bluuebunny/crossref_metadata_2025_split huggingface dataset:
Limitations of Variational Transition State Theory for Barrierless Radical–Radical Recombination Reactions
Authors: Troe Jürgen 
Published: April 2004

Abstract
Variational transition state theory (VTST) is widely used for the modelling of barrierless radical-radical recombination reactions. In this application, VTST suffers from a number of limitations some of which are of more technical, others of more fundamental nature. The former are caused by inappropriate averaging over individual adiabatic channel potentials or by the neglect of quantum effects, the latter are due to deviations from adiabatic dynamics. It is shown that most radical-radical recombination reactions are characterized by Massey parameters which are smaller than unity such that the dynamics is nonadiabatic. VTST treatments which generally assume adiabatic dynamics, therefore, have a fundamental problem. Calculations of rate constants by VTST often exceed classical trajectory results by about 10 to 20percent. This is normally attributed to “recrossing trajectories”. In the present work it is shown, however, that deviations of this magnitude also have to be expected for nonadiabatic dynamics in comparison to adiabatic dynamics. It is, therefore, suggested that “recrossing” at least in part has to be attributed to nonadiabatic dynamics. A way out of the dilemma is the use of a combination of statistical adiabatic channel and classical trajectory concepts.
A Kinetic Study of the Reaction between the 2-Ċ3H7 Radical and i-C4H8: Enthalpy of Formation of the (CH3)2CHCH2Ċ(CH3)2 Radical
Authors: Seres László , Dinse Martin , Görgényi Miklós 
Published: April 2004

Abstract
The reversible addition reaction

2-Ċ
3H7 + i-C4H8 ⇔ (CH3)2CHCH2
Ċ(CH3)2

was studied in the temperature range 491–543K by product analysis in experiments in which 2-Ċ
3H7 radicals were generated by the thermal decomposition of azoisopropane. The enthalpy of formation of the radical (CH3)2CHCH2
Ċ(CH3)2 was determined, the value obtained being Δf
H° = -21.8 ± 5.2kJ mol-1. From this result, the following group value was deduced: Δf
H°[Ċ–(C)3] = 177.1kJ mol-1. From the latter, Δf
H°(t-Ċ
4H9) = 51.6kJ mol-1 was estimated.
The rate constant of self-combination of the radical (CH3)2CHCH2
Ċ(CH3)2 was determined for the first time: log(k
12/(dm3mol-1s-1)) = 7.3.
Direct Kinetic Study of Reactions of Hydroxyl Radicals with Alkyl Formates
Authors: Szilágyi István , Dóbé Sándor , Bérces Tibor , Márta Ferenc , Viskolcz Béla 
Published: April 2004

Abstract
Rate coefficients were determined for the gas phase reactions of hydroxyl radicals with a series of alkyl formats. Experiments were carried out using the isothermal fast flow method coupled with resonance fluorescence detection. The obtained room temperature rate coefficients are (in 10−13cm3 molecule−1s−1 units): 1.83 ± 0.33 (methyl formate), 9.65 ± 0.43 (ethyl formate), 18.73 ± 0.83 (isopropyl formate), 6.77 ± 0.38 (tert-butyl formate) and 1.62 ± 0.13 (methyl chloroformate). These results are compared with the literature data. In addition estimations are made for the partial reactivities of the formate group and for the hydrocarbon groups adjacent to HC(O)O. Moreover, it has been found that the partial reactivity of the HC(O)O group (in reactions of OH with formates) is two orders of magnitude smaller than that of the HC(O) group (in reactions of OH with aldehydes). This has been explained using the results of ab initio calculations at the G3MP2//MP2(full)/6-31G(d) level of theory.
Gas-Phase Kinetics of the Reactions of the CH2F Radicals with the Radicals CHF2, CH3, and C2H5
Authors: Beiderhase T. , Hoyermann Karlheinz , Nothdurft Jörg , Olzmann Matthias 
Published: April 2004

