Supramolecular chemistry: Self-constructed folded macrocycles with low symmetry

Molecules that are made up of multiple repeating subunits, known as monomers, which may vary or not in their chemical structure, are classified as macromolecules or polymers. Examples exist in nature, including proteins and nucleic acids, which are at the heart of all biological systems. Proteins not only form the basis of structural elements in cells, they also serve as enzymes — which catalyze essentially all of the myriad of chemical transformations that take place in living systems. In contrast, nucleic acids such as DNA and RNA serve as informational macromolecules. DNA stores the cell’s genetic information, which is selectively copied into RNA molecules that provide the blueprints for the synthesis of proteins. In addition, long chains comprised of sugar units provide energy reserves in the form of glycogen, which is stored in the liver and the muscles. These diverse classes of polymeric molecules all have one feature in common: They spontaneously fold into characteristic spatial conformations, for example the famous DNA double helix, which in most cases are essential for their biochemical functions.

Professor Ivan Huc (Department of Pharmacy, LMU) studies aspects of the self-organization processes that enable macromolecules to adopt defined folded shapes. The molecular structures found in nature provide him with models, whose properties he tries to reproduce in the laboratory with non-natural molecules that are neither proteins, nucleic acids or sugar-like. More specifically, he uses the tools of synthetic chemistry to elucidate the underlying principles of self-organization — by constructing molecules that are expressly designed to fold into predetermined shapes. Beginning with monomers that his group has developed, he sets out to produce what he calls ‘foldamers’, by assembling the monomers one by one to generate a folded macromolecule.

Structures with low degrees of symmetry

“The normal way to get the complex structure of proteins is to use different types of monomers, called amino acids,” as Huc reports. “And the normal method to connect different amino acids in the the correct order is to link them one by one.” The sequence of amino acids contains the folding information that allows different protein sequences to fold in different ways.

“But we discovered something unexpected and spectacular,” comments Huc. He and his colleagues in Munich, Groningen, Bordeaux and Berlin used organic, sulfur-containing monomers to spontaneously get cyclic macromolecules with a complex shape, as illustrated by their low degree of symmetry, without requiring a specific sequence. The macromolecules self-synthesize — no further conditions are necessary. “We only put one monomer type in a flask and wait,” Huc says. “This is typical for a polymerization reaction, but polymers from a single monomer usually don´t adopt complex shapes and don’t stop growing at a precise chain length.”

To further control the reaction, the scientists also used either a small guest molecule or a metal ion. The regulator binds within the growing macromolecule and causes monomers to arrange themselves around it. By choosing a regulator with the appropriate characteristics, the authors of the new study were able to produce structures with a predetermined number of subunits. The cyclic macromolecules exhibited low levels of symmetry. Some consisted of either 13, 17 or 23 subunits. Since 13, 17 and 23 are prime numbers, the corresponding folded shapes exhibit low degrees of symmetry.

A model for biological and industrial processes

Interest in the elucidation of such mechanisms is not restricted to the realm of basic research. Huc and his colleagues hope that their approach will lead to the fabrication of designer plastics. Conventional polymers usually consist of mixtures of molecules that vary in length (i.e. the number of monomers they contain). This heterogeneity has an impact on their physical properties. Hence, the ability to synthesize polymer chains of an exact length and/or geometry is expected to lead to materials with novel and interesting behaviors.

Furthermore, foldamers like those that have now been synthesized show close structural resemblances to biopolymers. They therefore offer an ideal model system in which to study the properties of proteins. Every protein is made up of a defined linear (i.e. unbranched) sequence of amino acids, which constitutes its ‘primary structure’. But most amino-acid chains fold into local substructures such as helically coiled stretches, or parallel strands that can form sheets. These units represent the protein’s secondary structure. The term ‘tertiary structure’ is applied to the fully folded single chain. This in turn can interact with other chains to form a functional unit or quaternary structure.

