Abstract
The control of freezing saline water at the micrometer level has become very important in cryosurgery and cryopreservation of stem cells and foods. Adding antifreeze protein to saline water is a promising method for controlling the freezing because the protein produces a gap between the melting point and the freezing point. Furthermore, a synergistic effect of the solutes occurs in which the freezing point depression of a mixed solution is more noticeable than the sum of two freezing point depressions of single-solute solutions. However, the mechanism of this effect has not yet been clarified. Thus, we have carried out a molecular dynamics simulation on aqueous solutions of winter flounder antifreeze protein and sodium chloride or calcium chloride with an ice layer. The results show that the cations inhibit the hydrogen bond among water molecules not only in the salt solutions but also in the mixed solutions. This inhibition depends on the local number of ions and the valence of cations. The space for water molecules to form the hydrogen bonds becomes small in the case of the mixed solution of the protein and calcium chloride. These findings are consistent with the synergistic effect. In addition, it is found that the diffusion of ions near positively-charged residues is attenuated. This attenuation causes an increase in the possibility of water molecules staying near or inside the hydration shells of the ions. Furthermore, the first hydration shells of the cations become weak in the vicinity of the arginine, lysine and glutamic-acid residues. These factors can be considered to be possible mechanisms of the synergistic effect.
Highlights
The control of freezing water at micrometer levels has become very important in recent years in various fields: (1) cryopreservation of food and food ingredients [1,2]; (2) cryopreservation of blood, stem cells and organs to be transplanted [3]; (3) cryosurgery [4]; and (4) ice slurry for cooling or energy storage [5].Several methods have been developed for this control of freezing
We carry out molecular dynamics simulations for the dilute aqueous solution of HPLC6, sodium ions, calcium ions and chloride ions near a thin ice layer covered with secondary prism or pyramidal faces, in order to analyze the interaction between the ice and Antifreeze proteins (AFPs) and the effect of ions on the interaction
4th, and 6th layers indicates lower values for. This is in thethe result of 5th, hydrogen bonds between water molecules salt solutions the number for pure water. the
Summary
The motion enhancement of the mixed solution [19] described in the Introduction. The motion enhancement of ions and ions and water molecules a reason for theeffect. The higher values of HBCF for the cations near alanine residues show that the first hydration. The higher values of HBCF for the cations near alanine residues show that the first hydration shells of the cations in the vicinity of these residues remain robust. Theshells robustness of the hydrophobic shellsin around these residues expected. Robust contribute to the hydration shells around these residues is expected. The discussion is consistent with the discussion in Sectionto the synergistic.
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