Hybrid hard- and soft-modelling applied to analyze ultrafast processes by femtosecond transient absorption spectroscopy: study of the photochromism of salicylidene anilines.

Multivariate curve resolution-alternating least squares (MCR-ALS) of multi-experiment data analysis was successfully applied to elucidate the photodynamics of the N-(3-methylsalicylidene)-3-methylaniline by analyzing UV-vis femtosecond transient absorption spectra. The two-way data obtained present some specific difficulties linked to the nature of the transient spectra collected and to the overlapping of the photodynamics of the solvent and other contributions at short time scale (below 1 ps). Advantage was taken from the flexibility of the hybrid hard-soft multivariate curve resolution (HS-MCR) approach to consider a non-absorbing contribution in the kinetic model and to provide a functional description of the solvent in soft-modelling. The results obtained confirm the existence of an intermediate excited state in the process, which is created just after the ESIPT. It was observed that this intermediate relaxes in a few hundreds of femtosecond to the S(1) fluorescent cis-keto excited state and a decay time constant of 219 fs was found. These results confirm other femtosecond time-resolved fluorescence studies on salicylidene aniline molecules. Previous hypothesis on the formation of the trans-keto photoproduct from the S(1) fluorescent cis-keto state (time constant 14 ps) is also confirmed.

Contribution made by multivariate curve resolution applied to gel permeation chromatography-Fourier transform infrared data for an in-depth characterization of styrene-butadiene rubber blends.

We evaluate the contribution made by multivariate curve resolution-alternating least squares (MCR-ALS) for resolving gel permeation chromatography-Fourier transform infrared (GPC-FT-IR) data collected on butadiene rubber (BR) and styrene butadiene rubber (SBR) blends in order to access in-depth knowledge of polymers along the molecular weight distribution (MWD). In the BR-SBR case, individual polymers differ in chemical composition but share almost the same MWD. Principal component analysis (PCA) gives a general overview of the data structure and attests to the feasibility of modeling blends as a binary system. MCR-ALS is then performed. It allows resolving the chromatographic coelution and validates the chosen methodology. For SBR-SBR blends, the problem is more challenging since the individual elastomers present the same chemical composition. Rank deficiency is detected from the PCA data structure analysis. MCR-ALS is thus performed on column-wise augmented matrices. It brings very useful insight into the composition of the analyzed blends. In particular, a weak change in the composition of individual SBR in the MWD's lowest mass region is revealed.

Genetic algorithm optimisation combined with partial least squares regression and mutual information variable selection procedures in near-infrared quantitative analysis of cotton-viscose textiles.

In this work, different approaches for variable selection are studied in the context of near-infrared (NIR) multivariate calibration of textile. First, a model-based regression method is proposed. It consists in genetic algorithm optimisation combined with partial least squares regression (GA-PLS). The second approach is a relevance measure of spectral variables based on mutual information (MI), which can be performed independently of any given regression model. As MI makes no assumption on the relationship between X and Y, non-linear methods such as feed-forward artificial neural network (ANN) are thus encouraged for modelling in a prediction context (MI-ANN). GA-PLS and MI-ANN models are developed for NIR quantitative prediction of cotton content in cotton-viscose textile samples. The results are compared to full-spectrum (480 variables) PLS model (FS-PLS). The model requires 11 latent variables and yielded a 3.74% RMS prediction error in the range 0-100%. GA-PLS provides more robust model based on 120 variables and slightly enhanced prediction performance (3.44% RMS error). Considering MI variable selection procedure, great improvement can be obtained as 12 variables only are retained. On the basis of these variables, a 12 inputs ANN model is trained and the corresponding prediction error is 3.43% RMS error.

Multivariate curve resolution of rapid-scan FTIR difference spectra of quinone photoreduction in bacterial photosynthetic membranes.

Photosynthetic reaction centres and membranes are systems of particular interest and are often taken as models to investigate the molecular mechanisms of selected bioenergetic reactions. In this work, a multivariate curve resolution by alternating least squares procedure is detailed for resolution of time-resolved difference FTIR spectra probing the evolution of quinone reduction in photosynthetic membranes from Rhodobacter sphaeroides under photoexcitation. For this purpose, different data sets were acquired in the same time range and spectroscopic domain under slightly different experimental conditions. To enable resolution and provide meaningful results the different data sets were arranged in an augmented matrix. This strategy enabled recovery of three different species despite rank-deficiency conditions. It also results in better definition (identity and evolution) of the contributions. From the resolved spectra, the species have been attributed to: 1. the formation of ubiquinol, more precisely the disappearance of Q/appearance of QH(2); 2. conformational change of the protein in the surrounding biological medium; 3. oxidation of diaminodurene, a redox mediator. Because, moreover, results obtained from augmented data sets strategies enable quantitative and qualitative interpretation of concentration profiles, other effects, for example the consequence of repeated light excitation of the same sample, choice of illumination power, or the number of spectra accumulated could be compared and discussed.

