In the depth of oligosaccharidic structural complexity The example of multiply branched glycans

International audienceRandom clivage of branched reserve polysaccharides composed of two different (malto-, m) and (isomalto-, i) linking types lead to complex oligomeric mixtures of various polymeric degree (DP). Each DP is a mixture of molecules containing potentially all combinations of (m) and/or (i) sub-structures. Industrial hydrolysis of starches polysaccharides produce syrups with a low DP (typically from 1 to 20). The number of potential oligosaccharidic structures accessible by random hydrolysis grow exponentially with the DP. The number of isomeric structures for each given DP (n) is a Catalan number, noted C(n), calculated as (2n choose n)/(n+1) = (2n)!/(n!(n+1)!). The calculation gives 2 isomers (maltose and isomaltose) for (DP2), 16796 deca-saccharides potential isomers (DP10) and more than 6 billions eicosasaccharide isomers (DP20)

Synthesis of Polysaccharide Macrobolaforms

International audienceNeutral polysaccharides are very abundant renewable natural products that have been identified as alternative substrates for use in the field of polymer commmodities. Unfortunately beside other obstacles such as hydrophilicity, polysaccharides can display very low shape factors (molecular length/width) as compared to common synthetic polymers. This shape factor is often unsuited for creating the molecular entanglements, necessary for material physical cohesion for applications in the field of plastic material. In order to overcome this drawback various strategies have been applied to extend the length of these macromolecules, from controlled chemical cross-linking to macromolecular fractionation. Due to the very large number of chemically similar hydroxyl functions present on the macromolecular polymer backbone, selective chemical intermolecular-linking of hydroxyl groups is almost impossible to control, and very rapidly leads to unsuited tri-dimensional networks. Taking advantage of the unique chemical nature of one of the extremities (the reducing end) we developed several techniques of selective dimerisation of oligo-and polysaccharide, using diamine and dicarboxylic linkers. These dimerisations resulted in saccharidic bolaforms with improved shape factor by doubling of the molecular length. In the case of large polysaccharides the obtained macrobolaforms displayed interesting improved mechanical properties. Preliminary investigations of the structure/property relationships of these macrobolaforms show an improvement of mechanical behaviour, which was linked to the shape factor improvement and also to the ability to form oriented structures during material extrusion + dimerisation of polysaccharide

A Fast and Selective HPLC Determination of Ulose Formation during Enzymatic Isomerisation of Pentose Rich Syrups

International audienceXylose, and arabinose rich syrups obtained by hydrolysis of wheat bran represent a large potential as fermentation substrates in the production of second generation biofuels (1), providing that pentoses are isomerised into the 2-ulose form previously, or during in the fermentation process. The transformation of arabinose and xylose present in pentose rich syrups into the corresponding ketoses using immobilised isomerases produces a very effective fermentation medium. (2). Existing analytical protocols to monitor the isomerisation rate, such as the carbazol test (3) or the resorcinol method (4) do poorly on concentrated syrups containing a mixture of various types of aldoses, especially at low and medium ulose concentrations. In order to closely monitor the action of the isomerase on the sugar mixture we developed a new fast and selective high performance liquid chromatographic (HPLC) analysis of the produced uloses, directly in the concentrated complex carbohydrate mixtures (5). This method uses the UV absorption specificity of the open-chain ketose form at 210 nm. The test is linear up to a concentration of 20 g/L ketose even in the presence of 50 g/L D-xylose or L-arabinose. The sensitivity of th method is 0.5 g/L for D-xylulose and L-ribulose

Cellulose Gum: a new additive for wine tartaric stability. Tentative of structures determination involved in the haze formation after CMC addition in wine

