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PubMed2004

(Butadiene)metallocene/B(C6F5)3 pathway to catalyst systems for stereoselective methyl methacrylate polymerization: evidence for an anion dependent metallocene catalyzed polymerization process.

The ansa-zirconocene dichlorides [Me(2)Si(C(5)H(4))(3-R-C(5)H(3))]ZrCl(2) 7a-e (R = H, CH(3), cyclohexyl, -CHMe(2), -CMe(3)) were reacted with butadiene-magnesium to yield the respective (eta(4)-butadiene)metallocenes 17a-e. The chiral examples give a mixture of two s-cis and two s-trans diastereomers. The strong Lewis acid B(C(6)F(5))(3) adds selectively to a terminal butadiene carbon atom to yield the (butadiene)metallocene/B(C(6)F(5))(3) betaine complexes 18a-e. Initially, the formation of the Z-18 isomers is preferred. These consecutively rearrange to the thermodynamically favored isomers E-18. The dipolar systems 18 are active single component metallocene catalysts for the stereospecific polymerization of methyl methacrylate. With increasing steric bulk of the attached single alkyl substituent an increasingly isotactic poly(methyl methacrylate) is obtained. A similar trend is observed in the methyl methacrylate polymerization at the [Me(2)Si(C(5)H(4))(3-R-C(5)H(3))]ZrCH(3)(+) catalysts (9a-e) that were conventionally prepared by methyl abstraction from the corresponding ansa-zirconocene dimethyl complexes by treatment with B(C(6)F(5))(3). A comparison of the poly(methyl methacrylates) obtained at these two series of catalysts has revealed substantial differences in stereoselectivity that probably originate from an influence of the respective counteranions. An initial reactive intermediate of methyl methacrylate addition to the dipolar single component metallocene catalyst E-18a was experimentally observed and characterized by NMR spectroscopy at 253 K. The subsequently formed series of [PMMA-C(4)H(6)(-)B(C(6)F(5))(3)](-) anion oligomers (at the catalyst 18c) was monitored (after quenching) and characterized by electrospray mass spectrometry.

Journal Article↗
PubMed2005

Chemical polymerization of aniline on a poly(styrene sulfonic acid) membrane: Controlling the polymerization site using different oxidants.

Poly(styrene sulfonic acid) membranes (Neosepta CMX, Tokuyama Corp.) have been modified by in situ polymerization of aniline. (NH4)2S2O8, FeCl3, H2O2, and KIO3 were used as oxidizing agents, and two different modification methods (single-step versus two-step) were studied. The composite membranes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, elemental analysis, electrodialysis, ion-exchange capacity, and conductivity measurements. Our results demonstrate that it is possible to control the polymerization site of aniline which in turn affects the membrane selectivity properties. Hence, composite membranes having a very thin and homogeneous surface polyaniline layer lead to a very low transport of Zn 2+ without increasing significantly the resistance to H+ conductivity. On the other hand, membranes containing about the same quantity of PANI but inside the membrane do not block the transport of Zn 2+.

Journal Article↗
PubMed2006

A test of the transition-metal nanocluster formation and stabilization ability of the most common polymeric stabilizer, poly(vinylpyrrolidone), as well as four other polymeric protectants.

