Determination of the maximum bioaccumulation capacity of various metals in leaves of two Tillandsia species.

Tillandsia species are plants from the Bromeliaceae family which display biomonitoring capacities in both active and passive modes. The bioaccumulation potential of Tillandsia aeranthos (Loisiel.) Desf. and Tillandsia bergeri Mez acclimated to Southern/Mediterranean Europe has never been studied. More generally, few studies have detailed the maximum accumulation potential of Tillandsia leaves through controlled experiments. The aim of this study is to evaluate the maximum accumulation values of seven metals (Co, Cu, Mn, Ni, Pb, Pt, and Zn) in T. aeranthos and T. bergeri leaves. Plants were immersed in different mono elemental metallic solutions of Co (II), Cu (II), Mn (II), Ni (II), Pb (II), Pt (IV), and Zn (II) ions at different concentrations. In addition, cocktail solutions of these seven metals at different concentrations were prepared to study the main differences and the potential selectivity between metals. After exposure, the content of these metals in the leaves were measured by inductively coupled plasma-optical emission spectrometry. Data sets were evaluated by a fitted regression hyperbola model and principal component analysis, maximum metal loading capacity, and thermodynamic affinity constant were determined. The results showed important differences between the two species, with T. bergeri demonstrating higher capacity and affinity for metals than T. aeranthos. Furthermore, between the seven metals, Pb and Ni showed higher enrichment factors (EF). T. bergeri might be a better bioaccumulator than T. aeranthos with marked selectivity for Pb and Ni, metals of concern in air quality biomonitoring.

Behavior of a Dynamic Covalent Library Driven by Combined Pd(II) and Biphasic Effectors for Metal Transport between Phases.

This work reports the effect of Pd(II) as chemical effector on an acylhydrazone-based dynamic covalent library (DCL) in biphasic systems (water/chloroform). The constituents of the DCL are self-built and distributed in the two phases, two of them are lipophilic enough to play the role of a carrier agent that may transfer Pd(II) from the aqueous phase to the organic phase. Upon addition of Pd(II), the DCL of components exhibits a strong amplification of the constituent that is the most adapted to stabilize Pd(II) in chloroform as well as its agonist in water. This evolution is driven by the combination of the interaction of the DCL with Pd(II) and the presence of the two phases. This study paves the way to a novel approach for liquid/liquid extraction and metal recovery by means of adaptive extractant species generated in situ by a DCL.

Short Alternative Route for Nuclear Fuel Reprocessing Based on Organic Phase Self-Splitting.

A more sustainable management of natural resources and the establishment of processes allowing a joint management of nuclear materials to avoid their diversion from their civilian use are two issues for the nuclear industry. Short alternatives to existing processes have therefore been proposed based on known systems available, tributylphosphate (TBP), for the separation of actinides by liquid/liquid extraction. Proof of concept of such alternative has been established on the uranium(VI)/thorium(IV) system. From an organic phase consisting of a mixture of TBP/n-dodecane loaded with uranium and thorium, two fluxes have been obtained: the first contains almost all of the thorium in the presence of uranium in a controlled ratio, the second contains surplus uranium. Two levers were selected to control the spontaneous separation of the organic phase: the addition of concentrated nitric acid, or the temperature variation. Best results have been obtained using a temperature drop in the liquid/liquid extraction process, and variations in process conditions have been studied. Final metal recovery and solvent recycling have also been demonstrated, opening the door for further process development.

From Electronic Waste to Suzuki-Miyaura Cross-Coupling Reaction in Water: Direct Valuation of Recycled Palladium in Catalysis.

Invited for this month's cover is the group of Damien Bourgeois at the Marcoule Institute for Separation Chemistry (ICSM). The image shows how a short process chain can efficiently transform our waste into an active catalyst. The Full Paper itself is available at 10.1002/cssc.202001155.

From Electronic Waste to Suzuki-Miyaura Cross-Coupling Reaction in Water: Direct Valuation of Recycled Palladium in Catalysis.

From electronic waste to Pd-catalyzed reaction! The straightforward valuation of palladium recovered from electronic waste is reported here. Following a classical leaching stage, palladium is selectively extracted from a complex aqueous mixture of metallic cations into an organic phase. Afterwards, the judicious choice of a surfactant enables stabilization of palladium during back extraction cycles, and the direct preparation of an aqueous micellar solution, which can be employed in a model Suzuki-Miyaura cross-coupling reaction. Clean phase separation is observed, and distribution of all components between organic and aqueous phases is mastered. The proposed process avoids several waste generating steps dedicated to palladium isolation and ultimate purification, as well as the preparation of palladium pre-catalyst. This novel approach enables a better use of both natural resources and industrial wastes, through new cycles in circular economy.

Fireproofing of domestic upholstered furniture: Migration of flame retardants and potential risks.

