Contact Ion Pair Formation between Hard Acids and Soft Bases in Aqueous Solutions Observed with 2DIR Spectroscopy

被引：36

作者：

Sun, Zheng ^{[1
]}

Zhang, Wenkai ^{[1
]}

Ji, Minbiao ^{[1
]}

Hartsock, Robert ^{[1
]}

Gaffney, Kelly J. ^{[1
]}

机构：

[1] Stanford Univ, PULSE Inst, SLAC Natl Accelerator Lab, Stanford, CA 94305 USA

来源：

JOURNAL OF PHYSICAL CHEMISTRY B | 2013年 / 117卷 / 49期

关键词：

LIGAND-EXCHANGE DYNAMICS; HYDROGEN-BOND EXCHANGE; DIELECTRIC-RELAXATION; ELECTROLYTE-SOLUTIONS; VIBRATIONAL-ENERGY; SOLVENT RELAXATION; ULTRAFAST DYNAMICS; SOLVATION; HYDRATION; IR;

D O I：

10.1021/jp4033854

中图分类号：

O64 [物理化学（理论化学）、化学物理学];

学科分类号：

070304 ; 081704 ;

摘要：

The interaction of charged species in aqueous solution has important implications for chemical, biological, and environmental processes. We have used 2DIR spectroscopy to study the equilibrium dynamics of thioc-yanate chemical exchange between free ion (NCS-) and contact ion pair configurations (MNCS+), where M2+ = Mg2+ or Ca2+. Detailed studies of the influence of anion concentration and anion speciation show that the chemical exchange observed with the 2DIR measurements results from NCS- exchanging with other anion species in the first solvation shell surrounding Mg2+ or Ca2+. The presence of chemical exchange in the 2DIR spectra provides an indirect, but robust, determinant of contact ion pair formation. We observe preferential contact ion pair formation between soft Lewis base anions and hard Lewis acid cations. This observation cannot be easily reconciled with Pearson's acid-base concept or Collins' Law of Matching Water Affinities. The anions that form contact ion pairs also correspond to the ions with an affinity for water and protein surfaces, so similar physical and chemical properties may control these distinct phenomena.

引用

页码：15306 / 15312

页数：7