Water bound

The term bound water and equivalent terms, such as hydration shell, solvent shell, or hydration water, have been commonly used to refer to water affected by the protein surface, particularly in solution measurements. The point of the following discussion is that the bound water can be defined sufficiently precisely and independently of the type of measurement to make both the term and the concept useful. 

Consider again the heat capacity data of Fig. 38. The isotherm defines the phase diagram of a protein—water system. Below 0.38 h th re is a solution of water in protein—more accurately, water on the prote in. At 0.38 h there is phase separation, and at higher hydration levels the hydrated protein phase is constant in composition. This end point is well 

With this picture the terms hydration shell and bound water are understood to mean the water at the hydration end point. With this definition several questions should be addressed. 

Some apparent conflicts between the hydration dependence of dynamic properties and the time-average picture may be treated relatively simply, as noted above. There is additional discussion in Section III. 

Do some measurements detect the effects of hydration beyond the end point defined above The answer is, clearly, yes. Electrostatic interactions may be longer range. Hydration forces have been discussed. Measurements of this kind are treated by use of a different model, which may not include a distinct water monolayer at the protein surface. The point to be made, however, is that water beyond the monolayer is not strongly perturbed and differs substantially from water adjacent to the surface. 

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Goldanskii V I and Krupyanskii Y F 1989 Protein and protein-bound water dynamics studied by Rayleigh scattering of Mdssbauer radiation (RSMR) Q. Rev. Biophys. 22 39-92... 

Free Moisture. The free moisture of a filler is the water present on the surface of the particles. This weakly bound water can sometimes contribute to iaterparticle bonding (reinforcing) or filler—matrix iateraction, ie, biader adsorption or catalysis. A determination of free moisture is usually made by measuriag the percent loss on drying the sample at either 100 or 110°C. 

The mechanism of the tarmage is accepted to be largely one of replacement of the bound water molecules by the phenoHc groups of the tannin and subsequent formation of hydrogen bonds with the peptide bonds of the protein. The effect of this bonding is to make the leather almost completely biorefractive. 

Pure talc is thermally stable up to 930°C, and loses its crystalline bound water (4.8%) between 930 and 970°C, leaving an enstatite (dehydrated magnesium siUcate) residue. Most commercial talc products have thermal loss below 930°C on account of the presence of carbonates, which lose carbon dioxide at 600°C, and chlorite, which loses water at 800°C. Talc is an insulator for both heat and electricity. 

The actual amount and stmcture of this "bound" water has been the subject of debate (83), but the key factor is that in water, PVP and related polymers are water stmcture organi2ers, which is a lower entropy situation (84). Therefore, it is not unexpected that water would play a significant role in the homopolymeri2ation of VP, because the polymer and its reactive terminus are more rigidly constrained in this solvent and termination k is reduced... 

The combination of electrostatic interaction (induced dipole—dipole interaction) with an increase in entropy resulting from the discharge of bound water is fundamental to PVP s abiUty to complex with a variety of large anions. 

The resulting sludge contains less chemically bound water and can be more easily dewatered. 

Ion-Dipole Forces. Ion-dipole forces bring about solubihty resulting from the interaction of the dye ion with polar water molecules. The ions, in both dye and fiber, are therefore surrounded by bound water molecules that behave differently from the rest of the water molecules. If when the dye and fiber come together some of these bound water molecules are released, there is an increase in the entropy of the system. This lowers the free energy and chemical potential and thus acts as a driving force to dye absorption. 

Note that in Ref. 55 the "c values for the P-bound and N-bound water molecules were eiToneously interchanged. Source Ref. 55. 

Apart from the application of XPS in catalysis, the study of corrosion mechanisms and corrosion products is a major area of application. Special attention must be devoted to artifacts arising from X-ray irradiation. For example, reduction of metal oxides (e. g. CuO -> CU2O) can occur, loosely bound water or hydrates can be desorbed in the spectrometer vacuum, and hydroxides can decompose. Thorough investigations are supported by other surface-analytical and/or microscopic techniques, e.g. AFM, which is becoming increasingly important. 

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