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      Assembly of silver Trigons into a buckyball-like Ag 180 nanocage


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          Here we present a striking outcome from the alliance between chemistry and mathematics in the design, synthesis, and characterization of a silver cage, Ag 180. In principle, the design replaces each carbon atom of C 60 with a triplet of argentophilicity-bonded silver atoms to produce a (1,1) polyhedron with sixty 3-gons, ninety 4-gons, twelve 5-gons, and twenty 6-gons. Results from mass spectroscopy suggest an assembly mechanism in solution based on such triplets––the Silver-Trigon Assembly Road (STAR). Indeed, the STAR mechanism may be a general synthetic pathway toward even larger silver polyhedral cages. Besides its fundamental appeal, this synthetic cage may be considered for use as a molecular luminescent thermometer.


          Buckminsterfullerene (C 60) represents a perfect combination of geometry and molecular structural chemistry. It has inspired many creative ideas for building fullerene-like nanopolyhedra. These include other fullerenes, virus capsids, polyhedra based on DNA, and synthetic polynuclear metal clusters and cages. Indeed, the regular organization of large numbers of metal atoms into one highly complex structure remains one of the foremost challenges in supramolecular chemistry. Here we describe the design, synthesis, and characterization of a Ag 180 nanocage with 180 Ag atoms as 4-valent vertices (V), 360 edges (E), and 182 faces (F)––sixty 3-gons, ninety 4-gons, twelve 5-gons, and twenty 6-gons––in agreement with Euler’s rule V − E + F = 2. If each 3-gon (or silver Trigon) were replaced with a carbon atom linked by edges along the 4-gons, the result would be like C 60, topologically a truncated icosahedron, an Archimedean solid with icosahedral ( I h) point-group symmetry. If C 60 can be described mathematically as a curling up of a 6.6.6 Platonic tiling, the Ag 180 cage can be described as a curling up of a Archimedean tiling. High-resolution electrospray ionization mass spectrometry reveals that {Ag 3} n subunits coexist with the Ag 180 species in the assembly system before the final crystallization of Ag 180, suggesting that the silver Trigon is the smallest building block in assembly of the final cage. Thus, we assign the underlying growth mechanism of Ag 180 to the Silver-Trigon Assembly Road (STAR), an assembly path that might be further employed to fabricate larger, elegant silver cages.

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          Self-assembly of DNA into nanoscale three-dimensional shapes

          Molecular self-assembly offers a ‘bottom-up’ route to fabrication with subnanometre precision of complex structures from simple components1. DNA has proven a versatile building block2–5 for programmable construction of such objects, including two-dimensional crystals6, nanotubes7–11, and three-dimensional wireframe nanopolyhedra12–17. Templated self-assembly of DNA18 into custom two-dimensional shapes on the megadalton scale has been demonstrated previously with a multiple-kilobase ‘scaffold strand’ that is folded into a flat array of antiparallel helices by interactions with hundreds of oligonucleotide ‘staple strands’19, 20. Here we extend this method to building custom three-dimensional shapes formed as pleated layers of helices constrained to a honeycomb lattice. We demonstrate the design and assembly of nanostructures approximating six shapes — monolith, square nut, railed bridge, genie bottle, stacked cross, slotted cross — with precisely controlled dimensions ranging from 10 to 100 nm. We also show hierarchical assembly of structures such as homomultimeric linear tracks and of heterotrimeric wireframe icosahedra. Proper assembly requires week-long folding times and calibrated monovalent and divalent cation concentrations. We anticipate that our strategy for self-assembling custom three-dimensional shapes will provide a general route to the manufacture of sophisticated devices bearing features on the nanometer scale.
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            Physical Principles in the Construction of Regular Viruses

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              Self-assembled M24L48 polyhedra and their sharp structural switch upon subtle ligand variation.

              Self-assembly is a powerful technique for the bottom-up construction of discrete, well-defined nanoscale structures. Large multicomponent systems (with more than 50 components) offer mechanistic insights into biological assembly but present daunting synthetic challenges. Here we report the self-assembly of giant M24L48 coordination spheres from 24 palladium ions (M) and 48 curved bridging ligands (L). The structure of this multicomponent system is highly sensitive to the geometry of the bent ligands. Even a slight change in the ligand bend angle critically switches the final structure observed across the entire ensemble of building blocks between M24L48 and M12L24 coordination spheres. The amplification of this small initial difference into an incommensurable difference in the resultant structures is a key mark of emergent behavior.

                Author and article information

                Proc Natl Acad Sci U S A
                Proc. Natl. Acad. Sci. U.S.A
                Proceedings of the National Academy of Sciences of the United States of America
                National Academy of Sciences
                14 November 2017
                27 October 2017
                : 114
                : 46
                : 12132-12137
                [1] aKey Lab of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University , Jinan, 250100, People’s Republic of China;
                [2] bState Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University , Xiamen, 361005, People’s Republic of China;
                [3] cCalifornia NanoSystems Institute, University of California, Los Angeles , CA 90095-1563;
                [4] dDepartment of Psychology, University of California, Los Angeles , CA 90095-1563;
                [5] eSchool for Radiological and Interdisciplinary Sciences, Soochow University , Jiangsu 215123, People’s Republic of China
                Author notes
                2To whom correspondence may be addressed. Email: stan.schein@ 123456gmail.com or dsun@ 123456sdu.edu.cn .

                Edited by Vivian Wing-Wah Yam, The University of Hong Kong, Hong Kong, China, and approved September 28, 2017 (received for review July 07, 2017)

                Author contributions: D.S. conceived and designed the experiments; Z.W. conducted synthesis and characterization; H.-F.S., Y.-Z.T., S.-C.L., W.L., S.-A.W., and D.S. performed research; H.-F.S., Y.-Z.T., S.-C.L., W.L., S.-A.W., and D.S. analyzed data; S.S. analyzed the mathematics of the polyhedral structure; and Z.W., S.S., W.-G.W., C.-H.T., D.S., and L.-S.Z. wrote the paper.

                1Z.W. and H.-F.S. contributed equally to this work.

                Author information
                PMC5699068 PMC5699068 5699068 201711972

                Published under the PNAS license.

                Page count
                Pages: 6
                Funded by: National Science Foundation of China
                Award ID: 21571115
                Funded by: National Science Foundation of China
                Award ID: 21227001
                Funded by: Young Scholars Program of Shandong University
                Award ID: 2015WLJH24
                Funded by: Fundamental Research Funds of Shandong University
                Award ID:
                Physical Sciences

                coordination assembly,supramolecular chemistry,symmetry,silver cage,Goldberg cage


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