Selective Anion Sensing by a Tris-Amide CTV Derivative:  ¹H NMR Titration, Self-Assembled Monolayers, and Impedance Spectroscopy

Abstract

A hydrogen-bond forming tris(amide) receptor based on cyclotriveratrylene (CTV) was prepared. Self-assembled monolayers (SAMs) of the receptor were formed on gold surfaces. Desorption experiments show a surface coverage of 2.26 x 10(-10) mol/cm(2). (1)H NMR and UV measurements confirm that the receptor exhibits the highest affinity for acetate ions among the anions studied. Electrochemical impedance was used to investigate anion sensing by the SAMs and proved to be an efficient and convenient technique for detecting anions in aqueous solutions. Upon binding acetate anions, the monolayer-modified gold electrodes show a drastic increase of the R(ct) values when Fe(CN)(6)(3-/4-) is used as the redox probe. When the probe was changed to a positively charged one, Ru(NH3)(6)(3+/2+), the R(ct) values decreased monotonically as the acetate concentration was increased, thus confirming the accumulation of negative surface charge upon anion binding. H(2)PO(4-) shows some interference when sensing AcO-. Other monovalent anions such as Cl-, Br-, NO3(-) and HSO4(-) do not bind to the CTV receptor either in solution or on the surfaces.

Electrochemical investigation on the film of L-cysteine self-assembled to nanoparticles on a gold electrode

“…When the bare gold electrode was modified with gold nanoparticles, the peak current increased obviously in the solution of either 1 mM K 3 Fe(CN) 6 or 1 M H 2 SO 4 . Compared with the bare and nanogold electrode, the electrode modified with gold nanoparticles and L-cysteine showed the better reversible CV response in K 3 Fe(CN) 6 . This may be the protonation of -NH 2 in L-cysteine and the electrostatic interaction with K 3 Fe(CN) 6 [19].…”

“…Compared with the bare and nanogold electrode, the electrode modified with gold nanoparticles and L-cysteine showed the better reversible CV response in K 3 Fe(CN) 6 . This may be the protonation of -NH 2 in L-cysteine and the electrostatic interaction with K 3 Fe(CN) 6 [19]. Figure 1(B) showed the electrochemical impedance spectroscopy (EIS) of Nyquist plots.…”

“…Figure 1(A) showed CVs for 1 mM K 3 Fe(CN) 6 containing 0.1 M KCl at a) a clean gold electrode, b) a gold electrode modified with nano gold, c) L-cysteine self-assembled to the nanogold electrode.…”

“…The 25 m diameter Pt ultramicroelectrode (UME), which is made by our own laboratory, were used to investigate the modified gold electrode surface and record the feedback approach curve at the different concentration of the mediator solution (K 3 Fe(CN) 6 ). In the SECM experiments, the modified electrode was used as the substrate.…”

“…Surface-enhanced Raman spectroscopy (SERS) and surface-enhanced second-harmonic generation (SESHG) were employed to investigate the adsorption of L-cysteine on a polycrystalline silver electrode [4]. What matters most was that self-assemble monolayers (SAMs) was a simple and stable method in the study of modified electrode, and it can obtain spontaneously high-order monolayer on gold via the thiol end group [5][6][7][8]. The electrode modified directly with Lcysteine SAMs can investigate various performances, including the following several aspects, voltammetric behavior of vitamin B 2, selective response of dopamine in ascorbic acid and electrochemical behavior of epinephrine [9][10][11].…”