The Effect of pH upon the Bacteriostatic Activity of Certain Nitrophenols

Abstract

An investigation of the bacteriostatic powers of 6 nitrophenols against Escherichia coli and Bacillus mesentericus showed that, the more acidic the compound, the greater is the effect of a change in the pH of the medium. For example, [image]-nitro-phenol (pKa 8.3) was inhibitive against E. coli in almost the same concn. throughout a culture pH range of 8.5 to 5.5, but 2,4-dinitrophenol (pKa 4) underwent a 60-fold increase in potency at the lower pH value. The activity appears to be due to the undissociated molecule of the drug concerned. From mass action principles, 3 equations are presented, one of which affords a semi-quantitative agreement with the exptl. findings. The unavailability of equilibrium constants precludes more concise expressions from the other 2 approaches which the authors consider to be more logical.