New stage in living cationic polymerization: An array of effective Lewis acid catalysts and fast living polymerization in seconds

Our recent extensive research on Lewis acid catalysts with a weak base for the cationic polymerization of vinyl ethers led to unprecedented living reaction systems: fast living polymerization within 1–3 s; a wide choice of metal halides containing Al, Sn, Fe, Ti, Zr, Hf, Zn, Ga, In, Si, Ge, and Bi; and heterogeneously catalyzed living polymerization with Fe₂O₃. The use of added bases for the stabilization of the propagating carbocation and the appropriate selection of Lewis acid catalysts were crucial to the success of such new types of living polymerizations. In addition, the base‐stabilized living polymerization allowed the quantitative synthesis of star‐shaped polymers with a narrow molecular weight distribution via polymer‐linking reactions and the precision synthesis and self‐assembly of stimuli‐responsive block copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1801–1813, 2007.     

Conductometric study of cationic and anionic complexes in propylene carbonate

Conductivity data are used to determine thermodynamic complex formation constants for cases in which both the initial electrolyte and the complexed electrolyte form ion pairs. Using the method described in the text, the complex formation constants of Li⁺, Na⁺ and K⁺ with the crown ether 18-crown-6 and of Li⁺ with the ligand triphenylphosphine oxide in propylene carbonate have been evaluated from conductance data. The complexation of AgBr in propylene carbonate solutions of n-etrabutylammonium bromide has also been studied by the measurement of molar conductivities. The results of these studies indicate that ion pairing should not be neglected, even in high permittivity solvents such as propylene carbonate, and that the ion pair association constants correlate well with structural studies on cation-crown ether molecular conformations.     

Photochemistry of perfluoroacyl halides in the presence of O2 and CO

Photolyses of CF₃C(O)X and C₂F₅C(O)X (X=Cl, F) at 254 nm in the presence of O₂ yield the perfluorinated radicals C₂F₅O (C₂) and CF₃O (C₁), respectively. The C₂ radicals decompose to give CF₃ radicals:

C₂F₅O→CF₃+CF₂O

which, in turn, react with O₂ leading to the formation of C₁ radicals. When in addition to O₂, CO is present, the C₁ radicals react with it leading to its catalytic oxidation to CO₂. The trioxide CF₃OC(O)O₃C(O)OCF₃ was observed following the photolysis of all four halides in the presence of O₂ and CO.

The other radical partners coming from the initial step in the photolysis (XC(O)) as well as the products of their reaction with O₂ (XC(O)O_y, y=1, 2) do not react with CO but when X=F they lead to the formation of a new stable peroxy molecule with the formula CF₃OC(O)O₂C(O)F. Some of the properties of this new molecule, its stability and its IR features are presented in this work.     

Adsorption of the fluoride ion on the surface of various faces of a single crystal of silver: a quantum-chemical study

The fluoride ion adsorption from a gas phase on various faces of a single crystal of silver is studied by a density functional method within a cluster model for metal. The adsorption bond energy is found to increase in the series Ag(100) < Ag(111) < Ag(311) < Ag(110). A substantial structural and energetic heterogeneity of various adsorption sites is revealed. The results are utilized to simulate the electrochemical interface between individual faces of a single crystal of silver and aqueous solutions containing the fluoride ion. It is assumed that the adsorption potential may be represented as the sum of two contributions, one of which describes the metal–ion interaction and the other, the ion solvation energy. The plotted adsorption terms take into account partial degradation of the fluoride ion when adsorbed from an aqueous solution. Estimates of discreteness of the electrical double layer are presented. A conclusion on the maximum manifestation of specific adsorption of the fluoride ion for the Ag(100) face is made.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 232–238.Original Russian Text Copyright © 2005 by Nazmutdinov, Zinkicheva.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Novel synthesis of 4-halo-3-hydroxy-2-pyrone: one pot rearrangement-cyclization reaction by magnesium halide

Treatment of acetonide protected 4,5-dihydroxy-2-chloroglycidic ester or its rearrangement product, the acetonide protected 4,5-dihydroxy-3-chloro-2-oxo ester, with magnesium halides gave 4-halo-3-hydroxy-2-pyrone in excellent to reasonable yields in one pot. The mechanism of this novel one pot rearrangement-cyclization reaction is also proposed.     

An efficient route to regioselective opening of N-tosylaziridines with zinc(II) halides

An efficient route for the regio- and stereoselective ring opening of N-tosylaziridines with zinc dihalides (ZnX₂, X = Cl, Br, I) is described. Depending on the solvent and Zn(II) halide, β-halo amines or imidazolines are obtained selectively in good to excellent yields.     

