Emulsion polymerisation

rounded by a polymer shell (1-3). The technique of poly-Polymer encapsulation of small silica particles, using dispermer encapsulation is becoming more and more popular since sion polymerization of styrene in aqueous ethanol medium with polymer-encapsulated particles offer very interesting actual poly(N-vinyl pyrrolidone) (PVP) as stabilizer, is described. Siland potential applications. Encapsulated pigments are inica particles, directly synthesized by the Stö ber process in an volved in the manufacture of cosmetics, inks, and paints to aqueous ethanol medium, are either unreacted (hydrophilic improve the compatibility between the filler and the binder. character) or coated with 3-(trimethoxysilyl) propyl methacry-The process of encapsulation is of particular interest in agrilate (MPS) (hydrophobic character) , which is grafted at the culture and pharmaceutical industries to produce controlledsilica particle surface. When the bare silica particles are used release products such as encapsulated pesticides and drugs as the seed, there is a strong tendency of the silica beads to cover the surface of the polystyrene particles and obviously en-(4). Encapsulation technologies have developed to reduce capsulation does not occur. On the contrary, when the silica toxicity, to mask taste and odor, to facilitate storage or transsurface is made hydrophobic by coating, the inorganic particles port, and to improve the stability of the encapsulated product. are entirely contained in the polystyrene particles as evidenced Polymer-encapsulated inorganic particles may also have inby microscopy techniques (TEM, SEM, AFM). It is shown that teresting properties in areas such as adhesives, textiles, opsome polystyrene chains are then chemically bonded to the silica tics, and electronics (5). particles, through the coupling agent MPS, and that only a small Most methods of encapsulation employ, so far, mechaniamount of bonded polystyrene, compared to the total polystycal processes. Recently, a new encapsulation technology has rene synthesized, is sufficient to obtain encapsulation of the been developed which consists in the coating of fine inorsilica particles with the entire amount of polystyrene syntheganic powders (submicrometer in size) in aqueous system sized during the polymerization. Under our experimental condiby emulsion polymerization. This new polymer-encapsulations, each polystyrene latex particle contains, on average, 4 to 23 silica beads depending, in particular, on the size of the silica. tion process is of particular interest in the paint industry We believe that it is possible to control the composite particle where a uniform distribution of the pigment in the matrix size and morphology by a convenient choice of the composition is required. Latex-encapsulated pigments offer many advanof the system. Moreover, this new polymer-encapsulation protages. The encapsulation of titanium dioxyde with poly cess could be used to synthesize other organic-inorganic com-(methyl methacrylate) has been extensively studied by Caris posite particles, using, for example, other monomers or mineret al. (6-9), who used titanate coupling agents to improve als.

Chloroquine is thought to exert its antimalarial activity by preventing the polymerisation of toxic haematin released during proteolysis of haemoglobin in the Plasmodium digestive vacuole. However, the molecular mechanisms by which this inhibition occurs and the universality of this mechanism for other quinoline antimalarials remain to be established. We demonstrate here a correlation for eight antimalarial quinolines between inhibition of haematin polymerisation in vitro and inhibition of P. falciparum growth in culture, confirming haematin polymerisation as the likely target of quinoline blood schizonticides. Furthermore, using isothermal titration microcalorimetry, a correlation was observed between the haematin binding constant of these compounds and their ability to inhibit haematin polymerisation, suggesting that these compounds mediate their activity through binding to haematin. It was also observed that the compounds bind primarily to the-oxo dimer form of haematin rather than the monomeric form. It is postulated that this binding inhibits haematin polymerisation by shifting the haematin dimerisation equilibrium to the-oxo dimer, thus reducing the availability of monomeric haematin for incorporation into haemozoin. These data reconcile the haematin polymerisation theory with the Fitch hypothesis, which states that chloroquine mediates its activity through binding to haematin.

Tissue engineering (TE) aims to regenerate critical size defects, which cannot heal naturally, by using highly porous matrices called TE scaffolds made of biocompatible and biodegradable materials. There are various manufacturing techniques commonly used to fabricate TE scaffolds. However, in most cases, they do not provide materials with a highly interconnected pore design. Thus, emulsion templating is a promising and convenient route for the fabrication of matrices with up to 99% porosity and high interconnectivity. These matrices have been used for various application areas for decades. Although this polymer structuring technique is older than TE itself, the use of polymerised internal phase emulsions (PolyHIPEs) in TE is relatively new compared to other scaffold manufacturing techniques. It is likely because it requires a multidisciplinary background including materials science, chemistry and TE although producing emulsion templated scaffolds is practically simple. To date, a number of excellent reviews on emulsion templating have been published by the pioneers in this field in order to explain the chemistry behind this technique and potential areas of use of the emulsion templated structures. This particular review focusses on the key points of how emulsion templated scaffolds can be fabricated for different TE applications. Accordingly, we first explain the basics of emulsion templating and characteristics of PolyHIPE scaffolds. Then, we discuss the role of each ingredient in the emulsion and the impact of the compositional changes and process conditions on the characteristics of PolyHIPEs. Afterward, current fabrication methods of biocompatible PolyHIPE scaffolds and polymerisation routes are detailed, and the functionalisation strategies that can be used to improve the biological activity of PolyHIPE scaffolds are discussed. Finally, the applications of PolyHIPEs on soft and hard TE as well as in vitro models and drug delivery in the literature are summarised.

