Ligand-aided ¹H Nuclear Magnetic Resonance Spectroscopy for Non-destructive Estimation of Sulfate Content in Sulfated Saccharides

Sulfated saccharides exhibit diverse physiological activities, but a lack of any convenient assay hinders their evaluation. Herein, an assay for the analysis of sulfated saccharides is described using ¹H nuclear magnetic resonance (NMR) spectroscopy by employing ligands that can form ionic complexes with the sulfate groups. Based on the change in the chemical shift (Δδ) of the ligands by sulfated mono- to tetrasaccharide, imidazole was found to be a good ligand, showing the maximum Δδ; neutral saccharides do not show any change in the δ value. A marked and constant downfield δ value observed was changed dramatically at a molar ratio of >1:1 (imidazole: sulfated saccharides), allowing a sulfate content estimation based on the concentration of imidazole at the Δδ inflection point. By the proposed ligand-aided ¹H NMR assay, the sulfate content of natural sulfated polysaccharide, fucoidan, was non-destructively estimated to be 2.1 mmol/g-fucoidan.