Category: Chemistry

The atomic structure of solid substances can often be analyzed quickly, easily and very precisely using X-rays. However, this requires that crystals of the corresponding substances exist. Chemist Professor Oliver Oeckler from Leipzig University and his team are developing methods to make this possible even for very small crystals that cannot be seen with the naked eye.

These include phosphorus oxide nitrides, which consist of phosphorus, nitrogen and oxygen and do not occur in nature. Unusual properties are attributed to this novel class of compounds, which have been difficult to access until now, because of their unusual structures.

Working with Professor Wolfgang Schnick from the Ludwig Maximilian University of Munich, Oeckler and his team have developed a method that made it possible, over a decade of research, to determine the complex crystal structure of new phosphorus oxide nitrides. The scientists have just published their findings in Chemistry—A European Journal.

When analyzing crystal structure, the combination of electron microscopy and synchrotron radiation—particularly intense X-rays generated using a special technique at a large-scale research facility—plays a decisive role. However, the analysis of phosphorus oxide nitride shows that this is sometimes not enough.

The substance, which could form the basis for novel phosphors in future studies, for example, was already produced for the first time in 2014, but its structure has not yet been elucidated, because it was previously considered a class of compounds that was difficult to access. Daniel Günther, a doctoral researcher in Oeckler’s working group, has now been able to solve the puzzle together with his mentor.

“It was not due to the data, but to a trick of nature. We are not talking about just one substance, but three very complicated, intergrown compounds,” explains Günther, who is the first author of the study.

Sections of the atomic arrangements formed a kind of modular system from which complicated and also disordered structures can emerge.

“Such an investigation requires extremely meticulous work, for which only a few staff members can muster the necessary patience and concentration. Without a research sabbatical and such a dedicated member of staff, it probably wouldn’t have worked. Most people would have been horrified by what at first glance appeared to be ‘unanalyzable’ data and would never have mentioned it again,” says Oliver Oeckler.

He points out that the significant factor here is not only the structure of oxonitridophosphates, which the researchers find very interesting, but also the method of analysis. The procedure described in their article could be used to solve similar analytical problems with completely different substances.

More information: Daniel Günther et al, Modular Principle for Complex Disordered Tetrahedral Frameworks in Quenched High‐pressure Phases of Phosphorus Oxide Nitrides, Chemistry—A European Journal (2023). DOI: 10.1002/chem.202203892

Journal information: Chemistry – A European Journal 

Provided by Leipzig University 

Orange, starchy sweet potatoes are great mashed, cut into fries or just roasted whole. But you likely haven’t considered grinding them into a flour and baking them into your next batch of cookies—or at least, not yet. Recent research published in ACS Food Science & Technology has reported the best method to turn sweet potatoes into gluten-free flours that are packed with antioxidants and perfect for thickening or baking.

Wheat flour has been used for tens of thousands of years, and likely isn’t going away anytime soon. But for those who face gluten intolerance or have celiac disease, the gluten proteins in wheat flour can lead to stomach pain, nausea and even intestinal damage.

Several gluten-free options are either already available or in development, including those made from banana peels, almonds and various grains. But an up-and-coming contender is derived from sweet potatoes, as the hearty tuber is packed with antioxidants and nutrients, along with a slightly sweet flavor and hint of color.

Before it can become a common ingredient in store-bought baked goods, the best practices for processing the flour need to be established. Though previous studies have investigated a variety of parameters, including the way the potatoes are dried and milled, none have yet determined how these different steps could interact with one another to produce flours best suited for certain products.

So, Ofelia Rouzaud-Sández and colleagues wanted to investigate how two drying temperatures and grinding processes affected the properties of orange sweet potato flour.

To create their flours, the team prepared samples of orange sweet potatoes (Ipomoea batatas) dried at either 122 or 176 F then ground them once or twice. They investigated many parameters for each sample, comparing them to store-bought sweet potato flour and a traditional wheat one. Regardless of drying temperature, grinding once damaged just enough of the starch to make it ideal for fermented products, such as gluten-free breads.

