Structural and dynamical properties of Li+-dibenzo-18-crown-6(DB18C6) complex in pure solvents and at the aqueous-organic interface.

Microstructure of dibenzo-18-crown-6 (DB18C6) and DB18C6/Li(+) complex in different solvents (water, methanol, chloroform, and nitrobenzene) have been analyzed using radial distribution function (RDF), coordination number (CN), and orientation profiles, in order to identify the role of solvents on complexation of DB18C6 with Li(+), using molecular dynamics (MD) simulations. In contrast to aqueous solution of LiCl, no clear solvation pattern is found around Li(+) in the presence of DB18C6. The effect of DB18C6 has been visualized in terms of reduction in peak height and shift in peak positions of g(Li-Ow). The appearance of damped oscillations in velocity autocorrelation function (VACF) of complexed Li(+) described the high frequency motion to a "rattling" of the ion in the cage of DB18C6. The solvent-complex interaction is found to be higher for water and methanol due to hydrogen bond (HB) interactions with DB18C6. However, the stability of DB18C6/Li(+) complex is found to be almost similar for each solvent due to weak complex-solvent interactions. Further, Li(+) complex of DB18C6 at the liquid/liquid interface of two immiscible solvents confirm the high interfacial activity of DB18C6 and DB18C6/Li(+) complex. The complexed Li(+) shows higher affinity for water than organic solvents; still they remain at the interface rather than migrating toward water due to higher surface tension of water as compared to organic solvents. These simulation results shed light on the role of counter-ions and spatial orientation of species in pure and hybrid solvents in the complexation of DB18C6 with Li(+).