In this work we study the effect of zigzag single walled nanotubes (ZNT's) of varying sizes on the complexation of simple polar molecules by adsorption. We have considered two ZNT's (with constant lengths of 13.5 angstrom), the (8, 0) which corresponds to 6.3 angstrom and the (14,0) species that has a diameter of 11.4 angstrom. This was performed in order to compare the relative complexation energies of the polar molecules adsorbed on the inside and on the surface of the nanotube structures. (C) 2008 Published by Elsevier B.V.