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At least 1,315 records · Page 73Linked to original sources
PubMed2002

Effects of acute stimulation through contacts placed on the motor cortex for chronic stimulation.

OBJECTIVES: We tried to determine which neural elements were activated in awake subjects by stimulation through contacts placed chronically on the motor cortex. METHODS: We recorded the motor effects of stimulation through 4 disc contacts placed in the subdural space over the motor cortex in 9 patients undergoing chronic stimulation for the control of pain or for the control of the rigidity of multiple system atrophy. RESULTS: Single stimuli could elicit short latency motor evoked potentials or facilitate active motoneurons in the contralateral limbs. The responsible neural elements had a short chronaxie (the pulse duration necessary to reach threshold with a stimulus intensity twice that required to reach threshold at the longest pulse duration used) and refractory period implying that they were myelinated axons. The facilitation was larger with cathodal than with anodal monopolar stimulation. The short latency facilitation in response to the second of two stimuli was greater at condition test intervals of 2-5 ms. This enhancement could be demonstrated with conditioning stimuli subthreshold for the excitation of active motoneurons suggesting that it arose, in part, at the level of the cortex. Single cortical stimuli could result in inhibition of voluntarily activated motoneurons. The inhibition was larger with cathodal than anodal monopolar stimulation. The responsible neural elements also had a short chronaxie and refractory period. CONCLUSIONS: Stimulation in awake subjects through contacts placed chronically over the motor cortex appears to activate axons in the cortex, which excite both corticospinal neurons and inhibitory neurons.

Adult↗
PubMed2004

Effect of transcranial DC sensorimotor cortex stimulation on somatosensory evoked potentials in humans.

OBJECTIVE: To study the after-effect of transcranial direct current stimulation (tDCS) over the sensorimotor cortex on the size of somatosensory evoked potentials (SEPs) in humans. METHODS: SEPs were elicited by electrical stimulation of right or left median nerve at the wrist before and after anodal or cathodal tDCS in 8 healthy subjects. tDCS was applied for 10 min to the left motor cortex at a current strength of 1 mA. RESULTS: Amplitudes of P25/N33, N33/P40 (parietal components) and P22/N30 (frontal component) following right median nerve stimulation were significantly increased for at least 60 min after the end of anodal tDCS, whereas P14/N20, N20/P25 (parietal components) and N18/P22 (frontal component) were unaffected. There was no effect on SEPs evoked by left median nerve stimulation. Cathodal tDCS had no effect on SEPs evoked from stimulation of either arm. CONCLUSIONS: Anodal tDCS over the sensorimotor cortex can induce a long-lasting increase in the size of ipsilateral cortical components of SEPs. SIGNIFICANCE: tDCS can modulate cortical somatosensory processing in humans and might be a useful tool to induce plasticity in cortical sensory processing.

Adult↗
PubMed2002

A glucose/hydrogen peroxide biofuel cell that uses oxidase and peroxidase as catalysts by composite bulk-modified bioelectrodes based on a solid binding matrix.

An improved composite bulk-modified bioelectrode setup based on a solid binding matrix (SBM) has been used to develop a glucose/hydrogen peroxide biofuel cell. Fuel is combined through a catalytically promoted reaction with oxygen into and oxidized species and electricity. The present work explores the feasibility of a sugar-feed biofuel cell based on SBM technology. The biofuel cell that utilizes mediators as electron transporters from the glucose oxidation pathway of the enzyme directly to electrodes is considered in this work. The anode was a glucose oxidase (GOx, EC 1.1.3.4)/ferrocene-modified SBM/graphite composite electrode. The cathode was a horseradish peroxidase (HRP, EC 1.11.1.7)/ferrocene-modified SBM/graphite composite electrode. The composite transducer material was layered on a wide polymeric surface to obtain the biomodified electrodic elements, anodes and cathodes and were assembled into a biofuel cell using glucose and H(2)O(2) as the fuel substrate and the oxidizer. The electrochemical properties and the characteristics of single composite bioelectrodes are described. The open-circuit voltage of the cell was 0.22 V, and the power output of the cell was 0.15 microW/cm(2) at 0.021 V. The biofuel cell proved to be stable for an extended period of continuous work (30 days). The reproducibility of the biotransducers fabrication was also investigated. In addition, an application of presented biofuel cell, e.g. the use of hydrolyzed corn syrup as renewable biofuels, was discussed.

