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Issue 53, 2014
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A non-Bornian analysis of the Gibbs energy of hydration for organic ions

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Recently, a non-Bornian model was successfully applied to evaluate the Gibbs energy of hydration (ΔG°hyd) for spherical ions (mainly inorganic ions). In this model, the long-range, Born-type electrostatic ion–solvent interaction is not explicitly included in the calculation of ΔG°hyd, since its contribution is small, whereas the short-range interaction, including Coulomb, polarization, and charge-transfer interactions, is considered as the dominant factor that determines the ΔG°hyd of ions. The ΔG°hyd scaled by the surface area of an ion can be given by a quadratic function of the surface field strength (E) of the ion. In this study, the non-Bornian model was further applied to organic ions with charged groups. Using the Gaussian 09 program package, the geometries of ions in vacuum were optimized at the B3LYP/6-311++G(2d,p) level, and the partial atomic charges were computed in the Mulliken, Merz-Kollman (MK), natural population analysis (NPA), Hirshfeld, and ChelpG methods. Introducing a new subprogram, we could estimate local electric fields on the ion surface (van der Waals surface or solvent-accessible surface (SAS)). This enabled us to perform regression analyses based on the non-Bornian model, by using the experimental values of ΔG°hyd for 109 ions. When the NPA-SAS combination was chosen, the best regression result was obtained, giving the mean absolute error of 4.3 kcal mol−1. The non-Bornian model would provide a simple and relatively accurate way of determining ΔG°hyd of ions.

Graphical abstract: A non-Bornian analysis of the Gibbs energy of hydration for organic ions

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The article was received on 19 Mar 2014, accepted on 10 Jun 2014 and first published on 11 Jun 2014

Article type: Paper
DOI: 10.1039/C4RA02422B
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Citation: RSC Adv., 2014,4, 27634-27641
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    A non-Bornian analysis of the Gibbs energy of hydration for organic ions

    W. Murakami, M. Yamamoto, K. Eda and T. Osakai, RSC Adv., 2014, 4, 27634
    DOI: 10.1039/C4RA02422B

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