bluuebunny/crossref_metadata_2025_split huggingface dataset:
Car–Parrinello Molecular Dynamics Study of the Rearrangement of the Valeramide Radical Cation
Authors: Semialjac Marija , Schröder Detlef , Schwarz Helmut 
Published: September 2003

AbstractCar–Parrinello molecular dynamics (CPMD) studies of neutral (1) and ionized (1+.) valeramide are performed with the aim of providing a rationalization for the unusual temperature effect on the dissociation pattern of 1+. observed in mass spectrometric experiments. According to CPMD simulations of neutral valeramide 1 performed at approximately 500 K, the conformation with the fully relaxed carbon backbone predominates (96 %). Conformational changes involving folding of the carbon backbone into conformers that would allow intramolecular H transfers are predicted not to take place spontaneously at this temperature because of the barrier heights associated with these transitions (3.5 and 6.9 kcal mol−1), which cannot be overcome by thermal motion alone. For 1+., CPMD simulations performed at ≈300 K reveal a substantial stability of a conformation in which the carbon backbone is fully relaxed; no reaction is observed even after 7 ps. However, when conformers with already folded carbon‐backbones are used as initial geometries in the CPMD simulations, the γ‐hydrogen migration (McLafferty rearrangement resulting in C3H6) is already completed within 2 ps. For this important process, the free activation energy associated with both a required conformational change and the subsequent H transfer equals 4.5 kcal mol−1, while for the formally related δ‐H shift (which eventually gives rise to the elimination of C2H4/C2H5.) it amounts to 7.0 kcal mol−1. Since the barriers associated with conformational changes are energetically more demanding than those of the corresponding hydrogen transfers, 1+. is essentially trapped by conformational barriers and long‐lived at ≈300 K. At elevated temperatures (500 K), the preferred reaction (within 7.3 ps) in the CPMD simulation corresponds to the McLafferty rearrangement. The estimated free activation energy associated with this process amounts to 2.5 kcal mol−1, while the free activation energy for the δ‐H transfer equals 4.4 kcal mol−1. This relatively small free activation energy for the McLafferty rearrangement might cause dissociation of a substantial fraction of 1+. prior to the time‐delayed mass selection, which would reduce the C3/C2 ratio in the experiments conducted with metastable ions that have a lifetime in the order of some μs at a source temperature of 500 K.
Structure defects and optical damage resistance in doubly doped In:Nd:LiNbO3 crystal waveguide substrates
Authors: Zhen X. H. , Zhao L. C. , Xu Y. H. 
Published: September 2003

AbstractA series of In:Nd:LiNbO3 crystals were grown by Czochralski technique and were made into waveguide substrates. The optical damage resistance of the In:Nd:LiNbO3 waveguide substrates was characterized by measurement of the holographic method. The optical damage resistance of In (3.0 mol%):Nd:LiNbO3 was much higher than that of other In:Nd:LiNbO3. The ultraviolet‐visible (UV‐Vis) absorption spectra the In:Nd:LiNbO3 crystals were measured and investigated. The structure defects were discussed in this paper to explain the enhance of the optical damage resistance in the In:Nd:LiNbO3 crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the Crystallization Solvent on Molecular and Supramolecular Structures of Silver(I) Tris(3‐Phenylpyrazolyl)methane Complexes
Authors: Reger Daniel L. , Semeniuc Radu F. , Smith Mark D. 
Published: September 2003

AbstractThe compound [{HC(3‐Phpz)3}Ag](BF4) (pz = pyrazolyl ring) has been prepared and shown to crystallize in four different forms depending on the solvent. Vapor‐phase diffusion of diethyl ether into nitromethane solutions of the complex produces two polymorphs, an orthorhombic form (1) and triclinic form (2). Both polymorphs are coordination polymers constructed by a κ2−κ1 coordination of the tris(3‐Phpz)methane units and have similar, but different, supramolecular structures. In 1 there are two independent chains linked by C−H···π interactions. In 2 only one type of chain is present, with a different internal structure than in 1. Non‐covalent forces, mainly C−H···π interactions, organize the chains into sheets and the sheets into a final 3‐D supramolecular structure in the case of 1, while in the case of 2 only a 2‐D supramolecular structure forms. In contrast, vapor‐phase diffusion of diethyl ether into acetonitrile or acetone solutions produces [{HC(3‐Ph‐pz)3}Ag{(CH3)2CO}](BF4) (3) and [{HC(3‐Phpz)3}Ag{CH3CN}](BF4) (4). In these compounds, the ligand shows tripodal coordination to a single silver center and coordination of one solvent molecule to the metallic center. Both compounds form 3‐D supramolecular structures organized by both C−H···π interactions and weak C−H···F hydrogen bonds and in the case of 4 π−π stacking. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Organocalcium Compounds with Catalytic Activity for the Ring‐Opening Polymerization of Lactones
Authors: Westerhausen Matthias , Schneiderbauer Stefan , Kneifel Alexander N. , Söltl Yvonne , Mayer Peter , Nöth Heinrich , Zhong Zhiyuan , Dijkstra Pieter J. , Feijen Jan 
Published: September 2003

