Using the Tsallis distribution and the fractional differentiation to resolve the overlapping bands

Using the Tsallis distribution, which facilitates the generalization of well-known distributions such as Gaussian and Lorentzian by varying a non-extensivity parameter q as a model of the individual band to correctly assign overlapping bands and the fractional differentiation as mathematical tool to help to determine the spectral parameters of the individual band, a new resolution method for the overlapping bands is presented. According to variation of the maximum and the zero-crossing of the Tsallis distribution at different differential order, two types of parameter estimators are obtained, which are utilized to calculate the parameters of position, height, and width of Tsallis distribution. To verify the suggested method, separation of several kinds of overlapping bands simulated by computer and the experimental infrared spectrum of 1,2-bromofluoroethane have been performed and discussed. Figure α-Order differentiation of the overlapping band     

Ensemble preprocessing of near-infrared (NIR) spectra for multivariate calibration

Preprocessing of raw near-infrared (NIR) spectral data is indispensable in multivariate calibration when the measured spectra are subject to significant noises, baselines and other undesirable factors. However, due to the lack of sufficient prior information and an incomplete knowledge of the raw data, NIR spectra preprocessing in multivariate calibration is still trial and error. How to select a proper method depends largely on both the nature of the data and the expertise and experience of the practitioners. This might limit the applications of multivariate calibration in many fields, where researchers are not very familiar with the characteristics of many preprocessing methods unique in chemometrics and have difficulties to select the most suitable methods. Another problem is many preprocessing methods, when used alone, might degrade the data in certain aspects or lose some useful information while improving certain qualities of the data. In order to tackle these problems, this paper proposes a new concept of data preprocessing, ensemble preprocessing method, where partial least squares (PLSs) models built on differently preprocessed data are combined by Monte Carlo cross validation (MCCV) stacked regression. Little or no prior information of the data and expertise are required. Moreover, fusion of complementary information obtained by different preprocessing methods often leads to a more stable and accurate calibration model. The investigation of two real data sets has demonstrated the advantages of the proposed method.     

Application of near infrared spectroscopy (NIR), X-ray fluorescence (XRF) and chemometrics to the differentiation of marmora samples from the Mediterranean basin

Abstract

Near-infrared (NIR) and X-ray fluorescence spectra were recorded for 15 different samples of marmora, from the Mediterranean Basin and of different colours. After appropriate pretreatment (SNV transform + second derivative), the results were subjected to principal component analysis (PCA) treatment with a view to differentiating them. The observed differences among the samples were chemically interpreted by highlighting the NIR wavelengths and minerals, respectively, contributing the most to the PCA models. Moreover, a mid-level data fusion protocol allowed integrating the information from the different techniques and, in particular, to correctly identify (based on the distance in the score space) three test samples of known type. Moreover, it should be stressed that positive results on the differentiation and identification of marmora were obtained using two completely non-invasive, non-destructive and relatively inexpensive techniques, which can also be used in situ.     

Effect of temperature variation on the visible and near infrared spectra of wine and the consequences on the partial least square calibrations developed to measure chemical composition

Many studies have reported the use of near infrared (NIR) spectroscopy to characterize wines or to predict wine chemical composition. However, little is known about the effect of variation in temperature on the NIR spectrum of wine and the subsequent effect on the performance of calibrations used to measure chemical composition. Several parameters influence the spectra of organic molecules in the NIR region, with temperature being one of the most important factors affecting the vibration intensity and frequency of molecular bonds. Wine is a complex mixture of chemical components (e.g. water, sugars, organic acids, and ethanol), and a simple ethanol and water model solution cannot be used to study the possible effects of temperature variations in the NIR spectrum of wine. Ten red and 10 white wines were scanned in triplicate at six different temperatures (25 °C, 30 °C, 35 °C, 40 °C, 45 °C and 50 °C) in the visible (vis) and NIR regions (400-2500 nm) in a monochromator instrument in transmission mode (1 mm path length). Principal component analysis (PCA) and partial least squares (PLS) regression models were developed using full cross validation (leave-one-out). These models were used to interpret the spectra and to develop calibrations for alcohol, sugars (glucose + fructose) and pH at different temperatures. The results showed that differences in the spectra around 970 nm and 1400 nm, related to OH bonding were observed for both varieties. Additionally an effect of temperature on the vis region of red wine spectra was observed. The standard error of cross validation (SECV) achieved for the PLS calibration models tended to inverse as the temperature increased. The practical implication of this study it is recommended that the temperature of scanning for wine analysis using a 1 mm path length cuvette should be between 30 °C and 35 °C.     

Crystal structure and infrared spectra of dicesium trans-tetraaquadichlorochromium(III) chloride

