TEMPO-mediated oxidation of maltodextrins and D-glucose: effect of pH on the selectivity and sequestering ability of the resulting polycarboxylates

Maltodextrins were oxidized to polyglucuronic acids with the ternary oxidat ion system: NaOCl-NaBr-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). The ch emoselective oxidation at the primary alcohol groups was shown to be strong ly pH dependent. Oxidation of polysaccharides was best achieved at pH 9.5 i n order to minimize depolymerization, whereas oxidation of oligosaccharides required stronger alkaline conditions (pH 11-11.5). The resulting sodium p olyglucuronates present interesting sequestering properties, the best of wh ich being obtained from maltodextrins with the highest degrees of polymeriz ation. The same oxidation process allowed the convenient conversion of D-gl ucose to D-glucaric acid in high yield (> 90%), under strongly basic condit ions (pH > 11.5). (C) 2001 Elsevier Science Ltd. All rights reserved.