bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis, Crystal Structures, and Photophysical Properties of Lanthanide Complexes Containing Pyrrole‐Derivatized Carboxylate Ligands
Authors: Law Ga‐Lai , Wong Ka‐Leung , Lau Kok‐Kin , Tam Hoi‐Lam , Cheah Kok‐Wai , Wong Wing‐Tak 
Published: October 2007

AbstractTwo pyrrole‐deriviatized carboxylic acids [L1 = 1‐methylpyrrole‐2‐carboxylate] and [L2 = N‐methyl‐3‐indoleglyoxylate] were used as ligands to prepare six lanthanide coordination compounds [(L1)3Ln]n (Ln = Eu, 1; Gd, 2; Tb, 3) and [(L2)nLn(NO3)(MeOH)2]n (Ln = Eu, 4; Gd, 5; Tb, 6). These complexes have been synthesized and structurally characterized by single‐crystal X‐ray diffraction. The phosphorescence behavior of the ligands in the Gd3+ complexes show that modification of the ligands can tune the triplet energy levels of the ligands so that they match the 5D0 energy level of Eu3+ and the 5D4 energy level of Tb3+; thus, the energy transfer efficiency from antenna to Eu3+ and Tb3+ is improved, and the Eu3+ and Tb3+ emission intensity is enhanced. This concept can be applied towards improving the luminescent properties of Ln3+ complexes by the modification of coordinating ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
First NiII–LnIII Coordination Polymers Constructed by Using [Ni(bpca)2] as a Building Block [Hbpca = bis(2‐pyridylcarbonyl)amine]: Synthesis, Crystal Structures and Magnetic Properties
Authors: Madalan Augustin M. , Bernot Kevin , Pointillart Fabrice , Andruh Marius , Caneschi Andrea 
Published: October 2007

AbstractThree new heterobimetallic 1D coordination polymers have been obtained by assembling the [Ni(bpca)2] complex, as a building block, with lanthanide cations: [{Ln(O2NO)(H2O)3}{Ni(bpca)2}](NO3)2·3H2O (Ln Gd 1; Tb 2; Dy 3). The three compounds are isostructural and their structure consists of infinite cationic chains with LnIII ions connected by [Ni(bpca)2] complexes acting as bridging bis‐bidentate ligands. The charge of the chains is counterbalanced by uncoordinated nitrate ions. The LnIII ions display a coordination number of nine: four oxygen atoms from the carbonyl groups of the bpca ligands belonging to two {Ni(bpca)2} moieties, two oxygen atoms from a chelating nitrato ion and three water molecules. The magnetic investigation of the gadolinium derivative 1 revealed very weak intrachain NiII–GdIII‐ferromagnetic interactions (θ = +0.15 K). The weak intrachain‐exchange interactions, as well as the bad magnetic isolation of the chains in the crystals, preclude the single‐chain magnet behaviour of compounds 2 and 3. The out‐of‐phase, χ″, signal observed with compounds 2 and 3 can be ascribed to the magnetic slow relaxation of the lanthanide ions (TbIII, DyIII).(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
A New Donor‐Stabilized Ditungsten Amido Alkoxido Species: Synthesis, Crystal Structure, Fluxionality, and Grafting onto Silica
Authors: Coutelier Olivier , Gauvin Régis M. , Nowogrocki Guy , Trébosc Julien , Delevoye Laurent , Mortreux André 
Published: October 2007

AbstractA new dimeric tungsten(III) complex containing amidoand chelating pyridine–alkoxido ligands was synthesized through protonolysis of [W2(NMe2)6] by 2‐(2‐pyridyl)propan‐2‐ol and fully characterized by X‐ray diffraction and infrared and NMR spectroscopy. Intramolecular exchange processes were studied by variable‐temperature NMR spectroscopy. The compound was grafted onto dehydroxylated silica by protonolysis of an amido–tungsten bond, and the structure of the supported species was investigated by infrared and solid‐state (bidimensional) NMR spectroscopy. The reactivity of the molecular and grafted species toward alkynes was probed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
The Structure of Potassium and Tetramethylammonium Salts of the Cyclic Organohydroborate Anion [H2BC8H14]– with Different Solvent Ligands
Authors: Chen Xuenian , Liu Shengming , Du Bin , Meyers Edward A. , Shore Sheldon G. 
Published: October 2007

