Gram negative bacteria perform oxidative phosphorylation in their periplasmic regions, between the inner and outer membrane where a proton gradient is maintained and used by the ATP synthase to make ATP.
Gram positive bacteria do not have a second membrane, but only a porous polysaccharide capsule. Oxidative phosphorylation then would on try to pump protons to the outside of the bacterium and it could diffuse out into the surrounding environment. Does this cause gram positive bacteria to operate less efficiency? does it make them more vulnerable to a basic pH in their environment?