Bibliografie tematiche / Activations C-H

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Letteratura scientifica selezionata sul tema "Activations C-H"

Autore: Grafiati
Pubblicato: 16 novembre 2024

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Articoli di riviste sul tema "Activations C-H"

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Yang, Yajie, Jiaqi Huang, Hailu Tan, Lingkai Kong, Mengdan Wang, Yang Yuan e Yanzhong Li. "Synthesis of cyano-substituted carbazoles via successive C–C/C–H cleavage". Organic & Biomolecular Chemistry 17, n. 4 (2019): 958–65. http://dx.doi.org/10.1039/c8ob03031f.

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Choi, Isaac, Julia Struwe e Lutz Ackermann. "C–H activation by immobilized heterogeneous photocatalysts". Photochemical & Photobiological Sciences 20, n. 12 (16 novembre 2021): 1563–72. http://dx.doi.org/10.1007/s43630-021-00132-9.

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AbstractDuring the last decades, the merger of photocatalysis with transition metal chemistry has been surfaced as a sustainable tool in modern molecular syntheses. This Account highlights major advances in synergistic photo-enabled C‒H activations. Inspired by our homogenous ruthenium- and copper-catalyzed C‒H activations in the absence of an exogenous photosensitizer, this Account describes the recent progress on heterogeneous photo-induced C‒H activation enabled by immobilized hybrid catalysts until September 2021, with a topical focus on recyclability as well as robustness of the heterogeneous photocatalyst.
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Ackermann, Lutz, Korkit Korvorapun, Ramesh C. Samanta e Torben Rogge. "Remote C–H Functionalizations by Ruthenium Catalysis". Synthesis 53, n. 17 (19 aprile 2021): 2911–46. http://dx.doi.org/10.1055/a-1485-5156.

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AbstractSynthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences, and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we discuss important mechanistic insights by experiments and computation, illustrating the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes.1 Introduction2 Stoichiometric Remote C–H Functionalizations3 meta-C–H Functionalizations4 para-C–H Functionalizations5 meta-/ortho-C–H Difunctionalizations6 Conclusions
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Li, Shuai-Shuai, Liu Qin e Lin Dong. "Rhodium-catalyzed C–C coupling reactions via double C–H activation". Organic & Biomolecular Chemistry 14, n. 20 (2016): 4554–70. http://dx.doi.org/10.1039/c6ob00209a.

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Zhu, Haoran, Sen Zhao, Yu Zhou, Chunpu Li e Hong Liu. "Ruthenium-Catalyzed C–H Activations for the Synthesis of Indole Derivatives". Catalysts 10, n. 11 (29 ottobre 2020): 1253. http://dx.doi.org/10.3390/catal10111253.

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The synthesis of substituted indoles has received great attention in the field of organic synthesis methodology. C–H activation makes it possible to obtain a variety of designed indole derivatives in mild conditions. Ruthenium catalyst, as one of the most significant transition-metal catalysts, has been contributing in the synthesis of indole scaffolds through C–H activation and C–H activation on indoles. Herein, we attempt to present an overview about the construction strategies of indole scaffold and site-specific modifications for indole scaffold via ruthenium-catalyzed C–H activations in recent years.
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Kerr, M. E., I. Ahmed, A. Gunay, N. J. Venditto, F. Zhu, E. A. Ison e M. H. Emmert. "Non-directed, carbonate-mediated C–H activation and aerobic C–H oxygenation with Cp*Ir catalysts". Dalton Transactions 45, n. 24 (2016): 9942–47. http://dx.doi.org/10.1039/c6dt00234j.

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Ackermann, Lutz. "(Keynote) Metallaelectro-Catalyzed Bond Activations". ECS Meeting Abstracts MA2023-02, n. 52 (22 dicembre 2023): 2478. http://dx.doi.org/10.1149/ma2023-02522478mtgabs.

