RESEARCH NEWS

With climate change firmly on the

global agenda, the need to burn

fossil fuels for power generation

directly conflicts with the desire to

reduce the emission of greenhouse

gases. One possible solution is

to capture CO2 and store it deep

underground. Hence there is a great

deal of interest in materials that can

capture CO2 both efficiently and

cheaply.

Now a team at the Pacific

Northwest National Laboratory

(PNNL) in Washington, University

of Missouri–Columbia and the

Università di Salerno in Italy has

discovered a porous organic solid

that can capture 6.9 wt.% of CO2 at

room temperature and pressure, which is significantly

better than commercially available materials, they

claim [Thallapally et al., Chem. Mater. (2007) 19,

3355]. For comparison, Selexol, an industrial solvent

for removing acid gases, absorbs only 3 wt.% of CO2

at high pressure, which reduces the overall energy

efficiency of the process.

The new material, 1,2-dimethyoxy-p-tert-butylcalix-

[4]dihydroquinone, self-assembles via Van der Waals

forces and hydrogen bonding with

water molecules to form a crystal

containing both water-filled channels

and unoccupied lattice voids within

the structure. Six molecules stack

in a circular fashion to form a

supramolecular unit, which is in

turn linked octahedrally to six more

supramolecular units around it

(as shown). The structure remains

intact when the water molecules are

removed by heating, leaving a porous

solid with an estimated free volume

of 988 Å3 per unit cell.

Although higher gas sorption has

been reported for metal-organic

frameworks, organic crystals can

have the advantage of being gas

selective. This new compound shows no detectable

absorption of hydrogen gas at 20 atm pressure.

“High selectivity for CO2 over hydrogen is an

important requirement if these materials are to

be used for separation of flue gases”, says Praveen

Thallapally of PNNL. Future work will investigate new

materials, focusing on those that show selectivity to

gases including CO2, NOx, SO2, and H2S.

Pauline Rigby

A space-filling model of

calix[4]dihydroquinone. Void space

is shown in yellow. (Courtesy of

Praveen Thallapally.)

Scientists at Virginia Commonwealth

University (VCU) and Luna Innovations

have discovered a new biological

function for fullerenes – the ability

to inhibit the basic inflammatory

response in an allergic reaction [Ryan

et al. J. Immunol. (2007) 179, 665].

This could lead to new therapies for

a range of conditions from hayfever

to autoimmune diseases such as

inflammatory arthritis.

Mast cells are present in all tissues

except blood. They are packed with

granules containing histamine, which is

rapidly released in an allergic reaction

along with other inflammatory

substances. Histamine-containing cells

in the blood are known as peripheral

blood basophils (PBBs).

The researchers found that human

mast cells and PBBs incubated with

modified water-soluble fullerenes

release significantly less histamine

and cytokine in response to an

antigen compared with those that

have not. The researchers report that

an injection of fullerenes prevents

anaphylaxis in mice, and does not

appear to be toxic to them.

Immunohistochemistry staining on

the human cells shows that most

of the fullerenes are located within

the cytoplasm, suggesting that the

inhibitory mechanism operates

inside the cell. “Unlike most allergy

medications out there, these molecules

turn off the allergic cells before the

allergic mediators are released” says

Christopher L. Kepley of VCU.

The exact mechanism has not been

fully investigated, although the

researchers believe that the powerful

antioxidant properties of fullerenes

may play an important role.

The next step is to modify the

fullerene molecules with functional

groups so that they target only the

mast cell and PBB.

Pauline Rigby

Fullerenes can’t be sneezed atNANOMEDICINE

Organic crystals capture CO2POROUS MATERIALS

Oxide phase separation produces chessboard pattern

Researchers have previously observed,

but been unable to explain, complex

satellite reflections in the diffraction

patterns of the perovskite-based Li ion

conductor (Nd2/3-xLi3x)TiO3. A team from

from the University of Pennsylvania have

now shown that this effect is the result

of periodic two-dimensional nanoscale

phase separation [Guiton and Davies, Nat.

Mater. (2007), doi:10.1038/nmat1953].

The resulting superlattices could be used

as templates for bottom-up fabrication of

nanostructures or molecular monolayers.

Transmission electron microscopy

(TEM) with the electron beam parallel to [001] of several

(Nd2/3-xLi3x)TiO3 powder samples (range 0.047 < x < 0.151)

reveal two distinct contrast patterns with identical periodicity:

a nanoscale chessboard and a diamond design. Higher-

resolution TEM images show the two patterns simultaneously,

suggesting that they represent aspects of the same structural

feature.

Z-contrast imaging shows that the

diamond patterning is a result of the oxide

undergoing phase separation into Li-rich

squares and Li-poor boundary regions. By

varying the ratio of Nd to Li in the bulk,

the periodicity of the patterns can be

controlled. Estimates of the composition

of the two phases, made from TEM

images, were verified using multislice

simulations.

“Spontaneous phase separation with

such long range periodicity has not, to

our knowledge, been observed previously

in any inorganic material,” says Beth

S. Guiton. “It is particularly interesting in this case because

it occurs both on the nanometer length scale and two

dimensionally.” The range of ordering and the ability to tune

unit cell dimensions implies that inexpensive standard ceramic

processing methods could be used to engineer nanostructures

with great precision.

Paula Gould

NANOSTRUCTURED MATERIALS

TEM images of chessboard- and

diamond-type superlattice contrast.

(© 2007 Macmillan.)

AUGUST 2007 | VOLUME 2 | NUMBER 4 9

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