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Journal articles on the topic 'Effet de ligand'

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Published: 20 April 2024

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1

Khamyath, Mélanie, Amélie Bonaud, Karl Balabanian, and Marion Espéli. "La signalisation de CXCR4, un rhéostat de la réponse immunitaire à médiation humorale." médecine/sciences 39, no. 1 (January 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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2

Hecini, Linda, and 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, no. 3 (December 15, 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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3

Crawford, Sarah M., Craig A. Wheaton, Vinayak Mishra, and 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, no. 6 (June 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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4

Drouet, M., F. Mourcin, N. Grenier, J. F. Mayol, V. Leroux, J. J. Sotto, and 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, no. 7 (July 1, 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: 2–10 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·mL–1 (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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5

Tatarchuk, T. R., H. O. Sirenko, and 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, no. 1 (March 15, 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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6

Wang, Yanan, and Thomas Bürgi. "Evidence for stereoelectronic effects in ligand exchange reactions on Au25 nanoclusters." Nanoscale 14, no. 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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7

van Heerden, Tracey, and 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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8

Yu, Baoyi, Zhixiong Luo, Fatma B. Hamad, Karen Leus, Kristof van Hecke, and 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, no. 7 (2016): 2092–100. http://dx.doi.org/10.1039/c5cy01506e.

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9

Liu, Xiaochun, Haifeng Zhao, Linfeng Wei, Xinjian Ren, Xinyang Zhang, Faming Li, Peng Zeng, and Mingzhen Liu. "Ligand-modulated electron transfer rates from CsPbBr3 nanocrystals to titanium dioxide." Nanophotonics 10, no. 8 (June 1, 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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10

Monteiro, Jorge H. S. K., Ana de Bettencourt-Dias, Italo O. Mazali, and 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, no. 3 (2015): 1883–91. http://dx.doi.org/10.1039/c4nj01701c.

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11

Gadgoli, Umesh B., Yelekere C. Sunil Kumar, and Deepak Kumar. "An Insight into the Metabolism of 2,5-Disubstituted Monotetrazole Bearing Bisphenol Structures: Emerging Bisphenol A Structural Congeners." Molecules 28, no. 3 (February 2, 2023): 1465. http://dx.doi.org/10.3390/molecules28031465.

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The non-estrogenic 2,5-disubstituted tetrazole core-bearing bisphenol structures (TbB) are being researched as emerging structural congeners of Bisphenol A, an established industrial endocrine disruptor. However, there is no understanding of TbB’s adverse effects elicited via metabolic activation. Therefore, the current study aimed to investigate the metabolism of TbB ligands, with in silico results serving as a guide for in vitro studies. The Cytochrome P450 enzymes (CYP) inhibitory assay of TbB ligands on the seven human liver CYP isoforms (i.e., 1A2, 2A6, 2D6, 2C9, 2C8, 2C19, and 3A4) using human liver microsomes (HLM) revealed TbB ligand 223-3 to have a 50% inhibitory effect on all the CYP isoforms at a 10 μM concentration, except 1A2. The TbB ligand 223-10 inhibited 2B6 and 2C8, whereas the TbB ligand 223-2 inhibited only 2C9. The first-order inactivity rate constant (Kobs) studies indicated TbB ligands 223-3, 223-10 to be time-dependent (TD) inhibitors, whereas the TbB 223-2 ligand did not show such a significant effect. The 223-3 exhibited a TD inhibition for 2C9, 2C19, and 1A2 with Kobs values of 0.0748, 0.0306, and 0.0333 min−1, respectively. On the other hand, the TbB ligand 223-10 inhibited 2C9 in a TD inhibition manner with Kobs value 0.0748 min−1. However, the TbB ligand 223-2 showed no significant TD inhibition effect on the CYPs. The 223-2 ligand biotransformation pathway by in vitro studies in cryopreserved human hepatocytes suggested the clearance via glucuronidation with the predominant detection of only 223-2 derived mono glucuronide as a potential inactive metabolite. The present study demonstrated that the 223-2 ligand did not elicit any significant adverse effect via metabolic activation, thus paving the way for its in vivo drug–drug interactions (DDI) studies.
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Kim, Hye Yeon, Ae Nim Pae, Yeon Joo Lee, Joon Kyu Park, Dae Sung Kim, Kwang Yeon Hwang, Myeong-Hee Yu, and Eunice EunKyeong Kim. "Structural Comparison of Ligand-Binding Domains in Estrogen-Related Receptors." Key Engineering Materials 277-279 (January 2005): 107–12. http://dx.doi.org/10.4028/www.scientific.net/kem.277-279.107.

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Estrogen-related receptors (ERRs), orphan nuclear receptors, share a significant amino acid sequence homology with estrogen receptors (ERs), yet their ligands do not respond in the same manner. In fact, some of the ligands that are known as agonists of ERs show antagonistic effect in ERRs. Accordingly, the current study investigated the structures of the ligand-binding domains using homology model building and docking studies. The results showed clear differences between the ligand-binding pockets of ERRs and ERs, thereby providing structural insights into the activities related to the ligands.
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13

Korbecki, Jan, Mateusz Bosiacki, Dariusz Chlubek, and Irena Baranowska-Bosiacka. "Bioinformatic Analysis of the CXCR2 Ligands in Cancer Processes." International Journal of Molecular Sciences 24, no. 17 (August 27, 2023): 13287. http://dx.doi.org/10.3390/ijms241713287.

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Human CXCR2 has seven ligands, i.e., CXCL1, CXCL2, CXCL3, CXCL5, CXCL6, CXCL7, and CXCL8/IL-8—chemokines with nearly identical properties. However, no available study has compared the contribution of all CXCR2 ligands to cancer progression. That is why, in this study, we conducted a bioinformatic analysis using the GEPIA, UALCAN, and TIMER2.0 databases to investigate the role of CXCR2 ligands in 31 different types of cancer, including glioblastoma, melanoma, and colon, esophageal, gastric, kidney, liver, lung, ovarian, pancreatic, and prostate cancer. We focused on the differences in the regulation of expression (using the Tfsitescan and miRDB databases) and analyzed mutation types in CXCR2 ligand genes in cancers (using the cBioPortal). The data showed that the effect of CXCR2 ligands on prognosis depends on the type of cancer. CXCR2 ligands were associated with EMT, angiogenesis, recruiting neutrophils to the tumor microenvironment, and the count of M1 macrophages. The regulation of the expression of each CXCR2 ligand was different and, thus, each analyzed chemokine may have a different function in cancer processes. Our findings suggest that each type of cancer has a unique pattern of CXCR2 ligand involvement in cancer progression, with each ligand having a unique regulation of expression.
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Arslan Biçer, F., and O. Z. Yeşilel. "Synthesis, Characterization and The Effect of the Auxiliary Ligands on the Dimensionality of Two Cobalt(II)-Fumarate Coordination Polymers with Bis(imidazole) Ligands." Журнал структурной химии 64, no. 8 (2023): 114396. http://dx.doi.org/10.26902/jsc_id114396.

