Carbon-13 chemical shift anisotropy in DNA bases from field dependence of solution NMR relaxation rates

Knowledge of (13)C chemical shift anisotropy (CSA) in nucleotide bases is important for the interpretation of solution-state NMR relaxation data in terms of local dynamic properties of DNA and RNA. Accurate knowledge of the CSA becomes particularly important at high magnetic fields, prerequisite for adequate spectral resolution in larger oligonucleotides. Measurement of (13)C relaxation rates of protonated carbons in the bases of the so-called Dickerson dodecamer, d(CGCGAATTCGCG)(2), at 500 and 800 MHz (1)H frequency, together with the previously characterized structure and diffusion tensor yields CSA values for C5 in C, C6 in C and T, C8 in A and G, and C2 in A that are closest to values previously reported on the basis of solid-state FIREMAT NMR measurements, and mostly larger than values obtained by in vacuo DFT calculations. Owing to the noncollinearity of dipolar and CSA interactions, interpretation of the NMR relaxation rates is particularly sensitive to anisotropy of rotational diffusion, and use of isotropic diffusion models can result in considerable errors.