Literatura académica sobre el tema "Effet de ligand"
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Artículos de revistas sobre el tema "Effet de ligand"
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Khamyath, Mélanie, Amélie Bonaud, Karl Balabanian y Marion Espéli. "La signalisation de CXCR4, un rhéostat de la réponse immunitaire à médiation humorale". médecine/sciences 39, n.º 1 (enero de 2023): 23–30. http://dx.doi.org/10.1051/medsci/2022192.
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CXCR4 est un récepteur de chimiokine qui joue un rôle central dans la migration cellulaire mais également dans d’autres mécanismes essentiels, tels que le développement du système immunitaire. De concert avec son ligand naturel, la chimiokine CXCL12, cet axe de signalisation joue un rôle important dans la biologie des lymphocytes B, des stades précoces de différenciation dans la moelle osseuse à leur activation et différenciation en cellules sécrétrices d’anticorps, aussi appelées plasmocytes. Des mutations gain de fonction de CXCR4 sont retrouvées dans une immunodéficience rare, le Syndrome WHIM. Ces mutations affectent le mécanisme de désensibilisation du récepteur et entraînent un gain de fonction en réponse à CXCL12. Cette revue résume le rôle de CXCR4 dans la réponse immune humorale et, à travers l’étude du Syndrome WHIM, souligne le rôle régulateur essentiel de la désensibilisation de CXCR4 dans ces processus. Des travaux récents rapportent en effet qu’une signalisation correcte de CXCR4 est essentielle pour limiter la réponse immune dite « extra-folliculaire » et pour permettre une protection au long terme assurée par les anticorps.
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Hecini, Linda y Samia Achour. "Coagulation-floculation au sulfate d’aluminium de composés organiques phénoliques et effet de sels de calcium et de magnésium". Revue des sciences de l’eau 27, n.º 3 (15 de diciembre de 2014): 271–80. http://dx.doi.org/10.7202/1027810ar.
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L’objectif de la présente étude est d’observer l’efficacité de la coagulation-floculation par le sulfate d’aluminium sur l’élimination des composés organiques à fonctions phénoliques (phénol et pyrogallol). L’intérêt s’est porté plus particulièrement sur l’incidence de sels minéraux constitutifs de la dureté « calcium et magnésium » et souvent présents dans la matrice minérale des eaux algériennes. Des essais de Jar-Test ont été réalisés sur les deux composés phénoliques dissous dans l’eau distillée seule, puis enrichie en sels minéraux. Ces essais ont été réalisés sur des solutions synthétiques d’eau distillée enrichies par les ions de calcium et de magnésium introduits sous différentes formes (CaCl2•2H2O; CaSO4•2H2O; CaCO3; MgCl2•6H2O; MgSO4•7H2O) et, enfin, avec les eaux souterraines de la région. Différents paramètres réactionnels ont été variés (ex. : l’effet du pH et l’influence de la teneur en sels) et cette approche a permis une meilleure compréhension des mécanismes d’interactions composés phénoliques / sels calciques et magnésiens. Les résultats obtenus indiquent que l’efficacité du procédé dépend du nombre et de la position des groupements phénoliques sur les molécules. Les principaux mécanismes seraient soit une adsorption physique, soit un échange de ligand ou une complexation à la surface des flocs d’hydroxydes d’aluminium. L’ajout de sels minéraux semble améliorer les rendements d’élimination de composés phénoliques testés et avoir un effet sur la gamme optimale de pH de coagulation. Une application de ce procédé à des eaux minéralisées (eaux de forage) de la région de Biskra, située au sud-est de l’Algérie, a abouti à une amélioration des rendements comparés à ceux dans de l'eau distillée.
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Crawford, Sarah M., Craig A. Wheaton, Vinayak Mishra y Mark Stradiotto. "Probing the effect of donor-fragment substitution in Mor-DalPhos on palladium-catalyzed C–N and C–C cross-coupling reactivity". Canadian Journal of Chemistry 96, n.º 6 (junio de 2018): 578–86. http://dx.doi.org/10.1139/cjc-2017-0749.
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The competitive catalytic screening of 18 known and newly prepared Mor-DalPhos ligand variants in the palladium-catalyzed cross-coupling of chlorobenzene with aniline, octylamine, morpholine, indole, ammonia, or acetone is presented, including ligands derived from the new secondary phosphine HP(Me2Ad)2 (Me2Ad = 3,5-dimethyladamantyl). Although triarylphosphine ancillary ligand variants performed poorly in these test reactions, ligands featuring either PAd2 or P(Me2Ad)2 donors (Ad = 1-adamantyl) gave rise to superior catalytic performance. Multiple Mor-DalPhos variants proved effective in cross-couplings involving aniline, octylamine, or morpholine; conversely, only a smaller subset of ligands proved useful in related cross-couplings of indole, ammonia, or acetone. In the case of the N-arylation of indole, a Mor-DalPhos ligand variant featuring ortho-disposed PAd2 and dimethylmorpholino donor fragments (L13) proved superior to all other ligands surveyed, including the parent ligand Mor-DalPhos (L5). Conversely, L5 was found to be superior to all other ligands in the palladium-catalyzed monoarylation of ammonia. Ligand L6 (i.e., the P(Me2Ad)2 variant of L5) proved superior to all other ligands in the monoarylation of acetone and, with the exception of indole N-arylation, was the most broadly useful of the Mor-DalPhos ligands surveyed herein.
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Drouet, M., F. Mourcin, N. Grenier, J. F. Mayol, V. Leroux, J. J. Sotto y F. Hérodin. "Effet des rayonnements ionisants sur les cellules souches et progéniteurs hématopoïétiques: place de l'apoptose et intérêt thérapeutique potentiel des traitements antiapoptotiques". Canadian Journal of Physiology and Pharmacology 80, n.º 7 (1 de julio de 2002): 700–709. http://dx.doi.org/10.1139/y02-071.
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Bone marrow aplasia observed following ionizing radiation exposure (Total Body Irradiation; gamma dose range: 210 Gy) is a result, in particular, of the radiation-induced (RI) apoptosis in hematopoietic stem and progenitor cells (HSPC). We have previously shown in a baboon model of mobilized peripheral blood CD34+ cell irradiation in vitro that RI apoptosis in HSPC was an early event, mostly occurring within the first 24 hours, which involves the CD95 Fas pathway. Apoptosis may be significantly reduced with a combination of 4 cytokines (4F): Stem Cell Factor (SCF), FLT-3 Ligand (FL), thrombopoietin (TPO), and interleukin-3 (IL-3), each at 50 ng·mL1 (15% survival versus <3% untreated cells, 24 h post-irradiation at 2.5 Gy). In this study we show that addition of TNF-alpha(800 IU/ml) induces an increase in 4F efficacy in terms of cell survival 24 h after incubation (26% survival after 24 h irradiation exposure at 2.5 Gy) and amplification (k) of CD34+ cells after 6 days in a serum free culture medium (SFM) (kCD34+ = 4.3 and 6.3 respectively for 4F and successive 4F + TNF-alpha/ 4F treatments). In addition, the 4F combination allows culture on pre-established allogenic irradiated stromal cells in vitro at 4 Gy (kCD34+ = 4.5). Overall this study suggests (i) the potential therapeutic interest for an early administration of anti-apoptotic cytokines with or without hematopoiesis inhibitors (emergency cytokine therapy) and (ii) the feasibility in the accidentally irradiated individual, of autologous cell therapy based on ex vivo expansion in order to perform autograft of residual HSPC collected after the accident.Key words: apoptosis, cytokine, hematopoiesis, irradiation, bone marrow aplasia.[Journal translation]
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Tatarchuk, T. R., H. O. Sirenko y U. L. Kush. "The Solution of Applied Problems of Complex Compounds with the d-Elements Central Atoms Surrounded by Octahedral Ligand Based on the Theory of Crystal Field". Фізика і хімія твердого тіла 16, n.º 1 (15 de marzo de 2015): 145–54. http://dx.doi.org/10.15330/pcss.16.1.145-154.
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The crystal field theory as applied to complex compounds of d-elements surrounded by octahedral ligans was described. Ligand field causes the splitting of d-orbitals, which is characterized by the energy splitting Δo. The spectrochemical series of ligands and examples of high-spin and low-spin complex compounds depending on the degree of force field were presented. Deformation of octahedral complexes by the Jahn-Teller effect was described. It shows the calculation of gains power as a result of complex formation, called the crystal field stabilization energy (CFSE) depending on the electronic structure of the central ion and the ligand position in spectrochemical series. It shows the distribution of electrons in orbitals of eg and t2g complex ions with different electronic configurations (from d1 to d10), examples values of energy orbitals and energy of crystal field stabilization for high-spin and low-spin octahedral complexes.
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Wang, Yanan y Thomas Bürgi. "Evidence for stereoelectronic effects in ligand exchange reactions on Au25 nanoclusters". Nanoscale 14, n.º 6 (2022): 2456–64. http://dx.doi.org/10.1039/d1nr07602g.
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Fluoro-substituted ligands attached on a gold cluster slow down subsequent ligand exchange reactions. The clusters obtained through ligand exchange with mixtures show non-statistical ligand distribution, revealing a stereoelectronic effect.
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van Heerden, Tracey y Eric van Steen. "Metal–support interaction on cobalt based FT catalysts – a DFT study of model inverse catalysts". Faraday Discussions 197 (2017): 87–99. http://dx.doi.org/10.1039/c6fd00201c.
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It is challenging to isolate the effect of metal–support interactions on catalyst reaction performance. In order to overcome this problem, inverse catalysts can be prepared in the laboratory and characterized and tested at relevant conditions. Inverse catalysts are catalysts where the precursor to the catalytically active phase is bonded to a support-like ligand. We can then view the metal–support interaction as a ligand interaction with the support acting as a supra-molecular ligand. Importantly, laboratory studies have shown that these ligands are still present after reduction of the catalyst. By varying the quantity of these ligands present on the surface, insight into the positive effect SMSI have during a reaction is gained. Here, we present a theoretical study of mono-dentate alumina support based ligands, adsorbed on cobalt surfaces. We find that the presence of the ligand may significantly affect the morphology of a cobalt crystallite. With Fischer–Tropsch synthesis in mind, the CO dissociation is used as a probe reaction, with the ligand assisting the dissociation, making it feasible to dissociate CO on the dense fcc Co(111) surface. The nature of the interaction between the ligand and the probe molecule is characterized, showing that the support-like ligands’ metal centre is directly interacting with the probe molecule.
