The influence of sunlight on the localized corrosion of UNS S31600 in natural seawater

Tests were conducted on the performance of UNS S31600 stainless steel (SS) in a natural day/night cycle vs full darkness under conditions of natural marine biofilm accumulation. In quiescent flowing seawater tests in the laboratory as well as under natural immersion in the sea, diffuse sunlight (～10% of natural) counteracted the influence of marine biofilms and produced substantial inhibition of the corrosion of SS. Thus, the probabilities (percentage attack) and propagation rates (depths of attack) in multiple crevice tests were substantially lower in the day/night cycle than in the dark. A benefit was also observed for welded SS in terms of the time to corrosion initiation and the mass loss. SS in the passive state showed broader passive regions, well-defined breakdown potentials and markedly smaller anodic and cathodic current densities under the diurnal cycle. The overall reduction in corrosion is attributed to a combination of electrochemical photoinhibition and simultaneous photoinactivation of microbially mediated metal redox reactions linked to cathodic kinetics. These data offer fresh insights into the behaviour of SS under practical seawater situations and the proposed potential use of illumination in the mitigation of biologically influenced consequences.     

Oxygen and pH microprofiles above corroding mild steel covered with a biofilm

O₂ and pH microprofiles were measured above corroding mild steel covered with a biofilm. The pH in the anodic areas (tubercles) ranged from 5 to 7 and was always 9.45 at the surface of the cathodic areas. After 1 month of biofilm development, O₂ was depleted at the anodic area but could reach the cathodic surface where it was reduced. Consequently, differential O₂ concentration cells were the driving force for corrosion. The O₂ microprofiles indicated that O₂ was consumed in the tubercles, probably by microbial activity, while O₂ was reduced electrochemically in the cathodic areas. It was concluded that O₂ transfer to the cathodic surface was the rate limiting step for the corrosion process.     

The role of bacteria in pit propagation of carbon steel

Pit propagation in carbon steel exposed to a phosphate-containing electrolyte required either stagnant conditions or microbial colonization of anodic regions. A scanning vibrating electrode (SVE) was used to resolve formation and inactivation of anodic and cathodic sites on carbon steel. In sterile, continuously aerated medium, pits initiated and repassivated, while in the absence of aeration, pits initiated and propagated. Pit propagation was also observed in continuously aerated medium inoculated with a heterotrophic bacterium, originally isolated from a corrosion tubercle formed on a steel pipe in a fresh water environment. Autoradiography of bacteria following uptake of (14)C-acetate into cellular material in combination with SVE analysis demonstrated that sites of anodic activity coincided with sites of bacterial activity. Prelabeled bacteria also preferentially attached to corrosion products over the anodic sites. Confocal laser scanning microscopy demonstrated that attraction to anodic sites did not depend on bacterial viability and was not specific for iron as a substratum. The results suggest that bacteria may preferentially attach to the corrosion products formed over corrosion pits. The biofilms over these anodic sites may create stagnant conditions within corrosion pits that result in pit propagation.     

The influence of sunlight on the localized corrosion of UNS S31600 in natural seawater

Tests were conducted on the performance of UNS S31600 stainless steel (SS) in a natural day/night cycle vs full darkness under conditions of natural marine biofilm accumulation. In quiescent flowing seawater tests in the laboratory as well as under natural immersion in the sea, diffuse sunlight (～10% of natural) counteracted the influence of marine biofilms and produced substantial inhibition of the corrosion of SS. Thus, the probabilities (percentage attack) and propagation rates (depths of attack) in multiple crevice tests were substantially lower in the day/night cycle than in the dark. A benefit was also observed for welded SS in terms of the time to corrosion initiation and the mass loss. SS in the passive state showed broader passive regions, well-defined breakdown potentials and markedly smaller anodic and cathodic current densities under the diurnal cycle. The overall reduction in corrosion is attributed to a combination of electrochemical photoinhibition and simultaneous photoinactivation of microbially mediated metal redox reactions linked to cathodic kinetics. These data offer fresh insights into the behaviour of SS under practical seawater situations and the proposed potential use of illumination in the mitigation of biologically influenced consequences.     