Electrodes↗
PubMed1992

Influence of tyrosine on the dual electrode electrochemical detection of copper(II)-peptide complexes.

The bluret reaction makes peptides electrochemically active. This is the basis of an electrochemical method for the detection of peptides following their liquid chromatographic separation. This paper discusses the influence of tyrosine, an electroactive amino acid, on the detection of Cu(II)-peptide (bluret) complexes containing it. The dual electrode detector has an upstream anode and a downstream cathode. Tyrosine-containing peptides yield anodic signals that are approximately the sum of the tyrosine signal and the signal from the bluret complex of a nonelectroactive model peptide, phenylalanylglycyl-glycine (FGG). The cathodic signal is depressed in comparison to FGG. This is traced to the presence of an intramolecular reaction between Cu(III) and a reaction product resulting from the oxidation of the tyrosinyl residue. The rate constant for the corresponding intermolecular reaction is significant (10(6)-10(7) M-1 s-1), but in practical analytical situations, the concentrations of the reactants will be small, so the reaction will not be a major factor. Sensitivities for several bioactive peptides are reported. The dependence of the signals on the position of tyrosine in a tripeptide is also studied.

Amino Acid Sequence↗
PubMed1995

Rotating ring-disk electrode study of copper(II) complexes of the model peptides triglycine, tetraglycine, and pentaglycine.

The reversible electrochemistry of the Cu(II)/Cu(III) couple was investigated for the copper(II) complexes of triglycine (G3), tetraglycine (G4), and pentaglycine (G5) in alkaline solution using a rotating ring-disk electrode (RRDE). The study was motivated by the need to elucidate electrochemical processes occurring in dual electrode postcolumn detection of peptides. The disk electrode served as the anode and the ring electrode as the cathode. The electrode was used in both linear sweep voltammetry and constant potential, varied rotation speed modes. Redox waves for two generic forms of the complexes, Cu(II)-NNNN and Cu(II)-NNNO, were identified, with respective E1/2 values of approximately 0.45 and 0.7 V. It was found that the G3 complex underwent an ECE-like process at the anode that magnified the anodic signal and suppressed the cathodic signal. The G4 and G5 complexes were subject to two CE processes, the C reactions being (i) deprotonation of Cu(II)-NNNO to Cu(II)-NNNN and (ii) loss of hydroxide ion by Cu(II)-NNN(OH-), a variant of Cu(II)-NNNO. An additional C reaction, dissociation of a carbonate variant of Cu(II)-NNNO, occurred in 0.2 M carbonate buffer. Visible absorbance measurements assisted in assignment of these forms. Measurements of diffusion coefficients of the complexes were performed by Taylor-Aris laminar flow axial dispersion measurements. The analytical implications for these findings are discussed.

Buffers↗
PubMed2001

Use of dyes to investigate migration of the chiral selector in CFFE and the impact on the chiral separations.

Continuous free flow electrophoresis was investigated as a tool for the preparative chiral separation of piperoxan enantiomers using sulfated beta-cyclodextrin (sbeta-CD) as the chiral additive. Bulk migration of sbeta-CD was confirmed using LC-MS analysis of the individual fractions collected and visualized with the addition of crystal violet to the separation buffer. In the absence of sbeta-CD, the crystal violet-containing buffer was reddish/purple and the crystal violet was deflected cathodically in the chamber. In the presence of sbeta-CD, the crystal violet-containing buffer was blue and was deflected anodically. However, formation of accumulation and depletion zones was apparent in both cases. The addition of sbeta-CD to the cathodic wash solution allowed for almost complete resolution of the piperoxan enantiomers with a processing rate of 0.45 mg/ h.

