Showing papers on "Fourier transform infrared spectroscopy published in 1996"

Infrared spectroscopy of biomolecules

Abstract: Theoretical Analyses of the Amide I Infrared Bands of Globular Proteins (H. Torii & M. Tasumi). Fourier Transform Infrared Spectroscopy of Enzyme Systems (J. Alben). Light--Induced Fourier Transform Infrared Difference Spectroscopy of the Primary Electron Donor in Photosynthetic Reaction Centers (E. Nabedryk). Equipment: Slow and Fast Infrared Kinetic Studies (F. Siebert). Ultrafast Infrared Spectroscopy of Biomolecules (B. Cohen & R. Hochstrasser). Infrared Spectroscopy of Nucleic Acids (J. Liquier & E. Taillandier). Fourier Transform Infrared Spectroscopy in the Study of Hydrated Lipids and Lipid Bilayer Membranes (R. Lewis & R. McElhaney). Fourier Transform Infrared Spectroscopic Studies of Cell Surface Polysaccharides (K. Brandenburg & U. Seydel). Fourier Transform Infrared Spectroscopy of Biomembrane Systems (P. Haris & D. Chapman). What Can Infrared Spectroscopy Tell Us About the Structure and Composition of Intact Bacterial Cells? (D. Naumann, et al.). Biomedical Infrared Spectroscopy (M. Jackson & H. Mantsch). New Trends in Isotope--Edited Infrared Spectroscopy (H. Fabian, et al.). Index.

Fourier transform infrared spectroscopy of the solution-mediated conversion of amorphous calcium phosphate to hydroxyapatite: New correlations between X-ray diffraction and infrared data

Abstract: Fourier Transform infrared spectroscopic analysis of maturing, poorly crystalline hydroxyapatite (HA) formed from the conversion of amorphous calcium phosphate (ACP) at constant pH or variable pH show only subtle changes in the v1, v3 phosphate absorption region (900 cm-1-1200 cm-1). This region is of interest because it can be detected by analysis of mineralized tissue sections using FT-IR microscopy. To evaluate the subtle spectral changes occurring during the maturation, second derivatives of the spectra were calculated. HA formed at constant pH showed little or no variation in the second derivative peak positions with bands occurring at 960 cm-1, 985 cm-1, 1030 cm-1, 1055 cm-1, 1075 cm-1, 1096 cm-1, 1116 cm-1, and 1145 cm-1. These bands can be assigned to molecular vibrations of the phosphate (PO4(3-)) moiety in an apatitic/stoichiometric environment of HA. In contrast, during the early stages of maturation of the HA formed at variable pH, second derivative peak positions occurring at 958 cm-1, 985 cm-1, 1020 cm-1, 1038 cm-1, 1112 cm-1, and 1127 cm-1 shifted in position with maturation, indicating that the environment of the phosphate species is changing as the crystals mature. Peaks at 1020 cm-1, 1038 cm-1, 1112 cm-1, and 1127 cm-1 were attributable to nonstoichiometry and/or the presence of acid phosphate-containing species. This concept was supported by the lower Ca:P molar ratios measured by chemical analysis of the synthetic material made at variable pH. Using the second derivative peak positions as initial input parameters, the v1, v3 phosphate region of the synthetic HAs prepared at constant pH were curve fit. X-ray diffraction patterns of these same materials were also curve fit to calculate the changes in crystallinty (size/perfection) in the c-axis 002 reflection as well as the 102, 210, 211, 112, 300, 202, and 301 planes. Linear regression analysis showed that the changes in the percent area of the underlying bands at 982 cm-1, 999 cm-1, 1030 cm-1, 1075 cm-1, 1096 cm-1, 1116 cm-1, and 1145 cm-1 were correlated with changes in crystallinity in one or more of the reflection planes. It is suggested that a combination of second-derivative and curve-fitting analysis of the v1, v3 phosphate contour allows the most reproducible evaluation of these spectra.