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Two new Co(II) coordination polymers, namely {[Co(m-fum)0.5(m-obix)2(H2O)](NO3)}n (1), {[Co(m-fum)0.5(m-mbix)2(H2O)](NO3)}n (2), (H2fum: fumaric acid, obix:1,2-bis(imidazol-1-yl-methyl)benzene, mbix: 1,3-bis(imidazol-1-yl-methyl)benzene), have been successfully synthesized under hydrothermal conditions. They have been structurally characterized by elemental analysis, IR spectra, single crystal X-ray diffraction, powder X-ray diffraction (PXRD), magnetic properties. Single-crystal X-ray analysis reveals that the asymmetric units of both CPs contain a Co(II) ion, half fumarate ligand, two bis(imidazole) ligands, one aqua ligand and a nitrate ion. While two symmetry-related Co1 ions are connected by one fumarate ligand to generate a dinuclear unit and obix ligand links adjacent dinuclear units through the nitrogen atoms to form a 1D double chains in 1, each mbix ligand links two Co1 ions to form 1D double chains, and the adjacent chains are further linked together by fumarate ligands to form a 2D network in 2. The effect of bis(imidazole) ligands, which are o- and m-isomers, on the dimensionality of the formed coordination polymer was investigated. The reason for this great effect of bis(imidazole) ligands is that adjustments in the framework occur result of the bending of the semi-rigid imidazole ligands. Thermal analysis shows that 1 and 2 possess similar thermal behaviors. The optical band gap energy values of 1 and 2 observed 3.24 eV and 3.21 eV, respectively. This small difference in the band gap energy may be due to the difference in structural arrangement.
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15

Wu, Jing, Shuang Li, Tete Li, Xinping Lv, Mingyou Zhang, Guoxia Zang, Chong Qi, Yong-Jun Liu, Liang Xu, and Jingtao Chen. "pDC Activation by TLR7/8 Ligand CL097 Compared to TLR7 Ligand IMQ or TLR9 Ligand CpG." Journal of Immunology Research 2019 (April 9, 2019): 1–10. http://dx.doi.org/10.1155/2019/1749803.

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Plasmacytoid dendritic cells (pDCs) express high levels of the toll-like receptors (TLRs) TLR7 and TLR9. In response to TLR7 and TLR9 ligands, pDCs are primary producers of type I interferons. Our previous study demonstrated that pDCs activated by the TLR7 ligand imiquimod (IMQ) and the TLR9 ligand CpG A can kill breast cancer cells in vitro and inhibit tumor growth in vivo. Moreover, we observed a distinctive morphological, phenotypic change in pDCs after activation by IMQ and CpG A. However, the effect of other TLR7 and TLR9 ligands on pDCs remains less understood. In this study, we treat pDCs with the TLR7 ligand IMQ, TLR7/8 ligands (CL097 and CL075), and three TLR9 ligands (different types of CpGs). The size of pDCs increased significantly after activation by TLR7, or TLR7/8 ligands. TLR7, TLR7/8, and TLR9 ligands similarly modulated cytokine release, as well as protein expression of pDC markers, costimulatory molecules, and cytotoxic molecules. Interestingly, TLR7/8 ligands, especially CL097, induced stronger responses. These results are relevant to the further study of the role and mechanism of pDC-induced antitumor effects and may aid in the development of a new strategy for future tumor immunotherapy.
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Okumura, Takeshi, Yasuhiro Funahashi, Tomohiro Ozawa, Koichiro Jitsukawa, and Hideki Masuda. "Structure and Characterization of Fe(III) Complexes with a Square Planar Ligand and the Effect by the Introduction of External Monodentate Axial Ligands." Advanced Materials Research 11-12 (February 2006): 335–38. http://dx.doi.org/10.4028/www.scientific.net/amr.11-12.335.

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A square planar iron complex with H2babp was synthesized and its coordination behaviors with monodentate axial ligands were studied. Cl– or imidazole ligand coordinated at the axial positions of the complex, but pyridine could not be introduced. The heterocyclic nitrogen donors, such as pyridine and imidazole, abstracted the amide protons of the ligand H2babp [1]. The oxidation reactivity was controlled by the presence or absence of amide protons of planar ligand H2babp rather than the axial ligands. The oxidation of cyclohexene by their complexes in the presence of PhIO proceeded catalytically when the iron complexes with protonated H2babp was used, while only a slight amount of oxidation products were obtained when the complexes with deprotonated babp2– were used.
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17

Ruff, Kiersten M., Furqan Dar, and Rohit V. Pappu. "Ligand effects on phase separation of multivalent macromolecules." Proceedings of the National Academy of Sciences 118, no. 10 (March 2, 2021): e2017184118. http://dx.doi.org/10.1073/pnas.2017184118.

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Biomolecular condensates enable spatial and temporal control over cellular processes by concentrating biomolecules into nonstoichiometric assemblies. Many condensates form via reversible phase transitions of condensate-specific multivalent macromolecules known as scaffolds. Phase transitions of scaffolds can be regulated by changing the concentrations of ligands, which are defined as nonscaffold molecules that bind to specific sites on scaffolds. Here, we use theory and computation to uncover rules that underlie ligand-mediated control over scaffold phase behavior. We use the stickers-and-spacers model wherein reversible noncovalent cross-links among stickers drive phase transitions of scaffolds, and spacers modulate the driving forces for phase transitions. We find that the modulatory effects of ligands are governed by the valence of ligands, whether they bind directly to stickers versus spacers, and the relative affinities of ligand–scaffold versus scaffold–scaffold interactions. In general, all ligands have a diluting effect on the concentration of scaffolds within condensates. Whereas monovalent ligands destabilize condensates, multivalent ligands can stabilize condensates by binding directly to spacers or destabilize condensates by binding directly to stickers. Bipartite ligands that bind to stickers and spacers can alter the structural organization of scaffold molecules within condensates even when they have a null effect on condensate stability. Our work highlights the importance of measuring dilute phase concentrations of scaffolds as a function of ligand concentration in cells. This can reveal whether ligands modulate scaffold phase behavior by enabling or suppressing phase separation at endogenous levels, thereby regulating the formation and dissolution of condensates in vivo.
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Jiang, Xiaolin, Jiahui Zhang, Dongmei Zhao, and Yuehui Li. "Aldehyde effect and ligand discovery in Ru-catalyzed dehydrogenative cross-coupling of alcohols to esters." Chemical Communications 55, no. 19 (2019): 2797–800. http://dx.doi.org/10.1039/c8cc10315a.

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19

Bagchi, Abhinav, Kasuni T. Gamage, Scott R. Gilbertson, and Chin-Yo Lin. "Abstract 3336: Regulation of liver X receptor protein stability by novel ligands in pancreatic cancer cells." Cancer Research 84, no. 6_Supplement (March 22, 2024): 3336. http://dx.doi.org/10.1158/1538-7445.am2024-3336.