AbstractSolvated potassium salts of the 9‐BBN hydroborate anion have been prepared and their structures have been determined by single‐crystal X‐ray diffraction analyses. A tetrameric complex {LK[(μ‐H)2BC8H14]}4 is formed when L is toluene, MeTHF, toluene/THF, THF/Et2O mixtures. The basic framework consists of a distorted K4B4 cube in which potassium and boron are at alternate corners of the cube linked by bridging hydrogen atoms and α‐C–H hydrogen atoms from the 9‐BBN hydroborate that appear to form agostic interactions with potassium. There are two types of bridging hydrogen atoms: one is connected to three potassium atoms and one boron atom in a μ4‐coordination arrangement, and the other one is connected to two potassium atoms and one boron atom in a μ3‐coordination arrangement. There are four μ4‐hydrogen arrangements in the structure. They are located inside of the K4B4 cube. The four μ3‐hydrogen arrangements are located outside of the distorted K4B4 cube. The coordination number of potassium is 8 with the three μ4‐, two μ3‐bridging hydrogen atoms, two α‐C–H hydrogen atoms, and one oxygen atom of the solvent, L (there is a weak π‐η6 interaction when the solvent is toluene). On the other hand, in the chelating solvent DME, a dimeric structure is formed in which the inner part is planar with potassium and boron located at alternate corners. The potassium is connected to four μ3‐bridging hydrogen atoms, two apparent agostic α‐C–H bonding hydrogen atoms, and four oxygen atoms of two DME molecules. Its coordination number is 10 including the agostic interactions. The structure of the uncoordinated [H2BC8H14]– anion is observed in the tetramethylammonium salt. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Chiral separability of hydrophobic boron cluster anions with native cyclodextrins in water–methanol background electrolytes
Authors: Horáková Hana , Vespalec Radim 
Published: October 2007

AbstractCluster anions of boron are built up on three‐center two‐electron bonds in contrast to naturally occurring compounds and their synthetic analogs. Methanol works as a solvent and as a competing agent, which advantageously adjusts reasonable strength of their interaction with native CDs in water–organic BGE. The highest methanol concentration preserving chiral discrimination of atropoisomers of individual anions is approximately 35, 55 and 75% v/v for α‐, β‐ and γ‐CD, respectively. α‐CD separates anionic 7, 8‐nido‐dicarbaundecaborate clusters with small exo‐skeletal substituents. β‐CD separates anions of all four tested structural types. The efficiency of separation of a compound with α‐ or β‐CD is always markedly lower than the separation efficiency at the absence of a CD in BGE. The efficiency of separation of a compound with β‐CD is always lower than the efficiency of separation of the compound with α‐CD. γ‐CD was proved to be unsuitable as a chiral selector because in BGEs with γ‐CD, effective mobilities of analytes as well as their differences continuously decrease. The decrease was ascribed to the decomposition of the γ‐CD. The assessment of analytical prospect of α‐ and β‐CDs as chiral selectors for chiral separations of boron cluster anions requires knowledge of stability of individual CDs at the conditions of analyses and recognition of the chance to eliminate low separation efficiency.
Analysis of sub‐ppb levels of Fe(II), Co(II), and Ni(II) by electrokinetic supercharging preconcentration, CZE separation, and in‐capillary derivatization
Authors: Urbanek Marek , Delaunay Nathalie , Michel Régis , Varenne Anne , Gareil Pierre 
Published: October 2007

AbstractThe analysis of sub‐ppb levels of Fe(II), Co(II), and Ni(II) in heat exchanger fluids of nuclear power plants is needed to monitor corrosion. A method involving preconcentration with electrokinetic supercharging (electrokinetic injection with transient ITP), CZE separation, and in‐capillary derivatization with ortho‐phenanthroline (o‐Phe) for direct UV detection was thus developed. First, a multizone BGE was loaded into the capillary by successive hydrodynamic introduction of zones of (i) o‐Phe‐containing BGE, (ii) BGE for the zonal separation, and (iii) ammonium‐based leading electrolyte. Metal cations were electrokinetically injected and stacked at the capillary inlet behind this last leading zone. Finally, a terminating electrolyte zone was hydrodynamically introduced. When a constant voltage was applied, metal ions kept on concentrating isotachophoretically, then separated in CZE mode, were complexed by migrating through an o‐Phe zone, and finally detected by direct absorbance. To detect extremely thin peaks, it was attempted for the first time to focus the derivatization reagent by inducing a second transient ITP, before labeling analytes, already separated in CZE mode. With this arrangement, LODs were about 30 ppt in pure water. In heat exchanger fluid matrices containing 1000 ppm bore and 2 ppm lithium, only Fe(II) cation was detected among the three cations of interest at the 1 ppb level using the present method, and its LOD was about ten times higher, due to the lower loading rate during electrokinetic injection.
A rapid CE‐potential gradient detection method for determination of quinolones
Authors: Fan Yongxia , Gan Xiao , Li Shuo , Qin Weidong 
Published: October 2007