Chitosan Film Acylation and Effects on Biodegradability

Abstract: Chitosan films were acylated under heterogeneous conditions in methanol with acetic and hexanoic anhydrides and characterized by proton nuclear magnetic resonance, elemental analysis, and multiple internal reflective Fourier transform infrared spectroscopy. The disappearance of the NH2 vibrational band at 1590 cm-1, the appearance of the amide II band at 1555 cm-1, and the relatively low intensity of the ester band at 1735 cm-1 showed that acylation at the surface was site-selective for the amino (N) functionalities. Furthermore, N-acylation at the surface region appeared complete within 1 h. The acylated chitosan films were fractionated in aqueous acetic acid for compositional analysis. Acetylation of chitosan films for 3 h gave 52% of aqueous acetic acid insoluble chitin (outer film region) and 48% unreacted chitosan. In contrast, 3 h hexanoylation reactions resulted in 99% aqueous acetic acid soluble product. Thus, film N-acetylation was more rapid than N-hexanoylation. Moreove...

X-ray photoelectron spectroscopy studies of lithium surfaces prepared in several important electrolyte solutions. A comparison with previous studies by Fourier transform infrared spectroscopy

Abstract: Li electrodes prepared in situ in solutions and then stored in them for different periods were studied by X-ray photoelectron spectroscopy (XPS) including depth profiling performed by argon sputtering followed by XPS. A set of solvents, propylene carbonate (PC), ethylene carbonate (EC)−dimethyl carbonate (DMC) mixtures, and 1,3-dioxolane, and a set of salts, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiC(SO2CF3)3, were investigated with respect to the effect of storage time. The results of this study were compared with previous studies of Li electrodes in the same solutions by in situ and ex situ Fourier transform infrared spectroscopy. Basically, the results thus obtained are in line with the previous studies. The Li surface chemistry is dominated by solvent reactions. However, all the above salt anions are also reduced to form insoluble species which also contribute to the build-up of the surface films (e.g., the salt anions of the type MFy- (M = As, P, B) are reduced to LiF and species of the LixMFz type)...

Structural and Spectroelectrochemical Investigations of Sol-Gel Derived Electrochromic Spinel Co[sub 3]O[sub 4] Films

Abstract: Thin films of the cubic spinel Co{sub 3}O{sub 4} were prepared by the sol-gel route from a Co(II) sulfate precursor using a dip-coating technique. The films (50 to 60 nm thick) were deposited on indium-tin oxide glass substrates with a single dipping. The electrochromic properties of the films were studied in an aqueous alkaline electrolyte (0.1 M LiOH) using cyclic voltammetry (CV) and in situ UV-vis spectroelectrochemistry. The intermediate oxide products that appeared during cycling at current peak potentials were analyzed by x-ray diffraction (XRD) and ex situ Fourier transform infrared (FTIR) reflection-absorption spectroscopy performed at near-grazing incidence angle conditions (NGIA). High hydration of the spinel structure enables complex redox processes to take place inside the structure or on the surface of the film when potential cycling is performed. Vibrational bands characteristic of the formation of CoO, Co(OH){sub 2}, and hydrated Co{sub 3}O{sub 4} phases have been assigned and discussed according to the results obtained from ex situ NGIA FTIR, CV, and XRD studies. The change in transmittance ({lambda} = 634 nm) between bleached and colored states for single-dipped films was 25%, and for electrochromic efficiency ({eta}) was approximately 25 cm{sup 2}/C.

Formation of Cyclic Anhydride Intermediates and Esterification of Cotton Cellulose by Multifunctional Carboxylic Acids: An Infrared Spectroscopy Study:

Abstract: Multifunctional polycarboxylic acids have been used as nonformaldehyde cross linking agents for cotton fabrics to replace the traditional N-methylol reagents. Ester ification of cotton cellulose by seventeen aliphatic and aromatic polycarboxylic acids is studied using Fourier transform infrared spectroscopy. Five-membered cyclic an hydride intermediates formed under the curing conditions are identified on cotton fabrics treated with these acids. Only those polycarboxylic acids that form cyclic an hydride intermediates esterify cotton cellulose. Formation of the cyclic anhydride intermediates and esterification of cotton cellulose take place in the same curing tem perature regions. The infrared spectroscopy data also indicate that the second carboxyl group in a bifunctional carboxylic acid is not able to esterify cotton cellulose effectively. Therefore, we can conclude that a polycarboxylic acid esterifies cotton cellulose through the formation of a cyclic anhydride intermediate. The infrared spectroscopy ...

