Electrochemical study of the interaction between cytochrome c and DNA at a modified gold electrode

The direct electron transfer of surface-confined horse heart cytochrome c (Cyt c) was achieved using COOH-terminated alkanethiolate-modified gold electrode. Later DNA was immobilized on the two-layer modified electrode. The quantitative determination of DNA was explored and the interaction between cytochrome c and DNA was studied. The binding site sizes were determined to be 15 bp per Cyt c molecule with double-stranded (ds) DNA and 30 nucleotides binding one Cyt c molecule with single-stranded (ss) DNA. At the dsDNA/Cyt c/MUA/Au electrode, the rate constant of oxidation electron transfer k(s,ox)=1.59x10(-3)cms-1 was obtained, at the ssDNA/Cyt c/MUA/Au electrode, the value was 2.43x10(-3)ms-1 when the scan rate was 1.0V/s. The different electrodes were characterized with electrochemical quartz crystal microbalance and atomic force microscope.     

Precise blood lead analysis using a combined internal standard and standard addition approach with disposable screen-printed electrodes

We report here a highly accurate and efficient method for blood lead analysis (BLA) through the use of a disposable electrode. A new type of mercury-plated preanodized screen-printed carbon electrode, together with a thallium(III) internal standard, simplifies calibration and gives easily quantifiable signals for accurate BLA. A preanodization procedure improves the preconcentration ability of the working electrode through the effect of lead (Pb) complexing with an electrogenerated surface functional group, mainly >C=O. Under optimized conditions, the ratio of the anodic stripping peak currents of Pb and Tl (i.e., i(Pb)/i(Tl)) is linear against [Pb] in the window of 1-300 ppb with a correlation coefficient and detection limit (signal-to-noise ratio=3) of 0.999 and 0.23 ppb, respectively. This approach was used to analyze blood samples (n=55) from workers at a local battery factory. The results are consistent with those obtained from graphite furnace atomic absorption spectroscopy and confirm the applicability of the proposed method.     

Salicylate poly(vinyl chloride) membrane electrode based on (2-[(E)-2-(4-nitrophenyl) hydrazono]-1-phenyl-2-(2-quinolyl)-1-ethanone) Cu(II)

A new salicylate-selective electrode based on the complex of (2-[(E)-2-(4-nitrophenyl)hydrazono]-1-phenyl-2-(2-quinolyl)-1-ethanone) Cu(II) as the membrane carrier was developed. The electrode exhibited a good Nernstian slope of -59.6+/-1.0 mV/decade and a linear range of 1.0 x 10(-6) to 1.0M for salicylate. The limit of detection was 5.0 x 10(-7) M. The electrode had a fast response time of 10 s and can be used for more than 3 months. The selective coefficients were determined by the fixed interference method and could be used in the pH range of 4.0 to 10.5. The electrode was employed as an indicator electrode for direct determination of salicylate in pharmaceutical and biological samples.     

Application of Non-invasive Microsensing System to Simultaneously Measure Both H+ and O2 Fluxes Around the Pollen Tube

Various ionic and molecular activities in the extracellular environment are vital to plant cell physiological processes. A noninvasive microsensing system (NMS) based on either the scanning ion-selective electrode technique (SIET) or the scanning polarographic electrode technique (SPET) is able to obtain information regarding the transportation of various ions/molecules in intact samples under normal physiological conditions. The two-probe simultaneous test system (2STS) is an integrated system composed of SIET,SPET, and a Xu-Kunkel sampling protocol. In the present study, 2STS was able to simultaneously measure fluxes of H+ and O2 of the lily (Lilium Iongiflorum Thunb. cv. Ace) pollen tube while avoiding interference between the two probes. The results indicate that the proton fluxes were effluxes, whereas the oxygen fluxes were influxes, and they were closely correlated to each other surrounding the constitutive alkaline band region. Specifically, when the proton effluxes increased, the oxygen influxes also increased. Therefore,the hypothesis of condensed active mitochondria existing in the alkalized area of the pollen tube proposed by Hepler's group is supported.     

Dynamics of the ion cyclotron resonance effect on amino acids adsorbed at the interfaces

In this study we show a reproduction of the Zhadin experiment, which consists of the transient increase of the electrolytic current flow across an aqueous solution of L-arginine and L-glutamic acid induced by a proper low frequency alternating magnetic field superimposed to a static magnetic field of higher strength. We have identified the mechanisms that were at the origin of the so-far poor reproducibility of the above effect: the state of polarization of the electrode turned out to be a key parameter. The electrochemical investigation of the system shows that the observed phenomenon involves the transitory activation of the anode due to ion cyclotron frequency effect, followed again by anode passivation due to the adsorption of amino acid and its oxidation products. The likely occurrence of similar ion cyclotron resonance (ICR) phenomena at biological membranes, the implications on ion circulation in living matter, and the consequent biological impact of environmental magnetic fields are eventually discussed.     

