Head-to-tail Aggregates of Sulfonatomethylated Calix[4]resorcinarene in Aqueous Solutions

Abstract

Two amphiphilic water-soluble sulfonatomethylated calix[4]resorcinarene derivatives were studied by various 1 H NMR techniques ( 1 H NMR titration, 2D NOESY, NMR diffusion measurements). The derivative with methyl moieties at the lower rim (1) was found to be nonaggregated in the range 0 -10 mM in aqueous solutions. Lengthening of the lower rim substituent to pentyl (2) results in self-aggregation of 2 in aqueous solutions with the aggregation number varying from 3 at 1 mM to 20 at 10 mM. The 2D NOESY 1 H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions. Binding of guests (tetramethylammonium and N-methylpyridinium) results in additional stabilization of the aggregates whilst the head-to-tail packing mode of the aggregate is retained.

Complexes of tetramethylensulfonatocalix[4]resorcinarene aggregates with methyl orange: Interactions with guests and driving force of color response

“…Their 95-99% binding efficiency toward suitable guests is accomplished by substrate binding with both the individual macrocycles and their aggregates (Fig. 7) [8,9]. Binding of organic cations with H often causes increase of the aggregate dimensions [9].…”

“…Hydrophilic analog of H with four methyl substituents at the lower rim forms no aggregates in 0-10 mM solutions and shows only a moderate binding efficiency. Amphiphilic H, on the other hand, exists in aqueous solutions as head-to-tail dimers or 3-4 nm large polydisperse aggregates [8,9]. Their 95-99% binding efficiency toward suitable guests is accomplished by substrate binding with both the individual macrocycles and their aggregates (Fig.…”

“…In our earlier works, we have demonstrated that aggregation plays a crucial role in the binding properties of amphiphilic macrocycles [6][7][8][9][10]. Hydrophilic analog of H with four methyl substituents at the lower rim forms no aggregates in 0-10 mM solutions and shows only a moderate binding efficiency.…”

“…Tetramethylensulfonated tetrapentylcalix [4]resorcinarene (H), reported here, in aqueous solutions is always aggregated either in dimers or in polydisperse aggregates that show a high (>90%) efficiency of guest binding. Sulfonated calix [4]resorcinarene forms inclusion complexes with ammonium-substituted guests of a suitable size, where bound guests are localized in the cavities formed by head-to-tail oriented molecules of H [8,9]. Binding efficiency of H toward earlier mentioned MO dye does not exceed 30% since it is not encapsulated in the layer of aggregated macrocycles and is bound exclusively on the surface of the aggregates.…”

Synthesis and properties of potassium salts of per-O-carboxymethyl-calix[4]pyrogallols and their complexes with Cu2+, Fe3+, and La3+

“…This value is also lower than that for calixarenes with close geometric sizes. For example, for the calix[4]resorcinol tetrasulfonate derivative with the methyl substituents at the lower rim 38,39 the experimental values D s (3.50•10 -10 m 2 s -1 ) and R H (7.7 Å) determined for aqueous solutions agree well with the theo retical values: D s = 3.73•10 -10 m 2 s -1 and R H = 7.4 Å.According to available data, 40-43 the decrease in D s of molecules by 25-30% indicates the formation of a dimer. When the concentration of compound 5 decreases from 35 to 0.5 mmol L -1 , the D s value remains unchanged, indicating the stability of the aggregated structures.…”