Sharma Bikramjit, Chandra Amalendu
Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur 208016, India.
J Phys Chem B. 2017 Nov 22;121(46):10519-10529. doi: 10.1021/acs.jpcb.7b06091. Epub 2017 Nov 14.
The structure and dynamics of solvation shells of the phosphate ion in deuterated water are studied by means of Born-Oppenheimer molecular dynamics simulation. The total number of molecules in the first and second solvation shells is found to be close to the effective hydration number reported experimentally. The OD bonds that are hydrogen bonded to the phosphate ion are found to be red shifted as compared to bulk water, which is consistent with experimental results. However, the two OD bonds of the same water molecule in the first hydration shell are found to be vibrationally distinct, which can be attributed to different strengths of the ion-water and water-water hydrogen bonds near the ion. Also, the hydrogen bonds formed by the second solvation shell OD bonds are somewhat stronger than the bulk. This finding shows a long ranged effect of the phosphate ion on water and also gives insights into the water structure making property of this anion. The dynamics of water in the first solvation shell is found to be significantly slower than that of the bulk. We have investigated the origin of the orientational slowing down of the first solvation shell water molecules and made connections to similar results observed experimentally.
通过玻恩-奥本海默分子动力学模拟研究了氘代水中磷酸根离子溶剂化壳层的结构和动力学。发现第一和第二溶剂化壳层中的分子总数接近实验报道的有效水合数。与本体水相比，发现与磷酸根离子形成氢键的OD键发生了红移，这与实验结果一致。然而，发现第一水合壳层中同一水分子的两个OD键在振动上是不同的，这可归因于离子附近离子-水和水-水氢键的不同强度。此外，第二溶剂化壳层OD键形成的氢键比本体中的氢键稍强。这一发现表明了磷酸根离子对水的长程效应，也为该阴离子的水结构形成性质提供了见解。发现第一溶剂化壳层中水的动力学明显比本体水慢。我们研究了第一溶剂化壳层水分子取向减慢的起源，并将其与实验观察到的类似结果联系起来。
