An electrochemical study of the stability of cytochrome c3 from Desulfovibrio desulfuricans Norway strain

The electrochemical behaviour of cytochrome c₃ from Desulfovibrio desulfuricans, Norway strain, remains unchanged within the pH range 5–9.5. Differential pulse polarography peaks disappear at pH < 5 and two transitions are noted at alkaline pH (10.5 and 12). In denaturation experiments, guanidinium chloride has a more marked effect than urea on differential pulse polarography and cyclic voltammetry peaks.The study of absorption spectra shows that the δ band at 351 nm of the oxidized form increases above pH ∼ 10.Neither absorption spectra nor polarograms are modified after the treatment of cytochrome c₃ for 10 min at 100°C.It is concluded that hydrogen bonds must play a prominent role in maintaining the tertiary structure of the protein. Cytochrome c₃ from D. desulfuricans Norway is a particularly stable molecule as regards pH, denaturing agents, temperature and ageing.     

Electrochemical investigations of cytochrome c3 from Desulfovibrio desulfuricans Norway at solid electrodes

Differential pulse and cyclic voltammetry studies with gold and glassy carbon electrodes of tetrahemic cytochrome c₃ from Desulfovibrio desulfuricans Norway show the existence of two well-separated reduction peaks. The four individual redox potentials have been evaluated from calculations on current—potential curves. It appears that hemes behave as four mono-electronic rather fast systems.Results from electrochemical data suggest that hemes are in non-equivalent sites, in agreement with structural data.     

Electrochemical investigations of the interconversions between catalytic and inhibited states of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans

Studies of the catalytic properties of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans by protein film voltammetry, under a H2 atmosphere, reveal and establish a variety of interesting properties not observed or measured quantitatively with other techniques. The catalytic bias (inherent ability to oxidize hydrogen vs reduce protons) is quantified over a wide pH range: the enzyme is proficient at both H2 oxidation (from pH > 6) and H2 production (pH < 6). Hydrogen production is inhibited by H2, but the effect is much smaller than observed for [NiFe]-hydrogenases from Allochromatium vinosum or Desulfovibrio fructosovorans. Under anaerobic conditions and positive potentials, the [FeFe]-hydrogenase is oxidized to an inactive form, inert toward reaction with CO and O2, that rapidly reactivates upon one-electron reduction under 1 bar of H2. The potential dependence of this interconversion shows that the oxidized inactive form exists in two pH-interconvertible states with pK(ox) = 5.9. Studies of the CO-inhibited enzyme under H2 reveals a strong enhancement of the rate of activation by white light at -109 mV (monitoring H2 oxidation) that is absent at low potential (-540 mV, monitoring H+ reduction), thus demonstrating photolability that is dependent upon the oxidation state.     

The electronic structure of the H-cluster in the [FeFe]-hydrogenase from Desulfovibrio desulfuricans: a Q-band 57Fe-ENDOR and HYSCORE study

The active site of the (57)Fe-enriched [FeFe]-hydrogenase (i.e., the "H-cluster") from Desulfovibrio desulfuricans has been examined using advanced pulse EPR methods at X- and Q-band frequencies. For both the active oxidized state (H(ox)) and the CO inhibited form (H(ox)-CO) all six (57)Fe hyperfine couplings were detected. The analysis shows that the apparent spin density extends over the whole H-cluster. The investigations revealed different hyperfine couplings of all six (57)Fe nuclei in the H-cluster of the H(ox)-CO state. Four large 57Fe hyperfine couplings in the range 20-40 MHz were found (using pulse ENDOR and TRIPLE methods) and were assigned to the [4Fe-4S](H) (cubane) subcluster. Two weak (57)Fe hyperfine couplings below 5 MHz were identified using Q-band HYSCORE spectroscopy and were assigned to the [2Fe](H) subcluster. For the H(ox) state only two different 57Fe hyperfine couplings in the range 10-13 MHz were detected using pulse ENDOR. An (57)Fe line broadening analysis of the X-band CW EPR spectrum indicated, however, that all six (57)Fe nuclei in the H-cluster are contributing to the hyperfine pattern. It is concluded that in both states the binuclear subcluster [2Fe](H) assumes a [Fe(I)Fe(II)] redox configuration where the paramagnetic Fe(I) atom is attached to the [4Fe-4S](H) subcluster. The (57)Fe hyperfine interactions of the formally diamagnetic [4Fe-4S](H) are due to an exchange interaction between the two subclusters as has been discussed earlier by Popescu and Münck [Popescu, C.V.; Münck, E., J. Am. Chem. Soc. 1999, 121, 7877-7884]. This exchange coupling is strongly enhanced by binding of the extrinsic CO ligand. Binding of the dihydrogen substrate may induce a similar effect, and it is therefore proposed that the observed modulation of the electronic structure by the changing ligand surrounding plays an important role in the catalytic mechanism of [FeFe]-hydrogenase.     

