C(6)-oxidation followed by C(5)-epimerization of guar gum studied by high field NMR.
Guar gum, a beta-D-(1-->4)-linked D-mannan with alpha-D-galactopyranosyl units attached as side groups, was treated with alpha-galactosidase, an enzyme that splits off the alpha-D-galactosyl units to obtain a galactomannan with a low galactose content. The galactose-depleted polysaccharide was then selectively oxidized in C(6) position and epimerized using mannuronan C(5)-epimerases, namely AlgE1, AlgE4, AlgE6, and their mixtures, obtaining new pseudo-alginates. In this paper, we report a full high field 1D and 2D NMR study of guar gum as such and of the galactose-depleted, oxidized and epimerized compounds, respectively. From the 1H NMR spectra, the degree of epimerization, the distribution of mannuronic acid (M) and guluronic acid (G) residues and the average G-block length, N(G>1), were obtained. By means of NMR diffusion experiments, it was also shown that no significant degradation of the polysaccharide occurs as a consequence of the epimerization reactions.
Department of Chemistry, University of Rome La Sapienza, Rome, Italy.
Vittorio
V
Crescenzi
Mariella
M
Dentini
Daniela
D
Risica
Sara
S
Spadoni
Gudmund
G
Skjåk-Braek
Donatella
D
Capitani
Luisa
L
Mannina
Stéphane
S
Viel
D002236:Carbohydrate Conformation; D005685:Galactans / Q000737:chemistry*; D008351:Mannans / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D010084:Oxidation-Reduction; D053149:Plant Gums; D013237:Stereoisomerism; D013816:Thermodynamics
D005685:Galactans; D008351:Mannans; D053149:Plant Gums; C007894:guar gum