RESUMO
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.
Assuntos
Bebidas Alcoólicas , Compostos de Bifenilo , Catecóis/química , Taninos Hidrolisáveis , Anti-Hipertensivos/química , Cromatografia Líquida de Alta Pressão , Etanol , Manipulação de Alimentos , Conformação Molecular , Estrutura Molecular , Soluções , Taninos/química , Taninos/isolamento & purificação , MadeiraRESUMO
Xyloglucan polymers have been isolated from cyclamen seeds and characterized by both liquid and CP-MAS 13C NMR spectroscopy. Treatment of the polysaccharides with cellulase from Trichoderma viride afforded XG oligomers which have been studied with both mass spectrometry and NMR spectroscopy. The repeating unit in the intact polymers and the most abundant hydrolysis product correspond to the Gal1 Xyl3 Glc4 (XXLG) fragment. However, detection of notable amounts of Xyl3 Glc4 (XXXG) and Gal2 Xyl3 Glc4 (XLLG) indicates that the galactose distribution in xyloglucan from cyclamen is irregular. FAB-MS analysis of a new derivative, prepared by forming the glycosamine of m-tetrafluoroethoxy aniline, has led to unambiguous sequence information for the XXLG oligomer.
Assuntos
Glucanos , Oligossacarídeos/química , Polissacarídeos/química , Sementes/química , Xilanos , Configuração de Carboidratos , Sequência de Carboidratos , Parede Celular/química , Celulase , Hidrólise , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Dados de Sequência Molecular , Estrutura Molecular , Polissacarídeos/isolamento & purificação , Trichoderma/enzimologiaRESUMO
The internal dynamics of four disaccharides, a galacturonic acid dimer, beta-ethyl-lactoside, sucralose and arabinobiose, have been studied using molecular dynamics and nuclear magnetic resonance methods. Theoretical motion models, which include order parameters and correlation times for internal motions, were extracted from dynamics trajectories in vacuo. In parallel, theoretical NOESY volumes were calculated from averaged distance matrices using 'model-free' spectral densities. These data were least-squares fitted to the normalized experimental NOESY volumes using the order parameters and internal motion correlation times as adjustable parameters. The resulting 'experimental' motional models were in good agreement with the theoretical ones with the exception of the galacturonic acid dimer which was best described by the rigid molecule approximation.
Assuntos
Dissacarídeos/química , Modelos Moleculares , Configuração de Carboidratos , Sequência de Carboidratos , Espectroscopia de Ressonância Magnética , Modelos Teóricos , Dados de Sequência Molecular , Relação Estrutura-AtividadeRESUMO
In the present study a combination of proton and carbon relaxation rates have been measured for several oligosaccharides at different temperatures. Correlation times, which have been calculated from both sets of data, have been compared in an attempt to establish the relative rate of internal motion. All the data suggest that these motions are not slow with respect to the overall tumbling.
Assuntos
Configuração de Carboidratos , Oligossacarídeos/química , Sequência de Carboidratos , Espectroscopia de Ressonância Magnética , Dados de Sequência Molecular , Movimento (Física) , TermodinâmicaRESUMO
The structure of an arabinogalactan-protein (AGP) isolated from grape juice was studied by methylation analysis, n.m.r. spectroscopy, and interactions with peanut lectin, after specific degradation with purified enzymes and/or Smith degradation. AGP appeared to be homogeneous with a weight-average molecular weight of 110,000. Treatment of AGP with arabinofuranosidase released 88% of the arabinose and left GP1. Hydrolysis of GP1 with an endo-(1----6)-beta-D-galactanase removed 50% of the galactose and left GP2. Smith degradation of GP1 gave a 3-linked galactan that still contained 3,6-linked residues. Endogalactanase- and Smith-degraded GP1, but not AGP and GP1, reacted strongly with peanut lectin. Thus, AGP is a 3-linked galactan cross-linked at positions 6. The core also carries, at positions 6, 6-linked galactan chains heavily 3-substituted with arabinofuranose residues.
Assuntos
Frutas/química , Galactanos/química , Glicoproteínas/química , Sequência de Carboidratos , Galactanos/isolamento & purificação , Glicoproteínas/isolamento & purificação , Glicosídeo Hidrolases/metabolismo , Lectinas/metabolismo , Espectroscopia de Ressonância Magnética , Metilação , Dados de Sequência Molecular , Monossacarídeos/análise , Aglutinina de Amendoim , Lectinas de PlantasRESUMO
The fine structure of a beta-)1----4)-linked glucomannan from Asparagus officinalis has been determined by n.m.r. analysis of the oligosaccharides obtained by acidic and enzymic hydrolyses. Cleavage of the glucomannan with beta-D-mannase from Aspergillus niger and purification by h.p.l.c. gave oligosaccharide fractions that contained Man (mannose), GlcMan (beta-glucopyranosylmannose), Man2, Glc2Man, and Glc3Man as the major components. Simulated digestion of a polymer composed of randomly distributed monomers with the same Glc:Man ratio as glucomannan from A. officinalis led to the same polysaccharides. The random distribution of the monomers of glucomannan from A. officinalis was corroborated by the diffraction diagram of the raw flour, which indicated that the "in situ" glucomannan was amorphous, whereas both cellulose and mannans are crystalline.