The influence of electrolyte composition on pH of nickel hydrate formation

The influence of the composition of nickel plating electrolytes containing various ligands (Ac⁻, Gly⁻, and Asp²⁻) on pH of nickel hydrate formation (pH_hydr) was studied. The data obtained were interpreted from the point of view of ionic equilibria in the systems studied. The nature of sparingly soluble precipitates formed in these electrolytes when pH_hydr was reached was determined. Sparingly soluble precipitates were found to be pure Ni(OH)₂ hydroxides or basic salts with the composition Ni(OH) _n Cl_{2 − n} , in which the content of chloride ions increased as the concentration of NiCl₂ grew. Organic substance anions were absent in the precipitates formed and only influenced pH_hydr through changes in the concentration of free nickel ions as a result of complex formation. A principle of selecting the composition of nickel plating electrolytes was suggested on the basis of the results obtained.     

The influence of nickel ions on the buffer capacity of aqueous solutions of glycine

The influence of nickel ions on the buffer properties of solutions of glycine of various concentrations was studied. The trends observed were interpreted in terms of ionic equilibria in the systems under consideration. It was shown that the buffer properties of solutions could be predicted by analyzing the corresponding distribution diagrams.     

Investigation of bio-corrosion in galvanized steel by Desulfovibrio desulfuricans and its mitigation by Butea monosperma leaf extract as green inhibitor

This work is intended to examine the microbially influenced corrosion on galvanized steel (GS) caused by sulfate-reducing bacteria (SRB). The efficacy of Butea monosperma (palash) leaf extract to mitigate the corrosion caused by Desulfovibrio desulfuricans was investigated in modified Barr's medium. Weight loss and electrochemical analysis were performed to check the corrosion rate at regular time intervals. SEM images were performed to understand the level of deterioration of the metal surfaces. Image analysis of the unprotected sample showed the presence of pits. From the gravimetric study, the maximum inhibition efficiency (IE) of 98% was obtained with 500 ppm of Palash leaf extract for the fourth-week sample. With the addition of 500 ppm of palash extract, the sulfide concentration decreases to 0 ppm from 123 ppm. Outcomes of potentiodynamic polarization (PP) studies showed that the extract disturbs the cathodic reaction significantly and moves the corrosion potential to a more negative value and IE was about 71% from PP studies. FTIR and GC-MS analysis was performed to recognize the plausible chemical compounds present in Palash leaf powder. EIS results confirmed that the resistance to corrosion increases substantially with the addition of inhibitor. The mechanism for corrosion inhibition has been proposed based on the results obtained.     

The influence of monovalent cations on the stability of electrochemically formed nickel fluoride films

The stability of electrochemically formed NiF₂ film in 1.0 M perchloric acid containing monovalent fluorides namely, NH₄F, HF, NaF, KF and LiF, is investigated using cyclic voltammetry, chronoamperometry, atomic absorption spectroscopy and scanning electron microscopy. In addition to direct dissolution of nickel and dissolution through the oxide layer, a new mode of dissolution of NiF₂ film as NiF₃ ⁻ and NiF₄ ²⁻ through complex formation is proposed. This process is significantly influenced by the alkali metal fluorides. On a comparative basis the stability of NiF₂ decreases in the order NH₄F > HF > KF > LiF. Received: 29 July 1998 / Accepted: 3 November 1998     

Crystallographic and FTIR spectroscopic evidence of changes in Fe coordination upon reduction of the active site of the Fe-only hydrogenase from Desulfovibrio desulfuricans.

Fe-only hydrogenases, as well as their NiFe counterparts, display unusual intrinsic high-frequency IR bands that have been assigned to CO and CN(-) ligation to iron in their active sites. FTIR experiments performed on the Fe-only hydrogenase from Desulfovibrio desulfuricans indicate that upon reduction of the active oxidized form, there is a major shift of one of these bands that is provoked, most likely, by the change of a CO ligand from a bridging position to a terminal one. Indeed, the crystal structure of the reduced active site of this enzyme shows that the previously bridging CO is now terminally bound to the iron ion that most likely corresponds to the primary hydrogen binding site (Fe2). The CO binding change may result from changes in the coordination sphere of Fe2 or its reduction. Superposition of this reduced active site with the equivalent region of a NiFe hydrogenase shows a remarkable coincidence between the coordination of Fe2 and that of the Fe ion in the NiFe cluster. Both stereochemical and mechanistic considerations suggest that the small organic molecule found at the Fe-only hydrogenase active site and previously modeled as 1,3-propanedithiolate may, in fact, be di-(thiomethyl)-amine.     

