bluuebunny/crossref_metadata_2025_split huggingface dataset:
The cell‐plasma membranes as composite system of two‐dimensional liquid crystal and macromolecular network and how to mimick its physical properties
Authors: Duwe H.‐P. , Eggl P. , Sackmann E. 
Published: April 2003

AbstractThe evolution of the cell has become possible after nature had invented the composite membrane by combining two states of matter: the two‐dimensional liquid crystalline lipid/protein bilayer and the macromolecular network.In the first part we introduce the essential structural features of the cell plasma membrane (case of erythrocyte) and describe their extraordinary mechanical properties. These are unmatched by the technical materials and allow migrating cells to squeeze through narrow gaps of the tissue or of the extracellular protein networks without loss of material or lysis. As an example, how nature manages to alter the structure and function of biomenbranes drastically by minor biochemical signals we consider chemically induced shape changes of cells.In the second part we describe some efforts to mimick mechanical properties of cell membranes with composite membranes of monomeric and polymeric amphiphiles. These model systems exhibit promising new material properties for future applications in chemistry and biotechnology.
Polymerized model biomembranes
Authors: O'Brien David F. , Liman Ulrich 
Published: April 2003

AbstractOver the past two decades lipid bilayer membranes have served as effective models for biomembranes. Pure lipid membranes allow investigators to probe the behavior of different classes of lipids in lamellar and nonlamellar phases. Nonlamellar phases are of current interest because of their considerable importance in cellular permeability, fusion, endo‐ and exocytosis. The reconstitution of biological membranes from purified protein and lipid components has proven to be a convenient method for the study of protein‐lipid interactions and membrane protein functionality. The introduction of methods to polymerize lipid bilayers in the early 1980s, now provides researchers with new ways to prepare and characterize model biomembranes. This report summarizes three areas of research on polymerized model membranes: 1) the enhancement of chemical stability and reduction in bilayer permeability by polymerization of single component membranes; 2) the polymerization induced domain formation in two‐component membranes, which is accompanied by membrane destabilization when one of the lipid components prefers a nonlamellar structure; and 3) the successful reconstitution of a purified delipidated membrane protein, rhodopsin, into partially polymerized bilayer membranes with retention of both protein functionality and phospholipid surface biocompatibility.
Ordering and organization in ionic solutions and emulsions
Authors: Ise Norio , Matsuoka Hideki , Ito Kensaku 
Published: April 2003

AbstractRecent studies on ionic distribution in solutions and in suspensions were reviewed. Suspensions of latex particles, which were large enough to be seen under an ultramicroscope, were investigated by the 2‐D Fourier transformation. The micrograph showing ordered structures gave discrete scattering spots, whereas those of disordered arrangements displayed no spots or halos. The two‐state structure gave a limited number of halo, confirming our previous conclusion that the very frequently observed single, broad scattering peak was reminiscent of some kind of ordering of solute species. By using an image data analyser, the crystallization process was shown to follow the Ostwald ripening mechanism. The concurrent study by the quasi elastic light scattering method and by the Fourier analysis gave consistent scattering profiles, which indicated that the ordering phenomena took place in the entire volume of suspensions. The scattering intensity (correctly the lattice factor) was calculated for cubic systems with paracrystalline distortion. The peak intensity was lowered by enhanced distortion, while the peak position itself was not affected. This justifies our previous treatment of the single, broad peak in terms of the Bragg equation. The experimentally found scattering curve was compared with this theoretical calculation; the degree of distortion was evaluated.
Übermolekulare flüssigkristalline strukturen von hochkonzentrierten cellulosederivatlösungen
Authors: Siekmeyer Maria , Steinmeier Hans , Zugenmaier Peter 
Published: April 2003

AbstractLyotropic liquid crystalline phases of cellulose derivatives were explored as an analytical tool. Molar mass dependent measurements of the helicoidal cholesteric pitch of a cellulose tricarbanilate/solvent system may be used to determine the molar mass of this derivative by optical means. The compatibility of a ternary liquid crystalline system can be adequately investigated by a study of the supermolecular structure with spectroscopic measurements.
Phospholipid polymers & new haemocompatible materials
Authors: Hall Brenda , Bird Richard Le R. , Chapman Dennis 
Published: April 2003

