Tag: Physics

A new study in published in Scientific Reports suggests that the perfect cup of coffee is influenced by a complex blend of variables such as bean processing method, brewing time, and grind size, not just the roast level.

Caffeine content and extraction yield are two of the most vital variables for coffee enthusiasts, especially those who approach it with precision.

Extraction yield is a measure of the amount of soluble material from the coffee grounds that gets dissolved in the brewed coffee. It essentially reflects the efficiency of the brewing process in extracting compounds from the coffee grounds.

Led by Dr. Zachary R. Lindsey, Assistant Professor of Physics at Berry College, U.S., the study focuses on how the degree of roast affects these two variables. Phys.org spoke to Dr. Lindsey, a self-proclaimed coffee nerd about the study.

“Over 20 years ago, I heard a barista claim that dark roasts have more caffeine, but a decade later, I was exposed to the contrasting idea that light roasts were the king of caffeine. Yet, I couldn’t find any convincing data.”

“It wasn’t until I picked up coffee roasting as a hobby in 2022 that I started to see the missing pieces of the puzzle. Luckily, two passionate undergraduate students on my research team were also intrigued by this mystery, and we got to work,” said Dr. Lindsey.

Choice of coffee, roast, and brew method

The researchers chose Ethiopian coffee to conduct their study. Ethiopia has a long tradition of producing coffee dating back centuries as it is the country where Coffee arabica, aka the coffee plant, originates.

In this, they are investigating natural and washed processed coffee.

In the natural method, the coffee cherries are dried with the seeds still inside. The seeds are separated after drying, resulting in fruity and complex flavors in the coffee beans. On the other hand, in the washed method, the seeds are separated from the coffee cherries and then dried, leading to a cleaner and brighter flavor profile.

The researchers then used five different degrees of roasts for the green coffee beans, choosing a brewing time of one, two, and ten minutes.

The researchers chose the AeroPress brewing method with a 15:1 water-to-coffee ratio. The AeroPress is a pressure-based brewing method, similar to an espresso machine, but on a smaller scale. The AeroPress steeps the coffee and uses pressure to extract the brew through a paper filter.

Dr. Lindsey explained the choice behind the AeroPress, saying, “When selecting a brew method, the main goal was to implement a procedure that could consistently produce brews within a wide range of extraction yields by only varying the brew time.”

“The AeroPress stood out as a means to achieve these desired outcomes with minimal variation across all roast batches.”

Overall, the researchers had 30 unique combinations of brewed coffee to study.

Analyzing the coffee

The researchers used three analysis techniques to analyze caffeine content and extraction yield.

To measure compounds like caffeine, chlorogenic acids, and other soluble compounds in the brewed coffee, they used high-performance liquid chromatography (HPLC).

This method separates different compounds in the coffee based on their interactions with a standard material, quantifying individual concentrations.

Next, they used refractometry. This method measures the bending of light through the brewed coffee, indicating the extraction yield, i.e., how much soluble material is dissolved from the coffee grounds.

Finally, they used scanning electron microscopy (SEM) to observe the surface of the coffee beans and grounds. This helped them to examine the grain size and porosity. SEM provides information about the impact of roasting on the physical features of the coffee beans.

“SEM allows for a straightforward characterization approach that provides two-dimensional information about the structure of the roasted coffee. The evolving porosity of the roasting coffee plays a pivotal role in compound mobility during roasting and brewing,” explained Dr. Lindsey.

Porosity, caffeine, and extraction

The researchers found that caffeine content in the brewed coffee depended on the roasting process and the extraction yield.

“During roasting, the volume and porosity of the coffee seeds increase as the roast progresses, which makes it easier for compounds to move in or out of the system,” explained Dr. Lindsey.

A greater porosity implies more of the inner surface area of the coffee grounds is exposed, making it easier for water to penetrate and dissolve compounds like caffeine and flavors. This has an impact on the entire extraction process that occurs during brewing.

For the caffeine content, the researchers found that when using identical brewing setups, light and medium roasts had a higher caffeine content than darker roasts. This is due to the caffeine loss during roasting, resulting in typically lower extraction yields for darker roasts.

Conversely, they found that the darker roast’s caffeine content was higher when the extraction yield was kept consistent for all the roasts.

