bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the shielding effect of the Helmholtz equation
Authors: Chen Yu 
Published: July 2007

AbstractHadamard‐type instability has been known for over a century as a cause of ill‐posedness of the Cauchy problem for elliptic PDEs. This ill‐posedness manifests itself as evanescent modes growing exponentially when propagated in the reverse direction. Since every oscillating mode of the Laplace equation is evanescent, the ill‐posedness of its Cauchy problem is solely due to Hadamard‐type instability. The presence of the propagating modes and beams for the Helmholtz equation gives rise to an entirely different type of ill‐posedness, hitherto unknown to the practice, and untreated by the theory, of inverse scattering. We will present this fundamental phenomenon of ill‐posedness for the Helmholtz equation. © 2007 Wiley Periodicals, Inc.
A practical method to analyze workflow logic models
Authors: Huang Yu , Wang Hanpin , Zhao Wen , Xu Chunxiang 
Published: July 2007

AbstractThe analysis of workflow is crucial to the correctness of workflow applications. This paper introduces a simple and practical method for analyzing workflow logic models. Firstly, some definitions of the models and some properties, such as throughness, no‐redundant‐transition and boundedness, are presented. Then, we propose an approach based on synchronized reachability graphs (SRGs) to verify these properties. The SRG uses the characteristics of synchronizers in workflow logic models and mitigates the state explosion by constructing synchronized occurrence sequences rather than interleaving occurrence sequences. This paper also proposes some refined and feasible reduction rules which can preserve vital properties of workflow logic models. Using these two techniques, the SRG‐based verification method can achieve higher efficiency. Furthermore, this research also develops a verification tool based on the method, presents the analysis results of some practical cases and compares our method with others. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic and Structural Investigation of Mn2+‐Doped ZnSe Semiconductor Nanoparticles
Authors: Hofmann Andreas , Graf Christina , Boeglin Christine , Rühl Eckart 
Published: July 2007

AbstractX‐ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals were carried out to study the local electronic structure and magnetic properties of Mn2+ embedded in the lattice of ZnSe nanoparticles. It is shown that Mn2+ is exclusively present in the bulk of ZnSe nanoparticles. Neither Mn–Mn coupling nor traces of oxidation to higher Mn oxidation states was observed. This result, which is consistent with EPR spectroscopic data, provides clear proof of the location of Mn2+ in semiconductor nanoparticles. Further, it is shown that the magnetic ions are highly polarised inside the nanocrystals, where they reach about 50 % of the theoretical value of a pure d5 state under identical conditions.
Ab Initio Molecular Dynamics Free‐Energy Study of Microhydration Effects on the Neutral–Zwitterion Equilibrium of Phenylalanine
Authors: Rodziewicz Pawel , Doltsinis Nikos L. 
Published: July 2007

AbstractThe structures and relative energies of the most stable conformers of both naked and microsolvated phenylalanine, Phe⋅(H2O)n (n=0–3), are calculated by density functional theory. For selected structures, coordination‐constrained ab initio molecular dynamics simulations determine the proton‐transfer mechanism connecting neutral and zwitterionic forms of Phe. The associated free‐energy profiles are calculated by thermodynamic integration. While no zwitterionic free‐energy minimum is found for naked Phe, microsolvation is found to stabilize the zwitterionic form. For cluster sizes n≥3, the proton‐transfer equilibrium shifts towards the zwitterionic structure for specific proton‐transfer pathways. The energetically most favourable interconversion path between the neutral and zwitterionic forms is through a H2O bridge with free‐energy barriers as low as 14.4 kJ mol−1 for Phe⋅(H2O)3. The free energy required for breaking a carboxylic OH bond involved in intramolecular hydrogen bonding is typically lower than in the water‐assisted case. However, the resulting zwitterion turns out to be unstable with respect to the backward proton‐transfer reaction.
FeII Bistable Materials with Dissymmetrical Ligands: Synthesis, Crystal Structure, Magnetic and Mössbauer Properties of FeII Complexes Based on N4 Schiff Bases Possessing 2‐Pyridyl and 1‐R‐Imidazol‐2‐yl Rings
Authors: Bréfuel Nicolas , Shova Sergiu , Tuchagues Jean‐Pierre 
Published: July 2007

