PM FTIRRAS Studies of Potential-Controlled Transformations of a Monolayer and a Bilayer of 4-Pentadecylpyridine, a Model Surfactant, Adsorbed on a Au(111) Electrode Surface

Citations Over TimeTop 10% of 2002 papers

Abstract

Polarization modulation Fourier transform infrared reflection−absorption spectroscopy (PM FTIRRAS) has been combined with electrochemistry to monitor the potential-induced transformations of a monolayer and a bilayer formed by 4-pentadecylpyridine (C15−4Py), a model amphiphilic compound, at a Au(111) electrode surface. The optical constants for a solution of randomly oriented C15−4Py molecules have been determined and used to calculate the integrated band intensities for a monolayer and bilayer of randomly oriented molecules. The orientation of the hydrophobic and hydrophilic parts of the molecule with respect to the surface normal was determined from the ratio of the intensity of experimental to calculated bands. The CH stretch region of the spectra was used to determine the tilt angle between hydrocarbon chains and the surface normal. The tilt angle varied with potential. The minimum value of the tilt angle was 16° for the monolayer and 27° for the bilayer. In the monolayer, the headgroup of the C15−4Py molecule lies almost flat on the Au(111) surface. At negative potentials, the angle between the plane of the pyridine ring and the surface normal is 68°. As applied potential becomes more positive, the pyridine group stands up gradually and the tilt angle decreases to 63°. In the bilayer, the C2 axis of the pyridine group in the leaflet turned to the electrolyte solution is tilted at ∼70° with respect to the normal and this tilt angle changes little with potential. In the leaflet turned to the electrode, the angle between the C2 axis of the headgroup and the surface normal changes from 64° to 54° by moving from negative to positive potentials. The PM IRRAS data also show that in the bilayer, the plane of the pyridine group rotates with respect to the C2 axis when the electrode potential changes. In the monolayer, the tilt angle of the C2 axis changes but the plane of the pyridine moiety does not rotate with potential.

Related Papers

• → Orientational Changes of Amphotericin B in Langmuir Monolayers Observed by Brewster Angle Microscopy(2001)32 cited
• → Silver n-Octadecanethiolate Langmuir Monolayers Mimicking Self-Assembled Monolayers on Silver(1996)11 cited
• → Effect of Escherichia coli on phospholipid monolayers: surface tensiometry and Brewster angle microscopy measurements(2019)1 cited
• → Brewster Angle Microscopy(2012)2 cited
• → Langmuir monolayer of hypocrellins and their amino substituted derivatives at the air/water interface: Brewster angle microscopy study(2001)