亚磷酸酯对新型冷冻机油抗磨性能的影响

本文合成了一系列短链、长链和大分子的亚磷酸酯，用Timken试验机和扫描电镜研究了它们对新型冷冻机油抗磨性能的改进作用。     

The influence of aluminium and aluminium oxide on the effects of mechanical activation of nickel hydroxocarbonate

The chemical and physical processes occurring during the grinding of nickel hydroxocarbonate and mixtures of nickel hydroxocarbonate with aluminium and aluminium oxide were discussed. For mechanical treatment a planetary ball mill was used. The phase analyses of ground products were carried out using thermogravimetry and X-ray diffraction methods. The amount of Ni₂(OH)₂CO₃ undecomposed and Al₂O₃xH₂O, xNiO, Ni⁰, Ni_xAl_y alloys and remained Al⁰ in the systems strongly depends on the proportion of components and on the duration of grinding in a mill which was used in the study. The comparative results are presented.This revised version was published online in November 2005 with corrections to the Cover Date.     

超细非晶镍合金的化学制备及类金属元素对性质的影响

常温下分别使用KBH4和NaH2PO2在水溶液中还原Ni^2^+制得了Ni65B35和Ni89P11超细非晶合金(UFAAP), 同时使用KBH4和NaH2PO2还原Ni^2^+制得了Ni73P13B14UFAAP. Ni-P的粒径较大, 约为110nm, Ni-B的粒径较小, 约为20nm,Ni-P-B的粒径居其之间, 约为40nm。XPS表明, Ni-P间的相互作用强于Ni-B间的相互作用, Ni-P-B中P的电子状态与Ni-P中的相似。Ni-P-B比Ni-P的比表面积高得多,Ni-P-B比Ni-B和Ni-P具有更好的非晶态稳定性, 在573K热处理, 它的非晶态保持完好。晶化结果也表明Ni-P-B中Ni-P间的相互作用比Ni-B间的强。     

The influence of a high-frequency electromagnetic field on the adsorption ability of ionogenic surface-active substances

The influence of a high-frequency electromagnetic field on the adsorption characteristics of micelle-forming surface-active compounds (surfactants) at the solution-air boundary was studied. It was shown that not only the volume but also surface properties of surfactants could change under the action of a high-frequency electromagnetic field on their solutions.     

The influence of the nature of background anions on the buffer capacity of glycine-containing electrolytes for nickel electroplating

The buffer properties of acetate, sulfate, and chloride glycine-containing electrolytes for nickel electroplating were studied. Various forms of the amino acid and background anions were shown to act in solution as two buffer systems related by competitive complex formation. The buffer capacity of a solution was then the result of the joint action of these systems. The contribution of each of them was determined by its absolute concentration in solution on the one hand and changes in this concentration caused by the addition of H⁺ or OH^? ions on the other.     

The influence of a water-acetone solvent on the stability of nickel(II) complexes with glycylglycine

The stability constants of nickel(II) complexes with glycylglycine in water-acetone mixtures (mole fraction of acetone X = 0–0.40) were determined by potentiometric titration at 298 K and an ionic strength of 0.1 M (NaClO₄). With an increase in the content of the organic cosolvent, nickel(II) glycylglycinates become more stable, mainly because of the better coordination of the ligand through the carboxy group.     

The influence of ionic strength, nutrients and pH on bacterial adhesion to metals

Bacteria-metal interactions in aqueous solutions are important in biofilm formation, biofouling and biocorrosion problems in the natural environment and engineered systems. In this study, the adhesion forces of two anaerobes (Desulfovibrio desulfuricans and Desulfovibrio singaporenus) and an aerobe (Pseudomonas sp.) to stainless steel 316 in various aqueous systems were quantified using atomic force microscopy (AFM) with a cell probe. Results show that the nutrient and ionic strength of the solutions influence the bacteria-metal interactions. The bacteria-metal adhesion force was reduced in the presence of the nutrients in the solution, because a trace organic film was formed and thus decreased the metal surface wettability. Stronger ionic strength in the solution results in a larger bacteria-metal adhesion force, which is due to the stronger electrostatic attraction force between the positively charged metal surface and negatively charged bacterial surface. Solution pH also influences the interaction between the bacterial cells and the metal surface; the bacteria-metal adhesion force reached its highest value when the pH of the solution was near the isoelectric point of the bacteria, i.e. at the zero point charge. The adhesion forces at pH 9 were higher than at pH 7 due to the increase in the attraction between Fe ions and negative carboxylate groups.