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Letteratura scientifica selezionata sul tema "H₂ activation"

Autore: Grafiati

Pubblicato: 21 dicembre 2024

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Articoli di riviste sul tema "H₂ activation"

1

Qiu, Youai, Julia Struwe e Lutz Ackermann. "Metallaelectro-Catalyzed C–H Activation by Weak Coordination". Synlett 30, n. 10 (21 maggio 2019): 1164–73. http://dx.doi.org/10.1055/s-0037-1611568.

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The merger of organometallic C–H activation with electrocatalysis has emerged as a powerful strategy for molecular synthesis, avoiding the use of toxic and expensive chemical oxidants in stoichiometric quantities. This review summarizes recent progress in transition-metal-catalyzed electrochemical C–H activation by weak chelation assistance until March 2019.1 Introduction2 Ruthenaelectro-Catalyzed C–H Activation3 Rhodaelectro-Catalyzed C–H Activation4 Iridaelectro-Catalyzed C–H Activation5 Summary and Outlook

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2

Liu, Yunyun, e Baoli Zhao. "Step-Economical C–H Activation Reactions Directed by In Situ Amidation". Synthesis 52, n. 21 (18 maggio 2020): 3211–18. http://dx.doi.org/10.1055/s-0040-1707124.

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Owing to the inherent ability of amides to chelate transition-metal catalysts, amide-directed C–H activation reactions constitute a major tactic in directed C–H activation reactions. While the conventional procedures for these reactions usually involve prior preparation and purification of amide substrates before the C–H activation, the step economy is actually undermined by the operation of installing the directing group (DG) and related substrate purification. In this context, directed C–H activation via in situ amidation of the crude material provides a new protocol that can significantly enhance the step economy of amide-directed C–H activation. In this short review, the advances in C–H bond activation reactions mediated or initiated by in situ amidation are summarized and analyzed.1 Introduction2 In Situ Amidation in Aryl C–H Bond Activation3 In Situ Amidation in Alkyl C–H Bond Activation4 Annulation Reactions via Amidation-Mediated C–H Activation5 Remote C–H Activation Mediated by Amidation6 Conclusion

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3

Ilies, Laurean. "Iron-Catalyzed C-H Bond Activation". Journal of Synthetic Organic Chemistry, Japan 75, n. 8 (2017): 802–9. http://dx.doi.org/10.5059/yukigoseikyokaishi.75.802.

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4

LI, Chao-Jun. "C―H Activation". Acta Physico-Chimica Sinica 35, n. 9 (2019): 905. http://dx.doi.org/10.3866/pku.whxb201903057.

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5

Bergman, Robert G. "C–H activation". Nature 446, n. 7134 (21 marzo 2007): 391–93. http://dx.doi.org/10.1038/446391a.

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6

WILSON, ELIZABETH. "H ACTIVATION, REVERSIBLY". Chemical & Engineering News 84, n. 47 (20 novembre 2006): 21. http://dx.doi.org/10.1021/cen-v084n047.p021.

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7

Holland, Herbert L. "C–H activation". Current Opinion in Chemical Biology 3, n. 1 (febbraio 1999): 22–27. http://dx.doi.org/10.1016/s1367-5931(99)80005-2.

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8

Sauermann, Nicolas, Tjark H. Meyer, Youai Qiu e Lutz Ackermann. "Electrocatalytic C–H Activation". ACS Catalysis 8, n. 8 (18 giugno 2018): 7086–103. http://dx.doi.org/10.1021/acscatal.8b01682.

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9

Dioumaev, Vladimir K., Patrick J. Carroll e Donald H. Berry. "Tandemβ-CH Activation/SiH Elimination Reactions: Stabilization of CH Activation Products byβ-Agostic SiH Interactions". Angewandte Chemie International Edition 42, n. 33 (25 agosto 2003): 3947–49. http://dx.doi.org/10.1002/anie.200352078.

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Dioumaev, Vladimir K., Patrick J. Carroll e Donald H. Berry. "Tandemβ-CH Activation/SiH Elimination Reactions: Stabilization of CH Activation Products byβ-Agostic SiH Interactions". Angewandte Chemie 115, n. 33 (25 agosto 2003): 4077–79. http://dx.doi.org/10.1002/ange.200352078.

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Tesi sul tema "H₂ activation"

1

Weeks, Amanda. "C-H activation in organic synthesis". Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535205.

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2

Doyle, Claire Marie. "C-H activation reactions of tetrahydropyridines". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9469.

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This thesis is presented as five chapters: Chapter 1.0 is divided into two sections: the first is a review of palladium-catalysed C–C bond forming reactions. It covers palladium-catalysed cross-coupling reactions; C–H bond functionalisation; the Heck reaction and functionalisation of heteroaromatic C–H bonds. Secondly the use of tetrahydropyridines in organic synthesis is discussed, with a particular focus on methodology developed by the Craig group. Chapter 2.0 discusses the research carried out during this studentship. It is divided into six sections and discusses the results obtained from research efforts into: our initial strategy for tetrahydropyridine synthesis; an SN1 approach; an α,β-unsaturated lactam approach; synthesis of 3-methoxy aryl-substituted tetrahydropyridines; synthesis of heteroaromatic analogues and further elaboration of tricyclic tetrahydropyridines. Chapter 3.0 details future work proposed within the areas described above. Chapter 4.0 details the experimental procedures employed and spectroscopic data for the compounds discussed in chapter 2.0. Finally, chapter 5.0 lists the references sourced in this thesis.

