Category: Chemistry

Codonopsis lanceolata, more commonly referred to as “deodeok,” is used as a medicinal herb in South Korea. It is cultivated in large quantities and has been an integral part of Korean cuisine across history. Aster koraiensis, or Korean starwort, is a common flower that resembles a daisy, which is only found in the Korean peninsula.

A team of researchers led by Director C. Justin LEE from the Life Science Institute (Center for Cognition and Sociality) within the Institute for Basic Science (IBS), South Korea, recently announced the discovery of new antiviral compounds derived from these two Korean native plants.

The researchers discovered that the saponins found within these plants were particularly effective at inhibiting SARS-CoV-2 infection by blocking membrane fusion, which allows the viruses to invade the host cells. These findings were published in Antiviral Research in October 2022 and Antimicrobial Agents and Chemotherapy in November 2022.

Coronaviruses are known to enter human cells via endosomes or fusion at the plasma membranes. In both of these two pathways, a process known as “membrane fusion” must occur between the coronavirus envelope and the cell membrane. The research team revealed that two saponins (astersaponin I and lansemaside A) found within the two beforementioned plants are capable of blocking this fusion of the membrane between the coronavirus and human cells, thereby effectively blocking all the ways that the virus can infect its host.

The research team first made a SARS-CoV-2 infection model using human lung cells overexpressing ACE2 receptor protein and a pseudovirus that expresses the viral spike protein on its surface, which can be used in the relatively less restrictive biosafety level 2 research facility. The cells were treated with astersaponin I and lansemaside A to test the compounds’ inhibitory effect on virus infection.

Both saponins were found to have an IC₅₀ value (half maximal inhibitory concentration) of 2 μM, indicating that they were highly effective at stopping the coronavirus from entering the cell. The same results were confirmed in subsequent experiments using actual authentic coronaviruses, and infection was suppressed with almost the same efficiency. More importantly, the inhibitory effect was identical for all SARS-CoV-2 variants, such as omicron.

Astersaponin I and lansemaside A are triterpenoid saponins. They both have central ringed hydrocarbon (or core) structures very similar to that of cholesterol, which is the main component of cell membranes. in addition to a polysaccharide chain attached to one side. The central part of these saponins readily binds to the cell membrane thanks to their similarity to cholesterol. When the molecule penetrates into the cell membrane, the long sugar chain on protrudes out of the cell membrane. It is believed that this protruding sugar is what blocks the cell membrane from fusing with the coronavirus envelope.

SARS-CoV-2 variants such as omicron are more infectious than original one due to the mutations in the spike protein, which enhances their binding affinity with the ACE2 cell receptor. However, no matter how much the SARS-CoV-2 variants to increase its affinity, it will be unable to enter the cell if the whole membrane fusion process, which occurs after viral binding to the receptor, is blocked. That is, the membrane fusion inhibitor can effectively prevent the infection of SARS-CoV-2 variants regardless of the their affinity to human cell receptor.

• Left) 12 different synthetic saponins were synthesized using Platycodin D as the base. Right) One of the synthetic saponins showed twice higher ability to inhibit SARS-CoV-2 infection. Credit: Institute for Basic Science
• Coronaviruses enter cells through membrane fusion between the virus envelope and cell membrane. When cells expressing coronavirus spike protein (green) are cultivated with human lung cells (red), membrane fusion followed by fusion between the two cells can be observed. Lansemaside A inhibits this membrane fusion, thereby confirming that its mechanism is based on blocking membrane fusion. Credit: Institute for Basic Science
• Astersaponin I, lancemaside A, and platycodin D are triterpenoid saponins with central ringed hydrocarbon structures similar to that of cholesterol. This allows one side of the saponin to become readily embedded within the cell membrane. It is believed that the polysaccharide chain protruding from the cell membrane is what prevents membrane fusion from occurring. Credit: Institute for Basic Science
• Left) 12 different synthetic saponins were synthesized using Platycodin D as the base. Right) One of the synthetic saponins showed twice higher ability to inhibit SARS-CoV-2 infection. Credit: Institute for Basic Science
• Coronaviruses enter cells through membrane fusion between the virus envelope and cell membrane. When cells expressing coronavirus spike protein (green) are cultivated with human lung cells (red), membrane fusion followed by fusion between the two cells can be observed. Lansemaside A inhibits this membrane fusion, thereby confirming that its mechanism is based on blocking membrane fusion. Credit: Institute for Basic Science

