N. A. Aksenova

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.

Photocatalytic properties and structure of chitosan-based porphyrin-containing systems

The photocatalytic activity of the disodium salt of substituted hematoporphyrin in a model reaction of tryptophan oxidation in the presence of chitosan with different molecular masses and a block copolymer of ethylene and propylene oxides (Pluronic F-127) is studied. It is shown that, in the presence of the Pluronic, the catalytic activity of the chitosan-porphyrin system increases. The structure of chitosan-Pluronic systems, depending on the molecular mass of chitosan and the presence of porphyrin, is examined by AFM. A pleasible mechanism of the influence of the Pluronic on the photocatalytic activity of chitosan-por-phyrin systems is proposed.

Features of crystallization of chitosan with different molecular mass and its mixtures with pluronic F-127 according to atomic force microscopy and X-ray diffraction data

The structure of chitosan with different molecular mass and its mixtures with pluronic F-127 (triblock copolymer of ethylene and propylene oxide) crystallized from aqueous solutions was analyzed by atomic force microscopy and X-ray diffraction methods. It was established that the low-molecular-mass chitosan (Mw = 20000) had a highly ordered macrocrystalline structure, whereas the high-molecular-mass chitosan (Mw = 250000) was characterized by a poorly ordered quasi-crystalline structure. It was shown that, after evaporation of the aqueous solution of high-molecular-mass chitosan and pluronic F-127, chitosan formed a continuous film on the mica surface and pluronic formed dendritic structures on the chitosan surface. At the same time, the evaporation of the solution of the low-molecular-mass chitosan and pluronic F-127 mixture resulted in the formation of interpenetrating dendrites of chitosan and pluronic on the mica surface. In the low-molecular-mass chitosan-pluronic systems, a pluronic crystalline phase was formed at a lower pluronic content than in the case of high-molecular-mass chitosan-pluronic systems.

Effect of Pluronic F127 on the photosensitizing properties of dimegine in the presence of nanoparticles

It is shown that the activity of the water-soluble porphyrin photosensitizer dimegine (DMG) in the oxidation reaction of tryptophan, a test reaction for photodynamic therapy (PDT), can be enhanced by introducing silver, gold, and hydroxyapatite nanoparticles (NP) into the reaction medium if an amphiphilic polymer (AP) with the properties of a SAS is introduced into this mixture. It is concluded that the effect of enhancing the photosensitizing activity of dimegine is due to the formation of nanoparticle-Pluronic-porphyrin triple systems in which Pluronic (PL) plays the role of a bridge, forming complex and adsorption bonds with porphyrin and nanoparticles.

Peculiarities of pluronic crystallization in thin films

The peculiarities of the crystallization of Pluronics from chloroform and aqueous polymer solution on mica surfaces are investigated with the atomic force microscopy method. It is shown that Pluronics in thin films form quasi two-dimensional crystalline structures of 10–12 nm thickness. Pluronic crystallization proceeds predominantly via the mechanism of diffusion-limited aggregation with the formation of dendrites. Three main morphological types of formed structures are identified including two types of dendrites (with 45° and 90° angles between branches) and elongated “needles.” It is shown that the film morphology depends on the polymer concentration, rate of solvent evaporation, and, probably, local gradients of concentration and temperature. Interaction with porphyrins establishes conditions for the local three-dimensional crystallization of Pluronics.

Luminescent characteristics of liquid-phase systems and polymer compositions containing europium β-diketonates solubilized with pluronics

The solubilization of europium β-diketonate complexes with amphiphilic polymers, ternary block copolymers of ethylene and propylene oxides (Pluronics), was shown to change luminescence intensity in such complexes. The association of europium β-diketonate complexes with Pluronics was proved by atomic force microscopy of agglomerates crystallized on mica surfaces from chloroform solutions of Pluronic F-127 in the presence and absence of the luminophores under study. In the absence of luminophores, Pluronic F-127 crystallized on a mica surface had a dendrite-like structure, while the evaporation of chloroform solutions containing both europium β-diketonates and Pluronic F-127 gave crystallized luminophore-Pluronic associates as compact islands with a characteristic size of ∼0.5 μm.

Effect of metal-free porphyrins on the thermal–oxidative breakdown of biocompatible polymers

The inhibitory effect of metal-free porphyrins on the thermal–oxidative breakdown of several biocompatible polymers is observed for the first time. Differential thermal analysis shows that the thermal stability of poly(ethylene oxide) and triblock copolymers of ethylene oxide and propylene oxide increases by 80–100 K, compared to the initial breakdown temperatures of these polymers in the presence of metal-free porphyrins (up to 3 wt %).