Freezing organic solutions

It is well known, that in aqueous solutions the water molecules, which are in the inner coordination sphere of the complex, quench the lanthanide (Ln) luminescence in result of vibrations of the OH-groups (OH-oscillators). The use of D O instead of H O, the freezing of solution as well as the introduction of a second ligand to obtain a mixed-ligand complex leads to either partial or complete elimination of the H O influence. The same effect may be achieved by water molecules replacement from the inner and outer coordination sphere at the addition of organic solvents or when the molecule of Ln complex is introduced into the micelle of the surfactant. 

The freezing of complex organic solutions and suspensions is often difficult to predict theoretically. The methods to analyze the freezing process and the formed structure are described in Section 1.1.5. The freezing is influenced by several factors, which often act in opposing directions ... 

Flink, J., Karel, M. Retention of organic volatiles in freeze-dried solutions of carbohydrates. Reprinted with permission from Journal of Agricultural and Food Chemistry, Vol. 18, No. 2, S. 295, 1970, Copyright 1970 American Chemical Society, Washington, DC 20005, USA... 

Seager, H., Taskis, C.B., Syrop, M., Lee, T.J. Structures of products prepared by freeze-drying solutions containing organic solvents. PDA J. Parenteral Sci. Technol. 39,161-179,1985 Kahn-Wyler, A. Kaltlufttrocknung von pharmazeutischen Praparaten and... 

After washing several times with methanol, the microgel fraction is freeze-dried from benzene and residual solvents are. stripped off under reduced pressure (10-5 mbar). The microgels thus obtained are white, dust-like powders with a sedimentation volume of 20-50 ml/g. They can be redispersed to form colloidal organic solutions. 

Lipid blends made by freeze-drying from organic solutions... 

While the phosphorescence of solids is easily observed at room temperature, it is often impossible to observe the phosphorescence of solutions at room temperature apparently oxygen molecules, absorbing energy in collisions with the excited species involved, quench its phosphorescence. To avoid this, solutions are cooled in liquid nitrogen (77°K) and allowed to freeze such solutions are referred to as rigid solutions or glasses. Two organic solvents commonly used to prepare such solutions are ethanol and EPA, a mixture of ethyl ether, isopentane, and ethanol. 

Polarization transfer has also been observed between HP supercritical xenon and organic solutes. HP xenon was collected as a solid and then transferred to a 3 mm borosilicate tube containing the organic molecule (toluene or biphenyl) at a field of 1 T to avoid relaxation. Proton enhancements were observed to be three (biphenyl) or seven (toluene) times the Boltzmann equilibrium level as measured at 2T and with the xenon polarization at 2%. Several proton acquisitions could be made because the xenon Ty was approximately 7.5 min. The authors suggest that the low cross-relaxation rates observed in both the liquid and now supercritical phases could lead to better polarization transfer in the solid state, albeit with a highly dispersed xenon, such as provided by freezing a supercritical or liquid solution. 

The use of multipass zone-refining apparatus for preconcentration of trace components from water has not been reported, although the concentration of trace flavor components from a solvent extract has been described (J93). It is obvious that the low-temperature preconcentration of organic solutes is desirable if thermal decomposition or reactions are to be avoided. Nevertheless, the use of freezing to concentrate inorganic solutes is worthy of further study, especially if it is possible to use an internal standard to improve upon the reliability of the method to establish a concentration factor for the solutes. 

The precipitation of the eutectics from solutions upon cooling occurs when the free energy of the solute molecules in the crystalline state becomes less than that of the molecules in solution. Therefore, a change in the tanperature of precipitation of the eutectics indicates a change in the chanical potentials of the components of the solutions in the presence of protein molecules. On concentration of the solution, this may occur in the hydrate shells of the protein molecules. Since for the organic solute molecules close to the macromolecules not only do the molecules of the solvent but also the structural elanents of the protein molecules form the medium, it is most probable that the observed phenomenon of a rise in the temperature of freezing is based on the interaction of the molecules of the organic additive with the biopolymer. 

JM Flink, M Karel. Retention of organic volatiles in freeze-dried solutions of earbohydrates. J Agr Food Chem 18(2) 295-297, 1970. 

When the formulated solution contains essentially saline or organic solutes that crystallize easily, the interstitial phase will crystallize out abruptly as an eutectic or a mixture of eutectics. The crystallization results in an immediate hardening of the frozen system, which becomes fully rigid. At this point, the system has reached its maximum temperature for complete solidification (eutectic point, Te), which is a basic parameter of the freeze-drying process. 

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