Cationic Porphyrins as Antimicrobial and Antiviral Agents in Photodynamic Therapy

Antimicrobial photodynamic therapy (APDT) has received a great deal of attention due to its unique ability to kill all currently known classes of microorganisms. To date, infectious diseases caused by bacteria and viruses are one of the main sources of high mortality, mass epidemics and global pandemics among humans. Every year, the emergence of three to four previously unknown species of viruses dangerous to humans is recorded, totaling more than 2/3 of all newly discovered human pathogens. The emergence of bacteria with multidrug resistance leads to the rapid obsolescence of antibiotics and the need to create new types of antibiotics. From this point of view, photodynamic inactivation of viruses and bacteria is of particular interest. This review summarizes the most relevant mechanisms of antiviral and antibacterial action of APDT, molecular targets and correlation between the structure of cationic porphyrins and their photodynamic activity.

Changes in Structural and Thermodynamic Properties of Starch during Potato Tuber Dormancy

The main reserve polysaccharide of plants-starch-is undoubtedly important for humans. One of the main sources of starch is the potato tuber, which is able to preserve starch for a long time during the so-called dormancy period. However, accumulated data show that this dormancy is only relative, which raises the question of the possibility of some kind of starch restructuring during dormancy periods. Here, the effect of long-term periods of tuber rest (at 2-4 °C) on main parameters of starches of potato tubers grown in vivo or in vitro were studied. Along with non-transgenic potatoes, Arabidopsis phytochrome B (AtPHYB) transformants were investigated. Distinct changes in starch micro and macro structures-an increase in proportion of amorphous lamellae and of large-sized and irregular-shaped granules, as well as shifts in thickness of the crystalline lamellae-were detected. The degree of such alterations, more pronounced in AtPHYB-transgenic tubers, increased with the longevity of tuber dormancy. By contrast, the polymorphic crystalline structure (B-type) of starch remained unchanged regardless of dormancy duration. Collectively, our data support the hypothesis that potato starch remains metabolically and structurally labile during the entire tuber life including the dormancy period. The revealed starch remodeling may be considered a process of tuber preadaptation to the upcoming sprouting stage.

Optical and Electrophysical Properties of Vinylidene Fluoride/Hexafluoropropylene Ferroelectric Copolymer Films: Effect of Doping with Porphyrin Derivatives

Polymer films doped by different porphyrins, obtained by crystallization from the acetone solutions, differ in absorption and fluorescence spectra, which we attribute to the differences in the structuring and composition of the rotational isomers in the polymer chains. According to the infrared spectroscopy data, the crystallization of the films doped with tetraphenylporphyrin (TPP) proceeds in a mixture of α- and γ-phases with TGTG^- and T₃GT₃G^- conformations, respectively. Three bonds in the planar zigzag conformation ensures the contact of such segments with the active groups of the porphyrin macrocycle, significantly changing its electronic state. Structuring of the films in the presence of TPP leads to an increase in the low-voltage AC-conductivity and the registration of an intense Maxwell-Wagner polarization. An increased conductivity by an order of magnitude in TPP-doped films was also observed at high-voltage polarization. The introduction of TPP during the film formation promotes the displacement of the chemical attachment defects of "head-to-head" type in the monomeric units into the surface. This process is accompanied by a significant increase in the film surface roughness, which was registered by piezo-force microscopy. The latter method also revealed the appearance of hysteresis phenomena during the local piezoelectric coefficient d₃₃ measurements.

Design of A3B-Porphyrin Conjugates with Terpyridine as Potential Theranostic Agents: Synthesis, Complexation with Fe(III), Gd(III), and Photodynamic Activity

This paper reports on the design and synthesis of new multifunctional porphyrin-based therapeutic agents for potential therapeutic and diagnostic applications. Zinc complexes of A3B-type meso-arylporphyrins containing OH- and COOH- groups were modified with chelating ligands based on 4'-(4-methylphenyl)-2,2':6',2″-terpyridine derivatives in high yields. Novel complexes with Gd(III), Fe(III) were obtained for these conjugates. Aggregation behaviour in solutions of different solubilisers was studied to inform the selection of the optimal solubilising platform for the porphyrins obtained; their photophysical and photochemical properties were also characterised. Micellar Pluronic F127 formulation was found to be the most effective solubiliser for stabilising the fluorescence-active monomolecular form of the photosensitisers (PS). In vitro cytotoxicity of the compounds was studied on the HEP-2 cell line with and without irradiation for 1.5 and 24 h. As a result, the IC50 of compounds 12 and 14 at an irradiation dose of 8.073 J/cm2 was shown to be 1.87 ± 0.333 and 1.4 ± 0.152 μM, respectively; without irradiation, the compound had no toxic effect within the studied concentration range (1.5 h). A test for the inhibition of metabolic cooperation or promoter activity was also performed for the abovementioned compounds, showing the efficacy and safety of the conjugates obtained. Preliminary data have indicated the high potential of the new type of PS to be promising molecular theranostic agents.

Characterization of a Novel Amphiphilic Cationic Chlorin Photosensitizer for Photodynamic Applications

A novel amphiphilic cationic chlorin e₆ derivative was investigated as a promising photosensitizer for photodynamic therapy. Two cationic -N(CH₃)₃⁺ groups on the periphery of the macrocycle provide additional hydrophilization of the molecule and ensure its electrostatic binding to the mitochondrial membranes and bacterial cell walls. The presence of a hydrophobic phytol residue in the same molecule results in its increased affinity towards the phospholipid membranes while decreasing its stability towards aggregation in aqueous media. In organic media, this chlorin e₆ derivative is characterized by a singlet oxygen quantum yield of 55%. Solubilization studies in different polymer- and surfactant-based supramolecular systems revealed the effective stabilization of this compound in a photoactive monomolecular form in micellar nonionic surfactant solutions, including Tween-80 and Cremophor EL. A novel cationic chlorin e₆ derivative also demonstrates effective binding towards serum albumin, which enhances its bioavailability and promotes effective accumulation within the target tissues. Laser confocal scanning microscopy demonstrates the rapid intracellular accumulation and distribution of this compound throughout the cells. Together with low dark toxicity and a rather good photostability, this compound demonstrates significant phototoxicity against HeLa cells causing cellular damage most likely through reactive oxygen species generation. These results demonstrate a high potential of this derivative for application in photodynamic therapy.

Self-assembly of amphiphilic meso-aryl-substituted porphyrin derivatives in the presence of surfactants

Surfactant-assisted self-assembly of porphyrin molecules in aqueous solutions sometimes leads to the formation of hybrid supramolecular structures with unusual photophysical properties resulting from the dipole–dipole interactions between the neighboring aromatic systems. The macrocycle orientation and interchromophore distance in such assemblies are determined by the dye–surfactant interactions, and hence, strongly depend on the molecular structure of both surfactant and porphyrin molecules. In this paper we studied the influence of the number and position of the peripheral alkyl chains of amphiphilic meso-aryl-substituted porphyrins on their aggregation behavior and intermolecular interactions with different surfactants in aqueous solutions. The studies revealed a crucial role of the local acidity on the micellar surface in the protolytic equilibrium of the porphyrin derivatives, as well as the influence of the macrocycle hydrophilic–lipophilic balance on its solubilization site within a micellar system. These findings enable prediction of the photophysical properties of amphiphilic porphyrin derivatives in the presence of different solubilizing agents and membrane-mimetic systems, and hence, selection the most suitable drug delivery systems for the novel amphiphilic porphyrin-based photosensitizers.