Improved Skill of Rotaxanes to Recognize Cations: A Theoretical Perspective

Cations have significant applications in fields such as medicinal inorganic chemistry and catalysis. Rotaxanes are composed of a macrocyclic structure that is mechanically interlocked with a linear molecule. These mechanically interlocked molecules (MIMs) provide a potential chemical environment that allows for the interaction with cations. In this study, the bonding situations between rotaxanes or their acyclic/cyclic molecular derivatives and: (i) transition metal (Zn²⁺ and Cd²⁺); or (ii) alkali metal (Li⁺, Na⁺, and K⁺), cations have been studied. It is notable that among the MIMs structures, the rotaxanes demonstrate enhanced interactions with cations in comparison to the cyclic and, notably, the acyclic derivative molecules. The modification of rotaxane structures through structural changes and chemical reduction represents an intriguing approach to enhance cationic recognition, which is supported by the formation of more favorable electrostatic and/or orbital interaction energies in comparison with Pauli repulsive energies. The findings of this investigation can be employed in the synthesis of compounds with enhanced cation recognition capabilities.