bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of tritium labelled mecillinam
Authors: Frederiksen Søren Melsing , Grue‐Sørensen Gunnar 
Published: July 2003

AbstractThe potent β‐lactam antibiotic mecillinam has successfully been labelled with tritium. 2,3,4,7‐Tetrahydro‐1H‐azepin‐1‐carbaldehyde was formed in a ring‐closing metathesis reaction and then condensed with trimethylsilyl protected penicillanic acid to give dehydro‐mecillinam. Pd/C catalysed tritiation then gave [3H2]‐mecillinam (6‐β (([3,4‐3H2]hexahydro‐1H‐azepin‐1‐yl)methyleneamino)penicillanic acid) with a radiochemical purity of 96% and a specific activity of 24 Ci/mmol. Copyright © 2003 John Wiley & Sons, Ltd.
Interannual and seasonal variability of modelled soil moisture in Oklahoma
Authors: DeLiberty Tracy L. , Legates David R. 
Published: July 2003

AbstractThe temporal variability of soil moisture is examined for Oklahoma, where diverse land surface, soils, and precipitation regimes exist. Using readily available meteorological, vegetation, and soils data, a hydrologic model was used to estimate daily soil moisture at 258 evaluation locations for the 30 year period from 1 January 1962 through 31 December 1991. A geographic information system (GIS) was used for the analysis, to take advantage of its powerful analysis capabilities and visualization tools. Results document the long‐term average soil moisture conditions, the variability that occurred during this 30 year period and the temporal scale of soil moisture variability for Oklahoma. On average, the soil moisture conditions in both winter and spring in Oklahoma are about 70% of field capacity and decrease to below 30% during the summer. Thus, the seasonal cycle is pronounced, although periods of wetter and drier conditions are evident. Overall, the period from 1962 through to early 1967, 1970–72, and 1976 through to 1981 were drier than the long‐term average soil moisture conditions. By contrast, wetter soil moisture conditions prevailed in late 1972 through to early 1975 and 1985 to the early months of 1988, where winter and spring soil moisture values often exceeded the long‐term average. An empirical estimate of the temporal consistency in soil moisture over Oklahoma is 53 days (1.8 months), and the amount of variance explained by the soil moisture (red noise) signal is 86%. No significant seasonal differences in the temporal autocorrelation were observed. Copyright © 2003 Royal Meteorological Society
A 10 year cloud climatology over Scandinavia derived from NOAA Advanced Very High Resolution Radiometer imagery
Authors: Karlsson Karl‐Göran 
Published: July 2003

AbstractResults from a satellite‐based method to compile regional cloud climatologies covering the Scandinavian region are presented. Systematic processing of multispectral image data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) instrument has been utilized to provide monthly cloud climatologies covering the period 1991–2000. Considerable local‐scale variation of cloud amounts was found in the region. The inland Baltic Sea and adjacent land areas exhibited a large‐amplitude annual cycle in cloudiness (high cloud amounts in winter, low cloud amounts in summer) whereas a weak‐amplitude reversed annual cycle (high cloud amounts with a weak maximum in summer) was found for the Scandinavian mountain range. As a contrast, conditions over the Norwegian Sea showed high and almost unchanged cloud amounts during the course of the year. Some interesting exceptions to these patterns were also seen locally. The quality of the satellite‐derived cloud climatology was examined through comparisons with climatologies derived from surface cloud observations, from the International Satellite Cloud Climatology Project (ISCCP) and from the European Centre for Medium‐range Weather Forecasts ERA‐40 data set. In general, cloud amount deviations from surface observations were smaller than 10% except for some individual winter months, when the separability between clouds and snow‐covered cold land surfaces is often poor. The ISCCP data set showed a weaker annual cycle in cloudiness, generally caused by higher summer‐time cloud amounts in the region. Very good agreement was found with the ERA‐40 data set, especially for the summer season. However, ERA‐40 showed higher cloud amounts than SCANDIA and ISCCP during the winter season. The derived cloud climatology is affected by errors due to temporal AVHRR sensor degradation, but they appear to be small for this particular study. The data set is proposed as a valuable data set for validation of cloud description in numerical weather prediction and regional climate simulation models. Copyright © 2003 Royal Meteorological Society
Estimating extreme dry‐spell risk in the middle Ebro valley (northeastern Spain): a comparative analysis of partial duration series with a general Pareto distribution and annual maxima series with a Gumbel distribution
Authors: Vicente‐Serrano S. M. , Beguería‐Portugués S. 
Published: July 2003

