Showing papers on "Fourier transform infrared spectroscopy published in 1999"

Chemical characterization of silicon-substituted hydroxyapatite.

Abstract: Bioceramic specimens have been prepared by incorporating a small amount of silicon (0.4 wt %) into the structure of hydroxyapatite [Ca10(PO4)6(OH)2, HA] via an aqueous precipitation reaction to produce a silicon-substituted hydroxyapatite (Si-HA). The results of chemical analysis confirmed the proposed substitution of the silicon (or silicate) ion for the phosphorus (or phosphate) ion in hydroxyapatite. The Si-HA was produced by first preparing a silicon-substituted apatite (Si-Ap) by a precipitation process. A single-phase Si-HA was obtained by heating/calcining the as-prepared Si-Ap to temperatures above 700 degrees C; no secondary phases, such as tricalcium phosphate (TCP), tetracalcium phosphate (TeCP), or calcium oxide (CaO), were observed by X-ray diffraction analysis. Although the X-ray diffraction patterns of Si-HA and stoichiometric HA appeared to be identical, refinement of the diffraction data revealed some small structural differences between the two materials. The silicon substitution in the HA lattice resulted in a small decrease in the a axis and an increase in the c axis of the unit cell. This substitution also caused a decrease in the number of hydroxyl (OH) groups in the unit cell, which was expected from the proposed substitution mechanism. The incorporation of silicon in the HA lattice resulted in an increase in the distortion of the PO4 tetrahedra, indicated by an increase in the distortion index. Analysis of the Si-HA by Fourier transform infrared (FTIR) spectroscopy indicated that although the amount of silicon incorporated into the HA lattice was small, silicon substitution appeared to affect the FTIR spectra of HA, in particular the P-O vibrational bands. The results demonstrate that phase-pure silicon-substituted hydroxyapatite may be prepared using a simple precipitation technique.

FTIR spectroscopic characterization of protein structure in aqueous and non-aqueous media

Abstract: With increasing use of proteins in many different applications, ranging from phramaceuticals to biosensors and biomaterials, there has emerged a need for protein structural characterisation in diverse environments. In many cases it is not sufficient to just have the three-dimensional structure of a protein in H 2 O or in the crystalline state. Often information on the structural properties of a protein is required in the presence of organic solvents, detergent micelles, phospholipid membranes and so on. Fourier transform infrared spectroscopy (FTIR) has been identified as one of the few techniques that can be applied for structural characterisation of proteins in such environments. Here we discuss how this technique is being used to obtain information on protein structure and stability in both aqueous and non-aqueous media. Examples are drawn from our studies of water soluble proteins and membrane proteins.

Role of nitrogen in the formation of hard and elastic CN x thin films by reactive magnetron sputtering

Abstract: Carbon nitride films, deposited by reactive dc magnetron sputtering in Ar/N2 discharges, were studied with respect to composition, structure, and mechanical properties. CNx films, with 0

Synthesis and Characterization of Carboxylate-Modified Gold Nanoparticle Powders Dispersible in Water

Abstract: Carboxylate-modified gold nanoparticles have been synthesized in a single-phase system based on the reduction of hydrogen tetrachloroaurate(III) by sodium borohydride in methanol using mercaptosuccinic acid (MSA) as the stabilizing thiol ligand. Five samples with diameters of 10.2, 10.8, 12.8, 19.4, and 33.6 A have been prepared as water-redispersible powders through decreasing the initial MSA/HAuCl4 molar ratio from 2.5 to 0.5. These samples were characterized by X-ray diffraction, transmission electron microscopy, elemental analysis, thermogravimetric analysis, ζ-potential measurement, Fourier transform infrared spectroscopy, and UV−vis spectroscopy. The results show that a large number of the particles are fcc single crystals with the polyhedral morphology of a truncated octahedral motif and that a self-assembled monolayer of thiolates has indeed formed through the adsorption of mercapto groups on the gold particle surface; the maximum packing density of the thiolates is 15.23 A2 per mercapto group. Th...

