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Methyl Tert (methyl + tert)
Selected AbstractsMethyl tert -butyl ether (MTBE)-induced cytotoxicity and oxidative stress in isolated rat spermatogenic cellsJOURNAL OF APPLIED TOXICOLOGY, Issue 1 2007Dongmei Li Abstract Methyl tert -butyl ether (MTBE) is a class of synthetic organic chemical. In the USA, MTBE pollution is regarded as a serious environmental problem. The objective of the present study was to investigate the cytotoxic effects and oxidative stress induced by MTBE in isolated rat spermatogenic cells. In cytotoxic experiments, spermatogenic cells isolated from the testes of adult Sprague-Dawley rats by a mechanical procedure without the use of trypsin were incubated with medium alone (control), 0.5, 5, 50 mm MTBE, respectively, for 6, 12 and 18 h. MTT assay, staining with fluorescein diacetate (FDA) and propidium iodide (PI) and flow cytometric analyses were used. In oxidative stress experiments, the spermatogenic cells were incubated with medium alone (control) and with 0.5, 50 ,m, 5 mm MTBE. For 1, 2, 6, 12, 18 h incubation, ROS production was tested using a 2,,7,-dichlorofluorescein diacetate (DCHF-DA) probe; for 1, 3, 6, 12, 18 h incubation, cytosolic superoxide dismutase (SOD) and extracellular SOD (SODEX) activity was assessed; and for 18 h incubation, lipid peroxidation was assessed. The results showed that MTBE at high doses significantly decreased the spermatogenic cell viability and increased plasma membrane damage and the ratio of necrotic cells compared with the control. Assessment of the MTBE-induced oxidative stress revealed that MTBE increased the production of reactive oxygen species (ROS) and enhanced lipid peroxidation. In addition, although SODEX activity increased at a high dose level, cytosolic SOD activity decreased. These results suggest that an increase of MTBE-induced ROS production and an enhancement of membrane lipid peroxidation may play an important role in its cytotoxicity in isolated rat spermatogenic cells. Copyright © 2006 John Wiley & Sons, Ltd. [source] On choosing the right ether for peptide precipitation after acid cleavageJOURNAL OF PEPTIDE SCIENCE, Issue 3 2008Beatriz G. de La Torre Abstract Methyl tert -butyl ether (MTBE) and diethyl ether (DEE) tend to be regarded as interchangeable for the ,cold ether' workup concluding the final acidolytic cleavage and deprotection step of solid-phase peptide syntheses. However, the use of MTBE to precipitate peptides from strong acid solutions is shown to give rise to t -butyl alkylation byproducts, readily detectable by MALDI-TOF MS. The problem can attain undesirable dimensions in the cleavage of peptide resins containing high proportions of aromatic residues, particularly in peptide nucleic acid (PNA) syntheses. In those cases, DEE workup is advisable, as it consistently leads to cleaner products. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Measurement of Henry's law constant for methyl tert -butyl ether using solid-phase microextractionENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2001Britta G. Bierwagen Abstract Increasing groundwater contamination with methyl tert -butyl ether (MTBE) requires more efficient remediation technologies. Accurate measurement of MTBE's air,water partitioning coefficient (Henry's law constant, H) is important for the design and optimization of removal efficiency for many treatment systems as well as for predicting its fate and transport. Previously published data for MTBE appear to have some unusual nonlinearity at lower temperatures (15,30°C), and a wide range of values exists for dimensionless H at 25°C, from 0.0216 to 0.1226 in the published literature. We measured H for MTBE using headspace solid-phase microextraction (SPME) and a static method that considers equilibrium partitioning in a closed system, for temperatures between 15 and 40°C. To validate our methods, we measured H for benzene, toluene, and trichloroethylene and compared our results to previously published values, with excellent agreement. The Arrhenius plot for MTBE indicates that ln(HMBTE) = 6.85,2,900 T,1, with T in K. At 25°C, HMBTE = 0.0555 ± 0.0122. [source] A Practical Approach to the Design, Monitoring, and Optimization of In Situ MTBE Aerobic BiobarriersGROUND WATER MONITORING & REMEDIATION, Issue 1 2010Paul C. Johnson A paradigm for the design, monitoring, and optimization of in situ methyl tert -butyl ether (MTBE) aerobic biobarriers is presented. In this technology, an oxygen-rich biologically reactive treatment zone (the "biobarrier") is established in situ and downgradient of the source of dissolved MTBE contamination in groundwater, typically gasoline-impacted