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Genome-wide CRISPR-Cas9 knockout screens aim to elucidate the relationship between genotype and phenotype by ablating gene expression on a genome-wide scale and studying the resulting phenotypic alterations. The approach utilises the CRISPR-Cas9 gene editing system, coupled with libraries of single guide RNAs (sgRNAs), which are designed to target every gene in the genome. Over recent years, the genome-wide CRISPR screen has emerged as a powerful tool for performing large-scale loss-of-function screens, with low noise, high knockout efficiency and minimal off-target effects. Early studies in "Caenorhabditis elegans" and "Drosophila melanogaster" saw large-scale, systematic loss of function (LOF) screens performed through saturation mutagenesis, demonstrating the potential of this approach to characterise genetic pathways and identify genes with unique and essential functions. The saturation mutagenesis technique was later applied in other organisms, for example zebrafish and mice. Targeted approaches for gene knockdown emerged in the 1980s with techniques such as homologous recombination, trans-cleaving ribozymes, and antisense technologies. By the year 2000, RNA interference (RNAi) technology had emerged as a fast, simple, and inexpensive technique for targeted gene knockdown, and was routinely being used to study "in vivo" gene function in "C. elegans". Indeed, in the span of only a few years following its discovery by Fire "et al". (1998), almost all of the ~19,000 genes in "C. elegans" had been analysed using RNAi-based knockdown | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens The production of RNAi libraries facilitated the application of this technology on a genome-wide scale, and RNAi-based methods became the predominant approach for genome-wide knockdown screens. Nevertheless, RNAi-based approaches to genome-wide knockdown screens have their limitations. For one, the high off-target effects cause issues with false-positive observations. Additionally, because RNAi reduces gene expression at the post-transcriptional level by targeting RNA, RNAi-based screens only result in partial and short-term suppression of genes. Whilst partial knockdown may be desirable in certain situations, a technology with improved targeting efficiency and fewer off-target effects was needed. Since initial identification as a prokaryotic adaptive immune system, the bacterial type II clustered regularly interspaced short palindrome repeats (CRISPR)/Cas9 system has become a simple and efficient tool for generating targeted LOF mutations. It has been successfully applied to edit human genomes, and has started to displace RNAi as the dominant tool in mammalian studies. In the context of genome-wide knockout screens, recent studies have demonstrated that CRISPR/Cas9 screens are able to achieve highly efficient and complete protein depletion, and overcome the off-target issues seen with RNAi screens. In summary, the recent emergence of CRISPR-Cas9 has dramatically increased our ability to perform large-scale LOF screens | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens The versatility and programmability of Cas9, coupled with the low noise, high knockout efficiency and minimal off-target effects, have made CRISPR the platform of choice for many researchers engaging in gene targeting and editing. The clustered regularly interspaced short palindrome repeats (CRISPR)/Cas9 system is a gene-editing technology that can introduce double-strand breaks (DSBs) at a target genomic locus. By using a single guide RNA (sgRNA), the endonuclease Cas9 can be delivered to a specific DNA sequence where it cleaves the nucleotide chain. The specificity of the sgRNA is determined by a 20-nt sequence, homologous to the genomic locus of interest, and the binding to Cas9 is mediated by a constant scaffold region of the sgRNA. The desired target site must be immediately followed (5’ to 3’) by a conserved 3 nucleotide protospacer adjacent motif (PAM). In order to repair the DSBs, the cell may use the highly error prone non-homologous end joining, or homologous recombination. By designing suitable sgRNAs, planned insertions or deletions can be introduced into the genome. In the context of genome-wide LOF screens, the aim is to cause gene disruption and knockout. To perform CRISPR knockouts on a genome-wide scale, collections of sgRNAs known as sgRNA libraries, or CRISPR knockout libraries, must be generated. The first step in creating a sgRNA library is to identify genomic regions of interest based on known sgRNA targeting rules | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens For example, sgRNAs are most efficient when targeting the coding regions of genes and not the 5’ and 3’ UTRs. Conserved exons present as attractive targets, and position relative to the transcription start site should be considered. Secondly, all the possible PAM sites are identified and selected for. On- and off-target activity should be analysed, as should GC content, and homopolymer stretches should be avoided. The most commonly used Cas9 endonuclease, derived from "Streptococcus pyogenes", recognises a PAM sequence of NGG. Furthermore, specific nucleotides appear to be favoured at specific locations. Guanine is strongly favoured over cytosine on position 20 right next to the PAM motif, and on position 16 cytosine is preferred over guanine. For the variable nucleotide in the NGG PAM motif, it has been shown that cytosine is preferred and thymine disfavoured. With such criteria taken into account, the sgRNA library is computationally designed around the selected PAM sites. Multiple sgRNAs (at least 4-6) should be created against every single gene to limit false-positive detection, and negative control sgRNAs with no known targets should be included. The sgRNAs are then created by "in situ" synthesis, amplified by PCR, and cloned into a vector delivery system. Developing a new sgRNA library is a laborious and time-consuming process. In practice, researchers may select an existing library depending on their experimental purpose and cell lines of interest | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens As of February 2020, the most widely used resources for genome-wide CRISPR knockout screens have been the two Genome-Scale CRISPR Knock-Out (GeCKO) libraries created by the Zhang lab. Available through addgene, these lentiviral libraries respectively target human and mouse exons, and both are available as a one-vector system (where the sgRNAs and Cas9 are present on the same plasmid) or as a two-vector system (where the sgRNAs and Cas9 are present on separate plasmids). Each library is delivered as two half-libraries, allowing researchers to screen with 3 or 6 sgRNAs/gene. Aside from GeCKO, a number of other CRISPR libraries have been generated and made available through addgene. The Sabatini & Lander labs currently have 7 separate human and mouse libraries, including targeted sublibraries for distinct subpools such as kinases and ribosomal genes (Addgene #51043–51048). Further, improvements to the specificity of sgRNAs have resulted in ‘second generation’ libraries, such as the Brie (Addgene #73632) and Brunello (Addgene #73178) libraries generated by the Doench and Root labs, and the Toronto knockout (TKO) library (Addgene #1000000069) generated by the Moffat lab. Targeted gene knockout using CRISPR/Cas9 requires the use of a delivery system to introduce the sgRNA and Cas9 into the cell. Although a number of different delivery systems are potentially available for CRISPR, genome-wide loss-of-function screens are predominantly carried out using third generation lentiviral vectors | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens These lentiviral vectors are able to efficiently transduce a broad range of cell types and stably integrate into the genome of dividing and non-dividing cells. Third generation lentiviral particles are produced by co-transfecting 293T human embryonic kidney (HEK) cells with: The lentiviral particle-containing supernatant is harvested, concentrated and subsequently used to infect the target cells. The exact protocol for lentiviral production will vary depending on the research aim and applied library. If a two vector-system is used, for example, cells are sequentially transduced with Cas9 and sgRNA in a two-step procedure. Although more complex, this has the advantage of a higher titre for the sgRNA library virus. In general, there are two different formats of genome-wide CRISPR knockout screens: arrayed and pooled. In an arrayed screen, each well contains a specific and known sgRNA targeting a specific gene. Since the sgRNA responsible for each phenotype is known based on well location, phenotypes can be identified and analysed without requiring genetic sequencing. This format allows for the measurement of more specific cellular phenotypes, perhaps by fluorescence or luminescence, and allows researchers to use more library types and delivery methods. For large-scale LOF screens, however, arrayed formats are considered low-efficiency, and expensive in terms of financial and material resources because cell populations have to be isolated and cultured individually | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens In a pooled screen, cells grown in a single vessel are transduced in bulk with viral vectors collectively containing the entire sgRNA library. To ensure that the amount of cells infected by more than one sgRNA-containing particle is limited, a low multiplicity of infection (MOI) (typically 0.3-0.6) is used. Evidence so far has suggested that each sgRNA should be represented in a minimum of 200 cells. Transduced cells will be selected for, followed by positive or negative selection for the phenotype of interest, and genetic sequencing will be necessary to identify the integrated sgRNAs. Following phenotypic selection, genomic DNA is extracted from the selected clones, alongside a control cell population. In the most common protocols for genome-wide knockouts, a 'Next-generation sequencing (NGS) library' is created by a two step polymerase chain reaction (PCR). The first step amplifies the sgRNA region, using primers specific to the lentiviral integration sequence, and the second step adds Illumina i5 and i7 sequences. NGS of the PCR products allows the recovered sgRNAs to be identified, and a quantification step can be used to determine the relative abundance of each sgRNA. The final step in the screen is to computationally evaluate the significantly enriched or depleted sgRNAs, trace them back to their corresponding genes, and in turn determine which genes and pathways could be responsible for the observed phenotype | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens Several algorithms are currently available for this purpose, with the most popular being the Model-based Analysis of Genome-wide CRISPR/Cas9 Knockout (MAGeCK) method. Developed specifically for CRISPR/Cas9 knockout screens in 2014, MAGeCK demonstrated better performance compared with alternative algorithms at the time, and has since demonstrated robust results and high sensitivity across different experimental conditions. As of 2015, the MAGeCK algorithm has been extended to introduce quality control measurements, and account for the previously overlooked sgRNA knockout efficiency. A web-based visualisation tool (VISPR) was also integrated, allowing users to interactively explore the results, analysis, and quality controls. Over recent years, the genome-wide CRISPR screen has emerged as a powerful tool for studying the intricate networks of cellular signalling. Cellular signalling is essential for a number of fundamental biological processes, including cell growth, proliferation, differentiation, and apoptosis. One practical example is the identification of genes required for proliferative signalling in cancer cells. Cells are transduced with a CRISPR sgRNA library, and studied for growth over time. By comparing sgRNA abundance in selected cells to a control, one can identify which sgRNAs become depleted and in turn which genes may be responsible for the proliferation defect | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens Such screens have been used to identify cancer-essential genes in acute myeloid leukemia and neuroblastoma, and to describe tumour-specific differences between cancer cell lines. Targeted cancer therapies are designed to target the specific genes, proteins, or environments contributing to tumour cell growth or survival. After a period of prolonged treatment with these therapies, however, tumour cells may develop resistance. Although the mechanisms behind cancer drug resistance are poorly understood, potential causes include: target alteration, drug degradation, apoptosis escape, and epigenetic alterations. Resistance is well-recognised and poses a serious problem in cancer management. To overcome this problem, a synthetic lethal partner can be identified. Genome-wide LOF screens using CRISPR-Cas9 can be used to screen for synthetic lethal partners. For this, a wild-type cell line and a tumour cell line containing the resistance-causing mutation are transduced with a CRISPR sgRNA library. The two cell lines are cultivated, and any under-represented or dead cells are analysed to identify potential synthetic lethal partner genes. A recent study by Hinze "et al." (2019) used this method to identify a synthetic lethal interaction between the chemotherapy drug asparaginase and two genes in the Wnt signalling pathway NKD2 and LGR6. Due to their small genomes and limited number of encoded proteins, viruses exploit host proteins for entry, replication, and transmission | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens Identification of such host proteins, also termed host dependency factors (HDFs), is particularly important for identifying therapeutic targets. Over recent years, many groups have successfully used genome-wide CRISPR/Cas9 as a screening strategy for HDFs in viral infections. One example is provided by Marceau "et al." (2017), who aimed to dissect the host factors associated with dengue and hepatitis C (HCV) infection (two viruses in family "Flaviviridae"). ELAVL1, an RNA-binding protein encoded by the ELAVL1 gene, was found to be a critical receptor for HCV entry, and a remarkable divergence in host dependency factors was demonstrated between the two flaviviridae. Additional reported applications of genome-wide CRISPR screens include the study of: mitochondrial metabolism, bacterial toxin resistance, genetic drivers of metastasis, cancer drug resistance, West Nile virus-induced cell death, and immune cell gene networks. "This section will specifically address genome-wide CRISPR screens. For a review of CRISPR limitations see Lino et al. (2018)" Genome-wide CRISPR screens will ultimately be limited by the properties of the chosen sgRNA library. Each library will contain a different set of sgRNAs, and average coverage per gene may vary. Currently available libraries tend to be biased towards sgRNAs targeting early (5’) protein-coding exons, rather than those targeting the more functional protein domains. This problem was highlighted by Hinze "et al | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens " (2019), who noted that genes associated with asparaginase sensitivity failed to score in their genome-wide screen of asparaginase-resistant leukemia cells. If an appropriate library is not available, creating and amplifying a new sgRNA library is a lengthy process which may take many months. Potential challenges include: (i) effective sgRNA design; (ii) ensuring comprehensive sgRNA coverage throughout