CONFORMATION OF GELATIN CHAINS IN AQUEOUS-SOLUTIONS .1. A LIGHT AND SMALL-ANGLE NEUTRON-SCATTERING STUDY

Gelatin solutions in dilute and semi-dilute regimes were characterized by using light and small-angle neutron scattering techniques. Absolute intensity measurements allowed us to evaluate the molecular parameters of these protein chains (radius of gyration, persistence length, cross-section, mass per unit length) and to determine the quality of the solvent (0.1 M NaCl solutions in H2O or D2O at pH = 7). The classical model of worm-like chains was adopted for the theoretical interpretation of chain conformation in the sol state (T = 50-degrees-C) with a persistence length of about 20 angstrom. In semi-dilute solutions the correlation length was measured for different concentrations. Agreement was found with the scaling laws, although the description is not totally satisfactory: non-trivial scattering effects are detected in both static and dynamic light scattering experiments, which can be attributed to the presence of inhomogeneities having a different local density. Their apparent radius of gyration is of the order of several hundred angstroms. The nature and extension of these inhomogeneities are discussed.