Zenixole R. Tshentu

Synthesis and characterization of rhenium(III) and (V) pyridylimidazole complexes

Reaction of trans-[ReOCl3(PPh3)2] with 2-(2′-pyridyl)imidazole (pimH) in methanol led to the isolation of the rhenium(III) salt [ReCl2(pimH)(PPh3)2](ReO4) (1). However, with 2-(2′-pyridyl)-1-methylimidazole (pimMe) as ligand, the complex [ReCl3(pimMe)(PPh3)] (2) was obtained. The monooxorhenium(V) complexes [ReOCl3(pimR)] (R = H, Me) could only be prepared by the reduction of [ReO4]− with an equimolar amount of PPh3 in the presence of pimR and hydrochloric acid in acetic acid. With four equivalents of PPh3, compounds 1 and 2 were obtained. Using (n-Bu4N)[ReOCl4] as starting material, the μ-oxo dimers [Re2O3(pimR)2Cl4] were isolated as the only products. These new compounds have been characterized by X-ray crystallography, 1H NMR and IR spectroscopy. In 1 the [ReO4]− counterion is tightly associated with the cationic complex through N–H ···  hydrogen bonding. Despite being paramagnetic, 1H NMR spectra for 1 and 2 could be fully assigned.

Synthesis and structural characterization of cationic octahedral oxorhenium(V) complexes with bidentate imidazole derivatives

Cationic distorted octahedral complexes [ReOCl(OEt)(L)(PPh3)]X {L = 2-(1-ethylaminomethyl)-1-methylimidazole (eami), 2-(1-methylaminomethyl)-1-methylimidazole (mami), 2-(1-ethylthiomethyl)-1-methylimidazole (etmi); X=ReO4, PF6} were prepared by reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of L in ethanol under anaerobic conditions. X-ray structure determinations of [ReOCl(OEt)(eami)(PPh3)](ReO4) (1a) and its etmi equivalent (3a) were performed. In 1a coordination of the chloride occurs trans to the imidazole nitrogen. However, in 3a the chloride is coordinated trans to the ethereal sulfur donor of etmi.

Design, fabrication and evaluation of intelligent sulfone-selective polybenzimidazole nanofibers.

Molecularly imprinted polybenzimidazole nanofibers fabricated for the adsorption of oxidized organosulfur compounds are presented. The imprinted polymers exhibited better selectivity for their target model sulfone-containing compounds with adsorption capacities of 28.5±0.4mg g(-1), 29.8±2.2mg g(-1) and 20.1±1.4mg g(-1) observed for benzothiophene sulfone (BTO2), dibenzothiophene sulfone (DBTO2) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO2) respectively. Molecular modeling based upon the density functional theory (DFT) indicated that hydrogen bond interactions may take place between sulfone oxygen groups with NH groups of the PBI. Further DFT also confirmed the feasibility of π-π interactions between the benzimidazole rings and the aromatic sulfone compounds. The adsorption mode followed the Freundlich (multi-layered) adsorption isotherm which indicated possible sulfone-sulfone interactions. A home-made pressurized hot water extraction (PHWE) system was employed for the extraction/desorption of sulfone compounds within imprinted nanofibers at 1mL min(-1), 150°C and 30 bar. PHWE used a green solvent (water) and achieved better extraction yields compared to the Soxhlet extraction process. The application of molecularly imprinted polybenzimidazole (PBI) nanofibers displayed excellent sulfur removal, with sulfur in fuel after adsorption falling below the determined limit of detection (LOD), which is 2.4mg L(-1)S, and with a sulfur adsorption capacity of 5.3±0.4mg g(-1) observed for application in the fuel matrix.

Imidazole-functionalized polymer microspheres and fibers – useful materials for immobilization of oxovanadium(IV) catalysts

Both polymer microspheres and microfibers containing the imidazole functionality have been prepared and used to immobilize oxovanadium(IV). The average diameters and BET surface areas of the microspheres were 322 μm and 155 m2 g−1 while the fibers were 1.85 μm and 52 m2 g−1, respectively. XPS and microanalysis confirmed the incorporation of imidazole and vanadium in the polymeric materials. The catalytic activity of both materials was evaluated using the hydrogen peroxide facilitated oxidation of thioanisole. The microspheres were applied in a typical laboratory batch reactor set-up and quantitative conversions (>99%) were obtained in under 240 min with turn-over frequencies ranging from 21.89 to 265.53 h−1, depending on the quantity of catalyst and temperature. The microspherical catalysts also proved to be recyclable with no drop in activity being observed after three successive reactions. The vanadium functionalized fibers were applied in a pseudo continuous flow set-up. Factors influencing the overall conversion and product selectivity, including flow rate and catalyst quantity, were investigated. At flow rates of 1–4 mL h−1 near quantitative conversion was maintained over an extended period. Keeping the mass of catalyst constant (0.025 g) and varying the flow rate from 1–6 mL h−1 resulted in a shift in the formation of the oxidation product methyl phenyl sulfone from 60.1 to 18.6%.

Synthesis and Structural Characterization of Dinuclear Oxorhenium(V) Complexes with Bidentate Imidazole Derivatives

The oxo-bridged dinuclear complexes [(μ-O){ReOCl2(L)}2] [L = 2-(1-ethylaminomethyl)-1-methylimidazole (eami); 2-(1-methylaminomethyl)-1-methylimidazole (mami); 2-(1-ethylthiomethyl)-1-methylimidazole (etmi)] were prepared by reaction of trans-[ReOCl3(PPh3)2] with L in acetone. X-ray crystallographic studies of the eami and etmi complexes show that these ligands coordinate in a bidentate manner, and that the cis, cis-N2Cl2 and cis, cis-NSCl2 equatorial planes are nearly orthogonal to the O=Re-O-Re=O backbone.

