二价金属硫酸盐水溶液中的离子配对和溶剂壳极化。

IF 2.9 2区 化学 Q3 CHEMISTRY, PHYSICAL
Erik Bialik,  and , Zareen Abbas*, 
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引用次数: 0

摘要

二价金属阳离子与水溶液中其他物质的相互作用在活细胞的基本功能等方面具有重要意义。最近的证据表明,接触离子对在硫酸镁溶液中几乎不存在,而溶剂共享离子对占主导地位。目前尚不清楚二价金属盐的情况是否普遍如此。已知二价金属阳离子第一溶剂化壳水分子的极化能对于正确计算离子溶剂化能是必不可少的。在这里,我们证明了相同类型的溶剂壳极化对于金属硫酸盐模型电解质中的离子配对是重要的。与非极化模型相比,溶剂化水分子的极化能使它们更难被离子取代,因此抑制了离子接触。由于这种极化能随着溶剂化水分子位置的电场强度而强烈增加,而电场强度又取决于阳离子的大小,这就引入了离子大小的依赖性。在极化水模型中,接触离子对在小于某一最小尺寸的阳离子中完全被抑制。在非极化水模型中没有看到相应的趋势,对于所有考虑的阳离子大小,阳离子和阴离子之间的直接接触是普遍存在的。这一观察结果可以解释先前注意到的极小离子在某些方面表现为大离子的趋势。虽然这种效应以前被归因于小离子周围的强结合溶剂化壳,但目前的结果为小离子不成比例地强溶剂化提供了一种机制。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Ion Pairing and Solvent Shell Polarization in Aqueous Solutions of Divalent Metal Sulfates

The interactions of divalent metal cations with other species in aqueous solution are important in contexts such as the basic functioning of living cells. Recent evidence suggests that contact ion pairs are virtually absent in magnesium sulfate solutions and that solvent-shared ion pairs predominate. It is still unclear whether this is the case for divalent metal salts, in general. The polarization energy of the water molecules of the first solvation shell of divalent metal cations is known to be essential to correctly calculating the ionic solvation energy. Here, we show that the same type of solvent shell polarization is important for ion pairing in metal sulfate model electrolytes. The polarization energy of the solvating water molecules makes them harder to replace with ions compared to nonpolarizable models and therefore suppresses ion contact. As this polarization energy increases strongly with the electric field strength at the position of solvating water molecules, which, in turn, depends on cation size, this introduces an ion size dependence. With a polarizable water model, contact ion pairing is completely suppressed for cations below a certain minimum size. No corresponding tendency is seen with a nonpolarizable water model, for which direct contacts between cations and anions are prevalent for all cation sizes considered. This observation may explain the previously noted tendency of extremely small ions in certain respects to behave as large ions. While this effect has previously been ascribed to a strongly bound solvation shell around small ions, the current results provide a mechanism for why small ions are disproportionately strongly solvated.

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来源期刊
CiteScore
5.80
自引率
9.10%
发文量
965
审稿时长
1.6 months
期刊介绍: An essential criterion for acceptance of research articles in the journal is that they provide new physical insight. Please refer to the New Physical Insights virtual issue on what constitutes new physical insight. Manuscripts that are essentially reporting data or applications of data are, in general, not suitable for publication in JPC B.
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