Aromaticity of H-bonded and metal complexes of guanine tautomers

The effect of H-bonding and metal complexation (probed by HF, F−, Li+, Na+, and K+) on structural and π-electron delocalization changes in four most stable guanine tautomers and their structural subunits has been studied in the gas phase using the B3LYP/6−311++G(2d,2p) computational level. In both cases, i.e., H-bonding and metal complexation, the strongest interactions are found in bifurcated complexes of the keto guanine tautomers. Interactions in which the functional groups participate (NH2 or C=O) regularly lead to the greatest geometric and aromaticity changes. As a consequence, aromaticity of substituted six-membered rings is decisive for aromaticity of whole ring system in guanine tautomers. Aromaticity of guanine tautomers and their structural subunits changes in the same way (increase or decrease) depending on particular type of interactions.