bluuebunny/crossref_metadata_2025_split huggingface dataset:
Screen‐Printed Carbon Electrodes Modified with Cellobiose Dehydrogenase: Amplification Factor for Catechol vs. Reversibility of Ferricyanide
Authors: Dock Eva , Ruzgas Tautgirdas 
Published: April 2003

AbstractA number of screen‐printed carbon electrodes (SPCEs) have been electrochemically studied revealing strong correlation between the reversibility of the Fe(CN)$\rm{ {_{6}^{3-}}}$/Fe(CN)$\rm{ {_{6}^{4-}}}$ couple and the sensitivity for catechol at the same electrodes modified with cellobiose dehydrogenase (CDH). Pretreatment of the electrode surfaces increased both the heterogeneous ferricyanide reaction rate and the catechol sensitivity. From cyclic voltammetric and chronoamperometric measurements of Fe(CN)$\rm{ {_{6}^{3-}}}$ it was concluded that the tested SPCEs behave as microelectrode arrays. Using the “pinhole” model the fraction of electroactive area was determined to directly correlate to a faster heterogeneous electron transfer for ferricyanide and a higher CDH‐modified biosensor sensitivity for catechol. An electroactive area of 50% and higher is sufficient to create a sufficiently good biosensor for catechol.
Multivariate Resolution of Coeluted Peaks in Hyphenated Liquid Chromatography – Linear Sweep Voltammetry
Authors: Berbel Francisco , Kapoya Elisabeth , Díaz‐Cruz José Manuel , Ariño Cristina , Esteban Miquel , Tauler Romà 
Published: April 2003

AbstractA novel application of Multivariate Curve Resolution with Alternating Least Squares (MCR‐ALS) method for the background correction and for the resolution and quantitation of coeluted analyte mixtures in liquid chromatography with voltammetric detection is presented. The selected voltammetric technique for analyte detection was Linear Sweep Voltammetry (LSV), which provides richer multivariate information than the more widespread employed univariate amperometric detection. Use of other voltammetric detection techniques was also attempted but they gave much poorer results because of instrumental and software limitations concerning data acquisition times. The method is tested in the resolution and quantitation of mixtures of pyrocatechol, ascorbic acid and epinephrine coeluting mixtures. In spite of the extremely large background current contributions observed using this voltammetric technique, MCR‐ALS was shown to be able to model this background contribution satisfactory as well as to resolve and give good quantitative estimations of these three analyte in their mixtures. The proposed approach is recommended for resolution and quantitation of complex coeluted mixtures using liquid chromatography with voltammetric detection and also for fast initial screening of optimal potential when amperometric detection is preferred.
Permselective Properties of Electropolymerized Guaiacol Derivatives
Authors: Milczarek Grzegorz , Ciszewski Aleksander 
Published: April 2003

AbstractGuaiacol (2‐methoxyphenol) and its 5 derivatives such as 4‐allyl‐2‐methoxyphenol,2‐methoxy‐4‐propenylphenol, 2‐methoxy‐4‐propylphenol, 4‐hydroxy‐3‐methoxybenzylamine and 4‐chloro‐2‐methoxyphenol were oxidatively polymerized on platinum electrodes in 0.1 M NaOH solution. The polymer modified electrodes were then checked for their responses towards biologically important analytes such as hydrogen peroxide, ascorbic and uric acids, dopamine and acetaminophen under flow injection conditions. The effect of a monomer chosen on the permselective properties of the deposited film is thoroughly discussed. Feasibility of the application of these polymer modified electrodes in selective flow injection detection of hydrogen peroxide and dopamine is demonstrated.
Voltammetric Determination of Microparticles of Some Local Anesthetics and Antithusics Immobilized on the Graphite Electrode
Authors: Komorsky‐Lovrić Šebojka , Vukašinović Nevenka , Penovski Rahela 
Published: April 2003

AbstractSolid microparticles of local anesthetics benzocaine, cinchocaine, lidocaine and procaine, and the antithusic codeine were mechanically immobilized on the surface of the paraffin impregnated graphite electrode and investigated by square‐wave and cyclic voltammetry in order to develop a method for their qualitative determination. The measurements were performed in the pH range between 1 and 9. The square‐wave frequency and amplitude were changed between 100 and 1000 Hz, and from 15 to 85 mV, respectively. The scan rate in cyclic voltammetry was 1 V/s.
Fabrication of a Sub‐Micrometer Electrode Array: Electrochemical Characterization and Mapping of an Electroactive Species by Confocal Raman Microspectroscopy
Authors: Szunerits Sabine , Garrigue Patrick , Bruneel Jean‐Luc , Servant Laurent , Sojic Neso 
Published: April 2003

