Category: Chemistry

by Eindhoven University of Technology

Woody biomass and wheat straw are all sources of the natural polymer lignin with more than 50 megatons of lignin produced annually at commercial scale. However, most is burned to produce energy, which alternatively could be used to make useful chemicals. A major issue with producing chemicals from lignin is that the properties of lignin vary from source to source and from season to season. Such variability can affect the yield and quality of the chemicals produced from lignin.

In a TU/e-led study, researchers have developed and tested a new and efficient model to predict the yield of lignin with specific chemical properties that are important for the production of biobased chemicals, materials, or fuels. The new study is published in Green Chemistry.

To date, most lignin derived from sources such as agricultural waste materials or woody biomass is burned to produce energy. As a renewable raw material, this can be seen as a waste. Researchers are looking for ways to use organic lignin as a reliable raw material for the chemical industry to make resins, foams, and biofuels.

As a source, woody biomass can be grown relatively fast, and thus it provides easy access to lignin for the long-term production of chemicals.

This is an idealized view of the situation though. “The major problem is that the properties of lignin are both unpredictable and variable, and this affects its usability,” says Mark Vis, assistant professor in the Department of Chemical Engineering and Chemistry and research lead.

So why is the unpredictability of lignin properties a bad thing? Vis explains, “Let’s say that we want to make a certain chemical using lignin, but we need lignin with a specific chemical composition to make the chemical. In any sample of lignin, there could be a million distinct types of lignin units, and isolating the right lignin type to make the chemical is the heart of the problem. Lignin does not have a single well-defined chemical structure, in contrast to the raw materials used to make conventional chemicals.”

The needle in a lignin stack

This sounds like searching for the proverbial needle in a lignin stack.

A treatment process known as solvent fractionation can help isolate the desired lignin types from the stack whereby lignin types with desired chemical properties are dissolved using a solvent, which later can be purified further by removing them from the solvent.

“Fractionation can decrease the range of lignin types, but with millions of lignin types in a sample, it’s difficult to be sure that a particular solvent will isolate a particular type of lignin,” says Vis. “Theoretical calculations can help predict the outcome of fractionation, but current theories are too complex to apply to lignin. And this is the problem that we solved.”

The solution from Vis and his collaborators at TU/e (including first author Stijn van Leuken and postdoc Dannie van Osch), Maastricht University, and the spin-off Vertoro is a new model that accurately and quickly predicts the fractionation of lignin in a solvent blend containing methanol and ethyl acetate. As it turns out, a blend is better for isolating precisely the lignin fraction needed.

Model times

The researchers’ model is based on the Flory-Huggins solution theory, a famous mathematical way of quantifying polymer solubility. Usually, this model is applied to study how one polymer interacts with a solvent, but the researchers took the model a number of steps further.

“Our model is well suited if you have hundreds of different polymer types simultaneously, which means that we can model the interactions of numerous lignin polymer types with different chemical properties (such as polymer chain length and composition) with the solvent,” says Vis. “Gaining insight on these interactions is critical as they affect whether a certain lignin type will dissolve or not in a certain solvent.”

To validate the new model, the researchers calculated the fractionation of lignin derived from wheat straw and then compared the model data with experiments involving the same materials. Vis adds, “We tested our model on existing data related to a common industrial lignin in a different solvent blend (methanol and dichloromethane). Our model was applied with minimal effort, and described the data very well,” adds Vis.

To date, in terms of using numerical tools to predict lignin yields, it’s all quite speculative. “Not many people are using theory to predict yields,” says Remco Tuinier, professor in the Department of Chemical Engineering and Chemistry and also an author on the paper. “Our model makes it easy and possible to predict which lignin can be isolated with a certain solvent (mixture). It’s a significant development for the field.”

Next steps

With the model proving so successful in predicting lignin yields, how can this model make an impact in industry? Panos Kouris, Chief Technology Officer and co-founder of Vertoro and co-author of the paper states, “This model is now a stepping stone for all lignin valorization activities; both in academia and industry.”

Vertoro is a spin-off company from a public-private partnership including TU/e, and wants to offer viable and affordable bio-based alternatives to fossil resources, so Kouris and his colleagues are well aware of the impact that the model can have on both academia and industry.

