Simplified Fourier-transform mid-infrared spectroscopy calibration based on a spectra library for the on-line monitoring of bioprocesses

In order to significantly reduce the time involved in mid-infrared spectroscopy calibrations, a novel approach based on a library of pure component spectra was developed and tested with an aerobic Saccharomyces cerevisiae fermentation. Instead of the 30-50 standards that would have been required to build a chemometric model, only five solutions were used to assemble the library, namely one for each compound (glucose, ethanol, glycerol, ammonium and acetate). Concentration profiles of glucose, ethanol and ammonium were monitored with a fair accuracy, leading to standard error of prediction (SEP) values of 0.86, 0.98 and 0.15 g L⁻¹. Prediction of the two minor metabolites, acetate and glycerol, was less accurate and presented a detection limit of around 0.5 g L⁻¹. The overall performance of the library-based method proved to be very similar to a 49-standard chemometrics model. The model was shown to be very robust and uncorrelated, since it was able to predict accurately the concentration changes during a spiking experiment. Even though simple, this method allows more advanced calculations, such as determination of the explained variance and detection of unexpected compounds using residuals analysis.     

Prediction of total and volatile acidity in red wines by Fourier-transform mid-infrared spectroscopy and iterative predictor weighting

Fourier-transform mid-infrared (FT-MIR) spectroscopy, combined with partial least-squares (PLS) regression and IPW as feature selection method, was used to develop reduced-spectrum calibration models based on a few IR bands to provide near-real-time predictions of two key parameters for the characterization of finished red wines, which are essential from a quality assurance standpoint: total and volatile acidity. Separate PLS calibration models, correlating IR data (only considering those regions showing a high signal to noise ratio) with each response studied, were developed. Wavenumber selection was also performed applying IPW-PLS to take into account only significant predictors, in an attempt to improve the quality of the final models constructed. Using both PLS and IPW-PLS regression, prediction of the two responses modelled was performed with very high reliability, with RMSECV and RMSEP values on the order of 1% (comparable in terms of accuracy to the results provided by the respective reference analysis methods). An important advantage derived from the application of the IPW-PLS method had to do with the low number of original variables needed for modelling both total acidity (22 significant wavenumbers) and volatile acidity (only 11 selected predictor variables), in such a way that variable selection contributed to enhance the stability and parsimony properties of the final calibration models. The high quality of the calibration models proposed encourages the feasibility of implementing them as a fast and reliable tool in routine analysis for the determination of critical parameters for wine quality.     

Total synthesis of 4-epi-atpenin A5 as a potent nematode complex II inhibitor

It is clear that atpenins and their analogs are useful chemical tools for elucidation of complex II functionality and that they could act as lead compounds for the development of novel helminth complex II-specific inhibitors. Recently, we discovered 4-epi-atpenin A5 as a potent nematode complex II inhibitor during our SAR studies of atpenin A5. This result led us to embark on a concise total synthesis of 4-epi-atpenin A5. In this study, we describe the total synthesis of 4-epi-atpenin A5. Importantly, this was more concise and practical synthesis than our previous total synthesis of atpenin A5.     

Protein-protein interaction of a Pharaonis halorhodopsin mutant forming a complex with Pharaonis halobacterial transducer protein II detected by Fourier-transform infrared spectroscopy

Pharaonis halorhodopsin (pHR) functions as a light-driven inward chloride ion pump in Natoronomonas pharaonis, while pharaonis phoborhodopsin (ppR; also called pharaonis sensory rhodopsin II, pSRII), is a light sensor for negative phototaxis. ppR forms a 2:2 complex with its cognate transducer protein (pHtrII) through intramembranous hydrogen bonds: Tyr199(ppR)-Asn74(pHtrII) and Thr189(ppR)-Glu43 (pHtrII), Ser62(pHtrII). It was reported that a pHR mutant (P240T/F250Y), which possesses the hydrogen-bonding sites, impairs its pumping activity upon complexation with pHtrII. In this study, effect of the complexation with pHtrII on the structural changes upon formation of the K, L(1) and L(2) intermediates of pHR was investigated by use of Fourier-transform infrared spectroscopy. The vibrational changes of Tyr250(pHR) and Asn74(pHtrII) were detected for the L(1) and L(2) intermediates, supporting that Tyr250(pHR) forms a hydrogen bond with Asn74(pHtrII) as similarly to Tyr199(ppR). The conformational changes of the retinal chromophore were never affected by complexation with pHtrII, but amide-I vibrations were clearly different in the absence and presence of pHtrII. The molecular environment around Asp156(pHR) in helix D is also slightly affected. These additional structural changes are probably related to blocking of translocation of a chloride ion from the extracellular to the cytoplasmic side during the photocycle.     

