bluuebunny/crossref_metadata_2025_split huggingface dataset:
Potentiometric Study of Urease Kinetics over pH 5.36–8.21
Authors: Krajewska Barbara , Chudy Michal , Drozdek Marek , Brzózka Zbigniew 
Published: April 2003

AbstractTo meet the demand for a convenient method of urease assay we present the potentiometric measurement of urease activity with use of an ammonium ion‐selective electrode. The membrane of the electrode was plasticized poly(vinyl chloride) containing physically immobilized nonactine as an NH4+‐sensitive ionophore and a lipophilic salt as an anionic additive. The calibration in buffers covering pH 5.36–9.97 showed that the electrode had a Nernstian response at pH <9.17 down to about 0.06 mM NH4+ and that for each buffer the detection limit grew with an increase in pH, concentration and the presence of Na2EDTA. The response time of the electrode was 15 s. In the study of urease kinetics performed with use of the electrode over pH 5.36–8.21 we have shown that the Michaelis constant of the enzyme does not significantly change with pH and that the maximum reaction rate‐pH profile, unlike those hitherto reported, has two maxima located at a short distance of 0.7 pH unit (7.2 and 6.5). Such a profile may pave the way for a new interpretation of the acid‐base mechanism of urease action. The potentiometric method presented can be helpful in screening for urease inhibitors, the substances of importance in therapies of diseases induced by ureolytic bacteria and in agriculture for proper nitrogen management in soil.
Determination of Labile Chromium in Water Samples by Catalytic Adsorptive Stripping Voltammetry in On‐Line System
Authors: Grabarczyk Malgorzata , Korolczuk Mieczyslaw 
Published: April 2003

AbstractA sensitive and selective on‐line voltammetric procedure for determination of traces of labile chromium is presented. The pulsed potential accumulation was proposed for the minimization of interferences of surface active substances and foreign ions. The calibration plot was linear from 7×10−10 mol L−1 to 3×10−8 mol L−1 for an accumulation time of 60 s. The relative standard deviation was 4.7% (n=5) for a chromium concentration of 1.5×10−8 mol L−1. The detection limit estimated from (3 σ) for an accumulation time of 60 s was about 2×10−10 mol L−1. The method was applied for the determination of labile chromium in tap and river water samples.
The Electrooxidation of Halogeno‐Anilines at Microelectrodes in Acetonitrile Solution
Authors: Pusztai Szabolcs , Dankházi Tibor , Farsang George 
Published: April 2003

AbstractThe electrochemical oxidation of 4‐chloro‐, 2,4‐dichloro‐, 2,4,6‐trichloro‐anilines and 4‐bromo‐, 2,4‐dibromo‐, 2,4,6‐tribromo‐anilines and 4‐iodo‐aniline were investigated in unbuffered acetonitrile solution. The main reaction at the electrooxidation of these compounds is the dimerization which is accompanied by release of the p‐substituent halide and formation of protons. To complete the so far achieved results by the apparent electron exchange number (napp) determination in the voltammetric time scale have been attempted. These measurements were carried out with the aim, to have a clearer picture on the napp influencing role of the following complicating factors: The rejected halogenides in MeCN solvent at lower potential values as the substrates can be oxidized to the corresponding halogens, and these halogens except the iodine substitute the substrate which takes place even in the voltammetric time scale by increasing the napp value characteristic for the dimerization only. The measurable napp values are influenced by the protons produced at the oxidation as well, in the opposite direction. The explanation for the latter is, that the solvent is aprotic, therefore the differently basic primary amino groups of the diffusing substrate molecules binding partly the protons and in this way voltammetrically inactive substrate species are formed. This reaction is a typical equilibrium type and this inactivation effect decrease the measurable napp value. This effect depends on the quality and number of halogene substituent at a given substrate because these affect the protonation constant of the substrate. Therefore the protonation constants of the substrates had to be determined. In the knowledge of these quantitative data the explanation of the trends in the napp values measured in the voltammetric time scale is attempted. The mechanistic study of the dimerization reaction of these substrates is in progress in our laboratory.
Micellar electrokinetic chromatography estimation of size and composition of procyanidins after thiolysis with cysteine
Authors: Herrero‐Martínez José M. , Ràfols Clara , Rosés Martí , Bosch Elisabeth , Lozano Carles , Torres Josep L. 
Published: April 2003

