Desulfation of sulfated galactans with chlorotrimethylsilane. Characterization of beta-carrageenan by 1H NMR spectroscopy

A desulfation method using chlorotrimethylsilane for treatment of pyridinium salts of sulfated galactans was developed. It proved to be appropriate for desulfation of polysaccharides of both agar and carrageenan families. In order to evaluate its efficiency in presence of the maximum content of 3,6-anhydrogalactose, it was applied to commercial kappa-carrageenan, leading to obtention of a product mainly composed by beta-carrageenan. Best experimental conditions for achieving desulfation of kappa-carrageenan--in terms of low sulfate content, high recovery and low degradation of the product--were found. In addition, the complete assignment of the 1H NMR spectrum of beta-carrageenan was achieved by means of 1D and 2D NMR techniques.