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Submerging a mobile device into rice is a common repair advice for devices that suffered from water damage . This technique has not been shown to be effective in repairing them. [ 1 ] [ 2 ] [ 3 ] Submerging these devices into a desiccant may or may not be more effective than leaving them to dry in open air. Uncooked rice is inferior to other common desiccants such as silica gel or cat litter, [ 4 ] and Apple Support warn that small particles of rice could damage a phone. [ 5 ]
Rice has traditionally been used to keep camera equipment and films dry in tropical environments. [ 1 ]
In July 2007, less than a month after the original iPhone was released, a member of MacRumors named jorsuss started a thread titled "I dropped my iPhone in water" in which they said they had used "the rice trick" to recover it. [ 6 ] This may have been the first documented attempt to use the procedure on an iPhone. [ 1 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phone_repair_with_rice |
Phonetotopy is the concept that articulatory features as well as perceptual features of speech sounds are ordered in the brain in a similar way as tone ( tonotopy ), articulation and its somatosensory feedback ( somatotopy ), or visual location of an object ( retinotopy ). It is assumed that a phonetotopic ordering of speech sounds as well as of syllables can be found at a supramodal speech processing level (i.e. at a phonetic speech processing level) within the brain.
The concept of phonetotopy was introduced in Kröger et al. (2009) on the basis of modeling speech production, speech perception, as well as speech acquisition. [ 1 ] Moreover, fMRI measurements on ordering of vowels with respect to phonetic features [ 2 ] as well as EEG-array measurements on vowel and syllable articulation [ 3 ] support this concept. It underpins the concept of distinctive features , which are phonetically based features of speech sounds (i.e. based in perceptual as well as in articulatory domain), but which as well are linguistically (or phonologically ) relevant, and thus are realized in a language specific way in humans. | https://en.wikipedia.org/wiki/Phonetotopy |
A phoniton is a theoretical quasiparticle that emerges from the hybridization of a localized, long-lived phonon (a quantum of sound) with a matter excitation. It serves as a sound-based analogue of cavity quantum electrodynamics , where the phonon plays a role similar to that of a photon in coupling with a matter excitation to form a polariton .
The concept of phonitons was introduced in research conducted by Soykal et al. [ 1 ] In their study, they explore the possibility of realizing these hybrid objects based on sound and matter. By investigating strained silicon systems, the authors identify low-lying donor transitions that can be driven solely by acoustic phonons at wavelengths suitable for constructing high-Q phonon cavities. The strongly coupled regime of the phonon-matter resonance is achieved, surpassing the thresholds of spontaneous phonon emission, phonon leakage, anharmonicity , and scattering. The proposed micropillar distributed Bragg reflector Si/Ge cavity demonstrates the feasibility of achieving high-Q factors and small mode volumes.
Phonitons offer exciting prospects in manipulating quantized vibrations in nanoscale mechanical systems and gaining deeper insights into the nature of sound and heat at the quantum level. phonitons can serve as fundamental components in constructing new macroscopic artificial quantum systems. [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Phoniton |
Phono input is a set of input jacks, usually mini jacks or RCA connectors , located on the rear panel of a preamp, mixer or amplifier, especially on early radio sets , to which a phonograph or turntable is attached. [ 1 ]
Modern phono cartridges give a very low level output signal of the order of a few millivolts which the circuitry amplifies and equalizes. Phonograph recordings are made with high frequencies boosted and the low frequencies attenuated: during playback the frequency response changes are reversed. This reduces background noise, including clicks or pops, and also conserves the amount of physical space needed for each groove, by reducing the size of the larger low-frequency undulations. This is accomplished in the amplifier with a phono input that incorporates standardized RIAA equalization circuitry.
Through at least the 1980s, the phono input was widely available on consumer stereo equipment—even some larger boomboxes had them. By the 2000s only very sophisticated and expensive stereo receivers retained the phono input, since most users were expected to use digital music formats such as CD or satellite radio. Some newer low-cost turntables include built-in amplifiers to produce line-level (one volt) outputs; devices are available that perform this conversion for use with computers; or older amplifiers or radio receivers can be used. Nearly all DJ mixers have two or more phono inputs, together with two or more one-volt line inputs that also use RCA connectors.
This "phono input" designed for the millivolt signal from an unamplified turntable should not be confused with the modern standard one-volt line input and output that also uses RCA connectors and is found on video cameras, recorders and similar modern equipment.
This electronics-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phono_input |
A phono stage , also known as a phono amplifier or phono preamplifier , is an electronic audio component that amplifies the signal from a turntable to a level that will allow it to be heard when connected to a sound system. [ 1 ] A phono stage is needed to listen to any turntable otherwise the sound will be too low when heard through speakers or headphones. The phono stage can be a separate device that connects to the record player or it can be included as part of another audio component like a preamplifier or integrated amplifier . They can also be built into the record player itself. [ 2 ]
When the magnetic cartridge from a turntable touches a vinyl record, it produces a signal called a "phono signal". In order for the signal to be properly heard through an audio system, it needs to be converted into a "line signal", otherwise the sound would be too low. The bass notes from a signal are increased while the treble is decreased in a process called RIAA equalization . [ 3 ] This balance is due to the way the record was press in order to compensate for the sound and is done to create a balance listening experience.
There are 2 types of phono stages:
Tube phono stages were the original way that phono stages were built. The advancements in technology soon led to the transition to solid state builds. In recent years, companies have started to re-release tube versions of phono stages alongside modern solid state phono stages due to the demand and appeal of their different sounds.
Tube and solid state are two methods of building a phono stage that will power the device to amplify the sound but on top of that, a phono stage also has to be built to work with the type of cartridge that the turntable will utilize. There are 2 types of cartridges that a phono stage has to work with: Moving Magnet (MM) cartridge and Moving Coil (MC) cartridge. Moving Coil cartridges for example offer a weaker signal in comparison so a phono stage will need to be powerful enough to properly amplify the signal. [ 4 ] | https://en.wikipedia.org/wiki/Phono_stage |
Phonon drag is an increase in the effective mass of conduction electrons or valence holes due to interactions with the crystal lattice in which the electron moves. As an electron moves past atoms in the lattice its charge distorts or polarizes the nearby lattice. This effect leads to a decrease in the electron (or hole, as may be the case) mobility , which results in a decreased conductivity. However, as the magnitude of the Seebeck coefficient increases with phonon drag, it may be beneficial in a thermoelectric material for direct energy conversion applications. The magnitude of this effect is typically appreciable only at low temperatures (<200 K).
Phonons are not always in local thermal equilibrium; they move against the thermal gradient. They lose momentum by interacting with electrons (or other carriers) and imperfections in the crystal. If the phonon-electron interaction is predominant, the phonons will tend to push the electrons to one end of the material, losing momentum in the process. This contributes to the already present thermoelectric field. This contribution is most important in the temperature region where phonon-electron scattering is predominant. This happens for
where θ D is the Debye temperature . At lower temperatures there are fewer phonons available for drag, and at higher temperatures they tend to lose momentum in phonon-phonon scattering instead of phonon-electron scattering.
This region of the Seebeck coefficient-versus-temperature function is highly variable under a magnetic field.
Kittel, Charles (1996) Introduction to Solid State Physics , 7th Ed., John Wiley and Sons, Inc.
This condensed matter physics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phonon_drag |
Phonon noise , also known as thermal fluctuation noise , arises from the random exchange of energy between a thermal mass and its surrounding environment. This energy is quantized in the form of phonons . Each phonon has an energy of order k B T {\displaystyle k_{\text{B}}T} , where k B {\displaystyle k_{\text{B}}} is the Boltzmann constant and T {\displaystyle T} is the temperature . The random exchange of energy leads to fluctuations in temperature. This occurs even when the thermal mass and the environment are in thermal equilibrium , i.e. at the same time-average temperature. If a device has a temperature-dependent electrical resistance , then these fluctuations in temperature lead to fluctuations in resistance. Examples of devices where phonon noise is important include bolometers and calorimeters . The superconducting transition edge sensor (TES), which can be operated either as a bolometer or a calorimeter, is an example of a device for which phonon noise can significantly contribute to the total noise. [ 1 ]
Although Johnson–Nyquist noise shares many similarities with phonon noise (e.g. the noise spectral density depends on the temperature and is white at low frequencies), these two noise sources are distinct. Johnson–Nyquist noise arises from the random thermal motion of electrons , whereas phonon noise arises from the random exchange of phonons. Johnson–Nyquist noise is easily modeled at thermal equilibrium , where all components of the circuit are held at the same temperature. A general equilibrium model for phonon noise is usually impossible because different components of the thermal circuit are nonuniform in temperature and also often not time invariant , as in the occasional energy deposition from particles incident on a detector. The transition edge sensor typically maintains the temperature through negative electrothermal feedback associated with changes in internal electrical power. [ 1 ]
An approximate formula for the noise-equivalent power (NEP) due to phonon noise in a bolometer when all components are very close to a temperature T is
where G is the thermal conductance and the NEP is measured in W / H z {\displaystyle \mathrm {W/{\sqrt {Hz}}} } . [ 2 ] In calorimetric detectors, the rms energy resolution δ E {\displaystyle \delta E} due to phonon noise near quasi-equilibrium is described using a similar formula,
where C is the heat capacity. [ 3 ]
A real bolometer or calorimeter is not at equilibrium because of a temperature gradient between the absorber and the bath. Since G and C are generally nonlinear functions of temperature, a more advanced model may include the temperature of both the absorber and the bath and treat G or C as a power law across this temperature range. | https://en.wikipedia.org/wiki/Phonon_noise |
Phonons can scatter through several mechanisms as they travel through the material. These scattering mechanisms are: Umklapp phonon-phonon scattering , phonon-impurity scattering, phonon-electron scattering , and phonon-boundary scattering. Each scattering mechanism can be characterised by a relaxation rate 1/ τ {\displaystyle \tau } which is the inverse of the corresponding relaxation time.
All scattering processes can be taken into account using Matthiessen's rule . Then the combined relaxation time τ C {\displaystyle \tau _{C}} can be written as:
The parameters τ U {\displaystyle \tau _{U}} , τ M {\displaystyle \tau _{M}} , τ B {\displaystyle \tau _{B}} , τ ph-e {\displaystyle \tau _{\text{ph-e}}} are due to Umklapp scattering, mass-difference impurity scattering, boundary scattering and phonon-electron scattering, respectively.
For phonon-phonon scattering, effects by normal processes (processes which conserve the phonon wave vector - N processes) are ignored in favor of Umklapp processes (U processes). Since normal processes vary linearly with ω {\displaystyle \omega } and umklapp processes vary with ω 2 {\displaystyle \omega ^{2}} , Umklapp scattering dominates at high frequency. [ 1 ] τ U {\displaystyle \tau _{U}} is given by:
where γ {\displaystyle \gamma } is the Gruneisen anharmonicity parameter , μ is the shear modulus , V 0 is the volume per atom and ω D {\displaystyle \omega _{D}} is the Debye frequency . [ 2 ]
Thermal transport in non-metal solids was usually considered to be governed by the three-phonon scattering process, [ 3 ] and the role of four-phonon and higher-order scattering processes was believed to be negligible. Recent studies have shown that the four-phonon scattering can be important for nearly all materials at high temperature [ 4 ] and for certain materials at room temperature. [ 5 ] The predicted significance of four-phonon scattering in boron arsenide was confirmed by experiments.
Mass-difference impurity scattering is given by:
where Γ {\displaystyle \Gamma } is a measure of the impurity scattering strength. Note that v g {\displaystyle {v_{g}}} is dependent of the dispersion curves.
Boundary scattering is particularly important for low-dimensional nanostructures and its relaxation rate is given by:
where L 0 {\displaystyle L_{0}} is the characteristic length of the system and p {\displaystyle p} represents the fraction of specularly scattered phonons. The p {\displaystyle p} parameter is not easily calculated for an arbitrary surface. For a surface characterized by a root-mean-square roughness η {\displaystyle \eta } , a wavelength-dependent value for p {\displaystyle p} can be calculated using
where θ {\displaystyle \theta } is the angle of incidence. [ 6 ] An extra factor of π {\displaystyle \pi } is sometimes erroneously included in the exponent of the above equation. [ 7 ] At normal incidence, θ = 0 {\displaystyle \theta =0} , perfectly specular scattering (i.e. p ( λ ) = 1 {\displaystyle p(\lambda )=1} ) would require an arbitrarily large wavelength, or conversely an arbitrarily small roughness. Purely specular scattering does not introduce a boundary-associated increase in the thermal resistance. In the diffusive limit, however, at p = 0 {\displaystyle p=0} the relaxation rate becomes
This equation is also known as Casimir limit. [ 8 ]
These phenomenological equations can in many cases accurately model the thermal conductivity of isotropic nano-structures with characteristic sizes on the order of the phonon mean free path. More detailed calculations are in general required to fully capture the phonon-boundary interaction across all relevant vibrational modes in an arbitrary structure.
Phonon-electron scattering can also contribute when the material is heavily doped. The corresponding relaxation time is given as:
The parameter n e {\displaystyle n_{e}} is conduction electrons concentration, ε is deformation potential, ρ is mass density and m* is effective electron mass. [ 2 ] It is usually assumed that contribution to thermal conductivity by phonon-electron scattering is negligible [ citation needed ] . | https://en.wikipedia.org/wiki/Phonon_scattering |
A phonovoltaic ( pV ) cell converts vibrational ( phonons ) energy into a direct current much like the photovoltaic effect in a photovoltaic (PV) cell converts light ( photon ) into power. That is, it uses a p-n junction to separate the electrons and holes generated as valence electrons absorb optical phonons more energetic than the band gap , and then collects them in the metallic contacts for use in a circuit. [ 1 ] The pV cell is an application of heat transfer physics [ 2 ] and competes with other thermal energy harvesting devices like the thermoelectric generator .
While the thermoelectric generator converts heat , a broad spectrum of phonon and electron energy, to electricity, the pV cell converts only a narrow band of phonon energy, i.e., only the most energetic optical phonon modes. A narrow band of excited optical phonons has much less entropy than heat. Thus, the pV cell can exceed the thermoelectric efficiency. [ 1 ] [ 3 ] However, exciting and harvesting the optical phonon poses a challenge.
By the first law of thermodynamics , the excitation driving electron generation in both photo- and phonovoltaic cells, i.e., the photon or phonon, must have more energy than the semiconductor band gap . [ 1 ] For a PV cell, many materials are available with a band gap ( Δ E e , g {\displaystyle \Delta E_{e,g}} ) well matched to the solar photon spectrum , like Silicon or Gallium Arsenide . For a pV cell, however, no current semiconducting materials have a band gap smaller than the energy of their most energetic (optical) phonon modes ( E p , O {\displaystyle E_{p,\mathrm {O} }} ). Thus, novel materials are required with both energetic optical phonon modes ( E p , O ≥ 100 {\displaystyle E_{p,\mathrm {O} }\geq 100} meV, e.g., graphene , diamond , or boron nitride ) and a small band gap ( Δ E e , g < E p , O {\displaystyle \Delta E_{e,g}<E_{p,\mathrm {O} }} , e.g., graphene).
By the second law of thermodynamics , the excitation must be "hotter" than the cell for power generation to occur. In a PV, the light comes from an outside source, for example, the sun, which is nearly 6000 kelvins , whereas the PV is around 300 kelvins. Thus, the second law is satisfied and energy conversion is possible. However, the crystal vibrations driving power generation in a pV are intrinsic to the material itself. As such, they can not be imported from an outside source like the sun, but must instead be excited by some other process until they are hotter than the cell. The temperature of the optical phonon population is calculated by comparing the number of optical phonon to the number expected at a given temperature, which comes from the Bose–Einstein statistics .
There are a number of ways to excite a population of vibrations, i.e., create a hot optical phonon population. For example, if the electron population is excited, using a laser or electric field , they will typically relax by emitting optical phonons. Additionally, a hot molecular gas can impart its vibrations to a crystal when chemisorbed . Regardless of method, the conversion efficiency is limited by the optical phonon temperature achieved as compared to the electron temperature within the device due to Carnot's theorem .
In a nanoscale device, this temperature is approximately equal to the temperature of the device itself. [ 1 ] [ 4 ] However, in a macroscale device the generated electrons accumulate faster than they are collected. Thus, the electron population is heated up to the optical phonon temperature and further generation is inhibited. The down-conversion is simultaneously inhibited as the acoustic phonon population is heated to the optical phonon temperature. Thus, the large pV cell develops a near-equilibrium state where it is heated. At best, it will act like a thermoelectric generator and exhibit thermoelectric effects. Such a device is called a thermovoltaic, [ 5 ] [ 6 ] rather than a phonovoltaic.
Entropy generation and inefficiency in a PV cell is the result of photons more energetic than the band gap producing electrons with kinetic energy in addition to the potential energy provided by the band gap. Similarly, optical phonon energy in excess of the band gap generates an entropy flow in the pV cell, rather than electric power. The energy efficiency ( η ϕ {\displaystyle \eta _{\phi }} ) is quantified by the ratio of the band gap and optical phonon energy, that is [ 1 ]
In addition this typical inefficiency, hot optical phonon populations tend to downconvert into multiple low-energy, acoustic phonon modes (whereas photons typically do not downconvert into low energy infrared waves). This efficiency ( η Q E {\displaystyle \eta _{QE}} ) is quantified by the tendency of a hot optical phonon to downconvert rather than generate an electron-hole pair, that is [ 1 ]
where γ ˙ e − p {\displaystyle {\dot {\gamma }}_{e-p}} is the rate of generation and γ ˙ p − p {\displaystyle {\dot {\gamma }}_{p-p}} is the rate of downconversion, i.e., the rate at which an optical phonon produces multiple low-energy, acoustic phonons. This provides a second entropy flow reducing the efficiency of a pV cell.
Finally, entropy is generated in both pV and PV cells due to the inefficient separation of the generated electrons and holes. This efficiency ( η p n {\displaystyle \eta _{pn}} ) is limited by the Carnot efficiency given by [ 1 ]
where T p V {\displaystyle T_{\mathrm {pV} }} is the temperature of the pV cell and T p , O {\displaystyle T_{p,\mathrm {O} }} is the temperature of the optical phonon population, as dictated by the Bose–Einstein statistics . This efficiency is reduced the smaller the band gap is in comparison to the thermal energy ( k B T {\displaystyle k_{\mathrm {B} }T} , where k B {\displaystyle k_{\mathrm {B} }} is the Boltzmann constant and T {\displaystyle T} is the temperature). Indeed, the p-n junction efficiency is approximately [ 1 ]
Thus, the overall efficiency ( η p V {\displaystyle \eta _{\mathrm {pV} }} ) is [ 1 ]
where the temperature independent terms become the material figure of merit ( Z p V {\displaystyle Z_{\mathrm {pV} }} ), [ 1 ]
If the band gap and optical phonon mode are resonant, and the optical phonon tends to generate electrons, the phonovoltaic cell can approach the Carnot limit as T p v → 0 {\displaystyle T_{pv}\rightarrow 0} .
The electron-phonon coupling is responsible for electron generation in the pV cell. In this phenomenon, the phonon leads to ion motion which perturbs the highest occupied valence state (HOS). This state begins to overlap with the lowest unoccupied conduction state (LUS), and the electron can switch states if energy and momentum are conserved. If it does, an electron-hole pair is generated.
Using a taylor expansion of the change in electron potential, φ {\displaystyle \varphi } , due to the ionic displacement of a phonon provides a matrix element for use in Fermi's golden rule , and the derivation of a generation rate. This Taylor expansion gives the following matrix element [ 7 ]
⟨ f | H e − p ′ | i ⟩ = M e − p = ( ℏ 2 ⟨ m ⟩ ω κ p , α ) 1 / 2 ⟨ κ e + κ p , j | ∂ φ ∂ d κ p , α | κ e , i ⟩ , {\displaystyle {\begin{aligned}\langle f|\mathrm {H} _{e-p}'|i\rangle =M_{e-p}=({\frac {\hbar }{2\langle m\rangle \omega _{\kappa _{p},\alpha }}})^{1/2}\langle {\boldsymbol {\kappa }}_{e}+{\boldsymbol {\kappa }}_{p},j|{\frac {\partial \varphi }{\partial \mathbf {d} _{{\boldsymbol {\kappa }}_{p},\alpha }}}|{\boldsymbol {\kappa }}_{e},i\rangle ,\end{aligned}}}
where ⟨ m ⟩ {\displaystyle \langle m\rangle } is the average atomic mass, ω κ p , α {\displaystyle \omega _{\kappa _{p},\alpha }} and d κ p , α {\displaystyle \mathbf {d} _{{\boldsymbol {\kappa }}_{p},\alpha }} are the frequency and atomic displacement due to a phonon with polarization α {\displaystyle \alpha } and momentum κ p {\displaystyle {\boldsymbol {\kappa }}_{p}} , and | κ e , i ⟩ {\displaystyle |{\boldsymbol {\kappa }}_{e},i\rangle } is the electron wavefunction for an electron with momentum κ e {\displaystyle {\boldsymbol {\kappa }}_{e}} in band i . From Fermi's golden rule
γ ˙ e − p = 2 π ℏ | M e − p | 2 δ ( E e , i , κ e − E e , j , κ e + κ p ± ℏ ω κ p , α ) f e , i , κ e ( 1 − f e , i , κ e + κ p ) ( 1 2 ∓ 1 2 + f p , α , κ p ) {\displaystyle {\begin{aligned}{\dot {\gamma }}_{e-p}={\frac {2\pi }{\hbar }}|M_{e-p}|^{2}\delta (E_{e,i,\mathbf {\kappa } _{e}}-E_{e,j,\mathbf {\kappa } _{e}+\mathbf {\kappa } _{p}}\pm \hbar \omega _{\mathbf {\kappa } _{p},\alpha })f_{e,i,\mathbf {\kappa } _{e}}(1-f_{e,i,\mathbf {\kappa } _{e}+\mathbf {\kappa } _{p}})({\frac {1}{2}}\mp {\frac {1}{2}}+f_{p,\alpha ,\mathbf {\kappa } _{p}})\end{aligned}}}
where E e , i , κ e {\displaystyle E_{e,i,\mathbf {\kappa } _{e}}} is the energy of an electron in band i and momentum κ e {\displaystyle \mathbf {\kappa } _{e}} , f e , i , κ e {\displaystyle f_{e,i,\mathbf {\kappa } _{e}}} is the corresponding electron occupation, and f p , α , κ p {\displaystyle f_{p,\alpha ,\mathbf {\kappa } _{p}}} is the phonon occupancy.
Competing with the generation of electrons is the downconversion of optical phonons into multiple acoustic phonons. The coupling arises from the crystal Hamiltonian (H) expanded in terms of the ionic displacement ( d i α {\displaystyle d_{i\alpha }} ) from the equilibrium position ( r i {\displaystyle r_{i}} ) of atom i in direction α {\displaystyle \alpha } in direction, i.e., [ 2 ] [ 8 ]
H = H o + 1 2 ∑ i , j ∑ α , β ∂ 2 ⟨ φ ⟩ ∂ d i α ∂ d j β | o d i α d j β + 1 6 ∑ i , j , k ∑ α , β , γ ∂ 3 ⟨ φ ⟩ ∂ d i α ∂ d j β ∂ d k γ | o d i α d j β d k γ + ⋯ = H o + ∑ i , j ∑ α , β Γ i j , α β d i α d j β + ∑ i , j , k ∑ α , β , γ Ψ i j k , α β γ d i α d j β d k γ + ⋯ , {\displaystyle {\begin{aligned}\mathrm {H} &=\mathrm {H_{o}} +{\frac {1}{2}}\sum _{i,j}\sum _{\alpha ,\beta }{\frac {\partial ^{2}\langle \varphi \rangle }{\partial d_{i\alpha }\partial d_{j\beta }}}|_{\mathrm {o} }d_{i\alpha }d_{j\beta }+{\frac {1}{6}}\sum _{i,j,k}\sum _{\alpha ,\beta ,\gamma }{\frac {\partial ^{3}\langle \varphi \rangle }{\partial d_{i\alpha }\partial d_{j\beta }\partial d_{k\gamma }}}|_{\mathrm {o} }d_{i\alpha }d_{j\beta }d_{k\gamma }+\cdots \\&=\mathrm {H_{o}} +\sum _{i,j}\sum _{\alpha ,\beta }\Gamma _{ij,\alpha \beta }d_{i\alpha }d_{j\beta }+\sum _{i,j,k}\sum _{\alpha ,\beta ,\gamma }\Psi _{ijk,\alpha \beta \gamma }d_{i\alpha }d_{j\beta }d_{k\gamma }+\cdots ,\end{aligned}}}
where H o {\displaystyle \mathrm {H_{o}} } is the ground-state Hamiltonian, the linear term vanishes (as the ground state is found by minimizing the energy in terms of the ionic position), and Γ i j , α β {\displaystyle \Gamma _{ij,\alpha \beta }} and Ψ i j k , α β γ {\displaystyle \Psi _{ijk,\alpha \beta \gamma }} are the second- and third-order force constants between atoms i , j , and k when moved in along coordinate α {\displaystyle \alpha } , β {\displaystyle \beta } , and γ {\displaystyle \gamma } . The second order term is primarily responsible for the phonon dispersion , while the anharmonic (third order and higher) terms are responsible for thermal expansion as well as the phonon up- (multiple low-energy optical phonons combine to form a high-energy phonon) and downconversion (a high-energy phonon splits into multiple low-energy phonons).
Typically, up- and down-conversion is dominated by the third-order interaction. Thus, the perturbation Hamiltonian used in Fermi's golden rule for phonon up- and downconversion is [ 9 ]
H p − p ′ = Ψ κ p κ p ′ κ p ″ , α α ′ α ″ Ψ κ p κ p ′ κ p ″ , α α ′ α ″ = ∑ i j k ∑ α β γ Ψ i j k , α β γ s i α κ p s j α ′ κ p ′ s k α ″ κ p ″ ( ⟨ m ⟩ ω κ p , α ) 1 / 2 e x p [ i ( κ p ⋅ r i + κ p ′ ⋅ r j + κ p ⋅ r k ) ] , {\displaystyle {\begin{aligned}\mathrm {H} _{p-p}'&=\Psi _{{\boldsymbol {\kappa }}_{p}{\boldsymbol {\kappa }}_{p}'{\boldsymbol {\kappa }}_{p}'',\alpha \alpha '\alpha ''}\\\Psi _{{\boldsymbol {\kappa }}_{p}{\boldsymbol {\kappa }}_{p}'{\boldsymbol {\kappa }}_{p}'',\alpha \alpha '\alpha ''}&=\sum _{ijk}\sum _{\alpha \beta \gamma }\Psi _{ijk,\alpha \beta \gamma }{\frac {\mathbf {s} _{i\alpha {\boldsymbol {\kappa }}_{p}}\mathbf {s} _{j\alpha '{\boldsymbol {\kappa }}_{p}'}\mathbf {s} _{k\alpha ''{\boldsymbol {\kappa }}_{p}''}}{(\langle m\rangle \omega _{\kappa _{p},\alpha })^{1/2}}}\mathrm {exp} [i({\boldsymbol {\kappa }}_{p}\cdot r_{i}+{\boldsymbol {\kappa }}_{p}'\cdot r_{j}+{\boldsymbol {\kappa }}_{p}\cdot r_{k})],\end{aligned}}}
where s i α κ p {\displaystyle \mathbf {s} _{i\alpha \mathbf {\kappa _{p}} }} is the direction of displacement for atom i due to the phonon. The resulting downconversion rate, from Fermi's golden rule , is
γ ˙ p − p = ℏ π 16 | Ψ κ p κ p ′ κ p ″ , α α ′ α ″ | 2 × δ κ p , κ p ′ + κ p ″ δ ( ω κ p , α − ω κ p ′ , α ′ − ω κ ″ , α ″ ) × ( f p ′ + f p ″ + 1 ) , {\displaystyle {\dot {\gamma }}_{p-p}={\frac {\hbar \pi }{16}}|\Psi _{{\boldsymbol {\kappa }}_{p}{\boldsymbol {\kappa }}_{p}'{\boldsymbol {\kappa }}_{p}'',\alpha \alpha '\alpha ''}|^{2}\times \delta _{\kappa _{p},\kappa _{p}'+\kappa _{p}''}\delta (\omega _{\kappa _{p},\alpha }-\omega _{\kappa _{p}',\alpha '}-\omega _{\kappa '',\alpha ''})\times (f_{p}'+f_{p}''+1),}
where two phonons are produced with polarization α ′ {\displaystyle \alpha '} and α ″ {\displaystyle \alpha ''} and momentum κ p ′ {\displaystyle \mathbf {\kappa } _{p}'} and κ p ″ {\displaystyle \mathbf {\kappa } _{p}''} .
As outlined above, an efficient pV cell requires a material with an optical phonon mode more energetic than the bandgap, which in turn is much more energetic than the thermal energy at the intended operating temperature ( E p , O ≃ Δ E e , g ≫ k B T p V ) {\displaystyle (E_{p,\mathrm {O} }\simeq \Delta E_{e,g}\gg k_{\mathrm {B} }T_{\mathrm {pV} })} . Furthermore, the pV cell requires a material wherein a hot optical phonon prefers to produce an electron rather than multiple low energy acoustic phonons ( γ ˙ e − p ∗ → 1 {\displaystyle {\dot {\gamma }}_{e-p}^{*}\rightarrow 1} ).
Very few materials offer this combination of properties. Indeed, the vast majority of crystals have optical phonon energies limited to below 50 meV, and those with more energetic optical phonons tend to have much more energetic band gaps. In general, a material with a first-row element ( periodic table ) is required to have a highly energetic optical phonon. However, the high electronegativity of a first-row elements tends to create a very large band gap, as in diamond and the boron nitride allotropes. [ 10 ] Graphene is one of the few materials which diverges from this trend, with no bandgap and an exceptionally energetic optical phonon mode near 200 meV. [ 11 ] [ 12 ] Thus, graphene has been the initial target for development of a phonovoltaic material through the opening and tuning of its bandgap. [ 13 ] [ 3 ]
Opening and tuning the bandgap of graphene has received substantial attention, and numerous strategies have been suggested and investigated. These include the use of uniaxial strain, [ 14 ] electric fields, [ 15 ] and chemical doping and functionalization. [ 16 ] In general, these mechanisms work by either changing the symmetry of graphene (both Carbon atoms in the unit cell are identical) or hybridization ( s p 2 {\displaystyle sp^{2}} ).
In the first phonovoltaic material investigations, it has been suggested that the latter technique destroys the electron-phonon coupling while the former preserves it. [ 13 ] [ 3 ] In particular, these investigations predict that hydrogenating graphene, to produce graphane , reduces the electron-phonon coupling so substantially that the material figure of merit vanishes; [ 13 ] and that doping graphene with boron nitride maintains the strong electron-phonon coupling in graphene, such that its figure of merit is predicted to reach 0.65 and enable heat harvesting with twice the efficiency of a typical thermoelectric generator. [ 3 ] | https://en.wikipedia.org/wiki/Phonovoltaic |
Phorbol is a natural, plant-derived organic compound . It is a member of the tigliane family of diterpenes . Phorbol was first isolated in 1934 via the hydrolysis of croton oil , which is derived from the seeds of the purging croton, Croton tiglium . [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] The structure of phorbol was determined in 1967. [ 7 ] [ 8 ] Various esters of phorbol have important biological properties, the most notable of which is the capacity to act as tumor promoters through activation of protein kinase C . [ 9 ] They mimic diacylglycerols , glycerol derivatives in which two hydroxyl groups have reacted with fatty acids to form esters. The most common and potent phorbol ester is 12- O -tetradecanoylphorbol-13-acetate (TPA), also called phorbol-12-myristate-13-acetate (PMA), which is used as a biomedical research tool in contexts such as models of carcinogenesis .
Phorbol is a natural product found in many plants, especially those of the Euphorbiaceae and Thymelaeaceae families. [ 10 ] [ 11 ] Phorbol and phorbol esters are the active constituents of the highly toxic New World tropical manchineel tree ( Hippomane mancinella ). [ 12 ] It is very soluble in most polar organic solvents , as well as in water. In the manchineel, this leads to an additional exposure risk during rain, where liquid splashing from an undamaged tree may also be injurious. Contact with the tree or consumption of its fruit can lead to symptoms such as severe pain and swelling. [ 13 ] [ 14 ] [ non-primary source needed ]
The purging croton , Croton tiglium , is the source of croton oil from which phorbol was initially isolated. Its seeds and oil have been used for hundreds of years in traditional medicine, generally as a purgative, and the seeds were mentioned in Chinese herbal texts 2000 years ago. [ 15 ] The purgative effects of the oil are largely attributed to the high percentage of phorbol esters contained in the oil. Phorbol was isolated from C. tiglium seeds in 1934. [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] The structure of the compound was determined in 1967, [ 7 ] [ 8 ] and a total synthesis was described in 2015. [ 16 ]
Phorbol derivatives work primarily by interacting with protein kinase C (PKC), although they can interact with other phospholipid membrane receptors. [ 17 ] The esters bind to PKC in a similar way to its natural ligand, diacylglycerol , and activate the kinase. [ 18 ] Diacylglycerol is degraded quickly by the body, allowing PKC to be reversibly activated. When phorbol esters bind to the receptor, they are not degraded as efficiently by the body, leading to constitutively active PK. [ 17 ] PKC is involved in a number of important cell signaling pathways. Thus, phorbol ester exposure can show a wide range of results.
The main results of phorbol exposure are tumor promotion and inflammatory response. Although phorbol is not a carcinogen itself, it greatly enhances the action of other substances and promotes tumor proliferation. PKC is a key component in biological pathways controlling cell growth and differentiation. When phorbol esters bind to PKC, cell proliferation pathways are activated. This effect greatly promotes tumors when the cells are exposed to even a sub-carcinogenic amount of a substance. [ 17 ] PKC is also involved in activation of inflammation pathways such as the NF-κB pathway. Thus, exposure to phorbol products can induce an inflammatory response in tissues. [ 19 ] Symptoms can include edema and pain, especially to the skin and mucous membranes. [ 10 ] While phorbol itself does not have irritant activity, nearly all phorbol esters are highly irritant, with a wide range of half-maximal inhibitory concentration ( IC 50 ) values. [ 10 ] The median lethal dose ( LD 50 ) of phorbol esters for male mice was found to be about 27 mg/kg, with the mice showing hemorrhage and congestion of pulmonary blood vessels, as well as lesions throughout the body. [ 18 ]
A total synthesis of enantiopure phorbol was developed in 2015. While this synthesis will not replace natural isolation products, it will enable researchers to create phorbol analogs for use in research, especially creating phorbol derivatives that can be evaluated for anti-cancer activity. [ 16 ] Previously, the difficulty with synthesizing phorbol had been creating C–C bonds, especially in the six-membered ring at the top of the molecule. This synthesis starts from (+)- 3-carene , and uses a series of 19 steps to eventually create (+)-phorbol. [ 20 ] [ 21 ] [ 16 ]
Because of their mechanism of action, phorbol esters can be used to study tumor proliferation and pain response. [ citation needed ] TPA is most commonly used in the laboratory to induce a cellular response. [ citation needed ] For example, TPA can be used to measure response to pain and test compounds that may mitigate the inflammatory response. [ 22 ] TPA and other phorbol esters can also be used to induce tumor formation and to study mechanism of action. [ 10 ] TPA, together with ionomycin , can also be used to stimulate T-cell activation, proliferation, and cytokine production, and is used in protocols for intracellular staining of these cytokines. [ citation needed ]
The phorbol ester tigilanol tiglate reportedly has in vitro anti-cancer, antiviral, and antibacterial activities. [ 10 ] The phorbol derivatives in croton oil are used in folk medicine, with purported purgative, counter-irritant, or anthelmintic activities. [ 23 ] [ better source needed ] | https://en.wikipedia.org/wiki/Phorbol |
Phorbol 12,13-dibutyrate ( PDBu ) is a phorbol ester which is one of the constituents of croton oil . As an activator of protein kinase C , it is a weak tumor promoter compared to 12- O -tetradecanoylphorbol-13-acetate . [ 1 ]
PDBu is widely used as a chemical reagent because of its solubility in water and other organic solvents. | https://en.wikipedia.org/wiki/Phorbol_12,13-dibutyrate |
Phoresis or phoresy is a temporary commensalistic relationship when an organism (a phoront or phoretic) attaches itself to a host organism solely for travel. [ 2 ] It has been seen in ticks and mites since the 18th century, [ 3 ] and in fossils 320 million years old. [ 2 ] It is not restricted to arthropods or animals ; plants with seeds that disperse by attaching themselves to animals are also considered to be phoretic. [ 4 ]
Phoresis is rooted in the Greek words phoras (bearing) and phor (thief). [ 3 ] The term, originally defined in 1896 as a relationship in which the host acts as a vehicle for its passenger, clashed with other terminology being developed at the time, so constraints on the length of time, feeding, and ontogeny are now considered. [ 3 ] Phoresis is used as a strategy for dispersal , [ 5 ] [ 6 ] seasonal migration , [ 7 ] transport to new host/habitat, [ 8 ] escaping ephemeral habitats, [ 9 ] [ 3 ] and reducing inbreeding depression . [ 10 ] In addition to the benefits afforded to individuals and species, its presence can add to the ecological diversity and complexity of an ecosystem. [ 4 ]
The strict definition of phoresis excludes cases in which the relationship is permanent (e.g. that of a barnacle surviving on a whale ), or those in which the phoront gains any kind of advantage from the host organism (e.g. remoras attaching to sharks for transportation and food). [ 3 ] Phoresis is a commensal relationship, and deviations result in mutualistic or parasitic relationships. Phoretic relationships can become parasitic if a cost is inflicted upon the host, such as if the number of mites on a host begins impeding its movement. Parasitic relationships could also be selected from phoretic ones if the phoront gains a fitness advantage from the death of a host (e.g. nutrition). Mutualistic relationships could also develop if the phoront begins to confer a benefit to the host (e.g. predator defense). [ 2 ] The evolutionary plasticity of phoretic relationships allow them to potentially add to the complexity and diversity of ecosystems. [ 4 ]
Cases in which the phoront parasitizes or preys upon the host organism after travel are still considered phoresis, as long as the travel behaviour and the feeding or parasitizing behaviour are separate. [ 2 ] Similarly, some pseudoscorpions prey upon the same species that act as their phoretic host. The behaviours are completely separate however, since the pseudoscorpion utilizes anatomical features used specifically for predation when treating the host as prey, but employs anatomical features used for phoresis when travelling. [ 11 ]
Examples may be found in the arthropods associated with sloths . Coprophagous sloth moths, such as Bradipodicola hahneli and Cryptoses choloepi , are unusual in that they exclusively inhabit the fur of sloths, mammals found in central and South America . [ 12 ] [ 13 ] The sloth provides transport for the moths, the females of which oviposit in the droppings of sloths, which the larvae feed on, and the newly hatched moths move into the forest canopy in search of a new sloth host.
Larvae of the blister beetle ( Meloe franciscanus ) need to find the nests of their host, the solitary bee ( Habropoda pallida ), to continue their life cycle. The larvae gather in colonies, and emit chemicals that mimic the pheromones of the female solitary bee . Larvae attach to the attracted males when they visit the false source of pheromones, and then subsequently to any female the male mates with. The blister beetle larvae then infest and parasitize the female bee’s nest. [ 8 ]
Some species of Bromeliad treefrog ( Scinax littoreus and Scinax perpusillus ) carry ostracods ( Elpidium sp.), which in turn carry ciliates ( Lagenophrys sp.) from one bromeliad plant to another. The plants act as ecological islands to the ostracods, and phoresis allows them to disperse over a wider area than would be available to them otherwise. The term for a phoretic organism riding on another phoretic organism is hyperphoresis . [ 9 ] [ 14 ]
Some mites in the clade Astigmatina have a stage of their life cycle (the deutonymph or hypopus) that is modified specifically for phoresis. This stage has reduced mouthparts, a well-sclerotised body that resists desiccation , and usually a posteroventral organ for attaching to the host animal (which may be an invertebrate or a vertebrate). Astigmatans often live in patchy and ephemeral habitats such as fungal fruiting bodies, dung, carrion, animal nests, tree sap flows and decaying wood. Phoresis allows these mites to quickly leave a depleted habitat and travel to a new one. [ 15 ] A specific example is deutonymphs of Lardoglyphus dispersing on beetles in the genus Dermestes to reach new habitats (both phoront and host feed on animal materials). [ 16 ]
A specialist mite ( Parasitellus fucorum ) that parasitizes bumble bees ( Bombus spp.) avoids inbreeding depression in a single hive, and remains genetically independent of any specific host lineage by travelling to a new hive. This is accomplished by travelling on a foraging bee to a flower and detaching, and waiting for and attaching to another bee which may be from another hive, and infesting the new hive. These mites can survive on flowers for up to 24 hours, and have shown a preference for opened flowers, where they would be most likely to find a host. [ 10 ]
Dung and carrion are ephemeral habitats that are frequently visited by beetles ( dung beetles , burying beetles ). Phoretic nematodes (Rhabditoides) and mites (e.g. genera Macrocheles , Poecilochirus , Uroobovella ) use the beetles to reach these rich resources, where they themselves reproduce. [ 17 ] [ 18 ] [ 19 ]
The pseudoscorpion Cordylochernes scorpioides is frequently found riding harlequin beetles ( Acrocinus longimanus ). Initially, there were a number of alternate hypothesis for why the pseudoscorpions were found on the beetles: by accident, to forage for mites inhabiting the beetle, or as an obligate parasite . Evidence suggested, however, that the pseudoscorpions were using beetles to travel from tree to tree, where they preyed upon other beetle larvae. [ 5 ]
If their host dies, lice can opportunistically use phoresis to hitch a ride on a fly, and attempt to find a new host. [ 20 ]
The largest mammalian example of phoresis is human beings directly riding on horses or other animals, or using them to pull vehicles with humans in them. | https://en.wikipedia.org/wiki/Phoresis |
In botany , phorophytes are plants on which epiphytes grow. The term is composed of phoro , meaning bearer or carrier [ 1 ] and phyte , meaning plant. [ 2 ]
The epiphytes benefit from the habitats provided, but the phorophyte is unaffected. In other words, the obligate epiphytes utilize phorophytes as habitats, without parasitizing them. [ 3 ]
Different phorophytes provide different conditions to the plants, which grown on their surface. The bark pH, degree of bark shedding, the presence of milk sap and the density and size of bark lenticels influence the occurrence of epiphytes. [ 4 ] Bark ornamentations affect the establishment of seeds and the chemical composition of the bark may be inhibiting germination. [ 3 ] Some epiphytic orchids tend to grow on phorophytes with rough bark. Conservation efforts of orchids need to account for the conservation of phorophytes as well. [ 5 ] | https://en.wikipedia.org/wiki/Phorophyte |
A phoropter or refractor is an ophthalmic testing device. It is commonly used by eye care professionals during an eye examination , and contains different lenses used for refraction of the eye during sight testing, to measure an individual's refractive error and determine their eyeglass prescription . [ 1 ] It also is used to measure the patients' phorias and ductions , which are characteristics of binocularity .
Typically, the patient sits behind the phoropter, and looks through it at an eye chart placed at optical infinity (20 feet or 6 metres), then at near (16 inches or 40 centimetres) for individuals needing reading glasses. The eye care professional then changes lenses and other settings, while asking the patient for subjective feedback on which settings gave the best vision . The patient's habitual prescription or an automated refractor may be used to provide initial settings for the phoropter. Sometimes a retinoscope is used through the phoropter to measure the vision without the patient having to speak, which is useful for infants and people who do not speak the language of the practitioner.
Phoropters can also measure heterophorias (natural resting position of the eyes), accommodative amplitudes , accommodative leads/lags, accommodative posture, horizontal and vertical vergences , and more.
The major components of the phoropter are the battery of spherical and cylindrical lenses, auxiliary devices such as Maddox rods , filtered lenses, prisms, and the JCC ( Jackson cross cylinder ) used for astigmatism measurement. The prismatic lenses are used to analyze binocular vision and treat orthoptic problems.
From the measurements taken, the specialist will write an eyeglass prescription that contains at least three numerical specifications for each eye: sphere, cylinder, and axis, as well as pupillary distance (distance between eyes), and, rarely, prism for one or both eyes.
The lenses within a phoropter refract light in order to focus images on the patient's retina . The optical power of these lenses is measured in 0.25 diopter increments. By changing these lenses, the examiner is able to determine the spherical power, cylindrical power, and cylindrical axis necessary to correct a person's refractive error. The presence of cylindrical power indicates the presence of astigmatism , which has an axis measured from 0 to 180 degrees away from being aligned horizontally.
Phoropters are made with either plus or minus cylinders. Traditionally, ophthalmologists and orthoptists use plus cylinder phoropters and optometrists use minus cylinder phoropters. One can mathematically convert figures obtained from either type of phoropter to the other.
Phoroptor is a registered trademark currently owned by Reichert Technologies, filed April 25, 1921, by DeZeng Standard of New Jersey, with the USPTO , serial number 71146698. The word was coined at that time for the newest version of their phoro-optometer . DeZeng was purchased in 1925 by American Optical of Massachusetts, which continued to market the product, but the term, often spelled phoropter, has become a generic trademark for all brands of modern vision testers, especially since AO's main competitor, Bausch and Lomb , stopped making their Greens' Refractor in 1970s. Reichert bought AO's refracting equipment division in 1980s, and their current version is named "Ultramatic Rx Master Phoroptor".
The history of the phoropter, as a binocular refracting device which can also measure phorias , ductions , and other traits of binocularity , as distinct from the monocular optometer , which cannot, starts in the mid-1910s, with the introduction of the Ski-optometer by Nathan Shigon, and the Phoro-optometer by Henry DeZeng. These two inventions, as they continued to improve, were accompanied by a third device, the Greens' Refractor, which entered the market in 1934. European manufacturers were working on similar devices as well. [ 2 ]
In 1909, Nathan Shigon of New York City invented [ 3 ] a monocular optometer with a range of +0.25 to +6.00 diopters, consisting of a mechanism where a disc of low-powered lenses advanced a second disc of higher power lenses automatically with each rotation, as in a modern phoropter.
There is no evidence this was ever manufactured, but in 1915 he filed for a patent for a binocular version of this same optometer, [ 4 ] and called it the Ski-Optometer, so named for its usefulness in doing skiascopy . This was manufactured by Wm. F. Reimold of Philadelphia. It included a Stevens Phorometer for measuring phorias, and a disc of auxiliary spherical lenses on the back, giving it a range of -12.00 to +12.00. To extend the range, there were clips on the front of each eye hole for the insertion of hand held sphere or cylinder trial lenses, with a mechanism to rotate the axis with the thumb. It weighed 2 lb. 3 oz.
Around 1916 Michael Woolf, also of New York City, bought him out and added his own invention, [ 5 ] an innovative battery of cylinder lenses, ranging from 0.25 to 2.00 D to the device, as well as Risley prisms for each eye. Maddox rods were optional. It was also called the Ski-Optometer, and it weighed 3 lb. 13 oz.
Around 1924 the patents and rights were transferred to General Optical Company of Mount Vernon, NY, which had been making a much larger, heavier and more solidly encased instrument, called the Genothalmic Refractor, since around 1920, using Woolf's 1917 patent number, and with a user's manual dated 1921. This instrument had a range of +17.75 to - 22.50 sphere, and up to 3.75 cylinder, Maddox rods, Risley prisms, and a Steven's phorometer. It weighed 7 pounds 5 ounces, and unlike all earlier devices of this kind, it hung from a horizontal mounting bar instead of being supported from the bottom. Like the Woolf, it had no Jackson cross-cylinders (JCC) at first, so a separate hand-held one was required. Late models of the Genothalmic were fitted with JCCs.
General Optical sold out to Shuron Optical of Geneva, New York, in 1927, which sold the refractor until the late 1930s. [ 2 ] A refined and improved version of the Genothalmic Refractor was manufactured in London starting around 1932, and sold in the UK by S. R. Stearman, S. Pulzer & Son Ltd., and others, as the British Refracting Unit (B.R.U.).
Also in 1909, Henry DeZeng got a patent for what looks remarkably like a modern phoropter, [ 6 ] but the patent illustrations look nothing like the manufactured product, which was introduced around 1915—the DeZeng Phoro-Optometer model 570. This was a device produced in Camden, New Jersey, which contained a battery of convex lenses for each eye, a battery of concave lenses for each eye, and auxiliary lenses which gave it a total power range of +15.75 to -19.75, as well as a Maddox rod and Risley prism for each eye, and a Steven's phorometer.
There were no cylindrical lenses, so testing for astigmatism required the use of manual trial-lenses, for which there were rotating holders on the front of each eye hole, and there were stationary ones on the backs as well. Cross-cylinders were optional, but they did not flip like a Jackson cross cylinder, they rotated in the same plane, so they were probably meant for the near point cross-cylinder test for reading. [ 7 ] It weighed 3 lb. 2 oz. Around 1920 an improved model, No. 574, was introduced, reduced in size but with the same range (lenses reduced from 1 inch to 3 ⁄ 4 inch). The forehead rest was removed, and the rear trial lens clips were replaced with rubber eye guards. It weighed 2 lbs. 12 oz.
In 1922, DeZeng replaced No. 574 with No. 584, and shortened the name to Phoroptor. This device became so popular that its name became genericized, though often spelled phoropter. The Phoroptor was smaller (lenses reduced again, to 9/16 inch diameter), with a similar power range, and the front clips for hand-held trial lenses were removed and replaced with batteries of cylinder lenses ranging from 0.25 D to 4.75 D. The Steven's phorometer was dropped, and there were no Jackson cross cylinders. It weighed 2 lb. 8 oz.
In 1925, American Optical bought DeZeng, and in 1927 introduced No. 588, the AO Wellsworth DeZeng Phoroptor, which was slightly larger; the lenses were increased to 11/16 inch and it weighed 3 lb. 2 oz. This was the first in the DeZeng/AO line to hang from a horizontal mounting bar, the earlier ones were supported from a bar below it. This phoroptor was unique in that it was calibrated in 1/8 diopter steps throughout its whole range.