Quantitative analysis of cotton-polyester textile blends from near-infrared spectra.

Quantitative analysis of textile blends and textile fabrics is currently of particular interest in the industrial context. In this frame, this work investigates whether the use of Fourier transform (FT) near-infrared (NIR) spectroscopy and chemometrics is powerful for rapid and accurate quantitative analysis of cotton-polyester content in blend products. As samples of the same composition have many sources of variability that affect NIR spectra, indirect prediction is particularly challenging and a large sample population is required to design robust calibration models. Thus, a total of more than three-hundred cotton-polyester samples were selected covering the range from the 0% to 100% cotton and the corresponding NIR reflectance spectra were measured on raw fabrics. The data set obtained was used to develop multivariate models for quantitative prediction from reference measurements. A successful approach was found to rely on partial least squares (PLS) regression combined with genetic algorithms (GAs) for wavelength selection. It involved evaluating a set of calibration models considering different spectral regions. The results obtained considering 27.5% of the original variables yielded a prediction error (RMSEP) of 2.3 in percent cotton content. It demonstrates that FT-NIR spectroscopy has the potential to be used in the textile industry for the prediction of the composition of cotton-polyester blends. As a further consequence, it was observed that the spectral preprocessing and the complexity of the model are simplified compared to the full-spectrum approach. Also, the relevancy of the spectral intervals retained after variable selection can be discussed.

Time-resolved step-scan FT-IR spectroscopy: focus on multivariate curve resolution.

The present paper describes the application of step-scan FT-IR spectroscopy in combination with chemometric analysis of the spectral data for the study of the photocycle of bacteriorhodopsin. The focus is on the performance of this instrumentation for time-resolved experiments. Three-dimensional data-spectra recorded over time-are studied using various factor analysis techniques, e.g., singular values decomposition, evolving factor analysis, and multivariate curve resolution based on alternating least squares. Transient intermediates formed in the time domain ranging from 1 micros to 6.6 ms are clearly detected through reliable pure time evolving profiles. At the same time, pure difference absorbance spectra are provided. As a result, valuable information about transitions and dynamics of the protein can be extracted. We conclude first that step-scan FT-IR spectroscopy is a useful technique for the direct study of difficult photochemical systems. Second, and this is the essential motivation of this paper, chemometrics provide a step forward in the description of the photointermediates.

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.

FT-IR and X-ray spectroscopic investigations of Na-diclofenac-cyclodextrins interactions.

The association of DCF-Na (the salt of the 2-[(2,6-dichlorophenyl)amino]-phenyl-acetic acid) with beta-CD (cyclodextrin) in some therapeutic formulas can contribute to the optimisation of the physico-chemical and pharmaceutical properties of the parent drug. The understanding of the interaction between DCF with beta-CD represents the objective of this study. FT-IR spectroscopy is one of the methods which clarify the nature of these interactions in complexes of such type. Therefore the changes in FT-IR spectra of binary dispersed systems DCF/beta-CD in physical mixture and coprecipitate from methanol (molar ratios: 1/1, 1/2, 2/3, 3/4, 7/4) were analysed. The analysis of the broadening of the X-ray powder diffraction line has been applied to investigate the average effective crystallite size, the mean square of the microstrain caused by distortions within beta-CD crystallite and the fault probability in the binary dispersed DCF/beta-CD coprecipitate system.

The secondary structure and architecture of human elastin.

The presented work constitutes the first structural characterization of both insoluble human elastin and its solubilized form, kappa-elastin. Structural data were reached following the use of Fourier transform infrared, near infrared Fourier transform Raman and circular dichroism optical spectroscopic methods and their quantitative analysis permitted us to estimate approximately 10% alpha-helices, approximately 35% beta-strands and approximately 55% undefined conformations in the global secondary structure of insoluble human elastin in the solid state. Following the use of the LINK method, the probable local distribution of the secondary-structure elements along the sequence was determined and compared to that obtained for bovine elastin, the historical standard of elastin. This comparison led us to propose a globular architecture for the human elastomer and permitted us to delineate some elements of its structure-elasticity relationship.

Infrared and Raman microspectrometry study of fluor-fluor-hydroxy and hydroxy-apatite powders.

Visible Raman and infrared microspectrometry studies performed on fluorapatite and hydroxyapatite powders have shown similar results. Small modifications of the nu2 and nu4 PO(3-)4 tetrahedra bending modes are observed. A small frequency shift of the nu1 mode and modifications on the nu3 mode region accompanied with a simplification of the hydroxyapatite and fluorapatite respective spectra from seven to four bands were observed. A broad and weak band which could be attributed to the Ca-F bond is detected at 311 cm(-1) on the Raman fluorapatite spectra. The phosphate vibration modes are little disturbed by fluoride substitution. This could indicate that phosphate groups interact strongly between themselves and weakly with substituted atoms (i.e. hydroxyle and fluoride atoms). Whatever crystallographic model is considered, the number of bands observed is always lower than the number of calculated ones, even for hydroxyapatite, whose symmetry is lower than that of fluorapatite.

