Tag Archives: Chemistry

How To Make Lithium-ion Batteries Invincible? (Chemistry)

Berkeley Lab researchers are developing a family of cathode materials that have all of the advantages of conventional lithium batteries but without the supply constraints

In our future electrified world, the demand for battery storage is projected to be enormous, reaching to upwards of 2 to 10 terawatt-hours (TWh) of annual battery production by 2030, from less than 0.5 TWh today. However, concerns are growing as to whether key raw materials will be adequate to meet this future demand. The lithium-ion battery – the dominant technology for the foreseeable future – has a component made of cobalt and nickel, and those two metals face severe supply constraints on the global market.

Now, after several years of research led by Lawrence Berkeley National Laboratory (Berkeley Lab), scientists have made significant progress in developing battery cathodes using a new class of materials that provide batteries with the same if not higher energy density than conventional lithium-ion batteries but can be made of inexpensive and abundant metals. Known as DRX, which stands for disordered rocksalts with excess lithium, this novel family of materials was invented less than 10 years ago and allows cathodes to be made without nickel or cobalt.

“The classic lithium-ion battery has served us well, but as we consider future demands for energy storage, its reliance on certain critical minerals exposes us not only to supply-chain risks, but also environmental and social issues,” said Ravi Prasher, Berkeley Lab’s Associate Lab Director for Energy Technologies. “With DRX materials, this offers lithium batteries the potential to be the foundation for sustainable battery technologies for the future.”

The cathode is one of the two electrodes in a battery and accounts for more than one-third of the cost of a battery. Currently the cathode in lithium-ion batteries uses a class of materials known as NMC, with nickel, manganese, and cobalt as the key ingredients.

“I’ve done cathode research for over 20 years, looking for new materials, and DRX is the best new material I’ve ever seen by far,” said Berkeley Lab battery scientist Gerbrand Ceder, who is co-leading the research. “With the current NMC class, which is restricted to just nickel, cobalt, and an inactive component made of manganese, the classic lithium-ion battery is at the end of its performance curve unless you transfer to new cathode materials, and that’s what the DRX program offers. DRX materials have enormous compositional flexibility – and this is very powerful because not only can you use all kinds of abundant metals in a DRX cathode, but you can also use any type of metal to fix any problem that might come up during the early stages of designing new batteries. That’s why we’re so excited.”

Cobalt and nickel supply-chain risks

The U.S. Department of Energy (DOE) has made it a priority to find ways to reduce or eliminate the use of cobalt in batteries. “The battery industry is facing an enormous resource crunch,” said Ceder. “Even at 2 TWh, the lower range of global demand projections, that would consume almost all of today’s nickel production, and with cobalt we’re not even close. Cobalt production today is only about 150 kilotons, and 2 TWh of battery power would require 2,000 kilotons of nickel and cobalt in some combination.”

What’s more, over two-thirds of the world’s nickel production is currently used to make stainless steel. And more than half of the world’s production of cobalt comes from the Democratic Republic of Congo, with Russia, Australia, the Philippines, and Cuba rounding out the top five producers of cobalt.

In contrast, DRX cathodes can use just about any metal in place of nickel and cobalt. Scientists at Berkeley Lab have focused on using manganese and titanium, which are both more abundant and lower cost than nickel and cobalt.

“Manganese oxide and titanium oxide cost less than $1 per kilogram whereas cobalt costs about $45 per kilogram and nickel about $18,” said Ceder. “With DRX you have the potential to make very inexpensive energy storage. At that point lithium-ion becomes unbeatable and can be used everywhere – for vehicles, the grid – and we can truly make energy storage abundant and inexpensive.”

Ordered vs. disordered

Ceder and his team developed DRX materials in 2014. In batteries, the number and speed of lithium ions able to travel into the cathode translates into how much energy and power the battery has. In conventional cathodes, lithium ions travel through the cathode material along well-defined pathways and arrange themselves between the transition metal atoms (usually cobalt and nickel) in neat, orderly layers.

Berkeley Lab battery scientists Gerbrand Ceder (left) and Guoying Chen co-lead the “deep dive” into DRX materials. © Marilyn Sargent/Berkeley Lab

What Ceder’s group discovered was that a cathode with a disordered atomic structure could hold more lithium – which means more energy – while allowing for a wider range of elements to serve as the transition metal. They also learned that within that chaos, lithium ions can easily hop around.

