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to infer the what best medicine to administer to the patient is based on their medical history, such as if they have a certain cancer or other conditions, simply by examining the natural language used in the patient's medical records. This would allow the first responders to quickly and efficiently search for medicine without having worry about the patient’s medical history themselves, as the semantic reasoner would already have analyzed this data and found solutions. In general, this illustrates the incredible strength of using semantic data mining and ontologies. They allow for quicker and more efficient data extraction on the user side, as the user has fewer variables to account for, since the semantically pre-processed data and ontology built for the data have already accounted for many of these variables. However, there are some drawbacks to this approach. Namely, it requires a high amount of computational power and complexity, even with relatively small data sets. This could result in higher costs and increased difficulties in building and maintaining semantic data processing systems. This can be mitigated somewhat if the data set is already well organized and formatted, but even then, the complexity is still higher when compared to standard data processing. Below is a simple a diagram combining some of the processes, in particular semantic data mining and their use in ontology. The diagram depicts a data set being broken up into two parts: the characteristics of its domain, or domain knowledge, and then the actual acquired data. The domain characteristics are then processed to become user understood domain knowledge that can be applied to the data. Meanwhile, the data set is processed and stored so that the domain knowledge can applied to it, so that the process may continue. This application forms the ontology. From there, the ontology can
|
{
"page_id": 12386904,
"source": null,
"title": "Data preprocessing"
}
|
be used to analyze data and process results. Fuzzy preprocessing is another, more advanced technique for solving complex problems. Fuzzy preprocessing and fuzzy data mining make use of fuzzy sets. These data sets are composed of two elements: a set and a membership function for the set which comprises 0 and 1. Fuzzy preprocessing uses this fuzzy data set to ground numerical values with linguistic information. Raw data is then transformed into natural language. Ultimately, fuzzy data mining's goal is to help deal with inexact information, such as an incomplete database. Currently fuzzy preprocessing, as well as other fuzzy based data mining techniques see frequent use with neural networks and artificial intelligence. == References == == External links == Online Data Processing Compendium Data preprocessing in predictive data mining. Knowledge Eng. Review 34: e1 (2019)
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{
"page_id": 12386904,
"source": null,
"title": "Data preprocessing"
}
|
The lower flammability limit (LFL), usually expressed in volume per cent, is the lower end of the concentration range over which a flammable mixture of gas or vapour in air can be ignited at a given temperature and pressure. The flammability range is delineated by the upper and lower flammability limits. Outside this range of air/vapor mixtures, the mixture cannot be ignited at that temperature and pressure. The LFL decreases with increasing temperature; thus, a mixture that is below its LFL at a given temperature may be ignitable if heated sufficiently. For liquids, the LFL is typically close to the saturated vapor concentration at the flash point, however, due to differences in the liquid properties, the relationship of LFL to flash point (which is also dependent on the test apparatus) is not fixed and some spread in the data usually exists. The L F L m i x {\displaystyle LFL_{mix}} of a mixture can be evaluated using the Le Chatelier mixing rule if the L F L i {\displaystyle LFL_{i}} of the components i {\displaystyle i} are known: L F L m i x = 1 ∑ x i L F L i {\displaystyle LFL_{mix}={\frac {1}{\sum {\frac {x_{i}}{LFL_{i}}}}}} Where L F L m i x {\displaystyle LFL_{mix}} is the lower flammability of the mixture, L F L i {\displaystyle LFL_{i}} is the lower flammability of the i {\displaystyle i} -th component of the mixture, and x i {\displaystyle x_{i}} is the molar fraction of the i {\displaystyle i} -th component of the mixture. == See also == Flash point Minimum ignition energy Stoichiometry == References ==
|
{
"page_id": 13501019,
"source": null,
"title": "Lower flammability limit"
}
|
In molecular biology mir-153 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. == See also == MicroRNA == References == == Further reading == == External links == Page for mir-153 microRNA precursor family at Rfam
|
{
"page_id": 36373084,
"source": null,
"title": "Mir-153 microRNA precursor family"
}
|
Bite force quotient (BFQ) is a numerical value commonly used to represent the bite force of an animal adjusted for its body mass, while also taking factors like the allometry effects. The BFQ is calculated as the regression of the quotient of an animal's bite force in newtons divided by its body mass in kilograms. The BFQ was first applied by Wroe et al. (2005) in a paper comparing bite forces, body masses and prey size in a range of living and extinct mammalian carnivores, later expanded on by Christiansen & Wroe (2007). Results showed that predators that take relatively large prey have large bite forces for their size, i.e., once adjusted for allometry. The authors predicted bite forces using beam theory, based on the directly proportional relationship between muscle cross-sectional area and the maximal force muscles can generate. Because body mass is proportional to volume while muscle force is proportional to area, the relationship between bite force and body mass is allometric. All else being equal, it would be expected to follow a 2/3 power rule. Consequently, small species would be expected to bite harder for their size than large species if a simple ratio of bite force to body mass is used, resulting in bias. Applying the BFQ normalizes the data allowing for fair comparison between species of different sizes in much the same way as an encephalization quotient normalizes data for brain size to body mass comparisons. It is a means for comparison, not an indicator of absolute bite force. In short, if an animal or species has a high BFQ this indicates that it bites hard for its size after controlling for allometry. Hite et al., who include data from the widest range of living mammals of any bite force regression to date, produce from their
|
{
"page_id": 28377703,
"source": null,
"title": "Bite force quotient"
}
|
regression the BFQ equation: B F Q = 100 ( B F 10 0.5703 ( log 10 B M ) + 0.1096 ) {\displaystyle BFQ=100\left({\frac {BF}{10^{0.5703(\log _{10}BM)+0.1096}}}\right)} Or equivalently B F Q = 77.7 ( B F B M 0.5703 ) {\displaystyle BFQ=77.7\left({\frac {BF}{BM^{0.5703}}}\right)} where BF = Bite Force (N), and BM = Body Mass (g) == Carnivore BFQs == Table sources (unless otherwise stated): == Sex Differences for BFQ in Canids == In a 2020 paper, the results of an estimation of the BFQ of various canid species separated by sex were published. Below there is a table with the BFQ averaged from the BFQ for each espécimen of each sex and for each species. BFQ coming from a single specimen for each sex in a given species will be marked with an asterisk. == References ==
|
{
"page_id": 28377703,
"source": null,
"title": "Bite force quotient"
}
|
Eobard Thawne, also known as the Reverse-Flash and Professor Zoom, is a supervillain appearing in American comic books published by DC Comics. Created by John Broome and Carmine Infantino, the character first appeared in The Flash #139 (August 31st 1963) and has since endured as the archenemy of Barry Allen / The Flash. Eobard Thawne, as introduced by name in The Flash #153, is the first and most well-known character to assume the Reverse-Flash mantle, and is additionally a descendant of Malcolm Thawne and ancestor of Bart Allen, Thaddeus Thawne and Owen Mercer. In his comic book appearances, Professor Eobard Thawne is depicted as a scientist from the 25th century who originally idolized the Flash. He replicated the accident that gave the Flash his powers, but was driven insane and became obsessed with ruining the Flash's life upon learning that he was destined to become his greatest enemy–the Reverse-Flash. Fueled by jealousy and hatred, Thawne travels throughout time to torment and destroy the Flash's life. He has been established as one of the fastest speedsters in the DC Universe. Thawne has frequently died, but has made multiple returns through resurrections and time travel. The character has been adapted in various media incarnations, having been portrayed in live-action by Tom Cavanagh and Matt Letscher in The CW's Arrowverse franchise, most notably in the television series The Flash. Eobard Thawne was born in 2151. == Fictional character biography == Eobard Thawne found a time capsule in the 25th century containing a costume of the Flash and with a Tachyon device amplified the suit's speed energy, giving himself speedster abilities. Reversing the costume's colors, he adopted the moniker of "Professor Zoom the Reverse-Flash" and went on a crime spree. However, the time capsule also contained an atomic clock which, due to the effects
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"title": "Eobard Thawne"
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of time travel, altered into an atomic bomb. To prevent its detonation, Barry Allen pursued and defeated Zoom, hoping he knew where the clock was. He did not, but Barry later found the clock, detonated it safely, and destroyed Thawne's costume. Blaming the Flash for his defeat, Thawne became obsessed with "replacing" Barry and traveled back in time to exact his revenge. Iris West rejected his romantic pursuits, so Thawne killed Iris. After Barry had found love again, Thawne threatened to kill Fiona Webb (Barry's fiancée) on their wedding day. Fearful that history was repeating itself, Barry killed Thawne by breaking his neck. === Post-Crisis and Zero Hour origin === Prior to discovering the time capsule containing the Flash's costume, the Post-Crisis extended origin storyline "The Return of Barry Allen" revealed that Thawne was once a scientist obsessed with his idol, even undergoing cosmetic surgery to resemble his hero. Obtaining the Cosmic Treadmill from an antique shop, Thawne gained all of the Flash's powers after replicating the electrochemical accident behind the Flash. Seeking to use the Cosmic Treadmill to travel back in time and meet his idol, Thawne arrived at the Flash Museum several years after Barry's death, discovering that he was destined to be "Professor Zoom, the Reverse-Flash" and die at his idol's hands. As a result, the unstable Thawne convinced himself that he was Barry Allen (based on his intimate knowledge of his idol's life from his reading of an as-yet-unpublished biography) and subsequently attacked Central City for "forgetting him". Wally West ultimately tricked Thawne into returning to the 25th century with no memory of the incident. Despite this, Thawne still managed to bring the remains of his older self's costume with him, cluing him further into his destiny. After the events of Zero Hour: Crisis in Time!,
|
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"title": "Eobard Thawne"
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it is revealed that Malcolm Thawne is his ancestor and Barry's long-lost twin brother, meaning that Barry is Eobard Thawne's great-uncle. === The Flash: Rebirth === In 2009, Thawne was re-imagined as a major villain in the DC Universe by writer Geoff Johns in The Flash: Rebirth. His resurrection is foreshadowed to occur in a near-future event. It is later revealed that Thawne's recreation of the accident behind Barry's powers made Thawne able to lure Barry out of the Speed Force during Final Crisis and temporarily turn his nemesis into the Black Flash. When Thawne reappears, he murders the revived Johnny Quick, before proceeding to trap Barry and the revived Max Mercury inside the negative Speed Force. Thawne then attempts to kill Wally's children through their Speed Force connection in front of Linda Park-West, only to be stopped by Jay Garrick and Bart Allen. Thawne defeats Jay and prepares to kill Bart, but Barry, Max, Wally, Jesse Quick and Impulse arrive to prevent the villain from doing so. In the ensuing fight, Thawne reveals that he is responsible for every tragedy that has occurred in Barry's life, including Nora Allen's death. Thawne then decides to destroy everything Barry holds dear by killing Iris before the two even met. As Barry chases after Thawne, Wally joins Barry in the time barrier. The two Flashes reach Thawne and in doing so, they become the lightning bolt that turns Barry into a speedster as they are able to stop Thawne from killing Iris. The two Flashes push Thawne back through time, showing his past and future while the two return to the present, where the Justice League, the Justice Society, and the Outsiders have built a device originally intended to disconnect Barry from the Speed Force as the Black Flash. Barry tosses Thawne
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
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in and Jay activates the device, severing his connection to the negative Speed Force. As the Flashes tie him up to stop him from running, Iris discovers Thawne's weapon back in the past, which Iris keeps. In the present, he is imprisoned in Iron Heights. Hunter Zolomon speaks to him, saying they can help each other be better. In Gorilla City, one of the apes warns that he has done something horrible to their jungles, but just what he has done is something even they do not know. === Blackest Night === In the 2009–2010 storyline "Blackest Night", the Pre-Crisis version of Thawne's broken-necked corpse is reanimated as a member of the Black Lantern Corps. The black power ring downloaded the corpse's memories, resulting in him not knowing of Barry's death and resurrection. Declaring himself the "Black Flash", he hunts down and attacks Barry who manages to elude him for the moment. When the Black Lantern Rogues attack Iron Heights, the living Thawne is encountered and the Black Lanterns' rings strangely malfunction, displaying a strange symbol. When Thawne's corpse approaches his living counterpart, he stops moving and is then frozen by Captain Cold's "cold grenade". Thawne's corpse is brought back to life by the white light of creation, and manages to escape. In the follow-up "Brightest Day" storyline, the present Professor Zoom is still imprisoned in Iron Heights. When Deadman activates the White Power Battery, the Entity speaks to the 12 heroes and villains resurrected at the climax of the "Blackest Night" and tells each of them of their mission that must be accomplished to restore 'life' to the universe and prevent the Blackest Night from ever reoccurring. Thawne becomes the first to inadvertently fulfill his mission, which occurred in the events of The Flash: Rebirth when he freed Allen
|
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"page_id": 47972968,
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"title": "Eobard Thawne"
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from the Speed Force following the resurrection. The Entity proclaims Thawne has completed his task and his life is restored to him, later revealing that Thawne (having fulfilled his task) is now fully purged of all trace remnants of his Black Lantern ties – both present and future. Thawne is released from Iron Heights by Captain Boomerang who had hoped to better understand his version of the Entity's message. Thawne does not answer him directly, giving a cryptic response and eventually escaping as Captain Boomerang is confronted by the rest of the Rogues. === Post-Infinite Crisis origin === Thawne uses his powers to completely rewrite his own history; he erases his younger brother from existence and kills his parents when they try to interfere with his research. Thawne later falls in love with Rose, a reporter who had been hired to interview him, thus his future self wipes all of the reporter's romantic interests from existence. After finding out his would-be love interest did not return his affections, Thawne's future self traumatized the reporter as a child, causing the woman to be mute and institutionalized so that they never met each other. He later had his younger self find the time capsule containing his idol's costume to make himself the Flash of the 25th century. He sheds a tear as his altered past self runs past him while saying "It won't last long. You will never find love. You will never be the Flash. Barry Allen destroyed my future. It's time I destroyed his.". === Flashpoint === In the 2011 Flashpoint storyline, a new timeline is created through the alteration of history. Thawne reveals that his body is permanently connected to the Speed Force, enabling him to create a negative version, with which he escaped prison. He was unable to
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
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alter Barry's transformation into a speedster, however, as that would effectively erase himself from existence. Instead, Thawne decides to ruin his nemesis's life during Barry's childhood, killing Nora Allen. Thawne later reveals that the Flashpoint timeline was created when Barry went back in time to stop him from killing Nora. After Thawne is killed by this reality's Batman with a sword stab through the chest, Barry travels back in time to stop Barry's younger self from altering history but instead, under Pandora's manipulations, a third, new timeline is created, in which DC Comics' continuity takes place from 2011 onward. === DC Rebirth origin === Thawne's origin is revised once again in the DC Rebirth relaunch. An only child when his parents died in an accident, Thawne grew up obsessed with the Flash. After finding a time capsule with the speedster's costume, he uses traces of the Speed Force in it to turn himself into a version of the Flash. Due to a lack of threats in the 25th century, Thawne creates his own by endangering people, before "saving" them. He is overjoyed when Barry travels to his time and teaches him new tricks, but this deceit is soon found out. After Barry defeats him and has him arrested, Thawne promises to rehabilitate himself, to that end undergoing therapy and being a professor. He also eventually becomes the curator of the Flash Museum. Seeking to show Barry how much he's changed and be a partner, Thawne travels to the past. However, he is enraged after he witnesses Barry give Wally a talk on how "every second is a gift", similar to one that Barry gave him, and realises that he wasn't treated specially by Barry. Still seeking to spend time with Barry and be a friend, Thawne becomes the Reverse-Flash, vowing
