Methylmethacrylate complexes of sterically hindered aluminum aryloxides: activation of methacrylic esters

The interaction of AlR₂(BHT)(OEt₂) and AlMe(BHT)₂ with methylmethacrylate (MMA) leads to the formation of the Lewis acid-base complexes AlR₂(BHT)(MMA) [R = Me (1), Et (2)] and AlMe-(BHT)₂(MMA) (3), respectively. The molecular structure of 1 has been determined by X-ray crystallography. The decrease in the C=O and C=C stretching frequencies in the IR spectrum, and downfield shift in the ¹³C NMR spectrum of the - and γ-carbons of the MMA, when compared to free MMA, is presented with respect to the activator ability of sterically crowded aryloxide compounds of aluminum to aluminum-porphyrin catalyzed (Inoue) polymerization of MMA.     

Flow sorption calorimetry, a powerful tool to investigate the acid-base character of organic polymer surfaces

Flow sorption calorimetry (FSC) can be a useful tool to estimate the Lewis acid-base behaviour of the surface of organic polymers with less than 1 m²/g surface area. Polyethylene powders grafted with different amounts of acrylic acid have been chosen as samples. The surface of the powders was investigated by means of X-ray photoelectron spectroscopy (XPS) at first and than brought into contact with the strong electron donor triethylamine in a special FSC measuring system. The heat of the displacement isotherm together with the surface excess isotherm of triethylamine adsorbed onto the powders was determined. The results obtained with FSC and XPS were well correlated and gave a comprehensive picture of the acidic surface character of modified polyethylene. Received: 19 September 1996 / Revised: 22 January 1997 / Accepted: 26 January 1997     

The promotion of d-type ions during the low energy collision-induced dissociation of some cysteic acid-containing peptides

Low energy collisionally activated dissociations (CAD) of doubly protonated peptides incorporating cysteic acid and arginine residues have been studied. Deuterium labeling experiments have established that loss of the elements of H₂SO₃ occurs with cleavage of one CH bond and transfer of the hydrogen to a neutral fragment. Prominent d-type ions were observed corresponding to cleavage at the cysteic acid residue. The analysis of structural analogs suggested that the unexpectedly low energy requirement for this process is attributable to a charge-proximal process promoted by intra-ionic interaction of the arginine and cysteic acid side chains. CAD (in the collision hexapole of a tandem quadrupole instrument) of electrospray source-formed fragment ions established that the d-type ions can form via b-type ions; there was no evidence of formation via (a _n + 1) or (b _n — H₂SO₃) ions. The equivalent d-ion was observed, albeit with lesser abundance, when the cysteic acid residue was replaced by aspartic acid, but not by glutamic acid.     

Controlled synthesis of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles by interfacial post-cross-linking reactions

 The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA), and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4′-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state ¹³C cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods. Received: 28 June 1999 /Accepted: 27 August 1999     

Analysis of the electrolyte diode. Electro-diffusion and chemical reaction within a hydrogel reactor

A reaction–diffusion system describing the electrolyte diode is investigated. This consists of a chemically crosslinked polyvinylalcohol (PVA) hydrogel cylinder in which a pH gradient is provided by having an acid and a base maintained at constant concentrations in reservoirs at each end of the one-dimensional reactor. A potential difference of a given strength is also applied across the gel cylinder. Previous experimental studies of the current–voltage characteristics (CVC) have shown two distinct cases, depending on whether a positive or negative potential difference was applied. The slopes of the linear current–voltage response curve are substantially different in the two cases, that in the 'forward' case being typically several orders of magnitude greater than that in the 'backward' case. Thus the system behaves like a semiconductor diode. The stationary concentration distribution for the different ions is described by a system of reaction–diffusion equations involving migration caused by the electric field. An approximate solution of these equations, using a simplified model, is presented and compared with results obtained by solving the full system numerically. The concentration profiles obtained from the numerical solution confirm the validity of the simplified model.     

Tandem mass spectrometry of aminated fullerene derivatives

The products of the reaction between fullerenes (C₆₀/C₇₀) and dimethylamine were investigated by fast atom bombardment (FAB) mass spectrometry and tandem mass spectrometry (MS/MS). The FAB mass spectrum shows peaks corresponding to the addition of up to eight dimethylamine species, exclusively to C₇₀. MS/MS reveals an unusual fragmentation pattern. The mass spectrum of the reaction products, together with a number of tandem mass spectra, are shown.     

Direct electron transfer from modified glassy carbon electrodes carrying covalently immobilised mediators to a dissolved viologen accepting pyridine nucleotide oxidoreductase and dihydrolipoamide dehydrogenase

N,N′-Diaminopropyl-4,4′-bipyridinium dication (DAPV) and cobalt diaminosarcophagine (Co—diamsar) were covalently bound on functionalised glassy carbon electrodes. The electron transfer from the modified electrodes to dissolved dihydrolipoamide dehydrogenase (Lip-DH) or viologen accepting pyridine nucleotide oxidoreductase (VAPOR) was tested by NADH formation in potentiostatically controlled electrochemical cells. The NADH formed was used to reduce pyruvate to -lactate catalysed by -lactate dehydrogenase ( -LDH). The reaction kinetics between the modified electrodes and the dissolved enzymes have been examined.