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Di, Matteo Marco. "Selective C-H Activation of Terpenes". Electronic Thesis or Diss., Sorbonne université, 2024. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2024SORUS001.pdf.

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Ce travail de thèse porte sur la découverte de nouvelles stratégies pour l'activation/fonctionnalisation C-H des terpènes, avec un accent particulier sur le (+)-limonène et la catalyse au palladium. Tout d'abord, nous avons décrit le couplage C(sp2)-H/C(sp2)-H déshydrogénant catalysé par le Pd(II) entre le limonène et des alcènes pauvres en électrons, avec une extension à divers terpènes et terpénoïdes. Ensuite, nous avons étudié la post-fonctionnalisation d'un produit issu du couplage déshydrogénant développé et de l'éthynylbenzène en conditions micellaires. Par la suite, nous avons développé avec succès le couplage redox neutre C(sp2)-H/C(sp2)-X entre le (+)-limonène et des bromoalcènes. Cette stratégie, qui est complémentaire par rapport au couplage déshydrogénant, nécessite une charge plus faible du catalyseur au palladium et du sel d'argent par rapport au couplage étudié précédemment. Enfin, nous avons étudié de nouvelles approches pour la synthèse du cannabidiol (CBD). Des travaux futurs seront nécessaires pour évaluer les stratégies et atteindre la cible synthétique
This thesis work is dealing with the discovery of new strategies for the C-H activation/functionalization of terpenes, with particular emphasis on (+)-limonene and palladium catalysis. Firstly, we described the dehydrogenative Pd(II)-catalyzed C(sp2)-H/C(sp2)-H coupling between limonene and electron-poor alkenes, with extension to various terpenes and terpenoids. Therefore, we studied the post-functionalization of one product stemming from the dehydrogenative coupling and ethynylbenzene under micellar regime. Secondly, we successfully developed the Pd(II)-catalyzed redox neutral C(sp2)-H/C(sp2)-X coupling between (+)-limonene and bromoalkenes. This strategy, which is complementary with respect to the dehydrogenative coupling, needs a lower loading of the palladium catalyst and of the silver salt with respect to the previously studied coupling. Finally, we investigated the study of new approaches to cannabidiol (CBD). Of course, future work will be necessary to evaluate the strategies and reach the target

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Vastine, Benjamin Alan. "Understanding mechanisms for C-H bond activation". [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2679.

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5

Khamker, Qudsia. "Ambiphilic C-H activation routes to heterocycles". Thesis, University of Leicester, 2014. http://hdl.handle.net/2381/28919.

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This thesis describes investigations of Cp*Rh- and (p-Cy)Ru-catalysed C-H functionalisation reactions of various substrates with alkynes and alkenes for the formation of several heterocycles and carbocycles. Mechanistic studies and DFT calculations are also presented. Chapter One includes a discussion of different mechanisms of C-H activation namely oxidative addition, σ-bond metathesis, 1,2-addition, electrophilic activation and AMLA/CMD. The applications of these different mechanisms of C-H activation in catalysis are also discussed with a particular emphasis on the use of AMLA/CMD in direct arylation reactions. Chapter Two gives an overview of stoichiometric and catalytic studies of AMLA C-H activation and subsequent reactivity with alkynes at Ir, Rh, and Ru. The results of Cp*Rh- and some (p-Cy)Ru-catalysed reactions of C-phenylpyrazoles with alkynes are presented. N-H and C-H activation occurs, leading to heterocycles. Mechanistic studies and DFT calculations show that C-H activation is reversible and rate limiting in the cases examined. Chapter Three is similar to Chapter Two but focusses on reactions with alkenes. The Cp*Rh-catalysed reactions of C-phenylpyrazoles with alkenes lead to mono or divinyl products which may undergo further aza-Michael cyclisations if the alkene is a good Michael acceptor. Mechanistic studies and DFT calculations are also discussed. Chapter Four deals with Cp*Rh-catalysed coupling reactions of other directing groups, including imidazole, imidazoline, pyrazolidinone, hydrazine, carboxylic acid and oxime with alkynes. Again, there is discussion on the different factors affecting product selectivity. Chapter Five gives a summary of all the conclusions on the work presented in this thesis. Throughout the thesis, all new compounds are characterised spectroscopically and several compounds have been characterised by X-ray crystallography.

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Rossignol, Anne-Claude. "Activation métabolique par la prostaglandine H synthétase". Paris 5, 1993. http://www.theses.fr/1993PA05P111.

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Wiley, Jack Scott. "C-H bond activation in iridium complexes /". Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/8510.

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Bu, Qingqing. "Ruthenium- and Cobalt-Catalyzed C-H Activation". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E4FC-F.

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Hebert, Alexandra. "Mise au point de nouvelles techniques de radio-iodation et application au radiomarquage de molécules d'intérêt". Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC413/document.

