螺旋手性SWCNT的尺寸对赖氨酸分子手性转变反应的限域影响

采用量子力学与分子力学组合的ONIOM方法,研究了两种构象的赖氨酸分子限域在螺旋手性单壁碳纳米管内的手性转变机理.结构分析表明:纳米管管径越小,限域在其中的赖氨酸分子骨架形变越明显,手性碳上的氢原子与氨基上氮的氮原子距离越小.势能面计算表明,两种构象的赖氨酸分子限域在SWCNT(6,4)时,旋光异构反应决速步的吉布斯自由能垒分别是194.72和170.08kJ·mol~(-1),分别由质子从手性碳向氨基氮和质子从手性碳向氨基氮与氨基上的质子向羰基氧双质子协同迁移的过渡态产生的.与裸反应的此通道决速步能垒252.6kJ·mol~(-1)相比较有显著降低.两种构象的赖氨酸分子限域在SWCNT(6,4)内旋光异构反应的表观能垒分别是160.00和178.59kJ·mol~(-1).他们限域在SWCNT(7,4)内时,旋光异构反应决速步的能垒分别是238.28和217.18kJ·mol~(-1);限域在SWCNT(8,4)内时,旋光异构反应决速步的能垒分别是253.00和250.11kJ·mol~(-1).结果表明:螺旋手性单壁碳纳米管的孔径越小,对赖氨酸分子手性转变反应的限域催化作用越好;限域在SWCNT(6,4)内的赖氨酸分子构象1更容易旋光异构.

The Tonfined Effect of the Size of Helically Chiral SWCNT on the Chiral Transition Reaction of Lys Molecules

The chiral transitionmechanism of two conformations of Lys molecules confined in the helically chiral SWCNT was studied by introducing the ONIOM methodsusing combination of quantum mechanics and molecular mechanics.The structural analysis shows that the smaller the diameter of the nanotube,the more obvious the molecular skeleton deformation of the lysine in the confinement region,the smaller the distance between the hydrogen atom on the chiral carbon and the nitrogen atom of the amino.Calculations of potential energy surface indicate that when two conformations of Lys molecules confined in the SWCNT(6,4),the Gibbs free energy barrier of the rate-determining step of the optical isomerization reaction are 194.72 and 170.08 kJ · mol-1,which are respectively generated by the transition states that the proton transferred from the chiral carbon to nitrogen,and the double protons collaboratively transferred from the chiral carbon to the amino nitrogen and from amino and carbonyl oxygen,which is obviously lower than that the Gibbs free energy barrier of the rate-determining step of bare reaction in the same channel,i.e.252.6 kJ · mol-1.The apparent energy barrier of the optical isomerization reaction of two conformations of Lys molecules confined in the SWCNT(6,4) are 160.00 and 178.59 kJ · mol-1,respectively.They confined in the SWCNT(7,4),the energy barrier of the rate-determining step of the optical isomerization reaction are 238.28 and 217.18 kJ · mol-1.They confined in the SWCNT(8,4),the energy barrier of the rate-determining step of the optical isomerization reaction are 253.00 and 250.11 kJ · mol-1.The results show that the smaller the pore size of the helically chiral SWNT,the better the confined catalysis of the chiral transition reaction of Lys molecules,and the easier the optical isomerization reaction of the conformation on of Lys molecules confined in SWCNT(6,4).