Mussel-Inspired Catechol-Functionalized Redox-Active Polypeptides for Energy Applications

Mussel-inspired, catechol-functionalized polypeptides were synthesized from natural feedstocks and investigated as redox-active organic electrode materials, to combine electrochemical performance with sustainability and cytocompatibility. Postpolymerization grafting of dopamine onto pre-established poly(α-l-glutamic acid)s resulted in low conjugation, giving poor aqueous solubility and failing to function electrochemically in initial solution-state studies. Therefore, a direct strategy was adopted, whereby the redox-active catechol functionality was embedded into the monomer, followed by ring-opening polymerization to afford a polypeptide bearing a catechol group at each repeat unit. In the solid state, WAXS revealed short-range order, thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC) indicated thermal stability and low flammability, and electrochemical evaluation demonstrated a quasi-reversible catechol/<i>o</i>-quinone aqueous redox process. The composite thin film electrochemical signal intensity was significantly greater for this poly(l-DOPA) than for the original catechol-grafted poly(α-l-glutamic acid). Cell-viability assays further support these catechol-functionalized polypeptides as viable components in sustainable and safe energy storage media.