bluuebunny/crossref_metadata_2025 huggingface dataset:
Tandem Palladium‐Catalyzed Cyclocarbonylation of Isolimonene: A Mechanistic Investigation and Theoretical Calculations on the Fully Diastereoselective Step
Authors: Lenoble Géraldine , Lacaze‐Dufaure Corinne , Urrutigoïty Martine , Mijoule Claude , Kalck Philippe
Published: February 2004

Cyclocarbonylation of isolimonene catalyzed by complexes of the type [HPd(SnCl3)L2] provides two cyclopentanone isomers (2a and 2b) containing two new stereogenic centers with a good diastereomeric excess (up to 69 % with L2 = dppf). These results show that chiral phosphane ligands are not necessary to ensure asymmetric induction. The diastereomeric excess is due, in fact, to the substrate itself, assisted by the steric hindrance of the diphosphanes. A full characterization of the two isomers by 1H, 13C and DPFGSE NOE NMR spectroscopy gives all the signal assignations and all the positions of the substituents of interest on the chiral carbon atoms. In order to have a better understanding of the catalytic process, we also present a density functional study of the crucial intermediate species 4 involved in the proposed catalytic cycle. Our calculations show that there is no coordination of the C=C bond in an exo mode. Conversely, we have found a pentacoordinate species with a trigonal bipyramidal geometry in which the C=C bond is coordinated in an endo mode. Selected bond lengths and bond orders are reported. The calculated net charge distribution supports the cyclization process, which proceeds through a C−C(O) and a C−Pd coupling. A β‐hydride elimination reaction of 4 provides the two 2a and 2b isomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthetic and Structural Studies of PdII and PtII Complexes with Quincorine and Quincoridine Derivatives
Authors: Fild Manfred , Thöne Carsten , Tötös Stefania
Published: February 2004

A series of PdII‐quincorine and ‐quincoridine complexes in which the ligands are coordinated through N,O‐donor atoms have been synthesised, and their structural features determined by X‐ray crystallography. Additionally, new chiral tetradentate N,P‐ligands containing two quinuclidine cores bridged through a cis‐enediyne fragment have been obtained. The different coordinating properties of the new ligands, which contain two soft phosphorus and two hard nitrogen donors, to PdII and PtII are emphasised. Several typical complexes were structurally characterised by X‐ray crystallography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Hydration of Propargylic Alcohols by Ruthenium Catalysts, with Dominant Anti‐Markovnikov Regioselectivity, Formation of α,β‐Unsaturated Products and Catalytic Decarbonylation to 1‐Alkenes
Authors: d'Alessandro Nicola , Di Deo Milena , Bonetti Monica , Tonucci Lucia , Morvillo Antonino , Bressan Mario
Published: February 2004

Ruthenium catalysts — water‐soluble ruthenium sulfophthalocyanine and heterogeneous ruthenium hydroxyapatite complexes — proved to be effective for the hydration of propargylic alcohols in entirely aqueous media. 1‐Phenyl‐2‐propyn‐1‐ol underwent an unprecedented catalytic hydration‐decarbonylation‐dehydration reaction, giving rise to styrene and carbon monoxide; 2‐propyn‐1‐ol and 3‐butyn‐2‐ol gave predominantly the products of anti‐Markovnikov addition, together with products of hydration‐dehydration (α,β‐rearrangement) and, to a minor extent, the decarbonylation products, ethene or propene, respectively. Hydrations were also conducted in D2O, giving indications of the mechanism of the reactions and apparently ruling out the allenylidene route for the α,β‐rearrangement. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Anomalous Difference in Magnetic Behavior between Highly Saddled Iron(III) Porphyrin Complexes in the Solid State
Authors: Ohgo Yoshiki , Ikeue Takahisa , Takahashi Masashi , Takeda Masuo , Nakamura Mikio
Published: February 2004

