Bibliothek

Notizen: DNA oligonucleotides with dA and dU residues can form duplexes with trans d(A · U) base pairing and the sugar-phosphate backbone in a parallel-stranded orientation, as previously established for oligonucleotides with d(A · T) base pairs. The properties of such parallel-stranded DNA (ps-DNA) 25-mer duplexes have been characterized by absorption (uv), CD, ir, and fluorescence spectroscopy, as well as by nuclease sensitivity. Comparisons were made with duplex molecules containing (a) dT in both strands, (b) dU in one strand and dT in the second, and (c) the same base combinations in reference antiparallel-stranded (aps) structures. Thermodynamic analysis revealed that total replacement of deoxythymine by deoxyuridine was accompanied by destabilization of the ps-helix (reduction in Tm by -13°C in 2 mM MgGl2, 10 mM Na-cacodylate). The U-containing ps-helix (U1 · U2) also melted 14°C lower than the corresponding aps-helix under the same ionic conditions; this difference was very close to that observed between ps and aps duplexes with d(A · T) base pairs. Force field minimized structures of the various ps and aps duplexes with either d(A · T) or d(A · U) base pairs ps/aps and dT/dU combinations are presented. The energy-minimized helical parameters did not differ significantly between the DNAs containing dT and dU. © 1996 John Wiley & Sons, Inc.

Notizen: The structures of the cyclic hexapeptide cyclo(-Gly-Tyr-Val-Pro-Met-Leu-) (1) and its phosphotyrosyl (pTyr) derivative cyclo[-Gly-Tyr(PO3H2)-Val-Pro-Met-Leu-] (2), designed as constrained models of a sequence that interacts with the src homology 2 (SH2) region of the p85 subunit of phosphatidylinositol-3-OH kinase (PI-3 kinase), were studied in methanol/water solutions by 500 MHz nmr spectroscopy. Compound 1 was found to exist as a 2:1 mixture of isomers about the Val-Pro bond (trans and cis prolyl) between 292-330 K in 75% CD3O (D,H)/(D,H)2O solutions. A third species of undetermined structure (ca. 5%) was also observed. Compound 2, a model of phosphorylated peptide ligand that binds to the PI-3 kinase SH2 domain, exhibited similar conformational isomerism. When either compound was dissolved in pure solvent [i.e., 100% CD3O(H,D) or (H,D)2O] the ratio of cis to trans isomers was ca 1:1. A battery of one- and two-dimensional nmr experiments at different temperatures and solvent compositions allowed a complete assignment of both the cis and trans forms of 1 and indicated the trans compound to be the major isomer. The spectral properties of the phosphorylated derivative 2 paralleled those of 1, indicating like conformations for the two compounds. Analysis of rotating frame Overhauser spectroscopy data, coupling constants, amide proton temperature dependence, and amide proton exchange rates generated a set of constraints that were employed in energy minimization and molecular dynamics calculations using the CHARMM force field. The trans isomer exists with the tyrosine and C-terminal Tyr(+3) (Met) residues at opposite corners of the 18-membered ring separated by a distance of 16-18 Å, in contrast with the cis isomer where the side chains of these residues are much closer in space (7-14 Å). It was previously shown that the pTyr and the third amino acid C-terminal to this residue are the critical recognition elements for pTyr-peptide binding to the PI-3 kinase SH2 domain. Such cyclic structures may offer appropriate scaffolding for positioning important amino acid side chains of pTyr-containing peptides as a means of increasing their binding affinities to SH2 domains, and in turn provide a conceptual approach toward the design of SH2 domain directed peptidomimetics. © 1995 John Wiley & Sons, Inc.

Notizen: The formation of a topologically closed DNA loop is important in many biological processes, including the regulation of transcription, recombination, and replication. Modeling DNA as an isotropic elastic rod, we use finite element analysis to show that the dependence of the twist (ΔTw) and the writhe (Wr) upon the linking number deficit (ΔLk) is strongly influenced by intrinsic bends. We determine how the geometry of a DNA loop changes as a function of the number of uniformly spaced coplanar 20° bends, oriented so as to open toward the center of the loop. We also calculate the geometry of DNA rods that are smoothly bent to the same extent. The response of both ΔTw and Wr of a bent DNA to changes in ΔLk falls into one of three categories, depending upon the number of bends. For a single bend of 20°, Wr increases monotonically with ΔLk and the change in ΔTw with distance is constant along the entire DNA axis. For two to ten 20° bends, Wr passes first through a local maximum, then through a local minimum, and finally increases monotonically as ΔLk increases. For eleven to eighteen 20° bends, Wr again varies monotonically with ΔLk. For all numbers of bends greater than two, the ΔTw per unit length depends upon the distribution of intrinsic bends, being constant between any two adjoining bends but varying with their position relative to the cut location. Accompanying these ΔLk-associated changes in Wr and ΔTw per unit length are characteristic changes in geometry that are specific for each category. The results of these calculations raise the possibility that intrinsic bends can serve as a control factor in the biological functions associated with loop formation in DNA. © 1996 John Wiley & Sons, Inc.

Notizen: We have previously proposed a model of the δ-opioid receptor bound conformation for the cyclic tetrapeptide, Tyr-c[D-Cys-Phe-D-Pen]OH (JOM-13) based on its conformational analysis and from conformation-affinity relationships observed for its analogues with modified first and third residues. To further verify the model, it is compared here with results of conformational and structure-activity studies for other known conformationally constrained δ-selective ligands: the cyclic pentapeptide agonist, Tyr-c[D-Pen-Gly-Phe-D-Phe]OH (DPDPE); the peptide antagonist, Tyr-Tic-Phe-PheOH (TIPP); the alkaloid agonist, 7-spiroindanyloxymorphone (SIOM); and the related alkaloid antagonist, oxymorphindole (OMI). A candidate δ-bound conformer is identified for DPDPE that provides spatial overlap of the functionally important N-terminal N+3 and C-terminal COO- groups and the aromatic rings of the Tyr and Phe residues in both cyclic peptides. It is shown that all δ-selective ligands considered have similar arrangements of their pharmacophoric elements, i.e., the tyramine moiety and a second aromatic ring (i.e., the rings of Phe3, Phe4, and Tic2 residues in JOM-13, DPDPE, and TIPP, respectively; the indole ring system in OMI, and the indanyl ring system in SIOM). The second aromatic rings, while occupying similar regions of space throughout the analogues considered, have different orientations in agonists and antagonists, but identical orientations in peptide and alkaloid ligands with the same agonistic or antagonistic properties. These results agree with the previously proposed binding model for JOM-13, are consistent with the view that δ-opioid agonists and antagonists share the same binding site, and support the hypothesis of a similar mode of binding for opioid peptides and alkaloids. © 1996 John Wiley & Sons, Inc.

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Notizen: Xanthan gum is an exopolysaccharide secreted by the bacterium Xanthamonas campestris whose ability to make solutions viscous at low concentrations and over a pH and temperature range have generated much interest in both academic and industrial environments. Mutant Xanthamonas strains have been derived that produce xanthan gums with an altered or variant subunit chemical structure and different measured viscosities when compared with the wild type (wt) form of the polymer. Two variant gums were targeted as potentially interesting in this study, these being the nonacetylated tetramer (natct; and the acetylated tetramer (atet), which both lack a side-chain terminal mannose residue and in one case (natet) lacks an acetate group on an internal mannose residue. Solutions of these tetrameric gums possess viscosities higher (natet) and lower (atet) than the wt gum, and therefore we have attempted to determine whether these molecules possess unique conformational preferences when compared with the wt and with each other. In this manner we can initiate an understanding of how a polysaccharide's conformation contributes to its solution properties.The GEGOP software permits a sampling of the static and dynamic equilibrium states of carbohydrate molecules, and this software was employed to calculate equilibrium states of representative oligosaccharides with chemical structures representative of xanthan-like molecules. Energy minimization techniques revealed similar local minima for all three molecules. Some of these minima are comprised of elongate backbone conformations (A type) in which side chains fold onto backbone surfaces. Other minima with A backbones possessed side chains in less intimate backbone contact especially when calculations were performed with a low dielectric constant. This phenomenon was particularly pronounced in the wt molecule where an increased number of negatively charged side-chain residues experience charge repulsion resulting in reduced side-chain-backbone contact.Metropolis Monte Carlo (MMC) dynamic simulations performed with an elevated temperature factor (1000 K) allowed a better qualitative representation of conformational space than 300 K simulations. Employing a nonhierarchical cluster analysis method (population density profile: PDP) coupled with a classification scheme, it was possible to partition resulting MMC data sets into conformational families. This analysis revealed that in simulations performed with different dielectric constant values (10, 25, and ∞) all molecules possessed primarily A-type backbones. Less elongate, more open helical backbone forms (B, C, D, J, and Flat-a) did occur during the simulations but were populated to a lesser extent. In the natet molecule significantly open helical backbones existed (E, F, G, H, and I) that did not occur in the lower viscosity wt and atet molecules. PDP clustering methods and subsequent conformational classification applied to the first residue (mannose) of the side chain permitted a determination of side-chain orientation. Comparison of all three molecules indicated a larger population of side-chain conformational families in less direct backbone contact for the wt molecule than either of the variant molecules (natet/atet) suggesting that the side chains in the wt are more flexible. Thus, a major conformational difference between the high viscosity natet. In addition, the significant difference between the higher viscosity wt and the lower viscosity atet is the increase side-chain flexibility in the wt. We hypothesize that conformational differences of this kind could form a partial explanation of the observed differences in viscosity between these xanthan-like polymers. © 1996 John Wiley & Sons, Inc.