the genome; (iii) lentiviral vector backbone design; (iv) producing sufficient amounts of high-quality lentivirus; (v) overcoming low transformation efficiency; (vi) proper scaling of the bacterial culture. One of the largest hurdles for genome-wide CRISPR screening is ensuring adequate coverage of the sgRNA library across the cell population. Evidence so far has suggested that each sgRNA should be represented and maintained in a minimum of 200-300 cells. Considering that the standard protocol uses a multiplicity of infection of ~0.3, and a transduction efficiency of 30-40% the number of cells required to produce and maintain suitable coverage becomes very large. By way of example, the most popular human sgRNA library is the GeCKO v2 library created by the Zhang lab; it contains 123,411 sgRNAs. Studies using this library commonly transduce more than 1x10 cells As CRISPR continues to exhibit low noise and minimal off-target effects, an alternative strategy is to reduce the number of sgRNAs per gene for a primary screen | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens Less stringent cut-offs are used for hit selection, and additional sgRNAs are later used in a more specific secondary screen. This approach is demonstrated by Doench "et al". (2016), who found that >92% of genes recovered using the standard protocol were also recovered using fewer sgRNAs per gene. They suggest that this strategy could be useful in studies where scale-up is prohibitively costly. Lentiviral vectors have certain general limitations. For one, it is impossible to control where the viral genome integrates into the host genome, and this may affect important functions of the cell. Vannucci "et al." provide an excellent review of viral vectors along with their general advantages and disadvantages. In the specific context of genome-wide CRISPR screens, producing and transducing the lentiviral particles is relatively laborious and time consuming, taking about two weeks in total. Additionally, because the DNA integrates into the host genome, lentiviral delivery leads to long-term expression of Cas9, potentially leading to off-target effects. In an arrayed screen, each well contains a specific and known sgRNA targeting a specific gene. Arrayed screens therefore allow for detailed profiling of a single cell, but are limited by high costs and the labour required to isolate and culture the high number of individual cell populations. Conventional pooled CRISPR screens are relatively simple and cost effective to perform, but are limited to the study of the entire cell population | https://en.wikipedia.org/wiki?curid=63202233 |
Genome-wide CRISPR-Cas9 knockout screens This means that rare phenotypes may be more difficult to identify, and only crude phenotypes can be selected for e.g. cell survival, proliferation, or reporter gene expression. Emerging technologies are aiming to combine pooled CRISPR screens with the detailed resolution of massively parallel single-cell RNA-sequencing (RNA-seq). Studies utilising “CRISP-seq”, “CROP-seq”, and “PERTURB-seq” have demonstrated rich genomic readouts, accurately identifying gene expression signatures for individual gene knockouts in a complex pool of cells. These methods have the added benefit of producing transcriptional profiles of the sgRNA-induced cells. | https://en.wikipedia.org/wiki?curid=63202233 |
MNase-seq is one of four classes of methods used for assessing the status of the epigenome through analysis of chromatin accessibility. The other three techniques are DNase-seq, FAIRE-seq, and ATAC-seq. While is primarily used to sequence regions of DNA bound by histones or other chromatin-bound proteins, the other three are commonly used for: mapping Deoxyribonuclease I hypersensitive sites (DHSs), sequencing the DNA unbound by chromatin proteins, or sequencing regions of loosely packaged chromatin through transposition of markers, respectively. Micrococcal nuclease (MNase) was first discovered in "S. aureus" in 1956, protein crystallized in 1966, and characterized in 1967. MNase digestion of chromatin was key to early studies of chromatin structure; being used to determine that each nucleosomal unit of chromatin was composed of approximately 200bp of DNA. This, alongside Olins’ and Olins’ “beads on a string” model, confirmed Kornberg’s ideas regarding the basic chromatin structure. Upon additional studies, it was found that MNase could not degrade histone-bound DNA shorter than ~140bp and that DNase I and II could degrade the bound DNA to as low as 10bp. This ultimately elucidated that ~146bp of DNA wrap around the nucleosome core, ~50bp linker DNA connect each nucleosome, and that 10 continuous base-pairs of DNA tightly bind to the core of the nucleosome in intervals | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq In addition to being used to study chromatin structure, micrococcal nuclease digestion had been used in oligonucleotide sequencing experiments since its characterization in 1967. MNase digestion was additionally used in several studies to analyze chromatin-free sequences, such as yeast ("Saccharomyces cerevisiae") mitochondrial DNA as well as bacteriophage DNA through its preferential digestion of adenine and thymine-rich regions. In the early 1980s, MNase digestion was used to determine the nucleosomal phasing and associated DNA for chromosomes from mature SV40, fruit flies ("Drosophila melanogaster"), yeast, and monkeys, among others. The first study to use this digestion to study the relevance of chromatin accessibility to gene expression in humans was in 1985. In this study, nuclease was used to find the association of certain oncogenic sequences with chromatin and nuclear proteins. Studies utilizing MNase digestion to determine nucleosome positioning without sequencing or array information continued into the early 2000s. With the advent of whole genome sequencing in the late 1990s and early 2000s, it became possible to compare purified DNA sequences to the eukaryotic genomes of "S. cerevisiae," "Caenorhabditis elegans," "D. melanogaster," "Arabidopsis thaliana," "Mus musculus", and "Homo sapiens." MNase digestion was first applied to genome-wide nucleosome occupancy studies in "S. cerevisiae" and "C | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq elegans," accompanied by analyses through microarrays to determine which DNA regions were enriched with MNase-resistant nucleosomes. MNase-based microarray analyses were often utilized at genome-wide scales for yeast and in limited genomic regions in humans to determine nucleosome positioning, which could be used as an inference for transcriptional inactivation. It was not until 2008, around the time Next-Generation sequencing was being developed, when MNase digestion was combined with high-throughput sequencing, namely Solexa/Illumina sequencing, to study nucleosomal positioning at a genome-wide scale in humans. A year later, the terms “MNase-Seq” and “MNase-ChIP”, for micrococcal nuclease digestion with chromatin immunoprecipitation, were finally coined. Since its initial application in 2008, has been utilized to deep sequence DNA associated with nucleosome occupancy and epigenomics across eukaryotes. As of February 2020, is still applied to assay accessibility in chromatin. Chromatin is dynamic and the positioning of nucleosomes on DNA changes through the activity of various transcription factors and remodeling complexes, approximately reflecting transcriptional activity at these sites. DNA wrapped around nucleosomes are generally inaccessible to transcription factors. Hence, can be used to indirectly determine which regions of DNA are transcriptionally inaccessible by directly determining which regions are bound to nucleosomes | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq In a typical experiment, eukaryotic cell nuclei are first isolated from a tissue of interest. Then, uses the endo-exonuclease micrococcal nuclease to bind and cleave protein-unbound regions of DNA of eukaryotic chromatin, first cleaving and resecting one strand, then cleaving the antiparallel strand as well. The chromatin can be optionally crosslinked with formaldehyde. MNase requires Ca as a cofactor, typically with a final concentration of 1mM. If a region of DNA is bound by the nucleosome core (i.e. histones) or other chromatin-bound proteins (e.g. transcription factors), then MNase is unable to bind and cleave the DNA. Nucleosomes or the DNA-protein complexes can be purified from the sample and the bound DNA can be subsequently purified via gel electrophoresis and extraction. The purified DNA is typically ~150bp, if purified from nucleosomes, or shorter, if from another protein (e.g. transcription factors). This makes short-read, high-throughput sequencing ideal for as reads for these technologies are highly accurate but can only cover a couple hundred continuous base-pairs in length. Once sequenced, the reads can be aligned to a reference genome to determine which DNA regions are bound by nucleosomes or proteins of interest, with tools such as Bowtie. The positioning of nucleosomes elucidated, through MNase-seq, can then be used to predict genomic expression and regulation at the time of digestion. Recently, has also been implemented in determining where transcription factors bind on the DNA | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq Classical ChIP-seq displays issues with resolution quality, stringency in experimental protocol, and DNA fragmentation. Classical ChIP-seq typically uses sonication to fragment chromatin, which biases heterochromatic regions due to the condensed and tight binding of chromatin regions to each other. Unlike histones, transcription factors only transiently bind DNA. Other methods, such as sonication in ChIP-seq, requiring the use of increased temperatures and detergents, can lead to the loss of the factor. CUT&RUN sequencing is a novel form of an MNase-based immunoprecipitation. Briefly, it uses an MNase tagged with an antibody to specifically bind DNA-bound proteins that present the epitope recognized by that antibody. Digestion then specifically occurs at regions surrounding that transcription factor, allowing for this complex to diffuse out of the nucleus and be obtained without having to worry about significant background nor the complications of sonication. The use of this technique does not require high temperatures or high concentrations of detergent. Furthermore, MNase improves chromatin digestion due to its exonuclease and endonuclease activity. Cells are lysed in an SDS/[[Triton X-100\\ solution. Then, the MNase-antibody complex is added. And finally, the protein-DNA complex can be isolated, with the DNA being subsequently purified and [[massive parallel sequencing|sequenced]]. The resulting soluble extract contains a 25-fold enrichment in fragments under 50bp | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq This increased enrichment results in cost-effective high-resolution data. Single-cell micrococcal nuclease sequencing (scMNase-seq) is a novel technique that is used to analyze [[nucleosome]] positioning and to infer chromatin accessibility with the use of only a single-cell input. First, cells are sorted into single aliquots using [[Flow cytometry|fluorescence-activated cell sorting (FACS)]]. The cells are then lysed and digested with micrococcal nuclease. The isolated DNA is subjected to [[Polymerase chain reaction|PCR]] amplification and then the desired sequence is isolated and analyzed. The use of MNase in single-cell assays results in increased detection of regions such as [[DNase I hypersensitive site|DNase I hypersensitive sites]] as well as transcription factor binding sites. [[File:Sequencing table.png|thumb|]] As with MNase-seq, DNase-seq was developed by combining an existing DNA endonuclease with Next-Generation sequencing technology to assay chromatin accessibility. Both techniques have been used across several eukaryotes to ascertain information on nucleosome positioning in the respective organisms and both rely on the same principle of digesting open DNA to isolate ~140bp bands of DNA from nucleosomes or shorter bands if ascertaining transcription factor information. Both techniques have recently been optimized for single-cell sequencing, which corrects for one of the major disadvantages of both techniques; that being the requirement for high cell input | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq At sufficient concentrations, DNase I is capable of digesting nucleosome-bound DNA to 10bp, whereas micrococcal nuclease cannot. Additionally, DNase-seq is used to identify DHSs, which are regions of DNA that are hypersensitive to DNase treatment and are often indicative of regulatory regions (e.g. [[Promoter (genetics)|promoters]] or [[Enhancer (genetics)|enhancers]]). An equivalent effect is not found with MNase. As a result of this distinction, DNase-seq is primarily utilized to directly identify regulatory regions, whereas is used to identify transcription factor and nucleosomal occupancy to indirectly infer effects on gene expression. FAIRE-seq differs more from than does DNase-seq. FAIRE-seq was developed in 2007 and combined with Next-Generation sequencing three years later to study DHSs. FAIRE-seq relies on the use of formaldehyde to crosslink target proteins with DNA and then subsequent sonication and phenol-chloroform extraction to separate non-crosslinked DNA and crosslinked DNA. The non-crosslinked DNA is sequenced and analyzed, allowing for direct observation of open chromatin. does not measure chromatin accessibility as directly as FAIRE-seq. However, unlike FAIRE-seq, it does not necessarily require crosslinking, nor does it rely on sonication, but it may require [[phenol-chloroform extraction|phenol and chloroform extraction]]. Two major disadvantages of FAIRE-seq, relative to the other three classes, are the minimum required input of 100,000 cells and the reliance on crosslinking | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq Crosslinking may bind other chromatin-bound proteins that transiently interact with DNA, hence limiting the amount of non-crosslinked DNA that can be recovered and assayed from the aqueous phase. Thus, the overall resolution obtained from FAIRE-seq can be relatively lower than that of DNase-seq or and with the 100,000 cell requirement, the single-cell equivalents of DNase-seq or make them far more appealing alternatives. ATAC-seq is the most recently developed class of chromatin accessibility assays. ATAC-seq uses a hyperactive [[transposase]] to insert transposable markers with specific adapters, capable of binding primers for sequencing, into open regions of chromatin. PCR can then be used to amplify sequences adjacent to the inserted transposons, allowing for determination of open chromatin sequences without causing a shift in chromatin structure. ATAC-seq has been proven effective in humans, amongst other eukaryotes, including in frozen samples. As with DNase-seq and MNase-seq, a successful single-cell version of ATAC-seq has also been developed. ATAC-seq has several advantages over in assessing chromatin accessibility. ATAC-seq does not rely on the variable digestion of the micrococcal nuclease, nor crosslinking or phenol-chloroform extraction. It generally maintains chromatin structure, so results from ATAC-seq can be used to directly assess chromatin accessibility, rather than indirectly via MNase-seq | https://en.wikipedia.org/wiki?curid=63210872 |