Grinding twice further disrupted the starch’s crystallinity, producing thickening agents ideal for porridges or sauces. When baked into a loaf of bread, the high-temperature-dried, single-ground sample featured higher antioxidant capacity than both the store-bought version and the wheat flour. The researchers say that these findings could help expand the applications for orange sweet potato flour, both for home cooks and the packaged food industry.

More information: María Francelia Moreno-Ochoa et al, Technological Properties of Orange Sweet Potato Flour Intended for Functional Food Products as Affected by Conventional Drying and Milling Methods, ACS Food Science & Technology (2023). DOI: 10.1021/acsfoodscitech.2c00308

Provided by American Chemical Society 

There are somewhere between 20 and 74,963 forms of ice because water can do all kinds of weird stuff when it freezes.

So far, scientists have experimentally determined the crystal structures for 19 types of ice.

Or maybe 20, depending on who you ask.

In this video, we’re going to charge through as many as we can in 10 minutes or so.

Provided by American Chemical Society 

A team of researchers at Academia Sinica in Taiwan, working with two colleagues from Kyoto University in Japan and another from Taipei Medical University, also in Taiwan, has identified the toxic material emitted by oyster mushrooms as a means of killing prey.

In their paper published in Science Advances, the group describes using gas chromatography-mass spectrometry to identify the chemicals used by the carnivorous mushrooms and how they are used to kill prey.

Oyster mushrooms are fairly well known as an edible mushroom, often served at high-end restaurants. They have a taste reminiscent of anise, a flavor akin to licorice. In their natural environment, they are creamy gray and known as one of many carnivorous mushrooms that emit volatile organic compounds.

Prior research has shown that oyster mushrooms are carnivorous—they kill and consume nematodes. Prior research has also shown that the means by which the oysters are able to kill their prey involves emitting a chemical that paralyzes a nematode that happens to venture too closely, followed by the setting off of a calcium wave that kills nematode cells and then their host.

To learn more about the substance emitted by the mushrooms, the researchers used gas chromatography-mass spectrometry to identify the material released from the mushroom’s toxocysts. The popsicle-shaped structures extend into the water from the mushroom and emit chemicals from their rod-like tips on contact. The researchers discovered the material was 3-octanone, a type of ketone.

Testing of the ketone on nematodes showed it first led to the worm attempting to flee. Then the worm became sluggish, and soon thereafter, it was paralyzed. They also found that after paralysis set in, a calcium wave was trigged in the worm, leading to widespread cell death, killing the nematode. They further note that the chemical was able to penetrate the worm’s plasma membrane and that cell death occurred due to transformation of mitochondria.

Further testing showed that it took a certain amount of the ketone (approximately a 50% concentration) to paralyze and kill the nematodes. The researchers note that 3-octanone, a volatile organic compound, is commonly used as a communication medium for transferring signals between fungi.

A mitochondrial calcium wave propagating throughout the hypodermis tissue after contacting P. ostreatus. Credit: Ching-Han Lee

More information: Ching-Han Lee et al, A carnivorous mushroom paralyzes and kills nematodes via a volatile ketone, Science Advances (2023). DOI: 10.1126/sciadv.ade4809

Journal information: Science Advances 

Scientists from Tokyo Metropolitan University have developed a new electrode material for deep-ultraviolet (DUV) light-emitting diode applications. They used a cutting-edge deposition technique to form thin films of an alloy of tin oxide and germanium oxide with added tantalum, finding that they exhibit excellent electrical conductivity and unprecedented transparency for DUV light. The new electrodes promise to impact industry, as the same wavelengths are used for sterilization processes and the manufacture of microchips.

Deep ultraviolet (DUV) light, with a wavelength of 200 to 300 nanometers, has some very important roles to play in industry and society. It can be used to sterilize water and surfaces by inactivating bacteria and viruses and for curing adhesives which harden on exposure to DUV light. Crucially, it is used in the manufacture of the most advanced semiconducting chips and devices.

With adoption of DUV technology becoming more widespread, scientists are keen to develop deep UV light-emitting diode (LED) devices, tapping the unparalleled energy efficiency, scalability, and compactness of LED sources. LEDs feature light-emitting layers of material sandwiched between a pair of transparent electrodes, which have to let the light through as well as conduct electricity. Though such LEDs exist, existing electrode materials are yet to combine conductivity with optimal transparency; they still absorb a significant proportion of DUV light.