Notizen: Because of their wide use in molecular modeling, methods to compute molecular surfaces have received a lot of interest in recent years. However, most of the proposed algorithms compute the analytical representation of only the solvent-accessible surface. There are a few programs that compute the analytical representation of the solvent-excluded surface, but they often have problems handling singular cases of self-intersecting surfaces and tend to fail on large molecules (more than 10,000 atoms). We describe here a program called MSMS, which is shown to be fast and reliable in computing molecular surfaces. It relies on the use of the reduced surface that is briefly defined here and from which the solvent-accessible and solvent-excluded surfaces are computed. The four algorithms composing MSMS are described and their complexity is analyzed. Special attention is given to the handling of self-intersecting parts of the solvent-excluded surface called singularities. The program has been compared with Connolly's program PQMS [M. L. Connolly (1993) Journal of Molecular Graphics, Vol. 11, pp. 139-141] on a set of 709 molecules taken from the Brookhaven Data Base. MSMS was able to compute topologically correct surfaces for each molecule in the set. Moreover, the actual time spent to compute surfaces is in agreement with the theoretical complexity of the program, which is shown to be O[n log(n)] for n atoms. On a Hewlett-Packard 9000/735 workstation, MSMS takes 0.73 s to produce a triangulated solvent-excluded surface for crambin (1crn, 46 residues, 327 atoms, 4772 triangles), 4.6 s for thermolysin (3tln, 316 residues, 2437 atoms, 26462 triangles), and 104.53 s for glutamine synthetase (2gls, 5676 residues, 43632 atoms, 476665 triangles). © 1996 John Wiley & Sons, Inc.

Notizen: We have studied by Raman and ir spectroscopy the metastable complex formed by the self-association of polyinosinic acid in aqueous solution. The complex is easily prepared by quickly cooling to ca. 0°C a warm solution of the polyribonucleotide to which a small amount of rubidium salt has been added. Upon heating, this metastable form melts cooperatively near 13°C, well below the dissociation temperature of a stable four-stranded complex, which occurs at 47°C in the same conditions. The presence of several components in the stretching-mode region of the carbonyl groups in the vibrational spectra of the metastable complex suggests that it also has a parallel four-stranded structure. The difference in structure between the two forms is believed to be caused by the presence of fewer metal ions in the central channel of the metastable complex, in agreement with conclusions reached in previous investigations. The Raman spectra further show that the ribose units in the metastable form have a C3′-endo conformation, in contrast with the stable form, for which we have previously suggested a mixed C2′-endo/C3′-endo conformation. © 1996 John Wiley & Sons, Inc.

Notizen: The effect of hydrostatic pressure on the helix-coil transition temperature (Tm) was measured for the DNA oligomers (dA)n(dT)n, where n = 11, 15, and 19, in 50 mM NaCl. The data were analyzed in light of previously published data for the polymer, poly(dA)·poly(dT) under the same conditions. As has been observed for DNA polymers, increasing the hydrostatic pressure led to an increase in the Tm of the oligomers; however, the effect of pressure diminished with decreasing chain length. The value of dTm/dP decreased linearly with the inverse of the chain length varying from 3.15 × 10-2°C MPa-1 for the polymer to 0.7 × 10-2°C MPa-1 for the 11-mer. The two-state or van't Hoff enthalpy (ΔHvH) of the helix-coil transition was obtained by analysis of the half-width of the thermal transition. As expected, ΔHvH decreases with decreasing chain length. In contrast to the behavior of the polymer, poly(dA)·poly(dT), and (dA)19(dT)19, the ΔHvH of the two shorter duplex oligonucleotides displayed a small pressure dependence dΔHvH/dP≃-0.4 kJ MPa-1 in both cases. The changes observed in the Tm and ΔHvH were not sufficient to explain the magnitude of the chain-length dependence of the pressure effect. To interpret the large chain-length dependence of dTm/dP, we propose that the terminal base pairs contribute a negative volume change to the helix-coil transition. Base pairs distant from the ends exhibit behavior characterized by the polymer where end effects are assumed to be negligible, i.e., a positive volume change for the helix-coil transition. The negative volume change of separating terminal bases may originate from the imperfect interactions these base pairs form with water due to the existence of several energetically equivalent conformations. This is reminiscent of one of the mechanisms proposed to be important in the pressure-induced dissociation of multimeric proteins into their constituent subunits. © 1996 John Wiley & Sons, Inc.

Notizen: We report on the conformation of a tetrasaccharide fragment in the repeating subunit of the cell wall polysaccharide of Streptococcus mitis J22, a receptor for the lectin of Actinomyces viscosus T14V in a bacterial coaggregation that is important in the ecological interactions of oral bacteria. Although there is considerable overlap of the 1H-nmr signals, some cross peaks can be extracted from conventional two-dimensional nuclear Overhauser effect spectroscopy (NOESY) data on the polysaccharide. These data cannot be fit to a single conformation of the tetrasaccharide fragment. Therefore we have prepared a polysaccharide sample fully enriched in 13C from which we have determined accurate NOESY cross-peak volumes in a three-dimensional heteronuclear-resolved spectrum that allows accurate determination of many more NOESY cross peaks than does conventional two-dimensional spectroscopy. We have also used the 13C enriched polysaccharide to measure accurate values of long-range 13C-1H coupling constants that can be correlated with glycosidic dihedral angles. Molecular modeling calculations on the polysaccharide fragment, including molecular dynamics simulations, identify multiple low-energy conformations. This result is to be contrasted with previous calculations on blood group oligosaccharides in our laboratory using similar methods that showed relatively rigid conformations with little flexibility of the glycosidic linkages. The present NOESY and 3JCH data can be reconciled with a model for the antigenic tetrasaccharide in which three distinct conformations are in fast exchange. We propose that some carbohydrate epitopes such as those of the blood group oligosaccharides are relatively rigid while others such as the tetrasaccharide fragment in these studies exhibit much greater flexibility. © 1996 John Wiley & Sons, Inc.

Notizen: Techniques have been developed for the routine reliable imaging of polysaccharides by atomic force microscopy (AFM). The polysaccharides are deposited from aqueous solution onto the surface of freshly cleaved mica, air dried, and then imaged under alcohols. The rationale behind the development of the methodology is described and data is presented for the bacterial polysaccharides xanthan, acetan, and the plant polysaccharides 1-carrageenan and pectin. Studies on uncoated polysaccharides have demonstrated the improved resolution achievable when compared to more traditional metal-coated samples or replicas. For acetan the present methodology has permitted imaging of the helical structure. Finally, in addition to data obtained on individual polysaccharides, AFM images have also been obtained of the network structures formed by κ-carrageenan and gellan gum. © 1996 John Wiley & Sons, Inc.

Notizen: The lateral packing of a collagen-like molecule, CH3CO-(Gly-L-Pro-L-Pro)4-NHCH3, has been examined by energy minimization with the ECEPP/3 force field. Two current packing models, the Smith collagen microfibril twisted equilateral pentagonal model and the quasi-hexagonal packing model, have been extensively investigated. In treating the Smith microfibril model, energy minimization was carried out on various conformations including those with the symmetry of equivalent packing, i.e., in which the triple helices were arranged equivalently with respect to each other. Both models are based on the experimental observation of the characteristic axial periodicity, D = 67 nm, of light and dark bands, indicating that, if any superstructure exists, it should consist of five triple helices. The quasi-hexagonal packing structure is found to be energetically more favorable than the Smith microfibril model by as much as 31.2 kcal/mol of five triple helices. This is because the quasi-hexagonal packing geometry provides more nonbonded interaction possibilities between triple helices than does the Smith microfibril geometry. Our results are consistent with recent x-ray studies with synthetic collagen-like molecules and rat tail tendon, in which the data were interpreted as being consistent with either a quasi-hexagonal or a square-triangular structure. © 1997 John Wiley & Sons, Inc. Biopoly 40: 595-607, 1996

Notizen: „ChiuZ“ wird 30 Jahre alt! Runde Geburtstage sind nicht nur Grund zum Feiern; die Jubilare nehmen sie auch oft zum Anlaß, um einerseits Bilanz zu ziehen und um andererseits über Gegenwart und Zukunft nachzudenken. Wir haben nun unsere Kuratoren gebeten, einmal aus ihrer Sicht mögliche Entwicklungslinien aufzuzeigen und zu kommentieren, natürlich immer eingedenk der Warnung Niels Bohrs: „Prognosen sind schwierig, besonders wenn sie die Zukunft betreffen.“ Doch lesen Sie selbst!.

Notizen: Radiation-induced graft copolymerization of 4-vinyl pyridine (VP) and a binary mixture of VP and acrylonitrile (AN) onto polyamide-6 (PA6) fiber has been studied. Optimum reaction conditions leading to maximum percentage of grafting have been evaluated. The graft copolymers have been characterized by IR spectroscopy, thermogravimetric analysis and also by studying the dyeing behaviour of the grafted and ungrafted fiber. It has been observed that, although the thermal properties of fibers had changed upon grafting, the dyeing behaviour, with respect to the total dye uptake, did show only little improvement.

Notizen: Structural investigations of low-molecular-weight polyisobutenes synthesized by selective polymerization and of commercial polyisobutenes were made by 1H- and 13C-NMR spectroscopy. It is possible to attribute the signals to “normal” and to some unusual olefinic structures. A comparison was made to literature data.

