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Abstract

Addition of electrolytes to solutions of non-crystallizing solutes can cause a significant decrease in the glass transition temperature (Tg') of the maximally freeze-concentrated solution. For example, addition of 2% sodium chloride to 10% solutions of dextran, PVP, lactose, and sucrose causes a decrease in Tg' of 14 degrees to 18 degrees C. Sodium phosphate has a smaller effect on Tg' and is unusual in that 1% to 2% sodium phosphate in 10% PVP causes a second glass transition to be observed in the low-temperature thermogram, indicating a phase separation in the freeze concentrate. Comparison of DSC thermograms of fast-frozen solutions of sucrose with and without added sodium chloride shows that electrolyte-induced reduction of Tg' is not caused by a direct plasticizing effect of the electrolyte on the freeze concentrate. Measurement of unfrozen water content as a function of temperature by a pulsed nmr method shows that the most likely mechanism for electrolyte-induced changes in Tg' is by increasing the quantity of unfrozen water in the freeze concentrate, where the unfrozen water acts as a plasticizer and decreases Tg'. The correlation time (tau c) of water in the freeze concentrate is in the range of 10(-7) to 10(-8) seconds. The results underscore the importance of minimizing the amount of added salts to formulations intended for freeze drying.

Characteristics and Significance of the Amorphous State in Pharmaceutical Systems

“…One can only say for certain that at T g the mean molecular relaxation time (τ) associated with the predominant molecular motions is about 100 s and that T g can be expected to vary with experimental heating and cooling rates, sample molecular mass, 12,13 sample history, sample geometry, 14,15 and sample purity. 16 The experimental glass transition temperature is also influenced by the choice of technique used to measure it because of the varying sensitivities of available techniques to different types and speeds of molecular motions.…”

Protein Cryoprotectant Ability of the Aqueous Zwitterionic Solution

“…Unfortunately, the value of T g for these three media could not be measured in this study due to equipment limitations (193 K). However, the amount of unfrozen water, which arises from the solute hydration water molecules, is related to glass formation . Given the broadening of the endothermic peak and the changes in T m and Δ H fus as shown in Figure d, e, we speculate that the unfrozen water content of the OE 2 imC 3 C solution is higher than that of the two CPA solutions.…”

“…The increase in the number of hydration water molecules with the solute in the binary aqueous solutions increases the amount of unfrozen water (hydration water species) because of a decrease in the number of bulk water molecules (free water species) forming ice (frozen water) at a low temperature . Here, we measured the water activity ( a w ) of aqueous OE 2 imC 3 C, glycerol, and DMSO solutions to determine the direct free water content (Figure S2).…”

Sonochemical application reduces monosaccharide levels and improves cryoprotective effect of Jerusalem artichoke extract on Leuconostoc mesenteroides WiKim33 during freeze-drying

“…Sonication treatment has been applied in various processes, which can improve oxidation and water decontamination, enhance biodegradability, minimize toxicity, assist Maillard reaction, and destroy refractory compounds [39] , [53] , [54] , [55] , [56] . Ultrasound generates a gas-phase phenomenon in liquids, which is mostly coupled with free radicals.…”