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An extreme ultraviolet pump and visible-light probe transmission experiment in crystalline LiF, carried out at the Free Electron Laser facility FERMI, revealed an oscillating time dependence of the plasmon mode excited in the high-density high-temperature electron plasma. The effect is interpreted as a fingerprint of the electron-ion interaction: the ion motion, shaped by the electron dynamic screening, induces, in turn, electron density fluctuations that cause the oscillation of the plasmon frequency at the timescale of the ion dynamics. Fitting the high resolution transmission data with an RPA model for the temperature-dependent dielectric function, which includes electron self-energy and electron-ion coupling, confirms the interpretation of the time modulation of the plasmon mode.
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The optical properties of a GaTa(4)Se(8) single crystal are investigated under high pressure. At ambient pressure, the optical conductivity exhibits a charge gap of ≈0.12 eV and a broad midinfrared band at ≈0.55 eV. As pressure is increased, the low energy spectral weight is strongly enhanced and the optical gap is rapidly filled, pointing to an insulator to metal transition around 6 GPa. The overall evolution of the optical conductivity demonstrates that GaTa(4)Se(8) is a Mott insulator which undergoes a bandwidth-controlled Mott metal-insulator transition under pressure, in remarkably good agreement with theory. With the use of our optical data and ab initio band structure calculations, our results were successfully compared to the (U/D, T/D) phase diagram predicted by dynamical mean field theory for strongly correlated systems.
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We present an analysis of the liquid and of a small isolated cluster of n-ethyl ammonium nitrate based on "first principles" molecular dynamics. We discover that the peculiar properties of ionic liquids make such compounds ideal candidates for such an analysis. We have been able to characterize some important features of the liquid structure and we have validated our simulations by comparing our findings with experimental vibrational spectra of the liquid phase. Theoretical spectra, which present a remarkable agreement with the measurements, besides the assignment of the main spectra features, allow an interpretation of the spectra at high frequencies where the vibrational motions involve the hydrogen-bonded atoms, thus providing a picture of the hydrogen bonding network that exists in such compounds.
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BACKGROUND: Strokes are the leading cause of epileptic seizures in adults and account for 50% of seizures in those over the age of 65 years. The use of antiepileptic drugs to prevent recurrent poststroke seizures is recommended. METHODS: One hundred and twenty-eight patients with poststroke seizures were randomly allocated to treatment with either levetiracetam (LEV) or sustained-release carbamazepine (CBZ) in a multicenter randomized open-label study. After a titration study phase (2 weeks), the optimal individual dose of trial medication was determined and treatment was continued for another 52 weeks. The primary endpoint was defined as the proportion of seizure-free patients; the secondary endpoints were: evaluation of time recurrence to the first seizure, EEG tracings, cognitive functions and side effects. RESULTS: Of 128 patients, 22 discontinued the trial prematurely; thus a total of 106 patients (52 treated with LEV and 54 treated with CBZ) were included in the analysis. The results of the study were as follows: no significant difference in number of seizure-free patients between LEV and CBZ (p = 0.08); time to the first recurrence tended to be longer among patients on LEV; there was no correlation between the therapeutic effect and the EEG findings in either treatment group; LEV caused significantly fewer (p = 0.02) side effects than CBZ; attention deficit, frontal executive functions and functional scales (Activities of Daily Living and Instrumental Activities of Daily Living indices) were significantly worse in the CBZ group. CONCLUSIONS: This trial suggests that LEV may be a valid alternative to CBZ in poststroke seizures, particularly in terms of efficacy and safety. In addition, our results show that LEV has significant advantages over CBZ on cognitive functions. This trial also indicates that LEV in monotherapy is a safe and effective therapeutic option in elderly patients who have suffered epileptic seizures following a stroke.
