bluuebunny/crossref_metadata_2025_split huggingface dataset:
Redox Materials by the Covalent Entrapment of Redox‐Active Dirhodium(II,II) Species in a Siloxane Network
Authors: Lo Schiavo Sandra , Forte Claudia , Pignataro Bruno , Tresoldi Giuseppe , Piraino Pasquale 
Published: May 2004

AbstractSummary: Hydrolysis and polycondensation of the coupling agent (aminopropyl)triethoxysilane (APS), axially coordinated to the redox‐active complex [Rh2(form)2(CH3COO)2(APS)2], lead to the insertion of redox‐active inorganic microdomains into a siloxane network; the new polymers undergo cyclic redox reactions indicating that dirhodium(II,II) centres retain their redox activity even when incorporated into siloxane networks.The redox‐active complex [Rh2(form)2(CH3COO)2(APS)2] (form = N,N′‐di‐p‐tolylformamidinate) incorporated into a siloxane network here.magnified imageThe redox‐active complex [Rh2(form)2(CH3COO)2(APS)2] (form = N,N′‐di‐p‐tolylformamidinate) incorporated into a siloxane network here.
Synthesis and Properties of a Novel Thiophene‐Based Conducting Copolymer with Mesogenic Groups Attached Parallel to the Polymer Backbone
Authors: Brown John W. , Lambe Gillian J. , Foot Peter J. S. , Clipson Jacqueline A. 
Published: May 2004

AbstractSummary: A novel thiophene‐based conducting copolymer has been synthesised with mesogenic groups attached parallel to the conducting polymer backbone; preliminary data are reported on its properties. These indicate that as the nonmesogenic intermediate polymer is converted into a liquid‐crystalline polymer there is a significant increase in conductivity. Measurement of the temperature‐dependent conductivity indicates a reduction of the activation energy in the liquid‐crystalline phase.Poly[(1‐(thiophene‐3‐methyloxy)‐6‐(4‐n‐hexyloxy‐2‐oxybenzoic acid)hexane)‐co‐(3‐n‐hexylthiophene)].magnified imagePoly[(1‐(thiophene‐3‐methyloxy)‐6‐(4‐n‐hexyloxy‐2‐oxybenzoic acid)hexane)‐co‐(3‐n‐hexylthiophene)].
Copolymerization of Propene and Buta‐1,3‐diene in the Presence of Highly HinderedC2‐Symmetric Zirconocene‐Based Catalyst
Authors: Pragliola Stefania , Costabile Chiara , Di Bartolomeo Francesca , Longo Pasquale 
Published: May 2004

AbstractSummary:Copolymerizations of propene and buta‐1,3‐diene performed in the presence ofrac‐[CH2(3‐tert‐butyl‐1‐indenyl)2]ZrCl2and methylaluminoxane (MAO) have been investigated. Buta‐1,3‐diene gives prevailingly primary coordination to the metal, producing overall 1,2 units. Cyclopropane and cyclopentane rings, although in low amounts, are also obtained. The presence of butadiene would be responsible for some regioirregular 2,1‐inserted propene units, which at high temperatures give rearrangement to 3,1 units.magnified image
MAO‐Free Activation of Metallocenes and other Single‐Site Catalysts for Ethylene Polymerization using Spherical Supports based on MgCl2
Authors: Severn John R. , Chadwick John C. 
Published: May 2004

AbstractSummary: Supports of type MgCl2/AlRn(OEt)3−n, obtained by reaction of AlR3 with adducts of MgCl2 and ethanol, have been shown to be effective for the immobilization and activation of [Cp2TiCl2] and other single‐site olefin polymerization catalysts without the use of methylaluminoxane or a borate activator. Polyethylene with a spherical particle morphology and narrow molecular weight distribution was obtained.magnified image
Synthesis and properties in solution of rodlike polyelectrolytes
Authors: Ballauff Matthias , Blaul Jürgen , Guilleaume Birgit , Rehahn Matthias , Traser Steffen , Wittemann Matthias , Wittmeyer Patrick 
Published: May 2004

