Showing papers on "Fourier transform infrared spectroscopy published in 1987"

Fourier transform infrared spectroscopic investigation of the interaction between myelin basic protein and dimyristoylphosphatidylglycerol bilayers.

Abstract: The interaction of basic protein from human myelin with dimyristoylphosphatidylglycerol (DMPG) bilayers was investigated by Fourier transform infrared spectroscopy. The effect of protein on the lipid conformation and also the effect of lipid on the protein secondary structure were examined. The association of myelin basic protein with DMPG results in a broadening of the lipid phase transition, accompanied by an increase in the conformational order of the acyl chains at temperatures below the phase transition. While the direct contact between myelin basic protein and acidic phospholipids is believed to involve the polar region of the bilayer, infrared spectra indicate that the association between DMPG head groups and protein does not result in drastic changes in the conformation of the lipid phosphate moiety. Infrared spectra of myelin basic protein in the amide I region were analyzed quantitatively by using resolution enhancement and band fitting procedures. The above analysis suggests that in aqueous solution the protein is devoid of alpha-helical and beta-conformations but that it contains a significant amount of turns. Upon binding to DMPG bilayers, the secondary structure of the protein is dramatically altered. The lipid-complexed basic protein adopts a highly ordered secondary structure. According to the quantitative infrared analysis, the main components of this structure are antiparallel beta-sheet (53%), alpha-helix (15%), and turns (15%).

FTIR-ATR spectroscopic determination of the distribution of surfactants in latex films

Abstract: FTIR-ATR (Fourier Transform Infra-Red-Attenuated Total Reflection) has been used to analyze the surface composition of coalesced acrylic latex films. The behavior of two anionic surfactants has been characterized. It has been found that surfactant distribution depends on the nature of the surfactant. A comparison between the normalized absorbance in transmission and in reflection has shown an enrichment of surfactants at the surfaces of films with a coalescence time of 3 days. The surfactant concentration at the film-air interface is higher than at the film substrate interface. A concentration gradient exists through the film thickness. In addition, the incompatible surfactant migrates towards the interface as coalescence proceeds.

Fourier transform Raman spectroscopy

Abstract: The basic experimental aspects of Fourier transform Raman Spectroscopy are reviewed with an emphasis on detector technology. The sensitivity is comparable to dispersive Raman Spectroscopy using visible lasers. The ease of spectral subtraction is demonstrated and examples are given showing the elimination of fluorescence.

Laboratory methods in vibrational spectroscopy

Abstract: Introduction Terminology and Definitions in Vibrational Spectroscopy Group Frequency Correlation Table Selected Properties of Infrared Transmitting Materials Spectra of Solvents and Frequently Encountered Contaminants The Dispersive Infrared Spectrometer Mid Infrared Fourier Transform Spectrometry Quantitative Analysis from the Infrared Spectrum Simple Sampling Preparation of Polymer Samples for IR Examination Reflection Spectroscopy Micro-Sampling Methods in Infrared Spectroscopy Techniques for Vibrational Spectroscopic Measurements under High Pressures Matrix Isolation Modern Methods for GC/IR and GC/FTIR Capillary GC/FT-IR Species Adsorbed at Surfaces Reactive, Unstable, Explosive and Energetic Materials Infrared Spectroscopy of Inorganic Compounds Methods of Obtaining Spectra at High and Low Temperatures The Infrared Emission Spectrum Raman Instrumentation Raman Sampling Concise Theory of Infrared Spectroscopy.

Fourier transform infrared spectroscopy of molecular clusters: The structure and internal mobility of clustered carbon dioxide

Abstract: Infrared spectra of supersonic jets of carbon dioxide seeded in helium are reported: Features assignable to clusters were observed for the ν2, ν3, ν1+ν3, and 2ν2+ν3 bands A detailed study was made of the ν3 band, from which it was concluded that the clusters do not adopt the face‐centered cubic crystal structure of solid carbon dioxide The observed spectra indicate that the cluster geometry is largely determined by pairwise interactions between adjacent molecules Furthermore, expansions of pure carbon dioxide produced clusters whose spectra indicate motional averaging: such clusters seem to be fluid on a picosecond time scale

Quantitative Estimation of α-Helix Coil Content in Bovine Serum Albumin by Fourier Transform-Infrared Spectroscopy

Abstract: Heat denaturation of albumin aqueous solution enables us to control the α-helix content to a reasonable level, and denatured albumin, whose conformation is different, can be obtained. Fourier transform-infrared absorption spectra in the amide I, II, and III band regions of these albumins have been measured and compared with each other. As a result, the characteristic frequencies associated with each conformation of α-helix, β-sheet, and random structure have been observed; moreover it has been newly proved that the intensity ratio of the amide II band to the amide I band depends on the α-helix content in albumin. In this paper, we demonstrate that this intensity ratio is very useful for quantitative estimation of α-helix content in albumin and apply this method to analysis of ATR spectra of albumin adsorbed on polyethylene surface.