Flame retardants (FRs) are widely incorporated in polyurethane foams to decrease their fire reaction. Currently, the risks associated with the use of FRs in domestic upholstered furniture (UF) are evaluated according to FRs volatility and potency to be emitted into the atmosphere. However, exposure via contact and dermal penetration, mediated by sweat, has not been considered so far. Our study provides an identification of the latest-generation of FRs most commonly used in UF, and an evaluation of their potency to migrate into artificial sweat. First of all, an extensive literature search, along with surveys with professionals, led to the identification of twenty-two FRs and synergists commonly used in France and Europe. Then, migration into artificial sweat of various FRs embedded into synthetic or commercially available polymer matrix was studied and evidenced. These results were analysed in the light of their potential effects on human health and the environment. Based on the migration's data, it is not possible to clearly rule out potential effects of FRs on human and environment health. Therefore, the authors consider that the use of FRs in domestic upholstery does not seem to be justified due to potential risks and a lack of clear benefits.

Impact of the Long-Range Electronic Effect of a Fluorous Ponytail on Metal Coordination during Solvent Extraction.

With the need for a precise description of the long-range electronic effects of a perfloroalkyl chain (F-ponytail) grafted onto metal chelators, we studied in detail the effect of a spacer inserted between the polar complexing head and the F-ponytail, in relation to the metal coordination ability of the resulting molecules. The prepared molecules were then applied for the extraction of various metals from an aqueous phase into an organic phase, and the optimum spacer length could be estimated to be between three and four methylene units, according to the extraction conditions. The study also revealed the difficulty of modeling and anticipating the tiny energy differences involved in the extraction process and the importance in peculiar cases to go beyond only these studied inductive effects to understand better the factors that govern the stabilization of a metallic cation in a complex fluorous phase.

Reactivity of U-associated osteopontin with lactoferrin: a one-to-many complex.

Uranium is the heaviest natural element, mainly found in aqueous medium as the hexavalent uranyl ion (UO22+). Bones are the main organs in which uranium accumulates, depending on as yet unknown molecular and cellular mechanisms. Recently, it has been revealed that osteopontin (OPN), a protein involved in bio-mineralization processes, and its main naturally occurring cleaved form (fOPN), have nanomolar affinities for UO22+. The binding of UO22+ is due to both the phosphorylation sites and acidic residues of these proteins and is accompanied by a slight gain in secondary structure. OPN is an Intrinsically Disordered Protein (IDP), a family of proteins which play a crucial role in several interaction networks, where phosphorylations are thought to be key elements. OPN has been shown to bind lactoferrin (LF) and the two proteins have antagonist functions in the modulation of the bio-mineralization process. However, to date, there has been no evidence that UO22+ and LF compete in their binding to OPN or not. Based on a series of convergent experimental data, this study first addressed in detail the LF/fOPN interaction and proposed a LF:fOPN 4/1 maximal stoichiometry. Moreover the phosphorylations were demonstrated to be necessary for the stability of such complexes. The interaction of preformed UO22+/fOPN complexes with LF was also investigated and the occurrence of several entities involving the three partners was demonstrated. These complexes did not reveal any significant conformational changes compared to those obtained in the absence of UO22+. The results have shown not only that LF and UO22+ do not compete, but also that these complexes are likely to be more stable than LF/fOPN complexes, as indicated by their melting temperature (Tm) values. The potential impact of those uranyl-stabilized ternary complexes on some biological pathways now remains to be assessed. Nonetheless, this work has contributed to shedding light on the formation of stable ternary complexes involving a large structured protein, an IDP and an exogenous metal.

Metal Recognition Driven by Weak Interactions: A Case Study in Solvent Extraction.

Tuning the affinity of a medium for a given metallic cation with the sole modification of weak interactions is a challenge for molecular recognition. Solvent extraction is a key technique employed in the recovery and purification of valuable metals, and it is facing an increased complexity of metal fluxes to deal with. The selectivity of such processes generally relies on the use of specific ligands, designed after their coordination chemistry. In the present study, we illustrate the possibility to employ the sole control of weak interactions to achieve the selective extraction of Pd(II) over Nd(III) : the control over selectivity is obtained by tuning the self-assembly of the organic phase. A model is proposed, after detailed experimental analysis of molecular (XRD, NMR) and supra-molecular (SAXS) features of the organic phases. We thus demonstrate that Pd(II) extraction is driven by metal coordination, whereas Nd(III) extraction requires aggregation of the extractant in addition to metal coordination. These results are of general interest for the applications which rely on the stabilization of metals in organic phases.

Micro-distribution of uranium in bone after contamination: new insight into its mechanism of accumulation into bone tissue.

After internal contamination, uranium rapidly distributes in the body; up to 20 % of the initial dose is retained in the skeleton, where it remains for years. Several studies suggest that uranium has a deleterious effect on the bone cell system, but little is known regarding the mechanisms leading to accumulation of uranium in bone tissue. We have performed synchrotron radiation-based micro-X-ray fluorescence (SR µ-XRF) studies to assess the initial distribution of uranium within cortical and trabecular bones in contaminated rats' femurs at the micrometer scale. This sensitive technique with high spatial resolution is the only method available that can be successfully applied, given the small amount of uranium in bone tissue. Uranium was found preferentially located in calcifying zones in exposed rats and rapidly accumulates in the endosteal and periosteal area of femoral metaphyses, in calcifying cartilage and in recently formed bone tissue along trabecular bone. Furthermore, specific localized areas with high accumulation of uranium were observed in regions identified as micro-vessels and on bone trabeculae. These observations are of high importance in the study of the accumulation of uranium in bone tissue, as the generally proposed passive chemical sorption on the surface of the inorganic part (apatite) of bone tissue cannot account for these results. Our study opens original perspectives in the field of exogenous metal bio-mineralization.

