Low-frequency Raman spectra and fragility of imidazolium ionic liquids

Raman spectra within the 5-200 cm(-1) range have been recorded as a function of temperature for different ionic liquids based on imidazolium cations. A correlation has been found between fragility and the temperature dependence of the strength of fast relaxational motions. Understanding quasielastic scattering as the relaxational contribution to ionic mean-squared displacement elucidates some effects on ionic liquids' fragility resulting from modifications in the chemical structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3462962]

Classification System of Raman Spectra using Cluster Analysis to Diagnose Coronary Artery Lesions

The traditional methods employed to detect atherosclerotic lesions allow for the identification of lesions; however, they do not provide specific characterization of the lesion`s biochemistry. Currently, Raman spectroscopy techniques are widely used as a characterization method for unknown substances, which makes this technique very important for detecting atherosclerotic lesions. The spectral interpretation is based on the analysis of frequency peaks present in the signal; however, spectra obtained from the same substance can show peaks slightly different and these differences make difficult the creation of an automatic method for spectral signal analysis. This paper presents a signal analysis method based on a clustering technique that allows for the classification of spectra as well as the inference of a diagnosis about the arterial wall condition. The objective is to develop a computational tool that is able to create clusters of spectra according to the arterial wall state and, after data collection, to allow for the classification of a specific spectrum into its correct cluster.

Independent component analysis applied to raman spectra for classification of in vitro human coronary arteries

Optical diagnostic methods, such as near-infrared Raman spectroscopy allow quantification and evaluation of human affecting diseases, which could be useful in identifying and diagnosing atherosclerosis in coronary arteries. The goal of the present work is to apply Independent Component Analysis (ICA) for data reduction and feature extraction of Raman spectra and to perform the Mahalanobis distance for group classification according to histopathology, obtaining feasible diagnostic information to detect atheromatous plaque. An 830nm Ti:sapphire laser pumped by an argon laser provides near-infrared excitation. A spectrograph disperses light scattered from arterial tissues over a liquid-nitrogen cooled CCD to detect the Raman spectra. A total of 111 spectra from arterial fragments were utilized.

Diagnostic model based on Raman spectra of normal, hyperplasia and prostate adenocarcinoma tissues in vitro

This study evaluated the use of Raman spectroscopy to identify the spectral differences between normal (N), benign hyperplasia (BPH) and adenocarcinoma (CaP) in fragments of prostate biopsies in vitro with the aim of developing a spectral diagnostic model for tissue classification. A dispersive Raman spectrometer was used with 830 nm wavelength and 80 mW excitation. Following Raman data collection and tissue histopathology (48 fragments diagnosed as N, 43 as BPH and 14 as CaP), two diagnostic models were developed in order to extract diagnostic information: the first using PCA and Mahalanobis analysis techniques and the second one a simplified biochemical model based on spectral features of cholesterol, collagen, smooth muscle cell and adipocyte. Spectral differences between N, BPH and CaP tissues, were observed mainly in the Raman bands associated with proteins, lipids, nucleic and amino acids. The PCA diagnostic model showed a sensitivity and specificity of 100%, which indicates the ability of PCA and Mahalanobis distance techniques to classify tissue changes in vitro. Also, it was found that the relative amount of collagen decreased while the amount of cholesterol and adipocyte increased with severity of the disease. Smooth muscle cell increased in BPH tissue. These characteristics were used for diagnostic purposes.

Classification model based on Raman spectra of selected morphological and biochemical tissue constituents for identification of atherosclerosis in human coronary arteries

This study presents the results of Raman spectroscopy applied to the classification of arterial tissue based on a simplified model using basal morphological and biochemical information extracted from the Raman spectra of arteries. The Raman spectrograph uses an 830-nm diode laser, imaging spectrograph, and a CCD camera. A total of 111 Raman spectra from arterial fragments were used to develop the model, and those spectra were compared to the spectra of collagen, fat cells, smooth muscle cells, calcification, and cholesterol in a linear fit model. Non-atherosclerotic (NA), fatty and fibrous-fatty atherosclerotic plaques (A) and calcified (C) arteries exhibited different spectral signatures related to different morphological structures presented in each tissue type. Discriminant analysis based on Mahalanobis distance was employed to classify the tissue type with respect to the relative intensity of each compound. This model was subsequently tested prospectively in a set of 55 spectra. The simplified diagnostic model showed that cholesterol, collagen, and adipocytes were the tissue constituents that gave the best classification capability and that those changes were correlated to histopathology. The simplified model, using spectra obtained from a few tissue morphological and biochemical constituents, showed feasibility by using a small amount of variables, easily extracted from gross samples.

