A New Quantum Mechanical Approach in Determining the Octanol Water Partition Coefficients of Organic Aromatic Compounds

Overview

Objectives/Goals The octanol-water partition coefficient (Kow) measures a solute's distribution between competing organic and aqueous phases, determining its environmental fate and safety. Current experimental methods to determine Kow are subject to human error and require many resources. How can quantum computational modeling be used to determine the Kow of organic aromatic compounds? The objective is to develop a new efficient and practical method to predict Kow. Methods/Materials The calculations were run with the Gaussian 98 program. The project considers two organic families, chlorophenol and chlorobenzene. Four probes molecules simulate the aqueous and organic phase. A water molecule represents immersion in water. Argon, neon, and benzene represent the organic phase because octanol itself is too large and inefficient. First, I optimized the geometry and vibrational frequencies of all molecules. Second, I added a probe molecule above the center of the ring. Next, I calculated the zero-point energy of the complex using the counterpoise method. Finally, I plotted the various energy parameters versus experimental logKow and assessed the strength of linear correlation. The procedures are repeated for different probe molecules, probe distances, and molecular geometries. Results There is a moderately strong linear correlation between logKow and Electron Correlation energy, or pure dispersion forces, of the octanol probe-solute complex (r^2=0.95). Stronger correlations were found between logKow and the Hartree-Fock energy, or pure dipole-dipole interactions of the water-solute complex (r^2=0.98). Finally, the strongest linear correlations were found when plotting logKow with the difference of the dispersion and electrostatic contributions (r^2=0.99). The strengths of the linear correlations are statistically acceptable for the extrapolation of logKow of similar compounds. Conclusions/Discussion The results confirm that Kow can be derived from computational methods. Also, the logKow of four chlorophenol congeners were predicted from the linear correlations. Because the water probe correlations are strong enough, dipole-dipole interactions can be used solely to predict Kow. Overall, the project successfully validated a new method to determine Kow, which can be applied to other organic compounds with limited experimental data. The computational approach saves many resources and diminishes the chance of human error.

Awards (1)

• Category Award

Competition history

• CSEF 2006 Chemistry · Entry S0513

Resources

• CSEF project summary ↗

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