Category: Chemistry

by Okayama University

Artificial lipid bilayer vesicle liposomes, also called proteoliposomes, are specialized systems capable of incorporating various molecules, such as chemicals and drugs. Their unique properties make them ideal carriers for delivering substances inside cells. However, they must possess the dual characteristics of high stability in extracellular environments and low stability in intracellular environments.

Several techniques have been developed to regulate the stability of liposomes in a condition-dependent manner, with pH-sensitive liposomes being widely employed. A standard measure of acidity or basicity, the pH scale ranges from 1 to 14, with 7 standing for “neutral,” like water, a pH below 7 indicating acidity and that above 7 indicating basicity. Interestingly, pH-sensitive liposomes can be triggered to release their contents when exposed to an acidic pH below 5.5.

In a new study, a team of researchers, led by Professor Yuki Sudo from Okayama University, Japan, have developed a precise method of releasing contents from pH-sensitive liposomes using light. “The study presents a novel nanomaterial called light-induced disruptive liposome (LiDL) and applies it to light-controlled intracellular substance delivery,” explains Prof. Sudo. Their work, co-authored by Mr. Taichi Tsuneishi of Okayama University and Prof. Yuma Yamada of Hokkaido University in Japan, was published in the journal Chemical Communications .

The researchers utilized a protein called Rubricoccus marinus Xenorhodopsin (RmXeR), derived from a marine bacterium, to initiate acidification inside liposomes using light. To study the functionality of RmXeR within liposomes without interference from pH-dependent properties, they first developed pH-insensitive proteoliposomes using the lipid hydration method, combining phosphatidylcholine from egg yolk with cholesterol. Then, purified RmXeR was incorporated via the dilution method. The researchers estimated that the pH inside the thus obtained liposomes changed from 7.0 to 4.8 upon exposure to green light, rendering them suitable for light-induced disruption.

Subsequently, the team developed pH-sensitive proteoliposomes based on 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine and cholesteryl hemisuccinate. Interestingly, before introducing RmXeR within the liposomes, the researchers incorporated a water-soluble fluorescent dye called calcein as a testing substance to evaluate their release capability.

By monitoring the fluorescence of calcein, they observed that its release from the liposomes occurred in a light-dependent manner, indicating that the liposomes effectively released substances when triggered by light. These pH-sensitive proteoliposomes, or LiDLs, displayed exceptional stability in the absence of light, maintaining their physiochemical properties when exposed to a temperature of 4°C for two weeks.

In the next phase of the study, the researchers introduced LiDL into mammalian HeLa cells to evaluate their effectiveness as carriers for delivering substances inside the cells. They monitored the cellular uptake for LiDLs, finding that the presence of LiDL, regardless of the inclusion of RmXeR, enhanced the uptake of liposomes by HeLa cells. This demonstrated the potential of LiDL as a carrier for intracellular substance delivery. To further improve the intracellular delivery efficiency, the researchers introduced a chemical called stearyl octaarginine into LiDL. This enhanced version, called LiDL-R8, exhibited significantly better performance compared to LiDL.

These findings highlight the utility of LiDL for the intracellular delivery of chemicals as well as biomolecules. “With LiDL, drug delivery can be controlled by light, potentially leading to advances in various therapies,” emphasizes Prof. Sudo. Going forward, the team aims to enhance the content release efficiency by thoroughly characterizing the structure of the liposomes and optimizing the experimental conditions.

In effect, LiDLs hold great promise as optically controllable carriers for improved drug delivery. These liposomes offer enhanced efficacy without causing side effects, showcasing exceptional extracellular stability and controllable intracellular instability. “Our study will contribute towards ensuring healthy lives and promoting well-being for people of all ages, which ties in with one of the Sustainable Development Goal (SDG3) of the United Nations,” concludes Prof. Sudo.

More information: Taichi Tsuneishi et al, Development of light-induced disruptive liposomes (LiDL) as a photoswitchable carrier for intracellular substance delivery, Chemical Communications (2023). DOI: 10.1039/D3CC02056H

Journal information: Chemical Communications 

Provided by Okayama University 

by University of Münster

Hydrogen is seen as an energy source of the future—at least, when it is produced in a climate-friendly way. Hydrogen can also be important for the production of active ingredients and other important substances. To produce hydrogen, water (H₂O) can be converted into hydrogen gas (H₂) by means of a series of chemical processes. However, as water molecules are very stable, splitting them into hydrogen and oxygen presents a big challenge to chemists. For it to succeed at all, the water first has to be activated using a catalyst; then it reacts more easily.

