Colloquium on November 16, 2009

Dean Astumian
University of Maine

Thermodynamics and kinetics of molecular motors

Protein molecular motors—perfected over the course of millions of years of evolution—play an essential role in moving and assembling biological structures. Recently chemists have been able to synthesize molecules that emulate in part the remarkable capabilities of these biomolecular motors (for extensive reviews see the recent papers: E. R. Kay, D. A. Leigh and F. Zerbetto, Angew. Chem., Int. Ed., 2006, 46, 72–191; W. R. Browne and B. L. Feringa, Nat. Nanotechnol., 2006, 1, 25–35; M. N. Chatterjee, E. R. Kay and D. A. Leigh, J. Am. Chem. Soc., 2006, 128, 4058–4073; G. S. Kottas, L. I. Clarke, D. Horinek and J. Michl, Chem. Rev., 2005, 105, 1281–1376; M. A. Garcia- Garibay, Proc. Natl. Acad. Sci., U. S. A., 2005, 102, 10771–10776)). Like their biological counter- parts, many of these synthetic machines function in an environment where viscous forces dominate inertia—to move they must ‘‘swim in molasses’’. Further, the thermal noise power exchanged rever- sibly between the motor and its environment is many orders of magnitude greater than the power provided by the chemical fuel to drive directed motion. One might think that moving in a specific direction would be as difficult as walking in a hurricane. Yet biomolecular motors (and increasingly, synthetic motors) move and accomplish their function with almost deterministic precision and very high efficiency. By using chemical design to control the labilities of transitions, and the relative stabilities of states, it is possible to constructively use thermal noise and viscous drag to create a motor that, in the presence of energy input, carries out the function of a motor with high efficiency and power output.