MNase-seq ATAC-seq can also be completed within a few hours, whereas the other three techniques typically require overnight incubation periods. The two major disadvantages to ATAC-seq, in comparison to MNase-seq, are the requirement for higher sequencing coverage and the prevalence of mitochondrial contamination due to non-specific insertion of DNA into both mitochondrial DNA and nuclear DNA. Despite these minor disadvantages, use of ATAC-seq over the alternatives is becoming more prevalent. [[Category:Molecular biology techniques]] | https://en.wikipedia.org/wiki?curid=63210872 |
Thermoneutral voltage In electrochemistry, a thermoneutral voltage is a voltage drop across an electrochemical cell which is sufficient not only to drive the cell reaction, but to also provide the heat necessary to maintain a constant temperature. For a reaction of the form The thermoneutral voltage is given by where formula_3 is the change in enthalpy and "F" is the Faraday constant. For a cell reaction characterized by the chemical equation: at constant temperature and pressure, the thermodynamic voltage (minimum voltage required to drive the reaction) is given by the Nernst equation: where formula_6 is the Gibbs energy and "F" is the Faraday constant. The standard thermodynamic voltage (i.e. at standard temperature and pressure) is given by: and the Nernst equation can be used to calculate the standard potential at other conditions. The cell reaction is generally endothermic: i.e. it will extract heat from its environment. The Gibbs energy calculation generally assumes an infinite thermal reservoir to maintain a constant temperature, but in a practical case, the reaction will cool the electrode interface and slow the reaction occurring there. If the cell voltage is increased above the thermodynamic voltage, the product of that voltage and the current will generate heat, and if the voltage is such that the heat generated matches the heat required by the reaction to maintain a constant temperature, that voltage is called the "thermoneutral voltage" | https://en.wikipedia.org/wiki?curid=63211357 |
Thermoneutral voltage The rate of delivery of heat is equal to formula_8 where "T" is the temperature (the standard temperature, in this case) and "dS/dt" is the rate of entropy production in the cell. At the thermoneutral voltage, this rate will be zero, which indicates that the thermoneutral voltage may be calculated from the enthalpy. For water at standard temperature (25 C) the net cell reaction may be written: Using Gibbs potentials (formula_11 kJ/mol) , the thermodynamic voltage at standard conditions is Just as the combustion of hydrogen and oxygen generates heat, the reverse reaction generating hydrogen and oxygen will absorb heat. The thermoneutral voltage is (using formula_13 kJ/mol): | https://en.wikipedia.org/wiki?curid=63211357 |
Transition metal phosphinimide complexes are metal complexes that contain phosphinimide ligands of the general formula NPR (R = organic substituent). Several coordination modes have been observed, including terminal and various bridging geometries. In the terminal bonding mode the M-N=P core is usually linear but some are quite bent. The preferred coordination type varies with the oxidation state and coligands on the metal and the steric and electronic properties of the R groups on phosphorus. Many transition metal phosphinimide complexes have been well-developed and, more recently, main group phosphinimide complexes have been synthesized. Complexes of Phosphinimide are generally prepared by two routes. For highly electrophilic metal chlorides, the silyl derivative is convenient since is generates volatile trimethylsilyl chloride: The synthesis of CpTi(NPR)Cl is prepared by this route. More common are salt-elimination reactions: Phosphinimide ligands have shown promise in the area of ethylene polymerization. In terms of homogeneous catalysts, this field has been dominated by metallocene-based catalysts inspired by the Kaminsky catalyst in 1976. Initially phosphinimide ligands were suggested for polyethylene synthesis due to the fact they have similar steric and electronic properties to metallocene polyethylene catalysts. In most respects the steric and electronic properties, of phosphinimides and Cylclopentadienyl are comparable ligands. Metal bound t-BuPN has a cone angle of 87° vs 83 for cylclopentadienyl | https://en.wikipedia.org/wiki?curid=63211888 |
Transition metal phosphinimide complexes Compared to Cp, the bulky substituents of the phosphinimide ligand are more distant from the metal, which increase the exposure of the metal centre to substrate. The less sterically crowded metal centre appears to be particularly susceptible to deactivation however. The precatalyst are prepared by alkylation and arylation of the phosphinimide complexes is possible through alkyllithium or Grignard reagents, giving products such as CpTi(NPR)Me. The zirconium complexes (RPN)ZrCl can be alkylated or arylated through simple substitution. These organoTi and organoZr complexes are activated by treatment with MAO and B(CF) as a cocatalyst to activate polymerization through methyl abstraction. The phosphinimide catalyst is thought to be homogeneous and single sited. It therefore produces reactivity comparable to metallocene catalysts which are also believed to be homogeneous, single sited catalysts. The catalytic process is assumed to proceed in much of the same way as metallocene based catalysts, as the chemistry is thought to occur primarily with the metal centre and not through the bulky ligands. | https://en.wikipedia.org/wiki?curid=63211888 |
List of copper salts Copper is a chemical element with the symbol Cu (from Latin: "cuprum") and the atomic number of 29. It is easily recognisable, due to its distinct red-orange color. Copper also has a range of different organic and inorganic salts, having varying oxidation states ranging from (0,I) to (III). These salts (mostly the (II) salts) are often blue to green in color, rather than the orange color copper is known for. Despite being considered a semi-noble metal, copper is one of the most common salt-forming transition metals, along with iron. | https://en.wikipedia.org/wiki?curid=63213352 |
Andrée Marquet Andrée Marquet, born in 1934, is a French chemist specializing in organic chemistry and chemical biology, professor emeritus at the Pierre and Marie Curie University and correspondent at the French Academy of sciences since 1993. studied engineering at the École nationale supérieure de chimie de Paris, then defended a thesis prepared at the Collège de France under the direction of Jean Jacques (1961), followed by a post-doctoral internship at the ETH in Zurich with Professor Duilio Arigoni. After a career at the CNRS, she was appointed professor at the Pierre-et-Marie-Curie University (1978) and founded the organic biological chemistry laboratory there. She contributed, with a few others, to the development of this interface sub-discipline at the national level, which was still in its infancy, and created at UPMC adapted teaching courses where chemists and biochemists could meet. In addition to her work as a teacher-researcher, she has held various positions of general interest. Between 1984 and 1986, she chaired the organic chemistry division of the Société chimique de France, and from 1987 to 1991, the Société Franco-japonaise de chimie fine et thérapeutique. She chaired section 20 of the CNRS National Committee (1991-1995) and was a member of the CNRS Scientific Council from 1992 to 1997. In 1998, she became Scientific Director of the Chemistry Department at the Research Department of the MENRT | https://en.wikipedia.org/wiki?curid=63215180 |
Andrée Marquet Between 1999 and 2003, she was a member of the Board of Directors of the Palais de la Découverte, and between 2007 and 2008, she was a member of the Board of Directors of the MENRT. 2011, member of the Ethics Committee of the CNRS. In 2002, she founded the "Chemistry and Society" Commission, within the Fondation de la Maison de la Chimie, of which she remains president until 2011. This commission seeks to analyse the origin of the misunderstanding that has developed between chemistry and society, and to contribute to the search for solutions by organising actions resolutely directed towards the general public. and her collaborators have been interested in reaction mechanisms in organic chemistry, in particular those involving carbanions (enolates, alpha anions of sulfoxides), and have used the results of these studies in synthesis, for example for total synthesis of biotin. She then turned to mechanistic enzymology, applying the approach used in organic chemistry to the functioning of enzymes. The main areas covered are : They have shown that it belongs to the newly discovered family of proteins (Fe-S) dependent on S-Adenosylmethionine, catalysing radical reactions. This is a family that opens a new chapter in enzymology. Another field of activity of the laboratory, the result of a collaboration with the neurobiology laboratory of the Collège de France (Prof. Jacques Glovinski) concerns the activity of a family of peptide neurotransmitters, the tachykinins | https://en.wikipedia.org/wiki?curid=63215180 |
Andrée Marquet 1961: Eugène Schuëller Prize (ENSCP) 1971: prize of the Organic Chemistry Division of the French Chemical Society 1986: La Caze Prize of the French Academy of sciences and Berthelot Medal of the French Academy of sciences 1988: CNRS silver medal 1993: Corresponding member of the French Academy of sciences. 1994: Achille-Le-Bel Grand Prize of the Chemical Society of France. 2000: Officier of the Ordre National du Mérite 2012: Officier of the Ordre national de la Légion d'Honneur 2018: Commandeur in the Ordre des Palmes Académiques | https://en.wikipedia.org/wiki?curid=63215180 |
Lamb–Chaplygin dipole The model is a mathematical description for a particular inviscid and steady dipolar vortex flow. It is a non-trivial solution to the two-dimensional Euler equations. The model is named after Horace Lamb and Sergey Alexeyevich Chaplygin, who independently discovered this flow structure. A two-dimensional (2D), solenoidal vector field formula_1 may be described by a scalar stream function formula_2, via formula_3, where formula_4 is the right-handed unit vector perpendicular to the 2D plane. By definition, the stream function is related to the vorticity formula_5 via a Poisson equation: formula_6. The Lamb–Chaplygin model follows from demanding the following characteristics: The solution formula_2 in cylindrical coordinates (formula_14), in the co-moving frame of reference reads: formula_15 where formula_16 are the zeroth and first Bessel functions of the first kind, respectively. Further, the value of formula_17 is such that formula_18, the first non-trivial zero of the first Bessel function of the first kind. Since the seminal work of P. Orlandi, the Lamb–Chaplygin vortex model has been a popular choice for numerical studies on vortex-environment interactions. The fact that it does not deform make it a prime candidate for consistent flow initialization. A less favorable property is that the second derivative of the flow field at the dipole's edge is not continuous. Further, it serves a framework for stability analysis on dipolar-vortex structures. | https://en.wikipedia.org/wiki?curid=63216140 |
SnRNA-seq snRNA-seq, also known as single nucleus RNA sequencing, single nuclei RNA sequencing or sNuc-seq, is an RNA sequencing method for profiling gene expression in cells which are difficult to isolate, such as those from tissues that are archived or which are hard to be dissociated. It is an alternative to single cell RNA seq (scRNA-seq), as it analyzes nuclei instead of intact cells. snRNA-seq minimizes the occurrence of spurious gene expression, as the localization of fully mature ribosomes to the cytoplasm means that any mRNAs of transcription factors that are expressed after the dissociation process cannot be translated, and thus their downstream targets cannot be transcribed.. Additionally, snRNA-seq technology enables the discovery of new cell types which would otherwise be difficult to isolate. The basic snRNA-seq method requires 4 main steps: tissue processing, nuclei isolation, cell sorting, and sequencing. In order to isolate and sequence RNA inside the nucleus, snRNA-seq involves using a quick and mild nuclear dissociation protocol. This protocol allows for minimization of technical issues that can affect studies, especially those concerned with immediate early gene (IEG) behavior. The resulting dissociated cells are suspended and the suspension gently lysed, allowing the cell nuclei to be separated from their cytoplasmic lysates using centrifugation. These separated nuclei/cells are sorted using FACS into individual wells, and amplified using microfluidics machinery | https://en.wikipedia.org/wiki?curid=63223403 |
SnRNA-seq Sequencing occurs as normal and the data can be analyzed as appropriate for its use. This basic snRNA-seq methodology is capable of profiling RNA from tissues that are preserved or cannot be dissociated, but it does not have high throughput capability due to its reliance on nuclei sorting by FACS. This technique cannot be scaled easily to profiling large numbers of nuclei or samples. Massively parallel scRNA-seq methods exist and can be readily scaled but their requirement of a single cell suspension as input is not ideal and eliminates some of the flexibility that is available with the snRNA-seq method in regards to the types of tissues and cells that can be examined. In response, the DroNc-Seq method of massively parallel snRNA-seq with droplet technology was developed by researchers from the Broad Institute of MIT and Harvard. In this technique, nuclei that have been isolated from their fixed or frozen tissue are encapsulated in droplets with uniquely barcoded beads that are coated with oligonucleotides containing a 30-terminal deoxythymine (dT) stretch. This coating captures the polyadenylated mRNA content produced when the nuclei are lysed inside the droplets. The captured mRNA is reverse transcribed into cDNA after emulsion breakage. Sequencing this cDNA produces the transcriptomes of all the single nuclei being looked at and these can be used for many purposes, including identification of unique cell types | https://en.wikipedia.org/wiki?curid=63223403 |
SnRNA-seq The sequencing tools and equipment used in scRNA-seq can be used with modifications for snRNA-seq experiments. Illumina outlines a workflow for the basic snRNA-seq method which can be performed with existing equipment. DroNc-Seq can be accomplished with microfluidic platforms which are meant for the Drop-seq scRNA-seq method. However, Dolomite Bio has adapted one of their instruments, the automated Nadia platform for scRNA-seq, to be used natively for DroNc-Seq as well. This instrument could simplify the generation of single nuclei sequencing libraries, as it is being used for its intended purpose. In regard to data analysis after sequencing, a computational pipeline known as dropSeqPipe was developed by the McCarroll Lab at Harvard. Although the pipeline was originally developed for use with Drop-seq scRNA-seq data, it can be used with DroNc-Seq data as it also utilizes droplet technology. snRNA-seq uses isolated nuclei instead of the entire cells to profile gene expression. That is to say, scRNA-seq measures both cytoplasmic and nuclear transcripts, while snRNA-seq mainly measures nuclear transcripts (though some transcripts might be attached to the rough endoplasmic reticulum and partially preserved in nuclear preps). This allows for snRNA-seq to proceed only the nucleus and not the entire cell. For this reason, compared to scRNA-seq, snRNA-Seq is more appropriate to profile gene expression in cells that are difficult to isolate (e.g. adipocytes, neurons), as well as preserved tissues | https://en.wikipedia.org/wiki?curid=63223403 |
