Fluorescence lifetime and quantum yield of TMPyPH 2 associated with micelles and DNA

Abstract

In this work, we have determined the fluorescence lifetime and quantum yield of meso-tetrakis (4- N-methylpyridyl)porphine (TMPyPH 2) in cationic, anionic and non-ionic micellar media and in buffer phosphate solutions of DNA in order to evaluate how their electrostatic domain affects the photophysical properties of TMPyPH 2. The results obtained indicated that each specific electrostatic domain in micellar medium and in DNA solution affect the photophysical properties of the porphyrin. In anionic micellar medium of sodium dodecylsulfate (SDS) the electrostatic interacting of TMPyPH 2 with the medium leads to a Φ f value higher and τ f longer than those obtained in cationic medium of cetyltrimethylammonium bromide (CTAB) micelles. The interaction of TMPyPH 2 with a biological staff as DNA results initially in two different populations of a complex DNA–TMPyPH 2. The τ 1 for the first complex species changes in the function of DNA concentration in the ranges from 5.25 (‘free’ porphyrin species) to 11.3 ns (‘completely bound’ species) and the τ 2 for the second complex remains constant around 3 ns. It also was observed that DNA binding leads to a reduction in the fluorescence quantum yield of TMPyPH 2 to all DNA concentrations. This is an indication that the photodynamic properties of this porphyrin interacting with DNA are susceptible to the environmental properties affecting directly their photodynamic action.