Salting in Peptides: Conformationally Dependent Solubilities and Phase Behavior of a Tripeptide Zwitterion in Electrolyte Solution

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• 作者：John S. Perkyns ; Yiyang Wang ; and B. Montgomery Pettitt
• 刊名：Journal of the American Chemical Society
• 出版年：1996
• 出版时间：February 7, 1996
• 年：1996
• 卷：118
• 期：5
• 页码：1164 - 1172
• 全文大小：261K
• 年卷期：v.118,no.5(February 7, 1996)
• ISSN：1520-5126

文摘

The dielectrically consistent interaction site model theory isapplied to a model system consisting of azwitterion tripeptide of sequence Gly-Ala-Gly at infinite dilution in asolvent mixture of water and sodium chloridewith only the central mages/gifchars/phi.gif" BORDER=0 >,mages/gifchars/psi.gif" BORDER=0 > dihedrals for conformationaldegrees of freedom. The peptide is found to be saltedintosolution by the cosolvent, with its solubility depending strongly onconformation of the central mages/gifchars/phi.gif" BORDER=0 >,mages/gifchars/psi.gif" BORDER=0 > pair.Thedistribution of cosolvent relative to the bulk solvent mixture isexamined and relatively little specific association isfound. Instead, the ionic concentration around the peptide isincreased, especially near the phase boundary, and theincreased concentration extends up to eight solvent diameters into thebulk. The consequences of such an ionicdistribution on thermodynamic measures of association are discussed.Similarities between this model system andthe unusual solubility behavior of mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-lactoglobulin found inexperiments are shown. The molecular distributionscalculated are found to be consistent with a separation of the solventmixture into two non-miscible phases, one ofwhich contains the solute and has a higher cosolvent concentration thanthe other. Since turbid solutions have beenobserved in the mages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-lactoglobulin system, it is suggested that aseparation into two liquid phases could be common toboth systems.