“However, darker roasts consistently exhibited lower extraction yields than light and medium roasts, so it was not always possible to achieve a common extraction yield for all degrees of roast,” added Dr. Lindsey.

New insights

The competing mechanisms of increased porosity improving extraction efficiency and darker roasts losing extractable compounds revealed a unique insight contradicting previous assumptions.

Caffeine sublimation—the process of caffeine transitioning directly from a solid to a gas—occurs at higher temperatures than previously thought.

“Although the interplay between roast degree and caffeine content has been addressed over 20 times in the literature, the prevailing theory is that caffeine remains stable during the roasting process.”

“However, we establish a clear relationship between roast degree, caffeine content, and extraction yield,” said Dr. Lindsey.

The researchers plan to extend this work to study the relationship between roast degree and extraction yield for decaffeinated coffees. They also aim to test it with percolation-based brewing methods to see if they yield similar results.

The bottom line is, if you want a cup of coffee with the maximum caffeine content choose a medium roast, says Dr. Lindsey.

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A researcher’s team at Chungnam National University has unlocked new potential for copper-zinc (CuZn) electrodes in electrochemical CO₂ reduction (EC CO₂R). This research, led by Professor Youngku Sohn, explores the performance and recyclability of CuZn electrodes, comparing them with single-metal alternatives like copper and zinc, and highlighting their superior catalytic properties.

This research is published in the journal Applied Surface Science.

“Electrochemical methods present a promising solution for repurposing CO₂, but electrode stability has always been challenging,” says Prof. Sohn. “Our study shows that CuZn electrodes can stabilize over time through recycling, preserving their catalytic effectiveness and selectivity for valuable hydrocarbons.”

A key highlight of the study was the use of laser techniques to control the oxidation states of the electrodes, allowing researchers to fine-tune their catalytic properties. By analyzing the performance of these electrodes through multiple recycling cycles, the team found that CuZn alloys outperformed single-metal electrodes, providing insights into the importance of surface oxidation states for catalytic efficiency and product selectivity.

The team utilized advanced techniques such as depth-profiling X-ray photoelectron spectroscopy (XPS) to track the changes in oxidation states and compositions of the electrodes. This method revealed that the CuZn electrodes not only stabilize over time but also exhibited a superior ability to maintain selectivity for complex hydrocarbons compared to the single-metal electrodes.

“We also explored the influence of oxidation states on product selectivity,” adds Ms. Seon Young Hwang, a co-author and master’s student in the Department of Chemistry at Chungnam National University. “By controlling the oxidation states, we were able to significantly enhance the electrodes’ performance in reducing CO₂ to valuable products.”

This study is particularly relevant for real-world applications, as it enhances the understanding of electrode recyclability and the design of more selective catalysts. The findings could help create high-efficiency CO₂ reduction systems for the conversion of CO₂ into sustainable fuels or valuable chemicals, potentially transforming industries such as energy, manufacturing, and environmental conservation.

“The long-term implications of this work are profound,” says Prof. Sohn. “This research could play a crucial role in developing carbon-neutral industrial processes, contributing to a circular carbon economy by efficiently recycling CO₂ into useful products.”

While the study marks a significant milestone, further research is needed to optimize the scalability of these electrodes for industrial applications. The team’s next step is to examine these electrodes under real-world conditions to understand their capabilities better.

The interactions between light and nitroaromatic hydrocarbon molecules have important implications for chemical processes in our atmosphere that can lead to smog and pollution. However, changes in molecular geometry due to interactions with light can be very difficult to measure because they occur at sub-Angstrom length scales and femtosecond time scales.

In a study, published in the journal Physical Chemistry Chemical Physics, researchers used an ultrafast electron camera to image the motions of hydrocarbon molecules on scales 10,000 times smaller than the width of a human hair.

This ultra-precise and ultrafast imaging technique, supported by advanced computations, reveals a proton transfer step followed by an out-of-plane twisting motion as key components of energy relaxation. (Relaxation is the process by which the molecule moves from an excited, high-energy state to a lower energy ground state after absorbing light.)

Previous studies have proposed various ways that hydrocarbon molecules may relax after interacting with light. However, scientists lacked experimental data to verify which process occurs.