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
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to making Barry's life a living hell until his nemesis learns to "make time" for him. === The Button === Leading up to the 2017 The Button crossover, Thawne returns with his Pre-New 52 memories restored after a mysterious wave of energy strikes his alternate self, and he recalls being killed by Thomas Wayne during Flashpoint. Seeking revenge, Thawne attacks Bruce Wayne in the Batcave and destroys Thomas's letter. Thawne brutally beats and verbally taunts Bruce before picking up the Comedian's smiley-face pin, which teleports him away to an unknown location. Thawne is then teleported back to the Batcave, having been bathed in radiation by a mysterious entity. As he collapses, Thawne says "God...I saw...God." Batman and Barry later come across Thawne in possession of the Button shortly before his apparent death, and follow him in an attempt to prevent it. As he follows the traces leading to the entity, Thawne muses that he may go back in time to raise his nemesis as a "family friend" after killing Nora, but is killed by Doctor Manhattan and teleported back to the Batcave. In the immediate aftermath of The Button, Thawne's corpse is taken to S.T.A.R. Labs, but he is resurrected via his connection to the Negative Speed Force and returns to the future, to examine the difference between the pre and post-Flashpoint timelines. He is present at Iris's house when Iris arrives with Wallace West, who Thawne brutally beats and denounces as a fake, before kidnapping Iris and bringing her to the 25th century. Barry arrives and is quickly beaten by Thawne, who reveals his identity as the Flash to Iris. Thawne subsequently shows the couple's future and tricks Barry into being trapped in the Negative Speed Force, but his nemesis gets connected to it and escapes. The pleased Thawne
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
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implores Barry to "ditch the loser sidekicks" and become his friend and partner, but his nemesis refuses and strips him of his speed. Nevertheless, Thawne vows to regain his powers and keep coming back to torment Barry, before being killed by Iris with a vaporisation gun. === Flash War and return to Flashpoint === In the 2018 event Flash War, Zolomon sends the Renegades to arrest Iris for Thawne's death, as part of a plan to instigate a conflict between Barry and Wally. It is revealed that, after being freed from prison by Captain Boomerang in Brightest Day, Thawne broke Zolomon out of prison and took him to the 25th Century, accepting his offer to work together. The pair secretly took over the Temporal Courts and formed the Renegades, but eventually had a falling out over a difference in motives, culminating in Thawne returning to the past. Thawne's repeated deaths infuriated Zolomon, triggering a change in his own motives. Zolomon eventually discovers that Thawne himself was responsible for his transformation into his successor Zoom, with Thawne having given the Clown the gun with which he killed Zolomon's father-in-law and changed the course of Zolomon's history. It is later revealed that Thawne pulled Thomas out of the Flashpoint timeline just as Manhattan erased it, to torment Thomas with the reality where Bruce is Batman. Thawne is briefly resurrected again in the 2022 storyline Flashpoint Beyond, when Bruce restores the Flashpoint timeline. Thawne seeks out Thomas, who had also been sent back to that timeline, but is murdered by Martha Wayne / Joker shortly afterwards. == Powers and abilities == Eobard Thawne already possessed genius-level intellect by the standards of the 25th Century even prior to gaining his metahuman abilities, making him possibly one of the smartest individuals when in the 21st
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
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century. The Flash: Rebirth revealed that duplicating the accident behind Barry Allen's powers corrupted the Speed Force which created a negative version. The Reverse-Flash is therefore able to travel at superhuman speeds faster than the speed of light, deliver blows of extreme force by hitting the victim hundreds of times a second, run on water, generate vacuums, create afterimages ("speed mirages") of himself, and vibrate his molecules to pass through solid objects. Unlike original Speed Force users, Thawne has the ability to travel through and manipulate time, being able to drastically alter history and completely erase people from existence (other speedsters cannot change the past without dramatic consequences). Thawne developed numerous new powers in the events leading up to Flashpoint, including the ability to cross over to other dimensions, create shock waves across time and space at the snap of his fingers, absorb another's memories via physical contact, and alter the age of anyone or anything. Thawne has also displayed superhuman strength, as well as electrokinetic abilities. The presence of his lightning is able to disrupt and fry nearby electronics, in addition to allowing him to manipulate magnetism. The events of Flashpoint turned him into a "living paradox", making him immune to timeline alterations and unable to be erased from existence. In the DC Rebirth relaunch, Thawne also gains the abilities to possess others, by phasing into their bodies, and to hypnotize others, by whispering at hyperspeed to implant subconscious suggestions into their minds. == Other versions == Several alternate universe variants of Eobard Thawne appear in Impulse #35: one who became a scientific advisor to dictator Julian Tremain, one who joined a rebellion against Tremain, and one who was a gorilla in a modern society identical to that of ancient Egypt. An alternate universe variant of Eobard Thawne appears
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
}
|
in The New 52. This version gained the ability to manipulate time after being struck by lightning. Believing himself to have been "chosen" by the Speed Force as the Flash's replacement, Thawne dons a costume similar to the hero's and begins to terrorize the Gem Cities as Zoom. An alternate universe variant of Eobard Thawne who became the leader of the Legion of Zoom appears in Finish Line. After Barry infuses Zoom with Speed Force energy, he rewrites history so that the latter never became a villain and is instead the curator of the Flash Museum. An alternate universe variant of Zoom from the Dark Multiverse appears in Tales from the Dark Multiverse. == In other media == === Television === Eobard Thawne / Professor Zoom appears in the Batman: The Brave and the Bold episode "Requiem for a Scarlet Speedster!", voiced by John Wesley Shipp. Eobard Thawne / Reverse-Flash appears in series set in The CW's Arrowverse, with Matt Letscher portraying his original likeness and Tom Cavanagh portraying him in the form of Harrison Wells. Introduced and featured most prominently in The Flash, Thawne makes further appearances in the spin-off series Legends of Tomorrow and the crossover events "Crisis on Earth-X" and "Elseworlds". Eobard Thawne / Professor Zoom appears in Robot Chicken, voiced by Seth Green and Tom Cavanagh. Thawne also appears in Robot Chicken DC Comics Special 2: Villains in Paradise and Robot Chicken DC Comics Special III: Magical Friendship, voiced by Matthew Senreich in the former and with no dialogue in the latter. This version is a member of the Legion of Doom. Eobard Thawne / Reverse-Flash makes non-speaking cameo appearances in Harley Quinn as a member of the Legion of Doom. === Film === Eobard Thawne / Professor Zoom appears in films set in the DC
|
{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
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Animated Movie Universe, voiced by C. Thomas Howell. First appearing in Justice League: The Flashpoint Paradox, he attempts to kill the Flash via the Rogues, but is thwarted by his nemesis and the Justice League. Despite this, Zoom taunts the Flash over Nora Allen's death before Superman takes the former to prison. After the Flash creates the "Flashpoint" timeline and fails to restore the original, Zoom returns to reveal that as long as he is alive, the Flash cannot draw enough energy from the Speed Force to travel through time again. However, Batman shoots Zoom, allowing the Flash to undo the "Flashpoint" timeline. In Suicide Squad: Hell to Pay, immediately after Batman shot him, Zoom drew energy from the Speed Force to slow down the moment of his death and survive into the new timeline the Flash created. As this limited the use of his speed, Thawne recruits Silver Banshee, Blockbuster, and Killer Frost to help him acquire a "Get Out of Hell Free" card so he can cheat death, only to encounter the Suicide Squad, who defeat him and send him to die in the "Flashpoint" timeline. Eobard Thawne / Reverse-Flash appears in Lego DC Comics Super Heroes: The Flash, voiced by Dwight Schultz. Eobard Thawne / Reverse-Flash makes a cameo appearance in Injustice. === Video games === Eobard Thawne / Professor Zoom appears in DC Universe Online. Eobard Thawne / Reverse-Flash, based on Tom Cavanagh's portrayal, appears as a playable character in the mobile version of Injustice: Gods Among Us. Eobard Thawne / Professor Zoom appears as a character summon in Scribblenauts Unmasked: A DC Comics Adventure. Eobard Thawne / Reverse-Flash appears as an unlockable playable character in Lego Batman 3: Beyond Gotham, voiced by Liam O'Brien. Eobard Thawne / Reverse-Flash appears as a "premier skin" for the
|
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"page_id": 47972968,
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"title": "Eobard Thawne"
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Flash in Injustice 2, voiced again by Liam O'Brien. This version was stranded in the 21st century after being trapped in a paradox due to the Regime killing one of his ancestors, leading to him joining Gorilla Grodd's Society to seek revenge on the Flash, who previously supported the Regime. Eobard Thawne / Reverse-Flash appears in Lego DC Super-Villains, voiced again by C. Thomas Howell. This version is a member of the Legion of Doom. === Miscellaneous === Eobard Thawne / Reverse-Flash appears in Justice League Adventures #6. Eobard Thawne / Reverse-Flash appears in the Death Battle! episode "Goku Black VS Reverse-Flash". == Reception == IGN ranked Eobard Thawne as the 31st Greatest Comic Book Villain Of All Time in 2009 and #2 on their Top 5 Flash Villains list in 2015. == References == == External links == Professor Zoom at the DC Database Reverse-Flash at dccomics.com Professor Zoom at Those Who Ride the Lightning Professor Zoom at the DCU Guide Archived 2014-05-17 at the Wayback Machine
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{
"page_id": 47972968,
"source": null,
"title": "Eobard Thawne"
}
|
CIDNP (chemically induced dynamic nuclear polarization), often pronounced like "kidnip", is a nuclear magnetic resonance (NMR) technique that is used to study chemical reactions that involve radicals. It detects the non-Boltzmann (non-thermal) nuclear spin state distribution produced in these reactions as enhanced absorption or emission signals. CIDNP was discovered in 1967 by Bargon and Fischer, and, independently, by Ward and Lawler. Early theories were based on dynamic nuclear polarisation (hence the name) using the Overhauser effect. The subsequent experiments, however, have found that in many cases DNP fails to explain CIDNP polarization phase. In 1969 an alternative explanation which relies on the nuclear spins affecting the probability of a radical pair recombining or separating. It is related to chemically induced dynamic electron polarization (CIDEP) insofar as the radical-pair mechanism explains both phenomena. == Concept and experimental set-up == The effect is detected by NMR spectroscopy, usually using 1H NMR spectrum, as enhanced absorption or emission signals ("negative peaks"). The effect arises when unpaired electrons (radicals) are generated during a chemical reaction involving heat or light within the NMR tube. The magnetic field in the spectrometer interacts with the magnetic fields that are caused by the spins of the protons. The two spins of protons produce two slightly different energy levels. In normal conditions, slightly more nuclei, about 10 parts in a million are found in the lower energy level. In contrast, CIDNP produces greatly imbalanced populations, with far greater numbers of spins in upper energy level in some products of the reaction and greater numbers in the lower energy level in other products. The spectrometer uses radio frequencies to detect these differences. == Radical pair mechanism == The radical pair mechanism is currently accepted as the most common cause of CIDNP. This theory was proposed by Closs, and, independently, by
|
{
"page_id": 1901162,
"source": null,
"title": "CIDNP"
}
|
Kaptein and Oosterhoff. There are, however, exceptions, and the DNP mechanism was found to be operational, for example, in many fluorine-containing radicals. The chemical bond is a pair of electrons with opposite spins. Photochemical reactions or heat can cause an electron in the bond to change its spin. The electrons are now unpaired, in what is known as a triplet state, and the bond is broken. The orientation of some of the nuclear spins will favour some unpaired electrons changing their spins and so revert to the normal pairs as chemical bonds. This quantum interaction is known as spin–orbit coupling. Other nuclear spins will exert a different influence on the triplet pairs, giving the radical pairs more time to separate and react with other molecules. Consequently, the products of recombination will have different distributions of nuclear spins from the products produced by separated radicals. == Typical photochemical reaction == The generation of CIDNP in a typical photochemical system (target + photosensitizer, flavin in this example) is a cyclic photochemical process shown schematically in Figure 1. The chain of reactions is initiated by a blue light photon, which excites the flavin mononucleotide (FMN) photosensitizer to the singlet excited state. The fluorescence quantum yield of this state is rather low, and approximately half of the molecules undergo intersystem crossing into the long-lived triplet state. Triplet FMN has a remarkable electron affinity. If a molecule with a low ionization potential (e.g. phenols, polyaromatics) is present in the system, the diffusion-limited electron transfer reaction forms a spin-correlated triplet electron transfer state – a radical pair. The kinetics are complicated and may involve multiple protonations and deprotonations, and hence exhibit pH dependence. The radical pair may either cross over to a singlet electron state and then recombine, or separate and perish in side reactions. The
|
{
"page_id": 1901162,
"source": null,
"title": "CIDNP"
}
|
relative probability of these two pathways for a given radical pair depends on the nuclear spin state and leads to the nuclear spin state sorting and observable nuclear polarization. == Applications == Detected as enhanced absorptive or emissive signals in the NMR spectra of the reaction products, CIDNP has been exploited for the last 30 years to characterise transient free radicals and their reaction mechanisms. In certain cases, CIDNP also offers the possibility of large improvements in NMR sensitivity. The principal application of this photo-CIDNP technique, as devised by Kaptein in 1978, has been to proteins in which the aromatic amino acid residues histidine, tryptophan and tyrosine can be polarized using flavins or other aza-aromatics as photosensitisers. The key feature of the method is that only solvent accessible histidine, tryptophan and tyrosine residues can undergo the radical pair reactions that result in nuclear polarization. Photo-CIDNP has thus been used to probe the surface structure of proteins, both in native and partially folded states, and their interactions with molecules that modify the accessibility of the reactive side chains. Although usually observed in liquids, the photo-CIDNP effect has also been detected in solid state, for example on 13C and 15N nuclei in photosynthetic reaction centres, where significant nuclear polarization can accumulate as a result of spin selection processes in the electron transfer reactions. == See also == Dynamic nuclear polarisation Electron paramagnetic resonance Magnetoreception – a sense in birds that appears to rely on a radical pair mechanism == References == == Further reading == Muus, L. T.; Atkins, P.W.; McLauchlan, K.A.; Pedersen, J. B., eds. (1977). Chemically Induced Magnetic Polarisation. Dordrecht: D. Reidel. Goez, Martin (2007). "Photochemically Induced Dynamic Nuclear Polarization". Advances in Photochemistry. pp. 63–163. doi:10.1002/9780470133545.ch2. ISBN 9780470133545. Kaptein, Robert (1982). "Photo-CIDNP Studies of Proteins". Biological Magnetic Resonance. pp. 145–191.
|
{
"page_id": 1901162,
"source": null,
"title": "CIDNP"
}
|
doi:10.1007/978-1-4615-6540-6_3. ISBN 978-1-4615-6542-0. Kaptein, R.; Dijkstra, K.; Nicolay, K. (1978). "Laser photo-CIDNP as a surface probe for proteins in solution". Nature. 274 (5668): 293–294. Bibcode:1978Natur.274..293K. doi:10.1038/274293a0. PMID 683312. S2CID 4162279. Hore, J.; Broadhurst, R.W. (1993). "Photo-CIDNP of biopolymers". Progress in Nuclear Magnetic Resonance Spectroscopy. 25 (4): 345–402. doi:10.1016/0079-6565(93)80002-B. Kuprov, I.; Hore, P.J. (2004). "Chemically amplified 19F–1H nuclear Overhauser effects". Journal of Magnetic Resonance. 168 (1): 1–7. Bibcode:2004JMagR.168....1K. doi:10.1016/j.jmr.2004.01.011. PMID 15082243. Prakash, Shipra; Alia; Gast, Peter; De Groot, Huub J. M.; Matysik, Jörg; Jeschke, Gunnar (2006). "Photo-CIDNP MAS NMR in Intact Cells ofRhodobactersphaeroidesR26: Molecular and Atomic Resolution at Nanomolar Concentration". Journal of the American Chemical Society. 128 (39): 12794–12799. doi:10.1021/ja0623616. hdl:1887/3455644. PMID 17002374.
