Frozen aqueous solutions concentration

Frozen Aqueous Solutions Concentration Effects. As solute is rejected by the growing ice and as its concentration increases in the shrinking liquid phase, the temperature drops toward the eutectic point, where the entire system approaches complete solidification. Of major importance is the fact that a highly concentrated liquid phase can persist indefinitely at any point above the eutectic temperature. 

Fig. 6.10 Mossbauer spectra of amorphous frozen aqueous solutions with the indicated concentrations of [Fe(H20)6]. The spectra were obtained at 80 K. Rough estimates of the relaxation times are given...

Figure 2. Dependence of H atom yields on solute concentration in 7-irradiated frozen aqueous solutions at 77 °K.

The effect of dithiothreitol (DTT) on DNA radiolysis at cryogenic temperatures was investigated by the EPR technique in order to elucidate its properties as a radioprotector and to establish which DNA radicals can be repaired. The DTT, even at concentrations up to 1 M, does not repair more than 30% of DNA radicals. However, the ability of DTT to donate hydrogen atoms to damaged DNA in frozen aqueous solutions is limited to the allyl radical of thymine [reaction (7)] and guanine radical cation [reaction (8)] ... 

FIGURE 9.1 A comparison of two calibration curves, one prepared from the reference standard and another from the lyophilized formulated dose. The reference standard was provided as a frozen aqueous solution. Each was spiked into assay buffer and dilutions were made to provide the corresponding calibrators with the same concentrations. 

A typical pharmaceutical formulation will serve as model, frozen aqueous solutions that are contained in loosely stoppered glass vials. They stand directly on the freeze-drier shelves. Such a model appears deceptively simple but is in fact subject to considerable complexities that bedevil the modelling of optimum processing conditions and the estimation of a realistic drying cycle time. As emphasised in earlier chapters, for the case where the product does not display eutectic behaviour, it is imperative to freeze the solution to below Tg, in order to ensure maximal freeze-concentration and minimise deleterious chemical reactions that have been shown to occur at high rates in part frozen, supersaturated mixtures.By the same token, the temperature during the removal of ice by sublimation must on no account be allowed to rise above T at... 

Two groups have used physical measurements e.g. density, viscosity, refractive index, and optical rotation) to determine the compositions of solutions of water-sucrose-D-glucose (or invert sugar) at various temperatures. The diffusion coefficient for self-diffusion of D-fructose in an aqueous system has been measured over a range of concentrations and temperatures. The yields of trapped electrons and radicals have been determined following y-irradiation of frozen aqueous solutions of sugars. ... 

In an aqueous solution of DNA, the water outside of the solvation shell is referred to as bulk water. When DNA solutions are frozen, the bulk water crystallizes as a separate phase—ice. Ice does not form if the concentration of DNA is brought to a level where only the solvation shell remains, about 20-22 waters/nucleotide. If brought to this concentration slowly, a film is formed. Freezing a film does not create ice. Another type of sample is prepared by first lyophilizing DNA and then letting it sit at a preselected humidity that determines the level of hydration, typically 2.5 < F < 22. Subsequent freezing of these cotton-like samples does not yield ice. 

Figure 14. Variation of radical yields with solute concentration in y-irradiated frozen aqueous NaOH solutions at 77°K. (O) G(T ) in polycrystalline phase ( ) G(T ) in glassy phase ( ) G(0 ) in polycrystalline phase at...

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