E. V. Rumyantsev

Thermal properties of ligands, salts and metal complexes of linear oligopyrroles

The effect of structure on the thermal properties of dipyrrolylmethanes, dipyrrolylmethenes, bis (dipyrrolylmethenes), their salts, and chelates is analyzed proceeding from the results of thermogravimetric analysis. The common tendency is a decrease in the thermal stability of compounds with a disturbed symmetry of alkyl substitution of ligands and with a higher degree of their alkylation, with the increased size of alkyl substituents, with the nitrogen atom in the five-member cycles replaced by S or O. The opposite effect occurs at the change in the mode of attaching methylene spacer in going from 2,2′- to 3,3′-bis(dipyrrolylmethenes). The effects of the themostabilization of the ligands of linear oligopyrroles in the composition of chelates and HBr salts are evaluated quantitatively.

Spectral and Photophysical Properties, Photo and Heat Resistance of Dipyrrolylmethene Borofluoride Complex and Its Hybrid Material with Polymethylmethacrylate

A hybrid material based on polymethylmethacrylate with immobilized borofluoride dipyrrolylmethene complex. The inclusion of the chromophore in the polymer environment is shown to result in a reduced polarization due to the weakening of the forces of intermolecular interactions. Study of spectral properties, photo and thermal stability showed that inclusion of the complex in the polymer matrix can significantly increase the photo and thermal stability and mechanical strength of the material while preserving the spectral characteristics inherent to the individual compound.

Thermodynamic stability of Ni(II) and Cu(II) chelates with biladiene-a,c in DMF

The equilibria of the reactions of complex formation between alkyl-substituted biladiene-a,c and Ni(II) and Cu(II) acetates in DMF were studied by the electronic spectroscopy. Porphyrin-like complexes (1:1) were shown to form in the systems under study. Concentration constants of complex formation were calculated and extrapolated to infinite dilution in order to obtain standard thermodynamic quantities. The role of the nature of a metal cation on thermodynamic parameters of complex formation processes was discussed.

Effect of Structural and Solvation Factors on the Chromophore Properties and Stability of Chemical Forms of Linear Tetrapyrroles

Electronic absorption spectra of solutions of salts formed by alkyl-substituted biladiene-ac and bilatriene with hydrobromic acid were analyzed with respect to salt concentration and solvent nature. The major light-absorbing species of the pigments in benzene and dimethyl sulfoxide were found to be the corresponding onium ions. Reduction of the pigment concentration in dimethylformamide and pyridine favors solvolytic dissociation of the salt with formation of neutral ligand species. Structural and solvation factors responsible for the stability of chemical forms of linear tetrapyrroles in solution are discussed.

The Kinetics of Oxidation of Bilirubin and Ascorbic Acid in Solution

The results of a comparative study of the oxidation of bilirubin, ascorbic acid, and their mixture in aqueous solutions under the action of air oxygen and hydrogen peroxide are presented. The observed and true rate constants for the oxidation reactions were determined. It was shown that the oxidation of tetrapyrrole pigment occurred under these conditions bypassing the stage of biliverdin formation to monopyrrole products. Simultaneous oxidation of bilirubin and ascorbic acid was shown to be accompanied by the inhibition of ascorbic acid oxidation by bilirubin, whereas ascorbic acid itself activated the oxidation of bilirubin.

Actual aspects of the chemistry of dipyrrin dyes and prospects for their application in molecular sensorics

The results of research on the correlation between molecular structure and spectral luminescent and photophysical properties for a new class of dyes and luminophores based on dipyrrins, bis(dipyrrins), and their coordination compounds in different media are summarized. The new perspective applications of dipyrrin dyes and luminophores as fluorescent sensors for measuring the polarity, viscosity, and temperature of the medium and highly sensitive and selective fluorescent “off-on” chemosensors for detecting Zn2+, Cd2+, and Hg2+ cations in weakly polar and nonpolar organic solvents and biological systems are discussed.

Synthesis, spectral properties and stability towards protolytic dissociation of the palladium(II) complexes with dipyrrolylmethene and its bis-derivatives

Palladium(II) complexes with alkylated dipyrrolylmethene (Hdpm) and its bis-derivative, biladienea, c (H2bd), of the composition [Pd(dpm)2] and [Pd(bd)] were synthesized and were characterized by IR, UVVIS, and NMR spectroscopy. It was shown that the nature of the solvent has almost no effect on the spectral characteristics of the complexes due to the square-planar configuration of the coordination nodes in them and, respectively, the impossibility of further coordination. From the results of the kinetic study of the complexes stability to the action of acids in the C6H6-CCl3COOH mixtures it was concluded that the Pd(II) complexes are much more stable compared to the other d-metal dipyrrolylmethenates. Kinetic manifestation of polychelate effect was observed consisting in a sharp decrease in the dissociation rate of the palladium(II) complex with biladiene as compared to that with dipyrrolylmetene.

The thermodynamic characteristics of formation of mono-and binuclear biladiene Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) chelates in dimethylformamide solutions

The spectral and calorimetric data on complex formation between alkyl substituted a,c-biladiene and Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates in dimethylformamide are discussed. The stability of mononuclear biladiene chelates was shown to be determined by steric factors characterizing the formation of coordination polyhedra with the tetradentate ligand. The thermodynamic characteristics of the differential polychelate effect caused by the replacement of the bidentate dipyrrolylmetene ligand with the tetradentate biladiene anion in mononuclear zinc(II) complexes were estimated. The results showed that the largest contribution to the polychelate effect was made by the enthalpy component of the Gibbs energy.

Electronic absorption spectra and acid-base and ligand properties of alkyl-substituted biladiene-a,c

The influence of the nature of a solvating medium on the chromophore properties and stability of alkyl-substituted biladiene-a,c dihydrobromide, a synthetic analogue of a bile pigment bilirubin, was analyzed. The results of the spectrophotometric study of the protonation of a tetrapyrrol ligand and of the complex formation with Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) acetates in DMF at 298.15 K were considered. Depending on the nature of a complex-forming cation and concentrations of reagents in solution the formation of complexes of three various types is possible: porphyrin-like (1:1), binuclear with different ligands (2:1), and binuclear biligand (2:2). The nature of metal cation renders essential influence on the formation of coordination polyhedra of the metal chelates with various structure.

Formation kinetics of heteroligand Ni(II) complex with alkyl-substituted 2,2′-dipyrrolylmethenes

The formation kinetics of heteroligand Ni(II) complexes with alkylated dipyrrolylmethenes of symmetric and asymmetric structure was studied. The kinetic and activation parameters of the reactions were determined. The spectral and kinetic data obtained, as well as available data on the solvation of Ni(II) acetate in electron-donor solvents, allowed us to propose an associatively activated concerted mechanism. The Ni(II) complex formation is mainly determined by the rate of substitution of the entering ligand for solvent molecules in the initial Ni(II) complex, that is, by creation of conditions for efficient donor-acceptor interaction.