Calibration of the photoluminescence technique for measuring B, P and Al concentrations in Si in the range 1012 to 1015 cm-3 using Fourier transform spectroscopy

Abstract: Calibrations are reported for measuring boron, phosphorus and aluminium concentrations in silicon by comparing the intensities of bound-exciton and free-exciton luminescence features. Particular attention has been directed towards investigating the effects of excitation density and instrumental resolution. The luminescence spectra have been corrected for the system response so that the calibrations are independent of the equipment used and are hence transferable. Fourier transform rather than dispersive spectroscopy has been employed to measure the luminescence spectra. Since Fourier transform photoluminescence spectroscopy is a relatively new technique, it is described in some detail.

Preparation of silicon carbide from organosilicon gels: I. Synthesis and characterization of precursor gels

Abstract: Polymeric organosilicon gel precursors to SiC have been prepared using trifunctional chloro and alkoxysilanes that contain both the Si and C necessary for SiC formation. Crosslinked gels having the ideal formula (RSiO{sub 1.5}){sub n} have been synthesized by a hydrolysis/condensation scheme for a series of saturated and unsaturated R groups. The starting gels have been characterized by elemental analysis and by a variety of spectroscopic and physical measurements including Fourier transform infrared spectroscopy, XRD, surface-area and pore-volume determination, and thermal gravimetric analysis. {sup 13}C and {sup 29}Si solid-state NMR analysis proved to be particularly powerful for characterizing these gels by showing the degree of crosslinking and the residual hydroxy/alkoxy content. Under an inert atmosphere, the gels decompose to produce an intimate mixture of C and SiO{sub 2} which can react to form SiC at higher temperatures. The pyrolysis of these gels to produce SiC is described in Part II.

Reflection Absorption Infrared Spectroscopy

Abstract: Much of the information concerning the bonding and symmetry of molecules in the gaseous, liquid, and solid states has come from the study of molecular vibrations using infrared spectroscopy. It seemed, therefore, only natural that infrared spectroscopy should be extended to provide a vibrational spectroscopic technique for the study of the adsorbed phase. The first step in this direction appears to have been taken by Buswell et al. in 1938,(1) extending the traditional transmission ir technique to the study of adsorbed water on montmorillonite clay surfaces. It was not until the 1950s that the ir transmission method was again taken up by several groups to study adsorbed species on high surface area materials.(2-4) Perhaps the most remarkable of these experiments was the work of Eischens and co-workers in 1956,(4) who studied the adsorption of CO on supported nickel, palladium, and platinum catalysts. A comparison of the spectra obtained on the catalysts with those of various metal carbonyl complexes enabled then to assign bands to various adsorption configurations (i.e., linear and bridging), and to recognize the influence of vibrational coupling on the C-O stretch vibration of adsorbed CO. Indeed, their results and interpretations have been largely substantiated in work on single-crystal surfaces, as will be seen in Section 3 of this chapter.

The Structure of Hexane Soot. Part III: Ozonation Studies

Abstract: The gravimetric estimation of CO2-evolved, FT-IR monitoring of the rate of formation of surface species, as well as several other measurements during the n-hexane soot/ozone reaction, has led to the conclusion that soot is a layered structure whose layers are chemically bonded, unlike the graphite structure where the layers are ordered by van der Waals forces. Fourier transform infrared spectroscopy, electrochemical analysis, microgravimetry, scanning electron microscopy (SEM), and the classical BET surface area determination technique have been employed in this work.

Dispersive Fourier Transform Spectroscopy

Abstract: A review is presented of recent developments in the methods of dispersive Fourier transform spectroscopy that have demonstrated the unique value of this broad band method for determining the optical constants of gases, liquids and solids.

