Spectroscopic Studies on Molecular Interactions. IV. Charge-Transfer Properties and Antibacterial Activity of Sulfonamides

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Charge-transfer properties of 12 sulfonamides, together with diaminodiphenyl sulfone, p-aminobenzoic acid, and aniline, were investigated by their interactions with p-chloranil. The equilibrium constant was determined and the ionization potential (I_D) was estimated by utilizing the charge-transfer band arising in the 500-550 mμ region. The relation of hv_CT (charge-transfer transition energy) or I_D to the Michaelis constant for the acetylation of sulfonamides with liver extract indicated that the affinity of the drugs to acetylation enzymes increased as the ability of the charge-transfer of the drugs increased. The relationships between hv_CT or I_D and in vitro bacteriostatic activities were expressed with parabolic curves, which indicated the optimum value of I_D being about 2.37 eV for the potent sulfonamides. The relationships were explained from the dependence of the affinity to enzymes on the charge-transfer ability of the drugs.