Carrageenans. Part IV. Variations in the structure and gel properties of κ-carrageenan, and the characterisation of sulphate esters by infrared spectroscopy

Abstract

Structures of the ' masked repeating ' type seem to occur generally in K-carrageenans from Chondfus crispus and Gigartina species and will account for the analytical variation between one sample and another. Most-possibly all--of the variation is in the 4-linked units which occur as 3.6-anhydrogalactose, 3.6-anhydrogalactose 2-sulphate, galactose 6-sulphate, and galactose 2.6-disulphate. In K-carrageenan from G. stellata, as from C. crispus, all galactose units are believed to have the D-configuration. Samples from Chondrus were similar to each other and had a lower content of both types of 2-sulphate than those from Gigartina. The separation of a Chondrus sample into a series of subfractions which differed in the relative proportions of the various 4-linked units, suggests that K-carrageenan might normally contain a mixture of related molecules. Evidence is given that absorption bands shown by sulphated 3.6-anhydrogalactose units in the 800-850 cm.-I region of the infrared spectrum cannot be interpreted in the simple stereochemical terms used previously. However, many carrageenans show a band at about 805 cm.-l which is characteristic of 3,6-anhydrogalactose sulphate and potentially useful because it is easily recognised, even in the presence of other sulphate esters. Gel formation by K-carrageenan is enhanced by removal of 6-sulphate with conversion into 3.6-anhydrogalactose, but is much less sensitive to an excess of 2sulphate. The variation of gel strength with polysaccharide structure provides some evidence on the molecular basis of gel formation.

Characteristics of polysaccharides and protein associated with them from dried and freshly collected red alga Tichocarpus crinitus

“…IR spectra of KCl-insoluble polysaccharides from both freshly collected and dried alga contained absorption bands characteristic of N/E-carrageenan. The absorption band at 930 cm -1 belonged to 3,6-anhydrogalactose; at 846, to a C-4 sulfate of galactose; at 893, to unsulfated galactose [8,9]. IR spectra of KCl-soluble polysaccharides corresponded to that found by us earlier for an X-type carrageenan [2].…”

Comparative study of carrageenans from reproductive and sterile forms of Tichocarpus crinitus (Gmel.) Rupr (Rhodophyta, Tichocarpaceae)

“…These spectra exhibited an intense absorption band at 932 cm -1 that is characteristic for 3,6 anhydrogalactose and an absorption band at 847 cm -1 of the sulfate group at the O 4 of galactose [27]. Based on these data, the polysaccha rides of the gelling fractions can be identified as κ car rageenans [28]. The weak absorption band at 893 cm -1 indicates the presence of non sulfated galactose residue, this being characteristic for both β and α carrageenans [29,30].…”

Conformation and intermolecular interactions of carbohydrate chains

“…These are alternating copolymers, containing variable amounts of sulphate ester, and "junction forming" sequences contain 1,3-linked P-D-galactose and either 1,4-linked 3,6-anhydro-a-D-or -L-galactose residues for carrageenans (IVa) and agarose (Va) respectively (25,26). Associated helices are terminated by "soluble kinks" (IVb and Vb) of sequences involving deviations from the regular 3,6-anhydro residues.…”