Influence of Rose Bengal Dimerization on Photosensitization

Protein crosslinking photosensitized by rose Bengal (RB 2− ) has multiple medical applications and understanding the photosensitization mechanism can improve treatment effectiveness. To this end, we investigated the photochemical efficiencies of monomeric RB 2− (RB M 2− ) and dimeric RB 2− (RB D 2− ) and the optimal pH for anaerobic RB 2− photosensitization in cornea. Absorption spectra and dynamic light scattering (DLS) measurements were used to estimate the fractions of RB M 2− and RB D 2− . RB 2− self‐photosensitized bleaching was used to evaluate the photoactivity of RB M 2− and RB D 2− . The pH dependence of anaerobic RB 2− photosensitization was evaluated in ex vivo rabbit corneas. The 549 nm/515 nm absorption ratio indicated that concentrations > 0.10 m m RB contained RB D 2− . Results from DLS gave estimated mean diameters for RB M 2− and RB D 2− of 0.70 ± 0.02 nm and 1.75 ± 0.13 nm, respectively, and indicated that 1 m m RB 2− contained equal fractions of RB M 2− and RB D 2− . Quantum yields for RB 2− bleaching were not influenced by RB D 2− in RB 2− solutions although accounting for RB 2− concentration effects on the reaction kinetics demonstrated that RB D 2− is not a photosensitizer. Optimal anaerobic photosensitization occurred at pH 8.5 for solutions containing 200 m m Arg. These results suggest potential approaches to optimizing RB M 2− ‐photosensitized protein crosslinking in tissues.