In 1934, AO introduced No. 589, the Additive Effective Power Phoroptor, once again enlarged and improved. The lenses were increased to 3 ⁄ 4 inch diameter, the permanent size, and the unit was much more massive, with a weight of 7 lb. 9 oz., and with a range of +16.87 to -19.12 sphere and 6.00 cylinder, with auxiliary lenses to increase these to +18.87/-21.12 sphere and 8.00 cylinder. All these models resembled the original DeZeng model in design, but No. 590 of 1948 was a completely re-designed device, much larger and heavier, and more modern. It weighed 10 lbs. 7 oz. This was followed by another complete re-design in 1956, the RxMaster, [ 2 ] which became the prototype of all modern phoropters, and was updated to the Ultramatic RxMaster in 1967, which is the current model.
AO sold their phoroptor division to Reichert in 1982, who still make the Ultramatic.
In the early 20th century, ophthalmologists A. S. Green, L. D. Green, and M. I. Green, of San Francisco, CA, designed an optometer , [ 8 ] which they developed slowly over many years. The Greens teamed up with inventor Clyde L. Hunsicker of San Francisco, who applied for a patent on October 25, 1926. The title of their invention was simply an "optometrist instrument", and the text described it as an optometer. Patent 1,804,690 was granted to the Greens and Hunsicker in 1931, and sold to Bausch & Lomb (B&L), which had them redesign it (patent 1,873,356, granted 1932).
B&L trademarked it as "Greens' Refractor" and introduced it in 1934. It was far more advanced than the competition in many ways. The power could be read right off the dial without having to do mental calculations, the range was far higher, from +19.75 to -28.00 and with cylinders up to 7.50, the battery of cylinders was much more intuitive and easy to use, and it was the first to have Jackson cross cylinders affixed, (the first AO Phoroptors with JCC's were late models of the Additive, and very late Genothalmic Refractors also had them). It weighed 13 lbs. 1 oz. The Greens' Refractor soon became the gold standard among eyecare professionals. It helped put the Shigon/Woolf/Genothalmic line out of the market and forced AO to completely redesign their phoroptor from scratch, not once, but twice, (the 590 failed to compete).
The Greens' Refractor remained unchanged for over four decades, but sales slipped when AO introduced the Ultramatic RxMaster with its revolutionary yoked JCC in 1967, and production of the Greens' Refractor finally ended in the mid-1970s. In 1978, B&L introduced the Greens II refractor, also called the Bausch and Lomb Refractor, or the Greens' Mark II Refractor. [ 9 ] It included yoked JCC, but AO had already patented the yoking of the JCC, and production of the Greens' II was halted. Very few were made, and they are a rarity. It weighed 11 pounds 13 ounces. As for the original Greens' Refractor, in spite of the fact that production stopped decades ago, many are still being used today, as they are virtually indestructible, and have a devoted rank who still swear by them. [ 2 ]
Starting in the mid-20th century, companies in Europe and Asia have made phoropters of their own design, as well as copied American models. The Moeller Wedel Visutest of Germany, the Magnon RT 500 of France, and the Nikon Optester and Takagi MT3, both of Japan, are all of original design. The Topcon VT S of Japan is of original design, but Topcon has also made knock-offs of the Greens' Refractor and the AO Ultramatic. Rodenstock in Germany has developed many of their own models, as well as copied the Ultramatic with their Phorovist 200. The Marco RT-300 of Japan is an original design which borrows heavily from the Ultramatic. In the 1930s, Stearman in the UK and Ellis Optical Co., also in the UK, both made an improved version of the Genothalmic Refractor called the British Refracting Unit, and Stearman also made a knockoff of the Greens Refractor. China makes numerous unbranded knockoffs of the Ultramatic. | https://en.wikipedia.org/wiki/Phoropter |
Phosgene is an organic chemical compound with the formula COCl 2 . It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. [ 7 ] It can be thought of chemically as the double acyl chloride analog of carbonic acid , or structurally as formaldehyde with the hydrogen atoms replaced by chlorine atoms. In 2013, about 75–80 % of global phosgene was consumed for isocyanates , 18% for polycarbonates and about 5% for other fine chemicals . [ 8 ]
Phosgene is extremely poisonous and was used as a chemical weapon during World War I , where it was responsible for 85,000 deaths . It is a highly potent pulmonary irritant and quickly filled enemy trenches due to it being a heavy gas.
It is classified as a Schedule 3 substance under the Chemical Weapons Convention . In addition to its industrial production, small amounts occur from the breakdown and the combustion of organochlorine compounds , such as chloroform . [ 9 ]
Phosgene is a planar molecule as predicted by VSEPR theory . The C=O distance is 1.18 Å , the C−Cl distance is 1.74 Å and the Cl−C−Cl angle is 111.8°. [ 10 ] Phosgene is a carbon oxohalide and it can be considered one of the simplest acyl chlorides, being formally derived from carbonic acid . [ citation needed ]
Industrially, phosgene is produced by passing purified carbon monoxide and chlorine gas through a bed of porous activated carbon , which serves as a catalyst : [ 9 ]
This reaction is exothermic and is typically performed between 50 and 150 °C. Above 200 °C, phosgene reverts to carbon monoxide and chlorine, K eq (300 K) = 0.05. World production of this compound was estimated to be 2.74 million tonnes in 1989. [ 9 ]
Phosgene is fairly simple to produce, but is listed as a Schedule 3 substance under the Chemical Weapons Convention . As such, it is usually considered too dangerous to transport in bulk quantities . Instead, phosgene is usually produced and consumed within the same plant, as part of an "on demand" process. This involves maintaining equivalent rates of production and consumption, which keeps the amount of phosgene in the system at any one time fairly low, reducing the risks in the event of an accident. Some batch production does still take place, but efforts are made to reduce the amount of phosgene stored. [ 11 ]
Simple organochlorides slowly convert into phosgene when exposed to ultraviolet (UV) irradiation in the presence of oxygen . [ 12 ] Before the discovery of the ozone hole in the late 1970s large quantities of organochlorides were routinely used by industry, which inevitably led to them entering the atmosphere. In the 1970-80s phosgene levels in the troposphere were around 20-30 pptv (peak 60 pptv). [ 12 ] These levels had not decreased significantly nearly 30 years later, [ 13 ] despite organochloride production becoming restricted under the Montreal Protocol .
Phosgene in the troposphere can last up to about 70 days and is removed primarily by hydrolysis with ambient humidity or cloudwater. [ 14 ] Less than 1% makes it to the stratosphere , where it is expected to have a lifetime of several years, since this layer is much drier and phosgene decomposes slowly through UV photolysis . It plays a minor part in ozone depletion .
Carbon tetrachloride ( CCl 4 ) can turn into phosgene when exposed to heat in air. This was a problem as carbon tetrachloride is an effective fire suppressant and was formerly in widespread use in fire extinguishers . [ 15 ] There are reports of fatalities caused by its use to fight fires in confined spaces . [ 16 ] Carbon tetrachloride's generation of phosgene and its own toxicity mean it is no longer used for this purpose. [ 15 ]
Phosgene is also formed as a metabolite of chloroform , likely via the action of cytochrome P-450 . [ 17 ]
Phosgene was synthesized by the Cornish chemist John Davy (1790–1868) in 1812 by exposing a mixture of carbon monoxide and chlorine to sunlight . He named it "phosgene" from Greek φῶς ( phos , light) and γεννάω ( gennaō , to give birth) in reference of the use of light to promote the reaction. [ 18 ] It gradually became important in the chemical industry as the 19th century progressed, particularly in dye manufacturing.
The reaction of an organic substrate with phosgene is called phosgenation . [ 9 ] Phosgenation of diols give carbonates (R = H , alkyl , aryl ), which can be either linear or cyclic:
An example is the reaction of phosgene with bisphenol A to form polycarbonates . [ 9 ] Phosgenation of diamines gives di-isocyanates, like toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). In these conversions, phosgene is used in excess to increase yield and minimize side reactions. The phosgene excess is separated during the work-up of resulting end products and recycled into the process, with any remaining phosgene decomposed in water using activated carbon as the catalyst. Diisocyanates are precursors to polyurethanes . More than 90% of the phosgene is used in these processes, with the biggest production units located in the United States (Texas and Louisiana), Germany, Shanghai, Japan, and South Korea. The most important producers are Dow Chemical , Covestro , and BASF . Phosgene is also used to produce monoisocyanates, used as pesticide precursors ( e.g. methyl isocyanate (MIC).
Aside from the widely used reactions described above, phosgene is also used to produce acyl chlorides from carboxylic acids :
For this application, thionyl chloride is commonly used instead of phosgene.
The synthesis of isocyanates from amines illustrates the electrophilic character of this reagent and its use in introducing the equivalent synthon "CO 2+ ": [ 19 ]
Such reactions are conducted on laboratory scale in the presence of a base such as pyridine that neutralizes the hydrogen chloride side-product.
Phosgene is used to produce chloroformates such as benzyl chloroformate :
In these syntheses, phosgene is used in excess to prevent formation of the corresponding carbonate ester .
With amino acids , phosgene (or its trimer) reacts to give amino acid N-carboxyanhydrides . More generally, phosgene acts to link two nucleophiles by a carbonyl group. For this purpose, alternatives to phosgene such as carbonyldiimidazole (CDI) are safer, albeit expensive. [ 20 ] CDI itself is prepared by reacting phosgene with imidazole .
Phosgene is stored in metal cylinders . In the US, the cylinder valve outlet is a tapered thread known as " CGA 160" that is used only for phosgene.
In the research laboratory, due to safety concerns phosgene nowadays finds limited use in organic synthesis . A variety of substitutes have been developed, notably trichloromethyl chloroformate (" diphosgene "), a liquid at room temperature, and bis(trichloromethyl) carbonate (" triphosgene "), a crystalline substance. [ 21 ]
Phosgene reacts with water to release hydrogen chloride and carbon dioxide :
Analogously, upon contact with ammonia, it converts to urea :
Halide exchange with nitrogen trifluoride and aluminium tribromide gives COF 2 and COBr 2 , respectively. [ 9 ]
It is listed on Schedule 3 of the Chemical Weapons Convention : All production sites manufacturing more than 30 tonnes per year must be declared to the OPCW . [ 22 ] Although less toxic than many other chemical weapons such as sarin , phosgene is still regarded as a viable chemical warfare agent because of its simpler manufacturing requirements when compared to that of more technically advanced chemical weapons such as tabun , a first-generation nerve agent . [ 23 ]
Phosgene was first deployed as a chemical weapon by the French in 1915 in World War I. [ 24 ] It was also used in a mixture with an equal volume of chlorine, with the chlorine helping to spread the denser phosgene. [ 25 ] [ 26 ] Phosgene was more potent than chlorine, though some symptoms took 24 hours or more to manifest.
Following the extensive use of phosgene during World War I , it was stockpiled by various countries. [ 27 ] [ 28 ] [ 29 ]
Phosgene was then only infrequently used by the Imperial Japanese Army against the Chinese during the Second Sino-Japanese War . [ 30 ] Gas weapons, such as phosgene, were produced by the IJA's Unit 731 .
Phosgene is an insidious poison as the odor may not be noticed and symptoms may be slow to appear. [ 31 ]
At low concentrations, phosgene may have a pleasant odor of freshly mown hay or green corn, [ 32 ] but has also been described as sweet, like rotten banana peels.
The odor detection threshold for phosgene is 0.4 ppm, four times the threshold limit value (time weighted average). Its high toxicity arises from the action of the phosgene on the −OH , −NH 2 and −SH groups of the proteins in pulmonary alveoli (the site of gas exchange), respectively forming ester, amide and thioester functional groups in accord with the reactions discussed above. This results in disruption of the blood–air barrier , eventually causing pulmonary edema . The extent of damage in the alveoli does not primarily depend on phosgene concentration in the inhaled air, with the dose (amount of inhaled phosgene) being the critical factor. [ 33 ] Dose can be approximately calculated as "concentration" × "duration of exposure". [ 33 ] [ 34 ] Therefore, persons in workplaces where there exists risk of accidental phosgene release usually wear indicator badges close to the nose and mouth. [ 35 ] Such badges indicate the approximate inhaled dose, which allows for immediate treatment if the monitored dose rises above safe limits. [ 35 ]
In case of low or moderate quantities of inhaled phosgene, the exposed person is to be monitored and subjected to precautionary therapy, then released after several hours. For higher doses of inhaled phosgene (above 150 ppm × min) a pulmonary edema often develops which can be detected by X-ray imaging and regressive blood oxygen concentration . Inhalation of such high doses can eventually result in fatality within hours up to 2–3 days of the exposure.
The risk connected to a phosgene inhalation is based not so much on its toxicity (which is much lower in comparison to modern chemical weapons like sarin or tabun ) but rather on its typical effects: the affected person may not develop any symptoms for hours until an edema appears, at which point it could be too late for medical treatment to assist. [ 36 ] Nearly all fatalities as a result of accidental releases from the industrial handling of phosgene occurred in this fashion. On the other hand, pulmonary edemas treated in a timely manner usually heal in the mid- and longterm, without major consequences once some days or weeks after exposure have passed. [ 37 ] [ 38 ] Nonetheless, the detrimental health effects on pulmonary function from untreated, chronic low-level exposure to phosgene should not be ignored; although not exposed to concentrations high enough to immediately cause an edema, many synthetic chemists ( e.g. Leonidas Zervas ) working with the compound were reported to experience chronic respiratory health issues and eventual respiratory failure from continuous low-level exposure.
If accidental release of phosgene occurs in an industrial or laboratory setting, it can be mitigated with ammonia gas; in the case of liquid spills ( e.g. of diphosgene or phosgene solutions) an absorbent and sodium carbonate can be applied. [ 39 ] | https://en.wikipedia.org/wiki/Phosgene |
Phosgene oxime , or CX , is an organic compound with the formula Cl 2 C = N − O H . It is a potent chemical weapon , specifically a nettle agent . The compound itself is a colorless solid, but impure samples are often yellowish liquids. It has a strong, disagreeable and irritating odor. It is used as a reagent in organic chemistry . [ 2 ]
Phosgene oxime can be prepared by reduction of chloropicrin using a combination of tin metal and hydrochloric acid as the source of the active hydrogen reducing agent :
The observation of a transient violet color in the reaction suggests intermediate formation of trichloronitrosomethane (Cl 3 CNO). Early preparations, using stannous chloride as the reductant, also started with chloropicrin. [ 3 ]
The compound is electrophilic and thus sensitive to nucleophiles , including bases , which destroy it:
Phosgene oxime has been used to prepare heterocycles that contain N-O bonds, such as isoxazoles . [ 4 ]
Dehydrohalogenation upon contact with mercuric oxide generates chlorine fulminate , a reactive nitrile oxide : [ 5 ]
Phosgene oxime is classified as a vesicant even though it does not produce blisters. [ 6 ] It is toxic by inhalation, ingestion, or skin contact. The effects of the poisoning occur almost immediately. No antidote for phosgene oxime poisoning is known. Generally, any treatment is supportive. Typical physical symptoms of CX exposure are as follows: | https://en.wikipedia.org/wiki/Phosgene_oxime |
Phoslactomycin ( PLM ) is a natural product from the isolation of Streptomyces species. This is an inhibitor of the protein serine/threonine phosphatase which is the protein phosphate 2A (PP2A). The PP2A involves the growth factor of the cell such as to induce the formation of mitogen-activated protein interaction [ 1 ] and playing a role in cell division and signal transduction. Therefore, PLM is used for the drug that prevents the tumor, cancer, or bacteria. There are nowsaday has 7 kinds of different PLM from PLM A to PLM G which differ the post-synthesis from the biosynthesis of PLM.
Phoslactomycin B ( PLM B ) is the product of the post synthase of the biosynthesis of phoslactomycin and the intermediate to produce the other PLMs. The biosynthesis of phoslactomycin belongs to type I polyketide synthase (PKS). A polyketide is are characterized by a macrocyclic lactone and is produced by bacteria and fungi. From the PLM B, there are many articles wrote about the synthesis of different PLM A through PLM G.
The domains in the polyketide synthase type I: [ 3 ]
The PKS of phoslactomycin has one loading domain, 7 modules and 6 proteins that encode PnA, PnB, PnC, PnD, PnE, and PnF. The biosynthesis starts the loading with the cyclohexyl- CoA. Stepping in each module, there always need the keto synthase (KS) to create the new linkage of carbon-carbon to elongate the chain, the acyl transferase to transfer acyl to ACP domain. Then ACP serves as the acyl carrier protein to the further reaction, and each module has the keto reductase at the end to reduce the ketone to hydroxyl group with more stable. Module 1 uses the precursor malonyl-CoA and dehydrase domain to create the double bond.
Similarly, module 2, module 5, and module 7 have the same 5 domains KS-AT-ACP-DH-KR, but module 7 has one more domain at the end is thioesterase (TE) to create the ring member of the phoslactomycin product. Module 4 and module 6 have 4 domains which are KS-AT-ACP-KR and use the precursor ethylmalonyl-CoA. The final product is phoslactomycin.
Isolation from Streptomyces platensis , PLM is produces. Genes PnT1 and PnT2 regulate the post-synthesis of PLM to form PLM B by the phosphorylation and added the amine group . Figure 4 is based on the biosynthesis analysis on the Gene journal introduced that PLM B is used to produce PLM A, and 4 more PLMs C-F. [ 4 ] The PLM A-F are the post synthesis product of the biosynthesis of PLM with the modification of many enzyme PnT1-T8.
PLMs regulates the actin cytoskeleton as they induce actin depolymerization by the indirect way. In the experiment, PLM F does not affect to the polymerization of purified actin in vitro. [ 5 ] However, PLM F enhances the phosphorylation of intracellular vimentin. | https://en.wikipedia.org/wiki/Phoslactomycin_B |
Phoslock is the commercial name for a bentonite clay in which the sodium and/or calcium ions are exchanged for lanthanum . The lanthanum contained within Phoslock reacts with phosphate to form an inert mineral known as rhabdophane ( LaPO 4 ⋅ n H 2 O {\displaystyle {\ce {LaPO4.{\mathit {n}}H2O}}} ). Phoslock is used in lake restoration projects to remove excess phosphorus from aquatic systems, thereby improving water quality and inducing biological recovery in impaired freshwater systems. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]
It was developed in Australia by the CSIRO in the late 1990s by Dr Grant Douglas (US Patent 6350383) as a way of utilising the ability of lanthanum to bind phosphate in freshwater natural aquatic systems. The first large-scale trial took place in January 2000 in the Canning River , Western Australia. [ 7 ]
During its development, patenting and commercialisation by CSIRO and subsequent commercial production, Phoslock has been a subject in academic research [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] and has been used globally in lake restoration projects. The largest number of whole lake applications and the most comprehensive pre- and post-application monitoring has taken place in Europe, primarily Germany (where it is sold under the tradename Bentophos), the Netherlands and the UK. [ 14 ]
There are studies indicating that lanthanum release due to application of this clay could lead to increased concentrations of this rare element in water and soils, resulting in bioaccumulation in animal tissues [ 15 ] and there are still concerns and precautions to be taken as currently there is not enough complete and independent information. [ 16 ] | https://en.wikipedia.org/wiki/Phoslock |
Phosphaalkenes ( IUPAC name: alkylidenephosphanes ) are organophosphorus compounds with double bonds between carbon and phosphorus(III) with the formula R 2 C=PR. In the compound phosphorine one carbon atom in benzene is replaced by phosphorus. The reactivity of phosphaalkenes is often compared to that of alkenes and not to that of imines because the HOMO of phosphaalkenes is not the phosphorus lone pair (as in imines the amine lone pair) but the double bond. Therefore like alkenes, phosphaalkenes engage in Wittig reactions , Peterson reactions , Cope rearrangements and Diels-Alder reactions .
The first phosphaalkene discovered was a phosphabenzene , by Mërkl in 1969. The first localized phosphaalkene was reported in 1976 by Gerd Becker [ 1 ] as a keto-enol tautomerism akin a Brook rearrangement :
In the same year Harold Kroto established spectroscopically that thermolysis of Me 2 PH generates CH 2 =PMe. A general method for the synthesis of phosphaalkenes is by 1,2-elimination of suitable precursors, initiated thermally or by base such as DBU , DABCO or triethylamine : [ 2 ]
The Becker method is used in the synthesis of the phosphorus pendant of Poly(p-phenylene vinylene) : [ 3 ]
The reduction or oxidation of phosphaalkenes can produce radical phosphorus ions . | https://en.wikipedia.org/wiki/Phosphaalkene |
In chemistry , a phosphaalkyne ( IUPAC name: alkylidynephosphane ) is an organophosphorus compound containing a triple bond between phosphorus and carbon with the general chemical formula R−C≡P . [ 2 ] Phosphaalkynes are the heavier congeners of nitriles , though, due to the similar electronegativities of phosphorus and carbon, possess reactivity patterns reminiscent of alkynes . [ 3 ] Due to their high reactivity, phosphaalkynes are not found naturally on earth, but the simplest phosphaalkyne, phosphaethyne ( H−C≡P ) has been observed in the interstellar medium. [ 4 ]
The first of preparation of a phosphaalkyne was achieved in 1961 when Thurman Gier produced phosphaethyne by passing phosphine gas at low pressure over an electric arc produced between two carbon electrodes. Condensation of the gaseous products in a −196 °C (−321 °F) trap revealed that the reaction had produced acetylene, ethylene, phosphaethyne, which was identified by infrared spectroscopy . [ 5 ]
Following the initial synthesis of phosphaethyne, it was realized that the same compound can be prepared more expeditiously via the flash pyrolysis of methyldichlorophosphine ( CH 3 PCl 2 ), resulting in the loss of two equivalents of hydrogen chloride . This methodology has been utilized to synthesize numerous substituted phosphaalkynes, including the methyl, [ 6 ] vinyl, [ 7 ] chloride, [ 2 ] and fluoride [ 8 ] derivatives. Fluoromethylidynephosphane ( F−C≡P ) can also be prepared via the potassium hydroxide promoted dehydrofluorination of trifluoromethylphosphine ( CF 3 PH 2 ). It is speculated that these reactions generally proceed via an intermediate phosphaethylene with general structure RClC=PH. This hypothesis has found experimental support in the observation of F 2 C=PH by 31 P NMR spectroscopy during the synthesis of F−C≡P . [ 9 ]
The high strength of silicon – halogen bonds can be leveraged toward the synthesis of phosphaalkynes. Heating bis -trimethylsilylated methyldichlorophosphines ( ((CH 3 ) 3 Si) 2 C(R)−PCl 2 ) under vacuum results in the expulsion of two equivalents of chlorotrimethylsilane and the ultimate formation of a new phosphaalkyne. This synthetic strategy has been applied in the synthesis of 2-phenylphosphaacetylene [ 10 ] and 2-trimethylsilylphosphaacetylene. [ 11 ] As in the case of synthetic routes reliant upon the elimination of a hydrogen halide, this route is suspected to involve an intermediate phosphaethylene species containing a C=P double bond, though such a species has not yet been observed. [ 2 ]
Like the preceding method, the most popular method for synthesizing phosphaalkynes is reliant upon the expulsion of products containing strong silicon-element bonds. Specifically, it is possible to synthesize phosphaalkynes via the elimination of hexamethyldisiloxane (HMDSO) from certain silylated phosphaalkenes with the general structure RO−( Me 3 Si)C=P−SiMe 3 . These phosphaalkenes are formed rapidly following the synthesis of the appropriate acyl bis -trimethylsilylphosphine, which undergoes a rapid [1,3]-silyl shift to produce the relevant phosphaalkene. This synthetic strategy is particularly appealing because the precursors (an acyl chloride and tris -trimethylsilylphosphine or bis -trimethylsilylphosphide) are either readily available or simple to synthesize. [ 2 ]
This method has been utilized to produce a variety of kinetically stable phosphaalkynes, including aryl, [ 2 ] [ 12 ] [ 13 ] tertiary alkyl, [ 14 ] secondary alkyl, [ 2 ] and even primary alkyl [ 15 ] phosphaalkynes in good yields.
Dihalophospaalkenes of the general form R−P=CX 2 , where X is Cl, Br, or I, undergo lithium-halogen exchange with organolithium reagents to yield intermediates of the form R−P=CXLi . These species then eject the corresponding lithium halide salt, LiX, to putatively give a phospha-isocyanide, which can rearrange, much in the same way as an isocyanide, [ 16 ] to yield the corresponding phosphaalkyne. [ 17 ] This rearrangement has been evaluated using the tools of computational chemistry , which has shown that this isomerization process should proceed very rapidly, in line with current experimental evidence showing that phosphaisonitriles are unobservable intermediates, even at −85 °C (−121 °C). [ 18 ]
It has been demonstrated by Cummins and coworkers that thermolysis of compounds of the general form C 14 H 10 PC(=P Ph 3 )R leads to the extrusion of C 14 H 10 (anthracene), triphenylphosphine, and the corresponding substituted phosphaacetylene: R−C≡P . Unlike the previous method, which derives the phosphaalkyne substituent from an acyl chloride , this method derives the substituent from a Wittig reagent . [ 19 ]
The carbon-phosphorus triple bond in phosphaalkynes represents an exception to the so-called " double bond rule ", which would suggest that phosphorus tends not to form multiple bonds to carbon, and the nature of bonding within phosphaalkynes has therefore attracted much interest from synthetic and theoretical chemists. For simple phosphaalkynes such as H−C≡P and Me−C≡P , the carbon-phosphorus bond length is known by microwave spectroscopy , and for certain more complex phosphaalkynes, these bond lengths are known from single-crystal X-ray diffraction experiments. These bond lengths can be compared to the theoretical bond length for a carbon-phosphorus triple bond predicted by Pekka Pyykkö of 1.54 Å. [ 20 ] By bond length metrics, most structurally characterized alkyl and aryl substituted phosphaalkynes contain triple bonds between carbon and phosphorus, as their bond lengths are either equal to or less than the theoretical bond distance.
The carbon-phosphorus bond order in phosphaalkynes has also been the subject of computational inquiry, where quantum chemical calculations have been utilized to determine the nature of bonding in these molecules from first principles. In this context, natural bond orbital (NBO) theory has provided valuable insight into the bonding within these molecules. Lucas and coworkers have investigated the electronic structure of various substituted phosphaalkynes, including the cyaphide anion ( − C≡P ), using NBO, natural resonance theory (NRT), and quantum theory of atoms in molecules (QTAIM) in an attempt to better describe the bonding in these molecules. For the simplest systems, − C≡P and H−C≡P , NBO analysis suggests that the only relevant resonance structure is that in which there is a triple bond between carbon and phosphorus. For more complex molecules, such as Me−C≡P and Me 3 C−C≡P , the triple bonded resonance structure is still the most relevant, but accounts for only some of the overall electron density within the molecule (81.5% and 72.1%, respectively). This is due to interactions between the two carbon-phosphorus pi-bonds and the C-H or C-C sigma-bonds of the substituents, which can be visualized by inspecting the C-P pi-bonding molecular orbitals in these molecules. [ 24 ]
Phosphaalkynes possess diverse reactivity profiles, and can be utilized in the synthesis of various phosphorus-containing saturated of unsaturated heterocyclic compounds .
One of the most developed areas of phosphaalkyne chemistry is that of cycloadditions . Like other multiply bonded molecular fragments, phosphaalkynes undergo myriad reactions such as [1+2] cycloadditions, [ 26 ] [ 27 ] [ 28 ] [3+2] cycloadditions, [ 29 ] [ 30 ] and [4+2] cycloadditions. [ 2 ] [ 31 ] This reactivity is summarized in graphical format below, which includes some examples of 1,2-addition reactivity [ 32 ] [ 33 ] (which is not a form of cycloaddition).
The pi-bonds of phosphaalkynes are weaker than most carbon-phosphorus sigma bonds, rendering phosphaalkynes reactive with respect to the formation of oligomeric species containing more sigma bonds. These oligomerization reactions are triggered thermally, or can be catalyzed by transition or main-group metals .
Phosphaalkynes with small substituents ( H , F , Me , Ph , etc.) undergo decomposition at or below room temperature by way of polymerization/oligimerization to yield mixtures of products which are challenging to characterize. The same is largely true of kinetically stable phosphaalkynes, which undergo oligomerization reactions at elevated temperature. [ 35 ] In spite of the challenges associated with isolating and identifying the products of these oligimerizations, however, cuboidal tetramers of tert -butylphosphaalkyne and tert -pentylphosphaalkyne have been isolated (albeit in low yield) and identified following heating of the respective phosphaalkyne. [ 36 ]
Computational chemistry has proved a valuable tool for studying these synthetically complex reactions, and it has been shown that while the formation of phosphaalkyne dimers is thermodynamically favorable, the formation of trimers, tetramers, and higher order oligomeric species tends to be more favorable, accounting for the generation of intractable mixtures upon inducing oligomerization of phosphaalkynes experimentally. [ 37 ] [ 38 ]
Unlike thermally initiated phosphaalkyne oligomerization reactions, transition metals and main group metals are capable of oligomerizing phosphaalkynes in a controlled manner, and have led to the isolation of phosphaalkyne dimers, trimers, tetramers, pentamers, and even hexamers. [ 35 ] A nickel complex is capable of catalytically homocoupling t Bu-C≡P to yield a diphosphatetrahedrane. [ 39 ] | https://en.wikipedia.org/wiki/Phosphaalkyne |
The phosphaethynolate anion , also referred to as PCO , is the phosphorus-containing analogue of the cyanate anion with the chemical formula [PCO] − or [OCP] − . [ 1 ] The anion has a linear geometry and is commonly isolated as a salt. When used as a ligand, the phosphaethynolate anion is ambidentate in nature meaning it forms complexes by coordinating via either the phosphorus or oxygen atoms. [ 1 ] [ 2 ] [ 3 ] This versatile character of the anion has allowed it to be incorporated into many transition metal and actinide complexes but now the focus of the research around phosphaethynolate has turned to utilising the anion as a synthetic building block to organophosphanes. [ 3 ] [ 4 ]
The first reported synthesis and characterisation of phosphaethynolate came from Becker et al. in 1992. [ 5 ] They were able to isolate the anion as a lithium salt (in 87% yield) by reacting lithium bis(trimethylsilyl)phosphide with dimethyl carbonate ( see Scheme 1 ). [ 5 ] [ 6 ] The x-ray crystallographic analysis of the anion determined the P-C bond length to be 1.555 Å (indicative of a phosphorus-carbon triple bond) and the C-O bond length to be 1.198 Å . [ 7 ] Similar studies were performed on derivatives of this structure and the results indicated that dimerisation to form a four-membered Li ring is favoured by this molecule. [ 5 ]
Ten years later, in 2002, Westerhausen et al. published the use of Becker's method to make a family of alkaline earth metal salts of PCO ( see Scheme 2 ); this work involved the synthesis of the magnesium , calcium , strontium and barium bis-phosphaethynolates. [ 5 ] [ 8 ] Like the salts previously reported by Becker, the alkali-earth metal analogues were unstable to moisture and air and thus were required to be stored at low temperatures (around −20 °C ) in dimethoxyethane solutions. [ 5 ] [ 6 ] [ 8 ]
It was not until 2011 that the first stable salt of the phosphaethynolate anion was reported by Grutzmacher and co-workers ( see Scheme 3 ). [ 9 ] They managed to isolate the compound as a brown solid in 28% yield. [ 9 ] The structure of the stable sodium salt, formed by carbonylation of sodium phosphide, contains bridging PCO units in contrast to the terminal anions found in the previously reported structures. [ 9 ] The authors noted that this sodium salt could be handled in air as well as water without major decomposition; this emphasises the significance of the accompanying counter cation in stabilisation of PCO. [ 6 ] [ 9 ]
Direct carbonylation was a method also employed by Goicoechea in 2013 in order to synthesis a phosphaethynolate anion stabilised by a potassium cation sequestered in 18-crown-6 ( see Scheme 4 ). [ 10 ] This method required the carbonylation of solutions of K 3 P 7 at 150 °C and produced by-products that were readily separated during aqueous work ups. The use of aqueous work ups reflects the high stability of the salt in water. [ 6 ] [ 10 ] This method afforded the PCO anion in reasonable yields around 43%. Characterisation of the compound involved infra-red spectroscopy ; the band indicative of the P≡C triple bond stretch was observed at 1730 cm−1 . [ 10 ]
The phosphaethynolate anion is the heavier isoelectronic congener of the cyanate anion. It has been shown that it behaves in a similar way to its lighter analogue, as an ambidentate nucleophile. [ 3 ] This ambidentate character of the anion means that it is able to bind via both the phosphorus and oxygen atoms depending on the nature of the centre being coordinated. [ 3 ]
Computational studies carried out on the anion such as Natural Bond Orbital (NBO) and Natural Resonance Theory (NRT) analyses can go part way to explain why PCO can react in such a manner ( Figure 1 ) . [ 11 ] The two dominant resonance forms of the phosphaethynolate anion localise negative charge on either the phosphorus or oxygen atoms meaning both are sites of nucleophilicity . [ 11 ] The same applies for the cyanate anion hence why PCO is observed to have similar pseudo-halogenic behaviour. [ 3 ] [ 12 ]
Coordination via the oxygen atom is favoured by hard , highly electropositive centres. [ 6 ] This is due to the fact that oxygen is a more electronegative atom and thus prefers to bind via more ionic interactions. [ 6 ] Examples of this type of coordination were presented in the work of Arnold et al. from 2015. [ 2 ] The group found that actinide complexes of PCO involving uranium and thorium both coordinated through the oxygen. This is the result of the contracted nature of the actinide orbitals which makes the metal centres more 'core-like' thus favouring ionic interactions. [ 2 ]
On the other hand, softer, more polarisable centres prefer to coordinate in a more covalent manner through the phosphorus atom. [ 6 ] Examples of this include complexes accommodating a neutral or sparsely charged transition metal centre. [ 12 ] [ 13 ] The first example of this nature of PCO binding was published by Grutzmacher and co-workers in 2012. [ 12 ] The group's studies used a Re(I) complex and the analysis of its bonding parameters and electronic structure showed that the phosphaethynolate anion coordinated in a bent fashion. [ 12 ] This suggested the Re(I) – P bond possessed a highly covalent character thus the complex would be best described as a metallaphosphaketene. [ 12 ] It wasn't until four years later that a second example of this coordination nature of PCO was identified. This time it came in the form of a W(0) pentacarbonyl complex produced by the Goicoechea group. [ 13 ]
There is one particular reaction studied by Grutzmacher et al. that exhibits the rearrangement of coordination character of PCO. [ 3 ] Initially when reacting the anion with triorganyl silicon compounds, it binds via the oxygen forming the kinetic oxyphosphaalkyne product. [ 3 ] The thermodynamic silyl phosphaketene product is generated when the kinetic product rearranges to allow PCO to coordinate through phosphorus. [ 3 ]
The formation of the kinetic product is charged controlled and thus explains why it is formed by oxygen coordination. [ 3 ] The oxygen atom favours a larger degree of ionic interactions as a result of its greater electronegativity . Contrastingly, the thermodynamic product of the reaction is generated under orbital control. [ 3 ] This comes in the form of phosphorus coordination as the largest contribution in the HOMO of the anion resides on the phosphorus atom; this is clearly visible in Figure 3 . [ 3 ] [ 11 ] [ 14 ]
Extensive studies involving the phosphaethynolate anion have shown that it can react in a variety of ways. It has documented use in cycloadditions, as a phosphorus transfer agent, a synthetic building block and as pseudo halide ligands ( as described above ).
In these types of reactions, CO is released as the phosphaethynolate anion acts as either a mild nucleophilic source of phosphorus or a Brønsted base . Examples of these types of reactions involving PCO include work conducted by Grutzmacher and Goicoechea. [ 15 ] [ 16 ]
In 2014, Grutzmacher et al. reported that an imidazolium salt would react with the phosphaethynolate anion to produce a phosphinidine carbene adduct. [ 1 ] [ 15 ] Computational mechanistic studies were conducted on this reaction using density functional theory at the B3LYP/6-31+G* level. [ 15 ] The results of these investigations suggested that the lowest energy and therefore most likely pathway involves PCO acting as a Brønsted base initially deprotonating the acidic imidazolium cation to generate the intermediate phosphaketene, HPCO. [ 1 ] [ 15 ] [ 17 ] The highly unstable protonated PCO remains hydrogen bonded to the newly produced N-heterocylic carbene prior to rearrangement and formation of the observed product. [ 6 ] [ 15 ] In this case, PCO does not act as a mild nucleophile due to the augmented stability of the starting imidazolium cation. [ 15 ]
On the other hand, in the work published by Goicoechea and co-workers in 2015, the phosphaethynolate anion can be seen to act as a source of nucleophilic phosphide ( P − ). [ 16 ] The anion was seen to add across the Si=Si double bond of cyclotrisilene thus introducing a phosphorus vertex into its scaffold (after undergoing decarbonylation). [ 16 ]
After synthesising the potassium salt of the phosphaethynolate anion in 2013, Goicoechea et al. began to look into the potential of PCO towards cycloadditions . [ 10 ] They found that the anion could react in a [2+2] fashion with a diphenyl ketene to produce the first isolatable example of a four-membered monoanionic phosphorus containing heterocycle . [ 1 ] [ 10 ] They employed the same method to test other unsaturated substrates such as carbodiimides and found that the likelihood of cyclisation heavily relies on the nature of the substituents on the unsaturated substrate. [ 10 ]
Cycloaddition reactions involving the phosphaethynolate anion have also been shown by Grutzmacher and co-workers to be a viable synthetic route to other heterocycles. [ 18 ] One simple example is the reaction between the NaPCO and an α-pyrone . This reaction yields the sodium phosphinin-2-olate salt which is stable to both air and moisture. [ 1 ] [ 18 ]
A large part of the research involving PCO is now looking into utilising the anion as a synthetic building block to derive phosphorus containing analogues of small molecules.
The first major breakthrough in this area came from Goicoechea et al. in 2013; they published the reaction between the PCO anion and ammonium salts which yielded the phosphorus containing analogue of urea in which phosphorus replaces a nitrogen atom. [ 4 ] The group predict that this heavier congener could have applications in new materials, anion sensing and coordination chemistry. [ 4 ]
Goicoechea and co-workers were also able to isolate the heavily sought after phosphorus containing analogue of isocyanic acid , HPCO, in 2017. [ 17 ] This molecule is thought to be a crucial intermediate in a lot of reactions involving PCO (including P-transfer to an imidazolium cation). [ 6 ] [ 17 ]
Moreover, the most recent addition to this class of small molecules is the phosphorus containing analogue of N,N-dimethylformamide . [ 19 ] This work in which the phosphorus again replaces a nitrogen atom was published in 2018 by Stephan and co-workers. [ 19 ] Generating acylphosphines in this manner is considered a much milder route than other current strategies that require multi-step syntheses involving toxic , volatile and pyrophoric reagents. [ 19 ]
The other analogues of the phosphaethynolate anion all obey the general formulae E-C-X and are made by varying E and X. When changing either atom, unique trends amongst the different analogues become apparent.
As 'E' is varied by descending group 15, there is a clear shift in the weights of the resonance structures towards the phosphaketene analogue ( Figure 5 ) . [ 11 ] This reflects the decrease in effective orbital overlap between E and C which in turn disfavours multiple bond formation. This increasing tendency to form double and not triple E-C bonds is also reflected in calculated E-C bond lengths ( Table 1 ) . [ 14 ] The data from Table 1 is evidence of E-C bond elongation which correlates with the change from triple to double bond. [ 7 ]
In addition, NBO analysis highlights that the greatest electron delocalisation within the anions stems from the donation of an oxygen lone pair into the E−C π antibonding orbital. The energy value associated with this donation is seen to increase down the group ( Table 1 ) . This explains the increasing resonance weight towards the ketene like isomer as populating antibonding orbitals usually suggests the breaking of a bond. [ 11 ]
The shift towards the ketene isomer will also cause an increase in charge density on the elemental 'E' atom; this makes the elemental atom an increasing source of nucleophilicity ( see Figure 5 and Figure 6 ). [ 11 ]
The simplest analogue that can be formed as 'X' is varied is PCS − . This anion was first isolated by Becker et al. by reacting the phosphaethynolate anion with carbon disulphide. [ 20 ] Unlike PCO, PCS shows ambidentate nucleophilic tendencies towards the W(0) complex mentioned above. [ 11 ]
This is the result of a reduced difference in electronegativity between E and X thus neither atom offers a substantial advantage over the other in terms of providing ionic contributions to bonding. As a result, the average electron density in PCS is spread over the entire anion ( Figure 8 ) whereas in PCO, most electron density is localised on the phosphorus atom ( Figure 7 ) as this is the atom which bonds to form the thermodynamically favourable product. [ 11 ] | https://en.wikipedia.org/wiki/Phosphaethynolate |
Phosphagens , also known as macroergic compounds, are high energy storage compounds, also known as high-energy phosphate compounds, chiefly found in muscular tissue in animals . They allow a high-energy phosphate pool to be maintained in a concentration range, which, if it all were adenosine triphosphate (ATP), would create problems due to the ATP-consuming reactions in these tissues. As muscle tissues can have sudden demands for much energy, these compounds can maintain a reserve of high-energy phosphates that can be used as needed, to provide the energy that could not be immediately supplied by glycolysis or oxidative phosphorylation . Phosphagens supply immediate but limited energy.
The actual biomolecule used as a phosphagen is dependent on the organism. The majority of animals use arginine as phosphagen; however, the phylum Chordata (i.e., animals with spinal cords) use creatine . Creatine phosphate (CP), or phosphocreatine (PCr), is made from ATP by the enzyme creatine kinase in a reversible reaction:
However, annelids (segmented worms) use a set of unique phosphagens; for example, earthworms use the compound lombricine .
Phosphagens were discovered by Philip Eggleton and his wife Grace Eggleton. [ 1 ]
The Phosphagen System ( ATP-PCr ) occurs in the cytosol (a gel-like substance) of the sarcoplasm of skeletal muscle , and in the myocyte 's cytosolic compartment of the cytoplasm of cardiac and smooth muscle . [ 2 ]
During muscle contraction:
Muscle at rest:
When the Phosphagen System has been depleted of phosphocreatine (creatine phosphate), the resulting AMP produced from the adenylate kinase (myokinase) reaction is primarily regulated by the Purine Nucleotide Cycle . [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Phosphagen |
Phosphates are the naturally occurring form of the element phosphorus . [ 2 ]
In chemistry , a phosphate is an anion , salt , functional group or ester derived from a phosphoric acid . It most commonly means orthophosphate , a derivative of orthophosphoric acid, a.k.a. phosphoric acid H 3 PO 4 .
The phosphate or orthophosphate ion [PO 4 ] 3− is derived from phosphoric acid by the removal of three protons H + . Removal of one proton gives the dihydrogen phosphate ion [H 2 PO 4 ] − while removal of two protons gives the hydrogen phosphate ion [HPO 4 ] 2− . These names are also used for salts of those anions, such as ammonium dihydrogen phosphate and trisodium phosphate .
In organic chemistry , phosphate or orthophosphate is an organophosphate , an ester of orthophosphoric acid of the form PO 4 RR′R″ where one or more hydrogen atoms are replaced by organic groups. An example is trimethyl phosphate , (CH 3 ) 3 PO 4 . The term also refers to the trivalent functional group OP(O − ) 3 in such esters. Phosphates may contain sulfur in place of one or more oxygen atoms ( thiophosphates and organothiophosphates ).
Orthophosphates are especially important among the various phosphates because of their key roles in biochemistry , biogeochemistry , and ecology , and their economic importance for agriculture and industry. [ 2 ] The addition and removal of phosphate groups ( phosphorylation and dephosphorylation ) are key steps in cell metabolism .
Orthophosphates can condense to form pyrophosphates .
The phosphate ion has a molar mass of 94.97 g/mol, and consists of a central phosphorus atom surrounded by four oxygen atoms in a tetrahedral arrangement. It is the conjugate base of the hydrogen phosphate ion [HPO 4 ] 2− , which in turn is the conjugate base of the dihydrogen phosphate ion [H 2 PO 4 ] − , which in turn is the conjugate base of orthophosphoric acid , H 3 PO 4 .
Many phosphates are soluble in water at standard temperature and pressure . The sodium, potassium, rubidium , caesium , and ammonium phosphates are all water-soluble. Most other phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates.
In water solution, orthophosphoric acid and its three derived anions coexist according to the dissociation and recombination equilibria below [ 3 ]
Values are at 25 °C and 0 ionic strength.
The p K a values are the pH values where the concentration of each species is equal to that of its conjugate bases . At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two p K a values) the dihydrogen phosphate ion, [H 2 PO 4 ] − , is practically the only species present. Around pH 9.8 (mid-way between the second and third p K a values) the monohydrogen phosphate ion, [HPO 4 ] 2− , is the only species present. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, [PO 4 ] 3− .
This means that salts of the mono- and di-phosphate ions can be selectively crystallised from aqueous solution by setting the pH value to either 4.7 or 9.8.
In effect, H 3 PO 4 , [H 2 PO 4 ] − and [HPO 4 ] 2− behave as separate weak acids because the successive p K a differ by more than 4.
Phosphate can form many polymeric ions such as pyrophosphate , [P 2 O 7 ] 4− , and triphosphate , [P 3 O 10 ] 5− . The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of [PO 3 ] − and are found in many compounds.
In biological systems , phosphorus can be found as free phosphate anions in solution ( inorganic phosphate ) or bound to organic molecules as various organophosphates . [ 5 ]
Inorganic phosphate is generally denoted P i and at physiological ( homeostatic ) pH primarily consists of a mixture of [HPO 4 ] 2− and [H 2 PO 4 ] − ions. At a neutral pH, as in the cytosol (pH = 7.0), the concentrations of the orthophoshoric acid and its three anions have the ratios [ H 2 PO 4 − ] [ H 3 PO 4 ] ≈ 7.5 × 10 4 [ HPO 4 2 − ] [ H 2 PO 4 − ] ≈ 0.62 [ PO 4 3 − ] [ HPO 4 2 − ] ≈ 2.14 × 10 − 6 {\displaystyle {\begin{aligned}{\frac {[{\ce {H2PO4-}}]}{[{\ce {H3PO4}}]}}&\approx 7.5\times 10^{4}\\[4pt]{\frac {[{\ce {HPO4^2-}}]}{[{\ce {H2PO4-}}]}}&\approx 0.62\\[4pt]{\frac {[{\ce {PO4^3-}}]}{[{\ce {HPO4^2-}}]}}&\approx 2.14\times 10^{-6}\end{aligned}}}
Thus, only the [H 2 PO 4 ] − and [HPO 4 ] 2− ions are present in significant amounts in the cytosol (62% [H 2 PO 4 ] − , 38% [HPO 4 ] 2− ). In extracellular fluid (pH = 7.4), this proportion is inverted (61% [HPO 4 ] 2− , 39% [H 2 PO 4 ] − ).
Inorganic phosphate can also be present as pyrophosphate anions [P 2 O 7 ] 4− , which give orthophosphate by hydrolysis :
Organic phosphates are commonly found in the form of esters as nucleotides (e.g. AMP , ADP , and ATP ) and in DNA and RNA . Free orthophosphate anions can be released by the hydrolysis of the phosphoanhydride bonds in ATP or ADP. These phosphorylation and dephosphorylation reactions are the immediate storage and source of energy for many metabolic processes. ATP and ADP are often referred to as high-energy phosphates , as are the phosphagens in muscle tissue. Similar reactions exist for the other nucleoside diphosphates and triphosphates .
An important occurrence of phosphates in biological systems is as the structural material of bone and teeth. These structures are made of crystalline calcium phosphate in the form of hydroxyapatite . The hard dense enamel of mammalian teeth may contain fluoroapatite , a hydroxy calcium phosphate where some of the hydroxyl groups have been replaced by fluoride ions.
Phosphates are medicinal salts of phosphorus. Some phosphates, which help cure many urinary tract infections , are used to make urine more acidic. To avoid the development of calcium stones in the urinary tract, some phosphates are used. [ 6 ] For patients who are unable to get enough phosphorus in their daily diet, phosphates are used as dietary supplements, usually because of certain disorders or diseases. [ 6 ] Injectable phosphates can only be handled by qualified health care providers. [ 6 ]
Plants take up phosphorus through several pathways: the arbuscular mycorrhizal pathway and the direct uptake pathway.
Hyperphosphatemia , or a high blood level of phosphates, is associated with elevated mortality in the general population. The most common cause of hyperphosphatemia in people, dogs, and cats is kidney failure. In cases of hyperphosphatemia, limiting consumption of phosphate-rich foods, such as some meats and dairy items and foods with a high phosphate-to-protein ratio, such as soft drinks, fast food, processed foods, condiments, and other products containing phosphate-salt additives is advised. [ 7 ]
Phosphates induce vascular calcification , and a high concentration of phosphates in blood was found to be a predictor of cardiovascular events . [ 8 ]
Phosphates are the naturally occurring form of the element phosphorus , found in many phosphate minerals . In mineralogy and geology, phosphate refers to a rock or ore containing phosphate ions. Inorganic phosphates are mined to obtain phosphorus for use in agriculture and industry. [ 2 ]
The largest global producer and exporter of phosphates is Morocco . Within North America, the largest deposits lie in the Bone Valley region of central Florida , the Soda Springs region of southeastern Idaho , and the coast of North Carolina . Smaller deposits are located in Montana , Tennessee , Georgia , and South Carolina . The small island nation of Nauru and its neighbor Banaba Island , which used to have massive phosphate deposits of the best quality, have been mined excessively. Rock phosphate can also be found in Egypt, Israel, Palestine, Western Sahara, Navassa Island , Tunisia, Togo, and Jordan, countries that have large phosphate-mining industries.
Phosphorite mines are primarily found in:
In 2007, at the current rate of consumption, the supply of phosphorus was estimated to run out in 345 years. [ 9 ] However, some scientists thought that a " peak phosphorus " would occur in 30 years and Dana Cordell from Institute for Sustainable Futures said that at "current rates, reserves will be depleted in the next 50 to 100 years". [ 10 ] Reserves refer to the amount assumed recoverable at current market prices. In 2012 the USGS estimated world reserves at 71 billion tons, while 0.19 billion tons were mined globally in 2011. [ 11 ] Phosphorus comprises 0.1% by mass of the average rock [ 12 ] (while, for perspective, its typical concentration in vegetation is 0.03% to 0.2%), [ 13 ] and consequently there are quadrillions of tons of phosphorus in Earth's 3×10 19 -ton crust, [ 14 ] albeit at predominantly lower concentration than the deposits counted as reserves, which are inventoried and cheaper to extract. If it is assumed that the phosphate minerals in phosphate rock are mainly hydroxyapatite and fluoroapatite, phosphate minerals contain roughly 18.5% phosphorus by weight. If phosphate rock contains around 20% of these minerals, the average phosphate rock has roughly 3.7% phosphorus by weight.
