Melanin is a ubiquitous biopolymer found in a diverse array of living organisms known for its variety of functions such as radical scavenging, radiation protection, and thermoregulation. There are many different classes of melanin materials including eumelanin, found in commonly in animals, and allomelanin, a nitrogen-free melanin found in fungi and plants. Melanin and its synthetic analogues have demonstrated strong adhesive properties attributed to its strong hydrogen bonding, pi-pi stacking, and covalent bonding capabilities. Furthermore, melanin in nature suggests that it has certain toxin and metal remediating properties as shown in melanized turtleheaded seasnakes and self-poisoning protection in butter clams. Melanin’s ability to bind to small molecules and metals motivated our synthesis of highly porous synthetic analogues of melanin to further optimize its adsorption capabilities. Previously, mesoporous eumelanin and microporous allomelanin particles were synthesized that not only demonstrated high porosity and surface area, but also an affinity for chemical warfare agent (CWA) simulants. While melanin’s affinity for these toxins have been established, a remediation mechanism after adsorption has not been established for these synthetic materials. In nature, several species of microorganisms can remediate such toxins through enzymatic degradation under mild conditions, making it an attractive way to remediate these compounds in a way that is safe for humans and the environment.<br/><br/>This work shows that a high loading of CWA remediating enzyme, organophosphorus acid anhydrolase (OPAA) can be immobilized onto these synthetic porous eumelanin and allomelanin nanoparticles while still maintaining the native activity of OPAA. The activity of these enzymatically-active particles have been measured at various temperatures and pH in order to probe the thermal and pH stability offered through the immobilization onto the porous particles. Furthermore, these particles can be coated onto polymeric scaffolds such as fabrics to facilitate the reusability of these enzymes. The generalizability of this facile enzyme immobilization procedure further increases the potential use of these materials in relevant applications in which enzymatic catalysis is used such as in chemical synthesis and other pollutant remediation.

Enzyme-loaded synthetic porous melanin for chemical warfare agent remediation

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