Molecular Dynamics simulations of liquid isoquinoline as a function of temperature

Abstract Molecular Dynamics simulations of isoquinoline in liquid phase have been conducted in the temperature range 300–365 K corresponding to the normal liquid phase in order to investigate the evolution of translational and rotational diffusion with temperature. Molecules are supposed to be rigid and interact through an all-atom potential composed of Coulombic and Lennard-Jones terms. Translational diffusion coefficients are computed from velocity autocorrelation functions and mean square displacement. Anisotropic rotational diffusion coefficients are computed from angular velocity autocorrelation functions. The evolution of the 13 C spin–lattice relaxation time with temperature has been obtained from the simulations and compared with experimental results. A small non-Arrhenius behavior, more pronounced than what was observed experimentally, has been found for this property. The structure has been analyzed in terms of populations of different kinds of first-neighbor dimers. A continuous evolution of the structure with temperature has been observed. The general trend is thus a continuous smooth evolution of the structure at dimer level and a slight non-Arrhenius evolution for diffusion coefficients and reorientational correlation times. These results are compared with those obtained for liquid quinoline where a clear non-Arrhenius break around 290 K was observed for the 13 C spin–lattice relaxation time from experiments [D. Jalabert, J.-B. Robert, H. Roux-Buisson, J.-P. Kintzinger, J.-M. Lehn, R. Zinzius, D. Canet, P. Tekely, Europhys. Lett. 15 (1991) 435] and from simulations [C. Millot, J.-C. Soetens, N. Ahmad, R. Adnan, Europhys. Lett. 96 (2011) 43002]. Moreover, the identification of break temperatures for liquid isoquinoline appears to be less clear than for quinoline.