Vibrational Raman Spectra Research Articles

Identification of Penicillium Species of Fruits Using Morphology and Spectroscopic Methods

This study aimed to investigate and identify the isolated five species of Penicillium from different rot fruits. The P.implicatum, P.aurantiogriseum, P.purpurogenum, P.citrinum, and P.notatum Penicillium species were found. Penicillium species are important in the field of medicine, industry, and produces secondary metabolite, some penicillium species are contaminant for bread, grains, fruits, and processed food, so the identification and characterization of these species are very important. By using the microscopic technique and spectroscopic methods for identification and characterization that species isolated from infected fruits. The spectroscopic methods are Raman spectroscopy and UV-Visible spectrophotometry, they are fast analysis techniques, sensitive, use a small quantity of sample, and depend on biochemical components for the discriminate of Penicillium spp. Raman vibrational spectra and UV-Visible absorption spectra showed differences for five Penicillium species. Our results proved that spectroscopic techniques showed spectral differences for five Penicillium species, and this agreed with the study of morphological characteristics for that species. The conclusions of this study demonstrate that spectroscopic methods in combination with morphological techniques could be accurate and reliable approach for discrimination between different Penicillium species.

Black metal hydrogen above 360 GPa driven by proton quantum fluctuations

Hydrogen metallization under stable conditions is a substantial step towards the realization of the first room-temperature superconductor. Recent low-temperature experiments1–3 report different metallization pressures, ranging from 360 GPa to 490 GPa. In this work, we simulate the structural properties and vibrational Raman, infrared and optical spectra of hydrogen phase III, accounting for proton quantum effects. We demonstrate that nuclear quantum fluctuations downshift the vibron frequencies by 25%, introduce a broad lineshape into the Raman spectra and reduce the optical gap by 3 eV. We show that hydrogen metallization occurs at 380 GPa in phase III due to band overlap, in good agreement with transport data2. Our simulations predict that this state is a black metal—transparent in the infrared—so the shiny metal observed at 490 GPa (ref. 1) is not phase III. We predict that the conductivity onset and optical gap will substantially increase if hydrogen is replaced by deuterium, underlining that metallization is driven by quantum fluctuations and is thus isotope-dependent. We show how hydrogen acquires conductivity and brightness at different pressures, explaining the apparent contradictions in existing experimental scenarios1–3. Numerical calculations that include the quantum fluctuations of protons explain the optical properties of hydrogen at high pressure.

Theoretical study on spectral differences of polypeptides constituted by L- and D-amino acids

Amino acids, polypeptides and proteins, which are all chiral, are the most important living substances. Most living organisms are made up of L-amino acids. Chirality is of great significance in exploring biomolecules. Studying polypeptides with a large number of atoms is a great challenge for quantum chemistry calculation. We conduct structural studies and perform vibrational and electronic spectra investigations on two polypeptides consisting of 14 L- and D-amino acids, both of which are right-handed α-helical. We find that the two polypeptides have similar IR and Raman vibrational spectra except that the polypeptide constituted by D-amino acids has an intramolecular hydrogen bond peak, but their chiral and excited state spectra are different and the chiral spectra are not mirror symmetric, which can be applied to distinguish them and shows that they have different structures in detail. Thus they may have different properties and functions. In addition, the amide III vibrations of the polypeptide include the information of the backbone and side chains. Therefore, care should be taken to apply the amide III vibrations to determine the secondary structure of polypeptide.

Structural properties and Raman spectra of columbite-type NiNb2−xVxO6 synthesized under high pressure

The complete set of structural parameters of the new series of compounds NiNb2−xVxO6 (0 ​≤ ​x ​≤ ​2) with the unusual columbite-type structure is presented here. In the samples containing vanadium, this crystalline structure was stabilized by synthesis in conditions of high pressure and high temperature. Here we report the first Raman spectrum for the NiV2O6-Pbcn polymorph and extend the list of the previously observed modes for the NiNb2O6. The evolution of the vibrational Raman spectrum produced when the vanadium is substituted for niobium along the series is also presented and discussed. This evolution is interpreted by taking into account the changes in the local structural environment of the niobium/vanadium atoms and its influence over the nickel-oxygen bonds around them. The presence of vanadium atoms favors an increase of the symmetry in the arrangement of oxygen atoms around the nickel-ones; in counterpart, the vanadium is in an octahedral environment which is more distorted than that of the niobium. Because of these apparently subtle differences, the homogeneous distribution of vanadium in the solid solution NiNb2−xVxO6 is not possible.