SnRNA-seq Additionally, the nuclei required for snRNA-seq can be obtained quickly and easily from fresh, lightly fixed, or frozen tissues, whereas isolating single cells for single-cell RNA-seq (scRNA-seq) involves extended incubations and processing. This gives researchers the ability to obtain transcriptomes which are not as perturbed during isolation. In neuroscience, neurons have an interconnected nature which makes it extremely hard to isolate intact single neurons. As snRNA-seq has emerged as an alternative method of assessing a cell's transcriptome through the isolation of single nuclei, it has been possible to conduct single-neuron studies from postmortem human brain tissue. snRNA-seq has also enabled the first single neuron analysis of immediate early gene expression (IEGs) associated with memory formation in the mouse hippocampus. In 2019, Dmitry et al used the method on cortical tissue from ASD patients to identify ASD-associated transcriptomic changes in specific cell types, which is the first cell-type-specific transcriptome assessment in brains affected by ASD. Outside of neuroscience, snRNA-seq has also been used in other research areas. In 2019, Haojia et al compared both scRNA-seq and snRNA-seq in a genomic study around the kidney. They found snRNA-seq accomplishes an equivalent gene detection rate to that of scRNA-seq in adult kidney with several significant advantages (including compatibility with frozen samples, reduced dissociation bias and so on ) | https://en.wikipedia.org/wiki?curid=63223403 |
SnRNA-seq In 2019, Joshi et al used snRNA-seq in a human lung biology study in which they found snRNA-seq allowed unbiased identification of cell types from frozen healthy and fibrotic lung tissues. Adult mammalian heart tissue can be extremely hard to dissociate without damaging cells, which does not allow for easy sequencing of the tissue. However, in 2020, German scientists presented the first report of sequencing an adult mammalian heart by using snRNA-seq and were able to provide practical cell‐type distributions within the heart | https://en.wikipedia.org/wiki?curid=63223403 |
One-way wave equation A one-way wave equation is a [[partial differential equation], used in fields such as [[geophysics]] - whose solutions include only [[wave]]s that propagate in a single direction on one of the axes. In the one-dimensional case, the one-way wave equation allows the calculation of wave propagation without disturbing reflected waves (e.g. at the border of different layers). Several methods (approximations) use the 1D one-way wave equation for 3D seismic calculations. The standard [[wave equation|2nd order wave equation]] can be written in the form (formula_1 is the coordinate, displacement formula_2, formula_3 wave velocity [[[Sound|speed of sound]]]): This has two solutions that propagate in the forward (formula_5) direction. It also has solutions that propagate in the backward (formula_6) direction, making it a "Two-way wave equation". Due to the ambiguity, formula_7, the two-way wave equation does not contain information about the wave direction. However, the general solution contains a wave travelling in the forward formula_8 and backward formula_9 directions: formula_10 [= Sum of a forward and a backward travelling wave] So for one-directional wave propagation calculation, the wave propagation direction has to be selected accordingly, i.e. from the formula above one of the respective sums, and has to be selected | https://en.wikipedia.org/wiki?curid=63245755 |
One-way wave equation [[Factorization|Factoring]] the operator on the left side of the two-way wave equation yields a pair of one-way wave equations, one applying to forward propagation and the other to backward propagation. From the forward- and backward-travelling waves are described by, respectively, The one-way wave equations (in a homogeneous medium, e.g. air) can also be derived directly from the characteristic specific acoustical impedance. In a longitudinal plane wave, the specific impedance determines the local proportionality of (sound) pressure formula_13 and particle velocity formula_14 (formula_15: density): The conversion of the impedance equation leads to: A longitudinal plane wave of angular frequency formula_18 has the displacement formula_2. The pressure formula_20 and the particle velocity formula_21 can be expressed in terms of the displacement formula_22 (formula_23: [[Elastic Modulus]]): These relations inserted into the equation above (*) yields: With the local wave velocity definition ([[Sound|speed of sound]]) directly follows the 1st order partial differential equation respectively one-way wave equation The wave velocity formula_3 can be set yet within this wave equation as formula_33 or formula_34 according on the direction of wave propagation | https://en.wikipedia.org/wiki?curid=63245755 |
One-way wave equation For a wave propagation in the direction of formula_33 the unique solution follows formula_36 and vice versa for wave propation in formula_33 direction the respective solution is formula_38 [[Category:Geophysics]] [[Category:Wave mechanics]] [[Category:Acoustics]] [[Category:Sound]] [[Category:Continuum mechanics]] | https://en.wikipedia.org/wiki?curid=63245755 |
1,6-Dioxecane-2,7-dione is a chemical described as a cyclic lactone or lactide, which is formed as an impurity in the manufacture of polymer resins and biodegradable polyesters. It is the cyclic dimer of GHB. | https://en.wikipedia.org/wiki?curid=63247646 |
Transhalogenation (also: "halide metathesis") is a substitution reaction in which a halogen atom of a halogen compound is exchanged for another halogen atom, for example the reaction of an alkyl chloride to an alkyl fluoride by means of sodium fluoride: R-Cl + NaF → R-F + NaCl If the halogen compound is an organic compound, this is called Finkelstein reaction. However, it is also possible, for example, to produce phosphorus fluoride compounds by transhalogenating chlorine, bromine or iodine bound to phosphorus with a metal fluoride. As a halogen source for transhalogenation, metal halides (such as sodium fluoride or lithium fluoride) are often used, but also the use of onium halides is possible. has been described as a gentle method for the synthesis of fluoroorganylboranes. It is also possible to produce aryliodides from the corresponding aryl chlorides or aryl bromides. One investigation showed a possibility to perform transhalogenation by means of genetically modified enzymes (haloalkanes dehalogenases, HLDs). | https://en.wikipedia.org/wiki?curid=63252675 |
Extreme tribology refers to tribological situations under extreme operating conditions which can be related to high loads and/or temperatures, or severe environments. Also, they may be related to high transitory contact conditions, or to situations with near-impossible monitoring and maintenance opportunities. In general, extreme conditions can typically be categorized as involving abnormally high or excessive exposure to e.g. cold, heat, pressure, vacuum, voltage, corrosive chemicals, vibration, or dust.. The extreme conditions should include any device or system requiring a lubricant operating under any of the following conditions: Operation in such extreme conditions is a great challenge for tribologists to develop tribosystems that could meet these extreme requirements. Often, only multifunctional materials fulfill such requirements. The progression of the humanity suggested new technologies, devices, materials and surface treatments which required novel lubricants and lubrication systems. Likewise, the development of high-speed trains, aircraft, space stations, computer hard discs, artificial implants, and bio-medical and many other engineering systems, have only been possible through the advances in tribology. Challenges in tribology including sustainability, climate change and gradual degradation of the environment require new solutions and innovative approaches. In many tribological applications, the system components are exposed to extreme temperatures (very high or ultra-low temperatures) | https://en.wikipedia.org/wiki?curid=63257483 |
Extreme tribology Examples of such applications can be found in the aerospace, mining, power generation, metalworking industries, and steel plants. In tribology, an application can be considered to operate at elevated temperatures when the use of conventional lubricants, i.e. oils and greases is no longer effective due to their rapid decomposition at around 300 C. Smart lubricating materials and multifunctional lubricating materials are developed as new class materials with increased safety, long-term durability and as less amount of repairing costs as possible. Such materials are designed to be self-diagnosis, self-repair, and self-adjust. These materials include structural/lubricating integrated material, anti-radiation lubricating material, conductive or insulation lubricating material, etc. At low temperatures and in cryogenic environments, liquid lubricants can solidify or become highly viscous and not be effective. On the other end, solid lubricants have usually been found to be better than liquid lubricants or greases. The most common solid lubricants for cryogenic temperature are Polytetrafluoroethylene (PTFE), Polycarbonate (PC), Tungsten disulphide (WS), and Molybdenum disulphide (MoS). In addition, ice could be a possible lubricant for deformation in cryogenic environments which provides a method of self-lubrication in the sense that no active mechanism is needed to supply a lubricant | https://en.wikipedia.org/wiki?curid=63257483 |
Extreme tribology The fundamental difference that distinguishes micro/nano tribology from classical macro tribology is that micro/nano tribology considers the friction and wear of two objects in relative sliding whose dimensions range from micro-scales down to molecular and atomic scales. MEMS refer to micro-electromechanical systems that have a characteristic length of 100 nm to 1 mm, while NEMS are the nano-electromechanical systems that have a characteristic length of less than 100 nm.. There are great challenges in the development of a fundamental understanding of tribology, surface contamination and environment in MEMS/NEMS. One of these challenges in such extreme tribological situations is the adhesion force which can be up to a million times greater than the force of gravity. This is due to the fact that the adhesion force decreases linearly with size, whereas the gravitational force decreases with the size cubed. Low surface energy, hydrophobic coatings applied to oxide surfaces are promising for minimizing adhesion and static-charge accumulation. Under vacuum environment, it is a problem to achieve acceptable endurance of tribological components due to the fact that the lubricant may either freeze, evaporate or decompose and hence become ineffective. Tribological properties of materials exhibit different characteristics at the space vacuum as compared to the atmospheric pressure. Adhesive and fatigue wear are the two important types of wear encountered in a vacuum environment | https://en.wikipedia.org/wiki?curid=63257483 |
Extreme tribology Vacuum not only radically affects the wear behavior of metals and alloys in contact, but also has a pronounced influence on nonmetals as well.. Different new kinds of materials are developed for potentially operating in vacuum environments. For instance, copper alloy CuZnPb and Ni(Si,Ti) alloys have excellent anti-wear properties in all the vacuum conditions. Types of solid lubricants used in space applications: The most common way to utilize a solid lubricant is to apply it to a metal surface as a film or surface coating of a thin layer of soft film, typically molybdenum disulphide, artificially deposited on the surfaces. Coatings of solid lubricant are built up atom by atom yielding a mechanically strong surface layer with a long service life and the minimum quantity of solid lubricant. The term ""geotribology"" was first stated by Harmen Blok with no significant discussion. Later, geotribology framework was employed to analyze the flow mechanics of granular sand. Even though tribological concepts can be utilized to many geosciences phenomena, the two research communities are separated. In earth science, many tribological concepts were applied successively, particularly in rock friction analyses. The asperity-asperity contact mechanism was applied to rock friction experiments that led to the rate-state friction law that prevails in earthquake analyses. High dust areas and dirt environments can weigh profoundly on a lubricant due to the high risk of particle contamination | https://en.wikipedia.org/wiki?curid=63257483 |
Extreme tribology These contaminants readily form a grinding paste, causing failure of tribosystems and subsequently damaging of equipment. This type of contamination most frequently takes place when airborne or stagnant particles gain access to the lubrication system through open ports and hatches, especially in systems with negative pressure. Half of a bearing loss of usefulness can be attributed to wear. This wear, which occurs through surface abrasion, fatigue and adhesion, is often the result of particle contamination. In radiation environments, liquid lubricants can decompose. Suitable solid lubricants can extend the operation of systems beyond 10 rads while maintaining relatively low coefficients of friction. In weight-limited spacecraft and rovers, solid lubrication has the advantage of weighing substantially less than liquid lubrication. The elimination (or limited use) of liquid lubricants and their replacement by solid lubricants would reduce spacecraft weight and, therefore, have a dramatic impact on mission extent and craft maneuverability. | https://en.wikipedia.org/wiki?curid=63257483 |
Metal cluster compound Metal cluster compounds are a molecular ion or neutral compound composed of three or more metals and featuring significant metal-metal interactions. The development of metal carbonyl clusters such as Ni(CO) and Fe(CO) led quickly to the isolation of Fe(CO) and Fe(CO). Rundle and Dahl discovered that Mn(CO) featured an "unsupported" Mn-Mn bond, thereby verifying the ability of metals to bond to one another in molecules. In the 1970s, Paolo Chini demonstrated that very large clusters could be prepared from the platinum metals, one example being [Rh(CO)H]. This area of cluster chemistry has benefited from single-crystal X-ray diffraction. Many metal carbonyl clusters contain ligands aside from CO. For example, the CO ligand can be replaced with myriad alternatives such as phosphines, isocyanides, alkenes, hydride, etc. Some carbonyl clusters contain two or more metals. Others contain carbon vertices. One example is the methylidyne-tricobalt cluster [Co(CH)(CO)]. The above-mentioned cluster serves as an example of an overall zero-charged (neutral) cluster. In addition, "cationic" (positively charged) rather than neutral organometallic trimolybdenum or tritungsten clusters are also known. The first representative of these ionic organometallic clusters is [Mo(CCH)(OCCH)(HO)]. The halides of low-valent early metals often are clusters with extensive M-M bonding. The situation contrasts with the higher halides of these metals and virtually all halides of the late transition metals, where metal-halide bonding is replete | https://en.wikipedia.org/wiki?curid=63262069 |
