Showing papers on "Fourier transform infrared spectroscopy published in 1993"

Solution effects on the surface reactions of a bioactive glass.

Abstract: The in vitro surface reactions of a 45S5 bioactive glass in three simulated body fluids (SBF) are analyzed using Fourier transform infrared (FTIR) spectroscopy. Five reaction stages are observed. Calcium and phosphate ions in SBF accelerate to a small extent the repolymerization of silica (Stage 3) and formation of an amorphous calcium-phosphate (a-CP) layer (Stage 4) on the glass surface. The a-CaP layer is crystallized to form hydroxy-carbonate apatite (HCAp) (Stage 5) more rapidly in the Ca- and P-containing SBF solutions (in 90 min rather than 120 min). However, Mg ions in SBF slow down formation of the a-CaP layer and greatly retard crystallization of HCAp on the glass surface.

An IR and NMR study of the chemisorption of titanium tetrachloride on silica

Abstract: The atomic layer epitaxy (ALE) reactions, i.e., the saturating gas-solid reactions of TiCl 4 at 175 and 450 o C with silica preheated at 200-820 o C, were studied by nuclear magnetic resonance and Fourier transform infrared spectroscopy, while etching experiments with sulfuric acid were carried out to determine the amount of amorphous titanium species. At 175 o C TiCl 4 reacted directly with the OH groups of silica either monofunctionally or bifunctionally depending on the preheat temperature of silica

Rapid quantitative determination of free fatty acids in fats and oils by Fourier transform infrared spectroscopy.

Abstract: Rapid direct and indirect Fourier transform infrared (FTIR) spectroscopic methods were developed for the determination of free fatty acids (FFA) in fats and oils based on both transmission and attenuated total reflectance approaches, covering an analytical range of 0.2–8% FFA. Calibration curves were prepared by adding oleic acid to the oil chosen for analysis and measuring the C=O band @ 1711 cm–1 after ratioing the sample spectrum against that of the same oil free of fatty acids. For fats and oils that may have undergone significant thermal stress or extensive oxidation, an indirect method was developed in which 1% KOH/methanol is used to extract the FFAs and convert them to their potassium salts. The carboxylate anion absorbs @ 1570 cm–1, well away from interfering absorptions of carbonyl-containing oxidation end products that are commonly present in oxidized oils. Both approaches gave results comparable in precision and accuracy to that of the American Oil Chemists’ Society reference titration method. Through macroprogramming, the FFA analysis procedure was completely automated, making it suitable for routine quality control applications. As such, the method requires no knowledge of FTIR spectroscopy on the part of the operator, and an analysis takes less than 2 min.

Vapour-phase oxidation of diamond surfaces in O2 studied by diffuse reflectance Fourier-transform infrared and temperture-programmed desorption spectroscopy

Abstract: Thermal oxidizing treatments of hydrogenated diamond surfaces have been performed in an O2 environment. Chemisorption of oxygen on diamond surfaces has been investigated by diffuse reflectance Fourier-transform infrared (FTIR), temperature-programmed desorption (TPD), temperature-programmed reaction (TPR) and thermogravimetry (TG). Oxidation of the hydrogenated diamond occurred above 300 °C and diamond started to burn out above 480 °C in 20% O2. Diffuse reflectance FTIR spectra indicated that the oxidation gave species containing CO and C—O—C structures on the diamond surface above 300 °C. The structures of the chemisorbed species changed with the oxidation temperature. The maximum coverage of oxygen was obtained between 480 and 500 °C. TPD spectra of oxidized diamond indicated that the oxygen-containing species were desorbed as CO and CO2 above 480 °C. This paper deals with the mechanistic considerations for the oxidation of diamond surfaces.