In this research, scientists used the relativistic ultrafast electron diffraction (UED) instrument to observe the relaxation of photoexcited o-nitrophenol. Then, they used a genetic structure fitting algorithm to extract new information about small changes in the molecular shape from the UED data that were imperceptible in previous studies.

Specifically, the experiment resolved the key processes in the relaxation of o-nitrophenol: proton transfer and deplanarization (i.e., a rotation of part of the molecule out of the molecular plane). Ab-initio multiple spawning simulations confirmed the experimental findings.

The researchers were able to identify a key relaxation pathway involving proton transfer and molecular “twisting.” This result lays the groundwork for studies of more complex molecules that scientists believe undergo similar interactions. It will also help researchers better understand how pollution forms.

Researchers at Lawrence Livermore National Laboratory (LLNL) have developed a new approach that combines generative artificial intelligence (AI) and first-principles simulations to predict three-dimensional atomic structures of highly complex materials.

This research highlights LLNL’s efforts in advancing machine learning for materials science research and supporting the Lab’s mission to develop innovative technological solutions for energy and sustainability.

The study, recently published in Machine Learning: Science and Technology, represents a potential leap forward in the application of AI for materials characterization and inverse design.

The approach uses X-ray absorption near edge structure (XANES) spectroscopy. Accurately determining atomic structures from spectroscopic data has long posed a challenge, particularly for complex systems, such as shapeless materials.

In response, LLNL scientists have introduced a generative framework based on diffusion models, which are an emerging machine learning technique. The authors demonstrate how this framework enables the prediction of 3D atomic arrangements from XANES spectra.

“Our method bridges a crucial gap between spectroscopic analysis and precise structure determination,” said Hyuna Kwon, a materials scientist in LLNL’s Quantum Simulations Group, Materials Science Division. “By conditioning the generative model on XANES data, we can reconstruct atomic structures that align closely with the target spectra, offering a powerful tool for material analysis and custom design.”

The project was a collaborative effort, with Kwon and Tim Hsu from LLNL’s Center for Applied Scientific Computing contributing equally. The team demonstrated that their AI model also scales effectively from small datasets for generating realistic, large-scale structures. This scale-agnostic property demonstrates the model’s ability to bridge scales from nanoscale to microscale, enabling detailed atomic structure generation even at complex features like grain boundaries and phase interfaces.

“This approach can be leveraged beyond just structural analysis,” said Anh Pham, the principal investigator of the project. “It can be extended to inverse design—where we start from a desired material property and engineer the corresponding atomic structure—accelerating the discovery of materials with tailored functionalities.”

Fluorescence is a well-known phenomenon with many practical applications that has been studied for decades. Despite this, a commonly used mathematical formalism to describe how it evolves over time does not make physical sense under certain conditions, as researchers from the Institute of Physical Chemistry, Polish Academy of Sciences have recently discovered.

Namely, they showed that a mathematical tool that can be safely used in solids, where molecules are practically immobile, cannot always be used in liquids, where they can move freely. If applied incorrectly, this widely used approach can lead to erroneous interpretations of experimental data and wrong conclusions. This is what their paper in the The Journal of Chemical Physics warns us about.

Everything glows, but not in the same way. It has been known for more than a century that anybody at a given temperature above the inaccessible absolute zero emits photons. Some substances also emit light after undergoing a chemical or biochemical reaction, an electrochemical reaction, or after being excited by another light source. These phenomena are known as chemi-, bio-, electrochemi- and photo-luminescence, respectively.

You may have seen photos of Australian coastlines full of bright blue algae at night, or glowing fireflies in the forest. You may have noticed the green and blue flakes in banknotes under an ultraviolet lamp. In all these examples, the observed light is a luminescence process in which molecules in excited states of their electrons relax back to the comfortable relaxed state, giving off the excess energy in the form of photons, and not just heating up their environment.

This phenomenon of luminescence was first described in Europe in the 16th century by Nicolas de Monardes: lucky enough to be at the center of the world at the time, he received some wood samples from Mexico that, when soaked in alkaline water, glowed blue. The Americans had known for a long time that this was a sign of a well-prepared medicine against kidney diseases from a certain plant known to Monardes as Lignum nephriticum.

