Characterization of thalidomide using Raman spectroscopy

Thalidomide is a potent anticancer therapeutic drug whose mechanism of action has not yet been elucidated. In this report, experimental Raman spectroscopy is used to determine and characterize the vibrational frequencies of the drug. These normal modes are then compared to their quantum mechanical counterparts, which have been computed using density functional theory. Upon analysis of the spectra, we found that there was a high level of agreement between the wavenumbers. As such, this spectroscopic technique may be a viable tool for examining the way in which this drug interacts with its target molecules.     

Aromatic amino acids providing characteristic motifs in the Raman and SERS spectroscopy of peptides

Raman and surface-enhanced Raman spectroscopies (SERS) are potentially important tools in the characterization of biomolecules such as proteins and DNA. In this work, SERS spectra of three cysteine-containing aromatic peptides: tryptophan-cysteine, tyrosine-cysteine, and phenylalanine-cysteine, bound to Au nanoshell substrates, were obtained, and compared to their respective normal Raman spectra. While the linewidths of the SERS peaks are significantly broadened (up to 70%), no significant spectral shifts (<6 cm (-1)) of the major Stokes modes were observed between the two modalities. We show that the Raman and SERS spectra of penetratin, a cell-penetrating peptide oligomer, can be comprised quite reliably from the spectra of its constituent aromatic amino acids except in the backbone regions where the spectral intensities are critically dependent on the length and conformations of the probed molecules. From this study we conclude that, together with protein backbone groups, aromatic amino acid residues provide the overwhelmingly dominant features in the Raman and SERS spectra of peptides and proteins when present. It follows that the Raman modes of these three small constructed peptides may likely apply to the assignment of Raman and SERS features in the spectra of other peptides and proteins.     

Characterization of diatomaceous silica by Raman spectroscopy

The network characteristic of a selection of diatomaceous silica derived from China has been investigated using Raman spectroscopy. Before any thermal treatment of the sample, two prominent bands of 607 and circa 493 cm(-1) are resolved in the Raman spectra of diatomaceous silica, corresponding to the (SiO)3-ring breathing mode of D2-line and the O3SiOH tetrahedral vibration mode of D1-line, respectively. This is more similar to the pyrogenic silica rather than the silica gel. For the latter, to obtain a (SiO)3-ring, the sample must be heated between 250 and 450 degrees C. Significant difference is also found between the diatomaceous silica and other natural silicas, e.g. in the Raman spectra of sedimentary and volcanic opals, neither D1 nor D2 band is detected in previous reports.     

Polarized Raman spectra and intensities of aliphatic amino acids

Raman spectra of aliphatic α-l-amino acids, glycine, alanine, and valine were re-investigated both in aqueous solution and deuterium oxide solution. The spectra were taken of the zwitterionic and of the completely deprotonated form of the amino acids. Spectra of leucine and isoleucine were studied in water at the isoelectric point. Spectra were recorded both with parallel and perpendicular polarization and the isotropic and anisotropic scattering components were isolated.The integrated intensities of CH stretch, CC stretch and carboxylate bend vibrations are discussed. Linear relations between the number of CC and CH bonds and the total scattered intensity in the appropriate spectral regions are observed. The sum over the carboxylate modes shows characteristic intensities for the first three members of the aliphatic amino acids.An increase of isotropic scattering of ϱ_co2 near 510 cm⁻¹ with increasing chain length of the amino acid (or with increasing concentration) is interpreted as the result of micelle formation.     

Characterization of fuel gases with fiber-enhanced Raman spectroscopy

Common gaseous fuels are mixtures of several components. As the properties of the fuels can vary with the composition, but combustion needs to be stable, reliable analytical methods are highly sought after. Raman spectroscopic methods have proved their suitability for the characterization of diverse gaseous mixtures. They have the potential to overcome existing limitations of established technologies, since they are fast, non-consumptive, and accurate. Here, we demonstrate a gas sensor based on fiber-enhanced Raman spectroscopy (FERS) for fuel gas monitoring. Online detection of all gas components, including alkanes, carbon dioxide (CO₂), nitrogen (N₂), and hydrogen sulfide (H₂S), for varying concentration ranges from tens of vol% down to the ppm level enables a comprehensive characterization of the fuels. The developed sensor system features a pinhole assembly which sufficiently reduces the background signal from the fiber to enable the detection of C2–C4 alkanes occurring in low concentrations. Detection limits in the low ppm region were achieved for the minor components of fuel gases, which allow the online monitoring of necessary purification steps, e.g., for biogas. The obtained results indicate that fiber-enhanced Raman sensors have the potential for comprehensive online and onsite gas sensing for fuel gas quality control.