Abstract
The mechanisms and the rates of the reactions of the fluorinated hydrocarbon radical CH2F with the fluorinated and pure hydrocarbon radicals CHF2, CH3, and C2H5, respectively, have been studied at low pressure (around 2 mbar) and room temperature using the discharge-flow reactor technique. Mass spectrometry either with electron impact or laser induced multiphoton ionization was applied for the detection of labile and stable species.
The cross combination of the radicals is mainly followed by HF elimination from the chemically activated adduct. The overall rate coefficients at 298K for

CH2F + CHF2 → C2H2F2 + HF (1)

CH2F + CH3 → C2H4 + HF (2)

CH2F + C2H5 → C3H6 + HF (3)

were derived from the analysis of the radical-time profiles by fit procedures; the following values were obtained:

CH2F + CHF2 → C2H2F2 + HF (1)

CH2F + CH3 → C2H4 + HF (2)

CH2F + C2H5 → C3H6 + HF (3)

k
1 = (3.0 + 1.5/ − 0.7) × 1012cm3mol−1s−1

k
2 = (4.0 ± 1.5) × 1013cm3mol−1s−1

k
3 = (9.0 ± 3) × 1012cm3mol−1s−1.

The results are discussed in terms of chemical activation mechanisms.
Polymer Complexes: supramolecular assemblies and structures of poly[N‐(2′‐pyridyl)propenamide] complexes
Authors: Mubarak A. T. A. , El‐Sonbati A. Z. , El‐Bindary A. A. 
Published: April 2004

AbstractA number of new polymer complexes of palladium(II), platinum(II) and copper(II) containing homopolymer (N‐(2′‐pyridyl)propenamide; APH) and various anions (Cl−, Br−, I− or NO3−) have been synthesized and characterized by elemental analyses, magnetic susceptibility, electron paramagnetic resonance, IR and reflectance spectral measurements. The homopolymer shows three types of coordination behavior. In the mononuclear polymer complexes 1–6 and 9 it acts as a neutral bidentate ligand chelated through the pyridine‐nitrogen and amide‐oxygen atoms, whereas in the square‐planar [Pd(APH)2X2] (X = Cl, Br) unidentate APH is coordinated through the pyridine‐nitrogen atom alone. Under alkaline conditions APH is deprotonated in the presence of palladium(II) to form [Pd(AP)2] (10), AP being an anionic bidentate ligand and chelating through the pyridine‐nitrogen and amide‐oxygen atoms. The poly‐chelates are of 1:1 and 1:3 (metal:homopolymer) stoichiometry and exhibit six‐coordination. The polymer complexes of stoichiometric [(APH)2CuX2] contain square planar (APH)2 Cu2+ units and the anions X− are in the axial positions, giving distorted octahedral configurations. From the electron paramagnetic resonance and spectral data, the orbital reduction factors were calculated. Copyright © 2004 John Wiley & Sons, Ltd.
High‐resolution 15N solid‐state NMR investigations on borazine‐based precursors
Authors: Toury Bérangère , Gervais Christel , Dibandjo Philippe , Cornu David , Miele Philippe , Babonneau Florence 
Published: April 2004

AbstractReference compounds based on borazine units and polyborylborazines have been characterized by 15N solid‐state NMR. The various nitrogen sites (B3N, B2NH, B2NX (X = H, Me, iPr), BN(H)X and BNX2 (X = Me, iPr) have been discriminated according to their cross‐polarization behaviour and chemical shift values, which range from −265 to −350 ppm. This has permitted the elucidation of the polymerization mechanism associated with the polycondensation of two borazine‐based derivatives. In particular, this technique appears to be a powerful investigation tool for finding whether the B3N3 rings are linked through three‐atom NBN aminoboryl bridges or connected by direct BN bonds. Copyright © 2004 John Wiley & Sons, Ltd.
Crystallographic report: Bis(µ2‐chloro)‐{bis(diethylether)‐lithium}‐bis(η5‐pentamethyl‐cyclopentadienyl)samarium(III)
Authors: Junk Peter C. , Smith Matthew K. 
Published: April 2004