A team of researchers led by Prof. Armido Studer at the Institute of Organic Chemistry at Münster University (Germany) has developed a photocatalytic process in which water, under mild reaction conditions, is activated through triaryl phosphines, and not—as in most other processes—through transition metal complexes.

This strategy, which has now been published in Nature, will open a new door in the highly active field of research relating to radical chemistry, says the team. Radicals are, as a rule, highly reactive intermediates. The team uses a special intermediate—a phosphine-water radical cation—as activated water, from which hydrogen atoms from H₂O can be easily split off and transferred to a further substrate. The reaction is driven by light energy.

“Our system,” says Prof. Studer, “offers an ideal platform for investigating unresearched chemical processes which use the hydrogen atom as a reagent in synthesis.”

Dr. Christian Mück-Lichtenfeld, who analyzed the activated water complexes using theoretical methods, says, “The hydrogen-oxygen bond in this intermediate is extraordinarily weak, making it possible to transfer a hydrogen atom to various compounds.”

Dr. Jingjing Zhang, who carried out the experimental work, adds, “The hydrogen atoms of the activated water can be transferred to alkenes and arenes under very mild conditions, in so-called hydrogenation reactions.”

Hydrogenation reactions are enormously important in pharmaceutical research, in the agrochemical industry and in materials sciences.

More information: Jingjing Zhang et al, Photocatalytic phosphine-mediated water activation for radical hydrogenation, Nature (2023). DOI: 10.1038/s41586-023-06141-1

Journal information: Nature 

Provided by University of Münster 

by International Journal of Extreme Manufacturing

Publishing in the International Journal of Extreme Manufacturing, scientists from Jilin University and Edith Cowan University comprehensively reviewed the latest preparation techniques of copper matrix composites and the effect of ceramic particles on the mechanical properties, thermal conductivity and thermal expansion behavior of the composites. Four main aspects of particle characterization were included: particle content, particle size, particle morphology and interfacial bonding of particles to copper matrix.

Team leader, Feng Qiu, said, “By reviewing the preparation techniques and effect mechanisms of particle reinforced copper matrix composites, it is hoped that this will serve as a basis for more precise design and manipulation of composite microstructure to meet the growing demand for copper matrix composites in a wide range of application fields.”

So far, endeavors have been focusing on how to choose suitable ceramic components and fully exert the strengthening effect of ceramic particles in the copper matrix. Currently, the preparation of copper matrix composites by powder metallurgy is the most mature technique, but it still faces many unresolved process drawbacks.

Mechanical alloying and spark plasma sintering have a more prominent contribution to the improvement of grain refinement and densification of composite, as well as the dispersion of particles. While the internal oxidation and in-situ method could greatly enhance the interfacial bonding between the ceramic phase and the metal matrix. Further combinations of these advanced preparation techniques and the full utilization of each technical advantage remain to be explored in more detail.

The co-leading author, Prof. Hongyu Yang, added that, “practical challenges in manipulating particle characteristics reinforce the value of the preparation and mechanistic exploration, which contribute to further optimize the physical and chemical performance of composites.”

“Currently, the manipulation of ceramic particles in most copper matrix composites is mainly focused on particle content and size, while particle distribution, morphology, and interfacial bonding still need to be optimized, especially for the exploration of in-situ synthesis techniques.”

First author, Dr. Yifan Yan said, “Regarding the study of the effect mechanism of ceramic particle reinforced copper matrix composites, while experimental studies and mathematical models can reflect the influence of particle characteristics on material properties, finite element simulations provide a more intuitive perspective for predicting and studying the mechanism of intensifying action. However, optimal design of composites by computational simulation techniques in the definition of the constitutive model and the precise reconfiguration of the composite are largely unexplored.”

Prof. Laichang Zhang, an expert in advanced materials and also the co-leading author of the article, said, “Ongoing research in the field of ceramic reinforced copper matrix composites has yielded promising results in recent studies. Composites mixed with high-performance carbon nanotubes, carbon fibers, and advanced MAX-phase ceramic materials have demonstrated favorable comprehensive performance. However, there is limited information available on the interaction and distribution of strengthening phases.”

