Photoreactivite des carboxylates de cuivre. II – Etude de l'acide ortho-coumarique et de ses sels de cuivre (I) et (II)

Le comportement photochimique des ortho-coumarates de cuivre (I) et (II) ainsi que celui de l'acide ortho-coumarique en solution dans le DMSO sont décrits. L'acide ortho-coumarique est caractérisée par un rendement quantique d'isomérisation trans→cis élevé et la présence d'une double émission de fluorescence dans le cas de l'isomère trans. Les formes ioniques RH— et R2— obtenues par déprotonations successives ont par contre de faibles rendements quantiques d'isomérisation et des propriétés émissives très différentes.Une solution diluée ortho-coumarate de cuivre dans le DMSO contient essentiellement de l'acide ortho-coumarique sous forme neutre (caractérisée par ses propriétés spectrales, émissives et photochimiques). Un complexe structuré de nature vraisemblablement dimère est présent dans les solutions de concentration en sel de cuivre supérieure à 10-3 M. Le spectre d'absorption présente alors à 715 nm une transition de type d-d centrée sur le métal ; cette transition apparaît également pour le sel de cuivre (I). Simultanément, on observe une importante inhibition de photo-isomérisation et de l'émission de fluorescence du ligand. Dans ce complexe structuré, le cuivre est capable de désactiver l'état singulet du ligand

Émission des différentes formes de la fluorescéine en solution aqueuse

La fluorescéine est susceptible d’exister en solution aqueuse sous quatre formes différentes : cationique, neutre, anionique et dianionique. Ces formes participent à trois équilibres protolytiques à l’état fondamental. Une technique de détermination relative de rendements quantiques de fluorescence sous différentes longueurs d’onde d’excitation permet d’atteindre les propriétés émissives des formes à l’état excité singulet. Les rendements quantiques de fluorescence des formes anionique et neutre sont respectivement 0,26 et 0,14 ; celui du cation n’a pas été déterminé puisque ce cation n’existe pas à l’état excité aux pH étudiés. Par ailleurs, un calcul cinétique classique montre qu’il ne peut pas s’établir un équilibre prololytique à l’état excité singulet à un pH voisin de 6 ; nos résultats expérimentaux sont compatibles avec cette prévision

Photolyse et photo-oxydation d'aldéhydes satures normaux

Le niveau triplet T1 (nπ*) d'aldéhydes saturés à chaîne droite se désactive essentiellement par un processus bimoléculaire d'autodésactivation, lorsque la concentration de l'aldéhyde est comprise entre 10–2 et 10–1 M. Le rendement quantique de population du niveau triplet T1 (nπ*) de l’aldéhyde est alors égal à la moitié du rendement quantique de disparition réelle. La photo-oxydation du n-propanal, du n-butanal et du n-hexanal implique un processus d’amorçage des chaînes d'oxydation issu du niveau excité singulet plus efficace que celui issu de l'état excité triplet

Photolyse et photo-oxydation d'aldéhydes saturés ramifiés

L’étude cinétique de la photolyse d'aldéhydes saturés à chaîne ramifiée et de son inhibition par le napthalène permet de préciser le comportement de ces molécules dans le domaine de concentration 10–2M – 10–1M ; on peut déduire du mécanisme un procédé simple de mesure du rendement quantique de transition inter-systèmes S1 → T1, l'état excité triplet T1 (nπ*) se désactivant essentiellement par un processus bimoléculaire d'autodésactivation. Le rendement quantique de population du triplet est égal à 0,295, 0,34 et 0,41 respectivement pour l'éthyl-2 butanal, le diméthyl-2,2 propanai et l'isobutanal.L'étude cinétique de la photo-oxydation de ces mêmes aldéhydes, inhibée par le napthalène montre que la durée de vie de l'état triplet n'est pas perturbée par l'oxygène dissous dans le n-heptane. La comparaison entre photolyse et photo-oxydation permet de préciser les processus d'amorçage de la réaction en chaînes d'oxydation

Extractability of water-soluble soil organic matter as monitored by spectroscopic and chromatographic analyses