“In academia, the model can instigate new research lines on new solvents and lignin types, in addition to looking at ways to target particular lignin chemical properties for particular applications,” notes Kouris. “And in the biomass biorefining industry, the model could be very insightful and contribute to the design of new lignin-based products.”

Getting ready

In theory, the model can already be used by biorefineries to explore the valorization of certain lignin types, but there’s still a lot to be done before the model is ready for large-scale commercial use.

First, the model needs to be validated for the most common lignin types processed by the industry. Next, the solvent fractionation technology itself must have reached the level where the technology is ready for commercial use, and finally, clear applications of the final products are needed in the market, such as biobased packaging or biofuels.

Satisfying these requirements will take time, yet Kouris and his colleagues at Vertoro are optimistic that the model will have an impact on biorefineries sooner rather than later. “We at Vertoro expect that in the first half of 2024, the model will be extended to test several commercially available lignin sources, especially from second-generation cellulosic ethanol biorefineries that are actively looking for lignin valorization technologies and solutions.”

More information: Stijn H. M. van Leuken et al, Quantitative prediction of the solvent fractionation of lignin, Green Chemistry (2023). DOI: 10.1039/D3GC00948C

Journal information: Green Chemistry 

Provided by Eindhoven University of Technology 

by Chiba University

Transition metals form catalytic complexes that can speed up various chemical processes, especially in the production of pharmaceuticals as well as various pigments, dyes, and laboratory reagents like sulfuric acid. The use of light emitting diodes (LEDs) has boosted the use of visible light in reaction catalysis, and scientists have developed photo-redox catalysts made of iridium and ruthenium, which facilitate catalysis when irradiated with specific wavelengths of light.

Additionally, scientists have even demonstrated visible light photoreactions with palladium complexes without the use of photo-redox catalysts. While several such transition metal-catalyzed photoreactions have been developed, there has been limited development of new ligands for these reactions; most studies used existing ligands that were developed for thermal reactions.

Thus, there has been a notable lack of development of ligands that interact specifically with transition metal catalysts in photoreactions, preventing us from unlocking the true potential of such reactions.

Recently, a team of researchers, led by Professor Tetsuhiro Nemoto from the Graduate School of Pharmaceutical Sciences at Chiba University in Japan, developed novel ligands that can be used in photoreactions with transition metal catalysts. They also demonstrated how the developed ligands interacted with different transition metals to produce different catalytic results for photoreactions.

The team included Mr. Yu Matsuda from the Graduate School of Pharmaceutical Sciences at Chiba University and Dr. Masaya Nakajima, who was affiliated with the same institute at the time of the study but is now affiliated to the Graduate School of Pharmaceutical Sciences at the University of Tokyo. Their work was published in ACS Catalysis.

The researchers utilized commercially available 9-phenylacridine to prepare four acridine-containing PNP-pincer ligands, which were then used to create complexes with nickel, palladium, platinum, copper, and cobalt.

The team evaluated the catalytic activity of the complexes for a specific photoreaction called transfer hydrogenation, a common reaction used in various industries. While the nickel complex did not react efficiently, the palladium and platinum complexes successfully catalyzed the reaction to provide a high yield of the final products.

Specifically, the researchers found that the newly developed ligands allowed the platinum complex to successfully catalyze a reaction in the presence of visible light (blue LED irradiation) in a stoichiometric manner. This means that the exact values of reagents needed, and the quantity of product obtained, can be mathematically calculated.

The preciseness of the catalysis will allow the streamlining of industrial processes, such as in the production of medicines. Furthermore, the new platinum complex could catalyze the hydroxy/alkoxy alkylation of olefins—a reaction that could not be catalyzed with existing well-known ligands.

The fact that these photoreactions did not occur in the presence of well-known ligands highlights how the newly designed ligands could help define new reaction capabilities. Explaining the results, Dr. Nakajima says, “This research reveals a new reactivity of platinum that was previously unknown. As a result, it has become possible to synthesize new kinds of molecules more efficiently, potentially finding applications in the manufacturing of novel materials and pharmaceuticals.”

The present study is also expected to have numerous long-term implications. “Visible light is utilized as the energy source for such reactions. Thus, sunlight can be used as an endless source of energy, and technological advancement could allow us to perform photoreactions without the constraints that come with the arrangements necessary for thermal reactions, ultimately helping us resolve emerging energy issues,” concludes Dr. Nakajima.