Pressure/temperature phase diagram of hexanitrohexaazaisowurtzitane

Abstract: The five shown polymorphs of hexanitrohexaazaisowurtzitanc (chemical name: 2,4,6,8,10,12-hexanitro2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0 5,9 .0 3,11 ]dodecane), α, β, γ, e, and ζ, were studied by optical polarizing light microscopy (OPLM) and Fourier transform infrared spectroscopy (FTIR) as a function of temperature and pressure. A high-temperature/high-pressure diamond anvil cell specially designed for these studies was employed. Four reversible and five unidirectional phase transformations were observed and identified by FTIR spectra

Matrix infrared spectra of NUN formed by the insertion of uranium atoms into molecular nitrogen

Abstract: Pulsed‐laser ablated uranium atoms were codeposited with 14N2(15N2) and excess Ar at 12 K. The Fourier transform infrared (FTIR) spectrum revealed a single product, UN2, which exhibited a ν3 absorption at 1051.0 cm−1. Ultraviolet (UV) photolysis increased the yield of UN2 by threefold and showed that electronic excitation facilitated the insertion reaction. N2 perturbed UN2 bands at 1041.3 and 1031.5 cm−1 grew sharply during matrix annealings. In 14N15N experiments the ν1 and ν3 modes of 14NU15N were observed at 987.2 and 1040.7 cm−1, respectively; FG matrix calculations were performed to determine Fr=8.27 mdyn/A and Frr=0.12 mdyn/A and to estimate the IR‐inactive ν1 modes of U14N2 and U15N2 at 1008.3 and 985.7 cm−1, respectively. Energetic considerations suggest that the U+N2 insertion reaction has little exothermicity and that the activation energy for this reaction may be provided by hypothermal uranium atoms.

Chemical Surface Modification of Porous Silicon

Abstract: Resistance to room temperature oxidation and control over wetting properties can be achieved by chemical modification of a porous‐silicon surface. Fourier transform infrared spectroscopy was used in the transmission mode to monitor the surface chemistry of both treated and untreated porous‐silicon samples before and after exposure to humid air at room temperature. Surface modification methods investigated include: (i) vapor‐phase silation using either hexamethyl‐disilazane or trimethylchlorosilane, and (ii) rapid thermal annealing in nitrogen, ammonia, or argon ambients. The silation treatments, carried out in the presence of trace moisture, were successful both in creating surface trimethylsilyl groups and in suppressing room temperature oxidation. Rapid thermal annealing at temperatures as low as 500°C for 30 s eliminates all silicon hydrides. Nitrided porous‐silicon layers are formed at 1100°C in either ammonia or nitrogen; in both cases the silicon nitride infrared absorption peaks scale with the porous layer thickness, indicating that the compounds are distributed throughout the porous layer.

Thermal hydrogenation of diamond surfaces studied by diffuse reflectance Fourier-transform infrared, temperature-programmed desorption and laser Raman spectroscopy

Abstract: The chemisorbed species on diamond surfaces have been studied by Fourier-transform infrared (FTIR), temperature-programmed desorption (TPD) and laser Raman spectroscopy. Oxidized diamond powders were treated thermally in an H2 environment. IR spectral changes were followed during the hydrogenation of oxidized diamond powders. We observed CH bonding on diamond surfaces. The amount of CH bonding increased with the temperature of treatment below 900 °C. Above 900 °C, the amount of the CH bonding decreased. Thermally desorbed species were analysed by mass spectrometry. H2 was desorbed from hydrogenated diamond powders above ca. 800 °C. Close agreement between FTIR and TPD results was obtained. Raman spectra indicated that the disordered graphitic carbon phase was formed above 900 °C.

Fourier transform-infrared studies of thin H2SO4/H2O films: Formation, water uptake, and solid-liquid phase changes

Abstract: Fourier transform-infrared (FTIR) spectroscopy was used to examine films representative of stratospheric sulfuric acid aerosols. Thin films of sulfuric acid were formed in situ by the condensed phase reaction of SO3 with H2O. FTIR spectra show that the sulfuric acid films absorb water while cooling in the presence of water vapor. Using stratospheric water pressures, the most dilute solutions observed were greater than 40 wt % before simultaneous ice formation and sulfuric acid freezing occurred. FTIR spectra also revealed that the sulfuric acid films crystallized mainly as sulfuric acid tetrahydrate (SAT). Crystallization occurred either when the composition was about 60 wt% H2SO4 or after ice formed on the films at temperatures 1-4 K below the ice frost point. Finally, we determined that the melting point for SAT depended on the background water pressure and was 216-219 K in the presence of 4 x 10(exp -4) Torr H2O. Our results suggest that once frozen, sulfuric acid aerosols in the stratosphere are likely to melt at these temperatures, 30 K colder than previously thought.

