mV pH Research Articles

Immobilization of hemoglobin on electrodeposited cobalt-oxide nanoparticles: Direct voltammetry and electrocatalytic activity

Cyclic voltammetry at potential range − 1.1 to 0.5 V from aqueous buffer solution (pH 7) containing CoCl 2 produced a well defined cobalt oxide (CoOx) nanoparticles deposited on the surface of glassy carbon electrode. The morphology of the modified surface and cobalt oxide formation was examined with SEM and cyclic voltammetry techniques. Hemoglobin (Hb) was successfully immobilized in cobalt-oxide nanoparticles modified glassy carbon electrode. Immobilization of hemoglobin onto cobalt oxide nanoparticles have been investigated by cyclic voltammetry and UV–visible spectroscopy. The entrapped protein can take direct electron transfer in cobalt-oxide film. A pair of well defined, quasi-reversible cyclic voltammetric peaks at about − 0.08 V vs. SCE (pH 7), characteristic of heme redox couple (Fe(III)/Fe(II)) of hemoglobin, and the response showed surface controlled electrode process. The dependence of formal potential ( E 0′) on the solution pH (56 mV pH − 1 ) indicated that the direct electron transfer reaction of hemoglobin was a one-electron transfer coupled with a one proton transfer reaction process. The average surface coverage of Hb immobilized on the cobalt oxide nanoparticles was about 5.2536 × 10 − 11 mol cm − 2 , indicating high loading ability of nanoparticles for hemoglobin entrapment. The heterogeneous electron transfer rate constant ( k s) was 1.43 s − 1 , indicating great of facilitation of the electron transfer between Hb and electrodeposited cobalt oxide nanoparticles. Modified electrode exhibits a remarkable electrocatalytic activity for the reduction of hydrogen peroxide and oxygen. The Michaels–Menten constant K m of 0.38 mM, indicating that the Hb immobilized onto cobalt oxide film retained its peroxidases activity. The biosensor exhibited a fast amperometric response < 5 s, a linear response over a wide concentration range 5 μM to 700 μM and a low detection limit 0.5 μM. According to the direct electron transfer property and enhanced activity of Hb in cobalt oxide film, a third generation reagentless biosensor without using any electron transfer mediator or specific reagent can be constructed for determination of hydrogen peroxide in anaerobic solutions.

PH Sensitivity of Gallium Arsenide (GaAs) Electrodes Functionalized with Methyl−mercaptobiphenyl Monolayers

GaAs electrodes coated with hydrophobic, methyl−mercaptobiphenyl (CH3−MBP) monolayers exhibited an excellent electrochemical stability. We found that the interface resistance of the chemically functionalized GaAs shows linear relationships with electrolyte pH and bias potential in a reproducible manner. The impedance spectra measured in a wide frequency range ( f = 100 kHz to 50 mHz) are analyzed with several equivalent circuit models in a quantitative manner, and the pH sensitivity extrapolated from two linear relationships (35 mV pH-1) can be attributed to the absorption of the OH- ions on the hydrophobic surface.

Preparation and characteristics of ruthenium dioxide for pH array sensors with real-time measurement system

Abstract Ruthenium oxide (RuO2) thin film was used as the sensing layer of hydrogen ion selective electrodes (ISE) for pH array sensors. The RuO2 sensing membrane was deposited onto a silicon wafer substrate using radio frequency sputtering technology. We measured the IDS–VG curves of the RuO2 sensing membranes connected to a MOSFET with conducting wire and immersed in the pH buffer solutions at different pH concentrations using a Keithley 236 Instrument. The results obtained the pH sensitivity of the RuO2 sensing membrane for the ISE devices at about 55.64 mV/pH. From the nonideal characteristic experimental results, the drift rate of the RuO2 ISE device was obtained at 0.38 mV/h at pH 7. The hysteretic widths of the RuO2 ISE device were 4.36 mV and 2.2 mV in pH 7–4–7–10–7 and pH 7–10–7–4–7 loop cycles, respectively. The RuO2 ISE was used for the pH array sensors structure to reduce the measurement error and testing time for four single sensors. And the reproducibility, stability, selectivity and response time of RuO2 array sensors were investigated. A real-time measurement system for pH array sensors was achieved. The system has the following advantages: portable USB DAQ card, easy to setup and use, with an application program development by the Visual Basic software, which is easily used in other computers.

