Temperature-dependence of riboflavin phosphorescence in cryosolvents

The molecular mobility of amorphous excipients is important for the stability of biomaterials during preservation, facilitating matrix formulation and product design. Phosphorescence spectroscopy is a sensitive optical method to study molecular mobility. However, there is a need to expand the pool of probes available for analysis since molecules differ in sensitivity. This research explored the feasibility and limitations of using riboflavin as a phosphorescent probe for monitoring matrix molecular mobility. Phosphorescence decays of riboflavin in four amorphous cryosolvents (aqueous solutions of glycerol, ethanol, sucrose, and dextran) were collected at 77 K to capture its natural phosphorescence lifetime (estimated at 170 ms). Decays were also collected during ballistic heating to assess the sensitivity of riboflavin towards changes in matrix molecular mobility. Riboflavin exhibited good sensitivity towards matrix secondary relaxations in the glass, indicating that riboflavin has excellent potential as an edible phosphorescent probe for molecular mobility in food and pharmaceutical products.