D. B. Berezin

Thermal stability of porphyrins with chemicaly active NH bond and their associates with electron-donor solvents

The composition and stability of the crystalline H associates of NH active tetrapyrroles with electron-donor solvents were investigated by thermogravimetry. It was found that common porphyrins and their analogs can form 1: 1 and 1: 2 macrocycle solvent H associates whose energy of formation depends on their composition and ranges from 20 to 115 kJ/mol. Based on the results from an analysis of the Stokes shifts, we concluded that the formation of H associates in a solution is accompanied by variations in the degree of macrocycle nonplanarity. The stability of a series of tetrapyrroles with regard to thermal destruction in argon atmosphere and in the presence of atmospheric oxygen was shown to drastically vary.

Thermochemistry of ethyl acetate solvation in the 1-octanol-N,N-dimethylformamide system

The thermal effects of ethyl acetate (EtOAc), 1-octanol (OctOH), and N,N-dimethylformamide (DMF) solution in a OctOH-DMF model system were measured using a calorimeter of variable temperature with an isothermal shell at 298 K. The standard enthalpies of solution and ester transfer from an alcohol to a binary mixture, and partial mole enthalpies of mixed solvent components were determined. The state of non-electrolyte molecules in OctOH-DMF and OctOH-DMF-EtOAc systems were studied using extended coordination model. It was found that the binary solvent is subjected to microclusterization, since the fraction of the single-type molecules in the solvation sphere of both components of a mixture is significantly higher than in the liquid phase volume. The conclusion was drawn that in the triple system, the ethyl acetate solvation sphere in the whole range of compositions is significantly enriched with amide owing to stronger esteramide dipole-dipole interaction.

Synthesis and physico-chemical properties of 2,7,12,17-tetraphenylporphycene and its metal complexes

Porphycene, β-phenyl-substituted analog of tetraphenylporphyrin, and its complexes with Cu(II) and Zn(II) have been prepared. Spectral parameters of the porphycene, its acid-base properties and thermal stability in the solid phase as well as its complexes stability towards dissociation in acidic medium have been studied by means of electronic absorption and NMR spectrometry, mass spectroscopy, thermogravimetry, and quantum chemistry simulation.

Synthesis, stability, and electrocatalysis by Cu(II) and Zn(II) complexes of meso-bridged isomeric porphyrinoid tetraphenylporphycene

Spectral characteristics (electronic absorption spectra, fluorescence emission spectra, 1H NMR) of prepared Cu(II) and Zn(II) complexes of 2,7,12,17-tetraphenylporphycene {H2(β-Ph)4Por}, their thermal stability, and persistence toward acids, as well as electrochemical and electrocatalytic properties have been discussed. It has been found by cyclic voltammetry that the electrocatalytic activity of metalloporphycenes M(β-Ph)4Por in the reaction of molecular oxygen reduction is close to that of metalloporphyrins M(ms-Ph)4P. Thermal stability and persistence of M(β-Ph)4Por in acidic medium are considerably lower than those of porphyrin analogs. Thus, the kinetic stability of copper(II) complex of 2,7,12,17-tetraphenylporphycene in HOAc–H2SO4 medium as compared with Cu(ms-Ph)4P is lower by more than an order of magnitude, while its thermal stability is almost 200°С lower, which is caused by sterically unfavorable change in the shape of coordination center of ligand H2(β-Ph)4Por upon complexation.

Thermal stability of chlorophyll a derivatives containing hydrophilic groups

Trends in thermal stability of aromatic macroheterocycles based of pheophorbide a and chlorin e6 containing hydrophilic groups have been revealed by means of thermogravimetric analysis at 298–1223 K under inert atmosphere. Methylpheophorbide a and 13(1)-N-methylamide of chlorin e6 are the most stable, the decomposition onset temperature being to 351 and 333°С. Their functional substitution leads to the reduction in thermal stability. Depending on the macrocycle structure the decrease in to can reach 20–200°С.

