Sequence selective coordination of Mg2+(aq) to DNA.

Thermodynamic parameters for magnesium binding to a series of DNA molecules of defined sequence have been evaluated by 25Mg NMR spectroscopy. These results demonstrate that G/C-DNA binds Mg2+(aq) up to 40 to 100-fold more strongly than A/T-DNA, i.e., coordination of Mg2+(aq) to G/C-DNA is ca. 2.1-2.7 kcal (mole Mg2+)-1 more stable relative to A/T-DNA. Activation free energies [delta G* approximately (12.7-13.3) x 10(3) kcal] and exchange rates [k(ex) approximately (0.5-3.0) x 10(3)s-1] were estimated by variable temperature experiments. The low value of the quadrupole coupling constants (chi B = 0.2-0.6 MHz) is indicative of outer-sphere coordination by Mg(H2O)6(2+).