Reaction of nucleic acid bases with the mercury electrode: Determination of purine derivatives at submicromolar concentrations by means of cathodic stripping voltammetry

It was found that adenine, guanine, hypoxanthine, 8-hydroxyadenine, and a number of further purine derivatives react in alkaline media with mercury of the electrode charged to potentials close to zero V (against the saturated calomel electrode) and form sparingly soluble compounds. Formation of these compounds with mercury is manifested on the polarographic (voltammetric) curves by characteristic anodic waves (peaks) which can be exploited for analytical purposes. Differential pulse polarography renders it possible to determine bases at concentrations of 10^?5–10^?6m. Substantially higher sensitivity can be reached by cathodic stripping voltammetry (CSV). This method is based on a slow accumulation of the sparingly soluble compound at the electrode surface and its subsequent rapid cathodic stripping. A number of purine derivatives can be determined by CSV at concentrations as low as 10^?8m (the limit of adenine detection is about 2 × 10^?9m). As compared with sulphur-containing substances CSV analysis of the purine derivatives is limited to a narrower range of deposition potentials. It was shown that the presence of an excess of proteins or DNA does not interfere with determination of purine bases.     

Electrochemical reactions of horse heart cytochrome c at graphite electrodes

The interaction of cytochrome c with a paraffin-wax-impregnated spectroscopic graphite electrode (WISGE) was studied in a medium consisting of 0.1 M potassium phosphate, pH 7.0, by means of differential pulse and cyclic voltammetry. Ferricytochrome c yields on voltammograms a single cathodic peak C around a potential of -0.3 V (vs. Ag/AgCl) and two anodic peaks AI and AII around the potentials of 0.66 and 0.89 V, respectively. Cathodic peak C corresponds to a catalytic reaction during which ferricytochrome c is reduced to ferrocytochrome c: ferricytochrome c is then regenerated by chemical oxidation of ferrocytochrome c by oxygen adsorbed at the WISGE surface. The first, more negative anodic peak AI corresponds to anodic electrochemical oxidation of tyrosine residues, whereas the second, more positive anodic peak (peak AII) corresponds to an anodic reaction of haemin. Voltammetry at a WISGE may provide a valuable technique for obtaining data about cytochrome c properties on electrically charged surface.     

The steady-state distribution of gating charge in crayfish giant axons.

Progressive shifts of holding potential (Vh) in crayfish giant axons, from -140 to -70 mV, reduce gating currents seen in depolarizing steps (to 0 mV test potential) while proportionately increasing gating currents in hyperpolarizing steps (to -240 mV). The resulting sigmoid equilibrium charge distribution (Q-Vh curve) shows an effective valence of 1.9e and a midpoint of -100 mV. By contrast, Q-V curves obtained using hyperpolarizing and/or depolarizing steps from a single holding potential, change their "shape" depending on the chosen holding potential. For holding potentials at the negative end of the Q-Vh distribution (e.g., -140 mV), negligible charge moves in hyperpolarizing pulses and the Q-V curve can be characterized entirely from depolarizing voltage steps. The slope of the resulting simple sigmoid Q-V curve also indicates an effective valence of 1.9e. When the axon is held at less negative potentials significant charge moves in hyperpolarizing voltage steps. The component of the Q-V curve collected using hyperpolarizing pulses shows a significantly reduced slope (approximately 0.75e) by comparison with the 1.9e slope found using depolarizing pulses or from the Q-Vh curve. As holding potential is shifted in the depolarizing direction along the Q-Vh curve, an increasing fraction of total charge movement must be assessed in hyperpolarizing voltage steps. Thus charge moving in the low slope component of the Q-V curve increases as holding potential is depolarized, while charge moving with high apparent valence decreases proportionately. Additional results, together with simulations based on a simple kinetic model, suggest that the reduced apparent valence of the low slope component of the Q-V curve results from gating charge immobilization occurring at holding potential. Immobilization selectively retards that fraction of total charge moving in hyperpolarizing pulses. Misleading conclusions, as to the number and valence of the gating particles, may therefore be derived from Q-V curves obtained by other than depolarizing pulses from negative saturated holding potentials.     

