Influence of Solvent Polarity on Preferential Solvation of Molecular Recognition Probes in Solvent Mixtures
Influence of Solvent Polarity on Preferential Solvation of Molecular Recognition Probes in Solvent Mixtures
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DOI：
10.1021/jp310379h
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发表时间：
2012-12-13
影响因子：
3.3
通讯作者：
Vinter, Jeremy G.
中科院分区：
文献类型：
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作者：
Amenta, Valeria;Cook, Joanne L.;Vinter, Jeremy G.
在一系列不同的溶剂混合物中测量了氢键受体（三正丁基氧化膦）和氢键供体（4-苯基偶氮苯酚）之间形成 1:1 配合物的缔合常数。已经研究了正辛烷和极性较大的溶剂（醚、酯、酮、腈、亚砜、叔酰胺以及卤代和芳香族溶剂）的二元混合物。在所有情况下都观察到类似的行为。当极性较大的溶剂浓度较低时，缔合常数与纯正辛烷中观察到的缔合常数相同。一旦达到极性较大的溶剂的阈值浓度，缔合常数的对数与极性较大的溶剂的浓度的对数成正比地减小。这表明两种溶质之一优先被极性较大的溶剂溶剂化，并且与该溶剂化平衡的竞争决定了观察到的缔合常数。发生优先溶剂化的极性较大的溶剂的浓度取决于溶剂极性：甲苯为 700 mM，1,1,2,2-四氯乙烷为 60 mM，醚、酯、酮和腈为 20 mM，叔酰胺为 0.2 mM，亚砜溶剂为 0.1 mM。结果可以通过一个简单的模型来解释，该模型仅考虑溶质和溶剂表面特定位点之间的成对相互作用，这意味着溶剂的整体性质对溶剂化热力学影响很小。
The association constants for formation of 1:1 complexes between a H-bond acceptor, tri-n-butylphosphine oxide, and a H-bond donor, 4-phenylazophenol, have been measured in a range of different solvent mixtures. Binary mixtures of n-octane and a more polar solvent (ether, ester, ketone, nitrile, sulfoxide, tertiary amide, and halogenated and aromatic solvents) have been investigated. Similar behavior was observed in all cases. When the concentration of the more polar solvent is low, the association constant is identical to that observed in pure n-octane. Once a threshold concentration of the more polar solvent in reached, the logarithm of the association constant decreases in direct proportion to the logarithm of the concentration of the more polar solvent. This indicates that one of the two solutes is preferentially solvated by the more polar solvent, and it is competition with this solvation equilibrium that determines the observed association constant. The concentration of the more polar solvent at which the onset of preferential solvation takes place depends on solvent polarity: 700 mM for toluene, 60 mM for 1,1,2,2-tetrachloroethane, 20 mM for the ether, ester, ketone, and nitrile, 0.2 mM for the tertiary amide, and 0.1 mM for the sulfoxide solvents. The results can be explained by a simple model that considers only pairwise interactions between specific sites on the surfaces of the solutes and solvents, which implies that the bulk properties of the solvent have little impact on solvation thermodynamics.