|
{
"page_id": 1901162,
"source": null,
"title": "CIDNP"
}
|
In biochemistry, dephosphorylation is the removal of a phosphate (PO3−4) group from an organic compound by hydrolysis. It is a reversible post-translational modification. Dephosphorylation and its counterpart, phosphorylation, activate and deactivate enzymes by detaching or attaching phosphoric esters and anhydrides. A notable occurrence of dephosphorylation is the conversion of ATP to ADP and inorganic phosphate. Dephosphorylation employs a type of hydrolytic enzyme, or hydrolase, which cleaves ester bonds. The prominent hydrolase subclass used in dephosphorylation is phosphatase, which removes phosphate groups by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl (–OH) group. The reversible phosphorylation-dephosphorylation reaction occurs in every physiological process, making proper function of protein phosphatases necessary for organism viability. Because protein dephosphorylation is a key process involved in cell signalling, protein phosphatases are implicated in conditions such as cardiac disease, diabetes, and Alzheimer's disease. == History == The discovery of dephosphorylation came from a series of experiments examining the enzyme phosphorylase isolated from rabbit skeletal muscle. In 1955, Edwin Krebs and Edmond Fischer used radiolabeled ATP to determine that phosphate is added to the serine residue of phosphorylase to convert it from its b to a form via phosphorylation. Subsequently, Krebs and Fischer showed that this phosphorylation is part of a kinase cascade. Finally, after purifying the phosphorylated form of the enzyme, phosphorylase a, from rabbit liver, ion exchange chromatography was used to identify phosphoprotein phosphatase I and II. Since the discovery of these dephosphorylating proteins, the reversible nature of phosphorylation and dephosphorylation has been associated with a broad range of functional proteins, primarily enzymatic, but also including nonenzymatic proteins. Edwin Krebs and Edmond Fischer won the 1992 Nobel Prize in Physiology or Medicine for the discovery of reversible protein phosphorylation. == Function == Phosphorylation and dephosphorylation of hydroxyl groups belonging
|
{
"page_id": 1704568,
"source": null,
"title": "Dephosphorylation"
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|
to neutral but polar amino acids such as serine, threonine, and tyrosine within specific target proteins is a fundamental part of the regulation of every physiologic process. Phosphorylation involves the covalent modification of the hydroxyl with a phosphate group through the nucleophilic attack of the alpha phosphate in ATP by the oxygen in the hydroxyl. Dephosphorylation involves removal of the phosphate group through a hydration reaction by addition of a molecule of water and release of the original phosphate group, regenerating the hydroxyl. Both processes are reversible and either mechanism can be used to activate or deactivate a protein. Phosphorylation of a protein produces many biochemical effects, such as changing its conformation to alter its binding to a specific ligand to increase or reduce its activity. Phosphorylation and dephosphorylation can be used on all types of substrates, such as structural proteins, enzymes, membrane channels, signaling molecules, and other kinases and phosphatases. The sum of these processes is referred to as phosphoregulation. The deregulation of phosphorylation can lead to disease. === Post-translational modification === During the synthesis of proteins, polypeptide chains, which are created by ribosomes translating mRNA, must be processed before assuming a mature conformation. The dephosphorylation of proteins is a mechanism for modifying behavior of a protein, often by activating or inactivating an enzyme. Components of the protein synthesis apparatus also undergo phosphorylation and dephosphorylation and thus regulate the rates of protein synthesis. As part of posttranslational modifications, phosphate groups may be removed from serine, threonine, or tyrosine. As such, pathways of intracellular signal transduction depend on sequential phosphorylation and dephosphorylation of a wide variety of proteins. === ATP === ATP4− + H2O ⟶ ADP3− + HPO2−4 + H+ Adenosine triphosphate, or ATP, acts as a free energy "currency" in all living organisms. In a spontaneous dephosphorylation reaction 30.5
|
{
"page_id": 1704568,
"source": null,
"title": "Dephosphorylation"
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|
kJ/mol is released, which is harnessed to drive cellular reactions. Overall, nonspontaneous reactions coupled to the dephosphorylation of ATP are spontaneous, due to the negative free energy change of the coupled reaction. This is important in driving oxidative phosphorylation. ATP is dephosphorylated to ADP and inorganic phosphate. On the cellular level, the dephosphorylation of ATPases determines the flow of ions into and out of the cell. Proton pump inhibitors are a class of drug that acts directly on ATPases of the gastrointestinal tract. === Other reactions === Other molecules besides ATP undergo dephosphorylation as part of other biological systems. Different compounds produce different free energy changes as a result of dephosphorylation. Psilocybin also relies on dephosphorylation to be metabolized into psilocin and further eliminated. No information on psilocybin's effect on the change in free energy is currently available. === Photosystem II === The first protein complex of the photosynthesis component light-dependent reactions is referred to as photosystem II. The complex utilizes an enzyme to capture photons of light, providing the greater photosynthesis process with all of the electrons needed to produce ATP. Photosystem II is particularly temperature sensitive, and desphosphorylation has been implicated as a driver of plasticity in responding to varied temperature. Accelerated protein dephosphorylation in photosynthetic thylakoid membranes occurs at elevated temperatures, directly impacting the desphosphorylation of key proteins within the photosystem II complex. == Pathology == Excessive dephosphorylation of the membrane ATPases and proton pumps in the gastrointestinal tract leads to higher secretory rates of caustic peptic acids. These result in heartburn and esophagitis. In combination with Helicobacter pylori infection, peptic ulcer disease is caused by the elevated pH dephosphorylation elicits. The microtubule-associated protein tau is abnormally hyperphosphorylated when isolated from the brain of patients who suffer from Alzheimer's disease. This is due to the dysfunction of
|
{
"page_id": 1704568,
"source": null,
"title": "Dephosphorylation"
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|
dephosphorylation mechanisms at specific amino acids on the tau protein. Tau dephosphorylation is catalysed by protein phosphatase-2A and phosphatase-2B. Deficiency or modification of one or both proteins may be involved in abnormal phosphorylation of tau in Alzheimer's disease Dephosphorylation has also been linked to cardiac disease, particularly the alteration of actin-myosin interactions that are key for providing the underlying force of a heartbeat. Dephosphorylation is a key part of the myosin cycling kinetics that directly control the actin-myosin interactions. When the dephosphorylation process is interrupted, calcium dependent cardiac contraction is impaired or fully disabled. Research has also suggested that modifications to dephosphorylation impact physiological processes implicated in Diabetes mellitus. The kinetics of dephosphorylation of insulin receptor substrate-1/2, Akt, and ERK1/2, phosphoproteins are shown to be involved in insulin receptor signaling, and in vitro models demonstrate that changes to dephosphorylation kinetics impact upstream and downstream insulin stimulation. == Treatment == Inhibition of proton pumps significantly decreases the acidity of the gastrointestinal tract, reducing the symptoms of acid-related diseases. The resulting change in pH decreases survival of the bacteria H.pylori, a major cause of peptic ulcer disease. Once the proton pump inhibitor eradicates this bacteria within the gut, reversing erosive reflux. Treating heart disease has improved with the use of drugs that inhibit AMPK via dephosphorylation. In the treatment of diabetes, sulfonylurea drugs are able to stimulate dephosphorylation of the glucose transporter GLUT4, decreasing insulin resistance and increasing and glucose utilization. == Research applications == Dephosphorylation can play a key role in molecular biology, particularly cloning using restriction enzymes. The cut ends of a vector may re-ligate during a ligation step due to phosphorylation. By using a desphosphorylating phosphatase, re-ligation can be avoided. Alkaline phosphatases, which remove the phosphate group present at the 5′ terminus of a DNA molecule, are often sourced
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{
"page_id": 1704568,
"source": null,
"title": "Dephosphorylation"
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|
naturally, most commonly from calf intestine, and are abbreviated as CIP. == Underlying evolutionary forces == The natural selection power for dephosphorylation is less understood. A recent study has found that IRF9, which is from the interferon-regulatory factors family (IRFs), a critical family for anti-viral immune response, could be influenced by natural selection during Human species evolution. The positive selection has been found on the amino acid site Val129 (NP_006075.3:p.Ser129Val) of human IRF9. The ancestral state (Ser129) is conserved among mammals, while the novel state (Val129) was fixed before the "out-of-Africa" event ~ 500,000 years ago. This young amino acid (Val129) may serve as a dephosphorylation site of IRF9. The dephosphorylation may affect the immune activity of IRF9. == See also == Phosphorylation Phosphatase == References ==
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{
"page_id": 1704568,
"source": null,
"title": "Dephosphorylation"
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|
Algae (UK: AL-ghee, US: AL-jee; sg.: alga AL-gə) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, such as cyanobacteria, Chlorella, and diatoms, to multicellular macroalgae such as kelp or brown algae which may grow up to 50 metres (160 ft) in length. Most algae are aquatic organisms and lack many of the distinct cell and tissue types, such as stomata, xylem, and phloem that are found in land plants. The largest and most complex marine algae are called seaweeds. In contrast, the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and stoneworts. Algae that are carried passively by water are plankton, specifically phytoplankton. Algae constitute a polyphyletic group because they do not include a common ancestor, and although eukaryotic algae with chlorophyll-bearing plastids seem to have a single origin (from symbiogenesis with cyanobacteria), they were acquired in different ways. Green algae are a prominent example of algae that have primary chloroplasts derived from endosymbiont cyanobacteria. Diatoms and brown algae are examples of algae with secondary chloroplasts derived from endosymbiotic red algae, which they acquired via phagocytosis. Algae exhibit a wide range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction via spores. Algae lack the various structures that characterize plants (which evolved from freshwater green algae), such as the phyllids (leaf-like structures) and rhizoids of bryophytes (non-vascular plants), and the roots, leaves and other xylemic/phloemic organs found in tracheophytes (vascular plants). Most algae are autotrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy or phagotrophy. Some unicellular species of green algae,
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{
"page_id": 633,
"source": null,
"title": "Algae"
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|
many golden algae, euglenids, dinoflagellates, and other algae have become heterotrophs (also called colorless or apochlorotic algae), sometimes parasitic, relying entirely on external energy sources and have limited or no photosynthetic apparatus. Some other heterotrophic organisms, such as the apicomplexans, are also derived from cells whose ancestors possessed chlorophyllic plastids, but are not traditionally considered as algae. Algae have photosynthetic machinery ultimately derived from cyanobacteria that produce oxygen as a byproduct of splitting water molecules, unlike other organisms that conduct anoxygenic photosynthesis such as purple and green sulfur bacteria. Fossilized filamentous algae from the Vindhya basin have been dated to 1.6 to 1.7 billion years ago. Because of the wide range of types of algae, there is a correspondingly wide range of industrial and traditional applications in human society. Traditional seaweed farming practices have existed for thousands of years and have strong traditions in East Asian food cultures. More modern algaculture applications extend the food traditions for other applications, including cattle feed, using algae for bioremediation or pollution control, transforming sunlight into algae fuels or other chemicals used in industrial processes, and in medical and scientific applications. A 2020 review found that these applications of algae could play an important role in carbon sequestration to mitigate climate change while providing lucrative value-added products for global economies. == Etymology and study == The singular alga is the Latin word for 'seaweed' and retains that meaning in English. The etymology is obscure. Although some speculate that it is related to Latin algēre, 'be cold', no reason is known to associate seaweed with temperature. A more likely source is alliga, 'binding, entwining'. The Ancient Greek word for 'seaweed' was φῦκος (phŷkos), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, fūcus, meant primarily the
|
{
"page_id": 633,
"source": null,
"title": "Algae"
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|
cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך (pūk), 'paint' (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue. The study of algae is most commonly called phycology (from Greek phykos 'seaweed'); the term algology is falling out of use. == Description == The algae are a heterogeneous group of mostly photosynthetic organisms that produce oxygen and lack the reproductive features and structural complexity of land plants. This concept includes the cyanobacteria, which are prokaryotes, and all photosynthetic protists, which are eukaryotes. They contain chlorophyll a as their primary photosynthetic pigment, and generally inhabit aquatic environments. However, there are many exceptions to this definition. Many non-photosynthetic protists are included in the study of algae, such as the heterotrophic relatives of euglenophytes or the numerous species of colorless algae that have lost their chlorophyll during evolution (e.g., Prototheca). Some exceptional species of algae tolerate dry terrestrial habitats, such as soil, rocks, or caves hidden from light sources, although they still need enough moisture to become active. === Morphology === A range of algal morphologies is exhibited, and convergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellular thalli are the reds and browns, and some chlorophytes. Apical growth is constrained to subsets of these groups: the florideophyte reds, various browns, and the charophytes. The form of charophytes is quite different from those of reds and browns, because they have distinct nodes, separated by internode 'stems'; whorls of branches reminiscent of the horsetails occur at the nodes. Conceptacles are another polyphyletic trait; they appear in the coralline algae and the Hildenbrandiales, as well as
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{
"page_id": 633,
"source": null,
"title": "Algae"
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|
the browns. Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and nonmotile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the lifecycle of a species, are Colonial: small, regular groups of motile cells Capsoid: individual non-motile cells embedded in mucilage Coccoid: individual non-motile cells with cell walls Palmelloid: nonmotile cells embedded in mucilage Filamentous: a string of connected nonmotile cells, sometimes branching Parenchymatous: cells forming a thallus with partial differentiation of tissues In three lines, even higher levels of organization have been reached, with full tissue differentiation. These are the brown algae,—some of which may reach 50 m in length (kelps)—the red algae, and the green algae. The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The innovation that defines these nonalgal plants is the presence of female reproductive organs with protective cell layers that protect the zygote and developing embryo. Hence, the land plants are referred to as the Embryophytes. ==== Turfs ==== The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps, and they are usually less than 15 cm tall. Such a turf may consist of one or more species, and will generally cover an area in the order of a square metre or more. Some common characteristics are listed: Algae that form aggregations that have been described as turfs include diatoms, cyanobacteria, chlorophytes, phaeophytes and rhodophytes. Turfs are often composed of numerous species at a wide range of spatial scales, but monospecific turfs are frequently reported. Turfs can be morphologically
|
{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
highly variable over geographic scales and even within species on local scales and can be difficult to identify in terms of the constituent species. Turfs have been defined as short algae, but this has been used to describe height ranges from less than 0.5 cm to more than 10 cm. In some regions, the descriptions approached heights which might be described as canopies (20 to 30 cm). === Physiology === Many algae, particularly species of the Characeae, have served as model experimental organisms to understand the mechanisms of the water permeability of membranes, osmoregulation, salt tolerance, cytoplasmic streaming, and the generation of action potentials. Plant hormones are found not only in higher plants, but in algae, too. === Life cycle === Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have life cycles which show considerable variation and complexity. In general, an asexual phase exists where the seaweed's cells are diploid, a sexual phase where the cells are haploid, followed by fusion of the male and female gametes. Asexual reproduction permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote. To ensure a successful mating, the development and release of gametes is highly synchronized and regulated; pheromones may play a key role in these processes. Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle. However, sexual reproduction is more costly than asexual reproduction. Meiosis has been shown to occur in many different species of algae. == Diversity == The most recent estimate (as of January 2024) documents 50,605 living and 10,556 fossil algal species, according to the online database AlgaeBase.
|
{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
They are classified into 15 phyla or divisions. Some phyla are not photosynthetic, namely Picozoa and Rhodelphidia, but they are included in the database due to their close relationship with red algae. The various algal phyla can be differentiated according to several biological traits. They have distinct morphologies, photosynthetic pigmentation, storage products, cell wall composition, and mechanisms of carbon concentration. Some phyla have unique cellular structures. === Prokaryotic algae === Among prokaryotes, five major groups of bacteria have evolved the ability to photosynthesize, including heliobacteria, green sulfur and nonsulfur bacteria and proteobacteria. However, the only lineage where oxygenic photosynthesis has evolved is in the cyanobacteria, named for their blue-green (cyan) coloration and often known as blue-green algae. They are classified as the phylum Cyanobacteriota or Cyanophyta. However, this phylum also includes two classes of non-photosynthetic bacteria: Melainabacteria (also called Vampirovibrionia or Vampirovibrionophyceae) and Sericytochromatia (also known as Blackallbacteria). A third class contains the photosynthetic ones, known as Cyanophyceae (also called Cyanobacteriia or Oxyphotobacteria). As bacteria, their cells lack membrane-bound organelles, with the exception of thylakoids. Like other algae, cyanobacteria have chlorophyll a as their primary photosynthetic pigment. Their accessory pigments include phycobilins (phycoerythrobilin and phycocyanobilin), carotenoids and, in some cases, b, d, or f chlorophylls, generally distributed in phycobilisomes found in the surface of thylakoids. They display a variety of body forms, such as single cells, colonies, and unbranched or branched filaments. Their cells are commonly covered in a sheath of mucilage, and they also have a typical gram-negative bacterial cell wall composed largely of peptidoglycan. They have various storage particles, including cyanophycin as aminoacid and nitrogen reserves, "cyanophycean starch" (similar to plant amylose) for carbohydrates, and lipid droplets. Their Rubisco enzymes are concentrated in carboxysomes. They occupy a diverse array of aquatic and terrestrial habitats, including extreme environments from
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{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
hot springs to polar glaciers. Some are subterranean, living via hydrogen-based lithoautotrophy instead of photosynthesis. Three lineages of cyanobacteria, Prochloraceae, Prochlorothrix and Prochlorococcus, independently evolved to have chlorophylls a and b instead of phycobilisomes. Due to their different pigmentation, they were historically grouped in a separate division, Prochlorophyta, as this is the typical pigmentation seen in green algae (e.g., chlorophytes). Eventually, this classification became obsolete, as it is a polyphyletic grouping. Cyanobacteria are included as algae by most phycological sources and by the International Code of Nomenclature for algae, fungi, and plants, although a few authors exclude them from the definition of algae and reserve the term for eukaryotes only. === Eukaryotic algae === Eukaryotic algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. Many groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely. ==== Primary algae ==== These algae, grouped in the clade Archaeplastida (meaning 'ancient plastid'), have "primary chloroplasts", i.e. the chloroplasts are surrounded by two membranes and probably developed through a single endosymbiotic event with a cyanobacterium. The chloroplasts of red algae have chlorophylls a and c (often), and phycobilins, while those of green algae have chloroplasts with chlorophyll a and b without phycobilins. Land plants are pigmented similarly to green algae and probably developed from them, thus the Chlorophyta is a sister taxon to the plants; sometimes the Chlorophyta, the Charophyta, and land plants are grouped together as the Viridiplantae. ==== Secondary algae ==== These algae appeared independently in various distantly related lineages after acquiring a
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{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
chloroplast derived from another eukaryotic alga. Two lineages of secondary algae, chlorarachniophytes and euglenophytes have "green" chloroplasts containing chlorophylls a and b. Their chloroplasts are surrounded by four and three membranes, respectively, and were probably retained from ingested green algae. Chlorarachniophytes, which belong to the phylum Cercozoa, contain a small nucleomorph, which is a relict of the algae's nucleus. Euglenophytes, which belong to the phylum Euglenozoa, live primarily in fresh water and have chloroplasts with only three membranes. The endosymbiotic green algae may have been acquired through myzocytosis rather than phagocytosis. Another group with green algae endosymbionts is the dinoflagellate genus Lepidodinium, which has replaced its original endosymbiont of red algal origin with one of green algal origin. A nucleomorph is present, and the host genome still have several red algal genes acquired through endosymbiotic gene transfer. Also, the euglenid and chlorarachniophyte genome contain genes of apparent red algal ancestry. Other groups have "red" chloroplasts containing chlorophylls a and c, and phycobilins. The shape can vary; they may be of discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon shaped. They have one or more pyrenoids to preserve protein and starch. The latter chlorophyll type is not known from any prokaryotes or primary chloroplasts, but genetic similarities with red algae suggest a relationship there. In some of these groups, the chloroplast has four membranes, retaining a nucleomorph in cryptomonads, and they likely share a common pigmented ancestor, although other evidence casts doubt on whether the heterokonts, Haptophyta, and cryptomonads are in fact more closely related to each other than to other groups. The typical dinoflagellate chloroplast has three membranes, but considerable diversity exists in chloroplasts within the group, and a number of endosymbiotic events apparently occurred. The Apicomplexa, a group of closely related parasites, also have plastids called apicoplasts, which are not
|
{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
photosynthetic. The Chromerida are the closest relatives of apicomplexans, and some have retained their chloroplasts. The three alveolate groups evolved from a common myzozoan ancestor that obtained chloroplasts. == History of classification == Linnaeus, in Species Plantarum (1753), the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are currently considered among algae. In Systema Naturae, Linnaeus described the genera Volvox and Corallina, and a species of Acetabularia (as Madrepora), among the animals. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves. W. H. Harvey (1811–1866) and Lamouroux (1813) were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae. At this time, microscopic algae were discovered and reported by a different group of workers (e.g., O. F. Müller and Ehrenberg) studying the Infusoria (microscopic organisms). Unlike macroalgae, which were clearly viewed as plants, microalgae were frequently considered animals because they are often motile. Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals. Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753), de Jussieu (1789), Lamouroux (1813), Harvey (1836), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864), in further classifications, the "algae" are seen as an artificial, polyphyletic group. Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and
|
