Biological applications of infrared spectrometry

Summary A brief overview of infrared studies of biological systems is presented. Relevant studies of the four classes of biomolecules, the proteins, the lipids, the carbohydrates and the nucleic acids are exemplified with results from the recent literature. The great potential of infrared spectrometry for biological studies is demonstrated.

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Biologische Anwendungen der Infrarot-Spektrometrie

Zusammenfassung Es wird ein kurzer Überblick über infrarotspektroskopische Untersuchungen von biologischen Systemen gegeben. Die wesentlichen Studien der vier Klassen von Biomolekülen, nämlich Proteine, Lipide, Kohlenhydrate und Nucleinsäuren, werden mit exemplarischen Ergebnissen aus der neueren Literatur vorgestellt. Das hohe Potential der Infrarot-Spektroskopie für biologische Untersuchungen wird demonstriert.

     

Active infrared thermography applied to the investigation of art and historic artefacts

Infrared thermography (IRT) is a non-destructive technique that has recently been extensively applied to the investigation of cultural heritage. It provides information on the surface and subsurface structure of the artefacts by the analysis of the heat diffusion process within the sample. IRT has been successfully applied to the study of historic large structures and buildings most of the time by means of the so-called passive approach, where only the naturally occurring temperature changes in the sample are analysed. On the other hand, IRT has also been applied to the study of other art and historic artefact by applying the so-called active method where the thermal stimulation of the sample is required. In this article, an overview of the applications of active thermography to the investigation of art and historic artefacts will be presented and discussed.     

Quantitative applications of photoacoustic spectroscopy in the infrared

Quantitative photoacoustic and transmission infrared spectroscopy have been compared for a highly overlapped three component mixture with concentrations varying from 0 to 60%. A partial leastsquares model has been employed for the quantitative analysis. High correlation coefficients were obtained for both the transmission and photoacoustic model.     

Detection of defects in components made of dispersion-filled polymeric materials by the method of infrared thermography

A method allowing one to determine the presence of hidden defects in dispersion-filled polymeric materials by means of a thermal imager is studied. The results of studies of the determination of hidden defects in samples of dispersion-filled polymeric materials are reported. The dependence of the determination of hidden defects in samples of dispersion-filled polymeric materials on the method of the transfer of excess temperatures to the tested object is established.     

Biochemical applications of surface-enhanced infrared absorption spectroscopy

An overview is presented on the application of surface-enhanced infrared absorption (SEIRA) spectroscopy to biochemical problems. Use of SEIRA results in high surface sensitivity by enhancing the signal of the adsorbed molecule by approximately two orders of magnitude and has the potential to enable new studies, from fundamental aspects to applied sciences. This report surveys studies of DNA and nucleic acid adsorption to gold surfaces, development of immunoassays, electron transfer between metal electrodes and proteins, and protein–protein interactions. Because signal enhancement in SEIRA uses surface properties of the nano-structured metal, the biomaterial must be tethered to the metal without hampering its functionality. Because many biochemical reactions proceed vectorially, their functionality depends on proper orientation of the biomaterial. Thus, surface-modification techniques are addressed that enable control of the proper orientation of proteins on the metal surface. Figure Surface enhanced infrared absorption spectroscopy (SEIRAS) on the studies of tethered protein monolayer (cytochrome c oxidase and cytochrome c) on gold substrate (left), and its potential induced surface enhanced infrared difference absorption (SEIDA) spectrum     

Fundamentals and applications of near infrared spectroscopy in spectroelectrochemistry

Near infrared spectroscopy as a tool for in situ spectroelectrochemical investigations of electrochemical systems is reviewed with particular attention to experimental approaches and typical results from all parts of chemistry and applied chemistry     

Sensor applications of attenuated total reflection infrared spectroscopy

Attenuated total reflection Fourier transform infrared spectroscopy is one of the most powerful methods for recording infrared spectra of biological materials in general, and of biological membranes in particular. It is fast, yields a strong signal with only a few micrograms of sample and recent ATR devices allow the recording of nanogram quantities. Importantly, it allows information about the orientation of various parts of the molecules under study to be evaluated in an oriented system. While mid-infrared radiation has been most used for fundamental research on molecular structure, it is becoming an interesting alternative for sensor research. In addition to the usual sensor response, one of its advantages is its sensitivity to molecular conformation. In turn, the binding of a drug onto a receptor may be monitored as for other detection methods but in addition the evaluation of the structural response of the receptor to this binding is likely to bring invaluable information on the mechanism of action of the drug. The present review focuses only on the ATR-mid IR spectroscopy with a special interest for proteins and biological membranes.     