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Abstract Liver X Receptors (LXRs) are nuclear receptors that act as ligand-modulated transcription factors. LXRs are overexpressed in various cancers, including pancreatic cancer, and targeting LXR with small molecule ligands has emerged as a promising therapeutic strategy in cancer. Current small molecule LXR ligands were originally developed for the treatment of atherosclerosis and other metabolic diseases. To identify ligands specifically targeting cancer cells, we screened a focused library of drug-like molecules predicted to bind to LXR using molecular docking. In the screen, novel LXR ligand GAC0001E5 (1E5) exhibited significant anti-proliferative effects in human pancreatic ductal adenocarcinoma (PDAC) cell lines. Functionally, 1E5 is an LXR inverse agonist which decreases LXR target gene expression and a “degrader” of LXR proteins following prolonged treatment. We posit that this novel ligand inhibits PDAC cells by downregulating the expression of LXR target genes. To test this hypothesis, we treated cancer cells with the previously described LXR inverse agonist SR9238 and examined its effect on cancer cell proliferation. Interestingly, treatments with SR9238 had no effect on pancreatic cancer cell proliferation as compared to the novel ligand 1E5 and the 1E5 derivative KD-95, suggesting that LXR inverse agonism was insufficient to inhibit cell proliferation. To determine whether SR9238 has similar effects on LXR protein levels as novel ligands, we performed western analysis of protein expression following ligand treatment. In contrast to the novel ligands 1E5 and KD-95, treatments with SR9238 increased LXR protein levels. Furthermore, time-course studies in cycloheximide treated cells indicated that novel ligands decreased protein stability whereas SR9238 had the opposite effect. Inhibition of proteasomal degradation and autophagy abolished the effects of 1E5 and KD-95 in a cell line-dependent manner. Related to these observations, previously published data revealed that knockdown of LXR expression greatly diminished PDAC cell proliferation. Taken together, these findings indicate that LXR expression is essential in pancreatic cancer cells and suggest that the novel ligands may disrupt its involvement in protein-protein interactions and non-genomic mechanisms. Citation Format: Abhinav Bagchi, Kasuni T. Gamage, Scott R. Gilbertson, Chin-Yo Lin. Regulation of liver X receptor protein stability by novel ligands in pancreatic cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3336.
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Díaz-González, F., J. Forsyth, B. Steiner, and M. H. Ginsberg. "Trans-dominant inhibition of integrin function." Molecular Biology of the Cell 7, no. 12 (December 1996): 1939–51. http://dx.doi.org/10.1091/mbc.7.12.1939.

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Occupancy of integrin adhesion receptors can alter the functions of other integrins and cause partition of the ligand-occupied integrin into focal adhesions. Ligand binding also changes the conformation of integrin extracellular domains. To explore the relationship between ligand-induced conformational change and integrin signaling, we examined the effect of ligands specific for integrin alpha IIb beta 3 on the functions of target integrins alpha 5 beta 1 and alpha 2 beta 1. We report that binding of integrin-specific ligands to a suppressive integrin can inhibit the function of other target integrins (trans-dominant inhibition). Trans-dominant inhibition is due to a blockade of integrin signaling. Furthermore, this inhibition involves both a conformational change in the extracellular domain and the presence of the beta cytoplasmic tail in the suppressive integrin. Similarly, ligand-induced recruitment of alpha IIb beta 3 to focal adhesions also involves a conformational rearrangement of its extracellular domain. These findings imply that the ligand-induced conformational changes can propagate from an integrin's extracellular to its intracellular face. Trans-dominant inhibition by integrin ligands may coordinate integrin signaling and can lead to unexpected biological effects of integrin-specific inhibitors.
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Crujeiras, Pablo, José Luis Rodríguez-Rey, and Antonio Sousa-Pedrares. "Deactivation of the coordinating ability of the iminophosphorane group by the effect of ortho-carborane." Dalton Transactions 46, no. 8 (2017): 2572–93. http://dx.doi.org/10.1039/c6dt04592h.

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22

Sorkin, A., B. Westermark, C. H. Heldin, and L. Claesson-Welsh. "Effect of receptor kinase inactivation on the rate of internalization and degradation of PDGF and the PDGF beta-receptor." Journal of Cell Biology 112, no. 3 (February 1, 1991): 469–78. http://dx.doi.org/10.1083/jcb.112.3.469.

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The complementary DNAs for wildtype and tyrosine kinase-inactivated (K634A) forms of the PDGF beta-receptor were expressed in porcine aortic endothelial cells. We examined the internalization and degradation of ligands and receptors after exposure of receptor expressing cells to PDGF-BB, which binds to the beta-receptor with high affinity, and PDGF-AB, which binds with lower affinity. Cells expressing wildtype beta-receptors were able to internalize and degrade the receptor, as well as the ligand, after exposure to PDGF-BB or -AB. Cells expressing the kinase-inactivated mutant receptor also internalized and degraded both receptor and ligand, but with lower efficiency compared with the wildtype receptor cells. The degradation of either form of receptor was inhibited by treatment of the cells with the lysosomotropic drug chloroquine. Exposure of wildtype and K634A receptor expressing cells to PDGF-AB resulted in a twofold slower rate of internalization of this ligand as compared with PDGF-BB, whereas the relative rate of degradation was similar for the two ligands. Our data indicate that tyrosine kinase activity promotes, but is not a prerequisite for, ligand-induced internalization and degradation of the ligand-receptor complex.
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Holubová, Jana, Zdeněk Černošek, and Ivan Pavlík. "Niobocene Dichloride and Niobocene Diiodide: Electronic Absorption Spectra and Electron Spin Resonance." Collection of Czechoslovak Chemical Communications 63, no. 5 (1998): 628–35. http://dx.doi.org/10.1135/cccc19980628.

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The effect of the halide ligand on the bonding of niobium in niobocene dichloride and niobocene diiodide was investigated. The electronic absorption spectra of the two compounds in the range of d-d transitions were resolved into four bands corresponding to transitions of the d1 electron between five frontier orbitals in a molecule of symmetry point group C2v. The energies of the frontier molecular orbitals were determined relatively to the energy of the orbitals in the spherically symmetric ligand field formed by the appropriate halide ligands. The effect of the halide ligands on the spin-orbital interaction of the HOMO orbital is discussed qualitatively on the basis the ESR spectra.
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24

Varnum-Finney, B., L. Wu, M. Yu, C. Brashem-Stein, S. Staats, D. Flowers, J. D. Griffin, and I. D. Bernstein. "Immobilization of Notch ligand, Delta-1, is required for induction of notch signaling." Journal of Cell Science 113, no. 23 (December 1, 2000): 4313–18. http://dx.doi.org/10.1242/jcs.113.23.4313.

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Cell-cell interactions mediated by Notch and its ligands are known to effect many cell fate decisions in both invertebrates and vertebrates. However, the mechanisms involved in ligand induced Notch activation are unknown. Recently it was shown that, in at least some cases, endocytosis of the extracellular domain of Notch and ligand by the signaling cell is required for signal induction in the receptive cell. These results imply that soluble ligands (ligand extracellular domains) although capable of binding Notch would be unlikely to activate it. To test the potential activity of soluble Notch ligands, we generated monomeric and dimeric forms of the Notch ligand Delta-1 by fusing the extracellular domain to either a series of myc epitopes (Delta-1(ext-myc)) or to the Fc portion of human IgG-1 (Delta-1(ext-IgG)), respectively. Notch activation, assayed by inhibition of differentiation in C2 myoblasts and by HES1 transactivation in U20S cells, occurred when either Delta-1(ext-myc) or Delta-1(ext-IgG) were first immobilized on the plastic surface. However, Notch was not activated by either monomeric or dimeric ligand in solution (non-immobilized). Furthermore, both non-immobilized Delta-1(ext-myc) and Delta-1(ext-IgG) blocked the effect of immobilized Delta. These results indicate that Delta-1 extracellular domain must be immobilized to induce Notch activation in C2 or U20S cells and that non-immobilized Delta-1 extracellular domain is inhibitory to Notch function. These results imply that ligand stabilization may be essential for Notch activation.
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25

Hemmingsen, Lars, Ulf Ryde, and Rogert Bauer. "Nuclear Quadrupole Interactions in Cadmium Complexes: Semiempirical and ab initio Calculations." Zeitschrift für Naturforschung A 54, no. 6-7 (July 1, 1999): 422–30. http://dx.doi.org/10.1515/zna-1999-6-713.

