Hierarchical Self‐Assembly Induced by Dilution‐Enhanced Hydrophobic Hydration

Abstract

Hydrophobic hydration (HH) is crucial in protein chemistry. Its role in the organization of molecules in water, however, remains elusive and difficult to investigate without appropriate model systems. Metal carbonyl vesicles (MCsomes), assembled from hydrophobic Fp(CH ) Azobenzene (Fp head=(PPh )(Cp)Fe(CO)(CO-); hydrocarbon tail=(CH ) Azobenzene ; trans:trans configuration) is dispersible in water via HH of the Fp heads. We examined the dependence of this HH on solution conditions by taking advantage of redox activity and fluorescence quenching ability of hydrated Fe elements. A subtle variation in the HH substantially varied the solution behaviour of the MCsomes for hierarchical structural evolutions. This scrutiny resolved a long-standing challenge to explicate the role of HH in self-assembly at molecular levels, an imperative step to understand the biological systems.

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

“…The hydrated CO groups possess a partially negative charge on the O atoms, while the Fe atoms with a partially positive charge are less hydrated. This charge imbalance explains the negative surface charges for the colloids as we have reported before (Scheme b). , The TEM images reveal spherical particles with a dark periphery, suggesting the formation of vesicles (Figures c and S13a). Based on a computer simulation, the hydration of the backbone is responsible for a long-range hydration interaction that drives the macromolecules to a parallel association into the membrane. , The diameter of the vesicles estimated from the TEM image is ca.…”

“…84/1) are illustrated in Figure . The fractions of a strongly and weakly bound water ( T 2 S and T 2 W ) are larger than those for the solutions with 0.5 μL of water (Figure S9b) because a higher water content enhances the hydration . The fraction of T 2 W for the solutions of P­(FpP) (8.0%) and P + [BPh 4 ] − (8.2%; Figure S9b) is similar because T 2 W is attributed to the water interacting with the CO groups in the same macromolecular backbone (Figure a,b).…”

“…This investigation started from the FT-IR analysis of P­(FpP) 7 in tetrahydrofuran (THF) (1 mL, 40 mg/mL) in the presence of various amounts of water (up to 20 μL to avoid HE-caused aggregation). As shown in Figure a, upon the addition of water, the absorption peak for the terminal CO groups (CO–Fe– in the repeating unit) shifts by 14 cm –1 with a shoulder remaining at 1914 cm –1 , indicating the interaction of the CO groups with water. ,,− This interaction also occurs for the solution of P + [BPh 4 ] − , as indicated by the FT-IR spectra (Figure b), suggesting that the ionic end group with a hydrophobic [BPh 4 ] − does not disturb the hydration. However, there is no detectable water carbonyl interaction for the solution of P + I – because no shift of the CO absorption bands is observed before and after the addition of water (Figure c).…”

“…The migration insertion polymerization (MIP) of FpP (Fp = (Cp)­Fe­(CO) 2 , P = alkylphosphine group) produces P­(FpP), − which is able to assemble in water into vesicles via a lateral association of the macromolecular chains into a vesicular membrane. , The interaction of water with CO groups is detectable by Fourier transform infrared (FT-IR). − It suggests that hydration is responsible for the assembly, but the role of water is still a matter of research. By converting the phosphine end group to phosphonium cation (Scheme ), we create P + X – (P + = P­(FpP) phosphonium cation, X – = I – or [BPh 4 ] − ) to study the dependence of water carbonyl interaction on the water structure perturbated by an ionic end group.…”

“…This charge imbalance explains the negative surface charges for the colloids as we have reported before (Scheme 1b). 33,38 The TEM images reveal spherical particles with a dark periphery, suggesting the formation of vesicles (Figures 5c and S13a). Based on a computer simulation, 27 the hydration of the backbone is responsible for a long-range hydration interaction that drives the macromolecules to a parallel association into the membrane.…”