AbstractThe equimolar reaction of calcium bis[bis(trimethylsilyl)amide] with 2,2,6,6‐tetramethylheptane‐3,5‐dione (Htmhd) in THF yields liquid mononuclear [Ca(tmhd){N(SiMe3)2}(THF)3] (1). A similar reaction in toluene with a stoichiometric ratio of 2:3 gives the dinuclear complex [{(THF)Ca}2(tmhd)2(µ‐tmhd){µ‐N(SiMe3)2}] (2). The calcium atoms of these complexes are in a distorted octahedral environment. In 2 the complex consists of two octahedra connected by a common face of one nitrogen base and two oxygen atoms; the bridging Ca−N bond lengths are extremely large. The metalation of the tetradentate Jacobsen reagent with calcium bis[bis(trimethylsilyl)amide] in 1,2‐dimethoxyethane (DME) gives the corresponding calcium complex 3, nearly quantitatively, as its DME adduct. The calcium atom is in an unusual trigonal prismatic coordination sphere. The metathesis reaction of 3 with tin(II) chloride yields the corresponding yellow tin(II) complex with the metal atom in a distorted square‐pyramidal environment. Complexes 2 and 3 show catalytic reactivity in the ring‐opening polymerization of cyclic esters such as lactones and lactides. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses and Crystal Structures of Highly Diastereomerically Enriched Lithiated Benzylsilanes in the Presence of External Donor Molecules: Experiment and Theory
Authors: Strohmann Carsten , Buchold Daniel H. M. , Seibel Timo , Wild Kerstin , Schildbach Daniel 
Published: September 2003

AbstractThe solid‐state structures of the lithiated (aminomethyl)benzylsilanes Me2Si[(R)‐(CHPhLi·0.5TMEDA)](CH2SMP) [{(R,S)‐2}2·TMEDA] and Me2Si[(R)‐(CHPhLi·DABCO)](CH2SMP) [(R,S)‐2·DABCO] [CH2SMP = (S)‐2‐(methoxymethyl)pyrrolidinomethyl] and the absolute configurations at the stereogenic metallated carbon centres of these compounds were determined by single‐crystal X‐ray diffraction methods. The crystal structures of the TMEDA‐bridged dimer [(R,S)‐2]2·TMEDA and monomeric (R,S)‐2·DABCO were compared to that of the parent compound (R,S)‐2, a coordination polymer. By computational methods [B3LYP/6−31+G(d)], the mechanism of the deprotonation of the starting compound, (aminomethyl)benzylsilane [(S)‐1], as well as the stability of configuration of the lithiated derivatives of (R,S)‐2, were examined. For the highly diastereoselective substitution reactions of the derivatives of (R,S)‐2 with iodomethane, inversion of the configuration at the metallated carbon centre was observed and correlated with the results of the quantum‐chemical studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Solvent‐Free and TMEDA‐Solvated Mixed Alkali Metal‐Magnesium Tris‐diisopropylamides
Authors: Hevia Eva , Kenley Fiona R. , Kennedy Alan R. , Mulvey Robert E. , Rowlings René B. 
Published: September 2003