Huc’s ultimate goal is to mimic complex biological mechanisms using structurally defined, synthetic precursors. He wants to understand how, for example, enzymes fold into the correct, biologically active conformation following their synthesis in cells. Molecules whose properties can be precisely controlled in the laboratory provide ideal models with which to work out the answers and perhaps to go beyond enzymes themselves.

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Materials provided by Ludwig-Maximilians-Universität München. Note: Content may be edited for style and length.

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Oil droplet ‘predators’ chase oil droplet prey

Oil droplets can be made to act like predators, chasing down other droplets that flee like prey. The behavior, which is controlled by chemical signaling produced by the droplets, mimics behavior seen among living organisms but, until now, had not been recreated in synthetic systems. This tunable chemical system could potentially serve a model to help understand interactions in many-body systems such as schools of fish, bacterial colonies, or swarms of insects.

An international team of researchers led by Penn State scientists describe the system in a paper published November 16, 2020 in the journal Nature Chemistry.

“By controlling the chemistry of the oil droplets, we can create a system in which the droplets behave actively and communicate with each other through chemical gradients,” said Lauren Zarzar, assistant professor of chemistry at Penn State and the leader of the research team. “The exciting thing that we found is that you can design a system of droplets that exhibit ‘non-reciprocal’ interactions. One droplet is attracted to the other, while the other is repelled, similar to the behavior of predator and prey.”

The researchers place microscale droplets of the two different oils into a solution of water and a surfactant — a compound commonly found in soaps that lowers the surface tension of liquids. One of the oils dissolves more easily in the surfactant solution causing those droplets to emit a chemical gradient of oil molecules into its surroundings. Droplets are repelled by the dissolved oil.

“Initially this cloud of oil around the droplets is basically symmetrical and the droplets don’t move,” said Caleb Meredith, a graduate student at Penn State and co-first author of the paper. “But what we discovered is that the prey droplets can actually uptake some of the oil released by the predator droplets, setting up a source-sink exchange of oil between the droplets. When the droplets get close enough, it creates an asymmetry in the chemical gradient between the two droplets and causes the predator droplet to move towards the prey, setting up a chase.”

The asymmetry of the oil chemical gradient generated by the source and sink causes a difference in the surface tension across the surface of both the predator and prey droplets. The gradient causes the predator droplet (source) to move toward the prey droplet (sink). Similarly, due to the effect of the predator’s emitted chemical gradient, the prey is repelled by the approaching predator.

“One of the surprising results is that the two oil droplets don’t need to be very different chemically from each other to elicit this behavior,” said Zarzar. “We looked at a wide variety of chemical compositions for the oils and surfactant, which allowed us to establish a set of rules that govern these interactions. We can use these rules to tune the strength of the interactions by controlling the compositions of the droplet oils or surfactant.”

The research team also developed a model, which based on measurements of the speeds of chasing between individual pairs of droplets, was able to accurately simulate the motion of many droplets and show how they organize into larger clusters that move in a variety of fashions.

“They really look to me like they’re alive sometimes,” said Meredith. “When multiple droplets get together into clusters they can start to rotate, stop-and-go, move in spirals, and even split apart into smaller clusters.”

The researchers say that by understanding the types of rules that govern these interactions, their system could eventually be used for experimentally modeling many-body systems ranging from the behavior of large numbers of animals to the interactions that might have played a role in the evolution of early life.

“What we are doing is really basic, fundamental research where the motivation is to understand the processes at work that can control the activity of inanimate things like the oil droplets,” said Zarzar. “But, these ideas could find application in other areas, like self-assembly, group behaviors, and even in thinking about the origins of life on Earth where mixtures of simple chemical components had to somehow organize into non-equilibrium structures. Clearly, we are not looking at the same chemicals, but we may be able to establish parameters or conditions that, for example, give rise to similar types of interactions that occurred.”

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Materials provided by Penn State. Original written by Sam Sholtis. Note: Content may be edited for style and length.