Fourier transform infrared spectroscopy of a single aerosol particle

Abstract: Throughout this thesis, the phenomenon of radiation-induced particle size change is studied both on a theoretical as well as experimental level. The thrust of this study is aimed at using the size changes due to heat absorption to develop a technique for obtaining the particle chemical composition. The experiments here involve charged particles, generated with an impulse jet, and trapped by the electric field of an electrodynamic balance. The particles under study are all aqueous solutions of non-volatile salts, where upon heating a partial evaporation of water occurs. The evaporation and subsequent condensation processes are modeled in both the continuum and the transition regimes. The models developed are tested and the agreement between theory and experimental results is demonstrated. The models are also used to extract the values of the water, thermal, and mass accommodation coefficients from the data. The results for the thermal accommodation show that its value is near unity, however the corresponding results for the mass accommodation are not conclusive. A method is developed for obtaining the molecular composition of a single suspended microparticle by Fourier transform infrared spectroscopy. The particle is irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The laser is tuned to an edge of an optical resonance of the particle while the IR beam is chopped. Through evaporation and condensation the chopped IR beam causes a size modulation of the droplet, which in turn induces a fluctuation in the laser light scattered from the particle. The scattered light is detected at 90° with a photomultiplier, and the amplitude of the light fluctuation is measured with a lock-in amplifier. The lock-in signal is then inverted by a discrete fast Fourier transform routine (FFT), to yield the particle absorption spectrum. Spectra of (NH4)2SO4 droplets at different solute concentrations are presented.

Near-Surface Analysis and Depth Profiling by FT-IR Photoacoustic Spectroscopy:

Abstract: Fourier transform photoacoustic spectroscopy (FT-IR/PAS) has proven to be a powerful technique for the near-surface characterization of solid materials. The effective sampling depth of FT-IR/PAS can be varied by using different interferometer mirror velocities, so that nondestructive depth profiling can be performed. In this research, sized cotton yarns, treated glass fibers, chemically modified poly(ethylene terephthalate) fibers, and a naturally weathered poly(vinyl chloride) composite were investigated with the use of FT-IR/PAS at different mirror velocities. Penetration of the chemical additives in these materials was studied. It was demonstrated that FT-IR/PAS has the ability to investigate the changes in chemical nature within the detectable surface layers of solid samples.

High resolution interferometric Fourier transform infrared absorption spectroscopy in a supersonic free jet expansion

Abstract: The absorption spectrum of CHF3 in a free jet expansion has been recorded at a resolution of 0·004 cm-1 in the 8–9 μm region. The line width is found to be essentially Doppler limited. An approximate rotational temperature of 40K has been determined from the spectrum. Relative intensities and transition moments for the interacting bands are discussed.

Fourier Transform Infrared Photoacoustic Spectroscopy Characterization of Sulfur-Oxygen Species Resulting from the Reaction of SO2 with CaO and CaCO3:

Abstract: Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) has been used to investigate the reaction of SO2 in He with CaO and CaCO3 particles at temperatures between 25 and 900°C. The reaction of SO2 with CaO occurs at 25°C, while the reaction of CaCO3 with SO2 is first evident at 550°C. The initial product of both of these reactions is CaSO3. The CaSO3 then further reacts with SO2 to form CaSO4, CaS2O3, and CaS at higher temperatures. At 900°C and above, the net production of SO4− and S2O3− is decreased because of the decomposition of SO3−. FTIR/PAS depth-profiling experiments indicate the formation of a reaction-limiting product layer of SO3− and SO4− from the above reactions on the surface of the CaO and CaCO3 particles.

Characterization of interfacial phenomena occurring during exposure of a thin copper film to an aqueous suspension of an acidic polysaccharide

Abstract: A Fourier transform infrared spectrometer equipped with a cylindrical internal reflection element was used to sample the solid—liquid interface of a metallic copper film submerged in an aqueous acidic polysaccharide solution. The presence of a polysaccharide absorption band at 1050 cm−1 in a water-subtracted spectrum supported previous spectroscopic data indicating polymer accumulation at the surface of the film. Firm binding of the polysaccharide to the surface after a 17-day exposure period was demonstrated by the retention of the 1050-cm−1 absorption band in spectra obtained after gentle rinsing of the film surface with polymer-free water. The sampling technique also provided evidence which suggests that acidic polysaccharides, including the firmly bound exopolymers produced by adherent cells of a freshwater sediment bacterium, promoted deterioration of the copper film. Internal reflection Fourier transform infrared spectroscopy appeared to be a useful, nondestructive method to study the sorption of biomolecules to a solid metal surface submerged in an aqueous medium.

Use of Fourier transform infrared spectroscopy for quantitative analysis: a comparative study of different detection methods.