AbstractThis paper analyses a 50 year time series of daily precipitation in a region of the middle Ebro valley (northeastern Spain) in order to predict extreme dry‐spell risk. A comparison of observed and estimated maximum dry spells (50 year return period) showed that the generalized Pareto (GP) distribution combined with partial duration series (PDS) gives better results than the Gumbel distribution fitted to annual maximum series. Indeed, the classical Gumbel approach underestimated the empirical duration of dry spells. The PDS–GP approach was successfully applied in the study of extreme hydro‐climatic variable values. The results reported here could be applied in estimating climatic drought risks in other geographical areas. Copyright © 2003 Royal Meteorological Society
Determination of cholesterol oxides content in milk products by solid phase extraction and gas chromatography‐mass spectrometry
Authors: Calvo María V. , Ramos Lourdes , Fontecha Javier 
Published: July 2003

AbstractA method for quick and reliable analysis of cholesterol oxidation products (COPs) in dairy products has been developed. After lipid extraction, fat was transesterified under mild conditions to avoid degradation of the target compounds. Isolation of the COPs studied from other components in the lipid fraction was carried out on an aminopropyl SPE cartridge. Finally, analytes were analysed by GC‐MS without derivatisation. The method developed provides high specificity and good sensitivity, allowing the direct and unambiguous determination of the underivatized COPs investigated. Application of the method to dairy food analysis revealed the presence of COPs in powder milks and milk‐based infant formulas commercially available in Spain, showing that attention should be focused on reduction of cholesterol oxidation levels during both the processing and the storage of these types of foodstuffs.
Determination of tribromophenol and pentachlorophenol and its metabolite pentachloroanisole in Asparagus officinalis by gas chromatography/mass spectrometry
Authors: Mardones Claudia , Palma Julie , Sepúlveda Carlos , Berg Alex , von Baer Dietrich 
Published: July 2003

AbstractA GC‐MS method was developed and optimized for simultaneous determination of pentachlorophenol (PCP), 2,4,6‐tribromophenol (TBP), and pentachloroanisole (PCA) residues in the edible part of Asparagus officinalis. For this purpose, two procedures were evaluated: the direct separation of PCP, TBP, and PCA and the separation of acetyl‐PCP, acetyl‐TBP, and non‐acetylated PCA. Better sensitivity and quantitative results, especially for PCP, were obtained after acetylation. The residues of PCP and TBP were extracted as phenolates and acetylated in a carbonate solution. Acetylated compounds were extracted by liquid‐liquid extraction with hexane, while PCA was directly leached with this solvent. The proposed method allows the rapid quantification of traces of PCP, TBP, and PCA in a concentration ranging between 1.0 and 8.0 ng mL–1 in solution (corresponding to 0.3 and 8.0 μg kg–1 in asparagus). In this concentration range, typical recoveries for PCA, TBP, and PCP from asparagus samples were 59%, 86%, and 97% respectively (RSDs 3–7%).
Stability of ceftriaxone in water and cerebrospinal fluid determined by high‐performance liquid chromatography
Authors: de Diego Glaría Marta , Moscciati Gloria Godoy , Ramos Ricardo Godoy , Riquelme Marcelo Maturana 
Published: July 2003

AbstractA study of the stability of ceftriaxone in water and cerebrospinal fluid in the presence or the absence of buffer at different storage temperatures was performed by liquid chromatography on a C18 column (125×4 mm, 5 μm) using a mobile phase consisting of acetonitrile (300 mL), 0.1 M phosphate buffer (pH 7.4; 50 mL), tetrabutylammonium bromide (3.2 g) made up to a volume of 1 L with water. Detection was at 270 nm with a 50 μL loop and 1 mL/min flow. The study was performed with an without 0.05 M phosphate buffer (pH 6.0) and at room temperature (25 ± 2°C), +8°C, –20°C, and –40°C, over 15 days, 78 days, and 111 days (–20°C and –40°C), respectively. At all the temperatures studied, the degradation of ceftriaxone followed first‐order kinetics. Degradation of the drug was greater at higher temperatures and in the absence of phosphate buffer. Lower storage temperatures and the presence of 0.05 M phosphate buffer (pH 6.0) therefore improved the stability of ceftriaxone in water and cerebrospinal fluid.
Development and validation of a high‐performance liquid chromatographic procedure for the determination of herbicide residues in surface and agriculture waters
Authors: Zanella Renato , Primel Ednei G. , Gonçalves Fábio F. , Kurz Márcia H. S. , Mistura Clóvia M. 
Published: July 2003