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This tableware made from sugarcane and bamboo breaks down in 60 days

Scientists have designed a set of “green” tableware made from sugarcane and bamboo that doesn’t sacrifice on convenience or functionality and could serve as a potential alternative to plastic cups and other disposable plastic containers. Unlike traditional plastic or biodegradable polymers — which can take as long as 450 years or require high temperatures to degrade — this non-toxic, eco-friendly material only takes 60 days to break down and is clean enough to hold your morning coffee ordinner takeout. This plastic alternative is presented November 12 in the journal Matter.

“To be honest, the first time I came to the US in 2007, I was shocked by the available one-time use plastic containers in the supermarket,” says corresponding author Hongli (Julie) Zhu of Northeastern University. “It makes our life easier, but meanwhile, it becomes waste that cannot decompose in the environment.” She later saw many more plastic bowls, plates, and utensils thrown into the trash bin at seminars and parties and thought, “Can we use a more sustainable material?”

To find an alternative for plastic-based food containers, Zhu and her colleagues turned to bamboos and one of the largest food-industry waste products: bagasse, also known as sugarcane pulp. Winding together long and thin bamboo fibers with short and thick bagasse fibers to form a tight network, the team molded containers from the two materials that were mechanically stable and biodegradable. The new green tableware is not only strong enough to hold liquids as plastic does and cleaner than biodegradables made from recycled materials that might not be fully de-inked, but also starts decomposing after being in the soil for 30-45 days and completely loses its shape after 60 days.

“Making food containers is challenging. It needs more than being biodegradable,” said Zhu. “On one side, we need a material that is safe for food; on the other side, the container needs to have good wet mechanical strength and be very clean because the container will be used to take hot coffee, hot lunch.”

The researchers added alkyl ketene dimer (AKD), a widely used eco-friendly chemical in the food industry, to increase oil and water resistance of the molded tableware, ensuring the sturdiness of the product when wet. With the addition of this ingredient, the new tableware outperformed commercial biodegradable food containers, such as other bagasse-based tableware and egg cartons, in mechanical strength, grease resistance, and non-toxicity.

The tableware the researchers developed also comes with another advantage: a significantly smaller carbon footprint. The new product’s manufacturing process emits 97% less CO2 than commercially available plastic containers and 65% less CO2 than paper products and biodegradable plastic. The next step for the team is to make the manufacturing process more energy efficient and bring the cost down even more, to compete with plastic. Although the cost of cups made out of the new material ($2,333/ton) is two times lower than that of biodegradable plastic ($4,750/ton), traditional plastic cups are still slightly cheaper ($2,177/ton).

“It is difficult to forbid people to use one-time use containers because it’s cheap and convenient,” says Zhu. “But I believe one of the good solutions is to use more sustainable materials, to use biodegradable materials to make these one-time use containers.”

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Materials provided by Cell Press. Note: Content may be edited for style and length.

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3D-printed weather stations could enable more science for less money

Across the United States, weather stations made up of instruments and sensors monitor the conditions that produce our local forecasts, like air temperature, wind speed and precipitation. These systems aren’t just weather monitors, they are also potent tools for research on topics from farming to renewable energy generation.

Commercial weather stations can cost thousands of dollars, limiting both their availability and thus the amount of climate data that can be collected. But the advent of 3D printing and low-cost sensors have made it possible to build a weather station for a few hundred dollars. Could these inexpensive, homegrown versions perform as well as their pricier counterparts?

” I didn’t expect that this station would perform nearly as well as it did. Even though components started to degrade, the results show that these kinds of weather stations could be viable for shorter campaigns.” — Adam Theisen, Argonne atmospheric and Earth scientist

The answer is yes — up to a point, according to researchers, who put a 3D-printed weather station to the test in Oklahoma. Adam K. Theisen, an atmospheric and Earth scientist at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, led the project, which compared the printed station with a commercial-grade station for eight months to see whether it was accurate and how well it could hold up against the elements.

