Author: MIT News

Moving perovskite advancements from the lab to the manufacturing floor

by MIT.Nano |

The following was issued as a joint announcement from MIT.nano and the MIT Research Laboratory for Electronics; CubicPV; Verde Technologies; Princeton University; and the University of California at San Diego.

Tandem solar cells are made of stacked materials — such as silicon paired with perovskites — that together absorb more of the solar spectrum than single materials, resulting in a dramatic increase in efficiency. Their potential to generate significantly more power than conventional cells could make a meaningful difference in the race to combat climate change and the transition to a clean-energy future.

However, current methods to create stable and efficient perovskite layers require time-consuming, painstaking rounds of design iteration and testing, inhibiting their development for commercial use. Today, the U.S. Department of Energy Solar Energy Technologies Office (SETO) announced that MIT has been selected to receive an $11.25 million cost-shared award to establish a new research center to address this challenge by using a co-optimization framework guided by machine learning and automation.

A collaborative effort with lead industry participant CubicPV, solar startup Verde Technologies, and academic partners Princeton University and the University of California San Diego (UC San Diego), the center will bring together teams of researchers to support the creation of perovskite-silicon tandem solar modules that are co-designed for both stability and performance, with goals to significantly accelerate R&D and the transfer of these achievements into commercial environments.

“Urgent challenges demand rapid action. This center will accelerate the development of tandem solar modules by bringing academia and industry into closer partnership,” says MIT professor of mechanical engineering Tonio Buonassisi, who will direct the center. “We’re grateful to the Department of Energy for supporting this powerful new model and excited to get to work.”

Adam Lorenz, CTO of solar energy technology company CubicPV, stresses the importance of thinking about scale, alongside quality and efficiency, to accelerate the perovskite effort into the commercial environment. “Instead of chasing record efficiencies with tiny pixel-sized devices and later attempting to stabilize them, we will simultaneously target stability, reproducibility, and efficiency,” he says. “It’s a module-centric approach that creates a direct channel for R&D advancements into industry.”

The center will be named Accelerated Co-Design of Durable, Reproducible, and Efficient Perovskite Tandems, or ADDEPT. The grant will be administered through the MIT Research Laboratory for Electronics (RLE).

David Fenning, associate professor of nanoengineering at UC San Diego, has worked with Buonassisi on the idea of merging materials, automation, and computation, specifically in this field of artificial intelligence and solar, since 2014. Now, a central thrust of the ADDEPT project will be to deploy machine learning and robotic screening to optimize processing of perovskite-based solar materials for efficiency and durability.

“We have already seen early indications of successful technology transfer between our UC San Diego robot PASCAL and industry,” says Fenning. “With this new center, we will bring research labs and the emerging perovskite industry together to improve reproducibility and reduce time to market.”

“Our generation has an obligation to work collaboratively in the fight against climate change,” says Skylar Bagdon, CEO of Verde Technologies, which received the American-Made Perovskite Startup Prize. “Throughout the course of this center, Verde will do everything in our power to help this brilliant team transition lab-scale breakthroughs into the world where they can have an impact.”

Several of the academic partners echoed the importance of the joint effort between academia and industry. Barry Rand, professor of electrical and computer engineering at the Andlinger Center for Energy and the Environment at Princeton University, pointed to the intersection of scientific knowledge and market awareness. “Understanding how chemistry affects films and interfaces will empower us to co-design for stability and performance,” he says. “The center will accelerate this use-inspired science, with close guidance from our end customers, the industry partners.”

A critical resource for the center will be MIT.nano, a 200,000-square-foot research facility set in the heart of the campus. MIT.nano Director Vladimir Bulović, the Fariborz Maseeh (1990) Professor of Emerging Technology, says he envisions MIT.nano as a hub for industry and academic partners, facilitating technology development and transfer through shared lab space, open-access equipment, and streamlined intellectual property frameworks.

“MIT has a history of groundbreaking innovation using perovskite materials for solar applications,” says Bulović. “We’re thrilled to help build on that history by anchoring ADDEPT at MIT.nano and working to help the nation advance the future of these promising materials.”

MIT was selected as a part of the SETO Fiscal Year 2022 Photovoltaics (PV) funding program, an effort to reduce costs and supply chain vulnerabilities, further develop durable and recyclable solar technologies, and advance perovskite PV technologies toward commercialization. ADDEPT is one project that will tackle perovskite durability, which will extend module life. The overarching goal of these projects is to lower the levelized cost of electricity generated by PV.

Research groups involved with the ADDEPT project at MIT include Buonassisi’s Accelerated Materials Laboratory for Sustainability (AMLS), Bulović’s Organic and Nanostructured Electronics (ONE) Lab, and the Bawendi Group led by Lester Wolfe Professor in Chemistry Moungi Bawendi. Also working on the project is Jeremiah Mwaura, research scientist in the ONE Lab.

Nanoparticles provoke immune response against tumors but avoid side effects

by Anne Trafton | MIT News Office |

Cancer drugs that stimulate the body’s immune system to attack tumors are a promising way to treat many types of cancer. However, some of these drugs produce too much systemic inflammation when delivered intravenously, making them harmful to use in patients.

MIT researchers have now come up with a possible way to get around that obstacle. In a new study, they showed that when immunostimulatory prodrugs — inactive drugs that require activation in the body — are tuned for optimal activation timing, the drugs provoke the immune system to attack tumors without the side effects that occur when the active form of the drug is given.

