Hydration diffraction

KEY TERMS amorphous crystalline diffraction hydrate solid emulsion... 

Naphthoic acid, 3-hydroxy-7-sulfonato-metal complexes structure, 482 1,8-Naphthyridine metal complexes, 92,93 Neoeupferron metd complexes, 509-512 Neptunium complexes cupferron, 510 Neutron diffraction hydrates... 

In general, anions are less strongly hydrated than cations, but recent neutron diffraction data have indicated that even around the halide ions there is a well defined primary hydration shell of water molecules, which, in... 

Structural investigations of metal-ion hydration have been carried out by spectroscopic, scadering and diffraction teclmiques, but these teclmiques do not always give identical results since they measure in different timescales. There are tliree distinct types of measurement ... 

The mineralogical, structural, physical, and thermodynamic properties of the various crystalline alumiaa hydrates are Hsted ia Tables 1, 2, and 3, respectively. X-ray diffraction methods are commonly used to differentiate between materials. Density, refractive iadex, tga, and dta measurements may also be used. 

Amorphous silica, ie, silicon dioxide [7631-86-9] Si02, does not have a crystalline stmcture as defined by x-ray diffraction measurements. Amorphous silica, which can be naturally occurring or synthetic, can be either surface-hydrated or anhydrous. Synthetic amorphous silica can be broadly divided into two categories of stable materials (1) vitreous silica or glass (qv), which is made by fusing quart2 at temperatures greater than approximately 1700°C (see Silica, vitreous silica), and microamorphous silica, which is discussed herein. 

These hydrated salts contain bidentate carbonate ligands and no water molecules are bound directly to the central metal atom. The only single-crystal x-ray diffraction studies available are those for salts of (4) (52—54) and the mineral tuliokite [128706 2-3], Na2BaTh(C03)2 -6H20], which contains the unusual Th(C02) 2 anion (5) (55). 

Bleaching Powder. This material, known siace 1798, is made by chlorination of slightly moist hydrated lime, calcium hydroxide [1305-62-0] Ca(OH)2- It has the empirical formula Ca(OCl)2 CaCl2 Ca(OH)2 2H20. Its compositioa, loag a subject of coatroversy, was estabHshed by phase studies, microscopy, and x-ray diffraction techniques (241). The initial chlorination products are monobasic calcium chloride [14031-38-4] and dibasic calcium hypochlorite [12394-14-8] ... 

X-ray diffraction patterns yield typical 1.2—1.4 nm basal spacings for smectite partially hydrated in an ordinary laboratory atmosphere. Solvating smectite in ethylene glycol expands the spacing to 1.7 nm, and beating to 550°C collapses it to 1.0 nm. Certain micaceous clay minerals from which part of the metallic interlayer cations of the smectites has been stripped or degraded, and replaced by expand similarly. Treatment with strong solutions of... 

The hydrated alumina minerals usually occur in ooUtic stmctures (small spherical to eUipsoidal bodies the size of BB shot, about 2 mm in diameter) and also in larger and smaller stmctures. They impart harshness and resist fusion or fuse with difficulty in sodium carbonate, and may be suspected if the raw clay analyzes at more than 40% AI2O2. Optical properties are radically different from those of common clay minerals, and x-ray diffraction patterns and differential thermal analysis curves are distinctive. 

Table 1 Comparison of MD and X-Ray Diffraction Results for Structural Parameters of Fully Hydrated DPPC Bilayers...

Early diffraction photographs of such DNA fibers taken by Rosalind Franklin and Maurice Wilkins in London and interpreted by James Watson and Francis Crick in Cambridge revealed two types of DNA structures A-DNA and B-DNA. The B-DNA form is obtained when DNA is fully hydrated as it is in vivo. A-DNA is obtained under dehydrated nonphysiological conditions. Improvements in the methods for the chemical synthesis of DNA have recently made it possible to study crystals of short DNA molecules of any selected sequence. These studies have essentially confirmed the refined fiber diffraction models for A- and B-DNA and in addition have given details of small structural variations for different DNA sequences. Furthermore, a new structural form of DNA, called Z-DNA, has been discovered. 

Pure HCIO4 is a colourless mobile, shock-sensitive, liquid d(25°) 1.761 gem" . At least 6 hydrates are known (Table 17.23). The structure of HCIO4. as determined by electron diffraction in the gas phase, is as shown in Pig, 17,20. This... 

Cationic quaternary ammonium compounds such as distearyldimethylammonium-chloride (DSDMAC) used as a softener and as an antistatic, form hydrated particles in a dispersed phase having a similar structure to that of the multilayered liposomes or vesicles of phospholipids 77,79). This liposome-like structure could be made visible by electron microscopy using the freeze-fracture replica technique as shown by Okumura et al. 79). The concentric circles observed should be bimolecular lamellar layers with the sandwiched parts being the entrapped water. In addition, the longest spacings of the small angle X-ray diffraction pattern can be attributed to the inter-lamellar distances. These liposome structures are formed by the hydrated detergent not only in the gel state but also at relatively low concentrations. 

Protein crystals contain between 25 and 65 vol% water, which is essential for the crystallisation of these biopolymers. A typical value for the water content of protein crystals is 45% according to Matthews et al. l49,150). For this reason it is possible to study the arrangement of water molecules in the hydration-shell by protein-water and water-water interactions near the protein surface, if one can solve the structure of the crystal by X-ray or neutron diffraction to a sufficiently high resolution151 -153). 

The mechanism responsible for the formation of gas hydrates became clear when von Stackelberg and his school 42 49 in Bonn succeeded in determining the x-ray diffraction patterns of a number of gas hydrates and Claussen6 helped to formulate structural arrays fitting these patterns. Almost simultaneously Pauling and Marsh26 determined the crystal structure of chlorine hydrate. 

Hydrazine Salt. Fine yellow crysts, mp 123° with decompn (Ref 25). It is prepd by the addn of hydrazine hydrate to TNMe in w (Ref 25), or by the addn of anhyd hydrazine to TNMe in iso-Pr ale (Ref 48). The cryst structure and X-ray diffraction pattern of the pure salt are given in Ref 45. Impact sensy (2.5kg wt), the 50% expln height was found to be 10cm (Ref 25). It is stable to 100° (Ref 48). It is claimed as an ingredient in a thixotropic propint formulation (Ref 41)... 

The diffraction pattern of the sample of chlorine hydrate consisted of powder lines on which were superimposed a large number of more intense single-crystal reflections for some planes only the latter were visible. The intensities of the lines were estimated by comparison with a previously calibrated powder photograph, and were averaged for several films pre-... 

Many ionic compounds contain what used to be referred to as water of crystallization . For example, magnesium chloride can exist as a fully hydrated salt which was formerly written MgCla.bHjO, but is more appropriately written Mg(OH2)eCl2, since the water molecules occupy coordination sites around the magnesium ions. This is typical. In most compounds that contain water of crystallization, the water molecules are bound to the cation in an aquo complex in the manner originally proposed by Alfred Werner (1866-1919) in 1893 (Kauffman, 1981). Such an arrangement has been confirmed in numerous cases by X-ray diffraction techniques. 

These special features are explained by an interaction between the proton and one of the water molecules, which is not merely electrostatic but also covalent. This yields a new chemical species, the hydroxonium ion, HjO. The existence of such ions was demonstrated in the gas phase by mass spectrometry and in the solid phase by X-ray diffraction and nuclear magnetic resonance. The H -H20 bond has an energy of 712kJ/mol, which is almost two-thirds of the total proton hydration energy. 

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