Abstract Structures of irinotecan (CPT-11) in neutral lactone, carboxyl, and anionic carboxylate forms singlet ground states their complexes with Cu(II) doublet are optimized using B3LYP/6-311G* treatment. Metal ion affinities (MIA), Cu charges Laplacians Cu-ligand bond critical points possible CPT active sites evaluated. The formation the ligand leads to release CO 2 that can cause a decrease ...