Molecular spectroscopic investigation, quantum chemical, molecular docking and biological evaluation of 2-(4-Chlorophenyl)-1-[3-(4-chlorophenyl)-5-[4-(propan-2-yl) phenyl-3, 5-dihydro-1H-pyrazole-yl] ethanone

2-(4-Chlorophenyl)-1-[3-(4-chlorophenyl)-5-[4-(propan-2-yl)phenyl-3, 5-dihydro-1H-pyrazole-yl] ethanone (CCPPE) has been studied experimentally and theoretically. The structure of CCPPE was characterized by X-ray diffraction (XRD), and determined theoretically by the ab initio Hartree-Fock (HF) method and by the density functional theory(DFT) method B3LYP using the 6-311++G (d, p) basis set. Theoretical topological analysis of the electron density, according to the Quantum Theory of Atoms in Molecule (AIM), electron localization function (ELF) and the localized orbital locator (LOL) have been performed. Fourier Transform Infrared (FTIR) and Fourier Transform Raman (FT-Raman) vibrational spectra were recorded and the observed frequencies were compared to those obtained from B3LYP/6-311G (d, p) and B3LYP/6-311++G (d, p) calculations. The HOMO and LUMO energy results show that good exchange of charge happened inside the molecule. Molecular electrostatic potential was also performed. From the MEP it is evident that the negative charges cover the C=O group, the region having the positive potential are over the phenyl rings and the remaining species are surrounded by zero potential. Theoretical (TD-DFT) and experimental UV-Vis absorption wavelengths (λ) were compared with each other. The stability of the molecule arising from hyper-conjugative interaction and charge delocalization has been analyzed using NBO analysis. The antimicrobial activity of the CCPPE was determined against bacterial strains such as Bacillus subtilis,Staphylococcus aureus, E.coli, Pseudomonas and fungal strains such as Candida albicans and A.niger. The obtained results show that the compound exhibited good to moderate antimicrobial activity. Molecular docking studies were executed to understand the inhibitory activity of CCPPE against antibacterial, antifungal, anti-inflammatory, antioxidant, antiviral activities.

Crystal structure and optical properties of a new nickel magnesium diphosphate

A new member of (A,M)2P2O7 diphosphate family, MgNiP2O7, has been synthesized and structurally characterized. The structure was determined using powder X-ray diffraction. MgNiP2O7 crystallizes in the monoclinic system, space group P21/c, with the unit cell parameters a= 6.4903(3) Å; b= 8.2772(3) Å; c=9.0131(4) Å and β= 113.767(9) °, Z=4 and V= 473.867(3) Å3. The structure of MgNiP2O7 is isotypic with β-Mg2P2O7 and α-Ni2P2O7. The Mg and Ni atoms are distributed randomly between MO5 pyramid and MO6 octahedron. The infrared and Raman vibrational spectra have been investigated and all the modes have been attributed. CIE L* a* b* parameters values are determined and UV-Visible spectrum consists of weak and narrow band between 680 and 720 nm assigned to the forbidden d-d transition of Ni2+ ions due to the square pyramid environment of Ni2+ in MgNiP2O7 which is in a good agreement with the structure refinement results.

A combined theoretical and experimental investigation of the electronic and vibrational properties of red lead pigment

The electronic and vibrational properties of red lead pigment, the mixed valence lead oxide compound Pb3O4, known as minium, have been studied by means of first principle calculations based on Density Functional Theory (DFT) and Fourier Transform–Infra Red (FT-IR) and Raman spectroscopies. The aim of the present investigation is to validate an integrated theoretical-experimental approach for modelling the structural, electronic and spectroscopic properties of minium and to define its structure-properties relationships. The calculated band gap performed using GW approximation is in excellent agreement with the experimental one and improves previous results found in literature. The simulated vibrational IR and Raman spectra are able to reproduce the main features of the experimental spectra and to assign the normal modes related to the experimental bands. The combined theoretical and experimental study of the electronic and vibrational properties of Pb3O4 allows to clarify the mechanism of lead whitening as well as to interpret ambiguous Raman spectra of minium in terms of resonance effects.

