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Cation Interaction (cation + interaction)
Selected AbstractsSynthesis of Ene-ynamide Derivatives Starting from Baylis,Hillman Adducts: Isomerization with the Aid of ,-Cation Interaction.CHEMINFORM, Issue 5 2006Saravanan Gowrisankar Abstract For Abstract see ChemInform Abstract in Full Text. [source] Innentitelbild: Stable Pentavalent Uranyl Species and Selective Assembly of a Polymetallic Mixed-Valent Uranyl Complex by Cation,Cation Interactions (Angew. Chem.ANGEWANDTE CHEMIE, Issue 45 200945/2009) Oligomere Komplexe mit kationischen Actinyleinheiten sind entscheidend für die Aufarbeitung von radioaktivem Abfall und die Verteilung von Actinoiden in der Umwelt. In ihrer Zuschrift auf S.,8629,ff. zeigen M. Mazzanti et,al., dass der N,N,-Bis(salicyliden)ethylendiamin-Ligand (Salen) fünfwertiges Uran stabilisieren kann. Ein entsprechender Vierkernkomplex, in dem eine antiferromagnetische Kopplung zwischen den vier oxoverbrückten Uranzentren vorliegt, ist stabil gegen Disproportionierung und Hydrolyse. [source] Stable Pentavalent Uranyl Species and Selective Assembly of a Polymetallic Mixed-Valent Uranyl Complex by Cation,Cation Interactions,ANGEWANDTE CHEMIE, Issue 45 2009Victor Mougel Nützliche Verbindung: Vier Salenkomplexe von fünfwertigen Uranylionen aggregieren zu einem Vierkernkomplex, der sehr beständig gegen Disproportionierung und Hydrolyse ist und eine deutliche antiferromagnetische Kopplung zwischen den vier oxoverbrückten Uranzentren aufweist (siehe Bild: O,rot, U,grün). Ausgehend von diesem Komplex wurde auch die erste gemischtvalente UV3/UVI -Verbindung selektiv synthetisiert. [source] Structural basis for preferential binding of non- ortho -substituted polychlorinated biphenyls by the monoclonal antibody S2B1JOURNAL OF MOLECULAR RECOGNITION, Issue 4 2005Jean-Luc Pellequer Abstract Polychlorinated biphenyls (PCBs) are a family of 209 isomers (congeners) with a wide range of toxic effects. In structural terms, they are of two types: those with and those without chlorines at the ortho positions (2, 2,, 6 and 6,). Only 20 congeners have no ortho chlorines. Three of these are bound by the aryl hydrocarbon receptor and are one to four orders of magnitude more toxic than all others. A monoclonal antibody, S2B1, and its recombinant Fab have high selectivity and nanomolar binding affinities for two of the most toxic non- ortho -chlorinated PCBs, 3,4,3,,4,-tetrachlorobiphenyl and 3,4,3,,4,,5,-pentachlorobiphenyl. To investigate the basis for these properties, we built a three-dimensional structure model of the S2B1 variable fragment (Fv) based on the high-resolution crystallographic structures of antibodies 48G7 and N1G9. Two plausible conformations for the complementarity-determining region (CDR) H3 loop led to two putative PCB-binding pockets with very different shapes (models A and B). Docking studies using molecular mechanics and potentials of mean force (PMF) indicated that model B was most consistent with the selectivity observed for S2B1 in competition ELISAs. The binding site in model B had a deep, narrow pocket between VL and VH, with a slight constriction at the top that opened into a wider pocket between CDRs H1 and H3 on the antibody surface. This binding site resembles those of esterolytic antibodies that bind haptens with phenyl rings. One phenyl ring of the PCB fits into the deep pocket, and the other ring is bound in the shallower one. The bound PCB is surrounded by the side chains of TyrL91, TyrL96 and TrpH98, and it has a ,-cation interaction with ArgL46. The tight fit of the binding pocket around the ortho positions of the bound PCBs indicates that steric hindrance of ortho chlorines in the binding site, rather than induced conformational change of the PCBs, is responsible for the selectivity of S2B1. Copyright © 2005 John Wiley & Sons, Ltd. [source] Humic acid metal cation interaction studied by spectromicroscopy techniques in combination with quantum chemical calculationsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2010M. Plaschke Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III),HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K -edge and laser scanning luminescence microscopy (LSLM) at the 5D0,7F1,2 fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s -NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV),HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a `pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material. [source] Bis[2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidin-1-ium] dl -malateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009S. Franklin Racemic malic acid and trimethoprim [5-(3,4,5-trimethoxybenzyl)pyrimidine-2,4-diamine] form a 1:2 salt (monoclinic, P21/c), 2C14H19N4O3+·C4H4O52,, in which the malate component is disordered across a centre of inversion. The crystal structure of the salt consists of protonated trimethoprim residues and a malate dianion. The carboxylate group of the malate ion interacts with the trimethoprim cation in a linear fashion through pairs of N,H...O hydrogen bonds to form a cyclic hydrogen-bonded motif. This is similar to the carboxylate,trimethoprim cation interaction observed earlier in the complex of dihydrofolate reductase with trimethoprim. The structure of the salt of trimethoprim with racemic dl -malic acid reported here is the first of its kind. The present study investigates the conformations and the hydrogen-bonding interactions, which are very important for biological functions. The pyrimidine plane makes a dihedral angle of 78.08,(7)° with the benzene ring of the trimethoprim cation. The cyclic hydrogen-bonded motif observed in this structure is self-organized, leading to novel types of hydrogen-bonding motifs in supramolecular patterns. [source] | ||||||||||