Direct electron transfer reaction of glucose oxidase at bare silver electrodes and its application in analysis

The direct electron transfer reaction of glucose oxidase (GOx) at a bare silver electrode is verified. The electron transfer number n = 2, electron transfer coefficient α = 0.45 and rate constant of the electrochemical reaction K_s = 0.1 s⁻¹ are obtained. This communication presents a multimolecular adsorption model to explain the properties of the direct electron reaction between GOx and bare silver electrodes. The residual valence force may be an important factor to ensure a direct electron transfer reaction on the bare electrode. On the basis of the experimental fact that only biologically active GOx exhibits electrochemical activity in solution, a facile analytical method for analyzing the active GOx concentration is developed. The results determined correspond very well to that of a spectrometric method.     

Characterization of peptides by liquid chromatography/electrospray ionization mass spectrometry using silver nitrate as a post-column complexant

Two model peptides, des-Arg1-bradykinin (DAB) and bradykinin (B), were cationized by Ag+ after their separation by reversed-phase liquid chromatography (RPLC) prior to mass spectrometry (MS). Silver nitrate solution was used as a post-column reagent. The RPLC and MS experimental conditions were optimized using flow injection in order to obtain sufficiently abundant silver adducts to permit MS/MS experiments. The use of water-methanol with 0.1% formic acid as mobile phase allowed a good chromatographic separation of the two peptides with a polymeric stationary phase and sufficiently abundant silver-containing adducts, [M + Ag + H]2+ and [M + 2Ag]2+. The gas-phase dissociation of [DAB + Ag + H]2+ and [DAB + 2Ag]2+ led to interpretable mass spectra during the on-line cationization experiment. Most of the ions obtained by dissociating [DAB + Ag + H]2+ and [DAB + 2Ag]2+ species are silver-containing ions but the ions produced depend on the parent. The ions coming from the dissociation of the doubly charged silver adducts [DAB + Ag + H]2+ or [DAB + 2Ag]2+ are of interest compared with those coming from the singly charged silver species or doubly charged protonated species. The fragmentation of the doubly charged silver adducts provides ions over the entire mass range. Although the presence of several prolines in des-Arg1-bradykinin prevents the formation of some expected ions, the observation of triplets [an-H + Ag]+, [bn-H + Ag]+ and [bn + OH + Ag]+ produced by the dissociation of on-line Ag(+)-cationized peptides could contribute to greater success of automatic sequencing of peptides.     

Carbenium ion pairs on silica: UV-spectroscopic and electrokinetic measurements of triarylmethylium/halide-aerosil in 1,2-dichloroethane

The interaction of carbenium ion pairs with silica is studied by means of UV-spectroscopy, electrokinetic and adsorption measurements using triphenylmethyl derivatives, (RC₆H₄)₃CX, (X=F, Cl, Br, SCN, OH; R=Cl, I, H, CH₃, C(CH₃)₃, OCH₃, N(CH₃)₂) in interaction with silica particles suspended in 1,2-dichloroethane. The adsorption of triarylmethyl-halides onto silica is accompanied by the heterolytic dissociation of the tertiary carbonhalogen bond. The degree of ionization depends on the basicity of the counter anion and acidity of the cation, respectively. The influences of both concentration and structure of triarylmethyl halides on the zeta-potential are discussed with regard to steric and electronic factor. The zeta-potential values of the adsorbates decrease significantly, as compared with the free silica surface, from a certain triarylmethyl halide concentration where ionization takes place, to a constant level which is characteristic of the carbenium ion pair. These constant zeta-potential values of the adsorbates depend on the basicity of the counter ion and the _p Hammett constants of the ring substitutents, with exclusion of sterically hindered substituents and salt derivatives, e.g., crystal violet and malachite green.     

[Rb2(H2O)2][Re3(μ-Cl)3Br7(H2O)2]2 · H2O,ein gemischtes Halogenid-Hydrat mit anionischen Dimeren {[Re3(μ-Cl)3Br7(H2O)2]2 · H2O}2−

[Rb₂(H₂O)₂][Re₃(μ-Cl)₃Br₇(H₂O)₂]₂ · H₂O, a Mixed Halide-Hydrate with the Anionic Dimer {[Re₃(μ-Cl)₃Br₇(H₂O)₂]₂ · H₂O}^2? [Rb₂(H₂O)₂][Re₃(μ-Cl)₃Br₇(H₂O)₂]₂ · H₂O crystallizes as dark redbrown single crystals from an hydrobromic-acid solution of ReCl₃ and RbBr at 0°C. An important feature of the crystal structure (monoclinic, C2/c; a = 1494.61(8); b = 835.71(4); c = 3079.96(19) pm; β = 97.801(4)°; V_m = 573.9(4) cm³mol^?1; R = 0.060; R_w = 0.038) is the connection of two anions [Re₃(μ-Cl)₃Br₇(H₂O)₂]^? via a water molecule to dimers, {[Re₃(μ-Cl)₃Br₇(H₂O)₂]₂ · H₂O}^2?. These dimeric units are contained in slabs that are stacked in the [001] direction and held together by Rb⁺ cations and crystal water.