AbstractA trio of heterobimetallic tris‐diisopropylamides, the solvent‐free potassium‐magnesium amide [{KMg(NiPr2)3}∞], its TMEDA solvate [KMg(NiPr2)3·TMEDA] and the sodium congener [NaMg(NiPr2)3·TMEDA] has been synthesised by mixing the appropriate metal alkyl reagents with three molar equivalents of diisopropylamine in a hydrocarbon medium, to which, in the last two cases, TMEDA is added. All three amides have been successfully crystallographically characterised by X‐ray diffraction studies. Representing the first pure s‐block mixed‐metal diisopropylamide free of solvent molecules or other stabilising anionic co‐ligands, the first compound adopts an infinite spiral chain of ···K‐(μ‐N)2‐Mg‐N··· links, the metal‐N framework of which is supported by agostic K···C intra‐dinuclear and inter‐dinuclear contacts. The dinuclear tris‐amido motif is maintained in both TMEDA complexes, the metal‐N cores of which are essentially isostructural, but the presence of the chelating diamine blocks the propagating terminal site on the alkali metal and so gives rise to discrete molecular structures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Homo‐ and Heteroleptic Hypersilylcuprates — Valuable Reagents for the Synthesis of Molecular Compounds with a Cu−Si Bond
Authors: Klinkhammer Karl W. , Klett Jan , Xiong Yun , Yao Shenglai 
Published: September 2003

AbstractUnsolvated hypersilanides MHyp [Hyp = Si(SiMe3)3] of the heavier alkali metals (MI = Na, K, Cs) react with copper tert‐butoxide in toluene to yield crystalline heteroleptic cuprates [MI(toluene)][tBuOCuHyp]. These cuprates proved to be valuable sources for pure hypersilylcopper and other cuprates bearing hypersilyl ligands such as the di(hypersilyl)‐ cuprates MI[CuHyp2]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Direct Introduction of a Boryl Substituent into the 2‐Position of Azulene: Application of the Miyaura and Smith Methods to Azulene
Authors: Kurotobi Kei , Miyauchi Masato , Takakura Katsuto , Murafuji Toshihiro , Sugihara Yoshikazu 
Published: September 2003

AbstractThe 4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolanyl group was directly introduced into the 2‐positions of azulenes with high selectivity by the C−H activation method with use of iridium catalysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Briarane, Erythrane, and Aquariane Diterpenoids from the Caribbean Gorgonian Erythropodium caribaeorum
Authors: Taglialatela‐Scafati Orazio , Craig Kyle S. , Rebérioux Delphine , Roberge Michel , Andersen Raymond J. 
Published: September 2003

AbstractSeven new diterpenoids belonging to the briarane [erythrolides R (5), S (6), T (7), and U (8)], erythrane [erythrolide V (9)], and aquariane [aquariolides B (10) and C (11)] skeletal classes have been isolated from the encrusting gorgonian Erythropodium caribaeorum. The structures of the new compounds were elucidated by spectroscopic analysis and chemical interconversions. A biogenetic proposal that links carbon skeletons found in E. caribaeorum diterpenoids is presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Oxidative Coupling Reactions Mediated by MoCl5 Leading to 2,2′‐Cyclolignans: The Specific Role of HCl
Authors: Kramer Beate , Fröhlich Roland , Waldvogel Siegfried R. 
Published: September 2003

AbstractThe scope and performance of oxidative coupling reaction using MoCl5 can be significantly improved by employing Lewis‐acidic additives such as TiCl4, SnCl4, or SiCl4. Since the by‐product, HCl, plays a particular function as an inhibitor for MoCl5 by forming chloro complexes, exploiting typical chloride scavengers, like silver salts or molecular sieves, is also successful. A variety of differently substituted 1,4‐diarylbutanes 4a−g, which were easily synthesized by a modular approach, were subjected to the dehydrodimerization reaction. For the oxidative coupling reaction, a para‐substitution pattern — with a donor group on the aryl system — is pivotal for allowing access to the 2,2′‐cyclolignans 5a,e−g. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Utilization of raffinose and melibiose by a mutant of Saccharomyces cerevisiae
Authors: Atiyeh Hasan , Duvnjak Zdravko 
Published: September 2003

AbstractThe mutant Saccharomyces cerevisiae ATCC 36858 was used in the production of ethanol and/or fructose from synthetic media in batch processes with raffinose, melibiose or sucrose. The mutant was able to hydrolyze all the sugars used and to selectively ferment glucose and galactose to ethanol while fructose accumulated in the fermentation medium. The fructose yield was above 89% of the theoretical value in the media with either raffinose or sucrose, when initial concentrations were between 131.5 g dm−3 and 242.0 g dm−3. The ethanol yields were 82% and 77% of the theoretical values in the media with melibiose and sucrose, respectively, and about 72% of the theoretical value when raffinose was used. The fructose fraction in the carbohydrate content of the produced syrups was more than 96% when raffinose concentration was below 189.1 g dm−3. However, even at a sucrose concentration of 187.9 g dm−3, the produced syrup contained 100% fructose. Some oligosaccharides were also produced in all tested media. The produced oligosaccharides were consumed by the end of the fermentation process. These findings can be useful in the production of ethanol and high fructose syrups using raw materials based on sucrose and raffinose such as molasses. Copyright © 2003 Society of Chemical Industry
Effect of xylanase on ozone bleaching kinetics and properties of Eucalyptus kraft pulp
Authors: Roncero M Blanca , Torres Antonio L , Colom José F , Vidal Teresa 
Published: September 2003