Following an introduction to the nanocluster stabilization literature and DLVO (Derjaugin-Landau-Verwey-Overbeek) theory of colloidal stability, the most common steric stabilizer of transition-metal nanoclusters, poly(vinylpyrrolidone) (PVP), has been examined for its efficacy in the formation, stabilization, and subsequent catalytic activity of prototype, test case Ir(0)n nanoclusters. First, the five criteria established previously for ranking nanocluster protectants for their nanocluster formation and stabilization ability were evaluated for 1 monomer equiv of 10000 average molecular weight (MWav) PVP in the absence, and then presence, of the traditionally weakly coordinating anion BF4- as well as the absence and presence of the strongly coordinating, superior anionic stabilizer P2W15Nb3O62(9-), all in propylene carbonate solvent. It is found that neither 1 equiv of BF4- in propylene carbonate nor 1 monomer equiv of (undried) PVP alone allows for isolable and redissolvable nanoclusters without bulk Ir(0)n metal formation. Careful predrying of the PVP, and by implication other polymers, is shown to be necessary for the formation and stabilization of the nanoclusters. Next, 40 monomer equiv of 10000 MWav PVP and 1 equiv of BF4- in propylene carbonate are shown to allow isolable, redissolvable nanoclusters. Control experiments reveal little difference on nanocluster stabilization by 3500 or 55000 (i.e., vs 10,000) MWav PVP, but yield interesting effects on nanocluster nucleation by the 3500 MWav PVP, as well as by the polymer poly(bis(ethoxy)phosphazene) (PBEP). Four other key polymers reported in the literature to be nanocluster stabilizers are tested by the five criteria method for their efficacy in the formation and stabilization of Ir0n nanoclusters (now in acetone due to the polymers' solubility) and in comparison to each other, specifically, poly(methyl methacrylate) (PMMA), poly(styrene) (PS), poly(methylhydrosilane) (PMHS), and PBEP. Only 40 monomer equiv dried PMMA allows isolable and redissolvable nanoclusters in acetone. Control/reference point experiments show that the electrostatic stabilizer P2W15Nb3O62(9-) is superior to each of the five polymeric stabilizers studied herein in both acetone and propylene carbonate, at least for the test case of Ir(0)n nanoclusters. Further controls show that 40 monomer equiv of PVP added to P2W15Nb3O(62)9--stabilized nanoclusters has no discernible effect on the five criteria other than to reduce by approximately 50% the nanocluster catalytic activity and total catalytic lifetime for cyclohexene hydrogenation. The main finding of this work is that DLVO theory as applied to nanocluster stabilization is fully supported; that is, surface-bound anions in high dielectric constant solvents provide superior stabilization. The importance of even traditionally weakly coordinating anions such as BF4- in nanocluster stabilization is a second, important finding of this work. The fact that HPO4(2-) has been shown to be a simple, cheap, commercially available, thermally robust, and 31P-NMR-handle-containing analogue of the more esoteric P2W15Nb3O62(9-) stabilizer is also discussed in the 14 total Conclusions from this first study ranking polymeric stabilizers of modern transition-metal nanoclusters.

Journal Article↗
PubMed1992

Thrombin promotes actin polymerization in U937 human monocyte-macrophage cells. Analysis of the signalling mechanisms mediating actin polymerization.

The U937 human monocyte-macrophage cell line was used to examine the effect of thrombin, an ill-defined chemoattractant, on the polymerization of actin, a process essential for cell motility. In differentiated macrophage-like U937 cells, thrombin (0.5-50 units/ml) caused a rapid dose-dependent increase in the formation of filamentous (F-) actin, detected by the staining of F-actin with the fluorescent toxin, 7-nitrobenz-2-oxa-1,3-diazole-phallacidin. In contrast with other chemoattractants such as N-formylmethionyl-leucylphenylalanine or C5a, actin polymerization in response to thrombin occurred via a pertussis-toxin-insensitive G1-(inhibitory G-protein) independent signalling pathway. Further, this response was not affected by the Ca2+ chelator EGTA or by the specific protein kinase C (PKC) inhibitor RO-31-8220. The response to thrombin was not mimicked by the Ca2+ ionophore ionomycin or by the direct PKC activator phorbol 12-myristate 13-acetate. The thrombin response was, however, inhibited by the non-specific protein kinase inhibitor staurosporine. The present results suggest that in U937 cells thrombin stimulates the formation of F-actin via a signalling pathway independent of (i) the activation of PKC, (ii) the mobilization of intracellular Ca2+ and (iii) the activation of Ca(2+)-dependent protein kinases, but dependent on the activation of an undefined staurosporine-sensitive protein kinase.

Actins↗
PubMed1983

A rat monoclonal antibody reacting specifically with the tyrosylated form of alpha-tubulin. I. Biochemical characterization, effects on microtubule polymerization in vitro, and microtubule polymerization and organization in vivo.

