Amino acid end-group in commercial heparin. II. Reaction kinetics of the amino end groups with 2,4,6-trinitrobenzenesulfonic acid

Three different commercial heparins were trinitophenylated with 2,4,6-trinitrobenzenesulfonic acid (TNBS) under aqueous conditions. The reaction kinetics of amino groups in heparin with TNBS showed that the reactivities of amino groups were significantly different for free amino groups on heparin, compared to reactivities in peptides and amino acid residues attached to heparin molecules. With TNBS, unreactive amino groups were always present during the reaction.     

Solvent free amination reactions of aryl bromides at room temperature catalyzed by a (pi-allyl)palladium complex bearing a diphosphinidenecyclobutene ligand

An air- and moisture-stable (pi-allyl)palladium complex bearing a unique diphosphinidenecyclobutene ligand effectively catalyzes amination reactions of aryl bromides with amines, where the reactions proceed under mild conditions without solvent, with 2 mol % of catalyst and 1 equiv of t-BuOK at room temperature. Under these conditions the amination products were obtained in good to excellent isolated yields.     

Preparation of sterically protected 3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene derivatives having ring-fused structures

[reaction: see text] Sterically protected 3,4-diphosphinidenecyclobutenes, having ring-fused structures, were prepared. Structures of 8,9-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]bicyclo[5.2.0]non-1(7)-ene and its dichloropalladium(II) complex were analyzed by X-ray crystallography. A geometrical change induced by the complex formation was exhibited by X-ray crystallographic analysis. The geometrical change in solution was also suggested by (1)H NMR spectroscopy in CDCl(3).     

Endgroup analysis of isolated poly(methyl methacrylate) from graft copolymers of wool

In order to elucidate the termination mechanism in the graft copolymerization of methyl methacrylate to unreduced and reduced wool fibers, graft copolymers were prepared by means of the LiBr–K₂S₂O₈ redox sytem without homopolymer or with K₂S₂O₈ only with homopolymer at 30°C. The graft polymers (PMMA) were isolated almost completely from the wool trunk by an HCI-digestion method, leaving a few amino acid residues on the end of the graft polymers. Dinitrophenylation of the isolated polymer was carried out by various methods. The spectral features were almost the same as for dinitrophenylated amino acids of the usual type such as valine, leucine, and methionine, with a maximum in ultraviolet light at 340–345 mμ. From colorimetric analysis of the number of dinitrophenylated amino acid endgroups and the measurement of the average molecular weight of the isolated polymers, the number of amino acid endgroups linked to the graft polymers was calculated to be about one and two per polymer chain in reduced and unreduced wool, respectively, independent of the reaction system, graft-on, and molecular weight of graft polymers. From these facts, it was suggested that the most of isolated polymers are the truly grafted polymers. Also, the termination reactions have been explained as follows. In the unreduced wool, the restriction of mobility of the radical end might be expected, for the confinement of growing chains in wool fibers. This would be favorable to termination by recombination rather than by the disproportionation, since the former has a lower activation energy than the latter. Thus, the formation of intra- or intermolecular crosslinks might be considered between polypeptide chains. On the other hand, in the reduced wool, the mobility of graft polymers might be considered to be greater than that of unreduced wool because of its open structure. Therefore, termination would be principally by disproportionation between graft polymer radicals.     

Isomerization kinetics of panipenem in aqueous solution

The isomerization kinetics of panipenem (INN: (+)-(5R,6S)-3-[(S)-1-(acetimidoylpyrrolidin-3-yl)thio]-6-[(R)-hydroxyethyl]-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid, CAS No. 87726-17-8) in aqueous solution were investigated. An equilibrium between the Z-form and E-form was observed, and it was found that the isomerization rates were affected by the pH of the solution. Under acidic conditions, the isomerization rates were small. However, the isomerization rates were increased with the pH value. This phenomenon resulted from the extent of proton dissociation from the acetimidoyl group.     

