A new Co(III)–hypocrellin B complex with enhanced photonuclease activity

Abstract

Hypocrellin B (HB), a naturally occurring photosensitizer, has been extensively and intensively studied as a promising photodynamic therapy (PDT) agent. In this work, a new Co(III) complex [Co 2(HB)(tmp) 4] 4+ (tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) was designed and synthesized with HB as bridging ligand and tmp as terminal ligand. [Co 2HB(tmp) 4] 4+ exhibits improved water solubility, enhanced absorptivity in the phototherapeutic window, increased binding affinity and DNA photocleavage capability toward dsDNA with respect to HB. The photodynamic activity of [Co 2(HB)(tmp) 4] 4+ stems from its 1O 2 photosensitization ability, in sharp contrast to [Cu 2(HB)(tmp) 2] 2+ which relies on superoxide anion radical (O 2 - ) and hydroxyl radical (·OH) to photocleave DNA, though the both complexes possess similar electrochemical properties. The remarkable difference between the photodynamic mechanisms of [Co 2(HB)(tmp) 4] 4+ and [Cu 2(HB)(tmp) 2] 2+ was discussed in detail.