Champ de forces de symetrie locale de molecules cycliques: Partie I. L'hexachlorocyclotriphosphazène (NPCl2)3

Normal coordinate analysis of hexachloroeyclotriphosphazene (NPCl₂)₃ using a local symmetry force field gives good agreement between the calculated and observed frequencies and permits assignments for the 30 normal vibrational modes to be proposed. The redundancy relations lead to the definition of 12 coordinates which are characteristic of the ring. These may be transferred to more complex molecules where this ring is present.     

Comparison of supervised pattern recognition methods with McNemar’s statistical test: Application to qualitative analysis of sugar beet by near-infrared spectroscopy

The application of supervised pattern recognition methodology is becoming important within chemistry. The aim of the study is to compare classification method accuracies by the use of a McNemar’s statistical test. Three qualitative parameters of sugar beet are studied: disease resistance (DR), geographical origins and crop periods. Samples are analyzed by near-infrared spectroscopy (NIRS) and by wet chemical analysis (WCA). Firstly, the performances of eight well-known classification methods on NIRS data are compared: Linear Discriminant Analysis (LDA), K-Nearest Neighbors (KNN) method, Soft Independent Modeling of Class Analogy (SIMCA), Discriminant Partial Least Squares (DPLS), Procrustes Discriminant Analysis (PDA), Classification And Regression Tree (CART), Probabilistic Neural Network (PNN) and Learning Vector Quantization (LVQ) neural network are computed. Among the three data sets, SIMCA, DPLS and PDA have the highest classification accuracies. LDA and KNN are not significantly different. The non-linear neural methods give the less accurate results. The three most accurate methods are linear, non-parametric and based on modeling methods. Secondly, we want to emphasize the power of near-infrared reflectance data for sample discrimination. McNemar’s tests compare classification developed with WCA or with NIRS data. For two of the three data sets, the classification results are significantly improved by the use of NIRS data.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

Local symmetry force field of the silatrane cage

The problem of the redundancies inherent to the tricyclic structure of the silatranes is solved and the symmetry coordinates of the reduced space for the cage are settled. In this space, the local symmetry force field of the skeleton is built, then refined looking at the wavenumbers common to numerous silatranes. These parameters are used to interpret the spectra of simple derivatives. Moreover, it constitutes transferable information available for performing an a priori computation of the vibrational normal modes of homologous molecules.     

Champ de forces de symetrie locale de molecules cycliques: III. Interprétation des spectres de vibration du glucose cristallisé sous les deux formes α et β

This paper reports complete infrared and Raman spectra of crystalline α and β glucose. Some high frequency bands are shown to be characteristic of the anomeric forms but there are significant differences in the low frequency region, despite the fact that the two forms crystallize in the same space group.These spectral data have been interpreted using a normal coordinate treatment of intra and intermolecular vibrations. Firstly, it was necessary to take into account both “tree” and “cycle” redundancies. Concerning the intermolecular vibrations, hydrogen bonds and atom-atom contacts were considered. Assignments of frequencies are given. A relation between the observed differences and the molecular structure modification is established and it is shown that hydrogen bonding is responsible for the differentiation of the α and β glucose low frequency spectra.     

Structure moleculaire de composes nitro aromatiques : Partie II. Spectres de vibration et analyse en coordonnées normales du 1,3,5 trinitrobenzene (TNB)

Infrared and Raman spectra of 1,3,5-trinitrobenzene are reported with a normal coordinate treatment taking redundancies into account. Assignments are given with particular emphasis on low frequency and overall vibrations, and the local symmetry force field is described.     

Multivariate curve resolution methods in imaging spectroscopy: influence of extraction methods and instrumental perturbations

Imaging spectroscopy is becoming a key field of analytical chemistry. In the face of more and more complex samples, we actually need accurate microscopic insight. Nowadays, the methods used to produce concentration maps of the pure compounds from spectral data sets are based on the classical univariate approach although multivariate approaches are sometimes investigated. But in any case, the analytical quality of the chemical images thus provided cannot be discussed since no reference methods are at our disposal. Thus the proposed research focuses on the application of multivariate methods such as Orthogonal Projection Approach (OPA), SIMPLE-to-use Self-modeling Mixture Analysis (SIMPLISMA), Multivariate Curve Resolution - Alterning Least Squares (MCR-ALS), and Positive Matrix Factorization (PMF) for imaging spectroscopy. A systematic and quantitative characterization of the accuracy of spectra and images extraction is investigated on mid-infrared spectral data sets. Of special interest is the influence of instrumental perturbations such as noise and spectral shift on the extraction ability to access the algorithm's robustness.     

Direct structural identification of polysaccharides from red algae by FTIR microspectrometry II: Identification of the constituents ofGracilaria verrucosa

The use of the infrared microspectrometry analytical technique as a new tool for the identification of the polysaccharides contained in the red algaeGracilaria verrucosa has demonstrated that in addition to agar spectra, features of the other coexisting constituents can also be obtained. Indeed, the infrared spectra recorded previously, all exhibit two important bands at about 1645 and 1530cm^–1. These two bands were not present in the infrared spectra of the extracted agars and they are expected to be due to the amide I and amide II protein vibrations. In order to confirm this supposition, we have applied some enzymatic treatments, firstly on the whole algae and secondly on the ground algae (the algae has been previously depigmented and then dehydrated). Agarase, xylanase and cellulase were successively carried out on the algae. The last resulting spectrum, i.e. the spectrum obtained from the fraction which has undergone the three treatments, has been identified to be characteristic of proteins. This spectrum contained, both the amide I and II vibrations and in addition, weak absorption at 1230 cm^–1 due probably to the amide III, was observed. Additional weak bands in the 1400–1300 cm^–1 due to the different skeletal modes of the proteins were also present in this spectrum.The infrared spectra also revealed that the use of the enzymatic treatments on the ground algae is more efficient than when it is carried out on the whole algae.