mid-IR Spectra Research Articles

Application of quantitative IR spectral analysis of bacterial cells to acetone–butanol–ethanol fermentation monitoring

Clostridium acetobutylicum ATCC 824 was grown under three different acetone–butanol–ethanol (ABE) fermentation conditions: (1) strictly anaerobic conditions with vegetative inoculum; (2) semi-anaerobic conditions with vegetative inoculum; and (3) strictly anaerobic conditions with spore inoculum. Semi-anaerobic fermentation with vegetative inoculum and strictly anaerobic fermentation with spore inoculum produced solvents at high level. Strictly anaerobic fermentation with vegetative inoculum showed an “acid crash”, i.e. produced mainly acids and did not switch to predominant solvent production. The content of carbohydrates, nucleic acids, proteins and lipids in Clostridium cells during the fermentation were evaluated from the mid-IR spectra. The content of nucleic acids decreased with process time, and the lipid content increased, corresponding to ceasing growth and formation of the toxic fermentation products. It was shown that the physiological states of either solvent production or acid crash are reflected in the microbial biomass composition, which can be assessed by IR spectroscopy.

Ice features in the mid-IR spectra of galactic nuclei

Mid infrared spectra provide a powerful probe of the conditions in dusty galactic nuclei. They variously contain emission features associated with star forming regions and absorptions by circumnuclear silicate dust plus ices in cold molecular cloud material. Here we report the detection of 6-8um water ice absorption in 18 galaxies observed by ISO. While the mid-IR spectra of some of these galaxies show a strong resemblance to the heavily absorbed spectrum of NGC 4418, other galaxies in this sample also show weak to strong PAH emission. The 18 ice galaxies are part of a sample of 103 galaxies with good S/N mid-IR ISO spectra. Based on our sample we find that ice is present in most of the ULIRGs, whereas it is weak or absent in the large majority of Seyferts and starburst galaxies. This result is consistent with the presence of larger quantities of molecular material in ULIRGs as opposed to other galaxy types. Like NGC 4418, several of our ice galaxy spectra show a maximum near 8um that is not or only partly due to PAH emission. While this affects only a small part of the galaxy population studied by ISO, it stresses the need for high S/N data and refined diagnostic methods, to properly discriminate spectra dominated by PAH emission and spectra dominated by heavy obscuration. The spectral variation from PAH emission to absorbed continuum emission near 8um shows strong similarities with Galactic star forming clouds. This leads us to believe that our classification of ice galaxy spectra might reflect an evolutionary sequence from strongly obscured beginnings of star formation (and AGN activity) to a less enshrouded stage of advanced star formation (and AGN activity), as the PAHs get stronger and the broad 8um feature weakens.

Mid-IR microspectroscopic imaging of breast tumor tissue sections.

IR microspectroscopic imaging is a relatively new approach for the examination of tissue sections. In contrast to standard light microscopy based procedures, the IR approach requires neither sample staining nor fixation. The IR spectra of breast tumor tissue sections are obtained via a microscope equipped with a focal plane array detector. This enabled the simultaneous collection of individual mid-IR spectra from thousands of different sample positions with a spatial resolution near the diffraction limit. The analysis of the IR data reveals a high sensitivity of the IR approach toward changes in tissue biochemistry and variations in breast tissue architecture. Moreover, the data demonstrate the need for collecting spectra with high spatial resolution at the level of individual cells. This minimizes problems associated with tissue microheterogeneity and is an essential prerequisite for future studies aimed at developing IR microspectroscopic imaging as a complement to present diagnostic tools for breast cancer.

A first glimpse at the acidic proton vibrations in HCl–water clusters via supersonic jet FTIR spectroscopy

The first mid-IR spectra of the proton vibrational dynamics in isolated HCl–water clusters are presented. Pulsed expansions of HCl and water in rare gases through a slit nozzle are probed by an FTIR spectrometer in the 2000–3300 cm−1 range. Distinct absorptions by small HCl and HCl–water clusters are superimposed on broad bands, partly due to electrolytically dissociated HCl. A firm assignment of the 1 : 1 complex (at 2723.5 cm−1) is provided together with a more tentative assignment of the 1 : 2 complex (near 2464 cm−1). The results are compared to condensed phase, matrix isolation and theoretical studies as well as exploratory quantum-chemical calculations. A rationale for the low abundance of small molecular HCl–water clusters beyond the 1 : 1 complex is given.