Listeria monocytogenes is able to escape from the phagolysosome and grow within the host cell cytoplasm. By 3 h after initiation of infection, actin filaments begin to concentrate at one end of the bacterium. Polarization of F-actin is associated with ...

Enteropathogenic Escherichia coli (EPEC) strains have recently been shown to invade tissue culture cells. We describe a set of 22 Tn5 IS50L::phoA (TnphoA) insertion mutants of EPEC strain E2348-69 that are unable to invade HEp-2 cells. Each mutant was tested for the ability to adhere to and to induce the polymerization of actin in HEp-2 cells. Southern hybridization of plasmid and total DNA of each strain was performed to determine the location of each TnphoA insert, and each TnphoA insert along with flanking EPEC sequences was cloned. These studies resulted in the grouping of the mutants into five main categories. These include strains with plasmid and chromosomal insertions that alter adherence, chromosomal insertions that alter the ability to induce actin polymerization, and chromosomal insertions that do not affect adherence or actin polymerization. These studies indicate that genes affecting EPEC adherence may be located on both the plasmid and chromosome, that several genes ar...

A photochemically curable transparent hard coating material has been developed to improve the wear resistance of organic polymers. Methacrylate functionalized silanes and nanoscaled boehmite particles were used for the preparation of the UV curable hard coatings by the sol gel technique. The inorganic network is formed as a result of the controlled hydrolysis and condensation of the methacryloxysilanes in the presence of nanoparticles (particle size: 15 nm). The hydrolysis and condensation of the methacryloxy silane, for two hours in presence of boehmite nanoparticles (43 wt.%), at 1008C leads to a degree of condensation of 80% of the inorganic network, as determined by 29 Si NMR spectroscopy. The organic network is formed by photoinitiated polymerisation of the methacrylic functions in only a few minutes, using UV light from a Hg high pressure lamp. Transparent coatings on plastic substrates (PC, PMMA) were produced by spray coating with good optical quality and thicknesses of several micrometers. The transparent coatings show excellent adhesion on PMMA and PC (GT=TT 0=0, DIN 53151), even without using primers, and also good abrasion resistance after the Taber abraser test with haze values of 10% after 1000 cycles (CS 10F rolls, 5,4 N, DIN 52347). The water exposition test (658C, deionized water) and the Suntest, without using ®lters, did not result in any crack formation, loss of adhesion or yellowing within the test period of two weeks.

We constructed a series of BspMI cassettes that simplify the introduction of specific point mutations in the polymerase domain of human immunodeficiency virus type 1 reverse transcriptase. A series of point mutants were constructed by using these cassette vectors. The RNA-dependent DNA polymerase and RNase H activities of 20 point mutations in the conserved portion of the polymerase domain were assayed. All the mutations analyzed are conservative substitutions of evolutionarily conserved amino acids. The mutations were divided into four classes. The first class has little effect on either polymerase or RNase H activity. The second class affects RNase H but not polymerase activity, while the third class has a normal RNase H activity with diminished polymerase activity. The fourth class affects both activities.

, whereby his undergraduate research was performed in the group of Professor Jöns Hilborn. He performed his degree project at IBM Almaden Research Center (San José, CA, USA) dealing with organo-catalysis, block-copolymer synthesis, and hydrogels under the supervision of Dr. James L. Hedrick. He is currently pursuing his Ph.D. in polymer chemistry at The Royal Institute of Technology (KTH) (Stockholm, Sweden) under the supervision of Professor Anders Hult and Assistant Professor Michael Malkoch. His research interests include synthesis of well-defined block-copolymer architectures and use of block co-polymers in antifouling coatings.