In 2018, the Vehicle Technologies Office in DOE’s Office of Energy Efficiency and Renewable Energy provided funding for Berkeley Lab to take a “deep dive” into DRX materials. In collaboration with scientists at Oak Ridge National Laboratory, Pacific Northwest National Laboratory, and UC Santa Barbara, Berkeley Lab teams led by Ceder and Guoying Chen have made tremendous progress in optimizing DRX cathodes in lithium-ion batteries.

For example, the charge rate – or how fast the battery can charge – of these materials was initially very low, and its stability was also poor. The research team has found ways to address both of these issues through modeling and experimentation. Studies on using fluorination to improve stability have been published in Advanced Functional Materials and Advanced Energy Materials; research on how to enable a high charging rate was recently published in Nature Energy.

Illustration of a DRX cathode’s “disordered” atomic structure (right) versus the “ordered” atomic structure of a conventional cathode. A disordered cathode structure can store more lithium – which means more energy – while allowing for a wider range of elements to serve as the transition metal. © Berkeley Lab

Since DRX can be made with many different elements, the researchers have also been working on which element would be best to use, hitting the sweet spot of being abundant, inexpensive, and providing good performance. “DRX has now been synthesized with almost the whole periodic table,” Ceder said.

“This is science at its best – fundamental discoveries that will serve as the bedrock of systems in future homes, vehicles, and grids,” said Noel Bakhtian, director of Berkeley Lab’s Energy Storage Center. “What has made Berkeley Lab so successful in battery innovation for decades now is our combination of breadth and depth of expertise – from fundamental discovery to characterization, synthesis, and manufacturing, as well as energy markets and policy research. Collaboration is key – we partner with industry and beyond to solve real-world problems, which in turn helps galvanize the world-leading science we do at the Lab.”

Fast progress

New battery materials have traditionally taken 15 to 20 years to commercialize; Ceder believes progress on DRX materials can be accelerated with a larger team. “We’ve made great progress in the last three years with the deep dive,” Ceder said. “We’ve come to the conclusion that we’re ready for a bigger team, so we can involve people with a more diverse set of skills to really refine this.”

An expanded research team could move quickly to address the remaining issues, including improving the cycle life (or the number of times the battery can be recharged and discharged over its lifetime) and optimizing the electrolyte, the chemical medium that allows the flow of electrical charge between the cathode and anode. Since being developed in Ceder’s lab, groups in Europe and Japan have also launched large DRX research programs.

“Advances in battery technologies and energy storage will require continued breakthroughs in the fundamental science of materials,” said Jeff Neaton, Berkeley Lab’s Associate Lab Director for Energy Sciences. “Berkeley Lab’s expertise, unique facilities, and capabilities in advanced imaging, computation, and synthesis allow us to study materials at the scale of atoms and electrons. We are well poised to accelerate the development of promising materials like DRX for clean energy.”

Featured image: Jingyang Wang holds up a ceramic palette sample prepared for the DRX research program co-led by Gerbrand Ceder and Guoying Chen at Berkeley Lab. © Marilyn Sargent/Berkeley Lab


Reference: Huang, J., Zhong, P., Ha, Y. et al. Non-topotactic reactions enable high rate capability in Li-rich cathode materials. Nat Energy (2021). https://doi.org/10.1038/s41560-021-00817-6


Provided by LBL

MOF Metallic Mastery (Chemistry)

The tightly defined ratios of metals in metallic organic frameworks makes them ideal starting materials for novel catalyst creation.

The tightly defined ratios of metals in MOFs makes them ideal starting materials for novel catalyst creation.

Heating bimetallic metal organic frameworks (MOFs) until their porous structure collapses into nanoparticles can be a highly effective way to make catalysts. This novel approach to catalyst design has now been used by KAUST and Spanish researchers to make a robust catalyst that converts carbon dioxide (CO2) into carbon monoxide (CO) gas with unprecedented selectivity. 

The benefit of this method pioneered at KAUST is that it can generate mixed metal catalytic nanoparticles that have proven challenging or impossible to make by conventional means.

