On the aromatic character of the heterocyclic bases of DNA and RNA |
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Authors: | Cyrański Micha? K Gilski Miros?aw Jaskólski Mariusz Krygowski Tadeusz Marek |
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Institution: | Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland. |
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Abstract: | 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. |
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