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Le radiomarquage de molécules d’intérêt avec des isotopes radioactifs est d'un grand intérêt pour la communauté scientifique, car il influe fortement sur le processus de découverte dans les sciences de la vie et en médecine nucléaire. Les molécules radiomarquées ont été largement utilisées pour évaluer les réactions biochimiques, pour mesurer la distribution in vivo d'une substance ou pour réaliser des tests RIA (RadioImmunoAssay). En médecine nucléaire, des radiopharmaceutiques pour la thérapie par ra-dio-isotopes (RIT) et des radiotraceurs pour des expériences d'imagerie telles que la TEP (tomographie par émission de positons), la tomographie par émission monophotonique (TEMP) ou la scintigraphie ont été décrites. Plusieurs isotopes de l'iode peuvent être utilisés à la fois pour le diagnostic et le traite-ment : 123I pour l'imagerie TEMP, 124I pour la TEP, 125I pour l'analyse biologique et 131I pour la radio-thérapie et la scintigraphie.Les méthodes classiques de radio-iodation reposent sur l'utilisation d'un précurseur pré-fonctionna-lisé, qui doit être synthétisé, isolé et purifié avant d'être introduit à l'étape de radio-iodation. La méthode par radioiododéstannylation est la méthode la plus populaire, bien que les précurseurs stannylés soient connus pour leur synthèse difficile et leur toxicité. Le développement de nouvelles méthodes de radio-iodation représente donc un grand intérêt dans le domaine de la radiochimie.Sur la base de travaux antérieurs, notre groupe a mis au point une méthode de radio-iodation de N-acylsulfonamides au moyen d’une radio-iodation C-H médiée par le palladium à température ambiante. Cette stratégie originale permet le radiomarquage de molécules d’intérêt dans des conditions très douces sans utiliser de précurseurs chimiques.Sur la base de la littérature, notre groupe développe actuellement une nouvelle méthode de radio-iodation de dérivés d’arylsilanes par radioiododésilylation dans des conditions douces. Cette méthodo-logie générale permet pour le moment le radiomarquage de dérivés d'arylsilanes activés en conditions douces
Labeling of (bio)molecules with radioactive isotopes is of high interest to for the scientific commu-nity, as it strongly impacts the discovery process in life science and nuclear medicine. Radiolabeled molecules have been extensively used to assess biochemical reactions, to measure in vivo distribution of a substance or to preform RIA (RadioImmunoAssay). In nuclear medicine, radio-therapeutics for RIT (RadioIsotope Therapy) and radio-tracers for molecular imaging experiments such as PET (Positron Emission Tomography), SPECT (Single Photon Emission Computed Tomography) or scintigraphy have been described. Several useful isotopes of iodine can be used for both diagnosis and therapy: 123I for SPECT imaging, 124I for PET imaging, 125I for biological assays and 131I for radio-therapy and scintig-raphy.Classical methods of radioiodination methods use a prefunctionalized precursor, which must be syn-thesized, isolated and purified before being introduced to the radio-iodination step. The radioiodode-stannylation method is the most popular method, although stannylated precursors are known for their difficult synthesis and their toxicity. The development of new methods of radioiodination is therefore of great interest in the field of radiochemistry.Based on a previous work, our group has developed a method to radio-iodinate N-acylsulfonamides through a room temperature palladium mediated C-H radio-iodination. This original strategy allows radiolabeling of biomolecules in very mild conditions without the use of chemical precursors.Based on literature, our group is now developping a new method to radio-iodinate arylsilyl derivates through radioiododesilylation in mild conditions. This general methodology allows for the moment the radiolabeling of activated arylsilyl derivates in mild conditions

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Chow, Catherine. "C-H activation by a tungsten trimethylsilylallyl complex". Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42646.

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Thermolysis of Cp*W(NO)(Np)(η³-CH₂CHCHSiMe₃) generates a 16-electron allene intermediate complex that selectively activates hydrocarbons at their methyl groups. In the case of linear alkanes, only terminal activation is observed. This selectivity persists in the presence of an ether functionality, but not of other oxygen-containing substrates such as aldehydes and alcohols. With these latter substrates, oxidation of the complex to Cp*W(O)₂Np has been noted. The existence of the allene intermediate has been verified by two thermolytic experiments, and kinetic studies show that Cp*W(NO)(Np)(η³- CH₂CHCHSiMe₃) is consumed according to pseudo-first-order kinetics during C–H bond activation. The neopentyl ligand can be functionalized by reaction with CO, and the resulting acyl complexes undergo chemical exchange on a slow timescale. The congeneric Mo complex has also been synthesized, and although this complex is equally capable of generating the η²-allene intermediate, its preferred mode of reactivity is coupling of the allyl and alkyl ligands. As a result, the Mo complex is inferior to the W system for C–H activation. The thermolysis of Cp*W(NO)(Np)(η³-CH₂CHCHSiMe₃) in benzene has been studied since the major products of this reaction each contain a 1,3-disubstituted allyl ligand which might reduce reactivity at the allyl ligand in subsequent chemistry. In thermolytic conditions, the resulting disubstituted allyl hydride complex undergoes no apparent reaction with alkanes, but with deuterobenzene, deuterium incorporation into the allyl ligand is observed. In addition to H/D exchange, the hydride ligands in these complexes can also migrate onto the allyl ligand, forming an η²-olefin complex that can be trapped as the pyridine adduct. The activation of fluorobenzenes by Cp*W(NO)(Np)(η³-CH₂CHCHSiMe₃) was also studied, and in these substrates, exclusive activation of the C–H bond is observed. Migration of the newly formed aryl ligands onto the allyl ligand does not occur when there is a fluorine atom in the ortho position, which is probably due to the reduced nucleophilicity of the ligand relative to the unfluorinated phenyl ligand. Selectivity in the activation of C–H bonds in fluorobenzenes appears to be determined by sterics.

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Libri sul tema "H₂ activation"

1

Yu, Jin-Quan, Lutz Ackermann e Zhangjie Shi. C-H activation. Heidelberg: Springer, 2010.

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2

Yu, Jin-Quan, e Zhangjie Shi, a cura di. C-H Activation. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-12356-6.

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Goldberg, Karen I., e Alan S. Goldman, a cura di. Activation and Functionalization of C—H Bonds. Washington, DC: American Chemical Society, 2004. http://dx.doi.org/10.1021/bk-2004-0885.