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Yu, Baoyi, Zhixiong Luo, Fatma B. Hamad, Karen Leus, Kristof van Hecke y Francis Verpoort. "Effect of the bulkiness of indenylidene moieties on the catalytic initiation and efficiency of second-generation ruthenium-based olefin metathesis catalysts". Catalysis Science & Technology 6, n.º 7 (2016): 2092–100. http://dx.doi.org/10.1039/c5cy01506e.
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Liu, Xiaochun, Haifeng Zhao, Linfeng Wei, Xinjian Ren, Xinyang Zhang, Faming Li, Peng Zeng y Mingzhen Liu. "Ligand-modulated electron transfer rates from CsPbBr3 nanocrystals to titanium dioxide". Nanophotonics 10, n.º 8 (1 de junio de 2020): 1967–75. http://dx.doi.org/10.1515/nanoph-2020-0631.
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Abstract In most perovskite nanocrystal (PeNC)-based optoelectronic and photonic applications, surface ligands inevitably lead to a donor–bridge–acceptor charge transfer configuration. In this article, we demonstrate successful modulation of electron transfer (ET) rates from all-inorganic CsPbBr3 PeNCs to mesoporous titanium dioxide films, by using different surface ligands including single alkyl chain oleic acid and oleylamine, cross-linked insulating (3-aminopropyl)triethoxysilane and aromatic naphthoic acid molecules as the ligand-bridge. We systematically investigated the ET process through time-resolved photoluminescence spectroscopy. Calculations verified the ligand-bridge barrier effect of the three species upon the ET process. Transient absorption measurements excluded carrier-delocalization effect of the naphthoic acid ligands and confirmed the bridge-barrier effect. Our work provides a perspective for composable and appropriate ligands design for diverse practical purposes.
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Monteiro, Jorge H. S. K., Ana de Bettencourt-Dias, Italo O. Mazali y Fernando A. Sigoli. "The effect of 4-halogenobenzoate ligands on luminescent and structural properties of lanthanide complexes: experimental and theoretical approaches". New Journal of Chemistry 39, n.º 3 (2015): 1883–91. http://dx.doi.org/10.1039/c4nj01701c.
Texto completoTesis sobre el tema "Effet de ligand"
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Montalvo, Acosta Joel José. "Computational approaches to molecular recognition : from host-guest to protein-ligand binding". Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF051/document.
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La reconnaissance moléculaire est un problème très intéressant et surtout un défi actuel pour la chimie biophysique. Avoir des prévisions fiables sur la reconnaissance spécifique entre les molécules est hautement prioritaire, car il fournira un aperçu des problèmes fondamentaux et suscitera des applications technologiques pertinentes. La thèse présentée ici est centrée sur une analyse quantitatif de la reconnaissance moléculaire en solution pour la liaison l'hôte-invité, la liaison protéine-ligand et la catalyse. Le cadre de la mécanique statistique utilisé pour décrire l'état de la technique de liaison récepteur-ligand est un point d'inflexion pour le développement de nouvelles méthodes améliorées. En fait, un modèle très performant et précis a été obtenu pour l'analyse de la liaison hôte-invité. Enfin, les modèles présentés ont été utilisés comme outils prédictifs fiables pour la découverte de nouvelles entités chimiques destinées à améliorer la catalyse en solutionMolecular recognition is a very interesting problem, and foremost, a current challenge for biophysical chemistry. Having reliable predictions on the specific recognition between molecules is highly priority as it will provide an insight of fundamental problems and will raise relevant technological applications. The dissertation presented here is centered on a quantitative analysis of molecular recognition in solution for host-guest, protein-ligand binding and catalysis. The statistical mechanics framework used to describe the state-of-the-art for receptor-ligand binding is an inflection point for the developing of new improved and methods. In fact, a highly performanced and accurate model was obtained for the analysis of host-guest binding. Finally, the presented models were used as a reliable predictive tools for discovering new chemical entities for enhance catalysis in solution
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Marchenko, Nataliia. "Effets de ligand sur les propriétés de nanoparticules ultra-petites à base de platine". Electronic Thesis or Diss., Toulouse, INSA, 2023. http://www.theses.fr/2023ISAT0061.
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Les nanoparticules (NP) métalliques ultra-petites possèdent des propriétés uniques en raison de leur taille : un rapport surface sur volume élevé et une quantification de leurs propriétés physiques. Ces caractéristiques en font des objets d'étude populaires en catalyse, en auto-assemblage (AA), en photophysique ou en transport de charge. Des ligands stabilisants sont généralement utilisés pour préserver la petite taille et la dispersion des NP, en plus d'influencer leurs propriétés fonctionnelles. Dans cette thèse, nous étudions comment les ligands peuvent moduler les propriétés intrinsèques des NP de platine et comment ces connaissances peuvent être appliquées dans différentes sphères, de l'auto-assemblage à la catalyse. Cette thèse est composée de cinq chapitres : une revue de la littérature et quatre études expérimentales qui couvrent des projets indépendants, où les NP UP à base de platine sont l'objet principal de la recherche.Le chapitre 1 regroupe des exemples représentatifs de l'influence des ligands sur la synthèse, l'AA et les propriétés catalytiques de NP à base de métal. Dans la première partie, les ligands organiques classiques tels que les thiols ou les polymères sont pris en compte, tandis que la deuxième partie couvre des exemples de ce que l'on appelle les "systèmes hybrides" où des complexes métalliques stabilisent ou interagissent avec les NP.Le chapitre 2 présente la synthèse, la caractérisation et les propriétés catalytiques des nanoparticules de platine stabilisées par des macrocycles de pyranose - les cyclodextrines (CD). L'influence du groupement fonctionnel de la CD (motifs thiol ou oxyde de phosphine secondaire) et l'effet de la quantité relative de ligand sur la performance d'hydrogénation des NP de Pt sont discutés.Le chapitre 3 est consacré à la synthèse de NP de FePt immobilisées sur des phases liquides ioniques supportées (SILP) à base de silice, et à leur utilisation en tant que catalyseurs. Dans ce chapitre, l'importance de la modulation de la teneur en Fe ainsi que le rôle du support modifié par le liquide ionique sont démonstrés en hydrogénation et l'hydrodésoxygénation catalytiques sélectives de cétones et d’aldéhydes.Le chapitre 4 décrit des systèmes hybrides composés de NP de Pt et de porphyrines ou de porphyrines métalliques fonctionnalisées. En particulier, la formation d’AA de différentes formes et les changements évidents dans les propriétés photophysiques des systèmes sont rationalisés et corrélés à la force des interactions entre les NP de Pt et les porphyrines.Le chapitre 5 décrit la synthèse et la caractérisation de systèmes hybrides contenant des NP de Pt UP et des complexes de ruthénium(II) bipyridyle modifiés par des fragments imidazolium attachés de manière covalente. Les systèmes NP-antennes préparés sont des candidats prometteurs pour la photocatalyse.En conclusion, cette thèse présente des résultats de valeur sur le contrôle par les ligands de la synthèse, de l'AA et des propriétés catalytiques des NP de Pt ultra-petites. Cette étude souligne l'importance d'un choix minutieux des ligands pour produire des NP stables et actives. Les résultats de cette recherche peuvent servir de ligne directrice pour la conception rationnelle de nanocomposites afin de former des systèmes auto-assemblés ou des catalyseurs sélectifsUltra-small metal nanoparticles (NPs) have unique properties originating from their size such as a high surface-to-volume ratio and a quantization of their physical properties. These characteristics make them a popular object of investigation in catalysis, self-assembly (SA), photophysics or charge transport. Stabilizing ligands that are generally used to preserve the small size and the dispersion of NPs can also influence their functional properties. In this thesis, we investigate how ligands can modulate the intrinsic properties of platinum NPs and how this knowledge can be applied in different spheres, from self-assembly to catalysis. This manuscript consists of five chapters: a literature review and four experimental studies that cover independent projects, where US platinum-based NPs are the main object of investigation.Chapter 1 gathers representative examples of ligand influence on the synthesis, SA, and catalytic properties of metal-based NPs. In the first part, classical organic ligands like thiols or polymers are considered, while the second part covers examples of so-called “hybrid systems” where metal complexes stabilize or interact with NPs.Chapter 2 reports the synthesis, characterization and catalytic properties of Pt NPs stabilized with pyranose macrocycles - cyclodextrins (CD). The influence of the functional group of the CD (thiol or secondary phosphine oxide moieties) and the effect of the ligand relative quantity on the hydrogenation performance of Pt NPs are discussed.Chapter 3 is dedicated to FePt NPs immobilized on silica-based supported ionic liquid phases (SILP). In this chapter, the importance of the Fe content modulation as well as the role of the ionic liquid-modified support are demonstrated in selective catalytic hydrogenation and hydrodeoxygenation of ketones and aldehydes.Chapter 4 describes hybrid systems made of Pt NPs and functionalized porphyrins or metal porphyrins. Particularly, the formation of SAs of different shapes and obvious changes in the photophysical properties of the systems are rationalized and correlated to the strength of interactions between the Pt NP and the porphyrins.Chapter 5 describes the synthesis and the characterization of hybrid systems containing Pt NPs and covalently attached ruthenium (II) bipyridyl complexes modified with imidazolium fragments. The prepared NP-antenna systems are promising candidates in photocatalysis.In conclusion, this thesis demonstrates valuable findings about ligand control of the synthesis, SA, and catalytic properties of ultra-small Pt NPs. This study highlights the importance of a thorough ligand choice to produce stable and active NPs. The results of this research can serve as a guideline for a rational design of nanocomposites to form self-assembled systems or selective catalysts
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Darbandi-Tehrani, Kévin. "Etude de la structure du CX3CR1 par BRET : effet anti-tumoral de son ligand, le CX3CL1". Paris 6, 2010. http://www.theses.fr/2010PA066396.
