Development of stimuli-responsive artificial peroxidase system based on a dimanganese complex and its application

Abstract

Peroxidase, which catalyzes a variety of oxidation reactions by using hydrogen peroxide (H2O2) or other peroxides as oxidants, has a wide variety of applicability in various fields such as biosensing and organic synthesis. In this dissertation, a study on the development of a stimuli-responsive artificial peroxidase system is described by exploiting a previously reported dimanganese complex-based artificial peroxidase called Mn2(bpmp) (bpmp: 2,6-bis((bis(pyridin-2-ylmethyl)amino)methyl)-4-methylphenolate). Caged artificial peroxidase system (Caged Mn2(bpmp)), whose intrinsic activity was completely blocked by masking the active site, was established based on a new design and synthesis of bpmp ligand by introducing stimuli-responsive trigger to a hydroxyl group of bpmp ligand. The peroxidase-like activity could be restored via specific stimuli-induced release of trigger within caged Mn2(bpmp). Based on the feature that various external stimuli can be employed by varying the structure of the trigger, we presented a new application of the caged artificial peroxidase system in peroxidase-based sensing and hydrogel synthesis. In the study on analyte-triggered artificial peroxidase system, we report a straightforward strategy to develop a peroxidase activity-based sensing platform for the detection of a wide range of analytes using caged Mn2(bpmp). An analyte-activatable artificial peroxidase system was established by introducing an analyte-cleavable trigger to cage the hydroxyl moiety in Mn2(bpmp). The sensing platform based on this caged Mn2(bpmp) operated by cascade reaction involving the analyte-induced release of trigger and generation of a detectable signal by restored peroxidase-like activity upon commercial peroxidase substrates. By utilizing the caged Mn2(bpmp), we successfully developed a versatile enzyme assay for leucine aminopeptidase (LAP) and γ-glutamyl transpeptidase (GGT). This assay enabled selective monitoring of enzyme activity by colorimetric and/or fluorescence change in real-time, screening of the efficiency of enzyme inhibitors, and determining enzyme activity in a human serum sample. In the study on light-triggered artificial peroxidase system, it is focused on the development of a photoactivatable artificial peroxidase system using Mn2(bpmp) to address the applicability of artificial peroxidase as a more broadly used tool. By exploiting a photoremovable protecting group (PPG) to construct photocaged Mn2(bpmp), it enabled the complete inhibition of intrinsic peroxidase-like activity. The operating principle of photocaged Mn2(bpmp) relied on the irreversible cleavage of PPG upon irradiation with a specific wavelength. In this study, the most widely used PPG, o-nitrobenzyl group, was used, and the irradiation with 365 nm UV LED light induced successful activation of the artificial peroxidase system. Kinetics of the reaction catalyzed by peroxidase-like activity was finely tuned in situ and on-demand by varying the irradiation time and light intensity. Based on the ability of Mn2(bpmp) to catalyze the synthesis of hydrogel, which is a 3D hydrophilic polymer network serving as an effective platform for various fields such as biomedical and sensing applications, we established the method for light-controlled synthesis of a hydrogel. Efficient oxidative coupling of catechol moiety in polymer backbone by light-triggered peroxidase-like activity led to crosslinking to generate a hydrogel. Moreover, spatiotemporal controllability of light enabled the synthesis of a desired shape of the hydrogel by site-specific activation and the regulation of mechanical property of the resultant hydrogel depending on the irradiation time.