Effect of dimethyl sulfoxide on the electron transfer reactivity of hemoglobin

Electrochemical characterization of natural organic matter by direct voltammetry in an aprotic solvent

The complex and indeterminant composition of NOM makes characterization of its redox properties challenging. Approaches that have been taken to address this challenge include chemical probe reactions, potentiometric titrations, chronocoulometry, and voltammetry. In this study, we revisit the use of direct voltammetric methods in aprotic solvents by applying an expanded and refined suite of methods to a large set of NOM samples and model compounds (54 NOM samples from 10 different sources, 7 NOM model compounds, and 2 fresh extracts of plant materials that are high in redox-active quinonoid model compounds dissolved in DMSO). Refinements in the methods of fitting the data obtained by staircase cyclic voltammetry (SCV) provided improved definition of peaks, and square wave voltammetry (SWV), performed under the same conditions as SCV, provided even more reliable identification and quantitation of peaks. Further evidence is provided that DMSO improves the electrode response by unfolding some of the tertiary structure of NOM polymers, thereby allowing greater contact between redox active functional groups and the electrode surface. We averaged experimental peak potentials for all NOM compounds and calculated potentials in water. Average values for Epa1, Epc1, and Ep1 in DMSO were -0.866 ± 0.069, -1.35 ± 0.071, and -0.831 ± 0.051 V vs. Ag/Ag+, and -0.128, -0.613, and -0.0930 V vs. SHE in water. In addition to peak potentials, the breadth of SCV peaks was quantified as a way to characterize the degree to which the redox activity of NOM is due to a continuum of contributing functional groups. The average breadth values were 1.63 ± 0.24, 1.28 ± 0.34, and 0.648 ± 0.15 V for Epa1, Epc1, and Ep1 respectively. Comparative analysis of the overall dataset-from SCV and SWV on all NOMs and model compounds-revealed that NOM redox properties vary over a narrower range than expected based on model compound properties. This lack of diversity in redox properties of NOM is similar to conclusions from other recent work on the molecular structure of NOM, all of which could be the result of selectivity in the common extraction methods used to obtain the materials.

Mechanisms of Enhanced Hemoglobin Electroactivity on Carbon Electrodes upon Exposure to a Water-Miscible Primary Alcohol

Exposing a carbon electrode to hemoglobin (Hb) and alcoholic solvents, such as methanol, ethanol or 1-propanol, drastically changes Hb electroactivity, but until this work, the important underlying mechanisms were unclear. For the first time, we show that these alcohols impact Hb electroactivity via three mechanisms: modification of the carbon surface oxides on the glassy carbon (GC) electrode, Hb film formation, and structural changes to Hb. C_1s X-ray photoelectron spectroscopy provided evidence for significant alcohol-induced modification of the carbon surface oxides, and differential pulse voltammetry showed links between these modifications and Hb electroactivity. Spectroscopic ellipsometry showed that Hb films formed during exposure to Hb- and alcohol-containing electrolytes increased in thickness with increasing alcohol content, although film thickness played only a minor role in Hb electroactivity. Alcohol-induced structural changes in Hb are confirmed with UV-visible absorption and fluorescence data, showing that Hb denaturation also was a significant factor in increasing Hb electroactivity. Carbon-surface-oxide modification and Hb denaturation worked in tandem to maximally increase the Hb electroactivity in 60% methanol. While in ethanol and 1-propanol, the significant increases in Hb electroactivity caused by Hb denaturation were offset by an increase in Hb-inhibiting carbon surface oxides. Knowledge of these mechanisms shows the impact of alcohols on both Hb and carbon electrodes, allows for thoughtful design of the Hb-sensing system, is vital for proper analysis of Hb electroactivity in the presence of these alcohols (e.g., when used as binder solvents for immobilizing Hb into films), and provides fundamental understanding of the Hb-carbon interactions.

Direct electrochemistry and bioelectrocatalysis of hemoglobin immobilized on carbon black

It is reported for the first time that hemoglobin (Hb) was immobilized on the surface of carbon black powders modified at the surface of a glassy carbon electrode. The cyclic voltammetric results showed that the immobilized Hb could undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E(0), is -0.330 V in phosphate buffer solution (pH 6.9) at a scan rate of 100 mV/s and is almost independent of the scan rate in the range of 40-200 mV/s. The dependence of E(0), on the pH of the buffer solution indicated that the conversion of Hb-Fe(III)/Hb-Fe(II) is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized Hb retained its bioelectrocatalytic activity for the reduction of H(2)O(2). Furthermore, the immobilized Hb can be stored at 4 degrees C for several weeks without any loss of the enzyme activity. Thus, the immobilized Hb may be used as a biocathodic catalyst in biofuel cells.

In situ electrochemical contact angle study of hemoglobin and hemoglobin–Fe3O4 nanocomposites

The electrochemical redox-induced contact angle changes of hemoglobin droplets in the absence and presence of tetraheptylammonium-capped Fe3O4 nanoparticles have been explored by using in situ electrochemical contact angle measurements. The results indicate that the electrochemical redox process may lead to some structure changes of hemoglobin (Hb), which could further induce the hydrophobic-to-hydrophilic changes of the relative droplets. Our observations demonstrate that hemoglobin could self-assemble on the surface of the functionalized Fe3O4 nanoparticles as Hb-Fe3O4 nanocomposites, which may contribute to much more significant change of the electrochemical redox-induced contact angle values than that with free nano-Fe3O4. These results suggest that in situ electrochemical contact angle measurements could be readily applied as a new and convenient method to detect some specific biological process.

