Journal of Porphyrins and Phthalocyanines

This paper summarizes what was discussed in a lecture at the IXth International Conference on Porphyrin Chemistry held in Suzdal (Russia) in September 2003. The development of porphyrin chemistry in former Soviet Union countries and over the world are discussed. Some ideas which were cultivated during three conditional porphyrin periods (1930-1960, 1960-1980 and 1980-2000) are also discussed.

The influence of free bases of meso-tetrakis(3,5-di-tert-butyl-4-hydroxy-phenyl)porphyrins and meso-tetraphenylporphyrins and their complexes of Co, Ni, Cu, Pt upon the radical chain oxidation of oleic acid as model substrates for lipid peroxidation has been studied. It was shown that the introduction of the antioxidative phenolic fragment into the porphyrin ring leads to the dual activity of phenolic porphyrins when compared with their tetraphenyl substituted analogues in substrate oxidation. Free base phenolic porphyrins and their nickel, copper, platinum complexes demonstrate acute inhibitory effect upon oleic acid peroxidation due to the key role of 2,6-di-tert-butylphenol moities, whereas cobalt porphyrin exhibits dual activity associated with the presence of both the redox active metal center and phenolic group.

Upon interaction of hydrazine hydrate with bacteriopurpurin, the initially formed monohydrazide in an acidic medium readily reacts with the second carboxyl group to give a six-membered N-aminocycloimide of bacteriochlorin p₆. The free amino group at the fused imide ring makes it easy to obtain N-alkyl and N-acyl derivatives. The compounds thus obtained exhibit high light-induced cytotoxicity on A549 human adenocarcinoma cells.

Structurally defined nanoscale self-assembled multiporphyrin arrays of variable geo-metry and composition (up to eight tetrapyrrole macrocycles) have been formed via two-fold extra-ligation in solutions at 77-293 K. The array formation is based on non-covalent binding interactions of the phenyl bridged Zn octaethylporphyrin chemical dimers or trimers, (ZnOEP)₂Ph or (ZnOEP)₃Ph₂, with di- and tetrapyridyl substituted tetrapyrrole extra-ligands (porphyrin, pentafluorophenyl substituted porphyrin, Cu porphyrin, tetrahydroporphyrin). Using steady-state and time-resolved measurements, spectral properties as well as pathways and dynamics of non-radiative relaxation processes (energy migration, photoinduced electron transfer, exchange d-π effects, realized in nano-femtosecond time scale) have been studied in these complexes upon variation of the composition, mutual geometry, redox and photophysical properties of interacting subunits as well as on the tempera-ture and polarity of surrounding.

The antimicrobial activity of new meso-tetrakis(N-methyl-6-quinolinyl)-substituted porphyrins and meso-tetrakis(N-methyl-6-quinolinyl)-substituted chlorins is described. The dark toxicity and photosensitising potentials of free-base (TQP and TQC) and its Sn(IV)-complexes [(TQP)Sn(IV) and (TQC)Sn(IV)] were tested on Gram-positive (Staphylococus aureus), Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria and two species of yeasts (Candida albicans and Rhodotorula bogoriensis). The results described in this paper show that TQP and (TQP)Sn(IV) did not inhibit the growth of S. aureus in the dark, but efficiently photosensitize the inactivation of this Gram-positive bacteria. These porphyrins have no appreciable photosensitizing activity towards Gram-negative bacteria. However, (TQP)Sn(IV) shows high dark toxicity against E. coli and P. aeruginosa. The free-base derivatives demonstrated dark activity only in the case of P. aeruginosa. We suppose that these meso-tetrakis(N-methyl-6-quinolinyl)-substituted porphyrins can bind to the Gram-negative bacteria outer membrane receptors that transported vitamin B₁₂. The meso-substituted chlorins TQC and (TQC)Sn(IV) have shown similar efficiency in the dark- and photoinactivation of S. aureus. They revealed a middle level of dark toxicity towards Gram-negative bacteria. The Sn(IV)-complex of chlorin in comparison with free base and metalloporphyrins are more effective in photoinactivation of Gram-negative bacteria. Yeasts, such as Candida albicans and Rhodotorula bogoriensis are more sensitive to photodynamic inactivation as bacterial cells. The effects of (TQP)Sn(IV) and (TQC)Sn(IV) are more expressed than effects of free bases.

A series of 2(α,β-unsaturated-γ-keto)-5,10,15,20-tetraphenylporphyrins was obtained by condensation of 2-formyl-5,10,15,20-tetraphenylporphyrin with acetone, 1,4-diacetylbenzene, 2-acetylthiophene, acetylacetone and acetophenone according to the Claisen-Schmidt reaction. The condensation product with 1,4-diacetylbenzene could react similarly with another formyl derivative – quinoxalin-6-carboxaldehyde and 2-formyl-5,10,15,20-tetraphenylporphyrin. It is shown that this reaction passes through formation of iminium salt formylporphyrin in presence of free base piperidine and perchloric acid.

Photophysical properties of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMpyP4) and its metallocomplexes M(II)TMpyP4 (M = Zn, Cu, Ni, Co) bound to natural DNA and synthetic poly-, oligo- and mononucleotides are considered with a primary emphasis placed upon intermolecular interaction of the photoexcited porphyrins with the nearest environment. Quenching of the fluorescent S₁ (but not triplet T₁) state due to guanine to porphyrin electron transfer is observed for TMpyP4 intercalated between GC base pairs of the double-strand helixes, whereas in the case of TMpyP4 complexed with guanosine monophosphate (GMP) both S₁ and T₁ states of the porphyrin are quenched. Furthermore, a dependence of the efficiency of TMpyP4 triplet state quenching by the dissolved molecular oxygen from air on the porphyrin localization enables one to readily distinguish porphyrin groove binding mode from intercalation. Excited states of the TMpyP4 complexes with transition metals, in spite of their very short lifetimes, also interact with nucleic acid components by means of an axial ligand binding/release to/from the metal. A possible structure of the five-coordinate excited complex (“exciplex”) formed in case of CuTMpyP4 groove binding to some single- and double-strand polynucleotides is discussed.