title: DFT analysis of NMR scalar interactions across the glycosidic bond in DNA.
abstract: The relationship between the glycosidic torsion angle chi, the three-bond couplings (3)J(C2/4-H1') and (3)J(C6/8-H1'), and the one-bond coupling (1)J(C1'-H1') in deoxyribonucleosides and a number of uracil cyclo-nucleosides has been analyzed using density functional theory. The influence of the sugar pucker and the hydroxymethyl conformation has also been considered. The parameters of the Karplus relationships between the three-bond couplings and chi depend strongly on the aromatic base. (3)J(C2/4-H1') reveals different behavior for deoxyadenosine, deoxyguanosine, and deoxycytidine as compared to deoxythymidine and deoxyuridine. In the case of (3)J(C6/8-H1'), an opposite trans to cis ratio of couplings is obtained for pyrimidine nucleosides in contrast to purine nucleosides. The extremes of the Karplus curves are shifted by ca. 10 degrees with respect to syn and anti-periplanar orientations of the coupled nuclei. The change in the sugar pucker from S to N decreases (3)J(C2/4-H1') and (3)J(C6/8-H1'), while increasing (1)J(C1'-H1') for the syn rotamers, whereas all of the trends are reversed for the anti rotamers. The influence of the sugar pucker on (1)J(C1'-H1') is interpreted in terms of interactions between the n(O4'), sigma*(C1'-H1') orbitals. The (1)J(C1'-H1') are related to chi through a generalized Karplus relationship, which combines cos(chi) and cos(2)(chi) functions with mutually different phase shifts that implicitly accounts for a significant portion of the related sugar pucker effects. Most of theoretical (3)J(C2/4-H1') and (3)J(C6/8-H1') for uracil cyclo-nucleosides compare well with available experimental data. (3)J(C6/8-H1') couplings for all C2-bridged nucleosides are up to 3 Hz smaller than in the genuine nucleosides with the corresponding chi, revealing a nonlocal aspect of the spin-spin interactions across the glycosidic bond. Theoretical (1)J(C1'-H1') are underestimated with respect to the experiment by ca. 10% but reproduce the trends in (1)J(C1'-H1') vs chi.
authors.affiliation: National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlárská 2, CZ-611 37 Brno, Czech Republic. marketa@ncbr.chemi.muni.cz
authors.forename: Markéta L
authors.initials: ML
authors.lastname: Munzarová
authors.forename: Vladimír
authors.initials: V
authors.lastname: Sklenár
mesh_terms: D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D006027:Glycosides / Q000737:chemistry* / Q000378:metabolism; D008956:Models, Chemical; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009705:Nucleosides / Q000737:chemistry* / Q000378:metabolism
chemical_list: D006027:Glycosides; D009705:Nucleosides; D004247:DNA