title: Optimizing rotary processes in synthetic molecular motors.
abstract: We deal with the issue of quantifying and optimizing the rotation dynamics of synthetic molecular motors. For this purpose, the continuous four-stage rotation behavior of a typical light-activated molecular motor was measured in detail. All reaction constants were determined empirically. Next, we developed a Markov model that describes the full motor dynamics mathematically. We derived expressions for a set of characteristic quantities, i.e., the average rate of quarter rotations or "velocity," V, the spread in the average number of quarter rotations, D, and the dimensionless Péclet number, Pe = V/D. Furthermore, we determined the rate of full, four-step rotations (Omega(eff)), from which we derived another dimensionless quantity, the "rotational excess," r.e. This quantity, defined as the relative difference between total forward (Omega(+)) and backward (Omega(-)) full rotations, is a good measure of the unidirectionality of the rotation process. Our model provides a pragmatic tool to optimize motor performance. We demonstrate this by calculating V, D, Pe, Omega(eff), and r.e. for different rates of thermal versus photochemical energy input. We find that for a given light intensity, an optimal temperature range exists in which the motor exhibits excellent efficiency and unidirectional behavior, above or below which motor performance decreases.
authors.affiliation: Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands.
authors.forename: Edzard M
authors.initials: EM
authors.lastname: Geertsema
authors.forename: Sense Jan
authors.initials: SJ
authors.lastname: van der Molen
authors.forename: Marco
authors.initials: M
authors.lastname: Martens
authors.forename: Ben L
authors.initials: BL
authors.lastname: Feringa
mesh_terms: D000465:Algorithms; D006841:Hydrocarbons, Aromatic / Q000138:chemical synthesis* / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D049329:Nanostructures / Q000737:chemistry; D012399:Rotation; D013237:Stereoisomerism
chemical_list: D006841:Hydrocarbons, Aromatic