Today, luminescence, in particular fluorescence, is used intensively for the same purpose: to report on the structure and properties of biological samples. Fluorescence microscopy techniques have evolved to the point where single molecules can be observed.

An interesting characteristic of fluorescent samples is that the duration of light emission depends on many external factors. Therefore, not only the color of the emission is used in the above applications, but also its temporal decay. In the simplest case, this fluorescence decay is well described by an exponential function. This is analogous to the exponential decay of the intensity of ionizing radiation (alpha, beta, or gamma) emitted by a sample containing a single type of radioactive isotope.

It is often observed that when the sample is structurally complex, non-homogeneous or very viscous, a simple mathematical function such as the exponential is not sufficient to describe the temporal evolution of fluorescence. Sometimes a sum of several such functions is sufficient.

If the complexity is high enough, the number of these functions can be very large, so it makes more sense to use continuous distributions of decays. This is a very elegant formalism that can provide a lot of insight into the structure of the environment in which the fluorescent species is embedded. For example, in a living cell, a fluorophore (our little reporter) might be located in places in the membrane, or in the citoplasm, or in the mitochondria, or attached to some proteins.

All these different environments will affect the properties of the fluorophore in such a way that its luminescent relaxation will vary, leading to slightly different colors of luminescence with distinct decay times.

One important phenomenon that occurs to excited molecules is called quenching. This is usually a chemical reaction that impedes the molecules from emitting light, reducing, quenching, the total amount of light observed from the sample. This also shortens the observed duration of the fluorescent glow: it is then said that the decay kinetics are affected by quenching.

Merging both scenarios, complex environments and quenching by chemical reactions with other substances, is not an easy thing to study, but it happens all the time. One might be tempted to use the same sums of exponential functions or continuous distributions of lifetimes to explain the observations. Until now, we did not know that this was wrong:

“We have shown that this mathematical approach has a clear physical interpretation only when the fluorophore and quencher molecules are stationary, as in the solid state. However, if we consider the mobility of the fluorophore with respect to the quencher, such an interpretation becomes impossible. Therefore, for systems in which the relative motion of fluorophores and quenchers cannot be ignored, it is not appropriate to use the time-independent rate or decay time distributions to explain, fit, or rationalize experimental results on fluorescence decay,” says Prof. Gonzalo Angulo of ICP PAS.

In addition, ICP PAS scientists have provided a new insight into the description of molecular systems where the relative motion of fluorophore and quencher is taken into account. They have shown that it is possible to use a theoretical approach to predict the time-dependent decay rate distribution, provided that the initial microscopic properties of the system, such as the distribution of quenchers around the fluorophore and the microscopic transfer rates, are known. Such a time-dependent distribution can correctly describe fluorescence decay even in the presence of molecular motion.

As is usually the case in theoretical studies, a few simplifying assumptions were made, “First, we assumed that the quenchers interact with a fluorophore but do not “feel” each other: their interactions are neglected. Furthermore, although we considered the fluorophore-quencher excluded volume—through the presence of the pair distribution function—we neglected the quencher-quencher excluded volume effect. Therefore, we can assume that the quencher positions are independent,” says Dr. Jakub Jędrak.

However, he emphasizes that the main result is very general and does not depend on the presence and exact form of interactions between molecules in solution.

Their results show how important it is to re-examine existing theories and models and to look at well-studied assumptions. So there is still a lot of work to be done, even if we think that everything is well studied and well known.

The Stach Group in Penn Engineering has led a collaborative team identifying how chemical catalysts drive the creation of liquid fuels from sunlight, paving the way for more efficient removal of greenhouse gases from the atmosphere.

“Imagine standing in a desert under a clear, starlit sky,” says Eric Stach, Robert D. Bent Professor of Engineering at the University of Pennsylvania. “With just your naked eye, you might spot the shimmering band of the Milky Way or the fuzzy glow of Andromeda. But without a telescope and other sophisticated tools, it’s nearly impossible to distinguish individual stars or truly understand their arrangement in the cosmos.”

Stach likens this experience to the challenge the team faced in trying to visualize molecular catalysts, the microscopic structures key to chemical reactions like converting carbon dioxide (CO₂) into usable fuels, on surfaces of semiconductor materials.