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Abstract Semiempirical calculations, based on the so-called angular overlap model, have been compared with ab initio methods (MP2) for the calculation of nuclear quadrupole interactions (NQI’s) in cadmium complexes with biologically relevant ligands (H2O, OH-, cysteinate, carboxylate, and imidazole). The assumptions on which the semiempirical model is based have been tested and the comparison indicates that: 1) A change in the Cd-ligand bond length by 0.1 A may change the electric field gradient (EFG) by about 0.2 a. u.. A simple scheme to incorporate such effects in the semiempirical method is suggested. 2) The effect of ligand-ligand interactions is up to about 0.2 a. u. for the largest diagonal element of the EFG tensor for the tested complexes, and such effects can significantly influence the so-called asymmetry parameter. 3) The position of non-coordinating atoms on the ligands can in some cases (e. g. the hydrogen atoms of water) significantly influence the EFG. The combined effect of non-coordinating atoms and ligand-ligand interactions may cause deviations of up to 0.35 a.u. between ab initio and the semiempirical calculations. 4) In the semiempirical model each ligand is characterised by one parameter, the so-called partial nuclear quadrupole interaction. This parameter has been evaluated by ab initio calculations, and agreement was found within about 0.2 a. u. (≈ 40 Mrad/s) for all ligands except imidazole. 5) A change in the coordination number from 2 to 6 may change the partial NQI by about 0.3 a. u.
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26

Urien, S., F. Brée, B. Testa, and J. P. Tillement. "pH-dependency of basic ligand binding to α1-acid glycoprotein (orosomucoid)." Biochemical Journal 280, no. 1 (November 15, 1991): 277–80. http://dx.doi.org/10.1042/bj2800277.

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The binding interactions of a series of basic ligands with alpha 1-acid glycoprotein (AAG) were examined as a function of pH. The binding to AAG increased with increasing pH, and the binding data were satisfactorily fitted to a model that incorporates the effect of pH and discriminates the association constants of neutral (non-protonated) and protonated forms of ligands. It was shown that ligands in the neutral form have a markedly higher affinity for AAG than the protonated forms, resulting in a concomitant decrease in the pKa of bound ligands. The u.v.-visible difference spectra generated upon binding of a representative ligand to AAG also showed that there was a contribution to the binding arising from the deprotonation of the ligand. It is suggested that all tested ligands bind similarly to AAG and that hydrophobic interactions dominate high-affinity binding to AAG.
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27

Ishihara, Kazuaki, and Kazuki Nishimura. "Thorpe–Ingold Effect on High-Performance Chiral π–Copper(II) Catalyst." Synlett 33, no. 06 (January 26, 2022): 585–88. http://dx.doi.org/10.1055/a-1750-8481.

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AbstractThe Thorpe–Ingold effect was applied to the design of a chiral ligand of π–copper(II) catalysts for the enantioselective α-fluorination of N-acyl-3,5-dimethylpyrazoles, and also for the enantioselective Mukaiyama–Michael, Diels–Alder, and 1,3-dipolar cycloaddition reactions of N-acryloyl-3,5-dimethylpyrazoles. The use of β,β-dimethyl-β-arylalanine-type ligand gave desired products with higher enantioselectivity compared to with previously reported β-arylalanine-type ligands.
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Tokumaru, Sho, Shigeki Higashiyama, Takeshi Endo, Takatoshi Nakagawa, Jun-ichiro Miyagawa, Katsumi Yamamori, Yasushi Hanakawa, et al. "Ectodomain Shedding of Epidermal Growth Factor Receptor Ligands Is Required for Keratinocyte Migration in Cutaneous Wound Healing." Journal of Cell Biology 151, no. 2 (October 16, 2000): 209–20. http://dx.doi.org/10.1083/jcb.151.2.209.

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Keratinocyte proliferation and migration are essential to cutaneous wound healing and are, in part, mediated in an autocrine fashion by epidermal growth factor receptor (EGFR)–ligand interactions. EGFR ligands are initially synthesized as membrane-anchored forms, but can be processed and shed as soluble forms. We provide evidence here that wound stimuli induce keratinocyte shedding of EGFR ligands in vitro, particularly the ligand heparin-binding EGF-like growth factor (HB-EGF). The resulting soluble ligands stimulated transient activation of EGFR. OSU8-1, an inhibitor of EGFR ligand shedding, abrogated the wound-induced activation of EGFR and caused suppression of keratinocyte migration in vitro. Soluble EGFR–immunoglobulin G-Fcγ fusion protein, which is able to neutralize all EGFR ligands, also suppressed keratinocyte migration in vitro. The application of OSU8-1 to wound sites in mice greatly retarded reepithelialization as the result of a failure in keratinocyte migration, but this effect could be overcome if recombinant soluble HB-EGF was added along with OSU8-1. These findings indicate that the shedding of EGFR ligands represents a critical event in keratinocyte migration, and suggest their possible use as an effective clinical treatment in the early phases of wound healing.
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29

Paris, R., and K. V. Desboeufs. "Effect of atmospheric organic complexation on iron-bearing dust solubility." Atmospheric Chemistry and Physics 13, no. 9 (May 14, 2013): 4895–905. http://dx.doi.org/10.5194/acp-13-4895-2013.

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Abstract. Recent studies reported that the effect of organic complexation may be a potentially important process to be considered by models estimating atmospheric iron flux to the ocean. In this study, we investigated this process effect by a series of dissolution experiments on iron-bearing dust in the presence or the absence of various organic compounds (acetate, formate, oxalate, malonate, succinate, glutarate, glycolate, lactate, tartrate and humic acid as an analogue of humic like substances, HULIS) typically found in atmospheric waters. Only 4 of tested organic ligands (oxalate, malonate, tartrate and humic acid) caused an enhancement of iron solubility which was associated with an increase of dissolved Fe(II) concentrations. For all of these organic ligands, a positive linear dependence of iron solubility to organic concentrations was observed and showed that the extent of organic complexation on iron solubility decreased in the following order: oxalate >malonate = tartrate > humic acid. This was attributed to the ability of electron donors of organic ligands and implies a reductive ligand-promoted dissolution. This study confirms that among the known atmospheric organic binding ligands of Fe, oxalate is the most effective ligand promoting dust iron solubility and showed, for the first time, the potential effect of HULIS on iron dissolution under atmospheric conditions.
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30

Jung, Minho, and Eun Young Choi. "TLR5 and TLR7 amplify different stage of myeloid cells." Journal of Immunology 202, no. 1_Supplement (May 1, 2019): 126.40. http://dx.doi.org/10.4049/jimmunol.202.supp.126.40.