AbstractThe synthesis and characterization of two symmetrical FeII complexes, [FeLB4(NCS)2], 1, and [FeLB5(NCS)2], 2 {LBx =N,N′‐bis[(2‐N‐R‐imidazol‐1‐yl)methylene]‐2,2‐dimethylpropane‐1,3‐diamine ligands; 1: x = 4, R = H; 2: x = 5, R = Me} are reported. Whereas the tetradentate ligand LB4 is planar in 1, the X‐ray structure of 2 illustrates the folded conformation of LB5. Ferrous [FeLEx(NCS)2] complexes were synthesized {LEx = N‐[(1‐N‐R2‐imidazol‐2‐yl)methylene]‐N′‐(1‐pyridin‐2‐yl‐ethylidene)‐2,2‐R1‐propane‐1,3‐diamine; 3: x = 1, R1 = H, R2 = H; 4: x = 2, R1 = H, R2 = Me; 5: x = 3, R1 = Me, R2 = H; 6: x = 4, R1 = Me, R2 = Me}. These dissymmetrical Schiff bases, possessing pyridine and imidazole rings, are obtained through the reaction of 2‐methyl‐2‐pyridin‐2‐yl‐hexahydropyrimidine (R1 = H; 3, 4) or 2,5,5‐trimethyl‐2‐pyridin‐2‐yl‐hexahydropyrimidine (R1 = Me; 5, 6) aminals with imidazole‐2‐carboxaldehyde (R2 = H: 3, 5) or 1‐N‐methylimidazole‐2‐carboxaldehyde (R2 = Me: 4, 6) and iron(II) thiocyanate.Single‐crystal X‐ray structures were determined for [FeLE1(NCS)2] 3 [FeLE3(NCS)2] 5 and [FeLE4(NCS)2] 6; these complexes are in the low‐spin state at 180 K. Magnetic susceptibility and Mössbauer measurements showed a smooth and incomplete spin crossover involving ca. 50 % of the iron centres between 200 and 400 K for 5 and 6; 3 and 4 remain low spin up to 350 K; the slight χMT increase between 350 and 400 K results from the onset of spin crossover for 3 and 4. The spin crossover properties in the [FeLEx(NCS)2] series may thus be tuned by the ligand substituents: by changing R1 from H (for 3, 4) to Me (for 5, 6) the spin crossover is lowered from above 400 K to ca. 350 K; the effect of the imidazolyl substituent is weaker: by changing R2 from H (for 5) to Me (for 6) the spin crossover temperature is lowered by ca. 35 K. The electronic effect of the highly conjugated Fe–N=C–C=N– imidazolyl fragment overpasses and qualitatively and quantitatively modifies the effects of R1 and R2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Recent Developments in Phosphole‐Containing Oligo‐ and Polythiophene Materials (Eur. J. Inorg. Chem. 23/2007)
Authors: Hobbs Matthew G. , Baumgartner Thomas 
Published: July 2007

AbstractThe cover picture shows the schematic structures of a 2,5‐dithienylphosphole and a dithieno[3,2‐b:2′,3′‐d]phosphole, as well as the fluorescence properties of materials based on the latter system. These scaffolds are two of the most promising organophosphorus‐based building blocks for organic electronics to date. Extensive investigations of their structure–property relationships has laid ground for a variety of applications such as sensing or as an active component in electronic devices. Details on the syntheses, their systematic modifications, as well as the resulting (opto)electronic properties of the materials are presented in the Microreview by M. G. Hobbs and T. Baumgartner on p. 3611 ff.
Synthesis of Methyleneisoxazolidine Nucleoside Analogues by Microwave‐Assisted Nitrone Cycloaddition
Authors: Chiacchio Ugo , Corsaro Antonino , Iannazzo Daniela , Piperno Anna , Romeo Giovanni , Romeo Roberto , Saita Maria G. , Rescifina Antonio 
Published: July 2007

