Characterization of riboflavin-photosensitized changes in aqueous solutions of alginate by dynamic light scattering.

The effect of irradiation, in the wavelength range of 310-800 nm, on aqueous solutions (pH = 7.4) of alginate in the presence of the photosensitizer riboflavin (RF) has been investigated with the aid of dynamic light scattering (DLS). Under aerobic conditions light irradiation of RF causes scission of the polymer chains which affects the polymer dynamics. The time correlation data obtained from DLS experiments showed at all conditions the existence of two relaxation modes: one single exponential at short times, followed by a stretched exponential at longer times. The slow relaxation time revealed, over the whole considered concentration range, lower values for the alginate/RF system, whereas no effect of photochemical degradation was observed for the fast relaxation time in the semidilute regime. The results suggest that the photochemically induced fragmentation of alginate affects the slow relaxation mode, associated with disengagement relaxation of individual chains or cluster relaxation, in a similar way as the zero-shear viscosity. These findings provide detailed insight into the dynamics of the polymer matrix, and this knowledge can be useful in the context of controlled-release delivery of drugs. The chemical units of alginate (M = mannuronic acid and G = guluronic acid).