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Abstract Balance between immune activation and immune suppression is important for immune homeostasis. Toll-like receptors (TLRs) play key roles in the innate immune system, initiating inflammatory responses against pathogen infections and internal danger signals. Different TLRs recognize different kinds of ligands, but not all the TLRs do have same effect: some TLRs are immune stimulatory, while the others are immune suppressive. For instance, TLR5 ligand has been known to be immune suppressive, while TLR7 ligand has been used for immune activation. To understand how these TLR ligands lead to opposite immune outcomes, we investigated the effects of the ligands on myeloid cell differentiation. Treatment of TLR5 ligand flagellin resulted in the increase of CD11b+ Ly6C+Ly6G+ myeloid-derived suppressor cells (MDSCs) on days 2 and 3 after culture initiation. However, TLR7 ligand gardiquimod led to enhancement of dendritic cell differentiation on day 1, and then increase of CD11c− MHCII− CD11b− Ly6C− Ly6G− progenitor population on day 2, which differentiate into CD11c− MHCIIow CD11b+ Ly6C+ cells with DC differentiation potential afterwards. Based on these results, we suggest that different immune outcomes of TLR ligands would depend on the stages of myeloid cells at which corresponding TLRs act, contributing to overall immune homeostasis.
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31

Zhang, Dongdong, Xiuli Ren, and Lixin Zhou. "Theoretical analysis of trans-[PtCl2(NH3)(thiazole)] and trans-[PtCl2(thiazole)2] binding to biological targets — Factors influence binding kinetics and adduct stability." Canadian Journal of Chemistry 88, no. 12 (December 2010): 1240–46. http://dx.doi.org/10.1139/v10-139.

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Full reaction energy profiles for trans-[PtCl2(NH3)(thiazole)] and trans-[PtCl2(thiazole)2] binding to sulfur- and nitrogen-containing biorelevant ligands were constructed by the density functional theory (DFT) method. Calculated results demonstrate that trans-platinum complexes can interact with biological targets, affording cis and trans products via very similar transition states. For different substituents, sulfur-containing ligands constitute kinetically preferred targets for platination, whereas the platination of nitrogen-containing ligands is more favorable thermodynamically. This is consistent with previous experimental studies. Calculated results also suggest that the trans effect, the influence of the ligand, the size of the ligand, and hydrogen bonding play important roles in binding kinetics and stabilizing adducts.
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32

Deng, Meng, Shuhui Chi, and Yunjie Luo. "Rare-earth metal bis(alkyl) complexes bearing pyrrolidinyl-functionalized cyclopentadienyl, indenyl and fluorenyl ligands: synthesis, characterization and the ligand effect on isoprene polymerization." New Journal of Chemistry 39, no. 10 (2015): 7575–81. http://dx.doi.org/10.1039/c5nj00279f.

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33

Karukurichi, Kannan R., Xiang Fei, Robert A. Swyka, Sylvain Broussy, Weijun Shen, Sangeeta Dey, Sandip K. Roy, and David B. Berkowitz. "Mini-ISES identifies promising carbafructopyranose-based salens for asymmetric catalysis: Tuning ligand shape via the anomeric effect." Science Advances 1, no. 6 (July 2015): e1500066. http://dx.doi.org/10.1126/sciadv.1500066.

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This study introduces new methods of screening for and tuning chiral space and in so doing identifies a promising set of chiral ligands for asymmetric synthesis. The carbafructopyranosyl-1,2-diamine(s) and salens constructed therefrom are particularly compelling. It is shown that by removing the native anomeric effect in this ligand family, one can tune chiral ligand shape and improve chiral bias. This concept is demonstrated by a combination of (i) x-ray crystallographic structure determination, (ii) assessment of catalytic performance, and (iii) consideration of the anomeric effect and its underlying dipolar basis. The title ligands were identified by a new mini version of the in situ enzymatic screening (ISES) procedure through which catalyst-ligand combinations are screened in parallel, and information on relative rate and enantioselectivity is obtained in real time, without the need to quench reactions or draw aliquots. Mini-ISES brings the technique into the nanomole regime (200 to 350 nmol catalyst/20 μl organic volume) commensurate with emerging trends in reaction development/process chemistry. The best-performing β-d-carbafructopyranosyl-1,2-diamine–derived salen ligand discovered here outperforms the best known organometallic and enzymatic catalysts for the hydrolytic kinetic resolution of 3-phenylpropylene oxide, one of several substrates examined for which the ligand is “matched.” This ligand scaffold defines a new swath of chiral space, and anomeric effect tunability defines a new concept in shaping that chiral space. Both this ligand set and the anomeric shape-tuning concept are expected to find broad application, given the value of chiral 1,2-diamines and salens constructed from these in asymmetric catalysis.
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34

Ferreira-Faria, Diogo, and M. Ângela Taipa. "Thermal Stabilization of Lipases Bound to Solid-Phase Triazine-Scaffolded Biomimetic Ligands: A Preliminary Assessment." Processes 12, no. 2 (February 11, 2024): 371. http://dx.doi.org/10.3390/pr12020371.

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Biomimetic ligands are synthetic compounds that mimic the structure and binding properties of natural biological ligands. The first uses of textile dyes as pseudo-affinity ligands paved the way for the rational design and de novo synthesis of low-cost, non-toxic and highly stable triazine-scaffolded affinity ligands. A novel method to assess and enhance protein stability, employing triazine-based biomimetic ligands and using cutinase from Fusarium solani pisi as a protein model, has been previously reported. This innovative approach combined the concepts of molecular modeling and solid-phase combinatorial chemistry to design, synthesize and screen biomimetic compounds able to bind cutinase through complementary affinity-like interactions while maintaining its biological functionality. The screening of a 36-member biased combinatorial library enabled the identification of promising lead ligands. The immobilization/adsorption of cutinase onto a particular lead (ligand 3′/11) led to a noteworthy enhancement in thermal stability within the temperature range of 60–80 °C. In the present study, similar triazine-based compounds, sourced from the same combinatorial library and mimicking dipeptides of diverse amino acids, were selected and studied to determine their effectiveness in binding and/or improving the thermal stability of several lipases, enzymes which are closely related in function to cutinases. Three ligands with different compositions were screened for their potential thermostabilizing effect on different lipolytic enzymes at 60 °C. An entirely distinct enzyme, invertase from Saccharomyces cerevisiae, was also assessed for binding to the same ligands and functioned as a ‘control’ for the experiments with lipases. The high binding yield of ligand 3′/11 [4-({4-chloro-6-[(2-methylbutyl)amino]-1,3,5-triazin-2-yl}amino)benzoic acid] to cutinase was confirmed, and the same ligand was tested for its ability to bind lipases from Aspergillus oryzae (AOL), Candida rugosa (CRL), Chromobacterium viscosum (CVL), Rhizomucor miehei (RML) and Rhizopus niveus (RNL). The enzymes CRL, CVL, RNL and invertase showed significant adsorption yields to ligand 3′/11—32, 29, 36 and 94%, respectively, and the thermal stability at 60 °C of free and adsorbed enzymes was studied. CVL and RNL were also stabilized by adsorption to ligand 3′/11. In the case of CRL and invertase, which bound but were not stabilized by ligand (3′/11), other ligands from the original combinatorial library were tested. Between the two alternative ligands, one was effective at stabilizing C. rugosa lipase, while none stabilized invertase.
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35

Nin-Hill, Alba, Nicolas Pierre Friedrich Mueller, Carla Molteni, Carme Rovira, and Mercedes Alfonso-Prieto. "Photopharmacology of Ion Channels through the Light of the Computational Microscope." International Journal of Molecular Sciences 22, no. 21 (November 8, 2021): 12072. http://dx.doi.org/10.3390/ijms222112072.

