Melanin and related polyphenolic pigments are versatile functional polymers that serve diverse aesthetic and protective roles across the living world. These polymeric pigments continue to inspire the development of adhesive, photonic, electronic and radiation-protective materials and coatings. The properties of these structures are dictated by covalent and non-covalent interactions in ways that, despite progress, are not fully understood. It remains a major challenge to direct oxidative polymerization of their precursors (amino acids, (poly-)phenols, thiols) toward specific structures. By taking advantage of supramolecular pre-organization of tyrosine-tripeptides and reactive sequestering of selected amino acids during enzymatic oxidation, we demonstrate the spontaneous formation of distinct new chromophores with optical properties that are far beyond the range of those found in biological melanins, in terms of color, UV absorbance and fluorescent emission.

Inspired by the role of intracellular liquid-liquid phase separation (LLPS) in formation of membraneless organelles, there is great interest in developing dynamic compartments formed by LLPS of intrinsically disordered proteins (IDPs) or short peptides. However, the molecular mechanisms underlying the formation of biomolecular condensates have not been fully elucidated, rendering on-demand design of synthetic condensates with tailored physico-chemical functionalities a significant challenge. To address this need, here we design a library of LLPS-promoting peptide building blocks composed of various assembly domains. We show that the LLPS propensity, dynamics, and encapsulation efficiency of compartments can be tuned by changes to the peptide composition. Specifically, with the aid of Raman and NMR spectroscopy, we show that interactions between arginine and aromatic amino acids underlie droplet formation, and that both intra- and intermolecular interactions dictate droplet dynamics. The resulting sequence-structure-function correlation could support the future development of compartments for a variety of applications.

The accumulation of metal ions in organisms and the presence of heavy metals in water cause adverse effects on ecosystems and results in numerous human health issues such as cancer and neurogenerative diseases. Therefore, the development of novel platforms for metal‐scavenging and rapid metal detection for in situ applications are of high importance. Here, this challenge is tackled by taking advantage of the metal chelation ability of a melanin‐inspired material in combination with the near‐infrared (NIR) fluorescence response of single‐walled carbon nanotubes (SWCNTs) to surface binding. SWCNTs are functionalized by a melanin‐like substance, obtained by enzymatic oxidative polymerization of a fluorenylmethyloxycarbonyl‐tyrosine (FmocY) precursor. The resulting multicomponent system (SWCNT‐FmocYOx) serves as a metal‐ion scavenging platform that concurrently reports on metal binding with optical signal transduction. Upon binding of a library of mostly divalent transition metal‐ions, the fluorescence emission of the functionalized SWCNTs is modulated, showing a concentration‐dependent response with a limit of detection in the nanomolar range. Metal‐binding and removal from water of up to 98% is further shown via inductively coupled plasma mass spectrometry. The SWCNT‐FmocYOx hybrid system presents a novel platform with NIR optical signal for real‐time feedback on metal‐ion scavenging.

Melanins are natural biopolymers that have remarkable properties including UV-protection, coloration, and antioxidant activity. Their biosynthesis is regulated both spatially and temporally and involves supramolecular templating and compartmentalization of enzymes and reactants within specialized organelles called melanosomes. In contrast, the laboratory-based bulk synthesis of melanin by tyrosine or dopamine oxidation is a poorly controlled process, resulting in materials with undefined properties. Inspired by the pigment’s biosynthesis, we developed a methodology to spatiotemporally regulate melanin formation in liquid droplets. The spatial control is achieved by sequestration of the reaction in dextran-rich droplets of a polyethylene glycol/dextran aqueous two-phase system, where the use of a photocleavable protected tyrosine provides a temporal control over its enzymatic oxidation–polymerization. We show that the liquid droplets allow for confined local reactivity as they serve as reaction centers for melanin synthesis and compartmentalize the melanin product. This methodology opens tremendous opportunities for applications in skincare and biomedicine.

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