Specific Co-Absorption of Purines and Pyrimidines by Montmorillonite (Clay-Organic Studies XV)

Abstract

The co-absorptions of various purines and pyrimidines from aqueous solutions by Na- and Ca-montmorillonite are studied in the range of pH 1-6. The pyrimidines, thymine and uracil, which are not absorbed from solutions of these compounds alone, are appreciably absorbed from solutions containing also adenine or 2,6-diaminopurine, are weakly absorbed from solutions containing hypo- xanthine, and are not absorbed from solutions containing purine, cytosine, and caffeine. The specific co-absorption is tentatively attributed to hydrogen-bond formation between the molecules in solution rather than to an overlapping of the molecular configurations (vertical stacking). The montmorillonite- organic associations have a basal spacing of about 12.5 -~ which permits only a single molecular layer between successive silicate layers.