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Biomedical subjects

V A Davankov

Publications and source records attributed to V A Davankov.

At least 19 recordsLinked to original sources
PubMed2005

Selectivity in preparative separations of inorganic electrolytes by size-exclusion chromatography on hypercrosslinked polystyrene and microporous carbons.

Preparative-scale separation of concentrated solutions of simplest mineral electrolytes by size-exclusion chromatography was performed on three samples of commercially available microporous hypercrosslinked polystyrene sorbents "Macronet Hypersol" and two experimental samples of activated carbons. Selectivity of separation of a pair of electrolytes was found to be determined by the largest ions in each pair. Fortunately, selectivity rises at higher concentrations of electrolytes, which was explained by exclusion of smaller species from the concentrated solution, i.e., mobile phase, into small pores of the column packing that are inaccessible to large species. The separation of concentrated mixtures revealed another remarkable advantage of the new process - self-concentrating of each of two separated components in the corresponding fractions. Self-concentration is more pronounced for the minor component that occupied less space in the initial mixture. The new method may prove productive in processing pickle bath solutions.

Carbon↗
PubMed2004

Elucidation of retention mechanisms on hypercrosslinked polystyrene used as column packing material for high-performance liquid chromatography.

Establishing of basic retention mechanisms was considered the key target during the development of new column packing materials. To extract, from an appropriate retention data matrix on hypercrosslinked polystyrene Chromalite 5HGN, certain factors that can be brought in an obvious correspondence with known retention mechanisms, the principal component analysis (PCA) was applied. The approach was used to elucidate the adsorption properties of the above novel HPLC packing. Besides HPLC, knowledge of retention mechanisms helps to reveal perspective application area for the hypercrosslinked polystyrene-type materials in solid-phase extraction (SPE) and low-pressure preparative LC.

Chromatography, High Pressure Liquid↗
PubMed2003

Hypercrosslinked polystyrene as a novel type of high-performance liquid chromatography column packing material. Mechanisms of retention.

An experimental material, Chromalite 5HGN (Purolite, UK), that represents hypercrosslinked polystyrene as a new type of neutral stationary phase for HPLC was examined. The material contains no functional groups, but is compatible with any kind of nonpolar and highly polar mobile phase, and even with water. It is chemically resistant and thermally stable. When using aqueous organic mobile phases, Chromalite 5HGN works similar to standard C18 reversed-phase packings, but is characterized by much greater hydrophobicity and, sometimes, unusual selectivity. When using nonpolar mobile phases, i.e. under "quasi normal-phase" conditions, the retention is mostly governed by the interactions between pi-electronic systems of the adsorbent and adsorbate. Adding highly polar, even hydrophilic solvents into the mobile phase, leads to a shift of retention times toward the "reversed-phase" kind of chromatography, which gives an additional possibility in fine tuning the column selectivity.

Chromatography, High Pressure Liquid↗
PubMed2001

Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation.

Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.4 nm in ML. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water is obtained with the HPS-Pt-THF complex prior to H2 reduction. During an induction period of about 100 min, L-sorbose conversion is negligible while catalytic species develop in situ. The structure of the catalyst isolated after the induction period is analyzed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electron micrographs reveal a broad distribution of Pt nanoparticles, 71% of which measure less than or equal to 2.0 nm in diameter. These nanoparticles are most likely responsible for the high catalytic activity and selectivity observed. The formation of nanoparticles measuring up to 5.9 nm in diameter is attributed to the facilitated intercavity transport and aggregation of smaller nanoparticles in swollen HPS. The catalytic properties of these novel Pt nanoparticles are highly robust, remaining stable even after 15 repeated uses.

Catalysis↗
PubMed2000

30 years of chiral ligand exchange.

The history of the discovery and some benchmark achievements of enantioselective ligand exchange chromatography (LEC) are briefly reviewed. Some of the most important results of investigations into the structure of Cu(II) complexes with nitrogen-substituted alpha-amino acids are summarized, and the role of water molecules that are coordinated in two axial positions of these complexes in the mediation of between-ligand interactions is underlined. UV and circular dichroism spectroscopy are shown to be very convenient for studying and quantifying the thermodynamic and kinetic enantioselectivity phenomena in the complex formation. Polystyrene-based chiral ligand exchange resins served as the first highly selective column packing in the development of enantioselective liquid chromatography. These resins were then followed by more efficient silica bonded monomeric and polymeric HPLC phases. The latter proved to be especially stable in aqueous media at elevated temperatures. Finally, chiral coated ligand exchanging RP phases presented the most inexpensive, but highly efficient and selective phases for the resolution of chelate-forming racemic solutes in LC and TLC. The mechanism of chiral resolution on these last phases involves an essential interaction of both the selector and selectand with the achiral hydrophobic surface. The same is valid for chiral resolutions according to chiral mobile phase techniques. Perspectives on further development of enantioselective LEC are discussed.

Journal Article↗
PubMed1997

Novel polymeric solid-phase extraction material for complex biological matrices. Portable and disposable artificial kidney.

The replacement of conventional hemodialysis treatment for a patient with malfunctioning kidneys by providing him/her with a portable and disposable "artificial kidney" which is connected to implanted artery and veneous cannulas on a patient's wrist is discussed. During a continuous flow of blood, plasma diffuses through a plasmapheretic membrane, passes through a bed of plasmacompatible sorbent Styrosorb, and arrives at an ultrafiltration membrane. Vacuum-operated ultrafiltration removes excess water together with dissolved urea and other small molecules, and Stryosorb removes medium-sized toxic substances. The hemocompatibility of the sorbent is improved by chemical modification of the surface.

Biocompatible Materials↗
PubMed1995

Mass-spectrometric analysis of N-acetylchitooligosaccharides prepared through enzymatic hydrolysis of chitosan.

