Development of Surface-SFED Models for Polar Solvents Page: 441
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Journal of Chemical Information and Modeling
paper.16 However, some modifications are needed to describe
the solvation free energies of polar solutes in polar solvents
in which the hydrogen bonding contributes significantly.
On the basis of the assumption that the solvation free energy
can be partitioned into the different contributions, the solva-
tion free energy of a molecule is described as a sum of three
AGsolv = AGinter + AGHB + AGcav (1)
The free energy of interactions, AGinter, is described as a
linear combination of four basis functions, h(rk), representing
the contribution of the interaction between interacting
compartments of the solute and the kth grid point on the
cavity surface (Figure 1).
van der Waals like Swface
basicity of the solute, Asolute and Bsolute, respectively.
AGHB = AGa + AGd = CaAsolute + CdBsolute
The values of Asolute and Bsolute were obtained from
Abraham's et al.,21-23 Aexp and Bexp, and empirical model, Aca1
and Bcal. Application of Ae" and Be" to the Surface-SFED
model produced results in good agreement with the
experimental solvation free energy.6 However, because there
are a limited number of Abraham's hydrogen bond parameters,
application of the Surface-SFED model can be limited to a
molecule for which AexP and BexP were determined. For the
general purpose of the Surface-SFED model, Acal and Bcal are
given by the sum of the acidities, ai, and basicities, /A, of the
acidic and basic atoms of the solute, respectively.
Acal = ai and Bcal = 1i
i i (4)
where ai and f/iwere meant to reproduce the values published
by Abraham, et al.
The free energy of cavity formation by the solute, AGcav, was
expressed by a term proportional to the SAS area, Ss, of the
solute as follows
AGcav = CsSS + C
Figure 1. Solute and solvent of a solution are described as an
assemblage of interacting compartments. Furthermore, the solvent
accessible surface (SAS), Rw, Rshell, Al, and van der Waals-like surface
of the model are described.
The final formula for the SFED computation of a solute is
AGsolv = AGinter + AGHB + AGcav
= Z Z Chj(rik) + CdAsolute + CaBsolute + CsSs + C
B. Solvation Free Energy Database Construction. Most
of the experimental solvation free energies were obtained from
the experimental gas/solvent partition coefficients database of
Acree et al.24-3s The partition coefficient is the ratio of
concentrations of a solute between solvent A and solvent B at
where S and NA are the number of grid points on the cavity
surface and the number of atoms in the solute, respectively.
Atom-centered net atomic charges, qi, were calculated with an
empirical net atomic charge calculation method, the modified
partial equalization of orbital electronegativity
(MPEOE),18"19 and effective atomic polarizabilities, al, were
calculated using an empirical method, the charge dependent
effective atomic polarizability (CDEAP).20
The hydrogen bond stabilization term, AGHB, was divided
into two terms on the basis of the role of the solvent in
hydrogen bonding, with the acceptor and donor represented
with the subscripts "a" and "d", respectively. These two terms
were simple functions of the hydrogen bond acidity and
The gas/solvent partition coefficient, K, is a specific case of eq 7
where solvent B is replaced with gas. The base-10 logarithm of
the gas/solvent partition coefficient is related to the standard
state free energy of solvation as follows
log K = log[soluteG (8)
AGsoly = - 2.303RTlog K (9)
The gas/solvent partition coefficient was calculated from either
the Raoult's law infinite dilution activity coefficient, Yoluteo
from the Henry's law constant, KHenry, for solutes dissolved in
anhydrous organic solvents, or from partition coefficients of a
solute between water and organic solvent saturated with water,
and the gas/water partition coefficient of the solute, K,, as
shown in eqs 10-12.
log K= log o RT
dx.doi.org/10.1021/ci2004913 I J. Chem. Inf. Model. 2012, 52, 440-448
AGinter = Cjhj(rik)
k i=l rik
+ C3 - - iC4
i=1 rik i=l
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Lee, Sehan; Cho, Kwang-Hwi; Acree, William E. (William Eugene) & No, Kyoung Tai. Development of Surface-SFED Models for Polar Solvents, article, January 13, 2012; [Washington, DC]. (digital.library.unt.edu/ark:/67531/metadc174730/m1/2/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.