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Oxidative C–H activation has emerged as an increasingly powerful tool in molecular syntheses.[ 1] Despite major progress towards atom and step economy, these transformations largely rely on precious metal catalysts and stoichiometric amounts of toxic metal oxidants, compromising the overall sustainability of the C–H activation strategy. In contrast, employing electrooxidation in lieu of reactive chemical oxidants prevents undesired waste formation through oxidant economyand offers efficient use of renewable energies from sustainable sources for chemical bond formation.[2] Inexpensive Earth-abundant 3d metal[3] cobaltaelectrocatalysis set the stage for molecular syntheses at a unique level of resource economy.[4] Our studies towards metallaelectrocatalytic C–H and C–C activation will be discussed, with a topical focus on sustainable base metals.[5] References [1] a) L. Ackermann, Acc. Chem. Res. 2014, 47, 281–295; b) C. S. Yeung, V. M. Dong, Chem. Rev. 2011, 111, 1215–1292. [2] a) P. Gandeepan, L. H. Finger, T. H. Meyer, L. Ackermann, Chem. Soc. Rev. 2020, 49, 4254–4272; b) LA, Acc chem Rex 2020, C. Ma, P Fang, T.-S. Mei, ACS Catal. 2018, 7179–7189. [3] P. Gandeepan, T. Müller, D. Zell, G. Cera, S. Warratz, L. Ackermann, Chem. Rev. 2019, 111, 2192–2452. [4] Y. Qiu, M. Stangier, T. H. Meyer, J. C. A. Oliveira, L. Ackermann, Angew. Chem. Int. Ed. 2018, 57, 14179–14183; b) Y. Qiu, W.-J. Kong, J. Struwe, N. Sauermann, T. Rogge, A. Scheremetjew, L. Ackermann, Angew. Chem. Int. Ed. 2018, 57, 5828–5832. [5] a) R. Mei, N. Sauermann, J. C. A. Oliveira, L. Ackermann, J. Am. Chem. Soc. 2018, 140, 7913–7921;N. Sauermann, T. H. Meyer, C. Tian, L. Ackermann, J. Am. Chem. Soc. 2017, 139, 18452–18455. Figure 1
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Gunay, Ahmet, e Klaus H. Theopold. "C−H Bond Activations by Metal Oxo Compounds". Chemical Reviews 110, n. 2 (10 febbraio 2010): 1060–81. http://dx.doi.org/10.1021/cr900269x.

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Volla, Chandra M. R., Rahul K. Shukla e Akshay M. Nair. "Allenes: Versatile Building Blocks in Cobalt-Catalyzed C–H Activation". Synlett 32, n. 12 (31 marzo 2021): 1169–78. http://dx.doi.org/10.1055/a-1471-7307.

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AbstractThe unique reactivity of allenes has led to their emergence as valuable coupling partners in transition-metal-mediated C–H activation reactions. On the other hand, due to its high abundance and high Lewis acidity, cobalt is garnering widespread interest as a useful catalyst for C–H activation. Here, we summarize cobalt-catalyzed C–H activations involving allenes as coupling partners and then describe our studies on Co(III)-catalyzed C-8 dienylation of quinoline N-oxides with allenes bearing a leaving group at the α-position for realizing a dienylation protocol.
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Jun, Chul-Ho, e Chang-Hee Lee. "Chelation-Assisted C–H and C–C Bond Activation of Allylic Alcohols by a Rh(I) Catalyst under Microwave Irradiation". Synlett 29, n. 06 (16 novembre 2017): 736–41. http://dx.doi.org/10.1055/s-0036-1591697.

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Chelation-assisted Rh(I)-catalyzed ketone synthesis from allylic alcohols and alkenes through C–H and C–C bond activations under microwave irradiation was developed. Aldimine is formed via olefin isomerization of allyl alcohol under Rh(I) catalysis and condensation with 2-amino-3-picoline, followed by continuous C–H and C–C bond activations to produce a dialkyl ketone. The addition of piperidine accelerates the reaction rate by promoting aldimine formation under microwave conditions.
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Tesi sul tema "Activations C-H"

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Henderson, William Howell. "Palladium-Mediated C-H Activations". The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1318003095.

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Bechtoldt, Alexander. "Aerobic Ruthenium-Catalyzed C–H Activations". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2018. http://hdl.handle.net/11858/00-1735-0000-002E-E492-A.

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Korvorapun, Korkit. "Site-Selectivity in Ruthenium-Catalyzed C–H and C–C Activations". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://hdl.handle.net/21.11130/00-1735-0000-0005-148C-7.

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Wang, Hui. "Cobalt(III)- and Manganese(I)-Catalyzed C-H and C-C Activations". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2019. http://hdl.handle.net/11858/00-1735-0000-002E-E5EF-5.

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Pal, S. "Non-metallic approaches for C-H and C-Si bond activations". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2013. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/1921.

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Korvorapun, Korkit [Verfasser]. "Site-Selectivity in Ruthenium-Catalyzed C–H and C–C Activations / Korkit Korvorapun". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1218299231/34.

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Tian, Cong. "Metallaelectro-Catalyzed C─H Activations by 3d Transition Metals". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://hdl.handle.net/21.11130/00-1735-0000-0005-1482-1.

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Mo, Jiayu. "Iron-Catalyzed C–H/N–H Activations for Annulation of Allenes, Alkynes, and Bicyclopropylidenes". Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://hdl.handle.net/21.11130/00-1735-0000-0005-14F0-5.

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Kossen, Hanno. "Exploration of Brønsted base catalysis for formal C–H bond activations". Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23598.