AbstractThis paper describes the characterization of procyanidin mixtures by acid depolymerization in the presence of cysteine (thiolysis with cysteine) and micellar electrokinetic chromatography (MEKC). Reversed‐phase liquid chromatography (RP‐HPLC) and MEKC were investigated for the separation of the major components of the depolymerized mixtures (catechins and their cysteinyl derivatives). The solutes could only be effectively separated using MEKC. Two background electrolytes (BGEs) are recommended: (i) 50 mM phosphate at pH 7, containing 40 mM sodium cholate (SC) and 10 mM sodium dodecyl sulfate (SDS); (ii) a BGE with the same composition but containing only 50 mM SDS. The MEKC procedures here reported, are cheap, reliable and fast, and their potential in the determination of the size and composition in procyanidin mixtures has been shown. The proposed MEKC methods were validated by comparison with our intralaboratory reference RP‐HPLC method using cysteamine as thiol donor.
Application of capillary zone electrophoresis in the separation and determination of the principal gum opium alkaloids
Authors: Reddy Mudiam Mohanakrishna , Suresh Velayudhan , Jayashanker Gurumurthy , Rao Beedu Sashidhar , Sarin Rajendra Kumar 
Published: April 2003

AbstractWe describe the use of capillary zone electrophoresis (CZE) for the qualitative and quantitative determination of major alkaloids (i.e., thebaine, codeine, morphine, papavarine and narcotine) in gum opium involving the analysis of alkaloids without derivatization or purification. Three extractions with 2.5% w/v aqueous acetic acid quantitatively extracted major alkaloids. The separation was carried out by CZE using a 7:3 mixture of methanol and sodium acetate (100 mM, pH 3.1) at a potential of 15 kV, with UV detection at 224 nm. Spiking of pure reference alkaloid standards in the opium extract was used for peak identification. The influences of buffer composition, pH and voltage on the separation of alkaloids were studied. The detection limit of each alkaloid dissolved in methanol was found to be 850 ng/mL (morphine), 450 ng/mL (thebaine), 500 ng/mL (codeine), 550 ng/mL (papaverine), and 500 ng/mL (narcotine) at an injection pressure of 300 mbar (injection volume, 4 nL) with a signal‐to‐noise ratio of 3:1. The external standard method was used for the quantification of alkaloids. The calibration plot was based on linear regression analysis. The relative standard deviation (RSD) for peak area and migration time was in the range of 1.03–3.56% and 0.34–0.69%, respectively. Percentage compositions (g%) of opium alkaloids in five gum opium samples were found to be in the range of 14.45–15.95 (morphine), 2.0–3.45 (codeine), 1.32–2.73 (thebaine), 0.92–2.37 (papavarine), and 3.85–5.77 (narcotine). The method developed is suitable for the routine analysis of major gum opium alkaloids in samples of forensic importance.
Surface characterization using chemical force microscopy and the flow performance of modified polydimethylsiloxane for microfluidic device applications
Authors: Wang Bin , Abdulali‐Kanji Zamin , Dodwell Emily , Horton J. Hugh , Oleschuk Richard D. 
Published: April 2003

AbstractThe widespread interest in micro total analysis systems has resulted in efforts to develop devices in cheaper polymer materials such as polydimethylsiloxane (PDMS) as an alternative to expensive glass and silicon devices. We describe the oxidation of the PDMS surface to form ionizable groups using a discharge from a Tesla coil and subsequent chemical modification to augment electroosmotic flow (EOF) within the microfluidic devices. The flow performance of oxidized, amine‐modified and unmodified PDMS materials has been determined and directly compared to conventional glass devices. Exact PDMS replicas of glass substrates were prepared using a novel two step micromolding protocol. Chemical force microscopy has been utilized to monitor and measure the efficacy of surface modification yielding information about the acid/base properties of the modified and unmodified surfaces. Results with different substrate materials correlates well with expected flow modifications as a result of surface modification. Oxidized PDMS devices were found to support faster EOF (twice that of native PDMS) similar to glass while those derivatized with 3‐aminopropyl triethoxysilane (APTES) showed slower flow rates compared to native PDMS substrates as a result of masking surface charge. Results demonstrate that the surface of PDMS microdevices can be manipulated to control EOF characteristics using a facile surface derivatization methodology allowing surfaces to be tailored for specific microfluidic applications and characterized with chemical force microscopy.
Reversed‐phase high‐performance liquid chromatography prefractionation prior to two‐dimensional difference gel electrophoresis and mass spectrometry identifies new differentially expressed proteins between striate cortex of kitten and adult cat
Authors: Van den Bergh Gert , Clerens Stefan , Vandesande Frans , Arckens Lutgarde 
Published: April 2003