Indeed, the development of new ligands for transition metal complex photocatalysis can create new possibilities and redefine reaction capabilities, allowing novel solutions to the challenges we face today.

More information: Yu Matsuda et al, Acridine PNP-Pincer Ligands Enabling Transition Metal-Catalyzed Photoreactions, ACS Catalysis (2023). DOI: 10.1021/acscatal.3c01654

Journal information: ACS Catalysis 

Provided by Chiba University 

by JooHyeon Heo, Ulsan National Institute of Science and Technology

The rapid advancements in flexible electronic technology have led to the emergence of innovative devices such as foldable displays, wearables, e-skin, and medical devices. These breakthroughs have created a growing demand for flexible adhesives that can quickly recover their shape while effectively connecting various components in these devices.

However, conventional pressure-sensitive adhesives (PSAs) often face challenges in achieving a balance between recovery capabilities and adhesive strength. In an extraordinary study conducted at UNIST, researchers have successfully synthesized new types of urethane-based crosslinkers that address this critical challenge.

Led by Professor Dong Woog Lee from the School of Energy and Chemical Engineering at UNIST, the research team developed novel crosslinkers utilizing m-xylylene diisocyanate (XDI) or 1,3-bis(isocyanatomethyl)cyclohexane (H₆XDI) as hard segments along with poly(ethylene glycol) (PEG) groups serving as soft segments. By incorporating these newly synthesized materials into pressure-sensitive adhesives, they achieved significantly improved recoverability compared to traditional methods.

The PSA formulated with H₆XDI-PEG diacrylate (HPD) demonstrated exceptional recovery properties while maintaining high adhesion strength (~25.5 N 25 mm⁻¹). Through extensive folding tests totaling 100k folds and multi-directional stretching tests spanning 10k cycles, the PSA crosslinked with HPD exhibited remarkable stability under repeated deformation—showcasing its potential for applications requiring both flexibility and recoverability.

Furthermore, even after subjecting the adhesive to strains up to 20%, it displayed high optical transmittance (>90%), making it suitable for fields such as foldable displays that demand not only flexibility but also optical clarity.

“This breakthrough in adhesive technology offers promising possibilities for electronic products that require both high flexibility and rapid recovery characteristics,” said Professor Lee. “Our research addresses the long-standing challenge of balancing adhesion strength and resilience, opening up new avenues for the development of flexible electronic devices.”

Hyunok Park, a researcher involved in the study, emphasized the significance of this research by stating, “The introduction of this new crosslinking structure has led to an adhesive with exceptional adhesion and recovery properties. We believe it will drive future advancements in adhesive research while contributing to further developments in flexible electronics.”

The study findings have been published in Advanced Functional Materials.

More information: Hyunok Park et al, Tailoring Pressure Sensitive Adhesives with H6XDI‐PEG Diacrylate for Strong Adhesive Strength and Rapid Strain Recovery, Advanced Functional Materials (2023). DOI: 10.1002/adfm.202305750

Journal information: Advanced Functional Materials 

Provided by Ulsan National Institute of Science and Technology 

by Chinese Academy of Sciences

The global energy crisis is exacerbated by the continuous consumption of fossil fuels during the rapid development of modern industries. In addition, the survival and development of human beings is also being seriously affected by the emission of greenhouse gases.

As we know, natural photosynthesis can convert solar illumination to sustainable energy. Inspired by this, a carbon-neutral strategy that uses sunlight to convert carbon dioxide to fuels has attracted great attention.

The successful implementation of photosynthesis depends on the design of photocatalysts. Inorganic semiconductors have been extensively studied for CO₂ photoreduction reaction (CO₂PRR), which presents shortcomings. For example, the band gaps of metal oxides and metal chalcogenides are difficult to adjust, resulting in poor light absorption. In addition, the high carrier recombination rate and the low Brunauer-Emmett-Teller (BET) specific surface area impair the photocatalytic efficiency, thus limiting photon utilization.

Photocatalysts based on porous organic frameworks (POFs) have attracted tremendous interest owing to their facile bandgap and charge separation tunability via designable functional building blocks. Nevertheless, a considerable portion of previously reported POFs still rely on the metal reactive sites. The photosensitizer and sacrificial reagent are required for promoting their performances on CO₂PRR.

