• Camptothecins;
  • Oneutral and protonated forms;
  • Topoisomerase I–DNA complex;
  • quantum chemical calculations;
  • optical properties;
  • structures


The structure and properties of the 11 Camptothecin derivatives (CPTs) and their different mono-, di-, and triprotonated forms, depending on the number of proton accepting centers in the molecules are studied both theoretically and experimentally by quantum chemical approaches, electronic absorption, and CD spectroscopy. The study of the protonated forms of the CPTs and search of the electron-withdrawing groups is crucial of the water-solubility of the novel medications. Thus, the model interaction of the different protonated molecular species with the Topoisomerase I–DNA complex are elucidated and discussed with a view to understand the mode of binding of the CPTs depending on the type of the substituents and pH of the medium. © 2011 Wiley Periodicals, Inc. Biopolymers 97: 134–144, 2012.