Metal ion interaction with a novel anthracene pendant-armed fluorescent molecular probe. Synthesis, characterization, and fluorescence studies

A new scorpionate system (L) containing an emissive anthracene pendant arm, derived of O¹,O⁷-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren, has been synthesized and characterized. The sensing capability of L towards a range of metal ions has been studied. Protonation and complexation studies, using UV-Vis and fluorescent emission measurements, have been performed with alkaline and alkaline earth metal ions (M = Na(I), K(I), Li(I), Ca(II), Mg(II)), as well as transition and post-transition metal ions (M = Cr(III), Cu(II) and Zn(II), Cd(II), Hg(II) and Al(III)). An increase in the fluorescence emission (CHEF effect) was observed in methanol and in methanol/water mixtures in the presence of Cd(II) (5.0-fold), Zn(II) (4.5-fold), Cr(III) (2.0-fold) and Al(III) (1.8-fold); these results suggest a notable sensing ability of this new N₃O₄ ligand for these metals; these experiments were also performed in the presence of large amounts of alkaline and alkaline earth metal ions.     

Anthracene Removal using Activated Soil Reactors

The aim of this study was to evaluate anthracene removal using activated soil reactors, previously inoculated, under both aerobic and anaerobic conditions. In the reactors, the soil was maintained at 60% moisture (weight basis), room temperature, in the dark, and under constant agitation at 100 rpm. Two experiments were run during and after acclimatization to evaluate anthracene removal under both aerobic and anaerobic conditions. The first one took place during inoculum acclimatization using three different concentrations of anthracene (50, 100, and 500 mg anthracene/L per day) during 90 days. The second experiment took place after acclimatization (during 132 days). The results of anthracene removal were compared with controls in which no additional inoculum was added. During the two experiments, the behavior of pH, chemical oxygen demand (COD), and biogas production was evaluated. Results indicate that the bacterial community adapted for removal of anthracene became enriched through the acclimatization process. Anthracene biodegradation occurred in the soil model with both types of reactors (aerobic and anaerobic), but the rates and extent of biodegradation in the aerobic reactor were higher (95%) than those in anaerobic conditions (74%). Microbial activity also contributed to enhancing bioremediation in the soil by reducing anthracene sorption.     

Phenanthrene stimulates the degradation of pyrene and fluoranthene by <Emphasis Type="Italic">Burkholderia</Emphasis> sp. VUN10013

Pyrene and fluoranthene, when supplied as the sole carbon source, were not degraded by Burkholderia sp. VUN10013. However, when added in a mixture with phenanthrene, both pyrene and fluoranthene were degraded in liquid broth and soil. The amounts of pyrene and fluoranthene in liquid media (initial concentrations of 50 mg l⁻¹ each) decreased to 42.1% and 41.1%, respectively, after 21 days. The amounts of pyrene and fluoranthene in soil (initial concentrations of 75 mg kg⁻¹ dry soil each) decreased to 25.8% and 12.1%, respectively, after 60 days. None of the high molecular weight (HMW) polycylic aromatic hydrocarbons (PAHs) tested adversely affected phenanthrene degradation by this bacterial strain and the amount of phenanthrene decreased rapidly within 3 and 15 days of incubation in liquid broth and soil, respectively. Anthracene also stimulated the degradation of pyrene or fluoranthene by Burkholderia sp. VUN10013, but to a lesser extent than phenanthrene. The extent of anthracene degradation decreased in the presence of these HMW PAHs.     

Synthesis, photophysical characterisation and metal ion binding properties of new ligands containing anthracene chromophores

Two new fluorescent chemosensors for heavy metal ions have been synthesised and their photophysical properties have been investigated. They present a pyridyl-thioether-based binding site and the anthracene moiety as a chromophore. In the experimental conditions used, no evidence is found for the formation of complexes with Pb²⁺, Zn²⁺, Cd²⁺, and Ag⁺ ions. On the contrary, in acetonitrile solutions both ligands strongly bind Cu²⁺ and Hg²⁺ cations according to a 1:1 and a 1:2 (metal:ligand) stoichiometry. In these complexes, the intense luminescence typical of anthracene derivatives is almost completely quenched and this phenomenon can be mainly attributed to an intraligand electron transfer process from the anthracene chromophore to the complexed pyridine. These results are of interest for the development of new chemosensors for the design of efficient electronic tongues for the detection of transition metal ions.     

