UCLA supramolecular chemists report in the journal Science an artificial molecular machine that functions like a nanoelevator.
"Such nanoscale robotic devices could find use in slow-release drug delivery systems and in the control of chemical reactions within nanofluidic systems conducted in laboratories on a chip," said Jovica Badjic, postdoctoral researcher in the laboratory of Fraser Stoddart, holder of the Fred Kavli Chair in nanosystems sciences and director of the California NanoSystems Institute at UCLA.
In Badjic's incrementally staged design of the nanoelevator — a rig-like construct with three legs embracing an interlocked deck-like component, can be made to move between two levels, he had to get the matching components to fit together just perfectly.
The challenge is similar to one that nature has already solved in creating the multivalent interactions that exist between cells for the purpose of communicating information throughout the body.
"The first step in the synthesis can be likened to learning how to put a glove on one's hand blindfolded. You will make countless mistakes but eventually you find out by trial and error how to get the match just right. That's how the multivalency gets expressed during my template-directed synthesis," Badjic said.
In order to demonstrate the operation of the elevator, the UCLA chemists entered into collaboration with an Italian team at the University of Bologna: professor Vincenzo Balzani, assistant professor Alberto Credi and graduate student Serena Silvi.
The elevator is about 3.5 nanometers in diameter and 2.5 nanometers in height. Each leg of the rig has two stations — one, a strong one, which relies on hydrogen bonds, and another much weaker one. The strong hydrogen bonds between the rig and the deck can be destroyed by taking a proton away from each leg one at a time with base. The result is a stepwise movement of the deck down to the now preferred stations lower down the rig. By taking steps one at a time, the elevator is more reminiscent of a legged animal than it is of a passenger elevator. The deck can be returned to the top level by the addition of acid. The elevator has been made to go up and down 10 times by the consecutive addition of acid and base, respectively.
Although it has been commented in the article that distance traveled by the deck is just a little less than one nanometer, 1,000 times smaller than the thickness of a human hair, and that the force generated could be as much as 200 picoNewtons, Stoddart urged caution with respect to this claim, based on calculations carried out in Bologna, until it is backed up by experiments, and also by an all-encompassing theory.