AbstractA new series of conformationally locked N,O‐nucleoside analogues was synthesized by exploiting allenic nucleobases as dipolarophiles in 1,3‐dipolar nitrone cycloadditions. The regio‐ and sitoselectivity of the reaction were rationalized according to the frontier orbital treatment of the nitrone cycloaddition by AM1 calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
DFT Study on the SnII‐Catalyzed Diastereoselective Synthesis of Tetrahydrofuran from D–A Cyclopropane and Benzaldehyde
Authors: Zhang Jinsheng , Shen Wei , Li Ming 
Published: July 2007

AbstractBy means of density functional theory (DFT), the regio‐ and diastereoselective mechanism for the synthesis of 2,5‐disubstituted tetrahydrofuran from a donor–acceptor (D–A) cyclopropane cycloaddition reaction with benzaldehyde catalyzed by Sn(OTf)2 was investigated. As demonstrated, the overall reaction includes the activation of the D–A cyclopropane (S)‐1, an unusual SN2 attack on the activated cyclopropane, the formation of the tetrahydrofuran coordination complex and the regeneration of the catalyst. The D–A cyclopropane is activated by its combination with Sn(OTf)2, which leads to a decrease in the natural bond orbital (NBO) energy ofσ*(C1–C2) and an increase in the dipole moment and angular deviation of the bent bond σ(C1–C2). Two nucleophilic reactions generates two chiral carbon centres, and the first one is rate controlling. In the SN2 reaction, one molecule of trifluoromethane sulfonate forms a hydrogen‐bond H(CHO)···O(OTf), which can control the stretching direction of the benzaldehyde. On the whole, the solvation energies of the species increase with increases in the molecular dipole moments, and the solvent effects increase the reaction barriers. The theoretically predicted dominant product is cis‐(2R,5R)‐tetrahydrofuran. So these can satisfactorily account for the experimental observations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Ring Expansion Induced by DAST: Synthesis of Substituted 3‐Fluoropiperidines from Prolinols and 3‐Fluoroazepanes from 2‐Hydroxymethylpiperidines
Authors: Déchamps Ingrid , Gomez Pardo Domingo , Cossy Janine 
Published: July 2007

AbstractOptically active prolinols can be converted into optically active 3‐fluoropiperidines by treatment with DAST. The reaction often produces 2‐fluoromethylpyrrolidines as byproducts. The ring expansion was also applied to 2‐hydroxypiperidines to produce 3‐fluoroazepanes. The rearrangement proceeds via an aziridinium intermediate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Chlorodifluorothioacetic Acid, CF2ClC(O)SH: Synthesis, Characterization, X‐ray Structure and Conformational Properties
Authors: Erben Mauricio F. , Boese Roland , Willner Helge , Della Védova Carlos O. 
Published: July 2007

