Letteratura scientifica selezionata sul tema "C-S bond formation"
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Articoli di riviste sul tema "C-S bond formation"
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Xu, Yulong, Xiaonan Shi e Lipeng Wu. "tBuOK-triggered bond formation reactions". RSC Advances 9, n. 41 (2019): 24025–29. http://dx.doi.org/10.1039/c9ra04242c.
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Gao, Jian, Jie Feng e Ding Du. "Shining Light on C−S Bonds: Recent Advances in C−C Bond Formation Reactions via C−S Bond Cleavage under Photoredox Catalysis". Chemistry – An Asian Journal 15, n. 22 (14 ottobre 2020): 3637–59. http://dx.doi.org/10.1002/asia.202000905.
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Modha, Sachin G., Vaibhav P. Mehta e Erik V. Van der Eycken. "Transition metal-catalyzed C–C bond formation via C–S bond cleavage: an overview". Chemical Society Reviews 42, n. 12 (2013): 5042. http://dx.doi.org/10.1039/c3cs60041f.
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Sun, Fengli, Xuemin Liu, Xinzhi Chen, Chao Qian e Xin Ge. "Progress in the Formation of C-S Bond". Chinese Journal of Organic Chemistry 37, n. 9 (2017): 2211. http://dx.doi.org/10.6023/cjoc201703038.
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Jean, Mickaël, Jacques Renault, Pierre van de Weghe e Naoki Asao. "Gold-catalyzed C–S bond formation from thiols". Tetrahedron Letters 51, n. 2 (gennaio 2010): 378–81. http://dx.doi.org/10.1016/j.tetlet.2009.11.025.
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Choudhuri, Khokan, Milan Pramanik e Prasenjit Mal. "Noncovalent Interactions in C–S Bond Formation Reactions". Journal of Organic Chemistry 85, n. 19 (25 agosto 2020): 11997–2011. http://dx.doi.org/10.1021/acs.joc.0c01534.
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Wang, Haibo, Lu Wang, Jinsai Shang, Xing Li, Haoyuan Wang, Jie Gui e Aiwen Lei. "Fe-catalysed oxidative C–H functionalization/C–S bond formation". Chem. Commun. 48, n. 1 (2012): 76–78. http://dx.doi.org/10.1039/c1cc16184a.
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Stenfors, Brock A., Richard J. Staples, Shannon M. Biros e Felix N. Ngassa. "Crystal structure of 1-[(4-methylbenzene)sulfonyl]pyrrolidine". Acta Crystallographica Section E Crystallographic Communications 76, n. 3 (28 febbraio 2020): 452–55. http://dx.doi.org/10.1107/s205698902000208x.
Testo completoAbstract (sommario):
The molecular structure of the title compound, C11H15NO2S, features a sulfonamide group with S=O bond lengths of 1.4357 (16) and 1.4349 (16) Å, an S—N bond length of 1.625 (2) Å, and an S—C bond length of 1.770 (2) Å. When viewing the molecule down the S—N bond, both N—C bonds of the pyrrolidine ring are oriented gauche to the S—C bond with torsion angles of −65.6 (2)° and 76.2 (2)°. The crystal structure features both intra- and intermolecular C—H...O hydrogen bonds, as well as intermolecular C—H...π and π–π interactions, leading to the formation of sheets parallel to the ac plane.
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Shen, Chao, Pengfei Zhang, Qiang Sun, Shiqiang Bai, T. S. Andy Hor e Xiaogang Liu. "Recent advances in C–S bond formation via C–H bond functionalization and decarboxylation". Chemical Society Reviews 44, n. 1 (2015): 291–314. http://dx.doi.org/10.1039/c4cs00239c.
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Saidalimu, Ibrayim, Shugo Suzuki, Etsuko Tokunaga e Norio Shibata. "Successive C–C bond cleavage, fluorination, trifluoromethylthio- and pentafluorophenylthiolation under metal-free conditions to provide compounds with dual fluoro-functionalization". Chemical Science 7, n. 3 (2016): 2106–10. http://dx.doi.org/10.1039/c5sc04208a.
Testo completoTesi sul tema "C-S bond formation"
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Arambasic, Milan. "Carbon-carbon bond formation via rhodium-catalysed C-S activation processes". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:e9e29a73-e637-4844-9a37-58b5ae4a3f99.
Testo completoAbstract (sommario):
In the following thesis, new methodologies towards harnessing C-S activation processes are documented. These methods utilise rhodium catalysis and are focused on the activation of aryl methyl sulfides. Chapter 1 provides an overview of the development of metal-catalysed C-S activation chemistry, with a focus on the catalytic systems, reagents and starting materials used to facilitate various C-C bond forming transformations. Chapter 2 describes a novel rhodium-catalysed cross-coupling reaction of aryl and alkyl terminal alkynes with simple aryl sulfides. This resulted in a Sonogashira-type transformation which exhibited orthogonality with traditional palladium catalysed Sonogashira chemistry. Chapter 3 documents a new catalytic system which allowed for the practical and efficient alkyne carbothiolation reactions of ketone-baring methyl sulfides. The carbothiolation products can be conveniently utilised in a one-pot three-component reaction to form highly substituted isoquinolines. Chapter 4 discusses the potential for future work. Chapter 5 presents the experimental data.
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Garcia, Civit Marc. "Activation of B-interElement (E=S, Se) reagents towards selective C-S and C-Se bond formation". Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/454746.
Testo completoAbstract (sommario):
Aquetsa tesi descriu el treball realitzat amb reactius que contenen enllaços bor-sofre o bor-seleni. Aquest reactius s’han fet servir en reaccions de tioboració i selenoboració de substrats amb insaturacions conjugades a cetones o esters i en reaccions d’inserció amb grups diazo per a sintetitzar nous compostos organosulfurats i organoselenats. La tesi es divideix en quatre capítols. El primer d’ell és una breu introducció al compostos organosulfurats i organoselenats, parlant sobre les seves principals aplicacions i els mètodes per sintetitzar-los més representatius fins al moment. En aquest primer capítol també és parla de la síntesis dels reactius de bor-sofre i bor-seleni i les reaccions en les que s’han fet servir. El segon capítol parla de la reactivitat dels compostos de bor-sofre amb cetones i aldehids α,β-insaturats. S’ha observat que el propi grup carboxil és capaç d’activar el reactiu i fer entrar la unitat de sofre en la posició beta. El tercer capítol parla de la reacció amb triples enllaços conjugat a cetones i esters per sintetitzar vinil sulfats i vinil selenats. Aquesta mateixa reacció en presència d’una fosfina permet obtenir compostos anti-3,4-selenoborats que són precursors de compostos amb el grup seleni en la posició alfa. L’últim capítol parla sobre les reaccions d’inserció de compostos diazo en l’enllaç bor-sofre que permet obtenir molècules molt funcionalitzades amb grups Si, B, S i H que degut a les seves diferents propietats químiques poden continuar sent funcionalitzades per sintetizar una gran varitat de compostos orgànics.Esta tesis describe el trabajo realizado con reactivos que contienen enlaces boro-azufre o boro-selenio. Estos reactivos se han usado en reacciones de tioboración y selenoboración de sustratos con insaturaciones conjugadas a cetonas o esteres y en reacciones de inserción con grupos diazo para sintetizar nuevos compuestos organosulfurados y organoselenados. La tesis se divide en cuatro capítulos. El primero es una breve introducción a los compuestos organosulfurados y organoselenados, hablando sobre sus principales aplicaciones y los métodos para sintetizarlos más representativos hasta el momento. En este primer capítulo también se presenta el método de síntesis de los reactivos de boro-azufre y boro-selenio y las reacciones en las que se han usado. El segundo capítulo habla de la reactividad de los compuestos de boro-azufre con cetonas y aldehídos α,β-insaturados. Se ha observado que el propio grupo carboxilo es capaz de activar el reactivo y hacer entrar la unidad de azufre en la posición beta. El tercer capítulo habla de la reacción con triples enlaces conjugado a cetonas y esters para sintetizar vinilo sulfatos y vinilo selenatos. Esta misma reacción en presencia de una fosfina permite obtener compuestos anti-3,4-selenoborats que son precursores de compuestos con el grupo selenio en la posición alfa. El último capítulo habla sobre las reacciones de inserción de compuestos diazo en el enlace boro-azufre que permite obtener moléculas muy funcionalizadas con los grupos Si, B, S y H que debido a sus diferentes propiedades químicas pueden continuar siendo funcionalizados.