Imidazolate coordination of 2,6-bis(2-benzimidazolyl) pyridine in a dimeric rhenium(V) complex

The oxo-bridged dinuclear complex [(μ-O){ReOCl2(pimH)}2]·2H2O·2DMF was prepared by reaction of trans-[ReOCl3(PPh3)2] and 2,6-bis(2-benzimidazolyl)pyridine (pimH2) in acetonitrile, with recrystallization from CH2Cl2/DMF. An X-ray crystallographic study shows that pimH is coordinated as a tridentate monoanionic chelate, with deprotonation of an imidazolyl N(1)H group. The axis of the molecule is formed by the O=Re–O–Re=O moiety, with the bridging oxygen lying on a crystallographic inversion center. The two O–Re=O angles are therefore equal [172.7(1)°].

Synthesis and structure of oxorhenium(V) complexes containing a terdentate imidazole ligand. A route to mixed ‘3 + 2’ complexes

The neutral mononuclear complex [ReOBr2(ami)] (1) [Hami = 2-(1-ethanolaminomethyl)-1-methylimidazole] was prepared by reaction of (n-Bu4N)[ReOBr4(OPPh3)] with an equimolar amount of Hami in acetonitrile. Further reaction of 1 with disodium oxalate (Na2ox) in methanol yielded the mixed didentate–terdentate complex [ReO(ox)(ami)] (2). These compounds were characterized by spectroscopy and X-ray crystallography. Both complexes have distorted octahedral geometry with the alcoholate oxygen of ami– coordinated trans to the oxo group. In 1 the Br–Re–Br angle equals 89.91(3)° and in 2 the oxalate has a bite angle of 81.0(2)°.

The Ratios of Vanadium-to-nickel and Phenanthrene-to-dibenzothiophene as Means of Identifying Petroleum Source and Classification of Nigeria Crude Oils

Nigeria light, medium, and heavy crude oils were categorized based on the ratio of vanadium-to-nickel (V/Ni) and the ratio of phenanthrene-to-dibenzothiophene (PHEN/DBT) derivatives. V/Ni ratio of 0.47, 1.36, and 2.77 were observed for light, medium, and heavy crude oils, respectively, while the PHEN/DBT ratio was observed to be 8.35, 4.33, and 1.09 for the light, medium, and heavy crude oils, respectively. From the results obtained, light crude oil was suggested to originate from marine organic matter while the heavy oil originates from the terrestrial organic matter.

Selective removal of isoquinoline and quinoline from simulated fuel using 1,1′-binaphthyl-2,2′-diol (BINOL): crystal structure and evaluation of the adduct electronic properties

1,1′-Binaphthyl-2,2′-diol/quinoline (BINOL/QUN) and 1,1′-binaphthyl-2,2′-diol/isoquinoline (BINOL/ISOQUN) adducts were successfully synthesized. X-ray single crystals of BINOL/QUN and BINOL/ISOQUN were grown and analysed. The crystal packing of the molecules in both adducts confirmed that they are held in aggregates by strong hydrogen bonds (O2–H2⋯O3), (O3–H3⋯N1), (O2–H2⋯O1), (O1–H1⋯N1), (O2–H2⋯O1) and weak hydrogen C–H⋯π bonds. The patterns of the hydrogen bonding network as well as the conformation of BINOL contribute to the formation of the shape of the voids that entrap quinoline and isoquinoline. Molecular modelling which was employed to investigate the electronic properties of BINOL/QUN and BINOL/ISOQUN shows that the HOMO positions of the adducts are localized around the 1,1′-binaphthyl-2,2′-diol (BINOL), while the LUMO is positioned on isoquinoline and quinoline. Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) revealed a stronger isoquinoline/BINOL interaction compared to quinoline/BINOL. 6-Vinyl-1,1′-binaphthyl-2,2′-diol was co-polymerized with styrene to form [DBN-co-STY]. Electrospun [DBN-co-STY] exhibited selectivity for quinoline and isoquinoline in a model simulated fuel presenting an adsorption capacity of 2.2 and 2.4 mg g−1 respectively. The adsorption study showed a higher adsorption capacity for isoquinoline compared to quinoline. This may be attributed to the more favourable electronic properties (HOMO–LUMO properties) of isoquinoline. This concept demonstrates the possibility of extracting/separating isoquinoline and quinoline from fuel.

pH-metric chemical speciation modeling and studies of in vitro antidiabetic effects of bis[(imidazolyl)carboxylato]oxidovanadium(IV) complexes.

A range of bidentate N,O-donor ligands of the imidazolyl-carboxylate moiety, which partially mimic naturally occurring bioligands, were prepared and reacted with the oxidovanadium(IV) ion to form the corresponding bis-coordinated oxidovanadium(IV) complexes. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry, which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave evidence that the bis[(imidazolyl)carboxylato]oxovanadium(IV) complexes possess a broad pH-metric stability. The complexes improved glucose uptake in cell cultures using 3T3-L1 adipocytes, C2C12 muscle cells and Chang liver cells. The PTP inhibition studies indicated that the mechanism underlying insulin-stimulated glucose uptake was possibly via the protein tyrosine phosphorylation through the inhibition of the protein tyrosine phosphatase 1B (PTP 1B). The vanadium compounds also demonstrated the inhibition of D-dimer formation, suggesting that these compounds could potentially relieve a hypercoagulative state in diabetic patients.