  Using semiempirical PM6 method, the structures of a rod-like [Ti40O124H81]-7
model cluster and of the [Ti40O124H81Cu]-5 ones with Cu2+ coordinated at
various sites were optimized. If the relative toxicity of individual Ti centers
in rod-like rutile nanoparticles can be evaluated by the electron density
transfer to a Cu2+ probe, its maximal values may be ascribed to the
pentacoordinated corner and hexacoordinated edge ones with three Ti-OH bonds.
However, these centers exhibit the least negative interaction energies which
can be compensated by the significantly better accessibility of the corner Ti
center in comparison with the remaining ones. The Ti centers with the most
negative interaction energy parameters exhibit the lowest extent of the
electron density transfer to a Cu2+ probe. The rutile nanoparticles destruction
starts at pentacoordinated Ti face centers
