Characteristic Raman Bands Research Articles

The crystal structure, infrared, Raman and density functional studies of bis(2-aminophenyl) diselenide

Bis(2-aminophenyl) diselenide exhibits a broad spectrum of biological activity against viruses, bacteria, yeasts and pathogenic fungi. In this work, for the first time the structure of bis(2-NH 2Ph)Se 2 has been determined by single crystal X-ray diffraction and vibrational spectroscopy methods. The compound crystallizes in the triclinic system, space group P 1 ¯ . There are two symmetrically independent molecules, each containing two seleno-2-aminophenyl moieties bound by the diselenide bridge. The Se–Se distances are 2.3565(2) and 2.3600(3) Å. The N–H⋯N intermolecular hydrogen bonds contribute to the formation of the zig-zag chains along the b axis. The Raman and FT-IR spectra of the title compound are reported. Comprehensive theoretical studies have been performed by using density functional B3LYP method with the 6-311+G(d,p) basis set. The calculated atom distances, bond angles and vibrational frequencies are in good agreement with experiment. Detailed assignments of the spectra have been made on the basis of the calculated potential energy distribution, PED. The ν(C–Se) stretching vibrations are assigned at 288 and 280 cm −1 (Raman). The most intense and characteristic Raman band at 252 cm −1 arises from the Se–Se stretching vibration. The presented vibrational assignment will be helpful in the spectroscopic studies of other organoselenium compounds.

Characterization of an iron smelting slag from Zimbabwe by Raman microscopy and electron beam analysis

A sample of archaeological iron slag from Northern Zimbabwe was characterised by Raman microscopy (RM) and electron beam analysis (EBA). The phases identified in a slag found at an ironmaking site not only reflect the chemical composition of the slag but can also provide crucial information regarding the reconstruction and interpretation of the metallurgical operations, such as the prevailing redox conditions in a furnace at the time of cooling. Free iron oxides, such as haematite, magnetite and wüstite, are important indicators of these redox conditions. But while classical techniques of phase identification can be used to identify the different iron oxides, they cannot distinguish between dissimilar oxidation states due to their non‐stoichiometric nature, and also the effect of substituting elements in iron oxides. RM proved invaluable in both respects. By combining the results provided by RM and EBA, it was possible to identify (1) the free iron oxides, haematite and magnetite in the original ore, and magnetite and wüstite in the slag, (2) oxidised magnetite and wüstite, characterized by a shift to higher wavenumbers of their intense characteristic Raman bands and (3) Al3+‐substituted magnetite and a solid solution between magnetite and hercynite (FeAl2O4). This pilot study aims to develop a model that enables close identification of the redox conditions by analysing the free iron oxides from a variety of smelting processes. It is hoped that this will provide an independent and quantifiable criterion to distinguish smithing slags (more oxidising) from smelting slags (more reducing), and to understand better the actual smelting process that transforms highly oxidised iron ore to fully reduced iron metal. Copyright © 2011 John Wiley & Sons, Ltd.

Study on the electrodissolution and roughening of a palladium electrode in chloride containing solutions

Potential-dependent surface electrooxidation processes of a Pd electrode in chloride containing solutions have been investigated in detail by means of in situ confocal Raman spectroscopy for the first time. In a solution of HCl, characteristic Raman bands for the oxidative coordination of Pd with Cl−, the transformation of soluble Pd(II) to Pd(IV) complexes, the electrooxidation of Cl− into Cl2, and the redox between Cl2 and Pd were all detected unambiguously during the potential ascending. While in a solution of KCl, insoluble salt films of K2PdCl4 and K2PdCl6 were found on the electrode surface due to their poor solubility. Moreover, electrochemical roughing of Pd electrode by electrodissolution–electrodeposition cycling in the HCl solution with a surfactant have been utilized to construct micro-nanostructures of Pd, which display high activity toward the electrooxidation of ethanol in an alkaline medium and obvious surface enhanced Raman spectroscopy (SERS) signals for pyridine probe molecules.