Controlled Orientation of Cyclodextrin Derivatives Immobilized on Gold Surfaces

Abstract: Several different cyclodextrinthiol derivatives have been immobilized on gold surfaces through a chemisorption process to form films which exhibit significantly different features. Three monothiolated cyclodextrin derivatives with different spacers between the cyclodextrin cavity and the thiol group and a mixture of multithiolated cyclodextrins were synthesized and characterized. Chemisorption of these compounds onto gold surfaces gave films which were investigated by Fourier transform infrared (FTIR) spectroscopy, time-of-flight mass spectrometry, contact angle measurements, plasmon surface polariton (PSP) spectroscopy, and cyclic voltammetry. It was found that the chemical structure of each cyclodextrin derivative had a strong influence on the molecular architecture in the resulting films, and in particular on the orientation of the cyclodextrin torus. Models were developed to describe the molecular arrangement in the films.

Glu46 Donates a Proton to the 4-Hydroxycinnamate Anion Chromophore During the Photocycle of Photoactive Yellow Protein †

Abstract: Photoactive yellow protein (PYP) is a photoreceptor containing a unique 4-hydroxycinnamic acid (pCA) chromophore. The trans to cis photoisomerization of this chromophore activates a photocycle involving first a short-lived red-shifted intermediate (pR), then a long-lived blue-shifted intermediate (pB), and finally recovery of the original receptor state (pG). The pCA chromophore is deprotonated in pG and protonated in pB, but the proton donor for this process has not yet been identified. Here we report the first FTIR spectroscopic data on pG, pR, and pB. The IR difference signals in the carbonyl stretching region of COOH groups (1700−1800 cm-1) reveal that a buried carboxylic group close to the chromophore (i) is protonated in pG, (ii) develops a stronger hydrogen bonding in pR, and (iii) becomes deprotonated in pB. These signals are unambiguously assigned to Glu46, on the basis of the IR data and the 1.4 A X-ray structure of PYP [Borgstahl et al. (1995) Biochemistry 34, 6278−6287]. Our data demonstrate t...

Effects of physicochemical factors on the secondary structure of β-lactoglobulin

Abstract: Fourier transform infrared spectroscopy and differential scanning calorimetry were used as complementary techniques to study changes in the secondary structure of beta-lactoglobulin under various physicochemical conditions. The effects of pH (3-9), NaCl (0-2 M), and lactose, glucose and sucrose (100-500 g/l) in the temperature range 25-100 degrees C on the conformation sensitive amide I band in the i.r. spectrum of beta-lactoglobulin in D2O solution were examined. The 1692 cm-1 band in the amide I band profile had not been definitively assigned in previous studies of the i.r. spectrum of beta-lactoglobulin. The decrease in this band at ambient temperature with time or upon mild heating was attributed to slow H-D exchange, indicating that it was due to a structure buried deep within the protein. The disappearance of the 1692 cm-1 band on heating was accompanied by the appearance of two bands at 1684 and 1629 cm-1, assigned to beta-sheets. The 1692 cm-1 band was therefore attributed to a beta-type structure. beta-Lactoglobulin showed maximum thermal stability at pH 3 and was easily denatured at pH 9. On denaturation, the protein unfolded into more extensive random coil structures at pH 9 than at pH 3. After 10 h at pH 9 (25 degrees C), beta-lactoglobulin was partly denatured. Heating to 60-80 degrees C generally resulted in the loss of secondary structure. At all pH values studied, two new bands at 1618 and 1684 cm-1, characteristic of intermolecular beta-sheet structure and associated with aggregation, were observed after the initial denaturation. Differential scanning calorimetry studies indicated that the thermal stability of beta-lactoglobulin was enhanced in the presence of sugars. The Fourier transform i.r. results obtained provide evidence that sugars promoted the unfolding of beta-lactoglobulin via multiple transition pathways leading to a transition state resisting aggregation.

