Behaviour of cis- and trans-N-methylformamide in liquid mixture: Dynamical properties at varying pressure and temperature, and ion solvation scenario

Classical molecular dynamics simulations have been carried out to investigate dynamical properties of cis-trans mixture of liquid N-methylformamide at eight different temperatures (278-423 K) and four pressures ranging from 0.1 MPa to 300 MPa. At 298 K and 0.1 MPa, it is observed that cis-NMF is impeded by approximately 4.12% in its diffusion rate than trans-NMF. Higher pressures evoke slower dynamics concomitantly with enhanced caging effect, which is appreciable in case of cis-NMF. Calculated activation energy values for diffusion (13.465 +/- 0.21-15.641 +/- 0.51 kJ/mol) are in agreement with experimental observations, particularly at 0.1 MPa. Unlike self-diffusion behaviour, the orientational relaxation time of N-H bond vector follows Arrhenius behaviour even at lower temperature and higher pressure. Hydrogen bonding patterns are observed to be different for H-bonds involving amide-hydrogen of either trans-NMF or cis-NMF molecules and overall interaction probability is boosted by the participation of cis-NMF conformers. Solvation scenario of ions of different charge and size in cis/trans-NMF mixture has also been explored. It is found that cations favour oxygen of cis-NMF and anions are attracted towards hydrogen sites of trans-NMF while intermediately-sized potassium and bromide ions may deviate in their preferences from the usual trend. (C) 2018 Elsevier B.V. All rights reserved.