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R, Leone Stephen, e United States. National Aeronautics and Space Administration., a cura di. Rate coefficients of C₂H with C₂H₄, C₂H₆, and H₂ from 150 to 359 K. [Washington, DC: National Aeronautics and Space Administration, 1996.

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Dixneuf, Pierre H., e Henri Doucet, a cura di. C-H Bond Activation and Catalytic Functionalization II. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-29319-6.

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Dixneuf, Pierre H., e Henri Doucet, a cura di. C-H Bond Activation and Catalytic Functionalization I. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-24630-7.

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Wu, Xiao-Feng, a cura di. Transition Metal-Catalyzed Heterocycle Synthesis via CH Activation. Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, 2016. http://dx.doi.org/10.1002/9783527691920.

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Pérez, Pedro J., a cura di. Alkane C-H Activation by Single-Site Metal Catalysis. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-90-481-3698-8.

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Maiti, Debabrata, e Upendra Sharma, a cura di. Functionalisation of Heterocycles through Transition Metal Catalyzed C-H Activation. Cham: Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-70843-5.

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Matsumoto, Arimasa. Iron-Catalyzed Synthesis of Fused Aromatic Compounds via C–H Bond Activation. Tokyo: Springer Japan, 2014. http://dx.doi.org/10.1007/978-4-431-54928-4.

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Capitoli di libri sul tema "H₂ activation"

1

Shi, Feng, e Richard C. Larock. "Remote C–H Activation via Through-Space Palladium and Rhodium Migrations". In C-H Activation, 123–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2008_46.

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Daugulis, Olafs. "Palladium and Copper Catalysis in Regioselective, Intermolecular Coupling of C–H and C–Hal Bonds". In C-H Activation, 57–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_10.

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Davies, Huw M. L., e Allison R. Dick. "Functionalization of Carbon–Hydrogen Bonds Through Transition Metal Carbenoid Insertion". In C-H Activation, 303–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_11.

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Bouffard, Jean, e Kenichiro Itami. "Rhodium-Catalyzed C–H Bond Arylation of Arenes". In C-H Activation, 231–80. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_12.

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Martins, Andrew, Brian Mariampillai e Mark Lautens. "Synthesis in the Key of Catellani: Norbornene-Mediated ortho C–H Functionalization". In C-H Activation, 1–33. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_13.

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Fagnou, Keith. "Mechanistic Considerations in the Development and Use of Azine, Diazine and Azole N-Oxides in Palladium-Catalyzed Direct Arylation". In C-H Activation, 35–56. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_14.

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Beck, Elizabeth M., e Matthew J. Gaunt. "Pd-Catalyzed C–H Bond Functionalization on the Indole and Pyrrole Nucleus". In C-H Activation, 85–121. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_15.

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Liu, Guosheng, e Yichen Wu. "Palladium-Catalyzed Allylic C–H Bond Functionalization of Olefins". In C-H Activation, 195–209. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_16.

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Yoo, Woo-Jin, e Chao-Jun Li. "Cross-Dehydrogenative Coupling Reactions of sp3-Hybridized C–H Bonds". In C-H Activation, 281–302. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_17.

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You, Shu-Li, e Ji-Bao Xia. "Palladium-Catalyzed Aryl–Aryl Bond Formation Through Double C–H Activation". In C-H Activation, 165–94. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/128_2009_18.

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Atti di convegni sul tema "H₂ activation"

1

Yann, Theara, Charinee Winotapun, Phanny Yos, Lee Hwei Voon e Orathai Boondamnoen. "Particle Characteristics of Diatomite Activated by Alkaline Solution". In 2024 8th International Conference on Materials Engineering and Nano Sciences & 2024 8th International Conference on Material Engineering and Manufacturing, 37–43. Switzerland: Trans Tech Publications Ltd, 2024. http://dx.doi.org/10.4028/p-d4jwe2.

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In this study, the activation of natural diatomite was done with alkaline solution. The diatomite powder was sieved and purified prior to activation at room temperature (Alk-DA RT) and 85 °C (Alk-DA 85 °C). The effect of activation time of Alk-DA 85 °C samples was observed for 1 h, 2 h and 5 h. At temperature interval from room temperature to 530 °C, the weight loss for all of Alk-DA are less than R-DA. The reduction of particle aggregation was found in Alk-DA at both RT and 85 °C as shown in SEM images, indicating the activation by NaOH that effectively breaks down the bulky structure. The formation of silanol group (Si-OH) were obtained on the surface of Alk-DA. However, BET result revealed there is no increment of surface area and porosity in case of RT. In addition, Alk-DA 85 °C samples at 1 h and 2 h provided the spongy surfaces with obvious improvement of surface area, and reduction in porosity and pore size. In contrast, Alk-DA 85 °C 5 h showed more cluster of particle aggregation. Moreover, it can be observed that Alk-DA 85 °C 1 h is the most interesting for further study since it potentially provides high gas adsorption but only requires a shorter activation time.

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Ulin-Avila, Erick, e Akhilesh Kumar Mishra. "Graphene-based Photonic C-H bond activation". In Frontiers in Optics. Washington, D.C.: OSA, 2021. http://dx.doi.org/10.1364/fio.2021.jtu1a.55.

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3

Nyambo, Silver, Dong-Sheng Yang e Yuchen Zhang. "PROBING SELECTIVE BOND ACTIVATION IN ALKYLAMINES: LANTHANUM-MEDIATED C-H AND N-H BOND ACTIVATION STUDIED BY MATI SPECTROSCOPY." In 73rd International Symposium on Molecular Spectroscopy. Urbana, Illinois: University of Illinois at Urbana-Champaign, 2018. http://dx.doi.org/10.15278/isms.2018.fb01.

