Abstract
Two-dimensional sheet-like supramolecules have attracted much attention from the viewpoints of their potential application as functional (nano)materials due to unique physical and chemical properties. One of the supramolecular sheet-like nanostructures in nature is visible in the self-assemblies of bacteriochlorophyll-c–f pigments inside chlorosomes, which are major components in the antenna systems of photosynthetic green bacteria. Herein, we report artificial chlorosomal supramolecular nanosheets prepared by the self-assembly of a synthetic zinc 31-methoxy-chlorophyll derivative having amide and urea groups in the substituent at the 17-position. The semi-synthetic zinc chlorophyll derivative kinetically formed dimeric species and transformed into more thermodynamically stable chlorosomal J-aggregates in the solid state. The kinetically and thermodynamically formed self-assemblies had particle-like and sheet-like supramolecular nanostructures, respectively. The resulting nanosheets of biomimetic chlorosomal J-aggregates had flat surfaces and well-ordered supramolecular structures. The artificial sheet-like nanomaterial mimicking chlorosomal bacteriochlorophyll-c–f J-aggregates was first constructed by the model molecule, and is potentially useful for various applications including artificial light-harvesting antennas and photosyntheses.
Highlights
Two-dimensional sheet-like nanostructures have been made by organic and/or inorganic materials, for example, graphene, supramolecules, polymers, covalent organic frameworks, metal organic frameworks, and hexagonal boron nitride, and interested in wide fields such as electronics, optoelectronics, catalysts, energy storage, energy generation, sensors, separation, and biomedicines due to their unique physical and chemical properties[1,2,3]
This is the first report of biomimetic supramolecular nanosheets of chlorosomal J-aggregates being prepared from a synthetic zinc chlorophyll derivative
Zinc chlorophyll derivatives Zn-1 and Zn-2 (Fig. 2a) were synthesized from methyl 3-devinyl-3methoxymethyl-pyropheophorbide-a, which was prepared from naturally occurring chlorophyll-a extracted from commercially available Spirulina powders according to reported procedures
Summary
Two-dimensional sheet-like nanostructures have been made by organic and/or inorganic materials, for example, graphene, supramolecules, polymers, covalent organic frameworks, metal organic frameworks, and hexagonal boron nitride, and interested in wide fields such as electronics, optoelectronics, catalysts, energy storage, energy generation, sensors, separation, and biomedicines due to their unique physical and chemical properties[1,2,3]. A single chlorosome contains a large amount of bacteriochlorophyll-c, d, e, and f pigments (Fig. 1b), magnesium complexes of 31-hydroxy-131-oxo-chlorin, which are surrounded by lipid monolayers and form J-aggregates in hydrophobic environments without any protein assistance[14,15] Their self-assembly is mainly organized by coordination bonding (31-O∙∙∙Mg), hydrogen bonding (31-O–H∙∙∙O=C-13), and π–π stacking of chlorin skeletons[16,17]. Their supramolecular (nano)structures are still in discussion, but suggested to be rods, tubes, and/or lamellar sheets. Model compounds of such chlorosomal bacteriochlorophyll-c–f pigments have been synthesized from naturally occurring chlorophyll-a18,19. This is the first report of biomimetic supramolecular nanosheets of chlorosomal J-aggregates being prepared from a synthetic zinc chlorophyll derivative
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