bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Evaluation of the Interaction between Avidin and Biotin at Biotinylated Polypyrrole Electrode Using a Redox Marker
Authors: Kuramitz Hideki , Matsuda Mari , Sugawara Kazuharu , Tanaka Shunitz 
Published: March 2003

AbstractThe interaction between avidin and biotin was evaluated electrochemically by monitoring the change in the electrode response of redox markers. Biotin was immobilized on the electrode surface by means of the electrochemical polymerization of biotinylated pyrrole and pyrrole. When avidin was introduced onto the biotinylated polypyrrole electrode surface, the large change in the electrode response of the redox marker was detected. The fact that the change in the electrode response of a marker ion could be attributed to the electrostatic interaction between avidin on the electrode surface and the redox marker ion present in a solution was verified by replacing avidin with NutrAvidin. At a pH lower than the isoelectric point of avidin, the electrode response of ferrocyanide as an anionic marker ion increased linearly within the range of 5.0×10−9 −3.0×10−8 M avidin. The relative standard deviation at 1.5×10−8 M avidin was about 5.4% (n=5). The detection of biotin was also performed using a competitive reaction between biotin in solution and biotin that had been immobilized on the electrode surface in the form of the biotinylated polypyrrole.
Voltammetric Oxidation of Ambroxol and Application to Its Determination in Pharmaceuticals and in Drug Dissolution Studies
Authors: Demircigil B. Tolga , Uslu Bengi , Özkan Yalçin , Özkan Sibel A. , Sentürk Zühre 
Published: March 2003

AbstractA detailed study of the electrochemistry of ambroxol at a glassy carbon electrode was carried out in the pH range 1.8–11.0 in aqueous solution using cyclic and differential pulse voltammetry. The compound was oxidized irreversibly at high positive potentials resulting in the formation of a chemical product at less positive potentials, which was more readily oxidized than the parent compound. In addition, a differential pulse voltammetric method was proposed for the determination of the drug in different pharmaceutical formulations, and in drug dissolution studies.
Study of a Catalytic Mechanism in Additive Differential Pulse Techniques
Authors: Molina Angela , Moreno Marién M. , Serna Carmen , Martínez‐Ortiz Francisco 
Published: March 2003

AbstractThe new electrochemical double pulse technique, known as additive differential normal pulse voltammetry (ADNPV) when there is no restriction on the duration of both pulses, and additive differential pulse voltammetry (ADPV) when t2≪t1, has been applied to a pseudo‐first‐order catalytic mechanism. The expressions obtained here are applicable to planar and spherical electrodes, of any radius. This is of great interest since the size of the electrode plays an important role in the preponderating of diffusive and kinetics processes. The signal obtained with this technique presents the same morphological characteristics as the triple pulse technique, double differential pulse voltammetry (DDPV) and is more advantageous than DDPV and than the double pulse one, differential pulse voltammetry (DPV).
Electrocatalytic Oxidation of Methanol at Lower Potentials on Glassy Carbon Electrode Modified by Platinum and Platinum Alloys Incorporated in Poly(o‐Aminophenol) Film
Authors: Golabi S. M. , Nozad A. 
Published: March 2003

AbstractThe electrocatalytic oxidation of methanol at a glassy carbon electrode modified by a thin film of poly(o‐aminophenol) (PoAP) containing Pt, Pt‐Ru and Pt‐Sn microparticles has been investigated using cyclic voltammetry as analytical technique and 0.10 M perchloric acid as supporting electrolyte. It has been shown that the presence of PoAP film increases considerably the efficiency of deposited Pt microparticles toward the oxidation of methanol. The catalytic activity of Pt particles is further enhanced when Ru or specially Sn is co‐deposited in the polymer film. The effects of various parameters such as the thickness of polymer film, concentration of methanol, medium temperature as well as the long term stability of modified electrodes have also been investigated.
Adsorption of Tri‐n‐Butyl Phosphate (TBP) from NaClO4 Aqueous Solution on Hg Electrode
Authors: Dogić R. , Krznarić D. 
Published: March 2003

