I. V. Blagodatskikh

Antifungal activity of oligochitosans (short chain chitosans) against some Candida species and clinical isolates of Candida albicans: molecular weight-activity relationship.

A series of oligochitosans (short chain chitosans) prepared by acidic hydrolysis of chitosan and characterized by their molecular weight, polydispersity and degree of deacetylation were used to determine their anticandidal activities. This study has demonstrated that oligochitosans show a high fungistatic activity (MIC 8-512 μg/ml) against Candida species and clinical isolates of Candida albicans, which are resistant to a series of classic antibiotics. Flow cytometry analysis showed that oligochitosan possessed a high fungicidal activity as well. For the first time it was shown that even sub-MIC oligochitosan concentration suppressed the formation of C. albicans hyphal structures, cause severe cell wall alterations, and altered internal cell structure. These results indicate that oligochitosan should be considered as a possible alternative/additive to known anti-yeast agents in pharmaceutical compositions.

A new approach to the synthesis of cage-like metallasiloxanes

Abstract A new approach to the synthesis of cage-like metallasiloxanes has been proposed. Copper-containing metallasiloxanes {Na4[(RSiO2)12Cu4](R′OH)n} (1a, R=Ph, R′=n-Bu; 1b, R=Ph, R′=Me; 2, R=Vi, R′=Me) were prepared from PhSi(OR)3·(R=n-Bu, Me) and ViSi(OMe)3, respectively. Compound 2 was characterized by X-ray single structure analysis. The structures of compounds 1a,b were deduced by their follow up reactions with Me3SiCl.

Molecular mass characterization of polymers with strongly interacting groups using gel permeation chromatography–light scattering detection

This work is aimed at studying dilute solution behavior and developing techniques for the proper Mr characterization of polymers with strongly interacting groups. In particular, we have studied ionomers based on poly(dimethylcarbosiloxane) with carboxylic groups and hydrophobically modified polyacrylamide and its charged terpolymer. Gel permeation chromatography-light scattering (GPC-LS) study of organosilicon ionomers allowed us to follow molecular mass distribution evolutions during approximately a week that evidenced the gradual dissolution of clusters formed in bulk polymers. The rate of this process depends on the polymer composition and its preliminary treatment. Observed aggregates arre found to be stable during the procedure of chromatographic analysis. For characterization of hydrophobically modified polyacrylamide and its charged derivatives, we have used aqueous NaNO3-acetonitrile mixed solvent. Fluorescence spectroscopy with pyrene as a probe did not reveal any hydrophobic association in this solvent in contrast to aqueous solutions. Reversed-phase retention as well as polyelectrolyte exclusion were suppressed at GPC analysis. GPC-LC and classical LS methods gave consistent results for uncharged and weakly charged polymers. In the case of highly charged and highly hydrophobic terpolymers LS results evidenced association, while OPC-LC gave credible Mr values. We can conclude that in the last case, the observed association was weak enough to be disrupted in the coarse of chromatography.

Hydrolytic condensation of trialkoxysilanes in the presence of alkali metal and copper(II) ions. Influence of the reaction conditions on the structure of Cu/M organosiloxanes

The formation of polyhedral copper/sodium(potassium) organosiloxanes was examined as a result of hydrolytic condensation of organotrialkoxysilanes in the presence of copper(ii) and sodium or potassium ions. High selectivity of the synthesis of copper/sodium(potassium) organosiloxanes having desired structures can be achieved by choosing the reaction conditions.

Synthesis and molecular-mass characteristics of some cardo poly(benzimidazoles)

The GPC procedure for analyzing molecular mass characteristics of cardo poly(benzimidazoles) has been developed. In most cases, the reaction between 4,4′-oxydibenzene-1,2-diamine and 4,4′-(3-oxo-1,3-dihydroisobenzofuran-1,1-diyl)dibenzoic acid in Eaton’s reagent is accompanied by formation of a microgel. Depending on the synthesis conditions (temperature, duration of heating, and content of phosphorus pentoxide in the reaction mixture), polymers with both unimodal and bimodal molecular mass distributions can be prepared. Formation of the microgel fraction is observed for many representatives of poly(benzimidazoles) of various chemical structures. Based on the experimental evidence, the most probable pathway is suggested for the branching side reaction of poly(benzimidazoles) during their synthesis in Eaton’s reagent.

