The Effect of Fluorination on the Interfacial Properties of Alcohols and Carboxylic Acids

The Effect of Fluorination on the Interfacial Properties
of Alcohols and Carboxylic Acids

Molecular dynamic simulations are
used to investigate the effect of the fluorination on surfactant-like
moleculesÕ physical properties and interfacial behavior at air-water and
octanol-water interfaces. The project includes comparisons between the
properties of molecules such as methanol, pentanol, and octanol to their
fluorinated counterparts and various C8-fluorotelomers. Interfacial tension and
octanol-water partition coefficients are calculated in an effort to predict the
biological and environmental impact of these molecules. Understanding the
partitioning and interfacial behavior of these molecules is expected to inform
the development of alternative surfactants that could, potentially, serve the
same purpose with lower potential for bioaccumulation.

To date, we have collected preliminary
results for the octanol-water partitioning coefficients [1] and surface tension
behavior of 8-carbon fluorotelomers.  The Adaptive Biasing Force (ABF)
method was used to calculate the change in free energy for hydration and
solvation [2-4] of the C8-fluorotelomers and the partitioning coefficient was
then modeled by the equation

Ultimately, the change in free energies are calculated as
the difference between the two plateaus.  Values for the change in free
energies and the octanol-water partition coefficients are recorded in Table 1.

Table 1:  Calculated octanol-water partition
coefficients

Simulations were performed in NAMD, version 2.9[5]. For the fluorotelomer surface tension
calculations, an interface 50 slab of TIP3P water
molecules, with a density of 1 g/cm³, in the center of a box was used[6].  Calculations were only made for TIP3P water
model at 300K.  Figure 3 represents the surface tension as a function of
concentration of the fluorotelomer at the TIP3P water interface.

References:

1.         Bhatnagar,
N., G. Kamath, and J.J. Potoff, Prediction of 1-octanolÐwater and airÐwater
partition coefficients for nitro-aromatic compounds from molecular dynamics
simulations. Physical Chemistry Chemical Physics, 2013. 15(17): p.
6467-6474.

2.         Darve,
E. and A. Pohorille, Calculating free energies using average force. The
Journal of Chemical Physics, 2001. 115(20): p. 9169-9183.

3.         Darve,
E., M.A. Wilson, and A. Pohorille, Calculating free energies using a
scaled-force molecular dynamics algorithm. Molecular Simulation, 2002. 28(1-2):
p. 113-144.

4.         Rodriguez-Gomez,
D., E. Darve, and A. Pohorille, Assessing the efficiency of free energy
calculation methods. The Journal of chemical physics, 2004. 120(8):
p. 3563-3578.

5.         Phillips,
J.C., et al., Scalable molecular dynamics with NAMD. Journal of computational
chemistry, 2005. 26(16): p. 1781-1802.

6.         Vega,
C. and E. De Miguel, Surface tension of the most popular models of water by
using the test-area simulation method. The Journal of chemical physics,
2007. 126(15): p. 154707.