bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compositional variability of ice‐rafted debris in Heinrich layers 1 and 2 on the northwest European continental slope identified by environmental magnetic analyses
Authors: Walden John , Wadsworth Emilie , Austin William E. N. , Peters Clare , Scourse James D. , Hall Ian R. 
Published: July 2006

AbstractThe composition of ice‐rafted debris (IRD) within a sediment core from the European continental slope (core OMEX‐2K; 49° 5′ N, 13° 26′ W) has been examined using environmental magnetic analyses. The data demonstrate compositional variability of the IRD within Heinrich layers 2 (H2) and 1 (H1) and these differences are most readily explained by changes in the contribution of different IRD sources to the core site. Some IRD within the main Heinrich layers show magnetic signatures that are similar to IRD derived from the Laurentide ice sheet found in cores from within the main North Atlantic IRD‐belt. In contrast, other IRD‐rich layers, both prior to and within the main Heinrich layers, demonstrate different magnetic behaviour, suggesting a contribution from a non‐Laurentide sourced IRD, most likely derived from ice streams discharging from northeast Atlantic ice sheets such as the British and Fennoscandian ice sheets. These data are consistent with published compositional data from the same core and, given the rapid, highly sensitive and non‐destructive nature of the method, suggest that environmental magnetic analysis has considerable potential for characterising IRD materials within Heinrich layers for the purposes of defining provenance. Copyright © 2006 John Wiley & Sons, Ltd.
Synthesis of 3‐ and 4‐ Arm Star‐Block Copolypeptides using Multifunctional Amino Initiators and High Vacuum Techniques
Authors: Aliferis Thrasyvoulos , Iatrou Hermis , Hadjichristidis Nikos , Messman Jamie , Mays Jimmy 
Published: July 2006

AbstractThree‐ and four‐arm star‐block copolypeptides, (BL‐b‐G)3 and (G‐b‐BL)4, of poly(ε‐butyloxycarbonyl‐L‐lysine) (BL) and poly(γ‐benzyl‐L‐glutamate) (G), were synthesized under high vacuum conditions, using three different multifunctional amino‐initiators for the ring opening polymerization of the corresponding α‐aminoacid N‐carboxyanhydrides. When the initiator contained only primary amine groups {2(aminomethyl)‐2‐methyl‐1,3‐propanediamine, AMPDA}, well‐defined star‐block copolypeptides with monomodal molecular weight distribution were produced. However, if the multifunctional initiator contained both primary and tertiary amine groups {polypropylenimine tetraamine dendrimer, generation 1.0 (DAB); amidoethylethanolamine dendrimer, 1,4‐diaminobutane core, generation 0.0 (PAMAM)}, bimodal high polydispersed copolypeptides were formed. The different behaviors are due to the participation of both the primary and tertiary amino groups, each following different polymerization kinetics.
Successive Synthesis of Regular and Asymmetric Star‐Branched Polymers by Iterative Methodology Based on Living Anionic Polymerization Using Functionalized 1,1‐Diphenylethylene Derivatives
Authors: Hirao Akira , Inoue Kyoichi , Higashihara Tomoya 
Published: July 2006

AbstractIn order to achieve the successive synthesis of star‐branched polymers, we have developed a new iterative methodology which involves only three sets of the reactions in each iterative process: (a) a coupling reaction of a living anionic polymer with 1,1‐bis(3‐chloromethylphenyl)ethylene to prepare a DPE‐chain‐functionalized polymer, (b) an addition reaction of sec‐BuLi to the DPE‐chain‐functionalized polymer, followed by treatment with 1‐(4‐(4‐bromobutyl)phenyl)‐1‐phenylethylene to prepare a new DPE‐chain‐functionalized polymer whose DPE is separated by four methylene units from the main chain, and (c) a coupling reaction of 1,1‐bis(3‐chloromethylphenyl)ethylene with the polymer anion derived from the newly prepared DPE‐chain‐functionalized polymer and sec‐BuLi. With this methodology, a series of well‐defined 4‐arm, 8‐arm, and 16‐arm regular star‐branched polystyrenes as well as 4‐arm A2B2, 8‐arm A4B4, and 16‐arm A8B8 asymmetric star‐branched polymers comprising polystyrene and poly(α‐methylstyrene) segments have been successively synthesized.
Progress in Polymerization of Cyclic Esters: Mechanisms and Synthetic Applications
Authors: Biela Tadeusz , Kowalski Adam , Libiszowski Jan , Duda Andrzej , Penczek Stanisław 
Published: July 2006

