High pressure Raman spectra of DL-lysine hydrochloride

DL-lysine hydrochloride crystals were studied by Raman spectroscopy under hydrostatic pressure using a diamond anvil cell from ambient pressure up to 9.8 GPa in the spectral range from 1150 to 40 cm⁻¹. Changes in the Raman spectrum were observed in all spectral regions analyzed. In particular, modifications in the lattice modes indicate that the crystal undergoes a phase transition. The classification of the vibrational modes, the behavior of their band wavenumber as a function of the pressure and the reversibility of the phase transitions are also discussed.     

Raman spectroscopic study of the uranyl sulphate mineral zippeite: low wavenumber and U–O stretching regions

The uranyl sulphate mineral zippeite was studied by Raman spectroscopy. The phase purity of the sample was initially checked by X-ray powder diffraction and its chemical composition was defined by electron microprobe (wavelength dispersive spectroscopy, WDS) analysis. The Raman spectroscopy research focused on the low wavenumber and uranyl stretching vibration regions. Vibration bands down to 50 cm^–1 were tentatively assigned. The U–O bond lengths were calculated based on empirical relations. Inferred values are consistent with those obtained from the crystal structure analysis of synthetic zippeite. Number of bands was interpreted on the basis of factor group analysis.     

In situ FT‐Raman spectroscopic study of the conformational changes occurring in isotactic polypropylene during its melting and crystallization processes

The conformational changes occurring in isotactic polypropylene during the melting and crystallization processes have been carefully investigated using FT‐Raman spectroscopy at temperatures below, at, and above the polymer melting point. Results confirmed the retention of some crystallinity up to +210 °C, which is 50 °C above the melting point. It was found that, at temperatures just above the melting point (1–10 °C), there is still some short range order of at least 12 monomer units long in certain regions of the melt. At 10 °C above the melting point, the short range order drops below 12 monomer units resulting in the disappearance of the Raman band at 841 cm^–1. Vice versa, the experimental measurements show that the iPP melt system is stable when the persistence length of helical sequences is less than 12 monomer units. As soon as the helix length exceeds 12 units, the 3₁ helix conformation extends quickly and then crystallization occurs. These results are discussed in terms of Imai's microphase separation theory and it agreed very well with it. Also, from our observations for correlation splitting, Raman bands related to conformational states were identified. This analysis indicates the existence of three different conformational states at 808, 830, and 841 cm^–1. The 808 cm^–1 band was assigned to helical chains within crystals (representing crystalline phase). The 841 cm^–1 band was shown to be composed of a band at 841 cm^–1, assigned to shorter chains in helical conformation with isomeric defects (representing the isomeric defect phase), and a broader band at 830 cm^–1 assigned to chains in nonhelical conformation (representing the melt‐like amorphous phase). This indicates the detection of a three‐phase structure in iPP, where a third phase could be due to the presence of defect regions within the crystalline region, or due to the presence of an amorphous–crystal interphase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2173–2182, 2006     

Chemical composition of bio-oil produced by co-pyrolysis of biopolymer/polypropylene mixtures with K2CO3 and ZnCl2 addition

The chemical composition of liquid products of cellulose and lignin co-pyrolysis with polypropylene at 450 °C with and without the potassium carbonate or zinc chloride as an catalyst was investigated. The yield of liquid products of pyrolysis was in the range of 26–45 wt% and their form was liquid or semi-solid highly depending on the composition of sample and pyrolysis conditions. The potassium carbonate and zinc chloride addition to blends has also influenced the range of samples decomposition as well as the chemical composition of resulted bio-oils. All bio-oils from biopolymer and polypropylene mixtures were three-phase (water, oil and solid). While zinc chloride acted as catalyst, all bio-oils obtained from biopolymer and polypropylene mixtures were yellow liquids with well-separated water and oil phases. All analyses proved that the structure and quality of bio-oil strongly depends on both the composition of the blend and the presence of the additive. The FT-IR and GC–MS analyses of oils showed that oxygen functionalities and hydrocarbons contents highly depend on the composition of biomass/polypropylene mixture. Results confirmed the significant removal and/or transformation of oxygen containing organic compounds, i.e. levoglucosan, 1,6-anhydro-β-d-glucofuranose and phenol derivatives due to the zinc chloride presence during pyrolysis process. All analyses showed that zinc chloride as catalyst was generally much more effective for removal of hydroxyl and methoxy groups than was potassium carbonate. It was demonstrated in this study that catalysts used in present work lead to the increased char yield and improved the fuel quality of bio-oil.     

