Colette Belin

Fluorescence spectroscopy of coastal and marine waters

Abstract Fluorescence measurements were performed on a large variety of water samples collected in different estuaries and oceans over the world. Spectra were recorded with a high-sensitivity spectrofluorometer without preconcentration of the samples. Qualitative and quantitative parameters of fluorescence were determined on fully corrected emission, excitation and synchronous fluorescence spectra. Critical conditions required to record the corrected fluorescence spectra of open marine water are emphasized. General results show that with an adequate excitation wavelength (313 nm) the fluorescence signature can be used to differentiate water masses. The variation of the emission wavelength maxima for excitation ranging from 250 to 410 nm give strong evidence that as far as the humic substances themselves are concerned, the fluorescence spectra of the natural water samples we investigated contain at least two distinctive classes of fluorophores. Synchronous spectra as well as all other fluorescence results we have obtained can be accounted for on the basis of a model which includes both the existence of these two classes of fluorophores in different proportions and variations in nature and the distribution of the fluorophores within each class.

Giant dendritic molecular electrochrome batteries with ferrocenyl and pentamethylferrocenyl termini.

Giant redox dendrimers were synthesized with ferrocenyl and pentamethylferrocenyl termini up to a theoretical number of 3(9) tethers (seventh generation). Lengthening of the tethers proved to be a reliable strategy to overcome the bulk constraint at the dendrimers periphery. These redox metallodendrimers were characterized by (1)H, (13)C, and (29)Si NMR; MALDI-TOF mass spectrometry (for the low generations); elemental analysis; UV-vis spectroscopy; dynamic light scattering (DLS); atomic force microscopy (AFM); electron-force microscopy (EFM) for half- or fully oxidized dendrimers; cyclic voltammetry; and coulometry. UV-vis spectroscopy, coulometry, and analytical data are consistent with an increasing amount of defects as the generation number increases, with this amount remaining relatively weak up to G(5). AFM shows that the dendrimers form aggregates of discrete size on the mica surface, recalling the agglomeration of metal atoms in monodisperse nanoparticles. Cyclic voltammetry reveals full chemical and electrochemical reversibility up to G(7), showing that electron transfer is fast among the flexible peripheral redox sites. Indeed, the redox stability of these new electrochromic dendrimers, i.e., a battery behavior, was established by complete chemical oxido-reduction cycles, and the blue 17-electron ferrocenium and deep-green mixed-valence Fe(III)/Fe(II) dendritic complexes were isolated and characterized. AFM studies also show the reversible dendrimer size changes from upon redox switching between Fe(II) and Fe(III), suggesting a breathing mechanism controlled by the redox potential. Considerable adsorption of high-generation dendrimers on Pt electrodes such as G(7)-Fc allows the easy formation of modified electrodes that sense the ATP anion only involving the electrostatic factor even in the absence of any other type of interaction with the redox tethers.

High-sensitivity fluorescence spectroscopy of mediterranean waters using a conventional or a pulsed laser excitation source

Abstract Instrumental efforts have been made to record the fluorescence spectra of coastal and marine waters of the Mediterranean Sea for different excitation wavelengths without preconcentration of the samples. A fluorescence spectrophotometer, using a pulsed nitrogen laser as excitation source, was developed and spectra obtained on marine waters were compared with those obtained with a high-sensitivity commercial spectrofluorometer. Fluorescence emission spectra recorded with this high-resolution instrument, using the laser excitation source, do not show resolved structured bands. Other results obtained on a high-sensitivity fluorometer with a very low stray light level show that, on the same sample, fluorescence spectra present a difference in the position between the maximum of the emission spectra when recorded with an excitation wavelength of 313 or 370 nm. The positions of the maxima of the emission spectra also show shifts between samples collected at different locations. No difference is observed between coastal and marine waters for a 370-nm excitation wavelength. On the other hand, an important blue shift (up to 20 nm) is observed between coastal and marine samples when 313 nm is used as the excitation wavelength. These results clearly show that marine and coastal waters have different fluorescence signatures, and demonstrate that high-sensitivity fluorescence spectroscopy is a promising tool for better elucidation of the behaviour of part of the complex dissolved organic matter in the ocean.

