V. I. Parfenyuk

Electrochemical properties of derivatives of tetraphenylporphyrin in dichloromethane

The method of cyclic voltammetry was used to study electrochemical properties of derivatives of tetraphenylporphyrin in dichloromethane. In the case of substituted tetraphenylporphyrin, as dependent on the nature of substituents at the periphery of the porphyrin ring, reduction of porphyrins occurs in the range of negative potentials resulting in formation of a π-anion-radical and dianion, while oxidation of porphyrins with formation of a π-cation-radical and dication occurs in the range of positive potentials. In the case of tetrakis(p-aminophenyl)porphyrin, a poly-porphyrin film is formed on the electrode in the course of electrooxidation. The method of chronoamperometry was used to determine the potential of initiation of electropolymerization of H2T(p-NH2Ph)P.

Substituent position influence on the electrochemical properties and antioxidant activity of tetra(aminophenyl)porphyrins

Free radicals and reactive oxygen species (ROS) are important intermediate products in physiological processes. In the healthy cell, they are generated and regulated by enzymes and low molecular weight antioxidants. Overproduction of ROS leads to a large list of diseases, so the determination of antioxidant activity of perspective natural and synthetic compounds is necessary for drugs development. In this paper cyclic voltammetry (CV) method was applied to the electrochemical and superoxide scavenging properties of 5,10,15,20-tetrakis(4′-aminophenyl)porphyrin (H2T(p-NH2Ph)P) and 5,10,15,20-tetrakis(3′-aminophenyl)porphyrin (H2T(m-NH2Ph)P) investigation. It is shown that the studied porphyrins have very similar electrochemical behavior and slight effect on the quantity of superoxide produced during first CV cycle therefore the estimation of superoxide scavenging properties may be performed by the oxidation peak current monitoring. The antioxidant properties of porphyrins were estimated in terms of binding constants. The strong effect of NH2 group position on the superoxide scavenging activity are shown: the H2T(p-NH2Ph)P (kb = 12.7 × 102 mol-1) demonstrates the significant superoxide scavenging activities whereas H2T(m-NH2Ph)P (kb = 0.83 × 102 mol-1) — negligible. The most probable mechanism of superoxide scavenges explaining the observed differences are the H-atoms transfer due to N–H bond breaking in the aminophenyl substituent.

Effect of anodic potential on process of formation of polyporphyrin film in solutions of tetrakis(p-aminophenyl)porphin in dichloromethane

The electrode impedance spectroscopy technique was used to study the process of formation of a conducting polyporphyrin film on a Pt electrode from a 10−3 M solution of tetrakis(p-aminophenyl)porphin in dichloromethane. An equivalent circuit is suggested for simulation of interface impedance in a wide range of working electrode potentials. It is shown that regions with a different mechanism of film formation are observed at an increase in potential from 0.0 to +1.0 V. The kinetics of film formation are studied at the potentials of +0.40, +0.60, and +0.80 V. It is found that good agreement is observed between the model and experimental data when the growing film is simulated using a Warburg element with a finite diffusion length. Conductivity and the diffusion coefficient of charge carriers in it are estimated on the basis of the suggested model for a film obtained at the potential of +0.40 V. It is shown that conductivity of a polyporphyrin film grows by more than an order of magnitude at an increase in deposition potential from +0.40 to +0.80 V.

The coulometric approach to the superoxide scavenging activity determination: The case of porphyrin derivatives influence on oxygen electroreduction

The electrochemical and antioxidant properties of 5,10,15,20-tetrakis(3′-hydroxyphenyl)porphyrin (H2T(m-OHPh)P) and 5,10,15,20-tetrakis(4′-hydroxyphenyl)porphyrin (H2T(p-OHPh)P) were tested by the cyclic voltammetry (CV) method. It is shown that in dimethylsulfoxide (DMSO) the electroreduction processes of oxygen and porphyrins are under diffusion control. The electroreduction of H2T(m-OHPh)P and H2T(p-OHPh)P with potentials about -1 V are irreversible due to the chemical step (EC process) which leads to products with oxidation potentials about -0.5 V. Additionally in case of oxygen and porphyrin coreduction, both H2T(m-OHPh)P and H2T(p-OHPh)P influence the O2•- electrosynthesis. The nonlinear dependence of the O2•- peak current vs. porphyrin concentrations makes the available amperometric approach unsuitable for antioxidant activity estimation. To solve this problem, the coulometric parameters were calculated. The excellent linearity of the coulometric response of superoxide ion vs. porphyrins concentration was demonstrated for a wide concentration range. On the basis of coulometric responses, we constructed a parameter which separated the radical scavenging activity and variation of oxygen electroreduction. The superoxide scavenging activities of H2T(m-OHPh)P and H2T(p-OHPh)P were determined using the developed approach. The effect of OH group position on the superoxide scavenge activity is shown: H2T(p-OHPh)P has a higher activity (slope = 0.75 L.mmol-1) than H2T(m-OHPh)P (slope = 0.60 L.mmol-1).

