[H-1, N-15] NMR INVESTIGATIONS OF N-H HYDROGEN-BONDING IN D(GPG) AND D(TPGPG) N7,N7-ADDUCTS OF [PT(EN)](2+) IN AQUEOUS SOLUTION

We report studies of the pH and temperature dependences of N-H NMR resonances of [Pt(N-15-en){d(GpG)-N7(1),N7(2)}](2+) (1), [Pt(N-15-en){d(pGpG)-N7(1),N7(2)}](2+) (2), and [Pt(N-15-en){d(TpGpG)-N7(2),N7(3)}](2+) (3) in aqueous solution using N-15-edited H-1 and [H-1, N-15] heteronuclear multiple quantum coherence (HMQC) 2D NMR spectroscopy. The data for 2 are consistent with strong stereospecific intramolecular H bonding involving only one of the en NH hydrogens and the deprotonated dianionic terminal 5'-phosphate group, for which the pK(a) is lowered by ca. 0.5 units to 6.46. The NMR data for complex 1 are similar to those of complex 3, suggesting either that such H bonding is very weak for a bridging monoanionic 5'-phosphate (diester) or, more likely, that these NMR methods are insensitive to its presence.