Poster (Scientific congresses and symposiums)
Use of 13C-NMR in structural elucidation of polysaccharides: case of locust bean gum
Gillet, Sébastien; Aguedo, Mario; Blecker, Christophe et al.
2014Young Belgium Magnetic Resonance Scientist 2014 (YBMRS 2014)
 

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Keywords :
RMN; Polysaccharides; galactomannans
Abstract :
[en] Locust bean gum (LBG) galactomannans are polysaccharides consisting of a β-(1→4) D-mannopyranosyl backbone substituted to varying degrees in α-(1→6) with single D-galactopyranosyl residues. This basic structure is the same for all galactomannans (Fig. 2). However, when locust bean gum is extracted at different temperatures, the generated fractions exhibit different properties in aqueous solution (viscosity, viscoelasticity, gel formation, thermohydrolysis resistance, etc.). This means that there are differences within the fine structure of the polymers (although the basic structure is the same). Analysis of [13C]-NMR spectra of galactomannans, in combination with other techniques, can provide capital information about fine structural elucidation of the polymers. The method specifies the distribution of lateral galactosyls along the main chain of mannans. Two fractions extracted from locust bean gum at 25 and 80 °C (respectively GM25 and GM80) were comparatively studied by [13C]-NMR. Mannosyls/Galactosyls (M/G) ratios can be determined by considering the intensities of C-1 mannose and galactose signals in [13C]-NMR spectra. This method provides results relatively close to those obtained by GC-MS analysis. Spectra also showed that resonance from C4 of D-mannose residues were split, in evident dependence upon the nearest-neighbor probabilities (“diad frequencies”) of D-galactosyl groups along the mannan chains (Fig. 2). Diad frequencies were obtained by integrating C4(Man) peak areas. F11, F21/F12 and F22 gave respectively the di-, mono- or non-substituted mannose pairs proportions. High percentages of F11 and F22 therefore indicate a more non-homogeneous distribution of lateral galactosyls along the polysaccharide backbone as observed for GM80. The percentages of total lateral substituents obtained by C4(Man) peak analysis [F11 + (F21 or F12)/2] were fairly well correlated with M/G ratios. Splitting of the C-6 substituted D-mannose resonance provides, therefore the basis for determining the next-nearest-neighbor probabilities (triad frequencies) (Fig. 2). However, the spectrum is often not sufficiently resolved to accurately quantify and interpret the results.
Disciplines :
Chemistry
Author, co-author :
Gillet, Sébastien ;  Université de Liège - ULiège > Chimie et bio-industries > Chimie biologique industrielle
Aguedo, Mario ;  Université de Liège - ULiège > Chimie et bio-industries > Chimie biologique industrielle
Blecker, Christophe ;  Université de Liège - ULiège > Chimie et bio-industries > Science des alim. et formul.
Jacquet, Nicolas  ;  Université de Liège - ULiège > Chimie et bio-industries > Chimie biologique industrielle
Richel, Aurore  ;  Université de Liège - ULiège > Chimie et bio-industries > Chimie biologique industrielle
Language :
English
Title :
Use of 13C-NMR in structural elucidation of polysaccharides: case of locust bean gum
Publication date :
25 November 2014
Event name :
Young Belgium Magnetic Resonance Scientist 2014 (YBMRS 2014)
Event organizer :
YBMRS
Event place :
Spa, Belgium
Event date :
24th-25th November
By request :
Yes
Audience :
International
Available on ORBi :
since 09 December 2014

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