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Performing Chemistry in Floating Droplets

Performing Chemistry in Floating Droplets

Could chemists be ready to ditch the venerable test tube, the very symbol of chemistry in the minds of many people? Maybe not quite yet, but Caltech’s Jack Beauchamp is working on it.

Beauchamp is doing work in what he calls “lab-in-a-drop” chemistry, in which chemical reactions are performed within a drop of liquid suspended in midair through acoustic levitation.

Acoustic levitation works by creating areas of high and low pressure in the air through the use of ultrasonic transducers. These transducers act like tiny but powerful speakers that operate at a frequency above what human ears can hear. The sonic energy emitted by these transducers is focused in such a way that the high- and low-pressure zones they create form “traps” that can hold small objects in place in the air. An object placed in one of the low-pressure zones is held there by the high-pressure zones that surround it. An acoustic levitator of this sort can be constructed for about $75 from off-the-shelf parts using 3D-printing techniques.

An animated gif showing a hand place a pellet in the levitator. Graphics showing high- and low-pressure zones are superimposed.

Credit: Caltech

In a new paper, Beauchamp and his colleagues describe the use of the technique to study how a skin-cancer drug works at a chemical level. The research, he says, represents the first successful use of acoustic levitation as a “wall-less” reactor in a detailed study of chemical reactions.

In the work, Beauchamp and his team coated a droplet of water with lipids, biomolecules that make up cell membranes. They then applied an anti-cancer drug to the droplet and used a mass spectrometer to “sniff” the chemical signature given off by the droplet as the drug reacted with the lipid when illuminated with a red laser pointer.

In the experiment, the researchers added a small amount of one of two lipids, cardiolipin and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol)), to each drop of water. The lipids migrated to the surface of the droplet, where they organized to form a thin film that is similar in composition to the cell membrane of a living cell.

With the membrane established, a chemical called temoporfin was added to the droplet. Temoporfin, a ring-like molecule, is excited by red light. In this state, the temoporfin transfers energy to molecular oxygen, forming an excited electronic state that easily oxidizes molecules it comes into contact with, including those that make up cell membranes. This makes temoporfin useful as a treatment for some skin cancers. A doctor could apply the drug to a cancerous lesion and then illuminate it with red light, which easily shines through tissues. As the compound is illuminated and excited, it oxidizes vital cellular materials, including lipids, proteins, and nucleic acids, triggering cell death.

It was this cancer-killing process that Beauchamp wanted to study. “When you’re doing this chemistry, you’d like to be able to carry out these reactions under conditions where you don’t have any contact of the liquid with surfaces,” he says. “We achieve this goal by performing chemistry in a levitated droplet.”

The acoustic levitator allowed Beauchamp and his team to suspend in midair a 1 millimeter droplet of water containing a mixture of the lipid and temoporfin. The droplet was then illuminated by red laser light, exciting the temoporfin and causing it to oxidize the molecules of the membrane layer.

As this oxidation was occurring, a pair of high-voltage electrodes placed near the droplet pulled minute amounts of material off the droplet and into the sensor of a mass spectrometer, which provided readings that allowed researchers to deduce the molecular structures of compounds within the drop. By continually monitoring these readings, the researchers were able to see how the compounds on the surface became progressively more oxidized. By looking at these reaction products, Beauchamp says the research team could determine how the oxidation processes work.

“As far as I know, we’re the only people doing serious chemistry this way, examining the kinetics and mechanism of the reactions involved” Beauchamp says.

Acoustic levitation could find use in other fields as well, he says. As an example, he cites the research of Caltech’s Joe Parker, an assistant professor of biology and biological engineering who studies the symbiotic relationship between certain species of ants and beetles. Beauchamp says it would be possible to levitate an ant and a beetle in close proximity to one another and then use the apparatus to analyze the pheromones they emit.

The technique could have other applications as well. In collaborative studies with Caltech’s John Seinfeld, Louis E. Nohl Professor of Chemical Engineering, Beauchamp previously revealed details of the complex environmental chemistry that leads to the formation of organic aerosols in the atmosphere in studies using droplets hanging on the end of a capillary. With the new levitation methodology, that capillary would no longer be required.

The paper describing Beauchamp’s research, titled “Mass Spectrometric Study of Acoustically Levitated Droplets Illuminates Molecular-Level Mechanism of Photodynamic Therapy for Cancer Involving Lipid Oxidation,” appears in the April 23 issue of Angewandte Chemie, the flagship journal of the German Chemical Society. Beauchamp’s co-authors include Chaonan Mu, Jie Wang, and Xingxing Zhang of Nankai University, and Kevin J. Barraza, a postdoctoral scholar in chemistry at Caltech.

