A CHIRAL SPHERICAL MOLECULAR ASSEMBLY HELD TOGETHER BY 60 HYDROGEN-BONDS

Spontaneous self-assembly processes that lead to discrete spherical mo lecular structures are common in nature. Spherical viruses' (such as h epatitis B) and fullerenes(2) are well-known examples in which non-cov alent and covalent forces, respectively, direct the assembly of smalle r subunits into larger superstructures. A common feature of these shel l-like architectures is their ability to encapsulate neutral and/or ch arged guests whose size, shape and chemical exteriors complement those of the host's inner surface(3,4). Their interiors can often be regard ed as a new phase of matter(5), capable of controlling the flow of rea ctants, transients and products, and of catalysing reactions of both c hemical and biological relevance. Such properties have inspired the re cent emergence of monomolecular(5-7) and supramolecular dimeric molecu lar capsules(8,9), many of which have been based on the head-to-head a lignment of bowl-shaped polyaromatic macrocycles such as calix[4]arene s(5,7,9). But true structural mimicry of frameworks akin to viruses an d fullerenes, which are based on the self-assembly of n > 3 subunits, and where surface curvature is supplied by edge sharing of regular pol ygons, has remained elusive. Here we present an example of such a syst em: a chiral spherical molecular assembly held together by 60 hydrogen bonds (1) (Fig, 1). We demonstrate the ability of 1, which consists o f six calix[4]resorcinarenes 2 and eight water molecules, to self-asse mble and maintain its structure in apolar media and to encapsulate gue st species within a well-defined cavity that possesses an internal vol ume of about 1,375 Angstrom(3). Single crystal X-ray analysis shows th at its topology resembles that of a spherical virus(1) and conforms to the structure of a snub cube, one of the 13 Archimedean solids(10).