Mobilities of poly-L-lysine molecules in low-salt solutions

Publisher Website
Google Scholar
Abstract
We have studied the ordinary–extraordinary phase transition of poly‐L‐lysine solutions using the techniques of quasielastic light scattering (QELS), electrophoreticlight scattering (ELS), and fluorescence photobleaching recovery (FPR). Polymer of molecular weight 90 kg/mol was examined in aqueous solutions at a concentration of 1 g polymer/l. The apparent mutual diffusion coefficient, as measured by QELS, was observed to increase sharply by an order of magnitude (from 0.8 to 7×10− 7 cm2/s) as the KCl concentration was increased from 2 to 5 mM, in agreement with previous reports by Schurr and co‐workers. On the other hand, the tracer diffusion coefficient (measured by FPR) varies only by about 50% (from 4 to 6×10− 7 cm2/s) in a broader trend over the range from 0 KCl to 10 mM KCl. The electrophoretic mobility (measured by ELS) mirrors the change in the tracer diffusion coefficient (from 1.9 to 2.6 μm cm/V s). The ELS and FPR data indicate that poly‐L‐lysine exists primarily as a random coil with little restriction of translational motion due to intermolecular interactions. The QELS data must then be interpreted in terms of fluctuation mobilities whose lifetimes are not characteristic of the motion of individual molecules.