The researchers designed prodrugs with bottlebrush-like structures based on a class of compounds called imidazoquinolines (IMDs). Mice treated with these bottlebrush prodrugs designed with optimized activation kinetics showed a significant reduction in tumor growth, with no side effects. The researchers hope that this approach could be used to boost immune system responses in cancer patients, especially when combined with other immunotherapy drugs or cancer vaccines.

“Our bottlebrush prodrug library enabled us to show an immunological effect of controlling immunotherapy kinetics, allowing us to boost immune responses while minimizing the side effects,” says Sachin Bhagchandani, an MIT graduate student who is the lead author of the study. “This kind of approach opens up avenues for scientists who want to decouple toxicity from some promising immunotherapy agents.”

Jeremiah Johnson, an MIT professor of chemistry, and Darrell Irvine, the Underwood-Prescott Professor with appointments in MIT’s departments of Biological Engineering and of Materials Science and Engineering, are the senior authors of the paper, which appears today in Science Advances. Irvine is also an associate director of MIT’s Koch Institute for Integrative Cancer Research and a member of the Ragon Institute of MGH, MIT, and Harvard.

Tailored prodrugs

Organic molecules known as IMDs bind to cell receptors called Toll-like receptors that are found on macrophages and other cells of the innate immune system. When activated, these cells begin producing cytokines and other inflammatory molecules.

In 1997, the FDA approved topical IMD drugs to treat certain types of skin cancer. Since then, many other IMD drugs have been tested in clinical trials for a variety of types of cancer, but none of these were approved, in part because the drugs produced too much systemic inflammation.

The MIT team set out to explore whether prodrugs of IMDs, which are inactivated until turned “on” in the tumor microenvironment, could reduce those side effects. In recent years, Johnson’s lab has developed a novel type of prodrug platform shaped like a bottlebrush. These nanoscale, cylindrical structures consist of chains that extend from a central backbone, giving the molecule a bottlebrush-like structure. Inactivated drugs are bound along the bottlebrush backbone through cleavable linkers that define the rate of active IMD release.

The researchers generated and compared six bottlebrush prodrugs that only differed by their release rate, in order to investigate how prodrug activation kinetics impact antitumor responses. Using these bottlebrush prodrugs, the researchers hoped they could deliver active IMDs to tumors while avoiding release into the bloodstream.

“Our ability to synthesize six bottlebrush prodrugs with identical sizes and shapes uniquely allows us to isolate and study release kinetics as a key variable. Excitingly, we find that it is possible to identify prodrug structures that limit IMD exposure to the whole body, thereby avoiding toxicity, and that activate in tumors to give antitumor efficacy,” Johnson says.

In preliminary studies in cells and mice, the researchers found that the fastest-activating prodrugs did cause immune-related side effects, including weight loss and elevated cytokine levels. However, the medium- and slow-releasing versions did not produce these effects.

The researchers then tested the IMD bottlebrush prodrugs in two different mouse models of colon cancer. Because the prodrugs are so small (approximately10 nanometers), they are able to efficiently accumulate in tumors. Once there, they get taken up by innate immune cells, where their linkers are cleaved. The resulting release of active IMDs causes immune cells to release cytokines and other molecules that create a pro-inflammatory environment. This series of events activates nearby T cells to attack the tumor.

In both models, mice treated with the bottlebrush prodrugs showed significantly slowed tumor growth. When the treatment was combined with a checkpoint blockade inhibitor — another class of immunotherapy drug — tumors were completely eliminated in about 20 percent of the mice.

While mice treated with the IMD used in this study, known as resiquimod, showed weight loss, elevated cytokine levels, and reduction in white blood cell count, as expected, mice given resiquimod bottlebrush prodrugs did not show any of these effects.

“Our molecules were able to safely reduce these effects by controlling how much of the active drug is released in the blood,” Bhagchandani says. “If you minimize release of the active compound there, then you’re able to get anti-tumor effects at the tumor site without the systemic side effects.”

Enhanced response

The findings suggest that the most promising use for IMD bottlebrush prodrugs could be to give them along with another drug that stimulates the immune response. Another possibility is using IMD bottlebrush prodrugs as adjuvants to enhance the immune system’s response to cancer vaccines.

“The ability of the bottlebrush prodrug strategy to change both where the drug accumulates in the body and when it is active is very attractive for activating immune responses against cancer or other disease safely,” Irvine says.

This research was funded by the Marble Center for Cancer Nanomedicine; the Ragon Institute of MGH, MIT and Harvard; the Koch Institute Frontier Research Program via the Curt and Kathy Marble Cancer Research Fund; a graduate fellowship from the Ludwig Center at the Koch Institute; and the National Cancer Institute.

Other authors of the paper include Farrukh Vohidov, Lauren Milling, Evelyn Yuzhou Tong, Christopher Brown, Michelle Ramseier, Bin Liu, Timothy Fessenden, Hung Nguyen, Gavin Kiel, Lori Won, Robert Langer, Stefani Spranger, and Alex Shalek.

Scientists use computational modeling to design “ultrastable” materials

by Anne Trafton | MIT News Office |

Materials known as metal-organic frameworks (MOFs) have a rigid, cage-like structure that lends itself to a variety of applications, from gas storage to drug delivery. By changing the building blocks that go into the materials, or the way they are arranged, researchers can design MOFs suited to different uses.

