Molecular structure-interfacial activity relation\-ship of N-substituted aminoacids, adsorption of N-Dansylglycine at the Mercury/aqueous solution interface

The adsorption of N-dansylglycine (5-dimethylaminonaphthalene-I-sulphanylglycine) in monoaniomcand dianionic forms has been characterized in aqueous solution at a mercury electrode. At pH 6(only the monoanionic form present in the bulk), N-dansylglycine is arranged on the metal surface m aperpendicular manner through the naphthyl moiety, and an attractive interaction factor among theadsorbed molecules is observed. At pH 12 (dianionic form), the molecules is still arranged in a perpendicularway show a greater molecular area and no interaction factor is revealed. These features. together withthose regarding a series of other N-substituted glycine derivatives previously studied, are related to somecalculated structural indices, and a relationship is obtained between the adsorption Gibbs energy andAE, n (the energy difference between the lowest unoccupied molecular orbital and the highest occupiedone). Moreover, some local theoretical indices (net atomic charges, partial net charges) are used in atentative molecular interpretation of the disposition of the sorbate on the surface and of the significanceof the Frumkin interaction factor. To offer a more general grounding to the argument, a group ofnaphthyl and benzoyl denvatives studied by Bockris and co-workers (J. Phys. Chem., 65 (1961) 2000) invery similar conditions is also considered.