AbstractEnvironmental pressure has led the pulp and paper industry to develop new technologies in order to reduce or suppress the presence of various pollutants in effluents from bleaching plants. One of the choices for this purpose is enzyme‐based biotechnology. This study deals with the effect of using a xylanase‐based enzymatic pretreatment, in a TCF (Totally Chlorine Free) sequence, on the properties of the resulting paper pulps. The hexenuronic acid content in the pulp and the physical properties of the paper were also studied. The performance of the xylanase was analysed through kinetic studies on ozone bleaching. The enzymatic pretreatment results in easier bleaching and delignification of the pulp, causing a bleach‐boosting effect. The decreased consumption of reagent is related to a decreased content of hexenuronic groups. The physical properties of the treated pulp are similar to those of untreated pulps. Cellulose degradation, delignification and chromophores' removal show first‐order kinetics. Enzyme pretreatment leads to differences between the kinetic constants of cellulose degradation and chromophores' removal, due to an increased accessibility to bleaching agents. The xylanase treatment leads to a lower floor kappa number (IK∞) during the ozone stage. Copyright © 2003 Society of Chemical Industry
Removal of fluoride using some lanthanum(III)‐loaded adsorbents with different functional groups and polymer matrices
Authors: Fang Luo , Ghimire Kedar Nath , Kuriyama Masayuki , Inoue Katsutoshi , Makino Kenjiro 
Published: September 2003

AbstractAlthough fluoride is beneficial for human beings in small quantities, it causes dental fluorosis when consumed in larger quantities over a period of time. In recent years, considerable work has been conducted for the purpose of developing new and low cost absorbents for adsorptive removal of fluoride, especially chelating resins loaded with metal ions. In the present study, several types of adsorbents with different functional groups loaded with lanthanum(III) were prepared to be used for fluoride removal from water. The optimum conditions for loading lanthanum(III) on the adsorbents and the effects of pH and initial fluoride concentration as well as shaking time and solid–liquid ratio on the removal of fluoride have been investigated. Based on these fundamental data, the removal of fluoride from actual hot spring water was also tested as a practical application by comparing the efficiency of different adsorbents for the removal of fluoride from hot spring water. The following conclusions were obtained. (1) The different chemical composition and chemical structure of the polymer matrix play the most important role in fluoride adsorption, (2) strongly acidic adsorbents are more effective on fluoride removal at neutral pH than weakly acidic adsorbents, (3) the order of fluoride removal in the neutral pH range of 4.5–8.0 by the different La(III)‐loaded adsorbents employed in the present work is as follows: 200CT resin > POJRgel > IR124resin > SOJR gel ≥ CPAgel ≥ WK11 resin. The column experiments showed that the 200CT resin loaded with lanthanum(III) at pH 6.0 can be successfully employed for the removal of fluoride ions from actual hot spring water. Copyright © 2003 Society of Chemical Industry
Transport of chromium(VI) through a Cyanex 921‐supported liquid membrane from HCl solutions
Authors: Alguacil Francisco José , Caravaca Concepción , Martín María Isabel 
Published: September 2003

AbstractThe transport of chromium(VI) through a flat‐sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921‐based flat‐sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. Copyright © 2003 Society of Chemical Industry
Electrochemical decomplexing and oxidation of organic (chelating) additives in effluents from surface treatment and metal finishing
Authors: Lissens Geert , Verhaege Marc , Pinoy Luc , Verstraete Willy 
Published: September 2003

