ADVANCES
Graphic by Amanda MontañezPABLO BEREA NUÑEZBIOCHEMISTRY
Venomous
Secrets
Synthesized scorpion compounds
can help fight dangerous infections
We rarely think of scorpions as beneficial.
But researchers have isolated two new
compounds in the arachnids’ venom that
show promise for treating staph infections
and drug-resistant tuberculosis.
Scorpion venom is beyond expensive:
harvesting a milliliter would cost about
$10,300, says Richard Zare, a chemist at
Stanford University and
senior author of a study
published in June in the
Proceedings of the National
Academy of Sciences USA.
He estimates that “milking”
venom from one scorpion
can yield only a few thou-
sandths of a milliliter at a
time at most, and it takes
two or more weeks for an individual’s sup-
plies to replenish. The substance can still
be worth studying, however. Some of its
constituent compounds have intriguing
medicinal properties and can be synthe-
sized more cheaply in the laboratory.
Researchers at the National Autono-
mous University of Mexico milked scorpi-
ons of the eastern Mexican species Diplo
centrus melici, whose venom had never
been studied before. They separated its
components and tested some on Staphylo
coccus aureus, Escherichia coli and Myco
bacterium tuberculosis bacteria. Two of
these components—one of which happens
to be red when isolated and the other
blue—killed staph and TB microorganisms,suggesting their potential as antibiotics.
The researchers sent small samples
of the isolated compounds to Zare’s group
at Stanford to determine the substances’
compositions and molecular structures.
The group then chemically synthesized the
compounds and shipped them to the Sal-
vador Zubirán National Institute of Medi-
cal Sciences and Nutrition in Mexico City.
There pathologists testedthe synthe-
sized substances in mice infected with
tuberculosis and on human tissue samples
hosting staph bacteria. The red compound
proved more effective at killing staph, and
the blue one worked better on TB—includ-
ing a drug-resistant strain—without dam-
aging the lining of the mice’s lungs.
Christine Beeton, a molecular physiolo-
gist and biophysicist at Baylor College of
Medicine, who studies therapeutic uses for
venom but was not involved with the new
work, says the study’s approach seems
promising. But she cautions that the com-
pounds still need to be tested in larger ani-
mals—and they could also be challenging
to synthesize on the scales required for
testing in humans. — Rachel Crowell20 nanometersMOF particleTrapped CO 2 moleculeMATERIALS SCIENCE
A Molecular Trap
New views reveal single molecules of captured CO 2
For the first time, researchers have obtained images of individual carbon dioxide mole-
cules trapped in a series of molecular “cages”—and they borrowed an imaging technique
from biologists to do it. Metal-organic frameworks (MOFs) are exceptionally porous
polymers designed to capture particular gas molecules, letting scientists separate or puri-
fy various vapors. Even small amounts can slurp up a lot of gas: a single gram can have
a gas-grabbing surface area nearly the size of two football fields. MOFs have been pro-
posed for holding hydrogen in automobile tanks or fuel cells (without the need for extra
cooling) and for grabbing and storing planet-warming carbon dioxide emissions, among
many other uses.
When Yuzhang Li, a materials scientist at Stanford University, and his colleagues exam-
ined a sample of a CO 2 -trapping MOF with a transmission electron microscope, they found
the instrument’s powerful electron beam “just melted” the honeycomblike framework, Li
says. So the researchers tried an approach that biologists often turn to when imaging deli-
cate proteins, viruses and cell organelles: they used liquid nitrogen to freeze and stabilize
the material at a nippy –170 degrees Celsius and also dialed back the strength of their elec-
tron beam. This method let them take long-exposure pictures—not only of a slice through
the material itself, called ZIF-8 ( top and middle ) but of the CO 2 molecules trapped within it
( bottom ). The team reported its results in the August issue of Matter.
This flash-freezing process will allow detailed studies of how MOFs trap gas, says
Jeffrey Long, a materials chemist at the University of California, Berkeley, who was not
involved in the study. For example, Li says, future work might generate 3-D images to
investigate how quickly and efficiently the materials pull in gases. — Sid Perkins SOURCE: “CRYO-EM STRUCTURES OF ATOMIC SURFACES AND HOST-GUEST CHEMISTRY IN METAL-ORGANIC
FRAMEWORKS,” BY YUZHANG LI ET AL., IN
M AT TER, VOL. 1, NO. 2; AUGUST 7, 2019 (micrographs)Diplocentrus melici20 Scientific American, October 2019