AbstractRecent advances in the controlled ring‐opening polymerization of aliphatic cyclic esters are briefly reviewed. Particular attention is paid to the high molecular weight linear, branched, and star‐shaped poly(lactide)s and poly(ε‐caprolactone) synthesis. It is concluded that despite the plethora of initiating and/or catalytic systems applied for this purpose the best results so far were achieved with Al‐ and Sn(II) derivatives. Analytical methods employed for aliphatic polyesters of various architectures characterization, including SEC‐MALLS, LC‐CC, and fluorescence spectroscopy, are also discussed.
Anionic Copolymerization of ε‐Caprolactam with ω‐Laurolactam
Authors: Budín Jan , Roda Jan , Brožek Jiří , Kříř Jaroslav 
Published: July 2006

AbstractPolyamide 6/12 copolymers were prepared by employing two different initiation systems containing activator N‐benzoyl‐ε‐caprolactam (BzCL) and initiator either sodium salt of ε‐caprolactam (CLNa) or ε‐caprolactam magnesium bromide (CLMgBr). Materials prepared by initiation with CLNa show one melting endotherm and are random copolymers. Materials prepared by initiation with CLMgBr show two melting endotherms and are probably composed from random copolymer and block copolymer containing blocks of random copolymer and blocks of copolymer with ε‐caprolactam rich segments. The character of copolymers and fractionalized materials was evaluated by means of DSC and NMR.
Self‐Nucleation Behavior of the Polyethylene Block as Function of the Confinement Degree in Polyethylene‐Block‐Polystyrene Diblock Copolymers
Authors: Müller A. J. , Lorenzo A. T. , Arnal M. L. , de Fierro A. Boschetti , Abetz V. 
Published: July 2006

AbstractA series of well defined polyethylene‐b‐polystyrene diblock copolymers (ExSyz, where x and y represent the composition in weight % and z the molecular weight in Kg/mol) has been synthesized in a wide composition range by sequential anionic polymerization. The molecular weight of the PE block was kept constant. A fractionated crystallization behavior was observed for the PE block within E26S74105(PE cylinders) and E11S89244(PE spheres). When the PE blocks form a continuous or percolated phase (PE, E79S2141and E53S4751), a “classic” self‐nucleation behavior (where the usual three self‐nucleation domains are obtained) was observed. When the PE block is located within isolated microphases (having dimensions on the nanometer scale) and a fractionated crystallization was detected (E26S74105and E11S89244), the fraction of crystals formed at higher temperatures exhibits a “classic” self‐nucleation behavior, while those crystals that crystallized at the largest supercooling (lower exotherms) can only be self‐nucleated at lower temperatures where annealing of unmolten material has already started. An unusual fractionated crystallization behavior for isolated, spherical PE microphases (E11S89244) is reported.
Siloxane‐containing Bifunctional Epoxide Together with Multi‐functional Acrylates to Improve the Performance of Holographic Gratings
Authors: Kawakami Yusuke , Cho Yeong Hee 
Published: July 2006

AbstractWell‐defined transmission holographic gratings with high diffraction efficiency were fabricated by irradiating a mixture of dipentaerythritol penta‐/hexa‐functional acrylates, 1‐vinyl‐2‐pyrrolidone and 1,3‐bis(3‐glycidoxypropyl)‐1,1,3,3‐tetramethyldisiloxane or 1,3‐bis[2‐(1,2‐epoxycyclohex‐4‐yl)ethyl]‐1,1,3,3‐tetramethyldisiloxane in the absence (photo‐polymer systems, 30 : 10 : 60 in weight ratio; 80 or 55% efficiency) or presence (holographic polymer dispersed liquid crystal systems: 45 : 9 : 36 : 10 in weight ratio; 83 or 67% efficiency) of commercial liquid crystalline compound E7 with diphenyliodonium hexafluorophosphate and 3,3′‐carbonylbis(7‐diethylaminocoumarin) photo‐initiating system by Nd:YAG laser (λ = 532 nm). When the ratio of dipentaerythritol penta‐/hexaacrylate and 1,3‐bis(3‐glycidoxypropyl)‐1,1,3,3‐tetramethyldisiloxane was changed to 50 : 40 in photo‐polymer system, the diffraction efficiency increased to 84%. They had smooth surface morphologies with regulated spacing. In polymer dispersed liquid crystal system, the same ratio of dipentaerythritol penta‐/hexaacrylate and siloxane‐containing epoxides gave the best results. 1,5‐Bis(3‐glycidoxypropyl)‐1,1,3,3,5,5‐hexamethyltrisiloxane and 1,5‐bis[2‐(1,2‐epoxycyclohex‐4‐yl)ethyl]‐1,1,3,3,5,5‐hexamethyltrisiloxane gave high diffraction efficiency with 10% E7 (97% and 75%). The trisiloxane derivatives gave gratings with considerably or moderately reduced angular deviation (0.83, 0.66 degree for trisiloxane from 1.2, 0.7 degree for disiloxane derivatives, respectively for signal beam, and 0.76, 0.70 degree from 1.1, 1.0 degree for the reference beam at 32 degree of external incident angle) from Bragg profile, namely 5.2 and 4.5% volume shrinkage for trisiloxane, and 7.5, 5.6% for disiloxane derivatives, respectively. Gratings with diffraction efficiency over 95% with the narrowest angular selectivity of 4.0 degree was obtained when trimethylolpropane triacrylate was used together with 1,5‐bis[2‐(1,2‐epoxycyclohex‐4‐yl)ethyl]‐1,1,3,3,5,5‐hexamethyltri‐siloxane (50 : 40) and 5% E7. These gratings were actually used to store real images.
The Effect of Alkyl Side Chain and Additives on the Anionic Polymerization of Isocyanates with Carbamate Group
Authors: Shin Yeong‐Deuk , Rahman M. Shahinur , Samal Shashadhar , Lee Jae‐Suk 
Published: July 2006