AbstractThe structure is mononuclear with samarium bound by two η5‐cyclopentadienyl ligands and two chloride ligands, the latter of which bridge to a doubly ether‐solvated lithium centre. Copyright © 2004 John Wiley & Sons, Ltd.
Photo‐induced single electron transfer addition of triphenylgermane to conjugated carbonyl compounds: competitive radical addition
Authors: Feddouli A. , El Kadib A. , Rivière P. , Delpech F. , Rivière‐Baudet M. , Castel A. , Manriquez M. J. , Chavez I. , Ait Itto M. Y. , Ahbala M. 
Published: April 2004

AbstractConjugated ketones are poorly reactive towards triphenylgermane under radical conditions, but in their excited state they can undergo single electron transfer (SET) reactions. The SET reaction, through the formation of a germanium‐centred radical, initiates a competitive and divergent radical addition. In the case of carvone, the SET adduct was isolated pure from the reaction of triphenylgermyllithium with the same ketone. Copyright © 2004 John Wiley & Sons, Ltd.
Coordination behaviour of the 2‐(N,N‐dimethylaminomethyl)phenyl ligand towards the di‐t‐butylchlorotin(IV) moiety
Authors: Novák Petr , Císařová Ivana , Jambor Roman , Rûžička Aleš , Holeček Jaroslav 
Published: April 2004

Abstract{2‐(N,N‐Dimethylaminomethyl)phenyl}(di‐t‐butyl)tin(IV)chloride, {2‐[(CH3)2NCH2]C6H4}Sn(t‐Bu)2 Cl, has been prepared and characterized using NMR and crystallography. This is the first example of a triorganotin(IV) halide containing the 2‐[(CH3)2NCH2]C6H4—group as a C,N‐chelating ligand with a weak intramolecular Sn—N interaction because of the steric hindrance of t‐butyl groups. The interatomic Sn—N distance is elongated to 2.904(14) Å and the central tin atom is distorted trigonal bipyramidal. Copyright © 2004 John Wiley & Sons, Ltd.
Structural comparisons between analogously substituted gallane–pnictine adducts
Authors: Kuczkowski Andreas , Schulz Stephan , Nieger Martin 
Published: April 2004

AbstractThe syntheses and solid‐state structures of five Lewis acid–base adducts Et3Ga–E(SiMe3)3 (E = P (1), As (2), Sb (3)), i‐Bu(t‐Bu)2Ga–P(i‐Pr)3 (4) and (t‐Bu)3Ga–As(i‐Pr)3 (5) are described and the structural trends observed within these adducts are discussed and compared with those reported for the corresponding alane adducts. GaC bond distances and CGaC bond angles were found to be useful structural parameters to estimate the strength of the Lewis acid–base interaction in the solid state. In addition, the solid‐state structure of uncomplexed t‐Bu3Ga (6) is reported. Copyright © 2004 John Wiley & Sons, Ltd.
Improving performance of text categorization by combining filtering and support vector machines
Authors: Díaz Irene , Ranilla José , Montañes Elena , Fernández Javier , Combarro Elías F. 
Published: April 2004

AbstractText Categorization is the process of assigning documents to a set of previously fixed categories. A lot of research is going on with the goal of automating this time‐consuming task. Several different algorithms have been applied, and Support Vector Machines (SVM) have shown very good results. In this report, we try to prove that a previous filtering of the words used by SVM in the classification can improve the overall performance. This hypothesis is systematically tested with three different measures of word relevance, on two different corpus (one of them considered in three different splits), and with both local and global vocabularies. The results show that filtering significantly improves the recall of the method, and that also has the effect of significantly improving the overall performance.
Information retrieval by metabrowsing
Authors: Wiesman F. , van den Herik H.J. , Hasman A. 
Published: April 2004

