bluuebunny/crossref_metadata_2025 huggingface dataset:
Enzyme‐catalyzed direct electron transfer: Fundamentals and analytical applications
Authors: Ghindilis Andrey L. , Atanasov Plamen , Wilkins Ebtisam
Published: May 2005

This article overviews the fundamentals of the phenomenon of direct electron transfer in enzyme‐catalyzed electrode reactions and the development of electroanalytical applications of the bioelectrocatalytic systems. A brief description of the enzymes capable of catalyzing electrochemical reactions by means of direct electron transfer is given. The physico‐chemical background of bioelectrocatalysis is discussed in terms of the different concepts underlying the mechanism of electron transfer. The concept of a “molecular transducer” is introduced to designate a complex, formed by the electrocatalytically active enzyme on the electrode‐electrolyte interface, which is directly responsible for the transduction of the chemical signal to an electric one. The role of this “molecular transducer” in enzyme electrodes and immunoelectrodes is discussed. The analytical applications of bioelectrocatalysis are categorized as systems employing either amperometric or potentiometric detection. Discussion focuses on the advantages of systems based on enzyme‐catalyzed direct electron transfer as opposed to other enzyme‐catalyzed electroanalytical devices. In conclusion, the trends towards upcoming practical applications are suggested as well as some directions in fundamental studies of bioelectrocatalysis as a phenomenon.
Determination of antimony(III) and antimony(V) in copper plant electrolyte by anodic stripping voltammetry
Authors: Bond Alan M. , Kratsis Steven , Newman O. Michael G.
Published: May 2005

The concentration of antimony in copper plant electrolyte needs to be known at the ppm level. Spectroscopic techniques for trace metal determination in this electrolyte, such as atomic absorption and inductively coupled plasma (ICP) spectrometry only enable total antimony to be determined, whereas ideally the concentration of both the antimony(III) and antimony(V) oxidation states needs to be known. For the determination of antimony(III) and antimony(V) by differential pulse anodic stripping voltammetry (DPASV), the similar stripping peak potentials of −0.37 V(vs. Ag/AgCl) for copper and −0.27 V(vs. Ag/AgCl) for antimony in 5 M HCl mean that concentrations of copper greater than 6 times that of antimony cause difficulties in resolving the antimony and copper stripping peaks. In this article, a simple procedure is reported for the determination of antimony(III) and (V) in copper plant electrolyte after separation of antimony from copper by passing an ammoniacal solution of plant electrolyte through a column of Chelex‐100 ion‐exchange resin. Most of the copper is retained on the column so that the determination of antimony(III) and (V) by DPASV is possible after addition of hydrochloric acid to the eluent. Total antimony is determined in 5 M HCl and antimony(III) in 0.1 M HCl. Total antimony concentrations correlate well with data obtained by ICP and recoveries of antimony in both oxidation states are > 96%.
Investigation of the performance of microelectrodes with micrometer size structural diameters
Authors: Tian Min , Jing Xinli
Published: May 2005

A microelectrode was fabricated by coating a silicon dioxide film on the Pt wire surface. The fabricated electrode was then characterized by scanning electron micrographs, energy spectrum, cyclic voltammetry, differential pulse voltammetry and AC impedance spectroscopy. A welldefined sigmoidal response for reduction of potassium ferricyanide showed that the electrode has a high mass transport rate, which is the feature of the microelectrode. The micrometer scale size permits it to be used in vivo, and the absence of epoxy resin (as insulator material) also makes the presented microdisk electrode suitable for electroanalysis in nonaqueous media.
A new electrochemical method for the investigation of the aggregation of dyes in solution
Authors: Gooding Justin J. , Compton Richard G. , Brennan Colin M. , Atherton John H.
Published: May 2005

A new electrochemical technique is presented for the investigation of aggregation phenomena in solution over a wide range of solution conditions. Developed nominally for dyes, the method is, in principle, applicable to any electroactive compound. The method employs microelectrodes to measure the change in the diffusion limited current, with concentration, of the aggregating species of interest. At the onset of aggregation, the relationship between this limiting current and concentration deviates from linearity. This deviation, due to the slower rate of diffusion of aggregates, is related to the degree of association of the molecule, assuming a molecular weight distribution of aggregates and using an established relationship between the effective diffusion coefficient and molecular weight. The technique is contrasted with an existing spectroscopic method.
Fabrication of a polyglycine chemically modified electrode and its electrocatalytic oxidation to ascorbic acid
Authors: Yu Ai‐Min , Zhang Hai‐Li , Chen Hong‐Yuan
Published: May 2005

Cyclic voltammetry was used to investigate the electrochemical polymerization of glycine at the glassy carbon electrode. The applied voltage range, pH of electrolyte, concentration of monomer, and cyclic number were found to affect the polymerization process. The resulting film displayed a catalytic activity towards the oxidation of ascorbic acid (AA), reducing the overpotential by 350 mV. A catalytic reaction rate constant of 5.86 × 104 M−1 s−1 was determined using a rotating electrode. Hydrodynamic voltammetric experiments were performed to characterize the electrode as an amperometric sensor for the determination of AA. At 0.4 V (in pH 7.0 PBS) the detection limit is 4.0 × 10−8 M (SIN = 3). The linear dynamic range was wide, from 6.0 × 10−8 to 2.5 × 10−4 M.
Carbon paste electrodes plated with a gold film for the voltammetric determination of mercury(II)
Authors: Švancara Ivan , Matoušek Milan , Sikora Eugen , Schachl Klemens , Kalcher Kurt , Vytřas Karel
Published: May 2005

