Solvation free energy profile of the SCN- ion across the water-1,2-dichloroethane liquid/liquid interface. A computer simulation study

The solvation free energy profile of a single SCN- ion is calculated across the water-1,2-dichloroethane liquid/liquid interface at 298 K by the constraint force method. The obtained results show that the free energy cost of transferring the ion from the aqueous to the organic phase is about 70 kJ/mol, The free energy profile shows a small but clear well at the aqueous side of the interface, in the subsurface region of the water phase, indicating the ability of the SCN- ion to be adsorbed in the close vicinity of the interface. Upon entrance of the SCN- ion to the organic phase a coextraction of the water molecules of its first hydration shell occurs. Accordingly, when it is located at the boundary of the two phases the SCN- ion prefers orientations in which its bulky S atom is located at the aqueous side, and the small N atom, together with its first hydration shell, at the organic side of the interface

Photoinduced Excited State Electron Transfer at Liquid/Liquid Interfaces

Several aspects of the photoinduced electron transfer (ET) reaction betweencoumarin 314 (C314) and N,N-dimethylaniline (DMA) at the water/DMA interface areinvestigated by molecular dynamics simulations. New DMA and water/DMA potentialenergy surfaces are developed and used to characterize the neat water/DMA interface.The adsorption free energy, the rotational dynamics and the solvation dynamics of C314at the liquid/liquid interface are investigated and are generally in reasonable agreementwith available experimental data. The solvent free energy curves for the ET reactionbetween excited C314 and DMA molecules are calculated and compared with thosecalculated for a simple point charge model of the solute. It is found that thereorganization free energy is very small when the full molecular description of the soluteis taken into account. An estimate of the ET rate constant is in reasonable agreement withexperiment. Our calculations suggest that the polarity of the surface “reported” by thesolute, as reflected by solvation dynamics and the reorganization free energy, is strongly solute-dependent