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The same antifreeze proteins that keep organisms from freezing in cold
environments also can prevent ice from melting at warmer temperatures,
according to a new Ohio University and Queen's University study
published today in the Early Edition of the journal Proceedings of
the National Academy of Sciences.
Antifreeze proteins are found in insects, fish, bacteria and other
organisms that need to survive in cold temperatures. These proteins
protect the organisms by arresting the growth of ice crystals in their
bodies. The new study not only has implications for understanding this
process in nature, but also for understanding the superheating of
crystals in technologies that use superconductor materials and
Twenty years ago, researchers proposed that antifreeze proteins can
create superheating by suppressing melting at temperatures higher than
the equilibrium melting point.
"During recrystallization, a larger ice crystal grows while a smaller
one melts. Antifreeze proteins can help control both of these
processes," explained Ido Braslavsky, an associate professor of physics
and astronomy at Ohio University who worked on the study with lead
author Yeliz Celik, a doctoral student in physics at Ohio University,
and Professor Peter Davies of Queen's University in Canada.
The team's study, supported by the National Science Foundation and
the Canadian Institutes for Health Research, presents the first direct
measurements of the superheating of ice crystals in antifreeze protein
solutions, Celik said.
In addition, the researchers provide the first experimental evidence
that superheated ice crystals can be stabilized above the melting point
for hours, at a maximum temperature of about .5 degree Celsius.
Superheated crystals rarely stay stable for long periods of time, and
previous studies showed that stabilization only occurs under unique
conditions, Braslavsky explained.
The researchers used two techniques in the study, fluorescence
microscopy and sensitive temperature control of a solution within a thin
cell. In order to track the position of the antifreeze protein on an
ice crystal, the researchers attached a second protein to the antifreeze
protein -- the green fluorescent protein, which glows under certain
conditions. The scientists then placed the antifreeze protein solution
in the thin cell, which allowed them to observe the fluorescence signal
from the protein while finely controlling the ice crystal's temperature.
Although the study reveals that these proteins can suppress ice
melting up to a certain point, the protein's ability to suppress ice
growth is much stronger. The hyperactive antifreeze proteins used in the
study were more capable of suppressing melting than the moderately
active ones, Braslavsky said.
These findings potentially could make the process of ice
recrystallization inhibition more efficient for applications such as
maintaining the quality of frozen foods, Braslavsky said.
"Antifreeze proteins that inhibit growth and melt are essential for
protection against freeze and thaw damages," he said. "Big crystals
(that occur in the recrystalization process) separate cell walls and
damage the integrity of the tissue."
In additional to Celik, Braslavsky and Davies, co-authors of the
study include Maya Bar of the Weizmann Institute of Science and Laurie
Graham and Yee-Foong Mok of Queen's University.
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