Blockade of sodium channels by Bistramide A in voltage-clamped frog skeletal muscle fibres.

The effect of Bistramide A, a toxin isolated from Bistratum lissoclinum Sluiter (Urochordata), on the peak sodium current (INa) of frog skeletal muscle fibres was studied with the double sucrose gap voltage clamp technique. External or internal application of Bistramide A inhibited INa without alteration of the kinetic parameters of the current nor of the apparent reversal potential for Na. The steady-state activation curve of INa was unchanged while the steady-state inactivation curve of INa was shifted towards more negative membrane potentials. Dose-response curves indicated an apparent dissociation constant for Bistramide A of 3.3 microM and a Hill coefficient of 1.2 which suggested a one to one relation between the toxin and Na channel. The inhibition of INa occurred at rest, and was more important at more positive holding potentials. Bistramide A exhibited only a weak frequency-dependent effect. The toxin did not interact with the use-dependent effect of lidocaine. It mainly blocked Na channels at more depolarized holding potentials. The toxin blocked Na channels when it was internally applyed and when the inactivation gating system has been previously destroyed by internal diffusion of iodate. The data suggest that Bistramide A inhibited the Na channel both at rest and in the inactivated state and occupied a site which was not located on the inactivation gate.     

Local Treatment of Murine Tumors by Electric Direct Current

Low-level direct current (0.2–1.8 mA) was demonstrated to be an antitumor agent on two different murine tumor models (fibrosarcoma Sa-1 and melanoma B-16), and has been suggested for regional cancer treatment. Its antitumor effect was achieved by introduction of single or multiple–array needle electrodes (Pt-Ir alloy) in the tumor and (an)other electrode(s) subcutaneously in its vicinity. The electrode inserted in the tumor was made anodic (anodic electrotherapy, ET) or cathodic (cathodic ET). In control groups, animals were subjected to exactly the same procedures with needle electrodes inserted at usual sites without current. In single-stimulus ET performed after the tumors have reached approximately 50 mm3 in volume with 0.2, 0.6, and 1.O mA for 30, 60, and 90 min, cathodic ET exhibited better antitumor effect than anodic ET. In both cases and at all ET durations, the antitumor effect depended proportionally on the current level applied. The antitumor effect was evaluated by following tumor growth and by microscopic estimation of the necrotization of the tumor area immediately after ET, and 24, 48, and 72 h posttreatment.

Necrotization produced by cathodic ET was observed to be immediate and extensive whereas anodic ET resulted in increased necrotization only at 24 h posttreatment. In both cases the extent of necrosis was significantly higher than in control and was centrally located (site of electrode), whereas in controls it was sporadic, distributed randomly over the whole tumor area. When current was delivered via multiple–array electrode ET, the antitumor effect was slightly better in cathodic ET compared to single-electrode ET. Employing cathodic multiple-array electrode ET and using higher currents, i.e., 1.0, 1.4, and 1.8 mA in melanoma B-16, 20% and 40% cures were achieved by 1.4 and 1.8 mA single-shot ET of 1 h duration, respectively, whereas in fibrosarcoma Sa-1 no cures were accomplished. In general, different susceptibility of the two tumor models to ET was noticeable. Comparing tumor growth and necrotization after the application of direct current (0.6 mA) and alternating current (0.0 mA mean, 0.6 mA RMS), it appeared that alternating current had no impact either on necrotization of tumor tissue or on tumor growth. ET was performed on normal tissues as well. In subcutaneous tissue, thigh muscle, and liver of healthy mice immediately after 1 h of treatment using 0.6 mA in both cathodic and anodic modes, local necrotization at the site of electrode insertion was evident, with signs of acute inflammation in the vicinity. In anodic ET, vacuolization around the electrode was noticed.     

