Synthesis, crystal structure from PXRD of a MnII(purp)2 complex, interaction with DNA at different temperatures and pH and lack of stimulated ROS formation by the complex

Abstract

The formation of reactive oxygen species (ROS) by anthracycline anticancer drugs is essential for their antitumor activity but they also make these drugs cardiotoxic. When complexed with metal ions there is a decrease in ROS formation and therefore in cardiotoxicity. Interestingly, in spite of producing fewer ROS, some of the complexes are effective antitumor agents, often better than the parent anthracycline. Purpurin (LH₃), a hydroxy-9,10-anthraquinone, resembles doxorubicin at the core. An Mn^II complex of LH₃ [Mn^II(LH₂)₂] was synthesized to see the extent to which the complex resembles metal–anthracyclines with regard to structure and function. The crystal structure was determined by Rietveld refinement of PXRD data using an appropriate structural model developed on the basis of spectroscopic information. This is only the second report on the crystal structure of a hydroxy-9,10-anthraquinone with a 3d-transition metal ion. Bond lengths and bond angles were obtained by structural refinement. The structure is supported by DFT calculations. DNA binding of the complex is slightly better than for purpurin but more importantly unlike purpurin, the binding constant values remained constant even with an increase in the pH of the medium. The NADH dehydrogenase assay and the DCFDA-ROS generation assay showed that generation of superoxide in the former and ROS in general in the latter were significantly less for the complex than for purpurin. Even with decreased ROS formation, the complex is able to maintain the biological activity of purpurin.