Showing papers in "Russian Chemical Bulletin in 2001"
TL;DR: A review of modern methods for the determination of unknown crystal structures of organic and inorganic compounds from powder diffraction data can be found in this paper, where the main stages of this process, from the preparation of the specimen to a search for the structural motif followed by the Rietveld refinement, are considered.
Abstract: The review surveys modern methods for the determination of unknown crystal structures of organic and inorganic compounds from powder diffraction data. The main stages of this process, from the preparation of the specimen to a search for the structural motif followed by the Rietveld refinement, are considered. The results obtained on different diffractometers using X-ray, synchrotron, and neutron radiations are demonstrated to be well reproducible. Examples of successful structure solution are cited, which provide evidence that powder diffraction is a reliable tool in establishing structures of a wide range of compounds for which single crystals are unavailable.
94 citations
TL;DR: In this paper, it was shown that the model isotherms in single slit-shaped micropores can be fitted to the Hill-de Boer isotherm, in agreement with mathematical studies of the origin of the Dubinin-Astakhov equation.
Abstract: Dubinin"s theory for the volume filling of micropores (TVFM), originally developed for the adsorption of single vapours by microporous solids such as activated carbons and zeolites, has gradually been extended to other areas. They include immersion calorimetry, the adsorption of water vapour and of mixtures, as well as adsorption from aqueous solutions. Recent studies in the field of adsorption from aqueous solutions, by activated carbons, suggest that the principle of temperature invariance is fulfilled and in the case of phenolic compounds a modified DRK equation can be used to predict the adsorption equilibrium over a certain range of temperatures. Computer modelling of CO2 adsorption by carbons at 273 K leads to micropore distributions, which are in good agreement with those derived from other techniques. It also appears that the model isotherms in single slit-shaped micropores can be fitted to the Hill-de Boer isotherm, in agreement with mathematical studies of the origin of the Dubinin—Astakhov equation.
60 citations
TL;DR: In this article, the structure and properties of the enzyme organophosphate hydrolase exhibiting catalytic activity with respect to orthophosphates are reviewed and the role of two metal ions involved in the enzyme active site is considered.
Abstract: The available investigations on the structure and properties of the enzyme organophosphate hydrolase exhibiting catalytic activity with respect to orthophosphates are reviewed. Recent data on the mechanism of enzymatic hydrolysis of paraoxon are surveyed. The role of two metal ions involved in the enzyme active site is considered. The substrate specificity and the influence of various inhibitors on the kinetic characteristics of the enzyme are discussed.
59 citations
TL;DR: In this article, a procedure for the synthesis of 4,5-bis[2,5dimethyl(3-thienyl)]-1,3-azoles based on 1,2-bis[2.5-dimethyl[3]-diametrizoles was presented, where the thienyl rings are linked through the azole rings.
Abstract: Procedures for the synthesis of 4,5-bis[2,5-dimethyl(3-thienyl)]-1,3-azoles based on 1,2-bis[2,5-dimethyl(3-thienyl)]-2-hydroxyethan-1-one, 2-chloro-1,2-bis[2,5-dimethyl(3-thienyl)]ethan-1-one, and 1,2-bis[2,5-dimethyl(3-thienyl)]ethane-1,2-dione were developed. Dithienylethenic compounds in which the thienyl rings are linked through the azole rings exhibit photochromic properties.
52 citations
TL;DR: The applications of transition metal hexacyanoferrates in electroanalysis are surveyed in this paper, where it is recognized as the most promising low-potential transducer for hydrogen peroxide reduction among all known systems.
Abstract: The applications of transition metal hexacyanoferrates in electroanalysis are surveyed Prussian Blue (ferric hexacyanoferrate) is recognized as the most promising low-potential transducer for hydrogen peroxide reduction among all known systems The advantages of Prussian Blue over platinum or peroxidase electrodes for hydrogen peroxide detection are discussed Various types of biosensors based on transition metal hexacyanoferrates and oxidase enzymes are considered Amperometric biosensors based on Prussian Blue-modified electrodes allow the detection of glucose and glutamate down to 10–7 mol L–1 in the flow-injection mode The future prospects of Prussian Blue-modified electrodes in analytical chemistry for the monitoring of chemical toxic agents, in clinical diagnostics, and in food control are outlined
44 citations
TL;DR: In this paper, the deformation electron density and atomic displacements were analyzed based on the results of precision low-temperature X-ray diffraction studies of a series of isostructural mixed metallocenes.
