"Flexiball" toolkit: A modular approach to self-assembling capsules

We report the synthesis and characterization of new, self-assembling molecu lar capsules. The modular strategy makes use of glycoluril building blocks available in multigram amounts combined with aromatic spacer elements. The lengthy syntheses encountered with earlier generations of capsules are avoi ded, and several capsules of nanometer dimensions are now accessible, Singl e bond attachments between spacers and glycoluril modules result in monomer s as dimeric capsules that are less rigid than their earlier counterparts. The host-guest properties of the homo- and heterodimeric capsules were stud ied using a combination of NMR and ESI-mass spectrometry. They show a less pronounced selectivity for guests of different sizes, and their increased f lexibility prevents self-assembly when no rigidifying elements are present on the central spacer unit. Some of the new capsules bear inwardly directed , secondary amide N-H protons. These can be further functionalized, as show n by their methylation to give tertiary analogues. The structures hold broa der implications for the placement of functional groups on concave molecula r surfaces.