Simultaneous determination of dopamine, ascorbic acid, and uric acid using carbon ionic liquid electrode

A recently constructed carbon composite electrode using room temperature ionic liquid as pasting binder was employed as a novel electrode for sensitive, simultaneous determination of dopamine (DA), ascorbic acid (AA), and uric acid (UA). The apparent reversibility and kinetics of the electrochemical reaction for DA, AA, and UA found were improved significantly compared to those obtained using a conventional carbon paste electrode. The results show that carbon ionic liquid electrode (CILE) reduces the overpotential of DA, AA, and UA oxidation, without showing any fouling effect due to the deposition of their oxidized products. In the case of DA, the oxidation and reduction peak potentials appear at 210 and 135mV (vs Ag/AgCl, KCl, 3.0M), respectively, and the CILE shows a significantly better reversibility for dopamine. The oxidation peak due to the oxidation of AA occurs at about 60mV. For UA, a sharp oxidation peak at 340mV and a small reduction peak at 250mV are obtained at CILE. Differential pulse voltammetry was used for the simultaneous determination of ternary mixtures of DA, AA, and UA. Relative standard deviation for DA, AA, and UA determinations were less than 3.0% and DA, AA, and UA can be determined in the ranges of 2.0x10(-6)-1.5x10(-3), 5.0x10(-5)-7.4x10(-3), and 2.0x10(-6)-2.2x10(-4)M, respectively. The method was applied to the determination of DA, AA, and UA in human blood serum and urine samples.     

Effects of changes in the shape of the intracellular action potential on the peak-to-peak ratio of single muscle fibre potentials

In situ recording of the intracellular action potential (IAP) of human muscle fibres is not yet feasible, and consequently, knowledge about certain IAP characteristics of these IAPs is still limited. The ratio between the amplitudes of the second and first phases (the so-called peak-to-peak ratio, PPR) of a single fibre action potential (SFAP) is known to be closely related to the IAP profile. The PPR of experimentally recorded SFAPs has been found to be largely independent of changes in the fibre-to-electrode (radial) distance. The main goal of this paper is to analyze the effect of changes in different aspects of the IAP spike on the relationship between PPR and radial distance. Based on this analysis, we hypothesize about the characteristics of IAPs obtained experimentally. It was found that the sensitivity of the SFAP PPR to changes in radial distance is essentially governed by the duration of the IAP spike. Assuming that, for mammals, the duration of the IAP rising phase lies within the range 0.2-0.4 ms, we tentatively suggest that the duration of the IAP spike should be over approximately 0.75 ms, with the shape of the spike strongly asymmetric. These IAP characteristics broadly coincide with those observed in mammal IAPs.     

Tailoring Electrode/Electrolyte Interfacial Properties in Flexible Supercapacitors by Applying Pressure

Electrode/electrolyte interfacial properties of flexible supercapacitors assembled with nanostructured activated carbon fabric (ACF) electrodes can be tailored by applying a pressure and tuning electrolyte ion size relative to electrode pore size. Experimental results reveal that increasing pressure between the supercapacitor electrodes can significantly improve capacitive performance. The ratio of solvated ion size in the electrolyte to the pore size on the electrodes determines the minimum pressure necessary to achieve an optimum performance. For a specific electrode material, this minimum pressure for optimum performance is primarily governed by the size of the larger solvated ions (either the anions or cations), and is lower (～689 KPa) when the ratio of the solvated ion size to the pore size is higher than 0.6, and is higher (at least 1379 KPa) when the ratio is lower than 0.6. An analytical model capable of predicting the experimental performance data has been developed. These results together provide a fundamental understanding of pressure dependence of electrode/electrolyte interfacial properties and pave the way for practical applications of flexible supercapacitors.     

A D-pathway mutation decouples the Paracoccus denitrificans cytochrome c oxidase by altering the side-chain orientation of a distant conserved glutamate

Asparagine 131, located near the cytoplasmic entrance of the D-pathway in subunit I of the Paracoccus denitrificans aa(3) cytochrome c oxidase, is a residue crucial for proton pumping. When replaced by an aspartate, the mutant enzyme is completely decoupled: while retaining full cytochrome c oxidation activity, it does not pump protons. The same phenotype is observed for two other substitutions at this position (N131E and N131C), whereas a conservative replacement by glutamine affects both activities of the enzyme. The N131D variant oxidase was crystallized and its structure was solved to 2.32-A resolution, revealing no significant overall change in the protein structure when compared with the wild type (WT), except for an alternative orientation of the E278 side chain in addition to its WT conformation. Moreover, remarkable differences in the crystallographically resolved chain of water molecules in the D-pathway are found for the variant: four water molecules that are observed in the water chain between N131 and E278 in the WT structure are not visible in the variant, indicating a higher mobility of these water molecules. Electrochemically induced Fourier transform infrared difference spectra of decoupled mutants confirm that the protonation state of E278 is unaltered by these mutations but indicate a distinct perturbation in the hydrogen-bonding environment of this residue. Furthermore, they suggest that the carboxylate side chain of the N131D mutant is deprotonated. These findings are discussed in terms of their mechanistic implications for proton routing through the D-pathway of cytochrome c oxidase.