soils resulting from leaks and spills at service station sites or other fuel storage and distribution facilities. The system is designed so that groundwater containing dissolved MTBE flows to, and through, the biobarrier treatment zone, ideally under natural gradient conditions so that no pumping is necessary. As the groundwater passes through the biobarrier, the MTBE is converted by microorganisms to innocuous by-products. The system also reduces concentrations of other aerobically degradable chemicals dissolved in the groundwater, such as benzene, toluene, xylenes, and tert -butyl alcohol. This design paradigm is based on experience gained while designing, monitoring, and optimizing pilot-scale and full-scale MTBE biobarrier systems. It is largely empirically based, although the design approach does rely on simple engineering calculations. The paradigm emphasizes gas injection,based oxygen delivery schemes, although many of the steps would be common to other methods of delivering oxygen to aquifers. [source] Evaluation of TCE and MTBE in situ Biodegradation: Integrating Stable Isotope, Metabolic Intermediate, and Microbial Lines of EvidenceGROUND WATER MONITORING & REMEDIATION, Issue 4 2007Jennifer R. McKelvie Compound specific isotope analysis (CSIA) was used to investigate biodegradation of trichloroethene (TCE) and methyl tert -butyl ether (MTBE) at contaminated field sites in Alaska and New York State, respectively. At both sites, geochemical conditions and the presence of metabolic intermediates (cis -1-2-dichloroethene and tert -butyl alcohol [TBA]) suggested the potential for biodegradation of TCE and MTBE, respectively. Given that in both cases these metabolic intermediates could also have been present as cocontaminants in the source zone, CSIA was undertaken to evaluate the possibility of in situ biodegradation. At the TCE-contaminated field site in Alaska, ,13C values of TCE in ground water determined in this study showed no evidence of biodegradation (mean ,13C of ,27.0 ± 1.0, for nine wells), and quantitative-polymerase chain reaction analyses of ground water from four wells found no evidence of dechlorinator Dehalococcoides sp. at this site. At the MTBE-contaminated field site in New York, TBA was present in the ground water but was not present in gasoline sampled from underground storage tanks (UST) on-site, suggesting that at this site, TBA was potentially a metabolite of MTBE biodegradation rather than a cocontaminant. However, at all sampling times and locations, ,13C and ,2H values of MTBE in ground water were within range of published values for undegraded MTBE in gasoline. While the occurrence of a small extent of in situ MTBE biodegradation cannot be ruled out, the findings suggest that it is more likely that multiple gasoline spills occurred through time, and while present day USTs do not contain TBA as a cocontaminant, gasoline spilled at the site in the past may have. At both contaminated field sites, CSIA, chemical, and microbiological lines of evidence suggest that biodegradation was not a significant attenuation process. The results of these two studies underscore the need for an integrated approach to site assessment that draws on measurements of metabolic intermediates, analysis of stable isotopes, and microbial evidence to give a reliable assessment of in situ biodegradation at contaminated field sites. [source] Effect of H2 and Redox Condition on Biotic and Abiotic MTBE TransformationGROUND WATER MONITORING & REMEDIATION, Issue 4 2006P.M. Bradley Laboratory studies conducted with surface water sediment from a methyl tert -butyl ether (MTBE)-contaminated site in South Carolina demonstrated that, under methanogenic conditions, [U- 14C] MTBE was transformed to 14C tert -butyl alcohol (TBA) with no measurable production of 14CO2. Production of TBA was not attributed to the activity of methanogenic microorganisms, however, because comparable transformation of [U- 14C] MTBE to 14C-TBA also was observed in heat-sterilized controls with dissolved H2 concentrations > 5 nM. The results suggest that the transformation of MTBE to TBA may be an abiotic process that is driven by biologically produced H2 under in situ conditions. In contrast, mineralization of [U- 14C] MTBE to 14CO2 was completely inhibited by heat sterilization and only observed in treatments characterized by dissolved H2 concentrations < 2 nM. These results suggest that the pathway of MTBE transformation is influenced by in situ H2 concentrations and that in situ H2 concentrations may be an useful indicator of MTBE transformation pathways in ground water systems. [source] Enantioselective Copper-Catalysed Allylic Alkylation of Cinnamyl Chlorides