AbstractThe adsorption of TBP on Hg electrode from aqueous NaClO4 media has been studied using differential capacity and chronocoulometric measurements. TBP adsorbs in two steps, the first corresponding to a flat and second to a perpendicular orientation. Both orientations were observed in the entire investigated potential range. The maximal measured surface concentration (Γmax) of TBP reaches a value of 1.55×10−10 mol cm−2, which corresponds to the theoretical value for densely packed molecules in perpendicular orientation. Γ value of the first isotherm step plateau is about 7 to 15% smaller than Γmax and decreases strongly at potentials more negative than −0.9 V due to the repelling of negative charges between the electrode and the phosphate group. The standard Gibbs energy of adsorption was found to reach the value of −34 kJ mol−1.
Determination of octanol‐water partition coefficients for carbonate esters and other small organic molecules by microemulsion electrokinetic chromatography
Authors: Østergaard Jesper , Hansen Steen Honoré , Larsen Claus , Schou Christian , Heegaard Niels H. H. 
Published: March 2003

AbstractMicroemulsion electrokinetic chromatography (MEEKC) was assessed as a tool for determination of octanol‐water partition coefficients using 34 solutes encompassing 8 carbonate esters. It was confirmed that microemulsions containing 1.44–2.88% w/w SDS, 6.49% w/w 1‐butanol, and 0.82% w/w n‐heptane constitute a good model of octanol‐water partitioning in the pH range of 1.4–7.4. Use of the migration index concept led to improved repeatability of the MEEKC method compared to the use of retention factors. Using a dynamical coating, a high electroosmotic flow at pH 1.4 and 4.75 was achieved expanding the practical pH working range of the MEEKC system. The correlation obtained between the migration index and log P was unaffected by pH indicating that the properties of the microemulsion droplets and, thus, partitioning are independent of pH. No evidence for congeneric behavior was found for the sample set comprising solutes with different hydrogen bonding properties suggesting that simple reference compounds can be used as calibrators. Lipophilicity estimates for the series of carbonate esters were obtained. The increase in lipophilicity with chain length was smaller than expected from the Hansch substituent constant, π.
Monitoring liposome‐mediated delivery and fate of an antisense drug in cell extracts and in single cells by capillary electrophoresis with laser‐induced fluorescence
Authors: Malek Amir H. , Khaledi Morteza G. 
Published: March 2003

AbstractCapillary electrophoresis with laser‐induced fluorescence (CE‐LIF) detection was used for evaluation of the effectiveness of delivery and fate of a model 25‐mer DNA‐based phosphorothiate antisense drug in cells. The antisense molecule was delivered to the cells through a simple incubation and by using a cationic liposome (Cytofectin GS 3815). The cationic lipid interacted with the negatively charged antisense to form a more positively charged complex. It was observed that uptake of the liposome‐antisense complex by the cell was dependent on concentration of lipid, duration of transfection, and the cell type. The antisense drug interacted with intracellular components such as proteins and additional steps were needed to quantify the free antisense. Proteinase‐K was able to release antisense from proteins. However, the addition of sodium dodecyl sulfate (SDS) to the sample or running buffer was more effective than Proteinase‐K to release both naked and liposome‐bound antisense from the cellular materials. Analysis of single HeLa cells for uptake of the unbound and liposome‐complexed antisense revealed averages of 8.9×10‐19 moles and 4.9×10‐18 moles, respectively. The amount of uptake, however, varied greatly among individual cells and depended on the delivery method. With liposome‐mediated delivery, the relative standard deviation (RSD) for the amount of antisense in individual cells was 130%, while the variation was much smaller (RSD = 45%) when the cells were incubated with the unbound antisense. These uptake variations agreed with those obtained from flow cytometry analysis.
Separation of capsular polysaccharide K4 and defructosylated K4 derived disaccharides by high‐performance capillary electrophoresis and high‐performance liquid chromatography
Authors: Volpi Nicola 
Published: March 2003

