RIVERSIDE – There is a basic similarity between some molecules and some racehorses, scientists at UC Riverside have learned, and although molecules have been around longer than racehorses, they haven’t developed nanosized parimutuel betting and you won’t find them in the morning line (by the way nanometers are one billionth of a meter).
On the molecular side there are trotters and pacers just as there are in harness racing. Trotters travel by advancing opposite legs. For example, the left foreleg moves with the right rear leg and then it’s right foreleg and left rear leg. Pacers move both legs on the same side at the same time. There’s another similarity between molecules and the equine breeds, the pacers are faster than trotters but neither has to pull carts and drivers. There are no molecular sulkies, but the molecules can definitely carry the weight.
But most of the similarities end about here . . . at the door of Ludwig Bartels lab at UCR. “In our work,” the professor of chemistry said, “we want to understand what the basic principles mechanics are for machines that are only one molecule in size.
“We made a horse-like structure with four ‘hooves’ to study how molecular machinery can organize the motion of multiple parts,” said Bartels, whose lab led the research. “A couple of years ago, we discovered how we can transport carbon dioxide molecules along a straight line across a surface using a molecular machine with two ‘feet’ that moved one step at a time. For the new research, we wanted to create a species that can carry more cargo – which means it would need more legs. But if a species has more than two legs, how will it organize their motion?”
“Nature uses such machines everywhere: the acid in your stomach is created by a proton pump in the cells lining your stomach. In every cell proteins are dragged to the places where they are needed by kinesin motors . . .” Bartels said. A web definition of kinesin: any of a class of proteins that convert chemical into mechanical energy and power movement along microtubules.
Such motors are too big for his work, Bartels said. They can be modeled but if they they behave like real world machines, different rules may apply.
Bartels and his colleague Mike Marsella “make molecules that are sufficiently small that we can understand them and which behave like walkers and carriers.” Their set up – working on a flat copper surface – is simpler than using biology, he said. “It allows us to image and understand their motion in detail.”
“My group develops instrumentation to image molecular motion at surfaces; we also use simulation software to simulate their behavior, so that we can draw conclusion why they behave as we see them behave. This software runs on supercomputers. In the case of this study, the bulk of the calculations were done on computers of the NCSA computer center, which is part of the NSF Teragrid of supercomputer resources available to US institutions of higher education.
A couple of years ago, he said, they found a simple molecule – anthraquinone – which could not only walk in a straight line across the copper surface, it could carry carbon dioxide molecules. It was bipedal, like a man. They were excited at the cargo carrying ability and mystified by its speed. In order to slow it down, they had to cool it to minus-300 degrees Farenheit. They wanted a molecule that moved slower and was easier to study, he said. That was pentacenetetrone, which proved to have four legs, remember the horses, instead of two. They expected it to be slower, Bertals said, but it proved to be a million times slower. It required much less cooling to observe the motion of the molecule.
It was then they learned the difference between the pacers and the trotters in speed at the molecular level. The trotter required much more torsion in order to move ahead, which put it at a disadvantage..
But even the pacer was a million times slower than the bipedal molecule, Bartels said. The two-legged molecule was able to tunnel its way through the rough surface and the less coordinated quadripedal molecule had to drag its burden over the bumps instead of through. Try moving a double-door fridge from the U-Haul down a rocky driveway and around to the back stairs and into the house. You’ll get the idea no matter how many legs you have.
More tests on more molecules lie ahead to learn their speed and carrying capacity. Some will be linked, giving them more legs going from a pacer to a molecular centipede.
Visit the university web site and see moving models of the molecular pacers and trotters by going to http://newsroom.ucr.edu/news_item.html?action=page&id=2423