Video: KAUST researchers develop a novel approach to catalyst design using metal organic frameworks. © 2021 KAUST. https://discovery.kaust.edu.sa/en/article/1126/mof-metallic-mastery

Capturing CO2 emissions and catalytically converting the greenhouse gas into CO, a valuable chemical feedstock, is one option for reducing greenhouse gases associated with climate change. Precious metals can catalyze this reaction, but they are costly and supplies are limited, says Samy Ould-Chikh, a research engineer in KAUST.

“Iron oxide catalysts are an inexpensive alternative,” Ould-Chikh says. “However, in the presence of CO, the iron is carburized forming iron carbide, which leads to by-product formation and catalyst deactivation.”

Adding titanium to the catalyst particles could stabilize iron oxide against carburization. Chemical incompatibilities between iron and titanium precursors, however, had made it impossible to synthesize nanoparticles incorporating a homogenous mixture of the two metals in the necessary ratio. To overcome this limitation, the team turned to MOFs, porous materials made from metal ions connected together by carbon-based linkers.

“The use of MOFs allows us to perfectly control the iron-titanium ratio on the parent MOF,” says research engineer Adrian Ramirez Galilea. Heating decomposes the organic part of the MOF, leaving the two metals behind, homogenously mixed in the desired ratio and in neat octahedral nanoparticles that mirror the structure of the parent MOF.

The nanoparticles converted CO2 to CO with 100 percent selectivity, with no sign of deactivation after several days of use. “Our initial calculations suggested that nanoparticles with such atomic ratios should be able to do the job; however, the results far exceeded our original expectations,” Gascon says.

As well as continuing to explore the properties and reactivity of the iron-titanium nanocatalyst, the team is examining other metal catalyst systems made from MOFs in the same way. “The use of MOFs opens the way to synthesize new catalysts that were not possible to make using conventional approaches,” Ramirez Galilea says.

“We are looking at different metal combinations for applications ranging from traditional thermal catalysis to photo and photothermal catalysis,” adds Jorge Gascon, who led the research. “This paper is just the tip of the iceberg.”

Featured image: The use of MOFs opens the way to make new catalysts that are not possible to synthesize using conventional approaches. Adapted from Castells-Gil et al. 2021.


References

  1. Castells-Gil, J., Ould-Chikh, S., Ramirez, A., Ahmad, R., Prieto, G., Rodriguez Gómez, A., Garzon-Tovar, L., Telalovic, S., Liu, L., Genovese, A., Padial, N.M., Aguilar-Tapia, A., Bordet, P., Cavallo, L., Martí-Gastaldo, C. & Gascon, J. Unlocking mixed oxides with unprecedented stoichiometries from heterometallic Metal Organic Frameworks. Implications for the catalytic hydrogenation of CO2Chem Catalysis, advance online publication 26 April 2021.| article

Provided by KAUST

Researchers Realize Controlled Self-assembly and Multistimuli-responsive Interconversions of 3 Conjoined Twin-cages (Chemistry)

Supramolecular transformations within coordination-assembled architectures have attracted great attention over the past two decades because fundamental biomolecules are found to be capable of achieving biological functions through conformational changes.

Well-controlled interconversion between topologically complex superstructures may lay the foundation for achieving a variety of functions within a switchable system. The size, shape and nature properties between interconvertible cage-shaped molecules have been altered accompanied by the structural interconversions with the output of structurally dependent properties and functions.

In a study published in J. Am. Chem. Soc., the research group led by Prof. Sun Qingfu from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported the controlled self-assembly of three topologically-unprecedented conjoined twin-cages, i.e. one stapled interlocked Pd12L6 cage 2 and two helically-isomeric Pd6L3 cages 3 and 4, made from the same cis-blocked palladium corners and a new bis-bidentate ligand.

The researchers provided reliable evidence for these unique conjoined twin-cage structures by X-ray crystallographic analysis.

Cage 2 features three mechanically-coupled cavities, while cages 3 and 4 are topologically-isomeric helicate-based twin-cages based on the same metal/ligand stoichiometry. Cage 2 shows a S6 molecular symmetry, containing six ligands, with each ligand from the left interlocking with the other two ligands for the right and vice versa. The structure of 3 has a C2 symmetry, where two pyridinium ligands intertwines with each other, and the third one is independent. While cage 4 possesses a higher D3 symmetry with three ligands arranged in a triple helicate conformation. These structures are in good agreement with the nuclear magnetic Resonance (NMR) analysis.

