On the aromatic character of the heterocyclic bases of DNA and RNA.
Studies based on ab initio optimized geometries (at B3LYP/6-311+G** and MP2/6-311+G** levels) and on experimental structures retrieved from the Cambridge Structural Database (CSD) reveal that the nucleobases constituting DNA and RNA differ significantly in their aromatic character, as shown by the geometry-based index of aromaticity HOMA that ranges from 0.466 for thymine to 0.917 for adenine, based on B3LYP/6-311+G** calculations, and 0.495-0.926, respectively, if based on the MP2/6-311+G** level. Aromaticity of the bases decreases markedly with an increase of the number of double-bond C=X (X = N, O) substituents at the rings. H-bonds involving C=O groups in Watson-Crick pairs cause an increase of the aromatic character of the rings.
Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
Michał K
MK
Cyrański
Mirosław
M
Gilski
Mariusz
M
Jaskólski
Tadeusz Marek
TM
Krygowski
D000225:Adenine / Q000737:chemistry; D020029:Base Pairing; D003596:Cytosine / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry; D006860:Hydrogen Bonding; D008432:Mathematical Computing; D009690:Nucleic Acid Conformation; D011789:Quantum Theory; D012313:RNA / Q000737:chemistry*; D013237:Stereoisomerism; D013941:Thymine / Q000737:chemistry; D014498:Uracil / Q000737:chemistry
D014498:Uracil; D006147:Guanine; D012313:RNA; D003596:Cytosine; D004247:DNA; D000225:Adenine; D013941:Thymine