Electrochemical degradation of tetracycline

Oxidation of tetracycline® in an electrochemical cell with separated cathodic and anodic compartments on smooth platinum was studied. The extent of electrochemical degradation of tetracycline and the energy consumption for eliminating the biological activity of its aqueous solutions were estimated.     

Diffusion-viscometric analysis and conformational characteristics of sodium polystyrenesulfonate molecules

Samples of sodium polystyrenesulfonate of molecular weights varying in a 20-fold range were synthesized. The hydrodynamic behavior of the samples was studied in a 0.2 M NaCl solution in which the initial polyelectrolyte effects are suppressed. Relationships between the molecular weight and the translational friction coefficient and intrinsic viscosity were obtained. The theory describing the hydrodynamic behavior of wormlike chains with taking into account both the percolation effects and the excluded-volume effects was applied to estimation of the length of the statistical segment and the cross section of the sodium polystyrenesulfonate molecules in 0.2 M NaCl solution.     

Epithermal neutron activation analysis of Spirulina platensis biomass and extracted C-phycocianin and DNA

Epithermal neutron activation analysis (ENAA) was used for study the biomass of Spirulina platensis. The background levels of concentration 27 macro-, micro- and trace elements ranging from 10^-3 to 10⁴ ppm was determined. It was found that the biomass of Spirulina does not contain toxic element concentrations above the tolerance level and can be utilized as a matrix of pharmaceuticals. The conentrations of basic elements in C-phycocianin and DNA extracted from Spirulina platensis were determined by ENAA. A comparison of the element content of a whole Spirulina biomass with that of a refined C-phycocianin preparation was made.     

Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization

The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes.     

Measuring the ignition delay time for hydrogen-oxygen mixtures behind the front of an incident shock wave

The delay time τ has been measured for the formation of the ^·OH radical in igniting hydrogenoxygen mixtures diluted with argon (79–97%). The experiments have been carried out under incident shock wave conditions at temperatures of 900–3000 K, pressures of 0.5–2.5 atm, and H₂/O₂ ratios of 0.2–20. The dependence of τ on the pressure P _s of the stoichiometric part of the combustible mixture (2H₂-O₂) has been investigated for different mixture compositions. Under the above conditions, τ depends practically linearly on 1/P _s at P _s = 0.02−0.1 atm, irrespective of the mixture composition. This allows the measured τ data to be converted to one quantity, τP _s. The temperature dependence of τP _s in the P _s range from 0.02 to 0.1 atm is Arrhenius-like. For the hydrogen-rich mixtures (H₂/O₂ = 2–20), this dependence appears as τP _s= 0.057 + 0.0256exp(7470/T) μs atm; for the lean mixtures (H₂/O₂ = 0.125–1), τP _s = 0.021 + 0.0069exp(7470/T) μs atm. The length of the shock-heated gas plug in the incident shock wave poses limitations on the ignition delay time measurements at T < 900 K.     

Synthesis of 5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one derivatives

The reaction of 2-aminothiazoles with ethyl acetoacetate in acetic or polyphosphoric acid gave a series of 5H-[1,3]thiazolo[3,2-a]pyrimidin-5-one derivatives which were nitrated with a mixture of nitric and sulfuric acid to 6-nitro-5H-[1,3]thiazolo[3,2-a]pyrimidin-5-ones, and the latter were reduced to the corresponding amines.     

Chemosensors and biosensors based on polyelectrolyte microcapsules containing fluorescent dyes and enzymes

The concept of enzyme-assisted substrate sensing based on use of fluorescent markers to detect the products of enzymatic reaction has been investigated by fabrication of micron-scale polyelectrolyte capsules containing enzymes and dyes in one entity. Microcapsules approximately 5 μm in size entrap glucose oxidase or lactate oxidase, with peroxidase, together with the corresponding markers Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) dichloride (Ru(dpp)) complex and dihydrorhodamine 123 (DHR123), which are sensitive to oxygen and hydrogen peroxide, respectively. These capsules are produced by co-precipitation of calcium carbonate particles with the enzyme followed by layer-by-layer assembly of polyelectrolytes over the surface of the particles and incorporation of the dye in the capsule interior or in the multilayer shell. After dissolution of the calcium carbonate the enzymes and dyes remain in the multilayer capsules. In this study we produced enzyme-containing microcapsules sensitive to glucose and lactate. Calibration curves based on fluorescence intensity of Ru(dpp) and DHR123 were linearly dependent on substrate concentration, enabling reliable sensing in the millimolar range. The main advantages of using these capsules with optical recording is the possibility of building single capsule-based sensors. The response from individual capsules was observed by confocal microscopy as increasing fluorescence intensity of the capsule on addition of lactate at millimolar concentrations. Because internalization of the micron-sized multi-component capsules was feasible, they could be further optimized for in-situ intracellular sensing and metabolite monitoring on the basis of fluorescence reporting.     

Gas-sensitive properties of thin nickel oxide films

The results of a study of the gas-sensitive properties of nickel oxide layers with respect to n-hexane, acetone, ethanol, benzene, o-xylene, toluene and ammonia are presented. NiO layers 100 ± 5 nm thick were obtained by chemical vapor deposition in the systems (EtCp)₂Ni–О₂–Ar and (EtCp)₂Ni–О₃–О₂–Ar. The electrical resistance of the layers changes in the presence of hexane, ethanol, benzene, and ammonia vapors. The electrical resistance of the obtained layers changed in the presence of vapors of hexane, ethanol, benzene and ammonia. Response and recovery time of the sensing element of the gas sensors did not exceed 6 s in the temperature range 500–600 K.     

Synthesis and NMR spectroscopy of 1,3,3,5,5-pentaalkoxy-1-chlorocyclotriphosphazenes

A series of pentaalkoxychlorocyclotriphosphazenes was synthesized. The spectral characteristics of the synthesized compounds (³¹Р, ¹H, ¹³С NMR) were studied. It was shown that the complexity of the NMR spectra of pentaalkoxychlorocyclotriphosphazenes is associated with the magnetic nonequivalence of the phosphorus atoms in the triphosphazene cycle and the hydrogen and carbon atoms in the alkoxy groups on these phosphorus atoms, as well as the cis/trans isomerism of the latter groups.