AbstractTwo‐dimensional difference gel electrophoresis (2‐D DIGE), in combination with mass spectrometry, is a highly effective method for the rapid and reproducible detection of differentially expressed proteins. This approach, however, has the unfortunate drawback that it preferentially displays rather abundantly expressed proteins. Nevertheless, comparison of the protein expression levels of the striate cortex of adult cats and 30‐day‐old kittens, resulted in the identification of several proteins related to postnatal brain development and possibly age‐dependent plasticity as well (Van den Bergh et al., J. Neurochem. 2003, in press). The goal of the present study was the selective enrichment and identification of less abundant proteins within the same paradigm. Hereto, we performed a reversed‐phase chromatography prefractionation of our tissue lysate to separate the proteins in four fractions based on their hydrophobicity prior to 2‐D DIGE analysis. This approach not only confirmed the differential expression levels of a number of proteins from the previous study, but also identified three additional proteins preferentially expressed in kitten visual cortex and five additional proteins with higher expression levels in adult cat visual cortex. These spots were not visible on the total tissue lysate protein maps, indicating that the high‐performance liquid chromatography (HPLC) prefractionation enabled us to visualize additional, less abundant proteins.
Torsional response of symmetric buildings to incoherent and phase‐delayed earthquake ground motion
Authors: Heredia‐Zavoni Ernesto , Leyva Adrián 
Published: April 2003

AbstractThis paper studies the effect of coherency loss and wave passage on the seismic torsional response of three‐dimensional, multi‐storey, multi‐span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase‐delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd.
14‐3‐3γ Is upregulated by in vitro ischemia and binds to protein kinase Raf in primary cultures of astrocytes
Authors: Chen Xiao Qian , Chen Jian Guo , Zhang Yun , Hsiao Wendy Wen Luan , Yu Albert Cheung Hoi 
Published: April 2003

AbstractThe 14‐3‐3 protein family comprises critical regulatory molecules involved in signaling during cell division, proliferation, and apoptosis. Despite extensive study, the functions of the 14‐3‐3 proteins in brain remain unclear. 14‐3‐3γ, a subtype of the 14‐3‐3 family of proteins, was thought to be brain‐ and neuron‐specific. Using RNA arbitrarily primed PCR, we identified an upregulated cDNA fragment of the 14‐3‐3γ gene in primary cultures of astrocytes. Using Northern blot analysis, we confirmed this fragment was brain‐specific. In cultures of astrocytes, 14‐3‐3γ genes and proteins were differentially expressed at different ages and the proteins were distributed only in the cytoplasm. These results indicated that 14‐3‐3γ was not neuron‐specific but also expressed in astrocytes. The function of this protein in brain is unclear. Northern and Western blot analyses demonstrated that 14‐3‐3γ mRNA and protein were upregulated in cultured astrocytes in an anaerobic chamber‐induced ischemia model. The induction of 14‐3‐3γ proteins was neither suppressed by an MAP kinase inhibitor (U0126) nor a PI‐3 kinase inhibitor (LY294002). These data indicated that induction of 14‐3‐3γ might not involve PI‐3 and MAP kinase‐dependent pathways. Using coimmunoprecipitation, we demonstrated that endogenous 14‐3‐3γ bound to c‐Raf‐1 and p‐Raf 259. As Raf is one of the critical serine/threonine kinases controlling cell growth, differentiation, and death, the binding of 14‐3‐3γ to Raf indicates the critical role of this protein in ischemia‐induced apoptosis and the changes in signal transduction in astrocytes in culture. GLIA 42:315–324, 2003. © 2003 Wiley‐Liss, Inc.
Malignant peripheral nerve sheath tumor cell invasion is facilitated by Src and aberrant CD44 expression
Authors: Su Weiping , Sin Mihaela , Darrow Andrea , Sherman Larry S. 
Published: April 2003