Coherent effects in femtosecond infrared spectroscopy

The accessible time resolution in femtosecond infrared experiments is shorter than the typical phase relaxation time of a vibronic transition. Therefore, coherent interaction of the light pulses with the sample may disturb the observed absorbance signals. Coherence results in an artifact known as perturbed free induction decay, which may be misinterpreted as an intrinsic incoherent temporal evolution of the sample. In the present paper, a model is presented describing this effect for the general situation, where a complex molecule containing many overlapping vibrational modes is investigated. The model leads to an efficient linear least square fit algorithm allowing the analysis of huge data sets. The model and the fit algorithm are applied to transient absorbance changes observed in a large dye molecule. It is demonstrated that it is possible to separate an ultrafast energy relaxation process from the perturbed free induction decay signal. In addition, the analysis of the perturbed free induction decay effect itself allows one to obtain information on the instantaneous absorbance change of the sample.     

Industrial applications of computerized dispersive infrared spectroscopy for analysis in solution

Today, with the relatively low cost of data processing equipment, it is possible to interface a dedicated minicomputer to a computer-compatible scientific instrument to give a total system that is ideal for routine operation. This article describes some basic chemical applications of a commercial system for computerized infrared spectroscopy that are relevant to analytical problems encountered in industrial laboratories. In the initial stages of the article some examples are given of the different experimental procedures that are available to handle infrared data from solutions. The remaining sections illustrate the direct application of data handling to specific applications in both organic and aqueous media.     

Line shape distortion effects in infrared spectroscopy

This paper explores different phenomena that cause distortions of infrared absorption spectra by mixing of reflective and absorptive band shape components of infrared spectra, and the resulting distortion of observed band shapes. In the context of this paper, we refer to the line shape of the variations of the refractive index in spectral regions of an absorption maximum (i.e., in regions of "anomalous dispersion") as "dispersive" or "reflective" line shape contributions, in analogy to previous spectroscopic literature. These distortions usually result in asymmetric bands with a negative intensity contribution at the high wavenumber of the band, accompanied by a shift toward lower wavenumber, and confounded band intensities. In extreme cases of band distortions caused by the "resonance Mie" (RMie) mechanism, spectral peaks may be split into doublets of peaks, change from positive to negative peaks, or appear as derivative-shaped features.     

Thermal transfer,interfacial, and mechanical properties of carbon fiber/polycarbonate-CNT composites using infrared thermography

Electrical resistance (ER) and thermogram measurements were used to evaluate thermal transfer, interfacial and mechanical properties of carbon fiber reinforced thermoplastic polycarbonate composites. Carbon nanotubes (CNTs) were fairly uniformly dispersed in polycarbonates using a solvent dispersion method. The CNTs were then further dispersed with an additional time using a twin screw extruder. The effect of CNT on the mechanical properties of polycarbonate was evaluated using a thin film tensile test. For thermogram to evaluate the transferring temperature the composite was placed on a hotplate and copper wires were inserted in the composite at uniform thickness intervals. Due to the different inherent thermal conductivity of CNT, ER was measured to detect thermal changes in the carbon fiber/CNT-polycarbonate composites. The comparison of interlaminar shear strength (ILSS) was to investigate effects of CNT on mechanical and interfacial properties. The uniform distribution of CNTs affected all of these properties in carbon fiber-reinforced thermoplastic composite. Furthermore, heat transfer and heat release become more rapid with the addition of CNT than the without case.     

Near infrared spectroscopic imaging assessment of cartilage composition: Validation with mid infrared imaging spectroscopy

Disease or injury to articular cartilage results in loss of extracellular matrix components which can lead to the development of osteoarthritis (OA). To better understand the process of disease development, there is a need for evaluation of changes in cartilage composition without the requirement of extensive sample preparation. Near infrared (NIR) spectroscopy is a chemical investigative technique based on molecular vibrations that is increasingly used as an assessment tool for studying cartilage composition. However, the assignment of specific molecular vibrations to absorbance bands in the NIR spectrum of cartilage, which arise from overtones and combinations of primary absorbances in the mid infrared (MIR) spectral region, has been challenging. In contrast, MIR spectroscopic assessment of cartilage is well-established, with many studies validating the assignment of specific bands present in MIR spectra to specific molecular vibrations. In the current study, NIR imaging spectroscopic data were obtained for compositional analysis of tissues that served as an in vitro model of OA. MIR spectroscopic data obtained from the identical tissue regions were used as the gold-standard for collagen and proteoglycan (PG) content. MIR spectroscopy in transmittance mode typically requires a much shorter pathlength through the sample (≤10 microns thick) compared to NIR spectroscopy (millimeters). Thus, this study first addressed the linearity of small absorbance bands in the MIR region with increasing tissue thickness, suitable for obtaining a signal in both the MIR and NIR regions. It was found that the linearity of specific, small MIR absorbance bands attributable to the collagen and PG components of cartilage (at 1336 and 856 cm⁻¹, respectively) are maintained through a thickness of 60 μm, which was also suitable for NIR data collection. MIR and NIR spectral data were then collected from 60 μm thick samples of cartilage degraded with chondroitinase ABC as a model of OA. Partial least squares (PLS) regression using NIR spectra as input predicted the MIR-determined compositional parameters of PG/collagen within 6% of actual values. These results indicate that NIR spectral data can be used to assess molecular changes that occur with cartilage degradation, and further, the data provide a foundation for future clinical studies where NIR fiber optic probes can be used to assess the progression of cartilage degradation.     

