bluuebunny/crossref_metadata_2025_split huggingface dataset:
Covalent Inorganic Azides
Authors: Tornieporth‐Oetting Inis C. , Klapötke Thomas M. 
Published: December 2003

AbstractThe chemistry of covalent inorganic azides originated with the synthesis of aqueous HN3 solutions by Tony Curtis in 1890. A little later, in 1900, it proved possible to prepare iodine azide, IN3, as the first member of the meanwhile complete series of halogen azides. Since then it has been possible to synthesize, in addition to HN3 and the stable salt H2NSbF, azide compounds of elements from Groups 13 to 17. In these compounds the N3 moiety acts as a pseudohalogen and is primarily covalently coordinated to the nonmetal. Only a few organic azides, however, as well as HN3, H2N, and all halogen azides have been thoroughly studied with respect to structure and bonding. The combined application of diffraction methods (X‐ray and electron diffraction) and microwave spectroscopy together with quantum chemical approaches such as ab initio SCF and density functional calculations have led in the last few years to an improved understanding of the molecular properties of numerous nonmetal azides, almost all of which are explosive. This interaction of theory and experiment has greatly enhanced the development of azide chemistry and has led to realistic expectations for the synthesis of as yet unknown nonmetal azides.
Solventothermal Synthesis of Solid‐State Chalcogenidometalates
Authors: Sheldrick William S. , Wachhold Michael 
Published: December 2003

AbstractDevelopment of solventothermal methods in the intermediate‐temperature (100–600°C) range has been motivated by current interest in the design of solid‐state compounds with open framework structures. The preparation of nanoporous chalcogenidometalates by this technique is particularly promising, as a combination of the typical ion‐exchanging and catalytic features of zeolite‐like phases with the unique optoelectronic properties of transition metal and group 13–16 chalcogenides could afford novel multifunctional materials. Superheated strongly polarizing solvents such as water, methanol, and amines at temperatures in the range 110–200°C provide reaction conditions adequate to greatly enhance solubility, diffusion, and crystallization but still mild enough to leave molecular building blocks such as chains and rings intact to participate in the formation of polymeric anions. Such intermediate temperatures often allow the isolation of metastable solid‐state compounds and thermodynamically stable phases that decompose at higher temperatures. The dimensionality and pore size of the anion network can be influenced by the choice of a suitable structure‐directing alkali metal or alkyl‐ammonium cation. Methanolothermal conditions have been found to be particularly suitable for the preparation of selenido‐ and telluridometalates, and have afforded a new class of very tellurium‐rich alkali metal tellurides such as RbTe6 and Cs3Te22. This article presents a comprehensive review of the application of mild solventothermal techniques to the preparation of heavier group 14–16 and transition metal chalcogenidometalates.
The Chemistry of Spider Toxins and Spider Silk
Authors: Schulz Stefan 
Published: December 2003

AbstractSpiders have a bad reputation because of their predacious and hidden way of life. Nevertheless, they developed a finely tuned system, based on the use of venom and silk, which enabled them to compete successfully in evolution. Only recently has the mystery of the chemistry of their silk and venom begun to unravel, although the first investigations were performed at the beginning of this century and in the fifties. The silk and toxins are made of proteins, but low molecular weight compounds are also present, too. Among these small molecules are compounds not known from any other natural source. For this reason the following article will focus on the structure and function of the low molecular weight components of the silk and the venom.
Unifying the Current Data on the Mechanism of Cleavage–Transesterification of RNA
Authors: Perreault Denise M. , Anslyn Eric V. 
Published: December 2003

AbstractThe various mechanisms by which RNA is hydrolyzed are currently under intense investigation. The first step in the hydrolysis pathway is a cleavage–transesterification in which a 2′‐OH group attacks a 3′,5′‐phosphodiester linkage with departure of the 5′ group. The second step involves the opening of a 2′,3′‐cyclic phosphodiester. Complications in these steps arise from multiple possible pathways involving specific acid and base as well as general acid and base catalysis. In addition, controversy exists concerning the protonation states of the phosphodiesters and any intermediate phosphoranes under various experimental conditions. A summary of mechanistic studies involving general and specific acid/base catalysis of RNA hydrolysis and the hydrolysis of RNA analogs is presented herein, along with the interpretations given by the original authors. Included are theoretical calculations, kinetic studies, pKa determinations, isotope effects, Hammett and Brønsted correlations, and model studies. Recent analyses of the mechanism of RNase A are also briefly reviewed. Two limiting mechanisms for the cleavage–transesterification step that unify the data in the literature and differ only in the role of the phosphorane and its protonation state are given at the outset. An analysis of the literature studies supporting these mechanisms is then provided.
Enantioselective Synthesis with Lithium/(−)‐Sparteine Carbanion Pairs
Authors: Hoppe Dieter , Hense Thomas 
Published: December 2003

