Surface Chemistry of Synthetic Protein Analogues. IV. On the Monolayers of Electrolytic Synthetic Polypeptides, Poly-l-Glutamic Acid and the Copolypeptide of l-Lysine, l-Leucine and l-Glutamic Acid

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Abstract
The surface pressure and surface viscosity of the spread monolayers of the copolypeptide of l-lysine, l-leucine and l-glutamic acid and of poly-l-glutamic acid were measured in relation to substrate pH. The copolypeptide of l-lysine, l-leucine and l-glutamic acid.—The F—A curves in the range of pH 5.8 and 9.4 were of condensed type, but at both outsides of this pH range they were of expanded type. The area at constant pressure or surface viscosity against pH curves were of W-shape and a maximum appeared at pH 7. That the iso-electric point of the copolypeptide may lie at pH 7 was concluded from the observations of the monolayer properties. The W-shaped curve could be interpreted in terms of the ionization degree of amino and carboxyl groups. At the isoelectric point, pH 7, the surface viscosity became maximum. This is in contrast to the bulk viscometric behaviour of polyampholytes. Poly-l-glutamic acid.—The area at constant pressure or surface viscosity and the pressure at constant area decreases rapidly if the pH of the substrate exceeds 4.6. This fact corresponds to the viscometric behaviour of electrolytic polypeptides in solution, i. e., when the elongation of a molecule by the electrical repulsion of ionized groups occurs, the rapid increase in viscosity and in solubility appears in solution and at monolayer, respectively.