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Literatura académica sobre el tema "Formation of C-N bonds"

Autor: Grafiati

Publicado: 25 de mayo de 2024

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Artículos de revistas sobre el tema "Formation of C-N bonds"

Meng, Ge, Pengfei Li, Kai Chen y Linghua Wang. "Recent Advances in Transition-Metal-Free Aryl C–B Bond Formation". Synthesis 49, n.º 21 (26 de septiembre de 2017): 4719–30. http://dx.doi.org/10.1055/s-0036-1590913.

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Arylboronic acids and their derivatives are widely used in organic synthesis. Conventional methods for their preparation require either reactive organometallic reagents or transition-metal-mediated processes. In recent years, transition-metal-free reactions for aryl C–B bond formation that obviate preformed organometallic reagents have gained interest and have developed rapidly. These new reactions have shown significant advantages for the preparation of functionalized molecules. In this review, an overview of the recent advances in transition-metal-free aromatic borylation reactions is provided.1 Introduction2 Transition-Metal-Free Transformations of CAr–N Bonds to CAr–B Bonds3 Transition-Metal-Free Transformations of CAr–X Bonds to CAr–B Bonds4 Transition-Metal-Free Transformations of CAr–H Bonds to CAr–B Bonds5 Conclusion

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Zeng, Xiaoming y Xuefeng Cong. "Chromium-Catalyzed Cross-Coupling Reactions by Selective Activation of Chemically Inert Aromatic C–O, C–N, and C–H Bonds". Synlett 32, n.º 13 (11 de mayo de 2021): 1343–53. http://dx.doi.org/10.1055/a-1507-4153.

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AbstractTransition-metal-catalyzed cross-coupling has emerged as one of the most powerful and useful tools for the formation of C–C and C–heteroatom bonds. Given the shortage of resources of precious metals on Earth, the use of Earth-abundant metals as catalysts in developing cost-effective strategies for cross-coupling is a current trend in synthetic chemistry. Compared with the achievements made using first-row nickel, iron, cobalt, and even manganese catalysts, the group 6 metal chromium has rarely been used to promote cross-coupling. This perspective covers recent advances in chromium-catalyzed cross-coupling reactions in transformations of chemically inert C(aryl)–O, C(aryl)–N, and C(aryl)–H bonds, offering selective strategies for molecule construction. The ability of low-valent Cr with a high-spin state to participate in two-electron oxidative addition is highlighted; this is different from the mechanism involving single-electron transfer that is usually assigned to chromium-mediated transformations.1 Introduction2 Chromium-Catalyzed Kumada Coupling of Nonactivated C(aryl)–O and C(aryl)–N Bonds3 Chromium-Catalyzed Reductive Cross-Coupling of Two Nonactivated C(aryl)–Heteroatom Bonds4 Chromium-Catalyzed Functionalization of Nonactivated C(aryl)–H Bonds5 Conclusions and Outlook

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Henry, Martyn, Mohamed Mostafa y Andrew Sutherland. "Recent Advances in Transition-Metal-Catalyzed, Directed Aryl C–H/N–H Cross-Coupling Reactions". Synthesis 49, n.º 20 (28 de agosto de 2017): 4586–98. http://dx.doi.org/10.1055/s-0036-1588536.

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Amination and amidation of aryl compounds using a transition-metal-catalyzed cross-coupling reaction typically involves prefunctionalization or preoxidation of either partner. In recent years, a new class of transition-metal-catalyzed cross-dehydrogenative coupling reaction has been developed for the direct formation of aryl C–N bonds. This short review highlights the substantial progress made for ortho-C–N bond formation via transition-metal-catalyzed chelation-directed aryl C–H activation and gives an overview of the challenges that remain for directed meta- and para-selective reactions.1 Introduction2 Intramolecular C–N Cross-Dehydrogenative Coupling2.1 Nitrogen Functionality as Both Coupling Partner and Directing Group2.2 Chelating-Group-Directed Intramolecular C–N Bond Formation3 Intermolecular C–N Cross-Dehydrogenative Coupling3.1 ortho-C–N Bond Formation3.1.1 Copper-Catalyzed Reactions3.1.2 Other Transition-Metal-Catalyzed Reactions3.2 meta- and para-C–N Bond Formation4 C–N Cross-Dehydrogenative Coupling of Acidic C–H Bonds5 Conclusions

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Chang, Denghu, Dan Zhu, Peng Zou y Lei Shi. "Cleavage of C–N bonds in guanidine derivatives and its relevance to efficient C–N bonds formation". Tetrahedron 71, n.º 11 (marzo de 2015): 1684–93. http://dx.doi.org/10.1016/j.tet.2015.01.050.

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Wang, Congyang y Ting Liu. "Manganese-Catalyzed C(sp2)–H Addition to Polar Unsaturated Bonds". Synlett 32, n.º 13 (27 de marzo de 2021): 1323–29. http://dx.doi.org/10.1055/a-1468-6136.

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AbstractTransition-metal-catalyzed nucleophilic C–H addition of hydrocarbons to polar unsaturated bonds could intrinsically avoid prefunctionalization of substrates and formation of waste byproducts, thus featuring high step- and atom-economy. As the third most abundant transition metal, manganese-catalyzed C–H addition to polar unsaturated bonds remains challenging, partially due to the difficulty in building a closed catalytic cycle of manganese. In the past few years, we have developed manganese catalysis to enable the sp2-hydrid C–H addition to polar unsaturated bonds (e.g., imines, aldehydes, nitriles), which will be discussed in this personal account.1 Introduction2 Mn-Catalyzed N-Directed C(sp2)–H Addition to Polar Unsaturated Bonds3 Mn-Catalyzed O-Directed C(sp2)–H Addition to Polar Unsaturated Bonds4 Conclusion

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Rit, Raja K., Majji Shankar y Akhila K. Sahoo. "C–H imidation: a distinct perspective of C–N bond formation". Organic & Biomolecular Chemistry 15, n.º 6 (2017): 1282–93. http://dx.doi.org/10.1039/c6ob02162j.

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Zinser, Caroline M., Katie G. Warren, Fady Nahra, Abdullah Al-Majid, Assem Barakat, Mohammad Shahidul Islam, Steven P. Nolan y Catherine S. J. Cazin. "Palladate Precatalysts for the Formation of C–N and C–C Bonds". Organometallics 38, n.º 14 (2 de julio de 2019): 2812–17. http://dx.doi.org/10.1021/acs.organomet.9b00326.

