P-31 Chemical Shift Tensors in Nucleic Acids from the Quantum Chemistry Point of View
| Authors | |
|---|---|
| Year of publication | 2008 |
| Type | Article in Proceedings |
| Conference | 23rd NMR Valtice |
| MU Faculty or unit | |
| Citation | |
| Field | Physical chemistry and theoretical chemistry |
| Keywords | NMR, DFT, nucleic acids, chemical shift |
| Description | Phosphorus-31 nuclei are known for their large chemical shift anisotropy (CSA), which gives rise to resonance offsets to isotropic chemical shifts upon partial alignment. The so-called induced chemical shifts delta_csa can be used as restraints for structure refinement provided the elements and orientation of the 31P CSA tensor are known. Unfortunately, experimental data are only sparse. Therefore, we have applied density functional theory (DFT) to calculate 31P CSA tensors in canonical as well as non-canonical DNA and RNA backbone conformations using hexahydrated dimethyl phosphate as a model. Separate ranges of isotropic chemical shifts and of delta_11 components of the traceless chemical shift tensor have been found for gauche-gauche and gauche-trans conformations, respectively, which is an evidence of the major effect of torsion angles alpha and zeta on the two quantities. Different directional properties of delta_22 and delta_33 compared to delta_11 account for no clear distinction between the gg- and gt-ranges of the two components, respectively. Generally, 31P CSA tensors display considerable variations resulting in large spans of about 16 ppm for delta_11, and about 22 ppm for delta_22 and delta_33. Differences among the 31P CSA tensors of the conformations inspected have important implications for 31P NMR studies. We examine the consequences not only for induced chemical shifts delta_csa but also for CSA order parameters derived from relaxation measurements. |
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