Monolayer properties of poly-L-tyrosine (D.P.39) and poly-DL-alanine (D.P.24) were studied at air-water interphase prior to, and after their gamma irradiation in dilute aqueous solutions at a dose rate of 1.5× 105 R/hr. Both these polyamino acids spread to a lesser extent than$1\ {\rm m}^{2}/{\rm mg}$ and also exhibited strong "association" phenomena. From the observed significantly low values for packing areas as well as areas at minimum compressibility, a possibility of the molecules being in α-configuration at the interphase has been suggested. Marked reductions in the spread areas were noted in the irradiated samples. Examination of changes in the molecular weights, and in total and actual areas occupied by the molecules indicated relative stability of the peptide bond against radiation attack. This was further confirmed in the case of poly-DL-alanine by the study of ultraviolet absorption at 200 mμ, due to the peptide chromophore. Cross-linking effect of irradiation was also evident in this molecule. Radiation did not seem to affect "association" in either poly-L-tyrosine or poly-DL-alanine.

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