In the past, the IBS team worked jointly with Dr. Kim Seungtaek from Korea Pasteur Institute and discovered another natural triterpenoid saponin called platycotin D from the balloon flower. This saponin was also found to be effective against SARS-CoV-2 infection. This research was published in the journal Experimental & Molecular Medicine in May 2021.

Armed with this knowledge, the IBS researchers in collaboration with Prof. Han Sunkyu’s team from Korea Advanced Institute for Science and Technology (KAIST) explored the creation of synthetic saponins with potentially even more powerful effects. The joint team made and tested a dozen synthetic saponins possessing different polysaccharide chains with varying lengths and types of sugars. One of these saponins was found to have up to twice higher activity as that of platycodin D. This research was published in the 2022 October issue of the journal Bioorganic Chemistry.

Director C. Justin Lee stated, “Natural saponins contained in these plants are major constituents in many foods and herbal medicines that are readily accessible in everyday life. When ingested, it can be delivered at high concentrations to the epithelial cells of the upper respiratory tract, which means it can be effective in an asymptomatic or early stage of COVID-19 infection.” He added, “While their effects have been confirmed only in vitro at the moment, clinical trials may be possible in the future if positive results are obtained in animal tests.”

Senior Researcher Kim Taeyoung from the IBS said, “Historically, many important drugs such as penicillin, aspirin, or the antimalarial drug artemisinin have been derived from natural organisms. As these saponins’ mechanism of action relies on inhibiting membrane fusion, it may even be possible to develop broad-spectrum antiviral drugs based on this principle.”

More information: Tai Young Kim et al, Astersaponin I from Aster koraiensis is a natural viral fusion blocker that inhibits the infection of SARS-CoV-2 variants and syncytium formation, Antiviral Research (2022). DOI: 10.1016/j.antiviral.2022.105428

Tai Young Kim et al, Lancemaside A from Codonopsis lanceolata: studies on antiviral activity and mechanism of action against SARS-CoV-2 and its variants of concern, Antimicrobial Agents and Chemotherapy (2022). Accepted for publication. d197for5662m48.cloudfront.net/ … 84348128900f0fd5.pdf

Tai Young Kim et al, Platycodin D, a natural component of Platycodon grandiflorum, prevents both lysosome- and TMPRSS2-driven SARS-CoV-2 infection by hindering membrane fusion, Experimental & Molecular Medicine (2021). DOI: 10.1038/s12276-021-00624-9

Youngho Jang et al, Synthesis and structure–activity relationship study of saponin-based membrane fusion inhibitors against SARS-CoV-2, Bioorganic Chemistry (2022). DOI: 10.1016/j.bioorg.2022.105985

Journal information: Antimicrobial Agents and Chemotherapy 

Provided by Institute for Basic Science 

Oak Ridge National Laboratory scientists designed a recyclable polymer for carbon-fiber composites to enable circular manufacturing of parts that boost energy efficiency in automotive, wind power and aerospace applications.

Carbon-fiber composites, or fiber-reinforced polymers, are strong, lightweight materials that can help lower fuel consumption and reduce emissions in critical areas such as transportation. However, unlike metal competitors, carbon-fiber composites are not typically recyclable, meaning wider adoption could present waste challenges.

“Our goal is to extend the lifecycle of these materials by making reuse possible without sacrificing performance,” said ORNL’s Md Anisur Rahman.

The team’s approach incorporates dynamic covalent bonds that are reversible, enabling both carbon fiber and polymer recycling. The new polymer maintained mechanical strength in six reprocessing cycles, a sharp contrast to previously reported polymers.