Assessment of CE-ICP/MS hyphenation for the study of uranyl/protein interactions.

Identification of uranyl transport proteins is key to develop efficient detoxification approaches. Therefore, analytical approaches have to be developed to cope with the complexity of biological media and allow the analysis of metal speciation. CE-ICP/MS was used to combine the less-intrusive character and high separation efficiency of CE with the sensitive detection of ICP/MS. The method was based on the incubation of samples with uranyl prior to the separation. Electrophoretic buffers were compared to select a 10 mM Tris to 15 mM NaCl buffer, which enabled analyses at pH 7.4 and limited dissociation. This method was applied to the analysis of a serum. Two main fractions were observed. By comparison with synthetic mixtures of proteins, the first one was attributed to fetuin and in a lesser extent to HSA, and the second one to uranyl unbound to proteins. The analysis showed that fetuin was likely to be the main target of uranyl. CE-ICP/MS was also used to investigate the behavior of the fetuin-uranyl complex, in the presence of carbonate, an abundant complexing agent of uranyl in blood. This method enabled association constants determination, suggesting the occurrence of both FETUA(UO2(2+)) and FETUA(UO2(2+))(CO3(2-)) complexes, depending on the carbonate concentration.

Incorporation of uranium into a biomimetic apatite: physicochemical and biological aspects.

Bone is the main target organ for the storage of several toxic metals, including uranium. But the mode of action of uranium on bones remains poorly understood. To better assess the impact of uranium on bone cells, synthetic biomimetic apatites encompassing a controlled amount of uranium were prepared and analyzed. This study revealed the physicochemical impact of uranium on apatite mineralization: the presence of the metal induces a loss of crystallinity and a lower mineralization rate. The prepared samples were then used as substrates for bone cell culture. Osteoblasts were not sensitive to the presence of uranium in the support, whereas previous results showed a deleterious effect of uranium introduced into a cell culture solution. This work should therefore have some original prospects within the context of toxicological studies concerning the effect of metallic cations on bone cell systems.

Alternate dipping preparation of biomimetic apatite layers in the presence of carbonate ions.

The classical simulated body fluids method cannot be employed to prepare biomimetic apatites encompassing metallic ions that lead to very stable phosphates. This is the case for heavy metals such as uranium, whose presence in bone mineral after contamination deserves toxicological study. We have demonstrated that existing methods, based on alternate dipping into calcium and phosphate ions solutions, can be adapted to achieve this aim. We have also especially studied the impact of the presence of carbonate ions in the medium as these are necessary to avoid hydrolysis of the contaminating metallic cations. Both the apatite-collagen complex method and a standard chemical (STD) method employing only mineral solutions lead to biomimetic apatites when calcium and carbonate ions are introduced simultaneously. The obtained materials were fully characterized and we established that the STD method tolerates the presence of carbonate ions much better, and this leads to homogeneous samples. Emphasis was set on the repeatability of the method to ensure the relevancy of further work performed on series of samples. Finally, osteoblasts cultured on these samples also proved a similar yield and standard-deviation in their adenosine triphosphate content when compared to commercially available substrates designed to study of such cell cultures.

Bone as target organ for metals: the case of f-elements.

The skeleton is a target organ for most metals. This leads to their bioaccumulation, either as storage of useful oligoelements or as a protection against damage by toxic elements. The different events leading to their accumulation in this organ, under constant remodeling, are not fully understood, nor the full subsequent impact on bone metabolism. This lack of knowledge is particularly true for lanthanides and actinides, whose use has been increasing over recent decades. These metals, known as f-elements, present chemical similarities and differences. After a comparison of the biologically relevant physicochemical properties of lanthanides and actinides, and a brief reminder of the main events of bone metabolism, this review considers the results published over the past decade regarding the interaction between bones and f-elements. Emphasis will be given to the molecular events, which constitute the basis of the most recent toxicological studies in this domain but still need further investigation. Ionic exchanges with the inorganic matrix, interactions with bone proteins, and cellular mechanism disturbances are mainly considered in this review.

Diastereoselective synthesis of (+/-)-1',4'-dimethyluridine.

The de novo synthesis of racemic 1',4'-dimethyluridine was accomplished in 12 steps starting from 2,5-dimethylfuran and vinylene carbonate. Key steps of the sequence include the stereoconvergent preparation of a meso diacid, and a stereoselective glycosylation without neighboring group participation. Such 1',4'-disubstituted ribonucleoside analogues are undisclosed compounds, which may present interesting biological activities.