Guvench Olgun, Mackerell Alexander D
Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, 20 Penn Street, HSF II-629, Baltimore, Maryland 21201, USA.
J Phys Chem A. 2006 Aug 17;110(32):9934-9. doi: 10.1021/jp0623241.
A proper understanding of the conformational energetics of 1,2-ethanediol (ethylene glycol) is important to the construction of molecular mechanics force fields for the treatment of carbohydrates since these biologically important molecules have a prevalence of vicinal hydroxyl groups. In the present study, quantum mechanical analysis of the 10 unique minimum-energy conformations of ethylene glycol is performed by using 10 model chemistries ranging from HF/6-311++G(d,p) up to a hybrid method that approximates CCSD(T)/cc-pVQZ. In addition, natural bond orbital (NBO) analysis of these conformations with deletion of pairings of CO bond/antibonding and lone pair/antibonding orbitals is used to investigate contributions from the "gauche" effect to ethylene glycol conformational energetics. MP2 with the "correlation consistent" basis sets and DFT/6-311++G(d,p) do the best job of matching the approximate CCSD(T)/cc-pVQZ energies while MP2/6-31G(d) and Hartree-Fock both fare poorly. NBO analysis shows the conformational energies to be independent of the deletion of matrix elements associated with (i) CO bonding and antibonding orbital interactions and (ii) lone pair and antibonding orbital interactions, whereas the energetic ordering correlates with geometric parameters consistent with internal hydrogen bonds. Thus, the present results suggest that standard molecular mechanics potential energy functional forms, which lack explicit terms to account for stereoelectronic effects, are appropriate for carbohydrates.
正确理解1,2 - 乙二醇（乙二醇）的构象能量学对于构建用于处理碳水化合物的分子力学力场很重要，因为这些具有生物学重要性的分子中邻位羟基普遍存在。在本研究中，通过使用从HF/6 - 311++G(d,p)到近似CCSD(T)/cc - pVQZ的混合方法等10种模型化学方法，对乙二醇的10种独特的最低能量构象进行了量子力学分析。此外，对这些构象进行自然键轨道（NBO）分析，并删除CO键/反键和孤对/反键轨道的配对，以研究“gauche”效应对乙二醇构象能量学的贡献。采用“相关一致”基组的MP2和DFT/6 - 311++G(d,p)在匹配近似CCSD(T)/cc - pVQZ能量方面表现最佳，而MP2/6 - 31G(d)和Hartree - Fock的表现都很差。NBO分析表明，构象能量与删除与（i）CO键合和反键轨道相互作用以及（ii）孤对和反键轨道相互作用相关的矩阵元素无关，而能量排序与与内部氢键一致的几何参数相关。因此，本研究结果表明，缺乏明确项来考虑立体电子效应的标准分子力学势能函数形式适用于碳水化合物。