Simulation and experimental characterization of plug distortion in hybrid microchannels

The plug distortion for on-chip capillary zone electrophoresis systems with rectangular separation channels, manufactured in a hybrid layer system with different material properties of the vertical and the horizontal walls has been examined. Experimental data and simulation results indicate that plug widening caused by different values of the ζ-potential of the walls in contact with the fluid depends strongly on the aspect ratio of the channel cross section. If the height to width ratio is much greater or much smaller than 1, as is often the case for commonly used labchip architectures, plug widening may be negligible. The difference of the ζ-potentials between the vertical and the horizontal sidewalls has been determined from the shape of the plug edges. For an architecture using glass for the top and bottom walls, but SU-8 for the sidewalls, the difference of the ζ-potentials was measured to be on the order of only 2.4 mV for a pH of 9.2, suggesting that such device architectures may be used for on-chip electrophoresis analysis without uniform coating of the channel inside for less-demanding applications.

Electrochemistry and Electrocatalysis of a Nafion/Nano‐CaCO3/Hb Film Modified Carbon Ionic Liquid Electrode Using BMIMPF6 as Binder

AbstractIn this paper a room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF6) was used as binder for the construction of carbon ionic liquid electrode (CILE) and a new electrochemical biosensor was developed for determination of H2O2 by immobilization of hemoglobin (Hb) in the composite film of Nafion/nano‐CaCO3 on the surface of CILE. The Hb modified electrode showed a pair of well‐defined, quasi‐reversible redox peaks with Epa and Epc as −0.265 V and −0.470 V (vs. SCE). The formal potential (E°′) was got by the midpoint of Epa and Epc as −0.368 V, which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The peak to peak separation was 205 mV in pH 7.0 Britton–Robinson (B–R) buffer solution at the scan rate of 100 mV/s. The direct electrochemistry of Hb in the film was carefully investigated and the electrochemical parameters of Hb on the modified electrode were calculated as α=0.487 and ks=0.128 s−1. The Nafion/nano‐CaCO3/Hb film electrode showed good electrocatalysis to the reduction of H2O2 in the linear range from 8.0 to 240.0 μmol/L and the detection limit as 5.0 μmol/L (3σ). The apparent Michaelis–Menten constant (KMapp) was estimated to be 65.7 μmol/L. UV‐vis absorption spectroscopy and FT‐IR spectroscopy showed that Hb in the Nafion/nano‐CaCO3 composite film could retain its native structure.

Silicate HinderingIn SituFormed Ferric Hydroxide Precipitation: Inhibiting Arsenic Removal from Water

The effects and dominant mechanism of silicate hindering arsenic removal with in situ formed ferric hydroxides were investigated. Zeta potential analysis showed that 10 mg/L silicate as Si obviously decreased ζ potential from −11.9 mV (pH 8.61) to −29.9 mV (pH 8.84) for ferric hydroxides; more significant effects was observed at higher pH levels. Photometric dispersion analysis indicated that silicate apparently hindered ferric hydroxides precipitation and aggregation, with more apparent influence at elevated pH values. Furthermore, in high pH ranges silicate led to filtered iron concentration increase. These adverse effects resulted in a significant decrease of arsenic removal with in situ formed ferric hydroxides, especially in higher pH ranges. Sequential filtration analysis showed the presence of aqueous arsenic species in liquid phase, demonstrating that silicate increasing repulsive charges between ferric precipitates and decreasing surface sites available for arsenic, rather than contributing to the formation of tiny ferric colloids with adsorbed arsenic, was more significant in silicate hindering arsenic removal by ferric hydroxides.

Carbon nanotube-modified electrodes for electrochemical DNA-sensors

Glassy-carbon electrodes (GCEs) are modified with preoxidized multiwalled carbon nanotubes (CNTs). According to the data of atomic force microscopy, the layers of CNTs on GCEs possess a homogeneous nanostructurized surface. The voltammetric properties of a GCE/CNT depend on the modifier load. Guanine and deoxyguanosine monophosphate are strongly adsorbed on GCE/CNT and oxidized at +690 and +930 mV (pH 7.0), respectively. The oxidation current of guanine DNA nucleotides adsorbed on a GCE/CNT is significantly higher for the thermally denaturated biopolymer than for the native one. Our results are of interest for the development of sensors based on the electrochemical properties of nucleic acids.

