ZHAO Xiaobo, LI Chenjie, WANG Zuocheng, et al. Chiral transition mechanism and water solvation effect of leucine molecules based on the amino proton transfer bridge[J]. Acta Scientiarum Naturalium Universitatis SunYatseni, 2017,56(3):85-92.
ZHAO Xiaobo, LI Chenjie, WANG Zuocheng, et al. Chiral transition mechanism and water solvation effect of leucine molecules based on the amino proton transfer bridge[J]. Acta Scientiarum Naturalium Universitatis SunYatseni, 2017,56(3):85-92.DOI:
The title reaction mechanism was explored by using the B3LYP density functional theory
the MP2 method of perturbation theory and smd model method of self consistent reaction field theory. The study of reaction channels showed that there are two channels a
b in the chiral transition reaction
and in the one the proton is transferred from one side to the other of chiral carbon with only the amino as a bridge
in the other with carbonyl and amino N as the bridge successively. The molecular structure analysis showed that the sevenring structure in the transition state aTS2·2H
2
O is almost coplanar and each hydrogen bond angles of the seven-ring structure approach straight angle. Calculations of potential energy surface pointed out that the channel a is the dominant reaction channel and the free energy barrier of the rate-determining step is 249.5 kJ·mol
-1
which is caused by the transition state with proton migration from chiral carbon to amino nitrogen. Moreover
with consideration of two water molecules as H transfer media and with inclusion of the water solvation effect of the continuous medium model
the free energy barrier of the rate-determining step is reduced to 113.2 kJ·mol
-1
and the reaction rate constant is 5.85×10
-8
s
-1
and the water solvation effect enables the energy barrier of the amino heterogeneous reaction increased from 13.4 kJ·mol
-1
to 19.3 kJ·mol
-1
. Therefore
water solvation effect can hinder the heterogeneous reaction of non proton transfer
and the interaction of the catalytic action of water molecules and water solvation effect can cooperatively reduce the proton transfer reaction energy barrier to a large degree.