Conformational and Infrared Spectral Studies of l-Methionine and Its N-Deuterated Isotopomer as Isolated Zwitterions

The mid-IR spectra of l-methionine and its N−D3 deuterated isotopomer as isolated zwitterions in a KBr solid solvent have been obtained by means of a newly developed infrared sampling technique, which involves the production of thin films. Ab initio calculations of the nonaqueous self-consistent reaction field type, using the Onsager dipole-sphere model have been carried out at both the Hartree−Fock and density functional levels of theory for the prediction of the vibrational spectra and molecular structures of Met zwitterions isolated in KBr matrixes. Seven stable conformers of Met zwitterion were located, of which three were shown to be characterized by strong intramolecular H-bonding. Another conformer was found to have the same conformation, and similar molecular structure, as one of the two forms of Met crystals. The calculated structural data supplement the limited crystal data obtained by X-ray diffraction studies. Comparison of the calculated spectra of the seven conformers with the measured spectra favors the presence of zwitterions of conformer GtG in the KBr solid solvent. However, the evidence against a number of the other conformers, in particular, gtt and tGG, is not overwhelming.

Near-infrared and mid-infrared spectroscopic study of sepiolites and palygorskites

Near-IR spectroscopy has been used to distinguish between palygorskites and sepiolites. Three near-IR spectral regions contain bands due to (a) the high frequency region between 6400 and 7400 cm −1 attributed to the first overtone of the hydroxyl stretching mode, (b) the 4800–5400 cm −1 region attributed to water combination modes and (c) the 4000–4800 cm −1 region attributed to the combination of the stretching and deformation modes of the M–MgOH units of palygorskites and sepiolites. Near-IR bands are observed in the first region and are assigned to the first overtone of the hydroxyl stretching frequency observed at 3620 and 3410 cm −1 in the mid-IR spectra. The near-IR bands observed in the second region are assigned to the combination of the water OH stretching and deformation vibrational modes. A complex set of low intensity bands are observed in the 4100–4600 cm −1 region and are attributed to the combination of the cation hydroxyl stretching, deformation and translation modes. The difference between the near-IR spectra of palygorskites and sepiolites depends on the dioctahedral nature of the palygorskites and the trioctahedral structure of the sepiolites. Changes in the near-IR spectra are therefore related to the Mg 3(OH) and Mg 2(OH) units in the palygorskites.

Infrared and Raman spectra, ab initio calculations and conformational equilibria of chloromethyl methyl dichlorosilane

Chloromethyl methyl dichlorosilane (ClCH2CH3SiCl2) was synthesized and the infrared spectra of its vapour, and of the amorphous and crystalline states, cooled to the temperature of liquid nitrogen were recorded. Additional mid IR spectra of the compound, isolated in both argon and nitrogen matrices, were taken at 5K. Raman spectra of the liquid were recorded in a capillary at various temperatures between 298 and 223K. The crystal was also studied in a capillary at 210K and deposited onto a copper finger cooled with liquid nitrogen.The compound occurs as anti and gauche conformers in its vapour and liquid states. Approximately five Raman bands, some of them weak, present in the fluid phases vanished upon crystallization. An additional eight IR bands disappeared or were reduced in intensity after crystallization. Two band pairs in the Raman spectra were used to calculate the enthalpy difference between the conformers in the liquid phase giving a value: ΔH(liq)(anti–gauche) of 0.0(±0.4kJmol−1. In the argon and nitrogen matrices, various small intensity variations in the IR bands were observed after annealing to ca. 36K (argon) or 32K (nitrogen). The gauche bands generally increased and the anti bands decreased in intensity, suggesting that gauche has a lower energy in the matrices. The conformational barrier was estimated to be 8–10kJmol−1.The optimized geometries, infrared and Raman intensities, and scaled vibrational frequencies for the anti and gauche conformers were derived from ab initio calculations at the RHF/6-311G∗level. The derived conformational energy difference was 7.2kJmol−1, gauche being the conformer of lowest energy. The calculated dipole moments of the anti and gauche conformers were 4.2 and 2.0D, respectively. Correlation between the observed and calculated wave numbers of both conformers revealed that gauche was present in the crystal, and assignments of the spectra have been carried out.

