Showing papers in "Russian Chemical Reviews in 2002"

Cryogels on the basis of natural and synthetic polymers: preparation, properties and application

Abstract: This review deals with cryotropic gelation in polymeric systems, which takes place on moderate freezing, storing in a frozen state and subsequent thawing of solutions or colloidal dispersions containing monomeric or polymeric precursors. The polymer materials formed under these conditions are termed as cryogels. They are macroporous heterophase gels in which polycrystals of the frozen solvent act as porogens during gel formation. The current knowledge about the structure of moderately frozen solutions of low- and high-molecular-mass compounds is considered, the general regularities of the cryotropic gelation processes and their similarity to and differences from gelation at positive temperatures are discussed, the fields of application of cryotropic gelation techniques are described, and examples of using polymeric cryogel-based materials for solving applied problems are given. The bibliography includes 433 references.

Supramolecular chemistry of cucurbiturils

Abstract: The main principles of the design of supramolecular compounds starting from organic macrocyclic cavitands,viz., cucurbit[n]urils [C 6 H 6 N 4 O 2 ] n (n=5–10), are considered. The presence of the hydrophobic inner cavity along with polar carbonyl groups forming the cucurbituril portals are responsible for high specificity of the formation of host–guest complexes. The unique ability of cucurbiturils to act as synthetic molecular containers is discussed. In these containers, bimolecular reactions between specially selected guests proceed with high regio- and stereoselectivity. The review surveys new data on the directed construction of supramolecular organic–inorganic compounds through the formation of an extensive network of hydrogen bonds between the portal oxygen atoms of cucurbiturils and water molecules of metal aqua complexes. The bibliography includes 108 references.

Spirooxazines: synthesis, structure, spectral and photochromic properties

Abstract: The review surveys synthetic approaches to spiro[1,4]oxazines belonging to one of the most promising classes of organic photochromes. The relationships between the structures of spirooxazines and their spectral properties as well as characteristics of thermal and photoinduced processes are considered. The bibliography includes 201 references.

Structure of X-ray photoelectron spectra of lanthanide compounds

Abstract: The results of the X-ray photoelectron spectroscopy studies of the electronic structures of trifluorides, oxides and other compounds of Sc, Y and lanthanides (Ln) from La to Lu, except for Pm, in the binding energy range from 0 to 1350 eV are generalised. The established dependences of the Ln4f binding energies and the relative intensities of lines on the atomic number Z do not contradict the theoretical data stating that the Ln4f atomic orbitals (AO) participate markedly in the formation of molecular orbitals (MO) in the lanthanide compounds. It is established that inner valence molecular orbitals (IVMO) composed of the metal Sc3p, Y4p, Ln5p AO and the ligand L(O,F)2s AO are formed in these systems in addition to the outer valence molecular orbitals (OVMO). It is shown that the spectral fine structure caused by multiplet splitting, many-body perturbation and dynamic effects is correlated with the lanthanide oxidation state, the spin state of ions and the mechanisms of the secondary electronic processes accompanying the photoemission and can serve as a characteristic for identification of lanthanide compounds. Charge induction is discussed using titanium and niobium double oxides as examples. The bibliography includes 206 references.

Norbornadiene–quadricyclane as an abiotic system for the storage of solar energy

Abstract: Data on the valence isomerisation of norbornadiene and its derivatives into the corresponding quadricyclanes published between 1990 and 2001 are considered and described systematically. The applicability of this reaction for the storage of solar energy is discussed. The bibliography includes 112 references.

Non-carbon nanotubes: synthesis and simulation

Abstract: The discovery of a new allotropic form of carbon, extended nanometre-sized quasi-unidimensional tubular structures (carbon nanotubes), as well as broad prospects for the use of nanomaterials based on them initiated numerous studies in the search for, and design of, nanotubular structures based in other compounds. Some properties and the main methods for the synthesis of non-carbon nanotubes are considered. Studies on the simulation of the electronic structures of these unique objects are analysed. Results of experimental and theoretical studies along these lines are discussed. The bibliography includes 328 references.