AbstractThe electrochemical decomplexing and oxidation of two frequently used complexing agents in surface treatment and metal finishing—EDTA (ethylenediaminetetraacetic acid) and NTA (nitrilotriacetic acid)—and of organic non‐complexing additives used in nickel‐plating baths were the subject of this study. Using a Ti–RuO2 electrode, a partial indirect oxidation by in‐situ electrochemical generation of chlorine compounds could be achieved for EDTA and NTA. At a boron‐doped diamond (BDD) electrode however, complete decomplexing and high COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) (up to 95%) removal occurred at an average current density of 2 A dm−2. It is shown that direct electrochemical oxidation at a BDD electrode resulted in lower energy consumption and higher treatment rates than indirect oxidation at a Ti–RuO2 electrode. Decomplexing at the BDD electrode occurred at high current efficiencies ranging from 71% to 95% with decomplexing rates in the order of 3.13 mmol (Ah)−1 and 5.02 mmol (Ah)−1 for EDTA and NTA respectively. COD removal rates obtained were 0.090 g (Ah)−1 for EDTA, 0.100 g (Ah)−1 for NTA and 0.205 g (Ah)−1 for the nickel‐plating additives. Electrochemical decomplexing and oxidation of common chelating agents can render the subsequent metal precipitation and biological wastewater treatment of surface treatment and metal finishing effluents more efficient. Copyright © 2003 Society of Chemical Industry
Selective catalytic reduction by urea in a fluidized‐bed reactor
Authors: Roh Seon Ah , Jung Soon Hwa , Jeong Sang Mun , Kim Sang Done 
Published: September 2003

AbstractThe selective catalytic reduction (SCR) of NOx by urea as a reducing agent was carried out over fresh and sulfated CuO/γ‐Al2O3 catalysts in a fluidized‐bed reactor. The optimum temperature ranges for NO reduction on the fresh and sulfated CuO/γ‐Al2O3 catalysts were 300–350 °C and 400–450 °C, respectively. NO reduction with the sulfated CuO/γ‐Al2O3 catalyst was somewhat higher than that with the fresh CuO/γ‐Al2O3 catalyst. N2O formation increased with increasing reaction temperature. Ammonia (NH3) slip increased with increasing gas velocity and decreased with increasing reaction temperature. Copyright © 2003 Society of Chemical Industry
Absence of eigenvalues of Dirac operators with potentials diverging at in‐finity
Authors: Kalf Hubert , Ōkaji Takashi , Yamada Osanobu 
Published: September 2003

AbstractWe investigate the non‐existence of eigenvalues of Dirac operators α · p +m(r)β + V(x) in the Hilbert space L2(R3)4 with a variable massm(r) and a matrix‐valued function V(x), which may decay or diverge at infinity. As a result we show that there are no eigenvalues of Dirac operators for a large class of m(r) and V(x) such that |m(r)| ≪ |V(x)| →∞ as r → ∞ and V(x) is positive or negative definite at infinity. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Weak type estimates for Calderón‐Zygmund operators on Herz spaces at critical indexes
Authors: Komori Yasuo 
Published: September 2003

AbstractWe define weak Herz spaces $ \dot K ^{\alpha , p, \infty} _{q} $(ℝn) which are the weak version of the ordinary Herz spaces $ \dot K ^{\alpha , p} _{q} $(ℝn). We consider the boundedness of Calderón‐Zygmund operators from $ \dot K ^{\alpha , p} _{q} $ to $ \dot K ^{\alpha , p, \infty} _{q} $ at critical indexes α = −n/q, n(1− 1/q) and q = 1. We also consider weighted estimates. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modular quintics in ℙ4
Authors: Meyer Christian 
Published: September 2003

AbstractWe will examine the arithmetic of some of the members of a pencil of symmetric quintics in projective 4‐space. We will give evidence for the modularity of some of the exceptional members (even the non‐rigid ones) and give a proof in one rigid case. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some ratio inequalities for iterated stochastic integrals
Authors: Yan Litan 
Published: September 2003

AbstractLet X = (Xt, ℱt) be a continuous local martingale with quadratic variation 〈X〉 and X0 = 0. Define iterated stochastic integrals In(X) = (In(t, X), ℱt), n ≥ 0, inductively by

with I0(t, X) = 1 and I1(t, X) = Xt. Let (ℒ︁xt(X)) be the local time of a continuous local martingale X at x ∈ ℝ. Denote ℒ︁*t(X) = supx∈ℝ ℒ︁xt(X) and X* = supt≥0 |Xt|. In this paper, we shall establish various ratio inequalities for In(X). In particular, we show that the inequalities

hold for 0 < p < ∞ with some positive constants cn,p and Cn,p depending only on n and p, where G(t) = log(1+ log(1+ t)). Furthermore, we also show that for some γ ≥ 0 the inequality

holds with some positive constant Cn,p,γ depending only on n, p and γ, where Un is one of 〈In(X)〉1/2∞ and I*n(X), and V one of the three random variables X*, 〈X〉1/2∞ and ℒ︁*∞(X). (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)