For longer versions of these and other
Molecules stories, visit www.sciencenews.org
Explosive goes boom, not too soon
By Rachel Ehrenberg
Look out, Road Runner: There’s a new
explosive for Wile E. Coyote’s arsenal.
By reining in a supersensitive explosive
with good old-fashioned TNT, chemists
have created a new compound that can
be stored safely and then quickly converted to a superexplosive form.
The new “cocrystal” comprises a zigzagging chain of the explosive CL- 20 and
TNT that, after heating, reverts to a form
of CL- 20 that detonates more readily
than either explosive alone, researchers
report online August 25 in Angewandte
Chemie International Edition.
“You want an explosive to deliver a
lot of destructive energy,” says Thomas
Klapötke of the Ludwig Maximilians University of Munich, an expert in energetic
materials. And it should explode fairly
easily. “But then it often becomes more
dangerous to handle,” Klapötke says.
Seeking a magical mix of stability and
By combining two explosives, TNT and
CL- 20, scientists have created a new
crystal (pictured) that’s very explosive
yet relatively safe to transport.
explosive power that would also provide
a good bang for the buck, materials chemist Adam Matzger and his University of
Michigan colleague Onas Bolton experimented with CL- 20, a relatively new
material developed by the U.S. Navy.
“CL- 20 has wonderful power, but it’s
a little sensitive — it tends to go off eas-
ily,” says Matzger. “If you’re on a ship
transporting munitions you don’t want
a little hit to set everything off.”
So the researchers put CL- 20 in a sol-
vent with Wile E.’s old standby, TNT.
Mixed together, the two substances form
a solid crystal that is much less sensitive
than CL- 20, the researchers report. They
tested the material using a detonation
yardstick known as a drop test, which is
just what it sounds like: The researchers
repeatedly dropped a weight on the new
material from different heights to find the
distance that causes it to explode 50 per-
cent of the time.
Science gets
details on DEET
Repellent appears to deter
insects by confusing them
By Rachel Ehrenberg
The insect repellent DEET doesn’t actually repel insects — it confuses them.
New research suggests that DEET gums
up sniffing machinery, sabotaging an
insect’s sense of smell.
Nerve cells that send odor-related signals to the brain respond differently to
DEET if it’s sniffed alone or with other
scents, experiments with fruit flies reveal.
DEET’s effects also vary depending on
what variety of smell-receiving machinery catches the scent, and whether it’s a
whopping dose or just a whiff, researchers report online September 21 in Nature .
“The effects of DEET are not
straightforward,” says neuroscientist
Maurizio Pellegrino of the University
of California, Berkeley, a member of the
research team. “We think it confuses the
odor coding — the insect doesn’t know
exactly what it is smelling.”
While DEET has protected people for
decades from loathsome mosquitoes,
ticks and chiggers, it hasn’t been clear
how it does its stuff. Some evidence sug-
gests that the compound, technically
N,N-diethyl-meta-toluamide, hits a spe-
cific cellular baseball mitt, an odor receiver
that catches repellent scents, triggering
a “get-the-heck-out-of-here” signal.
But the new work suggests that DEET
isn’t repulsive or frightening to bugs.
It’s baffling, blinding them to the
delicious scent of human.