AbstractA rapid CE coupled with potential gradient detection (PGD) for the separation and detection of four quinolones, namely, enoxacin, ofloxacin (OFL), fleroxacin, and pazufloxacin, was described. Separation was performed in a fused‐silica capillary (75 μm×8.5 cm) using a buffer of 30 mM Tris and 4 mM phosphoric acid at pH 8.9. Under the separation voltage of 3 kV, the quinolones were separated within 2.8 min with good linearity (r2 ≥ 0.985). The method was successfully applied in determining OFL in a pharmaceutical formulation. Also, a liquid–liquid extraction (LLE) method was developed and coupled to CE‐PGD in determining quinolones that spiked in milk samples. With dichloromethane and hexane for enrichment and purification, the LLE recoveries of the four quinolones were in the range of 77–106%. The detection limits of the quinolones with LLE‐CE‐PGD were from 23 to 65 ng/mL. The proposed CE‐PGD method was validated with an HPLC method, and the results indicated consistency between the two methods.
Enhanced pH‐mediated stacking of anions for CE incorporating a dynamic pH junction
Authors: Arnett Stacy D. , Lunte Craig E. 
Published: October 2007

AbstractA technique has been developed to enhance analyte focusing for CE for the analysis of physiological samples. High‐ionic‐strength samples are titrated to low‐ionic‐strength on‐line using pH‐mediated sample stacking in conjunction with a dynamic pH junction. This method concentrates analytes by reducing their electrophoretic mobility during field‐amplification. Parameters responsible for enhanced focusing were investigated, and an enhanced pH‐mediated stacking method was optimized for anionic nucleosides. The process results in ultra‐narrow peak widths, for example, 0.28 s for thymidine with a 10 min analysis time. Peak width and resolution with the enhanced stacking method were also compared to normal base stacking and electrokinetic injection. With this technique, mass‐loading capacity can be increased without degradation in peak shape and resolution is dramatically improved.
Determination of iodine and bromine compounds in foodstuffs by CE‐inductively coupled plasma MS
Authors: Chen Jing‐Huan , Wang Kai‐en , Jiang Shiuh‐Jen 
Published: October 2007

AbstractA CE‐inductively coupled plasma mass spectrometric (CE‐ICP‐MS) method for iodine and bromine speciation analysis is described. Samples containing ionic iodine (I− and IO3−) and bromine (Br− and BrO3−) species are subjected to electrophoretic separation before injection into the microconcentric nebulizer (CEI‐100). The separation has been achieved in a 50 cm length×75 μm id fused‐silica capillary. The electrophoretic buffer used is 10 mmol/L Tris (pH 8.0), while the applied voltage is set at −8 kV. Detection limits are 1 and 20–50 ng/mL for various I and Br compounds, respectively, based on peak height. The RSD of the peak areas for seven injections of 0.1 μg/mL I−, IO3− and 1 μg/mL Br−, BrO3− mixture is in the range of 3–5%. This method has been applied to determine various iodine and bromine species in NIST SRM 1573a Tomato Leaves reference material and a salt and seaweed samples obtained locally. A microwave‐assisted extraction method is used for the extraction of these compounds. Over 87% of the total iodine and 83% of the total bromine are extracted using a 10% m/v tetramethylammonium hydroxide (TMAH) solution in a focused microwave field within a period of 10 min. The spike recoveries are in the range of 94–105% for all the determinations. The major species of iodine and bromine in tomato leaves, salt, and seaweed are Br−, IO3−, I−, and Br−, respectively.
Peak splitting in the CE separation of enantiomers caused by organic solvents in the sample
Authors: Stapf Fabian I. , Oehme Michael , Kiessig Steffen , Schwarz Maria A. , Kálmán Franka 
Published: October 2007

AbstractTwo robust chiral standard separation systems were developed for the analysis of the chiral purity of chemically different model compounds applied in homogeneous asymmetric hydrogenation catalysis. Sulfated CDs were used as chiral selectors as they allow the analysis of neutral, acidic as well as basic compounds in the same electrophoretic system. Poorly water‐soluble amines were dissolved in different organic solvent/buffer mixtures. Reproducibly, depending on the amount of organic solvent in the sample solution, peak splitting occurred and/or more peaks than expected were observed, implying impure model compounds. The dependence of the “chiral purity” on experimental parameters, e.g., kind and amount of sample solvent, length of injection plug, inner surface modification of the capillary, kind of sulfated CD, hydrophobicity, and basicity of the analytes, etc. was investigated. It is gathered that different equilibrium constants of the strong binding basic analytes and highly sulfated CD complex in the organic phase of the injection plug and the aqueous electrolyte phase are resulting in two different mobility zones for each enantiomer. It follows that each enantiomer is showing two peaks instead of one. Experimental strategies are shown to avoid these peak splitting/artificial impurity effects and obtain the “real” chiral purity picture of the samples.
Assay of aromatic amino acid enantiomers in rice‐brewed suspensions by chiral ligand‐exchange CE
Authors: Qi Li , Liu Meirong , Guo Zhenpeng , Xie Mingyi , Qiu Changgui , Chen Yi 
Published: October 2007