The spin states of microcrystalline samples of [Fe(OMTPP)L2]+ (L = DMAP or Py) have been examined and interpreted using Mössbauer spectroscopy, SQUID magnetometry and X‐ray crystallography. The Mössbauer spectra of [Fe(OMTPP)(DMAP)2]+ and [Fe(OMTPP)Py2]+ showed that both of these complexes maintain the low‐spin (S = 1/2) state over the 77−300 K temperature range. The spin states of these complexes were further confirmed by SQUID magnetometry. Thus, the magnetic behavior of [Fe(OMTPP)Py2]+ is quite different from that of the structurally related species [Fe(OETPP)Py2]+. The latter complex exhibits a novel spin crossover between the S = 3/2 and S = 1/2 states as revealed by the spectroscopic and magnetic measurements. In order to understand the reasons for the absence of the spin crossover process in [Fe(OMTPP)Py2]+, we have compared the crystal and molecular structures of [Fe(OMTPP)Py2]+ with those of the recently reported species [Fe(OETPP)Py2]+. In the case of [Fe(OMTPP)Py2]+, the Fe−Naxial bond lengths hardly change with temperature and are 2.058(6) and 2.024(4) Å at 298 and 80 K, respectively. These results are in sharp contrast to those of the spin crossover complex [Fe(OETPP)Py2]+, in which the Fe−Naxial bonds contract from 2.201(3) Å at 298 K to 1.993(3) Å at 80 K. We have ascribed the difference in magnetic behavior between [Fe(OMTPP)Py2]+ and [Fe(OETPP)Py2]+ to the difference in molecular packing; the former adopts a densely packed cubic crystal system while the latter shows a less condensed monoclinic system. A cavity calculation has further confirmed the above mentioned assumption. While the cavity sizes around the pyridine ligands in [Fe(OETPP)Py2]+ are 32.08 and 28.88 Å3 at 298 K, that in [Fe(OMTPP)Py2]+ is only 19.81 Å3. Furthermore, the cavities contract by 17.7% in [Fe(OETPP)Py2]+ when the temperature is lowered from 298 to 80 K whereas the contraction is only 5.3% in the case of [Fe(OMTPP)Py2]+. On the basis of these results, we have concluded that the loosely packed crystal system and the wide cavities around the axial ligands are the important requirements for the occurrence of the spin crossover process in the solid state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Preparation of 17 Sulfur‐Rich Chain‐Like Thiaalkanes R−Sx−R′−Sy−R and R−Sx−R′−Sy−R′−Sz−R (x, y, z > 2) from Titanocene Thiolate Complexes
Authors: Münchow Vera , Steudel Ralf
Published: February 2004

Two novel Cp2Ti(Cl)S3R′S3Tr complexes have been prepared by reaction of the six‐membered metallacycles Cp2TiS4R′ (Cp = η5‐C5H5, R′ = CMe2, 1,1‐C6H10) with the sulfenyl chloride TrSCl (Tr = CPh3) at 20 °C. These complexes were treated with: (a) sulfenyl chlorides (RSCl or RSSCl) to obtain 11 new thiaalkanes of the type R−Sx−R′−Sy−R (R = Tr, 4‐ClC6H4, 2‐C10H7; x = 3, y > 2), or (b) with SO2Cl2, SCl2 or S2Cl2 to prepare six sulfur‐rich species of the type Tr−Sx−R′−Sy−R′−Sz−Tr (x, z = 3, y > 3), as well as Cp2TiCl2. The thiaalkanes decompose upon heating to give mixtures of various linear and cyclic polysulfanes R2Sn and R′Sm. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Inorganic−Organic Hybrid Compounds: Synthesis and Structures of New Metal Organic Polymers Synthesized in the Presence of Mixed Dicarboxylates
Authors: Thirumurugan A. , Natarajan Srinivasan
Published: February 2004

A hydrothermal reaction of a mixture of 1,2‐dicyanobenzene (1,2‐DCB), 1,4‐benzene‐dicarboxylic acid (1,4‐BDC) along with the corresponding lanthanide salts at a pH of ≈︁ 5, gives rise to a new series of carboxylate coordination polymers, [M2(H2O)4{(1,2BDC)2(1,4BDC)}], (M = La, Pr, Gd, Dy, and Y), which are three‐dimensional in structure. The 1,2‐DCB oxidized to the corresponding dicarboxylic acid, phthalic acid (1,2‐BDC), during the reaction. The structures are of two types with the larger La and Pr lanthanides forming type‐1 and the smaller ones, Gd, Dy, and Y, forming type‐2. While La and Pr have an idealizedD3htriply capped trigonal prism coordination environment, Gd, Dy, and Y have a distorted dodecahedral arrangement with respect to the oxygen atoms. The three‐dimensional structure consists of a column of M atoms connected through the 1,2‐BDC, and is cross‐linked through 1,4‐BDC giving rise to rhombic one‐dimensional channels. The water molecules, bound to the M atoms, project into the channels. The compounds also illustrate the lanthanide contraction principle. The compounds have been characterized using powder X‐ray diffraction, TGA, IR, and photoluminescence measurements. Our continuing investigations clearly reveal that related compounds can be formed with all the rare earth metal ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Non‐Heme Iron Complexes for Stereoselective Oxidation: Tuning of the Selectivity in Dihydroxylation Using Different Solvents
Authors: Klopstra Marten , Roelfes Gerard , Hage Ronald , Kellogg Richard M. , Feringa Ben L.
Published: February 2004