by Grignard Reagents using Chiral Phosphine-Phosphite LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Wibke Lölsberg Abstract The copper(I)-catalysed SN2,-type allylic substitution of E -3-aryl-allyl chlorides (cinnamyl chlorides) using Grignard reagents represents a powerful method for the synthesis of compounds carrying a benzylic stereocentre. By screening a small library of modular chiral phosphine-phosphite ligands a new copper(I)-based catalyst system was identified which allows the performance of such reactions with exceptional high degrees of regio- and enantioselectivity. Best results were obtained using TADDOL-derived ligands (3,mol%), copper(I) bromide,dimethyl sulfide (CuBr,SMe2) (2.5,mol%) and methyl tert -butyl ether (MTBE) as a solvent. Various (1-alkyl-allyl)benzene derivatives were prepared with up to 99% ee (GC) in isolated yields of up to 99%. In most cases the product contained less than 3% of the linear regioisomer (except for ortho -substituted substrates). Both electron-rich and electron-deficient cinnamyl chlorides were successfully employed. The absolute configuration of the products was assigned by comparison of experimental and calculated CD spectra. The substrates were prepared from the corresponding alcohols by reaction with thionyl chloride. Initially formed mixtures of regioisomeric allylic chlorides were homogenised by treatment with CuBr,SMe2 (2.5,mol%) in the presence of triphenyl phosphine (PPh3) (3,mol%) in MTBE at low temperature to give the pure linear isomers. In reactions with methylmagnesium bromide (MeMgBr) an ortho -diphenylphosphanyl-arylphosphite ligand with an additional phenyl substituent in ortho, -position at the aryl backbone proved to be superior. In contrast, best results were obtained in the case of higher alkyl Grignard reagents (such as ethyl-, n -butyl-, isopropyl-, and 3-butenylmagnesium bromides) with a related ligand carrying an isopropyl substituent in ortho, -position. The method was tested on a multi-mmol scale and is suited for application in natural product synthesis. [source] Theoretical study of adsorption of methyl tert -butyl ether on broken clay minerals surfacesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2005A. Michalkova Abstract The interactions between methyl tert -butyl ether (MTBE) and differently defected tetrahedral and octahedral fragments of clay minerals containing Si4+, Al3+, and Mg2+ central cations have been studied at the B3LYP and MP2 levels of theory in conjunction with the 6-31G(d) basis set. MTBE interacts with defect clay structures due to the formation of multiple CH,O and OH,O hydrogen bonds. Interactions of MTBE with systems containing different types of defected mineral fragments were found to vary. Systems containing the same type of defected mineral fragment with different central cation interact almost the same way with MTBE. The formation of hydrogen bonds leads to changes in the geometrical parameters and to the polarization of MTBE. The values of the interaction energies depend on the charge of the mineral fragment. They amount to 5 kcal/mol,35 kcal/mol. MTBE interacts more preferably with octahedral fragments than with tetrahedral fragments that contain an Al3+ central cation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] (R,S)-Azolides as Novel Substrates for Lipase-Catalyzed Hydrolytic Resolution in Organic SolventsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Pei-Yun Wang Abstract Azolides, that is, N -acylazoles, as versatile acylation reagents are well characterized in the literature, in which the azole structure can not only act as a better leaving group but also make the carbonyl carbon more electrophilic and susceptible to nucleophilic attack. It is therefore desirable to combine this unique property and lipase resolution ability in the development of a new resolution process for preparing optically pure carboxylic acids. With the Candida antarctica lipase B (CALB) - catalyzed hydrolysis of (R,S)- N -profenylazoles in organic solvents as the model system, (R,S)- N -profenyl-1,2,4-triazoles instead of their corresponding ester analogues were exploited as the best substrates for preparing optically pure profens, i.e., 2-arylpropionic acids. The structure-reactivity correlations for the (R,S)-azolides in water-saturated methyl tert -butyl ether (MTBE) at 45,°C coupled with a thorough kinetic analysis were further employed for elucidating the rate-limiting formation of a tetrahedral adduct without CN bond breaking or with moderate CN bond breaking concerted with CO bond formation in the acylation step. The advantages of easy substrate preparation, high enzyme reactivity and enantioselectivity, and easy