Now, a team led by Professor Yasushi Hirose of Tokyo Metropolitan University have developed a thin film transparent electrode with excellent conductivity and, crucially, unprecedented transparency for deep UV light. They combined a widely used ingredient of transparent electrodes, tin oxide, and mixed it together with germanium oxide, a material with a similar crystalline structure but better transparency.

These two materials are usually not soluble in each other, so the team used pulsed laser deposition, a method that allows insoluble materials to be deposited together without them spontaneously separating out into distinct regions. They showed that deep UV transmittance (the proportion of light let through) gets better and better with more germanium oxide addition. By adding some tantalum, they also improved the electrical conductivity of the films.

By optimizing the recipe, the films that were produced showed low resistivity and some of the best transmittance of DUV light out of all known electrode materials, including the most common transparent electrode material, indium tin oxide (ITO). Importantly, they showed that the films could be formed on aluminum nitride (AlN) substrates by using a crystalline “seed” layer of tin oxide. Aluminum nitride is a key material in deep UV LEDs; the compatibility of the team’s newly designed tantalum tin germanium oxide (Ta:SGO) films with AlN makes their work extremely promising for real-world applications in the next generation of light sources for chip manufacture, and beyond.

The work is published in the journal Chemistry of Materials.

More information: Yo Nagashima et al, Deep Ultraviolet Transparent Electrode: Ta-Doped Rutile Sn_1–xGe_xO₂, Chemistry of Materials (2022). DOI: 10.1021/acs.chemmater.2c01758

Journal information: Chemistry of Materials 

Provided by Tokyo Metropolitan University

A research team has improved the solar energy absorption of titanium oxo clusters. Their work demonstrates an effective strategy for regulating the light absorption behaviors of these clusters by importing electron-rich heterometals. These results have potential applications in the field of solar energy where solar conversion currently faces certain limitations.

The team’s work is published in the journal Polyoxometalates on December 2, 2022.

Solar energy offers the potential to ease the gradual exhaustion of global energy resources. Scientists consider titanium dioxide to be one of the most promising material candidates for solar conversion because of its excellent stability, durability, and activity. However, titanium dioxide suffers from a large bandgap, which results in only a small amount of the solar spectrum being utilized. Similarly, the metal doping strategy is well adopted to improve the solar absorption and performance because it creates impurity levels within forbidden bands.

The team successfully constructed two heterometallic clusters to improve the solar absorption and performance of titanium oxo clusters. Heterometallic describes any compound where one or more atoms are replaced by atoms of a different metal. The research team conducted single-crystal X-ray diffraction analysis where the heterometallic clusters were well-determined and found to feature the common presence of molybdenum interactions.

The team’s solid-state ultraviolet-visible absorption studies indicate that these structures exhibit enhanced visible-light absorption and significantly reduce optical band gaps which can be mainly attributed to the introduction of electron-rich molybdenum (Mo) pairs as heterometals. “We discovered that the electron-rich Mo–Mo pairs could be introduced to titanium oxo clusters to enhance visible-light absorption,” said Lei Zhang, a professor at the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences.

Crystalline titanium oxo clusters with their precise and tailorable structures are functional molecular titanium dioxide materials. Most of the metals in the periodic table have been incorporated into titanium oxo clusters, with their microscopic electronic structure and macroscopic performance capable of being modified. However, little investigation has been done on molybdenum-doped titanium oxo clusters.

With their distinct molecular and electronic structures, scientists have a special interest in electron-rich metal oxo clusters that have metal-metal bonds, because of their potential for use in the areas of catalysts, electronics, and batteries. Clusters that are modified by heterometals with delocalized electrons have shown potential advantages in band gap engineering and catalysis. For these reasons, the team used molybdenum chloride as a low-valent metal source. Working with carboxylic acid in alcohol media, they manipulated the flexible hydrolysis condensation process and various arrangements of the low-valent heterometallic molybdenum-titanium-oxo clusters.