However, not all possible MOF structures are stable enough to be deployed for applications such as catalyzing reactions or storing gases. To help researchers figure out which MOF structures might work best for a given application, MIT researchers have developed a computational approach that allows them to predict which structures will be the most stable.

Using their computational model, the researchers have identified about 10,000 possible MOF structures that they classify as “ultrastable,” making them good candidates for applications such as converting methane gas to methanol.

“When people come up with hypothetical MOF materials, they don’t necessarily know beforehand how stable that material is,” says Heather Kulik, an MIT associate professor of chemistry and chemical engineering, and the senior author of the study. “We used data and our machine-learning models to come up with building blocks that were expected to have high stability, and when we recombined those in ways that were considerably more diverse, our dataset was enriched with materials with higher stability than any previous set of hypothetical materials people had come up with.”

MIT graduate student Aditya Nandy is the lead author of the paper, which appears today in the journal Matter. Other authors are MIT postdoc Shuwen Yue, graduate students Changhwan Oh and Gianmarco Terrones, Chenru Duan PhD ’22, and Yongchul G. Chung, an associate professor of chemical and biomolecular engineering at Pusan National University.

Modeling MOFs

Scientists are interested in MOFs because they have a porous structure that makes them well-suited to applications involving gases, such as gas storage, separating similar gases from each other, or converting one gas to another. Recently, scientists have also begun to explore using them to deliver drugs or imaging agents within the body.

The two main components of MOFs are secondary building units — organic molecules that incorporate metal atoms such as zinc or copper — and organic molecules called linkers, which connect the secondary building units. These parts can be combined together in many different ways, just like LEGO building blocks, Kulik says.

“Because there are so many different types of LEGO blocks and ways you can assemble them, it gives rise to a combinatorial explosion of different possible metal organic framework materials,” she says. “You can really control the overall structure of the metal organic framework by picking and choosing how you assemble different components.”

Currently, the most common way to design MOFs is through trial-and-error. More recently, researchers have begun to try computational approaches to designing these materials. Most such studies have been based on predictions of how well the material will work for a particular application, but they don’t always take into account the stability of the resulting material.

“A really good MOF material for catalysis or for gas storage would have a very open structure, but once you have this open structure, it may be really hard to make sure that that material is also stable under long-term use,” Kulik says.

In a 2021 study, Kulik reported a new model that she created by mining a few thousand papers on MOFs to find data on the temperature at which a given MOF would break down and whether particular MOFs can withstand the conditions needed to remove solvents used to synthesize them. She trained the computer model to predict those two features — known as thermal stability and activation stability — based on the molecules’ structure.

In the new study, Kulik and her students used that model to identify about 500 MOFs with very high stability. Then, they broke those MOFs down into their most common building blocks — 120 secondary building units and 16 linkers.

By recombining these building blocks using about 750 different types of architectures, including many that are not usually included in such models, the researchers generated about 50,000 new MOF structures.

“One of the things that was unique about our set was that we looked at a lot more diverse crystal symmetries than had ever been looked at before, but [we did so] using these building blocks that had only come from experimentally synthesized highly stable MOFs,” Kulik says.

Ultrastability

The researchers then used their computational models to predict how stable each of these 50,000 structures would be, and identified about 10,000 that they deemed ultrastable, both for thermal stability and activation stability.

They also screened the structures for their “deliverable capacity” — a measure of a material’s ability to store and release gases. For this analysis, the researchers used methane gas, because capturing methane could be useful for removing it from the atmosphere or converting it to methanol. They found that the 10,000 ultrastable materials they identified had good deliverable capacities for methane and they were also mechanically stable, as measured by their predicted elastic modulus.

“Designing a MOF requires consideration of many types of stability, but our models enable a near-zero-cost prediction of thermal and activation stability,” Nandy says. “By also understanding the mechanical stability of these materials, we provide a new way to identify promising materials.”

The researchers also identified certain building blocks that tend to produce more stable materials. One of the secondary building units with the best stability was a molecule that contains gadolinium, a rare-earth metal. Another was a cobalt-containing porphyrin — a large organic molecule made of four interconnected rings.

Students in Kulik’s lab are now working on synthesizing some of these MOF structures and testing them in the lab for their stability and potential catalytic ability and gas separation ability. The researchers have also made their database of ultrastable materials available for researchers interested in testing them for their own scientific applications.

The research was funded by the U.S. Defense Advanced Research Projects Agency, a National Science Foundation Graduate Research Fellowship, the Office of Naval Research, the Department of Energy, an MIT Portugal Seed Fund, and the National Research Foundation of Korea.

QS World University Rankings rates MIT No. 1 in 11 subjects for 2023

by MIT News Office |

QS World University Rankings has placed MIT in the No. 1 spot in 11 subject areas for 2023, the organization announced today.

The Institute received a No. 1 ranking in the following QS subject areas: Chemical Engineering; Civil and Structural Engineering; Computer Science and Information Systems; Data Science and Artificial Intelligence; Electrical and Electronic Engineering; Linguistics; Materials Science; Mechanical, Aeronautical, and Manufacturing Engineering; Mathematics; Physics and Astronomy; and Statistics and Operational Research.

MIT also placed second in five subject areas: Accounting and Finance; Architecture/Built Environment; Biological Sciences; Chemistry; and Economics and Econometrics.

For 2023, universities were evaluated in 54 specific subjects and five broader subject areas. MIT was ranked No. 1 in the broader subject area of Engineering and Technology and No. 2 in Natural Sciences.