STRUCTURE, LUMINESCENCE, AND RAMAN SPECTROSCOPY OF EUROPIUM AND TERBIUM DIPIVALOYLMETHANATES AND OTHER β-DIKETONATES WITH 2,2′-BIPYRIDINE

The study reveals the relationship between structural and spectroscopic characteristics of lanthanide dipivaloylmethanates with 2,2′-bipyridine derivatives [Ln(DPM)3L] (Ln = Eu, Tb; L = 2,2′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 4,4′-diphenyl-2,2′-bipyridine) and fluorinated β-diketonates [Ln(β)3Bpy] (β = TTFA, TFAA, BTFA) with the CN (Ln3+) = 8 and the LnN2O6 coordination polyhedron in the form of a square antiprism. We discuss structural regularities resulting from the difference between Eu–O and Eu–N bond lengths in β-diketonates due to the changes in donor-acceptor properties of substituents and the steric factor. The effect of the main distortion Δ = r(Eu–N) – r(Eu–O) of the Eu coordination polyhedron on the luminescence spectra and vibrational Raman spectra is considered. A qualitative correlation is demonstrated between the relative intensity of the 5D0–7F2 (Eu3+) electric dipole transition, which characterizes the degree of distortion of the nearest environment of the Eu3+ ion, and the lifetimes of excited electronic states 5D0 (Eu3+) and 5D4 (Tb3+). The contribution of nonradiative processes caused by high-frequency vibrations of ligands to the decay rate of 5D0 (Eu3+) and 5D4 (Tb3+) levels is discussed. The Raman spectra are analyzed in terms of studying the changes in vibrational frequencies of the Bpy molecule depending on the distortion Δ of the Eu coordination polyhedron.

Predicting a Novel Phase of 2D SiTe2.

Layered IV–VI2 compounds often exist in a CdI2 structure. Using the evolution algorithm and first-principles calculations, we predict a novel layered structure of silicon ditelluride (SiTe2) that is more stable than the CdI2 phase. The structure has a triclinic unit cell in its bulk form. The atomic arrangement indicates the competition between the Si atoms’ tendency to form tetrahedral bonds and the Te atoms’ tendency to form hexagonal close-packing. The electronic and vibrational properties of the predicted phase are investigated. The effective mass of an electron is small among two-dimensional (2D) semiconductors, which is beneficial for applications such as field-effect transistors. The vibrational Raman and IR spectra are calculated to facilitate future experimental investigations.

Influence analysis of the detection accuracy of atmospheric water vapor using the solar-blind ultraviolet Raman lidar

Solar-blind ultraviolet Raman lidar can realize the daytime detection of atmospheric water vapor, as the transmitting wavelength of 266.0 nm and its excited vibrational Raman spectra of N2, O2 and H2O are within the solar-blind region. However, the spectra of the O3, NO2, SO2 absorptions and fluorescence are within the solar-blind region as well, and Raman channel of H2O still has a small amount of residual solar background noise, which will influence the detection accuracy and detection capability of the solar-blind ultraviolet Raman lidar. Moreover, although a high efficiency polychromator is required to extract the vibrational Raman spectra of N2, O2 and H2O, the suppression of aerosol Mie scattering and molecular Rayleigh scattering, and optical cross-talks are still required to discuss carefully in detail. Simulation results show that the retrieval accuracy of water vapor mixing ratio using the solar-blind Raman lidar are mainly influenced by the O3 absorption and the optical cross-talk of aerosol Mie scattering and molecular Rayleigh scattering. The rejection ratio with more than 5 orders of magnitude to elastic scattering signal is required in the design of polychromator to avoid the optical cross-talk between each extracted spectrum. The influences of NO2, SO2 absorptions, solar background noise and fluorescence on the retrieval of water vapor mixing ratio can be neglected. The theoretical analysis of the solar-blind ultraviolet Raman lidar on the retrieval of water vapor mixing ratio can further enhance the performance of the system detection accuracy and detection capability.

