B. N. Tarasevich

Oxidation of Organosulfur Compounds by Hydrogen Peroxide in the Presence of Niobium and Vanadium Peroxo Complexes

New niobium(V) peroxo complexes containing aspargine and Schiff base ligands were synthesized, and their structures were solved by IR, NMR, and mass spectrometric methods. They were found to be catalytically active for the peroxidation of methyl phenyl sulfide and benzothiophene to the corresponding sulfoxide and sulfones. It was shown that vanadium(V) peroxo complexes with the same ligands are less active in the oxidation of methyl phenyl sulfide than the niobium complexes.

Properties of Interfacial Layers in Multicomponent Systems Containing Gelatin

The review is devoted to the analysis of the effect of the addition of various surfactants on the composition, structure, and the properties of the interfacial adsorption layers (IALs) formed at equilibrium in the aqueous gelatin solution–hydrocarbon system. Associates of variable compositions that are determined by the component ratio and the concentration of added surfactant are formed due to the interaction between gelatin and surfactant. The formation of associates is equivalent to the modification of gelatin. The properties of the IALs of modified gelatins are discussed on the basis of our own results and published data on the interfacial tension, the mass accumulation of surface-active components at the interfaces during the IAL formation, the IAL rheological properties and the stability of emulsion films varied with the conditions of IAL formation (the nature of low-molecular-weight surfactant, component concentrations, pH of aqueous phase, and temperature). It was concluded that modified gelatins can be considered as new surfactants governing the dynamics of the formation and fracture mechanism of the IALs and the stability of emulsion films. The properties of the IALs of modified gelatins are compared with those of IALs formed by gelatin and low-molecular-weight surfactants under the conditions when associates are formed directly at the interface due to the use of oil-soluble surfactants.

Synthesis and spectral properties of autocomplexes of the nitroquinoline series

A number of new NH-bridged nitroquinoline derivatives with intramolecular charge transfer (autocomplexes) were synthesized starting from 8-chloro-5,7-dinitroquinoline and aromatic N,O-heterocyclic amines characterized by different donor powers and substitution patterns. The charge transfer in their molecules may occur via both direct polar conjugation through the bond sequence including the bridging nitrogen atom and through space between spatially close molecular fragments (contact charge transfer).

Adsorption of lipids on silicalite-1

The adsorption of egg lecithin and cholesterol from chloroform solutions onto silicalite-1 (hydrophobic silica with MFI zeolite structure) is investigated. Adsorption isotherms of the L-type for lecithin and the S-type for cholesterol are obtained in the 0.05–4.5 mg/mL range of equilibrium lipid concentrations. The maximum adsorption for lecithin is 30 mg/g; for cholesterol it is 70 mg/g. Chloroform treatment results in the desorption of no more than 10% of the lecithin and up to 50% of the cholesterol from the silicalite-1 surface. The lecithin molecules in the monolayer on the silicalite-1 are oriented such that their hydrophobic tails are oriented toward the surface and are partially inside the pores of the adsorbent.

Thermal Inactivation of Alkali Phosphatases under Various Conditions

The thermal inactivation of alkali phosphatases from bacteria Escherichia coli (ECAP), bovine intestines (bovine IAP), and chicken intestines (chicken IAP) was studied in different buffer solutions and in the solid state. The conclusion was made that these enzymes had maximum stability in the solid state, and, in a carbonate buffer solution, their activity decreased most rapidly. It was found that the bacterial enzyme was more stable than animal phosphatases. It was noted that, for ECAP, four intermediate stages preceded the loss of enzyme activity, and, for bovine and chicken IAPs, three intermediate stages were observed. The activation energy of thermal inactivation of ECAP over the range 25–70°C was determined to be 80 kJ/mol; it corresponded to the dissociation of active dimers into inactive monomers. Higher activation energies (∼200 kJ/mol) observed at the initial stage of thermal inactivation of animal phosphatases resulted from the simultaneous loss of enzyme activity caused by dimer dissociation and denaturation. It was shown that the activation energy of denaturation of monomeric animal alkali phosphatases ranged from 330 to 380 kJ/mol depending on buffer media. It was concluded that the inactivation of solid samples of alkali phosphatases at 95°C was accompanied by an about twofold decrease in the content of β structures in protein molecules.

IR Spectroscopic Study of the Structure of Isotactic Polypropylene Deformed by the Crazing Mechanism

The deformation of isotropic isotactic polypropylene with a spherulitic initial structure has been studied. Fourier transform IR spectra of polypropylene deformed to various stretch ratios in air and in a physically active medium have been recorded. From the spectroscopy data, the dichroic ratios and orientation functions have been calculated for the amorphous and crystalline polypropylene phases. It turned out that the orientations of macromolecules in the amorphous and crystalline polypropylene phases change identically while stretching in a physically active (water–ethanol) medium. However, the deformation in air leads to a more pronounced orientation of macromolecules in the crystalline phase as compared with the orientation in the amorphous phase. The maximum values of the orientation function in the deformation in air coincide with the stretch ratio at the yield point. This is how a physically active medium acts in crazing in comparison with shear deformation in air.

