Europium(II) compounds: simple synthesis of a molecular complex in water and coordination polymers with 2,2'-bipyrimidine-mediated ferromagnetic interactions

Reaction between EuCl(2) and 2,2'-bipyrimidine (bpm) in de-oxygenated water afforded a cationic molecular complex [EuCl(bpm)(2)(H(2)O)(4)][Cl]·H(2)O (1). When performed in an organic solvent such as THF or methanol, the same reaction yielded a 3-dimensional coordination polymer of formula [EuCl(2)(bpm)(MeOH)(0.5)](∞) (2) in which both bpm and the chloride ions act as linkers between the Eu(II) ions. Upon replacing Cl(-) by I(-), two coordination polymers of formula {[Eu(bpm)(2)(H(2)O)(3)][I](2)·0.5bpm}(∞) (3) and {[Eu(I)(bpm)(MeOH)][I]}(∞) (4) were obtained from reaction in water and methanol, respectively. All these compounds were characterized by X-ray crystallography. Investigations of the magnetic properties revealed a weak antiferromagnetic coupling in 2, while 3 and 4 showed a weak ferromagnetic coupling at low temperature.     

An oxacalix[2]arene[2]pyrimidine-bis(Zn-porphyrin) tweezer as a selective receptor towards fullerene C70

An oxacalix[2]arene[2]pyrimidine-bis(Zn^II-porphyrin) conjugate was readily prepared via nucleophilic aromatic substitution of a phenolic AB₃-Zn-porphyrin on the upper rim of a (1,3-alternate) 5,17-bis(methylsulfonyl)oxacalix[4]arene precursor. Efficient 1:1 complex formation between the ‘jaws’ bisporphyrin tweezer and fullerene C₇₀ was evidenced by ¹H NMR titrations (K = 3.0 × 10⁴ M⁻¹), while no detectable complexation could be observed with C₆₀. On the other hand, an analogous oxacalix[4]arene-bis(Cu-corrole) conjugate did not show any measurable (C₆₀ or C₇₀) fullerene binding.     

Comparative evaluation of software for retention time alignment of gas chromatography/time-of-flight mass spectrometry-based metabonomic data

In chromatography-based metabonomic research, retention time (RT) alignment of chromatographic peaks poses a challenge for the accurate profiling of biomarkers. Although a number of RT alignment software has been reported, the performance of these software packages have not been comprehensively evaluated. This study aimed to evaluate the RT alignment accuracy of publicly available and commercial RT alignment software. Two gas chromatography/mass spectrometry (GC/MS) datasets acquired from a mixture of standard metabolites and human bladder cancer urine samples, were used to assess three publicly available software packages, MetAlign, MZmine and TagFinder, and two commercial applications comprising the Calibration feature and Statistical Compare of ChromaTOF software. The overall RT alignment accuracies in aligning standard compounds mixture were 93, 92, 74, 73 and 42% for Calibration feature, MZmine, MetAlign, Statistical Compare and TagFinder, respectively. Additionally, unique trends were observed for the individual software with regards to the different experimental conditions related to extent and direction of RT shifts. Conflicting performance was observed for human urine samples suggesting that RT misalignments still occurred despite the use of RT alignment software. While RT alignment remains an inevitable step in data preprocessing, metabonomic researchers are recommended to perform manual check on the RT alignment of important biomarkers as part of their validation process.     

Synthesis of oxazolo[4,5-c]quinoline TRPV1 antagonists

An efficient synthesis of 2-amino-oxazolo[4,5-c]quinoline TRPV1 antagonists is described via a thiourea formation/carbodiimide cyclization sequence. Synthetic route optimization eliminates intermediate isolations and facilitates the rapid preparation of a series of novel pentacyclic TRPV1 antagonists. From this series, compound (S)-4 was identified as a potent and selective ligand for the TRPV1 ion channel.     

Fundamentals of melt infiltration for the preparation of supported metal catalysts. The case of Co/SiO2 for Fischer-Tropsch synthesis

We explored melt infiltration of mesoporous silica supports to prepare supported metal catalysts with high loadings and controllable particle sizes. Melting of Co(NO(3))(2)·6H(2)O in the presence of silica supports was studied in situ with differential scanning calorimetry. The melting point depression of the intraporous phase was used to quantify the degree of pore loading after infiltration. Maximum pore-fillings corresponded to 70-80% of filled pore volume, if the intraporous phase was considered to be crystalline Co(NO(3))(2)·6H(2)O. However, diffraction was absent in XRD both from the ordered mesopores at low scattering angles and from crystalline cobalt nitrate phases at high angles. Hence, an amorphous, lower density, intraporous Co(NO(3))(2)·6H(2)O phase was proposed to fill the pores completely. Equilibration at 60 °C in a closed vessel was essential for successful melt infiltration. In an open crucible, dehydration of the precursor prior to infiltration inhibited homogeneous filling of support particles. The dispersion and distribution of Co(3)O(4) after calcination could be controlled using the same toolbox as for preparation via solution impregnation: confinement and the calcination gas atmosphere. Using ordered mesoporous silica supports as well as an industrial silica gel support, catalysts with Co metal loadings in the range of 10-22 wt % were prepared. The Co(3)O(4) crystallite sizes ranged from 4 to 10 nm and scaled with the support pore diameters. By calcination in N(2), pluglike nanoparticles were obtained that formed aggregates over several pore widths, while calcination in 1% NO/N(2) led to the formation of smaller individual nanoparticles. After reduction, the Co/SiO(2) catalysts showed high activity for the Fischer-Tropsch synthesis, illustrating the applicability of melt infiltration for supported catalyst preparation.     

