Periodate oxidation and the shapes of glycosaminoglycuronans in solution

Abstract

1. It is proposed that periodate oxidation of glycol groups in the repeating units of polysaccharide molecules can be used to probe differences in polymer shapes in solution. 2. Measurement of second-order rate constants (k2) of periodate-glycol reactions may be compared between polymers and relevant monomers, to assess perturbations due to polymer configuration. 3. Factors effecting the measurement and interpretation of k2 are discussed. Over-oxidation, free-radical side reactions, end-group effects, Donnan equilibria and polymer (or molecular-weight) effects are relevant, but their importance is either small or can be minimized in practice. 4. A small group of glycosaminoglycuronans (chondroitin 4- and 6-sulphates and hyaluronate) are oxidized 50--100 times more slowly than three other glycosaminoglycuronans of similar composition, relevant monomers or three homopolyuronides. 5. A stable configuration in solution is postulated for the periodate-resistant polymers, involving carboxylate, acetamido and hydroxy groups in hydrogen-bonded sequences on alternate sides of the molecule. The more easily oxidizable polyuronides are unable to form this configuration. 6. The effect of temperature on the postulated configuration is investigated through the Arrhenius plot of k2, measured to hyaluronate, chondroitin 6-sulphate and methyl 4-O-methyl-alpha-D-glucopyranoside. Probable transitions at high (around 90 degrees C) temperatures were observed for both polymers, with an additional transition at about 37 degrees C in the case of hyaluronate. 7. L-Iduronic acid can take up different conformations depending on the polymer environment.