AbstractWhen blood comes into contact with an artificial surface, a number of events occur which include protein adsorption, platelet activation and the activation of the intrinsic pathway of blood coagulation. With the increased application of blood containing artificial devices, there is a great demand to develop new biomaterials which retard thrombus formation. Our new approach to solving this problem is to mimic the non‐thrombogenic surface of natural biological membranes at least in a simple form. We have developed a polymerisable phospholipid and polyesters based on the major phospholipid polar head group present on the erythrocyte outer membrane surface. The coagulation of blood exposed to these polymers was examined by the technique of Material Thrombelastography, a relatively simple test for the in vitro screening of polymer thrombogenicity. We present results which indicate that the polymerised phospholipid and polyesters show reduced thrombogenicity, and may therefore have potential for future biomaterials.
Modifizierung von polymeroberflächen zur erhöhung der zelladhäusion
Authors: Klee D. , Breuers W. , Bilo‐Jung M. , Mittermayer C. , Höcker H. 
Published: April 2003

AbstractAfter implantation a stable bond between the implant and the surrounding tissue is required. Therefore a high cell adhesion of the polymer surface of the implant must be achieved. Depending on the treatment time of a polydimethylsiloxane foil with oxygen plasma, the cell adhesion can be improved. FT‐IR spectroscopy and ESCA analysis were used to characterize the surface modification. The cell spreading and cell adhesion increase with increasing hydrophilic character of the polymer surface after plasma treatment. A pronounced correlation was found between the efficiency of DNA and protein content, characterizing cell growth, and the spreading of the cells.Polydimethylsiloxane, Glow‐Discharge, Surface Modification, Cell Adhesion, Cell Proliferation.
Explorations in cell biology and pharmacology using synthetic polymers
Authors: Lloyd J. B. 
Published: April 2003

AbstractWe have used synthetic polymers as tools to probe endocytosis and lysosome function. Their particular value lies in their well‐defined chemical constitution and in the possibility to custom‐synthesize molecules with desired characteristics. Polyvinylpyrrolidone, Percoll and polystyrene beads have been 125I‐labelled and used to explore the borderland of pinocytosis and phagocytosis. Derivatized poly(aspartamide), poly(hydroxypropylmethacrylamide) and a polylysine‐poly(ethylene oxide) block copolymer have been used to investigate the effects of hydrophobic moieties and sugar residues on substrate‐selection in pinocytosis. The effect of cationic moieties has been studied using vinylpyrrolidone‐vinylamine copolymers.Poly(hydroxypropylmethacrylamide) with certain oligopeptide side‐‐‐chains have been shown to be susceptible to lysosomal peptidases. Ethylene glycol oligomers are being used to study the basal permeability of the lysosome membrane.Soluble macromolecules have considerable potential in targeted drug‐delivery. Drugs attached to appropriate polymers by covalent links that are susceptible to lysosomal enzymes can deliver drug to target cells and avoid unwanted sideeffects. Synthetic macromolecules have several advantages over their natural counterparts: they are chemically more robust, less immunogenic, and easier and cheaper to prepare in bulk.
Preparation, properties and uses of polymer‐enzyme conjugates
Authors: Katchalski‐Katzir Ephraim 
Published: April 2003

AbstractEnzymes can be immobilized by gel entrapment, by microencapsulation, by physical or ionic adsorption, by covalent binding to inorganic or organic carriers, or by whole cell immobilization. Of particular interest is the large number of chemical reactions developed for the covalent binding of enzymes via their nonessential functional groups to inorganic carriers such as glass, ceramics and iron, to natural polymers such as cellulose and Sepharose, and to synthetic polymers such as nylon, polyacrylamide, and other vinyl polymers and copolymers possessing reactive chemical groups. The stability of certain enzymes is markedly increased on their immobilization. It was thus possible to transform the biologically active polymer derivatives into active enzyme beads, enzyme capsules, enzyme columns and enzyme membranes and these enabled the construction of enzyme reactors such as the batch‐stirred tank reactors, the continuous packed bed reactors, and fluidized bed reactors. So far mainly immobilized hydralases and isomerases are being used in industry on a large scale. It seems likely, however, that once adequate techniques become available for cofactor recycling, the use of immobilized enzymes will be extended to other organic reactions, particularly those involving stereospecific synthesis of simple or complex organic molecules. Among the industrial processes in which immobilized enzymes are being used, it is worth mentioning the industrial‐scale continuous production of fructose enriched syrup from glucose by immobilized glucose‐isomerase, the batch process for the production of 6‐aminopenicillanic acid (6‐APA) from penicillin G with the aid of immobilized penicillin amidase; the production of aspartame from aspartic acid and phenylalanine by immobilized thermoase; the large scale production of optically active amino acids with immobilized amino acid acylase; and the large scale production and application of immobilized lactase for the hydrolysis of lactose. The recently developed process for acrylamide production using immobilized nitrilase containing microbial cells should also be referred to. The successful use of an NAD‐polyethylene glycol conjugate (NAD‐PEG) as a nondialyzable water‐soluble coenzyme derivative in the enzymic synthesis of leucine from α‐ketoisocaproic acid and ammonia, in a membrane‐enclosed reactor containing L‐leucine dehydrogenase, NAD‐PEG, formate and formate dehydrogenase, illustrates the new possibilities opened up by making use of cofactor‐polymer conjugates. The use of enzyme‐polymer conjugates in analytical and clinical is also illustrated.
Makromolekulare schalter für doppelschichtmembranen
Authors: Schröder Ulrich K. O. , Tirrell David A. 
Published: April 2003

