Hydration thermodynamic parameters

T. Ooi, M. Oobatake, G. Nemethy and H. A. Scheraga, Accessible surface areas as a measure of the thermodynamic parameters of hydration of peptides, Proc. Natl. Acad. Sci. USA 84 3086 (1987). 

Often, it is difficult to distinguish definitely between inner sphere and outer sphere complexes in the same system. Based on the preceding discussion of the thermodynamic parameters, AH and AS values can be used, with cation, to obtain insight into the outer vs. inner sphere nature of metal complexes. For inner sphere complexation, the hydration sphere is disrupted more extensively and the net entropy and enthalpy changes are usually positive. In outer sphere complexes, the dehydration sphere is less disrupted. The net enthalpy and entropy changes are negative due to the complexation with its decrease in randomness without a compensatory disruption of the hydration spheres. 

From measurements of the temperature dependency of the equilibrium constant, thermodynamic parameters may be deduced (section 3.4). Very few enthalpy and entropy constants have been derived for the distribution reaction MAj(aq) MA2(org) of neutral complexes such investigations give information about hydration and organic phase solvation. 

The tonic compound caesium chloride, Cs + CI-, dissolves readily in water to give a solution containing the individually hydrated Cs+ (aq) and Cl-(aq) ions. The thermodynamic parameters for the formation reaction of Cs hCl and for the reaction of its solution in water are ... 

Table 2 Thermodynamic Parameters of Hydrated Lanthanide Ions191 192...

The base-catalysed ring fission of several substituted 2,2-dihydroxymdane-l,3-diones [(71) in Scheme 4, i.e. hydrates of the indanetrione system (70)] has been studied in aqueous dioxane.106 Rate constants, thermodynamic parameters, substituent, salt,... 

In Eq. 1.3, i A = -1 for any A and uB = +1 for any B. Since Eq. 1.3 is an overall reaction, the assumption of constant stoichiometry underlying the definition of is not trivial, as discussed in Section 1.1. For example, at high pH, Eq. 1.28 would not always be applicable because of the influence of the reactions in Eqs. 1.1 and 1.5. On the other hand, at equilibrium, when the hydration reaction is described by Eq. 1.10, the application of Eq. 1.28 is possible. This fact serves to emphasize the difference between equilibrium chemical species that figure in thermodynamic parameters (e.g., Eq. 1.11) and kinetic species that figure in the mechanism of a reaction. The set of kinetic species is in general larger than the set of equilibrium species for any overall chemical reaction. 

Here we compare the thermodynamic parameters of trehalose, maltose and sucrose because they have the same chemical formula (C12H22O11) and mass (molecular weight 342.3), but different structures which could be responsible for their different hydration properties. The anomaly of hydration of trehalose is understood from the following observation [10]. Namely, the amount of water used for the preparation of 1.5 M trehalose solution is smaller than the amount used for the preparation of other sugar solutions. In a 1.5 M solution, trehalose itself occupies 37.5% of the volume of the solution. However, in a 1.5 M solution, sucrose occupies 13% and maltose occupies 14%. These data suggest that trehalose has a larger hydrated volume than the other sugars. This hypothesis can be demonstrated from various thermodynamic parameters as shown in Table 12.1. 

Finally, it should be noted that the thermodynamic parameters of trehalose are not anomalous compared with those of lactose (Table 12.1). This means that the peculiarity of trehalose in hydration is not necessarily deduced from the macroscopic properties of the solution alone. 

Choppin [24] examined some aspects of lanthanide-organic ligand interaction in aqueous solutions. An interpretation of thermodynamic parameters (AG, AH and AS) of complexation have been given in terms of hydration, inner versus outer sphere character, stability vs. chelate ring size and ligand charge polarization. 

Hydration and conformation of protective polymers generally depend on the thermodynamic parameters. The thickness of an adsorbed layer of polymer has been studied using latex as the substrate. An apparent hydrodynamic thickness... 

While a temperature-dependent IR spectrum allows one to examine specific elements of a transition, a DSC thermogram enables the visualization of transitions in their entirety and the calculation of associated thermodynamic parameters. The IR and DSC thermal profiles for identically treated samples of hydrated porcine SC are shown in Fig. 3. The results of a series of thermograms for intact, delipidized, fractionated, and reheated SC as well as extracted lipids suggest that these three major transitions near 60,70, and 95°C in intact SC are due to intercellular lipid, a lipid-protein complex associated with the comeocyte membrane, and intracellular keratin, respectively. Evidence supporting these deductions is elegantly presented by Golden et al. [33]. More recently, the presence of a subzero lipid transition at -9°C has also been reported [34]. 

A DSC heating scan of a fully hydrated aqueous dispersion of dipalmitoylphosphatidylcholine (DPPC), which has been annealed at 0°C for 3.5 days, is displayed in Fig. 2. The sample exhibits three endothermic transitions, termed (in order of increasing temperature) the subtransition, pretransition, and main phase transition. The thermodynamic parameters associated with each of these lipid phase transitions are presented in Table 1. The presence of three discrete thermotropic phase transitions indicates that four different phases can exist in aimealed, fully hydrated bilayers of this phospholipid, depending on temperature and thermal history. All of these phases are lamellar or bilayer phases differing only in their degree of organization. 

Clearly, first and foremost, more data of higher quality are needed for the thermochemistry of nanoparticles and their composites. Measurements of surface enthalpies, hydration enthalpies, excess heat capacities, and other thermodynamic parameters on well defined chemical systems are needed. The question of apparenf versus true surface properties raised by Diakonov (1998b) needs to be resolved and consistent nomenclature adopted. Surface (solid/gas), interface (solid/solid) and wef (solid/water) parameters each need to be measured and systematized. 

In order to examine the effect of the Kihara parameters on the predicted hydrate equilibrium pressures, a sensitivity analysis was carried out (see also Cao et al. ). In this study we report results for methane (si hydrate former) and propane (sll hydrate former). The Kihara parameter values, as well as the thermodynamic property values, reported by Sloan were taken as the base-reference case and hydrate equilibrium pressures were calculated by perturbing the reference values in the range +(1%-10%). On the other hand, the reported thermodynamic parameters zl// and Ah have a wider range, but as it is going to be discussed later, have a less significant effect on the predictions. 

According to the Langmuir model (Eq.2) the adsorption capacity qm for Cd is 2.5 times grater than for Zn and adsorption capacity qm for Pb is 2 times grater than Zn when granular activated carbon is used. When natural zeolite is used as adsorbent, the adsorption capacity qm for Zn is 5 times lower than Cd and Pb. So, qm varied in the order Cd (II)> Pb(II) >Zn(II) for GAC, and Pb(II) = Cd(II)>Zn(II) for the natural zeolite as adsorbent. Ricordel et al (2001) and Tsoi and Zhao (2004) reported a similar relationship when different adsorbents were used. This can be explained on the basis of their ionic radii, hydration energy, ionic mobility and diffusion coefficient. The explanations of different authors were given on the basis of the surface covered by the adsorbed metal ions or on the basis of metal surface complexation constants and thermodynamic parameters values. 

For the purpose of the analysis of the energetics of protein unfolding, the temperature dependence of the thermodynamical parameters of the transfer to water of various low-molecular-weight compounds has been used to estimate hydration effects, applying the group additivity method in conjunction with the determination of water-accessible surface area changes upon unfolding of proteins of... 

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