Scientists have discovered that water molecules determine the materials around us

For decades, the fields of physics and chemistry have maintained that the atoms and molecules that make up the natural world determine the nature 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 metallic bonds between iron or copper atoms, and rubber gets its stretchability from the elastic bonds within the polymers that make up the rubber. The same principle applies to materials such as fungi, bacteria, and wood.

Or so the story goes.

A new paper has been published in nature He flips this model around, and argues that the nature of many biological materials is actually created by the water that permeates these materials. Water produces a solid and continues to characterize that solid, while maintaining its liquid properties. In their paper, the authors group these and other materials into a new class of matter they call “fluidized solids,” which they say “gain the rigidity of their structure, the hallmark of the solid state, from the liquid that permeates their pores.” A new understanding of biological matter could help answer questions that have plagued scientists for years.

“I think this is a really special moment in science,” said Ozgur Şahin, professor of biological sciences and physics and one of the authors of the paper. “It unites something incredibly diverse and complex with simple explanation. It’s a great surprise, an intellectual treat.”

Stephen G. Harrelson, who recently completed his doctoral studies in the Columbia Department of Physics and an author on the study, used the metaphor of a building to describe the team’s discovery: “If you think of biological materials like a skyscraper, the molecular building blocks are the steel frames that hold them together, and the water between the molecular building blocks.” It is the air inside the steel frames. We discovered that some skyscrapers are not supported by their steel frames, but by the air inside those frames.”

Shaheen added, “This idea may seem hard to believe, but it solves mysteries and helps predict the presence of interesting phenomena in materials.”

When water is in its liquid form, its molecules strike a delicate balance between order and disorder. But when the molecules that make up biological materials combine with water, they tip the balance toward the system: the water wants to return to its original state. As a result, water molecules push away molecules of biological matter. This driving force, called the rehydration force, was identified in the 1970s, but its effect on biological matter was thought to be limited. This new paper’s argument that the strength of water is what determines almost the entire nature of biological matter, 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 expanding during a wet spell. However, this research shows that the surrounding water is more important to the traits of wood, fungi, plants, and other natural materials than we previously knew.

The team found that bringing water front and center allowed them to describe the properties displayed by familiar organic materials with very simple arithmetic. Previous models of how water interacts with organic matter required advanced computer simulations to predict the material’s properties. The simplicity of the formulas the team found can predict these properties indicating they are present in something.

To take one example, the team found that the simple equation E = Al/ accurately describes how a material’s elasticity changes based on factors including moisture, temperature, and particle size. (E in this equation denotes the elasticity of the material; A is a factor dependent on the temperature and humidity of the environment; l is the approximate size of biological particles and is the distance at which hydration forces lose their strength.)

“The more we work on this project, the simpler the answers become,” Harrelson said, adding that the experiment is “very rare in science.”

The new findings emerged from Professor Shaheen’s ongoing research into the strange behavior of germs and dormant bacterial cells. For years, Shaheen and his students have studied microbes to understand why they expand strongly when water is added to them and contract when water is removed. Several years ago, Shaheen and his colleagues garnered media coverage for harnessing this ability to create tiny, motor-like progenitors powered by spores.

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

After years of pondering possible explanations, it occurred to Shaheen that the puzzles the team constantly faces could be explained if the force of hydration controlled the way water travels in the spores.

“When we initially tackled the project, it seemed impossibly complicated. We were trying to explain several different effects, each with its own unsatisfying formula. Once we started using the hydrating powers, each of the old formulas could be stripped away. When only the water’s forces were left It just felt like our feet finally hit the ground. It was amazing, so relaxing; things made sense,” he said.

The paper’s findings apply to vast amounts of the world around us: hygroscopic biological materials—that is, biological materials that allow water in and out—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 such as bamboo, cotton, pine cones, wool, hair, nails, pollen 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, “hydrous solids,” applies to any natural material that responds to the ambient moisture around it. Using the equations the team determined, they and other researchers can predict the mechanical properties of materials from basic principles of physics. Until now this was mainly true of gases, thanks to the well-known general gas equation, which scientists have known since the 19th century.

“When we walk through the forest, 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,” Shaheen said. water.”