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Wei, Wenting, Wenming Zhu, Yi Wu, Yiling Huang y Hongze Liang. "Progress in C—N Bonds Formation Using t-BuONO". Chinese Journal of Organic Chemistry 37, n.º 8 (2017): 1916. http://dx.doi.org/10.6023/cjoc201703039.

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Zhao, Binlin, Torben Rogge, Lutz Ackermann y Zhuangzhi Shi. "Metal-catalysed C–Het (F, O, S, N) and C–C bond arylation". Chemical Society Reviews 50, n.º 16 (2021): 8903–53. http://dx.doi.org/10.1039/c9cs00571d.

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Sun, Qiu, Ling He, Jiaxin Cheng, Ze Yang, Yuansheng Li y Yulan Xi. "Synthesis of Isoxazolines and Isoxazoles via Metal-Free Desulfitative Cyclization". Synthesis 50, n.º 12 (14 de mayo de 2018): 2385–93. http://dx.doi.org/10.1055/s-0037-1609480.

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A novel, one-pot reaction for the synthesis of isoxazolines and isoxazoles is developed via a cascade process under metal-free conditions. The approach involves the formation of intramolecular C–N and C–O bonds and intermolecular C–C bonds from aromatic alkenes or alkynes and N-hydroxysulfonamides using hypervalent iodine(VII) and iodine as the oxidant. Activation of C–H and C–C bonds/construction of C–O bonds/elimination of SO2/C–N bond formation is achieved in sequence in the reaction system.

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Tesis sobre el tema "Formation of C-N bonds"

Bowen, John George. "C-H activation in the formation of C-N and C-O Bonds". Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685335.

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The regioselective activation of C-H bonds and subsequent transformation into desirable functional groupS is an attractive prospect in organic synthesis. We have developed two novel C-H functionalisation reactions; the first is an intramolecular, sulfonamide directed, C-H amination reaction for the synthesis of 3_phenylisoindolinone derivates and the second is a sulfonamide directed ortho C-H acetoxylation reaction. Both isoindolinones and phenol derivatives of sulfonamides are important motifs in numerous pharmaceutically relevant compounds. The Cull-catalysed intramolecular C-H amination reaction for the synthesis of substituted 3-phenylisolindolinone derivatives (Scheme i) was found to be tolerant to substitution on both aromatic rings, however, no reaction was observed on exchanging the tethered aryl group for an alkyl group. Mechanistic investigations revealed that C-H cleavage was not part of the rate-determining step which is likely to be coordination of the copper catalyst to the sulfonyl amide. Substitution of the tethered phenyl ring (R2 ) and a subsequent Hammett analysis indicated that this coordination may be accelerated by a cation-IT interaction between CU11 and the pie system of the aryl group.

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Persson, Andreas K. Å. "Palladium(II)-Catalyzed Oxidative Cyclization Strategies : Selective Formation of New C-C and C-N Bonds". Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-75435.

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The main focus of this thesis has been directed towards preparation and oxidative carbocyclization of en-, dien- and aza-enallenes. In the first part of this thesis, a stereoselective oxidative carbocyclization of dienallenes was realized. By employing cheap and readily available palladium trifluoroacetate we were able to efficiently cyclize a variety of dienallenes into hydroxylated carbocycles in high yield and high selectivity. This oxidative process was compatible with two different reoxidation protocols: one relying on p-benzoquinone (BQ) as the oxidant and the other employing molecular oxygen as the oxidant. In the second part of the thesis the carbocyclization methodology was extended to include carbocyclization of aza-enallenes. This was achieved in two distinct steps. First, a copper-catalyzed coupling of allylic sulfonamides with bromoallenes was developed, giving access to the corresponding aza-enallenes. Subjecting these substrates to catalytic amounts of palladium acetate, along with BQ as the oxidant, rendered N-heterocycles in good yield. The reactivity of these N-heterocycles towards activated dienophiles was later exploited in a tandem (aerobic) oxidative carbocyclization/Diels-Alder reaction. The third topic involves efficient oxidative arylative/borylative carbocyclization of enallenes. These reactions, catalyzed by palladium acetate, relies on transmetallation of a (σ-alkyl)palladium(II) intermediate with diboranes or arylboronic acids. With this novel methodology we were able to obtain an array of arylated or borylated carbocycles, as single diastereomers, in high yield. Finally, we developed a palladium(II)-catalyzed cyclization of allylic carbamates. This mild, operationally simple, and scalable catalytic reaction opens up access to an array of oxazolidinones in high yield and excellent diastereoselectivity.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Manuscript.

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Lishchynskyi, Anton. "Development of new methods for the asymmetric formation of C-N bonds". Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAF026.

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Au cours de ce travail de nouvelles méthodes pour la formation de liaison C-N ont été développées. Dans la première partie de cette thèse une application de catalyse métal-ligand bifonctionnelle pour la réaction énantiosélective aza-Michael est démontrée. Dans la deuxième partie nous présentons le travail sur les cyclisations, en utilisant des alcaloïdes du quinquina facilement disponibles, comme catalyseurs des plus prometteurs, fournissant des β-amino-acides d’indoline avec jusqu'à 98% ee. Parmi eux, l’hydroquinidine ressort du lot comme étant le catalyseur donnant le meilleur excès énatiomérique. La troisième partie est liée à l'élaboration d'un nouveau processus intermoléculaires de diamination de styrènes, diènes et triènes, utilisant des bis-sulfonylimides comme source d'azote, en combinaison avec le diacétate de iodosobenzène, qui fournit une approche intéressante et efficace de diamines vicinales biologiquement et chimiquement important. La réaction peut être effectuée à température ambiante sans avoir besoin de protection par atmosphère inerte
The concept of metal-ligand bifunctionality was successfully applied for an enantioselective aza-Michael reaction by employing well-defined ruthenium amido complexes. The catalyst was optimised and the corresponding chiral indoline β-amino acid derivatives were obtained with high enantioselectivities. Next, a straightforward enantioselective bifunctional organocatalytic approach was also developed. Employing hydroquinidine as catalyst the corresponding cyclic products were obtained in excellent enantioselectivities and quantitative yields. These compounds can be selectively deprotected and applied to peptide synthesis. Finally, we have developed unprecedented diamination reactions of styrenes, butadienes and hexatrienes employing easily accessible hypervalent iodine(III) reagents under robust reaction conditions. The first examples of the metal-free 1,2-diamination of butadienes were demonstrated and this oxidation methodology was further extended to the highly attractive 1,4 installation of two nitrogen atoms within a single step

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Mane, K. D. "Enantioselective synthesis of bioactive molecule and development of synthetic methodologies involving formation of C-C, C-N bonds". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2022. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/6140.

