89999-10-0Relevant academic research and scientific papers
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
Walmsley, Judith A.,Barr, Richard G.,Bouhoutsos-Brown, Elene,Pinnavaia, Thomas J.
, p. 2599 - 2605 (1984)
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.
Structure-Directing Properties of Na+ in the Solution Ordering of Guanosine 5'-Monophosphate. Stoichiometry of Aggregation, Binding to Ethidium, and Modes of Na+ Complexation
Bouhoutsos-Brown, Elene,Marshall, Christopher L.,Pinnavaia, Thomas J.
, p. 6576 - 6584 (1982)
Tetramethylammonium has been found to be a structure-inert cation in the solution ordering of guanosine 5'-monophosphate (5'-GMP) at neutral or slightly basic pH.This finding has made it possible to study quantitatively by 1H NMR spectroscopy the stoichiometry of nucleotide ordering in the presence of Na+ as a structure-directing counterion.The dependence of the ordered-structures on total nucleotide concentration is consistent with the formation of octamers.Independent evidence for octamer formation is provided by the binding of ethidium to the ordered nucleotide.Two octamer-ethidium complexes are observed with octamer to ethidium ratios of 1:1 and 1:2.The dependence of ordered structure formation on Na+ concentration indicates the binding of four Na+ ions per octamer unit.The types of Na+ binding sites are inferred from mixed Na+-K+ experiments.One binding site is a highly Na+-specific structure-directing site.The second site is less Na+ specific, but it plays an important role in stabilizing the ordered structures.The replacement of Na+ by K+ at the second site dramatically stabilizes the Na+-directed self-structures.A model involving coaxial stacking of planar hydrogen-bonded tetramer units is proposed for the ordered structures.Normal and inverted tetramer stacking arrangement account for the presence of three NMR-observable isomers, provided that twisting about the C4 symmetry axis is rapid.The hole defined by the four carbonyl oxygens of a tetramer unit is believed to be the highly Na+-specific binding site.Chelation of Na+ (or structure-stabilizing K+) by phosphate oxygens on adjacent tetramer plates is proposed as the less specific binding site.Model building studies suggest that interplate hydrogen bonding also may be involved in stabilizing the stacked tetramers.
