bluuebunny/crossref_metadata_2025_split huggingface dataset:
Catalytic Voltammetric Determination of Cladribine in Biological Samples
Authors: de‐los‐Santos‐Álvarez Noemí , Lobo‐Castañón María Jesús , Miranda‐Ordieres Arturo J. , Tuñón‐Blanco Paulino 
Published: April 2003

AbstractAn electrochemical method for the citotoxic prodrug cladribine determination is proposed. Graphite electrodes modified with cladribine showed a redox process with a formal potential of 0.173 V at pH 6, after the oxidation of the adenine moiety of the drug, whose current can be employed as analytical signal with a detection limit of 75 nM by square‐wave voltammetry. As these oxidation products exhibit great electrocatalytic activity toward the electro‐oxidation of NADH at low potentials, the analytical response can further be amplified. As a result, the detection limit was improved up to 1 nM using differential pulse voltammetry. The method was applied to the determination of cladribine in serum and urine samples after solid‐phase extraction. No electroactive interferences were found in both fluids. The method allows the selective detection of the drug in the presence of the main metabolite, 2‐chloroadenosine, which is not able to electrocatalize the NADH oxidation.
Eighty Years of Polarography – History and Future
Authors: Barek Jiří , Zima Jiří 
Published: April 2003

AbstractSince 1922, when Professor Jaroslav Heyrovský carried out his pioneering experiment with a dropping mercury electrode, polarography showed remarkable ability to adjust to ever increasing demands on the sensitivity and selectivity and up to now mercury electrodes are among the best sensors for electroanalytical measurements. The aim of this contribution is to show both the historical development of these techniques and their presence and possible future developments and to show that even today in certain cases polarographic and voltammetric techniques on mercury electrodes can successfully compete with modern separation and spectrometric techniques.
Amperometric Ion Sensing Using Polypyrrole Membranes
Authors: Michalska Agata , Walkiewicz Sebastian , Maksymiuk Krzysztof 
Published: April 2003

AbstractOxidation/reduction of conducting polymers, coupled with ion exchange between the polymer and electrolyte solution can be utilized for amperometric ion sensing. Electrochemically deposited “model” polypyrrole membranes doped by chloride (PPyCl) and hexacyanoferrate (PPyFeCN) anions were studied from the point of view of their advantages and limits for amperometric determination of electroinactive anions and cations, respectively. Monotonous dependences of the current on electrolyte concentration were obtained for short reading times after potential step application (in the range of ms). The experimental conditions were optimized to obtain linear dependences: log (current) vs. log (KCl concentration) within the range 10−6−1 M. The advantages of the amperometric method over the potentiometric one are highlighted: much lower effect of redox and pH interferences, wider concentration range, elimination of long conditioning procedure.
Statistical performance analysis of seismic‐excited structures with active interaction control
Authors: Zhang Yunfeng , Iwan Wilfred D. 
Published: April 2003

AbstractThis paper presents a statistical performance analysis of a semi‐active structural control system for suppressing the vibration response of building structures during strong seismic events. The proposed semi‐active mass damper device consists of a high‐frequency mass damper with large stiffness, and an actively controlled interaction element that connects the mass damper to the structure. Through actively modulating the operating states of the interaction elements according to pre‐specified control logic, vibrational energy in the structure is dissipated in the mass damper device and the vibration of the structure is thus suppressed. The control logic, categorized under active interaction control, is defined directly in physical space by minimizing the inter‐storey drift of the structure to the maximum extent. This semi‐active structural control approach has been shown to be effective in reducing the vibration response of building structures due to specific earthquake ground motions. To further evaluate the control performance, a Monte Carlo simulation of the seismic response of a three‐storey steel‐framed building model equipped with the proposed semi‐active mass damper device is performed based on a large ensemble of artificially generated earthquake ground motions. A procedure for generating code‐compatible artificial earthquake accelerograms is also briefly described. The results obtained clearly demonstrate the effectiveness of the proposed semi‐active mass damper device in controlling vibrations of building structures during large earthquakes. Copyright © 2003 John Wiley & Sons, Ltd.
Optimal location of sensors for reconstruction of seismic responses through spline function interpolation
Authors: Limongelli M. P. 
Published: April 2003

