The reaction mechanism of α-Ala chiral transition confined in different sizes of armchair SWCNT， which achieved based on using amino as the proton transfer bridge， was studied using the combined method of quantum mechanics and molecular mechanics at ONIOM (MP2/6-311++G(3df

3pd):UFF)//ONIOM(B3LYP/6-31+G(d

p):UFF). The result of reaction channel analysis showed that armchair SWCNT two channels a and b in different sizes were both found in the chiral transition reaction. Moreover

the amino N was used as a transfer bridge of the proton in the chiral carbon in the channel a

and that in the channel b the carbonyl O and amino N were successively used as a transfer bridge of the proton in the chiral carbon. The calculation of potential energy surface showed that the smaller the pore size of SWCNT

the lower the reaction energy barrier. In SWCNT(5

5)

the highest energy barrier (198.7 kJ·mol

-1

) was obviously lower than that (266.1 kJ·mol

-1

) of the single in channel a

and the highest energy barrier (285.0 kJ·mol

-1

) in channel b was significantly lower than that (326.6 kJ·mol

-1

) of the single. The result implied that the chiral transformation of α-Ala in the biological channels was mainly achieved by using amino as the proton transfer bridge

and that for the chiral transition of α-Ala

the confinement effect of the smaller size of nanotubes reactor in catalysis was more obvious.