AbstractThe fabrication of an ordered electrode array based on an etched optical fiber bundle is described. The high density sub‐micrometer electrode array is characterized electrochemically using cyclic voltammetry and geometrically via scanning electron microscopy. The observed steady‐state current indicates that individual diffusion layers do not overlap and that the electrodes are diffusively independent. Spatially resolved chemical information of the etched and insulating paint‐covered surface of the electrode array is obtained from confocal Raman microspectroscopy (CRM) experiments. Finally electroactive spots are probed using CRM through the different Raman spectra of the electroactive species of the redox couple Fe(CN)63−/Fe(CN)64−.
A Voltammetric Assay of Antioxidants and Inhibitors of Soybean Lipoxygenase
Authors: Pérusse Pascal , Leech Dónal 
Published: April 2003

AbstractAntioxidant activity and/or the inhibition of lipoxygenases may contribute to the cell and tissue protective properties of flavonoids. Soybean lipoxygenase‐1 (LOX‐1), is a useful paradigm for lipoxygenases isolated from different sources, and can be used to devise assays of oxygenase inhibitors and antioxidants. Here we describe the voltammetric detection of methylene blue (MB) to assay for antioxidant and lipoxygenase inhibition activity. MB is formed by the catalytic action of hydroperoxide, produced by soybean lipoxygenase reaction on linoleic acid, on benzoyl‐leuco methylene blue (BLMB). Every compound which blocks either the enzymatic reaction, lipoxygenase inhibitors, or the oxidation of BLMB, antioxidants, can thus be detected using this method. The assay involves reaction for a period of one hour of linoleic acid, lipoxygenase, BLMB and inhibitor, followed by injection into a flow‐injection system and detection by square‐wave voltammetry of the methylene blue produced. The problem of irreproducibility induced by adsorption at the solid platinum working electrode is alleviated using the method of alternate injections of control and assay solutions. Assays of several known lipoxygenase inhibitors were undertaken. All of these inhibitors were also, however, shown to be antioxidants. Extension of the assay to the rapid evaluation of novel therapeutic antioxidants and lipoxygenase inhibitors is proposed.
Voltammetric Determination of Free and Total Sulfur Dioxide in Beer
Authors: Almeida P. J. , Rodrigues J. A. , Guido L. F. , Santos J. R. , Barros A. A. , Fogg A. G. 
Published: April 2003

AbstractA voltammetric method for the determination of free and total sulfur dioxide in beer is described. First, volatile aldehydes (mainly acetaldehyde) are purged with nitrogen from a beer sample diluted in alkaline medium, collected in an appropriate electrolyte trapping solution and determined, after derivatization with hydrazine, by voltammetry using a hanging mercury drop electrode. Then, the remaining beer solution is strongly acidified and (total) sulfur dioxide is purged with nitrogen, collected in an appropriate electrolyte trapping solution and determined by voltammetry. The free sulfur dioxide concentration is calculated by difference between (total) sulfur dioxide and acetaldehyde concentrations. The proposed method has a relative standard deviation of about 2.1% and 4.4%, respectively for (total) sulfur dioxide and free sulfur dioxide concentrations normally found in beer, and results are in good agreement with those obtained by the p‐rosaniline reference method.
A Novel Catalytic Adsorptive Stripping Voltammetric Method of Iron Determination as Its 1,2‐Cyclohexanedione Dioxime Complex
Authors: Bobrowski Andrzej , Królicka Agnieszka 
Published: April 2003

AbstractThe sensitive catalytic adsorptive stripping voltammetric method for the determination of trace iron in the supporting electrolyte consisting of 0.1 M ammonia buffer, 0.05–0.15 mM 1,2‐cycloheksanedione dioxime and 0.14 M NaNO2 is presented. The method is based on adsorptive accumulation of an iron‐nioxime complex on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of the catalytic reduction current of the adsorbed complex in the presence of sodium nitrite. The detection limit obtained for a 20 s accumulation time was 0.90 nM iron, the RDS was 3%, and the linearity range amounted from 3.6 to 107.4 nM of iron. Possible interferences from the coexisting ions and surface‐active substances were investigated.
Delivery of bioactive, gel‐isolated proteins into live cells
Authors: Taylor Jennifer E. , Fernandez‐Patron Carlos 
Published: April 2003

