ammonium compounds are less effective against gram-negative bacteria and more effective against gram-positive bacteria.

Quartenary.

Explanation:

Quaternary ammonium compounds (QACs) are cationic salts of organically substituted ammonium compounds and have a broad range of activity against microorganisms, i.e more effective against Gram-positive bacterium at lower concentrations than Gram-negative bacteria.

It was also reported previously that monoalkyl QACs bind by ionic and hydrophobic interactions to microbial membrane surfaces, with the cationic head group facing outwards and the hydrophobic tails inserted into the lipid bilayer, causing the rearrangement of the membrane and the subsequent leakage of intracellular constituents.