Metal cluster compound Transition metal halide clusters are prevalent for the heavier metals: Zr, Hf, Nb, Ta, Mo, W, and Re. For the earliest metals Zr and Hf, interstitial carbide ligands are also common. One example is ZrCCl. One structure type features six terminal halides and 12 edge-bridging halides. This motif is exemplified by tungsten(III) chloride, [TaCl], Another common structure has six terminal halides and 8 bridging halides, e.g. MoCl. Many of the early metal clusters can only be prepared when they incorporate intertitial atoms. In terms of history, Linus Pauling showed that "MoCl" consisted of Mo octahedra. F. Albert Cotton established that "ReCl" in fact features subunits of the cluster ReCl, which could be converted to a host of adducts without breaking the Re-Re bonds. Because this compound is diamagnetic and not paramagnetic the rhenium bonds are double bonds and not single bonds. In the solid state further bridging occurs between neighbours and when this compound is dissolved in hydrochloric acid a ReCl complex forms. An example of a tetranuclear complex is hexadecamethoxytetratungsten W(OCH) with tungsten single bonds. A related group of clusters with the general formula MMoX such as PbMoS. These sulfido clusters are called Chevrel phases. In the 1970s, ferredoxin was demonstrated to contain FeS clusters and later nitrogenase was shown to contain a distinctive MoFeS active site. The Fe-S clusters mainly serve as redox cofactors, but some have a catalytic function | https://en.wikipedia.org/wiki?curid=63262069 |
Metal cluster compound In the area of bioinorganic chemistry, a variety of Fe-S clusters have also been identified that have CO as ligands. FeMoco, the active site of most nitrogenases, features a FeMoSC cluster. Zintl compounds feature naked anionic clusters that are generated by reduction of heavy main group "p" elements, mostly metals or semimetals, with alkali metals, often as a solution in anhydrous liquid ammonia or ethylenediamine. Examples of Zintl anions are [Bi], [Sn], [Pb], and [Sb]. Although these species are called "naked clusters," they are usually strongly associated with alkali metal cations. Some examples have been isolated using cryptate complexes of the alkali metal cation, e.g., [Pb] anion, which features a capped square antiprismatic shape. According to Wade's rules (2n+2) the number of cluster electrons is 22 and therefore a closo cluster. The compound is prepared from oxidation of KPb by Au in PPhAuCl (by reaction of tetrachloroauric acid and triphenylphosphine) in ethylene diamine with 2.2.2-crypt. This type of cluster was already known as is the endohedral Ni@Pb (the cage contains one nickel atom). The icosahedral tin cluster Sn or stannaspherene anion is another closed shell structure observed (but not isolated) with photoelectron spectroscopy. With an internal diameter of 6.1 Ångstrom, it is of comparable size to fullerene and should be capable of containing small atoms in the same manner as endohedral fullerenes, and indeed exists a Sn cluster that contains an Ir atom: [Ir@Sn] | https://en.wikipedia.org/wiki?curid=63262069 |
Metal cluster compound Elementoid clusters are ligand-stabilized clusters of metal atoms that possess more direct element-element than element-ligand contacts. Examples of structurally characterized clusters feature ligand stabilized cores of Al, Ga, and Pd. These clusters consist of at least two different (semi)metallic elements, and possess more direct metal-metal than metal-ligand contacts. The suffix "oid" designate that such clusters possess at a molecular scale, atom arrangements that appear in bulk intermetallic compounds with high coordination numbers of the atoms, such as for example in Laves phase and Hume-Rothery phases. Ligand-free intermetalloid clusters include also endohedrally filled Zintl clusters. A synonym for ligand-stabilized intermetalloid clusters is "molecular alloy". The clusters appear as discrete units in intermetallic compounds separated from each other by electropositive atoms such as [Sn@Cu@Sn], as soluble ions [As@Ni@As] or as ligand-stabilized molecules such as [Mo(ZnCH)(ZnCp*)]. | https://en.wikipedia.org/wiki?curid=63262069 |
Hemolithin is an iron and lithium-containing protein, found inside two CV3 meteorites, Allende and Acfer-086, and thought to be the first protein discovered that may be of extraterrestrial origin. The protein was detected by teams of scientists, led by biochemist Julie McGeoch, from Harvard University, and from the biotech and physics companies of Bruker Scientific and the superconductor X-ray source supplier PLEX Corporation. The study is an extension of published and unpublished results by the teams. The detected hemolithin protein was reported to have been found inside two CV3 meteorites Allende and Acfer 086. Acfer-086, where the complete molecule was detected rather than fragments (Allende), was discovered in Agemour, Algeria in 1990. Hemolithin, the newly found protein, was found, aided by the use of "state-of-the-art" mass spectrometry, to be largely composed of glycine and hydroxyglycine amino acids. also contained atoms of oxygen, lithium and iron in an up-to-now unobserved arrangement. The researchers noted that the protein was related to “very high extraterrestrial" ratios of Deuterium/Hydrogen (D/H); such high D/H ratios are not found anywhere on Earth, but are "consistent with long-period comets" and suggest, as reported, "that the protein was formed in the proto-solar disc or perhaps even earlier, in interstellar molecular clouds that existed long before the Sun’s birth" | https://en.wikipedia.org/wiki?curid=63264796 |
Hemolithin A natural development of hemolithin may have started with glycine forming first, and then later linking with other glycine molecules into polymer chains, and later still, combining with iron and oxygen atoms. The iron and oxygen atoms reside at the end of the newly found molecule. The researchers speculate that the iron oxide grouping formed at the end of the molecule may be able to absorb photons, thereby enabling the molecule to split water (HO) into hydrogen and oxygen and, as a result, produce a source of energy that might be useful to the development of life. Nonetheless, exobiologist and chemist Jeffrey Bada expressed concerns about the possible protein discovery commenting, "The main problem is the occurrence of hydroxyglycine, which, to my knowledge, has never before been reported in meteorites or in prebiotic experiments. Nor is it found in any proteins. ... Thus, this amino acid is a strange one to find in a meteorite, and I am highly suspicious of the results." Although some scientists seem supportive of the study, other scientists may be less so. ""Hydroxyglycine was first detected in the meteorite Allende and this was published in 2015. At that point in time, only fragments of were detected. There is presented in the MS very clear evidence of multiple oxidations of a 17 glycine polymer: The hemolithin MS (arXiv) shows in figure S3.3 a characteristic oxidation series in which 2, 3, 4, 5, and 6 oxygen atoms bond to glycine residues within a 17 glycine chain | https://en.wikipedia.org/wiki?curid=63264796 |
Hemolithin This converts the corresponding numbers of mass 57 glycine residues into mass 73 hydroxy glycine residues (MS pages 27 and 28)."" The possible finding of the hemolithin protein supports the notion that life on Earth may not have started on Earth after all, but may have come from outer space instead – a process known as panspermia. Besides this possible discovery of an extraterrestrial protein, other evidences of complex chemistry (amino acids, polycyclic aromatic hydrocarbons, sugars, ribose, tholins) occurring in outer space have been accumulating from recent astrobiology studies, including those related to meteorites and comets. The presence of such complex chemistry occurring in the cosmos, as well as the observation by biologist Stephen Blair Hedges that life may have arisen quickly on the very early Earth, suggests that life may be widespread throughout the universe. is the name given to a protein molecule isolated from two CV3 meteorites, Allende and Acfer-086. Its deuterium to hydrogen ratio is 26 times terrestrial which is consistent with it having formed in an interstellar molecular cloud, or later in the protoplanetary disk at the start of our solar system 4.567 billion years ago. The elements hydrogen, lithium, carbon, oxygen, nitrogen and iron that it is composed of, were all available for the first time 13 billion years ago after the first generation of massive stars ended in nucleosynthetic events | https://en.wikipedia.org/wiki?curid=63264796 |
Hemolithin The horizontal arrow in the below shows, on the scale of the start of the Universe to the present, when could have formed and reformed. The research leading to the discovery of started in 2007 when another protein, one of the first to form on Earth, was observed to entrap water. That property being useful to chemistry before biochemistry on earth developed, we performed theoretical enthalpy calculations on the condensation of amino acids in gas phase space asking: “whether amino acids could polymerize to protein in space?” - they could, and their water of condensation aided their polymerization. Since 2013 we have used meteorites as a source of extraterrestrial material to determine experimentally whether our theory had validity. This led to several manuscripts of isotope and mass information on Hemolithin. | https://en.wikipedia.org/wiki?curid=63264796 |
Diphoterine is a chemical solution used for the emergency treatment of chemical spills to the eyes and body. contains an amphoteric molecule, that is, a substance which is capable of reacting with both acids and alkalis. When applied to either type of chemical spill, the appropriate part of the molecule neutralises the spilt chemical, halting the reaction with the body. Efficacy has been shown in studies in a clinical setting and also in studies on animals. | https://en.wikipedia.org/wiki?curid=63280303 |
Edible gold is a particular type of gold authorized by the European Union and the United States as a food additive, under the code E 175. The precious metal can be used for culinary purposes as it can be safely consumed. It is widely used in the haute cuisine in a gastronomical trend towards extravagant and rich meals. It can be employed in several foods and beverages such as in cookies decoration, in wines or liquors, as sushi garnishment or over ice cream. There are neither side effects nor benefits from eating gold since it is a biologically inert metal and it is suitable for use in food since it does not oxidize or corrode in moist air, unlike many other metals. is possible only with a specific type of gold(E-175) and it has to be pure, to avoid any type of infections or perils for the body. Gold usually undergoes one of these processes: it could be hammered, or pounded and rolled, or just a leaf or powder. In the first case, the gold needs to reach the measure of about 1/8000 of a millimeter thick, in the second one it could be used as a normal leaf (the measure depends on the purpose) or smashed in powder. dates back in time and it could be found in many regions of the World and in different ages. The earliest evidence about the use of edible gold is among the ancient Egyptians, almost 5000 years ago, where the use of gold were well-known in many fields such as: architecture, decoration, ornament, religion, jewelry and medicine | https://en.wikipedia.org/wiki?curid=63280480 |
Edible gold The Egyptians used also the gold for mental, bodily and spiritual purification because they believed in the divine effects of the precious metal. The alchemists of Alexandria developed various medicine and elisir with drinkable gold, which they believed, had effects on restoring and rejuvenating the body. It is believed that Cleopatra practiced these treatments with gold every night, as though having baths with gold and using facemask of pure gold. Ancient Egyptians were not the only ones to use gold as a decorative food and beverage garnish; it could be found also in the eastern countries such as Japan, China and India, mostly for medicine or mysterious elisir made by court physicians. was famous among the courts of the kings of European countries in the Middle Age, implemented as food decoration and as symbol of extreme luxury and prestige among vassals and courtiers. Ancients court physicians believed that gold helps with arthritis and other body problems such as sore limbs. During the Renaissance, Paracelsus (1493-1541) – considered the founder of the modern pharmacology – developed a variety of medicines using few quantities of edible gold in the form of pills or gold powder. From the Modern age – and until the XX century – gold was associated with medicines. It was common to find the application of some piece of gold in articulated and expensive drugs, using little pills or powder inside the medicine, or as a supplement for food to refill minerals in the human body | https://en.wikipedia.org/wiki?curid=63280480 |
Edible gold Gold is a noble metal and for this reason does not react inside our body. This means that it is not absorbed during the digestion process, so it is safe to eat. However, there are no nutritional or health benefits associated with its consumption. This type of gold must be 23-24 karats, which is different from the one used in jewelry that may contain other metals and can be toxic and dangerous if consumed because gold that sits below this carat limit contains more impurities, thus it can be dangerous for the body. The effects and safety of E-175 were first evaluated back in 1975 and recently re-evaluated in 2016 by EFSA ( European Food Safety Authority) when using the metal as an additive or food coloring. The agency has authorized the use of gold as food additive at quantum satis in the external coating of confectionery, decoration of chocolates and in liqueurs. Nevertheless, it states that: “"the specifications for gold (E 175) should include the mean particle size and particle size distribution (± SD), as well as the percentage (in number) of particles in the nanoscale (with at least one dimension below 100 nm), present in the powder form of gold (E 175). The methodology applied should comply with the EFSA Guidance document. Exposure estimates of gold (E 175) reached up to 1.32 µg/kg body weight (bw)/day in the maximum level exposure assessment scenario and up to 0.33 µg/kg bw/day in the refined, non-brand-loyal, exposure scenario | https://en.wikipedia.org/wiki?curid=63280480 |
Edible gold ”" Worldwide there are several manufacturers specialized in the production of edible gold. In Italy, for example, Giusto Manetti Battiloro S.p.a produces gold and silver leaf for both cuisine and beauty purposes; in the UK, one of the biggest suppliers of edible gold and silver is Conneisseur Gold with a customer range from major supermarket chains, Christmas pudding manufactures, distillers, Michelin starred restaurants, food distributors, specialist cake makers, cosmetic companies and individuals (for home use). CornucAupia is one the famous distributors in the US, with a supply chain that begins and ends in North America in order to guarantee purity along the way. In the Asian market, Horikin Ltd is the pioneer of gold leaf in Japan, where there is a strong cultural use of gold in tea. There are several manufacturers in Germany, like Goldmarie, rooted in Bavaria, or GoldGourmet and the Swiss DeLafée. The main buyers of edible gold are luxurious restaurants that want to provide an effect of wealth on their food and a new experience to their customers. The most well known restaurants that include in their menu some dishes with gold are based in Dubai, Malta, New York, Washington, D.C. and London. However, the trend starts spreading even in little restaurants. The restaurant “Finger’s Garden”, in Milan, started offering sushi-dishes covered in gold. sheets, flakes or powder can be easily found in the online market as well | https://en.wikipedia.org/wiki?curid=63280480 |