Lewis Acid Mediated Hydrosilylation on Porous Silicon Surfaces

Abstract: Lewis acid mediated hydrosilylation of alkynes and alkenes on non-oxidized hydride-terminated porous silicon derivatizes the surface with alkenyl and alkyl functionalities, respectively. A very broad range of chemical groups may be incorporated, allowing for tailoring of the interfacial characteristics of the material. The reaction is shown to protect and stabilize porous silicon surfaces from atmospheric or direct chemical attack without compromising its valuable material properties such as high porosity, surface area and visible room-temperature photoluminescence. The reaction is shown to act on alkenes and alkynes of all possible regiochemistries (terminal and internal alkynes; mono-, cis- and trans-, di-, tri-, and tetrasubstituted alkenes). FTIR as well as liquid- and solid-state NMR spectroscopies show anti-Markovnikov addition and cis stereochemistry in the case of hydrosilylated terminal alkynes. Material hydrosilylated with long-chain hydrophobic alkynes and alkenes shows a substantially slower surface oxidation and hydrolysis rate in air as monitored by long-term FTIR monitoring and chemography. BJH and BET measurements reveal that the surface area and average pore size of the material are reduced only slightly after hydrosilylation, indicating that the porous silicon skeleton remains intact. Elemental analysis and SIMS depth profiling show a consistent level of carbon incorporation throughout the porous silicon which demonstrates that the reaction occurs uniformly throughout the depth of the film. The effects of functionalization on photoluminescence were investigated and are shown to depend on the organic substituents.

Synthesis of Alkyl-Terminated Silicon Nanoclusters by a Solution Route

Abstract: We describe the synthesis and characterization of alkyl-capped nanocrystalline Si (R-n−Si) prepared by the reaction of SiCl4 with Mg2Si in ethylene glycol dimethyl ether (glyme) and surface-terminated with various alkyl groups, R-n−Si (R = methyl, ethyl, n-butyl, and n-octyl). This reaction produces crystalline nanoparticles with surfaces that can be chemically modified. The resultant crystalline nanoparticles can be suspended in organic solvents or isolated as a powder. The nanoclusters were characterized by transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, UV−vis absorption, and photoluminescence spectroscopy. The average cluster size depends on the reflux time of Mg2Si with SiCl4, which provided nanoclusters with an average size of 2−5 nm. HRTEM confirms the presence of crystalline nanoclusters, and SAED is consistent with diamond-structured sil...

Effect of Activated Carbon Surface Oxygen- and/or Nitrogen-Containing Groups on Adsorption of Copper(II) Ions from Aqueous Solution†

Abstract: The adsorption properties of a modified activated carbon with various oxygen- and/or nitrogen-containing surface groups toward copper ions was studied. Previously de-ashed and chemically modified commercial activated carbon D-43/1 (Carbo-Tech, Essen, Germany) was used. The chemical properties of the modified carbon surface were estimated by standard neutralization titration with HCl, NaOH, and NaOC2H5. The adsorption of Cu2+ ions on three modified activated carbons from aqueous CuSO4 solution of various pH was measured. The carbon samples with adsorbed Cu2+ ions were analyzed by spectroscopic methods (X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy). In addition, an electrochemical measurement (cyclic voltammetry) was performed using powdered activated carbon electrodes.While the modification procedures employed alter the surface only slightly, they strongly influence the surface chemical structure. Basic groups are predominant in the heat-treated samples; acidic functional group...

Reaction of benzoxazine-based phenolic resins with strong and weak carboxylic acids and phenols as catalysts

Abstract: The reaction of 3,4-dihydro-3,6-dimethyl-2H-1,3-benzoxazine using strong and weak carboxylic acids and phenols as catalysts has been studied using Fourier transform infrared (FTIR) spectroscopy. The auto-accelerated curing using sebacic acid as catalyst is further documented using 1H-nuclear magnetic resonance (NMR) and dielectric analysis. Termination of curing, using strong acids or no catalyst, are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1913–1921, 1999

Investigations of CH4, C2H2 and C2H4 dusty RF plasmas by means of FTIR absorption spectroscopy and mass spectrometry

Abstract: Infrared (IR) absorption spectroscopy and mass spectrometry have been simultaneously applied to dusty radiofrequency (RF) plasmas in methane, acetylene and ethylene. The combination of IR absorption spectroscopy and mass spectrometry allows the chemical composition and structure of the most relevant plasma-produced neutral species, the ionic plasma composition and the chemical composition of the nanometer-sized particles to be precisely identified. The production of acetylenic compounds (C2Hx) seems to be a key mechanism for the powder formation in all the investigated hydrocarbon plasmas. Electron attachment to acetylenic compounds and the following ion-neutral reactions might lead to the high-mass carbon anions, which are trapped in the plasma and finally end in powder formation. The hydrogenation of the monomer strongly influences the composition of the ions. Finally the composition of the plasma-produced particles is mainly sp3 bonded carbon and the infrared spectra show similarities to that of polyethylene.