AbstractThe delivery of proteins into live cells is a promising strategy for the targeted modulation of protein‐protein interactions and the manipulation of specific cellular functions. Cellular delivery can be facilitated by complexing the protein of interest with carrier molecules. Recently, an amphipatic peptide was identified, Pep‐1 (KETWWETWWTE WSQPKKKRKV), which crosses the plasma membrane of many cell types to carry and deliver proteins as large as antibodies. Pep‐1 effectively delivers proteins in solution; but Pep‐1 is not suitable for delivering sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) isolated proteins because Pep‐1 complexes with cargo proteins are destroyed by SDS. Here, we report cellular delivery of SDS‐PAGE‐isolated proteins, without causing cellular damage, by using a nonionic detergent, Triton X‐100, as carrier. To determine the specificity of our method, we separated antibodies against different intracellular targets by nonreducing SDS‐PAGE. Following electrophoresis, the antibody bands were detected by zinc‐imidazole reverse staining, excised, in‐gel refolded with Triton X‐100, and eluted in detergent‐free phosphate‐buffered saline. When overlaid on cultured NIH 3T3 cells, the antibodies penetrated the cells localizing to their corresponding intracellular targets. These results are proof‐of‐principle for the delivery of gel‐isolated bioactive proteins into cultured cells and suggest new ways for experimental protein therapy and for studying protein‐protein interactions using gel‐isolated protein.
Sol‐gel column technology for capillary isoelectric focusing of microorganisms and biopolymers with UV or fluorometric detection
Authors: Horká Marie , Planeta Josef , Růzička Filip , Šlais Karel 
Published: April 2003

AbstractThe sol‐gel surface modification is used for capillary isoelectric focusing of microorganisms and biopolymers. The coating strongly decreases the electroosmotic flow so that it enables the use of the short capillaries down to 100 mm in the separation length. The examples of capillary isoelectric focusing of the low‐molecular‐mass pI markers and mixed cultures of microbial populations of Escherichia coli, Candida albicans, Staphylococcus epidermidis, and Enteroccocus faecalis with UV detection are shown. It is possible to quantify bacterial cells according to their peak areas; the minimum detectable number of microbial cells was 5×102–1×103. The compatibility of sol‐gel capillaries with sensitive fluorometric detection of fluorescent pI markers together with fluorescein labeled proteins is demonstrated.
Size‐based separations of proteins by capillary electrophoresis using linear polyacrylamide as a sieving medium: Model studies and analysis of cider proteins
Authors: Gomis Domingo Blanco , Junco Sara , Expósito Yoana , Gutiérrez Dolores 
Published: April 2003

AbstractElectrophoretic conditions to separate sodium dodecyl sulfate (SDS)‐protein complexes according to their relative molecular mass by capillary electrophoresis (CE) using linear polyacrylamide as a sieving matrix were examined. Five purified proteins with relative molecular masses between 14 400 and 66 200 Da were separated on a coated fused‐silica capillary with an internal diameter of 100 μm and an effective length of 24 cm (total length, 32.5 cm). Benzoic acid was added to the solution of purified proteins as internal standard; β‐mercaptoethanol was also added as reducing agent. The running buffer composition was 0.05 M tris(hydroxymethyl)aminomethane (Tris), 0.035 M aspartic acid, 0.1% m/v SDS, 4% m/v acrylamide, the resulting pH being 8.0. The applied voltage was 7 kV (reversed voltage polarity) in order to avoid high current intensities. Under optimized conditions, the five proteins were separated in less than 15 min, with a % relative standard deviation (RSD) between 0.2 and 0.4 for migration times in the same day. Good efficiency (values between 150 000 and 40 000 N/m) and resolution (values between 2 and 2.8) were obtained. The inverse of relative migration times was found to correlate with the logarithm of their relative molecular mass. Finally, cider proteins were analyzed and their relative molecular masses were determined. These results were compared with those obtained by SDS‐polyacrylamide gel electrophoresis (SDS‐PAGE).
Speciation of chromium (III) and chromium (VI) by capillary electrophoresis with contactless conductometric detection and dual opposite end injection
Authors: Kubáň Pavel , Kubáň Petr , Kubáň Vlastimil 
Published: April 2003

