Scan Rate Dependence Research Articles

Electrolyte Dependence of CO2 Electroreduction: Tetraalkylammonium Ions Are Not Electrocatalysts

The ability of tetraalkylammonium ions (NR4+) to facilitate CO2 electroreduction at various electrode surfaces has been investigated. Scan rate dependence shows this process to be diffusion-controlled and largely independent of working electrode material. Variation of the R groups on NR4+ is shown to have little effect on the reduction potential, indicating that catalysis via reduced NR4• species, as previously proposed in the literature, is not a viable mechanism for CO2 electroreduction. Rather, CO2 is reduced via outer-sphere electron transfer according to the mechanism put forth by Saveant and co-workers [Lamy, E.; Nadjo, L.; Saveant, J.-M. J. Electroanal. Chem. 1977, 78, 403−407]. This view is supported by a full analysis of the reaction products, which consist exclusively of CO and CO32–, as well as solvent decomposition products formed at the counter electrode. No degradation of NR4+ ions is observed, which rules out the transient formation of NR4• radical species during electroreduction. However, ...

Electrochemical and nanogravimetric studies of iron phthalocyanine microparticles immobilized on gold in acidic and neutral media

An electrochemical quartz crystal nanobalance has been used to study the redox behavior of iron phthalocyanine (FePc) microparticles attached to gold in contact with acidic and neutral aqueous solutions at different pH values in the absence and presence of oxygen, respectively. Five redox transformations have been detected: one has been assigned to the Fe2+/Fe3+ redox process, while four of those have been assigned to the oxidation and reduction of the Pc ring; however, the reduction of Fe2+ and the reoxidation of Fe+ cannot be entirely excluded at potentials more negative than ca. −0.4 V vs. saturated calomel electrode (SCE). The redox processes are accompanied with significant mass changes which are related to the sorption and desorption of counterions and solvent molecules. An extensive solvent swelling occurs. The relatively slow motion of solvent molecules introduces a substantial scan rate dependence regarding the mass change during potential cycling. Due to the participation of H+ ions, the processes related to the oxidation and reduction of the Pc ring show pH dependence. Simultaneous with the charge transfer processes, solid-solid phase transitions can be assumed, especially in the case of the redox transformations occurring at most cathodic potentials. The mass change that can be detected in the presence of oxygen indicates a bonding of oxygen to FePc. During a cathodic voltammetric scan, the reduction of oxygen (ORR) starts when the central iron (III) ion of FePc is converted to Fe(II) during reduction. It follows that the electrocatalytic efficiency of FePc, which is comparable with that of Pt in acid and neutral solutions, cannot be expected at even lower overpotentials because the redox transformation of the central Fe ion of FePc determines the rate of the ORR.

Enhancement of Capacitance by Electrochemical Oxidation of Nanodiamond Derived Carbon Nano-Onions

Electrode responsiveness and electrochemical capacitance behavior of nanodiamond-derived carbon nano-onions (N-CNOs) were studied. N-CNOs were prepared by thermal annealing of nanodiamond powders. A thin film of N-CNOs was mounted on glassy carbon (GC) current collector and showed an excellent electrochemical behavior with rectangular voltammetric curves as well as great scan rate dependence of capacitance. The capacitance showed negligible drops over a wide range of scan rates (50mV/s - 5V/s) in both KCl and H2SO4. This excellent capacitive behavior was attributed to good electrical conductivity and mesoporous nature of N-CNOs. In order to further enhance capacitance, electrochemical oxidation of N-CNOs was carried out by iterating anodic cycling in acidic electrolytes. The capacitance enhancement of oxidized N-CNOs was probed by cyclic voltammetry as well as galvanostatic charging-discharging measurement. This study demonstrates that electrochemical oxidation can be an effective method to improve capacitance and energy density of carbon nanomaterials while maintaining a good scan rate performance.

