[nano] eurekalert: simulation studies of nanopropelling liquids

[Alejandro Dubrovsky]

(
http://www.eurekalert.org/pub_releases/2007-07/uoia-npp071607.php
)

Contact: Paul Francuch
francuch at uic.edu
312-996-3457
University of Illinois at Chicago
Nano propellers pump with proper chemistry

The ability to pump liquids at the cellular scale opens up exciting
possibilities, such as precisely targeting medicines and regulating flow
into and out of cells. But designing this molecular machinery has proven
difficult.

Now chemists at the University of Illinois at Chicago have created a
theoretical blueprint for assembling a nanoscale propeller with
molecule-sized blades.

The work is featured in Research Highlights in the July 12 issue of
Nature and was described in the June 28 cover story of Physical Review
Letters.

Using classical molecular dynamics simulations, Petr Král, assistant
professor of chemistry at UIC, and his laboratory coworkers were able to
study realistic conditions in this microscopic environment to learn how
the tiny propellers pump liquids.

While previous research has looked at how molecular devices rotate in
flowing gases, Král and his group are the first to look at molecular
propeller pumping of liquids, notably water and oils.

"We want to see what happens when the propellers get to the scale where
it's impossible to reduce the size of the blades any more," said Král.

Král's group found that at the molecular level -- unlike at the macro
level -- the chemistry of the propeller's blades and their sensitivity
to water play a big role in determining whether the propeller pumps
efficiently or just spins with little effect. If the blades have a
hydrophobic, or water-repelling nature, they pump a lot of water. But if
they are hydrophilic -- water-attracting -- they become clogged with
water molecules and pump poorly.

"Pumping rates and efficiencies in the hydrophilic and hydrophobic forms
can differ by an order of magnitude, which was not expected," he said.

The UIC researchers found that propeller pumping efficiency in liquids
is highly sensitive to the size, shape, chemical or biological
composition of the blades.

"In principle, we could even attach some biological molecules to the
blades and form a propeller that would work only if other molecules
bio-compatible with the blades are in the pumped solution," he said.

The findings present new factors to consider in developing nanoscale
liquid-pumping machines, but Král added that such technology probably
won't become reality for several years, given the difficult nature of
constructing such ultra-small devices.

Král's laboratory studies how biological systems, like tiny flagella
that move bacteria, offer clues for building motors, motile systems and
other nanoscale devices in a hybrid environment that combines biological
and inorganic chemistry.

"The 21st century will be about hybrid biological and artificial
nanoscale systems and their mutual co-evolution," Král predicts. "My
group alone is working on about a half-dozen such projects. I'm
optimistic about such nanoscale developments."

###

The PRL article was co-authored by UIC chemistry graduate student Boyang
Wang.