Multi-residue analysis and ultra-trace quantification of 36 priority substances from the European Water Framework Directive by GC-MS and LC-FLD-MS/MS in surface waters

A multi residue analysis was developed for screening, quantification and confirmation of 36 priority organic compounds included in the 2000/60/EC European Water Framework Directive. The compounds analyzed included 19 pesticides, 8 PAH, 5 endocrine-disruptors and 4 organochlorine compounds. The method was developed in three steps. First, automated off-line solid-phase extraction using Strata X cartridges was optimized to trap simultaneously the 36 studied compounds. Second, the more volatile compounds were analysed by gas chromatography coupled to mass spectrometry with electron impact ionisation in selected ion monitoring mode (SIM). Third, the last 20 compounds were detected and quantified, in one run, by liquid chromatography coupled to fluorescence detector and tandem mass spectrometry. The excellent selectivity and sensitivity allowed us satisfactory quantification and confirmation at levels as low as 0.2-67 ng L⁻¹ with recoveries between 59 and 105%. Such methodology was then applied to French surface waters: all the waters present organic contaminants, and their concentration varied according to the origin and nature of substances.     

5-Aminooxazole as an internal traceless activator of C-terminal carboxylic acid: rapid access to diversely functionalized cyclodepsipeptides

A conceptually novel macrolactonization protocol has been developed. It is a domino process involving a sequence of: 1) protonation of 5-aminooxazole leading to the electrophilic iminium salt; 2) trapping of the iminium species by the neighboring C-terminal carboxylic acid leading to a putative spirolactone; and 3) intramolecular nucleophilic addition of the tethered alcohol to the spirolactone followed by fragmentation. The strategically incorporated 5-aminooxazole serves as an internal traceless activator of the neighboring C-terminal carboxylic acid, since it became an integral part of the peptide backbone after cyclization. No coupling reagent is required and the entire sequence is triggered by just a few equivalents of trifluoroacetic acid under very mild conditions (MeCN as the solvent at room temperature). The spirolactone as an activated form of the carboxylic acid has been evidenced by a sulfur-migration experiment. By combining with a three-component synthesis of 5-aminooxazole, a two-step synthesis of structurally complex cyclodepsipeptides from readily accessible starting materials was developed.     

Ultrasoft pseudopotentials for lanthanide solvation complexes: core or valence character of the 4f electrons

The 4f electrons of lanthanides, because of their strong localization in the region around the nucleus, are traditionally included in a pseudopotential core. This approximation is scrutinized by optimizing the structures and calculating the interaction energies of Gd(3+)(H(2)O) and Gd(3+)(NH(3)) microsolvation complexes within plane wave Perdew-Burke-Ernzerhof calculations using ultrasoft pseudopotentials where the 4f electrons are included either in the core or in the valence space. Upon comparison to quantum chemical MP2 and CCSD(T) reference calculations it is found that the explicit treatment of the 4f electrons in the valence shell yields quite accurate results including the required small spin polarization due to ligand charge transfer with only modest computational overhead.     

Production and reactions of organic-soluble lanthanide complexes of the monolacunary Dawson [alpha1-P2W17O61]10- polyoxotungstate

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.     

A new family of mono- and dicarboxylic ruthenium complexes [Ru(DIP)2(L2)]2+ (DIP = 4,7-diphenyl-1,10-phenanthroline): synthesis, solution behavior, and X-ray molecular structure of trans-[Ru(DIP)2(MeOH)2][OTf]2

A new family of ruthenium complexes of general formula [Ru(DIP)2(L2)]2+, where DIP = 4,7-diphenyl-1,10-phenanthroline, a bidentate ligand with an extended aromatic system, was prepared and fully characterized. When L is a monodentate ligand, the following complexes were obtained: L = CF3SO3(-1) (2), CH3CN (3), and MeOH (4). When L2 is a bidentate ligand, the compounds [Ru(DIP)2(Hcmbpy)][Cl]2 (5) and [Ru(DIP)2(H2dcbpy)][Cl]2 (6) were prepared (Hcmbpy = 4-carboxy-4'-methyl-2,2-bipyridine, H2dcbpy = 4,4'-dicarboxy-2,2'-bipyridine). Complex [Ru(DIP)2(MeOH)2][OTf]2 (4) displayed a trans configuration of the DIP ligands, which is rare for octahedral complexes featuring DIP bidentate ligands. DFT calculations carried out on 4 showed that the cis isomer is more stable by 12.2 kcal/mol relative to the trans species. The solution behaviors of monocarboxylic complex [Ru(DIP)2(Hcmbpy)][Cl]2 (5) and dicarboxylic complex [Ru(DIP)2(H2dcbpy)][Cl]2 (6) were investigated by 1H NMR spectroscopy. VT-NMR, concentration dependence, and reaction with NaOD allowed us to suggest that aggregation of the cationic species in solution, especially for 6, originates mainly from hydrogen bonding interactions.     

