Complexation of M3+ lanthanide cations by calix[4]arene-CMPO ligands: A molecular dynamics study in methanol solution and at a water/chloroform interface

We report a molecular dynamics study on the 1:1 M3+ lanthanide (La3+, Eu3and Yb3+) inclusion complexes of an important extractant molecule L: calix[ 4]arene-tetraalkyl ether substituted at the wide rim by four NH-C(O)-CH2-P( O)Ph-2 arms. The M(NO3)(3) and MCl3 complexes of L are compared in methanol solution and at a water / chloroform interface. In the different environme nts the coordination sphere of M3+ involves the four phosphoryl oxygens and three to four loosely bound carbonyl oxygens of the CMPO-like arms. Based on free energy simulations, we address the question of ion binding selectiv ity in pure liquid phases and at the liquid-liquid interface where L and th e complexes are found to adsorb. According to the simulations, the enhancem ent of M3+ cation extraction in the presence of the calixarene platform, ex amined by comparing L to the (CMPO)(4) "ligand" at the interface, is relate d to the fact that (i) the (CMPO)(4)Eu(NO3)(3) complex is more hydrophilic than the LEu(NO3) one and (ii) the free CMPO ligands spread at the interfac e, and are therefore less organized for cation capture than L.