AbstractIn this paper, a criterion is proposed for the choice of the optimal location of a limited number of recording sensors for reconstruction of seismic responses of multistorey frames. Reconstruction of unknown responses is performed by modelling through a spline shape function the evolution of the relative acceleration along the height of the building. The coefficients of the spline function are determined by interpolating available responses in terms of absolute accelerations taking into account boundary conditions. The optimal location for a given number of recording sensors is defined as the one corresponding to the minimum value of the global error evaluated on the whole set of reconstructed responses. The criterion has been verified by using simulated responses of numerical models of multistorey frames and responses recorded on real buildings during the Northridge earthquake.A physical characterization of the location of available sensors leading to the minimum global error between calculated and real responses is proposed in terms of effective modal participation factors relevant to the principal modes of the structure. This characterization allows for frames of known modal characteristics the definition of a criterion for the choice of the location of a limited number of sensors for monitoring or vibration control purposes. Copyright © 2003 John Wiley & Sons, Ltd.
Empirical attenuation relationship for Arias Intensity
Authors: Travasarou Thaleia , Bray Jonathan D. , Abrahamson Norman A. 
Published: April 2003

AbstractArias Intensity is a ground motion parameter that captures the potential destructiveness of an earthquake as the integral of the square of the acceleration–time history. It correlates well with several commonly used demand measures of structural performance, liquefaction, and seismic slope stability. A new empirical relationship is developed to estimate Arias Intensity as a function of magnitude, distance, fault mechanism, and site category based on 1208 recorded ground motion data from 75 earthquakes in active plate‐margins. Its functional form is derived from the point‐source model, and the coefficients are determined through non‐linear regression analyses using a random‐effects model. The results show that for large magnitude earthquakes (M > 7) Arias Intensity was significantly overestimated by previous relationships while it was underestimated for smaller magnitude events (M ⩽ 6). The average horizontal Arias Intensity is not significantly affected by forward rupture directivity in the near‐fault region. The aleatory variability associated with Arias Intensity is larger than that of most other ground motion parameters such as spectral acceleration. However, it may be useful in assessing the potential seismic performance of stiff engineering systems whose response is dominated by the short‐period characteristics of ground motions. Copyright © 2003 John Wiley & Sons, Ltd.
Chlorotoxin‐sensitive Ca2+‐activated Cl− channel in type R2 reactive astrocytes from adult rat brain
Authors: Dalton Stanislava , Gerzanich Volodymyr , Chen Mingkui , Dong Yafeng , Shuba Yaroslav , Simard J. Marc 
Published: April 2003

AbstractAstrocytes express four types of Cl− or anion channels, but Ca2+‐activated Cl− (ClCa) channels have not been described. We studied Cl− channels in a morphologically distinct subpopulation (∼ 5% of cells) of small (10–12 μm, 11.8 ± 0.6 pF), phase‐dark, GFAP‐positive native reactive astrocytes (NRAs) freshly isolated from injured adult rat brains. Their resting potential, −57.1 ± 4.0 mV, polarized to −72.7 ± 4.5 mV with BAPTA‐AM, an intracellular Ca2+ chelator, and depolarized to −30.7 ± 6.1 mV with thapsigargin, which mobilizes Ca2+ from intracellular stores. With nystatin‐perforated patch clamp, thapsigargin activated a current that reversed near the Cl− reversal potential, which was blocked by Cl− channel blockers, 5‐nitro‐2‐(3‐phenylpropylamino)‐benzoate (NPPB) and Zn2+, by I− (10 mM), and by chlorotoxin (EC50 = 47 nM). With conventional whole‐cell clamp, NPPB‐ and Zn2+‐sensitive currents became larger with increasing [Ca2+]i (10, 150, 300 nM). Single‐channel recordings of inside‐out patches confirmed Ca2+ sensitivity of the channel and showed open‐state conductances of 40, 80, 130, and 180 pS, and outside‐out patches confirmed sensitivity to chlorotoxin. In primary culture, small phase‐dark NRAs developed into small GFAP‐positive bipolar cells with chlorotoxin‐sensitive ClCa channels. Imaging with biotinylated chlorotoxin confirmed the presence of label in GFAP‐positive cells from regions of brain injury, but not from uninjured brain. Chlorotoxin‐tagged cells isolated by flow cytometry and cultured up to two passages exhibit positive labeling for GFAP and vimentin, but not for prolyl 4‐hydroxylase (fibroblast), A2B5 (O2A progenitor), or OX‐42 (microglia). Expression of a novel chlorotoxin‐sensitive ClCa channel in a morphologically distinct subpopulation of NRAs distinguishes these cells as a new subtype of reactive astrocyte. GLIA 42:325–339, 2003. © 2003 Wiley‐Liss, Inc.
Thyroid hormone modulates the extracellular matrix organization and expression in cerebellar astrocyte: Effects on astrocyte adhesion
Authors: Gonçalves Trentin Andréa , De Aguiar Cláudia Beatriz Nedel Mendes , Castilho Garcez Ricardo , Alvarez‐Silva Marcio 
Published: April 2003

