Water molecules define materials that surround us

June 7 () –

a new study published in Nature holds that materials such as wood, bacteria, and fungi belong to a newly identified class of matter, the “solids of hydration”.

For decades, the fields of physics and chemistry have held that the atoms and molecules that make up the natural world define the character of solid matter. Salt crystals get their crystal quality from ionic bonding between sodium and chloride ions, metals like iron or copper get their strength from metallic bonds between iron or copper atoms, and gums get their elasticity from flexible bonds within the polymers that make up the rubber. The same principle applies to materials such as fungi, bacteria, and wood.

The new study dismantles this paradigm and argues that the character of many biological materials is actually due to the water that impregnates them. Water gives rise to a solid and defines its properties, while maintaining its liquid characteristics.

In their article, the authors group these and other materials into a new class of matter they call “hydration solids,” which they say “acquire their structural rigidity, the defining characteristic of the solid state, from the fluid that permeates their bodies.” pores”. The new understanding of biological matter may help answer questions that have dogged scientists for years.

“I think this is a very special moment for science,” he says. it’s a statement Ozgur Sahin, professor of Biological and Physical Sciences at Columbia University and one of the study’s authors. It’s unifying something incredibly diverse and complex with a simple explanation. It’s a big surprise, an intellectual delight.”

Steven G. Harrellson, who just finished his doctoral studies in Columbia’s Physics department and is one of the study’s authors, used the metaphor of a building to describe the team’s finding.

“If we think of biological materials as a skyscraper, the molecular blocks are the steel frames that support it, and the water between the molecular blocks is the air inside the steel frames,” he explains. We discovered that some skyscrapers are not supported by their steel frames, but by the air that is inside those frames”.

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

When water is in a liquid state, its molecules maintain a delicate balance between order and disorder. But when the molecules that make up biological materials combine with water, they tip the scales toward order: The water wants to go back to its original state. As a result, the water molecules push the molecules of biological matter.

That buoyant force, called the hydration force, was identified in the 1970s, but its impact on biological matter was thought to be limited. The argument of this new work that the hydration force is the one that almost completely defines the character of biological matter, including its degree of softness or hardness, is surprising.

Biological materials have long been known to absorb ambient moisture, such as a wooden door that swells when wet. This research, however, shows that environmental water is far more fundamental to the character of wood, fungi, plants, and other natural materials than we have ever known.

The team found that putting water in the foreground allowed them to describe the characteristics of familiar organic materials with very simple mathematics. Previous models of the interaction of water with organic matter required advanced computer simulations to predict material properties. The simplicity of the formulas used by the team to predict these properties suggests that they have hit the nail on the head.

For example, the team found that the simple equation E=Al/lambda perfectly describes how the elasticity of a material changes based on factors such as moisture, temperature, and molecular 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 the biological molecules and lambda is the distance from which the forces of hydration lose their strength).

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 and contract when water is removed. Several years ago, Sahin and his colleagues captured the attention of the media for harnessing that ability to create small spore-powered engine-like contraptions.

Around 2012, Sahin decided to take a step back to ask why spores behave the way they do. He was joined by researchers Michael S. DeLay and Xi Chen, authors of the new paper, who were then members of his lab. His experiments did not solve the mysterious behavior of the spores.

“We ended up with more mysteries than when we started,” recalls Sahin. They were stuck, but the mysteries they found hinted that there was something worth investigating. After years of pondering possible explanations, it occurred to Sahin that the mysteries the team continually found they could be explained if the hydration force governed the way water moves in the spores.

The team had to do more experiments to test the idea. In 2018, Harrellson, who is now a software engineer at data analytics company Palantir, joined the project.

“When we initially approached the project, it seemed impossibly complicated. We were trying to explain several different effects, each with its own unsatisfactory formula,” he recalls. “When we started using hydration forces, we were able to eliminate any and all old formulas When only the forces of hydration remained, we felt as if our feet had finally touched the ground. It was amazing and a huge relief; everything made sense“, it states.