Corrected fluorescence spectra of fulvic acids isolated from soil and water.

The fluorescence of humic matter is a ubiquitous phenomenon that occurs for isolated soil and aquatic matter and for natural water samples. This property is used to compare humic substances, but uncorrected emission spectra can be especially misleading for spectra taken on different instruments. This paper details the corrections of emission fluorescence spectra of well-characterized fulvic acids isolated from soil and a fresh-water river. The corrections significantly modify the uncorrected spectra. This effect demonstrates the need for emission spectra corrections before comparing the fluorescence properties of diverse humic matter samples.

Characterization by fluorescence of the dissolved organic matter in natural water. application to fractions obtained by tangential ultrafiltration and XAD resin isolation

Abstract A tangential ultrafiltration procedure has been applied to separate the dissolved organic matter in the order of decreasing molecular weights of two water samples from a dam reservoir. Four fractions have been isolated and their fluorescence emission spectra, fluorescence excitation spectra and their fluorescence quantum efficiencies were compared with those of macroporous XAD8 and XAD4 extracts isolated from the same water samples. A clear one to one correspondence between the ultrafiltrated fractions and the resin extracts was observed which indicates that the two methods lead to isolate very similar type of organic material. The “apparent”; mean molecular weights deduced for humic, fulvic and hydrophilic acids appear consistent with previous values drawn from waters of various origins. Moreover, by using the fluorescence spectra characterizing each of these acids we have been able to estimate the contribution of their respective fluorescence to the total fluorescence spectra of the two studied...

Interferences generated by organic and inorganic compounds during organotin speciation using hydride generation coupled with cryogenic trapping, gas chromatographic separation and detection by atomic absorption spectrometry

Abstract Hydride generation reactions are frequently used for the speciation analysis of organotin compounds in a wide variety of matrices. However, the organotin determination procedure may be altered by different interferences mechanisms. This work evaluates the interferences likely to occur in the determination of tributyltin in a harbour sediment candidate reference material for the EEC Community Bureau of Reference with the method of hydride generation combined on-line with cryogenic trapping, gas chromatographic separation and detection by atomic absorption spectrometry. First, a full geochemical characterization of the sediment and of its acetic acid leachate was achieved to evaluate interfering compounds that may inhibit the determination of TBT by hydride generation in this sediment. Second, interference studies on various organic and inorganic compounds likely to alter the overall organotin determination were carried out with simple model solutions. These model solutions were spiked successively with different possible interfering compounds mixed with the organotins under study, i.e., monomethyltin (MMT), monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in a mixed solution at concentrations of 5 ng as Sn of each compound in 50 ml of water. Organic interferents studied were organic pollutants (organic solvents, polychlorinated biphenyls, pesticides, n -alkanes), humic substances and a complexing agent, EDTA. The inorganic interferents were represented by a mixture of fourteen inorganic metals. The addition of organic compounds to the hydride generation reaction had little effect on the signal suppression for all organotin species. Reproducibility was significantly affected only by the presence of humic substances in solution. Signal suppression was observed only for the monoalkyltins (MMT and MBT) in the presence of EDTA. Solutions of mixed inorganic metals were found to be highly efficient in inducing severe signal suppression for all organotin compounds at a level of 100 μg of each element. Interference mechanisms during the speciation determination step are outlined and discussed.

The effect of freshwater UV-irradiation prior to resin preconcentration of trace metals

Abstract Trace metal concentrations in natural freshwater samples are often below detection limits for determination by inductively coupled plasma-mass spectrometry (ICP-MS). This is especially so following size fractionation of the sample. Preconcentration is therefore necessary, and sorption on a chelating resin such as Chelex-100 is often used. In order to chelate metals strongly complexed with organics, the metal–organic association has to be severed. In this study, ultra violet (UV)-irradiation was used to oxidize organic matter in a humic acid reference solution, and in a natural sample spiked with Ag, Cd, Cu and Pb, where the recoveries of the metals were calculated. Except for Ag, recoveries of Cd, Cu and Pb increased significantly up to almost 100% after irradiation. If preconcentration on Chelex-100 is used, UV-irradiation appears to be an essential step in achieving accurate concentrations of organically chelated trace metals in freshwater.