AbstractThe synthesis of new isocyanate monomers and their polymerization by anionic route is reported. Reaction of 1,6‐diisocyanatohexane with aliphatic alcohols such as methanol, n‐propanol and n‐pentanol in 1:0.5 molar ratios was carried out in the presence of pyridine such that one NCO group remained unreacted. The anionic polymerization of n‐alkoxycarbonylaminohexyl isocyanates was carried out using sodium napthalenide (Na‐Naph) initiator in the presence of 15‐crown‐5 (15C5) and sodium tetraphenylborate as the additives. While polymerization of n‐propyloxycarbonylaminohexyl isocyanate (PAHI) and n‐pentanoxycarbonylaminohexyl isocyanate (PEAHI) was feasible that of methoxycarbonylaminohexyl isocyanate (MAHI) led to an insoluble material. The polymers were isolated in high yields with NaBPh4 as the additive.
Improvement of Synthetic Vectors for Gene Therapy Using Ring‐Opening Cationic Polymerization
Authors: Cheradame H. , Brissault B. , Guis C. , Guégan P. , Pomel C. , Kichler A. , Gau J. , Auvray L. 
Published: July 2006

AbstractFor efficirent gene transfer, DNA has to be associated with a carrier which can be either of biological (i.e. recombinant viruses) or synthetic origin. In the domain of polymeric synthetic vectors two general types can be envisaged, namely positive polyelectrolytes or neutral amphiphilic block copolymers. Both types can be synthesized by ring‐opening cationic polymerization. Several examples show that the versatility of this polymerization technique can be used for the design of structures which after transfection studies, either in vitro or in vivo, can allow conclusions on the most important parameters which govern transfection efficacy. The present study allowed to conclude on the importance of physico‐chemical characteristics of these vectors, i.e. the linear macrostructure for the positive polyelectrolytes, and the amphiphilic nature for the neutral block copolymers.
Diphenyldiselenide As Novel Non–salt Photoinitiator for Photosensitized Cationic Polymerization of N‐Vinyl Carbazole
Authors: Gupta Mukesh Kumar , Singh Raj Pal 
Published: July 2006

AbstractPhotoinitiated cationic polymerization of N‐vinyl carbazole (NVC) with diphenyldiselenide (DPDS) as an initiator and aromatic nitriles such as dicyanonaphthalene (DCN) and dicyanoanthracene (DCA) as sensitizer was studied at λ > 290 nm in CH2Cl2 solvent using single electron transfer (SET) reactions in this investigation. Aromatic nitriles were found to be effective photosensitizer in initiating polymerization at wavelength λ > 290 nm where DPDS (λmax = 246 nm) do not absorb. However, the DPDS works well as an initiator with both DCN and DCA. An initiation mechanism is also proposed that involves the formation of selenium radical cation as actual initiating species. Upon photoirradiation, these radical cations are formed by single electron transfer between the excited singlet state sensitizer and the ground state of DPDS.
New Segmented Copolymers by Combination of Atom Transfer Radical Polymerization and Ring Opening Polymerization
Authors: Jakubowski Wojciech , Matyjaszewski Krzysztof 
Published: July 2006

