Shifting the Triangle-Square Equilibrium of Self-Assembled Metallocycles by Guest Binding with Enhanced Photosensitization.

ABSTRACT

Shifting a triangle-square equilibrium in one direction is an important problem in supramolecular self-assembly. Reaction of a benzothiadiazole-based diimidazole donor with a cis-Pt(II) acceptor yielded an equilibrium mixture of a triangle ([C18H24N10O6S1Pt1]3≡ PtMCT) and a square ([C18H24N10O6S1Pt1]4≡ PtMCS). We report here the shifting of such equilibrium toward a triangle using a guest (pyrene aldehyde, G1). While both benzothiadiazole and pyrene aldehyde can form reactive oxygen species (ROS) in organic solvents, their therapeutic use in water is restricted due to aqueous insolubility. The enhanced water solubility of the benzothiadiazole unit and G1 by macrocycle formation and host-guest complexation, respectively, enabled enhanced ROS generation by the host-guest complex (G1' ⊂ PtMCT) in water (G1' = hydrated form of G1). The guest-encapsulated metallacycle (G1' ⊂ PtMCT) has shown synergistic antibacterial activity compared to the mixture of macrocycles upon white-light irradiation due to enhanced ROS generation. The mechanism for such enhanced activity was established by measuring the oxidative stress and relative internalization of PtMCs and G1' ⊂ PtMCT.