{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g., Bolidophyceae), and others were splintered from older groups: charophytes and glaucophytes (from chlorophytes), many heterokontophytes (e.g., synurophytes from chrysophytes, or eustigmatophytes from xanthophytes), haptophytes (from chrysophytes), and chlorarachniophytes (from xanthophytes). With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included in Protista, later also abandoned in favour of Eukaryota. However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists). Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis, while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red algae Pterocladiophila and Gelidiocolax mammillatus, parasites of other red algae, or the dinoflagellates Oodinium, parasites of fish) had their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., Chlorochytrium), but later were seen as endophytic algae. Some filamentous bacteria (e.g., Beggiatoa) were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae. == Evolution == === Origin of oxygenic photosynthesis === Prokaryotic algae, i.e., cyanobacteria, are the only group of organisms where oxygenic photosynthesis has evolved. The oldest undisputed fossil evidence of cyanobacteria is dated at 2100 million years ago, although stromatolites, associated with cyanobacterial biofilms, appear as early as 3500 million years ago in the fossil record. === First endosymbiosis === Eukaryotic algae are polyphyletic thus their origin cannot be traced back to single hypothetical common ancestor. It is thought that they came into existence
|
{
"page_id": 633,
"source": null,
"title": "Algae"
}
|
when photosynthetic coccoid cyanobacteria got phagocytized by a unicellular heterotrophic eukaryote (a protist), giving rise to double-membranous primary plastids. Such symbiogenic events (primary symbiogenesis) are believed to have occurred more than 1.5 billion years ago during the Calymmian period, early in Boring Billion, but it is difficult to track the key events because of so much time gap. Primary symbiogenesis gave rise to three divisions of archaeplastids, namely the Viridiplantae (green algae and later plants), Rhodophyta (red algae) and Glaucophyta ("grey algae"), whose plastids further spread into other protist lineages through eukaryote-eukaryote predation, engulfments and subsequent endosymbioses (secondary and tertiary symbiogenesis). This process of serial cell "capture" and "enslavement" explains the diversity of photosynthetic eukaryotes. The oldest undisputed fossil evidence of eukaryotic algae is Bangiomorpha pubescens, a red alga found in rocks around 1047 million years old. === Consecutive endosymbioses === Recent genomic and phylogenomic approaches have significantly clarified plastid genome evolution, the horizontal movement of endosymbiont genes to the "host" nuclear genome, and plastid spread throughout the eukaryotic tree of life. It is accepted that both euglenophytes and chlorarachniophytes obtained their chloroplasts from chlorophytes that became endosymbionts. In particular, euglenophyte chloroplasts share the most resemblance with the genus Pyramimonas. However, there is still no clear order in which the secondary and tertiary endosymbioses occurred for the "chromist" lineages (ochrophytes, cryptophytes, haptophytes and myzozoans). Two main models have been proposed to explain the order, both of which agree that cryptophytes obtained their chloroplasts from red algae. One model, hypothesized in 2014 by John W. Stiller and coauthors, suggests that a cryptophyte became the plastid of ochrophytes, which in turn became the plastid of myzozoans and haptophytes. The other model, suggested by Andrzej Bodył and coauthors in 2009, describes that a cryptophyte became the plastid of both haptophytes and ochrophytes, and
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{
"page_id": 633,
"source": null,
"title": "Algae"
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it is a haptophyte that became the plastid of myzozoans instead. In 2024, a third model by Filip Pietluch and coauthors proposed that there were two independent endosymbioses with red algae: one that originated the cryptophyte plastids (as in the previous models), and subsequently the haptophyte plastids; and another that originated the ochrophyte plastids, where the myzozoans obtained theirs. === Relationship to land plants === Fossils of isolated spores suggest land plants may have been around as long as 475 million years ago (mya) during the Late Cambrian/Early Ordovician period, from sessile shallow freshwater charophyte algae much like Chara, which likely got stranded ashore when riverine/lacustrine water levels dropped during dry seasons. These charophyte algae probably already developed filamentous thalli and holdfasts that superficially resembled plant stems and roots, and probably had an isomorphic alternation of generations. They perhaps evolved some 850 mya and might even be as early as 1 Gya during the late phase of the Boring Billion. == Distribution == The distribution of algal species has been fairly well studied since the founding of phytogeography in the mid-19th century. Algae spread mainly by the dispersal of spores analogously to the dispersal of cryptogamic plants by spores. Spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms. Whether a spore is to grow into an adult organism depends on the species and the environmental conditions where the spore lands. The spores of freshwater algae are dispersed mainly by running water and wind, as well as by living carriers. However, not all bodies of water can carry all species of algae, as the chemical composition of certain water bodies limits the algae that can survive within them. Marine spores are often spread by ocean currents. Ocean water presents
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{
"page_id": 633,
"source": null,
"title": "Algae"
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many vastly different habitats based on temperature and nutrient availability, resulting in phytogeographic zones, regions, and provinces. To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is, therefore, possible to identify species occurring by locality, such as "Pacific algae" or "North Sea algae". When they occur out of their localities, hypothesizing a transport mechanism is usually possible, such as the hulls of ships. For example, Ulva reticulata and U. fasciata travelled from the mainland to Hawaii in this manner. Mapping is possible for select species only: "there are many valid examples of confined distribution patterns." For example, Clathromorphum is an arctic genus and is not mapped far south of there. However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies." === Regional algae checklists === The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown). Estimates vary widely. For example, according to one standard textbook, in the British Isles, the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species ..." Regional and group estimates have been made, as well: 5,000–5,500 species of red algae worldwide "some 1,300 in Australian Seas" 400 seaweed species for the western coastline of South Africa, and 212
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{
"page_id": 633,
"source": null,
"title": "Algae"
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species from the coast of KwaZulu-Natal. Some of these are duplicates, as the range extends across both coasts, and the total recorded is probably about 500 species. Most of these are listed in List of seaweeds of South Africa. These exclude phytoplankton and crustose corallines. 669 marine species from California (US) 642 in the check-list of Britain and Ireland and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton. == Ecology == Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as on snow and ice. Seaweeds grow mostly in shallow marine waters, under 100 m (330 ft) deep; however, some such as Navicula pennata have been recorded to a depth of 360 m (1,180 ft). A type of algae, Ancylonema nordenskioeldii, was found in Greenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet. The same algae was found in the Italian Alps, after pink ice appeared on parts of the Presena glacier. The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, or asphyxiate other life forms. Algae can be used as indicator organisms to monitor pollution in various aquatic systems. In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants. To detect these changes, algae can be sampled from the environment and maintained in laboratories
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{
"page_id": 633,
"source": null,
"title": "Algae"
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with relative ease. On the basis of their habitat, algae can be categorized as: aquatic (planktonic, benthic, marine, freshwater, lentic, lotic), terrestrial, aerial (subaerial), lithophytic, halophytic (or euryhaline), psammon, thermophilic, cryophilic, epibiont (epiphytic, epizoic), endosymbiont (endophytic, endozoic), parasitic, calcifilic or lichenic (phycobiont). === Symbiotic algae === Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples are: ==== Lichens ==== Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure". The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature, they do not occur separate from lichens. It is unknown when they began to associate. One or more mycobiont associates with the same phycobiont species, from the green algae, except that alternatively, the mycobiont may associate with a species of cyanobacteria (hence "photobiont" is the more accurate term). A photobiont may be associated with many different mycobionts or may live independently; accordingly, lichens are named and classified as fungal species. The association is termed a morphogenesis because the lichen has a form and capabilities not possessed by the symbiont species alone (they can be experimentally isolated). The photobiont possibly triggers otherwise latent genes in the mycobiont. Trentepohlia is an example of a common green alga genus worldwide that can grow on its own or be lichenised. Lichen thus share some of the habitat and often similar appearance with specialized species of algae (aerophytes) growing on exposed surfaces such as tree trunks and rocks and sometimes discoloring them. ==== Animal
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{
"page_id": 633,
"source": null,
"title": "Algae"
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symbioses ==== Coral reefs are accumulated from the calcareous exoskeletons of marine invertebrates of the order Scleractinia (stony corals). These animals metabolize sugar and oxygen to obtain energy for their cell-building processes, including secretion of the exoskeleton, with water and carbon dioxide as byproducts. Dinoflagellates (algal protists) are often endosymbionts in the cells of the coral-forming marine invertebrates, where they accelerate host-cell metabolism by generating sugar and oxygen immediately available through photosynthesis using incident light and the carbon dioxide produced by the host. Reef-building stony corals (hermatypic corals) require endosymbiotic algae from the genus Symbiodinium to be in a healthy condition. The loss of Symbiodinium from the host is known as coral bleaching, a condition which leads to the deterioration of a reef. Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species. == In human culture == In classical Chinese, the word 藻 is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao (藻鑒堂島), which thus simultaneously means "Island of the Algae-Viewing Hall" and "Island of the Hall for Reflecting on Literary Talent". == Cultivation == === Seaweed farming === === Bioreactors === == Uses == === Biofuel === To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae-based fuels hold great promise, directly related to the potential to produce more biomass per unit area in a year than any
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{
"page_id": 633,
"source": null,
"title": "Algae"
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other form of biomass. The break-even point for algae-based biofuels is estimated to occur by 2025. === Fertilizer === For centuries, seaweed has been used as a fertilizer; George Owen of Henllys writing in the 16th century referring to drift weed in South Wales: This kind of ore they often gather and lay on great heapes, where it heteth and rotteth, and will have a strong and loathsome smell; when being so rotten they cast on the land, as they do their muck, and thereof springeth good corn, especially barley ... After spring-tydes or great rigs of the sea, they fetch it in sacks on horse backes, and carie the same three, four, or five miles, and cast it on the lande, which doth very much better the ground for corn and grass. Today, algae are used by humans in many ways; for example, as fertilizers, soil conditioners, and livestock feed. Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places. Maerl is commonly used as a soil conditioner. === Food industry === Algae are used as foods in many countries: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable; Japan, over 20 species such as nori and aonori; Ireland, dulse; Chile, cochayuyo. Laver is used to make laverbread in Wales, where it is known as bara lawr. In Korea, green laver is used to make gim. Three forms of algae used as food: Chlorella: This form of alga is found in freshwater and contains photosynthetic pigments in its chloroplast. Klamath AFA: A subspecies of Aphanizomenon flos-aquae found wild in many bodies of water worldwide but harvested
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{
"page_id": 633,
"source": null,
"title": "Algae"
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only from Upper Klamath Lake, Oregon. Spirulina: Known otherwise as a cyanobacterium (a prokaryote or a "blue-green alga") The oils from some algae have high levels of unsaturated fatty acids. Some varieties of algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain. The natural pigments (carotenoids and chlorophylls) produced by algae can be used as alternatives to chemical dyes and coloring agents. The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularly high-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples. Carrageenan, from the red alga Chondrus crispus, is used as a stabilizer in milk products. === Gelling agents === Agar, a gelatinous substance derived from red algae, has a number of commercial uses. It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar. Alginic acid, or alginate, is extracted from brown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field of biotechnology as a biocompatible medium for cell encapsulation and cell immobilization. Molecular cuisine is also a user of the substance for its gelling properties, by which it becomes a delivery vehicle for flavours. Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in New Mexico for alginate extraction and abalone feed. === Pollution control and bioremediation === Sewage can be treated with algae, reducing the
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{
"page_id": 633,
"source": null,
"title": "Algae"
}
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use of large amounts of toxic chemicals that would otherwise be needed. Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer. Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber. Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years. They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers. Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds. The alga Stichococcus bacillaris has been seen to colonize silicone resins used at archaeological sites; biodegrading the synthetic substance. === Bioplastics === Various polymers can be created from algae, which can be especially useful in the creation of bioplastics. These include hybrid plastics, cellulose-based plastics, poly-lactic acid, and bio-polyethylene. Several companies have begun to produce algae polymers commercially, including for use in flip-flops and in surf boards. Even algae is also used to prepare various polymeric resins suitable for coating applications. == Additional images == == See also == AlgaeBase AlgaePARC Eutrophication Iron fertilization
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{
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"title": "Algae"
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Marimo algae Microbiofuels Microphyte Photobioreactor Phycotechnology Plants Toxoid – anatoxin == Notes == == References == == Bibliography == == External links == Guiry, Michael; Guiry, Wendy. "AlgaeBase". – a database of all algal names including images, nomenclature, taxonomy, distribution, bibliography, uses, extracts "Algae – Cell Centered Database". CCDb.UCSD.edu. San Diego: University of California. Anderson, Don; Keafer, Bruce; Kleindinst, Judy; Shaughnessy, Katie; Joyce, Katherine; Fino, Danielle; Shepherd, Adam (2007). "Harmful Algae". US National Office for Harmful Algal Blooms. Archived from the original on 5 December 2008. Retrieved 19 December 2008. "About Algae". NMH.ac.uk. Natural History Museum, United Kingdom.
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{
"page_id": 633,
"source": null,
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The Kohn-Sham equations are a set of mathematical equations used in quantum mechanics to simplify the complex problem of understanding how electrons behave in atoms and molecules. They introduce fictitious non-interacting electrons and use them to find the most stable arrangement of electrons, which helps scientists understand and predict the properties of matter at the atomic and molecular scale. == Description == In physics and quantum chemistry, specifically density functional theory, the Kohn–Sham equation is the non-interacting Schrödinger equation (more clearly, Schrödinger-like equation) of a fictitious system (the "Kohn–Sham system") of non-interacting particles (typically electrons) that generate the same density as any given system of interacting particles. In the Kohn–Sham theory the introduction of the noninteracting kinetic energy functional Ts into the energy expression leads, upon functional differentiation, to a collection of one-particle equations whose solutions are the Kohn–Sham orbitals. The Kohn–Sham equation is defined by a local effective (fictitious) external potential in which the non-interacting particles move, typically denoted as vs(r) or veff(r), called the Kohn–Sham potential. If the particles in the Kohn–Sham system are non-interacting fermions (non-fermion Density Functional Theory has been researched), the Kohn–Sham wavefunction is a single Slater determinant constructed from a set of orbitals that are the lowest-energy solutions to ( − ℏ 2 2 m ∇ 2 + v eff ( r ) ) φ i ( r ) = ε i φ i ( r ) . {\displaystyle \left(-{\frac {\hbar ^{2}}{2m}}\nabla ^{2}+v_{\text{eff}}(\mathbf {r} )\right)\varphi _{i}(\mathbf {r} )=\varepsilon _{i}\varphi _{i}(\mathbf {r} ).} This eigenvalue equation is the typical representation of the Kohn–Sham equations. Here εi is the orbital energy of the corresponding Kohn–Sham orbital φ i {\displaystyle \varphi _{i}} , and the density for an N-particle system is ρ ( r ) = ∑ i N | φ i ( r ) | 2
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"page_id": 4457082,
"source": null,
"title": "Kohn–Sham equations"
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. {\displaystyle \rho (\mathbf {r} )=\sum _{i}^{N}|\varphi _{i}(\mathbf {r} )|^{2}.} == History == The Kohn–Sham equations are named after Walter Kohn and Lu Jeu Sham, who introduced the concept at the University of California, San Diego, in 1965. Kohn received a Nobel Prize in Chemistry in 1998 for the Kohn–Sham equations and other work related to density functional theory (DFT). == Kohn–Sham potential == In Kohn–Sham density functional theory, the total energy of a system is expressed as a functional of the charge density as E [ ρ ] = T s [ ρ ] + ∫ d r v ext ( r ) ρ ( r ) + E H [ ρ ] + E xc [ ρ ] , {\displaystyle E[\rho ]=T_{s}[\rho ]+\int d\mathbf {r} \,v_{\text{ext}}(\mathbf {r} )\rho (\mathbf {r} )+E_{\text{H}}[\rho ]+E_{\text{xc}}[\rho ],} where Ts is the Kohn–Sham kinetic energy, which is expressed in terms of the Kohn–Sham orbitals as T s [ ρ ] = ∑ i = 1 N ∫ d r φ i ∗ ( r ) ( − ℏ 2 2 m ∇ 2 ) φ i ( r ) , {\displaystyle T_{s}[\rho ]=\sum _{i=1}^{N}\int d\mathbf {r} \,\varphi _{i}^{*}(\mathbf {r} )\left(-{\frac {\hbar ^{2}}{2m}}\nabla ^{2}\right)\varphi _{i}(\mathbf {r} ),} vext is the external potential acting on the interacting system (at minimum, for a molecular system, the electron–nuclei interaction), EH is the Hartree (or Coulomb) energy E H [ ρ ] = e 2 2 ∫ d r ∫ d r ′ ρ ( r ) ρ ( r ′ ) | r − r ′ | , {\displaystyle E_{\text{H}}[\rho ]={\frac {e^{2}}{2}}\int d\mathbf {r} \int d\mathbf {r} '\,{\frac {\rho (\mathbf {r} )\rho (\mathbf {r} ')}{|\mathbf {r} -\mathbf {r} '|}},} and Exc is the exchange–correlation energy. The Kohn–Sham equations are found by varying the total energy expression with
|
{
"page_id": 4457082,
"source": null,
"title": "Kohn–Sham equations"
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|
respect to a set of Kohn-Sham orbitals subject to the constraint that they are orthogonal, this yields a time-independent Schrödinger equation with a scalar potential equal to the Kohn–Sham potential v eff ( r ) = v ext ( r ) + e 2 ∫ ρ ( r ′ ) | r − r ′ | d r ′ + δ E xc [ ρ ] δ ρ ( r ) , {\displaystyle v_{\text{eff}}(\mathbf {r} )=v_{\text{ext}}(\mathbf {r} )+e^{2}\int {\frac {\rho (\mathbf {r} ')}{|\mathbf {r} -\mathbf {r} '|}}\,d\mathbf {r} '+{\frac {\delta E_{\text{xc}}[\rho ]}{\delta \rho (\mathbf {r} )}},} where the last term v xc ( r ) ≡ δ E xc [ ρ ] δ ρ ( r ) , {\displaystyle v_{\text{xc}}(\mathbf {r} )\equiv {\frac {\delta E_{\text{xc}}[\rho ]}{\delta \rho (\mathbf {r} )}},} is the exchange–correlation potential. This term, and the corresponding energy expression, are the only unknowns in the Kohn–Sham approach to density functional theory. An approximation that does not vary the orbitals is Harris functional theory. The Kohn–Sham orbital energies εi, in general, have little physical meaning (see Koopmans' theorem). The sum of the orbital energies is related to the total energy as E = ∑ i N ε i − E H [ ρ ] + E xc [ ρ ] − ∫ δ E xc [ ρ ] δ ρ ( r ) ρ ( r ) d r . {\displaystyle E=\sum _{i}^{N}\varepsilon _{i}-E_{\text{H}}[\rho ]+E_{\text{xc}}[\rho ]-\int {\frac {\delta E_{\text{xc}}[\rho ]}{\delta \rho (\mathbf {r} )}}\rho (\mathbf {r} )\,d\mathbf {r} .} Because the orbital energies are non-unique in the more general restricted open-shell case, this equation only holds true for specific choices of orbital energies (see Koopmans' theorem). == References ==
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{
"page_id": 4457082,
"source": null,
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In molecular biology mir-154 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms. == See also == MicroRNA == References == == Further reading == == External links == Page for mir-154 microRNA precursor family at Rfam
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{
"page_id": 36373118,
"source": null,
"title": "Mir-154 microRNA precursor family"
}
|
GenGIS merges geographic, ecological and phylogenetic biodiversity data in a single interactive visualization and analysis environment. A key feature of GenGIS is the testing of geographic axes that can correspond to routes of migration or gradients that influence community similarity. Data can also be explored using graphical summaries of data on a site-by-site basis, as 3D geophylogenies, or custom visualizations developed using a plugin framework. Standard statistical test such as linear regression and Mantel are provided, and the R statistical language can be accessed directly within GenGIS. Since its release, GenGIS has been used to investigate the phylogeography of viruses and bacteriophages, bacteria, and eukaryotes. == See also == Phylogeography Biogeography == References == == External links == GenGIS homepage
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{
"page_id": 35586688,
"source": null,
"title": "GenGIS"
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The Amadori rearrangement is an organic reaction describing the acid or base catalyzed isomerization or rearrangement reaction of the N-glycoside of an aldose or the glycosylamine to the corresponding 1-amino-1-deoxy-ketose. The reaction is important in carbohydrate chemistry, specifically the glycation of hemoglobin (as measured by the HbA1c test). The rearrangement is usually preceded by formation of a α-hydroxyimine by condensation of an amine with an aldose sugar. The rearrangement itself entails intramolecular redox reaction, converting this α-hydroxyimine to an α-ketoamine: The formation of imines is generally reversible, but subsequent to conversion to the keto-amine, the attached amine is fixed irreversibly. This Amadori product is an intermediate in the production of advanced glycation end-products (AGE)s. The formation of an advanced glycation end-product involves the oxidation of the Amadori product. == Food chemistry == The reaction is associated with the amino-carbonyl reactions (also called glycation reaction, or Maillard reaction) in which the reagents are naturally occurring sugars and amino acids. One study demonstrated the possibility of Amadori rearrangement during interaction between oxidized dextran and gelatine. == History == The Amadori rearrangement was discovered by the organic chemist Mario Amadori (1886–1941), who in 1925 reported this reaction while studying the Maillard reaction. == See also == Fructoselysine, the Amadori product derived from glucose and lysine Glycated hemoglobin, the Amadori product used in the HbA1c diagnostic test for diabetes == References == == External links == Amadori Rearrangement, PowerPoint presentation detailing the reaction mechanism
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"page_id": 7668353,
"source": null,
"title": "Amadori rearrangement"
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Richard Edwin Cutkosky (29 July 1928 – 17 June 1993) was a physicist, best known for the Cutkosky cutting rules in quantum field theory, which give a simple way to calculate the discontinuity of the scattering amplitude by Feynman diagrams. Richard Edwin Cutkowsky was born in Minneapolis as son of Oscar F. and Edna M. (Nelson) Cutkosky. His entire career was related to Carnegie, Pittsburgh, Pennsylvania. At the Carnegie Institute of Technology he made his Bachelor and Master of Science both in 1950, followed by a Doctor of Philosophy in 1953. 1954-1961 he was assistant professor of physics at the Carnegie Mellon University, professor since 1961 and the first Buhl professor since 1963 until his death in 1993. He was a fellow of the American Physical Society and of the American Association for the Advancement of Science. He was married with Patricia A. Klepfer, August 28,1952. Children: Mark, Carol, Martha. == Footnotes == == Publications == R. E. Cutkosky (1960), "Singularities and Discontinuities of Feynman Amplitudes", J. Math. Phys., 1 (5): 429, Bibcode:1960JMP.....1..429C, doi:10.1063/1.1703676 == References == Wolfenstein, Lincoln (April 1994). "Richard E. Cutkosky". Physics Today. 47 (4): 75–76. Bibcode:1994PhT....47d..75W. doi:10.1063/1.2808481. An obituary. Physics department news of CMU, Bob Kramer (1993), Interactions (PDF), p. 2.
