An investigation on ion association betweeen MgCl2 and CaCl2 with Alanine

• 1、State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082

Abstract：The interaction between magnesium or calcium ions with amino acids has not been revealed at the molecular level. Density functional theory and classical molecular dynamics were used to invetigate the association between magnesium and calcium ions with alanine at the molecular level. In the gas phase, the calculated binding energies indicate that the bidentate structures are more stable. In magnesium chloride and calcium chloride aqueous solution, the interactions between magnesium or calcium ions and alanine will not only hinder the association of alanine molecules to some extent, and the hydration of magnesium or calcium ions results in the transformation of the associated structures of alanine molecules in the aqueous solution. The association of magnesium ion with alanine molecule is stronger than that of calcium ion. In dulit salt concentration, magnesium ion directly contacts with alanine molecule, while the association structure of calcium ion with alanine molecule is solvent-shared ion pair. As in the concentrated salt solutions, tthe association between alanine molecules will enhance, and thus become weak in calcium chloride aqueous solution.The analyses show that the association between alanine molecules can be more easily effected by calcium ion in aqueous solutions, and such trend can be contributed to the characteristics of calcium ion.

Keywords： Density functional theory Classical molecular dynamics Alanine Association Intermolecular interaction