[3.3]Ferrocenophanes with Guanidine Bridging Units as Multisignalling Receptor Molecules for Selective Recognition of Anions, Cations, and Amino Acids
✍ Scribed by Francisco Otón; Arturo Espinosa; Alberto Tárraga; Carmen Ramírez de Arellano; Pedro Molina
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 474 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The synthesis, electrochemical, and optical properties of a new [3.3]ferrocenophane framework in which two ferrocene subunits, with similar electronic environments, are linked through two substituted guanidine moieties, are reported. The receptors 4–7 have been prepared in good yields by the reaction of bis(carbodiimide) 3 with primary amines. This architecture is exceptionally “tunable” because a variety of “legs” may be appended to the basic [3.3]ferrocenophane scaffold to give a wide range of signaling units. These receptors show remarkable ion‐sensing properties, due to the presence of a redox active unit (ferrocene), and an amphoteric binding site (guanidine). In this nitrogen‐rich structural motif the guanidine bridges act as multipoint binding sites for anions, cations, and amino acids. Sensing of anions takes place both by unprecedented redox‐ratiometric measurements (F^−^, Cl^−^, AcO^−^, NO~3~^−^, HSO~4~^−^, H~2~PO~4~^−^, and HP~2~O~7~^3−^), and colorimetric change (F^−^, AcO^−^, H~2~PO~4~^−^, and HP~2~O~7~^3−^). Sensing and discrimination of amino acids takes place by redox‐ratiometric measurements, whereas the recognition of metal cations (Zn^2+^, Ni^2+^, and Cd^2+^) is achieved either by electrochemical or fluorescence measurements. Moreover, the reported receptors display splitting of the oxidation wave of the Fe^II^/Fe^III^ redox couple, and form the mixed‐valence species 4^+.^‐7^+.^ by electrochemical partial oxidation which, interestingly, show intervalence charge‐transfer transitions associated to the appearance of absorption bands in the near infrared spectral region.