Ice Nucleation by Proteins and Surface Films

Abstract

DURING an investigation of the icing characteristics of solid surfaces, Schaefer¹ observed that certain protein films induced supercooled water drops to freeze at temperatures near zero. The possible importance of proteins as a source of natural ice nuclei cannot be over-emphasized because proteins are able to concentrate irreversibly at water surfaces and thereafter find their way into the atmosphere in particles large enough to act as ice nuclei. The ocean surface, in particular, would be an immense source of air-borne protein². Furthermore, protein films are of great fundamental interest because they possess the unique property that their state of compression, and therefore their geometric similarity to an ice lattice, can be varied continuously, thus providing a means of testing the relationship between ‘fit’ and nucleation temperature. It is therefore surprising that while several authors^3–5 have accepted proteins as ice nucleators, no confirmation or extension of Schaefer's work has been reported.