Kationische metallorganische Komplexe der Elemente der Gruppen 3 (mit Lanthanoiden), 4 und 13 zeigen eine hçhere Lewis-Acidität und Elektrophilie als die neutralen Stammverbindungen. Diese Verbindungen finden Verwendung als effiziente Polymerisationskatalysatoren und als Reagentien mit besonderen Reaktivitätsmustern in stçchiometrischen Reaktionen. [1-3] Auch die Lewis-Acidität neutraler Bismut-(III)-Verbindungen ist bekannt und in bismutkatalysierten (Co)polymerisationen sowie organischen Transformationen genutzt worden. [4] Dagegen ist die Zahl der isolierten und charakterisierten kationischen Organobismut(III)-Verbindungen begrenzt, und es wurde noch nicht über detaillierte Reaktivitätsstudien berichtet. [5, 6] Lediglich zwei Systeme mit chelatisierenden Di(aryl)liganden wurden als Lewis-Säure/ Base-Katalysatoren bei organischen Reaktionen eingesetzt. [6] Wir berichten hier über die Isolierung und Charakterisierung eines Salzes mit einem Bis(allyl)bismut-Kation und dessen Anwendung als Allylierungsreagens und Initiator für die kontrollierte, radikalische Styrolpolymerisation. Tris(allyl)bismut (1) wurde erstmals vor ca. 50 Jahren synthetisiert und später als Bismutquelle bei der metallorganischen chemischen Gasphasenabscheidung eingesetzt. [7] Der Bindungsmodus der Allylliganden wurde noch nicht im Detail untersucht. 1 wurde nach einer vereinfachten Literaturmethode hergestellt. Die gelbe Flüssigkeit ist temperatur-, licht-, luft-und vakuumempfindlich und zersetzt sich langsam (über Monate) bei Aufbewahrung unter Argon bei À30 8C unter Lichtausschluss. Die Zersetzung erfolgt hauptsächlich über radikalische Kupplung der Allylliganden unter Bildung eines Bismutspiegels. [8] Versuche, 1 durch Abkühlen einer Probe in der abgeschmolzenen Kapillare auf dem Diffraktometer zu kristallisieren, blieben zunächst erfolglos. Stattdessen wurde das noch nicht beschriebene Tris(methallyl)bismut (2) als gelbe Flüssigkeit (Schmp. = 176 K) in geringer Ausbeute isoliert (siehe Hintergrundinformationen) und in situ kristallisiert (Schema 1). [9, 37] Die Methallylliganden zeigen einen h 1-Bindungsmodus und lokalisierte CC -Bindungen. Die durchschnittliche Bi-C-Bindungslänge von 2.32(2) ist ähnlich wie der entsprechende Wert in der einzigen vollständig charakterisierten Allylbismutverbindung [Bi(h 1-C 3 H 3){2,6-(Me 2 NCH 2) 2 C 6 H 3 } 2 ] (Bi-C Allyl : 2.331(2)). [5g] Das Zentralatom in 2 ist pyramidal koordiniert, mit kleinen C-Bi-C-Winkeln von ca. 948. [10] 2 ist ein typischer Molekülkristall ohne gerichtete Wechselwirkungen zwischen benachbarten Molekülen. Bi•••H(Methyl)-Abstände von ca. 3.2 sind die kürzesten intermolekularen Kontakte und lassen sich auf eine Packung entlang der kristallographischen b-Achse zurückführen (siehe Hintergrundinformationen). Im Vergleich dazu zeigt [Bi(C 5 H 5) 3 ] intermolekulare Bi•••C-Wechselwirkungen im Festkçrper. [11] In Lçsung wird ein h 1-Bindungsmodus der Allylliganden von 1 und 2 ohne fluxionales Verhalten bei 23 8C beobachtet, wogegen die Cyclopentadienylliganden in [Bi(C 5 H 5) 3 ] fluxionales Verhalten zeigen. [11] Organobismutkationen wurden bisher durch Salzeliminierungsreaktionen hergestellt. [5, 12] Beim Einsatz von [Bi(C 3 H 5) 2 X] (X = Halogenid) war diese Herangehensweise jedoch wegen der geringen Stabilität der Verbindungen nicht praktikabel (siehe Hintergrundinformationen). Die Protonolyse von 1 mit der ausreichend aciden Brønsted-Säure [PhNMe 2 H][B(C 6 H 3 Cl 2) 4 ] ermçglichte die Isolierung des Bis-(allyl)bismut-Salzes 3 in Form eines gelben Feststoffs (Schema 1). Unter Argon und Lichtausschluss kann 3 über Monate zersetzungsfrei aufbewahrt werden. Laut Rçntgenstrukturanalyse kristallisiert 3 in der orthorhombischen Raumgruppe Pbca mit Z = 16 (Schema 1). [37] Das Zentral-Schema 1. Synthese von 3; [A] = [B(C 6 H 3 Cl 2) 4 ]. Molekülstrukturen von 2 und dem kationischen Teil von 3. Auslenkungsellipsoide sind mit 50 % Aufenthaltswahrscheinlichkeit gezeigt, H-Atome sind weggelassen. Wegen ihrer ¾hnlichkeit wird nur eines der beiden kristallographisch unabhängigen Kationen von 3 dargestellt und diskutiert. Ausgewählte Bindungslängen

