Our computational studies suggest that 3-substituted xanthines are good candidates
for tetrad and quadruplex structures. 3-Methylxanthine (3MX) has been synthesized
from 7-benzylxanthine, and the existence of tetrameric and octameric aggregates of
3MX with NH4+, Na+ and K+ ions in the gas phase (MS) and in DMSO-d6 solution (NMR)
has been observed. The "internal" H-bonds (N1H - - - O6) are stronger than the "external"
ones (N7H - - - O2) in these clusters (NMR).