Hydration powders

Fig. 9. Scanning electron micrograph of hydrated Powder River Basin high-Ca fly ash. The phases identified by XRD included ettringite (bumps on surface), monosulphate, and stratlingite (the latter are both platy).

Savolainen et al. investigated the role of Raman spectroscopy for monitoring amorphous content and compared the performance with that of NIR spectroscopy [41], Partial least squares (PLS) models in combination with several data pre-processing methods were employed. The prediction error for an independent test set was in the range of 2-3% for both NIR and Raman spectroscopy for amorphous and crystalline a-lactose monohydrate. The authors concluded that both techniques are useful for quantifying amorphous content however, the performance depends on process unit operation. Rantanen et al. performed a similar study of anhydrate/hydrate powder mixtures of nitrofurantoin, theophyllin, caffeine and carbamazepine [42], They found that both NIR and Raman performed well and that multivariate evaluation not always improves the evaluation in the case of Raman data. Santesson et al. demonstrated in situ Raman monitoring of crystallisation in acoustically levitated nanolitre drops [43]. Indomethazine and benzamide were used as model... 

Fig. 59.—Anti-firming effect of the monoglyceride preparations in white bread. Diglyceryl octadecanoate (DGMS) at pH 6.8 (open points), at pH 7.3 (solid points) DGMS hydrate (solid squares) DGMS hydrate powder (open squares) DGMS powder (solid triangles) mono- and diglyceride emulsion (open triangles) control (crosses). (Reprinted with permission from N. Krog and B. N. Jensen, J. Food Technol., 5 (1970) 77-87.)...

Ruggiero et al. (1986) measured the ESR spectra of samples of lysozyme, myoglobin, and hemoglobin with covalently bound spin labels and noncovalently bound spin probes, in solution and in the partially hydrated powder, over the temperature range 120—260 K. The several proteins behaved similarly. The solution samples differed from the powders in showing a change in spectrum shape at 210 K, understood to represent freezing of water in the hydration shell. 

The activities of several enzymes have been studied in partially hydrated powders as a funcuon of water activity or water content. Experiments of this type are not difficult to perform. Solutions of substrate and enzyme are mixed quickly, and the mixture is immediately frozen and lyophilized, which stops the reaction and gives a stable dry powder. If appropriately high concentrations of enzyme and substrate are mixed, the powder is of the enzyme-substrate complex. The sample is rehydrated under a controlled atmosphere to give the desired final hydration level. Conditions, particularly the pH of the sample, are set such that the hydration equilibrium is substantially complete (within several hours) before appreciable enzyme reaction has taken place. The problem of defining pH in partially hydrated powders was discussed in Section II,D in connection with hydrogen-exchange measurements. The pH of a powder appears to equal the nominal pH (that of the solution from which the powder was lyophilized) above about 0.15 A. 

In solution the hexasaccharide is cleaved by lysozyme relatively cleanly to tetramer and dimer. This is true also in the hydrated powder, at hydrations below 40 wt% water. Between 40 wt% water and the dilute solution the pattern undergoes changes, reflecting the contribution of transfer reactions. The reaction rate at full hydration in the powder (i.e., 0.38 h) is about 10% of the solution rate. 

The dependence of protein and solvent dynamics on hydration fits well into the above three-stage picture for some, but not all, properties. For dynamic properties that do not fit well, analysis on a case-by-case basis within the framework of the time-average picture can be informative. For example, consider protonic conduction, measured by the megahertz frequency dielectric response for partially hydrated powders of lysozyme. The capacitance grows explosively above a hydration level of 0.15 A, in a way characteristic of a phase transition (Section HI, A). The hydration dependence of thermodynamic properties shows, however. 

Packer, A., and H.S. Dhillon. 1968. Reactions of aluminum hydrate powders with aqueous sodium hydroxide solutions. Chem. Ind. (London) 1968 1806-1807. 

Relaxation Measurements. NMR measurements have been used to examine water-protein interactions in solution and in hydrated powders (2). Hilton et al (24) have shown that the motional properties of water in partially hydrated powders of lysozyme are best characterized as those of a viscous liquid. Dielectric relaxation spectra of water in lysozyme powders (28) distinguish... 

Electron Spin Resonance. ESR spectra (Figure 4) were measured for partially hydrated powders of lysozyme containing a nltroxlde spin probe, TEMPONE. Figure 5 shows the change with hydration level of a parameter which characterizes the relative amplitudes of various spectral lines. 