Some phosphate rock deposits, such as Mulberry in Florida, [ 15 ] are notable for their inclusion of significant quantities of radioactive uranium isotopes. This is a concern because radioactivity can be released into surface waters [ 16 ] from application of the resulting phosphate fertilizer .
In December 2012, Cominco Resources announced an updated JORC compliant resource of their Hinda project in Congo-Brazzaville of 531 million tons, making it the largest measured and indicated phosphate deposit in the world. [ 17 ]
Around 2018, Norway discovered phosphate deposits almost equal to those in the rest of Earth combined. [ 18 ] [ 19 ]
In July 2022 China announced quotas on phosphate exportation. [ 20 ]
The largest importers in millions of metric tons of phosphate are Brazil 3.2, India 2.9 and the USA 1.6. [ 21 ]
The three principal phosphate producer countries (China, Morocco and the United States) account for about 70% of world production.
In ecological terms, because of its important role in biological systems, phosphate is a highly sought after resource. Once used, it is often a limiting nutrient in environments , and its availability may govern the rate of growth of organisms. This is generally true of freshwater environments, whereas nitrogen is more often the limiting nutrient in marine (seawater) environments. Addition of high levels of phosphate to environments and to micro-environments in which it is typically rare can have significant ecological consequences. For example, blooms in the populations of some organisms at the expense of others, and the collapse of populations deprived of resources such as oxygen (see eutrophication ) can occur. In the context of pollution, phosphates are one component of total dissolved solids , a major indicator of water quality, but not all phosphorus is in a molecular form that algae can break down and consume. [ 23 ]
Calcium hydroxyapatite and calcite precipitates can be found around bacteria in alluvial topsoil. [ 24 ] As clay minerals promote biomineralization, the presence of bacteria and clay minerals resulted in calcium hydroxyapatite and calcite precipitates. [ 24 ]
Phosphate deposits can contain significant amounts of naturally occurring heavy metals. Mining operations processing phosphate rock can leave tailings piles containing elevated levels of cadmium , lead , nickel , copper , chromium , and uranium . Unless carefully managed, these waste products can leach heavy metals into groundwater or nearby estuaries. Uptake of these substances by plants and marine life can lead to concentration of toxic heavy metals in food products. [ 25 ] | https://en.wikipedia.org/wiki/Phosphate |
Phosphate-buffered saline ( PBS ) is a buffer solution (pH ~ 7.4) commonly used in biological research . It is a water-based salt solution containing disodium hydrogen phosphate , sodium chloride and, in some formulations, potassium chloride and potassium dihydrogen phosphate . The buffer helps to maintain a constant pH. The osmolarity and ion concentrations of the solutions are isotonic , meaning they match those of the human body.
PBS has many uses because it is isotonic and non-toxic to most cells. These uses include substance dilution and cell container rinsing. PBS with EDTA is also used to disengage attached and clumped cells. Divalent metals such as zinc , however, cannot be added as this will result in precipitation. For these types of applications, Good's buffers are recommended. PBS has been shown to be an acceptable alternative to viral transport medium regarding transport and storage of RNA viruses, such as SARS-CoV-2. [ 1 ]
There are many different ways to prepare PBS solutions, common ones are Dulbecco's phosphate-buffered saline (DPBS) [ 2 ] and the Cold Spring Harbor protocol. [ 3 ] Some formulations of DPBS do not contain potassium and magnesium, while other ones contain calcium and/or magnesium (depending on whether or not the buffer is used on live or fixed tissue: the latter does not require CaCl 2 or MgCl 2 ). [ citation needed ]
Start with 800 mL of distilled water to dissolve all salts. Add distilled water to a total volume of 1 liter. The resultant 1× PBS will have a final concentration of 157 mM Na + , 140mM Cl − , 4.45mM K + , 10.1 mM HPO 4 2− , 1.76 mM H 2 PO 4 − and a pH of 7.96. Add 2.84 mM of HCl to shift the buffer to 7.3 mM HPO 4 2− and 4.6 mM H 2 PO 4 − for a final pH of 7.4 and a Cl − concentration of 142 mM. [ citation needed ]
The pH of PBS is ~7.4. When making buffer solutions, it is good practice to always measure the pH directly using a pH meter. If necessary, pH can be adjusted using hydrochloric acid or sodium hydroxide. [ citation needed ]
PBS can also be prepared by using commercially made PBS buffer tablets or pouches. [ 4 ]
If used in cell culturing, the solution can be dispensed into aliquots and sterilized by autoclaving or filtration . Sterilization may not be necessary depending on its use. PBS can be stored at room temperature or in the refrigerator. However, concentrated stock solutions may precipitate when cooled and should be kept at room temperature until precipitate has completely dissolved before use. [ citation needed ]
The Henderson–Hasselbalch equation gives the pH of a solution relative to the p K a of the acid–base pair. However the p K a is dependent on ionic strength and temperature, and as it shifts so will the pH of a solution based on that acid–base pair. Because the doubly charged [HPO 4 ] 2− is stabilized more by high ionic strength than is the singly-charged [H 2 PO 4 ] − , their p K a is somewhat dependent on ionic strength. The often-cited p K a of ~7.2 is the value extrapolated to zero ionic strength, and is not applicable at physiological ionic strength. [ citation needed ]
Phillips et al. [ 5 ] measured the p K a at 10, 25, and 37 °C at various ionic strengths. For the latter two temperatures they report p K a in Debye-Hückel equations (plotted in the accompanying figure for μ up to 0.5 M): [ citation needed ] at 25 °C: pKa 2 = 7.18 − 1.52 sqrt(μ) + 1.96 μ at 37 °C: pKa 2 = 7.15 − 1.56 sqrt(μ) + 1.22 μ
The p K a 0 is weakly dependent on temperature. Phillips et al. reported ∆H 0 at 25 °C of 760 cal/mol (3180 J/mol) and a linear dependence of p K a 0 on 1/ T ( Van 't Hoff equation ). The positive ∆H 0 results in an increase in K a , and thus a decrease in p K a 0 with rising temperature, the change in pKa 0 being 166 × the change in (1/ T ), which around 25 °C results in a change in p K a 0 of −0.00187 per degree. This applies strictly to the extrapolated thermodynamic p K a 0 at infinite dilution, and as the figure shows, the temperature effect can be much larger at higher ionic strength. [ citation needed ] | https://en.wikipedia.org/wiki/Phosphate-buffered_saline |
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron , zinc , or manganese phosphates to improve corrosion resistance or lubrication or as a foundation for subsequent coatings or painting. [ 1 ] [ 2 ] [ 3 ] It is one of the most common types of conversion coating . The process is also called phosphate coating , phosphatization , [ 4 ] phosphatizing , or phosphating . It is also known by the trade name Parkerizing , especially when applied to firearms and other military equipment . [ 5 ] : 393
A phosphate coating is usually obtained by applying to the steel part a dilute solution of phosphoric acid , possibly with soluble iron, zinc, and/or manganese salts. The solution may be applied by sponging, spraying, or immersion. [ 6 ] Phosphate conversion coatings can also be used on aluminium , zinc , cadmium , silver and tin . [ 7 ] [ 8 ]
The phosphatizing of firearms was discovered around 1910, when it was found that the surface of steel if changed to a phosphate acquires significant corrosion resistance. [ 5 ] : 393 Until the 1940s it was very popular in the USA until more modern but similar methods of metal finishes were introduced. [ 5 ] : 393
The main types of phosphate coatings are manganese, iron, and zinc. [ 9 ]
The process takes advantage of the low solubility of phosphates at medium or high pH . The bath is a solution of phosphoric acid ( H 3 PO 4 ), containing the desired iron, zinc or manganese cations and other additives. [ 10 ] The acid reacts with the iron metal producing hydrogen and iron cations:
The reaction consuming protons raises the pH of the solution in the immediate vicinity of the surface, until eventually the phosphates become insoluble and get deposited over it. The acid and metal reaction also creates iron phosphate locally which may also be deposited. When depositing zinc phosphate or manganese phosphate the additional iron phosphate may be an undesired impurity.
The bath often includes an oxidizer, such as sodium nitrite ( NaNO 2 ), to consume the hydrogen gas ( H 2 ) — which otherwise would form a layer of tiny bubbles over the surface, slowing down the reaction. [ 10 ]
The main phosphating step can be preceded by an "activation" bath that creates tiny particles of titanium compounds on the surface. [ 10 ]
The performance of a phosphate coating depends on its crystal structure as well as its thickness. A dense microcrystalline structure with a low porosity is usually best for corrosion resistance or subsequent painting. A coarse grain structure impregnated with oil may be best for wear resistance. These factors can be controlled by varying the bath concentration, composition, temperature, and time. [ 6 ]
Parkerizing is a method of protecting a steel surface from corrosion and increasing its resistance to wear through the application of a chemical phosphate conversion coating. It was usually applied to firearms. [ 5 ] : 393 Parkerizing is usually considered to be an improved zinc or manganese phosphating process, and not to be an improved iron phosphating process, although some use the term parkerizing as a generic term for applying phosphating (or phosphatizing) coatings that do include the iron phosphating process.
Bonderizing , phosphating , and phosphatizing are other terms associated with the Parkerizing process but were often used for finishes of car parts as it gave finer grain on the surface. [ 5 ] : 394 It has also been known as pickling in the context of wrought iron and steel . [ 11 ]
Parkerizing is commonly used on firearms as a more effective alternative to bluing , which is an earlier-developed chemical conversion coating . It is also used extensively on automobiles to protect unfinished metal parts from corrosion.
The Parkerizing process cannot be used to protect non-ferrous metals such as aluminium , brass , or copper but can be used for chemical polishing or etching instead. It similarly cannot be applied to steels containing a large amount of nickel , or on stainless steel . Passivation can be used for protecting other metals.
Development of the process was started in England and continued by the Parker family in the United States . The terms Parkerizing , Parkerize , and Parkerized are all registered U.S. trademarks of Henkel Adhesives Technologies , although the terminology has largely passed into generic use for many years. The process was first used on a large scale in the manufacture of firearms for the United States military during World War II . [ 12 ]
The earliest work on phosphating processes was developed by British inventors William Alexander Ross, British patent 3119, in 1869, and by Thomas Watts Coslett, British patent 8667, in 1906. Coslett, of Birmingham, England , subsequently filed a patent based on this same process in America in 1907, which was granted U.S. patent 870,937 in 1907. It essentially provided an iron phosphating process, using phosphoric acid .
An improved patent application for manganese phosphating based in large part on this early British iron phosphating process was filed in the US in 1912, and issued in 1913 to Frank Rupert Granville Richards as U.S. patent 1,069,903 .
Clark W. Parker acquired the rights to Coslett's and Richards' U.S. patents, and experimented in the family kitchen with these and other rust-resisting formulations. The ultimate result was that Parker, along with his son Wyman C. Parker, working together, set up the Parker Rust-Proof Phosphating Company of America in 1915.
R. D. Colquhoun of the Parker Rust-Proof Phosphating Company of America then filed another improved phosphating patent application in 1919. This patent was issued in 1919 as U.S. patent 1,311,319 , for an improved manganese phosphating (Parkerizing) technique.
Similarly, Baker and Dingman of the Parker Rust-Proof Company filed an improved manganese phosphating (Parkerizing) process patent in 1928 that reduced the processing time to 1 ⁄ 3 of the original time that had been required through heating the solution to a temperature in the precisely controlled range of 500 to 550 °F (260 to 288 °C). This patent was issued as U.S. patent 1,761,186 in 1930.
Manganese phosphating, even with these process improvements, still required the use of expensive and difficult-to-obtain manganese compounds. Subsequently, an alternative technique was developed by the Parker Company to use easier-to-obtain compounds at less expense through using zinc phosphating in place of manganese phosphating. The patent for this zinc phosphating process (using strategic compounds that would remain available in America during a war) was granted to inventor Romig of the American Chemical Paint Company in 1938 as U.S. patent 2,132,883 , just prior to the loss of easy access to manganese compounds that occurred during World War II .
Somewhat analogous to the improved manganese phosphating process improvements discovered by Baker and Dingman, a similarly improved method was found for an improved zinc phosphating process as well. This improvement was discovered by Darsey of the Parker Rust Proof Company, who filed a patent in February 1941, which was granted in August 1942, U.S. patent 2,293,716 , that improved upon the zinc phosphatizing (Parkerizing) process further. He discovered that adding copper reduced the acidity requirement over what had been required, and that also adding a chlorate to the nitrates that were already used would additionally permit running the process at a much lower temperature in the range of 115 to 130 °F (46 to 54 °C), reducing the cost of running the process further. With these process improvements, the end result was that a low-temperature (energy-efficient) zinc phosphating (Parkerizing) process, using strategic materials to which the United States had ready access, became the most common phosphating process used during World War II to protect American war materials such as firearms and planes from rust and corrosion.
Glock Ges.m.b.H. , an Austrian firearms manufacturer, uses a black Parkerizing process as a topcoat to a Tenifer process to protect the slides of the pistols they manufacture. After applying the Tenifer process, a black Parkerized finish is applied and the slide is protected even if the Parkerized finish were to wear off. Used this way, Parkerizing is thus becoming a protective and decorative finishing technique that is used over other underlying improved techniques of metal protection.
Various of similar recipes for stovetop kitchen Parkerizing circulate in gun publications at times, and Parkerizing kits are sold by major gun-parts distributors such as Brownells.
Phosphate coatings are also commonly used as an effective surface preparation for further coating and/or painting, providing excellent adhesion and electric isolation. [ 6 ]
Phosphate coatings are often used to protect steel parts against rusting and other types of corrosion. However, they are somewhat porous, so this use requires impregnating the coating with oil, paint, or some other sealing substance. The result is a tightly adhering dielectric (electrically insulating) layer that can protect the part from electrochemical and under-paint corrosion. [ 6 ]
Zinc and manganese coatings are used to help break in components subject to wear [ 1 ] and help prevent galling . [ 6 ]
While a zinc phosphate coating by itself is somewhat abrasive , it can be turned into a lubricating layer for cold forming operations by treatment with sodium stearate ( soap ). The soap reacts with the phosphate crystals forming a very thin insoluble and hydrophobic zinc stearate layer, that helps to hold the unreacted sodium stearate even under extreme deformation of the part, such as in wire drawing . [ 1 ] [ 13 ] | https://en.wikipedia.org/wiki/Phosphate_conversion_coating |
Phosphate solubilizing bacteria (PSB) are beneficial bacteria capable of solubilizing inorganic phosphorus from insoluble compounds. [ 1 ] P-solubilization ability of rhizosphere microorganisms is considered to be one of the most important traits associated with plant phosphate nutrition. It is generally accepted that the mechanism of mineral phosphate solubilization by PSB strains is associated with the release of low molecular weight organic acids , through which their hydroxyl and carboxyl groups chelate the cations [an ion that have positive charge on it.] bound to phosphate, thereby converting it into soluble forms. PSB have been introduced to the Agricultural community as phosphate Biofertilizer . Phosphorus (P) is one of the major essential macronutrients for plants and is applied to soil in the form of phosphate fertilizers. However, a large portion of soluble inorganic phosphate which is applied to the soil as chemical fertilizer is immobilized rapidly and becomes unavailable to plants. [ 2 ] Currently, the main purpose in managing soil phosphorus is to optimize crop production and minimize P loss from soils. PSB have attracted the attention of agriculturists as soil inoculums to improve the plant growth and yield. When PSB is used with rock phosphate , it can save about 50% of the crop requirement of phosphatic fertilizer. [ citation needed ] The use of PSB as inoculants increases P uptake by plants. Simple inoculation of seeds with PSB gives crop yield responses equivalent to 30 kg P 2 O 5 /ha or 50 percent of the need for phosphatic fertilizers. Alternatively, PSB can be applied through fertigation or in hydroponic operations. Many different strains of these bacteria have been identified as PSB, including Pantoea agglomerans (P5), Microbacterium laevaniformans (P7) and Pseudomonas putida (P13) strains are highly efficient insoluble phosphate solubilizers. Recently, researchers at Colorado State University demonstrated that a consortium of four bacteria, synergistically solubilize phosphorus at a much faster rate than any single strain alone. [ 3 ] Mahamuni and Patil (2012) isolated four strains of phosphate solubilizing bacteria from sugarcane (VIMP01 and VIMP02) and sugar beet rhizosphere (VIMP03 and VIMP 04). Isolates were strains of Burkholderia named as VIMP01, VIMP02, VIMP03 and VIMP04. VIMP (Vasantdada Sugar Institute Isolate by Mahamuni and Patil) cultures were identified as Burkholderia cenocepacia strain VIMP01 (JQ867371), Burkholderia gladioli strain VIMP02 (JQ811557), Burkholderia gladioli strain VIMP03 (JQ867372) and Burkholderia species strain VIMP04 (JQ867373). [ 4 ]
Additionally, phosphate (P) compounds are capable of immobilizing heavy metals, especially Pb, in contaminated environments through phosphate-heavy metal precipitation. However, most P compounds are not readily soluble in soils so it is not readily used for metal immobilization. Phosphate solubilizing bacteria (PSB) have the potential to enhance phosphate-induced immobilization of metals to remediate contaminated soil. However, there is a limit on the amount of phosphate which can be added to the environment due to the issue of eutrophication. [ 5 ]
Phosphate is often adsorbed onto the surface of different type of minerals, for example iron containing minerals. Recent data suggest that bacteria growing under phosphorus starvation release iron-chelating molecules. Considering the geochemical interaction between these two elements, the authors suggest that some bacteria can dissolve iron-containing minerals in order to access the adsorbed phosphate. [ 6 ] | https://en.wikipedia.org/wiki/Phosphate_solubilizing_bacteria |
A range of qualitative and quantitative tests have been developed to detect phosphate ions ( PO 3− 4 ) in solution. Such tests find use in industrial processes, scientific research, and environmental water monitoring .
A quantitative method to determine the amount of phosphate present in samples, such as boiler feedwater , is as follows. A measured amount of boiler water is poured into a mixing tube and ammonium heptamolybdate reagent is added. The tube is then stoppered and vigorously shaken. The next step is to add dilute stannous chloride reagent, which has been freshly prepared from concentrated stannous chloride reagent and distilled water, to the mixture in the tube. This will produce a blue colour (due to the formation of molybdenum blue ) and the depth of the blue colour indicates the amount of phosphate in the boiler water. The absorbance of the blue solution can be measured with a colorimeter and the concentration of phosphate in the original solution can be calculated. Alternatively, a direct (but approximate) reading of phosphate concentration can be obtained by using a Lovibond comparator . This method for phosphate determination is known as Denigés' method. [ 1 ] [ 2 ] [ 3 ]
A simple qualitative method to determine the presence of phosphate ions in a sample is as follows. A small amount of the sample is acidified with concentrated nitric acid , to which a little ammonium molybdate is added. The presence of phosphate ions is indicated by the formation of a bright yellow precipitate layer of ammonium phosphomolybdate . The appearance of the precipitate can be facilitated by gentle heating. This test is also used to detect arsenic , a yellow precipitate being formed. | https://en.wikipedia.org/wiki/Phosphate_test |
Phosphatidic acids are anionic phospholipids important to cell signaling and direct activation of lipid-gated ion channels . Hydrolysis of phosphatidic acid gives rise to one molecule each of glycerol and phosphoric acid and two molecules of fatty acids. They constitute about 0.25% of phospholipids in the bilayer. [ 1 ]
Phosphatidic acid consists of a glycerol backbone, with, in general, a saturated fatty acid bonded to carbon -1, an unsaturated fatty acid bonded to carbon -2, and a phosphate group bonded to carbon -3. [ 2 ] [ 3 ]
Besides de novo synthesis, PA can be formed in three ways:
The glycerol 3-phosphate pathway for de novo synthesis of PA is shown here:
In addition, PA can be converted into DAG by lipid phosphate phosphohydrolases (LPPs) [ 6 ] [ 7 ] or into lyso-PA by phospholipase A (PLA).
The role of PA in the cell can be divided into three categories:
The first three roles are not mutually exclusive. For example, PA may be involved in vesicle formation by promoting membrane curvature and by recruiting the proteins to carry out the much more energetically unfavourable task of neck formation and pinching.
PA is a vital cell lipid that acts as a biosynthetic precursor for the formation (directly or indirectly) of all acylglycerol lipids in the cell. [ 11 ]
In mammalian and yeast cells, two different pathways are known for the de novo synthesis of PA, the glycerol 3-phosphate pathway or the dihydroxyacetone phosphate pathway. In bacteria, only the former pathway is present, and mutations that block this pathway are lethal, demonstrating the importance of PA. In mammalian and yeast cells, where the enzymes in these pathways are redundant, mutation of any one enzyme is not lethal. However, it is worth noting that in vitro , the various acyltransferases exhibit different substrate specificities with respect to the acyl-CoAs that are incorporated into PA. Different acyltransferases also have different intracellular distributions, such as the endoplasmic reticulum (ER), the mitochondria or peroxisomes, and local concentrations of activated fatty acids. This suggests that the various acyltransferases present in mammalian and yeast cells may be responsible for producing different pools of PA. [ 11 ]
The conversion of PA into diacylglycerol (DAG) by LPPs is the commitment step for the production of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylserine (PS). In addition, DAG is also converted into CDP-DAG, which is a precursor for phosphatidylglycerol (PG), phosphatidylinositol (PI) and phosphoinositides (PIP, PIP 2 , PIP 3 ). [ 11 ]
PA concentrations are maintained at extremely low levels in the cell by the activity of potent LPPs. [ 6 ] These convert PA into DAG very rapidly and, because DAG is the precursor for so many other lipids, it too is soon metabolised into other membrane lipids. This means that any upregulation in PA production can be matched, over time, with a corresponding upregulation in LPPs and in DAG metabolising enzymes.
PA is, therefore, essential for lipid synthesis and cell survival, yet, under normal conditions, is maintained at very low levels in the cell.
PA is a unique phospholipid in that it has a small highly charged head group that is very close to the glycerol backbone. PA is known to play roles in both vesicle fission [ 12 ] and fusion, [ 13 ] and these roles may relate to the biophysical properties of PA.
At sites of membrane budding or fusion, the membrane becomes or is highly curved. A major event in the budding of vesicles, such as transport carriers from the Golgi , is the creation and subsequent narrowing of the membrane neck. Studies have suggested that this process may be lipid-driven, and have postulated a central role for DAG due to its, likewise, unique molecular shape. The presence of two acyl chains but no headgroup results in a large negative curvature in membranes. [ 14 ]
The LPAAT BARS-50 has also been implicated in budding from the Golgi. [ 12 ] This suggests that the conversion of lysoPA into PA might affect membrane curvature. LPAAT activity doubles the number of acyl chains, greatly increasing the cross-sectional area of the lipid that lies ‘within’ the membrane while the surface headgroup remains unchanged. This can result in a more negative membrane curvature. Researchers from Utrecht University have looked at the effect of lysoPA versus PA on membrane curvature by measuring the effect these have on the transition temperature of PE from lipid bilayers to nonlamellar phases using 31 P-NMR. [ 15 ] The curvature induced by these lipids was shown to be dependent not only on the structure of lysoPA versus PA but also on dynamic properties, such as the hydration of head groups and inter- and intramolecular interactions. For instance, Ca 2+ may interact with two PAs to form a neutral but highly curved complex. The neutralisation of the otherwise repulsive charges of the headgroups and the absence of any steric hindrance enables strong intermolecular interactions between the acyl chains, resulting in PA-rich microdomains. Thus in vitro , physiological changes in pH, temperature, and cation concentrations have strong effects on the membrane curvature induced by PA and lysoPA. [ 15 ] The interconversion of lysoPA, PA, and DAG – and changes in pH and cation concentration – can cause membrane bending and destabilisation, playing a direct role in membrane fission simply by virtue of their biophysical properties. However, though PA and lysoPA have been shown to affect membrane curvature in vitro ; their role in vivo is unclear.
The roles of lysoPA, PA, and DAG in promoting membrane curvature do not preclude a role in recruiting proteins to the membrane. For instance, the Ca 2+ requirement for the fusion of complex liposomes is not greatly affected by the addition of annexin I, though it is reduced by PLD. However, with annexin I and PLD, the extent of fusion is greatly enhanced, and the Ca 2+ requirement is reduced almost 1000-fold to near physiological levels. [ 13 ]
Thus the metabolic, biophysical, recruitment, and signaling roles of PA may be interrelated.
PA is kept low in the bulk of the membrane in order to transiently burst and signal locally in high concentration. [ 16 ] For example TREK-1 channels are activated by local association with PLD and production of PA. [ 17 ] The dissociation constant of PA for TREK-1 is approximately 10 micromolar. [ 18 ] The relatively weak binding combined with a low concentration of PA in the membrane allows the channel to turn off. The local high concentration for activation suggests at least some restrictions in local lipid diffusion. The bulk low concentration of PA combined with high local bursts is the opposite of PIP2 signaling. PIP2 is kept relatively high in the membrane and then transiently hydrolized near a protein in order to transiently reduce PIP2 signaling. [ 19 ] PA signaling mirrors PIP2 signaling in that the bulk concentration of signaling lipid need not change to exert a potent local effect on a target protein.
As described above, PLD hydrolyzes PC to form PA and choline . Because choline is very abundant in the cell, PLD activity does not significantly affect choline levels; and choline is unlikely to play any role in signaling. [ citation needed ]
The role of PLD activation in numerous signaling contexts, combined with the lack of a role for choline, suggests that PA is important in signaling. However, PA is rapidly converted to DAG, and DAG is also known to be a signaling molecule. This raises the question as to whether PA has any direct role in signaling or whether it simply acts as a precursor for DAG production. [ 20 ] [ 21 ] If it is found that PA acts only as a DAG precursor, then one can raise the question as to why cells should produce DAG using two enzymes when they contain the PLC that could produce DAG in a single step.
PA produced by PLD or by DAGK can be distinguished by the addition of [γ- 32 P]ATP. This will show whether the phosphate group is newly derived from the kinase activity or whether it originates from the PC. [ 22 ]
Although PA and DAG are interconvertible, they do not act in the same pathways. Stimuli that activate PLD do not activate enzymes downstream of DAG, and vice versa. For example, it was shown that addition of PLD to membranes results in the production of [ 32 P]-labeled PA and [ 32 P]-labeled phosphoinositides. [ 23 ] The addition of DAGK inhibitors eliminates the production of [ 32 P]-labeled PA but not the PLD-stimulated production of phosphoinositides.
It is possible that, though PA and DAG are interconvertible, separate pools of signaling and non-signaling lipids may be maintained. Studies have suggested that DAG signaling is mediated by polyunsaturated DAG, whereas PLD-derived PA is monounsaturated or saturated. Thus functional saturated/monounsaturated PA can be degraded by hydrolysing it to form non-functional saturated/monounsaturated DAG, whereas functional polyunsaturated DAG can be degraded by converting it into non-functional polyunsaturated PA. [ 20 ] [ 24 ]
This model suggests that PA and DAG effectors should be able to distinguish lipids with the same headgroups but with differing acyl chains. Although some lipid-binding proteins are able to insert themselves into membranes and could hypothetically recognize the type of acyl chain or the resulting properties of the membrane, many lipid-binding proteins are cytosolic and localize to the membrane by binding only the headgroups of lipids. Perhaps the different acyl chains can affect the angle of the head-group in the membrane. If this is the case, it suggests that a PA-binding domain must not only be able to bind PA specifically but must also be able to identify those head-groups that are at the correct angle. Whatever the mechanism is, such specificity is possible. It is seen in the pig testes DAGK that is specific for polyunsaturated DAG [ 25 ] and in two rat hepatocyte LPPs that dephosphorylate different PA species with different activities. [ 26 ] Moreover, the stimulation of SK1 activity by PS in vitro was shown to vary greatly depending on whether dioleoyl (C18:1), distearoyl (C18:0), or 1-stearoyl, 2-oleoyl species of PS were used. [ 27 ] Thus it seems that, though PA and DAG are interconvertible, the different species of lipids can have different biological activities; and this may enable the two lipids to maintain separate signaling pathways.
As PA is rapidly converted to DAG, it is very short-lived in the cell. This means that it is difficult to measure PA production and therefore to study the role of PA in the cell. However, PLD activity can be measured by the addition of primary alcohols to the cell. [ 28 ] PLD then carries out a transphosphatidylation reaction, instead of hydrolysis, producing phosphatidyl alcohols in place of PA. The phosphatidyl alcohols are metabolic dead-ends, and can be readily extracted and measured. Thus PLD activity and PA production (if not PA itself) can be measured, and, by blocking the formation of PA, the involvement of PA in cellular processes can be inferred. | https://en.wikipedia.org/wiki/Phosphatidic_acid |
Phosphatidylethanols ( PEth ) are a group of phospholipids formed only in the presence of ethanol via the action of phospholipase D (PLD). [ 1 ] It accumulates in blood and is removed slowly, making it a useful biomarker for alcohol consumption. [ 2 ] PEth is also thought to contribute to the symptoms of alcohol intoxication . [ 3 ]
Chemically, phosphatidylethanols are phospholipids carrying two fatty acid chains , which are variable in structure, and one phosphate ethyl ester .
When ethanol is present, PLD substitutes ethanol for water and covalently attaches the alcohol as the head group of the phospholipid; hence the name phosphatidylethanol. Normally PLD incorporates water to generate phosphatidic acid (PA); the process is termed transphosphatidylation. [ 4 ] PLD continues to generate PA in the presence of ethanol and while PEth is generated and the effects of ethanol transphosphatidlyation are through the generation of the unnatural lipid not depletion of PA. [ 3 ]
The lipid accumulates in the human body and competes at agonists sites of lipid-gated ion channels contributing to alcohol intoxication. [ 3 ] The chemical similarity of PEth to phosphatidic acid (PA) and phosphatidylinositol 4,5-bisphosphate (PIP2) suggest a likely broad perturbation to lipid signaling ; the exact role of PEth as a competitive lipid ligand has not been studied extensively.
Levels of phosphatidylethanols in blood are used as markers of previous alcohol consumption. [ 5 ] [ 6 ] An increase of alcohol intake by ~20 g ethanol/day will raise the PEth 16:0/18:1 concentration by ~0.10 μmol/L, and vice versa if the alcohol consumption has decreased. However, it has been demonstrated that there can be significant inter-personal variation, leading to potential misclassification between moderate and heavy drinkers. [ 7 ] After cessation of alcohol intake, the half-life of PEth is between 4.5 and 10 days in the first week and between 5 and 12 days in the second week. [ 2 ] As a blood marker PEth is more sensitive than carbohydrate deficient transferrin (CDT), urinary ethyl glucuronide (EtG) and ethyl sulfate (EtS). [ 8 ]
The Society of PEth Research [ 9 ] published a harmonization document (2022 Consensus of Basel) for the interpretation of phosphatidylethanol concentrations in the clinical and forensic setting. [ 10 ] This consensus represents the first internationally established harmonization document on PEth. The consensus defined the target measurand (PEth 16:0/18:1 in whole blood), cutoff concentrations (20 ng/mL and 200 ng/mL), and minimal requirements for the applied analytical method ( accuracy and precision within 15%). [ citation needed ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphatidylethanol |
Phosphatidylinositol-4-phosphate ( PtdIns4 P , PI-4-P , PI4P , or PIP ) is a precursor of phosphatidylinositol (4,5)-bisphosphate . PtdIns4 P is prevalent in the membrane of the Golgi apparatus .
In the Golgi apparatus , PtdIns4 P binds to the GTP-binding protein ARF and to effector proteins , including four-phosphate-adaptor protein 1 and 2 ( PLEKHA3 and PLEKHA8 ). [ 1 ] This three molecule complex recruits proteins that need to be carried to the cell membrane . [ 2 ]
There is now evidence that PI-4-P is capable of deforming lipid systems into tightly curved assemblies, [ 3 ] [ 4 ] this is consistent with similar behaviour observed in phosphatidylinositol .
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphatidylinositol_4-phosphate |
The phosphatome of an organism is the set of phosphatase genes in its genome . Phosphatases are enzymes that catalyze the removal of phosphate from biomolecules . Over half of all cellular proteins are modified by phosphorylation which typically controls their functions. Protein phosphorylation is controlled by the opposing actions of protein phosphatases and protein kinases .
Most phosphorylation sites are not linked to a specific phosphatase, so the phosphatome approach allows a global analysis of dephosphorylation, screening to find the phosphatase responsible for a given reaction, and comparative studies between different phosphatases, similar to how protein kinase research has been impacted by the kinome approach.
Protein phosphatases remove phosphates from proteins, usually on Serine, Threonine, and Tyrosine residues, reversing the action of protein kinases. The PTP family of protein phosphatases is tyrosine-specific, and several other families (PPPL, PPM, HAD) appear to be serine/threonine specific, while other families are unknown or have a variety of substrates (DSPs dephosphorylate any amino acid, while some protein phosphatases also have non-protein substrates). In the human genome, 20 different folds of protein are known to be phosphatases, of which 10 include protein phosphatases. [ 1 ]
Protein phosphatomes have been cataloged for human and 8 other key eukaryotes, [ 1 ] for Plasmodium and Trypanosomes [ 2 ] [ 3 ] [ 4 ] and phosphatomes have been used for functional analysis, by experimentally investing all known protein phosphatases, in the yeast Fusarium, [ 5 ] in Plasmodium [ 6 ] and in human cancer [ 7 ] [ 8 ]
Large scale databases exist for human and animal phosphatomes Phosphatome.net , parasitic protozoans ProtozPhosDB and for the substrates of human phosphatases DEPOD .
Non-protein phosphorylation has three general forms
The human non-protein phosphatome has been cataloged, [ 1 ] but most phosphatome analyses are restricted to protein and lipid phosphatases that have regulatory functions.
The phosphatome includes proteins that are structurally closely related to phosphatases but lack catalytic activity. These retain biological function, and may regulate pathways that involve active phosphatases, or bind to phosphorylated substrates without cleaving them. [ 1 ] [ 9 ] Examples include STYX , where the phosphatase domain has become a phospho-tyrosine binding domain, and GAK , whose inactive phosphatase domain instead binds phospholipids. | https://en.wikipedia.org/wiki/Phosphatome |
Phosphinates or hypophosphites are a class of phosphorus compounds conceptually based on the structure of hypophosphorous acid . IUPAC prefers the term phosphinate in all cases, however in practice hypophosphite is usually used to describe inorganic species (e.g. sodium hypophosphite ), while phosphinate typically refers to organophosphorus species.
The hypophosphite ion is (H 2 PO 2 ) − . The salts are prepared by heating white phosphorus in warm aqueous alkali e.g. Ca(OH) 2 : [ 1 ]
Hypophosphites are reducing agents : [ 1 ]
Hypophosphites are used in electroless nickel plating as the reducing agent to deposit for example Ni metal from Ni salts. [ 1 ] The hypophosphite ion is thermodynamically unstable, and disproportionates on heating to phosphine and phosphate salts :
Hypophosphite (usually sodium hypophosphite) acts as a reducing agent to deposit nickel onto surfaces without using electricity. Common in electronics, automotive, and aerospace industries for corrosion resistance and hardness. Some hypophosphite compounds are used in medicines, particularly as sources of phosphorus or as stabilizers in formulations.
In polymer and plastic stabilization, they are used today as antioxidants and thermal stabilizers to prevent degradation during the processing of plastics like PVC. Beyond nickel plating, hypophosphites are used in general chemical synthesis where a mild reducing agent is needed.
Additionally, in wood science , sodium hypophosphite in combination with other agents, such as ammonium-, nitrogen- or aluminium-containing chemicals, has been used for in solid wood and particleboard to improve the fire retarding properties. [ 2 ] [ 3 ] | https://en.wikipedia.org/wiki/Phosphinate |
Phosphine ( IUPAC name: phosphane ) is a colorless, flammable, highly toxic compound with the chemical formula P H 3 , classed as a pnictogen hydride . Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting fish, due to the presence of substituted phosphine and diphosphane ( P 2 H 4 ). With traces of P 2 H 4 present, PH 3 is spontaneously flammable in air ( pyrophoric ), burning with a luminous flame. Phosphine is a highly toxic respiratory poison, and is immediately dangerous to life or health at 50 ppm. Phosphine has a trigonal pyramidal structure.
Phosphines are compounds that include PH 3 and the organophosphines , which are derived from PH 3 by substituting one or more hydrogen atoms with organic groups. [ 4 ] They have the general formula PH 3− n R n . Phosphanes are saturated phosphorus hydrides of the form P n H n +2 , such as triphosphane . [ 5 ] Phosphine ( PH 3 ) is the smallest of the phosphines and the smallest of the phosphanes.
Philippe Gengembre (1764–1838), a student of Lavoisier , first obtained phosphine in 1783 by heating white phosphorus in an aqueous solution of potash (potassium carbonate). [ 6 ] [ NB 1 ]
Perhaps because of its strong association with elemental phosphorus , phosphine was once regarded as a gaseous form of the element, but Lavoisier (1789) recognised it as a combination of phosphorus with hydrogen and described it as phosphure d'hydrogène (phosphide of hydrogen). [ NB 2 ]
In 1844, Paul Thénard, son of the French chemist Louis Jacques Thénard , used a cold trap to separate diphosphine from phosphine that had been generated from calcium phosphide , thereby demonstrating that P 2 H 4 is responsible for spontaneous flammability associated with PH 3 , and also for the characteristic orange/brown color that can form on surfaces, which is a polymerisation product. [ 7 ] He considered diphosphine's formula to be PH 2 , and thus an intermediate between elemental phosphorus, the higher polymers, and phosphine. Calcium phosphide (nominally Ca 3 P 2 ) produces more P 2 H 4 than other phosphides because of the preponderance of P-P bonds in the starting material.
The name "phosphine" was first used for organophosphorus compounds in 1857, being analogous to organic amines ( NR 3 ). [ NB 3 ] [ 8 ] The gas PH 3 was named "phosphine" by 1865 (or earlier). [ 9 ]
PH 3 is a trigonal pyramidal molecule with C 3 v molecular symmetry . The length of the P−H bond is 1.42 Å , the H−P−H bond angles are 93.5 ° . The dipole moment is 0.58 D, which increases with substitution of methyl groups in the series: CH 3 PH 2 , 1.10 D; (CH 3 ) 2 PH , 1.23 D; (CH 3 ) 3 P , 1.19 D. In contrast, the dipole moments of amines decrease with substitution, starting with ammonia , which has a dipole moment of 1.47 D. The low dipole moment and almost orthogonal bond angles lead to the conclusion that in PH 3 the P−H bonds are almost entirely pσ(P) – sσ(H) and phosphorus 3s orbital contributes little to the P-H bonding. For this reason, the lone pair on phosphorus is predominantly formed by the 3s orbital of phosphorus. The upfield chemical shift of it 31 P NMR signal accords with the conclusion that the lone pair electrons occupy the 3s orbital (Fluck, 1973). This electronic structure leads to a lack of nucleophilicity in general and lack of basicity in particular (p K aH = −14), [ 10 ] as well as an ability to form only weak hydrogen bonds . [ 11 ]
The aqueous solubility of PH 3 is slight: 0.22 cm 3 of gas dissolves in 1 cm 3 of water. Phosphine dissolves more readily in non-polar solvents than in water because of the non-polar P−H bonds. It is technically amphoteric in water, but acid and base activity is poor. Proton exchange proceeds via a phosphonium ( PH + 4 ) ion in acidic solutions and via phosphanide ( PH − 2 ) at high pH, with equilibrium constants K b = 4 × 10 −28 and K a = 41.6 × 10 −29 . Phosphine reacts with water only at high pressure and temperature, producing phosphoric acid and hydrogen: [ 12 ] [ 13 ]
Burning phosphine in the air produces phosphoric acid : [ 14 ] [ 12 ]
Phosphine may be prepared in a variety of ways. [ 15 ] Industrially it can be made by the reaction of white phosphorus with sodium or potassium hydroxide , producing potassium or sodium hypophosphite as a by-product.
Alternatively, the acid-catalyzed disproportionation of white phosphorus yields phosphoric acid and phosphine. Both routes have industrial significance; the acid route is the preferred method if further reaction of the phosphine to substituted phosphines is needed. The acid route requires purification and pressurizing.
It is prepared in the laboratory by disproportionation of phosphorous acid : [ 16 ]
Alternative methods are the hydrolysis zinc phosphide :
[ 17 ] Some other metal phosphides could be used including aluminium phosphide , or calcium phosphide . Pure samples of phosphine, free from P 2 H 4 , may be prepared using the action of potassium hydroxide on phosphonium iodide :
Phosphine is a worldwide constituent of the Earth's atmosphere at very low and highly variable concentrations. [ 18 ] It may contribute significantly to the global phosphorus biochemical cycle . The most likely source is reduction of phosphate in decaying organic matter, possibly via partial reductions and disproportionations , since environmental systems do not have known reducing agents of sufficient strength to directly convert phosphate to phosphine. [ 19 ]
It is also found in Jupiter 's atmosphere. [ 20 ]
In 2020 a spectroscopic analysis was reported to show signs of phosphine in the atmosphere of Venus in quantities that could not be explained by known abiotic processes . [ 21 ] [ 22 ] [ 23 ] Later re-analysis of this work showed interpolation errors had been made, and re-analysis of data with the fixed algorithm do not result in the detection of phosphine. [ 24 ] [ 25 ] The authors of the original study then claimed to detect it with a much lower concentration of 1 ppb. [ 26 ] [ disputed – discuss ]
Phosphine is a precursor to many organophosphorus compounds . It reacts with formaldehyde in the presence of hydrogen chloride to give tetrakis(hydroxymethyl)phosphonium chloride , which is used in textiles. The hydrophosphination of alkenes is versatile route to a variety of phosphines. For example, in the presence of basic catalysts PH 3 adds of Michael acceptors . Thus with acrylonitrile , it reacts to give tris(cyanoethyl)phosphine : [ 27 ]
Acid catalysis is applicable to hydrophosphination with isobutylene and related analogues:
where R is CH 3 , alkyl, etc.
Phosphine is used as a dopant in the semiconductor industry, and a precursor for the deposition of compound semiconductors . Commercially significant products include gallium phosphide and indium phosphide . [ 28 ]
Phosphine is an attractive fumigant because it is lethal to insects and rodents, but degrades to phosphoric acid, which is non-toxic. As sources of phosphine, for farm use , pellets of aluminium phosphide (AlP), calcium phosphide ( Ca 3 P 2 ), or zinc phosphide ( Zn 3 P 2 ) are used. These phosphides release phosphine upon contact with atmospheric water or rodents' stomach acid. These pellets also contain reagents to reduce the potential for ignition or explosion of the released phosphine.
An alternative is the use of phosphine gas itself which requires dilution with either CO 2 or N 2 or even air to bring it below the flammability point. Use of the gas avoids the issues related with the solid residues left by metal phosphide and results in faster, more efficient control of the target pests.
One problem with phosphine fumigants is the increased resistance by insects. [ 29 ]
Deaths have resulted from accidental exposure to fumigation materials containing aluminium phosphide or phosphine. [ 30 ] [ 31 ] [ 32 ] [ 33 ] It can be absorbed either by inhalation or transdermally . [ 30 ] As a respiratory poison, it affects the transport of oxygen or interferes with the utilization of oxygen by various cells in the body. [ 32 ] Exposure results in pulmonary edema (the lungs fill with fluid). [ 33 ] Phosphine gas is heavier than air so it stays near the floor. [ 34 ]
Phosphine appears to be mainly a redox toxin, causing cell damage by inducing oxidative stress and mitochondrial dysfunction. [ 35 ] Resistance in insects is caused by a mutation in a mitochondrial metabolic gene. [ 29 ]
Phosphine can be absorbed into the body by inhalation. The main target organ of phosphine gas is the respiratory tract. [ 36 ] According to the 2009 U.S. National Institute for Occupational Safety and Health (NIOSH) pocket guide, and U.S. Occupational Safety and Health Administration (OSHA) regulation, the 8 hour average respiratory exposure should not exceed 0.3 ppm. NIOSH recommends that the short term respiratory exposure to phosphine gas should not exceed 1 ppm. The Immediately Dangerous to Life or Health level is 50 ppm. Overexposure to phosphine gas causes nausea, vomiting, abdominal pain, diarrhea, thirst, chest tightness, dyspnea (breathing difficulty), muscle pain, chills, stupor or syncope, and pulmonary edema. [ 37 ] [ 38 ] Phosphine has been reported to have the odor of decaying fish or garlic at concentrations below 0.3 ppm. The smell is normally restricted to laboratory areas or phosphine processing since the smell comes from the way the phosphine is extracted from the environment. However, it may occur elsewhere, such as in industrial waste landfills. Exposure to higher concentrations may cause olfactory fatigue . [ 39 ]
Phosphine is used for pest control , but its usage is strictly regulated due to high toxicity. [ 40 ] [ 41 ] Gas from phosphine has high mortality rate [ 42 ] and has caused deaths in Sweden and other countries. [ 43 ] [ 44 ] [ 45 ]
Because the previously popular fumigant methyl bromide has been phased out in some countries under the Montreal Protocol , phosphine is the only widely used, cost-effective, rapidly acting fumigant that does not leave residues on the stored product. Pests with high levels of resistance toward phosphine have become common in Asia, Australia and Brazil. High level resistance is also likely to occur in other regions, but has not been as closely monitored. Genetic variants that contribute to high level resistance to phosphine have been identified in the dihydrolipoamide dehydrogenase gene. [ 29 ] Identification of this gene now allows rapid molecular identification of resistant insects.
Phosphine gas is denser than air and hence may collect in low-lying areas. It can form explosive mixtures with air, and may also self-ignite. [ 12 ]
Anne McCaffrey 's Dragonriders of Pern series features genetically engineered dragons that breathe fire by producing phosphine by extracting it from minerals of their native planet.
In the 2008 pilot of the crime drama television series Breaking Bad , Walter White poisons two rival gangsters by adding red phosphorus to boiling water to produce phosphine gas. However, this reaction in reality would require white phosphorus instead, and for the water to contain sodium hydroxide . [ 46 ] | https://en.wikipedia.org/wiki/Phosphine |
In chemistry a phosphine imide (sometimes abbreviated to phosphinimide ) also known as a iminophosphorane is a functional group with the formula R 3 P=NR. While structurally related to phosphine oxide its chemistry has more in common with phosphonium ylides .
Anions of this group, with the structure R 3 P=N − , are called phosphinoimidates and are used as ligands to form phosphinimide complexes which are highly active catalysts in some olefin polymerization reactions. [ 1 ]
Phosphine imides can be isolated as intermediates in the Staudinger reaction and have also been prepared by the action of hydroxylamine-O-sulfonic acid on phosphines , proceeding via a p-aminophosphonium salt. [ 2 ]
The functional group will readily hydrolyse to give a phosphine oxide and an amine
Phosphinimide ligands of the general formula NPR 3 − form transition metal phosphinimide complexeses . Some of these complexes are potential catalysts for the synthesis of polyethylene . [ 1 ] | https://en.wikipedia.org/wiki/Phosphine_imide |
Phosphine oxides are phosphorus compounds with the formula OPX 3 . When X = alkyl or aryl , these are organophosphine oxides. Triphenylphosphine oxide is an example. An inorganic phosphine oxide is phosphoryl chloride (POCl 3 ). [ 1 ] The parent phosphine oxide (H 3 PO) remains rare and obscure.
Tertiary phosphine oxides are the most commonly encountered phosphine oxides. With the formula R 3 PO, they are tetrahedral compounds. They are usually prepared by oxidation of tertiary phosphines. The P-O bond is short and polar. According to molecular orbital theory , the short P–O bond is attributed to the donation of the lone pair electrons from oxygen p-orbitals to the antibonding phosphorus-carbon bonds. [ 2 ] The nature of the P–O bond was once hotly debated. Some discussions invoked a role for phosphorus-centered d-orbitals in bonding, but this analysis is not supported by computational analyses. In terms of simple Lewis structure , the bond is more accurately represented as a dative bond , as is currently used to depict an amine oxide . [ 3 ] [ 4 ]
Secondary phosphine oxides (SPOs), formally derived from secondary phosphines (R 2 PH), are again tetrahedral at phosphorus. [ 5 ] One commercially available example of a secondary phosphine oxide is diphenylphosphine oxide . SPOs are used in the formulation of catalysts for cross coupling reactions . [ 6 ]
Unlike tertiary phosphine oxides, SPOs often undergo further oxidation, which enriches their chemistry:
These reactions are preceded by tautomerization to the phosphinous acid (R 2 POH):
Primary phosphine oxides, formally oxidized derivatives of primary phosphines, are again tetrahedral at phosphorus. With four different substituents (O, OH, H, R) they are chiral. The primary phosphine oxides subject to tautomerization, which leads to racemization, and further oxidation, analogous to the behavior of SPOs. Additionally, primary phosphine oxides are susceptible to disproportionation to the phosphinic acid and the primary phosphine: [ 7 ]
Phosphine oxide are typically produced by oxidation of organophosphines . The oxygen in air is often sufficiently oxidizing to fully convert trialkylphosphines to their oxides at room temperature:
This conversion is usually undesirable. In order to suppress this reaction, air-free techniques are often employed when handling say, trimethylphosphine .
Less basic phosphines, such as methyldiphenylphosphine are converted to their oxides by treatment with hydrogen peroxide: [ 8 ]
Phosphine oxides are generated as a by-product of the Wittig reaction :
Another albeit unconventional route to phosphine oxides is the thermolysis of phosphonium hydroxides:
The hydrolysis of phosphorus(V) dihalides also affords the oxide: [ 9 ]
A special nonoxidative route is applicable secondary phosphine oxides, which arise by the hydrolysis of the chlorophosphine. An example is the hydrolysis of chlorodiphenylphosphine to give diphenylphosphine oxide :
Transition metal complexes of phosphine oxides are numerous.