Quacquarelli Symonds Limited subject rankings, published annually, are designed to help prospective students find the leading schools in their field of interest. Rankings are based on research quality and accomplishments, academic reputation, and graduate employment.

MIT has been ranked as the No. 1 university in the world by QS World University Rankings for 11 straight years.

Mining the right transition metals in a vast chemical space

by Leda Zimmerman | Department of Chemical Engineering |

Swift and significant gains against climate change require the creation of novel, environmentally benign, and energy-efficient materials. One of the richest veins researchers hope to tap in creating such useful compounds is a vast chemical space where molecular combinations that offer remarkable optical, conductive, magnetic, and heat transfer properties await discovery.

But finding these new materials has been slow going.

“While computational modeling has enabled us to discover and predict properties of new materials much faster than experimentation, these models aren’t always trustworthy,” says Heather J. Kulik  PhD ’09, associate professor in the departments of Chemical Engineering and Chemistry. “In order to accelerate computational discovery of materials, we need better methods for removing uncertainty and making our predictions more accurate.”

A team from Kulik’s lab set out to address these challenges with a team including Chenru Duan PhD ’22.

A tool for building trust

Kulik and her group focus on transition metal complexes, molecules comprised of metals found in the middle of the periodic table that are surrounded by organic ligands. These complexes can be extremely reactive, which gives them a central role in catalyzing natural and industrial processes. By altering the organic and metal components in these molecules, scientists can generate materials with properties that can improve such applications as artificial photosynthesis, solar energy absorption and storage, higher efficiency OLEDS (organic light emitting diodes), and device miniaturization.

“Characterizing these complexes and discovering new materials currently happens slowly, often driven by a researcher’s intuition,” says Kulik. “And the process involves trade-offs: You might find a material that has good light-emitting properties, but the metal at the center may be something like iridium, which is exceedingly rare and toxic.”

Researchers attempting to identify nontoxic, earth-abundant transition metal complexes with useful properties tend to pursue a limited set of features, with only modest assurance that they are on the right track. “People continue to iterate on a particular ligand, and get stuck in local areas of opportunity, rather than conduct large-scale discovery,” says Kulik.

To address these screening inefficiencies, Kulik’s team developed a new approach — a machine-learning based “recommender” that lets researchers know the optimal model for pursuing their search. Their description of this tool was the subject of a paper in Nature Computational Science in December.

“This method outperforms all prior approaches and can tell people when to use methods and when they’ll be trustworthy,” says Kulik.

The team, led by Duan, began by investigating ways to improve the conventional screening approach, density functional theory (DFT), which is based on computational quantum mechanics. He built a machine learning platform to determine how accurate density functional models were in predicting structure and behavior of transition metal molecules.

“This tool learned which density functionals were the most reliable for specific material complexes,” says Kulik. “We verified this by testing the tool against materials it had never encountered before, where it in fact chose the most accurate density functionals for predicting the material’s property.”

A critical breakthrough for the team was its decision to use the electron density — a fundamental quantum mechanical property of atoms — as a machine learning input. This unique identifier, as well as the use of a neural network model to carry out the mapping, creates a powerful and efficient aide for researchers who want to determine whether they are using the appropriate density functional for characterizing their target transition metal complex. “A calculation that would take days or weeks, which makes computational screening nearly infeasible, can instead take only hours to produce a trustworthy result.”

Kulik has incorporated this tool into molSimplify, an open source code on the lab’s website, enabling researchers anywhere in the world to predict properties and model transition metal complexes.

Optimizing for multiple properties

In a related research thrust, which they showcased in a recent publication in JACS Au, Kulik’s group demonstrated an approach for quickly homing in on transition metal complexes with specific properties in a large chemical space.

Their work springboarded off a 2021 paper showing that agreement about the properties of a target molecule among a group of different density functionals significantly reduced the uncertainty of a model’s predictions.

Kulik’s team exploited this insight by demonstrating, in a first, multi-objective optimization. In their study, they successfully identified molecules that were easy to synthesize, featuring significant light-absorbing properties, using earth-abundant metals. They searched 32 million candidate materials, one of the largest spaces ever searched for this application. “We took apart complexes that are already in known, experimentally synthesized materials, and we recombined them in new ways, which allowed us to maintain some synthetic realism,” says Kulik.

After collecting DFT results on 100 compounds in this giant chemical domain, the group trained machine learning models to make predictions on the entire 32 million-compound space, with an eye to achieving their specific design goals. They repeated this process generation after generation to winnow out compounds with the explicit properties they wanted.

“In the end we found nine of the most promising compounds, and discovered that the specific compounds we picked through machine learning contained pieces (ligands) that had been experimentally synthesized for other applications requiring optical properties, ones with favorable light absorption spectra,” says Kulik.

Applications with impact

While Kulik’s overarching goal involves overcoming limitations in computational modeling, her lab is taking full advantage of its own tools to streamline the discovery and design of new, potentially impactful materials.

In one notable example, “We are actively working on the optimization of metal–organic frameworks for the direct conversion of methane to methanol,” says Kulik. “This is a holy grail reaction that folks have wanted to catalyze for decades, but have been unable to do efficiently.”

The possibility of a fast path for transforming a very potent greenhouse gas into a liquid that is easily transported and could be used as a fuel or a value-added chemical holds great appeal for Kulik. “It represents one of those needle-in-a-haystack challenges that multi-objective optimization and screening of millions of candidate catalysts is well-positioned to solve, an outstanding challenge that’s been around for so long.”

