Complexes of arabinogalactan of Pereskia aculeata and Co2+, Cu2+, Mn2+, and Ni2+

The main interest in the biopolymer arabinogalactan is that it is edible. C omplementing its high protein percentage, when complexed to essential metal ions, widens the use in food and pharmacology industries and technologies. The binding constants of Co2+, Cu2+, Mn2+ and Ni2+ with arabinogalactan, e xtracted from the leaves of Pereskia aculeata from Brazil were determined b y potentiometric titrations and also the speciation according to pH values. The complexed species proposed by potentiometric titrations and the unique complexing ability of galacturonic acid groups towards Cu2+ and Ni2+ in th e tridimensional web structure of arabinogalactan were confirmed by IR and EPR spectroscopies. The thermal stability of the complexed species also var ied with the metal ion employed in the complexation when compared to the bi opolymer alone. These complexes are new sources of additives for the food a nd pharmacology industries and carriers of essential metal ions to animal a nd vegetal biochemistry. (C) 2000 Elsevier Science Ltd. All rights reserved .