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The optical control and investigation of neuronal activity can be achieved and carried out with photoswitchable ligands. Such compounds are designed in a modular fashion, combining a known ligand of the target protein and a photochromic group, as well as an additional electrophilic group for tethered ligands. Such a design strategy can be optimized by including structural data. In addition to experimental structures, computational methods (such as homology modeling, molecular docking, molecular dynamics and enhanced sampling techniques) can provide structural insights to guide photoswitch design and to understand the observed light-regulated effects. This review discusses the application of such structure-based computational methods to photoswitchable ligands targeting voltage- and ligand-gated ion channels. Structural mapping may help identify residues near the ligand binding pocket amenable for mutagenesis and covalent attachment. Modeling of the target protein in a complex with the photoswitchable ligand can shed light on the different activities of the two photoswitch isomers and the effect of site-directed mutations on photoswitch binding, as well as ion channel subtype selectivity. The examples presented here show how the integration of computational modeling with experimental data can greatly facilitate photoswitchable ligand design and optimization. Recent advances in structural biology, both experimental and computational, are expected to further strengthen this rational photopharmacology approach.
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36

Zhang, Manlin, Michael Lindner-D’Addario, Mahdi Roohnikan, Violeta Toader, Robert Bruce Lennox, and Linda Reven. "Polymer Functionalized Nanoparticles in Blue Phase LC: Effect of Particle Shape." Nanomaterials 12, no. 1 (December 29, 2021): 91. http://dx.doi.org/10.3390/nano12010091.

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Ethylene oxide oligomers and polymers, free and tethered to gold nanoparticles, were dispersed in blue phase liquid crystals (BPLC). Gold nanospheres (AuNPs) and nanorods (AuNRs) were functionalized with thiolated ethylene oxide ligands with molecular weights ranging from 200 to 5000 g/mol. The BPLC mixture (ΔTBP ~6 °C) was based on the mesogenic acid heterodimers, n-hexylbenzoic acid (6BA) and n-trans-butylcyclohexylcarboxylic acid (4-BCHA) with the chiral dopant (R)-2-octyl 4-[4-(hexyloxy)benzoyloxy]benzoate. The lowest molecular weight oligomer lowered and widened the BP range but adding AuNPs functionalized with the same ligand had little effect. Higher concentrations or molecular weights of the ligands, free or tethered to the AuNPs, completely destabilized the BP. Mini-AuNRs functionalized with the same ligands lowered and widened the BP temperature range with longer mini-AuNRs having a larger effect. In contrast to the AuNPs, the mini-AuNRs with the higher molecular weight ligands widened rather than destabilized the BP, though the lowest MW ligand yielded the largest BP range, (ΔTBP > 13 °C). The different effects on the BP may be due to the AuNPs accumulating at singular defect sites whereas the mini-AuNRs, with diameters smaller than that of the disclination lines, can more efficiently fill in the BP defects.
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37

Ghosh, Subrata, Sukanya Bagchi, Sujit Kamilya, and Abhishake Mondal. "Effect of ligand substituents and tuning the spin-state switching in manganese(iii) complexes." Dalton Transactions 50, no. 13 (2021): 4634–42. http://dx.doi.org/10.1039/d1dt00284h.

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This work unravels the magneto-structural behavior of mononuclear manganese(iii) complexes with judiciously chosen substituted Schiff-base ligands, showcasing the role of ligand substitutions in spin-state switching.
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38

Castro, Caio B., Rafael G. Silveira, Felippe M. Colombari, André Farias de Moura, Otaciro R. Nascimento, and Caterina G. C. Marques Netto. "Solvent Effect on the Regulation of Urea Hydrolysis Reactions by Copper Complexes." Chemistry 2, no. 2 (June 2, 2020): 525–44. http://dx.doi.org/10.3390/chemistry2020032.

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Abiotic allosterism is most commonly observed in hetero-bimetallic supramolecular complexes and less frequently in homo-bimetallic complexes. The use of hemilabile ligands with high synthetic complexity enables the catalytic center by the addition or removal of allosteric effectors and simplicity is unusually seen in these systems. Here we describe a simpler approach to achieve kinetic regulation by the use of dimeric Schiff base copper complexes connected by a chlorido ligand bridge. The chlorido ligand acts as a weak link between monomers, generating homo-bimetallic self-aggregating supramolecular complexes that generate monomeric species in different reaction rates depending on the solvent and on the radical moiety of the ligand. The ligand exchange was observed by electron paramagnetic resonance (EPR) and conductivity measurements, indicating that complexes with ligands bearing methoxyl (CuIIL2) and ethoxyl (CuIIL5) radicals were more prone to form dimeric complexes in comparison to ligands bearing hydrogen (CuIIL1), methyl (CuIIL3), or t-butyl (CuIIL4) radicals. The equilibrium between dimer and monomer afforded different reactivities of the complexes in acetonitrile/water and methanol/water mixtures toward urea hydrolysis as a model reaction. It was evident that the dimeric species were inactive and that by increasing the water concentration in the reaction medium, the dimeric structures dissociated to form the active monomeric structures. This behavior was more pronounced when methanol/water mixtures were employed due to a slower displacement of the chlorido bridge in this medium than in the acetonitrile/water mixtures, enabling the reaction kinetics to be evaluated. This effect was attributed to the preferential solvation shell by the organic solvents and in essence, an upregulation behavior was observed due to the intrinsic nature of the complexes to form dimeric structures in solution that could be dismantled in the presence of water, indicating their possible use as water-sensors in organic solvents.
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39

Paris, R., and K. V. Desboeufs. "Effect of atmospheric organic complexation on iron-bearing dust solubility." Atmospheric Chemistry and Physics Discussions 13, no. 2 (February 4, 2013): 3179–202. http://dx.doi.org/10.5194/acpd-13-3179-2013.

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Abstract. Recent studies reported that the effect of organic complexation may be a potentially important process to be considered in models to estimate atmospheric iron flux to the ocean. In this study, we investigated this effect by a series of dissolution experiments on iron-bearing dust in presence or absence of various organic compounds typically found in the atmospheric waters (acetate, formate, oxalate, malonate, succinate, glutarate, glycolate, lactate, tartrate and humic acid as an analogue of humic like substances (HULIS)). Only 4 of tested organic ligands (oxalate, malonate, tartrate and humic acid) caused an enhancement of iron solubility which was associated with an increase of dissolved Fe(II) concentrations. For all of these organic ligands, a positive linear dependence of iron solubility to organic concentrations was observed and showed that the extent of organic complexation on iron solubility decreased in order oxalate > malonate = tartrate > humic acid. This was attributed to the ability of electron donors of organic ligands and implied a reductive ligand-promoted dissolution. This study confirmed that oxalate is the most effective ligand playing on dust iron solubility and showed, for the first time, the potential effect of HULIS on iron dissolution in atmospheric conditions.
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40

Paulmurugan, Ramasamy, Anobel Tamrazi, John A. Katzenellenbogen, Benita S. Katzenellenbogen, and Sanjiv S. Gambhir. "A Human Estrogen Receptor (ER)α Mutation with Differential Responsiveness to Nonsteroidal Ligands: Novel Approaches for Studying Mechanism of ER Action." Molecular Endocrinology 22, no. 7 (July 1, 2008): 1552–64. http://dx.doi.org/10.1210/me.2007-0570.