In Situ FT-IR/ATR Spectroelectrochemistry of Prussian Blue in the Solid State

Abstract: Interfacial oxidation and reduction of Prussian Blue (PB), KFeIII[FeII(CN)6]·nH2O (n ≈ 10), powder were probed in situ with Fourier transform infrared attenuated total reflection (FT-IR/ATR) spectroscopy. The combination of electrochemistry in the absence of liquid electrolyte with internal reflectance FT-IR spectroscopy was accomplished using a simple two-electrode sandwich-type cell in which a crystalline germanium served both as a working electrode and an infrared transparent element. Application of sufficiently large potential differences to sandwich electrodes led to oxidation and reduction of PB at opposing interfaces. The spectra, which were monitored by difference, clearly show changes in the cyanide stretching frequency range upon oxidation and reduction.

Fourier transform measurement of NO2 absorption cross-section in the visible range at room temperature

Abstract: New laboratory measurements of NO2 absorption cross-section were performed using a Fourier transform spectrometer at 2 and 16 cm-1 (0.03 and 0.26 nm at 400 nm) in the visible range (380–830 nm) and at room temperature. The use of a Fourier transform spectrometer leads to a very accurate wavenumber scale (0.005 cm-1, 8×10-5 nm at 400 nm). The uncertainty on the new measurements is better than 4%. Absolute and differential cross-sections are compared with published data, giving an agreement ranging from 2 to 5% for the absolute values. The discrepancies in the differential cross-sections can however reach 18%. The influence of the cross-sections on the ground-based measurement of the stratospheric NO2 total amount is also investigated.

The anhydride content of some commercial PP-g-MA: FTIR and titration

Abstract: A set of anhydride-grafted polypropylenes was collected from various companies. They were studied in light of our recent results on polypropylene melt grafted with maleic anhydride.(1) This work confirmed that an important decrease of the anhydride content is recorded on heating or washing, due to the elimination of free, ungrafted products, respectively, by sublimation of maleic anhydride and by polymaleic anhydride solubilization. The deconvolution of the infrared spectra of washed anhydride-grafted polypropylenes (PP-g-MA) revealed two types of grafted anhydride: succinic anhydride form and polymaleic anhydride form. All in all, four forms of anhydride functions were detected: two grafted and two free, each being either on monomeric or polymeric forms. Nevertheless, one PP-g-MA (Hercoprime) can be distinguished by its very high grafting level. This polymer is therefore discussed in more detail. Finally, all the present results are discussed with regard to the principal applications of the PP-g-MA as a blend compatiblizer or as an adhesion promoter. (C) 1996 John Wiley & Sons, Inc.

Infrared Amide I‘ Band of the Coiled Coil†

Abstract: The Fourier transform infrared (FTIR) spectra of several coiled-coil proteins have been shown to possess unusual features in the amide I‘ region. Band maxima occur in the vicinity of 1630 cm-1, with component bands at higher frequency. This is well below the observed band at 1650 cm-1 found in standard α-helical polypeptides such as poly-l-alanine. Normal mode calculations on models of the coiled-coil structure have been performed to investigate this issue. We find that the observed band profile can be reproduced with very small random variations on the φ,ψ of tropomyosin. We believe that the shift to lower frequency is due to additional hydrogen bonding of the solvent accessible backbone CO groups to water.

Characterization of transfer layers forming on surfaces sliding against diamond-like carbon☆

Abstract: Metallic and ceramic surfaces may become covered with a carbon-rich transfer layer during sliding against diamond-like carbon (DLC) films. The presence of such layers at sliding interfaces may dominate the long-term friction and wear performance of these films. In this study, we use Raman and infrared spectroscopies to characterize the chemical structure of such transfer layers forming on the surface of magnesia/partially-stabilized ZrO2 (MgOPSZ) balls. The DLC film (≈ 2 μm thick) was prepared by ion-beam deposition at room temperature, with methane used as the source gas. Tribological tests were performed on a ball-on-disk machine in open air at room temperature (≈22 ± 1°C) and humidity of 30–50%. Sliding velocity ranged from 1 to 6 m s−1 and the tests were continued until the DLC films were effectively worn through. The results showed that the friction coefficients of DLC against MgOPSZ were initially 0.08–0.12 but decreased to 0.05–0.06 after about 200 000–500 000 sliding passes, depending on velocity. They remained constant at 0.05 for the duration of the tests, which was 1.5 million cycles at 6 m s−1 but > 4 million cycles at 1 m s−1. The low friction coefficients observed in each test coincided with the formation of a carbon-rich transfer layer on the rubbing surfaces of MgOPSZ balls. Micro-laser-Raman and Fourier transformed infrared (FTIR) spectroscopies confirmed that these carbon-rich transfer layers had a disordered graphitic structure.