These catalysts, which contain heavy metal atoms, are scattered across surfaces in ways that are crucial to their performance, yet, like stars in the night sky, “their precise placement and clustering are difficult to discern with conventional techniques,” Stach says.

To that end, Stach and his collaborators at the University of North Carolina at Chapel Hill (UNC) and Yale University—working together as part of the Center for Hybrid Approaches in Solar Energy to Liquid Fuels— combined atomic-resolution imaging with machine learning analysis to better characterize the distribution of molecular catalysts.

The team published their findings on the determination of the conditions, behaviors, and qualities of different catalysts in the journal Matter.

“The project brought together researchers with complementary expertise in imaging, molecular synthesis, catalysis, and surface chemistry,” says Jillian L. Dempsey of UNC. “The collaboration was essential for visualizing how individual catalysts are distributed across semiconductor photoelectrodes.”

By providing a new understanding of how molecular catalysts behave on semiconductor surfaces, the team’s findings pave the way for more efficient catalytic systems. Advances could accelerate developments in renewable energy technologies, such as CO₂ conversion and hydrogen production, and offer insights applicable to a wide range of industrial processes.

“The elegance of our approach really lies in a simple yet powerful idea,” says Sungho Jeon, a postdoctoral researcher in the Stach Group and co-first author of the paper. “If you want to correlate variables, like how molecular coverage and distribution influence catalyst performance, you first have to measure them accurately.

“Our work shows how to precisely and robustly measure surface coverage, quantify distributions, and see how changing conditions, like the type of molecule or functionalization process, alters those properties.”

Making an atomic map

The team used High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) carried out at the Singh Center for Nanotechnology at Penn. This generates images with atomic-level resolution by highlighting the contrast between heavy atoms, such as rhenium or platinum, and their lighter surroundings. While techniques like HAADF-STEM provide extraordinary detail, they only capture small regions at a time and give researchers massive datasets that can be tricky to analyze manually.

“Enter Sungho’s convolutional neural networks (CNNs),” Stach says. “It’s a type of machine learning that excels at pattern recognition. Sungho trained CNNs to detect individual atoms in HAADF-STEM images, which let us see them to systematically map the surface coverage and distribution of catalysts across their supports.”

This allowed the researchers to not only quantify the number of immobilized molecules but also understand whether they were clustered, evenly spaced, or randomly scattered—insights critical for optimizing catalytic performance.

Why does this matter? The spatial arrangement of catalysts can dramatically influence their efficiency and selectivity. Molecules that are too densely packed might interfere with each other, reducing their effectiveness. Conversely, evenly dispersed catalysts can increase reaction rates and improve outcomes.

“Understanding these details is a game-changer,” says Stach. “It’s the first step toward designing catalytic systems with precision, tailoring their structure to enhance their function.”

Do not destroy

The team also overcame major practical hurdles, like the fragility of molecular catalysts under the intense electron beams used for imaging. They developed sample preparation methods and stabilization techniques to protect the molecules, ensuring the images accurately reflected real-world conditions.

Stach explains that there was an initial concern that the high-energy electrons would “destroy everything” upon impact, potentially “knocking atoms around like pinballs,” rendering the images unreliable and making it impossible to accurately determine their true arrangement. So, the researchers employed new sample preparation techniques, including backfilling the surface with stabilizing molecules to minimize electron beam damage.

“We had to convince ourselves—and reviewers—that what we were imaging was real and not an artifact of the imaging process,” says Stach. He notes that this ensured that the molecular catalysts’ true distribution was captured without distortion. Through this approach, the researchers uncovered distinct patterns in how catalysts interacted with their surfaces.

The researchers observed that some molecules, like the CO₂-reducing Re-Phen, tended to cluster, while others, such as the hydrogen-evolving Pt-Porph, exhibited more dispersed arrangements. These differences, they found, were influenced by variables such as the choice of attachment group and the functionalization process used to bond the molecules to the surface.

“This work would not have been possible without the combined expertise of researchers across institutions,” says Nilay Hazari of Yale. “Each team brought unique skills that enabled us to perform these imaging experiments. The superb instrumentation at Penn, in particular, was crucial to our success.”