recovery of the product and remaining substrate by aqueous extraction demonstrate the potential of using (R,S)-azolides as novel substrates for the enzymatic resolution process. [source] Photocatalytic degradation of methyl tert -butyl ether (MTBE) in contaminated water by ZnO nanoparticlesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2008Akbar Eslami Abstract BACKGROUND: Over the past several decades methyl tert -butyl ether (MTBE) as additive to gasoline, intended to either boost ratings of fuel or to reduce air pollution, has been accepted worldwide. Since MTBE has high water solubility, the occurrence of fuel spills or leaks from underground storage tanks or transferring pipeline has led to the contamination of natural waters. In this study the degradation of aqueous MTBE at relatively high concentrations was investigated by a UV-visible/ZnO/H2O2 photocatalytic process. The effects of important operational parameters such as pH, amount of H2O2, catalyst loading and irradiation time were also investigated. Concentration of MTBE and intermediates such as tert -butyl formate and tert -butyl alcohol were measured. RESULTS: Time required for complete degradation increased from 20 to 150 min when the initial concentration was increased from 10 to 500 mg L,1. The first-order rate constants for degradation of MTBE were estimated to be 0.183,0.022 min,1 as the concentration increased from 10 to 500 mg L,1. Study of the overall mineralization monitored by total organic carbon analysis showed that at an initial concentration of 100 mg L,1 MTBE complete mineralization was obtained after 100 min under UV-visible/ZnO/H2O2 photocatalysis. CONCLUSION: The data presented in this paper clearly indicated that UV-visible/ZnO/O2 as an advanced oxidation process provides an efficient treatment alternative for the remediation of MTBE-contaminated waters. Copyright © 2008 Society of Chemical Industry [source] Biodegradation kinetics of benzene, methyl tert -butyl ether, and toluene as a substrate under various substrate concentrationsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2007Chi-Wen Lin Abstract Owing to the complexity of conventional methods and shortcomings in determining kinetic parameters, a convenient approach using the nonlinear regression analysis of Monod or Haldane type nonlinear equations is presented. This method has been proven to provide accurate estimates of kinetic parameters. The major work in this study consisted of the testing of aromatic compound-degrading cultures in batch experiments for the biodegradation of benzene, methyl tert -butyl ether (MTBE), and toluene. Additionally, batch growth data of three pure cultures (i.e., Pseudomonas aeruginosa YAMT421, Ralstonia sp. YABE411 and Pseudomonas sp. YATO411) isolated from an industrial petrochemical wastewater treatment plant under aerobic conditions were assessed with the nonlinear regression technique and with a trial-and-error procedure to determine the kinetic parameters. The growth rates of MTBE-, benzene-, and toluene-degrading cultures on MTBE, benzene, and toluene were significant. Monod's model was a good fit for MTBE, benzene and toluene at low substrate concentrations. In contrast, Haldane's equation fitted well in substrate inhibition concentration. Monod and Haldane's expressions were found to describe the results of these experiments well, with fitting values higher than 98%. The kinetic parameters, including a maximum specific growth rate (µm), a half-saturation constant (Ks), and an inhibition constant (Ki), were given. Copyright © 2007 Society of Chemical Industry [source] Mobile phase additives for enhancing the chromatographic performance of astaxanthin on nonendcapped polymeric C30 -bonded stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 1 2009Philipp Kaiser Abstract Astaxanthin shows peak deformation and reduced peak area response when eluted with methanol and methyl tert -butyl ether on nonendcapped polymeric C30 -bonded HPLC phases. The present study tested different column manufacturers, column batches, and ten mobile phase additives including acids, bases, buffers, complexing and antioxidant agents for improvement of peak shape and peak area response. Concerning chromatographic benefits and feasibility, ammonium acetate was found to be the best additive followed by triethylamine for all columns tested. Variation of the mobile phase pH equivalent and the column temperature showed no synergistic effects on peak shape and peak area response. Results indicate that peak tailing and variation of peak area response are due to different on-column effects. Possible mechanisms of the observed phenomenon will be discussed. [source] Separation