Materials provided by the California Institute of Technology

ZTF Spots Asteroid with Shortest Year 2019 LF6

ZTF Spots Asteroid with Shortest Year

Astronomers have spotted an unusual asteroid with the shortest “year” known for any asteroid. The rocky body, dubbed 2019 LF6, is about a kilometre in size and circles the sun roughly every 151 days. In its orbit, the asteroid swings out beyond Venus and, at times, come closer in than Mercury, which circles the sun every 88 days. 2019 LF6 is one of only 20 known “Atira” asteroids, whose orbits fall entirely within Earth’s.

“You don’t find kilometre-size asteroids very often these days,” says Quanzhi Ye, a postdoctoral scholar at Caltech who discovered 2019 LF6 and works with Tom Prince, the Ira S. Bowen Professor of Physics at Caltech and a senior research scientist at JPL, and George Helou, the executive director of IPAC, an astronomy center at Caltech.

“Thirty years ago, people started organizing methodical asteroid searches, finding larger objects first, but now that most of them have been found, the bigger ones are rare birds,” he says. “LF6 is very unusual both in orbit and in size—its unique orbit explains why such a large asteroid eluded several decades of careful searches.”

2019 LF6 was discovered via the Zwicky Transient Facility, or ZTF, a state-of-the-art camera at the Palomar Observatory that scans the skies every night for transient objects, such as exploding and flashing stars and moving asteroids. Because ZTF scans the sky so rapidly, it is well-suited for finding Atira asteroids, which have short observing windows.

“We only have about 20 to 30 minutes before sunrise or after sunset to find these asteroids,” says Ye.

To find the Atira asteroids, the ZTF team has been carrying out a dedicated observing campaign, named Twilight after the time of day best suited for discovering the objects. Twilight was developed by Ye and Wing-Huen Ip of the National Central University in Taiwan. So far, the program has discovered one other Atira asteroid, named 2019 AQ3. Before 2019 LF6 came along, 2019 AQ3 had the shortest known year of any asteroid, orbiting the sun roughly every 165 days.

“Both of the large Atira asteroids that were found by ZTF orbit well outside the plane of the solar system,” says Prince. “This suggests that sometime in the past they were flung out of the plane of the solar system because they came too close to Venus or Mercury,” says Prince.

In addition to the two Atira objects, ZTF has so far found around 100 near-Earth asteroids and about 2,000 asteroids orbiting in the Main Belt between Mars and Jupiter.

Ye says he hopes the Twilight program will lead to more Atira discoveries, and he looks forward to the possible selection by NASA of the Near-Earth Object Camera (NEOCam) mission, a proposed spacecraft designed to look for asteroids closer to the sun than previous surveys. NEOCam would pick up the infrared, or heat, signatures of asteroids. (Ye works at IPAC, which would process and archive data for the NEOCam mission, but is not part of that team.)

“Because Atira asteroids are closer to the sun and warmer than other asteroids, they are brighter in the infrared,” says Helou.”NEOCam has the double advantage of its location in space and its infrared capability to find these asteroids more easily than telescopes working at visible wavelengths from the ground.”

The International Astronomical Union Minor Planet Center listing for 2019 LF6 is at https://minorplanetcenter.net/mpec/K19/K19M45.html.

Materials provided by the California Institute of Technology

A Bioengineer's Guide to Design

A Bioengineer’s Guide to Design

A team of researchers at Caltech has developed a set of guidelines for designing biological circuits using tools from mechanical and electrical engineering. Like electric circuits—but made out of cells and living matter—biological circuits show promise in producing pharmaceuticals and biofuels.

For example, the antimalarial compound artemisinin is produced by an expensive tropical plant, so scientists at UC Berkeley have engineered the plant’s metabolism into yeast cells in order to synthesize artemisinin without using plants or soil. However, the ability to predict the behavior of these circuits—to design them on paper and then successfully implement the design—is still rudimentary.

The set of bioengineering design principles described in this new work could make building cellular systems more efficient and predictable.

