Internal Sodium Ions and Water Molecules in Guanine Quadruplexes: Magnetic Relaxation Dispersion Studies of [d(G3T4G3)]2 and [d(G4T4G4)]2
The structural stability of guanine quadruplexes depends critically on an unusual configuration of dehydrated Na+ or K+ ions, closely spaced along the central axis of the quadruplex. Crystallography and NMR spectroscopy indicate that these internal ions can be located between the G-quartet planes as well as in the thymine loops, but the precise ion coordination has been firmly established in only