Graphical abstract

     

Study of N-aldonoyl amino acids by IR spectroscopy

Conclusions IR spectroscopy is suggested as a convenient method for determining the difference in the cyclic (dioxomorpholine) and acyclic forms of N-aldonoyl amino acid derivatives. It has been shown that in the acyclic forms, unlike the cyclic, there are strong absorption bands at 1570 cm^–1 and 690–720 cm^–1 corresponding to the amide II and V vibrations.M. M. Shemyakin Institute of the Chemistry of Natural Compounds of the Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 381–384, May–June, 1974.     

Raman spectra of amino acids and their aqueous solutions

Amino acids are the basic "building blocks" that combine to form proteins and play an important physiological role in all life-forms. Amino acids can be used as models for the examination of the importance of intermolecular bonding in life processes. Raman spectra serve to obtain information regarding molecular conformation, giving valuable insights into the topology of more complex molecules (peptides and proteins). In this paper, amino acids and their aqueous solution have been studied by Raman spectroscopy. Comparisons of certain values for these frequencies in amino acids and their aqueous solutions are given. Spectra of solids when compared to those of the solute in solution are invariably much more complex and almost always sharper. We present a collection of Raman spectra of 18 kinds of amino acids (L-alanine, L-arginine, L-aspartic acid, cystine, L-glutamic acid, L-glycine, L-histidine, L-isoluecine, L-leucine, L-lysine, L-phenylalanine, L-methionone, L-proline, L-serine, L-threonine, L-tryptophan, L-tyrosine, L-valine) and their aqueous solutions that can serve as references for the interpretation of Raman spectra of proteins and biological materials.     

Polymer crystallinity studied using Raman spectroscopy

The application of Raman spectroscopy to the study of crystallinity in polymers has been examined. In particular, Fourier transform (FT)-Raman spectroscopy has been applied in a number of studies in recent years to investigate crystallinity in a variety of polymers. The polymers discussed in this review are polyethylene, polystyrene, poly(ether ether ketone), polyamides, poly(ethylene terephthalate), elastomers, liquid crystalline polymers, inorganic polymers and certain polymer blends.     

Characterization and determination of someα-amino acids using optical rotatory dispersion spectroscopy

Summary The optical rotatory dispersion spectra of 16-amino acids have been recorded over wave lengths down to 200 nm. The linear relationship between the molecular rotation in 0.1N HCl and the concentration permits the rapid and simple microdetermination of various-amino acids in the range of 0.2 to 500 mg/ml with an average recovery of 98%. The data on the molecular rotation of the various acids and their relation with the nature of the substituent groups are also presented.

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Charakterisierung und Bestimmung einiger -Aminosäuren mit Hilfe der optischen Rotations-Dispersions-Spektroskopie

Zusammenfassung Die Spektren der optischen Rotations-Dispersion von 16-Aminosäuren wurden bei Wellenlängen bis herunter auf 200 nm gemessen. Das lineare Verhältnis zwischen der molekularen Rotation in 0,1N HCl und der Konzentration ermöglicht die rasche und einfache Mikrobestimmung verschiedener-Aminosäuren zwischen 0,2 und 500 mg/ml mit durchschnittlich 98% Genauigkeit. Die Daten der molekularen Rotation der verschiedenen Aminosäuren und deren Abhängigkeit von der Art der Substituenten-Gruppen wurden ebenfalls angegeben.