High pressure Raman spectra of d-threonine crystal

Raman spectra of d-threonine crystal were recorded for pressures up to 8.5 GPa. Modifications in the lattice modes indicate that the crystal undergoes two structural phase transitions, the first in the 1.9–2.4 GPa pressure range and the second in the 5.1–6.0 GPa pressure range. Splitting of modes and changes in the intensity of several bands suggest a conformational reorientation of the molecule in the crystal framework between 3.5 and 4.3 GPa. We discussed ours results by comparing with previous high-pressure investigation on l-conformer.     

Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition

Polarized Raman spectroscopy was used to study the lattice structure of BiFeO₃ films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO₃ films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50–700 cm⁻¹ were identified based on group theory. The symmetries of the high order Raman modes in 900–1500 cm⁻¹ of BiFeO₃ are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400–700 cm⁻¹ in return. Moreover, the lattice structures of BiFeO₃ films are identified consequently on the basis of Raman spectroscopy. BiFeO₃ films on SrRuO₃ coated SrTiO₃ (0 0 1) substrate, CaRuO₃ coated SrTiO₃ (0 0 1) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO₃ film on SrRuO₃ coated Nb: SrTiO₃ (0 0 1) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO₃ films.     

Synthesis and characterization of a new organic nonlinear optical crystal: l-Phenylalaninium maleate

l-Phenylalaninium maleate (abbreviated as LPM) chemical formula C₉H₁₂NO₂⁺·C₄H₃O₄⁻, a new organic nonlinear optical crystal was grown by slow evaporation technique. Transparent needle shaped crystal of dimensions 7 mm × 1 mm × 0.5 mm was obtained. Single crystals of LPM have been subjected to X-ray diffraction analysis to estimate the lattice parameters and the space group. The powder X-ray diffractogram of the crystal has been recorded and the reflections from various planes are identified. The XRD studies confirm the crystalline nature. The qualitative analysis on the crystal has been carried out using Fourier transform infrared (FTIR) and Fourier transform Raman (FTRaman) spectral measurements. The presence of hydrogen and carbon in the grown crystal was confirmed by using proton and carbon nuclear magnetic resonance (NMR) spectral analyses. Optical behaviour of the crystal was investigated using UV–vis spectroscopy. The thermal stability of the crystal was analysed with the aid of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The nonlinear optical (NLO) property of the crystal was tested by Nd:YAG laser source.     

Pressure dependent Raman studies in the K2Mo2O7·H2O crystal

The pressure dependent Raman scattering in the potassium molybdenum oxide hydrate crystal, K₂Mo₂O₇·H₂O, was measured. The high pressure Raman study showed, that the compound remains in the triclinic structure within the 0.0–3.81 GPa range and undergoes a structural phase transition between 3.81 and 4.13 GPa. This particular phase transition is most likely connected with changes in the Raman spectrum, in which the number of modes associated originally with the stretching vibrations in the MoO₅ and MoO₆ units is increased. However, the phase at atmospheric pressure shows bands due to the presence of only one equivalent site, while in the high-pressure phase, two bands are associated with the stretching modes. Continuing the pressure evolution up to 17.04 GPa, two further phase transitions occurred in this crystal in the 6.3–8.1 GPa and the 12.3–14.0 GPa range, respectively. The Raman spectra measured at about 17.04 GPa presented a crystal structure, which experienced a pre-amorphization with a total loss of all lattice modes. This particular result is indicative that this material may have undergone a complete amorphization at pressures larger than 17.04 GPa. Then, the reversible character in the triclinic P-1 (C_i¹) structure was recovered after releasing the pressure.     

