(NH4+)-N-15 ion movement inside d(G(4)T(4)G(4))(2) G-quadruplex is accelerated in the presence of smaller Na+ ions

2D NMR studies demonstrate that the residence lifetime of (NH4+)-N-15 ions within the bimolecular G-quadruplex adopted by d(G(4)T(4)G(4)) is reduced from 270 ms in the presence of ammonium ions alone to 36 ms in the presence of Na+ ions.