CHARGE-TRANSFER EFFECTS ON THE FLUORESCENCE-SPECTRA OF 9-AMINOCAMPTOTHECIN - STEADY-STATE AND TIME-RESOLVED FLUORESCENCE STUDIES

The steady-state and time-resolved fluorescence of 9-amino-20 (S) -cam ptothecin (ACAM) were measured in a series of organic solvents. The mo lecule exhibits charge-transfer (CT) fluorescence in nonhydrogen-bondi ng polar solvents. The solvatochromic data have been utilized to estim ate the dipole moment of the molecule in the lowest excited singlet st ate. The CT fluorescence of ACAM is quenched in polar and hydrogen-bon ding solvents. The fluorescence quenching of ACAM by methanol, water, and 2,2,2-trifluoroethanol were studied in 1,4-dioxane. The quenching efficiency is linearly related to hydrogen bond-donating capacity of t he quencher molecule. Semiempirical AM1 molecular orbital calculations have been performed to calculate excitation energies, oscillator stre ngths, and ground and excited-state dipole moments of ACAM as well of the parent drug, camptothecin. (C) 1998 Elsevier Science S.A. All righ ts reserved.