Showing papers on "Fourier transform infrared spectroscopy published in 2000"

The infrared absorption of amino acid side chains.

Abstract: Amino acid side chains play fundamental roles in stabilising protein structures and in catalysing enzymatic reactions. These fields are increasingly investigated by infrared spectroscopy at the molecular level. To help the interpretation of the spectra, a review of the infrared absorption of amino acid side chains in H(2)O and 2H(2)O is given. The spectral region of 2600-900cm(-1) is covered.

Polyethylene glycol-coated biocompatible surfaces.

Abstract: Surfaces covered with polyethylene glycol (PEG; HO-(CH(2)-CH(2)-O)(n)-H) have been shown to be biocompatible because PEG's properties yield nonimmunogenicity, nonantigenicity, and protein rejection. To produce a biocompatible surface coating, we have developed a method for grafting PEG onto activated silica films. We first deposited an amorphous silica film by plasma-enhanced chemical vapor deposition from SiH(4) and O(2) gases, which provided the flexibility to coat diverse materials with different chemistries and shapes. The silica films were activated by exposure to water plasma, increasing the number of silanol groups (Si-OH) on their surface. The surface silanol groups were then chemically reacted with the hydroxyl end of PEG to form an ester bond, Si-O-C, and to cover the surface with PEG. The surface reactions were monitored using attenuated total reflection Fourier transform infrared spectroscopy. The vibrational absorption bands of the C-O and -CH(2) bonds increased with time and saturated, indicating that PEG was adsorbed to saturation coverage on the surface. Simultaneously, the Si-OH absorption band decreased, showing that the surface silanols reacted with PEG and were depleted. The PEG-covered surfaces were physically characterized by atomic force microscopy, Auger electron spectroscopy, ellipsometry, and contact angle measurements. These characterization techniques provided additional evidence for the existence of chemically bonded PEG on the surfaces. Efficacy of protein rejection on PEG-covered surfaces was studied through measurements of the fluorescence intensity of Texas red-labeled bovine serum albumin brought in contact with such surfaces in solution. Significantly less protein adsorption was observed on surfaces covered with PEG compared to uncovered surfaces.

Change in Hydration State during the Coil−Globule Transition of Aqueous Solutions of Poly(N-isopropylacrylamide) as Evidenced by FTIR Spectroscopy†

Abstract: Coil−globule transition of poly(N-isopropylacrylamide) (PIPA), followed by intermolecular association in H2O and D2O, was investigated by Fourier transform infrared (FTIR) spectroscopy. IR spectra of the solutions were measured as a function of temperature, and spectral changes induced by the transition were observed. The intensities of the difference IR bands due to the vibrational modes of isopropyl and amide groups critically increased at the lower critical solution temperature (LCST). Heating of the PIPA solutions above the LCST led shifts of the amide II, C−H-stretching, and C−H-bending bands to lower wavenumbers during a shift of the amide I band to a higher wavenumber. The amide I band of the PIPA observed below the LCST could be fitted with a single component centered at 1625 cm-1, whereas two components (1625 and 1650 cm-1) were necessary to fit the band above the LCST. These components may be assigned to the CO group which is bound to water molecules as the solvent (1625 cm-1) and to the N−H in ...

The mechanical properties and molecular dynamics of plant cell wall polysaccharides studied by Fourier-transform infrared spectroscopy.

Abstract: Polarized one- and two-dimensional infrared spectra were obtained from the epidermis of onion (Allium cepa) under hydrated and mechanically stressed conditions. By Fourier-transform infrared microspectroscopy, the orientation of macromolecules in single cell walls was determined. Cellulose and pectin exhibited little orientation in native epidermal cell walls, but when a mechanical stress was placed on the tissue these molecules showed distinct reorientation as the cells were elongated. When the stress was removed the tissue recovered slightly, but a relatively large plastic deformation remained. The plastic deformation was confirmed in microscopic images by retention of some elongation of cells within the tissue and by residual molecular orientation in the infrared spectra of the cell wall. Two-dimensional infrared spectroscopy was used to determine the nature of the interaction between the polysaccharide networks during deformation. The results provide evidence that cellulose and xyloglucan associate while pectin creates an independent network that exhibits different reorientation rates in the wet onion cell walls. The pectin chains respond faster to oscillation than the more rigid cellulose.

Insight into protein structure and protein-ligand recognition by Fourier transform infrared spectroscopy.

