SEQUENCE SELECTIVE COORDINATION OF MG2+(AQ) TO DNA

Thermodynamic parameters for magnesium binding to a series of DNA mole cules of defined sequence have been evaluated by Mg-25 NMR spectroscop y. These results demonstrate that G/C-DNA binds Mg2+(aq) up to 40 to 1 00-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 Gsimilar to(12.7-13.3)X10(3) k cal] and exchange rates [k(ex)similar to(0.5-3.0)x10(3)s(-1)] were est imated by variable temperature experiments. The low value of the quadr upole coupling constants (chi(B)=0.2-0.6 MHz) is indicative of outer-s phere coordination by Mg(H2O)(6)(2+).