Effect of gelatin on molecular mobility in amorphous sucrose detected by erythrosin B phosphorescence

We have used phosphorescence from the triplet probe erythrosin B (Ery B) to evaluate the effect of gelatin on the molecular mobility of the amorphous sucrose matrix as a function of temperature. Ery B was dispersed in amorphous sucrose and sucrose-gelatin films at ratios of approximately 1:10(4) (probe/sucrose), and delayed emission spectra and emission decay transients were measured over the temperature range from 5 to 100 degrees C. Analysis of spectra using a lognormal function provided the peak energy and bandwidth of the emission. The emission peak frequency decreased at low (0.00022-0.0007) gelatin concentrations and increased at high (above 0.0022) gelatin concentrations, indicating that gelatin increased the extent, and thus the rate, of dipolar relaxation at low gelatin content and decreased the extent at higher gelatin content. Decay transients were well fit to a stretched exponential function at all gelatin contents and temperatures. Analysis of the emission lifetimes provided a measure of the rate of non-radiative decay to the ground state, an indicator of matrix molecular mobility. This rate increased at low (0.00022-0.0022) and decreased at high (>0.0073) gelatin wt ratios. Analysis of the effect of gelatin on the emission bandwidth, the stretching exponent beta, and the variation of lifetime across the emission band indicated that matrix dynamic site heterogeneity increased at low and decreased at high gelatin wt ratios. These results provide a novel insight into the complex dynamic effects of the gelatin polymer on the molecular mobility of the amorphous sucrose matrix.