Photophysics of melatonin in different environments

Melatonin (N-acetyl-5-methoxytryptamine) is a naturally occurring hormone w ith a structural resemblance to tryptophan. Its fluorescence is solvent dep endent and strongly quenched in the presence of oxygen. Fluorescence quench ing in aqueous and organic solutions have been studied in the presence of d ifferent quenchers. A 1:1 inclusion complex formation between melatonin and different cyclodextrins in aqueous solution has been observed. The effects of microheterogeneous media provided by cyclodextrins, micelles and revers e micelles on the fluorescence characteristics of melatonin have been inves tigated. The water-soluble inorganic quenchers like I(Br and KI were unable to quench the fluorescence of melatonin dissolved in a microemulsion consi sting of surfactant + cyclohexane + 1-propanol + water, whereas the organic quenchers like CCl4, and CHCl3 were able to quench the fluorescence with a rate constant ton the order of 10(8) dm(3) mol(-1) s(-1)) quite similar to that in neat organic solvents.