Intrinsic Ladders of Affinity for Amino-Acid-Analogues on Boron Nitride Nanomaterials: A B3LYP-D2*Periodic Study

A systematic computational study of the gas-phase adsorption of different amino-acid-analogues (AA-ans) on a (6,0) boron nitride nanotube (BNNT) and on a boron nitride monolayer (BNML) has been performed by means of B3LYP-D2* periodic calculations. The AA-ans are CH3-R molecules, where R represents functional groups present in amino acid side chains, i.e., OH, COOH, CONH2, NH2, imidazole, guanidine, phenyl, phenol, indole, and CONHCH3. On (6,0) BNNT, AA-an species containing N electron donor groups (i.e., R = NH2, imidazole, and guanidine) are strongly chemisorbed through dative interactions between the N atom of the AA-an and a B atom of the nanotube and present the largest adsorption energies (Delta E-ads). For AA-an bearing aromatic rings (i.e., R = phenyl, phenol and indole) and R = CONHCH3, adsorption is driven by p-stacking interactions (with lower Delta E-ads values than the previous group), while for AA-an with O electron donor groups and H-bonding donor groups (i.e., R = OH, COOH, and CONH2) adsorption is dictated by dispersion of moderate strength alongside weak dative and H-bond interactions, thus presenting the lowest Delta E-ads. Significant differences are found on BNMLs. All adducts form by means of dispersion interactions of a different nature. The most stable adducts are those establishing pi-stacking interactions, in which the pi-systems of the AA-ans are aromatic rings (i.e., R = phenyl, phenol, indole, and imidazole). The AA-an group presenting the second most favorable Delta E-ads also presents p-stacking interactions, but the p-system is a single double-bond (i.e., R = COOH, CONH2, guanidine, and CONHCH3), whereas for R = NH2 and OH adsorption is due to CH-pi interactions. On the basis of the computed adsorption energies, intrinsic affinity scales of the considered AA-ans for BN nanomaterials are proposed, which can give hints about those lateral chains responsible for the protein/BN nanomaterial interaction.