title: Hydrophobic effect as a driving force for host-guest chemistry of a multi-receptor Keplerate-type capsule.
abstract: The effectiveness of the interactions between various alkylammonium cations and the well-defined spherical Keplerate-type {Mo132} capsule has been tracked by (1)H DOSY NMR methodology, revealing a strong dependence on the self-diffusion coefficient of the cationic guests balanced between the solvated and the plugging situations. Analysis of the data is fully consistent with a two-site exchange regime involving the 20 independent {Mo9O9} receptors of the capsule. Furthermore, quantitative analysis allowed us to determine the stability constants associated with the plugging process of the pores. Surprisingly, the affinity of the capsule for a series of cationic guests increases continuously with its apolar character, as shown by the significant change of the stability constant from 370 to 6500 for NH4(+) and NEt4(+), respectively. Such observations, supported by the thermodynamic parameters, evidence that the major factor dictating selectivity in the trapping process is the so-called "hydrophobic effect". Computational studies, using molecular dynamics simulations, have been carried out in conjunction with the experiments. Analysis of the radial distribution functions g(r) reveals that NH4(+) and NMe4(+) ions behave differently in the vicinity of the capsule. The NH4(+) ions do not exhibit well-defined distributions when in close vicinity. In contrast, the NMe4(+) ions displayed sharp distributions related to different scenarios, such as firmly trapped or labile guest facing the {Mo9O9} pores. Together, these experimental and theoretical insights should aid in the exploitation of these giant polyoxometalates in solution for various applications.
authors: †Institut Lavoisier de Versailles UMR 8180, Université de Versailles Saint-Quentin, 78035 Versailles, France.|‡Inorganic and Organometallic Coordination Chemistry Laboratory, Faculty of Sciences, Lebanese University, R. Hariri University Campus, Beyrouth, Hadath, Lebanon.
authors: Nancy
authors: N
authors: Watfa
authors: §Institute of Chemical Research of Catalonia (ICIQ), Av. dels Països Catalans, 16, Tarragona 43007, Spain.|⊥Departament d'Enginyeria Química, ETSEQ, Universitat Rovira i Virgili, Av. dels Països Catalans, 26, 43007 Tarragona, Spain.
authors: Dolores
authors: D
authors: Melgar
authors: †Institut Lavoisier de Versailles UMR 8180, Université de Versailles Saint-Quentin, 78035 Versailles, France.
authors: Mohamed
authors: M
authors: Haouas
authors: †Institut Lavoisier de Versailles UMR 8180, Université de Versailles Saint-Quentin, 78035 Versailles, France.
authors: Francis
authors: F
authors: Taulelle
authors: ‡Inorganic and Organometallic Coordination Chemistry Laboratory, Faculty of Sciences, Lebanese University, R. Hariri University Campus, Beyrouth, Hadath, Lebanon.
authors: Akram
authors: A
authors: Hijazi
authors: ‡Inorganic and Organometallic Coordination Chemistry Laboratory, Faculty of Sciences, Lebanese University, R. Hariri University Campus, Beyrouth, Hadath, Lebanon.
authors: Daoud
authors: D
authors: Naoufal
authors: ⊥Departament d'Enginyeria Química, ETSEQ, Universitat Rovira i Virgili, Av. dels Països Catalans, 26, 43007 Tarragona, Spain.
authors: Josep Bonet
authors: JB
authors: Avalos
authors: †Institut Lavoisier de Versailles UMR 8180, Université de Versailles Saint-Quentin, 78035 Versailles, France.
authors: Sébastien
authors: S
authors: Floquet
authors: §Institute of Chemical Research of Catalonia (ICIQ), Av. dels Països Catalans, 16, Tarragona 43007, Spain.|∥Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Av. dels Països Catalans, 26, 43007 Tarragona, Spain.
authors: Carles
authors: C
authors: Bo
authors: †Institut Lavoisier de Versailles UMR 8180, Université de Versailles Saint-Quentin, 78035 Versailles, France.
authors: Emmanuel
authors: E
authors: Cadot