Polar host–guest interactions. Solubilization of some polar compounds with lipophilic calix[6]arenes containing polar groups in apolar media

Abstract

Alkylation of three of the six hydroxy groups in calix[6]arene (2) with 1-bromo-7,7-di(ethoxycarbonyl)pentacosane (3) followed by hydrolysis and subsequent condensation with NH₃ gives rise to a hexa-amide derivative (6); the structural formula refers to a mixture of regioisomers of unknown composition. 1-Ethyl-4-methoxycarbonylpyridinium iodide (12) and formamide (HCONH₂) as polar guests are solubilized in apolar organic solvents such as hexane and CCl₄via host–guest (1:1) complex formation with (6) as a lipophilic polar host. The absorption maximum at 365 nm of (12) thus solubilized indicates that the binding site of (6) for (12) is relatively polar. The solubilization of (12) and HCONH₂ is discussed in terms of micro-solvation interactions of the polar core of (6) with the guests.