The Burgeoning of Mechanically Interlocked Molecules in Chemistry

MIMs have been synthesized using various synthetic strategies that are constantly being optimized to reach higher yields that lead to novel architectures. The rational design of these architectures integrating multiple subcomponents that are not connected by covalent bonds is key to advancing the field of MIMs. Designing atomically precise molecules implies reaching a high level of understanding of their behavior and working processes. Recent analytical characterization techniques (e.g., spectroscopic, ensemble, single molecule) are being used to obtain precise descriptions of MIMs at the nanoscale. MIM-based proof-of-concept research is now flourishing, especially in the artificial molecular machine community. The next evolutionary step is to address applications that employ unprecedented molecular functionalities to relocate MIMs from ‘basic chemistry’ to ‘applied nanoengineering’. Mechanically interlocked molecules (MIMs), such as rotaxanes, catenanes, and molecular knots, have attracted significant interest because of their unique properties originating from their mechanically bonded components. Recently, MIMs have been employed in increasingly diverse architectures thanks to the tools of rational molecular design and the ability to incorporate functions in a precise manner. Here, we discuss advances in MIM synthesis, the fundamental understanding of their working processes, and applications exploiting their singular behavior. This review covers some of the most recent studies demonstrating the widespread interest in MIMs by scientists pursuing the ultimate goal of designing functional molecular machines that surpass their natural analogs or exhibit unprecedented properties. Mechanically interlocked molecules (MIMs), such as rotaxanes, catenanes, and molecular knots, have attracted significant interest because of their unique properties originating from their mechanically bonded components. Recently, MIMs have been employed in increasingly diverse architectures thanks to the tools of rational molecular design and the ability to incorporate functions in a precise manner. Here, we discuss advances in MIM synthesis, the fundamental understanding of their working processes, and applications exploiting their singular behavior. This review covers some of the most recent studies demonstrating the widespread interest in MIMs by scientists pursuing the ultimate goal of designing functional molecular machines that surpass their natural analogs or exhibit unprecedented properties. use of a metal ion as a template and catalyst for a reaction. modification (increase or decrease) of a second-site binding activity depending on the binding of an effector molecule at a first binding site of a molecule (commonly employed in biochemistry). spatial arrangement of interlocked components in a mechanomolecule; (co-)conformational changes appear through translation or pirouetting motions and potentially lead to important changes in molecules’ shapes and properties. spatial arrangement of atoms in a molecule; conformational changes appear through rotations about single bonds. doubly interlocked rotaxane, leading to cyclic or acyclic architectures. component part of a rotaxane comprising a stoppered axle. mechanism involving the raising and lowering of thermodynamic wells, possibly leading to directed motion in molecular machines. molecule that differs from another stereoisomer by the configuration of only one stereogenic center. a cyclic molecule; the term is mainly used here to describe the component part of a rotaxane or catenane (also mentioned as the ring). molecule presenting chirality arising from the relative orientation of its mechanically interlocked components (even with component parts devoid of covalent chirality). cyclic arrangement of connected aromatic rings. molecules that exhibit distinct behaviors on measurement. complex of two molecular components (an axle and a macrocycle) held together by noncovalent bonding interactions instead of mechanical bonds (no stoppering of the axle). element of a molecule bearing ligands or groups such that the interchange of two of these ligands leads to a stereoisomer. arrangement of atoms ordered by face-to-face stabilizing interactions between aromatic moieties. molecules presenting identical chemical formulas but differences in molecular topology. lowering of the transition state of a reaction using a catalyst.