DFT study of the mechanism of benzocyclobutene formation by palladium-catalysed C(sp3)-H activation: role of the nature of the base and the phosphine

DFT(B3PW91) calculations of the mechanism of the intramolecular C(sp(3))-H arylation of 2-bromo-tert-butylbenzene to form benzocyclobutene catalysed by Pd(PR(3)) (R = Me, (t)Bu) and a base (acetate, bicarbonate, carbonate) show that the preferred mechanism is highly dependent on the nature of the phosphine and the base used in the calculations. With the experimental reagents (P(t)Bu(3) and carbonate) the rate-determining step is C-H activation with the base coordinated trans to the C-H bond. An agostic interaction of a geminal C-H bond with respect to the bond to be cleaved induces a lowering of the activation barrier.     

Potentiometric determination of coextraction constants of potassium salts in ion-selective electrodes utilizing a nitrobenzene liquid membrane phase

A theoretical treatment of potentiometric data is applied to calculate coextraction constants (K_IA) for three potassium salts from water into a liquid nitrobenzene phase. The experiment involves treating nitrobenzene as a membrane and contacting it with two aqueous solutions of different ion activities. In the presence of either a cation or anion exchanger, the ratio of activities of ions in the two aqueous phases gives rise to a potential difference across the membrane that depends upon the nature and charge of the counter ion of the ion-exchanger in excess. Here, the cation exchanger was chosen to be potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and the anion exchanger was tetradodecylammonium chloride (TDDACl). TDDACl was incrementally added to the nitrobenzene phase containing a fixed concentration of KTpClPB, and the corresponding emf was recorded as a function of concentration of TDDACl. The membrane changes from one with cation exchanger properties (excess KTpClPB) to one with anion exchanger properties (excess TDDACl). The potential difference and shape of the titration curve can be predicted by theory based on the phase boundary potential model. Log(K_IA) values calculated for KCl, KNO₃ and KClO₄ in nitrobenzene were found as: −10.53 (± 0.09), −8.16 (± 0.05) and −5.63 (± 0.03) respectively, in accordance with the Hofmeister series of lipophilicity, and similar to those observed in PVC membranes containing other plasticizers. The method presented here offers the advantage over other methods to calculate K_IA, in that it is relatively experimentally simple without compromising the accuracy of the calculated coextraction constants. The ability to titrate directly into the liquid membrane phase affords a higher precision compared to the preparation of a series of PVC/plasticizer membranes with different compositions.     

High-throughput salting-out assisted liquid/liquid extraction with acetonitrile for the simultaneous determination of simvastatin and simvastatin acid in human plasma with liquid chromatography

Simvastatin (SS) is an effective cholesterol-lowering medicine, and is hydrolyzed to simvastatin acid (SSA) after oral administration. Due to SS and SSA inter-conversion and its pH and temperature dependence, SS and SSA quantitation is analytically challenging. Here we report a high-throughput salting-out assisted liquid/liquid extraction (SALLE) method with acetonitrile and mass spectrometry compatible salts for simultaneous LC-MS/MS analysis of SS and SSA. The sample preparation of a 96-well plate using SALLE was completed within 20 min, and the SALLE extract was diluted and injected into an LC-MS/MS system with a cycle time of 2.0 min/sample. The seamless interface of SALLE and LC-MS eliminated drying down step and thus potential sample exposure to room or higher temperature. The stability of SS and SSA in various concentration ratios in plasma was evaluated at room and low (4 °C) temperature and the low temperature (4 °C) was found necessary to maintain sample integrity. The short sample preparation time along with controlled temperature (2-4 °C) and acidity (pH 4.5) throughout sample preparation minimized the conversion of SS → SSA to ≤0.10% and the conversion of SSA → SS to 0.00% The method was validated with a lower limit of quantitation (LLOQ) of 0.094 ng mL⁻¹ for both SS and SSA and a sample volume of 100 μL. The method was used for a bioequivalence study with 4048 samples. Incurred sample reproducibility (ISR) analysis of 362 samples from the study exceeded ISR requirement with 99% re-analysis results within 100 ± 20% of the original analysis results.