“Selecting and manipulating the strengthening phases in a rational manner could meet the performance requirements of copper matrix composites in various applications, but presents significant challenges in the design and preparation of composites. More complex material configuration designs, such as network structures and gradient structures, offer new opportunities to prepare anisotropic functional materials or speciality composites.”

More information: Yi-Fan Yan et al, Ceramic particles reinforced copper matrix composites manufactured by advanced powder metallurgy: preparation, performance, and mechanisms, International Journal of Extreme Manufacturing (2023). DOI: 10.1088/2631-7990/acdb0b

Provided by International Journal of Extreme Manufacturing

by Zhang Nannan, Chinese Academy of Sciences

Prof. Huang Qunying’s team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has developed a novel inorganic silica-based adsorbent for the highly selective separation of strontium from acidic medium. The results were published in Separation and Purification Technology.

Radioactive strontium (⁹⁰Sr) is considered to be one of the most dangerous radionuclides due to its high biochemical toxicity. During the vitrification process of high-level liquid waste, the presence of ⁹⁰Sr can cause instability of the vitrification substrate, resulting in radionuclide leaching. Removal of ⁹⁰Sr can reduce the heat generation and shorten the cooling time of the vitrification substrate in the repository, which is favorable for further deep geological disposal of the radioactive waste.

To address the above issues, Prof. Huang’s team developed a novel silica-based adsorbent Sb₂O₅/SiO₂ by a two-step method, i.e., vacuum impregnation followed by oxidation, and investigated the adsorption behavior of the adsorbent on strontium stable nuclide in low and high acid mediums (i.e., pH 6 and 1 M HNO₃).

The experimental results showed that the prepared adsorbent possessed good acid resistance stability and exhibited favorable adsorption on strontium stable nuclide in both low and high acid mediums. The mechanistic results revealed that the adsorption mechanism was ion exchange, and the adsorption was accompanied by charge transfer and reduction of adsorption energy.

This study not only develops a novel method for the preparation of highly stable silica-based adsorbent, but also provides relevant experimental data and theoretical basis for the selective separation of strontium in acidic environments.

More information: Shichang Zhang et al, Efficient separation of strontium in different environments with novel acid-resistant silica-based ion exchanger, Separation and Purification Technology (2023). DOI: 10.1016/j.seppur.2023.124347

Provided by Chinese Academy of Sciences 

by Ecole Polytechnique Federale de Lausanne

Tubulin is a protein that plays a crucial role in the structure and function of cells. It is the main component of microtubules, which are long, hollow fibers that provide structural support, help the cell divide, give it its shape, and act as tracks for moving molecular cargo around inside the cell.

There are two types of tubulin: alpha-tubulin and beta-tubulin. Together, they form dimeric (two-part) building blocks, spontaneously assembling into microtubules that undergo further continuous cycles of assembly and disassembly.

To fine-tune microtubules, the dimers undergo various post-translational modifications (PTMs), which are chemical modifications that occur after they are synthesized, and can affect their structure, activity, and interactions with other molecules.

Two important PTMs take place on the unstructured tail of alpha-tubulin: Polyglutamylation, which adds chains of glutamate amino acids, and detyrosination, which removes the final tyrosine amino acid. These PTMs, among others, are found together in stable microtubules, e.g. in neurons.

Combinations of PTMs form what scientists refer to as a “tubulin code,” which is connected to specific functions of microtubules. Tubulin PTMs are critical for the proper functioning of microtubules.

Dysregulation of PTMs have been linked to various diseases, including cancer, neurodegeneration, and developmental disorders. Therefore, understanding the importance of tubulin PTMs is crucial for advancing our knowledge of these diseases and developing potential therapies. The problem is that the mechanisms that govern such PTM patterns are not well understood, mostly because we don’t have the tools to dissect the function and regulation of tubulin PTMs.

Cracking the tubulin code

Scientists at EPFL and the University of Geneva (UNIGE) have now developed a chemical method to engineer fully functional tubulin carrying precise combinations of post-translational modifications (PTMs). The study was led by Professors Beat Fierz (EPFL) and Assistant Professor Charlotte Aumeier (UNIGE), in collaboration with the labs of Pierre Gönczy (EPFL) and Carsten Janke (Institute Curie), and provides insight into how specific PTMs regulate the function of tubulin in cells. Their findings have been published in Nature Chemistry.

The method uses chemo-enzymatic protein splicing to attach synthetic alpha-tubulin tails that were modified with varying degrees of polyglutamate to human tubulin molecules. Using these “designer” tubulins allowed the researchers for the first time to assemble homogenously modified microtubules.