Besides, the researchers realized the controllable structural conversions by fine-tuning experimental conditions, including solvents, temperature, anions, and guest molecules, and controlled the sole formation of cage 2 or a dynamic mixture of cage 3 and 4 by changing the solvents employed during the self-assembly.

Once acetone was added into the self-assembly, a mixture of cages 3 and 4 was formed. BF4 anion plays an important role in the structure conversion from cages 3 and 4 to cage 2, which is favorable due to enthalpic benefits from the host-guest interaction. Structural conversions between cages 3 and 4 can been both triggered by changes in temperature/solvent and induce-fit guest encapsulations.

Through variable-temperature NMR spectra, the researchers calculated thermodynamic parameters based on the van’t Hoff equation. The results showed that the system favors the transformation from cage 3 to cage 4 at higher temperature.

Interestingly, induced-fit guest encapsulations triggered the structural conversion from 3 to 4 completely. Addition of 1-adamantanecarboxylic acid or 1-adamantanol to the mixture of cage 3 and 4 resulted in the distinct change in 1H NMR spectra, where a simple set of host signals of the inclusion complex of cage 4 was observed finally.

The researchers obtained the X-ray structure of the host-guest complex, which shows the encapsulation of eight 1-adamantanol molecules in the two pockets of cage 4. They inferred that the strong host-guest interactions are the origin of induced-fit structural conversion from cage 3 to 4.

In this study, stimuli-responsive structural transformations between discrete coordination supramolecular architectures provide a versatile molecular-level platform to mimic the biological transformation process.

Featured image: Schematic illustration of the research (Image by Prof. SUN’s group)


Reference

Controlled Self-Assembly and Multistimuli-Responsive Interconversions of Three Conjoined Twin-Cages


Provided by Chinese Academy of Sciences

Novel Approach to Precisely Control Gas-liquid Taylor Flow Pattern for Continuous Flow Chemistry

Microreactor exhibits great potential for intensified synthesis of advanced materials and chemicals in continuous flow mode, for its various advantages such as excellent heat and mass transfer efficiency, high controllability, easy scale-up, etc. Among numerous flow patterns, gas-liquid Taylor Flow has been proven as an ideal flow regime to enhance chemical reactions. However, the method to precisely control the Taylor flow pattern is still lacking. 

Motivated by such a challenge, a research team led by Prof. TANG Zhiyong and Associate Prof. ZHANG Jie at the Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences (CAS) reported a novel approach of adding pulsation field to precisely regulate the gas-liquid Taylor Flow. Results were published in Chemical Engineering Journal

In this research, the research team used a simple valve arrangement to introduce the pulsation filed, thus producing periodic acceleration and deceleration motion of liquid slugs.

Space-time distribution of gas fraction in bubble formation process (Image by SARI)

By combing visual flow experiments with computational fluid dynamics (CFD) simulation, the temporal-spatial migration of the Taylor flow pattern under pulsating gas intake conditions was investigated. A high-speed camera was used to track the trajectory of gas-liquid interface by the Lagrangian method, while the numerical simulation is used to acquire the flow field distribution at different moments using the Euler method.

Meanwhile, the involved forces during bubble formation and the characteristics of bubble length and velocity under pulsation were analyzed in detail.

(a) Forces versus pulse frequency f at the T-junction, (b) Bubble velocities at downstream (Image by SARI) 

Through studying the temporal-spatial migration of the pattern, the researchers found that the pulsation can increase the power of inertial force on the Taylor flow pattern. Moreover, the pattern can be destroyed when the pulsation energy exceeds a certain value. 

This work provides a new route to regulate precisely the gas-liquid Taylor flow, and will contribute to future applications of this technique to intensify various gas-liquid reactions in continuous flow. 

This work was supported by the Youth Innovation Promotion Association of CAS, the STS Program of CAS and the Frontier Scientific Research Project funded by Shell.  

Featured image: Regulation of Gas-Liquid Taylor Flow by Pulsating Gas Intake in Micro-channel (Image by SARI)


Reference: Yaheng Zhang, Jie Zhang, Zhiyong Tang, Qing Wu, Regulation of gas-liquid Taylor flow by pulsating gas intake in micro-channel, Chemical Engineering Journal, Volume 417, 2021, 129055, ISSN 1385-8947, https://doi.org/10.1016/j.cej.2021.129055. (https://www.sciencedirect.com/science/article/pii/S138589472100646X)


Provided by Chinese Academy of Sciences

UBCO Researchers Find A New Use for Waste (Chemistry)

Pulp mill waste hits the road instead of the landfill

Waste materials from the pulp and paper industry have long been seen as possible fillers for building products like cement, but for years these materials have ended up in the landfill. Now, researchers at UBC Okanagan are developing guidelines to use this waste for road construction in an environmentally friendly manner.

