Christine Le Guernevé

Bio: Christine Le Guernevé is an academic researcher from University of Montpellier. The author has contributed to research in topics: Glyoxylic acid & Dimer. The author has an hindex of 19, co-authored 32 publications receiving 1233 citations. Previous affiliations of Christine Le Guernevé include SupAgro & Institut national de la recherche agronomique.

Synthesis and properties of biobased epoxy resins. part 1. Glycidylation of flavonoids by epichlorohydrin

Abstract: Biobased epoxy resins were synthesized from a cate- chin molecule, one of the repetitive units in natural flavonoid biopolymers also named condensed tannins. The reactivity of catechin toward epichlorohydrin to form glycidyl ether deriva- tives was studied using two model compounds, resorcinol and 4-methylcatechol, which represent the A and B rings of catechin, respectively. These model molecules clearly showed differences in reactivity upon glycidylation, explaining the results found with catechin monomer. The reaction products were character- ized by both FTIR and NMR spectroscopy and chemical assay. The glycidyl ether of catechin (GEC) was successfully cured in various epoxy resin formulations. The GECs thermal properties showed that these new synthesized epoxy resins displayed interesting properties compared to the commercial diglycidyl ether of bisphenol A (DGEBA). For instance, when incorporated up to 50% into the DGEBA resin, GEC did not modify the glass- transition temperature. Epoxy resins formulated with GEC had slightly lower storage moduli but induced a decrease of the swelling percentage, suggesting that GEC-enhanced crosslink- ing in the epoxy resin networks. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2261-2270, 2011

Phenolic composition of Litchi fruit pericarp

Abstract: Litchi (Litchi chinensis, Sapindaceae) is a nonclimacteric subtropical fruit that, once harvested, loses its red pericarp color because of browning reactions probably involving polyphenols. Low-pressure chromatography, high-pressure liquid chromatography, UV−visible spectral analysis, mass spectrometry, and nuclear magnetic resonance studies have allowed the determination and quantification of the polyphenolic composition of litchi pericarp. Litchi skins contain significant amounts of polyphenolic compounds. The principal characteristic of the litchi skin polyphenolic compounds is their ortho-diphenolic structure, which gives them high oxidability. Four major pigments were formally identified as cyanidin 3-rutinoside, cyanidin glucoside, quercetin 3-rutinoside (rutin), and quercetin glucoside. The tannin content was characterized after the depolymerization thiolysis reaction. Tannins (polymeric proanthocyanidins) are mainly constituted with epicatechin units linked by A- and B-type bonds. The different ph...

Xanthylium salts formation involved in wine colour changes

Abstract: Summary The reaction of (+)-catechin in wine-like model solution was investigated. First appearance of colourless dimeric compounds consisting of two flavanol units linked by carboxy-methine bridge was observed. Their isolation and further incubation was found to yield two types of yellowish pigments showing visible absorption maxima at 440 and 460 nm, respectively. Mass spectroscopy (MS) spectral analysis showed that the first type were xanthylium salt pigments formed by dehydration of the colourless compounds followed by an oxidation process. The loss of a water molecule was shown to take place between two A ring hydroxyl groups of the colourless dimers. The second type were shown to be ester derivatives of the first ones. Thus ethylester of xanthylium salt was obtained and fully characterized by mass and nuclear magnetic resonance (NMR) spectroscopy. Esterification was found to involve the colourless compound before dehydration and thus a general scheme for xanthylium salt formation was postulated. The proposed scheme constitutes a new xanthylium formation pathway as up to now only anthocyanin-flavanol reactions were supposed to form xanthylium salt derivatives during wine ageing. This work also provides new support to the contribution of xanthylium salt in colour evolution observed during wine ageing which is generally expressed in an increase of absorption in the 400–500 nm, region of xanthylium salt absorption maxima.

Characterization of a colorless anthocyanin-flavan-3-ol dimer containing both carbon-carbon and ether interflavanoid linkages by NMR and mass spectrometry.

Abstract: Direct addition of anthocyanins and flavan-3-ols was investigated in a model system by incubating malvidin 3-glucoside and (-)-epicatechin in ethanol. Analysis of reaction products by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC/ESI-MS) before and after thiolysis showed the formation of colorless dimers detected at m/z 781 in the negative ion mode, with retention times and spectroscopic characteristics identical to those of compounds detected in wine, which contain one malvidin 3-glucoside unit and one flavanol unit. On the basis of their resistance to thiolysis, these compounds were postulated to be bicyclic dimers linked with both carbon-carbon and ether bonds as observed in the case of A type proanthocyanidins. The major dimer analyzed by NMR experiments was identified as malvidin 3-glucoside(C2-O-C7,C4-C8)epicatechin, confirming this hypothesis. A similar assay was performed with (+)-catechin instead of (-)-epicatechin, and the formation of bicyclic dimers was also observed.

Proanthocyanidins and tannin-like compounds – nature, occurrence, dietary intake and effects on nutrition and health

Abstract: Proanthocyanidins (syn condensed tannins) are complex flavonoid polymers naturally present in cereals, legume seeds and particularly abundant in some fruits and fruit juices. They share some common structural features—phenolic nature and high molecular weight—with phenolic polymers found in black tea and red wine (called here tannin-like compounds). The polymeric nature of proanthocyanidins makes their analysis and estimation in food difficult. For this reason, little is known about their consumption, although they likely contribute a large part of the daily polyphenol intake. They also share common physicochemical properties: they form stable complexes with metal ions and with proteins and are, like other polyphenols, good reducing agents. Many of their biological effects of nutritional interest derive from these properties. As metal ion chelators, they influence the bioavailability of several minerals. The nutritional significance of the non-specific complexation of proteins is less clear. As reducing agents, they may participate in the prevention of cancers, both of the digestive tract and inner organs. They may also protect LDLs against oxidation and inhibit platelet aggregation and therefore prevent cardiovascular diseases. In vitro, animal and human studies on the prevention of these chronic diseases are reviewed with particular attention to wine and tea polyphenols. The lack of data on their bioavailability and the paucity of human studies are emphasised. © 2000 Society of Chemical Industry

Biobased thermosetting epoxy: present and future.

Abstract: Reḿi Auvergne,† Sylvain Caillol,† Ghislain David,*,† Bernard Boutevin,† and Jean-Pierre Pascault‡,§ †Institut Charles Gerhardt UMR CNRS 5253 Laboratoire Ingeńierie et Architecture Macromolećulaire, Ecole Nationale Supeŕieure de Chimie de Montpellier, 8 rue de l’Ecole Normale, 34296 Montpellier Cedex 05, France ‡INSA-Lyon, IMP, UMR5223, F-69621, Villeurbanne, France Universite ́ de Lyon, F-69622, Lyon, France