This thesis describes the work done with reagents that contain links boron-sulphur or boron-selenium. These reagents have used in reactions of thioboration and selenoboration of substrates with unsaturation conjugated to ketones or esters and in reactions of insertion with diazo compounds to synthesize new organosulfides and organoselenides compounds. The thesis is divided in four chapters. The first is a brief introduction to the organosulfides and organoselenides compounds, reporting its main applications and its more representative methods of synthesis. The first chapter also reported the synthesis of the boron-sulphur and boron-selenium reagents and the reactions where they have been used. The second chapter is about the reactivity of the compounds of boron-sulphur with α,β-unsaturated ketones and aldehydes. It has observed that the carboxyl group is able to activate the B-S reagent and deliver the sulphur unit in the beta position. The third chapter shows the reactivity with triple bonds conjugated to ketones and esters to synthesise vinyl sulphates and vinyl selenates. The same reaction in presence of a phosphine allow to obtain anti-3,4-selenoborated compounds that they are precursors of compounds with the selenium moiety in the alpha position. The last chapter is about the insertion reactions of diazo compounds into the boron-sulphur bond that allow to obtain molecules very functionalized with groups Si, B, S and H than due to its different chemical behaviour can be further functionalized.
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Vuong, Khuong Quoc Chemistry Faculty of Science UNSW. "Metal complex catalysed C-X (X = S, O and N) bond formation". Awarded by:University of New South Wales. Chemistry, 2006. http://handle.unsw.edu.au/1959.4/23015.
Testo completoAbstract (sommario):
This thesis describes the catalysed addition of X-H bonds (X = S, O and N) to alkynes using a range of novel rhodium(I) and iridium(I) complexes containing hybrid bidentate phosphine-pyrazolyl, phosphine-imidazolyl and phosphine-N heterocyclic carbene (NHC) donor ligands. The synthesis of novel bidentate phosphine-pyrazolyl, phosphine-imidazolyl (P-N) and phosphine-NHC (PC) donor ligands and their cationic and neutral rhodium(I) and iridium(I) complexes [M(P N)(COD)]BPh4, [M(PC)(COD)]BPh4, [Ir(P-N)(CO)2]BPh4 and [M(P-N)(CO)Cl] were successfully performed. An unusual five coordinate iridium complex with phosphine-NHC ligands [Ir(PC)(COD)(CO)]BPh4 was also obtained. Seventeen single crystal X-ray structures of these new complexes were determined. A range of these novel rhodium and iridium complexes were effective as catalysts for the addition of thiophenol to a variety of alkynes. Iridium complexes were more effective than rhodium analogues. Cationic complexes were more effective than neutral complexes. Complexes with hybrid phosphine-nitrogen donor were more effective than complexes containing bidentate nitrogen donor ligands. An atom-economical, efficient method for the synthesis of cyclic acetals and bicyclic O,O-acetals was successfully developed based on the catalysed hydroalkoxylation. Readily prepared terminal and non-terminal alkyne diols were cyclised into bicyclic O,O-acetals in quantitative conversions in most cases. The efficiency of a range of rhodium and iridium complexes containing bidentate P-N and PC donor ligands as catalysts for the cyclisation of 4-pentyn-1-amine to 2-methyl-1-pyrroline varied significantly. The cationic iridium complexes with the bidentate phosphine-pyrazolyl ligands, [Ir(R2PyP)(COD)]BPh4 (2.39-2.42) were extremely efficient as catalysts for this transformation. Increasing the size of the substituent on or adjacent to the donor led to improvement in catalytic activity of the corresponding metal complexes. The mechanism of the catalysed hydroalkoxylation was proposed to proceed by the initial activation of the alkyne via ?? coordination to the metal centre. The ?? binding of both aliphatic and aromatic alkynes to [Ir(PyP)(CO)2]BPh4 (2.44) was observed by low temperature NMR and no reaction between 2.44 and alcohols was observed. In contrast, the facility in which thiol and amine oxidatively added to 2.44 led the proposal that in the hydrothiolation and hydroamination reaction, the catalytic cycle commences with the activation of the X-H bond (X = S, N) by an oxidative addition process.
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Fusillo, Vincenzo. "New insights into scale up processing and C-S bond formation reactions". Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/28635/.
Testo completoAbstract (sommario):
This thesis describes the development of a new microwave-mediated methodology for C–S bond formation and the issues regarding scaling up heterocyclic transformations. Chapter 1 provides an overview on the current understanding of microwave-mediated synthesis and on the use of microwave technology in copper- and palladium-mediated synthesis. A separate part is dedicated to the current advancements in the use of flow reactors within the chemical community. Chapter 2 describes the application of the current batch and continuous flow technology for the scale-up of selected heterocyclic transformations, starting with the well known Bohlmann- Rahtz pyridine synthesis and moving to other reactions, including pyrimidine and Hantzsch dihydropyridine synthesis. Chapter 3 describes the development of a new methodology for the microwave-mediated C–S bond formation, starting from an investigation on the current available methods and moving to the application of new methodology to the synthesis of a library of compounds. Further application was found in the synthesis of a drug candidate with anti-ageing properties and in the synthesis of a new class of anti-HIV compounds.
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Aota, Yusuke. "Development of New Methodologies for the Asymmetric Synthesis of Chiral Sulfoximines via C-S Bond Formation". Kyoto University, 2020. http://hdl.handle.net/2433/253103.
