This new design works a bit like a molecular Sterling Cycle. A new miniature Sterling Engine seems very impressive – Deskarati
By using light to change the elasticity of a DNA molecule, scientists have designed a molecular motor that can turn light into mechanical work. Unlike most previously reported molecular motors, the proposed setup involves an atomic force microscope, which acts as an interface with the outside world and enables the work to be extracted.
The researchers, Martin McCullagh, Ignacio Franco, Mark A. Ratner, and George C. Schatz, from the Department of Chemistry and the Non-equilibrium Energy Research Center (NERC) at Northwestern University, have published their study in a recent issue of the Journal of the American Chemical Society.
The molecule that the scientists propose using as the central component of the motor is a DNA hairpin that includes two guanine-cytosine base pairs capped by an azobenzene compound. The scientists designed a computational model of the system including the attachment of one end of the DNA hairpin to a surface and the other end to an atomic force microscope coupled to a cantilever.
“The greatest significance of this work is showing how the structure of DNA can be exploited to amplify the transduction ability of azobenzene in a setup in which the work can be extracted,” Schatz told PhysOrg.com. “To our knowledge, this is the first proposed DNA-based molecular motor with an interface to the outside world.”
In their molecular dynamics simulations, the researchers used light to change the structure of the azobenzene. In this process, called “isomerization,” the DNA-motor reversibly changes between the cis isomer and the trans isomer. Although this photoinduced isomerization is only a structural change, it has important implications, such as changing the length of the molecule (the trans isomer is longer) and altering the stability of the bonds between the guanine and cytosine bases (the trans isomer’s intra base pair interactions are stable across a greater range of lengths).
As the chemists showed, these two differences between the cis and trans isomers alter the molecule’s elasticity, and can be exploited to extract work from the system. For modest extensions, the trans isomer of the DNA hairpin is stiffer because it has a geometry that favors DNA base pairing, which makes it more difficult to extend the DNA hairpin.