AbstractThe effects of thyroid hormone (T3) on extracellular matrix (ECM) expression and organization in cerebellar astrocytes were studied. Control astrocytes exhibit laminin immunostaining distributed in a punctate configuration and fibronectin concentrated in focal points at the cell surface. These cells attach to the substratum by membrane points, as shown by scanning microscopy, possibly by focal points stained to fibronectin. In contrast, after T3 treatment, laminin assumes a fibrillary pattern and fibronectin becomes organized in filaments homogeneously distributed on the cell surface; the cells acquire a very flat and spread morphology. T3 treatment also modulates astrocyte adhesion. In addition, increased expression of both laminin and fibronectin was detected by Western blot. These alterations in fibronectin and/or laminin production and organization may be involved in the flat and spread morphology and in altered adhesion. We observed that fibroblast growth factor‐2 (FGF2) added to cultures had similar effects to those described to T3. Neutralizing antibodies against FGF2 reversed T3 effects on fibronectin and laminin distribution. We also observed that cerebellar neurons co‐cultured on T3‐treated astrocytes had an increase in the number of cells and presented longer neurites. Thus, we propose a novel mechanism of the effect of thyroid hormone on cerebellar development mediated by astrocytes: T3 may induce astrocyte secretion of growth factors, mainly FGF2, that autocrinally stimulate astrocyte proliferation, reorganization in ECM proteins, and alterations in cell spreading and adhesion. These effects may indirectly influence neuronal development. GLIA 42:359–369, 2003. © 2003 Wiley‐Liss, Inc.
Synthesis of a Tridentate Ligand for Use in TiIV‐Catalyzed Acetate Aldol Addition Reactions
Authors: Singer Robert A. , Brock Jane R. , Carreira Erick M. 
Published: April 2003

AbstractA facile, practical synthesis and resolution of (±)‐2′‐amino‐[1,1′‐binaphthalen]‐2‐ol (1) is described, as well as the preparation of the tridentate Schiff base ligand 2 derived from condensation of 1 with 3‐bromo‐5‐(tert‐butyl)salicylaldehyde, which has been used in catalytic enantioselective acetate aldol addition reactions.
Myth and Reality in the Attitude toward Valence‐Bond (VB) Theory: Are Its ‘Failures’ Real?
Authors: Shaik Sason , Hiberty Philippe C. 
Published: April 2003

AbstractAccording to common wisdom propagated in textbooks and papers, valence‐bond (VB) theory fails and makes predictions in contradiction with experiment. Four iconic ‘failures’ are: a) the wrong prediction of the ground state of the O2 molecule, b) the failure to predict the properties of cyclobutadiene (CBD) viz. those of benzene, c) the failure to predict the aromaticity/anti‐aromaticity of molecular ions like C5H$\rm{_{5}^{+}}$ and C5H$\rm{_{5}^{-}}$, C3H$\rm{_{3}^{+}}$ and C3H$\rm{_{3}^{-}}$, C7H$\rm{_{7}^{+}}$ and C7H$\rm{_{7}^{-}}$, etc; and d) the failure to predict that, e.g., CH4 has two different ionization potentials. This paper analyzes the origins of these ‘failures’ and shows that two of them (stated in a and d) are myths of unclear origins, while the other two originate in misuse of an oversimplified version of VB theory, i.e., simple resonance theory that merely enumerate resonance structures. It is demonstrated that, in each case, a properly used VB theory at a simple and portable level leads to correct predictions, as successful as those made by use of molecular‐orbital (MO) theory. This notion of VB ‘failure’, which is traced back to the VB‐MO rivalry, in the early days of quantum chemistry, should now be considered obsolete, unwarranted, and counterproductive. A modern chemist should know that there are two ways of describing electronic structure, which are not two contrasting theories, but rather two representations or two guises of the same reality. Their capabilities and insights into chemical problems are complementary, and the exclusion of any one of them undermines the intellectual heritage of chemistry.
Cocrystallization with Acetylene. The 1 : 1 Complex with Benzene: Crystal Growth, X‐Ray Diffraction and Molecular Simulations
Authors: Boese Roland , Clark Timothy , Gavezzotti Angelo 
Published: April 2003

