Metastable states in the system water–ethanol. Existence of a second hydrate; curious properties of both hydrates

Principles of Ice-Free Cryopreservation by Vitrification

Vitrification is an alternative to cryopreservation by freezing that enables hydrated living cells to be cooled to cryogenic temperatures in the absence of ice. Vitrification simplifies and frequently improves cryopreservation because it eliminates mechanical injury from ice, eliminates the need to find optimal cooling and warming rates, eliminates the importance of differing optimal cooling and warming rates for cells in mixed cell type populations, eliminates the need to find a frequently imperfect compromise between solution effects injury and intracellular ice formation, and can enable chilling injury to be "outrun" by using rapid cooling without a risk of intracellular ice formation. On the other hand, vitrification requires much higher concentrations of cryoprotectants than cryopreservation by freezing, which introduces greater risks of both osmotic damage and cryoprotectant toxicity. Fortunately, a large number of remedies for the latter problem have been discovered over the past 35 years, and osmotic damage can in most cases be eliminated or adequately controlled by paying careful attention to cryoprotectant introduction and washout techniques. Vitrification therefore has the potential to enable the superior and convenient cryopreservation of a wide range of biological systems (including molecules, cells, tissues, organs, and even some whole organisms), and it is also increasingly recognized as a successful strategy for surviving harsh environmental conditions in nature. But the potential of vitrification is sometimes limited by an insufficient understanding of the complex physical and biological principles involved, and therefore a better understanding may not only help to improve present outcomes but may also point the way to new strategies that may be yet more successful in the future. This chapter accordingly describes the basic principles of vitrification and indicates the broad potential biological relevance of this alternative method of cryopreservation.

Interactions of methanol, ethanol, and 1-propanol with polar and nonpolar species in water at cryogenic temperatures

Methanol is known as a strong inhibitor of hydrate formation, but clathrate hydrates of ethanol and 1-propanol can be formed in the presence of help gases. To elucidate the hydrophilic and hydrophobic effects of alcohols, their interactions with simple solute species are investigated in glassy, liquid, and crystalline water using temperature-programmed desorption and time-of-flight secondary ion mass spectrometry. Nonpolar solute species embedded underneath amorphous solid water films are released during crystallization, but they tend to withstand water crystallization under the coexistence of methanol additives. The CO₂ additives are released after crystallization along with methanol desorption. These results suggest strongly that nonpolar species that are hydrated (i.e., caged) associatively with methanol can withstand water crystallization. In contrast, ethanol and 1-propanol additives weakly affect the dehydration of nonpolar species during water crystallization, suggesting that the former tend to be caged separately from the latter. The hydrophilic vs. hydrophobic behavior of alcohols, which differs according to the aliphatic group length, also manifests itself in the different abilities of surface segregation of alcohols and their effects on the water crystallization kinetics.

Structurability: a collective measure of the structural differences in vodkas

Although vodka is a reasonably pure mixture of alcohol and water, beverage drinks typically show differences in appeal among brands. The question immediately arises as to the molecular basis, if any, of vodka taste perception. This study shows that commercial vodkas differ measurably from ethanol-water solutions. Specifically, differences in hydrogen-bonding strength among vodkas are observed by (1)H NMR, FT-IR, and Raman spectroscopy. Component analysis of the FT-IR and Raman data reveals a water-rich hydrate of composition E x (5.3 +/- 0.1)H(2)O prevalent in both vodka and water-ethanol solutions. This composition is close to that of a clathrate-hydrate observed at low temperature, implying a cage-like morphology. A structurability parameter (SP) is defined by the concentration of the E x (5.3 +/- 0.1)H(2)O hydrate compared to pure ethanol-water at the same alcohol content. SP thus measures the deviation of vodka from "clean" ethanol-water solutions. SP quantifies the effect of a variety of trace compounds present in vodka. It is argued that the hydrate structure E x (5.3 +/- 0.1)H(2)O and its content are related to the perception of vodka.

Structural basis of the 1H-nuclear magnetic resonance spectra of ethanol-water solutions based on multivariate curve resolution analysis of mid-infrared spectra

The (1)H-nuclear magnetic resonance (NMR) chemical shifts of ethanol and water hydroxyl groups show a pattern change at a critical ethanol concentration. Below the critical value (20 mol% at 400 Hz), only one hydroxyl peak appears due to fast proton exchange, whereas above the critical concentration, the ethanol hydroxyl peak splits from the water peak emerging as an individual chemical shift. The structural basis of the NMR pattern change was interpreted by a multivariate curve resolution-alternating least squares (MCR-ALS) analysis of the mid-infrared (mid-IR) spectra obtained for ethanol-water solutions. Results suggest that the NMR pattern change is due to the formation of ethanol-ethanol clusters. Below the critical concentration, no ethanol-ethanol clusters exist. Therefore, the NMR does not detect the ethanol environment. Above the critical ethanol concentration, ethanol-ethanol clusters first appear such that a distinct ethanol hydroxyl peak emerges. The basis for the dependence of the critical concentration on working frequency is also interpreted. High frequency NMR measurements are more sensitive to ethanol content, resulting in a lower critical ethanol concentration.