High-Fidelity Fourier Transform Infrared Spectroscopic Imaging of Primate Brain Tissue

Abstract: We demonstrate a new mid-infrared and near-infrared imaging approach which is ideally suited to microscopic applications. The method employs an indium antimonide (InSb) focal-plane array detector and a commercially available step-scan Fourier transform infrared spectrometer (FTIR). With either a KBr or a CaF2 beamsplitter, images from 1 to 5.5 μm (10,000–1818 cm-1) can be rapidly acquired with the use of all the available pixels on the detector. The spectral resolution for each image is easily varied by changing the number of acquired images during the interferometer scan. We apply this technique to noninvasively generate image contrast in sections of monkey brain tissue and to relate these data to specific lipid and protein fractions. In addition, we describe several computational methods to highlight the spatial distributions of components within a sample.

SiCN alloys deposited by electron cyclotron resonance plasma chemical vapor deposition

Abstract: Silicon–carbon–nitrogen alloys have been deposited by electron cyclotron resonance plasma chemical vapor deposition. Nitrogen, methane, and argon diluted silane have been used as precursor gases. The properties of the deposited films were studied by spectroscopic ellipsometry, Fourier transform infrared spectroscopy, X‐ray photoelectron, and Auger electron spectroscopy. The structure and bond formation in the SiCN films is discussed in terms of the present results.

Study of surface reactions during plasma enhanced chemical vapor deposition of SiO2 from SiH4, O2, and Ar plasma

Abstract: In situ attenuated total reflection Fourier transform infrared spectroscopy was employed in proposing possible surface reaction mechanisms during plasma enhanced chemical vapor deposition of SiO2 from a mixture of SiH4, O2, and Ar in a helical resonator plasma reactor. Infrared spectra taken during the oxide deposition revealed that the oxide surface is covered with OH when the deposition is conducted with a low SiH4 to O2 ratio (≪1). Both associated hydroxyls (SiOHassoc) and isolated hydroxyls (SiOHisol) were detected on the surface during growth. Two kinds of OH attached to Si exist on the surface: weakly bound OH that thermally desorb at 250 °C and strongly bound OH that desorb under ion bombardment. The thermal removal of weakly bound OH does not lead to SiO2 formation, but the ion‐assisted removal of strongly bound OH by Ar+ ion bombardment results in oxide growth via the reaction 2SiOH(s)+Ar+→Si–O–Si(s)+H2O(g)+Ar+. Experiments undertaken to delineate the possible heterogeneous reaction paths between...

Characterization and catalytic activity of titanium containing SSZ-33 and aluminum-free zeolite beta

Abstract: The post-synthetic incorporation of titanium in the borosilicate SSZ-33 and the direct synthesis of an aluminum-free titanium-containing zeolite Beta (Ti-Beta) are reported. These materials are characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), FT-Raman, and diffuse reflectance ultraviolet (DR-UV) spectroscopies. The molecular sieves are shown to catalyze the epoxidation of various olefins using aqueous hydrogen peroxide as the oxidant. The physicochemical properties as found by the characterization methods are correlated to the catalytic data and the results compared to a high quality sample of TS-1. The modified SSZ-33 samples contain titanium primarily in the form of isolated tetrahedrally coordinated Ti atoms, although some extra-framework Ti is observed by Raman and DR-UV spectroscopies. Ti-Beta samples show no evidence of extra-framework titanium. For the epoxidation of cis -cyclooctene, the Ti-Beta catalysts give quantitative conversion to epoxide, and both the Ti-Beta and Ti-SSZ-33 catalysts are able to epoxidize substrates too large to be oxidized by TS-1.