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  • 1.
    Daver, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Algarra, Andrés G.
    Rebek, Julius
    Harvey, Jeremy N.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Mixed Explicit-Implicit Solvation Approach for Modeling of Alkane Complexation in Water-Soluble Self-Assembled Capsules2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 39, p. 12527-12537Article in journal (Refereed)
    Abstract [en]

    The host-guest binding properties of a water-soluble resorcinarene-based cavitand are examined using density functional theory methodology. Experimentally, the cavitand has been observed to self-assemble in aqueous solution into both 1:1 and 2:1 host/guest complexes with hydrophobic guests such as n-alkanes. For n-decane, equilibrium was observed between the 1:1 and 2:1 complexes, while 1:1 complexes are formed with shorter n-alkanes and 2:1 complexes are formed with longer ones. These findings are used to assess the standard quantum chemical methodology. It is first shown that a rather advanced com- putational protocol (B3LYP-D3(BJ)/6-311+G(2d,2p) with COSMO-RS and quasi-rigid-rotor-harmonic-oscillator) gives very large errors. Systematic examination of the various elements of the methodology shows that the error stems from the implicit solvation model. A mixed explicit-implicit solvation protocol is developed that involves a parametrization of the hydration free energy of water such that water cluster formation in water is predicted to be thermoneutral. This new approach is demonstrated to lead to a major improvement in the calculated binding free energies of n-alkanes, reproducing very well the 1:1 versus 2:1 host/guest binding trends.

  • 2.
    Daver, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Harvey, Jeremy N.
    Rebek, Jr., Julius
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Quantum Chemical Modeling of Cycloaddition Reaction in a Self-Assembled Capsule2017In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 139, no 43, p. 15494-15503Article in journal (Refereed)
    Abstract [en]

    Dispersion-corrected density functional theory is used to study the cycloaddition reaction between phenyl acetylene and phenyl azide inside a synthetic, self-assembled capsule. The capsule is first characterized computationally and a previously unrecognized structure is identified as being the most stable. Next, an examination of the free energies of host-guest complexes is conducted, considering all possible reagent, solvent and solvent impurity combinations as guests. The experimentally observed relative stabilities of host-guest complexes are quite well reproduced, when the experimental concentrations are taken into account. Experimentally, the presence of the host capsule has been shown to accelerate the cycloaddition reaction and to yield exclusively the 1,4-regioisomer product. Both these observations are reproduced by the calculations. A detailed energy decomposition analysis shows that reduction of the entropic cost of bringing together the reactants along with a geometric destabilization of the reactant supercomplex are the major contributors to the rate acceleration compared to the background reaction. Finally, a sensitivity analysis is conducted to assess the stability of the results with respect to the choice of methodology.

  • 3. Harvey, Jeremy N.
    et al.
    Himo, Fahmi
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maseras, Feliu
    Perrin, Lionel
    Scope and Challenge of Computational Methods for Studying Mechanism and Reactivity in Homogeneous Catalysis2019In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 9, no 8, p. 6803-6813Article in journal (Refereed)
    Abstract [en]

    Computational methods based on quantum mechanical modeling are increasingly used to provide insight into mechanistic aspects of homogeneous catalysis. While the potential and value of such methods are obvious, it is also clear that it remains challenging to obtain reliable and predictive mechanistic insights from modeling. In this Perspective, we assess the various factors influencing the quality of computational studies. While the type of electronic structure theory methodology used is of course of great importance, we argue that many other aspects can play a large role also. The other factors emphasized here include the treatment of entropic effects, solvation, the choice of the structural model, conformational complexity, the translation of computed relative Gibbs energies into a kinetic model, and the high demands required for the prediction of selectivity.

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