Showing papers on "Fourier transform infrared spectroscopy published in 1990"

Secondary structure and dosage of soluble and membrane proteins by attenuated total reflection Fourier-transform infrared spectroscopy on hydrated films.

Abstract: Attenuated total reflection Fourier-transform infrared spectroscopy of thin hydrated films of soluble and membrane protein included in a phospholipid bilayer is shown to provide useful information as to the secondary structure of the protein. The analysis of the amide I band of deuterated samples by Fourier self-deconvolution followed by a curve fitting was performed by a new procedure in which all the input parameters are generated by the computer rather than by the investigator. The results of this analysis provide a correct estimation of the alpha-helix and beta-sheet structure content with a standard deviation of 8.6% when X-ray structures are taken as a reference. We also show that the orientation of the different secondary structures resolved by the Fourier self-deconvolution/curve-fitting procedure and of the phospholipid acyl chains can be simultaneously evaluated for membrane proteins reconstituted in a lipid bilayer. Of special interest for reconstitution of membrane proteins, the lipid/protein ratio can be accurately and quickly determined from the infrared spectrum.

Resolution-enhanced Fourier transform infrared spectroscopy study of the environment of phosphate ion in the early deposits of a solid phase of calcium phosphate in bone and enamel and their evolution with age: 2. Investigations in the nu3PO4 domain.

Abstract: In order to investigate the possible existence in biological and poorly crystalline synthetic apatites of local atomic organizations different from that of apatite, resolution-enhanced, Fourier transform infrared spectroscopy studies were carried out on chicken bone, pig enamel, and poorly crystalline synthetic apatites containing carbonate and HPO4 2− groups. The spectra obtained were compared to those of synthetic well crystallized apatites (stoichiometric hydroxyapatite, HPO4 2−-containing apatite, type B carbonate apatite) and nonapatitic calcium phosphates which have been suggested as precursors of the apatitic phase [octacalcium phosphate (OCP), brushite, and β tricalcium phosphate and whitlockite]. The spectra of bone and enamel, as well as poorly crystalline, synthetic apatite in thev 4 PO4 domain, exhibit, in addition to the three apatitic bands, three absorption bands that were shown to be independent of the organic matrix. Two low-wave number bands at 520–530 and 540–550 cm−1 are assigned to HPO4 2−. Reference to known calcium phosphates shows that bands in this domain also exist in HPO4 2−-containing apatite, brushite, and OCP. However, the lack of specific absorption bands prevents a clear identification of these HPO4 2− environments. The third absorption band (610–615 cm−1) is not related to HPO4 2− or OH− ions. It appears to be due to a labile PO4 3− environment which could not be identified with any phosphate environment existing in our reference samples, and thus seems specific of poorly crystalline apatites. Correlation of the variations in band intensities show that 610–615 cm−1 band is related to an absorption band at 560 cm−1 superimposed on an apatite band. All the nonapatitic phosphate environments were shown to decrease during aging of enamel, bone, and synthetic apatites. Moreover, EDTA etching show that the labile PO4 3− environment exhibited a heterogeneous distribution in the insoluble precipitate.

Group-delay measurement using the Fourier transform of an interferometric cross correlation generated by white light.

Abstract: A new method and apparatus for measuring the group delay in optical components and laser cavities are described. Cross-correlational fringes are fully recorded with a Michelson interferometer, in one of whose arms the optics to be measured are inserted. The path difference of the interferometer is calibrated to subwavelength accuracy, and the group delay is calculated from the phase of the Fourier transform of the measured fringe. The group delay for the entire visible-wavelength region is evaluated after a single measurement in approximately 10 min, using white light.

Alcohol Interaction with Zirconia Powders

Abstract: The mechanism by which alcohol washing of ceramic powders produces soft agglomerates has been investigated by studying the interaction of ethanol with hydrous ZrO{sub 2} powders using Fourier transform infrared (FTIR) spectroscopy. Unambiguous evidence of ethoxide formation has been found, which apparently prevents bond formation between adjacent particles and thus the formation of hard agglomerates.

An FTIR study of the catalytic activity of a 85:15 Pt:Ru alloy for methanol oxidation.

Abstract: In situ Fourier Transform Infrared Spectroscopy is used to study the catalytic properties of a Pt/Ru alloy as compared to pure platinum. Spectra taken at different potentials show the different behaviour of both metals with respect to methanol adsorption and oxidation. In the potential region below 700 mV the presence of Ru atoms increases the electrocatalytic activity of platinum. In the case of the alloy the poisoning adsorbate COad is adsorbed to a less extent and its seems to be weaker bonded to the Pt/Ru than to the Pt surface.

