Great expectations

November 25, 2011

Physicist Richard Feynman in his famous 1959 talk, "Plenty of Room at the Bottom," described the precise control at the atomic level promised by molecular machines of the future. More than 50 years later, synthetic molecular switches are a dime a dozen, but synthetically designed molecular machines are few and far between.

Northwestern University chemists recently teamed up with a University of Maine physicist to explore the question, "Can artificial molecular machines deliver on their promise?" Their provocative analysis provides a roadmap outlining future challenges that must be met before full realization of the extraordinary promise of synthetic molecular machines can be achieved.

The tutorial review will be published Nov. 25 by the journal Chemical Society Reviews.

The senior authors are Sir Fraser Stoddart, Board of Trustees Professor of Chemistry, and Bartosz A. Grzybowski, the K. Burgess Professor of Physical Chemistry, both in Northwestern's Weinberg College of Arts and Sciences, and Dean Astumian, professor of physics at the University of Maine. (Grzybowski is also professor of chemical and biological engineering in the McCormick School of Engineering and Applied Science.)

One might ask, what is the difference between a switch and a machine at the level of a molecule? It all comes down to the molecule doing work.

"A simplistic analogy of an artificial molecular switch is the piston in a car engine while idling," explains Ali Coskun, lead author of the paper and a postdoctoral fellow in Stoddart's laboratory. "The piston continually switches between up and down, but the car doesn't go anywhere. Until the pistons are connected to a crankshaft that, in turn, makes the car's wheels turn, the switching of the pistons only wastes energy without doing useful work."

Astumian points out that this analogy only takes us part of the way to understanding molecular machines. "All nanometer-scale machines are subject to continual bombardment by the molecules in their environment giving rise to what is called 'thermal noise,'" he cautions. "Attempts to mimic macroscopic approaches to achieve precisely controlled machines by minimizing the effects of thermal noise have not been notably successful."

Scientists currently are focused on a chemical approach where thermal noise is exploited for constructive purposes. Thermal "activation" is almost certainly at the heart of the mechanisms by which biomolecular machines in our cells carry out the essential tasks of metabolism. "At the nanometer scale of single molecules, harnessing energy is as much about preventing unwanted, backward motion as it is about causing forward motion," Astumian says.

In order to fulfill their great promise, artificial molecular machines need to operate at all scales. A single molecular switch interfaced to its environment can do useful work only on its own tiny scale, perhaps by assembling small molecules into chemical products of great complexity. But what about performing tasks in the macroscopic world?

To achieve this goal, "there is a need to organize the molecular switches spatially and temporally, just as in nature," Stoddart explains. He suggests that "metal-organic frameworks may hold the key to this particular challenge on account of their robust yet highly integrated architectures."

What is really encouraging is the remarkable energy-conversion efficiency of artificial molecular machines to perform useful work that can be greater than 75 percent. This efficiency is quite spectacular when compared to the efficiency of typical car engines, which convert only 20 to 30 percent of the chemical energy of gasoline into mechanical work, or even of the most efficient diesel engines with efficiencies of 50 percent.

"The reason for this high efficiency is that chemical energy can be converted directly into mechanical work, without having to be first converted into heat," Grzybowski says. "The possible uses of artificial molecular machines raise expectations expressed in the fact that the first person to create a nanoscale robotic arm, which shows precise positional control of matter at the nanoscale, can claim Feynman's Grand Prize of $250,000."
-end-
The title of the paper is "Great Expectations: Can Artificial Molecular Machines Deliver on Their Promise?" In addition to Stoddart, Grzybowski, Coskun and Astumian, the other co-author of the paper is Michal Banaszak from Adam Mickiewicz University, Poland.

Northwestern University

Related Molecules Articles from Brightsurf:

Finally, a way to see molecules 'wobble'
Researchers at the University of Rochester and the Fresnel Institute in France have found a way to visualize those molecules in even greater detail, showing their position and orientation in 3D, and even how they wobble and oscillate.

Water molecules are gold for nanocatalysis
Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals.

Water molecules dance in three
An international team of scientists has been able to shed new light on the properties of water at the molecular level.

How molecules self-assemble into superstructures
Most technical functional units are built bit by bit according to a well-designed construction plan.

Breaking down stubborn molecules
Seawater is more than just saltwater. The ocean is a veritable soup of chemicals.

Shaping the rings of molecules
Canadian chemists discover a natural process to control the shape of 'macrocycles,' molecules of large rings of atoms, for use in pharmaceuticals and electronics.

The mysterious movement of water molecules
Water is all around us and essential for life. Nevertheless, research into its behaviour at the atomic level -- above all how it interacts with surfaces -- is thin on the ground.

Spectroscopy: A fine sense for molecules
Scientists at the Laboratory for Attosecond Physics have developed a unique laser technology for the analysis of the molecular composition of biological samples.

Looking at the good vibes of molecules
Label-free dynamic detection of biomolecules is a major challenge in live-cell microscopy.

Colliding molecules and antiparticles
A study by Marcos Barp and Felipe Arretche from Brazil published in EPJ D shows a model of the interaction between positrons and simple molecules that is in good agreement with experimental results.

Read More: Molecules News and Molecules Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.