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Anticonvulsivantes/uso terapêutico , Carbamazepina/uso terapêutico , Piracetam/análogos & derivados , Convulsões/tratamento farmacológico , Acidente Vascular Cerebral/complicações , Atividades Cotidianas , Idoso , Idoso de 80 Anos ou mais , Anticonvulsivantes/efeitos adversos , Carbamazepina/efeitos adversos , Feminino , Humanos , Levetiracetam , Masculino , Pessoa de Meia-Idade , Piracetam/efeitos adversos , Piracetam/uso terapêutico , Estudos Prospectivos , Convulsões/etiologia , Resultado do TratamentoRESUMO
High pressure is a proven effective tool for modulating inter-layer interactions in semiconducting transition metal dichalcogenides, which leads to significant band structure changes. Here, we present an extended infrared study of the pressure-induced semiconductor-to-metal transition in 2H-[Formula: see text], which reveals that the metallization process at 13-15 GPa is not associated with the indirect band-gap closure, occurring at 24 GPa. A coherent picture is drawn where n-type doping levels just below the conduction band minimum play a crucial role in the early metallization transition. Doping levels are also responsible for the asymmetric Fano line-shape of the [Formula: see text] infrared-active mode, which has been here detected and analyzed for the first time in a transition metal dichalcogenide compound. The pressure evolution of the phonon profile under pressure shows a symmetrization in the 13-15 GPa pressure range, which occurs simultaneously with the metallization and confirms the scenario proposed for the high pressure behaviour of 2H-[Formula: see text].
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High pressure, low temperature Raman measurements performed on LaMnO3 up to 34 GPa provide the first experimental evidence for the persistence of the Jahn-Teller distortion over the entire stability range of the insulating phase. This result resolves the ongoing debate about the nature of the pressure driven insulator to metal transition (IMT), demonstrating that LaMnO3 is not a classical Mott insulator. The formation of domains of distorted and regular octahedra, observed from 3 to 34 GPa, sheds new light on the mechanism behind the IMT suggesting that LaMnO3 becomes metallic when the fraction of undistorted octahedra domains increases beyond a critical threshold.
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GaAs nanowires were heated locally under ambient air conditions by a focused laser beam which led to oxidation and formation of crystalline arsenic on the nanowire surface. Atomic force microscopy, photoluminescence and Raman spectroscopy experiments were performed on the same single GaAs nanowires in order to correlate their structural and optical properties. We show that the local changes of the nanowires act as a barrier for thermal transport which is of interest for thermoelectric applications.
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Nowadays, practice of tattooing is very common worldwide and, along with this increasing trend, there is also an increased risk of adverse reactions to tattoo pigments that are well known and described in literature. Previous studies have reported that cutaneous and allergic reactions to a particular pigment can manifest in several ways (allergic contact dermatitis and photo-allergic dermatitis). In this paper, a new high-throughput method is presented, in order to achieve a new system for the quality control on tattoo inks based on chromatographic-spectroscopic approach. The samples, twenty-one tattoo inks and three permanent makeup, comprised the following colors: black inks, yellow, blue, green, white, pink and various shades of red (pigment that gives many allergic responses) were analyzed through the combination of chromatographic and spectroscopic techniques, the HPTLC-Raman. In particular, Raman technique has been chosen because of its high sensitivity towards the inorganic and organic pigments, main constituents of tattoo inks. Moreover, the advantage of this hyphenated technique is to overcome the problem of analysing the complex mixture of tattoo inks, allowing to obtain a Raman spectrum of each single component, isolated by chromatographic separation. This approach aims at developing a powerful instrument to establish the nature of tattoo inks and substances that could be cause adverse reactions in tattooed patients.
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Cromatografia em Camada Fina/métodos , Corantes/análise , Tinta , Análise Espectral Raman/métodos , Tatuagem , Corantes/química , Corantes/normas , Ensaios de Triagem em Larga Escala , Controle de QualidadeRESUMO
Fibrillogenesis of monomeric human insulin in the presence or absence of (-)-epigallocatechin-3-gallate and melatonin was here investigated using a multi-technique approach. Results from Raman and Infrared spectroscopy pointed out that a high content of intermolecular ß-sheet aggregates is formed after long-term incubation. However, near UV experiments, Dynamic Light Scattering, Thioflavin-T fluorescence measurements and Atomic Force Microscopy revealed that the kinetics from native-to-fibrillar state of insulin is hampered only in the presence of (-)-epigallocatechin-3-gallate. Molecular dynamic simulations indicated that this compound binds near the B11-B18 protein segment, where hydrophobic residues responsible for the beginning of cooperative aggregation are located. Such a preferential binding region is not recognized by melatonin, a highly mobile molecule, which indeed does not affect fibril formation. The results of the present study demonstrate that (-)-epigallocatechin-3-gallate interferes with the insulin nucleation phase, giving rise to amorphous aggregates in the early stages of the aggregation process.