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4

Siffert, W., P. Scheid e JW N. Akkerman. "PROTEIN KINASE C CONTROLS CA2+ MOBILIZATION IN HUMAN PLATELETS". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1644509.

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Platelet stimulation has been shown to result in a rise of cytosolic pH (pHi) as a result of an activation of a Na+/H+ antiport. We have investigated the role of pH in Ca2+ mobilization in human platelets. pHi and free Ca2+, {Ca2+)i, were measured in platelets loaded with the fluorescent indicators BCECF and quin2, respectively. Stimulation of platelets by either thrombin or OAG, an activator of protein kinase C (Pk-C), increased pHi. Pretreatment of platelets with inhibitors of Pk-C, trifluoperazine (TFP) or sphingosine (SPH), blocked the stimulus-induced rise in pHi, suggesting a role of Pk-C in the activation of Na+/H+ exchange. Blocking Na+/H+ exchange by an amiloride analogue or by TFP similarly suppressed the thrombin-induced increase in {Ca2*}i. This effect could be prevented by increasing pHi with the Na+/H+ ionophore monensin or with NH4Cl. The thrombin-induced (0.05 U/ml) rise in {Ca2+}i was more than 3-fold enhanced when the pH was raised from 6.8 to 7.4.Our results demonstrate that pHi controls Ca2+ mobilization in human platelets and suggest that Pk-C contributes to this control by activating the Na+/H+ exchanger.Supported by the Deutsche Forschungsgemeinschaft. No Sche 46/5-2.

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5

Akkerman, JW N. "INTRACELLULAR PH CHANGES AND PLATELET ACTIVATION". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1644774.

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It is long known that platelet aggregation and secretion are accompanied by acidification of the extracellular medium. Much of the proton extrusion results from hydrolysis of ATP generated in the glycolytic pathway and liberation of secretion granules, which are slightly acidic. Recent eyidence points at a third source for extracellular protons.Following early observations (1) that epinephrine-induced platelet functions depended on extracellular Na+ (Na+ o ), it became evident that platelets possess a Na+ /H+ antiport, which regulates the cytosolic pH (pH.) via stochiometric exchange of intracellular protons with extracellular Na+ (2). Platelet functions triggered by epinephrine, AdP or low doses of thrombin are impaired by (i) the absence of Na+ o, and (ii) the presence of EIPA, an amiloride analogue which blocks the antiport. Ionophores which enhance proton efflux enhance the platelet responses. Thus, the antiport affects platelet functions via changes in pHi, but this has been difficult to establish experimentally. Early studies by Simons based on 6-carboxyfluorescein indeed reported a rise in pHi. during platelet activation, but more precise analysis awaited the development of more sensitive pHi-indicators. Recently (3),1studies employing BCECF, have confirmed that resting platelets maintain a pH. of about 7.1 via an EIPA-sensitive mechanism.Platelet activation induces a rise of 0.1-0.2 pH units, which lasts for several minutes unless the antiport is inhibited. When Na+/H+ exchange is gradually inhibited by lowering Na+ o , EIPA-sensitive proton efflux, mobilization of Ca2+ ions and aggregation are inhibited in parallel following stimulation with a low dose of thrombin. Artificial alkalinization reverses these effects. Alkalinization alone is not a trigger for platelet functions. Furthermore, high doses of thrombin (> 0.2 U/ml) initiate Ca2+ -mobilization and aggregation independent of changes in pHi Possibly, Na+ /H+ exchange enhances Ca mobilization by inositol-P3, generated by weak stimulation of the thrombin receptor, wfiich accords with the pH profile of IP3-induced Ca2+ liberation from isolated dense tubular membranes. However, concurrent measurement of Quin-2 and BCECF-fluoresence indicate that Ca2+ mobilization slightly precedes the rise in pHi which would make Ca+ mobilization a trigger for Na+ /H+ exchange is stead of one of its effects. Recent data favour a role for protein kinase C in activation of the antiport. A rise in pHi. is seen during incubation with OAG, an activator of protein kinase C. Thrombin (low dose)-induced Na /H exchange is inhibited by TFP, an inhibitor of this enzyme. These findings are bes^explained by assuming that low doses of thrombin initiate phospholipase C-mediated formation of inositol-P3, which triggers Ca2+ mobilization. Concurrently, diacylglycerol is formed, which activates protein kinase C. The result is a rise in pHi, which enhances the mobilization of Ca2+ by inositol-P3.This scheme differs from the sequence seen during activation by ADP or epinephrine (1), where Na+ /H2+ exchange is an early step after receptor occupancy and precedes phospholipid A2-mediated PG-endoperoxides/TxA2 formation. These metabolites activate phospholipase C resulting in diacylglycerol and inositol-P3-formation at a rather late stage in signal processing. Recent evidence (4) indicates that in epinephrine-stimulated platelets Na+ /H+ exchange requires fibrinogen binding, which opens the intriguing possibility that occupancy of GPIIb-IIIa starts a process that affects signal processing pathways in platelets.Sweatt, J.D., Limbird, L.E, et al. J.B.C. 1983, 1985, 1986Siffert, W., Akkerman, J.W.N., et al. FEBS Lett 1984, 1987; Nature 1987.Zavoico, G.B., Feinstein, M.B st al. J.B.C. 1986Banga, H.D., Rittenhouse, S.E. PNAS 1986

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6

Lian, T., S. E. Bromberg, H. Yang, M. Asplund, R. G. Bergman e C. B. Harris. "Femtosecond IR Studies of Alkane C-H Bond Activation by Organometallic Compounds". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/up.1996.fe.27a.