AbstractChlorodifluoroacetic anhydride, [CF2ClC(O)]2O, and chlorodifluoroacetyl chloride, CF2ClC(O)Cl, react with hydrogen sulfide to yield chlorodifluorothioacetic acid, CF2ClC(O)SH. This novel thiocarboxylic acid has been obtained in pure form and characterized by NMR, IR and Raman spectroscopy. By extrapolation of the vapour pressure curve, log p = 6.102–2068/T (p [bar], T [K]), the boiling point was determined to be 66(1) °C. The melting point of the pure substance is –83(2) °C. The conformational properties of the gas‐phase molecule have been studied by vibrational spectroscopy [IR (vapour), Raman (liquid)] and quantum chemical calculations [B3LYP and MP2 methods with 6‐311++G(d,p) and 6‐311++G(3df,2p) basis sets]. The most stable form has C1 symmetry with a synperiplanar (syn) orientation of the C=O double bond with respect to the S–H single bond whereas in the chlorodifluoroacetyl group the gauche orientation of the ClC–C=O moiety is preferred (gauche‐syn form). The analysis of the IR spectrum of gaseous CF2ClC(O)SH suggests the presence of two other conformations in equilibrium at room temperature. These forms have been fully characterized by high‐level quantum chemical calculations. The structure of a single crystal, grown by a miniature zone‐melting procedure using focused infrared laser radiation, was determined by X‐ray diffraction analysis at low temperature. The crystalline solid [monoclinic, space group C2/c, a = 17.6165(14), b = 5.8848(5), c = 11.0877(9) Å, β = 113.5330(11)°] consists exclusively of molecules adopting the gauche‐syn conformation. These molecules associate, forming pairs of cyclic dimers in the crystal through S–H···O=C hydrogen bonds.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Synthesis of Positional Thiol Analogs of β‐D‐Galactopyranose
Authors: Pei Zhichao , Dong Hai , Caraballo Rémi , Ramström Olof 
Published: July 2007

AbstractApproaches toward the synthesis of thio‐β‐D‐galactose derivatives are described. These compounds were prepared from the parent carbohydrates: D‐galactose, methyl β‐D‐galactoside and methyl β‐D‐glucoside, respectively. It was found that not only the strategies of protecting group introduction and selective deprotection, but also the choices of solvent and nucleophilic reagent concentration were crucial to allow the efficient introduction of sulfur at different positions of the galactose ring. The effects from the solvent, the nucleophilic reagent concentration, and the protecting group patterns have been investigated. The results clearly show that ester protecting groups play highly important roles for the synthesis of thio‐containing carbohydrates, requiring nonpolar solvents to suppress the neighboring group participation. For the Lattrell–Dax (nitrite‐mediated) inversion reaction, employed in the synthetic route to the 2‐thio‐β‐D‐galactoside, intramolecular nucleophilic attack, as well as strongerstereospecific ester activation, are necessary to overcome hindrance from 4,6‐O‐benzylidene protection.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Ferrocenyliminophosphites as Easy‐to‐Modify Ligands for Asymmetric Catalysis
Authors: Gavrilov Konstantin N. , Maksimova Marina G. , Zheglov Sergey V. , Bondarev Oleg G. , Benetsky Eduard B. , Lyubimov Sergey E. , Petrovskii Pavel V. , Kabro Anzhelika A. , Hey‐Hawkins Evamarie , Moiseev Sergey K. , Kalinin Valery N. , Davankov Vadim A. 
Published: July 2007

AbstractSeveral N,P bidentate phosphite‐type ligands derived from readily available ferrocene‐based iminoalcohols were successfully used in Rh‐catalysed hydrogenations and Pd‐catalysed allylic substitutions of a variety of substrates. Moderate‐to‐high catalytic activities under standard conditions were observed, and the enantiomeric excess of the products were up to 97 %. Results obtained under systematic variation of the ligand parameters indicate that the enantioselectivity is largely determined by the nature of the phosphocentre and also by the substituent in the C*HN‐fragment. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
tert‐Butyl‐calix[4]arenes Substituted at the Narrow Rim with Cobalt Bis(dicarbollide)(1–) and CMPO Groups – New and Efficient Extractants for Lanthanides and Actinides
Authors: Mikulášek Libor , Grüner Bohumír , Dordea Crenguta , Rudzevich Valentyn , Böhmer Volker , Haddaoui Jaouad , Hubscher‐Bruder Véronique , Arnaud‐Neu Françoise , Čáslavský Josef , Selucký Pavel 
Published: July 2007

