Unidirectional rotary motion in a molecular system

The conversion of energy into controlled motion plays an important role in both man-made devices and biological systems. The principles of operation o f conventional motors are well established, but the molecular processes use d by 'biological motors' such as muscle fibres, flagella and cilia(1-9) to convert chemical energy into co-ordinated movement remain poorly understood (10-12). Although Brownian ratchets'(13-16) are known to permit thermally a ctivated motion in one direction only, the concept of channelling random th ermal energy into controlled motion has not pet been extended to the molecu lar level. Here we describe a molecule that uses chemical energy to activat e and bias a thermally induced isomerization reaction, and thereby achieve unidirectional intramolecular rotary motion. The motion consists of a 120 d egrees rotation around a single bond connecting a three-bladed subunit to t he bulky remainder of the molecule, and unidirectional motion is achieved b y reversibly introducing a tether between the two units to energetically fa vour one of the two possible rotation directions. Although our system does not achieve continuous and fast rotation, the design principles that we hav e used may prove relevant for a better understanding of biological and synt hetic molecular motors producing unidirectional rotary motion.