AbstractAtom transfer radical polymerization (ATRP) and ring opening polymerization (ROP) were combined to synthesize various polymers with various structures and composition. Poly(ε‐caprolactone)‐b‐poly(n‐octadecyl methacrylate), PCL‐PODMA, was prepared using both sequential and simultaneous polymerization methods. Kinetic studies on the simultaneous process were performed to adjust the rate of both polymerizations. The influence of tin(II) 2‐ethylhexanoate on ATRP was investigated, which led to development of new initiation methods for ATRP, i.e., activators (re)generated by electron transfer (AGET and ARGET). Additionally, block copolymers with two crystalizable blocks, poly(ε‐caprolactone)‐b‐poly(n‐butyl acrylate)‐b‐poly(n‐octadecyl methacrylate), PCL‐PBA‐PODMA, block copolymers for potential surfactant applications poly(ε‐caprolactone)‐b‐poly(n‐octadecyl methacrylate‐co‐dimethylaminoethyl methacrylate), PCL‐P(ODMA‐co‐DMAEMA), and a macromolecular brush, poly(hydroxyethyl methacrylate)‐graft‐poly(ε‐caprolactone), PHEMA‐graft‐PCL, were prepared using combination of ATRP and ROP.
Controlled Radical Polymerization of Furfuryl Methacrylate
Authors: Kavitha Amalin A. , Choudhury Anusuya , Singha Nikhil K. 
Published: July 2006

AbstractAtom transfer radical polymerization provides a new method of controlled radical polymerization. The most important advantage of ATRP is that it is tolerant to the different functional groups present in the initiator as well as in the monomer. Furfuryl Methacrylate (FMA) is a specialty monomer, which has applications in coatings, adhesives and in biomedicals. Conventional radical polymerization of FMA leads to excessive gel formation, which limits its applications. In this investigation homo and co‐polymerization of FMA has been carried out via ATRP. ATRP of FMA was carried out using CuBr as catalyst and 1, 1, 4, 7, 10, 10 hexamethyltriethylenetetramine (HMTETA) as ligand. There was no gel formation during the polymerization. ATRP of FMA was well controlled with a linear increase of molecular weight (Mn) with monomer conversion. The polymers were characterized by using 1HNMR, FT‐IR and GPC analysis. Interestingly, it was observed that the furfuryl ring was not affected during polymerization.
Copper Catalyzed ATRP of Methyl Methacrylate Using Aliphatic α‐Bromo Ketone Initiator
Authors: Mittal Anuj , Baskaran Durairaj , Sivaram Swaminathan 
Published: July 2006

AbstractThe atom transfer radical polymerization (ATRP) of MMA was examined using 3‐bromo‐3‐methyl‐butanone‐2 (MBB) as an initiator in the presence of CuBr as catalyst and 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl]pyridine (BPIEP) as a tridentate N‐donor ligand. The effect of various other N‐donor ligands including a bisoxazoline ligand, namely, 2,6‐bis(4,4‐dimethyl‐2‐oxazolin‐2‐yl) pyridine (dmPYBOX) was studied in ATRP and reverse ATRP of MMA. The ATRP of MMA in toluene at 90 °C using MBB as initiator was relatively slow in the case of bidentate and faster in the case of tridentate N‐donor ligands. The apparent rate constant, kapp, with MBB as initiator and BPIEP as ligand in toluene (50%, v/v) at 90 °C was found to be 7.15 × 10−5 s−1. In addition, reverse ATRP of MMA in diphenylether at 70 °C using BPIEP/CuBr2 as catalyst system was very effective in reducing the reaction time from several hours to 24 h for polymerization of MMA.
Atom Transfer Radical Polymerization (ATRP) of Ethyl Acrylate: Its Mechanistic Studies
Authors: Datta Haimanti , Bhowmick Anil K. , Singha Nikhil K. 
Published: July 2006

AbstractAtom transfer radical polymerization (ATRP) of ethyl acrylate was carried out in bulk using ethyl 2‐bromoisobutyrate as initiator, CuBr as well as CuCl as catalyst in combination with different ligands e.g., 2,2′ bipyridine (bpy)andN,N, N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA). In most of the cases very high conversion (72–98%) was achieved. The polymerization was well controlled with a linear increase of molecular weight (MnSEC) with conversion and relatively narrow molecular weight distributions (polydispersity index 1.2–1.3). Use of PMDETA as the ligand resulted in faster polymerization rate (98% conversion in 1 h) than those using bipyridine (72% conversion in 5 h). The MALDI‐TOF‐MS analysis of poly (ethyl acrylate) (PEA) prepared by using bpy as ligand showed the presence of halogen as the end group. On the contrary, when PMDETA was used as the ligand, the mass analysis showed no trace of this end group.
Effects of voltage‐gated calcium channel subunit genes on calcium influx in cultured C. elegans mechanosensory neurons
Authors: Frøkjær‐Jensen Christian , Kindt Katie S. , Kerr Rex A. , Suzuki Hiroshi , Melnik‐Martinez Katya , Gerstbreih Beate , Driscol Monica , Schafer William R. 
Published: July 2006

