Bom theory of solvation

The Bom theory of solvation applies continuum dielectric theory to the calculation of the solvation energy of an ion of charge q and radius a in a solvent characterized by a static dielectric constant, The well known result for the solvation free energy, i.e., the reversible work needed to transfer an ion from flic interior of a dielectric solvent to vacuum, is... 

The values of -AG soin) for the positive ions in Table 8 are seen to decrease successively with size of the alkyl groups, as expected on the basis of the Bom theory of solvation. The magnitude of AG(soin ° for (CH3)2S is only slightly less... 

Pliego JR (2011) Shells theory of solvation and the long-range bom correction. Theor Chem Acc 128 275-283... 

Continuum models have a long and honorable tradition in solvation modeling they ultimately have their roots in the classical formulas of Mossotti (1850), Clausius (1879), Lorentz (1880), and Lorenz (1881), based on the polarization fields in condensed media [32, 57], Chemical thermodynamics is based on free energies [58], and the modem theory of free energies in solution is traceable to Bom s derivation (1920) of the electrostatic free energy of insertion of a monatomic ion in a continuum dielectric [59], and Kirkwood and Onsager s... 

In chapter 2, Profs. Contreras, Perez and Aizman present the density functional (DF) theory in the framework of the reaction field (RF) approach to solvent effects. In spite of the fact that the electrostatic potentials for cations and anions display quite a different functional dependence with the radial variable, they show that it is possible in both cases to build up an unified procedure consistent with the Bom model of ion solvation. The proposed procedure avoids the introduction of arbitrary ionic radii in the calculation of insertion energy. Especially interesting is the introduction of local indices in the solvation energy expression, the effect of the polarizable medium is directly expressed in terms of the natural reactivity indices of DF theory. The paper provides the theoretical basis for the treatment of chemical reactivity in solution. 

The Born solvation equation is based on the difference in the energy needed to charge a sphere of radius r,- in a solvent of dielectric constant e, and in vacuum having a dielectric constant of unity. Thae are basic flaws in the concept of the Born solvation equation (5) on which the continuum theory of ET reactions is based. First, Bom Eq. (5) does not take into account the interaction of ions with a water solvent that has a dielectric constant of approximately 80 at room temperature. Hence, the Born solvation energy will have negligible contribution from solvents with high dielectric constants. Consequently, for solvents of high dielectric constant, Eq. (5) can be written as... 

With respect to the solvation energy, this is usually approximated by modeling the reactants and products as spheres and the solvent as a dielectric continuum (Bom theory), which in the case of an interface electron transfer gives rise to the following expression [30, 36] ... 

The half-wave potentials (corrected for changes in liquid-junction potential) for the one-electron reduction of aromatic hydrocarbons generally become more positive (the reduction is easier) as the dielectric constant of the solvent increases.44 This is in accord with the direction of the variation in solvation energy of the radical anions that is predicted by the simple Bom theory... 

In the geochemical literature, theoretical models of metal complexation have been based on the dielectric continuum theory of Bom (1920). In the original Bom formalism, the solvation free energy of a metal ion with radius R and charge q is... 

Dielectric properties describe the polarization, P, of a material as its response to an applied electric field E (bold symbols indicate vectors) [1—3], In the field of solution chemistry, the discussion of dielectric behavior is often reduced to the equilibrium polarization, Pq = So(s — V) Eq (eq is the electric field constant), of the isotropic and nonconducting solvent in a static field, Eq. Characteristic quantity here is the static relative permittivity (colloquially dielectric constant ), , which is a measure for the efficiency of the solvent to screen Coulomb interactions between charges (i.e., ions) embedded in the medium. As such, enters into classical electrolyte theories, like Debye-Hiickel theory or the Bom model for solvation free energy [4, 5] and is used... 

In the Bom like approaches to solvation energy, the electrostatic potential of the ion appears as the basic variable of the theory. From Eq (1), it may be seen that if we have accurate electron densities at hand, the electrostatic potential strongly depends on the ionic radius r. The choice of suitable ionic radii usually introduces some arbitrariness in the calculation of AESolv there is no a physical criterium to justify the use of empirical rA values coming from different sources [15-16],... 

Electron transfer reactions, treated by continuum theory, suggested that the Franck-Condon barrier (the barrier for the vertical transition of electrons), which is about four times the activation barrier for the isotopic electron transfer in solution, is due to Bom continuum solvation processes. Specific contributions for the activation of ions come from the solvent continuum far from the ion the important contribution from the solvent molecules oriented toward the central ion in the first and second solvation shells is neglected. ... 

Thus, current versions of the model allow sorption of inner-sphere complexes directly to surface hydroxyls whereas outer-sphere complexes are located at the [3-plane. Recent modifications have included an extension to allow parameter estimation of surface site densities, surface acidity constants and site densities using Bom solvation and crystal chemical theory (Sverjensky, 1993, 1994 Sverjensky Sahai, 1996 Sahai Sverjensky, 1997a,b) and to treat electrolyte ions as nonspecific adsorbing species that screen charge in the p-plane (Robertson Leckie, 1997). 

A computationally attractive alternative to a direct solution of Eq. (1) is the popular Generalized Bom (GB) formalism [5,27] given in Eq. (2) which empirically approximates electrostatic solvation free energies from Poisson theory ... 

Tsui, V., Case, D. Theory and applications of fhe Generalized Bom solvation model in macromolec-ular simulations. Biopolymers 2001, 56,275-91. 

---