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Huang, Xiaohua 1973. "Palladium-catalyzed C-C, C-N and C-O bond formation". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29639.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.
Vita.
Includes bibliographical references.
New methods for Pd-catalyzed cross-coupling reactions of aryl halides or arenesulfonates are described. Key to the success of these transformations is the proper choice of ligand and reaction conditions. Palladium catalysts supported by bulky, monodentate phosphine ligands with a biaryl backbone or the bidentate ligand, Xantphos, effectively promote the formation of ca-aryl carbonyl compounds. Base-sensitive functional groups are better tolerated when a weak base, such as K3PO4, is used. One of the most difficult transformations in Pd catalysis, the intermolecular C-O bond formation between primary alcohols and electron-neutral or even electron-rich aryl halides, was effectively promoted by the use of a new generation of ligands, 3-methyl-2-di-t-butylphosphinobiaryl. The one-step synthesis of ligands from cheap starting materials, as well as the mild reaction conditions employed for the coupling reactions, enables the practical use of Pd catalysis to access aryl alkyl ethers for the first time. Continuing study of Pd-catalyzed C-N bond-forming processes using biaryl monophosphine ligands led to the discovery of a structural derivative of these ligands, 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl. This ligand, in combination with a Pd source, produces a catalyst system with both a greater degree of activity and of stability than those that use our previous ligands. Substrates that were not amenable to Pd catalysis previously are reexamined using this new catalyst system, and excellent results are obtained.
by Xiaohua Huang.
Ph.D.

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Correia, Camille. "Oxidative C-C bond formation via metal-catalyzed coupling of two C-H bonds". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114441.

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This thesis describes the formation of new C-C bonds from the direct oxidative coupling of two C-H bonds, through the use of metal catalysts for activation. First, three different oxidative Cross-Dehydrogenative-Coupling (CDC) reactions will be presented. Initially, through the use of an organic co-catalyst, N-hydroxyphthalimide (NHPI), oxygen could be utilized as the terminal oxidant for the metal catalyzed alkylation of benzylic C-H bonds with 1,3-dicarbonyls and ketones in Chapter 2. The reaction was found to be feasible for a variety of substrates with readily enolizable C-H bonds. Next, the 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) mediated alkynylation of sp3 C-H bonds was studied. A novel copper (I) triflate catalyzed CDC reaction of unactivated benzylic C-H bonds and terminal aromatic alkynes is presented in Chapter 3. After further studies, the alkynylation of benzylic ethers could also be realized in the presence of a catalytic amount of silver (I) triflate, as described in Chapter 4. Both procedures were found to be amendable for aromatic terminal alkynes, however could not be extended to aliphatic alkynes. Finally, a palladium catalyzed Minisci-type reaction will be described in Chapter 6. Peroxide generated α-hydroxyalkyl radicals could be reacted with azines in moderate to good yields. A stoichiometric amount of acid, used in the traditional Minisci reaction, was replaced by a catalytic amount of palladium dichloride.
Cette thèse décrit la formation de nouvelles liaisons C-C par activation oxydative directe de deux liaisons C-H grâce à l'utilisation de métaux de transition comme catalyseurs. La première partie présentera trois différentes réactions de Cross-Dehydrogenative-Coupling (CDC) oxydantes. Dans un premier temps, sera présentée dans le chapitre 2, la réaction d'alkylation de liens C-H benzylique par 1,3-dicarbonyles et cétones. Ce system a démontré son efficacité sur une large variété de substrats contenant des liaisons C-H enolysable. De plus il a été rendu possible, grâce à l'utilisation d'un co-catalyseur organique, le N-Hydroxyphthalimide (NHPI), d'utiliser l'oxygène moléculaire comme oxydant terminal. Dans un second temps, nous étudierons l'utilisation du 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) comme médiateur pour l'alkynylation de liaisons sp3 C-H. Une nouvelle CDC réaction catalysée par le triflate de cuivre (I) sera présentée dans le chapitre 3, entre un alcyne et une liaison C-H benzylique. Le chapitre 4 présentera le développement de cette réaction à l'alcynation d'éthers benzyliques en présence d'une quantité catalytique de triflate d'argent (I). Ces deux procédures sont seulement applicables pour les alcynes vrais aromatiques. Finalement, le chapitre 6 portera sur la réaction de Minisci catalysée par le palladium. Le peroxyde radical α-hydroxyalkyl généré lors de la réaction est capable de réagir avec les azines. La quantité stœchiométrique d'acide nécessaire lors de la traditionnelle réaction de Minisci, a été remplacée par une quantité catalytique de dichloro palladium.

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Laren, Martijn Wouter van. "Palladium-catalyzed C-H and C-N bond formation". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2004. http://dare.uva.nl/document/75422.

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Karabal, P. U. "Asymmetric synthesis of bioactive molecules and formation of C-N, C-Br and C-I bonds via olefin functionalization". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2014. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2219.

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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.

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Midya, S. P. "Transition metal catalyzed (de) hydrogenative C-C and C-N bond formation". Thesis(Ph.D.), CSIR-National Chemical laboratory, Pune, 2018. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4568.

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Libros sobre el tema "Formation of C-N bonds"

Taillefer, Marc y Dawei Ma, eds. Amination and Formation of sp2 C-N Bonds. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-40546-4.

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C-X bond formation. Heidelberg: Springer, 2010.

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Zucherman, Jerry J. The Formation of bonds to C, Si, Ge, Sn, Pb (part 2). New York, N.Y: VCH Publishers, 1989.

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Vigalok, Arkadi, ed. C-X Bond Formation. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12073-2.

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Krische, Michael J., ed. Metal Catalyzed Reductive C–C Bond Formation. Berlin, Heidelberg: Springer Berlin Heidelberg, 2007. http://dx.doi.org/10.1007/978-3-540-72879-5.

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Catalyst Design for the Ionic Hydrogenation of C=N Bonds. [New York, N.Y.?]: [publisher not identified], 2015.

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M, Coates Robert y Denmark Scott E, eds. Reagents, auxiliaries and catalysts for C-C bond formation. Chichester: Wiley, 1999.

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Mahrwald, Rainer. Enantioselective Organocatalyzed Reactions II: Asymmetric C-C Bond Formation Processes. Dordrecht: Springer Science+Business Media B.V., 2011.

