PHOTOCHEMICAL REACTIONS 85 the dye occurs (7). Acriflavin and fluorescein-type dyes undergo photo- reduction in the presence of aqueous solutions of mild reducing agents such as ascorbic acid, but the rate of the reaction is considerably enhanced in presence of PVP (8-11). It has been shown that these dyes bind to the polymer and that the bound dyes are more readily promoted to the reac- tive triplet state upon irradiation (12). The enhancement of photoreduction which Oster and coworkers have demonstrated with polymers such as PVP and PMA can also be accom- plished with surface active agents. Data obtained using one of the sys- tems utilized by Oster for studies with PMA are presented to illustrate the effects of nonionic, anionic, and cationic surface active agents. Solu- tions containing malachite green and ascorbic acid are, under the condi- tions of this study, relatively stable to light in absence of a macromolecule. Malachite green binds to the nonionic surface active agent polysorbate 80 as indicated by the equilibrium dialysis data presented in Fig. 1. The polysorbate 80 causes the malachite green-ascorbic acid system to un- dergo rapid photodecomposition. Figure 2 illustrates the rate of photo- reduction of malachite green in the presence of varying polysorbate 80 concentrations in an anaerobic system. In an aerobic system (Fig. 3), 7 6 TOTAL FREE 5 4 $ 2 I I I i I I 0 i 2 3 4 5 POLYS ORBATE 80 (% W/V) Figure 1. Binding of malachite green to polysorbate 80, pH 5.0 acetate buffer, 25øC. Mala- chite green concentration 1.0 X 10-*M

86 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS A 0.5 I I I 2 .'.'5 MINUTES Figure 2. Anaerobic photobleaching of 2 X 10-SM malachite green in prcscnce of 1 X 10-•M ascorbic acid, pH 5.0 acetate buffer, 25øC. A, no additive B, 1% polysorbate 80 C, 3% polysorbate 80 D, 5% polysorbate 80 1.0 0.9 = 0.8 o ,,0 0.7 bJ z 0.6 o cn 0.,5 Y o o 0,4 I I i 5 I I I 5 I0 I 20 25 .30 MINUTES Figure 3. Aerobic photobleaching of 2 X 10-*M malacbite green in pre•ncc of 1 X 10-•M ascorbic acid and 5% polysorbate 80, pH 5.0 acetate buffer, 25øC there is no photoreduction of malachite green until all of the oxygen in the system is consumed. In the presence of oxygen, excited dye species react readily with oxygen to form an intermediate which is a powerful