Abstract: The electron density distribution and atomic displacements were analyzed based on the results of precision low-temperature X-ray diffraction studies of a series of isostructural (Pnma, Z = 4) mixed metallocenes (η5-C5H5)M(η5-C7H7) (M = Ti, V, or Cr) and (η5-C5H5)Ti(η8-C8H8). The barriers to rotation of the cyclic ligands were evaluated based on rms libration amplitudes. Analysis of the deformation electron density demonstrated that the character of the M--(π-ligand) chemical bond depends substantially both on the nature of the metal atom and the size of the ligand. Lowering of the local symmetry of the (η5-C5H5)M(η5-C7H7) complexes to CS leads to distortion of the cylindrical symmetry of the electron density distribution observed in vanadocene (η5-C5H5)2V and titanocene (η5-C5H5)Ti(η8-C8H8).
40 citations
TL;DR: The conformation of a free β-cyclodextrin molecule optimized by the MNDO/PM3 quantum-chemical calculations has C7 symmetry as discussed by the authors, where the 2-OH groups act as the proton donors and the O atoms of the nearby 3"-OH groups function as proton acceptors, is advantageous for thermodynamic reasons.
Abstract: The conformation of a free β-cyclodextrin molecule optimized by the MNDO/PM3 quantum-chemical calculations has C7 symmetry. The “right” orientation of the interglucose hydrogen bonds in β-cyclodextrin, in which the 2-OH groups act as the proton donors and the O atoms of the nearby 3"-OH groups function as the proton acceptors, is advantageous for thermodynamic reasons. The ring of seven H bonds thus formed stabilizes the symmetrical form of β-cyclodextrin. The β-cyclodextrin head-to-head dimer has D
7 symmetry and consists of molecules whose 2-OH groups partcipate as proton donors in the formation of fourteen complementary intermolecular hydrogen bonds. The energy of H bonds in the β-cyclodextrin monomer and dimer was estimated to be 1.0--1.4 kcal mol–1. Of the two possible β-cyclodextrin dimers, the “head-to-tail” dimer is more thermodynamically stable. The thermodynamic preference of the right orientation of the inter-glucose H bonds in β-cyclodextrin was confirmed by the MP2/6-31G(d,p)//6-31G(d,p) ab
initio calculations for maltose (α-glucodioside). The maltose molecule with inter-glucose H bonds of the type 2-OH→O(3")-H is more stable than the structure with the H-(2)O←H-O(3") orientation of H bonds with a difference of ∼2.7 kcal mol–1. According to the MNDO/PM3 method, the maltose structure with the right H bond orientation is more stable by ∼3.1 kcal mol–1.
33 citations
TL;DR: In this paper, the properties of dilute and concentrated solutions of dibenzoylmethanatoboron difluoride and its crystals were studied.
Abstract: Fluorescence properties of dilute and concentrated solutions of dibenzoylmethanatoboron difluoride and its crystals were studied. Excimers are formed in concentrated solutions and crystals of dibenzoylmethanatoboron difluoride. The crystal structure of dibenzoylmethanatoboron difluoride was determined by X-ray diffraction analysis. It was found that the molecules of dibenzoylmethanatoboron difluoride are coplanar with an interplanar distance of 3.6 A.
32 citations
TL;DR: In this paper, carbon dioxide adsorption and carbon dioxide-induced deformation of crystalline NaX zeolite at pressures of 0.2-5.4 MPa and temperatures of 195-423 K were measured.
Abstract: Isotherms of carbon dioxide adsorption and adsorption-induced deformation of pelletized crystalline NaX zeolite at pressures of 0.2--5.4 MPa and temperatures of 195--423 K are measured. The adsorption deformation is positive at low zeolite micropore filling (a 7 mmol g-1) the NaX zeolite shows dramatic expansion.
30 citations
TL;DR: The triterpenoids methyl ursonate, acetylbetulone, and allobetulone with atmospheric oxygen in the presence of ButOK in ButOH yielded 2,3-diketo derivatives in 90-97% yields.