A sugar-aza-crown ether-based fluorescent sensor for Hg and Cu

A fluorescent sensor, 5, based upon the sugar-aza-crown ether structure with two anthracenetriazolymethyl groups was prepared and its fluoroionophoric properties toward transition metal ions were investigated. In methanol, the sensor exhibits highly selective recognition of Cu²⁺ and Hg²⁺ ions among a series of tested metal ions. The association constant for 5·Cu²⁺ and 5·Hg²⁺ in methanol was calculated to be 4.0 × 10⁵ M⁻¹ and 1.1 × 10⁵ M⁻¹, respectively. The detection limits for the sensing of Cu²⁺ and Hg²⁺ ions were 1.39 × 10⁻⁶ M and 1.39 × 10⁻⁵ M, respectively.     

Enrichment and identification of polycyclic aromatic compound-degrading bacteria enriched from sediment samples

The degradation of polycyclic aromatic compounds (PACs) has been widely studied. Knowledge of the degradation of PACs by microbial populations can be utilized in the remediation of contaminated sites. To isolate and identify PAC-degrading bacteria for potential use in future bioremediation programmes, we established a series of PAC enrichments under the same experimental conditions from a single sediment sample taken from a highly polluted estuarine site. Enrichment cultures were established using the pollutants: anthracene, phenanthrene and dibenzothiophene as a sole carbon source. The shift in microbial community structure on each of these carbon sources was monitored by analysis of a time series of samples from each culture using 16S rRNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Significantly, our findings demonstrate that shifts in the constituent species within each degradative community are directly attributable to enrichment with different PACs. Subsequently, we characterized the microorganisms comprising the degradative communities within each enrichment using 16S rRNA sequence data. Our findings demonstrate that the ability to degrade PACs is present in five divisions of the Proteobacteria and Actinobacteria. By determining the precise identity of the PAC-degrading bacterial species isolated from a single sediment sample, and by comparing our findings with previously published research, we demonstrate how bacteria with similar PAC degrading capabilities and 16S rRNA signatures are found in similarly polluted environments in geographically very distant locations, e.g., China, Italy, Japan and Hawaii. Such a finding suggests that geographical barriers do not limit the distribution of key PAC-degrading bacteria; this finding is in accordance with the Baas-Becking hypothesis “everything is everywhere; the environment selects” and may have significant consequences for the global distribution of PAC-degrading bacteria and their use in bioremediation.     

Synthesis and inclusion ability of anthracene appended β-cyclodextrins: unexpected effect of triazole linker

A new fluorescent β-cyclodextrin has been synthesized by coupling an anthracene moiety to the cyclic oligosaccharide via click chemistry. The influence of the triazole spacer was compared to the simple amino and amido linkers. While a sensing ability toward adamantan-1-ol was observed with the latter two spacers, the absence of inclusion capacity prevents the triazole modified cyclodextrin from showing any fluorescence variations. The difference in the binding behaviors studied by Isothermal Titration Calorimetry, UV–vis and fluorescence spectroscopies, was highlighted by the NOESY NMR spectra of the modified cyclodextrins: whereas a free cavity was observed for the amino and amido linkers, an important obstruction was obtained in the case of the triazole.     

Assessment of phytotoxicity of anthracene in soybean (Glycine max) with a quick method of chlorophyll fluorescence

A decrease in photosynthetic efficiency may indicate the toxic effects of environmental pollutants on higher plants. Measurement of chlorophyll (Chl) a fluorescence to assess the performance of photosystem II (PSII) was used as an bioindicator of toxicity of the polycyclic aromatic hydrocarbon (PAH) anthracene (ANT) in soybean plants. The results revealed that ANT treatment caused a reduction in quantum yield of PSII, damage to the oxygen evolving complex, as well as a significant reduction in performance index of PSII. However, change in performance index was more prominent, and it seems that the performance index is a more sensitive parameter to environmental contaminants. Moreover, a change in heterogeneity of PSII was also observed. The number of active reaction centres decreased with increasing concentration of ANT, as secondary plastoquinone reducing centres were converted into non‐reducing centres, and PSIIα centres were converted into PSIIβ and PSIIγ centres. The influence of ANT on PSII heterogeneity could be an important reason for reductions in the PSII performance.     