Development of multi-walled carbon nanotube/poly(vinyl alcohol) composite as electrode for capacitive deionization

To improve the electrode performance in capacitive deionization, a multi-walled carbon nanotubes (MWCNTs) and poly(vinyl alcohol) (PVA) composite electrode was prepared in this study. The electrosorption performance of this composite electrode was evaluated in terms of capacitive characteristics, number cycles, desalting capability, and compared to that of commercial activated carbon. Results showed that the MWCNT/PVA composite electrode had strong hydrophilicity, high mesoporosity, and excellent capacitor characteristics. The cyclic voltammetry curves of the MWCNT/PVA composite represented less scan-rate and concentration dependency, reflecting better rate capacity for ion electrosorption. From the desalination experiments of 0.001M NaCl at 1.2V, the MWCNT/PVA composite electrode exhibited a larger ion removal capacity (13.07mgg−1), higher electrosorption rate (0.073min−1), and less energy consumption (0.038kWhm−3) as compared to that of the activated carbon electrode. The good electrosorption performance could be attributed to the mesoporous structure that is less affected by double-layer overlapping and then facilitates ion transport. Additionally, the MWCNT/PVA composite electrode revealed a higher effective surface area of 26.04% of the Brunauer–Emmett–Teller surface area, which was −10 fold than that of activated carbon electrode. Overall, because of its excellent electrode properties and morphology advantage, the composite electrode is a desirable material for the removal of ions in capacitive deionization.

Electrochemical Characterization of an Electroactive Ureidopyrimidinone Derivative, a Four Hydrogen Bond Array Containing a Dimethylaminophenylurea

Electron transfer reactions can be used to perturb the strength of hydrogen bonding interactions between organic molecules. When molecular redox centers are integrated onto hydrogen bond arrays, this combination can become a powerful tool for controlling binding strength in supramolecular complexes. Whether used for sensing devices, molecular machines or self-assembly, the strength of a hydrogen bond can also be enhanced simply by arrangement of hydrogen donor interactions (D) versus hydrogen acceptor interactions (A). Indeed, because of secondary interactions, dimerization constants of the DDAA 4 H-Bond array typically exceed that of the DADA 4 H-Bond array.1 By combining a DDAA 4 H-bond array such as Meijer’s ureidopyrimidinone1with an electroactive center such as the dimethylaminophenylurea, the strength of hydrogen bonding becomes tunable.Cyclic voltammetry investigation, in nonaqueous solvents, of dimethylaminophenylurea (UHH), a DD 2H-bond array, show that without a guest present, there is one reversible oxidation wave in methylene chloride of one electron height. CV Digital simulations as well as UV-vis spectroelectrochemistry indicate a proton transfer from the radical species to the reduced U(H)H, followed by another electron transfer due to potential inversion to give the quinoidal cation, Scheme 1. With the integration of the dimethylphenylamino redox center, this mechanism would certainly complicate the dimerization of Meijer’s DDAA array.Scheme 1. Proposed oxidation mechanism of UHH undergoing an overall one electron transfer due to proton transfer.Due to the acidity of the urea NH that is part of the electroactive center, proton transfer could also occur as part of the electrochemistry associated with the DDAA dimer. We hypothesize that depending on the ratio of arrays substituted with an electroactive center versus those without, the DDAA sequence could change to a DDAD array. With all arrays containing an electroactive center the hydrogen bonding array would form an ADDA homodimer.This presentation will cover cyclic voltammetry studies that includes concentration and scan rate dependence investigations on Meijier’ DDAA dimer equipped with a dimethyphenylurea electroactive center. Digital CV simulations and spectroelectrochemistry will be used to analyze experimental CV ‘s.Figure 1. Meijer’s ureidopyrimidinone (Upy) 4 H-bond system without redox functionality as a DDAA homodimer.Figure 2. Structure of the proposed heterodimer, DDAD array, as a result of half the concentration with an electroactive center and the other half without.

