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10.1002/anie.202103447
Angewandte Chemie International Edition
RESEARCH ARTICLE
Anisotropic Synthetic Allomelanin Materials via Solid State
Polymerization of Self-Assembled 1,8-Dihydroxynaphthalene
Dimers
Xuhao Zhou, Xinyi Gong, Wei Cao, Christopher J. Forman, Julia Oktawiec, Liliana D’ Alba, Hao Sun,
Matthew P. Thompson, Ziying Hu, Utkarsh Kapoor, Naneki C. McCallum, Christos D. Malliakas, Omar
K. Farha, Arthi Jayaraman, Matthew D. Shawkey and Nathan C. Gianneschi*
[*]
X. Zhou, X. Gong, Dr. W. Cao, Dr. C. J. Forman, Dr. J. Oktawiec, Dr. H. Sun, Dr. M. P. Thompson, Dr. Z. Hu, Dr. N. C. McCallum, Dr. C. D. Malliakas, Prof.
O. K. Farha, Prof. N. C. Gianneschi
Department of Chemistry, International Institute of Nanotechnology, Simpson-Querrey Institute, Chemistry of Life Processes Institute, Lurie Cancer Center.
Northwestern University
Evanston, Illinois 60208, United States of America
E-mail: nathan.gianneschi@northwestern.edu
Prof. N. C. Gianneschi
Department of Materials Science and Engineering, and Department of Biomedical Engineering. Northwestern University
Evanston, Illinois 60208, United States of America
Dr. U. Kapoor, Prof. A. Jayaraman
Department of Chemical and Biomolecular Engineering, Colburn Laboratory and Department of Materials Science and Engineering, University of Delaware
Newark, Delaware 19716, United States of America
Dr. L. D’ Alba, Prof. M. D. Shawkey
Department of Biology, Evolution and Optics of Nanostructures Group, University of Ghent
Ghent 9000, Belgium
Supporting information for this article is given via a link at the end of the document.
Abstract: Melanosomes have diverse morphologies in nature,
including spheres, rods, and platelets. By contrast, shapes of
synthetic melanins have been almost entirely limited to spherical
nanoparticles with few exceptions produced by complex templated
synthetic methods. Here, we report a non-templated method to
access synthetic melanins with a variety of architectures including
spheres, sheets, and platelets. Three 1,8-dihydroxynaphthalene
dimers (4-4′, 2-4′ and 2-2′) were used as self-assembling synthons.
These dimers pack to form well-defined structures of varying
morphologies depending on the isomer. Specifically, distinctive
ellipsoidal platelets can be obtained using 4-4′ dimers. Solid-state
polymerization of the preorganized dimers generates polymeric
synthetic melanins while maintaining the initial particle morphologies.
This work provides a new route to anisotropic synthetic melanins,
where the building blocks are preorganized into specific shapes,
followed by solid-state polymerization.
In contrast to this diversity found in nature, synthetic melanin is
mostly produced as spherical nanoparticles. Although some
anisotropic structures of polydopamine have been achieved
a more convenient,
scalable, and direct route towards non-spherical synthetic
melanin materials is desirable.
using DNA-origami-based templates,[9]
Allomelanin, the class of melanin targeted in this work, is a
heterogeneous group of polymers found mostly in fungi, bacteria,
10]
and plants.[7,
These organisms synthesize allomelanins
through oxidative polymerization of nitrogen-free precursors,
such as 1,8-dihydroxynaphthalene (1,8-DHN) and catechols.[10b,
11]
Typically, allomelanin generated by fungi utilizes 1,8-DHN
and is referred to as DHN melanin. The existence of DHN
melanin may be critical in the survival of fungi in hostile
environments, protecting them against ionizing radiation,
extreme temperatures, and oxidizing agents.[12] Previously, we
reported
a route for the chemical synthesis of artificial
allomelanin nanoparticles via oxidative oligomerization of 1,8-
DHN.[13] The resulting nanoparticles showed well-defined
spherical nanostructures and free radical scavenging activity.
Experimentally, we determined that spherical nanostructures
formed upon dimerization of 1,8-DHN, inspiring Kapoor and
Jayaraman to probe the self-assembly behavior of the three
DHN dimers (4-4′, 2-4′ and 2-2′) (Figure 1) via atomistic
molecular dynamics simulations.[14] These simulations revealed
that 4-4′ dimers adopt an anisotropic shape as they assemble,
as opposed to 2-2′ dimers that self-assemble into spherical
morphologies.[14] Inspired by the simulations, we hypothesized
that different isomers of DHN dimers would exhibit differences in
hierarchical self-assembly behavior that would be reflected in
their nanoscale or microscale morphologies. Specifically, 4-4′
dimers would have the propensity to generate synthetic
allomelanins with anisotropic morphologies. Furthermore, we
Introduction
Melanin is the term for a class of natural pigments ubiquitously
found in most organisms.[1] Melanin serves a variety of functions,
including as a pigment in human skin and hair,[2] in thermal
regulation,[3] in radiation protection,[4] in metal ion
sequestration,[5] and in neuroprotection.[6] In nature,
melanosomes, or melanin-containing organelles, possess
various morphologies and sizes.[7] Unique melanosome shapes,
including rods, disks, and platelets, are ubiquitous across
different biological kingdoms, particularly in bird feathers.[7-8]
A
wide array of spectacular bird colors emerges as a direct
consequence of the diversity of melanosomes morphologies. For
example, the green hermit hummingbird (Phaethornis guy)
applies densely packed ellipsoidal platelet-like melanosomes in
the gorget feathers to generate bright structural color (Figure S1).
1
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