bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tris(trimethylsilyl)‐Substituted Heavy Group 14‐Element‐Centered Anions: Unsolvated Trimeric Germyllithium and Solvated Dimeric Silyl‐ and Stannyllithiums
Authors: Nanjo Masato , Nanjo Emi , Mochida Kunio 
Published: May 2004

AbstractTris(trimethylsilyl)‐substituted group 14‐element‐centered anion monomers [LiE(SiMe3)3·3THF] (E = Si, Ge, and Sn) can be distilled under reduced pressure to give dimeric silyllithium 4 and stannyllithium 6, and trimeric germyllithium 5 without pyrolysis products such as dilithiometallanes. The molecular structures of 4, 5, and 6 were unequivocally determined by X‐ray diffraction. Dimer 4 has a symmetrical bent four‐membered‐ring structure consisting of two anionic silicon atoms and two cationic lithium atoms with coordinated THF molecules. Dimer 6 has an unsymmetrical distorted four‐membered‐ring structure consisting of two anionic tin atoms, a bridged unsolvated lithium atom, and a bridged lithium atom solvated by a THF molecule. Interestingly, 6 aggregates to form dimers of dimers by an intermolecular CH3···Li interaction. Trimeric germyllithium 5 forms an equilateral triangular lithium cluster without solvation. Compound 5 has a crystallographic threefold axis with three anionic germanium atoms and three cationic lithium atoms lying in the same plane. The lithium atoms in 5 are stabilized by an intramolecular CH3···Li interaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis, Crystal Structure and Thermal Reactivity of New Copper(I) Halide Pyrimidine‐Containing Coordination Polymers
Authors: Näther Christian , Jeß Inke 
Published: May 2004

AbstractReaction of copper(I) chloride with pyrimidine in acetonitrile leads to the formation of the ligand‐rich 1:1 compound poly[CuCl(μ2‐pyrimidine‐N,N′)] (1). “Zig‐zag”‐like CuCl chains are found in the crystal structure that are connected by the pyrimidine ligands to form layers. This compound loses half of its ligands upon heating and transforms into the new l2:1 coordination polymer poly[(CuCl)2(μ2‐pyrimidine‐N,N′)] (2). In this structure, ladder‐like CuCl double chains occur which are connected by the pyrimidine ligands to form layers. If copper(I) iodide is used in the synthesis, the new 1:1 coordination polymer poly[CuI(μ2‐pyrimidine‐N,N′)] (3) forms. In contrast to compound 1, CuI single chains and (CuI)2 dimers are found as the CuX substructure, and these are connected by the ligands to form sheets. On heating this compound a similar behaviour as for compound 1 is observed, and a transformation into the new 2:1 compound poly[(CuI)2(μ2‐pyrimidine‐N,N′)] (4) occurs. This compound is not isotypic to 2 even though the topology of the coordination network is identical (CuI double chains are connected into layers by the pyrimidine ligands). The thermal behaviour of the known compounds poly[CuBr(μ2‐pyrimidine‐N,N′)] (5) and poly[(CuBr)2(μ2‐pyrimidine‐N,N′)] (6) was also investigated. A transformation of the ligand‐rich 1:1 compound 5 into the 2:1 compound 6 is also observed in the thermal decomposition reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Characterization of [OsCl2(=C=CHR)(PPh3)2] and Related Complexes
Authors: Wen Ting Bin , Hung Wai Yiu , Zhou Zhong Yuan , Lo Man Fung , Williams Ian D. , Jia Guochen 
Published: May 2004