Carbon pastes of different compositions were tested as supports for gold film electrodes. A paste containing highly‐viscous silicone oil as a binder was found the most suitable. Experimental conditions were optimized in order to develop a differential pulse anodic stripping voltammetric method for the determination of mercury in water samples. In a supporting electrolyte containing HNO3 (0.1 mol/L), (KCl 0.02 mol/L) and tetrachloroaurate(III) for in situ plating with a gold film, the response of Hg was found to be linear in a concentration range from 1 × 10−9 up to 2.5 × 10−7 mol/L (0.2–50 μg/L; accumulation potential +0.2V (vs. Ag/AgCl); accumulation time 30 s–5 min) with a detection limit of about 2.5 × 10−10 mol/L (50 ng/L) after accumulating for 30 min. Reliability of the method depended mainly on the concentration of AuIII in the electrolyte which had to be chosen adequately, with respect to the concentration level of HgII in the sample. Interferences from some ions with the determination of mercury were also studied. The method was tested on both model and real samples and the results agreed well with those obtained by reference determinations.
Effect of varying quaternary ammonium salt concentration on the potentiometric properties of some trifluoroacetophenone derivative‐based solvent‐polymeric membranes
Authors: Hong Young Ki , Yoon Woo Jin , Oh Hyun Jun , Jun Young Moo , Pyun Hyung‐Jung , Cha Geun Sig , Nam Hakhyun
Published: May 2005

Potentiometric properties of carbonate‐selective membranes based on some trifluroacetophenone derivatives [e.g., trifluoroacetyl‐p‐decylbenzene (TFADB), 1,7‐bis(4′‐trifluoro‐acetophenyl)‐4‐decyl‐1,7‐dioxo‐2,6‐dioxy‐heptane (compound I) and 1,2‐bis(4‐trifluoroacetylbenzoyloxymethyl)‐benzene (compound II)] with varying concentration of tridedecylmethyl ammonium chloride (TDMACl) have been examined. It was observed that both TFADB‐ and compound‐II‐based membranes with about 50 mol % TDMACl (relative to the carrier) exhibit the maximum selectivity for carbonate. On the other hand, the compound‐I‐based membranes with about 50 mol % TDMACl showed the greatest discrimination of lipophilic anions (ClO4−, salicylate, SCN3−) including NO, but those with about 80 mol % against Cl− and CH3COO−. These results conform well to the theoretical model developed by Simon et al. if we assume trifluroacetophenone derivatives form 2:1 and/or 3:1 complexes with the anions in the plasticized PVC‐based membranes. Molecular mechanics calculations indicated that bis‐trifluroacetophenones may not form 1:1 complex with the carbonate ion because of a large steric hindrance between the two bulky adjacent chains.
On‐line flow sensor for measuring acetylcholine combined with microdialysis sampling probe
Authors: Horiuchi Tsutomu , Torimitsu Keiichi , Yamamoto Katsunobu , Niwa Osamu
Published: May 2005

We have developed an on‐line electrochemical sensor for the continuous measurement of acetylcholine (ACh). The sensor comprises a small volume prereactor containing immobilized choline oxidase (ChOx) and catalase (or horseradish peroxidase, HRP), a small volume enzymatic reactor containing immobilized acetylcholine esterase (AChE) and ChOx and a glassy carbon electrode modified with Os‐polyvinylpyrridine ‐HRP. The sensor can measure ACh selectively even when the choline (Ch) concentration is more than 1000 times that of ACh, when th ChOx and catalase are immobilized in the prereactor. The sensor shows a wide linear relationship from 5 nM to 1 μM and a detection limit of 5 nM (S/N = 2), which is comparable to the ACh detection limit achieved by liquid chromatography/electrochemistry. It also shows high selectivity against other neurotransmitters and interferents. The properties of the sensor combined with a microdialysis (MD) probe were also studied by measuring a solution containing a much higher concentration of Ch than ACh.
Redox and adsorption processes of hydrolyzed uranyl species on a mercury electrode from sodium chloride solutios
Authors: Djogić Renata , Krznarić Damir , Branica Marko
Published: May 2005

Reduction and adsorption processes of hydrolyzed uranyl species on the mercury drop electrode, from 0.55 mol L−1 NaCl, were studied by electrochemical cathodic stripping techniques: cyclic voltammetry, alternating current voltammetry, chronoamperometry and double potential step chronocoulometry. The only uranyl species adsorbed on the Hg electrode (between pH 5 and 7) was found to be uncharged uranyl dihydroxide, as well as its reduction product. At bulk concentrations between 3 and 5 μmol L−1 that reactant forms an adsorbed compact film as a result of surface polymerization, nucleation or other condensation processes. The adsorption isotherm at pH 6.2 and −0.2 V was measured. It was fitted with a Frumkin type isotherm. At the plateau. a reduction current corresponding to 6.7 × 10−9 mol cm−2 of uranyl ions was measured. This represents on the average 7 adsorbed layers of UO2(OH), presuming an orthorhombic crystal cell structure. Multilayer adsorption is certain even if a polymeric form of uranyl dihydroxide was considered.
Adsorptive stripping voltammetric measurements of chromium accumulation in mice organs using mercury film microelectrodes
Authors: Pereira Maria C. , Pereira Maria L. , Sousa João P.
Published: May 2005

