Resolution Of Nuclear Magnetic Resonance Spectra Research Articles

Zipper-like Watson-Crick base-pairs

A series of DNA heptadecamers containing the DNA analogues of RNA E-like 5′-d(GXA)/(AYG)-5′ motifs (X/Y is complementary T/A, A/T, C/G, or G/C pair) were studied using nuclear magnetic resonance (NMR) methodology and distance geometry (DG)/molecular dynamics (MD) approaches. Such oligomers reveal excellent resolution in NMR spectra and exhibit many unusual nuclear Overhauser effects (NOEs) that allow for good characterization of an unusual zipper-like conformation with zipper-like Watson-Crick base-pairs; the potential canonical X · Y H-bonding is not present, and the central X/Y pairs are transformed instead into inter-strand stacks that are bracketed by sheared G · A base-pairs. Such phenomenal structural change is brought about mainly through two backbone torsional angle adjustments, i.e. δ from C2′-endo to C3′-endo for the sugar puckers of unpaired residues and γ from gauche+ to trans for the following 3′-adenosine residues. Such motifs are analogous to the previously studied (GGA)2 motif presumably present in the human centromeric (TGGAA)n tandem repeat sequence. The novel zipper-like motifs are only 4–7 deg. C less stable than the (GGA)2 motif, suggesting that inter-strand base stacking plays an important role in stabilizing unusual nucleic acid structures. The discovery that canonical Watson-Crick G · C or A · T hydrogen-bonded pairs can be transformed into stacking pairs greatly increases the repertoire for unusual nucleic acid structural motifs.

Resolution of the NMR Spectrum Using Wavelet Transform

A novel method for resolution of an overlapping nuclear magnetic resonance (NMR) spectrum using the wavelet transform (WT) is proposed. Due to the localization character in terms of both space and scale of the wavelet transform, an NMR spectrum can be decomposed into a series of localized contributions (details and approximations) at different resolution levels, which represent the spectral information of different resolutions. With amplification of the contributions at fine resolution level and then reconstruction (inverse transform), the resolution of the reconstructed NMR spectrum will increase. Therefore, the resolved spectrum can be obtained from a low-resolution spectrum or an overlapping spectrum. Simulated data sets and a spectrum of a biological sample (gramicidin-S) were investigated by this method. It was proven that resolution of NMR spectra can be greatly improved by this approach.

Solid-phase 31P NMR spectra of peat and mineral soils, humic acids and soil solution components: influence of iron and manganese

Solid-phase31P nuclear magnetic resonance (NMR) offers a direct means to determine the chemical environment of P present in soil and soil fractions. Iron is often a major component in soil and it has been thought that the presence of paramagnetic Fe and Mn in soil components is responsible for loss of resolution in NMR spectra. We have found that the resolution of signals in the solid-phase 31P NMR spectra of a Fe- and Mn-rich mineral soil was no worse than that for a series of four peat soils with a comparable concentration of P. Similarly, the resolution in the solid-phase 31P NMR spectra of the humic acid from the mineral soil was not much changed by extraction of the humic acid with acetylacetone in diethyl ether which removed around 40% of its Fe and 30% of its Mn. Removal of up to 50% of the Fe from organic rich, freeze-dried soil solutions from a soil catena with different land uses produced little change in spectral resolution. It was concluded that the limitations to resolution in solid-phase 31P NMR spectroscopy of soil humic substances do not stem from the presence of paramagnetic substances, but from the variable way P species are physically held in the amorphous milieu of the organic phase.