Charge separation reactions of doubly charged benzene ions

Photoion-photoion coincidence spectra of benzene and benzene-d₆ photoionized by He(II) light and synchrotron radiation show the existence of six major and eight minor charge-separation reactions of the [C₆H₆]²⁺ ion. Three main groups of ion pairs are related to [C₃H₃]⁺ + [C₃H₃]⁺, [C₂H₃]⁺ + [C₄H₃]⁺ and [CH₃]⁺ + [C₅H₃]⁺, with appearance energies of 32.2 ± 0.5 eV, 31.3 ± 0.5 eV and 28.4 ± 0.3 eV. The kinetic energy release is the same for all pairs within a group, irrespective of hydrogen number, but differs from group to group. Results are interpreted in terms of fast, direct charge separation of [C₆H₆]²⁺, and subsequent hydrogen loss by the singly charged fragments.     

Adapting a thermobalance to constrained rate thermogravimetry

A thermobalance has been converted to allow interactive control of the heating rate from the rate of mass loss of the sample (Constrained Rate Thermogravimetry). The interfacing of the balance and temperature controller both to an ACORN RISC microcomputer and to a PC microcomputer is described along with an outline of the software required. This provides an economic route for the conversion of existing thermobalances. Problems of achieving effective control and acceptable data recording are outlined. The nature of the TG curves obtained from interactive temperature control and the influence of control parameters is discussed.     

Biosynthesis inspired Diels-Alder route to pyridines: synthesis of the 2,3-dithiazolylpyridine core of the thiopeptide antibiotics

Reaction of serine derived 1-alkoxy-2-azadienes with dehydroalanine derived dienophiles results in Diels-Alder reaction and aromatisation to give 2,3,6-trisubstituted pyridines, thereby establishing the viability of the proposed biosynthetic route to the pyridine ring of the thiopeptide antibiotics originally proposed by Bycroft and Gowland.     

Evidence for the existence of methyl hypofluorite: methanolysis of xenon difluoride

Methyl hypofluorite is indicated as an intermediate in the reaction of xenon difluoride with alkenes in methanol as solvent.     

Analysis of anionic metallized azo and formazan dyes by capillary electrophoresis-mass spectrometry

Capillary electrophoresis-mass spectrometry was applied to the separation of several anionic dyes containing copper(II), chromium(III), or cobalt(III) as part of the dye molecule. The dyes were separated using a 110 cm x 50 microm uncoated fused-silica capillary and a 5 mM ammonium acetate buffer (pH 9) containing 40% acetonitrile. Excellent separation efficiencies (N = 500,000 plates/column) and low detection limits of 20-50 pg (selected ion monitoring, S/N = 10) were achieved. Mass spectra were acquired at different cone voltages. At low cone voltages (low collision energies), sensitivity was maximized and the mass spectra contained only signals of the (multiply charged) molecular ions and low levels of sodium ion and proton adducts. At higher cone voltages, the 2:1 (ligand:metal) chromium and cobalt dyes showed losses of one of the two dye ligands, accompanied by a reduction of the metal. The copper dyes showed signals due to loss of SO2 and SO3-, but no release of metal. Azo cleavage, otherwise typical of azo dyes, was not observed with the metallized dyes.     

Catalytic hydroxylation of polypropylenes

The regioselective functionalization of both model and commercial polypropylenes of varying tacticity has been conducted by a rhodium-catalyzed functionalization of the methyl C-H bonds of the polymer with diboron reagents. Rhodium-catalyzed borylation of the polypropylenes, followed by oxidation of the boron-containing material, produced polymers containing 0.2-1.5% hydroxymethyl side chains. Both the number-average molecular weights and molecular weight distributions of the polypropylenes were essentially unchanged after the catalytic and oxidative functionalization process. The efficiency of the borylation process was affected by the molecular weight of the polymer, the steric hindrance around the methyl groups, and the ratio of the diboron reagent to the monomer repeat unit. The hydroxylated derivative of the commercial isotactic polypropylene was used as macroinitiator for the aluminum-mediated ring-opening polymerization of epsilon-caprolactone to prepare polypropylene-graft-polycaprolactone. This graft copolymer was an effective compatibilizer for melt blends of polypropylene and polycaprolactone.     

Bis-1,2,3-thiaselenazolyl radicals and their sigma-bonded dimers

Resonance stabilized bis-1,2,3-thiaselenazolyl radicals associate in the solid state to afford Se-Se sigma-bonded dimers.     

Synthesis and characterization of water-soluble amino fullerene derivatives

[formula: see text] A series of amino-substituted methanofullerene derivatives were prepared by mono-, tris-, and hexa-Bingel-Hirsch reactions using an N-protected malonate derivative. Upon scission of the protecting groups, the e,e,e-tris- and octahedral Th hexa-methano amino fullerenes were found to be among the most water-soluble fullerene derivatives yet prepared. 3He NMR data on corresponding adducts of 3He/C60 helped verify the assigned structures. UV spectral studies confirmed the influence of aggregation on solubility of these adducts in water.     

Conformational changes of a calix[8]arene derivative at the air-water interface

The particular behavior of a p-tert-butyl calix[8]arene derivative (C8A) has been studied at the air-water interface using surface pressure-area isotherms, surface potential-area isotherms, film relaxation measurements, Brewster angle microscopy (BAM), and infrared spectroscopy for Langmuir-Blodgett films. Thus, it is observed that the properties of the film, for example, isotherms, domain formation, and FTIR spectra, recorded during the first compression cycle differ appreciably from those during the second compression and following cycles. The results obtained are interpreted on the basis of the conformational changes of the C8A molecules by surface pressure, allowing us to inquire into the inter- and intramolecular interactions (hydrogen bonds) of those molecules. Thus, the compression induces changes in the kind of hydrogen bonds from intra- and intermolecular with other C8A molecules to hydrogen bonds with water molecules.     

Continuous and simultaneous fermentation and recovery of lactic acid in a biparticle fluidized-bed bioreactor

Applied Biochemistry and Biotechnology - A continuous biparticle fluidized-bed reactor (BFBR) is developed for the simultaneous fermentation and recovery of lactic acid. In this processing scheme,...