AbstractEfficient synthetic strategies are described for the preparation of rodlike polyelectrolytes based on the intrinsically rigid poly(p‐phenylene). Uncharged precursors were first prepared via the Suzuki coupling and then characterized by different methods of polymer analysis. Finally, they were transformed into polyelectrolytes using macromolecular substitution reactions. Depending on the substitution pattern, the obtained polyelectrolytes are either soluble or insoluble in water. Using water‐soluble derivatives, the Poisson‐Boltzmann cell model was tested by osmotic measurements and small‐angle X‐ray scattering. It is shown that the cell model provides a good first approximation of the distribution of the counterions around the macroion but still underestimates their correlation. Moreover, the PPP polyelectrolytes show a very pronounced polyelectrolyte effect. Since the rodlike PPPs are very rigid in shape, this observation proves that the polyelectrolyte effect is caused by long‐range intermolecular electrostatic repulsion of the dissolved macroions rather than due to conformational changes.
Particle scattering factor of pearl necklace chains
Authors: Schweins Ralf , Huber Klaus 
Published: May 2004

AbstractThe particle scattering behaviour of a pearl necklace chain is derived. The chain is composed of sphere‐like pearls, separated by rod‐like segments of fixed length, which have no angular restrictions. By calculating several series of model scattering curves, the important structural features are retrieved. The model is believed to be useful in interpreting intermediate structures of collapsing macromolecules or polyelectrolytes. A first application to a shrinking polyelectrolyte coil generated by molecular dynamic simulations (Limbach and Holm, J.Phys.Chem. 2003) is presented and used to discuss the potentials and limits of the model.
Conformations and solution structure of polyelectrolytes in poor solvent
Authors: Limbach Hans Jörg , Holm Christian , Kremer Kurt 
Published: May 2004

AbstractUsing extensive Molecular Dynamics (MD) simulations we study the behavior of polyelectrolytes in poor solvents, where we take explicitely care of the counterions. The resulting pearl‐necklace structures are subject to strong conformational fluctuations, only leading to small signatures in the form factor, which is a severe obstacle for experimental observations. In addition we study how the necklace collapses as a function of Bjerrum length. At last we demonstrate that the position of the first peak in the inter‐chain structure factor varies with the monomer density close to $&#x003C1;^{1/3}_{m}$ for all densities. This is in strong contrast to polyelectrolyte solutions in good solvent.
Counterion mobility and effective charge of polyelectrolytes in solution
Authors: Böhme Ute , Scheler Ulrich 
Published: May 2004

AbstractPolyelectrolytes are macromolecules containing dissociable or charged groups. The charge, that is effectively accessible, is determined by counterion condensation, which is strongly influenced by the ionic strength of the solution under study. In general a rapid exchange between free and condensed counterions is expected. In the present study diffusion and electrophoretic mobility of poly(diallyldimethylammoniumchloride) and perfluorinated succinic acid have been monitored simultaneously. Condensation of the perfluorinated succinic acid to the macroion shows in the electrophoretic mobility of succinic acid monitored by pulsed field gradient NMR. In the concentration dependence of the averaged diffusion coefficient and electrophoretic mobility an exchange fast on the time scale of the NMR experiment is manifested.
Poly(styrene sulfonate) self‐organization: electrostatic and secondary interactions
Authors: Ahrens H. , Büscher K. , Eck D. , Förster S. , Luap C. , Papastavrou G. , Schmitt J. , Steitz R. , Helm C.A. 
Published: May 2004

