Surface Chemistry of Synthetic Protein Analogues. VII. Polytyrosine and its Related Polypeptides

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Abstract
The monolayer properties of synthetic polypeptides which have phenolic OH groups in the side chains such as poly-l-tyrosile and poly-Dl-tyrosine were studied to investigate the effect of hydrogen bonding by tyrosyl OH groups. Poly-o-benzyl-Dl-tyrosine and poly-Dl-phenylalanine were also studied for comparison. At air/water interface poly-l-tyrosine and poly-Dl-tyrosine occupy much smaller aerea per residue than any other poly peptide films, and have very small surface moment, if they were spread from the solution in pyridine and isopropyl alcohol mixture. These polypeptides might be spread in a strict sense not in an extended monolayer but in a coiled state, suggesting the hydrogen bond between phenolic OH and –CO– or –NH– groups in the main chain. On the alkaline substrate the film expands considerably because of the breaking of hydrogen bonds by the ionization of phenolic OH. At petroleum ether/water interface, the film is also expanded by releasing of van der Waals force. Interfacils moment changes its sign due to whether the aqueous phase is acid. or alkaline. It suggests that p-hydroxybenzyl groups are in the oil phase at oil/acid solution, whereas they are in the aqueous phase at oil/alkaline solution. Poly-l-tyrosine assumes the configuration very similar that of poly-l-tyrosine is spread from a solution in dichloroacetic acid which is a strong hydrogen bond braking agent. Poly-o-benzyl-Dl-tyrosine gives a monolayer which is somewhat more condensed than poly-Dl-phenylalanine at air/water interface, whereas it occupies a larger area per residue than poly-l-tyrosine, poly-Dl-tyrosine and poly-Dl-phenylalanine at oil/water interface. All these findings are caused by the existence of very large side chains in poly-o-benzyl-Dl-tyrosine.

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