Nitrogen-15 chemical shifts in AT (adenine-thymine) and CG (cytosine-guanine) nucleic acid base pairs

This paper presents ab initio (DFT) calculations of the N-15 chemical shift s in AT (Adenine-Thymine) and CG (Cytosine-Guanine) nucleic acid base pairs . Calculations were done on 14 AT and 18 CG base pairs using experimental ( X-ray) geometries obtained from several DNA decamers. The calculated chemic al shifts are compared with the experimental values in the pure bases and s ubjected to statistical analysis to explore their sensitivity to the local geometry and pair helix parameters. The results indicate that the N-15 chem ical shifts, isotropic and principal components are quite sensitive to smal l changes in the geometry of the pairs, but they do not correlate well with the helix pair parameters. From the statistical analysis, several linear c orrelations between structural parameters and chemical shifts emerge. These relationships may serve as a foundation to extract information on molecula r structure from N-15 chemical shift measurements.