Impedance study of thallous ion movement through gramicidin–dioleoylphosphatidylcholine self-assembled monolayers supported on mercury electrodes: the C–(C)–CE mechanism

Application of electrochemical impedance spectroscopy to the study of surface processes

The application of Electrochemical Impedance Spectroscopy to the study of surface electrode processes is reviewed. The impedance expressions and the physical meaning of the parameters included in them are shown for three surface processes: adsorption kinetics, diffusion towards partially blocked electrodes and surface confined redox reactions. The models are applied to selected examples, showing the capability of Electrochemical Impedance Spectroscopy to obtain fundamental kinetic information of these processes. A review with 83 references.

Electrochemical properties of phospholipid monolayers at liquid-liquid interfaces

Biomembrane models built at the interface between two immiscible electrolytes (ITIES) are useful systems to study phenomena of biological relevance by means of their electrochemical processes. The unique properties of ITIES allow one either to control or measure the potential difference across the biomimetic membranes. Herein we focus on phospholipid monolayers adsorbed at liquid-liquid interfaces, and besides discussing recent developments on the subject, we describe electrochemical techniques that can be used to get insight on the interfacial processes and electrostatic properties of phospholipid membranes at the ITIES. In particular, we examine the electrochemical and physicochemical properties of (modified) phospholipid monolayers and their interaction with other biologically relevant compounds. The use of liquid-liquid electrochemistry as a powerful tool to characterize drug properties is outlined. Although this review is not a survey of all the work in the field, it provides a comprehensive referencing to current research.

Electrochemical and PM-IRRAS studies of the effect of the static electric field on the structure of the DMPC bilayer supported at a Au(111) electrode surface

Differential capacity, charge density measurements, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) were employed to study the fusion of small unilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) on a Au(111) electrode surface. The differential capacity and charge density data showed that the vesicles fuse onto the gold surface at charge densities between -10 microC/cm(2) < sigma(M) < 10 microC/cm(2) to form a bilayer. When sigma(M) < -10 microC/cm(2), the film is detached from the surface but it remains in close proximity to the surface. PM-IRRAS experiments provided IR spectra for the bilayer in the adsorbed and the desorbed state. Ab initio normal coordinate calculations were performed to assist interpretation of the IR spectra. The IR bands were analyzed quantitatively, and this analysis provided information concerning the conformation and orientation of the acyl chains and the polar head region of the DMPC molecule. The orientation of the chains, hydration, and conformation of the headgroup of the DMPC molecule strongly depend on the electrode potential.

Self-Assembly of Phospholipid Molecules at a Au(111) Electrode Surface

We described the first scanning tunneling microscopy study of spreading unilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) at a Au(111) electrode surface. At the initial stage of the film formation, the molecular resolution images revealed that DMPC molecules are adsorbed flat with the acyl chains oriented parallel to the surface. The molecules assemble into double rows by aligning the acyl chains in the nearest neighbor direction of the reconstructed Au(111) surface and assuming a 90 +/- 10 degrees angle with respect to line of the molecular row. After approximately 30 min, this film is transformed into a hemimicellar state with long rows characteristic for the formation of hemicylindrical surface micelles. At hydrophilic surfaces such as glass, spreading of vesicles involves adsorption, rupture, and sliding of a single bilayer on a lubricating film of the solvent. We have provided the first evidence that a different mechanism is involved in spreading the vesicles at gold. The molecules released by rupture of vesicles self-assemble into an ordered film, and the assembly is controlled by the chain-substrate interaction.