AbstractA sensitive, rapid and inexpensive capillary electrophoretic method for the determination of Cr(III) and Cr(VI) species is presented. The method is based on the dual opposite end injection principle and contactless conductometric detection. The sample containing cationic and anionic species is injected into the opposite ends of the separation capillary and after the high voltage is applied, the analytes migrate towards the capillary center, where the cell of a contactless conductivity detector is placed. The method does not require any sample pretreatment, except dilution with deionized water. The separation of Cr(III), Cr(VI) and other common inorganic anions and cations is achieved in less than 4 min. The parameters of the separation electrolyte solution, such as pH and concentration of L‐histidine, were optimized. Best results were achieved with electrolyte solution consisting of 4.5 mM L‐histidine, adjusted to pH 3.40 with acetic acid. The detection limits achieved for Cr(III) and Cr(VI) were 10 and 39 μg·L–1, respectively. The repeatability of migration times and peak areas was better than 0.3% and 2.8%, respectively. The developed method was applied to the analyses of rinse water samples from the galvanic industry. The results for the determination of Cr(III) and Cr(VI) were in good agreement with the results obtained by certified differential spectrophotometric method using diphenylcarbazide (CN 83 0520‐40) and with the results for the total chromium concentrations determined by electrothermal atomic absorbance spectrometry (ET‐AAS) and inductively coupled plasma‐mass spectrometry (ICP‐MS).
Investigation of a capillary electrophoretic approach for direct quantification of apolipoprotein A‐I in serum
Authors: Lehmann Rainer , Friess Ulrich , Häring Hans‐Ulrich , Voelter Wolfgang , Liebich Hartmut , Beck Alexander 
Published: April 2003

AbstractIn the present study a rapid, reproducible and robust capillary electrophoresis (CE) procedure for the quantification of apolipoprotein A‐I (Apo A‐I) in serum without pretreatment has been developed (total run time, 11 min). The coefficients of variation (CV; n = 10) for the relative peak area are 1.8% at a concentration of 145 mg/dL and 1.6% at 196 mg/dL; and for the inter‐assay 8.9% at 161 mg/dL (10 consecutive days), i.e., similar to the CVs of a high‐throughput immunonephelometric routine assay. The CV for the migration time is 0.4% (n = 20). The robustness of the CE approach was tested in patient samples with hemolysis, hyperbilirubinemia and hyperlipidemia. A comparison of 99 Apo A‐I serum values with results of a fixed‐time immunonephelometric routine assay showed a positive constant bias of 60% (mean) for the immunonephelometric values, no deviation from linearity, but significant deviations in several samples. Investigations on interferences in the CE analyses gave no evidence that CE failed. Our study shows that CE is amenable to a fast analysis and a reproducible and reliable quantification of Apo A‐I level in sera of various clinical samples.
Proteome analysis of Saccharomyces cerevisiae under metal stress by two‐dimensional differential gel electrophoresis
Authors: Hu Yi , Wang Gang , Chen Grace Y. J. , Fu Xin , Yao Shao Q. 
Published: April 2003

AbstractThe defense mechanism by which cells combat metal stress remains poorly understood. By utilizing a newly developed technique – the differential gel electrophoresis (DIGE) – we evaluated the biological alterations of metal stress on Saccharomyces cerevisiae at its translational level. By simultaneously comparing the differential expression profiles of thousands of proteins as results of 15 different metal treatments, we were able to closely examine the response of a large number of proteins within the yeast proteome towards individual metals, as well as the response of the same proteins towards different metals. This, to our knowledge, is the first case which demonstrates the potential of DIGE as a high‐throughput tool for large‐scale proteome analysis. From our studies, where yeast cells were exhaustively treated with exogenous metals, 20–30% of all proteins detected showed statistically significant changes. According to different effects (up‐/downregulation) of protein expression levels observed, we were able to tentatively divide the 15 metals into three groups. By mass spectrometric analysis, more than 50 protein spots were positively identified, both quantitatively and qualitatively. One of the proteins was identified to be Cu/Zn superoxide dismutase (SOD1), and its expression levels as a result of 15 different metal treatments was further examined in greater details. Significant changes in SOD1 expression were observed throughout all 15 DIGE gels.
Representation of radiation damping by fractional time derivatives
Authors: Ruge P. , Trinks C. 
Published: April 2003

AbstractWhen modelling unbounded domains, formulation of a matrix‐valued force–displacement relationship which can take radiation damping into account is of major importance. In this paper, a method to describe the dynamic stiffness by a system of fractional differential equations in the time‐domain is presented. Here, a doubly asymptotic rational approximation of the low‐frequency force–displacement relationship is used, whereas a direct interpretation of the asymptotic part as a fractional derivative is possible. The numerical solution of the corresponding system of fractional differential equations is demonstrated using the infinite beam on elastic foundation as an example. Copyright © 2003 John Wiley & Sons, Ltd.
Bisubstrate Inhibitors for the Enzyme Catechol O‐Methyltransferase (COMT): Dramatic Effects of Ribose Modifications on Binding Affinity and Binding Mode
Authors: Lerner Christian , Siegrist Romain , Schweizer Eliane , Diederich François , Gramlich Volker , Jakob‐Roetne Roland , Zürcher Gerhard , Borroni Edilio 
Published: April 2003