AbstractKontrollierte Adsorption von Polyelektrolyten kann ein wirksames Werkzeug im Design von dünnen molekularen Filmen sein. Man kann erwarten, daß die Adsorption von Polyelektrolytketten das empfindliche Kräftegleichgewicht erheblich beeinflußt, das die strukturellen und funktionellen Eigenschaften von geordneten Strukturen wie Einzel‐, Doppel‐ und Mehrfachschichten bestimmt. Andererseits ist die Adsorption von Polyelektrolyten außerordentlich sensitiv auf Umgebungsparameter, z.B. pH, Temperatur oder lonenstärke. Kontrollierte Adsorption kann daher zu Sensitivität auf bestimmte chemische oder physikalische Stimuli führen, sodaß auf diese Weise ein molekularer Schaltmechanismus entworfen werden kann. Durch Umsetzen dieser ldee in reale Systeme gelang es uns, molekulares Schalten in Mischungen von Poly(2‐ethylacrylsäre) mit natürlichen oder synthetischen Phosphatidylcholinen zu bewirken. Insbesondere haben wir Phosphatidylcholinvesikel hergestellt, die ihren lnhalt nach einer Änderung von pH, Temperatur, Glukosekonzentration oder nach Bestrahlung mit Licht schnell und quantitativ freisetzen. Die Entwicklung und die Herstellung von Doppelschichtmembranen, die auf solche Änderungen reagieren, sowie die Kinetik und der Mechanismus des damit verbundenen molekularen Schaltprozesses werden im vorliegenden Artikel diskutiert.
Die nutzung gentechnischer methoden zur produktion wertvoller proteine in mikroorganismen
Authors: Heilmann Hans‐Jürgen , Strauß Michael , Stollwerk Jürgen , Appelhans Heribert , Weiler Hartmut , Gassen Hans Günter 
Published: April 2003

AbstractThe genetic make‐up of living systems especially of isolated cells can be altered by a variety of methods including chemical or light‐induced mutation. More modern procedures are the in vitro recombination of nucleic acids and the cell‐cell fusion.The new methods are especially useful to reprogram microorganisms to produce valuable proteins or other natural products in excess quantties. In the following we will elucidate the importance of the new techniques by describing the bacterial production of glucose dehydrogenase, of the proteinase inhibitor stefin A and by outlining the methods and promisses of substractive cloning. Although the economic value of genetic engineering techniques still awaits justification, the importance of the methodology for basic biological research is well documented.
Synthesis and evaluation of pyridazines in natural rubber
Authors: Yehia A. A. , Doss N. L. , Ismail M. N. 
Published: April 2003

AbstractFour pyridazine derivatives were synthesized and evaluated as accelerators in natural rubber (NR) mixes. The rheological characteristics were determined by a Monsanto Rheometer 100. The kinetic constants for the vulcanization reaction in the presence of the synthetic compounds were calculated using the rheometric data. The compounds showed a good accelerating efficiency compared with mercaptobenzothiazole (MBT), which is widely used in rubber industry.
N‐substituted maleimides as thermal stabilizers for rigid polyvinylchloride
Authors: Sabaa M. W. , Mikhael M. G. , Mohamed N. A. , Yassin A. A. 
Published: April 2003

AbstractN‐substituted maleimides have been investigated as thermal stabilizers for rigid polyvinylchloride (PVC) at 180°C in air by measuring the rate of dehydrochlorination and the extent of discoloration of the polymer. The results reveal the higher stabilizing efficiency of these products relative to basic lead carbonate, dibutyl tin maleate, and cadmium‐barium stearate stabilizers commonly used in industry. The induction period (Ts) increases as a function of the positive resonance effect of the substituents (+R). Moreover, the investigated stabilizers impart better color stability for the degraded samples as compared with the stearate stabilizer. The stabilizer efficiencies are attributed to their radical trapping potency which intervenes with the radical degradation process of PVC, while the good color stability is due to the ability of the stabilizer to interact with the conjugated double bonds formed on the PVC chains as a result of degradation. A mechanism illustrating the stabilizer's action is proposed.
Reaction of diimide compounds with diglycidyl ether of 4,4′‐dihydroxybiphenyl
Authors: Bertrán Manel , Mantecón Ana , Cádiz Virginia 
Published: April 2003