Diamondlike carbon films obtained by low energy cluster beam deposition: Evidence of a memory effect of the properties of free carbon clusters.

Abstract: Free carbon clusters with various selected sizes (C 20 ,C 60 ,C 900 ) have been deposited on different substrates to obtain continuous thin films (thickness ∼100 nm). The characterization of nanostructures and electronic structures of the films have been performed using various complementary techniques (atomic force microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy). A memory effect of the free carbon cluster properties permits the synthesis of amorphous diamond or graphite films depending on the deposited incident species (C 20 or C 900 , respectively)

Thermal Desorption and Infrared Studies of Plasma-Enhanced Chemical Vapor Deposited SiO Films with Tetraethylorthosilicate

Abstract: Thermal desorption and Fourier transform infrared spectroscopies were used to study plasma-enhanced chemical vapor deposited SiO films from tetraethylorthosilicate. Significant water desorption and concomitant structural changes were observed for the films during subsequent heat treatments between 100 and 700°C. The films exhibited three distinct water desorption states. The desorption temperatures were approximately 100-200°C for the first state, 150-300°C for the second state, and 350-650°C for the third state. Air exposure experiments revealed that the first and second states resulted from absorbed water and the third state from constitution water. The first and second desorption states were confirmed to originate from liquid like water and water molecules hydrogen-bonded to Si-OH bonds at macropore sites in the films, respectively. The third desorption state was found to result from Si-OH bonds formed during the film growth. This desorption of constitution water was considered to be accompanied by a microstructural change of the films.

Layer-by-layer deposited multilayer assemblies of polyelectrolytes and proteins: from ultrathin films to protein arrays

Abstract: We have recently introduced a new method of creating ultrathin films of polyelectrolytes based on the electrostatic attraction between opposite charges. Multilayer assemblies are adsorbed in a layer-by-layer fashion from aqueous solutions of the polymers. The total film thickness can easily be adjusted by varying the ionic strength of the solution. Here, we report on the temperature stability and the water content of the multilayer assemblies. Furthermore, we have extended our concept to the incorporation of protein layers into films of synthetic polyelectrolytes. The well established system biotin/streptavidin was used to construct such multilayers, also by biospecific recognition. Adsorption of streptavidin onto previously photostructured precursor films leads to the deposition of the protein on selected areas on the substrate. The films were investigated by small-angle x-ray scattering (SAXS), Fourier Transform Infrared Spectroscopy (FTIR), and by fluorescence microscopy.

Structure and integrity of a plasma sprayed hydroxylapatite coating on titanium

Abstract: Plasma sprayed hydroxylapatite (HA) coatings on titanium substrates were analyzed for process-induced compositional and structural changes. The HA starting powder and the resulting HA coatings were characterized using x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The integrity of the ceramic-to-substrate bond strength was also determined, by subjecting plasma sprayed HA coatings to shear/cantilever bond testing. The ceramic coatings retained the basic apatitic crystal structure of the starting powder; however, a considerable amount of amorphous material was created during the plasma spray process. FTIR and Raman spectroscopy revealed that the resulting coatings were partially dehydroxylated. Both XRD and FTIR spectroscopy results also suggested that amorphous material, as well as additional calcium phosphate phases such as alpha-tricalcium phosphate (TCP) not in the starting powder, were present in the HA coating. Average bond strengths of the HA coatings to Ti were determined to be 14.8 MPa +/- 3.5, with fracture occurring at the interface and within the coating itself.

