The mechanisms of α-H and proton transfers of glycine induced by Mg²⁺

Abstract

A MP2/6-31++G(d,p)//B3LYP/6-31++G(d,p) method was used to investigate the mechanisms of α- H and proton transfers of glycine induced by Mg 2+. Eight complexes were obtained, six of which were neutral and the other two were zwitterionic. Among them, the zwitterion with a binding energy of 159.4 kcal/mol was the most stable structure. Conformation transformations of the complexes caused by the rotation of single bond and the transfers of α- H and proton were completed via seven transition states. The inductive effect of Mg 2+ made the electron cloud of glycine deviate to Mg 2+, which activated the covalent bond involving the transferred proton. The neutral complex can be turned into the zwitterionic one by the transfers of both carboxyl hydrogen and α- H , and the energy barrier of each reaction was less than 9.2 kcal/mol. After the transfer of α- H , a delocalized π bond was formed in glycine skeleton and the α- C atom took 0.19 positive charges. So the chemical activity of the glycine enhanced, and glycine was readily available for addition and nucleophilic substitution reactions. The path from the most stable glycine conformer G1 to the zwitterionic conformation I is G1 → G1–G3 → G3 → G3–G4 → G4 → G2–G4 → G2 → VI → I–VI → I, and the highest energy barrier of this path is 9.2 kcal/mol.

Interaction of Cysteine with Li+ and LiF in the Presence of (H2O)n (n = 0–6) Clusters

“…14 Cation–amino acid clusters have been intensively studied in solution and in the gas phase over recent years to provide insights into ion–amino acid interactions. 14 − 25 However, the study of anionic species is substantially less intensive, despite the fact that proteins and enzymes usually are negatively charged. 26 − 29 The investigation 29 of the complexation of the halide ion to the gas-phase amino acids reveals that the zwitterionic and canonical minima are very close in energy for arginine·Br – , whereas the canonical form is significantly lower for arginine·Cl – .…”

“…Therefore, further investigations on how ions interact with biological molecules and how these interactions affect, adjust, or control the functions of biological molecules are essential for a better understanding of the role and effect of ions in biological systems . Cation–amino acid clusters have been intensively studied in solution and in the gas phase over recent years to provide insights into ion–amino acid interactions. − However, the study of anionic species is substantially less intensive, despite the fact that proteins and enzymes usually are negatively charged. − The investigation of the complexation of the halide ion to the gas-phase amino acids reveals that the zwitterionic and canonical minima are very close in energy for arginine·Br – , whereas the canonical form is significantly lower for arginine·Cl – . It is noteworthy that the cation–anion correlation effect profoundly affects the ion–amino acid interactions and needs to be taken into consideration.…”