Aromatic Bands Research Articles

Warm dust and aromatic bands as quantitative probes of star-formation activity

We combine samples of spiral galaxies and starburst systems observed with ISOCAM on board ISO to investigate the reliability of mid-infrared dust emission as a quantitative tracer of star formation activity. The total sample covers very diverse galactic environments and probes a much wider dynamic range in star formation rate density than previous similar studies. We find that both the monochromatic 15 µm continuum and the 5−8.5 µm emission constitute excellent indicators of the star formation rate as quantified by the Lyman continuum luminosity LLyc, within specified validity limits which are different for the two tracers. Normalized to projected surface area, the 15 µm continuum luminosity Σ15 µm,ct is directly proportional to ΣLyc over several orders of magnitude. Two regimes are distinguished from the relative offsets in the observed relationship: the proportionality factor increases by a factor of ≈5 between quiescent disks in spiral galaxies, and moderate to extreme star- forming environments in circumnuclear regions of spirals and in starburst systems. The transition occurs near ΣLyc ∼ 10 2 Lpc −2 and is interpreted as due to very small dust grains starting to dominate the emission at 15 µm over aromatic species above this threshold. The 5−8.5 µm luminosity per unit projected area is also directly proportional to the Lyman continuum luminosity, with a single conversion factor from the most quiescent objects included in the sample up to ΣLyc ∼ 10 4 Lpc −2 ,w here the relationship then flattens. The turnover is attributed to depletion of aromatic band carriers in the harsher conditions prevailing in extreme starburst environments. The observed relationships provide empirical calibrations useful for estimating star formation rates from mid-infrared observations, much less affected by extinction than optical and near-infrared tracers in deeply embedded H  regions and obscured starbursts, as well as for theoretical predictions from evolutionary synthesis models.

Atmospheric aging of poly[methyl(phenyl)silanediyl] monitored by FTIR spectroscopy

AbstractPoly[methyl(phenyl)silanediyl] films were irradiated in ATLAS Weather‐O‐Meter Ci 3000+ for ca 3 h. Changes in the region of siloxane, carbonyl, hydroxyl, and C‐H (aromatic) bands were monitored by FTIR. Main attention was paid to changes in siloxane formation, which could be reduced in the presence of phenolic UV absorber 1 and oxalanilide 3.

Resonance Raman spectroscopy of highly fluorescing lignin containing chemical pulps: Suppression of fluorescence with an optical Kerr gate

Abstract Raman spectroscopy using 400 nm excitation was successfully applied to chemical pulp samples and the fluorescence background that usually limits the application of this method to such samples was effectively suppressed. This enabled the detection of much weaker Raman bands from the pulps. The rejection ratio of the fluorescence background to Raman scattering was estimated to be about 250. The resonance Raman spectra of peroxide bleached chemical pulps had chromophoric lignin bands at 1605 and 1655 cm−1, whereas the chlorine dioxide bleached pulps had only the aromatic band at 1605 cm−1. The square root of the aromatic chromophore band relative to cellulose band correlated linearly with the brightness which is in accordance with the Kubelka-Munk theory. This correlation indicated that the resonance enhanced Raman bands were mainly due to chromophoric lignin structures. Chlorine dioxide and peroxide bleached pulps gave different correlations to brightness, which was an indication of different kinds of chromophores in these pulps. The intensity of the aromatic band relative to the cellulose band was about 20 times higher with the ultraviolet (257 nm) than with the visible (400 nm) excitation. This clearly illustrated the importance of working with different excitation wavelengths. On one hand the UV excitation is more sensitive towards aromatic residual lignin in pulp, and on the other hand the visible excitation enables the selective detection of chromophoric lignin structures.

