bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mesogeneous Catalysts: A New Concept in Nanotechnology
Authors: Rodríguez Rogelio , Nava Rufino , Halachev Todor , Castaño Victor M. 
Published: March 2004

AbstractSummary: A novel type of catalysis, neither homogeneous nor heterogeneous, is presented. This new “mesogeneous catalysis” combines the high efficiency characteristic of the homogeneous process with the advantages of the heterogeneous one (i.e., the possibility of removing and reusing the catalyst and obtaining catalyst‐free products). The reactions are performed on the surface of nano‐particles, where catalytic‐active sites have been previously chemically anchored by a short dangling organic chain, thus forming a nanohybrid system.Methanol produced by the different catalysts, after 60 min.imageMethanol produced by the different catalysts, after 60 min.
The Critical Lowest Molecular Weight for PEG to Crystallize in Cross‐Linked Networks
Authors: Qiao Congde , Jiang Shichun , Dong Dewen , Ji Xiangling , An Lijia , Jiang Bingzheng 
Published: March 2004

AbstractSummary: Poly(ethylene glycol) (PEG) networks were synthesized by γ‐irradiation. The crystalline behavior of PEG was investigated by differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). It was shown that the crystallinity of PEG is dramatically lower in the cross‐linked networks than in pure PEG. When the molecular weight of PEG in the networks decreased to 1 000, it could not crystallize at all. Moreover, we also found that the melting temperature of PEG is greatly affected by the presence of a cross‐linked network.The DSC curves of PEG ($\overline M _{\rm w}$ = 1 500) and the corresponding cross‐linked PEG.imageThe DSC curves of PEG ($\overline M _{\rm w}$ = 1 500) and the corresponding cross‐linked PEG.
Synthesis of a Novel Oligoaniline: “Dumbbell‐Shaped” Oligoaniline
Authors: Yu Youhai , Mao Huaping , Chen Liang , Lu Xiaofeng , Zhang Wanjin , Wei Yen 
Published: March 2004

AbstractSummary: A new kind of aniline oligomer with a “dumbbell” shape was synthesized through a simple oxidative coupling reaction with a new rigid aromatic amine as starting material. The oligomer was characterized with mass spectrometry, IR and NMR spectroscopies. Its redox property was checked by cyclic voltammetry and chemical oxidation/reduction process was monitored by UV spectroscopy. We found it has a reversible electrochemical property like common oligoanilines. Combined with its well‐defined structure, it is expected to act as a model compound for a molecular electronic switch.The “dumbbell‐shaped” oligoaniline compound synthesized here.imageThe “dumbbell‐shaped” oligoaniline compound synthesized here.
Synthesis and Characterization of Amphiphilic Poly(caprolactone) Star Block Copolymers
Authors: An Sung Guk , Cho Chang Gi 
Published: March 2004

AbstractSummary: Novel, star‐shaped, amphiphilic block copolymers composed of fully degradable poly(caprolactone) were synthesized by sequential addition polymerization. In the first step, four‐arm macroinitiators were produced by ring‐opening polymerization of caprolactone by initiation with pentaerythritol. Then, block copolymers were synthesized by sequential addition of 4‐(2‐benzyloxyethyl)‐ε‐caprolactone to the four‐arm macroinitiators. Star‐shaped, amphiphilic block copolymers containing poly(caprolactone)‐block‐poly[4‐(2‐hydroxyethyl)caprolactone] segments were obtained by catalytic debenzylation.Four‐arm amphiphilic polycaprolactone star block copolymer.imageFour‐arm amphiphilic polycaprolactone star block copolymer.
Photoregulated Sol‐Gel Transition of Novel Azobenzene‐Functionalized Hydroxypropyl Methylcellulose and Its α‐Cyclodextrin Complexes
Authors: Zheng Peijie , Hu Xiao , Zhao Xiongyan , Li Lin , Tam Kam Chiu , Gan Leong Huat 
Published: March 2004