Remarkable Scan Rate Dependence for a Highly Constrained Dinuclear Iron(II) Spin Crossover Complex with a Wide Thermal Hysteresis Loop

The abrupt [HS-HS] ↔ localized [HS-LS] spin crossovers of a new triazole-based diiron(II) complex result in a record-equaling thermal hysteresis loop width for a dinuclear complex (ΔT = 22 K by SQUID magnetometer in "settle" mode) and show a remarkable scan rate dependence of only the cooling branch, as revealed by detailed magnetic, DSC, and Mössbauer studies.

Study on the Electrochemical Kinetics of Manganese Dioxide/Multiwall Carbon Nanotube Composite by Voltammetric Charge Analysis

Electrochemical properties of MnO2/multiwall carbon nanotube (MWCNT) composites were investigated by using cavity microelectrodes (CME). Electrochemical kinetics of the MnO2/MWCNT composites were studied by analyzing the scan rate dependence of voltammetric charge, which was measured by cyclic voltammetry (CV) at various scan rates ranging from 20 mV s−1 to 1000 mV s−1. Based on several mathematical models, the relationship between voltammetric charge and scan rate was interpreted systematically. At slow scan rates, ion diffusion in MnO2 dominantly determined the rate of the overall electrochemical process. However, the faradaic reaction of Mn3+/Mn4+ at the MnO2 surface competed with mass transfer in terms of kinetics when the potential scan rate was higher than 400 mV s−1.

Electrochemical mechanism and sensitive assay of antiretroviral drug Abacavir in biological sample using multiwalled carbon nanotube modified pyrolytic graphite electrode

Multiwalled carbon nanotube modified edge plane pyrolytic graphite electrode (MWCNT/EPPGE) was developed and implemented for the determination of antiretroviral drug Abacavir using differential pulse adsorptive stripping voltammetry (DP AdSV). Cyclic voltammogram showed two oxidation peaks located at+0.91V and+1.10V on (MWCNT/EPPGE). Dependency of peak potential and peak current on pH was investigated as details. The oxidation potentials affected by the pH indicating protons are involved in the electrochemical oxidation of Abacavir. Mass transport to the electrode surface was found as a combination of diffusion and adsorption which was concluded by studying the potential scan rate dependency of both peak currents. The oxidation mechanism was proposed using the obtained data and discussed. A large enhancement in both of the peak currents was observed with applying an accumulation step presenting the effect of adsorption. Peak currents showed a linear relation upon the Abacavir concentration within a range of 1×10−7–2×10−5M with (r=0.999) for both peak responses. The method was fully validated related with selectivity, sensitivity, precision and accuracy studies. Abacavir was also determined with the proposed method in its pharmaceutical dosage forms and human serum samples. No interferences from the excipients of the dosage form or endogenous substances from biological material were found.

Kinetic Control in Protein Folding for Light Chain Amyloidosis and the Differential Effects of Somatic Mutations

Light chain amyloidosis is a devastating disease where immunoglobulin light chains form amyloid fibrils, resulting in organ dysfunction and death. Previous studies have shown a direct correlation between the protein thermodynamic stability and the propensity for amyloid formation for some proteins involved in light chain amyloidosis. Here we investigate the effect of somatic mutations on protein stability and in vitro fibril formation of single and double restorative mutants of the protein AL-103 compared to the wild-type germline control protein. A scan rate dependence and hysteresis in the thermal unfolding and refolding was observed for all proteins. This indicates that the unfolding/refolding reaction is kinetically determined with different kinetic constants for unfolding and refolding even though the process remains experimentally reversible. Our structural analysis of AL-103 and AL-103 delP95aIns suggests a kinetic coupling of the unfolding/refolding process with cis–trans prolyl isomerization. Our data reveal that the deletion of proline 95a (AL-103 delP95aIns), which removes the trans–cis di-proline motif present in the patient protein AL-103, results in a dramatic increment in the thermodynamic stability and a significant delay in fibril formation kinetics with respect to AL-103. Fibril formation is pH dependent; all proteins form fibrils at pH2; reactions become slower and more stochastic as the pH increases up to pH7. Based on these results, we propose that, in addition to thermodynamic stability, kinetic stability (possibly influenced by the presence of cis proline 95a) plays a major role in the AL-103 amyloid fibril formation process.