The clustering of catalysts like Re-Phen was found to potentially hinder catalytic efficiency due to interactions between neighboring molecules, while dispersed arrangements optimized performance.

Looking ahead, the team is already exploring how this methodology can be adapted to study catalysts on more complex surfaces, such as “porous materials that offer greater surface area but pose additional imaging challenges,” Stach says. “We would’ve never bothered with something this tricky a couple of years ago, but the information we got from this paper’s already paying tremendous dividends in the preliminary data.”

Hydrogen sulfide, a colorless gas that smells like rotten eggs, is produced naturally from decaying matter. This gas is lethal to breathe in, and hydrogen sulfide present in high concentrations can cause death very rapidly.

Its relative density is also greater than air, causing it to accumulate at lower altitudes and posing an enormous threat to workers at sites, such as manholes, sewage systems and mining operations.

Why is hydrogen sulfide so dangerous? It binds strongly to the heme-containing cytochrome c oxidase (CcO) enzyme and blocks the cellular process of aerobic (oxygen-dependent) respiration.

What is even more concerning is that, as of now, there is no identified antidote that can treat hydrogen sulfide poisoning. Hence, there is an urgent need to develop therapeutic agents that can be stored for long durations and are effective against hydrogen sulfide poisoning immediately.

A study led by Professor Hiroaki Kitagishi at Doshisha University and published online on December 10, 2024, in Scientific Reports has proposed a novel antidote for hydrogen sulfide poisoning.

Atsuki Nakagami, Ph.D. students in the Department of Applied Chemistry at the Graduate School of Doshisha University, Dr. Qiyue Mao, Specially Appointed Assistant Professor at Doshisha University, Associate Professor Masaki Horitani at the Faculty of Agriculture, Saga University, and Professor Masahito Kodera at the Faculty of Science and Engineering, Doshisha University, also contributed to the results of this study.

They decided to tackle this problem by using artificial heme-model compounds that would have a higher affinity towards hydrogen sulfide than the native hemes present in our bodies.

Providing more context to their approach, Prof. Kitagishi explains, “We have developed and studied synthetic heme-model compounds (hemoCDs) over the last two decades. The series of hemoCDs, which consist of porphyrin and cyclodextrins, is our original heme-model system that realizes the biological functions of hemes (like hemoglobin) while using completely synthetic materials.”

Previously, Prof. Kitagishi and his collaborators used two novel hemoCDs dubbed “hemoCD-Twins”—met-hemoCD-P and met-hemoCD-I—to successfully treat carbon monoxide and hydrogen cyanide poisoning in mice.

In this study, they decided to test if these two complexes had the potential to “scavenge” hydrogen sulfide in an aqueous medium. Interestingly, they found that met-hemoCD-I in particular had a very high affinity for hydrogen sulfide under normal physiological conditions—almost 10 times higher than that of human met-hemoglobin.

Met-hemoCD-I was able to convert toxic hydrogen sulfide into nontoxic sulfite and sulfate ions, indicating that it could be used to treat hydrogen sulfide poisoning.

To test this antidote, they injected hydrogen sulfide-treated mice with met-hemoCD-I. The results were very promising—mice injected with met-hemoCD-I showed improved survival rates compared to mice that were not given the antidote. Additionally, CcO activity in the brain and heart tissues (which had decreased because of poisoning) recovered and returned to normal.

Another aspect of met-hemoCD-I that makes it a very promising antidote is its demonstrated safety—it was found that injected met-hemoCD-I was excreted in the urine of the rats without undergoing any chemical decomposition in their body.

The results of this study show that hemoCD-Twins could be used as a powerful antidote to treat carbon monoxide, hydrogen cyanide, and now hydrogen sulfide poisoning without the risk of any side effects.

Explaining their vision for this treatment, Prof. Kitagishi says, “Using hemoCD-Twins, we can provide one powerful solution for multiple gas poisoning, even if the cause of poisoning is unknown. Worldwide, we still do not have an actual solution for accidentally occurring gas poisoning—we would like to supply hemoCD to fulfill this unmet medical need.”

In the future, they hope to bring this rapid and effective treatment to clinics and other medical settings. “We will proceed with non-clinical and clinical trials in cooperation with medical doctors in order to implement this compound as a therapeutic agent actually used in the world,” adds Prof. Kitagishi.

