The chiral conversion mechanism and water solvation effect of three kinds of the most stable configurations of tyrosine molecules were researched by using the B3LYP method of density functional theory

the MP2 method of perturbation theory

and smd model method of self consistent reaction field theory. The study of reaction channels shows that there are three channels a

b and c in the title reaction. For the configuration one and two

the proton of the chiral carbon is transferred with amino group after the carboxyl cistrans isomerism

amino group and carboxyl/amino groups as the bridge

respectively. For the configuration three

the proton is transferred with amino group and carboxyl/amino groups as the bridge

and transferred proton of the carboxyl is transferred with amino group as the bridge

respectively. Calculations of potential energy surface show that channel a is the dominant reaction path in the configuration one and two

stepdetermining gibbs free energy barriers are 257.0 and 264.0（kJ·mol

-1

），respectively. In addition

channel b and c are the dominant reaction paths in the configuration three

step-determining gibbs free energy barriers are 257.4 and 257.0 kJ·mol

-1

which are generated by the transition state of proton transfer from the chiral carbon to the amino N. The water solvation effect enables the stepdetermining energy barrier is reduced to 113.1 kJ·mol

-1

for the dominant reaction path in the configuration one. The results show that: monomer tyrosine molecule is stable

tyrosine chiral conversion can be proceeded slowly in water environment.