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{
"page_id": 43123332,
"source": null,
"title": "Richard E. Cutkosky"
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This page provides supplementary chemical data on Hydrochloric acid. == Material Safety Data Sheet == 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 and follow its directions. [1] == Structure and properties == == References ==
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{
"page_id": 4194949,
"source": null,
"title": "Hydrochloric acid (data page)"
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Anisic acid or methoxybenzoic acid is an organic compound which is a carboxylic acid. It exists in three forms, depending on arene substitution patterns: p-Anisic acid (4-methoxybenzoic acid) m-Anisic acid (3-methoxybenzoic acid) o-Anisic acid (2-methoxybenzoic acid)
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{
"page_id": 3408525,
"source": null,
"title": "Anisic acid"
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In chemistry, the mesomeric effect (or resonance effect) is a property of substituents or functional groups in a chemical compound. It is defined as the polarity produced in the molecule by the interaction of two pi bonds or between a pi bond and lone pair of electrons present on an adjacent atom. This change in electron arrangement results in the formation of resonance structures that hybridize into the molecule's true structure. The pi electrons then move away from or toward a particular substituent group. The mesomeric effect is stronger in compounds with a lower ionization potential. This is because the electron transfer states will have lower energies. == Representations of the mesomeric effect == The effect is used in a qualitative way and describes the electron withdrawing or releasing properties of substituents based on relevant resonance structures and is symbolized by the letter M. The mesomeric effect is negative (−M) when the substituent is an electron-withdrawing group, and the effect is positive (+M) when the substituent is an electron donating group. Below are two examples of the +M and −M effect. Additionally, the functional groups that contribute to each type of resonance are given below. === +M effect === The +M effect, also known as the positive mesomeric effect, occurs when the substituent is an electron donating group. The group must have one of two things: a lone pair of electrons, or a negative charge. In the +M effect, the pi electrons are transferred from the group towards the conjugate system, increasing the density of the system. Due to the increase in electron density, the conjugate system will develop a more negative charge. As a result, the system under the +M effect will be more reactive towards electrophiles, which can take away the negative charge, than a nucleophile. +M effect
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{
"page_id": 66189,
"source": null,
"title": "Mesomeric effect"
}
|
order: −O− > −NH2 > −NHR > −NR2 > −OH > −OR > −NHCOR > −OCOR > −Ph > −F > −Cl > −Br > −I > −NO === −M effect === The −M effect, also known as the negative mesomeric effect, occurs when the substituent is an electron-withdrawing group. In order for a negative mesomeric (−M) effect to occur the group must have a positive charge or an empty orbital in order to draw the electrons towards it. In the −M effect, the pi electrons move away from the conjugate system and towards the electron drawing group. In the conjugate system, the density of electrons decreases and the overall charge becomes more positive. With the −M effect the groups and compounds become less reactive towards electrophiles, and more reactive toward nucleophiles, which can give up electrons and balance out the positive charge. −M effect order: −NO2 > −CN > −SO3H > −CHO > −COR > −COOCOR > −COOR > −COOH > −CONH2 > −COO− == Mesomeric effect vs. inductive effect == The net electron flow from or to the substituent is determined also by the inductive effect. The mesomeric effect as a result of p-orbital overlap (resonance) has absolutely no effect on this inductive effect, as the inductive effect has purely to do with the electronegativity of the atoms and their topology in the molecule (which atoms are connected to which). Specifically the inductive effect is the tendency for the substituents to repel or attract electrons purely based on electronegativity and not dealing with restructuring. The mesomeric effect however, deals with restructuring and occurs when the electron pair of the substituents shift around. The inductive effect only acts on alpha carbons, while the mesomeric utilizes pi bonds between atoms. While these two paths often lead to the similar molecules
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{
"page_id": 66189,
"source": null,
"title": "Mesomeric effect"
}
|
and resonance structures, the mechanism is different. As such, the mesomeric effect is stronger than the inductive effect. The concepts of mesomeric effect, mesomerism and mesomer were introduced by Ingold in 1938 as an alternative to Pauling's synonymous concept of resonance. "Mesomerism" in this context is often encountered in German and French literature, but in English literature the term "resonance" dominates. == Mesomerism in conjugated systems == Mesomeric effect can be transmitted along any number of carbon atoms in a conjugated system. This accounts for the resonance stabilization of the molecule due to delocalization of charge. It is important to note that the energy of the actual structure of the molecule, i.e. the resonance hybrid, may be lower than that of any of the contributing canonical structures. The difference in energy between the actual inductive structure and the (most stable contributing structures) worst kinetic structure is called the resonance energy or resonance stabilization energy. For the quantitative estimation of the mesomeric/resonance effect strength various substituent constants are used, i.e. Swain-Lupton resonance constant, Taft resonance constant or Oziminski and Dobrowolski pEDA parameter. Additionally, the resulting resonance structures can give the molecule properties that are not inherently evident from looking at one structure. Some of these properties include different reactivities, local diamagnetic shielding in aromatics, deshielding, and acid and base strengths. == References ==
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{
"page_id": 66189,
"source": null,
"title": "Mesomeric effect"
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Codon reassignment is the biological process via which the way the genetic code of a cell is read is changed as a response to the environment. Typically codons, sets of three mRNA nucleotides, correspond to one specific amino acid. Codon reassignment is the exception to this rule. When a codon is reassigned, it codes for a new amino acid. This change in code can have immense consequences for the cell as protein structures are altered. == Mechanics of Codon Reassignment == === Normal Codon Behavior === Proteins are essential to life, preforming many necessary cellular functions. Cells construct proteins with amino acids using DNA instructions. Typically, DNA is transcribed into messenger RNA (mRNA) and the mRNA is translated into a sequence of amino acids. The complex that facilitates translation from mRNA to amino acid is called the ribosome. Ribosomes hold and read mRNA in three nucleotide chunks called codons. Codons have a corresponding transport RNA (tRNA) that binds to the ribosome. tRNAs are responsible for bringing amino acids to the ribosome so they can be incorporated into the protein. Though each codon only codes for a single tRNA, a tRNA can represent multiple codons. This is because there are 64 possible codon combinations and 20 natural amino acids. Each tRNA codes for a single amino acid. Each amino acid is added to the growing chain of amino acids that will form the final protein. The initial chain of amino acids, also called the primary structure of the protein, determines the final shape and functional capacity of the protein. === Reassigned Codon Behavior === When codon reassignment occurs, it is usually due to a change in tRNAs. A tRNA can be assigned to a new codon or the tRNA can be altered to pick up a different amino acid. For the
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{
"page_id": 70386320,
"source": null,
"title": "Codon reassignment"
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protein, this means either swapping one amino acid for another, or in the case of a stop codon, adding an amino acid where there was none before. Since the primary structure determines the functionality of a protein, changing even one amino acid in this way can drastically impact what the final protein is able to do. == Examples of Codon Reassignment == === Amino acid deficiencies === In bacteria and yeast, codon reassignment can be caused by a shortage of required amino acids. Instead of halting protein production all together, tRNA molecules select another amino acid to add to the amino acid chain. This amino acid may have similar properties to the intended amino acid, or it may not. This may cause deformities in the proteins, making them less efficient or even nonfunctional. A hypothesis as to why this phenomenon persists despite the loss of efficiency is that it is preferable for the organism to have a worse version of the protein than to have no protein at all. In some human cancer cells, such as melanoma cells, a similar tactic is used. As an immune response, to try and destroy the cancer, T cells release an enzyme that destroys the essential amino acid tryptophan within the cancer cells. This typically deprives the cancer of many key proteins, killing the cancer cells. However, some cancer cells are able to use codon reassignment to replace the tryptophan with a similar amino acid called phenylalanine. This amino acid replacement and resulting functional protein allows the cancer cell to survive and continue dividing. === Alteration of tRNAs === In some bacteriophages, tRNAs have been assigned to stop codons TAG and TGA to code for amino acids glutamine and tryptophan respectively. The reasons for this codon reassignment are still being studied, it may be
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{
"page_id": 70386320,
"source": null,
"title": "Codon reassignment"
}
|
related to the infection process. Exposure to outside environmental factors can alter tRNA molecules enough to result in codon reassignment. For example, after being infected with a certain virus, rat liver cells can replace the amino acid selenocysteine with cysteine, a structurally similar amino acid. == Implications of Codon Reassignment == === Not-So Universal Genetic Code === It has been well documented that there are variations in genetic code within between nucleic DNA, mitochondrial DNA and chloroplast DNA. However, it was previously thought that the genetic code was consistent across species within the nucleus. The existence of codon reassignment challenges this idea. The same codon may code for different amino acids in different species. Codon reassignment shows flexibility and adaptability within genetic code. === Potential Uses of Codon Reassignment === Artificial, synthetic, unnatural, or non-proteinogenic amino acids are used in research to help understand the construction and functionality of proteins. These artificial amino acids are also used in some medications. Researchers normally use stop codons, which do not code for an amino acid, to insert these amino acids into proteins. Since there are only three stop codons, researchers were previously limited to using only one or two artificial amino acids. There was also an option to use artificial tRNA molecules to insert artificial amino acids, but these artificial tRNA molecules are not as high quality as natural tRNA molecules, often making mistakes. The ability to reassign natural tRNA to artificial amino acids through codon reassignment unlocks many possibilities for this research. Since there are 64 possible combinations and only about 20 natural amino acids, this method would allow researchers to hypothetically insert 43 artificial amino acids into a protein, preserving one stop codon to complete the translation process properly. These advancements in genetic and protein manipulation may help scientists and
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{
"page_id": 70386320,
"source": null,
"title": "Codon reassignment"
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doctors to deepen humanity's understanding of cellular functions and produce more effective and efficient medicines. == See also == Expanded genetic code Transcription (biology) Translation (biology) Gene expression Cancer genome sequencing == References ==
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{
"page_id": 70386320,
"source": null,
"title": "Codon reassignment"
}
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An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted–Lowry or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H+. Aqueous Arrhenius acids have characteristic properties that provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus, meaning 'sour'. An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as "acid" (as in "dissolved in acid"), while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic. Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride that is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong
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"page_id": 656,
"source": null,
"title": "Acid"
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acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid. The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF3), whose boron atom has a vacant orbital that can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH3). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H+) into the solution, which then accept electron pairs. Hydrogen chloride, acetic acid, and most other Brønsted–Lowry acids cannot form a covalent bond with an electron pair, however, and are therefore not Lewis acids. Conversely, many Lewis acids are not Arrhenius or Brønsted–Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as such. == Definitions and concepts == Modern definitions are concerned with the fundamental chemical reactions common to all acids. Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, so the Arrhenius and Brønsted–Lowry definitions are the most relevant. The Brønsted–Lowry definition is the most widely used definition; unless otherwise specified, acid–base reactions are assumed to involve the transfer of a proton (H+) from an acid to a base. Hydronium ions are acids according to all three definitions. Although alcohols and amines can be Brønsted–Lowry acids, they can also function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms. === Arrhenius acids === In 1884, Svante Arrhenius attributed the properties of acidity to hydrogen ions
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"page_id": 656,
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"title": "Acid"
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(H+), later described as protons or hydrons. An Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in the water. Chemists often write H+(aq) and refer to the hydrogen ion when describing acid–base reactions but the free hydrogen nucleus, a proton, does not exist alone in water, it exists as the hydronium ion (H3O+) or other forms (H5O2+, H9O4+). Thus, an Arrhenius acid can also be described as a substance that increases the concentration of hydronium ions when added to water. Examples include molecular substances such as hydrogen chloride and acetic acid. An Arrhenius base, on the other hand, is a substance that increases the concentration of hydroxide (OH−) ions when dissolved in water. This decreases the concentration of hydronium because the ions react to form H2O molecules: H3O+(aq) + OH−(aq) ⇌ H2O(liq) + H2O(liq) Due to this equilibrium, any increase in the concentration of hydronium is accompanied by a decrease in the concentration of hydroxide. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, while an Arrhenius base increases it. In an acidic solution, the concentration of hydronium ions is greater than 10−7 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidic solutions thus have a pH of less than 7. === Brønsted–Lowry acids === While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923, chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid–base reactions involve the transfer of a proton. A Brønsted–Lowry acid (or simply Brønsted acid) is a species that donates a proton to a Brønsted–Lowry base. Brønsted–Lowry acid–base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic
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"page_id": 656,
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"title": "Acid"
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acid (CH3COOH), the organic acid that gives vinegar its characteristic taste: CH3COOH + H2O ⇌ CH3COO− + H3O+ CH3COOH + NH3 ⇌ CH3COO− + NH+4 Both theories easily describe the first reaction: CH3COOH acts as an Arrhenius acid because it acts as a source of H3O+ when dissolved in water, and it acts as a Brønsted acid by donating a proton to water. In the second example CH3COOH undergoes the same transformation, in this case donating a proton to ammonia (NH3), but does not relate to the Arrhenius definition of an acid because the reaction does not produce hydronium. Nevertheless, CH3COOH is both an Arrhenius and a Brønsted–Lowry acid. Brønsted–Lowry theory can be used to describe reactions of molecular compounds in nonaqueous solution or the gas phase. Hydrogen chloride (HCl) and ammonia combine under several different conditions to form ammonium chloride, NH4Cl. In aqueous solution HCl behaves as hydrochloric acid and exists as hydronium and chloride ions. The following reactions illustrate the limitations of Arrhenius's definition: H3O+(aq) + Cl−(aq) + NH3 → Cl−(aq) + NH+4(aq) + H2O HCl(benzene) + NH3(benzene) → NH4Cl(s) HCl(g) + NH3(g) → NH4Cl(s) As with the acetic acid reactions, both definitions work for the first example, where water is the solvent and hydronium ion is formed by the HCl solute. The next two reactions do not involve the formation of ions but are still proton-transfer reactions. In the second reaction hydrogen chloride and ammonia (dissolved in benzene) react to form solid ammonium chloride in a benzene solvent and in the third gaseous HCl and NH3 combine to form the solid. === Lewis acids === A third, only marginally related concept was proposed in 1923 by Gilbert N. Lewis, which includes reactions with acid–base characteristics that do not involve a proton transfer. A Lewis acid is a
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"page_id": 656,
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"title": "Acid"
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species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor. Brønsted acid–base reactions are proton transfer reactions while Lewis acid–base reactions are electron pair transfers. Many Lewis acids are not Brønsted–Lowry acids. Contrast how the following reactions are described in terms of acid–base chemistry: In the first reaction a fluoride ion, F−, gives up an electron pair to boron trifluoride to form the product tetrafluoroborate. Fluoride "loses" a pair of valence electrons because the electrons shared in the B—F bond are located in the region of space between the two atomic nuclei and are therefore more distant from the fluoride nucleus than they are in the lone fluoride ion. BF3 is a Lewis acid because it accepts the electron pair from fluoride. This reaction cannot be described in terms of Brønsted theory because there is no proton transfer. The second reaction can be described using either theory. A proton is transferred from an unspecified Brønsted acid to ammonia, a Brønsted base; alternatively, ammonia acts as a Lewis base and transfers a lone pair of electrons to form a bond with a hydrogen ion. The species that gains the electron pair is the Lewis acid; for example, the oxygen atom in H3O+ gains a pair of electrons when one of the H—O bonds is broken and the electrons shared in the bond become localized on oxygen. Depending on the context, a Lewis acid may also be described as an oxidizer or an electrophile. Organic Brønsted acids, such as acetic, citric, or oxalic acid, are not Lewis acids. They dissociate in water to produce a Lewis acid, H+, but at the same time, they also yield an equal amount of a Lewis base (acetate, citrate, or oxalate, respectively, for the acids mentioned). This
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"page_id": 656,
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article deals mostly with Brønsted acids rather than Lewis acids. == Dissociation and equilibrium == Reactions of acids are often generalized in the form HA ⇌ H+ + A−, where HA represents the acid and A− is the conjugate base. This reaction is referred to as protolysis. The protonated form (HA) of an acid is also sometimes referred to as the free acid. Acid–base conjugate pairs differ by one proton, and can be interconverted by the addition or removal of a proton (protonation and deprotonation, respectively). The acid can be the charged species and the conjugate base can be neutral in which case the generalized reaction scheme could be written as HA+ ⇌ H+ + A. In solution there exists an equilibrium between the acid and its conjugate base. The equilibrium constant K is an expression of the equilibrium concentrations of the molecules or the ions in solution. Brackets indicate concentration, such that [H2O] means the concentration of H2O. The acid dissociation constant Ka is generally used in the context of acid–base reactions. The numerical value of Ka is equal to the product (multiplication) of the concentrations of the products divided by the concentration of the reactants, where the reactant is the acid (HA) and the products are the conjugate base and H+. K a = [ H + ] [ A − ] [ HA ] {\displaystyle K_{a}={\frac {{\ce {[H+] [A^{-}]}}}{{\ce {[HA]}}}}} The stronger of two acids will have a higher Ka than the weaker acid; the ratio of hydrogen ions to acid will be higher for the stronger acid as the stronger acid has a greater tendency to lose its proton. Because the range of possible values for Ka spans many orders of magnitude, a more manageable constant, pKa is more frequently used, where pKa = −log10 Ka.