Chromium is the metallic species of most concern with the use of stainless steel implants. To study the distribution of chromium in mice organs with time, several animals were subcutaneously injected with 2.70 × 10−3 mol/L of chromium solution during a certain period of time. Square wave voltammetry using adsorptive collection of Cr3+ ‐DTPA complex on a mercury film microelectrode (MFM) was used for quantitation. Optimized conditions included DTPA concentration of 2.0 × 10−2 mol/L, sodium acetate 4.0 × 10−2 mol/L, sodium nitrate 0.40 mol/L, potassium permanganate 1.0 × 10−3 mol/L, pH ca. 6.1, deposition potential of −1.15 V, deposition time 20 s, frequency 100 Hz, step 2.5 mV and an amplitude of 20 mV. The detection limit of the method was 1.54 × 10−8 mol/L after deposition of 20s. Other species presented in the biological material such as calcium and iron do not interfere with the chromium determinations. The accuracy of the proposed method was checked by comparing the results with those obtained by atomic absorption spectrometry (AAS) yielding good agreement. The results showed an increase of chromium levels with time in liver, kidney and spleen, indicating that this metal is partially accumulated in the studied organs.
Differential pulse voltammetric determination of fenobucarb at the glassy carbon electrode, after its alkaline hydrolysis to a phenolic product
Authors: Cabanillas Agustina Guiberteau , Díaz Teresa Galeano , Salinas Francisco , Ortiz Juan Manuel , Kauffmann Jean Michel
Published: May 2005

A differential pulse voltammetric method for the determination of fenobucarb is proposed. This N‐methylcarbamate pesticide is hydrolyzed in alkaline medium (0.02 M NaOH during ten min), and the resulting product 2‐sec‐butylphenol is oxidized at the glassy carbon electrode giving rise to a peak at a potential near 750 mV (pH 3.5). The linear relationship between Ip and fenobucarb concentration was established up to 1.00 × 10−4 M concentration, the detection limit was 3.68 × 10−6 M. The RSD is 3.74% for a 1.0 × 10−5 M concentration (n = 11, p = 0.05). The method has been satisfactorily applied to the analysis of water samples spiked with the pesticide.
Electrical contact of redox enzyme layers associated with electrodes: Routes to amperometric biosensors
Authors: Willner Itamar , Katz Eugenii , Willner Bilha
Published: May 2005

Tailoring of electrically contacted enzyme electrodes provides the grounds for bioelectronic and biosensor systems. Redox‐enzymes organized onto electrodes as monolayer assemblies, and chemically functionalized by redox‐relay groups, yield electrically contacted enzyme electrodes exhibiting bioelectrocatalytic features. The sensitivity of the enzyme electrode can be enhanced, or tuned, by the organization of multilayer enzyme electrodes and the application of rough metal supports. Enzyme electrodes of extremely efficient electrical communication with the electrode are generated by the reconstitution of apo‐flavoenzymes onto relay‐FAD monolayers associated with electrodes. The reconstitution process results in an aligned enzyme on the surface, and its effective electrical contact with the electrode yields selective enzyme electrodes of unprecedented high current responses. Integrated electrodes consisting of relay‐NAD(P)+‐cofactor and enzyme units are generated by the reconstitution of NAD(P)+‐dependent enzymes onto a relay‐NAD(P)+ monolayer assembly followed by lateral crosslinking of the enzyme network.
Stabilization of an osmium bis‐bipyridyl polymer‐modified carbon paste amperometric glucose biosensor using polyethyleneimine
Authors: Jezkova Jitka , Iwuoha Emmanuel I. , Smyth Malcolm R. , Vytras Karel
Published: May 2005

The modification of carbon paste electrodes by incorporation of the enzyme glucose oxidase (GOx) and a conducting redox osmium bis‐bipyridyl poly(4‐vinylpyridine) polymer (Os‐polymer) is described. The resulting enzyme electrodes were operated as amperometric glucose sensors in the presence or absence of a stabilizer, polyethyleneimine (PEI), mixed into the paste. Cyclic voltammetric studies showed that Os‐polymer containing Os2+/3+ redox couple mediated the electron transfer from reduced GOx to the carbon paste electrode material. Steady‐state amperometric responses of the sensors to 2–120 mM glucose at an operating potential of 350 mV (vs. Ag/AgCl) were determined in 0.1 M phosphate buffer (pH 7.0) medium. The study showed that PEI enhances both, the sensitivity and stability of the carbon paste enzyme electrode and that a diffusion‐limited step precedes electrocatalytic reactions of the biosensor. Cyclic voltammetric data and the Arrhenius analysis of the apparent turnover rate constant, k′cat showed that PEI decreases the diffusion limitations of CPE, thereby increasing the frequency of collision of reacting species in this biosensor format.
A new macrocyclic polystyrene based membrane sensor for zinc
Authors: Singh Ashok K. , Bhattacharjee G. , Singh Manendra , Chandra Sudeshna
Published: May 2005

A quadridentate dihydrogen perchlorate macrocyclic membrane is found to exhibit quite promising selectivity for Zn2+. It can be used to estimate zinc in the range 2.5 × 10−6 to 1.0 × 10−1 mol dm−3 (0.16 to 6.50 × 103 mg dm−3) with a near‐Nernstian slope of ≈︁ 28 mV per decade of concentration. The working pH range of the sensor is 3.0 to 7.0. The polystyrene based membrane electrode is found to possess adequate stability and specific selectivity with a response time of 10 s. Most of the ions that interfere with Zn2+ electrode do not cause any significant disturbance with this assembly and the sensor can be used for more than three months in aqueous as well as in partially nonaqueous media. The utility of the membrane sensor has also been observed in solutions contaminated with detergent matter. The membrane sensor has also been used successfully to analyse some baby food products and soft drinks for the determination of Zn2+ ions.
Voltammetric response of myoglobin at a modified silver electrode
Authors: Zhu Junjie , Gong Yue , Zhang Jinjie , Shen Pingping , Chen Hongyuan
Published: May 2005