These are obviously uneconomical. The photoreduction of CO₂ tends to produce mixed products with different ratios as the number of electrons and protons reacting with CO₂ varies. The quantity and purity of the targeted product are generally low due to insufficient conversion, which requires overcoming the high chemical inertness of CO₂. Therefore, achieving highly efficient and selective CO₂ conversion have been very challenging.

A research team led by Prof. Yong Yang from Nanjing University of Science and Technology and Prof. Yong Zhou from Nanjing University, China, reported a series of three-dimensional Tröger’s base-derived porous aromatic frameworks (3D-X-TB-PAFs (X = TEPE, TEPM, SPF)) featuring designated reaction sites and unique charge transfer properties. The results were published in Chinese Journal of Catalysis.

The incorporation of V-shaped Tröger’s base (TB) units and aromatic alkynes both endow polymers with permanent porosity, additional photon scattering cross-sections and enhanced CO₂ adsorption/activation capability. Both density functional theory (DFT) calculations and optoelectronic measurements reveal the formation of intramolecular built-in polarization and electron-trap sites brought about by TB, which modulate the charge separation and customize reaction sites in collaboration with the enhanced CO₂ accumulation.

Also, the product allocation in the photoreduction of CO₂ is hereby regulated together with the photooxidation of H₂O. Among the 3D-PAFs, the most efficient electron transport channel is constructed in TEPE-TB-PAF with the full conjugated TEPE-T.

In the absence of cocatalysts and sacrificial agents, TEPE-TB-PAF presents a competitive CO formation rate (194.50 μmol g^-1 h^-1) with near-unity selectivity (99.74%). Significantly, the low energy barrier for CO desorption and high energy barrier for *CHO formation commonly contribute to the high efficiency of TEPE-TB-PAF, which is demonstrated by computational explorations and in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectra.

This work provides efficient building blocks for the synthesis of multifunctional organic photocatalysts and a ground-breaking insight for the simultaneous enhancement of photocatalytic reactivity and selectivity.

More information: Nan Yin et al, Tröger’s base derived 3D-porous aromatic frameworks with efficient exciton dissociation and well-defined reactive site for near-unity selectivity of CO2 photo-conversion, Chinese Journal of Catalysis (2023). DOI: 10.1016/S1872-2067(23)64474-2

Provided by Chinese Academy of Sciences 

by Kobe University

The Vilsmeier reagent is necessary for producing a large range of pharmaceuticals, but its unstable nature and toxic precursor phosgene are challenges for its use. A new process that efficiently produces phosgene, the Vilsmeier reagent and the desired products in one flow is poised to make the industry greener and safer.

For the production of many active pharmaceutical ingredients, a chemical called Vilsmeier reagent is necessary, but it is extremely unstable. That’s why it is produced on-site and on-demand wherever possible. In addition, the currently used methods for producing the reagent either use phosgene, which is itself an unstable and highly toxic chemical, or if phosgene is avoided result in toxic or difficult-to-remove by-products.

Kobe University chemist Tsuda Akihiko specializes on on-demand systems and using a unique UV-radiation approach, his group previously achieved the production of both phosgene and the Vilsmeier reagent from relatively safe and stable starting chemicals directly in the same vessel as their intended reaction substrates. This means they could achieve the whole reaction as if phosgene or the Vilsmeier reagent were never there.

While their technique was at first limited by being a batch process and thus being not easily scalable, they recently developed a completely novel flow system for the production of phosgene, creating an opportunity for the scalable on-demand production of other chemicals requiring phosgene. Tsuda explains, “Our group discovered for the first time that chloroform, a common organic solvent, underwent photochemical oxidation to form phosgene with high efficiency when irradiated with ultraviolet light. Our ‘photo-on-demand organic synthesis method’ based on this chemical reaction is a big step for phosgene-based organic synthesis.”

In a study published in the journal Organic Process Research & Development, the group adapted their unique process to create a flow system that produces the Vilsmeier reagent on demand from phosgene for direct reaction with any desired substrate. The phosgene was itself produced in the same on-demand flow system from chloroform, a relatively safe and stable starting compound, thus creating a scalable, safe and efficient reaction system to produce a wide range of useful chemicals.

