Dynamic light scattering studies of poly-L-lysine HBr in the presence of added salt.

Abstract

AbstractClipped autocorrelation functions for the fluctuating intensity of light scattered from dilute solutions of poly‐L‐lysine in 0.2 M NaBr have been observed over a wide range of time scales down to 1.83 μsec, and over a wide range of pH. Two poly‐L‐lysine samples of molecular weight 35,000 and 200,000, respectively, were compared to determine the extent of draining of the so‐called random‐coil configuration. The observed correlation functions were in general very satisfactorily represented by simple translation diffusion of single molecules. At high pH ∼10–10.4, there was evidence of considerable aggregation, but no indication whatsoever of any unusually fast component, as reported recently by Jamieson et al. for poly‐L‐lysine HBr in the absence of salt.A 30% rise in the diffusion coefficient to a peak at pH 10 parallels the previously reported dip in the intrinsic viscosity, and is interpreted in terms of a more compact structure in that pH region between the coil and helix extremes.