M. Ya. Mel’nikov

Reaction of donor-acceptor cyclopropanes with 1,3-diphenylisobenzofuran. Lewis acid effect on the reaction pathway

Reaction of donor-acceptor cyclopropanes with 1,3-diphenylisobenzofuran in the presence of lanthanide triflates, as well as CuOTf, Sn(OTf)2, SnCl2, ZnCl2, GaCl3, and MgI2, proceeds as a formal [3+4]-cycloaddition leading to a newly formed seven-membered ring. This reaction was found to be typical of cyclopropane-1,1-diesters and dinitriles, as well as 1-nitrocyclo-propanecarboxylates containing aromatic, heteroaromatic, and vinylic substituents at the C(2) atom of the small ring. When Me3SiOTf, TiCl4, SnCl4, or BF3·OEt2 were used as initiators, unusual cyclic hemiacetals were formed via the conjugate 1,4-addition of a cyclopropane and a nucleophile to the diene moiety.

Photochemistry of Tetraalkylammonium Tetrachlorocuprates in Low-Temperature Matrices

The product composition and the principles of photochemical transformations of tetrahexylammonium tetrachlorocuprate [(RH)4N+]2[CuIICl4]2− (RH = C6H13) in 2-chlorobutane at 77 K have been found out by ESR spectroscopy. It has been shown that the photolysis of [(RH)4N+]2 [CuIICl4]2− results in the formation of alkyl radicals (R⊙), presumably, anions [CuICl3]2− and organic copper(II) compounds {CuIIR}. A reduction in the quantum yield of primary photolysis products during the reaction, nonequivalence of the quantum yield of the buildup of paramagnetic photolysis products to that of [CuIICl4]2− consumption, and a decrease in the total number of paramagnetic particles in the system during the photolysis have been revealed. A photolysis mechanism involving both photochemical and thermal processes is proposed.

Activation of Molecular Oxygen in Trifluoroacetic Acid

The interaction of molecular oxygen with aqueous trifluoroacetic acid (TFA) led to an increase in pH. This effect was explained by a decrease in the concentration of the protonated CF3CO2H2+ and H3O+ species after oxygen was fed in the reactor. Quantum-chemical calculations show that a radical pair can be formed in an activation-free exothermal reaction involving the radical residue of the acid, the CF3CO2H2+...3O2...CF3CO2− peroxide radical, and the acid molecule in the CF3C2·...HOO· collision complex. It was assumed that the activation of molecular oxygen in aqueous TFA solutions, providing the activity of the system in oxidations of various organic and inorganic substrates, is related to the formation of peroxide radicals in them.

A fluorescence study of the excited-state dynamics of boron dipyrrin molecular rotors

Noticeable viscosity dependence has been revealed for fluorescence spectra of three phenyl derivatives of boron dipyrrin in aqueous glycerol solutions. This dependence is less pronounced for the fluorescence lifetimes. Such behavior is characteristic of molecular rotors used as media microviscosity sensors. A significant growth of the radiative deactivation constant is observed in the range 298-150 K. Quantumchemical calculation of the model fluorophore support the assumption on barrier-free relaxation of the excited state from the pretwisted to the flattened conformation. The spectral-kinetic parameters of fluorophores have been determined, and viscosity graduation curves are presented.

Conversion of CO2 in a trifluoroacetic acid

It is determined that the conversion of carbon dioxide in anhydrous trifluoroacetic acid (TFA) takes place at room temperature and atmospheric pressure, yielding a resinous product. Activation of CO2 by the oxygen dissolved in a TFA is investigated.

The mechanism of formation of the hydroperoxyl radical in the CF3COOH + 3O2 system: a quantum-chemical study

Ab initio quantum-chemical calculations of the (CF3CO2H2+…3O2) and (CF3CO2−…3O2) complexes were performed by the MP2 method. It was found that these complexes were characterized by low complex formation energies, of 2.97 and 1.72 kcal/mol, respectively. According to the MP2(full)/6-311++G(d, p) calculation data, the bridge stabilization of oxygen by linking with both the CF3CO2H2+ cation and CF3CO2− anion is much more favorable energetically. A study of the potential energy surface of the joint molecular system (CF3CO2H2+…3O2…CF3CO2−) shows that proton experiences activationless transfer from the cation to the 3O2 molecule accompanied by electron transfer from the CF3COO− anion. An analysis of spin density distribution shows that two radicals are stabilized in the (CF3CO2….OOH….O=C(OH)CF3) complex in the triplet state observed on the potential energy surface.

Peculiarities of exited state intramolecular proton transfer in 2-amino-3-(2′-benzazolyl)-quinolines

It has been shown that a low fluorescence quantum yield of 2-amino-3-(2′-benzoxazolyl)-quinoline (ABO) and 2-amino-3-(2′-benzothiazolyl)-quinoline (ABT) is due to the relaxation process caused by excited state intramolecular proton transfer (ESIPT). Quantum-chemical calculations have revealed that ESIPT in these compounds is characterized by overcoming a potential barrier, with the lower basicity of the proton-accepting moiety in ABO resulting in a higher barrier than in ABT and, thereby, determining a substantial difference in their fluorescence quantum yields.

Aggregation state of amphiphilic cationic tetraphenylporphyrin derivatives in aqueous microheterogeneous systems

The conditions for the formation of ionic associates and J- and H-aggregates from amphiphilic cationic tetraphenylporphyrin derivatives in aqueous solutions of anionic surfactants and polyelectrolytes in a wide range of concentrations and pH are considered. The aggregation behaviors of tetraphenylporphyrin and its cationic derivatives in aqueous microheterogeneous systems are compared illustrating the influence of the porphyrin molecular structure on its ability to form supramolecular aggregates of a certain structure. The mechanism of the promoting action of premicellar solutions of anionic surfactants on the formation of J-aggregates of the diprotonated form of cationic porphyrins was proposed. The acid-base properties of a number of new synthetic meso-aryl-substituted porphyrins in aqueous microheterogeneous systems were characterized.

Application of nonspecific biosensors in controlling the pharmaceutical activity of drugs

Here we explore the principal opportunity of using a erythrocyte sedimentation rate as a nonspecific biosensor to study variations in activity in different batches of the same pharmaceutical substance.

Structural reorganization in the excited state of transition metal complexes

The lifetimes of the lowest excited state and the Raman spectra of Pt(bpy)(4-X-PhS)2 complexes were measured. The results are consistent with the assumption about the formation of transient three-electron sulfur-sulfur bond in the excited state and show that this bonding can be employed for controlling the excited-state reactivity.