“We like to put it this way: if you were designing an airplane, you wouldn’t start by making 1,000 different planes and launching them all into the sky to see which ones flew,” says lead author Noah Olsman (PhD ’19), a former Caltech graduate student who is now a postdoctoral scholar at Harvard. “Instead, you would begin by studying the math and physics that are important to flight. In the same way, the process of designing biological circuits can really benefit from some quantitative guiding principles.”

Biological systems are constantly measuring their environments and adapting to maintain homeostasis—a balanced, steady state. Our eyes adjust in response to light and dark, and our bodies maintain roughly the same internal temperature whether we are in searing heat or a freezing snowstorm. Even single cells, the fundamental units of life, are confronted with vastly variable conditions and make precise measurements and adjustments to survive. The process of measuring the outside world and making changes internally in response is called feedback.

Feedback is commonly studied in engineering. One example of a designed feedback system is a car’s cruise-control mode—the car measures its speed and changes acceleration or deceleration accordingly, makes another measurement of speed, makes any needed changes, and so on. Additionally, the thermostat in a house is designed to use feedback, measuring the external temperature and then heating or cooling as needed.

Ideally, a system would reach a desired state quickly and be robust against large or small perturbations. But when designing systems, engineers often cannot have it all. For example, the features that make a motorcycle more efficient and maneuverable than a car also make it much easier to crash. A branch of engineering called control theory describes these performance trade-offs mathematically.

Now, in two new research papers, Olsman and his colleagues use control theory to lay out design principles for constructing biological systems.

“A major question in biology is: Can we understand biological systems the way we understand electrical circuits or mechanical devices? Can we understand how cells put together molecular components to make life, and can we engineer that ourselves?” says Olsman. “Like an understanding of digital circuits leads to engineering a laptop, an understanding of cellular networks would enable us to build biological systems ourselves.”

Olsman and his collaborators studied a simple bacterial model of feedback, developed by another Caltech team, using Escherichia coli. In colonies of these bacteria, each bacterium emits small molecules in order to send signals to one another. The bacteria were engineered to simultaneously produce a toxin when emitting these signaling molecules. The larger the bacterial population, the higher the toxin concentration. At a high enough concentration of toxin, some bacteria begin to die and thus reduce the toxin concentration. This system of feedback regulates bacterial population growth.

The researchers characterized this system to develop mathematical descriptions of biological feedback.

“Cells are sophisticated machines, but so are airplanes and satellites. The right mathematical thinking can reveal simple principles that govern a complicated world,” says Olsman.

A paper describing the research appears in the journal Cell Systems and is titled “Hard Limits and Performance Tradeoffs in a Class of Antithetic Integral Feedback Networks.” In addition to Olsman, additional co-authors are former Caltech graduate student Ania-Ariadna Baetica (PhD ’18), now of UC San Francisco; graduate student Fangzhou Xiao; former graduate student Yoke Peng Leong (PhD ’18); Richard Murray (BS ’85), Thomas E. and Doris Everhart Professor of Control and Dynamical Systems and Bioengineering; and John Doyle, Jean-Lou Chameau Professor of Control and Dynamical Systems, Electrical Engineering, and Bioengineering.

A second paper describing the work appears in the journal iScience and is titled “Architectural Principles for Characterizing the Performance of Antithetic Integral Feedback Networks.” In addition to Olsman, Fangzhou Xiao, and John Doyle are co-authors.

Materials provided by California Institute of Technology

Chris Martin KCWI Cold flow

Spiraling Filaments Feed Young Galaxies

Galaxies grow by accumulating gas from their surroundings and converting it to stars, but the details of this process have remained murky. New observations, made using the Keck Cosmic Web Imager (KCWI) at the W. M. Keck Observatory in Hawaii, now provide the clearest, most direct evidence yet that filaments of cool gas spiral into young galaxies, supplying the fuel for stars.

“For the first time, we are seeing filaments of gas directly spiral into a galaxy. It’s like a pipeline going straight in,” says Christopher Martin, a professor of physics at Caltech and lead author of a new paper appearing in the July 1 issue of the journal Nature Astronomy. “This pipeline of gas sustains star formation, explaining how galaxies can make stars on very fast timescales.”

For years, astronomers have debated exactly how gas makes its way to the center of galaxies. Does it heat up dramatically as it collides with the surrounding hot gas? Or does it stream in along thin dense filaments, remaining relatively cold? “Modern theory suggests that the answer is probably a mix of both, but proving the existence of these cold streams of gas had remained a major challenge until now,” says co-author Donal O’Sullivan (MS ’15), a PhD student in Martin’s group who built part of KCWI.

