α-螺旋型寡聚L-乳酸的计算研究

Computational Study on the L-Lactic Acid Oligomers in α-Helix

在CAM-B3LYP/6-311+G*水平,对气相中α-螺旋型寡聚L-乳酸的几何结构、热力学性质和谱学性质进行了详细的计算研究,并根据概念密度泛函理论对各稳定结构的化学性质进行考察。链长与聚合度满足拟合方程:Y=0.37087×e(n2.88711)+8.61611,R2=0.90099。寡聚L-乳酸通过三种氢键形成螺旋状寡聚物。热力学数据显示,熵值与聚合度呈较好线性相关,其拟合方程为Y=27.75?n+88.711,R2=0.9964。计算得到的各结构中C=O、COO-H和O-H键的伸缩振动频率与实验值相比,发生蓝移。PLLA7的亲电指数最小,酸性最强。

The geometrical structures, thermodynamics, spectral property and the conceptual density func-tional analysis of L-lactic acid oligomers in α-helix were calculated at CAM-B3LYP/6-311+G* level in gas phase. The chain length of PLLAn and the degree of polymerization obey the equation: Y=0.37087 ×e(n/2.88711) +8.61611,R2=0.90099 . The results showed that three types of intramolecular hydrogen bonds were beneficial to form the L-lactic acid oligomers in α-helix. The values of ther-modynamics showed linear correlation of entropy (S) of PLLAn and the degree of polymerization: Y=27.75·n+88.711,R2=0.9964 . Compared with the experimental values, the stretching vibrational frequencies of the C=O, COO-H and O-H bonds exhibit a general blue shift. Among all of the structures, the electrophilicity indexes of PLLA7 are the smallest, but its acidity is the strongest.