AbstractTreatment of [OsCl2(PPh3)3] with HC≡CR (R = Ph, p‐tolyl, CMe3) in the presence of HCl gives the corresponding trichloro(carbyne) complexes [OsCl3(≡CCH2R)(PPh3)2] in good yields. The vinylidene complexes [OsCl2(=C=CHR)(PPh3)2] (R = Ph, p‐tolyl, CMe3) are, in turn, prepared from the reactions of the carbyne complexes [OsCl3(≡CCH2R)(PPh3)2] with NEt3. These new vinylidene complexes are hygroscopic and react with H2O to give (aqua)(vinylidene) complexes [OsCl2(H2O)(=C=CHR)(PPh3)2]. The structures of several of these new complexes have been determined by X‐ray diffraction studies. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Subsequent Hydride Substitution in (Arene)trihydridodiruthenium Complexes: Synthesis and Structure of Thiolato‐Bridged Diruthenium Cations of the Type [H2(arene)2Ru2(p‐X−C6H4−S)]+ and [H(arene)2Ru2(p‐X−C6H4−S)2]+
Authors: Tschan Mathieu J.‐L. , Chérioux Frédéric , Therrien Bruno , Süss‐Fink Georg 
Published: May 2004

AbstractThe cationic complexes [HRu2(η6‐arene)2{μ2‐(p‐X−C6H4)−S}2]+ and [H2Ru2(η6‐arene)2{μ2‐(p‐X−C6H4)−S}]+ (arene = 1,2,4,5‐Me4C6H2 or C6Me6; X = Br and Me) are accessible in good yields from p‐X−C6H4−SH with [H3Ru2(1,2,4,5‐Me4C6H2)2][BF4] and [H3Ru2(C6Me6)2][BF4], respectively. The dibromo derivative [HRu2(C6Me6)2(p‐Br−C6H4−S)2]+ is found to undergo double Suzuki coupling reactions with 3‐thiophene boronic acid to give [HRu2(C6Me6)2(p‐C4H3S−C6H4−S)2]+. This dibromo complex is a potential precursor for the insertion of dinuclear hydrido organometallic entities in the main chain of conjugated molecules. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Phenyl 2‐Pyridyl Ketone and Its Oxime in Manganese Carboxylate Chemistry: Synthesis, Characterisation, X‐ray Studies and Magnetic Properties of Mononuclear, Trinuclear and Octanuclear Complexes
Authors: Milios Constantinos J. , Stamatatos Theocharis C. , Kyritsis Panayotis , Terzis Aris , Raptopoulou Catherine P. , Vicente Ramon , Escuer Albert , Perlepes Spyros P. 
Published: May 2004

AbstractThe use of phenyl 2‐pyridyl ketone [(ph)(2‐py)CO] and its oxime [(ph)(2‐py)CNOH] in manganese benzoate chemistry has been investigated. The reaction of an excess of (ph)(2‐py)CNOH with Mn(O2CPh)2·2H2O affords the mononuclear complex [MnII(O2CPh)2{(ph)(2‐py)CNOH}2]·1.2H2O (1·1.2H2O) in high yield. The MnII ion is coordinated by two monodentate benzoates and two N,N′‐bidentate chelating (ph)(2‐py)CNOH molecules in a cis‐cis‐trans fashion. The comproportionation reaction between Mn(O2CPh)2·2H2O and NnBu4MnO4 (3:1) in the presence of (ph)(2‐py)CNOH in MeCN/EtOH/CH2Cl2 leads to the isolation of the mixed‐valent cluster [Mn8O2(OH)2(O2CPh)10{(ph)(2‐py)CNO}4]· 4CH2Cl2 (2·4CH2Cl2) in about 55% yield. A second synthetic procedure that leads to pure 2 involves the reaction between the known starting material (NnBu4)[Mn4IIIO2(O2CPh)9(H2O)] and four equivalents of the oxime ligand in CH2Cl2. The centrosymmetric octanuclear molecule contains four MnII and four MnIII ions held together by two μ4‐O2− ligands and two μ3‐OH− ions to give the unprecedented [Mn8(μ4‐O)2(μ3‐OH)2]14+ core, with peripheral ligation provided by ten PhCO2− (two η1, four syn,syn η1:η1:μ2 and four η1:η2:μ3) and four η1:η1:η1:μ2 (ph)(2‐py)CNO− ions. The 1:1 reaction between Mn(O2CPh)2·2H2O and the ketone (ph)(2‐py)CO affords the trinuclear complex [Mn3(O2CPh)6{(ph)(2‐py)CO}2] (3) in more than 80% yield. As judged from single‐crystal X‐ray crystallography, the complex adopts a linear structure with one η1:η2:μ2 and two η1:η1:μ2 benzoates spanning each pair of metal ions. The terminal MnII ions are capped by bidentate chelating (ph)(2‐py)CO ligands. The three complexes have been characterised by IR spectroscopy. The CV study of complex 2 in CH2Cl2 reveals irreversible reduction and oxidation processes. The magnetic properties of 2 and 3 have been studied by variable‐temperature dc magnetic‐susceptibility techniques. As the temperature approaches zero, the value of the χMT product for 2 approaches zero and, thus, the octanuclear complex has an S = 0 ground state. This S = 0 ground state is explained in terms of the magnetic behaviour of the central, butterfly‐like [Mn4III(μ3‐O)2]8+ subcore. The results for 3 reveal weak antiferromagnetic coupling, with J = −2.7 cm−1 for adjacent MnII ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
[1,2]‐Rearrangement of Imino‐N‐heterocyclic Carbenes − Synthesis and Structures of Chelating Iminoimidazole Pd and Ni Complexes
Authors: Steiner Georg , Krajete Alexander , Kopacka Holger , Ongania Karl‐Hans , Wurst Klaus , Preishuber‐Pflügl Peter , Bildstein Benno 
Published: May 2004