The haemoglobin system of the mudfish, Labeo capensis: adaptations to temperature and hypoxia

The effect of temperature and hypoxic acclimation on the haemoglobin system and intraerythrocytic organic phosphate concentrations in the South African mudfish, Labeo capensis, have been investigated. Exposure to hypoxia or increased temperature raised haemoglobin concentration and decreased NTP/Hb ratio. Temperature acclimation did not effect the oxygenation characteristics of the haemolysate or haemoglobin multiplicity, as evident from isoelectric focussing experiments that showed one cathodic (Hb I) and three anodic haemoglobins (Hb II, III and IV). Oxygen equilibria of the isolated components showed a smaller Bohr effect and lower temperature and organic phosphate sensitivities in the cathodic than in the anodic haemoglobins. Unlike the trout and eel haemoglobin systems, both the anodic and cathodic haemoglobins from L. capensis exhibited sensitivity to organic phosphates but the effect was smaller in the latter. The results indicate that oxygen transport in mudfish blood is supported by variations in the red cell organic phosphate\haemoglobin ratio and the functional differentiation between anodic and cathodic haemoglobins.     

Schistosoma japonicum: immunological characterization and detection of circulating polysaccharide antigens from adult worms

The antigenic constituents of a trichloroacetic acid (TCA)-soluble fraction of adult Schistosoma japonicum were studied with immunoelectrophoresis, and compared with those of Schistosoma mansoni. Eight TCA-soluble antigens of S. japonicum were demonstrated, five of which showed immunological identity with S. mansoni antigens. Of the eight antigens, five antigens with anodic motility were found as circulating antigens in S. japonicum-infected hamster and rabbit sera; the major circulating antigen was the circulating anodic antigen (CAA). Two other antigens, with cathodic motility, including the circulating cathodic antigen (CCA), were demonstrable as circulating antigens in S. mansoni infections, but not in S. japonicum infections. Most of the circulating antigens were shown to be gut-associated. Only one antigen, line 2, which was not demonstrable as circulating antigen and which was present in the parenchyma of the worms, was found to be specific for S. japonicum. Using an ELISA for the detection of CAA in the sera of S. japonicum-infected rabbits, a lower detection level of 100 ng CAA/ml serum was achieved. Moreover, at 7-8 weeks after infection, a direct relationship between worm burden and CAA level was demonstrated.     

The Relation of Water Absorption by Wheat Seeds to Water Potential

The progress of water absorption by wheat grains was studiedby supplying water in the vapour phase, at controlled potentials. At a potential of –250 metres of water, the curve forwater uptake against time shows exponential approach to equilibriummoisture content. Living and dead seeds behave similarly untilgermination effects are apparent. Water uptake in the earlystages is probably due to physical rather than physiologicalprocesses. When germination occurs, it causes an exponentialincrease in the rate of water uptake. At higher potentials, up to zero, the uptake curves for deadseeds depart from the simple exponential relationship; in additionto the exponential component, there is a component the rateof which increases with time to a constant rate. The first componentmay represent the physical process of imbibition by the starch,and the second the initiation and progress of starch hydrolysis. A parameter a of the formula derived for the curves is interpretedas representing the diffusivity of water vapour in the seedmaterial, depending upon the physical properties and dimensionsof the seed.     

Effect of W–TiO2 composite to control microbiologically influenced corrosion on galvanized steel

Microorganisms tend to colonize on solid metal/alloy surface in natural environment leading to loss of utility. Microbiologically influenced corrosion or biocorrosion usually increases the corrosion rate of steel articles due to the presence of bacteria that accelerates the anodic and/or cathodic corrosion reaction rate without any significant change in the corrosion mechanism. An attempt was made in the present study to protect hot-dip galvanized steel from such attack of biocorrosion by means of chemically modifying the zinc coating. W–TiO₂ composite was synthesized and incorporated into the zinc bath during the hot-dipping process. The surface morphology and elemental composition of the hot-dip galvanized coupons were analyzed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The antifouling characteristics of the coatings were analyzed in three different solutions including distilled water, seawater, and seawater containing biofilm scrapings under immersed conditions. Apart from electrochemical studies, the biocidal effect of the composite was evaluated by analyzing the extent of bacterial growth due to the presence and absence of the composite based on the analysis of total extracellular polymeric substance and total biomass using microtiter plate assay. The biofilm-forming bacteria formed on the surface of the coatings was cultured on Zobell Marine Agar plates and studied. The composite was found to be effective in controlling the growth of bacteria and formation of biofilm thereafter.     