AbstractA procedure has been developed for the determination of quinclorac, bentazone, 2,4‐D, clomazone, and propanil residues in surface and agriculture waters by SPE and HPLC‐UV. The method was validated and was applied for levels between 0.1 and 0.5 g/L, after a 500‐fold pre‐concentration. Average recoveries ranged from 85.7 to 109.8% with overall relative standard deviations of 1.8 to 13.4%.
Analysis of volatile composition of honey by solid phase microextraction and gas chromatography‐mass spectrometry
Authors: Soria Ana Cristina , Martínez‐Castro Isabel , Sanz Jesús 
Published: July 2003

AbstractHoney aroma is largely dependent on its volatile fraction, which in turn is influenced by nectar composition and by possible modifications after harvesting. Solid phase microextraction (SPME) allows a simple and rapid fractionation of volatile compounds in honey as a prior step to their GC‐MS qualitative and quantitative determination. A simple SPME‐based procedure has been developed for GC‐MS analysis of honey volatiles and applied to the study of 6 different commercial honeys. The possibility of honey characterization from the analytical data obtained by the SPME method is discussed.
Enantioseparation of dansyl amino acids on terguride‐based chiral selectors. Part I: Capillary electrophoretic separation
Authors: Honzátko Aleš , Votruba Jaroslav , Olšovská Jana , Flieger Miroslav , Bachechi Fiorella , Ferrantelli Paola , Sinibaldi Massimo , Cvak Ladislav 
Published: July 2003

AbstractA method of separation of dansyl amino acid (Dns‐AA) enantiomers by capillary electrophoresis (CE) using terguride‐based chiral selectors (CSs) was developed using linear polyacrylamide coated capillaries. Due to the high UV absorption of all studied CSs, only the capillary was filled with CS, while the inlet and outlet vials contained buffer solution only. Conditions were found for baseline separation of all Dns‐AA under study. L‐Dns‐AAs were eluted prior to D‐Dns‐AAs on all studied CSs. Use of the optical antipode of allyl‐terguride resulted in reversal of elution order of all Dns‐AAs (the D‐form was eluted prior to the L‐form). The best enantioselectivity was achieved for hydroxyl group‐containing AAs, i. e. serine and threonine. This finding is in good agreement with the proposed mechanism of chiral recognition of these AAs determined by X‐ray studies. Seven CSs with different N(1)‐side chain units, five of them designed for the preparation of silica based HPLC chiral stationary phases, were tested for their ability to resolve enantiomers of Dns‐AAs. Different polarity and hydrophobicity of N(1)‐side chains of the CSs resulted in different CS mobilities, thus influencing the effective separation time in the capillary. 1‐(5‐Aminopentyl)‐terguride showed the best enantioseparation and resolution for the Dns‐AAs studied.
Characterisation of a new minor urinary metabolite of piperine, an omnipresent food component, by LC‐MS/MS
Authors: Bajad Sunil , Khajuria Ravi K. , Suri Om P. , Bedi Kasturi L. 
Published: July 2003

AbstractThis study describes the detection and characterisation of a new minor metabolite of piperine in rat urine by LC‐MS/MS. The metabolite was partially purified using Sephadex®–LH20 column chromatography. Even in partially purified samples, the concentration was so low that NMR data could not be obtained using LC/NMR. However, comparative LC‐MS/MS as well as UV data of piperine (m/z 285) and the metabolite (m/z 287) gave very specific information to explain the difference of two mass units in the structures of these molecules. The proposed structure of the metabolite is E,E‐1‐[5‐(3‐methoxy‐4‐hydroxy‐phenyl)‐1‐oxo‐2,4‐pentadienyl]piperidine. Like human urinary metabolites, this metabolite retains the conjugated side chain and piperidine ring of the parent molecule while the methylenedioxy ring is cleaved. The study emphasises the role of LC‐MS/MS as a powerful tool in drug metabolism studies, particularly in identifying unstable or minor metabolites.
Experimental and modeling study of shock‐tube oxidation of acetylene
Authors: Eiteneer Boris , Frenklach Michael 
Published: July 2003