The Periplasmic Molecular Chaperone Protein SurA Binds a Peptide Motif That Is Characteristic of Integral Outer Membrane Proteins

The Escherichia coli SurA protein is a periplasmic molecular chaperone that facilitates correct folding of outer membrane porins. The peptide binding specificity of SurA has been characterized using phage display of heptameric peptides of random sequence. The consensus binding pattern of aromatic-polar-aromatic-nonpolar-proline amino acids emerges for both SurA and a SurA "core domain," which remains after deletion of a peripheral peptidyl-proline isomerase domain. Isothermal titration calorimetry with a high affinity heptameric peptide of sequence WEYIPNV yields peptide affinities in the range of 1-14 microm for both SurA and its core domain. Although the peptide consensus aromatic-polar-aromatic-nonpolar-proline occurs infrequently in E. coli proteins, the less restrictive tripeptide motif aromatic-random-aromatic appears with greater-than-random frequency in outer membrane proteins and is prevalent in the "aromatic bands" of the porin beta barrel structures. Thus, SurA recognizes a peptide motif that is characteristic of integral outer membrane proteins.

Mid-Infrared Spectroscopy of Infrared-Luminous Galaxies with Subarcsecond Resolution

Low spectral resolution (Δλ/λ ∼ 50) mid-infrared observations with high angular resolution (03–05) using the Long Wavelength Spectrometer on the Keck I Telescope are reported of the nuclei of five highly luminous infrared-bright galaxies. Spectra of eight distinct nuclei, ranging in luminosity from ∼1011 to more than 1012 L⊙ have been obtained. Four of the nuclei show the characteristic polycyclic aromatic hydrocarbon (PAH) emission features, i.e., 11.3 μm emission, as well as the 8.6 μm shoulder of the 7.7 μm band. The other nuclei show either weak PAH emission bands or no evidence for these bands. The high spatial resolution of the observations reveals extended emission in the 11.3 μm PAH band associated with several of the compact nuclear sources. When proper account is taken of the diffuse PAH emission, most of the compact sources show little or no directly associated PAH emission. The diffuse PAH emission is extended over spatial scales of 100–500 pc; its presence shows that there is significant circumnuclear UV–optical emission exciting the aromatic bands, most likely associated with circumnuclear starbursts. After the spectra of the nuclear sources are corrected for the spectrum of the diffuse PAH emission, the peak apparent silicate optical depth at 9.7 μm can be as large as 15, corresponding to more than 150 mag of visible light extinction. Because of the large silicate optical depths, mid-infrared spectra are not probing the nature of the true nuclei in the most opaque compact sources.

Subarcsecond Mid‐Infrared Imaging of Two Post–Asymptotic Giant Branch 21 Micron Sources

High-resolution (FWHM 04) mid-infrared images have been obtained for two proto-planetary nebulae possessing the 21 μm emission feature (IRAS 07134+1005 and Z02229+6208). Images through five filters were obtained, covering the 11.3 and 21 μm emission features as well as the adjacent dust continuum. The images of IRAS 07134+1005 show a clearly resolved shell structure, but no significant variation in morphology is seen between the different filters. The uniform morphology between the emission features and the continuum suggests that both the carriers of the 11.3 μm aromatic band and the 21 μm feature originate from the material ejected during the asymptotic giant branch phase of evolution.

Hydrogen bonding to Trp beta37 is the first step in a compound pathway for hemoglobin allostery.

Human hemoglobin is widely thought to change from the R to the T quaternary structure in a single rate process requiring tens of microseconds. Here we present kinetic evidence that the R --> T allosteric pathway in hemoglobin requires more than one step. We use magnetic circular dichroism (MCD) spectroscopy of the aromatic amino acid bands to show that formation of a tryptophan-aspartate hydrogen bond in the hinge region of the dimer-dimer interface is part of an obligatory R --> T step proceeding more than a factor of 10 faster than the kinetic step previously identified in heme-band absorption studies.

FTIR and py-GC-MS spectra of true-fern and seed-fern sphenopterids (Sydney Coalfield, Nova Scotia, Canada, Pennsylvanian)