Effects of direct electric current on Herpetomonas samuelpessoai: An ultrastructural study

The literature shows that the effects of direct electric currents on biological material are numerous, including bactericidal, fungicidal, parasiticidal, and anti‐tumoral, among others. Non‐pathogenic trypanosomatids, such as Herpetomonas samuelpessoai, have emerged as important models for the study of basic biological processes performed by a eukaryotic cell. The present study reports a dose‐dependent anti‐protozoan effect of direct electric treatment with both cathodic and anodic current flows on H. samuelpessoai cells. The damaging effects can be attributable to the electrolysis products generated during electric stimulation. The pH of the cell suspension was progressively augmented from 7.4 to 10.5 after the cathodic treatment. In contrast, the anodic treatment caused a pH decrease varying from 7.4 to 6.5. Transmission electron microscopy analyses revealed profound alterations in vital cellular structures (e.g., mitochondrion, kinetoplast, flagellum, flagellar pocket, nucleus, and plasma membrane) after exposure to both cathodic and anodic current flows. Specifically, cathodic current flow treatment induced the appearance of autophagic‐like structures on parasite cells, while those submitted to an anodic current flow presented marked disorganization of plasma membrane and necrotic appearance. However, parasites treated in the intermediary chamber (without contact with the electrodes) did not present significant changes in viability or morphology, and no pH variation was detected in this system. The use of H. samuelpessoai as a biological model and the direct electric current experimental approach used in our study provide important information for understanding the mechanisms involved in the cytotoxic effects of this physical agent. Bioelectromagnetics 33:334–345, 2012. © 2011 Wiley Periodicals, Inc.     

Increase in the effectiveness of microbial absorption on activated charcoal upon sorbent polarization

The effect of Staphylococcus albus and the contact time on hydrolytic adsorption of ions on activated charcoal SKN-2K in the physiological solution (0.9% NaCl) was investigated. Experiments were performed without polarization or with cathodic and anodic polarization of the adsorbent. The adsorbed microorganisms decreased the rate of electrolyte ion adsorption, especially in case of cathodic polarization. When activate charcoal was at negative potential (-0.2 V), up to 95% of active microorganisms was adsorbed at the initial concentration of 5.75.10(6) microorganisms per ml, while in case of anodic polarization only 43-44% of microorganisms was adsorbed.     

The hemoglobin system of the serpent eel Ophisurus serpens: structural and functional characterization

The hemoglobin system of the serpent eel Ophisurus serpens was structurally and functionally characterized with the aim of comparing it to the hemoglobin system of other fish species, as oxygen loading under the severe habitat conditions experienced by O. serpens could have necessitated specific adaptation mechanisms during evolution. The hemoglobin system of O. serpens includes one cathodic and four anodic components. The molecular mass of the α and β chains of the cathodic component as well as the 2 α and 4 β of the anodic components were determined. Analysis of the intact α and β chains from cathodic hemoglobin and their proteolytic digestion products by high-resolution MS and MS/MS experiments resulted in 92 and 95 % sequence coverage of the α and β globins, respectively. The oxygen binding properties of both hemoglobin components were analyzed with respect to their interactions with their physiological effectors. Stripped cathodic hemoglobin displayed the highest oxygen affinity among Anguilliformes with no significant effect of pH on O₂-affinity. In the presence of both chloride and organic phosphates, O₂-affinity was strongly reduced, and cooperativity was enhanced; moreover, cathodic hemoglobin contains two indistinguishable GTP-binding sites. Stripped anodic hemoglobins exhibited both low O₂-affinity and low cooperativity and a larger Bohr effect than cathodic hemoglobin. The cathodic hemoglobin of O. serpens and the corresponding component of Conger conger share the greatest structural and functional similarity among hemoglobin systems of Anguilliformes studied to date, consistent with their phylogenetic relationship.     

