The adsorptions of proton and hydroxide on the perfect and defect armchair (5,5) single-walled carbon nanotubes (SWCNTs) of cap-ended C-80, C-120 and open-elided C80H20 and on their protonated structures in the systems with and without water were studied using the Hartree-Fock and two-layered ONIOM(MO:MO) methods. The binding energies of all the adsorptions on various types of armchair (5,5) SWCNTs were obtained at the ONIOM(B3LYP/6-31G(d):AM1) level of theory. The strain energies for all the adsorbed-state structures of SWCNTs and thermodynamic properties for all the adsorptions computed at various levels of theory were obtained. (C) 2007 Elsevier B.V. All rights reserved.