The researchers were particularly interested in wood-based pulp mill fly ash (PFA), which is a non-hazardous commercial waste product. The North American pulp and paper industry generates more than one million tons of ash annually by burning wood in power boiler units for energy production. When sent to a landfill, the producer shoulders the cost of about $25 to $50 per ton, so mills are looking for alternative usages of these by-products.

“Anytime we can redirect waste to a sustainable alternative, we are heading in the right direction,” says Dr. Sumi Siddiqua, associate professor at UBC Okanagan’s School of Engineering. Dr. Siddiqua leads the Advanced Geomaterials Testing Lab, where researchers uncover different reuse options for industry byproducts.

This new research co-published with Postdoctoral Research Fellow Dr. Chinchu Cherian investigated using untreated PFA as an economically sustainable low-carbon binder for road construction.

“The porous nature of PFA acts like a gateway for the adhesiveness of the other materials in the cement that enables the overall structure to be stronger and more resilient than materials not made with PFA,” says Dr. Cherian. “Through our material characterization and toxicology analysis, we found further environmental and societal benefits that producing this new material was more energy efficient and produced low-carbon emissions.”

But Dr. Siddiqua notes the construction industry is concerned that toxins used in pulp and paper mills may leach out of the reused material.

“Our findings indicate because the cementation bonds developed through the use of the untreated PFA are so strong, little to no release of chemicals is apparent. Therefore, it can be considered as a safe raw material for environmental applications.”

While Dr. Cherian explains that further research is required to establish guidelines for PFA modifications to ensure its consistency, she is confident their research is on the right track.

“Overall, our research affirms the use of recycled wood ash from pulp mills for construction activities such as making sustainable roads and cost-neutral buildings can derive enormous environmental and economic benefits,” she says. “And not just benefits for the industry, but to society as a whole by reducing waste going to landfills and reducing our ecological footprints.”

In the meantime, while cement producers can start incorporating PFA into their products, Dr. Cherian says they should be continually testing and evaluating the PFA properties to ensure overall quality.

The research was published in the Journal of Cleaner Production with support from the Bio-Alliance Initiative — an organization representing BC pulp and paper mills — and Mitacs.

Featured image: UBCO postdoctoral research fellow Chinchu Cherian, along with Associate Professor Sumi Siddiqua, examines a road-building material created partly with recycled wood ash. © UBCO


Reference: Chinchu Cherian, Sumi Siddiqua, Engineering and environmental evaluation for utilization of recycled pulp mill fly ash as binder in sustainable road construction, Journal of Cleaner Production, Volume 298, 2021, 126758, ISSN 0959-6526, https://doi.org/10.1016/j.jclepro.2021.126758. (https://www.sciencedirect.com/science/article/pii/S095965262100977X)


Provided by University of British Columbia

Commercially Available Ultralong Organic Room-temperature Phosphorescence (Chemistry)

Purely organic room-temperature phosphorescence (RTP) materials have been a hot research topic. Currently, the pure RTP materials have been realized by the introduction of heavy halogen atoms, carbonyls groups or some heteroatoms, hydrogen bonding, H-aggregation, strong intermolecular electronic coupling, molecular packing, host-guest interaction, etc. However, the complicated synthesis and high expenditure are still inevitable in these systems. In addition, their performances in air are not satisfactory and the introduction of halogen atoms is generally necessary. Therefore, a new facile and robust host-guest strategy utilizing only electron-rich materials is a promising alternative for constructing RTP systems.