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J, Krische Michael y Breit B, eds. Metal catalyzed reductive C-C bond formation: A departure from preformed organometallic reagents. Berlin: Springer, 2007.

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Horvath, Michael John. Initial studies into selective C-F bond formation via the reactions of fluoride ion with organometallic complexes. Ottawa: National Library of Canada = Bibliothèque nationale du Canada, 1991.

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Capítulos de libros sobre el tema "Formation of C-N bonds"

Toffano, M. "Formation of C—N Bonds". En Organophosphorus Compounds (incl. RO-P and RN-P), 1. Georg Thieme Verlag KG, 2009. http://dx.doi.org/10.1055/sos-sd-042-00432.

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Brown, J. M. y B. N. Nguyen. "C—N Bond Formation". En Stereoselective Synthesis 1 Stereoselective Reactions of Carbon—Carbon Double Bonds, 1. Georg Thieme Verlag KG, 2011. http://dx.doi.org/10.1055/sos-sd-201-00185.

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"C–C Bond Formation". En Biocatalysis in Organic Synthesis: The Retrosynthesis Approach, 217–53. The Royal Society of Chemistry, 2018. http://dx.doi.org/10.1039/bk9781782625308-00217.

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This chapter covers enzyme classes that are capable of catalysing reactions to form carbon–carbon bonds, including aldolases, hydroxynitrile lyases, thiamine-dependent lyases, terpene cyclases, carboxylases, Pictet–Spenglerases, P450 monooxygenase variants and methyltransferases. The chapter is divided into separate sections, each detailing the formation of carbon–carbon bonds by a specific enzyme class. Each section begins with a review of chemical methods of carrying out similar transformations, followed by a description of the enzyme class itself. The substrate scope of each enzyme class, including its chemo-, regio- and stereoselectivity, is discussed and a general mechanism for the enzyme-catalysed reaction is presented. This should give the reader a good understanding of when and how to carry out carbon–carbon bond forming reactions using enzymes.

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von Angerer, S. "By Formation of Two N–C Bonds and Two C–C Bonds". En Science of Synthesis Knowledge Updates KU 2011/1, 1. Georg Thieme Verlag KG, 2011. http://dx.doi.org/10.1055/sos-sd-116-00079.

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"C–X Bond Formation". En Biocatalysis in Organic Synthesis: The Retrosynthesis Approach, 179–216. The Royal Society of Chemistry, 2018. http://dx.doi.org/10.1039/bk9781782625308-00179.

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This chapter covers enzyme classes that are capable of catalysing reactions to form carbon–heteroatom bonds, including transaminases, ammonia lyases, hydratases, halohydrin dehalogenases and methyltransferases. The chapter is divided into separate sections, each detailing the formation of a specific carbon–heteroatom bond, including carbon–nitrogen, carbon–oxygen, carbon–halogen and carbon–sulfur bonds. Each section begins with a review of chemical methods of making each bond type, followed by a description of the enzyme classes capable of catalysing each bond formation. The substrate scope of each enzyme class, including its chemo-, regio- and stereoselectivity, is discussed and a general mechanism for the enzyme-catalysed reaction is presented. Where appropriate, strategies for co-factor recycling are also included. This should give the reader a rounded understanding of when and how to carry out C–X bond forming reactions using enzymes.

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Jones, R. Alan. "Formation of C—C Bonds". En Quaternary Ammonium Salts, 229–301. Elsevier, 2001. http://dx.doi.org/10.1016/b978-012389171-6/50007-6.

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Kaufmann, D. E. y M. Kster. "Formation of C—C Bonds". En Boron Compounds, 1. Georg Thieme Verlag KG, 2005. http://dx.doi.org/10.1055/sos-sd-006-00987.

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Boysen, M. M. K. "Formation of C—C Bonds". En Nitro, Nitroso, Azo, Azoxy, and Diazonium Compounds, Azides, Triazenes, and Tetrazenes, 1. Georg Thieme Verlag KG, 2010. http://dx.doi.org/10.1055/sos-sd-041-00451.

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Toffano, M. "Formation of C—C Bonds". En Organophosphorus Compounds (incl. RO-P and RN-P), 1. Georg Thieme Verlag KG, 2009. http://dx.doi.org/10.1055/sos-sd-042-00429.

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Yang, Y. y C. Wang. "2.15 Manganese-Catalyzed C—H Functionalization". En Base-Metal Catalysis 2. Stuttgart: Georg Thieme Verlag KG, 2023. http://dx.doi.org/10.1055/sos-sd-239-00231.

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AbstractManganese-catalyzed directed C—H functionalization is an efficient and straightforward approach for the formation of a variety of C—C and C—heteroatom bonds. In this review, we summarize the most significant advances in manganese-catalyzed C(sp2)—H functionalizations, including C—H alkenylation, alkylation, allylation, cyclization, amination, cyanation, borylation, and hydroxymethylation. The chapter is classified based on the type of newly formed chemical bond (C—C, C—N, C—B, and C—D bonds) and the reacting partner.

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Actas de conferencias sobre el tema "Formation of C-N bonds"

PRASAD, DIPAK y NILANJAN MITRA. "EVOLUTION OF VISCOSITY UPON CROSSLINKING IN EPOXY RESIN: AN ATOMISTIC INVESTIGATION". En Proceedings for the American Society for Composites-Thirty Eighth Technical Conference. Destech Publications, Inc., 2023. http://dx.doi.org/10.12783/asc38/36619.

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Adhesive materials such as epoxy resin (DGEBA/DETDA) are crucial in formation of any laminated and sandwich composites. Typically for these thermoset polymeric adhesives, crosslinking is an important step which eventually determines the thermomechanical response of the resultant composite. During this process of cross linking of epoxy resin, one observes changes in the viscosity of the resultant composite mixture of the resin and the hardener as well as change in temperature. This crosslinking of thermoset resins (DGEBA/DETDA at 2:1 ratio) is a complex chemical reaction process involving breaking of oxirane ring (C-O bond) in DGEBA, breaking of N-H bond in the amine (DETDA) and creation of N-C covalent bonds between the resin and the hardener. Apart from formation of new covalent bonds in the process, numerous non-covalent bonds such as hydrogen bonds and van der Waals interactions are also formed. This study is aimed at fundamental understanding of the correlation between viscosity changes in the composite upon crosslinking with the evolution of these non-covalent bonds. The study is primarily based upon molecular/atomistic investigations.