Studies on direct electron transfer and biocatalytic properties of hemoglobin in polyacrylonitrile matrix

The direct electrochemistry of hemoglobin (Hb) immobilized in polyacrylonitrile (PAN) modified glassy carbon electrode was described. The protein-PAN film exhibited a pair of well-defined and quasi-reversible cyclic voltammetric peaks for Hb Fe(III)/Fe(II) redox couple in a pH 7.0 phosphate buffer. The formal potential of Hb heme Fe(III)/Fe(II) couple varied linearly with the increase of pH in the range of 5.0–9.0 with a slope of 54 mV pH − 1 , which implied that a proton transfer was accompanied with each electron transfer in the electrochemical reaction. Position of Soret absorption band of Hb-PAN film suggested that the Hb kept its secondary structure similar to its native state in the PAN matrix. The Hb in PAN matrix acted as a biologic catalyst to catalyze the reduction of hydrogen peroxide. The electrocatalytic response showed a linear dependence on the H 2O 2 concentration ranging from 8.3 × 10 − 6 to 5 × 10 − 4 mol L − 1 with a detection limit of 8.3 × 10 − 6 mol L − 1 at 3 σ. The apparent Michaelis–Menten constant K M app for H 2O 2 sensor was estimated to be 0.9 mmol L − 1 .

Adsorptive behaviors of humic acid onto freshly prepared hydrous manganese dioxides

This study focused on the adsorptive behaviors of humic acid onto freshly prepared hydrous MnO2(s) (δMnO2), and investigated the feasibility of employing δMnO2 for humic acid removal from drinking water. Effects of such parameters as molecular mass of humic acid, kinds of divalent cations on adsorptive behaviors and possible mechanisms involved were investigated. This study indicated that humic acid with higher molecular mass exhibited more tendency of adsorbing onto δMnO2 than that with lower molecular mass. Ca2+ facilitated more humic acid adsorption than Mg2+; UV-Vis spectra analysis indicated higher capabilities of Ca2+ coordinating with acidic functional groups of humic acid than that of Mg2+. Additionally, ζ potential characterization indicated that Ca2+ showed higher potential of increasing gz potential of δMnO2 than Mg2+. Ca2+ of 1.0 mmol/L increased ζ potential of δMnO2 from −37 mV (pH 7.9) to +7 mV (pH 7.2), while 1.0 mmol/L Mg2+ increased to lower value as −9 mV (pH 6.5), correspondingly. Fourier transform infrared (FTIR) spectra demonstrated the adsorption of humic acid onto δMnO2, showing the important roles of-COO− functional groups and surface Mn-OH in the adsorption of humic acid onto δMnO2.

Electrochemistry and Electrocatalysis of Hemoglobin in Nafion/nano-CaCO3 Film on a New Ionic Liquid BPPF6 Modified Carbon Paste Electrode

Room temperature ionic liquid N-butylpyridinium hexafluorophosphate (BPPF6) was used as a binder to construct a new carbon ionic liquid electrode (CILE), which exhibited enhanced electrochemical behavior as compared with the traditional carbon paste electrode with paraffin. By using the CILE as the basal electrode, hemoglobin (Hb) was immobilized on the surface of the CILE with nano-CaCO3 and Nafion film step by step. The Hb molecule in the film kept its native structure and showed good electrochemical behavior. In pH 7.0 Britton-Robinson (B-R) buffer solution, a pair of well-defined, quasi-reversible cyclic voltammetric peaks appeared with cathodic and anodic peak potentials located at -0.444 and -0.285 V (vs SCE), respectively, and the formal potential (E degrees') was at -0.365 V, which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The formal potential of Hb shifted linearly to the increase of buffer pH with a slope of -50.6 mV pH-1, indicating that one electron transferred was accompanied with one proton transportation. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FT-IR) spectroscopy studies showed that Hb immobilized in the Nafion/nano-CaCO3 film still remained its native arrangement. The Hb modified electrode showed an excellent electrocatalytic behavior to the reduction of H2O2, trichloroacetic acid (TCA), and NaNO2.

