FAB CIDMS/MS analysis of partially methylated maltotrioses derived from methylated amylose: a study of the substituent distribution

Amylose was methylated with CH3I in alkaline aqueous suspension, yielding m ethylated amylose (MeAl) with a degree of substitution of 1.44 (s < 0.01). Determination of the monomer composition showed that HO-6 and HO-2 were hig hly substituted in contrast to HO-3 (7:2:5.5, HO-2:HO-3:HO-6). By using par tial acid hydrolysis, oligomers were prepared that varied both in degree of polymerisation and in methyl-content. Studies on the distribution of subst ituents in trimers showed large deviations from random distributions. By us ing CID tandem mass spectrometry, the substituent distribution in these tri mers was determined in more detail. Various sets of trimers with equal amou nts of methyl-groups but differing in substituted positions were quantified . From the monomer composition of MeAl, the probability of each trimer was calculated and compared to the outcome of the measured distributions. It wa s concluded that trimers with terminal tri- or non-substituted glucose mono mers at the non-reducing end were formed preferentially during partial hydr olysis and that partial hydrolysis of MeAl yielded oligomers in a non-rando m way. This is the first study that describes the partial hydrolysis of MeA l in such detail. (C) 2000 Elsevier Science Ltd. All rights reserved.