AbstractThe crystal structure of an unusual 1 : 1 molecular complex between benzene and acetylene, two very small and apolar molecules, has been determined by X‐ray‐analysis of crystals grown by first mixing the two liquids under conditions of low temperature and high pressure in a capillary, followed by repeated zone melting to form crystals directly on the goniometer head of a diffractometer. Each acetylene molecule is clamped between two parallel benzene rings, with its molecular axis apparently perpendicular to the benzene planes. Closer inspection of thermal‐motion data from the diffraction experiment suggests that the acetylene molecule undergoes a wobbling, or precession, motion between the two rings so that it is perpendicular to them only in a time‐averaged sense. The results of quantum‐chemical calculations on isolated molecular dimers and trimers support this conclusion. In addition, the calculation of separate coulombic, dispersion, polarization and repulsion contributions to intermolecular bonding reveals that the CH⋅⋅⋅π‐bond interaction between acetylene and benzene in a T‐shaped dimer consists of a mixture of coulombic and polarization interactions. In the benzeneacetylene cocrystal, its magnitude is quantitatively comparable with that of other dispersive interactions. 5.4 ns Molecular‐dynamics simulations of the liquid mixture reveal that the two components are persistently miscible, a possible key to the formation of the cocrystal. No structure is, however, observed in the solution during the relatively short simulation time.
Structural Correlations for Nucleophilic Addition to the CO Group: The Solvation Angle
Authors: Davies John E. , Kirby Anthony J. , Komarov Igor V. 
Published: April 2003

AbstractWe report some new observations in BürgiDunitz territory – structurestructure correlations for the addition of N nucleophiles to the CO group. The amino aldehyde 1 exists predominantly in polar solvents, and exclusively in the crystal, as the carbonyl‐addition structure 2, but appears to demand hydrogen‐bonding solvation as part of the process. In terms of CO bond lengthening, the new system lies somewhere nearly half‐way between an amino aldehyde and a stable quaternary ammonium aminal: we present the structure 2⋅Me of the N+COMe derivative of 2 as an example. We have investigated the effects on the cyclisation equilibrium in this system of hydration, which is important, and of the degree of methylation of the azaadamantane skeleton, which – unexpectedly – is not. In terms of the reverse process, i.e., breaking the CN+ bond: in each case, the bond is lengthened by (n(O)σ*(CN)) electron‐pair donation from the O‐atom (the generalised anomeric effect, as in 2⋅Me↔3, below) [4]. This effect is strongest when the O‐atom is negatively charged, reduced by hydrogen‐bonding, and minimised by alkylation.
Crystal Structures and Magnetic Properties of Nitronyl Nitroxide Radicals
Authors: Zakrassov Alexander , Shteiman Vitaly , Sheynin Yana , Botoshansky Mark , Kapon Moshe , Kaftory Menahem , Del Sesto Rico E. , Miller Joel S. 
Published: April 2003

AbstractThe crystal structures and magnetic properties of the nitronyl nitroxide radicals 4,5‐dihydro‐4,4,5,5‐tetramethyl‐3‐oxido(1H‐imidazol‐1‐yloxyl) (1), 4,5‐dihydro‐2,4,4,5,5‐pentamethyl‐3‐oxido(1H‐imidazol‐1‐yloxyl) (2), 2‐(4‐chlorophenyl)‐4,5‐dihydro‐4,4,5,5‐tetramethyl‐3‐oxido(1H‐imidazol‐1‐yloxyl) (3), and 4,5‐dihydro‐2‐(2‐hydroxy‐5‐nitrophenyl)‐4,4,5,5‐tetramethyl‐3‐oxido(1H‐imidazol‐1‐yloxyl) (4) are reported. Compound 1 has two polymorphic forms: the α phase is monoclinic (P21/n space group), with a single molecule in the asymmetric unit, and the β phase is monoclinic (P21/c space group), with four molecules in the asymmetric unit. In the two polymorphs, the molecules are arranged in dimers formed by hydrogen bonds of the type CH⋅⋅⋅ON. The crystal structure of 3 contains layers of antiparallel ribbons of molecules. Compound 4 crystallizes with solvent molecules, and an intramolecular hydrogen bond is formed between the 2‐OH group of the phenyl ring and the nitroxide O‐atom. Compound 4 also loses the two O‐atoms of the nitroxide moiety upon heating to 90°. Magnetic measurements showed that both α and β polymorphs of 1 exhibit antiferromagnetic coupling. The best fit to the experimental data was obtained using BleanyBower's singlet‐triplet model (H=−2JSaSb): J=−11.2 K for the α phase and J=−15.0 K for the β phase. Compounds 3 and 4 show no evidence for spin coupling.
Distorted Fivefold‐Diamond Structure of 4,4‐Bis(2‐carboxyethyl)pimelic Acid (‘Methanetetrapropionic Acid’)
Authors: Ermer Otto , Kusch Andreas , Röbke Christof 
Published: April 2003