AbstractThe aim of this work was to assay seasoning D‐ or L‐aromatic amino acids (AAs) in rice‐brewed suspensions, Laozao in Chinese, by chiral ligand‐exchange CE with UV detection and Zn(II) complex as a chiral selecting system. Resolution and peak retention were found to be parallel to the basicity of the AA chiral ligands, and basic L‐Arg was known to work the best at pH 8.20 compared with L‐Lys and other AA ligands. Baseline separation of DL‐aromatic AAs and partially separation of some FMOC‐labeled nonaromatic AAs have been achieved using a running buffer of 5 mM ammonium acetate, 100 mM boric acid, 3 mM ZnSO4, and 6 mM L‐Arg at pH 8.20. The aromatic amino acids in four brands of Laozao were measured in a range of 0.25–20 μg/mL for Typ, 1.00–120 μg/mL for Phe, and 2.50–200 μg/mL for Tyr, with linear regression coefficient all over 0.999. The LOD (S/N = 3) was 0.15 μg/mL for Typ, 0.50 μg/mL for Phe, and 1.25 μg/mL for Tyr. The recovery of the method determined by spiking with the supernates of Laozao as background was 94.0–112.9%. The RSDs of migration time and peak area measured from six injections of tyrosine were 0.2 and 2.7%, respectively, for run‐to‐run, and 1.6 and 3.2%, respectively for day‐to‐day. Interestingly, there were only L‐Trp, D‐Tyr, and L‐Tyr found in the assayed four brands of Laozao. They may serve as an index to recognize the brand of Laozao.
Reliable electrophoretic mobilities free from Joule heating effects using CE
Authors: Evenhuis Christopher J. , Hruska Vlastimil , Guijt Rosanne M. , Macka Miroslav , Gaš Bohuslav , Marriott Philip J. , Haddad Paul R. 
Published: October 2007

AbstractIonic electrophoretic mobilities determined by means of CE experiments are sometimes different when compared to generally accepted values based on limiting ionic conductance measurements. While the effect of ionic strength on electrophoretic mobility has been long understood, the increase in the mobility that results from Joule heating (the resistive heating that occurs when a current passes through an electrolyte) has been largely overlooked. In this work, a simple method for obtaining reliable and reproducible values of electrophoretic mobility is described. The electrophoretic mobility is measured over a range of driving powers and the extrapolation to zero power dissipation is employed to eliminate the effect of Joule heating. These extrapolated values of electrophoretic mobility can then be used to calculate limiting ionic mobilities by making a correction for ionic strength; this somewhat complicated calculation is conveniently performed by using the freeware program PeakMaster 5. These straightforward procedures improve the agreement between experimentally determined and literature values of limiting ionic mobility by at least one order of magnitude. Using Tris‐chromate BGE with a value of conductivity 0.34 S/m and ionic strength 59 mM at a modest dissipated power per unit length of 2.0 W/m, values of mobility for inorganic anions were increased by an average of 12.6% relative to their values free from the effects of Joule heating. These increases were accompanied by a reduction in mobilities due to the ionic strength effect, which was 11% for univalent and 28% for divalent inorganic ions compared to their limiting ionic mobilities. Additionally, it was possible to determine the limiting ionic mobility for a number of aromatic anions by using PeakMaster 5 to perform an ionic strength correction. A major significance of this work is in being able to use CE to obtain reliable and accurate values of electrophoretic mobilities with all its benefits, including understanding and interpretation of physicochemical phenomena and the ability to model and simulate such phenomena accurately.
Determination of olive oil acidity by CE
Authors: Balesteros Manoela R. , Tavares Marina F. M. , Ribeiro Sidney J. L. , Polachini Ferminio C. , Messaddeq Younes , de Oliveira Marcone A. L. 
Published: October 2007

