Biomedical subjects

C Le Guernevé

Publications and source records attributed to C Le Guernevé.

11 recordsLinked to original sources

PubMed2000

New phenolic compounds formed by evolution of (+)-catechin and glyoxylic acid in hydroalcoholic solution and their implication in color changes of grape-derived foods.

The reaction between (+)-catechin and glyoxylic acid in model solution system was investigated by LC/DAD and LC/ESI-MS analyses. The formation of phenolic compounds exhibiting absorption maxima near 300 nm and presenting a shoulder around 350 nm was observed. Their structures consisted of a (+)-catechin unit with one or two aldehyde groups linked at positions 6, 8 or 6 and 8 of the A ring. In addition, new yellow pigments exhibiting UV-visible spectra similar to those of xanthylium salts with absorption maxima at 450 and 280 nm were also detected. The major yellow compound was isolated and identified by ESI-MS and 1D and 2D NMR spectroscopy. The implication of these compounds in color change and browning observed during aging of grape-derived beverages is also discussed.

Alcohols↗

PubMed2000

Identification of a precursor of beta-methyl-gamma-octalactone in the wood of sessile oak (Quercus petraea (Matt.) Liebl.).

The 6'-O-gallate derivative of (3S, 4S)-4-beta-D-glucopyranosyloxy-3-methyloctanoic acid was isolated for the first time from the wood of Sessile oak (Quercus petraea (Matt.) Liebl.) and shown to be a precursor of cis-beta-methyl-gamma-octalactone. The structure of this precursor was determined by HRFAB-MS, NMR, LCMS, and chiral analysis of the liberated (3S,4S)-beta-methyl-gamma-octalactone on a chiral fused silica capillary column. Optical rotation was shown to be identical to that of the same compound previously isolated from the wood of Platycarya strobilacea Sieb. et Zucc. by Tanaka and Kouno in 1996. Moreover, the 6'-O-gallate derivative of a threo-4-beta-D-glucopyranosyloxy-3-methyloctanoic acid was tentatively identified as a minor precursor of trans-beta-methyl-gamma-octalactone in the same wood of Sessile oak.

Lactones↗

PubMed2000

Phenolic composition of litchi fruit pericarp.

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 phenolic compounds of litchi cv. Kwai Mi were quantified by HPLC. Condensed tannins were the most abundant (4 mg x g(-1) of fresh skin), followed by epicatechin and procyanidin A2 (1.7 and 0.7 mg x g(-1) of fresh pericarp, respectively). The amount of anthocyanins was found to be comparable to that of flavonols, with a value of approximately 0.4 mg x g(-1) of fresh pericarp.

Chromatography, Liquid↗

PubMed2000

Phenolic composition of grape stems.

Grape stems contain significant amounts of polyphenolic compounds, especially phenolic acids, flavonols, and flavanonols such as astilbin. The tannin content was characterized after the depolymerization reaction thiolysis. Tannins consisted of polymeric proanthocyanidins (up to 27 units) mainly consisting of (-)-epicatechin units along with smaller amounts of (+)-catechin, (-)-epicatechin gallate, and (-)-epigallocatechin. Flavanonols (astilbin) have been identified for the first time in stem and characterized by LC/MS and NMR. All phenolic compounds in grape stems were quantified by HPLC: quercetin 3-glucuronide was the most important, followed by catechin, caffeoyltartaric acid, and dihydroquercetin 3-rhamnoside (astilbin). Comparison was made of proanthocyanidin characteristics in different white and red grape varieties and also among parts of the cluster (skin, seed, and stem). Stem-condensed tannins were qualitatively intermediate between seed and skin but could not be differentiated between red and white varieties.

Flavonoids↗

PubMed1999

Evolution of castalagin and vescalagin in ethanol solutions. Identification of new derivatives.

Brandies, cognac, armagnac, whiskeys, and rums are aged in oak barrels to improve their organoleptic properties. During this period, numerous compounds such as ellagitannins are extracted from the wood and can subsequently be transformed into new derivatives by chemical reactions. Model solutions of castalagin and vescalagin have been studied to determine the behavior of polyphenols in ethanol-water. Upon prolonged exposure to 40 and 70% (v/v) ethanol at room temperature, hemiketal derivatives containing ethoxy groups have been characterized by LC/MS and NMR. These compounds further evolve to afford the corresponding ketals. They have also been detected in the extracts of oak wood stored under similar conditions.

