BUFFALO, N .Y. -- Using clever but elegant design, University at
Buffalo chemists have synthesized tiny, molecular cages that can be
used to capture and purify nanomaterials.
Sculpted from a special kind of molecule called a "bottle-brush
molecule," the traps consist of tiny, organic tubes whose interior
walls carry a negative charge. This feature enables the tubes to
selectively encapsulate only positively charged particles.
In addition, because UB scientists construct the tubes from
scratch, they can create traps of different sizes that snare
molecular prey of different sizes. The level of fine tuning
possible is remarkable: In the Journal of the American Chemical
Society, the researchers report that they were able to craft
nanotubes that captured particles 2.8 nanometers in diameter, while
leaving particles just 1.5 nanometers larger untouched.
These kinds of cages could be used, in the future, to expedite
tedious tasks, such as segregating large quantum dots from small
quantum dots, or separating proteins by size and charge.
"The shapes and sizes of molecules and nanomaterials dictate
their utility for desired applications. Our molecular cages will
allow one to separate particles and molecules with pre-determined
dimensions, thus creating uniform building blocks for the
fabrication of advanced materials," said Javid Rzayev, the UB
assistant professor of chemistry who led the research.
"Just like a contractor wants tile squares or bricks to be the
same size so they fit well together, scientists are eager to
produce nanometer-size particles with the same dimensions, which
can go a long way toward creating uniform and well-behaved
materials," Rzayev said.
To create the traps, Rzayev and his team first constructed a
special kind of molecule called a bottle-brush molecule. These
resemble a round hair brush, with molecular "bristles" protruding
all the way around a molecular backbone.
After stitching the bristles together, the researchers hollowed
out the center of each bottle-brush molecule, leaving behind a
structure shaped like a toilet paper tube.
The carving process employed simple but clever chemistry: When
building their bottlebrush molecules, the scientists constructed
the heart of each molecule using molecular structures that
disintegrate upon coming into contact with water. Around this core,
the scientists then attached a layer of negatively charged
carboxylic acid groups.
To sculpt the molecule, the scientists then immersed it water,
in effect hollowing the core. The resulting structure was the
trap—a nanotube whose inner walls were negatively charged due
to the presence of the newly exposed carboxylic acid groups.
To test the tubes' effectiveness as traps, Rzayev and colleagues
designed a series of experiments involving a two-layered chemical
The cocktail's bottom layer consisted of a chloroform solution
containing the nanotubes, while the top layer consisted of a
water-based solution containing positively charged dyes. (As in a
tequila sunrise, the thinner, water-based solution floats on top of
the denser chloroform solution, with little mixing.)
When the scientists shook the cocktail for five minutes, the
nanotubes collided with and trapped the dyes, bringing the dyes
into the chloroform solution. (The dyes, on their own, do not
dissolve in chloroform.)
In similar experiments, Rzayev and his team were able to use the
nanotubes to extract positively charged molecules called dendrimers
from an aqueous solution. The nanotubes were crafted so that
dendrimers with a diameter of 2.8 nanometers were trapped, while
dendrimers that were 4.3 nanometers across were left in
To remove the captured dendrimers from the nanotubes, the
researchers simply lowered the pH of the chloroform solution, which
shuts down the negative charge inside the traps and allows the
captured particles to be released from their cages.
The research on nanotubes is part of a larger suite of studies
Rzayev is conducting on bottle-brush molecules using a National
Science Foundation CAREER award. His other work includes the
fabrication of bottle-brush-based nanomembranes that could be
adapted for water filtration, and the assembly of layered,
bottle-brush polymers that reflect visible light like the wings of
a butterfly do.
The University at Buffalo is a premier research-intensive public
university, a flagship institution in the State University of New
York system and its largest and most comprehensive campus. UB's
more than 28,000 students pursue their academic interests through
more than 300 undergraduate, graduate and professional degree
programs. Founded in 1846, the University at Buffalo is a member of
the Association of American Universities.
Nanomembranes Made From Bottle-Brush Molecules Could Filter
Bacteria From Water: http://www.buffalo.edu/news/12288.