LU3-1 and IL4 are the molecular pair found for PqsR agonist, LU3-1 has a chain with seven carbons while IL4 has a chain with nine carbons, but agonist activity is around one hundred and seventy times greater for LU3-1, finding relationships between the chain size and the agonist activity. In another perspective, compounds with code LU2 and LU10 were activity cliffs related to antagonist activity, these have a lateral chain with six carbons, but LU2 has oxygen in position four, while for LU10 all are carbons; this variation generates a loss of potency in sixteen orders of magnitude; this loss should be explained by the lack of a hydrogen bond acceptor. Activity cliffs for RhlR agonist are molecules with a thiolactone ring and a lateral chain, here the chain change in methyl group in position four for BO2-4 while BO11 does not have it, activity for BO2-4 is eight times greater than BO11; furthermore, the natural autoinducer of RhlR has an EC 50 ) lower than these compounds, and its difference is a lactonic ring versus thiolactone ring, as reported by Boursier and coworkers . The substitution of the phenyl ring in molecular pairs found for antagonist activity generates a change of this activity, while EI29 is disubstituted by two chlorines, EI24 is monosubstituted by a methyl group, linking the size and inductive effects with this activity .