A silver electrode coated with captopril, 1‐[(2S)‐3‐mercapto‐2‐methyl‐1‐oxopropyl]‐L‐proline, was prepared by covalent bonding method. The modified electrode was long‐lived and stable. Experimental results revealed that myoglobin (Myb) could exhibit good voltammetric response at the modified electrode. Square wave voltammetric measurements of Myb with the modified electrode gave a linear relationship between the anodic peak current and the protein concentration in the range of 4 × 10−6 −5 × 10−5 mol/L. The relative standard deviation is 5 % for 6 successive determinations in 2 × 10−5 mol/L Myb.
Chronopotentiometric detection of DNA strand breaks with mercury electrodes modified with supercoiled DNA
Authors: Fojta M. , Havran L. , Paleček E.
Published: May 2005

Chronopotentiometry is used for detecting damage to scDNA. The technique offers useful detection of DNA strand break at a supercoiled DNA modified mercury electrode.
A carbon dioxide biosensor based on hemoglobin incorporated in metal supported bilayer lipid membranes (BLMs): Investigations for enhancement of response characteristics by using platelet‐activating factor
Authors: Siontorou Christina G. , Nikolelis Dimitrios P. , Krull Ulrich J.
Published: May 2005

The present article reports the development of a novel electrochemical carbon dioxide minisenso based on hemoglobin which is incorporated into self‐assembled bilayer lipid membranes (s‐BLMs) on a metal support. The presence of carbon dioxide in solution was found to modulate the ion conductivity of BLMs containing hemoglobin, when using a lipid composition containing egg phosphatidylcholine (egg PC) and dipalmitoylphosphatidic acid (DPPA). The use of stabilized metal‐supported BLMs has allowed the electrochemical investigation of the reversibility of the response to carbon dioxide and of hemoglobin binding to lipid membranes. The effects of hemoglobin concentration, composition of BLMs in DPPA and pH on the sensitivity of the response were examined. The sensor provides the advantages of fast response times (on the order of ca. 10 s) to alterations of carbon dioxide concentration, low detection limits (ca. 0.4 × 10−6 M) and capability of analysing small sample volumes. Semisynthetic platelet‐activating factor (PAF; 1‐O‐alkyl‐2‐acetyl‐sn‐glyceryl‐3‐phosphorylcholine, AGEPC) was found to improve the response characteristics of the carbon dioxide sensor (i.e., decrease of the detection limit to nM range and increase of the dynamic range of carbon dioxide determination). The biosensor was routinely mechanically stable and functional for over 48 h. During this time it showed reproducible sensitivity and response to a given concentration of carbon dioxide in solution.
Detection of carbamate pesticides in vegetable samples using cholinesterase‐based biosensors
Authors: Skládal Petr , Nunes Gilvanda Silva , Yamanaka Hideko , Ribeiro Maria Lucia
Published: May 2005

Biosensors for determination of carbamates in vegetables based on five different cholinesterase as biorecognition elements and a screen‐printed electrode system as an amperometric transducer were developed. Measurements were simply performed by dropping solutions (either sample or substrate) directly on the biosensor. The response of biosensors to selected carbamates (aldicarb, carbaryl, carbofuran, methomyl and propoxur) was characterized. The performance was evaluated on extracts of potatoes and carrots, the results from the AChE biosensor and a standard HPLC procedure were compared. Finally, the biosensor was used for the direct analysis of vegetable juices without any pretreatment steps. In this case, 10 μg/L levels of added carbofuran and propoxur were reliably identified. The whole procedure takes less than 20 min including 10 min incubation with samples. The concentrations of carbamates determined with biosensor agreed well for carbofuran. Lower response was observed for propoxur.
Ion‐exchange voltammetry of trace mercury(II) at glassy carbon electrodes coated with a cationic polypyrrole derivative. Application to pore‐waters analysis
Authors: Ugo Paolo , Sperni Laura , Moretto Ligia M.
Published: May 2005

Glassy carbon electrodes modified with coatings of poly‐[1‐methyl‐3‐(pyrrol‐1‐ylmethyl)pyridinium], poly‐MPP, were prepared by electrochemical oxidation of the suitable monomer in acetonitrile solutions. The anion exchange properties of the coated electrode were exploited in aqueous solutions for preconcentrating and detecting the anionic complex HgCl42−, which is the prevailing inorganic HgII species in seawater and other chloride media. The partition coefficients for the ion‐exchange equilibrium involved were calculated from voltammetric data and compared with those obtained at electrodes coated with Tosflex, a perfluorinated anion exchanger, and poly(vinylpyridine). The selectivity of the poly‐MPP coated electrodes towards the rejection of copper interference was also studied. The optimization of experimental conditions allowed the development of a differential pulse voltammetric method for the determination of submicromolar mercury concentrations with a detection limit of 0.1 nM. The method was applied to the analysis of mercury in the pore‐waters of tidal sediments of the Lagoon of Venice (Italy), determining HgII concentration values in the 70–80 nM range.
Modeling of a CdII–N‐(2‐hydroxyethyl)ethylenediamine system and optimization of stability constants by the use of complex formation curves. A polarographic study at a fixed L:M ratio and varied pH
Authors: Cukrowski Ignacy
Published: May 2005