Abstract“Chiral carbanions”—that is, enentiomerically enriched lithium–carbanion pairs in which the carbanionic center carries the chiral information—were regarded until recently as “exotic species.” In the past ten years it has become clear that they can, in fact, play a meaningful role in enantioselective synthesis, since substitution for lithium occurs here stereospecifically, usually with retention of configuration. They are also more readily and commonly accessible than was originally assumed. The trick lies in the use of lithium cations with chiral ligands, whether in the form of alkyllithium species used as bases in kinetically controlled, enantiotopically discriminating deprotonation, or in thermodynamically controlled equilibration in configurationally labile epimeric ion pairs. The lupine alkaloid (−)‐sparteine has shown itself admirably suited as a chiral bidentate ligand, and its efficiency and breadth of application are so far unsurpassed. This contribution constitutes an overview of the preparation of chiral reagents, convering primarily “umpoled” synthons such as homoenolates. 1‐oxyalkanides with a broad pattern of substitution, and α‐aminobenzyl anions.
Homoleptic Metal Carbonyl Cations of the Electron‐Rich Metals: Their Generation in Superacid Media Together with Their Spectroscopic and Structural Characterization
Authors: Willner Helge , Aubke Friedhelm 
Published: December 2003

AbstractHomoleptic carbonyl cations of the electron‐rich metals in Groups 8 through 12 are the newest members of the large family of transition metal carbonyls. They can be distinguished from typical metal carbonyl complexes in several respects. Their synthesis entails carbonylation of metal salts in such superacids as fluorosulfuric acid and “magic acid” HSO3FSbF5. Thermally stable salts with [Sb2F11]− as counterion are obtained with antimony pentafluoride as reaction medium. Both the [Sb2F11]− anion and superacid reaction media have previously found little application in the organometallic chemistry of d‐block elements. Also unprecedented in metal carbonyl chemistry are the coordination geometries with coordination numbers 4 (square‐planar coordination) and 2 (linear coordination) for the cation. Formal oxidation states of the metals, and the charges of the complex cations, extend from + 1 to +3: thus CO is largely σ‐bonded to the metal, and the CO bond is strongly polarized. Minimal metal → CO π‐backbonding and a positive partial charge on carbon are manifested in long MC bonds, short CO bonds, high frequencies for CO stretching vibrations (up to 2300 cm−1), and small 13C NMR chemical shifts (up to δc, = 121). Prominent examples of these unusual homoleptic carbonyl cations, which were recently the subject of a Highlight in this journal, include the first carbonyl cation of a p‐block metal [Hg(CO)2]2+, the first trivalent carbonyl cation [Ir(CO)6]3+, and the first multiply charged carbonyl cation of a 3d metal [Fe(CO)6]2+. In this overview we propose to (a) outline the historical origins of cationic metal carbonyls and their methods of synthesis; (b) present a summary of the general field of carbonyl cations, which has developed over a yery short period of time; (c) discuss the structural and spectroscopic characteritics of metal–CO bonding; (d) discuss the special significance associated with reaction media and the [Sb2F11]− anion; and (e) point to the most recent results and anticipated future developments.
Immobilization of horseradish peroxidase by entrapment in natural polysaccharide
Authors: Shukla Sachin P. , Modi Kalpana , Ghosh P. K. , Devi Surekha 
Published: December 2003