Very recently, Zheng and Qin et al. developed a series of novel host-guest organic phosphorescence systems, in which N,N,N’,N’-tetraphenylbenzidine (TPB) acted as a guest, triphenylphosphine (TPP) or triphenylamine (TPA) served as a host. The maximum phosphorescence efficiency and the longest lifetime could reach 23.6% and 362 ms, respectively. Experimental results and theoretical calculation revealed that the host molecules not only play a vital role in providing a rigid environment and suppressing non-radiative decay of the guest, but also show a synergistic effect to the guest in the photo-physical process through Förster resonance energy transfer (FRET). These new host-guest RTP systems enjoy the integrated merits of commercially available compounds with electron-rich features and low cost, absence of halogen atoms, facile preparation and excellent performances, etc., which shows great potentials in practical applications. Therefore, this work broadens the way for the fabrication of purely organic RTP materials and offers a novel platform for the development of diverse applications.

Featured image : The chemical structures of TPB, TPP and TPA, the phosphorescence of TPB/TPP and TPB/TPA crystalline powders, the advantages of these new host-guest RTP systems. ©Science China Press


Reference: Ning, Y., Yang, J., Si, H. et al. Ultralong organic room-temperature phosphorescence of electron-donating and commercially available host and guest molecules through efficient Förster resonance energy transfer. Sci. China Chem. (2021). https://link.springer.com/article/10.1007/s11426-020-9980-4 https://doi.org/10.1007/s11426-020-9980-4


Provided by Science China Press

Chemists Achieve Breakthrough in the Production of Three-dimensional Molecular Structures (Chemistry)

New dimensions in organic chemistry through light-mediated synthesis / Publication in “Science”

A major goal of organic and medicinal chemistry in recent decades has been the rapid synthesis of three-dimensional molecules for the development of new drugs. These drug candidates exhibit a variety of improved properties compared to predominantly flat molecular structures, which are reflected in clinical trials by higher efficacy and success rates. However, they could only be produced at great expense or not at all using previous methods. Chemists led by Prof. Frank Glorius (University of Münster) and his colleagues Prof. M. Kevin Brown (Indiana University Bloomington, USA) and Prof. Kendall N. Houk (University of California, Los Angeles, USA) have now succeeded in converting several classes of flat nitrogen-containing molecules into the desired three-dimensional structures. Using more than 100 novel examples, they were able to demonstrate the broad applicability of the process. This study will be published by Science on Friday, 26 March 2021.

Light-mediated energy transfer overcomes energy barrier

One of the most efficient methods for synthesizing three-dimensional architectures involves the addition of a molecule to another, known as cycloaddition. In this process, two new bonds and a new ring are formed between the molecules. For aromatic systems – i.e. flat and particularly stable ring compounds – this reaction was not feasible with previous methods. The energy barrier that inhibits such a cycloaddition could not be overcome even with the application of heat. For this reason, the authors of the “Science” article explored the possibility of overcoming this barrier through light-mediated energy transfer.

“The motif of using light energy to build more complex, chemical structures is also found in nature,” explains Frank Glorius. “Just as plants use light in photosynthesis to synthesize sugar molecules from the simple building blocks carbon dioxide and water, we use light-mediated energy transfer to produce complex, three-dimensional target molecules from flat basic structures.”

New drug candidates for pharmaceutical applications?

The scientists point to the “enormous possibilities” of the method. The novel, unconventional structural motifs presented by the team in the “Science” paper will significantly expand the range of molecules that medicinal chemists can consider in their search for new drugs: for example, basic building blocks containing nitrogen and highly relevant to pharmaceuticals, such as quinolines, isoquinolines and quinazolines, which have been scarcely used owing to selectivity and reactivity problems. Through light-mediated energy transfer, they can now be coupled with a wide range of structurally diverse alkenes to obtain novel three-dimensional drug candidates or their backbones. The chemists also demonstrated a variety of innovative transformations for the further processing of these synthesized backbones, using their expertise to pave the way for pharmaceutical applications. The method’s great practicality and the availability of the required starting materials are crucial for the future use of the technology: the molecules used are commercially available at low cost or easy to produce.

“We hope that this discovery will provide new impetus in the development of novel medical agents and will also be applied and further investigated in an interdisciplinary manner,” explains Jiajia Ma. Kevin Brown adds: “Our scientific breakthrough can also gain great significance in the discovery of crop protection agents and beyond.”

Synergy of experimental and computational chemistry

Another special feature of the study: the scientists clarified the reaction mechanism and the exact structure of the molecules produced for the first time not only analytically and experimentally in detail, but also via “computational chemistry”: Kendall Houk and Shuming Chen conducted detailed computer-aided modeling of the reaction. They were able to show how these reactions work and why they occur very selectively. “This study is a prime example of the synergy of experimental and computational theoretical chemistry,” emphasizes Shuming Chen, now a professor at Oberlin College in Ohio. “Our detailed mechanistic elucidation and understanding of reactivity concepts will enable scientists to develop complementary methods and to use what we learned to design more efficient synthetic routes in the future,” adds Kendall Houk.