Differential pulse voltammetric determination of albendazole in pharmaceutical tablets using a cathodically pretreated boron-doped diamond electrode

A sensitive, simple, and rapid electrochemical method was developed for the determination of albendazole (ABZ) in anthelminthic pharmaceutical formulations using differential pulse voltammetry (DPV) with a cathodically pretreated boron-doped diamond (BDD) electrode and 0.05molL−1 H2SO4 as supporting electrolyte. The electrochemical behavior of ABZ obtained with cyclic voltammetry (CV) showed two oxidation peaks at 0.95 and 1.30V vs. Ag/AgCl (3.0molL−1 KCl). The total number of electrons (four) transferred during the oxidation process was estimated from the scan rate dependence of this CV response. The proposed method resulted in an analytical curve ranging from 0.0797 to 8.36μmolL−1, with a detection limit (based on 3-sigma) of 0.0625μmolL−1. This novel DPV method was successfully applied to determine ABZ in three pharmaceutical formulations (tablets), with results similar to those obtained using a reference HPLC method.

Influence of morphologies and pseudocapacitive contributions for charge storage in V2O5 micro/nano-structures

Three pure V2O5 micro/nano-structures including rods, hierarchical wires and porous tubes are synthesized via a chemical vapor deposition process by adjusting the oxidation temperature. Their surface-to-volume ratio increases significantly because of particle size decrease, pore quantity increase and hollow structure formation. Lithium-ion storage investigation in aqueous electrolyte indicates that the enlargement of surface area can suppress irreversible phase transition and lead to significant improvement of cycling stability, storage capacity and electrochemical kinetics. Furthermore, scan-rate dependence cyclic voltammetry analysis demonstrates that both pseudocapacitive and bulk Li+ storage are within these V2O5 electrodes and the relative contributions of them depend strongly on the scan rate. In porous V2O5 micro/nano-tubes, the surface pseudocapacitive storage dominates the total storage capacity at scan rates above 0.06Vs−1, whereas the bulk Li+ storage is the domination effect for V2O5 micro/nano-rods at the scan rate ranging from 0.02 to 0.3Vs−1. At the special scan rate, the maximum and minimum capacity is observed in V2O5 porous micro/nano-tubes and micro/nano-rods, respectively. These studies should be useful for elucidating the morphological effects on Li-ion storage for V2O5-based electrodes. By varying key morphological parameters, the pseudocapacitive properties of V2O5 micro/nano-structure electrodes are expected to be affected.

Generation and electrochemical nanogravimetric response of the third anodic hydrogen peak on a platinum electrode in sulfuric acid media

Platinum electrodes have been investigated in sulfuric acid solutions in the hydrogen adsorption–desorption region by electrochemical quartz crystal nanobalance (EQCN). It was found that a well-developed peak (the so-called third peak) between the two main peaks appeared when, following the cycling in the oxide region, the electrode was kept at potentials just more positive than the potential of hydrogen evolution under the same conditions. The extent of this third peak and its ratio to oxidation peaks of the strongly and weakly adsorbed hydrogen depend on the waiting time at potentials mentioned above as well as on the scan rate. Similarly to the other two peaks, the simultaneous EQCN response shows a slight mass increase which can be assigned to adsorption of HSO4 − ions at the platinum surface. Because the third peak appears only after a potential excursion in the oxide region, it is related to the formation of specific surface sites on which hydrogen can be adsorbed with an energy which falls between the energies of the weakly and strongly bound hydrogen. The waiting time effect indicates that this adsorption is a slow process, and it is the very reason that it cannot be observed during the second cycle. The scan rate dependence can be elucidated by the transformation of this type of adsorbed hydrogen to the other two forms.

