Studies on the metal binding properties of the seeds of Strychos potatorum linn

Abstract

The seed of irmali tree Strychnos potatorum linn which grows wild in the Vindhyan and southern region of India are lenticular in shape and have previously been studied for their coagulation properties in clarifying turbidwater. This property was attributed to the presence of anionic polyelectrolytes having -COOH and free -OH surface groups that are present in the seed protein. However, the metal binding property of these seeds is of recent interest where some bench scale experiments were conducted at NML in order to establish the binding of metal ions from dilute HCl solutions. The seeds collected from the trees of S. potatorum Linn were ground to 0.5 mm size for experimentation purpose. The binding of different transition metals from aqueous solutions by these seeds was studied for Au (I), Ag (I), Cu (I), Cu (II), Co (II), Ni (II), Pb(II), Zn (II), Fe(II) and Fe (III) by shaking 1.0 g of the powdered seed in a 5% v/v HCl solution containing 50.0 ppm 1.0 ppm of the respective metal ion in a 50 ml solution for 5 min. The filtrate obtained after each experiment was analyzed for the respective metal ions and the results obtained are Au (I)=40.80 ppm; Ag (I)=41.10 ppm; Cu (I) =38.00 ppm; Zn (II) = 41.70 ppm; Fe (II) = 42.10 ppm and Fe (III) = 38.20 ppm. On an average the seeds binds 0.5 mg of the respective metals per 1.0 g of the seed. These seeds were fractionated into three different fractions, namely, fraction A, fraction B and fraction C using solvent extraction, distillation and centrifuging techniques in order to investigate what fraction of the seed is responsible in metal ion binding, and the weight percentages of each fraction were found to be 65%, 5% and 30%, respectively. Fraction A is mostly comprising of carbohydrates and some protein, whereas, fraction C is pure protein. Fractions A and C are found to be equally responsible for the binding of metals.