Publication details

Structural Dependence of 31P Chemical Shielding Tensors: DFT Study



Year of publication 2004
Type Monograph
MU Faculty or unit

Faculty of Science

Description Our study aims to assess the influences of the alpha, zeta and epsilon torsional angles, as well as the OPO bond angle on the 31P isotropic chemical shielding (CSI) and the chemical shielding anisotropy (CSA) in the suga-phosphate backbone of B-DNA. For this purpose, a model compound comprising two sugars connected by a phosphate group has been used. During the geometry optimizations of the model, only the torsional angle studied has been varied within its experimental range while all other backbone torsions have been constrained to average experimental values. Our results reveal that when either alpha or zeta goes up from 270 degs to 330 degs (the former) or from 240 to 300 degs (the latter), an increase in CSI as well as CSA is introduced. In the case of CSI the increase is as small as a few ppm for both torsional angles. By contrast, in the case of CSA it is as large as 30 ppm for alpha and 10 ppm for zeta. The larger ranges of CSI/CSA as a function of alpha (compared with zeta) suggest higher sensitivity of the 31P chemical shielding to the alpha torsional angle. The plots of CSI/CSA against alpha (zeta) obtained for various values of zeta=240-300 degs (alpha=270-330 degs) show that the trends of CSI/CSA are conserved and shifted to higher values when zeta (alpha) increases from 240 degs to 300 degs (from 270 to 330 degs). Interestingly, the extent into which the epsilon torsional angle influences CSI is of the same order as that we found for alpha and zeta. On the contrary, CSA remains almost unaffected by epsilon. Last but not least, the trend uncovered in the dependence of CSI on alpha correlates with changes in the OPO bond angle which in turn correlates with the alpha torsional angle.
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