Supercapacitors based on carbons with tuned porosity derived from paper pulp mill sludge biowaste

Hydrothermal carbonization followed by chemical activation is utilized to convert paper pulp mill sludge biowaste into high surface area (up to 2980m2g−1) carbons. This synthesis process employs an otherwise unusable byproduct of paper manufacturing that is generated in thousands of tons per year. The textural properties of the carbons are tunable by the activation process, yielding controlled levels of micro and mesoporosity. The electrochemical results for the optimized carbon are very promising. An organic electrolyte yields a maximum capacitance of 166Fg−1, and a Ragone curve with 30Whkg−1 at 57Wkg−1 and 20Whkg−1 at 5450Wkg−1. Two ionic liquid electrolytes result in maximum capacitances of 180–190Fg−1 with up to 62% retention between 2 and 200mVs−1. The ionic liquids yielded energy density–power density combinations of 51Whkg−1 at 375Wkg−1 and 26–31Whkg−1 at 6760–7000Wkg−1. After 5000 plus charge–discharge cycles the capacitance retention is as high at 91%. The scan rate dependence of the surface area normalized capacitance highlights the rich interplay of the electrolyte ions with pores of various sizes.

Electrochemical, electrochromic behaviour and effects of supporting electrolyte on nano-thin film of poly (3,4-ethylenedioxy thiophene)

3,4-Ethylenedioxy thiophene is polymerized electrochemically in p-toluene sulphonic acid (a), phosphate buffer (b) and borax buffer (c) on glassy carbon and Indium tin oxide (ITO) surface. The scan rate dependence studies of the polymer redox processes were carried out. A linear relationship was observed between the peak current and scan rate with good correlation, r2=0.998 indicating adsorption controlled behaviour of polymer film. The SEM photograph showed the differences in surface morphology of polymers modified electrode. The XRD studies revealed semi-crystalline nature of doped polymers. Spectroelectrochemical behaviors of Indium tin oxide coated glass electrode covered with thin film of poly-3,4-ethylenedioxythiophene a, b, c in 0.1M KCl were obtained at different electrode potentials between 1100 and 200nm. Poly-3,4-ethylenedioxythiophene-a, poly-3,4-ethylenedioxythiophene-b and poly-3,4-ethylenedioxythiophene-c film exhibits transparent clear blue, opaque violet and dark maroon colours respectively at reduced potential. Further probing the potential between 400mV and 800mV coated film shows greenish blue colour for poly-3,4-ethylenedioxythiophene-a, poly-3,4-ethylenedioxythiophene-b and poly-3,4-ethylenedioxythiophene -c shows opaque violet and yellowish maroon colours respectively. Increasing the applied potential between 1000mV and 1200mV over oxidation of polymer film shows dark greenish blue for poly-3,4-ethylenedioxythiophene -a, dark brown for poly-3,4-ethylenedioxythiophene-b and transparent red colour for poly-3,4-ethylenedioxythiophene-c. Electrochromic parameters such as colouration efficiency, response time and optical contrast were calculated for all three films.

Introduction of a thermophile-sourced ion pair network in the fourth beta/alpha unit of a psychophile-derived triosephosphate isomerase from Methanococcoides burtonii significantly increases its kinetic thermal stability

