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 mm 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 mm 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 mm Arg. These results suggest potential approaches to optimizing RB_M ^2- -photosensitized protein crosslinking in tissues.