Subambient behavior of mannitol in ethanol-water co-solvent system

PURPOSE

The purpose of this study is to characterize the freezing behavior of mannitol in ethanol-water co-solvent systems in comparison with the corresponding aqueous solution.

METHODS

Subambient differential scanning calorimetry (DSC) and microscopy techniques were used to investigate the freezing behavior of mannitol in aqueous solutions and in ethanol-water co-solvent systems.

RESULTS

The DSC thermogram of the frozen aqueous solution, which was warmed after cooling at 5.0 degrees C/min, consisted of a glass transition, an endothermic transition, and a crystallization exotherm from mannitol, respectively. The thermograms of ethanol-containing solutions were different in view of including some thermal events attributable to ethanol hydrates. The glass transition of amorphous mannitol was also observed in the thermograms, but became unclear with increasing ethanol in the co-solvent system. The microscopy experiments enabled understanding of the subambient behavior of mannitol. Ethanol was largely removed by vacuum drying rather than freeze-drying. In addition, such manipulations as annealing during the freezing process and slower cooling (0.5 degrees C/min) enhanced the crystallization of mannitol in the frozen system.

CONCLUSIONS

In the presence of ethanol, crystallization of mannitol was inhibited under subambient conditions. Annealing or slower cooling promoted the crystallization of mannitol during the freezing process.

Ultrasonic velocity and volumetric properties of isomeric butanediols plus water systems

Ultrasonic velocities and densities of binary aqueous solutions of isomeric butanediols were measured in the temperature range 298-318 K at 10 degree intervals over the entire composition range, and 5 degree intervals in the water-rich region. The experimental data in the dilute region, with mole fraction of water less than 0.1, was analysed to determine the partial molar volumes and adiabatic compressibilities of water at infinite dilution. The standard thermodynamic transfer functions were calculated to evaluate the environment of water at infinite dilution in these systems. From the compressibility isotherms, as a function of temperature in the water-rich region, the formation and the composition of clathrate-like structures in the liquid solutions was determined, and the nature of these structures was discussed.Key words: ultrasonic velocity, adiabatic compressibility, density, partial molar quantities, standard thermodynamic transfer functions.

Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

The presence of clathrate hydrates in cometary ice has been suggested to account for anomalous gas release at large radial distances from the sun as well as the retention of volatiles in comets to elevated temperatures. However, how clathrate hydrates can form in low-pressure environments, such as in cold interstellar molecular clouds, in the outer reaches of the early solar nebula, or in cometary ices, has been poorly understood. Experiments performed with the use of a modified electron microscope demonstrate that during the warming of vapor-deposited amorphous ices in vacuo, clathrate hydrates can form by rearrangements in the solid state. Phase separations and microporous textures that are the result of these rearrangements may account for a variety of anomalous cometary phenomena.

Glass-forming tendency and stability of the amorphous state in the aqueous solutions of linear polyalcohols with four carbons. I. Binary systems water-polyalcohol

All the aqueous solutions of linear saturated polyalcohols with four carbons have been investigated at low temperature. Only ice has been observed in the solutions of 1,3-butanediol and 1,2,3- and 1,2,4-butanetriol. For same solute concentration, the glass-forming tendency on cooling is highest with 2,3-butanediol, where it is comparable to that with 1,2-propanediol, the best solute reported to date. However, the quantity of ice and hydrate crystallized is particularly high on slow cooling or on subsequent rewarming. The highest stability of the amorphous state is observed on rewarming the 1,2-butanediol and 1,3-butanediol solutions. With respect to this property, these compounds come just after 1,2-propanediol and before all the other compounds studied so far. They are followed by dimethylsulfoxide and 1,2,3-butanetriol. The glass-forming tendency of the 1,3-butanediol solutions is also very high; it is third only to that of 1,2-propanediol and 2,3-butanediol. The glass-forming tendency is a little smaller with 1,2-butanediol, but it is cubic instead of ordinary hexagonal ice which crystallizes on cooling rapidly with 35% 1,2-butanediol. Cubic ice is thought to be innocuous. A gigantic glass transition is observed with 45% of this strange solute. 1,4-Butanediol, 45% also favors cubic ice greatly. Therefore, 1,2- and 1,3-butanediol with comparable physical properties are perhaps as interesting as 1,2-propanediol for cryopreservation of cells or organs by complete vitrification. Together with 1,2-propanediol, 1,2- and 1,3-butanetriol, 1,2,3-butanetriol, and perhaps 2,3-butanediol provide an interesting battery of solutions for cryopreservation by vitrification.