PHOTOSTABILITY OF ANILINE-BLUE (CP-42755) AND METHYL-BLUE (CI-42780)

Commercially available and purified samples of Aniline Blue and Methyl Blue (both dyes having the synonym ''Cotton Blue'') in aqueous soluti on appeared to be reasonably photostable wizen subjected to simulated sunlight. The compounds were, however, degraded in the presence of hyd rogen peroxide (100 vol.), rite reaction following second order kineti cs with Aniline Blue and first order kinetics with Methyl Blue. Inclus ion of mannitol greatly increased the rare constants for, both dyes. I rradiation of the dyes separately with 2,2'azobis(2'-amidinopropane) d ihydrochloride (ABAP) resulted in rapid degradation of both dyes. Addi tion of acetaldehyde to both dyes resulted in a reduced rare constant, thus suggesting that the reaction was hydroperoxy radical mediated. W hen the dyes were treated with singlet oxygen whilst being protected f rom light or irradiated with simulated sunlight, they under went decom position, suggesting that they were singlet oxygen sensitive. These fi ndings may have considerable practical implications when the dyes are used in a diagnostic setting; if they are not protected fr om light ex posure, their staining capability is likely to be considerably reduced . (C) 1997 Elsevier Science Ltd.