Peroxidase-Like Reactivity at Iron-Chelation Sites in a Mesoporous Synthetic Melanin

Abstract

High catalytic activity and substrate specificity make enzymes a rich source of inspiration for catalyst development. Co-opting the advantages of natural materials while tuning them to a modified form and purpose, however, is not a straightforward synthetic task. Polymerization of L-3,4-dihydroxyphenylalanine (L-DOPA) results in amorphous polymer nanoparticles that are similar in many ways to natural eumelanin. Herein, the authors introduce mesoporosity and iron ion chelation to synthesize a variant of the L-DOPA polymer with high peroxidase-like activity. Our results indicate catalytic reaction with peroxide under mildly acidic conditions (pH 5.4 and 6) with a greater maximum reaction velocity (V max ) than horseradish peroxidase (HRP) at optimal pH 3.5-4.5. Comparison between Fe(III) and Fe(II) loading indicates that either can be used as a starting point to trigger reactivity, though Fe(II) loading leads to materials with twice the V max of the Fe(III)-loaded sample. The lack of catalyst degradation despite the redox changes and presence of radical species is consistent with the robust nature and redox versatility of polydopamine-based materials and demonstrates strong potential as a versatile redox-catalysis platform.

Fe3O4/Ag/Bi2MoO6 Photoactivatable Nanozyme for Self‐Replenishing and Sustainable Cascaded Nanocatalytic Cancer Therapy

“…Moreover, nanozymes may be designed to be photoactivatable for localized treatment. [11][12][13][14][15] But most of current nanozymes mimic peroxidase (POD) and a few simulate catalase (CAT) to convert H 2 O 2 into •OH for chemodynamic therapy (CDT) or into oxygen to enhance O 2 -dependent photodynamic therapy (PDT). [16][17][18] The effectiveness of these strategies is, however, not sustainable owing to limited supply of H 2 O 2 and suppression of the generated reactive oxygen species (ROS) by the elevated antioxidants in TME.…”

Quaternary Ammonium Assisted Synthesis of Melanin-like Poly(l-DOPA) Nanoparticles with a Boosted Photothermal Effect

“…Inspired by nature, polydopamine nanoparticle (PDA NP)-based melanin-like materials have been popularly shining in biomedical, − energy, − and other fields. ,,− It is worth noting that poly­(levodopa) nanoparticles (P­( l -DOPA) NPs), as another typical kind of melanin mimetic, have also emerged in recent years, showing superior performance and great potential in many areas. − Several methods have been developed for the preparation of P­( l -DOPA) NPs, such as employing ammonia, strong oxidants, and enzymes. ,,,, However, these strategies are plagued by problems including poor controllability, high cost, or damaged functional groups. Very recently, metal ions were found to be efficient in achieving the controlled synthesis of P­( l -DOPA) NPs .…”

Hydrophobic Melanin via Post-Synthetic Modification for Controlled Self-Assembly

“…Synthetic mimics have been developed to unravel the structure and function of natural melanins and to further explore a range of functions and applications. − Over the past two decades, polydopamine, used to mimic natural eumelanin, has been the most common synthetic analogue. Synthetic mimics of other melanins have received far less attention. − Allomelanin, the focus of this work, is a nitrogen-free class of melanin often derived from the precursor 1,8-dihydroxynaphthalene (1,8-DHN) and found predominantly in fungi. − Natural allomelanins serve as protective agents in fungi, which allow them to withstand radiation . Recently, synthetic allomelanin materials have been developed using chemical synthetic routes to polymerize monomeric 1,8-DHN and related dimers .…”