“ORNL’s carbon-fiber composites enable fast processing and can be repaired or reprocessed multiple times, opening pathways to circular, low-carbon manufacturing,” said ORNL’s Tomonori Saito.

The research was published in Cell Reports Physical Science.

More information: Zhengping Zhou et al, Unraveling a path for multi-cycle recycling of tailored fiber-reinforced vitrimer composites, Cell Reports Physical Science (2022). DOI: 10.1016/j.xcrp.2022.101036

Journal information: Cell Reports Physical Science 

Provided by Oak Ridge National Laboratory 

For the past two centuries, humans have relied on fossil fuels for concentrated energy; hundreds of millions of years of photosynthesis packed into a convenient, energy-dense substance. But that supply is finite, and fossil fuel consumption has tremendous negative impact on Earth’s climate.

“The biggest challenge many people don’t realize is that even nature has no solution for the amount of energy we use,” said University of Chicago chemist Wenbin Lin. Not even photosynthesis is that good, he said: “We will have to do better than nature, and that’s scary.”

One possible option scientists are exploring is “artificial photosynthesis“—reworking a plant’s system to make our own kinds of fuels. However, the chemical equipment in a single leaf is incredibly complex, and not so easy to turn to our own purposes.

A Nature Catalysis study from six chemists at the University of Chicago shows an innovative new system for artificial photosynthesis that is more productive than previous artificial systems by an order of magnitude. Unlike regular photosynthesis, which produces carbohydrates from carbon dioxide and water, artificial photosynthesis could produce ethanol, methane, or other fuels.

Though it has a long way to go before it can become a way for you to fuel your car every day, the method gives scientists a new direction to explore—and may be useful in the shorter term for production of other chemicals.

“This is a huge improvement on existing systems, but just as importantly, we were able to lay out a very clear understanding of how this artificial system works at the molecular level, which has not been accomplished before,” said Lin, who is the James Franck Professor of Chemistry at the University of Chicago and senior author of the study.

‘We will need something else’

“Without natural photosynthesis, we would not be here. It made the oxygen we breathe on Earth and it makes the food we eat,” said Lin. “But it will never be efficient enough to supply fuel for us to drive cars; so we will need something else.”

The trouble is that photosynthesis is built to create carbohydrates, which are great for fueling us, but not our cars, which need much more concentrated energy. So researchers looking to create alternates to fossil fuels have to re-engineer the process to create more energy-dense fuels, such as ethanol or methane.

In nature, photosynthesis is performed by several very complex assemblies of proteins and pigments. They take in water and carbon dioxide, break the molecules apart, and rearrange the atoms to make carbohydrates—a long string of hydrogen-oxygen-carbon compounds. Scientists, however, need to rework the reactions to instead produce a different arrangement with just hydrogen surrounding a juicy carbon core—CH₄, also known as methane.

This re-engineering is much trickier than it sounds; people have been tinkering with it for decades, trying to get closer to the efficiency of nature.

Lin and his lab team thought that they might try adding something that artificial photosynthesis systems to date haven’t included: amino acids.

The team started with a type of material called a metal-organic framework or MOF, a class of compounds made up of metal ions held together by an organic linking molecules. Then they designed the MOFs as a single layer, in order to provide the maximum surface area for chemical reactions, and submerged everything in a solution that included a cobalt compound to ferry electrons around. Finally, they added amino acids to the MOFs, and experimented to find out which worked best.

They were able to make improvements to both halves of the reaction: the process that breaks apart water and the one that adds electrons and protons to carbon dioxide. In both cases, the amino acids helped the reaction go more efficiently.

Even with the significantly improved performance, however, artificial photosynthesis has a long way to go before it can produce enough fuel to be relevant for widespread use. “Where we are now, it would need to scale up by many orders of magnitude to make an sufficient amount of methane for our consumption,” Lin said.

The breakthrough could also be applied widely to other chemical reactions; you need to make a lot of fuel for it to have an impact, but much smaller quantities of some molecules, such as the starting materials to make pharmaceutical drugs and nylons, among others, could be very useful.