The two heterometallic clusters the team created both have Mo^V-Mo^V bonds in common. The X-ray photoelectron spectroscopy measurements the researchers obtained reveal the simultaneous presence of Mo^V and Mo^VI in one of the clusters, indicating the first example of mixed-valent Mo^V/VI doping in heterometallic titanium oxo clusters.

In optoelectronics, a semiconductor’s band gap determines its potential applications. The team investigated the band gaps of their two heterometallic clusters using diffuse reflectance spectroscopy analysis. They found that the optical band gaps of these two compounds are dramatically reduced.

They attribute this reduction in the band gaps to the introduction of electron-rich Mo-Mo pairs as heterometals. In addition, the team found that the bands shift effectively toward the visible-light region, as shown by the solid state ultraviolet-visible spectroscopy measurements. The team’s work not only enriches the structural diversities of metal oxo clusters, but it also provides a simple route for the property modulation of electron-rich molybdenum-doped titanium oxo clusters.

Looking ahead the team hopes to construct heterometallic oxo clusters with further enhanced visible-light absorption and improved stability. “The ultimate goal is to develop efficient cluster catalysts to split water into hydrogen using solar energy,” said Zhang.

More information: Weizhou Chen et al, Heterometallic Mo–Ti oxo clusters with metal–metal bonds: Preparation and visible-light absorption behaviors, Polyoxometalates (2022). DOI: 10.26599/POM.2022.9140013

Provided by Tsinghua University Press

The composition of foodstuffs, but also the sequence of dishes, is important for the perfect taste experience of a menu. This insight, based on experience, is well known. The molecular causes of the pleasure-enhancing effects, on the other hand, are still poorly understood.

Using the example of chicory, surrogate and roasted coffee, a study by the Leibniz Institute for Food Systems Biology at the Technical University of Munich (LSB) now explains for the first time why the order in which we eat food can be decisive for bitter taste perception and what role bitter taste receptors play in this process.

Chicory (Cichorium intybus L.) is a popular salad ingredient, and its bitterness harmonizes well with apples or balsamic vinegar. The roasted and ground bitter roots of the plant, on the other hand, contribute to the flavor similarity to roasted coffee in many coffee substitutes. The reason for this, however, is not clear. To investigate this question and learn more about the molecular basis of taste perception, the research team led by Maik Behrens, head of the Taste & Odor Systems Reception group at LSB, conducted extensive experiments.

Three bitter taste receptor types identified for chicory

The experiments focused on the three main known bitter substances present in chicory and chicory root-containing surrogate coffee. To determine which human bitter taste receptor types they activate, the team used an established cellular assay system.

As the test results show for the first time, the chicory bitter compounds activate only three of the approximately 25 bitter taste receptor types. However, these belong to the group of five receptor types identified to date that respond to bitter substances in roasted coffee. “Chicory bitter compounds thus exhibit a receptor activation profile that overlaps with those of the roasted coffee compounds tested to date and appear to mimic the bitterness of roasted coffee well. However, the profiles are not completely identical,” says Tatjana Lang of the LSB, who was substantially involved in the study.

It’s the sequence that counts

To check the extent to which the similarities and differences in the receptor activation profiles affect taste perception, the team also conducted sensory tests. If the test subjects evaluated roasted coffee shortly before eating chicory or drinking a coffee substitute, both foods tasted significantly less bitter than before. Conversely, consumption of chicory or surrogate coffee did not affect the perceived bitterness of a subsequently tasted roasted coffee.

“Our results suggest that the bitter substances of roasted coffee briefly make all three bitter taste receptor types that respond to chicory compounds less sensitive to the latter. Conversely, this debittering effect does not work, as presumably the chicory bitter substances are not able to desensitize all receptor types that detect bitter compounds in roasted coffee,” explains Roman Lang, who heads the Biosystems Chemistry & Human Metabolism group at LSB.

“Ultimately, our results suggest that precise knowledge of the receptor activation profiles of bitter compounds could in principle be used to predict or positively modulate the taste perception of foods,” adds principal investigator Maik Behrens. “Moreover, it can be assumed that such effects are not limited to the perception of bitter substances. Therefore, there is still much to be explored to understand the molecular mechanisms underlying complex taste sensations.”