AbstractHorseradish peroxidase (HRP), which catalyzes oxidation reduction reactions of large number of substrates, was entrapped in K‐carrageenan beads using polyethyleneimine as hardening agent. The heat and storage stability was found to be better for entrapped horseradish peroxidase than free enzyme. The entrapped enzyme showed 50% retention of its activity after 4 cycles. Effective diffusion coefficient for diffusion of hydroquinone into K‐carrageenan beads was found to be 0.27 × 10−10 m2/s during enzyme‐catalyzed oxidation of hydroquinone. Kinetic parameters calculated from Lineweaver–Burke plots were observed to be Km = 8 × 10−5 and Vmax = 1.53 for free enzyme, and Km = 8.3 × 10−5 and Vmax = 2.18 for entrapped enzyme when enzyme concentration was kept constant and Km = 4 × 10−11 and Vmax = 0.45 for free enzyme and Km = 4.5 × 10−11 and Vmax = 0.58 for entrapped enzyme when substrate concentration was kept constant. This indicates that there is no conformational change during entrapment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2063–2071, 2004
Conductive polymer composites: Influence of extrusion conditions on positive temperature coefficient effect of poly(butylene terephthalate)/poly(olefin)–carbon black blends
Authors: Feller J. F. 
Published: December 2003

AbstractProcessing conditions determine both the morphology and the carbon black (CB) distribution in conductive polymer composites (CPCs). Good control of these parameters is essential to obtain reproducible electrical properties. We found that for extruded tapes of poly(butylene terephthalate) (PBT)/poly(olefin) (OLE)–CB blends, an increase of both processing temperature and screw speed leads to a significant decrease of resistivity. This shift factor, more important with PBT/poly(ethylene)–CB than with PBT/poly(ethylene‐co‐ethyl acrylate)–CB, is attributed to viscosity variations of all compounds. A decrease of viscosity promotes CB aggregation at the PBT/OLE interface and creates larger conductive channels by coalescence. Nevertheless, the CB concentration effect appears predominant compared to the morphology effect to explain resistivity variations. This interesting finding can be used either to improve reproducibility of electrical properties or to adjust electrical properties without changing CPC formulation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2151–2157, 2004
Poly(dimethylsiloxane) coatings for controlled drug release. II. Mechanism of the crosslinking reaction in emulsion
Authors: Gao Zongming , Schulze Nahrup Julia , Mark James E. , Sakr Adel 
Published: December 2003

AbstractEarlier work focused on the crosslinking of hydroxyl‐terminated poly(dimethylsiloxane) (PDMS) particles in a stable latex suitable for spraying onto drug tablets, and established the conditions for eliminating the usual toxic catalysts that would be unacceptable in such pharmaceutical coating materials. Use of these coatings for controlling the rate of release of a drug, however, requires a better understanding of their properties and thus clarification of the mechanism through which the crosslinking occurs. The present study approaches this goal by documenting the effects of anionic, cationic, and nonionic surfactants at various concentrations, and in acidic, neutral, or basic media. FTIR spectroscopy was used to monitor the transportation of crosslinker from the water phase into the hydrophobic PDMS phase. The results suggest a possible mechanism for the crosslinking in sufficient detail to be used to optimize the coatings for drug‐release applications. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2186–2194, 2004
Dynamics of lipase catalyzed enzymatic degradation of poly(bisphenol‐A carbonate)
Authors: Sivalingam G. , Madras Giridhar 
Published: December 2003

AbstractPoly(bisphenol‐A carbonate) (PC) was degraded in solution at various temperatures (26–70°C) by different lipases, Candida Rugosa (CR), Hog Pancreas (HP), Lipolase (LL), and Novozyme (NV), in various solvents. The degradation of PC was monitored using gel permeation chromatography (GPC). The molecular weights of oligomers obtained were around ∼1,400 irrespective of the lipases used. Continuous distribution kinetics was proposed to determine the rate coefficients of the polymers and deactivation of the enzyme. The FTIR analysis of the polymer before and after degradation showed that there is large reduction of carbonate linkages and generation of hydroxyl and acidic groups in the broken chains. The optimal temperatures for HP and other lipases were 50 and 60°C, respectively. HP showed higher degradation activity at lower temperatures and the overall degradability of the lipases was in the order of LL > CR > NV > HP. The effect of viscosity and polarity of the solvents on the degradation of the polycarbonate was also investigated. While the degradation rate decreased with viscosity, it increased with polarity for the solvents. © 2003 Wiley Periodicals, In6c. J Appl Polym Sci 91: 2391–2396, 2004
Dielectric and conductivity studies on cobalt phthalocyanine tetramers
Authors: Saravanan S. , Joseph Mathai C. , Anantharaman M. R. , Venkatachalam S. , Prabhakaran P. V. 
Published: December 2003