The ligand N‐(2‐hydroxyethyl)ethylenediamine (HEEN) was studied with CdII by differential pulse polarography (DPP) at fixed total ligand (LT) to total metal (MT) concentration ratios and varied pH at 25°C and an ionic strength μ = 0.5 mol dm−3. The polarographic experimental complex formation curve (ECFC) and calculated complex formation curve (CCFC) were used for modeling of the metal‐ligand system and the refinement of stability constants. The ECFC, in which experimental parameters of polarographic peaks are included (a shift in a peak potential and a variation in a peak height) appears to be a characteristic function for a particular metal‐ligand system studied at a particular LT : MT ratio. The CCFC is a theoretical curve calculated for the assumed metal‐ligand model from mass‐balance equations. The final model of metal species formed is the one for which the CCFC fits best the ECFC. Four cadmium complexes CdL2+, CdL, CdL, and CdL2 (OH)+ and their stability constants as log β found from DPP 5.08 ± 0.03, 9.44 ± 0.04, 11.25 ± 0.05, 12.06 ± 0.03, respectively, are reported. The complex CdL was found for the first time. Results obtained in this work are compared with literature data.
Electrochemical detection of mercury adsorbed from flowing gas samples on porous carbon electrodes
Authors: Huang Min , Huang Meiju J. , Faguy Peter W. , Pan Wei‐Ping
Published: May 2005

The adsorption of mercury from flowing gas streams onto reticulated vitreous carbon (RVC) is combined with postadsorption stripping voltammetric determination. This novel analytical method achieves gas stream detection limits of 1.1 μg/m3 for unmodified RVC electrodes at 52°C and 1.8 μg/m3 for modified RVC electrodes at 25°C. Due to the unique features of this detection technique, it is possible and feasible that it could be applied for mercury analysis in coal fired power plant plumes and waste incinerator stacks.
Peroxidase‐based amperometric sensor of hydrogen peroxide generated in oxidase reaction: Application to creatinine and creatine assay
Authors: Kinoshita Hideaki , Torimura Masaki , Kano Kenji , Ikeda Tokuji
Published: May 2005

Peroxidase (POD) was entrapped on a ferrocene (Fc)‐embedded carbon paste (CP) electrode with a dialysis membrane to construct a POD‐Fc‐CP electrode for the reductive amperometric determination of hydrogen peroxide (H2O2). The electrode allowed the H2O2 detection down to 10 nM (under stirring), with a linear relation up to 15 μM, and without change of the response over one month. On the other hand, a plastic‐formed carbon (PFC) electrode can donate electrons to POD without any specific mediator. The POD‐entrapped PFC electrode produced a relative current density of 24% compared with the POD‐Fc‐CP electrode. The reductive detection of H2O2 with the POD‐Fc‐CP electrode was applied to the determination of creatinine and creatine in serum and urine using sarcosine oxidase, creatine amidinohydrolase, and creatinine amidohydrolase as the reagents. The significance of the membrane‐covered POD‐Fc‐CP electrode in the coupling of the oxidase reaction is also discussed.
Split square‐wave voltammograms of surface redox reactions
Authors: Mirčeski Valentin , Lovrić Milivoj
Published: May 2005

A fast and simple method for the estimation of kinetic parameters of surface redox reactions, based on the splitting of their square‐wave voltammograms, is proposed. A mathematical procedure for simulation of these processes is developed. The method can be applied for the fast and chemically reversible redox reactions which are characterized by the kinetic parameter K ≥ 0.8 (K = ks/f). The standard rate constant, transfer coefficient and standard redox potential of the redox reaction of alizarine‐red S adsorbed on the mercury electrode in pH 9 medium are ks = 60 ± 10s−1, α = 0.45 ± 0.03 and E° = −0.810 ± 0.005V (vs. Ag/AgCl‐KCl).
A novel iron‐porphyrin‐derived oxygen sensor working near 0 V (vs. Ag/AgCl) in neutral solution
Authors: Wu Xuanzheng , Li Yijun , Gründig Bernd , Yu Nai‐Teng , Renneberg Reinhard
Published: May 2005

A metalloporphyrin film modified platinum (Pt) electrode was prepared by electrochemical polymerizing of iron(III)‐tetra(3‐methoxy‐4‐hydroxy‐phenyl) porphyrin on a platinum electrode. Cyclic voltammetry of the electrode in PBS pH 7.0 shows the dioxygen reduction peak close to 0 V (vs. Ag/AgCl). Rotating disk electrode experiments indicate a four‐electron transfer mechanism of dioxygen reduction. The chemically modified electrode is recommended as a potential oxygen sensor working at a relatively low potential.
Anodic stripping voltammetry at hydrodynamic mercury thin film electrodes. Part 2. Numerical simulation of stripping peaks for irreversible and quasireversible processes
Authors: Ball Jon C. , Compton Richard G.
Published: May 2005

The time dependent backwards implicit method is used to simulate the shape and position of the stripping peaks in DC (linear scan) anodic stripping voltammetry at mercury thin film hydrodynamic electrodes for electrochemically irreversible and quasireversible systems assuming that the electrode diffusion layer thickness is uniform, as in the case of a rotating disk electrode. The effect of the electrochemical rate constant in influencing both the peak potential and peak shape is examined and the conditions identified under which electrochemically reversible behavior is approached.
Polyion‐sensitive membrane electrodes for detecting phosphate‐rich biological polyanions
Authors: Esson Joan M. , Meyerhoff Mark E.
Published: May 2005

Appropriately formulated polymeric membrane electrodes are shown to exhibit analytically useful nonequilibrium potentiometric responses to biologically important polyanions with high phosphate content, including polyphosphates and nucleic acids, in the μg/mL concentration range This response is dependent on the charge density, lipophilicity, and molecular weight of the polyanion species. The application of these electrodes for monitoring enzymatic activities is also demonstrated, using acid phosphatase/polyphosphate as a model system. The detection limit of this assay was found to be 0.9 ± 0.4 mU/mL with a linear range of 5–100 mU/mL. A similar electrochemical assay scheme can be utilized to monitor ribonuclease activity, using a RNA homopolymer as the substrate.
Catalytic hydrogen evolution in the presence of sulfide and cobalt ions. A study by cathodic stripping voltammetry on the hanging mercury drop electrode
Authors: Bǎnicǎ Florinel Gabriel , Spǎtaru Nicolae , Spǎtaru Tanţa
Published: May 2005

