Laser-Induced Anisotropic Effects on Raman Intensities and Depolarization Ratios

Abstract

A major impetus for the extensive research on the water-soluble derivatives of porphyrins over the past decade, has been not only that they can be used as model chromophores for porphyrins in vivo that participate in many of the essential function of life in procaryotes and eucaryotes, but as well their clinically useful photosensitizing properties which produce singlet oxygen causing tumour cell wall damage in photodynamic therapy of cancer cells and their binding (intercalation, groove-binding) mechanisms to DNA used in chemotherapy [1]. Several techniques were used [2–4], such as circular dichroism (CD), picosecond laser induced fluorescence polarization, laser induced dichroism effect (LIDE) spectroscopy, and resonance Raman (RR) spectroscopy to probe the nature of the meso-tetrakis(N-methyl-4-pyridyl) porphine, H2TMpyP(4), complex formed with DNA, H2TMpyP(4)-DNA. A thorough study of the RR spectra and depolarization ratios, ρ n, of the free H2TMpyP(4) is required before interpreting the information obtained from ρ n values of the H2TMpyP(4)-DNA. In this study we present an analysis of the behaviour of ρ n versus laser power I1(mW) of the ν 2(C β -C β ), A1g, \( \Delta \bar{\upsilon } = 1558{{\operatorname{cm} }^{{ - 1}}} \) and δ(pyr), A1g, \( \Delta \bar{\upsilon } = 1643{{\operatorname{cm} }^{{ - 1}}} \) RR peaks of the H2TMpyP(4) in a phosphate buffer solution [3].