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Gehrtz, Paul Henry [Verfasser], e Ivana [Akademischer Betreuer] Fleischer. "Pd- and Ni-based catalysts for mild C-S bond activation and formation / Paul Henry Gehrtz ; Betreuer: Ivana Fleischer". Tübingen : Universitätsbibliothek Tübingen, 2020. http://d-nb.info/120277394X/34.
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Gehrtz, Paul [Verfasser], e Ivana [Akademischer Betreuer] Fleischer. "Pd- and Ni-based catalysts for mild C-S bond activation and formation / Paul Henry Gehrtz ; Betreuer: Ivana Fleischer". Tübingen : Universitätsbibliothek Tübingen, 2020. http://d-nb.info/120277394X/34.
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Huadsai, Wimonsiri. "Activation du dioxyde de carbone par des composés de Lewis hautement acidés". Electronic Thesis or Diss., Université de Toulouse (2023-....), 2024. http://www.theses.fr/2024TLSES053.
Testo completoAbstract (sommario):
Cette recherche visait à étudier les applications potentielles des complexes d'hydrure de Mg et de Ca soutenus par des ligands ß-diketiminate et amidinate pour la réduction des molécules de CO2. Les capacités catalytiques de ces complexes ont été explorées dans le contexte de l'hydroboration et de l'hydrosilylation du CO2. Dans la première partie de l'étude, nous avons examiné la réactivité des hydrures ß-diketiminato de Mg et de Ca avec le CO2. Il a été observé que le complexe d'hydrure de Mg incorporait rapidement le CO2, conduisant à la formation de divers intermédiaires avec différentes nucléarités. Cela implique l'insertion de la liaison Mg—H dans le CO2, ce qui entraîne la génération de groupements formate. Sous l'effet de la chaleur, des complexes de formiate hexamériques ont été formés par un mécanisme de "retournement de ligand", libérant les entraves stériques autour des centres métalliques. Pour les réactions à l'hydrure de Ca et au CO2, l'analyse RMN in situ a été principalement réalisée. En outre, un nouveau complexe amidinate dihydride de Mg a été synthétisé avec succès et a réagi avec du CO2 pour donner un produit unique de complexe formate Mg dimérique, contrairement à l'échafaudage ß-diketiminate, où plusieurs espèces de formate ont été détectées. La deuxième partie de la recherche s'est concentrée sur l'hydroboration catalytique du CO2 à l'aide de complexes d'hydrures alcalino-terreux. En particulier, le système à base de Ca a démontré une grande efficacité dans la production de la réduction à quatre électrons du CO2 ou du produit BBA. Il s'agit du premier exemple d'utilisation de composés hydrides de Mg et de Ca pour catalyser l'hydroboration du CO2, produisant sélectivement le produit BBA. Le BBA généré in situ a ensuite été utilisé comme réactif de transfert de méthylène dans des réactions de condensation avec des thiols, ce qui a entraîné la formation de nouveaux composés hémithioacétals stables [RS—CH2—OBR2] dans des conditions douces et neutres. L'activation des composés hémithioacétals a été réalisée dans des conditions acides, conduisant à la formation de dithioacétals et d'hémithioaminals. La condensation du deuxième fragment OBR2 avec des amines secondaires, qui agissent comme des nucléophiles plus puissants, a abouti à la génération de sulfures d'aryle et de méthyle [RS—CH2—NR2]. Dans la dernière section, nous avons étudié l'hydrosilylation en tandem du CO2 en utilisant divers hydrosilanes en combinaison avec des complexes d'hydrures à base de [Ae] et l'acide de Lewis B(C6F5)3 comme catalyseurs. Cette recherche a élargi les études précédentes sur l'hydrosilylation du CO2 médiée par le Mg et a introduit le premier exemple d'hydrosilylation du CO2 catalysée par le Ca avec des hydrosilanes. L'efficacité de la réduction du CO2 en CH4 ou en bis(silyl)acétal [H2C(Ph3SiO)2] ou en BSA dépend de la nature des silanes et des encombrements stériques autour de la liaison Si—H du substrat. Le choix du catalyseur [Ae] a également influencé de manière significative la vitesse globale de la réaction. En outre, les analyses d'Eyring et d'Arrhenius ont permis de mieux comprendre les paramètres d'activation de la réduction du CO2 par certains catalyseurs, révélant que cette réaction est principalement régie par une contribution entropique. En résumé, cette recherche a démontré la réactivité des complexes d'hydrure de Mg et de Ca pour la réduction du CO2 et a exploré leurs applications dans les réactions d'hydroboration et d'hydrosilylation. Les recherches futures pourraient explorer les possibilités mécanistiques, les différences cinétiques et la réactivité des complexes d'hydrures métalliques du groupe 2 avec le monoxyde de carbone pour l'homologation du COThis research aimed to investigate the potential applications of Mg and Ca hydride complexes supported by ß-diketiminate and amidinate ligands for the reduction of CO2 molecules. The catalytic abilities of these complexes were explored in the context of hydroboration and hydrosilylation of CO2. In the first part of the study, we examined the reactivity of ß-diketiminato Mg and Ca hydrides with CO2. It was observed that the Mg hydride complex rapidly incorporated CO2, leading to the formation of various intermediates with different nuclearities. This involved the insertion of Mg—H bond into CO2, resulting in the generation of formate moieties. Under heat, hexameric formate complexes were formed through a "ligand flip" mechanism, releasing steric hindrances around the metal centers. For Ca hydride and CO2 reactions, in situ NMR analysis was mainly conducted. Additionally, a novel Mg amidinate dihydride complex was successfully synthesized and reacted with CO2 to yield a unique single product of dimeric formate Mg complex, in contrast to the ß-diketiminate scaffold, where several formate species were detected. The second part of the research focused on the catalytic hydroboration of CO2 using alkaline-earth hydride complexes. In particular, the Ca-based system demonstrated high efficiency in the production of the four-electron reduction of CO2 or BBA product. This was the first example of using Mg and Ca hydride compounds to catalyze the hydroboration of CO2, selectively producing the BBA product. The in situ generated BBA was further used as a methylene transfer reagent in condensation reactions with thiols, resulting in the formation of novel stable hemithioacetal [RS—CH2—OBR2] compounds under mild and neutral conditions. Activation of the hemithioacetal compounds was achieved under acidic conditions, leading to the formation of dithioacetals and hemithioaminals. The condensation of the second OBR2 fragment with secondary amines, which act as stronger nucleophiles, resulted in the generation of aryl methyl sulfides [RS—CH2—NR2]. In the final section, we investigated the tandem hydrosilylation of CO2 using various hydrosilanes in combination with [Ae]-based hydride complexes and Lewis acid B(C6F5)3 as catalysts. This research expanded on previous studies of Mg-mediated hydrosilylation of CO2 and introduced the first example of Ca-catalyzed CO2 hydrosilylation with hydrosilanes. The effectiveness of reducing CO2 to CH4 or bis(silyl)acetal [H2C(Ph3SiO)2] or BSA depended on the nature of the silanes and the steric hindrances around the substrate Si—H bond. The choice of [Ae] catalyst also significantly influenced the overall reaction rate. Furthermore, Eyring and Arrhenius analyses provided insight into the activation parameters for reducing CO2 by certain catalysts, revealing that this reaction is primarily governed by an entropic contribution. In summary, this research has demonstrated the reactivity of Mg and Ca hydride complexes for CO2 reduction and explored their applications in hydroboration and hydrosilylation reactions. Future investigations may explore mechanistic possibilities, kinetic differences, and the reactivity of group 2 metal hydride complexes with carbon monoxide for CO homologation
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Roberts, Deborah Elizabeth. "Palladium N-neterocyclic carbene complexes as catalysts for C-N, C-Si and C-S bond formations". Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/45342/.