Passive location of chemical compounds using a Fourier-transform spectroradiometer

Fourier-transform spectroradiometers designed for searching, identifying, and determining the integral concentrations of vaporous chemical compounds in open atmosphere by the method of passive location are described. Characteristics and experimental data of field tests of the developed Fourier-transform spectroradiometers are presented.     

Fourier-transform raman spectroscopy of minerals

The FTR spectra of a variety of minerals are reported, comprising carbonates, phosphates, arsenates, vanadates, sulphates, molybdates, tungstates, oxides and sulphides. It is shown that FTR can be a fast, non-destructive technique for the study of such minerals.     

Application of a digital signal processor to Fourier-transform infrared spectroscopy

Summary The application of a digital signal processor (DSP) to Fourier-transform infrared spectroscopy is described, which allows for near real-time display of the transformed interferograms as spectra.     

Fourier-transform Raman spectroscopic study of a Neolithic waterlogged wood assemblage

The use of Fourier-transform Raman spectroscopy for characterising lignocellulosics has increased significantly over the last twenty years. Here, an FT-Raman spectroscopic study of changes in the chemistry of waterlogged archaeological wood of Pinus sp. and Quercus sp. from a prehistoric assemblage recovered from northern Greece is presented. FT-Raman spectral features of biodeteriorated wood were associated with the depletion of lignin and/or carbohydrate polymers at various stages of deterioration. Spectra from the archaeological wood are presented alongside spectra of sound wood of the same taxa. A comparison of the relative changes in intensities of spectral bands associated with lignin and carbohydrates resulting from decay clearly indicated extensive deterioration of both the softwood and hardwood samples and the carbohydrates appear to be more deteriorated than the lignin. The biodeterioration of the archaeological timbers followed a pattern of initial preferential loss of carbohydrates causing significant loss of cellulose and hemicellulose, followed by the degradation of lignin.     

Combined Fourier-transform infrared imaging and desorption electrospray-ionization linear ion-trap mass spectrometry for analysis of counterfeit antimalarial tablets

This paper reports use of a combination of Fourier-transform infrared (FTIR) spectroscopic imaging and desorption electrospray ionization linear ion-trap mass spectrometry (DESI MS) for characterization of counterfeit pharmaceutical tablets. The counterfeit artesunate antimalarial tablets were analyzed by both techniques. The results obtained revealed the ability of FTIR imaging in non-destructive micro-attenuated total reflection (ATR) mode to detect the distribution of all components in the tablet, the identities of which were confirmed by DESI MS. Chemical images of the tablets were obtained with high spatial resolution. The FTIR spectroscopic imaging method affords inherent chemical specificity with rapid acquisition of data. DESI MS enables high-sensitivity detection of trace organic compounds. Combination of these two orthogonal surface-characterization methods has great potential for detection and analysis of counterfeit tablets in the open air and without sample preparation.     

In-line monitoring of esterification using a miniaturised mid-infrared spectrometer

A miniaturised mid-infrared (MIR) spectrometer attached directly to an in-line immersion probe with an attenuated total reflectance crystal has been used to monitor the progression of the batch reaction of crotonic acid and 2-butanol in toluene. Univariate calibration, using the signal at 1188 cm(-1) in the 2nd derivative spectrum, gave accurate (average error, 1.6%) and precise (average relative standard deviation, 5.2%) estimation of 2-butyl crotonate concentrations in the range 0.08-0.49 mol dm(-3). Calibration by partial least squares was of no additional benefit in this application. The performance of in-line MIR spectrometry was comparable to that of an off-line reference gas chromatography method and superior to that of other in-line process analysis techniques (near-infrared, Raman or UV-visible spectrometries).     

Fourier-transform infrared photoacoustic spectroscopy of zeolites

Photoacoustic detection is shown to be very valuable for obtaining infrared-spectroscopic data for samples with characteristics that involve very difficult sampling. The modification reactions on the zeolite mordenite, a highly scattering material, are investigated by this technique and by gas-adsorption experiments. The mechanism of the reactions between borane groups inside the channels of the mordenite and amines at different reaction temperatures is described. At low temperatures, amine- and amino-boranes are formed that polymerize at elevated temperatures if steric hindrance is absent. The implantation of boron-nitrogen compounds inside the channels of the mordenite allow a continuous and controlled variation of the accessibility of the mordenite for gas molecules such as krypton and xenon at 273 K.     

