Stability and compatibility of resorcin[4]arene hexamer cages with amphiphilic random copolymers in organic solvents

Abstract

The structural integrity and guest–hosting capabilities of resorcin[4]arene-based hexamer cages ([Rs₄]₆ and [Rs₁₁]₆) bearing different side chains (–C₄H₉, butyl or –C₁₁H₂₃, undecyl) is explored using water-soluble copolymers mapped in different solvents (CHCl₃, CH₂Cl₂, toluene and THF). We here identify significant differences between the length of the macrocycle's “footing” chains (–C₄H₉ or –C₁₁H₂₃) and their intrinsic stability. NMR and DLS size analyses reveal that while both cages are stable in chloroform, the undecyl-footed [Rs₁₁]₆ cage demonstrates superior intrinsic stability in toluene and dichloromethane, self-assembling into discrete hexamers (D_h = 3.6 nm) even in the absence of embedded guests. In contrast, the butyl-footed [Rs₄]₆ cage requires an alkylammonium salt template to avoid formation of large and unstable aggregates. When mixed with amphiphilic random copolymers, the cage [Rs₁₁]₆ maintains high encapsulation efficiencies at molar ratios of up to 1 : 6 (cage : copolymer), regardless of the copolymer's philicity, displaying either aliphatic or fluorinated sidechains. A competitive interaction between the copolymers' polyethylene glycol (PEG) side chains and structural water molecules is proposed, establishing the cage [Rs₁₁]₆ as a robust and versatile scaffold for the development of complex, water-soluble nano-assemblies. This now offers a resilient platform for biomimetic carrier and catalytic applications.