Traces of sulfide ion produce a cathodic peak on the HMDE at about −1.50 V (vs. SCE) after preconcentration at −0.5 V in the borax buffer containing 0.01 mM CoII. This peak is due to the catalytic hydrogen evolution, as demonstrated by the influence of the buffer concentration, the effect of water substitution by deuterium oxide and by the formation of hydrogen bubbles on the electrode. The effect of sulfide ion concentration, deposition time and deposition potential demonstrate that a positively charged cobalt complex is adsorptively accumulated during the deposition step. The reduction of CoII in this species produces a catalytically active compound which is involved in the reduction of the hydrogen ion according to the proposed mechanism. The potential analytical applications of this process for the determination of the sulfide ion have been assessed. The peak current is directly proportional to the concentration of the sulfide ion enabling the application of the standard addition method. The detection limit (using either normal or derivative LSV) is about 1 nM for 10 min accumulation time. The accuracy and reproducibility are fairly good and some of the common interferences in CSV of sulfide ion are removed or at least diminished.
Comparison of metalloporphyrins interacting with DNA
Authors: Qu Feng , Li Nan‐Qiang
Published: May 2005

A series of metalloporphyrins (CuTMpyP, CuTMAP. CuTPPS, NiTMpyP, ZnTMpyP and CdTMpyP) reacting with DNA were compared. The interaction of metalloporphyrin with DNA shows different binding modes and electrochemical behavior when either the metal ion or porphyrin ligand is different. Due to electrostatical repulsion interaction between the anionic substitute group and a phosphate group on DNA molecular backbone, it is difficult for the anionic porphyrin to interact with DNA. The ability of cationic porphyrins to react with DNA depends on the size of the substitute group and the metal ion in the porphyrin plane center. Metalloporphyrin with or without axial ligand, which depends on the metal ion, results in outside binding or intercalating modes, and shows different interaction capability with DNA. The conditional binding constants of NiTMpyP, CuTMpyP and CuTMAP, which mainly show intercalating mode to DNA, were evaluated.
A new cerium(IV) vanadate‐based solid membrane electrode for bismuth(III)
Authors: Jain Ajay K. , Gupta Vinod K. , Singh Lok P. , Khurana Upendra
Published: May 2005

A 20% (w./w.) polystyrene‐based heterogeneous membrane of inorganic ion‐exchanger, cerium(IV) vanadate, has been prepared and used as a bismuth(III) selective electrode. The electrode gives linear potential response in the concentration range 8.0 × 10−5‐1.0 × 10−1 mol L−1 with a slope of 19.2 mV per decade of concentration and a fast response time of 50s. The electrode functions well in the pH range 2.0–4.0, in partially nonaqueous media up to 25% (v./v.) alcoholic content and was used over a period of 4 months without any significant drift in potentials. It exhibits selectivity for Bi3+ over a large number of metal ions and can be used as an indicator electrode to determine Bi3+ by potentiometric titration with EDTA.
Fabrication of a multilayer film electrode containing 12‐tungstosilicic acid and its electrocatalytic reduction for nitrite
Authors: Sun Changqing , Zhang Jidong
Published: May 2005

A novel multilayer film electrode was designed based on the interaction between molecules of 12‐tungstosilicic acid and poly(4‐vinylpyridine) in organic phase. The electrochemical behavior of the modified electrode is characterized. The modified electrode exhibits an excellent and stable electrocatalytic response for the reduction of nitrite.
Mesoporous TiO2 films: New catalytic electrode fabricating amperometric biosensors based on oxidases
Authors: Cosnier Serge , Gondran Chantal , Senillou Anne , Grätzel Michael , Vlachopoulos Nicholas
Published: May 2005

A novel catalytic material (mesoporous TiO2 films) for the cathodic detection of hydrogen peroxide in air‐saturated aqueous solution is described. The immobilization of glucose oxidase (GOD) as enzyme model onto the TiO2 electrode provides an efficient biosensor for the amperometric detection of glucose at −0.15 V (vs. SCE). GOD molecules were immobilized in an inorganic laponite gel and cross‐linked by glutaraldehyde. The highest sensitivity and detection limit were 3.33 mAM−1 cm−2 and 15 μM, respectively. In addition different procedures of enzyme immobilization including cross‐linking with glutaraldehyde and physical entrapment in a functionalized polypyrrole film have been compared.
A Murine Model of Acute Liver Injury Induced by Human Monoclonal Autoantibody *
Authors: Yamauchi Katsumi , Yamaguchi Naoko , Furukawa Takaji , Takatsu Kazuko , Nakanishi Toshimi , Ishida Kohji , Komatsu Tatsuji , Tokushige Katsutoshi , Nagahara Hikaru , Hashimoto Etsuko , Shiratori Keiko
Published: May 2005

