Theoretical Studies on Complexes of Calcium Ion with Amino Acids

The complexes formed by calcium ion and 12 common amino acids were investigated systematically in the gas phase at the level of MP2/6-311++G(d,p)//MP2/6-31G(d,p). The results show that the salt-bridge structure is the most preferred motif for Ca2+ binding aliphatic amino acids without heteroatom in the side chain, while charge-solvated(CS) structure is the most preferred motif for Ca2+ binding other amino acids except for glutamine and lysine. IR spectra of Gln-Ca2+ and Asn-Ca2+ complexes were calculated and compared well with the available experiments. From the study in aqueous solution, the bidentate salt-bridge structure was determined to be the most favorable for all the twenty kinds of amino acids to chelate Ca2+ to both the oxygen atoms of the negatively carboxylate group in the backbone.