bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of Axially Chiral N,N′‐Diarylimidazolium and N‐Arylthiazolium Salts and Evaluation of Their Catalytic Potential in the Benzoin and in the Intramolecular Stetter Reactions
Authors: Pesch Jens , Harms Klaus , Bach Thorsten 
Published: April 2004

AbstractN‐Aryl‐substituted imidazoles 14b, 15b and thiazoles 17−22, 25 were prepared which contain a stereogenic axis and which can occur as atropisomers. The imidazolium salts 15b could be obtained from 2‐isopropylaniline (12b) and diacetyl (11) in three steps (19% yield) whereas the synthesis of their tert‐butyl analogues failed. The meso‐isomer meso‐15b prevailed (dr = 90/10). The chiral thiazolium salts rac‐17 (53% yield) and rac‐22 (49% yield) were prepared in two steps from 2‐tert‐butylaniline (12a). The enantiomerically pure thiazolium salt 19 was obtained from α‐bromomenthone (23) and the aniline 12a (27% overall yield). In contrast to the imidazolium salts 15b, the thiazolium salts proved to be suitable catalysts in the benzoin condensation of benzaldehyde (1 → 2) and in the intramolecular Stetter reaction of the α,β‐unsaturated ester 9a. The best results obtained with catalyst 19 (20 mol %) were 85% yield of product 2 (40% ee) and 75% yield of product 10a (50% ee). The stereogenic axis of catalyst 19 is not configurationally stable in the catalytically active carbene intermediate 28. The catalyst is recovered as a mixture of diastereomeric atropisomers 19 and 26 in a ratio of 70:30 to 75:25. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The cis‐Specific Pictet−Spengler Reaction
Authors: Alberch Laura , Bailey Patrick D. , Clingan Paul D. , Mills Timothy J. , Price Richard A. , Pritchard Robin G. 
Published: April 2004

AbstractThe Pictet−Spengler reaction of tryptophan allyl ester with aryl aldehydes generates cis‐tetrahydro‐β‐carbolines with complete stereo‐control and with complete retention of optical integrity, when the reaction is carried out under kinetically controlled conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
An Efficient Enantioselective Synthesis of (+)‐(R,Z)‐5‐Muscenone and (−)‐(R)‐Muscone − An Example of a Kinetic Resolution and Enantioconvergent Transformation
Authors: Fehr Charles , Galindo José , Etter Olivier 
Published: April 2004

AbstractAn efficient catalytic kinetic resolution by CBS reduction and an original enantioconvergent transformation involving a PdII‐catalyzed position‐selective cyclization are the key steps for the synthesis of the exceptional musk odorant (R,Z)‐5muscenone [(R)‐1] and (R)‐muscone [(R)‐3]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Stroboscopic sampling in comprehensive high‐performance liquid chromatography‐capillary electrophoresis via a pneumatic sampler
Authors: Ehala Sille , Kaljurand Mihkel , Kudrjashova Marina , Vaher Merike 
Published: April 2004

AbstractA new approach is presented to solve the problem of a long separation time in the second dimension of comprehensive two‐dimensional chromatography. The need for a rapid separation in the second column is overcome by repeating analysis of a sample many times. In each of these individual analysis cases the sample is injected into the first dimension column and after a delay a low amount of the effluent at the end of the first column is sampled to the second‐dimensional column. The time interval between the samplings from the first column to the second column is constantly increased. Thus, the system enables a comprehensive analysis of the effluent emerging from the first into the second column. This approach, which we call stroboscopic sampling, is tested for coupling high‐performance liquid chromatography (HPLC) to capillary electrophoresis (CE) by an interface which operates on the principle of transporting the effluent from the HPLC column to the capillary inlet by small pressure pulses (0.5 MPa). The performance of the interface for accomplishing the comprehensive HPLC‐CE analysis was demonstrated for an on‐line connection of a short ion‐exchange column and an ion‐exclusion column to the CE capillary.
Narrow‐band fractionation of proteins from whole cell lysates using isoelectric membrane focusing and nonporous reversed‐phase separations
Authors: Zhu Yi , Lubman David M. 
Published: April 2004