AbstractThis article investigates a new, effective browsing approach called metabrowsing. It is an alternative for current information retrieval systems, which still face six prominent difficulties. We identify and classify the difficulties and show that the metabrowsing approach alleviates the difficulties associated with query formulation and missing domain knowledge. Metabrowsing is a high‐level way of browsing through information: instead of browsing through document contents or document surrogates, the user browses through a graphical representation of the documents and their relations to the domain. The approach requires other cognitive skills from the user than what is currently required. Yet, a user evaluation in which the metabrowsing system was compared with an ordinary query‐oriented system showed only some small indicatory differences in effectiveness, efficiency, and user satisfaction. We expect that more experience with metabrowsing will result in a significantly better performance difference. Hence, our conclusion is that the development of new cognitive skills requires some time before the technologies are ready to be used.
An entropy‐based interpretation of retrieval status value‐based retrieval, and its application to the computation of term and query discrimination value
Authors: Dominich Sándor , Góth Júlia , Kiezer Tamás , Szlávik Zoltán 
Published: April 2004

AbstractThe concepts of Shannon information and entropy have been applied to a number of information retrieval tasks such as to formalize the probabilistic model, to design practical retrieval systems, to cluster documents, and to model texture in image retrieval. In this report, the concept of entropy is used for a different purpose. It is shown that any positive Retrieval Status Value (RSV)‐based retrieval system may be conceived as a special probability space in which the amount of the associated Shannon information is being reduced; in this view, the retrieval system is referred to as Uncertainty Decreasing Operation (UDO). The concept of UDO is then proposed as a theoretical background for term and query discrimination power, and it is applied to the computation of term and query discrimination values in the vector space retrieval model. Experimental evidence is given as regards such computation; the results obtained compare well to those obtained using vector‐based calculation of term discrimination values. The UDO‐based computation, however, presents advantages over the vector‐based calculation: It is faster, easier to assess and handle in practice, and its application is not restricted to the vector space model. Based on the ADI test collection, it is shown that the UDO‐based Term Discrimination Value (TDV) weighting scheme yields better retrieval effectiveness than using the vector‐based TDV weighting scheme. Also, experimental evidence is given to the intuition that the choice of an appropriate weighting scheme and similarity measure depends on collection properties, and thus the UDO approach may be used as a theoretical basis for this intuition.
Interaction of dexloxiglumide, a cholecystokinin type‐1 receptor antagonist, with human cytochromes P450
Authors: Hall Michael , Persiani Stefano , Cheung Yen‐Ling , Matthews Anne , Cybulski Z. Richard , Holding Jeremy D. , Kapil Ram , D'Amato Massimo , Makovec Francesco , Rovati Lucio C. 
Published: March 2004

AbstractDexloxiglumide (DEX) is a cholecystokinin type‐1 receptor antagonist under development for the treatment of constipation‐predominant irritable bowel syndrome. Studies of the potential interaction of DEX with human cytochromes P450 (CYPs) were conducted in vitro. DEX (300µM), both with and without a 15‐min pre‐incubation, was incubated with pooled human liver microsomes and substrates selective for each of eight CYPs. This resulted in >30% inhibition of tolbutamide 4‐methyl‐hydroxylase (CYP2C9/10) and lauric acid 11‐hydroxylase (CYP2E1) activities. Mean Ki (SD) for CYP2C9/10 and CYP2E1 were 69.0 (24.3) and 426 (60)µM, respectively. Incubations of [14C]DEX with pooled human liver microsomes produced one major phase I metabolic fraction, with Vmax=131 pmol/min/mg protein and Km=23.7µM. Further incubations with (i) liver microsomes from 16 individual donors (correlation analysis), (ii) Supersomes™ and (iii) selective chemical inhibitors, implicated CYP3A4/5, CYP2B6 and CYP2C9 in the formation of this component. Thus, DEX interacts with CYP2C9 both as inhibitor (Ki=69.0µM) and as substrate in vitro. However, based on the maximum concentration (27µM) after repeated oral doses of 200mg t.i.d. and the unbound fraction (0.03) of DEX in human plasma, no clinically relevant metabolic interactions with other CYP substrates are predicted. Copyright © 2004 John Wiley & Sons, Ltd.
Pharmacokinetics of mebudipine, a new calcium antagonist, following single intravenous and oral administrations in rats
Authors: Bohlooli Shahab , Keyhanfar Fariborz , Mahmoudian Massoud 
Published: March 2004

