THEORETICAL-STUDIES ON TRI-N-BUTYL PHOSPHATE - MD SIMULATIONS IN-VACUO, IN WATER, IN CHLOROFORM, AND AT A WATER CHLOROFORM INTERFACE/

We report Molecular Dynamics studies on TBP, representative of neutral organophosphorous ligands used in metal ion extraction experiments. F irst, the conformation of the TBP monomer is analyzed as a function of its environment (in the gas phase, in pure water or pure chloroform p hases, and at a water/chloroform interface). Then the structure and st ability of (TBP)(n) clusters are studied (n = 2 and 10), and shown to be markedly dependent on the environment. For instance, the dimer (n=2 ), unstable in a dry organic phase, remains bound in the gas phase or in chloroform via two bridging water molecules. In an aqueous phase, a nother type of the dimer is found, stabilized by hydrophobic interacti ons between butyl chains. The (TBP)(10) aggregate behaves differently in pure water and in pure chloroform solutions. The simulations of (TB P)(l) and (TBP)(10) at the water/chloroform interface demonstrate the strong adsorption and orientational preference of TBP at the interface , related to its amphiphilic nature. With different starting configura tions, a monolayer forms at the interface during the simulation, with the phosphoryl dipoles pointing towards the aqueous phase and the alky l chains more or less in the organic phase. These results are discusse d in relation with experimental data.