Assessment of Raman microscopy coupled with principal component analysis to examine egg yolk–pigment interaction based on the protein CH stretching region (3100–2800 cm−1)

This work seeks to identify the slight changes in the characteristic CH stretching region (3100–2800 cm−1) of a protein‐based binder and fatty acid esters from egg yolk, which may occur in complex paint samples due to the presence of particular pigments. To date, this protein region—where historic pigments do not show characteristic Raman bands—has not been used to identify possible interactions between painting materials, in spite of its potential due to the mentioned feature. This study is based on the investigation of pure egg yolk model samples and tempera model samples prepared by mixing this binder with some historic pigments (cinnabar, raw Sienna, lead white, gypsum, calcite, azurite, lapis lazuli and smalt) as binary samples. All samples were analyzed in this region by Raman microscopy (RM) coupled with principal component analysis (PCA) for three color groups (red, white and blue) separately. The results show relevant spectral changes in the CH stretching region of amino acids and polyunsaturated fatty acids esters of the egg yolk binder, particularly in the azurite, lead white and gypsum‐based tempera samples. Lesser interactions were discerned in the tempera samples made with smalt, as well as shift in the region of polyunsaturated fatty acid esters of the egg yolk binder in the cinnabar and raw Sienna‐based tempera paintings. No interactions were recognized between the egg yolk and the pigments calcite and lapis lazuli. The effectiveness of applying RM combined with PCA for identifying interaction processes between binders and pigments is demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.

A study of heavy oil fractions by Fourier-transform near-infrared Raman spectroscopy

Oil fractions with a boiling-point step size of 20°C (300 to 560°C) for six different crude oils of Western Siberia have been studied by Fourier-transform Raman and Fourier-transform IR spectroscopy. Weak bands have been more clearly revealed, previously noninterpreted bands have been attributed, and corrections to the published assignment of their characteristic Raman bands have been made. The capabilities and the informative value of the method have been shown, as applied to the determination of nitrogen heterocycles and the ratios between mono-, bi-, tri-, and polycyclic aromatic hydrocarbons or between CH2 and CH3 groups. The true band envelopes of polycyclic aromatic hydrocarbons have been found with the use of corrected difference Fourier-transform Raman spectroscopy at different temperature increments, and the tendency toward their approach to the Raman band envelopes of disordered carbon (in particular, for the case of sedimentary rocks) has been shown. A complementary application of Fourier-transform Raman and Fourier-transform near-infrared absorption spectroscopy to the monitoring of industrial streams and processes in the near-infrared region through integrated fiber-optic networks has been suggested.

Oxygen-doped activated carbon fiber cloth as electrode material for electrochemical capacitor

Novel oxygen-doped activated carbon fiber cloths (OACFC), with different compositions of surface oxygen functionalities, have been prepared by direct electrooxidative/reductive methods in an undivided electrolytic cell filled with high purity water without a supporting electrolyte under high voltage conditions. The morphology and surface chemical composition of the materials have been investigated by SEM, Raman and XPS spectroscopies. They revealed an electrochemical erosion of the CF surface upon activation, concomitant with a strong change of the D/G ratio of characteristic Raman bands and the surface O/C atomic ratio, respectively. Thus pretreated material was tested as electrodes for an electrochemical capacitor by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 3.75 M H 2SO 4. The performance of the electrochemical capacitor based on modified carbon electrodes was compared to that of an analogous device with unmodified carbon. The measurements revealed altered electrochemical behavior of the OACFC in terms of the determined capacitances. The proposed activation method is also superior to other electrochemical activation procedures, since it uses much less energy per CF surface or mass.

Raman Spectroscopic Study of Tungsten(VI) Oxosulfato Complexes in WO3−K2S2O7−K2SO4 Molten Mixtures: Stoichiometry, Vibrational Properties, and Molecular Structure