Rational design of metal coordination compounds with azomethine ligands

Abstract: This review surveys the state of art in the coordination chemistry of chelating azomethine systems, viz., amino(hydroxy)-azomethines, β-aminovinyl ketones, β-aminovinylimines and their sulfur- and selenium-containing analogues. Variations in the fine structure of azomethine ligands allow one to perform the targeted synthesis of chelate and molecular, mono-, bi- and polynuclear, homo- and heterometallic structures. The bibliography includes 425 references.

Non-classical structures of organic compounds: unusual stereochemistry and hypercoordination

Abstract: Non-classical structures of organic compounds are defined as molecules containing non-tetrahedral tetracoordinate and/or hypercoordinate carbon atoms. The evolution of the views on this subject is considered and the accumulated theoretical and experimental data on the structures and dynamic transformations of non-classical organic compounds are systematised. It is shown that computational analysis using the methods and the software potential of modern quantum chemistry has now acquired high predictive capacity and is the most important source of data on the structures of non-classical compounds. The bibliography includes 227 references.

Barium borate β-BaB2O4 as a material for nonlinear optics

Abstract: Data on the structure, polymorphism, phase equilibria, growth techniques, properties and applications of single crystals of the low-temperature modification of barium borate are analysed. The bibliography includes 201 references.

Electrocatalysis on polymer-modified electrodes

Abstract: The procedures for applying polymeric films onto conductive supports and doping them with active microparticles of metal-catalysts or functional redox groups are considered. General principles of the electrocatalytic action of these systems are discussed. Experimental results on the electrocatalysis on electrodes modified by polymeric films are analysed. Attention is drawn to systems involving particles of platinum-group metals incorporated into polymeric matrices. The properties of electrodes modified by ion-conducting and electron-conducting polymers are compared. Certain problems to be solved in future studies of the electrode systems under discussion are formulated. The bibliography includes 265 references.

Proton-conducting electrolyte membranes based on aromatic condensation polymers

Abstract: The results of investigations in the field of development and applications of proton-conducting electrolyte membranes based on aromatic condensation polymers are analysed and summarised. Primary attention is paid to the properties of the starting polymers, such as the thermal stability, water uptake and proton conductivity. General approaches to the preparation of aromatic condensation polymers with high proton conductivity are considered, including sulfonation, synthesis from monomers containing sulfonic acid groups, incorporation of alkylsulfonated substituents and formation of acid–basic polymer complexes. The bibliography includes 115 references.

Theoretical studies of transition metal complexes with nitriles and isocyanides

Abstract: Theoretical studies of transition metal complexes with nitriles and isocyanides are reviewed. The electronic structures and the nature of coordination bonds in these complexes are discussed. The correlation between the electronic structures of transition metal complexes with nitriles and isocyanides and their structural properties, spectroscopic characteristics, and reactivities are considered. The bibliography includes 121 references.

Metal complex catalysis in organic electrosynthesis

Abstract: Data on the use of electrochemically generated metal complex catalysts in organic synthesis are analysed, systematised and generalised. The considerable potential of organic electrochemistry is shown. Some electrochemical methods provide advantages in the synthesis of compounds where conventional chemical methods fail, are experimentally complicated or have environmental limitations. Particular attention is given to the mechanisms of electrocatalytic reactions. The bibliography includes 333 references.

Chemical aspects of implantation of high-energy ions into polymeric materials

Abstract: Data on the study of the influence of accelerated ion beams on polymeric materials are generalised. The mechanisms of chemical processes occurring in a polymer matrix upon ion implantation and resulting in crucial changes in the electrical conductivity, microhardness, hydrophilicity and other characteristics of the irradiated polymer surface are discussed. Main fields of applications of ion-implanted polymeric materials are considered. The bibliography includes 188 references.

Isothiazoles (1,2-thiazoles): synthesis, properties and applications

Abstract: The most recent achievements in the chemistry of isothiazoles are generalised and systematised. The main applications of isothiazole derivatives are surveyed. The bibliography includes 293 references.

