Conformational Switching between Carboxylic Acid and Carboxylate Anion States by NH...O Hydrogen Bonding

摘要

Biologically important Ca-proteins and Ca-biominerals as metal-polymer complexes are often regulated by the complexation and demetalation with the biopolymers. Metal-oxygen bond is supported by NH...O hydrogen bonds between coordinating oxyanion and neighboring amide NH and by the successive hydrogen bonding networks. Carboxylate anion under hydrophobic conditions has a high basicity that leads to a covalent Ca-O bond character that is significantly affected by the NH...O hydrogen bond. The hydrogen bonds in Asp-containing tripeptide fragments in Ca-proteins presumably control coordination/dissociation of metal-oxygen bonds. Our systematic studies of Carboxylate, sulfonate and phosphate Ca(II) complexes demonstrate a relationship between the basicity of oxyanion in Carboxylate and hydrogen bonds as cooperating with the oligopeptide conformation in Asp-containing Ca(II) complexes. Hydrogen bonds between Carboxylate oxyanion and amide NH, controlled by a conformational switching of oligopeptide fragments, seem to be one of essential factors for the regulatory formation of Ca-proteins and nano-architectures in connection with the interface structure of inorganic and organic phases in biominerals.