International audienceCellulose gum (or sodium carboxymethylcellulose / CMC) is a new additive permitted by the European Community for tartaric stabilization (maximum dosage: 10g/HL). CMC is known to have a high eciency for potassium bitartrate and calcium tartrate crystallization inhibition in white and sparkling wines. Hypotheses suggest an inhibition of the nuclei growth at the beginning of their formation. However some problems remain, such as the formation of a low increase of the turbidity in white wine (from 0,1 to 0,4 NTU at room temperature) requiring a ltration step and the formation of a high lumps volume when CMC is used in some red wines. The goal of the following experiments was to determine which molecules are involved in the haze formed in white or red wines. 1. On white wines: A unique Sauvignon wine is treated from 0 up to 600mg/L of activated bentonite. After ltration, each batch was added (or not) with 100mg/L of CMC previously dissolved in tap water (conc.:50g/L). After 1 week of storage at 13°C, samples were heated at 80°C during ½ h and then stored at RT during 24h before running turbidity. 2. On red wines: 1L of red wine (blend of Cinsault, Merlot and Cab. Sauvignon) was added with 100mg/L of CMC (see above) and stored at-4°C for 4 days. After this time, the wine showed a high level of red clouds. At negative temperature, the deposit was ltered on 0.2 µm nitrocellulose lter membrane and extensively washed with a hydro-alcoholic solution (12% ethanol v/v-pH: 3,5/HCl) kept at-4°C. The membrane was then dried under vacuum and the deposit was collected and exchanged 3 times with D2O for H1-NMR study (HRMAS)

Analyse prédictive de structures potentielles des dextrines MOS et MIMOS

National audienceL'Analyse Prédictive de Structures Potentielles (APSP) permet de calculer et de décrire un nombre fini de structures isomères discrètes pour chaque DP: N=f(DP) pour des oligomères ramifiés avec des caractéristiques structurales données. L'application à des fractions de DP croissants, isolées à partir de sirops de dextrines issus de la dégradation enzymatique d'amylopectines est présentée ici

Analyse prédictive de structures potentielles des dextrines MOS et MIMOS

National audienceL'Analyse Prédictive de Structures Potentielles (APSP) permet de calculer et de décrire un nombre fini de structures isomères discrètes pour chaque DP: N=f(DP) pour des oligomères ramifiés avec des caractéristiques structurales données. L'application à des fractions de DP croissants, isolées à partir de sirops de dextrines issus de la dégradation enzymatique d'amylopectines est présentée ici

ChemInform Abstract: Glycosylation of Acids under Phase-Transfer Conditions. Partial Synthesis of Saponins.

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Properties of starch based blends. Part 2. Influence of poly vinyl alcohol addition and photocrosslinking on starch based materials mechanical properties

International audienceMechanical properties of starch/PVA blends (maximum 5% wt PVA), with or without crosslinking, have been analyzed in order to study how the increase in the linear to branched chain can improve the material's performances. As a result, elongation is enhanced without significant strength decrease for both casting and extrusion processes. Water sorption and photocrosslinking ability have also been measured showing a fairly good compatibility between the two macromolecular components: PVA and starch. For example, a decrease in water sorption on PVA addition was observed which could not simply be related to additivity between the two polymers. Finally, systems composed of pure glycerol plasticized starch blends were photocrosslinked at very low rates in order to ‘lengthen’ the macromolecules. The results of the mechanical tests on these materials showed an enhancement of the elongation at break. These results highlighted the fact that a modification of the molecular weight distribution (or linear long chains ratio, i.e. PVA) led to the development of entanglements or long distance interactions (strain at break increase)

<b>Sapelenin E and F: new acyclic triterpenoids from the stem bark of <i>Entandrophragma cylindricum</i></b>

New acyclic triterpenoids, sapelenin E (1) and F (2) were isolated from the stem bark of Entandrophragma cylindricum. Their full structure including absolute configuration in sapelenin E (1) were determine from spectroscopic data and by chemical transformation

SAPELENIN E AND F: NEW ACYCLIC TRITERPENOIDS FROM THE STEM BARK OF ENTANDROPHRAGMA CYLINDRICUM

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