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

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 Å which permits only a single molecular layer between successive silicate layers.