科研之友
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摘要
The catalysis of water molecules and the chiral transition of two stable configurations of alanine (Ala) and Ca2+ complexes in gas phase have been studied using the M06 method based on density functional theory. The study shows that the Ala_1?Ca2+ chiral transition has two pathways a and b. In pathway a, α-H is transferred merely using carbonyl O atom as a bridge. In pathway b, the proton on the amino group transfers to α-C from inside paper after α-H is transferred to carbonyl O atom. The Ala_2?Ca2+ chiral transition has four pathways a, b, c and d. In pathway a, α-H is transferred merely using carbonyl O atom as a bridge after the transition of proton on the carboxyl group. In pathway b, α-H is transferred to carbonyl O atom and then proton transfers from the amino group N atom to α-C after the transition of proton on the carboxyl group. In pathway c, α-H is transferred to the amino group N atom after the coordination bond between calcium and nitrogen is broken. In pathway d, the coordination bond between calcium and nitrogen is broken and Ala_2?Ca2+ is isomerized to Ala_1?Ca2+, then Ala_1?Ca2+ achieves the chiral transition. The potential energy surface calculation shows that the dominant pathway of the chiral transition of Ala_1?Ca2+ is pathway a, and the total energy barrier is 134.8 kJ?mol-1. The dominant pathway of the chiral transition of Ala_2?Ca2+ is pathway d, and the total energy barrier is 235.3 kJ?mol-1. The catalysis of water molecules then reduces them to 40.8 kJ?mol-1 and 141.3 kJ?mol-1 respectively. The results show that Ca2+ has a catalytic effect on the chiral transition of Ala, and water molecule has an excellent catalytic effect on the chiral transition of Ala and Ca2+ complexes.
