Showing papers on "Fourier transform infrared spectroscopy published in 1992"

Fourier Transform Infrared Spectroscopy

Abstract: Typically, lignins are characterized by IR spectroscopy in the solid state. The examination of lignins in solution has long been a domain of UV and NMR spectroscopy. However, with the advent of the FTIR technique, the IR spectra of liquid samples now can be readily obtained. The need to measure IR spectra in solution exists when there is not enough time to isolate lignin from solution as, for example, is the case when spent pulping liquors have to be analyzed rapidly during a pulping process for process control. This section describes briefly the common liquid sampling accessories and applications of solution state FTIR spectroscopy to lignins. For more details on FTIR spectroscopy, the reader is referred to Chapter 4.1.

Characterization of Humic Acids, Composts, and Peat by Diffuse Reflectance Fourier-Transform Infrared Spectroscopy

Abstract: Transmission infrared (IR) spectroscopy, either dispersive or Fourier transformed (FTIR), has been used extensively in studies on humic substances. A variety of bands characteristic of molecular structures and functional groups have been identified for these substances. The development of an attachment mounted onto FTIR spectrophotometers has allowed the determination of diffuse reflectance Fourier-transformed infrared (DRIFT) spectra. The purpose of this work was to study the applicability of DRIFT to soil organic-matter research and to compare the use of this instrumentation to dispersive and Fourier-transformed transmission IR spectroscopy. The DRIFT spectra were determined for humic acids, peat samples, and composts. In addition, the possibility of using DRIFT spectra to quantitatively measure sample concentration and measuring the relative concentration of functional groups was assessed. Sample preparation for DRIFT is much simpler than for transmission IR spectroscopy, interferences due to water adsorption are reduced, and resolution is improved. The spectra obtained using DRIFT had a higher degree of resolution as compared with dispersive and Fourier-transform transmission IR spectroscopy. Bands indicative of aliphatic C-H, carboxyl and corboxylate functional groups, aromatic C=C, and C-O stretch of polysaccharides were prominent and very well resolved. The DRIFT spectra obtained can also he used to fingerprint organic matter acquired from various sources. Spectra obtained at various concentrations of humic acid indicated that DRIFT cannot be used to estimate concentrations of organic matter in a given mixture. Relative concentrations of functional groups, however, were found to be fairly constant regardless of sample concentration. Therefore, changes in the relative concentration of functional groups can he measured during the humification process. It is expected that the application of DRIFT to organic-matter research will prove especially useful for characterizing bulky heterogeneous samples such as peat and composts.

Infrared spectroscopy of DNA.

Abstract: Publisher Summary This chapter presents a general survey of the Fourier-transform infrared (FTIR) spectrum of a nucleic acid, describes the characterization of the different classic families of DNA conformations, and then discusses the way FTIR spectroscopy can be used in the study of DNA recognition, particularly in the case of triple-stranded structures and DNA–drug interactions. Compared to other techniques some of the advantages of infrared spectroscopy in the study of nucleic acids are (1) the possibility of obtaining data from samples under an extremely wide variety of physical states, (2) no limitation introduced by the size of the investigated molecule—that is, it can work well with short oligonucleotides as well as long polynucleotides, DNA fragments obtained by enzymatic or chemical cleavage, or high molecular weight native DNAs, (3) infrared spectroscopy is a nondestructive technique, which requires only small amounts of samples, and (4) it gives vibrational information characteristic of the helical conformations of the nucleic acids.

Luminescence and structural study of porous silicon films

Abstract: The luminescence properties of 3 μm thick, strongly emitting, and highly porous silicon films were studied using a combination of photoluminescence, transmission electron microscopy, and Fourier transform infrared spectroscopy. Transmission electron micrographs indicate that these samples have structures of predominantly 6–7 nm size clusters (instead of the postulated columns). In the as‐prepared films, there is a significant concentration of Si—H bonds which is gradually replaced by Si—O bonds during prolonged aging in air. Upon optical excitation these films exhibit strong visible emission peaking at ≊690 nm. The excitation edge is shown to be emission wavelength dependent, revealing the inhomogeneous nature of both the initially photoexcited and luminescing species. The photoluminescence decay profiles observed are highly nonexponential and decrease with increasing emission energy. The 1/e times observed typically range from 1 to 50 μs. The correlation of the spectral and structural information suggest...