The deoxygenation of phosphine oxides has been extensively developed because many useful stoichiometric reactions convert tertiary phosphines to the corresponding oxides. Regeneration of the tertiary phosphine requires cheap oxophilic reagents, which are usually silicon-based. These deoxygenation reactions can be subdivided into stoichiometric and catalytic processes. [ 10 ]
Use of trichlorosilane is a standard laboratory method. Industrial routes use phosgene or equivalent reagents, which produce chlorotriphenylphosphonium chloride, which is separately reduced. [ 11 ] For chiral phosphine oxides, deoxygenation can proceed with retention or inversion of configuration. Classically, inversion is favored by a combination of trichlorosilane and triethylamine, whereas in the absence of the Lewis base, the reaction proceeds with retention. [ 12 ]
The popularity of this method is partly attributable to the availability of inexpensive trichlorosilane. Instead of HSiCl 3 , other perchloropolysilanes, e.g. hexachlorodisilane (Si 2 Cl 6 ), can also be used. In comparison, using the reaction of the corresponding phosphine oxides with perchloropolysilanes such as Si 2 Cl 6 or Si 3 Cl 8 in benzene or chloroform, phosphines can be prepared in higher yields.
Deoxygenation has been effected with boranes and alanes. [ 10 ]
Phosphoric acids ((RO) 2 PO 2 H) catalyze the deoxygenation of phosphine oxides by hydrosilanes. [ 13 ]
Some phosphine oxides are well-known in photopolymerization processes, where they react with UV/LED exposure via a type I Norrish reaction mechanism to form free radicals , leading to the polymerization of the photopolymer . An example is 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO), which has been noted as a very efficient photoinitiator that absorbs in the long-wavelength UV, specifically at 380-410nm. [ 14 ]
Phosphine oxides are ligands in various applications of homogeneous catalysis . In coordination chemistry , they are known to have labilizing effects to CO ligands cis to it in organometallic reactions. The cis effect describes this process. | https://en.wikipedia.org/wiki/Phosphine_oxides |
In organic chemistry , phosphinites are organophosphorus compounds with the formula P(OR)R 2 . They are used as ligands in homogeneous catalysis and coordination chemistry . [ 1 ]
Phosphinites are prepared by alcoholysis of organophosphinous chlorides. For example, treatment of chlorodiphenylphosphine with methanol and base gives methyl diphenylphosphinite:
Although they are esters of phosphinous acids (R 2 POH), phosphinites are not made via such intermediates.
Oxidation of phosphinites gives phosphinates :
Phosphinites are ligands, giving derivatives similar to metal phosphine complexes . They are stronger pi-acceptors than typical phosphine ligands. [ 2 ] | https://en.wikipedia.org/wiki/Phosphinite |
Phosphinooxazolines (often abbreviated PHOX ) are a class of chiral ligands used in asymmetric catalysis . Colorless solids, PHOX ligands feature a tertiary phosphine group, often diphenyl, and an oxazoline ligand in the ortho position. The oxazoline, which carries the stereogenic center, coordinates through nitrogen, the result being that PHOX ligands are P,N-chelating ligands. Most phosphine ligands used in asymmetric catalysis are diphosphines , so the PHOX ligands are distinctive. Some evidence exists that PHOX ligands are hemilabile . [ 1 ]
The synthesis of phosphinooxazolines is modular. Methods exist for installing the phosphine ligand before the oxazoline and the reverse. [ 2 ] Commonly a phenyloxazoline is combined with a source of diphenylphosphine. Methods for doing this depend on the nature of the substituent in the X position:
Of these methods, the copper iodide catalysed reaction method is popular. [ 7 ]
Phosphinooxazoline complexes have been widely tested in homogeneous catalysis . [ 8 ] [ 9 ] [ 10 ]
PHOX-based palladium complexes catalyse enantioselective allylic substitutions.
Substitutions include allylic alkylations ( Tsuji-Trost reaction ), [ 11 ] aminations, [ 12 ] and sulfonylations. [ 13 ]
Palladium complexes containing chiral phosphinooxazolines are efficient catalysts for the Heck reaction . [ 14 ] [ 15 ] Pd-PHOX catalysts have also been used for intramolecular Heck reactions and examples exist where they have been shown to be superior to more common ligands such as BINAP . [ 16 ]
In asymmetric hydrogenation iridium complexes of phosphinooxazolines catalyse 'classic' hydrogenation . [ 17 ] Related ruthenium and palladium catalysts effect transfer hydrogenation . [ 1 ] In addition to theoretical studies, [ 18 ] the structural [ 19 ] and kinetic properties [ 20 ]
Other oxazoline based ligands
Structurally related ligands | https://en.wikipedia.org/wiki/Phosphinooxazolines |
Phosphinous acid is the inorganic compound with the formula H 2 POH. It exists, fleetingly, as a mixture with its less stable tautomer H 3 PO ( phosphine oxide ). This mixture has been generated by low temperature oxidation of phosphine with ozone . [ 1 ] H 2 POH is mainly of pedagogical interest. Organophosphinous acids are more prevalent than the parent H 2 POH.
Phosphinous acids exist mainly as minor tautomers of secondary phosphine oxides . For example diphenylphosphinous acid, which is not detectable directly, is invoked as the tautomer of diphenylphosphine oxide .
Highly electron-withdrawing substituents stabilize the phosphinous acid tautomer as illustrated by (CF 3 ) 2 POH. [ 2 ] | https://en.wikipedia.org/wiki/Phosphinous_acid |
Phosphinous acids are usually organophosphorus compounds with the formula R 2 POH. They are pyramidal in structure. Phosphorus is in the oxidation state III. Most phosphinous acids rapidly convert to the corresponding phosphine oxide, which is tetrahedral and is assigned oxidation state V.
Only one example is known, bis(trifluoromethyl)phosphinous acid, (CF 3 ) 2 POH. [ 1 ] It is prepared in several steps from phosphorus trichloride (Et = ethyl ): [ 2 ]
With the lone exception of the bis(trifluoromethyl) derivative, the dominant reaction of phosphinous acids is tautomerization :
Even the pentafluorophenyl compound P(C 6 F 5 ) 2 OH is unstable with respect to the phosphine oxide . [ 2 ]
Although phosphinous acids are rare, their P-bonded coordination complexes are well established, e.g. Mo(CO) 5 P(OH) 3 . [ 3 ]
Tertiary phosphine oxides, compounds with the formula R 3 PO cannot tautomerize. The situation is different for the secondary and primary phosphine oxides, with the respective formulas R 2 (H)PO and R(H) 2 PO. [ 4 ] | https://en.wikipedia.org/wiki/Phosphinous_acids |
Phosphirene is the hypothetical organophosphorus compound with the formula C 2 H 2 PH. As the simplest cyclic, unsaturated organophosphorus compound, phosphirene is the prototype of a family of related compounds that have attracted attention from researchers. [ 1 ]
Phosphirenes , that is substituted phosphirene compounds where one or more of the H's are replaced by organic substituents, are far more commonly discussed than the parent phosphirene. The first example of a phosphirene, 1,2,3-triphenylphosphirene was prepared via trapping of the phosphinidine complex Mo(CO) 5 PPh with diphenylacetylene . [ 2 ]
Placement of the double bond between the carbon atoms provides a 1Hphosphirene in which the phosphorus center is bonded to two carbon atoms and a hydrogen atom. Alternatively, placement of the double bond between the phosphorus center and a carbon atom generates a 2H-phosphirene. The first 2H-phosphirene was synthesized as early as 1987 by Regitz group. However, the chemistry of 2H-phosphirenes was relatively dormant until a series of reports by Stephan group. [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Phosphirene |
Phosphonite
A phosphite ion in inorganic chemistry usually refers to [HPO 3 ] 2− but includes [H 2 PO 3 ] − ([HPO 2 (OH)] − ). These anions are the conjugate bases of phosphorous acid (H 3 PO 3 ). The corresponding salts, e.g. sodium phosphite (Na 2 HPO 3 ) are reducing in character.
The IUPAC recommended name for phosphorous acid is phosphonic acid . Correspondingly, the IUPAC-recommended name for the HPO 2− 3 ion is phosphonate . In the US the IUPAC naming conventions for inorganic compounds are taught at high school, but not as a 'required' part of the curriculum. [ 2 ] A well-known university-level textbook follows the IUPAC recommendations. [ 3 ] In practice any reference to "phosphite" should be investigated to determine the naming convention being employed.
From the commercial perspective, the most important phosphite salt is basic lead phosphite . Many salts containing the phosphite ion have been investigated structurally, these include sodium phosphite pentahydrate (Na 2 HPO 3 ·5H 2 O). (NH 4 ) 2 HPO 3 ·H 2 O, CuHPO 3 ·H 2 O, SnHPO 3 and Al 2 (HPO 3 ) 3 ·4H 2 O. [ 4 ] The structure of HPO 2− 3 is approximately tetrahedral. [ 5 ] [ 6 ]
HPO 2− 3 has a number of canonical resonance forms making it isoelectronic with bisulfite ion, HSO − 3 , which has a similar structure. [ 7 ]
Acid or hydrogen phosphites are called hydrogenphosphonates or acid phosphites. IUPAC recommends the name hydrogenphosphonates). They are anions HP(O) 2 OH − . A typical derivative is the salt [NH 4 ][HP(O) 2 OH]. [ 7 ] [ 6 ] Many related salts are known, e.g., RbHPHO 3 , CsHPHO 3 , TlHPHO 3 . These salts are prepared by treating phosphorous acid with the metal carbonate . These compounds contain a layer polymeric anion consisting of HPO 3 tetrahedra linked by hydrogen bonds. These layers are interleaved by layers of metal cations. [ 8 ]
Organic esters of hydrogen phosphites are anions with the formula HP(O) 2 OR − (R = organic group). One commercial example is the fungicide fosetyl-Al with the formula [C 2 H 5 OP(H)O 2 ] 3 Al. [ 9 ]
Pyrophosphites (diphosphites) can be produced by gently heating acid phosphites under reduced pressure. They contain the ion H 2 P 2 O 2− 5 , which can be formulated [HP(O) 2 O−P(O) 2 H] 2− . [ 7 ] [ 6 ]
In contrast to the paucity of evidence for PO 3− 3 , the corresponding arsenic ion, ortho- arsenite , AsO 3− 3 is known. An example is Ag 3 AsO 3 as well as the polymeric meta-arsenite (AsO − 2 ) n . [ 7 ] The iso-electronic sulfite ion, SO 2− 3 is known from its salts. [ 7 ]
Inorganic phosphites (containing HPO 2− 3 ) have been applied to crops to combat fungus-like pathogens of the order oomycetes (water molds). The situation is confusing because of the similarity in name between phosphite and phosphate (a major plant nutrient and fertilizer ingredient), and controversial because phosphites have sometimes been advertised as fertilizers, even though they are converted to phosphate too slowly to serve as a plant's main phosphorus source. In fact, phosphites may cause phytotoxicity when a plant is starved of phosphates. [ 10 ] Lemoynie [ 11 ] and others have described this complicated situation and noted that calling phosphites fertilizers avoided the regulatory complication and negative public perceptions that might have been incurred by registering them as fungicides. [ 10 ]
A major form of inorganic phosphite used in agriculture is monopotassium phosphite . This compound does serve as a potassium fertilizer. | https://en.wikipedia.org/wiki/Phosphite_(ion) |
In organic chemistry , a phosphite ester or organophosphite usually refers to an organophosphorous compound with the formula P(OR) 3 . They can be considered as esters of an unobserved tautomer phosphorous acid , H 3 PO 3 , with the simplest example being trimethylphosphite , P(OCH 3 ) 3 . Some phosphites can be considered esters of the dominant tautomer of phosphorous acid (HP(O)(OH) 2 ). The simplest representative is dimethylphosphite with the formula HP(O)(OCH 3 ) 2 . Both classes of phosphites are usually colorless liquids.
Phosphite esters are typically prepared by treating phosphorus trichloride with an alcohol . For alkyl alcohols the displaced chloride ion can attack the phosphite, causing dealkylation to give a dialkylphosphite and an organochlorine compound . [ 1 ] [ 2 ] The overall reaction is as follows:
Alternatively, when the alcoholysis is conducted in the presence of proton acceptors (typically an amine base), one obtains the C 3 -symmetric trialkyl derivatives: [ 3 ]
A base is not essential when using aromatic alcohols such as phenols, as they are not susceptible to attack by chloride, however it does catalyse the esterification reaction and is therefore often included. [ 4 ]
Phosphite esters can also be prepared by transesterification , as they undergo alcohol exchange upon heating with other alcohols. [ 5 ] This process is reversible and can be used to produce mixed alkyl phosphites. Alternatively, if the phosphite of a volatile alcohol is used, such as trimethyl phosphite , then the by product ( methanol ) can be removed by distillation, allowing the reaction to be driven to completion.
Phosphites are oxidized to phosphate esters:
This reaction underpins the commercial use of some phosphite esters as stabilizers in polymers. [ 6 ]
Alkyl phosphite esters are used in the Perkow reaction for the formation of vinyl phosphonates, and in the Michaelis–Arbuzov reaction to form phosphonates . Aryl phosphite esters may not undergo these reactions and hence are commonly used as stabilizers in halogen-bearing polymers such as PVC .
Phosphite esters may be used as reducing agents in more specialised cases. For example, triethylphosphite is known to reduce certain hydroperoxides to alcohols formed by autoxidation [ 7 ] ( scheme ). In this process the phosphite is converted to a phosphate ester . This reaction type is also utilized in the Wender Taxol total synthesis .
Phosphite esters are Lewis bases and hence can form coordination complexes with various metal ions. Representative phosphite ligands include trimethylphosphite ((MeO) 3 P), triethylphosphite ((EtO) 3 P), trimethylolpropane phosphite , and triphenylphosphite ((PhO) 3 P). Phosphites exhibit a smaller ligand cone angles than the structurally related phosphine ligand family . Phosphite ligands are components of industrial catalysts for hydroformylation and hydrocyanation . [ 8 ]
Diorganophosphites are derivatives of phosphorus(V) and can be viewed as the di-esters of phosphorous acid ((HO) 2 P(O)H). They exhibit tautomerism , however, the equilibrium overwhelmingly favours the right-hand (phosphonate-like) form: [ 11 ] [ 12 ]
The P-H bond is the site of high reactivity in these compounds (for example in the Atherton–Todd reaction and Hirao coupling ), whereas in tri-organophosphites the lone pair on phosphorus is the site of high reactivity. Diorganophosphites do however undergo transesterification. | https://en.wikipedia.org/wiki/Phosphite_ester |
In chemistry , a phosphodiester bond occurs when exactly two of the hydroxyl groups ( −OH ) in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds. The "bond" involves this linkage C−O−PO − 2 O−C . [ 1 ] Discussion of phosphodiesters is dominated by their prevalence in DNA and RNA , but phosphodiesters occur in other biomolecules, e.g. acyl carrier proteins , phospholipids and the cyclic forms of GMP and AMP ( cGMP and cAMP ). [ 2 ]
Phosphodiester bonds make up the backbones of DNA and RNA . In the phosphodiester bonds of nucleic acids, a phosphate is attached to the 5' carbon of one nucleoside and to the 3' carbon of the adjacent nucleoside. Specifically, it is the phosphodiester bonds that link the 3' carbon atom of one sugar molecule and the 5' carbon atom of another (hence the name 3', 5' phosphodiester linkage used with reference to this kind of bond in DNA and RNA chains). [ 3 ] The involved saccharide groups are deoxyribose in DNA and ribose in RNA. In order for the phosphodiester bond to form , joining the nucleosides , the tri-phosphate or di-phosphate forms of the nucleotide building blocks are broken apart to give off energy required to drive the enzyme -catalyzed reaction. [ 4 ] In DNA replication, for example, formation of the phosphodiester bonds is catalyzed by a DNA polymerase enzyme , using a pair of magnesium cations and other supporting structures. [ 3 ] Formation of the bond occurs not only in DNA and RNA replication, but also in the repair and recombination of nucleic acids, and may require the involvement of various polymerases, primers, and/or ligases. During the replication of DNA, for example, the DNA polymerase I leaves behind a hole between the phosphates in the newly formed backbone. DNA ligase is able to form a phosphodiester bond between the nucleotides on each side of the gap. [ 2 ]
Phosphodiesters are negatively charged at pH 7. [ 5 ] The negative charge attracts histones , metal cations such as magnesium , and polyamines [needs citation]. Repulsion between these negative charges influences the conformation of the polynucleic acids.
Hydrolysis (breaking) of phosphodiester bonds can be promoted in several ways. Phosphodiesterases are enzymes that catalyze the hydrolysis of the phosphodiester bond. These enzymes are involved in repairing DNA and RNA sequences, nucleotide salvage, and in the conversion of cGMP and cAMP to GMP and AMP, respectively. [ 2 ] Hydrolysis of the phosphodiester bond also occurs chemically and spontaneously, without the aid of enzymes. For example, simple ribose (in RNA) has one more hydroxyl group than deoxyribose (in DNA), making the former less stable and more susceptible to alkaline hydrolysis , wherein relatively high pH conditions induce the breaking of the phosphodiester linkage between two ribonucleotides . The relative instability of RNA under hydroxyl attack of its phosphodiester bonds makes it inadequate for the storage of genomic information, but contributes to its usefulness in transcription and translation . [ 2 ] | https://en.wikipedia.org/wiki/Phosphodiester_bond |
A phosphodiesterase ( PDE ) is an enzyme that breaks a phosphodiester bond . Usually, phosphodiesterase refers to cyclic nucleotide phosphodiesterases, which have great clinical significance and are described below. However, there are many other families of phosphodiesterases, including phospholipases C and D , autotaxin , sphingomyelin phosphodiesterase , DNases , RNases , and restriction endonucleases (which all break the phosphodiester backbone of DNA or RNA ), as well as numerous less-well-characterized small-molecule phosphodiesterases.
The cyclic nucleotide phosphodiesterases comprise a group of enzymes that degrade the phosphodiester bond in the second messenger molecules cAMP and cGMP . They regulate the localization, duration, and amplitude of cyclic nucleotide signaling within subcellular domains. PDEs are therefore important regulators of signal transduction mediated by these second messenger molecules.
These multiple forms (isoforms or subtypes) of phosphodiesterase were isolated from rat brain using polyacrylamide gel electrophoresis in the early 1970s by Weiss and coworkers, [ 1 ] [ 2 ] and were soon afterward shown to be selectively inhibited by a variety of drugs in brain and other tissues, also by Weiss and coworkers. [ 3 ] [ 4 ]
The potential for selective phosphodiesterase inhibitors to be used as therapeutic agents was predicted in the 1970s by Weiss and coworkers . [ 5 ] This prediction has now come to pass in a variety of fields (e.g. sildenafil as a PDE5 inhibitor and Rolipram as a PDE4 inhibitor ).
The PDE nomenclature signifies the PDE family with an Arabic numeral, then a capital letter denotes the gene in that family , and a second and final Arabic numeral then indicates the splice variant derived from a single gene (e.g., PDE1C3: family 1, gene C, splicing variant 3). [ 6 ]
The superfamily of PDE enzymes is classified into 11 families, namely PDE1 - PDE11 , [ 7 ] in mammals . The classification is based on:
Different PDEs of the same family are functionally related despite the fact that their amino acid sequences can show considerable divergence. [ 8 ] PDEs have different substrate specificities. Some are cAMP-selective hydrolases ( PDE4 , 7 and 8 ); others are cGMP-selective ( PDE5 , 6 , and 9 ). Others can hydrolyse both cAMP and cGMP ( PDE1 , 2 , 3 , 10 , and 11 ). PDE3 is sometimes referred to as cGMP-inhibited phosphodiesterase. Although PDE2 can hydrolyze both cyclic nucleotides, binding of cGMP to the regulatory GAF-B domain will increase cAMP affinity and hydrolysis to the detriment of cGMP. This mechanism, as well as others, allows for cross-regulation of the cAMP and cGMP pathways. PDE12 cleaves 2',5'-phosphodiester bond linking adenosines of the 5'-triphosphorylated oligoadenylates. [ 9 ] [ 10 ] PDE12 is not a member of the cyclic nucleotide phosphodiesterase superfamily that contains PDE1 through PDE11.
Phosphodiesterase enzymes have been shown to be different in different types of cells, including normal and leukemic lymphocytes [ 11 ] and are often targets for pharmacological inhibition due to their unique tissue distribution, structural properties, and functional properties. [ 12 ]
Inhibitors of PDE can prolong or enhance the effects of physiological processes mediated by cAMP or cGMP by inhibition of their degradation by PDE. [ 13 ]
Sildenafil (Viagra) is an inhibitor of cGMP-specific phosphodiesterase type 5 , which enhances the vasodilatory effects of cGMP in the corpus cavernosum and is used to treat erectile dysfunction . Sildenafil is also currently being investigated for its myo- and cardioprotective effects, with particular interest being given to the compound's therapeutic value in the treatment of Duchenne muscular dystrophy [ 14 ] and benign prostatic hyperplasia . [ 15 ]
Paraxanthine , the main metabolite of caffeine , is another cGMP-specific phosphodiesterase inhibitor which inhibits PDE9, a cGMP preferring phosphodiesterase. [ 16 ] PDE9 is expressed as high as PDE5 in the corpus cavernosum. [ 17 ]
PDE inhibitors have been identified as new potential therapeutics in areas such as pulmonary arterial hypertension , coronary heart disease , dementia , depression , asthma , COPD , protozoal infections (including malaria ) and schizophrenia . [ citation needed ]
PDE also are important in seizure incidence. For example, PDE compromised the antiepileptic activity of adenosine. In addition, using of a PDE inhibitor (pentoxifylline) in pentylenetetrazole-induced seizure indicated the antiepileptic effect by increasing the time latency to seizure incidence and decreasing the seizure duration in vivo. [ 18 ]
Cilostazol (Pletal) inhibits PDE3 . This inhibition allows red blood cells to be more able to bend. This is useful in conditions such as intermittent claudication , as the cells can maneuver through constricted veins and arteries more easily. [ citation needed ]
Dipyridamole inhibits PDE-3 and PDE-5. This leads to intraplatelet accumulation of cAMP and/or cGMP, inhibiting platelet aggregation. [ 19 ]
Zaprinast inhibits the growth of asexual blood-stage malaria parasites ( Plasmodium falciparum ) in vitro with an ED 50 value of 35 μM, and inhibits PfPDE1, a P. falciparum cGMP-specific phosphodiesterase, with an IC 50 value of 3.8 μM. [ 20 ]
Xanthines such as caffeine and theobromine are cAMP -phosphodiesterase inhibitors. However, the inhibitory effect of xanthines on phosphodiesterases are only seen at dosages higher than what people normally consume. [ citation needed ]
Sildenafil, Tadalafil and Vardenafil are PDE-5 inhibitors and are widely used in the treatment of erectile dysfunction.
Recently a PDE was found to break down and release human body grime found on laundry. With the help of this newly discovered nuclease, the yellow stains and odors, that normally remain on clothes with classical detergents, can easily be removed. [ 21 ] | https://en.wikipedia.org/wiki/Phosphodiesterase |
PDE3 is a phosphodiesterase . The PDEs belong to at least eleven related gene families , which are different in their primary structure , substrate affinity , responses to effectors , and regulation mechanism .
Most of the PDE families are composed of more than one gene. PDE3 is clinically significant because of its role in regulating heart muscle, vascular smooth muscle and platelet aggregation. PDE3 inhibitors have been developed as pharmaceuticals, but their use is limited by arrhythmic effects and they can increase mortality in some applications.
PDE3 enzymes are involved in regulation of cardiac and vascular smooth muscle contractility. Molecules that inhibit PDE3 were originally investigated for the treatment of heart failure , but, because of unwanted arrhythmic side-effects , they are not studied for that indication any longer. Nonetheless, the PDE3 inhibitor milrinone is approved for use in heart failure in intravenous form. [ 1 ]
Both PDE3A and PDE3B are expressed in vascular smooth muscle cells and are likely to modulate contraction. Their expression in vascular smooth muscle is altered under specific conditions such as elevated cAMP and hypoxia . [ 1 ]
The PDE3 family in mammals consists of two members, PDE3A and PDE3B. The PDE3 isoforms are structurally similar, containing an N-terminal domain important for the localization and a C-terminus end. [ 2 ] The 44-amino acid insertion in the catalytic domain differs in the PDE3 isoforms, and the N-terminal portions of the isoforms are quite divergent. PDE3A and PDE3B have strikingly similar pharmacological and kinetic properties , but the distinction is in expression profiles and affinity for cGMP. [ 3 ]
The PDE3 family is composed of two genes , PDE3A and PDE3B . In cells expressing both genes, PDE3A is usually dominant. Three different variants of PDE3A (PDE3A1-3) are products of alternate startcodon usage of the PDE3A gene. The PDE3B encodes a single isoform only. [ 1 ] [ 4 ]
In their full-length both PDE3A and PDE3B contain two N-terminal hydrophobic membrane association regions, NHR1 and NHR2 (figure 2). The difference of the PDE3A1-3 variants lies in whether they include:
The last can be predicted to be exclusively on soluble / cytosolic form. [ 4 ] [ 5 ]
PDE3A is mainly implicated in cardiovascular function and fertility but PDE3B is mainly implicated in lipolysis. [ 3 ] Table 1 is an overview of localization of the PDE3 isoforms.
In general, PDE3 can be either cytosolic or membrane-bound and has been associated to plasma membrane , sarcoplasmic reticulum , golgi , and nucleus envelope. [ 2 ]
PDE3B is predominantly membrane-associated, and is localized to endoplasmic reticulum and microsomal fractions. [ 1 ]
PDE3A can be either membrane-associated or cytosolic, depending on the variant and the cell type it is expressed in. [ 1 ]
PDE3A and PDE3B activity is regulated by several phosphorylation pathways. Protein kinase A and protein kinase B both activate PDE3A and PDE3B via phosphorylation at two different phosphorylation sites (P1 and P2) between NHR1 and NHR2 (figure 2). Hydrolysis of cAMP by PDE3 isoforms is also directly inhibited by cGMP , although PDE3B is only ≈10% as sensitive to cGMP inhibition as PDE3A. [ 4 ] The PDE3B has been extensively studied for its importance in mediating the antilipolytic and antiglycogenlytic effect of insulin in adipose and liver tissues . The activation of PDE3B in adipocytes is associated with phosphorylation of serine residue by an insulin-stimulated protein serine kinase (PDE3IK). By blocking insulin activation of PDE3IK, and in turn phosphorylation/activation of PDE3B, the antilipolytic effect of insulin can be antagonized. Activation of PDE3B decreases concentrations of cAMP, which in turn reduces protein kinase A activity. Protein kinase A is responsible for activation of lipase , which induces lipolysis as well as other physiological pathways. [ 6 ] [ 4 ]
Whether phosphorylation pathways, which regulate activity of PDE3A or PDE3B, could serve as potential drug targets rather than the catalytic domain of the PDE3 enzyme itself is unclear and beyond the scope of this text.
The mammalian PDEs share a common structural organization and contain three functional domains, which include the conserved catalytic core, a regulatory N-terminus , and the C-terminus . The conserved catalytic core is much more similar within PDE families, with about 80% amino acid identity, than between different families. It is believed that the core contains common structural elements that are important for the hydrolysis of cAMP and cGMP phosphodiester bonds. It is also believed that it contains family-specific determinants for differences in affinity for substrates and sensitivity for inhibitors. [ 6 ]
The catalytic domain of PDE3 is characterized by a 44-amino acid insert, but this insert is unique to the PDE3 family, and is a factor when determining a structure for a potent and selective PDE3 inhibitor . [ 6 ]
The crystal structure of the catalytic domains of several PDEs, including PDE3B, have shown that they contain three helical subdomains:
At the interface of these domains a deep hydrophobic pocket is formed by residues that are highly conserved among all PDEs. This pocket is the active site and is composed of four subsites :
The M site is at the bottom of the hydrophobic binding pocket and contains two divalent metal binding sites. The metal ions that can bind to these sites are either zinc or magnesium. The zinc binding site has two histidine and two aspartic acid residues that are absolutely conserved among those PDEs studied to date. [ 3 ] [ 1 ]
The N-terminal portions of PDEs are widely divergent and contain determinants that are associated with regulatory properties specific to different gene families. For PDE3, those determinants are the hydrophobic membrane association domains and cAMP-dependent protein kinase phosphorylation sites. [ 6 ]
At first, the PDE3s were purified and described as enzymes that hydrolyse both cGMP and cAMP with K m values of 0.1–0.8 μM. However the V max for cAMP hydrolysis is 4–10 times higher than V max for cGMP hydrolysis. [ 6 ]
When different PDEs were first identified, two types of PDEs (PDE3 and PDE4) that exhibited high affinities for cAMP were isolated. PDE3 exhibited high affinity for both cGMP and cAMP, but PDE4 had high affinity for only cAMP. For that reason, the PDE3 was called the cGMP-inhibited PDE to distinguish it from PDE4. [ 6 ]
The 44-amino acid insertion in the catalytic domain of PDE3s is believed to be involved in PDE3's interaction with its substrate and inhibitors, but that remains to be established. [ 6 ]
The proposed molecular mechanism of cyclic nucleotide specificity of PDEs is the so-called glutamine switch mechanism.
In the PDEs that have had their structure solved, there seems to be an invariant glutamine residue that stabilizes the binding of the purine ring in the active site (binding pocket). The g-amino group of the glutamine residue can alternatively adopt two different orientations:
In PDEs that can hydrolyse both cGMP and cAMP (PDE3s), the glutamine can rotate freely and therefore switch between orientations. [ 3 ] [ 1 ]
From early studies an initial model of PDE, active site topography was derived. This early model can be summarized into the following steps concerning cAMP active site topography:
PDE3 inhibitors :
It has been demonstrated that PDE3A inhibition prevents oocyte maturation in vitro and in vivo . [ 1 ] For example, when mice are made completely deficient of PDE3A, they become infertile. [ 2 ]
Aggregation of platelets is highly regulated by cyclic nucleotides. PDE3A is a regulator of this process, and PDE3 inhibitors effectively prevent aggregation of platelets. Cilostazol is approved for treatment of intermittent claudication and is thought to involve inhibition of platelet aggregation and also inhibition of smooth muscle proliferation and vasodilation.
The most studied roles of PDE3B have been in the areas of insulin , IGF1 , and leptin signaling. [ 1 ] When PDE3B is overexpressed in β-cells in mice, it causes impaired insulin secretion and glucose intolerance. [ 2 ]
PDE3a expression has been described as a biomarker for sensitivity for PDE3-inhibitor Zardaverine in different types of cancer. [ 8 ]
Targeting PDE3 with optimal doses and timing, enoximone prevents allergic inflammation in HDM-driven models of allergic airway inflammation. [ 9 ] PDE3 inhibitors enoximone and milrinone can be used as a rescue drug in life-threatening bronchial asthma/ acute severe asthma . [ 10 ] [ 11 ] [ 12 ] | https://en.wikipedia.org/wiki/Phosphodiesterase_3 |
At least four types of the enzyme phosphodiesterase 4 ( PDE4 ) are known: | https://en.wikipedia.org/wiki/Phosphodiesterase_4 |
Phosphoenolpyruvate carboxylase (also known as PEP carboxylase , PEPCase , or PEPC ; EC 4.1.1.31 , PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO 3 − ) to phosphoenolpyruvate (PEP) to form the four-carbon compound oxaloacetate and inorganic phosphate : [ 1 ]
This reaction is used for carbon fixation in CAM (crassulacean acid metabolism) and C 4 organisms, as well as to regulate flux through the citric acid cycle (also known as Krebs or TCA cycle) in bacteria and plants. The enzyme structure and its two step catalytic, irreversible mechanism have been well studied. PEP carboxylase is highly regulated, both by phosphorylation and allostery .
The PEP carboxylase enzyme is present in plants and some types of bacteria, but not in fungi or animals (including humans). [ 2 ] The genes vary between organisms, but are strictly conserved around the active and allosteric sites discussed in the mechanism and regulation sections. Tertiary structure of the enzyme is also conserved. [ 3 ]
The crystal structure of PEP carboxylase in multiple organisms, including Zea mays (maize), and Escherichia coli has been determined. [ 3 ] The overall enzyme exists as a dimer-of-dimers: two identical subunits closely interact to form a dimer through salt bridges between arginine (R438 - exact positions may vary depending on the origin of the gene) and glutamic acid (E433) residues. [ 4 ] This dimer assembles (more loosely) with another of its kind to form the four subunit complex. The monomer subunits are mainly composed of alpha helices (65%), [ 1 ] and have a mass of 106kDa each. [ 5 ] The sequence length is about 966 amino acids . [ 6 ]
The enzyme active site is not completely characterized. It includes a conserved aspartic acid (D564) and a glutamic acid (E566) residue that non-covalently bind a divalent metal cofactor ion through the carboxylic acid functional groups. [ 1 ] This metal ion can be magnesium , manganese or cobalt depending on the organism, [ 1 ] [ 2 ] and its role is to coordinate the phosphoenolpyruvate molecule as well as the reaction intermediates. A histidine (H138) residue at the active site is believed to facilitate proton transfer during the catalytic mechanism. [ 1 ] [ 4 ]
The mechanism of PEP carboxylase has been well studied. The enzymatic mechanism of forming oxaloacetate is very exergonic , and thereby irreversible, in biochemical standard conditions; the biological standard Gibbs free energy change (∆G°’) is −30 kJ⋅mol −1 . [ 1 ] The substrates and cofactor bind in the following order: metal cofactor (either Co 2+ , Mg 2+ , or Mn 2+ ), PEP, bicarbonate (HCO 3 − ). [ 1 ] [ 2 ] The mechanism proceeds in two major steps, as described below and shown in figure 2:
The metal cofactor is necessary to coordinate the enolate and carbon dioxide intermediates; the CO 2 molecule is only lost 3% of the time. [ 2 ] The active site is hydrophobic to exclude water , since the carboxyphosphate intermediate is susceptible to hydrolysis . [ 1 ]
The three most important roles that PEP carboxylase plays in plants and bacteria metabolism are in the C 4 cycle , the CAM cycle , and the citric acid cycle biosynthesis flux.
The primary mechanism of carbon dioxide assimilation in plants is through the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (also known as RuBisCO ), that adds CO 2 to ribulose-1,5-bisphosphate (a 5 carbon sugar), to form two molecules of 3-phosphoglycerate (2x3 carbon sugars). However, at higher temperatures and lower CO 2 concentrations, RuBisCO adds oxygen instead of carbon dioxide, to form the unusable product glycolate in a process called photorespiration . To prevent this wasteful process, plants increase the local CO 2 concentration in a process called the C 4 cycle . [ 3 ] [ 8 ] PEP carboxylase plays the key role of binding CO 2 in the form of bicarbonate with PEP to create oxaloacetate in the mesophyll tissue . This is then converted back to pyruvate (through a malate intermediate), to release the CO 2 in the deeper layer of bundle sheath cells for carbon fixation by RuBisCO and the Calvin cycle . Pyruvate is converted back to PEP in the mesophyll cells, and the cycle begins again, thus actively pumping CO 2 . [ 2 ] [ 9 ] [ 10 ]
The second important and very similar biological significance of PEP carboxylase is in the CAM cycle . This cycle is common in organisms living in arid habitats. Plants cannot afford to open stomata during the day to take in CO 2 , as they would lose too much water by transpiration . Instead, stomata open at night, when water evaporation is minimal, and take in CO 2 by fixing with PEP to form oxaloacetate though PEP carboxylase. Oxaloacetate is converted to malate by malate dehydrogenase , and stored for use during the day when the light dependent reaction generates energy (mainly in the form of ATP ) and reducing equivalents such as NADPH to run the Calvin cycle . [ 2 ] [ 3 ] [ 10 ]
Third, PEP carboxylase is significant in non-photosynthetic metabolic pathways. Figure 3 shows this metabolic flow (and its regulation). Similar to pyruvate carboxylase , PEP carboxylase replenishes oxaloacetate in the citric acid cycle. At the end of glycolysis , PEP is converted to pyruvate , which is converted to acetyl-coenzyme-A ( acetyl-CoA ), which enters the citric acid cycle by reacting with oxaloacetate to form citrate . To increase flux through the cycle, some of the PEP is converted to oxaloacetate by PEP carboxylase. Since the citric acid cycle intermediates provide a hub for metabolism, increasing flux is important for the biosynthesis of many molecules, such as for example amino acids . [ 11 ]
PEP carboxylase is mainly subject to two levels of regulation: phosphorylation and allostery . Figure 3 shows a schematic of the regulatory mechanism.
Phosphorylation by phosphoenolpyruvate carboxylase kinase turns the enzyme on, whereas phosphoenolpyruvate carboxylase phosphatase turns it back off. Both kinase and phosphatase are regulated by transcription . It is further believed that malate acts as a feedback inhibitor of kinase expression levels, and as an activator for phosphatase expression (transcription). [ 12 ] Since oxaloacetate is converted to malate in CAM and C 4 organisms, high concentrations of malate activate phosphatase expression - the phosphatase subsequently de-phosphorylates and thus de-actives PEP carboxylase, leading to no further accumulation of oxaloacetate and thus no further conversion of oxaloacetate to malate. Hence malate production is down-regulated. [ 1 ] [ 12 ]
The main allosteric inhibitors of PEP carboxylase are the carboxylic acids malate (weak) and aspartate (strong). [ 5 ] [ 12 ] Since malate is formed in the next step of the CAM and C 4 cycles after PEP carboxylase catalyses the condensation of CO 2 and PEP to oxaloacetate, this works as a feedback inhibition pathway. Oxaloacetate and aspartate are easily inter-convertible through a transaminase mechanism; thus high concentrations of aspartate are also a pathway of feedback inhibition of PEP carboxylase.
The main allosteric activators of PEP carboxylase are acetyl-CoA [ 13 ] and fructose-1,6-bisphosphate (F-1,6-BP). [ 1 ] [ 13 ] Both molecules are indicators of increased glycolysis levels, and thus positive feed-forward effectors of PEP carboxylase. They signal the need to produce oxaloacetate to allow more flux through the citric acid cycle . Additionally, increased glycolysis means a higher supply of PEP is available, and thus more storage capacity for binding CO 2 in transport to the Calvin cycle . It is also noteworthy that the negative effectors aspartate competes with the positive effector acetyl-CoA , suggesting that they share an allosteric binding site. [ 14 ]
Studies have shown that energy equivalents such as AMP , ADP and ATP have no significant effect on PEP carboxylase. [ 15 ]
The magnitudes of the allosteric effects of these different molecules on PEP carboxylase activity depend on individual organisms. [ 16 ] | https://en.wikipedia.org/wiki/Phosphoenolpyruvate_carboxylase |
Phosphohydroxypyruvic acid is an organic acid most widely known as an intermediate in the synthesis of serine . [ 1 ]
Phosphohydroxypyruvic acid is a moderately weak acid .
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphohydroxypyruvic_acid |
Phosphoinositide phospholipase C ( PLC , EC 3.1.4.11, triphosphoinositide phosphodiesterase, phosphoinositidase C, 1-phosphatidylinositol-4,5-bisphosphate phosphodiesterase, monophosphatidylinositol phosphodiesterase, phosphatidylinositol phospholipase C, PI-PLC, 1-phosphatidyl- D - myo -inositol-4,5-bisphosphate inositoltrisphosphohydrolase ; systematic name 1-phosphatidyl-1 D - myo -inositol-4,5-bisphosphate inositoltrisphosphohydrolase ) is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. [ 1 ] These enzymes belong to a larger superfamily of Phospholipase C . Other families of phospholipase C enzymes have been identified in bacteria and trypanosomes . Phospholipases C are phosphodiesterases .
Phospholipase Cs participate in phosphatidylinositol 4,5-bisphosphate (PIP 2 ) metabolism and lipid signaling pathways in a calcium-dependent manner. At present, the family consists of six sub-families comprising a total of 13 separate isoforms that differ in their mode of activation, expression levels, catalytic regulation, cellular localization, membrane binding avidity and tissue distribution. All are capable of catalyzing the hydrolysis of PIP 2 into two important second messenger molecules, which go on to alter cell responses such as proliferation , differentiation , apoptosis , cytoskeleton remodeling, vesicular trafficking, ion channel conductance , endocrine function and neurotransmission .
All family members are capable of catalyzing the hydrolysis of PIP 2 , a phosphatidylinositol at the inner leaflet of the plasma membrane into the two second messengers, inositol trisphosphate (IP 3 ) and diacylglycerol (DAG).
The chemical reaction may be expressed as:
PLCs catalyze the reaction in two sequential steps. The first reaction is a phosphotransferase step that involves an intramolecular attack between the hydroxyl group at the 2' position on the inositol ring and the adjacent phosphate group resulting in a cyclic IP 3 intermediate. At this point, DAG is generated. However, in the second phosphodiesterase step, the cyclic intermediate is held within the active site long enough to be attacked by a molecule of water, resulting in a final acyclic IP 3 product. It should be mentioned that bacterial forms of the enzyme, which contain only the catalytic lipase domain, produce cyclic intermediates exclusively, whereas the mammalian isoforms generate predominantly the acyclic product. However, it is possible to alter experimental conditions (e.g., temperature, pH) in vitro such that some mammalian isoforms will alter the degree to which they produce mixtures of cyclic/acyclic products along with DAG. [ citation needed ] This catalytic process is tightly regulated by reversible phosphorylation of different phosphoinositides and their affinity for different regulatory proteins. [ 2 ] [ 3 ] [ 4 ]
Phosphoinositide phospholipase C performs its catalytic function at the plasma membrane where the substrate PIP 2 is present. This membrane docking is mediated mostly by lipid-binding domains (e.g. PH domain and C2 domain ) that display affinity for different phospholipid components of the plasma membrane. It is important to note that research has also discovered that, in addition to the plasma membrane, phosphoinositide phospholipase C also exists within other sub-cellular regions such as the cytoplasm and nucleus of the cell. At present, it is unclear exactly what the definitive roles for these enzymes in these cellular compartments are, particularly the nucleus.
Phospholipase C performs a catalytic mechanism, depleting PIP2 and generating inositol trisphosphate (IP 3 ) and diacylglycerol (DAG).
Depletion of PIP2 inactivates numerous effector molecules in the plasma membrane, most notably PIP2 dependent channels and transporters responsible for setting the cell's membrane potential. [ 5 ]
The hydrolytic products also go on to modulate the activity of downstream proteins important for cellular signaling. IP3 is soluble, and diffuses through the cytoplasm and interacts with IP3 receptors on the endoplasmic reticulum , causing the release of calcium and raising the level of intracellular calcium .
DAG remains within the inner leaflet of the plasma membrane due to its hydrophobic character, where it recruits protein kinase C (PKC), which becomes activated in conjunction with binding calcium ions. This results in a host of cellular responses through stimulation of calcium-sensitive proteins such as Calmodulin .
In terms of domain organization, all family members possess homologous X and Y catalytic domains in the form of a distorted Triose Phosphate Isomerase (TIM) barrel with a highly disordered, charged, and flexible intervening linker region. Likewise, all isoforms possess four EF hand domains, and a single C2 domain that flank the X and Y catalytic core. An N-terminal PH domain is present in every family except for the sperm-specific ζ isoform.
SH2 (phosphotyrosine binding) and SH3 (proline-rich-binding) domains are found only in the γ form (specifically within the linker region), and only the ε form contains both guanine nucleotide exchange factor (GEF) and RA ( Ras Associating) domains. The β subfamily is distinguished from the others by the presence of a long C-terminal extension immediately downstream of the C2 domain, which is required for activation by G αq subunits, and which plays a role in plasma membrane binding and nuclear localization.
The phospholipase C family consists of 13 isoenzymes split between six subfamilies, PLC-δ (1,3 & 4), -β(1-4), -γ( 1 ,2), -ε, -ζ, and the recently discovered -η(1,2) isoform. Depending on the specific subfamily in question, activation can be highly variable. Activation by either G αq or G βγ G-protein subunits (making it part of a G protein-coupled receptor signal transduction pathway) or by transmembrane receptors with intrinsic or associated tyrosine kinase activity has been reported. In addition, members of the Ras superfamily of small GTPases (namely the Ras and Rho subfamilies) have also been implicated. It should also be mentioned that all forms of phospholipase C require calcium for activation, many of them possessing multiple calcium contact sites in the catalytic region. The only isoform that is known to be inactive at basal intracellular calcium levels is the δ subfamily of enzymes suggesting that they function as calcium amplifiers that become activated downstream of other PLC family members.
PLC-β(1-4) (120-155kDa) are activated by G αq subunits through their C2 domain and long C-terminal extension. Gβγ subunits are known to activate the β2 and β3 isozymes only; however, this occurs through the PH domain and/or through interactions with the catalytic domain. The exact mechanism still requires further investigation. The PH domain of β2 and β3 plays a dual role, much like PLC-δ1, by binding to the plasma membrane, as well as being a site of interaction for the catalytic activator. However, PLC-β binds to the lipid surface independent of PIP 2 with all isozymes preferring phosphoinositol-3-phosphate or neutral membranes.
Members of the Rho GTPase family (e.g., Rac1, Rac2, Rac3, and cdc42 ) have been implicated in their activation by binding to an alternate site on the N-terminal PH domain followed by subsequent recruitment to the plasma membrane . A crystal structure of Rac1 bound to the PH domain of PLCβ2 has been solved. Like PLC-δ1, many PLC-β isoforms (in particular, PLC-β1) have been found to take up residence in the nuclear compartment. A basic amino acid region within the enzyme's long C-terminal tail appears to function as a Nuclear Localization Signal for import into the nucleus. PLC-β1 seems to play unspecified roles in cellular proliferation and differentiation.
PLC-γ (120-155kDa) is activated by receptor and non-receptor tyrosine kinases due to the presence of two SH2 and a single SH3 domain situated between a split PH domain within the linker region. Although this particular isoform does not contain classic nuclear export or localization sequences, it has been found within the nucleus of certain cell lines. [ citation needed ] There are two main isoforms of PLCγ expressed in human specimens, PLC-γ1 and PLC-γ2. [ 6 ]
PLC-γ2 plays a major role in BCR signal transduction . Absence of this enzyme in knockout specimens severely inhibits the development of B cells because the same signaling pathways necessary for antigen mediated B cell activation are necessary for B cell development from CLPs . [ 6 ]
In B cell signaling, PI 3-kinase is recruited to the BCR early in the signal transduction pathway. PI-3K phosphorylates PIP 2 ( Phosphatidylinositol 4,5-bisphosphate ) into PIP 3 ( Phosphatidylinositol 3,4,5-trisphosphate ). The increase in concentration of PIP 3 recruits PLC-γ2 to the BCR complex which binds to BLNK on the BCR scaffold and membrane PIP 3 . PLC-γ2 is then phosphorylated by Syk on one site and Btk on two sites. PLC-γ2 then competes with PI-3K for PIP 2 which it hydrolyzes into IP 3 (inositol 1,4,5-trisphosphate), which ultimately raises intercellular calcium, and diacylglycerol (DAG), which activates portions of the PKC family. Because PLC-γ2 competes for PIP 2 with the original signaling molecule PI3K, it serves as a negative feedback mechanism. [ 6 ]
The PLC-δ subfamily consists of three family members, δ1, 2, and 3. PLC-δ1 (85kDa) is the most well understood of the three. The enzyme is activated by high calcium levels generated by other PLC family members, and therefore functions as a calcium amplifier within the cell. Binding of its substrate PIP 2 to the N-terminal PH domain is highly specific and functions to promote activation of the catalytic core. In addition, this specificity helps tether the enzyme tightly to the plasma membrane in order to access substrate through ionic interactions between the phosphate groups of PIP2 and charged residues in the PH domain. While the catalytic core does possess a weak affinity for PIP 2 , the C2 domain has been shown to mediate calcium-dependent phospholipid binding as well. In this model, the PH and C2 domains operate in concert as a "tether and fix" apparatus necessary for processive catalysis by the enzyme.
PLC-δ1 also possesses a classical leucine -rich nuclear export signal (NES) in its EF hand motif, as well as a Nuclear localization signal within its linker region. These two elements combined allow PLC-δ1 to actively translocate into and out of the nucleus. However, its function in the nucleus remains unclear.
The widely expressed PLC-δ1 isoform is the best-characterized phospholipase family member, as it was the first to have high-resolution X-ray crystal structures available for analysis. In terms of domain architecture, all of the enzymes are built upon a common PLC-δ backbone, wherein each family displays similarities, as well as obvious distinctions, that contribute to unique regulatory properties within the cell. Because it is the only family found expressed in lower eukaryotic organisms such as yeast and slime molds , it is considered the prototypical PLC isoform. The other family members more than likely evolved from PLC-δ as their domain architecture and mechanism of activation were expanded. Although a full crystal structure has not been obtained, high-resolution X-ray crystallography has yielded the molecular structure of the N-terminal PH domain complexed with its product IP3, as well as the remainder of the enzyme with the PH domain ablated. These structures have provided researchers with the necessary information to begin speculating about other family members such as PLCβ2.