Edible gold can be used in mainly three different shapes to garnish foods and beverages: leaf-shaped, in flakes or in powder. Among the dishes and beverages in which edible gold is implemented there are cakes and sweet desserts, soups, pastas, risottos, sushi, cocktails and wines. Since it is used as tasteless garnish, edible gold is usually the ingredient at the top of the dish at direct contact with food. In most of the recipes requiring gold in flakes or dust, it is usually dabbed with a knife or sprinkled on the top. Gold is added during the bottling of wines and liqueurs and it is generally mixed during cocktails’ preparation. More recently, gold leaves have been used to garnish steak and hamburgers: Hard Rock Café’s “24-Karat Gold Leaf Steak Burger” was sold in USA for 7$ extra than the one without the metallic garnish. Salt Bae, the chef owner of the Nusr-Et restaurants chain, includes in his menu a steak entirely covered by gold, sold at 650€ in Greece. The emphasis in edible gold consumption is on sight and this is strictly linked to the edible gold foods spreading on social media pictures. As a consequence, conspicuous consumption of luxury becomes the driver of the development of edible gold consumption and its today’s dissemination on almost every region of the world. Started as a viral phenomenon in Dubai, a proliferation of restaurants and pastries using edible gold in their recipes reached more countries and more popular and accessible cafés and restaurants | https://en.wikipedia.org/wiki?curid=63280480 |
Edible gold Symbolism is the pivotal feature of edible gold consumption, since it is exclusively an aesthetic garnish. By decorating food with gold, chefs’ desire is that to provide a dish that can be quickly recognized as luxurious and extravagant, elevating the chef’s status to “culinary artist”. The importance of the artistic value of a dish decorated with gold gains relevance in the contemporary society due to the general prioritization of sight over the rest of the senses, thus influencing even the culinary environment. is considered luxurious because it is rare in the ever-competitive arena of fine dining, even though its spread is reaching more and more regions of the World. Furthermore, the visual impact of a golden – and edible – dish gives it an artistic, precious, and extravagant aura that is what mainly attract consumers. Gold is worldwide accepted and recognized as a valuable metal and an undeniable symbol of luxury even thanks to its long history as bargaining chip and once nations adopted the gold standard in 19th and 20th century. In addition to its physical characteristic – its shiny and sunny color – gold embodies several social values – especially the displaying of social power – that are extremely relevant from earlier eras. Once added gold on a dish or drink, it gains immediately the values described. Moreover, eating gold has no taste or health benefits, thus indicating the display of wealth in a form of luxury which allows the consumer of the dish to distance from the world of practical necessity | https://en.wikipedia.org/wiki?curid=63280480 |
Edible gold * Nowadays, many chefs are including edible gold in their restaurants’ offer, among them: “Nusr-Et Steakhouse”, Dubai “Serendipity 3”, New York “ Margo’s Pizzeria”, Malta “Hard Rock Cafe’s”, New York, Times Square “ Il Marchesino”, Milan, chef: Gualtiero Marchesi (italian "risotto"). | https://en.wikipedia.org/wiki?curid=63280480 |
Monobenzyl phthalate (MBzP) also known as benzene-1, 2-dicarboxylic acid is an organic compound with the condensed structural formula CHCHOOCCHCOOH. It is the major metabolite of butyl benzyl phthalate, more than monobutyl phthalate (MBP). Like many phthalates, MBP has attracted attention as a potential endocrine disruptor. | https://en.wikipedia.org/wiki?curid=63288959 |
Marcy Zenobi-Wong is an American engineer and professor of Tissue Engineering and Biofabrication at the Swiss Federal Institute of Technology (ETH Zurich). She is known for her work in the field of Tissue Engineering. Zenobi-Wong completed her undergraduate degree in mechanical engineering at the Massachusetts Institute of Technology, and a graduate degree at Stanford University. She completed her PhD on the role of mechanical forces in skeletal development in 1990. After this, she first worked for a year as a postdoc in the Orthopaedic Research Laboratories, University of Michigan, before moving to the University of Bern as group leader Cartilage Biomechanics in 1992, where she habilitated in 2000. In 2003, she moved to ETH Zürich, first to the Institute for Biomedical Engineering, and later to the Department of Health Sciences and Technology, where she became an associate professor in 2017. Zenobi-Wong works in the area of tissue engineering, in particular for cartilage regeneration. She develops functional biomaterials which mimic the extracellular matrix. The biofabrication techniques used to develop these materials include electrospinning, casting, two-photon polymerization and bioprinting. Zenobi-Wong holds four licensed patents in the fields of tissue engineering, tissue engineering techniques, and gene expression assays. She was one of the originators of the MSc Biomedical Engineering program at ETH Zürich, and developed several graduate level courses in tissue engineering and biomedical engineering | https://en.wikipedia.org/wiki?curid=63291291 |
Marcy Zenobi-Wong Zenobi-Wong currently serves as President of the Swiss Society for Biomaterials and Regenerative Medicine, and as secretary general of the International Society of Biofabrication. | https://en.wikipedia.org/wiki?curid=63291291 |
Chemical Workers' Union (Finland) The Chemical Workers' Union (, KTL) was a trade union representing workers in the chemical industry in Finland. The union was founded in 1970, with the merger of the Finnish General Workers' Union and many workers from the General and Speciality Workers' Union. The new union affiliated to the Central Organisation of Finnish Trade Unions. By the 1980s, the union was keen to collaborate with others in the light industries, and in 1990, it began investigating a merger with the Rubber and Leather Workers' Union. The two eventually merged in 1993, with a new Chemical Union founded on 24 October. | https://en.wikipedia.org/wiki?curid=63292069 |
Vanessa Allen Sutherland Vanessa Lorraine Allen Sutherland is a corporate lawyer and former chairperson of the U.S. Chemical Safety and Hazard Investigation Board (CSB). Sutherland was born at Sibley Memorial Hospital in Washington, D.C. She lived in Tantallon, Maryland, where she attended Queen Anne School. She graduated from high school at the age of 16 and enrolled at Drew University, where she received a B.A. in political science and art history, and later attended American University, where she received a J.D. and M.B.A. After graduating from college, she moved to Fort Washington, Maryland. After graduating from Drew, Sutherland worked at the office of the Inspector General of the Department of Energy prior to attending law school. While attending American University, she served as an associate at Federal Deposit Insurance Corporation and a clerk at Fulbright & Jaworski. After graduating from law school, she worked as a corporate attorney at the telecommunications company MCI Inc. At this company, she became vice president and deputy general counsel of Digex, a subsidary. She later worked as a counsel for the tobacco product producer Altria (formerly Philip Morris Companies, Inc.). In 2011, Sutherland began government service as chief counsel for the Pipeline and Hazardous Materials Safety Administration. Sutherland was nominated by President Barack Obama to the U.S. Chemical Safety Board in March 2015 after the resignation of Rafael Moure-Eraso over allegations of mismanagement. She was confirmed by the Senate in August 2015 | https://en.wikipedia.org/wiki?curid=63303989 |
Vanessa Allen Sutherland In 2017, Sutherland was chairperson of the agency when the Trump administration attempted to defund the CSB for the 2018 United States federal budget. In March 2018, the Office of Management and Budget informed Sutherland that the Trump administration had again proposed to shut down the agency as part of the 2019 United States federal budget. This caused Sutherland to resign despite having two years left in her five-year term. After leaving the CSB, Sutherland joined Norfolk Southern Railway as a vice president. The agency was ultimately not defunded after the House Appropriations Committee opposed the Trump administration's proposal and proposed a $1 million increase in the agency's 2019 budget. Kristen Kulinowski became the interim executive after Sutherland's departure until Katherine Lemos was confirmed as chair in March 2020. CSB says it closed thirteen incident investigations under Sutherland. | https://en.wikipedia.org/wiki?curid=63303989 |
Stratingh Institute for Chemistry The is a research institute of the Faculty of Science and Engineering of the University of Groningen (The Netherlands). It is named after Sibrandus Stratingh, who is known for being the inventor of the first battery powered electric car. As of 2020, about 150 people (from over 30 nationalities) are employed within the Stratingh Institute for Chemistry. The staff members include Ben Feringa, who won the 2016 Nobel Prize in Chemistry "for the design and synthesis of molecular machines", Nathalie Katsonis and Sijbren Otto. The institute is currently located on the Zernike Campus in Groningen, in the Nijenborgh 4 and Linnaeusborg buildings. The research carried out within the institute falls within the following research areas: | https://en.wikipedia.org/wiki?curid=63321233 |
Keeper (chemistry) Keepers are substances (typically solvents, but sometimes adsorbent solids) added in relatively small quantities during an evaporative procedure in analytical chemistry, such as concentration of an analyte-solvent mixture by rotary evaporation. The purpose of a keeper is to reduce losses of a target analyte during the procedure. Keepers typically have reduced volatility and are added to a more volatile solvent. In the case of volatile target analytes, it is difficult to totally avoid loss of the analyte in an evaporative procedure, but the presence of a keeper solvent or solid is intended to preferentially solvate or adsorb the analyte, so that the volatility of the analyte is reduced as the evaporative procedure continues. In the case of non-volatile target analytes, the presence of the keeper solvent or solid is intended to prevent all the solvent from being evaporated off, thereby preventing the loss of analytes which might irreversibly adsorb to the container walls when completely dried, or if it is totally dried (in the case of a solid keeper), provide a surface where the analyte can be reversibly rather than irreversibly adsorbed A solid keeper of sodium sulfate was effective for reducing losses of polycyclic aromatic hydrocarbons (PAHs) in an evaporative procedure. | https://en.wikipedia.org/wiki?curid=63322305 |
National Chemical Emergency Centre The (NCEC) is a former UK government agency, now privately owned as part of Ricardo plc, providing information related to chemical accidents (spillages and fires) to emergency services in the United Kingdom and other countries. The NCEC is headquartered on the Harwell Science and Innovation Campus in the Vale of White Horse in Oxfordshire. The NCEC was formed in 1973 as a government agency. On 1 March 1979 the Centre launched, in cooperation with the Home Office, its Hazfile computer database, made available to fifteen British fire services, listing over 10,000 chemical compounds; this was later replaced by the Chemdata system. A similar system in the USA is called RTECS (Registry of Toxic Effects of Chemical Substances). Most chemical safety legislation in the UK covers the transport of hazardous chemicals by road. Companies carrying dangerous substances must comply with the legislation. The NCEC worked with the European Chemical Industry Council (CEFIC) to develop a set of safety codes for carrying dangerous chemicals for National Intervention in Chemical Transport Emergencies Centres across Europe. In the 1980s the NCEC developed the Chemdata hazardous material database, which was provided to British fire services for us in case of chemical accidents. Chemdata lists over 61,600 safety data sheets (SDS) for dangerous substances. It is published in six languages. | https://en.wikipedia.org/wiki?curid=63326444 |
Julie Kovacs is an American chemist and academic. She is professor of chemistry at the University of Washington. Her research involves investigations into the function of non-heme iron enzymes and the mechanisms of oxygen-evolving complexes. She is Chair of the American Chemical Society Division on Inorganic Chemistry. Kovacs studied chemistry at Michigan State University. She moved to Harvard University for her doctoral degree and completed her PhD under the supervision of Richard H. Holm in 1986. Her doctoral research considered transition metal complexes and Kovacs was a postdoctoral researcher at the University of California, Berkeley, where she worked with Robert Bergman. She joined the University of Washington as an Assistant Professor in 1988. She was promoted to Professor in 2001. Her research involves investigations into the role of thiolates in dioxygen chemistry. Non-heme iron enzyomes are known to promote biological reactions, but the mechanisms by which cysteinates impact their function is not well understood. Kovacs has studied the activity of meta-stale cis-thiolate ligated dioxygen intermediates. Kovacs is interested in the formation of the oxygen–oxygen bond. In nature, it is this oxygen-evolving complex (OEC) that stores solar energy in chemical bonds. By creating a series of small molecule analogues, Kovas studies the radical coupling mechanism by which Mn-oxyl radicals attach briding oxo groups. She also investigates nucleophilic attack of Mn-oxo due to hydroxyl groups on the OEC | https://en.wikipedia.org/wiki?curid=63326845 |
Julie Kovacs The small molecules include nitrogen and sulphur and a particular stereochemistry. Through synthesis of organic molecules with a variety of different molecular frameworks, Kovacs investigates their structure-property relationships and the reactivity of the resulting transition-metal complexes. Kovacs was elected President of the American Chemical Society Division on Inorganic Chemistry in 2019. Her publications include: | https://en.wikipedia.org/wiki?curid=63326845 |
Ideal electrode In electrochemistry, there are two types of ideal electrode, the ideal polarizable electrode and the ideal non-polarizable electrode. Simply put, the ideal polarizable electrode is characterized by charge separation at the electrode-electrolye boundary and is electrically equivalent to a capacitor, while the ideal non-polarizable electrode is characterized by no charge separation and is electrically equivalent to a short. An ideal polarizable electrode (also ideally polarizable electrode or ideally polarized electrode or IPE) is a hypothetical electrode characterized by an absence of net DC current between the two sides of the electrical double layer, i.e., no faradic current exists between the electrode surface and the electrolyte. Any transient current that may be flowing is considered non-faradaic. The reason for this behavior is that the electrode reaction is infinitely slow, with zero exchange current density, and behaves electrically as a capacitor. The concept of the ideal polarizability has been first introduced by F.O. Koenig in 1934. An ideal non-polarizable electrode, is a hypothetical electrode in which a faradic current can freely pass (without polarization). Its potential does not change from its equilibrium potential upon application of current. The reason for this behavior is that the electrode reaction is infinitely fast, having an infinite exchange current density, and behaves as an electrical short | https://en.wikipedia.org/wiki?curid=63339701 |
