Volume 66, Nº 5 (2017)

The review is dedicated to the elaboration and application of hybrid quantum mechani-cal/molecular mechanical methods for heterogeneous catalytic systems, including single atoms and clusters of transition metals immobilized on covalent oxide supports. The following issues are considered: (1) elaboration of the hybrid covEPE method for modeling of covalent sys-tems of the zeolite and silicate types, (2) computations of the properties of atoms and small titanium, rhodium, iridium, and gold clusters localized in cavities or embedded in the zeolite framework, and (3) computations of small silver and tantalum clusters anchored at the dehydr-oxylated and hydroxylated silica surfaces. The calculations were performed by the density functional theory (DFT) with the Becke—Perdew (BP) exchange-correlation potential.

The results of theoretical and experimental studies of the structure and properties of poly-meric carbon nitrides are reviewed. Various routes of the synthesis of these compounds using nitrogen-rich precursors, viz., cyanamide, dicyandiamide, carbamide, melamine, etc., are described. Particular attention is paid to the catalytic properties of graphite-like carbon nitrides and methods of their texture and chemical modification. The main trends for the synthesis of meso- and nanostructured materials based on graphite-like carbon nitrides are considered. Prospects of their practical application as efficient photo-, electro-, and heterogeneous metal-free catalysts are discussed.

The results of theoretical search for model transition states of electrophilic substitution in 1H-tetrazole (1) without preceding formation of N-protonated azolium salts are presented. Two routes of the reaction were proposed: A, attack of molecule 1 by the nucleophile HO^–(aq)) to form the anion to which the electrophile H₃O⁺(aq)) is added further; and B, attack of molecule 1 by the same electrophile with the subsequent addition of the same nucleophile to the specifically solvated protonated species. The thermodynamic parameters were calculated earlier at the indicated routes. In this article, the kinetic characteristics of the reactions were estimated by the DFT/B3LYP/6-31G(d) method using the scanning pro-cedure of the potential energy surface. Both steps of route A turned out to be barrier-less, while in route B only its first step is barrier-less and the second step is conjugated with surmounting an activation barrier of ~35 kcal mol^–1 between the formed prereaction complex and the products of electrophilic substitution.

The decomposition of two neutral binuclear nitrosyl iron complexes (NICs) of the µ-S structural type and general composition [Fe₂(SR)₂(NO)₄]⁰ was studied in comparison. The exchange reaction of the thiophenol or 2-aminothiophenol thiolate ligand by glutathione (GSH) in neutral NICs was studied. The reaction system was analyzed by spectrophotometry to prove the presence of a new NICs with the GS^– ligand in it. It was found that, unlike the earlier studied binuclear cationic NICs of the µ-S type and general composition [Fe₂(µ-SR)₂(NO)₄]²⁺SO₄•nH₂O with cysteamine and penicillamine ligands in which both thiolate ligands exchange by GS^–, in these neutral complexes both thiolate ligands are de-tached by only one GSH ligand is attached. A water molecule is inserted into the second free site. It is assumed that the antitumor activity of the neutral NICs can be determined not only by their NO-donor activity but also by their ability to exchange the thiolate ligand by GS^–, i.e., "to remove" GSH from the medium as in the case of cationic NICs. The discovered reaction can prevent, most likely, the S-glutathionylation of important metabolites in the presence of GSH and is very significant for metabolism of NICs.

The mathematical model of the accelerated thermal decomposition of a composite explo-sive, the rate of which is nonadditive with respect to the decomposition rates of the compo-nents, is considered using a solid composite explosive of nitrotriazolone with trinitrotoluene with the weight ratio 1: 1 as an example. The formation of an unstable 1: 1 complex at the stage of preliminary heating up of the composition is assumed to be a reason for this decom-position. The subsequent fast thermal decomposition of the complex imparts a necessary acceleration to the decomposition of the composite explosive as a whole, which occurs with a high rate to the end of experiment.

Using a high-precision volumetric—gravimetric experimental unit, the adsorption iso-therms of methane, argon, and nitrogen were measured at pressures of 0.1—40 MPa and at temperatures of 303—373 K on four carbon adsorbents with different porosities. To calculate the characteristic energy and average heat of adsorption of gases in the supercritical region, two parameters, which characterize an adsorptive were introduced: critical temperature T_c of the gas and the analog of the saturated vapor pressure “P_s”, which is defined assuming that densities of an adsorbate and an adsorptive are equal. The average heats of gas adsorption well agree with the average isosteric heats for the adsorption systems over the entire pressure and temperature intervals under study.

trans-1-Alkoxy-2-(phenylethynyl)cyclopropanes undergo lithiation at the hydrogen atom in the α-position to the triple bond on treatment with BuLi in THF at–(65—70) °C. The resulting organolithium derivatives react with acetaldehyde, acetone, dimethyl disulfide, and methyl chloroformate giving the corresponding alcohols, sulfides, and esters with the yields up to 69% with complete retention of cyclopropane ring stereoconfiguration. The obtained methyl 3-alkoxy-2,2-dimethyl-1-(phenylethynyl)cyclopropanecarboxylates and the corre-sponding acid readily undergo ring opening with addition of water molecule or HCl.