“So many of these fundamental processes are the same,” said Lin. “If you develop good chemistries, they can be plugged into many systems.”

More information: Guangxu Lan et al, Biomimetic active sites on monolayered metal–organic frameworks for artificial photosynthesis, Nature Catalysis (2022). DOI: 10.1038/s41929-022-00865-5

Journal information: Nature Catalysis 

Provided by University of Chicago 

It is possible to capture carbon dioxide (CO₂) from the surrounding atmosphere and repurpose it into useful chemicals usually made from fossil fuels, according to a study from the University of Surrey.

The technology could allow scientists to both capture CO₂ and transform it into useful chemicals such as carbon monoxide and synthetic natural gas in one circular process.

Dr. Melis Duyar, senior lecturer of chemical engineering at the University of Surrey explained: “Capturing CO₂ from the surrounding air and directly converting it into useful products is exactly what we need to approach carbon neutrality in the chemicals sector. This could very well be a milestone in the steps needed for the U.K. to reach its 2050 net-zero goals.

“We need to get away from our current thinking on how we produce chemicals, as current practices rely on fossil fuels which are not sustainable. With this technology we can supply chemicals with a much lower carbon footprint and look at replacing fossil fuels with carbon dioxide and renewable hydrogen as the building blocks of other important chemicals.”

The technology uses patent-pending switchable Dual Function Materials (DFMs) that capture carbon dioxide on their surface and catalyze the conversion of captured CO₂ directly into chemicals. The “switchable” nature of the DFMs comes from their ability to produce multiple chemicals depending on the operating conditions or the composition of the added reactant. This makes the technology responsive to variations in demand for chemicals as well as availability of renewable hydrogen as a reactant.

Loukia-Pantzechroula Merkouri, Postgraduate student leading this research at the University of Surrey added, “Not only does this research demonstrate a viable solution to the production of carbon neutral fuels and chemicals, but it also offers an innovative approach to combat the ever-increasing CO₂ emissions contributing to global warming.”

The research is published in Nanoscale.

More information: Loukia-Pantzechroula Merkouri et al, Feasibility of switchable dual function materials as a flexible technology for CO2 capture and utilisation and evidence of passive direct air capture, Nanoscale (2022). DOI: 10.1039/D2NR02688K

Journal information: Nanoscale 

A research group led by Susumu Kitagawa of Kyoto University’s Institute for Cell-Material Sciences (iCeMS), Japan and Cheng Gu of South China University of Technology, China have made a material that can effectively separate heavy water from normal water at room temperature.

Until now, this process has been very difficult and energy intensive. The findings have implications for industrial—and even biological—processes that involve using different forms of the same molecule. The scientists reported their results in the journal Nature.

Isotopologues are molecules that have the same chemical formula and whose atoms bond in similar arrangements, but at least one of their atoms has a different number of neutrons than the parent molecule. For example, a water molecule (H₂O) is formed of one oxygen and two hydrogen atoms.

The nucleus of each of the hydrogen atoms contains one proton and no neutrons. In heavy water (D₂O), on the other hand, the deuterium (D) atoms are hydrogen isotopes with nuclei containing one proton and one neutron. Heavy water has applications in nuclear reactors, medical imaging and in biological investigations.

“Water isotopologues are among the most difficult to separate because their properties are so similar,” explains materials scientist Cheng Gu. “Our work provided an unprecedented mechanism for separating water isotopologues using an adsorption-separation method.”

Gu and chemist Susumu Kitagawa, together with colleagues, based their separation technique on a copper-based porous coordination polymer (PCP). PCPs are porous crystalline materials formed of metal nodes connected by organic linkers. The team tested two PCPs made with different types of linkers.

What makes their PCPs especially important for isotopologue separation is that the linkers flip when moderately heated. This flipping action acts like a gate, allowing molecules to pass from one ‘cage’ in the PCP to another. Movement is blocked when the material is cooled.