Abstract: An overview of the application of Fourier transform infrared spectroscopy for the analysis of the structure of proteins and protein-ligand recognition is given. The principle of the technique and of the spectra analysis is demonstrated. Spectral signal assignments to vibrational modes of the peptide chromophore, amino acid side chains, cofactors and metal ligands are summarized. Several examples for protein-ligand recognition are discussed. A particular focus is heme proteins and, as an example, studies of cytochrome P450 are reviewed. Fourier transform infrared spectroscopy in combination with the various techniques such as time-resolved and low-temperature methods, site-directed mutagenesis and isotope labeling is a helpful approach to studying protein-ligand recognition.

Bioactivity of a CaO−SiO2 Binary Glasses System

Abstract: Five glasses in the CaO−SiO2 binary system with different silica content (50−90% in mol) have been prepared by the sol−gel method. The referred glasses have been characterized by thermogravimetric and differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) showing clear differences in composition and specific surface and porosity between those glasses with low SiO2 content (50−70% in mol) and those with high SiO2 content (80−90% in mol). The in vitro bioactivity study of all glasses prepared were carried out by soaking in a simulated body fluid (SBF) at 37 °C. The FTIR, XRD, SEM, and EDS analysis of the surface of these glasses after the in vitro assays reveal the formation of a hydroxycarbonate apatite (HCA) layer. The formation process of this layer on the glass is a function of the glass composition. The rate of formation increases in those glasses with lower SiO2 (50−70...

Insights into the Formation Mechanisms of Si−OR Monolayers from the Thermal Reactions of Alcohols and Aldehydes with Si(111)−H1

Abstract: Hydrogen-terminated Si(111) reacts thermally at moderate temperatures with alcohols (RCH2OH) and aldehydes (RCHO) to form the corresponding Si−OCH2R films. The films are characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). While FTIR and XP spectroscopies suggest that films of similar composition are formed, AFM and the relative chemical stabilities of the organic films show that the two reactions do not result in structurally identical films. A mechanism for the reaction of the aldehyde with Si(111)−H is proposed which is analogous to the well-known hydrosilylation of aldehydes. The reaction proceeds either by nucleophilic addition/hydride transfer or by a radical chain mechanism via adventitious radical initiation. The alcohol reaction is similar to the chemical etching of Si(111)−H by water and short-chain alcohols. This reaction proceeds by nucleophilic attack followed by loss of dihydrogen. Traces of ammonium fluor...

Metal−Support Interactions in Co/Al2O3 Catalysts: A Comparative Study on Reactivity of Support

Abstract: Co/Al2O3 catalysts have been prepared with conventional impregnation and sol−gel methods to vary the chemical reactivity of the alumina support. The material system has been investigated with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance Fourier transform spectroscopy (DRIFT), Brunauer−Emmett−Teller (BET) method, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) (with thermogravimetric analysis (TGA) and differential thermal analysis (DTA)), and gas chromotography (GC) for the catalytic oxidation of CO. It had been found that the reactivity of the support changes the surface structure and chemical composition of catalysts significantly. When the metal−support interaction is weak, Co3O4 is a predominant surface phase (which is interfaced by a “cobalt surface phase”). With an increase in support reactivity, CoO and CoAl2O4 are found to be present on the surface. The cobalt content on the surface decreases upon the increase in suppor...

Some of the most significant changes in the Fourier transform infrared spectra of edible oils under oxidative conditions

Abstract: The oxidation of a broad collection of commercial edible oils, including extra virgin olive, olive, sesame, sunflower, corn, unknown seed, soybean, safflower, rapeseed, peanut and walnut oils, was monitored by Fourier transform infrared spectroscopy. Samples were kept in a convection oven with air circulating at 70 °C. Duplicate spectra were collected each day of the experiment by applying a film of pure oil between two KBr disks. The frequency and absorbance of each infrared band were automatically registered by a macro program. Ratios between absorbances of different bands of the spectra were calculated. Changes in frequency values of different bands and in ratios between absorbances of some bands allow different stages of the oxidation process to be distinguished as well as determining their oxidative stability in a simple and fast way, showing the usefulness of this technique in monitoring oil oxidation processes. © 2000 Society of Chemical Industry

Chemical Preparation of Pure and Strontium- and/or Magnesium-Doped Lanthanum Gallate Powders

Abstract: Powder compositions of LaGaO3 ,L a 0.9Sr0.1GaO2.95, and La0.8Sr0.2Ga0.83Mg0.17O2.815 were prepared via a Pechini-type process that uses citric acid and ethylene glycol. The calcination behavior of the precursor powders of the abovementioned phases was studied in the temperature range of 200°‐1400°C in an air atmosphere. Characterization of the powder samples were performed using several processes, including X-ray diffractometry, thermogravimetry/differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, inductively coupled plasma‐ atomic emission spectroscopy, and carbon and nitrogen analyses.

