title: Dinuclear Calcium Complexes with Intramolecularly NH.O Hydrogen-Bonded Dicarboxylate Ligands.
abstract: A novel dinuclear calcium complex, [Ca(2){(2-OCO-3-CH(3)C(6)H(3)NHCO)(2)C(CH(3))(2)}(2)(CH(3)OH)(6)] (1), was synthesized as a structural model of 8-coordinated Ca(II) ions in the double calcium-binding site of thermolysin. The complex has four NH.O hydrogen bonds between the amide NH and the carboxylate oxygen anion. Two types of bridging coordination of the carboxylate ligand to Ca(II) were found in 1. The amide NH forms a strong NH.O hydrogen bond with the anionic oxygen of the two carboxylate oxygens. A ligand-exchange reaction between the dinuclear calcium complex and eight equimolar amounts of 2,4,6-trimethylbenzoic acid or 2-CH(3)-6-t-BuCONHC(6)H(3)COOH indicates that the NH.O hydrogen bond prevents the dissociation of the Ca-O bond.
authors.affiliation: Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba 274-0072, Japan.
authors.forename: Norikazu
authors.initials: N
authors.lastname: Ueyama
authors.forename: Jiro
authors.initials: J
authors.lastname: Takeda
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Yamada
authors.forename: Akira
authors.initials: A
authors.lastname: Onoda
authors.forename: Taka-aki
authors.lastname: Okamura Ta
authors.forename: Akira
authors.initials: A
authors.lastname: Nakamura