bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generation and Characterization of Multilayer Systems Consisting of Au55(PPh3)12Cl6 Double Layers and SiO2 Barrier Films
Authors: Reuter Torsten , Neumeier Stefan , Schmid Günter , Koplin Eva , Simon Ulrich 
Published: July 2005

AbstractMultilayer systems, consisting of Au55(PPh3)12Cl6 double layers and SiO2 barrier films of different thickness, have been generated and characterised. The formation of the double layer between the barrier films was carried out by using spin‐coating techniques. For the generation of the SiO2 films, a plasma‐assisted physical vapour deposition (PAPVD) procedure has been applied, based on an anodic plasma arc process. Samples of up to nine cluster/SiO2 combinations have been produced and have been characterised by AFM and SEM. Impedance measurements showed that there is a characteristic thermally activated frequency dependence of the capacitance of the different systems. The cluster layers interact by dipoles formed in the double layers at low frequencies. It has also been shown that multilayer systems with SiO2 films thicker than 15 nm tend to spontaneously crystallise. Furthermore, wetting problems during the spin‐coating processes have been investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Bis(trimethylsilyl)ketene Acetals as C,O‐Dinucleophiles: One‐Pot Formation of Polycyclic γ‐ and δ‐Lactones from Pyridines and Pyrazines
Authors: Rudler Henri , Denise Bernard , Xu Yiming , Parlier Andrée , Vaissermann Jacqueline 
Published: July 2005

AbstractBis(trimethylsilyl)ketene acetals react with pyridines, quinoline and isoquinoline in the presence of stoichiometric amounts of methyl chloroformate to give the corresponding dihydropyridine‐, dihydroquinoline‐ and dihydroisoquinoline‐substituted carboxylic acids in satisfactory yields. The regio‐ and diastereoselectivities of the addition reactions, together with the presence or absence of rotamers, have been established. The isolated acids react with peracids to give β‐hydroxy‐δ‐lactones through an intramolecular reaction. Similar lactonizations could also be brought about directly from the azaaromatic compounds in one‐pot reactions with silica gel, iodine or bromine. In these cases δ‐lactones or β‐halo‐δ‐lactones were produced. The behaviour of pyrazines in these transformations is peculiar, since methyl chloroformate on its own induces the formation, through interaction with both nitrogen atoms, of polycyclic γ‐lactones, a reaction formally reminiscent of the double nucleophilic addition of the same ketene acetals to (arene)tricarbonylchromium complexes. Most of the new structures were assigned through X‐ray crystal structure determinations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Extended Cavitands of Nanoscale Dimensions
Authors: Menozzi Edoardo , Onagi Hideki , Rheingold Arnold L. , Rebek Julius 
Published: July 2005

AbstractNew tetrabenzimidazole cavitands with upper rims extended by aromatic groups have been prepared and their X‐ray structures were analyzed. The reversible encapsulation of a series of n‐alkylammonium guests was studied by NMR spectroscopy and mass spectrometry. These guests showed different binding modes and unique interactions with the hydrophobic cavity. The trimethylammonium guests bearing n‐butyl to n‐hexyl substituents stabilize the C4v conformation of the cavitand by additional CH···π interactions with the aromatic upper part. The longest n‐hexylammonium salt adopts a minimal gauche conformation to fit in the cavity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
1,3‐Selenazole
Authors: Below Harald , Pfeiffer Wolf‐Diethard , Geisler Karlheinz , Lalk Michael , Langer Peter 
Published: July 2005

AbstractThe parent 1,3‐selenazole was prepared by cyclization of selenoformamide with α‐bromoacetaldehyde. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Ring Opening of 1‐Azabicyclo[1.1.0]butanes with Hydrazoic Acid – a Facile Access to N‐Unsubstituted Azetidin‐3‐Amines
Authors: Mlostoń Grzegorz , Celeda Małgorzata 
Published: July 2005