PLCB1 ; PLCB2 ; PLCB3 ; PLCB4 ; PLCD1 ; PLCD3 ; PLCD4 ; PLCE1 ; PLCG1 ; PLCG2 ; PLCH1 ; PLCH2 ; PLCL1 ; PLCL2 ; PLCZ1 | https://en.wikipedia.org/wiki/Phosphoinositide_phospholipase_C |
Phospholipid-derived fatty acids ( PLFAs ) are widely used in microbial ecology as chemotaxonomic markers of bacteria and other organisms. Phospholipids are the primary lipids composing cellular membranes . Phospholipids can be saponified , which releases the fatty acids contained in their diglyceride tail. Once the phospholipids of an unknown sample are saponified, the composition of the resulting PLFA can be compared to the PLFA of known organisms to determine the identity of the sample organism. PLFA analysis may be combined with other techniques, such as stable isotope probing to determine which microbes are metabolically active in a sample. PLFA analysis was pioneered by D.C. White at the University of Tennessee, in the early to mid 1980s. [ 1 ]
PLFAs are an essential structural component of all microbial cellular membranes . PLFA analysis is a technique widely used for estimation of the total biomass and to observe broad changes in the community composition of the living microbiota of soil and aqueous environments. There has been a surge of interest in PLFAs in recent years, evident from the large increase in peer-reviewed journal references on the subject. [ 2 ] However, there is increasing concern that some researchers are assigning PLFAs to specific microbial classes when in fact those PLFAs are present in a broad range of life forms. [ 2 ] Phospholipids can occur in many biological classes (such as in plant roots, fungi, as well as in soil bacteria), so care has to be taken in over-assigning PLFA biomarkers to the wrong class. Even though phospholipids occur in many different life forms, the fatty acid side chains between differing life forms can be quite unique. Polyunsaturated fatty acids ( e.g. 18:3 ω3c) are found in plants, algae and cyanobacteria, but are often not present in bacteria. Monounsaturated fatty acids (particularly at the omega-7 position), odd-chain saturated fatty acids ( e.g. 15:0), branched-chain fatty acids (mainly iso or anetiso and 10-methyl) and cyclopropane fatty acids ( e.g. 19:0 cyclo ω7c) are mostly synthesized by bacteria. The polyunsaturated fatty acid, 18:2 ω6c ( linoleic acid ), is found in soil fungi , whereas the monounsaturated fatty acid, 16:1 ω5c, is predominant in Arbuscular mycorrhizal fungi (AMF).
The basic premise is that as individual organisms (especially bacteria and fungi) die, phospholipids are rapidly degraded and the remaining phospholipid content of the sample is assumed to be from living organisms. As the phospholipids of different groups of bacteria and fungi contain a variety of somewhat unusual fatty acids , they can serve as useful biomarkers for such groups. PLFA profiles and composition can be determined by purifying the phospholipids and then cleaving the fatty acids for further analysis. Knowledge of the composition and metabolic activity of the microbiota in soils, water and waste materials is useful in optimizing crop production, in bioremediation and in understanding microbial ecosystems . Soil microbial community analysis by PLFA has been a widely used technique due to the sensitive, reproducible measurement of the dominant portions of the soil microbiota and the fact that PLFA does not require cultivation of the organisms. [ 3 ] Sampling of soil populations by culturing has proven not cost effective and results in biased results due to the differing ease of culturing of some organisms. The main drawback of PLFA has been that the extraction time is very long and cumbersome. A new 96-well plate PLFA extraction procedure has been developed which represents a 4-to-5 fold increase in throughput over traditional PLFA extraction methods. This new method, coupled to new software tools for analyzing the PLFA data, will be useful to laboratories performing large numbers of PLFA analyses, or for laboratories wanting to begin PLFA research. [ 4 ]
Early studies of the living soil microbial communities were largely based on attempts at culturing bacteria and fungi of soil. However, due to difficulty in culturing many of the organisms, the differential growth rates of the organisms, and labor involved, this proved to be not satisfactory. A 1965 article proposed using molecules produced by the organisms as biomarkers for the microbial communities. [ 5 ] In the following two decades, rapid progress was made in development of gas chromatographs (GC) and of fused silica capillary columns for the GC instruments, enabling better analysis of biological materials, including fatty acid methyl esters (FAMEs). PLFA analysis can be used for microbial community structure and activity through the use of “signature” fatty acids. [ 6 ] The basic concept is that the phospholipid content represents living organisms as these compounds are rapidly decomposed in aerobic mixed communities and that some of the neutral lipid components such as the lipopolysaccharides of Gram-negative bacteria do not reflect organisms alive at the time of sampling.
Although the method of sample collection is different for soil, water samples, etc., the extraction-derivatization is generally similar to the following protocol from an article on soil microbial communities. [ 7 ] The lipids were extracted from the dried soil sample by use of a chloroform-methanol-phosphate buffer mixture by use of a brief sonication followed by shaking for 2 hours and centrifugation to pellet the soil material. The liquid above the soil had additional chloroform and water added to cause separation of the lipid-containing chloroform from the buffer/methanol phase. The lipids were fractionated on a solid-phase extraction column and the neutral lipids, free fatty acids and other materials discarded and the phospholipid phase then dried, prior esterification to form the fatty acid methyl esters (FAMEs) [ 7 ] to make them suitable for analysis.
Gas chromatography (GC) analysis of fatty acid methyl esters (FAMEs) is the method of choice for analysis of PLFAs from soil. The GC is coupled with either a mass spectrometer detector (MSD) or a flame ionization detector (FID). The GC-MS system is more expensive to purchase and maintain, requires considerable skill to operate, and is typically used for qualitative analysis only. Identification of fatty acids using the GC-FID system is typically use for both qualitative and quantitative analysis of FAMEs, and is usually dependent on comparison of retention times of the unknown fatty acid compounds in comparison to purchased FAME standards. A commercially available, fatty-acid based microbial identification system (using GC-FID), which reproducibly names and quantitates the FAMEs, has been widely adopted for PLFA analysis. [ 8 ]
Actinomycetes are Gram-positive bacteria that are some of the most common bacteria in soil, freshwater and marine environments. Actinomycetes are active in decomposition of organic matter and give rise to the rich "earthy" smell of freshly tilled soils. This group of bacteria produce distinctive biomarker fatty acids having a methyl branch at the 10th carbon, such as 16:0 10-methyl and 18:0 10-methyl. [ 9 ] Some common species of soil actinomycetes include Rhodococcus , Nocardia , Corynebacterium , and Streptomyces .
Gram-positive bacteria include aerobic Bacillus species especially those related to B. cereus and to B. subtilis. These bacteria are common in the bulk soil and increase in numbers in the rhizosphere. The PLFA profiles of these Gram-positive species have high percentages of biomarker branched-chain fatty acids such as 15:0 iso and 15:0 anteiso. Thus, the sum of the iso and anteiso fatty acids in a PLFA analysis may provide an estimate of the abundance of the Gram-positive bacteria (other than actinomycetes) in the sample.
Gram-negative bacteria are a major component of the plant rhizosphere and improve plant growth by increasing solubility of phosphate , producing ionophore compounds that increase uptake of iron or other minerals and may produce antifungal compounds. [ 10 ] Gram-negative bacteria produce high levels of monounsaturated fatty acids ( e.g. 16:1 omega-7 and 18:1 omega-9) during active metabolism but convert much of the unsaturated fatty acid composition to cyclopropane fatty acids ( e.g. 17:0 cyclopropane and 19:0 cyclopropane) when metabolism and cell division slow due to shortage of nutrition or other stress. Thus, in PLFA analysis, the sum of monounsaturated and cyclopropane fatty acids may provide an estimate of the abundance of Gram-negative bacteria. A high ratio of cyclopropane to monounsaturated fatty acid indicates stress conditions. [ 3 ]
Anaerobic bacteria in agriculture are primarily a factor in soils of low-oxygen levels such as occur in greater depths or of wet conditions such as in rice paddies. Using PLFA analysis in early sampling, the bacteria- archaea consortia in rice paddy soil was about 44% aerobic bacteria, 32% facultatively anaerobic- bacteria and 24% archaea. Under longer term flooding, the levels were 27%, 36% and 37% respectively and with total biomass being significantly lower. [ 11 ] Dimethyl acetals (DMA) formed during derivatization are considered to be biomarkers of anaerobic bacteria. [ citation needed ]
Archaea are universally distributed in soils and have been shown to control nitrification in acidic conditions [ 12 ] and to contribute to ammonia oxidation in agricultural and forest soils. [ 13 ] However, as the phospholipids of archaea are not ester linked as in bacteria, but are ether linked, they are not significantly present in routine PLFA sample preparation which is designed to cleave ester-linked fatty acids.
Arbuscular mycorrhizae fungi (AMF) penetrate the walls of cortical cells of about 80% of all vascular plant families, generating a symbiotic relationship. The fungi form membrane structures adjacent to the plant cell membrane allowing exchange of phosphorus, nitrogen compounds and minerals from the fungus and the plant provides the fungus primarily with photosynthesis-derived sugars. As the AMF are obligate symbiotic fungi, they are not free-living in the soil. The AMF hyphae in the root form lipid materials which then are transported to the hyphae that extend into the soil from the root and thus may occur in a soil sample. [ 14 ] Vesicles are lipid storage organs of AMF and these and the hyphae in the soil contain the fatty acids 18:2 w6c (often used as an indicator of fungal content of the PLFA analysis) as well as containing the fatty acid 16:1 w5c which has been recommended as a biomarker for AMF (PLFA fraction:AMF hyphae and NLFA fraction:AMF spores). [ 15 ]
Sampling of agricultural soils for analysis of chemical composition ( e.g. pH, N, P, K, Ca, Mg, etc .) has long been practiced in crop production and while there has been recognition of the importance of the soil microbiota, tools for studying the microbiota have been developed relatively recently.
Many high-value vegetable crops easily justify soil testing both for chemical content and the soil microbiota. [ 16 ] Conventional, low-input and organic farming systems showed a rapid response of the soil microbial communities to wet/dry cycles and that increases in bacterial cyclopropyl fatty acids were useful to detect periods of stress. [ 17 ] Lines of transgenic corn (maize) expressing Bacillus thuringiensis endotoxins were found to have small effect on soil microbial communities when compared by PLFA analysis to their non-transgenic isolines. [ 7 ] Successful exotic invasive plant species can have profound effects on the microbial communities of the soil [ 18 ] perhaps thus improving their competitiveness. Grassland restoration practices of tillage , weeding and herbicide use showed an impact on microbial communities of the upper soil but very small changes on the microbiota of lower soil layers and that after 4 years of recovery the communities were very similar to untreated plots. [ 19 ]
Bioremediation has been studied using PLFA analysis of soil microbiota from sites contaminated by diesel fuel , [ 20 ] crude oil, [ 21 ] explosives, [ 22 ] olive mill waste, [ 23 ] pentachlorophenol , [ 24 ] coal tar [ 25 ] and PCBs. [ 26 ] There are reports of the effects on PLFAs of heavy metals on arbuscular fungi [ 27 ] and on bacteria, [ 9 ] of polycyclic aromatic hydrocarbons on rice paddy bacteria [ 28 ] and of methylene chloride on bacteria. [ 29 ]
Phytoplankton ( eukaryotic algae ) are microscopic photosynthesizing plants that inhabit the sunlit layers of oceans and bodies of freshwater. As the primary source of elaborated carbon compounds, they are vital to the aquatic food web. Phytoplankton produce considerable amounts of polyunsaturated fatty acids (PUFA), including Eicosapentaenoic acid (EPA, 20:5 w3c), with microalgae being the origin of omega-3 fatty acids in fish oil. [ 30 ] The diverse taxonomic groups in algae vary in abundance dependent on environmental conditions such as temperature, salinity, sunlight, and nutrient availability. The PLFA biomarker compositions were found to enable determination of the prevalence of the major groups in several marine environments. [ 31 ] In a study of reservoir sedimentary deposits, an assumption was made that the community PUFA content constituted ca . 50% of the total microeukaryotic PLFAs. [ 32 ] It was also assumed that "The ratio of omega-3 to omega-6 fatty acids describes the relative contribution of phototrophic to heterotrophic members of the microeukaryotic community…." [ 32 ]
In contrast to the considerable microbial diversity in soils, free-living microbes distributed by marine currents and exposed to algal exudates exhibit global distributions for a few dominant microbial groups of relatively few species. [ 33 ] Streambed sediments displayed a variation in microbial community structure (as measured by PLFA) related to the forest environment and geographic location of the stream, with much of the variation determined by use of the algal biomarker fatty acid 18:3 w3. [ 34 ] By PLFA analysis, considerable spatial and seasonal variations were determined in a freshwater reservoir sedimentary microbial community. [ 32 ]
Coniferous forests are dependent on available nutrients in soil rather than agricultural fertilizers and thus are routinely colonized by symbiotic mycorrhizal fungi. The mycorrhizae may be ectomycorrhizae (EMF) and/or arbuscular (AMF) in type in the forest. [ 35 ] The amount of total PLFA in soil provides an estimate of the total soil fungi (not including AMF). The AMF can be estimated by the amount of 16:1 w5c fatty acid in the PLFA. [ 35 ] Water stress was indicated by an increase in [PLFA ratios of saturated, monounsaturated and (cyclo 17:0 + cyclo 19:0) / (16:1 w7c + 18:1 w7c)] in a Douglas fir forest. [ 36 ] Boreal forests with low soil pH values had elevated EM PLFAs and raising the pH of the soil increased bacterial PLFAs. [ 37 ] The introduction of photosynthates through tree roots is a major source of carbon for soil microbiota and influences the composition of fungal and bacterial communities. [ 38 ] Forest areas without tree roots had less fungal biomarkers and more actinobacterial biomarkers than areas with tree roots. [ 39 ] Addition of nitrogen fertilizer to an oak forest reduced the ectomycorrhizal fungal content of the soil microbiota. [ 40 ]
Composting of organic materials is the microbial degradation of heterogeneous organic material under moist, self-heating, aerobic conditions. Initially, activity by mesophilic organisms leads to a rapid rise in temperature, followed by thermophilic organisms dominating the degradation process leading to a cooling period in which mesophilic bacteria again dominate populations. A commercial FAME extraction protocol developed for identification of bacteria, a mild alkaline methanolysis protocol and PLFA-extraction/derivatization were compared for effectiveness. [ 41 ] The PLFA protocol gave the most detailed information about community succession, however, the other two protocols were much simpler and appeared suitable for analysis of microbial FAME profiles in compost. [ 41 ]
Activated sludge technology is the most widely used method for wastewater treatment. Complex microbial communities in activated sludge processes are needed for the stable removal efficiency of organic pollutants. PLFA analysis can be used to monitor the microbial community composition of activated sludge reactors, which microbial groups are predominant, and the efficiency of such systems. [ 42 ] [ 43 ]
Soil microbial community composition in high mountain areas is less known when compared to other plant communities. The microbial community PLFA can be characterized by
composition and its relation with soil N availability, N mineralization and nitrification potential. [ 44 ] | https://en.wikipedia.org/wiki/Phospholipid-derived_fatty_acids |
3CH4
10654
68603
ENSG00000163344
ENSMUSG00000027952
Q15126
Q9D1G2
NM_006556 NM_001323011 NM_001323012 NM_001348696
NM_026784 NM_027348 NM_001310640
NP_001309940 NP_001309941 NP_006547 NP_001335625
NP_001297569 NP_081060 NP_081624
Phosphomevalonate kinase is an enzyme ( EC 2.7.4.2 ) in the mevalonate pathway [ 5 ] [ 6 ] [ 7 ] that in humans is encoded by the PMVK gene.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphomevalonate_kinase |
Phosphomevalonic acid is an intermediate in the Mevalonate pathway . [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphomevalonic_acid |
Phosphomimetics are amino acid substitutions that mimic a phosphorylated protein , thereby activating (or deactivating) the protein. Within cells, proteins are commonly modified at serine , tyrosine and threonine amino acids by adding a phosphate group. Phosphorylation is a common mode of activating or deactivating a protein as a form of regulation. However some non-phosphorylated amino acids appear chemically similar to phosphorylated amino acids. Therefore, by replacing an amino acid, the protein may maintain a higher level of activity. For example, aspartic acid can be considered chemically similar to phospho-serine, due to it also carrying a negative charge. Therefore, when an aspartic acid replaces a serine, it is a phosphomimetic of phospho-serine and can imitate the protein always in its phosphorylated form. However, differences between the phosphomimetic compound and the phosphorylated residue, notably differences in Ramachandran distributions, [ 1 ] charge states [ 2 ] and size, can alter the protein sufficiently to result in significant differences in behavior. [ 3 ] Phosphonate-based compounds have been used as phosphotyrosine analogues, as they are less enzyme labile and are physiologically more stable. [ 4 ]
This chemical similarity can be exploited in cancer, where a protein may mutate into an "always on" (constitutively active) state. A mutation may occur to replace a tyrosine (which needs to be phosphorylated in order to activate the protein) with an aspartic acid (which would not need to be phosphorylated). In a laboratory setting, the use of recombinant proteins to artificially introduce phosphomimetics is a common tool for studying phosphorylation and protein activation. For example, the IRF3 protein must be phosphorylated for its normal activity (transcription of its target genes, like IFNβ ), but when serine amino acid residues were mutated to aspartic acid, the activity increased 90-fold. [ 5 ] Phosphomimetics are commonly used in a gain of function experiment with respect to phosphorylation. For example, aspartate mutants were successfully used to probe the biological function of the phosphorylation of a threonine residue of a ribosomal protein both in vivo [ 6 ] and in vitro [ 7 ] to investigate a gain-of-function mutation on a kinase that is related to Parkinson's disease . Phosphomimetics were also used to investigate the therapeutic potential of proteins or peptides. For example, phosphomimetic mutants (using glutamate to mimic serine phosphorylation) have been used to demonstrate that the phosphorylated glycoprotein may have stronger anti-melanoma effects that the wildtype protein. [ 8 ] This approach is in particularly useful as up to three serine residues can be phosphoylated on the said protein, [ 8 ] and hence phosphomimetic mutants are useful to probe the function of the individual phosphorylation.
This protein -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphomimetics |
In organic chemistry , phosphonates or phosphonic acids are organophosphorus compounds containing C−PO(OR) 2 groups , where R is an organic group ( alkyl , aryl ). If R is hydrogen then the compound is a dialkyl phosphite , which is a different functional group. Phosphonic acids, typically handled as salts, are generally nonvolatile solids that are poorly soluble in organic solvents , but soluble in water and common alcohols .
Many commercially important compounds are phosphonates, including glyphosate (the active molecule of the herbicide Roundup ), and ethephon , a widely used plant growth regulator. Bisphosphonates are popular drugs for treatment of osteoporosis . [ 1 ]
In biochemistry and medicinal chemistry , phosphonate groups are used as stable bioisosteres for phosphate, such as in the antiviral nucleotide analog, Tenofovir , one of the cornerstones of anti- HIV therapy. And there is an indication that phosphonate derivatives are "promising ligands for nuclear medicine ." [ 2 ]
Phosphonates feature tetrahedral phosphorus centers. They are structurally closely related to (and often prepared from) phosphorous acid . [ 3 ]
Phosphonate salts are the result of deprotonation of phosphonic acids, which are diprotic acids:
Phosphonate esters are the result of condensation of phosphonic acids with alcohols.
Several methods exist for the preparation of phosphonic acids and their salts.
Most processes begin with phosphorous acid (aka phosphonic acid, H 3 PO 3 ), exploiting its reactive P−H bond. [ 1 ] [ 3 ]
Phosphonic acid can be alkylated via the Kabachnik–Fields reaction or Pudovik reaction to give aminophosphonate , which are useful as chelating agents. One example is the industrial preparation of nitrilotris(methylenephosphonic acid) :
Phosphonic acid also can be alkylated with acrylic acid derivatives to afford carboxyl functionalized phosphonic acids. This reaction is a variant of the Michael addition :
In the Hirao coupling dialkyl phosphites (which can also be viewed as di-esters of phosphonic acid: (O=PH(OR) 2 ) undergo a palladium-catalyzed coupling reaction with an aryl halide to form a phosphonate.
Phosphonic esters are prepared using the Michaelis–Arbuzov reaction . For example, methyl iodide catalyses the conversion of trimethylphosphite to the phosphonate ester dimethyl methylphosphonate :
These esters can be hydrolysed to the acid (Me = methyl):
In the Michaelis–Becker reaction , a hydrogen phosphonate diester is first deprotonated and the resulting anion is alkylated.
Vinylphosphonic acid can be prepared by the reaction of PCl 3 and acetaldehyde :
This adduct reacts with acetic acid:
This chloride undergoes dehydrochlorination to afford the target:
In the Kinnear–Perren reaction alkylphosphonyl dichlorides and esters are generated by alkylation of phosphorus trichloride in the presence of aluminium trichloride . Alkyltrichlorophosphonium salts are intermediates: [ 1 ]
The RPCl + 3 product can then be decomposed with water to produce an alkylphosphonic dichloride RP(=O)Cl 2 .
Phosphonate esters are generally susceptible to hydrolysis under both acidic and basic conditions. Cleavage of the P-C bond is harder but can be achieved under aggressive conditions.
In the Horner–Wadsworth–Emmons reaction dialkyl-phosphonates are deprotonated to give stabilized carbanions , which react with aldehydes to give E-alkenes with elimination of a dialkyl- phosphate . [ 4 ]
Compounds containing 2 geminal phosphonate groups are known as bisphosphonates . They were first synthesized in 1897 by Von Baeyer and Hofmann and now form the basis for an important class of drugs, used to treat osteoporosis and similar diseases. Examples include HEDP (etidronic acid or Didronel), which is prepared from phosphorous acid and acetic anhydride : [ 1 ]
A thiophosphonate group is a functional group related to phosphonate by substitution of an oxygen atom for a sulphur. They are a reactive component of many pesticides and nerve agents . Substituted thiophosphonates can have two main structural isomers bonding though either O or S groups to give thione and thiol forms respectively. This is a property they share with related functional groups such as thiocarboxylic acids and organothiophosphates .
Phosphonamidates are related to phosphonates by substitution of an oxygen atom for a nitrogen. They are a rarely encountered functional group. The nerve agent Tabun is an example.
Phosphonates are one of the three sources of phosphate intake in biological cells. [ citation needed ] The other two are inorganic phosphate and organophosphates.
The naturally occurring phosphonate 2-aminoethylphosphonic acid was first identified in 1959 in plants and many animals, where it is localized in membranes. Phosphonates are quite common among different organisms, from prokaryotes to eubacteria and mushrooms , mollusks , insects and others. They were first reported in natural soils by Newman and Tate (1980). The biological role of the natural phosphonates is still poorly understood. Bis- or polyphosphonates have not been found to occur naturally.
A number of natural product phosphonate substances with antibiotic properties have been identified. [ 5 ] Phosphonate natural product antibiotics include fosfomycin which is approved by FDA for the treatment of non-complicated urinary tract infection as well as several pre-clinically investigated substances such as Fosmidomycin (inhibitor isoprenyl synthase), SF-2312 (inhibitor of the glycolytic enzyme enolase , [ 6 ] and substances of unknown mode of actions such as alahopcin . Although phosphonates are profoundly cell impermeable, natural product phosphonate antibiotics are effective against a number of organisms, because many bacterial species express glycerol-3-phosphate and glucose-6-phosphate importers, which can be hijacked by phosphonate antibiotics. Fosfomycin resistant bacterial strains frequently have mutations that inactivate these transporters; however, such mutations are not maintained in the absence of antibiotic because of the fitness cost they impose.
In 1998 the consumption of phosphonates was 56,000 tons worldwide – 40,000 tons in the US, 15,000 tons in Europe and less than 800 tons in Japan. The demand of phosphonates grows steadily at 3% annually.
Since the work of Gerold Schwarzenbach in 1949, phosphonic acids are known as effective chelating agents . The introduction of an amine group into the molecule to obtain −NH 2 −C−PO(OH) 2 increases the metal binding abilities of the phosphonate. Examples for such compounds are NTMP, EDTMP and DTPMP. These phosphonates are the structural analogues to the well-known aminopolycarboxylate such as EDTA . The stability of the metal complexes increases with increasing number of phosphonic acid groups. Phosphonates are highly water-soluble while the phosphonic acids are only sparingly so.
Phosphonates are effective chelating agents. That is, they bind tightly to di- and trivalent metal ions, which is useful in water softening . In this way, they prevent formation of insoluble precipitates (scale). The binding of these ligands also suppresses the catalytic properties of metal ions. They are stable under harsh conditions. For these reasons, an important industrial use of phosphonates is in cooling waters, desalination systems, and in oil fields to inhibit scale formation. Phosphonates are also regularly used in reverse osmosis systems as antiscalants. Phosphonates in cooling water systems also serve to control corrosion of iron and steel. In pulp and paper manufacturing and in textile industry they serve as "peroxide bleach stabilizers", by chelating metals that could inactivate the peroxide. In detergents they are used as a combination of chelating agent, scale inhibitor, and bleach stabilizer. Phosphonates are also increasingly used in medicine to treat disorders associated with bone formation and calcium metabolism. Furthermore, they serve as carriers for radionuclides in bone cancer treatments (see samarium-153-ethylene diamine tetramethylene phosphonate ).
Phosphonates are also used as concrete retarder. [ 7 ] [ 8 ] They delay the cement setting time, allowing a longer time to place the concrete or to spread the cement hydration heat on a longer period of time to avoid too high temperature and resulting cracks. They also have favourable dispersing properties and so are investigated as a possible new class of superplasticizers. However, presently, phosphonates are not commercially available as superplasticizers. Superplasticizers are concrete admixtures designed to increase the concrete fluidity and workability of concrete or to decrease its water-to-cement (w/c) ratio. By reducing the water content in concrete, it decreases its porosity, improving so the mechanical properties (compressive and tensile strength) and the durability of concrete (lower water, gas and solutes transport properties). [ 9 ]
Phosphonates and specially diarylphosphonates are also reported to be used as "warhead" or reactive site in proteomics analysis. [ 10 ]
In medicine, phosphonates and bisphosphonates are commonly used as inhibitors of enzymes which utilize phosphates and diphosphates as substrates. Most notably, these enzymes include those that produce the intermediates of cholesterol biosynthesis. [ 11 ]
Phosphonate nucleotide analogues such as tenofovir , cidofovir and adefovir are critical antiviral medications, which in various pro-drug forms are used for the treatment of HIV , hepatitis B and others.
In conjunction with organosilicates, phosphonates are also used to treat "sudden oak death", which is caused by the fungus-like eukaryote Phytophthora ramorum .
The toxicity of phosphonates to organisms living in water is low. Reported values for 48-hour LC 50 values for fish are between 0.1 and 1.1 mM. Also the bioconcentration factor for fish is very low.
In nature bacteria play a major role in the degradation of phosphonates. [ 12 ] Due to the presence of natural phosphonates in the environment, bacteria have evolved the ability to metabolize phosphonates as nutrient sources. Some bacteria use phosphonates as a phosphorus source for growth. Aminophosphonates can also be used as sole nitrogen source by some bacteria. The polyphosphonates used in industry differ greatly from natural phosphonates such as 2-aminoethylphosphonic acid, because they are much larger, carry a high negative charge and are complexed with metals. Biodegradation tests with sludge from municipal sewage treatment plants with HEDP and NTMP showed no indication for any degradation. An investigation of HEDP, NTMP, EDTMP and DTPMP in standard biodegradation tests also failed to identify any biodegradation. It was noted, however, that in some tests due to the high sludge to phosphonate ratio, removal of the test substance from solution observed as loss of DOC was observed. This factor was attributed to adsorption rather than biodegradation. However, bacterial strains capable of degrading aminopolyphosphonates and HEDP under P-limited conditions have been isolated from soils, lakes, wastewater, activated sludge and compost.
"No biodegradation of phosphonates during water treatment is observed but photodegradation of the Fe(III)-complexes is rapid. Aminopolyphosphonates are also rapidly oxidized in the presence of Mn(II) and oxygen and stable breakdown products are formed that have been detected in wastewater. The lack of information about phosphonates in the environment is linked to analytical problems of their determination at trace concentrations in natural waters. Phosphonates are present mainly as Ca and Mg-complexes in natural waters and therefore do not affect metal speciation or transport." [ 13 ] Phosphonates interact strongly with some surfaces, which results in a significant removal in technical and natural systems. | https://en.wikipedia.org/wiki/Phosphonate |
In organic chemistry , phosphonites are organophosphorus compounds with the formula P(OR) 2 R. They are found in some pesticides and are used as ligands . [ 1 ]
Although they are derivatives of phosphonous acid (RP(OH) 2 ), [ 2 ] they are not prepared from such precursors. Phosphonites are prepared by alcoholysis of organophosphinous chlorides. For example, treatment of dichlorophenylphosphine with methanol and base gives dimethyl phenylphosphonite:
Oxidation of phosphonites gives phosphonates :
Phosphonites can function as ligands in homogeneous catalysis . [ 3 ] | https://en.wikipedia.org/wiki/Phosphonite |
In chemistry , the term phosphonium (more obscurely: phosphinium ) describes polyatomic cations with the chemical formula P R + 4 (where R is a hydrogen or an alkyl , aryl , organyl or halogen group). These cations have tetrahedral structures . The salts are generally colorless or take the color of the anions. [ 1 ]
The parent phosphonium is PH + 4 as found in the iodide salt, phosphonium iodide . Salts of the parent PH + 4 are rarely encountered, but this ion is an intermediate in the preparation of the industrially useful tetrakis(hydroxymethyl)phosphonium chloride :
Many organophosphonium salts are produced by protonation of primary, secondary, and tertiary phosphines :
The basicity of phosphines follows the usual trends, with R = alkyl being more basic than R = aryl. [ 2 ]
The most common phosphonium compounds have four organic substituents attached to phosphorus. The quaternary phosphonium cations include tetraphenylphosphonium , (C 6 H 5 ) 4 P + and tetramethylphosphonium P(CH 3 ) + 4 .
Quaternary phosphonium cations ( PR + 4 ) are produced by alkylation of organophosphines. [ 3 ] For example, the reaction of triphenylphosphine with methyl bromide gives methyltriphenylphosphonium bromide :
The methyl group in such phosphonium salts is mildly acidic, with a p K a estimated to be near 15: [ 5 ]
This deprotonation reaction gives Wittig reagents . [ 6 ]
Solid phosphorus pentachloride is an ionic compound , formulated [PCl 4 ] + [PCl 6 ] − (tetrachlorophosphonium hexachlorophosphate(V)), that is, a salt containing the tetrachlorophosphonium cation. [ 7 ] [ 8 ] Dilute solutions dissociate according to the following equilibrium:
Triphenylphosphine dichloride (Ph 3 PCl 2 ) exists both as the pentacoordinate phosphorane and as the chlorotriphenylphosphonium chloride, depending on the medium. [ 9 ] The situation is similar to that of PCl 5 . It is an ionic compound (PPh 3 Cl) + Cl − in polar solutions and a molecular species with trigonal bipyramidal molecular geometry in apolar solution. [ 10 ]
The Michaelis–Arbuzov reaction is the chemical reaction of a trivalent phosphorus ester with an alkyl halide to form a pentavalent phosphorus species and another alkyl halide. Commonly, the phosphorus substrate is a phosphite ester (P(OR) 3 ) and the alkylating agent is an alkyl iodide. [ 11 ]
Tetrakis(hydroxymethyl)phosphonium chloride has industrial importance in the production of crease-resistant and flame-retardant finishes on cotton textiles and other cellulosic fabrics. [ 12 ] [ 13 ] A flame-retardant finish can be prepared from THPC by the Proban Process, [ 14 ] in which THPC is treated with urea. The urea condenses with the hydroxymethyl groups on THPC. The phosphonium structure is converted to phosphine oxide as the result of this reaction. [ 15 ]
Organic phosphonium cations are lipophilic and can be useful in phase transfer catalysis , much like quaternary ammonium salts. Salts or inorganic anions and tetraphenylphosphonium ( PPh + 4 ) are soluble in polar organic solvents. One example is the perrhenate (PPh 4 [ReO 4 ]). [ 16 ]
Wittig reagents are used in organic synthesis . They are derived from phosphonium salts. A strong base such as butyllithium or sodium amide is required for the deprotonation:
One of the simplest ylides is methylenetriphenylphosphorane (Ph 3 P=CH 2 ). [ 6 ]
The compounds Ph 3 PX 2 (X = Cl, Br) are used in the Kirsanov reaction . [ 17 ] The Kinnear–Perren reaction is used to prepare alkylphosphonyl dichlorides (RP(O)Cl 2 ) and esters (RP(O)(OR′) 2 ). A key intermediate are alkyltrichlorophosphonium salts, obtained by the alkylation of phosphorus trichloride : [ 18 ]
The main industrial procedure for the production of ammonia today is the thermal Haber-Bosch process , which generally uses fossil gas as a source of hydrogen, which is then combined with nitrogen to produce ammonia. In 2021, Professor Doug MacFarlane and collaborators Alexandr Simonov and Bryan Suryanto of Monash University devised a method of producing green ammonia that has the potential to make Haber-Bosch plants obsolete. [ 19 ] Their process is similar to the electrolysis approach for producing hydrogen. While working with local company Verdant, which wanted to make bleach from saltwater by electrolysis, Suryanto discovered that a tetraalkyl phosphonium salt allowed the efficient production of ammonia at room temperature. [ 20 ] | https://en.wikipedia.org/wiki/Phosphonium |
In organic chemistry , phosphonium coupling is a cross-coupling reaction for organic synthesis . It is a mild, efficient, chemoselective and versatile methodology for the formation of C–C, C–N, C–O, and C–S bond of unactivated and unprotected tautomerizable heterocycles . The method was originally reported in 2004. [ 1 ] The C–OH bond of a tautomerizable heterocycle is activated with a phosphonium salt ( PyBroP , PyBOP , BroP, or BOP ), and subsequent functionalization with either a nucleophile through SNAr displacement or an organometallic through transition metal catalyzed cross coupling reaction . The in situ activation of the C-OH bond in phosphonium coupling has been applied to cross coupling reactions of tautomerizable heterocycles and arenols using other types of activating reagents. [ 2 ] [ 3 ]
Phosphonium coupling generates in situ a pseudo aryl or heteroaryl halide (the intermediate phosphonium species ), which subsequently reacts with its coupling partner . [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] | https://en.wikipedia.org/wiki/Phosphonium_coupling |
Phosphonium iodide is a chemical compound with the formula PH 4 I . It is an example of a salt containing an unsubstituted phosphonium cation ( PH + 4 ). Phosphonium iodide is commonly used as storage for phosphine [ 2 ] and as a reagent for substituting phosphorus into organic molecules. [ 3 ]
Phosphonium iodide is prepared by mixing diphosphorus tetraiodide ( P 2 I 4 ) with elemental phosphorus and water at 80 °C and allowing the salt to sublime. [ 4 ] [ 5 ]
Its crystal structure has the tetragonal space group P4/nmm, which is a distorted version of the NH 4 Cl crystal structure; the unit cell has approximate dimensions 634×634×462 pm. [ 6 ] The hydrogen bonding in the system causes the PH + 4 cations to orient such that the hydrogen atoms point toward the I − anions. [ 7 ]
At 62 °C and atmospheric pressure, phosphonium iodide sublimates and dissociates reversibly into phosphine and hydrogen iodide (HI). [ 1 ] It oxidizes slowly in air to give iodine and phosphorus oxides ; it is hygroscopic [ 4 ] and is hydrolyzed into phosphine and HI: [ 8 ]
Phosphine gas may be devolved from phosphonium iodide by mixing an aqueous solution with potassium hydroxide : [ 9 ]
It reacts with elemental iodine and bromine in a nonpolar solution to give phosphorus halides; for example:
Phosphonium iodide is a powerful substitution reagent in organic chemistry; for example, it can convert a pyrilium into a phosphinine via substitution. [ 3 ] In 1951, Glenn Halstead Brown found that PH 4 I reacts with acetyl chloride to produce an unknown phosphine derivative, possibly CH 3 C(=PH)PH 2 ·HI . [ 4 ] | https://en.wikipedia.org/wiki/Phosphonium_iodide |
Phosphopantetheine , also known as 4'-phosphopantetheine , is a prosthetic group of several acyl carrier proteins including the acyl carrier proteins (ACP) of fatty acid synthases , ACPs of polyketide synthases , the peptidyl carrier proteins (PCP), as well as aryl carrier proteins (ArCP) of nonribosomal peptide synthetases (NRPS). [ 1 ] It is also present in formyltetrahydrofolate dehydrogenase . [ 2 ]
Subsequent to the expression of the apo acyl carrier protein , 4'-phosphopantetheine moiety is attached to a serine residue. The coupling involves formation of a phosphodiester linkage. This coupling is mediated by acyl carrier protein synthase (ACPS), a 4'-phosphopantetheinyl transferase . [ 3 ]
Phosphopantetheine prosthetic group covalently links to the acyl group via a high energy thioester bond . The flexibility and length of the phosphopantetheine chain (approximately 2 nm) allows the covalently tethered intermediates to access spatially distinct enzyme-active sites. This accessibility increases the effective molarity of the intermediate and allows an assembly line-like process. [ citation needed ]
This article about metabolism is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphopantetheine |
Phosphoproteomics is a branch of proteomics that identifies, catalogs, and characterizes proteins containing a phosphate group as a posttranslational modification . Phosphorylation is a key reversible modification that regulates protein function, subcellular localization, complex formation, degradation of proteins and therefore cell signaling networks. With all of these modification results, it is estimated that between 30–65% of all proteins may be phosphorylated, some multiple times. [ 1 ] [ 2 ] Based on statistical estimates from many datasets, 230,000, 156,000 and 40,000 phosphorylation sites should exist in human, mouse, and yeast, respectively. [ 2 ]
Compared to expression analysis, phosphoproteomics provides two additional layers of information. First, it provides clues on what protein or pathway might be activated because a change in phosphorylation status almost always reflects a change in protein activity. Second, it indicates what proteins might be potential drug targets as exemplified by the kinase inhibitor Gleevec. While phosphoproteomics will greatly expand knowledge about the numbers and types of phosphoproteins, its greatest promise is the rapid analysis of entire phosphorylation based signalling networks. [ 3 ]
A sample large-scale phosphoproteomic analysis includes cultured cells undergo SILAC encoding; cells are stimulated with factor of interest (e.g. growth factor, hormone); stimulation can occur for various lengths of time for temporal analysis, cells are lysed and enzymatically digested, peptides are separated using ion exchange chromatography ; phosphopeptides are enriched using phosphospecific antibodies , immobilized metal affinity chromatography or titanium dioxide (TiO 2 ) chromatography ; phosphopeptides are analyzed using mass spectrometry , and peptides are sequenced and analyzed. [ 4 ]
The analysis of the entire complement of phosphorylated proteins in a cell is certainly a feasible option. This is due to the optimization of enrichment protocols for phosphoproteins and phosphopeptides, better fractionation techniques using chromatography, and improvement of methods to selectively visualize phosphorylated residues using mass spectrometry. Although the current procedures for phosphoproteomic analysis are greatly improved, there is still sample loss and inconsistencies with regards to sample preparation, enrichment, and instrumentation. Bioinformatics tools and biological sequence databases are also necessary for high-throughput phosphoproteomic studies. [ 5 ]
Previous procedures to isolate phosphorylated proteins included radioactive labeling with 32 P-labeled ATP followed by SDS polyacrylamide gel electrophoresis or thin layer chromatography. These traditional methods are inefficient because it is impossible to obtain large amounts of proteins required for phosphorylation analysis. Therefore, the current and simplest methods to enrich phosphoproteins are affinity purification using phosphospecific antibodies, immobilized metal affinity chromatography ( IMAC ), strong cation exchange (SCX) chromatography, or titanium dioxide chromatography. Antiphosphotyrosine antibodies have been proven very successful in purification, but fewer reports have been published using antibodies against phosphoserine- or phosphothreonine-containing proteins. IMAC enrichment is based on phosphate affinity for immobilized metal chelated to the resin. SCX separates phosphorylated from non-phosphorylated peptides based on the negatively charged phosphate group. Titanium dioxide chromatography is a newer technique that requires significantly less column preparation time. Many phosphoproteomic studies use a combination of these enrichment strategies to obtain the purest sample possible.
Mass spectrometry is currently the best method to adequately compare pairs of protein samples. The two main procedures to perform this task are using isotope-coded affinity tags (ICAT) and stable isotopic amino acids in cell culture (SILAC). In the ICAT procedure samples are labeled individually after isolation with mass-coded reagents that modify cysteine residues. In SILAC, cells are cultured separately in the presence of different isotopically labeled amino acids for several cell divisions allowing cellular proteins to incorporate the label. Mass spectrometry is subsequently used to identify phosphoserine, phosphothreonine, and phosphotyrosine-containing peptides. [ 6 ]
Intracellular signal transduction is primarily mediated by the reversible phosphorylation of various signalling molecules by enzymes dubbed kinases . Kinases transfer phosphate groups from ATP to specific serine , threonine or tyrosine residues of target molecules. The resultant phosphorylated protein may have altered activity level, subcellular localization or tertiary structure.
Phosphoproteomic analyses are ideal for the study of the dynamics of signalling networks. In one study design, cells are exposed to SILAC labelling and then stimulated by a specific growth factor. The cells are collected at various timepoints, and the lysates are combined for analysis by tandem MS. [ 4 ] This allows experimenters to track the phosphorylation state of many phosphoproteins in the cell over time. The ability to measure the global phosphorylation state of many proteins at various time points makes this approach much more powerful than traditional biochemical methods for analyzing signalling network behavior. [ 7 ]
One study was able to simultaneously measure the fold-change in phosphorylation state of 127 proteins between unstimulated and EphrinB1-stimulated cells. [ 8 ] Of these 127 proteins, 40 showed increased phosphorylation with stimulation by EphrinB1. The researchers were able to use this information in combination with previously published data to construct a signal transduction network for the proteins downstream of the EphB2 receptor.
Another recent phosphoproteomic study included large-scale identification and quantification of phosphorylation events triggered by the anti-diuretic hormone vasopressin in kidney collecting duct. [ 9 ] A total of 714 phosphorylation sites on 223 unique phosphoproteins were identified, including three novel phosphorylation sites in the vasopressin-sensitive water channel aquaporin-2 (AQP2).
Since the inception of phosphoproteomics, cancer research has focused on changes to the phosphoproteome during tumor development. Phosphoproteins could be cancer markers useful to cancer diagnostics and therapeutics. In fact, research has shown that there are distinct phosphotyrosine proteomes of breast and liver tumors. There is also evidence of hyperphosphorylation at tyrosine residues in breast tumors but not in normal tissues. Findings like these suggest that it is possible to mine the tumor phosphoproteome for potential biomarkers .
Increasing amounts of data are available suggesting that distinctive phosphoproteins exist in various tumors and that phosphorylation profiling could be used to fingerprint cancers from different origins. In addition, systematic cataloguing of tumor-specific phosphoproteins in individual patients could reveal multiple causative players during cancer formation. By correlating this experimental data to clinical data such as drug response and disease outcome, potential cancer markers could be identified for diagnosis, prognosis, prediction of drug response, and potential drug targets. [ 3 ]
While phosphoproteomics has greatly expanded knowledge about the numbers and types of phosphoproteins, along with their role in signaling networks, there are still several limitations to these techniques. To begin with, isolation methods such as anti-phosphotyrosine antibodies do not distinguish between isolating tyrosine-phosphorylated proteins and proteins associated with tyrosine-phosphorylated proteins. Therefore, even though phosphorylation dependent protein-protein interactions are very important, it is important to remember that a protein detected by this method is not necessarily a direct substrate of any tyrosine kinase. Only by digesting the samples before immunoprecipitation can isolation of only phosphoproteins and temporal profiles of individual phosphorylation sites be produced. Another limitation is that some relevant proteins will likely be missed since no extraction condition is all encompassing. It is possible that proteins with low stoichiometry of phosphorylation, in very low abundance, or phosphorylated as a target for rapid degradation will be lost. [ 10 ] Bioinformatics analyses of low-throughput phosphorylation data together with high-throughput phosphoproteomics data (based mostly on MS/MS) estimate that current high-throughput protocols, after several repetitions are capable of capturing 70% to 95% of total phosphoproteins, but only 40% to 60% of total phosphorylation sites. [ 2 ] | https://en.wikipedia.org/wiki/Phosphoproteomics |
A phosphor is a substance that exhibits the phenomenon of luminescence ; it emits light when exposed to some type of radiant energy . The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or visible light, and cathodoluminescent substances which glow when struck by an electron beam ( cathode rays ) in a cathode-ray tube .
When a phosphor is exposed to radiation, the orbital electrons in its molecules are excited to a higher energy level ; when they return to their former level they emit the energy as light of a certain color. Phosphors can be classified into two categories: fluorescent substances which emit the energy immediately and stop glowing when the exciting radiation is turned off, and phosphorescent substances which emit the energy after a delay, so they keep glowing after the radiation is turned off, decaying in brightness over a period of milliseconds to days.
Fluorescent materials are used in applications in which the phosphor is excited continuously: cathode-ray tubes (CRT) and plasma video display screens, fluoroscope screens , fluorescent lights , scintillation sensors , white LEDs , and luminous paints for black light art. Phosphorescent materials are used where a persistent light is needed, such as glow-in-the-dark watch faces and aircraft instruments, and in radar screens to allow the target 'blips' to remain visible as the radar beam rotates. CRT phosphors were standardized beginning around World War II and designated by the letter "P" followed by a number.
Phosphorus , the light-emitting chemical element for which phosphors are named, emits light due to chemiluminescence , not phosphorescence. [ 1 ]
The scintillation process in inorganic materials is due to the electronic band structure found in the crystals . An incoming particle can excite an electron from the valence band to either the conduction band or the exciton band (located just below the conduction band and separated from the valence band by an energy gap ). This leaves an associated hole behind, in the valence band. Impurities create electronic levels in the forbidden gap .
The excitons are loosely bound electron–hole pairs that wander through the crystal lattice until they are captured as a whole by impurity centers. They then rapidly de-excite by emitting scintillation light (fast component).
In the conduction band, electrons are independent of their associated holes. Those electrons and holes are captured successively by impurity centers exciting certain metastable states not accessible to the excitons. The delayed de-excitation of those metastable impurity states, slowed by reliance on the low-probability forbidden mechanism , again results in light emission (slow component).
In the case of inorganic scintillators , the activator impurities are typically chosen so that the emitted light is in the visible range or near-UV , where photomultipliers are effective.
Phosphors are often transition-metal compounds or rare-earth compounds of various types. In inorganic phosphors, these inhomogeneities in the crystal structure are created usually by addition of a trace amount of dopants , impurities called activators . (In rare cases dislocations or other crystal defects can play the role of the impurity.) The wavelength emitted by the emission center is dependent on the atom itself and on the surrounding crystal structure.
Phosphors are usually made from a suitable host material with an added activator . The best known type is a copper-activated zinc sulfide (ZnS) and the silver -activated zinc sulfide ( zinc sulfide silver ).
The host materials are typically oxides , nitrides and oxynitrides, [ 2 ] sulfides , selenides , halides or silicates of zinc , cadmium , manganese , aluminium , silicon , or various rare-earth metals . The activators prolong the emission time (afterglow). In turn, other materials (such as nickel ) can be used to quench the afterglow and shorten the decay part of the phosphor emission characteristics.
Many phosphor powders are produced in low-temperature processes, such as sol-gel , and usually require post-annealing at temperatures of ~1000 °C, which is undesirable for many applications. However, proper optimization of the growth process allows manufacturers to avoid the annealing. [ 3 ]
Phosphors used for fluorescent lamps require a multi-step production process, with details that vary depending on the particular phosphor. Bulk material must be milled to obtain a desired particle size range, since large particles produce a poor-quality lamp coating, and small particles produce less light and degrade more quickly. During the firing of the phosphor, process conditions must be controlled to prevent oxidation of the phosphor activators or contamination from the process vessels. After milling, the phosphor may be washed to remove minor excess of activator elements. Volatile elements must not be allowed to escape during processing. Lamp manufacturers have changed compositions of phosphors to eliminate some toxic elements formerly used, such as beryllium , cadmium , or thallium . [ 4 ]
The commonly quoted parameters for phosphors are the wavelength of emission maximum (in nanometers, or alternatively color temperature in kelvins for white blends), the peak width (in nanometers at 50% of intensity), and decay time (in seconds ).
Examples:
Many phosphors tend to lose efficiency gradually by several mechanisms. The activators can undergo change of valence (usually oxidation ), the crystal lattice degrades, atoms – often the activators – diffuse through the material, the surface undergoes chemical reactions with the environment with consequent loss of efficiency or buildup of a layer absorbing the exciting and/or radiated energy, etc.
The degradation of electroluminescent devices depends on frequency of driving current, the luminance level, and temperature; moisture impairs phosphor lifetime very noticeably as well.
Harder, high-melting, water-insoluble materials display lower tendency to lose luminescence under operation. [ 7 ]
Examples:
Phosphor layers provide most of the light produced by fluorescent lamps , and are also used to improve the balance of light produced by metal halide lamps . Various neon signs use phosphor layers to produce different colors of light. Electroluminescent displays found, for example, in aircraft instrument panels, use a phosphor layer to produce glare-free illumination or as numeric and graphic display devices. White LED lamps consist of a blue or ultra-violet emitter with a phosphor coating that emits at longer wavelengths, giving a full spectrum of visible light. Unfocused and undeflected cathode-ray tubes have been used as stroboscope lamps since 1958. [ 15 ]
Phosphor thermometry is a temperature measurement approach that uses the temperature dependence of certain phosphors. For this, a phosphor coating is applied to a surface of interest and, usually, the decay time is the emission parameter that indicates temperature. Because the illumination and detection optics can be situated remotely, the method may be used for moving surfaces such as high speed motor surfaces. Also, phosphor may be applied to the end of an optical fiber as an optical analog of a thermocouple. [ citation needed ]
In these applications, the phosphor is directly added to the plastic used to mold the toys, or mixed with a binder for use as paints.
ZnS:Cu phosphor is used in glow-in-the-dark cosmetic creams frequently used for Halloween make-ups .
Generally, the persistence of the phosphor increases as the wavelength increases.
See also lightstick for chemiluminescence -based glowing items.
Quenching of the triplet state by O 2 (which has a triplet ground state) as a result of Dexter energy transfer is well known in solutions of phosphorescent heavy-metal complexes and doped polymers. [ 16 ] In recent years, phosphorescence porous materials(such as Metal–organic frameworks and Covalent organic frameworks ) have shown promising oxygen sensing capabilities, for their non-linear gas-adsorption in ultra-low partial pressures of oxygen. [ 17 ] [ 18 ]
Phosphor banded stamps first appeared in 1959 as guides for machines to sort mail. [ 19 ] Around the world many varieties exist with different amounts of banding. [ 20 ] Postage stamps are sometimes collected by whether or not they are "tagged" with phosphor (or printed on luminescent paper).
Zinc sulfide phosphors are used with radioactive materials, where the phosphor was excited by the alpha- and beta-decaying isotopes, to create luminescent paint for dials of watches and instruments ( radium dials ). Between 1913 and 1950 radium-228 and radium-226 were used to activate a phosphor made of silver doped zinc sulfide (ZnS:Ag), which gave a greenish glow. The phosphor is not suitable to be used in layers thicker than 25 mg/cm 2 , as the self-absorption of the light then becomes a problem. Furthermore, zinc sulfide undergoes degradation of its crystal lattice structure, leading to gradual loss of brightness significantly faster than the depletion of radium. ZnS:Ag coated spinthariscope screens were used by Ernest Rutherford in his experiments discovering atomic nucleus .