Sphenopterid specimens from the Late Pennsylvanian of Sydney Coalfield, Canada, are investigated by FTIR and py-GC-MS techniques as part of an on-going research project into the biochemistry and chemotaxonomy of Pennsylvanian-age pteridophylls. Included in the investigation are samples of the true-fern species Oligocarpia brongniartii and Zeilleria delicatula that are preserved as naturally macerated cuticles (NMC), and the seed-fern Eusphenopteris neuropteroides that is also preserved as a compression/impression. FTIR spectra of NMC seed-fern E. neuropteroides, and fern sphenopterid O. brongniartii are very similar, except that the latter does not have aromatic bands in the 700–900 cm −1 out-of-plane region. py-GC-MS show more aromatic compounds for the seed fern than for the two true-fern sphenopterids. Another difference between seed-fern and true-fern sphenopterids is a lower ratio of CH 2 to CH 3 in chemically treated specimens (CTC) for the seed fern. These observations suggest slightly higher aromaticity for the seed ferns, perhaps related to some chemotaxonomic differences. Comparison of FTIR and py-GC-MS characteristics of sphenopterids and other plant groups shows that these two techniques have potential to identifying chemotaxonomic signals from Carboniferous pteridophylls in general, although more data are needed to confirm this.

ISOCAM observations of the Ursa Major cirrus:

We present mid-IR imaging observations of a high Galactic latitude cirrus obtained with the ISO camera ISOCAM at 6'' angular resolution. The observations were done with two filters LW2 (5–8.5 μm) and LW3 (12–18 μm) that measure respectively the aromatic carbon bands and the underlying continuum emission from small dust particles. Three 0.05 square degree images sample atomic and molecular sections in the Ursa Major cirrus. These images are compared with Hi, CO and IRAS observations. In such a cloud transparent to stellar light () the mid-infrared to 100 μm and the mid-IR emissivity per hydrogen are related to the abundance and the optical properties of small dust particles independently of any modelling of the penetration of the radiation. Within the atomic section of the cloud, the comparison between ISOCAM images and 21 cm interferometric data highlights an enhancement of the mid-IR emitters abundance by a factor ∼5 in an Hi filament characterized by a large transverse velocity gradient suggestive of rotation. Furthermore, a drop in the abundance of the same mid-IR emitters is observed at the interface between the atomic and molecular cirrus sections. We propose that these abundance variations of the mid-IR emitters are related to the production of small dust particles by grain shattering in energetic grain-grain collisions generated by turbulent motions within the cirrus and inversely by their disappearance due to coagulation on large grains. At the Hi-H2 interface we also observe a change in the (LW2)/(LW3) ratio by a factor 2. This color variation indicates that the amplitude of the continuum near 15 μm, relative to the aromatic bands, rises inside the molecular region. It could result from a modification of the dust size distribution or of the intrinsic optical properties of the small dust particles.

FTIR investigation of structural modifications during low-temperature ageing of polycarbonate

Conformational changes are sought during low-temperature ageing of solution-cast films of BPA-polycarbonate, by observing the conformationally sensitive IR aromatic breathing band at 1600 cm−1. Preliminary results using the carbonyl band at 1775 cm−1 had shown some indication of ageing-induced changes in the distribution of conformations. The present results obtained on the 1600 cm−1 band show no indication whatever of conformational rearrangements. This result, at variance with observations of conformational rearrangements accompanying sub-Tg annealing, lends support to the concept that sub-Tg annealing and low temperature ageing are two distinct processes.

The Low Metallicity ISM of Dwarf Galaxies

The properties of the low metallicity environments of dwarf galaxies are studied through dust observations in conjunction with the FIR fine-structure cooling lines. There is a striking enhancement of the I[CII]/I(CO) in dwarf galaxies that is explained by the decreased attenuation of the UV light in molecular clouds. An important consequence is that a significant mass of the molecular gas mass inventory can be missed through CO observations alone. Modeling the infrared spectral energy distribution into submillimeter wavelengths in dwarf galaxies reveals the presence of very cold (∼ 8K) dust,which accounts for a large fraction of the dust mass, until now missed by models using IRAS observations alone. In spite of the striking defficiency of the mid-infrared aromatic band carriers, cooling in the photodissociation regions, via [CII] line emission is a very efficient process.

