Quantum electronic stability in selective enrichment of carbon nanotubes.

We have studied the structural and electronic stability of a helical ribbon of flavin mononucleotide wrapping around single-walled carbon nanotubes using first-principles density-functional calculations. The helical ribbon is formed through hydrogen bonding between adjacent uracil moieties of the isoalloxazine ring and stabilized through concentric pi-pi interactions. The electronic structure calculations reveal quantum electronic stability associated with lattice registry and band alignment between the helical assembly and the (8,6) nanotube. The electronic stability plays an essential role in the experimentally observed highly selective enrichment of specific chirality tubes.