The fluorescence from an open volume of a solution of fluorescent molecules fluctuates as the molecules randomly diffuse into and out of the volume. The distribution of degrees of aggregation or polymerization of the fluorescent molecules can be characterized without perturbing the system by measuring either the moments or the amplitude distribution of these fluctuations. We present an experimental verification of this approach applied to simple model systems consisting of solutions of fluorescent particles of well-defined size. We have also characterized the response of the photon-detection device (typically a photomultiplier), which is essential to the analysis of the fluorescence fluctuations, and have compared two methods for determining shot-noise contributions.

We investigated the condition of unique self-written channel and multichannel propagation inside bulk photopolymerizable materials. Light was introduced in the medium by a single-mode optical fiber. At a very low beam power of 5 mW, a unique uniform-channel waveguide without any broadening was obtained by polymerization. When the input power is increased to 100 mW, the guide becomes chaotic and multichannel. We connected two fibers separated by a 1-cm distance. The results open the door to studies of the optical and electro-optical properties of photopolymerized guides doped by nonlinear optical chromophores and to possible applications in integrated optical devices.

We have successfully prepared monodisperse poly(N-isopropylacrylamide) (PNIPAM) microspheres and hollow microcapsules by employing monomer-contained water-in-oil (W/O) emulsions as the polymerizing templates and introducing proper initiators into the disperse water phase or continuous oil phase, respectively. First, monodisperse monomer-contained W/O emulsions were prepared by SPG membrane emulsification method; then, UV irradiation was used to polymerize the monomer-contained W/O emulsions at a temperature below the lower critical solution temperature of PNIPAM. The prepared PNIPAM microspheres and hollow microcapsules were featured with good monodispersity and excellent thermo-responsive properties. The preparation methodology demonstrated in this study provided a unique approach for preparing monodisperse microspheres and hollow microcapsules with single W/O emulsions.

C5Me5, 1,3-diphenyl-&methylindene) affords novel RCe(OAr)z (R = C5Mes, 2; R = 1,3-diphenyl-2-methylindene, 3) compounds. Metathesis of the remaining aryloxide ligands in 2 with bulky main-group alkyl and amide compounds (LiCH(SiMe& and NaN(SiMe3)z) pro?de neutral C5Me5CeRz complexes (R = CH(SiMe3)z, 5; R = N(SiMe&, 6). Compound 5 is a polymerization catalyst for ethylene but not for propylene. Compounds 2 and 6 disproportionate in solution with formation of equilibrium mixtures containing C5Me5CeXz, (C5Me5)&eX, and CeX, complexes. Structural studies on 2, 5, and 6 show monomeric, formally five-coordinate compounds in the solid state. Compound 2 crystallizes in the monoclinic space group P2, with a = 9.575 (1) A, b = 17.026 (2) A, c = 11.530 (1) A, /3 = 112.02 (1)O, and 2 = 2. Compound 5 crystallizes in the hexagonal space group B3 with a = 18.477 (2) A, c = 15.991 (3) A, and 2 = 6. Compound 6 crystallizes in the monoclinic space group P 2 J c with a = 19.252 (6) A, b = 13.430 (4) A, c = 12.503 (3) A, / 3 = 90.28 (2) O , and 2 = 4. All compounds display interesting secondary interactions of the metal with C-H and/or Si-C bonds in the solid state. (1) In this paper the following abbreviations are used Ln = lanthanide or group 3 element; Ind* = 1,3-diphenyl-2-methylindenyl; OAr = 2,6-di-tert-butylphenoxo.

In comparison to the well-recognized adaptogenic herb Rhodiola rosea, phytochemical constituents of two other Rhodiola species (R. heterodonta and R. semenovii) were elucidated and characterized. Two major phytochemical groups; phenolic and/or cyanogenic glycosides and proanthocyanidins, were isolated and identified in the three species. Chemical similarities among the three species were observed; however, each species displayed differences in phytochemical constituents. R. heterodonta contained a newly detected phenylethanoid glycoside, heterodontoside, in addition to the known compounds tyrosol, viridoside, salidroside, and rhodiocyanoside A. Both R. heterodonta and R. rosea contained phenylethanoid/propanoid compounds that were not detected in R. semenovii. For R. semenovii, the cyanogenic glucosides rhodiocyanoside A and lotaustralin were detected. Although the three species have proanthocyanidins composed of (À)-epigallocatechin and its 3-O-gallate esters in common, the degree of polymerization greatly differed between them. In contrast to R. heterodonta and R. semenovii, R. rosea has higher molecular weight polymeric proanthocyanidins. This study resulted in the identification and isolation of phytochemical constituents for direct cross-comparison between three Rhodiola species of medicinal and pharmacological value.