Nonlinear regression by visualization of the sum of residual space applied to the integrated copolymerization equation with errors in all variables. II. Application to the system methyl methacrylate-α-methylene-γ-butyrolactone using on-line Raman spectroscopy

The copolymerization of α-methylene-γ-butyrolactone and methyl methacrylate in DMSO was studied by on-line Raman spectroscopy. Reactivity ratios for this system were estimated from the in situ conversion measurements. The estimates are in good agreement with estimates obtained from low-conversion experiments where the composition of the copolymer was analyzed by ¹H-NMR. In order to obtain reliable estimates from the Raman data in combination with the integrated copolymerization equation, at least two experiments starting from different initial monomer feed fractions should be conducted. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3804–3816, 1999     

Optical and Raman studies of Zn1-xMgxO ceramic pellets

The undoped and Mg-doped ZnO ceramics have been successfully synthesized using the conventional solid state sintering method. The doping effect of MgO content on the structural properties of ZnO/MgO composites has been investigated by X-ray diffraction (XRD) and Raman spectroscopy. The XRD patterns reveal that all the samples are polycrystalline and have a prominent hexagonal crystalline structure with (002) and (101) as preferred growth directions. The formation of the hexagonal ZnMgO alloy phase and the segregation of MgO-cubic phase took place for an MgO composition x ≥ 20 wt%. This finding is in good agreement with the Raman spectroscopy measurements which prove the existence of multiple-order Raman peaks originating from ZnO-like and MgO phonons. The band gap energy and the carrier concentration of ZnO pellets were found to be dependent upon the Mg doping whose values vary from 3.287 to 3.827 eV and from 1.6 × 10¹⁷ to 5.2 × 10²⁰ cm⁻³, respectively.     

A combined laser-induced breakdown and Raman spectroscopy Echelle system for elemental and molecular microanalysis

Raman and laser-induced breakdown spectroscopy is integrated into a single system for molecular and elemental microanalyses. Both analyses are performed on the same ~ 0.002 mm² sample spot allowing the assessment of sample heterogeneity on a micrometric scale through mapping and scanning. The core of the spectrometer system is a novel high resolution dual arm Echelle spectrograph utilized for both techniques. In contrast to scanning Raman spectroscopy systems, the Echelle–Raman spectrograph provides a high resolution spectrum in a broad spectral range of 200–6000 cm^? 1 without moving the dispersive element. The system displays comparable or better sensitivity and spectral resolution in comparison to a state-of-the-art scanning Raman microscope and allows short analysis times for both Raman and laser induced breakdown spectroscopy. The laser-induced breakdown spectroscopy performance of the system is characterized by ppm detection limits, high spectral resolving power (15,000), and broad spectral range (290–945 nm). The capability of the system is demonstrated with the mapping of heterogeneous mineral samples and layer by layer analysis of pigments revealing the advantages of combining the techniques in a single unified set-up.     

Microstructural,magnetic and crystal field investigations of nanocrystalline Dy3+ doped zinc oxide

Dy³⁺ doped zinc oxide was prepared by co-precipitation method. The as-prepared samples were annealed at different temperatures to obtain the samples with different particle sizes. The crystallographic phases of all the samples were confirmed by X-ray diffraction (XRD) patterns. Rietveld analysis of the XRD pattern of the sample annealed at 80 °C showed that most of the Dy³⁺ ions were substituted in the Zn²⁺ site of the hexagonal ZnO lattice. But in case of samples annealed at higher temperatures, a fraction of Dy³⁺ ions comes out from the ZnO lattice and this fraction increases with the increase of annealing temperature. The sizes of nanoparticles and the lattice strains of all the samples were obtained from the Hall–Williamson plot. High resolution transmission electron microscopy showed that ZnO nanoparticles are more or less spherical. Magnetic susceptibilities (χ) of some selected samples measured in the temperature range of 300–14 K indicate that the samples are paramagnetic. Values of χ were successfully fitted by Curie–Weiss law. A good theoretical simulation of χ of the sample annealed at 80 °C has been achieved using the one-electron crystal field interaction of the Dy³⁺ ions with its diamagnetic neighbors in the hexagonal single crystal.     