Ideal electrode The classical examples of the two nearly ideal types of electrodes, polarizable and non-polarizable, are the platinum electrode and the silver/silver chloride electrode, respectively. | https://en.wikipedia.org/wiki?curid=63339701 |
Adiabatic electron transfer Adiabatic electron-transfer is the basis of oxidation-reduction processes, which are ubiquitous in nature in both the inorganic and biological spheres. The mechanism of these reactions—the simplest of which proceed without making or breaking chemical bonds—remained unknown until the mid 1950s, when several independent theoretical studies showed that it was due to modulation of coupling between electronic and vibrational motions. According to his Royal Society election citation, Noel Hush's research in the area of homogeneous and heterogeneous electron transfer showed that electron transfer occurring during a collision between a molecule and either another molecule or else an electrode surface occurs adiabatically on a continuous potential-energy surface, and that electron transfer can occur by either optical or thermal mechanisms with the corresponding rates being closely connected. Figure 1 sketches the basic elements of adiabatic electron-transfer theory. Two chemical species (ions, molecules, polymers, protein cofactors, etc.) labelled D (for “donor”) and A (for “acceptor”) become a distance "R" apart, either through collisions, covalent bonding, location in a material, protein or polymer structure, etc. These species have different chemical bonding environments and they polarize any surrounding condensed media. A key feature is that both species must be able to sustain different charge (valence) states | https://en.wikipedia.org/wiki?curid=63340505 |
Adiabatic electron transfer Electron-transfer theories specify equations describing the rate of charge transfer processes that utilize these different charged states. All electrochemical reactions occur by this mechanism. Adiabatic electron-transfer theory stresses that intricately coupled to such charge transfer is the ability of any D-A system to absorb or emit light. Hence fundamental understanding of any electrochemical process demands simultaneous understanding of the optical processes that the system can undergo. Figure 2 sketches what happens if light is absorbed by just one of the chemical species, taken to be the charge donor. This produces an excited state of the donor. As the donor and acceptor are close to each other and surrounding matter, they experience a coupling formula_1. If the free energy change formula_2 is favorable, this coupling facilitates primary charge separation to produce D-A , producing charged species. In this way, solar energy is captured and converted to electrical energy. This process is typical of natural photosynthesis as well as modern organic photovoltaic and artificial photosynthesis solar-energy capture devices. The inverse of this process is also used to make organic light-emitting diodes (OLEDs). Unifying standard electrochemical electron-transfer processes with this type of solar energy harvesting, adiabatic electron-transfer theory also depicts a third application in which the donor and acceptor are both involved in light absorption, as sketched in Figure 3 | https://en.wikipedia.org/wiki?curid=63340505 |
Adiabatic electron transfer Here, light absorption directly leads to charge separation D-A. Hush's theory for this process considers the donor-acceptor coupling formula_1, the energy formula_4 required to rearrange the atoms from their initial geometry to the preferred local geometry and environment polarization of the charge-separated state, and the energy change formula_2 associated with charge separation. In the weak-coupling limit ( formula_6), Hush showed that the rate of light absorption (and hence charge separation) is given from the Einstein equation by This theory explained how the worlds first modern synthetic dye, Prussian blue absorbes light, creating Hush's theory also provides theoretical underpinning for the Robin-Day classification system for mixed-valence systems. Mixed valence is widespread in chemistry, from superconductors to minerals, magnetic molecular clusters and enzymes. It occurs when the same chemical species is found in two formally different oxidation states in the same system. The synthesis of the mixed-valence Creutz-Taube ion, an event leading significantly to the award of the 1983 Nobel Prize in Chemistry to Henry Taube, demonstrated the successfulness of adiabatic electron-transfer theory. In this molecule, the coupling formula_1 is not small, delivering unprecedented chemical phenomena in which charge is not localized on just one chemical species but is shared quantum mechanically between two, presenting classically forbidden half-integral valence states | https://en.wikipedia.org/wiki?curid=63340505 |
Adiabatic electron transfer Hush showed that the critical requirement for this phenomenon is Adiabatic electron-transfer theory stems from London's approach to charge-transfer and indeed general chemical reactions applied by Hush using parabolic potential-energy surfaces. Hush himself has carried out many theoretical and experimental studies of mixed valence complexes and long range electron transfer in biological systems. Hush's quantum-electronic adiabatic approach to electron transfer was unique; directly connecting with the Quantum Chemistry concepts of Mulliken, it forms the basis of all modern computational approaches to modeling electron transfer. Its essential feature is that electron transfer can never be regarded as an “instantaneous transition”; instead, the electron is partially transferred at all molecular geometries, with the extent of the transfer being a critical quantum descriptor of all thermal, tunneling, and spectroscopic processes. It also leads seamlessly to understanding electron-transfer transition-state spectroscopy pioneered by Zewail. In adiabatic electron-transfer theory, the ratio formula_10 is of central importance. In the very strong coupling limit when Eqn. (2) is satisfied, intrinsically quantum molecules like the Crautz-Taube ion result. Most intervalence spectroscopy occurs in the weak-coupling limit described by Eqn. (1), however | https://en.wikipedia.org/wiki?curid=63340505 |
Adiabatic electron transfer In both natural photosynthesis and in artificial solar-energy capture devices, formula_11 is maximized by minimiming formula_4 through use of large molecules like chlorophylls, pentacenes, and conjugated polymers. The coupling formula_1 can be controlled by controlling the distance "R" at which charge transfer occurs- the coupling typically decreases exponentially with distance. When electron transfer occurs during collisions of the D and A species, the coupling is typically large and the “adiabatic” limit applies in which rate constants are given by transition state theory. However, in biological applications as well as modern organic conductors and other device materials, "R" is externally constrained and so the coupling set at low or high values. In these situations, weak-coupling scenarios often become critical. In the weak-coupling (“non-adiabatic”) limit, the activation energy for electron transfer is given by the expression derived independently by Kubo and Toyozawa and by Hush. Using adiabatic electron-transfer theory, in this limit Levich and Dogonadze then determined the electron-tunneling probability to express the rate constant for thermal reactions as This approach is widely applicable to long-range ground-state intramolecular electron transfer, electron transfer in biology, and electron transfer in conducting materials. It also typically controls the rate of charge separation in the excited-state photochemical application described in Figure 2 and related problems | https://en.wikipedia.org/wiki?curid=63340505 |
Adiabatic electron transfer Marcus showed that the activation energy in Eqn. (3) reduces to formula_15 in the case of symmetric reactions with formula_16. In that work, he also derived what is the standard expression for the solvent contribution to the reorganization energy, making the theory readily applicable to practical problems. Use of this solvation description (instead of the form that Hush originally proposed) in approaches spanning the adiabatic and non-adiabatic limits is often termed “Marcus-Hush Theory”. These and other contributions, including the widespread demonstration of the usefulness of Eqn. (3), led to the award of the 1992 Nobel Prize in Chemistry to Marcus. Adiabatic electron-transfer theory is often also widely applied in Molecular Electronics. In recent years it has been generalized to arbitrary chemical reactions, providing a single conceptual basis covering many different aspects of chemical research. In particular, this reconnects adiabatic electron-transfer theory with its roots in proton-transfer theory and hydrogen-atom transfer, leading back to London's theory of general chemical reactions. In this approach, most chemical processes can be depicted in terms of the three critical parameters formula_1, formula_4 and formula_2, with for example the "resonance energy" that makes benzene and all aromatic compounds unique being nothing other than formula_1 | https://en.wikipedia.org/wiki?curid=63340505 |
Adiabatic electron transfer This approach also leads to a simple explanation in terms of the orbital Rydbergization processes discovered by Mulliken as to why first-row elements like nitrogen have bond angles around the tetrahedral angles while later-row elements have very much larger angles. Adiabatic electron-transfer theory applied in a simple one-dimensional form also provides analytical or numerically exact solutions for chemical processes not involving conical intersections, providing critical testbeds for examining failure of the Born-Oppenheimer approximation that is fundamental to chemical understanding. Similarly, it provides a basis for classifying the usefulness of general chemical reactions for applications as qubits in quantum information processors. | https://en.wikipedia.org/wiki?curid=63340505 |
Bert Poolman Berend (Bert) Poolman is a Dutch biochemist, as specialist in bioenergetics of microorganisms and membrane transport. He is a professor of Biochemistry at the University of Groningen and an elected member of the Royal Netherlands Academy of Arts and Sciences (KNAW) since 2009. Poolman is a pioneer in the field of bottom-up synthetic biology, that is, the construction from molecular building blocks of functional metabolic networks and autonomously operating functional systems, which are typical of living cells. Poolman is a lecturer in membrane biology and synthetic biology. Poolman pursued studies in Biochemistry and Microbiology at the University of Groningen, the Netherlands, and the University of Bern (Switzerland), obtaining a MSc degree in 1984. He gained his PhD in 1987 with a thesis on bioenergetics of streptococci, under the supervision of Wil Konings and Hans Veldkamp. After a brief stint as a scientist at Genencor Inc (now Dupont Industrial Biosciences) in San Francisco (USA), he returned to the Netherlands in the end of 1989 to start his own research group on biochemistry and molecular biology of membrane transport at the University of Groningen, supported by a fellowship from the Royal Netherlands Academy of Arts and Sciences. He has been professor of biochemistry at the Groningen since 1998. In 2008 he was appointed Program Director of its Centre for Synthetic Biolog), and in 2013 he became Scientific Director of its Biomolecular Sciences and Biotechnology Institute | https://en.wikipedia.org/wiki?curid=63347153 |
Bert Poolman In 1993 Poolman has done a sabbatical at Transgene SA, Strasbourg (France). Thanks to a Fulbright fellowship, he was visiting professor in biochemistry at California Institute of Technology, Pasadena (USA) in 2003. Poolman has been Chair of the KNAW Earth and Life Sciences Board, and has been vice-chair of KNAW Council for Natural and Technical Sciences since 2017. From 2016 to 2018, he was a member of the Dutch Council for Physics and Chemistry, and currently he is a member of the core team of the Council for Chemistry. Since 2009 he led the focus area on ‘Biomolecular and Bioinspired Functionality’ at the Zernike Institute for Advanced Materials (University of Groningen, together with Nobel laureate Ben Feringa, and, from 2010 to 2017, he managed a national Synthetic Biology program of the University of Groningen. Poolman has made seminal contributions to the understanding of the dynamics and permeability of biological membranes and to the field of vectorial biochemistry, that is, the role of electrochemical gradients in the fuelling and regulation of membrane transport. He demonstrated that the exchange of different sugars can be more advantageous for a cell than sugar-proton symport, and showed that cells exploit the coupling of substrate import to product exchange to conserve metabolic energy. He is an expert in the field of ATP-binding cassette transporters, one of the largest known protein families, by combining functional and structural studies | https://en.wikipedia.org/wiki?curid=63347153 |
Bert Poolman Highlights include: discovery of export of hydrophobic compounds from the inner leaflet of the lipid bilayer; elucidation of sensing and gating mechanism of ABC importers involved in cell volume regulation; single-molecule fluorescence studies to elucidate the mechanism of solute capture and translocation; structural basis for peptide selection by receptors involved in nitrogen uptake; structural basis for vitamin recognition and transport by a new class of ABC importers; and the energy coupling stoichiometry of ABC importers. Poolman has advanced of membrane transport by combining mechanistic in vitro studies with in vivo analyses of transporter regulation. His group has developed innovative technologies in membrane reconstitution and the probing of the physicochemical state of both the cytoplasm and the cell membrane. His group was the first to show that changes in the ionic strength are used to gate the activity of osmoregulatory transporters, providing the cell with a simple on/off switch to control its cytoplasmic volume. In parallel, his group developed sensors to quantify changes in ionic strength and excluded volume (macromolecular crowding). His main current research areas include: (i) bacterial cell-volume regulation: elucidation of the homeostatic mechanisms that control the physicochemistry of the cell; (ii) building of synthetic cells: construction of functional out-of-equilibrium systems for metabolic energy conservation and development of cell volume regulatory networks | https://en.wikipedia.org/wiki?curid=63347153 |
