T. E. Grigor’ev

Synthesis of Ag and Cu-chitosan metal-polymer nanocomposites in supercritical carbon dioxide medium and study of their structure and antimicrobial activity

This paper is dedicated to the design of efficient antimicrobial pharmaceuticals based on chitosan. Chitosan with a deacetylation degree of 0.98 preliminarily treated with supercritical carbon dioxide (scCO2) was impregnated with organometallic complexes (silver cyclooctadiene(hexafluoroacetylacetonate) and copper hexafluoroacetylacetonate) from an scCO2 solution followed by reduction with hydrogen to form metal-chitosan composites. Their structure was studied by small-angle X-ray scattering (SAXS). A narrow virtually monodisperse size distribution with a preferable particle size of 1–3 nm was found for silver and a wider polymodal size distribution with a particle size of up to 1–40 nm was revealed for copper. An X-ray fluorescent analysis showed the content of silver and copper metal to be 6 and 4.6%, respectively. The composites prepared by fluid technology were tested for antimicrobial activity toward bacteria S. epidermidis, E. coli, and a spore form of bacteria B. cereus in comparison with Cu2+-chitosan complexes obtained by the routine solution procedure. Ag0-chitosan nanocomposites were found to show bactericidal activity toward all the noted bacteria and spore forms, whereas Cu2+-chitosan complexes exhibit bacteriostatic activity toward the above bacteria and a lack of bactericidal properties toward the spore forms. The reasons for the bactericidal activity of the prepared composites are discussed.

Electrocatalysts for fuel cells synthesized in supercritical carbon dioxide

We applied the method of directly depositing an organometallic precursor from a solution in supercritical carbon dioxide on a dispersed carbon substrate surface followed by reduction to obtain a number of electrocatalytic materials in the form of nanoscale platinum particles on dispersed carbon supports (Vulcan XC72r carbon black, acetylene black, nanotubes). The synthesized materials persistently showed a monodisperse size distribution of platinum particles with an average diameter of 2–3 nm, regardless of the substrate nature, and a uniform distribution over the support surface. The synthesized electrocatalysts (ECs) were tested as part of an operating cathode electrode of a phosphoric acid fuel cell (FC) with a PBI matrix. In this case, the membrane-electrode assembly with this cathode showed current-voltage characteristics as good as the reference characteristics achieved with electrodes produced by BASF.

AFM study of the structuration of an ionic surfactant and phenylalanine with κ-carrageenan

Local networks of κ-carrageenan adsorbed in the presence of an ionic surfactant and phenylalanine were examined by atomic force microscopy (AFM). Polymer chains of adsorbed carrageenan are aligned with crystallographic axes. The helical and globular conformations of carrageenan effectively bind the surfactant. Phenylalanine is not involved in the structuration of the carrageenan gel.

Interaction of polymer matrix and bound water in poly(N-vinylcaprolaktam) films

Interaction of water molecules and the polymer matrix of poly(N-vinylcaprolaktam) (PVCL), depending on temperature (−100 and 50°C) and water concentration (less than 1, 5 and 24 wt %), was investigated using the dielectric spectroscopy method (at 10−1–107 Hz). The presence of characteristic temperature points of changes of system properties, whose values depend on the quantity of water molecules in the polymer, was identified. It was found that the mechanism of temperature influence and water concentrations changes the characteristics of hydrogen bonds.

Synthesis and properties of new functionalized poly(imides) based on 1,1-bis(4-aminophenyl)-1-z{4′-bis(4′’-bromophenyl)amino}phenyl-2,2,2-trifluoroethane

A new aromatic diamine, 1,1-bis(4-aminophenyl)-1-{4′-bis(4″-bromophenyl)amino}phenyl-2,2,2-trifluoroethane, is synthesized. Its interaction with various dianhydrides of aromatic carboxylic acids via high-temperature polycondensation yields a number of new functionalized poly(imides) combining high thermal and mechanical characteristics with solubility in organic solvents. The values of Tg vary from 208 to 230°C, and temperatures corresponding to 10% weight loss fall within the intervals 330–370 and 550–660°C (in air and argon, respectively). Spectroelectrochemical characteristics of poly(imides) are studied by cyclic voltammetry and UV-VIS spectrometry. Poly(imides) exhibit high reversible stability of electrochromic properties, and their color changes from colorless (the neutral form) to green (the oxidized form) as the applied potential is varied from 0 to 1.25 V.

Formation of Fe2+-phenanthroline complexes in the volume of hydrogel

The interaction of weakly crosslinked gels of poly(methacrylic acid) and a nonionic gel based on N-vinylcaprolactam and N-vinylimidazole with Fe2+ ions in aqueous solutions has been studied. A comparative study of the conformational state and of the absorption ability of the gels for their interaction with iron and ferroin ions has been performed. It has been shown that Fe2+ ions are efficiently absorbed by both poly(methacrylic acid) gels and the gels based on N-vinylcaprolactam and N-vinylimidazole. In this case, the poly(methacrylic acid) gels undergo contraction, while nonionic gels derived from N-vinylcaprolactam and N-vinylimidazole experience swelling. During the interaction of gels containing immobilized Fe2+ ions with phenanthroline, the efficient absorption of the complexon and the formation of Fe2+-phenanthroline complexes in the gel volume take place, thus inducing the contraction of gels. The interaction of poly(methacrylic acid) gels with ferroin is accompanied by the absorption of the complex, the formation of the tertiary complexes, and the collapse of the gel. The efficiency of formation of tertiary complexes in the gel volume is independent of their preparation procedure.

Solvent effect on the structure of composite films obtained from chitosan solutions with a precursor of silver nanoparticles

The solvent effect on the structure of nanocomposite films cast from chitosan solutions with AgNO3 as a precursor of silver nanoparticles was studied for the first time. The size and concentration of silver nanoparticles in the chitosan matrix can be controlled by varying the chitosan-dissolving ability of the solvent with carbonic acid.

Biological Xenogenic Vessel Prostheses: Effect of H 2 O/CO 2 and EtOH Media on the Structure and Mechanical Properties of the Bovine Jugular Veins

The effect of the H2O/CO2 and EtOH/CO2 media at pressures and temperatures corresponding to the formation of supercritical (sc) carbon dioxide on the structure and mechanical properties of bovine jugular veins was studied for the first time. Treatment of bovine jugular veins in an sc-CO2 + ethanol or sc-CO2 + water medium considerably devitalized the tissue and increased the tissue elasticity, which allows considering the treated veins as promising vascular grafts with expected high capacity to suppress calcification and good hemodynamic properties.

New Electrochromic Polymeric Pyridinium Salts

A series of new anode-cathode conjugated electrochromic polymeric pyridinium salts containing mainchain triphenylamine units and demonstrating multicolor electrochromism has been synthesized. All of the polymers exhibit intense UV absorption with maxima of absorption and fluorescence at 340–343 and 336–338 nm in DMF solutions and 460–461 and 410–438 nm in films. The electrochromic properties of the films are investigated by electrochemical and spectroelectrochemical methods. Reversible redox signals with stable electrochromic characteristics are found in cyclic voltamperograms. The electrochromic properties of the polymers remain highly stable after 50 cycles in the range 0–1.2 V.

Specific features of interaction of ionogenic surface-active substance with κ-carrageenan

Atomic force microscopy was used for the investigation of local lattices of κ-carrageenan adsorbed on a surface in the presence of an ionogenic surface-active substance. The effective binding of the surface-active substance by helical and native forms of carrageenan is demonstrated.