Mid-infrared spectroscopy coupled to sequential injection analysis for the on-line monitoring of the acetone–butanol fermentation process

Fourier transform infrared (FTIR) spectroscopy, coupled to sequential injection analysis (SIA) was employed for the on-line monitoring of an acetone–butanol fermentation by simultaneously determining acetone, acetate, n-butanol, butyrate and glucose from the mid-IR spectra of the samples. The analysis system (SIA-FTIR) developed was completely computer controlled, requiring only minute amounts of NaOH and Na 2CO 3 as reagents and was capable of performing 30 analyte determinations per hour. From a batch fermentation run of 55 h duration, samples were automatically drawn and analysed at 14 different points of time. The analysis by SIA-FTIR comprised of triplicate injections, from each of which two spectra one with 4 cm −1 the other with 8 cm −1 spectral resolution were obtained. In addition, triplicate reference analysis by gas chromatography and enzymatic test kits were also done at corresponding points of time. Based on the data of the reference analysis a partial least squares (PLS) model was established and validated by a leave-one-out cross validation. Best results were obtained using the second derivatised spectra collected at 8 cm −1 resolution. The regression coefficients and standard errors of prediction (S.E.P.) were as follows: acetone, r=0.999, S.E.P.=0.077 g/l; acetate, r=0.998, S.E.P.=0.063 g/l; butyrate, r=0.955 and S.E.P.=0.058 g/l; n-butanol, r=0.999, S.E.P.=0.301 g/l and glucose, r=0.999, S.E.P.=0.493 g/l. The high quality of the results obtained, and the observation that the precision of the SIA-FTIR analysis was as good and often better than those of the reference methods, showed that SIA-FTIR is a powerful tool for rapid on-line bioprocess monitoring.

Mid- and far-infrared spectroscopic studies of the influence of temperature, ultraviolet photolysis and ion irradiation on cosmic-type ices

Infrared (IR) studies of laboratory ices can provide information on the evolution of cosmic-type ices as a function of different simulated space environments involving thermal, ultraviolet (UV), or ion processing. Laboratory radiation experiments can lead to the formation of complex organic molecules. However, because of our lack of knowledge about UV photon and ion fluxes, and exposure lifetimes, it is not certain how well our simulations represent space conditions. Appropriate laboratory experiments are also limited by the absence of knowledge about the composition, density, and temperature of ices in different regions of space. Our current understanding of expected doses due to UV photons and cosmic rays is summarized here, along with an inventory of condensed-phase molecules identified on outer solar system surfaces, comets and interstellar grains. Far-IR spectra of thermally cycled H 2O are discussed since these results reflect the dramatic difference between the amorphous and crystalline phases of H 2O ice, the most dominant condensed-phase molecule in cosmic ices. A comparison of mid-IR spectra of products in proton-irradiated and UV-photolyzed ices shows that few differences are observed for these two forms of processing for the simple binary mixtures studied to date. IR identification of radiation products and experiments to determine production rates of new molecules in ices during processing are discussed. A new technique for measuring intrinsic IR band strengths of several unstable molecules is presented. An example of our laboratory results applied to Europa observations is included.

ISOCAM Observations of a Galaxy Merging Sequence

We present mid-IR (5–16μm) images and spectra of a sequence of interacting galaxies, observed by ISOCAM. The galaxies were selected as being at progressive stages in the time evolution of a merging event and having no detected contribution from an active galactic nucleus (AGN) in their mid-IR spectrum. To trace the intensity of the global star formation in those galaxies, we use the ratio of the 15μm to 7μm flux. Our analysis indicates that this ratio increases from ∼ 1 to ∼ 5 as galaxies move from the pre-starburst to the merging/starburst phase only to decrease to∼ 1 again in the post-starburst phase of the evolved merger remnants. Moreover, we find that the variation of this ratio is well correlated with the one of the IRAS 25μm/12μm and 60μm/100μm flux ratios. Improving upon these results using the Infrared Spectrograph (IRS) on board the Space Infrared Telescope Facility (SIRTF) is briefly discussed.

Fourier transform infrared quantitative analysis of sugars and lignin in pretreated softwood solid residues.