AbstractWe investigate the self‐organization of PSS in brushes and polyelectrolyte multilayers with X‐ray, neutron and optical reflectivity. The electrostatic force dominates brush phases and adsorption behavior, additionally we find evidence of a strong hydrophobic force: (ι) within amphiphilic diblock copolymer monolayers, a PSS monolayer adsorbs flatly to the hydrophobic block, (ιι) on temperature increase (and with screened electrostatic forces), more PSS is adsorbed onto oppositely charged surfaces, and (ιιι) a polyelectrolyte multilayers shrinks when heated at 100% r.h. The latter two effects are consistent with the well‐known increase of the hydrophobic force on heating: The increased PSS surface coverage can be attributed to deteriorating solvent conditions. Within a polyelectrolyte multilayer, an increase of the hydrophobic force maximizes the local contact of hydrophobic polymer segments, causing a reduction of swelling and an increased mass density.
Charge density, solvent polarity and counterion nature effects on the solution properties of some polycations
Authors: Dragan Stela , Ghimici Luminita , Wandrey Christine 
Published: May 2004

AbstractThe electrolytic conductivity and solution viscosity of some strong polycations, which possess the ammonium quaternary centers either attached to an acrylic macromolecular chain (polycation PDMAEMQ type), or in the backbone (polycation PCA type), have been measured in order to identify how charge density, polyelectrolyte concentration, solvent polarity as well as counterion nature influence the ultimate solution properties. The investigations reveal for all polycations an increase of the equivalent conductivity with decreasing concentration. The onset of the strong increase shifts to lower concentration if the charge density augments. Polyelectrolyte behavior was observed for PCA5D1 in the mixture of water/methanol for all solvent compositions employed and in the mixture of water/acetone up to 60 vol% of acetone content. At all experimental concentrations the reduced viscosity decreases with the dielectric constant of the mixed solvent. Furthermore, the specific interaction between several mono‐ and divalent counterions with some of these polycations was clearly proved by conductometric measurements.
Self‐assembly in ternary systems: cross‐linked polyelectrolyte, linear polyelectrolyte and surfactant
Authors: Zezin Alexander B. , Rogacheva Valentina B. , Novoskoltseva Olga A. , Kabanov Victor A. 
Published: May 2004

AbstractThe competitive interactions in ternary systems consisting of a slightly cross‐linked polyelectrolyte hydrogel and the mixture of linear polyelectrolyte and micelle forming surfactant both oppositely charged relative to the polyelectrolyte network were studied. It was shown that the equilibrium in the competitive reactions depends on the linear polyion charge density and the length of the surfactant aliphatic radical. Dependency on these characteristics the interpolyelectrolyte complex formed by cross‐linked and linear polyelectrolytes can uptake surfactant ions from water solution transforming into the cross‐linked polyelectrolyte‐surfactant complex and releasing the linear polyelectrolyte or vice versa. The ternary systems of this kind are perspective to design the novel family of delivery constructs.
Polyelectrolytes on block copolymer surfaces
Authors: Brehmer Martin , Funk Lutz , Conrad Lars , Allard Dirk , Theato Patrick 
Published: May 2004

AbstractSoft lithography and properties of amphiphilic block copolymers are combined in a new technique for the generation of patterned substrates, which can be used in different ways as templates for further processing. In these processing steps the deposition of polyelectrolytes, metals and grafting from polymerizations are used for the construction of different structures.
Comparison of polyelectrolyte multilayers built up with polydiallyldimethylammonium chloride and poly(ethyleneimine) from salt‐free solutions by in‐situ surface plasmon resonance measurements
Authors: Schwarz Simona , Nagel Jürgen , Jaeger Werner 
Published: May 2004

