Department of Chemistry, University of Catania , viale A. Doria 6, Catania -95125, Italy.
J Phys Chem A. 2013 Jun 20;117(24):5184-94. doi: 10.1021/jp403155q. Epub 2013 Jun 7.
Ab initio and density functional theory calculations have been carried out on dipole moments (μ), polarizabilities (α), and second-order hyperpolarizabilities (γ) of single chain β-strand oligoglycines in the gas phase. Basis set and electron correlation effects have been investigated. The long-range corrected CAM-B3LYP and ωB97X-D functionals furnish satisfactory results in agreement with correlated ab initio computations. The dependence of μ, α, and γ values per unit cell on chain length has been explored, extrapolating the properties in the limit of the polymer. The increase of the response electronic properties with the number of glycine units has been rationalized through the two-state model involving the typical π-π* NV1 electronic transition of peptides. The effect of the secondary structure on the electric properties has been discussed. At variance from the dipole moments, the γ values increase on going from the α-helices to the β-strands, whereas the α values are little influenced by the conformation of the oligoglycines.
采用从头算和密度泛函理论方法，对气相中单链 β-折叠寡肽的偶极矩（μ）、极化率（α）和二阶超极化率（γ）进行了计算。研究了基组和电子相关效应对计算结果的影响。长程修正的 CAM-B3LYP 和 ωB97X-D 泛函与相关从头算计算结果吻合良好。研究了单位细胞中 μ、α 和 γ 值随链长的变化，将聚合物极限下的性质外推。通过涉及典型的肽 π-π* NV1 电子跃迁的两态模型，解释了响应电子性质随甘氨酸单元数增加而增加的原因。讨论了二级结构对电性质的影响。与偶极矩不同，γ 值从α-螺旋增加到β-折叠，而α 值受寡肽构象的影响很小。
