  We report the first theoretical study of hydroxyl vacancies in
aluminosilicate and aluminogermanate single-walled metal-oxide nanotubes. The
defects are modeled on both sides of the tube walls and lead to occupied and
empty states in the band gap which are highly localized both in energy and in
real space. We find different magnetization states depending on both the
chemical composition and the specific side with respect to the tube cavity. The
defect-induced perturbations to the pristine electronic structure are related
to the electrostatic polarization across the tube walls and the ensuing change
in Br{\o}nsted acid-base reactivity. Finally, the capacity to counterbalance
local charge accumulations, a characteristic feature of these systems, is
discussed in view of their potential application as insulating coatings for
one-dimensional conducting nanodevices.