and purification of harmine and harmaline from Peganum harmala using pH-zone-refining counter-current chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2008Xiao Wang Abstract pH-zone-refining counter-current chromatography was successfully applied to the separation of alkaloids from a crude extract of Peganum harmala L. using a multilayer coil planet centrifuge. The experiment was performed with a two-phase solvent system composed of methyl tert -butyl ether/THF/water (2:2:3 by volume) where triethylamine (10 mM) was added to the upper organic stationary phase as a retainer and hydrochloric acid (5 mM) to the aqueous mobile phase as an eluter. From 1.2 g of the crude extract, 554 mg harmine and 325 mg harmaline were obtained each with a purity of over 96% as determined by HPLC. The structures of the isolated compounds were identified by electron ionization MS (EI-MS), 1H NMR, and 13C NMR. [source] Simultaneous determination of simvastatin and simvastatin acid in human plasma by LC-MS/MS without polarity switch: Application to a bioequivalence studyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2008Bhavin N. Patel Abstract A simple, specific and sensitive LC-MS/MS assay for simultaneous determination of simvastatin (SV) and its active ,-hydroxy acid metabolite, simvastatin acid (SVA) in human plasma was developed using a statin analog as internal standard (IS). The method was validated over a dynamic linear range of 0.20,100.00 ng/mL for SV and 0.10,50.00 ng/mL for SVA with correlation coefficient r , 0.9987 and 0.9989, respectively. The analytes and IS were extracted from 500 ,L aliquots of human plasma via liquid-liquid extraction using methyl tert -butyl ether and separated through an Aquasil C18 column (100 mm×2.1 mm, 5 ,m). Detection of analytes and IS was done by MS/MS with a turbo ion spray interface operating in positive ion and selective reaction monitoring acquisition mode. The total chromatographic run time was 3.0 min. Flash freezing of the aqueous phase was an added advantage during liquid-liquid extraction, which considerably reduced time and labour. The method was extensively validated for its accuracy, precision, recovery, stability studies and matrix effect. The method was successfully used for bioequivalence study of 40 mg SV tablet formulation in 12 human subjects under fasting condition. [source] VOLATILE ORGANIC COMPOUNDS IN GROUND WATER FROM RURAL PRIVATE WELLS, 1986 TO 1999,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2004Michael J. Moran ABSTRACT: The U.S. Geological Survey (USGS) collected or compiled data on volatile organic compounds (VOCs) in samples of untreated ground water from 1,926 rural private wells during 1986 to 1999. At least one VOC was detected in 12 percent of samples from rural private wells. Individual VOCs were not commonly detected with the seven most frequently detected compounds found in only 1 to 5 percent of samples at or above a concentration of 0.2 microgram per liter (,g/l). An assessment level of 0.2 ,g/l was selected so that comparisons of detection frequencies between VOCs could be made. The seven most frequently detected VOCs were: trichloromethane, methyl tert -butyl ether, tetrachloroethene, dichlorodifluoromethane, methylbenzene, 1,1,1-trichloroethane, and 1,2-dibromo-3-chloropropane. Solvents and trihalomethanes were the most frequently detected VOC groups in private wells. The distributions of detections of gasoline oxygenates and fumigants seemed to be related to the use patterns of compounds in these groups. Mixtures were a common mode of occurrence of VOCs with one-quarter of all samples with detections including two or more VOCs. The concentrations of most detected VOCs were relatively small and only 1.4 percent of samples had one or more VOC concentrations that exceeded a federally established drinking water standard or health criterion. [source] Separation of VOCs from N2 using poly(ether block amide) membranesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Li Liu Abstract This work deals with the separation of volatile organic compounds (VOCs) from nitrogen streams for organic vapour emission control by poly(ether block amide) membranes. As representative air pollutant VOCs, n -pentane, n -hexane, cyclohexane, n -heptane, methanol, ethanol, n -propanol, n -butanol, acetone, dimethyl carbonate, and methyl tert -butyl ether were used in this study. The separation of both binary VOC/N2 and multicomponent VOCs/N2 gas mixtures was carried out, and the membranes exhibited good separation performance. A VOC concentration of more than 90 mol% was achieved at a feed VOC concentration of 5 mol%. It was found that the permeances of the VOCs were mainly