Notizen: New polymers were synthesized by addition of epichlorohydrin to the polyamides or poly(amideimide)s derived from the polycondensation of poly(alkylenepolyamide)s with some Diels-Alder adducts of resin acids. The adducts were prepared by the reaction between resin acids (extracted from rosin) and acrylic acid or maleic anhydride. The obtained polymers, which were investigated by usual physical and chemical methods, are three-dimensional, thermosetting and fairly thermostable.

Notizen: Zur Beurteilung des viskoelastischen Verhaltens von Synthesefasern sind zeitaufwendige Relaxationsuntersuchungen erforderlich. Um zu schnelleren Aussagen zu gelangen, werden mathematische Modelle benötigt. Charakteristisch für Synthesefasern ist, daß bereits bei sehr kleinen Dehnungen 〈 1% kein lineares viskoelastisches Verhalten angenommen werden kann. Es wird ein auf der Grundlage der Boltzmann-Theorie erweitertes Modell vorgestellt, welches das nichtlineare viskoelastische Verhalten von Synthesefasern beschreibt. Unter Anwendung des hier vorgestellten Modells wird das Relaxationsverhalten der Synthesefasern Nomex® und PEEK beschrieben und ein Konzept zur Messung und Auswertung des Ergebnisses vorgestellt.

Notizen: Electrorheological (ER) fluids composed of a dispersing medium with a low dielectric constant and polyaniline particles, deprotonated with ammonia or sodium hydroxide at different concentrations for 24 h were studied. The effects of dielectric constant, conductivity and volume fraction of the polyaniline particles, the kind of dispersing medium, addition of surfactant, as well as the electric field strength and temperature on the ER properties of the ER fluids were investigated. The results showed that a moisture-insensitive, highly ER-active fluid can be obtained from chlorinated paraffin oil and polyaniline particles deprotonated with ammonia water at certain pH values and exhibited a static yield stress 〉 10 kPa and current density 〈 40 μA cm-2 at 2.8 kV mm-1 DC electric field.

Notizen: A phenolic resin/polyurethane copolymer was synthesized by reaction of a phenolic resin, a blocked-polyurethane and p-toluene sulfonic acid. The copolymer provides a good balance between the processability (including pot life, reactivity) and toughness. The reactions that proceeded during the synthesis of the copolymer was investigated by IR spectroscopy. It was found that blocked polyurethane reacted with the hydroxy group of the phenolic resin. Glass fiber-reinforced composites showed excellent bonding between fiber and matrix as revealed by SEM photographs. An overlap peak was found from the DMA diagram; it indicated that an interaction existed between phenolic resin and polyurethane and that improved the toughness of the phenolic resin.

Notizen: A systematic study of filled natural rubber (NR) vulcanizates has been carried out to investigate the effect of a crosslinkable processing aid, trans-polyoctenylene (TOR) on stress-strain properties at high temperature and after ageing. Three different crosslinking systems, i. e., conventional (CV), semi-efficient (SEV) and efficient (EV), are included in this study. Retention of 200% modulus and tensile strength (TS) at high temperature as well as after ageing has been found to be better with TOR in the CV system. TGA results of gum polymeric blends showed enhanced stability with addition of TOR in both oxygen and nitrogen atmosphere. Enhanced thermal stability is also exhibited by higher onset and peak temperature while determining the rescan enthalpy of the filled vulcanized sample by means of DSC. FTIR (ATR) spectra however show no polymeric interaction between NR and TOR. The improvement of properties in the CV system has been explained with the help of DSC results and a probable mechanism has been suggested on the changes of network structure.

Notizen: Surface functionalization of porous polymer networks was investigated using the sulfonation of macroporous styrene-divinylbenzene (S-DVB) copolymers as model reaction. Reaction conditions for the surface sulfonation were studied. Sulfonation with sulfuric acid in the presence of nitromethane was found to be a suitable method. Models and ideas of network structure are developed in order to estimate surface capacities and to show that surface-sulfonated networks were obtained.

Notizen: Die chemische Modifizierung von Polyacrylnitril-Ultrafiltrations(PAN-UF)-Membranen mit Hydroxylamin führt zu Niederdruckumkehrosmose-Membranen, die neben verbleibenden Nitrilguppen sowohl Amidoxim- als auch Hydroxamsäuregruppen enthalten und bei einem pH von 4,0 bis 6,5 positiv geladen sind.Die Wasserdurchlässigkeit der Membranen sinkt durch diese Modifizierung von 400 L h-1 m-2 auf 15 L h-1 m-2 (p = 0,3 MPa). Eine umfassende Charakterisierung erfolgte anhand von Trennkurven, IR- und NMR-Spektren, der Hg-Porosimetrie, der Membranpotentialmessung und der Trennleistung für verschiedene Metallsalze. Infolge des Donnan-Ausschlusses haben diese Membranen für zweiwertige Metallionen, wie die Härtebildner des Wassers Ca2+ und Mg2+, eine Rückhaltung von 88% bei einem Filtratfluß von 8 L h-1 m-2 (p = 0.3 MPa). Für Schwermetallionen wie Cu2+ und In3+ sind bei annähernd gleicher Rükhaltung wesentlich höhere Durchflußraten von 90 bis 100 L h-1 m-2 (p = 0,3 MPa) möglich.Im wäßrigen, schwermetallionenfreien Medium unterliegen die Amidoxim- und Hydroxamsäuregruppen der Hydrolyse, und es entstehen an der Membranoberfläche Carboxylgruppen, durch die mehrwertige Anionen zurückgehalten werden. Ihr Vermögen zur Wasserenthärtung bleibt erhalten.

Notizen: Acetone was polymerized under the action of NaOH, NaOEt or KOH in ethanolic or methanolic solutions at a molar ratio acetone/base ranging from 1.5 : 1 to 12:1 to give a liquid resin. The liquid resin was obtained with a maximum yield of 60% over initial acetone and was always accompanied by variable quantities of isophorone. The polyenic nature of the ketonic resin obtained was shown by infrared and electronic spectroscopy, as well as by using an isophorone resin as model compound. It is proposed that the structure of the acetone resin should be a condensation product of acetone/ isophorone and isophorone/isophorone. Acetone resins (PCA) obtained both with Brönsted acids (PCA-B), Lewis acids (PCA-L) and alkaline catalysts (PCA-A) can be easily halogenated up to certain degrees of saturation. All PCA resins form Diels-Alder adducts with maleic anhydride, p-benzoquinone and fumaric acid. The adducts can contain from 1 to 2 dienophile molecules per molecule of resin.

Notizen: A new uniform process for the solution chlorination of PVC, PE, and natural rubber has been developed with initiation by γ-irradiation or radical initiators (azocompounds). The solvent used is dichloromethane instead of the industrially used tetrachloroethane or tetrachloromethane. The reaction is carried out in an autoclave with stirrer at temperatures between 70 and 100°C and pressures from 4 to 7 bar. As a result of the simultaneous chlorination of the solvent, trichloromethane is formed and only less than 1 wt.-% tetrachloromethane. Characterization of the chlorinated polymers by DSC and NMR measurements showed no differences to conventionally chlorinated products.

Notizen: The proton-catalyzed polycondensation of aromatic aldehydes with aliphatic and aromatic α,ω-dithiols leads to polymercaptals. The reaction may be carried out in bulk or solution. The bulk polycondensation was catalyzed by hexafluorophosphorous acid (HPF6), formed photochemically by irradiation of the samples containing diaryliodonium salt. The polymers were obtained in high yields but with low molecular weights of Mn 2300-5700 determined by vapour pressure osmometry (VPO). High-molecular-weight products of Mn 9100-24000 (VPO) were obtained by solution polycondensation in dichloromethane catalyzed by p-toluenesulfonic acid. The polymers have been characterized by NMR, VPO, GPC and TGA. Cyclic side products have been isolated and identified. Polyrotaxane structures were found under special conditions.

Notizen: A poly(vinyl alcohol)-β-cyclodextrin (PVA-BCD) copolymer was prepared by successive reaction of BCD with toluylene diisocyanate and PVA. Copolymer formation was evidenced by infrared spectroscopy, differential scanning calorimetry and gel permeation chromatography. Scanning electron micrographs show morphological differences between PVA and the copolymer. The copolymer, being almost insoluble in common solvents with an equilibrium swelling in water of 50%, is a potential membrane material.

Notizen: Isotactic poly(propylene) (iPP) was modified in bulk by addition of low-molecular compounds, e.g. maleic anhydride, sodium maleate, fatty acids or their sodium salts and dibutyl phthalate. It was found that the dependence of the mechanical work of adhesion in the system modified iPP-poly(vinyl acetate) on the concentration of the low-molecular compound in iPP exhibited a maximum. It was shown that the highest value of the mechanical work of adhesion was reached in iPP containing 5 wt.-% of maleic anhydride or sodium maleate and 1 or 1.2 wt.-% of fatty acids or their salts, respectively. It was found that sodium oleate is the most efficient modifier and its addition increased the mechanical work of adhesion by 6.4 times.

Notizen: A series of ethynyl-terminated aromatic imide monomers containing phosphine oxide in the backbone were synthesized by the reaction of tris(3-aminophenyl) phosphine oxide (TAP) or bis(3-aminophenyl)methyl phosphine oxide (BAP) with pyromellitic dianhydride (PMDA) or 3, 3′,4, 4′-benzophenone tetracarboxylic acid dianhydride (BTDA) or 4, 4′-perfluoroisopropylidenebis(phthalic anhydride), and 3-ethynyl aniline. Structural characterization was done by infrared, nuclear magnetic resonance spectroscopy and elemental analysis. Thermal characterization was done by differential scanning calorimetry and thermogravimetric analysis. The decomposition temperatures of cured resins were above 500°C in nitrogen atmosphere. Char yield at 800°C ranged from 52-63.5%.