Using N-vinylpyrrolidone as polymer of choice, it has been pointed out that radiation formation of hydrogels in aqueous solutions proceeds according to the radical mechanism. Both in the processes of polymerization and crosslinking, the main role is played by indirect effect, i.e., these processes are initiated by intermediate products of radiolysis of water. In the presence of oxygen in the irradiated solutions, the process of gel formation is accompanied by the reactions leading to the scission of polymer main chain. Analysing the course of gel formation the use of modified Chadesby equation was suggested. This equation has an universal character. In order to calculate the values of the yield of radiation crosslinking a new method was used. It allows to obtain results without previous determination of the molecular weights of polymer to be crosslinked. I 0

In order to describe and quantify the reactivity of silicate melts, the ionic notation provided by the Temkin formalism has been historically accepted, giving rise to the study of melt chemical equilibria in terms of completely dissociated ionic species. Indeed, ionic modelling of melts works properly as long as the true extension of the anionic matrix is known. This information may be attained in the framework of the Toop-Samis (1962a,b) model, through a parameterisation of the acid-base properties of the dissolved oxides. Moreover, by combining the polymeric model of Toop and Samis with the «group basicity» concept of Duffy and Ingram (1973, 1974a,b, 1976) the bulk optical basicity (Duffy and Ingram, 1971; Duffy, 1992) of molten silicates and glasses can be split into two distinct contributions, i.e. the basicity of the dissolved basic oxides and the basicity of the polymeric units. Application to practical cases, such as the assessment of the oxidation state of iron, require bridging of the energetic gap between the standard state of completely dissociated component (Temkin standard state) and the standard state of pure melt component at P and T of interest. On this basis it is possible to set up a preliminary model for iron speciation in both anhydrous and hydrous aluminosilicate melts. In the case of hydrous melts, I introduce both acidic and basic dissociation of the water component, requiring the combined occurrence of H + cations, OH − free anions and, to a very minor extent, of T-OH groups. The amphoteric behaviour of water revealed by this study is therefore in line with the earlier prediction of Fraser (1975).

Mechanistic dynamic models often contain unknown parameters whose values are difficult to determine even with highly specialized laboratory experiments. A practical approach is to estimate such parameters from available process data. Typically only a subset of the parameters can be estimated due to restrictions imposed by the model structure, lack of measurements, and limited data. We present a simple parameter selection method which accounts for the first two factors independent of the data available for parameter estimation. The magnitude of each parameter effect on the measured variables is quantified by applying principal-component analysis to the steady-state parameter-output sensitivity matrix. The uniqueness of each parameter effect is determined by computing the minimum distance between the sensitivity vector of the particular parameter and the vector spaces spanned by sensitivity vectors of the parameters already selected for estimation. A recursive algorithm that provides a tradeoff between the magnitude and linear independence of parameter effects yields a ranking of the parameters according to their inherent ease of estimation. The parameter-selection procedure is applied to the problem of kinetic parameter estimation for an industrial model of a polymerization reactor. For this specific example, the proposed method yields superior estimation results than those obtained with a parameter-selection technique based on the Fisher information matrix (FIM).

Homogeneous complexes of Ti (IV) bearing sterically hindered bidentate diols such as 1,1-binaphthalene 2,2 diol (Binol) and substituted Binol were prepared and characterized. These catalyst precursors formulated as [Ti(O ∧ O) 2 ] or [Ti(O ∧ O)X 2 ] are found to be active in polymerization of ethylene at high temperatures in combination with alkyl aluminum sesquichloride (Et 3 Al 2 Cl 3) as co-catalyst. The polyethylenes obtained are linear, crystalline and display narrow polydispersities. The unique low molecular weight PE waxes formed in this reaction exhibit properties that have potential applications in surface coating and ink formulations. The influence of various reaction conditions on polymerization is discussed.