dominated by their solubilities in the membrane, whereas the permeance of N2 was affected by the presence of the VOCs. The permeance of N2 in the VOC/N2 mixtures was shown to be higher than pure N2 permeance due to membrane swelling induced by the VOCs dissolved in the membrane. Nevertheless, theVOC/N2 selectivity increased with an increase in the feed VOC concentration. Among the VOCs studied, the membrane showed a higher permeance to alcohol VOCs than paraffin VOCs. The effects of feed VOC concentration, temperature, stage cut, and permeate pressure on the separation performance were investigated. Ce travail porte sur la séparation des composés organiques volatils (COV) présents dans des courants d'azote pour le contrôle des émissions de vapeur organique par des membranes de poly(éther amide bloc). Comme polluants atmosphériques représentatifs des COV, on a utilisé dans cette étude le n-pentane, le n-hexane, le cyclohexane, le n-heptane, le méthanol, l'éthanol, le n-propanol, le n-butanol, l'acétone, le carbonate de diméthyle et le méthyl tertio-butyl. On a procédé à la séparation du mélange de gaz de COV/N2 binaire et du mélange de gaz multicomposant COV/N2, et les membranes montrent une bonne performance de séparation. Une concentration de COV de plus de 90% en poids moléculaire a été obtenue à une concentration d'alimentation de COV de 5% en poids moléculaire. On a trouvé que les perméances de N2 était sensibles à la présence de COV. La perméance de N2 dans les mélanges de COV/N2 s'avère plus élevée que la perméance du N2 pur en raison du gonflement de la membrane provoqué par les COV dissous dans la membrane. Néanmoins, la sélectivité des COV/N2 augmente avec la concentration de COV d'alimentation. Parmi les COV étudiés, la membrane montre la plus haute perméance aux COV d'alcool qu'aux COVde paraffine. Les effets de la concentration de COV d'alimentation, de la température, la coupure de phase et la pression des perméats ont été étudiés. [source] Determination of ibudilast in human serum by high-performance liquid chromatography for pharmacokinetic studyBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Hwa Yoon Abstract A simple, accurate, precise and cost effective reversed-phase HPLC method was developed to determine the concentration of ibudilast in human serum. Ibudilast and an internal standard, butyl 4-hydroxybenzoate, were extracted by liquid,liquid extraction with methyl tert -butyl ether. HPLC analysis was carried out under the following conditions: a Luna C18(2) 5,,m column, a mobile phase of acetonitrile,0.02% phosphoric acid (50,:,50, v/v, adjusted to pH 6.0 with triethylamine) and a UV detector at 319,nm. The chromatograms showed good resolution and sensitivity as well as no interference from the human serum. The calibration curves were linear over the concentration range, 1,100,ng/mL, for serum with correlation coefficients >0.999. The intra- and inter-day assay precision as well as the accuracy fulfilled the international requirements. The mean absolute recovery for human serum was 101.7 ± 6.1%. The lower limit of quantitation in human serum was 1,ng/mL, which is sensitive enough for pharmacokinetic studies. Stability studies revealed that ibudilast in human serum was stable during storage as well as during the assay procedure. This method was applied successfully to an examination of the pharmacokinetics of ibudilast in human subjects following a single oral dose of an ibudilast (10,mg) capsule. Copyright © 2009 John Wiley & Sons, Ltd. [source] Direct enantioselective HPLC monitoring of lipase-catalyzed kinetic resolution of tiaprofenic acid in nonstandard HPLC organic solvents,CHIRALITY, Issue 8 2008Ashraf Ghanem Abstract The first straightforward lipase-catalyzed enantioselective access to enantiomerically enriched tiaprofenic acid as a versatile method in chiral separation of racemates is demonstrated. The latter was directly monitored by enantioselective HPLC using a 3,5-dimethylphenylcarbamate derivative of cellulose-based chiral stationary phase namely Chiralpak IB (the immobilized version of Chiralcel OD). Non-standard HPLC organic solvents were used as diluent to dissolve the "difficult to dissolve" enzyme substrate (the acid) and as eluent for the simultaneous enantioselective HPLC baseline separation of both substrate and product in one run without any further derivatization. The existence of a non-standard HPLC organic solvent (e.g., methyl tert -butyl ether) in the mobile phase composition is mandatory to accomplish the simultaneous enantioselective HPLC baseline separation of both substrate and product. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source] | |||||||||||||||||||||||||