Effect of electric currents on bacterial detachment and inactivation

Since biofilms show strong resistance to conventional disinfectants and antimicrobials, control of initial bacterial adhesion is generally accepted as one of the most effective strategies for preventing biofilm formation. Although electrical methods have been widely studied, the specific properties of cathodic, anodic, and block currents that influence the bacterial detachment and inactivation remained largely unclear. This study investigated the specific role of electric currents in the detachment and inactivation of bacteria adhered to an electrode surface. A real-time bacterial adhesion observation and control system was employed that consisted of Pseudomonas aeruginosa PAO1 (PAO1) with green fluorescent protein as the indicator microorganism and a flow cell reactor mounted on a fluorescent microscope. The results suggest that the bacteria that remained on the electrode surface after application of a cathodic current were alive, although the extent of detachment was significant. In contrast, when an anodic current was applied, the bacteria that remained on the surface became inactive with time, although bacterial detachment was not significant. Further, under these conditions, active bacterial motions were observed, which weakened the binding between the electrode surface and bacteria. This phenomenon of bacterial motion on the surface can be used to maximize bacterial detachment by manipulation of the shear rate. These findings specific for each application of a cathodic or anodic electric current could successfully explain the effectiveness of block current application in controlling bacterial adhesion.     

Electrochemical investigation of the effect of some organic phosphates on haemoglobin

The effects of DPG, IHP, GTP, GDP and GMP on the structure and stability of haemoglobin were electrochemically investigated with an iodide-modified silver electrode in 0.01 M KNO₃ at pH 7.0. Anodic and cathodic peaks of haemoglobin were observed at 250 mV and 12 mV with a formal potential value of 133 mV vs. Ag/AgCl. The effects of different concentrations of DPG, IHP, GTP, GDP and GMP on the anaerobic redox reaction were determined. The results showed that DPG and IHP can lead to a positive shift in the reduction peak of haemoglobin, indicating that the oxidation peak shift of haemoglobin was small as a result of stabilization of the reduced state and destabilization of the R-like state of haemoglobin. GTP elicited a more positive shift in the cathodic and anodic peaks of haemoglobin at a higher concentration, signifying that it has a low-affinity binding site on haemoglobin. The positive shift of the cathodic and anodic peaks revealed a slight variation in the structure and indicated the unfolding of haemoglobin in the presence of high concentrations of GTP. Our study also showed that GDP and GMP did not cause significant shift the cathodic and anodic peaks of haemoglobin even at high concentrations, refuting the existence of specific GDP-and GMP-binding sites on the protein. Moreover, the iodide-modified silver electrode method proved to be easy and useful in investigating the effects of ligands or other effectors on haemoglobin in solution.     

Allosteric water and phosphate effects in Hoplosternum littorale hemoglobins.

This paper reports the results obtained using the osmotic stress method applied to the purified cathodic and anodic hemoglobins (Hbs) from the catfish Hoplosternum littorale, a species that displays facultative accessorial air oxygenation. We demonstrate that water potential affects the oxygen affinity of H. littorale Hbs in the presence of an inert solute (sucrose). Oxygen affinity increases when water activity increases, indicating that water molecules stabilize the high-affinity state of the Hb. This effect is the same as that observed in tetrameric vertebrate Hbs. We show that both anodic and cathodic Hbs show conformational substrates similar to other vertebrate Hbs. For both Hbs, addition of anionic effectors, especially chloride, strongly increases the number of water molecules bound, although anodic Hb did not exhibit sensitivity to saturating levels of ATP. Accordingly, for both Hbs, we propose that the deoxy conformations coexist in at least two anion-dependent allosteric states, T(o) and T(x), as occurs for human Hb. We found a single phosphate binding site for the cathodic Hb.     

A Graphic Comparison Between the Current-Voltage Curves of an Electrochemical Generator and Living Unstressed Rabbit Tibia

Unstressed living bone exhibits bioelectric potential differences along its surface. This electrogenic behavior has been characterized by a V=f(l) curve which is linear up to a certain limit. To better understand the origin and meaning of these potentials and to better describe this electrogenic behavior an electrochemical generator (a silver-oxide cell) was included, instead of bone, into the same measurement situation used to describe the V=f(I) curve of the rabbit tibia. The V=f(I) curve of the cell was graphically compared with the V=f(I) curve of the living unstressed rabbit tibia: the two curves were superimposable. This suggests that an electrochemical mechanism may be at the origin of the bioelectric potentials in unstressed living bone.