Degree of hydration

If a dilute acid is added to this solution, a white gelatinous precipitate of the hydrated tin(IV) oxide is obtained. It was once thought that this was an acid and several formulae were suggested. However, it now seems likely that all these are different forms of the hydrated oxide, the differences arising from differences in particle size and degree of hydration. When some varieties of the hydrated tin(IV) oxide dissolve in hydrochloric acid, this is really a breaking up of the particles to form a colloidal solution—a phenomenon known as peptisation. 

In addition to an array of experimental methods, we also consider a more diverse assortment of polymeric systems than has been true in other chapters. Besides synthetic polymer solutions, we also consider aqueous protein solutions. The former polymers are well represented by the random coil model the latter are approximated by rigid ellipsoids or spheres. For random coils changes in the goodness of the solvent affects coil dimensions. For aqueous proteins the solvent-solute interaction results in various degrees of hydration, which also changes the size of the molecules. Hence the methods we discuss are all potential sources of information about these interactions between polymers and their solvent environments. 

The Hydrate and Enol Form. In aqueous solutions, acetaldehyde exists in equihbrium with the acetaldehyde hydrate [4433-56-17, (CH2CH(0H)2). The degree of hydration can be computed from an equation derived by BeU and Clunie (31). Hydration, the mean heat of which is —21.34 kJ/mol (—89.29 kcal/mol), has been attributed to hyperconjugation (32). The enol form, vinyl alcohol [557-75-5] (CH2=CHOH) exists in equihbrium with acetaldehyde to the extent of approximately 1 molecule per 30,000. Acetaldehyde enol has been acetylated with ketene [463-51-4] to form vinyl acetate [108-05-4] (33). 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Methylmorpholine-4-oxide monohydrate [7529-22-8] M 135.2, m 71-73 . When dried for 2-3h at high vacuum it dehydrates. Add MeOH to the oxide and distil off the solvent under vacuum until the temp is ca 95°. Then add Me2CO at reflux then cool to 20°. The crystals are filtered off washed with Me2CO and dry. The degree of hydration may vary and may be important for the desired reactions, [van Rheenan et al. Tetrahedron Lett 1973 1076 Schneider and Hanze US Pat 2 769 823 see also Sharpless et al. Tetrahedron Lett 2503 / 976.1... 

In this case, the elements of the crosslinked structure exhibit higher mobility, the permeability of the crosslinked structure depends on the degree of hydration. It should be noted that the pore size in hydrated crosslinked copolymers is determined by small-angle X-ray scattering or with the aid of electron microscopy using special methods of preparation for the CP samples [15],... 

Uses. A Mn perchlorate (degree of hydration unspecified) has been patented as a burning rate accelerator for solid pro pints (Ref 4)... 

Ref 2). This was followed by Will in 1906 (Ref 3), Silberrad and Phillips in 1908 (Ref 4), and Kast in 1911 (Ref 5). More recently (1938), Hopper of PicArsn (Ref 6) detd and described the expl properties of the following metallic picrates Ai, Cd, Cr, Cu, Fe+3, Fe+2, Na, Ni and Zn. In general,he prepd the salts as cryst hydrates from aq solns by methods outlined by Silberrad Phillips, and Kast. These were then dehydrated by heating at temps of 80 to 150°, depending on the ease with which the w of crystn could be driven off, to obtain the desired degree of hydration... 

By using an alkali-metal hydroxide in situ as a proton acceptor, the alkali-metal dithiocarbamate salts, having various degrees of hydration, may be obtained (17). 

The two strands, in which opposing bases are held together by hydrogen bonds, wind around a central axis in the form of a double helix. Double-stranded DNA exists in at least six forms (A-E and Z). The B form is usually found under physiologic conditions (low salt, high degree of hydration). A single turn of B-DNA about the axis of the molecule contains ten base pairs. The distance spanned by one turn of B-DNA is 3.4 nm. The width (helical diameter) of the double helix in B-DNA is 2 nm. 

From the above, derives the fundamental concept that the newborn infant must be maintained in an adequate degree of hydration and in electrolyte balance in order for the infant to thrive. In some cases, where for one reason or other, the infant is not able to take fluids by mouth in the normal manner, one may need to resort to supplementary fluid therapy by vein. For a rational approach to this problem one needs to have available from the clinical chemical laboratory> rapid response in order to continuously monitor changes in electrolyte levels so that fluids can be modified so as to correct these abnormal-ities. 

The processes taking place on the positive electrode actually are more comph-cated. Several modifications of nickel oxides exist which in particular differ in their degrees of hydration, so the equations above do not correctly describe the water balance in the reaction. The hydroxide of divalent nickel is formed as p-Ni(OH)2 and... 

Permeability control of solutes through thermosensitive hydrogel membranes may be thought of in terms of the degree of hydration and kinetics of... 

The transport of many compounds takes place through interstices of polymer chains filled with aqueous medium [52], In such cases, the rate of mass transport is directly proportional to the degree of hydration of the membranes [53]. The most widely accepted method for determining the hydration of membranes is to equilibrate the membranes in water or buffer and weigh these membranes after blotting [54], In a newer method, the matrices to be studied are placed on a sintered glass funnel which is attached to a capillary filled with water. The absorption of water results in the movement of the capillary front [55],... 

Yasuda s free volume theory [57] has been proposed to explain the mechanism of permeation of solutes through hydrated homogeneous polymer membranes. The free volume theory relates the permeability coefficients in water-swollen homogeneous membranes to the degree of hydration and molecular size of the permeant by the following mathematical expression ... 

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