The occurrence of covalent grafting of polymer chains onto graphene oxide (GO) sheets during aqueous miniemulsion radical polymerizations of common vinyl monomers has been investigated. Styrene, benzyl methacrylate and t-butyl methacrylate were polymerized via miniemulsion polymerization using GO as sole surfactant, and the characterization of GO isolated post-polymerization was investigated by a range of experimental techniques (Fourier-Transform Near Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Photoelectron spectroscopy (XPS), Raman spectroscopy and X-Ray Diffraction (XRD)). All experimental techniques show consistently that significant grafting occurs for all three monomers under these conditions. Furthermore, Raman spectroscopy indicated that the mechanism of grafting involves the sp 2 carbons present in the GO structure, and not the oxygen-containing functional groups (e.g. epoxy, hydroxyl and carboxyl). The extent of grafting was quantified by XPS, revealing that polymer grafting occurred at levels in the approximate range of 20e60 wt% (grafted polymer relative to total mass of GO and grafted polymer). Miniemulsion polymerization using GO as surfactant is an attractive approach for synthesis of polymer/GO nanocomposites, and the present results are important in regards to the specific structures and performances of such materials.

Cellulose is the main constituent of such plant fibres as flax, ramie, cotton, and wood. The structural parameters of cellulose, like lattice type, crystallinity, crystallite size, and degree of polymerization, contribute significantly to the physical properties of the fibre. The crystallinity of cellulose influences, for example, the accessibility for chemical derivatization, swelling, and water-binding properties * Corresponding author. 0008~6215/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDZ 0008-6215(94)00091-S

A new ATRP initiator, 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid, has been synthesized and grafted as a film on a mechanically polished stainless steel (ASI304) substrate. Molecular integrity of the grafted initiator in the film, alkyl chain ordering, wettability were determined by X-ray photoelectron spectroscopy, infrared, and water contact angles. Polystyrene, poly(methyl methacrylate) and diblock copolymer (polystyrene-b-poly(methyl methacrylate)) brushes have been grafted from the flat stainless steel surfaces through surface-initiated atom transfer radical polymerization (ATRP) and characterized to check the effectiveness of the new initiator for future uses in surface-initiated ATRP.

We have developed a method to distinguish microtubule associated protein (MAP)containing regions from MAP-free regions within a microtubule, or within microtubule subpopulations. In this method, we measure the MAP-dependent stabilization of microtubule regions to dilution-induced disassembly of the polymer. The appropriate microtubule regions are identified by assembly in the presence of [3H]GTP, and assayed by filter trapping and quantitation of microtubule regions that contain label. We find that MAPs bind very rapidly to polymer binding sites and that they do not exchange from these sites measurably once bound. Also, very low concentrations of MAPs yield measurable stabilization of local microtubule regions. Unlike the stable tubule only polypeptide (STOP) proteins, MAPs do not exhibit any sliding behavior under our assay conditions. These results predict the presence of different stability subclasses of microtubules when MAPs are present in less than saturating amounts. The data can readily account for the observed "dynamic instability" of microtubules through unequal MAP distributions. Further, we report that MAP dependent stabilization is quantitatively reversed by MAP phosphorylation, but that calmodulin, in large excess, has no specific influence on MAP protein activity when MAPs are on microtubules.

Hybrid poplar (Populus nigra × P. maximowiczii) chips were pretreated using an organosolv ethanol process. The effect of pretreatment conditions (temperature, time, catalyst, and ethanol concentration) on the substrate characteristics, including fiber size, crystallinity, and degree of polymerization of cellulose, was investigated using an experimental matrix designed with response surface methodology. The conditions ranged 155-205°C, 26-94 min, 0.83-1.67% catalyst (H 2 SO 4) on oven-dry wood chip (w/w), and 25-75% ethanol concentration (v/v). The results indicated that the substrate characteristics are controllable and predictable. Desirable substrates can be prepared by fine-tuning the processing parameters. The regression models developed, allowed the quantitative prediction of the substrate characteristics from the pretreatment conditions used. Index Entries: Crystallinity; degree of polymerization; fiber size; hybrid poplar; organosolv ethanol pretreatment; substrate characteristics.

Molecularly imprinted polymers (MIPs) for 2,4-dichlorophenoxyacetic acid were synthesized via a noncovalent approach with 4-vinylpyridine as functional monomer and ethylene glycol dimethacrylate as cross-linker in a methanol/water mixture. Templated polymers synthesized in this self-assembly approach rely on complex formation between the target analyte and functional monomers in porogenic solution prior to radical polymerization. Consequently, the achievable selectivity is governed by the nature and stability of these complexes. The nature of noncovalent interactions responsible for complex formation during imprinting of the template 2,4-dichlorophenoxyacetic acid (2,4-D) with the functional monomer 4-vinylpyridine has been investigated. Fourier transform infrared and 1 H NMR spectroscopies provide the fundamental analytical basis for rationalizing the mechanisms of recognition during the imprinting process probing the governing interactions for selective binding site formation at a molecular level. Molecular modeling studies in explicit solvent (chloroform and water) corroborate the importance of hydrogen bonding in aprotic solvents and of hydrophobic interactions in protic media in agreement with the experimental spectroscopic investigations of prepolymerization solutions. Furthermore, chromatographic studies of the synthesized MIPs provided insight on the importance of size, shape, and functionality during selective 2,4-D rebinding processes confirming the results obtained during the prepolymerization studies.