Three-dimensional printing uses digital models to produce physical objects on the fly. Its low cost and the ability to print parts wherever you can lug a printer could help expand the number of these stations, helping to bring data collection to remote areas and educate tomorrow’s researchers.

A team at the University of Oklahoma followed the guidance and open source plans developed by the 3D-Printed Automatic Weather Station (3D-PAWS) Initiative at the University Corporation for Atmospheric Research to print over 100 weather station parts. Instead of using polylactic acid, more commonly used in 3D printing, they turned to acrylonitrile styrene acrylate, a type of plastic filament considered more durable outdoors. Coupled with low-cost sensors, the 3D-printed parts provide the basis for these new systems, which the 3D-PAWS Initiative established as promising in earlier experiments.

“In order for this to get more widespread adoption, it has to go through verification and validation studies like this,” Theisen said.

While the 3D-printed system did start showing signs of trouble about five months into the experiment — the relative humidity sensor corroded and failed, and some parts eventually degraded or broke — its measurements were on par with those from a commercial-grade station in the Oklahoma Mesonet, a network designed and implemented by scientists at the University of Oklahoma and at Oklahoma State University.

“I didn’t expect that this station would perform nearly as well as it did,” said Theisen. “Even though components started to degrade, the results show that these kinds of weather stations could be viable for shorter campaigns.”

Theisen, who was based at the University of Oklahoma when the research began, continued to oversee the effort after joining Argonne.

In the experiment, the low-cost sensors accurately measured temperature, pressure, rain, UV and relative humidity. With the exception of a couple of instruments, the plastic material held up in the Oklahoma weather from mid-August 2018 to mid-April the following year, a period that saw strong rainstorms, snow and temperatures ranging from 14 to 104°F (-10 to 40°C). A 3D-printed anemometer, which measures wind speed, did not perform as well, but could be improved partly with better printing quality.

The project, which was led by undergraduate students at the University of Oklahoma, confirmed both the accuracy of a 3D-printed weather station and its value as an education tool.

“The students learned skill sets they would not have picked up in the classroom,” Theisen said. “They developed the proposal, designed the frame, and did most of the printing and wiring.”

The ability to print specialized components could make weather stations more feasible in remote areas because replacement parts could be fabricated right away when needed. And even if a cheaper sensor breaks after a few months, the math still works out for a low budget.

“If you’re talking about replacing two or three of these inexpensive sensors versus maintaining and calibrating a $1,000 sensor every year, it’s a strong cost-benefit to consider,” noted Theisen.

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Using robotic assistance to make colonoscopy kinder and easier

Scientists have made a breakthrough in their work to develop semi-autonomous colonoscopy, using a robot to guide a medical device into the body.

The milestone brings closer the prospect of an intelligent robotic system being able to guide instruments to precise locations in the body to take biopsies or allow internal tissues to be examined.

A doctor or nurse would still be on hand to make clinical decisions but the demanding task of manipulating the device is offloaded to a robotic system.

The latest findings — ‘Enabling the future of colonoscopy with intelligent and autonomous magnetic manipulation’ — is the culmination of 12 years of research by an international team of scientists led by the University of Leeds.

The research is published today (Monday, 12 October) in the scientific journal Nature Machine Intelligence

Patient trials using the system could begin next year or in early 2022.

Pietro Valdastri, Professor of Robotics and Autonomous Systems at Leeds, is supervising the research. He said: “Colonoscopy gives doctors a window into the world hidden deep inside the human body and it provides a vital role in the screening of diseases such as colorectal cancer. But the technology has remained relatively unchanged for decades.

“What we have developed is a system that is easier for doctors or nurses to operate and is less painful for patients. It marks an important a step in the move to make colonoscopy much more widely available — essential if colorectal cancer is to be identified early.”

Because the system is easier to use, the scientists hope this can increase the number of providers who can perform the procedure and allow for greater patient access to colonoscopy.