AbstractNine mixtures of acetylene and oxygen diluted in argon were studied behind reflected shock waves at temperatures of 1150–2132 K and pressures of 0.9–1.9 atm. Initial compositions were varied from very fuel‐lean to moderately fuel‐rich, covering equivalence ratios of 0.0625–1.66. Two more mixtures with added ethylene were used to boost the sensitivity to reactions of vinyl oxidation. The progress of reaction was monitored by laser absorption of CO molecules. The collected experimental data were subjected to extensive detailed chemical kinetics analysis. The initial kinetic model was assembled based on recent literature data and then optimized using the solution mapping technique. The analysis was extended to include recent experimental observations of Hidaka and co‐workers (Combust Flame 1996, 107, 401). The derived model reproduces closely both sets of experimental data, the result obtained by modifying nine rate coefficients and three enthalpies of formation of intermediate species. The identified parameter tradeoffs and justification for the changes are discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 391–414, 2003
H‐atom abstraction from selected CH bonds in 2,3‐dimethylpentanal, 1,4‐cyclohexadiene, and 1,3,5‐cycloheptatriene
Authors: Tuazon Ernesto C. , Aschmann Sara M. , Nguyen Marie V. , Atkinson Roger 
Published: July 2003

AbstractThe gas‐phase reactions of OH radicals with 1,4‐cyclohexadiene, 1,3,5‐cycloheptatriene, and 2,3‐dimethylpentanal have been investigated to determine the importance of H‐atom abstraction at specific positions in these molecules. Benzene was observed as a product of the reaction of OH radicals with 1,4‐cyclohexadiene in 12.5 ± 1.2% yield, in good agreement with a previous study and indicating that this is the fraction of the reaction proceeding by H‐atom abstraction from the allylic CH bonds. In contrast, no formation of tropone from 1,3,5‐cycloheptatriene was observed, suggesting that in this case H‐atom abstraction is not important. For the reaction of OH radicals with 2,3‐dimethylpentanal, formation of 3‐methyl‐2‐pentanone was observed in 5.4 ± 1.0% yield (after correction for reaction of 3‐methyl‐2‐pentanone with OH radicals), and this product is predicted to be formed after initial H‐atom abstraction from the 2‐position CH group. Acetaldehyde and 2‐butanone were also observed as products, with initial yields of ∼90% and ∼26%, respectively, and their formation appeared to involve, at least in part, an intermediary acyl peroxy radical. Using a relative rate method, the measured rate constants for the reactions of OH radicals with 2,3‐dimethylpentanal, 3‐methyl‐2‐pentanone, and tropone are (in units of 10−12cm3molecule−1s−1) 2,3‐dimethylpentanal, 42 ± 7; 3‐methyl‐2‐pentanone, 6.87 ± 0.08; and tropone, 42 ± 6. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 415–426, 2003
Temperature and pressure dependence of the reaction of OH and CO: Master equation modeling on a high‐level potential energy surface
Authors: Senosiain Juan P. , Musgrave Charles B. , Golden David M. 
Published: July 2003

AbstractThe temperature and pressure dependence of the reaction of OH + CO has been modeled using the (energy‐resolved) master equation and RRKM theory. These calculations are based on the coupled‐cluster potential energy surface of Yu and co‐workers (Chem Phys Lett 349, 547–554, 2001). As is well known, this reaction shows a strong non‐Arrhenius behavior at moderate and low temperatures because of the stabilization of the HOCO intermediate. Kinetic simulations are in excellent agreement with experiments at temperatures above 300 K, but the agreement is only modest at temperatures below 250 K. Our calculations indicate that the contribution of tunneling to the rate constant is marginal, given the small energy difference between the transition states corresponding to formation and decomposition of the HOCO intermediate. Parametric fits to the calculated rate constants are provided for modeling purposes. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 464–474, 2003
Supramolecular Control of Ester Hydrolysis in Poly(ethylene glycol)‐Interlocked Hydrogels
Authors: Ichi Takahiro , Ooya Tooru , Yui Nobuhiko 
Published: July 2003

AbstractPoly(ethylene glycol) (PEG)‐interlocked hydrogels were prepared by linking the PEG with α‐cyclodextrins (α‐CDs) threaded onto a PEG chain having ester linkages at the terminals (hydrolyzable polyrotaxane). These hydrogels were examined to clarify the effect of ionic strength of phosphate buffers, pH, and the addition of ethanol on erosion time in relation to inclusion states of α‐CDs with the ester linkages. The most characteristic phenomenon of the hydrogel erosion was observed in an ethanol/PBS cosolvent system: the time to reach the complete erosion time was shortened with decreasing water content. NMR analysis revealed that the ester linkages were exposed to the aqueous environment due to the aggregation of α‐CDs. These results suggest that the movement of α‐CDs in the polyrotaxanes from the terminal ester region to the another region gives the ester linkages a chance to interact with water.
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Conjugates of Antibody‐Targeted PEG Multiblock Polymers with Doxorubicin in Cancer Therapy
Authors: Pechar Michal , Ulbrich Karel , Jelínková Markéta , Říhová Blanka 
Published: July 2003