The researchers also found that polyglutamylation of alpha-tubulin facilitated its detyrosination by enhancing the activity of the protein complex vasohibin/SVBP, the key enzyme responsible for this modification. The team confirmed their findings by changing the levels of polyglutamate in living cells and observing the effects on tyrosine removal.

The study presents a novel approach to designing tubulins with specific PTMs and uncovers a new interplay between two key regulatory systems that control the function of tubulin: polyglutamylation and detyrosination.

The new method of producing tubulins with defined PTMs can advance our understanding of their molecular function, and provide insights into how dysregulation of these PTMs leads to diseases.

Based on this work, the labs of Fierz and Aumeier, together with Jens Stein at the University of Fribourg and Michael Sixt at ISTA Vienna will next investigate how tubulin PTMs control the cytoskeleton in migrating immune cells.

More information: Eduard Ebberink et al. Tubulin engineering by semi-synthesis reveals that polyglutamylation directs detyrosination, Nature Chemistry (2023). DOI: 10.1038/s41557-023-01228-8. www.nature.com/articles/s41557-023-01228-8

Journal information: Nature Chemistry 

Provided by Ecole Polytechnique Federale de Lausanne 

by Kristi L. Bumpus, Oak Ridge National Laboratory

Oak Ridge National Laboratory researchers have developed a method to simplify one step of radioisotope production—and it’s faster and safer.

ORNL produces several radionuclides from irradiated radium-226 targets, including actinium-227 and thorium-228, both used in cancer treatments. Continuously improving isotopes for human health is one of the lab’s missions.

Currently, it takes workers two weeks to prepare radium-226 targets for irradiation in the High Flux Isotope Reactor. The targets are exposed to radiation throughout the process, which involves pressing radium carbonate aluminum composite into 10 pellets—one each day—and sealing them into an aluminum capsule.

The new method uses a single, seamless aluminum liner with aluminum powder caps to press and seal the radium carbonate. This minimizes the time required to prepare targets, significantly decreasing radiation doses to workers, and also reduces the targets’ failure rate.

Provided by Oak Ridge National Laboratory 

by University of California – Riverside

Some molecules exist in two forms, such that their structures and their mirror images are not superimposable, like our left and right hands. Called chirality, it is a property these molecules have due to their asymmetry. Chiral molecules tend to be optically active because of how they interact with light. Oftentimes, only one form of a chiral molecule exists in nature, for example, DNA. Interestingly, if a chiral molecule works well as a drug, its mirror image could be ineffective for therapy.

In trying to produce artificial chirality in the lab, a team led by chemists at the University of California, Riverside, has found that the distribution of a magnetic field is itself chiral. The research paper titled, “A magnetic assembly approach to chiral superstructures,” appears in the journal Science.

“We discovered that the magnetic field lines produced by any magnet, including a bar magnet, have chirality,” said Yadong Yin, a professor of chemistry, who led the team. “Further, we were also able to use the chiral distribution of the magnetic field to coax nanoparticles into forming chiral structures.”

Traditionally, researchers have used “templating” to create a chiral molecule. A chiral molecule is first used as the template. Achiral (or non-chiral) nanoparticles are then assembled on this template, allowing them to mimic the structure of the chiral molecule. The drawback to this technique is that it cannot be universally applied, being heavily dependent on the specific composition of the template molecule. Another shortcoming is the newly formed chiral structure cannot be easily positioned at a specific location on, say, an electronic device.

“But to gain an optical effect, you need a chiral molecule to occupy a particular place on the device,” Yin said. “Our technique overcomes these drawbacks. We are able to rapidly form chiral structures by magnetically assembling materials of any chemical composition at scales ranging from molecules to nano- and microstructures.”

Yin explained that his team’s method uses permanent magnets that consistently rotate in space to generate the chirality. He said transferring chirality to achiral molecules is done by doping, that is incorporating guest species, such as metals, polymers, semiconductors, and dyes into the magnetic nanoparticles used to induce chirality.

Yin said chiral materials acquire an optical effect when they interact with polarized light. In polarized light, light waves vibrate in a single plane, reducing the overall intensity of the light. As a result, polarized lenses in sunglasses cut glare to our eyes, while non-polarized lenses do not.

