Diffraction profile water

Bredehoeft JD, Papadopulos IS (1965) Rates of vertical groundwater movement estimated from the earth s thermal profile. Water Resources Research I(2) 325-328 Brown G, Brindley GW (1980) X-ray diffraction procedures for clay minerals identification. In Brindley GW, Brown G (eds) Crystal structures of clay minerals and their X-ray identification. Mineralogi-cal Society, London, pp 305-360... 

Fig. 9 X -ray powder diffraction profiles of Ireslily prepared PVA cryogels (samples GEL-n) obtained by different numbers n of freeze-thaw cycles (solid lines). The X-ray diffraction profile of liquid water is also shown (dashed lines). The 101 and 101 reflections of PVA crystals in the monoclinic form, in the 29 range 18-21°, are shown in gray. In the case of GEL-1, the crystalline reflections are evidenced in the inset at an enlarged scale. (Reproduced with permission from [42]. Copyright 2(X)4 by the American Chemical Society)...

The exact dimensions of a phospholipid bilayer membrane in terms of the in-plane area and the height of the lipid molecules as well as the thickness of the water layer that is associated with them is dependent on the chemical identity of the phospholipid head group, the length and the degree of saturation of the acyl chains, and the degree of hydration. This information may be obtained from a combination of small-angle X-ray diffraction by MLV or oriented multi-bilayer samples of phospholipids in excess water, electron and/or neutron density profiles across lipid bilayers, and atomic level molecular dynamics simulations of hydrated lipid bilayers. H-NMR studies on selectively deuter-ated phospholipids have also been important in elucidating acyl... 

To determine the shape of the hydrophobic barrier of bilayer membranes, fatty acids and PC molecules spin labeled with nitroxides at various positions along the lipid chains were diffused into vesicles and their solvent-sensitive isotropic coupling constants were measured [54]. Results are plotted in Figure 5 in terms of distance of the probe from the bilayer center. Also shown is the profile of the dielectric constant along the membrane normal evaluated from the fluorescence lifetime distribution of fluorescence probes in PC liposomes [55]. These data correlate well with results from neutron diffraction studies that map the positional distribution of water and lipid moieties along the bilayer normal [56]. 

Figure 4 Pore-water profiles showing coupled removal of dissolved phosphate and fluoride from pore waters with depth in sediments, suggesting active growth of CFA in these Baja California sediments. Stippled bands indicate position and width of discrete phosphorite layers, as detected visually and confirmed by X-ray diffraction. Downward extent of concentration gradients indicates that CFA can precipitate simultaneously in two or more phosphorite layers...

Non-specific hydration, or hydration of the lattice without a first-order phase transition, also must be considered. Cox, Woodard, and McCrone reported the moisture uptake profile of cromolyn sodium, and the related effects on the physical properties of this substance. Although up to nine molecules of water per molecule of cromolyn sodium are sorbed into the crystalline lattice at 90 /o relative humidity, the sorption profile does not show any sharp plateaus corresponding to fixed hydrates. Rather, the uptake profile exhibits a gradual increase in moisture content as relative humidity increases, which results in marked changes in X-ray diffraction patterns, density, and other physical properties. For this example, moisture uptake onto cromolyn sodium was correlated with expansion of the lattice in the b crystallographic direction, which was shown to be reversible on dehydration. 

Figure 8.5 The densitometered profiles from the monochromatic diffraction patterns recorded from (a) a glass mounting tube, (b) a mounting tube filled with double distilled water, (c) a mounting tube filled with double distilled water ethanol mixture (60 40v/v). From Glover et al (1991) with permission.

Figure 8.6 (a) Densitometered profiles from the recorded, monochromatic diffraction patterns of (i) RNAse and (ii) Yu crystallin showing the overall envelope of the observed diffuse scattering intensity (/) recorded parallel (full line) and perpendicular (chain line) to the crystal mounting axis. The scattering from water (dotted line) is plotted for comparison. 

The thermograms of DTA and TG of the precursors showed different profiles, depending on the method used to prepare the solids. The precursors of the LFA and ALF samples showed an exothermic peak at 240 and 250 °C, assigned to the hematite production [7]. On the other hand, the LFAW sample displayed no exothermic peak, indicating that no crystalline hematite was produced. We can thus conclude that when lanthanum and iron nitrate are added to the ammonium solution (LFA), and vice-versa (ALF), lanthanum favors hematite production. However, when the reactants are added to water (LFAW), the formation of hematite is delayed, in accordance with the X-ray diffraction results. In all cases, there is a large endothermic peak bellow 100 C, due to the loss of physically adsorbed volatiles in the solids, in agreement with TG curves. 

---