As a pervasive biopolymer, melanin is present throughout biology. Melanin has a myriad of different functions including radiation protection, radical scavenging, thermal regulation, and small molecule and metal adsorption. Five types of melanin have been discovered: eumelanin, pheomelanin, neuromelanin, pyomelanin, and allomelanin. The utility of function differs depending on the type of melanin, where it is located, and the organisms it is found in. Classically, melanin is known as a pigment. It has a broad absorption spectrum and one of the highest refractive indices for any known biological material (~1.8-2.0). Due to these properties, melanin has abundant interaction with the electromagnetic spectrum. In animals, melanin is a dark pigment dyeing the skin or hair. Conversely, when melanin is arranged into layers along with other biopolymers it can produce bright iridescent and non-iridescent structural coloration as seen in bird feathers. Predominately, animal melanin is composed of a combination of black or brown eumelanin and red pheomelanin. Both types of melanin are formed through the Raper-Mason pathway starting with a tyrosine precursor, but pheomelanin is formed through the addition of cysteine. Eumelanin and pheomelanin haven’t been well characterized, so their chemical structures and corresponding color properties remain elusive.<br/>Here, a pheomelanin film is formed at the air-water interface through the addition of cysteine during dopamine polymerization. Dopamine is the most common monomer used to mimic eumelanin and can be oxidatively polymerized to form polydopamine. Polydopamine films have been previously created at the air-water interface but are dark in color and consist largely of nanoparticles. With the addition of cysteine during the polymerization the resulting film is more uniform, forms vibrant colors, and iridescence. Through different characterization techniques, including XPS, FT-IR, ssNMR, and HETCOR, it is evident that cysteine binds to dopamine during the polymerization and incorporates into the film resulting in a biomimetic sulfur-containing free-standing colorful melanin film that can be easily scaled-up and deposited onto different surfaces for various applications.

Vibrant, colored pheomelanin films formed at the air-water interface

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.