Thermal stabilization of aliphatic polyamides and fibres based on them. A review

The analysis of the published data shows that most thermal stabilizers (of the amine and phenol type, metal complexes) are added in the stage of synthesis of the polymer. Since thermooxidative processes in the finished fibre take place on the surface of the fibre under the effect of heat and light in the presence of oxygen, this method of adding an oxidation inhibitor is evidently not very promising due to the low utilization factor during thermal degradation because of the distribution of the inhibitor in the entire bulk of the fibre. The method of diffusion stabilization based on application of a thermal stabilizer on the surface of the fibre during drawing and finishing of the fibre is more promising. From this point of view, water-soluble stabilizers containing transition metal complexes are promising. Copper complexes and the combination of copper complexes with alkali metal halides are most effective. Copper-containing complexes are also promising since they are effective photostabilizers. For this reason, the development of new types of copper-containing complexes which would not only be efficient as thermal stabilizers but also as antistatic preparations in the spinning composition is of great practical interest.Moscow State Textile Academy. Translated from Khimicheskie Volokna, No. 6, pp. 30–34, November–December, 1993.     

Fabrication of New Water-Soluble Chitosan Derivatives

A new water-soluble derivative of chitosan — chitosan oligoethylene oxide sulfonate — was synthesized. The ratio and concentration of reacting substances and temperature and duration of the chitosan modification reaction affect the composition and properties of the reaction products. The conditions that ensure a 100% yield of water-soluble chitosan derivatives were determined. Using potentiometric titration and IR spectroscopy, the formation of a new water-soluble chitosan derivative — oligoethylene oxide sulfonate — was confirmed. __________ Translated from Khimicheskie Volokna, No. 4, pp. 41–44, July–August, 2005.     

Optimization and characterization of TiO2-based solar cell design using diverse plant pigments

The design of electrochemical solar cells (SCs), including those composed of biological pigments is an actively developing direction of obtaining alternative energy. SCs were studied under different temperatures, light intensities and spectral conditions. Furthermore, to understand processes occurring in the SCs, investigations characterizing the efficiency and stability with regard to environmental factors are also required. For this aim, novel instrumentation for the investigation of environmental effects on photocurrent generated by SCs has been designed and constructed. The system can be a model, which reflects conditions required for effective and stable functioning of the solar cells. Preliminary results are shown for two types of solar cells with two photosensitizers: thylakoid membrane preparations and anthocyanin-enriched raspberry extracts. It was shown that electrogenic activity decreased by a half at 40 °C and returned back to the initial value under gradual cooling. Maximum current obtained from the thylakoid-based SC was 0.46 μA, while maximum current generated by the anthocyanin-based SC was 1.75 μA. The goal of this investigation is to find new ways to increase efficiency and stability of bio-based SCs. In future, this measuring system can be used for investigation of solar cells based on long-wave forms of chlorophylls (Chls d and f) and components of the photosynthetic apparatus comprising these chlorophylls.     

Concentration-dependent effects of metronidazole,inhibiting nitrogenase,on hydrogen photoproduction and proton-translocating ATPase activity of Rhodobacter sphaeroides

Rhodobacter sphaeroides MDC6522 is able to produce hydrogen (H₂) during photofermentation. Metronidazole (2-methyl-5-nitroimidazole-1-ethanol) has been shown to affect bacterial growth under anaerobic nitrogen-limited conditions in a concentration-dependent manner (within the range of 0.1–2 mM) by increasing lag phase duration and decreasing growth rate. The addition of metronidazole into the growth medium resulted in a delayed decrease of redox potential (E_h): by the addition of 0.1 mM metronidazole E_h decreased to −590 ± 25 mV, whereas in the presence of 2 mM E_h drop down was to −175 ± 15 mV. H₂ production during R. sphaeroides growth disappeared in the presence of metronidazole. By addition of 0.5 mM metronidazole H₂ yield was ∼8 fold lower in comparison with control; whereas the bacterium was unable to produce H₂ in the presence of 1–2 mM. The effects of metronidazole on nitrogenase-dependent H₂ production by R. sphaeroides might be explained by change of general photosynthetic electron transport with metronidazole as an alternative electron acceptor instead of nitrogenase. ATPase activity of membrane vesicles was determined with and without N,N'-dicyclohexylcarbodiimide (DCCD), an inhibitor of the F₀F₁-ATPase. It was revealed that DCCD-inhibited ATPase activity increased in the presence of metronidazole. It is possible that this effect may be resulted in either by direct affect of metronidazole on the F₀F₁-ATPase, or by its effect on E_h regulating ATPase activity.     

Growth of low temperature silicon nano-structures for electronic and electrical energy generation applications

This paper represents the lowest growth temperature for silicon nano-wires (SiNWs) via a vapour-liquid–solid method, which has ever been reported in the literature. The nano-wires were grown using plasma-enhanced chemical vapour deposition technique at temperatures as low as 150°C using gallium as the catalyst. This study investigates the structure and the size of the grown silicon nano-structure as functions of growth temperature and catalyst layer thickness. Moreover, the choice of the growth temperature determines the thickness of the catalyst layer to be used.The electrical and optical characteristics of the nano-wires were tested by incorporating them in photovoltaic solar cells, two terminal bistable memory devices and Schottky diode. With further optimisation of the growth parameters, SiNWs, grown by our method, have promising future for incorporation into high performance electronic and optical devices.     

Leishmania major pteridine reductase 1 belongs to the short chain dehydrogenase family: stereochemical and kinetic evidence

Pteridine reductase 1 (PTR1) is a novel broad spectrum enzyme of pterin and folate metabolism in the protozoan parasite Leishmania. Overexpression of PTR1 confers methotrexate resistance to these protozoa, arising from the enzyme's ability to reduce dihydrofolate and its relative insensitivity to methotrexate. The kinetic mechanism and stereochemical course for the catalyzed reaction confirm PTR1's membership within the short chain dehydrogenase/reductase (SDR) family. With folate as a substrate, PTR1 catalyzes two rounds of reduction, yielding 5,6,7, 8-tetrahydrofolate and oxidizing 2 equiv of NADPH. Dihydrofolate accumulates transiently during folate reduction and is both a substrate and an inhibitor of PTR1. PTR1 transfers the pro-S hydride of NADPH to carbon 6 on the si face of dihydrofolate, producing the same stereoisomer of THF as does dihydrofolate reductase. Product inhibition and isotope partitioning studies support an ordered ternary complex mechanism, with NADPH binding first and NADP+ dissociating after the reduced pteridine. Identical kinetic mechanisms and NAD(P)H hydride chirality preferences are seen with other SDRs. An observed tritium effect upon V/K for reduction of dihydrofolate arising from isotopic substitution of the transferred hydride was suppressed at a high concentration of dihydrofolate, consistent with a steady-state ordered kinetic mechanism. Interestingly, half of the binary enzyme-NADPH complex appears to be incapable of rapid turnover. Fluorescence quenching results also indicate the existence of a nonproductive binary enzyme-dihydrofolate complex. The nonproductive complexes observed between PTR1 and its substrates are unique among members of the SDR family and may provide leads for developing antileishmanial therapeutics.