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Ali, Ibrahim y Walid Fathalla. "Synthesis of N-substituted-3,4,5,6-tetrachlorophthalimide using trichloroacetimidate C-C bond formation method". En The 13th International Electronic Conference on Synthetic Organic Chemistry. Basel, Switzerland: MDPI, 2009. http://dx.doi.org/10.3390/ecsoc-13-00180.

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Hirn, U. y R. Schennach. "Fiber-Fiber Bond Formation and Failure: Mechanisms and Analytical Techniques". En Advances in Pulp and Paper Research, Oxford 2017, editado por W. Batchelor y D. Söderberg. Fundamental Research Committee (FRC), Manchester, 2017. http://dx.doi.org/10.15376/frc.2017.2.839.

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In this paper we give a literature overview on three different aspects of pulp fiber-fiber bonding. First we are reviewing how the adhesion between the pulp fibers is created by the capillary pressure during drying of a sheet. Second we are discussing the individual mechanisms relevant for fiber-fiber bonding. They can be grouped in three different groups: (a) The area in molecular contact, which also includes interdiffusion; (b) the intermolecular bonding mechanisms hydrogen bonding, Van der Waals forces and Coulomb interaction; (c) the mechanical bonding mechanisms which are capillary bridges and mechanical interlocking. The third and last part of the review discusses the failure process of fiber-fiber bonds and related single fiber-fiber bond testing methods. The general emphasis of the paper is set on providing a general understanding of the processes responsible for how bonds between fibers are created, how they work and how they are failing.

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Kim, Bioh, Thorsten Matthias, Markus Wimplinger, Paul Kettner y Paul Lindner. "Comparison of Enabling Wafer Bonding Techniques for TSV Integration". En ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40002.

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In this study are compared the technical merits and demerits of three bonding methods suitable for manufacturing 3D-ICs. Patterned metal thermo-compression bonding facilitates fine-pitch, high-density TSV stacking with lower electrical resistance and higher mechanical strength. Direct Cu-Cu bonding is preferred over transient liquid phase bonding with Sn or Sn alloys, but reliable Cu-Cu bonds result only from high process temperature and long process time. Both bonding temperature and post-bond annealing temperature have the most significant influence on Cu-Cu bond properties. The pre-bonding of silicon oxide bonds occurs at room temperature and thus does not induce any run-out errors in wafer alignment, resulting in higher post-bond alignment accuracy. Subsequent heating to high temperatures is necessary to achieve covalent bonds, but modifying the surface chemistry by plasma activation allows the formation of strong chemical bonds at significantly lower annealing temperatures (200–400°C). Adhesive bonding has such advantages as low bonding temperature and process time compared to metal bonding, the tolerance to wafer topography and surface conditions, and the ability to join any wafer materials. However, the material reflow imposes some challenges for maintaining the alignment accuracy and another major concern is the reliability of polymer adhesives during the post-bond processes.

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Duan, Shanzhong y Andrew Ries. "An Efficient O(N) Algorithm for Computer Simulation of Rigid Body Molecular Dynamics". En ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-42032.

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Molecular dynamics is effective for a nano-scale phenomenon analysis. There are two major computational costs associated with computer simulation of atomistic molecular dynamics. They are calculation of the interaction forces and formation/solution of equations of motion. In this paper, an O(N) (order N) procedure is presented for calculation of the interaction forces and formation/solution of equations of motion. For computational costs associated with potentials or interaction forces, an internal coordinate method is used. Use of the internal coordinate method makes application of multi-rigid body molecular dynamics to an atomistic molecular system become possible. The algorithm based on the method makes the calculation considerably more practical for large-scale problems encountered in molecular dynamics such as conformation dynamics of polymers. For computational costs associated with formation/solution of equations of motion, Kane method and the internal coordinate method are used for recursive formation and solution of equations of motion of an atomistic molecular system. However, in computer simulation of atomistic molecular dynamics, the inclusion of lightly excited all degrees of freedom of an atom, such as inter-atomic oscillations and rotation about double bonds with high frequencies, introduces limitations to the simulation. The high frequencies of these degrees of freedom force the use of very small integration step sizes, which severely limit the time scales for the atomic molecular simulation over long periods of time. To improve this, holonomic constraints such as strictly constant bond lengths and bond angles are introduced to freeze these high frequency degrees of freedom since they have insignificant effect on long time scale processes in conformational dynamics. In this way, the procedure developed in multibody dynamics can be utilized to achieve higher computing efficiency and an O(N) computational performance can be realized for formation/solution of equations of motion.

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Almubarak, Tariq, Majed Almubarak, Abdullah Almoajil y Fares Alotaibi. "Vitamin C: An Environmentally Friendly Multifunctional Additive for Hydraulic Fracturing Fluids". En ADIPEC. SPE, 2022. http://dx.doi.org/10.2118/211113-ms.

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Abstract There exists a need for high temperature fracturing fluids as we expand exploration into deeper, lower permeability, and hotter formations. Fracturing fluid stability depends on two main bonds: the crosslinker to polymer bond and the monomer to monomer bond. To preserve the crosslinker to polymer bond, a proper crosslinker with a suitable delay additive is typically utilized. On the other hand, the monomer to monomer bond is challenging to protect since it’s susceptible to a variety of factors with the main culprit being oxygen radical attacks. Consequently, the most common high temperature stabilizers used are oxygen scavengers such as sodium thiosulfate or sodium sulfite. Unfortunately, both additives create their own issues. Sodium thiosulfate is known to degrade at high temperature to generate H2S, while sulfites generate sulfates that end up causing inorganic scale precipitation or feeding sulfate reducing bacteria creating another source of H2S in the reservoir. Additionally, Sodium thiosulfate is a high pH additive which can cause formation damage through fines migration and precipitation of hydroxides. Vitamin C is renowned for its antioxidative and oxygen scavenging properties throughout many industries. It is commonly used as an extremely cheap supplement to boost the immune system and as a food preservative to increase shelf life. Moreover, it has an acidic pH and offers a chemical structure capable of delaying crosslinking reactions. For that reason, this work aims to study the influence of Vitamin C as a multifunctional additive in fracturing fluids. The tests mainly utilized the high-pressure/high-temperature (HPHT) rheometer. The performance of Vitamin C was assessed with a guar derivative at temperatures between 250-300°F for 1.5 hours. Moreover, zeta potential and coreflood were used to evaluate the formation damage tendencies of using this additive. The results showed that the use of Vitamin C was able to provide a pH reduction, crosslinking delay, and enhance the high temperature stability of fracturing fluids. Zeta potential and coreflood experiments showed that clays were more stable at lower pH conditions minimizing fines migration. Vitamin C is a cheap and readily manufactured environmentally friendly additive that offers solutions to the use of fracturing fluids at high temperatures. Utilizing it not only offers oxygen scavenging ability, but also replaces additives that lower pH and provides crosslinking delaying properties.