A liquid chromatography‐atmospheric pressure photoionization tandem mass spectrometric (LC‐APPI‐MS/MS) method for the determination of triterpenoids in medicinal plant extracts

An analytical method using liquid chromatography‐atmospheric pressure photoionization tandem mass spectrometry with toluene as a dopant was developed for the determination of triterpenes in medicinal plant extracts. The 12 compounds determined have been shown to exhibit biological activity, such as gastroprotective, hepatoprotective, anti‐inflammatory, antiviral and anti‐tumor effects. The parameters of the atmospheric pressure photoionization interface were optimized to obtain the highest possible sensitivity for all of the compounds. The limits of detection and quantification ranged from 0.4 to 157.9 µg l^?1 and 1.3 to 526.4 µg l^?1, respectively. The method was validated and applied to extracts of five medicinal plants species (Mansoa alliacea (Lam.) A.H.Gentry, Bauhinia variegata var variegata, Bauhinia variegata var alboflava, Cecropia obtuse Trécul and Cecropia palmate Willd) from the Amazonian region. The concentrations of the six triterpenes quantified in the samples ranged from 0.424 mg kg^?1 for ursolic acid to 371.96 mg kg^?1 for β‐amyrin, which were quantified by using the standard addition method (n = 3). Copyright © 2016 John Wiley & Sons, Ltd.     

Toward accurate solvation dynamics of lanthanides and actinides in water using polarizable force fields: from gas-phase energetics to hydration free energies

In this contribution, we focused on the use of polarizable force fields to model the structural, energetic, and thermodynamical properties of lanthanides and actinides in water. In a first part, we chose the particular case of the Th(IV) cation to demonstrate the capabilities of the AMOEBA polarizable force field to reproduce both reference ab initio gas-phase energetics and experimental data including coordination numbers and radial distribution functions. Using such model, we predicted the first polarizable force field estimate of Th(IV) solvation free energy, which accounts for −1,638 kcal/mol. In addition, we proposed in a second part of this work a full extension of the SIBFA (Sum of Interaction Between Fragments Ab initio computed) polarizable potential to lanthanides (La(III) and Lu(III)) and to actinides (Th(IV)) in water. We demonstrate its capabilities to reproduce all ab initio contributions as extracted from energy decomposition analysis computations, including many-body charge transfer and discussed its applicability to extended molecular dynamics and its parametrization on high-level post-Hartree–Fock data.     

Mapping the synthesis of low nuclearity polyoxometalates from octamolybdates to Mn-Anderson clusters

A comprehensive study of the isomer-independent synthesis of TRIS ((HOCH(2))(3)CNH(2)) Mn-Anderson compounds from Na(2)MoO(4)·2H(2)O, via the corresponding octamolybdate species, is presented. Three octamolybdate salts of [Mo(8)O(26)](4-) in the β-isomer form, with tetramethylammonium (TMA), tetraethylammonium (TEA) and tetrapropylammonium (TPA) as the counter cation, were synthesised from the sodium molybdate starting material. Fine white powdery products for the three compounds were obtained, which were fully characterised by elemental analysis, TGA, solution and solid state Raman, IR and ESI-MS, revealing a set ratio of Na and organic cations for each of the three compounds; (TMA)(2)Na(2)[Mo(8)O(26)] (1), (TEA)(3)Na(1)[Mo(8)O(26)] (2) and (TPA)(2)Na(2)[Mo(8)O(26)] (3), and the analyses also confirmed that the three compounds all consisted of the octamolybdate in the β-isomeric form. ESI-MS analyses of 1, 2 and 3 show similar fragmentation for these β-isomers compared to the previously reported study for the α-isomer ((TBA)(4)[α-Mo(8)O(26)]) (A) in the synthesis of ((TBA)(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)]) (B), and compounds 1, 2 and 3 were successfully used to synthesise equivalent TRIS Mn-Anderson compounds: (TMA)(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (4), (TEA)(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (5) and (TPA)(2)Na(1)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (6), as well as Na(3)[MnMo(6)O(18)((OCH(2))(3)CNH(2))(2)] (7). This is the first example where symmetric organically-grafted Mn-Anderson compounds have been synthesised in DMF from anything but the {Mo(8)O(26)} α-isomer.