Research Center of Laser Fusion, China Academy of Engineering Physics , Mianyang 621900, China.
J Phys Chem A. 2014 Mar 6;118(9):1684-96. doi: 10.1021/jp411403w. Epub 2014 Feb 21.
Extensive ab initio molecular calculations have been first performed to thoroughly characterize the gas-phase potential energy surfaces (PES) of the 21th amino acid selenocysteine and related ions (neutral, protonated and deprotonated). A wide range of trial structures generated by considering the combinations of all internal single-bond rotamers was surveyed at the BHandHLYP/6-31G(d) level, and then refined at the BHandHLYP/6-311++G(d,p) level. A total of 76, 23, 38, and 3 unique stable conformers respectively for neutral, protonated, deprotonated, and doubly deprotonated selenocysteine is identified, and neutral zwitterionic forms are found to be as local minima on the gas-phase PES. The properties of the low energy conformers, such as relative energies, dipole moments, rotational constants, and intramolecular hydrogen bonds, were determined and analyzed. The thermochemical properties of proton affinity (PA), gas-phase basicity (GB), proton dissociation energy (PDE), gas-phase acidity (GA), and the vertical ionization energies (VIEs) were computed by the theoretical approaches of BHandHLYP, B3LYP, MP2, and CCSD(T). Moreover, the conformational equilibrium effect (CEE) on thermochemical properties was analyzed. The statistical simulation predicts that the CEE generally yields a physical correction on about a 1 kBT scale in GA/GB calculations for multi-conformer systems.
已首次进行了广泛的从头算分子计算，以彻底表征第 21 种氨基酸硒代半胱氨酸及相关离子（中性、质子化和去质子化）的气相势能面（PES）。在 BHandHLYP/6-31G(d)水平上，考察了考虑所有内部单键旋转异构体组合生成的各种试探结构，然后在 BHandHLYP/6-311++G(d,p)水平上进行了优化。分别确定了中性、质子化、去质子化和双去质子化硒代半胱氨酸的 76、23、38 和 3 种独特稳定构象，并且发现中性两性离子形式是气相 PES 上的局部最小值。确定并分析了低能构象的性质，如相对能量、偶极矩、转动常数和分子内氢键。通过 BHandHLYP、B3LYP、MP2 和 CCSD(T）等理论方法计算了质子亲和能（PA）、气相碱度（GB）、质子离解能（PDE）、气相酸度（GA）和垂直电离能（VIE）的热化学性质。此外，还分析了构象平衡效应对热化学性质的影响。统计模拟预测，对于多构象体系的 GA/GB 计算，CEE 通常会在 GA/GB 计算中产生约 1 kBT 尺度的物理校正。
