1. Department of Chemistry, E. F. Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, USA

Correspondence to: T. Ross Kelly Correspondence and requests for materials should be addressed to T.R.K. (e-mail: Email: ross.kelly@bc.eduEmail: ).

Abstract

The conversion of energy into controlled motion plays an important role in both man-made devices and biological systems. The principles of operation of conventional motors are well established, but the molecular processes used by 'biological motors' such as muscle fibres, flagella and cilia^{1, 2, 3, 4, 5, 6, 7, 8, 9} to convert chemical energy into co-ordinated movement remain poorly understood^{10, 11, 12}. Although 'brownian ratchets'^{13, 14, 15, 16} are known to permit thermally activated motion in one direction only, the concept of channelling random thermal energy into controlled motion has not yet been extended to the molecular level. Here we describe a molecule that uses chemical energy to activate and bias a thermally induced isomerization reaction, and thereby achieve unidirectional intramolecular rotary motion. The motion consists of a 120° rotation around a single bond connecting a three-bladed subunit to the bulky remainder of the molecule, and unidirectional motion is achieved by reversibly introducing a tether between the two units to energetically favour one of the two possible rotation directions. Although our system does not achieve continuous and fast rotation, the design principles that we have used may prove relevant for a better understanding of biological and synthetic molecular motors producing unidirectional rotary motion.