Differences in Cucurbit[7]uril: Surfactant Complexation Promoted by the Cationic Head Group

Authors

  • Márcia Pessêgo,

    1. Departamento de Química Física, Centro de Investigación en Química Biológica y Materiales Moleculares (CIQUS), Universidad de Santiago, 15782 Santiago (Spain)
    2. CIQA, Departamento de Química e Farmácia, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal)
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  • Dr. José P. Da Silva,

    1. CIQA, Departamento de Química e Farmácia, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal)
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  • Dr. José A. Moreira,

    1. CIQA, Departamento de Química e Farmácia, Faculdade de Ciências e Tecnologia, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal)
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  • Prof. Luis García-Río

    Corresponding author
    1. Departamento de Química Física, Centro de Investigación en Química Biológica y Materiales Moleculares (CIQUS), Universidad de Santiago, 15782 Santiago (Spain)
    • Departamento de Química Física, Centro de Investigación en Química Biológica y Materiales Moleculares (CIQUS), Universidad de Santiago, 15782 Santiago (Spain)
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Abstract

The formation of host/guest complexes between cucurbit[7]uril (CB7) and tetradecyltrialkylammonium bromide surfactants with trimethyl (C14TMA+), triethyl (C14TEA+), and tripropyl (C14TPA+) head groups was studied. Complexation was studied by ESI-MS, isothermal titration calorimetry (ITC), and NMR spectroscopy. The structure of the complexes is strongly dependent on the surfactant head group. Both 1:1 and 2:1 complexes are formed with all cationic surfactants. The magnitude of the K1:1 binding constants decreases with the alkyl length of the head group, whereas that of the K2:1 binding constants is independent of the nature of the surfactant head group. Distinct structures were found for the 1:1 and 2:1 complexes. C14TMA+ and C14TPA+ surfactants form 1:1 inclusion complexes that comprise the head group close to the CB7 portal and 2:1 external complexes with both host molecules near the head group. The 1:1 complexes between C14TEA+ and CB7 showed that the head group was centered inside the CB7 cavity, whereas in the 2:1 complex the second molecule of CB7 was located at the end of the main alkyl chain.

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