The dissolution reaction of WO3 in pure molten K2S2O7 and in molten K2S2O7-K2SO4 mixtures is studied under static equilibrium conditions in the XWO3(0) = 0-0.33 mol fraction range at temperatures up to 860 °C. High temperature Raman spectroscopy shows that the dissolution leads to formation of W(VI) oxosulfato complexes, and the spectral features are adequate for inferring the structural and vibrational properties of the complexes formed. The band characteristics observed in the W=O stretching region (band wavenumbers, intensities, and polarization characteristics) are consistent with a dioxo W(=O)2 configuration as a core unit within the oxosulfato complexes formed. A quantitative exploitation of the relative Raman intensities in the binary WO3-K2S2O7 system allows the determination of the stoichiometric coefficient, n, of the complex formation reaction WO3 + nS2O7(2-) --> C(2n-). It is found that n = 1; therefore, the reaction WO3 + S2O7(2-) > WO2(SO4)2(2-) with six-fold W coordination is proposed as fully consistent with the observed Raman features. The effects of the incremental dissolution and presence of K2SO4 in WO3-K2S2O7 melts point to a WO3 · K2S2O7 · K2SO4 stoichiometry and a corresponding complex formation reaction in the ternary molten WO3-K2S2O7-K2SO4 system according to WO3 + S2O7(2-) + SO4(2-) --> WO2(SO4)3(4-). The coordination sphere of W in WO2(SO4)2(2-) (binary system) is completed with two oxide ligands and two chelating sulfate groups. A dimeric [{WO2(SO4)2}2(μ-SO4)2](8-) configuration is proposed for the W oxosulfato complex in the ternary system, generated from inversion symmetry of aWO2(SO4)3(4-) moiety resulting in two bridging sulfates. The most characteristic Raman bands for the W(VI) oxosulfato complexes pertain to W(=O)2 stretching modes (i) at 972 (polarized) and 937 (depolarized) cm(-1) for the ν(s) and ν(as) W(=O)2 modes of WO2(SO4)2(2-), and (ii) at 933 (polarized) and 909 (depolarized) cm(-1) for the respective modes of [{WO2(SO4)2}2(μ-SO4)2](8-).

Deep UV resonant Raman spectroscopy for photodamage characterization in cells

We employed deep UV (DUV) Raman spectroscopy for characterization of molecular photodamage in cells. 244 nm light excitation Raman spectra were measured for HeLa cells exposed to the excitation light for different durations. In the spectra obtained with the shortest exposure duration (0.25 sec at 16 µW/µm2 irradiation), characteristic resonant Raman bands of adenine and guanine at 1483 cm−1 and tryptophan and tyrosine at 1618 cm−1 were clearly visible. With increasing exposure duration (up to 12.5 sec), these biomolecular Raman bands diminished, while a photoproduct Raman band at 1611 cm−1 grew. By exponential function fitting analyses, intensities of these characteristic three bands were correlated with sample exposure duration at different intensities of excitation light. We then suggest practical excitation conditions effective for DUV Raman observation of cells without photodamage-related spectral distortion.

Raman spectroscopic study on sodium hyaluronate: an effect of proton and γ irradiation

AbstractRaman spectroscopy was applied to the analysis of structural changes in lyophilised sodium hyaluronate after proton and γ irradiation (0.5, 5, 50, 100, 200 and 600 Gy). Characteristic Raman bands of the polysaccharide were sensitive to irradiation. Significant damage was observed at doses of 50 Gy or higher. The spectral changes confirmed radiation‐induced loss of native solution conformation, destruction of primary structure, fragmentation, cross‐linking and elimination of functional groups. Differences in the effects of proton and γ radiation on sodium hyaluronate are discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Feasibility of Raman microspectroscopic identification of biomarkers through gypsum crystals

The miniaturized Raman spectrometer is considered to be a candidate instrument for the Pasteur payload (the ExoMars mission scheduled for 2018). This mission will, for the first time, combine mobility and access to subsurface locations where organic molecules might be well preserved. Evaporitic crystals are among the potential protected habitats that have been postulated. Various concentrations of biomarkers (beta-carotene, glycine and phthalic acid) dispersed in a gypsum matrix were analyzed through transparent mineral (gypsum) plates of different thicknesses. By doing so, conditions were simulated in which biomarkers were trapped within evaporitic crystals. Using a long-working distance objective, all studied concentrations of biomarkers mixed in gypsum powder were detected. The characteristic Raman bands were easily observable for a 10% mixture of all chosen biomarkers not only through a 3.3 mm plate and but even through a 5.2 mm plate. It was possible to detect key Raman bands of 1% phthalic acid/gypsum mixture and 1% beta-carotene/gypsum mixture even through a 5.2 mm gypsum plate. The 1% beta-carotene/gypsum mixture was still clearly distinguishable through an 8.5 mm gypsum crystal due to the known resonance Raman effect of the molecule.

Design and synthesis of Raman reporter molecules for tissue imaging by immuno‐SERS microscopy

The design and synthesis of Raman reporter molecules comprising olefin or alkyne moieties with strong and characteristic vibrational Raman bands is presented. Chemisorption onto the surface of colloidal Au/Ag shells yields a self-assembled monolayer. Hydrophilic stabilization of such SERS labels can be achieved by short terminal ethylene glycol units attached to the Raman reporter. Encapsulation by silica with subsequent functionalization of the glass surface allows the conjugation to biomolecules such as antibodies. We demonstrate the use of SERS-labeled antibodies for tissue imaging of the tumor suppressor p63 in prostate biopsies.

