CNRS Laboratory of Infrared and Raman Spectrochemistry

Lille, France

CNRS Laboratory of Infrared and Raman Spectrochemistry

Lille, France
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Smirnov K.S.,CNRS Laboratory of Infrared and Raman Spectrochemistry
Physical Chemistry Chemical Physics | Year: 2017

The interaction of water with the hydroxylated (010) surface of silicalite-1 was studied by classical molecular dynamics simulations. Interatomic interactions in the system were described using a set of effective potentials combining well-tested BKS and SPC models. The extended force field is shown to correctly reproduce the structural, energy, and dynamical characteristics of the silica surface OH groups. The interaction of water with the hydrophilic silanols leads to an ordering of H2O molecules in the vicinity of the surface. The ordering is found to be limited to two molecular layers extending to 7 Å above the surface. Despite the hydrophobic nature of the silicalite structure and the presence of hydrophilic surface sites, water molecules are capable of penetrating the porous silicalite system, where they form an H-bonded network blocking further access to the bulk. Water uptake by the zeolite was computed to be small in the time-scale of the simulations. The vibrational dynamics of the surface OH groups and adsorbed water molecules is discussed in detail. In agreement with the results of spectroscopic experiments, water molecules in the ordered surface layer have a spectral signature different from that of molecules more distant from the surface. © 2017 the Owner Societies.

Baddour-Hadjean R.,CNRS East Paris Institute of Chemistry and Materials Science | Smirnov M.B.,Saint Petersburg State University | Kazimirov V.Y.,Joint Institute for Nuclear Research | Smirnov K.S.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Pereira-Ramos J.-P.,CNRS East Paris Institute of Chemistry and Materials Science
Journal of Raman Spectroscopy | Year: 2015

Structure and vibrational dynamics of γ-V2O5 synthesized from a pristine γ-LiV2O5 sample via a chemical oxidation route was studied by means of Raman spectroscopy and quantum-chemical calculations. The calculations based on density functional theory reliably reproduce the experimental structure of the γ-V2O5 lattice. The calculated Raman spectrum agrees remarkably well with the experimental one. Making use of the agreement, a complete assignment of Raman bands to vibrations of particular structural units is proposed. The comparison of Raman spectra and structural features of α-V2O5 and γ-V2O5 polymorphs allowed establishing reliable 'structure-spectrum' correlations and identifying Raman peaks characteristic for different structural units. © 2015 John Wiley and Sons, Ltd.

Deschamps T.,Ecole Polytechnique - Palaiseau | Deschamps T.,Lyon Institute of Nanotechnologies | Vezin H.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Gonnet C.,Draka Comteq France | Ollier N.,Ecole Polytechnique - Palaiseau
Optics Express | Year: 2013

Using a combination of experimental techniques such as optical absorption, Raman scattering, continuous wave and pulse Electron Spin Resonance (ESR), we characterize a set of γ-irradiated Yb3+ doped silica glass preforms with different contents of phosphorous and aluminum. We demonstrate that when P is introduced in excess compared to Al, nearly no radiodarkening is induced by γ-rays. On the other hand, when Al>P, a large absorption band is induced by radiation. Thermal annealing experiments reveal the correlation between the decrease of the optical absorption band and the decrease of the Al-Oxygen Hole Center (AlOHC) ESR signal, demonstrating the main role of AlOHC defects in the fiber darkening. HYSCORE (HYperfine Sublevel CORElation) pulse-ESR experiments show a high Al-P nuclear spin coupling when P>Al and no coupling when Al>P. This result suggests that both AlOHC and POHC creation is inhibited by Al-O-P linkages. Confronting our data with previous works, we show that the well-known photodarkening process, meaning losses induced by the IR pump, can also be explained in this framework. © 2013 Optical Society of America.

Devos O.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Downey G.,Teagasc | Duponchel L.,CNRS Laboratory of Infrared and Raman Spectrochemistry
Food Chemistry | Year: 2014

Classification is an important task in chemometrics. For several years now, support vector machines (SVMs) have proven to be powerful for infrared spectral data classification. However such methods require optimisation of parameters in order to control the risk of overfitting and the complexity of the boundary. Furthermore, it is established that the prediction ability of classification models can be improved using pre-processing in order to remove unwanted variance in the spectra. In this paper we propose a new methodology based on genetic algorithm (GA) for the simultaneous optimisation of SVM parameters and pre-processing (GENOPT-SVM). The method has been tested for the discrimination of the geographical origin of Italian olive oil (Ligurian and non-Ligurian) on the basis of near infrared (NIR) or mid infrared (FTIR) spectra. Different classification models (PLS-DA, SVM with mean centre data, GENOPT-SVM) have been tested and statistically compared using McNemar's statistical test. For the two datasets, SVM with optimised pre-processing give models with higher accuracy than the one obtained with PLS-DA on pre-processed data. In the case of the NIR dataset, most of this accuracy improvement (86.3% compared with 82.8% for PLS-DA) occurred using only a single pre-processing step. For the FTIR dataset, three optimised pre-processing steps are required to obtain SVM model with significant accuracy improvement (82.2%) compared to the one obtained with PLS-DA (78.6%). Furthermore, this study demonstrates that even SVM models have to be developed on the basis of well-corrected spectral data in order to obtain higher classification rates. © 2013 Elsevier Ltd. All rights reserved.

