title: CO2 capture by multivalent amino-functionalized calix[4]arenes: self-assembly, absorption, and QCM detection studies.
abstract: The reactivity of CO(2) with polyamino substrates based on calix[4]arenes and on a difunctional, noncyclic model has been studied. All the compounds react with CO(2) in chloroform to form ammonium carbamate salts. However, the number, topology, and conformational features of the amino-functionalized arms present on the multivalent scaffold have a remarkable influence on the reaction efficiency and on the product composition. Tetraaminocalix[4]arenes 1-3 rapidly and efficiently react with 2 equiv of CO(2), yielding highly stable hydrogen-bonded dimers formed by the self-assembly of two bis-ammonium bis-carbamate intramolecular salts. 1,3-Diaminocalix[4]arene 4 absorbs 1 mol of CO(2), affording less stable zwitterionic ammonium carbamates. Gemini compound 5 reacts with CO(2) in a 1:1 stoichiometry, forming hydrogen-bonded dimers of ammonium carbamate derivatives of moderate stability. For upper rim 1,3-diaminocalix[4]arene 6, in addition to the labile intramolecular salt, the presence of a self-assembled polymer was also detected. These systems were fully characterized in solution by (1)H and (13)C NMR spectroscopy, whereas the corresponding gas-solid reactions were further investigated by QCM measurements. Interestingly, the high affinity and reversibility of CO(2) uptake shown by 1,3-diamino calix[4]arene 4 enabled us to attain a promising QCM device for carbon dioxide sensing.
authors.affiliation: Dipartimento di Chimica Organica e Industriale, Università di Parma, Parco Area delle Scienze 17/A, I-43124, Parma, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Baldini
authors.forename: Monica
authors.initials: M
authors.lastname: Melegari
authors.forename: Valentina
authors.initials: V
authors.lastname: Bagnacani
authors.forename: Alessandro
authors.initials: A
authors.lastname: Casnati
authors.forename: Enrico
authors.initials: E
authors.lastname: Dalcanale
authors.forename: Francesco
authors.initials: F
authors.lastname: Sansone
authors.forename: Rocco
authors.initials: R
authors.lastname: Ungaro