Testo completoAbstract (sommario):
This work is foremost a study of various palladium-bearing N-heterocyclic carbenes complexes and their catalytic potential to form C-N bonds. Both alkyl amination and aryl amination are considered. Further elucidation on the mechanism of such catalytic activity is investigated. The viability of alkyl amination using palladium complexes bearing the ligands, ITMe, 1,2,3,4- tetramethylimidazol-2-ylidene, and ICy, 1,3- bis-cyclohexylimidazol-2-ylidene, as catalysts, is investigated. This includes the synthesis of [Pd(ITMe)(neopentyl)Cl]2,[Pd(ITMe)2(neopentyl)Cl], [Pd(ITMe)(neopentyl)(tbutylamine)Cl], [Pd(ITMe)(neopentyl)(hexylamine)Cl], with successful elimination of the alkyl-amination reaction product in low yield from the latter complex. [Pd(ICy)(neopentyl)Cl]2, [Pd(ICy)2(neopentyl)Cl] are also isolated. Unsuccessful attempts were made to vary the electronic properties of the complexes by replacing the amine with a hydrazine. Work was also done on indirect alkylation using tBuLi which led to a new method for synthesis of [Pd(ItBu)2] and novel complex, [Pd(ItBu)Cl3. ItBuH] (ItBu = 1,3- bis-tertbutylimidazol-2-ylidene). Aryl amination catalysed by complexes of palladium bearing the ligand, ITMe, is considered. This includes an improved synthesis of [Pd(ITMe)2] and synthesis of [Pd(ITMe)2(anisole)Cl]. Unsuccessful attempts at the elucidation of the mechanism of [Pd(ITMe)2(anisole)] formation led to the unexpected formation of [Pd(ITMe)2(SiMe3)(Si(SiMe3)3)] and [Pd(ITMe)2(SiMe3)2]. Aryl amination with using [Pd(ITMe)2(SiMe3)2] led to two aryl amination products, 4-ortho-methoxyphenyl morpholine as well as the expected para isomer. The use of complexes [Pd(ItBu)2] and [Pd(SIPr)2] (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) in C-S bond formation was explored. Addition of mesityl magnesium bromide to Pd(1,5-COD)Cl2 led to addition of mesityl substrate across 1,5-COD double bond and the addition of ITMe formed the Heck cycle intermediate [Pd(8-mesityl-1,4,5-η3 – C8H12)X2] (X=Cl, Br). Addition of 4-tolyl magnesium chloride resulting in the formation of Pd(ItBu)2(tolyl)Cl via an indirect route.
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Thakur, V. V. "Asymmetric synthesis of bioactive molecules and formation of C-C, C-N, C-Br, S-O bonds by transition metal catalysis". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2002. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2338.
Testo completoCapitoli di libri sul tema "C-S bond formation"
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Eisen, Moris S. "Catalytic C–N, C–O, and C–S Bond Formation Promoted by Organoactinide Complexes". In C-X Bond Formation, 157–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2_7.
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Di Giuseppe, Andrea, Ricardo Castarlenas e Luis A. Oro. "Rhodium Catalysts for C–S Bond Formation". In Topics in Organometallic Chemistry, 31–67. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/3418_2016_171.
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Della Sala, Giorgio, e Alessandra Lattanzi. "C-Other Atom Bond Formation (S, Se, B)". In Stereoselective Organocatalysis, 493–527. Hoboken, New Jersey: John Wiley & Sons, Inc., 2013. http://dx.doi.org/10.1002/9781118604755.ch14.
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Gross, Johannes, Tamara Reiter, Christiane Wuensch, Silvia M. Glueck e Kurt Faber. "Non-Redox Lyases and Transferases for C-C, C-O, C-S, and C-N Bond Formation". In Practical Methods for Biocatalysis and Biotransformations 3, 75–134. Chichester: John Wiley & Sons, Ltd, 2016. http://dx.doi.org/10.1002/9781118697856.ch04.
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Mase, N. "C—S and C—Se Bond Formation". In Water in Organic Synthesis, 1. Georg Thieme Verlag KG, 2012. http://dx.doi.org/10.1055/sos-sd-206-00162.
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Argyropoulos, N. G. "By Formation of One S—S Bond, Two S—C Bonds, and One N—C Bond". In Five-Membered Hetarenes with Three or More Heteroatoms, 1. Georg Thieme Verlag KG, 2004. http://dx.doi.org/10.1055/sos-sd-013-00028.
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Aitken, R. A. "By Formation of Two S—S Bonds and One C—C Bond". In Five-Membered Hetarenes with Three or More Heteroatoms, 1. Georg Thieme Verlag KG, 2012. http://dx.doi.org/10.1055/sos-sd-113-00013.
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Rayner, C. M., e M. A. Graham. "By Formation of One S—C Bond". In Fused Five-Membered Hetarenes with One Heteroatom, 1. Georg Thieme Verlag KG, 2001. http://dx.doi.org/10.1055/sos-sd-010-00212.
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Andrews, M. D. "By Formation of One S—C Bond". In Fused Five-Membered Hetarenes with One Heteroatom, 1. Georg Thieme Verlag KG, 2001. http://dx.doi.org/10.1055/sos-sd-010-00290.
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Perst, H., e C. Klenke. "By Formation of One S—C Bond". In Five-Membered Hetarenes with One Chalcogen and One Additional Heteroatom, 1. Georg Thieme Verlag KG, 2002. http://dx.doi.org/10.1055/sos-sd-011-00089.
Testo completoAtti di convegni sul tema "C-S bond formation"
1
Besson, Thierry, Damien Hédou, Carole Dubouilh-benard, Nadège Loaëc, Laurent Meijer e Corinne Fruit. "Synthesis of Bioactive 2-(arylamino)thiazolo[5,4-f]-quinazolin-9-ones via the Hügershoff Reaction or Cu- Catalyzed Intramolecular C-S Bond Formation". In 2nd International Electronic Conference on Medicinal Chemistry. Basel, Switzerland: MDPI, 2016. http://dx.doi.org/10.3390/ecmc-2-a010.