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En interagissant avec leurs récepteurs couplés aux protéines G, les chimiokines, ou cytokines chimio-attractantes, induisent le recrutement spécifique des leucocytes et participent ainsi à la réponse immune et à de multiples processus homéostatiques, inflammatoires et pathologiques. En particulier, le couple adhésif formé par la chimiokine CX3CL1 et son récepteur, le CX3CR1, joue un rôle important dans, entre autres, l'athérosclérose, le glioblastome et la DMLA. Ce travail de thèse comprend deux aspects : d'une part une approche biophysique de la structure du CX3CR1 et d'autre part une étude de l'effet anti-tumoral de la molécule F2, un analogue du CX3CL1. Par la technique de BRET (Bioluminescence Resonance Energy Transfer), j'ai testé le CX3CR1 et l'effet des variations naturelles V249I et T280M. Les résultats suggèrent que tous les variants du CX3CR1 forment des oligomères et que la technique de BRET est suffisamment sensible pour détecter les différences conformationnelles entre variants. Les résultats ont été confirmés par FRET entre CX3CL1 fluorescentes. La modélisation moléculaire propose des éléments d'explication sur l'impact qu'ont les variations V249I et T280M sur les positions respectives des domaines transmembranaires I, VI et VII du CX3CR1. Par ailleurs, j'ai constaté dans un modèle murin de tumeurs sous-cutanées EG7 que l'injection intra-tumorale de protéines de fusion à base du super-agoniste F2 et d'immunoglobuline (F2-Ig) inhibait la croissance tumorale mais au même niveau que la protéine CX3CL1-Ig. Cependant, la poursuite de la caractérisation de F2 devrait permettre d'identifier des super-agonistes pouvant donner lieu à des molécules thérapeutiques
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Sidibe, Assitan. "Effet de ligands de G-quadruplexes sur la séquence terminale des télomères". Paris, Muséum national d'histoire naturelle, 2012. http://www.theses.fr/2012MNHN0017.
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Les télomères sont des complexes nucléoprotéiques situés à lʼextrémité des chromosomes. Le rôle des télomères dans la protection du génome, et leur implication dans la sénescence et le cancer en font une cible privilégiée dans la lutte contre le cancer. Une stratégie originale consiste à bloquer lʼaccès de lʼextrémité télomérique aux protéines nécessaires à sa réplication et à sa stabilité comme par exemple la télomérase qui est activée dans 85% des cancers ou les protéines POT1 et TRF2 qui protègent lʼextrémité télomérique. A cause de la répétition en guanines du brin G, lʼextrémité des télomères peut former des structures en quadruplexes de guanines (G- quadruplexes) dont la stabilisation par des ligands spécifiques (Ligands G4) bloque la réplication des télomères et altère son intégrité. Le traitement de cellules tumorales par des ligands G4 provoque une dysfonction télomérique associée à une dissociation des protéines POT1 et TRF2 et conduit à une apoptose ou une sénescence des cellules. Lʼanalyse de la séquence terminale de lʼextrémité télomérique par la méthode STELA (Single Telomere Length Analysis) montre que la séquence terminale du brin C se termine majoritairement par la séquence ATC-5ʼ. La protéine POT1 est responsable de la résection du brin C des télomères en recrutant une exo- nucléase capable de créer le substrat simple-brin pour la télomérase. La déplétion de POT1 par ARN interférence provoque une dérégulation de la terminaison du brin C. Nous avons étudié au cours de notre travail lʼeffet de ligands G4 sur la séquence terminale du brin C télomérique au niveau des télomères du chromosome XpYp et au niveau de lʼensemble des télomères en utilisant une modification de la technique de STELA. Nos résultats montrent quʼune faible concentration des dérivés de la série des pyridines dicarboxamides provoque un effet mineur mais significatif au niveau de la séquence terminale des télomères XpYp et au niveau de lʼensemble des télo- mères dans la lignée HT1080. Au contraire, une concentration plus importante ne modifie pas la séquence terminale du brin C dans les cellules HT1080, A549 et HeLa, mais induit un stress réplicatif. Lʼeffet modeste de ces ligands sʼexplique par une activité de dissociation incomplete de la protéine POT1 des télomères comparativement à sa déplétion par ARN interférence. En effet, nous avons également montré que la déplétion quasi complète de POT1 par shARN induit une randomisation de la séquence terminale du brin CThe role of telomeres in protecting the genome, and their involvement in senescence and cancer make them a prime target in the fight against cancer. An original strategy is to block the access of proteins to the telomeric end necessary for replication and stability, such as telomerase which is activated in 85% of cancers or TRF2 and POT1, proteins that protect the telomeric end. Because of the guanine repetition on the G strand, telomeric ends can form quadruplex structures in guanine (G-quadruplexes) whose stabilization by specific ligands (G4 ligands) blocks the replication of telomeres and alters its integrity. Treatment of tumor cells with G4 ligands causes a dysfunction associated with the dissociation of telomeric proteins POT1 and TRF2 and leads to apoptosis or cell senescence. The analysis of the telomeric end terminal sequence by the STELA method (Single Telomere Length Analysis) shows that the C-terminal sequence of the strand ends mainly by the sequence ATC-5 ʼ. POT1 protein is responsible for the resection of the C strand of telomeres by recruiting an exonuclease capable of creating a single-stranded substrate for telomerase. Depletion of POT1 by RNA interference causes a deregulation of the C strand end. We studied in our work the effect of G4 ligands on the terminal sequence of the telomeric C strand at the telomere of chromosome XpYp and at all telomeres using a modification of the technique of STELA. Our results show that a low concentration of derivatives of the pyridine dicarboxamides series causes a minor but significant effect on the terminal sequence of XpYp telomeres and of all telomeres in HT1080 cell line. On the contrary, a higher concentration does not alter the C strand termination in HT1080, A549 and HeLa cells but induces a replicative stress. The modest effect of these ligands can be explained by an incomplete activity of dissociation of the protein POT1 of telomeres compared to its depletion by RNA interference. Indeed, we also showed that the nearly complete depletion of POT1 by shRNA randomizes the terminal sequence of the C strand
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Pocquet, Lucrèce. "Ancrage supramoléculaire de complexes organométalliques dans la béta-lactoglobuline pour la catalyse asymétrique dans l'eau. Effet des ligands prochiraux hémilabiles". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066322/document.
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Ce travail de thèse est consacré à la conception de métalloenzymes artificielles. Un tel concept permet de combiner les avantages des catalyseurs enzymatiques et organométalliques, tels que la sélectivité catalytique élevée et l'efficacité des systèmes enzymatiques et la large portée de substrats des catalyseurs des métaux de transition. Notre approche repose sur l’utilisation de complexes de métaux de transition avec un ligand prochiral hémilabile, qui une fois insérés dans la protéine hôte sera forcé d’adopter une configuration spécifique. La chiralité sera ainsi amenée au plus près du centre métallique et permettra d’augmenter l’énantioselectivité des réactions catalysées. Dans cette thèse, nous rapportons la synthèse de nouveaux complexes de palladium à ligands pinces NCN hémilabiles prochiraux et l’étude de leurs propriétés structurales. De plus, l’ancrage supramoléculaire de ces complexes dans la β-lactoglobuline (β-LG) bovine a été étudié expérimentalement et théoriquement par modélisation moléculaire. Ces constructions ont montré une activité catalytique dans la condensation d’aldol dans l’eau, et permettent d’obtenir, dans certains cas, le produit Cis. Cette diastéréosélectivité inhabituelle résulte de la seconde sphère de coordination apportée par l'hôte protéique. Dans une deuxième partie, on rapporte la synthèse de nouveaux complexes semi-sandwich de ruthénium avec des ligands β-aminothioéther hémilabiles, ainsi que l'étude de leur insertion dans la protéine. Les hybrides catalysent l'hydrogénation par transfert d'arylcétones avec une énantiosélectivité élevée. L'amélioration de la sélectivité a été attribuée au transfert de chiralité de la protéine vers le complexe et à son tour vers le produit de réactionThis PhD work focused on the development of artificial metalloenzymes. Such a concept allows to combine typical advantages of both enzymatic and organometallic catalysts, such as high catalytic selectivity and efficiency of enzymatic systems and wide substrate scope of transition metals catalysts. Our approach consists in the utilization of transition metal complexes with a prochiral hemilabile ligand, once embedded within the protein host, could be forced to adopt a specific stereoconfiguration. This would in turn make possible to bring the chirality centers closer to the catalytic metal center and, therefore, to increase the enantioselectivity of catalyzed reactions.In this thesis, we report the synthesis of new palladium complexes of prochiral hemilabile NCN pincer ligands and the study of their structural properties. Furthermore, the supramolecular anchoring of these complexes to bovine β-lactoglobulin (β-LG) was studied both experimentally and theorically by computational calculation. These constructs were shown to catalyze aldol condensation reactions in aqueous media, affording, in some cases, the less-favorable cis product. This unusual diastereoselectivity was ensued by the second sphere of coordination brought by the protein host. In a second part, the synthesis of new half sandwich ruthenium complexes of prochiral hemilabile β-aminothioether ligands is reported as well as the study of their insertion in the protein. The hybrids catalyzed the transfer hydrogenation of arylketones with high enantioselectivity. The enhancement of selectivity was attributed to chirality
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Ávila, Gutiérrez Mario Alberto. "Effet de la nanocristallinité sur les croissances homogènes et hétérogènes des supercristaux magnétique de cobalt". Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS008.
