First Principles Calculations of Alanine Radicals Adsorbed on Pristine and Functionalized Carbon Nanotubes

The structural and electronic properties of alanine radicals adsorbed on pristine and carboxyl-functionalized (5,5) single-walled carbon nanotubes (SWCN) are investigated through ab initio calculations based on density functional theory. We find that the bonds between the alanine radicals and pristine SWCNs are stronger when the interaction occurs via the amine group. In particular, the strongest bond occurs for a structure where all C atoms belonging to the SWCN keep sp 2 -like hybridization. Interestingly, this is the only case where the system remains metallic. In all other cases, the systems result in a semiconductor or semiconductor with a half-filled level in the gap, depending on how the alanine radical is adsorbed. On the other hand, for carboxyl-functionalized SWCNs the properties of the systems do not significantly depend on how the alanine radical is absorbed.