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The Physics of Freezing Frogs

Posted by on January 13, 2017

By Ellie Welch, science media researcher at STFC’s ISIS Neutron and Muon Source

Water is the most ubiquitous substance on the planet, not only covering 70% of the Earth’s surface but also being the most abundant substance found in living things. However, our understanding of water on the molecular level is still limited. Researchers are using a number of techniques, including neutron studies, to further understand the properties and dynamics of water.

Using the Science and Technology Facilities Council’s ISIS Neutron and Muon Source in Oxfordshire, researchers from the University of Leeds have been looking at water at low temperatures, and its interaction with glycerol, nature’s answer to antifreeze. Glycerol is an example of a cryoprotectant molecule, which prevents damage occurring to cells, tissues, or other biological material when it is cooled to very low temperature for preservation (cryopreservation).

When biological material is cryopreserved, harmful ice crystals can form and damage the material. If tissues are cooled slowly then ice can form in the extracellular space, the space outside of the cell, too much ice can then damage the cell membrane and kill cells. Ice forming in the intracellular space, inside the cell, can interrupt the inner mechanism of cells, often killing them.


Image: Brian Gratwicke

Cryoprotectant molecules are particularly useful for creatures who survive freezing temperatures, such as the Eastern Wood frog of North America, which is able to survive at temperatures as low as -8°C. Creatures that are able to survive such low temperatures are known as psychrophiles, which are a sub-group of extremophiles – creatures who thrive in environments where most others would not survive. The research group in Leeds explores ‘the physics of living systems’ to try and further understand how extremophiles survive in such environments.

The team from Leeds recreated the freezing conditions that would be experienced by the frog, and studied the interaction between water and glycerol using neutron beams at the ISIS Neutron and Muon Source. The results showed that the water molecules form clusters that are then surrounded by glycerol, preventing the formation of harmful ice crystals.

The key advantage to using the technique of neutron diffraction that ISIS offered was that the team were able to study water at low temperatures over the course of six to eight hours, whilst it remained as a low density liquid. Trying to study the structure of water at low temperatures with other investigative techniques is incredibly challenging, as the water just freezes.

Dr Lorna Dougan, who leads the group at the University of Leeds said, “The experiments provide more insight into the fundamental properties of water. It’s important because it raises questions about what cryoprotectants are doing in living organisms and could help us take steps to understanding how these organisms survive.”

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