AbstractSterically congested 1‐azabicyclo[1.1.0]butanes 1 add hydrazoic acid smoothly at 0–5°, giving 3‐azidoazetidines 2 in good to excellent yields. After hydrogenolysis over Pd/C catalyst, compounds 2 were converted into N‐unsubstituted azetidin‐3‐amines 4. Attempted reduction of 2a with Raney‐Ni led to a mixture of the expected azetidin‐3‐amine 4a and the ring‐enlarged 2,5‐dihydro‐1H‐imidazole derivative 5.
New Synthesis of Pyrrolidines via Reaction of γ‐Halocarbanions with Imines
Authors: Mąkosza Mieczysław , Judka Marek 
Published: July 2005

Abstractγ‐Chlorocarbanions of proper nucleophilicity, generated from 3‐chloropropyl pentachlorophenyl sulfone (=pentachloro[(3‐chloropropyl)sulfonyl]benzene; 1; Ar=C6Cl5), add to electron‐deficient formal imines 3a–l to produce anionic adducts that enter intramolecular substitution leading to substituted pyrrolidines. This new and simple synthesis of pyrrolidines mimics a 1,3‐dipolar cycloaddition, although it proceeds in two distinct steps.
Activation Energies and Reaction Energetics for 1,3‐Dipolar Cycloadditions of Hydrazoic Acid with CC and CN Multiple Bonds from High‐Accuracy and Density Functional Quantum Mechanical Calculations
Authors: Jones Gavin O. , Ess Daniel H. , Houk Kendall N. 
Published: July 2005

AbstractThe reactions of hydrazoic acid (HN3) with ethene, acetylene, formaldimine (H2CNH), and HCN were explored with the high‐accuracy CBS‐QB3 method, as well as with the B3LYP and mPW1K density functionals. CBS‐QB3 predicts that the activation energies for the reactions of hydrazoic acid with ethylene, acetylene, formaldimine, and HCN have remarkably similar activation enthalpies of 19.0, 19.0, 21.6, and 25.2 kcal/mol, respectively. The reactions are calculated to have reaction enthalpies of −21.5 for triazoline formation from ethene, and −63.7 kcal/mol for formation of the aromatic triazole from acetylene. The reaction to form tetrazoline from formaldimine has a reaction enthalpy of −8 kcal/mol (ΔGrxn=+5.6 kcal/mol), and the formation of tetrazole from HCN has a reaction enthalpy of −23.0 kcal/mol. The trends in the energetics of these processes are rationalized by differences in σ‐bond energies in the transition states and adducts, and the energy required to distort hydrazoic acid to its transition‐state geometry. The density functionals predict activation enthalpies that are in relatively good agreement with CBS‐QB3, the results differing from CBS‐QB3 results by ca. 1–2 kcal/mol. Significant errors are revealed for mPW1K in predicting the reaction enthalpies for all reactions.
Application of the ‘Direct Amide Cyclization’ to Peptides Containing an Anthranilic Acid Residue
Authors: Philipova Irena , Linden Anthony , Heimgartner Heinz 
Published: July 2005

AbstractThe 2,2‐disubstituted 2H‐azirin‐3‐amines 7a–7c were used as amino acid synthons to prepare linear peptides derived from anthranilic acid. These linear peptides, which contain α,α‐disubstituted α‐amino acids, were synthesized by using the ‘azirine/oxazolone method’ (Schemes 2–5) and were subjected to the acid‐catalyzed ‘direct amide cyclization’. Unfortunately, all attempts to isolate the ten‐membered cyclotripeptides, by starting with different precursors, failed. Instead of the expected cyclotripeptides, the corresponding 1,3a,7‐triazabenz[e]azulene‐3,6‐diones 12 and 17 (Schemes 2 and 3) were obtained in up to 44% yield. Most likely, these products were formed by a transannular ring contraction of the desired products, followed by dehydration. In the case of the linear precursor 24, the 20‐membered cyclodimer 25 was formed in 50% yield, together with traces of the 1,3a,7‐triazabenz[e]azulene‐3,6‐dione 27 and the completely unexpected quinazolinone 26 (Scheme 5). In the cases of the linear precursors 30 and 34, no ring closure was observed under the conditions of the ‘direct amide cyclization’, which indicates the limitations of this method.
Quantification of the β‐Stabilizing Effect of the Dicarbonyl(η5‐cyclopentadienyl)iron Group
Authors: Dulich Felix , Müller Karl‐Heinz , Ofial Armin R. , Mayr Herbert 
Published: July 2005

