title: Host-guest interactions between cyclodextrins and surfactants with functional groups at the end of the hydrophobic tail.
abstract: The aim of this work was to investigate the influence of the incorporation of substituents at the end of the hydrophobic tail on the binding of cationic surfactants to α-, β-, and γ-cyclodextrins. The equilibrium binding constants of the 1:1 inclusion complexes formed follow the trend K1(α-CD)>K1(β-CD)≫K1(γ-CD), which can be explained by considering the influence of the CD cavity volume on the host-guest interactions. From the comparison of the K1values obtained for dodecyltriethylammonium bromide, DTEAB, to those estimated for the surfactants with the substituents, it was found that the incorporation of a phenoxy group at the end of the hydrocarbon tail does not affect K1, and the inclusion of a naphthoxy group has some influence on the association process, slightly diminishing K1. This makes evident the importance of the contribution of hydrophobic interactions to the binding, the length of the hydrophobic chain being the key factor determining K1. However, the presence of the aromatic rings does influence the location of the host and the guest in the inclusion complexes. The observed NOE interactions between the aromatic protons and the CD protons indicate that the aromatic rings are partially inserted within the host cavity, with the cyclodextrin remaining close to the aromatic rings, which could be partially intercalated in the host cavity. To the authors' knowledge this is the first study on the association of cyclodextrins with monomeric surfactants incorporating substituents at the end of the hydrophobic tail.
authors.affiliation: Department of Physical Chemistry, University of Seville, C/Profesor García González 1, 41012 Seville, Spain.
authors.forename: Victoria Isabel
authors.initials: VI
authors.lastname: Martín
authors.affiliation: Department of Physical Chemistry, University of Seville, C/Profesor García González 1, 41012 Seville, Spain.
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Ostos
authors.affiliation: NMR Service, University of Seville, Apartado 1203, E-41071 Seville, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Angulo
authors.affiliation: Department of Physical Chemistry, University of Seville, C/Profesor García González 1, 41012 Seville, Spain.
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Márquez
authors.affiliation: Department of Physical Chemistry, University of Seville, C/Profesor García González 1, 41012 Seville, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: López-Cornejo
authors.affiliation: Department of Chemical Engineering, Physical Chemistry and Materials Science, Faculty of Experimental Sciences, Campus de El Carmen, Avda. de las Fuerzas Armadas s/n, 21071 Huelva, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: López-López
authors.affiliation: Department of Organic Chemistry, University of Seville, C/Profesor García González 1, 41012 Seville, Spain.
authors.forename: Ana Teresa
authors.initials: AT
authors.lastname: Carmona
authors.affiliation: Department of Physical Chemistry, University of Seville, C/Profesor García González 1, 41012 Seville, Spain. Electronic address: moya@us.es.
authors.forename: María Luisa
authors.initials: ML
authors.lastname: Moyá
keywords: Aromatic substituents; Conductivity; Cyclodextrins; Inclusion complexes; NMR; Surfactants