Abstract: Using the ONIOM methods by combining quantum mechanics and molecular mechanics, we studied the reaction mechanism of the chiral transition of lysine (Lys) molecules conf ined in the armchair single walled boron nitride nanotube (SWBNNT). Using atom centered density matrix propagation (ADMP) molecular dynamics methods, we studied Lys molecules in the SWBNNT(5,5) dynamic reaction path in the inlet and outlet of the potential energy surface in chiral transition reaction channel, and gave images of the microscopic dynamic reaction of intermediates and products. The results show that with the decrease of diameter of nanotube, the bond angle between the skeletal carbon atoms of Lys molecules confined in nanotubes increases obviousl y, and the distance between H and amino N on chiral carbon gradually becomes sma ller. The chiral transition of Lys molecules is achieved by a two\|s tep elementary reaction in SWBNNT(5,5), whereas it is achieved by the three\|ste p and four\|step elementary reactions in SWBNNT(6,6) and SWBNNT(7,7), respective ly. The free energy barrier of the rate\|determining step of Lys molecule chiral transition reaction is reduced to a minimum value of 190.1 kJ/mol in SWCNT(5,5) . The energy barrier of the rate\|determining step is similar to that of bare reaction in SWBNNT(7,7).

Key words: ONIOM method, nanotube, transition state, lysine, chiral transition, density functional