AbstractCalix[4]arene derivatives bearing two residues A(–) derived from cobalt bis(dicarbollide)(1–) (1) and two CMPO groups B at their narrow rim were synthesized from tBu‐calix[4]arene in four steps. The first step involved the preparation of tBu‐calix[4]arene diether derivatives with appropriate precursors for amino groups (mostly nitriles 3). These were O‐alkylated through ring‐opening reactions with the zwitterionic dioxane derivative [(8‐O(CH2CH2)2O‐1,2‐C2B9H10)‐(1′,2′‐C2B9H11)‐3,3′‐Co]0 (10) to produce ionic nitrile derivatives 4. Reduction of the nitrile groups with BH3·SMe2 (or deprotection in the case of the corresponding phthalimido or Boc derivatives 8) led to a series of diamines 5a–f, which were subsequently converted into the corresponding CMPO derivatives 6a–f by acylation with p‐nitrophenyl(diphenylphosphoryl) acetate. Pure cone conformers were isolated in moderate to excellent yields after the second or third reaction step, although the presence of other conformers in the reaction mixtures was sometimes observed by NMR spectroscopy and HPLC, and in one case a di‐A(–)‐di‐B derivative 6c* in the 1,3‐alternate conformation was prepared. The novel ionic ligands 6a–f showed dramatically enhanced extraction abilities for trivalent actinides and lanthanides in relation to the previously reported simple covalent combination of one A(–) with one B group or to various synergistic mixtures of calixarenes substituted exclusively with two A(–) or two B moieties. A 1:1 mixture of calix[4]arenes containing four A(–) anions (13) and four CMPO functions (14), however, showed similarly high extraction efficiency, comparable to that of the best calixarenes 6b–d with mixed substitution. Complexation studies with 6c for La3+, Eu3+ and Yb3+ in methanol carried out by UV spectrophotometry and microcalorimetry revealed the formation of 1:1 and 1:2 metal‐to‐ligand complexes with log β values ranging from 9.6 to 11.7.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
First Total Synthesis of (+)‐Adenophorine, a Naturally Occurring Inhibitor of Glycosidases
Authors: Pearson Morwenna S. M. , Evain Michel , Mathé‐Allainmat Monique , Lebreton Jacques 
Published: July 2007

AbstractThe first total synthesis of a naturally occurring iminosugar, (+)‐adenophorine, in 14 steps from the (+)‐enantiomer ofGarner's aldehyde, is reported. The strategy is based onthe preparation and functionalization of enantiomericallypure trans‐6‐ethyl‐2‐hydroxymethyl‐1,2,5,6‐tetrahydropyridine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Silyl‐Substituted Tetrathia[7]helicenes: Synthesis, X‐ray Characterization and Reactivity
Authors: Bossi Alberto , Maiorana Stefano , Graiff Claudia , Tiripicchio Antonio , Licandro Emanuela 
Published: July 2007

AbstractWe describe the synthesis of trialkylsilyl‐substituted trans‐1,2‐bis(thieno[3,2‐e]benzothiophene‐2‐yl)ethenes as suitable soluble precursors for the preparation of the corresponding silylated tetrathia[7]helicenes, which, in turn, can be desilylated or transformed into dihalogen‐substituted derivatives through electrophilic substitution of silyl substituents. X‐ray structural studies showed that the presence of the two triisopropylsilyl groups on the terminal thiophene rings accounts for the high solubility of the alkene and for the very large dihedral angle in the helicene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Electrophoretic screening of ligands under suppressed EOF with an inert phospholipid coating
Authors: White Christian M. , Luo Ruijuan , Archer‐Hartmann Stephanie A. , Holland Lisa A. 
Published: July 2007