Strongly Correlated Molecular Magnet with Curie Temperature above 60 K

Summary Two-dimensional crystals with ferromagnetic ordering would lead to unprecedented possibilities for magnetic, magneto-optic, and magnetoelectric applications. However, long-range ferromagnetic ordering in two-dimensional van der Waals materials is strongly diminished by thermal fluctuation, while three-dimensional systems show the stiffness of magnetic ordering temperature to magnetic fields. Here, we report the discovery of intrinsic ferromagnetic ordering temperature of 60 K in an iron/tetracyanoquinodimethane layer via superconducting precursor. In such a molecular ferromagnet, an unprecedented control of ferromagnetic fluctuation temperature by ∼200% improvement is realized through magnetic fields. We demonstrate magnetodielectric coupling with a concomitant transition in magnetic ordering. A small magnetic field of 0.01 T enables an effective route to realize a sizable transition shift in magnetodielectric states. Stimulated by photoirradiation, it manifests a hidden metallic conducting state, declaring a metallic ferromagnet. The molecular ferromagnet and photoirradiation-induced hidden metallic phase present a “holy grail” in the field of molecular conducting magnets.

Effects of Surface in the IR and Raman Spectrum of Porous Silicon Carbide

Porous Silicon carbide has been identified as an attractive material for its use as electrode in supercapacitors, however the theoretical investigations about its properties, specially its vibrational properties, are still scarce. In this work the effect of the Si-C surface ratio on the vibrational properties, IR and Raman spectrum of porous silicon carbide was studied using the first principles density functional perturbation theory. The porous structures were modelled by removing atoms in the [001] direction from an otherwise perfect SiC crystal using the supercell scheme. The morphology of the pores was chosen so there would be more Si or C in the pore surface. The results show that the vibrational properties, and thus the IR and Raman spectrum of the porous SiC change depending if the pore surface is either Si or C rich, having the Si-rich pores more low frequency modes due to its higher mass. Also, the effects of phonon confinement are lessened by the effect of surface passivation, thus indicating that the surface plays an important role in the IR and Raman characterization of these structures.

Vibrational and optical studies of Na0.45K1.55Cu3(MoO4)4

Sodium potassium copper(II) tetra-[molybdate(VI)], Na0.45K1.55Cu3(MoO4)4, was synthesized using solid-state reaction route, and its crystal structure (monoclinic P21/c) was solved using single-crystal X-ray diffraction method. Na0.45K1.55Cu3(MoO4)4 forms 3D framework with elongated cavities occupied by alkali ions. The factor group analysis of Na0.45K1.55Cu3(MoO4)4 was applied for determination of number and activity of internal and external modes. Infrared and Raman vibrational spectra were investigated, and assignment of observed IR and Raman modes was proposed. The three crystallographically independent Cu2+ cations of Na0.45K1.55Cu3(MoO4)4 adopt the [4 + 2] CuO6 Jahn–Teller distortion giving rise to an intense d–d transition observed in UV–Vis absorption spectra. The energies of indirect (3.01 eV) and direct (2.17 eV) band gaps were calculated using Kubelka–Munk method combined with the Tauc equation.

Two-Dimensional Antimony Oxide.

Two-dimensional (2D) antimony, so-called antimonene, can form antimonene oxide when exposed to air. We present different types of single- and few-layer antimony oxide structures, based on density functional theory (DFT) calculations. Depending on stoichiometry and bonding type, these novel 2D layers have different structural stability and electronic properties, ranging from topological insulators to semiconductors with direct and indirect band gaps between 2.0 and 4.9eV. We discuss their vibrational properties and Raman spectra for experimental identification of the predicted structures.