PHENOLIC OH GROUP ESTIMATION BY FTIR AND UV SPECTROSCOPY. APPLICATION TO ORGANOSOLV LIGNINS

The phenolic hydroxyl group content of 34 acetylated organosolv lignins, obtained by ethanol or methanol autocatalyzed pulping of Eucalyptus globulus was measured by FTIR spectroscopy. The absorbance of aromatic IR ester bands of acetylated lignins at 1765 cm−1 was employed to estimate the lignin phenolic hydroxyl group content. To compare different samples the spectra recorded were baseline corrected and normalized with the bands around 1500, 1600 and 1423 cm−1. Partial least-squares (PLS) and multiple linear regression (MLR) calibrations were carried out to establish a mathematical correlation between UV data sets and FTIR spectra. The best results were shown by the models obtained by PLS regression. In these models the band at 1766 cm−1 was normalized using the band at 1744 cm−1 and the baseline corrections were performed with the bands at 1423 cm−1 (ethanol lignin) and 1507 cm−1 (methanol lignin).

Effects of Freeze-Thaw and Photobleaching on the Ultraviolet Resonance Raman Spectra of Human Colon Biopsies

We studied the effects of sample freezing and thawing, laser fluence, temperature, and oxygen on the ultraviolet resonance Raman (UVRR) spectra of human colon biopsies at 251 nm excitation. We show that the total adenylate content of the tissue decreases as a result of freezing and subsequent thawing to room temperature. We also show that photobleaching is the result of oxidative as well as thermal damage. Photobleaching consisted of a decrease in the intensity of the purine spectral bands and broadening and intensity increase of the aromatic amino acid bands. Both bio- and photodegradation of the tissue can be minimized by keeping the biopsy samples refrigerated during testing and the laser fluence under 0.2 mJ/μm2. Unlike amino acid photobleaching, purine photobleaching was also greatly reduced by placing the samples in an argon atmosphere. Sample storage could be achieved by refrigerating the fresh specimens and testing them within 30 h of surgical resection, without freezing. Alternatively, the fresh specimens could be snap-frozen in liquid nitrogen, then thawed and tested for up to 30 min. Altogether, these studies can be utilized to guide future experimental design and data interpretation during ultraviolet spectroscopy of biological tissues.

Change of the Structure of Coals from the Kozlu K20 G Borehole of Zonguldak Basin with Burial Depth 1. Chemical Structure

The present paper is a part of the studies on the structure and properties of the Zonguldak bituminous coal samples from the Kozlu K20 G borehole. The changes in the values of parameters characterizing the properties of the tested coals with an increase in the degree of coalification at increasingly greater depths in the borehole were reported. Changes in elemental and proximate analyses results, calorific value, FTIR aromatic bands, ESR values, and aromaticity of the samples were described.

ISOCAM‐CVF 5–12 Micron Spectroscopy of Ultraluminous Infrared Galaxies

We present low-resolution mid-infrared (MIR) spectra of 16 ultraluminous infrared galaxies (ULIRGs) obtained with the circular variable filter (CVF) spectroscopy mode of ISOCAM on board the Infrared Space Observatory (ISO). Our sample completes previous ISO spectroscopy of ultra- and hyperluminous infrared galaxies toward higher luminosities. The combined samples cover an infrared luminosity range of ~1012-1013.1 L☉. To discriminate active galactic nucleus (AGN) and starburst activity, we use the AGN-related MIR continuum and the starburst-related 6.2, 7.7, 8.6, and 11.3 μm MIR emission bands attributed to aromatic carbonaceous material. For about half of the high-luminosity ULIRGs studied here, strong aromatic emission bands suggest starburst dominance. Other spectra are dominated by a strong AGN-related continuum with weak superposed emission features of uncertain nature. Our sample contains one unusual example, IRAS F00183-7111, of an AGN that is highly obscured even in the MIR. An improved method to characterize quantitatively the relative contribution of star formation and AGN activity to the MIR emission of ULIRGs is presented. The ULIRG spectra are fitted by a superposition of a starburst and an AGN spectrum, both of which may be obscured at different levels. Models in which starburst and AGN obscuration differ are significantly more successful than models with a single extinction. Previous results based on a simpler line-to-continuum measure of aromatic emission strength are confirmed, further supporting the robustness of the aromatic emission feature as a diagnostic of ULIRG power sources. As dominant sources of the bolometric luminosity, starbursts prevail at the lower end and AGNs at the higher end of this range. The transition between mostly starburst and mostly AGN powered occurs at ~1012.4-1012.5 L☉, and individual luminous starbursts are found up to ~1012.65 L☉.