Adsorption and Decomposition of Dimethyl Methylphosphonate on TiO2

Abstract: By using Fourier transform infrared spectroscopy (FTIR) we have witnessed the sequential steps of surface diffusion, weak chemical bonding, and decomposition of dimethyl methylphosphonate (DMMP) on TiO2 powder. At temperature lower than ∼160 K, DMMP condenses as an ice layer on the outer surface of the TiO2 sample. In the temperature range 160− 200 K, diffusion into the TiO2 interior occurs and hydrogen bonding of DMMP to isolated TiOH groups is observed. In addition, bonding to Lewis acid sites occurs. Above 214 K, cleavage of P−OCH3 groups takes place, with the production of Ti−OCH3 surface species and this is accompanied by the consumption of surface hydroxyl groups. A reduction of P−O bond order then occurs as adsorbed phosphonate species are formed.

FTIR Spectroscopic Investigation of the Mechanism and Kinetics of the Heterogeneous Reactions of NO2 and HNO3 with Soot

Abstract: Soot samples from a spark generator, a flame, and a diesel passenger car were either collected on a Teflon filter and transferred to an IR-transparent window or deposited directly from a flame onto the window and investigated by Fourier transform infrared (FTIR) spectroscopy. The soot-covered windows were mounted in a 10 cm vacuum cell connected to a standard flow system with He as carrier gas. Reactive gases, such as NO2 and HNO3, were added to the carrier gas flow at a concentration of (0.016 to 2.5) × 1014 molecule cm-3. FTIR spectra of soot samples before and after exposure to HNO3, NO2, and O3 are presented. Formation of IR absorption bands was analyzed as a function of exposure time. IR bands attributable to soot surface oxidation products and nitrogen containing species, e.g. −CO, R−NO2, R−ONO2, and R−ONO were observed. The observed time dependence of the absorption bands of the spark generator soot can be fitted by two parallel reactions, a slow and a fast process. Both processes have a reaction o...

Atomic Layer Deposition of Tungsten Nitride Films Using Sequential Surface Reactions

Abstract: Tungsten nitride films were deposited with atomic layer control using sequential surface reactions. The tungsten nitride film growth was accomplished by separating the binary reaction 2WF 6 + NH 3 → W 2 N + 3HF + 9/2F 2 into two half-reactions. Successive application of the WF 6 and NH 3 half-reactions in an ABAB... sequence produced tungsten nitride deposition at substrate temperatures between 600 and 800 K. Transmission Fourier transform infrared (FTIR) spectroscopy monitored the coverage of WF* x and NH y * surface species on high surface area particles during the WF 6 and NH 3 half-reactions. The FTIR spectroscopic results demonstrated that the WF 6 and NH 3 half-reactions were complete and self-limiting at temperatures ≥600 K. In situ spectroscopic ellipsometry monitored the film growth on Si(100) substrates as temperature and reactant exposure. A tungsten nitride deposition rate of 2.55 A/AB cycle was measured at 600-800 K for WF 6 and NH 3 reactant exposures ≥3000 L and 10,000 L, respectively, X-ray photoelectron spectroscopy depth-profiling experiments determined that the films had a W 2 N stoichiometry with low C and O impurity concentrations. X-ray diffraction investigations revealed that the tungsten nitride films were microcrystalline. Atomic force microscopy measurements of the deposited films observed remarkably flat surfaces indicating smooth film growth. These smooth tungsten nitride films deposited with atomic layer control should be useful as diffusion barriers for Cu on contact and via holes.

A new application of UV-ozone treatment in the preparation of substrate-supported, mesoporous thin films

Abstract: A nominally room temperature photochemical method, simply employing ultraviolet light- (187−254 nm) generated ozone environment, is shown to provide an efficient alternative for the removal of surfactant templates for a routine production of mesoporous silica thin films at low temperatures. The treatment concomitantly strengthens the silicate phase by fostering the condensation of unreacted silanols leading to mesoporous thin films with well-defined mesoscopic morphologies. The surfactant/silicate thin film mesophases were prepared onto a polycrystalline Au surface by dip-coating or spin-casting methods using sub-critical micelle concentration (cmc) nonionic ethylene oxide surfactant in an oligomeric silica sol mixture. The structures and compositions of the thin film mesophases before and after exposure to UV/ozone were determined using a combination of reflection−absorption Fourier transform infrared spectroscopy, transmission electron microscopy, and thin film X-ray diffraction measurements. The pore c...