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{
"page_id": 656,
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Stronger acids have a smaller pKa than weaker acids. Experimentally determined pKa at 25 °C in aqueous solution are often quoted in textbooks and reference material. == Nomenclature == Arrhenius acids are named according to their anions. In the classical naming system, the ionic suffix is dropped and replaced with a new suffix, according to the table following. The prefix "hydro-" is used when the acid is made up of just hydrogen and one other element. For example, HCl has chloride as its anion, so the hydro- prefix is used, and the -ide suffix makes the name take the form hydrochloric acid. Classical naming system: In the IUPAC naming system, "aqueous" is simply added to the name of the ionic compound. Thus, for hydrogen chloride, as an acid solution, the IUPAC name is aqueous hydrogen chloride. == Acid strength == The strength of an acid refers to its ability or tendency to lose a proton. A strong acid is one that completely dissociates in water; in other words, one mole of a strong acid HA dissolves in water yielding one mole of H+ and one mole of the conjugate base, A−, and none of the protonated acid HA. In contrast, a weak acid only partially dissociates and at equilibrium both the acid and the conjugate base are in solution. Examples of strong acids are hydrochloric acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr), perchloric acid (HClO4), nitric acid (HNO3) and sulfuric acid (H2SO4). In water each of these essentially ionizes 100%. The stronger an acid is, the more easily it loses a proton, H+. Two key factors that contribute to the ease of deprotonation are the polarity of the H—A bond and the size of atom A, which determines the strength of the H—A bond. Acid strengths are also often
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{
"page_id": 656,
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discussed in terms of the stability of the conjugate base. Stronger acids have a larger acid dissociation constant, Ka and a lower pKa than weaker acids. Sulfonic acids, which are organic oxyacids, are a class of strong acids. A common example is toluenesulfonic acid (tosylic acid). Unlike sulfuric acid itself, sulfonic acids can be solids. In fact, polystyrene functionalized into polystyrene sulfonate is a solid strongly acidic plastic that is filterable. Superacids are acids stronger than 100% sulfuric acid. Examples of superacids are fluoroantimonic acid, magic acid and perchloric acid. The strongest known acid is helium hydride ion, with a proton affinity of 177.8kJ/mol. Superacids can permanently protonate water to give ionic, crystalline hydronium "salts". They can also quantitatively stabilize carbocations. While Ka measures the strength of an acid compound, the strength of an aqueous acid solution is measured by pH, which is an indication of the concentration of hydronium in the solution. The pH of a simple solution of an acid compound in water is determined by the dilution of the compound and the compound's Ka. == Lewis acid strength in non-aqueous solutions == Lewis acids have been classified in the ECW model and it has been shown that there is no one order of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by C-B plots. It has been shown that to define the order of Lewis acid strength at least two properties must be considered. For Pearson's qualitative HSAB theory the two properties are hardness and strength while for Drago's quantitative ECW model the two properties are electrostatic and covalent. == Chemical characteristics == === Monoprotic acids === Monoprotic acids, also known as monobasic acids, are those acids that are able to donate one proton
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{
"page_id": 656,
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per molecule during the process of dissociation (sometimes called ionization) as shown below (symbolized by HA): HA (aq) + H2O (l) ⇌ H3O+ (aq) + A− (aq) Ka Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO3). On the other hand, for organic acids the term mainly indicates the presence of one carboxylic acid group and sometimes these acids are known as monocarboxylic acid. Examples in organic acids include formic acid (HCOOH), acetic acid (CH3COOH) and benzoic acid (C6H5COOH). === Polyprotic acids === Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic (or dibasic) acid (two potential protons to donate), and triprotic (or tribasic) acid (three potential protons to donate). Some macromolecules such as proteins and nucleic acids can have a very large number of acidic protons. A diprotic acid (here symbolized by H2A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, Ka1 and Ka2. H2A (aq) + H2O (l) ⇌ H3O+ (aq) + HA− (aq) Ka1 HA− (aq) + H2O (l) ⇌ H3O+ (aq) + A2− (aq) Ka2 The first dissociation constant is typically greater than the second (i.e., Ka1 > Ka2). For example, sulfuric acid (H2SO4) can donate one proton to form the bisulfate anion (HSO−4), for which Ka1 is very large; then it can donate a second proton to form the sulfate anion (SO2−4), wherein the Ka2 is intermediate strength. The large Ka1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid (H2CO3) can lose one proton to form
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{
"page_id": 656,
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bicarbonate anion (HCO−3) and lose a second to form carbonate anion (CO2−3). Both Ka values are small, but Ka1 > Ka2 . A triprotic acid (H3A) can undergo one, two, or three dissociations and has three dissociation constants, where Ka1 > Ka2 > Ka3. H3A (aq) + H2O (l) ⇌ H3O+ (aq) + H2A− (aq) Ka1 H2A− (aq) + H2O (l) ⇌ H3O+ (aq) + HA2− (aq) Ka2 HA2− (aq) + H2O (l) ⇌ H3O+ (aq) + A3− (aq) Ka3 An inorganic example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid. All three protons can be successively lost to yield H2PO−4, then HPO2−4, and finally PO3−4, the orthophosphate ion, usually just called phosphate. Even though the positions of the three protons on the original phosphoric acid molecule are equivalent, the successive Ka values differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged. An organic example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion. Although the subsequent loss of each hydrogen ion is less favorable, all of the conjugate bases are present in solution. The fractional concentration, α (alpha), for each species can be calculated. For example, a generic diprotic acid will generate 3 species in solution: H2A, HA−, and A2−. The fractional concentrations can be calculated as below when given either the pH (which can be converted to the [H+]) or the concentrations of the acid with all its conjugate bases: α H 2 A = [ H + ] 2 [ H + ] 2 + [ H + ] K 1 + K 1 K 2 = [ H 2 A ] [ H 2 A ] + [ H A −
|
{
"page_id": 656,
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] + [ A 2 − ] α HA − = [ H + ] K 1 [ H + ] 2 + [ H + ] K 1 + K 1 K 2 = [ HA − ] [ H 2 A ] + [ H A − ] + [ A 2 − ] α A 2 − = K 1 K 2 [ H + ] 2 + [ H + ] K 1 + K 1 K 2 = [ A 2 − ] [ H 2 A ] + [ H A − ] + [ A 2 − ] {\displaystyle {\begin{aligned}\alpha _{{\ce {H2A}}}&={\frac {{\ce {[H+]^2}}}{{\ce {[H+]^2}}+[{\ce {H+}}]K_{1}+K_{1}K_{2}}}={\frac {{\ce {[H2A]}}}{{\ce {{[H2A]}}}+[HA^{-}]+[A^{2-}]}}\\\alpha _{{\ce {HA^-}}}&={\frac {[{\ce {H+}}]K_{1}}{{\ce {[H+]^2}}+[{\ce {H+}}]K_{1}+K_{1}K_{2}}}={\frac {{\ce {[HA^-]}}}{{\ce {[H2A]}}+{[HA^{-}]}+{[A^{2-}]}}}\\\alpha _{{\ce {A^{2-}}}}&={\frac {K_{1}K_{2}}{{\ce {[H+]^2}}+[{\ce {H+}}]K_{1}+K_{1}K_{2}}}={\frac {{\ce {[A^{2-}]}}}{{\ce {{[H2A]}}}+{[HA^{-}]}+{[A^{2-}]}}}\end{aligned}}} A plot of these fractional concentrations against pH, for given K1 and K2, is known as a Bjerrum plot. A pattern is observed in the above equations and can be expanded to the general n -protic acid that has been deprotonated i -times: α H n − i A i − = [ H + ] n − i ∏ j = 0 i K j ∑ i = 0 n [ [ H + ] n − i ∏ j = 0 i K j ] {\displaystyle \alpha _{{\ce {H}}_{n-i}A^{i-}}={{[{\ce {H+}}]^{n-i}\displaystyle \prod _{j=0}^{i}K_{j}} \over {\displaystyle \sum _{i=0}^{n}{\Big [}[{\ce {H+}}]^{n-i}\displaystyle \prod _{j=0}^{i}K_{j}}{\Big ]}}} where K0 = 1 and the other K-terms are the dissociation constants for the acid. === Neutralization === Neutralization is the reaction between an acid and a base, producing a salt and neutralized base; for example, hydrochloric acid and sodium hydroxide form sodium chloride and water: HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq) Neutralization is the basis of titration, where a pH indicator shows
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equivalence point when the equivalent number of moles of a base have been added to an acid. It is often wrongly assumed that neutralization should result in a solution with pH 7.0, which is only the case with similar acid and base strengths during a reaction. Neutralization with a base weaker than the acid results in a weakly acidic salt. An example is the weakly acidic ammonium chloride, which is produced from the strong acid hydrogen chloride and the weak base ammonia. Conversely, neutralizing a weak acid with a strong base gives a weakly basic salt (e.g., sodium fluoride from hydrogen fluoride and sodium hydroxide). === Weak acid–weak base equilibrium === In order for a protonated acid to lose a proton, the pH of the system must rise above the pKa of the acid. The decreased concentration of H+ in that basic solution shifts the equilibrium towards the conjugate base form (the deprotonated form of the acid). In lower-pH (more acidic) solutions, there is a high enough H+ concentration in the solution to cause the acid to remain in its protonated form. Solutions of weak acids and salts of their conjugate bases form buffer solutions. == Titration == To determine the concentration of an acid in an aqueous solution, an acid–base titration is commonly performed. A strong base solution with a known concentration, usually NaOH or KOH, is added to neutralize the acid solution according to the color change of the indicator with the amount of base added. The titration curve of an acid titrated by a base has two axes, with the base volume on the x-axis and the solution's pH value on the y-axis. The pH of the solution always goes up as the base is added to the solution. === Example: Diprotic acid === For each diprotic
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acid titration curve, from left to right, there are two midpoints, two equivalence points, and two buffer regions. ==== Equivalence points ==== Due to the successive dissociation processes, there are two equivalence points in the titration curve of a diprotic acid. The first equivalence point occurs when all first hydrogen ions from the first ionization are titrated. In other words, the amount of OH− added equals the original amount of H2A at the first equivalence point. The second equivalence point occurs when all hydrogen ions are titrated. Therefore, the amount of OH− added equals twice the amount of H2A at this time. For a weak diprotic acid titrated by a strong base, the second equivalence point must occur at pH above 7 due to the hydrolysis of the resulted salts in the solution. At either equivalence point, adding a drop of base will cause the steepest rise of the pH value in the system. ==== Buffer regions and midpoints ==== A titration curve for a diprotic acid contains two midpoints where pH=pKa. Since there are two different Ka values, the first midpoint occurs at pH=pKa1 and the second one occurs at pH=pKa2. Each segment of the curve that contains a midpoint at its center is called the buffer region. Because the buffer regions consist of the acid and its conjugate base, it can resist pH changes when base is added until the next equivalent points. == Applications of acids == === In industry === Acids are fundamental reagents in treating almost all processes in modern industry. Sulfuric acid, a diprotic acid, is the most widely used acid in industry, and is also the most-produced industrial chemical in the world. It is mainly used in producing fertilizer, detergent, batteries and dyes, as well as used in processing many products such like
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"page_id": 656,
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removing impurities. According to the statistics data in 2011, the annual production of sulfuric acid was around 200 million tonnes in the world. For example, phosphate minerals react with sulfuric acid to produce phosphoric acid for the production of phosphate fertilizers, and zinc is produced by dissolving zinc oxide into sulfuric acid, purifying the solution and electrowinning. In the chemical industry, acids react in neutralization reactions to produce salts. For example, nitric acid reacts with ammonia to produce ammonium nitrate, a fertilizer. Additionally, carboxylic acids can be esterified with alcohols, to produce esters. Acids are often used to remove rust and other corrosion from metals in a process known as pickling. They may be used as an electrolyte in a wet cell battery, such as sulfuric acid in a car battery. === In food === Tartaric acid is an important component of some commonly used foods like unripened mangoes and tamarind. Natural fruits and vegetables also contain acids. Citric acid is present in oranges, lemon and other citrus fruits. Oxalic acid is present in tomatoes, spinach, and especially in carambola and rhubarb; rhubarb leaves and unripe carambolas are toxic because of high concentrations of oxalic acid. Ascorbic acid (Vitamin C) is an essential vitamin for the human body and is present in such foods as amla (Indian gooseberry), lemon, citrus fruits, and guava. Many acids can be found in various kinds of food as additives, as they alter their taste and serve as preservatives. Phosphoric acid, for example, is a component of cola drinks. Acetic acid is used in day-to-day life as vinegar. Citric acid is used as a preservative in sauces and pickles. Carbonic acid is one of the most common acid additives that are widely added in soft drinks. During the manufacturing process, CO2 is usually pressurized to
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{
"page_id": 656,
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dissolve in these drinks to generate carbonic acid. Carbonic acid is very unstable and tends to decompose into water and CO2 at room temperature and pressure. Therefore, when bottles or cans of these kinds of soft drinks are opened, the soft drinks fizz and effervesce as CO2 bubbles come out. Certain acids are used as drugs. Acetylsalicylic acid (Aspirin) is used as a pain killer and for bringing down fevers. === In human bodies === Acids play important roles in the human body. The hydrochloric acid present in the stomach aids digestion by breaking down large and complex food molecules. Amino acids are required for synthesis of proteins required for growth and repair of body tissues. Fatty acids are also required for growth and repair of body tissues. Nucleic acids are important for the manufacturing of DNA and RNA and transmitting of traits to offspring through genes. Carbonic acid is important for maintenance of pH equilibrium in the body. Human bodies contain a variety of organic and inorganic compounds, among those dicarboxylic acids play an essential role in many biological behaviors. Many of those acids are amino acids, which mainly serve as materials for the synthesis of proteins. Other weak acids serve as buffers with their conjugate bases to keep the body's pH from undergoing large scale changes that would be harmful to cells. The rest of the dicarboxylic acids also participate in the synthesis of various biologically important compounds in human bodies. === Acid catalysis === Acids are used as catalysts in industrial and organic chemistry; for example, sulfuric acid is used in very large quantities in the alkylation process to produce gasoline. Some acids, such as sulfuric, phosphoric, and hydrochloric acids, also effect dehydration and condensation reactions. In biochemistry, many enzymes employ acid catalysis. == Biological occurrence ==
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"page_id": 656,
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Many biologically important molecules are acids. Nucleic acids, which contain acidic phosphate groups, include DNA and RNA. Nucleic acids contain the genetic code that determines many of an organism's characteristics, and is passed from parents to offspring. DNA contains the chemical blueprint for the synthesis of proteins, which are made up of amino acid subunits. Cell membranes contain fatty acid esters such as phospholipids. An α-amino acid has a central carbon (the α or alpha carbon) that is covalently bonded to a carboxyl group (thus they are carboxylic acids), an amino group, a hydrogen atom and a variable group. The variable group, also called the R group or side chain, determines the identity and many of the properties of a specific amino acid. In glycine, the simplest amino acid, the R group is a hydrogen atom, but in all other amino acids it is contains one or more carbon atoms bonded to hydrogens, and may contain other elements such as sulfur, oxygen or nitrogen. With the exception of glycine, naturally occurring amino acids are chiral and almost invariably occur in the L-configuration. Peptidoglycan, found in some bacterial cell walls contains some D-amino acids. At physiological pH, typically around 7, free amino acids exist in a charged form, where the acidic carboxyl group (-COOH) loses a proton (-COO−) and the basic amine group (-NH2) gains a proton (-NH+3). The entire molecule has a net neutral charge and is a zwitterion, with the exception of amino acids with basic or acidic side chains. Aspartic acid, for example, possesses one protonated amine and two deprotonated carboxyl groups, for a net charge of −1 at physiological pH. Fatty acids and fatty acid derivatives are another group of carboxylic acids that play a significant role in biology. These contain long hydrocarbon chains and a carboxylic
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"page_id": 656,
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acid group on one end. The cell membrane of nearly all organisms is primarily made up of a phospholipid bilayer, a micelle of hydrophobic fatty acid esters with polar, hydrophilic phosphate "head" groups. Membranes contain additional components, some of which can participate in acid–base reactions. In humans and many other animals, hydrochloric acid is a part of the gastric acid secreted within the stomach to help hydrolyze proteins and polysaccharides, as well as converting the inactive pro-enzyme, pepsinogen into the enzyme, pepsin. Some organisms produce acids for defense; for example, ants produce formic acid. Acid–base equilibrium plays a critical role in regulating mammalian breathing. Oxygen gas (O2) drives cellular respiration, the process by which animals release the chemical potential energy stored in food, producing carbon dioxide (CO2) as a byproduct. Oxygen and carbon dioxide are exchanged in the lungs, and the body responds to changing energy demands by adjusting the rate of ventilation. For example, during periods of exertion the body rapidly breaks down stored carbohydrates and fat, releasing CO2 into the blood stream. In aqueous solutions such as blood CO2 exists in equilibrium with carbonic acid and bicarbonate ion. CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO−3 It is the decrease in pH that signals the brain to breathe faster and deeper, expelling the excess CO2 and resupplying the cells with O2. Cell membranes are generally impermeable to charged or large, polar molecules because of the lipophilic fatty acyl chains comprising their interior. Many biologically important molecules, including a number of pharmaceutical agents, are organic weak acids that can cross the membrane in their protonated, uncharged form but not in their charged form (i.e., as the conjugate base). For this reason the activity of many drugs can be enhanced or inhibited by the use of antacids or acidic
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"page_id": 656,