Notizen: Die Feuchtigkeit stellt bei der Verwendung von Naturfasern in faserverstärkten Kunststoffen neben der geringen Faser-Matrix-Haftung eines der wesentlichen Problemfelder dar. Durch eine optimale Trocknung vor der Verarbeitung lassen sich bei Jute-EP-Verbunden die mechanischen Kennwerte um bis zu ca. 20% steigern.Durch den Einsatz von Haftvermittlern auf Silanbasis läßt sich neben einer Verbesserung der Faser-Matrix-Grenzschicht mit daraus resultierender deutlicher Erhöhung der mechanischen Verbundkennwerte auch der Feuchteeinfluß auf diese deutlich minimieren. So konnte die statische Zugfestigkeit durch die Silanisierung der Faseroberflächen unabhängig vom Feuchtegehalt der Verbunde eingestellt werden. Der Feuchteeinfluß auf den Verbund-E-Modul sowie auf die Wöhlerkurve konnte durch diese Art der Faserbehandlung auch deutlich reduziert werden.

Notizen: Low-molecular-weight stat-poly(ethylene oxide-co-propylene oxide) polymers have been prepared anionically using a new heterogeneous catalytic process previously reported. They were fully characterized by 1H and 13C NMR spectroscopy in order to determine the distribution of the ethylene oxide (EO)-centered triads, as well as the average lengths of poly(ethylene oxide) (PEO) sequences. Low degrees of crystallization were determined by DSC. These copolymers have been successfully used for applications in the solid polymer electrolytes field and high levels of conductivity at room temperature have been measured. The results are in good agreement with those obtained from a Monte Carlo simulation method using the copolymerization terminal model developed for radical polymerization.

Notizen: The preparation of single-phase toluene/sodium bis(2-ethylhexyl)sulfosuccinate(AOT)/water/acrylamide/sodium dodecyl sulfate(SDS) inverse microemulsions is described and their properties prior to polymerization (macroviscosity as a function of volume fraction Φaw of the dispersed aqueous (water + acrylamide(AAm) + SDS) phase, and of SDS/AAm mass ratio) are studied. At 20°C three viscosity maxima are observed. At 50°C all three peaks remain, the viscosity of the first and third peak, respectively, is lowered to 5-8 mPa· s while the second, most prominent peak still marks the level of ca. 250 mPa· s. The polymerization of acrylamide in dispersion systems is initiated by water-soluble ammonium peroxodisulfate (APS) and oilsoluble dibenzoyl peroxide (DBP) at 60°C. The polymerization rate of acrylamide for a given [toluene]/[AOT] molar ratio and AAm/water mass ratio monotonically decreases for Φaw values greater than 20%. The polyacrylamide viscosity molecular mass increases up to a Φaw value of ca. 30%, irrespective of the nature of initiator. For Φaw values over 30% the viscosity molecular mass of polyacrylamide seems to level off with some sings of shallow minimum close to Φaw of 50%.

Notizen: Das Zähigkeitsverhalten von Polycarbonat wird bei dynamischer Beanspruchung mittels instrumentierter Kerbschlagbiegeprüfung bestimmt. In Abhängigkeit von der Temperatur wird elastisches, elastisch-plastisches Werkstoffverhalten mit überwiegend instabilem Rißwachstum und elastisch-plastisches Werkstoffverhalten mit dominanten Anteilen an stabilem Rißwachstum beobachtet. Mit der energiebestimmten bruchmechanischen Kenngröße „J-Integral“ wird eine Auswertemethode zur Verfügung gestellt, die eine Bewertung der Temperaturabhängigkeit in einem weiten Temperaturbereich erlaubt. Die J-Integral-Werte zeigen ein kraftdeterminiertes lokales Maximum bei -60°C und ein globales Maximum bei 60°C, das mit einem spannungsinduzierten Scherfließprozeß in Beziehung steht. Der Schnittpunkt der Spur der ß-Relaxation mit der Bruchfrequenz im Arrhenius-Diagramm ergibt sich zu einer Temperatur von -60°C bei einer Frequenz von 300 Hz. Daraus ist zu ersehen, daß die Zähigkeitserhöhung bei -60°C durch die ß-Relaxation stimuliert wird. Im gewählten Temperaturbereich war es möglich, die quantitative Größe ausgewählter Bruchflächenphänomene mittels lichtmikroskopischer Untersuchungen zu ermitteln und in Beziehung zum Werkstoffverhalten zu setzen.

Notizen: This paper studies the effect produced by different vanadium oxides on the microstructure of PEO and PEO/PPO blends by means of the analysis of the crystallization kinetics under isothermal and nonisothermal conditions. The electrical properties of the samples were characterized by complex impedance analysis. Results suggest that the additives employed (considering both carbon black and vanadium oxides) promote changes in the microstructure of PEO/PPO polymer blends because of polymer-additive interactions. All samples tested show good conductivity properties.

Notizen: Ausgehend von den Grundlagen zur Kapillarrheometrie mit den bekannten Korrekturverfahren nach Rabinowitsch und Bagley wird das traditionelle Verfahren zur Ermittlung des Düseneinlaufdrucks sowie des Wandschubspannungswerts dargestellt. Dieses Verfahren kann bei manchen Materialien zur fehlerhaften Bewertung des Fließverhaltens führen, da ein linearer Druckabfall in den Meßdüsen unterstellt wird. Daher wird eine neue Methode zur direkten Schubspannungsermittlung vorgestellt sowie die dazu notwendige Meßeinrichtung beschrieben. Es handelt sich dabei um eine in-line integrierbare Düse, die auf der Basis eines auf Piezokraftaufnehmern gelagerten Düsenabschnitts die Reaktionskraft der strömenden Schmelze auf die Düsenwandung ermittelt.Die Meßergebnisse zeigen, daß bei der Ermittlung der Fließeigenschaften von Materialien, die ein Potential zur Strukturbildung während des Fließvorganges aufweisen, wie z. B. flüssigkristalline Polyester (LCP), mit der In-line-Düse korrekte Wandschubspannungen erhalten werden. Mit der klassischen Methode der Kapillarrheometrie hingegen können bei solchen Materialien nur dann vergleichbare Ergebnisse gewonnen werden, wenn zusätzliche Annahmen über den Druckverlauf in der Meßdüse gemacht werden.

Notizen: New azomethine-urethanic compounds were synthesized, starting from 2,2′-[methylenebis(nitrilomethylidyne)]diphenol and phenylisocyanate for the model compound and tolylene-2,4-diisocyanate for the polymer. The products were characterized by elemental analysis, IR and NMR spectroscopy as well as thermogravimetry, DSC and viscosimetry. Through heating, these compounds suffer chemical modification, both addition and condensation reactions being possible. Thermogravimetric studies have evidenced the formation of thermostable products, possibly due to hexahydrotriazinic structures resulted from the thermal treatment.

Notizen: The influence of CO2 laser radiation on the surface properties of a lamination resin (temperature resistant up to 120°C) which is used for carbon fibre-reinforced plastics (CFRP) is examined. It is shown by XPS and infrared spectroscopy that the hydroxy groups of the resin are eliminated by the laser radiation. Using a carbon dioxide atmosphere, also deeper parts of the resin are influenced compared to the treatment in air. The reproducibility of the bond strength is higher for the laser-treated samples than for untreated samples if a room temperature-curing adhesive is used, but the bond strength itself is lower. Laser treatment shows no influence at all if a hot-curing adhesive is used.

Notizen: A new macromonomeric peroxyinitiator (MMPI) was synthesized by the reaction of polytetrahydrofurandiol (p-THF-diol), Mw (1000), isophorone diisocyanate, 2,5-dimethylhexyl-2,5-dihydroperoxide and 2-isocyanatoethyl methacrylate. Homopolymerization of MMPI at 80°C gave crosslinked polytetrahydrofuran (poly-THF) with swelling ratios in CHCl3 varying between 1.4 and 4.2.Styrene polymerization initiated by MMPI at 80°C in bulk gave crosslinked poly-THF-b-polystyrene block copolymers. The overall rate constant, k, was found to be 1 · 10-4 (L mol-1)1/2 s-1 by keeping the polymer yield below 15%. Swelling ratios of the crosslinked block copolymers in CHCl3 were between 2.7 and 75 according to the concentration of MMPI and the polymerization time. In case the MMPI concentration was kept constant while the polymerization time was increased, swelling ratios were found between 3.55 and 7.07. Thermogravimetric analysis showed that the crosslinked block copolymers were still containing undecomposed peroxy groups, so they can thermally initiate styrene polymerization in order to obtain multicomponent cross-linked copolymers.

Notizen: Poly(methyl methacrylate) is a preferred material used in X-ray lithography. One effect observed after irradiation is a change of its chemical structure, combined with a decrease of the molar mass. This was analysed quantitatively using size exclusion chromatography combined with multi-angle laser-light scattering. Based on a kinetic model, an equation was derived which gives a satisfactory description of the dependence of the molar mass on the radiation dose.

Notizen: A cyanomethylated styrene-divinylbenzene copolymer was prepared by the reaction of a chloromethylated styrene-divinylbenzene copolymer with sodium cyanide. A polystyrene-based macroreticular resin containing a pair of neighboring nitrile groups in each monomeric styrene unit was obtained from the reaction of the cyanomethylated copolymer with 3-chloropropionitrile under phase transfer conditions. The resin was reacted with hydroxylamine to afford a chelating resin containing a pair of neighboring amidoxime groups in each monomeric styrene unit. The chelating resin showed high adsorption capacity for uranyl ions. It was found that the resin was an effective adsorbent for other heavy metal ions such as Hg2+ and Pb2+.

