Nina A. Kuznetsova

Photochemical studies of tetra-2,3-pyridinoporphyrazines

Tetra-2,3-pyridinoporphyrazines and the corresponding water-soluble N,N′,N′′,N′′′-tetramethyl-tetra-2,3-pyridinoporphyrazine complexes, containing central metal atoms; M=Ge, Sn, Si and Zn, were synthesized and their photochemical properties were investigated. The reductive quenching of pyridinoporphyrazines excited states, enhanced relative to phthalocyanines, was considered as the first photochemical step of dyes phototransformation in dimethylformamide (DMF) and dimethylsulfoxide (DMSO) solutions under irradiation with visible light. Efficiency of singlet oxygen photosensitization decreases significantly in the row phthalocyanines, unquaternized, quaternized tetra-2,3-pyridinoporphyrazine metallocomplexes.

Silicon octaphenoxyphthalocyanines: photostability and singlet oxygen quantum yields

Abstract Photochemical properties of series of axially substituted silicon octaphenoxyphthalocyanines with aryloxy, siloxy, aminoalkoxy, esters of carboxylic acids and sulphonic acid esters residues as axial ligands were studied in dimethylsulfoxide (DMSO) solution. It was found, that under Q-band excitation axial ligands in compounds studied have the propensity to be changed by hydroxyl groups with quantum yields in the range 10 −5 to 10 −2 depending on the nature of the axial ligand. Axial substituent phototransformation was followed by slow photobleaching of dihydroxysilicon octaphenoxyphthalocyanine (photoproduct) in self-sensitized singlet oxygen mediated oxidation of the macrocycle. Singlet oxygen quantum yields were found to be in the range 0.15–0.20 for majority of the phthalocyanines (Pc) studied.

Sulfonated phthalocyanines: aggregation and singlet oxygen quantum yield in aqueous solutions

The influence of sulfonation degree (n) and central atom nature on singlet oxygen quantum yield (ΦΔ) were studied for a series of sulfonated phthalocyanine metal complexes MPcSnmix. It was found that in DMSO, where the studied dyes exist as monomers, ΦΔ values are independent of number and position of the sulfogroups and are equal to 0.11 ± 0.02, 0.19 ± 0.03, 0.37 ± 0.05, 0.38 ± 0.05 and 0.68 ± 0.10 for the metal-free and Mg, Gd, Al and Zn complexes, correspondingly. However, in aqueous solutions, aggregation of the dyes determines their photochemical activity. Substitution in adjacent to macrocycle 3 and 6 benzene positions interferes with aggregation compared to 4 and 5 positions, presumably due to enhanced steric hindrances in the former case. In the ZnPcSnmix series (n varied from 2 to 4), as an example, the linear relationship between degree of aggregation and ΦΔ indicates that only the monomer fraction of the dye is responsible for singlet oxygen production. For less sulfonated samples the order of ...

Comparative photosensitised transformation of polychlorophenols with different sulphonated metallophthalocyanine complexes in aqueous medium

Abstract The relative efficiencies for the oxidation of trichlorophenol (TCP) and pentachlorophenol (PCP), sensitised by sulphonated phthalocyanine complexes containing Zn, Al, Sn and Si as central metals, were studied in aqueous solutions. For the first time, sulphonated silicon and tin phthalocyanines were synthesised and their activity towards photosensitisation of singlet oxygen and photo-oxidation of polychlorophenols was examined. The efficiency of the sensitised photo-oxidative degradation of polychlorophenols depends not only on singlet oxygen quantum yield of sensitiser, but also on its stability. The influence of substrate structure and the pH of the solution on the photo-oxidation efficiency, as well as on the sensitiser photodegradation were studied. It was found that the contribution of the Type II (singlet oxygen-mediated) mechanism to the relative efficiency of the photosensitised photo-oxidation of the phenol, decreased from phenol to p -chlorophenol, TCP and PCP, whereas Type I radical pathway increased. The results obtained for PCP give evidence that electron transfer from the excited sensitiser to the substrate in its unionised form is responsible for enhanced sensitiser photodegradation.

Electrostatic binding of substituted metal phthalocyanines to enterobacterial cells: Its role in photodynamic inactivation

The effect of ionic substituents in zinc and aluminum phthalocyanine molecules and of membrane surface charge on the interaction of dyes with artificial membranes and enterobacterial cells, as well as on photosensitization efficiency was studied. It has been shown that increasing the number of positively charged substituents enhances the extent of phthalocyanine binding to Escherichia coli cells. This, along with the high quantum yield of singlet oxygen generation, determines efficient photodynamic inactivation of Gram-negative bacteria by zinc and aluminum octacationic phthalocyanines. The effect of Ca2+ and Mg2+ cations and pH on photodynamic inactivation of enterobacteria in the presence of octacationic zinc phthalocyanine has been studied. It has been shown that effects resulting in lowering negative charge on outer membrane protect bacteria against photoinactivation, which confirms the crucial role in this process of the electrostatic interaction of the photosensitizer with the cell wall. Electrostatic nature of binding is consistent with mainly electrostatic character of dye interactions with artificial membranes of different composition. Lower sensitivity of Proteus mirabilis to photodynamic inactivation, compared to that of E. coli and Salmonella enteritidis, due to low affinity of the cationic dye to the cells of this species, was found.