AbstractImidazolium and benzimidazolium salts with an N‐iminoyl and an N′‐alkyl group are potential precursors for new bidentate [N,C] ligands which are of interest as novel steering ligands for applications of their metal complexes in homogeneous catalysis. Deprotonation of these azolium salts with potassium hydride does indeed occur, however, the initially formed imino‐N‐heterocyclic carbenes rearrange spontaneously under migration of the N‐iminoyl group from the nitrogen to the former carbene carbon with the formation of 2‐iminoyl(benz)imidazoles. These rearranged compounds are new [N,N] ligand systems, which can also be synthesized by aluminum‐assisted condensation of anilines with the corresponding 2‐acylimidazoles. Palladium and nickel [N,N] complexes have been prepared, characterized by single‐crystal X‐ray analysis, and briefly evaluated for their catalytic performance in ethylene polymerizations and in Suzuki cross‐coupling reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Surface modifications of alumina–silica glass fiber
Authors: Andrade A.L. , Ferreira J.M.F. , Domingues R.Z. 
Published: May 2004

AbstractA commercial glass fiber with Al2O3 (68.4%) and SiO2 (27.6%) as major components and CaO, TiO2, Fe2O3, and CuO as minor components was used as substrate in a silica sol–gel coating process. After cleaning, fiber samples were immersed into tetraethoxysilane (TEOS) at room temperature for 1 h, and then individual fiber samples were soaked into a simulated body fluid (SBF) solution,1 and removed after 5, 10, 15, and 20 days. Zeta potential and Energy Dispersive Spectroscopy (EDS) analyses showed that the fiber surfaces were effectively coated with a silica layer, which improved the formation of an HA layer upon immersion into SBF solution for 5 days. The coating became even more continuous after 10‐day immersion. Fourier Transform Infrared Spectroscopic (FTIR) analyses confirmed that the coating layer has PO vibration bands characteristic of hydroxyapatite (HA) near 1060 and 600 cm−1. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 70B: 378–383, 2004
Homocysteine increases the production of asymmetric dimethylarginine in cultured neurons
Authors: Selley Michael L. 
Published: May 2004

