Miscibility and thermodynamics of mixing of different models of formamide and water in computer simulation

The thermodynamic changes that occur upon mixing five models of formamide and three models of water, including the miscibility of these model combinations itself, is studied by performing Monte Carlo computer simulations using an appropriately chosen thermodynamic cycle and the method of thermodynamic integration. The results show that the mixing of these two components is close to the ideal mixing, as both the energy and entropy of mixing turn out to be rather close to the ideal term in the entire composition range. Concerning the energy of mixing, the OPLS/AA-mod model of formamide behaves in a qualitatively different way than the other models considered. Thus, this model results in negative, while the other ones in positive energy of mixing values in combination with all three water models considered. Experimental data supports this latter behavior. Although the Helmholtz free energy of mixing always turns out to be negative in the entire composition range, the majority of the model combinations tested either show limited miscibility, or, at least, approach the miscibility limit very closely in certain compositions. Concerning both the miscibility and the energy of mixing of these model combinations, we recommend the use of the combination of the CHARMM formamide and TIP4P water models in simulations of water-formamide mixtures.

Bálint Kiss (1, 2) , Balázs Fábián (3, 4) , Abdenacer Idrissi (1) , Milán Szőri (2) , Pál Jedlovszky (5)

1 LASIRE - Laboratoire Avancé de Spectroscopie pour les Intéractions la Réactivité et l'Environnement - UMR 8516
2 Institute of Chemistry
3 Department of Inorganic and Analytical Chemistry
4 UTINAM - Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
5 Department of Chemistry

Domaines: Chimie théorique et/ou physique

Bálint Kiss, Balázs Fábián, Abdenacer Idrissi, Milán Szőri, Pál Jedlovszky. Miscibility and thermodynamics of mixing of different models of formamide and water in computer simulation. Journal of Physical Chemistry B, 2017, 121 (29), pp.7147 - 7155. ⟨10.1021/acs.jpcb.7b04965⟩. ⟨hal-01593264⟩