Characterization of silica gels by infrared reflection spectroscopy

Abstract: The FTIR specular reflection spectra of porous silica gels, either dried at room temperature or subjected to partial densification at 400°C, are significantly different from the spectrum of bulk vitreous silica. Namely, the high frequency SiOSi stretching vibrational peak near 1100 cm −1 exhibits shifts in the gels of up to 40 cm −1 towards lower frequencies, whereas the relative intensity of the companion high frequency shoulder simultaneously increases. The origin and possible structural meaning of the observed changes were investigated by Kramers-Kronig analysis of the experimental near-normal infrared reflectivity spectra of a series of silica xerogels, porous Vycor and bulk vitreous silica. Major differences were found for the energy loss function Im(−1/ϵ ∗ ), the peaks of which have been associated with the LO components of the dominant vibrational modes, and the largest red shifts corresponded to the highest frequency mode. Simple calculations show that the observed behavior of the infrared spectra could in part be due to a certain degree of strain in the SiOSi bridging bonds at the surface of the gel pores.

Structural and electronic transitions in polyaniline: A Fourier transform infrared spectroscopic study

Abstract: Fourier transform infrared (FTIR) spectroscopic studies are carried out on different, potentiometric well defined oxidation states of polyaniline in aqueous acidic and organic electrolytes. During the oxidation process ring structures transform from benzenoid into quinoid states. The fully reduced state of polyaniline shows differences in the anion contents in acidic and organic electrolytes. The 400 mV vs saturated calomel electrode (SCE) oxidized state has the maximum number of the intercalated anions in aqueous acidic media in accordance with supporting potentiometric titration experiments. This conducting form of polyaniline shows similar FTIR spectra in organic as well as in acidic media. For the oxidized state at 800 mV vs SCE, a deintercalation of anions in aqueous acidic, or further intercalation in organic electrolyte is observed. Beyond 800 mV vs SCE, polyaniline shows degradation processes in aqueous acidic media which are found to proceed via formation of benzoquinone‐like structures and finally result in a complete dissolution of the polymer.

In situ CIR-FTIR characterization of salicylate complexes at the goethite/aqueous solution interface.

Abstract: The types of complexes that salicylate (2-hydroxy-benzoate) forms with the surface of goethite ({alpha}-FeOOH) in aqueous medium were studied in situ by using cylindrical internal reflection (CIR) Fourier transform infrared (FTIR) spectroscopy. Results obtained from CIR-FTIR studies were compared with adsorption isotherm experiments in order to relate the level of salicylate coverage to the nature of the surface complex. At lower surface coverages all the interfacial salicylate has a chelate structure in which one carboxylic oxygen and the ortho phenolic oxygen bind one Fe atom of the goethite surface. At higher surface coverages this chelate complex coexists with salicylate ions, which are weakly bound in the double layer.

Characterization of benzoic and phenolic complexes at the goethite/aqueous solution interface using cylindrical internal reflection Fourier transform infrared spectroscopy. 2. Bonding structures

Abstract: La spectrometrie IR a transformation de Fourier est utilisee in situ pour etudier la structure des complexes superficiels formes apres adsorption de benzoate et de phenolate sur des particules de α-FeOOH en suspension dans l'eau

An automatic molecular beam microwave Fourier transform spectrometer

Abstract: We present hardware and software details of the pulsed molecular beam microwave Fourier transform (MB‐MWFT) spectrometer used in the Kiel microwave group. We emphasize an automatic scanning facility which greatly increases the efficiency of MB‐MWFT spectroscopy for the measurement of unassigned spectra.

Determination of the total unsaturation in oils and margarines by fourier transform raman spectroscopy

Abstract: An improved Raman spectroscopic procedure for the determination of the total unsaturation in oils and fats using Fourier Transform Raman (FT-Raman) spectroscopy is described. An important advantage of FT-Raman for these samples is that the spectra are fluorescence-free unlike dispersive Raman which often uses visible excitation. Samples can be analyzed without any pre-treatment thus eliminating the need for dissolution in toxic solvents. The short acquisition time of FT-Raman and the ease of application allowed for a rapid sample turnover.

