Amino acids interacting with defected carbon nanotubes: ab initio calculations

The adsorption of a number of amino acids on a defected single-walled carbon nanotube (SWCNT) isinvestigated by using the density-functional theory (DFT) calculations. The adsorption energies andequilibrium distances are calculated for various configurations such as amino acid attaching to defectsites heptagon, pentagon and hexagon in defective tube and also for several molecular orientationswith respect to the nanotube surface. The results showed that amino acids prefer to be physisorbed onthe outer surface of the defected nanotube with different interaction strength following the hierarchyhistidine > glycine > phenylalanine > cysteine. Comparing these findings with those obtained forperfect SWCNTs reveals that the adsorption energy of the amino acids increase for adsorption ontodefected CNTs. The adsorption nature has also been evaluated by means of electronics structuresanalysis within the Mulliken population and DOS spectra for the interacting entities