When the scientists exposed their “flip-flop dynamic crystals” to vapor containing a mixture of normal, heavy and semi-heavy water and then slightly warmed it, they adsorbed normal water much faster than they did the other two isotopologues. Crucially, this process happened within room temperature ranges.

“The adsorptive separation of water isotopologues in our work is substantially superior to conventional methods due to very high selectivity at room temperature operation,” says Kitagawa. “We are optimistic that new materials guided by our work will be developed to separate other isotopologues.”

More information: Cheng Gu, Separating water isotopologues using diffusion-regulatory porous materials, Nature (2022). DOI: 10.1038/s41586-022-05310-y. www.nature.com/articles/s41586-022-05310-y

Journal information: Nature 

Provided by Kyoto University 

To convert heat into electricity, easily accessible materials from harmless raw materials open up new perspectives in the development of safe and inexpensive so-called “thermoelectric materials.” A synthetic copper mineral acquires a complex structure and microstructure through simple changes in its composition, thereby laying the foundation for the desired properties, according to a study published in the journal Angewandte Chemie.

The novel synthetic material is composed of copper, manganese, germanium, and sulfur, and it is produced in a rather simple process, explains materials scientist Emmanuel Guilmeau, CNRS researcher at CRISMAT laboratory, Caen, France, who is the corresponding author of the study. “The powders are simply mechanically alloyed by ball-milling to form a precrystallized phase, which is then densified by 600 degrees Celsius. This process can be easily scaled up,” he says.

Thermoelectric materials convert heat to electricity. This is especially useful in industrial processes where waste heat is reused as valuable electric power. The converse approach is the cooling of electronic parts, for example, in smartphones or cars. Materials used in this kind of applications have to be not only efficient, but also inexpensive and, above all, safe for health.

However, thermoelectric devices used to date make use of expensive and toxic elements such as lead and tellurium, which offer the best conversion efficiency. To find safer alternatives, Emmanuel Guilmeau and his team have turned to derivatives of natural copper-based sulfide minerals. These mineral derivatives are mainly composed of nontoxic and abundant elements, and some of them have thermoelectric properties.

Now, the team has succeeded in producing a series of thermoelectric materials showing two crystal structures within the same material. “We were very surprised at the result. Usually, slightly changing the composition has little effect on the structure in this class of materials,” says Emmanuel Guilmeau, describing their discovery.

The team found that replacing a small fraction of the manganese with copper produced complex microstructures with interconnected nanodomains, defects, and coherent interfaces, which affected the material’s transport properties for electrons and heat.

Emmanuel Guilmeau says that the novel material produced is stable up to 400 degrees Celsius, a range well within the waste heat temperature range of most industries. He is convinced that, based on this discovery, cheaper novel and nontoxic thermoelectric materials could be designed to replace more problematic materials.

More information: V. Pavan Kumar et al, Engineering Transport Properties in Interconnected Enargite‐Stannite Type Cu 2+ x Mn 1− x GeS 4 Nanocomposites, Angewandte Chemie International Edition (2022). DOI: 10.1002/anie.202210600

Journal information: Angewandte Chemie International Edition , Angewandte Chemie

Provided by Wiley

A team of researchers at the Chinese Academy of Sciences, working with a colleague from the State University of New Jersey, has developed a gel-based code-hiding system that uses combinations of water, light and heat to hide and reveal hidden codes. In their paper published in the journal Science Advances, the group describes how their gel is made and the possible uses for it.

A variety of techniques are used to keep sensitive information safe from prying eyes—requiring passcodes before gaining access to a bank account, for example. Other techniques are required to prevent counterfeiting of sensitive documents, such as passports or paper money. Currently, most methods that have been developed to prevent counterfeiting involve adding an attribute to the material to be protected—a watermark, for example, that glows under a UV light. In this new effort, the researchers developed a new means for preventing counterfeiting that can also be used to convey passcodes.

