Adsorption behaviour of aromatic nitro compounds on sephadex LH-20

Abstract

By classifying the mechanism of adsorption of solutes to gels into two groups, viz., ionic effects (ion exchange, ion exclusion and ion adsorption) and pure adsorption (hydrogen bonding and π-bonding), and by considering the gel structure as hydrochloric acid, potassium hydroxide, or potassium chloride in methanol are adsorbed on to the gels and the surface of the gel becomes positively charged, the adsorption behaviour of dinitrophenyl derivatives on Sephadex LH-20 in methanol, 0.05 N hydrochloric acid-methanol, 0.05 N potassium hydroxide-methanol and 0.05 N potassium chloride-methanol have been explained. The solutes that have no dissociative groups interact with the gel only by pure adsorption. The solutes that have an acidic group interact with the gel by ion adsorption under the dissociation conditions for the solutes, and those that have a basic group by ion exclusion under both the dissociation and non-dissociation conditions. These behaviours are compared with those in methanol. Benzene or pyridine added to methanol are assumed to block the interaction sites of gels and hence lower K d values for the solutes are obtained. The presence of two nitro groups and hydroxyl, carboxyl or amino groups on a benzene ring shows the potentiation effect of adsorption to the gel. The dissociative groups favour the ionic effects, which are than the sieving effect. A nitro group is assumed to be adsorbed to the gel by hydrogen bonding and this secondary effect is greater than the molecular sieving effect for low-molecular-weight compounds.