Low dielectric constant films prepared by plasma-enhanced chemical vapor deposition from tetramethylsilane

Abstract: Dielectric films have been prepared by radio-frequency plasma-enhanced chemical vapor deposition from mixtures of tetramethylsilane with oxygen. The films have been characterized as-deposited and after annealing at 400 °C to determine the thermal stability of their properties. Rutherford backscattering and forward recoil elastic scattering have been used for determination of the composition of the films. Optical properties were characterized by Fourier transform infrared spectroscopy and measurements of the index of refraction and optical gap. The electrical properties were measured in a Si/insulator/metal configuration. It has been found that the index of refraction decreases and the optical gap and dielectric constant increase with increasing oxygen concentration in the gas feed. While the materials did not show a mass or composition loss after annealing, the annealing resulted in a reduction of the dielectric constant of the films. Dielectric constants as low as 3.1 have been obtained after annealing the film deposited from pure tetramethylsilane.

Solid state 27Al NMR and FTIR study of lanthanum aluminosilicate glasses

Abstract: The structure of lanthanum aluminosilicate (LAS) glasses, containing: (15–25) mol% La2O3, (15–35) mol% Al2O3 and (40–70) mol% SiO2, were studied by 27Al nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The effects of La2O3 and Al2O3 content on the properties and structure of the LAS glasses were evaluated. Al3+ ion enters into the glass structure mainly in fourfold co-ordination, forming ( AlO 4/2 ) − tetrahedra, and only in small amounts in fivefold and sixfold co-ordination. La3+ acts as network modifier, producing more non-bridging oxygen atoms as its content increases.

Characterization of Barium Titanate Powders: Barium Carbonate Identification

Abstract: A range of methods for the detection of barium carbonate contaminant in barium titanate powder has been assessed, namely: X-ray diffraction (XRD), scanning electron microscopy (SEM), with EDS-X-ray microanalysis, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), gas chromatography (GC) for analysis of carbon, and X-ray photoelectron spectroscopy (XPS). The most satisfactory procedure for the detection of the small amounts of BaCO3 commonly present is FT-IR. Surface analyses by XPS show that the carbonate is present as a discrete phase and is not a surface film on barium titanate particles.

X-ray photoelectron spectroscopy study of surface films formed on Li electrodes freshly prepared in alkyl carbonate solutions

Abstract: Li samples were freshly prepared (shearing) and stored (2 days) in dimethyl carbonate (DMC), and ethyl carbonate−diethyl carbonate (EC−DEC), and dry (20 ppm of H2O) and wet (500 ppm of H2O) EC−DMC solutions of LiAsF6 (1 M), and were then studied by X-ray photoelectron spectroscopy (XPS). The XPS analysis, including depth profiling of these surface films, appears to be reliable on the qualitative level only, because both the X-ray beam and sputtering should be suspected as being partially destructive to the surface films on lithium. These studies basically confirm previous conclusions obtained by Fourier transform infrared spectroscopy spectroscopic studies of Li surfaces. Surface films formed on Li in alkyl carbonate solutions of LiAsF6 are comprised of ROCO2Li, Li2CO3, LiF, LixAsFy, and Li oxides. XPS could also detect surface species with Li−C bonds (e.g., LiCH2CH2OCO2Li). When EC is present, its reduction dominates the surface film formation. The presence of water suppresses both solvent and salt anion...

Miniaturized time-scanning Fourier transform spectrometer based on silicon technology

Abstract: We present a miniaturized Fourier transform spectrometer (FTS) based on optical microelectromechanical system technology The FTS is a Michelson interferometer with one scanning mirror A new type of electrostatic comb drive actuator moves the mirror We have measured a nonlinearity of the driving system of ±05 µm for a displacement of 385 µm A method is presented to correct the spectrum to get rid of the nonlinearity The driving reproducibility is ±25 nm The measured resolution of the spectrometer after the phase correction is 6 nm at a wavelength of 633 nm

Coating Carboxylic Acids on Amorphous Iron Nanoparticles

Abstract: Nanophased amorphous iron particles were coated by various carboxylic acids and their physical properties (differential scanning calorimetry, thermogravimetric analysis, temperature-programmed desorption, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and magnetism) were measured. The various properties were measured as a function of the alkyl chain length. The desorption pattern at 400 °C revealed a keto derivative.