A colonoscopy is a procedure to examine the rectum and colon. Conventional colonoscopy is carried out using a semi-flexible tube which is inserted into the anus, a process some patients find so painful they require an anaesthetic.

Magnetic flexible colonoscope

The research team has developed a smaller, capsule-shaped device which is tethered to a narrow cable and is inserted into the anus and then guided into place — not by the doctor or nurse pushing the colonoscope but by a magnet on a robotic arm positioned over the patient.

The robotic arm moves around the patient as it manoeuvres the capsule. The system is based on the principle that magnetic forces attract and repel.

The magnet on the outside of the patient interacts with tiny magnets in the capsule inside the body, navigating it through the colon. The researchers say it will be less painful than having a conventional colonoscopy.

Guiding the robotic arm can be done manually but it is a technique that is difficult to master. In response, the researchers have developed different levels of robotic assistance. This latest research evaluated how effective the different levels of robotic assistance were in aiding non-specialist staff to carry out the procedure.

Levels of robotic assistance

Direct robot control. This is where the operator has direct control of the robot via a joystick. In this case, there is no assistance.

Intelligent endoscope teleoperation. The operator focuses on where they want the capsule to be located in the colon, leaving the robotic system to calculate the movements of the robotic arm necessary to get the capsule into place.

Semi-autonomous navigation. The robotic system autonomously navigates the capsule through the colon, using computer vision — although this can be overridden by the operator.

During a laboratory simulation, 10 non-expert staff were asked to get the capsule to a point within the colon within 20 minutes. They did that five times, using the three different levels of assistance.

Using direct robot control, the participants had a 58% success rate. That increased to 96% using intelligent endoscope teleoperation — and 100% using semi-autonomous navigation.

In the next stage of the experiment, two participants were asked to navigate a conventional colonoscope into the colon of two anaesthetised pigs — and then to repeat the task with the magnet-controlled robotic system using the different levels of assistance. A vet was in attendance to ensure the animals were not harmed.

The participants were scored on the NASA Task Load Index, a measure of how taxing a task was, both physically and mentally.

The NASA Task Load Index revealed that they found it easier to operate the colonoscope with robotic assistance. A sense of frustration was a major factor in operating the conventional colonoscope and where participants had direct control of the robot.

James Martin, a PhD researcher from the University of Leeds who co-led the study, said: “Operating the robotic arm is challenging. It is not very intuitive and that has put a brake on the development of magnetic flexible colonoscopes.

“But we have demonstrated for the first time that it is possible to offload that function to the robotic system, leaving the operator to think about the clinical task they are undertaking — and it is making a measurable difference in human performance.”

The techniques developed to conduct colonoscopy examinations could be applied to other endoscopic devices, such as those used to inspect the upper digestive tract or lungs.

Dr Bruno Scaglioni, a Postdoctoral Research Fellow at Leeds and co-leader of the study, added: “Robot-assisted colonoscopy has the potential to revolutionize the way the procedure is carried out. It means people conducting the examination do not need to be experts in manipulating the device.

“That will hopefully make the technique more widely available, where it could be offered in clinics and health centres rather than hospitals.”

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Chemical innovation stabilizes best-performing perovskite formulation

Perovskites are a class of materials made up of organic materials bound to a metal. Their fascinating structure and properties have propelled perovskites into the forefront of materials’ research, where they are studied for use in a wide range of applications. Metal-halide perovskites are especially popular, and are being considered for use in solar cells, LED lights, lasers, and photodetectors.

For example, the power-conversion efficiency of perovskite solar cells (PSCs) have increased from 3.8% to 25.5% in only ten years, surpassing other thin-film solar cells — including the market-leading, polycrystalline silicon.

Perovskites are usually made by mixing and layering various materials together on a transparent conducting substrate., which produces thin, lightweight films. The process, known as “chemical deposition,” is sustainable and relatively cost-effective.

