CALORIMETRIC STUDY OF CRYSTAL-GROWTH OF ICE IN HYDRATED METHEMOGLOBINAND OF REDISTRIBUTION OF THE WATER CLUSTERS FORMED ON MELTING THE ICE

Calorimetric studies of the melting patterns of ice in hydrated methem oglobin powders containing between 0.43 and 0.58 (g water)/(g protein) , and of their dependence on annealing at subzero temperatures and on isothermal treatment at ambient temperature are reported. Cooling rate s were varied between approximate to 1500 and 5 K min(-1) and heating rate was 30 K min(-1) Recrystallization of ice during annealing is obs erved at T > 228 K. The melting patterns of annealed samples are chara cteristically different from those of unannealed samples by the shifti ng of the melting temperature of the recrystallized ice fraction to hi gher temperatures toward the value of ''bulk'' ice. The ''large'' ice crystals formed during recrystallization melt on heating into ''large' ' clusters of water whose redistribution and apparent equilibration is followed as a function of time and/or temperature by comparison with melting endotherms. We have also studied the effect of cooling rate on the melting pattern of ice with a methemoglobin sample containing 0.5 0 (g water)/(g protein), and we surmise that for this hydration coolin g at rates of greater than or equal to approximate to 150 K min(-1) pr eserves on the whole the distribution of water molecules present at am bient temperature.