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Catequina/análogos & derivados , Insulina/química , Melatonina/farmacologia , Multimerização Proteica/efeitos dos fármacos , Sequência de Aminoácidos , Catequina/farmacologia , Humanos , Simulação de Dinâmica Molecular , Conformação Proteica em Folha betaRESUMO
We report a study of the structural phase transitions induced by pressure in bulk black phosphorus by using both synchrotron x-ray diffraction for pressures up to 12.2 GPa and Raman spectroscopy up to 18.2 GPa. Very recently black phosphorus attracted large attention because of the unique properties of few-layers samples (phosphorene), but some basic questions are still open in the case of the bulk system. As concerning the presence of a Raman spectrum above 10 GPa, which should not be observed in an elemental simple cubic system, we propose a new explanation by attributing a key role to the non-hydrostatic conditions occurring in Raman experiments. Finally, a combined analysis of Raman and XRD data allowed us to obtain quantitative information on presence and extent of coexistences between different structural phases from ~5 up to ~15 GPa. This information can have an important role in theoretical studies on pressure-induced structural and electronic phase transitions in black phosphorus.
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The equilibrium optical phonons of graphene are well characterized in terms of anharmonicity and electron-phonon interactions; however, their non-equilibrium properties in the presence of hot charge carriers are still not fully explored. Here we study the Raman spectrum of graphene under ultrafast laser excitation with 3 ps pulses, which trade off between impulsive stimulation and spectral resolution. We localize energy into hot carriers, generating non-equilibrium temperatures in the ~1700-3100 K range, far exceeding that of the phonon bath, while simultaneously detecting the Raman response. The linewidths of both G and 2D peaks show an increase as function of the electronic temperature. We explain this as a result of the Dirac cones' broadening and electron-phonon scattering in the highly excited transient regime, important for the emerging field of graphene-based photonics and optoelectronics.
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A detailed Raman study has been carried out on the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI) over a wide pressure (0-8 GPa) and temperature (100-300 K) range. The explored thermodynamic region allowed us to study the evolution of the system across different solid and liquid phases. Calculated Raman spectra remarkably helped in the spectral data analysis. In particular, the pressure behavior of the most intense Raman peak and the shape analysis of the ruby fluorescence (used as a local pressure gauge) allowed us to identify a liquid-solid transition around 2.2 GPa at T = 300 K. The low-frequency Raman signal as well as the absence of remarkable spectral shape modifications on crossing the above threshold and the comparison with the spectra of the crystalline phase suggest a glassy nature of the high-pressure phase. A detailed analysis of the pressure dependence of the relative concentration of two conformers of TFSI allowed us to obtain an estimate of the volume variation between trans-TFSI and the smaller cis-TFSI, which is the favored configuration on applying the pressure. Finally, the combined use of both visual inspection and Raman spectroscopy confirmed the peculiar sequence of phase transitions observed as a function of temperature at ambient pressure and the different spectral/morphological characteristics of the two crystalline phases.
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The local structure of molybdenum dichalcogenide MoX2 (X = S, Se, Te) single crystal has been studied by means of multi-edge (Mo, Se, and Te K-edges) extended x-ray absorption fine-structure spectroscopy as function of temperature. The temperature dependences of the interatomic distances Mo-X, Mo-Mo and X-X (X = S, Se, and Te) and of the corresponding Debye-Waller factors have been extracted over the 70-500 K temperature range. Exploiting the correlated Einstein model, we found that the Einstein frequencies of Mo-X and X-X bonds obtained by present data are in close agreement with the frequencies of the optical (Raman and infrared) stretching modes for both MoS2 and MoSe2, whereas a significant deviation has been found for MoTe2. A similar anomaly has been found for the force constants related to the Mo-X bonds in the MoTe2 case. Our findings, accordingly with the results reported in a recent theoretical paper, support the idea that the optical vibrational modes have a dominant role in MoS2 and MoSe2, whereas the effects of acoustic vibrational modes cannot be neglected in the case of MoTe2.