Phase transition chromatography of polyesters on macroporous glycidyl methacrylate—ethylene dimethacrylate copolymers

Abstract The chromatographic behaviour of oligoesters of phenolphthalein and terephthalic acid in columns packed with a polymeric sorbent based on the macroporous strongly cross-linked copolymer glycidyl methacrylate—ethylene dimethacrylate was studied. The possibility of the effective separation of oligomers according to the type of terminal groups was demonstrated. For comparison the sorbent Silasorb 600 was used.

Thermal fractionation of vinyl acetate-vinyl alcohol copolymers

Thermal fractionation via the method of successive self-nucleation and annealing was used for the first time to study the crystallinity of vinyl acetate-vinyl alcohol copolymers with different random distributions of chain units. The lamella-thickness distribution was calculated through the Gibbs-Thomson equation. It was shown that, for all samples, the minimum lamella thickness is the same and corresponds to a block of no less than 15 vinyl alcohol units. On the basis of these data and with the use of the computer simulation of the polymer-analogous reaction via the Monte Carlo method, the block-length distribution in the crystalline phase was found. It was shown through a comparison of the lamella-thickness and block-length distributions that the maximum lamella thickness increases with the block length and vinyl alcohol content in the copolymer. In crystallites, blocks with lengths exceeding the maximum lamella thickness comprise a significant fraction. Thus, it is probable that these blocks form folds. The dependences of melting temperatures of crystalline lamellas on their thicknesses, as well as the dependences of the melting temperatures of copolymers not subjected to thermal fractionation on the chain-structure parameters, are adequately described by the Flory crystallization theory.

Influence of glucosamine on oligochitosan solubility and antibacterial activity

Light scattering studies indicate that oligochitosan (short-chain chitosan) solutions contain aggregates at pH values below the critical pH of phase separation, while at or above this point the gel phase coexists with the aggregate solution. This work demonstrates for the first time that the presence of D-glucosamine in an oligochitosan solution shifts the critical pH to a higher value and improves the oligochitosan antibacterial activity against Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermis in neutral and slightly alkaline aqueous media. By comparing the results of light scattering studies and antimicrobial assays one can conclude that the antimicrobial activity of oligochitosan is dependent on its unimolecular form, not its supramolecular structures. The widening of the homogeneity region of an oligochitosan solution could lead to promising biomedical applications.

Chemical modification of cardo poly(benzimidazole) using “click” reaction for membranes of high-temperature hydrogen fuel cells

Phosphonethylated poly(benzimidazole)s (PEP BIs) were obtained for the first time in the Nesmey anov Institute of Organoelement Compounds, Rus sian Academy of Sciences, by the polymer analogous reaction of high molecular weight PBI–O–PT poly mer [3] via the reaction with O,O diethyl vinylphos phonate [4] (Scheme 1) and successfully studied in the construction of the membrane electrode block (MEB) of the hydrogen HTFC.

GENERAL FEATURES OF THE REACTION OF 4,4'-DIFLUOROBENZOPHENONE WITH POTASSIUM DIPHENOXIDE OF 2,2-BIS(4-HYDROXYPHENYL)PROPANE

AbstractThe major factors determining molecular weights of polyarylene-ether ketones formed by the reaction of 4,4′-difluorobenzophenone with 2,2-bis(4-hydroxyphenyl)propane in the presence of K2CO3 were revealed. The optimum conditions for the preparation of high-molecular-weight polymers were found, and it was demonstrated that it is possible to control their molecular weights (