In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, James Tour, Stephan Link and Angel Marti of the William Marsh Rice University will develop and study molecules that exhibit controlled motion on a surface, "nanocars". The approach is to synthesize "nanocars" that incorporate fluorescent moieties within their frameworks and to continue expanding the repertoire of molecular parts that can be used to build these molecules. The PIs will also incorporate molecular entities into the "nanocars" that exhibit photon driven rotation and may acts as a propulsion mechanism for the molecules. Finally, the PIs will develop optical microscopy methods for tracking and characterizing the translation motion of the individual molecules and to utilize these methods to measure quantities such as collision frequencies and diffusion coefficients. The broader impacts involve training undergraduate students, graduate students and postdoctoral researchers. Additionally, the PIs plan to develop informal science learning approaches aimed at middle school students. Major principles in book chapters from middle school science curricula will be translated into bullet points, developed into dance songs (with professional help) and then added to open source Step Mania and Jamming software packages.
This work will enhance our fundamental understanding about controlling individual molecular movement across a surface. Ultimately, such work could lead to the development of molecular machines that could control chemical transport and fabrication at ultrasmall dimensions.
Biological machines such as RNA polymerase, ATP synthase and linear Kinesin that convert chemical energy to mechanical work inspired scientists to develop artificial nanomachines. For example rotatory motors, switches, shuttles, and nanovehicles. A family of nanovehicles, named nanocars has been developed, aiming to roll on surface and do work at the nanoscale. The challenges are how to convert energy inputs into controlled molecule transportation. In 2006, we reported the first light-driven motorized nanocar. The design included a unidirectional-rotatory motor, capable to rotate at 1.8 rotations per hour at 60 °C, and an oligo(phenylene ethylene) chassis and axle system with four carboranes to serve as the wheels. Later we reported the synthesis of a nanocar with a ~3 MHz rotation speed. We have also reported the synthesis of the first chemically-propelled nanocars. The propulsion was generated by a ring-opening metathesis polymerization (ROMP) that was achieved by incorporation of a Hoveyda-Grubbs catalyst.Although there are many examples of synthetic light-driven rotatory motors, their potential to promote solution-phase locomotion at the molecular level remains unexplored. However, it has been reported the diffusion enhancement in solution using micromotors, for example bimetallic nanowires that are propelled by the catalytic dismutation of H2O2, silica particles equipped with a H2O2 disproportionation catalyst and gold-silica Janus particles functionalized with a Grubbs catalyst propelled by ROMP process. Nevertheless, these machines are in the micrometer scale and the increase in diffusion of single molecules by chemical propulsion have been not reported. Motivated by the plethora of opportunities to generate work by single molecules, specifically, translational movement in solution, we are working in the development of new self-propelled nanomachines capable to increase its diffusion in response to energy inputs. At the nanometer scale the monitoring and tracking of nanomachines is a very difficult task to perform using optical techniques. In the past, scanning tunneling microscopy (STM) was used trying to track nanocars; however it was a time-consuming approach and required difficult imaging conditions. Therefore, alternative techniques are preferred. Using single molecule fluorescence microscopy (SMFM) we were able to monitor the motion of fluorescent nanocars on surfaces under ambient conditions. Nevertheless, it cannot be applied to imaging nanomachines in solution because they drift quickly out of focus producing trajectories that are too short to obtain accurate diffusion constants. The project has led to the synthesis of many new molecules and their analyses, most of which has been published in peer-reviewed journals. The project has also led to the education of several graduate students, with at least 3 obtaining Ph.D.s and others working toward their theses, clearly demonstrating the intellectual merit of the project. In addition, undergraduates have been trained in complex synthetic work during summer terms. All students have been trained in safe laboratory procedures, synthetic methods, use of complex analytical instruments and the presentation of their work to others. Broader impacts include educational outreach to grades K through 8 through the SciRave.org and STEMscopes.com web sites. There were almost 2 million visits to the STEMscopes web site from 2012 to 2014.
