Spontaneous Multi-scale Supramolecular Assembly Driven by Noncovalent Interactions Coupled with the Continuous Marangoni Effect.

Reported herein is the multi-scale supramolecular assembly (MSSA) process along with redox reactions driven by supramolecular interactions coupled with the spontaneous Marangoni effect in ionic liquid (IL)-based extraction systems. The black powder, the single sphere with a black exterior, and the single colorless sphere were formed step by step at the interface when an aqueous solution of KMnO was mixed with the IL phase 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (COHmimNTf) bearing octyl(phenyl)-,-diisobutylcarbamoylmethylphosphine oxide (CMPO). The mechanism of the whole process was studied systematically. The phenomena were related closely to the change in the valence state of Mn. The MnO ion could be reduced quickly to δ-MnO and further to Mn slowly by the hydroxyl-functionalized IL COHmimNTf. Based on Mn, Mn(CMPO), elementary building blocks (EBBs), and [EBB] clusters were generated step by step. The [EBB] clusters with the large enough size that were transferred to the interface, together with the remaining δ-MnO, assembled into the single sphere with a black exterior, driven by supramolecular interactions coupled with the spontaneous Marangoni effect. When the remaining δ-MnO was used up, the mixed single sphere turned completely colorless. It was found that the reaction site of COHmim with Mn(VII) and Mn(IV) was distributed mainly at the side chain with a hydroxyl group. The MSSA process presents unique spontaneous phase changes. This work paves the way for the practical application of the MSSA-based separation method developed recently. The process also provides a convenient way to observe in situ and characterize directly the continuous Marangoni effect.