Hydrate, powder. Practically insol in water, ale sol in mineral acids. 

We will illustrate the coupling of protein and water dynamics using results of MD simulations of several systems, including native and MG states of human a-lactalbumin (HaLA) in aqueous solution [5], ribonuclease A (RNase) in dry and hydrated powders and glycerol solution [6,7], maltose-binding protein (MBP) in a hydrated powder [8], and bacteriorhodopsin (BR) in purple membrane (PM) stacks [9,10]. Our choice of specific systems has generally been made based on the availability of experimental data to which the simulation results can be closely compared. We have accordingly set up the systems so that the simulations are very similar to the experiments, both in terms of sample composition and thermodynamic state points (i.e., temperature and pressure). 

Molecular Dynamics Simulations of Ribonuclease A in Dry AND Hydrated Powders and Glycerol Solution... 

Molecular Dynamics Simulations of Maltose-Binding Protein in a Hydrated Powder... 

A model for a hydrated powder of MBP was constructed based on a crystal structure (PDB entry 1JW4 [20]). The model contained four protein molecules generated from four unit cells (a 2a x 2b x c lattice) of the triclinic crystal with the water molecules removed. A large box of water molecules was overlaid on the protein supercell, and all but the 3460 water molecules that were closest to the protein molecules were removed to give h = 0.43, corresponding to samples used in neutron scattering experiments carried out in conjunction with the simulations [8]. A constant pressure and temperature MD simulation at 1 atm and 300 K was used to allow the cell to collapse and anneal the protein-protein and protein-water contacts. A series of production runs were performed at constant pressure over a range of temperature. 

FIGU RE 16.6 Temperature dependence of protein and water dynamical properties from MD simulations of a hydrated powder of MBP [8]. (a) MSFs of protein nonexchangeable H atoms averaged over 1 ns blocks of the trajectories, (b) Temperature dependence of the inverse of the correlation times, of the protein-water hydrogen bond correlation functions [73]. (c) Value of... 

FIGURE 1.52 (a) Scheme of silica nanoparticle location in the suspension and the hydrated powder of nanosilica OX-50 and (h) size distrihutions of clusters and domains of hound water. 

Thus, the difference in the hydration characteristics of silica OX-50 in the aqueous suspension and hydrated powder in different media depends on the particle-particle interactions (distances between particles) and the textural porosity in the powders. Nonpolar (methane) or weakly polar (chloroform) coadsorbates can reduce interaction of water with the silica surface because water-water and water-silica interactions are much stronger than that of water-organics. Therefore, rearrangement of the system organization leads to an increase in the size of water domains with parallel diminution of the contact area between water-organics and water-silica but with increasing silica-organics contact area. 

Characteristics of Bound Water in Hydrated Powders of Nanosilica A-380 with the Presence of Organic Solvents... 

FIGURE 1.54 Relationships between content of unfrozen water and changes in the Gibbs free energy of unfrozen water in differently hydrated powders of nanosilica A-380 at /i = (a) 1, (b) 0.5, (c) 0.15, (d) 0.08, and (c) 0.07 g/g and different amounts of organic solvents. 

To prepare hydrated powders, certain amounts of distilled water and DCl (or HCl) were added to air-dry silica samples. Before the measurements, samples (placed in closed NMR ampoules)... 

Concentrated aqueous suspension. Other samples are weakly hydrated powders. 

The NMR spectra of hydrated powders of SM4-SM6 (in chloroform) are shown at different temperatures (Figure 1.141). For SM1-SM3 (which are not shown in Figure 1.141), the 5h(T) graphs are akin to that for SM4. Since chloroform is a poor proton donor, its molecules are not capable to compete with water molecules on interaction with residual silanols on modified samples to form complexes =SiO(H)---H-X. Therefore, one can assume that chloroform weakly affects the structure of water clusters adsorbed on the hydrophilic surfaces. 

FIGURE 1.148 Dependence of interfacial free energy on concentration of chloroform-Colloid Interface Sci., 118, Gun ko, V.M., Turov, V.V., Bogatyrev, V.M. et al.. Unusual properties of water at hydrophilic/hydrophobic interfaces, 125-172, 2005a. Copyright 2005, with permission from Elsevier.)... 

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