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Absorbance spectra of two ionic liquids, the short alkyl chain N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) and the longer chain N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide (TMHA-TFSI) are reported as a function of pressure and temperature. The occurrence of various phase transitions is evidenced by the changes in the relative concentration of the cisoid and transoid conformers of their common TFSI anion. The infrared spectrum of TMPA-TFSI was measured at 300 K with an applied pressure varying over the 0-5 GPa range. Above 0.2 GPa only the trans conformer is detected, suggesting the occurrence of a pressure induced crystallization. When pressure is applied to TMHA-TFSI at T = 310 K, both TFSI conformers subsist up to â¼11 GPa. However, the clear change of their intensity ratio observed around 2 GPa, suggests the onset of a glass phase as supported by measurements carried out at 4.2 GPa along a cooling/heating cycle. A careful analysis of the spectra collected along different p-T thermodynamic paths shows the occurrence of a cold crystallization at 295 K on heating from 139 K along the p = 0.5 GPa isobar. The rich phase diagrams of the two ionic liquids is the result of the competition among the anion-cation intermolecular interactions, the lower energy of trans-TFSI with respect to cis-TFSI and the smaller volume of cis-TFSI with respect to trans-TFSI.
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Recent progress in nanotechnology and its application to biomedical settings have generated great advantages in dealing with early cancer diagnosis. The identification of the specific properties of cancer cells, such as the expression of particular plasma membrane molecular receptors, has become crucial in revealing the presence and in assessing the stage of development of the disease. Here we report a single cell screening approach based on Surface Enhanced Raman Scattering (SERS) microimaging. We fabricated a SERS-labelled nanovector based on the biofunctionalization of gold nanoparticles with folic acid. After treating the cells with the nanovector, we were able to distinguish three different cell populations from different cell lines (cancer HeLa and PC-3, and normal HaCaT lines), suitably chosen for their different expressions of folate binding proteins. The nanovector, indeed, binds much more efficiently on cancer cell lines than on normal ones, resulting in a higher SERS signal measured on cancer cells. These results pave the way for applications in single cell diagnostics and, potentially, in theranostics.
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Ácido Fólico/química , Nanopartículas Metálicas , Análise de Célula Única , Análise Espectral Raman , Linhagem Celular , Ouro , Humanos , Propriedades de SuperfícieRESUMO
The aim of the present work was to investigate how the native signal observed in the electron paramagnetic resonance (EPR) spectrum of tooth enamel and dentin is associated with the organic content of the two tissues. This was achieved by comparing the EPR native signal and the optical bands (Raman and infrared, IR) associated with organic components of tooth enamel and dentin, in natural and deproteinated samples. The main results were: (a) in natural samples, the organic optical bands are more intense in dentin than in enamel, in contrast with the EPR native signal which shows similar intensity in the two tissues; (b) after deproteination, the optical organic bands are completely suppressed in both dentin and enamel, while the EPR native signal is eliminated only in dentin. It is suggested that the IR and Raman organic bands are originated in the bulk of the organic matrix, while the paramagnetic centres associated with the EPR native signal are located in the organic-mineral interface.
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Esmalte Dentário/química , Dentina/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Dente Molar/química , Proteínas/química , Espectrofotometria Infravermelho/métodos , Análise Espectral Raman/métodos , Humanos , Técnicas In VitroRESUMO
We report on Raman and Ni K-edge x-ray absorption investigations of a NiS(2-x)Se(x) (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS(2-x)Se(x) Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS(2-x)Se(x) pyrites.
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The local structure and the electronic properties of FeSe under hydrostatic pressure were studied by means of dispersive x-ray absorption measurements at the Fe K-edge. The pressure dependence of the x-ray absorption near edge structure features seems to follow the behavior of the superconducting transition temperature Tc. The local structure, that has an important impact on the superconducting properties, appears to fall into two regimes: the pressure dependence of the Fe-Fe bond distance shows a clear change in the compressibility at p â¼ 5 GPa; in contrast, the Fe-Se bond distance decreases continuously with increasing pressure with a lower compressibility than the Fe-Fe bond. The results suggest that the pressure dependent changes in Tc of FeSe are closely related to the changes in local structure.
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We present an analysis of gas-phase structures of small clusters of n-alkylammonium nitrates (ethyl, propyl, and butyl) together with vibrational Raman spectroscopy of their respective liquid phases. The assignment and interpretation of the resonant frequencies have been performed by comparison with high-quality ab initio (DFT) computations. The theoretical spectra are in excellent agreement with the measured ones and allow the interpretation and assignment of almost all the spectral features. A careful analysis of the vibrational frequencies and of the electronic structure of the compounds has provided additional information on various structural features and on the rather complex hydrogen bonding network that exists in such compounds. A geometric structure of the short-range local arrangement in the bulk phases is also proposed.