AbstractIncreased circulating concentrations of homocysteine may be a risk factor for Alzheimer's disease and cognitive dysfunction in normal aging. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase (NOS). ADMA is metabolized in neurons by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). Nitric oxide plays an important role in synaptic events involved in learning and memory. We determined the effect of L‐homocysteine on ADMA accumulation and nitric oxide production in cultured rat neuronal granule cells. The incubation of neuronal granule cells with L‐homocysteine for 24 hr caused a dose‐dependent accumulation of ADMA and a dose‐dependent decrease in nitric oxide production. The addition of the sulfhydryl antioxidant pyrrolidine dithiocarbamate (PDTC) attenuated the effect of homocysteine on ADMA accumulation and nitric oxide production. DDAH activity had a decreasing dose–response relationship with increasing L‐homocysteine concentrations. The addition of PDTC caused a dose‐dependent increase in DDAH activity. The addition of the N‐methyl‐D‐aspartate receptor antagonists (±)‐2‐amino‐5‐phosphopentanoic acid and 7‐chlorokynurenate had no effect on the inhibition of DDAH by homocysteine. It is concluded that L‐homocysteine inhibits DDAH activity, thereby causing ADMA accumulation and decreasing nitric oxide production in cultured neurons. The protective effect of PDTC suggests that L‐homocysteine inactivates DDAH in neurons by reacting with the cysteine residue in its active site. The preservation of DDAH activity and the reduction of ADMA accumulation in neurons may be a new strategy for the treatment of Alzheimer's disease and cognitive impairment in normal aging. © 2004 Wiley‐Liss, Inc.
Cationic Polymerization of Vinyl Ethers in the Presence of Silyl Enol Ethers
Authors: Lang Weihong , Sarker Prodip K. , Rimmer Stephen 
Published: May 2004

AbstractSummary: Vinyl ether oligomers with reactive end groups were prepared by alkylation of silyl enol ethers during propagation. Silyl enol ethers were added to the cationic polymerization of isobutyl vinyl ether, ethyl vinyl ether and methyl vinyl ether. The polymerizations were carried out under non‐living conditions so that, in the absence of added silyl enol ether, MALDI TOF mass spectrometry gave evidence for end groups other than those derived from reaction with the methanol capping agent. Addition of either phenyl‐1‐(trimethylsilyloxy)ethylene or 1‐methoxyphenyl‐1‐(trimethylsilyloxy)ethylene significantly reduced the fraction of end groups derived from intramolecular termination reactions, such as elimination, at temperatures between 21 and −78 °C. However, as in living systems lowering the reaction temperature increased the proportion of chains with the desired chain‐end functionality (i.e. aryl ketone derived from alkylation of the silyl enol ether). α‐β Elimination also produced a population of isobutyl vinyl ether oligomers with α‐β unsaturated ketone end groups.Structure of an oligo(isobutyl vinyl ether) with a substituted phenyl ketone end group.imageStructure of an oligo(isobutyl vinyl ether) with a substituted phenyl ketone end group.
Light Scattering Studies on Ternary Polymer Blend Solutions Comprising Poly(hydroxybutyrate)
Authors: Chee Melinda J. K. , Kummerlöwe Claudia , Lechner Manfred D. , Kammer Hans‐Werner 
Published: May 2004

AbstractSummary: We report on light scattering studies of polymer blend solutions in trifluoroethanol (TFE). The polymer blends comprised poly(3‐hydroxybutyrate) (PHB) in combination with poly(ethylene oxide) (PEO) and poly(ε‐caprolactone) (PCL). PHBs of two different molecular masses were used. Relevant quantities were obtained from Zimm plots. All quantities display non‐linear dependencies on blend composition. For the blend system with PEO and PHB of lower molecular mass, we observed a negative excess of the second virial coefficient, which is indicative of the miscibility of the constituents. The opposite is observed for blends with PCL. The situation changes in blends with PEO and PHB of sufficiently high molecular mass. It turns out that PEO is only miscible with PHB of high molecular mass if it is the major component. This can be concluded from both light scattering and viscosity results.Apparent molecular mass as a function of blend composition for PEO/PHB(1) and PCL/PHB(1) solutions in TFE at 25 °C.imageApparent molecular mass as a function of blend composition for PEO/PHB(1) and PCL/PHB(1) solutions in TFE at 25 °C.
Inversion of Phase Morphology in Polymer‐Blend Thin Films on Glass Substrates
Authors: Zong Qi , Li Zhi , Xie Xuming 
Published: May 2004

