Scanning Electrochemical Microscopy Studies of Electron Transfer through Monolayers Containing Conjugated Species at the Liquid−Liquid Interface

Abstract

The rates of electron transfer (ET) between two redox species through a monolayer of saturated dipalmytoyl phosphocholine and polyconjugated 2(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3phosphocholine phospholipids adsorbed at the interface of two immiscible electrolyte solutions (ITIES) were measured by scanning electrochemical microscopy. Comparison of the ET rates shows that addition of phospholipids with conjugated hydrocarbon chains increases the ET rate by at least a factor of 2 compared to films with only saturated hydrocarbon chains. This difference was sufficiently high to obtain information about distribution of lipid molecules in monolayers formed by mixing two lipids. Lateral scanning of an ultramicroelectrode tip across the lipid monolayer comprised of two different phospholipids showed that each lipid forms microsize domains. The rate of ET across a monolayer of lipid adsorbed at the ITIES was also probed as a function of temperature. A sharp decrease in ET rate with temperature suggests a phase transition of the hydrocarbon chains of the lipid molecules. The phase transition increases the ET distance between the two redox centers with a resultant decrease in ET rate.

Scanning electrochemical microscopy: beyond the solid/liquid interface

“…However, electron transfer rate constants between redox couples with conjugated phospholipids at the interface were twice those measured with saturated phospholipids adsorbed at the interface [77]. SECM has also been used to image electron transfer rates across a mixed monolayer of conjugated and saturated phospholipids, revealing domains of relatively high and low electron transfer rates, respectively [77].…”

Investigation of Localized Catalytic and Electrocatalytic Processes and Corrosion Reactions with Scanning Electrochemical Microscopy (SECM)

“…At the same time, Liu et al [24] described unusually large currents in electrochemical scanning tunneling microscopy (ECSTM) at working distances at which electron tunneling should not occur. By 1989, Bard and coworkers had quantitatively described the effect [25] and the development started with the investigation of a broad range of model samples not restricted to heterogeneous electrode surfaces [26][27][28][29] but also including living cells [30][31][32], biomolecules [33][34][35], and liquid-liquid interfaces [36][37][38][39]. The development further intensified when commercial instrumentation became available that can nowadays be obtained from several commercial sources.…”

A gramicidin analogue that exhibits redox potential-dependent cation influx

“…The development of scanning electrochemical microscopy (SECM) techniques in the late 1980s by Bard and his co-workers, 7 resulted in several publications on the use of this technique in probing the kinetics of ion-transfer (IT) 8,9,10 and electron-transfer (ET) processes 11,12,13,14,15,16 on monolayers at the interface between two immiscible electrolyte solutions (ITIES). Tsionsky, Bard and co-workers 15 used SECM to probe the kinetics of ion-transfer processes on the surface of BLMs using approach curves.…”