Study: Smoke particles from wildfires can erode the ozone layer

by Jennifer Chu | MIT News Office |

A wildfire can pump smoke up into the stratosphere, where the particles drift for over a year. A new MIT study has found that while suspended there, these particles can trigger chemical reactions that erode the protective ozone layer shielding the Earth from the sun’s damaging ultraviolet radiation.

The study, which appears today in Nature, focuses on the smoke from the “Black Summer” megafire in eastern Australia, which burned from December 2019 into January 2020. The fires — the country’s most devastating on record — scorched tens of millions of acres and pumped more than 1 million tons of smoke into the atmosphere.

The MIT team identified a new chemical reaction by which smoke particles from the Australian wildfires made ozone depletion worse. By triggering this reaction, the fires likely contributed to a 3-5 percent depletion of total ozone at mid-latitudes in the Southern Hemisphere, in regions overlying Australia, New Zealand, and parts of Africa and South America.

The researchers’ model also indicates the fires had an effect in the polar regions, eating away at the edges of the ozone hole over Antarctica. By late 2020, smoke particles from the Australian wildfires widened the Antarctic ozone hole by 2.5 million square kilometers — 10 percent of its area compared to the previous year.

It’s unclear what long-term effect wildfires will have on ozone recovery. The United Nations recently reported that the ozone hole, and ozone depletion around the world, is on a recovery track, thanks to a sustained international effort to phase out ozone-depleting chemicals. But the MIT study suggests that as long as these chemicals persist in the atmosphere, large fires could spark a reaction that temporarily depletes ozone.

“The Australian fires of 2020 were really a wake-up call for the science community,” says Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies at MIT and a leading climate scientist who first identified the chemicals responsible for the Antarctic ozone hole. “The effect of wildfires was not previously accounted for in [projections of] ozone recovery. And I think that effect may depend on whether fires become more frequent and intense as the planet warms.”

The study is led by Solomon and MIT graduate student Peidong Wang, along with collaborators from the Institute for Environmental and Climate Research in Guangzhou, China; the U.S. National Oceanic and Atmospheric Administration; the U.S. National Center for Atmospheric Research; and Colorado State University.

Chlorine cascade

The new study expands on a 2022 discovery by Solomon and her colleagues, in which they first identified a chemical link between wildfires and ozone depletion. The researchers found that chlorine-containing compounds, originally emitted by factories in the form of chlorofluorocarbons (CFCs), could react with the surface of fire aerosols. This interaction, they found, set off a chemical cascade that produced chlorine monoxide — the ultimate ozone-depleting molecule. Their results showed that the Australian wildfires likely depleted ozone through this newly identified chemical reaction.

“But that didn’t explain all the changes that were observed in the stratosphere,” Solomon says. “There was a whole bunch of chlorine-related chemistry that was totally out of whack.”

In the new study, the team took a closer look at the composition of molecules in the stratosphere following the Australian wildfires. They combed through three independent sets of satellite data and observed that in the months following the fires, concentrations of hydrochloric acid dropped significantly at mid-latitudes, while chlorine monoxide spiked.

Hydrochloric acid (HCl) is present in the stratosphere as CFCs break down naturally over time. As long as chlorine is bound in the form of HCl, it doesn’t have a chance to destroy ozone. But if HCl breaks apart, chlorine can react with oxygen to form ozone-depleting chlorine monoxide.

In the polar regions, HCl can break apart when it interacts with the surface of cloud particles at frigid temperatures of about 155 kelvins. However, this reaction was not expected to occur at mid-latitudes, where temperatures are much warmer.

“The fact that HCl at mid-latitudes dropped by this unprecedented amount was to me kind of a danger signal,” Solomon says.

She wondered: What if HCl could also interact with smoke particles, at warmer temperatures and in a way that released chlorine to destroy ozone? If such a reaction was possible, it would explain the imbalance of molecules and much of the ozone depletion observed following the Australian wildfires.

Smoky drift

Solomon and her colleagues dug through the chemical literature to see what sort of organic molecules could react with HCl at warmer temperatures to break it apart.

“Lo and behold, I learned that HCl is extremely soluble in a whole broad range of organic species,” Solomon says. “It likes to glom on to lots of compounds.”

The question then, was whether the Australian wildfires released any of those compounds that could have triggered HCl’s breakup and any subsequent depletion of ozone. When the team looked at the composition of smoke particles in the first days after the fires, the picture was anything but clear.

“I looked at that stuff and threw up my hands and thought, there’s so much stuff in there, how am I ever going to figure this out?” Solomon recalls. “But then I realized it had actually taken some weeks before you saw the HCl drop, so you really need to look at the data on aged wildfire particles.”

When the team expanded their search, they found that smoke particles persisted over months, circulating in the stratosphere at mid-latitudes, in the same regions and times when concentrations of HCl dropped.

“It’s the aged smoke particles that really take up a lot of the HCl,” Solomon says. “And then you get, amazingly, the same reactions that you get in the ozone hole, but over mid-latitudes, at much warmer temperatures.”

When the team incorporated this new chemical reaction into a model of atmospheric chemistry, and simulated the conditions of the Australian wildfires, they observed a 5 percent depletion of ozone throughout the stratosphere at mid-latitudes, and a 10 percent widening of the ozone hole over Antarctica.