AbstractNew esterimide and ketoimide polymers containing a biphenyl group have been synthesized and characterized by spectral techniques. Their thermal properties have been studied by thermogravimetric (TGA) measurements, showing a different stability with regard to the imide structure. The analogous amide imide compounds have been tested as monomers, but their polymerization has not taken place as we expected and side reactions have been detected by 13C‐NMR spectroscopy.
Thermal and dyeing properties of acrylonitrile‐glycidyl methacrylate copolymers
Authors: Elsabee Maher Z. , Sabaa Magdy W. , Mikhael Michael G. , El Hamouly Sabrnal H. 
Published: April 2003

AbstractThe copolymerization of acrylonitrile (AN) with glycidyl methacrylate (GMA) has been investigated in tetrahydrofuran (THF). The reactivity ratios were estimated and the thermal behaviour of the homo‐ as well as the copolymers, both in air, and under nitrogen atmosphere was investigated using differential thermal analysis (DTA) and thermogravimetry (TG) techniques. GMA was found to initiate the nitrile oligomerization reaction in the copolymers upon heating. The dyeing ability, as well as the colour fastness towards UV light have also been investigated. It was found that the copolymers showed better affinity towards basic dyes compared to homopolyacrylonitrile. This affinity increases with increasing the GMA content in the copolymer.
Thermal stability of polyurethanes with carbon‐carbon crosslinks
Authors: Kościelecka Alicja 
Published: April 2003

AbstractThermal properties of polyurethanes based on 4,4′‐diphenylmethane diisocyanate and poly(ethylene adipate) crosslinked only by CC linkages were studied by isothermal and non‐isothermal thermogravimetry carried out in nitrogen atmosphere. Previously studied polyurethanes crosslinked only with allophanate groups were used for comparison.It was found that the structure of crosslinks determines the initial stage of degradation process.
Copolymer of cyclohexanone‐formaldehyde resin and polystyrene
Authors: Akar Ahmet , Acuner Ayşegül , Hizal Gürkan , Öztürk Turan 
Published: April 2003

AbstractThe reaction product of cyclohexanone‐formaldehyde resin with an acid chloride of a radical initiator, 4,4′‐azo‐bis(4‐cyano pentanoic acid) was used as initiator for styrene polymerization to form a cyclohexanone‐formaldehyde resin/polystyrene copolymer. The copolymer showed similar solubility as polystyrene.
Photoabbau von styrol‐acrylnitril‐1‐vinylnaphthalin‐copolymeren
Authors: Bratschkov C. , Braun D. 
Published: April 2003

AbstractTerpolymere aus Styrol, Acrylnitril und steigenden Gehalten an 1‐Vinylnaphthalin wurden photooxidative abgebaut, um den Einfluß des Comonomeren mit Naphthalinresten zu untersuchen. Es wurde festgestellt, daß bis zu 10 Gew.‐% 1‐Vinylnaphthalin‐Bausteine im Copolymeren keine Änderung des Abbauverhaltens gegenüber Styrol‐Acrylnitril‐Copolymeren bewirken. Bei 1‐Vinylnaphthalin‐Gehalten ab 20 Gew.‐% wird der Photoabbau deutlich unterdrückt.
Effect of charge groups in polyurethane and polystyrene interpenetrating polymer networks
Authors: Hsieh K. H. , Chou L. M. , Wong S. S. 
Published: April 2003

AbstractOpposite charges, namely tertiary amine and carboxyl groups, were introduced into polyurethane (PU) and polystyrene (PS), respectively, to prepare PU/PS interpenetrating polymer networks (IPNs) by means of simultaneous bulk polymerization. Four IPNs were synthesized: a full‐IPN, two semi‐IPNs and a linear blend. The effect of charge groups on the mechanical properties and morphology of the four polymer alloys was investigated.It is found that the PU/PS IPN which was incorporated with charge groups is free of any phase‐separation, and sufficiently uniformly distributed, as can be seen from the corresponding scanning electron microscopy (SEM) photographs. Dynamic mechanical analysis indicates that the transition peak of the loss modulus E″ will move towards the centre between the two transition peaks of both components in the absence of charge groups, as a function of an increase in the contents of the opposite charge groups. Meanwhile the storage modulus E′ will decrease in a single‐stage way from the previous two‐stage mode.The tensile strength in all the four polymer alloys increased markedly along with an increase in the contents of acrylic acid (AA) in the poly(styrene‐acrylic acid) (PSAA), which clearly can be seen for the PU/PSAA full‐IPN.
Thermal degradation of partially carboxymethylated cellulose grafted with 4‐vinylpyridine
Authors: Leza M. Lourdes , Cortazar Milagros , Casinos Ismael , Guzmán Gonzalo Martin 
Published: April 2003