AbstractThe molecules of 4,4‐bis(2‐carboxyethyl)pimelic acid (=4,4‐bis(2‐carboxyethyl)heptanedioic acid; 1) assemble to build up hollow, five‐fold interpenetrating diamond‐like networks in tetragonal crystals via standard pairwise H‐bonds between the carboxy groups. In keeping with the flat, extended molecular conformation of 1 of approximate D2d symmetry, the supramolecular diamondoid networks are tetragonally compressed. Their mode of interpenetration is unusual and corresponds to that of adamantane‐1,3,5,7‐tetracarboxylic acid, which has an undistorted five‐fold diamond structure. Both the degree and the mode of interpenetration of 1 differ from those of the lower homologue 3,3‐bis(carboxymethyl)glutaric acid (2), which adopts a more‐common tetragonally elongated triple‐diamond architecture in the solid state.
The History of Ozone. Part III
Authors: Rubin Mordecai B. 
Published: April 2003

AbstractThe introduction of ozone into organic chemistry is due to the work of C. D. Harries, first in Berlin but mainly in Kiel, during the period 1903–1916. He established experimental procedures for ozonolysis, demonstrated the generality of the reaction of unsaturated compounds with ozone, and showed that ozone could be used for the synthesis of a variety of sensitive compounds. Most important for the future development of organic chemistry, he established that ozonolysis could be an important tool for determining the structures of organic compounds. He also initiated investigations into the mechanism of ozone reactions with alkenes, which culminated about forty years later in the Criegee mechanism for ozonolysis.
Polyacetylenes and Cumulenes, Potential Elements for Molecular Machines and Precursors of Carbon Clusters: A Theoretical Study
Authors: Zahradník Rudolf , Šroubková Libuše 
Published: April 2003

AbstractA recently described very simple procedure for estimating Hartree–Fock (H. F.) energy and accurate nonrelativistic energy has been used with simple hydrocarbons possessing CC or CC bonds and for the acetylene dimer. Experimental characteristics (heats of formation, ionization potentials, electron affinities), structural features, and reactivity have been discussed in terms of quantum‐chemistry characteristics at the H. F. level and also at a level including a part of electron correlation. Deviations from linearity with derivatives of long polyacetylenes and cumulenes are ascribed to the lowest‐energy deformation vibrations, which decrease rapidly when passing from short to long acetylenic and cumulenic chains. The role of derivatives and heteroanalogues of hydrocarbons under study in atmospheric and interstellar chemistry is briefly mentioned. Derivatives with enhanced stability represent potentially promising construction materials for molecular devices and also resources for the preparation of defined clusters of C‐atoms.
Parental assessment of early childhood development: biological and social covariates
Authors: Pevalin David J. , Wade Terrance J. , Brannigan Augustine 
Published: April 2003

AbstractThis study uses data from the National Longitudinal Survey of Children and Youth (N=8605) to investigate the effects of unfavourable birth outcomes and dimensions of the family environment on the development of Canadian children aged 0–47 months. Among children under 24 months of age, it was found that sex of the child, birth order and low birthweight were significant covariates while the familial environment tended to have little influence. However, among children aged 24–47 months, effects of parenting style, social support, and positive social‐structural conditions of the family supplemented the effects of sex of the child and low birthweight. The results suggest that the cumulative effects of a positive family environment begin to occlude the neonatal disadvantages in the first 47 months of life. Copyright © 2003 John Wiley & Sons, Ltd.