AbstractA rapid, highly sensitive and reproducible high‐performance capillary electrophoresis (HPCE) method (electrokinetic chromatography with sodium dodecyl sulfate) is described for the determination of disaccharides present in the polysaccharide from the uropathogenic Escherichia coli K4 bacteria (05:K4:H4) and its defructosylated product. Following chondroitinase digestion of K4 and its derivative, the two disaccharides, ΔHexAFrc‐GalNAc for K4 and δHexA‐GalNAc for defructosylated K4, are separated and readily determined within 20 min on an uncoated fused‐silica capillary using normal polarity at 20 kV and detection at 230 nm. Comparison was made by separation of these two disaccharides in isocratic strong‐anion exchange HPLC. A linear relationship was found for the two unsaturated disaccharides over a wide range of concentrations, from approximately 0.5 to 5 μg for high‐performance liquid chromatography (HPLC) and from approximately 0.06 to 0.3 μg for HPCE. The HPCE separation produced a greater detection sensitivity (about 10 times greater) than HPLC. The described methods were used to evaluate the defructosylation process of K4 under drastic acid conditions. Good correspondence was found for the amount of unsaturated disaccharides for the two techniques.
Migration order of dipeptide and tripeptide enantiomers in the presence of single isomer and randomly sulfated cyclodextrins as a function of pH
Authors: Süß Falko , Sänger‐van de Griend Cari E. , Scriba Gerhard K. E. 
Published: March 2003

AbstractThe present study was conducted in order to evaluate the cyclodextrin (CD)‐mediated chiral separation of peptide enantiomers as uncharged analytes at pH 5.3 using randomly sulfated β‐cyclodextrin, heptakis‐6‐sulfato‐β‐CD and heptakis‐(2,3‐diacetyl‐6‐sulfato)‐β‐CD as chiral selectors. Although less effective compared to stronger acidic conditions, the CDs proved to be suitable chiral selectors for the present set of peptides at pH 5.3. The carrier ability of the negatively charged CDs upon reversal of the applied voltage may also be exploited leading to a reversal of the migration order. In addition, reversal of the enantiomer migration order upon increasing the buffer pH from 2.5 to 5.3 was also observed for Ala‐Tyr in the presence of randomly sulfated β‐CD, for Ala‐Phe, Ala‐Tyr, Phe‐Phe, Asp‐PheNH2 and Gly‐Ala‐Phe in the presence of heptakis‐6‐sulfato‐β‐CD, and for Phe‐Phe and Ala‐Leu in the presence of heptakis‐(2,3‐diacetyl‐6‐sulfato)‐β‐CD. The migration behavior could be explained on the basis of the complexation constants and the mobilities of the peptide‐CD complexes. While a change in the affinity pattern of the CDs upon increasing the pH was observed for some peptides, complex mobility was the primary factor for other peptide‐CD combinations affecting the enantiomer migration order at the two pH values studied.
Chiral separation of 3,4‐methylenedioxymeth‐ amphetamine and related compounds in clandestine tablets and urine samples by capillary electrophoresis/fluorescence spectroscopy
Authors: Huang Yu‐San , Liu Ju‐Tsung , Lin Li‐Chang , Lin Cheng‐Huang 
Published: March 2003

AbstractThe R‐(–)‐ and S‐(+)‐isomers of 3,4‐methylenedioxymethamphetamine (MDMA) and its metabolite 3,4‐methylenedioxyamphetamine (MDA) were prepared, identified by gas chromatography/mass spectrometry (GC/MS) and then used as standards in a series of capillary electrophoresis (CE) experiments. Using these R‐(–)‐ and S‐(+)‐isomers, the distribution of (RS)‐MDA and (RS)‐MDMA stereoisomers in clandestine tablets and suspect urine samples were identified. Several electrophoretic parameters, such as the concentration of β‐cyclodextrin used in the electrophoretic separation and the amount of organic solvents required for the separation, were optimized.
Determination of kanamycin by electrophoretically mediated microanalysis with in‐capillary derivatization and UV detection
Authors: Kaale Eliangiringa , Van Schepdael Ann , Roets Eugène , Hoogmartens Jos 
Published: March 2003

AbstractAn electrophoretically mediated microanalysis (EMMA) approach, used to perform on‐line chemistry between two small molecules, has been characterized and optimized. The plug‐plug type EMMA method involved electrophoretic mixing and subsequent reaction of nanoliter plugs of kanamycin‐containing samples and 1,2‐phthalic dicarboxaldehyde and mercaptoacetic acid within the confines of the capillary column, which acts as a microreactor. Analyses were performed by pressure‐injecting a plug of kanamycin sandwiched in two reagent plugs. A potential of 375 Vcm‐1 was then applied to electrophoretically mix the two reactants, and an incubation time of up to 5 min allowed the reaction to proceed prior to the application of a separation potential of 588 Vcm‐1. UV detection was at 335 nm. The background electrolyte was 30 mM sodium tetraborate at pH 10.0, containing 16% of methanol. The method was validated in terms of linearity, limits of quantitation and detection, and precision. The method allows determination of kanamycin in bulk samples as a fully automated procedure.
Open‐tubular capillary electrochromatography using a polymeric surfactant coating
Authors: Kamande Mary W. , Kapnissi Constantina P. , Zhu Xiaofeng , Akbay Cevdet , Warner Isiah M. 
Published: March 2003

