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The polysaccharides from Chondria macrocarpa and Ceramium rubrum were examined by 13C NMR spectroscopy and their spectra were analysed by means of set theory. The spectra of the polysaccharides from Chondria macrocarpa collected in autumn were in accord with previous chemical analysis but polysaccharides from seaweed collected in spring comprise a higher level of agar precursors, much lower levels of galactose 2-sulfate, and the polysaccharide is separable into two components, the predominant one of which is essentially free of anhydrogalactose. The signal subset due to the xylosyl unit substituted at the 3-position of 4-linked L-galactose could be assigned from the spectrum of desulfated polysaccharide from Chondria macrocarpa. The extract from Ceramium rubrum consisted of a backbone of 3-linked D-galactosyl units alternating with the 4-linked units 3,6-anhydro-L-galactosyl and L-galactosyl in a ratio of 2:1 respectively, to which substitution by xylose occurred at approximately 8% of the total sugar units. The natural polymer had moderate levels of sulfate ester, with galactose-6-sulfate being the predominant unit, some of which survives alkaline treatment and was consistent with being 3-linked. There is also evidence of low levels of 3-linked galactose-2-sulfate. [ABSTRACT FROM AUTHOR]

The 13C nuclear magnetic resonance spectra of unsubstituted algal galactans of simple diad structure, together with their sulfated, methylated and permethylated analogues, are recorded as sets of signals, and provisional assignments are presented in matrix form for those spectra previously unassigned. This use of discrete mathematics permits a concise and transparent presentation of changes in chemical shifts arising from various substitutions. Regularities in the chemical shifts due to substitution, represented in matrix form, are observed for methylation and to a lesser extent for sulfate ester. Different reference matrices are required for each conformational state about linkage bonds, and some irregularities, particularly where there is sulfate ester near the linkage bond, can be interpreted in terms of changes in conformation brought about by the substitution. The β-shifts due to substitution are provisionally interpreted in terms of changes of the magnetic vector potential from residual magnetization fields from the region of substitution. The chemical shifts of methoxyl carbon atoms vary by approximately 6 ppm, are characteristic of their location on the polymer and may be of use for structural analysis. Changes of chemical shift due to substitution are sufficiently regular for the examples described here that they should be useful for predicting spectra of unknown red algal galac tans. [ABSTRACT FROM AUTHOR]

The polysaccharide from Cladhymenia oblongifolia and some of its derivatives have been examined by 13C nuclear magnetic resonance spectroscopy and the spectra analysed with the techniques of set theory. The polysaccharide is an agaroid with significant levels of sulfation at most positions other than the axial hydroxyl group. The 4-linked units consist of anhydrogalactosyl and galactosyl units in the approximate ratio of 3:2. The galactose, but not the anhydrogalactose, units in the natural polymer have high levels of 2-sulfate ester, while low levels of galactose-3-sulfate are also present in the galactosyl residues. The 4-linked galactosyl units also contain significant levels of 6-sulfate, which is converted to anhydrogalactose by alkali treatment, including significant levels of anhydrogalactose-2-sulfate. The 3-linked units consist of high levels of galactose 2-sulfate, moderate levels of galactose 6-sulfate, and very low levels of pyruvate acetal. Methylation is largely absent from this polysaccharide. The approximate structure can be summarized in set theory nomenclature as 3DG|2S0.4(4,6)P0.05 6S0.4| - 4L(AG0.6, G0.4|2S0.353S0.16S0.3|). The polysaccharide is similar to those extracted from other members of the Rhodomelaceae to the extent that it is a non-gelling agaroid, but the high levels of 2-sulfation are unusual as is the total variation in sulfation. [ABSTRACT FROM AUTHOR]

In this report, the 13C NMR chemical shifts of some red algal galactans which are not based on one diad repeat unit, together with their methylated derivatives, are examined for regularities using the techniques of discrete mathematics. Evidence is found for a new carrageenan diad, 3-linked galactose-4-sulfate and 4-linked galactose 3-sulfate, from a commercial sample of t-carrageenan and from the α-carrageenan-bearing Catenella nipae. The utility of set theory is shown for the unravelling of features of spectra containing several diads. Further confirmation is found that the polysaccharide from Pachymenia lusoria occurs as a block copolymer in that selective hydrolysis of the anhydrogalactosyl bonds permitted a polymer fraction to be obtained which contained only 3-linked D-galactose-2-sulfate and 4-linked D-galactose or 2-O -methyl-D-galactose. [ABSTRACT FROM AUTHOR]

The polysaccharide from Cladhymenia oblongifolia and some of its derivatives have been examined by 13C nuclear magnetic resonance spectroscopy and the spectra analysed with the techniques of set theory. The polysaccharide is an agaroid with significant levels of sulfation at most positions other than the axial hydroxyl group. The 4-linked units consist of anhydrogalactosyl and galactosyl units in the approximate ratio of 3:2. The galactose, but not the anhydrogalactose, units in the natural polymer have high levels of 2-sulfate ester, while low levels of galactose-3-sulfate are also present in the galactosyl residues. The 4-linked galactosyl units also contain significant levels of 6-sulfate, which is converted to anhydrogalactose by alkali treatment, including significant levels of anhydrogalactose-2-sulfate. The 3-linked units consist of high levels of galactose 2-sulfate, moderate levels of galactose 6-sulfate, and very low levels of pyruvate acetal. Methylation is largely absent from this polysaccharide. The approximate structure can be summarized in set theory nomenclature as 3DG | 2S0.4(4,6)P0.05 6S0.4| - 4L(AG0.6, G0.4 | 2S0.353S0.16S0.3| ). The polysaccharide is similar to those extracted from other members of the Rhodomelaceae to the extent that it is a non-gelling agaroid, but the high levels of 2-sulfation are unusual as is the total variation in sulfation. [ABSTRACT FROM AUTHOR]

In this experiment, the observation that, for meta- and para-substituted styrene derivatives, the magnitude of the C-13 shielding value for the beta-carbon is linearly related to sigma for the ring substituent is used to determine sigma. (BB)