Bert Poolman What tasks should a living cell minimally perform and how this can be accomplished with a minimal set of components? and (iii) the molecular mechanisms of membrane transport proteins: understanding the dynamics, energetics and mechanisms of solute transporters in the plasma membrane. Poolman has received numerous awards, including the Biochemistry Award (1989) of the "Dutch Biochemistry and Molecular Biology Organisation" (NVBMB), a Royal Netherlands Academy of Arts and Sciences fellowship (1989), an "Human Frontiers Science Program Organization" award (1992), the SON ‘Jonge Chemici’ award (1997), the Federation European Biochemical Society Lecturer Award (2014), and the Joel Mandelstam Memorial Lecture award (2016). He obtained four TOP program grants from the Netherlands Organisation for Scientific Research (NWO)(2001, 2007, 2010, 2014)., two program grants from the Netherlands Proteomics Centre (2005 en 2008), and coordinated three large European networks (1996, 1999 and 2012). In 2015 he received an ERC Advanced Grant and in 2019 an ERC Proof-of-Concept Grant, and in 2017 the BaSyC consortium (with Poolman as one of the lead principal investigators) was awarded a multimillion Dutch Gravitation grant. Poolman was born in 1959 as the first son of Jelto Poolman and Neeltje Prinsse. In 1983 he married Heleen Stevenson (1959), with whom he has four children. | https://en.wikipedia.org/wiki?curid=63347153 |
John H. Wotiz John Henry Wotiz (12 April 1919 in Ostrava – 21 August 2001 in Morehead, Kentucky) was a Czech-American chemist in the areas of organic chemistry and chemical history. Wotiz began studying of chemical engineering at the Czech Technical University in Prague, but went to the USA with his brother in 1939 because of the German occupation of Czechoslovakia. In 1941 he received a Bachelor's degree in chemistry from Furman University and in 1943 a Master's degree from the University of Richmond. At the end of World War II he served in the United States Army as Lieutenant of chemical weaponry. In 1944 he became an US citizen. In 1948 he earned a PhD in chemistry under Melvin S. Newman at Ohio State University. Wotiz was an instructor and from 1954 an associate professor at the University of Pittsburgh. He went to work in industry at the Diamond Alkali Company in Painesville in 1957. There he was involved in authoring 44 patents. In 1962 he became a professor at Marshall University in Huntington, West Virginia, and in 1967 at Southern Illinois University in Carbondale. In 1980 Wotiz was Chairman of the History Division of the American Chemical Society. Starting in 1971 he organized trips to Europe regarding the history of chemistry. As a chemical historian, he was particularly concerned with August Kekulé. He was involved in establishing a center for the history of chemistry, the Chemical Heritage Foundation (now the Science History Institute). Wotiz retired in 1989 | https://en.wikipedia.org/wiki?curid=63349869 |
John H. Wotiz He was particularly committed to international exchange with Eastern Europe and was involved in comparative studies of chemical education in the Soviet Union, Eastern Europe and Asia. He and his wife Kathryn died as a result of a car accident on August 21, 2001. In 1982 Wotiz received the Dexter Award, in part for his contributions to the establishment of a center for the history of chemistry. In 1998 he was awarded an honorary doctorate by the Technical University of Ostrava (in his home town) after receiving their gold medal in 1982. | https://en.wikipedia.org/wiki?curid=63349869 |
Julia A. Kornfield is a Professor of Chemical Engineering at the California Institute of Technology. Her research considers the development of mega-supramolecular systems for fuel additives and intraocular lenses. She was elected to the National Academy of Engineering in 2020. Kornfield was born in Oakland, California and grew up in the San Francisco Bay Area. Her father is a surgeon and her mother was a chef. She studied chemistry at the California Institute of Technology (Caltech) and graduated in 1983. She specialised in chemical engineering for her graduate studies, and earned a master's degree at Caltech before joining Stanford University for her doctoral research with Gerald Fuller. She earned her doctorate at Stanford in 1988. After graduating, Kornfield joined the Max Planck Institute for Polymer Research, where she worked as a NATO postdoctoral scholar with Hans Spiess. Her early research considered the optical properties of polymers in their melt phase. She studied the molecular weight distributions of polymer melts, as well as investigating their nematic order. Kornfield studies the macroscopic properties of polymer materials. Her research considers the physics and chemistry of polymers, as well as treatments for eye disease. She was recruited to the faculty at Caltech in 1990. She was the first woman who earned her bachelor's in the department of chemical engineering to join the faculty. Here she built a range of optical methods for rheology, combining molecular level probes with rheology measurements | https://en.wikipedia.org/wiki?curid=63352967 |
Julia A. Kornfield These investigations included quantitative observations of the dynamics of polymers and the local level; including the molecular level motions that determine their glass transition temperature. Kornfield has considered the orientation of block co-polymers, polymer liquid crystals and how polymer sidechains impact their viscoelasticity. She showed that certain block co-polymers can form structures that contain multiple differently oriented states. Kornfield went on to show that certain topological structures, including rings, wedges and branched chains, demonstrate distinct relaxation responses. Alongside her research into the material properties of polymers, Kornfield looks to apply her understanding to societal challenges. After the September 11 attacks Kornfield was motivated to design new polymeric systems that can be added to fuels to minimise the risk of explosion. The polymers attach to one another "via" amine and carboxylic acids groups to form mega-supramolecules, which reduce the burn time, size and temperature of ignited fuel. Kornfield has worked with the United States Army to test the polymer additives in improvised explosives and projectiles. She has demonstrated intraocular lenses that contain a silicone polymeric material that can be shaped after being implanted through the use of laser light. She worked with a surgeon at the UCSF Medical Center to transfer the lenses out of the laboratory and into the clinic | https://en.wikipedia.org/wiki?curid=63352967 |
Julia A. Kornfield Kornfield is the only woman to win the Society of Rheology Bingham Medal since it began in 1948. She spent 2018 as an academic visitor at the East China University of Science and Technology. Kornfield holds several patents for polymer processing and devices to tackle eye disease. | https://en.wikipedia.org/wiki?curid=63352967 |
Cytokeratin 5/6 antibodies are antibodies that target both cytokeratin 5 and cytokeratin 6. These are used in immunohistochemistry, often called CK 5/6 staining, including the following applications: | https://en.wikipedia.org/wiki?curid=63355855 |
Martin Geoffrey Low Martin Low FRS (27 July 1950 — 6 August 2013) was a molecular cell biologist who discovered GPI (glycosylphosphatidylinositol) membrane anchors in eukaryotic cells. He was elected Fellow of the Royal Society in 1996. | https://en.wikipedia.org/wiki?curid=63363474 |
Selenium tetrabromide is an inorganic compound with a chemical formula SeBr. This yellowish or brownish crystal will produce selenous acid in wet air. could dissolve in carbon disulfide, chloroform and bromoethene. It could produce by mixing bromine and selenium elements: The compound is only stable under a bromine saturated atmosphere and in gas phase measurements of the gas density indicate that the compound decomposes into selenium bromide and bromine. | https://en.wikipedia.org/wiki?curid=63371375 |
Glossary of nanotechnology This glossary of nanotechnology is a list of definitions of terms and concepts relevant to nanotechnology, its sub-disciplines, and related fields. For more inclusive glossaries concerning related fields of science and technology, see Glossary of chemistry terms, Glossary of physics, Glossary of biology, and Glossary of engineering. | https://en.wikipedia.org/wiki?curid=63399479 |
Waterborne resins are sometimes called water-based resins. They are resins or polymeric resins that use water as the carrying medium as opposed to solvent or solvent-less. Resins are used in the production of coatings, adhesives, sealants, elastomers and composite materials..When the phrase waterborne resin is used it usually describes all resins which have water as the main carrying solvent. The resin could be water soluble, water reducible or water dispersed. Most coatings have four basic components. These are the resin, solvent, pigment and additive systems but the resin or binder is the key ingredient. Continuing environmental legislation in many countries along with geopolitics such as oil production are ensuring that chemists are increasingly turning to waterborne technology for paint/coatings and since resins or binders are the most important part of a coating, more of them are being developed and designed waterborne and there is a constantly increasing use by coating formulators. The use of waterborne coatings and hence waterborne resins really started to grow in the 1960’s led by the United States and was driven by: a) the need to reduce flammability; b) environmental legislation aimed at reducing the amount of solvent vapor (VOC - Volatile organic compound) discharged into the atmosphere; c) cost; d) political factors i.e. security of supply. All these factors helped the desire to reduce the reliance on oil derived solvents | https://en.wikipedia.org/wiki?curid=63417066 |
Waterborne resins The use of water as the carrying solvent for coatings and hence resins has been increasing ever since. The same holds true for adhesives. Water is generally a low cost(but not free) commodity in plentiful supply with no toxicity problems so there has always been a desire to produce paints, inks, adhesives and textile sizes etc. with water as the carrying solvent. This has required the production of waterborne resins designed for these systems. In recent years legislative pressure has ensured that waterborne systems and hence waterborne resins are coming increasingly to the fore. see also Epoxy An epoxy resin system generally consists of a curing agent and an epoxy resin. Both the curing agent and the epoxy resin can be made waterborne. Solid epoxy resin (molecular weight >1000) dispersions are available and consist of an epoxy resin dispersed in water sometimes with the aid of co-solvents and surfactants. The resin backbone is often modified to ensure water dispersibility. These resins dry in their own right by water/co-solvent evaporation and he particles coalescence.. To cure the resin and crosslink it, an amine based curing agent is usually added. This produces a two-component system. An alternative is to use standard medium viscosity liquid epoxy resins and emulsify them in a water soluble polyamine or polyaminoamide hardener resin which also gives a two component system | https://en.wikipedia.org/wiki?curid=63417066 |
Waterborne resins Polyaminoamides are made by reacting ethylene amines with dimerized fatty acids to give a species with amide links but still having amine functionality. Water is liberated during the condensation reaction. These resins can then be made water soluble by reacting further with glacial organic acids or formaldehyde. Resins like these are usually left with yet further amine functionality on the polymer backbone to enable them to cure and crosslink an epoxy resin. Paints may then be made from them by pigmenting either the epoxy or the amine hardener portion or even both. Polyamine curing resins as opposed to polyaminoamide resins are generally made by partially adducting polyfunctional amines with an epoxy resin and/or epoxy diluent and leaving the species with residual amine functionality. This adduct can then be dissolved in water and used to emulsify more epoxy resin and again either portion or both may be pigmented. The advantage with these systems is that they do not need glacial organic acids to solubilize them. This is an advantage if the coating is to be used over a highly alkaline substrate such as fresh concrete, as the alkali from the cement will neutralise the acid and cause instability on repeated dipping of a brush into the can. see also article Alkyd Water reducible alkyds are basically conventional alkyd resins i.e. polyesters based on saturated or unsaturated oils or fatty acids, polybasic acids and alcohols modified to confer water miscibility | https://en.wikipedia.org/wiki?curid=63417066 |
Waterborne resins Typical components are vegetable oils or fatty acids such as linseed, soyabean, castor, dehydrated castor, safflower, tung, coconut and tall oil. Acids include isophthalic, terephthalic, adipic, benzoic, succinic acids and phthalic, maleic and trimellitic anhydride. Polyols include glycerol, pentaerythritol, Trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, neopentyl glycol, 1,6-hexanediol and 1,4-butanediol. Typical methods for introducing varying degrees of water miscibility are similar to other resin systems. Methods basically involve introducing hydrophilic centres such as acid groups that can then be neutrazised to form a salt. Introducing polar groups onto the backbone is another method. With alkyds typical methods include maleinization of unsaturated fatty acids with maleic anhydride. This involves making a Diels-Alder adduct near the double bond sites. The acid groups introduced can then be further reacted with polyols. A Diels-Alder reaction only occurs where there is a conjugated double bond system. Simple addition occurs if not conjugated. Other techniques include synthesizing the resin with hydroxyl functional oligomers e.g. containing ethylene glycol then adding specific acid or hydroxyl containing substances towards the end of the reaction. Another technique is making an acrylic functional alkyd with an acrylic monomer blend rich in carboxylic acid groups | https://en.wikipedia.org/wiki?curid=63417066 |
Waterborne resins see also Polyester resin Saturated polyester resins contain many of the materials used in conventional alkyd resins but without the oil or fatty acid components. Typical components for these resins are poly carboxylic and polyhydroxyl components. The more commonly used polyacids are phthalic, isophthalic, terephthalic and adipic acid. Phthalic and trimellitic anhydrides may also be used. Polyols tend to be neopentyl glycol, 1,6-hexanediol and trimethylolpropane. To make them waterborne organic acids or anhydrides are added in a two-stage process but there are other methods too. see article Polyurethane dispersion Polyurethanes resins are available waterborne. The single component versions are usually referred to as Polyurethane dispersions. They are available in anionic, cationic and nonionic versions though anionic moieties are the most readily available commercially. Waterborne polyurethanes are also available in 2 component versions. As a 2 component polyurethane consists of polyol(s) and an isocyanate and isocyanates react with water this requires special formulating and production techniques. The polyisocyanate that is water-dispersible maybe modified with sulfonate for example. see main article Latex A latex is a stable dispersion (emulsion) of polymer in water. Synthetic lattices are usuaully made by polymerizing a monomer such as vinyl acetate that has been emulsified with surfactants dispersed in water | https://en.wikipedia.org/wiki?curid=63417066 |
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