But there is a problem. Since 2014, metal halide perovskites have been made by mixing cations or halides with formamidinium (FAPbI3). The reason is that this recipe results in high power-conversion efficiency in perovskite solar cells. But at the same time, the most stable phase of FAPbI3 is photoinactive, meaning that it does not react to light — the opposite of what a solar power harvester ought to do. In addition, solar cells made with FAPbI3 show long-term stability issues.

Now, researchers led by Michael Grätzel and Anders Hafgeldt at EPFL, have developed a deposition method that overcomes the formamidinium issues while maintaining the high conversion of perovskite solar cells. The work has been published in Science.

In the new method, the materials are first treated with a vapor of methylammonium thiocyanate (MASCN) or formamidinium thiocyanate FASCN. This innovative tweak turns the photoinactive FAPbI3 perovskite films to the desired photosensitive ones.

The scientists used the new FAPbI3 films to make perovskite solar cells. The cells showed more than 23% power-conversion efficiency and long-term operational and thermal stability. They also featured low (330 mV) open-circuit voltage loss and a low (0.75 V) turn-on voltage of electroluminescence.

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Materials provided by Ecole Polytechnique Fédérale de Lausanne. Original written by Nik Papageorgiou. Note: Content may be edited for style and length.

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Flutter Expands OS Support to Include Windows

Flutter made a name for itself by delivering an open-source framework that allows developers to build apps once, and distribute that app across multiple ecosystems (e.g. Android, iOS, etc.). One of the missing operating systems from Flutter’s support portfolio has been Windows. Last week, Flutter introduced an alpha release for Windows.

“Windows remains a popular choice for desktop and laptop devices, with Microsoft reporting over one billion active devices running Windows 10,” Flutter’s Chris Sells commented in a blog post announcement. “Our own statistics show that over half of all Flutter developers use Windows, so it’s a natural target for Flutter. Native desktop support opens up a variety of exciting possibilities for Flutter, including improved developer tooling, reduced friction for new users, and of course apps that can reach any device a user might have from a single codebase.”

Expanding the reach of Flutter to desktop-based operating systems comes with a host of challenges. Mobile device applications need not worry about keyboards, mice, mouse wheels, controllers, and more. But that’s just the beginning. Screen size, toolchain updates, shell, runner, plugins, and much more were all needed to expand Flutter to support Windows.

To help developers get started on Flutter for Windows, Flutter has published some sample apps. For example, Flokk is available on GitHub, including a guide to how it was built with Flutter. Check out more apps built with Flutter at its app gallery.

Flutter expects to release a stable version in the next few months. Currently, Flutter supports Windows 7 and above. To learn more, visit the Flutter architectural overview.

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Author: <a href="">ecarter</a>


Proof-of-concept for a new ultra-low-cost hearing aid for age-related hearing loss

A new ultra-affordable and accessible hearing aid made from open-source electronics could soon be available worldwide, according to a study published September 23, 2020 in the open-access journal PLOS ONE by Soham Sinha from the Georgia Institute of Technology, Georgia, US, and colleagues.

Hearing aids are a major tool for individuals with hearing loss — especially age-related hearing loss, which currently affects approximately 226 million adults over the age of 65 worldwide (and is projected to affect 900 million by 2050). However, hearing aid adoption remains relatively low among adults: fewer than 3 percent of adults in low-and-middle-income countries (LMIC) use hearing aids, versus around 20 percent of adults in non-LMIC countries. Though various reasons contribute to this poor uptake, cost is a significant factor. While the price to manufacture hearing aids has decreased over time, the retail price for a pair of hearing aids ranges from $1,000 to $8,000 USD, with the average pair costing $4,700 in the US.

