Ground and excited-state ionization behavior of 9-aminocamptothecin: An absorption and fluorescence spectral study

1143-1148<span style="font-size:14.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">The absorption and fluorescence spectra of 9-amino-20(S)-camptothecin (ACAM) have been measured as a function of pH. The photophysical properties. for example, fluorescence quantum yields and lifetimes, and radiative and nonradiative decay rates of different prototropic species of ACAM in aqueous solution have been estimated. The neutral lactone form as well as the ring-opened carboxylate form of the drug are found to be nonfluorescent in aqueous medium. The ground and excited-state acidities of the prototropic forms of the molecule have been determined. The semi-empirical AM1 calculations have been performed to calculate the ground and excited-state charge densities at the basic centers of the molecule. The results have been compared with that for the parent drug, 20(S)-camptothecin.</span

Spectroscopic and photophysical studies of the anticancer drug: Camptothecin

Electronic absorption and fluorescence spectra as well as the photophysical properties of 20-(S)-camptothecin were studied in a series of organic solvents and in aqueous solution. The fluorescence quantum yield and lifetime were measured. In contrast to previously reported results, this study has demonstrated that there is a marked increase of fluorescence quantum yield and fluorescence lifetime with an increase in solvent polarity and hydrogen-bonding capacity. The solvent dependence of the fluorescence quantum yield and lifetime are explained. The solvent effects indicate that the S1 state of CAM is 1π,π*-type with some contribution from a close-lying higher energy 1n,π* state. The fluorescence lifetime of the drug was measured in sucrose solutions of varying viscosity and it was observed that the lifetime decreased with an increase in viscosity. The fluorescence quenching of both camptothecin lactone and camptothecin carboxylate in interactions with I- ion in aqueous medium is reported. The fluorescence intensity of both forms are mainly quenched by the dynamic process. The quenching constant of the lactone form is twice as high as that of the carboxylate form

Dual fluorescence of 9-(N,N-dimethylamino)anthracene: Effect of solvent polarity and viscosity

Absorption and fluorescence spectra of 9-(N,N-dimethylamino)anthracene (9-DMA) have been studied in a series of organic solvents and water. The induced circular dichroic spectra of 9-DMA were measured in β-and γ-cyclodextrins to locate the position of the 1La and 1Lb transitions in the absorption spectrum. The fluorescence spectra of 9-DMA exhibit dual emission bands in the solvents employed. Absorption and fluorescence excitation spectra of 9-DMA exhibit a local and an underlying charge-transfer band. The effects of temperature, solvent polarity, and viscosity on these spectra have been studied. The steady-state fluorescence polarization spectra were used to examine the transitions involved. The fluorescence quantum yields and lifetimes of 9-DMA in neat solvents and solvent mixtures have been measured. The pKa value of nitrogen protonation was estimated in aqueous solution. Semiempirical AM1 calculations were performed to calculate energies and dipole moments of various conformers of 9-DMA obtained by twisting the -N(CH3)2 group around the C-N bond

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)-camptothecin (ACAM) were measured in a series of organic solvents. The molecule exhibits charge-transfer (CT) fluorescence in nonhydrogen-bonding polar solvents. The solvatochromic data have been utilized to estimate the dipole moment of the molecule in the lowest excited singlet state. The CT fluorescence of ACAM is quenched in polar and hydrogen-bonding 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 the quencher molecule. Semiempirical AM1 molecular orbital calculations have been performed to calculate excitation energies, oscillator strengths, and ground and excited-state dipole moments of ACAM as well of the parent drug, camptothecin. © 1998 Elsevier Science S.A. All rights reserved