The effect of water on NMR spin–spin couplings in DNA: Improvement of calculated values by application of two solvent models

Abstract

Influence of water on isotropic one-bond ¹J(X,H), ¹J(C,X) and two-bond ²J(X,H), (X = C,N) indirect NMR spin–spin coupling constants were investigated theoretically at ab initio levels by application of explicit and PCM solvent models. Sensitivity of the Fermi contact contribution to the total J coupling towards the solvent inclusion calculated using coupled perturbed density functional theory with the B3LYP hybrid functional is dominating, while solvent shifts of the other three J contributions are negligible. Consideration of the solvent leads to a noticeable shift of the ¹J(C,H) couplings; the largest shift of 6.1 Hz was found for ¹J(C8,H8) coupling in guanine. Further inclusion of solvent decreases the mean absolute deviation between the calculated and experimental J constants from 1.7 to 1.1 Hz for guanine, from 2.4 to 0.6 Hz for cytosine, and from 2.3 to 1.6 Hz for adenine. In the explicit solvent model, the ¹J(C8,H8) solvent shift seems to be sensitive to the magnitude of charge transfer from water σ bonding O–H and oxygen lone pair orbitals to the σ* antibonding C8–H8, C8–N7, and C8–N9 orbitals of guanine. Both explicit and PCM solvent models provide similar improvement of calculated couplings when comapred to the experimental data of the ¹³C, ¹⁵N-labeled DNA hairpin molecule d(GCGAAGC).