Stacking interactions of nucleobases: NMR-investigations. II. Self-association of purine-and pyrimidine-derivatives.

The self-association of various purine- and pyrimidine-derivatives in D2O has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model. Among the nucleobases investigated, the adenine-derivatives were found to be most suitable for quantitative determination. A comparison of methylated adenine-derivatives and the pH-dependence of the self-association lead to the conlcusion, that the stacking associates are stabilized by special van der Waals interactions based, essentially, on the polarizability of the pi-electron-system of the assciated molecules.