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Bolotov, Vasiliy Alexandrovich, Serguei Fedorovich Tikhov, Konstantin Radikovich Valeev, Vladimir Timurovich Shamirzaev y Valentin Nikolaevich Parmon. "SELECTIVE FORMATION OF LINEAR ALPHA-OLEFINS VIA MICROWAVE CATALYTIC CRACKING OF LIQUID STRAIGHT-CHAIN ALKANES". En Ampere 2019. Valencia: Universitat Politècnica de València, 2019. http://dx.doi.org/10.4995/ampere2019.2019.9894.

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Linear even-carbon-number alpha-olefins (LAO) with four or more carbon atoms are important compounds of high demand in chemical industry as precursors of a wide range of value-added chemicals [1]. LAO are used as co-monomers for polyethylene production, for the production of alcohols (mainly in detergents and plasticizers) and for synthesis of polyalphaolefins (used in synthetic lubricants). Alpha-olefins (C4, C6, C8 and C10) are mainly used to produce poly(vinyl chloride) plasticizers, high-density and linear low-density polyethylene to impart the stress-crack resistance. C10–C14 alpha-olefins can be used to synthesize linear alkylbenzene sulfonates (synthetic detergents). A conventional route to produce alpha-olefins is oligomerization of ethylene. The process provides production of high quality alpha-olefins but is very costly. If not oligomerization, LAO can be produced by thermal cracking of waxy paraffins but the product is not pure and contains numerous internal olefins, dienes and paraffin impurities. The process is conducted in the vapor phase at relatively low cracking temperatures and needs rapid quenching to prevent side reactions such as isomerization or cyclization. In our previous work [2], we showed that the selectivity to alpha-olefins can be increased considerably via catalytic cracking of n-alkanes under selective MW heating of catalysts. In the present work, the general regularities of MW cracking of n-alkanes are presented. Porous ceramic matrix Al2O3/Al composites (ceramometals) and various carbon materials (CM) having high dielectric losses were studied as supports of the catalysts. MW cracking was conducted with n-C16H34 and n-C28H58. The influence particle size and surface morphology of ceramometals and CM on the structural and group composition of the products was studied. It was established that LAO (C2-C23) and n-alkanes (C2-C26) were the main cracking products under selective MW heating of the used supports. The quantitative analysis of the products demonstrated that the liquid-phase process is more selective to alpha-olefins at the MW catalytic cracking than at the convectional thermal cracking. Silica modification of the surface of CM was shown to suppress spark discharge (usually observed at MW heating of CM); hence, the thermal cleavage of C-C bonds on the CM surface but not in the plasma discharge contributes the most to the formation of radicals. It was shown that the selectivity to liquid alpha-olefin could be more than 85 % under MW heating of cermets in region of the E - field node and decrease considerably in the region of H - field node.

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Henschen, A. y E. Müller. "ON THE FACTOR XIIIa-INDUCED CROSSLINKING OF HUMAN FIBRIN α-CHAINS". En XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1644649.

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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.

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Guan, Y. F., R. Zhu, J. C. Han, H. X. Liu, S. T. Li y C. K. Wu. "Multiphoton ionization process of CH3OH and C2H5OH induced by a XeCl excimer laser". En International Laser Science Conference. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/ils.1986.thl45.

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In the multiphoton ionization mass spectrum of CH3OH induced by the XeCl laser, three kinds of ion are found: CH+3, CH2OH+, and CH3OH+. The ionic signal dependences on the laser intensity and the sample pressure are measured. From these results, it is concluded that CH3OH+ is directly formed after CH3OH has absorbed four photons, and that the collisions between CH3OH+ and CH3OH produce CH 3 + and CH2OH+. At the same laser wavelength, the ions produced in the C2H5OH MPI process are C 2 H 5 + , CH2OH+, CH3OH+, C2H2OH+, C2H3OH+, C2H4OH+, and C2H5OH+. The relative ionic intensities are 74%(CH3OH+), 12 % ( C 2 H 5 + ) , 6.1%(CH2OH+), 4.1 %(C2H3OH+), and < 2% for others. On the basis of the consideration of the mass spectrum theory for organic molecules, brief explanations of the result are given. The breakdown of the C-O bond and the C-C bond results in the formation of C 2 H 5 + ; and CH2OH+, respectively. The McLaffety rearrangement process leads to the production of C2H3OH+. The analysis shows that the birth of CH3OH+ cannot be described in terms of the breakdown process of some molecular bonds; CH3OH+ is the product of a very complicated recombination reaction.

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Sahu, Sunil, Anil Tyagi, Yonghwee Kim y Arjun Puri. "Accurate Identification of Gas-Bearing Formation in a Mature Field Using Pulsed Neutron Logs Prevented Well Abandonment". En Gas & Oil Technology Showcase and Conference. SPE, 2023. http://dx.doi.org/10.2118/214153-ms.

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Abstract Operators typically update formation fluid saturation from producing wells as production impacts changes in formation fluid type and volume. An operator in India deployed a multi-detector pulsed neutron well logging tool on one of the old wells in a mature field to evaluate saturation profiles across multiple clastic formations. Production from the subject well had ceased due to water loading. The objective of the logging was to identify possible bypassed hydrocarbon zones before the operator decided on the well abandonment. A multi-detector pulsed neutron tool acquired a salinity-independent gas-sensitive time-based measurement from short-spaced and extra-long-spaced gamma-ray detectors. In addition, inelastic energy spectra-based carbon/oxygen (C/O) ratios were recorded to quantify formation oil saturation in a low water salinity environment. Another critical component in the saturation analysis workflow was the forward modeling of tool responses. We used the Monte Carlo N-particle (MCNP) stochastic method to predict gas-sensitive and C/O ratio responses in logging conditions. We had limited information on well conditions, such as cement bond condition and formation fluid properties, as no recent well logging was carried out to evaluate these. Thus, we performed saturation analyses in various conditions to reduce uncertainties in the results, including well-cemented, partially-cemented, and uncemented annulus conditions and different oil and gas densities. The analysis results identified one shallow sand unit containing gas. The sand was initially considered a water-dominant zone because the same zone produced water from adjacent wells. We evaluated the uncertainty in the gas saturation calculation attributed to cement bond quality and formation gas density. This helped to remove uncertainties in cement bond conditions and in-situ gas density on gas saturation. The identified sand unit was perforated and produced a large amount of gas. The accurate result of the gas saturation analysis saved the well from abandonment and increased reserves and production capacity. Additionally, the analysis revealed that water-filled formations were predominant in other sands. The C/O log analysis showed no bypassed oil in the lower sands. This paper further discusses case studies on candidate selection for pulsed neutron well logging, uncertainties in formation parameters, and the implications for saturation results.