Characterization of sulfided molybdenum/alumina catalysts by temperature-programmed reduction and low-temperature Fourier transform infrared spectroscopy of adsorbed carbon monoxide

Abstract: Sulfided Mo/Al[sub 2]O[sub 3] catalysts were studied by temperature-programmed reduction (TPRS) and transmission infrared spectroscopy of adsorbed CO at low temperatures. Reductive elimination of nonstoichiometric and stoichiometric sulfur from edge and corner sites creates coordinatively unsaturated Mo[sup 2+] sites. C-O stretching bands at 2100 cm[sup [minus]1] and at ca. 2060-2070 cm[sup [minus]1] were attributed to CO adsorption complexes on edge and corner sites, respectively. Evidence of morphological changes of MoS[sub 2] slabs during H[sub 2] treatment at 770 K is provided. IR spectroscopy of adsorbed CO at low temperature provides unique possibilities for the characterization of sulfided catalysts. 39 refs., 8 figs., 1 tab.

Determination of the global secondary structure of proteins by Fourier transform infrared (FTIR) spectroscopy

Abstract: In the development of new foods or in the control of traditional process, protein functionality plays a paramount role. It has long been theorized that changes in protein structure can alter functionality, but there has been a lack of reliable methodologies for observing protein structural changes in ‘real-world’ food samples. Here, a technique for determination of the global secondary structure of proteins using Fourier transform infrared (FTIR) spectroscopy in H2O instead of D2O is assessed and contrasted with other methodologies for structural determinations. A quantitative procedure is presented for preparing and analysing FTIR spectra of proteins for the determination of their global secondary structural components. As an example, an analysis of the FTIR spectra of egg-white lysozyme is presented and correlated with global secondary structure values calculated from its X-ray crystallographic structure. Other examples of FTIR analyses of food proteins are presented with consideration given to qualitative procedures for more rapid structural analysis of processed samples.

In situ FTIR Spectroelectrochemical Studies of Surface Films Formed on Li and Nonactive Electrodes at Low Potentials in Li Salt Solutions Containing CO 2

Abstract: In recent studies it was found that the presence of CO[sub 2] in Li battery electrolyte solutions considerably improves the cycling efficiency of Li electrodes. Surface films formed on Li and noble metal electrodes at low potentials in salt solutions saturated with CO[sub 2] were investigated using in situ Fourier transform infrared spectroscopy (FTIRS). Two methods have been used: subtractively normalized interfacial FTIRS (SNIFTIRS)-type measurements, external reflectance mode (thin layer cell configuration) and internal reflectance mode. The solutions used included LiAsF[sub 6] in propylene carbonate, tetrahydrofuran, and methylformate. It was found that Li[sub 2]CO[sub 3] is a major surface species formed, and its precipitation suppresses solvent-related surface reactions on the active electrode surfaces. A coproduct of Li carbonate seems to be CO gas.

Precision parts cleaning using supercritical fluids

Abstract: Supercritical fluid extraction and chromatography measurements were made on pieces of disk drive actuator components in order to understand how to clean and analyse these parts. Extract analyses were made by Fourier transform infrared (FTIR) and flame ionization detector measurements. Hydrocarbons, silicones, and fluorocarbons were seen on various pieces of different samples using FTIR, time‐of‐flight static secondary‐ion mass spectrometry (TOF‐SSIMS), and x‐ray photoelectron spectroscopy. In addition TOF‐SSIMS detected di‐isooctyl phthalate. Silicones and di‐isooctyl phthalate could be removed by CO2 extraction.

Phase‐modulated ellipsometer using a Fourier transform infrared spectrometer for real time applications

Abstract: A new Fourier transform infrared phase‐modulated ellipsometer is presented. It combines the high frequency provided by a photoelastic modulator (37 kHz) with the low frequency of the Fourier transform infrared spectroscopy (<1 kHz), by means of a numerical data acquisition system. A full spectrum recording (from 900 to 4000 cm−1) can be achieved in 2 s. Thus, it allows its adaptation for kinetic in situ studies. The optical setup and the data reduction procedure are presented. In particular, a self‐consistent spectral calibration procedure is described in detail. The precision in Ψ and Δ increases from 0.3° to 0.02° when increasing the integration time from 2 to 760 s. The examples shown in this article illustrate the high sensitivity to identify and analyze the absorption vibration variations of ultrathin films (a few angstroms thick).

