Changes In Intensity Of Bands Research Articles

Temperature dependence of bulk luminescence from ZnO.

X-Ray excited luminescence (radioluminescence, RL) spectra from nominally pure crystalline zinc oxide (ZnO) are reported. The temperature range is from 20 to 673K. Significant changes of emission band energies and intensities are observed across the temperature range. Photon energies of emission bands linked to the band gap decrease with increasing temperature in RL. This dependence fits the theoretical equations describing the temperature response of the ZnO band gap. Defect related luminescence includes a complex mixture of features at low temperature for RL. Thermoluminescence (TL) signals from 20 to 300K confirm the presence of an unresolved feature in the RL data. Comments on the possible origin of these bands are summarized. The data underline that it is essential to record the temperature dependence for the luminescence data in order to separate overlapping spectral features.

Two-trace two-dimensional (2T2D) correlation spectroscopy – A method for extracting useful information from a pair of spectra

Two-trace two-dimensional (2T2D) correlation spectroscopy, where a pair of spectra are compared as 2D maps by a form of cross correlation analysis, is introduced. In 2T2D, spectral intensity changes of bands arising from the same origin, which cannot change independently of each other, are synchronized. Meanwhile, those arising from different sources may and often do change asynchronously. By taking advantage of this property, one can distinguish and classify a number of contributing bands present in the original pair of spectra in a systematic manner. Highly overlapped neighboring bands originating from different sources can also be identified by the presence of asynchronous cross peaks, thus enhancing the apparent spectral resolution. Computational procedure to obtain 2T2D correlation spectra and their interpretation method, as well as an illustrative description of the basic concept in the vector phase space, are provided. 2T2D spectra may also be viewed as individual building blocks of the generalized 2D correlation spectra derived from a series of more than two spectral data. Some promising application potentials of 2T2D correlation and integration with established advanced 2D correlation techniques are discussed.

Color selection and red fluorescence enhancement through the controllable energy transfer in NaxCa1-2xWO4:Eux3+ phosphor for UV converted LEDs

Phosphor-converted warm white light-emitting diodes (pc-wLEDs) have played a key role in our daily lighting life, but they are difficult to realize without adding red-emitting phosphors. Conventional Eu3+ doped red phosphors, however, suffer greatly from the intrinsic shortcomings such as low quantum efficiency, limited absorption of UV LED light and chemical and thermal stability. In this work, we design the Eu3+ doped NaxCa1-2xWO4:Eux3+ (0 ≤ x ≤ 0.20) phosphors, which can exhibit enhanced Eu3+ red fluorescence and the tunable color at the same time. Phase purity analysis, which was checked by X-ray powder diffraction (XRD), shows all samples crystallize in a scheelite structure with the space group of I41/a (No.88). Our findings reveal that increasing the Eu3+ content gives rise to moving the XRD position to low angle direction and, in the meanwhile, decreasing the charge transfer (CT) intensity of samples. Spectral results show that controlling the charge compensation content and energy transfer efficiency from host to Eu3+ enables us to achieve the enhanced Eu3+ red fluorescence and simultaneously the tunable color. Unlike the decrease change in the CT band intensity, the Eu3+ emission upon excitation at 393 nm and 464 nm exhibits a continuous increase in the emission intensity. Due to the inefficiency energy transfer between host and Eu3+ dopant, controlling the x value enables tuning the relative photoemission intensity between host and Eu3+ dopant and therefore the color tuning from blue to red. Our time-resolved PL results indicate that the energy transfer between the CaWO4 host and Eu3+ dopant begins to occur at t = 5 μs. A feasible profile, which bases on the energy transfer, has been also established in the work. This work not only demonstrates simultaneous enhanced Eu3+ fluorescence and color tuning in CaWO4 matrix through charge compensation method, but also can provide new insight into improving the PL properties in other phosphors for UV converted pc-wLEDs.

Effect of interface in dielectric relaxation properties of PEMA–BaZrO3 nanocomposites

XRD peaks demonstrate the interaction of nanoparticles with polymer matrix. It is evident from the dielectric data that observed change in dielectric parameters would result from appropriate changes in chain mobility due to nanoparticles–polymer interactions. FT-IR spectra represent the significant changes in intensity, shape and position of the different vibrational bands corresponding to –OH stretching, C–O–C stretching, C–H stretching and C–O–C in C–H stretching modes occur as a result of the incorporation of BaZrO3 nanofiller. Thermally stimulated discharge current (TSDC) and transient discharging current study presented the dipolar and interfacial type of relaxations.

