The spectroscopic properties and the photodynamic activity of a highly water soluble
zinc(II)tetramethyltetrapyridino[2,3-
b:2',3'-g:2",3"-l:2"',3'''-q]porphyrazinium
salt (
ZnTM2,3PyPz) were investigated in aqueous homogeneous
solution and in biomimetic reverse
micelles medium bearing photooxidizable
biological substrates. Absorption and fluorescence spectroscopic studies indicate that
ZnTM2,3PyPz is dissolved as monomer in water and in
n-heptane/
sodium bis(2-ethylhexyl)sulfosuccinate (AOT, 0.1 M)/water (W0 = 30) micellar system. Fluorescence quantum yields (phi F) of 0.29 and 0.27 were calculated for
ZnTM2,3PyPz in water and in AOT
micelles, respectively. Spectroscopic analysis at different AOT concentrations showed interaction between
ZnTM2,3PyPz and AOT reverse
micelles with a binding constant (Kb) of 1.7 x 10(3) M(-1). The
photosensitization ability of
ZnTM2,3PyPz was evaluated using
9,10-dimethylanthracene (DMA). Singlet molecular
oxygen, O2(1 delta g), production yielded values of phi(delta) = 0.65 for
ZnTM2,3PyPz in AOT
micelles. Also,
ZnTM2,3PyPz induced efficiently the decomposition of the
amino acid L-tryptophan (Trp) and the
nucleotide guanosine 5'-monophosphate (GMP) in both media. A value of approximately 3.6 x 10(7) s(-1) M(-1) was found for the second order rate constant of Trp (k(r)(Trp)) decomposition in the AOT system, which is near to that found in pure water. Moreover,
ZnTM2,3PyPz formed stable complexes with GMP with a binding constant of K(GMP) = 1.0 x 10(3) M(-1). 1H NMR studies indicated that
ZnTM2,3PyPz interacts mainly with the
guanine moiety more than the
sugar part of GMP. On the other hand, the photodynamic activity of
ZnTM2,3PyPz produced decomposition of GMP. Quantification of GMP by HPLC indicates that the
nucleotide is photooxidized with a k(obs)(GMP) = 2.6 x 10(-4) s(-1) in water. Photooxidation of GMP considerably increases in deuteriated water indicating that
ZnTM2,3PyPz appears to perform its photosensitizing action via the intermediacy of O2(1delta g). Also, efficient sensitized decomposition was observed in micellar media resembling that in pure water. These results provide a better understanding of the effective photodynamic action produced by
ZnTM2,3PyPz like a potential phototherapeutic agent for the treatment of neoplastic diseases by
photodynamic therapy.