Synthesis, characterization and albumin binding capabilities of quinizarin containing ternary cobalt(III) complexes

Four Co(III) ternary complexes with the composition of [(Co(4 N))₂(quin)](ClO₄)₄ or [(Co(4 N))₂(quinS)](ClO₄)₃, where 4 N = tris(2-aminoethyl)amine (tren) or tris(2-pyridylmethyl)amine (tpa), quinH₂ = quinizarin (1,4-dihydroxy-9,10-anthraquinone), quinSH₃ = quinizarin-2-sulfonic acid (1,4-dihydroxy-9,10-anthraquinone-2-sulfonic acid), were synthesized, characterized and their human serum albumin (HSA) binding capabilities were also tested. The complexes can be considered as likely chaperons of quinizarins which are structural models for anthracycline-based anticancer drugs like doxorubicin. All the Co(III) complexes are dinuclear and were isolated as mixture of isomers. Comparison of the cyclic voltammograms of the free ligands and the appropriate Co(III) complexes revealed that the new signals belonging to reversible processes in the range -400-0 mV (vs. Ag/AgCl) for the complexes can be attributed to the reversible reduction of the Co(III) centre. These potentials are in the range of typical (O,O) chelated Co(III) ternary complexes bearing 4 N donor ligands and follow the order being more positive for the tpa containing complexes. Presence of the sulfonate group in the quinizarin results in slightly more negative reduction potential of the Co(III) complexes. HSA binding capabilities of the quinH₂ and quinSH₃ ligands as well as the appropriate complexes showed that quinSH₃ has higher affinity to the protein than quinH₂ while none of the complexes seem to bind to HSA.