title: Contribution of intramolecular NH···O hydrogen bonds to magnesium-carboxylate bonds.
abstract: A series of magnesium carboxylate complexes containing intramolecular NH···O hydrogen bonds were synthesized. Their molecular structures were determined by X-ray analysis. A direct NH···O hydrogen bond to the coordinated oxygen atom elongated the Mg-O bond, while a hydrogen bond to the carbonyl group shortened the Mg-O bond. Double NH···O hydrogen bonds significantly lowered the basicity of the carboxylate anion and prevented coordination to the Mg ion in a trans configuration; however, a cis-dicarboxylate complex was successfully obtained. Strong coordination of water to the Mg(2+) ion stabilizes the weak Mg-carboxylate bond at the trans position. In contrast, a weak Mg-carboxylate bond strengthens the Mg-O(water) bond, probably increasing the acidity. Based on the experimental results and theoretical calculations, a new switching mechanism is proposed. In the proposed mechanism, the acidity of the coordinated water on magnesium is controlled during catalytic hydrolysis in endonuclease.
authors.affiliation: Department of Macromolecular Science, Graduate School of Science, Osaka University , Toyonaka, Osaka 560-0043, Japan.
authors.forename: Taka-aki
authors.initials: TA
authors.lastname: Okamura
authors.forename: Junko
authors.initials: J
authors.lastname: Nakagawa
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008274:Magnesium / Q000737:chemistry*; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D002264:Carboxylic Acids; D008274:Magnesium; D009584:Nitrogen