     

Characterization of lipid extracts from brain tissue and tumors using Raman spectroscopy and mass spectrometry

Brain tissue is characterized by high lipid content. The amount of lipids decreases, and its composition changes in the most frequent primary brain tumor, the glioma. Scope of the current paper was to extract quantitatively lipids from porcine and human brain tissue as well as from five human gliomas using a modified protocol according to Folch. The lipid extracts were studied by Raman spectroscopy with 785 nm excitation and by mass spectrometry with electron impact ionization. Porcine and human brain tissues have similar water and lipid content and show similar Raman and mass spectra. In contrast, gliomas are characterized by increased water content and decreased lipid content. Elevated phosphatidylcholine to cholesterol ratios in lipid extracts of gliomas were indicated by Raman bands of the choline group and cholesterol. Due to its higher sensitivity, mass spectrometry detected increased levels of cholesterol ester relative to cholesterol in lipid extracts of gliomas. For comparison, thin tissue sections were prepared from the glioma specimens before lipid extraction; infrared spectroscopic images were recorded and analyzed by a supervised classification model. This study demonstrates how to improve the analysis of brain tumors and to complement the diagnosis of brain pathologies using a multimodal approach.     

Rapid monitoring of antibiotics using Raman and surface enhanced Raman spectroscopy

Comparatively few studies have explored the ability of Raman spectroscopy for the quantitative analysis of microbial secondary metabolites in fermentation broths. In this study we investigated the ability of Raman spectroscopy to differentiate between different penicillins and to quantify the level of penicillin in fermentation broths. However, the Raman signal is rather weak, therefore the Raman signal was enhanced using surface enhanced Raman spectroscopy (SERS) employing silver colloids. It was difficult by eye to differentiate between the five different penicillin molecules studied using Raman and SERS spectra, therefore the spectra were analysed by multivariate cluster analysis. Principal components analysis (PCA) clearly showed that SERS rather than the Raman spectra produced reproducible enough spectra to allow for the recovery of each of the different penicillins into their respective five groups. To highlight this further the first five principal components were used to construct a dendrogram using agglomerative clustering, and this again clearly showed that SERS can be used to identify which penicillin molecule was being analysed, despite their molecular similarities. With respect to the quantification of penicillin G it was shown that Raman spectroscopy could be used to quantify the amount of penicillin present in solution when relatively high levels of penicillin were analysed (>50 mM). By contrast, the SERS spectra showed reduced fluorescence, and improved signal to noise ratios from considerably lower concentrations of the antibiotic. This could prove to be advantageous in industry for monitoring low levels of penicillin in the early stages of antibiotic production. In addition, SERS may have advantages for quantifying low levels of high value, low yield, secondary metabolites in microbial processes.     

Fast Raman spectroscopy of cytochrome c using intracavity resonance Raman amplification

The resonance Raman spectrum of cytochrome c (5 × 10^?4 M) was obtained using the method of resonance Raman amplification (RRA) in a dye laser resonator in 30 ns. The second harmonic of a Q-switched Nd glass laser was used as an excitation source and the spectra were recorded using a photographic plate.     

A Rheumatoid arthritis study using Raman spectroscopy

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the joints and can lead to a progressive destruction of articular cartilage and bone. In this study, the specificity and sensitivity of the RA diagnostic methods based on the receiver-operating characteristic curves for monitoring C-reactive protein (CRP) and rheumatoid factor (RF) were compared with the Raman spectroscopic diagnostic method developed in this work. Sera from 24 patients with rheumatoid arthritis and from 16 healthy individuals were analyzed to assess the biochemical composition and presence of inflammatory activity by the aforementioned methods. By comparing with the clinical results for specificity and sensitivity from the RF and CRP tests, we show that the overall results from the newly developed Raman method were significantly better, with a specificity of 96%, a sensitivity of 88%, and correctly identifying 92% of the RA and healthy individuals, while the RF test gave a specificity of 100% and a sensitivity of 54%, and the CRP test gave a specificity of 87% and a sensitivity of 58%, respectively.     

Raman amplification spectroscopy using pulsed dye lasers

A picosecond laser system consisting of a mode-locked argon-ion laser synchronously pumping two dye lasers is used for studies of Raman amplification spectra. The two dye laser beams, one kept constant in frequency while the other is tunable, coincide in the Raman sample. Recording the gain or the loss in intensity of one of the lasers as a function of frequency difference produces the Raman spectrum. Good signal to noise ratios have been obtained for a variety of liquids and solids. Fluorescing samples can be studied in the Inverse Raman method where the loss on the higher frequency laser is monitored.     