AbstractKinetic investigations of the reactions of (prop‐2‐enyl)dicarbonyl(cyclopentadienyl)iron complexes 1 with benzhydrylium ions 3, and of dicarbonyl(cyclopentadienyl)[(1,2‐η)propene]iron(II) tetrafluoroborate (9⋅BF4) with π‐nucleophiles have been performed to elucidate the magnitude of the β‐effect of the [(CO)2FeCp] group (Fp group). Introduction of the Fp group into the allylic position of propene and 2‐methylpropene increases the nucleophilicity of the π‐bonds by nine and six orders of magnitude, respectively, with the result that the allyl‐Fp complexes 1a (N=6.78) and 1b (N=8.45) are among the strongest neutral π‐nucleophiles. Replacement of one β‐H‐atom in the isopropyl cation by the Fp group reduces the electrophilicity by more than 20 orders of magnitude, so that 9+ ranks among the weakest cationic C‐electrophiles (E=−11.2).
Fluorinated Diazo Diketones in Rhodium(II)‐Catalyzed Reactions with Sultams: Chemoselective O‐Functionalization of Amide Carbonyl Groups
Authors: Zakharova Valeria M. , Schulze Bärbel , Rodina Ludmila L. , Sieler Joachim , Nikolaev Valerij A. 
Published: July 2005

AbstractRhodium(II)‐catalyzed decomposition of fluorinated diazo diketones in the presence of isothiazole‐3(2H)‐one 1,1‐dioxides offers a chemoselective and useful tool for O‐functionalization of their CO groups by interaction with transient fluorine‐containing RhII‐diketocarbenoids. The resulting O‐alkylimidates of isothiazole 1,1‐dioxides, bearing (trifluoromethyl)acetyl groups, easily react with traces of H2O giving rise to stable hydrates of the perfluoroacetyl groups. No O→N isomerization of O‐alkylimidates (similar to the Lander–Chapman rearrangement) was observed under the reaction conditions studied.
Light‐Induced Cycloaddition of 2,3‐Dihydro‐2,2‐dimethyl‐4H‐thiopyran‐4‐one (a 4‐Thiacyclohex‐2‐enone) to Alkenes and Dienes
Authors: Schmidt Kerstin , Kopf Jürgen , Margaretha Paul 
Published: July 2005

AbstractThe reactivity of (thiacyclic)‐2,3‐dihydro‐2,2‐dimethyl‐4H‐thiopyran‐4‐one (1a) in light‐induced cycloadditions to furan (F), acrylonitrile (AN), or 2,3‐dimethylbut‐2‐ene (TME) is compared to that of (carbocyclic) 5,5‐dimethylcyclohex‐2‐enone (1b). Whereas for the more‐flexible thiacycle, the efficiency of [2+2]‐photocycloadduct formation with AN or TME is generally much lower, the diastereoselectivity regarding the ring fusion in the bicyclo[4.2.0]octanes is quite similar for both enones. In contrast, 1a affords exclusively trans‐fused [4+2] cycloadducts with F, while 1b gives predominantly the corresponding cis‐fused products.
Synthesis of the 2‐Alkenyl‐4‐alkylidenebut‐2‐eno‐4‐lactone (=α‐Alkenyl‐γ‐alkylidenebutenolide) Core Structure of the Carotenoid Pyrrhoxanthin via the Regioselective Dihydroxylation of Hepta‐2,4‐diene‐5‐ynoic Acid Esters
Authors: Schmidt‐Leithoff Joachim , Brückner Reinhard 
Published: July 2005

