Solubility prediction thermodynamic cycle

One of the popular methods for prediction of solubility from this thermodynamic cycle is the general solubility equation (GSE) [32, 33], which relates log5 to melting point TJ and the logarithm of the octanol-water partition coefficient (logP). 

Although it is not strictly a molecular simulation method, we mention the GSE here since it can be derived from the thermodynamic cycle of crystal to supercooled liquid to solution provided that some assumptions are made about the entropy of melting, AS. The GSE provides useful estimates of solubihty when experimental melting point and AS data are available [34], However, the GSE is not usually applicable to unsynthesized molecules as the best empirical methods for predicting melting point give predictive errors of 40-50°C [35, 36], The GSE has provided the basis of empirical methods to predict solubility such as the Solubihty Forecast Index [37]. 

The thermodynamic cycle for transfer from aystal to vapor to solntion (Fig. 11.2) provides a convenient method to compute solubility since both of the related thermodynamic parameters (sublimation and hydration free energy) are accessible by both experiment and computation. Perlovich et al. have published a series of papers that investigate the thermodynamic properties of a wide variety of structurally diverse drugs, by both experiment and computation, but they have not provided any molecular simulation methods for the prediction of solubility from structure alone without empirical parameterization [42,43]. 

With Ag2S based membranes thermodynamics predict extremely low detection limits down to 10 M or so, see Fig. 9.16. This can be achieved in sulfide solutions at elevated pH where the dissolved silver is extremely small. Note that this is in essence a thermodynamic cycle and one can equally state that the electrode is responsive to the abundant sulfide ion (the silver activity is calculated from the sulfide concentration and the known solubility pn)duct). However, if no such ion buffer is present and one aims to measure low total concentrations, one often finds the behavior shown in Fig. 9.17, which has been attributed to the presence of... 

The initiation of the cationic polymerisation of alkenes is examined in detail by means of simple thermodynamic concepts. From a consideration of the kinetic requirements it is shown that the ideal initiator will yield a stable, singly charged anion and a cation with a high reactivity towards the monomer by simple, well defined reactions. It must also be adequately soluble in the solvent of choice and for the experimental method to be used. The calculations are applied to carbocation salts as initiators and a method of predicting their relative solubilities is described. From established and predicted data for a variety of carbocation salts the position of their ion molecule equilibria and their reactivity towards alkenes are examined by means of Born-Haber cycles. This treatment established the relative stabilities of a number of anions and the reason for dityl, but not trityl salts initiating the polymerisation of isobutene. 

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