The reaction with HCl is likely the main pathway by which wildfires can deplete ozone. But Solomon guesses there may be other chlorine-containing compounds drifting in the stratosphere, that wildfires could unlock.

“There’s now sort of a race against time,” Solomon says. “Hopefully, chlorine-containing compounds will have been destroyed, before the frequency of fires increases with climate change. This is all the more reason to be vigilant about global warming and these chlorine-containing compounds.”

This research was supported, in part, by NASA and the U.S. National Science Foundation.

Gabriela Schlau-Cohen: Illuminating photosynthesis

by Anne Trafton | MIT News Office |

During photosynthesis, chlorophyll in plants absorbs packets of energy called photons from the sun’s rays. This energy is then transferred to a series of other chlorophyll molecules organized by protein scaffolds, funneling the energy into the next stage of photosynthesis.

Those early light-harvesting stages of photosynthesis involve repeated excitation of pigments, as photons are passed between them. To capture these highly dynamic processes, MIT Associate Professor Gabriela Schlau-Cohen employs ultrafast spectroscopy, a technique that uses extremely short laser pulses to study events that happen on timescales of femtoseconds to nanoseconds.

With this approach, Schlau-Cohen has made discoveries that reveal how photosynthesis is regulated under different light conditions, as well as how plants protect themselves from damage by dissipating excess sunlight.

“We are really interested in understanding the dynamics of electronically excited states, in photosynthesis and other systems,” she says. “We’re studying how energy can migrate through molecular systems and what controls the nature of that migration and its efficiency, particularly in the large protein networks that you find in photosynthesis.”

She also uses other spectroscopic techniques to study how proteins rapidly change their conformation when they bind to specific targets — for example, when receptors found on cell surfaces bind to stimuli such as growth factors or other signaling molecules.

Molecular interactions

As a high school student in the suburbs of Philadelphia, Schlau-Cohen enjoyed chemistry and was particularly intrigued by the phenomenon known as wave-particle duality: the concept that physical matter can have both wave-like and particle-like properties.

“I remember learning about wave-particle duality in my high school chemistry class, which is when I really became interested in chemistry. I had a really talented chemistry teacher who made all of the molecular interactions come alive,” she says.

At Brown University, she majored in chemical physics, which allowed her to explore the physical properties of molecules and molecular systems. There, she used ultrafast microscopy to study rapid processes such as energy moving between the electronic states of molecules.

After graduating from college, she spent three years in New York as a community organizer for the Working Families Party, where she worked on campaigns such as helping to raise the minimum wage for New York State.

“Social and economic justice causes were always something that was really important to me and that I was involved in throughout high school and college, so that was an interest that was present along with chemistry,” she says. “But as I was doing that work, I started to miss the intellectual challenge of science, and that led me to think about returning to science, so then I applied for grad school.”

She decided to go to the University of California at Berkeley, where she worked in a lab that used a type of ultrafast spectroscopy called multidimensional spectroscopy. Using this technique, she studied the energy transfer that occurs in photosynthetic light-harvesting complexes, down to the level of individual proteins within the complex.

“As we were studying these photosynthetic proteins, the simulations that I was doing in conjunction with the experimental work were showing that if you just looked at just one protein, the behavior of that protein was not just quantitatively but qualitatively different than what we could see in the ensemble,” she says.

As a postdoc at Stanford University, she went on to analyze the behavior of those individual photosynthetic proteins more closely, using single-molecule spectroscopy. She found that different copies of the same proteins could change shape, which changes how long they store energy from the sun.

Protein dynamics

When applying for faculty positions, Schlau-Cohen says she was drawn to MIT by the students’ talent and enthusiasm for science.

“When I visited MIT, one of the things that really stood out was the caliber of the students and the intellectual environment they were creating where we could have these really stimulating and exciting conversations about science,” she says. “Throughout MIT, there’s this real excitement about science and an interest in understanding how things work and how we can control how things work.”

Since starting her MIT lab in 2015, Schlau-Cohen has continued studying light-harvesting systems. She uses ultrafast spectroscopy to study how these systems transfer energy over long distances and how their efficiency is regulated in response to changes in sunlight. To help achieve that, she also works on improving the spectral bandwidth (which allows them to observe a wider range of energy levels) of ultrafast spectroscopy and the temporal resolution of single-molecule spectroscopy.

Her lab has published several papers in which they elucidated the mechanisms that allow plants to adjust the amount of energy captured from the sun when exposed to different weather conditions, and how they prevent sun damage. Single-molecule measurements of a protein called light-harvesting complex stress-related (LHCSR) revealed that it plays a key role in controlling these responses in green algae and moss.

Working with other MIT faculty members, including Mark Bathe, a professor of biological engineering, and Adam Willard, an associate professor of chemistry, she is also working on designing synthetic light-harvesting materials, using DNA origami structures as scaffolds.

“Our goal is to develop nanostructures with similar or even better emergent properties than photosynthetic light-harvesting systems, so that we can really achieve control over the evolution of light energy in a way that mimics or even exceeds the performance of nature,” she says.

In another area of research, Schlau-Cohen studies how proteins can respond to their environment by changing their structure. This shape shifting is a key element of cellular signal transduction systems, which control the flow of information within and between cells.