The work involved manipulating types of molecules called donor-acceptor Stenhouse adducts (DASAs)—they change from a given color to transparent when exposed to normal light. The researchers created 12 molecules that change from reflecting colors to transparency when exposed to certain combinations of water, light and heat. By allowing for mixing up the amount of each that are used, the three ingredients represent a cypher of sorts. To use such a cypher, the researchers embedded the molecules in a polymer.

In practice, a person would choose desired ratios of light, water and heat and then use the gel as a sort of ink to print number codes onto a piece of paper in the format of numbers displayed on a digital clock. Each of the segments making up a number would have different amounts of DASAs. The ratios would then be divulged only to those people who are supposed to have access to the code.

Such a system could be used to verify the authenticity of documents such as passports or cash money. It could also be used to convey passcodes. Banks, for example, could securely send passwords to customers via printed documents. The researchers suggest their gel could prove useful in a wide variety of applications because it would be difficult to mimic the conditions needed to access the hidden data.

More information: Yu Dong et al, Harnessing molecular isomerization in polymer gels for sequential logic encryption and anticounterfeiting, Science Advances (2022). DOI: 10.1126/sciadv.add1980

Journal information: Science Advances 

Rotary molecular motors were first created in 1999, in the laboratory of Ben Feringa, Professor of Organic Chemistry at the University of Groningen. These motors are driven by light. For many reasons, it would be good to be able to make these motor molecules visible. The best way to do this is to make them fluoresce. However, combining two light-mediated functions in a single molecule is quite challenging. The Feringa laboratory has now succeeded in doing just that, in two different ways. These two types of fluorescing light-driven rotary motors were described in Nature Communications (September 30) and Science Advances (November 4).

“After the successful design of molecular motors in the past decades, an important next goal was to control various functions and properties using such motors,” explains Feringa, who shared in the Nobel Prize in Chemistry in 2016. “As these are light-powered rotary motors, it is particularly challenging to design a system that would have another function that is controlled by light energy, in addition to the rotary motion.”

Feringa and his team were particularly interested in fluorescence since this is a prime technique that is widely used for detection, for example in biomedical imaging. Usually, two such photochemical events are incompatible in the same molecule; either the light-driven motor operates and there is no fluorescence or there is fluorescence and the motor does not operate. Feringa says, “We have now demonstrated that both functions can exist in parallel in the same molecular system, which is rather unique.”

Ryojun Toyoda, a postdoctoral researcher in the Feringa group, who now holds a professor position at Tohoku University in Japan, added a fluorescent dye to a classic Feringa rotary motor. “The trick was to prevent these two functionalities from blocking each other,” says Toyoda. He managed to quench the direct interactions between the dye and the motor. This was done by positioning the dye perpendicular to the upper part of the motor to which it was attached. “This limits the interaction,” Toyoda explains.

Different colors

In this way, the fluorescence and the rotary function of the motor can coexist. Furthermore, it turned out that changing the solvent allows him to tune the system: “By varying the solvent polarity, the balance between both functions can be changed.” This means that the motor has become sensitive to its environment, which could point the way for future applications.

Co-author Shirin Faraji, professor of Theoretical Chemistry at the university of Groningen, helped to explain how this happens. Kiana Moghaddam, a postdoc in her group, performed extensive quantum mechanical calculations and demonstrated how the key energetics governing the photo-excited dynamics strongly depend on the solvent polarity.

Another useful property of this fluorescing motor molecule is that different dyes could be attached to it as long as they have a similar structure. “So, it is relatively easy to create motors that are glowing in different colors,” says Toyoda.

Antenna

A second fluorescent motor was constructed by Lukas Pfeifer, also while working as a postdoctoral researcher in the Feringa group. He has since joined the École Polytechnique Fédérale in Lausanne, Switzerland: “My solution was based on a motor molecule that I had already made, which is driven by two low-energy near-infrared photons.” Motors that are powered by near-infrared light are useful in biological systems, as this light penetrates deeper into tissue than visible light and is less harmful to the tissue than UV light.