“This reaction system consumes less energy, produces less waste, and enables versatile as well as scalable chemical synthesis. These features contribute positively to the life cycle assessment of the products, which is especially important in the industry,” comments Tsuda.

Thus, this process is a huge step into the direction of a safer and greener production of pharmaceutical chemicals. In addition, it also enables a more local production of these key chemicals, reducing dependence on production abroad.

More information: Yue Liu et al, Flow Photo-on-Demand Synthesis of Vilsmeier Reagent and Acyl Chlorides from Chloroform and Its Applications to Continuous Flow Synthesis of Carbonyl Compounds, Organic Process Research & Development (2023). DOI: 10.1021/acs.oprd.3c00267

Journal information: Organic Process Research & Development 

Provided by Kobe University 

by University of Bath

An ultraportable, low-cost device invented by researchers at the University of Bath proves highly successful at detecting synthetic cannabinoids (SCs, e.g. “Spice,” K2).

A device that lights up in the presence of illegal drugs soaked into paper or fabric is expected to be cleared for rollout across the U.K. within months.

The pocket-sized device is intended to detect SCs—a class of psychoactive substances used predominantly in prisons and homeless communities in the U.K. The drug can be fatal and often causes severe side effects, including psychosis, stroke and seizures.

The researchers hope that in its current format, the drug detector will be used to stem the flow of SCs smuggled into prisons and reduce the devastating effects on users of these highly addictive drugs. With further engineering, they are confident their device will be able to detect all types of synthetic drugs.

Professor Christopher Pudney, who led the research from the Department of Life Sciences at Bath, said, “Our device is truly groundbreaking—it’s battery-operated, ultra-portable, low-cost and gives instant results that anyone can interpret.

“Detecting Spice is a major challenge with currently available technology, not least because the substance is usually smuggled into prisons absorbed into physical products like paper and fabric, and now also in vape liquid, which makes detection very difficult.”

The device, and it’s potential to revolutionize the detection of SCs, is described this week in the journal Analytical Chemistry, published by the American Chemical Society.

National rollout

The researchers expect that the new tool—designed to light up in the presence of synthetic drugs—will be ready for mass production this autumn. The team is currently looking for a company able to manufacture the device at scale and distribute it to prisons, probation services, homeless shelters and relevant charities—initially in the U.K. but eventually also overseas.

SCs can be soaked into paper or other solid materials like clothing, and this has become a common way to smuggle it into institutions, as most detection technologies struggle to produce a reliable result when testing “complex” materials.

Professor Pudney said, “Typically, Spice enters prisons on paper, and once it’s inside, it’s divided into smaller paper sheets in the prison and then sold. The paper is crumpled up and inserted into a vape pen and smoked, so detection in the prison environment is incredibly challenging.”

The device is unique, being able to detect drugs on a very broad range of different materials and with high accuracy (95%). The team has even shown detection in vape liquid and the caps of vape pens.

“We see our device being used to decrease the amount of Spice used by all vulnerable communities, and we hope that leads to a better chance for people to recover from addiction and decrease serious health outcomes,” said Professor Pudney.

Instant detection

The device works by detecting the fluorescent properties that make up the core part of the synthetic cannabinoid molecule.

When the device touches a material that is suspected to contain an absorbed SC, it first identifies the material it’s on and then tests for the presence of the drug. An “alarm” shows up as a glowing ring of LEDs, visible to the operator to alert them to the presence of the substance. The greater the concentration of the SC, the brighter the LEDs glow.

Professor Pudney’s team is now working on modifying the device to detect more complex cross-conjugated compounds, including highly addictive benzodiazepines and opioids. They believe this objective may be achieved within the next two years.

Much more dangerous and unpredictable than cannabis

Spice was originally designed to mimic the effects of natural cannabis, but it is much stronger than cannabis, making it considerably more dangerous and unpredictable.

Recently, Spice has also been added to liquids in vapes, putting unsuspecting smokers at risk.

Generally, smokers are duped into smoking Spice when they have bought their vape liquid from a dealer and believe they are smoking vape liquid containing THC (one of the psychoactive substances extracted from cannabis) or cannabis oil. Even when hidden this way, however, the drug can be easily detected by the new device.

“We can spot Spice easily simply by opening a vape and testing the mouth filter,” said Professor Pudney.

