Active Role of Water in the Hydration of Macromolecules with Ionic End Group for Hydrophobic Effect-Caused Assembly

The role of water in the hydration and aqueous assembly of hydrophobic P+X- (P+: Macromolecular phosphonium cation, X-: Anion) was investigated via complementary Fourier transform infrared (FT-IR) and low-field NMR analyses. The hydration of the macromolecular backbone was dependent on X-. When X- is I-, the ionic end group ordered water molecules that exerted a detectable long-range effect of dehydrating the backbone. The consequent hydrophobic interaction drove the aqueous assembly of P+I- into micelle-like aggregates, with the ionic group exposed to water. In contrast, the ion pair with a hydrophobic anion of [BPh4]- was not able to hold water and did not deplete the hydration water. The hydrated backbone endowed the assembly of P+[BPh4]- into vesicles that were driven by hydration interactions. This elucidation at the molecular level is craved to progress the aqueous supramolecular chemistry.