“I added an antenna to the motor molecule that collects the energy of two infrared photons and transfers it to the motor. While working on this, we discovered that with some modifications, the antenna could also cause fluorescence,” says Pfeifer. It turned out that the molecule can have two different excited states: in one state, the energy is transferred to the motor part and drives rotation, while the other state causes the molecule to fluoresce.

Power

“In the case of this second motor, the entire molecule fluoresces,” explains Professor Maxim Pshenichnikov, who performed spectroscopic analysis of both types of fluorescent motor and who is a co-author of both papers. “This motor is one chemical entity on which the wave function is not localized and, depending on the energy level, can have two different effects. By altering the wavelength of the light, and thus the energy that the molecule receives, you get either rotation or fluorescence.” Faraji adds, “Our synergized in-principle and in-practice approach highlights the interplay between theoretical and experimental studies, and it illustrates the power of such combined efforts.”

Now that the team has combined both motion and fluorescence in the same molecule, a next step would be to show motility and detect the molecule’s location simultaneously by tracing the fluorescence. Feringa says, “This is very powerful and we might apply it to show how these motors might traverse a cell membrane or move inside a cell, as fluorescence is a widely used technique to show where molecules are in cells. We could also use it to trace the movement that is induced by the light-powered motor, for instance on a nanoscale trajectory or perhaps trace motor-induced transport on the nanoscale. This is all part of follow-up research.”

More information: Ryojun Toyoda et al, Synergistic interplay between photoisomerization and photoluminescence in a light-driven rotary molecular motor, Nature Communications (2022). DOI: 10.1038/s41467-022-33177-0

Lukas Pfeifer et al, Dual Function Artificial Molecular Motors Performing Rotation and Photoluminescence, Science Advances (2022). DOI: 10.1126/sciadv.add0410. www.science.org/doi/10.1126/sciadv.add0410

Journal information: Science Advances  , Nature Communications 

Provided by University of Groningen 

Physicists at the Ural Federal University (UrFU) have created a theory for the solidification of iron-nickel (Fe-Ni) alloy (invar). They determined that an important role in the technology of creating invar products, namely in the solidification process, is played by the oncoming flow: when an alloy cools, the liquid layer flows on top of the solidified layer. If this process is regulated, it is possible to control the characteristics of the alloys, obtain a more uniform structure, and improve the properties of the final product.

Nickel and iron alloys are used to create high-precision instruments, including clocks, seismic sensors, chip substrates, valves and engines in aircraft structures, and instruments for telescopes. The right calculations will help to create an alloy of the required structure, which will affect the quality of the finished products. A description of the model and the behavior of melts, as well as analytical calculations, was published in the journal Scientific Reports.

“Let me explain the work with the help of an analogy. When the water freezes, it pushes out all the dirt. So you can take a piece of ice in your mouth, it will be clean. Approximately the same happens with melts during cooling. Only they do not push out all the impurities, but some of them. Some of the impurities come out and some remain in the melt.”

“What remains in the melt fills the gaps between the crystals that solidify and the voids that remain. Thus, the alloys are heterogeneous: one tiny piece is enriched, while the neighboring piece is not. And it affects the properties of the finished product,” says Dmitri Alexandrov, Head of the Ural Federal University’s Laboratory of Multi-Scale Mathematical Modeling.

The main thing that scientists have shown is the processes in a two-phase layer: a layer in which both solid and liquid phases are located, inside it there is a transformation from a liquid state to a solid one.

“This layer completely changes the crystallization scenario. Thus, for example, the temperature at each point of this layer is lower than the crystallization temperature, and crystallites and dendrites release the heat of phase transformation and thus partially compensate for supercooling.”

“In addition, the growing solid phase displaces the dissolved impurity, which lowers the crystallization temperature. These processes lead to the formation of complex branched structures of the solid phase, the gaps between which are filled by a liquid with a higher concentration of impurities,” says Liubov Toropova, senior researcher at the Laboratory of Mathematical Modeling of Physical and Chemical Processes at UrFU.

