The construction of interlocked structures has long been an area of intensive research in supramolecular chemistry. While cationic species have been widely used to effect motion in molecules; the use of anions is extremely rare despite the fact that anions are key components in many biological and chemical processes. A collaboration between Paul Beer, from the University of Oxford, UK and Vitor Felix, from Universidade de Aveiro, Portugal has resulted in development of anion-induced molecular motion in an artificially constructed assembly.   

The crucial ring rotation process is induced by the deprotonation of a phenol moiety attached to the periphery of one of the two cyclic rings of the catenane. This leads to a half rotation of an anion recognising macrocycle, bringing it into association with the resultant phenolate ion.   

'Such interlocked structures capable of performing molecular motion have enormous potential as a basis for construction of molecular machines,' explains Beer. 'Multiple stations can be incorporated into these structures and external inputs such as changes in pH, redox, photo-activity and recognition of guest species can be employed to control the movements of one component relative to the other.' 

Beer also found that the binding of chloride ions inside the catenane's cavity inhibits the rotation movement. This chloride-controlled locking mechanism is an excellent switch to control the on and off molecular motion process. These systems have an exciting variety of potential applications in nanotechnology; for example in sensing, switching and molecular machine-like behaviour.    

Future challenge lies mainly with increasing the degree of complexity of such systems. This means a higher degree of sophistication is required both in the construction of these assemblies and in their mechanical directional control. 

Kathleen Too