Structural study of polyacrylonitrile fibers during oxidative thermal degradation by pyrolysis-gas chromatography, solid-state carbon-13 NMR, and Fourier-transform infrared spectroscopy

Abstract: The main stabilization mechanism of the PAN fibers to form cyclic ladder structures was confirmed by PyGC, 13 C NMR, and FT-IR. Furthermore, the contribution of dehydrogenation and/or dehydrocyanide reactions to form conjugated polyene structures suggested by the data of PyGC, especially for the PAN fibers stabilized at relatively higher temperatures, was also supported by those of 13 C NMR and FT-IR

Fourier-transform infrared study of the surface properties of cobalt oxides

Abstract: The surface properties of cobalt oxide after two different pretreatments have been investigated by means of Fourier-transform infrared (FTIR) spectroscopy of adsorbed carbon monoxide, methanol and ammonia. The surface of evacuated Co3O4 exposes CO3+ cations that react rapidly with CO, producing Co2+ and probably CO+, together with carbonate ions. This surface is extremely reactive, and decomposes at room temperature both ammonia and methanol. After mild reduction in hydrogen, CoO is produced. After this treatment the surface exposes Co2+ and even more reduced sites that by contact with CO give small polycarbonyl clusters. This surface adsorbs methanol dissociatively and ammonia molecularly at room temperature.

Infrared study of carbon monoxide hydrogenation over rhodium/ceria and rhodium/silica catalysts

Abstract: Carbon monoxide hydrogenation over ceria-promoted Rh or Rh/SiO{sub 2} catalysts was investigated by means of Fourier transform infrared spectroscopy. In the chemisorption of CO at room temperature, a new absorption band was observed near 1,725 or 1,696 cm{sup {minus}1} on a reduced 5% Rh-5% CeO{sub 2}/SiO{sub 2} or 5% Rh/CeO{sub 2} catalyst, respectively. This new absorption band was attributed to a C- and O-bonded species, located at the metal/support interface. The appearance of this species was related to the shift to lower temperatures of the peak ascribed to CO dissociation in the temperature-programmed desorption spectra after CO adsorption. A flow high-pressure IR cell allowed to study the surface species in situ during CO + H{sub 2} reaction and to follow the reactivity of these species toward pure H{sub 2}. The results suggest that the drop in methane formation may be related to a lower reactivity of surface carbon in the presence of the promoter.

Reaction Mechanisms of Plasma‐ and Thermal‐Assisted Chemical Vapor Deposition of Tetraethylorthosilicate Oxide Films

Abstract: Plasma- and thermal-assisted chemical vapor deposited (CVD) tetrathylorthosilicate (TEOS) oxide films were deposited on silicon substrates using a single-wafer reactor. The deposition kinetics of both plasma and thermal CVD processes were studied as a function of temperature. Film properties and bonding structure were analyzed for as-deposited and annealed films using Fourier transform infrared spectroscopy (FTIR), Auger, x-ray photoelectron spectroscopy (XPS), and nuclear reaction analysis (NRA) techniques. The thermal TEOS films were found to be more porous and to contain more hydrogen, but were more conformal than plasma-deposited TEOS films. Without a plasma, thermal temperatures can assist gas-phase reactions between ozone and TEOS (oxidation) to form conformal oxide films at as low as 200°C. With a plasma, both gas-phase and subsequent surface CVD reactions between TEOS, ozone, and oxygen are substantially enhanced, thus result in CVD films with higher quality

Surface and bulk infrared modes of crystalline and amorphous silica particles: a study of the relation of surface structure to cytotoxicity of respirable silica.

Abstract: Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

Fourier transform infrared spectroscopy of the polymorphic forms of syndiotactic polystyrene

Abstract: Infrared spectra of syndiotactic polystyrene exhibiting various crystalline forms and modifications, and in the amorphous state, are reported in this contribution. In addition to strong conformational effects, the spectra demonstrate striking effects of chain packing. Several infrared spectral differences also exist between the two crystalline forms which present a trans-planer conformation of the chains. Spectral changes are also reported for solution-crystallized samples, which depend on the solvent present in the clathrate compound formed with the polymers.

Molecular orientation in LB films of azobenzene-containing long-chain fatty acids and their barium salts studied by FT-IR transmission and reflection-absorption spectroscopy

Abstract: Molecular orientations in Langmuir-Blodgett films of 4 kinds of azobenzene-containing long-chain fatty acids and their barium salts are quantitatively evaluated by Fourier transform infrared transmission and reflection-absorption spectroscopy. The effects of carbon chain length of the tail and spacer portions, the number of monolayers, and the head group difference between the carboxyl and carboxylate groups on the molecular orientation are examined. It is concluded that the barium salts are more highly oriented as compared with the corresponding acids. This tendency is remarkable between barium salts with an eight-carbon tail and their acids. These results are consistent with their previous results obtained by UV absorption spectroscopy. Further, the orientation of the hydrocarbon chain and the azobenzene chromophore is found to be almost independent of the number of monolayers, but the tilt angle of the symmetrical axis of the carboxylate group in the first monolayer is larger than those in the upper monolayers.