Quantitative Determination of the Biodegradable Polymer Poly(β-hydroxybutyrate) in a Recombinant Escherichia coli Strain by Use of Mid-Infrared Spectroscopy and Multivariative Statistics

Abstract: Fourier transform infrared (FTIR) spectroscopy in combination with the partial least squares (PLS) multivariative statistical technique was used for quantitative analysis of the poly(β-hydroxybutyrate) (PHB) contents of bacterial cells. A total of 237 replicate spectra from 34 samples were obtained together with gas chromatography-determined reference PHB contents. Using the PLS regression, we were able to relate the infrared spectra to the reference PHB contents, and the correlation coefficient between the measured and predicted values for the optimal model with a standard error of prediction of 1.49% PHB was 0.988. With this technique, there are no solvent requirements, sample preparation is minimal and simple, and analysis time is greatly reduced; our results demonstrate the potential of FTIR spectroscopy as an alternative to the conventional methods used for analysis of PHB in bacterial cells.

Thermal degradation of nylon polymers

Abstract: This paper is concerned with the processes of thermal degradation of nylon 6 and nylon 6,6, which lead to crosslinking and the production of involatile char. The techniques used in this study include thermogravimetric analysis (TG), differential scanning calorimetry (DSC), hot-stage Fourier transform infrared spectroscopy (hot-stage FTIR) and solution viscosity. TG results showed that nylon 6 and nylon 6,6 produce involatile char during thermal degradation. The formation of char lead to a deviation from first order kinetics of thermal degradation, and the amount of char yielded decreased with increasing temperature. Thermal degradation lead to a decrease in the amount of crystallinity attainable on cooling from the melt, which was considered to be due to crosslinking, and was accompanied by an increase in molecular weight and formation of colour. Hot-stage FTIR results showed that thermal degradation lead to the formation of an aromatic-conjugated structure, which may contain keteneimine groups.

Diffuse Reflectance Fourier Transform Infrared Study of the Adsorption of Oleate/Oleic Acid onto Titania

Abstract: Fourier transform infrared spectroscopy in diffuse reflectance mode is used to study the nature of the adsorbed species when rutile form titania is exposed to aqueous oleate/oleic acid over a range of pH values. Any of the oleic acid dimer, the monomer, or the anion may be adsorbed, depending on the oxide sample, in particular the incidence of surface Lewis acid sites. The results suggest that oleic acid monomer can be adsorbed by coordination as a σ-bonded ligand to Ti4+ Lewis acid sites, via its carbonyl group oxygen. The oleic acid dimer appears to simultaneously coordinate to two adjacent Lewis sites via the hydroxyl oxygens. At pH 3 there is evidence that the adsorbed amphiphiles make two-point contact with the oxide surface via an interaction of the CHCH group with surface OH2+ groups.

Conductive and Magnetic Properties of 3,4-Dimethoxy- and 3,4-Ethylenedioxy-Capped Polypyrrole and Polythiophene

Abstract: Electrochemically prepared poly(3,4-dimethoxypyrrole), poly(3,4-dimethoxythiophene), poly(3,4-ethylenedioxypyrrole), and poly(3,4-ethylenedioxythiophene) have been characterized by cyclic voltammetry (CV) and ultraviolet−visible (UV−vis) and Fourier transform infrared (FTIR) spectroscopy and were subsequently investigated by in situ conductivity, in situ electron spin resonance spectroscopy (ESR), and electrochemical quartz crystal microbalance (EQCM) analysis. Blocking the 3 and 4 positions of the heteroaromatic ring allows the display of a complete potential window of conductivity for the polypyrroles during the oxidative doping process, whereas a potential window of conductivity wider than usual, but still open, is displayed for the polythiophenes. The combination of redox-type conduction and solvation in poly(3,4-dimethoxypyrrole) gives this material unusual solvatoconductive properties.

Layered polymer-kaolinite nanocomposites

Abstract: Kaolinite (K) was reacted with liquid dimethyl sulfoxide (DMSO) producing K(DMSO)0.4. Highly ordered polymer/kaolinite materials were obtained by displacement of DMSO molecules in the K(DMSO)0.4 intercalate by polyethylene oxide (PEO) or bacterial polyhydroxybutyrate (PHB), both in the melt state at 130°C and 180°C, respectively. The hybrid nanocomposites obtained were characterized by powder X-ray diffractometry (PXRD), Fourier Transform Infrared spectrometry (FTIR) and thermal analysis (simultaneous TG/DSC). The obtained results are consistent with the total replacement of DMSO molecules by the macromolecular linear chains that lie flat building a monolayer of the polymer in the interlayer space of kaolinite. The stoichiometry of the compounds estimated from the TG/DSC measurements are: K(DMSO)0.40±0.02, K(PHB)0.82±0.02, K(PEO)3.40±0.02.