AbstractVoltage‐gated calcium channels (VGCCs) serve as a critical link between electrical signaling and diverse cellular processes in neurons. We have exploited recent advances in genetically encoded calcium sensors and in culture techniques to investigate how the VGCC α1 subunit EGL‐19 and α2/δ subunit UNC‐36 affect the functional properties of C. elegans mechanosensory neurons. Using the protein‐based optical indicator cameleon, we recorded calcium transients from cultured mechanosensory neurons in response to transient depolarization. We observed that in these cultured cells, calcium transients induced by extracellular potassium were significantly reduced by a reduction‐of‐function mutation in egl‐19 and significantly reduced by L‐type calcium channel inhibitors; thus, a main source of touch neuron calcium transients appeared to be influx of extracellular calcium through L‐type channels. Transients did not depend directly on intracellular calcium stores, although a store‐independent 2‐APB and gadolinium‐sensitive calcium flux was detected. The transients were also significantly reduced by mutations in unc‐36, which encodes the main neuronal α2/δ subunit in C. elegans. Interestingly, while egl‐19 mutations resulted in similar reductions in calcium influx at all stimulus strengths, unc‐36 mutations preferentially affected responses to smaller depolarizations. These experiments suggest a central role for EGL‐19 and UNC‐36 in excitability and functional activity of the mechanosensory neurons. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006
Physiological requirement for the glutamate transporter dEAAT1 at the adult Drosophila neuromuscular junction
Authors: Rival Thomas , Soustelle Laurent , Cattaert Daniel , Strambi Colette , Iché Magali , Birman Serge 
Published: July 2006

AbstractL‐Glutamate is the major excitatory neurotransmitter in the mammalian brain. Specific proteins, the Na+/K+‐dependent high affinity excitatory amino acid transporters (EAATs), are involved in the extracellular clearance and recycling of this amino acid. Type I synapses of the Drosophila neuromuscular junction (NMJ) similarly use L‐glutamate as an excitatory transmitter. However, the localization and function of the only high‐affinity glutamate reuptake transporter in Drosophila, dEAAT1, at the NMJ was unknown. Using a specific antibody and transgenic strains, we observed that dEAAT1 is present at the adult, but surprisingly not at embryonic and larval NMJ, suggesting a physiological maturation of the junction during metamorphosis. We found that dEAAT1 is not localized in motor neurons but in glial extensions that closely follow motor axons to the adult NMJ. Inactivation of the dEAAT1 gene by RNA interference generated viable adult flies that were able to walk but were flight‐defective. Electrophysiological recordings of the thoracic dorso‐lateral NMJ were performed in adult dEAAT1‐deficient flies. The lack of dEAAT1 prolonged the duration of the individual responses to motor nerve stimulation and this effect was progressively increased during physiological trains of stimulations. Therefore, glutamate reuptake by glial cells is required to ensure normal activity of the Drosophila NMJ, but only in adult flies. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006
Regulation of FGF10 by POU transcription factor Brn3a in the developing trigeminal ganglion
Authors: Cox Eric , Lanier Jason , Quina Lely , Eng S. Raisa , Turner Eric E. 
Published: July 2006

AbstractThe POU‐domain transcription factor Brn3a is expressed in specific neurons of the caudal CNS and peripheral sensory nervous system. The sensory neurons of mice lacking Brn3a exhibit marked defects in axon growth and extensive apoptosis in lategestation. Here we show that expression of thedevelopmental regulator FGF10 is approximately 35‐fold increased in the developing trigeminal ganglia of Brn3a‐null mice. In order to determine whether FGF10 regulates other changes in gene expression observed in Brn3a knock‐out ganglia, we have used a sensory‐specific enhancer to over‐express FGF10 in transgenic mice. Microarray analysis of trigeminal ganglia from individual transgenic founders effectivelyexcludes the cell‐autonomous activity of FGF10 as a mechanism for mediating the downstream effects of the loss of Brn3a, probably because developing sensory neurons lack the appropriate type of FGF receptor. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006