Entropy selected ions

Table A5.3 presents standard heat capacities, entropies, enthalpies of formation, and Gibbs free energies of formation for selected ions at...

ENTROPY-DRIVEN SELECTIVE ION EXCHANGE FOR HYDROPHOBIC IONIZABLE ORGANIC COMPOUNDS (HIOCs)... 

These examples and some others that are given in Table III show that for selected ions, which form strong complexes, it is possible to make unambiguous structure determinations from solution diffraction data and to obtain direct information on coordination changes that take place during the stepwise formation of complexes. Thermodynamic data provide only indirect information on these structural changes, indicated, for example, by abnormal changes in enthalpy and entropy values or in stability constants for the formation of the complexes. 

The results obtained at 445 K and 525 K were recalculated to 298.15 K using the second and third laws and the heat capacities and entropies selected by this review. For the third law evaluation, relative ion intensities were taken from Figure 3 of the paper and combined with the total pressures reported by Niwa and Shibata [40NIW/SHI] for the lower and by Yamdagni and Porter [68YAM/POR] for the higher temperature range. A third law evaluation for Se2(g) and Seg(g) could not be made because of the lack of partial pressure data. 

Values of hydration entropies, AjjydS , can be derived by assigning (by convention) a value of zero for the absolute entropy, S°, of gaseous H ". Table 6.6 lists values of Ahyd-S for selected ions, and the corresponding values of... 

The thermodynamic analysis of the selectivity of ion exchange with the participation of ions of quaternary ammonium bases [56--58] has shown that an increase in bonding selectivity, when metal ions are replaced by organic ions, which is usually accompanied by an increase in entropy of the system (Table 5). It follows from Table 5 that a drastic increase in bonding selectivity upon passing to a triethylbenzylammonium counterion (the most complex ion) is due to a considerable increase in the entropy of the system. 

The thermodynamic analysis of these systems played an important role in the interpretation of these data and of the high selectivity. It was found that selective sorption of complex organic ions is accompanied by an increase in the entropy of the system (Table 6). 

A comparison of the effects of increasing selectivity of sorption of organic counterions and the entropy control of the replacement of small ions by large organic ions in CP is a rational explanation of these phenomena. 

This pardaxin model is not unique. We have developed several similar models that are equally good energetically and equally consistent with present experimental results. It is difficult to select among these models because the helices can be packed a number of ways and the C-terminus appears very flexible. Our energy calculations are far from definitive because they do not include lipid, water, ions, membrane voltage, or entropy and because every conformational possibility has not been explored. The model presented here is intended to illustrate the general folding pattern of a family of pardaxin models in which the monomers are antiparallel and to demonstrate that these models are feasible. 

Yeager suggests that the major factor involved in the ion exchange selectivity of Nafion is the positive entropy change associated with the replacement of H+ with the metal ion, which is accompanied by water release and polymer contraction. 

In this section the standard molar entropies of a small selection of cations and anions are tabulated and the manner of their derivation discussed. The values themselves are required in the calculation of entropies of hydration of ions, discussed in Section 2.7.2. 

AS = 13 e.u. for the Cu-template resin, and AH = -0.8, AS = 9,8 (K - 540) for the resin synthesized without any template ion. The larger change in entropy observed in the complexation of the Cu-template resin indicated that die Cu-template resin selectively adsorbed Cu ions by entropic effect. Furthermore, the absorption spectrum of the Cu complex of the Cu template resin was located at a wavelength 10—20 nm shorter than those of the other resins70 and the ESR parameters of the Cu complex of the Cu-template resin were similar to those of the non-distorted planar Cu complex71. From these results, it was suggested that the conformation of the polymer-ligand chain in the Cu template resin remained the best one for the Cu ion. 

Figure 4.4. Driving forces in ion diffusion across selectively permeable membranes, a Entropy promotes diffusion down a con-centrationgradient,regardlessof charge, b Electroneutrality will oppose entropy, c The Nemst equation describes the membrane potential that ensues when entropy and electroneutrality are in equilibrium.

Sorption of Cu(tfac)2 on a column depends on the amount of the compound injected, the content of the liquid phase in the bed, the nature of the support and temperature. Substantial sorption of Cu(tfac)2 by glass tubing and glass-wool plugs was observed. It was also shown that sorption of the copper chelate by the bed is partialy reversible . The retention data for Cr(dik)3, Co(dik)3 and Al(dik)3 complexes were measured at various temperatures and various flow rates. The results enable one to select conditions for the GC separation of Cr, Al and Co S-diketonates. Retention of tfac and hfac of various metals on various supports were also studied and were widely used for the determination of the metals. Both adsorption and partition coefficients were found to be functions of the average thickness of the film of the stationary phase . Specific retention volumes, adsorption isotherms, molar heats and entropy of solution were determined from the GC data . The retention of metal chelates on various stationary phases is mainly due to adsorption at the gas-liquid interface. However, the classical equation which describes the retention when mixed mechanisms occur is inappropriate to represent the behavior of such systems. This failure occurs because both adsorption and partition coefficients are functions of the average thickness of the film of the stationary phase. It was pointed out that the main problem is lack of stability under GC conditions. Dissociation of the chelates results in a smaller peak and a build-up of reactive metal ions. An improvement of the method could be achieved by addition of tfaH to the carrier gas of the GC equipped with aTCD" orFID" . ... 

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