Abstract: Using the B3LYP method of density functional theory,  we investigated the chiral transition process of the methionine molecule under the cooperative a
ction of monoH₂O at the level of 6-311+-G(2-df-). We drawed a complete chiral transition path reaction potential energy surface by finding structures of the extreme value points including the transition states and intermediates, and analyzed the geometric and electronic structure properties of extreme value points. The results show that the hydrogen atom on the chiral carbon atom of Smethionine molecule can transfer to the other side of the carbon atom via the 10O-19O atoms of carboxyl atoms as a bridge, and achieve the chiral transition of methionine molecule from Stype to Rtype. On this path there are four intermediates and five transition states. The maximum reaction energy barrier is 199.275 5 kJ/mol, which comes from the second transition state TS₂-S-Met&1H₂O₂.

Key words: chirality, transition state, methionine, density functional theory (DFT)