This paper reports the studies made on the vacuum pyrolysis of deashed sugarcane bagasse, on the pyrolysis products. The present work is with an objective to understand the change in the quantity and quality of the oil fraction obtained from pyrolysis, upon pretreatment for deashing of original biomass. Ash, in the entrained char is believed to be catalyzing the polymerization reaction in the oils and thereby increases the viscosity. Three different pre-treatment processes used for deashing are water leaching, mild acid treatment with HCl and mild acid treatment with HF. 1 The study indicates the remarkable influence of pretreatment process for deashing, by enhancing the total energy distribution in oil fraction of the pyrolysis products. This is attributed to selective removal of ash elements along with removal of extractives and hemicellulose in different proportions. However, it was found that the pre-treatments do not improve the stability of oil. The water leachate, as expected, showed potential of making ethanol via fermentation.

In this report we describe the molecular defect underlying partial and severe quantitative von Willebrand factor (VWF) deficiencies in 3 families previously diagnosed with types 1 and 3 Von Willebrand-disease. Analysis of the VWF gene in affected family members revealed a novel C to T transition at nucleotide 1067 of the VWF complemetary DNA (cDNA), predicting substitution of arginine by tryptophan at amino acid position 273 (R273W) of pre-pro-VWF. Two patients, homozygous for the R273W mutation, had a partial VWF deficiency (VWF:Ag levels of 0.06 IU/mL and 0.09 IU/mL) and lacked high-molecular weight VWF multimers in plasma. A third patient, also homozygous for the R273W mutation, had a severe VWF deficiency (VWF:Ag level of less than 0.01 IU/mL) and undetectable VWF multimers in plasma. Recombinant VWF having the R273W mutation was expressed in COS-7 cells. Pulse-chase experiments showed that secretion of rVWFR273W was severely impaired compared with wild-type rVWF. However, the m...

This work was supported by the Fonds der Chemischen Industrie and the Deutsche Forschungsgemeinschaft. R.M. thanks the Alexander von Humboldt Foundation for a postdoctoral fellowship; G.-J.M. thanks the Graduiertenkolleg 440 ("Methoden der asymmetrischen Synthese") for a doctoral fellowship. We thank Prof. M. Schmidt, Mainz University, for kindly measuring MALDI TOF mass spectra.

The inhibition of the polymerization of tubulin from cultured cells of rose (Rosa. sp. cv. Paul's scarlet) by colchicine and the binding of colchicine to tubulin were examined in vitro and compared with data obtained in parallel experiments with bovine brain tubulin. Turbidimetric measurements of taxol-induced polymerization of rose microtubules were found to be sensitive and semiquantitative at low tubulin concentrations, and to conform to some of the characteristics of a nucleation and condensation-polymerization mechanism for assembly of filamentous helical polymers. Colchicine inhibited the rapid phase of polymerization at 24 ~ C with an apparent inhibition constant (Ki) of 1.4.10-4 M for rose tubulin and an apparent Ki= 8.8" 10-v M for brain tubulin. The binding of [3H]colchicine to rose tubulin to form tubulin-colchicine complex was mildly temperature-dependent and slow, taking 2-3 h to reach equilibrium at 24 ~ C, and was not affected by vinblastine sulfate. The binding of [3H]colchicine to rose tubulin was saturable and Scatchard analysis indicated a single class of low-affinity binding sites having an apparent affinity constant (K) of 9.7.102 M-1 and an estimated molar binding stoichiometry (r) of 0.47 at 24 ~ C. The values for brain tubulin were K=2.46" 106 M-1 and r=0.45 at 37 ~ C. The binding of [3H]colchicine to rose tubulin was inhibited by excess unlabeled colchicine, but not by podophyllotoxin or tropolone. The data demonstrate divergence of the colchicine-binding sites on plant and animal tubulins and indicate that the relative resistance of plant microtubule polymerization to

A novel, generic method for the synthesis of families of tri-block protein-polymer giant amphiphiles was designed and developed. We have synthesized a hydrophilic a-maleimido poly-1alkyne with M n = 9.5 kDa (1 H-NMR) and narrow PDi (1.15 as measured by SEC) via ATRP (Atom Transfer Radical Polymerization). This polymer was succesfully coupled to BSA to afford a hydrophilic multifunctional bioconjugate which was isolated using protein purification techniques and fully characterized. Following the post-functionalization approach, we introduced hydrophobicity to the resulting hydrophilic biohybrid by a straightforward, high yield ''click''-chemistry cycloaddition step. The resulting tri-block protein-polymer amphiphiles were isolated and showed interesting aggregation patterns (TEM, confocal microscopy).