AbstractSummary: Novel azobenzene‐functionalized hydroxypropyl methylcellulose (AZO‐HPMC) polymers and their α‐cyclodextrin (α‐CD) complexes have been prepared. These polymers show interesting sol‐gel transition behavior in aqueous solutions. In the absence of α‐CD, the gelation temperature increases after UV irradiation, while in the presence of α‐CD, the gelation temperature decreases after UV irradiation. The difference in the gelation temperatures between the trans and cis samples of AZO‐HPMC opens a wide operating window for reversible regulation of the sol‐gel transition behavior by photoirradiation.The UV‐induced cis/trans isomerism of azobenzene‐functionalized hydroxypropyl methylcellulose and its α‐cyclodextrin complexes.imageThe UV‐induced cis/trans isomerism of azobenzene‐functionalized hydroxypropyl methylcellulose and its α‐cyclodextrin complexes.
Thermotropic Liquid‐Crystalline Polymer Derived from Natural Cinnamoyl Biomonomers
Authors: Kaneko Tatsuo , Matsusaki Michiya , Hang Tran Thi , Akashi Mitsuru 
Published: March 2004

AbstractSummary: The compound 4‐hydroxycinnamic acid (4HCA), a natural biomonomer, is polymerized by melt polycondensation to yield a liquid‐crystalline biopolymer (P4HCA) with UV reactivity. L929 cells were successfully incubated on P4HCA films at 37 °C.Structure of poly(4‐hydroxycinnamic acid) (P4HCA) and its crossed‐polarizing optical micrograph in the nematic state. Inset image: optical micrograph of L929 mouse fibroblasts adhered on P4HCA film after 24 h incubation at 37 °C.imageStructure of poly(4‐hydroxycinnamic acid) (P4HCA) and its crossed‐polarizing optical micrograph in the nematic state. Inset image: optical micrograph of L929 mouse fibroblasts adhered on P4HCA film after 24 h incubation at 37 °C.
Preparation of Main‐Chain‐Type Quinolinol Polymers by Organometallic Polycondensation
Authors: Iijima Takayuki , Yamamoto Takakazu 
Published: March 2004

AbstractSummary: New main‐chain‐type polymers of 8‐quinolinol were prepared by organometallic polycondensation. They had a poly(aryleneethynylene)‐type structure and exhibited photoluminescence with a peak at about 470 nm and quantum yields of 21–39%. Metal ions such as Zn2+ and Al3+ modified the photoluminescence.Structure of the three main‐chain‐type polymers of 8‐quinolinol synthesized and studied here.imageStructure of the three main‐chain‐type polymers of 8‐quinolinol synthesized and studied here.
A Tandem Catalytic System for the Synthesis of Ethylene–Hex‐1‐ene Copolymers from Ethylene Stock
Authors: Ye Zhibin , AlObaidi Fahad , Zhu Shiping 
Published: March 2004

AbstractSummary: A tandem catalytic system, composed of (η5‐C5H4CMe2C6H5)TiCl3 (1)/MMAO (modified methyl aluminoxane) and [(η5‐C5Me4)SiMe2(tBuN)]TiCl2 (2)/MMAO, was applied for the synthesis of ethylene–hex‐1‐ene copolymers with ethylene as the only monomer stock. During the reaction, 1/MMAO trimerized ethylene to hex‐1‐ene, while 2/MMAO copolymerized ethylene with the in situ produced hex‐1‐ene to poly(ethylene–hex‐1‐ene). By changing the catalyst ratio and reaction conditions, a series of copolymer grades with different hex‐1‐ene fractions at high purity were effectively produced.The overall strategy of the tandem 1/2/MMAO catalytic system.imageThe overall strategy of the tandem 1/2/MMAO catalytic system.
Suppression of Thermochromism in a Poly(di‐n‐hexylsilane)‐Zirconia Hybrid
Authors: Matsuura Yukihito , Inoue Hiroshi , Matsukawa Kimihiro 
Published: March 2004

