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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Direct Absolute pK_a Predictions and Proton Transfer Mechanisms of Small Molecules in Aqueous Solution by QM/MM-MD
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Direct Absolute pK_a Predictions and Proton Transfer Mechanisms of Small Molecules in Aqueous Solution by QM/MM-MD

机译：QM / MM-MD直接预测水溶液中小分子的绝对pK_a和质子转移机理

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摘要

The pK_a values of HF, HCOOH, CH3COOH, CH3CH2COOH, H2CO3, HOCl, NH4~+, CH3NH3~+, H2O2, and CH3CH2OH in aqueous solution were predicted by QM/MM-MD in combination with umbrella samplings adopting the flexible asymmetric coordinate (FAC). This unique combination yielded remarkably accurate values with the maximum and root-mean-square errors of 0,45 and 0.22 in pK_a units, respectively, without any numerical or experimental adjustments. The stability 6f the initially formed Coulomb pair rather than the proton transfer stage turned out to be the rate-determining step, implying that the stabili2ations of the created ions require a large free energy increase. A remarkable correlation between DWR (degree of water rearrangements) and pK_a was observed. As such, the large pK_a of ethanol can be, in part, attributed to the large water rearrangement, strongly suggesting that proper samplings of water dynamics at dissociated regions are critical for accurate predictions of pK_a Current results exhibit a promising protocol for direct and accurate predictions of pK_a. The significant variations in the gas phase deprotbnation energies with level of theory appear to be mostly canceled by the similar changes in the averaged solute—solvent interactions, yielding accurate results.
机译：通过QM / MM-MD结合采用不对称柔性坐标的伞形采样（）预测水溶液中HF，HCOOH，CH3COOH，CH3CH2COOH，H2CO3，HOCl，NH4〜+，CH3NH3〜+，H2O2和CH3CH2OH的pK_a值FAC）。这种独特的组合产生了非常准确的值，最大误差和均方根误差分别为pK_a单位为0.45和0.22，而无任何数值或实验上的调整。最初形成的库仑对而不是质子转移阶段的稳定性6f证明是速率确定步骤，这意味着所产生离子的稳定化需要大量自由能的增加。观察到DWR（水重排程度）与pK_a之间存在显着相关性。因此，乙醇的大量pK_a可以部分归因于较大的水重排，强烈表明在离解区域正确采样水动力学对于准确预测pK_a至关重要。的pK_a。气相去质子化能随理论水平的显着变化似乎被平均的溶质-溶剂相互作用的相似变化所抵消，从而得出准确的结果。

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