Photophysical properties of dibucaine and primaquine : a comparison study
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The purpose of this thesis was to compare two different drugs, dibucaine and primaquine, in their photophysical properties and their interaction with bacteriorhodopsine (bR) purple membrane. Even though these two drugs have totally different pharmacological effects -- dibucaine is a local anesthetic while primaquine is an antimalarial drug -- they have similar molecular structures (quinoline analogue). The bR purple membrane was used as a model for investigating the interaction of membranes with different drugs. Dibucaine was shown to have rich optical properties and distinguishable photophysical properties for neutral, hydrogen-bonded, and protonated species. The absorption spectra of native (λ[submax] = 568 nm) and deionized (λ[submax] = 608 nm) bR with dibucaine∙HC1 added show that they are very sensitive to the amount of dibucaine∙HC1 added. The emission spectrum of dibucaine∙HC1 in neutral micellar solution, Triton X-100, was used to study the deprotonation process of dibucaine∙HC1 in a hydrophobic environment. The emission of dibucaine free base in Triton X-100 micellar solution and that of dibucaine∙HC1 in the retinal-free mutant bR solution were compared to identify the action mechanism of local anesthetics within the bR purple membrane. The phosphorescence emission of dibucaine at 77 K is completely quenched by bR, and the fluorescence-quenching rate for different quenchers suggests that the retinal chromophore is the center of quenching in the bR. The incorporation of dibucaine∙HC1 in bR inhibits the formation of the slow component of an M₄₁₂ decreases the amount M₄₁₂ of formation in the photocycle of bR. All observations suggest that the action site of the local anesthetic is near or at the retinal chromophore. The anesthetic action on bR purple membrane is a specific site binding, without a change in conformation. Primaquine, an antimalarial drug, also has a quinolinelike structure, but it does not have a tertiary amine group as dibucaine does. Unlike dibucaine, it does not have a clearly distiriguishable photophysical property for different ionization species, but the emission spectra of primaquine at different concentrations and pH values suggest that primaquine tends to aggregate in a way that is conformational dependent and only exists in the excited state. The temperature-dependent emission spectrum of primaquine suggests that such an aggregate is a dimer which results from an excited state double-proton transfer reaction. The emission spectrum of primaquine in Triton X-100 solution reveals that the monomer of the aggregate has emission of the neutral form. The incorporation of primaquine in native purple bR shows that the primaquine interacts with the lipids of bR while dibucaine interacts with protein.