February 27, 2012 - IMM@BUCT

SCIENCE & TECHNOLOGY CONCENTRATES
substitution had little effect on the compound’s
ability to bind to luciferase, but it
had less light output than amino- d -luciferin
in in vitro studies, in part because of its
lower quantum yield. In vivo, the seleniumsubstituted
compound was about as good
as amino- d -luciferin, presumably because
of a trade-off between its greater tissue
penetration and its lower quantum yield.
Because 77 Se is a stable nucleus for magnetic
resonance imaging (MRI), the researchers
believe the compound could find use in bimodal
bioluminescence-MRI studies. —BH
CATALYTIC PARTICLES
FEATURE SPATIAL-
ACTIVITY HOT SPOTS
The level of catalytic activity mediated by
one type of crystal facet can vary across the
surface of that facet and also among several
facets of a single type. This finding by
Cornell University chemists suggests that
knowing the surface structure of crystalline
catalyst particles alone is not sufficient
for predicting activity ( Nat. Nanotechnol.,
DOI: 10.1038/nnano.2012.18 ). Decades
ago, researchers found that some crystal
facets, or faces, of solid catalysts are more
catalytically active than others. Catalyst
manufacturers have used that information
to fine-tune preparation methods to
enhance exposure of the most active facets.
Cornell’s Peng Chen and coworkers used
fluorescence microscopy with single-molecule
resolution to monitor light-producing
catalytic reactions on gold nanorods and
discovered that facet-dependent activity
turns out to be unexpectedly complex.
By examining hundreds of highly faceted
nanorods they determined that catalytic
activity within a single facet exhibits a reactivity
gradient that tends to increase from
the center toward the facet edges. In addition,
the relative reactivities of the ends
and sides of nanorods vary widely among
samples even though they exhibit the same
types of facets, the team reports. — MJ
CHONDROITINS
FREAK FISH OUT
Behavioral ecologists have long noticed
that when a fish is injured nearby members
of the same species will rapidly flee. But
how this alarm signal is transmitted has
remained a mystery. Researchers led by
Suresh Jesuthasan of Singapore’s Duke-
SURESH JESUTHASAN
A spoonful of chondroitin scares these
zebra fish.
NUS Graduate Medical School and the
Agency for Science, Technology & Research
report that one component of this chemical
signal is chondroitin sulfate, a polysaccharide
that is part of fish skin ( Curr. Biol., DOI:
10.1016/j.cub.2012.01.061). Jesuthasan’s
team studied schools of zebra fish to discover
this fear factor. The researchers note
there are probably other molecules involved
in raising an alarm, because chondroitin sulfate
is common to many species of fish but
fish respond strongly only to injury signals
from members of their own species. The
search is now on for additional molecules
that trigger species-specific alarm responses,
as well as receptors in the olfactory epithelium
that detect the chemicals. —SE
PHOTOSWITCH MOLECULE
CONTROLS PAIN
A light-activated compound that resembles
the anesthetic lidocaine might lead
the way to future pain
therapy, according
to a report
( Nat. Methods,
DOI: 10.1038/
nmeth.1897 ).
Anesthetics typically
suppress pain, but they
take a while to wear off and
are indiscriminate in
which nerve cells they
inhibit. Now, Richard H.
Kramer of the University
of California, Berkeley;
Dirk Trauner of the University
of Munich; and coworkers have developed
a photoswitchable compound
that targets specific neurons and
can be turned on and off at will.
N
O
O
N
+ N
N
H
trans-QAQ
500-nm
light
WWW.CEN-ONLINE.ORG 53 FEBRUARY 27, 2012
O
380-nm
light
cis-QAQ
They demonstrated that the lidocaine-like
molecule, quaternary ammonium-azobenzene-quaternary
ammonium (QAQ),
blocks ion channels in pain-sensing nerve
cells when in its trans form. After exposure
to 380-nm light, QAQ switches to its cis
form, unblocking the channels and allowing
the neurons to transmit pain signals.
The researchers regenerated trans- QAQ
with 500-nm light. When applied to the
eyes of mice along with the chili-pepper
compound capsaicin, trans- QAQ slipped
into the rodents’ nerve cells through the
protein receptor TRPV1 and lessened the
critters’ response to pain. Fiber-optic systems
will be needed to use compounds like
QAQ inside humans, the scientists say, but
meanwhile these photoswitches can help
map pain circuitry in the body. —LKW
MISFOLDED PROTEINS
DIRECT NANOPARTICLES
N
+ N
N
H
O
+ N
N
H
In biological fluids, nanoparticles end up
coated with a mixture of proteins and lipids,
a process that determines the ultimate
destination of the nanoparticles. By exploiting
that so-called protein corona, Paul
Wentworth Jr. of the University of Oxford
and Scripps Research Institute and Oxford
graduate students Kanlaya Prapainop
and Daniel P. Witter have shown they can
direct diagnostic nanoparticles to specific
cell types (J. Am. Chem. Soc., DOI: 10.1021/
ja300537u ). The researchers chemically
modified the surface of CdSe/ZnS quantum
dots with cholesterol 5,6- seco sterol
atheronal-B, an inflammatory metabolite
that triggers misfolding of apolipoprotein B
in the corona. The conformational
change
+ N exposes binding sites
in apolipoprotein
B for receptors on
the surface of macrophages,
which take up the nanoparticles via
receptor-mediated endocytosis. Different
cell types can be targeted by
using different molecules to expose
binding sites for other receptors,
N
the researchers note. Kenneth A.
Dawson , an expert on proteinnanoparticle
interactions at
University College Dublin, calls
such reprogramming “a creative
NH
and inventive way of thinking of
the problem—working with the
corona, not trying to eliminate it
but using it wisely.” — CHA