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首页> 外文OA文献 >Molecular dynamics simulations of organic crystal dissolution: The lifetime and stability of the polymorphic forms of para-amino benzoic acid in aqueous environment
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Molecular dynamics simulations of organic crystal dissolution: The lifetime and stability of the polymorphic forms of para-amino benzoic acid in aqueous environment

机译：有机晶体溶解的分子动力学模拟：对氨基苯甲酸多晶型在水环境中的寿命和稳定性

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摘要

Para-amino benzoic acid (PABA) manifests crystalline solid-state properties that are typical of a class of chemical compounds with important industrial applications. Hence, it is particularly worthwhile to investigate the lifetime and stability of representative molecular-clusters of two polymorphic forms of PABA in aqueous solution using molecular dynamics simulations. Simulations of 5 ns duration in the isothermal-isobaric ensemble (constant particle number, pressure and temperature (NPT) ensemble) were performed for the two polymorphic forms at three different temperatures 0 °C, 50 °C and 100 °C. The simulations revealed that at 0 °C the representative molecular-clusters of the two polymorphic forms remain ordered while at 50 °C the molecular packing within the clusters becomes partially disordered for both polymorphic forms and at 100 °C the clusters lose long-range order rapidly and come to resemble liquid drops. Care should be taken when assessing the relative stability of polymorphic forms, as a function of temperature, from such computational experiments which explore the dissolution of nano-scale crystals. The long range order of the clusters of the α-form at 50 °C and 100 °C was, respectively, partially and completely lost after 5 ns which merits further investigation given that the α-form is the high-temperature stable polymorph. Importantly, the initial shape of clusters, as well as the number of solute molecules they contained, affected the extent to which order was lost and how rapidly the loss occurred. Given that the classical nucleation theory predicts a finite probability that clusters significantly larger than the critical size, in terms of number of molecules, may dissolve, building clusters containing a greater number of molecules could improve the simulated stability of the α polymorph at 50 °C and 100 °C. Furthermore, the simulations revealed that the selection of a suitable electrostatic potential is very important for the description of the dissolution process of the nano-sized crystals.
机译：对氨基苯甲酸（PABA）表现出结晶的固态性质，是具有重要工业应用的一类化合物的典型特征。因此，使用分子动力学模拟研究水溶液中PABA的两种多晶型形式的代表性分子簇的寿命和稳定性特别值得。在0°C，50°C和100°C的三种不同温度下，对两种多晶型进行了等温-等压集成（恒定粒子数，压力和温度（NPT）集成）中5 ns持续时间的仿真。模拟显示，在0°C时，两种多晶型形式的代表性分子簇保持有序，而在50°C时，两种多晶型形式的簇内分子堆积变得部分无序，在100°C时，簇失去长程有序迅速变得类似于液滴。当从探索纳米级晶体溶解的计算实验中评估多晶型形式的相对稳定性（随温度变化）时，应格外小心。 5 ns后，在50℃和100℃时，α-型团簇的长程有序部分或全部消失，鉴于α-型是高温稳定的多晶型物，值得进一步研究。重要的是，团簇的初始形状以及它们所包含的溶质分子的数量会影响顺序丢失的程度以及丢失发生的速度。鉴于经典的成核理论预测，在分子数量方面，明显大于临界尺寸的团簇可能会溶解的有限概率，构建包含更多分子的团簇可以改善50°C下α多晶型物的模拟稳定性和100°C。此外，模拟表明，对于描述纳米级晶体的溶解过程，选择合适的静电势非常重要。

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