Abstract: Oxidation of triterpenoids methyl ursonate, acetylbetulone, and allobetulone with atmospheric oxygen in the presence of ButOK in ButOH afforded the corresponding 2,3-diketo derivatives in 90-97% yields. These derivatives exist predominantly as tautomers containing the enolized keto group at the C(2) atom. Their reactions with o-phenylenediamine gave rise to the corresponding quinoxalines in 85-95% yields.
30 citations
TL;DR: In this paper, it was shown that the removal of phenol from mixtures with water depends on the relative concentrations, and the limiting factor for adsorption is either the effective surface area of the carbon, or the micropore volume.
Abstract: The removal of phenol and related compounds from dilute aqueous solutions by activated carbons corresponds to the coating of the micropore walls and of the external surface by a monolayer. This process is described by an analog of the Dubinin—Radushkevich—Kaganer equation. On the other hand, as suggested by immersion calorimetry at 293 K, in the case of concentrated solutions, the mechanism corresponds to the volume filling of the micropores, as observed for the adsorption of phenol from the vapor phase. The equilibrium is described by the Dubinin—Astakhov equation. It follows that the removal of phenol from mixtures with water depends on the relative concentrations, and the limiting factor for adsorption is either the effective surface area of the carbon, or the micropore volume.
TL;DR: In this article, Triphenylantimony dicarboxylates Ph3Sb(OAc)2 and Ph3 Sb (O2CEt)2 are efficient C-phenylating agents for methyl acrylate.
Abstract: Triphenylantimony dicarboxylates Ph3Sb(OAc)2 and Ph3Sb(O2CEt)2 are efficient C-phenylating agents for methyl acrylate. In the presence of the Pd(OAc)2, Li2PdCl4 or Pd2(dba)3(CHCl3) catalysts in MeCN at 50 °C, methyl cinnamate forms in 70—150% yield with respect to SbV. Copper(ii) salts do not increase the reaction yield.
TL;DR: The carbon nitride polymer of the previously unknown sphere-shaped structure was prepared both by a template-directed solid-state and solution phase syntheses from cyanuric chloride or fluoride and lithium nitride as discussed by the authors.
Abstract: The carbon nitride polymer of the previously unknown sphere-shaped structure was prepared both by a template-directed solid-state and solution phase syntheses from cyanuric chloride or fluoride and lithium nitride. The obtained polymer powder was characterized by SEM/EDAX, TEM, XRD, TGA, XPS, (13C) MAS NMR, LD/MS, FTIR, UV-visible, and Raman spectroscopy. Modification of the surface area of the template used demonstrated the possibility of producing the carbon nitride spheres with the particle sizes ranging from 20 μm to 50 nm. According to TEM data, the spheres are hollow and the material is shown to be essentially amorphous by powder XRD.
TL;DR: In this article, the reactivity of 16e half-sandwich complexes with a cisoidor transoid geometry has been investigated for cyclotrimerization reactions, which lead selectively to carboranes mono- or disubstituted in B(3,6) positions.
Abstract: The reactivity of the 16e half-sandwich complexes Cp*Rh[E2C2(B10H10)] (1a,b), Cp*Ir[E2C2(B10H10)] (2a,b) (E = S (a), Se(b)), (p-cymene)Ru[S2C2(B10H10)] (3), (p-cymene)Os[S2C2(B10H10)] (4) (p-cymene = 1-Me-4-Pri-benzene) towards various alkynes (acetylene, propyne, 3-methoxypropyne, methyl acetylenemonocarboxylate, dimethyl acetylenedicarboxylate, phenylacetylene, ferrocenylacetylene) was studied. The reactions start with an insertion into one of the M—E bonds, followed (except for MeO2C—C≡C—CO2Me) by intramolecular, metal-induced B—H activation, formation of an M—B bond, accompanied by simultaneous transfer of a hydrogen atom from boron via the metal atom to the alkyne. This leads to new complexes with a cisoidor transoid geometry (orientation of the E—C=C unit with respect to the C(1)—B bond). This geometry determines the course of further intramolecular reactions which lead selectively to carboranes mono- or disubstituted in B(3,6) positions. Numerous intermediates and final products were characterized by X-ray analysis in the solid state, and by multinuclear magnetic resonance in solution. First catalytic applications of 1a,b became evident by cyclotrimerization reactions.
