SPECIFIC CO-ABSORPTION OF PURINES AND PYRIMIDINES BY MONTMORILLONITE (CLAY-ORGANIC STUDIES 15)

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 hypoxanthine, 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. © 1969.