Cationic Zn and Al phthalocyanines: synthesis, spectroscopy and photosensitizing properties

Several Zn(II) and Al(III) phthalocyanines bearing eight or sixteen positive charges on substituents of different structure have been prepared. Synthesized polycationic phthalocyanines have been studied in aqueous and alcoholic media by UV-vis spectroscopy and tested for their efficacy in singlet oxygen photosensitization. It has been found that a minor structural modification at the periphery of the photosensitizer allows control over its key features such as singlet oxygen generation due to specific intermolecular interactions in solution. The efficacy of polycationic phthalocyanines to sensitize tryptophan photobleaching in aqueous media and inactivation of bacteria in sewage water is also structure-dependent. Among the complexes studied, two dyes - zinc octakis(pyridiniomethyl)- and octakis[N-(2-hydroxyethyl)-N,N-dimethylammoniomethyl]substituted phthalocyanines - are the best sensitizers and have high potential for photodynamic applications.

New heterogeneous photosensitizers with phthalocyanine molecules covalently linked to aminopropyl silica gel

New heterogeneous photosensitizers were synthesized, in which phthalocyanines of zinc and aluminum, tetrasubstituted at non-peripheral positions with modified thiophenyl groups, were grafted to aminopropyl silica gel. The absorption and fluorescence spectra, and the quantum yields of fluorescence and photosensitized singlet oxygen generation were estimated for aqueous suspensions of these sensitizers. It is shown that upon photoexcitation, silica gel-bound phthalocyanines produce singlet oxygen and display photobactericidal activity against bacteria E. coli.

Study on the photostability of water-soluble Zn(II) and Al(III) phthalocyanines in aqueous solution

The photodegradation of a series of water-soluble Zn(II) and Al(III) phthalocyanines has been studied in aerobic aqueous solutions. The photobleaching quantum yields of zinc phthalocyanine derivatives range from 2.2 × 10-4 for octacarboxy- to 1.5 × 10-5 for ZnPc, bearing 16 positively charged groups on periphery. Their aluminum counterparts are more photostable and photobleach with quantum yields in the narrow range (0.75 ÷ 2 × 10-6). The pH dependences of the photobleaching quantum yields for aluminum phthalocyanines show enhanced photodegradation for molecules with deprotonated axial H2O ligand. Some aspects of the mechanism of dyes photodegradation were studied and discussed. It was found that contribution to photooxidation of type II pathways depends upon a particular dye structure. Thus, no contribution of singlet oxygen to the photooxidation of cationic phthalocyanines has been found, even though singlet oxygen is involved in the photodegradation of negatively charged phthalocyanines.

Photophysical properties and photodynamic activity of octacationic oxotitanium(IV) phthalocyanines

The photophysical and photosensitizing properties of two octacationic oxotitanium phthalocyanines (TiOPcs), bearing pyridiniomethyl or cholinyl substituents, have been studied in aqueous and alcohol solutions. In water, both compounds were monomeric with the high quantum yields of fluorescence (Phi(F) = 0.17-0.19) and singlet oxygen formation (Phi(Delta) = 0.4-0.5). The Phi(F) and Phi(Delta) of both phthalocyanines decreased with the increase of solvent hydrophobicity from water to ethanol. This effect was much stronger in alcohol solutions of the pyridiniomethyl-substituted phthalocyanine and probably results from aggregation of TiOPc molecules caused by association of chloride anions with phthalocyanine cationic groups. Evidence is presented that under illumination aqueous TiOPc solutions also produce hydroxyl radicals, which probably appear owing to photocleavage of water molecules. The quantum yield of OH formation was (3-5) x 10(-5) after argon purging and twice as much in the presence of air. It is shown that irradiation of TiOPc solutions causes photobleaching of TiOPcs. The photobleaching quantum yield in water was found to be about 1 x 10(-4). The data suggest that photobleaching occurs owing to the reactivity of hydroxyl radicals, though singlet oxygen is generated by TiOPcs much more efficiently. The phototoxicity of the tested TiOPcs toward bacteria has been revealed. It is proposed that both OH and (1)O(2) might be responsible for the observed bactericidal effects.

Effects of the degree of substitution on the physicochemical properties and photodynamic activity of zinc and aluminum phthalocyanine polycations

A series of zinc and aluminum phthalocyanines containing 3–8 pyridiniomethyl or cholinyl substituents on average were synthesized. As the number of cation substituents increased, in aqueous solutions, the aggregation ability of phthalocyanines decreased, while the quantum yields of fluorescence and singlet oxygen generation increased. The photodynamic inactivation of coliform bacteria sensitized by zinc and aluminum phthalocyanine polycations with an increase in the substitution degree became more effective.