Modeling the conformational preference, spectroscopic properties, UV light harvesting efficiency, biological receptor inhibitory ability and other physico-chemical properties of five imidazole derivatives using quantum mechanical and molecular mechanics tools

Five imidazole derivatives, 1-boc-imidazole (B1), 1-(trifluoroacetyl)imidazole (B2), 1-(2-hydroxyethyl)imidazole (B3), 1-(aminopropyl)imidazole (B4) and 1-ethylimidazole (B5) were analyzed for the structural, nonlinear optical, electronic and biological properties. The functional nature of the compounds were analyzed using vibrational spectra and Raman spectra and was compared with the scaled, simulated spectra obtained using the density functional theory using appropriate functional and basis set with diffused orbitals and are found to be close agreement. Relaxed potential energy scan predicts the stable conformers. Analysis of the outermost molecular orbitals gave their energy difference, aiding in the forecasting stability and other electronic properties. Time dependent density functional theory was used to analyze the electron excitation and de-excitation dynamics of these molecules and to predict the use of these molecules as effective UV photo sensitizers. This work further discusses in detail, the natural bond orbital (NBO) studies for intra molecular stabilization factors, molecular electrostatic potential (MEP) and hyperpolarizability calculations. Further molecular docking studies were conducted for the compounds with Glucanendo-1,6-beta-glucosidase and Protein-glutamatemethylesterase to predict their utility as potential inhibitors.

Application of NIR Raman Spectroscopy to Probe the Flexibility of RNA Structure.

NIR Raman spectroscopy has great potential for the detection of very weak Stokes-shifted Raman scattering emitted by biomolecules. Reports relating Raman spectroscopy analyses of ribonucleic acids (RNAs) are minimal. Nevertheless, correlation between Raman vibrational spectra and specific structural features of RNA from Avocado sunblotch viroids (ASBVds) has been clearly established. In this chapter, we discuss how to obtain NIR Raman RNA spectra and applications of Raman spectroscopy for the structural analysis of RNA, based on the analysis of ASBVd RNA. This chapter includes the analysis of spectral changes upon thermal denaturation, deuteration, and self-cleavage perturbations.

Spectroscopic insight into the interplay between structural disorder and oxidation degree in melt‐grown Ce0.5Zr0.5O2‐y compounds

AbstractThe oxygen storage capacity of CexZr1‐xO2‐y compounds arises from the mixed‐valent character of cerium, which makes the system sensitive to external factors such as temperature and oxygen partial pressure through their influence in the Ce valence, cation ordering and oxygen content. In this work, we analyze the phase relations in Ce0.5Zr0.5O2‐y compounds fabricated by the laser floating zone technique in either oxidising or reducing atmosphere. Chemical, structural, and microstructural properties are studied by X‐ray diffraction, thermogravimetry, scanning electron microscopy (energy dispersive X‐ray spectroscopy and electron backscatter diffraction), and Raman spectroscopy. The latter proves to be determinant to discriminate between phases arising from subtle variations of atomic distribution that are hardly distinguished by X‐ray diffraction or energy dispersive X‐ray analyses. Cation disordered, fluorite‐like phases are obtained when processing is performed in air, whereas cation‐ordered, pyrochlore‐related phases are formed when processing in Ar+5%H2 atmosphere. Processing in a low but non‐negligible pO2 yields, besides the pyrochlore and fluorite‐like phases, an intermediate state with partial disorder that may be relevant for catalysis applications. The vibrational Raman spectrum of the Ce2Zr2O7 pyrochlore has been fully interpreted through polarisation measurements at room and low temperature. Bands arising from crystal field transitions within the ground and first excited multiplets of Ce3+ ions are also identified. The electronic Raman spectrum is found to be a sensitive probe of the degree of cation and oxygen order in these compounds.

Tuning the microstructural, optical and superexchange interactions with rare earth Eu doping in nickel ferrite nanoparticles

A methodical study on structural, magnetic and optical properties of Eu doped NiFe2O4 nanoparticles with generic composition NiEuxFe2-xO4 (x = 0.00, 0.02, 0.04 and 0.06), synthesized via co-precipitation technique has been reported in this article. The fabrication of single phase ferrite nanoparticles was verified using X-ray powder diffractograms. The analysis of W–H plots revealed the presence tensile strain in the samples along with an average crystallite size of 20 ± 4 nm. The existence lowering of cubic symmetry at octahedral sublattices was detected by vibrational Raman spectra recorded at 300 K. The values of indirect optical band gap were noted in the range of 1.76 ± 0.02 eV. The hysteresis loops at room temperature supported the paramagnetic character of Eu3+ ions in spinel structure. The evidence of reduced A-O-B superexchange interaction along with reduction of saturation magnetization was also found for higher Eu content nanoparticles at 300 K. The coercivity was observed to increase at 5 K. The blocking temperature and thermo-magnetic irreversibility was reduced with increasing Eu concentration.