The antigenic site recognized by a rat monoclonal antibody (clone YL 1/2) reacting with alpha-tubulin (Kilmartin, J.V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576-582) has been determined and partially characterized. YL 1/2 reacts specifically with the tyrosylated form of brain alpha-tubulin from different mammalian species. YL 1/2 reacts with the synthetic peptide Gly-(Glu)3-Gly-(Glu)2-Tyr, corresponding to the carboxyterminal amino acid sequence of tyrosylated alpha-tubulin, but does not react with Gly-(Glu)3-Gly-(Glu)2, the constituent peptide of detyrosylated alpha-tubulin. Electron microscopy as well as direct and indirect immunofluorescence microscopy shows that YL 1/2 binds to the surface of microtubules polymerized in vitro and in vivo. Further in vitro studies show that the antibody has no effect on the rate and extent of microtubule polymerization, the stability of microtubules, and the incorporation of the microtubule-associated proteins (MAP2) and tau into microtubules. In vivo studies using Swiss 3T3 fibroblasts injected with YL 1/2 show that; when injected at low concentration (2 mg IgG/ml in the injection solution), the antibody binds to microtubules without changing their distribution in the cytoplasm. Injection of larger concentration of YL 1/2 (6 mg IgG/ml) induces the formation of microtubule bundles, and still higher concentrations cause the aggregation of microtubule bundles around the nucleus (greater than 12 mg IgG/ml).

Animals↗
PubMed2005

Investigation of the DNA-dependent cyclohexenyl nucleic acid polymerization and the cyclohexenyl nucleic acid-dependent DNA polymerization.

DNA polymerases from different evolutionary families [Vent (exo-) DNA polymerase from the B-family polymerases, Taq DNA polymerase from the A-family polymerases and HIV reverse transcriptase from the reverse transcriptase family] were examined for their ability to incorporate the sugar-modified cyclohexenyl nucleoside triphosphates. All enzymes were able to use the cyclohexenyl nucleotides as a substrate. Using Vent (exo-) DNA polymerase and HIV reverse transcriptase, we were even able to incorporate seven consecutive cyclohexenyl nucleotides. Using a cyclohexenyl nucleic acid (CeNA) template, all enzymes tested were also able to synthesize a short DNA fragment. Since the DNA-dependent CeNA polymerization and the CeNA-dependent DNA polymerization is possible to a limited extend, we suggest CeNA as an ideal candidate to use in directed evolution methods for the development of a polymerase capable of replicating CeNA.

Biopolymers↗
PubMed1991

Cellular origins of human polymeric and monomeric IgA: enumeration of single cells secreting polymeric IgA1 and IgA2 in peripheral blood, bone marrow, spleen, gingiva and synovial tissue.

Using modified ELISA and spot-ELISA, which permit the parallel determination of heavy chain subclass and the presence of covalently linked J chain, we analysed IgA found in cell culture supernatants or secreted by individual cells from peripheral blood, spleen, bone marrow, gingiva and synovial tissue, with respect to its polymeric or monomeric IgA form (pIgA, mIgA) and IgA1 or IgA2 subclass. The ELISA for determination of J chain in tissue culture supernatants was specific and highly sensitive (detection limit in pg). The results demonstrated that IgA1-producing cells predominated in the tissues examined, and that J chain could be detected in association with the majority of IgA1 and IgA2 secreted by individual cells. With respect to the frequency of cells secreting polymeric, J chain-containing IgA, only 20-30% of cells from the bone marrow were engaged in the synthesis of PIgA. In other tissues the frequency of cells secreting pIgA1 and pIgA2 was considerably higher. Peripheral blood mononuclear cells secreting pIgA2 were easily inducible during stimulation with T cell-dependent pokeweed mitogen, whereas Epstein-Barr virus-transformed cells secreted preferentially mIgA1. When the frequencies of pIgA-, pIgA1- or pIgA2-secreting cells (determined by spot-ELISA technique) from different tissues were correlated with the proportion of pIgA to mIgA (and IgA subclasses) secreted in tissue culture supernatants, data obtained suggest that many individual IgA-producing cells could be engaged in simultaneous secretion of mIgA and pIgA.

Adult↗
PubMed1986

Stimulated cytokineplasts from human polymorphonuclear leukocytes mobilize calcium and polymerize actin. Cytoplasts made in cytochalasin B retain a defect in actin polymerization.

Biologically active fragments from polymorphonuclear leukocytes (PMN) are simplified systems that can be used to elucidate specific pathways by which cell function is altered. In the current study we have found that cytokineplasts, which are motile fragments derived from the leading front (protopod, lamellipodium) of human PMN, rapidly increase their intracellular free calcium concentration when stimulated by chemotactic formyl peptide or by leukotriene B4, as measured by Quin-2 acetoxymethyl ester fluorescence. As in the parent cell, extracellular EGTA blunts this response only partially. Hence, cytokineplasts retain a mobilizable internal calcium pool, despite a general lack of intracellular organelles. In addition, formyl peptide more than doubles the amount of cytoskeleton-associated (polymerized) actin. In contrast, cytoplasts made by high-speed, discontinuous gradient centrifugation of cytochalasin B-treated leukocytes also increase their intracellular free calcium on stimulation, but cytoskeleton-associated actin increases by only approximately 14%. Thus, defective motile function in the latter cytoplast is associated with compromised effector function (actin polymerization).

