Periodate oxidation of marine high molecular weight dissolved organic matter: Evidence for a major contribution from 6-deoxy- and methyl sugars

Nuclear magnetic resonance spectroscopy has been used to infer that marine high molecular weight dissolved organic matter (HMWDOM) is a mixture of carbohydrates, proteins, and lipids. However, acid and base catalyzed hydrolysis of HMWDOM followed by molecular level analyses using gas and liquid chromatography provide only low to modest yields of simple sugars, amino acids, and lipids. Here we use periodate over-oxidation to investigate the composition of HMWDOM. Our analyses show that the oxidation of HMWDOM carbohydrate consumes more periodate per carbon on a molar basis (1.3:1) than simple sugars (0.8:1) or linear polysaccharides (1.0:1), and that HMWDOM is highly branched. We also recover acetic acid and methanol as major oxidation products. Methanol and acetic acid are derived from the oxidation of methyl and 6-deoxy sugars, and our analyses suggest these sugars are major components of HMWDOM. Periodate over-oxidation shows that lipids are not major constituents of HMWDOM, and that most of the alkyl carbon observed in the 13CNMR spectra between 0–45 ppm that has been previously assigned to lipids is due to the methyl carbons of acetamide and 6-deoxy sugars.