Perrier A.,University Paris Diderot | Aloise S.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Olivucci M.,University of Siena | Olivucci M.,Bowling Green State University | And 2 more authors.
Journal of Physical Chemistry Letters | Year: 2013

The understanding of the intimate electronic processes in photochromes is essential to optimize the properties of light-controllable devices. For one of the most studied classes of molecular switches, namely, dithienylethenes, the relative efficiencies of the normal and inverse structures remained puzzling. Indeed, despite a larger ratio of the active antiparallel conformers for the latter, the quantum yields of cyclization of inverse dithienylethenes do not exceed those of its normal counterpart. In the present contribution, we provide the first explanation of this experimental outcome using multireference ab initio quantum chemistry. We demonstrate the existence of a fluorescent intermediate on the S1 state of the inverse system that generates a photochemically unreactive conformation in the ground state. This study paves the way toward a rational development of efficient molecular photochromes presenting a photon-quantitative response. © 2013 American Chemical Society.

Piqueras S.,University of Barcelona | Piqueras S.,CSIC - Institute of Environmental Assessment And Water Research | Duponchel L.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Tauler R.,CSIC - Institute of Environmental Assessment And Water Research | De Juan A.,University of Barcelona
Analytica Chimica Acta | Year: 2011

MCR-ALS is a resolution method that has been applied in many different fields, such as process analysis, environmental data and, recently, hyperspectral image analysis. In this context, the algorithm provides the distribution maps and the pure spectra of the image constituents from the sole information in the raw image measurement. Based on the distribution maps and spectra obtained, additional information can be easily derived, such as identification of constituents when libraries are available or quantitation within the image, expressed as constituent signal contribution. This work summarizes first the protocol followed for the resolution on two examples of kidney calculi, taken as representations of images with major and minor compounds, respectively.Image segmentation allows separating regions of images according to their pixel similarity and is also relevant in the biomedical field to differentiate healthy from non-healthy regions in tissues or to identify sample regions with distinct properties. Information on pixel similarity is enclosed not only in pixel spectra, but also in other smaller pixel representations, such as PCA scores. In this paper, we propose the use of MCR scores (concentration profiles) for segmentation purposes. K-means results obtained from different pixel representations of the data set are compared. The main advantages of the use of MCR scores are the interpretability of the class centroids and the compound-wise selection and preprocessing of the input information in the segmentation scheme. © 2011 Elsevier B.V.

Devos O.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Duponchel L.,CNRS Laboratory of Infrared and Raman Spectrochemistry
Chemometrics and Intelligent Laboratory Systems | Year: 2011

Spectral pre-processing and variable selection are often used to produce PLS regression models with better prediction abilities. We proposed here to optimize simultaneously the spectral pre-processing and the variable selection for PLS regression. The method is based on parallel genetic algorithm with a unique chromosome coding both for pre-processing and variable selections. A pool of 31 pre-processing functions with various settings is tested. In the same chromosome several pre-processing steps can be combined. Three near infrared spectroscopic datasets have been used to evaluate the methodology. The efficacy of the co-optimization is evaluated by comparing the prediction ability of the PLS models with those after pre-processing optimization only. The effect of the number of successive pre-processing steps has been also tested. Concerning the different datasets used here, one can observe two different behaviors. In a first case the GA co-optimization procedure is found to perform well, leading to important improvement of the prediction ability especially when three consecutive pre-processing techniques are applied. In a second case, only the preprocessing optimization is enough to obtain an optimal model. All these models are optimal and more accurate compared to the classical models (build with the "trial and error" methods). © 2011 Elsevier B.V.