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Les auto-organisations à 3D de nanocristaux (NCx) métalliques constituent une nouvelle génération de matériaux nanostructurés, appelés supercristaux. Ils présentent de nouvelles propriétés collectives, ce qui permet de les impliquer dans différentes applications technologiques. Dans cette thèse, nous proposons une étude comparative concernant la croissance hétérogène et homogène en absence ou présence d’un champ magnétique, de supercristaux de nanocristaux de cobalt obtenus par la voie micellaire (7,5 nm, σ: 11 %, type cfc) et par la dismutation d’un sel organométallique ([CoCl(PPh3)3]) (9 nm, σ: 10 %, type hc). Les premiers sont passivés avec l’acide dodécanoïque et les seconds avec l’oleylamine. En contrôlant la quantité d’oleylamine dans la solution colloïdale de NCx de Co-hc ainsi que le volume de solution déposée, nous favorisons la croissance de supercristaux, relativement similaires à ceux obtenus avec les NCx de Co-cfc. Une nouvelle méthode d’échange de ligands (de l’oleylamine à l’acide dodécanoïque) est proposée, favorisant des NCx de Co-hc dont l’interaction avec l’acide dodécanoïque est covalente. Les dépôts menés avec ces NCx favorisent pour la première fois des cristaux colloïdaux de NCx de Co-hc passivés d’acide dodécanoïque. En utilisant une méthode d’oxydation en solution, des nanocristaux cœur/coquille [Co (ferromagnétique)@ CoO (antiferromagnétique)] de taille uniforme, ont été obtenus avec un cœur métallique monocristallin (hc) et une coquille cfc. Les études préliminaires des propriétés magnétiques montrent un couplage d’échange magnétique à l’interface ferromagnétique/antiferromagnétiqueMetallic nanocrystals 3D self-organization (NCx) is a new generation of nanostructured materials, called supercrystals. They present a new collective property, which allows them to be involved in different technological applications. In this thesis, we propose a comparative study concerning heterogeneous and homogeneous growth in the absence or presence of a magnetic field, of cobalt nanocrystals, obtained by the micellar route (7.5 nm, σ: 11%, fcc type) and by the dismutation of an organometallic salt ([CoCl(PPh3)3]) (9 nm, σ: 10%, hc type). The former are passivated with dodecanoic acid and the latter with oleylamine. By controlling the amount of oleylamine in Co-hc NCx colloidal solution and the volume of solution deposited, we promote the growth of super crystals, relatively similar to those obtained with Co-fcc NCx. A new method of ligand exchange (from oleylamine to dodecanoic acid) is proposed, promoting Co-hc NCx whose interaction with dodecanoic acid is covalent. The deposits conducted with these NCx promote for the first time colloidal crystals of Co-hc NCx passivated with dodecanoic acid. Using a solution oxidation method, core/shell nanocrystals [Co (ferromagnetic)@ CoO (antiferromagnetic)] of uniform size were obtained with a monocrystalline metal core (hc) and an fcc shell. Preliminary studies of magnetic properties show magnetic exchange coupling at the ferromagnetic/antiferromagnetic interface
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Pittari, Gianfranco. "NK Cell Tolerance of Self-Specific Apecific Activating Receptor KIR2DS1 in Individuals with Cognate HLA-C2 Ligand". Thesis, Paris 11, 2013. http://www.theses.fr/2013PA11T043.
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Les cellules tueuses naturelles (NK) sont régulées par des récepteurs activateurs et inhibiteurs. La plupart des récepteurs inhibiteurs reconnaisse des molécules du complexe majeur d'histocompatibilité (CMH) de classe I, et protège les cellules saines des phénomènes d'auto-immunité médiés par les cellules NK. Cependant, certains récepteurs activateurs, incluant le récepteur killer cell Ig-like receptor (KIR) 2DS1, reconnaissent aussi des ligands CMH de classe I. Cela pose la question de savoir comment les cellules NK qui expriment des récepteurs activateurs deviennent tolérantes au soi. Nous avons cherché à déterminer si la présence de HLA-C2, le ligand du récepteurs 2DS1, peut induire les cellules NK qui expriment le 2DS1 à développer un état de tolérance au soi. Indépendamment de la présence ou de l'absence du ligand HLA-C2 dans le donneur, une activité anti-HLA-C2 a été identifiée in vitro dans certains clones NK 2DS1-positifs. La fréquence des clones NK avec réactivité anti-HLA-C2 était élevée parmi les donneurs homozygotes pour HLA-C1. De façon étonnante, nous n'avons pas constaté de différence statistiquement significative dans la fréquence de cytotoxicité anti-HLA-C2 entre les donneurs HLA-C2 hétérozygotes et les donneurs sans ligand HLA-C2. Par contre, les donneurs HLA-C2 homozygotes montrent une fréquence réduite de clones NK avec réactivité anti-HLA-C2 par rapport aux autres donneurs. Clones 2DS1-positifs qui co-expriment des KIR inhibiteurs spécifiques des molécules HLA de classe I du soi n’étaient pas communément cytotoxiques, et la cytotoxicité anti-HLA-C2 était limité presque exclusivement à des clones positifs seulement pour 2DS1 (« single positive » 2DS1 clones). Nous avons aussi identifié des clones 2DS1 « single positive » avec réactivité anti-HLA-C2 dans des patients recevant une greffe de cellules souches hématopoïétiques à partir de donneurs 2DS1. Ces résultats montrent que plusieurs cellules NK avec réactivité anti-HLA-C2 sont présentes dans des donneurs 2DS1 soit hétérozygotes soit homozygotes pour HLA-C1. En revanche, les clones 2DS1-positifs obtenus par des donneurs homozygotes pour HLA-C2 sont fréquemment tolérants aux antigènes HLA-C2NK cells are regulated by inhibiting and activating cell surface receptors. Most inhibitory receptors recognize MHC-class I antigens, and protect healthy cells from NK cell-mediated auto-aggression. However, certain activating receptors, including the human killer cell Ig-like receptor (KIR) 2DS1, also recognize MHC-class I. This raises the question of how NK cells expressing such activating receptors are tolerized to host tissues. We investigated whether the presence of HLA-C2, the cognate ligand for 2DS1, induces tolerance in 2DS1-expressing NK cells. Anti-HLA-C2 activity could be detected in vitro in some 2DS1 positive NK clones irrespective of presence or absence of HLA-C2 ligand in the donor. The frequency of anti-HLA-C2 reactivity was high in donors homozygous for HLA-C1. Surprisingly, there was no significant difference in frequency of anti-HLA-C2 cytotoxicity in donors heterozygous for HLA-C2 and donors without HLA-C2 ligand. However, donors homozygous for HLA-C2 had significantly reduced frequency of anti-HLA-C2 reactive clones as compared to all other donors. 2DS1 positive clones that express inhibitory KIR for self-HLA class I were commonly non-cytotoxic, and anti-HLA-C2 cytotoxicity was nearly exclusively restricted to 2DS1 single positive clones lacking inhibitory KIR. 2DS1 single positive NK clones with anti-HLA-C2 reactivity were also present post-transplantation in HLA-C2 positive recipients of hematopoietic stem cell transplants from 2DS1 positive donors. These results demonstrate that many NK cells with anti-HLA-C2 reactivity are present in HLA-C1 homozygous and heterozygous donors with 2DS1. In contrast, 2DS1 positive clones from HLA-C2 homozygous donors are frequently tolerant to HLA-C2
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Maurais, Emilie. "L'incorporation de CD154 par le VIH-1 et son effet sur l'activation des macrophages dérivés de monocytes humains". Thesis, Université Laval, 2008. http://www.theses.ulaval.ca/2008/25648/25648.pdf.
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Le CD154 joue un rôle crucial dans l’activation des cellules présentatrices d’antigènes. Il a été démontré que le CD154 est incorporé à la surface du VIH-1 et que de tels virus activent des lymphocytes B. Nous avons vérifié s’ils ont également la capacité d’activer des macrophages humains. Nous avons observé une augmentation de la production d’IL-8 par les macrophages dérivés de monocytes (MDM), mais celle-ci varie grandement en fonction des différentes productions virales et des donneurs utilisés. L’induction de la sécrétion d’IL-8 est spécifique au CD154 puisqu’une forme mutée ne l’induit pas et est indépendante de la gp120. L’expression des MMP-1 et -2 est influencée par le CD154 sur les cellules 293T, mais l’effet spécifique de CD154 est perdu lorsque des virus sont utilisés. L’ensemble de ces résultats suggère que l’incorporation de CD154 par le virus pourrait être un moyen additionnel d’attirer des cellules cibles au site d’infection et ainsi favoriser la réplication virale.CD154 interacts with CD40 found on antigen-presenting cells such as macrophages and plays a crucial role in activating these cells and initiating immune responses. We have previously reported that CD154 is incorporated within HIV-1 envelope and is effective at activating primary B lymphocytes. In this study, we tested if such CD154-bearing virions are also effective in activating human monocyte-derived-macrophages (MDM). We observed an increase in IL-8 secretion, but it is highly variable depending on viral productions and donors used. The induction of IL-8 production is specific to CD154 since a mutant form does not induce it and is independent of gp120. The production of MMP-1 and -2 is influenced by CD154 on 293T cells but the specificity is lost when viral particles are used. These results suggest a possible way used by the virus to attract target cells to the site of infection and thereby favour its own replication.
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Marcon, Lionel. "Détection électrique d'anticorps sériques humains à l'aide d'un nanocapteur". Lille 1, 2005. https://ori-nuxeo.univ-lille1.fr/nuxeo/site/esupversions/1cfe627c-1fb1-4dac-aa87-bfa288fa6c5c.
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Nous avons réalisé un nouveau type de biocapteur consacré à la détection d'une interaction biomoléculaire via un signal électrique. Le principe du dispositif repose sur l'immobilisation de complexes ligand/récepteur entre des nanoélectrodes puis leur caractérisation par un signal électrique. Nous avons choisi l'interaction modèle entre la protéine A, imprimée sur une surface en silicium, et les immunoglobulines issues du sérum humain elles-mêmes reconnues par un anticorps secondaire marqué par des nanoparticules d'or. La première étape analyse la capacité d'un nanogap à capter des biomolécules spécifiques. Les nanocompartiments doivent être accessibles pour confiner les solutions réactives pendant les traitements. Nous avons vérifié ces propriétés à l'aide de la microscopie à force chimique, de mesures d'angle de contact et des nanoparticules d'or fonctionnelles. L'étape suivante a impliqué la conception de microélectrodes. En raison du microgap, un courant direct n'a pas été détecté. Néanmoins, une précipitation à l'argent, catalysée par les nanoparticules, a court-circuité le gap et permis des changements de conductivité facilement mesurables. Enfin, l'expérience principale a exploité deux nanostructures : un large gap noté A (30 → 280 nanomètres) et un gap étroit B (30 → 90 nanomètres). Dans les deux cas, une variation de conductivité a été observée après incubation de l'anticorps secondaire-or. La géométrie A a révélé un comportement ohmique d'après les courbes intensité-tension (courant multiplié par 50). Inversement, un blocage de Coulomb est apparu via la forme B dans lequel le courant (x 5000) est probablement transmis par tunneling dans les particules métalliques.
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LEPETIT, POURCELOT CHRISTINE. "Mise au point de nouveaux catalyseurs de dimerisation du propylene a base de complexes supportes du nickel : controle de la stabilite et de la selectivite par effet de ligands : influence electronique sterique et mecanistique". Paris 6, 1987. http://www.theses.fr/1987PA066489.
Texto completoLibros sobre el tema "Effet de ligand"
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Parfenov, E. A. Biometals and ligands for anticancer drug design. Commack, N.Y: Nova Science Publishers, 1998.