Raman spectra of a pseudo-oxocarbon anion in ionic liquids

Raman and electronic spectra of the [3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate] dianion, the croconate violet (CV), are reported in solutions of ionic liquids based on imidazolium cations. Different normal modes of the CV anion, nu (C=O), nu (CO) + nu (CC) + nu (CCN), and nu(C N), were used as probes of solvation characteristics of ionic liquids, and were compared with spectra of CV in common solvents. The spectra of CV in ionic liquids are similar to those in dichloromethane solution, but distinct from those in protic solvents such as ethanol or water. The UV-vis spectra of CV in ionic liquids strongly suggest pi-pi interactions between the CV anion and the imidazolium cation. Copyright (C) 2009 John Wiley & Sons, Ltd.

Studies on the resonance Raman spectra of polyaniline obtained with near-IR excitation

The effects of near-IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANIES) and base (PANI-EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm-1 in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm-` were associated to vC-N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm-1 in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to vC=N modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 run causes the deprotonation of PANI-ES and the formation of cross-linking segments having phenazine and/or oxazine rings. For PANI-EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright (c) 2007 John Wiley & Sons, Ltd.

Raman spectra of acetonitrile in imidazolium ionic liquids

Raman spectra of dilute solutions of acetonitrile in ionic liquids reveal the characteristic features of ionic liquids` polarity. This is accomplished by investigating the Raman bandshape of the nu (CN) band, corresponding to the CN stretching mode of CH(3)CN, which is a very sensitive probe of the local environment. The amphiphilic nature of the CH(3)CN molecule allows us to observe the effect of electron pair acceptor and electron pair donor characteristics on ionic liquids. It has been found that the overall polarity of nine different ionic liquids based on 1-alkyl-3-methylimidazolium cations is more dependent on the anion than cation. The observed wavenumber shift of the nu (CN) band of CH(3)CN in ionic liquids containing alkylsulfate anions agrees with the significant different values previously measured for the dielectric constant of these ionic liquids. The conclusions obtained from the analysis of the nu (CN) band were corroborated by the analysis of the symmetric nu(1) (CD(3)) stretching mode of deuterated acetonitrile in different ionic liquids. Copyright (C) 2010 John Wiley & Sons, Ltd.

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether, lithium perchlorate, and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate

Raman spectra of polymer electrolytes based on poly(ethylene glycol) dimethyl ether (PEGdME) with LiClO(4), PEGdME/LiClO(4), and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, PEGdME/[bmim]PF(6), are compared. Raman spectroscopy suggests stronger interactions in PEGdME/LiClO(4) than PEGdmE/[bmim]PF(6), thus corroborating previous results obtained by molecular dynamics simulations. Quantum Chemistry methods have been used to calculate vibrational frequencies and the equilibrium structure of segments of the polymer chain around the cation. A consistent picture has been obtained from Raman spectroscopy, density functional theory (DFT) calculations, and molecular dynamics simulations for these polymer electrolytes. (C) 2010 Elsevier B.V. All rights reserved.

Phase transformation and residual stress probed by Raman spectroscopy in diamond-turned single crystal silicon

Single-point diamond turning of monocrystalline semiconductors is an important field of research within brittle materials machining. Monocrystalline silicon samples with a (100) orientation have been diamond turned under different cutting conditions (feed rate and depth of cut). Micro-Raman spectroscopy and atomic force microscopy have been used to assess structural alterations and surface finish of the samples diamond turned under ductile and brittle modes. It was found that silicon undergoes a phase transformation when machined in the ductile mode. This phase transformation is evidenced by the creation of an amorphous surface layer after machining which has been probed by Raman scattering. Compressive residual stresses are estimated for the machined surface and it is observed that they decrease with an increase in the feed rate and depth of cut. This behaviour has been attributed to the formation of subsurface cracks when the feed rate is higher than or equal to 2.5 mu m/rev. The surface roughness was observed to vary with the feed rate and the depth of cut. An increase in the surface roughness was influenced by microcrack formation when the feed rate reached 5.0 mu m/rev. Furthermore, a high-pressure phase transformation induced by the tool/material interaction and responsible for the ductile response of this typical brittle material is discussed based upon the presented Raman spectra. The application of this machining technology finds use for a wide range of high quality components, for example the creation of a micrometre-range channel for microfluidic devices as well as microlenses used in the infrared spectrum range.

Short-range structure of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) ceramic compounds probed by XAS and Raman scattering techniques

Ti K-edge x-ray absorption near-edge spectroscopy (XANES) and Raman scattering were used to study the solid solution effects on the structural and vibrational properties of Pb(1-x)Ba(x)Zr(0.65)Ti(0.35)O(3) with 0.0 < x < 0.40. Compared with x-ray diffraction techniques, which indicates that the average crystal symmetry changes with the substitution of Pb by Ba ions or with temperature variations for samples with x=0.00, 0.10, and 0.20, local structural probes such as XANES and Raman scattering results demonstrate that at local level, the symmetry changes are much less prominent. Theoretical XANES spectra calculation corroborate with the interpretation of the XANES experimental data.

