Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

We present new results on the liquid–liquid extraction of uranium (VI) from a nitric acid aqueous phase into a tri‐n‐butyl phosphate/1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (TBP/[C₄mim][Tf₂N]) phase. The individual solubilities of the ionic‐liquid ions in the upper part of the biphasic system are measured over the whole acidic range and as a function of the TBP concentration. New insights into the extraction mechanism are obtained through the in situ characterization of the extracted uranyl complexes by coupling UV/Vis and extended X‐ray absorption fine structure (EXAFS) spectroscopy. We propose a chemical model to explain uranium (VI) extraction that describes the data through a fit of the uranyl distribution ratio D_U. In this model, at low acid concentrations uranium (VI) is extracted as the cationic complex [UO₂(TBP)₂]²⁺, by an exchange with one proton and one C₄mim⁺. At high acid concentrations, the extraction proceeds through a cationic exchange between [UO₂(NO₃)(HNO₃)(TBP)₂]⁺ and one C₄mim⁺. As a consequence of this mechanism, the variation of D_U as a function of TBP concentration depends on the C₄mim⁺ concentration in the aqueous phase. This explains why noninteger values are often derived by analysis of D_U versus [TBP] plots to determine the number of TBP molecules involved in the extraction of uranyl in an ionic‐liquid phase.     

Ultratrace-level determination of N-Nitrosodimethylamine,N-Nitrosodiethylamine,and N-Nitrosomorpholine in waters by solid-phase extraction followed by liquid chromatography-tandem mass spectrometry

N-nitrosamines are a new class of emerging nitrogenous drinking water disinfection by-products. These compounds are probably carcinogenic which could seriously affect the safety of drinking water consumers. The aim of this study is to develop a simple, fast, and specific analytical method for the routine determination of low part per trillion levels of N-nitrosamines in waters. An ultra high pressure liquid chromatography coupled with tandem mass spectrometry (UHPLC/MS/MS) method was developed for the qualitative and quantitative analysis of N-nitrosamines in waters. N-nitrosamines were extracted, purified and concentrated from water samples in one step using a solid-phase extraction (SPE). The compounds were detected in multiple reaction monitoring via electrospray ionisation source with positive ionisation mode. To achieve symmetrical peak shapes and a short chromatographic analysis time, the mobile phase consisting of acetonitrile, water and formic acid (60:40:0.1, v/v/v) was used in the experiment. Chromatographic separation of N-nitrosamines was done in less than two minutes. All calibration curves had good linearity (r²≥ 0.9989). The intra- and inter-day precision of the assay ranged from 0.59% to 3.11% and accuracy ranged from 99.66% to 104.1%. The mean recoveries of N-nitrosamines in spiked water were 98%-101%. The reproducability was acceptable with relative standard deviations of less than 3.53%. The proposed method yielded detection limits very low which ranges from 0.04 to 0.16 ng L^?1. Finally, the developed analytical method was successfully applied to the analysis of N-nitrosamines in natural water sample     

Comparative Study on the Reactivity of 6‐Haloimidazo[1,2‐a]pyridine Derivatives towards Negishi‐ and Stille‐Coupling Reactions

The scope of the Suzuki‐cross‐coupling reaction of 6‐haloimidazo[1,2‐a]pyridines is dependent on the availability of the (hetero)arylboronic acids. Thus, with the aim to develop expanded applications of (hetero)arylations of imidazo[1,2‐a]pyridines, we investigated the Negishi‐ and Stille‐cross‐coupling reactions at the 6‐position. Remarkably, attempts to apply the Negishi‐cross‐coupling conditions to the organozinc derivative prepared from 6‐haloimidazo[1,2‐a]pyridine via a lithium? zinc exchange led to the 5‐phenyl compound 3 in 54% yield instead of the desired 6‐phenyl isomer (Scheme 1). In contrast, various commercially available halogenated five‐ or six‐membered‐ring heterocycles were efficiently coupled to the 6‐(trialkylstannyl)imidazo[1,2‐a]pyridine under Stille conditions (Table 2).     

The N-Terminal End Truncated Mu-Opioid Receptor: from Expression to Circular Dichroism Analysis

In order to evaluate the biochemical, biophysical, and pharmacological implication of the N-terminal domain of the human mu-opioid receptor (HuMOR), deletion mutants lacking 64 amino acids from the amino terminus of HuMOR were constructed and expressed in the yeast Pichia pastoris. The recombinant proteins differed with respect to the presence of the Saccharomyces cerevisiae α-factor prepropeptide and the enhanced green fluorescent protein fused to the N terminus of the receptor. Pharmacological studies indicated that deletion of the N-terminal domain produced little effect on ligand affinities. The N-terminal end truncated and c-myc/6his-tagged receptor was subsequently purified to homogeneity and a yield of 5 mg/l was obtained after purification. The N-terminal end truncated receptor was further characterized by circular dichroism in trifluoroethanol and showed a characteristic pattern of α-helical structure. A pH effect on the structure of the receptor was observed when it was solubilized in sodium dodecyl sulfate micelles, with an increase of helicity at low pH.     