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The mechanism of alkane C-H bond activation by transition metal complexes such as CpM(CO)2 (M=Rh, Ir) has been intensely studied because it represents a first step in a catalytic process using unreactive hydrocarbons.[1] The bond activation reaction starts with the formation of monocarbonyl intermediates such as CpRh(CO). These species have been detected in the gas phase[2] and in liquefied rare Kr and Xe[3] by µs time resolved IR spectroscopy. Unfortunately, the subsequent oxidative insertion of CpRh(CO) into the C-H bond is not well understood due to its rapid rate and low quantum yield (~1%) for formation of the C-H activated product. These properties have hindered previous femtosecond and picosecond time-resolved studies of activation reaction in room temperature alkane solution. [4]

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7

Kim, Jongsik, Marshall S. Abbott, David B. Go e Jason C. Hicks. "Tunable C-H activation via metal-plasma interaction at elevated temperatures". In 2016 IEEE International Conference on Plasma Science (ICOPS). IEEE, 2016. http://dx.doi.org/10.1109/plasma.2016.7533960.

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8

Ortiz de Elguea, Verónica, Nuria Sotomayor e Esther Lete. "Intramolecular Palladium-catalyzed C-H activation reactions: Synthesis of substituted quinolones". In MOL2NET 2016, International Conference on Multidisciplinary Sciences, 2nd edition. Basel, Switzerland: MDPI, 2016. http://dx.doi.org/10.3390/mol2net-02-h008.

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9

Sato, Tamotsu, Hirokazu Odaka, Kazuyoshi Hiragi, Tsunefumi Mizuno, Masatoshi Ohno, Yasushi Fukazawa, Masayuki Ohta et al. "In-orbit activation study of ASTRO-H X-ray observatory using Geant4". In 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference (2012 NSS/MIC). IEEE, 2012. http://dx.doi.org/10.1109/nssmic.2012.6551405.

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10

Schleef, R. R., M. P. Bevilacqua, M. Sawdey, M. A. Gimbrone e D. J. Loskutoff. "INTERLEUKIN 1 (IL-1) AND TUMOR NECROSIS FACTOR (TNF) ACTIVATION OF VASCULAR ENDOTHELIUM: EFFECTS ON PLASMINOGEN ACTIVATOR INHIBITOR (PAI-1) AND TISSUE-TYPE PLASMINOGEN ACTIVATOR (tPA)". In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642864.

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The regulation of the fibrinolytic system of cultured human umbilical vein endothelial cells (ECs) by two distinct monokines (IL-1 and TNF) was investigated. Conditioned media (CM) was collected from ECs cultured for 24 h in the presence of the monokines and analyzed in quantitative immunological assays for PAI-1 activity and tPA antigen. Both monokines induced a dose-dependent increase in extracellular PAI-1 activity, with a concomitant decrease in tPA antigen. Maximal effects were achieved with either 10 U/ml IL-1 or 200 U/ml of TNF, and resulted in a 4 fold increase in PAI-1 and a 50% decrease in tPA. The kinetics of the effects of both monokines on EC PAI-1 and tPA were similar, with maximal response detected at 24 h. Cell-associated PAI-1 also increased in response to these monokines. For example, a 24 h exposure of EC to TNF (250 U/ml) or IL-1 (5 U/ml) caused a 5-fold increase in cell-associated PAI-1. Northern blot analysis using a PAI-1 cDNA probe indicated that the monokines increased the levels of two RNA species, corresponding to PAI mRNAs of approximately 3.0 and 2.2 kb in length. To determine if the increase in cel 1-associated PAI-1 reflects a storage pool of rapidly releasable PAI-1, ECs were pretreated with IL-1 for 24 h, washed and the PAI-1 activity in CM measured after 5, 15 and 60 min treatment with known secretagogues (i.e., phorbol myristate acetate, calcium ionophore A23187). Although IL-1 treated ECs released PAI-1 at a rate which was 5-fold higher than controls, this rate was not increased further by treatment with phorbol myristate acetate or ionophore. The fact that both monokines act in a similar manner strengthens the hypothesis that the local development of immune and inflammatory processes could reduce endothelial fibrinolytic activity, thus leading to the pathologic formation of intravascular thrombi.

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Rapporti di organizzazioni sul tema "H₂ activation"

1

Lees, Alistair J. Photochemistry of Intermolecular C-H Bond Activation Reactions. Office of Scientific and Technical Information (OSTI), giugno 2000. http://dx.doi.org/10.2172/761218.

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2

Crabtree, Robert. Moving to Sustainable Metals: Multifunctional Ligands in Catalytic, Outer Sphere C-H, N-H and O-H Activation. Office of Scientific and Technical Information (OSTI), marzo 2015. http://dx.doi.org/10.2172/1171638.

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3

Rakowski-DuBois, Mary C. Aspects of C-H Activation in Metal Complexes Containing Sulfur Ligands. Office of Scientific and Technical Information (OSTI), ottobre 2004. http://dx.doi.org/10.2172/833244.

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4

Asplund, M. C. Time resolved infrared studies of C-H bond activation by organometallics. Office of Scientific and Technical Information (OSTI), giugno 1998. http://dx.doi.org/10.2172/290889.