The name “invar” comes from the word “unchanging,” as the alloy almost does not expand or contract when the temperature changes. The first invar alloy was discovered by Swiss scientist Charles Edouard Guillaume in 1896. In 1920 he received the Nobel Prize in Physics for it.

This alloy of nickel and iron is used when a serious dimensional stability of finished parts is required: in precision instruments, clocks, valves, etc. One of the first applications of invar is rods for pendulum clocks. At the time when the pendulum clock was invented, it was the most precise chronometer in the world. Today, invar is also used in astronomy, as components that support the size-sensitive optics of astronomical telescopes.

More information: Dmitri V. Alexandrov et al, The role of incoming flow on crystallization of undercooled liquids with a two-phase layer, Scientific Reports (2022). DOI: 10.1038/s41598-022-22786-w

Journal information: Scientific Reports 

Provided by Ural Federal University 

In recent years, many engineers and material scientists have been trying to develop sustainable energy solutions that could help to mitigate climate change on Earth. This includes carbon capture technologies, which are specifically designed to capture or absorb carbon dioxide (CO₂) in sites where it is widely produced, such as power generation plants or industrial facilities that rely on biomass or burning fossil fuels.

While some carbon capture solutions achieved promising results, those based on conventional wet chemical scrubbing methods utilizing sp³ amines often consume too much energy and are prone to corrosion and sorbent degradation. This significantly limits their widespread implementation, highlighting the need for alternative CO₂ separation strategies.

Researchers at Johns Hopkins University, the University of Texas at Austin and Massachusetts Institute of Technology (MIT) have recently introduced a series of redox-tunable Lewis bases (i.e., molecules with a lone pair of electrons that can be donated to a coordinate covalent bond) with sp² nitrogen centers that can reversibly capture and release CO₂. In their paper, published in Nature Energy, they also outline strategies to fine-tune the properties of these Lewis bases.

“We demonstrate a library of redox-tunable Lewis bases with sp²-nitrogen centers that can reversibly capture and release carbon dioxide through an electrochemical cycle,” Xing Li, Xunhua Zhao, Yuanyue Liu, T. Alan Hatton and Yayuan Liu wrote in their paper. “The mechanism of the carbon capture process is elucidated via a combined experimental and computational approach.”

The researchers’ recent work is based on the idea that due to their CO₂ affinity, Lewis bases with redox-active sp² nitrogen centers could be modulated using electrochemical potentials, enabling the development of alternative, more effective carbon capture solutions. To verify this hypothesis, the researchers compiled a library of organic bases containing sp² nitrogen centers, including pyradine, diazine, thiadizole and azo moieties.

“While in the oxidized form, none of these compounds shows strong interactions with CO₂,” the researchers wrote in their paper. “However, their electro-reduction and subsequent oxidation behavior can be drastically modulated by the presence of CO₂ in the electrolyte.”

Li and his colleagues clearly outlined the mechanism that allows the Lewis base sorbents to capture carbon in both computational simulations and experiments. Subsequently, they showed that the properties of these sorbents can be fine-tuned (i.e., tailored for specific uses) using both molecular design and electrolyte engineering methods. By fine-tuning the properties of the Lewis bases they created, the researchers were then able to identify a particularly promising Lewis base based on bifunctional azopyridine.

“We identify a bifunctional azopyridine base that holds promise for electrochemically mediated carbon capture, exhibiting >85% capacity utilization efficiency over cycling in a flow system under 15% carbon dioxide with 5% oxygen,” Li and his colleagues wrote in their paper. “This work broadens the structural scope of redox-active carbon dioxide sorbents and provides design guidelines on molecules with tunable basicity under electrochemical conditions.”

In the future, the bifunctional azopyridine base identified by Li and his colleagues could be used to create more energy-efficient and effective carbon capture technologies. In addition, their work could pave the way towards the development of other carbon capture solutions based on Lewis base sorbents.

More information: Xing Li et al, Redox-tunable Lewis bases for electrochemical carbon dioxide capture, Nature Energy (2022). DOI: 10.1038/s41560-022-01137-z

Journal information: Nature Energy 

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