Graziano Giuseppe
Dipartimento di Scienze e Tecnologie, Università del Sannio, Via Port'Arsa 11, 82100 Benevento, Italy.
ScientificWorldJournal. 2014 Jan 27;2014:870106. doi: 10.1155/2014/870106. eCollection 2014.
It has recently been shown that aqueous solutions of tetrapropylammonium chloride and sulphate salts destabilize the folded conformation of Trp-peptides (Dempsey et al., 2011). This result is rationalized by the application of a statistical thermodynamic approach (Graziano, 2010). It is shown that the magnitude of the solvent-excluded volume effect, the main contribution for the native state stability, decreases in both aqueous 2 M TPACl solution and aqueous 1 M TPA2SO4 solution. This happens because TPA(+) ions are so large in size and interact so weakly with water molecules, due to their very low charge density, to be able to counteract the electrostrictive effect of chloride and sulphate ions on the water structure, so that the density of their aqueous solutions is smaller or only slightly larger than that of water.
最近有研究表明，四丙基氯化铵和硫酸盐的水溶液会使色氨酸肽的折叠构象不稳定（登普西等人，2011年）。这一结果通过应用统计热力学方法得到了合理的解释（格拉齐亚诺，2010年）。结果表明，对于天然态稳定性起主要作用的溶剂排除体积效应的大小，在2 M四丙基氯化铵水溶液和1 M硫酸四丙基铵水溶液中均减小。出现这种情况是因为四丙基铵离子体积非常大，且由于其电荷密度极低，与水分子的相互作用非常弱，无法抵消氯离子和硫酸根离子对水结构的电致伸缩效应，因此它们水溶液的密度比水小或仅略大于水。
