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Metal Ion Binding by Amino Acids. - Preparation and Crystal Structures of two Calcium L-Aspartate Hydrates
Schmidbaur, Hubert,Bach, Ina,Wilkinson, Dallas L.,Mueller, Gerhard
, p. 1439 - 1444 (2007/10/02)
Crystalline calcium(II) L-aspartate dihydrate, Ca(L-Asp) * 2H2O (2), has been obtained in a three-step procedure from CaCO3 and L-aspartic acid L-AspH2 via calcium bis(L-hydrogenaspartate) Ca(L-AspH)2 and calcium hydrogen L-aspartate chloride dihydrate Ca(L-AspH)Cl * 2H2O.The crystals of 2 are orthorhombic, space group P212121.The structure is a coordination polymer with the metal atoms arranged in double chains interconnected by aspartate dianions.Each Asp(2-) ligand is coordinated to the metal ion as a N,Oα,Oβ tripod.In addition, two water molecules and three β-carboxylate oxygen atoms from neighbouring units are also coordinated to each metal atom, giving a coordination number of eight for each calcium.The β-carboxylate oxygen atoms form also a bridge between metals of a parallel chain of metal atoms. - A crystalline tetrahydrate (monoclinic, space group C2) Ca(L-Asp) * 4H2O (1) has been prepared from L-AspH2 and Ca(OH)2.The structure contains two molecules in the asymmetric unit.Each calcium atom is seven-coordinate and surrounded by an N,Oα-chelating L-Asp(2-) ligand, four water molecules, and one oxygen atom of the β-carboxylate group of a neighbouring molecule.Due to this interaction, the monomeric units are linked to give a one-dimensional coordination polymer chain. - In both structures the double strands and chains, respectively, are crosslinked by a network of hydrogen bonds. - Keywords: L-Aspartate complexes / Amino acid complexes / Calcium L-aspartate dihydrate / Calcium L-aspartate tetrahydrate / Hydrogen bonding