AbstractInhibition of the enzyme catechol O‐methyltransferase (COMT) is of significant interest in the therapy of Parkinson's disease. Described herein are structural analogs of the potent bisubstrate inhibitor (−)‐1 (IC50=9 nM; Table 1) for COMT, with target modifications of the central ribose moiety. Their synthesis involves, as key intermediates, adenosine derivatives, which are transformed to the potential bisubstrate inhibitors by a similar sequence of six steps (Schemes 1–4). The compounds were submitted to an enzymatic assay for determination of their in vitro inhibitory activity against COMT, and the inhibition mechanism with respect to the binding side of the cofactor S‐adenosylmethionine (SAM) was analyzed by kinetics measurements (Fig. 3). Both binding affinity and binding mode were exceedingly sensitive towards modifications of the ribose moiety (Table 1). Removal of the 2′‐OH group upon changing from (−)‐1 to (−)‐2 (IC50=28 μM) led to a reduction in binding affinity by more than three orders of magnitude. At the same time, competitive inhibition kinetics with respect to the SAM binding site was maintained, thereby supporting a bisubstrate binding mode. Unlike (−)‐2, the dideoxyribose inhibitor (−)‐3 (IC50=3 μM) showed a mixed and the cyclopentane derivative (+)‐4 (IC50=1 μM) an uncompetitive inhibition mechanism with respect to the SAM binding site. In the complex of the latter, the adenine‐substituted cyclopentane ring orients most probably towards the surface of the enzyme into the surrounding solution. The enantiomeric compounds (−)‐5 (IC50=43 μM) and (+)‐5 (IC50=141 μM), wherein the ribose had been replaced by a pyrrolidine ring, showed only low binding affinity.
7,8‐(Dichloromethano)homo[70]fullerene, an Unusual, but Unexceptional, Methanoannulene
Authors: Kiely Andrew F. , Meier Mark S. , Patrick Brian O. , Selegue John P. , Pratt Brock Carolyn 
Published: April 2003

AbstractThe crystal structure of 7,8‐(dichloromethano)homo[70]fullerene shows that addition of the dichlorocarbene (:CCl2) to C70 gives a surprisingly normal methano‐bridged [9]annulene. The structural changes caused by the addition are highly localized; the C(7)C(8) distance lengthens by 0.705(2) Å but no other distance changes by more than 0.022(3) Å. Bond angles within the [9]annulene increase by as much as 7.8(1)°, but changes outside the C9 ring are much smaller. The nearly ellipsoidal molecules form hexagonally close‐packed layers that interact in pairs through short Cl⋅⋅⋅C, and possibly short Cl⋅⋅⋅Cl and C⋅⋅⋅C, interactions.
Promiscuity in Antibody Catalysis: Esterolytic Activity of the Decarboxylase 21D8
Authors: Backes Alexander C. , Hotta Kinya , Hilvert Donald 
Published: April 2003

AbstractThe high structural similarity of decarboxylase antibody 21D8 and esterase antibody 48G7 suggests that 21D8 might also possess hydrolytic activity. Kinetic investigations show that 21D8 does promote the selective hydrolysis of methyl 4‐nitrophenyl carbonate and sodium 4‐(acetoxy)benzenesulfonate with catalytic proficiencies (kcat/Km)/kun of ca. 105 M−1. The ability of 21D8 to accelerate a reaction for which it was not developed suggests that certain antibody scaffolds are intrinsically predisposed toward catalysis, a property that can be enhanced and refined during affinity maturation in response to a transition‐state analog. At the same time, however, the restricted structural diversity of the immune system may ultimately limit the catalytic efficiency that can be achieved.
Crystal Packing: An Examination of the Packing of Molecules Approximately Isosteric with 4,5‐Dichlorophthalic Anhydride
Authors: Britton Doyle , Noland Wayland E. , Pinnow Matthew J. , Young Jr. Victor G. 
Published: April 2003

AbstractThe crystal structures of five 5,6‐disubstituted benzofurazan 1‐oxides are presented and compared with five previously reported structures: three polymorphs of 5,6‐dichlorobenzofurazan 1‐oxide plus 4,5‐dichloro‐ and 4,5‐dibromophthalic anhydride. All but one of these compounds pack with similar two‐dimensional layers. The benzofurazan oxides all show disorder about a crystallographic twofold or pseudo‐twofold axis. In addition, six complexes of phthalic anhydride and benzofurazan oxides are reported. With the packing in the complexes principally directed by the π complexing, the disorder, invariably found in the uncomplexed benzofurazan oxides, is diminished, and, in two cases, eliminated.