Application of infrared thermography for online monitoring of wall temperatures in inductively coupled plasma torches with conventional and low-flow gas consumption

Inductively coupled plasma (ICP) sources typically used for trace elemental determination and speciation were investigated with infrared (IR) thermography to obtain spatially resolved torch temperature distributions. Infrared thermographic imaging is an excellent tool for the monitoring of temperatures in a fast and non-destructive way. This paper presents the first application of IR thermography to inductively coupled plasma torches and the possibility to investigate temperatures and thermal patterns while the ICP is operating and despite background emission from the plasma itself. A fast and easy method is presented for the determination of temperature distributions and stress features within ICP torches.     

Semi-classical treatment of line mixing effects in infrared spectroscopy

Results of infrared linewidths measurements at room temperature in the ν₃ + ν₂ - ν₂ band at 5 μ of OCS diluted in Ar are compared to semiclassical calculations. We have shown that the cross relaxation rate is very sensitive to the details of the potential.     

Representative applications of heparin-sepharose in the removal of polyamines from biological materials

Many experimental systems would greatly benefit from the availability of a simple and effective technique to remove polyamines from biological materials. We have examined the possibility of utilizing heparin-sepharose in the removal of polyamines from rat heart mitochondria, DNA-spermine complex, and fetal calf serum. Heparin-sepharose removes 90% of spermine adsorbed to the cytoplasmic surface of rat heart mitochondria. Heparin-sepharose almost totally removes spermine from DNA-spermine complex, leaving less than 0.003 mol spermine/mol DNA phosphorus. Heparin-sepharose is highly effective in removing spermine and spermidine (99.5 and 95% adsorbed, respectively) from fetal calf serum. Under the same experimental conditions only 50% of putrescine is adsorbed. A higher amount of resin corresponding to an increased capacity for putrescine must be used to achieve a satisfactory removal of putrescine.     

Metabolic fingerprinting in disease diagnosis: biomedical applications of infrared and Raman spectroscopy

The ability to diagnose the early onset of disease, rapidly, non-invasively and unequivocally has multiple benefits. These include the early intervention of therapeutic strategies leading to a reduction in morbidity and mortality, and the releasing of economic resources within overburdened health care systems. Some of the routine clinical tests currently in use are known to be unsuitable or unreliable. In addition, these often rely on single disease markers which are inappropriate when multiple factors are involved. Many diseases are a result of metabolic disorders, therefore it is logical to measure metabolism directly. One of the strategies employed by the emergent science of metabolomics is metabolic fingerprinting; which involves rapid, high-throughput global analysis to discriminate between samples of different biological status or origin. This review focuses on a selective number of recent studies where metabolic fingerprinting has been forwarded as a potential tool for disease diagnosis using infrared and Raman spectroscopies.     

Toxicological applications of gas chromatography using Fourier transform infrared spectrometry detection

Fourier transform infrared spectrometry (FTIR) used as a detection method for gas chromatography (GC) enhances the analytical performance of GC for the identification of eluted compounds. GC—FTIR technology has a major application in toxicological and forensic analysis.     

Investigation of reconstructed three-dimensional active infrared thermography of buried defects: multiphysics finite elements modelling investigation with initial experimental validation

Journal of Thermal Analysis and Calorimetry - In this paper, we use a Multiphysics approach in COMSOL? Platform to develop and validate a finite element model that simulates thermal images...     

Angle dependent effects in polarized specular reflection infrared spectroscopy

Polarized specular reflection infrared spectra of crystalline NaNO₃ were measured in the ν₃ region at angles of incidence from 75° to 10°. In addition to the LO component, the TO component of ν₃ appeared in the 65° spectrum, and the intensity of ν₃(TO) increased relative to ν₃(LO) with decreasing angle. The frequency of ν₃(LO) shifted from 1460 cm^?1 at 75° to 1448 cm^?1 at 10° angle of incidence.     

Pronounced non-Condon effects in the ultrafast infrared spectroscopy of water

In the context of vibrational spectroscopy in liquids, non-Condon effects refer to the dependence of the vibrational transition dipole moment of a particular molecule on the rotational and translational coordinates of all the molecules in the liquid. For strongly hydrogen-bonded systems, such as liquid water, non-Condon effects are large. That is, the bond dipole derivative of an OH stretch depends strongly on its hydrogen-bonding environment. Previous calculations of nonlinear vibrational spectroscopy in liquids have not included these non-Condon effects. We find that for water, inclusion of these effects is important for an accurate calculation of, for example, homodyned and heterodyned three-pulse echoes. Such echo experiments have been "inverted" to obtain the OH stretch frequency time-correlation function, but by necessity the Condon and other approximations are made in this inversion procedure. Our conclusion is that for water, primarily because of strong non-Condon effects, this inversion may not lead to the correct frequency time-correlation function. Nevertheless, one can still make comparison between theory and experiment by calculating the experimental echo observables themselves.