MD SIMULATIONS ON IONOPHORES AT A WATER-CHLOROFORM INTERFACE .1. CALIX[4]ARENES UNCOMPLEXED AND THE 222-CRYPTAND

Computer experiments are reported on calixarene ionophores at the wate r-chloroform interface, using an explicit representation of the solven ts. The time evolution of the free carriers is simulated by molecular dynamics for timescales ranging from 250 to 600 ps, As ionophores, we consider the t-butylcalix[4]arene-tetra(diethyl)amide the t-butylcalix [4]arene-anion, the 1,3-alternate 1,3-dimethoxy-t-butylcalix[4]arene-c rown and calix[4]arene-bis-crown-6. For comparison, the 222 cryptand i s also considered. We find that they all behave like surfactants, i.e. , are adsorbed at the interface and sit almost entirely in chloroform, without migrating further to the organic phase. This contrasts with n -butane and Cl-, which migrate from the interface to the bulk organic phase and the aqueous phase, respectively. lonophores at the interface are partially hydrated, involving ''water fingers'' in some cases. Th e interface is found to be very sharp. On the basis of an energy compo nent analysis, we suggest that the ''stationary states'' of ionophores at the interface result from solvent cohesive forces rather than solu te-solvent interactions.