Conformation of poly‐L‐tyrosine in trimethyl phosphate solution

Absorption, circular dichroism (CD), and optical rotatory dispersion (ORD) measurements were carried out on poly‐ L ‐tyrosine in trimethyl phosphate solution over the spectral range 185–600 mμ. There is evidence in the CD spectrum for side chain‐side chain interactions in poly‐ L ‐tyrosine. ORD and CD data in dimethylformamide and pyridine closely parallel those in trimethyl phosphate, indicating a similarity in conformation of the polymer in all three solvents. In the polarized infrared spectrum both position and polarization of amide A, I, and II bands are characteristic of α‐helical polypeptides. Bands corresponding to side chain also exhibit dichroism, suggesting that the side chains are not randomly oriented. Viscosity and light‐scattering studies are consistent with α‐helical structure for the polymer that, remains rigid over a temperature range of 15–50°C and becomes somewhat flexible at higher temperatures. Optical rotatory properties were found to vary gradually and continuously with temperature over the range of −30 to +100°C. This suggested that all three electronic transitions of tyrosyl side chain are optically active, and that the side chains have some freedom of motion that decreases with decreasing temperature, disappearing only at about −30°C.