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5

Das, Jayabrata, e Debabrata Maiti. Transition Metal Catalyzed Remote C-H Activation: A New Direction Towards Site-Selective Chemical Reactions. The Israel Chemical Society, marzo 2023. http://dx.doi.org/10.51167/acm00036.

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6

Lees, A. J. [Photochemistry of intermolecular C-H bond activation reactions]. Progress report, [September 15, 1994--March 15, 1995]. Office of Scientific and Technical Information (OSTI), dicembre 1994. http://dx.doi.org/10.2172/35271.

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7

Moran, Nava, Richard Crain e Wolf-Dieter Reiter. Regulation by Light of Plant Potassium Uptake through K Channels: Biochemical, Physiological and Biophysical Study. United States Department of Agriculture, settembre 1995. http://dx.doi.org/10.32747/1995.7571356.bard.

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The swelling of plant motor cells is regulated by various signals with almost unknown mediators. One of the obligatory steps in the signaling cascade is the activation of K+-influx channels -K+ channels activated by hyperpolarization (KH channels). We thus explored the regulation of these channels in our model system, motor cell protoplasts from Samanea saman, using patch-clamp in the "whole cell" configuration. (a) The most novel finding was that the activity of KH channels in situ varied with the time of the day, in positive correlation with cell swelling: in Extensor cells KH channels were active in the earlier part of the day, while in Flexor cells only during the later part of the day; (b) High internal pH promoted the activity of these channels in Extensor cells, opposite to the behavior of the equivalent channels in guard cells, but in conformity with the predicted behavior of the putative KH channel, cloned from S. saman recently; (c) HIgh external K+ concentration increased (KH channel currents in Flexor cells. BL depolarized the Flexor cells, as detected in cell-attached patch-clamp recording, using KD channels (the K+-efflux channels) as "voltage-sensing devices". Subsequent Red-Light (RL) pulse followed by Darkness, hyperpolarized the cell. We attribute these changes to the inhibition of the H+-pump by BL and its reactivation by RL, as they were abolished by an H+-pump inhibitor. BL increased also the activity KD channels, in a voltage-independent manner - in all probability by an independent signaling pathway. Blue-Light (BL), which stimulates shrinking of Flexor cells, evoked the IP3 signaling cascade (detected directly by IP3 binding assay), known to mobilize cytosolic Ca2+. Nevertheless, cytosolic Ca2+ . did not activate the KD channel in excised, inside-out patches. In this study we established a close functional similarity of the KD channels between Flexor and Extensior cells. Thus the differences in their responses must stem from different links to signaling in both cell types.

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8

Rafaeli, Ada, e Russell Jurenka. Molecular Characterization of PBAN G-protein Coupled Receptors in Moth Pest Species: Design of Antagonists. United States Department of Agriculture, dicembre 2012. http://dx.doi.org/10.32747/2012.7593390.bard.

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The proposed research was directed at determining the activation/binding domains and gene regulation of the PBAN-R’s thereby providing information for the design and screening of potential PBAN-R-blockers and to indicate possible ways of preventing the process from proceeding to its completion. Our specific aims included: (1) The identification of the PBAN-R binding domain by a combination of: (a) in silico modeling studies for identifying specific amino-acid side chains that are likely to be involved in binding PBAN with the receptor and; (b) bioassays to verify the modeling studies using mutant receptors, cell lines and pheromone glands (at tissue and organism levels) against selected, designed compounds to confirm if compounds are agonists or antagonists. (2) The elucidation ofthemolecular regulationmechanisms of PBAN-R by:(a) age-dependence of gene expression; (b) the effect of hormones and; (c) PBAN-R characterization in male hair-pencil complexes. Background to the topic Insects have several closely related G protein-coupled receptors (GPCRs) belonging to the pyrokinin/PBAN family, one with the ligand pheromone biosynthesis activating neuropeptide or pyrokinin-2 and another with diapause hormone or pyrokinin-1 as a ligand. We were unable to identify the diapause hormone receptor from Helicoverpa zea despite considerable effort. A third, related receptor is activated by a product of the capa gene, periviscerokinins. The pyrokinin/PBAN family of GPCRs and their ligands has been identified in various insects, such as Drosophila, several moth species, mosquitoes, Triboliumcastaneum, Apis mellifera, Nasoniavitripennis, and Acyrthosiphon pisum. Physiological functions of pyrokinin peptides include muscle contraction, whereas PBAN regulates pheromone production in moths plus other functions indicating the pleiotropic nature of these ligands. Based on the alignment of annotated genomic sequences, the primary and secondary structures of the pyrokinin/PBAN family of receptors have similarity with the corresponding structures of the capa or periviscerokinin receptors of insects and the neuromedin U receptors found in vertebrates. Major conclusions, solutions, achievements Evolutionary trace analysisof receptor extracellular domains exhibited several class-specific amino acid residues, which could indicate putative domains for activation of these receptors by ligand recognition and binding. Through site-directed point mutations, the 3rd extracellular domain of PBAN-R was shown to be critical for ligand selection. We identified three receptors that belong to the PBAN family of GPCRs and a partial sequence for the periviscerokinin receptor from the European corn borer, Ostrinianubilalis. Functional expression studies confirmed that only the C-variant of the PBAN-R is active. We identified a non-peptide agonist that will activate the PBAN-receptor from H. zea. We determined that there is transcriptional control of the PBAN-R in two moth species during the development of the pupa to adult, and we demonstrated that this transcriptional regulation is independent of juvenile hormone biosynthesis. This transcriptional control also occurs in male hair-pencil gland complexes of both moth species indicating a regulatory role for PBAN in males. Ultimate confirmation for PBAN's function in the male tissue was revealed through knockdown of the PBAN-R using RNAi-mediated gene-silencing. Implications, both scientific and agricultural The identification of a non-peptide agonist can be exploited in the future for the design of additional compounds that will activate the receptor and to elucidate the binding properties of this receptor. The increase in expression levels of the PBAN-R transcript was delineated to occur at a critical period of 5 hours post-eclosion and its regulation can now be studied. The mysterious role of PBAN in the males was elucidated by using a combination of physiological, biochemical and molecular genetics techniques.

