Nanometric, soccer-like balls were prepared in the lab by self-assembly of “sticky” pentagonal molecules, mimicking the formation of spherical viral capsid.
Nature uses spherical containers ubiquitously in both the inanimate and living worlds, and the icosahedron or dodecahedron are the polyhedra that are closest in symmetry to the sphere. Consequently, the optimal bottom-up strategy to achieve spherical objects involves the construction of these Platonic solids. This notion has been applied at any scale, from dodecahedrane, Buckminsterfullerene, spherical virus capsids, as well as soccer balls and geodesic spheres. Spherical viruses use this approach to create particles ranging in size from 15 to 500 nm, which assemble spontaneously from their components under the proper conditions, and disassemble under other conditions, thus enabling the viral life cycle. The icosahedral virus capsids teach us important lessons, including the economy of surface area-to-volume ratio and the genetic efficiency of subunit-based symmetric assembly.
Chemical mimicry of viral capsids is highly desirable because stable structures of icosahedral symmetry can be applied in many ways, including microencapsulation and transport of sensitive cargo, drug delivery and targeting, synthesis of nanoparticles of uniform size, reactivity modulation of bound guests, molecular recognition, catalysis, formation of structural elements for supramolecular architecture, and even safe immunization by epitope presentation on the surface of non-viral spherical objects.
Part of the research team had proposed in 2007 a synthetic strategy to achieve chemical capsids, which is based on the self-assembly of twelve pentatopic tiles (tectons). These tiles can bind one another either directly or with the help digonal or trigonal connectors (Figure 1). Although this approach seems simple, its realization has been challenging. Following 12 years of unsuccessful attempts by the Technion team and other research groups, the goal was finally achieved by a joint effort of the Technion group and the group of Prof. Yi-Tsu Chan at the National Taiwan University. Spontaneous self-assembly of twelve tectons with 30 cadmium(II) cations produces a giant icosahedral capsid (of 6 nm external diameter and 1 nm thick shell) as a thermodynamically stable single product in high yield.
Chemical mimicry of viral capsid self-assembly via corannulene-based pentatopic tectons. Yu-Sheng Chen, Ephrath Solel, Yi-Fan Huang, Chien-Lung Wang, Tsung-Han Tu, Ehud Keinan & Yi-Tsu Chan. Nature Communications
volume 10, Article number: 3443 (2019).