AbstractPreparative isoelectric focusing (PIEF) is used to achieve narrow‐band fractionation of proteins from whole cell lysates of Escherichia coli (E. coli). Isoelectric membranes create well‐defined pH ranges that fractionate proteins by isoelectric point (pI) upon application of an electric potential. A commercial IsoPrime device (Amersham‐Pharmacia BioTech) is modified for the PIEF separation to lessen run volumes significantly. Two‐dimensional polyacrylamide gel electrophoresis (2‐D PAGE) analysis of chamber contents indicates that excellent pH fractionation is achieved with little overlap between chambers. PIEF pH fractions are further separated using nonporous reversed‐phase high‐performance liquid chromatography (NPS‐RP‐HPLC) and HPLC eluent is analyzed on‐line by electrospray ionization‐time of flight‐mass spectrometry (ESI‐TOF‐MS) for intact protein molecular weight (MW) analysis. The result is a pI versus MW map of bacterial protein content. IEF fractionation down to 0.1 pH units combined with intact protein MW values result in a highly reproducible map that can be used for comparative analysis of different E. coli strains.
Optimization of the separation of a group of triazine herbicides by micellar capillary electrophoresis using experimental design and artificial neural networks
Authors: Frías‐García Sergio , Sánchez M. Jesús , Rodríguez‐ Delgado Miguel Ángel 
Published: April 2004

AbstractThe micellar electrokinetic chromatography separation of a group of triazine compounds was optimized using a combination of experimental design (ED) and artificial neural network (ANN). Different variables affecting separation were selected and used as input in the ANN. A chromatographic exponential function (CEF) combining resolution and separation time was used as output to obtain optimal separation conditions. An optimized buffer (19.3 mM sodium borate, 15.4 mM disodium hydrogen phosphate, 28.4 mM SDS, pH 9.45, and 7.5% 1‐propanol) provides the best separation with regard to resolution and separation time. Besides, an analysis of variance (ANOVA) approach of the MEKC separation, using the same variables, was developed, and the best capability of the combination of ED‐ANN for the optimization of the analytical methodology was demonstrated by comparing the results obtained from both approaches. In order to validate the proposed method, the different analytical parameters as repeatability and day‐to‐day precision were calculated. Finally, the optimized method was applied to the determination of these compounds in spiked and nonspiked ground water samples.
Electroosmotic flow in a poly(dimethylsiloxane) channel does not depend on percent curing agent
Authors: Wheeler Aaron R. , Trapp Gabriele , Trapp Oliver , Zare Richard N. 
Published: April 2004

AbstractPoly(dimethylsiloxane) (PDMS) microfluidic devices were prepared from different ratios of “curing agent” (which contains silicon hydride groups) to “base” (which contains vinyl‐terminated noncross‐linked PDMS), to determine the effect of this ratio on electroosmotic flow (EOF). In fabricating devices for this purpose, a novel method for permanently enclosing PDMS channels was developed. As a supplement to the microfluidic method, the inner walls of capillaries were coated with PDMS formed from varying ratios of curing agent to base. EOF was found to be constant for PDMS formed with each ratio, which implies that the negative surface charges do not arise from chemical species present only in the base or the curing agent.
Thermoresponsive N,N‐dialkylacrylamide copolymer blends as DNA sieving matrices with a thermally tunable mesh size
Authors: Kan Cheuk‐Wai , Doherty Erin A. S. , Buchholz Brett A. , Barron Annelise E. 
Published: April 2004