Third-generation biosensors based on the direct electron transfer of proteins

Recent progress in third-generation electrochemical biosensors based on the direct electron transfer of proteins is reviewed. The development of three generations of electrochemical biosensors is also simply addressed. Special attention is paid to protein-film voltammetry, which is a powerful way to obtain the direct electron transfer of proteins. Research activities on various kinds of biosensors are discussed according to the proteins (enzymes) used in the specific work.

Electrochemical investigation of redox thermodynamics of immobilized myoglobin: ionic and ligation effects

In this study, we investigated redox thermodynamics of myoglobin as well as the ionic (phosphate ions) and ligation (imidazole) effects via a dynamic electrochemical approach. We employed a previously established system that features nonmediated, direct electrochemistry of myoglobin and myoglobin in an immobilized state (i.e., diffusionless electrochemistry). Thermodynamics parameters were obtained by measuring redox potential (E degrees ') of myoglobin at varied temperature (T), in the presence and in the absence of specific ions or axial ligands. As a step further, we evaluated contributions from allosteric effect and axial iron ligation by partitioning E degrees ' changes into entropic and enthalpic terms. Compensation phenomena between the entropic and enthalpic changes were observed in all these cases. On the basis of these studies, we also correlated these phenomena to possible structural variations.

An electrochemical study of hemoglobin in water–glycerol solutions

The effect the composition of a water-glycerol mixture has on the electrochemical properties of hemoglobin (Hb) is studied. With the increased glycerol concentrations, the peak-to-peak separation of hemoglobin is found to increase from approximately 40 to 200 mV, with the apparent standard potential of hemoglobin negatively shifted, which demonstrate that the electron-transfer activity of hemoglobin will decrease at relatively high glycerol concentrations and the oxidized state of hemoglobin will be more stable with the increasing glycerol concentrations. Meanwhile, the electrocatalytic activity of hemoglobin to hydrogen peroxide, as well as the binding of ligands or effectors to hemoglobin in the presence of glycerol, are also been investigated. Our studies indicate that glycerol will decrease the electrocatalytic activity of hemoglobin, while have little effect on the microenvironment around the heme site.

Direct electrochemistry and electrocatalysis of hemoglobin immobilized on carbon paste electrode by silica sol–gel film

Direct electrochemical and electrocatalytic behaviors of hemoglobin (Hb) immobilized on carbon paste electrode (CPE) by a silica sol-gel film derived from tetraethylorthosilicate (TEOS) were investigated for the first time. Hb/sol-gel film modified electrodes showed a pair of well-defined and nearly reversible cyclic voltammetric peaks for Hb Fe(III)/Fe(II) redox couple at about -0.312 V (versus Ag/AgCl) 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 5.0-10.0 with a slope of 49.44 mV pH(-1), which suggests that a proton transfer is accompanied with each electron transfer (ET) in the electrochemical reaction. The immobilized Hb displayed the features of peroxidase and gave excellent electrocatalytic performance to the reduction of O2, NO2(-) and H2O2. The calculated apparent Michaelis-Menten constant was 8.98 x 10(-4)M, which indicated that there was a large catalytic activity of Hb immobilized on CPE by sol-gel film toward H2O2. In comparison with other electrodes, the chemically modified electrodes, used in this direct electrochemical study of Hb, are easy to be fabricated and rather inexpensive. Consequently, the Hb/sol-gel film modified electrode provides a convenient approach to perform electrochemical research on this kind of proteins. It also has potential use in the fabrication of the third generation biosensors and bioreactors.

Direct electron transfer and bioelectrocatalysis of hemoglobin at a carbon nanotube electrode

A stable suspension of carbon nanotube (CNT) can be obtained by dispersing the CNT in the solution of the surfactant cetyltrimethylammonium bromide. CNT has promotion effects on the direct electron transfer of hemoglobin (Hb), which was immobilized onto the surface of CNT. The direct electron transfer rate of Hb was greatly enhanced after it was immobilized onto the surface of CNT. Cyclic voltammetric results showed a pair of well-defined redox peaks, which corresponded to the direct electron transfer of Hb, with the formal potential (E(0('))) at about -0.343V (vs. saturated calomel electrode) in the phosphate buffer solution (pH 6.8). The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (k(s)) and the value of formal potential (E(0('))) were estimated. The dependence of E(0(')) on solution pH indicated that the direct electron transfer reaction of Hb is a one-electron transfer coupled with a one-proton transfer reaction process. The experimental results also demonstrated that the immobilized Hb retained its bioelectrocatalytic activity to the reduction of H(2)O(2). The electrocatalytic current was proportional to the concentration of H(2)O(2) at least up to 20mM.

Direct electrochemical characterization of Vitreoscilla sp. hemoglobin entrapped in organic films

The redox properties of a prokaryotic, Vitreoscilla sp. hemoglobin (VHb) in fuzzy organic films are studied with electrochemistry. This VHb exhibits irreversible electrochemical response at bare pyrolytic graphite (PG) electrode surfaces. However, upon being entrapped in organic films, the heterogeneous electron transfer rate of VHb will be sufficiently high to produce a quasi-reversible electrochemical response. The observation of electrocatalysis (reduction of O2) by hemes suggests that the protein can retain its biological activity under these conditions.