The determination of captopril in Solution by Raman spectroscopy

Captopril, 1-[(2S)-3-mercapto-2-methyl propionyl]-Lproline, is an angiotensin converting enzyme (ACE) inhibitor, which reduces peripheral resistance and lowers blood pressure. It is widely used in the hypertensive ailments and incongestive heart failure treatment. Due to such crucial pharmacological importance, development of simple and accurate methods for the determination of captopril is desired. In this work, the normal Raman spectra of the captopril in different concentrations were studied, and the relationship between the Raman intensity and the concentrations of the captopril was quantificationally analysed. By selecting appropriate characteristic Raman bands of the cptopril, the solution of some captopril purchased in a local pharmacy was quantificationally determined. A quantificational linear relationship between the Raman intensity and the concentrations of captopril was obtained, and it is little affected by other compounds in the solution of captopril. This study provides an effective technique for the quantificational determination of captopril in solutions, and it has a potential application in the analysis of medicament.

Distribution and clearance of PEG-single-walled carbon nanotube cancer drug delivery vehicles in mice.

To study the distribution and clearance of polyethylene glycol (PEG)-ylated single-walled carbon nanotube (SWCNTs) as drug delivery vehicles for the anticancer drug cisplatin in mice. PEG layers were attached to SWCNTs and dispersed in aqueous media and characterized using dynamic light scattering, scanning transmission electron microscopy and Raman spectroscopy. Cytotoxicity was assessed in vitro using Annexin-V assay, and the distribution and clearance pathways in mice were studied by histological staining and Raman spectroscopy. Efficacy of PEG-SWCNT-cisplatin for tumor growth inhibition was studied in mice. PEG-SWCNTs were efficiently dispersed in aqueous media compared with controls, and did not induce apoptosis in vitro. Hematoxylin and eosin staining, and Raman bands for SWCNTs in tissues from several vital organs from mice injected intravenously with nanotube bioconjugates revealed that control SWCNTs were lodged in lung tissue as large aggregates compared with the PEG-SWCNTs, which showed little or no accumulation. Characteristic SWCNT Raman bands in feces revealed the presence of bilary or renal excretion routes. Attachment of cisplatin on bioconjugates was visualized with Z-contrast scanning transmission electron microscopy. PEG-SWCNT-cisplatin with the attached targeting ligand EGF successfully inhibited growth of head and neck tumor xenografts in mice. PEG-SWCNTs, as opposed to control SWCNTs, form more highly dispersed delivery vehicles that, when loaded with both cisplatin and EGF, inhibit growth of squamous cell tumors.

Stress-induced phase transitions in diamond

A phase transformation in diamond into an intermediate carbon phase (ICP) was revealed in regions of maximal shear stress of diamond anvils. The transition was stimulated by additional stresses supplied to the compressed anvils with torque by a rotation of the anvil around the anvil's axis; maximal shear stress approached 55 GPa during the rotation. Creation of an ICP is considered as a mechanism of the stress-induced stability loss of the diamond structure. The characteristic Raman bands of ICP near 250, 500, 650–850 and 1050–1390 cm−1 were observed in the failure regions.

Rapid in situ detection of street samples of drugs of abuse on textile substrates using microRaman spectroscopy

Trace amounts of street samples of cocaine hydrochloride and N-methyl-3,4-methylenedioxy-amphetamine (MDMA) on natural and synthetic textiles were successfully detected in situ using confocal Raman microscopy. The presence of some excipient bands in the spectra of the drugs did not prevent the unambiguous identification of the drugs. Raman spectra of the drugs were readily obtained without significant interference from the fibre substrates. Interfering bands arising from the fibre natural or synthetic polymer structure and/or dye molecules did not overlap with the characteristic Raman bands of the drugs. If needed, interfering bands could be successfully removed by spectral subtraction. Also, Raman spectra could be acquired from drug particles trapped between the fibres of highly fluorescent textile specimens. The total acquisition time of the spectra of the drug particles was 90 s accomplished non-destructively and without detachment from their substrates. Sample preparation was not required and spectra of the drugs could be obtained non-invasively preserving the integrity of the evidential material for further analysis.