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Abstract Estrogens, acting through the estrogen receptors (ERs), play crucial roles in regulating the function of reproductive and other systems under physiological and pathological conditions. ER activity in regulating target genes is modulated by the binding of both steroidal and synthetic nonsteroidal ligands, with ligand binding inducing ERs to adopt various conformations that control their interactions with transcriptional coregulators. Previously, we developed an intramolecular folding sensor with a mutant form of ERα (ERG521T) that proved to be essentially unresponsive to the endogenous ligand 17β-estradiol, yet responded very well to certain synthetic ligands. In this study, we have characterized this G521T-ER mutation in terms of the potency and efficacy of receptor response toward several steroidal and nonsteroidal ligands in two different ways: directly, by ligand effects on mutant ER conformation (by the split-luciferase complementation system), and indirectly, by ligand effects on mutant ER transactivation. Full-length G521T-ER shows no affinity for estradiol and does not activate an estrogen-responsive reporter gene. The synthetic pyrazole agonist ligand propyl-pyrazole-triol is approximately 100-fold more potent than estradiol in inducing intramolecular folding and reporter gene transactivation with the mutant ER, whereas both ligands have high potency on wild-type ER. This estradiol-unresponsive mutant ER can also specifically highlight the agonistic property of the selective ER modulator, 4-hydroxytamoxifen, by reporter gene transactivation, even in the presence of estradiol, and it can exert a dominant-negative effect on estrogen-stimulated wild-type ER. This system provides a model for ER-mutants that show differential ligand responsiveness to gene activation to gain insight into the phenomenon of hormone resistance observed in endocrine therapies of ER-positive breast cancers.
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41

Kerton, Francesca M., Stacey Holloway, Angela Power, R. Graeme Soper, Kristina Sheridan, Jason M. Lynam, Adrian C. Whitwood, and Charlotte E. Willans. "Accelerated syntheses of amine-bis(phenol) ligands in polyethylene glycol or “on water” under microwave irradiation." Canadian Journal of Chemistry 86, no. 5 (May 1, 2008): 435–43. http://dx.doi.org/10.1139/v08-043.

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Pure amine-bis(phenol) ligands are readily accessible in high yield, often >90%, when the Mannich condensation reactions are performed “on water” or in poly(ethyleneglycol) (PEG). Microwave-assisted synthesis dramatically reduces the time and energy required to prepare these molecules, typically from 24 h to 5 min. The approach seems to be widely applicable (7 amines and 5 phenols were tested to yield a diverse set of bis(phenol) ligands). Significant improvements in yield were observed for ligands derived from di-tert-amyl and di-tert-butyl phenols, possibly resulting from a hydrophobic effect. Single crystal X-ray diffraction data for the ligand derived from p-cresol and N,N′-dimethylethylenediamine is reported.Key words: amine-phenol, Mannich condensation, on water, microwave, ligand, high-throughput.
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42

Journal, Baghdad Science. "Synthesis and Characterization of Some Metal Complexes with their Sulfamethoxazoleand 4,4'-dimethyl-2,2'-bipyridyl and study Cytotoxic Effect on Hep-2 Cell Line." Baghdad Science Journal 12, no. 4 (December 6, 2015): 740–52. http://dx.doi.org/10.21123/bsj.12.4.740-752.

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The ligand 4-amino-N-(5-methylisoxazole-3-yl)-benzene-sulfonamide(L1) (as a chelating ligand) was treated with Pd(II),Pt (IV) and Au(III) ions in alcoholic medium in order to prepare a series of new metal complexes. Mixed ligand complexes of this primary ligand were prepared in alcoholic medium in presence of the co-ligand 4,4'-dimethyl-2,2'-bipyridyl(L2) with Cu(II) ,Pd(II) and Au(III) ions. The complexes were characterized in solid state using flame atomic absorption, elemental analysis C.H.N.S, FT-IR, UV-Vis Spectroscopy, conductivity and magnetic susceptibility measurements. The nature of some complexes formed in ethanolic solution has been studied following the molar ratio method, also stability constant was studied and the complexes found to be stable in molar ratio1:1.an octahedral geometry was suggested for PdL1L2, PtL1and AuL1L2 complexes, square planar was suggested for AuL1 and PdL1complexes,while CuL1L2 complex has a square pyramidal geometry. Cytotoxic effect of theprepared complexes as well as ligands was evaluated against Hep-2 cell line using four different concentrations (625, 1250, 2500&5000 µg/ml) respectively in an exposure time 48 hrs comparing this effect with control positive Cis-Pt as reference drug. The obtained results refers to the higher inhibition rates of all complexes and their ligands and ligand (L1) and its complexes give more activity against tested cell than ligand (L2) and its complexes comparable with control positive .
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43

Alias, Mahasin F., and Maysoon M. AbdulHassan. "Synthesis and Characterization of Some Metal Complexes with their Sulfamethoxazoleand 4,4'-dimethyl-2,2'-bipyridyl and study Cytotoxic Effect on Hep-2 Cell Line." Baghdad Science Journal 12, no. 4 (December 6, 2015): 740–52. http://dx.doi.org/10.21123/bsj.2015.12.4.740-752.

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The ligand 4-amino-N-(5-methylisoxazole-3-yl)-benzene-sulfonamide(L1) (as a chelating ligand) was treated with Pd(II),Pt (IV) and Au(III) ions in alcoholic medium in order to prepare a series of new metal complexes. Mixed ligand complexes of this primary ligand were prepared in alcoholic medium in presence of the co-ligand 4,4'-dimethyl-2,2'-bipyridyl(L2) with Cu(II) ,Pd(II) and Au(III) ions. The complexes were characterized in solid state using flame atomic absorption, elemental analysis C.H.N.S, FT-IR, UV-Vis Spectroscopy, conductivity and magnetic susceptibility measurements. The nature of some complexes formed in ethanolic solution has been studied following the molar ratio method, also stability constant was studied and the complexes found to be stable in molar ratio1:1.an octahedral geometry was suggested for PdL1L2, PtL1and AuL1L2 complexes, square planar was suggested for AuL1 and PdL1complexes,while CuL1L2 complex has a square pyramidal geometry. Cytotoxic effect of theprepared complexes as well as ligands was evaluated against Hep-2 cell line using four different concentrations (625, 1250, 2500&5000 µg/ml) respectively in an exposure time 48 hrs comparing this effect with control positive Cis-Pt as reference drug. The obtained results refers to the higher inhibition rates of all complexes and their ligands and ligand (L1) and its complexes give more activity against tested cell than ligand (L2) and its complexes comparable with control positive .
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44

Kuznetsov, Aleksei, and Jaak Järv. "Ligand structure controlled allostery in cAMP-dependent protein kinase catalytic subunit." Open Life Sciences 4, no. 2 (June 1, 2009): 131–41. http://dx.doi.org/10.2478/s11535-009-0012-6.

