SPECTROSCOPIC CHARACTERIZATION OF HYPOCRELLIN B: LANTHANIDE COMPLEXES FOR USE IN PHOTODYNAMIC THERAPY / Caracterização espectroscópica de complexos hipocrelina B: lantanídeos para uso em terapia fotodinâmica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

A study about the optical properties of the chromophore hypocrellin B (HB) and of its complexes with lanthanum (La3+), europium (Eu3+) and terbium (Tb3+) ions in ethanol solutions was realized. This pigment is a potential second generation photosensitizer due to its great properties, as high in vivo metabolism and mainly high singlet oxygen generation quantum yield (FD). The present work was carried out in two stages: the first one consisted of the spectroscopic study of the complexes of HB with lanthanide ions (Ln3+); the second one, of in vitro PDT tests against Candida albicans. In the first stage of the work, the best molar ratio between HB and Ln3+ was verified by monitoring the complexes longer wavelength absorption peaks. The larger red-shift (from 589 nm to 614 nm) was noted for the complexes with 1 mol of HB for 2 moles of lanthanide ions. It was observed that HB and its complexes emit from about 600 nm up to 750 nm. It was possible, from the absorption and emission spectra, to calculate the values of energy levels for the molecule and its complexes. All photosensitizers showed for the lower energy level value higher than 0,98 eV, which can indicate that they are able to generate singlet oxygen. The dimerization constants of the samples were determined, for verifying their tendency for giving rise to dimmers or higher order aggregates. The obtained values of this parameter for HB and its complexes with lanthanum, europium and terbium were, respectively, 4,7.104, 3,6.105, 2,1.105 and 1,0.105 M-1. All the samples showed to be stable against the action of light of 532 nm with intensity up to 400 mW/cm2 for the period of time of 1 hour. The capacities of generating singlet oxygen were determined by the direct (detection of the singlet oxygen emission around 1270 nm) and the indirect methods (changes in 440 nm absorption of RNO). The direct method indicated that HB can generate singlet oxygen, and the chemical method revealed that this specie is generated following a tax of 2,8.10-4 s-1; for HB:La3+ (1:1), it was obtained an enhancement of 32% on the singlet oxygen generation related to HB, and for HB:La3+ (1:2), the indirect method presented tax of 3,0.10-4 s-1. Based n the experimental data, the best among the studied complexes was HB:La3+ (1:2). Thus, this and its precursor, HB, were applied in antimicrobial PDT in vitro tests, the second stage of this work. The ideal concentration of HB was 10 M. With only 30 seconds of irradiation with LED in 460 nm and with 333 mW/cm2 of intensity, it was observed lethal effect for all the microorganisms, with both HB and its complex. However, with excitation at 660 nm at the same intensity, only HB:La3+ (1:2) was effective, reaching total photodynamic effect after 6 minutes of irradiation; the reduction caused by HB in the same time interval was lower, which proves the effectiveness of the produced photosensitizer.

ASSUNTO(S)

espectroscopia oxigênio singleto biofísica biofísica pdt espectroscopia hipocrelina b hipocrelina b pdt terapia fotodinâmica oxigênio singleto terapia fotodinâmica fotossensibilizador fotossensibilizador

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