“If we change the magnetic field that produces a material’s chiral structure, we can change the chirality, which then creates different colors that can be observed through the polarized lenses,” Yin said. “This color change is instantaneous. Chirality can also be made to disappear instantaneously with our method, allowing for rapid chirality tuning.”

The findings could have applications in anti-counterfeit technology. A chiral pattern that signifies the authenticity of an object or document would be invisible to the naked eye but visible when seen through polarized lenses. Other applications of the findings are in sensing and the field of optoelectronics.

“More sophisticated optoelectronic devices can be made by taking advantage of the tunability of chirality that our method allows,” said Zhiwei Li, the first author of the paper and former graduate student in Yin’s lab. “Where sensing is concerned, our method can be used to rapidly detect chiral or achiral molecules linked to certain diseases, such as cancer and viral infections.”

Yin and Li were joined in the research by a team of graduate students in Yin’s lab, including Qingsong Fan, Zuyang Ye, Chaolumen Wu, and Zhongxiang Wang. Li is now a postdoctoral researcher at Northwestern University in Illinois.

More information: Zhiwei Li et al, A magnetic assembly approach to chiral superstructures, Science (2023). DOI: 10.1126/science.adg2657. www.science.org/doi/10.1126/science.adg2657

Journal information: Science 

Provided by University of California – Riverside 

by Jason Daley, University of Wisconsin-Madison

Shear band formation is not typically a good sign in a material—the bands often appear before a material fractures or fails. But materials science and engineering researchers at the University of Wisconsin–Madison have found that shear bands aren’t always a negative; under the right conditions, they can improve the ductility, or the plasticity, of a material.

Led by Izabela Szlufarska, a professor of materials science and engineering at UW–Madison, the researchers published details of their work in the journal Nature Materials.

Using a combination of experimental characterization and simulations, the team identified potential strategies for encouraging shear bands. This could lead to new ways of increasing the toughness of a wide array of materials.

“In a previous paper, we demonstrated that shear bands in a material called samarium cobalt could actually be beneficial,” says Szlufarska. “That led to the questions, “When do shear bands form?” and “When do they support plasticity versus fracture? When do you want to avoid them and when do you want to promote them?'”

In materials with crystalline structures, like metals and ceramics, plasticity is determined by small structural irregularities within the crystal lattice called dislocations. These dislocations can move through the lattice and provide some give, which allows materials like metals to bend without ripping apart the bonds in their rigid structure. However, the more these dislocations are locked into place, either through hardening techniques or natural structural variations, the more brittle a material becomes.

That’s why Szlufarska and her team were surprised to find that in samarium cobalt, a brittle intermetallic material used to make strong magnets, amorphous, or unstructured, shear bands increased the material’s plasticity and were not a sign of failure. Instead, these areas acted as a lubricant, allowing planes of atoms to slide over one another without creating a fracture.

The team hypothesized that these types of beneficial shear bands can form in materials that easily transition between crystalline and amorphous phases. To test this, they looked at aluminum samarium, a glassy material studied extensively by Szlufarska and her colleagues in the Materials Research Science and Education Center at UW–Madison. Using atomic-level simulations, Szlufarska’s group predicted that the crystalline form of this material should also form shear bands under stress. They not only confirmed the finding in the lab, but also varied the atomic composition of the aluminum samarium, making versions where shear bands led either to fracture or to plasticity.

That understanding led the team to propose criteria for screening new materials that might exhibit similar properties and for identifying when shear bands are beneficial. The hope is that these parameters will make it possible to search databases to identify materials that could benefit from doping or engineering to promote shear band formation.

“Increasing toughness, or the amount of energy or stress a material can take before it breaks, by two or three or four times could be really powerful,” says Szlufarska. “In this paper, we extended our finding to a new class of materials. But this is not the end.”

The team intends to test traditional structural materials like oxides, carbides and borides to determine how they can be optimized.

“We understand so much more about how this happens and what to look for,” says Szlufarska. “I think we have identified the key to the design of these materials, and we want to now take them to other classes.”

Szlufarska has also published related research in the journal npj 2D Materials and Applications

More information: Jun Young Kim et al, Experimental and theoretical studies of native deep-level defects in transition metal dichalcogenides, npj 2D Materials and Applications (2022). DOI: 10.1038/s41699-022-00350-4

Journal information: Nature Materials 

Provided by University of Wisconsin-Madison 

by Society of Chemical Industry

Plastic food packaging accounts for a significant proportion of plastic waste in landfills. In the face of escalating environmental concerns, researchers are looking to bio-derived alternatives.

