"Flexiball" toolkit: a modular approach to self-assembling capsules.

We report the synthesis and characterization of new, self-assembling molecular 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 avoided, and several capsules of nanometer dimensions are now accessible. Single bond attachments between spacers and glycoluril modules result in monomers as dimeric capsules that are less rigid than their earlier counterparts. The host-guest properties of the homo- and heterodimeric capsules were studied using a combination of NMR and ESI-mass spectrometry. They show a less pronounced selectivity for guests of different sizes, and their increased flexibility 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 shown by their methylation to give tertiary analogues. The structures hold broader implications for the placement of functional groups on concave molecular surfaces.

On the way to rotaxane-based molecular motors: studies in molecular mobility and topological chirality.

ATP synthase represents a machine at the molecular level which couples the rotation of an axle in a wheel with the endergonic production of ATP, the general source of chemical energy in the cell. The natural system prototypically bears all features of a macroscopic motor: a rotor within a stator held by a membrane and fueled by a difference in chemical potential in the form of a proton gradient combined with a machine for ATP production. The assembly of axle and wheel to a rotor device reminds one very much of a rotaxane. In this Account, we discuss some important features of motors and their (potential) realization in simpler artificial model systems, that is, the molecular mobility of mechanically bound molecules, the importance of chirality for unidirectional motion, the sources of energy for driving the rotation, and the potential of using membranes and surfaces for ordering a large number of devices to achieve macroscopic effects.

Molecular recognition and supramolecular chemistry in the gas phase.

Supramolecular chemistry, in particular, the fields of molecular recognition and self-assembly, profit much from the development of soft ionization techniques and advanced methods for mass analysis and gas-phase chemistry. Vice versa, weakly bonded architectures and host-guest complexes represent a veritable challenge for the mass spectrometrist, leading to further development of methods and techniques. This review describes the state-of-the-art in this field, and includes topics such as the effects of solvation on meta binding to crown ethers, chiral discrimination of guests by chiral hosts, the elucidation of the secondary structure of self assembled complexes, and the mechanistic pathways of self assembly or the fragmentations of supramolecular complexes in the gas phase.