AbstractA new strategy for the stereoselective synthesis of 4‐alkylidenebut‐2‐eno‐4‐lactones (=γ‐alkylidenebutenolides) with (Z)‐configuration of the exocyclic CC bond at C(4) was developed. It is exemplified by the synthesis of 4‐alkylidenebutenolactone 31 (Scheme 4), which constitutes a substructure of the carotenoids pyrrhoxanthin (1) and peridinin. The formation of the precursor 4‐(1‐hydroxyalkyl)butenolactone 29 was accomplished either by cyclocarbonylation of the prop‐2‐yn‐1‐ol moiety of 27 (→29) or by hydrostannylation of the isopropylidene‐protected alkynoic acid ester 26 (→28) followed by transacetalization/transesterification (→30). The 4‐alkylidenebutenolactone was formed by the anti‐selective Mitsunobu dehydration 29→31.
Tautomerism in 5,8‐Diaza‐7,9‐dicarbaguanine (‘Alloguanine’)
Authors: Wagner Trixie , Han Bo , Koch Guido , Krishnamurthy Ramanarayanan , Eschenmoser Albert 
Published: July 2005

AbstractAn X‐ray structure analysis of the title compound reveals that this purinoid exists in the crystal as two tautomers which interact with each other in the mode of a reverse‐Watson–Crick base pair.
Studies on the oxidation of phenols catalyzed by a copper(II)–Schiff base complex in aqueous solution under mild conditions
Authors: Meng Xiang‐Guang , Zhu Jie , Yan Jie , Xie Jia‐Qing , Kou Xing‐Ming , Kuang Xiao‐Fan , Yu Li‐Feng , Zeng Xian‐Cheng 
Published: July 2005

AbstractThe catalytic oxidation of phenol with hydrogen peroxide using a synthetic copper(II)–Schiff base complex as catalyst has been investigated in phosphate buffer at pH 7 and 25 °C. In order to further investigate the reaction pathway, the catalytic oxidation of hydroquinone, p‐benzoquinone and catechol were also studied under the same conditions. These reactions were found to be pseudo‐first‐order with respect to the concentration of phenolic substances. The rate constants were also calculated. In the presence of catalyst, the kinetics and the HPLC analysis showed that for the first step phenol was oxidized to hydroquinone and catechol, and the catalyst easily promoted the formation of hydroquinone but not catechol, for the second step the dihydroxybenzenes were further oxidized to benzoquinone, and lastly short‐chain acids, including maleic acid and oxalic acid, were formed. The activity of the catalyst hardly decreased during the whole reaction. Addition of imidazole accelerated the oxidation of phenol. The catalytic decomposition of hydrogen peroxide using this catalyst was also investigated. Copyright © 2005 Society of Chemical Industry
Molecular recognition by mass spectrometry
Authors: Di Tullio Alessandra , Reale Samantha , De Angelis Francesco 
Published: July 2005

AbstractA recent major advance in the field of mass spectrometry in the biomolecular sciences is represented by the study of the supramolecular interactions among two or more partners in the gas phase. A great deal of chemistry and most of biochemistry concerns molecular interactions taking place in solution. The electrospray technique, which allows direct sampling from solution, and soft ionization of the solute without deposition into the analyte of large amounts of energy, guarantees in many cases the survival of noncovalent bondings and, hence, the direct analysis of the supramolecular complexes present in the condensed phase. The proper preparation of the solution to be studied and also the expert and accurate setting and use of the instrumental parameters are the prerequisites for gaining results as to the specific interactions between, for instance, a protein conformationally modified by its specific metal ion, eventually, and a ligand molecule. The analysis of the charge state of the protein itself and of the modifications of the complex integrity by activating collisions are also methods for studying the biomolecule–molecule interactions. Accordingly, this new mass spectrometric approach to the supramolecular chemistry, which could be also defined as ‘supramolecular mass spectrometry’, allows the study of ion–protein, protein–protein, protein–ligand and DNA–drug interactions. Chiral recognition can also be performed in the gas phase, studying by electrospray mass spectrometry the fragmentation of diastereomeric complex ions. Not the least, a deep insight can also be obtained into the formation and nature of inclusion complexes like those formed with crown ethers, cyclodextrins and calixarenes as host molecules. All these topics are treated to a certain extent in this special feature article. Copyright © 2005 John Wiley & Sons, Ltd.
Alpha‐synuclein immunohistochemistry in two cases of co‐occurring idiopathic Parkinson's disease and motor neuron disease
Authors: Klos Kevin J. , Josephs Keith A. , Parisi Joseph E. , Dickson Dennis W. 
Published: July 2005

