title: Competition between Hydrogen Bonding and Proton Transfer during Specific Anion Recognition by Dihomooxacalix[4]arene Bidentate Ureas.
abstract: Competition between hydrogen bonding and proton transfer reactions was studied for systems composed of electrogenerated dianionic species from dinitrobenzene isomers and substituted dihomooxacalix[4]arene bidentate urea derivatives. To analyze this competition, a second-order ErCrCi mechanism was considered where the binding process is succeeded by proton transfer and the voltammetric responses depend on two dimensionless parameters: the first related to hydrogen bonding reactions, and the second one to proton transfer processes. Experimental results indicated that, upon an increase in the concentration of phenyl-substituted dihomooxacalix[4]arene bidentate urea, voltammetric responses evolve from diffusion-controlled waves (where the binding process is at chemical equilibrium) into irreversible kinetic responses associated with proton transfer. In particular, the 1,3-dinitrobenzene isomer showed a higher proton transfer rate constant (∼25 M(-1) s(-1)) compared to that of the 1,2-dinitrobenzene (∼5 M(-1) s(-1)), whereas the 1,4-dinitrobenzene did not show any proton transfer effect in the experimental conditions employed.
authors.affiliation: Centro de Investigación y Desarrollo Tecnológico en Electroquímica, Parque Tecnológico Querétaro Sanfandila , 76703 Sanfandila, Pedro Escobedo, Querétaro, Mexico.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Martínez-González
authors.affiliation: Departamento de Química del Centro de Investigación y Estudios Avanzados del I.P.N., Av. Instituto Politécnico Nacional 2508 , Apdo. Postal 14-740, C. P. 07360, Mexico City, Mexico.
authors.forename: Felipe J
authors.initials: FJ
authors.lastname: González
authors.affiliation: Centro de Química Estrutural, Instituto Superior Técnico , Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors.forename: José R
authors.initials: JR
authors.lastname: Ascenso
authors.affiliation: Centro de Química Estrutural, Faculdade de Ciências da Universidade de Lisboa , Edifício C8, 1749-016 Lisboa, Portugal.|Faculdade de Farmácia da Universidade de Lisboa , Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
authors.forename: Paula M
authors.initials: PM
authors.lastname: Marcos
authors.affiliation: Centro de Investigación y Desarrollo Tecnológico en Electroquímica, Parque Tecnológico Querétaro Sanfandila , 76703 Sanfandila, Pedro Escobedo, Querétaro, Mexico.
authors.forename: Carlos
authors.initials: C
authors.lastname: Frontana