Fourier transform Raman and infrared vibrational study of human skin: Assignment of spectral bands

Abstract: Fourier transform (FT) Raman and infrared spectra of the outermost layer of human skin, the stratum corneum, were recorded. Assignments consistent with the FT Raman vibrations were made for the first time and compared with assignments from the FTIR spectrum. The results demonstrate that FT Raman spectroscopy holds several advantages over FTIR in studies of human skin. The molecular and conformational nature of human skin, and modifications induced by drug or chemical treatments, may be assessed by FT Raman spectroscopy.

Fourier transform infrared microspectroscopy is a new way to look at plant cell walls.

Abstract: Highly reproducible Fourier transform infrared (FTIR) spectra from both single onion (Allium cepa) cell walls and their constituent polymers were obtained under a variety of sampling conditions. The specificity of the chemical extraction sequence used in the preparation of the material was confirmed: pectins only are extracted by cyclohexanediaminetetraacetic acid and sodium carbonate, whereas xyloglucans are extracted by increasing concentrations of potassium hydroxide. There was very little contamination of the first potassium hydroxide extract with residual pectin. The low abundance of both phenolics and protein was also confirmed. The first sodium carbonate extraction almost completely removes esters remaining in the cell wall. We have demonstrated that FTIR spectroscopy can detect large conformational changes in pectic polymers on removal from the cell wall and on drying. FTIR spectroscopy provides a powerful and rapid assay for wall components and putative cross-links by identifying polymers and functional groups nondestructively in muro. The availability of micro-sampling and data acquisition techniques that permit subtraction of the blanket absorption of water make FTIR spectroscopy particularly suitable for studies of cell wall architecture. The use of polarizers with the microscope accessory permits determination of the orientation of particular functional groups with respect to the direction of cell elongation in carrot suspension cells.

Amide and Ester Surface Attachment Reactions for Alkanethiol Monolayers at Gold Surfaces As Studied by Polarization Modulation Fourier Transform Infrared Spectroscopy

Abstract: The modification of alkanethiol monolayers via amide and ester formation reactions is demonstrated as a methodology for attaching monolayer and submonolayer coveragea of specific chemical species onto metal electrodes. A monolayer of 11-mercaptoundecanolc acid (HSC 10 H 20 COOH) is used as a surface bifunctional linking agent on polycrystalllne gold surfaces. The reaction of these adsorbed molecules with gaseous thionyl chloride converts the carboxylic acid group to an acid chloride which can then be reacted further with an amine or alcohol to form an amide or ester linkage

Characterization of diamondlike carbon by infrared spectroscopy

Abstract: Comparison of Fourier transform infrared (FTIR) absorption spectroscopy, high resolution 13C nuclear magnetic resonance spectroscopy, and hydrogen evaluation by forward recoil elastic scattering (FRES) measurements shows that FTIR cannot be used to determine the carbon hybridization or total hydrogen content of diamondlike carbon films (DLC). FTIR absorption reflects only the optically active hydrogen in the DLC and, using it together with FRES, it can provide an estimate of the unbound hydrogen contained in the films. The fraction of unbound hydrogen can reach values of up to ∼50%.

Secondary structure and orientation of the surfactant protein SP-B in a lipid environment. A Fourier transform infrared spectroscopy study.

Abstract: Attenuated total reflection Fourier transform infrared spectroscopy was used to investigate the secondary structure of the surfactant protein SP-B. Nearly half of the polypeptide chain is folded in an alpha-helical conformation. No significant change of the secondary structure content was observed when the protein is associated to a lipid bilayer of dipalmitoylphosphatidylcholine (DPPC)/phosphatidylglycerol (PG) or of dipalmitoylphosphatidylglycerol (DPPG). The parameters related to the gamma w(CH2) vibration of the saturated acyl chains reveal no modification of the conformation or orientation of the lipids in the presence of SP-B. A model of orientation of the protein at the lipid/water interface is proposed. In this model, electrostatic interactions between charged residues of SP-B and polar headgroups of PG, and the presence of small hydrophobic alpha-helical peptide stretches slightly inside the bilayers, would maintain SP-B at the membrane surface.