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Chen, Ko-Ming. Effect of TLR2 ligands and IL-4 on Th2 cutaneous inflammation. [S.l: s.n.], 2013.
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K, Sen Amar y Lee Tyrone, eds. Receptors and ligands in psychiatry. Cambridge [England]: Cambridge University Press, 1988.
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M, Göthert, Molderings Gerhard J y Reis Donald J, eds. Imidazoline receptors and their endogenous ligands: Current concepts and therapeutic potential. New York: New York Academy of Sciences, 1999.
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Hestermann, Eli V. Mechanisms of action for aryl hydrocarbon receptor ligands in the PLHC-1 cell line. Cambridge, Mass: Massachusetts Institute of Technology, 2000.
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Kalthoff, Holger. Death receptors and cognate ligands in cancer. Heidelberg: Springer, 2009.
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J, Reis Donald, Bousquet Pascal, Parini Angelo y International Symposium on Imidazoline Receptors (2nd : 1994 : New York, N.Y.), eds. The imidazoline receptor: Pharmacology, functions, ligands, and relevance to biology and medicine. New York: New York Academy of Sciences, 1995.
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Sutaria, Adil Dinyar. The effect of heterodentate chelatin P-N ligands on allyl and alkyl complexes of palladium and platinum. Salford: University of Salford, 1995.
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1944-, Hindmarch I., Ott H y Collegium Internationale Neuro-psychopharmacologicum Congress, eds. Benzodiazepine receptor ligands, memory, and information processing: Psychometric, psychopharmacological, and clinical issues. Berlin: Springer-Verlag, 1988.
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E, Giesen-Crouse, ed. Peripheral benzodiazepine receptors. London: Academic Press, 1993.
Buscar texto completoCapítulos de libros sobre el tema "Effet de ligand"
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Onishi, Taku. "Ligand Bonding Effect". En Quantum Computational Chemistry, 187–97. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-5933-9_11.
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Pawar, Prasad V., Abraham J. Domb y Neeraj Kumar. "Systemic Targeting Systems-EPR Effect, Ligand Targeting Systems". En Advances in Delivery Science and Technology, 61–91. Boston, MA: Springer US, 2013. http://dx.doi.org/10.1007/978-1-4614-9434-8_3.
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Lucki, I. y K. Rickels. "The Effect of Anxiolytic Drugs on Memory in Anxious Subjects". En Benzodiazepine Receptor Ligands, Memory and Information Processing, 128–39. Berlin, Heidelberg: Springer Berlin Heidelberg, 1988. http://dx.doi.org/10.1007/978-3-642-73288-1_9.
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Yamamoto, Akira, Masaki Fujimura, Masamitu Hirano, Masashi Suwo y Atsumi Mori. "Effect of Laminin Receptor Ligands on Peritoneal Metastasis". En Recent Advances in Management of Digestive Cancers, 419–21. Tokyo: Springer Japan, 1993. http://dx.doi.org/10.1007/978-4-431-68252-3_115.
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Luo, Zhixun y Shiv N. Khanna. "Cluster Dissociation, Intracluster Reactivity and Effect of the Ligands". En Metal Clusters and Their Reactivity, 175–91. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-9704-6_11.
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Darkhovskiy, Mikhail. "Effect of Conformational Entropy on Affinity of Specific Ligands". En Molecular Recognition in Pharmacology, 83–90. Boca Raton: CRC Press, 2023. http://dx.doi.org/10.1201/9781003366669-6.
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Yamashita, Kanae. "Synergistic Effect of Sesame Lignans and Tocopherols". En Food and Free Radicals, 101–12. Boston, MA: Springer US, 1997. http://dx.doi.org/10.1007/978-1-4899-1837-6_9.
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Hasegawa, Miki y Yasuchika Hasegawa. "Triboluminescence of Lanthanide Complexes". En The Materials Research Society Series, 105–30. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-0260-6_7.
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AbstractThe photoluminescence of lanthanide complexes originating from f–f transitions is generally sensitized through energy transfer from the ligand to the lanthanide ion in the excited state under UV irradiation. This phenomenon is known as the photo-antenna effect. Luminescence driven by mechanical stimuli, such as tapping or rubbing, is called mechanoluminescence or triboluminescence (TL). In recent years, reports on TL in rare-earth complexes, which have attracted attention as novel luminescent materials that do not require an electrical excitation source, have steadily increased. In this chapter, we focus on triboluminescent lanthanide complexes. Specifically, we introduce the history and detection methods of TL and cite recent examples of materials demonstrating this phenomenon, particularly coordination polymer-like and discrete molecular crystalline lanthanide complexes. Finally, we summarize the application prospects of these complexes as soft crystals.
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Järv, Jaak. "A Novel Strategy of Effect-Directed Ligand Design for G-Protein Coupled Receptors". En Neurochemistry, 791–96. Boston, MA: Springer US, 1997. http://dx.doi.org/10.1007/978-1-4615-5405-9_130.
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Blackler, M. J., C. W. Wharton y M. P. Weir. "The Effect of Ligand Binding on the FTIR Spectra of Serine Proteinase Enzymes". En Spectroscopy of Biological Molecules, 155–56. Dordrecht: Springer Netherlands, 1995. http://dx.doi.org/10.1007/978-94-011-0371-8_71.
Texto completoActas de conferencias sobre el tema "Effet de ligand"
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Dzichenka, Yaraslau, Michail Shapira, Sergei Usanov, Marina Savić, Ljubica Grbović, Jovana Ajduković y Suzana Jovanović-Šanta. "NOVEL LIGANDS OF HUMAN CYP7 ENZYMES – POSSIBLE MODULATORS OF CHOLESTEROL BLOOD LEVEL: COMPUTER SIMULATION STUDIES". En 1st INTERNATIONAL Conference on Chemo and BioInformatics. Institute for Information Technologies, University of Kragujevac, 2021. http://dx.doi.org/10.46793/iccbi21.435d.
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Our in vitro studies showed that a couple of perspective steroidal derivatives showed previously biomedical potential via enzyme inhibition, receptor binding or antiproliferative effect against the cancer cells of reproductive tissues are able to bind to human CYP7 enzymes – key enzymes taking part in hydroxylation of cholesterol, 25-, 27-hydroxycholesterol and a number of steroidal hormones. In silico screening of binding affinity of the modified steroids toward CYP7 enzymes showed that interaction energy for the new ligands is comparable with consequent values, calculated for the ‘essential’ substrates of the enzymes – cholestenone (CYP7A1) and DHEA (CYP7B1). However, no correlation between binding energy and the affinity of the ligand was found. Novel ligands interact with conserved amino acids taking part in stabilization of natural substrates of CYP7 enzymes. A couple of structural features, governing ligand binding, were identified. Among which are planar structure of A-ring for CYP7A1 ligands, absence of many polar fragments in side-chain and presence of polar group at C3 position. Analysis of the docking results showed that CYP7B1 higher selectivity in comparison with CYP7A1 is connected by the structure of the cavity formed by α-helices I and B`. The data obtained will be used for the explanation of ligand specificity of human sterol- hydroxylases.
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Xu, Hua, Jeffery C. C. Lo, Xing Qiu, Yuanjie Cheng, Mian Tao, S. W. Ricky Lee, Lawrence C. L. Ko, Ho Ki Yeung y Chun Ho Yau. "Effect of Sintering Conditions on Electrical Resistivity of Printed Silver Inks". En ASME 2023 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/ipack2023-111648.
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Abstract Thermal sintering is a simple, cost-effective, and high-throughput option for printed silver inks with nanoparticles. Low-temperature sintering processes are necessary for printed electronics to accommodate substrates or polymer components that cannot withstand high temperatures. However, it is difficult to reach a low level resistivity with printed silver nanoparticles sintered at low temperatures. This study focused on the effect of solvent evaporation during the sintering process and the effect of ligands on the resistivity of the final product. The present investigation used commercial silver ink due to its excellent properties such as low cracking, high uniformity, and good adhesion to the substrate. The solvent was a mixture of propylene glycol monomethyl ether and diethylene glycol monomethyl ether. Thermal gravimetric analysis and differential scanning calorimetry were used to characterize the temperatures of solvent evaporation and ligand decomposition. The resistivities of the sintered silver inks were measured. The study found that preheating was effective in helping achieve lower resistivity and that the removal of ligands could further decrease the resistivity by about 20%.
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Jomeh, Sina y Mina Hoorfar. "Numerical Investigation of the Effect of Geometric and Physiochemical Parameters on Biomolecule Capture Efficiency". En ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels collocated with 3rd Joint US-European Fluids Engineering Summer Meeting. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30531.
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This paper presents and compares three different designs including open channel, circular pillar and screen-plate microreactors for capturing and detection of biomolecules in a buffer liquid. In general, these capturing/detection devices consist of a flow cell containing one or several reactive surfaces loaded with ligand molecules. The critical issue in the design of an efficient device is the proximity of the biomolecules to the ligands in the capturing stage since the latter is immobilized on the reactive surface and the former is freely moving in the flow. The flow pattern and the geometry of the device are the key factors in this regard. The presented designs are numerically modeled and compared in terms of capture efficiency. Immersed biomolecules are assumed to behave like a continuum medium. The Navier-Stokes and advection-diffusion equations are solved in two dimensions and the concentration profile is found after a certain sampling period. The chemical reaction between the ligand and the biomolecule is included in the model through solving the first order kinetic equation at the boundaries. The average surface concentrations of the adsorbed molecules are plotted and compared for all the geometries to determine the most efficient one. Considering the performance, ease of fabrication, and detection, the screen plates are found to be the best option for the purpose of biomolecule removal. The effects of the change in the geometric parameters (e.g., the flow path width in the microchannels) and physicochemical parameters (e.g., the diffusion constant, ligand surface density, and forward and backward reaction rates) involved in the problem on the adsorbed concentration are thoroughly inspected and the corresponding results are plotted.
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Xu, Chao, Yu Du, Tingting Liu y Suliang Yang. "Extraction of Nd(III), Eu(III), Am(III) and Cm(III) With 6-Carboxylic Di(2-Ethylhexyl) Amide Pyridine". En 2022 29th International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/icone29-90818.