Structure, stability, depolarized light scattering, and vibrational spectra of fullerenols from all-electron density-functional-theory calculations

We have investigated the stability, electronic properties, Rayleigh (elastic), and Raman (inelastic) depolarization ratios, infrared and Raman absorption vibrational spectra of fullerenols [C(60)(OH)(n)] with different degrees of hydroxylation by using all-electron density-functional-theory (DFT) methods. Stable arrangements of these molecules were found by means of full geometry optimizations using Becke's three-parameter exchange functional with the Lee, Yang, and Parr correlation functional. This DFT level has been combined with the 6-31G(d,p) Gaussian-type basis set, as a compromise between accuracy and capability to treat highly hydroxylated fullerenes, e.g., C(60)(OH)(36). Thus, the molecular properties of fullerenols were systematically analyzed for structures with n=1, 2, 3, 4, 8, 10, 16, 18, 24, 32, and 36. From the electronic structure analysis of these molecules, we have evidenced an important effect related to the weak chemical reactivity of a possible C(60)(OH)(24) isomer. To investigate Raman scattering and the vibrational spectra of the different fullerenols, frequency calculations are carried out within the harmonic approximation. In this case a systematic study is only performed for n=1-4, 8, 10, 16, 18, and 24. Our results give good agreements with the expected changes in the spectral absorptions due to the hydroxylation of fullerenes.

Evidences of the evolution from solid solution to surface segregation in Ni-doped SnO(2) nanoparticles using Raman spectroscopy

Ni-doped SnO(2) nanoparticles, promising for gas-sensing applications, have been synthesized by a polymer precursor method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO(2)) for Ni contents below 10 mol%. The mean crystallite size shows a progressive reduction with the Ni content. Room-temperature Raman spectra of Ni-doped SnO(2) nanoparticles show the presence of Raman active modes and modes activated by size effects. From the evolution of the A(1g) mode with the Ni content, a solubility limit at similar to 2 mol% was estimated. Below that content, Raman results are consistent with the occurrence of solid solution (ss) and surface segregation (seg.) of Ni ions. Above similar to 2 mol% Ni, the redshift of A(1g) mode suggests that the surface segregation of Ni ions takes place. Disorder-activated bands were determined and their integrated intensity evolution with the Ni content suggest that the solid-solution regime favors the increase of disorder; meanwhile, that disorder becomes weaker as the Ni content is increased. Copyright (C) 2010 John Wiley & Sons, Ltd.

USE OF DISPERSIVE RAMAN SPECTROSCOPY IN THE DETERMINATION OF UNSATURATED FAT IN COMMERCIAL EDIBLE OIL- AND FAT-CONTAINING INDUSTRIALIZED FOODS

The present study aims at the use of Raman spectroscopy in the quantification of unsaturated fats in fat-containing foods, compared to the information available in the Nutritional Table, to obtain a non-destructive optical quantification of unsaturation. Raman spectra of edible oil, margarine, mayonnaise, hydrogenated fat, and butter were obtained with a near-infrared Raman spectrometer (830nm). By analyzing selected bands in the regions of 1750, 1660, 1440, 1300, and 1260cm-1, the amount of total and unsaturated fat of samples of oil, margarine, and mayonnaise were correlated with the information displayed in the Nutritional Table. The amount of unsaturated trans fat in selected samples was correlated to the Raman shift of 1660cm-1. Dispersive Raman spectroscopy was shown to be effective in quantifying the unsaturated fats in oil, margarine, and mayonnaise, and trans fat in hydrogenated oils and butter.

Raman spectroscopy analysis of structural photoinduced changes in GeS(2) + Ga(2)O(3) thin films

Photoexpansion and photobleaching effects have been observed in amorphous GeS(2) + Ga(2)O(3) (GGSO) thin films, when their surfaces were exposed to UV light. The photoinduced changes on the surface of the samples are indications that the structure has been changed as a result of photoexcitation. In this paper, micro-Raman, energy dispersive X-ray analysis (EDX) and backscattering electrons (BSE) microscopy were the techniques used to identify the origin of these effects. Raman spectra revealed that these phenomena are a consequence of the Ge-S bonds` breakdown and the formation of new Ge-O bonds, with an increase of the modes associated with Ge-O-Ge bonds and mixed oxysulphide tetrahedral units (S-Ge-O). The chemical composition measured by EDX and BSE microscopy images indicated that the irradiated area is oxygen rich. So, the present paper provides fundamental insights into the influence of the oxygen within the glass matrix on the considered photoinduced effects. (C) 2010 Elsevier B.V. All rights reserved.