Bovine elastin and kappa-elastin secondary structure determination by optical spectroscopies.

Elastin is the macromolecular polymer of tropoelastin molecules responsible for the elastic properties of tissues. The understanding of its specific elasticity is uncertain because its structure is still unknown. Here, we report the first experimental quantitative determination of bovine elastin secondary structures as well as those of its corresponding soluble kappa-elastin. Using circular dichroism and Fourier transform infrared and near infrared Fourier transform Raman spectroscopic data, we estimated the secondary structure contents of elastin to be approximately 10% alpha-helices, approximately 45% beta-sheets, and approximately 45% undefined conformations. These values were very close to those we had previously determined for the free monomeric tropoelastin molecule, suggesting thus that elastin would be constituted of a closely packed assembly of globular beta structural class tropoelastin molecules cross-linked to form the elastic network (liquid drop model of elastin architecture). The presence of a strong hydration shell is demonstrated for elastin, and its possible contribution to elasticity is discussed.

[HPLC used in the validation of simple methods for research of degradation products in essential drug tablets]. / Validation par HPLC de méthodes simples pour la recherche de produits de dégradation dans les comprimés de médicaments essentiels.

HPLC have been used to validate simple methods to be employed in developing countries (DC) for the quality control of drugs. As the important lack of analytical material in DC, colorimetric methods have been used. These are subjected to visual appreciation of the color intensity. Two essential drugs have been selected: aspirin, hydrochlorothiazide. For each compound, standardization of concentration's degradation product by colorimetry and HPLC have been achieved in proximity of the restricted norms of pharmacopoeia. These results have been applied to tablets exposed to stressed conditions (t(0) = 60 and humidity = 75%). The results obtained by colorimetric method were similar to HPLC's ones.

[Non-destructive quality control of tablets by photoacoustic infrared spectrometry. Analysis in primary packaging]. / Contrôle de qualité non destructif de comprimés par spectrométrie infrarouge photoacoustique. Analyse sous conditionnement primaire.

We have studied the feasibility of the photoacoustic detection in Fourier transform infrared spectrometry for the quality control of drug tablets. Beyond the non destructive character of the method, the main advantage which has been established is the precocity of impurity detection on the tablet outside. The direct recording of spectra through PVC lead to interesting results for study of tablets under blister.

XeCl laser in biliary calculus fragmentation: fluence threshold and ablation products.

The in vitro action of a xenon-chlorine (XeCl) excimer laser on biliary calculi is reported: fluence threshold and rate for ablation process are given. An analysis of gaseous products evolved during irradiation of gallstones, performed through an infrared spectrophotometric technique is also reported. Based on the different results, we discuss the mechanism of destruction.

Gas chromatography with Fourier transform infrared spectrometry for biomedical applications.

The basic concepts relating to Fourier transform infrared spectroscopy (FTIR) have been set out to enable chromatographers to make use of gas chromatography (GC)-FTIR coupling. To describe the current position regarding applications, studies are briefly presented that are representative of the field of industrial products, natural vegetable extracts and pesticides. Biomedical applications are described in detail. The analyses of medicaments, metabolism studies and toxicological investigations are reviewed. Given the limited amount of published work in this field, it is possible to survey the limitations of GC-FTIR. The solutions provided by technological developments currently in progress are described.

[Not Available]. / Analyse de melanges complexes sur le couplage chromatographie en phase gazeuse/spectrometrie infrarouge par transformee de fourier equipe de colonnes capillaires.

To increase the analytical potential of the combination of gas chromatography and Fourier-transform infrared spectrometry, we have adapted our system to use of capillary columns, and automated the acquisition and treatment of the data. The performance of the method was tested by analysis of complex mixtures such as the essential oils of peppermint and lavender. The sensitivity and resolution are poorer than those obtained with classical GC detectors but the spectra are very useful for determining molecular structure.

[Drug addiction by inhalation of gasoline vapor. Clinical and toxicological aspects]. / Toxicomanies par inhalation de vapeur d'essence. Aspects cliniques et toxicologiques.

Following an epidemic of sniffing petrol fumes and the death of a child, the authors review published findings of this little-known type of toxicomania. They envisage the Clinical and Toxicological problems. Researching and identifying the petrol remain problems. It is possible to detect the traces of petrol directly in the blood by gaz chromatography on a capillary column coupled to flame ionisation detector but it not possible to identify the product with complete certainly. The gas liquid on a packed column detected by Fournier transformed infra-red spectrography can be given to identification with total accuracy.