Guar gum, a a-D-(1f4)-linked D-mannan with R-D galactopyranosyl units attached as side groups, was treated with R-galactosidase, an enzyme that splits off the R-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, NG>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
C(6)-oxidation followed by C(5)-epimerization of guar gum studied by high field NMR / Crescenzi, Vittorio; Dentini, Mariella; Risica, Daniela; Spadoni, Sara; G., Skjak Braek; Donatella, Capitani; Mannina, Luisa; Stephane, Viel. - In: BIOMACROMOLECULES. - ISSN 1525-7797. - ELETTRONICO. - 5:2(2004), pp. 537-546. [10.1021/bm034387k]
C(6)-oxidation followed by C(5)-epimerization of guar gum studied by high field NMR
CRESCENZI, Vittorio;DENTINI, Mariella;RISICA, Daniela;SPADONI, SARA;MANNINA, LUISA;
2004
Abstract
Guar gum, a a-D-(1f4)-linked D-mannan with R-D galactopyranosyl units attached as side groups, was treated with R-galactosidase, an enzyme that splits off the R-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, NG>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 reactionsI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