Oxidative stress in ageing and disease development studied by FT-IR spectroscopy

FT-IR spectroscopy was used to investigate the effect of oxidative stress and to approach the mechanism on cancer bone demineralization, aortic valve mineralization and heterotopic ossification on disease development. The FT-IR spectra obtained from paediatric, adult bone and ex vivo irradiated adult healthy bone with a dose of 20Gy were compared with those of healthy bone. The increase of band intensity changes of vasCH2,vsCH2 in the region 3000–2850cm−1 depended on aging, the disease progression and the dose of irradiation. The bands at 3080cm−1 and 1744cm−1, which originate from olefinic terminal bond (v=CH) and ester carbonyl group (vROCO), respectively, indicate the influence of oxidative stress on lipid degradation and peroxidation, respectively. The new bands at about 1690cm−1 and 1516cm−1 denote the presence of β-sheet conformation of the proteins due to the diseases, confirming the increasing amount of lipophilic environment and fibril formation. Comparison of the FT-IR spectra of calcified aortic valve and hip heterotopic ossification with that of normal bones showed that in the bone-like formation the peroxide anion free radicals play an important role in the disease.

Specific optical rotation is a versatile tool for the identification of critical micelle concentration and micellar growth of tartaric acid-based diastereomeric amphiphiles.

Four novel tartaric acid-based diastereomeric chiral amphiphiles, two being enantiomers of the other two, have been synthesized and investigated using chiroptical spectroscopic methods, along with tensiometry and dynamic light scattering experiments. We found that an inflection point in specific optical rotation (SOR) values at ~0.32mM corresponds to the critical micelle concentration (CMC). The increase in magnitude of SOR values beyond CMC corresponds to the growth of aggregates. For enantiomers, oppositely signed SOR values were observed, ruling out the possibility for the presence of aggregation size mediated artefacts. SOR values did not exhibit concentration dependence for a chiral tartaric acid based non-aggregating analogue further establishing the absence of artefacts or anomalous interaction of tartaric acid based head group with solvent. Electronic circular dichroism spectra showed no significant changes in band positions or intensities with concentration. Due to the requirement for higher concentrations (~200mM) needed to obtain vibrational circular dichroism spectra, these measurements are not found to be useful for studying concentration dependent properties of chiral amphiphiles.

Gold Nanoparticles as a Probe for Amyloid-β Oligomer and Amyloid Formation.

The process of amyloid-β (Aβ) amyloid formation is pathologically linked to Alzheimer's disease (AD). The identification of Aβ amyloids and intermediates that are crucial players in the pathology of AD is critical for exploring the underlying mechanism of Aβ aggregation and the diagnosis of the disease. Herein, we performed a gold nanoparticle (AuNP)-based study to detect the formation of Aβ amyloid fibrils and oligomers. Our results demonstrate that the intensity of the surface plasmon resonance (SPR) absorption band of the AuNPs is sensitive to the quantity of Aβ40 amyloids. This allows the SPR assay to be used for detection and semi-quantification of Aβ40 amyloids, and characterization of the kinetics of Aβ amyloid formation. Furthermore, our study demonstrates that the SPR band intensity of the AuNPs is sensitive to the presence of oligomers of both Aβ40 and an Aβ40 mutant, which forms more stable oligomers. The kinetics of the stable oligomer formation of the Aβ40 mutant can also be monitored following the SPR band intensity change of AuNPs. Our results indicate that this nanoparticle based method can be used for mechanistic studies of early protein self-assembly and fibrillogenesis.

