Ab-initio study of model guanine assemblies: The role of pi-pi coupling and band transport

摘要

Several assemblies of guanine molecules are investigated by means offirst-principle calculations. Such structures include stacked andhydrogen-bonded dimers, as well as vertical columns and planar ribbons,respectively, obtained by periodically replicating the dimers. Our results arein good agreement with experimental data for isolated molecules, isolateddimers, and periodic ribbons. For stacked dimers and columns, the stability isaffected by the relative charge distribution of the pi orbitals in adjacentguanine molecules. pi-pi coupling in some stacked columns induces dispersiveenergy bands, while no dispersion is identified in the planar ribbons along theconnections of hydrogen bonds. The implications for different materialscomprised of guanine aggregates are discussed. The bandstructure of dispersiveconfigurations may justify a contribution of band transport (Bloch type) in theconduction mechanism of deoxyguanosine fibres, while in DNA-like configurationsband transport should be negligible.