AbstractPartially carboxymethylated cellulose (PCMC) was grafted with 4‐vinylpyridine (4‐VP) using ceric ammonium nitrate (CAN) as initiator and the thermal behaviour of the grafted samples having different grafting yields was studied by means of thermogravimetric dynamic analysis (TGA). For comparison, the thermal behaviour of poly(4‐vinylpyridine), P(4‐VP), and the ungrafted cellulosic substrate were also examined. The activation energies were determined according to the Broido method.From the thermogravimetric curves the temperature range at which the main decomposition occurred was determined and showed that the thermal degradation of grafted samples was initiated at lower temperature than both PCMC and P(4‐VP).
Chemical dehydrofluorination and electrical conductivity of poly(vinylidene fluoride) films
Authors: Kise Hideo , Ogata Hiroshi , Nakata Masakazu 
Published: April 2003

AbstractThe dehydrofluorination of poly(vinylidene fluoride) (PVDF) powder and films was studied using several kinds of base solution. Especially the reactivity of 1,8‐diazabicyclo[5.4.0]‐7‐undecene (DBU) in ethanol, KOH in 2‐propanol and aqueous NaOH solution with tetrabutylammonium bromide was investigated by the change in infrared (IR) and ultraviolet‐visible (UV‐VI) absorptions of PVDF films. The elimination reactions by DBU or KOH were considered to be accompanied by substitution reaction. The electrical conductivity of dehydrofluorinated PVDF films increased markedly by doping with iodine, and the activation energies of conduction were found to be between 0.4 and 0.5 eV. When a drawn PVDF film was dehydrofluorinated and doped with iodine, anisotropy in conductivity was observed.
Mechanische eigenschaften von polyesterfasern bei kurzzeitiger zugbeanspruchung, 4. Strukturveränderungen durch kurzzeitverformung an polyester‐monofilamentgarn
Authors: Beier Manfred , Schollmeyer Eckhard 
Published: April 2003

AbstractInterferenzmikroskopische Messungen eines PETP‐Monofilamentgarns zeigen, daß die Orientierung des schon hoch vororientierten Materials durch Dehnen und wieder Entspannen abnimmt, langsame Verformung wirkt dabei stärker desorientierend auf das Material als eine schnelle Verformung. Die Packungsdichte nimmt durch Dehnen ab. Die größte Dehngeschwindigkeit bewirkt die größte Abnahme.Ein mit der Dehngeschwindigkeit ϵ = 104%/s gedehntes Monofilament zeigt interferenzmikroskopisch sichtbare „Crazes”︁. Diese „Crazes”︁ sind keine Risse, sondern nur rißförmige Orte verminderter Orientierung. Für kleinere Dehngeschwindigkeiten ist interferenzmikroskopisch Unsymmetrie der Orientierung sichtbar. DTA‐Kurven von PETP‐Fasern zeigen zwischen 30 und 80°C einen exothermen Peak, der spezifischen Strukturen der fehlgeordneten Bereiche zugeordnet werden kann. Bei niedrigen Dehngeschwindigkeiten verlagert sich dieser Peak zu niedrigeren Temperaturen. Durch Lagern des Materials kehrt er zur ursprünglichen Temperaturlage zurück. Für schnell deformiertes Material ändert dieser Peak seine Temperaturlage nicht.
Nylon 6/poly(ethylene terephthalate) polymer blends: Rheological properties of melts
Authors: Varma D. S. , Dhar V. K. 
Published: April 2003

AbstractMelt rheological studies of nylon 6/polyethylene terephthalate (PETP) blends (PETP content varying from 10 to 50%) were carried out using capillary rheometer in the shear rate range of 58 s−1 to 1.15 · 103 s−1. With increasing PETP content in the blend a decrease of the melt viscosity as well as non‐Newtonian behaviour was observed. The model equation developed by Uemura and Takayanagi for viscoelastic melt blends has been used to understand the state of dispersion and morphology of a nylon 6/PETP blend system. Further, an inverse relationship between polymer melt viscosity (η) and elastic modulus (E') of fibres was observed.