bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enantioseparation of chiral allenic acids by micellar electrokinetic chromatography with cyclodextrins as chiral selector
Authors: Wang Zhaoyan , Tang Zhongmei , Gu Zhenhua , Hu Zhide , Ma Shengming , Kang Jingwu 
Published: February 2005

AbstractEnantioseparation of chiral aryl allenic acids by micellar electrokinetic chromatography (MEKC) with cyclodextrins (CDs) as chiral selectors was described. The screen of chiral selectors (β‐CD, γ‐CD, and hydroxypropyl (HP)‐γ‐CD) showed that the enantioseparation was not only dependent on the type of CD but also the presence of 2‐propanol in the buffer. In order to optimize the operational parameters, the effect of the concentration of CDs, sodium dodecyl sulfate (SDS), and 2‐propanol, as well as the buffer ionic strength and pH on enantioseparation were studied. It was proved that the concentration of CDs, 2‐propanol, and the buffer ionic strength were the critical parameters. Under optimal conditions, baseline separations of all seven allenic acid enantiomers were achieved. Furthermore, the method validation in terms of repeatability, linearity, limit of detection (LOD), and limit of quantitation (LOQ) were performed. Using the present method, the optical purity of a nonracemic sample with the enantiomeric excess (e.e.%) value of 99.65% was determined.
Separation and on‐column preconcentration of some nonsteroidal anti‐inflammatory drugs by microemulsion electrokinetic capillary chromatography using high‐speed separations
Authors: Macià Alba , Borrull Francesc , Calull Marta , Aguilar Carme 
Published: February 2005

AbstractVarious strategies have been investigated for separating a group of nonsteroidal anti‐inflammatory drugs (NSAIDs) by microemulsion electrokinetic capillary chromatography (MEEKC) using high‐speed separations. The parameters that of affect the separation, such as the nature of the oil droplet and the buffer, and the surfactant concentration have been studied. In addition, several organic solvents were used to decrease the retention of the analytes in the oil droplet phase and to improve the resolution of the NSAIDs. The optimum microemulsion background electrolyte (BGE) solution made of 0.8% w/w ethyl acetate, 6.6% w/w butan‐1‐ol, 6.0% w/w acetonitrile, 1.0% w/w sodium dodecyl sulfate (SDS), and 85.6% w/w of 10 mM sodium tetraborate at pH 9.2 resolved the drugs within 8 min. The short‐end injection procedure is an alternative for reducing the analysis time. When this procedure was used, the microemulsion BGE solution consisted of 0.8% w/w ethyl acetate, 6.6% w/w butan‐1‐ol, 17.0% w/w methanol, 1.0% w/w SDS, and 74.6% w/w of 10 mM sodium tetraborate, pH 9.2, and the NSAIDs were separated within 3 min. The reversed electrode polarity stacking mode (REPSM) technique was applied to the on‐line concentration of the NSAIDs. In this technique, the sample matrix was pumped out of the capillary using a polarity‐switching step. When this technique was applied, the sensitivity was enhanced up to 40‐fold and the limits of detection (LODs) were in the low μg·L‐1 levels.
Amino acid analysis by micellar electrokinetic chromatography with laser‐induced fluorescence detection: Application to nanolitre‐volume biological samples from Arabidopsis thaliana and Myzus persicae
Authors: Zhu Xunlin , Shaw P. Nicholas , Pritchard Jeremy , Newbury John , Hunt Emma J. , Barrett David A. 
Published: February 2005

AbstractAmino acids were derivatised with 4‐fluoro‐7‐nitrobenzo‐2,1,3‐oxadiazol (NBD‐F), separated by micellar electrokinetic chromatography (MEKC), and detected by argon‐ion (488 nm) laser‐induced fluorescence. The optimised MEKC background electrolyte conditions were: 40 mM sodium cholate, 5 mM β‐cyclodextrin in 20 mM aqueous borate buffer, pH 9.1, with 7% v/v acetonitrile. Using these conditions, 19 amino acids were separated within 17 min. The limits of detection were in the range of 7.6–42.2 pmol/mL and limits of quantitation from 0.05–0.14 nmol/mL. The method was systematically validated for injection volume error, migration time variation, calibration linearity, accuracy, precision, and recovery. Nanolitre volume samples of phloem sap of individual sieve element cells from the plant Arabidopsis thaliana and honeydew from the aphid Myzus persicae were directly analysed with this method. Quantitative amino acid concentrations in these two biological matrices were profiled for the first time. This method is particularly important because it allows the complete profile of the amino acids obtained from individual phloem elements, allowing cell to cell and plant to plant variation to be quantified, which to date has not been possible with Arabidopsis thaliana.
Language processing within the human medial temporal lobe
Authors: Meyer Patric , Mecklinger Axel , Grunwald Thomas , Fell Juergen , Elger Christian E. , Friederici Angela D. 
Published: February 2005