AbstractSummary: Poly(di‐n‐hexylsilane) (PDHS)‐containing zirconia hybrid thin films were prepared by a sol‐gel reaction of PDHS copolymers and zirconium alkoxide, and it was found that the thermochromic properties of PDHS due to the transformation of the SiSi main chain were suppressed in the PDHS‐zirconia hybrid thin film.Structure of poly(di‐n‐hexylsilane)‐zirconia hybrid.imageStructure of poly(di‐n‐hexylsilane)‐zirconia hybrid.
Smectic A Elastomers with Uniform Homeotropic Orientation Obtained by Applying a Biaxial Mechanical Field
Authors: Nishikawa Etsushi , Yamamoto Jun , Yokoyama Hiroshi , Finkelmann Heino 
Published: March 2004

AbstractSummary: The orientation behavior of a smectic A elastomer is investigated by applying a biaxial mechanical field to the elastomer in a swollen state. The network is composed of a siloxane‐polymer backbone, a bi‐functional cross‐linker, and a monomer with a perfluorinated tail. In this work, biaxial deformation is successfully achieved to macroscopically orient the smectic A phase in a uniform, homeotropic fashion. We describe the orientation process in detail and discuss the microstructure of the smectic A phase organized in the monomer, the linear polymer, and the elastomer determined by using X‐ray diffraction data.A photograph of the oriented smectic A elastomer E4F (above) and a schematic model of its homeotropic orientation (below).imageA photograph of the oriented smectic A elastomer E4F (above) and a schematic model of its homeotropic orientation (below).
Double Yielding in a Styrene/Butadiene Star Block Copolymer
Authors: Adhikari Rameshwar , Buschnakowski Matthias , Henning Sven , Goerlitz Sylvia , Huy Trinh An , Lebek Werner , Godehardt Reinhold , Michler Georg Hannes , Lach Ralf , Geiger Kalman , Knoll Konrad 
Published: March 2004

AbstractSummary:The morphology and tensile deformation behaviour of a highly asymmetric styrene/butadiene star block copolymer (polystyrene (PS) content = 74%) containing random PS‐co‐PB (polybutadiene) copolymer as a rubbery phase were investigated. The existence of double yielding, similar to that observed in some semicrystalline polymers, was detected in this nanostructured amorphous polymer. The observed phenomenon may be correlated with two different micromechanical processes taking place at the initial stage of deformation.The stress‐strain curve of the star block copolymer prepared here (each curve represents a different method). The two yield points are clearly visible (labelled I and II).imageThe stress‐strain curve of the star block copolymer prepared here (each curve represents a different method). The two yield points are clearly visible (labelled I and II).
Polymeric Semiconductors with a Pre‐Specified Alternation of Conjugated Bonds and Metal Clusters
Authors: Tsetlin Boris L. , Golubev Vladimir N. , Vlasov Alexandr V. , Khokhlov Alexei R. , Vannikov Anatoly V. , Tameev Alek R. 
Published: March 2004

AbstractSummary:In this work the first samples of polymeric semiconductors of a new structure are produced. Their electric conductivity is of the order ∼10−2Ohm−1 · cm−1and it increases with temperature. Their synthesis includes a stage of radiation grafting of a matrix‐type on stretched polyamide films. Conducting molecular circuits in such materials include fragments with conjugated bonds and metal clusters. The alternation of these fragments is determined by the polyamide matrix.Plot of voltage versus current determined for new polymer semiconducting films where fragments with conjugated bonds alternate with silver clusters.imagePlot of voltage versus current determined for new polymer semiconducting films where fragments with conjugated bonds alternate with silver clusters.
Atom Transfer Radical Polymerization of N,N‐Dimethylacrylamide
Authors: Ding Shijie , Radosz Maciej , Shen Youqing 
Published: March 2004

