Dos Santos Hélio F, Chagas Marcelo A, De Souza Leonardo A, Rocha Willian R, De Almeida Mauro V, Anconi Cleber P A, De Almeida Wagner B
Laboratório de Química Computacional e Modelagem Molecular (LQC-MM), Departamento de Química, ICEx, Universidade Federal de Minas Gerais , Campus Pampulha, 31270-901 Belo Horizonte, MG, Brazil.
Laboratório de Química Computacional (LQC), Departamento de Química Inorgânica, Instituto de Química, Universidade Federal Fluminense (UFF) , 24020-150 Niterói, RJ, Brazil.
J Phys Chem A. 2017 Apr 13;121(14):2839-2846. doi: 10.1021/acs.jpca.7b01067. Epub 2017 Mar 30.
In this paper, density functional theory calculations of nuclear magnetic resonance (NMR) chemical shifts for l-quebrachitol isomer, previously studied in our group, are reported with the aim of investigating in more detail the water solvent effect on the prediction of H NMR spectra. In order to include explicit water molecules, 20 water-l-quebrachitol configurations obtained from Monte Carlo simulation were selected to perform geometry optimizations using the effective fragment potential method encompassing 60 water molecules around the solute. The solvated solute optimized geometries were then used in B3LYP/6-311+G(2d,p) NMR calculations with PCM-water. The inclusion of explicit solvent in the B3LYP NMR calculations resulted in large changes in the H NMR profiles. We found a remarkable improvement in the agreement with experimental NMR profiles when the explicit hydrated l-quebrachitol structure is used in B3LYP H NMR calculations, yielding a mean absolute error (MAE) of only 0.07 ppm, much lower than reported previously for the gas phase optimized structure (MAE = 0.11 ppm). In addition, a very improved match between theoretical and experimental H NMR spectrum measured in DO was achieved with the new hydrated optimized l-quebrachitol structure, showing that a fine-tuning of the theoretical NMR spectra can be accomplished once solvent effects are properly considered.
本文报道了我们小组之前研究过的 l-对映贝壳杉醇异构体核磁共振（NMR）化学位移的密度泛函理论计算，目的是更详细地研究水溶剂对 1H NMR 光谱预测的影响。为了纳入明确的水分子，从蒙特卡罗模拟中获得的 20 种水-l-对映贝壳杉醇构型被选中，使用有效片段势方法进行几何优化，该方法在溶质周围包含 60 个水分子。然后将溶剂化溶质的优化几何结构用于 B3LYP/6-311+G(2d,p) NMR 计算，并采用 PCM-水模型。在 B3LYP NMR 计算中纳入明确的溶剂导致 1H NMR 谱图发生了很大变化。我们发现，当在 B3LYP 1H NMR 计算中使用明确的水合 l-对映贝壳杉醇结构时，与实验 NMR 谱图的一致性有了显著提高，平均绝对误差（MAE）仅为 0.07 ppm，远低于之前报道的气相优化结构的平均绝对误差（MAE = 0.11 ppm）。此外，新的水合优化 l-对映贝壳杉醇结构在重水（D2O）中测量的理论和实验 1H NMR 光谱之间实现了非常好的匹配，表明一旦适当考虑溶剂效应，就可以对理论 NMR 光谱进行微调。
