Croatica Chemica Acta, Vol. 87 No. 4, 2014.
Original scientific paper
https://doi.org/10.5562/cca2431
Metal Complexation and H-bonding Effects on Electronic Structure of Cytosine Studied in the Gas Phase
Olga A. Stasyuk
; Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
Halina Szatylowicz
; Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
Tadeusz M. Krygowski
; Department of Chemistry, Warsaw University, Pasteura 1, 02-093 Warsaw, Poland
Abstract
The influence of H-bonding and complexation with cations (probed by HF, F–, Li+, Na+ and K+) on structural and π-electron changes in the six most stable cytosine tautomers has been studied in the gas phase using the B3LYP/6-311++G(2d,2p) computational level. The presence of two exo- groups (ami-no/imino and carbonyl/hydroxyl) in cytosine tautomers significantly increases their sensitivity to structur¬al changes due to intra- and intermolecular interactions. These interactions induce large changes in aroma¬ticity of the rings and in the CX (X = N, O) bond lengths of exocyclic groups. Three types of H-bonds, considering their strength, could be distinguished: (i) charge-assisted X–•••HF, X = N or O, as the strong¬est, (ii) neutral X•••HF, where X is the nitrogen atom of the ring or imino group or the keto form oxygen atom and (iii) also neutral X•••HF, where X being either amino N or alternatively hydroxylic O. Hydrogen bond energy decreases approximately twice in the above listed sequence of interactions. Structural conse¬quences of H-bonding and metal complexation have been observed not only in the immediate region of the interaction but also in other parts of the molecule (the shape of the amino group, changes in CO and CN bond lengths). Complexation of the cytosine tautomers with cations leads to monotonic changes in
aromaticity in line with an increase of their ionic radii.
Keywords
H-bonding; aromaticity; cytosine; tautomer; metal complexation
Hrčak ID:
131526
URI
Publication date:
22.12.2014.
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