A chiral spherical molecular assembly held together by 60 hydrogen bonds

Abstract

Spontaneous self-assembly processes that lead to discretespherical molecular structures are common in nature. Sphericalviruses¹ (such ashepatitis B) and fullerenes² are well-known examples inwhich non-covalent and covalent forces,respectively, direct the assembly of smaller subunits intolarger superstructures. A common feature of theseshell-like architectures is their ability to encapsulateneutral and/or charged guests whose size, shape and chemicalexteriors complement those of the host's innersurface³,⁴. Their interiors can often beregarded as a new phase of matter⁵, capable of controlling the flowof reactants, transients and products, and of catalysingreactions of both chemical and biological relevance. Suchproperties have inspired the recent emergence ofmonomolecular^5,6,7 and supramolecular dimeric molecularcapsules⁸,⁹, many of which have been basedon the head-to-head alignment of bowl-shapedpolyaromatic macrocycles such as calix[4]arenes⁵,⁷,⁹. But true structural mimicry offrameworks akin to viruses and fullerenes, which are based onthe self-assembly of n > 3 subunits,and where surface curvature is supplied by edge sharing of regularpolygons, has remained elusive. Here we present anexample of such a system: a chiral spherical molecular assemblyheld together by 60 hydrogen bonds (1) (Fig. 1). We demonstrate the ability of 1, which consists of six calix[4]resorcinarenes 2 and eight water molecules, to self-assemble and maintain its structure in apolar media and to encapsulate guest species within a well-defined cavity that possesses an internal volume of about 1,375 ų. Single crystal X-ray analysis shows that its topology resembles that of a spherical virus¹ and conforms to the structure of a snub cube, one of the 13 Archimedean solids¹⁰.