KCWI, designed and built at Caltech, is a state-of-the-art spectral imaging camera. Called an integral-field unit spectrograph, it allows astronomers to take images such that every pixel in the image contains a dispersed spectrum of light. Installed at Keck in early 2017, KCWI is the successor to the Cosmic Web Imager (CWI), an instrument that has operated at Palomar Observatory near San Diego since 2010. KCWI has eight times the spatial resolution and 10 times the sensitivity of CWI.

“The main driver for building KCWI was understanding and characterizing the cosmic web, but the instrument is very flexible, and scientists have used it, among other things, to study the nature of dark matter, to investigate black holes, and to refine our understanding of star formation,” says co-author Mateusz (Matt) Matuszewski (MS ’02, PhD ’12), a senior instrument scientist at Caltech.

The question of how galaxies and stars form out of a network of wispy filaments in space—what is known as the cosmic web—has fascinated Martin since he was a graduate student. To find answers, he led the teams that built both CWI and KCWI. In 2017, Martin and his team used KCWI to acquire data on two active galaxies known as quasars, named UM 287 and CSO 38, but it was not the quasars themselves they wanted to study. Nearby each of these two quasars is a growing galaxy within its own giant nebula, larger than the Milky Way and visible thanks to the strong illumination of the quasars. By looking at light emitted by hydrogen in the nebulas—specifically an atomic emission line called hydrogen Lyman-alpha—they were able to map the velocity of the gas. From previous observations at Palomar, the team already knew there were signs of rotation in the nebulas, but the Keck data revealed much more.

“When we used Palomar’s CWI previously, we were able to see what looked like a rotating disk of gas, but we couldn’t make out any filaments,” says O’Sullivan. “Now, with the increase in sensitivity and resolution with KCWI, we have more sophisticated models and can see that these objects are being fed by gas flowing in from attached filaments, which is strong evidence that the cosmic web is connected to and fueling this disk.”

Martin and colleagues developed a mathematical model to explain the velocities they were seeing in the gas and tested it on the galaxies near UM 287 and CSO 38 as well as on a simulated galaxy.

“It took us more than a year to come up with the mathematical model to explain the radial flow of the gas,” says Martin. “Once we did, we were shocked by how well the model works.”

The findings provide the best evidence to date for the cold-flow model of galaxy formation, which basically states that cool gas can flow directly into forming galaxies, where it is converted into stars. Before this model came into popularity, researchers had proposed that galaxies pull in gas and heat it up to extremely high temperatures. From there, the gas was thought to gradually cool, providing a steady but slow supply of fuel for stars. In 1996, research from Caltech’s Charles (Chuck) Steidel, the Lee A. DuBridge Professor of Astronomy and a co-author of the new study, threw this model into question. He and his colleagues showed that distant galaxies produce stars at a very high rate—too fast to be accounted for by the slow settling and cooling of hot gas that was a favored model for young galaxy fueling.

“Through the years, we’ve acquired more and more evidence for the cold-flow model,” says Martin. “We have nicknamed our new version of the model the ‘cold-flow inspiral,’ since we see the spiraling pattern in the gas.”

“These type of measurements are exactly the kind of science we want to do with KCWI,” says John O’Meara, the Keck Observatory chief scientist. “We combine the power of Keck’s telescope size, powerful instrumentation, and an amazing astronomical site to push the boundaries of what’s possible to observe. It’s very exciting to see this result in particular, since directly observing inflows has been something of a missing link in our ability to test models of galaxy formation and evolution. I can’t wait to see what’s coming next.”

The new study, titled, “Multi-Filament Inflows Fuel Young Star-Forming Galaxies,” was funded by the National Science Foundation (NSF), the W. M. Keck Observatory, Caltech, and the European Research Council. KCWI is funded by NSF, Keck Observatory, the Heising-Simons Foundation, and Caltech. The galaxy simulations were performed at NASA Advanced Supercomputing at NASA Ames Research Center. Other Caltech authors include former postdoc Erika Hamden, now at the University of Arizona; Patrick Morrissey, a visitor in space astrophysics who also works at JPL, which is managed by Caltech for NASA; and research scientist James D. (Don) Neill.

Materials provided by the California Institute of Technology

Europa

Table Salt Compound Spotted on Europa

A familiar ingredient has been hiding in plain sight on the surface of Jupiter’s moon Europa. Using a visible light spectral analysis, planetary scientists at Caltech and the Jet Propulsion Laboratory, which Caltech manages for NASA, have discovered that the yellow color visible on portions of the surface of Europa is actually sodium chloride, a compound known on Earth as table salt, which is also the principal component of sea salt.

