Abstract:

The molecular structure and chiral shift mechanism of α-alanine inside singlewalled armchair SWCNT(5,5),(6,6),(7,7), zigzag SWCNT(9,0),(10,0),(11,0), spiral SWCNT(8,2),(8,3),(8,4),(9,1),(9,2) and (9,3) were studied by  the combined method of quantum chemistry ONIOM (B3LYP/631++g*: UFF). The analysis of molecular structure shows that compared with that of the monomer α-alanine, the molecular structure of α-alanine which is limited to the carbon nanotube of small diameter is significantly stretched along the axial direction of the nanotube.   The bond angle of skeleton C—C—C and H—N—H significantly increased.  The dihedral angles of skeleton C—C—N—C significantly increased.  The researches on the reaction channel and paths of chiral shift show that there is a channel with the help of which hydrogen first transfers inside hydroxyl and then hydrogen in chiral carbon transfers, making hydroxyl 11O as a bridge. The calculation of potential energy surface in chiral shift reaction shows that when α-alanine is limited to the small diameter of the SWCNT(5,5),(9,0),(8,2),(9,1), the energy barriers of hydrogen transfer inside the carboxyl and hydrogen transfer from the chiral carbon to the carbonyl group are significantly reduced. The results show that when α-alanines are limited to carbon nanotubes, the energy barriers of hydrogen transfer of chiral transition decreases with the decreasing diameter of carbon nanotubes. The difference in nanotube chirality makes little effect on energy barrier in the process of hydrogen transfer.

Key words: single-walled carbon nanotubes (SWCNT), α-alanine, chiral transition, density functional theory, transition state, ONIOM method