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Abstract Solvent extraction has been widely used in spent fuel reprocessing because of its advantages such as high mass transfer rate, short production cycle, easy operation and large extraction capacity. The ligands containing soft S and N atoms usually have a good effect on the separation of trivalent lanthanides actinides. Herein, a novel extractant, 6-carboxylic di(2-ethylhexyl) amide pyridine (DEHAPA, HA), containing carboxyl and amide pyridine, was designed. The extraction of Nd(III), Eu(III), Am(III) and Cm(III), representing trivalent lanthanides and actinides, from nitric solution has been carried out by DEHAPA diluted in toluene as the organic phase. According to the slope analysis, the results show that the extraction of Ln(III) and An(III) with DEHAPA was governed by ion-exchange mechanism and the extraction equilibrium constants of Nd(III), Eu(III), Am(III) and Cm(III) have been calculated. The effect of concentration indicated that the structure of extraction complexes are 1:3/LnA3 and 1:3/AnA3. The temperature has a slight influence to distribution ratio of extraction Nd(III) and Eu(III). The infrared spectrum of DEHAPA and extracted complex analysis showed that -N-C = O and -O-C = O group coordinated with Nd(III). According to 1:3/LnA3 extracted complex structure, the Nd(III) ion in complex was coordinated with three -N-C = O, -O-C = O and pyridine group from three tridentate A− ligands by three tridentate A− ligand in organic solvent. This work reveals the unique extraction and coordination structure and provides a value reference to design more effective extraction ligands for Ln(III)/An(III) separation.
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Kesić, Ana S., Snežana Radisavljević y Biljana V. Petrović. "SUBSTITUTION REACTIONS OF THE MONOFUNCTIONAL GOLD(III) COMPLEX AND SULPHUR-DONOR BIOLOGICALLY IMPORTANT LIGANDS". En 1st INTERNATIONAL Conference on Chemo and BioInformatics. Institute for Information Technologies, University of Kragujevac, 2021. http://dx.doi.org/10.46793/iccbi21.391k.
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Gold(III) complexes have found application in catalysis, materials science and medical inorganic chemistry. Considering that the right choice of inert ligands in the structure of Au(III) complexes is crucial for their properties and reactivity toward biomolecules, we have studied the substitution reactions between monofunctional Au(III) complex, [Au(Cl-Ph-tpy)Cl]Cl2 (Cl- Ph-tpy = 4′-(4-chlorophenyl)-2,2′:6′, 2″-terpyridine) and sulfur-donor biomolecules, glutathione (GSH) and L-methionine (L-Met), in 25 mM Hepes buffer (pH = 7.2) and 40 mM NaCl. The reactions were followed under the pseudo-first-order conditions as a function of ligand concentration and temperature, using the stopped-flow technique. Calculations were made by Microsoft Excel 2019 and Origin2019b 64Bit. Observed kinetics traces follow a single exponential function, suggesting that the process of the substitution undergoes as one reversible step. Also, L-Met was more reactive than GSH. This order is related to the positive inductive effect of the methyl group, which increases the nucleophilicity of the thioether. According to the values of the activation parameters, the reactions follow an associative model. These results demonstrate the strong connection between the reactivity of Au(III) complexes and the structural and electronic characteristics of the biologically important ligands.
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Sigurdson, M., C. Meinhart, D. Wang, X. Liu, J. J. Feng, S. Krishnamoorthy y S. Sundaram. "AC Electrokinetics for Microfluidic Immunosensors". En ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41442.
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A technique is proposed to enhance microfluidic immuno-sensors, specifically, sensors in which a ligand immobilized within a microchannel binds analyte flowing through the channel for the purpose of detection of that analyte. These sensors can be limited in both response time and sensitivity by the diffusion of analyte to the sensing surface. The sensitivity and response of these heterogeneous immunoassays may be improved by using AC electrokinetically-driven microscale fluid motion to enhance antigen motion towards immobilized ligands. Specifically, electrothermal effects can produce swirling flow patterns that carry sample past the binding surface. Numerical simulations of antigen in a microchannel flow subjected to the electrothermal effect suggest that 14 V rms applied to electrodes strategically placed opposite a narrow binding region can increase binding in the first few minutes by a factor of five. Optimization of the electrode geometry and placement can render this technique useful for a large variety of microfluidic sensors.
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Pathak, Amit, Vikram S. Deshpande, Robert M. McMeeking y Anthony G. Evans. "Simulation of the Coupling of Cell Contractility and Focal Adhesion Formation". En ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176108.
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The remodeling of the cytoskeleton and focal adhesion distributions for cells on substrates with micro-patterned ligand patches is investigated using a bio-chemo-mechanical model. All the cells have approximately the same area and we investigate the effect of ligand pattern shape on the cytoskeletal arrangements and focal adhesion distributions. The model for the cytoskeleton accounts for the dynamic rearrangement of the actin/myosin stress fibers and entails the highly non-linear interactions between signaling, the kinetics of tension-dependent stress-fiber formation/dissolution and stress dependent contractility. This model is coupled with a focal adhesion (FA) model that accounts for the mechano-sensitivity of the adhesions from thermodynamic considerations. This coupled stress fiber and focal adhesion model is shown to capture a variety of key experimental observations including: (i) the formation of high stress fiber and focal adhesion concentrations at the periphery of circular and triangular, convex–shaped ligand patterns; (ii) the development of high focal adhesion concentrations along the edges of the V, T, Y and U shaped concave ligand patterns; and (iii) the formation of highly aligned stress fibers along the un-adhered edges of cells on the concave ligand patterns. When appropriately calibrated, the model also accurately predicts the radii of curvature of the un-adhered edges of cells on the concave-shaped ligand patterns.
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Sarvestani, Alireza. "A Theoretical Analysis for the Effect of Substrate Elasticity on Cellular Adhesion". En ASME 2010 First Global Congress on NanoEngineering for Medicine and Biology. ASMEDC, 2010. http://dx.doi.org/10.1115/nemb2010-13311.
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Cell behavior is mediated by variety of physiochemical properties of extracellular matrix (ECM). Material composition, surface chemistry, roughness, and distribution pattern of cell adhesive proteins are among the ECM properties which are known to modulate various cellular physiological functions. Mechanical stiffness of ECM in particular is found to be a major regulator for multiple aspects of cellular function. Experiments show that cells in general, exhibit an apparent adhesion preference for stiffer substrates with a larger projected spread area with increasing the substrate stiffness. In addition, it seems that the effect of substrates elasticity is strongly coupled with adhesivity of the substrate; on relatively stiff substrates the spread area of the cells exhibits strong biphasic dependence to the changes in ligand density, whereas on soft substrates their limited spreading is much less sensitive to the density of surface ligands. This study aims to propose a theoretical basis for the interplay between substrate elasticity and cellular adhesion, using an equilibrium thermodynamic model. Within this framework, the equilibrium contact area is assumed to ensure minimization of the free energy contributed by interfacial adhesive and repulsive interactions between the membrane and substrate as well as the deformation of cell and substrate. Hence, this thermodynamic model overlooks the contribution of intracellular signaling or actively regulated cytoskeleton and assumes that cell adhesion is solely a result of the balance between the membrane-substrate repulsive potentials, stored elastic energy, binding enthalpy, and mixing entropy of mobile receptors. The predictions of this purely mechanistic model for cell adhesion qualitatively follow the experimental results featuring the variation of cell spread area on compliant bio-adhesive substrates. This suggests that the mechanistic pathways inherent to membrane-substrate interactions may be equally important as intracellular signaling pathways to mediate the cellular adhesion.
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Peterson, Steven H., Edward J. Lahoda y John F. Jackovitz. "Isotope effect in photochemical ligand exchange of zirconium complexes". En Conference on Lasers and Electro-Optics. Washington, D.C.: OSA, 1986. http://dx.doi.org/10.1364/cleo.1986.tui3.
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Radovanović, Marko D., Ignjat Filipović, Maja Djukić, Marija Ristić, Matija Zlatar y Zoran D. Matović. "Relativistic DFT calculation and their effect on the accuracy of results". En 2nd International Conference on Chemo and Bioinformatics. Institute for Information Technologies, University of Kragujevac, 2023. http://dx.doi.org/10.46793/iccbi23.653r.
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This study explores the significance of density functional theory (DFT) calculations with relativistic effects for two ethylenediaminetetraacetate (edta) type complexes: trans(O5)-[M(eddadp)]- (M = Rh3+, Co3+). Relativistic effects affect the electronic structure of a molecule and, thus, its chemical and spectroscopic properties. With the use of scalar relativistic corrections (SR-ZORA), as implemented in the ADF package, with the B3LYP functional, the TZP basis set and the COSMO solvation model, structural analyses show improved predictions for the geometries of both complexes. In the case of the Rh3+ complex, the differences in metal-ligand bond lengths with and without the relativistic effects were small. In the case of the Co3+ complex, the changes in metal-ligand bond lengths due to the relativistic effects were slightly more pronounced. Compared to experimental values, excitation energies are better when including relativistic corrections, especially for the Rh3+ complex. These results indicate the importance of relativistic DFT calculations for heavy element compounds.
Informes sobre el tema "Effet de ligand"
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Rafaeli, Ada y Russell Jurenka. Molecular Characterization of PBAN G-protein Coupled Receptors in Moth Pest Species: Design of Antagonists. United States Department of Agriculture, diciembre de 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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Liang, Feixin. Effect of reactive oxygen species on the ligand-independent activation of EGFR in tongue squamous cell carcinoma. Science Repository, junio de 2018. http://dx.doi.org/10.31487/j.dobcr.2018.02.005.
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Scott A. Wood. The Effect of Organic Ligands on the Sorption of Neodymium, Gadolinium and Uranium onto Nontronite and Goethite. Office of Scientific and Technical Information (OSTI), junio de 2007. http://dx.doi.org/10.2172/908643.
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Altstein, Miriam y Ronald J. Nachman. Rational Design of Insect Control Agent Prototypes Based on Pyrokinin/PBAN Neuropeptide Antagonists. United States Department of Agriculture, agosto de 2013. http://dx.doi.org/10.32747/2013.7593398.bard.