Alcoholic Beverages↗

PubMed1999

New polyphenolic compounds with xanthylium skeletons formed through reaction between (+)-catechin and glyoxylic acid.

The reaction between (+)-catechin and glyoxylic acid was studied in a model solution system. The major (+)-catechin carboxymethine-linked dimer was isolated and shown to proceed to new polyphenolic compounds exhibiting absorption maxima around 440 and 460 nm. Three yellow pigments were obtained by incubation of the 8-8 colorless isomer. One was the previously reported xanthylium compound NJ2 with a maximum at 440 nm. The other two, showing absorption maxima at 460 nm, were obtained separately by incubation of the colorless dimer in hydroethanolic or methanolic medium. Structural elucidation of these two new yellow pigments was achieved by means of MS and 1D and 2D NMR techniques and showed that they were, respectively, ethyl and methyl esters of NJ2. The fact that these compounds were not obtained when NJ2 was incubated in hydromethanolic or ethanolic medium showed that esterification took place before the formation of the xanthylium chromophores. The detection of the esterified colorless compounds and the corresponding xanthene intermediates confirmed the postulated mechanism. New pigments exhibiting a strong absorption at 560 nm were also observed.

Catechin↗

PubMed1998

Interaction of the wheat endosperm lipid-binding protein puroindoline-a with phospholipids.

Puroindoline-a is the main component of a new family of proteins that has been suggested to exert an antimicrobial activity in plant seeds through an interaction with lipid membranes. Here the interaction of puroindoline-a with model phospholipid membranes and micelles has been studied using intrinsic tryptophan fluorescence, fluorescence polarization of diphenyl hexatriene, and proteolysis experiments. The protein appears to interact with both zwitterionic and negative phospholipids. The interaction with phosphatidylcholine is characterized by low-affinity surface binding with very limited penetration into the hydrophobic membrane interior. On the other hand, the interaction with phosphatidylglycerol displays a high affinity and involves a partial penetration of the protein into the bilayer interior that disrupts acyl chain packing. The specificity appears to be due to the presence of a stretch of positively charged residues in the protein sequence. In all, the lipid-binding properties of puroindoline-a resemble those of cardiotoxins, another family of proteins for which a disruptive effect on the membrane structure has been involved to explain their biological function.

Amino Acid Sequence↗

PubMed1998

Comparison between the dynamics of lipid/gramicidin A systems in the lamellar and hexagonal phases: a solid-state 13C NMR study.

We have investigated the effect of gramicidin A on the dynamics of two model membranes: dimyristoylphosphatidylcholine (DMPC) in the lamellar phase at a lipid-to-peptide molar ratio of 10:1 and dioleoylphosphatidylcholine (DOPC) in the hexagonal HII phase at a lipid-to-peptide molar ratio of 5:1. Natural abundance 13C nuclear magnetic resonance (NMR) spectroscopy was used in combination with magic angle spinning to increase the spectral resolution, therefore allowing the different regions of the lipid bilayers to be investigated from the same spectra. 31P NMR was also used to detect and confirm the formation of the DOPC HII phase in the presence of gramicidin A. In order to examine the effect of gramicidin A on both the fast and slow motions of DMPC and DOPC, the 1H spin-lattice relaxation times in the laboratory frame (HT1) as well as the 1H spin-lattice relaxation times in the rotating frame (HT1rho) were calculated for each resolved protonated lipid resonance in the 13C spectra. For both DMPC and DOPC, we found that the presence of gramicidin A does not significantly affect the fast motions of the lipid acyl chains but increases slightly the fast motions of the polar head group. However, the HT1rho are significantly decreased, this effect being more pronounced for DOPC most likely due to a decrease in the rate of the lipid lateral diffusion.

Carbon Isotopes↗

PubMed1996

Band-selective 3D NOESY-TOCSY: measurement of through-space correlations between aliphatic protons of membrane peptides and proteins in non-deuterated detergents.

