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The formation of water-soluble metalloporphyrin heterodimers from Fe(III), Cu(II) and Ni(II) complexes of 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin and 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin has been investigated using UV-vis, IR and electron paramagnetic resonance spectra. Absorption and IR spectra confirmed the formation of dimers and electron paramagnetic resonance spectra showed evidence for the metal-metal interactions in the dimers.

The in vitro photodynamic effect of bis(tri-n-hexylsiloxy)silicon phthalocyanine has been evaluated against the melanotic M6 cell line. The results showed that at 10^-5 M dose, LD₅₀ is obtained for a 150 J cm^-2 light dose and LD₉₀ for 540 J cm^-2. Electron spin resonance spectroscopy was used with spin traps to study the type I and type II photochemical pathways involved and to detect active oxygen intermediates such as singlet oxygen, oxygen superoxide and hydroxyl radical. The two mechanisms occurred simultaneously and no change was observed when the phthalocyanine was entrapped in liposomes.

Neutral double-decker radical lutetium(III) diphthalocyanine with eight crown ether substituents bound through oxymethyl bridges has been synthesized from 1-[(benzo-15-crown-5)-4′-yl]oxymethyl-3,4-dicyanobenzene and lutetium(III) acetate. The ESR spectrum confirmed the radical nature of the complex.

The double-decker lutetium(III) phthalocyanine [(C₆H₁₃S)₈Pc]₂Lu was investigated by electrochemical and spectroelectrochemical methods and comparisons made to previously investigated [(C₁₂H₂₅S)₄Pc]₂Lu and (Pc)₂Lu under the some experimental conditions. All three compounds undergo a single reversible one-electron oxidation and up to four reversible one-electron reductions in CH₂Cl₂ containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). The octa- and tetra substituted phthalocyanine derivatives exhibit one oxidation and three or four reductions in solution while five reductions can be detected for the two compounds in a gel-like cast film membrane of tetraoctylphosphonium bromide (4C₈P⁺Br⁻) at a basal plane pyrolytic graphite electrode which was immersed in aqueous 0.5 M KCl. The half-wave potentials of these SR substituted complexes in CH₂Cl₂ are negatively shifted by 210-490 mV from E_1/2 values for the same compounds in the aqueous 4C₈P⁺Br⁻ matrix and five reductions of these compounds are observed under the latter experimental conditions. The UV-visible spectra of the compounds were measured in five different oxidation states and ESR spectra were also characterized for the neutral and doubly reduced complexes. As was expected, [(Pc)₂Lu]⁻,{[(C₆H₁₃S)₈Pc]₂Lu}⁻ and {[(C₁₂H₂₅S)₄Pc]₂Lu}⁻ are ESR silent while electrogenerated [(Pc)₂Lu]²⁻, {[(C₆H₁₃S)₈Pc]₂Lu}²⁻ and {[(C₁₂H₂₅S)₄Pc]₂Lu}²⁻ show broad strong signals at g = 2.0046, 2.0041 and 2.0034 with linewidths of 13.9, 16.1 and 12.9, respectively. These signals are indicative of organic free radicals where the unpaired electrons of the dianion are delocalized over two macrocycles.

Self-exchange electron transfer rates between π-radical cations of zinc porphyrins and the neutral metalloporphyrins have been determined from the line-width broadening in the ESR spectra in different solvents at various temperatures. Fine tuning of the substituent on the porphyrin ring and the proper choice of the solvent have enabled us to observe negative activation enthalpies for the self-exchange electron transfer reactions. The observation of negative activation enthalpies indicates that the self-exchange electron transfer occurs via the charge-transfer π-complexes formed between zinc porphyrin radical cations and the neutral zinc porphyrins. The complete delocalization of the unpaired electron over two porphyrin moieties is observed in the radical cation of a zinc porphyrin dimer, 5,5'-bis(10,20-bis(3,5-di-tert-butylphenyl)porphyrinatozinc(II)). This is regarded as the extreme limit of the rapid self-exchange electron transfer between zinc porphyrin radical cation and the neutral form.

