PHOTOPHYSICAL AND REDOX PROPERTIES OF DIBUCAINE AND PRIMAQUINE - A COMPARISON STUDY

Absorption and emission (at 77 K) spectra and amperometric cyclic volt ammograms of dibucaine and primaquine were recorded at different conce ntrations and pH values. While dibucaine shows distinguishable photoph ysical properties for neutral, hydrogen-bonded, and protonated species , primaquine at 77 K aggregates to form an excited-state double-proton -transfer dimer (i.e., a J-type excimer) at concentrations higher than 5 x 10(-5) M and in the pH range 2.5-5.5. Dibucaine is electrochemica lly stable, but primaquine is not. The electrochemical instability of primaquine is probably associated with the observation that the 1 x 10 (-4) M primaquine in acetonitrile displays a highly accentuated signal of cyclic voltammogram in the reduction reaction H+. The proton disso ciative nature of primaquine supports the NMR measurement that the exc hange of C-5 aromatic proton in primaquine at pH <4 is unusually fast. The acidic nature of primaquine resulted from the dissociation of C-5 aromatic proton could assist the uptake of the antimalarial drugs. Th e spectroscopic investigations of native bacteriorhodopsin (bR) and de lipidated deionized bR incorporating with two drugs show that dibucain e interacts with the protein of bR, while primaquine affects its lipid and denatures the purple membrane. The results are discussed in light of the pharmacological actions of dibucaine (a local anesthetic drug) and of primaquine (an antimalarial drug).