Actins↗
PubMed1991

Importance of polymerization initiator systems and interfacial initiation of polymerization in adhesive bonding of resin to dentin.

Although various adhesive resins for dentin have been developed and used clinically, most attention has been directed to adhesion-promoting monomers and pre-treatment agents. The role of polymerization initiator systems in bonding has been overlooked. The purpose of this work was to study the role of initiators from the viewpoint of interfacial initiation of polymerization in dentin bonding. The bond strength between dentin and methyl methacrylate resin was significantly improved by a possible interfacial initiation with (1) the combination of ferric chloride, adsorbed onto dentin, and oxidized tri-n-butylborane (TBBO) and (2) the addition of tertiary butyl peroxymaleic acid (containing a carboxylic acid group, which has an affinity with dentin) to chemically- or light-activated initiator systems.

Acid Etching, Dental↗
PubMed2005

Self-assembled complexes of non-cross-linked amphiphilic polymeric ligands with inorganic species: highly active and reusable solid-phase polymeric catalysts.

I present herein the development of highly active and reusable polymeric catalysts produced by self-assembly process of non-cross-linked amphiphilic polymeric ligands with inorganic species. Thus, PWAA 1 prepared from H3PW12O40 and poly[(N-isopropylacrylamide)-co-(acrylamide with ammonium salt)] is suitable for oxidation of alcohols, amines, and sulfides in aqueous hydrogen peroxide. PdAS 2 produced by self-organization of (NH4)2PdCl4 and poly[(N-isopropylacrylamide)10-co-diphenylphosphinostyrene] is an excellent recyclable catalyst for Suzuki-Miyaura reaction in water, water-organic solvent, and organic solvent. It is commercially available from Tokyo Kasei Kogyo (TCI). PdAS-V 3 assembled from (NH4)2PdCl4 and poly[(N-isopropylacrylamide)5-co-diphenylphosphinostyrene] provides recycling system of itself for Mizorogi-Heck reaction. TiSS 4 made from Ti(O-i-Pr)4 and poly(styryl-linked binaphtholate-co-styrene) promotes an enantioselective carbonyl-ene reaction as a recyclable catalyst.

Amines↗
PubMed2006

Preparation and evaluation of uniform-size (-)-ephedrine-imprinted polymeric microspheres by multi-step swelling and suspension polymerization.

Ephedrine-imprinted polymeric microspheres have been prepared in an aqueous system by multi-step swelling and suspension polymerization, using methacrylic acid (MAA) as a functional monomer, and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Scanning electron microscopy (SEM) was used as a means to identify the structure features of the obtained polymers. Further, we examined the recognition mechanism of the polymers and the influences of some chromatographic conditions, such as the mobile-phase composition, flow-rate, column temperature and sample amount on the retentivity and selectivity for (-)-ephedrine and (+)-ephedrine. The results reveal that stable macroporous polymer beads with good size monodispersity were obtained, the average size of which was 3-5 microm. Baseline chiral separation of the template isomers was achieved on a short column (50 mmx4.6 mm i.d.) when the prepared polymer beads were used as a stationary phase, while the non-imprinted polymers (NIPs) did not show such ability. The optimized chromatographic condition was as follows: acetonitrile-acetic acid (99.8/0.2, v/v) as the mobile phase; sample amount, 40-80 microg; flow rate, 1.0 ml min-1; and column temperature, room temperature, respectively. It is assumed that two classes of binding sites exist in the porous polymers, one being hydrophilic binding sites, the other being hydrophobic binding sites.

Acetic Acid↗
PubMed1991

Mutual recognition between polymerized liposomes. III. Association processes between avidin and biotin on polymerized liposome surfaces.

Association processes between avidin and biotin in various liposome systems were studied. By incorporating biotin onto the polymerized liposome surface, association processes with free avidin were largely decelerated. When the number of binding sites on the liposome surface was taken into account, the corrected association rate constant was 4.3% of the theoretical value for binary collision. The association rate constant between avidin- and biotin-carrying polymerized liposomes was much smaller than those for both the free avidin-free biotin system and the free avidin/biotin-liposome system, probably due to the repulsive hydration phenomenon. The results are discussed both in terms of our understanding of cell-cell recognition phenomena and for the development of drug delivery systems.

