Determination of the quaternary phase diagram of the water–ethylene glycol–sucrose–NaCl system and a comparison between two theoretical methods for synthetic phase diagrams

Abstract

Characterization of the thermodynamic properties of multi-solute aqueous solutions is of critical importance for biological and biochemical research. For example, the phase diagrams of aqueous systems, containing salts, saccharides, and plasma membrane permeating solutes, are indispensible in the field of cryobiology and pharmacology. However, only a few ternary phase diagrams are currently available for these systems. In this study, an auto-sampler differential scanning calorimeter (DSC) was used to determine the quaternary phase diagram of the water-ethylene glycol-sucrose-NaCl system. To improve the accuracy of melting point measurement, a "mass redemption" method was also applied for the DSC technique. Base on the analyses of these experimental data, a comparison was made between the two practical approaches to generate phase diagrams of multi-solute solutions from those of single-solute solutions: the summation of cubic polynomial melting point equations versus the use of osmotic virial equations with cross coefficients. The calculated values of the model standard deviations suggested that both methods are satisfactory for characterizing this quaternary system.

Comparison of non-ideal solution theories for multi-solute solutions in cryobiology and tabulation of required coefficients

“…Such information could be used to help choose the optimal model for working with a given solution system of interest. Limited comparisons between these solution theories have been made in the past [3,14,21,55], but these have been restricted to only a few of the multi-solute systems for which data are available in the literature, and none have directly compared the molality-and mole fraction-based forms of the multi-solute osmotic virial equation. There has yet to be a comprehensive quantitative study comparing the abilities of all three of these models to predict non-ideal multi-solute solution behavior for the range of available cryobiologically-relevant multi-solute data in which the predictions of all three models are based on a single consistent set of binary solution data.…”

“…This article examines and evaluates some of the available theories for predicting water (i.e. solvent) chemical potential, in particular those that do not depend on multi-solute solution data.In cryobiology, water chemical potential is often expressed in terms of its composition dependence, osmolality [3,11,14,15,21,55,56,74], or in terms of the related properties freezing point depression [3,[14][15][16]21,38,[50][51][52]55,[74][75][76] and osmotic pressure [37,44,55,73]. Freezing point depression and osmotic pressure are physically measurable solution properties, and the relationships between them and osmolality (described below in Eqs.…”

Non-ideal Solution Thermodynamics of Cytoplasm

“…44 Although there have been other multi-solute solution theories able to make predictions directly from single solute information that apply accurately to specific examples, 49 our osmotic virial approach is the most broadly applied. 3,26,27,[42][43][44] It is important to point out that some nonlinear relationships have been presented for osmolality of cytoplasm in bacteria (i.e., Escherichia coli); 50,51 however, in those studies the nonlinearity arose from different phenomena than those being studied here. Specifically the nonlinear function in these works 50,51 described the dependence of osmolality on the molality of the growth medium in adaptation studies, while the osmotic coefficient was assumed to be independent of the solution osmolality in passive osmotic response studies.…”

“…26 This equation is able to predict directly the osmolality of the cytoplasmic solution of red blood cells in agreement with measurements. 3 Other research groups have applied our equation to v) a quaternary system of water-CPA-sugarsalt, 43 and vi) aqueous solutions of two micelle-forming non-ionic surfactants. 44 Although there have been other multi-solute solution theories able to make predictions directly from single solute information that apply accurately to specific examples, 49 our osmotic virial approach is the most broadly applied.…”

“…The osmotic virial equation has been shown by many researchers over decades to apply to a vast number of types of solutes in aqueous systems, including sugars, electrolytes, cryoprotectants, macromolecules, proteins, alcohols, and starches. 3,24,26,27,[31][32][33][34][35][36][37][38][39][40][41][42][43][44] Osmolality describes the concentration dependence of the chemical potential of water in a solution and is the solution thermodynamics quantity that appears directly in equations describing freezing point depression of a solution (see Eq. 12) or the driving force for passive osmotic transport.…”