A Fourier Transform Infrared Spectroscopy Study of the Passive Film Produced during Aqueous Acidic Phenol Electro‐oxidation

Abstract: In this work Fourier transform infrared spectroscopy was used to analyze samples of the passivating film produced on the anode during phenol electrolysis. Work by other researchers with p-terbutyl-phenol was extended to the acidic region where than main product was found to be a 1,2,4 substituted ether-linked polymer. The films produced by the oxidation of p-cresol, o,o'-biphenol, and phenol were also studied

Characterization of model polar stratospheric cloud films using Fourier transform infrared spectroscopy and temperature programmed desorption

Abstract: This study combines Fourier transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD) measurements of nitric-acid/ice films representative of type I polar stratospheric clouds (PSCs). Using this combination of techniques, we are able to correlate the FTIR spectra with measurements of the film stoichiometry. The results confirm the assignments for amorphous nitric-acid/ice films and for crystalline nitric acid trihydrate (NAT), dihydrate, and monohydrate proposed by Ritzhaupt and Devlin (1991). In addition to these films, we observe a new high temperature nitric-acid/ice film which we attribute to a more stable structure of NAT with fewer defects. When low temperature crystalline NAT is heated, such as during TPD or slow annealing, the IR absorption spectrum irreversibly changes around −88° to −75°C. Future IR absorption measurements of PSCs in the atmosphere should be compared with IR spectra of both amorphous and crystalline nitric acid/ice, including both forms of NAT.

FTIR separation of nylon‐6 chain conformations: Clarification of the mesomorphous and γ‐crystalline phases

Abstract: Specific infrared absorptions for each form of Nylon-6 have been indentified. Quenched films were prepared by melt casting and converted in turn to the α-crystalline and γ-crystalline structures. The films were examined using Fourier transform infrared spectroscopy (FTIR) with the attenuated total reflection configuration and by X-ray diffractometry. The FTIR spectrum of the pure mesomorphous component of the quenched film was calculated by subtracting away the contribution of α-crystalline peaks present due to incomplete quenching. A curve-fitting procedure was applied to the pure mesomorphous and gamma crystalline spectra. Several peaks in the mesomorphous spectrum are observed to develop a shoulder upon conversion to the γ-crystalline form. This is due to the extra gauche character imparted to the CN bond between the methylene unit and the amide group. These and other band assignments were confirmed by analysis of model compounds.

A Fourier transform infrared study of water—head group interactions in reversed micelles containing sodium bis(2-ethylhexyl) sulfosuccinate (AOT)

Abstract: Fourier transform infrared spectroscopy has been employed to study the state of water and water—head group interactions in AOT aggregates or microemulsions in n-heptane. Isotopic dilution of water (4% D2O and in H2O) has been used to monitor the uncoupled ν(OD) band of HOD as a function of W0 (the number of water molecules per head group). It is found that the feature always consists of a single-band profile and there is no evidence of coexisting multiple water species in these systems (on the vibrational time scale). By detailed examination of ν(SO) and ν(CO) bands of the head group it is found that up to W0 = 6 (severely perturbed) water molecules are bound closely to the sulfonate and Na+ ions at the water/organic interface. Beyond this point all the water molecules seem to have a similar vibrational relaxation rate but there are still gradual structural and electronic changes as the water molecules move farther away from the first hydration shell. At values of W0 higher than 12 there is some evidence that the water molecules are similar to those in the bulk, but up to 20 water molecules per head group are probably needed to form well-defined reversed micelles in these systems.

