Hydration phenomena

Bashin A A 1990. Hydration Phenomena, Classical Electrostatics, and the Boundary Element Methoc Journal of Physical Chemistry 94 1725-1733. 

A number of workers have observed that the strength of binding of monovalent counterions depends on ionic radius. However, the effect of ionic radius is somewhat obscure as it depends on hydration phenomena and whether the size of the bare ion or that of the hydrated ion is the significant parameter (Wilson Crisp, 1977). 

The recent theoretical approach based on the information theory (IT) in studying aqueous solutions and hydration phenomena [62 66] shows such a direction. IT is a part of the system based on a probabilistic way of thinking about communication, introduced in 1948 by Sharmon and subsequently developed [114]. It consists in the quantitative description of the information by defining entropy as a function of probability... 

Chapter 3 presents the fundamentals of the time-dependent hydrate phenomena of nucleation, growth, and decomposition. These fundamentals are presented with an objective of understanding how hydrate formation and decomposition occur, such that this knowledge may be applied to a range of hydrate applications, such as flow assurance, storage, separation, or gas production from hydrate reservoirs. 

The most challenging and intriguing questions regarding hydrates concern how hydrates form, dissociate, and are inhibited with time. The previous chapter provides the foundation required to understand these time-dependent processes. Time-dependent hydrate phenomena are substantially more challenging than time-independent phenomena of structure and thermodynamics. One can expect a decrease in accuracy of time-dependent measurements and models by at least one order of magnitude relative to their thermodynamic counterparts, as found in Chapters 4 through 6. 

For example, at 278.2 K, hydrates form at a pressure of approximately 5 bar and dissociate upon pressurization at approximately 600 bar. A more detailed explanation of the pseudo-retrograde hydrate phenomena can be found in the binary hydrates section which follows. Note that the hydrate formation pressure of propane hydrates along the Aq-sII-V line at 277.6 K is predicted to be 4.3 bar. 

In summary, the MD, MC, and LD (lattice dynamic) techniques are very powerful tools to investigate hydrate phenomena. Indeed, hydrate computer simulations may shortly outnumber hydrate experimental observations, because simulations are generally more accessible than experiments. However, such tools investigate phenomena which are on much smaller time and space dimensions than normally observed, outside of spectroscopy. Even with spectroscopy, the relevant peaks may be subject to some interpretation. As a result there may be several microscopic interpretations (based upon hundreds to thousands of molecules) of macroscopic phenomena which involve typically 1023 molecules. Such a scale-up may cause misinterpretation. 

Sucrose, like other simple carbohydrates, is used as additive in mineral suspensions, concrete, and ceramics. The hygroscopic character of the carbohydrates and their ability to interact with colloidal inorganic particles and ions modifies the hydration phenomena within the suspensions, and consequently on the rheology of the medium and the kinetics (most often slowing down) of the... 

In order to characterize the hydration phenomena in more detail, it is worthwhile to obtain information on the dynamics of water molecules involved in the hydration shell. One of the useful techniques for such a purpose is 170-NMR spectroscopy. In the so-called two-state model, 170 nuclei in the aqueous solution are assumed to be distributed between the following two motional states the water in the hydration shell and the bulk water. Under this assumption, the analysis of concentration-dependent changes of the spin-lattice relaxation time of 170 nucleus gives the following important parameter known as the dynamic hydration number [17] ... 

A. A. Rashin, Int. J. Quantum Chem., Quantum Biol. Symp., 15, 103 (1988). Continuum Electrostatics and Hydration Phenomena. 

AIMD simulations appear as a promising tool for a first-principles modeling of enzymes. Indeed, they enable in situ simulations of chemical reactions furthermore, they are capable of tEiking crucial thermal effects [53] into account finally, they automatically include many of the physical effects so difficult to model in force-field based simulations, such as polarization effects, many-body forces, resonance stabilization of aromatic rings and hydration phenomena. 

The use of experimental solubility data to analyze hydration phenomena... 

Rashin, A. A. (1990). Hydration phenomena, classical electrostatics and the boundary element method. J. Phys. Chem. 94 725-733. 

NMR signal along with the NIR spectra to investigate sugar solutions. By using outer product analysis (OPA), correlations between the NMR and NIR signals could be discerned, and provided insight into the hydration phenomena. This unique combination of spectral data should prove to be another fruitful area of future research. 

Peschel, G., and Ludwig, P., Cation exchange on oxide surfaces as influenced by surface hydration phenomena. 1. Alkali metal ions on silica, Ber. Bunsenges. Phys. Chem., 91, 536, 1987. 

