SCIENCE TECHNOLOGY: antifreeze

Friday, 25 November 2011

Simple compound with surprising antifreeze properties

ScienceDaily (Oct. 25, 2011) — A chemical compound used to stabilize particles in suspension has proved capable of controlling the growth of ice crystals. This finding was made by CNRS/Saint-Gobain researchers, in collaboration with CNRS-affiliated teams at INSA Lyon and Université Claude Bernard Lyon 1. Surprisingly, the compound in question is a simple molecule, not at all like the macromolecules previously known for their antifreeze properties. It offers many advantages, including low production costs, stability and ease of use, which should open the way to industrial applications.

Published in the online journal PLoS ONE, this work also provides new leads for the development of synthetic equivalents of antifreeze proteins, different from those currently produced.

The formation of ice crystals can have multiple, and often destructive, consequences. Cell degradation in living organisms, damage to land and roads in cold climates, ice crystals in ice creams… These are all examples of situations where it is useful to control ice growth. Many organisms and species that live in cold environments have adapted to control ice growth. Their resistance to low temperatures is based on the presence of antifreeze proteins, all of which are made up of very long organic chains with amphiphilic structures (partly hydrophilic, partly hydrophobic). How do these proteins interact with ice crystals? Researchers are trying to identify the mechanism enabling antifreeze proteins to identify these crystals, but the phenomenon is still not fully understood. In addition, since these proteins are extremely costly to extract, the preferred solution is to create synthetic equivalents inspired by natural structures. All proteins currently known for their "antifreeze" properties are macromolecules (like glycoproteins, polysaccharides, etc.).

A team led by Sylvain Deville(1), CNRS researcher at the LSFC (Laboratoire de Synthèse et Fonctionnalisation des Céramiques, Synthesis and Functionalization of Ceramics Laboratory, CNRS/Saint-Gobain), in collaboration with the Matériaux, Ingénierie et Sciences (Materials, Engineering and Sciences) laboratory (CNRS/INSA Lyon / Université Claude Bernard Lyon 1), has discovered that zirconium acetate, a chemical compound normally used to stabilize particles in suspension, can control ice crystal growth. The compound governs the morphology of the ice crystals obtained by freezing a solution in which it is combined with water. The crystals obtained when adding zirconium acetate are very homogenous, whereas those obtained without it show no particular uniformity.

These results are quite surprising, given that zirconium acetate is a "salt,"(2) a simple compound that is radically different from the macromolecules known for their antifreeze properties. It was not known as a substance capable of controlling ice crystal growth. Such control can be exerted in a number of ways: by reducing the speed of crystal growth (to slow their formation), by lowering the freezing point (to delay their formation), or by controlling their morphology, as in this case. Since this implies a direct interaction with the ice crystals, the researchers were surprised to find out that such radically different molecules as zirconium acetate and proteins could affect crystalline growth.

This compound offers significant advantages over existing equivalents, whether natural or synthetic. It is cheap to produce, stable, "simple" and easy to use, which bodes well for a wealth of future industrial applications. In addition, since it is totally different from all previously identified and/or developed substances with the same function, further research could lead to the development of other molecules with antifreeze properties.

This project relied on X-ray diffraction and imaging. These works were made possible by using the X-ray synchrotron (beam line ID19) at the ESRF in Grenoble, France. They are covered by two patents published on October 1, 2011.

Notes:

Laureate of an ERC Junior grant in 2011.In chemistry, a salt is an ionic compound made up of cations and anions, forming a neutral product with no net charge. This type of salt is much different from edible (table) salt.

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The above story is reprinted from materials provided by CNRS (Délégation Paris Michel-Ange), via AlphaGalileo.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Sylvain Deville, Céline Viazzi, Jérôme Leloup, Audrey Lasalle, Christian Guizard, Eric Maire, Jérôme Adrien, Laurent Gremillard. Ice Shaping Properties, Similar to That of Antifreeze Proteins, of a Zirconium Acetate Complex. PLoS ONE, 2011; 6 (10): e26474 DOI: 10.1371/journal.pone.0026474

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Saturday, 23 July 2011

Scientists a step closer to understanding 'natural antifreeze' molecules

ScienceDaily (June 23, 2011) — Scientists have made an important step forward in their understanding of cryoprotectants -- compounds that act as natural 'antifreeze' to protect drugs, food and tissues stored at sub-zero temperatures.

Researchers from the Universities of Leeds and Illinois, and Columbia University in New York, studied a particular type of cryoprotectants known as osmolytes. They found that small osmolyte molecules are better at protecting proteins than larger ones.

The findings, published in Proceedings of the National Academy of Sciences, could help scientists develop better storage techniques for a range of materials, including human reproductive tissue used in IVF.

Biological systems can usually only operate within a small range of temperatures. If they get too hot or too cold, the molecules within the system can become damaged (denatured), which affects their structure and stops them from functioning.

But certain species of fish, reptiles and amphibians can survive for months below freezing by entering into a kind of suspended animation. They are able to survive these extreme conditions thanks to osmolytes -- small molecules within their blood that act like antifreeze -preventing damage to their vital organs.

These properties have made osmolytes attractive to scientists. They are used widely in the storage and testing of drugs and other pharmaceuticals; in food production; and to store human tissue like egg and sperm cells at very low temperatures (below -40ºC) for a long period of time.

"If you put something like human tissue straight in the freezer, ice crystals start to grow in the freezing water and solutes -- solid particles dissolved in the water -- get forced out into the remaining liquid.

This can result in unwanted high concentrations of solutes, such as salt, which can be very damaging to the tissue," said Dr Lorna Dougan from the University of Leeds, who led the study. "The addition of cryoprotectants, such as glycerol, lowers the freezing temperature of water and prevents crystallisation by producing a 'syrupy' semi-solid state. The challenge is to know which cryoprotectant molecule to use and how much of it is necessary.

"We want to get this right so that we recover as much of the biological material as possible after re-thawing. This has massive cost implications, particularly for the pharmaceutical industry because at present they lose a large proportion of their viable drug every time they freeze it."

Dr Dougan and her team tested a range of different osmolytes to find out which ones are most effective at protecting the 3D structure of a protein. They used an atomic force microscope to unravel a test protein in a range of different osmolyte environments to find out which ones were most protective. They discovered that smaller molecules, such as glycerol, are more effective than larger ones like sorbitol and sucrose.

Dr Dougan said: "We've been able to show that if you want to really stabilise a protein, it makes sense to use small protecting osmolytes. We hope to use this discovery and future research to develop a simple set of rules that will allow scientists and industry to use the best process parameters for their system and in doing so dramatically increase the amount of material they recover from the freeze-thaw cycle."

The research was funded by the UK Engineering and Physical Sciences Research Council, the US National Institutes of Health and the China National Basic Research Program.