Coloring Agents↗
PubMed2001

Evaluations of the stability of sheathless electrospray ionization mass spectrometry emitters using electrochemical techniques.

The processes that cause the failure of sheathless electrospray ionization (ESI) emitters, based on different kinds of gold coatings on fused-silica capillaries, are described and explained. The methods chosen for this study include electrochemical methods, ICPMS analysis of the electrolytes used, SEM studies, and electrospray experiments. Generally, the failure occurs by loss of the conductive coating. It is shown that emitters with sputter-coated gold lose their coatings because of mechanical stress caused by the gas evolution accompanying water oxidation or reduction. Emitters with gold coatings on top of adhesion layers of chromium and nickel alloy withstand this mechanical stress and have excellent durability when operating as cathodes. When operating as anodes, the adhesion layer is electrochemically dissolved through the gold film, and the gold film then flakes off. It is shown that the conductive coating behaves as a cathode even in the positive electrospray mode when the magnitude of a superimposed reductive electrophoretic current exceeds that of the oxidative electrospray current. Fairy-dust coatings developed in our laboratory (see Barnidge, D. R.; etal.Anal. Chem. 1999, 71, 4115-4118,) bygluing gold dust onto the emitter, are unaffected by the mechanical stress due to gas evolution. When oxidized, the fairy-dust coatings show an increased surface roughness and decreased conductivities due to the formation of gold oxide. The resistance of this oxide layer is however negligible in comparison with that of the gas phase in ESI. Furthermore, since no flaking and only negligible electrochemical etching of gold was found, practically unlimited emitter lifetimes may be achieved with fairy-dust coatings.

Journal Article↗
PubMed2002

Anomalous radial migration of single DNA molecules in capillary electrophoresis.

We report the unexpected radial migration of DNA molecules in capillary electrophoresis (CE) with applied Poiseuille flow. Such movement can contribute to anomalous migration times, peak dispersion, and size and shape selectivity in CE. When Poiseuille flow is applied from the cathode to the anode, DNA molecules move toward the center of the capillary, forming a narrow, highly concentrated zone. Conversely, when the flow is applied from the anode to the cathode, DNA molecules move toward the walls, leaving a DNA-depleted zone around the axis. We showed that the deformation and orientation of DNA molecules under Poiseuille flow was responsible for the radial migration. By analyzing the forces acting on the deformed and oriented DNA molecules, we derived an expression for the radial lift force, which explained our results very well under different conditions with Poiseuille flow only, electrophoresis only, and the combination of Poiseuille flow and electrophoresis. Factors governing the direction and velocity of radial migration were elucidated. Potential applications of this phenomenon include an alternative to sheath flow in flow cytometry, improving precision and reliability of single-molecule detection, reduction of wall adsorption, and size separation with a mechanism akin to field-flow fractionation. On the negative side, nonuniform electroosmotic flow along the capillary or microfluidic channel is common in CE, and radial migration of certain analytes cannot be neglected.

DNA↗
PubMed2004

Electroanalytical determination of trace chloride in room-temperature ionic liquids.

The electroanalytical quantification of chloride in [C4mim][BF4], [C4mim][NTf2], and [C4mim][PF6] ionic liquids has been explored using linear sweep and square wave voltammetry. Cathodic stripping voltammetry at a silver disk electrode is found to be the most sensitive. The methodology is based on first holding the potential of the electrode at +2.0 V (vs Ag wire), to accumulate silver chloride at the electrode. On applying a cathodic scan, a stripping wave is observed corresponding to the reduction of the silver chloride. This stripping protocol was found to detect ppb levels of chloride in [C4mim][BF4], [C4mim][NTf2], and [C4mim][PF6]. Although other methods for chloride have been reported for [BF4](-)- and [PF6](-)-based ionic liquids, no methods have been reported for [NTf2](-) ionic liquids.