TL;DR: For a series of derivatives of symmetrical 3,6-di-tert-butyl-o-benzoquinone, the rate of photopolymerization of α,ω-bis(methacryloyloxyethyleneoxycarbonyloxy)ethylene oxideethylene (OCM-2) in the presence of N,N-dimethylaniline is determined by the free energy (ΔG fixmee) of electron transfer from the amine to photoexcited o-benzosquinone as discussed by the authors.
Abstract: o-Benzoquinones initiate radical polymerization of methacrylates under visible light irradiation in the presence of tertiary amines. Spectral sensitivity of the initiating system coincides with absorption bands of o-benzoquinone attributed to the S(π→π*) (λmax ≈ 400 nm) and S(n→π*) (λmax ≈ 600 nm) transitions. The amine radicals (Am·) initiating polymerization are generated by the photoreduction of Q in the presence of AmH from the triplet radical pair 3(QH·, Am·). The yield of Am· depends on the difference between the volumes of substituents in the 3 and 6 positions of the quinoid ring and is maximal for symmetrically substituted o-benzoquinones. For a series of derivatives of symmetrical 3,6-di-tert-butyl-o-benzoquinone, the rate of photopolymerization of α,ω-bis(methacryloyloxyethyleneoxycarbonyloxy)ethyleneoxyethylene (OCM-2) in the presence of N,N-dimethylaniline is determined by the free energy (ΔG
e) of electron transfer from the amine to photoexcited o-benzoquinone. The ΔG
e value includes the energies of oxidation of the amines and reduction of the o-quinones and the energy of the 0→0 transition of the triplet excited state of o-benzoquinones, which are equal to their redox potentials. The photopolymerization rate is maximal for ΔG
e ≈ 0.
TL;DR: In this paper, the structures of the mercury and cadmium pnictidehalides MaZbXc (M = Cd, Hg; Z = P, As, Sb; X = Cl, Br, I) are discussed on the basis of the Zintl-Klemm concept.
Abstract: The structures of the mercury and cadmium pnictidehalides MaZbXc (M = Cd, Hg; Z = P, As, Sb; X = Cl, Br, I) are discussed on the basis of the Zintl--Klemm concept. Primary attention is paid to the relationship between the crystal and electronic structures of the compounds in question.
TL;DR: The role of metal peroxo, -hydroperoxo and -oxo intermediates in activation of O2 and transfer of an oxygen atom to the C-H bond in biocatalysis by heme and non-heme monooxygenases and biomimetic oxidation of alkanes is reviewed in this article.
Abstract: The role of metal-peroxo, -hydroperoxo, and -oxo intermediates in activation of O2 and transfer of an oxygen atom to the C—H bond in biocatalysis by heme and non-heme monooxygenases and biomimetic oxidation of alkanes is reviewed.
TL;DR: The first mixed bismuth monohalides Bi4BrxI4-x (x = 1, 2, or 3) were prepared for the first time by the reactions of bismhuth metal with bismith trihalides taken in stoichiometric amounts as mentioned in this paper.
Abstract: New mixed bismuth monohalides Bi4BrxI4–x (x = 1, 2, or 3) were prepared for the first time by the reactions of bismuth metal with bismuth trihalides taken in stoichiometric amounts. Their crystal structures were established by single-crystal X-ray diffraction analysis. The Bi4Br3I and Bi4BrI3 compounds are isostructural and crystallize in the orthorhombic system, and Bi4Br2I2 crystallizes in the monoclinic system. The crystal structures of all three phases contain one-dimensionally infinite molecular chains consisting of the [Bi4X4] fragments whose structures are identical with those of the individual Bi4I4 and Bi4Br4 molecules. The molecules are packed in layers. Different packing modes of the layers were found for different bismuth monohalides. The Bi4ClI3 compound, which is apparently structurally similar to Bi4Br3I and Bi4BrI3, was also prepared.
TL;DR: Interactions of the enzyme with competitive inhibitors many of which are widely used in medicine as antitumor and antibacterial drugs are examined and the role of specific interactions and molecular motions of the protein and ligands in the mechanism of catalysis and in the binding of the ligands to the enzyme is discussed.
