​​There are some animals, plants, fungi and bacteria that are able to survive at sub-zero temperatures thanks to the presence of antifreeze proteins (AFPs). Understanding the antifreeze mechanism of these proteins in detail would be a step towards being able to develop them for use in commercial applications such as food storage or tissue preservation.

“As the extraction of natural AFPs are costly, laborious and difficult for mass production, the designing of synthetic products analogous to AFPs is a better alternative," explains author Xiang-Qiang Chu.

AFPs prevent the organisms from freezing by stopping the formation of large ice crystals, thanks to the presence of hydroxyl groups on their binding surface. Graphene oxide (GO) nanosheets have also been shown to form similar hydroxyl groups, and so their behaviour under freezing conditions could give us an insight into the details of how AFPs function.

To understand the structural changes taking place during freezing, the researchers used time-resolved small-angle X-ray scattering (TR-SAXS) at the Shanghai Synchrotron Radiation Facility (SSRF). They also used quasi-elastic neutron scattering (QENS) on the IRIS beamline to look at the dynamics of the water during the freezing process. In these experiments, they compared the system with an equivalent made of heavy water.

Using these techniques they were able to monitor the formation of ice crystals and how this is effected by the addition of GO nanosheets. As part of their study, published in Structural Dynamics, they compared two different sizes of GOs, finding that this was a critical factor when it came to regulating ice formation.

When the GOs were larger than 11nm, ice actually began to form at higher temperatures. The presence of the larger GO nanosheets caused the hydrogen motion to slow down and reduce the energy requirement for ice nucleation. An intermediate state was also seen under these conditions that had never been observed experimentally before.

As GO nanosheets are similar to AFPs, the results from this study will serve as a preliminary model for how AFPs work to reduce ice formation temperatures in the natural world.

“Since the size of natural proteins cannot be changed freely, while the size of synthesized GOs can be controlled precisely over a wide range, it is a great advantage to use GOs to systematically study the size effect in ice formation and build up our understanding from [a] fundamental science point of view," said Xiang-Qiang Chu.

Further information

The full paper can be found online at DOI: 10.1063/4.0000111

The article was also featured as an AIP Scilight at DOI: 10.1063/10.0006029