Recent advances in mass spectrometry studies of non-covalent complexes of macrocycles - A review

Non-covalent molecular interactions are crucial for the formation of supramolecular systems whose applications in the transport and release of drugs, the development of nanoreactors or the design of molecular sensors, among others, make them very hot topic of investigation. The use of mass spectrometry (MS) and soft ionization methods as electrospray ionization (ESI) and matrix assisted laser desorption ionization (MALDI) has allowed the characterization of supramolecular systems. This comprises the characterization of non-covalent complexes formed by synthetic molecules and biomolecules and the study of these host-guest systems with different molecular interactions and thermodynamic aspects. Mass spectrometry is capable of answering many questions regarding analytical characterization of these systems including composition, stoichiometry, and structural aspects as e.g., connectivities and building blocks in the supramolecular complex. These soft ionization techniques together with MS have become the technique of choice for characterizing molecular interactions allowing the design of new molecules capable of self-assembly in supramolecular systems. In this review, the synthetic macromolecules cucurbiturils, calixarenes, crown ethers, catenanes, rotaxanes and cyclodextrins are reviewed due to the wide range of non-covalent interactions that they are able to form in their supramolecular assemblies. Both the non-covalent interactions and the supramolecular structures of these synthetic molecules have been studied by mass spectrometry to characterize their structures, thus showing the power of the technique as a tool for supramolecular analysis.