A. B. Solov’eva

Porphyrin photosensitizers solubilized with pluronics in the oxidation of tryptophan

It was shown that water-insoluble porphyrins solubilized with pluronics (ternary block copolymers of ethylene oxide and propylene oxide) efficiently transfer photoexcitation energy to molecular oxygen dissolved in aqueous media to excite it into the singlet state, which is active in oxidizing organic substrates. It was established that the degree of solubilization of porphyrin photosensitizers (PPSs) γ defined as the proportion of PPS molecules passed into the aqueous phase in the dissolution of formed films depends on a single parameter, the initial ratio between the porphyrin and pluronic molar concentrations q. γ = γ(q) dependences for the solubilization of dissimilar water-insoluble porphyrins were analyzed. It was shown that the behavior of all the obtained γ = γ(q) dependences is changed at a characteristic value qmax: when q š qmax, γ ∼ 1, and, when q ≥ ?qmax, the degree of solubilization decreases. It was concluded that solubilized porphyrins are efficient photosensitizers in the oxidation of organic substrates (tryptophan).

The effect of Pluronics on the photocatalytic activity of water-soluble porphyrins

Solubilization of hydrophilic porphyrins, 2,7,12,18-tetramethyl-3,8-di(1-methoxyethyl)-13,17-di(2-oxycarbonylethyl) porphyrin disodium salt (dimegin) and N-methyl-di-D-glucose amine salt of chlorine e6 (photoditazine), as well water-insoluble meso-tetraphenylorphyrin in the micelles of Pluronics (triblock copolymers and propylene oxide and ethylene oxide), increases the photocatalytic activity of porphyrins in the course of the oxidation of L-tryptophan in aqueous salt-containing solutions. The maximum photocatalytic activity is attained for the photocatalysts based on the Pluronics P85 and F127 containing 50–70% ethylene oxide units. As a result of solubilization, the activity of tetraphenylporphyrin increases by a factor of 50, while the activities of hydrophilic dimegin and photoditazine increase by factors of 1.5 and 6, respectively. The increased activity of tetraphenylporphyrin is due to the dissolution and dissociation of aggregates in the presence of Pluronics. The increased activity of dimegin, which is known to aggregate in water, is primarily provided by disaggregation. In the case of photoditazine, which does not form aggregates in aqueous solutions and is likely to be localized in the polar micellar “crown,” the effect of a polymer is due to the local concentration of both a substrate and a catalyst in the micellar pseudophase.

The influence of amphiphilic polymers on the photocatalytic activity of water-soluble porphyrin photosensitizers

The influence of amphiphilic polymers polyvinylpyrrolidone, poly(ethylene oxide), poly(vinyl alcohol), and pluronic F127 (propylene oxide-ethylene oxide triblock copolymer) on the catalytic activity of a number of water-soluble metal-free porphyrin photosensitizers was studied in the reaction of tryptophan photooxidation in aqueous solution. The introduction of the specified polymers was found to enhance the activity of carbon-substituted tetrafluorophenylporpyrin, photoditazine, and dimegin. It was ascertained that introduction of polyvinylpyrrolidone had the strongest effect on the increase in the photooxidation process rate; the change in the activity of porphyrins was 30–70%. The introduction of poly(ethylene oxide), poly(vinyl alcohol), and pluronic F127 was shown to enhance the rate of the process by 10–40%. It was concluded that this polymer effect was connected with the dissociation of aggregates, in which form porphyrin molecules were present in aqueous solutions, as indicated by an increase in fluorescence intensity of porphyrins. The introduction of polymers resulted in a bathochromic shift of the fluorescence bands for all porphyrins, which accounted for the formation of complexes of porphyrin sensitizers with the polymers.

Structure of pluronic F-127 and its tetraphenylporphyrin complexes: X-ray diffraction study

The structure of pluronic F-127 and its complexes with tetraphenylporphyrin has been studied by SAXS and WAXS techniques. It has been shown that the samples prepared via evaporation of chloroform and aqueous solutions of pluronic and its mixtures with tetraphenylporphyrin have a semicrystalline layered structure with the crystalline phase composed of poly(ethylene oxide). The identity period of layers in the samples prepared from the aqueous solution of pluronic has been found to be larger than that in the samples prepared from chloroform solutions of the polymer. This result may apparently be explained by a more pronounced hydration of the samples prepared by the former method. The presence of tetraphenylporphyrin in the samples has an insignificant effect on the parameters of the crystalline and layered structures of pluronic. When the tetraphenylporphyrin content is not larger than its solubilization limit with pluronic, tetraphenylporphyrin concentrates in the amorphous layers of pluronic in the noncrystalline finely dispersed state.

Amphiphilic polymers in photodynamic therapy

It is shown that some amphiphilic polymers (AP), including, polyvinylpyrrolidone (PVP), which exhibit no their own photochemical activity, can increase the activity of porphyrin photosensitizers (PPS), the most effective and nontoxic types of dyes for photodynamic action on tumor cells. It is also shown that, under the model conditions of tryptophan photooxidation, addition of amphiphilic polymers increases the activity of carborane-substituted tetra(fluorophenyl)porphyrins, Photoditazine, and dimegin. According to NMR and fluorescence spectroscopy data, this phenomenon, known as polymer effect, is probably associated with the formation of AP-PPS complexes, a factor that prevents the aggregation of PPS, normally occurring in aqueous solutions, thereby enhancing the photosensitizing activity of PPS.