A flat molecule containing nitrogen is turned into a three-dimensional molecule through photochemical synthesis (illustration). The Chinese character on the arrow means “light”.© Peter Bellotti

The story behind the publication

Using the method of light-mediated energy transfer, both Jiajia Ma/Frank Glorius (University of Münster) and Renyu Guo/Kevin Brown (Indiana University) had success, independently. Through collaborations with Kendall Houk and Shuming Chen at UCLA, both research groups learned of the mutual discovery. The three groups decided to develop their findings further together in order to share their breakthrough with the scientific community as soon as possible and to provide medicinal chemists with this technology to develop novel drugs.

Funding

The study received financial support from the German Research Foundation (Leibniz Award, Priority Program 2102 and Collaborative Research Centre 858), the European Research Council (H2020 ERC) and the Alfred Krupp von Bohlen-und-Halbach Foundation. On the US side, the study was supported by funding from the National Institutes of Health and the National Science Foundation.

Featured image: Chemists use this experimental setup for photochemical reactions.© Peter Bellotti


Original publication

J. Ma, S. Chen, P. Bellotti, R. Guo, F. Schäfer, A. Heusler, X. Zhang, C. Daniliuc, M. K. Brown, K. N. Houk, F. Glorius (2021): Photochemical Intermolecular Dearomative Cycloaddition of Bicyclic Azaarenes with Alkenes. Science; DOI: 10.1126/science.abg0720.


Provided by University of Munster

RUDN University Chemists Found a way to Increase the Efficiency of Metathesis Reactions (Chemistry)

Chemists from RUDN University found out that fluorine and fluoroalkyl groups increase the efficiency of catalysts in metathesis reactions that are used in the pharmaceutical industry and polymer chemistry. The team also identified fluorine-containing compounds that can simplify the purification of the catalyst from the reaction product, making it reusable. The results of the study were published in the Russian Chemical Reviews journal.

Many medicinal drugs and polymers are based on olefins, organic compounds with a double bond between carbon atoms. To obtain useful substances from them, scientists used the metathesis reaction. In the course of metathesis, double bonds in the molecules are broken, and groups of different molecules attached to them are redistributed. However, this reaction requires powerful catalysts called ruthenium-carbene complexes. A team of chemists from RUDN University found a way to increase their catalytic activity with fluorine. The results of their work could be used in the pharmaceutical industry and industrial chemistry.

“We studied the scientific literature and summarized the data on the methods of adding fluorine atoms and fluoroalkyl groups into different ligands. This technology is used to create ruthenium-carbene complexes that would be active in the metathesis reaction. We have also analyzed the catalytic activity of complexes with different additives,” said Sergey Osipov, PhD, researcher at the Joint Institute for Chemical Research, RUDN University.

Ruthenium-based complexes consist of the transition metal ruthenium and different types of ligands, including carbene ligands (unstable bivalent carbon compounds). When donor ligands react with the electrophilic atom of ruthenium, they bring the parts of the complex together. Electrophilicity is the ability to receive electrons, and it is this quality of the atom of ruthenium in the middle of a complex that determines the activity of a catalyst. The team summarized the data from other studies and found out that electrophilicity could be increased by adding fluorine to the ligands. This method works because both fluorine and fluoroalkyl groups that contain it have a high accepting ability.

By changing the types and structures of fluoroalkyl groups, one can create a catalyst with desired qualities. For example, when the team added fluorine to asymmetrical ligands, an additional reaction between ruthenium and the atom of fluorine was observed. It added stability to the whole complex and increased its catalytic activity. By adding polyfloroalkyl groups to ligands, one can simplify the purification of the catalyst from reaction products and make it reusable.

The results of the study can help chemists improve ruthenium-based catalysts by choosing specific floroalkyl additives for particular requirements.

“Fluorine in ligands speeds up the beginning of catalysis because the bond between ruthenium and the atom of ligand weakens in the course of metathesis. Moreover, adding polyfloroalkyl groups to ligands solves the issue of purification of the catalyst from reaction products. This way, an expensive catalyst can be reused several times,” added Sergey Osipov from RUDN University.