Notizen: The graft polymerization of vinylidene chloride (VDC) onto cellulose initiated by ceric ions is reported. The grafting yield increases with reaction time and then levels off after 6 h. On the other hand, the grafting efficiency decreases rapidly from high initial values at short reaction times and then approaches to a constant value. The mechanism from of grafting is suggested for the present copolymerization. In order to determine both grafting yield and grafting efficiency, the separation of homopolymer and graft polymer is required. Sufficiently high temperatures are needed to dissolve poly(vinylidene chloride) (PVDC) because of its high crystallinity and melting point. Cyclohexanone dissolves the graft copolymer at 120°C bringing about some degradation of cellulose. Degradation is produced by hydrogen chloride formed throughout a slight dehydrochlorination of the synthetic polymer. A method inert for cellulose is suggested to retrieve the homopolymer from the polymerization crude by using a mixture of dry cyclohexanone and 4-methylpyridine as solvent.

Notizen: The Young's modulus E and Poisson's ratio v of various thermosets, including 6 amine crosslinked epoxies, one anhydride crosslinked epoxy, one styrene crosslinked polyester and one styrene crosslinked vinylester, were determined from tensile tests in the 220-393 K temperature range and 1.6710-4-1.6710-2 s-1 strain rate range. The bulk (B) and shear (G) modulus were calculated from E and v. Some observations about structure-property relationships can be derived from these data and their comparison with corresponding ones relative to linear polymers. B appears to depend essentially of the cohesion and packing density and does not depend, practically, of temperature and strain rate. In contrast, G depends sharply of the local molecular mobility, this latter being affected by an antiplasticization mechanism. The Poisson's ratio seems to be systematically higher for thermosets than for linear polymers.

Notizen: Standard epoxy resins have good mechanical properties, but their prolonged low temperature curing time limits their potential use in clinical applications as well as in many industrial applications. A fast-curing epoxy-episulfide resin has been developed. The gel time of epoxy-episulfide made from EPONTrade mark of Shell Chemical Company. 828 ranges from 2 to 10 minutes by changing the ratio of the ingredients. The heat of reaction of this system is low, resulting in low cure shrinkage. Water absorption of the episulfide network is low. The epoxy-episulfide system cured with polyamide curing agent V-40 exhibits two transition temperatures, at about 85°C and 130°C, as shown in dynamic mechanical analysis data. In order to solve the long term stability problem of the above episulfides, and also the mixing problem, a lower viscosity resin, Eponex, was used to make Eponex-sulfide. Eponex-sulfide systems show promise in that they remain in a stable liquid form without epoxy. The other advantages appear to be retained.

Notizen: Structure and properties of microgels prepared by emulsion copolymerization depend on the composition and concentration of the monomers at the reaction sites, on the reactivity ratios and on the solubility of the comonomers in water. By separate and joint solubilization of 1,4-divinyl benzene and various comonomers of different solubility it could be shown, that the diffusion control of the copolymerization rate is favoured by crosslinking, by a high concentration of an oil-soluble initiator and of the emulsifier and by a low solubility of the comonomer in water.

Notizen: This paper describes studies on the formation of microgels from high functionality mixtures of monomers which are able to polymerise by a step-growth process to polyurethanes in the specially selected solvent butan-2-one. Using the reactants poly(ethylene glycol) 6000, 1,2,6-hexanetriol and biscyclohexylmethane-4,4′-diisocyanate in formulations made to comprise exactly one isocyanate group per hydroxyl, it was found that microgels of number average molecular weight, as determined by Gel Permeation Chromatography, of less than 20,000 were obtained up to the Critical Gelation Concentration which ranged from w/w reactant to solvent concentrations of from ∼ 0.24 to 0.74 at PEG/HT ratios of 1:4 to 4:4 respectively. These polymerisations surprisingly, went to complete conversion without gelation and produced 95 - 99% yields of microgel product after precipitation into a non-solvent. Intrinsic viscosity determinations on the microgels dissolved in chloroform were determined and used to obtain estimates of the swollen coil densities at infinite dilution from which the critical packing concentration of these swollen coils in the solvent used for the solvent could be estimated. The critical packing concentration was in all cases well below the Critical Gelation Concentration. It was thus clearly demonstrated that the formation of “soluble” microgels is progressing in spite of the system being critically packed. This is a surprising observation and especially so when it is combined with the very low measured weight average molecular weights and high conversions of the products in the critically packed region. The GPC molecular weights decreased at the higher concentrations which is contrary to expectations. The ability to form microgels above critical packing confirms the results obtained and reported previously by us, that a similar phenomenom occurs in the case of the polymerisation of polyfunctional free-radically polymerised monomer systems. These observations will need to be taken into account when formulating mathematical analyses of the gelation process. This class of products are able to be crystallised from organic solvents and are soluble in water. They are potentially useful as components of pharmaceutical formulations for the controlled release of drugs, high molecular weight active materials and living microorganisms.

Notizen: In an early stage of the polycondensation of phenol/formaldehyde (Ph/F) systems catalyzed by bivalent metal acetates (Me2+(ac)2), 2-hydroxy-benzylalcohol (2-OH-BA) formation was selective in the weak acidic medium and only in the presence of the catalyst. The concentration change in 2-OH-BA and its hemiformal (HF) was followed by GPC as a function of the pH value of the system and the catalyst concentration and was found to be independent of the type of metal used in the catalyst but dependent on the pH value of the medium and on the catalyst concentration. An extremely high catalyst concentration does not cause further increase in the overall rate of 2-OH-BA formation. It was proved by 1H NMR that at higher conversion and in the presence of Me2+(ac)2 catalyst, the o-o′-Ar—CH2—Ar isomers are dominating over o, p′ and p,p′ ones. Novolacs with overwhelming o-diphenylmethane structures are thermally stable up to 400°C and can be crosslinked without hexamethylenetetramine (HEXA).

Notizen: Seven homologous samples of a thermoplastic polyurethane (TPU) were characterized in dilute solutions of N-methyl-2-pyrrolidinone (NMP) by size exclusion chromatography (SEC) on normal-phase silica gel, low-shear viscometry and membrane osmometry. The Staudinger-Mark-Houwink (SMH) constants of this homologous series were obtained by a new procedure of calculation on the basis of universal calibration of SEC with narrow polystyrene standards. The calculated SMH constants for these TPU samples in NMP at 298 K (K = 3.94 mL g-1, a = 0.29) prove the branched structure of this TPU samples and were further confirmed by osmometry.

Notizen: A new Monte Carlo (MC) algorithm is reported which enables RAfa +RBfb polymerisations to be simulated. It is based on the random reaction of pairs of groups for intermolecular reaction, with intramolecular reaction weighted according to Gaussian statistics and the size of ring structure being formed. The algorithm counts all the ring structures formed and enables polymerisations to be simulated efficiently up to complete reaction. Gel point and modulus results from trifunctional and tetrafunctional polyurethane-forming polymerisations are modelled, with particular emphasis on the effects on modulus of network defects at complete reaction. More in keeping with experiment, higher reductions in modulus at complete reaction are predicted using the the present algorithm than using Biosym MC software. However, it is shown that quantitative agreement with experiment cannot be obtained unless relationships defining the entropies of various ring structures are elucidated and more accurate modelling of the chain statistics governing the intramolecular reaction forming ring structures of various sizes is used.

Notizen: The present investigation concerns acrylic/silicone polymer networks formed by the hydrosilylation reaction. Acrylic polymers containing alkenyl groups have been obtained by radical polymerization of a monomer having an alkenyl group and other vinyl monomers. Also a silicone polymer containing SiH groups has been prepared by the equilibrium reaction in presence of sulfuric acid. They are compatible with each other and can be crosslinked by the hydrosilylation reaction. The cured films are approximately of uniform structure and their acid resistance is excellent.

Notizen: The effect of alumina particulates on a thermoplastic matrix is investigated, in particular the effect altering the alumina particle size and morphology has on the mechanical properties. Different grades of alumina are used and two thermoplastic matrices; namely poly(propylene) and poly(ethylene-co-vinyl acetate). Investigations showed that optimum properties were achieved with the alumina of smallest particle size and lowest aspect ratio. Preliminary work has also been performed on the use of silane coupling agents and they have proved effective in increasing the tensile properties of the composites.

Notizen: Based on an earlier paper of Chen and Lee, a procedure is developed to determine optimal reaction times for predetermined monomer conversions and number-average degrees of polymerization in an azeotropic free-radical batch copolymerization with one charge of monomers and initiator. The procedure allows for the calculation of the admissible range of monomer concentrations, the determination of an appropriate initiator and its most suited concentration to arrive at the goal in reaction times as short as possible. The validity of the model was tested in the free-radical copolymerization of acrylonitrile and butadiene in chlorobenzene at 343 K, using 1,1′-azocyclohexanenitrile (ACN) and 2,2′-azoisobutyronitrile (AIBN) as initiators. The agreement of theoretical and experimental data was satisfying. It is pointed out that the gel effect can be incorporated into the model, and that the procedure can also be used in the design of free-radical homopolymerizations.

Notizen: Eight samples of poly(ethylene-co-propylene-co-diene) (EPDM, containing 55 wt.-% ethylene) were vulcanized with 0.5-8.0 phr dicumyl peroxide. The influence of molar volumes V1 of cyclohexane, hexane, heptane, iso-octane, tetrachloromethane, carbon disulfide, xylene, benzene, toluene, tetrahydrofuran, trichloromethane and chlorobenzene on the swelling intensity of the EPDM vulcanizates was studied, and it was found that regardless of the solubility parameters, polarity, dielectric constants, acidity or basicity of solvents, a linear relationship exists between V1 and number of moles of solvent in the gels, n1. With increase of V1, n1 decreases.

