Solvent continuum model

It is often the case that the solvent acts as a bulk medium, which affects the solute mainly by its dielectric properties. Therefore, as in the case of electrostatic shielding presented above, explicitly defined solvent molecules do not have to be present. In fact, the bulk can be considered as perturbing the molecule in the gas phase , leading to so-called continuum solvent models [14, 15]. To represent the electrostatic contribution to the free energy of solvation, the generalized Bom (GB) method is widely used. Wilhin the GB equation, AG equals the difference between and the vacuum Coulomb energy (Eq. (38)) ... 

Zhou, R. Friesner, R.A. Ghosh, A. Rizzo, R.C. Jorgensen, W.L. Levy, R.M., New linear interaction method for binding affinity calculations using a continuum solvent model, J. Phys. Chem. B 2001,105,10388-10397... 

Incorporation of Continuum Solvent Models Using a Generalized Born Approach... 

An accurate quantitative prediction of their relative affinities by a combination of molecular mechanics and continuum solvent models, J. Med. Chem. 43 3786 (2000). 

We have also studied the coordination of the monocarbonate, bicarbonate, and tricarbonate complexes of neptunyl in water, by using both explicit water molecules and a continuum solvent model.84 The monocarbonate complex was shown to have a pentacoordinated structure, with three water molecules in the first coordination shell, and the bicarbonate complex has a hexacoordinated structure, with two water molecules in the first coordination shell. Overall good agreement with experimental results was obtained. 

General Comments Discrete Molecular and Continuum Solvent Models... 

To better understand the possible weak links in the decanio-bate ion that might give rise to oxygen exchange, a molecular dynamics calculation was carried out with the PQS quantum chemistry code (www.pqs-chem.com) of the decaniobate ion embedded in the COSMO continuum solvent model (55) (dielectric constant = 80, probe radius = 1.4 A). The time step was set at... 

At the heart of all continuum solvent models is a reliance on the Poisson equation of classical electrostatics to express the electrostatic potential as a function of the charge density and the dielectric constant. The Poisson equation, valid for situations where a surrounding dielectric medium responds in a linear fashion to the embedding of charge, is written... 

Storer etal. (1994) employed a SM.v GB continuum solvent model to investigate this question. Because of die efficiency of die continuum model, they were able to examine various levels of electronic-structure dieory in assessing the influence of aqueous solvation... 

Taylor, R. D., Jewsbury, P. J., and Essex, J. W. (2003) FDS flexible ligand and receptor docking with a continuum solvent model and soft-core energy function. J. Comput. Chem. 24, 1637-1656. 

Why is parameterizing a continuum solvent model with the conventional dielectric constant possibly physically unrealistic ... 

Continuum solvent models are normally parameterized with the solvent dielectric constant (but see the COSMO models, Chapter 8). First we note that dielectric constant and dipole moment are not in general well correlated from Chapter 8 ... 

Defining a Stem layer using hydrated radii of the ions is justified in the P—B framework, since ions must be fully hydrated in order for the uniform dielectric approximation to be valid. If ions were allowed to penetrate this layer, then additional physics would have to be introduced to account for ion—ion correlations, partial dehydration, and other considerations that fall well outside the realm of applicability for standard continuum solvent models. To generalize the P—B framework, new approaches are needed... 

Solvent effects for ions can be described by a similar continuum solvent model the so-called Born model. This model predicts a stabilization proportional to the square of the charge, and inversely proportional to the size (radius) of the ion that is, small and highly charged ions are strongly stabilized in solution. 

Since the development of the Onsager model, there have been a number of elaborations on the model [4,5]. For example, the spherical cavity has been replaced by molecularly-shaped cavities. The state of the art within the field of solvent effects described by continuum solvent models is now implemented in, e.g., the Gaussian program package. 

G. Scalmani, N. Rega, M. Cossi and V. Barone, Finite elements molecular surface in continuum solvent models for large chemical systems, J. Comput. Meth. Science Eng., 2 (2001) 159-164. 

In this chapter we consider the extension of continuum solvent models to nonlocal theories in the framework of the linear response approximation (LRA). Such an approximation is mainly applicable to electrostatic solute-solvent interactions, which usually obey the LRA with reasonable accuracy. The presentation is confined to this case. 

As shown in Figure 2.5, continuum solvent models (PCM) reproduce satisfactorily solvent effects on the aN parameter only for aprotic solvents (bulk effects), whereas there is a noticeable underestimation of solvent shifts for protic solvents (methanol and water). In these media also specific solute-solvent interactions have to be taken into account. 

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