AbstractPolyelectrolytes offer a widespread potential for the defined modification of planar inorganic or polymer surfaces. Essential parameters for the regular adsorption of subsequent polymer layers by electrostatic interactions are the charge of polyelectrolyte and of the outermost surface region, the surface of the substrate, and the molar mass of the polyelectrolyte.To study such effects in mono‐ and multilayers we used poly(diallyldimethylammonium chloride (PD) with a molar mass from 5000 to 400000 g/mol as a strong polycation and poly(ethyleneimine) (PEI) with 75000 g/mol as a weak polycation and poly(sodium styrenesulfonate) (PSS) from 70000 to 1Mio g/mol in the diluted and semi‐diluted region.The characterization of the layers was performed by streaming potential, in‐situ SPR and UV‐Vis spectroscopy. Thereby the layer built up at the solid/liquid‐interface could be followed and quantified at the molecular level. SPR revealed that the thicknesses of the multilayer depends strongly on pK values of the polyelectrolyte (strong or weak) and the molar masses. We observed a linear growth if both polyelectrolytes are strong and an exponential growth if one polyelectrolyte is weak. The thickness increased with higher molar masses of the polyelectrolytes. The process was followed in‐situ in short time steps.
Multilayers consisting of oriented charged α‐helical polypeptides
Authors: Müller Martin , Reihs Thomas , Kessler Bernd , Adler Hans‐Jürgen , Lunkwitz Klaus 
Published: May 2004

AbstractPolyelectrolyte Multilayers (PEMs) consisting of cationic α‐helical poly(L‐lysine) (PLL) and optionally anionic poly(vinysulfate) (PVS) (i) or α‐helical poly(L‐glutamic acid) (PLG) (ii) were deposited at substrates texturized by parallel nanoscopic surface grooves, respectively. Using dichroic Attenuated Total Reflexion Fourier Transform Infrared (ATR‐FTIR) spectroscopy the consecutive deposition, conformation and macromolecular order of stiff polyelectrolytes within PEMs were studied. From the dichroic ratios of the Amide I and Amide II bands order parameters S ⩾ 0.6 (S = 1 for high, S = 0 for low order) were obtained suggesting a significant alignment of charged α‐helical polypeptides in PEMs. For the PEM consisting of PLL/PVS the deposited amount as well as the order parameter S significantly depended on the molecular weight (contour length) of PLL. Furthermore, the related opening angle γ of a model cone consisting of α‐helical PLL rods was proven to be a function of both contour length and width of the confining surface grooves. AFM pictures on PEM‐PLL/PVS showed anisotropically oriented worm‐like structures As a second system PEMs of PLL and PLG, both in the α‐helical conformation, are introduced. A high order parameter of both spectroscopically indistinguishable polypeptides was found. A model of aligned rod/coil (i) and rod/rod (ii) structures was proposed. Finally, multilayers of stiff conductive polymers like polyaniline (PANI) alternating with poly(acrylic acid) (PAC) are introduced. Preliminary results on their deposition and alignment are given.
The infinitesimal rigid displacement lemma in Lipschitz co‐ordinates and application to shells with minimal regularity
Authors: Anicic Sylvia , Dret Hervé Le , Raoult Annie 
Published: May 2004

AbstractWe establish a version of the infinitesimal rigid displacement lemma in curvilinear Lipschitz co‐ordinates. We give an application to linearly elastic shells whose midsurface and normal vector are both Lipschitz. Copyright © 2004 John Wiley Sons, Ltd.
An operator approach for an oblique derivative boundary‐transmission problem
Authors: Castro L. P. , Santos A. Moura 
Published: May 2004

AbstractWe consider a boundary‐transmission problem for the Helmholtz equation, in a Bessel potential space setting, which arises within the context of wave diffraction theory. The boundary under consideration consists of a strip, and certain conditions are assumed on it in the form of oblique derivatives. Operator theoretical methods are used to deal with the problem and, as a consequence, several convolution type operators are constructed and associated to the problem. At the end, the well‐posedness of the problem is shown for a range of non‐critical regularity orders of the Bessel potential spaces, which include the finite energy norm space. In addition, an operator normalization method is applied to the critical orders case. Copyright © 2004 John Wiley & Sons, Ltd.
Structural assignment of regioisomeric 3‐[2‐ or 5‐anilino‐2‐(alkylamino)phenyl]propanoic acids, 2H‐1,4‐benzothiazin‐3(4H)‐ones and 2,3‐dihydro‐1,5‐benzothiazepin‐4(5H)‐ones by 1D NOE and gHMBC NMR techniques
Authors: Katritzky Alan R. , Akhmedov Novruz G. , Wang Mingyi , Rostek Charles J. , Steel Peter J. 
Published: May 2004