AbstractIn an earlier study we showed that a blend of thermoresponsive and nonthermoresponsive hydroxyalkylcelluloses could be used to create a thermally tunable polymer network for double‐stranded (ds) DNA separation. Here, we show the generality of this approach using a family of polymers suited to a wider range of DNA separations: a blended mixture of N,N‐dialkylacrylamide copolymers with different thermoresponsive behaviors. A mixture of 47% w/w N,N‐diethylacrylamide (DEA)/53% w/w N,N‐dimethylacrylamide (DMA) (DEA47; thermoresponsive, transition temperature = 55°C in water) and 30% w/w DEA/70% w/w DMA (DEA30; nonthermoresponsive, transition temperature > 85°C in water) copolymers in the ratio of 1:5 w/w DEA47:DEA30 was used to separate a dsDNA restriction digest (ΦX174‐HaeIII). We investigated the effects of changing mesh size on dsDNA separation, as controlled by temperature. We observed good DNA separation performance with the copolymer blend at temperatures ranging from 25°C to 48°C. The separation selectivity was evaluated quantitatively for certain DNA fragment pairs as a function of temperature. The results were compared with those obtained with a control matrix consisting only of the nonthermoresponsive DEA30. Different DNA fragment pairs of various sizes show distinct temperature‐dependent selectivities. Over the same temperature range, no significant temperature dependence of selectivity is observed for these DNA fragment pairs in the nonthermoresponsive control matrix. Overall, the results show similar trends in the temperature dependency of separation selectivity to what was previously observed in hydroxyalkylcellulose blends, for the same DNA fragment pairs. Finally, we showed that a ramped temperature scheme enables improved separation in the blended copolymer matrix for both small and large DNA fragments, simultaneously in a single capillary electrophoresis (CE) run.
Peptide and protein separations by capillary electrophoresis in the presence of mono‐ and diquaternarized diamines
Authors: Pontoglio Alessandro , Viganò Agnese , Sebastiano Roberto , Citterio Attilio , Maragnoli Luca , Righetti Pier Giorgio , Gelfi Cecilia 
Published: April 2004

AbstractTwo compounds, derivatives of 1,4‐diazobicyclo[2,2,2]octane (DABCO), have been evaluated as potential quenchers of silanol interactions with peptides and proteins during their capillary zone electrophoresis (CZE) separations. They are: 1‐(4‐iodobutyl)4‐aza‐1‐azoniabicyclo[2,2,2]octane iodide (M7C4I) and 1,4‐didecyl‐1,4‐diazoniabicyclo [2,2,2]octane dibromide (C10M7C10). The first compound is known to react with the wall, by forming a covalent bond via alkylation of silanols. On the contrary, the second one (C10M7C10) can only loosely interact with silica due to lack of reactive iodine and to a much too short distance (a C2) between the two quaternary nitrogens. Very good peptide maps of protein digests can be obtained in isoelectric glutamic acid (Glu) buffer, at pH 3.52 by utilizing the M7C4I. However, in the case of total tissue extracts, excellent resolution is obtained only with the first eluting part of the analyte spectrum (i.e., peptides and smaller proteins). With larger proteins, interaction with the wall and loss of resolution is experienced. When using the C10M7C10, good resolution of di‐ and tripeptides is obtained, while a loss of resolution is observed with entire protein digest. M7C4I does not seem to interact with the peptide/protein analytes, and simply repels them from the wall via its positive charges; it is believed that disalt (C10M7C10) acts by interacting with the same compounds, possibly by forming micelles in solution.
Separation and determination of biphenyl nitrile compounds by microemulsion electrokinetic chromatography with mixed surfactants
Authors: Gong Suxuan , Bo Tao , Huang Lan , Li Ke An , Liu Huwei 
Published: April 2004

AbstractA mixture of six biphenyl nitrile compounds and three related substances with high hydrophobicity and similar structures was successfully separated by microemulsion electrokinetic chromatography (MEEKC) within 30 min. The microemulsion system contained 100 mM sodium dodecyl sulfate (SDS), 80 mM sodium cholate (SC), 0.81% v/v heptane, 7.5% v/v n‐butanol, 10% v/v acetonitrile, and 10 mM borate. The addition of SC, organic modifiers, sample preparation, and temperature all showed remarkable effects on the separation. The capacity factor (k) was calculated by using dodecyl benzene as the marker for microemulsion, and the calculated partition coefficient log Po/w of the solutes was in the range of 3.35–7.38. The log k values matched well with the log Po/w with a correlation coefficient of 0.96. In addition, the linear correlation coefficients of each compound between peak area and concentration were from 0.996 to 0.998 with the repeatability RSD value < 1.2% for migration time and < 4.8% for peak area, and the highest theoretic plate number was > 586 000. MEEKC was compared with micellar electrokinetic chromatography (MEKC) indicating that the former method is more suitable for this separation and can be used for the quality control of biphenyl nitrile compounds in the synthesis of liquid crystals.
Fast and simple method for determination of iodide in human urine, serum, sea water, and cooking salt by capillary zone electrophoresis
Authors: Pantůčková Pavla , Křivánková Ludmila 
Published: April 2004

