The mobility of amorphous biomaterials, primarily carbohydrates and proteins, modulate the stability and shelf-life of foods, feeds, and pharmaceuticals, and the viability of spores, seeds, and even whole organisms during anhydrobiosis. We have developed phosphorescence methods to monitor the molecular mobility and dynamic site heterogeneity of amorphous solid biomaterials using steady-state and time-resolved emission and intensity from xanthene and indole chromophores. Measurements of peak frequency and linewidth monitor the rate and extent of solvent relaxation in the local amorphous environment around the probes. Measurements of intensity decay kinetics, analyzed using stretched exponential decay models in which the lifetime and the stretching exponent are the physically relevant fitting parameters, provide information about the rate and distribution of non-radiative quenching due to collisional interactions between the probe and the local matrix environment. And finally, systematic variations in the decay kinetics with emission wavelength provide a sensitive and novel indicator of the extent of dynamic site heterogeneity within the amorphous solid matrixes. The specific ways in which these chromophores respond to molecular mobility within amorphous solid sugars, sugar alcohols, and globular proteins as a function of temperature over the range from about -30 to 150C will be reviewed and correlated with rates of oxygen diffusion monitored by the extent of oxygen quenching of the probe phosphorescence. These studies provide insight into how luminescence can be used to monitor molecular mobility in amorphous solids and how this mobility controls the rate of an important degradative process (oxidation).
Back to Stars, Branched, Graft and Dendritic Polymers
Back to The 37th Middle Atlantic Regional Meeting (May 22-25, 2005)