Displacement, of water molecules

Figure 15 (a) Mean-square displacements of water molecules m three dimensions (see text for... 

The intermediate reaction complexes (after formation with rate constant, fc,), can undergo unimolecular dissociation ( , ) back to the original reactants, collisional stabilization (ks) via a third body, and intermolecular reaction (kT) to form stable products HC0j(H20)m with the concomitant displacement of water molecules. The experimentally measured rate constant, kexp, can be related to the rate constants of the elementary steps by the following equation, through the use of a steady-state approximation on 0H (H20)nC02 ... 

A hydrophobic bonding mechanism is the result of an overall entropy gain of the system due to the displacement of water molecules from the clay surface by sorbed organic compounds. The contributions of this mechanism will be more pronounced in the adsorption of high-molecular-weight organic matter (Parfitt and Greenland, 1970 Mortland, 1970). 

Displacement of water molecules by a coordinating anion is signalled by an increase in the emission intensity (as coordinated and closely diffusing OH and NH oscillators quench the 5D0 excited state of Eu) [23] as depicted in Figure 3. 

Kornienko et al. [32] have utilized wetproofed electrodes of acetylene black containing 40 wt.% PTFE to reduce CFC 113 to CTFE in 3 M LiCl at 35°C. The presence of tetraalkylammonium cations considerably facilitates the reduction process. It is assumed that CFC 113, like other halogenated compounds, forms a positively charged complex with the tetraalkylammonium cation, which is much more easily reduced than the CFC 113 itself. The largest effect was found for tetra-M-butylammonium ion (TBA+), giving a 96% yield of CTFE. The increase in CTFE current yield is explained by the shift of potential to less cathodic values and to the displacement of water molecules by organic cations in the layer next to the electrode because hydrogen evolution is slower. 

Other Vanadium(V) Compounds. When vanadates are strongly acidified, the a s-[V02(H20)4]+ ion is formed, and it can give complexes by displacement of water molecules, for example, [V02C14]3-, [V02(EDTA)]3, and [V02(ox)2]3-. The cis V02 arrangement is favored (as for other dP systems) because this allows better Op7T—> Mdn bonding than a linear arrangement would allow. 

The first systematic study of Zn shieldings by high-resolution pulse FT methods is that by Epperlein et al. (242) The non-linearity of the shift dependence on concentration for a variety of zinc salts is taken as evidence for complexation with the counter-ion through displacement of water molecules from the hexacoordinated hydration sphere. Generally the concentration shifts for the halides follow the order Cl > Br > I whereas nitrate, perchlorate, and sulphate do not show any concentration dependence. 

Further improvements are given by a high concentration of NaCl (possible reason displacement of water molecules needed for reaction (7) from the anodic reaction site). 

Metal ions dissolved in water are effectively complexed to water molecules. Displacing the set of water ligands, partially or entirely by another set in such aqua metal ions, results in forming what is more conventionally known as complexes. Displacement of water molecules by multidentate ligands results in more stable complexes than similar systems with none or fewer chelates. 

The binding of a ligand to a protein always leads to the displacement of water molecules. If the ligand can form more hydrogen bonds than the water molecule that are released, then a very tight binding can be achieved. 

Dehydration of lipids by heat drying and by osmotic stress promotes a shift of the P=0 frequency mode of vibration to higher values, denoting the displacement of water molecules (Table 34.1). 

Neutral molecules are also interesting as adsorbates, because they influence or participate in faradaic processes (2-, 6-8, 13, 16-19, 34). They can be detected and studied by the methods we have outlined above (see Problem 13.6). An interesting aspect of their behavior is that adsorption from aqueous solutions is often effective only at potentials relatively near the PZC. The usual rationale for this phenomenon rests on a recognition that adsorption of a neutral molecule requires the displacement of water molecules from the surface. When the interface is strongly polarized, the water is tightly bound and its displacement by a less dipolar substance is energetically unfavorable. Adsorption can take... 

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