Hyperthermophile proteins commonly have higher numbers of surface ionic interactions than homologous proteins from other domains of life. PfuTIM, a triosephosphate isomerase (TIM) from the hyperthermophile archaeon, Pyrococcus furiosus, contains an intricate network of 4 ion pairs in its 4th beta/alpha unit, (β/α)4, whereas MbuTIM, a triosephosphate isomerase from a psychrophile archaeon, Methanococcoides burtonii, lacks this network. Notably, (β/α)4 is the first element of the structure formed during folding of certain TIM-type (beta/alpha)8 barrel proteins. Previously, we have shown that elimination of PfuTIM's ion pair network in PfuTIM significantly decreases its kinetic structural stability. Here, we describe the reciprocal experiment in which this ion pair network is introduced into MbuTIM, to produce MutMbuTIM. Recombinant MbuTIM displays multi-state unfolding with apparent Tm values of autonomous structural elements approaching, or above, 70°C, when a temperature scanning rate of 90°C/h is used. The protein displays significant intrinsic kinetic stability, i.e., there is a marked temperature scan rate-dependence of the Tm values associated with unfolding transitions. The Tm values drop by as much as ~10°C when the temperature scanning rate is lowered to 5°C/h. MutMbuTIM, incorporating PfuTIM's ion pair network, shows significantly higher apparent Tm values (raised by 4–6°C over those displayed by MbuTIM). MutMbuTIM also displays significantly higher kinetic thermal stability. Thus, it appears that the thermal stability of triosephosphate isomerase can be increased, or decreased, by either enhancing, or reducing, the strength of ion pair interactions stabilizing (β/α)4, presumably through reduced cooperativity (and increased autonomy) in unfolding transitions.

Understanding the fast lithium storage performance of hydrogenated TiO2 nanoparticles

Anatase TiO2 is considered as one of the promising anode materials for lithium ion batteries (LIBs) because of its nontoxicity, safety, and excellent capacity retention. However, the poor rate capability of TiO2 electrodes, caused by the low electrical conductivity and lithium diffusion coefficient, strongly hinders its practical application in high power LIBs. Herein, we report on the fast lithium storage performance of hydrogenated anatase TiO2 nanoparticles (H-TiO2) prepared by a H2 plasma treatment. The scan-rate dependence of the cyclic voltammetry (CV) analysis reveals that the improved rate capability of H-TiO2 results from the enhanced contribution of pseudocapacitive lithium storage on the particle surface. Combined with the structural properties of H-TiO2, it is suggested that the disordered surface layers and Ti3+ species of H-TiO2 play an important role in the improvement of pseudocapacitive lithium storage. The results help to understand the fast lithium storage performance of H-TiO2 and might pave the way for further studies of other hydrogenated metal oxide electrodes for high power LIBs.

Polyproline fold—In imparting kinetic stability to an alkaline serine endopeptidase

Polyproline II (PPII) fold, an unusual structural element was detected in the serine protease from Nocardiopsis sp. NCIM 5124 (NprotI) based on far UV circular dichroism spectrum, structural transitions of the enzyme in presence of GdnHCl and a distinct isodichroic point in chemical and thermal denaturation. The functional activity and conformational transitions of the enzyme were studied under various denaturing conditions. Enzymatic activity of NprotI was stable in the vicinity of GdnHCl upto 6.0M concentration, organic solvents viz. methanol, ethanol, propanol (all 90% v/v), acetonitrile (75% v/v) and proteases such as trypsin, chymotrypsin and proteinase K (NprotI:protease 10:1). NprotI seems to be a kinetically stable protease with a high energy barrier between folded and unfolded states. Also, an enhancement in the activity of the enzyme was observed in 1M GdnHCl upto 8h, in organic solvents (75% v/v) for 72h and in presence of proteolytic enzymes. The polyproline fold remained unaltered or became more prominent under the above mentioned conditions. However, it diminished gradually during thermal denaturation above 60°C. Thermal transition studies by differential scanning calorimetry (DSC) showed scan rate dependence as well as irreversibility of denaturation, the properties characteristic of kinetically stable proteins. This is the first report of PPII helix being the global conformation of a non structural protein, an alkaline serine protease, from a microbial source, imparting kinetic stability to the protein.