AbstractA stable polyelectrolyte multilayer (PEM) coating was investigated for use in open‐tubular capillary electrochromatography (o‐CEC). In this approach, the PEM consisted of the cationic polymer of a quaternary ammonium salt, poly(diallyldimethylammonium chloride) and the anionic polymeric surfactant, poly(sodium undecylenic sulfate). Both the cationic and anionic polymers were physically adsorbed to the surface of a fused‐silica capillary by use of a simple coating procedure. This procedure involved an alternate rinse of the positively and negatively charged polymers. The performance of the PEM coating as a dynamic stationary phase was evaluated by use of electrochromatographic experiments and showed good selectivity for both phenols and benzodiazepines. Reproducibility of the PEM coating was also evaluated by calculating the relative standard deviations (RSDs) of the electroosomotic flow (EOF). The run‐to‐run and capillary‐to‐capillary RSD values of the EOF were less than 1.5%. The endurance of the coating was more than 100 runs. The importance of the PEM coating was illustrated by comparing separations on a bare uncoated capillary with the coated capillary. In addition, the chromatographic performance using o‐CEC and micellar electrokinetic chromatography (MEKC) was compared for the separation of benzodiazepines.
Molecularly imprinted polymer films grafted from porous or nonporous silica: Novel affinity stationary phases in capillary electrochromatography
Authors: Quaglia Milena , De Lorenzi Ersilia , Sulitzky Claudia , Caccialanza Gabriele , Sellergren Börje 
Published: March 2003

AbstractMolecularly imprinted composite materials were evaluated as chiral stationary phases in capillary electrochromatography (CEC). These consisted of spherical silica particles of different sizes and of different porosities, containing a surface‐immobilized layer of molecularly imprinted polymer (MIP) targeted to bind L‐phenylalanine anilide. Fused silica capillaries were packed over a length of 8.5 cm, using a pneumate amplification pump, and the stationary phase thus obtained was tested with respect to its electrochromatographic performance. The electroendosmotic flow (EOF) mobility was evaluated with respect to the content of grafted polymer, as well as the ionic strength and the acetonitrile content of the electrolyte. Moreover, the influence of the layer thickness and of the stationary phase porosity on the performance and on the sample load capacity was investigated. The packings exhibited different relative efficiencies for the two enantiomers. The results were discussed in terms of differencies in accessibility to the binding sites of the packings and of the mechanism of EOF generation. In the wide context of the different approaches so far proposed for MIP stationary phases in CEC, these materials can be a good alternative, worthy of further development and application, not restricted to chiral separations.
Alkyl‐modified siloxanes as pseudostationary phases for electrokinetic chromatography
Authors: Schulte Shannon , Palmer Christopher P. 
Published: March 2003

AbstractAnionic siloxane polymers with novel linker arm structures have been synthesized and characterized with respect to their performance and selectivity as pseudophases for electrokinetic chromatography. The linker arm between the siloxane backbone and the sulfonate head group is shorter and does not have the tertiary amine structure found in the siloxane pseudophases studied previously. This change in the linker arm structure and chemistry has dramatic effects on the chemical selectivity of the pseudophases. Linear solvation energy relationship (LSER) studies show that the greatest contributor to the difference in selectivity is that the new polymers are not as nonpolar as those previously studied. This result indicates that siloxane polymers are not by their nature more nonpolar or hydrophobic than other pseudophases. The LSER studies also demonstrate that siloxane pseudophases have a strong tendency to accept hydrogen bonds that cannot be attributed to the presence of the tertiary amine in the linker arm.
Direct coupling of micellar electrokinetic chromatography to mass spectrometry using a volatile buffer system based on perfluorooctanoic acid and ammonia
Authors: Petersson Patrik , Jörntén‐Karlsson Magnus , Stålebro Maria 
Published: March 2003

