Bernard Sombret

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 κ-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 ∼10% α-helices, ∼45% β-sheets, and ∼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 β 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.

Characterisation of the OO peroxide bond by vibrational spectroscopy

Abstract Only very few studies have been reported on organic peroxides, mainly because of their unstable and often explosive nature. Literature usually reports (P.A. Budinger, J.R. Mooney, J.G. Graselli and P.S. Fay, A.T. Guttmann, Anal. Chem., 53 (1981) 884) that the OO stretching vibration is weak by IR and leads to an intense band between 700 and 950 cm−1 by Raman spectroscopy. We have investigated by both these spectroscopie techniques some inorganic peroxides and 23 organic peroxides. Despite the fact that the OO stretch occurs in a region where carbon skeletal modes may interfere, we were able to determine a narrower range of frequencies for this vibration: 845–875 cm−1. This study has also demonstrated the influence of the peroxide group on the other functions of the molecule. We have noticed particularly some 40 cm−1 shifts on the frequencies of a carbonyl vibration in the α position from the peroxide bond.

Force field and vibrational spectra of oligosaccharides with different glycosidic linkages—Part II. Maltose monohydrate, cellobiose and gentiobiose

Abstract Complete Raman and IR spectra of maltose monohydrate, cellobiose and gentiobiose have been recorded in the crystalline state. These three disaccharides present the same monosaccharide composition of the glucose molecule and the remaining studied position (1–4 and 1–6) of the glycosidic linkage. Moreover, maltose and cellobiose present the different configurations of the glycosidic linkage α, 1–4 and β, 1–4, respectively. These data will constitute the support for theoretical calculations of normal modes of vibration. The assignments of the calculated bands of vibration will be made on the basis of the potential energy distributions using a modified Urey—Bradley—Shimanouchi intramolecular potential energy combined with a specific intermolecular potential energy function. The calculations show that using a correct initial force field, it is possible to reproduce correctly the density of observed vibrational states for large molecules such as disaccharides. The standard deviation between calculated and observed frequencies, below 1500 cm −1 , leads to values of 4.7, 4.2 and 4.6 cm − for maltose monohydrate, cellobiose and gentiobiose, respectively. Our previous investigations on trehalose dihydrate, sophorose monohydrate and laminaribiose are confirmed in this study and complete the previous assignments for the whole set of disaccharides.

Direct structural identification of polysaccharides from red algae by FTIR microspectrometry I: Localization of agar inGracilaria verrucosa sections

Unlike carrageenans, agars have not been studied very extensively by infrared spectroscopy, in so far as the structures of this kind of polygalactanes are not as well defined as carrageenans. However, in a previous work we have carried out a vibrational analysis of both carrageenans and agars and some important assignments of the main absorptions have been made. Consequently, the present work has been undertaken in order to identify agars without any extraction directly in various seaweeds using the infrared microspectrometry method. The main advantage of this method is that the sample consists only of a dehydrated algal section. The red algaeGradlaria verrucosa has been the subject of the present study. In the first place, spectra of extracted agars were recorded, as they can help us to confirm the nature of the compound identified by this technique. In a second stage, spectra of different parts of the sections have been carried out. The comparison between the resulting spectra with those of the extracted polysaccharides, has demonstrated, firstly that the best results are obtained from the cortical area, because, as expected, the agar is mainly located in the cell wall of this area of the algae. Indeed, the feature bands of agars are all observed, especially the intense ones between 1000 and 1100 cm−1 and the more characteristic absorptions in the wavenumbers range below 1000 cm−1 so as the ones at 988, 965, 930, 890, 870, 771 and 741 cm−1. Secondly, it may be also identified in smaller amounts in the medullar area, the cells are greater than in the cortical area and the cytoplasm is preponderent. However, in the latter case a coexisting polysaccharide, present in a considerable quantity and called floridean starch (Its structure is not very well known, as it varies from one algae to another), masks the spectra of agar, as its spectrum is very similar to those of polygalactanes.

In situ time-resolved FTIR spectroelectrochemistry: study of the reduction of TCNQ

The efficiency and versatility of time-resolved FTIR spectroscopy has been used to follow concentration profiles of species produced during a cyclic voltammetric scan. It has been tested in situ and in resolved time, by probing the reduction of tetracyanoquinodimethane (TCNQ) on its first and second electrochemical wave. Besides the establishment of the method, the individual concentrations of TCNQ, of the monoanion and of the dianion were monitored at distinct infrared frequencies and the time derivatives of the concentration profiles were compared to the voltammograms.

Self-Modeling Mixture Analysis Applied to FT-Raman Spectral Data of Hydrogen Peroxide Activation by Nitriles

In the analytical environment, spectral data resulting from analysis of samples often represent mixtures of several components. Extraction of information about pure components of these kinds of mixtures is a major problem, especially when reference spectra are not available or when unstable intermediates are formed. Self-modeling multivariate mixture analysis has been developed for this type of problem. In this paper two examples will be used to show the potential of this technique coupled with FT-Raman spectroscopy to elucidate reaction mechanisms and to follow in situ the kinetics of chemical transformations.

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.

On-Line Mid-Infrared Spectroscopic Data and Chemometrics for the Monitoring of an Enzymatic Hydrolysis

Multivariate models have been designed in order to be implemented at pilot plant scale. They allow the prediction of the degree of the enzymatic hydrolysis of bovine hemoglobin from on-line mid-infrared (MIR) attenuated total reflection (ATR) measurements. The procedure is very safe and practical, but the spectral information is unfortunately difficult to use. First, remote MIR optical fiber measurements induce a significant energy loss. Secondly, the spectra of proteins in aqueous solutions generally consist of broad and overlapping signals. Principal component analysis (PCA) of the full data set reveals some variations between the different batches as well as definite deviations from the ideal linear situation. This suggests the use of artificial neural networks (ANNs), which have the useful qualities of generalization ability and robustness. Preprocessing of the spectral data (including PCA and wavelet transforms) have been tested. In addition, the reliability of the calibration is ensured by the interpretation of the spectroscopic information. This permits the construction of very parsimonious models and contributes to greater confidence in the analytical tool built for process monitoring. Finally, the estimations of the prediction error are demonstrated to be acceptable. With an unknown proteolysis batch, this error is found to be lower than 0.4 for the degree of hydrolysis covering the range 0 to 8.7.

In situ characterisation of peroxybenzimidic acid by FT-Raman and ATR/FTIR spectroscopy

Abstract To elucidate the mechanism of the reaction of benzonitrile and hydrogen peroxide in alkaline medium, an experimental study was carried out by FT-Raman and ATR/FTIR. We were able to identify the intermediate peroxycarboximidic acid by assigning number of characteristic vibrations like νCN or νOO.

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.