Testo completo
2
Moskal, G., R. Swadźba, R. Białecki, T. Kruczek e W. Adamczyk. "S/TEM and TEM Investigations of Thermal Barrier Coatings Based on Gd2Zr2O7 Zirconate". In ITSC2017, a cura di A. Agarwal, G. Bolelli, A. Concustell, Y. C. Lau, A. McDonald, F. L. Toma, E. Turunen e C. A. Widener. DVS Media GmbH, 2017. http://dx.doi.org/10.31399/asm.cp.itsc2017p0784.
Testo completoAbstract (sommario):
Abstract Detailed investigations of thermally grown oxides (TGO) zone and areas adjoining to it were presented in this article. The thermal barrier coating (TBC) based on gadolinium zirconate (Gd2Zr2O7, GZ) and deposited by air plasma spraying (APS) on AMS 5599 superalloy with NiCrAlY type of bond-coat was the analysed material. Analyses were made on TBC system after spraying process and after time to 500 hours of oxidation at temperature 1100°C in atmosphere of laboratory air. Ultrahigh resolution scanning-transmission (S/TEM) electron microscope TITAN 80-300 was used to conduct the tests. Quanta 200i Dual Beam apparatus by FEI for precise and localized focused Ga+ ion beam (FIB) sample preparation was used as well.The basic aim of presented investigations was related with detailed characterization of interface zone between ceramic top-coat (TC) of Gd2Zr2O7 type and NiCrAlY bond-coat after spraying process and after 500 hours of deposition in oxidized atmosphere where the TGO zone was formed with the thickness ca. 5-10 µm. The special emphasis was placed on research of this zone and its morphology due to very strong influence of formed thermally grown oxides on overall life-time and destruction processes which took place on the interface between TGO and ceramic top-coat. Obtained data revealed that the most important factors influenced on destruction processes are related with the thickness of TGO zone (consisted mainly Al2O3, NiAl2O4 and eventually NiO) rather than formation of undesirable phases such as GdAlO3 complex oxide.
3
Molki, Majid, e Bahman Abbasi. "Experimental and Computational Study of Droplet Growth and Detachment Near the Inception Point". In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41433.
Testo completoAbstract (sommario):
An experimental and computational investigation was conducted to study the growth and detachment of a single liquid droplet. High-speed photography was employed to capture the droplet evolution from the onset to the breakup time. Three-dimensional computations were carried out to predict the droplet behavior and flow dynamics inside the droplet. The droplet fluid was water immersed in the surrounding atmospheric air. The computations were performed using the finite volume and Volume of Fluid (VOF) techniques. The computations and high-speed photography of the droplet formation were carried out at 20°C. Diameter of the injection port was 2.4 mm and the flow rate for generation of droplets was 1.1 × 10−4 kg/s. These values together with the choice of liquid resulted in a Bond number of 0.19, Capillary number of 3.4 × 10−4, and liquid-to-gas viscosity ratio of 56.05. The results indicated that the shape and evolution of the droplet as predicted by the computations were in good agreement with those captured on the high-speed photographs. The computations revealed details of the flow inside the droplet such as pressure and velocity.
4
Suzuki, K., J. Nishioka, H. Kusumoto e Y. Deyashiki. "BINDING SITE OF VITAMIN K-DEPENDENT PROTEIN S ON C4b-BINDING PROTEIN". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1644637.
Testo completoAbstract (sommario):
Protein S, a cofactor for activated protein C, reversibly complexes with a regulatory complement component C4b-binding protein (C4bp) in plasma. In plasma of patients with congenital protein S deficiency, most protein S exists as a complex with C4bp, which has no cofactor activity. C4bp (Mw 550,000) is composed of approximately seven subunits with Mw 75,000 which are linked by disulfide bonds near the carboxy1-terminus. We report here about the complex formation between protein S and C4bp particularly on the binding site of protein S on C4bp molecule. Protein S and C4bp were purified from human plasma. Seventeen mouse monoclonal antibodies against C4bp were prepared. Chymotrypsin-digested C4bp was separated on gel filtration into a fragment with Mw 160,000 derived from the carboxyl-terminal core of the intact C4bp and fragments with Mw 48,000 from the amino-terminus. The carboxy1-terminal fragment with Mw 160,000 was found to be composed of approximately seven polypeptides with Mw 25,000, which were linked by disulfide bonds.The experiments using these fragments and the monoclonal antibodies showed that: (1) Protein S bound not only to the intact C4bp, but also to the fragment with Mw 160,000. (2) The fragment with Mw 160,000 inhibited the binding of protein S to C4bp, but the fragment with Mw 48,000 did not. (3) One of the seventeen monoclonal antibodies blocked the inhibition of C4bp on the cofactor activity of protein S. (4) This antibody inhibited C4bp binding to protein S. (5) The antibody bound to the fragment with Mw 160,000. Based on these results, protein S was suggested to lose its cofactor activity for activated protein C by binding to the carboxyl-terminal core of C4bp where seven subunits are linked by disulfide bonds.
5
Ford, David A., Keith P. L. Fullagar, Harry K. Bhangu, Malcolm C. Thomas, Phil S. Burkholder, Paul S. Korinko, Ken Harris e Jacqueline B. Wahl. "Improved Performance Rhenium Containing Single Crystal Alloy Turbine Blades Utilising PPM Levels of the Highly Reactive Elements Lanthanum and Yttrium". In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-371.
Testo completoAbstract (sommario):
Turbine inlet temperatures have now approached 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and thrust levels approaching or exceeding 445 kN (100,000 lbs.). High reliability and durability must be intrinsically designed into these turbine engines to meet operating economic targets and ETOPS certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, computerized design technology for stresses and airflow and the development and application of rhenium (Re) containing, high γ′ volume fraction nickel-base single crystal superalloys, with advanced coatings, including prime-reliant ceramic thermal barrier coatings (TBCs). Re additions to cast airfoil superalloys not only improve creep and thermo-mechanical fatigue strength but also environmental properties, including coating performance. Re slows down diffusion in these alloys at high operating temperatures.(1) At high gas temperatures, several issues are critical to turbine engine performance retention, blade life and integrity. These are tip oxidation in particular for shroudless blades, internal oxidation for lightly cooled turbine blades and TBC adherence to both the airfoil and tip seal liner. It is now known that sulfur (S) at levels < 10 ppm but > 0.2 ppm in these alloys reduces the adherence of α alumina protective scales on these materials or their coatings by weakening the Van der Waal’s bond between the scale and the alloy substrate. A team approach has been used to develop an improvement to CMSX-4® alloy which contains 3% Re, by reducing S and phosphorus (P) levels in the alloy to < 2 ppm, combined with residual additions of lanthanum (La) + yttrium (Y) in the range 10–30 ppm. Results from cyclic, burner rig dynamic oxidation testing at 1093°C (2000°F) show thirteen times the number of cycles to initial alumina scale spallation for CMSX-4 [La + Y] compared to standard CMSX-4. A key factor for application acceptance is of course manufacturing cost. The development of improved low reactivity prime coats for the blade shell molds along with a viable, tight dimensional control yttrium oxide core body are discussed. The target is to attain grain yields of single crystal CMSX-4 (ULS) [La + Y] turbine blades and casting cleanliness approaching standard CMSX-4. The low residual levels of La + Y along with a sophisticated homogenisation/solutioning heat treatment procedure result in full solutioning with essentially no residual γ/γ′ eutectic phase, Ni (La, Y) low melting point eutectics and associated incipient melting pores. Thus, full CMSX-4 mechanical properties are attained. The La assists with ppm chemistry control of the Y throughout the single crystal turbine blade castings through the formation of a continuous lanthanum oxide film between the molten and solidifying alloy and the ceramic core and prime coat of the shell mold. Y and La tie up the < 2 ppm but > 0.2 ppm residual S in the alloy as very stable Y and La sulfides and oxysulfides, thus preventing diffusion of the S atoms to the alumina scale layer under high temperature, cyclic oxidising conditions. La also forms a stable phosphide. CMSX-4 (ULS) [La + Y] HP shroudless turbine blades will commence engine testing in May 1998.
