THE INTERACTION OF MELANIN WITH 8-METHOXYPSORALEN: EFFECT ON RADIATIVE and NONRADIATIVE TRANSITIONS. A FLUORESCENCE and PULSED PHOTOACOUSTIC STUDY |
| |
Authors: | Aba Losi Cristiano Viappiani Pier Raimondo Crippa |
| |
Institution: | Department of Physics, University of Parma, Viale delle Scienze, 43100 Parma, Italy |
| |
Abstract: | Abstract –The interaction of 8-methoxypsoralen (8-MOP) with synthetic eumelanin was investigated using static and time-resolved fluorescence and pulsed photoacoustic calorimetry. Due to the strong overlap of the absorption bands of melanin and 8-MOP, a method is presented to account for the systematic errors introduced by the optical filter effect exerted by each absorbing species in the fluorescence and the photoacoustic measurements. As a preliminary step to the understanding of the nonradiative behavior of the psoralen-melanin complexes, the photoacoustic parameters of 8-MOP in various solvents were determined. Spectroscopic data indicate the absence of interaction at the ground-state level, whereas the singlet excited state of 8-MOP is quenched by the pigment; the average fluorescence lifetimes are independent of the melanin concentration, thus indicating a static quenching mechanism. The photoacoustic data show that the quenching process involves an increased intersystem crossing probability, which is almost unaffected by the presence of oxygen, as expected for a molecule essentially acting as a type I photosensitizing agent. |
| |
Keywords: | |
|
|