AbstractAlthough the hippocampal formation is essential for verbal memory, it is not fully understood how it contributes to language comprehension. We recorded event‐related potentials (ERPs) directly from two substructures of the medial temporal lobe (MTL), the rhinal cortex and the hippocampus proper, while epilepsy patients listened to sentences that either were correct or contained semantic or syntactic violations. Semantic violations elicited a large negative ERP response peaking at ∼400 ms in the rhinal cortex. In contrast, syntactically incorrect sentences elicited a negative deflection of 500–800 ms in the hippocampus proper. The results suggest that functionally distinct aspects of integration in language comprehension are supported by different MTL structures: the rhinal cortex is involved in semantic integration, whereas the hippocampus proper subserves processes of syntactic integration. An analysis of phase synchronization within the gamma band between rhinal and hippocampal recording sites showed that both of the above‐mentioned ERP components were preceded by an increase of phase synchronization. In contrast to these short phasic increases of phase synchronization in both violation conditions, correct sentences were associated with a long‐lasting synchronization in a late time window, possibly reflecting the integration of semantic and syntactic information as required for normal comprehension. © 2005 Wiley‐Liss, Inc.
Effect of sucrose on nisin production in batch and fed‐batch culture by Lactococcus lactis
Authors: Lv Wenhua , Cong Wei , Cai Zhaoling 
Published: February 2005

AbstractThe effects of sucrose on cell growth and nisin production by Lactococcus lactis were investigated in batch and pH feed‐back controlled fed‐batch cultures. In batch cultures, nisin titer reached its maximum, 2658 IU cm−3, at the initial sucrose concentration of 30 g dm−3. With sucrose concentrations higher than 30 g dm−3, nisin production decreased while the biomass was not influenced significantly. By using the pH feed‐back controlled method, residual sucrose concentration could be controlled well in fed‐batch cultures and three conditions (sucrose maintained at 2, 16, 20 g dm−3, respectively) were evaluated. Maintaining a low sucrose concentration at 2 g dm−3 during feeding favored nisin biosynthesis, and the maximum nisin titer obtained was 4961 IU cm−3 compared with 3370 IU cm−3 (16 g sucrose dm−3)and 3498 IU cm−3 (20 g sucrose dm−3), respectively. Copyright © 2005 Society of Chemical Industry
Analysis of neutral oligosaccharides for structural characterization by matrix‐assisted laser desorption/ionization quadrupole ion trap time‐of‐flight mass spectrometry
Authors: Ojima Noriyuki , Masuda Katsuyoshi , Tanaka Koichi , Nishimura Osamu 
Published: February 2005

AbstractWe have acquired multi‐stage mass spectra (MSn) of four branched N‐glycans derived from human serum IgG by matrix‐assisted laser desorption/ionization quadrupole ion trap time‐of‐flight mass spectrometry (MALDI‐QIT‐TOF‐MS) in order to demonstrate high sensitivity structural analysis. [M + H]+ and [M + Na]+ ions were detected in the positive mode. The detection limit of [M + Na]+ in MS/MS and MS3 measurements for structural analysis was found to be 100 fmol, better than that for [M + H]+. The [M + H]+ ions subsequently fragmented to produce predominantly a Y series of fragments, whereas [M + Na]+ ions fragmented to give a complex mixture of B and Y ions together with some cross‐ring fragments. Three features of MALDI‐QIT‐CID fragmentation of [M + Na]+ were cleared by the analysis of MS/MS, MS3 and MS4 spectra: (1) the fragment ions resulting from the breaking of a bond are more easily generated than that from multi‐bond dissociation; (2) the trimannosyl–chitobiose core is either hardly dissociated, easily ionized or it is easy to break a bond between N‐acetylglucosamine and mannose; (3) the fragmentation by loss of only galactose from the non‐reducing terminus is not observed. We could determine the existence ratios of candidates for each fragment ion in the MS/MS spectrum of [M + Na]+ by considering these features. These results indicate that MSn analysis of [M + Na]+ ions is more useful for the analysis of complicated oligosaccharide structures than MS/MS analysis of [M + H]+, owing to the higher sensitivity and enhanced structural information. Furthermore, two kinds of glycans, with differing branch structures, could be distinguished by comparing the relative fragment ion abundances in the MS3 spectrum of [M + Na]+. These analyses demonstrate that the MSn technology incorporated in MALDI‐QIT‐TOF‐MS can facilitate the elucidation of structure of complex branched oligosaccharides. Copyright © 2005 John Wiley & Sons, Ltd.
Rapid characterization of Bacillus spores targeting species‐unique peptides produced with an atmospheric pressure matrix‐assisted laser desorption/ionization source
Authors: Pribil Patrick A. , Patton Elizabeth , Black Gavin , Doroshenko Vladimir , Fenselau Catherine 
Published: February 2005