Surface characterization of functional iron–gallium alloys annealed under different conditions

Fe–Ga alloys are functional magnetostrictive materials, which are promising for application in actuators and sensors. Because surface properties of these alloys such as corrosion resistance are important in technological applications, it is required to characterize the chemical composition and state of the surface of these alloys, which depend on annealing conditions. In this study, X-ray absorption spectroscopy (XAS) and secondary ion mass spectrometry (SIMS) were used to characterize surface layers formed on the Fe–Ga alloys annealed under different atmospheric conditions. The XAS spectra of the annealed sample showed that the amount of gallium in the surface layers increased due to annealing, whereas the XAS spectra of the as-polished alloys revealed that the amounts of iron and gallium arise from the bulk composition. The XAS spectra of the alloys annealed in argon–hydrogen with residual oxygen showed that gallium is increased for its preferential oxidation. SIMS depth profile also showed the enrichment of gallium on the surface and the inhomogeneous distribution of iron on the surface layers.     

Synthesis of water‐dispersible,fluorinated particles with grafting sulfonate chains by the core crosslinking of block copolymer micelles

Fluorinated polymer particles with grafting sulfonate chains, which showed high dispersion stability in aqueous media, were synthesized by the crosslinking of block copolymer micelles. A crosslinkable block copolymer, poly[(2,3,4,5,6‐pentafluorostyrene)‐co‐4‐(1‐methylsilacyclobutyl)styrene]‐b‐poly(neopentyl 4‐styrenesulfonate), composed of a statistical copolymer segment of 2,3,4,5,6‐pentafluorostyrene with 4‐(1‐methylsilacyclobutyl)styrene and a neopentyl 4‐styrenesulfonate segment, was prepared by the nitroxy‐mediated living radical polymerization of a 2,3,4,5,6‐pentafluorostyrene/4‐(1‐methylsilacyclobutyl)styrene mixture and neopentyl 4‐styrenesulfonate. The block copolymer formed micelles with a poly[(2,3,4,5,6‐pentafluorostyrene)‐co‐4‐(1‐methylsilacyclobutyl)styrene] core in acetonitrile, which were crosslinked via the ring‐opening reaction of silacyclobutyl groups in the core by a treatment with a platinum catalyst. The deprotection of sulfonate groups in the micelle corona by exposure to trimethylsilyl iodide and a treatment with aqueous HCl, followed by neutralization with aqueous NaOH, provided a polymer particle with polymer chains of sodium 4‐styrenesulfonate grafted on its surface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1316–1323, 2007     

Multifunctional Cyclic Carbonates Comprising Hyperbranched Polyacetals: Synthesis and Applications to Polymer Electrolytes and Networked Polymer Materials

Hyperbranched polyacetals (HBPAs) bearing cyclic carbonate (CC) terminals were synthesized from protocatechuric aldehydes bearing bifunctional trimethylolpropane (TMP) or glycerol (Gly) structures and then utilized to design polymer electrolytes and networked polymer materials. Since TMP‐based cyclic acetals (CAs) are thermodynamically more stable than Gly‐derived CSs, the copolymerization of these monomers favors to form HBPAs comprising TMP‐based acetal stems and Gly terminals. Consequently, HBPAs composed of larger amounts of TMP or Gly terminals were separately synthesized by changing monomer feed ratios. Their diol terminals react efficiently with diphenyl carbonate to give HBPAs bearing 5‐ or 6‐membered CC (5‐CC or 6‐CC) terminals. HBPAs bearing 5‐CC terminals were mixed homogeneously with lithium bis(trifluoromethanesulfonyl)imide to form uniform films showing lithium ion conductivity ranging from 8.2 × 10^?9 to 2.1 × 10^?3 S cm^?1 at 23–80 °C, whereas networked polycarbonate and polyhydroxyurethane films were successfully fabricated using HBPAs having CC terminals. These results apparently indicate that HBPAs having CC terminals are useful scaffolds to design functional polymer materials. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2295–2303