[1H, 15N] NMR Investigations of Pt-NH Hydrogen Bonding in d(GpG), d(pGpG), and d(TpGpG)-N7,N7 Adducts of [Pt(en)]2+ in Aqueous Solution

Abstract

We report studies of the pH and temperature dependences of N-H NMR resonances of [Pt(15N-en){d(GpG)­N7(1 ),N7(2)} ]2+ (1), [Pt(15N-en){ d(pGpG)-N7(1 ),N7(2)} ]2+ (2), and [Pt(15N-en){ d(TpGpG)-N7(2),N7(3)} ]2+ (3) in aqueous solution using 15N-edited 1H and [1H, 15N1 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 pKa 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.