The discovery suggests that the salty subsurface ocean of Europa may chemically resemble Earth’s oceans more than previously thought, challenging decades of supposition about the composition of those waters and making them potentially a lot more interesting for study. The finding was published in Science Advances on June 12.

Flybys from the Voyager and Galileo spacecrafts have led scientists to conclude that Europa is covered by a layer of salty liquid water encased by an icy shell. Galileo carried an infrared spectrometer, an instrument scientists use to examine the composition of the surface they’re examining. Galileo’s spectrometer found water ice and a substance that appeared to be magnesium sulfate salts—like Epsom salts, which are used in soaking baths. Since the icy shell is geologically young and features abundant evidence of past geologic activity, it was suspected that whatever salts exist on the surface may derive from the ocean below. As such, scientists have long suspected an ocean composition rich in sulfate salts.

That all changed when new, higher spectral resolution data from the W. M. Keck Observatory on Mauna Kea suggested that the scientists weren’t actually seeing magnesium sulfates on Europa. Most of the sulfate salts considered previously actually possess distinct absorptions that should have been visible in the higher-quality Keck data. However, the spectra of regions expected to reflect the internal composition lacked any of the characteristic sulfate absorptions.

“We thought that we might be seeing sodium chlorides, but they are essentially featureless in an infrared spectrum,” says Mike Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy at Caltech and co-author of the Science Advances paper.

However, Kevin Hand at JPL had irradiated ocean salts in a laboratory under Europa-like conditions and found that several new and distinct features arise after irradiation, but in the visible portion of the spectrum. He found that the salts changed colors to the point that they could be identified with an analysis of the visible spectrum. Sodium chloride, for example, turned a shade of yellow similar to that visible in a geologically young area of Europa known as Tara Regio.

“Sodium chloride is a bit like invisible ink on Europa’s surface. Before irradiation, you can’t tell it’s there, but after irradiation, the color jumps right out at you,” says Hand, scientist at JPL and co-author of the Science Advances paper.

“No one has taken visible wavelength spectra of Europa before that had this sort of spatial and spectral resolution. The Galileo spacecraft didn’t have a visible spectrometer. It just had a near-infrared spectrometer,” says Caltech graduate student Samantha Trumbo, the lead author of the paper.

“People have traditionally assumed that all of the interesting spectroscopy is in the infrared on planetary surfaces, because that’s where most of the molecules that scientists are looking for have their fundamental features,” Brown says.

By taking a close look with the Hubble Space Telescope, Brown and Trumbo were able to identify a distinct absorption in the visible spectrum at 450 nanometers, which matched the irradiated salt precisely, confirming that the yellow color of Tara Regio reflected the presence of irradiated sodium chloride on the surface.

“We’ve had the capacity to do this analysis with the Hubble Space Telescope for the past 20 years,” Brown says. “It’s just that nobody thought to look.”

While the finding does not guarantee that this sodium chloride is derived from the subsurface ocean (this could, in fact, simply be evidence of different types of materials stratified in the moon’s icy shell), the study’s authors propose that it warrants a reevaluation of the geochemistry of Europa.

“Magnesium sulfate would simply have leached into the ocean from rocks on the ocean floor, but sodium chloride may indicate that the ocean floor is hydrothermally active,” Trumbo says. “That would mean Europa is a more geologically interesting planetary body than previously believed.”

The study is titled Sodium chloride on the surface of Europa.” This research was supported by the NASA Earth and Space Science Fellowship Program, the Space Telescope Science Institute, and JPL.

Materials provided by California Institute of Technology

Konstantinos Giapis Oxygen

Comet Inspires Chemistry for Making Breathable Oxygen on Mars

Science fiction stories are chock full of terraforming schemes and oxygen generators for a very good reason—we humans need molecular oxygen (O2) to breathe, and space is essentially devoid of it. Even on other planets with thick atmospheres, O2 is hard to come by.

So, when we explore space, we need to bring our own oxygen supply. That is not ideal because a lot of energy is needed to hoist things into space atop a rocket, and once the supply runs out, it is gone.

