Water-freezing high-pressure condition

A study by Hayashi et al. demonstrates that less reactive electron-rich aromatic aldehydes efficiently undergo Mannich reactions under high pressure induced by water freezing [8], For instance, in the Mannich reaction of p-anisaldehyde, 3,4-dimethoxybenzaldehyde or N-acetyl-(4-formyl)aniline, with acetone and p-anisidine, good yields (61-99%) and excellent enantioselectivities (92-97%) have been obtained under water-freezing high-pressure conditions while there is no reaction at room temperature at 0.1 MPa (Scheme 9.6). 

Methane hydrates form when methane molecules become trapped within an ice lattice as water freezes. They can form in very cold conditions or under high-pressure conditions. Both of these conditions are met in deep oceans and in permafrost. In Canada, hydrates have already been found in large quantities in the Canadian Arctic. Methane hydrate has a number of remarkable properties. For example, when brought into an oxygen atmosphere, the methane fumes can be ignited, making it appear that the ice is burning ... 

Water is a very structurally versatile molecule. Water exists in all three physical states solid, liquid, and gas. Under extremely high temperature and pressure conditions, water can also become a supercritical fluid. Liquid water can be cooled carefully to below its freezing point without solidifying to ice, resulting in two possible forms of supercooled water. In the solid state, 13 different crystalline phases (polymorphous) and 3 amorphous forms (polyamorphous) of water are currently known. These fascinating faces of water are explored in detail in this section. 

Another technique—pres sure-shift freezing—also shows promise. In this technique the material is subjected to high pressure (200 MPa) and cooled to -15 C. Under these conditions the water does not freeze. However, when the pressure is released suddenly, many small ice crystals form. This has two results the small ice crystals do not rupture any structures present, but by dehydrating the unfrozen material the remaining stmcture is aggregated and stiffened by the introduction of secondary cross-links. At low concentration of solids there are too few interconnecting chains for there to be a load-bearing continuum, and the material tends to flocculate and settle out. 

Molybdenum sulfide nanoparticles in the size-range 3-10 nm have been synthesized in mild conditions using a microemulsion-based route. The reverse microemulsion phase, AOT/ n-heptane/ water, was first characterized by Transmission Electron Microscopy (TEM) of Freeze Fractures (FF) obtained via High Pressure Freezing (HPF) as well as Dynamic Light Scattering (DLS). The impacts of various parameters such as water-to-surfactant molar ratio w and the addition of a nonionic cosurfactant were then studied. The reverse microemulsion phase was further used to tailor the size of MoSx nanoparticles. The mean particle size obtained by this method makes those particles particularly interesting for further catalytic applications. 

Super-coohng is not an exelusive characteristic of water, it can be done with other liquids as well, but it is surprisingly easy for water because of the special hydrogen bonding network. In fact, under very special conditions at high pressure, water can even be super-eooled to -130 °C. This extremely unstable state can freeze upon heating ... 

The walls of erythrocytes (red blood cells) are permeable to water. In a salt solution, they shrivel (lose water) when the outside salt concentration is high and swell (take up water) when the outside salt concentration is low. In an experiment at 25°C, an aqueous solution of NaCl that has a freezing point of 0.406°C causes erythrocytes neither to swell nor to shrink, indicating that the osmotic pressure of their contents is equal to that of the NaCl solution. Calculate the osmotic pressure of the solution inside the erythrocytes under these conditions, assuming that its molarity and molality are equal. 

The lyophilization method is similar to ordinary vacuum distillation with one essential difference the material to be dried must first be solidly frozen and then subjected to a very low absolute pressure (high vacuum) and controlled heat input. Under these conditions, the water content, in the form of an ice matrix, is selectively removed via sublimation, completely bypassing the intermediate liquid phase. The solid particles are locked into the matrix during drying and cannot interact. The following conditions are necessary for freeze-drying ... 

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