Quantum confinement in multi-nanolayer sandwich systems

Presently we explored quantum confinement (QC) in three-nanolayer sandwich systems, composed of Au-SnO2-Fe, Au-SnO2-Si and Au-SnO2-Ag layers. We recorded the absorption spectra of these sandwich systems, all with discrete structure. We recorded the action spectra of the photocurrent for the Au-SnO2-Fe sandwich system, with the photocurrent quantum yields increasing with the photon energy, achieving 3.1 at 4.7 × 104 cm−1. The photocurrent action spectra correlate with high accuracy with optical absorption spectra. We discuss the mechanisms determining the absorption bandwidth value, including surface imperfections, thermal distribution of the vibrational level populations in the electronic ground state, and the diabatic coupling of levels of the excited state to those of a “dark” state. Volt-Ampere (V/A) characteristics were recorded for all three of the sandwich systems, quite similar to those of a Schottky diode. We report the parameter values of the V/A characteristics, found by fitting the experimental data with a theoretical curve. We also report charge density changes in the SnO2 layer caused by low constant voltage applied to the sandwich structure, observed as changes in the absorption band intensity.

Pressure dependence of the Raman signal intensity in high‐pressure gases

At present gas analysis based on Raman, spectroscopy is actively developed. In most cases, to achieve the required Raman signal intensity, compression of the gas medium is used. However, in comparison with normal conditions, the character of motion of molecules and their electric properties change in high‐pressure gas media, thereby violating a linear dependence of the Raman signal intensity on the concentration of molecules and the gas pressure. In the present work, a theoretical model is presented that describes the Raman signal intensity as a function of the pressure of the gas medium considering the compressibility factor, the internal field factor, and the instrumental factor. To verify the model, changes in the Raman signal intensities of vibrational bands of nitrogen and oxygen in the pressure range 1–80 atm and carbon dioxide in the pressure range 1–60 atm are investigated. Under these conditions, we observe a deviation of ~3% from a linear dependence for nitrogen, ~7% for oxygen and ~80% for carbon dioxide, which is in good agreement with the theoretical model. Raman shifts, half‐widths of Q‐branches of vibrational bands ν1 (and 2ν2 for carbon dioxide) of these molecules and also ratio of integral intensities I(2ν2)/I(ν1) for carbon dioxide under these conditions are investigated. Copyright © 2016 John Wiley & Sons, Ltd.

Simultaneous Time-Dependent Surface-Enhanced Raman Spectroscopy, Metabolomics, and Proteomics Reveal Cancer Cell Death Mechanisms Associated with Gold Nanorod Photothermal Therapy.

In cancer plasmonic photothermal therapy (PPTT), plasmonic nanoparticles are used to convert light into localized heat, leading to cancer cell death. Among plasmonic nanoparticles, gold nanorods (AuNRs) with specific dimensions enabling them to absorb near-infrared laser light have been widely used. The detailed mechanism of PPTT therapy, however, still remains poorly understood. Typically, surface-enhanced Raman spectroscopy (SERS) has been used to detect time-dependent changes in the intensity of the vibration frequencies of molecules that appear or disappear during different cellular processes. A complete proven assignment of the molecular identity of these vibrations and their biological importance has not yet been accomplished. Mass spectrometry (MS) is a powerful technique that is able to accurately identify molecules in chemical mixtures by observing their m/z values and fragmentation patterns. Here, we complemented the study of changes in SERS spectra with MS-based metabolomics and proteomics to identify the chemical species responsible for the observed changes in SERS band intensities during PPTT. We observed an increase in intensity of the bands at around 1000, 1207, and 1580 cm-1, which were assigned in the literature to phenylalanine, albeit with dispute. Our metabolomics results showed increased levels of phenylalanine, its derivatives, and phenylalanine-containing peptides, providing evidence for more confidence in the SERS peak assignments. To better understand the mechanism of phenylalanine increase upon PPTT, we combined metabolomics and proteomics results through network analysis, which proved that phenylalanine metabolism was perturbed. Furthermore, several apoptosis pathways were activated via key proteins (e.g., HADHA and ACAT1), consistent with the proposed role of altered phenylalanine metabolism in inducing apoptosis. Our study shows that the integration of the SERS with MS-based metabolomics and proteomics can assist the assignment of signals in SERS spectra and further characterize the related molecular mechanisms of the cellular processes involved in PPTT.

