Optical Rotation and Configuration of Poly-L-tyrosine

Abstract

IN a recent communication from this laboratory1 it was reported that the constant b0 in Moffitt's equation2 for the optical rotation of a helical polypeptide is positive for solutions of poly-L-tryosine in dimethyl formamide and in pyridine, and for the sodium salt of this polymer in solution and in films. It was implied that in spite of the unusual sign of b0 the polymer was in the α-helical form, and that the positive value is a consequence of the strong chromophoric group near the β carbon atom. We have since made further measurements of the optical rotation of a solution of this polymer in N sodium hydroxide and of films cast from a solution in dimethyl formamide at 60° C., together with observations of the infra-red spectrum and X-ray diffraction pattern of the films. These studies have led us to the conclusion that it is more probable that in dilute solutions in pyridine, in dimethyl formamide, and in aqueous alkali, poly-L-tyrosine is in the random coil configuration, as is its sodium salt in films.