A similar law may govern water freezing in minerals and living organisms

Abstract

THERE is an interesting similarity between the freezing of water in minerals and in biological tissues. Mazur^1,2 observed that many living organisms lose viability at threshold temperatures near −10 °C. After investigating this phenomenon from the point of view of possible mechanisms by which living cells suffer damage on freezing, he concluded that a key step in the freezing process is the penetration of ice into the cell to nucleate the internal water, and that at −10 °C ice can penetrate the membrane, whereas above this temperature, it cannot. This implies that the water in the cell-membrane pores or a portion of them, starts to freeze at about −10 °C. From the Kelvin equation which describes freezing in terms of the ice-water surface tension and the radius of cylindrical capillaries, Mazur deduced that¹ “the lower melting point of ice in a capillary can account for the barrier properties of the plasma membrane”. He observed, however, that “there is a large quantitative discrepancy. The evidence suggests that the plasma membrane ceases to be a barrier at approximately −10 °C. On the basis of equation (4), (ref. 1) the critical pore radius at −10 °C is 30 Å, whereas the estimated pore size from permeability studies is 3–8 Å”. To account for the discrepancy he postulated that the contact angle of water in the membrane pores is not 0 ° but 80 °. This enabled him to find the simple relationship where ΔT is the freezing point depression and a is the pore radius in Å, which predicts that water in 5 Å pores will freeze at −10 °C and thus agrees with experimental observations on membrane pore sizes.