Synthesis of Fe 3O 4\\SiO 2\\Ag nanoparticles and its application in surface-enhanced Raman scattering

To obtain a recyclable surface-enhanced Raman scattering (SERS) material, we developed a composite of Fe 3O 4\\SiO 2\\Ag with core\\shell\\particles structure. The designed particles were synthesized via an ultrasonic route. The Raman scattering signal of Fe 3O 4 could be shielded by increasing the thickness of the SiO 2 layer to 60 nm. Dye rhodamine B (RB) was chosen as probe molecule to test the SERS effect of the synthesized Fe 3O 4\\SiO 2\\Ag particles. On the synthesized Fe 3O 4\\SiO 2\\Ag particles, the characteristic Raman bands of RB could be observed when the RB solution was diluted to 5 ppm (1×10 −5 M). Furthermore, the synthesized particles could keep their efficiency till four cycles.

Discrimination of Green Arabica and Robusta Coffee Beans by Raman Spectroscopy

This paper presents an approach that may be applied as an accurate and rapid tool for classifying coffee beans on the basis of the specific kahweol content. Using Fourier-transform Raman spectroscopy with 1064 nm excitation it is possible to monitor the characteristic Raman bands of kahweol in green coffee beans without chemical and physical processing of the beans. The procedure was optimized on the basis of 83 and 125 measurements of whole and ground beans, respectively, using coffee samples of two different species, Coffea arabica L. and Coffea canephora L. (var. Robusta), and different origins (Asia, Africa, and South America). The relative contribution of the kahweol in individual beans can be determined quantitatively by means of a component analysis of the spectra, yielding a spectral kahweol index (σka) that is proportional to the relative content of kahweol in a coffee bean. The reproducibility of the spectroscopic measurement and analysis was found to be 3.5%. Individual beans of the same type and origin reveal a scattering of the σka values. Nevertheless, an unambiguous distinction between Arabica and Robusta samples is possible on the basis of single-bean measurements as the σka values are greater than and less than 10 for Arabica and Robusta coffees, respectively. Measurements of whole and ground beans afforded very similar results, despite the heterogeneous distribution of kahweol within a bean. Unlike conventional analytical techniques, the single-bean sensitivity of the present approach may also allow for a rapid detection of unwanted admixtures of low-value Robusta coffee to high-quality and more expensive Arabica coffee.

Lithocholic Acid Derivative as a Model for Artificial Receptors: A Raman Study

Two lithocholic acid (LCA) derivatives — mono- and diesters (newly synthetised) — are studied for their main conformational preferences, by Raman spectroscopy coupled to theoretical (DFT) methods. Raman bands characteristic of each compound were assigned, allowing an accurate and rapid identification of this kind of systems. The conformational preferences of the LCA diester were related with its ability to function as a model for artificial receptors, displaying a tailored structural profile. Keywords: Lithocholic acid derivatives, Artificial receptors, Conformational analysis, Raman spectroscopy

Raman spectroscopic approach to analytical astrobiology: the detection of key geological and biomolecular markers in the search for life

The compilation of this Theme Issue of Philosophical Transactions of the Royal Society on the theme of Raman spectroscopic analysis of materials from extreme environments is timely for several reasons, perhaps the most significant of these being the realization in the last decade that this technique

Identification of the chemical forms of uranium compounds in micrometer-size particles by means of micro-Raman spectrometry and scanning electron microscope

We used a micro-Raman spectrometer with two different laser excitation sources (514 and 785 nm) and variable laser powers to identify some uranium chemical species contained in airborne particulate matter. In the first part of this paper, we demonstrate that characteristic Raman bands mentioned in the literature for several uranium compounds relevant in the nuclear industry (UO 2, UO 4·(4H 2O), U 3O 8, UO 2F 2 and UF 4) can be identified in particles in the few μm to 30 μm size range. In the second part of the paper, we describe a method to carry out Raman analysis on airborne uranium particles sampled along with a majority of other kinds of particles simply by dabbing adhesive carbon disks on dusty surfaces. This methodology involves an SEM equipped with an energy dispersive X-ray analyser and software for automated detection of particles specifically to locate uranium particles on the substrate before the Raman analysis. Then the sample holder is transferred to the micro-Raman spectrometer and particles are relocated using landmarks and simple geometric calculations. Raman analyses are carried out with the laser that gives the best signal to noise ratio. With such a method particles as small as 5 μm can be efficiently analysed, although most of the smaller particles cannot be analysed due to limited precision of the relocation process. This methodology was successfully applied to 20 particles collected in a nuclear facility.