AbstractThe 1H and 13C NMR spectra of compounds 1–11 and 16–22 in CDCl3 and DMSO‐d6 solutions allowed structural assignment to regioisomers 1/5 and 2/6 and their regioselective cyclization products 16–18 utilizing one‐ and two‐dimensional NMR techniques (APT, DEPT, NOE difference, COSY, NOESY, HETCOR and gHMQC, gHMBC). Temperature‐dependent 1H NMR spectra of 8‐anilino‐5‐(4‐methyl‐2‐pentyl)‐2,3‐dihydro‐1,5‐benzothiazepin‐4(5H)‐one (18) indicated a free energy of activation (ΔG‡) of ca 17 kcal mol−1 for interconversion between rotamers. The 1H and 13C NMR spectra of 20 and 22 containing two chiral centers exhibit duplication of several signals, indicating the existence of two diastereomeric forms. The structure of 4 was unambiguously confirmed by x‐ray crystallography. Copyright © 2004 John Wiley & Sons, Ltd.
Acceleration of carbon‐13 spin–lattice relaxation times in amino acids by electrolytes
Authors: Tian Jinping , Yin Yingwu 
Published: May 2004

AbstractMeasurements of the enhancement, by various electrolytes, of the spin–lattice relaxation time of carbon‐13 at different locations in a number of amino acids are reported. Spin–lattice relaxation times T1 of all the carbons in amino acids generally tend to decrease with increase in the concentration of electrolytes, the largest effects often being observed for the charged carboxylate groups of the amino acids. Carboxylic carbons in amino acids are the sensitive ‘acceptor’ of the 13C spin–lattice relaxation accelerating effects offered by electrolytes, and the 13C spin–lattice relaxation accelerating ability of electrolytes decreases in the order Mg(ClO4)2 > MgCl2 > CaCl2 > NaCl > KCl > LiClO4 > NaOH. The mechanisms of the observed phenomena are discussed in terms of intermolecular interaction, paramagnetic impurities in electrolytes and other mechanisms; large contributions of intermolecular interactions with electrolytes are present on complex formation between amino acids and metal ions and the incoming ‘unsaturation’ of the primary solvation shell of cations with the increase in electrolyte concentration. Copyright © 2004 John Wiley & Sons, Ltd.
1H and13C NMR spectral assignments and conformational analysis of 14 19‐nor‐neoclerodane diterpenoids
Authors: Rodríguez Benjamín , Jimeno María L. 
Published: May 2004

AbstractUnambiguous and complete assignments of1H and13C NMR chemical shifts for 14 19‐nor‐neoclerodane diterpenoids, nine of them isolated from natural sources and five other synthetic derivatives, are presented. The assignments are based on 2D shift‐correlated (1H,1H‐COSY,1H,13C‐gHSQC and1H,13C‐gHMBC) and NOE experiments. The conformations of rings A and B of these compounds are supported by the3J(H,H) values and they agree with the low‐energy conformations obtained by semi‐empirical calculations. Moreover, the data obtained in this work for 2‐acetoxyteucvidin and a semisynthetic 18‐aldehyde derivative indicate that the configuration at C‐2 of the former and at C‐10 of the latter must be reversed with respect to those reported previously. Copyright © 2004 John Wiley & Sons, Ltd.
Reorientational dynamics of p‐sulfonatocalix[4]arene and of its La(III) complex in water
Authors: Israëli Yaël , Facey Glenn A. , Detellier Christian 
Published: May 2004