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The general objective of this study was to develop rationally designed mimetic antagonists (and agonists) of the PK/PBAN Np class with enhanced bio-stability and bioavailability as prototypes for effective and environmentally friendly pest insect management agents. The PK/PBAN family is a multifunctional group of Nps that mediates key functions in insects (sex pheromone biosynthesis, cuticular melanization, myotropic activity, diapause and pupal development) and is, therefore, of high scientific and applied interest. The objectives of the current study were: (i) to identify an antagonist biophores (ii) to develop an arsenal of amphiphilic topically active PK/PBAN antagonists with an array of different time-release profiles based on the previously developed prototype analog; (iii) to develop rationally designed non-peptide SMLs based on the antagonist biophore determined in (i) and evaluate them in cloned receptor microplate binding assays and by pheromonotropic, melanotropic and pupariation in vivo assays. (iv) to clone PK/PBAN receptors (PK/PBAN-Rs) for further understanding of receptor-ligand interactions; (v) to develop microplate binding assays for screening the above SMLs. In the course of the granting period A series of amphiphilic PK/PBAN analogs based on a linear lead antagonist from the previous BARD grant was synthesized that incorporated a diverse array of hydrophobic groups (HR-Suc-A[dF]PRLa). Others were synthesized via the attachment of polyethylene glycol (PEG) polymers. A hydrophobic, biostablePK/PBAN/DH analog DH-2Abf-K prevented the onset of the protective state of diapause in H. zea pupae [EC50=7 pmol/larva] following injection into the preceding larval stage. It effectively induces the crop pest to commit a form of ‘ecological suicide’. Evaluation of a set of amphiphilic PK analogs with a diverse array of hydrophobic groups of the formula HR-Suc-FTPRLa led to the identification of analog T-63 (HR=Decyl) that increased the extent of diapause termination by a factor of 70% when applied topically to newly emerged pupae. Another biostablePK analog PK-Oic-1 featured anti-feedant and aphicidal properties that matched the potency of some commercial aphicides. Native PK showed no significant activity. The aphicidal effects were blocked by a new PEGylated PK antagonist analog PK-dF-PEG4, suggesting that the activity is mediated by a PK/PBAN receptor and therefore indicative of a novel and selective mode-of-action. Using a novel transPro mimetic motif (dihydroimidazole; ‘Jones’) developed in previous BARD-sponsored work, the first antagonist for the diapause hormone (DH), DH-Jo, was developed and shown to block over 50% of H. zea pupal diapause termination activity of native DH. This novel antagonist development strategy may be applicable to other invertebrate and vertebrate hormones that feature a transPro in the active core. The research identifies a critical component of the antagonist biophore for this PK/PBAN receptor subtype, i.e. a trans-oriented Pro. Additional work led to the molecular cloning and functional characterization of the DH receptor from H. zea, allowing for the discovery of three other DH antagonist analogs: Drosophila ETH, a β-AA analog, and a dF analog. The receptor experiments identified an agonist (DH-2Abf-dA) with a maximal response greater than native DH. ‘Deconvolution’ of a rationally-designed nonpeptide heterocyclic combinatorial library with a cyclic bis-guanidino (BG) scaffold led to discovery of several members that elicited activity in a pupariation acceleration assay, and one that also showed activity in an H. zea diapause termination assay, eliciting a maximal response of 90%. Molecular cloning and functional characterization of a CAP2b antidiuretic receptor from the kissing bug (R. prolixus) as well as the first CAP2b and PK receptors from a tick was also achieved. Notably, the PK/PBAN-like receptor from the cattle fever tick is unique among known PK/PBAN and CAP2b receptors in that it can interact with both ligand types, providing further evidence for an evolutionary relationship between these two NP families. In the course of the granting period we also managed to clone the PK/PBAN-R of H. peltigera, to express it and the S. littoralis-R Sf-9 cells and to evaluate their interaction with a variety of PK/PBAN ligands. In addition, three functional microplate assays in a HTS format have been developed: a cell-membrane competitive ligand binding assay; a Ca flux assay and a whole cell cAMP ELISA. The Ca flux assay has been used for receptor characterization due to its extremely high sensitivity. Computer homology studies were carried out to predict both receptor’s SAR and based on this analysis 8 mutants have been generated. The bioavailability of small linear antagonistic peptides has been evaluated and was found to be highly effective as sex pheromone biosynthesis inhibitors. The activity of 11 new amphiphilic analogs has also been evaluated. Unfortunately, due to a problem with the Heliothis moth colony we were unable to select those with pheromonotropic antagonistic activity and further check their bioavailability. Six peptides exhibited some melanotropic antagonistic activity but due to the low inhibitory effect the peptides were not further tested for bioavailability in S. littoralis larvae. Despite the fact that no new antagonistic peptides were discovered in the course of this granting period the results contribute to a better understanding of the interaction of the PK/PBAN family of Nps with their receptors, provided several HT assays for screening of libraries of various origin for presence of PK/PBAN-Ragonists and antagonists and provided important practical information for the further design of new, peptide-based insecticide prototypes aimed at the disruption of key neuroendocrine physiological functions in pest insects.
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Yang, Nacy Y. C. Effect of Substrate Configuration on the Grain Structure and Morphology of Electrodeposited Ni for Prototyping LIGA. Office of Scientific and Technical Information (OSTI), julio de 2002. http://dx.doi.org/10.2172/797427.
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Eyal, Yoram y Sheila McCormick. Molecular Mechanisms of Pollen-Pistil Interactions in Interspecific Crossing Barriers in the Tomato Family. United States Department of Agriculture, mayo de 2000. http://dx.doi.org/10.32747/2000.7573076.bard.
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During the evolutionary process of speciation in plants, naturally occurring barriers to reproduction have developed that affect the transfer of genes within and between related species. These barriers can occur at several different levels beginning with pollination-barriers and ending with hybrid-breakdown. The interaction between pollen and pistils presents one of the major barriers to intra- and inter-specific crosses and is the focus of this research project. Our long-term goal in this research proposal was defined to resolve questions on recognition and communication during pollen-pistil interactions in the extended tomato family. In this context, this work was initiated and planned to study the potential involvement of tomato pollen-specific receptor-like kinases (RLK's) in the interaction between pollen and pistils. By special permission from BARD the objectives of this research were extended to include studies on pollen-pistil interactions and pollination barriers in horticultural crops with an emphasis on citrus. Functional characterization of 2 pollen-specific RLK's from tomato was carried out. The data shows that both encode functional kinases that were active as recombinant proteins. One of the kinases was shown to accumulate mainly after pollen germination and to be phosphorylated in-vitro in pollen membranes as well as in-vivo. The presence of style extract resulted in dephosphorylation of the RLK, although no species specificity was observed. This data implies a role for at least one RLK in pollination events following pollen germination. However, a transgenic plant analysis of the RLK's comprising overexpression, dominant-negative and anti-sense constructs failed to provide answers on their role in pollination. While genetic effects on some of the plants were observed in both the Israeli and American labs, no clear functional answers were obtained. An alternative approach to addressing function was pursued by screening for an artificial ligand for the receptor domain using a peptide phage display library. An enriched peptide sequence was obtained and will be used to design a peptide-ligand to be tested for its effect o pollen germination and tube growth. Self-incompatibility (SI) in citrus was studied on 3 varieties of pummelo. SI was observed using fluorescence microscopy in each of the 3 varieties and compatibility relations between varieties was determined. An initial screen for an S-RNase SI mechanism yielded only a cDNA homologous to the group of S-like RNases, suggesting that SI results from an as yet unknown mechanism. 2D gel electrophoresis was applied to compare pollen and style profiles of different compatibility groups. A "polymorphic" protein band from style extracts was observed, isolated and micro-sequenced. Degenerate primers designed based on the peptide sequence date will be used to isolate the relevant genes i order to study their potential involvement in SI. A study on SI in the apple cultivar Top red was initiated. SI was found, as previously shown, to be complete thus requiring a compatible pollinator variety. A new S-RNase allele was discovered fro Top red styles and was found to be highly homologous to pear S-RNases, suggesting that evolution of these genes pre-dated speciation into apples and pears but not to other Rosaceae species. The new allele provides molecular-genetic tools to determine potential pollinators for the variety Top red as well as a tool to break-down SI in this important variety.
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Amine, Razan y Fabrizio Santoro. Rendre obligatoires les outils fiscaux numériques en réponse à la Covid : l’exemple d’Eswatini. Institute of Development Studies, abril de 2023. http://dx.doi.org/10.19088/ictd.2023.020.
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Afin de réduire les contacts physiques, la Covid-19 a contraint de nombreuses administrations fiscales à adopter les technologies numériques pour les déclarations fiscales et les paiements d’impôts. Au-delà de la lutte contre la pandémie, la déclaration et le paiement électroniques sont très prometteurs pour faciliter le respect des obligations fiscales, accroître la transparence et réduire les possibilités de collusion (Okunogbe et Santoro, 2021). Eswatini a rendu obligatoire la déclaration électronique pour tous les contribuables à partir de septembre 2020, par le biais de la plateforme d’impôt en ligne (e-Tax). Par la suite, l’administration fiscale a lancé, en avril 2021, une politique visant à éliminer les opérations en espèces pour les paiements d’impôts. Notre étude a évalué l’impact de l’obligation de déclaration électronique sur le comportement des contribuables en matière de déclaration et de paiement, en examinant les questions suivantes : (i) quel est l’impact de l’obligation de déclaration électronique sur la conformité en matière de déclaration et de paiement ? (ii) existe-t-il des effets d’entraînement sur l’exactitude des déclarations et des paiements ? (iii) quels sont les principaux mécanismes qui expliquent les résultats ? Résumé du document de travail 140 par Fabrizio Santoro, Razan Amine et Tanele Magongo.
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Epel, Bernard y Roger Beachy. Mechanisms of intra- and intercellular targeting and movement of tobacco mosaic virus. United States Department of Agriculture, noviembre de 2005. http://dx.doi.org/10.32747/2005.7695874.bard.
