We describe the characterization of the B-type procyanidins in wine and the B-type dehydrodicatechins (dimeric flavan-3-ols) obtained for the autoxidation of (+)-catechin and (-)-epicatechin by tandem mass spectrometry (MS/MS) coupled to reversed-phase high-performance liquid chromatography (HPLC). The MS/MS analysis demonstrates that the interesting major fragments derive from the dissociations of the C-ring on the catechin or epicatechin unit, such as retro-Diels-Alder reactions. The two kinds of dimers give completely different fragmentations because of the striking effect of the C-C interflavan linkage (IFL). For the natural dimers in wine, a catechin or epicatechin unit linking to the C-4 position stabilizes the product ions by forming a large pi-pi hyperconjugated system, whereas a similar pi-pi system is formed within dehydrodicatechin B through the C-C IFL. Thus dissociation in MS/MS experiments was inhibited. Apparently, the fragmentations of the dimers differ from that of the monomer, which is very important in the study of the gas-phase ion behaviour of the polymeric flavan-3-ols. In addition, two specific fragment ions at m/z 451 for native dimers and at m/z 393 for autoxidation species in HPLC/MS/MS were found to be very useful for analysing mixtures of B-type procyanidins and B-type dehydrodicatechins in food and beverages.

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Al2O3-, TiO2-, SiO2-, and ZrO2-based mixed-oxide supports were synthesized by sol−gel techniques using 2,4-pentanedione as the complexing/templating agent. These materials have been investigated by employing nitrogen adsorption, 27Al, 29Si, and 1H solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), and Fourier transform laser Raman spectroscopy (FT-Raman). Nitrogen adsorption isotherms of the mixed oxides Al2O3−SiO2 and TiO2−SiO2 were of type IV, with hysteresis loops of type I, indicating well-defined pore structure, while other mixed oxides Al2O3−TiO2, Al2O3−ZrO2, TiO2−ZrO2, and ZrO2−SiO2 exhibited type II hysteresis loops, indicating pores of undefined nature. 27Al MAS NMR studies on the alumina-based mixed oxides showed the presence of four-, five-, and six-coordinated aluminum species, the number of four-coordinated framework aluminum sites being highest in the Al2O3−SiO2 mixed oxide. 29Si CP MAS NMR spectra of the oxides Al2O3−SiO2, TiO2−SiO2, and ZrO2−SiO2 indicated the substitutional insertion of the cations (Al, Ti, and Zr) into the silica framework. DRIFTS spectra of these mixed oxides, where the vibrations corresponding to Si−O−M‘ bonds were observed, are in conformity with 29Si CP MAS results. FT-Raman studies indicated the amorphous nature of the oxides, except in the case of the TiO2−SiO2 sample where the peaks corresponding to titania microcrystallites were noticed.

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LIN-ZHI CHEN and JACK M. MILLER. Can. J. Chem. 69,2002Chem. 69, (1991. First field-free region B/E linked scan studies of metastable and particularly collision-induced dissociations show that two competitive coordination processes ("end-on" and "side-on") exist in the complexation of metal ions (Ni+, Co+, Fe+, and Mn+) with alkanenitriles in the FAB source of an E/B configuration mass spectrometer. Analysis of the B/E linked scan CA spectra gives approximate percentages of the end-on coordination mode in the reactive complexes. An unusual @-methyl migration, involved in the elimination of CH, from end-on complexes, may be in competition with P-H migration/elimination of H2 and @-C-C bond cleavage/elimination of alkene. For the side-on complexes, the metal ions can insert into various C-C bonds followed by P-H transfer/competitive elimination of alkene and alkane or by a direct C-M+ bond cleavage to give an alkyl radical.Key words: FAB mass spectroscopy, metal-ion/nitrile reactions, collisional activation, coordination modes, ion-molecule reactions. [Traduit par la redaction] LIN-ZHI