AbstractFor the determination of iodide in urine, where 80–90% of consumed iodine is excreted, a fast, simple, and sensitive method of capillary zone electrophoresis was elaborated and tested also for additional complex matrices such as human serum, cooking salt, and seawater. Several approaches were examined for the separation of iodide from other macro‐ and microcomponents in the tested matrices, and the best results were obtained when host‐guest interaction with α‐cyclodextrin or ion‐pairing with polyethylenimine was employed. In both cases comparable resolution and sensitivity were reached. Due to the relatively high price of cyclodextrin only the method with polyethylenimine was further optimized and a simple procedure enabling the determination of iodide in untreated human urine, serum, cooking salt, and seawater was elaborated. The samples were injected for 20 s at 0.5 psi (3.45 kPa) into a fused‐silica capillary (0.18 mm ID, 50 cm effective length) coated with polyacrylamide (electroosmotic flow < 2×10−9 m2V−1s−1) and filled with the optimized background electrolyte composed of 20 mM KH2PO4 and 0.7% m/v polyethylenimine. For detection, UV absorption at 200 and 230 nm was measured. Concentration limits of detection reached at 230 nm were for human urine 0.14 μM, for human serum 0.17 μM, for seawater 0.17 μM, and for cooking salt 89 nM. Relative standard deviations of iodide peak area and height in all matrices ranged within 0.93 to 4.19%.
Micellar electrokinetic chromatography of enkephalin‐related peptides with laser‐induced fluorescence detection
Authors: Huang Ying , Duan Jianping , Chen Qiaoren , Chen Guonan 
Published: April 2004

AbstractEight enkephalin‐related peptides were derivatized using fluorescein isothiocyanate (FITC), and the derivatization products were separated and detected by capillary electrophoresis with laser‐induced fluorescence detection. The optimum molar ratio of FITC and peptide for derivatization was found to be 40:1, and 5 mmol/L sodium borate buffer (pH 9.2) was selected as derivatization media in order to get the high efficiency. Enkephalin‐related peptides were completely separated in the pH range of 10.51–10.60 in a running buffer consisting of 100 mmol/L sodium borate and 60 mmol/L sodium dodecyl sulfate (SDS). The detection limit for these eight enkephalins ranged from 0.18 to 2.25 nmol/L, and the linear response range was 1.0×10−6 to 1.0×10−9 mol/L with correlation coefficients between 0.9947–0.9988. A separation efficiency as high as 380 000 theoretical plates could be obtained for these analytes.
Development and modeling of a frictional wall damper and its applications in reinforced concrete frame structures
Authors: Cho Chang‐Geun , Kwon Minho 
Published: April 2004

AbstractA wall‐type friction damper is newly proposed in this paper to improve the performance of reinforced concrete (RC) framed structures under earthquake loads. Traditionally, the damper was generally invented as a brace‐type member. However, it has been seen to cause problems in the RC frame structures in that concrete is apt to be damaged in the connection regions of the RC member and the brace‐type damper under earthquake loads. The proposed wall‐type damper has an advantage in the retrofit of RC structures. The system consists of a Teflon® slider and a RC wall. The damper is also designed to control normal pressures acting on a frictional slider. The numerical applications show that the proposed damper can be effective in mitigating the seismic responses of RC frame structures and reducing the damage to RC structural members. Copyright © 2004 John Wiley & Sons, Ltd.
Case study: Environmental monitoring using remote optical sensing (OP‐FTIR) technology at the Oklahoma City Air Logistics Center industrial wastewater treatment facility
Authors: Hall Freddie E. 
Published: April 2004

