Guy Bourgeois

Characterisation of oligomeric and polymeric procyanidins from grape seeds by liquid secondary ion mass spectrometry

Abstract Several fractions of oligomeric and polymeric procyanidins have been obtained from grape seeds by gel chromatography on Fractogel TSK. Their molecular weights (Mw) were directly determined by Liquid Secondary Ion Mass Spectrometry (LSIMS). We observed that tannins were molecules with a wide range of Mw: from 290 to 3100 (decamers). Catechins (Mw 290), procyanidin dimers (Mw 578), (−)-epicatechin gallate (Mw 442), procyanidin dimer gallates (Mw 730), procyanidin dimer digallates (Mw 882), procyanidin trimers (Mw 866) and procyanidin trimer gallates (Mw 1018), were identified as (M−H) − quasimolecular ions by negative LSIMS. Some structures were elucidated by partial thiolysis and enzymatic hydrolysis.

The influence of various phenolic compounds on scavenging activity assessed by an enzymatic method

The effect of pure monomeric and dimeric procyanidins on superoxide anion radicals (O2°−) was studied with an enzymatic method and their IC50 was determined. A comparative study of the results suggested that the antiradical potential of these phenolic compounds closely depends on their stereochemical structure. Modification of the chiral carbon, C3 involved in the oxidation mechanism induces differences in the scavenging action of (+)-catechin (2R : 3S) or (−)-epicatechin (2R : 3R). The stereochemical conformation of the interflavan linkage (axial or pseudo) according to the chemical nature of dimeric procyanidin units also influences the radical oxidation mechanism. The nature of the interflavan linkage between the two units in dimeric procyanidins (C4–C8 or C4–C6 linkage) is an important factor responsible for effectiveness of the behaviour polyphenols towards O2°−. The extraction of oligomeric procyanidins in grape seeds enabled us to study the effect of polymerisation and galloylation on their scavenging activities. The results clearly showed that the molecular scavenging mechanism of these molecules is closely connected with their spatial conformation. © 1999 Society of Chemical Industry

Analysis of the variation of the essential oil composition of Eucalyptus globulus Labill. from Portugal using multivariate statistical analysis

Abstract Samples of Eucalyptus globulus Labill. subsp. globulus essential oil obtained from trees of different ages, growing in maritime and inland Portuguese regions, collected in May and November periods (1991–1992), were submitted to quantitative analysis. The results obtained were interpreted using principal component analysis and cluster analysis, considering the 25 abundantly found compounds. These compounds were grouped according to their variation patterns, leading to the definition of five groups, four of which have shown to be significant in the differentiation of young and adult leaves. Young leaves, when compared to adult leaves, were found to have higher oil yields, with lower percentage of group II (in which 1,8-cineole is included) and III compounds and higher percentages of compounds from groups I and IV. Variations in the oil composition due to season and geographic localisation were found not to be significant.

Determination of the Composition of Commercial Tannin Extracts by Liquid Secondary Ion Mass Spectrometry (LSIMS)

The composition of various commercial tannin extracts were determined by liquid secondary ion mass spectrometry (LSIMS). Spectra were obtained directly from tannin extracts without any pre-separation. Eight different tannin powders were analysed : three gallotannins (Chinese, Turkish, tara), three ellagitannins (sweet chestnut, pendunculata oak, sessile oak), one mixed hydrolysable tannin (myrabolans) and one proanthocyanidin (grape seeds). This method enabled the main molecules in these powders to be identified.

Structure simulation of two ellagitannins from Quercus robur L.

Abstract Two major ellagitannins from Quercus robur , vescalagin and castalagin, were studied by 1 HNMR and LSI-mass spectrometry, and molecular mechanics. A plausible 3D-structure is proposed for each of the two diastereoisomers. These structures were the most stable ones found after a conformational analysis study and their calculated NMR spectra are in good accordance with measured ones.

Essential Oil of Foeniculum vulgare Mill. (Fennel) subsp. piperitum (Ucria) Cout. Fruit

ABSTRACT For the first time, pentane extracts of the fruits of Foeniculum vulgare, subspecies piperitum, have been analyzed by GC. Two new compounds, piperitenone and piperitenone oxide, were identified by their mass spectra.

SYNTHESIS AND CHEMICAL PROPERTIES OF 1,3-DICHLORO-1,3-DIHYDRIDODISILAZANES

Abstract A trans-silylation route to 1,3-dichloro-l,3-dihydridodisilazanes, a novel class of polyfunctional disilazane, is described. Thus, heating hexamethyl- or heptamethyl-disilazane under reflux in the presence of an excess of dichlorohydrogenosilane R 1 SiHCl 2 , led to compounds of formula (R 1 ClHSi) 2 NR 2 (R 1 = Me, Et, Vi or Ph and R 2 = H; R 1 = Me and R 2 = Me) in high yield. The exchange of chlorinated organosilicon moieties was strongly facilited by a catalytic amount of ( π Bu 4 N)F. Interpretation of the results and a few chemical properties of these novel disilazanes are reported.

The secretory apparatus of Ginkgo biloba: structure, differentiation and analysis of the secretory product

SummaryThe differentiation of the secretory cavities of Ginkgo stem and the structural organization of the epithelial cells were followed by light and electron microscopy. The mode of formation of the cavities is schizo-lysigeneous. Functional complexes of leucoplasts and associated endoplasmic reticulum (ER) membranes are assumed to be the site of synthesis and translocation of the lipophilic secretory product. Most of the endoplasmic reticulum membranes are paired. The content of the cavities was directly collected and analysed by low- and high-resolution mass spectrometry. The cavities contain anacardic acids and cardanols, which are long-chain phenol lipids not characteristic of Ginkgo. The relationship between the plastid/ER complexes and the production of these secondary metabolites is discussed.

Composes organometalliques a cycle moyen : VI. Mise en evidence d'une interaction transannulaire O—Si en serie silacyclanique par spectrometrie de masse et resonance magnetique nucleaire de 29Si

Abstract A mass spectral study of a series of silacyclanones with 9—13-membered rings revealed the existence of the ion C 2 H 7 OSi ( m/e 75) whose formation was interpreted as resulting from a transannular interaction between the carbonyl oxygen and silicon. The 29 Si NMR results were in good agreement with the existence of this interaction.

Nouveaux polycarbosilanes modèles. 3-Synthèse et caractérisation de carbosilanes linéaires fonctionnels

Abstract A method for synthesizing novel linear polysilmethylenes of general formula Me(HMeSiCH 2 ) x SiMe 2 H (VII x ) is described. This strategy involves the cocondensation of chloromethylsilanes HMe 2 Si(CH 2 SiMeH) m CH 2 Cl ( m = 0 or 1) with methyldichlorosilane and 1,3-dichloro-1,3-dimethyl-1,3-disilapropane, respectively, by Grignard reactions. Thus, short-chain polycarbosilanes possessing terminal dimethylhydrogenosilyl groups were prepared (2 ≤ χ ≤ 5). They were then converted into the corresponding chlorinated derivatives Me(Cl MeSiCH 2 ) x SiMe 2 Cl (VIII x by reaction with CCl 4 in the presence of a palladium catalyst. The mass spectra (70 eV) of both series reveal that characteristic fragmentations occur. Moreover, the SiH-containing derivatives VII x exhibit analogous behavior during their rearrangement under electronic impact and during their pyrolysis.