AbstractThe synthesis and physico‐chemical characterisation of biodegradable multiblock polymer drug carriers based on poly(ethylene glycol) (PEG) are described. The blocks of PEG (${{\bar{M}}_{\rm w}}$ = 2 000) are interconnected by an enzymatically degradable tripeptide derivative consisting of one Lys and two Glu residues. An anticancer drug, doxorubicin (Dox), was attached to the polymer carrier by a Gly‐Phe‐Leu‐Gly tetrapeptide spacer, which is also susceptible to degradation by lysosomal enzymes. A targeting polyclonal antibody was covalently linked to the polymer‐Dox conjugate by the aminolytic reaction of reactive sulfosuccinimidyl ester groups of the polymer with the protein. The resulting antibody‐polymer‐drug conjugates were characterised by SEC, UV/VIS spectrophotometry and amino acid analysis. Although the studied polymers show only a moderate antiproliferative activity against concanavalin A‐stimulated murine splenocytes and a murine T‐cell EL 4 lymphoma in vitro, they exhibited significant antitumour efficiency against murine T‐cell EL 4 lymphoma in vivo.magnified image
Application of Electrospray Ionization Mass Spectrometry to the Elucidation of the Primary Structure of Lignin
Authors: Evtuguin Dmitry V. , Amado Francisco M. L. 
Published: July 2003

AbstractElectrospray ionization mass spectrometry (ESI‐MS) was successfully applied to the structural analysis of lignin. The structure of oligomers fractionated from Eucalyptus globulus dioxane lignin was elucidated using tandem mass spectrometry, and the information on fragmentation patterns was provided by experiments on dimeric model compounds. Data obtained revealed a significant abundance in the lignin macromolecules of linear fragments that were composed of 8‐O‐4′‐linked syringyl/guaiacyl units and syringaresinol.The proposed linear fragment of the E. globulus lignin molecule.magnified imageThe proposed linear fragment of the E. globulus lignin molecule.
Synthesis of Sequential Polypeptides Containing O‐Phospho‐L‐Serine
Authors: Yamamoto Hiroyuki , Saitoh Arihiro , Ohkawa Kousaku 
Published: July 2003

AbstractThe chemistry of phosphoserine [Ser(P)] containing peptides and polypeptides was extensively investigated to explore a new biomineralization material science. The selective cleavage of the O,O′‐diphenyl phospho‐protecting groups of Ser(PO3Ph2) was examined using hydrogenolysis catalysts. Among the catalysts examined, only PtO2 in 50% trifluoroacetic acid (TFA)/AcOH successfully cleaved the protecting group of Ser(PO3Ph2) to give Ser(P). Based on these characteristic new findings, Ser(P)‐containing dipeptides such as Gly‐Ser(P), Ala‐Ser(P), Ser‐Ser(P), Asp‐Ser(P), Glu‐Ser(P), and Lys‐Ser(P), and tetrapeptide [Asp‐Ser(P)]2 were synthesized by a facile method. When we used the Ser(PO3Ph2) residues at the C terminals, the amino functional groups of amino acids and peptides can be coupled by the unsymmetric mixed anhydride using isobutyl chloroformate but cannot be by the symmetric anhydride method using dicyclohexylcarbodiimide. Neither unsymmetric mixed anhydride nor symmetric anhydride can be coupled with p‐nitrophenol at their C terminals. High‐molecular‐weight sequential polypeptides containing Ser(P) such as poly[Ser(P)‐Xaa] (Xaa: Gly, Ala, Ser, Lys, Asp, Glu) and poly[Gly‐Ser(P)‐Gly] were first synthesized by the polycondensation of the di‐ and tripeptide p‐nitrophenyl active esters, followed by the quantitative elimination of the diphenyl protecting groups by PtO2 in TFA/AcOH. The new strategy to synthesize Ser(P)‐containing peptides and model proteins may help the development of hybrid formulations of marine and biomimetic protein minerals.magnified image