Copper doped zinc sulfide (ZnS:Cu) is the most common phosphor used and yields blue-green light. Copper and magnesium doped zinc sulfide (ZnS:Cu,Mg) yields yellow-orange light.
Tritium is also used as a source of radiation in various products utilizing tritium illumination .
Electroluminescence can be exploited in light sources. Such sources typically emit from a large area, which makes them suitable for backlights of LCD displays. The excitation of the phosphor is usually achieved by application of high-intensity electric field , usually with suitable frequency. Current electroluminescent light sources tend to degrade with use, resulting in their relatively short operation lifetimes.
ZnS:Cu was the first formulation successfully displaying electroluminescence, tested at 1936 by Georges Destriau in Madame Marie Curie laboratories in Paris.
Powder or AC electroluminescence is found in a variety of backlight and night light applications. Several groups offer branded EL offerings (e.g. IndiGlo used in some Timex watches) or "Lighttape", another trade name of an electroluminescent material, used in electroluminescent light strips . The Apollo space program is often credited with being the first significant use of EL for backlights and lighting. [ 21 ]
White light-emitting diodes are usually blue InGaN LEDs with a coating of a suitable material. Cerium (III)-doped YAG ( YAG:Ce 3+ , or Y 3 Al 5 O 12 :Ce 3+ ) is often used; it absorbs the light from the blue LED and emits in a broad range from greenish to reddish, with most of its output in yellow. This yellow emission combined with the remaining blue emission gives the "white" light, which can be adjusted to color temperature as warm (yellowish) or cold (bluish) white. The pale yellow emission of the Ce 3+ :YAG can be tuned by substituting the cerium with other rare-earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminium in the YAG with gallium. However, this process is not one of phosphorescence. The yellow light is produced by a process known as scintillation , the complete absence of an afterglow being one of the characteristics of the process.
Some rare-earth - doped Sialons are photoluminescent and can serve as phosphors. Europium (II)-doped β-SiAlON absorbs in ultraviolet and visible light spectrum and emits intense broadband visible emission. Its luminance and color does not change significantly with temperature, due to the temperature-stable crystal structure. It has a great potential as a green down-conversion phosphor for white LEDs ; a yellow variant also exists (α-SiAlON [ 22 ] ). For white LEDs, a blue LED is used with a yellow phosphor, or with a green and yellow SiAlON phosphor and a red CaAlSiN 3 -based (CASN) phosphor. [ 23 ] [ 24 ] [ 25 ]
White LEDs can also be made by coating near-ultraviolet-emitting LEDs with a mixture of high-efficiency europium-based red- and blue-emitting phosphors plus green-emitting copper- and aluminium-doped zinc sulfide (ZnS:Cu,Al) . This is a method analogous to the way fluorescent lamps work.
Some newer white LEDs use a yellow and blue emitter in series, to approximate white; this technology is used in some Motorola phones such as the Blackberry as well as LED lighting and the original-version stacked emitters by using GaN on SiC on InGaP but was later found to fracture at higher drive currents.
Many white LEDs used in general lighting systems can be used for data transfer, as, for example, in systems that modulate the LED to act as a beacon . [ 26 ]
It is also common for white LEDs to use phosphors other than Ce:YAG, or to use two or three phosphors to achieve a higher CRI, often at the cost of efficiency. Examples of additional phosphors are R9, which produces a saturated red, nitrides which produce red, and aluminates such as lutetium aluminum garnet that produce green. Silicate phosphors are brighter but fade more quickly, and are used in LCD LED backlights in mobile devices. LED phosphors can be placed directly over the die or made into a dome and placed above the LED: this approach is known as a remote phosphor. [ 27 ] Some colored LEDs, instead of using a colored LED, use a blue LED with a colored phosphor because such an arrangement is more efficient than a colored LED. Oxynitride phosphors can also be used in LEDs. The precursors used to make the phosphors may degrade when exposed to air. [ 28 ]
Cathode-ray tubes produce signal-generated light patterns in a (typically) round or rectangular format. Bulky CRTs were used in the black-and-white television (TV) sets that became popular in the 1950s, developed into color CRTs in the late 1960s, and used in virtually all color TVs and computer monitors until the mid-2000s. In the late 20th century, advanced electronics made new wide-deflection, "short tube" CRT technology viable, making CRTs more compact, but still bulky and heavy. As the original video display technology, having no viable competition for more than 40 years and dominance for over 50 years, the CRT ceased to be the main type of video display in use only around 2010. In addition to direct-view CRTs, CRT projection tubes were the basis of all projection TVs and computer video projectors of both front and rear projection types until at least the late 1990s.
CRTs have also been widely used in scientific and engineering instrumentation, such as oscilloscopes , usually with a single phosphor color, typically green. Phosphors for such applications may have long afterglow, for increased image persistence. A variation of the display CRT, used prior to the 1980s, was the CRT storage tube , a digital memory device which (in later forms) also provided a visible display of the stored data, using a variation of the same electron-beam excited phosphor technology.
The process of producing light in CRTs by electron-beam excited phosphorescence yields much faster signal response times than even modern (2020s) LCDs can achieve, which makes light pens and light gun games possible with CRTs, but not LCDs. Also in contrast to most other video display types, because CRT technology draws an image by scanning an electron beam (or a formation of three beams) across a phosphor surface, a CRT has no intrinsic "native resolution" and does not require scaling to display raster images at different resolutions; the CRT can display any raster format natively, within the limits defined by the electron beam spot size and, for a color CRT, the dot pitch of the phosphor. Because of this operating principle, CRTs can produce images using either raster and vector imaging methods. Vector displays are impossible for display technologies that have permanent discrete pixels, including all LCDs, plasma display panels , DMD projectors, and OLED (LED matrix, e.g. TFT OLED) panels.
The phosphors can be deposited as either thin film , or as discrete particles, a powder bound to the surface. Thin films have better lifetime and better resolution, but provide less bright and less efficient image than powder ones. This is caused by multiple internal reflections in the thin film, scattering the emitted light.
White (in black-and-white): The mix of zinc cadmium sulfide and zinc sulfide silver, the ZnS:Ag + (Zn,Cd)S:Ag is the white P4 phosphor used in black and white television CRTs. Mixes of yellow and blue phosphors are usual. Mixes of red, green and blue, or a single white phosphor, can also be encountered.
Red: Yttrium oxide - sulfide activated with europium is used as the red phosphor in color CRTs. The development of color TV took a long time due to the search for a red phosphor. The first red emitting rare-earth phosphor, YVO 4 :Eu 3+ , was introduced by Levine and Palilla as a primary color in television in 1964. [ 29 ] In single crystal form, it was used as an excellent polarizer and laser material. [ 30 ]
Yellow: When mixed with cadmium sulfide , the resulting zinc cadmium sulfide (Zn,Cd)S:Ag , provides strong yellow light.
Green: Combination of zinc sulfide with copper , the P31 phosphor or ZnS:Cu , provides green light peaking at 531 nm, with long glow.
Blue: Combination of zinc sulfide with few ppm of silver , the ZnS:Ag, when excited by electrons, provides strong blue glow with maximum at 450 nm, with short afterglow with 200 nanosecond duration. It is known as the P22B phosphor. This material, zinc sulfide silver , is still one of the most efficient phosphors in cathode-ray tubes. It is used as a blue phosphor in color CRTs.
The phosphors are usually poor electrical conductors. This may lead to deposition of residual charge on the screen, effectively decreasing the energy of the impacting electrons due to electrostatic repulsion (an effect known as "sticking"). To eliminate this, a thin layer of aluminium (about 100 nm) is deposited over the phosphors, usually by vacuum evaporation, and connected to the conductive layer inside the tube. This layer also reflects the phosphor light to the desired direction, and protects the phosphor from ion bombardment resulting from an imperfect vacuum.
To reduce the image degradation by reflection of ambient light, contrast can be increased by several methods. In addition to black masking of unused areas of screen, the phosphor particles in color screens are coated with pigments of matching color. For example, the red phosphors are coated with ferric oxide (replacing earlier Cd(S,Se) due to cadmium toxicity), blue phosphors can be coated with marine blue ( CoO · n Al 2 O 3 ) or ultramarine ( Na 8 Al 6 Si 6 O 24 S 2 ). Green phosphors based on ZnS:Cu do not have to be coated due to their own yellowish color. [ 7 ]
The black-and-white television screens require an emission color close to white. Usually, a combination of phosphors is employed.
The most common combination is ZnS:Ag + (Zn,Cd)S:Cu,Al (blue + yellow). Other ones are ZnS:Ag + (Zn,Cd)S:Ag (blue + yellow), and ZnS:Ag + ZnS:Cu,Al + Y 2 O 2 S:Eu 3+ (blue + green + red – does not contain cadmium and has poor efficiency). The color tone can be adjusted by the ratios of the components.
As the compositions contain discrete grains of different phosphors, they produce image that may not be entirely smooth. A single, white-emitting phosphor, (Zn,Cd)S:Ag,Au,Al overcomes this obstacle. Due to its low efficiency, it is used only on very small screens.
The screens are typically covered with phosphor using sedimentation coating, where particles suspended in a solution are let to settle on the surface. [ 31 ]
For displaying of a limited palette of colors, there are a few options.
In beam penetration tubes , different color phosphors are layered and separated with dielectric material. The acceleration voltage is used to determine the energy of the electrons; lower-energy ones are absorbed in the top layer of the phosphor, while some of the higher-energy ones shoot through and are absorbed in the lower layer. So either the first color or a mixture of the first and second color is shown. With a display with red outer layer and green inner layer, the manipulation of accelerating voltage can produce a continuum of colors from red through orange and yellow to green.
Another method is using a mixture of two phosphors with different characteristics. The brightness of one is linearly dependent on electron flux, while the other one's brightness saturates at higher fluxes—the phosphor does not emit any more light regardless of how many more electrons impact it. At low electron flux, both phosphors emit together; at higher fluxes, the luminous contribution of the nonsaturating phosphor prevails, changing the combined color. [ 31 ]
Such displays can have high resolution, due to absence of two-dimensional structuring of RGB CRT phosphors. Their color palette is, however, very limited. They were used e.g. in some older military radar displays.
The phosphors in color CRTs need higher contrast and resolution than the black-and-white ones. The energy density of the electron beam is about 100 times greater than in black-and-white CRTs; the electron spot is focused to about 0.2 mm diameter instead of about 0.6 mm diameter of the black-and-white CRTs. Effects related to electron irradiation degradation are therefore more pronounced.
Color CRTs require three different phosphors, emitting in red, green and blue, patterned on the screen. Three separate electron guns are used for color production (except for displays that use beam-index tube technology, which is rare). The red phosphor has always been a problem, being the dimmest of the three necessitating the brighter green and blue electron beam currents be adjusted down to make them equal the red phosphor's lower brightness. This made early color TVs only usable indoors as bright light made it impossible to see the dim picture, while portable black-and-white TVs viewable in outdoor sunlight were already common.
The composition of the phosphors changed over time, as better phosphors were developed and as environmental concerns led to lowering the content of cadmium and later abandoning it entirely. The (Zn,Cd)S:Ag,Cl was replaced with (Zn,Cd)S:Cu,Al with lower cadmium/zinc ratio, and then with cadmium-free ZnS:Cu,Al .
The blue phosphor stayed generally unchanged, a silver-doped zinc sulfide. The green phosphor initially used manganese-doped zinc silicate, then evolved through silver-activated cadmium-zinc sulfide, to lower-cadmium copper-aluminium activated formula, and then to cadmium-free version of the same. The red phosphor saw the most changes; it was originally manganese-activated zinc phosphate, then a silver-activated cadmium-zinc sulfide, then the europium(III) activated phosphors appeared; first in an yttrium vanadate matrix, then in yttrium oxide and currently in yttrium oxysulfide . The evolution of the phosphors was therefore (ordered by B-G-R):
For projection televisions , where the beam power density can be two orders of magnitude higher than in conventional CRTs, some different phosphors have to be used.
For blue color, ZnS:Ag,Cl is employed. However, it saturates. (La,Gd)OBr:Ce,Tb 3+ can be used as an alternative that is more linear at high energy densities.
For green, a terbium -activated Gd 2 O 2 Tb 3+ ; its color purity and brightness at low excitation densities is worse than the zinc sulfide alternative, but it behaves linear at high excitation energy densities, while zinc sulfide saturates. However, it also saturates, so Y 3 Al 5 O 12 :Tb 3+ or Y 2 SiO 5 :Tb 3+ can be substituted. LaOBr:Tb 3+ is bright but water-sensitive, degradation-prone, and the plate-like morphology of its crystals hampers its use; these problems are solved now, so it is gaining use due to its higher linearity.
Y 2 O 2 S:Eu 3+ is used for red emission. [ 31 ]
Some other phosphors commercially available, for use as X-ray screens, neutron detectors , alpha particle scintillators , etc., are: | https://en.wikipedia.org/wiki/Phosphor |
In organophosphorus chemistry , phosphoramidates (sometimes also called amidophosphates ) are a class of phosphorus compounds structurally related to phosphates (or organophosphates ) via the substitution of an −O − group for an amine group ( −N− ). They are derivatives of phosphoramidic acids , which possess the structure O=P(OH)(NR 2 ) 2 or O=P(OH) 2 (NR 2 ) .
A phosphorodiamidate is a phosphate that has two of its hydroxyl ( −OH ) groups substituted by amine ( NR 2 ) groups to give a species with the general formula O=P(OH)(NH 2 ) 2 . The substitution of all three OH groups gives the phosphoric triamides ( O=P(NR 2 ) 3 ), which are commonly referred to as phosphoramides . [ 1 ]
In the Stokes method, phosphoramidates are synthesized from phosphorus oxychloride . The compound reacts with phenol to form a chloro phosphonate ester or diester, depending on stoichiometry . The remaining chlorine substituents then react with an amine compound to give the phosphoramidate. [ 2 ]
Two examples of natural phosphoramidates are phosphocreatine and the phosphoramidate formed when histidine residues in histidine kinases are phosphorylated. [ 3 ] An example of a phosphorodiamidate is morpholino which is used in molecular biology . | https://en.wikipedia.org/wiki/Phosphoramidate |
Phosphoramide is a chemical compound with the molecular formula O=P(NH 2 ) 3 . It is a derivative of phosphoric acid in which each of the hydroxyl groups have been replaced with an amino group . In bulk, the compound is a white solid which is soluble in polar solvents .
Phosphoramide arises from the reaction of phosphoryl chloride with ammonia. In moist air, it hydrolyzes to an ammonium salt :
It reacts with sodium hydroxide with loss of ammonia : [ 2 ]
The related thiophosphoryl triamide compound S=P(NH 2 ) 3 was made from the reaction of thiophosphoryl chloride with ammonia.
Phosphoramide is also the parent compound for a range of derivatives called phosphoramides. [ 3 ] An example compound is the polar solvent hexamethylphosphoramide (HMPA). | https://en.wikipedia.org/wiki/Phosphoramide |
Phosphoramides are a class of phosphorus compounds with the formula O=P(NR 2 ) 3-n (OH) n . They can be considered derivatives of phosphoric acid where OH groups have been replaced with an amino or R-substituted amino group. In practise the term is commonly confined to the phosphoric triamides (P(=O)(NR 2 ) 3 ), essentially phosphoramide and derivatives thereof. [ 1 ] Derivatives with the general structures P(=O)(OH)(NR 2 ) 2 or P(=O)(OH) 2 (NR 2 ) are usually referred to as phosphoramidic acids . | https://en.wikipedia.org/wiki/Phosphoramides |
A phosphoramidite (RO) 2 PNR 2 is a monoamide of a phosphite diester. The key feature of phosphoramidites is their markedly high reactivity towards nucleophiles catalyzed by weak acids e.c ., triethylammonium chloride or 1 H - tetrazole . In these reactions, the incoming nucleophile replaces the NR 2 moiety.
Phosphoramidites derived from protected nucleosides are referred to as nucleoside phosphoramidites and are widely used in chemical synthesis of DNA , RNA, and other nucleic acids and their analogs.
Certain phosphoramidites are also used as monodentate chiral ligands in asymmetric synthesis. [ 1 ] A large group of such ligands is derived from the chiral diol BINOL and can be synthesised by reaction of BINOL with phosphorus trichloride to the chlorophosphite and then reaction with simple secondary amines . [ 2 ] This type of ligand was first used in 1996 in an asymmetric copper-catalysed addition of dialkylzincs to enones. [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Phosphoramidite |
A phosphorane ( IUPAC name: λ 5 -phosphane ) is a functional group in organophosphorus chemistry with pentavalent phosphorus . Phosphoranes have the general formula PR 5 .
Phosphoranes of the type PX 5 adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three equatorial bonds. Hypervalent bonding is described by inclusion of non-bonding MOs, as also invoked for the closely related molecule phosphorus pentafluoride . [ 1 ]
The parent hydride compound is the hypothetical molecule PH 5 .
Pentaphenylphosphorane (Ph 5 P) is stable. [ 2 ]
Pentaalkoxyphosphoranes are more common with electronegative substituents. Examples of P(OR) 5 (R = alkyl), have however been prepared by reaction of phosphites with benzene alkyl sulfenates : [ 3 ]
Phosphoranes of the type R 3 P=CR 2 are more common and more important. Phosphoranes are also considered to be one of the resonance structures of ylides , these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction , for instance methylenetriphenylphosphorane or Ph 3 P=CH 2 . | https://en.wikipedia.org/wiki/Phosphoranes |
Phosphorene is a two-dimensional material consisting of phosphorus . It consists of a single layer of black phosphorus , the most stable allotrope of phosphorus . [ 1 ] Phosphorene is analogous [ 2 ] to graphene (single layer graphite ). Among two-dimensional materials , phosphorene is a competitor to graphene because it has a nonzero fundamental band gap that can be modulated by strain and the number of layers in a stack. [ 2 ] [ 3 ] [ 4 ] Phosphorene was first isolated in 2014 by mechanical exfoliation. [ 2 ] [ 5 ] [ 6 ] Liquid exfoliation is a promising method for scalable phosphorene production. [ 7 ] [ 8 ] [ 9 ]
In 1914 black phosphorus , a layered, semiconducting allotrope of phosphorus, was synthesized. [ 1 ] This allotrope exhibits high carrier mobility . [ 10 ] In 2014, several groups [ 2 ] [ 5 ] [ 6 ] isolated single-layer phosphorene, a monolayer of black phosphorus. It attracted renewed attention [ 11 ] because of its potential in optoelectronics and electronics due to its band gap , which can be tuned via modifying its thickness, anisotropic photoelectronic properties and carrier mobility. [ 2 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ] [ 18 ] Phosphorene was initially prepared using mechanical cleavage, a commonly used technique in graphene production.
In 2023, alloys of arsenic-phosphorene displayed higher hole mobility than pure phosphorene and were also magnetic. [ 19 ]
Synthesis of phosphorene is a significant challenge. Currently, there are two main ways of phosphorene production: scotch-tape-based microcleavage [ 2 ] and liquid exfoliation , [ 8 ] [ 9 ] while several other methods are being developed as well. Phosphorene production from plasma etching has also been reported. [ 21 ]
In scotch-tape-based microcleavage, [ 2 ] phosphorene is mechanically exfoliated from a bulk of black phosphorus crystal using scotch-tape. Phosphorene is then transferred on a Si/SiO 2 substrate, where it is then cleaned with acetone , isopropyl alcohol and methanol to remove any scotch tape residue. The sample is then heated to 180 °C to remove solvent residue.
In the liquid exfoliation method, first reported by Brent et al. in 2014 [ 7 ] and modified by others, [ 8 ] bulk black phosphorus is first ground in a mortar and pestle and then sonicated in deoxygenated, anhydrous organic liquids such as NMP under an inert atmosphere using low-power bath sonication . Suspensions are then centrifuged for 30 minutes to filter out the unexfoliated black phosphorus. Resulting 2D monolayer and few-layer phosphorene unoxidized and crystalline structure, while exposure to air oxidizes the phosphorene and produces acid. [ 8 ]
Another variation of liquid exfoliation [ 9 ] is "basic N-methyl-2-pyrrolidone (NMP) liquid exfoliation". Bulk black phosphorene is added to a saturated NaOH/NMP solution, which is further sonicated for 4 hours to conduct liquid exfoliation. The solution is then centrifuged twice, first for 10 minutes to remove any unexfoliated black phosphorus and then for 20 minutes at a higher speed to separate thick layers of phosphorene (5–12 layers) from NMP. The supernatant then is centrifuged again at higher speed for another 20 minutes to separate thinner layers of phosphorene (1–7 layers). The precipitate from centrifugation is then redispersed in water and washed several times by deionized water. Phosphorene/water solution is dropped onto silicon with a 280-nm SiO 2 surface, where it is further dried under vacuum. NMP liquid exfoliation method was shown to yield phosphorene with controllable size and layer number, excellent water stability and in high yield. [ 9 ]
The disadvantage of the current methods includes long sonication time, high boiling point solvents, and low efficiency. Therefore, other physical methods for liquid exfoliation are still under development. A laser -assisted method developed by Zheng and co-workers [ 22 ] showed a promising yield of up to 90% within 5 minutes. The laser photon interacts with the surface of bulk black phosphorus crystal, causing a plasma and solvent bubbles to weaken the interlayer interaction. Depending on the laser energy, solvent ( ethanol , methanol, hexane , etc.) and irradiation time, the layer number and lateral size of the phosphorene were controlled.
The high yield production of phosphorene has been demonstrated by many groups in solvents, but to realize the potential applications of this material, it is crucial to deposit these free-standing nanosheets in solvents systematically on substrates. H. Kaur et al. [ 23 ] demonstrated the synthesis, interface-driven alignment and subsequent functional properties of few layer semiconducting phosphorene using Langmuir-Blodgett assembly. This is the first study which provides a straightforward and versatile solution towards the challenge of assembling nanosheets of phosphorene onto various supports and subsequently use these sheets in an electronic device. Therefore, wet assemblies techniques like Langmuir-Blodgett serves as a very valuable new entry point for the exploration of electronic as well as opto-electronic properties of phosphorene as well as other 2D layered inorganic materials.
It is still a challenge to directly epitaxially grow 2D phosphorene because the stability of black phosphorene is highly sensitive to substrate, which is understanding by theoretical simulations. [ clarification needed ] [ 24 ] [ 25 ]
Phosphorene 2D materials are composed of individual layers held together by van der Waals forces in lieu of covalent or ionic bonds that are found in most materials. There are three electrons within the 3p orbitals of the phosphorus atom, thus, giving rise to sp 3 hybridization of each phosphorus atom within the phosphorene structure. Monolayered phosphorene exhibits the structure of a quadrangular pyramid because three electrons of P atom bond with three other P atoms covalently at 2.18 Å leaving one lone pair. [ 8 ] Two of the phosphorus atoms are in the plane of the layer at 99° from one another, and the third phosphorus is between the layers at 103°, yielding an average angle of 102°.
According to density functional theory (DFT) calculations, phosphorene forms in a honeycomb lattice structure with notable nonplanarity in the shape of structural ridges. It is predicted that crystal structure of black phosphorus can be discriminated under high pressure. [ 26 ] This is mostly due to the anisotropic compressibility of black phosphorus because of the asymmetrical crystal structures. Subsequently, the van der Waals bond can be greatly compressed in the z-direction. However, there is a great variation in compressibility across the orthogonal x-y plane.
It is reported that controlling the centrifugal speed of production may aid in regulating the thickness of a material. For example, centrifuging at 18,000 rpm during synthesis produced phosphorene with an average diameter of 210 nm and a thickness of 2.8 ± 1.5 nm (2–7 layers). [ 8 ]
Phosphorene has a thickness dependent direct band gap that changes to 1.88 eV in a monolayer from 0.3 eV in the bulk. [ 9 ] Increase in band gap value in single-layer phosphorene is predicted to be caused by the absence of interlayer hybridization near the top of the valence and bottom of the conduction band. [ 2 ] A pronounced peak centered at around 1.45 eV suggests the band gap structure in few- or single-layer phosphorene difference from bulk crystals. [ 2 ]
In vacuum or on weak substrate, an interesting reconstruction with nanotubed termination of phosphorene edge is very easy to happen, transforming phosphorene edge from metallic to semiconducting. [ 27 ]
One major disadvantage of phosphorene is its limited air-stability. [ 29 ] [ 30 ] [ 31 ] [ 32 ] [ 33 ] [ 34 ] Composed of hygroscopic phosphorus and with extremely high surface-to-volume ratio , phosphorene reacts with water vapor and oxygen assisted by visible light [ 35 ] to degrade within the scope of hours. Through the degradation process, phosphorene (solid) reacts with oxygen/water to develop liquid phase acid 'bubbles' on the surface, and finally evaporate (vapor) to fully vanish (S-B-V degradation) and severely reducing overall quality. [ 9 ]
Researchers [ 2 ] have fabricated transistors of phosphorene to examine its performance in actual devices. Phosphorene-based transistor consists of a channel of 1.0 μm and uses few layered phosphorene with a thickness varying from 2.1 to over 20 nm. Reduction of the total resistance with decreasing gate voltage is observed, indicating the p-type characteristic of phosphorene. Linear I-V relationship of transistor at low drain bias suggests good contact properties at the phosphorene/metal interface. Good current saturation at high drain bias values was observed. [ 2 ] However, it was seen that the mobility is reduced in few-layer phosphorene when compared to bulk black phosphorus. Field-effect mobility of phosphorene-based transistor shows a strong thickness dependence, peaking at around 5 nm and decrease steadily with further increase of crystal thickness.
Atomic layer deposition (ALD) dielectric layer and/or hydrophobic polymer is used as encapsulation layers in order to prevent device degradation and failure. Phosphorene devices are reported to maintain their function for weeks with encapsulation layer, whereas experience device failure within a week when exposed to ambient condition. [ 29 ] [ 30 ] [ 31 ] [ 32 ] [ 33 ] [ 36 ]
Phosphorene is considered a promising anode material for rechargeable batteries, such as lithium-ion batteries. The interlayer space allows lithium storage and transfer. The layer number and lateral size of phosphorene affect the stability and capacity of the anode. [ 22 ]
Researchers have also constructed the CMOS inverter (logic circuit) by combining a phosphorene PMOS transistor with a MoS 2 NMOS transistor, achieving high heterogeneous integration of semiconducting phosphorene crystals as a new channel material for potential electronic applications. [ 2 ] In the inverter, the power supply voltage is set to be 1 V. The output voltage shows a clear transition from VDD to 0 within the input voltage range from −10 to −2 V. A maximum gain of ~1.4 is attained.
The potential applications of mixed bilayer phosphorene in solar-cell material was examined as well. [ 37 ] [ 36 ]
Phosphorene is a promising candidate for flexible nano systems due to its ultra-thin nature with ideal electrostatic control and superior mechanical flexibility. [ 39 ] Researchers have demonstrated the flexible transistors, circuits and AM demodulator based on few-layer phosphorus, showing enhanced am bipolar transport with high room temperature carrier mobility as high as ~310 cm 2 /Vs and strong current saturation. Fundamental circuit units including digital inverter, voltage amplifier and frequency doubler have been realized. [ 40 ] Radio frequency (RF) transistors with highest intrinsic cutoff frequency of 20 GHz has been realized for potential applications in high frequency flexible smart nano systems. [ 38 ] | https://en.wikipedia.org/wiki/Phosphorene |
Phosphorescence is a type of photoluminescence related to fluorescence . When exposed to light (radiation) of a shorter wavelength, a phosphorescent substance will glow, absorbing the light and reemitting it at a longer wavelength. Unlike fluorescence, a phosphorescent material does not immediately reemit the radiation it absorbs. Instead, a phosphorescent material absorbs some of the radiation energy and reemits it for a much longer time after the radiation source is removed.
In a general sense, there is no distinct boundary between the emission times of fluorescence and phosphorescence (i.e.: if a substance glows under a black light it is generally considered fluorescent, and if it glows in the dark it is often simply called phosphorescent). [ 1 ] In a modern, scientific sense, the phenomena can usually be classified by the three different mechanisms that produce the light, [ further explanation needed ] and the typical timescales during which those mechanisms emit light. Whereas fluorescent materials stop emitting light within nanoseconds (billionths of a second) after the excitation radiation is removed, phosphorescent materials may continue to emit an afterglow ranging from a few microseconds to many hours after the excitation is removed. [ 2 ]
There are two separate mechanisms that may produce phosphorescence, called triplet phosphorescence (or simply phosphorescence) and persistent phosphorescence (or persistent luminescence ):
Everyday examples of phosphorescent materials are the glow-in-the-dark toys, stickers, paint, and clock dials that glow after being charged with a bright light such as in any normal reading or room light. Typically, the glow slowly fades out, sometimes within a few minutes or up to a few hours in a dark room. [ further explanation needed ] [ 5 ]
The study of phosphorescent materials led to the discovery of radioactive decay .
The term phosphorescence comes from the Ancient Greek word φῶς ( phos ), meaning "light", and the Greek suffix -φόρος ( -phoros ), meaning "to bear", combined with the Latin suffix -escentem , meaning "becoming of", "having a tendency towards", or "with the essence of". [ 6 ] Thus, phosphorescence literally means "having a tendency to bear light". It was first recorded in 1766. [ 7 ]
The term phosphor had been used since the Middle Ages to describe minerals that glowed in the dark. One of the most famous, but not the first, was Bolognian phosphor. Around 1604, Vincenzo Casciarolo discovered a " lapis solaris " near Bologna, Italy. Once heated in an oxygen-rich furnace , it thereafter absorbed sunlight and glowed in the dark. In 1677, Hennig Brand isolated a new element that glowed due to a chemiluminescent reaction when exposed to air, and named it " phosphorus ". [ 8 ]
In contrast, the term luminescence (from the Latin lumen for "light"), was coined by Eilhardt Wiedemann in 1888 as a term to refer to "light without heat", while "fluorescence" by Sir George Stokes in 1852, when he noticed that, when exposing a solution of quinine sulfate to light refracted through a prism , the solution glowed when exposed to the mysterious invisible-light (now known to be UV light) beyond the violet end of the spectrum. Stokes formed the term from a combination of fluorspar and opalescence (preferring to use a mineral instead of a solution), albeit it was later discovered that fluorspar glows due to phosphorescence. [ 9 ]
There was much confusion between the meanings of these terms throughout the late nineteenth to mid-twentieth centuries. Whereas the term "fluorescence" tended to refer to luminescence that ceased immediately (by human-eye standards) when removed from excitation, "phosphorescence" referred to virtually any substance that glowed for appreciable periods in darkness, sometimes to include even chemiluminescence (which occasionally produced substantial amounts of heat). Only after the 1950s and 1960s did advances in quantum electronics , spectroscopy , and lasers provide a measure to distinguish between the various processes that emit the light, although in common speech the distinctions are still often rather vague. [ 10 ]
In simple terms, phosphorescence is a process in which energy absorbed by a substance is released relatively slowly in the form of light. This is in some cases the mechanism used for glow-in-the-dark materials which are "charged" by exposure to light. Unlike the relatively swift reactions in fluorescence, such as those seen in laser mediums like the common ruby , phosphorescent materials "store" absorbed energy for a longer time, as the processes required to reemit energy occur less often. However, timescale is still only a general distinction, as there are slow-emitting fluorescent materials, for example uranyl salts , and, likewise, some phosphorescent materials like zinc sulfide (in violet) are very fast. Scientifically, the phenomena are classified by the different mechanisms that produce the light, as materials that phosphoresce may be suitable for some purposes such as lighting, but may be completely unsuitable for others that require fluorescence, like lasers. Further blurring the lines, a substance may emit light by one, two, or all three mechanisms depending on the material and excitation conditions. [ further explanation needed ] [ 11 ]
When the stored energy becomes locked in by the spin of the atomic electrons , a triplet state can occur, slowing the emission of light, sometimes by several orders of magnitude. Because the atoms usually begin in a singlet state of spin, favoring fluorescence, these types of phosphors typically produce both types of emission during illumination, and then a dimmer afterglow of strictly phosphorescent light typically lasting less than a second after the illumination is switched off.
Conversely, when the stored energy is due to persistent phosphorescence, an entirely different process occurs without a fluorescence precursor. When electrons become trapped within a defect in the atomic or molecular lattice, light is prevented from reemitting until the electron can escape. To escape, the electron needs a boost of thermal energy to help spring it out of the trap and back into orbit around the atom. Only then can the atom emit a photon. Thus, persistent phosphorescence is highly dependent on the temperature of the material. [ 12 ]
Most photoluminescent events, in which a chemical substrate absorbs and then re-emits a photon of light, are fast, in the order of 10 nanoseconds . Light is absorbed and emitted at these fast time scales in cases where the energy of the photons involved matches the available energy states and allowed transitions of the substrate. In the special case of phosphorescence, the electron which absorbed the photon (energy) undergoes an unusual intersystem crossing into an energy state of different (usually higher) spin multiplicity ( see term symbol ), usually a triplet state . As a result, the excited electron can become trapped in the triplet state with only "forbidden" transitions available to return to the lower energy singlet state. These transitions, although "forbidden", will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. Most phosphorescent compounds are still relatively fast emitters, with triplet decay-times in the order of milliseconds.
Common examples include the phosphor coatings used in fluorescent lamps , where phosphorescence on the order of milliseconds or longer is useful for filling in the "off-time" between AC current cycles, helping to reduce "flicker". Phosphors with faster decay times are used in applications like the pixels excited by free electrons ( cathodoluminescence ) in cathode-ray tube television-sets , which are slow enough to allow the formation of a picture as the electron beam scans the screen, but fast enough to prevent the frames from blurring together. [ 13 ] [ 14 ] Even substances commonly associated with fluorescence may in fact be prone to phosphorescence, such as the liquid dyes found in highlighter pens, which is a common problem in liquid dye lasers . The onset of phosphorescence in this case can sometimes be reduced or delayed significantly by the use of triplet-quenching agents. [ 15 ]
S 0 + h ν → S 1 → T 1 → S 0 + h ν ′ {\displaystyle S_{0}+h\nu \to S_{1}\to T_{1}\to S_{0}+h\nu ^{\prime }\ } where S is a singlet and T a triplet whose subscripts denote states (0 is the ground state, and 1 the excited state). Transitions can also occur to higher energy levels, but the first excited state is denoted for simplicity.
Solid materials typically come in two main types: crystalline and amorphous. In either case, a lattice or network of atoms and molecules form. In crystals, the lattice is a very neat, uniform assembly. However, nearly all crystals have defects in the stacking sequence of these molecules and atoms. A vacancy defect , where an atom is simply missing from its place, leaving an empty "hole", is one type of defect. Sometimes atoms can move from place to place within the lattice, creating Schottky defects or Frenkel defects . Other defects can occur from impurities in the lattice. For example, when a normal atom is substituted by a different atom of much larger or smaller size, a substitutional defect occurs, while an interstitial defect occurs when a much smaller atom gets trapped in the "interstices", or the spaces between atoms. In contrast, amorphous materials have no "long-range order" (beyond the space of a few atoms in any direction), thus by definition are filled with defects.
When a defect occurs, depending on the type and material, it can create a hole, or a "trap". For example, a missing oxygen atom from a zinc oxide compound creates a hole in the lattice, surrounded by unbound zinc-atoms. This creates a net force or attraction that can be measured in electron-volts . [ further explanation needed ] When a high-energy photon strikes one of the zinc atoms, its electron absorbs the photon and is thrown out into a higher orbit. The electron may then enter the trap and be held in place (out of its normal orbit) by the attraction. To trigger the release of the energy, a random spike in thermal energy of sufficient magnitude is needed to boost the electron out of the trap and back into its normal orbit. Once in orbit, the electron's energy can drop back to normal (ground state) resulting in the release of a photon. [ 16 ]
The release of energy in this way is a completely random process, governed mostly by the average temperature of the material versus the "depth" of the trap, or how many electron-volts it exerts. [ citation needed ] A trap that has a depth of 2.0 electron-volts would require a great amount of thermal energy (very high temperature) to overcome the attraction, while at a depth of 0.1 electron-volts very little heat (very cold temperature) is needed for the trap to even hold an electron. Generally, higher temperatures cause a faster release of energy, resulting in a brighter yet short-lived emission, while lower temperatures produce a dimmer but longer-lasting glow. Temperatures that are too hot or cold, depending on the substance, may not allow the accumulation or release of energy at all. The ideal depth of trap for persistent phosphorescence at room temperature is typically between 0.6 and 0.7 electron-volts. [ 17 ] If the phosphorescent quantum yield is high, that is, if the substance has a large number of traps of the correct depth, this substance will release a significant amount of light over a long period of time, creating a so-called "glow in the dark" material.
Some examples of glow-in-the-dark materials do not glow by phosphorescence. For example, glow sticks glow due to a chemiluminescent process which is commonly mistaken for phosphorescence. In chemiluminescence, an excited state is created via a chemical reaction. The light emission tracks the kinetic progress of the underlying chemical reaction. The excited state will then transfer to a dye molecule, also known as a sensitizer or fluorophor , and subsequently fluoresce back to the ground state.
Common pigments used in phosphorescent materials include zinc sulfide and strontium aluminate . Use of zinc sulfide for safety related products dates back to the 1930s.
The development of strontium aluminate pigments in 1993 was spurred on by the need to find a substitute for glow-in-the-dark materials with high luminance and long phosphorescence, especially those that used promethium . [ 18 ] [ 19 ] This led to the discovery by Yasumitsu Aoki (Nemoto & Co.) of materials with luminance approximately 10 times greater than zinc sulfide and phosphorescence approximately 10 times longer. [ 20 ] [ 21 ] This has relegated most zinc sulfide based products to the novelty category. Strontium aluminate based pigments are now used in exit signs, pathway marking, and other safety related signage. [ 22 ]
Since both phosphorescence (transition from T 1 to S 0 ) and the generation of T 1 from an excited singlet state (e.g., S 1 ) via intersystem crossing (ISC) are spin-forbidden processes, most organic materials exhibit insignificant phosphorescence as they mostly fail to populate the excited triplet state, and, even if T 1 is formed, phosphorescence is most frequently outcompeted by non-radiative pathways. One strategy to enhance the ISC and phosphorescence is the incorporation of heavy atoms, which increase spin-orbit coupling (SOC). [ 23 ] Additionally, the SOC (and therefore the ISC) can be promoted by coupling n-π* and π-π* transitions with different angular momenta, also known as Mostafa El-Sayed 's rule. Such transitions are typically exhibited by carbonyl or triazine derivatives, and most organic room-temperature phosphorescent (ORTP) materials incorporate such moieties. [ 24 ] [ 25 ] In turn, to inhibit competitive non-radiative deactivation pathways, including vibrational relaxation and oxygen quenching and triplet-triplet annihilations, organic phosphors have to be embedded in rigid matrices such as polymers, and molecular solids (crystals, [ 26 ] covalent organic frameworks, [ 27 ] and others).
In 1974 Becky Schroeder was given a US patent for her invention of the "Glow Sheet" which used phosphorescent lines under writing paper to help people write in low-light conditions. [ 28 ]
Glow in the dark material is added to the plastic blend used in injection molds to make some disc golf discs, which allow the game to be played at night.
Often clock faces of watches are painted with phosphorescent colours. Therefore, they can be used in absolute dark environments for several hours after having been exposed to bright light.
A common use of phosphorescence is decoration. Stars made of glow-in-the-dark plastic are placed on walls, ceilings, or hanging from strings make a room look like the night sky. [ 29 ] Other objects like figurines, cups, posters, [ 30 ] lamp fixtures, toys [ 31 ] and bracelet beads may also glow. [ 32 ] Using blacklights makes these things glow brightly, common at raves , bedrooms, theme parks, and festivals.
A shadow wall is created when a light flashes upon a person or object in front of a phosphorescent screen which temporarily captures the shadow. The screen or wall is painted with a glow-in-the-dark product that contains phosphorescent compounds. [ 33 ] Publicly, these shadow walls can be found at certain science museums. [ 34 ] [ 35 ] | https://en.wikipedia.org/wiki/Phosphorescence |
Phosphorescent organic light-emitting diodes ( PHOLED ) are a type of organic light-emitting diode (OLED) that use the principle of phosphorescence to obtain higher internal efficiencies than fluorescent OLEDs. This technology is currently under development by many industrial and academic research groups.
Like all types of OLED, phosphorescent OLEDs emit light due to the electroluminescence of an organic semiconductor layer in an electric current. Electrons and holes are injected into the organic layer at the electrodes and form excitons , a bound state of the electron and hole.
Electrons and holes are both fermions with half integer spin . An exciton is formed by the coulombic attraction between the electron and the hole, and it may either be in a singlet state or a triplet state , depending on the spin states of these two bound species. Statistically, there is a 25% probability of forming a singlet state and 75% probability of forming a triplet state. [ 2 ] [ 3 ] Decay of the excitons results in the production of light through spontaneous emission .
In OLEDs using fluorescent organic molecules only, the decay of triplet excitons is quantum mechanically forbidden by selection rules , meaning that the lifetime of triplet excitons is long and phosphorescence is not readily observed. Hence it would be expected that in fluorescent OLEDs only the formation of singlet excitons results in the emission of useful radiation, placing a theoretical limit on the internal quantum efficiency (the percentage of excitons formed that result in emission of a photon) of 25%. [ 4 ]
However, phosphorescent OLEDs generate light from both triplet and singlet excitons, allowing the internal quantum efficiency of such devices to reach nearly 100%. [ 5 ]
This is commonly achieved by doping a host molecule with an organometallic complex . These contain a heavy metal atom at the centre of the molecule, for example platinum [ 6 ] or iridium, of which the green emitting complex Ir(mppy) 3 is just one of many examples. [ 1 ] The large spin–orbit interaction experienced by the molecule due to this heavy metal atom facilitates intersystem crossing , a process which mixes the singlet and triplet character of excited states. This reduces the lifetime of the triplet state, [ 7 ] [ 8 ] therefore phosphorescence is readily observed.
Due to their potentially high level of energy efficiency, even when compared to other OLEDs, PHOLEDs are being studied for potential use in large-screen displays such as computer monitors or television screens, as well as general lighting needs. One potential use of PHOLEDs as lighting devices is to cover walls with large area PHOLED light panels. This would allow entire rooms to glow uniformly, rather than require the use of light bulbs which distribute light unequally throughout a room. The United States Department of Energy has recognized the potential for massive energy savings via the use of this technology and therefore has awarded $200,000 USD in contracts to develop PHOLED products for general lighting applications. [ 9 ]
One problem that currently hampers the widespread adoption of this highly energy efficient technology is that the average lifetimes of red and green PHOLEDs are often tens of thousands of hours longer than those of blue PHOLEDs. This may cause displays to become visually distorted much sooner than would be acceptable for a commercially viable device. [ 10 ] | https://en.wikipedia.org/wiki/Phosphorescent_organic_light-emitting_diode |
The enzyme Phosphoribosylaminoimidazole carboxylase , or AIR carboxylase ( EC 4.1.1.21 ) is involved in nucleotide biosynthesis and in particular in purine biosynthesis . It catalyzes the conversion of 5'-phosphoribosyl-5-aminoimidazole ("AIR") into 5'-phosphoribosyl-4-carboxy-5-aminoimidazole ("CAIR") as described in the reaction:
Phosphoribosylaminoimidazole carboxylase is a fusion protein in plants and fungi , but consists of two non-interacting proteins in bacteria, PurK and PurE.
The crystal structure of PurE indicates a unique quaternary structure that confirms the octameric nature of the enzyme. [ 1 ]
In the bacterium Escherichia coli the reaction is catalyzed in two steps carried out by two separate enzymes, PurK and PurE.
PurK, N 5-carboxyaminoimidazole ribonucleotide synthetase , catalyzes the conversion of 5-aminoimidazole ribonucleotide ("AIR"), ATP , and bicarbonate to N 5-carboxyaminoimidazole ribonucleotide ("N5-CAIR"), ADP , and phosphate .
PurE, N 5-carboxyaminoimidazole ribonucleotide mutase , converts N5-CAIR to CAIR, the sixth step of de novo purine biosynthesis. In the presence of high concentrations of bicarbonate, PurE is reported able to convert AIR to CAIR directly and without ATP. Some members of this family contain two copies of this domain. [ 2 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphoribosylaminoimidazole_carboxylase |
In chemistry , a phosphoric acid , in the general sense, is a phosphorus oxoacid in which each phosphorus (P) atom is in the oxidation state +5, and is bonded to four oxygen (O) atoms, one of them through a double bond , arranged as the corners of a tetrahedron . Two or more of these PO 4 tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains , cycles , or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. The general formula of a phosphoric acid is H n +2−2 x P n O 3 n +1− x , where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure, between 0 and n + 2 / 2 .
Removal of protons ( H + ) from k hydroxyl groups –OH leaves anions generically called phosphates (if k = n − 2 x + 2 ) or hydrogen phosphates (if k is between 1 and n − 2 x + 1 ), with general formula [H n −2 x +2− k P n O 3 n +1− x ] k − . The fully dissociated anion ( k = n − 2 x + 2 ) has formula [P n O 3 n − x +1 ] ( n −2 x +2)− . The term phosphate is also used in organic chemistry for the functional groups that result when one or more of the hydrogens are replaced by bonds to other groups.
These acids, together with their salts and esters , include some of the best-known compounds of phosphorus, of high importance in biochemistry , mineralogy , agriculture , pharmacy , chemical industry , and chemical research .
The simplest and most commonly encountered of the phosphoric acids is orthophosphoric acid , H 3 PO 4 . Indeed, the term phosphoric acid often means this compound specifically (and this is also the current IUPAC nomenclature). [ citation needed ]
Two or more orthophosphoric acid molecules can be joined by condensation into larger molecules by elimination of water . Condensation of a few units yields the oligophosphoric acids , while larger molecules are called polyphosphoric acids . (However, the distinction between the two terms is not well defined.)
For example, pyrophosphoric , triphosphoric and tetraphosphoric acids can be obtained by the reactions 2 H 3 PO 4 ⟶ H 4 P 2 O 7 + H 2 O H 4 P 2 O 7 + H 3 PO 4 ⟶ H 5 P 3 O 10 + H 2 O H 5 P 3 O 10 + H 3 PO 4 ⟶ H 6 P 4 O 13 + H 2 O {\displaystyle {\begin{aligned}{\ce {2 H3PO4}}&\longrightarrow {\ce {H4P2O7 + H2O}}\\[2pt]{\ce {H4P2O7 + H3PO4}}&\longrightarrow {\ce {H5P3O10 + H2O}}\\[2pt]{\ce {H5P3O10 + H3PO4}}&\longrightarrow {\ce {H6P4O13 + H2O}}\end{aligned}}}
The "backbone" of a polyphosphoric acid molecule is a chain of alternating P and O atoms. Each extra orthophosphoric unit that is condensed adds 1 extra H ( hydrogen ) atom, 1 extra P ( phosphorus ) atom, and 3 extra O ( oxygen ) atoms. The general formula of a polyphosphoric acid is H n +2 P n O 3 n +1 or HO[−P(O)(OH)−O−] n H .
Polyphosphoric acids are used in organic synthesis for cyclizations and acylations ; an alternative is Eaton's reagent . [ 1 ] [ 2 ] [ 3 ]
Metaphosphoric acid ( HPO 3 ) is a colorless, vitreous, deliquescent solid, density 2.2 to 2.5 g/cc, which sublimes upon heating. It is soluble in ethanol. [ 4 ]
Phosphoric acid units can be bonded together in rings (cyclic structures). The simplest such compound is trimetaphosphoric acid or cyclo-triphosphoric acid having the formula H 3 P 3 O 9 . Its structure is shown in the illustration. Since the ends are condensed, its formula has one less H 2 O (water) than tripolyphosphoric acid.
The general formula of a phosphoric acid is H n −2 x +2 P n O 3 n − x +1 , where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure; that is, the minimum number of bonds that would have to be broken to eliminate all cycles.
The limiting case of internal condensation, where all oxygen atoms are shared and there are no hydrogen atoms ( x = n +2 / 2 ) is an anhydride P 2 n O 5 n , phosphorus pentoxide P 4 O 10 .
Removal of the hydrogen atoms as protons H + turns a phosphoric acid into a phosphate anion. Partial removal yields various hydrogen phosphate anions.
The anions of orthophosphoric acid H 3 PO 4 are orthophosphate (commonly called simply "phosphate") PO 3− 4 , monohydrogen phosphate HPO 2− 4 , and dihydrogen phosphate H 2 PO − 4 .
Dissociation of pyrophosphoric acid H 4 P 2 O 7 generates four anions, [H 4− k P 2 O 7 ] k − , where the charge k ranges from 1 to 4. The last one is pyrophosphate [P 2 O 7 ] 4− . The pyrophosphates are mostly water-soluble.
Likewise, tripolyphosphoric acid H 5 P 3 O 10 yields at least five anions [H 5− k P 3 O 10 ] k − , where k ranges from 1 to 5, including tripolyphosphate [P 3 O 10 ] 5− . Tetrapolyphosphoric acid H 6 P 4 O 13 yields at least six anions, including tetrapolyphosphate [P 4 O 13 ] 6− , and so on. Note that each extra phosphoric unit adds one extra P atom, three extra O atoms, and either one extra hydrogen atom or an extra negative charge.
Branched polyphosphoric acids give similarly branched polyphosphate anions. The simplest example of this is triphosphono phosphate [OP(OPO 3 ) 3 ] 9− and its partially dissociated versions.
The general formula for such (non-cyclic) polyphosphate anions, linear or branched, is [H n +2− k P n O 3 n +1 ] k − , where the charge k may vary from 1 to n + 2 . Generally in an aqueous solution, the degree or percentage of dissociation depends on the pH of the solution.
Salts or esters of cyclic polyphosphoric acids are often called "metaphosphates". What are commonly called trimetaphosphates actually have a mixture of ring sizes. A general formula for such cyclic compounds is [HPO 3 ] x where x = number of phosphoric units in the molecule.
