Nature of the Interaction
between Natural and Size-Expanded
Guanine with Gold Clusters: A Density Functional Theory Study
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Abstract
In this paper, we study the interaction of natural and
size-expanded
guanine molecules with small gold clusters, to shed light on the nature
of the N/O–Au bonds and of the unconventional NH···Au
hydrogen bonds, as well as on the dependence of these bonds on the
charge state of the systems. Based on density functional theory results,
it is found that the nature of the N/O–Au bonds between both
guanine and its size-expanded form and three- and four-atom Au clusters
is covalent in the neutral systems. In the −1 charged systems,
the binding energy decreases by almost 50% with a significant change
of geometry. Although the NH site in the spacer ring of size-expanded
guanine may supply a new acceptor opportunity for forming an additional
NH···Au hydrogen bond, this hardly emerges because
of the nonplanarity and the large steric effect. The introduction
of a spacer ring in guanine decreases the highest occupied molecular
orbital–lowest unoccupied molecular orbital gap and expands
the spatial distribution of electron wave functions, which make size-expanded
guanine appealing for charge transfer performance. At the same time,
it increases the steric hindrance, making the adsorption process more
orderly, which is also good in view of molecular electronic devices