AbstractElectrically conductive organic and metalloorganic polymers are of great interest and they have applications in electronic, optical, photonic, photoelectric, electrochemical, and dielectric devices. Tetrameric cobalt phthalocyanine was prepared by conventional chemical method. The dielectric permittivity of the tetrameric cobalt phthalocyanine sample was evaluated from the observed capacitance values in the frequency range 100 KHz to 5 MHz and in the temperature range of 300 to 383°K. It is found that the system obeys the Maxwell Wagner relaxation of space charge phenomenon. Further, from the permittivity studies AC conductivity was evaluated. The values of AC conductivity and DC conductivity were compared. Activation energy was calculated. To understand the conduction mechanism Mott's variable range hopping model was applied to the system. The T−1/4 behavior of the DC conductivity along with the values of Mott's Temperature (T0), density of states at the Fermi energy N (EF), and range of hopping R and hopping energy W indicate that the transport of charge carriers are by three‐dimensional variable range hopping. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2529–2535, 2004
Precipitation of PMMA/PCL blends using supercritical carbon dioxide
Authors: Vega‐González A. , Domingo C. , Elvira C. , Subra P. 
Published: December 2003

AbstractSolutions of a poly(methyl methacrylate)–poly(ε‐Caprolactone) (PMMA/PCL) polymer blend in dichloromethane (DCM) and mixtures of the same polymer blend and cholesterol in DCM were sprayed into supercritical carbon dioxide. Carbon dioxide was contacted with 0.23–1 wt % polymer solutions and with 0.3–1 wt % polymer plus 0.1–0.6 wt % cholesterol solutions in a continuous mode of operation. Pressure and temperature were constant for almost all of the experiments, 11 MPa and 314 K, respectively. Fibrous networks composed of many smaller microfibrils were obtained by spraying the different solutions through a conical nozzle into concurrently flowing supercritical carbon dioxide. This morphology suggests such an important degree of agglomeration that primary particles are no longer discernible. Processing the polymers with CO2 leads to the removal of contaminants as the precipitate was free of monomer and initiator. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2422–2426, 2004
Functionalization of poly(4‐vinyl pyridine) grafted cellulose by quaternization reactions and a study on the properties of postquaternized copolymers
Authors: Chauhan Ghanshyam S. , Singh Baljit , Dhiman Surya K. 
Published: December 2003

AbstractGraft copolymers of 4‐vinyl pyridine (4‐VP) synthesized by using simultaneous gamma irradiation method were further functionalized by post polymer quaternization reactions at N: of the pyridine ring of the graft copolymers. Using the optimum grafting conditions reported earlier for the grafting of 4‐VP onto extracted cellulose, graft copolymer was synthesized in bulk and was further functionalized by quaternization with hexyl bromide (C6H13Br), benzyl chloride (C6H5CH2Cl), n‐butyl bromide (C4H9Br), and maleic anhydride (MAnh). The quaternized polymers were studied for treatment of hardness of water, antibacterial action, emulsification properties, metal ion uptake and stability toward thermal degradation, and enzymatic and alkaline hydrolysis to evaluate the suitability of these polymers in harsh chemical, microbial, and thermal environments. The functionalized polymers were also characterized for surface morphology (SEM), elemental analysis and FTIR for investigations of structural aspects, and to obtain evidence for quaternization. The functionalized copolymers exhibit a range of properties that can be used in many fields of water purification technologies including antibacterial agents and ion exchangers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2454–2464, 2004
Structural material from waste plastic
Authors: Abdel‐Goad Mahmoud A.‐Halim 
Published: December 2003

AbstractIn efforts to contribute to community development, particularly in the context of Egyptian communities, waste plastics materials were successfully recycled without the difficult task of separation and reused to economically produce new structural material. Recycling was performed by mixing molten waste plastics with sand to produce these new materials. Samples with different percentages of plastics and different particle sizes of sand were used in the process. Materials showed acceptable density and high compressive strength, which was shown to be at a maximum with contents of about 30–40% waste plastic. Furthermore, certain types of sand having different colors were used to produce attractive materials, suitable for decorative uses. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2543–2547, 2004
Kinetics of heterogeneous polymerization of vinylidene chloride. I. Mechanism and modeling
Authors: Lu Qun , Weng Zhi‐Xue , Huang Zhi‐Ming , Tao Chun‐Yuan , Pan Zu‐Ren 
Published: December 2003

