Ferrocene–β‐Cyclodextrin Conjugates: Synthesis, Supramolecular Behavior, and Use as Electrochemical Sensors

• Published in: Chemistry : a European journal Vol. 15; no. 33; pp. 8146 - 8162
• Main Authors: Casas-Solvas, Juan M., Ortiz-Salmeron, Emilia, Fernandez, Ignacio, Garcia-Fuentes, Luis, Santoyo-Gonzalez, Francisco, Vargas-Berenguel, Antonio
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY‐VCH Verlag 17.08.2009; Wiley
• Subjects: beta-Cyclodextrins - chemical synthesis; beta-Cyclodextrins - chemistry; Bile Acids and Salts - chemistry; bile salts; Binding Sites; Calorimetry; Catalysis; Chemistry; Chemistry, Multidisciplinary; Copper - chemistry; cyclodextrins; Electrochemistry; ferrocene; Ferrous Compounds - chemical synthesis; Ferrous Compounds - chemistry; Magnetic Resonance Spectroscopy; Metallocenes; Molecular Structure; Oxidation-Reduction; Physical Sciences; Science & Technology; sensors; Stereoisomerism; voltammetry; GRADIENT SPIN-ECHO; voltammetry; BILE-SALTS; NUCLEAR-MAGNETIC-RESONANCE; INCLUSION COMPLEXES; cyclodextrins; STUDYING TRANSLATIONAL DIFFUSION; FERROCENECARBOXYLIC ACID; sensors; SELECTIVE BINDING; MOLECULAR RECOGNITION THERMODYNAMICS; bile salts; ferrocene; HOST-GUEST COMPLEXATION; SODIUM CHOLATE
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200900593

Ferrocene with a β‐cyclodextrin unit bound to one or both cyclopentadienyl rings through the secondary face were conveniently synthesized by regiospecific copper(I)‐catalyzed cycloaddition of 2‐O‐propargyl‐β‐cyclodextrin to azidomethyl or bis(azidomethyl)ferrocene. The supramolecular behavior of the synthesized conjugates in both the absence and presence of bile salts (sodium cholate, deoxycholate, and chenodeoxycholate) was studied by using electrochemical methods (cyclic and differential pulse voltammetry), isothermal titration calorimetry, and NMR spectroscopy (PGSE, CPMG, and 2D‐ROESY). These techniques allowed the determination of stability constants, mode of inclusion, and diffusion coefficients for complexes formed with the neutral and, in some cases, the oxidized states of the ferrocenyl conjugates. It was found that the ferrocenyl conjugate with one β‐cyclodextrin unit forms a redox‐controllable head‐to‐head homodimer in aqueous solution. The ferrocene–bis(β‐cyclodextrin) conjugate is present in two distinguishable forms in aqueous solution, each one having a different half‐wave oxidation potential for the oxidation of the ferrocene. By contrast, only one distinguishable form for the oxidized state of the ferrocene–β‐cyclodextrin conjugate is detectable. The redox‐sensing abilities of the synthesized conjugates towards the bile salts were evaluated based on the observed guest‐induced changes in both the half‐wave potential and the current peak intensity of the electroactive moiety. Guest room? Two ferrocene–β‐cyclodextrin conjugates were conveniently synthesized by click chemistry. The supramolecular behavior of both conjugates was studied in both the absence and presence of three bile salts, and their redox‐sensing abilities towards the bile salts were evaluated based on observed guest‐induced changes in the half‐wave potential and the current peak intensity (see figure).