AbstractSummary: The phase‐morphology inversion in two blend systems of polystyrene/poly(methyl methacrylate) (PS/PMMA) and polystyrene/poly(ε‐caprolactone) (PS/PCL) has been studied after their thin films were prepared on glass substrates by spin‐coating from a co‐solvent tetrahydrofuran (THF). Phase‐contrast microscopy (PCM), scanning‐electron microscopy (SEM) equipped with energy dispersive X‐ray spectroscopy (EDS), and atomic force microscopy (AFM) were used to obtain information on the morphology of the thin films during heat treatment. It was found that the PMMA‐rich and PCL‐rich phases are always continuous after annealing in either of the PS/PMMA and PS/PCL blend thin films, even though the PMMA and PCL are minor components in the blends. This should result from the better wetting abilities of PMMA and PCL on a glass substrate than PS in the blends. The effect of the viscosity in the evolution of the phase structure was also investigated by changing the molecular weight of PS in the PS/PCL blend thin films. Further more, it is found that the phase‐separation process and the wetting phenomenon of the blends on the glass substrate can be strongly suppressed after adding PS‐block‐PMMA diblock copolymer to the PS/PMMA blend system as a compatibilizer.Scheme of the longitudinal section of the evolution of the phase structure of a PS:PMMA (70:30 w:w) blend film.imageScheme of the longitudinal section of the evolution of the phase structure of a PS:PMMA (70:30 w:w) blend film.
Conformational Transition between Random Coil and Helix of Copolymers of N‐Propargylamides
Authors: Deng Jianping , Tabei Junichi , Shiotsuki Masashi , Sanda Fumio , Masuda Toshio 
Published: May 2004

AbstractSummary: Copolymerization of two N‐propargylamides bearing pendent groups with different lengths [monomer 4, HCCCH2NHCO(CH2)4H; monomer 8, HCCCH2NHCO(CH2)8H] was carried out and the conformational transition behavior of copolymers with different compositions was examined systematically. The copolymers could form relatively stable helices even though both of the corresponding homopolymers, poly(4) and poly(8), could not take a stable helical conformation under the same conditions. The helix content of copolymers reached a maximum when the content of monomer 8 was 61%. These results are explained in terms of the idea that the copolymers have higher cis‐content and that the intramolecular hydrogen bonding is more effective in these copolymers compared with the corresponding homopolymers.image
Inter‐ and Intramolecular Crosslinking Kinetics: Partitioning According to Number of Crosslinks
Authors: Li Rujun , McCoy Benjamin J. 
Published: May 2004

AbstractSummary: Intramolecular crosslinking is important in many processes, including nanoparticle fabrication, but quantitative models of the kinetics have not been extensively investigated. We propose a distribution kinetics analysis for simultaneous intramolecular and intermolecular crosslinking. For realistic cases, moment equations can be solved and crosslink density computed according to the number of crosslinks. An analytical solution for the ratio of intramolecular to intermolecular crosslinking rates varies inversely with the initial polymer concentration and initial molecular weight, in agreement with published experimental data.Time dependence of crosslink density pcd in a batch reactor for ω1 = ω2 = 1 with κ2 = 1 and κ1 = 0, 0.2, 0.5, and 1 (lines 1, 2, 3, and 4), and κ2 = 0 and κ1 = 1 (line 5). pcd increases linearly with time for all cases.imageTime dependence of crosslink density pcd in a batch reactor for ω1 = ω2 = 1 with κ2 = 1 and κ1 = 0, 0.2, 0.5, and 1 (lines 1, 2, 3, and 4), and κ2 = 0 and κ1 = 1 (line 5). pcd increases linearly with time for all cases.
Continuous Reversible Addition‐Fragmentation Chain Transfer Polymerization in Miniemulsion Utilizing a Multi‐Tube Reaction System
Authors: Russum James P. , Jones Christopher W. , Schork F. Joseph 
Published: May 2004

AbstractSummary: A unique, multi‐tube, continuous reactor has been successfully designed and implemented for the study of reversible addition‐fragmentation chain transfer (RAFT) in miniemulsions. Data collection is greatly enhanced by the ability to simultaneously collect samples at five different residence times. The results of a styrene homopolymerization show that kinetically, the reactor exhibits similar behavior to a batch reaction. Number‐average molecular weights increased linearly with conversion, typical of living polymerizations.The number‐average molecular weight of the polymers produced in the tubular reactor increased linearly with conversion, indicative of a controlled polymerization.imageThe number‐average molecular weight of the polymers produced in the tubular reactor increased linearly with conversion, indicative of a controlled polymerization.
Cover Picture: Macromol. Rapid Commun. 10/2004
Authors: Severn John R. , Chadwick John C. 
Published: May 2004

