Department of Chemistry, Texas A & M University, College Station, Texas 77843, USA.
J Phys Chem B. 2012 Jun 28;116(25):7389-97. doi: 10.1021/jp212243c. Epub 2012 Jun 14.
Thermodynamic and surface-specific spectroscopic investigations were carried with an elastin-like polypeptide (ELP) containing 16 aspartic acid residues. The goal was to explore the role of the carboxylate moieties in hydrophobic collapse and related Hofmeister effects. Experiments were conducted with a series of monovalent and divalent metal chloride salts. Both phase transition temperature and spectroscopic data demonstrated that the divalent cations showed relatively strong association to the carboxylate sites on the biopolymer with K(d) values in the range of 1 to 10 mM. The ordering of the divalent series was: Zn(2+) > Ca(2+) > Ba(2+) > Sr(2+) > Mg(2+). Monovalent cations displayed weaker binding which ranged from 78 mM for NH(4)(+) to 345 mM for Cs(+). The order for this series was: NH(4)(+) > Li(+) > Na(+) > NMe(4)(+) > K(+) > Rb(+) ≥ Cs(+). These results are in general agreement with the notion that strongly hydrated cations bind more tightly to carboxylate groups than do weakly hydrated cations. Moreover, the data for the monovalent series was partially consistent with the law of matching water affinity, although Li(+) and NH(4)(+) did not follow the model. The series for the divalent cations did not appear to obey the law of matching water affinity at all.
采用含有 16 个天冬氨酸残基的弹性蛋白样多肽 (ELP) 进行了热力学和表面特异性光谱研究。目的是探索羧酸盐在疏水性塌陷和相关的 Hofmeister 效应中的作用。实验采用了一系列一价和二价金属氯化物盐进行。相变温度和光谱数据均表明，二价阳离子与生物聚合物上的羧酸盐部位具有相对较强的结合作用，K(d) 值在 1 至 10mM 范围内。二价阳离子系列的排列顺序为：Zn(2+) > Ca(2+) > Ba(2+) > Sr(2+) > Mg(2+)。一价阳离子的结合较弱，范围从 NH(4)(+)的 78mM 到 Cs(+)的 345mM。该系列的顺序为：NH(4)(+) > Li(+) > Na(+) > NMe(4)(+) > K(+) > Rb(+) ≥ Cs(+)。这些结果与强水合阳离子比弱水合阳离子更紧密地结合羧酸盐基团的概念基本一致。此外，一价阳离子系列的数据部分符合水亲和力匹配定律，尽管 Li(+)和 NH(4)(+)不符合该模型。二价阳离子系列似乎根本不遵守水亲和力匹配定律。
