Synthesis and antioxidant activity of zinc(II) phthalocyanine tetranitroxide

Abstract Zinc(II) phthalocyanine (np-TEMPO-ZnPc) bearing four TEMPO fragments at the non-peripheral positions of the macrocycle was prepared through the cyclotetramerization of phthalonitrile derivative 3-TEMPO-Pht. Characterization of tetraradical was performed by electron paramagnetic resonance (EPR) at room temperature. A characteristic triplet was observed (g = 2.00715, hyperfine coupling constant of 15.73 G) in the EPR spectrum of np-TEMPO-ZnPc measured in chloroform. The np-TEMPO-ZnPc was also investigated for in vitro antioxidant activities. Antioxidant properties were determined for its free radical scavenging effect, reducing power, β-carotene bleaching and total antioxidant capacity assays. The results demonstrated that np-TEMPO-ZnPc has strong DPPH radical scavenging and β-carotene bleaching activities even more than the standard antioxidant BHT. Especially, the compound exhibited similar radical scavenging effect at low concentrations when compared with BHT.