More information: Gyles E. Cozier et al, Instant Detection of Synthetic Cannabinoids on Physical Matrices, Implemented on a Low-Cost, Ultraportable Device, Analytical Chemistry (2023). DOI: 10.1021/acs.analchem.3c01844

Journal information: Analytical Chemistry 

Provided by University of Bath 

by National University of Singapore

Spent coffee grounds (SCG) makes up the largest portion of waste generated from preparing coffee beverages and making instant coffee, producing close to 6 million metric tons of waste worldwide each year. To manage this vast amount of waste, scientists are finding ways of converting SCG into value-added products for various applications, from industrial materials to biofuels.

A team of researchers led by Associate Professor Liu Shao Quan from the NUS Department of Food Science and Technology under the Faculty of Science took a more innovative route to create an alcoholic beverage from fermented SCG as a way to sustainably manage the rising amount of waste generated from coffee consumption each year.

The team’s research on SCG-derived alcoholic beverages spanned across different studies where they worked on the flavor, aroma, and understanding its health benefits.

Achieving the best flavor and aroma

To prepare the alcoholic beverage from SCG, the researchers first prepared SCG hydrolysates, then fermented the SCG hydrolysates using a concoction of microorganisms, such as yeasts. Yeast plays an important role in the taste and aroma of the final product by influencing the chemical composition and quality of alcoholic beverages.

Assoc Prof Liu and his team demonstrated in a study published in 2021 in the journal LWT a method using two types of yeasts supplemented with yeast extracts for the fermentation process, allowing them to discover an effective way of creating an SCG-derived alcoholic beverage with a complex flavor palette.

“Alcoholic beverages are traditionally made using Saccharomyces yeasts. We took a different approach to making SCG-derived alcoholic beverages by exploring non-Saccharomyces yeasts for novel flavors and other characteristics,” said Assoc Prof Liu.

Following that study, the NUS team explored the use of other microorganisms, such as lactic acid bacteria with yeast, for fermentation to improve the smell and taste of the SCG-derived alcoholic beverage. The team used a mixture of yeast (Lachancea thermotolerans) and a lactic acid bacterium (Lactiplantibacillus plantarum) to ferment SCG hydrolysates to produce alcoholic beverages with different alcohol contents and physicochemical profiles.

This method resulted in higher contents of compounds related to a pleasant aroma and taste when compared to fermenting SCG hydrolysates with only yeast. The results of this fermentation strategy were published this year on 9 March 2023 in the journal Foods.

In their latest study, published in the journal Food Research International , the team adopted the fermentation strategy using this mixture of yeast and lactic acid bacteria for fermenting SCG hydrolysates. The team went a step further to conduct a detailed metabolomic analysis to identify the bioactive compounds present in the alcoholic beverage and determine its potential health benefits.

Identifying compounds that confer potential health benefits

The researchers adopted an advanced analytical technique known as liquid chromatography quadrupole time of flight mass spectrometry (LCQTOF-MS)—commonly used to identify and confirm the presence of chemical compounds in foods and beverages—to obtain a comprehensive picture of the chemical contents of the fermented SCG.

This study is the first time such an approach was used to determine a full profile of all the compounds present in SCG hydrolysates fermented by a combination of yeast and bacteria.

Through the analysis, the research team identified that fermentation of SCG hydrolysates through both yeast and bacteria boosted the presence of bioactive compounds associated with various health benefits, including anticancer, anti-inflammatory, and antimicrobial activities.

Dr. Liu Yunjiao, the first author of the most recent study, shared that the team developed several prototypes of the alcoholic beverages derived from SCG, all of which had varying flavor profiles.

“Some prototypes retained a coffee flavor, and for others, we’ve managed to achieve a pleasant flavor without a strong coffee flavor. Aside from the different flavor profiles, our tests showed that all the prototypes retained compounds that are known to confer health benefits, such as alkaloids and phenolic acids,” said Dr. Liu.