Hydrolysates were obtained from dilute sulfuric acid pretreatment of whole-tree softwood forest thinnings and softwood sawdust. Mid-infrared (IR) spectra were obtained on sample sets of wet washed hydrolysates, and 45 degrees C vacuum-dried washed hydrolysates, using a Fourier transform infrared (FTIR) spectrophotometer equipped with a diamond-composite attenuated total reflectance (ATR) cell. Partial least squares (PLS) analysis of spectra from each sample set was performed. Regression analyses for sugar components and lignin were generated using results obtained from standard wet chemical and high-performance liquid chromatography methods. The correlation coefficients of the predicted and measured values were >0.9. The root mean square standard error of the estimate for each component in the residues was generally within 2 wt% of the measured value except where reported in the tables. The PLS regression analysis of the wet washed solids was similar to the PLS regression analysis on the 45 degrees C vacuum-dried sample set. The FTIR-ATR technique allows mid-IR spectra to be obtained in a few minutes from wet washed or dried washed pretreated biomass solids. The prediction of the solids composition of an unknown washed pretreated solid is very rapid once the PLS method has been calibrated with known standard solid residues.

Automatic correction of peak shifts in Raman spectra before PLS regression

A simple algorithm is presented for the fast and fully automatic removal of peak shifts in large spectral data sets. It is able to remove peak shifts exceeding the discrete spectral resolution. The algorithm has been applied to Raman spectra of three solution copolymerizations of styrene (Sty) and butyl acrylate (BA) performed on three separate days. Small Raman peak shifts, smaller than the spectral resolution, and induced by the on/off switching of the laser and the repositioning of the grating, could successfully be removed prior to partial least squares (PLS) regression. It is demonstrated that after shift correction, the ability of PLS to predict Sty and BA concentrations is improved. Due to its speed, the algorithm is suitable to eliminate real time (on-line) spectral shifts from the spectra. This makes re-calibration or model adaptation forced by spectral shifts superfluous. The proposed algorithm may likewise be used to remove peak/wavelength shifts in mid-IR, near-IR, and NMR spectra, as well as to remove retention time shifts in chromatograms.

Conformations of Chiral Molecules in Solution: Ab Initio Vibrational Absorption and Circular Dichroism Studies of 4,4a,5,6,7,8-Hexahydro-4a-methyl-2(3H)-naphthalenone and 3,4,8,8a-Tetrahydro-8a-methyl-1,6(2H,7H)-naphthalenedione

Studies of the vibrational unpolarized absorption and vibrational circular dichroism (VCD) spectra of the bicyclic chiral molecules: 4,4a,5,6,7,8-Hexahydro-4a-methyl-2(3H)-naphthalenone (1) and 3,4,8,8a-Tetrahydro-8a-methyl-1,6(2H,7H)naphthalenedione (2) are reported. Experimental spectra are compared to spectra calculated using ab initio density functional theory (DFT), hybrid functionals (B3PW91 and B3LYP), gauge-invariant atomic orbitals (GIAOs), and the 6-31G* basis set. 1 and 2 are flexible molecules. Three conformations -“trans-chair” (I), “cis-chair” (II) and “trans-boat” (III)- of 1 and 2 have been studied. Predicted relative energies are I < II < III. Comparison of predicted spectra for the three conformations to experimental mid-IR spectra in CCl4 and CS2 solutions unambiguously demonstrates that for both 1 and 2 conformation I is the preferred conformation in these solvents. The predicted energy differences of conformations I and II are ∼1.8 and ∼1.2 kcal/mol in 1 and 2 respectively. Weak bands in the vibrational spectra of 2 can be attributed to conformation II. Their intensities are consistent with the predicted energy difference. Bands attributable to conformation II are not definitively observed in the vibrational spectra of 1, consistent with the greater energy difference predicted. X-ray crystallography has shown that conformation I is the conformation of 2 in the solid state; our work demonstrates that the conformation of 2 is the same in solution (in CCl4 and CS2) and in the crystalline solid state.

Dipole moment surfaces and the mid- and far-IR spectra of N2-Ar

An improved theoretical long-range dispersion plus induction dipole moment surface for N2-Ar is presented, and detailed numerical simulations are used to test its predictions against experimental far-IR and mid-IR spectra using two previously-reported potential energy surfaces. As was found in earlier work on the mid-IR spectrum using a pure induction dipole surface, the MMSVmod potential of Jäger et al. [J. Chem. Soc. Faraday Discuss. 97, 105 (1994)] yields distinctly better agreement with both experiments than does the XC-3 potential of Dham et al. [J. Chem. Phys. 103, 8477 (1995)]. However, the new dipole surface yields slightly poorer agreement with certain features of the experimental mid-IR and far-IR spectra, which suggests that the existing theoretical values and derivatives with respect to the bond length of some of the permanent moment and (hyper)polarizability properties of N2 need improvement.