Notizen: Differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to study the miscibility of blends of a graft copolymer of poly(methyl methacrylate) on linear low density polyethylene (LLDPE-g-PMMA, G-3) with poly(vinylidene fluoride)Systematic name: poly(1,1-difluoroethylene).(PVF2) and the compatibilization of blends of LLDPE/PVF2. The specific interaction between PMMA side chains and PVF2 in G-3/PVF2 binary blends is weaker than that between the homopolymers PMMA and PVF2. There are two states of PVF2 in the melt of a G-3/PVF2 (60/40, w/w) blend, one as pure PVF2 and the other interacting with PMMA side chains. The miscibility between PMMA side chains and PVF2 affects the crystallization of PVF2. LLDPE-g-PMMA was demonstrated to be a good compatibilizer in LLDPE/PVF2 blends, improving the interfacial adhesion and dispersion in the latter. Diffusion of PMMA side chains into PVF2 in the interfacial region reduces the crystallization rate and lowers the melting point (Tm) and the crystallization temperature (Tc) of PVF2 in the blends.

Notizen: New polythioesters were synthesized by interfacial polycondensation of bis(4-mercaptomethylphenyl)methane with selected aliphatic and isomeric phthaloyl dichlorides. To determine optimum polycondensation conditions, the influence of the following factors on reduced viscosity and yield were studied: type of organic phase, concentration of hydrogen chloride acceptor (NaOH), concentration of reagents, aqueous/organic phase ratio, rate of acid chloride addition, reaction time and reaction temperature.A thorough examination was carried out only for the polycondensation of dithiol with adipoyl and isophthaloyl dichlorides chosen as model systems. The structures of polythioesters were confirmed by elemental analysis, X-ray analysis and infrared spectroscopy. Some physicochemical, mechanical and electrical properties were determined. The molecular weights were not measured, because of the low solubility of the obtained polythioesters.

Notizen: Der Einfluß submikroner mineralischer Additive auf die rheologischen Eigenschaften von Polyamid 6 (PA 6) wurde untersucht. Üblicherweise steigt bei niedriger Schergeschwindigkeit die Viskosität nach der Einarbeitung zunehmender Mengen kommerzieller Füllstoffe (Mikronbereich der Korngrößen) stetig an, weil die Reibung in den Gleitschichten zunimmt.Nach intensiver Dispergierung submikroner Additive in Ethylenglykol unter Zusatz von Polyethylenimin als kationaktivem Dispergierhilfsmittel wurde eine agglomeratfreie Dispergierung aller untersuchten Additive erreicht. Unter Standardbedingungen wurden die glykolischen Suspensionen mit Hilfe eines Doppelschneckenextruders in die PA 6-Matrix eingearbeitet, dabei mittels einer Entgasungsstufe sofort der Glykolüberschuß entfernt. Die erwarteten Effekte verbesserten intramolekularen Gleitens zeigten sich in unterschiedlicher Höhe bei TiO2, Al2O3, SiO2, Kaolin und Talkum. CaCO3 dagegen schränkte auch im Submikronbereich das intramolekulare Gleiten schon in Konzentrationen unter 1 Gew.-% deutlich ein. Bei der Einarbeitung pulverförmiger Additive mittels eines Doppelschneckenextruders direkt in die PA 6-Matrix wurden analoge Effekte nicht erreicht.

Notizen: L'étude préliminaire des propriétés microlithographiques des résines obtenues en mélangeant un polyimide et un bis-azide a permis de montrer que de telles résines pourraient probablement être utilisées en tant que résines microlithographiques sensibles aux UV lointains. En effet ces résines donnent des couchages homogènes qui ont des épaisseurs convenables. De plus, elles sont très sensibles aux irradiations: elles subissent alors des modifications de structure lorsqu'on les irradie par des radiations de longueur d'onde égale à 254 nm. Les parties ainsi insolées sont insolubles dans les solvants constitués par des mélanges d'eau et de dioxane ou d'eau et de 1-N-méthylpyrrolidone alors que ces mêmes solvants solubilisent parties non insolées.

Notizen: Given a probability distribution from which the energy spectrum of a random peptide is to be sampled, we derive a general expression for the probability that such a peptide will fold to a unique native state and for the probability distribution of the native energy. This latter result allows us to localize the energy of folding based on model parameters and is one advantage of our formulation. Evidence from both the lattice theory of proteins and protein threading experiments suggest that the energy spectrum for the compact states of a peptide chain is Gaussian in form. For this reason we have derived from the more general framework the specific formulas that apply in the Gaussian case, where one requires only the number of states and the variance of the Gaussian distribution in order to apply the theory. This simplicity allows us to perform calculations that we compare with calculations previously made by others based on statistical thermodynamics. We find qualitative agreement, but a significant correction to prior estimates of folding probability derived from the Gaussian assumption is necessary. © 1996 John Wiley & Sons, Inc.

Notizen: Molecular mechanics calculations have been performed for the disaccharide neocarrabiose, one of the repeat units of β-carrageenan, as a general model for the (1 → 3)-linkage in the carrageenans. An adiabatic conformational energy map for this molecule has been prepared by constrained energy minimization and compared to previously reported relaxed maps. Neither the experimentally determined crystal structure of neocarrabiose nor the fiber diffraction conformation of β-carrageenan is a low energy conformation on the relaxed Ramachandran map. Molecular dynamics simulations in vacuum produced trajectories consistent with this relaxed vacuum surface. However, a simulation with explicitly included solvent water molecules produced a trajectory that remained in the region of the two experimental structures. This dramatic solvation effect is apparently the result of the breaking of an interring hydrogen bond between the O2 hydroxyl groups of neocarrabiose as both groups hydrogen bond to solvent. © 1996 John Wiley & Sons, Inc.

Notizen: Monte Carlo simulations are employed to investigate the thermodynamics of the first transition in writhe of a circular model filament corresponding to a 468 base-pair DNA. Parameters employed in these simulations are the torsional rigidity, C = 2.0 × 10-19 dyne cm2, and persistence length, P = 500 Å. Intersubunit interactions are modeled by a screened Coulomb potential. For a straight line of subunits this accurately approximates the nonlinear Poisson-Boltzmann potential of a cylinder with the linear charge density of DNA. Curves of relative free energy vs writhe at fixed linking difference (Δ1) exhibit two minima, one corresponding to slightly writhed circles and one to slightly underwrithed figure-8's, whenever Δ1 lies in the transition region. The free energies of the two minima are equal when Δ1c = 1.35, which defines the midpoint of the transition. At this midpoint, the free energy barrier between the two minima is found to be ΔGbar = (0.20) kBT at 298 K. Curves of mean potential energy vs writhe at fixed linking difference similarly exhibit two minima for Δ1 values in the transition region, and the two minimum mean potential energies are equal when Δ1 = 1.50. At the midpoint writhe, Δ1c = 1.35, the difference in mean potential energy between the minimum free energy figure-8 and circle states is (1.3) kBT, and the difference in their entropies is 1.3 kB. Thus, the entropy of the minimum free energy figure-8 state significantly exceeds that of the circle at the midpoint of the transition. The first transition in writhe is found to occur over a rather broad range of Δ1 values from 0.85 to 1.85. The twist energy parameter (ET), which governs the overall free energy of supercoiling, undergoes a sigmoidal decrease, while the translational diffusion coefficient undergoes a sigmoidal increase, over this same range. The static structure factor exhibits an increase, which reflects a decrease in radius of gyration associated with the circle to figure-8 transition. © 1996 John Wiley & Sons, Inc.

Notizen: Poly(dimethyldiallylammonium chloride) (PDMDAAC) exhibits a strong electrostatic interaction with bovine serum albumin (BSA) at pH 8.0 in 0.16M NaCl. Electrophoretic, dynamic, and static light scattering suggest that the mode of binding of BSA to PDMDAAC depends upon the weight concentration ratio (r) of BSA to PDMDAAC. When r is smaller than ca. 10, the system exhibits characteristics of cooperative binding, in that the BSA molecules are inhomogeneously distributed among the polymer chains, and free PDMDAAC molecules coexist with complex. When r reaches ca. 10, the amount of free PDMDAAC is too small to be observed. Further increase in r leads to a secondary binding process along with an increase in the amount of free protein. Hydrophobic interactions among the bound BSA are proposed as the driving force for the cooperative binding. © 1996 John Wiley & Sons, Inc.

Notizen: The thermostable sweet protein brazzein consists of 54 amino acid residues and has four intramolecular disulfide bonds, the location of which is unknown. We found that brazzein resists enzymatic hydrolysis at enzyme/substrate ratios (w/w) of 1:100-1:10 at 35-40°C for 24-48 h. Brazzein was hydrolyzed using thermolysin at an enzyme/substrate ratio of 1:1 (w/w) in water, pH 5.5. for 6 h and at 50°C. The disulfide bonds were determined, by a combination of mass spectrometric analysis and amino acid sequencing of cystine-containing peptides, to be between Cys4-Cys52, Cys16-Cys37, Cys22-Cys47, and Cys26-Cys49. These disulfide bonds contribute to its thermostability. © 1996 John Wiley & Sons, Inc.

Notizen: No abstract.