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Informes sobre el tema "Formation of C-N bonds"

I. A. Parshikov, Igor A. OXIDATION OF GERANYL-N-PHENYLCARBAMATE BY FUNGUS BEAUVERIA BASSIANA WITH AIM TO OBTANING OF NEW ANTI-CANCER DRUGS. Intellectual Archive, octubre de 2020. http://dx.doi.org/10.32370/iaj.2427.

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The microbial oxidation of geranyl-N-phenylcarbamate by fungus Beauveria bassiana was investigated. Oxidation of the C3 – C4 double bond of the parent molecule leads to regioselective formation of O-3,4-epoxyheranyl-N-phenylcarbamate in 30 % yield

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Mariam, Y. H. The synthesis, characterization and formation chemistry of Si-C-N-O-M ceramic and composite powders. Final technical report. Office of Scientific and Technical Information (OSTI), agosto de 1998. http://dx.doi.org/10.2172/638243.

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Glauz, W. D. y Cecil Chappelow. L51467A On-Site Assessment of Mill-Applied Fusion-Bonded Coating Quality. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), febrero de 1985. http://dx.doi.org/10.55274/r0010089.

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This report is an addendum to L51467. The commercial application of rapid cure fusion bonded epoxy (FBE) coatings to line pipe is a fast operation. Accordingly, it is possible to coat a large number of pipe joints improperly before the inferior coating quality can be detected and the cause remedied. The quality control techniques currently used in coating plants are too slow to meet the demands of this coating and its application procedures. The primary goal of this program was to develop on-site, repeatable, accurate, and operatively simple test procedures that are capable of determining (a) the degree of reaction (cure) of the applied FBE coating, (b) the adhesive bond strength of the coating to the steel pipe substrate, and (c) the void content of the coating created by bubble entrapment or gas formation during application. The secondary goal was to develop on-site test methods to monitor coating quality continuously and nondestructively on the coating production line.

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Rempel, K. U., A. E. Williams-Jones y K. Fuller. An experimental investigation of the solubility and speciation of uranium in hydrothermal ore fluids. Natural Resources Canada/CMSS/Information Management, 2021. http://dx.doi.org/10.4095/328995.

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Experimental data on the solubility and speciation of uranium in hydrothermal solution is required to improve genetic models for the formation of ore deposits, yet very few data of this type have been published. Of particular interest is the oxidation state of the uranium in solution, as conventional wisdom suggests that U is dissolved in the oxidized U(VI) state and precipitated as reduced U(IV) minerals, yet recent experiments have shown ppm-level solubility for U(IV). This study investigated the mobility of reduced U(IV) and oxidized U(VI) in acidic (pH = 2), fluoride- bearing and alkaline (pH = 10), chloride-bearing solutions at 100-200°C and 1 to 15.8 bars (0.1-1.58 MPa). Preliminary data for the mobility of U(IV) in pH 2 fluids with 0.01 m F- show concentrations of 1.76 to 3.92 ppm U at 200°C, indicating that, contrary to common belief, the reduced U(IV) can be transported in solution. We have also conducted experiments on U(VI) solubility in pH 2 fluoride-bearing, and pH 10 chloride-bearing solutions. Uranium concentrations in the F- -bearing experiments ranged from 624 to 1570 ppm (avg. 825 ppm, n = 6) at 100°C, 670 to 1560 ppm (avg. 931 ppm, n = 4) at 150°C, and 3180 to 7550 ppm (avg. 5240, n = 9) at 200°C. In comparison, U concentrations in the Cl- -bearing runs range from 86.1 to 357 ppm (avg. 185 ppm, n = 15) at 200°C. Clearly, oxidized U(VI) is very readily mobilized in hydrothermal fluids. However, the measured concentrations of U(VI) are independent of those of F- or Cl-, suggesting the formation of U oxide or hydroxide species rather than U chlorides or fluorides. These experimental data will be verified and supplemented in future experiments, which will be used to derive the stoichiometry and thermodynamic constants for the dominant uranium species in hydrothermal solutions. The data from this study will then be integrated into a comprehensive genetic model for uranium ore-forming systems.

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Ardakani, O. H. Organic petrography and thermal maturity of the Paskapoo Formation in the Fox Creek area, west-central Alberta. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/330296.

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The Paskapoo Formation, which ranges in age from middle to upper Paleocene, is the major shallow aquifer in Alberta. This study is part of a larger GSC-led study on the potential environmental impact of hydrocarbon development in the Fox Creek area (west-central Alberta) on shallow aquifers. Fox Creek is located near the northern limit of the Paskapoo Formation. In addition to the underlying organic-rich source rocks in the study area, including the Duvernay Formation that is currently exploited for hydrocarbon resources, the Paskapoo Formation contains organic-rich intervals and coal seams. In order to investigate any potential internal hydrocarbon sources within the Paskapoo Formation, ninety-seven (97) cutting samples from the formation obtained from eight shallow monitoring wells (50-90 m) in the study area were studied for total organic carbon (TOC) content, organic matter composition and thermal maturity of coal seams using programmed pyrolysis analysis and organic petrography. The TOC content of all samples ranges from 0.2 to 8.8 wt. %, with a mean value of 0.95 ± 1.6 wt. % (n=97). The Tmax values of studied samples range from 347 to 463 °C, with a mean value of 434 ± 20 °C that suggest a range of thermal maturity from immature to peak oil window. The random reflectance (Rr) measurement and fluorescence microscopy on eighteen (18) selected samples with TOC content &gt; ~1 wt. % shows a mean Rr value of 0.27% and 0.42% for the overlying till deposits and the underlying shallow depth sandstone, siltstone, shale and coal seams respectively, indicating a low rank coal ranging from lignite to sub-bituminous coal. Blue to green and yellow fluorescing liptinite macerals further confirmed the low maturity of studied samples. The low S2 yield of a large part of the samples (65%) resulted in unreliable Tmax values that overestimated the thermal maturity. Although the organic matter in the studied intervals are immature, exsudatinite, as secondary liptinite maceral, was observed in samples from the lower parts of the studied monitoring wells. Exsudatinite generally derives from the transformation of sporinite, alginite, resinite and varieties of vitrinite, which is a resinous or asphalt like material. Considering the thickness and distribution of coal seams in the studied samples, it is unlikely the exsudatinite will be a major source for aquifer hydrocarbon contamination in the study area. Additional stratigraphic studies and molecular geochemical analysis could provide an estimate of the total volume of possible organic compounds contribution to the aquifer in the study area. Due to the presence of coal seams in the studied intervals of the Paskapoo Formation, it is important to investigate the possibility of biogenic methane formation in Paskapoo shallow aquifers.

