Controllable vesicular structure and reversal of a surfactant-encapsulated polyoxometalate complex

An organic-inorganic complex, surfactant-encapsulated polyoxometalate (DDDA)(9)EuW10O36, demonstrates reversible self-assembly behavior in organic solvents and water. This hybrid complex can spontaneously organize into inverse vesicles by simply dispersing it in an organic solvent. Interestingly, by dissolving the water-insoluble complex in a water-miscible organic solvent such as ethanol and subsequently addition of water, it could be transferred into aqueous solution and the inverse vesicles in the organic solvent transformed into a regular bilayer structure in water. The vesicular aggregate, which had a regular structure, was studied by dynamic light scattering and transmission electron microscopy, as well as X-ray diffraction. The structural transformation was proved by zeta potential analysis and X-ray photoelectron spectroscopy, and the process was followed by H-1 NMR. These results provide the first example of aggregation behavior in this kind of complex, which is different from that exhibited by well known amphiphilic molecules with polar and non-polar ends, in water. Moreover, the reverse process, from a regular bilayer to inverse vesicles, can be conveniently carried out by simply extracting the complex from water into the organic phase. The results described may provide new opportunities in performing catalytic and biomimetic functions of polyoxometalates.