Recently the use of band-selective excitation to obtain 1H 2D NMR spectra of membrane peptides and proteins in non-deuterated detergents has been demonstrated [Seigneuret, M. and Levy, D. (1995) J. Biomol. NMR, 5, 345-352]. A limitation of the method was the inability to obtain through-space correlation between aliphatic protons. Here, a 3D F3-band-selective NOESY-TOCSY experiment is described that allows such correlations to be observed in the presence of an excess of non-deuterated detergent. Application to the measurement of proximities between aliphatic protons of the membrane peptide mastoparan X solubilized in non-deuterated n-octylglucoside is presented. With this additional experiment, it is now possible to obtain the same amount of structural constraints on membrane peptides and protein in non-deuterated detergent as in deuterated detergent and therefore to perform complete structural studies.

Detergents↗

PubMed1996

High-resolution mono- and multidimensional magic angle spinning 1H nuclear magnetic resonance of membrane peptides in nondeuterated lipid membranes and H2O.

High-speed (14 kHz) solid-state magic angle spinning (MAS) 1H NMR has been applied to several membrane peptides incorporated into nondeuterated dilauroyl or dimyristoylphosphatidylcholine membranes suspended in H2O. It is shown that solvent suppression methods derived from solution NMR, such as presaturation or jump-return, can be used to reduce water resonance, even at relatively high water content. In addition, regioselective excitation of 1H peptide resonances promotes an efficient suppression of lipid resonances, even in cases where these are initially two orders of magnitude more intense. As a consequence, 1H MAS spectra of the peptide low-field region are obtained without interference from water and lipid signals. These display resonances from amide and other exchangeable 1H as well as from aromatic nonexchangeable 1H. The spectral resolution depends on the specific types of resonance and membrane peptide. For small amphiphilic or hydrophobic oligopeptides, resolution of most individual amide resonance is achieved, whereas for the transmembrane peptide gramicidin A, an unresolved amide spectrum is obtained. Partial resolution of aromatic 1H occurs in all cases. Multidimensional 1H-MAS spectra of membrane peptides can also be obtained by using water suppression and regioselective excitation. For gramicidin A, F2-regioselective 2D nuclear Overhauser effect spectroscopy (NOESY) spectra are dominated by intermolecular through-space connectivities between peptide aromatic or formyl 1H and lipid 1H. These appear to be compatible with the known structure and topography of the gramicidin pore. On the other hand, for the amphiphilic peptide leucine-enkephalin, F2-regioselective NOESY spectra mostly display cross-peaks originating from though-space proximities of amide or aromatic 1H with themselves and with aliphatic 1H. F3-regioselective 3D NOESY-NOESY spectra can be used to obtain through-space correlations within aliphatic 1H. Such intrapeptide proximities should allow determination of the conformation of the peptide in membranes. It is suggested that high-speed MAS multidimensional 1H NMR of peptides in nondeuterated membranes and in H2O can be used for studies of both peptide structure and lipid-peptide interactions.

Dimyristoylphosphatidylcholine↗

PubMed1995

New approach to study fast and slow motions in lipid bilayers: application to dimyristoylphosphatidylcholine-cholesterol interactions.

Natural abundance 13C solid-state nuclear magnetic resonance spectroscopy was used to investigate the effect of the incorporation of cholesterol on the dynamics of dimyristoylphosphatidylcholine (DMPC) bilayers in the liquid-crystalline phase. In particular, the use of a combination of the cross-polarization and magic angle spinning techniques allows one to obtain very high resolution spectra from which can be distinguished several resonances attributed to the polar head group, the glycerol backbone, and the acyl chains of the lipid molecule. To examine both the fast and slow motions of the lipid bilayers, 1H spin-lattice relaxation times as well as proton and carbon spin-lattice relaxation times in the rotating frame were measured for each resolved resonance of DMPC. The use of the newly developed ramped-amplitude cross-polarization technique results in a significant increase in the stability of the cross-polarization conditions, especially for molecular groups undergoing rapid motions. The combination of T1 and T1 rho measurements indicates that the presence of cholesterol significantly decreases the rate and/or amplitude of both the high and low frequency motions in the DMPC bilayers. This effect is particularly important for the lipid acyl chains and the glycerol backbone region.

Carbon Isotopes↗