Infrared spectroscopy chain conformation

Novotny et al. [41] used p-polarized reflection and modulated polarization infrared spectroscopy to examine the conformation of 1 -1,000 nm thick liquid polyperfluoropropy-lene oxide (PPFPO) on various solid surfaces, such as gold, silver, and silica surfaces. They found that the peak frequencies and relative intensities in the vibration spectra from thin polymer films were different from those from the bulk, suggesting that the molecular arrangement in the polymer hlms deviated from the bulk conformation. A two-layer model has been proposed where the hlms are composed of interfacial and bulk layers. The interfacial layer, with a thickness of 1-2 monolayers, has the molecular chains preferentially extended along the surface while the second layer above exhibits a normal bulk polymer conformation. 

One of the initial spectroscopic methods applied to stationary-phase characterization was Fourier transform infrared spectroscopy (FTIR). This originated from several important studies of phase conformational order in crystalline n-alkanes conducted in the late 1960s and early 1980s by Snyder, Maroncelli, and coworkers [111-114], In this work, assignments of C—H bond wagging modes were associated with chain... 

By their nature, and in contrast with microscopic and scattering techniques that are used to elucidate long-ranged structure, spectroscopic methods interrogate short-range structure such as interactions between fixed ions in side chains and counterions, main chain conformations and conformational dynamics, and the fundamental hopping events of water molecules. The most common methods involve infrared (mid-IR and to a much lesser extent near- and far-IR) and solid-state NMR spectroscopies, although other approaches, such as molecular probes, have been utilized. 

In addition to describing the conformation of the hydrocarbon chains for amphiphilic molecules at the A/W interface, external reflectance infrared spectroscopy is also capable of describing the orientation of the acyl chains in these monolayers as a function of the monolayer surface pressure. The analysis of the orientation distribution for an infrared dipole moment at the A/W interface proceeds based on classical electromagnetic theory of stratified layers (2). In particular, when parallel polarized radiation interacts with the A/W interface, the resultant standing electric field has contributions from both the z component of the p-polarized radiation normal to the interface, as well as the x component of the p-polarized radiation in the plane of the interface. The E field distribution for these two... 

Modern methods of vibrational analysis have shown themselves to be unexpectedly powerful tools to study two-dimensional monomolecular films at gas/liquid interfaces. In particular, current work with external reflection-absorbance infrared spectroscopy has been able to derive detailed conformational and orientational information concerning the nature of the monolayer film. The LE-LC first order phase transition as seen by IR involves a conformational gauche-trans isomerization of the hydrocarbon chains a second transition in the acyl chains is seen at low molecular areas that may be related to a solid-solid type hydrocarbon phase change. Orientations and tilt angles of the hydrocarbon chains are able to be calculated from the polarized external reflectance spectra. These calculations find that the lipid acyl chains are relatively unoriented (or possibly randomly oriented) at low-to-intermediate surface pressures, while the orientation at high surface pressures is similar to that of the solid (gel phase) bulk lipid. 

The study of the raesophases by X-ray diffraction, electron microscopy, infrared spectroscopy and circular dichroism20-2S has shown that the structure is always lamellar and can be described as follows the lamellar structure consists of plane, parallel, and equidistant sheets of thickness d each sheet results from the superposition of two layers one of thickness dA formed by the polyvinyl chains in a more or less random coil conformation, the other with a thickness dB formed by the polypeptide chains in an a helix conformation, oriented perpendicular to the plane of the layers, arranged in a bidimensional hexagonal array, and generally folded. 

The study by low-angle X-ray diffraction of these mesophases provides X-ray patterns exhibiting a set of sharp lines with Bragg spadngs characteristic of a layered structure. This lamellar structure results from the superposition of plane, parallel, and equidistant sheets each sheet contains two layers one of thickness dA formed by the carbohydrate blocks, the other of thickness dB formed by the polypeptide blocks, there is a partition of the solvent between the two blocks 70% DMSO is localized in the carbohydrate layer284. Furthermore, the polypeptide chains are in a a-helix conformation as is demonstrated by infrared spectroscopy and X-ray diffraction and are oriented perpendicular to the plane of the sheets and assembled in a bidimensional hexagonal lattice as is revealed by X-rays284. ... 

RA. Quantitative determination of conformational disorder in the 38. acyl chains of phospholipid bilayers by infrared spectroscopy. Biochemistry 1989 28 8934-8939. 

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). 

Fourier transform infrared spectroscopy also provides information about conformation of bofh hydrocarbon chains and head groups. EPR spectios-copy (Box 8-C) with doxyl probes on carbon atoms at different depths within the bilayer has also been em-ployed. ... 

Copolymers of 0-Carbobenzoxy-L-tyrosine and Benzyl t-(or o-)glutamate Infrared spectroscopy and X-ray diffraction data have shown that the copolymers of 0-carbobenzoxy-L-tyrosine and benzyl L-(or D-)glutamate as well as benzyl L-aspartate possess a helical conformation in the solid state, even when they are very rich in carbobenzoxy-L-tyrosine residues (Vollmer and Spach, 1967). The ordering of the molecules of poly-O-carbobenzoxy-L-tyrosine in a purely helical structure appeared to be favored by the insertion of a small number of foreign residues in the polypeptide chain. 

Casal HL, McElhaney RN (1990) Quantitative determination of hydrocarbon chain conformational order in bilayers of saturated phosphatidylcholines of various chain lengths by fourier-transform infrared spectroscopy. Biochemistry 29 5423... 

Fourier transform infrared (FTIR) spectroscopy is a powerful and reliable technique that for many years has been an important tool for investigating chemical processes and structures. In the polymer fields, FTTR data is used in order to study characterization of chemical bonds, polymer microstructure, chain conformation, polymer morphology, crystallinity and etc, consequently is useful in SPR studies. 

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