In this study, Sinha and colleagues used mass-produced open source electronics to engineer a durable, affordable, self-serviceable hearing aid that meets most of the targets set by the WHO for mild-to-moderate age-related hearing loss: “LoCHAid.” When mass-produced at 10,000 units including earphones, a coin-cell battery, and holder, LoCHAid costs $0.98 (this doesn’t include labor costs) and is designed to be marketed over-the-counter — or even as a DIY project. LoCHAid doesn’t require specialty parts, and repairs can be completed by a minimally skilled user with access to a soldering iron and solder. Though it’s not currently programmable, simulations show that the LoCHAid is well fitted to a range of age-related hearing loss profiles for men and women between the ages of 60-79 years.

Potential limitations include the device lifetime (currently 1.5 years), as well as its relatively large size, which may not appeal to all consumers. The authors are currently working on a smaller prototype, but this costs more money to produce and would likely require third-party assemblers.

Despite these limitations, LoCHAid shows great potential to benefit individuals impacted by age-related hearing loss, especially those consumers challenged by the affordability and accessibility of current hearing aids available on the market.

The authors add: “In this work, we describe the development and rigorous audiological testing a minimal, 3d-printed and ultra low-cost ($1 in parts) hearing aid. The vision of the device is to make hearing aid accessible and affordable for elderly individuals with age related hearing loss in low- and middle-income countries.”

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Chemists make cellular forces visible at the molecular scale

Scientists have developed a new technique using tools made of luminescent DNA, lit up like fireflies, to visualize the mechanical forces of cells at the molecular level. Nature Methods published the work, led by chemists at Emory University, who demonstrated their technique on human blood platelets in laboratory experiments.

“Normally, an optical microscope cannot produce images that resolve objects smaller than the length of a light wave, which is about 500 nanometers,” says Khalid Salaita, Emory professor of chemistry and senior author of the study. “We found a way to leverage recent advances in optical imaging along with our molecular DNA sensors to capture forces at 25 nanometers. That resolution is akin to being on the moon and seeing the ripples caused by raindrops hitting the surface of a lake on the Earth.”

Almost every biological process involves a mechanical component, from cell division to blood clotting to mounting an immune response. “Understanding how cells apply forces and sense forces may help in the development of new therapies for many different disorders,” says Salaita, whose lab is a leader in devising ways to image and map bio-mechanical forces.

The first authors of the paper, Joshua Brockman and Hanquan Su, did the work as Emory graduate students in the Salaita lab. Both recently received their PhDs.

The researchers turned strands of synthetic DNA into molecular tension probes that contain hidden pockets. The probes are attached to receptors on a cell’s surface. Free-floating pieces of DNA tagged with fluorescence serve as imagers. As the unanchored pieces of DNA whizz about they create streaks of light in microscopy videos.

When the cell applies force at a particular receptor site, the attached probes stretch out causing their hidden pockets to open and release tendrils of DNA that are stored inside. The free-floating pieces of DNA are engineered to dock onto these DNA tendrils. When the florescent DNA pieces dock, they are briefly demobilized, showing up as still points of light in the microscopy videos.

Hours of microscopy video are taken of the process, then speeded up to show how the points of light change over time, providing the molecular-level view of the mechanical forces of the cell.

The researchers use a firefly analogy to describe the process.

“Imagine you’re in a field on a moonless night and there is a tree that you can’t see because it’s pitch black out,” says Brockman, who graduated from the Wallace H. Coulter Department of Biomedical Engineering, a joint program of Georgia Tech and Emory, and is now a post-doctoral fellow at Harvard. “For some reason, fireflies really like that tree. As they land on all the branches and along the trunk of the tree, you could slowly build up an image of the outline of the tree. And if you were really patient, you could even detect the branches of the tree waving in the wind by recording how the fireflies change their landing spots over time.”

“It’s extremely challenging to image the forces of a living cell at a high resolution,” says Su, who graduated from Emory’s Department of Chemistry and is now a post-doctoral fellow in the Salaita lab. “A big advantage of our technique is that it doesn’t interfere with the normal behavior or health of a cell.”

Another advantage, he adds, is that DNA bases of A, G, T and C, which naturally bind to one another in particular ways, can be engineered within the probe-and-imaging system to control specificity and map multiple forces at one time within a cell.