Journal Article↗
PubMed2003

Real-time determination of picomolar free Cu(II) in seawater using a fluorescence-based fiber optic biosensor.

We report real-time, in situ determination of free copper ion at picomolar levels in seawater using a fluorescence-based fiber optic biosensor. The sensor transducer is a protein molecule, site-specifically labeled with a fluorophore that is attached to the distal end of an optical fiber, which binds free Cu(II) with high affinity and selectivity. The transducer reports the metal's concentration as a change in fluorescence intensity or lifetime, using a frequency domain approach. The transducer's response time is diffusion-limited, with a typical measurement requiring 30 s. The sensor demonstrates a detection limit of 0.1 pM free Cu(II) in a seawater model. Accuracy and precision of the sensor were at least comparable to cathodic ligand exchange/adsorptive cathodic stripping voltammetry. Measurements of tidal flushing of a copper-contaminated inlet are shown.

Biosensing Techniques↗
PubMed2004

Protein characterization by on-line capillary isoelectric focusing, reversed-phase liquid chromatography, and mass spectrometry.

Two-dimensional polyacrylmide gel electrophoresis (2D-PAGE), perhaps the most widely used method in proteomics research, is often limited by sensitivity and throughput. Capillary isoelectric focusing (CIEF) coupled with electrospray ionization (ESI) mass spectrometry (MS) provides a liquid-based alternative to 2D-PAGE that can overcome these problems but is limited by ampholyte interference and signal quenching in ESI-MS. Inserting a reversed-phase liquid chromatography (RPLC) step between CIEF and MS can remove this interference. In this work, a CIEF-RPLC-MS system is described for separation and characterization of proteins in complex mixtures. CIEF is performed with a microdialysis membrane-based cathodic cell that also permits protein fractions to be collected, washed to remove ampholyte, and analyzed by RPLC-MS. CIEF performance with this cell is equivalent to that achieved with a conventional cathodic cell, and no loss of protein is observed during faction collection. The cell can be easily and safely retrofitted into commercial instrumentation and is applicable for peptide analysis as well. Protein detection at the low-femtomole level is demonstrated with little or no interference from ampholyte, and CIEF-RPLC-MS data are used to construct a plot of pI vs MW for a protein mixture. The current instrumental configuration allows seven fractions in the pI range 3-10 to be analyzed by RPLC-MS in 2 h.

Chromatography, Liquid↗
PubMed2005

Characterization of oligodeoxynucleotides by electron detachment dissociation fourier transform ion cyclotron resonance mass spectrometry.

Electron detachment dissociation (EDD), recently introduced by Zubarev and co-workers for the dissociation of multiply charged biomolecular anions via a radical ion intermediate, has been shown to be analogous to electron capture dissociation (ECD) in several respects, including more random peptide fragmentation and retention of labile posttranslational modifications. We have previously demonstrated unique fragmentation behavior in ECD compared to vibrational excitation for oligodeoxynucleotide cations. However, that approach is limited by the poor sensitivity for oligonucleotide ionization in positive ion mode. Here, we show implementation of EDD on a commercial Fourier transform ion cyclotron resonance mass spectrometer utilizing two different configurations: a heated filament electron source and an indirectly heated hollow dispenser cathode electron source. The dispenser cathode configuration provides higher EDD efficiency and additional fragmentation channels for hexamer oligodeoxynucleotides. As in ECD, even-electron d/w ion series dominate the spectra, but we also detect numerous a/z (both even-electron and radical species), (a/z - B), c/x, (c/x - B), and (d/w - B) ions with minimal nucleobase loss from the precursor ions. In contrast to previous high-energy collision-activated dissociation (CAD) and ion trap CAD of radical oligonucleotide anions, we only observe minimum sugar cross-ring cleavage, possibly due to the short time scale of EDD, which limits secondary fragmentation. Thus, EDD provides fragmentation similar to ECD for oligodeoxynucleotides but at enhanced sensitivity. Finally, we show that noncovalent bonding in a DNA duplex can be preserved following EDD, illustrating another analogy with ECD. We believe the latter finding implies EDD has promise for characterization of nucleic acid structure and folding.

