单壁碳纳米管尺寸和手性对α-丙氨酸分子手性转变限域的影响

摘要

用量子化学 ONIOM(B3LYP/6-31++ g*：UFF)方法,考察扶椅型单壁碳纳米管SWCNT(5,5),(6,6),(7,7)、锯齿型 SWCNT (9,0),(10,0),(11,0)和螺旋型 SWCNT (8,2),(8,3),(8,4),(9,1),(9,2),(9,3)中的α-Ala 分子结构和手性转变机制。结果表明：与单体相比,当α-Ala 分子限域在直径小的 SWCNT 中时,其 C—C—C 键角、C—C—N—C 二面角和 H—N—H 键角增加较大,其他结构参数值略有增减；只存在 H 先在羧基内转移,手性碳上的 H 再以羰基11 O 为桥梁转移的反应通道；当α-Ala 分子限域在 SWCNT(5,5),(9,0),(8,2),(9,1)中时,羧基内 H 转移和 H 从手性碳转移到羰基的能垒较低；α-Ala 分子限域在 SWCNT 中的 H 转移反应能垒随管径的减小而降低；不同手性的 SWCNT 对 H 转移反应能垒影响较小。%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),(1 1,0),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 1 1 O 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 whenα-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.