Photoactivatable Artificial Peroxidase System Using a Dimanganese Complex and Its Application to Light-Controlled Synthesis of Hydrogel

In this paper, we report a photoactivatable, artificial peroxidase system based on a photocaging approach. The photocaged Mn₂(bpmp) (bpmp: 2,6-bis((bis(2-pyridylmethyl)amino)-methyl)-4-methylphenolate) complex was developed by a simple design and synthesis of the corresponding bpmp ligand via the introduction of the 1-(o-nitrophenyl)-ethyl (NPE) group, a well-known photoremovable protecting group. Following 365 nm light irradiation of the resulting complex, the intrinsic peroxidase-like activity of the raw Mn₂(bpmp) was effectively restored. Interestingly, the degree of activation of the raw Mn₂(bpmp) system was found to be altered by varying the irradiation time and/or the light intensity, providing us with a method to tune the in situ reaction kinetics ad libitum. The photocaged Mn₂(bpmp) complex was further utilized for light-controlled hydrogelation by exploiting the ability of Mn₂(bpmp) to catalyze the synthesis of hydrogels under physiological conditions with a phenol-functionalized hydrophilic polymer as a precursor, and the photocontrollability of this catalytic activity using an external light source. Spatial control of light irradiation using a photomask enabled site-specific activation of peroxidase-like activity, allowing the preparation of a desired shape of the hydrogel. In addition, the mechanical properties of the resultant hydrogel, such as the adhesion strength, could be regulated depending on the light exposure time of the pre-gel solution containing the precursor, H₂O₂, and photocaged Mn₂(bpmp). Furthermore, the biocompatibility of the hydrogel synthesized using the photocaged Mn₂(bpmp) was confirmed by an in vitro assay.