Polarized attenuated total reflection infrared spectroscopy

E. Goormaghtigh and J. M. Ruysschaert, in Polarized Attenuated Total Reflection Infrared Spectroscopy as a Tool to Investigate the Conformation and Orientation of Membrane Components , CRC Press, Boca Raton, FL, 199.0, Vol. 1, pp. 285-329. 

The only piece of experimental evidence for the orientation of apoA-I helices on DMPC discoidal complexes has come from the use of polarized attenuated total reflection infrared (ATR-IR) spectroscopy (Brasseur et al. (1990 Wald et al., 1990). Although internal reflection spectroscopy is not new (Harrick, 1967), its combination with polarized IR measurements of oriented biological membranes is a more recent application, which allows the spectrum to be taken in the presence of water. The technique has been used most frequently to study the orientation of lipid functional groups relative to the membrane plane in pure lipid bilayers (Fringeli and Gunthard, 1981 Holmgre et al., 1987 Okamura et al., 1990 Hubner and Mantsch, 1991), but has also been applied to studies of... 

Fourier-transformed infrared spectroscopy (FT1R), either in the transmission mode(70), the grazing incidence reflection (GI) mode(7,5) or the attenuated total reflection (ATR) mode(7,2), has been the most widely used experimental tool for the characterization and structure determination of SA monolayers. GI-IR is especially useful in determining the molecular orientation in the film structures because it senses only the vibrational component perpendicular to the substrate surface(7,5). Polarized ATR-IR can also be used to study molecular orientation(7,77). McKeigue and Gula-ri(72) have used ATR-IR to quantitatively study the adsorption of the surfactant Aerosol-OT. 

For molecular properties of the TAG polymorphs, local molecular structural information such as methyl-end group, olefinic conformation, and chain-chain interaction are unveiled by infrared (IR) spectroscopy, especially Fourier-transformed infrared spectroscopy (FT-IR) (23, 24). Compared with a pioneering work by Chapman (25), great progress has been achieved by using various FT-IR techniques, such as polarized transmission FT-IR, reflection absorption spectroscopy (RAS), and attenuated total reflection (ATR) (26-28). 

Specialized techniques such as attenuated total reflection, polarized IR spectroscopy, etc. are also described by Amey and Chapman (1983). Another technique, which is potentially useful for lipid studies, is the combination of gas chromatography (GC) with Fourier transform infrared (FT-IR) spectroscopy, so that the column effluents are analysed by an on-line spectrometer. GC/FT-IR is discussed in detail by Erikson (1979). 

Electrochemically modulated infrared spectroscopy (EMIRS), polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and attenuated total reflectance (ATR) have also been used. (FTIR-ATR spectra are shown in Chap. 6, Fig. 6.11.)... 

Infrared attenuated total reflection spectroscopy (IR-ATR). This method [10] can be used to study lipid bilayer membranes and peptides associated with them in the dry and in the hydrated states [11, 12]. Position and shape of the IR bands allow the detection of peptide secondary structures their orientation with respect to the lipid molecules can be determined with polarized radiation. Adsorption from and escape into the aqueous surroundings, penetration through the membranes, and exchange can easily be studied. 

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