Periodate oxidized alginates: Depolymerization kinetics

Limited periodate oxidation (0–8%) of alginates results in enhanced degradability, extending the range of applications of alginates as biomaterials, e.g. in tissue engineering. Oxidation produces dialdehydes that are highly sensitive to alkaline β-elimination, even under physiological conditions (pH 7.4, 37 °C). Although all periodate is consumed during limited oxidation, not all of the resulting dialdehydes are equally degradable, leading to a characteristic level off in molecular weight upon prolonged degradation. A significant fraction (20–50%) of the oxidized residues were resistant even at pH 10.4. We tentatively assign this finding to the presence of particularly stable intramolecular hemiacetals known to form in periodate oxidized alginates (POA). The enhanced degradation of POA persists into the gel state, allowing tailoring of more biodegradable alginate gels. The activation energy for β-elimination of dialdehydes was 88 kJ/mol compared to 113 kJ/mol for unoxidized residues, presumably reflecting the absence of strain in the non-cyclic transition state of the former.