Abstract: The value of Fourier transform infrared spectroscopy in the mid-infrared region for the quantitative analysis of protein-starch mixtures is examined. Attenuated total reflectance, diffuse reflectance and photoacoustic detection are compared. It is concluded that photoacoustic detection is the best method of analysis for protein but that only attenuated total reflectance is of use in wet systems. Diffuse reflectance gave poorly resolved spectra, which severely limited its usefulness.

A study of the adsorption sites on thoria by scanning transmission electron microscopy and fourier-transform infrared spectroscopy. Adsorption and desorption of water and methanol

Abstract: A study of the adsorption sites of thoria has been made using scanning transmission electronic microscopy (STEM) and Fourier-transform infrared spectroscopy (FTIR). The STEM study showed that the thoria surface was composed mainly of (110)(211) and (111) faces in about equal proportions. The infrared study of activated ThO2 at 873 K indicated the existence of two remaining hydroxyl groups at 3660 and 3510 cm–1. With water adsorption, a third one appeared at 3745 cm–1 which was thermally less stable. Methanol adsorption gave rise to three kinds of species: (i) one reversibly adsorbed at room temperature and linked by hydrogen bonds in which thoria acts as a proton receiver; (ii) two methoxy species characterized by ν(CO) bands at 1127 cm–1(species I) and 1060 cm–1(species II). Species I desorption bands led to methanol whilst species II, much more thermally stable, gave methanol, dimethyl ether and carbon monoxide. Species I, which corresponds to the hydroxyl species at 3745 cm–1, are of the Th—OMe (Th—OH) type, and are formed on the (110) faces. Species II, which correspond to hydroxyl species at 3660 cm–1, are of the [graphic omitted] type, and are formed on the (211) faces. The third hydroxyl species, characterized by the ν(OH) band at 3510 cm–1, is probably due to species of the [graphic omitted] type appearing on (111) faces. The stability and reactivity of the methoxy species are shown to depend on their structure, and therefore on the local arrangement of the surface.

Multitechnique surface spectroscopic studies of plasma-modified polymers I: H2O/Ar plasma-modified polymethylmethacrylates

Abstract: Results from x-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion scattering spectrometry (LEIS or ISS); and Fourier transform infrared spectroscopy (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate) (PMMA) polymer films. Analysis of the unmodified PMMA polymers (isotactic, syndiotactic, and atactic) via ESCA, ISS, and FTIR, established the surface composition, bonding, and functionality before the modification was employed. An rf-plasma glow discharge created from an Ar/H2O gas mixture at different exposure times and power levels was used to treat the polymer surface. Subsequent ESCA, ISS, and FTIR analyses of these modified PMMA’s show the effects of surface modification in terms of a model of structural differences, over a limited depth (50–100 A). The composition and functionality changes of the resulting surfaces are discussed with respect to proposed mechanisms of the plasma reaction and differences in tacticity of the reactant. A two-step reaction mechanism involving reactive decarboxylation/reduction followed by H2O adsorption is proposed to understand the spectroscopic results.

Thermal characterization of a bis‐maleimide/bis‐cyanate/epoxy thermosetting resin for composites

Abstract: The thermosetting resin investigated here was a mixture of bis-maleimide and bis-cyanate, frequently referred to as BT (bis-maleimide triazine). Triazine is the reaction product of the cyclotrimerization of bis-cyanate during curing. For circuit board applications, a brominated epoxy resin was blended with BT to impact flame resistance. Resin cure was extensively investigated using a combination of thermoanalytical techniques (thermal analysis, heated cell infrared spectroscopy, and dynamic mechanical analysis). The ultimate glass transition temperature was found to be 240°C, which could only be obtained using cure temperatures above 225°C. At lower temperatures, the reaction does not reach full conversion, since the glass transition temperature of the curing network equals or slightly exceeds the cure temperature. Differential scanning calorimetry (DSC) indicates a minimum of two separate reactions. Fourier transform infrared spectroscopy provided more detailed information on the crosslinking reactions during cure. The onset of cyclotrimerization was found to start at 150°C, correlating with one of the peaks in the DSC. At higher temperatures, the epoxide reacts with the cyanate functionality forming oxazoline ring structures. It was not possible to unambiguously assign the origins of the high temperature peaks in the DSC. These high temperature peaks may be attributed to several reactions, including epoxy homopolymerization and polymerization of bis-maleimide. The high temperature reaction mechanisms warrant further investigation.