Voltammetrically Controlled Electron Transfer Reactions from Alkanethiol Modified Gold Electrode Surfaces to Low Molecular Weight Molecules Deposited within Lipid (Lecithin) Bilayers

Abstract

A procedure was developed for initiating electron transfer from a gold electrode to a low molecular weight electron acceptor present inside supported lipid (lecithin) bilayers, followed by further electron transfer to an electron acceptor present in an aqueous solution. The electron acceptors present in the lecithin bilayers and aqueous phase were 7,7,8,8-tetracyanoquinodimethane (TCNQ) and [Fe(III)(CN)(6)](3-), respectively. A polished planar gold disk electrode was first coated via self-assembly procedures with an alkanethiol monolayer. A phospholipid layer consisting of multiple bilayers of lecithin containing TCNQ was subsequently deposited onto the alkanethiol monolayer. The Au/alkanethiol/lecithin-TCNQ electrode was placed in an aqueous solution containing various amounts of [Fe(III)(CN)(6)](3-) and [Fe(II)(CN)(6)](4-), with 0.5 M KCl as the supporting electrolyte. In the absence of TCNQ inside the alkanethiol/lecithin layers, only a small background current was observed. When TCNQ was included in the alkanethiol/lecithin layers, the voltammetry showed features typical of a catalytic process, due to the TCNQ being reduced to TCNQ(-*) within the lecithin bilayers and then undergoing oxidation back to TCNQ via interaction with [Fe(III)(CN)(6)](3-) at the lecithin-aqueous solution interface. The procedures for preparing the alkanethiol/lecithin-TCNQ coatings were optimized in order to obtain the most reproducible voltammetric response. Experiments were also performed using tetrathiafulvalene (TTF) as an electron donor in the lipid bilayer phase.

Preparation and Characteristics of Novel Fibers Based on Cellulose Acetate and Soy Lecithin for Attracting and Binding POPs

“…Nevertheless, the presence of the Faradaic current indicated that electron transfer reactions were still occurring between ( ) (Figure 3(c)), indicating that the incorporation of SL into CA further reduces electron transfer between the GCE and the solution phase species. Although the distribution of SL in CA is a non-bilayer structure, its reduction of the current is similar to that of SL bilayers or multilayers [18]. The SL bilayer membrane is nearly completely insulative [19].…”

Voltammetric studies on vitamin K1 in organic solvents

“…Because the water molecules are reacting as Lewis acids for H-bonding with radical anions and dianions, the amphoteric (Lewis acid and Lewis base) properties of the solvents may also be important. 35 In addition to interactions between the solvent-water-analyte, it would also be expected that the Bu 4 N + cation would interact as an ion-pair with the charged compounds and thereby reduce the water interactions with VK 1 -• and VK 1 2-, especially in solvents with low dielectric constants. 36,37 Thus the data in Figure 2d…”

“…In unbuffered aqueous solutions, the initial reaction occurs via 2eto form the hydrogen-bonded dianion. 1,[24][25][26][27][28][29][30][31][32][33][34][35][36][37] Due to its basicity and depending on the exact solution pH, the dianion will exist in solution as a mixture of Q 2-, QH -, QH 2…”

“…In one instance, a solid electrode is first coated with a self-assembled monolayer (SAM), such as an alkanethiol, [16][17][18][19][20][21] and then a solution containing the molecule of interest and another bilayer forming molecule are allowed to spontaneously interact and form a membrane by attaching themselves to the tethered portion [a tethered bilayer membrane (t-BLM)]. [22][23][24][25][26][27][28][29][30][31][32][33][34][35] An alternative procedure simply involves placing a droplet of a volatile organic solvent (such as chloroform) that contains membrane forming molecules onto the surface of the electrode and allowing the bilayer to form during the evaporation process, [7][8][9][35][36][37][38][39] or allowing a clean electrode surface (such as a freshly cut Pt electrode)…”

“…[40][41][42][43] In order to improve the conductivity properties of the membrane, there are several reports where low molecular weight molecules such as TCNQ are incorporated into the s-BLM in order to promote the transfer of an electron through the membrane to a solution phase species (a mediated electron transfer). 17,35,[44][45][46][47][48][49][50][51] One major issue with interpreting the results from electrochemical studies on s-BLMs is that defect free bilayer membranes will only form on glass substrates, with metallic and carbon surfaces being poor substrates to obtain ideal membrane coverage. 52 Similarly, even with tethered molecules attached to the electrode surface, such as self-assembled layers of alkanethiols, it is highly likely that pin-holes will exist in the layers.…”