Now, scientists at The Chinese University of Hong Kong (CUHK) have developed an edible, transparent and biodegradable material with considerable potential for application in food packaging. Their work is published in the Journal of the Science of Food and Agriculture.

Heavy reliance on petrochemicals and inherent non-biodegradability of plastic packaging mean it has long been a significant contributor to environmental contamination. A team at CUHK has turned its attention to bacterial cellulose (BC), an organic compound derived from certain types of bacteria, which has garnered attention as a sustainable, easily available, and non-toxic solution to the pervasive use of plastics.

Professor To Ngai from the Department of Chemistry, CUHK and corresponding author of the study, explained that the impressive tensile strength and high versatility of BC are the key to its potential.

He said, “Extensive research has been conducted on BC, including its use in intelligent packaging, smart films, and functionalized materials created through blending, coating, and other techniques. These studies demonstrate the potential of BC as a replacement for single-use plastic packaging materials, making it a logical starting point for our research.”

Unlike the cellulose found in the cell walls of plants, BC can be produced through microbial fermentation, which eliminates the need for harvesting trees or crops. Ngai noted that as a result, “…this production method does not contribute to deforestation or habitat loss, making BC a more sustainable and environmentally friendly material alternative to plant cellulose.”

Up until now, the widespread adoption of BC has been limited by its unfavorable sensitivity to moisture in the air (hygroscopicity), which detrimentally impacts its physical properties.

In the paper, the researchers laid out a novel approach to address the limitations of BC-based materials. By incorporating certain soy proteins into the structure and coating it with an oil-resistant composite, they successfully created an edible, transparent, and robust BC-based composite packaging.

Ngai noted that this approach has a high feasibility for scale-up: “It does not require specific reaction conditions like chemical reactions, but rather a simple and practical method with mixing and coating. This approach offers a promising solution to the challenge of developing sustainable and environmentally friendly packaging materials that can replace single-use plastics on a large scale.”

The study demonstrated that the plastic alternative could be completely degraded within 1-2 months. Unlike other bio-derived plastics such as polylactic acid, the BC-based composite does not require specific industrial composting conditions to degrade.

Ngai explained, “The material developed in this research is completely edible, making it safe for turtles and other sea animals to consume without causing aquatic toxicity in the ocean.”

The researchers at CUHK are now exploring the directions for future research. They hope to enhance the versatility of modified BC films, making them suitable for a wider range of applications. Specifically, they are focused on developing a thermosetting glue that can create strong bonds between bacterial cellulose, allowing it to be easily molded into various shapes when heated.

“One of the main challenges with bacterial cellulose films is that they are not thermoplastic, which limits their potential for use in certain applications. By addressing this issue, we hope to make bacterial cellulose films more competitive with traditional plastics while maintaining their eco-friendliness,” explained Ngai.

Ngai hopes that the current study will help to combat the excessive use of single-use plastics, which can persist for hundreds of years after only a few days of being displayed on supermarket shelves.

“This research serves as a reminder that natural raw materials may already possess the necessary characteristics to perform beyond the functions of plastic packaging,” he concluded.

More information: Ka Man Cheung et al, Edible, strong, and low‐hygroscopic bacterial cellulose derived from biosynthesis and physical modification for food packaging, Journal of the Science of Food and Agriculture (2023). DOI: 10.1002/jsfa.12758

Journal information: Journal of the Science of Food and Agriculture 

Provided by Society of Chemical Industry

For decades, the fields of physics and chemistry have maintained that the atoms and molecules that make up the natural world define the character of solid matter. Salt crystals get their crystalline quality from the ionic bond between sodium and chloride ions, metals like iron or copper get their strength from the metallic bonds between iron or copper atoms, and rubbers get their stretchiness from the flexible bonds within polymers that constitute the rubber. The same principle applies for materials like fungi, bacteria, and wood.

Or so the story goes.

A new paper published in Nature upends that paradigm, and argues that the character of many biological materials is actually created by the water that permeates these materials. Water gives rise to a solid and goes on to define the properties of that solid, all the while maintaining its liquid characteristics. In their paper, the authors group these and other materials into a new class of matter that they call “hydration solids,” which they say “acquire their structural rigidity, the defining characteristic of the solid state, from the fluid permeating their pores.” The new understanding of biological matter can help answer questions that have dogged scientists for years.

