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| Titel |
Interactions between natural organic ligands and trace metals studied by fluorescence lifetime and fluorescence quenching |
| VerfasserIn |
Ayoub Nouhi, Houssam Hajjoul, Roland Redon, Jean-Pierre Gagné, Stéphane Mounier |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138799
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| Publikation (Nr.) |
 EGU/EGU2017-1922.pdf |
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| Zusammenfassung |
| Improved insight on the interactions between natural organic ligands and trace metals is of
paramount importance for better understanding transport and toxicity pathways of metal ions
in the environment. Fluorescence spectroscopy allows introspecting ligands-metals
interactions. Time-resolved laser fluorescence spectroscopy (TRLFS) measures fluorophore
lifetime probing the local molecular environment. Excitation Emission Fluorescence Matrices
(EEFMs) and their statistical treatment : parallel factor analysis (PARAFAC) using
PROGMEEF Matlab homemade program, can give insight on the number or nature of
organic fluorophores involved in the interactions. Quenching of fluorescence by metals can
occur following two processes: dynamic and static quenching (Lakowicz, 2013). In the first
case, quenching is caused by physical collisions among molecules and in the second case
fluorophores can form nonfluorescent complexes with quenchers. It is possible to
identify the different mechanisms because each type of quenching corresponds to
a different mathematical model (Lakowicz, 2013; Valeur and Berberan-Santos,
2012). In TRLFS, the study of fluorescence decay’s laws induced by nanosecond
pulsed laser will allow to exactly qualify the type of interaction. The crucial point
of the temporal deconvolution will be the evaluation of the best fitting between
the different physical models and the decays measured. From the most suitable
time decay model, it will be possible to deduce the quenching which modifies the
fluorescence.
The aim of this study was to characterize interactions between natural organic ligands and
trace metals using fluorescence tools to evaluate the fluorescence lifetime of the
fluorophore, the occurrence of quenching in presence of metal, discuss its mechanism
and estimate conditional stability constants if a complex organic ligand-metal is
formed.
This study has been done in two steps. First, we have examined the interactions between
salicylic acid and copper in order to calibrate our assays and compare our results with
literature. Several studies have shown that static quenching occurs in that case (Brun and
Schröder, 1975; Lavrik and Mulloev, 2010; Ventry et al., 1991; Babko, 1968). Indeed, after
processing the EEFMs and TRLFS data, we found a fluorescence intensity decay by about
50% and a constant lifetime for the fluorophore suggesting a static quenching, in agreement
with the literature.
In the second step, we have studied the interactions between metal and different types of
natural organic matters. In this case, EEMFs and TRLFS experiments were done on samples
prepared by dissolving copper in four different fractions of organic matter extracted from
estuarine water (St. Lawrence Estuary, Canada). Organic matter was obtained using DAX-8
and XAD-4 resins in series. Humic and fulvic acids are obtained following the IHSS
protocol.
The results of interaction between humic substances and copper gathered after processing
data on PROGMEEF have shown a fluorescence intensity decay by about 57% for the first
component and 88% for the second component. The fluorescence lifetime for both
components were close to 2 ns and 6 ns respectively and the pH range was stable and close to
6. This means that a static quenching takes place in this case in agreement with the
literature.
Our study also focused on the investigation of complexation of organic matter by other metals
in particular Aluminum, Arsenic, Europium and Uranium. |
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