Science + Technology

UCLA Chemists Create Nano Valve


UCLA chemists have created the first nanovalve that can be opened and closed at will to trap and release molecules. Thediscovery, federally funded by the National Science Foundation, will bepublished July 19 in the Proceedings of the NationalAcademy of Sciences.

"This paper demonstrates unequivocally that the machineworks," said Jeffrey I. Zink, a UCLA professor of chemistry and biochemistry, amember of the California NanoSystemsInstitute at UCLA, and a member of the research team. "With the nano valve, we can trap and release molecules on demand. Weare able to control molecules at the nano scale.

"A nano valve potentially could beused as a drug delivery system," Zink said.

"The valve is like a mechanical system that we can controllike a water faucet," said UCLA graduate student ThoiNguyen, lead author on the paper. "Trapping the molecule inside and shuttingthe valve tightly was a challenge. The first valves we produced leakedslightly."

"Thoi was a master nano plumber who plugged the leak with a tight valve," Zinksaid.

This nano valve consists of moving parts —switchable rotaxanemolecules that resemble linear motors designed by California NanoSystems Institute director Fraser Stoddart's team — attached to atiny piece of glass (porous silica), which measures about 500 nanometers, andwhich Nguyen is currently reducing in size. Tiny pores in the glass are only afew nanometers in size.

"It's big enough to let molecules in and out, but smallenough so that the switchablerotaxane molecules can block the hole," Zinksaid.

The valve is uniquely designed so one end attaches to theopening of the hole that will be blocked and unblocked, and the other end has the switchable rotaxanes whose movable component blocks the hole inthe down position and leaves it open in the up position. The researchers usedchemical energy involving a single electron as the power supply to open andshut the valve, and a luminescent molecule that allows them to tell fromemitted light whether a molecule is trapped or has been released.

Switchable rotaxanes are molecules composedof a dumbbell component with two stations between which a ring component can bemade to move back and forth in a linear fashion. Stoddart,who holds UCLA's Fred Kavli Chair in nanosystems sciences, has already shown how these switchable rotaxanes can be usedin molecular electronics. Stoddart's team is nowadapting them for use in the construction of artificial molecular machinery.

"The fact that we can take a bistablemolecule that behaves as a switch in a silicon-based electronic device at the nanoscale level and fabricate it differently to work aspart of a nano valve on porous silica is something Ifind really satisfying about this piece of research," Stoddart,said. "It shows that these little pieces of molecular machinery are highlyadaptable and resourceful, and means that we can move around in the nanoworld with the same molecular tool kit and adapt it todifferent needs on demand."

In future research, they will test how large a hole they canblock, to see whether they can get larger molecules, like enzymes, inside thecontainer; they are optimistic.

The research team also includes Hsian-RongTseng, a former postdoctoral scholar in chemistry who is now an assistantprofessor of molecular and medical pharmacology in UCLA's David Geffen Schoolof Medicine; Paul Celestre, a former undergraduatestudent in Stoddart's laboratory; AmarFlood, a former UCLA researcher in Stoddart's supramolecular chemistry group who is now an assistantprofessor of chemistry at Indiana University; and YiLiu, a former UCLA graduate student who is now a postdoctoral scholar at theScripps Research Institute in La Jolla.

"Ourteam and Fraser's have very different areas of expertise," Zink said. "Bycombining them and working together we were able to make something new thatreally works."

Stoddart has noted that it is onlyin the past 100 years that humankind has learned how to fly. Prior to the firstdemonstration of manned flight, there were many great scientists and engineerswho said it was impossible.

"Building artificial molecular machines and getting them tooperate is where airplanes were a century ago," Stoddartsaid. "We have come a long way in the last decade, but we have a very, verylong way to go yet to realize the full potential of artificial molecularmachines."

The nano valve is much smallerthan living cells. Could a cell ingest a nano valvecombined with bio-molecules, and could light energy then be used to release adrug inside a cell? Stay tuned.



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