Abstract
The triple-stranded polysaccharide scleroglucan was subjected to free-radical
depolymerisation with Fenton's reagent (H2O2/Fe2+), and partially
degraded samples in the molecular weight (M-w) range from 8 200 000
to 5200 were studied. Analyses of the chemical composition of partially
degraded samples by C-13 nuclear magnetic resonance spectroscopy
and by determination of reducing end-groups suggested that the degradation
was random. The decrease in M-w followed the kinetics expected for
a multiple-stranded polymer. Following an apparently initial stable
regime, degradation occurred with an exponential decrease (exponent
(nu) similar to 3.6) in M-w. Partially degraded samples displayed
bimodal molecular weight distributions. This was attributed to the
release of single-stranded oligomers having a degree of polymerisation
(DP) too low to remain incorporated in the tripler structure (DP
< DP,; the critical lower DP far tripler formation). The weight-average
molecular weight of the low-M-w fraction was estimated to about 36
000 (DP(w)similar to 56 tetrasaccharide units). Following a heat
treatment at 100 degrees C (15 min) of the partially degraded samples,
a reduction in M-w by a factor of 2 to 2.5 was observed. This was
attributed to the formation of more perfectly matched triple-stranded
molecules, without aggregation or ring formation, as shown by electron
microscopy. (C) 1998 Elsevier Science Ltd. All rights reserved.
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