AbstractNew and improved strategies are eagerly sought for the rapid identification of microorganisms, particularly in mixtures. Mass spectrometry remains a powerful tool for this purpose. Small acid‐soluble proteins (SASPs), which are relatively abundant in Bacillus spores, represent potential biomarkers for species characterization. Despite sharing extensive sequence homology, these proteins differ sufficiently in sequence for discrimination between species. This work focuses on the differences in sequence between SASPs from various Bacillus species. Compilation of SASP sequences from protein database searches, followed by in silico trypsin digestion and analysis of the resulting fragments, identified several species‐specific peptides that could be targeted for analysis using mass spectrometry. This strategy was tested and found to be successful in the characterization of Bacillus spores both from individual species and in mixtures. Analysis was performed using an ion trap mass spectrometer with an atmospheric pressure MALDI source. This instrumentation offers the advantage of increased speed of analysis and accurate precursor ion selection for tandem mass spectrometric analysis compared with vacuum matrix‐assisted laser desorption/ionization and time‐of‐flight instruments. The identification and targeting of species‐specific peptides using this type of instrumentation offers a rapid, efficient strategy for the identification of Bacillus spores and can potentially be applied to different microorganisms. Copyright © 2005 John Wiley & Sons, Ltd.
CHASE, a charge‐assisted sequencing algorithm for automated homology‐based protein identifications with matrix‐assisted laser desorption/ionization time‐of‐flight post‐source decay fragmentation data
Authors: Raucci Giuseppe , Gabrielli Meri , Novelli Sabrina , Picariello Gianluca , Collins Stephen H. 
Published: February 2005

AbstractWe describe CHASE, a novel algorithm for automated de novo sequencing based on the mass spectrometric (MS) fragmentation analysis of tryptic peptides. This algorithm is used for protein identification from sequence similarity criteria and consists of four steps: (1) derivatization of tryptic peptides at the N‐terminus with a negatively charged reagent; (2) post‐source decay (PSD) fragmentation analysis of peptides; (3) interpretation of the mass peaks with the CHASE algorithm and reconstruction of the amino acid sequence; (4) transfer of these data to software for protein identifications based on sequence homology (Basic Local Alignment Search Tool, BLAST). This procedure deduced the correct amino acid sequence of tryptic peptide samples and also was able to deduce the correct sequence from difficult mass patterns and identify the amino acid sequence. This allows complete automation of the process starting from MS fragmentation of complex peptide mixtures at low concentration (e.g. from silver‐stained gel bands) to identification of the protein. We also show that if PSD data are collected in a single spectrum (instead of the segmented mode offered by conventional matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) instrumentation), the complete workflow from MS‐PSD data acquisition to similarity‐based identification can be completely automated. This strategy may be applied to proteomic studies for protein identification based on automated de novo sequencing instead of MS or tandem MS patterns. We describe the Charge Assisted Sequencing Engine (CHASE) algorithm, the working protocol, the performance of the algorithm on spectra from MALDI‐TOFMS and the data comparison between a TOF and a TOF–TOF instrument. Copyright © 2005 John Wiley & Sons, Ltd.
Determination of micelle mass by electrospray ionization mass spectrometry
Authors: Nohara Daisuke , Kajiura Takatomo , Takeda Koji 
Published: February 2005