Cyclotrons↗
PubMed2004

Multichannel electrochemiluminescence of luminol in neutral and alkaline aqueous solutions on a gold nanoparticle self-assembled electrode.

The electrochemiluminescence (ECL) behavior of luminol on a gold nanoparticle self-assembled electrode in neutral and alkaline pH conditions was studied under conventional cyclic voltammetry (CV). The gold nanoparticle self-assembled electrode exhibited excellent electrocatalytic property and redox reactivity to the luminol ECL system. In neutral solution, four ECL peaks were observed at 0.69, 1.03, -0.45, and -1.22 V (vs SCE) on the curve of ECL intensity versus potential. Compared with a bulk gold electrode, two anodic and one cathodic ECL peaks were greatly enhanced, and one new cathodic ECL peak appeared. In alkaline solution, two anodic ECL peaks were obtained at 0.69 and 1.03 V, which were much stronger than those on a bulk gold electrode. These ECL peaks were found to depend on gold nanoparticles on the surface of the electrode, potential scan direction and range, the presence of O(2) or N(2), the pH and concentration of luminol solution, NaBr concentration, and scan rate. The emitter of all ECL peaks was identified as 3-aminophthalate by analyzing the ECL spectra. The spatial distribution of the luminol ECL peaks on the gold nanoparticle self-assembled electrode was studied by CCD. The surface state of the gold nanoparticle self-assembled electrode was characterized by scanning electron microscopy (SEM) and UV-visible reflection spectra. The mechanism for the formation of these ECL peaks has been proposed. The results indicate that the gold nanoparticle self-assembled electrode could lead to novel ECL properties, and strong luminol ECL in neutral and alkaline solutions could be obtained on such an electrode, which is of great analytical potential.

Journal Article↗
PubMed1981

Simian liver alcohol dehydrogenase: isolation and characterization of isoenzymes from Macaca mulatta.

Like human liver alcohol dehydrogenase, that of Macaca mulatta can be purified and separated into anodic and cathodic pyrazole-insensitive and cathodic pyrazole-sensitive enzyme forms. Their inhibition by 4-methylpyrazole and their substrate specificities are analogous to those observed for the corresponding isoenzymes of human liver. However, on the basis of data available so far, the physiochemical and compositional characteristics, i.e., molecular weight, zinc content, and dimeric structure, of all simian alcohol dehydrogenase forms are virtually identical with those of other mammalian alcohol dehydrogenases studied up to now. Zinc is essential for their enzymatic function, as demonstrated by inhibition with chelating agents.

Alcohol Dehydrogenase↗
PubMed1975

The macromolecular composition of Xenopus laevis egg jelly coat.

The three morphologically and functionally distinct jelly coat layers of Xenopus laevis eggs, J1, J2, and J3, were separated by manual dissection, solubilized with dithiothreitol, and physicochemically analyzed. The chemical composition of the three jelly layers varied from 37 to 48% protein and 63 to 52% carbohydrate. The carbohydrate consisted of hexosamines, galactose, and fucose. Some of the carbohydrate in each of the jelly layers was covalently linked to protein through O-glycosidic bonds as beta elimination of the carbohydrate moiety in the presence of alkali was observed. In agreement with a previous finding, covalently attached sulfate was localized within the innermost jelly coat layer, J1. Cellulose acetate electrophoresis at pH 8.0 resolved a total of nine macromolecular components from the three jelly coat layers differentially staining for protein and carbohydrate: J1 yielded two anodically migrating components; the middle layer J2 yielded two cathodically migrating macromolecular components; the outermost layer J3 contained five species, three anodic and two cathodic. Sodium dodecyl sulfate agarose gel electrophoresis analysis yielded nine unique species, six of which stained coincidently for protein and carbohydrate. Immunoelectrophoresis and Ouchterlony double diffusion analyses using antiserum to total jelly components resolved nine different antigenic species with cross-reactivity between one or two macromolecules in layers J1 and J3. Analytical sedimentation velocity centrifugation revealed eight distinct species all of which exhibited hypersharp schlieren patterns and whose s20,w values were highly concentration dependent. On the basis of these analyses, Xenopus laevis egg jelly layers are composed of at least 8-9 distinct macromolecular species. The majority of these macromolecules are uniquely associated with different jelly coat layers.