One place molecular oxygen does appear outside of Earth is in the wisps of gas streaming off comets. The source of that oxygen remained a mystery until two years ago when Konstantinos P. Giapis, a professor of chemical engineering at Caltech, and his postdoctoral fellow Yunxi Yao, proposed the existence of a new chemical process that could account for its production. Giapis, along with Tom Miller, professor of chemistry, have now demonstrated a new reaction for generating the oxygen that Giapis says could help humans explore the universe and perhaps even fight climate change at home. More fundamentally though, he says the reaction represents a new kind of chemistry discovered by studying comets.

Most chemical reactions require energy, which is typically provided as heat. Giapis’s research shows that some unusual reactions can occur by providing kinetic energy. When water molecules are shot like extremely tiny bullets onto surfaces containing oxygen, such as sand or rust, the water molecule can rip off that oxygen to produce molecular oxygen. This reaction occurs on comets when water molecules vaporize from the surface and are then accelerated by the solar wind until they crash back into the comet at high speed.

Comets, however, also emit carbon dioxide (CO2). Giapis and Yao wanted to test if CO2 could also produce molecular oxygen in collisions with the comet surface. When they found O2 in the stream of gases coming off the comet, they wanted to confirm that the reaction was similar to water’s reaction. They designed an experiment to crash CO2 onto the inert surface of gold foil, which cannot be oxidized and should not produce molecular oxygen. Nonetheless, O2 continued to be emitted from the gold surface. This meant that both atoms of oxygen come from the same CO2 molecule, effectively splitting it in an extraordinary manner.

“At the time we thought it would be impossible to combine the two oxygen atoms of a CO2molecule together because CO2 is a linear molecule, and you would have to bend the molecule severely for it to work,” Giapis says. “You’re doing something really drastic to the molecule.”

A stop-motion animation of carbon dioxide being converted to molecular oxygen.

In Giapis’s reactor, carbon dioxide is converted into molecular oxygen. Credit: Caltech

To understand the mechanism of how CO2 breaks down to molecular oxygen, Giapis approached Miller and his postdoctoral fellow Philip Shushkov, who designed computer simulations of the entire process. Understanding the reaction posed a significant challenge because of the possible formation of excited molecules. These molecules have so much energy that their constituent atoms vibrate and rotate around to an enormous degree. All that motion makes simulating the reaction in a computer more difficult because the atoms within the molecules move in complex ways.

“In general, excited molecules can lead to unusual chemistry, so we started with that,” Miller says. “But, to our surprise, the excited state did not create molecular oxygen. Instead, the molecule decomposed into other products. Ultimately, we found that a severely bent CO2 can also form without exciting the molecule, and that could produce O2.”

Tom Miller, professor of chemistry, stands in front of a rack of computers.

Tom Miller, professor of chemistry(Credit: Caltech)

The apparatus Giapis designed to perform the reaction works like a particle accelerator, turning the CO2 molecules into ions by giving them a charge and then accelerating them using an electric field, albeit at much lower energies than are found in a particle accelerator. However, he adds that such a device is not necessary for the reaction to occur.

“You could throw a stone with enough velocity at some CO2 and achieve the same thing,” he says. “It would need to be travelling about as fast as a comet or asteroid travels through space.”

That could explain the presence of small amounts of oxygen that have been observed high in the Martian atmosphere. There has been speculation that the oxygen is being generated by ultraviolet light from the sun striking CO2, but Giapis believes the oxygen is also generated by high-speed dust particles colliding with CO2 molecules.

He hopes that a variation of his reactor could be used to do the same thing at more useful scales—perhaps one day serving as a source of breathable air for astronauts on Mars or being used to combat climate change by pulling CO2, a greenhouse gas, out of Earth’s atmosphere and turning it into oxygen. He acknowledges, however, that both of those applications are a long way off because the current version of the reactor has a low yield, creating only one to two oxygen molecules for every 100 CO2 molecules shot through the accelerator.

“Is it a final device? No. Is it a device that can solve the problem with Mars? No. But it is a device that can do something that is very hard,” he says. “We are doing some crazy things with this reactor.”

The paper describing the team’s findings, titled “Direct dioxygen evolution in collisions of carbon dioxide with surfaces,” appears in the May 24 issue of Nature Communications. Caltech co-authors include Tom Miller, professor of chemistry; Philip Shushkov, a postdoctoral scholar in chemistry; and Yunxi Yao, postdoctoral researcher, formerly of Caltech. Funding for the research was provided by the National Science Foundation, the Joint Center for Artificial Photosynthesis, and the U. S. Department of Energy.

Materials provided by the California Institute of Technology