The effect of two fluorinated derivatives of tetrahydrocarbazoles on mitochondrial en-zymes catalyzing the oxidative deamination of biogenic amines such as monoamine oxidase A and B (MAO-A and MAO-B) has been investigated. A dose-dependent effect of the studied compounds on the enzymatic activity MAO-A was shown. It was revealed that both com-pounds are MAO-B inhibitors. Inhibition mechanisms were established and MAO-B inhibi-tion constants were calculated. The above derivatives exhibit strong antioxidant and antirad-ical activity.

General methods to access new 3-formyl-substituted 1-methoxypyrrolo[3,4-f]indole-5,7-diones were developed. The synthesized 3-formylindoles react with heterocyclic aceto-phenones under acid-catalyzed conditions to give different chalcones.

Preparative synthetic procedures towards new phosphorus-containing benzenesulfon-amides were elaborated. The synthesis is involved the reactions of trivalent phosphorus acids with high reactive N-methyl-N-chloromethylsulfonamide, phosphorylated methylamines bearing the NH and NSi groups, and methane-and benzenesulfonyl chlorides.

The effect of the solvent nature on the composition of the products formed upon the reaction between EtSi(H)Cl₂ and DMSO (molar ratio 1: 1, 0 °C) was revealed. This reaction in non-polar and low polar solvents (toluene, chloroform) gives oligoethyl(hydro)cyclo-siloxanes ((EtSi(H)O)_n, n = 3—8) as the major products in the yields up to 77%. In MeCN, oligoethyl(hydro)cyclosiloxanes are formed along with cyclic monochlorinated siloxanes ((EtSi(H)O)_n(EtSi(Cl)O), n = 2—7) in a ratio of ~7: 3 (68: 29 wt.%). In excess diethyl ether, the overall yield of oligoethyl(hydro)cyclosiloxanes does not exceed 25% and the major products are linear α,ω-diethoxyoligoethyl(hydro)siloxanes (EtO(EtSi(H)O)_nEt, n = 2—7) formed in 70—75% yields. A plausible reaction mechanism leading to the final products was suggested. Apparently, the reaction proceeds via ethyl(hydro)-and chloro(ethyl)silanones as intermediates.

Polysaccharide composition of 23 species of red algae collected from the coastal waters of Kamchatka and Commander Islands has been determined. Total acid hydrolysis of biomass was carried out in the presence of borane-4-methylmorpholine complex under the conditions where 3,6-anhydrogalactose liberating from sulfated galactans was protected from the acid degradation due to reduction into 3,6-anhydrogalactitol. Partial hydrolysis of biomass in the presence of the same reducing agent gave rise to diastereomeric agarobiitol or carrabiitol (3,6-anhydro-4-O-β-d-galactopyranosyl-l-or -d-galactitol, respectively). Identification of these fragments made it possible to attribute the algal galactans to agars or carrageenans. The data obtained was used to confirm the correlations between the taxonomic status and polysac-charide composition of the red algae.

Kinetic isotope effects (KIE) have been measured for oxidation reactions of ethylene by p-benzoquinone in Pd²⁺—MeCN—H₂O—HClO₄ system. Under the conditions of preferred formation of complex Pd(MeCN)(H₂O)₃²⁺ the ratio between the initial reaction rates \(R_{{C_2}{H_4}} 0/R_{{C_2}{D_4}} 0\) is equal to 1.14±0.06 and is close to the KIE for classical chloride systems. Based on the obtained results and previous data for C₂H₄—C₂D₄ and H₂O—D₂O (0.97±0.12) systems, the slow step was proposed in the reaction mechanism–a trans-addition of water molecule to the cationic p-complex LPd(H₂O)₂(CH₂CH₂)²⁺ with formation of metalcarben-ium ion solvated by water molecule (LPd(H₂O)₂(CH₂CH₂O+H₂)⁺).

Reaction between the nitric oxide donor, tetranitrosyl iron complex with thiosulfate ligand (TNIC), and phosphoenolpyruvic acid (PEP) was studied. Formation of products of the reaction between PEP and TNIC was confirmed by UV-, IR-spectroscopy, and mass spectrometry methods. Also, ions with mass numbers m/z 318 and m/z 256 were identi-fied among the reaction products, belonging to the compounds [O₃S₂—Fe—PEP]^2– and [S—Fe—PEP]^2–, respectively.