Applications of Quantitative PM IRRAS

Horswell et al. [80] made the first attempt to apply PM IRRAS to determine tilt angles of acyl chains of DM PC in a bilayer of this phospholipid deposited at an Au(lll) electrode surface in 2002. No correction of the measured spectra for the PEM response function was made at that time, and the tilt angle was determined using the relative method. It was assumed that the transition dipole of the asymmetric VaslCHs) stretch was randomly oriented. The tilt angle was then calculated from the ratio of the integrated intensity of the asymmetric Vas(CH2) and symmetric Vs(CH2) methylene stretches to the integrated intensity of the Vas(CH3) band using Eq. (43). 

The correction of the measured PM IRRAS signal for the PEM response functions was introduced in the studies of the potential-induced reorientation of a film formed by 4-pentadecyl pyridine [81], one year later. For the first time, the absorbance of a Langmuir film adsorbed at the electrode surface was determined in that paper. The theoretical spectrum of a film of randomly oriented molecules was calculated from independently measured optical constants, and tilt angles of the pentadecyl chain and the pyridine moiety were determined using the absolute method and Eq. (44). This work laid the methodological foundations for future PM IRRAS studies on monolayers and bilayers formed by amphiphilic molecules at electrode surfaces. 

quantitative PM IRRAS has been employed to investigate the orientation and the field-induced transformations of a monolayer [82] and a bilayer [83] of n-octadecanol at a gold electrode surface. The -octadecanol forms 2D solidlike films. These studies illustrate how to use PM IRRAS to determine not only the tilt angle of adsorbed molecules but also the packing and orientation of molecules into a unit cell of the 2D lattice of a solid film. 

Recently, Zawis2a et al. [84-86] and Bin et al. [87, 88] demonstrated that quantitative PM IRRAS has a very important application in biomimetic research. This technique provides unique information concerning potential-induced changes in the orientation and conformation of molecules in a model biological membrane supported at an electrode surface. This point is illustrated by the ap-phcation of PM IRRAS to study the stracture of a bilayer of DMPC formed at the Au(lll) electrode surface by fusion of unilamellar vesicles [87]. 

The angle 0 can be calculated from the ratio of the integrated intensity of a given band in the 2 spectrum to the integrated intensity of the 

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