“I think this is a really special moment in science,” Ozgur Sahin, a professor of Biological Sciences and Physics and one of the paper’s authors, said. “It’s unifying something incredibly diverse and complex with a simple explanation. It’s a big surprise, an intellectual delight.”

Steven G. Harrellson, who recently completed doctoral studies in Columbia’s physics department, and is an author on the study, used the metaphor of a building to describe the team’s finding: “If you think of biological materials like a skyscraper, the molecular building blocks are the steel frames that hold them up, and water in between the molecular building blocks is the air inside the steel frames. We discovered that some skyscrapers aren’t supported by their steel frames, but by the air within those frames.”

“This idea may seem hard to believe, but it resolves mysteries and helps predict the existence of exciting phenomena in materials,” Sahin added.

When water is in its liquid form, its molecules strike a fine balance between order and disorder. But when the molecules that form biological materials combine with water, they tip the balance toward order: Water wants to return to its original state. As a result, the water molecules push the biological matter’s molecules away. That pushing force, called the hydration force, was identified in the 1970s, but its impact on biological matter was thought to be limited. This new paper’s argument that the hydration force is what defines the character of biological matter almost entirely, including how soft or hard it is, thus comes as a surprise.

We have long known that biological materials absorb ambient moisture. Think, for example, of a wooden door, that expands during a humid spell. This research, however, shows that that ambient water is much more central to wood, fungi, plants, and other natural materials’ character than we had ever known.

The team found that bringing water to the front and center allowed them to describe the characteristics that familiar organic materials display with very simple math. Previous models of how water interacts with organic matter have required advanced computer simulations to predict the properties of the material. The simplicity of the formulas that the team found can predict these properties suggests that they’re onto something.

To take one example, the team found that the simple equation E=Al/λ neatly describes how a material’s elasticity changes based on factors including humidity, temperature, and molecule size. (E in this equation refers to the elasticity of a material; A is a factor that depends on the temperature and humidity of the environment; l is the approximate size of biological molecules and λ is the distance over which hydration forces lose their strength).

“The more we worked on this project, the simpler the answers became,” Harrellson said, adding that the experience “is very rare in science.”

The new findings emerged from Professor Sahin’s ongoing research into the strange behavior of spores, dormant bacterial cells. For years, Sahin and his students have studied spores to understand why they expand forcefully when water is added to them and contract when water is removed. Several years ago, Sahin and colleagues garnered media coverage for harnessing that capability to create small engine-like contraptions powered by spores.

Around 2012, Sahin decided to take a step back to ask why the spores behave the way they do. He was joined by researchers Michael S. DeLay and Xi Chen, authors on the new paper, who were then members of his lab. Their experiments did not provide a resolution to the mysterious behavior of spores. “We ended up with more mysteries than when we started,” Sahin remembers. They were stuck, but the mysteries they encountered were hinting that there was something worth pursuing.

After years of pondering potential explanations, it occurred to Sahin that the mysteries the team continually encountered could be explained if the hydration force governed the way that water moved in spores.

“When we initially tackled the project, it seemed impossibly complicated. We were trying to explain several different effects, each with their own unsatisfying formula. Once we started using hydration forces, every one of the old formulas could be stripped away. When only hydration forces were left, it felt like our feet finally hit the ground. It was amazing, and a huge relief; things made sense,” he said.

The paper’s findings apply to huge amounts of the world around us: Hygroscopic biological materials—that is, biological materials that allow water in and out of them–potentially make up anywhere from 50% to 90% of the living world around us, including all of the world’s wood, but also other familiar materials like bamboo, cotton, pine cones, wool, hair, fingernails, pollen grains in plants, the outer skin of animals, and bacterial and fungal spores that help these organisms survive and reproduce.

The term coined in the paper, “hydration solids,” applies to any natural material that’s responsive to the ambient humidity around it. With the equations that the team identified, they and other researchers can now predict materials’ mechanical properties from basic physics principles. So far that was true mainly of gases, thanks to the well-known general gas equation, which has been known to scientists since the 19th century.

“When we take a walk in the woods, we think of the trees and plants around us as typical solids. This research shows that we should really think of those trees and plants as towers of water holding sugars and proteins in place,” Sahin said, “It’s really water’s world.”

More information: Ozgur Sahin, Hydration solids, Nature (2023). DOI: 10.1038/s41586-023-06144-y. www.nature.com/articles/s41586-023-06144-y

Journal information: Nature 

Provided by Columbia University