Barras A.,Lille University of Science and Technology | Boussekey L.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Courtade E.,CNRS Atomic and Molecular Physics Laboratory | Boukherroub R.,Lille University of Science and Technology
Nanoscale | Year: 2013

Hypericin (Hy), a naturally occurring photosensitizer (PS), is extracted from Hypericum perforatum plants, commonly known as St. John's wort. The discovery of the in vitro and in vivo photodynamic activities of hypericin as a photosensitizer generated great interest, mainly to induce a very potent antitumoral effect. However, this compound belongs to the family of naphthodianthrones which are known to be poorly soluble in physiological solutions and produce non-fluorescent aggregates (A. Wirz et al., Pharmazie, 2002, 57, 543; A. Kubin et al., Pharmazie, 2008, 63, 263). These phenomena can reduce its efficiency as a photosensitizer for the clinical application. In the present contribution, we have prepared, characterized, and studied the photochemical properties of Hy-loaded lipid nanocapsule (LNC) formulations. The amount of singlet oxygen (1O2) generated was measured by the use of p-nitroso-dimethylaniline (RNO) as a selective scavenger under visible light irradiation. Our results showed that Hy-loaded LNCs suppressed aggregation of Hy in aqueous media, increased its apparent solubility, and enhanced the production of singlet oxygen in comparison with free drug. Indeed, encapsulation of Hy in LNCs led to an increase of 1O2 quantum yield to 0.29-0.44, as compared to 0.02 reported for free Hy in water. Additionally, we studied the photodynamic activity of Hy-loaded LNCs on human cervical carcinoma (HeLa) and Human Embryonic Kidney (HEK) cells. The cell viability decreased radically to 10-20% at 1 μM, reflecting Hy-loaded LNC25 phototoxicity. © 2013 The Royal Society of Chemistry.

Mutoh K.,Aoyama Gakuin University | Sliwa M.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Abe J.,Aoyama Gakuin University | Abe J.,Japan Science and Technology Agency
Journal of Physical Chemistry C | Year: 2013

Recently, we have developed a series of fast photochromic imidazole dimers with a [2.2]paracyclophane ([2.2]PC) moiety that bridge diphenylimidazole units and succeeded the acceleration of the thermal decoloration rate. The colorless [2.2]PC-bridged imidazole dimers show a photoinduced homolytic bond cleavage of the C-N bond between the imidazole rings to give a pair of colored imidazolyl radicals upon UV light irradiation, followed by the radical-radical coupling reaction to form the initial C-N bond between the imidazole rings. The decoloration reaction to give the initial imidazole dimer proceeds only thermally. The high quantum yield close to unity of the photochromic reaction and the large extinction coefficient of the radical achieve both high optical density at the photostationary state and rapid switching speed. The application to rapid fluorescence switching has been investigated to develop a new type of photochromic fluorescence switching molecule applicable to super-resolution microscopy. The widespread absorption of the colored radical lying between 500 and 900 nm enables the efficient quenching of the excited electronic state of the fluorophores by Förster resonance energy transfer (FRET) from the fluorophores to the radical moiety. We successfully developed a [2.2]PC-bridged imidazole dimer possessing a fluorescein moiety as a fluorescence unit. This photochromic dye shows fast photochromism to give a pair of imidazolyl radicals that quench the fluorescence from the fluorescent unit by the FRET mechanism. The fluorescence intensity can be switched rapidly with the fast photochromism. © 2013 American Chemical Society.

Falgayrac G.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Sobanska S.,CNRS Laboratory of Infrared and Raman Spectrochemistry | Bremard C.,CNRS Laboratory of Infrared and Raman Spectrochemistry
Journal of Hazardous Materials | Year: 2013

Laboratory experiments using in situ Raman imaging combined with ex situ TOF-S-SIMS demonstrate the behavior of CdSO4·8/3H2O microparticles in contact with 101̄4 CaCO3 (calcite) surface under three different experimental conditions representative of unpolluted atmosphere. The contact of CdSO4·8/3H2O particles with CaCO3 surface in humid air (RH∼40-80%) does not induce any chemical reaction. In contrast, the condensation of a water drop on CdSO4·8/3H2O/CaCO3 interface causes the free dissolution of CdSO4·8/3H2O particle in the drop. A CdSO4·8/3H2O microcrystal is reformed after gentle drying with a CdSO4·H2O coating of the CaCO3 surface. The TOF-S-SIMS image of the CaCO3 surface provides evidence of a thin layer corresponding probably to insoluble coating of CdCO3 (otavite) or CdxCa1-xCO3 solid solution at the liquid-solid interface. This layer armours the CaCO3 from further dissolution and stops the reaction. The deposition of CdSO4·8/3H2O particle in water drop previously in contact with CaCO3 for a long time generates CdCO3 small rhombohedral crystals while gentle drying provokes the crystallization of bar shape crystals of CaSO4·2H2O (gypsum). These laboratory results provide valuable chemical prediction for a possible fate of cadmium rich particles emitted in the atmosphere and thus, can contribute to realistic assessment of human exposure to Cd hazard. © 2013 Elsevier B.V.

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