Chemists redesign natural antifreeze.

Chemists have created a family of synthetic compounds akin to proteins that keep Arctic and Antarctic fish from freezing stiff. If the new molecules can work as well as the fish proteins do, they could offer a new route to protecting frozen foods and chilled transplant organs from destructive ice buildup.

Researchers discovered these so-called antifreeze proteins in the 1960s (SN: 4/19/97, p. 237). Scientists believe that the compounds bind to tiny ice crystals and make it harder for them to grow. Researchers have shown that the antifreeze proteins can thwart ice-crystal formation when added to food.

Yet, researchers haven't revealed molecular details of how the proteins work. Also, harvesting the proteins from fish is costly and time-consuming, says chemist Robert N. Ben of the State University of New York at Binghamton.

In the September-October BIOCONJUGATE CHEMISTRY, Ben and his colleagues report a new method for chemically synthesizing molecules that resemble sugar-containing antifreeze proteins called antifreeze glycoproteins.

The new chemical strategy creates a whole family of compounds, each one a variation on natural antifreeze glycoproteins, the team reports. Structural differences among the variants might help reveal the molecular motifs underlying the natural antifreeze proteins. Also, the variants might be more or less suited for specific anti-ice jobs, Ben says.

With an eye on commercial possibilities, the Binghamton team strengthened each of its molecules by creating a strong carbon-carbon bond in the location where the natural glycoproteins contain a weaker carbon-oxygen bond. With this added muscle, the synthetic molecules remain intact under certain chemical and biological conditions that destroy the natural glycoproteins, Ben says. That could make the new chemicals promising for ice-thwarting coatings, additives, or sprays for aircraft, concrete, or crops, he suggests.

Although the new molecules differ from the natural ones, Ben says preliminary evidence suggests his compounds bind to ice and inhibit crystal growth. Chi-Hing C. Cheng, a biologist at the University of Illinois at Urbana-Champaign, calls the report "a gallant attempt" at synthesizing antifreezes. However, she adds, Ben's group must show that the molecules' anti-ice powers rival those of the natural glycoproteins or are better.

"Nature evolves a particular compound for a purpose," Cheng says. The added carbon-carbon bonds might make the new molecules more stable, but the proteins might need the carbon-oxygen bonds for good antifreeze activity, she says.

If the new molecules do prove as effective as natural agents, then the new synthesis techniques Ben's team developed might suggest a route to commercially viable antifreeze products, comments biochemist Robert E. Feeney of the University of California, Davis. A specific application would be to prevent the buildup of gritty ice granules in ice cream, he says.