CONFORMATION OF GELATIN CHAINS IN AQUEOUS-SOLUTIONS .2. A QUASI-ELASTIC LIGHT-SCATTERING STUDY

We have characterized dilute and semi-dilute aqueous gelatin solutions by quasi-elastic light scattering. The concentration dependence of the scattering spectra has been explored. In semi-dilute solutions, two diffusive modes were determined: the fast mode, with a diffusion coefficient D(f), is attributed to the cooperative movements of the entangled transient network of chains and it increases with the concentration as D(f) approximately c0.6; the slow mode, whose diffusion coefficient D(s) is inversely proportional to the Newtonian viscosity of the solution, is interpreted as the self-diffusion of clusters of chains that have a constant hydrodynamic radius R(c) almost-equal-to 750 angstrom. The effects on the slow modes of the salt content of the solutions, the molecular weight of the chains and temperature are examined. Besides, it is shown that the addition of a surfactant (sodium dodecylsulphate) hinders the formation of the clusters, and it is concluded that the latter are probably stabilized by hydrophobic interactions between apolar lateral groups of the protein.