A semipreparative scale chromatography of N-acetylchitooligosaccharides (GlcNac)2-7 on a reversed-phase C-16 HPLC column is reported. The initial material was obtained by enzymatic hydrolysis of chitosan with a complex of chitinases from Streptomyces kurssanovii, followed by a complete acetylation of amino groups. Isolated N-acetylchitooligosaccharides were characterized by the mass-spectrometric method. On interacting with the sample, the fragments of 252Cf caused desorption of quasi-molecular ions of the substance. All mass spectra of chitin oligomers contained intense quasi-molecular ions [M + Na]+ and a less intense [M + K]+ ion. Fragment ions, compared to the quasi-molecular ion [M + K]+, had a lower intensity and confirmed the structure of samples under study. Due to this phenomenon, an accurate analysis of both individual compounds and mixtures of N-acetylchitooligosaccharides (n = 2-7) may be performed.

Acetylation↗
PubMed1994

One-step isolation of a chitinase by affinity chromatography of the chitinolytic enzyme complex produced by Streptomyces kurssanovii.

One of the four chitinases with a molecular mass of 42 kDa existing in the chitinolytic enzyme complex produced by Streptomyces kurssanovii was separated in homogeneous form using one-step affinity chromatography on cross-linked and phosphorylated chitin-type sorbents. Three other chitinases were not selectively bound by the sorbents and were not obtained in homogeneous form. The affinity sorbents were shown to be stable over the time of separation and could be used repeatedly.

Adsorption↗
PubMed1991

Ion-exchange high-performance liquid chromatography of nucleotides and polypeptides on new types of ion-exchange sorbents, based on polystyrene-coated silicas.

A novel type of ion exchanger was prepared by multipoint covalent binding of polystyrene chains onto the surface of porous silica followed by polymer-analogous modification of the bonded layer. Both anion and cation exchangers were synthesized and examined in the separation of nucleotides and proteins. Rapid and efficient separation of basic polypeptides on strong anion exchangers and that of acidic polypeptides on strong cation exchangers could be achieved. For the separation of complete mixtures of polypeptides the application of zwitter-ionic ion exchangers can be recommended.

Animals↗
PubMed1990

A vivid model illustrating chiral recognition induced by achiral structures.

If diastereomeric complexes are adsorbed on a surface or if they include a molecule of solvent, two points of attractive interaction between the chiral species of the complex can be sufficient for mutual chiral recognition of these species. In special cases even one single point of interaction is sufficient. This extension of the three-point contact rule of Dalgliesh, first observed in chiral ligand-exchange chromatography, can be demonstrated by using hands.

Hand↗
PubMed1990

[Ligand-exchange chromatography of proteins and enzymes].

Current state of the ligand-exchange chromatography (metal chelate affinity chromatography) of proteins and enzymes is reviewed. This technique is based on the ability of proteins to bind metal ions immobilized on chelate gels. The influence of pH, composition of buffer, type of stationary ligand and nature of metal ions on the chromatographic behaviour of proteins is discussed.

Chromatography, Affinity↗
PubMed1981

[Coordination-ionic enzyme immobilization. Dependence of properties of immobilized preparations of penicillinamidohydrolase on the nature of metal ion and stationary ligand].

Penicillinamidohydrolase was immobilized on heteroporous polystyrene supports containing groups of ethylenediamine, diethylenetriamine and triethylenetetramine, using Co(II), Ni(II), Cu(II), Fe(III), Co(III) ions. The effects of substrate concentrations and pH on the activity of the immobilized enzyme were investigated and the kinetic parameters of hydrolysis were determined, using N-phenacetylphenylglycine as substrate. The enzyme immobilization resulted in a slight decrease of Km(app), while the values of V decreased by a factor of two. Preparations possessing high thermal stability were obtained by oxidation of Co(II) to Co(III) in the enzyme sorption complex. High stability was also found for the Fe(III)-containing preparations.

Cobalt↗
PubMed1981

[Hydrolysis of N-acetyl-L- and N-acetyl-D,L-methionine by microbial aminacylase].

The kinetics of N-acetyl-L- and N-acetyl-D,L-methionine hydrolysis by aminoacylase from Asp. oryzae were studied. The maximal rate of the reaction was found to be about 2000 mu moles of L-methionine per mg of protein per hour; Km was equal to about 1.10(-1) M for both the racemic and optically active substrates. In the presence of Co(II) ions (the molar ratio of N-acetyl-L-methionine/Co(II) was 100:1) the reaction velocity was increased. The values of approximately 4500 and approximately 3000 mu moles per mg per hour were-attained with L-enantiomer and racemic substrates, respectively. The Km values were decreased down to 2.10(-2) M and 1.4.10(-2) M, respectively.

Amidohydrolases↗
PubMedDate not supplied

Evaluation of a hypercrosslinked polystyrene, MN-200, as a sorbent for the preconcentration of volatile organic compounds in air.

Breakthrough volumes, average percentage recoveries, and storage stabilities were obtained for vapors of 8 volatile organic compounds (pentane, octane, undecane, isooctane, cyclohexane, toluene, methanol, and dichloromethane) on a new adsorbent material, Hypersol-Macronet, MN-200. Breakthrough volumes were estimated as half of the gas chromatographic specific retention volumes at 20 degrees C for the compounds. Recoveries of the adsorbates were determined by both solvent extraction and thermal desorption methods. The results obtained compare favorably with those for Tenax GR (values reported in the published literature and others obtained in our laboratory). Results of storage stability studies on MN-200 meet the criterion for acceptability (<10% loss). High adsorption capacity for very volatile and polar compounds, combined with ease of desorption of less volatile compounds, render MN-200 a highly promising adsorbent for sampling volatile organic compounds in indoor and outdoor air.

Adsorption↗