We are confident that this antidote will prove invaluable for improving the safety of workers and rescue personnel around the world.

Helical structures are ubiquitous across biology, from the double-stranded helix of DNA to how heart muscle cells spiral in a band. Inspired by this twisty ladder, researchers from Hiroshima University’s Graduate School of Advanced Science and Engineering have developed an artificial polymer that organizes itself into a controlled helix.

They published their results on Oct. 24 in Angewandte Chemie.

“Motivated by elegant biological helical structures, considerable effort has been devoted to developing artificial helical organizations with defined handedness for wide potential applications, including memory, sensing devices, chiral stationary phases, asymmetric catalysts and spin filtering,” said corresponding author Takeharu Haino, professor at Hiroshima University’s Graduate School of Advanced Science and Engineering.

“The helical supramolecular polymer presented here is a new type of helical polymer.”

Polymers are a broad class of materials characterized by the large molecules that comprise them. They can be found in nature as proteins and more, including DNA, and in a number of industrial roles, including as synthetic components of plastics.

The molecules of a supramolecular polymer typically interact to form non-covalent bonds, which are highly directional and prompt specific behaviors depending on their arrangement.

The polymer that the Hiroshima University team developed is known as a pseudo-polycatenane, which contains mechanical bonds in addition to the non-covalent bonds. Mechanical bonds can be broken via force without disrupting the chemical structure of the non-covalent bonds—an attractive property when developing materials that require precise control.

Typically, such helical structures are categorized as “one-handed,” meaning their twist turns in one direction only. As such, the way they interact with other materials is dictated by the direction of their twist. If researchers can control whether that twist is left- or right-handed, so to speak, then researchers can control how the polymer behaves when applied in different scenarios.

“Helical polymers are potentially useful for various purposes; however, the synthesis of helical polymers with preferred handedness had remained challenging,” Haino said.

“Here, we present a novel synthetic method for helical polymers with preferred handedness via supramolecular polymerization controlled by complementary dimerization of the bisporphyrin cleft units.”

Bisporphyrin cleft units are molecular components that can join up with other components to form molecular complexes, including polymers. By strategically inducing joining of these units—dimerization—the researchers can pre-emptively determine the handedness of the resulting polymer.

“The proposed novel strategy for controlling the handedness of supramolecular helical pseudo-polycatenane polymers paves the way for the study of supramolecular polymer materials with functions directed by controlled helicity and mechanical bonding,” Haino said.

“Our goal is to apply these new helical supramolecular polymers to material separation and catalysis—or the acceleration of chemical reactions—and to create a new functional chemistry of helical supramolecular polymers.”

A team of physical chemists at Wageningen University and Research, Maastricht University and EnzyTag BV, all in the Netherlands, has uncovered the physical chemistry behind the ticks’ ability to adhere to the skin of its host. In their study, published in the journal Nature Chemistry, the group observed the evaporation of a drop of artificially synthesized amino acid similar to the kind produced in tick saliva to see if it would show phase separation.

Prior research has shown that when a tick catches a ride on a passing host, it adheres, then pierces the skin and feeds. In this new study, the research team noted that the sticking mechanism has not previously been well studied. They began by collecting samples of the saliva protein produced by the ticks, which they noted formed into solid cones when extruded onto the skin of its host. That meant that it was a bio-adhesive, the only one known to stick to a living substrate.

They found that the tick saliva had glycine-rich proteins, which was due to the tick upping its production just prior to latching onto a host. Prior research has shown that such proteins can prevent protein folding, which accounts for the degree of hardness of the cone that forms.

In studying the tick saliva and its proteins, the team found evidence of a possible liquid-to-liquid phase separation. To confirm it, they created a synthetic version of one of the main amino acids found in the saliva and placed a drop on a flat surface and watched it evaporate.

Prior research has shown that other liquid-to-liquid phase separations, such as those that occur in coffee, result in the creation of rings as they dry. After a few minutes, the research team found the rings they were expecting—they also noted fluorescence at the ring boundary and the creation of a rim. Finally, they observed tiny droplets of the synthesized protein floating in the rim.