AbstractSummary: The living polymerization of N,N‐dimethylacrylamide was achieved by atom transfer radical polymerization catalyzed by copper chloride complexed with a new ligand, N,N′‐bis(pyridin‐2‐ylmethyl 3‐hexoxo‐3‐oxopropyl)ethane‐1,2‐diamine (BPED). With methyl 2‐chloropropionate as the initiator, the polymerization reached high conversions (> 90%) at 80 °C and 100 °C, producing polymers with $\overline M _{\rm n}$ very close to theoretical values and low polydispersity. The ligand, temperature, and copper halide strongly affected the activity and control of the polymerization.PDMA molecular weight and polydispersity dependence on the DMA conversion in the DMA bulk polymerizations at different temperatures: DMA/CuCl/MCP/BPED = 100/1/1/1, 100 °C (♦, ⋄); 80 °C (▴, ▵); 60 °C (▪, □); and DMA/CuCl/MCP/BPED = 100/1/1/2, 80 °C (•, ○).imagePDMA molecular weight and polydispersity dependence on the DMA conversion in the DMA bulk polymerizations at different temperatures: DMA/CuCl/MCP/BPED = 100/1/1/1, 100 °C (♦, ⋄); 80 °C (▴, ▵); 60 °C (▪, □); and DMA/CuCl/MCP/BPED = 100/1/1/2, 80 °C (•, ○).
Cover Picture: Macromol. Rapid Commun. 5/2004
Authors: Nishikawa Etsushi , Yamamoto Jun , Yokoyama Hiroshi , Finkelmann Heino 
Published: March 2004

Cover: The picture displays the X‐ray pattern of a highly ordered smectic A Liquid Single Crystal Elastomer (LSCE). The higher order reflexes indicate a nearly solidlike state of order.Further details can be found in the Communication by E. Nishikawa, J. Yamamoto, H. Yokoyama, and H. Finkelmann* on page 611.
Chiral discrimination studies of (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid by high‐performance liquid chromatography and NMR spectroscopy
Authors: Lee Wonjae , Bang Eunjung , Baek Chae‐Sun , Lee Weontae 
Published: March 2004

AbstractChiral discrimination studies using (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid (18‐C‐6‐TA) as a chiral selector were performed by high‐performance liquid chromatography (HPLC) and NMR spectroscopy. The enantiomers of alanine (Ala) or alanine methyl ester (Ala‐ME) were well separated on the chiral stationary phases (CSPs) derived from (+)‐18‐C‐6‐TA by HPLC. The chiral selector, (+)‐18‐C‐6‐TA, used in the CSP was also applied for the chiral discrimination of the Ala and Ala‐ME enantiomers, and it discriminated these enantiomers successfully by NMR spectroscopy. The chemical shift differences (Δ Δ δ) of the α‐proton of these enantiomers in the presence of an equimolecular solution of 18‐C‐6‐TA were observed to be 0.10 ppm for Ala in methanol‐d4 containing 10 mM H2SO4 and 0.11 ppm for Ala‐ME in methanol‐d4. The observed NMR results agreed with the chromatographic data on the (+)‐18‐C‐6‐TA‐derived CSP by HPLC in terms of both the elution order and solvents effects. Copyright © 2004 John Wiley & Sons, Ltd.
47, 49Ti NMR spectra of half‐sandwich titanium(IV) complexes
Authors: Erben Milan , Růžička Aleš , Picka Michal , Pavlík Ivan 
Published: March 2004

