Self-association and solubility of peptides. Solvent-titration study of protected C-terminal segments of porcine secretin*

Abstract

Self‐association of peptides (related to the C‐terminal sequence of porcine secretin) in methylene chloride was disrupted by adding dimethylsulfoxide in increasing amounts. This structural transition was monitored by the disappearance of the amide‐I C = O stretching band of strongly intermolecularly hydrogen‐bonded molecules (1625–1630 cm^‐1) in the infrared absorption spectra. The effects induced by main‐chain length and sequence, type of Nα‐protection, and concentration were assessed. Hexamethylphosphortriamide was compared for its structure‐disrupting properties to dimethylsulfoxide. The increasing propensity to aggregate displayed by these peptides is paralleled by a decrease in their solubility. The impact of these results on the planning of peptide syntheses is briefly discussed.