AbstractIn this work, a CE method for the determination of olive oil acidity was proposed. The method was based on an ethanolic extraction (at 60°C) of the oil long‐chain free fatty acids (LC‐FFAs) components followed by CE determination in pH 6.86 phosphate buffer at 15 mmol/L concentration containing 4 mmol/L sodium dodecylbenzenesulfonate (SDBS), 10 mmol/L polyoxyethylene 23 lauryl ether (Brij 35®), 2% v/v 1‐octanol and 45% v/v ACN under indirect UV detection at 224 nm. Although this electrolyte promoted baseline separation of myristic acid (C14:0) (internal standard (IS)) and olive oil major components (palmitic acid (C16:0), oleic acid (C18:1c) and linoleic acid (C18:2cc)) in less than 8 min, after a few injections, the electropherogram profiles were severely altered (peak broadening, migration time shifts, etc.) and the current increased substantially. An adsorption study was conducted revealing that the dissolution of the capillary external polyimide coating during the electrophoretic run caused the detrimental effect. After removal of the capillary tip coating, ten consecutive injections could be performed without any disturbances and this simple procedure was, therefore, implemented during quantitative purposes. The reliability of the proposed method was further investigated by the determination of acidity of an extra virgin olive oil sample in comparison to the established methodology (AOCS method Ca 5a‐40, alkaline volumetric titration (AVT)). No statistical differences were found within 95% confidence level. A % acidity of 0.39 ± 0.02 was found for the olive oil sample under consideration.
Mixture‐designed electrolytes for the MEKC separation of natural and synthetic steroids
Authors: Silva Claudinei A. , Pereira Elisabete A. , Micke Gustavo A. , Farah João P. S. , Tavares Marina F. M. 
Published: October 2007

AbstractIn this work, the separation of 11 natural and synthetic steroids was studied using MEKC electrolytes modified by property‐selected organic solvents: ethanol, ACN, and THF. The interplay between electrophoretic behavior and structural features was disclosed and the effects of organic modifiers to modulate retention and to alter selectivity were discussed in terms of system linear solvation energy relationships (LSER). The LSER indicated the total organic solvent percentage in the electrolyte as a major parameter to control retention and as a minor contribution, the hydrogen bond acidity. By evaluating the electropherograms obtained from mixture‐designed electrolytes, a favorable separation condition for all solutes was achieved in ca. 25 min with an electrolyte composed of 20 mmol/L sodium tetraborate at pH 9.4, 20 mmol/L SDS and 20% EtOH (0.80% CV for migration time and 2.5% CV for peak area, n = five consecutive injections). The applicability of the proposed separation condition was demonstrated by the inspection of estrogens in urine sample (puberty stage).
A new game theory‐based solution methodology for generation maintenance strategy
Authors: Jia Dexiang , Cheng Haozhong , Zhang Wenjun , Hu Zechun , Yan Jianyong , Chen Ming 
Published: October 2007

AbstractA new maintenance scheduling of generating units (MSU) game in competitive electricity markets is presented to analyze strategic behaviors of generating companies (Gencos). The payoff of each player comprises the revenues from the energy auction market, production cost, maintenance cost, and risk loss over the horizon, which involves the compensation fee of interruptible load and the forced outage of generator. A simplified offer price methodology and a stochastic programming one are adopted to determine player's optimal bidding strategies for the day‐ahead market, whose trends of game result are similar. The maximal payoff of each Genco is obtained by tabu search algorithm. The solutions of non‐equilibrium, unique equilibrium, and multiple equilibria are coordinated. Numerical results for a two‐Genco system and a realistic system are used to illustrate the applicability of the proposed method. Copyright © 2007 John Wiley & Sons, Ltd.
Improvement of grounding resistances using a deep‐ground‐well method for indoor‐type substations located in complex soils
Authors: Chang Cheng‐Nan , Lee Chien‐Hsing , Wang Yaw‐Juen 
Published: October 2007

AbstractThe purpose of this paper is to investigate the performance of a deep‐ground‐well method used for improving the grounding resistances of indoor‐type substations located in complex soils in the system of Taiwan Power Company (TPC). Three and two ground wells are installed at Kungchia and Kuoan 161/23.9 ∼ 11.95 kV substations as examples for assessing the improvement. The grounding resistances of ground wells are calculated by one‐ and equivalent n‐layer soil models with the image method and the current distribution electromagnetic grounding and soil structure analysis (CDEGS) program. On the other hand, the grounding resistances of ground wells are measured by the fall‐of‐potential method. As a result, the calculated grounding resistances of ground wells based on an equivalent two‐layer soil model are approximately equal to the measured grounding resistances of ground wells. Moreover, the grounding resistances of Kungchia and Kuoan indoor‐type substations after installing ground wells are improved about 70.29 and 58.40%, respectively. Copyright © 2007 John Wiley & Sons, Ltd.