Micro-Raman mapping on an anatase TiO2 single crystal with a large percentage of reactive (0 0 1) facets

After it has been successfully synthesized in 2008, so far, no Raman investigations on the micro-sized anatase TiO₂ single crystal which has a large percentage of the reactive (0 0 1) facets have been conducted to the best of our knowledge. In the present work, this unique anatase TiO₂ single crystal was investigated by noninvasive and nondestructive Raman mapping technique. Raman images of both non-polarized and polarized measurements showed that the Raman features of the crystal varied with measurement position. The differences among the Raman spectra measured on different crystal facets were believed to result from the orientations and the symmetry rules. Whereas the differences among those measured at different points of the same crystal facet under the same measurement condition were supposed to indicate the defects of the crystal structure, such as oxygen vacancies, local lattice disorder etc. Furthermore, the appearance of the two second order Raman peaks of 803 and 918 cm⁻¹ as well as the blue-shift of 395 cm⁻¹ peak implies the anharmonicity of the crystal structure, which is also probably caused by the crystal defects. Our results provide useful information about the structure of this unique anatase TiO₂ material, and could be complementary to those that acquired by other characterization techniques.     

Construction of zinc selenide microspheres decorated with octadecylamine-functionalized reduced graphene oxide as an effective catalyst for the dual-mode detection of chloroquine phosphate

Zinc selenide microspheres were constructed using a simple hydrothermal technique at 180°C. It was ultrasonically treated with reduced graphene oxide modified with octadecylamine alkyl amine to form a hybrid nanocomposite. The optical, structural, and functional analysis by ultraviolet (UV) absorbance, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the crystal nature of the microspheres and the successful formation of the nanocomposite. Field emission scanning electron microscopy and transmission electron microscopy were done to study the morphological properties of the material. It was further used to fabricate a dual-modality sensor using both electrochemical and absorbance techniques for the detection of antimalarial drug chloroquine phosphate (CQP), which was used for the treatment of COVID-19 (SARS-CoV-2) virus. For electrochemical detection, the sensor showed a very low detection limit of 1.43 nM at a linear working range of 0.199–250.06 μM and a high sensitivity of 43.912 μA/μM/cm². For UV-based detection, the sensor showed a very low detection limit of 6.88 nM at a linear working range of 0.045–7.324 μM. The sensor showed excellent analyte recovery rate for real-time analysis in biological as well as environmental samples. The results suggested that the sensor is effective for the detection of CQP with feasibility for future commercialization.     

Raman spectroscopic study of mixed carbonate materials

The main parameters for precipitation of mixed carbonate materials have been studied by Raman microscopy. These carbonates are compounds of barium, strontium and calcium. It has been shown that the Raman spectrum of a sample is exclusively controlled by its composition, the precipitation parameters do not affect the crystal structure. Even at relatively low levels, the calcium content of a sample can dominate the vibrational frequencies as measured by Raman spectroscopy. Calcium contents greater than 17% show this effect to a considerable degree, and give the broadest or two Raman peaks and thus the least uniform unit cells. The analysis of the lattice modes demonstrates that each Raman shift observed for a mixed carbonate sample corresponds to a specific crystal structure. Some peaks lie within two or three shifts that are observed for different crystal structures.     

Density functional theory and surface-enhanced Raman spectroscopy studies on endocrine-disrupting chemical,dimethyl phthalate

A method to monitor endocrine-disrupting chemical contamination phthalate esters (PAEs) by surface-enhanced Raman scattering (SERS) spectroscopy has been investigated. The molecular structure and assignment of the vibrations of dimethyl phthalate (DMP), forming short chains in PAEs, has been studied by density functional theory (DFT) calculations. The structure of DMP with the dihedral angles of 1C-6C-11C-13O and 4C-5C-18C-20O being 133.78° and −24.00°, respectively, has the lowest energy. Theoretical vibrational frequencies using B3LYP/6-31 + G(d) (after scaling) show excellent agreement with the experimental normal Raman spectrum. In the region 200–1800 cm⁻¹, SERS spectra of DMP were measured using ordered gold nanosubstrates. All except the weak signals in the normal Raman spectrum of DMP were successfully enhanced. These results demonstrate that SERS technology could be developed as a rapid method for screening of DMP.     