Abstract: The mechanism of catalytic reduction of folic and dihydrofolic acids to tetrahydrofolate, which proceeds under the action of dihydrofolate reductase and the coenzyme NADPH, is considered The roles of the enzyme active site, the coenzyme, individual amino acid residues of the enzyme, and water molecules in the catalytic reaction are discussed Interactions of the enzyme with competitive inhibitors many of which are widely used in medicine as antitumor and antibacterial drugs are examined The factors controlling the selectivity of inhibitor binding to bacterial forms of the enzyme are analyzed The results of X-ray diffraction and NMR spectroscopic studies of the structures of the enzyme and its complexes with the substrate and inhibitors are surveyed The role of specific interactions and molecular motions of the protein and ligands in the mechanism of catalysis and in the binding of the ligands to the enzyme is discussed
TL;DR: In this paper, the structure of aphelasteroside D was elucidated as (24R)-29-O-[2-O-sulfo-β-D-glucopyranosyl]-24-ethyl-5α-cholestane-3β,5,6β,8β,15α,29-hexol sodium salt.
Abstract: Four sulfated steroid compounds were isolated from the Kuril population of the starfish Aphelasterias japonica. The structure of a new glycoside, aphelasteroside D, was elucidated as (24R)-29-O-[2-O-sulfo-β-D-glucopyranosyl]-24-ethyl-5α-cholestane-3β,5,6β,8β,15α,29-hexol sodium salt. Other three substances were identified as the known pycnopodioside C, 3-O-sulfo-24,25-dihydromarthasterone, and 3-O-sulfothornasterol A, the latter compound being isolated as a tyrammonium salt for the first time.
TL;DR: In this paper, a new stereoselective method was developed for the synthesis of β-bromostyrenes (E/Z > 5/1) starting from hydrazones of aromatic aldehydes and bromoform in the presence of CuCl.
Abstract: A new stereoselective method was developed for the synthesis of β-bromostyrenes (E/Z > 5/1) starting from hydrazones of aromatic aldehydes and bromoform in the presence of CuCl.
TL;DR: Bioluminescence spectra for various native and mutant luciferases from fireflies and beetles were analyzed in the light of the known theoretical concepts on the influence of the microenvironment of the emitter on its emission spectra.
Abstract: Bioluminescence spectra for various native and mutant luciferases from fireflies and beetles were analyzed in the light of the known theoretical concepts on the influence of the microenvironment of the emitter on its emission spectra. The mechanism for the explanation of the nature of changing bioluminescence spectra for natural and artificial mutations of the amino acid residues in the protein globule of luciferases was proposed.
TL;DR: In this paper, the azacrown derivatives of dibenzylidenecyclopentanone have two complex formation centers, Azacrown cycle and carbonyl group.
Abstract: The complex formation of 2,5-bis[4-(1,7,10,13-tetraoxa-4-azacyclopentadec-4-yl)benzylidene]cyclopentanone and several model compounds, prospective metal-sensitive fluorescent probes, with Mg2+, Ca2+, and Ba2+ ions in acetonitrile was studied. The azacrown derivatives of dibenzylidenecyclopentanone have two complex formation centers, azacrown cycle and carbonyl group. The sequence of binding to these sites is different for different ions. The efficient ejection of the Ca2+ and Ba2+ ions from their complexes with azacoronands was observed in the excited state, whereas in the case of the Mg2+ ion, this process occurred only partially.
TL;DR: In this article, a set of substituted 2-hydroxy-6-methoxynaphthazarins and 7-8-hydroxymethylcristazarin were synthesized.
Abstract: A set of substituted 2-hydroxy-6(7)-methoxynaphthazarins and 7(8)-hydroxypyranonaphthazarins were synthesized. The IR spectra of 2-hydroxy-6-methoxynaphthazarins and 7-hydroxypyranonaphthazarins, on the one hand, and of 2-hydroxy-7-methoxynaphthazarins and 8-hydroxypyranonaphthazarins, on the other hand, have the characteristic nonoverlapping intervals of stretching vibration frequencies of the β-hydroxy groups. These regularities confirm the structures of cristazarin and 6-methylcristazarin, which are metabolites of lichen Cladonia cristatella.
TL;DR: In this paper, an efficient procedure was developed for the two-step synthesis of 2,3-dihydroperimidinium salts in the synthesis of 1,8-bis(dialkylamino)naphthalenes (proton sponges) containing the Nisopropyl group along with the N-methyl groups.