Direct electrochemistry and electrocatalysis of hybrid film assembled by polyelectrolyte–surfactant polymer, carbon nanotubes and hemoglobin

Abstract Functional hybrid film based on the incorporation of multiwalled carbon nanotubes modified with hemoglobin into polyelectrolyte–surfactant polymer was fabricated. Such assembled films are found to possess facilitated electron transfer of hemoglobin. Cyclic voltammetric results showed a pair of well-defined redox peaks for the Hb heme Fe(III)/Fe(II) redox couple at about −0.273 (versus SCE) in a pH 7.0 phosphate buffer solution. The formal potential of the Hb heme Fe(III)/Fe(II) couple shifted linearly with pH with a slope of 52.8 mV pH−1, indicating that an electron transfer is coupled with a one-proton transportation. An FT-IR and UV–vis spectroscopy study confirms that the secondary structure of Hb entrapped in the hybrid film still maintains the original arrangement. It is suggested that the achieved faradic response of the hemoglobin be due to the ability of carbon nanotubes to promote the electron transfer of enzymes and the biomembrane properties of the polyelectrolyte–surfactant polymer. And the entrapped Hb exhibits the features of a peroxidase and acts in an electrocatalytic manner in the reduction of hydrogen peroxide, oxygen, and nitrite. The properties of the functional hybrid films, combined with the bioelectrochemical catalytic activity, could make them useful for the development of bioelectronic devices and investigation of protein electrochemistry at functional interface.

Direct electron transfer and electrocatalysis of hemoglobin adsorbed on mesoporous carbon through layer-by-layer assembly

Using chitosan as an effective linker between CMK-3 and glassy carbon electrode surface, {Hb/CMK-3}n multilayer film-modified electrodes were constructed through layer-by-layer assembly. The morphology of thus-formed {Hb/CMK-3}n film was characterized by scanning electron micrographs, and the interaction of hemoglobin (Hb) with CMK-3 was studied by UV-vis spectroscopy and electrochemical methods. Under optimal conditions, {Hb/CMK-3}6 film showed a couple of stable and well-defined redox peaks at about -377 and -296 mV in pH 7.0 buffers. Furthermore, the {Hb/CMK-3}6 film displayed excellent electrocatalysis to the reduction of both H2O2 and O2. Based on thus-formed film and its direct electron transfer behavior, a novel biosensor was presented for the determination of H2O2 ranging from 1.2 to 57 muM with the detection limit of 0.6microM at S/N=3. CMK-3 provided a desirable matrix for protein immobilization and biosensor preparation.

Modification of streaming potential by precipitation of calcite in a sand-water system: laboratory measurements in the pH range from 4 to 12

Spontaneous Potentials associated with volcanic activity are often interpreted by means of the electrokinetic potential, which is usually positive in the flow direction (i.e. Zeta potential of the rock is negative). The water-rock interactions in hydrothermal zones alter the primary minerals leading to the formation of secondary minerals. This work addresses the study of calcite precipitation in a sand composed of 98% quartz and 2% calcite using streaming potential measurements. The precipitation of calcite as a secondary mineral phase, inferred by high calcite saturation indices and by a fall in permeability, has a significant effect on the electrokinetic behaviour, leading to a significant reduction in the Zeta potential (in absolute value) and even a change in sign. The measured decrease in Zeta potential from -16 mV to -27±4 mV takes place as the pH rises from 4 to 7, while it remains constant at -25±1 mV as the pH increases from 8 to 10.5. For pH higher than 10.5, calcite precipitates and is expected to coat the quartz surface. The measured Zeta potential vary from -17 to +8 mV for pH ranging from 10.6 to 11.7 depending on the amount of precipitated calcite indicated by the decrease in permeability. The observed change in sign of the electrical surface potential rules out the usual qualitative interpretation of SP anomalies in order to determine fluid circulations, even at pH lower than 9 if calcite is widely present as a secondary mineral phase, since the electrical surface potential of calcite depends also on CO2 partial pressure and [Ca2+]. Therefore SP anomalies as measured in hydrothermal field, without mineralogical analyses of hydrothermal deposits, and without geochemical fluid survey, should be interpreted with caution.

