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Thermodynamics of the Quasi-Epitaxial Flavin Assembly around Various-Chirality Carbon Nanotubes

Sharifi, Roholah, Samaraweera, Milinda, Gascón, José A., Papadimitrakopoulos, Fotios
Journal of the American Chemical Society 2014 v.136 no.20 pp. 7452-7463
carbon nanotubes, dissociation, hydrogen bonding, mechanics, models, surfactants, thermodynamics, van der Waals forces
Establishing methods to accurately assess and model the binding strength of surfactants around a given-chirality single-walled carbon nanotube (SWNT) are crucial for selective enrichment, targeted functionalization, and spectrally sharp nanodevices. Unlike surfactant exchange, which is subject to interferences from the second surfactant, we herein introduce a thermal dissociation method based on reversible H⁺/O₂ doping to determine SWNT/surfactant thermodynamic stability values with greater fidelity. Thermodynamic values were reproduced using molecular mechanics augmented by ab initio calculations in order to better assess π–π interactions. This afforded detailed quantification of the flavin binding strength in terms of π–π stacking (55–58%), with the remaining portion roughly split 3:1 between electrostatic plus van der Waals flavin mononucleotide (FMN) interdigitation and H-bonding interactions, respectively. Quasi-epitaxial π–π alignment between the near-armchair FMN helix and the underlying nanotube lattice plays a crucial role in stabilizing these assemblies. The close resemblance of the thermal dissociation method to helix–coil and ligand-binding transitions of DNA opens up a unique insight into the molecular engineering of self-organizing surfactants around various-chirality nanotubes.