Invited
Sequence-encoded melanin-like nanomaterials formed by supramolecular peptides

Melanins are a class of pigments found across all life forms and have remarkable protective and aesthetic functionality through their chromophore-rich compositions. Their biosynthesis relies on tightly regulated processes, which are both temporally and spatially controlled and further fine-tuned by incorporation of locally available amino acids. By contrast, laboratory-based melanin synthesis is a poorly controlled process resulting in formation of insoluble precipitates, mainly due to lack of understanding of melanins’ structure-function relations.

Supramolecular self-assembly of molecular building blocks offers construction of functional materials with life-like properties that are tunable at the molecular level. Peptides are particularly attractive building blocks as they present a diverse set of simple chemical functionality and have the potential to be seamlessly interfaced with living systems.

Here, we developed a technology to form pigment materials by mimicking the biological manufacturing process of melanins, using supramolecular peptide assemblies with varying degree of order that pre-organize tyrosine substrates and provide steric and kinetic control of enzymatic oxidative polymerizationof tyrosine. In addition, we demonstrate a synthetic methodology to produce chromophoric microparticles, firstly to mimic biological black (eumelanin) and red (pheomelanin) pigments and subsequently, by addition of amino acids with varying side chains, to produce new chromophores not found in biology, dramatically expanding the optical properties that range from blue to far-red fluorescence and that can be rationally tuned. The microparticles can be utilized for cumulative sensing of amino acids by simultaneous incorporation and reporting through chromophore formation, and more generally for de novoconstruction of melanin-like materials with optical properties far beyond the range of properties accessible to biological melanins.