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Dickman, Martin B. y Oded Yarden. Role of Phosphorylation in Fungal Spore Germination. United States Department of Agriculture, agosto de 1993. http://dx.doi.org/10.32747/1993.7568761.bard.

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Spore germination is a common and fundamental event in fungal development and in many instances an essential phase of fungal infection and dissemination. Spore germination is also critical for hyperparasites to function as biocontrol agents as well as in fermentation proceses. Our common objective is to understand the mechanisms which regulated spore germination and identify factors involved in pathogenicity related prepenetration development. Our approach is to exploit the overall similarity among filamentous fungi using both a plant pathogen (Colletotricum trifolii) and a model system that is genetically sophisticated (Neurospora crassa). The simulataneous use of two organisms has the advantage of the available tools in Neurospora to rapidly advance the functional analysis of genes involved in spore germination and development of an economically important fungal phytopathogen. Towards this we have isolated a protein kinase gene from C. trifolii (TB3) that is maximally expressed during the first hour of conidial germination and prior to any visible gene tube formation. Based on sequence similarities with other organisms, this gene is likely to be involved in the proliferative response in the fungus. In addition, TB3 was able to functionally complement a N. crassa mutant (COT-1). Pharmacological studies indicated the importance of calmodulin in both germination and appressorium differentiation. Using an antisense vector from N. crassa, direct inhibition of calmodulin results in prevention of differentiation as well as pathogenicity. Both cAMP dependent protein kinase (PKA) and protein kinase C (PKC) like genes have been cloned from C. trifolii. Biochemical inhibition of PKA prevents germination; biochemical inhibitors of PKC prevents appressorium differentiation. In order to analyze reversible phosphorylation as a regulatory mechanism, some ser.thr dephosphorylative events have also been analyzed. Type 2A and Type 2B (calcineurin) phosphatases have been identified and structurally and functionally analyzed in N. crassa during this project. Both phosphatases are essential for hyphal growth and maintenance of proper hyphal architecture. In addition, a first novel-type (PPT/PP5-like) ser/thr phosphatase has been identified in a filamentous fungus. The highly collaborative project has improved our understanding of a fundamental process in fungi, and has identified targets which can be used to develop new approaches for control of fungal plant pathogens as well as improve the performance of beneficial fungi in the field and in industry. In addition, the feasibility of molecular technology transfer in comparative mycology has been demonstrated.

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Naim, Michael, Andrew Spielman, Shlomo Nir y Ann Noble. Bitter Taste Transduction: Cellular Pathways, Inhibition and Implications for Human Acceptance of Agricultural Food Products. United States Department of Agriculture, febrero de 2000. http://dx.doi.org/10.32747/2000.7695839.bard.

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Historically, the aversive response of humans and other mammals to bitter-taste substances has been useful for survival, since many toxic constituents taste bitter. Today, the range of foods available is more diverse. Many bitter foods are not only safe for consumption but contain bitter constituents that provide nutritional benefits. Despite this, these foods are often eliminated from our current diets because of their unacceptable bitterness. Extensive technology has been developed to remove or mask bitterness in foods, but a lack of understanding of the mechanisms of bitterness perception at the taste receptor level has prevented the development of inhibitors or efficient methods for reducing bitterness. In our original application we proposed to: (a) investigate the time course and effect of selected bitter tastants relevant to agricultural products on the formation of intracellular signal molecules (cAMP, IP3, Ca2+) in intact taste cells, in model cells and in membranes derived therefrom; (b) study the effect of specific bitter taste inhibitors on messenger formation and identify G-proteins that may be involved in tastant-induced bitter sensation; (c) investigate interactions and self-aggregation of bitter tastants within membranes; (d) study human sensory responses over time to these bitter-taste stimuli and inhibitors in order to validate the biochemical data. Quench-flow module (QFM) and fast pipetting system (FPS) allowed us to monitor fast release of the aforementioned signal molecules (cGMP, as a putative initial signal was substituted for Ca2+ ions) - using taste membranes and intact taste cells in a time range below 500 ms (real time of taste sensation) - in response to bitter-taste stimulation. Limonin (citrus) and catechin (wine) were found to reduce cellular cAMP and increase IP3 contents. Naringin (citrus) stimulated an IP3 increase whereas the cheese-derived bitter peptide cyclo(leu-Trp) reduced IP3 but significantly increased cAMP levels. Thus, specific transduction pathways were identified, the results support the notion of multiple transduction pathways for bitter taste and cross-talk between a few of those transduction pathways. Furthermore, amphipathic tastants permeate rapidly (within seconds) into liposomes and taste cells suggesting their availability for direct activation of signal transduction components by means of receptor-independent mechanisms within the time course of taste sensation. The activation of pigment movement and transduction pathways in frog melanophores by these tastants supports such mechanisms. Some bitter tastants, due to their amphipathic properties, permeated (or interacted with) into a bitter tastant inhibitor (specific phospholipid mixture) which apparently forms micelles. Thus, a mechanism via which this bitter taste inhibitor acts is proposed. Human sensory evaluation experiments humans performed according to their 6-n-propyl thiouracil (PROP) status (non-tasters, tasters, super-tasters), indicated differential perception of bitterness threshold and intensity of these bitter compounds by different individuals independent of PROP status. This suggests that natural products containing bitter compounds (e.g., naringin and limonin in citrus), are perceived very differently, and are in line with multiple transduction pathways suggested in the biochemical experiments. This project provides the first comprehensive effort to explore the molecular basis of bitter taste at the taste-cell level induced by economically important and agriculturally relevant food products. The findings, proposing a mechanism for bitter-taste inhibition by a bitter taste inhibitor (made up of food components) pave the way for the development of new, and perhaps more potent bitter-taste inhibitors which may eventually become economically relevant.

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