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foods. The charged form, however, is often more soluble in blood and cytosol, both aqueous environments. When the extracellular environment is more acidic than the neutral pH within the cell, certain acids will exist in their neutral form and will be membrane soluble, allowing them to cross the phospholipid bilayer. Acids that lose a proton at the intracellular pH will exist in their soluble, charged form and are thus able to diffuse through the cytosol to their target. Ibuprofen, aspirin and penicillin are examples of drugs that are weak acids. == Common acids == === Mineral acids (inorganic acids) === Hydrogen halides and their solutions: hydrofluoric acid (HF), hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI) Halogen oxoacids: hypochlorous acid (HClO), chlorous acid (HClO2), chloric acid (HClO3), perchloric acid (HClO4), and corresponding analogs for bromine and iodine Hypofluorous acid (HFO), the only known oxoacid for fluorine. Sulfuric acid (H2SO4) Fluorosulfuric acid (HSO3F) Nitric acid (HNO3) Phosphoric acid (H3PO4) Fluoroantimonic acid (HSbF6) Fluoroboric acid (HBF4) Hexafluorophosphoric acid (HPF6) Chromic acid (H2CrO4) Boric acid (H3BO3) === Sulfonic acids === A sulfonic acid has the general formula RS(=O)2–OH, where R is an organic radical. Methanesulfonic acid (or mesylic acid, CH3SO3H) Ethanesulfonic acid (or esylic acid, CH3CH2SO3H) Benzenesulfonic acid (or besylic acid, C6H5SO3H) p-Toluenesulfonic acid (or tosylic acid, CH3C6H4SO3H) Trifluoromethanesulfonic acid (or triflic acid, CF3SO3H) Polystyrene sulfonic acid (sulfonated polystyrene, [CH2CH(C6H4)SO3H]n) === Carboxylic acids === A carboxylic acid has the general formula R-C(O)OH, where R is an organic radical. The carboxyl group -C(O)OH contains a carbonyl group, C=O, and a hydroxyl group, O-H. Acetic acid (CH3COOH) Citric acid (C6H8O7) Formic acid (HCOOH) Gluconic acid HOCH2-(CHOH)4-COOH Lactic acid (CH3-CHOH-COOH) Oxalic acid (HOOC-COOH) Tartaric acid (HOOC-CHOH-CHOH-COOH) === Halogenated carboxylic acids === Halogenation at alpha position increases acid strength, so that the following acids are all
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stronger than acetic acid. Fluoroacetic acid Trifluoroacetic acid Chloroacetic acid Dichloroacetic acid Trichloroacetic acid === Vinylogous carboxylic acids === Normal carboxylic acids are the direct union of a carbonyl group and a hydroxyl group. In vinylogous carboxylic acids, a carbon-carbon double bond separates the carbonyl and hydroxyl groups. Ascorbic acid === Nucleic acids === Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) == References == Listing of strengths of common acids and bases Zumdahl, Steven S. (1997). Chemistry (4th ed.). Boston: Houghton Mifflin. ISBN 9780669417944. Pavia, D. L.; Lampman, G. M.; Kriz, G. S. (2004). Organic Chemistry Volume I. Mason, OH: Cengage Learning. ISBN 0759347271. == External links == Curtipot: Acid–Base equilibria diagrams, pH calculation and titration curves simulation and analysis – freeware
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Bitumen (UK: BIH-chuum-in, US: bih-TEW-min, by-) is an immensely viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American English, the material is commonly referred to as asphalt or tar. Whether found in natural deposits or refined from petroleum, the substance is classed as a pitch. Prior to the 20th century, the term asphaltum was in general use. The word derives from the Ancient Greek word ἄσφαλτος (ásphaltos), which referred to natural bitumen or pitch. The largest natural deposit of bitumen in the world is the Pitch Lake of southwest Trinidad, which is estimated to contain 10 million tons. About 70% of annual bitumen production is destined for road construction, its primary use. In this application, bitumen is used to bind aggregate particles like gravel and forms a substance referred to as asphalt concrete, which is colloquially termed asphalt. Its other main uses lie in bituminous waterproofing products, such as roofing felt and roof sealant. In material sciences and engineering, the terms asphalt and bitumen are often used interchangeably and refer both to natural and manufactured forms of the substance, although there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term bitumen for the naturally occurring material. For the manufactured material, which is a refined residue from the distillation process of selected crude oils, bitumen is the prevalent term in much of the world; however, in American English, asphalt is more commonly used. To help avoid confusion, the terms "liquid asphalt", "asphalt binder", or "asphalt cement" are used in the U.S. to distinguish it from asphalt concrete. Colloquially, various forms of bitumen are sometimes referred to as "tar", as
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in the name of the La Brea Tar Pits. Naturally occurring bitumen is sometimes specified by the term crude bitumen. Its viscosity is similar to that of cold molasses while the material obtained from the fractional distillation of crude oil boiling at 525 °C (977 °F) is sometimes referred to as "refined bitumen". The Canadian province of Alberta has most of the world's reserves of natural bitumen in the Athabasca oil sands, which cover 142,000 square kilometres (55,000 sq mi), an area larger than England. == Terminology == === Etymology === The Latin word traces to the Proto-Indo-European root *gʷet- "pitch". The word "asphalt" is derived from the late Middle English, in turn from French asphalte, based on Late Latin asphaltum, which is the latinisation of the Greek ἄσφαλτος (ásphaltos), a word meaning "asphalt/bitumen/pitch", which perhaps derives from ἀ-, "not, without", i.e. the alpha privative, and σφάλλειν (sphallein), "to cause to fall, baffle, (in passive) err, (in passive) be balked of". The first use of asphalt by the ancients was as a cement to secure or join various objects, and it thus seems likely that the name itself was expressive of this application. Specifically, Herodotus mentioned that bitumen was brought to Babylon to build its gigantic fortification wall. From the Greek, the word passed into late Latin, and thence into French (asphalte) and English ("asphaltum" and "asphalt"). In French, the term asphalte is used for naturally occurring asphalt-soaked limestone deposits, and for specialised manufactured products with fewer voids or greater bitumen content than the "asphaltic concrete" used to pave roads. === Modern terminology === Bitumen mixed with clay was usually called "asphaltum", but the term is less commonly used today. In American English, "asphalt" is equivalent to the British "bitumen". However, "asphalt" is also commonly used as a shortened form
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
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of "asphalt concrete" (therefore equivalent to the British "asphalt" or "tarmac"). In Canadian English, the word "bitumen" is used to refer to the vast Canadian deposits of extremely heavy crude oil, while "asphalt" is used for the oil refinery product. Diluted bitumen (diluted with naphtha to make it flow in pipelines) is known as "dilbit" in the Canadian petroleum industry, while bitumen "upgraded" to synthetic crude oil is known as "syncrude", and syncrude blended with bitumen is called "synbit". "Bitumen" is still the preferred geological term for naturally occurring deposits of the solid or semi-solid form of petroleum. "Bituminous rock" is a form of sandstone impregnated with bitumen. The oil sands of Alberta, Canada are a similar material. Neither of the terms "asphalt" or "bitumen" should be confused with tar or coal tars. Tar is the thick liquid product of the dry distillation and pyrolysis of organic hydrocarbons primarily sourced from vegetation masses, whether fossilized as with coal, or freshly harvested. The majority of bitumen, on the other hand, was formed naturally when vast quantities of organic animal materials were deposited by water and buried hundreds of metres deep at the diagenetic point, where the disorganized fatty hydrocarbon molecules joined in long chains in the absence of oxygen. Bitumen occurs as a solid or highly viscous liquid. It may even be mixed in with coal deposits. Bitumen, and coal using the Bergius process, can be refined into petrols such as gasoline, and bitumen may be distilled into tar, not the other way around. == Composition == === Normal composition === The components of bitumen include four main classes of compounds: Naphthene aromatics (naphthalene), consisting of partially hydrogenated polycyclic aromatic compounds Polar aromatics, consisting of high molecular weight phenols and carboxylic acids produced by partial oxidation of the material Saturated hydrocarbons;
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"page_id": 657,
"source": null,
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the percentage of saturated compounds in asphalt correlates with its softening point Asphaltenes, consisting of high molecular weight phenols and heterocyclic compounds Bitumen typically contains, elementally 80% by weight of carbon; 10% hydrogen; up to 6% sulfur; and molecularly, between 5 and 25% by weight of asphaltenes dispersed in 90% to 65% maltenes. Most natural bitumens also contain organosulfur compounds, nickel and vanadium are found at <10 parts per million, as is typical of some petroleum. The substance is soluble in carbon disulfide. It is commonly modelled as a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase. "It is almost impossible to separate and identify all the different molecules of bitumen, because the number of molecules with different chemical structure is extremely large". Asphalt may be confused with coal tar, which is a visually similar black, thermoplastic material produced by the destructive distillation of coal. During the early and mid-20th century, when town gas was produced, coal tar was a readily available byproduct and extensively used as the binder for road aggregates. The addition of coal tar to macadam roads led to the word "tarmac", which is now used in common parlance to refer to road-making materials. However, since the 1970s, when natural gas succeeded town gas, bitumen has completely overtaken the use of coal tar in these applications. Other examples of this confusion include La Brea Tar Pits and the Canadian tar sands, both of which actually contain natural bitumen rather than tar. "Pitch" is another term sometimes informally used at times to refer to asphalt, as in Pitch Lake. === Additives, mixtures and contaminants === For economic and other reasons, bitumen is sometimes sold combined with other materials, often without being labeled as anything other than simply "bitumen". Of particular note is the
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"page_id": 657,
"source": null,
"title": "Bitumen"
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use of re-refined engine oil bottoms – "REOB" or "REOBs" – the residue of recycled automotive engine oil collected from the bottoms of re-refining vacuum distillation towers, in the manufacture of asphalt. REOB contains various elements and compounds found in recycled engine oil: additives to the original oil and materials accumulating from its circulation in the engine (typically iron and copper). Some research has indicated a correlation between this adulteration of bitumen and poorer-performing pavement. == Occurrence == The majority of bitumen used commercially is obtained from petroleum. Nonetheless, large amounts of bitumen occur in concentrated form in nature. Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once-living things. These natural deposits of bitumen have been formed during the Carboniferous period, when giant swamp forests dominated many parts of the Earth. They were deposited in the mud on the bottom of the ocean or lake where the organisms lived. Under the heat (above 50 °C) and pressure of burial deep in the earth, the remains were transformed into materials such as bitumen, kerogen, or petroleum. Natural deposits of bitumen include lakes such as the Pitch Lake in Trinidad and Tobago and Lake Bermudez in Venezuela. Natural seeps occur in the La Brea Tar Pits and the McKittrick Tar Pits in California, as well as in the Dead Sea. Bitumen also occurs in unconsolidated sandstones known as "oil sands" in Alberta, Canada, and the similar "tar sands" in Utah, US. The Canadian province of Alberta has most of the world's reserves, in three huge deposits covering 142,000 square kilometres (55,000 sq mi), an area larger than England or New York state. These bituminous sands contain 166 billion barrels (26.4×10^9 m3) of commercially established oil reserves, giving Canada the third largest oil reserves
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
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in the world. Although historically it was used without refining to pave roads, nearly all of the output is now used as raw material for oil refineries in Canada and the United States. The world's largest deposit of natural bitumen, known as the Athabasca oil sands, is located in the McMurray Formation of Northern Alberta. This formation is from the early Cretaceous, and is composed of numerous lenses of oil-bearing sand with up to 20% oil. Isotopic studies show the oil deposits to be about 110 million years old. Two smaller but still very large formations occur in the Peace River oil sands and the Cold Lake oil sands, to the west and southeast of the Athabasca oil sands, respectively. Of the Alberta deposits, only parts of the Athabasca oil sands are shallow enough to be suitable for surface mining. The other 80% has to be produced by oil wells using enhanced oil recovery techniques like steam-assisted gravity drainage. Much smaller heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, US. The Tar Sand Triangle deposit, for example, is roughly 6% bitumen. Bitumen may occur in hydrothermal veins. An example of this is within the Uinta Basin of Utah, in the US, where there is a swarm of laterally and vertically extensive veins composed of a solid hydrocarbon termed Gilsonite. These veins formed by the polymerization and solidification of hydrocarbons that were mobilized from the deeper oil shales of the Green River Formation during burial and diagenesis. Bitumen is similar to the organic matter in carbonaceous meteorites. However, detailed studies have shown these materials to be distinct. The vast Alberta bitumen resources are considered to have started out as living material from marine plants and animals, mainly algae, that died millions of years ago when an
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{
"page_id": 657,
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ancient ocean covered Alberta. They were covered by mud, buried deeply over time, and gently cooked into oil by geothermal heat at a temperature of 50 to 150 °C (120 to 300 °F). Due to pressure from the rising of the Rocky Mountains in southwestern Alberta, 80 to 55 million years ago, the oil was driven northeast hundreds of kilometres and trapped into underground sand deposits left behind by ancient river beds and ocean beaches, thus forming the oil sands. == History == === Paleolithic times === Bitumen use goes back to the Middle Paleolithic, where it was shaped into tool handles or used as an adhesive for attaching stone tools to hafts. The earliest evidence of bitumen use was discovered when archeologists identified bitumen material on Levallois flint artefacts that date to about 71,000 years BP at the Umm el Tlel open-air site, located on the northern slope of the Qdeir Plateau in el Kowm Basin in Central Syria. Microscopic analyses found bituminous residue on two-thirds of the stone artefacts, suggesting that bitumen was an important and frequently-used component of tool making for people in that region at that time. Geochemical analyses of the asphaltic residues places its source to localized natural bitumen outcroppings in the Bichri Massif, about 40 km northeast of the Umm el Tlel archeological site. A re-examination of artifacts uncovered in 1908 at Le Moustier rock shelters in France has identified Mousterian stone tools that were attached to grips made of ochre and bitumen. The grips were formulated with 55% ground goethite ochre and 45% cooked liquid bitumen to create a moldable putty that hardened into handles. Earlier, less-careful excavations at Le Moustier prevent conclusive identification of the archaeological culture and age, but the European Mousterian style of these tools suggests they are associated with
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"page_id": 657,
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Neanderthals during the late Middle Paleolithic into the early Upper Paleolithic between 60,000 and 35,000 years before present. It is the earliest evidence of multicomponent adhesive in Europe. === Ancient times === The use of natural bitumen for waterproofing and as an adhesive dates at least to the fifth millennium BC, with a crop storage basket discovered in Mehrgarh, of the Indus Valley civilization, lined with it. By the 3rd millennium BC refined rock asphalt was in use in the region, and was used to waterproof the Great Bath in Mohenjo-daro. In the ancient Near East, the Sumerians used natural bitumen deposits for mortar between bricks and stones, to cement parts of carvings, such as eyes, into place, for ship caulking, and for waterproofing. The Greek historian Herodotus said hot bitumen was used as mortar in the walls of Babylon. The 1 kilometre (0.62 mi) long Euphrates Tunnel beneath the river Euphrates at Babylon in the time of Queen Semiramis (c. 800 BC) was reportedly constructed of burnt bricks covered with bitumen as a waterproofing agent. Bitumen was used by ancient Egyptians to embalm mummies. The Persian word for asphalt is moom, which is related to the English word mummy. The Egyptians' primary source of bitumen was the Dead Sea, which the Romans knew as Palus Asphaltites (Asphalt Lake). In approximately 40 AD, Dioscorides described the Dead Sea material as Judaicum bitumen, and noted other places in the region where it could be found. The Sidon bitumen is thought to refer to material found at Hasbeya in Lebanon. Pliny also refers to bitumen being found in Epirus. Bitumen was a valuable strategic resource. It was the object of the first known battle for a hydrocarbon deposit – between the Seleucids and the Nabateans in 312 BC. In the ancient Far
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{
"page_id": 657,
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East, natural bitumen was slowly boiled to get rid of the higher fractions, leaving a thermoplastic material of higher molecular weight that, when layered on objects, became hard upon cooling. This was used to cover objects that needed waterproofing, such as scabbards and other items. Statuettes of household deities were also cast with this type of material in Japan, and probably also in China. In North America, archaeological recovery has indicated that bitumen was sometimes used to adhere stone projectile points to wooden shafts. In Canada, aboriginal people used bitumen seeping out of the banks of the Athabasca and other rivers to waterproof birch bark canoes, and also heated it in smudge pots to ward off mosquitoes in the summer. Bitumen was also used to waterproof plank canoes used by indigenous peoples in pre-colonial southern California. === Continental Europe === In 1553, Pierre Belon described in his work Observations that pissasphalto, a mixture of pitch and bitumen, was used in the Republic of Ragusa (now Dubrovnik, Croatia) for tarring of ships. An 1838 edition of Mechanics Magazine cites an early use of asphalt in France. A pamphlet dated 1621, by "a certain Monsieur d'Eyrinys, states that he had discovered the existence (of asphaltum) in large quantities in the vicinity of Neufchatel", and that he proposed to use it in a variety of ways – "principally in the construction of air-proof granaries, and in protecting, by means of the arches, the water-courses in the city of Paris from the intrusion of dirt and filth", which at that time made the water unusable. "He expatiates also on the excellence of this material for forming level and durable terraces" in palaces, "the notion of forming such terraces in the streets not one likely to cross the brain of a Parisian of that generation".
