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1.
Govers HA Krop HB Parsons JR Tambach T Kubicki JD 《SAR and QSAR in environmental research》2002,13(2):271-280
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. 相似文献
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Near-thermal charge exchange between He+ and H2(D2O) is used as a source of OH+(OD+) A3Hi→ X3Σ? emission. A comparison between experimental emission branching ratios and those calculated in the r-centroid approximation suggests that the electronic transition moment varies as a function of the r-centroid. 相似文献
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The use of the molecular mechanics AMBER force field (FF) to predict product profiles for the hydroxylation of the monoterpenes 1R-camphor, 1S-camphor, 1R-norcamphor, 1S-norcamphor and camphane by the enzyme cytochrome P450cam from the soil bacterium Pseudomonas putida was investigated. Predictions were carried out by applying multiple substrate (starting) orientations in the enzyme pocket in two procedures: a procedure based on molecular dynamics (MD) and a procedure based on short MD simulations followed by geometry optimisations. The latter (GO) procedure is faster and enabled the use of more monoterpene starting orientations. Monoterpene orientations were transformed into product profiles by applying both energetic and geometrical criteria appropriate for the (monoterpene) hydrogen abstraction reaction. Good predictions compared to experimental data were obtained for most compounds in both the MD and GO procedures. Prior to the product profile calculations, the FF was calibrated by reproducing the experimental data for the binding energy of 1R-camphor and 1S-camphor to P450cam and the energy of vaporisation of water. Focus of the calibration was on the value for the scaling factor for the electrostatic interactions. 相似文献
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Determination of organic colorants in cosmetic products by high-performance liquid chromatography 总被引:2,自引:0,他引:2
Summary High-performance liquid chromatography (HPLC) with UV-vis detection was used for the determination of organic colorants in
cosmetic products. 126 colorants were characterized by their retention times in an ion-pair reversed-phase HPLC system with
gradient elution, and by their UV-vis spectra, recorded with a diode array detector (DAD). The method is rapid and efficient,
as is demonstrated by the analysis of 45 cosmetic samples. 相似文献
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Emission spectra between 185 and 600 nm have been investigated following near-thermal charge exchange between He+ and N2O and ≤ 100 eV electron impact on N2O. The charge exchange produces N2O+Ã→X?and N2+ B → X emission, but the two band systems account for at most 5% of all charge transfer products. These results and literature data on Ar+/N2O are discussed in the light of Franck—Condon and energy resonance criteria as applied to low-energy charge exchange. The electron-impact experiments revealed a weak (≈ 10?3) long-lived (≈ 50 × 10?6 s) component in the N2O+Ã→X?emission. 相似文献
7.
The use of the molecular mechanics AMBER force field (FF) to predict product profiles for the hydroxylation of the monoterpenes 1R-camphor, 1S-camphor, 1R-norcamphor, 1S-norcamphor and camphane by the enzyme cytochrome P450cam from the soil bacterium Pseudomonas putida was investigated. Predictions were carried out by applying multiple substrate (starting) orientations in the enzyme pocket in two procedures: a procedure based on molecular dynamics (MD) and a procedure based on short MD simulations followed by geometry optimisations. The latter (GO) procedure is faster and enabled the use of more monoterpene starting orientations. Monoterpene orientations were transformed into product profiles by applying both energetic and geometrical criteria appropriate for the (monoterpene) hydrogen abstraction reaction. Good predictions compared to experimental data were obtained for most compounds in both the MD and GO procedures. Prior to the product profile calculations, the FF was calibrated by reproducing the experimental data for the binding energy of 1R-camphor and 1S-camphor to P450cam and the energy of vaporisation of water. Focus of the calibration was on the value for the scaling factor for the electrostatic interactions. 相似文献
8.
Abstract A nonlinear thermodynamic model is applied to the prediction of both the bioconcentration factor (Kbw) in the guppy (Poecilia reticulata) and the n-octanol-water partition coefficient (Kow) of chlorinated dibenzofurans and dibenzo-p-dioxins. To this end molar liquid volumes, heats of vaporization and empirically fitted parameters of the pertinent solute and solvents are used. Calculated log Kbw and log Kow values are obtained with correlation coefficients (r = 0.85 and 0.992) and mean deviations (< dev > = 0.19 and 0.17), which compare favourably with experimental data. In addition the model enables an explanation of the well-known nonlinear log-log relationship between the two properties for compounds with high Kow values on the basis of differences between the properties of biotic lipid and n-octanol. It is suggested that the breakdown of the linear relationship is caused by entropic effects related to the number of chlorine atoms in the solute molecules and to the structures of the lipid and n-octanol. 相似文献
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A gas chromatographic method using Kováts retention indices has been applied to determine the liquid vapour pressure (P(i)), enthalpy of vaporization (DeltaH(i)) and difference in heat capacity between gas and liquid phase (DeltaC(i)) for a group of polycyclic aromatic hydrocarbons (PAHs). This group consists of 19 unsubstituted, methylated and sulphur containing PAHs. Differences in log P(i) of -0.04 to +0.99 log units at 298.15K were observed between experimental values and data from effusion and gas saturation studies. These differences in log P(i) have been fitted with multilinear regression resulting in a compound and temperature dependent correction. Over a temperature range from 273.15 to 423.15K, differences in corrected log P(i) of a training set (-0.07 to +0.03 log units) and a validation set (-0.17 to 0.19 log units) were within calculated error ranges. The corrected vapour pressures also showed a good agreement with other GC determined vapour pressures (average -0.09 log units). 相似文献