Title

Excited state tautomerization of camptothecin in aqueous solution

Document Type

Article

Publication Date

11-15-1996

Abstract

The effect of pH on the absorption and fluorescence spectral characteristics of 20(S)-camptothecin was studied in aqueous solution. In alkaline solution, the lactone ring of camptothecin hydrolyzes to produce camptothecin carboxylate. The equilibrium constants of the lactone ring hydrolysis of camptothecin at various pH values were determined using steady state fluorescence measurements. The 1H nuclear magnetic resonance (NMR) and circular dichroism spectra were measured to characterize the structure of camptothecin in strongly alkaline medium. The fluorescence intensity of camptothecin is quenched by OH- ions. A mechanism of fluorescence quenching of the carboxylate form by OH- ions, which involves tautomerization on electronic excitation, is proposed. The ground and excited state pKa values of the quinolinium ion are reported.

Publication Source (Journal or Book title)

Journal of Photochemistry and Photobiology A: Chemistry

First Page

21

Last Page

27

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