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Pigments by design

American Association for the Advancement of Science

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IMAGE: Polymeric pigments produced by guided oxidation of peptide assemblies. This material relates to a paper that appeared in the June 9, 2017, issue of Science, published by AAAS. The paper,... view more 

Credit: Photography by Matej Vakula, NYC

Researchers have discovered how to tune the optical and electrical properties of a synthetic polymer similar to melanin, a natural pigment that's the primary factor affecting skin color. They achieved this "tuning" of a melanin-like material, which has been very difficult to date, simply by juggling the order of its peptides. Melanin pigments are found in most life forms, including plants, bacteria, fungi, and animals, where they play a role in coloration and protection from various stresses that damage cells. The optical, electronic, and free-radical properties of these pigments make synthetic versions called analogs attractive for materials and biomedicine applications as well. Here, Ayala Lampel and colleagues identified a small subset of peptides containing tripeptide precursors that can serve as tunable precursors for melanin-like polymers. They found that constructing six different sequences of the three peptides resulted in noticeably different colors, ranging from beige to brown-black. Microscopy revealed that the sequence of peptides also affected the nanoscale morphology, stiffness and level of oxidation. In a related Perspective, Marco d'Ischia and Phillip B. Messersmith note that the scope of this chemistry can be expanded considerably given the structural and chemical diversity accessible with peptides.

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