Voltammetric and Spectroscopic Investigation of the Interaction Between 1,4-Benzodiazepines and Bovine Serum Albumin

The interaction of diazepam (DZ) and chlordiazepoxide hydrochloride (CPZ) with bovine serum albumin (BSA) was investigated by the application of cyclic and square wave voltammetry. The electrochemical behavior of DZ and CPZ in the absence and in the presence of BSA was studied using a Sonogel–Carbon electrode modified with 5 % bentonite. In the presence of BSA, the reductive peak current of DZ or CPZ was decreased apparently without any significant changes in peak potentials and the appearance of no new reduction or oxidation peaks. Electrochemical parameters such as formal potential (E°), standard rate constant (k s) and charge transfer coefficient (α) were calculated and compared in the absence and presence of BSA. The results showed that the interaction of DZ or CPZ with BSA resulted in formation of an electro-inactive bio-complex. The equilibrium constant (β s) and binding ratio (m) of the bio-complexes were calculated. UV–Vis spectrophotometry and Fourier transform infrared (FT-IR) techniques were used to assess the structural effects of DZ and CPZ binding on BSA. The formation of DZ–BSA and CPZ–BSA bio-complexes was proved and the binding constant was calculated from the UV–Vis measurements. There is little difference between the binding constant values calculated using the voltammetric and UV–Vis spectrophotometric techniques. The formation of DZ–BSA and CPZ–BSA bio-complexes was confirmed by recording the changes in both intensity and position of FT-IR spectral bands of BSA, DZ, CPZ and their bio-complexes DZ–BSA and CPZ–BSA.

On the Identification of Rayon/Viscose as a Major Fraction of Microplastics in the Marine Environment: Discrimination between Natural and Manmade Cellulosic Fibers Using Fourier Transform Infrared Spectroscopy.

This work was sparked by the reported identification of man-made cellulosic fibers (rayon/viscose) in the marine environment as a major fraction of plastic litter by Fourier transform infrared (FT-IR) transmission spectroscopy and library search. To assess the plausibility of such findings, both natural and man-made fibers were examined using FT-IR spectroscopy. Spectra acquired by transmission microscopy, attenuated total reflection (ATR) microscopy, and ATR spectroscopy were compared. Library search was employed and results show significant differences in the identification rate depending on the acquisition method of the spectra. Careful selection of search parameters and the choice of spectra acquisition method were found to be essential for optimization of the library search results. When using transmission spectra of fibers and ATR libraries it was not possible to differentiate between man-made and natural fibers. Successful differentiation of natural and man-made cellulosic fibers has been achieved for FT-IR spectra acquired by ATR microscopy and ATR spectroscopy, and application of ATR libraries. As an alternative, chemometric methods such as unsupervised hierarchical cluster analysis, principal component analysis, and partial least squares-discriminant analysis were employed to facilitate identification based on intrinsic relationships of sample spectra and successful discrimination of the fiber type could be achieved. Differences in the ATR spectra depending on the internal reflection element (Ge versus diamond) were observed as expected; however, these did not impair correct classification by chemometric analysis. Moreover, the effects of different levels of humidity on the IR spectra of natural and man-made fibers were investigated, too. It has been found that drying and re-humidification leads to intensity changes of absorption bands of the carbohydrate backbone, but does not impair the identification of the fiber type by library search or cluster analysis.

Systematic in Situ Infrared Study of the Electro-Oxidation of C3 Alcohols on Carbon-Supported Pt and Pt-Bi Catalysts for Energy Applications

The electrooxidation of C3 alcohols (1-propanol, 2-propanol, 1,2-propanediol, 1,3 propanediol and glycerol) has been studied in alkaline medium on Pt/C and Pt9Bi1/C catalysts by cyclic voltammetry and in situ FTIR spectroscopy. The modification of Pt by 10 at% of Bi decreases the oxidation onset potentials of C3 alcohols down to ca. 200 mV. In situ FTIR spectroscopy measurements indicated clearly that the presence of Bi also led to avoid the C-C bond cleavage during alcohol electrooxidation reactions. Systematic evaluation of the positions and intensity changes of absorption bands as a function of the electrode potential allowed determining reaction pathways of electrooxidation of C3 alcohols. It has been shown that the secondary alcohol groups are more reactive than the primary ones, but also that in the case of glycerol steric limitations due to the presence of two primary alcohol groups could be responsible of the higher oxidation onset potential. At potentials above 0.6 V, the linear1-propanol bearing a single primary alcohol group leads to the highest activity due to lower steric hindrance of the surface compared with the other alcohols studied. Figure 1

