Circular Dichroism Study of Supramolecular Assemblies of Guanosine 5′-Monophosphate

Abstract

Concentration and temperature dependent studies of the circular dichroism of dianionic guanosine 5’-monophosphate (5’-GMP), where the cation was Na+, K+, or Rb+ ion, were done to obtain information regarding the nature of the self-assembled 5’-GMP species in aqueous solution, including G-quartets and other structures. Concentrations in the 0.05 M – 0.85 M range and temperatures in the 5–50 °C range were used. At the highest concentrations and 5 °C, Na2(5’-GMP) and K2(5’-GMP) formed a cholesteric phase, but Rb2(5’-GMP) did not. Evidence for antiparallel base stacking (stacked with opposite polarity; head to head) was observed for Rb2(5’-GMP), but not for the Na+ or K+ salts. This structure, believed to be G-quartets, had a melting temperature of 15 °C and dissociated into a second associated species as the temperature increased. The latter was present to the greatest extent at ~40 °C and it is characterized by a prominent negative CD band at 306 nm, which may be indicative of an X-DNA type of structure (an expanded G-quartet) or base-stacked monomers or dimers. The same negative band appeared at 310 nm in the CD spectra of K2(5’-GMP) and Na2(5’-GMP), but was much less intense in the latter case. K2(5’-GMP) also formed a non-cholesteric phase containing at least two different species, one more stable at low temperatures and the other more stable at higher temperatures, similar to Rb2(5’-GMP). 1H NMR spectroscopy was used to assist in the interpretation of the CD spectra.

Guanine-Centric Self-Assembly of Nucleotides in Water: An Important Consideration in Prebiotic Chemistry

“…The CD spectral profiles of UMPdss are independent of concentration and correspond to the spectrum of the monomeric nucleotide. In contrast, the CD spectrum of GMPdss at 0.1 M corresponds to monomeric GMP, while at 0.2 M, the spectrum exhibits a ( + )220 nm shoulder, a ( -)260 nm peak, and a ( -)295 nm peak that indicate a different self-assembled structure, possibly due to base stacking (Panda and Walmsley, 2011). There is no clear evidence of higher-order, G-tetrad assemblies.…”

“…Spectra were measured at 5°C and 20°C . Thermal melt curves were obtained at 275 nm, which corresponds to the cholesteric G-tetrad (G4) gel phase formed by guanosine compounds (Panda and Walmsley, 2011) and therefore does not necessarily report on other coexisting or alternate structures in the solutions. Because the thermal melt curves varied in shape among different samples and did not always have the typical S shape associated with melt curves, we did not attempt to identify curve midpoints to calculate melting temperatures.…”

“…It is not surprising that Na + and K + would favor different structures. Na + is smaller than K + and fits into the center of a single tetrad, whereas the larger K + occupies the space between two tetrads (Walmsley and Burnett, 1999;Panda and Walmsley, 2011). Another consideration is the competition between G-tetrads and the continuous helix, which is promoted by K + (Walmsley and Burnett, 1999), although it may also occur in the presence of Na + (Sasisekharan et al, 1975).…”

“…The solutions of GMPdss/ XMPfa exhibited large, negative peaks at 220 nm and 275-280 nm (Fig. 6) that are indicative of a cholesteric G4 gel phase (Panda and Walmsley, 2011). There are differences among the different XMPfa with respect to both peak magnitudes and relative magnitudes of the two peaks.…”

Supramolecular Transcription of Guanosine Monophosphate into Mesostructured Silica

“…The latter is confirmed by circular dichroism measurements of hGMP-1 (see Figure S8 in the Supporting Information), which are consistent with previously reported spectra for a Na 2 (5'-GMP) in self-assembled G quartets with N-and S-type tetramers (antiparallel arrangement). [1,19] Barboui and co-workers recently characterized a mesostructured material made by the condensation of guaninesiloxane monomers, termed G Si , in the absence of any additional silica source. [20] The authors conclude that supramolecular assembled G si units form hexagonal p6mm symmetries, with chiral transcription from the template to the silica wall promoted through the rigid covalent linker between the silica and G quartet.…”