More information: Yunjiao Liu et al, Untargeted LC-QTOF-MS/MS-based metabolomics of spent coffee grounds alcoholic beverages fermented with Lachancea thermotolerans and Lactiplantibacillus plantarum, Food Research International (2023). DOI: 10.1016/j.foodres.2023.112733

Provided by National University of Singapore 

by Tokyo Institute of Technology

As we seek more efficient utilization of waste thermal energy, use of “phase change materials (PCMs)” is a good option. PCMs have a large latent heat capacity and the ability to store-and-release heat as they change from one state of matter to another. Among many PCMs, sugar alcohols (SAs), a class of organic compounds commonly used as sweeteners, stand out due to their low cost, non-toxic, non-corrosive, and biodegradable nature.

In particular, SAs generally have their melting point in 100–200 °C, which is an important temperature range where a huge amount of waste heat exists but is currently being discarded in our world.

However, SAs usually suffer from the issue of supercooling where, instead of solidifying, they remain in a liquid state even at temperatures well below the melting point. The supercooling degrades the quality (or “exergy”) of stored thermal energy because thermal energy at lower temperature has less usefulness. (Note: Thermal energy at room temperature is totally useless, no matter how much of it exists.)

Now, in a new study, researchers from Tokyo Institute of Technology (Tokyo Tech) led by Professor Yoichi Murakami have discovered that confining SAs in covalent organic framework (COF) crystals effectively resolves the issue of supercooling. Their findings, published in the journal Materials Horizons, have the potential to revolutionize SAs as heat-storage materials.

Dr. Murakami, who is a Professor at the Laboratory for Zero-Carbon Energy at Tokyo Tech, explains, “We propose a new materials concept with which the stored thermal energy can be retrieved at a much higher temperature than before, by largely mitigating the long-standing issue of supercooling that degrades the stored thermal energy. We have created a new class of solid-state PCMs based on abundant, non-toxic, and low-cost SAs.”

Normally, pure D-mannitol (Man), one of SAs, has a melting point of 167 °C, but it usually solidifies at random temperatures around 80–120 °C, which is a large supercooling of about 47–87 °C. To resolve this issue, the researchers introduced Man into the crystals of COF-300, one of the most typical COFs. They discovered that while the melting of Man confined in the COF occurred at around 150–155 °C, the freezing of the Man confined in the COF reproducibly occurred in the slightly lower temperature range of 130–145 °C. Therefore, the supercooling has been suppressed to only 10–20 °C, much smaller than the previous supercooling of about 47–87 °C.

“These results indicate that the fusion–freezing cycles of the Man–COF composite occur within a narrow temperature range of 130–155 °C without large or random supercooling,” says Prof. Murakami, highlighting the discovered effect of the COF confinement.

According to their published paper, earlier works confined SAs in rigid inorganic porous materials such as nanoporous silica and alumina to form solid-state PCMs, but they failed to resolve the supercooling issue of SAs. COFs are not only flexible porous materials but also have much smaller pores (in the order of single-nanometer scale) than those of previous inorganic nanoporous materials.

The present study is expected to pave the way for the new class of solid-state heat storage materials based on green and low-cost SAs for efficient thermal energy storage.

More information: Yoichi Murakami et al, Composite formation of covalent organic framework crystals and sugar alcohols for exploring a new class of heat-storage materials, Materials Horizons (2023). DOI: 10.1039/D3MH00905J

Journal information: Materials Horizons 

Provided by Tokyo Institute of Technology 

by University of Liverpool

New research by the University of Liverpool’s Chemistry Department represents an important breakthrough in the field of polymer science.

In their study, Liverpool researchers use mechanochemistry to characterize how a polymer chain in solution responds to a sudden acceleration of the solvent flow around it.

The paper, “Experimental quantitation of molecular conditions responsible for flow-induced polymer mechanochemistry,” is published in Nature Chemistry and is featured on the front cover.

This new approach answers a fundamental and technological question that has preoccupied polymer scientists for the past 50 years.

Since the 1980s, researchers have been trying to understand the unique response of dissolved polymer chains to suddenly accelerating solvent flows but had been constrained to highly simplified solvent flows that provided limited exploitable insights into the behavior of real-world systems.

The new discovery by Liverpool chemists Professor Roman Boulatov and Dr. Robert O’Neill has significant scientific implications for several areas of physical sciences as well as at a practical level for polymer-based rheological control used in many multi-million dollar industrial processes such as enhanced oil and gas recovery, long distance piping and photovoltaics manufacturing.