Disease pattern recognition in infrared spectra of human sera with diabetes mellitus as an example

To benefit from the full information content of the mid-IR spectra of human sera, we directly related the overall shape of the spectra to the donors' disease states. For this approach of disease pattern recognition we applied cluster analysis and discriminant analysis to the example of the disease states diabetes type 1, diabetes type 2, and healthy. In a binary, supervised classification of any pair of these disease states we achieved specificities and sensitivities of approximately 80% within our data set.

Optical, infrared and millimetre-wave properties of Vega-like systems—IV. Observations of a new sample of candidate Vega-like sources

Optical, infrared and millimetre-wave properties of Vega-like systems—IV. Observations of a new sample of candidate Vega-like sources

The infrared spectra and molecular structure of zwitterionic l-β-phenylalanine

The infrared absorption spectrum and molecular structure of zwitterionic l-β-phenylalanine (Phe) were studied by means of a new sampling technique and ab initio molecular orbital calculations. The self-consistent reaction field calculations at HF/6-311G(d,p) level were carried out on zwitterionic Phe present in a continuum of KBr. Good agreement in terms of both frequencies and intensities was found between the calculated and observed full mid-IR spectra. The predicted structure of monomeric zwitterionic Phe was discussed and compared with Phe analogues.

Molecular mechanisms involved in creep phenomena of paper

The phenomenon of mechanosorptive creep (i.e., the increasing creep occurring in some hygroscopic materials subjected to moisture cycling) was studied for paper from a molecular point of view. Paper was tested in creep at different loading levels in a constant high humidity of 90% relative humidity (RH) and in a cyclic climate between 30 and 90% RH. Throughout the creep tests, spectra from the mid- and near-IR, as well as dynamic mechanical data, were recorded to determine molecular changes occurring with time. In tensile stress scans the instantaneous, dynamic elastic modulus was found to increase. It is suggested that this increase was due to orientation of the cellulose molecules, which was detected as changes in the mid-IR spectra at 1160 cm−1 assigned to the C1OC4 stretching. During creep in constant and cyclic humidity, the modulus was found to increase with time, more so for the cyclic humidity. Changes in the mid-IR spectra at 1184 and 1030 cm−1, which is assigned to CH2, CH, and CO, may indicate sliding between the cellulose chains. The near-IR measurements mainly showed differences in the moisture content. In stress scans the moisture content increased with increasing tensile load. In creep at constant 90% RH, the moisture content was also found to increase in a manner similar to the stress scan. In the cyclic humidity with a conditioning time of 70 min at 90% RH the moisture content decreased successively with increasing numbers of cycles. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1590–1595, 2001

Interstellar and Circumstellar PAHs

ISO has shown that the mid–IR spectra of almost all sources are dominated by narrow emission features collectively known as the UIR bands. These bands are carried by a family of polycyclic aromatic hydrocarbon molecules containing about 50 C-atoms. Other classes of molecules such as C-chains as well as non-aromatic groups attached to the PAHs are much less abundant. ISO has revealed that the UIR spectrum is incredibly rich with a large number of weaker features, subfeatures, and shoulders; many of which were not known before. Some examples and the new insights they can provide are described. A systematic study of this spectral structure may well allow us to considerably narrow down the composition of the family of PAHs responsible for the observed emission.

Infrared spectra (MID-IR) classification of balsamic vinegars

Traditional and non Balsamic vinegars have been classified on the basis of Mid-IR spectra. After the most significant spectral bands were determined, the transmission values were elaborated statistically using Linear Discriminant Analysis. This approach has shown net differences between Traditional Balsamic vinegars from Modena and Balsamic ones and moreover it has confirmed, among the latter, the presence of two different vinegar groups These groups stand out in a similar way to the differentiation obtained as a function of 5-acetoxymethyl-2-furaldehyde and α-aminoadipic acid. which are indexes of the ageing process.