Hydrogen bonds of RNA are stronger than those of DNA, but NMR monitors only presence of methyl substituent in uracil/thymine.
Recently, Vakonakis and LiWang (J. Am. Chem. Soc. 2004, 126, 5688) reported experimental evidence for stronger hydrogen bonds in RNA A:U than in DNA A:T base pairs, which was based on differences in NMR shielding for adenine C2. We have analyzed the proposed correlation between NMR shielding and hydrogen-bond strength using density functional theory. Although we agree with the conclusion that A:U is more strongly bound, we find no correlation between the hydrogen-bond strength and the NMR shielding of C2. Our study shows that NMR merely probes the presence/absence of the methyl group in thymine/uracil, without any relation to the strength of the hydrogen bonds involved. In other words, one cannot infer the Watson-Crick hydrogen-bond strength from the NMR shielding constant of adenine C2.
Swart
Marcel
M
Afdeling Theoretische Chemie, Scheikundig Laboratorium der Vrije Universiteit, De Boelelaan 1083, NL-1081 HV Amsterdam, The Netherlands.
Fonseca Guerra
Célia
C
Bickelhaupt
F Matthias
FM
D000225:Adenine / Q000032:analysis / Q000737:chemistry*; D020029:Base Pairing; D004247:DNA / Q000737:chemistry*; D006860:Hydrogen Bonding; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D012313:RNA / Q000737:chemistry*; D013816:Thermodynamics; D013941:Thymine / Q000032:analysis / Q000737:chemistry*; D014498:Uracil / Q000032:analysis / Q000737:chemistry*
D014498:Uracil; D012313:RNA; D004247:DNA; D000225:Adenine; D013941:Thymine