Featured image: Chemists from RUDN University found out that fluorine and fluoroalkyl groups increase the efficiency of catalysts in metathesis reactions that are used in the pharmaceutical industry and polymer chemistry. The team also identified fluorine-containing compounds that can simplify the purification of the catalyst from the reaction product, making it reusable. ©§RUDN University


Reference: S M MasoudD V VorobyevaD A PetropavlovskikhCh BruneauS N Osipov, “Fluorine-containing ruthenium-based olefin metathesis catalysts”, Volume 90 (2021), Number 4, Pages 419–450. DOI: https://doi.org/10.1070/RCR4984


Provided by RUDN University

Size Matters When it Comes To Atomic Properties (Chemistry)

A study from Chalmers University of Technology, Sweden, has yielded new answers to fundamental questions about the relationship between the size of an atom and its other properties, such as electronegativity and energy. The results pave the way for advances in future material development. For the first time, it is now possible under certain conditions to devise exact equations for such relationships.

“Knowledge of the size of atoms and their properties is vital for explaining chemical reactivity, structure and the properties of molecules and materials of all kinds. This is fundamental research that is necessary for us to make important advances,” explains Martin Rahm, the main author of the study and research leader from the Department of Chemistry and Chemical Engineering at Chalmers University of Technology.

The researchers behind the study, consisting of colleagues from the University of Parma, Italy, as well as the Department of Physics at Chalmers University of Technology, have previously worked with quantum mechanical calculations to show how the properties of atoms change under high pressure. These results were presented in scientific articles in the Journal of the American Chemical Society and ChemPhysChem.

The new study, published in the journal Chemical Science, constitutes the next step in their important work, exploring the relationship between the radius of an atom and its electronegativity – a vital piece of chemical knowledge that has been sought since the 1950s.

Establishing useful new equations

By studying how compression affects individual atoms, the researchers have been able to derive a set of equations that explain how changes in one property – an atom’s size – can be translated and understood as changes in other properties – the total energy and the electronegativity of an atom. The derivation has been made for special pressures, at which the atoms can take one of two well-defined energies, two radii and two electronegativities.

“Knowledge of the size of atoms and their properties is vital for explaining chemical reactivity, structure and the properties of molecules and materials of all kinds. This is fundamental research that is necessary for us to make important advances,” explains Martin Rahm, the main author of the study and research leader from the Department of Chemistry and Chemical Engineering at Chalmers University of Technology. © Johan Bodell/Chalmers University of Technology

“This equation can, for example, help to explain how an increase in an atom’s oxidation state also increases its electronegativity and vice versa, in the case of a decrease in oxidation state,” says Martin Rahm.

A key question for the science of unexplored materials

One aim of the study has been to help identify new opportunities and possibilities for the production of materials under high pressure. At the centre of the earth, the pressure can reach hundreds of gigapascals – and such conditions are achievable in laboratory settings today. Examples of areas where pressure is used today include the synthesis of superconductors, materials which can conduct electric current without resistance. But the researchers see many further possibilities ahead.

“Pressure is a largely unexplored dimension within materials science, and the interest in new phenomena and material properties that can be realised using compression is growing,” says Martin Rahm.

Creating the database they themselves wished for

The large amounts of data that the researchers have computed through their work have now been summarised into a database, and made available as a user-friendly web application. This development was sponsored by Chalmers Area of Advance Materials and made possible through a collaboration with the research group of Paul Erhart at the Department of Physics at Chalmers.

In the web application, users can now easily explore what the periodic table looks like at different pressures. In the latest scientific publication, the researchers provide an example for how this tool can be used to provide new insight into chemistry. The properties of iron and silicon – two common elements found in the earth’s crust, mantle and core – are compared, revealing large differences at different pressures.

“The database is something I have been missing for many years. Our hope is that it will prove to be a helpful tool, and be used by many different chemists and materials researchers who study and work with high pressures. We have already used it to guide theoretical searches for new transition metal fluorides,” says Martin Rahm.

Featured image: An illustration of potassium atoms undergoing changes in fundamental characteristics such as radius, energy and electronegativity as they are compressed by surrounding neon atoms. © Neuroncollective, Daniel Spacek, Pavel Travnicek


Provided by Chalmers University of Technology