  We examine the effective force between two nanometer scale solutes in water
by Molecular Dynamics simulations. Macroscopic considerations predict a strong
reduction of the hydrophobic attraction between solutes when the latter are
charged. This is confirmed by the simulations which point to a surprising
constancy of the effective force between oppositely charged solutes at contact,
while like charged solutes lead to significantly different behavior between
positive and negative pairs. The latter exhibit the phenomenon of ``like-charge
attraction" previously observed in some colloidal dispersions.