6
Suzuki, Koji, Yoshihiro Deyashiki, Junji Nishioka, Kazunori Toma e Shuji Yamamoto. "THE INHIBITOR OF ACTIVATED PROTEIN C: STRUCTURE AND FUNCTION". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642963.
Testo completoAbstract (sommario):
In the final step of protein C pathway, activated protein C (APC) is neutralized with a plasma inhibitor, termed protein C inhibitor (PCI). PCI was first described by Marlar and Griffin (1980) and then isolated from human plasma as a homogeneous form and characterized by the authors (1983). PCI is a single chain glycoprotein with M 57,000 and a plasma concentration of 5 ug/ml. Analysis of a cDNA nucleotide sequence has clarified that a precursor of human PCI consists of a mature protein of 387 amino acid residues (M 43,759) and a signal peptide of 19 amino acid residues. Only one cysteine residue is present in the entire protein as in α1antitrypsin (α1AT) and α1antichymotrypsin (α1ACT). Three Asn-X-Ser/Thr sequences and two Ser/Thr-X-X-Pro sequences are present as potential attachment sites of carbohydrate chains. Based on the amino acid sequence of the carboxyl-terminal peptide released from the inhibitor by APC digestion, the reactive site peptide bond of PCI was found to be Arg(354)-Ser(355). It is similar to the reactive sites of the other serine protease inhibitors which are located to their carboxyl-terminal Arg(393)-Ser (394), Met(358)-Ser(359) and Leu(358)-Ser(359) in antithrombin III, α1AT and α1ACT, respectively. The alignment of the amino acid sequence of PCI with heparin cofactor II, α1plasmin inhibitor, ovalbumin, angiotensinogen and the above noted plasma inhibitors showed that PCI is a member of serine protease inhibitor superfamily. PCI inhibits APC noncompetitively in a 1:1 stoichiometry and forms a covalent acyl-bond with a Ser residue in the active center of APC. The half life of APC in plasma approximately 30 min, which is rather slow compared with the other protease inhibitors. However, optimal concentrations of heparin, dextran sulfate and its derivatives potentiate the rate of inhibition 30-60 fold. PCI has Ki of 10-8m for APC, and can inhibit thrombin, Factor Xa, urokinase and tissue plasminogen activator as well in the presence of heparin or dextran sulfate, though the Ki for these enzymes is slightly higher. During the complex formation with APC, PCI is cleaved by the complexed APC to form a modified form with M 54,000. PCI is synthesized in several hepatoma cell lines and decreased in plasma of patients with liver cirrhosis. It is also decreased in patients with DIC or those during cardiopulmonary bypass in parallel with the decrease in protein C, suggesting that PCI participates in regulation of the protein C pathway in intravascular coagulation. Recently, we have obtained the recombinant PCI from COS-1 cells which were transfected with expression vector pSV2 containing the cDNA of PCI. The recombinant PCI had the same Mr and specific activity as the protein purified from plasma. It also had an affinity for heparin and dextran sulfate. Moreover, we have predicted a three dimentional structure of the proteolytically modified PCI with computer graphics based on its amino acid sequence homology with the modified α1AT whose structure had been elucidated with X-ray crystallography. All potential carbohydrate attachment sites were estimated to exist on the surface of the protein. Succesively we have constructed the interaction model between the intact PCI predicted from the modified form and the active center of APC which was simulated from that of trypsin. From the model, it was observed that the amino-group of Arg (354, PI site) of PCI could strongly interact with the carboxy1-group of Asp (88, SI site) of the heavy chain of APC at the base of the active center pocket of the enzyme.
7
Dahiback, Bjorn, Ake Lundwall, Andreas Hillarp, Johan Malm e Johan Stenflo. "STRUCTURE AND FUNCTION OF VITAMIN K-DEPENDENT PROTEIN S, a cofactor to activated protein C which also interacts with the complement protein C4b-binding protein". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642960.
Testo completoAbstract (sommario):
Protein S is a single chain (Mr 75.000) plasma protein. It is a cofactor to activated protein C (APC) in the regulation of coagulation factors Va and Villa. It has high affinity for negatively charged phospolipids and it forms a 1:1 complex with APC on phospholipid surfaces, platelets and on endothelial cells. Patients with heterozygous protein S deficiency have a high incidence of thrombosis. Protein S is cleaved by thrombin, which leads to a loss of calcium binding sites and of APC cofactor activity. Protein S has two to three high affinity (KD 20uM) calcium binding sites - unrelated to the Gla-region - that are unaffected by the thrombin cleavage. In human plasma protein S (25 mg/liter) circulates in two forms; free (approx. 40%) and in a 1:1 noncovalent complex (KD 1× 10-7M) with the complement protein C4b-binding protein (C4BP). C4BP (Mr 570.000) is composed of seven identical 70 kDa subunits that are linked by disulfide bonds. When visualized by electron microscopy, C4BP has a spiderlike structure with the single protein S binding site located close to the central core and one C4b-binding site on each of the seven tentacles. When bound to C4BP, protein S looses its APC cofactor activity, whereas the function-of C4BP is not directly affected by the protein S binding. Chymotrypsin cleaves each of the seven C4BP subunits close to the central core which results in the liberation of multiple 48 kDa “tentacte” fragments and the formation of a 160 kDa central core fragment. We have successfully isolated a 160 kDa central core fragment with essentially intact protein S binding ability.The primary structure of both bovine and human protein S has been determined and found to contain 635 and 634 amino acids, respectively, with 82 % homology to each other. Four different regions were distinguished; the N-terminal Gla-domain (position 1-45) was followed by a region which has two thrombin-sensitive bonds positioned within a disulfide loop. Position 76 to 244 was occupied by four repeats homologous to the epidermal growth factor (EGF) precursor. In the first EGF-domain a modified aspartic acid was identified at position 95, B-hydroxaspartic acid (Hya), and in corresponding positions in the three following EGF-domains (positions 136,178 and 217) we found B-hydroxyasparagine (Hyn). Hyn has not previously been identified in proteins. The C-terminal half of protein S (from position 245) shows no homology to the serine proteases but instead to human Sexual Hormon Binding Globulin (SHBG)(see separate abstract). To study the structure-function relationship we made eighteen monoclonal antibodies to human protein S. The effects of the monoclonals on the C4BP-protein S interaction and on the APC cofactor activity were analysed. Eight of the antibodies were calciumdependent, four of these were against the Gla-domain, two against the thrombin sensitive portion and two against the region bearing the high affinity calcium binding sites. Three of the monoclonals were dependent on the presence of chelating agents, EDTA or EGTA, and were probably directed against the high affinity calcium binding region. Three other monoclonals inhibited the protein S-C4BP interaction. At present, efforts are made to localize the epitopes to gain information about functionally important regions of protein S.