Another polysaccharide which displays interesting hydration phenomena is (l->-3 )-B-D-g 1 ucan, often called paramylon ( ), curdlan ( ) or laminaran (16). The molecular crystalline arrangement o P this polysaccharide consists of a triple helix formed by three intertwining 6j hel ices. (, 23) Two polymorphs... 

Given the scope of this review, we desist from a detailed discussion of the energetics and vibrational spectra of the solvated aqueous clusters. However, the study of solvation phenomena can be extended to the hydration phenomena of biologically important chemical systems using Monte Carlo and molecular dynamics simulations [85-94]. More information on aqueous clusters can be obtained from our extensive work on these systems cited above. 

The behaviour of the lower alcohols in aqueous solution merits a special comment. Despite their apparent complete miscibility with one another and with water, the alcohols display an extremely complex series of eutectic, peritectic and hydration phenomena, which have usually been hidden from earlier observers because they appear at low temperatures. As one example, consider the mixture water-tert-butanol shown in Figure 17. A stable hydrate of composition A-2H20 and lA = 0.55°C is clearly shown, and there are also indications of several peritectic transitions and metastable hydrates. Similar complexities have been described for aqueous solutions of methanol, ethanol and propanol. ... 

In our recent study [59], we have utilized NMR spectroscopy at 400 MHz to study the selective hydration phenomena for typical univalent anions (X = Cl , Br , I , NO, CIO4, and SCN ) in deuterated nitrobenzene (NB-ds). For the respective anions, dependences of the chemical shift of water on water and ion concentrations have been examined. We have found that the selective hydration of these anions can be explained in terms of the successive reaction mechanim [e.g., Br Br (H20) Br (H20)2 Br (H20)3 Br (H20)4]. In addition, measurements of spin-lattice relaxation times have shown that the rate of rotational diffusion of water molecules is considerably slowed by the hydration of the ions. The results are summarized below. 

Hydration phenomena of ions in organic solvents and their roles in interfacial ion-transfer processes have been extensively discussed for many years.. As discussed in this chapter, a marked development in this field may be recognized, at least from a thermodynamic viewpoint. However, no detailed molecular pictures of hydrated ions in organic solvent have been provided yet. Further experimental and theoretical approaches seem to be required. Vibrational spectroscopic and molecular dynamics simulation studies on solvation of ions in the gas phase [70,71] would shed light on the microscopic structure and dynamics of hydrated ions in organic solvents. 

The property of dried citrus pulp to be "wet" by oils has been described by Kesterson and Braddock (8). Washed orange pulp solids normally contain 0.5-1.5% ether extractible lipids. Also present is cuticular wax which gives lipophilic character to the pulp solids (9). Both the water holding capacity (WHO) which encompasses sorption and hydration phenomena, and oil holding capacity (OHC) which can be described in terms of adsorption and capillary entrapment of... 

Additional questions are raised when the moving ion is immersed in water instead of a simple dipolar liquid discussed in Sec. 5.4.The hydration phenomena observed by many different experiments show a remarkable variety in its dependence on size and sign of ions, which may not be characterized by a simple chemical model such as ion-water complex formation, or a solventberg model. Such a model seems to apply to very small monovalent ions like Li+ and F and multi-valent ions which make a stable hydration shell with substantial lifetime. However, water molecules in the first hydration shell around ions with greater size are more mobile and disordered than those in bulk water. The behavior which has been referred to as structure breaking by Frank and Wen [85] and as negative hydration by Samoilov [86] is due to the competition between two forces acting on water molecules in the shell, the... 

Maisano, G., D. Majolino, P. Migliardo, S. Vraiuto, F. Ahotta, and S. Magazu. 1993. Sound velocity and hydration phenomena in aqueous polymeric solutions. Mol. Phys. 78 421-435. 

A. A. Rashin,/. Phys. Chem., 94,1725 (1990). Hydration Phenomena, Qassical Flectrosta-tics, and Boundary Element Method. 

The image revealed the 3D distribution of a hydration layer and adsorbed water molecules. Such direct information on the water distribution has not been available with other methods and hence invaluable in the studies on hydration phenomena. Therefore, the author expects that such a 3D force imaging technique should become a powerful tool in the various research fields related to the solid-liquid interface. 

The partition of DPPC and hydrated water moiecuies into QM and MM regions (Reprinted from Journai of Coiioid and Interface Science, 329, Yin J and Zhao YP, Hybrid QM/MM simuiation of the hydration phenomena of dipaimitoyiphosphatidyichoiine headgroup, 410-415, Copyright (2009), with permission from Eisevier)... 

Yin J, Zhao YP (2009) Hybrid QM/MM simulation of the hydration phenomena of dipalmitoylphosphati-dylcholine headgroup. J CoUoid Interface Sci 329... 

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