Theoretical study of gas and solvent phase stability and molecular adsorption of noncanonical guanine bases on graphene

The gas and solvent phase stability of noncanonical (Gua)n nucleobases is investigated in the framework of dispersion-corrected density functional theory (DFT). The calculated results strongly support the high tendency for the dimerization of (Gua)n bases in both gas and solvent phases. An interplay between intermolecular and bifurcated H-bonds is suggested to govern the stability of (Gua)n bases which bears a correlation with the description of dispersion correction terms employed in the DFT calculations. For example, a higher polarity is predicted for (Gua)n bases by the dispersion-corrected DFT in contrast to the non-polar nature of (Gua)3 and (Gua)4 predicted by the hybrid meta-GGA calculations. This distinct variation becomes significant under physiological conditions as polar (Gua)n is likely to exhibit greater stabilization in the gas phase compared to solvated (Gua)n. Graphene acting as a substrate induces modification in base configurations via maximization of π-orbital overlap between the base and substrate. In solvent, the substrate-induced effects are further heightened with lowering of the dipole moments of (Gua)n as also displayed by the corresponding isosurface of the electrostatic potential. The graphene-induced stability in both gas and solvent phases appears to fulfill one of the prerequisite criteria for molecular self-assembly. The DFT results therefore provide atomistic insights into the stability and molecular assembly of free-standing noncanonical (Gua)n nucleobases which can be extended to understanding the self-assembly process of functional biomolecules on 2D materials for potential biosensing applications.