Composition and block structure of alginates from New Zealand brown seaweeds

Alginates have been extracted from seven brown algae found in the Southern Hemisphere and characterized by 1H and 13C NMR analyses. The results are compared with similar analyses obtained in this work for three commercially available alginates isolated from Macrocystis pyrifera, a species of the Northern Hemisphere. Overall the ten alginates display a wide range of compositions, ranging from the very high mannuronic acid containing alginate extracted from Durvillaea antarctica (FM = 0.80) to the moderately high guluronic acid containing alginate from Marginariella boryana (FG = 0.56). All data are examined in terms of two addition copolymerization models, namely the Bernoullian and the first-order Markov models. Monomer distributions in the high M and intermediate composition alginates have M-diad frequencies calculated from the NMR analyses that agree closely with Bernoullian distributions, the best agreements being obtained for those alginates in which FM is greater than 0.72. However, as the monomer composition tends towards a higher G content, both of the above statistical models fail to satisfactorily describe the distributions of either the M or the G residues. A feature of this work is the excellent agreement obtained for the 1H and the 13C NMR analyses