Abstract: Efficient procedures were developed for the two-step synthesis of 1,2,2,3-tetramethyl-2,3-dihydroperimidines and for the one-step synthesis of 1,3-dimethyl-2,3-dihydroperimidines starting from 1,8-diaminonaphthalenes. New possibilities of the use of 2,3-dihydroperimidinium salts in the synthesis of 1,8-bis(dialkylamino)naphthalenes (“proton sponges”) containing the N-isopropyl group along with the N-methyl groups were demonstrated. The 1,1,2,2,3-pentamethyl-2,3-dihydroperimidinium cation exists in the acyclic iminium form responsible for its high reactivity.
TL;DR: In this article, a procedure for the synthesis of substituted bis(2,5-dimethyl-3-thienyl)furans based on 1,2-bis(2.5dimethyl)-3-THienyl)-2-hydroxyethanone was developed.
Abstract: Procedures were developed for the synthesis of substituted bis(2,5-dimethyl-3-thienyl)furans based on 1,2-bis(2,5-dimethyl-3-thienyl)-2-hydroxyethanone. Dithienylethene structures in which the ethene fragment is involved in the furan or furopyrimidine system possess photochromic properties and their open forms exhibit fluorescence.
TL;DR: The proton transfer and the character of the strong intramolecular O--HO hydrogen bond in 3-acetyl-4-hydroxycoumarin were analyzed based on the results of X-ray diffraction study in the temperature range from 100 to 353 K and quantum-chemical B3LYP/6-31G(d,p) calculations as discussed by the authors.
Abstract: The proton transfer and the character of the strong intramolecular O--HO hydrogen bond (OO 2442 A) in 3-acetyl-4-hydroxycoumarin were analyzed based on the results of X-ray diffraction study in the temperature range from 100 to 353 K and quantum-chemical B3LYP/6-31G(d,p) calculations The barrier to proton transfer along the H-bond line is low (2 kcal mol–1) However, no proton transfer was observed in the crystal at 100 K Bader's topological analysis of the electron density distribution both in the crystal and in the isolated molecule demonstrated that the hydrogen bond corresponds to an intermediate type of interatomic interactions (E(r) 0 at the critical point (3, –1))
TL;DR: In this article, the catalytic activity of supported chromites MCr2O4/γ-Al2O3 (M = Cu, Co, Mn, Zn, Mg) in the oxidation of CO, C3H6, and o-xylene and NOx reduction was studied.
Abstract: The catalytic activity of supported chromites MCr2O4/γ-Al2O3 (M = Cu, Co, Mn, Zn, Mg) in the oxidation of CO, C3H6, and o-xylene and NOx reduction was studied. The catalytic activity depends on the calcination temperature and cation nature. The features of the formation of the catalysts were studied by the UV-Vis diffuse reflectance and IR spectroscopies.
TL;DR: In this paper, the stereoselective synthesis of E,E-1,4-dialkenylbuta, 1,3-dienes, dienyl-1-4-bisphosphonates, E, E-1.4-diphenylphosphino, and e,E.1, 4-bis(thiophenyl)buta was presented.
Abstract: E,E-1,4-Diiodobuta-1,3-diene can enter into cross-coupling reactions with carbon- or other element-centered nucleophiles in the presence of Pd or Ni complexes as catalysts. Convenient procedures were developed for the stereoselective synthesis of E,E-1,4-dialkenylbuta-1,3-dienes, dienyl-1,4-bisphosphonates, E,E-1,4-bis(diphenylphosphino)buta-1,3-diene, E,E-1,4-diphenylbuta-1,3-diene, and E,E-1,4-bis(thiophenyl)buta-1,3-diene.
TL;DR: In this paper, the crystal structure of parkerite, Ni3Bi2S2, was studied by single-crystal X-ray diffraction analysis and refined by the extended Huckel and DFT--LMTO--ASA methods.
Abstract: The crystal structure of parkerite, Ni3Bi2S2, was studied by single-crystal X-ray diffraction analysis and refined. The single crystal was prepared by the method of chemical transport reactions. The electronic structure of Ni3Bi2S2 was calculated by the extended Huckel and DFT--LMTO--ASA methods. Substantial delocalization of electrons in the vicinity of the Fermi level and the presence of the strong Ni--S and Ni--Bi bonds were revealed. The Ni--Ni bonds are weak, which is in agreement with the X-ray diffraction data.