AbstractDirect coupling of micellar electrokinetic chromatography (MEKC) to mass spectrometry (MS) without employing partial filling is considered to be a challenge. One way of solving the problem would be the use of an MS‐compatible surfactant. In the present study, the applicability of a series of surfactants (sodium dodecyl sulfate (SDS), lauric acid, cholic acid and perfluorated carboxylic acids) have been investigated both in terms of separation performance and MS compatibility. It was found that a MEKC system based on perfluorooctanoic acid (PFOA) and ammonia gave excellent results. The separation performance of the suggested system is comparable to the one obtained with standard systems based on SDS and sodium borate buffer although the selectivity is different. The electrospray ionization MS signal of the analytes is not seriously suppressed even at a PFOA concentration of 100 mM. Clusters are formed but their intensities are relatively low and comparable to those obtained with acetic acid. PFOA is volatile enough to allow long‐term use, 30 h of continuous use has been recorded without any signs of decreasing performance. After use residual PFOA is easily removed from the ion‐source (no memory effects). Furthermore, quantitation of trace impurities is possible at 25 ppb level when employing selected ion monitoring.
Monitoring of Polymorphism – From Detection to Quantification
Authors: Giron D. 
Published: March 2003

AbstractThe polymorphic behavior of organic substances is driven by thermodynamic and kinetic factors. Therefore several solid phases may coexist. Since the properties of the solid state may be extremely relevant for the quality of medicines, the International Conference of Harmonization (ICH) requires a polymorphic study for new active ingredients. The different steps of investigations and the analytical methods which are used during the development phase in order to achieve adequately this challenging task, from detection to quantification are emphasized.
Crystallization of Pharmaceutical Compounds Polymorphs, Pseudo‐Polymorphs and Particle Formation
Authors: Beckmann W. 
Published: March 2003

AbstractThe crystallization of a pharmaceutical compound, of an active pharmaceutical ingredient, is governed by a set of interdependent requirements. Two of the most prominent parameters are polymorphism and crystal or particle size distribution. The requirements for these parameters are governed by regulatory issues as well as by demands arising from the formulation process and the use of the drug substance. This paper focuses on the optimal choice of the modification of the active pharmaceutical ingredient and on the controlled crystallization of the polymorph chosen. These requirements are checked against the processes used to control particle size.
Development of a New Coating Process in Pharmaceutical Industry by Crystallization
Authors: Kim J.‐W. , Ulrich J. 
Published: March 2003

AbstractThis study concentrates on the development of a new coating technology, which is applied via a solution crystallization process using heterogeneous seeds. Hemi‐sphere pastilles of different materials (seed particles) and isomaltulose solution are used as core materials and coating materials, respectively. The surface nucleation and the growth rate on the surface of seed particles are investigated. An effective crystalline coating, which is very compact in structure without cracking and uniform in shape, is achieved. The growth rate and the quality of coating are related to the degree of subcooling, the retention time and the surface characteristic of the used seed particles. This study focuses on how crystalline‐formed coatings are formed by a crystallization process, how an operating variable effects the quality of coatings and how a good quality of a coating can be achieved.
Polymorphism and Liquid‐Liquid Demixing in Supersaturated Drug Solution
Authors: Lafferrère L. , Hoff C. , Veesler S. 
Published: March 2003

AbstractIn the field of pharmaceutical compound crystallization, one of the challenging tasks is to control the nucleation and the polymorphism. With these objectives, it becomes clear that an important stage is the phase diagram determination of the considered substance. We have investigated the phase diagram of a pharmaceutical compound in a mixture of ethanol/water. We have observed and characterized, in this phase diagram, a solid‐solid (polymorphism) and a liquid‐liquid phase separation as a function of temperature and drug substance concentration.
Solubility Equilibria in Chiral Systems and Their Importance for Enantioseparation
Authors: Lorenz H. , Sapoundjiev D. , Seidel‐Morgenstern A. 
Published: March 2003

AbstractTernary solubility equilibria are studied for three chiral systems in various aqueous and nonaqueous solvents. The chosen systems were a pharmaceutical intermediate, threonine and mandelic acid. Measured solubility data are presented and the nature of the ternary solubility phase diagrams is described. On this basis possible procedures for a crystallization based enantioseparation are derived. Also, the impact of solubility equilibria on the resolution of racemates by liquid chromatography is analyzed and discussed for the systems under investigation. Finally, a hybrid approach coupling both separation techniques for an efficient chiral resolution is demonstrated by means of the fundamental solubility phase diagrams.