International audienceCold and hot water processes have been intensively used to recover soil organic matter, but the effect of extraction conditions on the composition of the extracts were not well investigated. Our objective was to optimize the extraction conditions (time and temperature) to increase the extracted carbon efficiency while minimizing the possible alteration of water extractable organic matter of soil (WEOM). WEOM were extracted at 20A degrees C, 60A degrees C, or 80A degrees C for 24 h, 10-60 min, and 20 min, respectively. The different processes were compared in terms of pH of suspensions, yield of organic carbon, spectroscopic properties (ultraviolet-visible absorption and fluorescence), and by chromatographic analyses. For extraction at 60A degrees C, the time 30 min was optimal in terms of yield of organic carbon extracted and concentration of absorbing and fluorescent species. The comparison of WEOM 20A degrees C, 24 h; 60A degrees C, 30 min; and 80A degrees C, 20 min highlighted significant differences. The content of total organic carbon, the value of specific ultraviolet absorbance (SUVA(254)), the absorbance ratio at 254 and 365 nm (E (2)/E (3)), and the humification index varied in the order: WEOM (20A degrees C, 24 h) < WEOM (80A degrees C, 20 min) < WEOM (60A degrees C, 30 min). The three WEOM contained common fluorophores associated with simple aromatic structures and/or fulvic-like and common peaks of distinct polarity as detected by ultra performance liquid chromatography. For the soil chosen, extraction at 60A degrees C for 30 min is the best procedure for enrichment in organic chemicals and minimal alteration of the organic matter

Analysis of electrophoretic soil humic acids fractions by reversed-phase high performance liquid chromatography with on-line absorbance and fluorescence detection

International audienceA combination of reversed-phase high performance liquid chromatography (RP HPLC) with on-line absorbance and fluorescence detection was used for analysis of chernozem soil humic acids (HAs) and their fractions A, B and C + D with different electrophoretic mobility (EM) and molecular size (MS). Samples were injected onto the column at the identical volume and absorbance. All chromatograms exhibit the resolution of seven peaks. The estimation of relative recovery of HAs and fractions from the reverse-phase column has been done. High MS fraction A, which possesses the low EM, is essentially more hydrophobic (73% of the fraction amount remained adsorbed on the column) and aliphatic than medium MS and EM fraction B (33% of the fraction amount remained adsorbed on the column). The most hydrophilic and aromatic properties belong to low MS fraction C + D, which possess the highest EM and practically was not adsorbed on the column. The hydrophobicity of the bulk HAs lies within the range of fractions hydrophobicity. The absorption spectra of bulk HAs, electrophoretic fractions A, B, C + D and corresponding RP HPLC peaks were featureless but had differences in the values of absorbance ratio at 300 and 400 nm (A3/A4). For fractions A and B this ratio gradually decreased from peak 1 to 7 (from 3.05 to 2.80 and 3.00 to 2.40, respectively). This trend was less pronounced in HAs and practically absent in fraction C + D, where ratio A3/A4 varied within a small range. The strong relationship between fluorescence properties, EM, MS, polarity and aliphaticity/aromaticity of HAs fractions was found. Humic and proteinlike fluorescence had different polarity nature. The protein-like fluorescence is located in humic material which irreversibly adsorbed on the reverse-phase column and not subjected to RP HPLC characterization. The humic-like fluorescence at Ex/Em 270/450 nm is mostly located in the hydrophilic peak of low MS fraction C + D. Taking into account that high MS fraction A consisted mainly of aliphatic components it is reasonable to suggest that these associations are capable of organizing into micellar structures. These data could be of great environmental importance, because the different fractions might reflect different soil physical-chemical properties

Spectral Properties of Probes Containing Benzothioxanthene Chromophore linked with Hindered Amine in Solution and in polymer Matrices

