THE PROTONATION STATE OF ONE-ELECTRON-REDUCED CYTOSINE AND ADENINE .1. INITIAL PROTONATION SITES AT LOW-TEMPERATURES IN GLASSY SOLIDS

Electron paramagnetic resonance spectra of cytosine and adenine, one-electron reduced in a 9 M LiCl glass at 4K, show that in each case protonation occurs at the amino group. In order to understand this, we produced a number of one-electron-reduced cytosine and adenine analogues in different glassy environments, at 4 K, and used Q-band EPR to determine the sites of protonation. We conclude that the specific association of Li+ with the ring nitrogen blocks protonation at the expected sites, N3 of cytosine and N1 of adenine, diverting protonation to the less basic amino group.