Proton affinity of polar amino acid sidechain analogues anchored to the outer wall of single walled carbon nanotubes

We investigate the proton affinity values of sidechain analogues of Ser, Asp, His and Tyr covalently attached to the the outer wall of single walled carbon nanotubes both in the gas phase and in the presence of a polar solvent. The proton affinity values, estimated by B3LYP/SVP method, show marked sensitivity to the anchoring hydrophobic surface. His and Tyr-like sidechains exhibit high propensities towards accepting a proton from a neighboring –OH group similarly tethered to the carbon nanotube wall. Compared to Tyr sidechain in the gas phase, a marked increase in proton affinity values of Tyr-like sidechains is observed in functionalized systems if, in addition to the proton donor –OH group, an additional –OH group is present covalently attached to the wall within hydrogen bonding distance of the proton acceptor sidechain.