The requirement for hydrogen peroxide (H 2 O 2) during suberization was demonstrated in woundinduced potato tubers by monitoring the extent of phenolic polymerization after the inhibition of H 2 O 2 production using diphenyleneiodonium (DPI). In DPI-treated tissues the extent of phenolic polymerization in suberized tissues, measured using DFRC (Derivatization Followed by Reductive Cleavage) and thioglycolic acid analyses, was greatly reduced relative to untreated controls. Concomitantly, a large quantity of new soluble phenolics accumulated in the DPI-treated tissue some of which were not present in the controls. We suggest that the inhibition of H 2 O 2 production prevented these phenolics from being oxidized by cell wall peroxidases. As a result, these phenolics were left unpolymerized and accumulated in the tissue. Several of the soluble phenolics were identified as hydroxycinnamic acid derivatives. From the data presented, it was concluded that H 2 O 2 is required for the polymerization step in the formation of the poly(phenolic) domain of suberized potato tubers.

Fruit stones and pericarps of Litchi chinensis, waste products of the food, were studied as a source of polymeric proanthocyanidins. The structures of the polymeric proanthocyanidins isolated from Litchi chinensis were characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) coupled with high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) analysis. The spectra obtained through MALDI-TOF MS analysis revealed that the dominant Atype procyanidin polymers occurred in each polymer length with one or more A-type linkages. The polymeric proanthocyanidins of litchi fruit stones exhibited longer polymer length than those of fruit pericarps, with polymerization degrees up to 20 and 11 for fruit stones and pericarps, respectively. After depolymerization with toluene-α-thiol, HPLC-ESI-MS analysis showed that epicatechin and A-type dimer were the major constituent units, and the mean polymerization degrees were 15.4 and 5.8 for polymeric proanthocyanidins of fruit stones and pericarps, respectively. The antioxidant properties investigated using DPPH, ABTS and FRAP methods showed that the higher polymerization degree of polymeric proanthocyanidins from litchi fruit stones exhibited higher antioxidant activities than those from litchi pericarps.

The kinetics of the ethylene polymerization of ethylene in toluene using a monometallic palladium catalyst containing phosphine ligands was investigated. The effect of both external and internal mass transfer limitations was assessed. The influence of several factors (temperature, monomer concentration, catalyst concentration) on the polymerization rate, molecular weights and crystallinity was studied. A polymerization mechanism was proposed and a mathematical model for the process was developed.

We describe a thermodynamic principle determining the phenomenon of protein self-assembly controlled by elastic stresses. This principle is based on the Gibbs-Dühem-like relationship between the chemical potential of the aggregated molecules and the stresses produced by forces acting on a protein aggregate. We present two biological systems whose operation can be driven by this principle: actin filament, a polymerizing processive capping by proteins of the formin family, and focal adhesions mediating a mechanical link between the cytoskeleton and extracellular substrates. We describe the major phenomenology of these systems and overview recent models, aimed at understanding the mechanisms of their functioning.

A new approach is presented to calculate both the distribution of particles with i radicals and the average number of radicals per particle in emulsion polymerizations carried out using oil-soluble initiators. The convergence and accuracy of the approach were examined. It was found that, in agreement with previously published experimental results, the present approach predicts a kinetic behavior similar to that found for water-soluble initiators. This effect is primarily due to the desorption of initiator radicals from the polymer particles rather than the contribution of the fraction of oil-soluble initiator dissolved in the aqueous phase.

Kinetic models describing the controlled radical polymerization (CRP) of vinyl and divinyl monomers are presented. The main focuses of this work are the atom-transfer radical polymerization (ATRP) of n-butyl acrylate/diacrylate monomers (nBA/diacrylate) and of methyl methacrylate with ethylene glycol dimethacrylate (MMA/EGDMA). Nitroxide-mediated radical polymerization (NMRP) of styrene with divinylbenzene (S/DVB) is also considered as a case study. For the three chemical systems, this analysis is restricted to the formation of soluble (hyperbranched) polymers. Particular kinetic mechanisms associated with the synthesis of hyperbranched polymers based on these chemical systems are considered, such as crosslinking involving radicals and double bonds with different reactivities, branching due to polymerization of terminal double bonds and/or chain transfer to polymers, the presence of two isomers in the commercial DVB and thermal polymerization of styrene. For the three polymerization systems, predicted values of dynamics of monomer conversion, molecular weights and z-average radius of gyration are compared with the measured values of these properties obtained through the characterization by SEC/RI/MALLS of the synthesized materials.