Characterization of the alumino–silico–oxygen clinoptilolite framework and its hydrogen forms via IR spectroscopy

In this work, clinoptilolite hydrogen forms are obtained from the Khonguruu zeolite locality (Republic of Sakha, Russia) using hydrochloric acid solutions of different concentrations. The chemical composition is identified via X-ray spectral microprobe analysis and thermogravimetry. IR vibrational spectra of the alumino–silico–oxygen framework are studied in its dealumination and decationization. The effect of the aluminum content in clinoptilolite hydrogen forms on the intensity change and frequencies of the principal vibrational bands of alumino–silico–oxygen framework is established as well.

Importance of Atomic Contacts in Vibrational Energy Flow in Proteins.

Vibrational energy flow in proteins was studied by monitoring the time-resolved anti-Stokes ultraviolet resonance Raman scattering of three myoglobin mutants in which a Trp residue substitutes a different amino acid residue near heme. The anti-Stokes Raman intensities of the Trp residue in the three mutants increased with similar rates after depositing excess vibrational energy at heme, despite the difference in distance between heme and each substituted Trp residue along the main chain of the protein. This indicates that vibrational energy is not transferred through the main chain of the protein but rather through atomic contacts between heme and the Trp residue. Distinct differences were observed in the amplitude of the band intensity change between the Trp residues at different positions, and the amplitude of the band intensity change exhibits a correlation with the extent of exposure of the Trp residue to solvent water. This correlation indicates that atomic contacts between an amino acid residue and solvent water play an important role in vibrational energy flow in a protein.

Ionic and tautomeric conformers of adenine at different pH investigated by Raman spectroscopy combined with DFT calculations

Raman spectroscopy and density functional theory studies have been done to determine the ionic and tautomeric conformers of adenine (Ade) in aqueous solution at pH 1.5 (acidic), 7.0 (neutral) and 12.5 (alkaline). The experimental Raman spectra of the aqueous solution of Ade have been recorded for the spectral range of 500–1800 cm−1. As expected, the recorded Raman spectra of the aqueous solution of Ade at different pH have noticeable differences. The change in the spectral features of Ade at different pH is a result of the change in structure (neutral, cation and anion) of Ade in the aqueous solution. The shifting in the wavenumber position of the Raman bands, along with the change in relative intensity and appearance of new bands with the change of pH, has been explained. In order to determine the structure of Ade at various pH, theoretical Raman spectra, corresponding to the most probable structure of Ade at that particular pH, are calculated by density functional theory‐based explicit model. The Raman bands observed at each pH of the aqueous solution of Ade are assigned with the help of a potential energy distribution calculation. The most plausible ionic and neutral conformers of Ade in aqueous solution at pH 1.5, 7.0 and 12.5 are determined by comparing the experimental and theoretical spectra. From this, it is concluded that at neutral pH (7.0), Ade‐N9 and Ade‐N7 tautomers of Ade predominantly exist along with some signature of imine form of Ade in the aqueous solution. However, single‐protonated and double‐protonated forms of Ade can exist simultaneously in the aqueous solution at pH 1.5. As per expectation, the anionic form of Ade has been found at alkaline pH (12.5). Copyright © 2016 John Wiley & Sons, Ltd.

A Systematicin SituInfrared Study of the Electrooxidation of C3 Alcohols on Carbon-Supported Pt and Pt–Bi Catalysts

The electrooxidation of C3 alcohols (1-propanol, 2-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol) has been studied in alkaline medium on Pt/C and Pt9Bi1/C catalysts by cyclic voltammetry and in situ FTIR spectroscopy. Both catalysts were synthesized with metal particle sizes below 5 nm and were characterized by TGA, AAS, and XRD. The modification of Pt by 10 at. % of Bi decreases the oxidation onset potentials of C3 alcohols down to ca. 200 mV. In situ FTIR spectroscopy measurements indicated clearly that the presence of Bi also led to avoid the C–C bond cleavage during alcohol electrooxidation reactions and, hence, to favor the formation of value-added C3 compounds. Moreover, with respect to a Pd-based catalyst, Pt9Bi1/C presented much higher electrocatalytic activity at low potentials. Systematic evaluation of the positions and intensity changes of absorption bands as a function of the electrode potential allowed determining reaction pathways of electrooxidation of C3 alcohols. It has been sh...