Relationship between conformation and enthalpy or volume relaxation in polycarbonate

Conformational changes are observed during sub- T g annealing of solution-cast films of BPA–polycarbonate by following changes in the conformationally sensitive IR aromatic breathing band at 1600 cm −1. The rate of conformational relaxation is compared with published data on enthalpy and volume relaxation on the same polymer. The relaxation rates and timescales converge in the immediate vicinity of T g, but diverge at temperatures below T g−15 K and conformational energy only accounts for a very small fraction of observed enthalpy relaxation. The results suggest that a single process is active in volume and conformational relaxation and that at least two processes contribute to enthalpy relaxation.

Interactions in chromatographic separation of resins from deasphaltened crude oils studied by means of infrared spectroscopy and principal component analysis

Resins were extracted from crude oils by adsorption onto various particles followed by desorption using various solvent combinations in a two-step desorption procedure. The extracted resins were analyzed using infrared spectroscopy, followed by local principal component analysis on the polar and aromatic absorption bands. It was found that the adsorption and desorption processes can be related to interactions involving specific functional groups such as amides, esters and aromatics in the resins with the adsorbents and solvents. The results are discussed in terms of polar forces, hydrogen bonds, dispersion forces and acid-based characteristics. Polar functional groups in the resins were found to interact with polar groups at the adsorbents and with solvents by polar forces and hydrogen bonds. It is also found that the aromatic character of the extracted resins is greater when benzene is used as solvent than if polar solvents are used. When using a low-polarity adsorbent the extracted resins contain less polar functional groups than when using a high-polarity solvent, showing that dispersion forces are important in the extraction. Some intercrude differences were also found and discussed.

Secretinite—reflectance and chemical data from two high volatile bituminous coals (Upper Carboniferous) of North America

Secretinite—a maceral of the inertinite group as recognized by the ICCP in 1996—is a noncellular maceral of seed fern origin. New reflectance data indicate that this maceral has primary anisotropy with bireflectances of 0.4% to 0.9% in high-volatile B bituminous (Ro=0.6%) Carboniferous coal of North America. The highest reflectance is in cross-section as opposed to longitudinal section. Characteristic feature of secretinite is the virtual absence of Si and Al, unlike that in associated vitrinite. This indicates the absence of submicron aluminosilicates in secretinite and their presence in vitrinites. Secretinite is highly aromatic as indicated by low O/C ratios and high contribution of aromatic hydrogen bands detected by FTIR analysis.

The Mid-Infrared Properties of Nearby Spiral Galaxies

The galaxies (~ 40) presented here are part of three ISOCAM guaranteed time programs. Observations consist of raster maps performed with a sampling of 3 and 6 arcsecond per pixel, in the 6.75 μm (LW2) and 15 μm (LW3) bands. The 6.75 μm band samples mostly emission from a blend of aromatic bands, while the 15 μm band is more complex since it generally samples aromatic bands and an associated continuum as well, but can also receive a significant, or even dominant, contribution from a sharply rising continuum emitted by small grains in HII regions or high radiation density environments.

Ab initio MO and experimental studies on the vibrational spectra and structure of 4-hydroxybenzonitrile and of its anion

The structures of 4-hydroxybenzonitrile ( p-cyanophenol) and its anion have been studied by IR spectra and ab initio HF and MP2 calculations. In agreement between theory and experiment, the conversion of the 4-hydroxybenzonitrile molecule into the oxyanion leads to essential spectral changes: decrease in the frequency of the cyano stretching band and strong increase in its integrated intensity, strong enhancement of the integrated intensities of the aromatic skeletal bands of ν 8 and ν 19 types, etc. According to the calculations (MP2 data in italics) the oxyanionic charge is delocalized over the cyano group (0.13 e −, 0.12e −), phenylene ring (0.44 e −, 0.39e −) and oxyanionic center (0.43 e −, 0.49e −). The conversion into the oxyanion results in an additional quinoidization of the phenylene ring.