Fourier transform infrared spectroscopy of molecular interactions of heptafluoro-1-butanol or 1-butanol in supercritical carbon dioxide and supercritical ethane

Abstract: Fourier transform infrared (FT-IR) spectroscopy was used to measure the degree of intermolecular hydrogen bonding for 2,2,3,3,4,4,4-heptafluoro-1-butanol-d and 1-butanol-d in supercritical carbon dioxide and supercritical ethane solvents. Supercritical binary solutions containing up to 0.10 mol fraction alcohol were examined under conditions ranging from 200 to 400 bar at 40{degree}C. In these fluids, an equilibrium appears to be established between the free non-hydrogen-bonded monomer and various hydrogen-bonded species. Aggregation numbers of these alcohols in carbon dioxide were in the range of 3.4-4.4 molecules per aggregate. The aggregate size in CO{sub 2} was, within experimental error, the same as found for supercritical ethane. Solute-solvent interactions were described using a semiempirical dielectric continuum model (Kirkwood-Bauer-Magat). The spectral evolution of a particular vibrational mode provided molecular level detail on the transition from a gas- to liquidlike solvation environment as the density of the supercritical fluid solvent was increased. The high solubility of the fluorinated alcohol in low dielectric constant fluids such as CO{sub 2} is primarily attributed to the weaker hydrogen-bonding energies of the fluorinated alcohol relative to those of the protonated alcohols. The contribution of fluorine repulsion to decreases in the attractive solute-solute interactions (i.e., steric hindrance) also acts to increase solubility inmore » low dielectric constant supercritical fluids. 45 refs., 13 figs., 2 tabs.« less

Rapid and direct lodine value and saponification number determination of fats and oils by attenuated total reflectance/fourier transform infrared spectroscopy

Abstract: A simple, rapid and reproducible method of determining the iodine value (IV) and saponification number (SN) for fats and oils was developed with an attenuated total reflectance/Fourier transform infrared spectrometer and commercially available triglycerides as calibration standards. Partial least squares was used to determine the spectral regions correlating with the known chemical IV and SN values, and the calibration set was augmented with additional standards generated by spectral co-adding techniques. The calibration model obtained was used to analyze commercially available fats and oils with a wide range of IV and SN values, and the results were compared to the values obtained by American Oil Chemists’ Society methods. With the spectrometer calibrated and programmed, IV and SN results could be obtained within 2–3 min per sample, a major improvement over conventional wet chemical methods.

Methylmercury determination as volatile methylmercury hydride by purge and trap gas chromatography in line with Fourier transform infrared spectroscopy

Abstract: We report a novel aqueous derivatization of methylmercury chloride by NaBH 4 to mehtymercury hydride (CH 3 HgH), a volatile and unexpectedly stable species which we determined has a half-life of approximately 2 h. The analytical apparatus consisted of a purge and trap (PT) unit linked to a gas chromatograph (GC), in line with a Fourier transform infrared spectrometer (FTIR). The sample was purged with nitrogen, and volatile compounds were concentrated in a cold trap

Water structural changes in the bacteriorhodopsin photocycle: analysis by Fourier transform infrared spectroscopy.

Abstract: The Fourier transform infrared difference spectra between light-adapted bacteriorhodopsin (BR) and its photointermediates, L and M, were analyzed for the 3750-3450-cm-1 region. The O-H stretching vibrational bands were identified from spectra upon substitution with 2H2O. Among them, the 3642-cm-1 band of BR was assigned to water by substitution with H2(18)O. By a comparison with the published infrared spectra of the water in model systems [Mohr, S.C., Wilk, W.D., & Barrow, G.M. (1965) J. Am. Chem. Soc. 87, 3048-3052], it is shown that the O-H bonds of the water in BR interact very weakly. Upon formation of L, the interaction becomes stronger. The O-H bonds of the protein side chain undergo similar changes. On the other hand, M formation further weakens the interaction of the same water molecules in BR. The appearance of a sharp band at 3486 cm-1, which was assigned tentatively to the N-H stretching vibration of the peptide bond, is unique to L. The results suggest that the water molecules are involved in the perturbation of Asp-96 in the L intermediate and that they are exerted from the protonated Schiff base which changes position upon the light-induced reaction.

Conformation of magainin-2 and related peptides in aqueous solution and membrane environments probed by Fourier transform infrared spectroscopy.

