Executive Summary Final - the Center for Nanoscale Science - an ...

IRG2: Powered Motion at the Nanoscale
IRG2: Powered Motion at the Nanoscale
Faculty: P. Butler, V. H. Crespi, T. J. Huang, T. E. Mallouk, A. Sen, D. Velegol, K. F. Kelly
(Rice), J. M. Tour (Rice), and P. S. Weiss (UCLA).
Students and Postdocs: Michael Ibele (Ph.D. 2010), Shakuntala Sundararajan (Ph.D. 2010),
Yang Wang (Ph.D. 2010), Shraddha Surve (M.S. 2010), Joseph McDermott, Ryan Pavlick,
Samudra Sengupta, Wei “Tiger” Wang, Amir Nourhani, Young-Moo Byun, Bala Krishna Pathem,
Ajeet Kumar, Tomohide Takami, Qingzhen Hao, Paul Lammert, Bala Krishna Juluri, Yue Bing
Zheng, Jinjie Shi, Yanhui Zhao, Yanjun Liu, Pin-Lei Edmund Chu (Rice) Tsong Chiang (Rice),
Jazmin Godoy-Vargas (Rice), Guillaume Vives (Rice), Jason M. Guerrero (Rice).
External Collaborators: Ubaldo. M. Córdova-Figueroa (Univ. Puerto Rico), Misael Diaz
(Univ. Puerto Rico).
Goals: IRG2 aims to control autonomous motion of objects spanning from the nano to the
microscale, to attack one of the grand challenges in science: How can we master energy and
information on the nano and microscale to create new technologies with capabilities ultimately
rivaling those of living things?
Catalytic motors are a novel class of nano- and microscale particles and assemblies that convert
chemical energy to mechanical forces. In the absence of information in the form of gradients,
individual motors move in random direction. In the presence of magnetic fields, or chemical,
ionic or light gradients they move directionally, exhibiting the phenomenon of taxis. The
observed movement is in accord with transport physics studied and modeled by our groups.
Collectively the motors give more complex behaviors, such as schooling or predator-prey
phenomena due to motor-motor interactions of diverse origin, such as overlapping ion gradients
generated by reactions at the motors’ surfaces. Because of the continuous input of energy, these
are driven systems that operate far from equilibrium. Many of the observed behavior are
strikingly similar to those in living systems and can be modeled accordingly.
The IRG has made several significant discoveries in catalytic motors over the past year. We have
discovered that individual nanometer-scale catalyst molecules, such as enzymes, display
enhanced movement in the presence of substrates, motion that increases with substrate
concentration. Further, this increase is attenuated by the addition of an inhibitor. The microscopic
origin of this enhanced movement – whether due to an imbalanced local environment (for
e.g. charged reactants or products) or modulations in local viscosity or otherwise – is an area of
current investigation. The observation of increased movement of molecular catalysts when they
are turning over substrates may alter our view of catalysis in a fundamental way. It is now
accepted that many molecular machines in living systems – proteins that perform crucial tasks of
life, from shuttling molecules through membranes to reading information off of DNA – function
as Brownian ratchets. They are powered through catalysis and it is conceivable that the
movements of these enzyme-based biological machines are facilitated by their increased
diffusion rates in the presence of substrates. The work on single catalyst molecules will link the
nano-scale molecular motors with micro-scale catalytic motors as we scale up from single
catalyst molecules (enzymes) to the same catalysts tethered to micro-scale objects.