AbstractBy electrospray ionization (ESI) mass spectrometry, micelle solutions of sodium cholate were investigated in detail in the presence and absence of ethanol. The average aggregation number could be evaluated from the spectra acquired under conditions where soft collisions adequate to measure the micelle solution were induced, and the value agreed well with that obtained previously by other methods. From the dependence on ethanol content, it was also found that the average aggregation number in aqueous solution without organic solvent could be reliably estimated. The ESI method proved to be a useful tool for determining the micelle mass in the original aqueous phase. Copyright © 2005 John Wiley & Sons, Ltd.
Quantification of urinary N‐acetyl‐S‐ (propionamide)cysteine using an on‐line clean‐up system coupled with liquid chromatography/tandem mass spectrometry
Authors: Li Chien‐Ming , Hu Chiung‐Wen , Wu Kuen‐Yuh 
Published: February 2005

AbstractAcrylamide has been reported to be present in high‐temperature processed foods and normal processed food intake could lead to significant acrylamide exposure. Acrylamide in vivo can be conjugated with glutathione in the presence of glutathione transferase. This conjugation product is further metabolized and excreted as N‐acetyl‐S‐(propionamide)cysteine (NASPC) in the urine. NASPC could be considered a biomarker for acrylamide exposure. The objective of this study was to develop a highly specific, rapid and sensitive method to quantify urinary NASPC, serving as a biomarker for acrylamide exposure assessment. Isotope‐labeled [13C3]NASPC was successfully synthesized and used as an internal standard. This urine mixture was directly analyzed using a newly developed liquid chromatographic/tandem mass spectrometric method coupled with an on‐line clean‐up system. The detection limit for this method was estimated as <5 µg l−1(0.4 pmol) on‐column. The method was applied to measure the urinary level of NASPC in 70 apparently health subjects. The results showed that the NASPC urinary level was highly associated with smoking. Smokers had a significantly higher urinary NASPC level (135 ± 88 µg g−1 creatinine) than non‐smokers (76 ± 30 µg g−1 creatinine). A highly sensitive and selective LC/MS/MS isotope dilution method was successfully established. With an on‐line clean‐up system, this system is capable of routine high‐throughput analysis and accurate quantitation of NASPC in urine. This could be a useful tool for health surveillance for acrylamide exposure in a population for future study. Copyright © 2005 John Wiley & Sons, Ltd.
Gas‐phase ion chemistry in XH4C3H4ZH3 (XSi, Ge; ZN, P) mixtures
Authors: Operti Lorenza , Rabezzana Roberto , Turco Francesca , Vaglio Gian Angelo 
Published: February 2005

AbstractThe gas‐phase ion chemistry of silane–allene–ammonia, germane–allene (or propyne)–ammonia (or phosphine) systems was studied by ion trap mass spectrometry. Reaction sequences were determined and rate constants were measured for the main processes observed. The mixture containing silane displays higher reactivity with respect to that with germane. Comparison with analogous systems provides useful information about the reactivity of different hydrocarbon molecules and the different affinities of silicon and germanium towards nitrogen and phosphorus. The most interesting product ions observed are those containing Si (or Ge), C and N (or P) elements together, as these ion species may be considered precursors of doped amorphous carbides, which are widely used in semiconductor devices. Copyright © 2005 John Wiley & Sons, Ltd.
Electrolytic electrospray ionization mass spectrometry of quaterthiophene‐bridged bisporphyrins: beyond the identification tool
Authors: Rondeau David , Rogalewicz Françoise , Ohanessian Gilles , Levillain Eric , Odobel Fabrice , Richomme Pascal 
Published: February 2005

