5-(4-PIRIDIL)-1,3,4-(OXADIAZOL)-2-TIOL E Na3[Fe(CN)5Hpyt].3H2O: Síntese, caracterização e estudos de formação de monocamadas automontadas.

Abstract

-(4-pyridinyl)-1,3,4-oxadiazole-2-thiol (Hpyt) and [Fe(CN)5Hpyt]3- (FeHpyt) species spontaneously adsorbed on gold forming SAM (Self-Assembled Monolayers) that, based on electrochemical data, contain pinholes through which [Fe(CN)6]4– and [Ru(NH3)6]3+ probe molecules access the underlying gold electrode. From the former molecule and the dependence of the faradaic current on the pH value of the electrolyte solution, the surface pKa of the Hpyt SAM was evaluated as 4.2. Taking into account the STM (Scanning tunneling Microscopy) results obtained for the Hpyt SAM on Au(111), it was possible to estimate that the Hpyt molecules are adsorbed in an hexagonal arrangement with an average distance between the sulfur atoms of 5.5 Å. These images also showed the presence of pinholes, which indicate that a strong lateral interaction does not effectively happen. The thermodynamics parameters ΔHads, ΔGads and ΔSads of the Hpyt and FeHpyt adsorption process were calculated from the correlation between the concentration of the adsorbates on the surface (Γ) and in solution (C) at different temperatures. The surface coverage data were obtained from the reductive desorption process RS-Au + e- �� RS- + Au°, where R = Hpyt or FeHpyt, observed at -555 and -566 mV vs Ag|AgCl|Cl- for Hpyt and FeHpyt SAM, respectively, indicating an enhancement of the Au–S bond as consequence of the π-backbonding interaction from iron metal center toward the Hpyt moiety. The heterogeneous electron transfer reaction of cytochrome c metalloprotein was successfully assessed by Hpyt and FeHpyt and SAM, presenting a quasi-reversible voltammograms with potentials consistent with the native form of the protein.