Aqueous solubilization of hydrophobic supramolecular metal–organic nanocapsules

Abstract

Micelles of metal-seamed C-propylpyrogallol[4]arene-based [(PgC₃)_nM_4nL_0–4n, L = ligand, M = metal] hexamers and dimers in water have been formulated using non-ionic surfactants and characterized using in situ scattering techniques. Polysorbitans (tween 20, tween 40, tween 80) are utilized to solubilize (PgC₃)₆Cu₂₄ and (PgC₃)₆Ni₂₄L₂₄ hexamers, (PgC₃)₂Ni₈L₈, (PgC₃)₂Zn₈L₈, and (PgC₃)₂Co₈L₈ dimers in water. The dimensions of micelles of tweens⊂(PgC₃)_nM_4nL_0–4n dimers and hexamers are studied using dynamic light scattering (DLS; hydrodynamic radius/R_h) and small-angle neutron scattering (SANS). SANS data is fitted to a polydisperse core–shell–sphere model (static radius/R_HS) and used to calculate the radius of gyration (R_g). An increase in radius of the tween 20 (C12)- and tween 40 (C16)-based micelles is observed with an increase in the radius of the nanocapsule (dimer vs. hexamer); however, given the longer alkyl tails of tween 80 (C18:1, cis-9), a progression in radius is not observed for tween 80-enclosed micelles due to the unsaturation (C9) and bent alkyl tail of the surfactant. The R_g : R_h ratios are close to 0.77 for the control (0.62), tween 20⊂dimeric (0.67) and tween 20⊂hexameric (0.68) micelles that demonstrates the sphericity of micelles in water. In contrast, the higher R_g/R_h ratio (0.76 to 0.93) of tween 80-based micelles is indicative of more elongated micellar species in aqueous solution.