More information: Roman Lang et al, Overlapping activation pattern of bitter taste receptors affect sensory adaptation and food perception, Frontiers in Nutrition (2022). DOI: 10.3389/fnut.2022.1082698

Provided by Leibniz-Institut für Lebensmittel-Systembiologie

Stress isn’t just the psychological pressure you feel in response to a looming deadline at work. It is also a description of the physical forces pushing, pulling, or twisting an object, structure, or material. Examples of stress include gravity dragging downward on a bridge, wind blowing against the side of a building, or even a waistband drawn taut by a big meal.

With stress affecting literally everything made and used by people, often in damaging ways, it is important to identify when and where it is happening and the extent to which it is occurring. This is not always easy, though, because many materials show no obvious signs of being under stress.

Caltech’s Maxwell Robb, an assistant professor of chemistry, has been working to make stress easier to identify through the creation of polymers that change color when a force is applied to them. Now, in a paper titled “Mechanically gated formation of donor–acceptor Stenhouse adducts enabling mechanochemical multicolour soft lithography” and published in Nature Chemistry, Robb shows how his team created a new type of these polymers that can be made to change to almost any colors the user wants. This is in contrast to the polymers he had previously developed, which could only change to a single, predetermined color.

To understand the Robb group’s latest research, it is helpful to first know how previously developed color-changing plastics work. To create a plastic that changes color in response to stress, you need a type of molecule known as a mechanophore. There are many kinds of these mechanophores, with only some being color changing, but almost all work in essentially the same way. The molecules exist in two states, and when they are subjected to an external force, they undergo a chemical reaction that converts them from one state to another. In the case of the mechanophores Robb’s team works with, one state is colorless and the other is colored.

When mechanophores are incorporated into a plastic, they experience the force that is applied to the plastic and thus will change color, allowing the location of that stress to be visualized.

The team’s latest work is based on similar principles but with a twist. The mechanophore they have developed doesn’t change color directly with force but rather produces an intermediate compound that can be converted to myriad brightly colored dyes called donor–acceptor Stenhouse adducts (DASAs).

The colorless mechanophore molecules are also incorporated into plastic, but, in this case, they remain essentially colorless even after they are subjected to stress. Instead, the change in their molecular structure makes them able to undergo a secondary chemical reaction, a process referred to as mechanochemical gating. Once in that chemically receptive state, they are “developed” with a chemical bath that tacks another molecular piece onto their structure. These pieces cause the larger molecule to become brightly colored; the researcher can tune the color to any desired hue by changing the molecular fragment that is tacked on.

“The beauty of this is we have one central mechanically responsive molecule,” Robb says. “And that makes it a general chemical platform, because just by changing the identity of the chemical that you use in the second step, you can generate this extremely diverse library of dyes.”

As a demonstration of the platform, researchers in Robb’s lab prepared a sheet of stretchy polymer containing their new mechanophore molecule and stamped it with a pattern that provided stress in specific areas. The material was then placed in a chemical bath that turned the pattern purple. The plastic was stamped a second time with a new pattern and developed with a different chemical that turned the newly stamped area blue. And finally, the plastic was stamped a third time and developed with a bath that turned the most recently stamped area green. Together, the three stamped patterns created a multicolor flower image within the plastic itself. And because DASAs also change their color with light, the image could be made to disappear using a flashlight.

Of course, the technology was not created just for the sake of printing simple pictures in plastics. Robb says the ability to leave chemically reactive imprints in three dimensions in polymer materials could also open the door to patterning other kinds of chemicals in three-dimensional space, such as proteins, which would have applications in tissue engineering. Additionally, he says that the lab is working to further take advantage of the time element associated with the photoresponse of DASAs, making the printing 4D.

“It’s actually really interesting for future directions of using this for things like encryption technologies,” he says.

More information: Anna C. Overholts et al, Mechanically gated formation of donor–acceptor Stenhouse adducts enabling mechanochemical multicolour soft lithography, Nature Chemistry (2023). DOI: 10.1038/s41557-022-01126-5

Journal information: Nature Chemistry 

Provided by California Institute of Technology 

Recently, a research team led by Prof. Chen Tao from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) revealed the formation and evolution of the point defect of antimony selenosulfide. This work was published in Advanced Materials.