AbstractWe report on two cases of sporadic idiopathic Parkinson's disease with motor neuron disease co‐occurring in the same individuals. Pathological analysis revealed the presence of Lewy bodies in brainstem nuclei and basal forebrain consistent with Lewy body disease (LBD), as well as motor neuron degeneration and argyrophilic grain disease. We compared our two cases to all previously published pathological cases of combined LBD and motor neuron degeneration. © 2005 Movement Disorder Society
Study on δ‐form complex in syndiotactic polystyrene–organic molecules systems. IV. Formation of complexes with a mixture of solvents and structural changes during the sorption of solvents by syndiotactic polystyrene mesophase membranes
Authors: Mahesh K. P. O. , Tsujita Y. , Yoshimizu H. , Okamoto S. , Mohan D. 
Published: July 2005

AbstractThe syndiotactic polystyrene (sPS) δ form was crystallized from mixtures with different compositions of p‐chlorotoluene–chlorobenzene (p‐CT–CB) and p‐chlorotoluene–1,1,2‐trichloroethane (p‐CT–TCE). The presence of the δ form and TTGG helical conformation was confirmed by Fourier transform infrared and wide‐angle X‐ray diffraction (WAXD) analyses. In sPS/p‐CT–CB and sPS/p‐CT–TCE δ‐form membranes, the relative absorbance (RA) of the p‐chlorotoluene (p‐CT) solvent peak was very high even at very low concentrations of p‐CT in comparison with the RA of higher concentrations of chlorobenzene (CB) or 1,1,2‐trichloroethane (TCE) in the mixtures. However, the RAs of both CB and TCE solvent peaks decreased with decreasing concentrations of CB and TCE in the mixtures. A negligible decrease in the RA of the TTGG helical content was observed with a decreasing concentration of CB or TCE. The WAXD results showed that the 2θ peak positions of the [010] and [$\bar{2}$10] planes of the sPS/p‐CT–CB and sPS/p‐CT–TCE δ‐form membranes appeared in the same position and were almost equal to those of the sPS–p‐CT δ‐form membrane. The mesophases of the sPS–p‐CT [p‐CT (A‐M)] and sPS–TCE [TCE (A‐M)] membranes were used for the sorption studies with different concentrations of various solvents. The sorption amount of aromatic solvents by both p‐CT (A‐M) and TCE (A‐M) mesophase membranes was higher than that of aliphatic solvents, regardless of the size, shape, and nature of the molecular cavity. The 2θ peak of the [010] plane of the sPS membranes slowly approached the original δ‐form value when the sPS mesophase membranes were immersed in various solvents of different concentrations for 48 h. The shifting of the 2θ peak of the [010] plane to the original δ form depended on the nature and concentration of the immersion solvents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2380–2387, 2005
Polymer–filler interactions in sol–gel derived polymer/silica hybrid nanocomposites
Authors: Bandyopadhyay Abhijit , de Sarkar Mousumi , Bhowmick Anil K. 
Published: July 2005

