Canadian Journal of Pure & Applied Sciences

Abstract: Photo bleaching of methylene blue with two aldohexoses (galactose and D-mannose) in 50% aqueous methanol in presence of acetate buffer has been investigated with steady illumination of high intensity radiation of 661 nm on specially designed optical processor in photochemical research laboratory. High power Hg bulb was used as source of radiation. Quantum yield of reduction of dye showed that configuration of aldoses has some bearing on rate of reduction and depends upon the concentration of reducing sugars. This follows the first order decay kinetics of triplet transient species of the dye with life time of 10.1?s. Transient intermediate of methylene blue rapidly convert into leuco form after abstraction of H ion from hexoses by following step. MBT+ + H+ MBH++ T Reduction was carried out at different parameters like concentration of dye, reducing sugars, acidity which was adjusted by Hammmett ‘s acidity function and temperature. A comparison of reduction of dye by two monosaccharides reflect that quantum yield (?) was higher when D-mannose was in the reaction mixture. The values of rate constants were obtained and compared with international data.