AbstractMalignant peripheral nerve sheath tumors (MPNSTs) are aggressive malignancies that arise within peripheral nerves. These tumors occur with increased incidence in patients with neurofibromatosis type 1 (NF1), exhibiting increased Ras activity due to loss of the NF1 gene product, neurofibromin, and abnormal expression of the epidermal growth factor receptor (EGFR). We previously found that MPNSTs express increased levels of the CD44 family of transmembrane glycoproteins that have been implicated in tumor cell invasion and metastasis. In two MPNST cell lines, we have found that elevated CD44 expression and cell invasion are dependent on Src kinase activity but are independent of mitogen‐activated protein kinases (MAPK) kinase (MEK) activity. In contrast, inhibition of Src kinase activity has no influence on MPNST cell proliferation. Reduction of CD44 levels, using antisense oligonucleotides, results in reduced MPNST cell invasion in vitro, suggesting that Src contributes in part to MPNST cell invasion by increasing CD44 levels. At least some of this increased CD44 expression results from elevated EGFR levels through a Src‐dependent mechanism, consistent with the notion that EGFR promotes constitutive Src activation in MPNSTs. These data indicate that Src and CD44 are putative targets for the treatment of MPNST invasion and metastasis. GLIA 42:350–358, 2003. © 2003 Wiley‐Liss, Inc.
Human malignant glioma cells express semaphorins and their receptors, neuropilins and plexins
Authors: Rieger Johannes , Wick Wolfgang , Weller Michael 
Published: April 2003

AbstractSemaphorins comprise a family of molecules implicated in the guiding of growing axons and neuronal progenitor cells. Further, semaphorins have been suggested to play a role in cancer metastasis. Neuropilins 1 and 2 are cell surface receptors for soluble class 3 semaphorins. Plexins are direct receptors for membrane‐bound semaphorins and, by binding to neuropilins, coreceptors necessary for class 3 semaphorin signaling. We here report that human malignant glioma cell lines express neuropilins 1 and 2 mRNA and protein, as well as either plexin A1, A2, or B1. Further, all glioma cell lines express SEMA3A and SEMA3C and exhibit SEMA3A binding sites. Exogenous SEMA3A expressed in 293 or U87MG cells has no collapsing or chemorepulsive activities on glioma cells as determined by F‐actin staining and collagen coculture assays. In summary, human glioma cells express class 3 semaphorins and receptors for soluble and membrane‐bound semaphorins, suggesting a possible role of the semaphorin/neuropilin system in the interactions of human malignant glioma with the host's central nervous and immune systems. GLIA 42:379–389, 2003. © 2003 Wiley‐Liss, Inc.
Sequential loss of myelin proteins during Wallerian degeneration in the rat spinal cord
Authors: Buss Armin , Schwab Martin E. 
Published: April 2003

AbstractAxotomy of nerve fibers leads to the subsequent degeneration of their distal part, a process termed Wallerian degeneration (WD). While WD in the peripheral nervous system is usually followed by regeneration of the lesioned axons, central nervous system (CNS) neurons are generally unable to regrow. In this study, we investigated the process of WD in the dorsal columns of the rat spinal cord rostral to a mid‐thoracic lesion. We confirm earlier studies describing a very delayed microglial and an early and sustained astroglial reaction finally leading to scar formation. Interestingly, we found a differential time course in the loss of myelin proteins depending on their location. Proteins situated on the periaxonal myelin membrane such as myelin associated glycoprotein disappeared early, within a few days after lesion, concomitantly with cytoskeletal axonal proteins, whereas compact myelin and outer myelin membrane proteins such as MBP and Nogo‐A remained for long intervals in the degenerating tracts. Two distinct mechanisms are probably responsible for this difference: processes of protein destruction emanating from and initially probably located in the axon act on a time scale of 1–3 days. In contrast, the bulk of myelin destruction is due to phagocytosis known to be slow, prolonged, and inefficient in the CNS. These results may also have implications for future intervention strategies aiming at enhancing CNS regeneration. GLIA 42:424–432, 2003. © 2003 Wiley‐Liss, Inc.
Differential effects of apotransferrin on two populations of oligodendroglial cells
Authors: García C.I. , Paez P. , Soto E.F. , Pasquini J.M. 
Published: April 2003