“Ultimately, we may be able to link various mechanical activities of a cell to specific proteins or to other parts of cellular machinery,” Brockman says. “That may allow us to determine how to alter the cell to change and control its forces.”

By using the technique to image and map the mechanical forces of platelets, the cells that control blood clotting at the site of a wound, the researchers discovered that platelets have a concentrated core of mechanical tension and a thin rim that continuously contracts. “We couldn’t see this pattern before but now we have a crisp image of it,” Salaita says. “How do these mechanical forces control thrombosis and coagulation? We’d like to study them more to see if they could serve as a way to predict a clotting disorder.”

Just as increasingly high-powered telescopes allow us to discover planets, stars and the forces of the universe, higher-powered microscopy allows us to make discoveries about our own biology.

“I hope this new technique leads to better ways to visualize not just the activity of single cells in a laboratory dish, but to learn about cell-to-cell interactions in actual physiological conditions,” Su says. “It’s like opening a new door onto a largely unexplored realm — the forces inside of us.”

Co-authors of the study include researchers from Children’s Healthcare of Atlanta, Ludwig Maximilian University in Munich, the Max Planck Institute and the University of Alabama at Birmingham. The work was funded by grants from the National Institutes of Health, the National Science Foundation, the Naito Foundation and the Uehara Memorial Foundation.

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Researchers make green chemistry advance with new catalyst for reduction of carbon dioxide

Researchers at Oregon State University have made a key advance in the green chemistry pursuit of converting the greenhouse gas carbon dioxide into reusable forms of carbon via electrochemical reduction.

Published in Nature Energy, the study led by Zhenxing Feng of the OSU College of Engineering and colleagues at Southern University of Science and Technology in China and Stanford University describes a new type of electrocatalyst.

The catalyst can selectively promote a CO2 reduction reaction resulting in a desired product — carbon monoxide was the choice in this research. A catalyst is anything that speeds the rate of a chemical reaction without being consumed by the reaction.

“The reduction of carbon dioxide is beneficial for a clean environment and sustainable development,” said Feng, assistant professor of chemical engineering. “In contrast to traditional CO2 reduction that uses chemical methods at high temperatures with a high demand of extra energy, electrochemical CO2 reduction reactions can be performed at room temperature using liquid solution. And the electricity required for electrochemical CO2 reduction can be obtained from renewable energy sources such as solar power, thus enabling completely green processes.”

A reduction reaction means one of the atoms involved gains one or more electrons. In the electrochemical reduction of carbon dioxide, metal nanocatalysts have shown the potential to selectively reduce CO2 to a particular carbon product. Controlling the nanostructure is critical for understanding the reaction mechanism and for optimizing the performance of the nanocatalyst in the pursuit of specific products, such as carbon monoxide, formic acid or methane, that are important for other chemical processes and products.

“However, due to many possible reaction pathways for different products, carbon dioxide reduction reactions have historically had low selectivity and efficiency,” Feng said. “The electrocatalysts need to promote the reaction with high selectivity to get one certain product, carbon monoxide in our case. Despite many efforts in this field, there had been little progress.”

Feng and his research co-leaders tried a new strategy. They made nickel phthalocyanine as a molecularly engineered electrocatalyst and found it showed superior efficiency at high current densities for converting CO2 to carbon monoxide in a gas-diffusion electrode device, with stable operation for 40 hours.

“To understand the reaction mechanism of our catalyst, my group at OSU used X-ray absorption spectroscopy to monitor the catalyst’s change during the reaction processes, confirming the role of the catalyst in the reaction,” Feng said. “This collaborative work demonstrates a high-performance catalyst for green processes of electrochemical CO2 reduction reactions. It also sheds light on the reaction mechanism of our catalyst, which can guide the future development of energy conversion devices as we work toward a negative-carbon economy.”

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Materials provided by Oregon State University. Original written by Steve Lundeberg. Note: Content may be edited for style and length.

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