AbstractThe similarities and differences between the heterogeneous polymerization of vinylidene chloride (VDC) and vinyl chloride (VC) were compared and analyzed. The effect of the poly(vinylidene chloride)(PVDC) crystal morphology on the kinetics of VDC polymerization was discussed. Based on the assumption that polymerization occurs in the monomer phase and on the edges of the PVDC lamellar crystals, a mechanism of VDC polymerization is proposed and then a kinetic model for VDC bulk/suspension polymerization is developed according to the elementary reactions. The model can be used to predict polymerization rate and conversion. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2576‐2581, 2004
Adsorption and complexation of chitosan wet‐end additives in papermaking systems
Authors: Li Houbin , Du Yumin , Xu Yongmei 
Published: December 2003

AbstractThe adsorption of several chitosan samples with different degrees of deacetylation (65, 73, 85, and 92%) and their interactions with the main components of reed pulp suspensions were investigated with gel permeation chromatography, phenol/sulfuric acid spectrophotometry, microelctrophoresis, and retention/drainage methods. The results showed that the chitosan additive was almost completely adsorbed onto the surfaces of the cellulosic fibers, especially onto the surfaces of fines in a variety of cellulosic systems at low dosages corresponding to those used in industrial operations. This adsorption increased as the degree of deacetylation of chitosan increased. Moreover, the aggregation of the fine cellulosic particles was maximum at a dosage of about 10 mg/kg of chitosan. The uptake of dissolved and colloidal carbohydrates always occurred in the cellulose suspensions upon the addition of chitosan. These phenomena were related to the maximum retention of fines and drainage performance of the pulp suspensions; the optimum drainage dosage was found to be about 5–8 mg of chitosan per gram of oven‐dried pulp. The interactions between chitosan and the cellulosic substrates were dominated by a bridging mechanism at pH ≈ 7 for these experiments. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2642–2648, 2004
Preparation and characterization of modified‐clay‐reinforced and toughened epoxy‐resin nanocomposites
Authors: Zhang Kailiang , Wang Lixin , Wang Fang , Wang Guangjian , Li Zuobang 
Published: December 2003

AbstractEpoxy–clay nanocomposites were prepared by the dispersion of an organically modified layered clay in an epoxy resin (diglycidyl ether of bisphenol A) and curing in the presence of methyl tetrahydro acid anhydride at 80–160°C. The nanometer‐scale dispersion of layered clay within the crosslinked epoxy‐resin matrix was confirmed by X‐ray diffraction and transmission electron microscopy, and the basal spacing of the silicate layer was greater than 100–150 Å. Experiments indicated that the hydroxyethyl groups of the alkyl ammonium ions, which were located in the galleries of organically modified clay, participated in the curing reaction and were directly linked to the epoxy‐resin matrix network. Experimental results showed that the properties of epoxy were improved, evidently because of the loading of organically modified clay. The impact strength and tensile strength of the nanocomposites increased by 87.8 and 20.9%, respectively, when 3 wt % organic clay was loaded, and this demonstrated that the composites were toughened and strengthened. The thermal‐decomposition and heat‐distortion temperatures were heightened in comparison with those of pure epoxy resin, and so were the dynamic mechanical properties, including the storage modulus and glass‐transition temperature. Moreover, experiments showed that most properties of the composites were ameliorated with low clay contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2649–2652, 2004
Preparation and performance testing of sulfonated poly(phenylene oxide) based composite membranes for nanofiltration
Authors: Nogami Nobuhiro , Chowdhury Geeta , Matsuura T. 
Published: December 2003

AbstractSulfonated brominated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPOBr) was synthesized by a sequence of bromination and sulfonation. A thin film of SPPOBr was coated on top of a commercial poly(ether sulfone) membrane. Pure butoxyethanol (BE) solvent or a BE/isopropyl alcohol (IPA) solvent mixture was used to dissolve SPPOBr in the coating process. The thin film composite membranes so prepared were then tested for the separation of carbohydrate and electrolyte solutes. We found that the flux and the carbohydrate separation both increased significantly with increasing IPA content in the solvent mixture. However, the separation of electrolyte solutes did not change significantly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2624–2628, 2004