Investigation of sport supplements quality by Raman spectroscopy and principal component analysis

In this work, sport supplements were investigated by Raman spectroscopy. Samples were obtained from health foods shops, gyms and sports centers covering a wide range of available supplement powders. A systematic comparison of Raman spectra of the analyzed supplements allowed identifying the supplement type through the characteristic vibrational modes of carbohydrates and proteins. The protein supplements were identified by Raman bands at 1650, 1250 and 1004 cm⁻¹, while the spectral range between 1200 and 800 cm⁻¹ was useful to identify the carbohydrate supplements. Due to the diversity in composition of sport supplements, a chemometric tool such as principal component analysis (PCA) was employed to assist in the interpretation of Raman spectra, allowing also the identification of compounds present in sport supplements. Especially, the Raman scattering of aromatic and aliphatic amino acids residues contributes to the existence of bands characteristic for the different types of proteins. This kind of information is very important for the quality control of these products, for detecting the presence of fraud or a sample composition in disagreement with the label, thus ensuring the provenance of the supplements.     

Molecular dynamics calculation to clarify the relationship between structure and mechanical properties of polymer crystals: the case of orthorhombic polyethylene

The molecular dynamics (MD) technique was used to calculate the temperature dependence of the structure, molecular motion, and mechanical property of the orthorhombic polyethylene (PE) crystal. The potential functional parameters reported by Karasawa et al. (J Phys Chem, 95 (1991) 2260) were refined further so that the vibrational frequencies of infrared and Raman bands, measured by us at ultra-low temperatures for the normal and fully deuterated PE, could be reproduced well. The flip-flop motion around the chain axis and the torsional motion of the skeletal chains were found to start above ca. 350 K and increase the amplitude of these motions progressively. Coupling these two types of chain motion resulted in a steep increase of the thermal vibration parameters or the mean-square-displacements of carbon and hydrogen atoms, corresponding well with the X-ray data. The lattice constants and the related linear thermal expansion coefficients were also found to be in good agreement with the observed data. The calculated Young's modulus along the chain axis decreased gradually with the increasing temperature: 330 GPa at 0 K to 280 GPa at room temperature. The latter was in good agreement with the value of 280–305 GPa evaluated from the Raman measurement of the longitudinal acoustic mode. Young's modulus was found to relate intimately with the chain contraction caused by the skeletal torsional motion. Only 0.3% contraction of the chain resulted in the reduction of the modulus by ca. 35%. A similar behavior was also seen in the trigonal polyoxymethylene and nylon 6 α forms.     

Micro-Raman Spectroscopy of Nanostructured Silver Sulfide

Nanostructured silver sulfide powder with an average particle size of about 45 nm, an acanthite α-Ag₂S monoclinic structure (space group P2₁/c), and nonstoichiometric composition Ag_1.93S has been synthesized by the chemical deposition method. The silver sulfide nanopowder has been studied by Raman spectroscopy. According to the Raman scattering data, heating the nanopowder with high-power laser radiation in air leads to photoinduced decomposition of the Ag_1.93S nanopowder to give silver metal. The Raman spectrum of the silver sulfide nanopowder shows a series of bands in the low-frequency range from 90 to 260 cm^–1 associated with vibrations of silver atoms, Ag–S bonds, and symmetric Ag–S–Ag longitudinal modes. Raman spectroscopy confirmed an acanthite monoclinic structure of synthesized silver sulfide nanopowder.     

Potential application of Raman spectroscopy for determining burial duration of skeletal remains

Raman spectroscopy was used to study trends in chemical composition of bones in a burial environment. A turkey bone was sectioned and buried for short intervals between 12 and 62 days. Buried sections were analyzed using Raman microspectroscopy with 785 nm excitation. The results indicate that chemical changes in bone due to soil bacteria are time-dependent. Spectroscopic trends within buried bone segments were correlated to burial duration. A preliminary model was constructed using peak integration of Raman bands. Data collected within buried bone segments fit very well in this model. The model constructed is sensitive to changes in bone composition in a scale of days. This study illustrates the great potential of Raman spectroscopy as a non-destructive method for estimating the burial duration of bone for forensic purposes.