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Ca2+ Cations (ca2+ + cation)
Selected AbstractsFormation of 2,4,D complexes on montmorillonites , an ab initio molecular dynamics studyEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007D. Tunega Summary Sorption of the anionic form of the pesticide 2,4,D (2,4,dichlorophenoxyacetic acid) on the surface of the clay mineral montmorillonite was investigated using a short-time ab initio molecular dynamics (MD) simulation at room temperature. Three different situations were modelled: sorption on a dry surface, on a hydrated surface and an intercalation between montmorillonite layers. In all three cases, the calcium cation compensates the excess negative charge of the montmorillonite layer and the negative charge of the 2,4,D anion. It was found that in all models with direct contact of the Ca2+ cation with the montmorillonite layer, the most stable position of Ca2+ is above the ditrigonal hole of the mineral layer. While in the case of a dry surface very stable bidentate binding is created between the 2,4,D anion and the Ca2+ cation, the formation of the monodentate complexes is preferred in all models that include water molecules. Hydrogen bonds formed between water molecules and the 2,4,D anion make a considerable contribution to the formation of the monodentate complexes. Tetrahedral substitutions in the montmorillonite layer have a significant effect on the formation of the complexes of any type. However, the MD simulations did not support the role of Ca2+ as a cation bridge in the adsorption mechanism. Calculations showed that hydrated 2,4,D···Ca2+ complexes are thermodynamically more stable than complexes in which the Ca2+ cation acts as a bridge to the surface. On the other hand, it is possible that phyllosilicates with a greater concentration of isomorphic substitutions (e.g. mica) will be able to form stable surface complexes with a cation bridge mechanism. [source] A non-twinned polymorph of CaTe2O5 from a hydrothermally grown crystalACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2008Matthias Weil In contrast with the multiple twinning and/or domain formation found in the mica-like polymorphs of CaTe2O5, calcium pentaoxidoditellurate(IV), that have been prepared by solid-state reactions and for which complete structure determinations have not been successful up to now, the crystal structure of a hydrothermally grown phase was fully determined from a non-twinned crystal. The structure is made up of alternating layers of Ca2+ cations and of 2,[Te2O5]2, anions stacked along [100]. The lone-pair electrons E of the TeIV atoms are stereochemically active and protrude into channels within the anionic layer. In comparison with analogous MIITe2O5 structures (M = Mg, Mn, Ni or Cu) with ditellurate(IV) anions that are exclusively made up of corner-sharing TeOx (x = 3,5) polyhedra resulting in flat 2,[Te2O5]2, layers, the anionic layers in CaTe2O5 are undulating and are built of corner- and edge-sharing [TeO4] polyhedra. [source] The double-layered hydroxide 3CaO·Al2O3·0.5CaBr2·0.5CaCl2·10H2OACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2001Jean-Philippe Rapin The title compound, calcium oxide,dialuminium trioxide,calcium dibromide,calcium dichloride hydrate (3/1/0.5/0.5/10), also formulated as Ca2Al(OH)6Br0.478Cl0.522·2H2O (dicalcium aluminium hydroxide hemibromide hemichloride dihydrate), is a double-layered hydroxide which belongs to the solid solution Ca2Al(OH)6BrxCl1,x·2H2O, where x can vary from 0 to 1. Chloride and bromide anions of the negatively charged interlayer [Br0.5Cl0.5·2H2O], share statistically the same crystallographic site. Al3+ and Ca2+ cations are coordinated by six and seven O atoms, respectively. All water molecules are bonded to Ca2+ cations and assume the seventh coordination position. Anions in the interlayer are surrounded by ten H atoms. Br, and Cl, are therefore connected to the main layer by ten hydrogen bonds, six of 2.74,(2),Å and four of 2.52,(5),Å, where the donors are hydroxyl groups and water molecules, respectively. Like the chloride equivalent, the title compound is a 6R polytype with trigonal space group Rc and lattice parameters a = 5.7537,(4),Å and c = 48.108,(4),Å. [source] Calcium(II) meso -2,3-diphenylsuccinate heptahydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000Gregory Morin The title compound, [Ca(C16H12O4)(H2O)6]·H2O, adopts a conformation about the central C,C bond that places the two carboxylate groups in an anti orientation. The crystal consists of layers of two-dimensional arrays of 2,3-diphenylsuccinate dianions which are linked by bridging Ca2+ cations. The unit cell contains two Ca2+ cations in an unusual four-membered Ca,O,Ca,O ring in which the bridging O atoms belong to water molecules rather than carboxylates, i.e. poly[[[di-,-aqua-bis[pentaaquacalcium(II)]]-,-(meso -2,3-diphenylsuccinato- O:O,)] succinate dihydrate]. [source] Live-Cell Imaging with Water-Soluble Aminophenoxazinone Dyes Synthesised through Laccase BiocatalysisCHEMBIOCHEM, Issue 10 2010Frédéric Bruyneel Dr. Abstract Aminophenoxazinone dyes with variable water solubilities were assayed for the first time in a live-cell imaging application. Among a library of ten sulfonylated chromophores, one compound gave excellent results as an endocytic marker, showing a precise subcellular distribution. The compound was compared to four commercial vital tracers, including Lucifer Yellow. The first laccase-mediated regioselective synthesis of a diphosphorylated 2-aminophenoxazinone dye was also described. This compound, water-soluble at 10,2,M, displayed modest fluorescence properties and the ability to complex Mg2+ and Ca2+ cations, therefore giving fluorescence quenching. [source] | ||||||||||