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9

Prusky, Dov, Noel T. Keen e Stanley Freeman. Elicitation of Preformed Antifungal Compounds by Non-Pathogenic Fungus Mutants and their Use for the Prevention of Postharvest Decay in Avocado Fruits. United States Department of Agriculture, gennaio 1996. http://dx.doi.org/10.32747/1996.7570573.bard.

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C. gloeosporioides attacks unripe avocado fruits in the orchard. Germinated spores produce appressoria that germinate and breach the cuticle, but the resultant subcuticular hyphae become quiescent and do not develop further until fruit is harvested and ripens. Resistance of unripe avocado to attach by C. gloeosporioides is correlated with the presence of fungitoxic concentrations of the preformed antifungal compound, 1-acetoxy-2-hydroxy-4-oxoheneicosa-12, 15 diene in the pericarp of unripe fruits. The objective of this proposal was to study the signal transduction process by which elicitors induce resistance in avocado. It was found that abiotic elicitors, infection of avocado fruit with C. gloeosporioides or treatment of avocado cell suspension with cell-wall elicitor induced a significant production of reactive oxygen species (ROS). Ripe and unripe fruit tissue differ with regard to the ROS production. The unripe, resistant fruit are physiologically able to react and to produce high levels of ROS and increased activity of H+ATPase that can enhance the phenylpropanoid pathway ad regulate the levels of the antifungal compound-diene, inhibit fungal development, resulting in its quiescence. Interestingly, it was also found that growth regulators like cytokinin could do activation of the mechanism of resistance. Postharvest treatments of cytokinins strongly activated the phenylpropanoid pathway and induce resistance. We have developed non-pathogenic strains of C. gloeosporioides by Random Enzyme Mediated Integration and selected a hygromycin resistance, non-pathogenic strain Cg-142 out of 3500 transformants. This non-pathogenic isolate activates H+ATPase and induces resistance against Colletotrichum attack. As a basis for studying the importance of PL in pathogenicity, we have carried out heterologous expression of pel from C. gloeosporioides in the non-pathogenic C. magna and determine the significant increase in pathogenicity of the non-pathogenic strain. Based on these results we can state that pectate lyase is an important pathogenicity factor of C. gloeosporioides and found that fungal pathogenicity is affected not by pel but by PL secretion. Our results suggest that PH regulates the secretion of pectate lyase, and support its importance as a pathogenicity factor during the attack of avocado fruit by C. gloeosporioides . This implicates that if these findings are of universal importance in fungi, control of disease development could be done by regulation of secretion of pathogenicity factors.

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10

Rafaeli, Ada, Russell Jurenka e Daniel Segal. Isolation, Purification and Sequence Determination of Pheromonotropic-Receptors. United States Department of Agriculture, luglio 2003. http://dx.doi.org/10.32747/2003.7695850.bard.

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Abstract (sommario):

Moths constitute a major group of pest insects in agriculture. Pheromone blends are utilised by a variety of moth species to attract conspecific mates, which is under circadian control by the neurohormone, PBAN (pheromone-biosynthesis-activating neuropeptide). Our working hypothesis was that, since the emission of sex-pheromone is necessary to attract a mate, then failure to produce and emit pheromone is a potential strategy for manipulating adult moth behavior. The project aimed at identifying, characterising and determining the sequence of specific receptors responsible for the interaction with pheromonotropic neuropeptide/s using two related moth species: Helicoverpa armigera and H. lea as model insects. We established specific binding to a membrane protein estimated at 50 kDa in mature adult females using a photoaffinity-biotin probe for PBAN. We showed that JH is required for the up-regulation of this putative receptor protein. In vitro studies established that the binding initiates a cascade of second messengers including channel opening for calcium ions and intracellular cAMP production. Pharmacological studies (using sodium fluoride) established that the receptor is coupled to a G-protein, that is, the pheromone-biosynthesis-activating neuropeptide receptor (PBAN-R) belongs to the family of G protein-coupled receptor (GPCR)'s. We showed that PBAN-like peptides are present in Drosophila melanogaster based on bioassay and immunocytochemical data. Using the annotated genome of D. melanogaster to search for a GPCR, we found that some were similar to neuromedin U- receptors of vertebrates, which contain a similar C-terminal ending as PBAN. We established that neuromedin U does indeed induce pheromone biosynthesis and cAMP production. Using a PCR based cloning strategy and mRNA isolated from pheromone glands of H. zea, we successfully identified a gene encoding a GPCR from pheromone glands. The full-length PBAN-R was subsequently cloned and expressed in Sf9 insect cells and was shown to mobilize calcium in response to PBAN in a dose-dependent manner. The successful progress in the identification of a gene, encoding a GPCR for the neurohormone, PBAN, provides a basis for the design of a novel battery of compounds that will specifically antagonize pheromone production. Furthermore, since PBAN belongs to a family of insect neuropeptides with more than one function in different life stages, this rationale may be extended to other physiological key-regulatory processes in different insects.

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