Fourier-transform infrared and Raman spectra,and ab initio calculations for cadmium-n-di-iso-propylphosphorylguanidine-di-chloride (CdDPGCl2) complex

Cadmium-n-di-isopropylphosphorylguanidine-di-chloride (CdDPGCl2) was synthesized in the solid phase and characterized previously. The Fourier transform infrared and Raman spectra of (CdDPGCl2) in the solid state were recorded and analyzed. Emphasis was placed on the vibrational assignment of the [(O2P=O-[CdCl2]-HN=C) fragment of the complete molecular structure. With the aim of assisting the vibrational assignment of the experimental spectra, a comparison with the spectra of N-di-isopropylphosphorylguanidine ligand was carried out and ab initio calculations have been performed with several effective core potentials and valence basis sets (Hay-Wadt (HW) and Stevens-Basch-Krauss (SBK)). Due to our limited computational resources, hydrogen atoms replaced the isopropyl groups. The calculated geometrical parameters showed excellent agreement with the experimental, as well as the RHF/MP2 calculated infrared wave numbers, when compared to the IR/Raman experimental wave numbers.     

A heterobimetallic ruthenium-gadolinium complex as a potential agent for bimodal imaging

Trinuclear heterobimetallic Ln(III)-Ru(II) complexes (Ln = Eu, Gd) based on a 1,10-phenanthroline ligand bearing a diethylenetriaminepentaacetic acid (DTPA) core have been synthesized and fully characterized by a range of experimental techniques. The (17)O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements of Gd(III)-Ru(II) show that, in comparison to the parent Gd-DTPA, this complex exhibits improved relaxivity, which is the result of an increase of the rotational correlation time. Relaxometry and ultrafiltration experiments indicate that the 1,10-phenanthroline ligand has a high affinity for noncovalent binding to human serum albumin, which results in a high relaxivity r(1) of 14.3 s(-1) mM(-1) at 20 MHz and 37 °C. Furthermore, the Ln(III)-Ru(II) complexes (Ln = Eu, Gd) show an intense light absorption in the visible spectral region due to metal-to-ligand charge transfer (MLCT) transitions. Upon excitation into the MLCT band at 440 nm, the complexes exhibit a bright-red luminescence centered at 610 nm, with a quantum yield of 4.7%. The luminescence lifetime equals 540 ns and is therefore long enough to exceed the fluorescent background. Monometallic lanthanide complexes have also been synthesized, and the Eu(III) analogue shows a characteristic red luminescence with a quantum yield of 0.8%. Taking into account the relaxometric and luminescent properties, the developed Gd(III)-Ru(II) complex can be considered as a potential in vitro bimodal imaging agent.     

Cocaine detection by a mid-infrared waveguide integrated with a microfluidic chip

A germanium (Ge) strip waveguide on a silicon (Si) substrate is integrated with a microfluidic chip to detect cocaine in tetrachloroethylene (PCE) solutions. In the evanescent field of the waveguide, cocaine absorbs the light near 5.8 μm, which is emitted from a quantum cascade laser. This device is ideal for (bio-)chemical sensing applications.     

Concept for a single-shot mid-infrared spectrometer using synchrotron radiation

Several attempts have been made to extend time-resolved mid infrared spectroscopy to higher time resolution. Such methods are either limited to specific samples that are cyclic and therefore allow the reaction under investigation to be repeated multiple times in the same manner, or they lack spectral resolution or sufficient signal-to noise ratio. Here, we report on a single-shot spectrometer concept which overcomes the aforementioned limitations utilizing fast linear detector arrays and highly brilliant infrared synchrotron radiation. The spectrometer may find applications, beside others, for the investigation of irreversible cascades of structural alterations in proteins.     

Fourier-transform infrared spectroscopic studies of dithia tetraphenylporphine

We present here infrared absorption spectra of dithia tetraphenylporphine and its cation in the 450–1600 and 2900–3400 cm⁻¹ regions. Most of the allowed IR bands are observed in pairs due to overallD _2h point group symmetry of the molecule. The observed bands have been assigned to the porphyrin skeleton and phenyl ring modes. Some weak bands, which are forbidden underD _2h , also appear in the spectra due to the distortion of the molecule from planarity-caused by the out-of-plane positioned N and S atoms. Increased intensity of some phenyl ring bands compared to free-base tetraphenylporphine is explained on the basis of rotation of phenyl rings towards the mean molecular plane. Contrary to the point group symmetry of cation of dithia tetraphenylporphine, certain bands are observed to be degenerate due to identical bonding arrangements in pyrrole rings of the cation     

Isolating stem cells in the inter-follicular epidermis employing synchrotron radiation-based Fourier-transform infrared microspectroscopy and focal plane array imaging

