Determination of thermodynamic p K a values of benzimidazole and benzimidazole derivatives by capillary electrophoresis
ABSTRACT Thermodynamic pK(a) values for benzimidazole and several substituted benzimidazoles were determined by CE. Electrophoretic mobilities of benzimidazoles were determined by CE at different pH levels and ionic strengths. The dependence of electrophoretic mobilities on pH was used to obtain pK(a) values at different ionic strengths. Extrapolations to zero ionic strength were used to determine the thermodynamic pK(a) values. Using this method the thermodynamic pK(a) values of 15 benzimidazoles were determined and found to range from 4.48 to 7.38. Results from the CE measurements were compared with spectrophotometric measurements which were evaluated at wavelengths where the highest absorbance difference for varying pH was recorded. The two analytical techniques were in good agreement.
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- "This suggests that one proton will be tightly held between the pyridyl and the imidazolyl nitrogen in weakly acidic solutions while the second proton is only accommodated in strongly acidic solutions. The pK 1 value is intermediate between that of imidazole (6.95) and pyridine (5.26) (Pettit and Powell, 2007), and is closer to that of benzimidazole (5.49) (Jerez et al., 2009). "
ABSTRACT: In this study, 1-octyl-2-(2′-pyridyl)imidazole (OPIM), along with dinonylnaphthalene sulfonic acid (DNNSA) as a synergist, was investigated as a potential selective extractant of Ni2+ from base metals in a solvent extraction system using 2-octanol/Shellsol 2325 (4:1) as a diluent and modifier, respectively. The separation of Ni2+ from the borderline and hard acids; Co2+, Cu2+, Zn2+, Fe2+, Fe3+, Mn2+, Mg2+ and Ca2+ was carried out at a pH range of 0.5–3.5 in sulfate and sulfate/chloride media. The separation of Ni2+ from Co2+ in 0.001 M solutions was achieved with an optimised concentration of 0.025 M OPIM along with 0.02 M DNNSA to the tune of a ΔpH½≈1.6. The extraction system further proved the rejection of 0.001 M Fe3+, Mn2+, Mg2+ and Ca2+. The absence of DNNSA resulted in very low extraction efficiencies of the Ni2+ metal ions in the pH range under investigation, thus highlighting the role of the synergist (DNNSA). The three-stage counter-current extraction of Ni2+, at the optimised pH of 1.89, from a synthetic mixture of Ni2+, Co2+ and Cu2+, yielded 99.01 (±1.79)%. The total co-extracted Cu2+ was 48.72 (±0.24)% of the original quantity in the mixture, and it was 19.85 (±0.28%) for Co2+. The co-extracted Cu2+ was scrubbed off from the loaded organic phase at pH≈8.5 by using an ammonium buffer, while co-extracted Co2+ was selectively and quantitatively stripped with H2SO4 at pH 1.64. The total recovery of Ni2+ by stripping at pH 0.32 was 94.05 (±1.70)%. The underlying chemistry in this extraction system was studied through solid state/solution studies for the complexation of the ligandwith the base metals, and it is apparent fromthe qualitative/semi-quantitative data that the separations achieved are of kinetic origin rather than thermodynamic, nor are they being driven by stereochemical preferences. Therefore, 1-octyl-2-(2′-pyridyl)imidazole can be effectively utilized alongside DNNSA as a co-extractant in the separation of Ni2+ from base metals in acidic sulfate and sulfate/chloride mediaHydrometallurgy 06/2012; 121-124:81-89. DOI:10.1016/j.hydromet.2012.04.002 · 1.93 Impact Factor
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ABSTRACT: Microencapsulation is used here as a new technique to immobilize enzymes in a microreactor coupled off-line to capillary electrophoresis (CE), allowing the determination of enzymatic reaction products. The redox enzyme laccase was encapsulated using the method of interfacial cross-linking of poly(ethyleneimine) (PEI). The 50 microm diameter capsules were slurry packed from a suspension into a capillary-sized reactor made easily and quickly from a short length of 530 microm diameter fused-silica tubing. The volume of the bed of laccase microcapsules in the microreactor was in the order of 1.1 microL through which 50 microL of the substrate o-phenylenediamine (OPD) was flowed. The oxidation product 2,3-diaminophenazine (DAP) and the remaining OPD were quantified by CE in a pH 2.5 phosphate buffer. Peak migration time reproducibility was in the order of 0.4% RSD and peak area reproducibility was less than 1.7% RSD within the same day. Using the OPD peak area calibration curve, a conversion efficiency of 48% was achieved for a 2-min oxidation reaction in the microreactor.Journal of Chromatography A 08/2009; 1216(47):8270-6. DOI:10.1016/j.chroma.2009.08.069 · 4.17 Impact Factor
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ABSTRACT: The elicitation of hydrolytic catalysts from a dynamic library of imine-zinc(II) complexes (and their precursor aldehydes and amines) via templating with pro-transition state analogs (pro-TSA) is described. pro-TSA (2-pyridyl)phosphonate 2 amplifies a benzimidazole-derived complex at the expense of an imidazole analogue; the amplified complex is also more active for the hydrolysis of the pyridyl ester 1a. Employing pro-TSA pyridyl hydrate 3 with libraries of Zn complexes of imines having nucleophilic side chains also perturbs the library in favor of imine-Zn complexes which prove to be the more active hydrolytic agents and catalysts. The catalytichydrolyses exhibit both saturation kinetics and inhibition by the pro-TSA. This process for catalyst evolution is operationally simple, amenable to high throughput screening, potentially applicable to a wide variety of catalytic reactions and thus could offer a practical alternative to catalytic antibodies and imprinted polymers.Berichte der deutschen chemischen Gesellschaft 04/2010; 2010(12):1847 - 1852. DOI:10.1002/ejic.201000129 · 2.94 Impact Factor