Development of Chemical Sensors Based on Redox-Dependent Receptors:  N,N‘-Dimethyldiazapyrenium-Modified Electrodes

Abstract

Electrodes modified with Nafion films containing 2,7-dimethyldiazapyrenium (DAP2+) were prepared and characterized with voltammetry by themselves and in the presence of organic substrates. The large, planar, electron-poor aromatic surface in DAP2+ facilitates pi-stacking interactions with other planar aromatic molecules, particularly those that are negatively charged or electron-rich. Previous studies showed that the reduction of DAP2+ decreases the strength of these interactions, making the binding redox-dependent, and resulting in negative shifts in the E(1/2) of DAP2+/+. This study shows that the redox-dependent binding ability of DAP2+ is retained in Nafion, but the selectivity is considerably different. Most significantly, the electron-rich, neutral aromatic compounds that produced small shifts in the E(1/2) of DAP2+/+ in solution cause much larger shifts, up to -110 mV, with the modified electrodes. With indole as a substrate, Nernstian behavior is observed (-60 mV shift per log[indole]) between 10 and 0.5 mM.

Organic Photoredox Catalysis

“…An intriguing aspect of this report is the proposed mechanism of the PET catalyst (Scheme 180), which is a two-photon process involving consecutive transfers and excitation of the radical anion PDI• − in order to generate the strong reductant PDI• − *. The researchers were prompted to consider this unusual mechanistic scenario after observing that this system was capable of hydrodehalogenation in aryl halides which possess reduction potentials that are too negative to be reduced by PDI• − or PDI*: for frame of reference, 4′-bromoacetophenone 180.1 has a reduction potential of −1.9 V vs SCE, 543 The ground state absorbance and fluorescence properties of dimethyldiazapyrenium (DAP 2+ ) 544 have been studied in relation to host-guest complexation 103,104,545 and the use of DAP 2+ as a sensor 546,547 in a variety of applications. This dicationic analogue to methyl viologen absorbs in the visible (∼420 nm) and is a potent oxidant in the singlet excited state.…”

One-step formation of ultra-thin chemically functionalized redox-active Langmuir–Schaefer Nafion films

“…1,2 The intrinsic cation-exchange capabilities of Nafion have led to widespread applications as a coating to modify electrodes, especially in sensor applications and electroanalysis. [3][4][5][6][7] Nafion has been used to preconcentrate a wide range of cationic species, including redox mediators, [8][9][10][11][12][13][14][15][16][17][18] enzymes [19][20][21][22][23] and dyes [24][25][26] or, more simply, has been used as a permselective layer to protect electrodes from interferences such as anions and biological macromolecules. [27][28][29][30][31][32] Composite materials have recently been prepared using Nafion in combination with metal nanoparticles, [33][34][35][36][37][38][39] carbon nanotubes [40][41][42] and conducting polymers, [43][44][45][46]…”

Electrochemical performance of l-cysteine–goldparticle nanocomposite electrode interface as applied to preparation of mediator-free enzymatic biosensors

“…CGN was immobilized in the network of a Nafion membrane used for fabrication of the interface of GC/NCGN. The thickness of the Nafion membrane could be estimated [39]. SEM was utilized to identify the form and microstructure of the interface of GC/NCGN.…”