We have previously reported an immunoglobulin (Ig) M autoantibody to hepatocyte-related 190-kd molecules in patients with type 1 autoimmune hepatitis (AIH). This molecule was first isolated by hepatocyte-specific human monoclonal antibody (MoAb). To elucidate the role of this IgM autoantibody in hepatocyte injury, we examined the reactivity of this MoAb to murine hepatocytes and then questioned whether acute hepatic injury could be induced in mice via injection of this MoAb. The reactivity of MoAb was examined via both FACS analysis using murine hepatocytes and immunostaining of liver tissues. We then identified the murine hepatocyte membrane molecule recognized by this MoAb. The role of this MoAb in the immunopathogenesis of AIH was assessed by testing whether its injection into mice could increase serum aminotransferase levels as well as cause changes in liver histology. The present results demonstrate that this MoAb cross-reacted with murine hepatocytes and recognized a 190-kd molecule on the murine hepatocyte membrane just as in human hepatocytes. One hour after the injection of MoAb, the deposition of both IgM and complement component 3 was found in liver tissues. At 8 hours after the injection, serum aminotransferase levels were significantly increased in MoAb-injected mice compared with controls. Histological study revealed massive hepatocyte necrosis in MoAb-injected mice.
In conclusion
, human MoAb recognized a 190-kd molecule of both human and murine hepatocytes, and the injection of this MoAb to mice resulted in acute liver injury, indicating that this type of autoantibody may play an important role in the immunopathogenesis of AIH. (Hepatology 2005.)
In vivo intrahippocampal microinfusion of carbachol and bicuculline induces theta‐like oscillations in the septally deafferented hippocampus
Authors: Colom Luis V. , Nassif‐Caudarella Siham , Dickson Clayton T. , Smythe James W. , Bland Brian H.
Published: May 2005

In their laboratory the authors have previously demonstrated that hippocampal slices could be induced to generate trains of “theta‐like” oscillations by whole‐bath perfusions of carbachol. Until recently, it has not been possible to generate similar activity in the septally deafferented hippocampus of an otherwise intact brain by microinfusions of carbachol. This study presents a full report of the first demonstration of a theta‐like oscillation in the in vivo, septally deafferented hippocampal formation. Rats were anesthetized with urethane and implanted with microinfusion cannulae in the region of the medial septum/vertical limb of the diagonal band of Broca (MS/vDBB) and at single or multiple sites in the stratum moleculare of the fascia dentata. The MS/vDBB was microinfused with procaine hydrochloride to produce a reversible suppression lasting for approximately 20 minutes. Intrahippocampal microinfusions of carbachol or bicuculline alone (in the postprocaine condition of the MS/vDBB) failed to produce any theta‐like oscillations. The combination of carbachol and bicuculline produced trains of theta‐like oscillations during suppression of the MS/vDBB very similar to those seen in the slice preparations. The oscillations were blocked by intravenous administration of atropine sulfate, and they had the same depth profile as that of theta. Theta‐on cells were shown to discharge in rhythmic bursts in synchrony with the oscillations. Thus, it would appear that the essential nature of the medial septal input to the hippocampal formation, for the generation of theta field activity in the intact brain, consists of a critical balance between cholinergic and GABAergic circuitry.
Isoproterenol increases the phosphorylation of the synapsins and increases synaptic transmission in dentate gyrus, but not in area CA1, of the hippocampus
Authors: Parfitt Karen D. , Van Doze A. , Madison Daniel V. , Browning Michael D.
Published: May 2005

Previous studies have shown that either norepinephrine (NE) or isoproterenol (ISO) enhances the slope of the field excitatory postsynaptic potential (EPSP) in the dentate gyrus of the rat hippocampal formation. In contrast, NE and ISO cause no increase in excitatory transmission in area CA1 of the hippocampus. The molecular mechanism underlying this brain region‐specific increase in synaptic transmission is not known. The phosphorylation of synapsin I and synapsin II, two homologous presynaptic vesicle‐associated proteins, is thought to promote neurotransmitter release. The authors have observed previously NE‐ and ISO‐enhanced phosphorylation of synapsins I and II in the dentate gyrus. The purpose of this study was to determine whether ISO‐stimulated phosphorylation also occurs in the CA1, where ISO has no effect on excitatory neurotransmission. These studies were correlated with electrophysiological studies in in vitro hippocampal slices. Superfusion of slices with ISO resulted in an increase in EPSP slope in the dentate but not in area CA1. The enhanced dentate EPSP returned to baseline levels within 30 minutes of washout of the drug. Isoproterenol produced corresponding increases in the phosphorylation of the synapsins in dentate slices but had no effect on these proteins in CA1 slices. Moreover, in dentate slices exposed to a 30‐minute wash following incubation with ISO, phosphorylation of the synapsins returned to control levels. This close temporal and brain regional correlation between ISO stimulation of both synapsin phosphorylation and synaptic transmission suggests that the synapsin proteins may play a role in the synaptic potentiation produced by ISO in the dentate.
Preserved configural learning and spatial learning impairment in rats with hippocampal damage
Authors: Gallagher Michela , Holland Peter C.
Published: May 2005

This study was undertaken to compare the effect of hippocampal neurotoxic lesions in rats on two behavioral tasks, one a test of spatial learning, and the other an operant discrimination task that is acquired by forming nonspatial configural associations. Lesions of the hippocampus were made with microinjections of ibotenic acid. After postoperative recovery, rats were trained initially to locate a camouflaged escape platform in a water maze using distal spatial cues. Rats also were trained in the maze apparatus with a visible escape platform under conditions in which spatial information was made irrelevant to performance, i. e., cue learning. In an operant task, the same rats were then trained on a discrimination that included simultaneous feature positive and feature negative components (trial types XA+, A−, XB−, B+). After completion of this nonspatial configural learning task, rats received additional training in the water maze using a new platform location for spatial learning. To the extent that proficient performance in both the maze and operant tasks depends on a common function of the hippocampus, i. e., configural learning, the expectation was that hippocampal lesions would prove equally detrimental to performance in both tasks. Contrary to this expectation, lesioned rats were severely impaired in spatial learning but readily acquired the operant discrimination, even exhibiting some evidence of enhanced performance on this nonspatial configural learning task. Performance of the lesioned rats during cue training in the water maze was also enhanced relative to the control group. These results demonstrate that a spatial learning deficit in rats with hippocampal damage does not necessarily occur in the setting of a general configural learning impairment, as originally suggested by Sutherland and Rudy (1989, Psychobiology 17:129–144).
Tracing of axonal connections by rhodamine‐dextran‐amine in the rat hippocampal‐entorhinal cortex slice preparation
Authors: Boulton Carolyn L. , v. Haebler Dorothea , Heinemann Uwe
Published: May 2005

