31P chemical shift anisotropy (CSA) tensors have been calculated for a set of selected DNA and RNA backboneconformations using density functional theory. The set includes canonical A-RNA, A-DNA, B
I-DNA, B
II-DNA, Z
I-DNA, and Z
II-DNA as well as four A-RNA-type, seven non-A-RNA-type, and three non-canonicalDNA conformations. Hexahydrated dimethyl phosphate has been employed as a model. The
31P chemicalshift tensors obtained are discussed in terms of similarities in the behavior observed for gauche-gauche (gg)and gauche-trans (gt) conformations around the P-O bonds. We show that torsion angles
![](/images/gifchars/alpha.gif)
and
![](/images/gifchars/zeta.gif)
are majordeterminants of the isotropic chemical shift
iso and of the
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10001.gif)
component of the traceless chemical shifttensor, which is revealed in separate ranges of both
iso and
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10002.gif)
for gg- and gt-conformers, respectively.A clear distinction between the two conformation types has not been found for the
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10003.gif)
and
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10004.gif)
components, which is attributed to their different directional properties. The
31P CSA tensors exhibitconsiderable variations resulting in large spans of ~16 ppm for
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10005.gif)
and ~22 ppm for
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10006.gif)
and
![](/isubscribe/journals/jpcbfk/112/i11/eqn/jp076073ne10007.gif)
. Weexamine the consequences of the CSA variations for predicting the chemical shift changes upon partialalignment
csa and for the values of CSA order parameters extracted from the analysis of
31P NMR relaxationdata. The theoretical
31P CSA tensors as well as the experimental
31P CSA tensor of barium diethyl phosphate(BDEP) are used to calculate
csa for two eclipsed orientations of the CSA and molecular alignment tensors.Percentage differences between the CSA order parameters obtained using the theoretical
31P CSA tensors andthe experimental
31P CSA tensor of BDEP, respectively, are also determined.