022 The theory of crystallization hydrolysis

Abstract

As an example of the phenomenon of crystallization hydrolysis, let us consider hydrolysis in the case of freezing of NaCl solution, with the initial concentration C0 and pH 7. It is known that Cl − ions are captured in ice better than Na + ions, i.e., the distribution coefficient K − > K + (K + @ 10 −3 ). This means the ice crystals are negatively charged relative to the NaCl solution, and the excess of Na + in the liquid phase is concentrated mainly in the Debye layer near the crystal surface. The ice-captured charge is eventually neutralized due to redistribution of ions OH − and H 3 O + arising spontaneously, with the rate dependent on the constant of disassociation. As a result of the neutralization process, the concentration of Na+ ions in the liquid phase would increase simultaneously with OH − ion concentration. In a theoretical analysis we can calculate the change of OH- ion concentration as Δn = kTS ∈ ∈ 0/e 2 @ 10 −7 S/V (mol/m 2 ), where S is the total interface area, V is the volume of the liquid phase, and d is the Debye radius. Since the volume of the liquid phase depends only on the temperature of the solution freezing, one can increase the pH by increasing the value of S. This can be realized by introducing cells or neutral polystyrol beads (latex) in the solution. In that case, the area of the ice-solution interface would be no less than the surface area of all beads and Δn would be no less than Δn > 3 ψ C(T)10 −7 /RC0 (mol/m 2 ) > 10 −2 mol/l, assuming that the volume concentration of beads ψ = 0.2, C(T)/C0 = 100, and the ball radius R = 1 μ m. Such considerable variation of pH at freezing can lead to anomalous cryochemical reactions and can damage the biological cells during low-temperature preservation. Experimental verification of the theory has been performed by studying the hydrolysis of K 3 Fe(CN) 6 during freezing of a 0.1 M NaCl solution in the presence of latex beads. It is known that the damage rate of slowly frozen erythrocytes is increased with the initial hematocrit value of the suspension. This fact is also in a good agreement with the theory of crystallization hydrolysis. Source of funding: Universal Stabilization Technologies, Inc. Conflict of interest: None declared. victorb@ustsd.com