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Zinc Cations (zinc + cation)
Selected AbstractsLigand-Exchange Processes on Solvated Zinc Cations: Water Exchange on [Zn(H2O)4(L)]2+,2,H2O (L=Heterocyclic Ligand)CHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2010Basam Abstract The water-exchange mechanisms of [Zn(H2O)4(L)]2+,2,H2O (L=imidazole, pyrazole, 1,2,4-triazole, pyridine, 4-cyanopyridine, 4-aminopyridine, 2-azaphosphole, 2-azafuran, 2-azathiophene, and 2-azaselenophene) have been investigated by DFT calculations (RB3LYP/6-311+G**). The results support limiting associative reaction pathways that involve the formation of six-coordinate intermediates [Zn(H2O)5(L)]2+,H2O. The basicity of the coordinated heterocyclic ligands shows a good correlation with the activation barriers, structural parameters, and stability of the transition and intermediate states. [source] Theoretical studies on farnesyl transferase: Evidence for thioether product coordination to the active-site zinc sphereJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2007Sérgio Filipe Sousa Abstract Farnesyltransferase (FTase), an interesting zinc metaloenzyme, has been the subject of great attention in anticancer research over the last decade. However, despite the major accomplishments in the field, some very pungent questions on the farnesylation mechanism still persist. In this study, the authors have analyzed a mechanistic paradox that arises from the existence of several contradicting and inconclusive experimental evidence regarding the existence of direct coordination between the active-site zinc cation and the thioether from the farnesylated peptide product, which include UV,vis spectroscopy data on a Co2+ -substituted FTase, two X-ray crystallographic structures of the FTase-product complex, and extended X-ray absorption fine structure results. Using high-level theoretical calculations on two models of different sizes, and QM/MM calculations on the full enzyme, the authors have shown that the farnesylated product is Zn coordinated, and that a subsequent step where this Zn bond is broken is coherent with the available kinetic results. Furthermore, an explanation for the contradicting experimental evidence is suggested. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Coordination polymers and hydrogen-bonded assemblies of 2,2,-[2,5-bis(carboxymethoxy)-1,4-phenylene]diacetic acid with ammonium, lanthanum and zinc cationsACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Hatem M. Titi We report the synthesis of the 2,2,-[2,5-bis(carboxymethoxy)-1,4-phenylene]diacetic acid (TALH4) ligand and the structures of its adducts with ammonium, namely diammonium 2,2,-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetate, 2NH4+·C14H12O102,, (I), lanthanum, namely poly[[aquabis[,4 -2,2,-(2-carboxylatomethyl-5-carboxymethyl-1,4-phenylenedioxy)diacetato]dilanthanum(III)] monohydrate], {[La2(C14H11O10)2(H2O)]·H2O}n, (II), and zinc cations, namely poly[[{,4 -2,2,-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetato}zinc(II)] trihydrate], {[Zn(C14H12O10)]·3H2O}n, (III), and poly[[diaqua(,2 -4,4,-bipyridyl){,4 -2,2,-[2,5-bis(carboxymethyl)-1,4-phenylenedioxy]diacetato}dizinc(II)] dihydrate], {[Zn2(C14H10O10)(C10H8N2)(H2O)2]·2H2O}n, (IV), the formation of all four being associated with deprotonation of TALH4. Adduct (I) is a diammonium salt of TALH22,, with the ions located on centres of crystallographic inversion. Its crystal structure reveals a three-dimensional hydrogen-bonded assembly of the component species. Reaction of TALH4 with lanthanum trinitrate hexahydrate yielded a two-dimensional double-layer coordination polymer, (II), in which the LaIII cations are nine-coordinate. With zinc dinitrate hexahydrate, TALH4 forms 1:1 two-dimensional coordination polymers, in which every ZnII cation is linked to four neighbouring TALH22, anions and each unit of the organic ligand is coordinated to four different tetrahedral ZnII cation connectors. The crystal structure of this compound accommodates molecules of disordered water at the interface between adjacent polymeric layers to give (III), and it has been determined with low precision. Another polymer assembly, (IV), was obtained when zinc dinitrate hexahydrate was reacted with TALH4 in the presence of an additional 4,4,-bipyridyl ligand. In the crystal structure of (IV), the bipyridyl and TAL4, entities are located on two different inversion centres. The ternary coordination polymers form layered arrays with corrugated surfaces, with the ZnII cation connectors revealing a tetrahedral coordination environment. The two-dimensional polymers in (II),(IV) are interconnected with each other by hydrogen bonds involving the metal-coordinated and noncoordinated molecules of water. TALH4 is doubly deprotonated, TALH22,, in (I) and (III), triply deprotonated, viz. TALH3,, in (II), and quadruply deprotonated, viz. TAL4,, in (IV). This report provides the first structural characterization of TALH4 (in deprotonated form) and its various supramolecular adducts. It also confirms the potential utility of this tetraacid ligand in the formulation of coordination polymers with metal cations. [source] | ||||||||||