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

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) (tmp=3,4,7,8-tetramethyl-1,10-phenanthroline) was designed and synthesized with HB as bridging ligand and tmp as terminal ligand. Co(2)HB(tmp)(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) stems from its (1)O(2) photosensitization ability, in sharp contrast to Cu(2)(HB)(tmp)(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) and Cu(2)(HB)(tmp)(2) was discussed in detail.