AbstractThe effect of polymer–filler interaction on solvent swelling and dynamic mechanical properties of the sol–gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica, and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites has been described for the first time. Tetraethoxysilane (TEOS) at three different concentrations (10, 30, and 50 wt %) was used as the precursor for in situ silica generation. Equilibrium swelling of the hybrid nanocomposites in respective solvents at ambient condition showed highest volume fraction of the polymer in the swollen gel in PVA/silica system and least in ACM/silica, with ENR/silica recording an intermediate value. The Kraus constant (C) also followed a similar trend. In dynamic mechanical analysis, the storage modulus dropped at higher strain (>1%), which indicated disengagement of polymer segments from the filler surfaces. This drop was maximum in ACM/silica, intermediate in ENR/silica, and minimum in PVA/silica, both at 50 and 70 °C. The drop in modulus with theoretical volume fraction of silica (ϕ) was interpreted with the help of a Power law model ΔE′ = a1ϕ, where a1 was a constant and b1 was primarily a filler attachment parameter. Strain dependence of loss modulus was observed in ACM/silica hybrid nanocomposites, while ENR/silica and PVA/silica nanocomposites showed almost strain‐independent behavior. The storage modulus showed sharp increase with increasing frequency in ACM/silica system, while that was lower in both ENR/silica (at higher frequency) and PVA/silica systems (in the entire frequency spectrum). The increase in modulus with ϕ also followed similar model ΔE′ = a2ϕ proposed in the strain sweep mode. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2399–2412, 2005
In situ study of K+ transport into the vacuole of Saccharomyces cerevisiae
Authors: Martínez‐Muñoz Gloria A. , Peña Antonio 
Published: July 2005

AbstractPermeable spheroplasts were prepared from two strains of Saccharomyces cerevisiae by incubating with zymolyase without a permeabilizing agent. The loss of the plasma membrane barrier was confirmed by the nucleotide release, the activity of glucose 6‐phosphate dehydrogenase with external substrates and by the effects on respiration of mitochondrial substrates and ADP. Mitochondrial integrity was maintained, as shown by respiration with lactate, pyruvate, glucose and ethanol, and its acceleration by ADP showed a coupled respiration. Potassium uptake into the vacuole was measured with a selective electrode and found to be taken up effectively by spheroplasts only in the presence of Mg‐ATP; it was reverted by CCCP and PCP and inhibited by bafilomycin A1, but not by sodium vanadate or sodium azide. Potassium ions did not alter ΔΨ of the vacuole, followed with oxonol V, but caused vacuolar alkalinization, as followed with pyranine. The increase of vacuolar pH was non‐selective and observed at 50–200 mM of several monovalent cations. Isolated vacuoles with pyranine inside showed similar changes of the internal pH in the presence of KCl. Results indicate that some strains do not require a permeabilizing agent to directly access the vacuole in spheroplasts prepared with zymolyase. The hypothesis about the existence of a K+/H+ antiporter in the vacuolar membrane of S. cerevisiae is discussed. Copyright © 2005 John Wiley & Sons, Ltd.
A Fixation with Floating: The Politics of Canada's Exchange Rate Regime
Authors: Helleiner Eric 
Published: July 2005

Abstract.Since the 1930s, Canadian policy makers have demonstrated an unusually strong commitment to a floating exchange rate regime. A fixed exchange rate regime was embraced for only two brief periods between 1939–1950 and 1962–1970. This article examines the political basis of Canada's longstanding “fixation with floating,” an issue that is unexplored in existing scholarly literature. Drawing on the growing literature examining the politics of exchange rate regimes, the article shows how Canada's longstanding commitment to floating has stemmed from a combination of distinct domestic private economic interests, the beliefs of state policy makers, and the unique nature of the US-Canada relationship.Résumé.Depuis les années 1930, les responsables de la politique monétaire canadienne ont manifesté une prédilection soutenue pour un taux de change flottant. Le pays n'a connu de taux de change fixe que pendant deux courtes périodes, de 1939 à 1950 et de 1962 à 1970. Cet article examine les fondements politiques de cette préférence, sujet qui reste inexploré dans la littérature existante. S'inspirant des travaux de plus en plus nombreux sur la politique des taux de change, l'article démontre que la source politique de cette préférence pour un taux de change flottant réside dans les intérêts économiques des entreprises, les convictions des décisionnaires et la nature unique de la relation entre le Canada et les États-Unis.