Abstract: The conformational properties of the magainin family of antimicrobial peptides in aqueous solution and in model membranes have been probed by Fourier transform infrared spectroscopy. The magainins were found to be structureless in aqueous solution at neutral pD, confirming other studies by Raman and circular dichroism spectroscopy. Increasing the pD to 10 induced the formation of predominantly alpha-helical secondary structures, with some beta-sheet. In the presence of negatively charged liposomes (dimyristoylphosphatidylglycerol), the peptides folded into alpha-helical secondary structures with some beta-sheet structure evident. On the other hand, in the presence of zwitterionic phospholipids (dimyristoylphosphatidylcholine), the spectra were identical to those in aqueous solution. For some magainins, the interaction with charged liposomes was modulated by the presence of cholesterol; cholesterol was found to promote the formation of beta-sheet structures, as evidenced by the appearance of amide I bands at 1614 and 1637 cm-1. Differences in structure were observed between the amidated and nonamidated forms of some peptides. From the data, a mechanism of antimicrobial action of the magainin family of peptides is proposed.

Specific Interactions and Ionic Aggregation in Miscible Blends of Nylon-6 and Zinc Sulfonated Polystyrene Ionomer

Abstract: Blends of a lightly sulfonated polystyrene (10.1 mol % sulfonation) neutralized with zinc (ZnSPS) and nylon-6 (N6) were found to be miscible over the entire compositional range. Miscibility was a coneequence of transition metal complexation between the metal sulfonate and the amide groups. Melting point depression data gave a value for the polymer-polymer interaction parameter of x = -1.3, which indicates very strong intermolecular interactions. FTIR and SAXS analyses indicated that the polyamide effectively solvated the ionic associations in the blends. (ZnSPS). Differential scanning calorimetry (DSC) was used to determine miscibility and x. Fourier transform infrared spectroscopy (FTIR) was used to characterize the local environment of the Zn sulfonate groups as a function of the blend composition. This yielded infor- mation about the specific interactions between ZnSPS and N6 as well as about the ionic associations within ZnSPS. Small-angle X-ray scattering (SAXS) was em- ployed to investigate the microstructural changes in the blends, specifically the effect on the cluster morphology. Experimental Section

Redox-induced conformational changes in myoglobin and hemoglobin: electrochemistry and ultraviolet-visible and Fourier transform infrared difference spectroscopy at surface-modified gold electrodes in an ultra-thin-layer spectroelectrochemical cell.

Abstract: Using suitable surface-modified electrodes, we have developed an electrochemical system which allows a reversible heterogeneous electron transfer at high (approximately 5 mM) protein concentrations between the electrode and myoglobin or hemoglobin in an optically transparent thin-layer electrochemical (OTTLE) cell. With this cell, which is transparent from 190 to 10,000 nm, we have been able to obtain electrochemically-induced Fourier-transform infrared (FTIR) difference spectra of both proteins. Clean protein difference spectra between the redox states were obtained because of the absence of redox mediators in the protein solution. The reduced-minus-oxidized difference spectra are characteristic for each protein and arise from redox-sensitive heme modes as well as from polypeptide backbone and amino acid side chain conformational changes concomitant with the redox transition. The amplitudes of the difference bands, however, are small as compared to the total amide I absorbance, and correspond to approximately 1% (4%) of the reduced-minus-oxidized difference absorbance in the Soret region of myoglobin (hemoglobin) and to less than 0.1% of the total amide I absorbance. Some of the bands in the 1560-1490-cm-1 spectral regions could be assigned to side-chain vibrational modes of aromatic amino acids. In the conformationally sensitive spectral region between 1680 and 1630 cm-1, bands could be attributed to peptide C = O modes because of their small (2-5 cm-1) shift in 2H2O. A similar assignment could be achieved for amide II modes because of their strong shift in 2H2O.(ABSTRACT TRUNCATED AT 250 WORDS)

Diethylsilane Decomposition on Silicon Surfaces Studied Using Transmission FTIR Spectroscopy