AbstractThe 47, 49Ti chemical shifts, resonance line half‐widths (Δν1/2) and energies of the first electronic charge‐transfer transitions $(\lambda_{\max}^{\rm 1.CT})$ of Cp′TiX3, where Cp′ = η5‐C5H5 (Cp), η5‐C5H4Me (MeCp), η5‐C5HMe4 (Me4Cp), η5‐C5Me5 (Me5Cp), η5‐C5H4SiMe3 (SiCp), η5‐C5H4SnMe3 (SnCp) and η5‐C5H4SiMe2Cl (Si′Cp) and X = Cl, Br, I and OBut, half‐sandwich complexes are reported. For the compounds studied, a direct linear relationship between δ(49Ti) and $\lambda_{\max}^{\rm 1.CT}$ was found. Copyright © 2004 John Wiley & Sons, Ltd.
Structure elucidation of 11‐amino‐8‐hydroxypentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane‐8,11‐lactam through selective acetylation and complete 1H and 13C NMR spectral assignment of the mono‐, di‐ and triacetates
Authors: Martins F. J. C. , Viljoen A. M. , Kruger H. G. , Wessels P. L. 
Published: March 2004

AbstractNMR techniques cannot unambiguously distinguish between 11‐amino‐8‐hydroxypentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane‐8,11‐lactam and 8‐amino‐11‐hydroxypentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane‐8,11‐lactam, both of which are possible products during the reaction of pentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane‐8,11‐dione with Strecker reagents. Treatment of 11‐amino‐8‐hydroxy‐pentacyclo[5.4.0.02, 6.03, 10.05, 9]undecane‐8,11‐lactam with acetic anhydride at room temperature produced a monoacetate. With acetic anhydride containing sodium acetate, a triacetate was obtained at reflux temperature. Treatment with acetyl chloride and N,N‐dimethylaniline produced a diacetate. High‐field 1H and 13C NMR techniques were used in the structure elucidation and assignment of the different NMR resonances of these three acetylated compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Phosphorylated amino acids: model compounds for solid‐state 31P NMR spectroscopic studies of proteins
Authors: Iuga Adriana , Brunner Eike 
Published: March 2004

AbstractSolid‐state 31P NMR spectroscopy was applied to measure the isotropic chemical shifts, chemical shift anisotropies and asymmetry parameters of three phosphorylated amino acids, O‐phospho‐L‐serine, O‐phospho‐L‐threonine and O‐phospho‐L‐tyrosine. The cross‐polarization buildup rates and longitudinal relaxation times of 31P and 1H were‐determined and compared with the values measured for a triphosphate (GppCH2p) bound to a crystalline protein (Ras). It is shown that the phosphorylated amino acids are well‐suited model compounds, e.g. for the optimization of experiments on crystalline proteins. Two‐dimensional exchange experiments on O‐phospho‐L‐tyrosine indicate the existence of an exchange between the two different conformations of the molecule. Copyright © 2004 John Wiley & Sons, Ltd.
Evidence of a phase transition of RbHCO3 from high‐resolution solid‐state 13C and 87Rb NMR by comparison with KHCO3
Authors: Odin Christophe 
Published: March 2004

AbstractA variable‐temperature high‐resolution 13C and 87Rb solid‐state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low‐temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non‐ferroic, non‐ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double‐well potential in the low‐temperature phase, and the double‐well potential becomes symmetric in the high‐temperature phase. By comparison with recent solid‐state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc ≈ 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar. Copyright © 2004 John Wiley & Sons, Ltd.
Assignment of 13C resonances of a nematic liquid crystal using off‐magic angle spinning
Authors: Vinay Deepak H. S. , Joy Anu , Suryaprakash N. , Ramanathan K. V. 
Published: March 2004

AbstractA novel method for assigning the resonances in the 13C NMR spectrum of a static liquid crystalline sample in its nematic phase is proposed. The method is based on the fact that the carbon chemical shifts in the isotropic phase and in the oriented phase under static and off‐magic angle spinning (OMAS) conditions are uniquely related by the tensorial property of the CSA tensor, requiring just one OMAS spectrum and the assignment in the isotropic phase. A computational procedure is proposed to take into account deviations arising out of non‐ideal experimental conditions and the assignments are made by identifying the minimum in the differences in the frequencies between calculated and experimental line positions. Practical implementation of the method has also been demonstrated in the case of the liquid crystal N‐(4‐ethoxybenzylidene)‐4‐n‐butylaniline. Copyright © 2004 John Wiley & Sons, Ltd.
Is high‐resolution magic angle spinning NMR a practical speciation tool for cheese samples? Parmigiano Reggiano as a case study
Authors: Shintu Laetitia , Ziarelli Fabio , Caldarelli Stefano 
Published: March 2004