Taken together, the behavior of the drop showed that liquid-to-liquid phase separation. The addition of salt helped to strengthen the bonds in the fluid, resulting in harder cones. To confirm that the natural tick saliva exhibited phase separation, they captured enough ticks to extract a quantity of saliva sufficient to repeat the earlier work using real saliva and found the same results.

© 2024 Science X Network

Screens for TVs, smartphones or other displays could be made with a new kind of organic LED material developed by an international team, co-led by University of Michigan engineers. The material maintains sharp color and contrast while replacing the heavy metal with a new hybrid material.

Curiously, the material also seemed to break a quantum rule.

OLED devices currently on the market include heavy metal components like iridium and platinum, which improve the efficiency, brightness and color range of the screen. But they come with drawbacks—significantly higher cost, a shorter device lifetime and increased health and environmental hazards.

In OLEDs, light emission through the more energy-efficient phosphorescence is preferred over fluorescence, but phosphorescence happens more slowly, taking milliseconds or longer without the heavy metal component. Speeding up phosphorescence to happen in microseconds is necessary to keep up with modern displays, which operate at 120 frames per second, without producing a lingering “ghost” image. This is a key role of the heavy metals.

“We found a way to make a phosphorescent organic molecule that can emit light on the microsecond scale, without including heavy metals in the molecular framework,” said Jinsang Kim, U-M professor of materials science and engineering and co-corresponding author of the study published in Nature Communications.

Dong Hyuk Park, professor of chemical and biomedical science and engineering at Inha University, and Sunkook Kim, professor of advanced materials science and engineering at Sungkyunkwan University, both in the Republic of Korea, are also co-corresponding authors.

The speed difference between fluorescence and phosphorescence is driven by what happens after electrons from the electrical current running through the OLED material slide into the high energy level within the molecule’s available electron orbitals, known as an excited state—sort of like jumping onto a rung of a ladder. In fluorescence, they can immediately release the energy as light, jumping back down to the ground state. But in phosphorescence, they have to make a conversion first.

The conversion has to do with the electron’s spin. Each electron has a partner in its ground state, and a quantum mechanical rule—Pauli Exclusion Principle—demands that they spin in opposite directions. But when an electron slides into that higher rung, it can end up spinning in either direction because each electron is now alone in its orbital. It only remains opposite its partner a quarter of the time, and this is the case that results in fluorescence.

Phosphorescence is three times more efficient because it harnesses the other 75% of excited electrons too, but it requires the electron to flip its spin before it can come back down. In conventional phosphorescent materials, the large atomic nucleus of the heavy metal generates a magnetic field that forces the same spin direction excited electron to turn quickly, resulting in faster light emission as it returns to its ground state.

The new material positions a 2D layer of molybdenum and sulfur near a similarly thin layer of the organic light emitting material, achieving the same effect by physical proximity without any chemical bonding. This hybrid construction sped up light emission by 1,000 times, achieving speeds fast enough for modern displays.

Light emission happens entirely within the organic material without having the weak metal-organic ligand bonding, helping the material last longer. Phosphorescent OLEDs that rely on heavy metals also use the metals to help produce the color, and the weaker chemical bonds between the metal and organic material can break apart when two excited electrons come into contact, dimming out the pixel.

Pixel burnout is a particular problem for high energy blue light that has yet to be solved, but the research team hopes their new design approach can help work towards stable, blue phosphorescent pixels. Current OLEDs use phosphorescent red and green pixels and fluorescent blue pixels, avoiding blue pixel burnout at the expense of lower energy efficiency.

Beyond the potential applications, analysis of this molecular hybrid system measured something once thought to be impossible—paired electrons sharing an orbital seemed to have a combined spin under dark conditions, suggesting a forbidden ‘triplet’ state when instead their spins should cancel one another out.

“We don’t yet fully understand what causes this triplet character in the ground state because this violates the Pauli Exclusion Principle. That is very impossible, but looking at the measurement data, yes, that seems to be the case,” Kim said. “That’s why we have a lot of questions about what really makes that happen.”

The research team will explore how the material achieves triplet character ground states while also pursuing potential spintronics device applications.

Collaborators from the University of California, Berkeley and Dongguk University contributed to the study. Jinsang Kim is also a director of academic programs for macromolecular science and engineering and a professor of chemistry.