Features of formation of magnetite coatings on low-carbon steel in hot nitrate solutions

The process of anticorrosion magnetite coating (MC) formation on low-carbon steel is studied in alkali-free nitrate converting media at the temperatures of 70–98°C reduced as compared to those used (130–145°C) in standard technologies of steel bluing: formation of such coatings in alkaline nitrate solutions. Alongside with the conventional corrosion-electrochemical methods of analysis of the formed MCs, the regularities of the MC surface reliefs were studied using the method of atomic force microscopy combined with the technique of flicker-noise spectroscopy (FNS) for processing digitized images and obtaining the parameters of the MC surface structure in different nanometer ranges. It was shown that it is necessary to introduce additives of metal nitrates with a low cation radius into the ammonium nitrate converting solution to obtain MCs with a high corrosion stability at the first stage of MC formation and the final stage must consist in the further “passivation” of MCs: MC treatment by aqueous solutions based on nontoxic carboxylates. According to the FNS analysis of the surface structure of the formed MCs, a significant decrease of the FNS “point” factor, an indicator of MC corrosion instability, occurred during the final treatment. On this basis, one could characterize quantitatively the results of accelerated corrosion tests: no steel corrosion occurred on the thus formed coatings for 42 days under standard severe conditions: 100% relative humidity and daily “showering”. The performed study reveals fundamental possibilities for solving the problems of standardization of the anticorrosion coating surface based on the analysis of their surface profile in the nanometer range.

The influence of ZnO-Sensor modification by porphyrins on to the character of sensor response to volatile organic compounds

The influence of modification of semi conductive ZnO and SnO2 sensors by porphyrins and their metal complexes on the parameters of sensor response to volatile organic compounds, ethanol, acetone and benzene, was analyzed. The concentration of volatile organic compounds (ci) varied in the range of 1–200 ppm. The sensor response was characterized by specific sensitivity γi = 100ΔRi/R0ci, where ΔRi = Ri − R0, Ri and R0 are measurable and initial resistance of the sensitive sensor layer correspondingly. It was established that the modification of sensors by porphyrins caused changes in sensor response and first of all decrease of ZnO sensor temperature at which the threshold of sensitivity is achieved (as used at this method cimin = 0.1 ppm) from 300 to 100°C. It also caused a change in sing of the parameter γ, which was of importance for creating “electronic nose” sensor systems. It was shown also, that the modification of ZnO sensor by metal complexes of porphyrin did not change sensor response parameters.

The character of the response of ZnO and SnO2 sensors modified with porphyrins to volatile organic compounds

The influence of the modification of the surface of ZnO and SnO2 sensors with 5,10,15,20-tetraphenylporphyrin on the parameters of sensor response to high-volatility organic substances was analyzed. The organic substances used were ethanol, acetone, and benzene. The sensor response was characterized by specific sensitivity γ determined as the ratio between a change in the resistance of the sensitive sensor layer and the volume concentration of high-volatility organic compounds introduced into the system. The modification of the sensors with tetraphenylporphyrin caused changes in sensor response, including a change in the sign of the γ parameter, which was of importance for creating “electronic nose” sensor systems.

Compatibility of cells of the nervous system with structured biodegradable chitosan-based hydrogel matrices

Hydrogel matrices for cell cultivation have been generated by two-photon laser polymerization of unsaturated chitosan derivatives and methacrylated hyaluronic acid. The adhesive and toxic properties of the matrices have been assessed, and the matrices have been shown to have a good compatibility with primary hippocampal cell cultures. The formation of morphologically normal neural networks by cells of the nervous system cultured on the surface of hydrogel matrices has been observed. The metabolic status of dissociated hippocampal cells cultured on the matrices was similar to that of the control cultures, as shown by the results of MTT reductase activity assay. Thus, matrices based on unsaturated polysaccharide derivatives crosslinked by laser irradiation showed good compatibility with differentiated cells of the nervous system and considerable potential for use in neurotransplantation.

Morphological changes of the polylactic acid microstructure under the action of supercritical carbon dioxide

The microstructure and properties of amorphous D,L-polylactide subjected to different treatments in supercritical carbon dioxide (SC-CO2) were investigated. Atomic force microscopy analysis demonstrated that plasticization and subsequent foaming of the polymer in SC-CO2 leads to significant changes in its internal structure, which are caused by the rearrangement of the supramolecular structure of polylactic acid. The formation of micro and meso pores and an accompanying increase of polylactide void volume are directly related to the destruction of polymer initial intermolecular bonds during the release of SC-CO2. These changes facilitate the formation of thermodynamically more stable conformations, which is manifested in a significant (1.7–5.0-fold) increase of the values of exothermic effects registered by differential scanning calorimetry in the temperature range from −30 to −10°C and near 30–40°C.