Surface area model

The first term (AGcav) is connected with the surface area model, and the y parameter has the same physical meaning as the one in the SGB/NP model. The second term (AGvdW) is the solute-solvent van der Waals free energy term, which introduces another set of parameters. The first one, B, corresponds to the Born radius of the atom i, the second, Rw = 1.4 A is the radius of the water molecule, the next one at = -fTTpwsiw[Pg.219]

Despite the fact that nonpolar hydration forces dominate whenever hydrophobic interactions [46] are important, the general availability of accurate models for the nonpolar component of the hydration-free energy is lacking. The structure and properties of proteins in water is highly influenced by hydrophobic interactions [47-50]. Hydrophobic interactions also play a key role in the mechanism of ligand binding to proteins [30,51-53], Empirical surface area models [54] for the nonpolar component of the solvation free energy are widely used [28,37,55-62]. Surface area models are useful as a first... 

The Generalized Born and Generalized Born/Surface Area Models in Molecular Mechanics... 

This combination of Equations [5] and [16] is called the Generalized Born/Surface Area model (GB/SA), and it is currently available in the Macro-ModeP computer package. The speed of the molecular mechanics calculations is not significantly decreased by comparison to the gas phase situation, making this model well suited to large systems. Moreover, the model takes account of some first-hydration-shell effects through the positive surface tension as well as the volume polarization effects. A selection of data for aqueous solution is provided later (Table 2), and the model is compared to experiment and to other models. Nonaqueous solvents have been simulated by changing the dielectric constant in the appropriate equations, 8 but to take the surface tension to be independent of solvent does not seem well justified. 

The surface area model for solubility in water or any solvent can be further investigated by measuring the effect of temperature or added salt. Preliminary measurements indicate that some of the above models are not satisfactory. We find that the solubility of butanol in water decreases while the magnitude of surface tension of aqueous NaCl solution increases. These kinds of data are important for such systems as EOR (enhanced oil recovery). 

Kawamura K, Suzuki I, Fujii Y, Watarrabe O (1994) Ice core record of polycyclic aromatic hydrocarbons over the past 400 years. Naturwissenschaften 81 502-505 Kelly CP, Cramer CJ, Truhlar DG (2004) Predicting adsorption coefficients at air-water interfaces using universal solvation and surface area models. J Phys Chem B 108 12882-12897... 

Because reaction rates between minerals and solutions are directly proportional to the interfacial area between the phases, it is necessary to quantify this area for rate models. There are various methods to measure the interfacial area, but a useful first step for model building is to develop idealized reference models for reacting surfaces. Idealized surface area models neglect important surface features in a trade-off for simplicity. As such they provide a handy approximation of the relationship between surface geometry and reaction rates. 

The model quality was adequate for all models except for the span model, which did not accomplish the required quality values as mentioned in Table 14.6 and Sect. 2.2.5 The particle size and BET surface area models exhibit an artificial lack of fit of the single measurements due to high reproducibility of experiments dried at the same conditions (centre point results). The resulting small pure error (single measurements) exceeds the model error (centre point results) and reduces the model validity (marked with a in Table 14.6). All models besides the span model give good 2 and measures, which qualifies this model to make valid predictions for further experiments. 

In the simulation of molecules in aqueous solution, treatment of the solvent and solvent ions is particularly demanding both theoretically and computationally. Continuum or implicit solvent models provide a computationally efficient alternative to the inclusion of explicit solvent molecules. These models typically treat electrostatic and nonpolar contributions separately. A popular approach is to treat, respectively, the former with a continuum electrostatics model and the latter with a surface area model. These models often provide free energies and enthalpies to an accuracy that is comparable to, or better than, that of explicit solvent models, but with two or more orders of magnitude less computation. Other properties such as solvent induced forces, solvent structural features and specific hydrogen-bonding interactions are better treated with explicit solvent models... 

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