Electrochemical biosensor for the selective determination of hydrogen peroxide based on the co-deposition of palladium, horseradish peroxidase on functionalized-graphene modified graphite electrode as composite

A sensitive and noble amperometric biosensor was developed by the co-deposition of palladium and horseradish peroxidase (HRP) on functionalized graphene (f-graphene) modified graphite electrode. The physical morphology of the modified electrodes was characterized using scanning electron microscopy and energy dispersive analysis of X-ray. The electrochemical behavior of the enzyme modified electrode towards hydrogen peroxide (H2O2) detection was evaluated using cyclic voltammetry and differential pulse voltammetry techniques where as the electrical conductivity and capacitance was investigated by electrochemical impedance spectroscopy. The effects of scan rate, pH, and temperature dependence on the current response of the biosensor were analyzed for sensitive analytical performance. The modified electrode exhibits a fast amperometric response of <2s, good linear range of 25μM–3.5mM, effective sensitivity of 92.82μAmM−1cm−2, activation energy of 9.84kJM−1 and extraordinary Michaelis–Menten’s constant (KMapp) of 0.11mM. This could be attributed to high affinity, bioactivity of HRP and also due to the synergistic effects of HRP, Pd and f-graphene on the developed biosensor. The KMapp value obtained in this study is lower than those of the electrodes reported earlier. The modified electrode also reports a remarkable decrease of over potential for the detection of H2O2 that decreases the interference of the other substances and retains the selectivity for H2O2. The biosensor showed better reproducibility and stability with a good electrochemical response indicating that it can be stored up to 4weeks without loosing its activity. In addition the modified electrode was utilized for real sample analysis that displayed good satisfactory results.

Voltammetry of dehaloperoxidase on self-assembled monolayers: Reversible adsorptive immobilization of a globin

Dehaloperoxidase (DHP), a monomeric hemoglobin, was adsorptively immobilized under low ionic strength conditions on binary self-assembled monolayers composed of OH- and COOH-terminated alkylthiols. Voltammetry of its Fe(III)/Fe(II) reactions revealed adsorbed DHP to be electroactive and native under both anaerobic and aerobic conditions. The chemically reversible nature of the adsorptive immobilization was established from voltammetric desorption/re-adsorption experiments. Cyclic voltammetric determination of electroactive surface concentration uncovered an unusual inverse scan rate dependence that was rationalized by means of Hoffman's dynamic docking electron transfer model [Z.-X. Liang et al., J. Am. Chem. Soc. 126 (2004) 2785]. This result represents the first evidence for dynamic docking control of protein electron transfer in an electrochemical setting.

Spectroelectrochemical Characterization of Small Hemoproteins Adsorbed within Nanostructured Mesoporous ITO Electrodes

3D nanostructured transparent indium tin oxide (ITO) electrodes prepared by glancing angle deposition (GLAD) were used for the spectroelectrochemical characterization of cytochrome c (Cyt c) and neuroglobin (Nb). These small hemoproteins, involved as electron-transfer partners in the prevention of apoptosis, are oppositely charged at physiological pH and can each be adsorbed within the ITO network under different pH conditions. The resulting modified electrodes were investigated by UV-visible absorption spectroscopy coupled with cyclic voltammetry. By using nondenaturating adsorption conditions, we demonstrate that both proteins are capable of direct electron transfer to the conductive ITO surface, sharing apparent standard potentials similar to those reported in solution. Preservation of the 3D protein structure upon adsorption was confirmed by resonance Raman (rR) spectroscopy. Analysis of the derivative cyclic voltabsorptograms (DCVA) monitored either in the Soret or the Q bands at scan rates up to 1 V s(-1) allowed us to investigate direct interfacial electron transfer kinetics. From the DCVA shape and scan rate dependences, we conclude that the interaction of Cyt c with the ITO surface is more specific than Nb, suggesting an oriented adsorption of Cyt c and a random adsorption of Nb on the ITO surface. At the same time, Cyt c appears more sensitive to the experimental adsorption conditions, and complete denaturation of Cyt c may occur as evidenced from cross-correlation of rR spectroscopy and spectroelectrochemistry.