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A computational study of ultrafast acid dissociation and acid-base neutralization reactions. I. the model

机译：超快酸解离和酸碱中和反应的计算研究。一，模型

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Ultrafast, time-resolved investigations of acid-base neutralization reactions have recently been performed using systems containing the photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) and various Br?nsted bases. Two conflicting neutralization mechanisms have been formulated by Mohammed [Science 310, 83 (2005)] and Siwick [J. Am. Chem. Soc. 129, 13412 (2007)] for the same acid-base system. Herein an ab initio molecular dynamics based computational model is formulated, which is able to investigate the validity of the proposed mechanisms in the general context of ground-state acid-base neutralization reactions. Our approach consists of using 2,4,6-tricyanophenol (exp. pKa?1) as a model for excited-state HPTS* (pKa?1.4) and carboxylate ions for the accepting base. We employ our recently proposed dipole-field/quantum mechanics (QM) treatment [P. Maurer and R. Iftimie, J. Chem. Phys. 132, 074112 (2010)] of the proton donor and acceptor molecules. This approach allows one to tune the free energy of neutralization to any desired value as well as model initial nonequilibrium hydration effects caused by a sudden increase in acidity, making it possible to achieve a more realistic comparison with experimental data than could be obtained via a full-QM treatment of the entire system. It is demonstrated that the dipole-field/QM model reproduces correctly key properties of the 2,4,6-tricyanophenol acid molecule including gas-phase proton dissociation energies and dipole moments, and condensed-phase hydration structure and pKa values.
机译：最近已使用包含光酸8-羟基py-1,3,6-三磺酸三钠盐（HPTS）和各种布朗斯台德碱的系统进行了酸碱中和反应的超快速，时间分辨的研究。 Mohammed [Science 310，83（2005）]和Siwick [J. Chem.Sci。，2001，3，2，3]提出了两种相互矛盾的中和机制。上午。化学Soc。 129，13412（2007）]。在此，从头开始建立了基于分子动力学的计算模型，该模型能够在基态酸碱中和反应的一般情况下研究所提出机制的有效性。我们的方法包括使用2,4,6-三氰基苯酚（实验值pKa？1）作为激发态HPTS *（pKa？1.4）的模型，并使用羧酸根离子作为接受碱。我们采用了我们最近提出的偶极场/量子力学（QM）处理方法[P. Maurer和R.Iftimie，化学杂志。物理132，074112（2010）]的质子供体和受体分子。这种方法可以将中和的自由能调节至任何所需值，并且可以对由于酸度突然增加而引起的初始非平衡水合效应进行建模，从而与通过完整方法获得的实验数据进行更现实的比较成为可能。 -整个系统的QM处理。结果表明，偶极场/ QM模型正确地再现了2,4,6-三氰基酚酸分子的关键特性，包括气相质子离解能和偶极矩，以及凝聚相水合结构和pKa值。

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