In one recent paper, she and Bin Zhang, an MIT associate professor of chemistry, analyzed how the epidermal growth factor receptor (EGFR) changes its conformation when it binds to its target. They discovered a large-scale structural shift that helps the receptor activate growth pathways inside the cell when activated by EGF.

“We’re interested in the structures of these proteins, and in how biological systems respond to changing environments by changing the structure and thus the function of their protein building blocks,” Schlau-Cohen says.

School of Science presents 2023 Infinite Expansion Awards

by Sarah Costello | School of Science |

The MIT School of Science has announced seven postdocs and research scientists as recipients of the 2023 Infinite Expansion Award. Nominated by their peers and mentors, the awardees are recognized not only for their exceptional science, but for mentoring and advising junior colleagues, supporting educational programs, working with the MIT Postdoctoral Association, or contributing some other way to the Institute.

The 2023 Infinite Expansion award winners in the School of Science are:

  • Kyle Jenks, a postdoc in the Picower Institute for Learning and Memory, nominated by professor and Picower Institute investigator Mriganka Sur;
  • Matheus Victor, a postdoc in the Picower Institute, nominated by professor and Picower Institute director Li-Huei Tsai.

A monetary award is granted to recipients, and a celebratory reception will be held for the winners this spring with family, friends, nominators, and recipients of the Infinite Expansion Award.

Jupneet Singh: Finding purpose through service

by Laura Rosado | MIT News correspondent |

As a first-year U.S. Air Force cadet in the Reserve Officers’ Training Corps (ROTC), Jupneet Singh never imagined she would rise to the rank of wing commander by the end of her MIT career. She approached her first year as a trial period without many expectations, but the close-knit community and inspiring leadership compelled her to continue in the program.

As commander, Singh is the highest-ranked cadet in Detachment 365, which includes students from MIT, Harvard University, Wellesley College, and Tufts University. The detachment was recently named best large detachment in the nation by Air Force ROTC. She oversees everything that happens and is the direct contact between the officer and cadet divisions.

Her decision to enroll in ROTC “really came down to believing in the values that the U.S. stands for, specifically freedom of religion,” says Singh, who is Sikh. “My parents were in India in 1985 during the Sikh Massacre, and hearing them talk about it is obviously very painful. Here in the U.S. that’s something that, in principle, doesn’t happen, and that makes me proud to serve.”

While Singh was growing up in Southern California, her family instilled in her the value of service to one’s community and often volunteered at Sikh Gurdwara community kitchens and religious retreats. Her mother would often mention how lucky they were to be able to give back, right in their backyard.

“I felt a lot of support from my community when I was growing up, and I want to make sure that other kids feel that same support and can also succeed and flourish,” says Singh, who has founded two organizations that do just that. “I feel a great connection to my community, and I always want to find a way to give back.”

Singh is a senior majoring in chemistry with a minor in history. In her research at MIT she has examined the biochemistry of human innate immunity and microbial pathogenesis through research on natural products at the Nolan Lab, and investigated fatty liver disease with computational biology at the Shalek Lab.

Following graduation, she will pursue a master’s degree focused on policy at Oxford University as a Rhodes Scholar — the first-ever scholar from the Air Force ROTC program. Then, she’ll commission as a second lieutenant in the Air Force and attend medical school with the goal of becoming a trauma surgeon. Looking ahead in her career, Singh wants to blend health and policy and continue to support grassroots efforts in addition to higher-level policy changes.

“Advocating for health and health care is the foundation for closing inequities in other aspects of life,” says Singh. “If someone isn’t able to access proper health care when they need it, then they can’t focus on education, income, or anything else. It’s also really important to me that whatever policy or programs I support are being looked at from a local, grassroots level. If a lot of changes are enacted but you don’t refer to the communities who are actually affected by them, they cannot be as effective.”

Making a lasting impact

In high school, Singh started the program Tennis for Tots. A longtime tennis player herself, she wanted to increase access to the sport that generally has a high cost to entry. By partnering with her high school’s tennis team, Tennis for Tots was able to provide rackets, balls, and a weekly clinic free of charge for underserved youth across multiple school districts.

Following the onset of the Covid-19 pandemic, Singh found herself spending an unplanned year at home, where she saw an opportunity to start another program that built upon the mission of Tennis for Tots. She worked with the Ventura County Family Justice Center to start Pathways to Promise, a program that provides support to children affected by domestic violence to help them achieve their goals. Pathways offers educational and vocational support through field trips, keynote speakers, and college-bound workshops.

“At big public schools, there may not be the one-on-one attention needed to give these kids motivation or expand their horizons,” says Singh. “This program was something that I was passionate about because while Tennis for Tots was improving the physical wellbeing of kids, Pathways was mental wellbeing, educational wellbeing, and giving social support. The other part that is important is the continuous nature of it. Every month we have this programming instead of just seeing them once a year.”

Singh followed up her work with Pathways to Promise by collaborating on and publishing a research paper as first author, examining domestic violence trends in the wake of the Covid-19 pandemic.

Though she doesn’t plan to return to her hometown in the near future, both Tennis for Tots and Pathways to Promise continue to expand and provide much needed resources to her community, and she returns periodically to stay involved.

Finding moments to be creative

Though the next few years of Singh’s life seem highly prescribed, she’s keeping an open mind to new opportunities.

“I like having a clear path, but within the next few years I’m going to keep creating spaces to take initiative,” says Singh.