'Click' synthesis and redox properties of triazolyl cobalticinium dendrimers.

The derivatization of macromolecules with redox-stable groups is a challenge for molecular electronics applications. The large majority of redox-derivatized macromolecules involve ferrocenes, and there are only a few reports with cobalticinium. We report here the first click derivatization of macromolecules with the cobalticinium redox group using ethynylcobalticinium hexafluorophosphate, 1. Cu(I) catalysis was used for these selective click metallodendrimer syntheses starting from 1 and providing the tripodal dendron 3 that contains three 1,2,3-triazolylcobalticinium termini and a phenol focal point and the dendrimers of generations 0, 1, and 2 containing 9, 27, and 81 triazolylcobalticinium units for the dendrimers 4, 5, and 6, respectively. Atomic force microscopy (AFM) statistical studies provided the progression of height upon increase of dendrimer generation. Cyclic voltammetry studies in MeCN and dimethylformamide (DMF) show the solvent-dependent reversibility of the Co(III/II) wave (18e/19e) and generation dependent reversibility of the Co(II/I) (19e/20e) wave in DMF. The H2PO4(-) anion is only recognized by the largest metallodendrimer 6 by a significant cathodic shift of the Co(III/II) wave.

Mixed-valent click intertwined polymer units containing biferrocenium chloride side chains form nanosnakes that encapsulate gold nanoparticles.

Polymers containing triazolylbiferrocene are synthesized by ROMP or radical chain reactions and react with HAuCl4 to provide class-2 mixed-valent triazolylbiferrocenium polyelectrolyte networks (observed inter alia by TEM and AFM) that encapsulate gold nanoparticles (AuNPs). With triazolylbiferrocenium in the side polymer chain, the intertwined polymer networks form nanosnakes, unlike with triazolylbiferrocenium in the main polymer chain. By contrast, simple ferrocene-containing polymers do not form such a ferricenium network upon reaction with Au(III), but only small AuNPs, showing that the triazolyl ligand, the cationic charge, and the biferrocenium structure are coresponsible for such network formations.

Hyperspectral imaging, spectrofluorimetry, FORS and XRF for the non-invasive study of medieval miniatures materials

BackgroundIlluminated manuscripts are complex multi-layer and multi-material objects. To this difficulty, from the analytical point of view, is added the impossibility of removing samples from these paintings for the study of their materials and techniques. There are relatively few analytical methods that satisfy these constraints as the availability of non-invasive techniques adapted to painted manuscripts is limited and mainly focused on the characterization of inorganic compounds. In the context of a research project on the analytical study of the forty miniatures in the Marcadé collection (Treasury of the Saint-André Cathedral of Bordeaux, XIII to XVI century), the potential of two non-invasive methods, hyperspectral imaging (HSI) and spectrofluorimetry is explored.ResultsThe methodological development of these techniques as well as preliminary tests on miniatures recreated according to medieval recipes and materials, allowed the validation of the analytical parameters and the creation of a database of reference spectra (parchments, pigments, binders). Hyperspectral imaging associates reflectance spectra with each pixel of the image and treats the signal received in various wavelengths. The characteristics of the spectral signal in VIS range or NIR are used to get an identification and a localization of the components. It allows the study of the entire image and offers lots of ways to work: comparison of spectra, mapping, principal component analyses and false color images. Spectrofluorimetry is a sensitive method which gives information on fluorescent organic compounds under UV or visible light. Emission and excitation spectra of five red pigments in binding media have been collected. These methods were compared with X-ray fluorescence spectrometry for the qualitative analysis and mapping of the inorganic elements in a facsimile which had been purposely reproduced by an illumination painter who worked with original medieval recipes for the sake of developing the present study.ConclusionsThe combination of all these techniques allows good identification of all the materials used on an illuminated manuscript. The pertinent selection of the wavelengths used with the HSI system and a preliminary database and study of materials under UV and white light is described in this paper.