Physisorption of bio oil nitrogen compounds onto montmorillonite

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Physical Chemistry Chemical Physics, Volume 38
We assess computationally the adsorption of a series of nitrogen containing heterocycles and fatty acid amides from bio-oil on a model clay surface, Na-montmorillonite. The adsorption energies and conformations predicted by atomistic detail molecular dynamics (MD) simulations are compared against density functional theory (DFT) based molecular electrostatic potentials (MEP) and Hirshfeld, AIM, Merz-Singh-Kollman, and ChelpG charges. MD predicts systematically adsorption via cation bridging with adsorption strength of the heterocycles following purine > pyridine > imidazole > pyrrole > indole > quinoline. The fatty acid amides adsorption strength follows the steric availability and bulkiness of the head group. A comparison against the DFT calculations shows that MEP predicts adsorption geometries and the MD simulations reproduce the conformations for single adsorption site species. However, the DFT derived charge distibutions show that MD force-fields with non-polarizable fixed partial charge representations parametrized for aqueous environments cannot be used in apolar solvent environments without careful accuracy considerations. The overall trends in adsorption energies are reproduced by the Charmm GenFF employed in the MD simulations but the adsorption energies are systematically overestimated in this apolar solvent environment. The work has significance both for revealing nitrogen compound adsorption trends in technologically relevant bio oil environments but also as a methodological assessment revealing the limits of state of the art biomolecular force-fields and simulation protocols in apolar bioenvironments.
The authors thank Rasmus Kronberg and Prof. Kari Laasonen for assistance with the electronic structure calculations and for useful discussions. This work was partly financed by the Fortum and Neste Foundation project 20210130 (M. V.). The authors acknowledge the financial support of the Academy of Finland Grant No. 309324 (M. S.). We are grateful for the support by the FinnCERES Materials Bioeconomy Ecosystem. Computational resources by CSC IT Centre for Science, Finland, RAMI – RawMatTERS Finland Infrastructure, and Aalto Science-IT project are also gratefully acknowledged.
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Vuorte , M , Kuitunen , S & Sammalkorpi , M 2021 , ' Physisorption of bio oil nitrogen compounds onto montmorillonite ' , Physical Chemistry Chemical Physics , vol. 23 , no. 38 , pp. 21840-21851 .