Influence of Rose Bengal Dimerization on Photosensitization.

Protein crosslinking photosensitized by rose Bengal (RB2- ) has multiple medical applications and understanding the photosensitization mechanism can improve treatment effectiveness. To this end, we investigated the photochemical efficiencies of monomeric RB2- (RBM 2- ) and dimeric RB2- (RBD 2- ) and the optimal pH for anaerobic RB2- photosensitization in cornea. Absorption spectra and dynamic light scattering (DLS) measurements were used to estimate the fractions of RBM 2- and RBD 2- . RB2- self-photosensitized bleaching was used to evaluate the photoactivity of RBM 2- and RBD 2- . The pH dependence of anaerobic RB2- photosensitization was evaluated in ex vivo rabbit corneas. The 549 nm/515 nm absorption ratio indicated that concentrations > 0.10 mm RB contained RBD 2- . Results from DLS gave estimated mean diameters for RBM 2- and RBD 2- of 0.70 ± 0.02 nm and 1.75 ± 0.13 nm, respectively, and indicated that 1 mm RB2- contained equal fractions of RBM 2- and RBD 2- . Quantum yields for RB2- bleaching were not influenced by RBD 2- in RB2- solutions although accounting for RB2- concentration effects on the reaction kinetics demonstrated that RBD 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 RBM 2- -photosensitized protein crosslinking in tissues.