AbstractDuring production and maintenance operations at Tinker Air Force Base in Oklahoma City, Oklahoma, industrial wastewater streams are generated that contain organic and heavy metal compounds. These waste streams result from chemical depainting operations, chemical cleaning processes, and electroplating operations. Processes discharging wastewater are treated at the on‐site industrial wastewater treatment facility (IWTF). Regulatory reporting mandates require identifying volatile organic compound emission sources, estimating emissions from the IWTF, quantifying ambient air concentrations surrounding the facility via air dispersion modeling, and evaluating computer‐generated numerical concentration estimates with respect to discontinuous field data and an open‐path optical remote monitoring system. The objective of this article is to compare three strategies for meeting air‐quality management requirements: (1) the use of a coupled model (air emission model and air dispersion model); (2) the use of air quality–monitoring data collected via discontinuous air sampling and analysis (i.e., periodic canister monitoring); and (3) the use of air‐quality data generated by open‐path optical remote monitoring using Fourier Transform Infrared Spectroscopy (OP‐FTIR). Validation of the predictive accuracy of the three strategies will be made based on (a) comparisons and statistical testing of receptor location predictions with air‐quality data from periodic canister monitoring; (b) comparisons and statistical testing of predictions along the open‐path optical remote monitoring boundary line with measured concentrations based on OP‐FTIR; and (c) comparisons and statistical testing of pertinent field canister monitoring data with open‐path monitoring results. © 2004 Wiley Periodicals, Inc.
Motivation for environmental construction
Authors: Siddiqi Khalid M. , Oberle Rita , Thomas‐Mobley Linda , Kangari Roozbeh 
Published: April 2004

AbstractEnvironmental laws are increasing and changing faster than they can be implemented in the construction industry. This is especially important for federal facilities and environmental construction because federal agencies are strongly averse to notices of violation to environmental regulations. Other industries, such as the Air Force aircraft development industry, are coping with problems related to impacts of environmental laws by integrating the concept of design for environment into their management strategy on a life‐cycle basis. The construction industry has historically addressed environmental regulations in a segregated and fragmented approach and seen environmental issues as restrictions and constraints. With the advent of sustainability in construction and bioremediation in environmental construction, federal agencies also need to address the problem in an integrated fashion by improving its project management, planning, and implementation strategies. This article presents a framework that can be used by the construction industry for analyzing construction alternatives in an integrated fashion with respect to environmental laws and regulations. The framework provides a holistic approach for taking into consideration public needs, construction processes, and regulatory governmental functions. The framework can be used by federal agencies for addressing life‐cycle environmental issues pertaining to compliance, conservation, and pollution prevention. Use of the holistic approach and integrated framework is expected to minimize remediation in new building and environmental construction projects. © 2004 Wiley Periodicals, Inc.
Biophysical and pharmacological characterization of hypotonically activated chloride currents in cortical astrocytes
Authors: Parkerson Kimberly A. , Sontheimer Harald 
Published: April 2004

AbstractRat cortical astrocytes regulate their cell volume in response to hypotonic challenge. This regulation is believed to depend largely on the release of chloride or organic osmolytes through anion channels. Using whole‐cell recordings, we identified weakly outwardly rectifying chloride currents that could be activated in response to hypotonic challenge. These currents exhibited the following permeability sequence upon replacement of chloride in the bathing solution with various anions: I−>NO3−>Cl−>Gluc− ≥MeS−>Ise−. Interestingly, extracellular I−, albeit showing the greatest permeability, blocked the currents with an IC50 of ≈50 mM. Currents were almost completely inhibited by 123 μM NPPB and partially inhibited by 200 μM niflumic acid or 200 μM DIDS. Additionally, the total number of Cl− ions effluxed through the hypotonically activated channels was markedly similar to the total solute efflux during volume regulation. We therefore propose the hypotonically activated chloride channel as a major contributor to volume regulation of astrocytes. To examine potential candidate chloride channel genes expressed by astrocytes, we employed RT‐PCR to demonstrate the presence of transcripts for ClC‐2, 3, 4, 5, and 7, as well as for VDAC and CFTR in cultured astrocytes. Moreover, we performed immunostaining with antibodies against each of these channels and showed the strongest expression of ClC‐2 and ClC‐3, strong expression of ClC‐5 and VDAC, weak expression of ClC‐7 and very weak expression of ClC‐4 and CFTR. Intriguingly, although we found at least seven Cl− channel proteins from three different gene families in astrocytes, none appeared to be active in resting cells. © 2004 Wiley‐Liss, Inc.