When metaphosphoric acids lose their hydrogens as H + , cyclic anions called metaphosphates are formed. An example of a compound with such an anion is sodium hexametaphosphate ( Na 6 P 6 O 18 ), used as a sequestrant and a food additive .
These phosphoric acids series are generally water - soluble considering the polarity of the molecules. Ammonium and alkali phosphates are also quite soluble in water. The alkaline earth salts start becoming less soluble and phosphate salts of various other metals are even less soluble.
In aqueous solutions (solutions of water), water gradually (over the course of hours) hydrolyzes polyphosphates into smaller phosphates and finally into ortho-phosphate, given enough water. Higher temperature or acidic conditions can speed up the hydrolysis reactions considerably. [ 5 ]
Conversely, polyphosphoric acids or polyphosphates are often formed by dehydrating a phosphoric acid solution; in other words, removing water from it often by heating and evaporating the water off.
Ortho-, pyro-, and tripolyphosphate compounds, such as sodium tripolyphosphate , have been commonly used in detergents (i. e. cleaners) formulations. Sometimes pyrophosphate, tripolyphosphate, tetrapolyphosphate, etc. are called diphosphate , triphosphate , tetraphosphate , etc., especially when they are part of phosphate esters in biochemistry . They are also used for scale and corrosion control by potable water providers . [ 6 ] As a corrosion inhibitor, polyphosphates work by forming a protective film on the interior surface of pipes. [ 7 ]
The −OH groups in phosphoric acids can also condense with the hydroxyl groups of alcohols to form phosphate esters . Since orthophosphoric acid has three −OH groups, it can esterify with one, two, or three alcohol molecules to form a mono-, di-, or triester. See the general structure image of an ortho- (or mono-) phosphate ester below on the left, where any of the R groups can be a hydrogen or an organic radical . Di- and tripoly- (or tri-) phosphate esters, etc. are also possible. Any −OH groups on the phosphates in these ester molecules may lose H + ions to form anions, again depending on the pH in a solution. In the biochemistry of living organisms, there are many kinds of (mono)phosphate, diphosphate, and triphosphate compounds (essentially esters ), many of which play a significant role in metabolism such as adenosine diphosphate (ADP) and triphosphate (ATP) . | https://en.wikipedia.org/wiki/Phosphoric_acids_and_phosphates |
Phosphoric monoester hydrolases (or phosphomonoesterases ) are enzymes that catalyse the hydrolysis of O-P bonds by nucleophilic attack of phosphorus by cysteine residues or coordinated metal ions.
They are categorized with the EC number 3.1.3.
Examples include:
This enzyme -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphoric_monoester_hydrolases |
In chemistry , a phosphorochloridate is a class of organophosphorus compounds with the formula (RO) 2 P(O)Cl (R = organic substituent). They are tetrahedral in shape, akin to regular phosphates (OP(OR) 3 ). They are usually colorless and sensitive toward hydrolysis. They are oxidized derivatives of phosphorochloridites , which have the formula (RO) 2 PCl. A popular example is diethyl phosphorochloridate .
Phosphochloridites are precursors to phosphate esters : [ 1 ]
Other nucleophiles have been employed, such as azide. [ 2 ] | https://en.wikipedia.org/wiki/Phosphorochloridate |
In chemistry , phosphorochloridites are a class of organophosphorus compound with the formula (RO) 2 PCl (R = organic substituent). They are pyramidal in shape, akin to regular phosphites (P(OR) 3 ). They are usually colorless and sensitive toward hydrolysis and, to some extent, oxidation to the corresponding phosphorochloridates ((RO) 2 P(O)Cl).
Phosphorochloridites are produced by partial alcoholysis of phosphorus trichloride , which proceeds stepwise: [ 1 ]
These reactions are readily controlled with aromatic diols , such as binaphthol and 2,2'-biphenol.
Phosphorochloridites are precursors to diphosphite ligands . When combined with rhodium precursors such as Rh(acac)(CO) 2 , these diphosphite ligands afford catalysts that are used industrially for the hydroformylation of alkenes. [ 2 ] it and related ligands have become popular in hydroformylation catalysis. [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Phosphorochloridite |
Phosphorolysis is the cleavage of a compound in which inorganic phosphate is the attacking group. It is analogous to hydrolysis . [ 1 ]
An example of this is glycogen breakdown by glycogen phosphorylase, which catalyzes attack by inorganic phosphate on the terminal glycosyl residue at the nonreducing end of a glycogen molecule. If the glycogen chain has n glucose units, the products of a single phosphorolytic event are one molecule of glucose 1-phosphate and a glycogen chain of n -1 remaining glucose units.
In addition, sometimes phosphorolysis is preferable to hydrolysis (like in the breakdown of glycogen or starch , as in the example above) because glucose 1-phosphate yields more ATP than does free glucose when subsequently catabolized to pyruvate .
Another example of phosphorolysis is seen in the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate in glycolysis. The mechanism involves phosphorolysis.
This chemical process -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphorolysis |
A phosphoroscope is piece of experimental equipment devised in 1857 by physicist A. E. Becquerel to measure how long it takes a phosphorescent material to stop glowing after it has been excited . [ 1 ]
It consists of two rotating disks with holes in them. The holes are arranged on each disk at equal angular intervals and a constant distance from the centre, but the holes in one disk do not align with the holes in the other. A sample of phosphorescent material is placed in between the two disks. Light coming in through a hole in one of the discs excites the phosphorescent material which then emits light for a short amount of time. The disks are then rotated and by changing their speed, the length of time the material glows can be determined.
This atomic, molecular, and optical physics –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphoroscope |
Phosphotothioate-based ligase-independent cloning [ 1 ] is a cloning method that uses the Phosphotothioate chemistry as a new universal cloning starting with the target's gene and vector's amplification with PCR. It is also commonly known as the PLICing method and it consists of three main steps: amplification, cleavage and hybridization. This method is important because it is a sequence-independent method to clone DNA fragments in an easier way than the traditional way which requires the use of restriction enzymes for DNA ligase, and it is also a really high efficient method. [ 2 ]
Primers and complementary phosphothioated nucleotides are used. It requires a recombination in order of short stretch of four amino acids among proteins. In the amplification step, the vector and the target gene are amplified by PCR with primers that have a complementary phosphothioated nucleotides in the 5' end. Then, the products of the PCR are cleaved in an iodine/ethanol solution and they produce single-stranded overhangs. Finally the ends hybridize at room temperature and the transformation into competent host cells happens with the resulting DNA.
This cloning procedure is also known for being simple since it only requires one single type of enzymatic reaction. [ 3 ] The reaction is required before transformation and it results in a high cloning efficiency, with the elimination of the nonrecombinant clones. It was also found and proven that the minimal length to have an efficient LIC is the 12-nucleotide ss tails. The 12-nucleotide products showed that it was cloned 5-10 times more efficiently compared to other ones with less nucleotides. The efficiency of the LIC is dependent on the length of the cohesive ends and the procedures used to purify the inserts. In another study, [ 4 ] it was also found that by having the 12-nucleotide, it permitted the formation of stable duplexes containing cohesive tails and it also eliminated the ligation step. Along with the cloning process being more efficient the process takes significant less time and no further steps need to be taken to get the final product. [ 1 ]
In the traditional way, there was not enzymatic activities after DNA was amplified/purified, but with this new cloning method, enzymatic activities are present which helps generating the libraries. Also, in the past it DNA cloning was known to be a really slow step, something that changed completed after the Phosphotothioate-based ligase-independent cloning method was created thanks to the appearance of enzyme/ligase-free type of method.
Thanks to this method, several industries were able to utilize the effectivity and efficiency of it to create and produce for example plant natural products. [ 5 ] By being able to do a DNA sequencing in a faster way and by using those biosynthetic pathways, plant natural products are able to be produced by specific compounds produced by those pathways.
In the medical area, it was found that the ligase-independent cloning can potentially be used to help with screening applications, [ 6 ] as well as the rapid generation of viruses like Influenza for research and the development of vaccines. [ 7 ] Studies have shown that this form of cloning also has led to further the study of protein function. [ 8 ]
This method has a lot of advantages since it is an enzyme-free method that only requires a short stretch of four amino acids in order to define and get a single crossover point. [ 2 ] It is easier and cheaper since only four amino acids are used along with the reagents PLICing, making it twelve times cheaper compared to standard restriction cloning. [ 1 ]
Standard cloning techniques often require long incubation and long processes. Ligation independent cloning (LIC) which was developed in the 1990's [ 9 ] was used to help resolve some of these issues. The majority of these LIC techniques still had their own restrictions. In 2010, a group of scientists: Milan Blanusa,Alexander Schenk, hengameh Sadeghi, Jan Marienhagen, and Ulrich Schwaneburg who were associated with Jacobs University Bremen in Germany worked to develop a process that was both an enzyme-free and sequence-independent known as Phosphorothioate-based ligase-independent gene cloning, or PLICing for short. [ 1 ] | https://en.wikipedia.org/wiki/Phosphorothioate-based_ligase-independent_cloning |
Phosphorus-31 NMR spectroscopy is an analytical chemistry technique that uses nuclear magnetic resonance (NMR) to study chemical compounds that contain phosphorus . Phosphorus is commonly found in organic compounds and coordination complexes (as phosphines ), making it useful to measure 31 - NMR spectra routinely. Solution 31 P-NMR is one of the more routine NMR techniques because 31 P has an isotopic abundance of 100% and a relatively high gyromagnetic ratio . The 31 P nucleus also has a spin of 1 / 2 , making spectra relatively easy to interpret. The only other highly sensitive NMR-active nuclei spin 1 / 2 that are monoisotopic (or nearly so) are 1 H and 19 F. [ 1 ] [ a ]
With a gyromagnetic ratio 40.5% of that for 1 H, 31 P-NMR signals are observed near 202 MHz on an 11.7- Tesla magnet (used for 500 MHz 1 H-NMR measurements). Chemical shifts are typically referenced to 85% phosphoric acid , which is assigned the chemical shift of 0, and appear at positive values (downfield of the standard). [ 2 ] Due to the inconsistent nuclear Overhauser effect , integrations are not useful. [ 2 ] Most often, spectra are recorded with protons decoupled .
31 P-NMR spectroscopy is useful to assay purity and to assign structures of phosphorus-containing compounds because these signals are well resolved and often occur at characteristic frequencies. Chemical shifts and coupling constants span a large range but sometimes are not readily predictable. The Gutmann-Beckett method uses Et 3 PO in conjunction with 31 P-NMR spectroscopy to assess the Lewis acidity of molecular species.
The ordinary range of chemical shifts ranges from about δ250 to −δ250, which is much wider than typical for 1 H-NMR. Unlike 1 H-NMR spectroscopy, but similar to most other nuclei, 31 P-NMR shifts are primarily not determined by the magnitude of the diamagnetic shielding, but are dominated by the so-called paramagnetic shielding tensor (unrelated to paramagnetism ). The paramagnetic shielding tensor, σ p , includes terms that describe the radial expansion (related to charge), energies of excited states , and bond overlap. Illustrative of the effects lead to big changes in chemical shifts, the chemical shifts of the two phosphate esters (MeO) 3 PO (δ2.1) and (t-BuO) 3 PO (δ-13.3). More dramatic are the shifts for phosphine derivatives H 3 P (δ-240), (CH 3 ) 3 P (δ-62), (i-Pr) 3 P (δ20), and (t-Bu) 3 P (δ61.9). [ 3 ]
One-bond coupling is illustrated by PH 3 where J(P,H) is 189 Hz. Two-bond couplings, e.g. P C H are an order of magnitude smaller. The situation for phosphorus-carbon couplings are more complicated since the two-bond couplings are often larger than one-bond couplings. The J( 13 C, 31 P) values for triphenylphosphine are respectively −12.5, 19.6, 6.8, and 0.3 for one-, two-, three-, and four-bond couplings. [ 4 ]
The convention surrounding 31 P-NMR (and other nuclei) changed convention in 1975: "The dimensionless scale should be defined as positive in the high frequency (low field) direction." [ 5 ] Therefore, note that manuscripts published before 1976 will generally have the opposite sign.
31 P-NMR spectroscopy is widely used for studies of phospholipid bilayers and biological membranes in native conditions. The analysis [ 6 ] of 31 P-NMR spectra of lipids could provide a wide range of information about lipid bilayer packing, phase transitions (gel phase, physiological liquid crystal phase, ripple phases, non bilayer phases), lipid head group orientation/dynamics, and elastic properties of pure lipid bilayer and as a result of binding of proteins and other biomolecules.
In addition, a specific N-H...(O)-P experiment (INEPT transfer using three-bond scalar coupling 3 J N-P ~5 Hz) could provide a direct information about formation of hydrogen bonds between amine protons of protein to phosphate of lipid headgroups, which is useful in studies of protein/membrane interactions. | https://en.wikipedia.org/wiki/Phosphorus-31_nuclear_magnetic_resonance |
The phosphorus cycle is the biogeochemical cycle that involves the movement of phosphorus through the lithosphere , hydrosphere , and biosphere . Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and phosphorus-based materials do not enter the gaseous phase readily, [ 1 ] as the main source of gaseous phosphorus, phosphine , is only produced in isolated and specific conditions. [ 2 ] Therefore, the phosphorus cycle is primarily examined studying the movement of orthophosphate ( PO 3− 4 ), the form of phosphorus that is most commonly seen in the environment, through terrestrial and aquatic ecosystems. [ 3 ]
Living organisms require phosphorus, a vital component of DNA , RNA , ATP , etc., for their proper functioning. [ 4 ] Phosphorus also enters in the composition of phospholipids present in cell membranes . Plants assimilate phosphorus as phosphate and incorporate it into organic compounds . In animals , inorganic phosphorus in the form of apatite ( Ca 5 (PO 4 ) 3 (OH,F) ) is also a key component of bones , teeth ( tooth enamel ), etc. [ 5 ] On the land, phosphorus gradually becomes less available to plants over thousands of years, since it is slowly lost in runoff . Low concentration of phosphorus in soils reduces plant growth and slows soil microbial growth, as shown in studies of soil microbial biomass . Soil microorganisms act as both sinks and sources of available phosphorus in the biogeochemical cycle. Short-term transformation of phosphorus is chemical, biological, or microbiological. In the long-term global cycle, however, the major transfer is driven by tectonic movement over geologic time and weathering of phosphate containing rock such as apatite . [ 6 ] Furthermore, phosphorus tends to be a limiting nutrient in aquatic ecosystems . [ 7 ] However, as phosphorus enters aquatic ecosystems, it has the possibility to lead to over-production in the form of eutrophication , which can happen in both freshwater and saltwater environments. [ 8 ] [ 9 ] [ 10 ]
Human activities have caused major changes to the global phosphorus cycle primarily through the mining and subsequent transformation of phosphorus minerals for use in fertilizer and industrial products. Some phosphorus is also lost as effluent through the mining and industrial processes as well.
Phosphorus is an essential nutrient for plants and animals. Phosphorus is a limiting nutrient for aquatic organisms. Phosphorus forms parts of important life-sustaining molecules that are very common in the biosphere. Phosphorus does enter the atmosphere in very small amounts when dust containing phosphorus is dissolved in rainwater and sea spray, but the element mainly remains on land and in rock and soil minerals. Phosphates which are found in fertilizers, sewage and detergents, can cause pollution in lakes and streams. Over-enrichment of phosphate in both fresh and inshore marine waters can lead to massive algae blooms . In fresh water, the death and decay of these blooms leads to eutrophication . An example of this is the Canadian Experimental Lakes Area.
Freshwater algal blooms are generally caused by excess phosphorus, while those that take place in saltwater tend to occur when excess nitrogen is added. [ 11 ] However, it is possible for eutrophication to be due to a spike in phosphorus content in both freshwater and saltwater environments. [ 11 ] [ 12 ] [ 10 ]
Phosphorus occurs most abundantly in nature as part of the orthophosphate ion (PO 4 ) 3− , consisting of a P atom and 4 oxygen atoms. On land most phosphorus is found in rocks and minerals. Phosphorus-rich deposits have generally formed in the ocean or from guano, and over time, geologic processes bring ocean sediments to land. Weathering of rocks and minerals release phosphorus in a soluble form where it is taken up by plants, and it is transformed into organic compounds. The plants may then be consumed by herbivores and the phosphorus is either incorporated into their tissues or excreted. After death, the animal or plant decays, and phosphorus is returned to the soil where a large part of the phosphorus is transformed into insoluble compounds. Runoff may carry a small part of the phosphorus back to the ocean . Generally with time (thousands of years) soils become deficient in phosphorus leading to ecosystem retrogression. [ 13 ]
There are four major pools of phosphorus in freshwater ecosystems: dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), particulate inorganic phosphorus (PIP) and particulate organic phosphorus (POP). Dissolved material is defined as substances that pass through a 0.45 μm filter . [ 14 ] DIP consists mainly of orthophosphate ( PO 3− 4 ) and polyphosphate, while DOP consists of DNA and phosphoproteins . Particulate matter are the substances that get caught on a 0.45 μm filter and do not pass through. POP consists of both living and dead organisms, while PIP mainly consists of hydroxyapatite , Ca 5 (PO 4 ) 3 OH . [ 14 ] Inorganic phosphorus comes in the form of readily soluble orthophosphate . Particulate organic phosphorus occurs in suspension in living and dead protoplasm and is insoluble. Dissolved organic phosphorus is derived from the particulate organic phosphorus by excretion and decomposition and is soluble.
The primary biological importance of phosphates is as a component of nucleotides , which
serve as energy storage within cells ( ATP ) or when linked together, form the nucleic acids DNA and RNA . The double helix of our DNA is only possible because of the phosphate ester bridge that binds the helix. Besides making biomolecules, phosphorus is also found in bone and the enamel of mammalian teeth, whose strength is derived from calcium phosphate in the form of hydroxyapatite . It is also found in the exoskeleton of insects, and phospholipids (found in all biological membranes ). [ 15 ] It also functions as a buffering agent in maintaining acid base homeostasis in the human body. [ 16 ]
Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles. [ 17 ] [ 18 ]
The global phosphorus cycle includes four major processes:
In terrestrial systems, bioavailable P (‘reactive P’) mainly comes from weathering of phosphorus-containing rocks. The most abundant primary phosphorus-mineral in the crust is apatite , which can be dissolved by natural acids generated by soil microbes and fungi, or by other chemical weathering reactions and physical erosion. [ 22 ] The dissolved phosphorus is bioavailable to terrestrial organisms and plants and is returned to the soil after their decay. Phosphorus retention by soil minerals (e.g., adsorption onto iron and aluminum oxyhydroxides in acidic soils and precipitation onto calcite in neutral-to-calcareous soils) is usually viewed as the most important process in controlling terrestrial P-bioavailability in the mineral soil. [ 23 ] This process can lead to the low level of dissolved phosphorus concentrations in soil solution. Various physiological strategies are used by plants and microorganisms for obtaining phosphorus from this low level of phosphorus concentration. [ 24 ]
Soil phosphorus is usually transported to rivers and lakes and can then either be buried in lake sediments or transported to the ocean via river runoff. Atmospheric phosphorus deposition is another important marine phosphorus source to the ocean. [ 25 ] In surface seawater, dissolved inorganic phosphorus, mainly orthophosphate ( PO 3− 4 ), is assimilated by phytoplankton and transformed into organic phosphorus compounds. [ 21 ] [ 25 ] Phytoplankton cell lysis releases cellular dissolved inorganic and organic phosphorus to the surrounding environment. Some of the organic phosphorus compounds can be hydrolyzed by enzymes synthesized by bacteria and phytoplankton and subsequently assimilated. [ 25 ] The vast majority of phosphorus is remineralized within the water column, and approximately 1% of associated phosphorus carried to the deep sea by the falling particles is removed from the ocean reservoir by burial in sediments. [ 25 ] A series of diagenetic processes act to enrich sediment pore water phosphorus concentrations, resulting in an appreciable benthic return flux of phosphorus to overlying bottom waters. These processes include
Additionally,
These processes are similar to phosphorus cycling in lakes and rivers.
Although orthophosphate ( PO 3− 4 ), the dominant inorganic P species in nature, is oxidation state +5, certain microorganisms can use phosphonate and phosphite ( +3oxidation state) as a P source by oxidizing it to orthophosphate. [ 29 ] Recently, rapid production and release of reduced phosphorus compounds has provided new clues about the role of reduced P as a missing link in oceanic phosphorus. [ 30 ]
The availability of phosphorus in an ecosystem is restricted by its rate of release during weathering. The release of phosphorus from apatite dissolution is a key control on ecosystem productivity. [ 31 ] The primary mineral with significant phosphorus content, apatite [Ca 5 (PO 4 ) 3 OH] undergoes carbonation . [ 17 ] [ 32 ]
Little of this released phosphorus is taken up by biota, as it mainly reacts with other soil minerals. This leads to phosphorus becoming unavailable to organisms in the later stage of weathering and soil development as it will precipitate into rocks. Available phosphorus is found in a biogeochemical cycle in the upper soil profile, while phosphorus found at lower depths is primarily involved in geochemical reactions with secondary minerals. Plant growth depends on the rapid root uptake of phosphorus released from dead organic matter in the biochemical cycle. Phosphorus is limited in supply for plant growth. Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles. [ 17 ] [ 18 ]
Low-molecular-weight (LMW) organic acids are found in soils. They originate from the activities of various microorganisms in soils or may be exuded from the roots of living plants. Several of those organic acids are capable of forming stable organo-metal complexes with various metal ions found in soil solutions. As a result, these processes may lead to the release of inorganic phosphorus associated with aluminum, iron, and calcium in soil minerals. The production and release of oxalic acid by mycorrhizal fungi explain their importance in maintaining and supplying phosphorus to plants. [ 17 ] [ 33 ]
The availability of organic phosphorus to support microbial, plant and animal growth depends on the rate of their degradation to generate free phosphate. There are various enzymes such as phosphatases , nucleases and phytase involved for the degradation. Some of the abiotic pathways in the environment studied are hydrolytic reactions and photolytic reactions. Enzymatic hydrolysis of organic phosphorus is an essential step in the biogeochemical phosphorus cycle, including the phosphorus nutrition of plants and microorganisms and the transfer of organic phosphorus from soil to bodies of water. [ 34 ] Many organisms rely on the soil derived phosphorus for their phosphorus nutrition. [ 35 ]
P deposition is quite important for ecosystem function, and is unevenly distributed across the planet. [ 36 ] Although phosphorus does not have a major atmospheric component, phosphorus sediments can be moved during dust storms. Large dust events can counteract natural imbalances where P occurs and allow for production in areas that would otherwise be P-limited. [ 37 ] This component of the phosphorus cycle has generally been overlooked by researchers, but its importance is starting to be understood. [ 36 ] Most of Earth's phosphorus is in rocks, and dust contains weathered rock particles from this parent material. [ 38 ] Dust also carries other nutrients such as potassium, calcium, and magnesium, making these storms of high importance to biogeochemical cycling. [ 39 ]
The source of most large-scale dust storms are arid climates, including the Sahara Desert. [ 36 ] Phosphorus carried in by wind from Northern Africa to the Amazon basin is thought to played a significant role supporting the rich biodiversity of the Amazon rainforest. [ 36 ]
These events are called dust-loading. [ 40 ] Smaller scale dust-loading events have been found to occur in midwestern US, where erosion of agricultural land provides ideal conditions for dust storms. [ 40 ] As the frequency of these dust storms increases, the amount of P left in the actual agricultural plots declines, leading to an increase of P fertilizer application. Retention of plant-available P becomes more difficult as erosion increases. [ 41 ]
Eutrophication is when waters are enriched by nutrients that lead to structural changes to the aquatic ecosystem such as algae bloom, deoxygenation, reduction of fish species. It does occur naturally, as when lakes age they become more productive due to increases in major limiting reagents such as nitrogen and phosphorus. [ 42 ] For example, phosphorus can enter into lakes where it will accumulate in the sediments and the biosphere. It can also be recycled from the sediments and the water system allowing it to stay in the environment. [ 43 ] Anthropogenic effects can also cause phosphorus to flow into aquatic ecosystems as seen in drainage water and runoff from fertilized soils on agricultural land. [ 44 ] Additionally, eroded soils, which can be caused by deforestation and urbanization, can lead to more phosphorus and nitrogen being added to these aquatic ecosystems. [ 45 ] These all increase the amount of phosphorus that enters the cycle which has led to excessive nutrient intake in freshwater systems causing dramatic growth in algal populations. When these algae die, their putrefaction depletes the water of oxygen and can toxify the waters. Both these effects cause plant and animal death rates to increase as the plants take in and animals drink the poisonous water. [ 46 ]
Oceanic ecosystems gather phosphorus through many sources, but it is mainly derived from weathering of rocks containing phosphorus which are then transported to the oceans in a dissolved form by river runoff. [ 47 ] Due to a dramatic rise in mining for phosphorus, it is estimated that humans have increased the net storage of phosphorus in soil and ocean systems by 75%. [ 48 ] This increase in phosphorus has led to more eutrophication in ocean waters as phytoplankton blooms have caused a drastic shift in anoxic conditions seen in both the Gulf of Mexico [ 49 ] and the Baltic Sea . [ 50 ] Some research suggests that when anoxic conditions arise from eutrophication due to excess phosphorus, this creates a positive feedback loop that releases more phosphorus from oceanic reserves, exacerbating the issue. [ 51 ] This could possibly create a self-sustaining cycle of oceanic anoxia where the constant recovery of phosphorus keeps stabilizing the eutrophic growth. [ 51 ] Attempts to mitigate this problem using biological approaches are being investigated. One such approach involves using phosphorus accumulating organisms such as, Candidatus accumulibacter phosphatis , which are capable of effectively storing phosphorus in the form of phosphate in marine ecosystems. [ 52 ] Essentially, this would alter how the phosphorus cycle exists currently in marine ecosystems. Currently, there has been a major influx of phosphorus due to increased agricultural use and other industrial applications, [ 51 ] thus these organisms could theoretically store phosphorus and hold on to it until it could be recycled in terrestrial ecosystems which would have lost this excess phosphorus due to runoff. [ 52 ]
Wetlands are frequently applied to solve the issue of eutrophication. Nitrate is transformed in wetlands to free nitrogen and discharged to the air. Phosphorus is adsorbed by wetland soils which are taken up by the plants. Therefore, wetlands could help to reduce the concentration of nitrogen and phosphorus to remit eutrophication. However, wetland soils can only hold a limited amount of phosphorus. To remove phosphorus continually, it is necessary to add more new soils within the wetland from remnant plant stems, leaves, root debris, and undecomposable parts of dead algae, bacteria, fungi, and invertebrates. [ 44 ]
Both N and P are widely used in agricultural fertilizers, as they are essential nutrients for plants. Human activity has resulted in an imbalance of normal N:P ratios, impacting the speed at which organisms synthesize proteins and DNA. In the last 40 years, the N:P ratio has increased from 19:1 to 30:1, meaning P is less available to ecosystems. [ 53 ] This imbalance is not only caused by more N pollution, but also because P is more likely to get trapped after water has been treated, preventing its release into ecosystems.
In an environment where neither nutrient is limited, where more P is present per N, organisms experience a faster growth rate. As this ratio increases, it is harder for organisms to grow. One example of organism response to this growing imbalance is rhizobia in legume root nodules. Research has shown that in low levels of P, the capacity for nitrogen-fixing bacteria to provide nutrients to the plant declines, negatively impacting both the host plant and its symbionts. [ 54 ] In addition, plants growing in P-limited environments will have more N content in their leaves. [ 55 ]
P and N are also unequally distributed across the globe, making certain geographical areas more favorable for crop growth than others. Disruption to these major biogeochemical cycles may exacerbate these inequities. [ 56 ]
Nutrients are important to the growth and survival of living organisms and, hence, are essential for developing and maintaining healthy ecosystems. Humans have greatly influenced the phosphorus cycle by mining phosphate rock. For millennia, phosphorus was primarily brought into the environment by weathering phosphate-containing rocks, which would replenish the phosphorus normally lost to the environment through processes such as runoff, albeit on a very slow and gradual time scale. [ 57 ] Since the 1840s, when the technology to mine and extract phosphorus became more prevalent, approximately 110 teragrams of phosphorus has been added to the environment. [ 58 ] This trend appears to be continuing in the future as from 1900-2022, the amount of phosphorus mined globally has increased 72-fold, [ 59 ] with an expected annual increase of 4%. [ 58 ] Most of this mining is done to produce fertilizers which can be used on a global scale. However, at the rate humans are mining, the geological system can not quickly restore what is lost. [ 60 ] Thus, researchers are examining ways to better recycle phosphorus in the environment, with one promising application including the use of microorganisms. [ 52 ] [ 61 ] Regardless, humans have had a profound impact on the phosphorus cycle with wide-reaching implications about food security , eutrophication , and the overall availability of the nutrient. [ 62 ]
Other human processes can have detrimental effects on the phosphorus cycle, such as the repeated application of liquid hog manure in excess to crops. Applying biosolids may also increase available phosphorus in soil. [ 63 ] In poorly drained soils or in areas where snowmelt can cause periodic waterlogging, reducing conditions can be attained in 7–10 days. This causes a sharp increase in phosphorus concentration in solution, and phosphorus can be leached. In addition, reducing the soil causes a shift in phosphorus from resilient to more labile forms. This could eventually increase the potential for phosphorus loss. This is of particular concern for the environmentally sound management of such areas, where disposal of agricultural wastes has already become a problem. It is suggested that soil water regimes used for organic waste disposal be considered when preparing waste management regulations. [ 64 ] | https://en.wikipedia.org/wiki/Phosphorus_cycle |
Phosphorus dioxide ( PO 2 ) is a gaseous oxide of phosphorus . It is a free radical that plays a role in the chemiluminescence of phosphorus and phosphine . [ 1 ] It is produced when phosphates are heated to high temperatures. [ 2 ]
In the ground state the molecule is bent, like nitrogen dioxide , but there is an excited state that is linear. [ 1 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphorus_dioxide |
Phosphorus monoxide is an unstable radical inorganic compound with molecular formula P O . [ 2 ]
Phosphorus monoxide is notable as one of the few molecular compounds containing phosphorus that has been detected outside of Earth. Other phosphorus containing molecules found in space include PN , PC , PC 2 , HCP and PH 3 . It was detected in the circumstellar shell of VY Canis Majoris and in the star forming region catalogued as AFGL 5142 . The compound has been found to have been initially produced in star-forming regions , and speculated to be carried by interstellar comets throughout outer space , including to the early Earth . [ 2 ] [ 3 ] [ 4 ]
Phosphorus monoxide plays a role in the phosphorescence of phosphorus.
In 1894 W. N. Hartley was the first to report an observation of ultraviolet emission from a phosphorus compound, that was later expanded on by Geuter. The source of the spectral lines and bands were known to be related to phosphorus, but the exact nature was unknown. In 1927 H. J. Emeléus and R. H. Purcell determined that the cause was a phosphorus oxide. But it was in 1921 that P. N. Ghosh and G. N. Ball determined that the oxide was phosphorus monoxide. [ 5 ]
Phosphorus monoxide is believed to be the most abundant phosphorus-containing molecule found in interstellar clouds . [ 6 ] Phosphorus was identified as a cosmically abundant element in 1998 after researchers found a cosmic ratio of phosphorus to hydrogen (P/H) of about 3×10 −7 . Even with the prevalence of phosphorus in interstellar clouds, very few phosphorus bearing molecules had been identified and found in very few sources; phosphorus nitride, PN, and the free radical CP were found in a carbon rich envelope of IRC +10215 in 1987. This suggested that more phosphorus containing molecules had to be found in interstellar space. While examining the oxygen-rich shell of the supergiant star VY Canis Majoris (VY CMa) the presence of PO was detected. VY CMa was studied using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). The telescope was able to observe the rotational frequencies of PO. ARO's 10 m SMT was able to measure the rotational transitions of PO showing J=5.5→4.5 at 240 GHz and J=6.5→5.5 at 284 GHz toward the evolved star, each consisting of well-defined lambda-doublets. Since the detection of PO towards the envelope of the VY CMa supergiant in 2001, PO has been found in many more interstellar clouds and is found in abundance around oxygen-rich shells. [ 7 ]
PO is formed when phosphorus is burnt in oxygen or ozone. It is a transient molecule observed in hot flames, or can be condensed into noble gas matrix. [ 8 ] PO can be formed in an inert gas matrix in the photolysis of P 4 S 3 O, a phosphorus oxysulfide . [ 9 ]
On Earth, phosphorus monoxide can be prepared for study by spraying phosphoric acid into a flame. Because commercial acetylene gas contains some phosphine , an oxy-acetylene flame will have weak PO emission bands in its spectrum also. In the flame, PO oxidises back to P 4 O 10 . [ 10 ]
As white phosphorus oxidises it gives out a greenish-white glow. The glow happens as PO is oxidised by one of these reactions: PO + O • → PO 2 ; or PO + O 2 →PO 2 + O • . [ 11 ] The possible ways that PO appears in this process is by breakup of the P 2 O molecule which in turn may come from P 4 O. [ 12 ]
Phosphorus monoxide can act as a ligand on transition elements such as molybdenum , ruthenium and osmium . The phosphorus forms a triple bond with the metal. [ 13 ] [ 14 ] The first to be discovered was on a nickel - tungsten cluster. The WNi 2 P 2 cluster was oxidised by a peroxide to yield a μ 3 -coordination, where each phosphorus atom is bound to three metal atoms. [ 15 ]
Phosphorus monoxide is a free radical with phosphorus double bonded to oxygen with phosphorus having an unpaired valence electron . The bond order is about 1.8. [ 5 ] The P=O bond in PO has a dissociation energy of 6.4 eV. [ 16 ] The bond length of the PO double bond is 1.476 Å, and free PO shows an infrared vibrational frequency of 1220 cm −1 due to the stretching of the bond. [ 17 ] The free radical nature of PO makes it highly reactive and unstable compared to other phosphorus oxides that have been further oxidized.
The visible to ultraviolet spectrum of phosphorus monoxide has three important bands. There is a continuum band near 540 nm. The β-system near 324 nm is due to the D 2 Σ→ 2 Π transition. The γ-system has bands near 246 nm due to a A 2 Σ→ 2 Π transition. Peaks in this band occur at 230, 238, 246, 253, and 260 nm in the ultraviolet. All these bands can be emission, absorption, or fluorescence depending on the method of illumination and temperature. [ 10 ] There is also a C' 2 Δ state. [ 18 ]
The γ-system band can be broken down into sub-bands based on the different vibrational transitions. (0,0), (0,1) and (1,0) are designations for the sub-bands produced by the transition between two vibration states, as the electronic transition occurs. Each of these contains eight series termed branches. These are o P 12 , P 2 , Q 2 , R 2 , P 1 , Q 1 , R 1 and s R 21 . [ 19 ]
The ionisation potential of PO is 8.39 eV. When ionised, PO forms the cation PO + . The adiabatic electron affinity of PO is 1.09 eV. On gaining an electron the PO − ion forms. [ 5 ]
r e in the ground state is 1.4763735 Å. [ 5 ]
The dipole moment of the molecule is 1.88 D. The phosphorus atom has a slight positive charge calculated as 0.35 of the electron. [ 5 ] | https://en.wikipedia.org/wiki/Phosphorus_monoxide |
In chemistry , phosphorus oxoacid (or phosphorus acid ) is a generic name for any acid whose molecule consists of atoms of phosphorus , oxygen , and hydrogen . [ 1 ] There is a potentially infinite number of such compounds. Some of them are unstable and have not been isolated, but the derived anions and organic groups are present in stable salts and esters . The most important ones—in biology, geology, industry, and chemical research—are the phosphoric acids , whose esters and salts are the phosphates .
In general, any hydrogen atom bonded to an oxygen atom is acidic, meaning that the –OH group can lose a proton H + leaving a negatively charged – O − group and thus turning the acid into a phosphorus oxoanion . Each additional proton lost has an associated acid dissociation constant K a 1 , K a 2 K a 3 , ..., often expressed by its cologarithm (pK a 1 , pK a 2 , pK a 3 , ...). Hydrogen atoms bonded directly to phosphorus are generally not acidic.
The phosphorus oxoacids can be classified by the oxidation state(s) of the phosphorus atom(s), which may vary from +1 to +5. The oxygen atoms are usually in oxidation state −2, but may be in state −1 if the molecule includes peroxide groups .
The most important members of this group are the phosphoric acids , where each phosphorus atom bonded to four oxygen atoms, one of them through a double bond , arranged as the corners of a tetrahedron . Two or more of these PO 4 tetrahedra may be connected by shared single-bonded oxygens, forming linear or branched chains, cycles, or more complex structures. The single-bonded oxygen atoms that are not shared are completed with acidic hydrogen atoms. Their generic formula is H n − x +2 P n O 3 n − x +1 , where n is the number of phosphorus atoms and x is the number of fundamental cycles in the molecule's structure.
These acids, and their esters and salts (" phosphates ") include some of the best-known and most important compounds of phosphorus.
The simplest member of this class is:
The smallest compounds of this class with two or more phosphorus atoms are called "oligophosphoric acids", and the larger ones, with linear –P–O– backbones, are "polyphosphoric acids"; with no definite separation between the two. Some of the most important members are:
The backbone may be branched, as in:
The PO 4 tetrahedra may be connected to form closed –P–O– chains, as in:
Metaphosphoric acid is a general term for phosphoric acids with a single cycle, (–P(O)(OH)–O–) n , whose elemental formula is HPO 3 .
Another compound that may be included in this class is
Some phosphorus oxoacids have two or more P atoms in different oxidation states. One example is | https://en.wikipedia.org/wiki/Phosphorus_oxoacids |
Phosphorus pentachloride is the chemical compound with the formula PCl 5 . It is one of the most important phosphorus chlorides/oxychlorides, others being PCl 3 and POCl 3 . PCl 5 finds use as a chlorinating reagent. It is a colourless, water-sensitive solid , although commercial samples can be yellowish and contaminated with hydrogen chloride .
The structures for the phosphorus chlorides are invariably consistent with VSEPR theory . The structure of PCl 5 depends on its environment. Gaseous and molten PCl 5 is a neutral molecule with trigonal bipyramidal geometry and ( D 3h ) symmetry . The hypervalent nature of this species (as well as of [PCl 6 ] − , see below) can be explained with the inclusion of non-bonding molecular orbitals ( molecular orbital theory ) or resonance ( valence bond theory ). This trigonal bipyramidal structure persists in nonpolar solvents, such as CS 2 and CCl 4 . [ 5 ] In the solid state PCl 5 is an ionic compound called tetrachlorophosphonium hexachlorophosphate formulated [PCl 4 ] + [PCl 6 ] − . [ 6 ]
In solutions of polar solvents, PCl 5 undergoes self- ionization . [ 8 ] Dilute solutions dissociate according to the following equilibrium:
At higher concentrations, a second equilibrium becomes more prevalent:
The cation [PCl 4 ] + and the anion [PCl 6 ] − are tetrahedral and octahedral , respectively. At one time, PCl 5 in solution was thought to form a dimeric structure, P 2 Cl 10 , but this suggestion is not supported by Raman spectroscopic measurements.
AsCl 5 and SbCl 5 also adopt trigonal bipyramidal structures. The relevant bond distances are 211 pm (As−Cl eq ), 221 pm (As−Cl ax ), 227 pm (Sb−Cl eq ), and 233.3 pm (Sb−Cl ax ). [ 9 ] At low temperatures, SbCl 5 converts to the dimer, dioctahedral Sb 2 Cl 10 , structurally related to niobium pentachloride .
PCl 5 is prepared by the chlorination of PCl 3 . [ 10 ] This reaction is used to produce around 10,000 tonnes of PCl 5 per year (as of 2000). [ 6 ]
PCl 5 exists in equilibrium with PCl 3 and chlorine , and at 180 °C the degree of dissociation is about 40%. [ 6 ] Because of this equilibrium, samples of PCl 5 often contain chlorine, which imparts a greenish coloration.
In its most characteristic reaction, PCl 5 reacts upon contact with water to release hydrogen chloride and give phosphorus oxides. The first hydrolysis product is phosphorus oxychloride :
In hot water, hydrolysis proceeds completely to orthophosphoric acid :
Phosphorus pentachloride is a Lewis acid. This property underpins many of its characteristic reactions, autoionization, chlorinations, hydrolysis. A well studied adduct is PCl 5 ( pyridine ) . [ 11 ]
In synthetic chemistry, two classes of chlorination are usually of interest: oxidative chlorinations and substitutive chlorinations. Oxidative chlorinations entail the transfer of Cl 2 from the reagent to the substrate. Substitutive chlorinations entail replacement of O or OH groups with chloride. PCl 5 can be used for both processes.
Upon treatment with PCl 5 , carboxylic acids convert to the corresponding acyl chloride . [ 12 ] The following mechanism has been proposed: [ 13 ]
It also converts alcohols to alkyl chlorides . Thionyl chloride is more commonly used in the laboratory because the resultant sulfur dioxide is more easily separated from the organic products than is POCl 3 .
PCl 5 reacts with a tertiary amides, such as dimethylformamide (DMF), to give dimethylchloromethyleneammonium chloride, which is called the Vilsmeier reagent , [(CH 3 ) 2 N=CClH] + Cl − . More typically, a related salt is generated from the reaction of DMF and POCl 3 . Such reagents are useful in the preparation of derivatives of benzaldehyde by formylation and for the conversion of C−OH groups into C−Cl groups. [ 14 ]
It is especially renowned for the conversion of C=O groups to CCl 2 groups. [ 15 ] For example, benzophenone and phosphorus pentachloride react to give the diphenyldichloromethane : [ 16 ]
The electrophilic character of PCl 5 is highlighted by its reaction with styrene to give, after hydrolysis , phosphonic acid derivatives. [ 17 ]
Both PCl 3 and PCl 5 convert R 3 COH groups to the chloride R 3 CCl . The pentachloride is however a source of chlorine in many reactions. It chlorinates allylic and benzylic CH bonds. PCl 5 bears a greater resemblance to SO 2 Cl 2 , also a source of Cl 2 . For oxidative chlorinations on the laboratory scale, sulfuryl chloride is often preferred over PCl 5 since the gaseous SO 2 by-product is readily separated.
As for the reactions with organic compounds, the use of PCl 5 has been superseded by SO 2 Cl 2 . The reaction of phosphorus pentoxide and PCl 5 produces POCl 3 : [ 18 ] [ page needed ]
PCl 5 chlorinates nitrogen dioxide to form unstable nitryl chloride :
PCl 5 is a precursor for lithium hexafluorophosphate , Li[PF 6 ] . Lithium hexafluorophosphate is a commonly employed salt in electrolytes in lithium ion batteries . [ 19 ] Li[PF 6 ] is produced by the reaction of PCl 5 with lithium fluoride , with lithium chloride as a side product:
PCl 5 is a dangerous chemical as it reacts violently with water. It is also corrosive when in contact with skin. It is toxic and can be fatal when inhaled.
Phosphorus pentachloride was first prepared in 1808 by the English chemist Humphry Davy . [ 20 ] Davy's analysis of phosphorus pentachloride was inaccurate; [ 21 ] the first accurate analysis was provided in 1816 by the French chemist Pierre Louis Dulong . [ 22 ] | https://en.wikipedia.org/wiki/Phosphorus_pentachloride |
Phosphorus pentaiodide is a hypothetical inorganic compound with formula P I 5 . The existence of this compound has been claimed intermittently since the early 1900s. [ 2 ] The claim is disputed: "The pentaiodide does not exist (except perhaps as PI 3 · I 2 , but certainly not as [PI 4 ] + I − ...)". [ 3 ]
Phosphorus pentaiodide was reported to be a brown-black crystalline solid melting at 41 °C produced by the reaction of lithium iodide and phosphorus pentachloride in methyl iodide , however, this claim is disputed and probably generated a mixture of phosphorus triiodide and iodine . [ 1 ] [ 4 ]
Although phosphorus pentaiodide has been claimed to exist in the form of [PI 4 ] + I − (tetraiodophosphonium iodide), experimental and theoretical data refutes this claim. [ 5 ] [ 1 ]
Unlike the elusive PI 5 , the [PI 4 ] + cation (tetraiodophosphonium cation) is widely known. This cation is known with the anions tetraiodoaluminate [AlI 4 ] − , hexafluoroarsenate [AsF 6 ] − , hexafluoroantimonate [SbF 6 ] − and tetraiodogallate [GaI 4 ] − . [ 4 ] [ 5 ]
This inorganic compound –related article is a stub . You can help Wikipedia by expanding it .
This article about theoretical chemistry is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphorus_pentaiodide |
Phosphorus pentoxide is a chemical compound with molecular formula P 4 O 10 (with its common name derived from its empirical formula , P 2 O 5 ). This white crystalline solid is the anhydride of phosphoric acid . It is a powerful desiccant and dehydrating agent .
Phosphorus pentoxide crystallizes in at least four forms or polymorphs . The most familiar one, a metastable form [ 1 ] (shown in the figure), comprises molecules of P 4 O 10 . Weak van der Waals forces hold these molecules together in a hexagonal lattice (However, in spite of the high symmetry of the molecules, the crystal packing is not a close packing [ 2 ] ). The structure of the P 4 O 10 cage is reminiscent of adamantane with T d symmetry point group . [ 3 ] It is closely related to the corresponding anhydride of phosphorous acid , P 4 O 6 . The latter lacks terminal oxo groups. Its density is 2.30 g/cm 3 . It boils at 423 °C under atmospheric pressure; if heated more rapidly it can sublimate. This form can be made by condensing the vapor of phosphorus pentoxide rapidly, and the result is an extremely hygroscopic solid. [ 4 ]
The other polymorphs are polymeric, but in each case the phosphorus atoms are bound by a tetrahedron of oxygen atoms, one of which forms a terminal P=O bond involving the donation of the terminal oxygen p-orbital electrons to the antibonding phosphorus-oxygen single bonds. The macromolecular form can be made by heating the compound in a sealed tube for several hours, and maintaining the melt at a high temperature before cooling the melt to the solid. [ 4 ] The metastable orthorhombic "O"-form (density 2.72 g/cm 3 , melting point 562 °C) adopts a layered structure consisting of interconnected P 6 O 6 rings, not unlike the structure adopted by certain poly silicates . The stable form is a higher density phase, also orthorhombic, the so-called O' form. It consists of a 3-dimensional framework, density 3.5 g/cm 3 . [ 1 ] [ 5 ] The remaining polymorph is a glass or amorphous form; it can be made by fusing any of the others.
P 4 O 10 is prepared by burning white phosphorus with a sufficient supply of oxygen: [ 6 ]
The dehydration of phosphoric acid to give phosphorus pentoxide is not possible, as on heating it forms various polyphosphates but will not dehydrate sufficiently to form P 4 O 10 .
Phosphorus pentoxide is a potent dehydrating agent as indicated by the exothermic nature of its hydrolysis producing phosphoric acid :
However, its utility for drying is limited somewhat by its tendency to form a protective viscous coating that inhibits further dehydration by unspent material. A granular form of P 4 O 10 is used in desiccators .
Consistent with its strong desiccating power, P 4 O 10 is used in organic synthesis for dehydration. The most important application is for the conversion of primary amides into nitriles : [ 7 ]
The indicated coproduct P 4 O 9 (OH) 2 is an idealized formula for undefined products resulting from the hydration of P 4 O 10 .
Alternatively, when combined with a carboxylic acid , the result is the corresponding anhydride : [ 8 ]
The "Onodera reagent", a solution of P 4 O 10 in DMSO , is employed for the oxidation of alcohols . [ 9 ] This reaction is reminiscent of the Swern oxidation .
The desiccating power of P 4 O 10 is strong enough to convert many mineral acids to their anhydrides. Examples: HNO 3 is converted to N 2 O 5 ; H 2 SO 4 is converted to SO 3 ; HClO 4 is converted to Cl 2 O 7 ; CF 3 SO 3 H is converted to (CF 3 ) 2 S 2 O 5 .
P 2 O 5 content is often used by industry as proxy value for all the phosphorus oxides in a material. For example, fertilizer grade phosphoric acid can also contain various related phosphorous compounds which are also of use. All these compounds are described collectively in terms of ' P 2 O 5 content' to allow convenient comparison of the phosphorous content of different products. Despite this, phosphorus pentoxide is not actually present in most samples as it is not stable in aqueous solutions.
Phosphorus pentoxide itself is not flammable. Just like sulfur trioxide , it reacts vigorously with water and water-containing substances like wood or cotton, liberates much heat and may even cause fire due to the highly exothermic nature of such reactions. It is corrosive to metal and is very irritating – it may cause severe burns to the eye, skin, mucous membrane , and respiratory tract even at concentrations as low as 1 mg/m 3 . [ 10 ] | https://en.wikipedia.org/wiki/Phosphorus_pentoxide |
Phosphorus tribromide is a colourless liquid with the formula P Br 3 . The liquid fumes in moist air due to hydrolysis and has a penetrating odour. It is used in the laboratory for the conversion of alcohols to alkyl bromides .
PBr 3 is prepared by treating red phosphorus with bromine . An excess of phosphorus is used in order to prevent formation of PBr 5 : [ 1 ] [ 2 ]
Because the reaction is highly exothermic, it is often conducted in the presence of a diluent such as PBr 3 . Phosphorus tribromide is also generated in situ from red phosphorus and bromine. [ 3 ]
Phosphorus tribromide, like PCl 3 and PF 3 , has both properties of a Lewis base and a Lewis acid . For example, with a Lewis acid such as boron tribromide it forms stable 1 :1 adducts such as Br 3 B · PBr 3 . At the same time PBr 3 can react as an electrophile or Lewis acid in many of its reactions, for example with amines .
An important reaction of PBr 3 is with alcohols , where it replaces an OH group with a bromine atom to produce an alkyl bromide . All three bromides can be transferred. [ 4 ]
Several detailed procedures are available. [ 5 ] [ 6 ] In some cases, triphenylphosphine /Br 2 is superior to PBr 3 . [ 7 ]
The mechanism for a primary alcohol involves formation of a phosphorous ester (to form a good leaving group), followed by an S N 2 substitution .
Because of the S N 2 substitution step, the reaction generally works well for primary and secondary alcohols , but fails for tertiary alcohols. If the reacting carbon centre is chiral , the reaction usually occurs with inversion of configuration at the carbon alpha to the alcohol, as is usual with an S N 2 reaction.