Avidin↗
PubMed2004

Crystal structure of a polymeric immunoglobulin binding fragment of the human polymeric immunoglobulin receptor.

The polymeric immunoglobulin receptor (pIgR) is a type I transmembrane protein that delivers dimeric IgA (dIgA) and pentameric IgM to mucosal secretions. Here, we report the 1.9 A resolution X-ray crystal structure of the N-terminal domain of human pIgR, which binds dIgA in the absence of other pIgR domains with an equilibrium dissociation constant of 300 nM. The structure of pIgR domain 1 reveals a folding topology similar to immunoglobulin variable domains, but with differences in the counterparts of the complementarity determining regions (CDRs), including a helical turn in CDR1 and a CDR3 loop that points away from the other CDRs. The unusual CDR3 loop position prevents dimerization analogous to the pairing of antibody variable heavy and variable light domains. The pIgR domain 1 structure allows interpretation of previous mutagenesis results and structure-based comparisons between pIgR and other IgA receptors.

Amino Acid Sequence↗
PubMed1996

Improved blood compatibility of segmented polyurethane by polymeric additives having phospholipid polar group. II. Dispersion state of the polymeric additive and protein adsorption on the surface.

To improve the blood compatibility of a segmented polyurethane (SPU), phospholipid polymer, i.e., 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymerized with cyclohexyl methacrylate or 2-ethylhexyl methacrylate, was blended into SPU as a polymeric additive. The blending was achieved by a solvent-evaporation technique from a homogeneous solution containing both the SPU and the MPC polymer. Surface analysis of the SPU membrane blended with the MPC polymer (SPU/MPC polymer membrane) revealed that the MPC polymer was concentrated at the surface of the SPU membrane which contacted the substrate, Teflon, compared with that which contacted air during the membrane-formation period. The dispersion state of the MPC polymer in the SPU membrane was evaluated in detail by staining the MPC unit with osmium tetraoxide. When sonication was applied during preparation of the mixed solution containing SPU and the MPC polymer, the dispersion of the MPC polymer in the SPU membrane was different from that without sonication. That is, the size of the domains of the MPC polymer became smaller but the number of the domains increased. The amount of the MPC polymer mixed with SPU affected the dispersion state. Plasma proteins adsorbed on the SPU/MPC polymer membrane surface after contact with human plasma were detected by gold-colloid-labeled immunoassay. Both albumin and fibrinogen were observed on the SPU membrane; however, the amount of these proteins was reduced on the SPU/MPC polymer membrane. Thus it was concluded that the blood compatibility of the SPU was effectively improved by the blending of the MPC polymer.

Adsorption↗
PubMed1987

Interactions between hepatitis B virus and polymeric human albumin. I. Production of monoclonal anti-idiotypes (anti-anti-polymeric human albumin) which recognize hepatitis B virus surface antigen.

In an attempt to characterize the polymeric human albumin (polyHSA) receptor expressed on hepatitis B virus and hepatocytes, we have used a human anti-polyHSA IgG to generate monoclonal anti-idiotypes (anti-Id) which bear the internal image of polyHSA and mimic its binding activity. Two monoclonal anti-Id antibodies, 63.14 and 70.F9, were strongly reactive in both radioimmunoassay and enzyme-linked immunosorbent assay (ELISA) with the F(ab')2 of the immunogen as well as with purified hepatitis B surface antigen (HBsAg) expressing various subtypes. The specificity of the binding of anti-Id to HBsAg was confirmed in direct ELISA and by Western blot analysis. These experiments also showed that the anti-Id bind to a site expressed on the major 24-kDa protein of HBsAg particles, and that this recognition is specifically inhibited by polyHSA. Experiments on cellular staining and radioimmunoprecipitation on HBsAg-positive and -negative cell lines showed that the anti-Id recognize intracellular HBsAg but not other liver cell proteins, including the putative polyHSA receptor. These data indicate, therefore, that the monoclonal anti-Id mimic the binding activity of polyHSA and recognize its binding site on the virus. The inability of both anti-Id to react with the hepatocyte surface suggests either the absence of a specific hepatic polyHSA receptor or the expression of one with a different configuration.

Antibodies, Monoclonal↗