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To cause disease, plant viruses must replicate and spread locally and systemically within the host. Cell-to-cell virus spread is mediated by virus-encoded movement proteins (MPs), which modify the structure and function of plasmodesmata (Pd), trans-wall co-axial membranous tunnels that interconnect the cytoplasm of neighboring cells. Tobacco mosaic virus (TMV) employ a single MP for cell- cell spread and for which CP is not required. The PIs, Beachy (USA) and Epel (Israel) and co-workers, developed new tools and approaches for study of the mechanism of spread of TMV that lead to a partial identification and molecular characterization of the cellular machinery involved in the trafficking process. Original research objectives: Based on our data and those of others, we proposed a working model of plant viral spread. Our model stated that MPᵀᴹⱽ, an integral ER membrane protein with its C-terminus exposed to the cytoplasm (Reichel and Beachy, 1998), alters the Pd SEL, causes the Pd cytoplasmic annulus to dilate (Wolf et al., 1989), allowing ER to glide through Pd and that this gliding is cytoskeleton mediated. The model claimed that in absence of MP, the ER in Pd (the desmotubule) is stationary, i.e. does not move through the Pd. Based on this model we designed a series of experiments to test the following questions: -Does MP potentiate ER movement through the Pd? - In the presence of MP, is there communication between adjacent cells via ER lumen? -Does MP potentiate the movement of cytoskeletal elements cell to cell? -Is MP required for cell-to-cell movement of ER membranes between cells in sink tissue? -Is the binding in situ of MP to RNA specific to vRNA sequences or is it nonspecific as measured in vitro? And if specific: -What sequences of RNA are involved in binding to MP? And finally, what host proteins are associated with MP during intracellular targeting to various subcellular targets and what if any post-translational modifications occur to MP, other than phosphorylation (Kawakami et al., 1999)? Major conclusions, solutions and achievements. A new quantitative tool was developed to measure the "coefficient of conductivity" of Pd to cytoplasmic soluble proteins. Employing this tool, we measured changes in Pd conductivity in epidermal cells of sink and source leaves of wild-type and transgenic Nicotiana benthamiana (N. benthamiana) plants expressing MPᵀᴹⱽ incubated both in dark and light and at 16 and 25 ᵒC (Liarzi and Epel, 2005 (appendix 1). To test our model we measured the effect of the presence of MP on cell-to-cell spread of a cytoplasmic fluorescent probe, of two ER intrinsic membrane protein-probes and two ER lumen protein-probes fused to GFP. The effect of a mutant virus that is incapable of cell-to-cell spread on the spread of these probes was also determined. Our data shows that MP reduces SEL for cytoplasmic molecules, dilates the desmotubule allowing cell-cell diffusion of proteins via the desmotubule lumen and reduces the rate of spread of the ER membrane probes. Replicase was shown to enhance cell-cell spread. The data are not in support of the proposed model and have led us to propose a new model for virus cell-cell spread: this model proposes that MP, an integral ER membrane protein, forms a MP:vRNAER complex and that this ER-membrane complex diffuses in the lipid milieu of the ER into the desmotubule (the ER within the Pd), and spreads cell to cell by simple diffusion in the ER/desmotubule membrane; the driving force for spread is the chemical potential gradient between an infected cell and contingent non-infected neighbors. Our data also suggests that the virus replicase has a function in altering the Pd conductivity. Transgenic plant lines that express the MP gene of the Cg tobamovirus fused to YFP under the control the ecdysone receptor and methoxyfenocide ligand were generated by the Beachy group and the expression pattern and the timing and targeting patterns were determined. A vector expressing this MPs was also developed for use by the Epel lab . The transgenic lines are being used to identify and isolate host genes that are required for cell-to-cell movement of TMV/tobamoviruses. This line is now being grown and to be employed in proteomic studies which will commence November 2005. T-DNA insertion mutagenesis is being developed to identify and isolate host genes required for cell-to-cell movement of TMV.
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Gruber, Verena, Ingrid Peignier y Elinora Pentcheva. Analyse des motivations d’achat de camions légers au Québec. CIRANO, febrero de 2023. http://dx.doi.org/10.54932/kzyi1849.
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Le présent rapport s’inscrit dans la continuité d’une vaste étude débutée en 2020 afin de mieux comprendre la préférence croissante de la population canadienne pour les véhicules énergivores ainsi que les facteurs (politiques, économiques, sociaux, etc.) qui contribuent à l’augmentation des ventes de ce type de véhicules. Le CIRANO a déjà participé à cette étude en publiant deux rapports de projet en 2021 et ce nouveau rapport traite plus en détail de la situation au Québec, avec une attention particulière portée sur les habitudes d’utilisation des véhicules. Pour ce faire, une étude empirique a été menée auprès d’un échantillon représentatif de 1 020 Québécois(es) propriétaires d’un véhicule à l’aide d’un questionnaire en ligne administré en juillet 2022. L’enquête par questionnaire a fait ressortir quatre aspects majeurs qui influencent l’intention d’acheter un véhicule de type VUS : les caractéristiques du véhicule (comme l’importance accordée à une position de conduite élevée et à une transmission à quatre roues motrices), les aspects démographiques (comme le fait de vivre dans une région rurale et d’avoir un revenu familial plus élevé) et les facteurs psychologiques (comme l’importance des valeurs hédoniques et égoïstes). Mais c’est surtout la nature du véhicule principal qui est la variable qui se distingue avec le plus grand effet (β = 0,451) sur l’intention d’achat de VUS. Ainsi, conformément aux résultats de 2020, le facteur le plus important pour expliquer l’intention d’achat futur d’un VUS est la possession préalable d’un VUS. 67 % des propriétaires de VUS ont affirmé qu’il était extrêmement probable ou très probable qu’ils achètent un VUS comme prochain véhicule contre seulement 24 % des propriétaires de berline. Ces résultats renforcent la conclusion que le fait de posséder un VUS est le meilleur prédicteur d’une haute intention d’achat de VUS pour le prochain véhicule et souligne l’importance des interventions visant les premiers acheteurs et les premières acheteuses. Les résultats de l’enquête suggèrent également que la réduction de la possession de voiture parmi les propriétaires sera fortement difficile, puisque ceux-ci considèrent leur véhicule comme indispensable, et ce quel que soit le type de véhicule possédé, quoique les propriétaires de berlines soient néanmoins significativement les moins nombreux à considérer leur véhicule comme indispensable. Bien que les répondant(e)s considèrent généralement leur véhicule comme indispensable, ils ou elles ne l’utilisent guère au maximum de sa capacité, ni en ce qui concerne les sièges du véhicule ni en ce qui concerne l’espace de rangement. En moyenne, 35 % des répondant(e)s indiquent qu’au moins 3 places de leur véhicule sur 5 sont occupées au moins une fois par semaine. La plus grande part affirme toutefois que cela n’arrive que quelques fois par année (40,1 %), voire jamais pour 13,6 % des répondant(e)s. Les mêmes ordres de grandeur sont observés en ce qui concerne l’utilisation de l’espace de chargement. En revanche, les conducteur(trice)s de VUS sont significativement plus nombreux que les conducteur(trice)s de berline à utiliser fréquemment la majorité des sièges de l’habitacle ainsi que la pleine capacité du coffre. Pourtant, lorsque l’on contrôle pour d’autres variables sociodémographiques, le type de véhicule conduit n’est généralement pas un facteur explicatif de la fréquence d’utilisation de la pleine capacité de notre véhicule, que l’on parle de sièges ou du coffre, mais c’est plutôt le fait d’avoir des enfants qui est la variable avec le plus grand pouvoir explicatif.
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Droby, Samir, Michael Wisniewski, Ron Porat y Dumitru Macarisin. Role of Reactive Oxygen Species (ROS) in Tritrophic Interactions in Postharvest Biocontrol Systems. United States Department of Agriculture, diciembre de 2012. http://dx.doi.org/10.32747/2012.7594390.bard.
Texto completoResumen
To elucidate the role of ROS in the tri-trophic interactions in postharvest biocontrol systems a detailed molecular and biochemical investigation was undertaken. The application of the yeast biocontrol agent Metschnikowia fructicola, microarray analysis was performed on grapefruit surface wounds using an Affymetrix Citrus GeneChip. the data indicated that 1007 putative unigenes showed significant expression changes following wounding and yeast application relative to wounded controls. The expression of the genes encoding Respiratory burst oxidase (Rbo), mitogen-activated protein kinase (MAPK) and mitogen-activated protein kinase kinase (MAPKK), G-proteins, chitinase (CHI), phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and 4-coumarate-CoA ligase (4CL). In contrast, three genes, peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), were down-regulated in grapefruit peel tissue treated with yeast cells. The yeast antagonists, Metschnikowia fructicola (strain 277) and Candida oleophila (strain 182) generate relatively high levels of super oxide anion (O2−) following its interaction with wounded fruit surface. Using laser scanning confocal microscopy we observed that the application of M. fructicola and C. oleophila into citrus and apple fruit wounds correlated with an increase in H2O2 accumulation in host tissue. The present data, together with our earlier discovery of the importance of H₂O₂ production in the defense response of citrus flavedo to postharvest pathogens, indicate that the yeast-induced oxidative response in fruit exocarp may be associated with the ability of specific yeast species to serve as biocontrol agents for the management of postharvest diseases. Effect of ROS on yeast cells was also studied. Pretreatment of the yeast, Candida oleophila, with 5 mM H₂O₂ for 30 min (sublethal) increased yeast tolerance to subsequent lethal levels of oxidative stress (50 mM H₂O₂), high temperature (40 °C), and low pH (pH 4). Suppression subtractive hybridization analysis was used to identify genes expressed in yeast in response to sublethal oxidative stress. Transcript levels were confirmed using semi quantitative reverse transcription-PCR. Seven antioxidant genes were up regulated. Pretreatment of the yeast antagonist Candida oleophila with glycine betaine (GB) increases oxidative stress tolerance in the microenvironment of apple wounds. ROS production is greater when yeast antagonists used as biocontrol agents are applied in the wounds. Compared to untreated control yeast cells, GB-treated cells recovered from the oxidative stress environment of apple wounds exhibited less accumulation of ROS and lower levels of oxidative damage to cellular proteins and lipids. Additionally, GB-treated yeast exhibited greater biocontrol activity against Penicillium expansum and Botrytis cinerea, and faster growth in wounds of apple fruits compared to untreated yeast. The expression of major antioxidant genes, including peroxisomal catalase, peroxiredoxin TSA1, and glutathione peroxidase was elevated in the yeast by GB treatment. A mild heat shock (HS) pretreatment (30 min at 40 1C) improved the tolerance of M. fructicola to subsequent high temperature (45 1C, 20–30 min) and oxidative stress (0.4 mol-¹) hydrogen peroxide, 20–60 min). HS-treated yeast cells showed less accumulation of reactive oxygen species (ROS) than non-treated cells in response to both stresses. Additionally, HS-treated yeast exhibited significantly greater (P≥0.0001) biocontrol activity against Penicillium expansum and a significantly faster (Po0.0001) growth rate in wounds of apple fruits stored at 25 1C compared with the performance of untreated yeast cells. Transcription of a trehalose-6-phosphate synthase gene (TPS1) was up regulated in response to HS and trehalose content also increased.