Lewis Strength Determines Specific-Ion Effects in Aqueous and Nonaqueous Solvents
Lewis Strength Determines Specific-Ion Effects in Aqueous and Nonaqueous Solvents
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DOI：
10.1021/acs.jpca.9b04004
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发表时间：
2019-08-01
影响因子：
2.9
通讯作者：
Page, Alister J.
中科院分区：
文献类型：
--
作者：
Gregory, Kasimir P.;Webber, Grant B.;Page, Alister J.
提出了使用能量分解分析来分析水性和非水性溶剂中的特定离子效应。特定离子效应诱导或影响物理化学现象的方式由存在的离子的特性决定，而不仅仅是由它们的电荷或浓度决定。自从霍夫迈斯特的开创性工作以来，这种效应就为人所知，并且通常根据著名的霍夫迈斯特级数进行分类。特定离子效应的例子在化学和生物学中无处不在，传统上是根据离子对水结构的影响来解释的。然而，这种解释并不令人满意，因为它无法充分解释和预测经常观察到的序列反转和异常。此外，最近的实验表明，在非水溶剂中观察到特定离子效应。通过对溶剂化离子-N-异丙基丙烯酰胺 (NIPAM) 络合物进行建模，我们在此表明，不仅在水中，而且在几种非水溶剂（甲醇、乙腈、DMSO）中都观察到特定离子对离子-NIPAM 相互作用自由能的影响，与离子的路易斯强度相对应。有趣的是，在完全没有溶剂环境的情况下也观察到相同的趋势。反离子对离子-NIPAM 相互作用自由能的影响对于解离的离子对来说可以忽略不计，但由于排斥离子-NIPAM 相互作用的调节，在相关离子对中很明显。我们基于离子-溶剂和离子-NIPAM相互作用的竞争强度及其相对路易斯强度，提出了一种解释特定离子效应逆转的机制。这扩展了有关水溶液中特定离子效应逆转的现有理论，因为我们表明还必须考虑溶剂性质以考虑在任意溶剂环境中预测的特定离子效应。
An analysis of specific-ion effects in aqueous and nonaqueous solvents using energy decomposition analysis is presented. Specific-ion effects induce or influence physicochemical phenomena in a way that is determined by the identity of the ions present, and not merely by their charge or concentration. Such effects have been known since the seminal work of Hofmeister and are often categorized according to the well-known Hofmeister series. Examples of specific-ion effects are ubiquitous throughout chemistry and biology and are traditionally explained in terms of the influence ions have on the structure of water. However, this explanation is unsatisfactory because it is unable to adequately explain and predict frequently observed series reversals and anomalies. Further, recent experiments have shown that specific-ion effects are observed in nonaqueous solvents. By modeling solvated ion-N-isopropylacrylamide (NIPAM) complexes, we show here that specific-ion effects on ion-NIPAM interaction free energies are observed not only in water, but also in several nonaqueous solvents (methanol, acetonitrile, DMSO) in correspondence with the ions' Lewis Strengths. Interestingly, the same trends are observed in the absence of a solvent environment altogether. Counterion effects on ion-NIPAM interaction free energies are negligible for dissociated ion pairs but are evident in associated ion pairs because of the modulation of repulsive ion-NIPAM interactions. We propose a mechanism for explaining reversals in specific-ion effects, based on the competing strengths of the ion-solvent and ion-NIPAM interaction and their relative Lewis strengths. This extends existing theories regarding specific-ion effect reversals in aqueous solutions, as we show that solvent properties must also be taken in to account for specific-ion effects to be predicted in arbitrary solvent environments.