The Determination of Quantum Yield in the Fluoresence Spectra of Porphyrins

Abstract

The porphyrins, natural macromolecules, and especially the glycosylated ones, are recently used in the photodynamic therapy of different kinds of tumor cells. The porphyrins are injected through intravenous way in the human body. Under appropriate radiation of tumor zone with light in UV region, oxidation processes of the porphyrins occur through different mechanizms. As a result, inside the tumor, is producing oxygen in singlet state which is lethal for the tumor cells. The spectroscopic study of the porphyrins, both the absorbtion and the fluoresence spectroscopy, reveals some properties of the porphyrins which are ralated with their eventual application in the photodynamic therapy. So, from the value of the quantum yield, which is an important quantity that derives from the measurement of fluoresence of porphyrins, one can judge, through which mechanizm, the oxidation process does occurs. This suggest how the porphyrin should be used in the therapy, as monomers or as aggregates. The porphyrins are sinthetised in the Laboratory of Chemistry of Natural Compaunds, in the University of Limoges. The spectra has been taken by means of a photospectrometer, in the University of Tirana. The fluoresence spectra of the “protected” and “unprotected” porphyrins are studied. The determination of the quantum yield has been done through the comparison of porphyrins spectra, with them of Rhodamine B, which has a large fluoresence, in the same region of spectrum where does occurr the fluoresence of porphyrins. In order to do that, the calculations of the surface under the fluoresence spectra and under the Rhodamine one, is necessary. Also, the extintion of the fluoresence of some “protected” porphyrins, in polar solution, has been detected. These extintion of fluoresence has to do with the formation of agregates, of dimers, which can be confirmed from the absorbtion spectra.