The study investigated the mechanism of optical isomerism of two stable conformations of lysine catalyzed by hydroxide ion groupwater clusters and the damage induced by hydroxy radicals in water environment of two conformations of valine molecules by using MP2/6-311++G(2df

pd)∥B3LYP/6-31+G(d

p) dualtheory. The result of reaction channels showed that there are two channels a and b in the optical isomer reaction of lysine. In channel a

the substrate was formed by hydrogen bonds of hydroxide ionwater clusters with

α

-H and N of amino groups; hydroxide ion abstracted

α

-H

and then

α

-C abstracted the hydrogen of two water clusters at the other side. And in channel b

the substrate was formed by hydrogen bonds of hydroxide ion-water clusters with

α

-H and O of carbonyl groups; hydroxide ion abstracted

α

-H

and then

α

-C abstracted the hydrogen of two water clusters at the other side. Lysine can be damaged by hydroxy radicals abstracting hydrogen in channel b. The potential energy surface calculation showed that the dominant optical isomerism reaction channels are channel b both in conformation 1(monohydrogen bond between amino- and carboxyl-group) and 2(dual-hydrogen bond between amino- and carboxyl-group)

and the energy barriers of rate-limiting steps are 49.94

60.41 kJ/mol

relatively. So the damage by hydroxy radical of conformation 1 and conformation 2 in channel b was low or non-barrier exothermic reactions.