Building C(sp3) Molecular Complexity on 2,2′-Bipyridine and 1,10-Phenanthroline in Rhenium Tricarbonyl Complexes

The reactions of [Re(N-N)(CO)₃(PMe₃)]OTf (N-N=2,2′-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt₃ have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt₃ reacted with [Re(bipy)(CO)₃(PMe₃)]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral Re^I products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to Re^I complexes containing bipy- and phen-derived chelates with several C(sp³) centers.     

In Vitro Antiplasmodial and Cytotoxic Activities of Compounds from the Roots of Eriosema montanum Baker f. (Fabaceae)

Malaria remains one of the leading causes of death in sub-Saharan Africa, ranked in the top three infectious diseases in the world. Plants of the Eriosema genus have been reported to be used for the treatment of this disease, but scientific evidence is still missing for some of them. In the present study, the in vitro antiplasmodial activity of the crude extract and compounds from Eriosema montanum Baker f. roots were tested against the 3D7 strain of Plasmodium falciparum and revealed using the SYBR Green, a DNA intercalating compound. The cytotoxicity effect of the compounds on a human cancer cell line (THP-1) was assessed to determine their selectivity index. It was found that the crude extract of the plant displayed a significant antiplasmodial activity with an IC₅₀ (µg/mL) = 17.68 ± 4.030 and a cytotoxic activity with a CC₅₀ (µg/mL) = 101.5 ± 12.6, corresponding to a selective antiplasmodial activity of 5.7. Bioactivity-guided isolation of the major compounds of the roots’ crude extract afforded seven compounds, including genistein, genistin and eucomic acid. Under our experimental conditions, using Artemisinin as a positive control, eucomic acid showed the best inhibitory activity against the P. falciparum 3D7, a well-known chloroquine-sensitive strain. The present results provide a referential basis to support the traditional use of Eriosema species in the treatment of malaria.     

Zirconium-Based Metal Organic Frameworks for the Capture of Carbon Dioxide and Ethanol Vapour. A Comparative Study

This paper reports on the comparison of three zirconium-based metal organic frameworks (MOFs) for the capture of carbon dioxide and ethanol vapour at ambient conditions. In terms of efficiency, two parameters were evaluated by experimental and modeling means, namely the nature of the ligands and the size of the cavities. We demonstrated that amongst three Zr-based MOFs, MIP-202 has the highest affinity for CO₂ (−50 kJ·mol⁻¹ at low coverage against around −20 kJ·mol⁻¹ for MOF-801 and Muc Zr MOF), which could be related to the presence of amino functions borne by its aspartic acid ligands as well as the presence of extra-framework anions. On the other side, regardless of the ligand size, these three materials were able to adsorb similar amounts of carbon dioxide at 1 atm (between 2 and 2.5 µmol·m⁻² at 298 K). These experimental findings were consistent with modeling studies, despite chemisorption effects, which could not be taken into consideration by classical Monte Carlo simulations. Ethanol adsorption confirmed these results, higher enthalpies being found at low coverage for the three materials because of stronger van der Waals interactions. Two distinct sorption processes were proposed in the case of MIP-202 to explain the shape of the enthalpic profiles.     

Inclusion Complexes of Cyproterone Acetate with Cyclodextrins in Aqueous Solution

Cyproterone acetate (CPA) is a steroidal antiandrogen with a progestogenic activity. Given that this molecule has a very poor water solubility (2.1 g/mL), different cyclodextrins (CDs) were tested to form inclusion complexes and to increase solubility. Two different techniques were compared to study the affinity between CPA and CDs: phase-solubility studies and NMR spectroscopy. The stoichiometry and the stability constant could be determined for most complexes with the aid of phase-solubility studies. The greatest increase in solubility was achieved with the methylated -CDs, but hydroxypropylated - and -CDs also gave enhanced solubilities. ¹H-NMR studies showed a solubility increase similar to that found with phase-solubility studies. The proof of inclusion in the2,6-dimethyl--CD (DIMEB) was shown by ¹H-NMR and t-ROESY spectra.     