Direct electrochemistry and electrocatalysis of hemoglobin in gelatine film modified glassy carbon electrode

Direct electrochemical and electrocatalytic behavior of hemoglobin (Hb) immobilized on glass carbon electrode (GCE) containing gelatine (Gel) films was investigated. The characteristics of Hb/Gel film modified GC electrode were performed by using SEM microscopy, UV–vis spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peak with a formal potential of −0.38 V (versus SCE) in 0.1 M pH 7.0 PBS. The formal potential changed linearly from pH 4.03 to 8.41 with a slope value of −52.0 mV pH −1, which suggested that a proton transfer was accompanied with each electron transfer (ET) in the electrochemical reaction. The Hb/gelatine/GCE displayed a rapid amperometric response to the reduction of H 2O 2 and nitrite.

Direct electrochemistry of glucose oxidase in a colloid Au–dihexadecylphosphate composite film and its application to develop a glucose biosensor

Colloid Au (Au nano) with a diameter of about 10 nm was prepared and used in combination with dihexadecylphosphate (DHP) to immobilize glucose oxidase (GOD) onto the surface of a graphite electrode (GE). The direct electrochemistry of GOD confined in the composite film was investigated. The immobilized GOD displayed a pair of redox peaks with a formal potential of − 0.475 mV in pH 7.0 O 2-free phosphate buffers at scan rate of 150 mV s − 1 . The GOD in the composite film retained its bioactivity and could catalyze the reduction of dissolved oxygen. Upon the addition of glucose, the reduction peak current of dissolved oxygen decreased, which could be developed for glucose determination. A calibration linear range of glucose was 0.5–9.3 mM with a detection limit of 0.1 mM and a sensitivity of 1.14 μA mM − 1 . The glucose biosensor showed good reproducibility and stability. The general interferences that coexisted in human serum sample such as ascorbic acid and uric acid did not affect glucose determination.

Measurement and modeling of the surface potential evolution of hydrated cement pastes as a function of degradation

Hydrated cement pastes (HCP) have a high affinity with a lot of (radio)toxic products and can be used as waste confining materials. In cementitious media, elements are removed from solution via (co)precipitation reactions or via sorption/diffusion mechanisms as surface complexation equilibria. In this study, to improve the knowledge of the surface charge evolution vs the degradation of the HCP particles, two cements have been studied: CEM-I (ordinary Portland cement, OPC) and CEM-V (blast furnace slag and fly ash added to OPC). Zeta potential measurements showed that two isoelectric points exist vs HCP leaching, i.e., pH. Zeta potential increases from −17 to +20 mV for pH 13.3 to pH 12.65 (fresh HCP states) and decreases from 20 to −8 mV for pH 12.65 to 11 (degraded HCP states). The use of a simple surface complexation model of C-S-H, limited in comparison with the structural modeling of C-S-H in literature, allows a good prediction of the surface potential evolution of both HCP. Using this operational modeling, the surface charge is controlled by the deprotonation of surface sites (>SO −) and by the sorption of calcium (>SOCa +), which brings in addition a positive charge. The calcium concentration is controlled by portlandite or calcium silicate hydrate (C-S-H) solubilities.

Removal of Cu(II) ions by activated poplar sawdust (Samsun Clone) from aqueous solutions

In this work, adsorption of Cu(II) ions on sawdust (SD) and activated sawdust (ASD) has been studied by using batch adsorption techniques. The equilibrium adsorption level was determined to be a function of the pH, initial Cu(II) concentration, and adsorbent dosage. The equilibrium nature of Cu(II) adsorption has been described by the Freundlich and Langmuir isotherms. The experimental adsorption data were fitted to the Langmuir adsorption model both sawdust and activated sawdust. The equilibrium capacity of sawdust and activated sawdust were 5.432 and 13.495 mg copper per g adsorbent, respectively at room temperature and natural pH. The maximum adsorption capacity was obtained at the maximum zeta potential value that −74.5 mV (pH 5) for activated sawdust and at −48.4 mV (pH 4) for sawdust. It was observed that activated sawdust was a suitable adsorbent than sawdust for removal of Cu(II) from aqueous solutions.

