Relationships between ~(31)P Chemical Shift Tensors and Conformation of Nucleic Acid Backbone:A DFT Study

摘要

Density functional theory(DFT)has been applied to study the conformational dependence of ~(31)P chemical shift tensors in B-DNA.The gg and gt conformations of backbone phosphate groups representing B_(I~-)and Bn-DNA have been examined.Calculations have been carried out on static models of dimethyl phosphate(dmp)and dinucleoside-3',5'-monophosphate with bases replaced by hydrogen atoms in vacuo as well as in an explicit solvent.Trends in ~(31)P chemical shift anisotropy(CSA)tensors with respect to the backbone torsion angles alpha,zeta,beta,and e are presented.Although these trends do not change qualitatively upon solvation,quantitative changes result in the reduction of the chemical shift anisotropy.For alpha and zeta in the range from 270° to 330° and from 240° to 300°,respectively,the delta_(22)and delta_(33)principal components vary within as much as 30 ppm,showing a marked dependence on backbone conformation.The calculated ~(31)P chemical shift tensor principal axes deviate from the axes of O-P-O bond angles by at most 5°.For solvent models,our results are in a good agreement with experimental estimates of relative gg and gt isotropic chemical shifts.Solvation also brings the theoretical delta_(iso)of the gg conformation closer to the experimental gg data of barium diethyl phosphate.