Electrothermal vaporisation ICP-mass spectrometry (ETV-ICP-MS) for the determination and speciation of trace elements in solid samples - A review of real-life applications from the author's lab

The use of electrothermal vaporisation (ETV) from a graphite furnace as a means of sample introduction in inductively coupled plasma mass spectrometry (ICP-MS) permits the direct analysis of solid samples. A multi-step furnace temperature programme is used to separate the vaporisation of the target element(s) and of the matrix components from one another. Sometimes, a chemical modifier is used to enable a higher thermal pre-treatment temperature, by avoiding premature analyte losses (stabilisation) or promoting the selective volatilisation of matrix components. In almost all instances, accurate results can be obtained via external calibration or single standard addition using an aqueous standard solution. Absolute limits of detection are typically ~1 pg, which corresponds to 1 ng/g for a typical sample mass of 1 mg. Real-life applications carried out in the author's lab are used to illustrate the utility of this approach. These applications aim at trace element determination in industrial and environmental materials. The industrial materials analysed include different types of plastics - Carilon, polyethylene, poly(ethyleneterephtalate) and polyamide - and photo- and thermographic materials. As samples from environmental origin, plant material, animal tissue and sediments were investigated. Some applications aimed at a multi-element determination, while in other, the content of a single, but often challenging, element (e.g., Si or S) had to be measured. ETV-ICP-MS was also used in elemental speciation studies. Separation of Se-containing proteins was accomplished using polyacrylamide gel electrophoresis (PAGE). Subsequent quantification of the Se content in the protein spots was carried out using ETV-ICP-MS. As the volatilisation of methylmercury and inorganic mercury could be separated from one another with respect to time, no chromatographic or electrophoretic separation procedure was required, but ETV-ICP-MS as such sufficed for Hg speciation in fish tissue.     

Comparison of mono- and polyatomic primary ions for the characterization of organic dye overlayers with static secondary ion mass spectrometry

Organic carbocyanine dye coatings have been analyzed by time-of-flight static secondary ion mass spectrometry (TOF-S-SIMS) using three types of primary ions: Ga(+) operating at 25 keV, and Xe(+) and SF(5) (+) both operating at 9 keV. Secondary ion yields obtained with these three primary ions have been compared for coatings with different layer thickness, varying from (sub)-monolayer to multilayers, on different substrates (Si, Ag and AgBr cubic microcrystals). For (sub)-monolayers deposited on Ag, Xe(+) and SF(5) (+) primary ions generate similar precursor ion intensities, but with Ga(+) slightly lower precursor ion intensities were obtained. Thick coatings on Ag as well as mono- and multilayers on Si produce the highest precursor and fragment ion intensities with the polyatomic primary ion. The yield difference between SF(5) (+) and Xe(+) can reach a factor of 6. In comparison with Ga(+), yield enhancements by up to a factor of 180 are observed with SF(5) (+). For the mass spectrometric analysis of dye layers on AgBr microcrystals, SF(5) (+) again proves to be the primary ion of choice.     

Structural change of the heme pocket due to disulfide bridge formation is significantly larger for neuroglobin than for cytoglobin

Human neuroglobin (hNgb) and human cytoglobin (hCygb), two recently discovered members of the vertebrate globin family, are known to be able to form an intramolecular disulfide bridge. Using electron paramagnetic resonance (EPR), we show that formation of a disulfide bridge in ferric hNgb causes a considerable change in the heme pocket structure, whereas this is not so clear for ferric hCygb. The structural results can be related nicely to earlier histidine and dioxygen affinity studies of the ferrous proteins.     

Rapid analysis of triterpenic acids by liquid chromatography using porous graphitic carbon and evaporative light scattering detection

An original system which uses Porous Graphitic Carbon as support and a mixture of organic solvents as mobile phase is proposed for the analysis of triterpenic acids by liquid chromatography. The separation of betulinic acid, ursolic acid, oleanolic acid, and 18alpha- and 18beta-glycyrrhetinic acids was carried out within a short time and monitored by evaporative light scattering detection as universal detection method. Molecular modelling studies show that the main contribution to the selectivity comes from the electrostatic interaction characterised by the dipole moment of the products.