AbstractHigh‐resolution magic angle spinning (HRMAS) NMR is probably the most apt NMR method to analyze complex materials involving a solid phase, e.g. foodstuffs. We present here an HRMAS analysis of grated cheese (Parmigiano Reggiano). A full NMR characterization of this cheese allows the identification of the presence of fatty acids (saturated and unsaturated), amino acids and other small organic molecules. Since the presence and relative concentration of these molecules have previously been shown to correlate with organoleptic, origin and age characterization, HRMAS NMR of cheese is likely to provide a good complimentary tool for the analysis of this food material. Copyright © 2004 John Wiley & Sons, Ltd.
Structural elucidation by 1D and 2D NMR of three isomers of a carotenoid lysophosphocholine and its synthetic precursors
Authors: Foss Bente Jeanette , Krane Jostein 
Published: March 2004

AbstractA carotenoic acid was used to obtain a long‐chain unsaturated lysophosphocholine. The carotenoid lysophosphocholine was synthesized by two methods. The first method resulted in mixtures of regioisomers for each step in the synthetic route. Homo‐ and heteronuclear 1D and 2D NMR methods were employed to elucidate the structures of the individual isomers and their intermediates. The pure regioisomer [1‐(β‐apo‐8′‐carotenoyl)‐2‐lyso‐glycero‐3‐phosphocholine] was obtained by a second method, but in low yield. The 1D 1H NMR subtraction spectrum of the mixture and the pure regioisomer was used to interpret the 1H shifts of the unsaturated acyl moieties. The 1H and 13C signals of the acyl chain show characteristic shifts depending on the positions of the choline and the acyl group attached to the glycerol backbone. Therefore, the unsaturated acyl chain signals have diagnostic values for the identification of isomers of unsaturated (lyso)phosphocholines. Chemical shifts and indirect coupling constants are reported for each of the major components of the mixtures. The methods used were 1D (1H, 13C and 31P) and 2D (H,H‐COSY, HMBC, HSQC and HETCOR) NMR. Copyright © 2004 John Wiley & Sons, Ltd.
Design of adaptive controllers using partial certainty equivalence principle
Authors: Filatov N.M. 
Published: March 2004

AbstractOptimal stochastic control problem for general non‐linear dynamic system with unknown parameters is considered. An approximative assumption, which has been named partial certainty equivalence (PCE) principle, is suggested for design of adaptive controllers of non‐linear and linear stochastic systems. For derivation of a suboptimal controller with the PCE principle the certainty equivalence (CE) assumption is used only for the part of the system states and unknown parameters. The PCE control policy has a simple form for linear systems with unknown parameters. It is suggested in the present paper to design adaptive dual control using the PCE assumption and bicriterial optimization to derive the adaptive controller with the optimal persistent excitation. Simulated examples are used to demonstrate the potential of the suggested method and its superiority over the generally used CE‐controllers. Copyright © 2004 John Wiley & Sons, Ltd.
Optimal exploitation of renewable resource stocks: necessary conditions
Authors: Baumeister J. , Leitão A. 
Published: March 2004

AbstractWe study a model for the exploitation of renewable stocks developed in Clark et al. (Econometrica 1979; 47:25–47). In this particular control problem, the control law contains a measurable and an impulsive control component. We formulate Pontryagin's maximum principle for this kind of control problems, proving first‐order necessary conditions of optimality. Manipulating the correspondent Lagrange multipliers we are able to define two special switch functions, that allow us to describe the optimal trajectories and control policies nearly completely for all possible initial conditions in the phase plane. Copyright © 2004 John Wiley & Sons, Ltd.