Synthesis of titanium oxide nanoparticles using Aloe barbadensis mill and evaluation of its antibiofilm potential against Pseudomonas aeruginosa PAO1

Titanium dioxide nanoparticles (TiO2-NPs) were synthesized using the aqueous leaf extract of Aloe barbadensis as a reducing and fabricating agent. The biosynthesis of the TiO2-NPs was initially confirmed by UV–vis spectroscopy. Based on the HRTEM and FESEM analysis, the biosynthesized NPs were found to be polydispersed and predominantly spherical in shape, with an average size of ~20 nm. A sharp and strong characteristic peaks of titanium (Ti) and oxygen (O) observed in the EDS pattern confirmed the synthesis of the TiO2-NPs. The FTIR spectroscopy suggested the presence of terpenoids, flavonoids and proteins which might be responsible for the biosynthesis and fabrication of the TiO2-NPs. The crystalline nature of the synthesized TiO2-NPs constituting of a mixture of brookite, anatase, and rutile phases was indicated by the XRD pattern. The spectral window around 180–1000 cm−1 covered the high-frequency Raman spectra of the TiO2-NPs. The Raman vibrational spectrum showed four Eg modes centered at 197.84, 399.24, 514.50, and 641.58 cm−1 representing the anatase phase of TiO2-NPs. The strongest and broadened peak of anatase was observed at the frequency of 641.58 cm−1. The metabolic activity of P. aeruginosa exposed to the MIC of TiO2-NPs was measured based on the reduction of tetrazolium salt by the dehydrogenase enzyme, produced by the metabolically active bacterial cells. The reduction in TTC was evident from the appearance of a red colored formazan in the solution. A noticeable suppression in the cell viability by 30.76 ± 3.96% of P. aeruginosa in the biofilm mode was found in presence of TiO2-NPs. Furthermore, the Minimum Inhibitory Concentration (MIC) of TiO2-NPs exhibited profound antibiofilm activity against P. aeruginosa by effectively preventing the adherence of the planktonic cells to the substratum. Thus, these NPs may be employed in controlling bacterial infections associated with biofilm.

Crystal-Chemical Properties of Synthetic Almandine-Pyrope Solid Solution by X-Ray Single-Crystal Diffraction and Raman Spectroscopy

Crystal-chemical properties of synthetic Almandine-Pyrope (Alm-Pyr) solid solutions were investigated by X-ray single-crystal diffraction and Raman spectroscopy. Garnet solid solution with different compositions were synthesized from powder at 4.0 GPa and annealed at 1200 °C for 48 h by a multi-anvil pressure apparatus. Garnet crystals with different sizes (about 60–1000 μm) were obtained from synthesis. The results of X-ray single-crystal diffraction show that the unit cell constants decrease with increasing Pyr contents in the synthetic Alm-Pyr crystals due to the smaller ionic radius of Mg2+ in eightfold coordination than that of Fe2+. The data exhibit obviously positive deviations from ideal mixing volumes across the Alm-Pyr join which may be caused by the distortion of the SiO4 tetrahedron. Moreover, the significant decrease in the average M-O bond length and volume of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell constant and volume. On the other hand, selected bond distances (average <M-O>, <Al-O>, and <D-O> distances) have a linear correlation with the unit-cell parameter, but the <Si-O> distance has nonlinear correlation. With increasing the unit-cell parameter, the average <M-O> distance increases significantly, followed by the average <D-O> and <Al-O> distances. While the <Si-O> distance changes negligibly further confirming the conclusion that the significant decrease of the average M-O bond length of the [MgO8]/[FeO8] dodecahedron with increasing Pyr contents are the most important factors to the decrease in the Alm-Pyr crystal unit cell volume. In the Raman spectra collected for the Alm-Pyr solid solutions, Raman vibration mode assignments indicate that the Raman vibrational spectra change along the Alm-Pyr binary solution. The mode frequencies of Si-O stretching, Si-O bending, and the rotation of the SiO4-tetrahedron (R(SiO4)) decrease linearly, while the translational modes of the SiO4-tetrahedron (T(SiO4)) increase with increasing Alm contents.