Two novel mononuclear Cu(II) coordination compounds of the type [Cu(dptaS)Cl₂] and [Cu(dptaS)Br₂] (dptaS=1,3-propanediamine, N¹-[3-aminopropyl]-N³-[2-thienylmethylidene] or Schiff mono-base of dipropylenetriamine with 2-thiophene-carboxaldehyde) were prepared by the hydrolysis of the di-bases, [Cu(dptaSS)Cl₂] and [Cu(dptaSS)Br₂] (dptaSS=1,3-propanediamine, N¹-[2-thienylmethylidene]-N³-[[2-thienylmethylidene]aminopropyl] or Schiff di-base of dipropylenetriamine with 2-thiophenecarboxaldehyde) to mono-bases with the release of one aldehyde molecule and freeing of the –NH₂ group of the coordinated dpta ligand. The X-ray determined structure of the compound [Cu(dptaS)Cl₂] was confirmed by spectroscopic methods, magnetic and molar conductivity measurements. The Cu(II) atom is a five-coordinated CuN₃Cl₂ chromophore with three nitrogen atoms coming up from the (dptaS) ligand and two chlorine atoms completing the square pyramidal geometry. Antiproliferative activity of both novel compounds was examined against a panel of different normal and cancer cell lines (MRC5, HeLa, MCF7, HT-29 and T47D) and showed that the Cu(II) Schiff mono-bases exhibit increased activity as compared to the starting materials. In vitro studies of plasmid DNA (pDNA) and double stranded DNA (dsDNA) interaction with the compounds under study support this difference. Some of the important factors contributing to the antiproliferative activity of the compounds under study, such as ionic character and dipole moment were also discussed in terms of the density functional theory calculated electronic structures of the ligands and their Cu(II) compounds.