Thermal stability of nanomaterials

Abstract: The main processes and phenomena (grain growth, phase transformations, relaxation, diffusion, and so on) in nanomaterials subjected to heat treatment are considered. Experimental data and theoretical views on the thermal stability of nanomaterials are analysed and generalised. Attention is drawn to unsolved problems. The bibliography includes 152 references.

The state-of-the-art and prospects for the development of rechargeable lithium batteries

Abstract: The state-of-the-art of investigations into the development and perfection of the most promising class of chemical power sources, namely, rechargeable lithium batteries, is considered. The main problems of designing the batteries with a metallic lithium electrode are formulated and the use of alternative negative electrodes is substantiated. Special attention is paid to the studies dealing with the principles of the performance of lithium-ion batteries as well as the key directions for the perfection of these devices, which mainly concern the elaboration of new materials for lithium-ion batteries. A separate section is devoted to the consideration of polymeric electrolytes for lithium and lithium-ion batteries. The bibliography includes 390 references.

Microwave radiation in analytical chemistry: the scope and prospects for application

Abstract: The key aspects of the effect of microwaves on the physicochemical processes in solutions and heterogeneous systems are analysed. Good prospects for the use of microwave radiation for intensifying various types of interaction are demonstrated in relation to dissolution, hydrolysis of organic and inorganic substances, complex formation by metal ions in solution and in the sorbent phase, oxidation of organic compounds, and synthesis of coordination and organic compounds. Specific features of analytical operations with microwave treatment are considered and the trends of development of analytical methods using microwaves are discussed. The bibliography includes 137 references.

Modern methods for the synthesis of peptide–oligonucleotide conjugates

Abstract: The published data on the methods of chemical solution and solid-phase synthesis of peptide–oligonucleotide conjugates are reviewed. The known methods are systematised and their advantages and disadvantages are considered. The approaches to the solution synthesis of peptide–oligonucleotide conjugates are systematised according to the type of chemical bonds between the fragments, whereas those to the solid-phase synthesis are classified according to the procedure used for the preparation of conjugates,viz., stepwise elongation of oligonucleotide and peptide chains on the same polymeric support or solid-phase condensation of two presynthesised fragments. The bibliography includes 141 references.

Polyurethane foams in chemical analysis: sorption of various substances and its analytical applications

Abstract: Data on the sorption properties of polyurethane foams including their modified forms are surveyed. Examples of application of polyurethane foams for the separation and preconcentration of inorganic and organic compounds are given. The mechanisms of sorption on polyurethane foams described in the literature are analysed. Advances in the development of combined and hybrid methods of analysis with the use of these sorbents are discussed. The bibliography includes 259 references.

Complex phosphates containing mono- and trivalent cations

Abstract: The review surveys the data on the synthesis, structures, thermal stability and physical properties of complex phosphates containing MI and MIII cations generated from double phosphates by the partial replacement M I →H + or PO 4 3- →X n- [X n- = F - , OH - , EO 4 n- (VO 4 3- , MoO 4 2- ) or S 2 O 3 2- ]. The sizes of the M I and M III cations and their ratio have a dominant role in the structure formation of complex phosphates. The prospects of the use of complex phosphates as polyfunctional materials are discussed. The bibliography includes 161 references.

The use of molecular-statistical methods for the calculation of thermodynamic characteristics of adsorption for identification of organic compounds by gas chromatography–mass spectrometry

Abstract: The current state of research on the theoretical description of adsorption in the Henry region by semiempirical molecular-statistical procedures, as applied to identification of organic compounds in complex mixtures, is considered. Various approaches to correcting the atom–atom potential parameters used to determine thermodynamic characteristics of adsorption are compared. Examples of calculations involved in the chromatographic and chromatography–mass spectrometric identification of model and real organic compounds including isomers are given. The bibliography includes 89 references.

Phase equilibria, phases and compounds in the Ti–C system

Abstract: The results of experimental and theoretical investigations of the phase equilibria in the titanium–carbon system are generalised. The generalised thermodynamic characteristics of disordered titanium carbide TiC y , are reported. Peculiarities of the crystal structures of all the known and hypothetical compounds of titanium with carbon are considered in detail. The X-ray diffraction patterns which allow identification of all these compounds are presented. The phase diagrams of the Ti–C system constructed with allowance for atomic ordering of non-stoichio metric carbide, TiC y , and for the existence of the molecular cluster-like compounds Ti 8 C 12 and Ti 13 C 22 (TiC 2 ) are discussed. The bibliography includes 142 references.