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This PhD project investigates the use of (Lewis or Brønsted) bases in catalysis. While the first chapter explores the use of main group metal amides in C–H bond activation reactions, the second chapter focusses on metal-free organocatalysis using so-called carbones. In the first chapter, formal allylic C(sp3)–H bond activations of unfuctionalised alkenes for C–C bond formations with imines were investigated. Alkali metal amides were used as catalysts for these transformations, giving homoallylic amine products. The investigations showed the unique reactivity of the Na-amide catalyst compared to other metal base complexes. The reaction scope and robustness was explored and initial insights into the reaction mechanism were obtained. A related K-amide catalyst was then developed for the isomerisation of allyl benzenes, as well as functionalised olefins such as allylic silanes, boronic esters, phosphines, amines, ethers, and thioethers. This part explored the use of ligands to increase the catalyst’s selectivity. Finally, the metal- or functional group-substituted classes of reagents were used in the functionalised allylation of imines, giving highly complex molecules with a diverse range of applications. Here, unprecedented reactivities were observed for the use of allyl–M reagents, as the allylation involved the activation of C–H bonds rather than C–X bonds. Furthermore, new catalytic formations of heteroatom-substituted homoallylic amines were described. The following chapter focussed on the use of carbodiphosphoranes (CDPs) in catalysis. These C(0) bases, or carbones, represent a class of heteroallene compounds that exhibit a high electron density on a P(V)-flanked carbon centre. Their potential as either a Lewis or Brønsted base was examined. Different CDPs were synthesised and reacted stoichiometrically with CO2, boron Lewis acids and metal salts. The generated intermediates were then studied in their reaction behaviour, taking advantage of a potentially available second pair of electrons. The results of these reactions were compared to other carbon bases, such as carbenes or other carbones. Finally, the Brønsted basicity of the CDP was examined in reactions with acidic pro-nucleophiles. The conjugate addition of alkylnitriles to α,β- unsaturated amides was developed using a catalytic amount of CDP. To the best of our knowledge, the first catalytic use of a CDP, as well as the first C–H bond activation of acetonitrile in Michael additions was reported.
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Tian, Cong [Verfasser]. "Metallaelectro-Catalyzed C─H Activations by 3d Transition Metals / Cong Tian". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/1217842853/34.

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Libri sul tema "Activations C-H"

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

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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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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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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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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 "Activations C-H"

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Beller, Matthias, e Xiao-Feng Wu. "Carbonylative C–H Activations". In Transition Metal Catalyzed Carbonylation Reactions, 115–32. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-39016-6_6.

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Kakiuchi, Fumitoshi, e Naoto Chatani. "Ruthenium-Catalyzed Reactions via sp CH, sp2 CH, sp3 CH, and CHalogen Bond Activations". In Ruthenium in Organic Synthesis, 219–55. Weinheim, FRG: Wiley-VCH Verlag GmbH & Co. KGaA, 2005. http://dx.doi.org/10.1002/3527603832.ch9.

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Knochel, Paul, Konstantin Karaghiosoff e Sophia Manolikakes. "Selective C–H Activations Using Frustrated Lewis Pairs. Applications in Organic Synthesis". In Topics in Current Chemistry, 171–90. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/128_2012_394.

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Legzdins, Peter, e Craig B. Pamplin. "Sequential Hydrocarbon C—H Bond Activations by 16-Electron Organometallic Complexes of Molybdenum and Tungsten". In ACS Symposium Series, 184–97. Washington, DC: American Chemical Society, 2004. http://dx.doi.org/10.1021/bk-2004-0885.ch011.

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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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Atti di convegni sul tema "Activations C-H"

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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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Abstract (sommario):
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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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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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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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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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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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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8

Kim, Jong, e Dong-Sheng Yang. "YTTRIUM-ASSISTED C-H AND C-C BOND ACTIVATION OF ETHYLENE PROBED BY MASS-ANALYZED THRESHOLD IONIZATION SPECTROSCOPY". In 71st International Symposium on Molecular Spectroscopy. Urbana, Illinois: University of Illinois at Urbana-Champaign, 2016. http://dx.doi.org/10.15278/isms.2016.ri06.

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9

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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Cao, Jianzhu, Tao Liu, Yuanyu Wu, Hong Li e Yuanzhong Liu. "Analysis of Radioactive Source Term for Modular HTGR During Normal Operation". In 18th International Conference on Nuclear Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/icone18-30075.

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The methods of radioactive source term analysis are introduced in detail for the modular high temperature gas cooled reactor in China. Radioactive fission products and activation products produced in the reactor are described. For fission products, the emphasis is on the process from production through release to the environment for noble gas, iodine and long-lived metallic nuclides. For activation products, it mainly introduces the behaviors of H-3 and C-14. Especially the permeation process from primary circuit to secondary circuit is described for H-3. Using the preliminary design parameters of demonstration HTGR in China, basic prediction of radioactive source term is done and the results are given.
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Rapporti di organizzazioni sul tema "Activations C-H"

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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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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3

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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4

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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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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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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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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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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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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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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