Comparison of Different Solvation Methods for the
Determination of the Free Energy of Solvation of Molecules and Ions
Sean McGovern ‘07, Andreu Viader Valls ‘05, and George C. Shields
Department of Chemistry, Hamilton College, Clinton, NY 13323
This particular project is part of a larger one, aimed at determining the most accurate way of finding pKa values. Using the thermodynamic cycle shown below, solvation free energies of reactants and products can be combined with the change in the gas phase free energy, to determine pKa values.1-5 The limiting factor in making this method general is the determination of accurate free energies of solvation for ions in aqueous solution.
Ggas
AHgas A-gas + H+gas
Gs (AH) Gs (A-) Gs(H+)
Gaq
AHaq A-aq + H+aq
Using B3LYP and HF optimized geometries of anions, cations, and neutral molecules, a series of solvation calculations were performed to determine the free energies of solvation, Gs. The different methods used to find Gs include PCM6 and CPCM7 calculations implemented in Gaussian,8 and the Poisson-Boltzmann solver9,10 implemented in Jaguar.11 The objective is to compare the obtained values to the accepted experimental values and hence to determine the most accurate method of finding G solvation.
We have also made an evaluation of the experimental Gs values from new values for Gs for H+ and OH-.
Stipend support for SM was provided by the Camille & Henry Dreyfus Foundation. This research was supported by an ACS/PRF grant to GCS and by NSF grant CHE-0116435 as part of the MERCURY supercomputer consortium ().
(1)Toth, A. M.; Liptak, M. D.; Phillips, D. L.; Shields, G. C. J. Chem. Phys. 2001, 114, 4595-4606.
(2)Pokon, E. K.; Liptak, M. D.; Feldgus, S.; Shields, G. C. J. Phys. Chem. A 2001, 105, 10483-10487.
(3)Liptak, M. D.; Shields, G. C. Int. J. Quantum Chem. 2001, 85, 727-741.
(4)Liptak, M. D.; Shields, G. C. J. Am. Chem. Soc. 2001, 123, 7314-7319.
(5)Liptak, M. D.; Gross, K. C.; Seybold, P. G.; Feldgus, S.; Shields, G. C. J. Am. Chem. Soc. 2002, 124, 6421-6427.
(6)Cossi, M.; Barone, V.; Cammi, R.; Tomasi, J. Chem. Phys. Lett. 1996, 255, 327-335.
(7)Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995-2001.
(8)Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.; Mennuci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.; Chem, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98; Gaussian, Inc.: Pittsburgh, PA, 1998.
(9)Tannor, D. J.; Marten, B.; Murphy, R.; Friesner, R. A.; Sitkoff, D.; Nicholls, A.; Ringnalda, M. N.; Goddard, W. A.; Honig, B. J. Am. Chem. Soc. 1994, 116, 11875-11882.
(10)Marten, B.; Kim, K.; Cortis, C.; Friesner, R. A.; Murphy, R. B.; Ringnalda, M. N.; Sitkoff, D.; Honig, B. J. Phys. Chem. 1996, 100, 11775-11788.
(11)Jaguar; Schrodinger, Inc.: Portland, OR, 1991-2001.