Quantitative studies of the avidity of naturally occurring substances for trace metals. 3. Pteridines, riboflavin and purines

8-Hydroxyquinoline (I) owes its well known avidity for metallic cations to the presence of an ionizable hydroxyl group peri to a tertiary heterocyclic nitro- gen atom.The presence of a similar configuration in several of the naturally occurring purines, e.g.* Derived by adopting any value for K' and working out values of -log [Sc] for regular increments of n, from equation (i).