Notizen: Antibacterial properties of the secretion from the female reproductive accessory glands of medfly Ceratitis capitata are mostly ascribed to the presence of two peptides, ceratotoxin A and B, which exhibit a strong activity against gram-positive and gram-negative bacterial strains, and show sequence and function homology with cecropins, melittin, and magainins.CD experiments performed in different solvents indicate the presence of a significant content of helical structures in organic solvent.Two-dimensional nmr results for ceratotoxin A in methanol show a helical behavior for the 8-25 region of the peptide. A Ramachandran classification of each residue for the structures obtained from distance geometry calculations lead to the definition of four structural families in which the central segment 10-19 is always helical and differences refer to residues 8-9 and 19-23.A sequence analysis of the two ceratotoxins and a systematic search on the protein data bank revealed the occurrence of a KX-hydrophobic-hydrophobic-P motif that seems to be important for helix stabilization. © 1996 John Wiley & Sons, Inc.

Notizen: The intramolecular interaction of protected dipeptides and tripeptides containing the amino acid units Ala, Phe, and Val was studied by means of ir spectroscopy. The NH and CO regions of the compounds dissolved in carbon tetrachloride clearly show the existence of different intramolecular hydrogen bonds. Using solvents with higher polarity such as chloroform and methylene chloride, the association bands disappear. Investigating the substances with the same amino acid sequence but opposite chirality of the central C atom in the peptide chain, we observed different band shapes in the CO and NH regions. Large effects were found when the chirality of the Phe unit in the second position was changed. This is probably due to the steric hindrance originated by the rotation of the aromatic ring in the side chain.The protecting groups, Z (benzyloxycarbonyl) or Boc (tert-butyloxycarbonyl) residues at the N-terminal group and methyl- or tert-butyl esters at the C-terminal group, influence the solubility of the substances in nonpolar solvent, as well as the NH and CO association band profiles in the methylene chloride solutions.The consequences of changing the sequence of the amino acids are discussed for the tripeptide derivatives.Besides a qualitative discussion, some quantitative considerations concerning the intramolecular interaction are also given to illustrate the different stabilities of the associates. © 1996 John Wiley & Sons, Inc.

Notizen: A laboratory-made sample of the polysaccharide xylinan (acetan) has been further characterized with respect to (i) purity, (ii) molar mass and polydispersity, and (iii) gross conformation by a combination of hydrodynamic measurements (sedimentation velocity and equilibrium analytical ultracentrifugation, viscometry, and dynamic light scattering) in aqueous NaCl (I = 0.10 mol·L-1). Sedimentation velocity diagrams recorded using Schlieren optics revealed highly pure material sedimenting as a single boundary [so20.w = 9.5 ± 0.7) S; ks = (273 ± 112) mL/g]. The hypersharp nature of these boundaries is symptomatic of a polydisperse and highly nonideal (in the thermodynamic sense) system. Low speed sedimentation equilibrium in the analytical ultracentrifuge using Rayleigh interference optics and two different types of extrapolation procedure (involving point and whole-cell molar masses) gave a weight average molar mass Mw of (2.5 ± 0.5) × 10-6 g·mol-1 and also a second virial coefficient, B = (2.8 ± 0.7) × 10-4 mL·mol·g-2, both values in good agreement with those from light scattering-based procedures (Part II of this series). A dynamic Zimm plot from dynamic light scattering measurements gave a z-average translational diffusion coefficient Do20.w = (3.02 ± 0.05) × 10-8 cm2·s-1 and the concentration-dependence parameter kD = (370 ± 15) mL/g. Combination of so20.w with Do20.w via the Svedberg equation gave another estimate for Mw of ≅ 2.4 × 106 g/mol, again in good agreement. Both the Wales-van Holde ratio (ks/[η]) ≅ 0.4 (with [η] = (760 ± 77) mL/g) and the ρ-parameter (ratio of the radius of gyration from static light scattering to the hydrodynamic radius from dynamic light scattering) as ρ 〉 2.0 all indicate an extended conformation for the macromolecules in solution. These findings, plus Rinde-type simulations of the sedimentation equilibrium data are all consistent with the interpretation in terms of a unimodal wormlike coil model performed earlier. © 1996 John Wiley & Sons, Inc.

Notizen: Incorporation of easily available achiral ω-amino acid residues into an oligopeptide results in substitution of amide bonds by polymethylene units of an aliphatic chain, thereby providing a convenient strategy for constructing a peptidomimetic. The central Gly-Gly segment of the helical octapeptide Boc-Leu-Aib-Val-Gly-Gly-Leu-Aib-Val-Ome(1) has been replaced by δ-amino-valeric acid (δ-Ava) residue in the newly designed peptide Boc-Leu-Aib-Val-δ-Ava-Leu-Aib-Val-OMe(2). 1H-nmr results clearly suggest that in the apolar solvent CDCl3, the δ-Ava residue is accommodated into a folded helical conformation, stabilized by successive hydrogen bonds involving the NH groups of Val(3), δ-Ava(4), and Leu(5). The δ-Ava residue must adopt a gauche-gauche-trans-gauche-gauche conformation along the central polymethylene unit of the aliphatic segment, a feature seen in an energy-minimized model conformation based on nmr parameters. The absence of hydrogen bonding functionalities, however, limits the elongation of the helix. In fact, in CDCl3, the folded conformation consists of an N-terminal helix spanning residues 1-4, followed by a Type II β-turn at residues 5 and 6, whereas in strongly solvating media like (CD3)2SO, the unfolding of the N-terminal helix results in β-turn conformations at Leu(1)-Aib(2). The Type II β-turn at the Leu(5)-Aib(6) segment remains intact even in (CD3)2SO. CD comparisons of peptides 1 and 2 reveal a “nonhelical” spectrum for 2 in 2,2,2-trifluoroethanol. © 1996 John Wiley & Sons, Inc.

Notizen: The combined use of several nuclear magnetic resonance and restrained molecular dynamics techniques allowed the formulation of a molecular model for the preferred solution conformation of a synthetic peptide reproducing the [1-20] processing domain of the pro-ocytocin-neurophysin precursor. In the model, the conformation of the 20-membered tocin ring, with the two Cys1 and Cys6 residues bridged by a disulphide bond, is very close to that observed for isolated ocytocin in the solid state; in addition, a type II β-turn is postulated for the 7-10 segment of the acyclic tail containing the Lys11-Arg12 processing site, and connecting ocytocin to the neurophysin domain, while the C-terminal 13-20 segment of the molecule is believed to assume a helical structure. This particular structural organization could be important in participating as the favorable conformation for optimal substrate-enzyme active site recognition and processing by specific endoproteases. © 1996 John Wiley & Sons, Inc.

Notizen: Recent x-ray structure analyses of peptides in Japan were reviewed. A series of peptides containing an aminoisobutyric acid (Aib) residue was analyzed and their helical types were investigated. Two convenient methods to determine helical types were obtained. One method was obtained by calculating averaged helical parameters and the other was obtained by investigating meridional intensity distributions. The conformations of some peptides, such as aureobasidin E, ascidiacyclamide, synthetic analogues of heat-stable enterotoxin, were studied by an x-ray diffraction method, and in some cases, with the help of nmr spectroscopy and molecular mechanics calculations. Since these peptides have physiologically important activities, the structure-activity relationships of these peptides were discussed. Several other peptide structures and the polymorphism of amino acids are also reported. © 1996 John Wiley & Sons, Inc.

Notizen: The X-ray diffraction experiments on peptides and related molecules which have been carried out in Western Europe, except Italy, in the last eight years are reviewed. The crystal structures of some bioactive peptides such as Leu-enkephalin (a neurotransmitter), cyclosporin A (an immunomodulator in both the free and protein-bound state), balhimycin (an antibiotic) and octreotide (a somatostatin analogue) are briefly presented. Crystallized N- and C-protected model peptides have given an insight into the folding tendency and folding modes depending on the peptide sequences. The crystal structures of various pseudopeptide molecules reveal how the three-dimensional structure of peptide analogues can be modulated by substituting non-peptide groups for the peptide bond. A few examples of structural mimetics of the β- and γ-turns, and of templates for α-helix induction are also presented. © 1996 John Wiley & Sons, Inc.

Notizen: The solid state structures of many opioid peptide agonists have been elucidated by x-ray diffraction analysis. Recently, the first structure of an opioid peptide antagonist has been determined. Theoretically, linear peptides can have many different backbone conformations, yet early x-ray studies (1983-1987) on enkephalin and its analogues showed only two different backbone conformations: extended and single β-bend. In 1989 enkephalin was observed in a third conformation, a double β-bend. Since that time diffraction studies have been completed on the rationally designed linear opioid peptide agonists DTLET (Tyr-D-Thr-Gly-Phe-Leu-Thr) and DADLE (D-Ala2, D-Leu5-enkephalin) as well as on several cyclic enkephalin analogues including DPDPE (Tyr-[D-Pen-Gly-Phe-D-Pen]) and JOM-13 (Tyr-[D-Cys-Phe-D-Pen]). The most recent review of the x-ray studies on this class of compounds was written in 1988. This paper will update that review to include the results of studies completed since that time. © 1996 John Wiley & Sons, Inc.