Towards single-microorganism detection using surface-enhanced Raman spectroscopy

The identification and discrimination of microorganisms is important not only for clinical reasons but also for pharmaceutical clean room production and food-processing technology. Vibrational spectroscopy such as IR, Raman, and surface-enhanced Raman scattering (SERS) can provide a rapid ‘fingerprint’ on the chemical structure of molecules and is used to obtain a ‘fingerprint’ from microorganisms as well. Because of the requirement that a single bacterium cell and noble metal nanoparticles must be in close contact and the lack of a significant physical support to hold nanoparticles around the single bacterium cell, the acquisition of SERS spectra for a single bacterium using colloidal nanoparticles could be a challenging task. The feasibility of SERS for identification down to a single bacterium is investigated. A Gram-negative bacterium, Escherichia coli, is chosen as a model for the investigation. Because the adsorption of silver nanoparticles onto the bacterial cell is an exclusive way for locating nanoparticles close to the bacterium cell, the absorption characteristics of silver nanoparticles with different surface charges are investigated. It is demonstrated that the citrate-reduced colloidal silver solution generates more reproducible SERS spectra. It is found that E. coli cells aggregate upon mixing with silver colloidal solution, and this may provide an additional benefit in locating the bacterial cell under a light microscope. It is also found that a laser wavelength in the UV region could be a better choice for the study due to the shallow penetration depth. It is finally shown that it is possible to obtain SERS spectra from a single cell down to a few bacterial cells, depending on the aggregation properties of bacterial cells for identification and discrimination.     

Investigating microcrystalline cellulose crystallinity using Raman spectroscopy

Cellulose - Microcrystalline cellulose (MCC) is a semi-crystalline material with inherent variable crystallinity due to raw material source and variable manufacturing conditions. MCC crystallinity...     

Quantitative monitoring of yeast fermentation using Raman spectroscopy

Compared to traditional IR methods, Raman spectroscopy has the advantage of only minimal interference from water when measuring aqueous samples, which makes this method potentially useful for in situ monitoring of important industrial bioprocesses. This study demonstrates real-time monitoring of a Saccharomyces cerevisiae fermentation process using a Raman spectroscopy instrument equipped with a robust sapphire ball probe. A method was developed to correct the Raman signal for the attenuation caused by light scattering cell particulate, hence enabling quantification of reaction components and possibly measurement of yeast cell concentrations. Extinction of Raman intensities to more than 50 % during fermentation was normalized with approximated extinction expressions using Raman signal of water around 1,627 cm^?1 as internal standard to correct for the effect of scattering. Complicated standard multi-variant chemometric techniques, such as PLS, were avoided in the quantification model, as an attempt to keep the monitoring method as simple as possible and still get satisfactory estimations. Instead, estimations were made with a two-step approach, where initial scattering correction of attenuated signals was followed by linear regression. In situ quantification measurements of the fermentation resulted in root mean square errors of prediction (RMSEP) of 2.357, 1.611, and 0.633 g/L for glucose, ethanol, and yeast concentrations, respectively.     

Normal Raman and surface enhanced Raman spectroscopic experiments with thin layer chromatography spots of essential amino acids using different laser excitation sources

A comparative study of the feasibility and efficiency of Raman spectroscopic detection of thin layer chromatography (TLC) spots of some weak Raman scatterers (essential amino acids, namely, glycine and L-forms of alanine, serine, valine, proline, hydroxyproline, and phenylalanine) was carried out using four different visible and near-infrared (NIR) laser radiations with wavelengths of 532, 633, 785, and 1064 nm. Three types of commercial TLC plates were tested and the possibility of inducing surface enhanced Raman scattering (SERS) by means of Ag-sol was also investigated. The spectra obtained from spotted analytes adsorbed on TLC plates were of very different quality strongly depending on the excitation wavelength, the wetness of the samples, and the compounds examined. The best results were obtained with the simple silica TLC plate, and it has been established that the longest wavelength (lowest energy) NIR excitation of a Nd:YAG laser is definitely more suitable for generating normal Raman scattering of analyte spots than any of the visible radiations. Concerning SERS with application of Ag-sol to the TLC spots, 1-3 orders of magnitude enhancement was observed with wet samples, the greatest with the 532 nm radiation and gradually smaller with the longer wavelength excitations. It is shown, however, that due to severe adsorption-induced spectral distortions and increased sensitivity to microscopic inhomogeneity of the sample, none of the SERS spectra obtained with the dispersive Raman microscope operating in the visible region were superior to the best NIR normal FT-Raman spectra, as far as sample identification is concerned.