AbstractThe applicability of dual injection CE for affinity selection of biopolymers that contain multiple binding sites is demonstrated. The efficient analysis of biomolecules such as carbohydrates and proteins, as well as pharmaceuticals by CE requires the reduction or elimination of nonspecific interactions with the capillary surface. Phospholipids are integral components of cell membranes and aqueous phospholipid liquid crystals adopt a bilayer structure on fused‐silica. This phospholipid surface does not interact significantly with the following biomolecules: serum albumin, the 96–110 heparin binding domain of amyloid precursor protein (APP), polydisperse glycosaminoglycans, and variable chain‐length oligosaccharides. Pharmaceuticals including five anionic nonsteroidal anti‐inflammatory drugs, three cationic analgesics, and two cationic β‐blockers, also show minimal interaction with the surface. In addition, the use of a phospholipid coating suppresses EOF, which enables reversed‐polarity separations, dual opposite injection CE, affinity screening via CE by dual opposite injection, and serial target‐ligand injections.
A selective and sensitive approach to characterize odour‐active and volatile constituents in small‐scale human milk samples
Authors: Buettner Andrea 
Published: July 2007

AbstractA sensitive and selective analytical approach was developed for the characterization of trace volatile and odorous substances in body fluids. The methodology was successfully applied for identification of more than 40 characteristic odorants in human milk. The technique comprises a modified stir bar sorptive extraction system in combination with two‐dimensional gas chromatographic separation and parallel mass spectrometric and olfactometric characterization of the analytes. The present study shows that the technique can be used for both direct extractive sampling and headspace analysis, and that it is applicable for small sample volumes. Copyright © 2007 John Wiley & Sons, Ltd.
Hippocampal theta sequences
Authors: Foster David J. , Wilson Matthew A. 
Published: July 2007

AbstractThe activity of individual hippocampal principal neurons is spatially localized such that each neuron is active only when the animal occupies an area of the environment known as the cell's place field. Additionally, the activity of hippocampal neurons exhibits a particular temporal relationship to the hippocampal EEG, such that spikes fired by the neuron occur at progressively earlier phases of the co‐occurring theta rhythm in the EEG as the animal traverses the place field. This relationship is known as theta precession. A long‐standing prediction following the observation of theta precession has been that among a collection of hippocampal neurons recorded simultaneously, the neurons will fire in sequences reflecting the behavioral order of the place fields. Here we examine this prediction. We show that clear, ordered sequences occur during theta, which we name theta sequences, in which a portion of the animal's spatial experience is played out in forwards order. We further investigate the relationship of theta sequences to phase precession by shuffling spike phases in such a way as to preserve the relationship between spike phase and position. This jitter significantly reduces the prevalence of theta sequences while leaving theta phase precession intact, suggesting that the presence of theta phase precession is not trivially predictive of theta sequences. Finally, we discuss the relationship between theta sequences and individual place fields, and the possible functional role of theta sequences in navigational learning. © 2007 Wiley‐Liss, Inc.
Contribution to the study of thermal waters in Greece: chemical patterns and origin of thermal water in the thermal springs of Lesvos
Authors: Lambrakis N. J. , Stamatis G. N. 
Published: July 2007

AbstractThe occurrence of thermal/spa waters on Lesvos Island is related to the presence of a major faulting system. Thermal waters are the result of mixing of meteoric and infiltrating seawater at great depth, and their total salinity depends on the percentage of seawater in their composition. According to the diagrams of main elements, trace elements and environmental isotopes, most of the components that determine the chemical composition of thermal waters such as sodium, chloride and sulphates originate from seawaters. On the other hand, the concentration of calcium, magnesium, boron, lithium, etc., was affected by water–rock interaction under high temperature conditions. Moving towards the surface, thermal waters may become polluted by influx of recent seawater, allowing their chemical composition to become similar to that of seawater. The thermal waters of Lesvos Island present relatively high concentrations of ammonia and redox sensitive metals because they are hosted in a reducing environment. They also exhibit low nitrate concentrations due to their mixture with recent fresh water. Finally, they show increased radon concentrations, ranging from 20 to 60 kBq m−3 in the eastern and southern parts of the island, and about 230 kBq m−3 in the north, in the area of Eftalou–Argenos. Copyright © 2007 John Wiley & Sons, Ltd.