Electrochemical and spectroelectrochemical studies are presented for nine copper corroles with electron-withdrawing or electron-donating substituents on the three meso-phenyl rings of the compounds or on the eight β-pyrrole positions of the macrocycle. Up to three reversible oxidations can be seen for each Cu(III) corrole in CH₂Cl₂ containing 0.1 M TBAP. Unlike the case of (OEC)Cu, no dimer is electrochemically detected upon the first oxidation of these compounds at room temperature. However, a dimer forms at low temperature (< -50°C) for compounds having strong electron-donating groups. Two reductions are observed for all nine corroles at low temperature in CH₂Cl₂, 0.1 M TBAP, but only one reduction is detected at room temperature for four of these compounds which have weak electron-withdrawing or electron-donating groups. The neutral, reduced or oxidized Cu corroles were also characterized by thin-layer UV-visible spectroelectrochemistry and ESR. The resulting data indicates that eight of the nine neutral complexes contain a Cu(III) center while only one complex, [Br₈(C₆F₅)₃Cor]Cu, exists in its Cu(II) form in CH₂Cl₂ containing 0.2 M TBAP.

Kinetics of the effect of three different tetrapyrrole-based photosenzitizers, pheophorbide a, meso-tetrahydroxyphenyl chlorin, and 3,7-bis(2-carboxyethyl)-2,8,12,17-tetramethyl-13,18-bis[(5-propoxycarbonyl-3-4-dihidroxy-phenyloxy) ethyl] porphyrin, on spin trapping with of 5,5-dymethyl-1-pyrroline N-oxide (DMPO) – a method widely applied in photodynamic therapy research – was investigated in the chemical model system of initiated oxidation of ethylbenzene. Spin adducts were measured by ESR spectroscopy, and kinetics of the consumption of the spin trap and accumulation of main products of oxidation (acetophenon, 1-phenyl-ethanol and 1-phenyl-ethyl-hydroperoxide) were followed using high performance liquid chromatography. The ESR spectrum of the non-illuminated system corresponded to an adduct formed between the spin trap and α–phenylethyl peroxyl radical, while under illumination, the spectrum indicated competitive formation of another adduct. Based on analysis of the corresponding g factor and hyperfine coupling constant values of the latter adduct (g = 2.00587, α_N = 13.57 G, α_H = 2.27 G), the nitrone ring has presumably been split up and an adduct was formed between α-phenylethyl radical and 4-methyl-4-nitrosopentanoic acid – a product of the oxidation of the parent spin trap by singlet oxygen. Computer modeling based on detailed reaction mechanism and fitted to the measured data confirmed this assumption. The rate constants gave values of 2.3 × 10⁵M⁻¹.s⁻¹ for the formation of the adduct and 1.0 × 10⁴M⁻¹.s⁻¹ for its decay by interaction with free radicals offering a more detailed quantitative understanding of spin trapping in the presence of tetrapyrrole photosensitizers under illumination.

Two cobalt porphyrazines, 2,3-tetrapyridoporphyrazine and 3,4-tetrapyridoporphyrazine, were examined in N,N-dimethylformamide, dimethyl sulfoxide and pyridine solutions as to their electrochemical, spectroelectrochemical and ESR spectroscopic properties. These results were compared with those of the unsubstituted cobalt phthalocyanine. At high concentrations, aggregation was observed for each investigated compound in the three solvents. The intensity of ESR signals of each derivative depends upon the extent of aggregation in its solution. The g values shift towards high field with an increase in the strength of the axial ligand and the number of axial ligands on the cobalt center. Both tetrapyridoporphyrazine complexes undergo one oxidation and three reductions in N,N-dimethylformamide, dimethyl sulfoxide or pyridine solution. Thin-layer UV-visible spectroelectrochemical results confirmed that the first oxidation and first reduction of both compounds are metal-centered while the second and third reductions are ring-centered. An overall electron transfer mechanism for both porphyrazine derivatives is proposed.