International audienceAbsorption and emission spectroscopy as well as laser flash photolysis was employed in order to characterize the spectral properties of novel probes based on benzothioxantheneimide chromophore covalently linked with different types of sterically hindered amines. These were chosen as 2-(2,2,6,6-tetramethyl-4- piperidyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTXINH), the equivalent stable nitroxyl radical, i.e. 2-(1-oxo-2,2,6,6-tetramethyl-4- piperidyl)thioxantheno[2,1,9dej]isoquinoline 1,3-dione (BTXINO) and the alkoxy derivative 2-(1-(1'-phenylethoxy)-2,2,6,6-tetramethyl-4-piperidyl)- thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTXINOR). Spectral properties, in solutions and in various polymer matrices such as polystyrene, polymethyl methacrylate, polyvinyl chloride and polypropylene, were compared with the compound 2-(1-dodecyl)-thioxantheno[2,1,9-dej]isoquinoline-1,3-dione (BTXID) taken in the present study as a reference compound. By means of the fluorescence decay and in the contrary to three other probes, BTXINO probe clearly showed a biexponential decay while the three other probes led to monoexponential decay. Two different singlet excited states with lifetimes of about 0.4 and 5 ns were proposed. They correspond to two dispositions of the nitroxyl radical chain above and along the fluorescent moiety of the molecule. Such behaviour depends on the surrounding media. Moreover, an efficient intramolecular quenching of the fluorescence emission was only observed with the short lived singlet excited state. The ratio BTXID/BTXINO was found equal to about 4 and 9 in solutions and polymer matrices respectively. Laser flash photolysis indicated that the novel probes as well as the model compound yielded transient absorption with maximum at 530 nm, corresponding to the triplet states. The intermolecular quenching of such species by molecular oxygen and by free N-oxyl, such as 1-oxy-2,2,6,6-teramethylpiperidine (TEMPO) and 1-oxy-2,2,6,6-teramethyl-4- hydroxypiperidine (TEMPOL), and the intramolecular quenching was not efficient

Fluorescence properties of the <5kDa molecular size fractions of a soil humic acid

International audienceSoil humic acids are complex mixtures displaying several still unexplained spectral properties. In this work, we aimed to investigate the fluorescent properties of soil humic acid macromolecules of molecular sizes less than 5 kDa. To recover the fraction < 5 kDa, we employed a protocol based on repeated ultrafiltration of a soil humic acid HA with a 5 kDa membrane. The obtained retentate did not show any fluorescence. In contrast, the ultrafiltrate, which accounted for 20% by mass of the starting HA, contained a significant amount of the fluorescent components. This ultrafiltrate was in turn ultrafiltered through 3 kDa and 1 kDa membranes, and three subfractions were obtained. Their emission spectra, measured at an absorbance of 0.1 at 300 nm, were different in shape and intensity. In particular, the contribution of the long-wavelength emissions decreased and the intensity of emission at the maximum increased as the molecular weight decreased. These results show that a large portion of the fluorescent moieties of the soil HA are contained in the fraction < 5 kDa and that the repartitioning of fluorophores depends on their molecular size. This finding represents an interesting starting point for further studies

Fluorescence analysis of humic-like substances extracted from composts: Influence of composting time and fractionation

International audienceHumic-like acids (HLA0, HLA70, HLA130, HLA730) were extracted from composts obtained from sewage sludges and trimmings after 0, 70, 130 and 730 days of composting, respectively. In addition, HLA130 was fractionated using SEC-PAGE set-up. Fluorescence spectroscopy revealed that HLA0 was the only sample to contain emission bands characteristic of protein-like compounds (λexc/λem: 280/350) and chlorophyll (λexc/λem: 420/660). Emission intensities above 400 nm and HIX both varied in the order: HLA70 > HLA130 > HLA730 > HLA0 and increased as the fraction molecular size decreased. Thus, the formation of long wavelength emitting fluorophores during composting is connected to the humification process. These fluorophores are mainly concentrated in the low molecular size fraction obtained by SEC-PAGE fractionation of compost

Photosensitizing properties of water extractable organic matter from soils.

International audienceWater-extractable organic matter (WEOM) was extracted using pure water from two black soils and from the Elliott reference soil of the International Humic Substances Society (IHSS). WEOMs were characterized by chemical and spectroscopic methods. The apparent quantum yields of singlet oxygen, triplet excited states and hydroxyl radicals formation upon irradiation within the wavelength range 290-450 nm were determined using chemical probes and compared to those of standard Elliott humic substances. In general, the aromatic content, as measured by the SUVA value, was close in WEOMs and humic substances, while the E2/E3 was higher and the humification index lower in the former. Quantum yield values measured for WEOMs fell within the range of those found for basic medium extracted humic substances or were even higher in one case. Thus, water soluble aromatic moiety of the soil organic matter, especially those with low humification degree, is important for the photosensitizing properties. We also found that WEOMs sensitized the bisphenol A phototransformation with rates of the same order of magnitude for all the samples