Orientation of polymers in polypropylene/poly(ethylene oxide) nanocomposites produced by crazing

177 Since recently, researchers have paid much atten tion to crystallization of polymers within a confined nanosized space, where the crystal growth is confined in one or several directions and the size of this confine ment is comparable to the size of a coil of macromol ecules in solution or melt. This may occur in thin films or thin layers in layered nanocomposites, polymer mixtures or block copolymers in which the glass tran sition or melting point of one of the components exceeds that of the other crystallizing component, nanoporous materials in the shape of nanotubes or nanoporous membranes, and composites consisting of polymers filled with nanofibers or nanotubes, etc. [1–3]. Research is made into the effect of the size and mor phology of the nanosized space on the kinetics of crys tallization of polymers, their degree of crystallinity, and the size and orientation of crystallites. In nanosys tems, of no less importance is the effect of the solid surface on the crystallization and structure of poly mers [3]. A method for producing nanoporous materials is deformation of polymers in adsorption active media, which occurs by a crazing mechanism and is accom panied by the formation of a fibrillar porous structure with nanosized (5–20 nm) pores and fibrils [4, 5]. If the deformation is performed in a solution containing various low molecular weight additives, they pene trate into the porous structure of crazes to form nano composites with finely dispersed components. How ever, the crazing method can produce nanocomposites with not only low molecular weight compounds. Previously [6, 7], we for the first time demonstrated that the deformation of polymers in solutions of flexi ble chain polymers also occurs by the crazing mecha nism and is accompanied by the penetration of macro molecules into the porous structure of crazes to give polymer–polymer nanocomposites. An important feature of crazing as a method for creating a porous structure in polymers is the fact that varying the defor mation conditions (stretching rate, temperature, and draw ratio) and the nature of the liquid medium enables one to vary the parameters of the fibrillar porous structure. In this context, it is obvious that polymer–polymer nanocomposites obtained by craz ing are convenient model systems for studying the polymer structuring under nanoconfined conditions. To study crystallization of polymers in nanoporous matrices of crazed polymers, we chose poly(ethylene oxide) (PEO), which can be crystallized to a high degree of crystallinity and is available as homopoly mers of various molecular weights. The purpose of this work was to investigate the structure of nanocompos ites based on isotactic polypropylene (PP) and PEO that were produced by crazing.

Properties of carrageenan gels with immobilized lysozyme

AbsractRheological properties of 3% carrageenan gels formed in 0.4 M sodium chloride solution in the presence of lysozyme are studied in detail. It is shown that the addition of protein results in an increase in the gel-sol transition temperature by 2°C (transition temperature of 3% gel is 48°C, lysozyme concentration is 0.5 mg/ml). Based on the frequency dependences of dynamic moduli at various temperatures, it is revealed that systems possess viscoelastic properties at low frequencies. Within a wide frequency range up to gel-sol transition temperature, systems become elastoviscous and, at higher frequencies, they demonstrate forced transition to glassy state. It is shown that carrageenan inhibits enzyme activity of lysozyme. The interaction between enzyme and carrageenan leads to changes in lysozyme conformations, i.e., the content of α-helices increases and that of turns decreases. It is demonstrated for the first time that, in the presence of a so-called nonspecific (for the gelation of carrageenan) sodium ion, it is possible to prepare gels with the necessary structure and rheological properties and gel-sol transition temperature. These gels can release a lysozyme under the conditions of transmucosal prolonged delivery.

Synthesis, molecular structure, and spectral properties of new metal chelates based on organic autocomplexes and charge transfer therein

A number of new chelate compounds based on 3d-transition metals and autocomplexes of the dinitroquinoline series were synthesized. The crystalline structure of the new complexes was determined by X-ray analysis, and their spectral properties were studied. The complexes have a conformation which gives rise to two modes of contact intramolecular charge transfer: intraligand, which is intrinsic to the initial ligand molecules, and interligand (as in binary charge-transfer complexes). The latter involves the corresponding pairs of donor and acceptor fragments of the initial ligand molecules, which appear spatially close as a result of complex formation.

Polymorphism of 2,4,6-trinitro-4′-iododiphenylamine

The experimental conditions for preparation of four differently colored polymorphs of 2,4,6-trinitro-4′-iododiphenylamine, a picryl autocomplex, have been determined. The specific features of intra-and intermolecular interactions in the resulting polymorphs, one of them being noncentrosymmetric, have been studied by IR spectroscopy and X-ray crystallography.