Secondary structure and temperature behavior of the acetylcholine receptor by Fourier transform infrared spectroscopy

Abstract: Fourier transform infrared spectroscopy (FT-IR) was used to test the secondary structure of purified acetylcholine receptor membranes from Torpedo californica. The secondary structure was estimated using the spectral features observed in the structure sensitive region of amide I and amide I' (between 1600 and 1700 cm-1), taking advantage of Fourier self-deconvolution and second-derivative techniques along with least-squares band fitting procedures. At least six different amide I' band components could be resolved in D2O and were tentatively assigned to beta-structures (1680 and 1636 cm-1), alpha-helices (1657 cm-1), aperiodic structures and/or distorted helices (1646-1648 cm-1), and turns (1690 and 1668 cm-1), respectively. The beta-band around 1637 cm-1, in particular, turned out to be complex since it reproducibly exhibited weak features near 1630 and 1627 cm-1, thereby suggesting the presence of different chain interacting beta-structures. The band near 1657 cm-1 was assigned to alpha-helices which transverse the membrane bilayers, while 1646-1648-cm-1 component was tentatively attributed to aperiodic structures and alpha-helices localized within the "globular head" of the receptor protein protruding from the membrane surface into the surrounding water. Least-squares band fitting procedures were applied in order to estimate relative amounts of secondary structures. The results suggest 36-43%, 32-33%, 14-24%, and 18-19% for beta-, alpha-helical, turn, and "rest" structures, respectively. Additionally, the temperature- and time-dependent variations of the secondary structure was tested by evaluating the changes of amide I and amide II band components of receptor membranes dispersed in H2O and D2O.(ABSTRACT TRUNCATED AT 250 WORDS)

Secondary structure and temperature behaviour of acetylcholinesterase. Studies by Fourier-transform infrared spectroscopy.

Abstract: The secondary structure of the acetylcholinesterase and its temperature behaviour have been investigated using Fourier-transform infrared (FTIR) spectroscopy. The data are compared to the structure obtained by X-ray analysis of the crystalline enzyme. The secondary structure was determined using the spectral features observed in the amide-I band (H2O buffer) and amide-I' band (D2O buffer) at 1600-1700 cm-1, taking advantage of resolution-enhancement techniques along with least-squares band-fitting procedures. The relative amounts of different secondary-structure elements, 34-36% for alpha-helices, 19-25% for beta-sheets, 15-16% for turns and 13-17% for irregular structures, were estimated. These data, obtained with the enzyme in solution, correlate well with X-ray data of the crystalline protein [Sussman, J. L., Hard, M., Frolow, F., Oefner, C., Goldman, A., Toker, L. & Silman, I. (1991) Science 253, 872-879]. These results are also in good agreement with those obtained by computing the psi and phi angles of the peptide backbone using the Kabsch and Sanders method [Kabsch, W. & Sanders, C. (1983) Biopolymers 22, 2577-2637]. In conjunction with the X-ray data, two bands in the FTIR spectra were assigned to different populations of long and short alpha-helices. Until now this phenomenon has only been described by theoretical calculations [Nevskaya, N. A. & Chirgadze, Yu. N. (1976) Biopolymers 15, 637-648]. The relationship between the thermally induced loss of enzyme activity and secondary-structure changes has also been investigated. The decrease in enzyme activity to zero at 30-40 degrees C was accompanied only by minor changes in the secondary structure. At 55-60 degrees C, denaturation of AChE occurs. In this temperature range, all bands assigned to the various secondary-structure elements abruptly disappear in a co-operative and irreversible manner, whereas the beta-aggregation bands (at 1622 cm-1 and the corresponding high-frequency band) increase in intensity at the same rate.

Phase diagram of mixtures of polymers in aqueous solution using Fourier-transform infrared spectroscopy

Abstract: A new method is presented to determine the phase diagram of mixed aqueous biopolymer systems using FTIR spectroscopy coupled with partial least-squares analysis. The equilibrium phase diagrams of aqueous amylopectin/gelatin mixtures allowed to phase separate at a temperature outside the range within which either polymer could gel were presented. The method is capable of detecting the changes in the phase diagram when the molecular weight of one of the components is altered. The phase diagrams are analyzed in terms of the Flory-Huggins theory for ternary systems