2-chlorophenyl zinc bromide: a convenient nucleophile for the mannich-related multicomponent synthesis of clopidogrel and ticlopidine

A methodological study devoted to the Mannich-like multicomponent synthesis of the antiplatelet agent (±)?clopidogrel (7) and the ethyl ester analogue 6 is described. The process involves the formation of 2-chlorophenyl zinc bromide (2) and its subsequent reaction with an alkyl glyoxylate and 4,5,6,7-tetrahydrothieno[3,2-c]pyridine (3). We demonstrate that the organozinc reagent 2 also constitutes a very convenient nucleophile for the multicomponent synthesis of the benzylamine core of ticlopidine (9).     

Photoinduced phase separation

A novel approach of photoinduced phase separation has been demonstrated with a photolabile anionic surfactant, mixed with an inert nonionic surfactant in the presence of salting-out electrolyte. Breakdown of the photolyzable surfactant results in hydrophobic photoproducts, which are emulsified by the remaining inert surfactant; added electrolyte resolves the emulsion into macroscopic oily and aqueous phases. The initial micellar systems can disperse an insoluble additive marker dye (shown), which may be spatially segregated from the aqueous environment by the action of UV light.     

Separation of 3'-azido-2',3'-dideoxythymidine pronucleotide diastereoisomers in biological samples by CZE with cyclodextrin addition

The possibility of using capillary electrophoresis as an alternative technique to HPLC for the separation of pronucleotide diastereoisomers of AZT was investigated. In the pH range 6.2-7.2 where the analytes are stable, a chiral additive, carboxymethyl-beta-CD, was found appropriate to enable the separation of the uncharged diastereoisomers. An experimental design strategy was used to study the influence of several parameters (CD and phosphate buffer concentration, methanol content of the electrolyte, injected volume, capillary length, electric field and separation temperature) on the separation and find suitable analytical conditions for monitoring the prodrugs in cell extracts. The diastereoisomers of the three tBuSATE phenylphosphotriester derivatives of AZT studied could be fully resolved within short analysis time (less than 10 min). Method validation results showed satisfactory results for linearity, accuracy and repeatability.     

Self-assembly of amphiphilic glycoconjugates into lectin-adhesive nanoparticles

This work describes the synthesis and self-assembly of carbohydrate-clicked rod-coil amphiphilic systems. Copper-catalyzed Huisgen cycloaddition was efficiently employed to functionalize the hydrophilic extremity of PEG-b-tetra(p-phenylene) conjugates by lactose and N-acetyl-glucosamine ligands. The resulting amphiphilic systems spontaneously self-assembled into nanoparticles when dissolved in aqueous media, as evidenced by dynamic light scattering (DLS), transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS). The formation of highly monodisperse micelles having a mean diameter of 10 nm was observed for systems containing a PEG 900 core, and a decrease in the hydrophilic moiety (PEG 600) led to the formation of vesicles with a broader size distribution. The presence of carbohydrate residues on the surfaces of the micelles and their ability to establish specific interactions with wheat germ agglutinin (WGA) and peanut agglutinin (PNA) were further highlighted by light-scattering measurements, thus confirming the attractive applications of such sugar micelles in biosensor devices.     

Structural influence on the photochromic response of a series of ruthenium mononitrosyl complexes

In mononitrosyl complexes of transition metals two long-lived metastable states corresponding to linkage isomers of the nitrosyl ligand can be induced by irradiation with appropriate wavelengths. Upon irradiation, the N-bound nitrosyl ligand (ground state, GS) turns into two different conformations: isonitrosyl O bound for the metastable state 1 (MS1) and a side-on nitrosyl conformation for the metastable state 2 (MS2). Structural and spectroscopic investigations on [RuCl(NO)py(4)](PF(6))(2)·1/2H(2)O (py = pyridine) reveal a nearly 100% conversion from GS to MS1. In order to identify the factors which lead to this outstanding photochromic response we study in this work the influence of counteranions, trans ligands to the NO and equatorial ligands on the conversion efficiency: [RuX(NO)py(4)]Y(2)·nH(2)O (X = Cl and Y = PF(6)(-) (1), BF(4)(-) (2), Br(-)(3), Cl(-) (4); X = Br and Y = PF(6)(-) (5), BF(4)(-) (6), Br(-)(7)) and [RuCl(NO)bpy(2)](PF(6))(2) (8), [RuCl(2)(NO)tpy](PF(6)) (9), and [Ru(H(2)O)(NO)bpy(2)](PF(6))(3) (10) (bpy = 2,2'-bipyridine; tpy = 2,2':6',2"-terpyridine). Structural and infrared spectroscopic investigations show that the shorter the distance between the counterion and the NO ligand the higher the population of the photoinduced metastable linkage isomers. DFT calculations have been performed to confirm the influence of the counterions. Additionally, we found that the lower the donating character of the ligand trans to NO the higher the photoconversion yield.