Professor Roman Boulatov said, “Our finding addresses a fundamental and technical question in polymer science and potentially upends our current understanding of chain behavior in cavitational solvent flows.”

Co-author of the paper, Dr. Robert O’Neill added, “Our proof-of-the-approach demonstration reveals that our understanding of how polymer chains respond to sudden accelerations of solvent flows in cavitating solutions was too simplistic to support systematic design of new polymer structures and compositions for efficient and economical rheological control in such scenarios or for gaining fundamental molecular insights into flow-induced mechanochemistry.

“Our paper has important implications for our ability to study non-equilibrium polymer chain dynamics at the molecular length scales, and thus our capacity to answer fundamental questions of how energy flows between molecules and within them, and how it transforms from kinetic to potential to free energies.”

The research team plans to focus on expanding the scope and capabilities of their new method and exploiting it to map molecular-level physics that would allow accurate predictions of flow behavior for an arbitrary combination of polymer, solvent and flow conditions.

More information: Robert T. O’Neill et al, Experimental quantitation of molecular conditions responsible for flow-induced polymer mechanochemistry, Nature Chemistry (2023). DOI: 10.1038/s41557-023-01266-2

Journal information: Nature Chemistry 

Provided by University of Liverpool 

by University of Science and Technology of China

Professor Huang Hanmin’s research team from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) proposed a new paradigm of metal electron-shuttle catalysis, which has been pioneeringly employed to achieve alkylative aminomethylation of unactivated alkene for the first time. Their work was published in Nature Catalysis on August 21.

Transition metal-catalyzed carbon-carbon bond formation has been an integral part of contemporary organic chemistry research. However, the development of transition metal-catalyzed C(sp³)-C(sp³) bond formation has been relatively slow due to the generation of unstable alkyl-metal intermediates during the reaction, which lead to various side reactions, making it difficult to apply the classical catalytic paradigm to C(sp³)-C(sp³) bond formation.

The dicarbofunctionalization of alkenes, where two carbon functional groups are introduced at both ends of the alkene in a single operation, has gained attention for its ability to efficiently connect carbon atoms, thereby facilitating the construction of complex molecules. Existing research is often limited to the introduction of C(sp²) functional groups, or they require the pre-installation of coordinating groups onto the alkenes to stabilize the alkyl-metal intermediates. This undeniably reduces the substrate applicability and step economy of the reaction.

To solve the challenges of alkene difunctionalization reactions, the research team proposed a new paradigm of metal electron-shuttle catalysis. Specifically, they utilized a metal catalyst as an electron shuttle to initiate and quench radicals, thereby achieving the construction of multiple alkyl-alkyl bonds through radical-unsaturated bond addition, effectively avoiding the generation of unstable alkyl-metal intermediates.

In this study, the team employed a nickel catalyst as the electron shuttle and used N, O-acetals and alkyl halides as the alkylating agents to accomplish the dialkylation of unactivated alkenes. This method demonstrated excellent compatibility with simple alkenes, unactivated alkenes and polysubstituted alkenes.

Additionally, various types of alkylating agents could be applied under such reaction conditions. Secondary amines and paraformaldehyde could also replace N, O-acetals in the four-component reaction, further broadening the scope of the reaction’s applications.

This reaction offers an efficient method for the synthesis of fluorinated and non-fluorinated δ-amino acids and other unnatural amino acid derivatives. Moreover, this reaction introduces various functional groups, which could further transform to produce more valuable complex molecules. For instance, by reducing and cyclizing the reaction products, one can swiftly construct piperidine compounds, which are prevalent in pharmaceutical molecules. Researchers synthesized the pharmaceutical molecule Mepazine and its corresponding fluorinated derivatives through this transformation strategy, demonstrating the practical value of the reaction.

This reaction not only offers significant synthetic applicability but also serves as an exemplar of the metal electron-shuttle catalysis paradigm, showcasing the promising prospects of this catalytic approach. Further research into the metal electron-shuttle catalysis will play a pivotal role in the development of drug and functional molecule synthesis.

More information: Changqing Rao et al, Double alkyl–alkyl bond construction across alkenes enabled by nickel electron-shuttle catalysis, Nature Catalysis (2023). DOI: 10.1038/s41929-023-01015-1

Journal information: Nature Catalysis 

Provided by University of Science and Technology of China