In order to demonstrate axonal connections preserved in rat temporal cortex slices the authors used rhodamine‐dextran‐amine as a tracer. The slices contained the neocortical areas Te2 and Te3, the medial and lateral entorhinal cortices (MEC and LEC), the subicular regions, and the dentate gyrus and hippocampus proper. Rhodamine‐dextran‐amine crystals were placed by microinjection into a given area. Following this local lesioning the dye was permitted to diffuse and migrate intraaxonally in antero‐and retrograde directions for about 8 hours. The slices were then formaldehyde‐fixed and analyzed by fluorescence microscopy. Most of the known connections within and between the entorhinal cortex and the hippocampus and denatate gyrus were preserved in the slice preparation, provided that the slices were cut with a near horizontal orientation corresponding to plates 99–108 in Paxinos and Watson (1986). Only the lateral perforant path between the LEC and the hippocampus could not be followed to its full extent. The authors conclude that most aspects of the intrinsic synaptic organization of the temporal lobe can be reliably studied in hippocampal‐entorhinal cortex slice preparations.
Postnatal development of mossy cells in the human dentate gyrus: A light microscopic Golgi study
Authors: Seress László , Mrzljak Ladislav
Published: May 2005

Mossy cells in the human dentate gyrus of adults and children of different ages were impregnated using the rapid‐Golgi method. In every case the cause of death was verified by autopsy and the brains were used when neither the history of the patient nor autopsy revealed brainrelated disease.

Mossy cells in the human share common light microscopic features with the same cell type in rats and monkeys. Their most characteristic feature is the extremely large and complex excrescences on their proximal dendrites. Distal dendrites display pedunculate spines. Mossy cells have a few somal spines. The axon of mossy cells originates from the cell body and gives rise to several collaterals in the hilar region. The axons could be followed for several hundred microns, but in only one case did an axon collateral enter the granule cell layer of the adult dentate gyrus.

In the newborn child, mossy cells display immature somal and dendritic features. The soma frequently bear spines. The dendrites are varicose and terminate in presumed growth cones. Both proximal and distal portions of the dendrites bear a few pedunculate spines and longirregular filopodia. A few small excrescences are present on the proximal dendrites. The first large, complex excrescences on the proximal dendrites of mossy cells appeared in the 7‐month‐old child. Both somata and dendrites dispaly adult‐like characteristics in mossy cells from a 5‐year‐old child. However, not all mossy cells are alike and some dendrites still display long filopodia. The axons of immature mossy cells were similar to adults.

The present results indicate that connections between granule cells and hilar mossy cells of the human dentate gyrus develop through an extended postnatal period of time that may last until the fifth year.
Intact verbal and nonverbal short‐term memory following damage to the human hippocampus
Authors: Cave Carolyn Backer , Squire Larry R.
Published: May 2005

Short‐term memory was assessed in two groups of amnesic patients. Six patients had confirmed or suspected damage to the hippocampal formation, and six patients had diencephalic damage as a result of alcoholic Korsakoff's syndrome. Verbal short‐term memory was evaluated with seven separate administrations of the standard digit span test in order to obtain a precise measure of short‐term memory. Nonverbal short‐term memory was evaluated with four tests that assessed apprehension, retention, and the ability to manipulate nonverbal material—all within the span of immediate memory. One of these four tests assessed short‐term memory for spatial location. Patients with damage to the hippocampal formation had a digit span equivalent to that of control subjects and also performed normally on the four tests of nonverbal short‐term memory. The patients with Korsakoff's syndrome had a marginally low digit span and performed poorly on three of the four nonverbal tasks, a finding consistent with the deficits in attention and visuospatial processing previously described for this patient group. These deficits are likely due to the frontal lobe atrophy typically associated with Korsakoff's syndrome, rather than to diencephalic damage. The results support the view that short‐term (immediate) memory, including short‐term spatial memory, is independent of the hippocampus.
The importance of comparative studies and ecological validity for understanding hippocampal structure and cognitive function
Authors: Bingman Verner P.
Published: May 2005

Building from the premise that hippocampal cognitive function has been molded by natural selection under natural environmental conditions, it is argued that traditional laboratory studies likely do not reveal the richness and complexity of hippocampal function. Research on the role of the hippocampal formation in the navigational behavior of homing pigeons is offerred as an example to illustrate the advantages of using an ecological approach to understand hippocampal function. It is further proposed that dissimilarities in hippocampal anatomy, physiology, and neurochemistry found between species reflect species differences in the range of functions served by the hippocampal formation, as well as possibly the molecular and cellular mechanisms that support such functions. These differences notwithstanding, it is suggested that, from an evolutionary perspective, the primary function of the hippocampal formation is a role in some aspect of spatial cognition. Dissimilarities in hippocampal structure and function among extant species are viewed as resulting from differences in evolutionary selective pressure and evolutionary history.