AbstractSeveral quaterthiophene‐bridged bisporphyrins were analyzed by electrospray ionization mass spectrometry (ESI‐MS). The active centers of these molecular assemblies are two porphyrins moieties complexed (Z) or not (H) with a metal ion, typically Zn2+, and the spacer is a quaterthiophene. The two end‐groups were chemically linked to the quaterthiophene spacers by (i) a CC single bond, (ii) a trans double bond or (iii) a triple bond. The formation of charged species either by protonation ([M + H]+ and [M + 2H]2+) or electron(s) loss (M+ and M2+), account for the occurrence of electrochemical processes in the basic operation of an electrospray source acting in a non‐aqueous solvent. The nature of the observed charged species is correlated with the electro‐oxidation properties and proton production by electro‐oxidation of residual water. The occurence of these electrochemical reaction is proposed when the electroactivity of the electrosprayed substrates is not sufficient to support the current demand of the ESI source. In this way, the results obtained from the analysed series suggest the occurrence of such a process when the interfacial potential of the metal capillary reaches a value of 0.75 V vs Ag/AgCl. The results of theoretical calculations confirm the importance of the ionization energy with regard to the protonation energy in the course of the ionization reaction. The structural differences at the porphyrin–linker junctions lead to significantly smaller ionization energy in the case of the trans double bond. The MS observation of discharged dimers from molecular assemblies, including two complexed porphyrins ZZ or two free bases HH as end‐group and a triple bond as the quaterthiophene–bisporphyrin junction, indicates together with molecular modelling (carried out at the semi‐empirical PM3 level), that the planar and symmetric structures favour stacking. Copyright © 2005 John Wiley & Sons, Ltd.
Analysis of the chiral composition of a carbon nanotube surface by means of second harmonic generation
Authors: De Dominicis L. , Fantoni R. , Botti S. , Ciardi R. , Asilyan L. , Fiori A. , Orlanducci S. 
Published: February 2005

AbstractThe second‐order susceptibility tensor χ(2)(2ω;ω, ω) of a carbon nanotube (CNT) surface was determined as a function both of the average tube orientation and CNT topology distribution. The transformation properties of the hyperpolarizability β tensor, as rooted in the CNT isogonal symmetry point group, make non‐vanishing only the chiral component of χ(2)(2ω;ω, ω), thus denying second harmonic generation (SHG) in racemic samples. Nevertheless, the rupture of the CNT spatial symmetry due to local deformations and to finite size can act as a source for SHG even in racemic samples. The study of SHG polarization and of the anisotropic dependence of the signal intensity on the angle Ω between the surface normal and the exciting laser beam direction are proposed as methods to discriminate between the two contributions. An experimental test of such a statement was performed on a sample grown by the laser annealing technique. A massive presence of chiral CNTs with strong local deformations was revealed by the low‐ and medium‐wavenumber Raman spectra measured on the sample. The SHG polarization and the anisotropic dependence of the signal intensity as a function of Ω were studied experimentally, allowing the racemic nature of the investigated sample to be elucidated. Copyright © 2005 John Wiley & Sons, Ltd.
Refined theory of two‐photon processes accounting for virtual electric quadrupole and magnetic dipole transitions
Authors: Egorova N. , Kouzov A. , Chrysos M. , Rachet F. 
Published: February 2005

AbstractTwo‐photon transition amplitudes, accounting for virtual double electric dipole–electric quadrupole (E1, E2) and electric dipole–magnetic dipole (E1, M1) transitions, are derived for isotropic molecular ensembles. The new‐type non‐resonant Raman scattering is shown to appear from the interfering emission fields generated by multipoles (electric dipole, electric quadrupole and magnetic dipole) induced on a scattering particle. The interference is found to affect strongly the angular distribution and polarization characteristics of the scattered radiation, damping the forward scattering while enhancing the backward scattering. When the excitation frequency approaches an absorption resonance, the interference features are shown to disappear from the Raman spectra. In the off‐resonance case, the Raman cross‐section equations for gases of linear and spherical (Td) molecules are elaborated in terms of the mixed electronic polarizabilities expressed via their invariants in the molecule‐fixed frame. Copyright © 2005 John Wiley & Sons, Ltd.
Photo‐fragment excitation spectroscopy (PHOFEX) by DFWM and LIF: propensities for H2CO → HCO + H near the So threshold
Authors: Tulej M. , Knopp G. , Beaud P. , Gerber T. , Radi P. P. 
Published: February 2005

AbstractA novel technique for photo‐fragment excitation spectroscopy (PHOFEX) is introduced by applying resonant‐enhanced degenerate four‐wave mixing (DFWM) and laser‐induced fluorescence (LIF). The method is applied to investigate the dynamics of the radical channel decomposition of H2CO. The DFWM configuration is used to excite H2CO to an energy level close to the threshold for dissociation to radical products on the S0 potential energy surface. Simultaneously, LIF is employed to detect the nascent HCO fragments. PHOFEX spectra are recorded by tuning the DFWM photon energy near the dissociation threshold and measuring specific HCO transitions by LIF. The PHOFEX spectra are subsequently normalized to the DFWM signals recorded simultaneously. The resulting fluorescence quantum yield spectra provide sensitive information on state‐specific propensities of the dissociation reaction. Copyright © 2005 John Wiley & Sons, Ltd.