The MIT Mock Trial team has kept her creative juices flowing at MIT, and another way Singh flexes her creative muscles is by playing the harmonium, an Indian instrument similar to an organ. Her grandmother was a harmonium teacher, and Singh has been playing and performing in Sikh temples since she was 2 years old.

Singh is also looking forward to her service in the Air Force and the opportunities she’ll have as a physician-leader.

“Being a doctor in the Air Force is so different from being a doctor in the civilian world, in terms of the people you serve and the opportunities you get to implement initiatives and programs so early in your career,” says Singh. “My dream would be to be the Surgeon General. The Air Force fits really well into that path of being able to serve as a doctor and also be a leader.”

A more sustainable way to generate phosphorus

by Anne Trafton | MIT News Office |

Phosphorus is an essential ingredient in thousands of products, including herbicides, lithium-ion batteries, and even soft drinks. Most of this phosphorus comes from an energy-intensive process that contributes significantly to global carbon emissions.

In an effort to reduce that carbon footprint, MIT chemists have devised an alternative way to generate white phosphorus, a critical intermediate in the manufacture of those phosphorus-containing products. Their approach, which uses electricity to speed up a key chemical reaction, could reduce the carbon emissions of the process by half or even more, the researchers say.

“White phosphorus is currently an indispensable intermediate, and our process dramatically reduces the carbon footprint of converting phosphate to white phosphorus,” says Yogesh Surendranath, an associate professor of chemistry at MIT and the senior author of the study.

The new process reduces the carbon footprint of white phosphorus production in two ways: It reduces the temperatures required for the reaction, and it generates significantly less carbon dioxide as a waste product.

Recent MIT graduate Jonathan “Jo” Melville PhD ’21 and MIT graduate student Andrew Licini are the lead authors of the paper, which appears today in ACS Central Science.

Purifying phosphorus

When phosphorus is mined out of the ground, it is in the form of phosphate, a mineral whose basic unit comprises one atom of phosphorus bound to four oxygen atoms. About 95 percent of this phosphate ore is used to make fertilizer. The remaining phosphate ore is processed separately into white phosphorus, a molecule composed of four phosphorus atoms bound to each other. White phosphorus is then fed into a variety of chemical processes that are used to manufacture many different products, such as lithium battery electrolytes and semiconductor dopants.

Converting those mined phosphates into white phosphorus accounts for a substantial fraction of the carbon footprint of the entire phosphorus industry, Surendranath says. The most energy-intensive part of the process is breaking the bonds between phosphorus and oxygen, which are very stable.

Using the traditional “thermal process,” those bonds are broken by heating carbon coke and phosphate rock to a temperature of 1,500 degrees Celsius. In this process, the carbon serves to strip away the oxygen atoms from phosphorus, leading to the eventual generation of CO2 as a byproduct. In addition, sustaining those temperatures requires a great deal of energy, adding to the carbon footprint of the process.

“That process hasn’t changed substantially since its inception over a century ago. Our goal was to figure out how we could develop a process that would substantially lower the carbon footprint of this process,” Surendranath says. “The idea was to combine it with renewable electricity and drive that conversion of phosphate to white phosphorus with electrons rather than using carbon.”

To do that, the researchers had to come up with an alternative way to weaken the strong phosphorus-oxygen bonds found in phosphates. They achieved this by controlling the environment in which the reaction occurs. The researchers found that the reaction could be promoted using a dehydrated form of phosphoric acid, which contains long chains of phosphate salts held together by bonds called phosphoryl anhydrides. These bonds help to weaken the phosphorus-oxygen bonds.

When the researchers run an electric current through these salts, electrons break the weakened bonds, allowing the phosphorus atoms to break free and bind to each other to form white phosphorus. At the temperatures needed for this system (about 800 C), phosphorus exists as a gas, so it can bubble out of the solution and be collected in an external chamber.

Decarbonization

The electrode that the researchers used for this demonstration relies on carbon as a source of electrons, so the process generates some carbon dioxide as a byproduct. However, they are now working on swapping that electrode out for one that would use phosphate itself as the electron source, which would further reduce the carbon footprint by cleanly separating phosphate into phosphorus and oxygen.

With the process reported in this paper, the researchers have reduced the overall carbon footprint for generating white phosphorus by about 50 percent. With future modifications, they hope to bring the carbon emissions down to nearly zero, in part by using renewable energy such as solar or wind power to drive the electric current required.

If the researchers succeed in scaling up their process and making it widely available, it could allow industrial users to generate white phosphorus on site instead of having it shipped from the few places in the world where it is currently manufactured. That would cut down on the risks of transporting white phosphorus, which is an explosive material.

“We’re excited about the prospect of doing on-site generation of this intermediate, so you don’t have to do the transportation and distribution,” Surendranath says. “If you could decentralize this production, the end user could make it on site and use it in an integrated fashion.”

In order to do this study, the researchers had to develop new tools for controlling the electrolytes (such as salts and acids) present in the environment, and for measuring how those electrolytes affect the reaction. Now, they plan to use the same approach to try to develop lower-carbon processes for isolating other industrially important elements, such as silicon and iron.

“This work falls within our broader interests in decarbonizing these legacy industrial processes that have a huge carbon footprint,” Surendranath says. “The basic science that leads us there is understanding how you can tailor the electrolytes to foster these processes.”

The research was funded by the UMRP Partnership for Progress on Sustainable Development in Africa, a fellowship from the MIT Tata Center for Technology and Design, and a National Defense Science and Engineering Graduate Fellowship.