The crystal structure of dicesium trans-tetraaquadichlorochromium(III) chloride Cs₂Cr^IIICl₅·4H₂O with trans-[M^IIIX₂(H₂O)₄]⁺ complex ions (space group C2/c, Z=4, a=1915.3(4) pm, b=614.1(1) pm, c=1392.0(3) pm, and β=118.24(3)°, final R1=0.0246 for 2100 unique reflections) was redetermined by single-crystal X-ray diffraction studies. It was found to crystallize in a 2c super structure of the structure reported previously (Inorg. Chem. 20 (1981) 1566; Inorg. Chem. 36 (1997) 2248). The obtained structure data now agree with the results of infrared spectroscopic studies, which has been confirmed in this work, namely that there are two different hydrate H₂O molecules in the structure. Phase transitions, static or dynamic disorder of the hydrate H₂O molecules, and space group C2/m proposed in the literature were ruled out. The coordinates of the four hydrogen positions derived from the X-ray data have been improved via the O–H distances derived from the wave numbers of the OD stretching modes of matrix isolated HDO molecules (2426, 2323, and 2306 cm⁻¹, 263 K) by using the ν_OD versus r_O–H correlation curve reported in the literature (J. Mol. Struct. 404 (1997) 63). The ν_OD versus r_HCl correlation curve reported by Mikenda (J. Mol. Struct. 147 (1986) 1) should be improved, especially for strong hydrogen bonds. The two hydrate H₂O molecules of the title compound are strongly distorted with a weak and a relatively strong O–HCl hydrogen bond each thus intramolecular coupling of the two OH stretching vibrations to coupled ones is largely reduced and, hence, the wavenumbers of the OH and OD stretching modes of the HDO molecules mainly resemble those of the H₂O and D₂O molecules. The strength of the hydrogen bonds is in accordance with the predictions of the competitive and synergetic effects. Chloro ligands are weaker hydrogen bond acceptor groups than chloride ions.     

Conformational stabilities of dimethylmethoxyphosphine and dimethyl(methylthio)phosphine from temperature dependent infrared spectra of rare gas solutions

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500 to 400 cm⁻¹) of dimethylmethoxyphosphine, (CH₃)₂POCH₃ and dimethyl(methylthio)phosphine, (CH₃)₂PSCH₃ dissolved in liquid krypton and/or xenon have been recorded. From these data, the enthalpy differences have been determined to be 393±50 cm⁻¹ (4.71±0.60 kJ/mol), for (CH₃)₂POCH₃ with the near-cis conformer the more stable rotamer and 80±10cm⁻¹ (0.96±0.12 kJ/mol) for (CH₃)₂PSCH₃ with the cis conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules.     

Vibrational and electronic studies on interactions of Cu (II) with protic amides: Structural aspects of biological importance

Raman, IR and UV–Vis–NIR experiments of formamide (FA), N-methylformamide (NMF) and their solutions with copper perchlorate at different compositions were carried out. The downshift of the ν_CO mode and the upshift of the νCN vibration have been observed for both amides and suggest that an ionic structure is stabilized by Cu (II). The quantitative Raman study at the νCN region reveals that six FA molecules are coordinated to Cu (II) while four NMF molecules are around the metal ion. The data are complemented by information at the region characteristic of the metal–ligand vibrations, which evidences coordination through the O atom. The spectral changes observed at the ν_CN region have been then combined to the electronic data and show that [Cu(FA)₆]²⁺ and [Cu(NMF)₄]²⁺ are described as distorted octahedral and square planar complexes.     

Electronic spectra of Cu(II) crystal complexes with S-methylthiosemicarbazones

Electronic spectra for a series of coordination compounds of copper(II) with tridentant ligands of salicyl aldehyde S-methylthiosemicarbazone and 8-quinoline aldehyde S-methylthiosemicarbazone were investigated. Coordinations of central ions were determined on the basis of X-ray data and IR spectra. Electronic transitions were detected by processing the diffusion-reflection spectra according to theKubelka-Munk theory. Identifications proved the presence of bands corresponding to intraligand transition, charge transfer spectra and the transition of d-d type which are the result of the elimination of d-orbital degeneration for Cu(II) ions in the crystal field. The effect of the symmetry of coordination polyhedrons is discussed.

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Elektronenspektren von Cu(II) Kristall-Komplexen mit S-Methylthiosemicarbazonen

Zusammenfassung Es wurden Elektronenspektren einer Serie von Koordinationsverbindungen des Kupfer(II) mit tridentaten Liganden (Salizylaldehyd-S-methylthiosemicarbazon und 8-Chinolinylaldehyd-S-methylthiosemicarbazon) untersucht. Die Zentralionkoordination wurde durch Röntgenstrahlenuntersuchungen und auf Grund der IR-Spektren festgestellt. Die Elektronenübergänge wurden nach derKubelka-Munk-Theorie aus den diffusen Reflexionsspektren ermittelt. Die Banden wurden den Intraligandübergängen, dem charge-transfer-Spektrum und den d-d-Typ-Übergängen, die als Resultat der Entartungsbeseitigung der Cu(II)-d-Orbitale im Kristallfeld verschiedener Symmetrie entstehen, zugeschrieben.

     

Vibrational spectra of Zn(II) complexes of the amino acids with hydrophobic residues

The infrared and Raman spectra of the bis-chelated Zn(II) complexes of the amino acids glycine, alanine, valine, leucine, isoleucine and phenylalanine were recorded and analyzed in relation to its structural peculiarities. Some comparisons between the recorded spectra are also presented and the characteristics of the carboxylate motions as well as those of the metal-to-ligand vibrations are discussed in detail.     

Synthesis,infrared spectra and thermal investigation of gold(III) and zinc(II) urea complexes. A new procedure for the synthesis of basic zinc carbonate

Reaction of urea with sodium tetrachloroaurate(III) dihydrate and zinc(II) chloride has been investigated at room and elevated temperature (～90°C) producing three new compounds: [Au(urea)₄]Cl₃·2H₂O, [Au₂(NH₂)₂Cl₂(NCO)(OH)]·H₂O and 2ZnCO₃·3Zn(OH)₂. The infrared spectra were recorded and the observed bands were assigned. The binuclear gold complex and basic zinc carbonate basic were also investigated by thermal analysis, and general mechanisms describing their decompositions are suggested.