NMR Studies of Nucleic Acids

Uridine in DMSO-d6 NOESY spectrum 500 msec mixing time 

Nucleic acid polymers are known to undergo transitions between single strands and double and triple helices. These transitions are readily detected by NMR because of the large differences in the line widths of a flexible random coil compared to a rigid helix. A mixture of adenosine, a mononucleoside, and poly U, a large single-stranded polymer, is known to form a triple helix at low temperatures.6 The down- 

The structure of small helices of 10 base pairs or less can be obtained from their NOES Y spectra and subsequent computer 

The chemical shift and cross-peak intensities are very sensitive to the secondary structure of the helix. Each of the 

H5 and Hg resonances are shifted downfield because each proton lies in the deshielding region of the neighboring guanosine base, and the two bases are in the same plane when they are hydrogen bonded. 

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The first reports showing 31P NMR study of nucleic acids were published in the 1970s.82 Terao et al. determined the size of the principal axis values of the 31P CSA tensor for RNA molecules (polyU, polyG, polyC, polyA and tRNA). Very recently, Rinnenthal et al.83 have reported the 31P NMR data for RNA cUUCGg tetraloop model hairpin prepared under various salt and hydration conditions. The experimental results were found to be consistent with theoretical DFT calculations published by Sklenar and co-workers.84... 

The NMR studies of nucleic acids can yield information about base sequences, conformations in solution, helix formation, and hydrogen bonding between base pairs. 

In the laboratory of R.A. Jones, A/ -methoxy derivatives of adenosine and 2 -deoxyadenosine were found to undergo a facile Dimroth rearrangement The high-yielding process allowed the efficient synthesis of [1,7- N2]- and [1,7, NH2- N3] adenosine and 2 -deoxyadenosine that are important tools in the NMR studies of nucleic acid structure and interactions. The rearrangement was carried out in weakly acidic refluxing methanol. 

Until recently 1 3C nmr studies of nucleic acids have not received the same attention as those of nucleosides and nucleotides. Poly-uridylic acid (poly U), polyadenylic acid (Poly ), and unfractionated baker s yeast transfer ribonucleic acid (tRNA) have been investigated by 13C nmr techniques (Table 11 Mantsch and Smith, 1972 Komoroski and Allerhand, 1972, 1974). Assignments for uridine monophosphates were based on changes in phosphorus-carbon splittings and on changes in the chemical shift of approximately 2-5 ppm on the phosphorylated carbon, which was caused by the deshielding effect of the phosphate group (Mantsch and Smith,... 

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