Abstract
The potassium chloride-soluble fraction of carrageenan from the red seaweed Iridaea undulosa Bory contains both μ-like and λ-like carrageenans. These were partly separated by extraction with hot dimethyl sulfoxide, and characterized by methylation analysis, both before and after alkaline modification. In addition to regions composed of μ- or λ-type repeating units, both fractions contained regions of structural irregularity. Unusual units were found in these last regions, namely: ( a) 2- and 6-linked galactose residues, ( b) 3-linked, 6-sulfated and 2,6-disulfated residues, and ( c) a small amount of branching with galacto- and xylo-pyranose units as nonreducing end groups. The determination of the changes in composition of the samples as a function of the number of methylation steps provided confidence in assignments of structural significance to minor components. These were characterized by g.l.c. and computerized g.l.c.-m.s. techniques under carefully chosen operating conditions, using two different sets of derivatives.
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