8
Suttie, W. J., A. Cheung e M. G. Wood. "ENZYMOLOGY OF THE VITAMIN K-DEPENDENT CARBOXYLASE: CURRENT STATUS". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643991.
Testo completoAbstract (sommario):
The vitamin K-dependent microsomal carboxylase converts glutamyl residues in precursor proteins to γ-carboxyglutamyl (Gla) residues in completed proteins. The enzyme activity is present in significant activities in most non-skeletal tissues but has been studied most extensively in rat and bovine liver. Early studies of the enzyme utilized bound precursors of vitamin K-dependent clotting factors as substrates for the enzyme and demonstrated that the enzyme requires the reduced form of vitamin K (vitamin KH2), O2, and CO2. Subsequent investigations have taken advantage of the observation that the enzyme will carboxylate low-molecular-weight peptide substrates with Glu-Glu sequences. Utilizing a substrate such as Phe-Leu-Glu-Glu-Leu, it has been possible to demonstrate that γ-C-H release from the Glu residue of a substrate is independent of CO2 concentration. The formation of vitamin K 2,3-epoxide can also be demonstrated in a crude microsomal system, and it can be shown that the formation of this metabolite can be stimulated by the presence of a peptide substrate of the carboxylase. These observations have led to the general hypothesis that the mechanism of action of the enzyme involves interaction of vitamin KH2 with O2 to form an oxygenated intermediate that can interact with a substrate Glu residue to abstract a γ-hydrogen and in the process he converted to vitamin K epoxide (KO). The current evidence suggests that, either directly or indirectly, removal of the γ-C-H results in the formation of a carbanion at the γ-position of the Glu residue which can interact with CO2 to form Gla. The Glu residue intermediate which is formed can be demonstrated to partition between accepting a proton in the media to reform Glu, or interacting with CO2 to form Gla. Current data do not distinguish between the direct formation of a carbanion coupled to proton removal, or the participation of a reduced intermediate. Recent studies have demonstrated that the enzyme will carry out a partial reaction, the formation of vitamin K epoxide, at a decreased rate in the absence of a Glu site substrate. Epoxide formation under these conditions has the same for O2 as the carboxylation reaction and is inhibited in the same manner as the carboxylation reaction. In the presence of saturating concentrations of a Glu site substrate and C02, the ratio of KO formed, γ-C-H released, and C02 formed is 1:1:1. However, KO formation can be uncoupled from and proceeds at a higher rate than γ-C-H bond cleavage and Gla formation at low Glu site substrate concentrations. At saturating concentrations of CO2, Gla formation is equivalent to γ-C-H bond cleavage, and this unity is not altered by variations in vitamin KH2 or peptide substrate concentrations. Natural compounds with vitamin K activity are 2-Me-l,4-naphthoquinones with a polyprenyl side chain at the 3-position. Studies of vitamin K analogs have demonstrated that a 2-Me group is essential for activity but that the group at the 3-position can vary significantly. Modification of the aromatic ring of the naphthoquinone nucleus by methyl group substitution can result in alterations of either the rate of the carboxylation reaction or the apparent affinity of the enzyme for the vitamin. Studies of a large number of peptide substrates have failed to reveal any unique primary amino acid sequence which is a signal for carboxylation. However, current evidence from a number of sources suggests that a basic amino acid rich "propeptide" region of the intracellular form of the vitamin K-dependent proteins is an essential recognition site for the enzyme. This region of the precursor is lost in subsequent processing, and the manner in which it directs this posttranslational event is not yet clarified. Supported by NIH grant AM-14881.
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Henschen, A., e E. Müller. "ON THE FACTOR XIIIa-INDUCED CROSSLINKING OF HUMAN FIBRIN α-CHAINS". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1644649.
Testo completoAbstract (sommario):
Factor XIIIa catalysis the formation of isopeptide bonds Between γ-carbamoyl groups of peptide-bound glutamines and ε-amino groups of lysines or lysine analogues. During fibrin crosslinking two such bonds are rapidly formed between the C-termini of two γ-chains in adjacent molecules and then several bonds are more slowly formed between several α-chains. The crosslinking sites in the γ-chain were identified already 15 years ago, those in the α-chain are still only tentatively or partially identified,, However, by determining the incorporation of lysine analogues in the α-chain it could be shown that the glutamines in positions 328, 366 and possibly also 237 may participate in crosslinking reactions. Analyses of cyanogen bromide fragments isolated from crosslinked fibrin indicated the segments 271-776 and 518-587 to contain the primary crosslinking sites.In the present study factor XHI-containing fibrinogen was incubated over night with thrombin in presence of calcium ions and cysteine or, as a control, in presence of EDTA. The fibrin material was cleaved with cyanogen bromide, mercaptolysed, pyri-dylethylated and then subjected to Sephacryl S-300 chromatography. The early protein fractions were tested by reversed-phase high-performance liquid chromatography (HPLC) using fibrinogen fragments as reference. In the control sample Aa-chain fragment 271-776 eluted first but in the crosslinked sample it was missing and instead a heterogeneous mixture of higher-molecular weight components was observed. N-Terminal sequence analysis showed the mixture to contain not only the expected fragments 241-476 and 518-584,but in fact all glutamine- or lysine-containing Aα-chain fragments between positions 208 and 611. In the corresponding 6 fragments a total of 6 glutamines and 21 lysines as potential crosslinking sites are present. Two fragments contain only one each of these residues which therefore must be true crosslinking sites. Remaining sites and the actual linkages were identified after reversed-phase HPLC of the tryptic peptide mixture by N-terminal sequence and total amino acid analyses.The linkage pattern will provide information about the localisation and conformation of the C-terminal part of the α-chain and its contribution to the fibrin polymer structure.
10
Comp, P. C., e C. T. Esmon. "Defects in the protein C pathway". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643715.
