Ordered Forms of Dianionic Guanosine 5'-Monophosphate with Na+ as the Structure Director. 1H and 31P NMR Studies of Hydrogen Bonding and Comparisons of Stacked Tetramer and Stacked Dimer Models

Article abstract of DOI:10.1021/j150656a035

The ordered forms of the guanosine 5'-monophosphate dianion in the presence of Na⁺ as the structure-directing cation (Na⁺/5'-GMP = 2.0) have been investigated in H2O solution by 1H NMR spectroscopy.The resonances assigned to H-bonded N(1)H (11.1-11.3 ppm) and N(2)H (8.8-10.4 ppm) in the orderer nucleotide have normalized intensities of 0.96 +/- 0.12 and 1.1 +/- 0.1 protons per orderer 5'-GMP, respectively.This results is compatible with the interbase H-bonding scheme expected for planar tetramer units (I) and supports the proposal that the orderer forms are isomeric octamers formed by stacking of tetramer units.An additional resonance at 7.69 ppm has been assigned on the basis of chemical shift, line width, and spin saturation transfer results to a ribose OH involved in extratetramer H bonding.The normalized intensity of the ribose OH proton (0.33 +/- 0.06) is equal within experimental uncertainty to the normalized intensity of an unusually high-field line at 2.2 ppm in the 31P NMR spectrum (0.30 +/- 0.06), suggesting that a phosphte oxygen on an adjacent tetramer may be acting as the hydrogen acceptor.Several plausible alternatives for the extratetramer H bond also are discussed.Finally, the merits of the stacked tetramer model are shown to be superior to those of a recently proposed stacked asymmetric dimer model when the two models are compared in light of all the relevant data.