Cover: Effective immobilization and activation of Cp2TiCl2 and other single‐site olefin polymerization catalysts has been achieved using spherical supports of type MgCl2/AlRn(OEt)3‐n, obtained by reaction of AlR3 with adducts of MgCl2 and ethanol. Polyethylene having spherical particle morphology and narrow molecular weight distribution was obtained, without the use of MAO or borate activators.Further details can be found in the Communication by J. R. Severn and J. C. Chadwick* on page 1024.
Cover Picture: Macromol. Theory Simul. 4/2004
Authors: de Jong Johan , ten Brinke Gerrit 
Published: May 2004

Cover: The picture on the cover shows the spontaneous curvature in an alternating copolymacromonomer brush with phase separated side chains.Further details can be found in the Full Paper by J. de Jong* and G. ten Brinke on page 318.
Acute stimulation in the external segment of the globus pallidus improves parkinsonian motor signs
Authors: Vitek Jerrold L. , Hashimoto Takao , Peoples John , DeLong Mahlon R. , Bakay Roy A.E. 
Published: May 2004

AbstractHigh frequency (>100Hz) electrical stimulation in both the external (GPe) and internal (GPi) segments of the globus pallidus was effective in improving parkinsonian motor signs. Improvement generally occurred at short latency (<5–10 seconds) in both GPe and GPi but was often (50% of the time) delayed in GPi. Dyskinetic movements were observed during stimulation within GPe and GPi but were more frequent in GPe (20% vs. 9%). These findings suggest that electrical stimulation in both GPe and GPi may ameliorate parkinsonian motor signs. The mechanisms responsible for these observations, however, may differ. The tendency for delayed responses with GPi stimulation suggests a more complex spatial–temporal profile of stimulation on the electrical activity of GPi neurons and/or its effect on network activity in pallido‐thalamo‐cortical circuitry. The rarity of delayed effects with GPe stimulation suggests a more direct role of synaptic inhibition or normalization of neuronal activity of GPi either directly by means of activation of striatopallidal fibers passing through GPe (direct pathway), by means of activation of GPe→GPi or GPe→subthalamic nucleus projections (indirect pathway) or indirectly by means of the tonic activation of adjacent fiber pathways. These data provide a rationale for the exploration of electrical stimulation in GPe in patients with medically intractable Parkinson's disease and provide a basis on which to develop further investigations into the use of chronic electrical stimulation for the treatment of Parkinson's disease and other movement disorders. © 2004 Movement Disorder Society
Pilot efficacy and tolerability: A randomized, placebo‐controlled trial of levetiracetam for essential tremor
Authors: Handforth Adrian , Martin Fredricka C. 
Published: May 2004

AbstractThe purpose of this pilot single‐site study was to assess efficacy and safety of levetiracetam for essential tremor, using a placebo‐controlled, double‐blind, randomized crossover design with an interim analysis planned after completion of the first 10 to 15 subjects. The study was designed to detect a mean 30% reduction in composite tremor score, comparable to that of primidone or propranolol, which can be demonstrated with 30 or fewer subjects. Each treatment arm included baseline tremor assessments, a 4‐week medication titration, 2 weeks of stable dose, and treatment tremor assessments. Levetiracetam was titrated to 3,000 mg/day or to a lower maximal tolerated dose. The median age was 72 years, with 28 years median tremor duration. There was no statistically significant difference in response between placebo and levetiracetam on any tremor rating scale or accelerometry measure. The 95% confidence interval for the true mean difference between placebo and levetiracetam treatments was +18.5 to −22.5%, which excludes the minimum 30% drop required to consider levetiracetam clinically effective to a degree comparable to primidone or propranolol. Whether levetiracetam has lesser‐degree antitremor efficacy was not addressed in this pilot study. © 2004 Movement Disorder Society