Abstract: Fourier transform infrared (FTIR) transmission spectroscopy was used to monitor the decomposition of diethylsilane (DES) on high surface area porous silicon samples. The FTIR spectra revealed that DES dissociatively adsorbs on porous silicon to form and species. The infrared absorbances of the stretching vibrations at 2955‐2879 cm−1 and the stretching vibration at 2088 cm−1 were employed to monitor the decomposition of the surface species. As the silicon surface was annealed to 500–750 K, the species decomposed to produce gas phase ethylene and additional surface species. These reaction products were consistent with a β‐hydride elimination reaction. Above 700 K, the surface species decreased concurrently with the desorption of from the porous silicon surface. The uptake of surface species was also monitored at various adsorption temperatures to determine the optimal DES exposure temperatures for silicon deposition. Carbon contamination was minimal at DES adsorption temperatures below 640 K prior to desorption. Because the DES adsorption process is self‐limiting at temperatures below 640 K, DES may be a useful molecular precursor for the atomic layer epitaxy of silicon.

Time‐resolved Fourier transform spectroscopy with 0.25 cm−1 spectral and <10−7 s time resolution in the visible region

Abstract: The development of a new time‐resolved Fourier transform spectrometer that is capable of 0.25 cm−1 spectral resolution and better than 10−7 s temporal resolution in the visible is reported. The time‐resolved capability of the spectrometer is achieved by coupling a step‐scan interferometer to a transient digitizer/laser system. The operation of the spectrometer is described in detail, and scattered light and laser‐induced fluorescence spectra from an I2 gas cell are presented to demonstrate the temporal and spectral resolution of the spectrometer.

Structures of aspartic acid-96 in the L and N intermediates of bacteriorhodopsin: analysis by Fourier transform infrared spectroscopy

Abstract: The light-induced difference Fourier transform infrared spectrum between the L or N intermediate minus light-adapted bacteriorhodopsin (BR) was measured in order to examine the protonated states and the changes in the interactions of carboxylic acids of Asp-96 and Asp-115 in these intermediates. Vibrational bands due to the protonated and unprotonated carboxylic acid were identified by isotope shift and band depletion upon substitution of Asp-96 or -115 by asparagine. While the signal due to the deprotonation of Asp-96 was clearly observed in the N intermediate, this residue remained protonated in L. Asp-115 was partially deprotonated in L. The C = O stretching vibration of protonated Asp-96 of L showed almost no shift upon 2H2O substitution, in contrast to the corresponding band of Asp-96 or Asp-115 of BR, which shifted by 9-12 cm-1 under the same conditions. In the model system of acetic acid in organic solvents, such an absence of the shift of the C = O stretching vibration of the protonated carboxylic acid upon 2H2O substitution was seen only when the O-H of acetic acid is hydrogen-bonded. The non-hydrogen-bonded monomer showed the 2H2O-dependent shift. Thus, the O-H bond of Asp-96 enters into hydrogen bonding upon conversion of BR to L. Its increased hydrogen bonding in L is consistent with the observed downshift of the O-H stretching vibration of the carboxylic acid of Asp-96.

Compositional and Microstructural Characterization of RuO2 ‐ TiO2 Catalysts Synthesized by the Sol‐Gel Method

Abstract: In this study mixtures were prepared from solution using and three different precursors for, , and and tris (2, 4‐pentanedionate) Ru(III). Multi‐layer coatings were deposited by spin coating onto fused silica slides with and without an intermediate, 200 nm thick, vacuum deposited Ti film. Samples heat treated at 200, 300, and 400°C were studied by several techniques (Rutherford backscattering spectrometry (RBS), elastic recoil detection, (ERD), nuclear reaction analysis (NRA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and x‐ray diffraction (XRD) to characterize morphological and compositional changes and to test the reproducibility of the preparation method. In all cases a single crystalline phase, the solid solution of the two component oxides, was detected by XRD. The films appeared to have a low density, and hydrogen and carbon were still found in the coatings after each heat treatment; their content was reduced only at 400°C for samples B and C. The surface of the films displayed increasing percentages of .