AbstractThe pharmacokinetics of a new calcium antagonist, mebudipine, was studied after a single intravenous (0.5 mg/kg) and oral (10 mg/kg) administration to rats. After intravenous dosing, the plasma concentration of mebudipine declined biexponentially with a terminal half‐life of 2.84 h. The blood clearance was 1.67 l/h/kg and the volume of distribution at steady state was found to be 6.26 l/kg. After oral dosing (10 mg/kg), the Cmax of mebudipine was 25.9±9.79 ng/ml. The oral bioavailability was low (< 2%) suggesting a marked first‐pass effect. The distribution of mebudipine into some tissues such as brain, heart, liver and kidney following intravenous administration (0.5 mg/kg) was studied and a rapid distribution of mebudipine into these tissues was found. It was concluded that brain, heart, liver and kidney are in the same compartment as plasma (central). Copyright © 2004 John Wiley & Sons, Ltd.
Decision framing: moderating effects of individual differences and cognitive processing
Authors: Simon Andrew F. , Fagley N. S. , Halleran Jennifer G. 
Published: March 2004

AbstractTwo studies examined the effect of an individual difference variable, need for cognition (NC), and processing of the options on the occurrence of risky choice framing effects. In Study 1 (N=206), frame interacted with NC and math skill such that no framing effect was observed among those high in both NC and math skill. No effect was found for the processing manipulation of requesting a reason for one's choices. Study 2 (N=257) enhanced the processing of the problems by asking participants to write out the options as they would describe them to a friend. Results showed that frame interacted with NC and depth of processing such that no framing effect was observed among those high in NC who were in the deep processing condition. These findings suggest that NC and depth of processing need to be considered in concert in order to understand their moderating effects on framing. Copyright © 2004 John Wiley & Sons, Ltd.
Teratogenic evaluation of metronidazole and ornidazole using Drosophila melanogaster as an experimental model
Authors: Palermo Ana María , Reynoso A.S. , López Nigro M. , Carballo M.A. , Mudry M.D. 
Published: April 2004

AbstractBACKGROUNDDrosophila and vertebrates show similarities that suggest that the mechanisms involved in the induction of developmental defects may be similar in both. Therefore, Drosophila has been proposed as a useful, rapid, and economical model in the preliminary screening for teratology studies. The objective of the present study was to investigate the effect of metronidazole (MTZ) and ornidazole (ONZ) on the developmental stages of Drosophila melanogaster.METHODSSamarkand wild‐type females were allowed to lay eggs for 24 hr in media containing MTZ or ONZ at concentrations of 0, 500, 1000, and 2000 μg/ml. When larvae completed their development, the emerging flies were counted and examined for morphological abnormalities.RESULTSAfter the analysis of 400–1000 flies for each concentration, ONZ‐treated flies did not show an incidence of malformations above control values, although a significant high number of individuals with reduced body size was observed (p < 0.005, χ2 test). On the other hand, the 1000‐ and 2000‐μg/ml MTZ‐treated series presented higher frequencies of total abnormalities than did concurrent and historic controls (p < 0.05, χ2 test), indicating an MTZ effect during developmental morphogenesis.CONCLUSIONSThese findings contribute to the characterization of both nitroimidazoles, which are widely used, especially in underdeveloped countries. At the same time, this Drosophila bioassay is sensitive enough to detect differential effects of MTZ and ONZ (abnormalities vs. growth effects), showing specificity and selectivity. Birth Defects Research (Part A), 2004. © 2004 Wiley‐Liss, Inc.
Enantioselective HPLC determination of E‐6087, a new COX‐2 inhibitor, in human plasma: Validation and pharmacokinetic application
Authors: Salgado Leonardo , Encina Gregorio , Farran Ramón , Puig Santiago , Martínez Luis 
Published: April 2004