AbstractIn the central nervous system (CNS), apotransferrin (aTf) is produced by oligodendroglial cells (OLGcs), and aTf is essential for cell survival. We previously demonstrated that a single intracranial injection of aTf in 3‐day‐old rats accelerates differentiation of OLGc and that aTf acts at early stages of development on certain populations of OLGcs, promoting accelerated maturation, with no effect on late markers of cell differentiation. The objective of the present study was to analyze OLGc maturation at two different stages of rat development, 4 and 10 days of age, in OLGcs isolated from the brain after intracranial injection of aTf at 3 days of age, and to explore the in vitro effect of aTf added to cultures of OLGc isolated from aTf‐injected and control brains. The maturational cell stages were identified by immunocytochemistry with different OLGc markers and by analysis of their morphological complexity. The OLGcs isolated from 4‐ and 10‐day‐old animals intracranially injected with aTf were more differentiated than control cells. Treatment with aTf of the cultures of OLGcs that were isolated from 4‐day‐old saline‐injected control animals induced their differentiation, while a similar treatment of the cultures of OLGcs that were isolated from 10‐day‐old animals did not induce further maturation of the cells. The results presented in the present report demonstrate that the in vivo effects of aTf on OLGc maturation can be reproduced in cultures and that the effects of aTf occur early in development during a narrow, transient “temporal window” within which OLGcs are sensitive to its action. GLIA 42:406–416, 2003. © 2003 Wiley‐Liss, Inc.
Generation and High‐Resolution Photoelectron Spectroscopy of Small Organic Radicals in Cold Supersonic Expansions
Authors: Willitsch Stefan , Dyke John M. , Merkt Frédéric 
Published: April 2003

AbstractA general method of generating radicals in cold supersonic expansions in the gas phase is presented. The method relies on excimer laser photolysis of suitable precursor molecules in a thin quartz capillary mounted at the orifice of a pulsed gas nozzle and can easily be combined with vacuum‐UV photoionization mass spectrometry and high‐resolution photoelectron spectroscopy to study the reactivity and the rovibronic energy level structure of neutral radicals and their ions, as well as to determine highly accurate adiabatic ionization energies. The characteristics of the radical source are described in detail, and its performance is illustrated by mass spectrometric and high‐resolution photoelectron spectroscopic investigations of NH2, CH2, CH3, C2H, C2H3, and C2H5. The radical source is not only suitable to produce cold samples (rotational temperature of ca. 30 K) of radicals of moderate reactivity, such as NH2, CH3, or C2H5, but it is also useful to prepare highly reactive radicals (e.g., C2H) for spectroscopic investigations.
Chiral and Achiral Crystal Structures
Authors: Flack Howard D. 
Published: April 2003

AbstractAn extensive study and analysis of the concepts, classification, presentation, and nomenclature of chirality and lack of chirality in crystal structures and their constituents is presented. Oriented crystal structures are classified. The chirality rules for existence of molecular crystal structures are examined and the relation to segmentation and latent symmetry highlighted. The nomenclature of chirality and related terms, and the relationship of chirality to optical activity is covered. The uses and limitations of the Euclidean normalizer are treated. An improved glossary of terms is included.
Magnetic Circular Dichroism of the Long‐Wavelength π‐π* Transitions in Nitrogen‐Containing Heteroconjugated Aromatic Compounds and in Selected Ruthenium Complexes
Authors: Kleindienst Peter , Belser Peter , Wagnière Georges H. 
Published: April 2003

AbstractThe long‐wavelength magnetic circular dichroism (MCD) spectra of some nitrogen‐containing heteroconjugated aromatic compounds have been recorded and interpreted on the basis of quantum‐chemical model calculations. In particular, the dependence of the MCD bands on the positions of the N‐atoms inside the aromatic rings and on substituents has been investigated.Some of the compounds considered form Ru2+ complexes. The influence of complexation on the long‐wavelength π‐π* bands of the ligands has also been recorded and discussed.