Synthetic Molecular Motors

The fascinating molecular motors ubiquitous in biological systems offer a great source of inspiration for the design of artificial motors and in the quest to achieve controlled movement at the molecular level. Synthetic chemists are involved in the challenging endeavor to exploit ormimic the properties of these intriguingmolecules found in nature. Movement in biological systems can be divided into linear motion, as found in, for example, kinesin and myosin (Vale and Milligan, 2000) or RNA polymerase (Yin et al., 1995), and rotary motion found in bacterial flagella (Berg and Anderson, 1973) or the F1-ATPase motor (Boyer, 1998, Walker, 1998). Nature’s sophisticated examples of (supra)molecular motors and especially the stunning direct observation of rotation for F1-ATPase (Noji et al., 1997) are a great stimulus for the synthetic chemist trying to mimic these systems. The major objective in designing amolecular motor is to generate controlledmotion which is different fromBrownian motion. In a molecular motor consumption of energy should result in controlled translational or rotary motion. Such motion could eventually enable a device to perform mechanical work, a particularly challenging goal in the context of future nanotechnology (Whitesides and Love, 2001). So far, only relatively simple artificial synthetic motors have been constructed. Also in these cases, one can roughly distinguish between linear molecular motors showing (intra)molecular translation and rotary molecular motors showing (unidirectional) (intra)molecular rotation. Translational and rotary motors will be treated separately in this chapter.