title: Dissolved organic carbon--contaminant interaction descriptors found by 3D force field calculations.
abstract: Enthalpies of transfer at 300 K of various partitioning processes were calculated in order to study the suitability of 3D force fields for the calculation of partitioning constants. A 3D fulvic acid (FA) model of dissolved organic carbon (DOC) was built in a MM+ force field using AMI atomic charges and geometrical optimization (GO). 3,5-Dichlorobiphenyl (PCB14), 4,4'-dichlorobiphenyl (PCB15), 1,1,1-trichloro-2,2-bis-(4-chlorophenyl)-ethane (PPDDT) and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (Atrazine) were inserted into different sites and their interaction energies with FA were calculated. Energies of hydration were calculated and subtracted from FA-contaminant interactions of selected sites. The resulting values for the enthalpies of transfer from water to DOC were 2.8, -1.4, -6.4 and 0.0 kcal/mol for PCB 14, PCB15, PPDDT and Atrazine, respectively. The value of PPDDT compared favorably with the experimental value of -5.0 kcal/mol. Prior to this, the method was studied by the calculation of the enthalpies of vaporization and aqueous solution using various force fields. In the MM + force field GO predicted enthalpies of vaporization deviated by +0.7 (PCB14), +3.6 (PCB15) and -0.7 (PPDDT)kcal/mol from experimental data, whereas enthalpies of aqueous solution deviated by -3.6 (PCB14), +5.8 (PCB15) and +3.7 (PPDDT) kcal/mol. Only for PCB14 the wrong sign of this enthalpy value was predicted. Potential advantages and limitations of the approach were discussed.
authors.affiliation: Department of Environmental and Toxicological Chemistry, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands. hgovers@science.uva.nl
authors.forename: H A J
authors.initials: HA
authors.lastname: Govers
authors.forename: H B
authors.initials: HB
authors.lastname: Krop
authors.forename: J R
authors.initials: JR
authors.lastname: Parsons
authors.forename: T
authors.initials: T
authors.lastname: Tambach
authors.forename: J D
authors.initials: JD
authors.lastname: Kubicki
mesh_terms: D001280:Atrazine / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D005544:Forecasting; D006540:Herbicides / Q000737:chemistry*; D011078:Polychlorinated Biphenyls / Q000737:chemistry*; D012995:Solubility; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014835:Volatilization; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D006540:Herbicides; D014874:Water Pollutants, Chemical; D002244:Carbon; D011078:Polychlorinated Biphenyls; C029861:4,4'-dichlorobiphenyl; C029904:3,5-dichlorobiphenyl; D001280:Atrazine