Bio-hydrogen production and the F0F1-ATPase activity of Rhodobacter sphaeroides: Effects of various heavy metal ions

Rhodobacter sphaeroides MDC 6521 isolated from Arzni mineral springs in Armenia is able to produce bio-hydrogen (H₂) in anaerobic conditions upon illumination in the presence of various metal ions. The significant aspect in regulation of H₂ production by these bacteria and its energetics is the requirement for F₀F₁-ATPase, the main membrane enzyme responsible for generation of proton motive force under anaerobic conditions. In order to determine the mediatory role of F₀F₁ in H₂ production, the effects of various metal ions (Mn²⁺, Mg²⁺, Fe²⁺, Ni²⁺, and Mo⁶⁺) on N,N′-dicyclohexylcarbodiimide inhibited ATPase activity of R. sphaeroides membrane vesicles were investigated. These ions in appropriate concentrations considerably enhanced H₂ production, which was not observed in the absence of Fe²⁺, indicate the requirement for Fe²⁺. The R. sphaeroides membrane vesicles demonstrated significant ATPase activity. In the absence of Fe²⁺ inhibition (∼80%) of ATPase activity was observed, which was increased by addition of metal ions. A higher ATPase activity was detected in the presence of Fe²⁺ (80 μM) and Mo⁶⁺ (16 μM). These results indicate a relationship between the F₀F₁-ATPase activity and H₂ production that might be a significant pathway to provide novel evidence of a requirement for F₀F₁-ATPase in H₂ production by R. sphaeroides.     

Ni (II) and Mg (II) ions as factors enhancing biohydrogen production by Rhodobacter sphaeroides from mineral springs

Various metal ions play a key role in biohydrogen (H₂) production by phototrophic bacteria through incorporation into or stimulating the responsible enzymes and/or related pathways. The Ni (II) and Mg (II) ions effects on growth and H₂ production by Rhodobacter sphaeroides strain MDC6521 isolated from mineral springs in Armenia were established. The highest growth specific rate was obtained with 4–6 μM Ni²⁺ and 5 mM Mg²⁺. pH of the growth medium changed from 7.0 to 9.2–9.4 during the bacterial growth up to 72 h in spite of Ni²⁺ added but pH increased in different manner with Mg²⁺. In the presence of 2–4 μM Ni²⁺ external oxidation-reduction potential (ORP) decreased to more negative values (−800 ± 15 mV). This decrease of ORP indicated ∼2.7-fold enhanced H₂ yield (9.80 mmol L⁻¹) with Ni²⁺ compared with the control (without Ni²⁺). The H₂ yield determined in the medium with Mg²⁺ was ∼2.2 fold higher than that with 1 mM Mg²⁺. These results reveal new regulatory ways to improve H₂ production by R. sphaeroides those were depending on Ni²⁺ and Mg²⁺ of different concentrations.     

Selecting the parameters of a reactive-power compensator at nonlinear loads

The possibility of improving the parameters of a reactive-power compensator operating in nonsinusoidal modes has been studied by means of supplementary assessment of the design power of the compensator. It is based on the decomposition of the instantaneous power into components in the modes of phase shift of current relative to supply voltage. The temporal distortion of the curve of current is also studied. To date, numerous attempts have been done to generalize the concept of reactive power to nonsinusoidal processes or to introduce other general concepts, but these attempts have not led to the creation of a generally accepted theory that would adequately reflect energetic processes in the general case in the presence of distortions of current and voltage. This paper aims to increase the efficiency of reactive power-compensator equipment for agricultural and industrial consumers operating in nonsinusoidal modes. This is achieved by the use of supplementary computational procedures in the controlling algorithm of a reactive-power compensator. In this case, the transmission-line resistance and internal resistance of the power supply are taken into account.     

Raman spectra and structural perfection of nominally pure lithium niobate crystals

We have studied the Raman spectra of nominally pure lithium niobate single crystals with congruent, near-stoichiometric, and stoichiometric compositions. The stoichiometric crystals have been grown by different procedures: from melts of congruent composition containing K₂O (4.5 and 6 wt %) as an alkaline solvent (flux) and by a conventional procedure from a melt containing a considerable excess of Li₂O (58.6 mol %). The results indicate that the growth procedure has a significant effect on the structural perfection and photorefractive properties of the crystals because it determines the nature and density of structural defects and, hence, the concentration of localized electrons. Stoichiometric crystals grown from a K₂O flux, though less perfect than stoichiometric crystals grown by a conventional procedure, exhibit a reduced photorefractive effect in comparison with both stoichiometric crystals grown with no flux and crystals of congruent composition.     

Relationship between molecular hydrogen production,proton transport and the F0F1-ATPase activity in Rhodobacter sphaeroides strains from mineral springs

This article aims to study hydrogen production and proton transport in two strains of purple non-sulfur bacterium Rhodobacter sphaeroides isolated from mineral springs of Armenia. This bacterium is able to grow and produce molecular hydrogen (H₂) in anaerobic conditions upon illumination. Along with H₂ production, a marked decrease in redox potential and the alkalization of the medium have been observed; the latter might be the evidence of proton influx. H₂ production and alkalization of the medium by whole cells both are suppressed by the F₀F₁-ATPase inhibitors – N,N′-dicyclohexylcarbodiimide (DCCD), sodium azide (NaN₃) and protonophore – carbonyl cyanide m-chlorophenylhydrazone (CCCP). Membrane vesicles of two strains of R. sphaeroides demonstrate ATPase activity, inhibited by DCCD and NaN₃, but not by CCCP. These results indicate a relationship between H₂ production, proton transport and the F₀F₁-ATPase activity that might be a pathway to regulate bacterial activity under anaerobic conditions.     

Complex-radical graft copolymerization of methacrylic acid with vinylic monomers in aqueous medium initiated with the K2S2O8-Na2S2O3 redox system in the presence of Cu2+ ions

Graft copolymerization and block copolymerization of methacrylic acid with vinylic monomers on polycaproamide fiber according to a complex-radical mechanism in the presence of Cu²⁺ ion in aqueous medium was investigated. It was found that the configurational correspondence of the propagation radical and the incorporated molecule of the monomer is the basic condition for the occurrence of graft copolymerization by this mechanism. Hypotheses were advanced concerning the mechanism of graft copolymerization of MAA with AA.     

An interference method for measuring parallelism of miniature optical components

A method for measuring parallelism of transparent optical components with small aperture size is described. It uses a Haidinger-type laser interferometer adapted for the measurement of optical components with millimeter and sub-millimeter aperture size. The method is based on the measurement of the optical thickness variation when the plate under test is translated across a focused laser beam. Measurement results for optical parts with 0.8 mm–10 mm aperture size are presented.