A water-soluble ribosyl-based fluorescent sensor for Hg and Cu ions

A water-soluble ribosyl-based fluorescent sensor 5 was prepared. The sensor contains an anthracene as the fluorophore and a set of complex groups as recognition sites, which bears two triazole ring spacers linked to two ribosyl carboxylic acids groups. The association constants of 5 in water are 2.15 × 10⁵ M⁻¹ and 9.57 × 10⁴ M⁻¹ for Cu²⁺ and Hg²⁺ ions, respectively, and both metals formed complexes with 5 at a 1:1 metal to ligand ratio. The binding of 5 to Cu²⁺ shows a broad pH range (5-10) and a low detection limit (57 ppb) in water, thus indicating it an efficient and promising cation probe.     

Homobimetallic anthracene-bridged η-cyclopentadienyl derivatives of rhodium(I) and iridium(I): large molecules or supramolecular species?

The reaction of 9,10-bis[(cyclopentadienylmethyl)thallium(I)]anthracene (2), obtained from 9,10-bis(cyclopentadienylmethyl)anthracene (1), with the chloro derivatives of rhodium(I) of formula [RhClL₂]₂ (L=η²-C₈H₁₄ or L₂=η⁴-C₈H₁₂) leads to the corresponding bimetallic complexes [L₂Rh{C₅H₄CH₂(9,10-anthrylene)CH₂C₅H₄}RhL₂] 3 (L=η²-C₈H₁₄) and 4 (L₂=η⁴-C₈H₁₂), in 22.8% and 15.0% yields, respectively. Analogously, by reacting 2 with [IrClL₂]₂ (L=η²-C₈H₁₄ or L₂=η⁴-C₈H₁₂), the corresponding bimetallic iridium(I) complexes [L₂Ir{C₅H₄CH₂(9,10-anthrylene)CH₂C₅H₄}IrL₂] 5 (L=η²-C₈H₁₄) and 6 (L₂=η⁴-C₈H₁₂) were obtained, in 24.5% and 43.0% yields, respectively. All complexes have been characterised by elemental analysis, mass spectrometry, and ¹H NMR. The structure of 4 was elucidated also by single crystal X-ray diffraction: it crystallises in the P2₁/c space group with a=19.932(11), b=6.4417(4), c=12.377(2) Å; α=90°, β=100.90(4)°, γ=90°. V=1560.5(9) ų. Z=2, D_calc=1.606 g cm⁻¹, R₁=0.0449 [I>σ(I)], wR₂=0.1121. The UV-Vis spectra (280-530 nm) of 3-6 are indicative of the existence of strong electronic interactions among the 9,10-anthrylene chromophore and the two cyclopentadienylML₂ moieties. When excited at ca. 370 nm, 1 results to be an efficient light-emitting molecule, while the fluorescence emission of the 9,10-anthrylene chromophore is almost completely quenched in complexes 3-6. The study of the electrochemical behaviour of 3-6 in strictly aprotic conditions allows a satisfactory interpretation of the observed electrode processes and gives information about the location of the redox sites along with the thermodynamic characterisation of the corresponding redox processes. These data show that the occurrence of an intramolecular charge-transfer process between the photo-excited 9,10-anthrylene group and the cyclopentadienylML₂ moiety is a possible route for the observed quenching of emission in the compounds 3-6. The one-electron oxidation of compounds 3-6 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals. Three of them, i.e., 3⁺, 5⁺ and 6⁺, give rise to good X-band EPR spectra that were fully interpreted by computer simulation as well as by semi-empirical calculations (PM3 level) of the spin density distribution.