Light wavelength influence on surface plasmon resonance in citrate–gold nanosystems

Citrate–gold particles were yielded according to classical method of auric salt reduction in two different synthesis media aiming to use them further applications in biomedical and environmental domains. The analysis of citrate–gold interaction was done through UV–vis and IR spectroscopy as well as by Transmission Electron Microscopy (TEM) and Dark Field (DF) Microscopy. Average particle size was higher for citrate–gold NPs synthesized with NaOH (32.5 nm) than for NPs synthesized with NaCl (15 nm). Dimensional histograms of one year aged colloidal suspensions presented mean size of 29 nm and respectively 18 nm. The influence of 90 min light exposure, analyzed by UV–vis, evidenced that for both NaOH synthesis protocol and NaCl protocol, plasmon band maxima at 528 nm and respectively 538 nm didn't changed, neither for white nor for green light. For one year aged samples this band shifted to 540 nm for green light irradiation in the case of citrate–gold NPs synthesized with NaOH. Also, for these NPs, both green and white light exposures resulted in plasmon band intensity changes for native as well as for aged samples. FTIR investigation showed also different changes at the level of the intensity of main vibration bands of citrate–gold after exposure to light, suggesting stronger adsorption of citrate in the case of NaCl addition in the initial reaction medium than in the case of NaOH. Finally, the utilization of NaCl in the synthesis protocol seems to favor the synthesis of more stable and lower toxicity colloidal suspensions, both during time and under the light irradiation.

Raman spectroscopy analysis of differences in composition of spent culture media of in vitro cultured preimplantation embryos isolated from normal and fat mice dams

The aim of the present study was to compare overall patterns of metabolic activity of in vitro cultured preimplantation embryos isolated from normal and fat mice dams by means of non-invasive profiling of spent culture media using Raman spectroscopy.To produce females with two different types of body condition (normal and fat), a previously established two-generation model was used, based on overfeeding of experimental mice during prenatal and early postnatal development. Embryos were isolated from spontaneously ovulating and naturally fertilized dams at the 2-cell stage of development and cultured to the blastocyst stage in synthetic oviductal medium KSOMaa. Embryos from fat mice (displaying significantly elevated body weight and fat) showed similar developmental capabilities in vitro as embryos isolated from normal control dams (displaying physiological body weight and fat).The results show that alterations in the composition of culture medium caused by the presence of developing mouse preimplantation embryos can be detected using Raman spectroscopy. Metabolic activity of embryos was reflected in evident changes in numerous band intensities in the 1620–1690cm−1 (amide I) region and in the 1020–1140cm−1 region of the Raman spectrum for KSOMaa. Moreover, multivariate analysis of spectral data proved that the composition of proteins and other organic compounds in spent samples obtained after the culture of embryos isolated from fat dams was different from that in spent samples obtained after the culture of embryos from control dams.This study demonstrates that metabolic activity of cultured preimplantation embryos might depend on the body condition of their donors.

Hydrogen Bonding in Liquid Water and in the Hydration Shell of Salts.

A near-IR spectral study on pure water and aqueous salt solutions is used to investigate stoichiometric concentrations of different types of hydrogen-bonded water species in liquid water and in water comprising the hydration shell of salts. Analysis of the thermodynamics of hydrogen-bond formation signifies that hydrogen-bond making and breaking processes are dominated by enthalpy with non-negligible heat capacity effects, as revealed by the temperature dependence of standard molar enthalpies of hydrogen-bond formation and from analysis of the linear enthalpy-entropy compensation effects. A generalized method is proposed for the simultaneous calculation of the spectrum of water in the hydration shell and hydration number of solutes. Resolved spectra of water in the hydration shell of different salts clearly differentiate hydrogen bonding of water in the hydration shell around cations and anions. A comparison of resolved liquid water spectra and resolved hydration-shell spectra of ions highlights that the ordering of absorption frequencies of different kinds of hydrogen-bonded water species is also preserved in the bound state with significant changes in band position, band width, and band intensity because of the polarization of water molecules in the vicinity of ions.