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{
"page_id": 657,
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But the substance was generally neglected in France until the revolution of 1830. In the 1830s there was a surge of interest, and asphalt became widely used "for pavements, flat roofs, and the lining of cisterns, and in England, some use of it had been made of it for similar purposes". Its rise in Europe was "a sudden phenomenon", after natural deposits were found "in France at Osbann (Bas-Rhin), the Parc (Ain) and the Puy-de-la-Poix (Puy-de-Dôme)", although it could also be made artificially. One of the earliest uses in France was the laying of about 24,000 square yards of Seyssel asphalt at the Place de la Concorde in 1835. === United Kingdom === Among the earlier uses of bitumen in the United Kingdom was for etching. William Salmon's Polygraphice (1673) provides a recipe for varnish used in etching, consisting of three ounces of virgin wax, two ounces of mastic, and one ounce of asphaltum. By the fifth edition in 1685, he had included more asphaltum recipes from other sources. The first British patent for the use of asphalt was "Cassell's patent asphalte or bitumen" in 1834. Then on 25 November 1837, Richard Tappin Claridge patented the use of Seyssel asphalt (patent #7849), for use in asphalte pavement, having seen it employed in France and Belgium when visiting with Frederick Walter Simms, who worked with him on the introduction of asphalt to Britain. Dr T. Lamb Phipson writes that his father, Samuel Ryland Phipson, a friend of Claridge, was also "instrumental in introducing the asphalte pavement (in 1836)". Claridge obtained a patent in Scotland on 27 March 1838, and obtained a patent in Ireland on 23 April 1838. In 1851, extensions for the 1837 patent and for both 1838 patents were sought by the trustees of a company previously formed by
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{
"page_id": 657,
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Claridge. Claridge's Patent Asphalte Company – formed in 1838 for the purpose of introducing to Britain "Asphalte in its natural state from the mine at Pyrimont Seysell in France", – "laid one of the first asphalt pavements in Whitehall". Trials were made of the pavement in 1838 on the footway in Whitehall, the stable at Knightsbridge Barracks, "and subsequently on the space at the bottom of the steps leading from Waterloo Place to St. James Park". "The formation in 1838 of Claridge's Patent Asphalte Company (with a distinguished list of aristocratic patrons, and Marc and Isambard Brunel as, respectively, a trustee and consulting engineer), gave an enormous impetus to the development of a British asphalt industry". "By the end of 1838, at least two other companies, Robinson's and the Bastenne company, were in production", with asphalt being laid as paving at Brighton, Herne Bay, Canterbury, Kensington, the Strand, and a large floor area in Bunhill-row, while meantime Claridge's Whitehall paving "continue(d) in good order". The Bonnington Chemical Works manufactured asphalt using coal tar and by 1839 had installed it in Bonnington. In 1838, there was a flurry of entrepreneurial activity involving bitumen, which had uses beyond paving. For example, bitumen could also be used for flooring, damp proofing in buildings, and for waterproofing of various types of pools and baths, both of which were also proliferating in the 19th century. One of the earliest surviving examples of its use can be seen at Highgate Cemetery where it was used in 1839 to seal the roof of the terrace catacombs. On the London stockmarket, there were various claims as to the exclusivity of bitumen quality from France, Germany and England. And numerous patents were granted in France, with similar numbers of patent applications being denied in England due to their similarity
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
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to each other. In England, "Claridge's was the type most used in the 1840s and 50s". In 1914, Claridge's Company entered into a joint venture to produce tar-bound macadam, with materials manufactured through a subsidiary company called Clarmac Roads Ltd. Two products resulted, namely Clarmac, and Clarphalte, with the former being manufactured by Clarmac Roads and the latter by Claridge's Patent Asphalte Co., although Clarmac was more widely used. However, the First World War ruined the Clarmac Company, which entered into liquidation in 1915. The failure of Clarmac Roads Ltd had a flow-on effect to Claridge's Company, which was itself compulsorily wound up, ceasing operations in 1917, having invested a substantial amount of funds into the new venture, both at the outset and in a subsequent attempt to save the Clarmac Company. Bitumen was thought in 19th century Britain to contain chemicals with medicinal properties. Extracts from bitumen were used to treat catarrh and some forms of asthma and as a remedy against worms, especially the tapeworm. === United States === The first use of bitumen in the New World was by aboriginal peoples. On the west coast, as early as the 13th century, the Tongva, Luiseño and Chumash peoples collected the naturally occurring bitumen that seeped to the surface above underlying petroleum deposits. All three groups used the substance as an adhesive. It is found on many different artifacts of tools and ceremonial items. For example, it was used on rattles to adhere gourds or turtle shells to rattle handles. It was also used in decorations. Small round shell beads were often set in asphaltum to provide decorations. It was used as a sealant on baskets to make them watertight for carrying water, possibly poisoning those who drank the water. Asphalt was used also to seal the planks on
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
ocean-going canoes. Asphalt was first used to pave streets in the 1870s. At first naturally occurring "bituminous rock" was used, such as at Ritchie Mines in Macfarlan in Ritchie County, West Virginia from 1852 to 1873. In 1876, asphalt-based paving was used to pave Pennsylvania Avenue in Washington DC, in time for the celebration of the national centennial. In the horse-drawn era, US streets were mostly unpaved and covered with dirt or gravel. Especially where mud or trenching often made streets difficult to pass, pavements were sometimes made of diverse materials including wooden planks, cobble stones or other stone blocks, or bricks. Unpaved roads produced uneven wear and hazards for pedestrians. In the late 19th century with the rise of the popular bicycle, bicycle clubs were important in pushing for more general pavement of streets. Advocacy for pavement increased in the early 20th century with the rise of the automobile. Asphalt gradually became an ever more common method of paving. St. Charles Avenue in New Orleans was paved its whole length with asphalt by 1889. In 1900, Manhattan alone had 130,000 horses, pulling streetcars, wagons, and carriages, and leaving their waste behind. They were not fast, and pedestrians could dodge and scramble their way across the crowded streets. Small towns continued to rely on dirt and gravel, but larger cities wanted much better streets. They looked to wood or granite blocks by the 1850s. In 1890, a third of Chicago's 2000 miles of streets were paved, chiefly with wooden blocks, which gave better traction than mud. Brick surfacing was a good compromise, but even better was asphalt paving, which was easy to install and to cut through to get at sewers. With London and Paris serving as models, Washington laid 400,000 square yards of asphalt paving by 1882; it became
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
the model for Buffalo, Philadelphia and elsewhere. By the end of the century, American cities boasted 30 million square yards of asphalt paving, well ahead of brick. The streets became faster and more dangerous so electric traffic lights were installed. Electric trolleys (at 12 miles per hour) became the main transportation service for middle class shoppers and office workers until they bought automobiles after 1945 and commuted from more distant suburbs in privacy and comfort on asphalt highways. === Canada === Canada has the world's largest deposit of natural bitumen in the Athabasca oil sands, and Canadian First Nations along the Athabasca River had long used it to waterproof their canoes. In 1719, a Cree named Wa-Pa-Su brought a sample for trade to Henry Kelsey of the Hudson's Bay Company, who was the first recorded European to see it. However, it wasn't until 1787 that fur trader and explorer Alexander MacKenzie saw the Athabasca oil sands and said, "At about 24 miles from the fork (of the Athabasca and Clearwater Rivers) are some bituminous fountains into which a pole of 20 feet long may be inserted without the least resistance." The value of the deposit was obvious from the start, but the means of extracting the bitumen was not. The nearest town, Fort McMurray, Alberta, was a small fur trading post, other markets were far away, and transportation costs were too high to ship the raw bituminous sand for paving. In 1915, Sidney Ells of the Federal Mines Branch experimented with separation techniques and used the product to pave 600 feet of road in Edmonton, Alberta. Other roads in Alberta were paved with material extracted from oil sands, but it was generally not economic. During the 1920s Dr. Karl A. Clark of the Alberta Research Council patented a hot water
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
oil separation process and entrepreneur Robert C. Fitzsimmons built the Bitumount oil separation plant, which between 1925 and 1958 produced up to 300 barrels (50 m3) per day of bitumen using Dr. Clark's method. Most of the bitumen was used for waterproofing roofs, but other uses included fuels, lubrication oils, printers ink, medicines, rust- and acid-proof paints, fireproof roofing, street paving, patent leather, and fence post preservatives. Eventually Fitzsimmons ran out of money and the plant was taken over by the Alberta government. Today the Bitumount plant is a Provincial Historic Site. === Photography and art === Bitumen was used in early photographic technology. In 1826, or 1827, it was used by French scientist Joseph Nicéphore Niépce to make the oldest surviving photograph from nature. The bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the bitumen and made it insoluble, so that when it was subsequently rinsed with a solvent only the sufficiently light-struck areas remained. Many hours of exposure in the camera were required, making bitumen impractical for ordinary photography, but from the 1850s to the 1920s it was in common use as a photoresist in the production of printing plates for various photomechanical printing processes. Bitumen was the nemesis of many artists during the 19th century. Although widely used for a time, it ultimately proved unstable for use in oil painting, especially when mixed with the most common diluents, such as linseed oil, varnish and turpentine. Unless thoroughly diluted, bitumen never fully solidifies and will in time corrupt the other pigments with which it comes into contact. The use of bitumen as a glaze to set in shadow or mixed with other colors to render a darker tone resulted in the eventual deterioration of many paintings, for
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
instance those of Delacroix. Perhaps the most famous example of the destructiveness of bitumen is Théodore Géricault's Raft of the Medusa (1818–1819), where his use of bitumen caused the brilliant colors to degenerate into dark greens and blacks and the paint and canvas to buckle. == Modern use == === Global use === The vast majority of refined bitumen is used in construction: primarily as a constituent of products used in paving and roofing applications. According to the requirements of the end use, bitumen is produced to specification. This is achieved either by refining or blending. It is estimated that the current world use of bitumen is approximately 102 million tonnes per year. Approximately 85% of all the bitumen produced is used as the binder in asphalt concrete for roads. It is also used in other paved areas such as airport runways, car parks and footways. Typically, the production of asphalt concrete involves mixing fine and coarse aggregates such as sand, gravel and crushed rock with asphalt, which acts as the binding agent. Other materials, such as recycled polymers (e.g., rubber tyres), may be added to the bitumen to modify its properties according to the application for which the bitumen is ultimately intended. A further 10% of global bitumen production is used in roofing applications, where its waterproofing qualities are invaluable. The remaining 5% of bitumen is used mainly for sealing and insulating purposes in a variety of building materials, such as pipe coatings, carpet tile backing and paint. Bitumen is applied in the construction and maintenance of many structures, systems, and components, such as: === Rolled asphalt concrete === The largest use of bitumen is for making asphalt concrete for road surfaces; this accounts for approximately 85% of the bitumen consumed in the United States. There are about 4,000
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
asphalt concrete mixing plants in the US, and a similar number in Europe. Asphalt concrete pavement mixes are typically composed of 5% bitumen (known as asphalt cement in the US) and 95% aggregates (stone, sand, and gravel). Due to its highly viscous nature, bitumen must be heated so it can be mixed with the aggregates at the asphalt mixing facility. The temperature required varies depending upon characteristics of the bitumen and the aggregates, but warm-mix asphalt technologies allow producers to reduce the temperature required. The weight of an asphalt pavement depends upon the aggregate type, the bitumen, and the air void content. An average example in the United States is about 112 pounds per square yard, per inch of pavement thickness. When maintenance is performed on asphalt pavements, such as milling to remove a worn or damaged surface, the removed material can be returned to a facility for processing into new pavement mixtures. The bitumen in the removed material can be reactivated and put back to use in new pavement mixes. With some 95% of paved roads being constructed of or surfaced with asphalt, a substantial amount of asphalt pavement material is reclaimed each year. According to industry surveys conducted annually by the Federal Highway Administration and the National Asphalt Pavement Association, more than 99% of the bitumen removed each year from road surfaces during widening and resurfacing projects is reused as part of new pavements, roadbeds, shoulders and embankments or stockpiled for future use. Asphalt concrete paving is widely used in airports around the world. Due to the sturdiness and ability to be repaired quickly, it is widely used for runways. === Mastic asphalt === Mastic asphalt is a type of asphalt that differs from dense graded asphalt (asphalt concrete) in that it has a higher bitumen (binder) content,
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
usually around 7–10% of the whole aggregate mix, as opposed to rolled asphalt concrete, which has only around 5% asphalt. This thermoplastic substance is widely used in the building industry for waterproofing flat roofs and tanking underground. Mastic asphalt is heated to a temperature of 210 °C (410 °F) and is spread in layers to form an impervious barrier about 20 millimeters (0.8 inches) thick. === Bitumen emulsion === Bitumen emulsions are colloidal mixtures of bitumen and water. Due to the different surface tensions of the two liquids, stable emulsions cannot be created simply by mixing. Therefore, various emulsifiers and stabilizers are added. Emulsifiers are amphiphilic molecules that differ in the charge of their polar head group. They reduce the surface tension of the emulsion and thus prevent bitumen particles from fusing. The emulsifier charge defines the type of emulsion: anionic (negatively charged) and cationic (positively charged). The concentration of an emulsifier is a critical parameter affecting the size of the bitumen particles—higher concentrations lead to smaller bitumen particles. Thus, emulsifiers have a great impact on the stability, viscosity, breaking strength, and adhesion of the bitumen emulsion. The size of bitumen particles is usually between 0.1 and 50 μm with a main fraction between 1 μm and 10 μm. Laser diffraction techniques can be used to determine the particle size distribution quickly and easily. Cationic emulsifiers primarily include long-chain amines such as imidazolines, amido-amines, and diamines, which acquire a positive charge when an acid is added. Anionic emulsifiers are often fatty acids extracted from lignin, tall oil, or tree resin saponified with bases such as NaOH, which creates a negative charge. During the storage of bitumen emulsions, bitumen particles sediment, agglomerate (flocculation), or fuse (coagulation), which leads to a certain instability of the bitumen emulsion. How fast this process occurs
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{
"page_id": 657,
"source": null,
"title": "Bitumen"
}
|
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