Solvent-dependent tautomerism of the inverted isomer of meso-tetraphenylporphine: Effect of the polarity of the medium

It is found that aza-imino tautomerism (a ⇆ b) of the inverted porphyrinoids and its mechanism are, along with the stability of tautomeric forms in the Solv–B system, determined by the nature of a base B and the polarity of a solvent Solv. It is shown that the transition from the C6H6–B system to MeCN–B is characterized by an approximate doubling of stability constants KT of the imine form (b), and by a change of the number of molecules B involved in the process (from two to one). According to quantum-chemical data (DFT, B3LYP, CC-pVDZ) and the results from spectral measurements (electronic absorption spectra, EAS), the stability of tautomer b (imino form) falls in the series of solvents DMF > Py ~ Et2NH > MeCN > Me2CO, and tautomer a is to a lesser extent stabilized in the given media by electron donors through the formation of hydrogen bonds (except for Me2CO: DMF > Py ≫ Me2CO ≫ MeCN, Et2NH).

Synthesis and redox characteristics of iron complexes with triphenylsubstituted corrols in the presence of argon and oxygen

Abstractpara-Substituted iron meso-triphenylcorrole derivatives [Fe(ms-p-R-Ph)3Cor] containing electron- donating (R = OMе) and electron-drawing (R = NO2) groups in phenyl rings are synthesized and characterized by 1H NMR, electronic absorption spectroscopy, and mass spectrometry. The effect of the nature of functional groups within iron complexes on the redox processes involving these complexes in water–alkaline solutions is analyzed. Electronic transitions in the ligand (Ered/ox = 0.820–0.850 V) and the metal (Ered/ox =–0.005 to–0.190 and–0.790 to–0.870 V for the Fe4+ ↔ Fe3+ and Fe3+ ↔ Fe2+ transitions, respectively) were found in the cyclic voltammograms. Iron in the synthesized complexes I–IV under the conditions under study exists in the +4 oxidation state. The activity of iron complexes in electroreduction of molecular oxygen significantly depends on the nature of a substituent, increases in the series: Fe(ms-p-NO2Ph)3Cor (II) < Fe(ms-p-MeOPh)3Cor (I) < Fe(β-Br)8(ms-Ph)3Cor (IV) < Fe(ms-Ph)3Cor (II) and is caused by the fact that low-energy redox electron transitions occur in the molecules. The electrocatalytic activity of iron corroles is much higher than that of metal porphyrins with a similar structure.

Photostability and fluorescence parameters of porphyrinoids: The effect of the macrocycle structure and the medium

The effects of the macrocycle structure and the medium nature on photodecomposition of porphyrinoids under UV irradiation have been studied. The influence of protonation, nonplanar structure of the molecule, and reactivity of NH bonds on the photostability of porphyrins and their analogs has been shown.

Thermal stability of meso-substituted metal corroles in inert and oxidative media

The thermal stability of 5,10,15-triphenylcorrole as the simplest representative of meso-substituted corroles and its complexes with d-metals (Cu3+, Mn3+, Mn4+, Co3+, Co4+, and Zn2+) is studied for the first time via thermogravimetry in oxidizing and inert atmospheres. It is shown that corroles, both as free ligands and in the form of metal complexes, are less thermally stable than porphyrins with a similar structure. It is found that if the free ligands of porphyrins are thermally more stable with respect to thermal oxidation than d-metal complexes, the thermal stability of metal corroles can be both lower and higher than those of free ligands. It is concluded that the order of thermal stability of compounds MnCor < CoCor < H3Cor < ZnCorH < CuCor is reversed upon moving from an oxidizing to an inert medium. It is shown that corroles complexes with many d-metals (Co, Mn, and others) readily participate in extracoordination reactions with electron-donating solvents, e.g., DMF, as is indicated by spectrophotometry and thermogravimetry.

Spectral parameters of derivatives of methylpheophorbide a and chlorin e 6, and their complex formation with Cu(II): The effects of structural fragments of the molecules and the solvent nature

Spectral (proton magnetic resonance and electronic absorption) parameters of the series of pyro-, meso-, and chlorin derivatives of methylpheophorbide a and kinetics of their complex formation with copper(II) nitrate in organic media have been studied.