NO removal in continuous BioDeNOx reactors: Fe(II)EDTA2− regeneration, biomass growth, and EDTA degradation

BioDeNOx is a novel technique for NOx removal from industrial flue gases. In principle, BioDeNOx is based on NO absorption into an aqueous Fe(II)EDTA2- solution combined with biological regeneration of that scrubber liquor in a bioreactor. The technical and economical feasibility of the BioDeNOx concept is strongly determined by high rate biological regeneration of the aqueous Fe(II)EDTA2- scrubber liquor and by EDTA degradation. This investigation deals with the Fe(II)EDTA2- regeneration capacity and EDTA degradation in a lab-scale BioDeNOx reactor (10-20 mM Fe(II)EDTA2-, pH 7.2 +/- 0.2, 55 degrees C), treating an artificial flue gas (1.5 m3/h) containing 60-155 ppm NO and 3.5-3.9% O2. The results obtained show a contradiction between the optimal redox state of the aqueous FeEDTA solution for NO absorption and the biological regeneration. A low redox potential (below -150 mV vs. Ag/AgCl) is needed to obtain a maximal NO removal efficiency from the gas phase via Fe(II)EDTA2- absorption. Fe(III)EDTA- reduction was found to be too slow to keep all FeEDTA in the reduced state. Stimulation of Fe(III)EDTA- reduction via periodical sulfide additions (2 mM spikes twice a week for the conditions applied in this study) was found to be necessary to regenerate the Fe(II)EDTA2- scrubber liquor and to achieve stable operation at redox potentials below -150 mV (pH 7.2 +/- 0.2). However, redox potentials of below -200 mV should be avoided since sulfide accumulation is unwanted because it is toxic for NO reduction. Very low values for biomass growth rate and yield, respectively, 0.043/d and 0.009 mg protein per mg ethanol, were observed. This might be due to substrate limitations, that is the electron acceptors NO and presumably polysulfide, or to physiological stress conditions induced by the EDTA rich medium or by radicals formed in the scrubber upon the oxidation of Fe(II)EDTA2- by oxygen present in the flue gas. Radicals possibly also induce EDTA degradation, which occurs at a substantial rate: 2.1 (+/-0.1) mM/d under the conditions investigated.

Simultaneous Determination of Dopamine and Ascorbic Acid at a Triazole Self-Assembled Monolayer-Modified Gold Electrode

A 3-amino-5-mercapto-1,2,4-triazole (TA) self-assembled monolayer-modified gold electrode (TA SAM/Au) is characterized by X-ray photoelectron spectroscopy, A.C. impedance, cyclic voltammetry, chronoamperometry and chronocoulometry. The TA SAM/Au exhibited good promotion of the electrochemical oxidation of dopamine. Some electrochemical parameters of dopamine such as electron transfer number, exchange current density, standard heterogeneous rate constant, diffusion coefficient, etc., were measured by different electrochemical methods. The peak currents of dopamine were linearly dependent on its concentration in the range of 1.5 × 10−6–1.0 × 10−4 mol L−1, with a detection limit of 5.0 × 10−7 mol L−1. The oxidative peak potentials of dopamine and ascorbic acid were well separated at about 190 ± 10 mV in pH 2.0 BR buffers at TA SAM/Au, the oxidation peak current increases approximately linearly with increasing concentration of both dopamine and ascorbic acid in the concentration range of 9.98 × 10−6–4.54 × 10−4 mol L−1. It can be used for simultaneous determination of dopamine and ascorbic acid.

Direct electrochemistry of hemoglobin in cetylpyridinium bromide film: Redox thermodynamics and electrocatalysis to nitric oxide

Hemoglobin was successfully immobilized in cetylpyridinium bromide (CPB) film on a polyacrylamide (PAM) modified glassy carbon electrode (GC). Cyclic voltammetry showed a pair of well-defined and nearly reversible CV peaks at about −0.2165 V vs SCE (pH = 4.22), indicating the character of Hb heme Fe(II)/heme Fe(III) redox couple. The apparent standard potentials of hemoglobin in the CPB were linearly varied with pH in the range from 4.22 to 9.18 with a slope of −48.85 mV pH −1, implying that one proton was accompanied with one electron transferred in the electrochemical reaction. The adsorption of Hb on the surface of PAM/GC electrode have been investigated by electrochemical impedance spectroscopy. The apparent standard potentials of hemoglobin were also studied through direct electrochemistry method as a function of temperature and the thermodynamic parameters (Δ S rc and Δ H rc) for the protein redox were calculated. Hemoglobin in the CPB exhibited catalytic activity for electrochemical reduction of NO.