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(054) Ab initio calculations of PAH-soot interaction energies for use in predicting parititioning onto soot.
Kubicki, James*,1, Ortiz, Grisselle1, 1 The Pennsylvania State University, University Park, PA, USA
ABSTRACT- The observation that soot can heavily influence the transport, bioavailability and fate of organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), has lead to research on the interactions of these two components of soils and sediments (Bucheli and Gustafsson, 2000, ES&T, 34, 5144). Two purposes may be served by performing molecular simulations that parallel the experimental adsorption studies. First, molecular-level interactions of PAH and soot can be studied. Second, partition coefficients may be predicted in less time than required to measure them. Molecular orbital calculations were applied to model systems. The "soot" in this case was a single coronene (C24H12) molecule. This simplification is justifiable if the soot-PAH adsorption occurs mainly through - interactions. The solvation energy was computed as the difference between the isolated gas-phase PAH molecule and the molecule enclosed in a dielectric continuum with a dielectric constant of 78.4. MP2 calculations with a 6-31G(d) basis set were used to obtain energies. Structures used were energy minimized with the COMPASS force field (Sun, 1998, J. Phys. Chem. 102, 7338) and with the MP2/6-31G(d) method. The difference between the adsorption and solvation energies correlates with the experimental log(Ksc) values of Bucheli and Gustafson (2000). The correlation has been used to predict log(Ksc) values for benzene, anthracene and fluoranthene. Future experimental work could measure these values and test the reliability of the model predictions. We are also performing calculations on dibenzo-p-dioxin and dibenzofuran to help explain their adsorption behavior. Upon testing of our methodology, adsorption energies will be calculated and used for predicting partitioning behavior of PAHs in the environment.
Key words: PAH, PCB, Adsorption, Ab initio
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