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Andersson M.P.,Copenhagen University | Bennetzen M.V.,Maersk Oil | Klamt A.,COSMOlogic GmbHandCOKG | Klamt A.,University of Regensburg | Stipp S.L.S.,Copenhagen University
Journal of Chemical Theory and Computation

The interfacial tension between two liquids is the free energy per unit surface area required to create that interface. Interfacial tension is a determining factor for two-phase liquid behavior in a wide variety of systems ranging from water flooding in oil recovery processes and remediation of groundwater aquifers contaminated by chlorinated solvents to drug delivery and a host of industrial processes. Here, we present a model for predicting interfacial tension from first principles using density functional theory calculations. Our model requires no experimental input and is applicable to liquid/liquid systems of arbitrary compositions. The consistency of the predictions with experimental data is significant for binary, ternary, and multicomponent water/organic compound systems, which offers confidence in using the model to predict behavior where no data exists. The method is fast and can be used as a screening technique as well as to extend experimental data into conditions where measurements are technically too difficult, time consuming, or impossible. © 2014 American Chemical Society. Source

Presselt M.,Friedrich - Schiller University of Jena | Presselt M.,Stanford University | Presselt M.,TU Ilmenau | Dehaen W.,Catholic University of Leuven | And 7 more authors.
Physical Chemistry Chemical Physics

The chemical and sensing properties of porphyrins are frequently tuned via the introduction of peripheral substituents. In the context of the exceptionally fast second protonation step in the case of 5,10,15,20-tetraphenylporphyrin (TPP), as compared to porphin and 5,10,15,20-tetramesitylporphyrin (TMesP), we investigated the macrocycle-substituent interactions of these three porphyrin derivatives in detail. Using quantum chemical thermodynamics calculations, the analysis of geometric structures, torsional profiles, electrostatic potential distributions, and particularly the analysis of molecular flexibilities via ab initio molecular dynamics simulations, we obtained a comprehensive picture of the reactivities of the studied porphyrins and how these are influenced by the meso-substituents. As compared to porphin and TMesP the second protonation of TPP is energetically more favorable and is particularly energetically comparable to its first protonation, instead of being significantly less favorable like in the case of porphyrin and TMesP. Additionally, the second TPP protonation is facilitated by an interplay between out-of-plane (oop) distortion of the protonation site and a pronounced electrostatic binding spot at the protonation site. Furthermore, the second protonation is particularly facilitated in the case of TPP by the large oop-flexibility of the diprotonated species as unraveled by ab initio molecular dynamics simulations. © 2015 Owner Societies. Source

Klamt A.,COSMOlogic GmbHandCOKG | Klamt A.,University of Regensburg | Diedenhofen M.,COSMOlogic GmbHandCOKG
Journal of Computer-Aided Molecular Design

The COSMO-RS method, a combination of the quantum chemical dielectric continuum solvation model COSMO with COSMO-RS, a statistical thermodynamics treatment of surface interactions, simulations, has been used for the direct, blind prediction of free energies of hydration within the SAMPL challenge. Straight application of the latest version of the COSMOtherm implementation in combination with a rigorous conformational sampling yielded a predictive accuracy of 1.56 kcal/mol (RMSE) for the 23 compounds of the blind prediction dataset. Due to the uncertainties of the extrapolations and assumptions involved in the derivation of the experimental data, the accuracy of the predicted data may be considered to be within the noise level of the experimental data. © 2010 Springer Science+Business Media B.V. Source

Bittermann K.,Helmholtz Center for Environmental Research | Spycher S.,Ecotoxicology Group | Endo S.,Helmholtz Center for Environmental Research | Pohler L.,COSMOlogic GmbHandCOKG | And 5 more authors.
Journal of Physical Chemistry B

The partition coefficient of chemicals from water to phospholipid membrane, Klipw, is of central importance for various fields. For neutral organic molecules, log Klipw correlates with the log of bulk solvent-water partition coe.cients such as the octanol-water partition coefficient. However, this is not the case for charged compounds, for which a mechanistic modeling approach is highly necessary. In this work, we extend the model COSMOmic, which adapts the COSMO-RS theory for anisotropic phases and has been shown to reliably predict Klipw for neutral compounds, to the use of ionic compounds. To make the COSMOmic model applicable for ionic solutes, we implemented the internal membrane dipole potential in COSMOmic. We empirically optimized the potential with experimental Klipw data of 161 neutral and 75 ionic compounds, yielding potential shapes that agree well with experimentally determined potentials from the literature. This model re.nement has no negative effect on the prediction accuracy of neutral compounds (root-mean-square error, RMSE = 0.62 log units), while it highly improves the prediction of ions (RMSE = 0.70 log units). The refined COSMOmic is, to our knowledge, the first mechanistic model that predicts Klipw of both ionic and neutral species with accuracies better than 1 log unit. (Figure Presented). © 2014 American Chemical Society. Source

Klamt A.,COSMOlogic GmbHandCOKG | Klamt A.,University of Regensburg | Reinisch J.,COSMOlogic GmbHandCOKG | Eckert F.,COSMOlogic GmbHandCOKG | And 2 more authors.
Physical Chemistry Chemical Physics

In this work, experimental hydrogen-bond (HB) enthalpies measured in previous works for a wide range of acceptor molecules in dilute mixtures of 4-fluorophenol in non-polar solvents are quantified from COSMO polarisation charge densities σ of HB acceptors (HBA). As well as previously demonstrated for quantum chemically calculated HB enthalpies, a good correlation of the experimental data with the polarisation charge densities is observed, covering an extended range of HBA (O, N, S, π systems and halogens) ranging from very weak to strong hydrogen bonds. Furthermore, for the first time, a quantitative analysis of experimental HB entropies is performed for such a chemical diversity of HBA. A good quantification of these entropies is achieved using the polarisation charge density σ as a descriptor in combination with the logarithm of a directional partition function ΩHB. This partition function covers the directional and multiplicity entropy of HBA and is based on the σ-proportional HB enthalpy expression taken from COSMO-RS. As a result, the experimental HB enthalpies and free energies of the ∼300 HB complexes are quantified with an accuracy of ∼2 kJ mol -1 based on COSMO polarisation charge densities. © 2013 the Owner Societies. Source

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