Chemical & Engineering News Digital Edition - January 11, 2010

write. The researchers acknowledge that
it is presently unclear how universal this
mechanism is and to what extent nature exploits
it in facilitating protein degradation.
They add that ubiquitin’s effect on protein
folding might be relevant to other cellular
processes regulated by the polypeptide, including
DNA repair and endocytosis. —SLR
SPEEDY NONLINEAR
OPTICAL ANALYSIS
Combining a novel laser-probe method
with a fast data-analysis technique enables
scientists to rapidly differentiate chemically
distinct thin films solely on the basis
of subtle differences in the optical properties,
according to a research team at Purdue
University ( Anal. Chem., DOI: 10.1021/
ac901832u). Changes in the polarization
of light reflected from thin films can serve
as a probe of the structure, orientation,
and symmetry of molecules at the film’s
surface. Yet those measurements can take
hours to complete. Purdue’s Nathan J.
Begue and Garth J. Simpson report that polarization
measurements can now be made
in fractions of a second by using a surfacesensitive
method they developed known
as nonlinear optical Stokes ellipsometry.
Time-consuming data analysis based on
traditional nonlinear curve fitting likewise
can be sped up by orders of magnitude,
they say, by combining linear curve fitting
with a statistical technique known as principal
component analysis. The researchers
showed that the new combination can be
used to quickly distinguish among monolayer
films of four similar dyes. The team
plans to apply the technique to probing
crystal polymorphism. —MJ
ATOM VERSUS
SUPERATOM
The concept of superatoms—molecules or
collections of atoms that behave like a single
atom—has received a boost from a new
photoelectron imaging spectroscopy study
( Proc. Natl. Acad. Sci. USA, DOI: 10.1073/
pnas.0911240107). A. Welford Castleman
Jr., Samuel J. Peppernick, and K. D. Dasitha
Gunaratne of Pennsylvania State University
compared the electron angular distributions
and electron-binding energies of
several diatomic molecules and their isoelectronic
atomic counterparts—titanium
monoxide versus nickel, zirconium mon-
SCIENCE & TECHNOLOGY CONCENTRATES
The binding
energies of electrons
in Ni – (top) and
a TiO – molecule
(bottom), shown
by bright spots, are
similar in these
photoelectron
images.
oxide versus palladium,
and tungsten
carbide versus
platinum. They
found the electronic
properties are
almost identical in
each case, suggesting
that an atom’s
corresponding
superatoms can be
predicted by simply
looking at the periodic
table and finding
combinations
that collectively
have the same
number of outershell
electrons as
the single atom,
Castleman says.
Although the study confirms the electronic
similarity of some transition-metal atoms
and their corresponding superatoms, the
researchers are now working to determine
if the similarities extend to the rest of the
periodic table and to atom-superatom
chemical reactivities. A periodic table of
superatoms could have many uses, the
researchers say. For example, tungsten carbide
has been shown to exhibit reactivity
similar to the much more expensive workhorse
catalyst platinum. —EKW
INFECTIOUS PRIONS
MUTATE STRUCTURALLY
Conversion of normal prion protein into
a misfolded, infectious form has generally
been viewed as a one-to-one process in
which each strain of prion protein misfolds
into a specific form. But in unexpected
findings with implications for drug design,
researchers have discovered that misfolded
prions can refold and thus evolve structurally.
Charles Weissmann and coworkers
of Scripps Florida report that prions from
infected brain cells change their properties,
and by implication their structures,
when transferred to cultured cells and
then change further when transferred back
( Science, DOI: 10.1126/science.1183218).
They also found that, in the presence of the
prion-inhibiting drug swainsonine, infectious
prions evolve into a drug-resistant
form. Prion diseases such as mad cow
disease and Creutzfeldt-Jakob disease in
people are lethal and incurable, so drugs
to fight the conditions are being sought.
WWW.CEN-ONLINE.ORG 34 JANUARY 11, 2010
COURTESY OF WELFORD CASTLEMAN
ACS APPL. MATER. INTERFACES
Weissmann and coworkers suggest that in
view of the newfound ability of infectious
prions to mutate and potentially evade
drugs designed against them, it might be
best to design drugs that target normal
prion protein instead of the shape-shifting
infectious forms. —SB
CLAY-POLYMER
NANOLAYERS IMPROVE
GAS-BARRIER FILMS
A composite sheet composed of alternating
nanolayers of clay and polymer could
provide improved transparent and flexible
gas-barrier films to protect electronics,
food, and pharmaceutical products, report
Morgan A. Priolo, Daniel Gamboa, and
Jaime C. Grunlan of Texas A&M University
A TEM image reveals the 40 bilayers of a
gas-barrier film made from clay platelets
(red) layered with polyethylenimine (blue)
on a polyethylene terephthalate substrate.
( ACS Appl. Mater. Interfaces, DOI: 10.1021/
am900820k). Currently, such films are
made from inorganic oxides, which are
prone to cracking, and bulk clay-polymer
composites, which offer poor transparency
and serve as only a weak barrier to gases
such as oxygen in the air. Grunlan and colleagues
tried a new approach by layering
sodium montmorillonite clay platelets with
branched polyethylenimine, tuning the
thickness of the polymer layers by adjusting
the pH of the solution. The researchers
liken the structure of the films to that of
a brick wall, with the clay platelets as the
bricks and the polymer as the mortar. A film
of 70 clay-polymer bilayers, 231 nm thick
when prepared at pH 10, remains flexible
and transparent and has oxygen permeability
lower than that reported for other claypolymer
composites, the researchers say.
Grunlan’s group is working toward developing
gas barriers with fewer layers to make
the composite sheets even more attractive
for commercial applications. —JK