Animals↗
PubMedDate not supplied

Complete deoxygenation from a hemoglobin solution by an electrochemical method and heat treatment for virus inactivation.

Hemoglobin (Hb) has been widely studied as a raw material for various types of oxygen carriers. In the purification of Hb from red blood cells including virus inactivation and denaturation of other proteins and the long-term storage of Hb vesicles (HbV), a deoxygenation process is one of the important processes because of the high stability of deoxygenated Hb to heating and metHb formation. Though an oxygenated Hb solution can be deoxygenated with an artificial lung, it is difficult to reduce the oxygen partial pressure of the Hb solution to less than 10 Torr. We developed an electrochemical system for complete deoxygenation of the Hb solution at the cathode compartment using hydrogen containing nitrogen gas at the anode compartment. Oxygen in the Hb solution was reduced to OH(-) at the cathode compartment within several minutes at a potential value of -1.67 V and was finally converted to water by neutralization with H(+) from the anode in the whole system. The resulting completely deoxygenated Hb could tolerate heat treatment at 62 degrees C for 10 h with no denaturation of deoxygenated Hb. The metHb formation rate of reoxygenated Hb at 37 degrees C was not changed after heat treatment. Furthermore, vesicular stomatitis virus (VSV) could be inactivated at an inactivation degree of more than 5.96 log by heat treatment.

Animals↗
PubMed2001

Major ion and electrical potential distribution in soil under electrokinetic remediation.

To assess the effect of pore water chemistry on the contaminant removal rate, we monitored major ion concentrations in the pore water and the electrical potential distribution of a soil during electrokinetic remediation treatment. On application of the voltage, the soil near the anode became acidic due to the electrolytic generation of H+, and the acid region gradually spread toward the cathode. The major cation in the acid region was, however, not H+ but Al3+ that arose from the acid-induced dissolution of soil minerals, and it migrated very slowly toward the cathode. The measured pH and accompanying ion concentrations indicated that the anomalously slow migration of Al3+ was due to its precipitation-dissolution reaction at the acid front. The stagnancy of Al3+ increased the ionic concentration, flattened the electrical potential profile, and in turn, diminished electromigration in the acid region. This seems to be one of the causes of the relatively low removal rate of cationic and anionic contaminants in electrokinetic treatments.

Aluminum↗
PubMed2002

An electrochemical system for removing and recovering elemental mercury from a gas stream.

The impending EPA regulations on the control of mercury emissions from the flue stacks of coal-burning electric utilities has resulted in the development of numerous advanced mercury control technologies such as sorbent injection and in-situ mercury oxidation. Although these technologies can effectively remove mercury from a flue stack they share, along with many other technologies, the common shortcoming of intermedia pollution transfer i.e. the traffic of mercury from the air phase to the solid phase and the subsequent generation of residue for landfill. This work addresses the need for an integrated system of mercury removal and recovery from flue stack gases and from the environment. The research explored the capture of elemental mercury from the gas phase at ambient temperature on an electrically conductive porous sorbent. The mercury loaded sorbent was regenerated at the anode in an electrochemical cell and the oxidized mercury recovered at the cathode as solid elemental mercury. Activated carbon cloth was selected as the most suitable sorbent as it had the highest mercury adsorption capacity of the sorbents tested and was electrically conductive. Direct and indirect electro-oxidation were shown to remove 95% and 100%, respectively, of the elemental mercury from the carbon cloth. After regeneration the carbon cloth was reused without any loss in mercury adsorption capacity. More than 99% of the mercury stripped from the cloth during regeneration was recovered at the cathode.

Adsorption↗