The influence of charge transfer complex formation on the antibacterial activity of some tricyclic drugs.

1. Phenothiazines and structurally related drugs are effective in eliminating bacterial plasmids. 2. Charge transfer complex formation between chlorpromazine and xanthine dyes with different electron acceptor activities (e.g. fluorescein, eosin, erythrosin and rose bengal) was detected by differential spectrophotometry. Charge transfer complexes were formed between the strong electron acceptor rose bengal and various tricyclic drugs. 3. On the basis of the wavelength shift, the binding energies of drugs and dyes were estimated. 4. The temperatures dependence of the reaction indicates charge transfer complex formation rather than a chemical reaction between drugs and dyes. 5. The anti-plasmid action of the phenothiazines was decreased in the presence of xanthine dyes. As a consequence of competitive inhibition between bacterial binding sites and xanthine dyes, the binding energy of drugs in the plasmid replication system could be determined in the presence of dyes. 6. Drugs with binding energies in the range of 0.23-2.31 kcal/mol can inactivate the plasmid replication system.