Testo completoAbstract (sommario):
Activated protein C functions as an anticoagulant by enzymatically degrading factors Va and Villa in the clotting cascade. Protein C may be converted to its enzymatically active form bythrombin. The rate at which thrombin cleavage of the zymogen occurs is greatly enhanced when thrombin is bound to an endothelial cell receptor protein, thrombomodulin. Activated proteinC has a relatively long half-life in vivo and the formation of activated protein C in response to low level thrombin infusion suggests that the protein C system may provide a feedback mechanism to limit blood clotting. Clinical support for such a physiologic role for activated protein C includes an increased incidence of thrombophlebitis and pulmonary emboli in heterozygous deficient individuals, and severe, often fatal, cutaneous thrombosis in homozygous deficient newborns. A third thrombotic condition associated with protein C deficiency is coumarin induced skin (tissue) necrosis. This localized skin necrosis occurs shortly after the initiation of coumarin therapy and is hypothesized to bedue to the rapid disappearance of protein C activity in the plasma beforean adequate intensity of anticoagulation is achieved. Recent estimates of heterozygous protein C deficiency range as high as 1 in 300 individuals in the general population. Since coumarin compounds are in routine clinical use throughout the world and skin necrosis remains a relatively rare clinical finding, this suggests that factors other than protein C deficiency alone may be involved in the pathogenesis of the skin necrosis.The anticoagulant properties of activated protein C are greatly enhanced by another vitamin K-dependent plasma protein, protein S. Protein S functions by increasing the affinity of activated protein C for cell surfaces.Protein S is found in two forms in plasma: free and in complex with C4b-binding protein, "an inhibitor of the complement system. Free protein S is functionally active and the complexed protein S is not active. Individuals congenitally deficient in protein S ae subject to recurrent thromboembolicevents. At least two classes of protin S deficiency occur.Some patienshavedecreased levels of protein S antigen and reduced protein S functional activity. A second group of deficient individuals have normal levels of protein S antigen but most or all their protein S is complexed to C4b-binding protein and they have little or no functional protein S activity. Such a protein S distribution could result from abnormal forms of protein S or C4b-binding protein or some other abnormal plasma or cellular component. Patients with functionally inactive forms of protein S have yet to be identified. Identification of protein S deficient individuals is complicated by thepossible effect of sex hormones on plasma protein S levels. Total protein S antigen is reduced during pregnancyand during oral contraceptive administration. This finding is of practicalclinical importance since the decrease in protein S which occurs during pregnancy may be an added risk factor for congenitally protein S deficient women and may explain why some proteinS deficient women experience their first episode of thrombosis during pregnancy.In addition to having anticoagulant properties, activated protein C enhances fibrinolysis, at least in part,by inhibiting the inhibitor of tissueplasminogen activator. This profibrinolytic effect is enhanced by protein S and cell surfaces. This protection of plasminogen activator activity suggests that the combination of tissue plasminogen activator and activated protein C may be useful in the treatment of coronary artery thrombi. Tissueplasminogen activator would promote clot lysis while activated protein C protected the plasminogen activatorfrom inhibition and also prevented further clot deposition. There is no evidence at present that fibrinolytic activity is reduced in protein C deficient individuals. The possible clinical relevance of this aspect of protein Cfunction in the predisposition of protein C deficient individuals to thrombosis remains to be defined.
Rapporti di organizzazioni sul tema "C-S bond formation"
1
Dickman, Martin B., e Oded Yarden. Genetic and chemical intervention in ROS signaling pathways affecting development and pathogenicity of Sclerotinia sclerotiorum. United States Department of Agriculture, luglio 2015. http://dx.doi.org/10.32747/2015.7699866.bard.
Testo completoAbstract (sommario):
Abstract: The long-term goals of our research are to understand the regulation of sclerotial development and pathogenicity in S. sclerotior11111. The focus in this project was on the elucidation of the signaling events and environmental cues involved in the regulation of these processes, utilizing and continuously developing tools our research groups have established and/or adapted for analysis of S. sclerotiorum, Our stated objectives: To take advantage of the recent conceptual (ROS/PPs signaling) and technical (amenability of S. sclerotiorumto manipulations coupled with chemical genomics and next generation sequencing) developments to address and extend our fundamental and potentially applicable knowledge of the following questions concerning the involvement of REDOX signaling and protein dephosphorylation in the regulation of hyphal/sclerotial development and pathogenicity of S. sclerotiorum: (i) How do defects in genes involved in ROS signaling affect S. sclerotiorumdevelopment and pathogenicity? (ii) In what manner do phosphotyrosinephosphatases affect S. sclerotiorumdevelopment and pathogenicity and how are they linked with ROS and other signaling pathways? And (iii) What is the nature of activity of newly identified compounds that affect S. sclerotiori,111 growth? What are the fungal targets and do they interfere with ROS signaling? We have met a significant portion of the specific goals set in our research project. Much of our work has been published. Briefly. we can summarize that: (a) Silencing of SsNox1(NADPHoxidase) expression indicated a central role for this enzyme in both virulence and pathogenic development, while inactivation of the SsNox2 gene resulted in limited sclerotial development, but the organism remained fully pathogenic. (b) A catalase gene (Scatl), whose expression was highly induced during host infection is involved in hyphal growth, branching, sclerotia formation and infection. (c) Protein tyrosine phosphatase l (ptpl) is required for sclerotial development and is involved in fungal infection. (d) Deletion of a superoxidedismutase gene (Sssodl) significantly reduced in virulence on both tomato and tobacco plants yet pathogenicity was mostly restored following supplementation with oxalate. (e) We have participated in comparative genome sequence analysis of S. sclerotiorumand B. cinerea. (f) S. sclerotiorumexhibits a potential switch between biotrophic and necrotrophic lifestyles (g) During plant microbe interactions cell death can occur in both resistant and susceptible events. Non pathogenic fungal mutants S. sclerotior111n also cause a cell death but with opposing results. We investigated PCD in more detail and showed that, although PCD occurs in both circumstances they exhibit distinctly different features. The mutants trigger a restricted cell death phenotype in the host that unexpectedly exhibits markers associated with the plant hypersensitive (resistant) response. Using electron and fluorescence microscopy, chemical effectors and reverse genetics, we have established that this restricted cell death is autophagic. Inhibition of autophagy rescued the non-pathogenic mutant phenotype. These findings indicate that autophagy is a defense response in this interaction Thus the control of cell death, dictated by the plant (autophagy) סr the fungus (apoptosis), is decisive to the outcome of certain plant microbe interactions. In addition to the time and efforts invested towards reaching the specific goals mentioned, both Pls have initiated utilizing (as stated as an objective in our proposal) state of the art RNA-seq tools in order to harness this technology for the study of S. sclerotiorum. The Pls have met twice (in Israel and in the US), in order to discuss .נחd coordinate the research efforts. This included a working visit at the US Pls laboratory for performing RNA-seq experiments and data analysis as well as working on a joint publication (now published). The work we have performed expands our understanding of the fundamental biology (developmental and pathogenic) of S. sclerotioז111וז. Furthermore, based on our results we have now reached the conclusion that this fungus is not a bona fide necrotroph, but can also display a biotrophic lifestyle at the early phases of infection. The data obtained can eventually serve .נ basis of rational intervention with the disease cycle of this pathogen.