AbstractE‐6087 is a nonsteroidal anti‐inflammatory compound that selectively inhibits cyclooxygenase‐2. Because E‐6087 has a chiral center, this compound is a racemic mixture of two stereoisomers, (+)‐(R)‐E‐6087 (E‐6231) and (−)‐(S)‐E‐6087 (E‐6232). A normal‐phase liquid‐chromatographic method for the enantioselective determination of E‐6087 in human plasma was developed and validated. The samples were extracted using solid‐phase extraction cartridges containing C18 sorbent, and the extracts were redissolved in absolute ethanol and injected into the chromatographic system. The enantiomeric separation was achieved on a chiral stationary‐phase column of derivatized amylose, and the enantiomers were quantified by fluorescence detection. The method was validated for drug concentrations ranging from 5 to 400 ng/ml for both enantiomers. No peaks interfering with the quantification of enantiomers were observed. The limit of quantification was 5 ng/ml, with precision expressed as a coefficient of variation lower than 10.6% and accuracy expressed as relative error lower than 12.2%. The utility of this method was demonstrated by analysis of plasma samples from healthy volunteers given an oral dose of rac‐E‐6087. Peak plasma levels of E‐6231 were higher than levels obtained for E‐6232. Results were consistent with those obtained with a conventional reversed‐phase method used for determination of the racemic compound. Chirality 16:302–308, 2004. © 2004 Wiley‐Liss, Inc.
Enantiomeric resolution of kielcorin derivatives by HPLC on polysaccharide stationary phases using multimodal elution
Authors: Sousa Emília P. , Tiritan M.E. , Oliveira Regina V. , Afonso C.M.M. , Cass Q.B. , Pinto Madalena M.M. 
Published: April 2004

AbstractAnalytical HPLC methods using carbamate chiral stationary phases of polysaccharide derivatives were developed for the enantiomeric resolution of five racemic mixtures of xanthonolignoids: rac‐trans‐kielcorin C, rac‐cis‐kielcorin C, rac‐trans‐kielcorin D, rac‐trans‐isokielcorin D, and rac‐trans‐kielcorin E. The separations were evaluated with the stationary phases cellulose tris‐3,5‐dimethylphenylcarbamate, amylose tris‐3,5‐dimethylphenylcarbamate, amylose tris‐(S)‐1‐phenylethylcarbamate, and amylose tris‐3,5‐dimethoxyphenylcarbamate under normal, reversed‐phase, and polar organic elution conditions. Chiral recognition of those chiral stationary phases, the influence of mobile phases on the enantiomers separation, and the effects of structural features of the solutes on the chiral discrimination observed are discussed. The best performance was achieved on an amylose tris‐3,5‐dimethylphenylcarbamate phase. Polar organic conditions gave shorter retention factors and better resolutions and were a valuable alternative to the alcohol‐hexane or reversed‐phase conditions. Chirality 16:279–285, 2004. © 2004 Wiley‐Liss, Inc.
The never‐ending controversies of screening mammography
Authors: Brem Rachel F. 
Published: March 2004

Controversies regarding the recommendations for screening mammography seen to be never ending. In this issue of Cancer, Gur et al. report their findings that breast cancer diagnosis improves with increasing recall rate above 10% in a study of experienced, high‐volume radiologists. This editorial discusses the implication of this well designed and executed study with bold and important conclusions.See also pages 000–000.