Conformational analysis and anion-binding properties of ferrocenyl-calixarene receptors

Novel synthetic approaches toward redox active calixarene-based receptors are described wherein ferrocene fragments have been introduced at the lower rim through anion-binding urea or amide connections. A thorough 1H NMR investigation on macrocycles was performed in order to estimate their hydrogen bonding-driven self-association properties and improve our understanding of the correlation between molecular structures and redox properties. The anion-binding properties of these artificial receptors have also been revealed by NMR spectroscopy and thoroughly investigated by electrochemical methods. We especially assessed the importance of the urea-phosphate bonds in the observed electrochemical response upon studying receptors wherein the ferrocene reporters and binding fragments are intimately associated or fully disconnected through a long alkyl chain. The experimental results clearly showed the utmost importance of ion pairing effects in the electrochemical recognition process accounting for most of the transduction signal in organic apolar media. [image omitted].