Antimony selenosulfide, i.e., Sb₂(S,Se)₃, features great stability, no inclusion of rare or toxic elements, excellent photovoltaic property, and low cost, which make it an ideal photovoltaic material. Due to the quasi-one-dimensional structure and high extinction coefficient of the material, it has unique advantages in fields such as ultralight devices, portable power sources, or building-integrated photovoltaics.

To improve the performance of devices, it is necessary to understand the basic properties of this new photovoltaic material.. The research team focused on the point defect of antimony selenosulfide. They utilized optical deep-level transient spectroscopy (O-DLTS) to detect the characteristics of the defect of antimony selenosulfide driven by temperature. Researchers then investigated the variation of the material composition during annealing to reveal the formation and evolution of the point defect.

The initial hydrothermal deposition results in the formation of point defects with high formation energy, which was the result of random deposition of ions driven in hydrothermal condition, according to the researchers. Post-annealing and the thin-film crystallization led to the loss of sulfur and selenium anions as well as the formation vacancy defect (V_S(e)). Since the formation energy of cation/anion inversion defects is relatively low, antimony ions would transfer and fill anion vacancies, eventually forming the Sb_S(e) inversion defect.

The study deepens the understanding of the formation and evolution of point defects of antimony selenosulfide and offers a new method to study such processes. It also provides a guidance for designing methods to produce films and inhibiting the formation of deep-level point defects.

More information: Bo Che et al, Thermally Driven Point Defect Transformation in Antimony Selenosulfide Photovoltaic Materials, Advanced Materials (2022). DOI: 10.1002/adma.202208564

Journal information: Advanced Materials 

Provided by University of Science and Technology of China

In the age-old battle against mosquitos, DEET has proven effective at keeping this nemesis at bay, but the repellent is smelly and its protection is short-lived. Now, researchers report in the Journal of Agricultural and Food Chemistry that they have designed safe alternatives that have some advantages over DEET, including a nice smell and much longer protection from bites.

DEET disrupts a mosquito’s ability to locate humans. Until recently, it was considered the gold standard among topical repellents, but some find its strong odor offensive. It has to be reapplied frequently, and at high concentrations, it can damage synthetic fabrics and plastics. Another popular repellent known as picaridin is now regarded as a better alternative, since its protective effect lasts longer, and it doesn’t have an odor or damage items. However, like DEET, it has to be reapplied after swimming or sweating.

So, Francesca Dani and colleagues wanted to look for alternatives to these established products. In prior work, the team used as starting materials two plant-based natural repellents that offered only short-term protection from mosquitos. The researchers converted these terpenoids into cyclic acetals and hydroxyacetals, thereby extending their protective timespan beyond that of DEET. But the researchers wanted to improve on these initial products.

In the current work, the team synthesized additional cyclic hydroxyacetals from inexpensive, commercially available carbonyls. The new cyclic compounds had pleasant, much fainter odors and were easier to dissolve in water, meaning they can be formulated without high concentrations of alcohol. Some were as effective as DEET and picaridin at repelling Asian tiger mosquitos, which have spread widely in the U.S. and carry diseases, including encephalitis, dengue and dog heartworm.

And like picaridin, they provided human volunteers more than 95% protection from bites for at least eight hours, while DEET’s protection rapidly declined below that level after just two hours. Toxicity of some of the most active new compounds was comparable to or lower than the traditional repellents.

Two hydroxyacetals were also less likely to cause immune reactions or to penetrate cell layers than picaridin. The researchers conclude that their compounds represent a new class of promising mosquito repellents that can compete favorably with DEET and picaridin in terms of efficacy and safety.

More information: Immacolata Iovinella et al, Cyclic Acetals as Novel Long-Lasting Mosquito Repellents, Journal of Agricultural and Food Chemistry (2023). DOI: 10.1021/acs.jafc.2c05537

Journal information: Journal of Agricultural and Food Chemistry 

Provided by American Chemical Society