AbstractThe reorientational dynamics of p‐sulfonatocalix[4]arene and of its La(III) complex in deuterated water were studied by 1H NMR longitudinal relaxation rates. It is shown that the relaxation is purely dipolar in the non‐extreme narrowing regime. The distance between the geminal protons could be determined from the NMR data, giving good agreement with the values generally used in correlation time calculations. The correlation times show an Arrhenius behaviour in good agreement with previously reported data from 13C measurements for a similar uncomplexed calixarene. The Arrhenius energies of activation are identical for the uncomplexed and the complexed calixarenes, suggesting a reorientational motion strongly dependent on the structure of the water cage around the complex. This is also in agreement with a complexation of the La(III) cation in the second sphere of solvation of the sulfonate groups, as shown by molecular dynamics simulations. Copyright © 2004 John Wiley & Sons, Ltd.
Adducts of Rh2[MTPA]4 with some phosphine chalcogenides: nature of binding and ligand exchange
Authors: Gáti Tamás , Simon András , Tóth Gábor , Magiera Damian , Moeller Stefan , Duddeck Helmut 
Published: May 2004

AbstractAdducts of four phosphine chalcogenides with the chiral dirhodium complex ([RhRh]) were investigated by variable‐temperature 1H and 31P NMR spectroscopy in order to compare their properties as axial ligands. Whereas the selenide (1) and the sulfide (2) are strong ligands with electrostatic attration and, in addition, a significant orbital (HOMO–LUMO) interaction, the phosphine oxide compounds (PO) bind primarily via electrostatic attraction and are relatively weak donors. Moreover, the overall bond strength in these adducts depends on steric congestion around the PO group. Copyright © 2004 John Wiley & Sons, Ltd.
Conformation analysis and molecular mobility of ethylene and tetrafluoroethylene copolymer using solid‐state 19F MAS and 1H → 19F CP/MAS NMR spectroscopy
Authors: Aimi Keitaro , Ando Shinji 
Published: May 2004

AbstractThe changes in the conformation and molecular mobility accompanied by a phase transition in the crystalline domain were analyzed for ethylene (E) and tetrafluoroethylene (TFE) copolymer, ETFE, using variable‐temperature (VT) solid‐state 19F magic angle spinning (MAS) and 1H → 19F cross‐polarization (CP)/MAS NMR spectroscopy. The shifts of the signals for fluorines in TFE units to higher frequency and the continuing decrease and increase in the T1ρF values suggest that conformational exchange motions exist in the crystalline domain between 42 and 145 °C. Quantum chemical calculations of magnetic shielding constants showed that the high‐frequency shift of TFE units should be induced by trans to gauche conformational changes at the CH2CF2 linkage in the E–TFE unit. Although the 19F signals of the crystalline domain are substantially overlapped with those of the amorphous domain at ambient probe temperature (68 °C), they were successfully distinguished by using the dipolar filter and spin‐lock pulse sequences at 145 °C. The dipolar coupling constants for the crystalline domain, which can be estimated by fitting the dipolar oscillation behaviors in the 1H → 19F CP curve, showed a significant decrease with increasing temperature from 42 to 145 °C. This is due to the averaging of 1H19F dipolar interactions originating from the molecular motion in the crystalline domain. The increase in molecular mobility in the crystalline domain was clearly shown by VT T1ρF and 1H → 19F CP measurements in the phase transition temperature range. Copyright © 2004 John Wiley & Sons, Ltd.
NMR characterization of new 10‐membered‐ring macrolactones and dihydrobenzophenazine‐5‐one, oxidized derivatives of benzo[a]phenazines
Authors: Goulart Marília O. F. , Machado Reys José Rui , Emery Flavio S. , Pinto Antônio V. , de Souza Filho José Dias 
Published: May 2004

AbstractPeroxidation of the phenazine of β‐lapachone using m‐ClC6H4CO3HCH2Cl2 furnished a macrolactone with a rigid 10‐membered ring, and the corresponding N‐oxide, along with a dihydrobenzophenazine‐5‐one. All of the new compounds were fully characterized by spectroscopic methods, with the unambiguous assignment of the hydrogens and carbon NMR signals for the N‐oxide, with the aid of 2‐D NMR, mainly COSY, HMQC, HSQC and HMBC. For the other two compounds some signals could not be assigned owing to their own intrinsic features. Copyright © 2004 John Wiley & Sons, Ltd.