title: Mediated oxidation of ascorbic acid on a homologous series of ferrocene-terminated self-assembled monolayers.
abstract: The kinetics of electrocatalytic oxidation of ascorbate was studied on a series of redox self-assembled monolayers (SAMs) of the general formula Fc(CH2)4COO(CH2)nSH as electron-transfer mediators, where Fc is the ferrocenyl group and n = 3, 6, 9, and 11. We show that the rate of electron transfer from ascorbate to the surface-confined Fc+ decreases with increasing n. The rationale for the dependence of the rate of electrocatalytic activity and n, in the presence of ClO4, is obtained from Fourier-transform surface-enhanced Raman spectroscopy (FT-SERS), cyclic voltammetry, and electrochemical quartz crystal microbalance (EQCM) data. In particular, FT-SERS shows decreasing amounts of surface-bound ClO4- upon oxidation of the ferrocene with decreasing n, while EQCM data show the effective electrode mass increase was consistently higher on the shorter chain SAMs. This mass increase is likely due to increasing ferricinium cation hydration. As n decreases, the SAMs become less ordered (FT-SERS data), as is widely known from previous literature. Disorder favors water penetration into the SAM, which, in turn, increases the hydration of the Fc+ (EQCM data). Increased hydration of the Fc+ impedes the formation of Fc+-ClO4- ion pairs (EQCM and FT-SERS data), which, consequently, accelerates the electrocatalytic electron transfer from the solution-dissolved ascorbate.
authors: Department of Bioelectrochemistry and Biospectroscopy, Institute of Biochemistry, Mokslininku 12, LT-08662 Vilnius, Lithuania.
authors: Birute
authors: B
authors: Kazakeviciene
authors: Gintaras
authors: G
authors: Valincius
authors: Gediminas
authors: G
authors: Niaura
authors: Zita
authors: Z
authors: Talaikyte
authors: Maryte
authors: M
authors: Kazemekaite
authors: Valdemaras
authors: V
authors: Razumas
authors: Deivis
authors: D
authors: Plausinaitis
authors: Ausra
authors: A
authors: Teiserskiene
authors: Vaclovas
authors: V
authors: Lisauskas
mesh_terms: D001205:Ascorbic Acid / Q000737:chemistry*; D003460:Crystallization; D004563:Electrochemistry; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008567:Membranes, Artificial; D000075163:Metallocenes; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011791:Quartz / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013499:Surface Properties
chemical_list: D005296:Ferrous Compounds; D008567:Membranes, Artificial; D000075163:Metallocenes; D011791:Quartz; D001205:Ascorbic Acid; C004998:ferrocene