Usefulness of the frequency data of the fourier transform infrared spectra to evaluate the degree of oxidation of edible oils.

Abstract: The oxidation process of 13 edible oil samples with different proportions of oleic, linoleic, and linolenic acyl groups has been studied using Fourier transform infrared spectroscopy. The oxidation experiments were carried out by heating the samples in a convection oven at 70 degrees C. Duplicate spectra were recorded from a film of pure oil between two disks of KBr for each sample every day during the course of the oxidation, and frequency data of each band of the spectrum were collected automatically. Changes in the values of the frequency of most of the bands of the spectra were observed. The shiftings of the frequency value of specific bands allowed one to distinguish between the different stages of the oxidation process and to establish the oxidation degree of each oil sample. This methodology could be useful to evaluate the oxidative stability of edible oils in a simple, fast, and accurate way.

Fourier transform infrared spectroscopy in analysis of protein deposits

Abstract: Publisher Summary The intrinsic insoluble nature of protein deposits (as in amorphous aggregates, inclusion bodies, amyloid fibrils, etc.) places severe restrictions on the availability of methods required for ascertaining the structure of the material. Fourier transform infrared (FTIR) spectroscopy is well suited for determining structural features of proteins, both in solution and as deposits. Proteins in the form of solutions, thin films (hydrated or dry), solids (including lyophilized or spray-dried powders), or suspensions of precipitates in various solvents can be used for FTIR analysis. The most commonly used methods for FTIR analysis of protein deposits are KBr pellets (in which the dry solid is dispersed in a KBr disk) and diffuse reflectance for dry samples, thin films (using transmission or attenuated total reflectance, or ATR modes) for samples in solution or suspension, and attenuated total reflectance mode for solid, liquid, or suspended samples. For dry solid samples there are several sampling techniques, including powder, mull, alkali halide pellet or disk, and film. Powdered samples can be difficult to analyze because of the high incidence of scattered light, which results in a loss of energy transmitted to the detector. To reduce scattering, samples should be ground to a powder of 5 μm particle size or less, smaller than the wavelength of the radiation.

Electrochemical and Spectroscopic Studies of Hydroxide Adsorption at the Au(111) Electrode

Abstract: The adsorption of hydroxide ions at a Au(111) single-crystal electrode has been investigated quantitatively using chronocoulometry and subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS). By thermodynamic analysis of the charge density data, the Gibbs excess, Gibbs energy of adsorption, and number of electrons flowing to the interface per one adsorbed hydroxide ion at a constant electrode potential (electrosorption valency) were determined. The electrosorption data indicate that the adsorption of OH- has a three-state character. The adsorbed OH- forms quite a polar surface bond at a negatively charged surface, while the polarity of the surface bond is significantly decreased at positive charge densities. Oxide formation begins at higher charge densities. Infrared spectroscopy shows that oxide formation takes place when the surface concentration of hydroxide ions exceeds one-third of a monolayer. The integrated infrared intensity of the O−H stretching band correlates ver...

FTIR-spectroscopy of molecular clusters in pulsed supersonic slit-jet expansions

Abstract: A new approach to the Fourier transform infrared (FTIR) absorption spectroscopy of molecular clusters in pulsed supersonic jets is developed to the point where it is competitive with high-sensitivity laser absorption techniques for intermediate and large molecular systems. A combination of rapid spectral acquisition and of a buffered jet chamber enables the use of intense gas pulses which cover complete interferometer scans. Applications to (N2O)n, (CH3OH)n and (HCl)n demonstrate the capabilities of this technique. Investigations of the association of bulky alcohols and of clusters within clusters illustrate some ongoing research.

Sorption and transport of water vapor in nylon 6,6 film

Abstract: The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture-sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water-vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (Tg's) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the Tg of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen-bond strength of the NH groups. However, an increase was seen for the CO groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 197–206, 1999