Development of copper-based oxidative bond cleavage reactions as new recognition and detection strategies for superoxide and ascorbate

Abstract

Abstract of thesis entitled

Development of Copper-based Oxidative Bond Cleavage Reactions as New Recognition and Detection Strategies for Superoxide and Ascorbate

Submitted by Zuo Hang Yu for the degree of Doctor of Philosophy at The University of Hong Kong in September 2019

Nature has been using different copper enzymes such as oxygenase for O2 activation and substrate oxidation. A variety of ligands with different basicity, denticities and ligand strength have been synthesized in order to mimic the active site of copper enzymes for understanding the underlying chemical reactivities. By utilizing the reactivity of these biomimetic copper complexes, a copper-based oxidative cleavage reaction is explored for developing fluorescent probes for the selective detection of challenging targets. In Chapter 1, a brief introduction on copper oxygenases and their synthetic model complexes are described. Emphasis has been put on the spectroscopic properties and reactivity of copper-oxygen intermediates involved in the oxidation. Fundamentals of fluorescent probe design for the detection of small molecule analytes are also described. In Chapter 2, the development of a series of selective superoxide probes is described. The superoxide probes are designed based on a copper-based oxidative cleavage featuring a Cu(II) complex supported by a hydroxyl-appended tris(2-pyridiyl)amine ligand. The superoxide probes (SOP) are selective towards superoxide against other ROS and RNS. The superoxide-induced C−O bond cleavage and fluorescent responses were investigated by a series of LCMS experiments. SOP-cyan and SOP-green are able to detect intracellular superoxide in HeLa, HEK293T and A431 cells by fluorescent imaging. In Chapter 3, the development of selective ascorbate probes is described. A copper-based oxidative cleavage reaction was used to design the ascorbate probes, which features a copper(II) complex supported by a tridentate ligand with three nitrogen donors inspired by the copper-dependent lytic polysaccharide monooxygenases (LPMOs). The ascorbate probes (AP) are selective towards ascorbate against dehydroascorbate, biological antioxidants, inorganic reducing agents, sugars, amino acids and vitamins. The ascorbate-induced C−O bond cleavage and fluorescent responses were further explored by LCMS and UV−Vis experiments. AP-cyan is able to detect ascorbate content in commercial drinks, human blood plasma, blood serum and detect intracellular ascorbate in HeLa cells by live-cell imaging. In Chapter 4, a concluding section with a brief description of future work is presented. In Chapter 5, experimental details including characterization of the synthesized molecules and experimental procedures are presented.