Fourier transform infrared difference spectroscopy shows no evidence for an enolization of chlorophyll a upon cation formation either in vitro or during P700 photooxidation.

Abstract: Molecular changes associated with the photooxidation of the primary electron donor P700 in photosystem I from cyanobacteria have been investigated with Fourier transform infrared (FTIR) difference spectroscopy. Highly resolved signals are observed in the carbonyl stretching frequency region of the light-induced FTIR spectra. In order to assign and to interpret these signals, the FTIR spectra of isolated chlorophyll a and pyrochlorophyll a (lacking the 10a-ester carbonyl) in both their neutral and cation states were investigated. Comparison of the redox-induced FTIR difference spectra of these two model compounds demonstrates that upon chlorophyll a cation formation in tetrahydrofuran the 7c-ester carbonyl is essentially unperturbed while the 10a-ester carbonyl is upshifted from 1738 to 1751 cm-1. For the 9-keto group, the shift is from 1693 to 1718 cm-1 in chlorophyll a and from 1686 to 1712 cm-1 in pyrochlorophyll a. The 1718-cm-1 band in the difference spectrum of chlorophyll a is thus unambiguously assigned to the 9-keto carbonyl of the cation. Comparison of the light-induced FTIR difference spectrum associated with the photooxidation of P700 in vivo with the difference FTIR spectrum of chlorophyll a cation formation leads to the assignment of the frequencies of the 9-keto carbonyl group(s) at 1700 cm-1 in P700 and at 1717 cm-1 in P700+.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroreduction of carbon dioxide on platinum single crystal electrodes: Electrochemical and in-situ ftir studies. (Reannouncement with new availability information). Technical report, 1990-1991

Abstract: Fourier transform infrared reflectance spectroscopy (FTIRRAS) has been used in conjunction with linear sweep voltammetry to examine the reduction of CO2 on platinum single crystal surfaces in 0.1 M HC104. The data indicate that CO2 reduction on the Pt(100) and Pt(110) surfaces, potentiostated in a CO2 saturated solution yields CO as a reduction product in the hydrogen adsorption region. The CO is adsorbed in two states; linear CO and a large amount of the bridge-bonded were found on the Pt(100) while linear CO and only a small amount of bridged CO were found on the Pt(110). The Pt(111) surface showed only a low activity for CO2 reduction in the hydrogen adsorption region.

Thermal degradation of poly(aryl‐ether‐ether‐ketone): Experimental evaluation of crosslinking reactions

Abstract: Poly(aryl-ether-ether-ketone) (PEEK) has been heated at 400°C in both nitrogen and air. The extent of thermal degradation has been monitored by a variety of techniques including: solution viscometry, UV-visible spectroscopy, 13C high-resolution cross-polarization/magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectroscopy. The results indicate, that in a nonoxidative environment such as nitrogen, PEEK is relatively stable at 400°C for periods up to 6 h. Under oxidative conditions chain scission reactions occur and crosslinks are formed causing a reduction in the crystallizability of the material and discoloration of the polymer. The spectroscopic evidence suggests that the chain cleavage occurs adjacent to the carbonyl functional groups. Subsequent hydrogen abstraction from the aromatic ring then leads to crosslinking between adjacent aryl rings.

Glow discharge polymerization of reactive functional silanes on poly(methyl methacrylate)

Abstract: Glow discharge polymerization among such reactive functional silances as 3-methacryloxypropyltrimethoxysilane (MSL), 3-glycidoxypropyltrimethoxysilane (ESL), and vinyltrimethoxysilane (VSL) on poly(methyl methacrylate) was investigated by means of Fourier transform infrared spectroscopy, ESCA analysis, and contact angle measurement. Flow rate of monomer influenced both polymer deposition rate and polymer elemental composition. Infrared spectra showed differences in chemical structure among the polymers prepared from the different silanes. All of the polymers obtained contained similar chemical groups such as CH3, CH2, SiOSi, and SiOC. Polymers deposited from MSL and ESL contained highly hydrophilic functional groups like COH, SiOH, and CO on the uppermost layer while that from VSL contained highly hydrophobic functional groups like CH3 groups. Chemical analysis by ESCA and contact angle measurement gave evidence for the similarity of the polymers prepared from MSL and ESL, in contrast with the differences of the polymers prepared from VSL.