Departamento de Física, Centro de Investigación en Ciencias-IICBA, Universidad Autónoma del Estado de Morelos, 62209 Cuernavaca, Morelos, México.
Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, 62209 Cuernavaca, Morelos, México.
J Phys Chem A. 2023 Mar 2;127(8):1803-1817. doi: 10.1021/acs.jpca.2c07476. Epub 2023 Feb 15.
Recent low-temperature infrared-based experimental studies provided information about the effects of aqueous microsolvation on the intramolecular hydrogen bond of protonated glycine and β-alanine [ , , 3355]. Here we address the temperature-dependent entropic effects on the aqueous microsolvation patterns of these protonated amino acids using the AAH(HO) ( = 1-8) cluster model at 50 K and room temperature with Born-Oppenheimer molecular dynamics using a calibrated hybrid density functional. The C-O, N-O, and center-of-mass-O radial distribution functions provide accurate structural data and temperature-dependent water coordination numbers vs. solvation degree. The solvation patterns for protonated glycine at 50 K show structural features in agreement with previous static optimizations. However, entropic effects at room temperature play a crucial role in the evolution of the intramolecular HB strength vs. solvation degree for both protonated amino acids. With increasing hydration entropic effects favor the making of solvent hydrogen bond networks over full solvation of protonated glycine. At room temperature four water molecules are needed to build the first solvation shell for protonated glycine while five are required for protonated β-alanine. A new statistical Cumulative Percentage of Structures (CPS) scheme is proposed; when the CPS data are analyzed in light of the empirical formula of Rozenberg et al. [ , , 2699] and the hydrogen bond relative strength (HBRS) criteria of Jeffrey [; Oxford University: 1997] we can provide a detailed molecular mechanism for the weakening of the intramolecular hydrogen bond based on the average dynamical structures, which clearly reveals the temperature dependence of this process. The new CPS-HBRS scheme proposed here can be utilized using any type of molecular dynamics trajectory (classical, BOMD, CPMD, etc.).
最近基于低温红外的实验研究提供了关于水微溶剂化对质子化甘氨酸和β-丙氨酸分子内氢键影响的信息[,, 3355]。在这里，我们使用 AAH(HO)（ = 1-8）簇模型在 50 K 和室温下使用经过校准的杂化密度泛函通过 Born-Oppenheimer 分子动力学研究了这些质子化氨基酸水微溶剂化模式的温度依赖性熵效应。C-O、N-O 和质心-O 径向分布函数提供了准确的结构数据和随溶剂化程度变化的温度依赖性水配位数。质子化甘氨酸在 50 K 下的溶剂化模式显示出与以前静态优化一致的结构特征。然而，在室温下的熵效应在质子化氨基酸的分子内 HB 强度与溶剂化程度的关系演变中起着至关重要的作用。随着水合熵效应的增加，有利于形成溶剂氢键网络而不是质子化甘氨酸的完全溶剂化。在室温下，需要四个水分子来构建质子化甘氨酸的第一个溶剂化壳，而质子化β-丙氨酸则需要五个水分子。提出了一种新的累积结构百分比（CPS）方案；当根据 Rozenberg 等人的经验公式[,, 2699]和 Jeffrey 的氢键相对强度（HBRS）标准[;牛津大学：1997]分析 CPS 数据时，我们可以根据平均动态结构提供分子内氢键减弱的详细分子机制，这清楚地揭示了该过程的温度依赖性。这里提出的新 CPS-HBRS 方案可以使用任何类型的分子动力学轨迹（经典、BOMD、CPMD 等）来使用。
