Westh Peter, Kato Hitoshi, Nishikawa Keiko, Koga Yoshikata
Department of Life Sciences and Chemistry, Roskilde University, Roskilde, DK-4000, Denmark.
J Phys Chem A. 2006 Feb 9;110(5):2072-8. doi: 10.1021/jp055036y.
We investigated the effects of NaF, NaCl, NaBr, and NaI on the molecular organization of H2O by a calorimetric methodology developed by us earlier. We use the third derivative quantities of G pertaining to 1-propanol (1P) in ternary 1P-a salt-H2O as a probe to elucidate the effects of a salt on H2O. We found that NaF and NaCl worked as hydration centers. The hydration numbers were 19 +/- 2 for NaF and 7.5 +/- 0.6 for NaCl. Furthermore, the bulk H2O away from the hydration shell was found unaffected by the presence of Na+, F-, and Cl-. For NaBr and NaI, in addition to the hydration to Na+, Br- and I- acted like a hydrophilic moiety such as urea. Namely, they formed a hydrogen bond to the existing H2O network and retarded the fluctuation nature of H2O. These findings were discussed with respect to the Hofmeister ranking. We suggested that more chaotropic anions Br- and I- are characterized as hydrophiles, whereas kosmotropes, F- and Cl-, are hydration centers.
我们采用我们之前开发的量热法研究了NaF、NaCl、NaBr和NaI对H₂O分子结构的影响。我们将三元体系1-丙醇（1P）-盐-H₂O中与1-丙醇（1P）相关的吉布斯自由能的三阶导数作为探针，以阐明盐对H₂O的影响。我们发现NaF和NaCl起到了水合中心的作用。NaF的水合数为19±2，NaCl的水合数为7.5±0.6。此外，发现远离水合壳的大量H₂O不受Na⁺、F⁻和Cl⁻存在的影响。对于NaBr和NaI，除了与Na⁺水合外，Br⁻和I⁻的作用类似于尿素等亲水性部分。也就是说，它们与现有的H₂O网络形成氢键，并抑制了H₂O的波动性质。这些发现结合霍夫迈斯特序列进行了讨论。我们认为，更多的离液序列高的阴离子Br⁻和I⁻表现为亲水剂，而促溶剂F⁻和Cl⁻则是水合中心。