Notizen: The methodology of regioselective cysteine pairings in synthetic multiple-cystine peptides has progressed in the past years to an efficiency that allows for at least three specific inter- and intrachain disulfide bridgings. Conformational studies on various multiple-cystine peptides like hormones, protease inhibitors, and toxins revealed that these bioactive peptides, generated by posttranslational processing of precursor proteins, are folded into miniprotein-like compact globular structures of remarkable stability. This strongly suggests protein domain or subdomain properties of these families of peptides, and thus sufficient sequence-encoded information for correct oxidative refolding under appropriate experimental conditions. From intensive research on the mechanisms and pathways of oxidative refolding of proteins in vivo and in vitro, the efficient methods have emerged for simulating nature in the regeneration of native folds not only for intact proteins, but also for protein domains and subdomains. In fact, the results obtained in the oxidative folding of excised protein fragments and of relatively low mass products of posttranslational processings show that this procedure is indeed a simple way of preparing peptides with several disulfide bonds, if optimization of reaction conditions is performed in terms of redox buffer, temperature, and additives capable of disrupting aggregates and of stabilizing nascent secondary structures. Moreover, with increased knowledge about stable, small natural cystine frameworks, their use instead of artificial templates should facilitate engineering of synthetic miniproteins with specific conformation and tailored functions. © 1996 John Wiley & Sons, Inc.

Notizen: N-Alkoxycarbonylamino acids are chirally stable under normal conditions of coupling. In the presence of tert.amine (tertiary amine), most activated N-alkoxycarbonylamino acids generate 2-alkoxy-5(4H)-oxazolone, which is not chirally stable in the presence of the base. Consequently, enantiomerization occurs in the presence of tert.amine if the activated residue is not immediately consumed by aminolysis. This paper reviews the situations in which 2-alkoxy-5(4H)-oxazolones are generated from N-alkoxycarbonylamino acids, the enantiomerization that occurs during and after the incorporation of N-alkoxycarbonylamino acids into peptides, the properties and methods of preparation of 2-alkoxy-5(4H)-oxazolones, and the practical use that has been made from our knowledge of the chemistry of 2-alkoxy-5(4H)-oxazolones. © 1996 John Wiley & Sons, Inc.

Notizen: Collagens can be distinguished from other proteins based on their triple-helical structure. Synthetic peptide models have been developed to better understand the triple helix structurally and to evaluate the triple helix as a recognition element for biological processes. Associated triple-helical peptides were first designed and assembled by solid-phase methodology in the late 1960s. Such peptides were used for triple-helical structural characterization by CD, nmr, and ir spectroscopies, and x-ray crystallography, and for studying the structural preferences of hydroxylases. In the late 1970s, methods were developed for covalently linking the three strands of triple-helical peptides. One benefit of “branched” peptides was the enhancement of triple-helical thermal stability. The incorporation of specific collagen sequences into thermally stable synthetic triple helices in the early 1990s has allowed for the mechanistic investigation of collagen-mediated cell adhesion and platelet aggregation. In time, discriminatory therapeutics may result from the continued exploration and further understanding of the biological effects of collagen primary, secondary, and tertiary structures via triple-helical peptide models. © 1996 John Wiley & Sons, Inc.

Notizen: Simple collagen-like peptides comprising a repeat Gly-Pro-Hyp sequence are highly platelet-reactive when presented to platelets in triple-helical and polymeric form. This activity is not mediated by the platelet collagen receptor integrin α2β1. This may imply the existence of an intrinsic platelet reactivity associated with the collagen triple helix as such or perhaps that the Gly-Pro-Hyp sequence in collagen serves as a specific cell-recognition site. In our view this basic α2β1-independent reactivity is modulated by the presence in collagen of sequences that may either enhance or diminish the interaction with platelets. Inhibition studies with short linear peptides have allowed the tentative identification of sequences in collagen such as XPGEP(Q)GPX and D(N)GE(Q)X that may promote the activation of platelets and so enhance collagen-platelet interaction. Sequences serving as integrin α2β1-binding sites may also promote platelet reactivity by permitting interaction with the collagen receptor. Using triple-helical peptides based on the sequence of the platelet-reactive collagen type III fragment α1(III)CB4, we have been able to locate an α2β1-binding site in collagen type III within a 30-mer sequence representing residues 508-537 of the α1(III) constituent α-chain. Despite their α2β1-independent platelet reactivity, signalling by the (Gly-Pro-Hyp)n-based peptides shows many features in common with signalling by collagen fibers, including activation of p72SYK and p125FAK the latter of which has until now been considered a specific consequence of ligand binding to α2β1. © 1996 John Wiley & Sons, Inc.

Notizen: Monoclonal antibodies against the main immunogenic region (MIR) of the muscle acetylcholine receptor (AChR) are capable of inducing experimental myasthenia gravis (MG) in animals. The epitope of these antibodies has been localized between residues 67 and 76 of the AChR α-subunit. The conformation in solution of the Torpedo californica MIR peptide and of its [A76] MIR analogue have been analyzed using molecular modeling based on nmr interproton distances and J-derived φ dihedral angles. Molecular dynamics simulations including dimethylsulfoxide as explicit solvent have been carried out on the free MIR peptide. Calculation of the structure of the [A76] MIR analogue bound to an anti-MIR monoclonal antibody have been performed in the presence of water molecules. A tightly folded structure appears for both peptides with a β-folded N-terminal N68-P-A-D71 sequence of type I in the free state and type III in the mAb6-bound state. The C-terminal sequence is folded in two different ways according to the result in the free and bound state of the peptides: two overlapping β / β or β / α turns result in a short helical sequence in the free MIR peptide, whereas the bound analogue is folded by an uncommon hydrogen bond closing an 11-membered cycle. This structural evolution is essentially the result of the reorientation of the hydrophobic side chains that are probably directly involved in peptide-antibody recognition. © 1997 John Wiley & Sons, Inc. Biopoly 40, 419-432, 1996

Notizen: The dielectric properties of poly(α-glutamic acid) and poly(γ-glutamic acid) aqueous solutions in the fully ionized state have been investigated in the frequency range from 1 MHz to 1 GHz by means of frequency-domain dielectric spectroscopy measurements. In this frequency range, micro-Brownian dynamics and internal motion of side-chain polar groups give rise to nonexponential relaxation processes resulting in an intermediate dielectric relaxation between that due to the counterion atmosphere polarization and that due to the orientational polarization of the water molecules. In this work, we study the influence of the polymer concentration in the dilute-semidilute regime on the dielectric parameters, i.e., the dielectric increment Δε and the relaxation time τ, and discuss their relevance in the light of some scaling pictures recently proposed by Dobrynin, Colby, and Rubinstein to describe the unentangled regime of flexible polyelectrolyte solutions. © 1997 John Wiley & Sons, Inc. Biopoly 40: 485-494, 1996

Notizen: Our previous studies showed that the nonapeptide fragment of human leukocyte antigen DQ with the TPQRGDVYT sequence strongly suppresses the immune response1 [Z. Szewczuk, I. Z. Siemion, and Z. Wieczorek (1996) Molecular Immunology, 33, 903-908]. The fragment contains the RGDVY sequence, which is very similar to thymopentin (pentapeptide RKDVY, an active fragment (32-36) of thymopoietin, an immune system activator produced in thymi), and at the same time contains the RGD sequence, known as an inhibitor of adhesion processes. In the present study we tested an influence of the nonapeptide and its shorter fragments on binding of activated platelets and K562 cells to fibrinogen and fibronectin, respectively. We also designed and synthesized a cyclic thymopentin-like peptide, C*RGDVYC* (where C* indicates Cys participating in disulfide bridge) to restrict its conformation. The cyclization product strongly suppresses the humoral and cellular immune response and selectively inhibits the adhesion of K562 cells to fibronectin. The results are discussed in the light of CD conformational studies. © 1997 John Wiley & Sons, Inc. Biopoly 40: 571-583, 1996

Notizen: Pulse gel electrophoresis was used to measure the reduction of mobilities of λ-DNA-Hind III fragments ranging from 23.130 to 2.027 kilobase pairs in Tris borate buffer solutions mixed with either hexammine cobalt(III), or spermidine3+ trivalent counterions that competed with Tris+ and Na+ for binding onto polyion DNA. The normalized titration curves of mobility were well fit by the two-variable counterion condensation theory. The agreement between measured charge fraction neutralized and counterion condensation prediction was good over a relatively wide range of trivalent cation concentrations at several solution conditions (pH, ionic strength). The effect of ionic strength, trivalent cation concentration, counterion structure, and DNA length on the binding were discussed based on the experimental measurements and the counterion condensation theory. © 1996 John Wiley & Sons, Inc.

Notizen: A theory of the polarization of counterions bound to a polyion, such as a DNA, in low and high electric field strengths is developed using statistical mechanics of inhomogeneous systems. For low fields, one finds that the polarizability p is (Zq)2 ρ0βL3/(12[1 + Lρ0σ(L, b, ζ, Z, I, ρ0)]J), where σ = ∫10 (λ′ - λ0 {dc(λ - λ′)/dλ}λ = λ0 dλ′J), Z and L are the valence and the length of the polyion, respectively, q is the proton charge, β = 1/kBT, T is the temperature, kB is the Boltzmann constant, I is the ionic strength, λ = x/L and λ0 = x0/L are scaled distances, x0 is a reference point such that the inhomogeneous counterion density at x0 is equal to ρ0 - the uniform density in the absence of an electric field E - and c(x) is the direct correlation function of the homogeneous counterion-polyion phase, which includes attractive and repulsive interactions. If Lσ(L, .) is much less than one, then the polarizability is proportional to L3. If the term Lσ(L, .) is much larger than one, the polarizability scales as L2. The induced dipole moment saturates and its value is the same as that of Mandel-Manning theories. The onset of the saturation, however, depends critically on the direct correlation function and hence polyelectrolyte effects. In the formalism, the polarization of the counterions is the equilibrium response to an electric field provided E is less than Esaturated. A dynamical scheme that incorporates the fact that in high fields the bound counterions conduct is discussed. © 1996 John Wiley & Sons, Inc.