Surface Chemistry of Synthetic Protein Analogues. VI. The Interaction of Urea and Salt with Non-electrolytic Polypeptides

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Abstract
The interaction of urea and potassium chloride with non-electrolytic polypeptide monolayers was investigated. The film of polypeptide was expanded considerably in the presence of urea in the substrate. The number of molecules was, however, not changed by the interaction with urea. The molecular weights of polypeptides determined by surface pressure measurement on the substrates with or without urea were the same. Whereas the co-area of the molecule was increased by increase of urea concentration in the substrate. Urea might be bound to the peptide linkages in backbone by hydrogen bonding and the formation of aduct seems improbable. Although potassium chloride affected the nature of electrolytic polypeptide film profoundly, it scarcely affected that of the nonelectrolytic polypeptide film. The interaction with urea was discussed in relation to the protein denaturation.