Physicochemical properties of an electroconductive film based on tetrakis(p-aminophenyl)porphine

A strong, optically transparent electroconductive polyporphyrin film is obtained during the electrooxidation of tetrakis(p-aminophenyl)porphine in dichloromethane on the surface of a platinum electrode. Analysis of electronic absorption and IR spectra indicates that tetrakis(p-aminophenyl)porphine is polymerized during electrooxidation via the formation of dihydrophenazine fragments. It is found that the film deposited on the electrode is insoluble in many organic solvents and mineral acids, is thermally stable when heated up to 200°C, and has a homogeneous surface with an even distribution of oligomer globules. It is found through differential scanning calorimetry that the compound deposited on the electrode is a partially crystalline polymer.

Kinetic parameters of the electroreduction of oxygen on a graphitized carbon electrode activated by tetrakis(4-methoxyphenyl)porphyrin and its cobalt complexes

Electrochemical and electrocatalytic properties of tetrakis(4-methoxyphenyl)porphyrin, tetrakis(4-methoxyphenyl)porphyrinatocobalt(II), and (tetrakis(4-methoxyphenyl)porphyrinato)chlorocobalt(III) are studied using the method of cyclic voltammetry. The redox-potentials of the electrode processes, the potentials of the half-wave and stationary rate constants for electroreduction of molecular oxygen are determined from an analysis of the voltammetric curves. The cobalt complex is found to be characterized by higher electrocatalytic activity than other analyzed compounds.

Effect of isopropyl alcohol on cathodic deposition of ultradispersed copper-containing powders from electrolyte solutions

The possibility of cathodic deposition of copper-containing powders of nanosize dispersity from solutions of copper dichloride in a mixed water-isopropanol solvent was studied.

Solvent and electrode influence on electrochemical forming of poly-Fe(III)-aminophenylporphyrin films

Fe(III)-complexes of amino-substituted tetraphenylporphyrins obtained from solutions in organic solvents: dichloromethane, ethanol, and dimethyl sulfoxide have been electropolymerized. The solvents’ effects on deposition and surface morphology of the obtained polyporphyrin film have been determined. It is only possible to obtain a polyporphyrin film from DMSO solutions through electrochemical activation of electropolymerization by a superoxide anion radical (O2•−). The activation effect of the dissolved oxygen becomes evident in porphyrin interaction with the superoxide anion radical (O2•−) that is synthesized in DMSO thanks to the quasi-reversible redox process. The size of particles forming the film is lowest when the film is deposited from DMSO and highest when it is deposited from dichloromethane. Therefore, the ratio of polyporphyrin phase grain growth rate to the nucleation rate has the highest value when the film is deposited from dichloromethane. Such films have the most developed surfaces, while ...

Electroconductive films based on amino-substituted tetraphenylporphyrins and their metal copper complexes

Amino-substituted tetraphenylporphyrins (5,10,15,20-tetrakis(4′-aminophenyl)porphyrin, 5-(4′-aminophenyl)–10,15,20-triphenylporphyrin) and their copper complexes in dichloromethane and ethanol were electropolymerized by the cyclic voltammetry method and their electrochemical properties were studied. The polyporphyrin films obtained by electro-oxidation transmit electricity and possess semiconductor properties of different types. The poly-5,10,15,20-tetrakis(4′-aminophenyl)porphyrin films obtained from different solvents are similar to each other in chemical composition but different in morphology. The polyporphyrin film surface morphology was studied by AFM microscopy.

Electrochemical preparation and properties of ultradisperce silver powder

The ultrafine powders of silver are prepared by the method of electrochemical deposition on cathode from water-ethanol solutions. Distribution of particles by size and quality of the synthesized powders are determined. A comparative evaluation of antimicrobial activity of silver nano-sized particles and foil is performed.