Endohedral metal derivatives and exohedral fluorine derivatives of fullerenes

Abstract: The thermodynamic studies of fullerenes and their stable derivatives, namely, endohedral metallofullerenes and exohedral fullerene fluorides, are generalised. The methods of synthesis and purification of fullerene fluorides are considered and the structures of these compounds are characterised. The thermodynamic properties of fullerenes and fullerene fluorides are discussed. The bibliography includes 150 references

1,3- and 1,4-substituted tetrazolium salts

Abstract: The published data on the synthesis, physicochemical properties, structures and reactions of 1,3-(1,3,5)- and 1,4-(1,4,5)-substituted tetrazolium salts are systematised and generalised. Their applications as starting compounds in the preparative chemistry of heterocyclic derivatives and some other branches of science and technology are reviewed. The bibliography includes 122 references.

Synthesis of C-vinylpyrroles

Abstract: The latest advances in the synthesis ofC-vinylpyrroles are generalised and systematised. Methods for the synthesis based on reactions of acylpyrroles and dicarbonyl compounds or their synthetic equivalents are still of most importance. New promising methods for the synthesis ofC-vinylpyrroles are considered, among them the reactions of alkenyl ketone oximes with acetylene in the KOH–DMSO system and base-catalysed condensation of pyrrolecarbodithioates, which have recently become available, with CH-acids. The bibliography includes 195 references.

Molecular polymer–polymer compositions. Synthetic aspects

Abstract: The main ways of improving the compatibility of polymer–polymer compositions containing polyolefins as one component are considered. Considerable attention is given to the preparation of polyolefins in the presence of an ingredient bound to the catalyst in the catalytic (including consecutive) polymerisation of olefins. The so-called reactor blends and the synthesis and structure of diblock and conducting composites are described. The important role of compatibilisation of polymers of different nature with the use of a third component is pointed out. The formation mechanism of molecular compositions, the structure and properties of the intermediate layer and the main fields of application of synthetic polyolefin–polymer compositions are discussed. The bibliography includes 335 references.

Nucleophilic attack on the unsubstituted carbon atom of azines and nitroarenes as an efficient methodology for constructing heterocyclic systems

Abstract: Data on new methods for the synthesis of fused azines by nucleophilic attack on the unsubstituted carbon atom of azines and nitroarenes are generalised. The review surveys tandem reactions of azines with binucleophiles comprising nucleophilic addition A N –A N nucleophilic addition–substitution A N –S ipso N , and nucleophilic substitutions S H N –S ipso N and S H N -S H N . Intramolecular S H N reactions of azines and nitroarenes and other methods for the synthesis of fused heterocycles based on S H N nucleophilic substitution are also discussed. The bibliography includes 69 references.

Some new views on the tautomerisation mechanism

Abstract: Published data on the prototropic tautomerism of some carbonyl and nitrogen-containing acyclic and heterocyclic compounds are systematised. Mechanisms of intramolecular and intermolecular proton transfer in tautomerisation reactions are considered. On the basis of the results of semiempirical and ab initio quantum-chemical calculations, preference is given to an intermolecular collective (dimeric, trimeric, tetrameric or oligomeric) mechanism. A new approach to the description of the solvent effect on the prototropic tautomeric equilibrium is proposed. The bibliography includes 107 references.

Applications of NMR tomography to mass transfer studies

Abstract: Modern physicochemical applications of NMR tomography, or magnetic resonance imaging (MRI), to the investigation of mass transfer processes are described. The mass transfer involved in the sorption of gases, fluids and solutes, swelling of polymers and coal and drying of various materials is considered. Various methods of studying isotropic, anisotropic and restricted diffusion in porous media are discussed. The approaches to the investigation of filtration and the flow of fluids, gases and granulated materials are presented. The bibliography includes 373 references.