In a similar reaction, PBr 3 also converts carboxylic acids to acyl bromides : [ 8 ]
The main use for phosphorus tribromide is for conversion of primary or secondary alcohols to alkyl bromides , [ 9 ] as described above . PBr 3 usually gives higher yields than hydrobromic acid , and it avoids problems of carbocation rearrangement- for example even neopentyl bromide can be made from the alcohol in 60% yield. [ 10 ]
Another use for PBr 3 is as a catalyst for the α-bromination of carboxylic acids . Although acyl bromides are rarely made in comparison with acyl chlorides , they are used as intermediates in Hell-Volhard-Zelinsky halogenation . [ 11 ] Initially PBr 3 reacts with the carboxylic acid to form the acyl bromide, which is more reactive towards bromination. The overall process can be represented as
On a commercial scale, phosphorus tribromide is used in the manufacture of pharmaceuticals such as alprazolam , methohexital and fenoprofen . It is also a potent fire suppression agent marketed under the name PhostrEx .
Phosphorus tribromide is used for doping in microelectronics . [ 12 ]
PBr 3 evolves corrosive HBr , which is toxic, and reacts violently with water and alcohols.
In reactions that produce phosphorous acid as a by-product, when working up by distillation be aware that this can decompose above about 160 °C to give phosphine which can cause explosions in contact with air. [ 9 ] | https://en.wikipedia.org/wiki/Phosphorus_tribromide |
This page provides supplementary chemical data on phosphorus tribromide .
External MSDS sheets: | https://en.wikipedia.org/wiki/Phosphorus_tribromide_(data_page) |
This page provides supplementary chemical data on phosphorus trichloride .
The handling of this chemical may incur notable safety precautions. It is highly recommend that you seek the Material Safety Datasheet ( MSDS ) for this chemical from a reliable source such as SIRI , and follow its directions. | https://en.wikipedia.org/wiki/Phosphorus_trichloride_(data_page) |
This page provides supplementary chemical data on phosphorus trifluoride . | https://en.wikipedia.org/wiki/Phosphorus_trifluoride_(data_page) |
This page provides supplementary chemical data on phosphoryl chloride . | https://en.wikipedia.org/wiki/Phosphoryl_chloride_(data_page) |
A phosphoryl group is a trivalent >P(=O)− group, consisting of a phosphorus atom (symbol P) and an oxygen atom (symbol O), where the three free valencies are on the phosphorus atom. While commonly depicted as possessing a double bond (P=O) the bonding is in fact non-classical. [ 1 ]
Despite that, the meaning of the term "phosphoryl" varies, depending on the branch of scientific discipline . For example, in biology , biochemistry and biomedicine branches, the term "phosphoryl" refers to groups consisting of phosphorus atom attached to three oxygen atoms, with the simplified chemical formula −PO 3 (there are several groups called "phosphoryl" in those branches, with the chemical formulas −P(=O)(−O − ) 2 , −P(=O)(−O − )(−OH) , −P(=O)(−OH) 2 , −P(=O)(−O − )−O− , −P(=O)(−OH)−O− and −P(=O)(−O−) 2 ). In the branches mentioned above, the "phosphoryl" and phosphate groups are sometimes abbreviated by the letter "P", or represented by a symbol of encircled letter "P". [ 2 ] [ 3 ] "Phosphoryl" groups are covalently bonded by a single bond to an organic molecule , phosphate group(s) or another "phosphoryl" group(s), and those groups are sp 3 hybridized at the phosphorus atom. [ 4 ] The term "phosphoryl" in the mentioned branches is usually used in the description of catalytic mechanisms in living organisms. The "phosphoryl" group plays a central role in phosphorylation . In biochemical reactions involving phosphate groups (e.g. adenosine triphosphate), a "phosphoryl" group is usually transferred between the substrates by the "phosphoryl transfer reactions" (see phosphorylation ). Examples of molecules containing those groups in biology, biochemistry and biomedicine are adenosine monophosphate (AMP), adenosine diphosphate (ADP), adenosine triphosphate (ATP), phosphocreatine (PCr) and DNA .
Contrary to biology , biochemistry and biomedicine branches, in organic and inorganic chemistry branches, and in the branch of chemical nomenclature (see IUPAC ), the correct name for the −P(=O)(−O − ) 2 group is not "phosphoryl", but phosphonato , and the correct name for the −P(=O)(−OH) 2 group is phosphono , and the term phosphoryl correctly refers to the trivalent >P(=O)− group. [ 2 ] [ 5 ] Example of molecules containing that trivalent phosphoryl group are phosphoryl chloride ( O=P(−Cl) 3 ), methylphosphonyl dichloride ( O=P(−CH 3 )(−Cl) 2 ) and phosphoramide ( O=P(−NH 2 ) 3 ).
A phosphoryl group should not be confused with a phosphate group. | https://en.wikipedia.org/wiki/Phosphoryl_group |
In biochemistry , phosphorylation is described as the "transfer of a phosphate group" from a donor to an acceptor. [ 1 ] A common phosphorylating agent (phosphate donor) is ATP and a common family of acceptor are alcohols :
This equation can be written in several ways that are nearly equivalent that describe the behaviors of various protonated states of ATP, ADP, and the phosphorylated product.
As is clear from the equation, a phosphate group per se is not transferred, but a phosphoryl group (PO 3 - ). Phosphoryl is an electrophile . [ 2 ] This process and its inverse, dephosphorylation , are common in biology . [ 3 ] Protein phosphorylation often activates (or deactivates) many enzymes . [ 4 ] [ 5 ]
Phosphorylation is essential to the processes of both anaerobic and aerobic respiration , which involve the production of adenosine triphosphate (ATP), the "high-energy" exchange medium in the cell. During aerobic respiration, ATP is synthesized in the mitochondrion by addition of a third phosphate group to adenosine diphosphate (ADP) in a process referred to as oxidative phosphorylation . ATP is also synthesized by substrate-level phosphorylation during glycolysis . ATP is synthesized at the expense of solar energy by photophosphorylation in the chloroplasts of plant cells.
Phosphorylation of sugars is often the first stage in their catabolism . Phosphorylation allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter . Phosphorylation of glucose is a key reaction in sugar metabolism. The chemical equation for the conversion of D-glucose to D-glucose-6-phosphate in the first step of glycolysis is given by:
Glycolysis is an essential process of glucose degrading into two molecules of pyruvate , through various steps, with the help of different enzymes. It occurs in ten steps and proves that phosphorylation is a much required and necessary step to attain the end products. Phosphorylation initiates the reaction in step 1 of the preparatory step [ 6 ] (first half of glycolysis), and initiates step 6 of payoff phase (second phase of glycolysis). [ 7 ]
Glucose, by nature, is a small molecule with the ability to diffuse in and out of the cell. By phosphorylating glucose (adding a phosphoryl group in order to create a negatively charged phosphate group [ 8 ] ), glucose is converted to glucose-6-phosphate, which is trapped within the cell as the cell membrane is negatively charged. This reaction occurs due to the enzyme hexokinase , an enzyme that helps phosphorylate many six-membered ring structures. Phosphorylation takes place in step 3, where fructose-6-phosphate is converted to fructose 1,6-bisphosphate . This reaction is catalyzed by phosphofructokinase .
While phosphorylation is performed by ATPs during preparatory steps, phosphorylation during payoff phase is maintained by inorganic phosphate. Each molecule of glyceraldehyde 3-phosphate is phosphorylated to form 1,3-bisphosphoglycerate . This reaction is catalyzed by glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The cascade effect of phosphorylation eventually causes instability and allows enzymes to open the carbon bonds in glucose.
Phosphorylation functions is an extremely vital component of glycolysis, as it helps in transport, control, and efficiency. [ 9 ]
Glycogen is a long-term store of glucose produced by the cells of the liver . In the liver , the synthesis of glycogen is directly correlated with blood glucose concentration. High blood glucose concentration causes an increase in intracellular levels of glucose 6-phosphate in the liver, skeletal muscle , and fat ( adipose ) tissue. Glucose 6-phosphate has role in regulating glycogen synthase .
High blood glucose releases insulin , stimulating the translocation of specific glucose transporters to the cell membrane; glucose is phosphorylated to glucose 6-phosphate during transport across the membrane by ATP-D-glucose 6- phosphotransferase and non-specific hexokinase (ATP-D-hexose 6-phosphotransferase). [ 10 ] [ 11 ] Liver cells are freely permeable to glucose, and the initial rate of phosphorylation of glucose is the rate-limiting step in glucose metabolism by the liver. [ 10 ]
The liver's crucial role in controlling blood sugar concentrations by breaking down glucose into carbon dioxide and glycogen is characterized by the negative Gibbs free energy (ΔG) value, which indicates that this is a point of regulation with. [ clarification needed ] The hexokinase enzyme has a low Michaelis constant (K m ), indicating a high affinity for glucose, so this initial phosphorylation can proceed even when glucose levels at nanoscopic scale within the blood.
The phosphorylation of glucose can be enhanced by the binding of fructose 6-phosphate (F6P), and lessened by the binding fructose 1-phosphate (F1P). Fructose consumed in the diet is converted to F1P in the liver. This negates the action of F6P on glucokinase, [ 12 ] which ultimately favors the forward reaction. The capacity of liver cells to phosphorylate fructose exceeds capacity to metabolize fructose-1-phosphate. Consuming excess fructose ultimately results in an imbalance in liver metabolism, which indirectly exhausts the liver cell's supply of ATP. [ 13 ]
Allosteric activation by glucose-6-phosphate, which acts as an effector, stimulates glycogen synthase, and glucose-6-phosphate may inhibit the phosphorylation of glycogen synthase by cyclic AMP -stimulated protein kinase . [ 11 ]
Phosphorylation of glucose is imperative in processes within the body. For example, phosphorylating glucose is necessary for insulin-dependent mechanistic target of rapamycin pathway activity within the heart. This further suggests a link between intermediary metabolism and cardiac growth. [ 14 ]
Protein phosphorylation is the most abundant post-translational modification in eukaryotes. Phosphorylation can occur on serine , threonine and tyrosine side chains (in other words, on their residues) through phosphoester bond formation, on histidine , lysine and arginine through phosphoramidate bonds , and on aspartic acid and glutamic acid through mixed anhydride linkages . Recent evidence confirms widespread histidine phosphorylation at both the 1 and 3 N-atoms of the imidazole ring. [ 15 ] [ 16 ] Recent work demonstrates widespread human protein phosphorylation on multiple non-canonical amino acids, including motifs containing phosphorylated histidine, aspartate, glutamate, cysteine , arginine and lysine in HeLa cell extracts. [ 17 ] However, due to the chemical lability of these phosphorylated residues, and in marked contrast to Ser, Thr and Tyr phosphorylation, the analysis of phosphorylated histidine (and other non-canonical amino acids) using standard biochemical and mass spectrometric approaches is much more challenging [ 17 ] [ 18 ] [ 19 ] and special procedures and separation techniques are required for their preservation alongside classical Ser, Thr and Tyr phosphorylation. [ 20 ]
The prominent role of protein phosphorylation in biochemistry is illustrated by the huge body of studies published on the subject (as of March 2015, the MEDLINE database returns over 240,000 articles, mostly on protein phosphorylation).
[ 21 ] [ 22 ] [ 23 ] [ 24 ] | https://en.wikipedia.org/wiki/Phosphorylation |
A phosphorylation cascade is a sequence of signaling pathway events where one enzyme phosphorylates another, causing a chain reaction leading to the phosphorylation of thousands of proteins. This can be seen in signal transduction of hormone messages. A signaling pathway begins at the cell surface where a hormone or protein binds to a receptor at the extracellular matrix . The interactions between the molecule and receptor cause a conformational change at the receptor, which activates multiple enzymes or proteins. These enzymes activate secondary messengers, which leads to the phosphorylation of thousands of proteins. The end product of a phosphorylation cascade is the changes occurring inside the cell. These cascades work to amplify the signal where binding of one extracellular ligand can activate thousands of proteins downstream since these are allosterically regulated enzymes that make many products, amplifying the signal.
An example of a signaling pathway that uses phosphorylation cascades is with the activation of mitogen-activated protein (MAP) kinase or ERK kinase . To activate this kinase, an epidermal growth factor must bind to the epidermal growth factor receptor at the extracellular domain, causing a conformational change to the receptor tyrosine kinase that activates it and results in dimerization and autophosphorylation of intracellular tyrosine residues. This allows for the binding of the adaptor protein GRB2 with its SH2 domain , which recognizes the phosphorylated tyrosines. [ 1 ] A pair of SH3 domains on the adaptor protein will recruit the SOS protein by recognition of proline-containing consensus sequences. SOS will subsequently act as a GEF protein to catalyze the exchange of GDP to GTP on the Ras GTPase . [ 2 ] Activated Ras-GTP now activates the Raf Kinase enzyme which will phosphorylate MEK enzymes, which in turn phosphorylate MAP/ERK kinases, which continue to phosphorylate other enzymes to regulate their activity and lead to regulation of gene expression. [ 2 ] MAP kinase not only plays an important function during growth of cell in the M phase phosphorylation cascade but also plays an important role during the sequence of signaling pathway. [ 3 ] In order to regulate its functions so it does not cause chaos, it can only be active when both tyrosine and threonine/serine residues are phosphorylated. [ 4 ]
Tumor cells may possess mutations in key receptors related to cell division and growth. A loss in the ability to properly regulate these receptors and the phosphorylation cascades they result in is deleterious to the organism. Fibroblast growth factors (FGF) bind to their fibroblast growth factor receptors (FGFR) and lead to activation of multiple signaling pathways by phosphorylation cascades to result in proliferation, differentiation and survival of the cell. [ 5 ] Mutations or gene fusions with these receptors leads to a loss of regulation of the intracellular enzymes, resulting in excessive proliferation which drives tumor growth. [ 5 ] Similarly, vascular endothelial growth factors (VEGF) bind to their vascular endothelial growth factor receptors (VEGFR) leads to activation of similar pathways along with those that lead to increased vessel permeability and angiogenesis . This is normally regulated by hypoxic conditions , but cancer cells can bypass this to stimulate vessel growth when not appropriate to aid in tumor growth. [ 5 ] Targeting and inhibiting these receptors and they cascades they initiate has been an effective means of battling some cancers and even with its great developments is a very active area of research. [ 5 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Phosphorylation_cascade |
Photo-Induced Cross-Linking of Unmodified Proteins (PICUP) is a protein cross-linking method by visible light irradiation of a photocatalyst in the presence of an electron acceptor and the protein of interest. [ 1 ] Irradiation results in a highly reactive protein radical that forms a covalent bond between the amino acid side chains of the proteins to be linked. Cross-linking methods developed prior to PICUP, including the use of physical, oxidative, and chemical cross-linkers, often require more time and result in protein byproducts. [ 2 ] In addition, the cross-linked protein yield is very low due to the multifunctionality of the cross-linking reagents.
The process was invented (US6613582B1) in 1999 to utilize protein cross-linking techniques to analyze the interactions between polypeptides as well as structural differences proteins undergo in a catalytic pathway . The techniques in the 20th century were not sufficient to be applied to cross-link fast and transient changes of these proteins in high yield. PICUP allowed for rapid (<1 second) and high production of covalently-linked proteins in close proximity with each other. [ 2 ]
Fancy and Kodadek's invention of PICUP in 1999 was the first time proteins cross-linking was able to be performed in such a short period of time (1 second) and without modifying the structure of the proteins in question. [ 2 ] Additionally, PICUP was able to be performed at physiological pH of 7.4, which opened doors for further application of protein cross-linking such as studying the biochemical mechanisms that proteins participate in the human body. In addition, irradiation by visible light in PICUP is useful because many biomolecules that participate in metabolic pathways to be analyzed do no absorb light with wavelengths below the range for UV light , allowing for cross-links without denaturation. [ 2 ]
In 2001, Gal Bitan, Aleksey Lomakin, and David B. Teplow applied PICUP to study amyloid β-protein (Aβ) oligomerization, which is observed in Alzheimer's disease. [ 3 ] PICUP allowed for identifying and quantifying the Aβ oligomers that are metastable because of its ability to rapidly cross-link. [ 3 ] Coupling PICUP with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) , the distribution of oligomers in rapid equilibrium was quantified. [ 3 ] This application allowed for the study of amyloidogenic proteins associated with neurodegenerative diseases and opened doors for possible future therapeutic mechanisms. Neurodegenerative diseases are currently suggested to be the result of neurotoxic proteins, so the ability to study their oligomer distribution is effective in understanding how and under what conditions these oligomers are formed.
The mechanism of PICUP require the tris(bipyridyl)Ru(II) complex , an electron acceptor, ammonium persulfate (APS) , and reactive amino acid side chains. [ 2 ] Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate, a tris(bipyridyl)Ru(II) complex, initially contains a Ru 2+ . [ 4 ] Upon visible light irradiation and in the presence of ammonium persulfate (APS), Ru 2+ enters its excited state and is oxidized to Ru 3+ . [ 4 ] Ru 3+ is now an extremely reactive oxidizer that only wants to accept one electron instead of the standard two. [ 4 ] The reaction can proceed in the absence of an electron acceptor, but it will have a much lower efficiency, producing byproducts resulting from the excited Ru(Bpy) 3 reacting with oxygen. [ 5 ] As an effective single electron oxidizer, Ru 3+ will pick up a single electron from amino acids of the neighboring proteins, most commonly Tryptophan and Tyrosine . [ 4 ] This produces a radical that is highly unstable on the amino acid side chains, which proceeds through reactions to reach a more stable state.
The unpaired single electron on the side chain reacts with another amino acid side chain of a polypeptide in the vicinity, resulting in a dimer with a covalent bond. [ 4 ] With the regeneration of Ru 2+ when Ru 3+ picks up an electron from the amino acids allows for continuous formation of radicals with Ru 3+ being oxidized by APS. [ 2 ]
In the PCR tube that the reaction takes place in, numerous unstable protein radicals come in contact with each other through simple diffusion and react both intra- and intermolecularly to achieve a more stable state. The monomeric protein radicals are able to achieve a lower energy state through forming a covalent bond to produce a dimer and releasing a hydrogen atom. [ 4 ] PLEASE NOTE: The image mistakenly shows the release of a proton and should not be used in this form (See also ref. 4). The creator has been contacted. This newly formed dimer is also able to react with numerous other monomers or dimers through the same mechanism, creating higher numbers of cross-linked oligomers. [ 4 ] This allows for a distribution of variety of oligomers to be present in the mixture.
In every experiment, it is important to determine the relative concentration of the protein in question, ammonium persulfate, and Tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate that will be used in the protein cross-linking experiment. Previous experiments have shown that for amyloid β-protein (Aβ), the peptide assumed to cause toxicity in Alzheimer's disease , the ratio of protein: Ru(Bpy) 3 : APS is 1:2:40. [ 3 ] The ratio of Ru(Bpy) 3 and APS is suggested to be kept at this ratio, but the appropriate concentration of a given protein can vary. For many proteins that PICUP has not yet been used for, finding the appropriate concentrations can be done through trial and error. Generally, protein concentrations would fall in between 10 and 50μM, dissolved in the corresponding buffer, most likely sodium phosphate if testing for conditions at physiological pH. However, some studies of pure protein suggest that the protein to Ru(Bpy) 3 ratio should be kept at 1:2 as well. [ 4 ] This level arises from the fact that the lower amount of Ru(Bpy) 3 can lead to the protein sample appearing to have more than the actual number of higher order oligomers, and a greater amount of Ru(Bpy) 3 can allow for artificial cross-linking byproducts.
The general method for PICUP is as follows:
Using PICUP on protein complexes is useful in providing catalytic and kinetic information about these proteins, as catalytic mechanisms are rapid and PICUP allows for fast and highly efficient cross-linking of proteins. [ 5 ] Some epitope and affinity tags were shown to be unaffected by the PICUP reaction, enabling visualization of the cross-linked proteins. [ 5 ]
Furthermore, PICUP allows for visualization of quantitative bands of protein oligomer distribution when it is coupled with protein fractionation techniques. This combination is especially useful when examining the oligomers of neurodegenerative diseases, such as Alzheimer's disease , Parkinson's disease , and Huntington's disease , that result from protein aggregation. [ 1 ] PICUP is extremely important when possible prevention and treatment procedures for these diseases are explored, as it is necessary to investigate the aggregation propensity of the respective amyloidogenic proteins . | https://en.wikipedia.org/wiki/Photo-induced_cross-linking_of_unmodified_proteins |
In high-energy astrophysics , a photo-meson is a meson (most often a pion ) produced in the interaction of a photon with a nucleon within an astrophysical object. This interaction is commonly referred to as photo-hadronic process. The decay of charged mesons ultimately results in the production of neutrinos and electrons , with muons as an intermediate state. The decay of neutral mesons produces high-energy gamma-rays . Photo-meson production is one of the hadronic processes that can occur in cosmic ray sources as gamma-ray bursts and active galactic nuclei , and that can result in an observable multi-messenger signature. [ 1 ]
This astrophysics -related article is a stub . You can help Wikipedia by expanding it .
This particle physics –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Photo-meson |
In polymer chemistry , photo-oxidation (sometimes: oxidative photodegradation ) is the degradation of a polymer surface due to the combined action of light and oxygen. [ 1 ] It is the most significant factor in the weathering of plastics. [ 2 ] Photo-oxidation causes the polymer chains to break ( chain scission ), resulting in the material becoming increasingly brittle. This leads to mechanical failure and, at an advanced stage, the formation of microplastics . In textiles , the process is called phototendering .
Technologies have been developed to both accelerate and inhibit this process. For example, plastic building components like doors, window frames and gutters are expected to last for decades, requiring the use of advanced UV- polymer stabilizers . Conversely, single-use plastics can be treated with biodegradable additives to accelerate their fragmentation.
Many pigments and dyes can similarly have effects due to their ability to absorb UV-energy.
Susceptibility to photo-oxidation varies depending on the chemical structure of the polymer. Some materials have excellent stability, such as fluoropolymers , polyimides , silicones and certain acrylate polymers . However, global polymer production is dominated by a range of commodity plastics which account for the majority of plastic waste . Of these polyethylene terephthalate (PET) has only moderate UV resistance and the others, which include polystyrene , polyvinyl chloride (PVC) and polyolefins like polypropylene (PP) and polyethylene (PE) are all highly susceptible.
Photo-oxidation is a form of photodegradation and begins with formation of free radicals on the polymer chain, which then react with oxygen in chain reactions . For many polymers the general autoxidation mechanism is a reasonable approximation of the underlying chemistry. The process is autocatalytic , generating increasing numbers of radicals and reactive oxygen species. These reactions result in changes to the molecular weight (and molecular weight distribution ) of the polymer and as a consequence the material becomes more brittle. The process can be divided into four stages:
Photo-oxidation can occur simultaneously with other processes like thermal degradation , and each of these can accelerate the other.
Polyolefins such as polyethylene and polypropylene are susceptible to photo-oxidation and around 70% of light stabilizers produced world-wide are used in their protection, despite them representing only around 50% of global plastic production. [ 1 ] Aliphatic hydrocarbons can only adsorb high energy UV-rays with a wavelength below ~250 nm, however the Earth's atmosphere and ozone layer screen out such rays, with the normal minimum wavelength being 280–290 nm. [ 3 ] The bulk of the polymer is therefore photo-inert and degradation is instead attributed to the presence of various impurities, which are introduced during the manufacturing or processing stages. These include hydroperoxide and carbonyl groups, as well as metal salts such as catalyst residues.
All of these species act as photoinitiators . [ 4 ] The organic hydroperoxide and carbonyl groups are able to absorb UV light above 290 nm whereupon they undergo photolysis to generate radicals. [ 5 ] Metal impurities act as photocatalysts , [ 6 ] although such reactions can be complex. [ 7 ] [ 8 ] It has also been suggested that polymer-O 2 charge-transfer complexes are involved. [ 9 ] [ 10 ] Initiation generates radical-carbons on the polymer chain, sometimes called macroradicals (P•).
Chain initiation
Chain propagation
Chain branching
Termination
Classically the carbon-centred macroradicals (P•) rapidly react with oxygen to form hydroperoxyl radicals (POO•), which in turn abstract an H atom from the polymer chain to give a hydroperoxide (POOH) and a fresh macroradical. Hydroperoxides readily undergo photolysis to give an alkoxyl macroradical radical (PO•) and a hydroxyl radical (HO•), both of which may go on to form new polymer radicals via hydrogen abstraction. Non-classical alternatives to these steps have been proposed. [ 11 ] The alkoxyl radical may also undergo beta scission , [ 12 ] generating an acyl- ketone and macroradical. This is considered to be the main cause of chain breaking in polypropylene. [ 13 ]
Secondary hydroperoxides can also undergo an intramolecular reaction to give a ketone group, although this is limited to polyethylene. [ 1 ] [ 14 ] [ 15 ] [ 16 ]
The ketones generated by these processes are themselves photo-active, although much more weakly. At ambient temperatures they undergo Type II Norrish reactions with chain scission. [ 17 ] They may also absorb UV-energy, which they can then transfer to O 2 , causing it to enter its highly reactive singlet state . [ 18 ] Singlet oxygen is a potent oxidising agent and can go on to cause further degradation.
For polystyrene the complete mechanism of photo-oxidation is still a matter of debate, as different pathways may operate concurrently [ 20 ] and vary according to the wavelength of the incident light. [ 21 ] [ 22 ] Regardless, there is agreement on the major steps. [ 19 ]
Pure polystyrene should not be able to absorb light with a wavelength below ~280 nm and initiation is explained though photo-labile impurities (hydroperoxides) and charge transfer complexes, [ 23 ] all of which are able to absorb normal sunlight. [ 24 ] Charge-transfer complexes of oxygen and polystyrene phenyl groups absorb light to form singlet oxygen , which acts as a radical initiator. [ 23 ] Carbonyl impurities in the polymer (cf. acetophenone ) also absorb light in the near ultraviolet range (300 to 400 nm), forming excited ketones able to abstract hydrogen atoms directly from the polymer. [ 24 ] Hyroperoxide undergoes photolysis to form hydroxyl and alkoxyl radicals.
These initiation steps generate macroradicals at tertiary sites, as these are more stabilised. The propagation steps are essentially identical to those seen for polyolefins; with oxidation, hydrogen abstraction and photolysis leading to beta scission reactions and increasing numbers of radicals.
These steps account for the majority of chain-breaking, however in a minor pathway the hydroperoxide reacts directly with polymer to form a ketone group ( acetophenone ) and a terminal alkene without the formation of additional radicals. [ 25 ]
Polystyrene is observed to yellow during photo-oxidation, which is attributed to the formation of polyenes from these terminal alkenes. [ 25 ]
Pure organochlorides like polyvinyl chloride (PVC) do not absorb any light above 220 nm. The initiation of photo-oxidation is instead caused by various irregularities in the polymer chain, such as structural defects [ 26 ] [ 27 ] as well as hydroperoxides, carbonyl groups, and double bonds. [ 28 ] Hydroperoxides formed during processing are the most important initiator to begin with, [ 29 ] however their concentration decreases during photo-oxidation whereas carbonyl concentration increases, [ 30 ] as such carbonyls may become the primary initiator over time. [ 29 ] [ 31 ] [ 32 ]
Propagation steps involve the hydroperoxyl radical, which can abstract hydrogen from both hydrocarbon (-CH 2 -) and organochloride (-CH 2 Cl-) sites in the polymer at comparable rates. [ 29 ] [ 31 ] Radicals formed at hydrocarbon sites rapidly convert to alkenes with loss of radical chlorine. This forms allylic hydrogens (shown in red) which are more susceptible to hydrogen abstraction leading to the formation of polyenes in zipper-like reactions.
When the polyenes contain at least eight conjugated double bonds they become coloured, leading to yellowing and eventual browning of the material. This is off-set slightly by longer polyenes being photobleached with atmospheric oxygen, [ 33 ] however PVC does eventually discolour unless polymer stabilisers are present. Reactions at organochloride sites proceed via the usual hydroperoxyl and hydroperoxide before photolysis yields the α-chloro-alkoxyl radical. This species can undergo various reactions to give carbonyls, peroxide cross-links and beta scission products. [ 34 ]
Unlike most other commodity plastics polyethylene terephthalate (PET) is able to absorb the near ultraviolet rays in sunlight. Absorption begins at 360 nm, becoming stronger below 320 nm and is very significant below 300 nm. [ 1 ] [ 35 ] [ 36 ] Despite this PET has better resistance to photo-oxidation than other commodity plastics , this is due to a poor quantum yield or the absorption. [ 37 ] The degradation chemistry is complicated due to simultaneous photodissociation (i.e. not involving oxygen) and photo-oxidation reactions of both the aromatic and aliphatic parts of the molecule. Chain scission is the dominant process, with chain branching and the formation of coloured impurities being less common. Carbon monoxide, carbon dioxide, and carboxylic acids are the main products. [ 35 ] [ 36 ] The photo-oxidation of other linear polyesters such as polybutylene terephthalate and polyethylene naphthalate proceeds similarly.
Photodissociation involves the formation of an excited terephthalic acid unit which undergoes Norrish reactions . The type I reaction dominates, which cause chain scission at the carbonyl unit to give a range of products. [ 1 ] [ 38 ]
Type II Norrish reactions are less common but give rise to acetaldehyde by way of vinyl alcohol esters. [ 36 ] This has an exceedingly low odour and taste threshold and can cause an off-taste in bottled water. [ 39 ]
Radicals formed by photolysis may initiate the photo-oxidation in PET. Photo-oxidation of the aromatic terephthalic acid core results in its step-wise oxidation to 2,5-dihydroxyterephthalic acid. The photo-oxidation process at aliphatic sites is similar to that seen for polyolefins, with the formation of hydroperoxide species eventually leading to beta-scission of the polymer chain. [ 1 ]
Perhaps surprisingly, the effect of temperature is often greater than the effect of UV exposure. [ 5 ] This can be seen in terms of the Arrhenius equation , which shows that reaction rates have an exponential dependence on temperature. By comparison the dependence of degradation rate on UV exposure and the availability of oxygen is broadly linear. As the oceans are cooler than land plastic pollution in the marine environment degrades more slowly. [ 40 ] [ 41 ] Materials buried in landfill do not degrade by photo-oxidation at all, though they may gradually decay by other processes.
Mechanical stress can effect the rate of photo-oxidation [ 42 ] and may also accelerate the physical breakup of plastic objects. Stress can be caused by mechanical load (tensile and shear stresses ) or even by temperature cycling , particularly in composite systems consisting of materials with differing temperature coefficients of expansion. Similarly, sudden rainfall can cause thermal stress .
Dyes and pigments are used in polymer materials to provide colour, however they can also effect the rate of photo-oxidation. Many absorb UV rays and in so doing protect the polymer, however absorption can cause the dyes to enter an excited state where they may attack the polymer or transfer energy to O 2 to form damaging singlet oxygen . Cu-phthalocyanine is an example, it strongly absorbs UV light however the excited Cu-phthalocyanine may act as a photoinitiator by abstracting hydrogen atoms from the polymer. [ 43 ] Its interactions may become even more complicated when other additives are present. [ 44 ] Fillers such as carbon black can screen out UV light, effectively stabilisers the polymer, whereas flame retardants tend to cause increased levels of photo-oxidation. [ 45 ]
Biodegradable additives may be added to polymers to accelerate their degradation. In the case of photo-oxidation OXO-biodegradation additives are used. [ 46 ] These are transition metal salts such as iron (Fe) , manganese (Mn) , and cobalt (Co) . Fe complexes increase the rate of photooxidation by promoting the homolysis of hydroperoxides via Fenton reactions .
The use of such additives has been controversial due to concerns that treated plastics do not fully biodegrade and instead result in the accelerated formation of microplastics . [ 47 ] Oxo-plastics would be difficult to distinguish from untreated plastic but their inclusion during plastic recycling can create a destabilised product with fewer potential uses, [ 48 ] [ 49 ] potentially jeopardising the business case for recycling any plastic. OXO-biodegradation additives were banned in the EU in 2019 [ 50 ]
UV attack by sunlight can be ameliorated or prevented by adding anti-UV polymer stabilizers , usually prior to shaping the product by injection moulding . UV stabilizers in plastics usually act by absorbing the UV radiation preferentially, and dissipating the energy as low-level heat. The chemicals used are similar to those in sunscreen products, which protect skin from UV attack. They are used frequently in plastics , including cosmetics and films . Different UV stabilizers are utilized depending upon the substrate, intended functional life, and sensitivity to UV degradation. UV stabilizers, such as benzophenones , work by absorbing the UV radiation and preventing the formation of free radicals . Depending upon substitution, the UV absorption spectrum is changed to match the application. Concentrations normally range from 0.05% to 2%, with some applications up to 5%.
Frequently, glass can be a better alternative to polymers when it comes to UV degradation. Most of the commonly used glass types are highly resistant to UV radiation. Explosion protection lamps for oil rigs for example can be made either from polymer or glass. Here, the UV radiation and rough weathers belabor the polymer so much, that the material has to be replaced frequently.
Poly(ethylene-naphthalate) (PEN) can be protected by applying a zinc oxide coating, which acts as protective film reducing the diffusion of oxygen. [ 51 ] Zinc oxide can also be used on polycarbonate (PC) to decrease the oxidation and photo-yellowing rate caused by solar radiation. [ 52 ]
The photo-oxidation of polymers can be investigated by either natural or accelerated weather testing. [ 53 ] Such testing is important in determining the expected service-life of plastic items as well as the fate of waste plastic .
In natural weather testing, polymer samples are directly exposed to open weather for a continuous period of time, [ 54 ] while accelerated weather testing uses a specialized test chamber which simulates weathering by sending a controlled amount of UV light and water at a sample. A test chamber may be advantageous in that the exact weathering conditions can be controlled, and the UV or moisture conditions can be made more intense than in natural weathering. Thus, degradation is accelerated and the test is less time-consuming.
Through weather testing, the impact of photooxidative processes on the mechanical properties and lifetimes of polymer samples can be determined. For example, the tensile behavior can be elucidated through measuring the stress–strain curve for a specimen. This stress–strain curve is created by applying a tensile stress (which is measured as the force per area applied to a sample face) and measuring the corresponding strain (the fractional change in length). Stress is usually applied until the material fractures, and from this stress–strain curve, mechanical properties such as the Young's modulus can be determined. Overall, weathering weakens the sample, and as it becomes more brittle, it fractures more easily. This is observed as a decrease in the yield strain , fracture strain , and toughness , as well as an increase in the Young's modulus and break stress (the stress at which the material fractures). [ 55 ]
Aside from measuring the impact of degradation on mechanical properties, the degradation rate of plastic samples can also be quantified by measuring the change in mass of a sample over time, as microplastic fragments can break off from the bulk material as degradation progresses and the material becomes more brittle through chain-scission. Thus, the percentage change in mass is often measured in experiments to quantify degradation. [ 56 ]
Mathematical models can also be created to predict the change in mass of a polymer sample over the weathering process. Because mass loss occurs at the surface of the polymer sample, the degradation rate is dependent on surface area. Thus, a model for the dependence of degradation on surface area can be made by assuming that the rate of change in mass − d m d t {\displaystyle -{\operatorname {d} \!m \over \operatorname {d} \!t}} resulting from degradation is directly proportional to the surface area SA of the specimen: [ 57 ]
− d m d t = k d ρ S A {\displaystyle -{\operatorname {d} \!m \over \operatorname {d} \!t}=k_{d}\rho SA}
Here, ρ {\displaystyle \rho } is the density and k d is known as the specific surface degradation rate (SSDR), which changes depending on the polymer sample's chemical composition and weathering environment. Furthermore, for a microplastic sample, SA is often approximated as the surface area of a cylinder or sphere. Such an equation can be solved to determine the mass of a polymer sample as a function of time.
Degradation can be detected before serious cracks are seen in a product by using infrared spectroscopy , [ 58 ] which is able to detect chemical species formed by photo-oxidation. In particular, peroxy-species and carbonyl groups have distinct absorption bands.
In the example shown at left, carbonyl groups were easily detected by IR spectroscopy from a cast thin film. The product was a road cone made by rotational moulding in LDPE , which had cracked prematurely in service. Many similar cones also failed because an anti-UV additive had not been used during processing. Other plastic products which failed included polypropylene mancabs used at roadworks which cracked after service of only a few months.
The effects of degradation can also be characterized through scanning electron microscopy (SEM). For example, through SEM, defects like cracks and pits can be directly visualized, as shown at right. These samples were exposed to 840 hours of exposure to UV light and moisture using a test chamber. [ 56 ] Crack formation is often associated with degradation, such that materials that do not display significant cracking behavior, such as HDPE in the right example, are more likely to be stable against photooxidation compared to other materials like LDPE and PP. However, some plastics that have undergone photooxidation may also appear smoother in an SEM image, with some defects like grooves having disappeared afterwards. This is seen in polystyrene in the right example. | https://en.wikipedia.org/wiki/Photo-oxidation_of_polymers |
Photo-reactive amino acid analogs are artificial analogs of natural amino acids that can be used for crosslinking of protein complexes. [ 1 ] Photo-reactive amino acid analogs may be incorporated into proteins and peptides in vivo or in vitro . [ 2 ] Photo-reactive amino acid analogs in common use are photoreactive diazirine analogs to leucine and methionine , and para -benzoylphenylalanine. Upon exposure to ultraviolet light , they are activated and covalently bind to interacting proteins that are within a few angstroms of the photo-reactive amino acid analog.
L -Photo-leucine and L -photo-methionine are analogs of the naturally occurring L - leucine and L - methionine amino acids that are endogenously incorporated into the primary sequence of proteins during synthesis using the normal translation machinery. They are then ultraviolet light (UV)-activated to covalently crosslink proteins within protein–protein interaction domains in their native in-vivo environment. The method enables the determination and characterization of both stable and transient protein interactions in cells without the addition of chemical crosslinkers and associated solvents that can adversely affect the cell biology being studied in the experiment.
When used in combination with limiting media that is devoid of leucine and methionine, the photo-activatable derivatives are treated like naturally occurring amino acids by the cellular protein synthesis machinery. As a result, they can be substituted for leucine or methionine in the primary structure of proteins. Photo-leucine and photo-methionine derivatives contain diazirine rings that are activated when exposed to UV light to become reactive intermediates that form covalent bonds with nearby protein side chains and backbones. Naturally interacting proteins within the cell can be instantly trapped by photoactivation of the diazirine-containing proteins in the cultured cells. Crosslinked protein complexes can be detected by decreased mobility on SDS-PAGE followed by Western blotting , size exclusion chromatography , sucrose density gradient sedimentation or mass spectrometry . | https://en.wikipedia.org/wiki/Photo-reactive_amino_acid_analog |
Photo-reflectance is an optical technique for investigating the material and electronic properties of thin films . Photo-reflectance measures the change in reflectivity of a sample in response to the application of an amplitude modulated light beam. In general, a photo-reflectometer consists of an intensity modulated "pump" light beam used to modulate the reflectivity of the sample, a second "probe" light beam used to measure the reflectance of the sample, an optical system for directing the pump and probe beams to the sample, and for directing the reflected probe light onto a photodetector , and a signal processor to record the differential reflectance. The pump light is typically modulated at a known frequency so that a lock-in amplifier may be used to suppress unwanted noise, resulting in the ability to detect reflectance changes at the ppm level.
The utility of photo-reflectance for characterization of semiconductor samples has been recognized since the late 1960s. In particular,
conventional photo-reflectance is closely related to electroreflectance [ 1 ] [ 2 ] [ 3 ] [ 4 ] in that the sample's internal electric field is modulated by the photo-injection of electron-hole pairs. [ 5 ] [ 6 ] The electro-reflectance response is sharply peaked near semiconductor interband transitions, which accounts for its usefulness in semiconductor characterization. [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] Photo-reflectance spectroscopy has been used to determine semiconductor bandstructures , internal electric fields, and other material properties such as crystallinity , composition , physical strain, and doping concentration . [ 12 ] [ 13 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ] [ 18 ]
The name "photo-reflectance" or "photoreflectance" is shortened from the term "photo-modulated reflectance," which describes the use of an intensity modulated light beam to perturb the reflectance of a sample. The technique has also been referred to as "modulated photo-reflectance," "modulated optical reflectance," and "photo-modulated optical reflectance." It has been known at least since 1967. [ 19 ]
Photo-reflectance is a particularly convenient type of modulation spectroscopy , as it may be performed at room temperature and only requires the sample have a reflecting surface. [ 20 ] It is an established tool for non-contact determination of material and electronic properties of semiconductor films. [ 21 ] In photo-reflectance, a pump laser beam is used to modulate the free charge density in a semiconductor sample (via photo-injection), thereby modulating one or more physical quantities (e.g. the internal electric field). The measured signal ΔR is the change in amplitude of the reflected probe light as the intensity modulated pump radiation interacts with the sample. The normalized signal is ΔR/R, i.e. the pump-induced change in reflectance (AC) divided by the baseline reflectance (DC). The conventional photo-reflectance apparatus uses a spectroscopic source for the probe beam, such that the signal may be recorded as a function of the probe light's wavelength. Generally, the signal may be written:
where ΔR/R is the normalized change in reflectance, α (≡1/R×∂R/∂ε 1 ) and β (≡1/R×∂R/∂ε 2 ) are the "Seraphin coefficients" which contain filmstack information, and Δε 1 and Δε 2 are the pump induced changes in the complex dielectric function . [ 22 ] However, in conventional photo-reflectance analysis, it is not necessary to independently determine the refractive and absorptive components (the first and second terms in ΔR/R, respectively) of the signal. Rather, a fit to the overall signal is performed using the third derivative functional form given by Aspnes . [ 20 ] This fit procedure yields the interband transition energies, amplitudes, and widths. However, because the signal depends on the uniformity of the perturbation, the extraction of such parameters must be treated with care. [ 23 ] [ 24 ]
The conventional photo-reflectance experimental setup uses a xenon or tungsten based lamp source passed through a monochromator to form the incident probe beam. The pump beam may be formed by the output of a continuous wave (CW) laser (e.g. a He-Ne or He-Cd laser) passed through a chopper wheel, or may be formed by the output of a directly modulated semiconductor diode laser . The pump beam is focused to a spot on the sample where it interacts with the sample. The probe beam is co-focused onto the sample where it is reflected. The reflected probe beam is collected and passed through an optical filter to eliminate any unwanted pump light and/or photoluminescence signal. Thereafter the probe beam is directed onto a photodetector (e.g. a Si or InGaAs photodiode ), which converts the probe intensity to an electrical signal. The electrical signal is processed to eliminate unwanted noise, typically using a lock-in circuit referenced to the modulation frequency. The photo-reflectance signal is then recorded as a function of probe beam wavelength using a computer or the like. [ 12 ] [ 25 ] [ 26 ]
In photo-reflectance, the sample's internal electric field is modulated by the photo-injection of electron-hole pairs (thus reducing the latent field). In order to achieve photo-injection, the energy of photons in the pump beam must exceed the band gap of material within the sample. Furthermore, semiconductors with little or no electric field will exhibit little or no electro-reflectance response. While this situation is not common, this point makes clear the importance of maintaining the probe intensity at a minimum, since any photo-injection of electron-hole pairs from the probe will necessarily offset the sample baseline condition by reducing the latent field. [ 27 ] [ 28 ] (Likewise, any CW component of the pump is undesirable.) Conversely, if the probe intensity is too low, detection may not be possible with conventional photodiodes. A further consideration is that phase-locked detection is a practical necessity due to the small size of the experimental signals (~ppm) and the unique ability of phase-locked detection methods to reject noise outside a narrow bandwidth centered on the modulation frequency.
Photo-reflectance is a highly sensitive measurement technique and provides unmatched capability for characterizing the material and electronic properties of thin films. Photo-reflectance has been particularly important in basic research on semiconductors due to its ability to precisely determine semiconductor bandstructures (even at room temperature). As an optical technique, photo-reflectance would appear suited to industrial applications because it is non-contact, and because it has good spatial resolution. However, the need for spectroscopic information limits measurement speed, and consequently the adoption of spectroscopic photo-reflectance in industrial applications such as process control of microelectronics manufacturing.
Nevertheless, where spectroscopic information is not required, photo-reflectance techniques have been implemented in semiconductor manufacturing process control. For example, in the late 1980s, Therma-Wave, Inc. introduced the "Therma-Probe" photo-modulated reflectance system to the market for semiconductor process control equipment. The original Therma-Probe focused an intensity modulated pump laser beam onto a spot on a silicon sample, modulating the sample reflectance. The reflectance changes were detected by a coincident laser probe beam of 633 nanometer wavelength. At this wavelength no electro-reflectance signal is present, since it is far removed from any interband transitions in silicon. Rather, the mechanisms responsible for the Therma-Probe signal are thermo-modulation and the Drude free carrier effect. [ 29 ] [ 30 ] [ 31 ] The Therma-Probe was used primarily for monitoring of the ion implantation process in silicon semiconductor manufacturing. [ 32 ] Measurement systems such as the Therma-Probe are particularly desirable in process control of microelectronics manufacturing because they provide the ability to quickly verify the correct execution of process steps, without contacting the wafer or removing the wafer from the clean room. [ 33 ] Generally a number of measurements will be made on certain areas of the wafer and compared with expected values. As long as the measured values are within a certain range, the wafers are passed for continued processing. (This is known as statistical process control .) Other photo-modulated reflectance systems marketed for process control of implant processes are the "TWIN" metrology system marketed by PVA TePla AG , and the "PMR-3000" marketed by Semilab Co. Ltd (originally Boxer-Cross, Inc.).
However, by the mid 2000s, new manufacturing processes were requiring new process control capabilities, for example the need for control of new "diffusion-less" annealing processes and advanced strained silicon processes. To address these new process control requirements, in 2007, Xitronix Corporation introduced a photo-reflectance system to the semiconductor process control market. Like the Therma-Probe, the Xitronix metrology system utilized a fixed wavelength probe beam generated by a laser. However, the probe beam of the Xitronix system had a wavelength of approximately 375 nanometers, near the first major interband transition in silicon. At this wavelength the electro-modulation signal is dominant, which enabled the Xitronix system to precisely measure active doping concentration in diffusion-less annealing processes. [ 34 ] This probe beam wavelength also provided excellent sensitivity to strain in strained silicon processes. [ 35 ] More recently, the use of laser photo-reflectance technology for precision measurement of carrier diffusion lengths, recombination lifetimes , and mobilities has been demonstrated. [ 36 ] [ 37 ]
Spectroscopic photo-reflectance employs a broad band probe light source , which may cover wavelengths from the infrared to the ultraviolet . By fitting spectroscopic photo-reflectance data with the conventional third derivative functional form, a comprehensive set of interband transition energies, amplitudes, and widths may be obtained, providing an essentially complete characterization of the electronic properties of the sample of interest. However, owing to the need to keep the probe light intensity to a minimum and to the practical necessity of phase-locked detection, spectroscopic photo-reflectance measurements must be made sequentially, i.e. probe one wavelength at a time.
This constraint limits the speed of spectroscopic photo-reflectance measurements, and coupled with the need for a careful fit procedure, renders spectroscopic photo-reflectance more suitable for analytical applications. Conversely, laser photo-reflectance employs a monochromatic light source, and hence is well suited for industrial applications. Moreover, in commonly encountered situations, the coherent wavefront of laser probe beam may be used to isolate the refractive component of the photo-reflectance signal, greatly simplifying the data analysis. [ 38 ] | https://en.wikipedia.org/wiki/Photo-reflectance |
PhotoStage Slideshow Producer is a video slideshow creator using photos , videos , and music . [ 3 ] [ 4 ] [ 5 ] [ 6 ] It can also be used as an organizational and basic editing tool. [ 7 ] [ 8 ]
A slideshow can be made by importing the desired photos. [ 9 ] [ 10 ] The software includes a timeline thumbnail with duration and transition types for each photo. [ 11 ] [ 10 ] Text tool can be used to add one or two lines of text to the slides. [ 11 ] [ 10 ]
Whilst using the software, one can add their own recorded narration or soundtrack by accessing the NCH Sound Effect Library. [ 11 ] [ 12 ] The slideshow file is exportable in fifteen formats. [ 13 ]
The software has been reviewed by Top Ten Reviews , Softonic , and others. [ 13 ] [ 14 ]
This software article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/PhotoStage |
Photoacids are molecules that become more acidic upon absorption of light. Either the light causes a photodissociation to produce a strong acid , or the light causes photoassociation (such as a ring forming reaction ) that leads to an increased acidity and dissociation of a proton.
There are two main types of molecules that release protons upon illumination: photoacid generators (PAGs) and photoacids (PAHs). PAGs undergo proton photodissociation irreversibly, while PAHs are molecules that undergo proton photodissociation and thermal reassociation. [ 1 ] In this latter case, the excited state is strongly acidic, but reversible.
An example due to photodissociation is triphenylsulfonium triflate. This colourless salt consists of a sulfonium cation and the triflate anion. Many related salts are known including those with other noncoordinating anions and those with diverse substituents on the phenyl rings.
The triphenylsulfonium salts absorb at a wavelength of 233 nm, which induces a dissociation of one of the three phenyl rings. This dissociated phenyl radical then re-combines with remaining diphenylsulfonium to liberate an H + ion. [ 2 ] The second reaction is irreversible, and therefore the entire process is irreversible, so triphenylsulfonium triflate is a photoacid generator. The ultimate products are thus a neutral organic sulfide and the strong acid triflic acid .
Applications of these photoacids include photolithography [ 3 ] and catalysis of the polymerization of epoxides .
An example of a photoacid which undergoes excited-state proton transfer without prior photolysis is the fluorescent dye pyranine (8-hydroxy-1,3,6-pyrenetrisulfonate or HPTS). [ 4 ]
The Förster cycle was proposed by Theodor Förster [ 5 ] and combines knowledge of the ground state acid dissociation constant (pK a ), absorption, and fluorescence spectra to predict the pK a in the excited state of a photoacid.
The name photoacid can be abbreviated PAH, where the H does not stand for a word starting with H, but rather for a hydrogen atom which is lost when the molecule reacts as a Brønsted acid . This use of PAH should not be confused with other meanings of PAH in chemistry and in medicine . | https://en.wikipedia.org/wiki/Photoacid |
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