Surface Chemistry of the Polyamide Series. I. Effect of Hydrogen Bonding on the Nature of Poly-α-amino Acid Monolayers

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Abstract
The effect of hydrogen bonding on the nature of poly-α-amino acid monolayers has been studied at the air/water and oil/water interfaces with poly-l-alanine, poly-Dl-alanine, polysarcosine, copoly-1 : 1-(glycine, sarcosine), copoly-1 : 1-(Dl-alanine, sarcosine) and poly-α-aminoisobutyric acid. Poly-l-alanine and poly-Dl-alanine gave monolayers of the condensed type on distilled water, and the surface viscosity of poly-Dl-alanine was first detected at a much larger area than its close-packed area where the surface pressure was sufficiently low. This fact suggests that there exists a strong interaction between peptide bonds of polyalanine. Both polymers would assume a β-configration. On the concentrated sulfuric acid subsolutions, the film of poly-Dl-alanine was expanded and an increase in surface moment was observed because of the breaking of hydrogen bonds between peptide linkages. A steric hindrance to the hydrogen bond formation was observed with the film of poly-α-amino isobutyric acid. This polypeptide gave an expanded monolayer on distilled water, and its surface viscosity could be first detected at a very small area where the surface pressure was remarkably high. The film of copoly-1 : 1-(Dl-alanine, sarcosine) was of the expanded type on the 3 m potassium chloride subsolution because of the decrease in the number of hydrogen bonds and that in the double-bond nature of the main chain. At the oil/distilled water interface, a marked difference was found between the monolayers of poly-Dl-alanine and polysarcosine, although these polymers have the same side chains. Poly-Dl-alanine gave a considerably condensed monolayer, even at the oil/water interface. On the other hand, the film of polysarcosine was of the expanded type. The difference between the films of these polymers is mainly to be ascribed to the presence or the absence of hydrogen bonds. The 1 : 1-copolymer of sarcosine with glycine or Dl-alanine also gave an expanded monolayer.