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AbstractProtein kinase A (cAMP dependent protein kinase catalytic subunit, EC 2.7.11.11) binds simultaneously ATP and a phosphorylatable peptide. These structurally dissimilar allosteric ligands influence the binding effectiveness of each other. The same situation is observed with substrate congeners, which reversibly inhibit the enzyme. In this review these allosteric effects are quantified using the interaction factor, which compares binding effectiveness of ligands with the free enzyme and the pre-loaded enzyme complex containing another ligand. This analysis revealed that the allosteric effect depends upon structure of the interacting ligands, and the principle “better binding: stronger allostery” observed can be formalized in terms of linear free-energy relationships, which point to similar mechanism of the allosteric interaction between the enzyme-bound substrates and/or inhibitor molecules. On the other hand, the type of effect is governed by ligand binding effectiveness and can be inverted from positive allostery to negative allostery if we move from effectively binding ligands to badly binding compounds. Thus the outcome of the allostery in this monomeric enzyme is the same as defined by classical theories for multimeric enzymes: making the enzyme response more efficient if appropriate ligands bind.
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45

Moreno-da Costa, David, César Zúñiga-Loyola, Federico Droghetti, Stephania Robles, Alondra Villegas-Menares, Nery Villegas-Escobar, Ivan Gonzalez-Pavez, Elies Molins, Mirco Natali, and Alan R. Cabrera. "Air- and Water-Stable Heteroleptic Copper (I) Complexes Bearing Bis(indazol-1-yl)methane Ligands: Synthesis, Characterisation, and Computational Studies." Molecules 29, no. 1 (December 20, 2023): 47. http://dx.doi.org/10.3390/molecules29010047.

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A series of four novel heteroleptic Cu(I) complexes, bearing bis(1H-indazol-1-yl)methane analogues as N,N ligands and DPEPhos as the P,P ligand, were synthesised in high yields under mild conditions and characterised by spectroscopic and spectrometric techniques. In addition, the position of the carboxymethyl substituent in the complexes and its effect on the electrochemical and photophysical behaviour was evaluated. As expected, the homoleptic copper (I) complexes with the N,N ligands showed air instability. In contrast, the obtained heteroleptic complexes were air- and water-stable in solid and solution. All complexes displayed green-yellow luminescence in CH2Cl2 at room temperature due to ligand-centred (LC) phosphorescence in the case of the Cu(I) complex with an unsubstituted N,N ligand and metal-to-ligand charge transfer (MLCT) phosphorescence for the carboxymethyl-substituted complexes. Interestingly, proper substitution of the bis(1H-indazol-1-yl)methane ligand enabled the achievement of a remarkable luminescent yield (2.5%) in solution, showcasing the great potential of this novel class of copper(I) complexes for potential applications in luminescent devices and/or photocatalysis.
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46

Ogura, Yusaku, Masahiro Nakano, Hajime Maeda, Masahito Segi, and Taniyuki Furuyama. "Cationic Axial Ligand Effects on Sulfur-Substituted Subphthalocyanines." Molecules 27, no. 9 (April 26, 2022): 2766. http://dx.doi.org/10.3390/molecules27092766.

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Herein, we report the synthesis of sulfur-substituted boron(III) subphthalocyanines (SubPcs) with cationic axial ligands. Subphthalocyanines were synthesized by a condensation reaction using the corresponding phthalonitriles and boron trichloride as a template. An aminoalkyl group was introduced on the central boron atom; this process was followed by N-methylation to introduce a cationic axial ligand. The peripheral sulfur groups shifted the Q band of SubPcs to a longer wavelength. The cationic axial ligands increased the polarity and enhanced the hydrophilicity of SubPcs. The effect of axial ligands on absorption and fluorescence properties is generally small. However, a further red shift was observed by introducing cationic axial ligands into the sulfur-substituted SubPcs. This change is similar to that in sulfur-substituted silicon(IV) phthalocyanines. The unique effect of the cationic axial ligand was extensively investigated by theoretical calculations and electrochemistry. In particular, the precise oxidation potential was determined using ionization potential measurements. Thus, the results of the present study provide a novel strategy for developing functional dyes and pigments based on SubPcs.
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47

Калиновская, И. В. "Разнолигандные комплексные соединения европия (III) с o-метоксибензойной кислотой и фосфорсодержащими нейтральными лигандами." Журнал технической физики 128, no. 5 (2020): 612. http://dx.doi.org/10.21883/os.2020.05.49318.310-19.

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The luminescent coordination multi-ligand compounds of europium (III) with o-methoxybenzoic acid and island-containing phosphorus-containing neutral ligands of the composition Eu (MOBA) 3 • 3Н2О and Eu (MOBA) 3 • L, where MOBA is o-methoxybenzoic acid, D is hmpa (D hexamethylphosphoric triamide), tppo (triphenylphosphine oxide), Et6pa (hexaethylphosphotriamide). The composition, structure, and thermal properties of complex multi-ligand compounds of europium (III) were studied. It was shown that during thermolysis, detachment of a neutral ligand molecule occurs in one stage with an endothermic effect, complex compounds are stable up to 280 С.Based on the data of IR spectroscopy, it was found that in the europium (III) o-methoxybenzoates, the o-methoxybenzoic acid is coordinated to the europium (III) o-methoxybenzoic ion in a bidentate manner. The low luminescence intensity of multi-ligand europium (III) compounds is explained by the inefficient transfer of electronic excitation energy from o-methoxybenzoic acid and phosphorus-containing neutral ligands to the europium ion.
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48

Tang, Qing, Runhai Ouyang, Ziqi Tian, and De-en Jiang. "The ligand effect on the isomer stability of Au24(SR)20 clusters." Nanoscale 7, no. 6 (2015): 2225–29. http://dx.doi.org/10.1039/c4nr05826g.

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Density functional calculations show that the relative isomer stability of the Au24(SR)20 nanocluster depends on the ligand and that the stereochemical interaction among ligands is crucial in affecting the relative energetics.
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49

Shi, Changhua, Qing Meng, and David W. Wood. "Analysis of the roles of mutations in thyroid hormone receptor-β by a bacterial biosensor system." Journal of Molecular Endocrinology 52, no. 1 (October 30, 2013): 55–66. http://dx.doi.org/10.1530/jme-13-0108.

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Mutations in thyroid hormone receptors (TRs) often lead to metabolic and developmental disorders, but patients with these mutations are difficult to treat with existing thyromimetic drugs. In this study, we analyzed six clinically observed mutations in the ligand-binding domain of the human TRβ using an engineered bacterial hormone biosensor. Six agonist compounds, including triiodothyronine (T3), thyroxine (T4), 3,5,3′-triiodothyroacetic acid (Triac), GC-1, KB-141, and CO-23, and the antagonist NH-3 were examined for their ability to bind to each of the TRβ mutants. The results indicate that some mutations lead to the loss of ability to bind to native ligands, ranging from several fold to several hundred fold, while other mutations completely abolish the ability to bind to any ligand. Notably, the effect of each ligand on each TRβ mutant in this bacterial system is highly dependent on both the mutation and the ligand; some ligands were bound well by a wide variety of mutants, while other ligands lost their affinity for all but the WT receptor. This study demonstrates the ability of our bacterial system to differentiate agonist compounds from antagonist compounds and shows that one of the TRβ mutations leads to an unexpected increase in antagonist ability relative to other mutations. These results indicate that this bacterial sensor can be used to rapidly determine ligand-binding ability and character for clinically relevant TRβ mutants.
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50

Martínez-Prieto, L. M., I. Cano, A. Márquez, E. A. Baquero, S. Tricard, L. Cusinato, I. del Rosal, et al. "Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts." Chemical Science 8, no. 4 (2017): 2931–41. http://dx.doi.org/10.1039/c6sc05551f.

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Pt NPs covered with zwitterionic amidinates as ligands exhibit an exciting ligand effect in the hydrogenation of carbonyl groups when electron donor/acceptor groups are introduced in theN-substituents.
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