Normal function and physiology of the epidermis is maintained by the regenerative capacity of this tissue via adult stem cells (SCs). However, definitive identifying markers for SCs remain elusive. Infrared (IR) spectroscopy exploits the ability of cellular biomolecules to absorb in the mid-IR region (λ?=?2.5–25?μm), detecting vibrational transitions of chemical bonds. In this study, we exploited the cell’s inherent biochemical composition to discriminate SCs of the inter-follicular skin epidermis based on IR-derived markers. Paraffin-embedded samples of human scalp skin (n?=?4) were obtained, and 10-μm thick sections were mounted for IR spectroscopy. Samples were interrogated in transmission mode using synchrotron radiation-based Fourier-transform IR (FTIR) microspectroscopy (15?×?15?μm) and also imaged employing globar-source FTIR focal plane array (FPA) imaging (5.4?×?5.4?μm). Dependent on the location of derived spectra, wavenumber–absorbance/intensity relationships were examined using unsupervised principal component analysis. This approach showed clear separation and spectral differences dependent on cell type. Spectral biomarkers concurrently associated with segregation of SCs, transit-amplifying cells and terminally-differentiated cells of epidermis were primarily PO ₂ ^? vibrational modes (1,225 and 1,080?cm^?1), related to DNA conformational alterations. FPA imaging coupled with hierarchical cluster analysis also indicated the presence of specific basal layer cells potentially originating from the follicular bulge, suggested by co-clustering of spectra. This study highlights PO ₂ ^? vibrational modes as potential putative SC markers.

Infrared absorption of gaseous CH3OO detected with a step-scan Fourier-transform spectrometer

CH(3)OO radicals were produced upon irradiation of a flowing mixture of CH(3)I and O(2) with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved IR absorption spectra of reaction intermediates. Transient absorption bands with origins at 3033, 2954, 1453, 1408, 1183, 1117, 3020, and 1441 cm(-1) are assigned to nu(1)-nu(6), nu(9), and nu(10) modes of CH(3)OO, respectively, close to wavenumbers reported for CH(3)OO isolated in solid Ar. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predicted the geometry and the vibrational wavenumbers of CH(3)OO; the vibrational wavenumbers and relative IR intensities of CH(3)OO agree satisfactorily with these observed features. The rotational contours of IR spectra of CH(3)OO, simulated based on ratios of predicted rotational parameters for the upper and lower states and on experimental rotational parameters of the ground state, agree satisfactorily with experimental results; the mixing ratios of a-, b-, and c-types of rotational structures were evaluated based on the direction of dipole derivatives predicted quantum chemically. A feature at 995 cm(-1), ascribed to CH(3)OOI from a secondary reaction of CH(3)OO with I, was also observed.     

Fourier-transform infrared spectroscopy discriminates a spectral signature of endometriosis independent of inter-individual variation

Endometriosis is the growth of endometrial tissue outside of the uterine cavity. Its aetiology remains obscure, and it is difficult to diagnose ranging from asymptomatic to debilitating disease. Mid-infrared (IR) spectroscopy has become recognised as a potential clinical diagnostic tool. Biomolecules absorb mid-IR (4000 cm(-1) to 400 cm(-1)) and from this, a biochemical-cell fingerprint in the form of an absorbance spectrum can be derived. We set out to determine if IR spectroscopy could be used to identify underlying biochemical differences between endometrial tissues growing outside of the uterus (ectopic) from endometrial tissue of the uterus (eutopic). For comparative purposes, endometrial tissues from endometriosis-free women were also obtained (benign eutopic). Attenuated total reflection Fourier-transform IR (ATR-FTIR) spectroscopy or transmission FTIR microspectroscopy was employed for spectral acquisition. Principal component analysis (PCA)-linear discriminant analysis (LDA) was used for chemometric analysis. A clear segregation was exhibited between the three categories independent of inter-individual confounding differences. Importantly, there was a marked difference between eutopic endometrial tissue from patients with or without endometriosis. This indicates that IR spectroscopy coupled with multivariate analysis (e.g., PCA-LDA) may provide a non-invasive diagnostic tool for endometriosis. By analysing the underlying biochemistry of these endometrial tissues, this approach may facilitate a better understanding of this pathology.     

The time domain in co-stained cell imaging: time-resolved emission imaging microscopy using a protonatable luminescent iridium complex

The intense luminescence of the new complex Ir(ppy)(2)(pybz) (1) within the cytoplasm of live cells can be discriminated from the fluorescence of an organic stain, solely on the basis of the emission timescale {pybzH = 2-pyridyl-benzimidazole}. The protonated form of 1 displays red-shifted emission, and may be implicated in a superior uptake compared to Ir(ppy)(3).