A new class of functional models for non‐heme iron‐based dioxygenases, including [(N3Py‐Me)Fe(CH3CN)2](ClO4)2 and [(N3Py‐Bn)Fe(CH3CN)2](ClO4)2 {N3Py‐Me = [di(2‐pyridyl)methyl]methyl(2‐pyridyl)methylamine; N3Py‐Bn = [di(2‐pyridyl)methyl]benzyl(2‐pyridyl)methylamine}, is presented here. NMR, UV and X‐ray analyses revealed that six‐coordinate low‐spin FeII complexes with the pyridine N‐atoms and the tertiary amine functionality of the ligand bound to Fe are formed. The two remaining coordination sites located cis to each other are occupied by labile CH3CN groups that are easily exchanged by other ligands. We demonstrate that the reactivity and stereoselectivity of the complexes investigated depend on the choice of the solvent. The complexes have been examined as catalysts for the oxidation of both alkanes and olefins in CH3CN. In this solvent alkanes are oxidized to alcohols and ketones and olefins to the corresponding cis‐epoxides and cis‐diols. In acetone as solvent a different reactivity pattern was found, with, as the most striking example, the trans‐dihydroxylation of cis‐olefins. 18O‐labeling studies in CH3CN establish incorporation of 18O from H218O2 and H218O in both the epoxide and the diol implicating an HO‐FeV=18O active intermediate originating from an H218O‐FeIIIOOH species. These results are in full agreement with mechanistic schemes derived for other dioxygenase model systems. Based on labeling studies in acetone an additional oxidation mechanism is proposed for this solvent, in which the solvent acetone is involved. This is the first example of a catalyst that can give cis‐ or trans‐dihydroxylation products, just by changing the solvent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Stannaborate Chemistry: Nucleophilic Substitution at the Cluster Sphere
Authors: Ronig Benno , Bick Torsten , Pantenburg Ingo , Wesemann Lars
Published: February 2004

Nucleophilic substitution at (γ‐chloropropyl)stanna‐closododecaborate [Cl(CH2)3SnB11H11]− with RLi [R = Ph, Me2NC6H4, ferrocenyl (Fc)] and RMgBr (R = vinyl, benzyl) affords the substitution products containing the anion [RSnB11H11]−. The reaction products have been characterized by elemental analysis, NMR spectroscopy and in the cases where R = Ph, Me2NC6H4, Fc and vinyl by X‐ray structure analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Some Properties and Molecular Orbitals of Planar Heterodinuclear Phthalocyanines (Eur. J. Inorg. Chem. 4/2004)
Authors: Kobayashi Nagao , Ogata Hiroshi
Published: February 2004

The cover picture shows planar heterodinuclear phthalocyanine (Pc) dimers consisting of Pc and pyrazinoporphyrazine and of Pc and naphthalocyanine. In the picture, red spheres indicate nitrogen atoms. These dimers commonly show broad absorption bands between ca. 500 and 1000 nm, while the differential pulse voltammetry and molecular orbital calculations suggest that the dimers are unstable to oxidation, and that the two relatively independent chromophore units interact. Details are discussed in the article by N. Kobayashi and H. Ogata on p. 906 ff.
Determination of the fatty acid profile by 1H‐NMR spectroscopy
Authors: Knothe Gerhard , Kenar James A.
Published: February 2004

The common unsaturated fatty acids present in many vegetable oils (oleic, linoleic and linolenic acids) can be quantitated by 1H‐nuclear magnetic resonance spectroscopy (1H‐NMR). A key feature is that the signals of the terminal methyl group of linolenic acid are shifted downfield from the corresponding signals in the other fatty acids, permitting their separate integration and quantitation of linolenic acid. Then, using the integration values of the signals of the allylic and bis‐allylic protons, oleic and linoleic acids can be quantitated. The procedure was verified for mixtures of triacylglycerols (vegetable oils) and methyl esters of oleic, linoleic and linolenic acids as well as palmitic and stearic acids. Generally, the NMR (400 MHz) results were in good agreement with gas chromatographic (GC) analyses. As the present 1H‐NMR‐based procedure can be applied to neat vegetable oils, the preparation of derivatives for GC would be unnecessary. The present method is extended to quantitating saturated (palmitic and stearic) acids, although in this case the results deviate more strongly from actual values and GC analyses. Alternatives to the iodine value (allylic position equivalents and bis‐allylic position equivalents) can be derived directly from the integration values of the allylic and bis‐allylic protons.
Editorial: Electrophoresis 4‐5/2004
Authors: El Rassi Ziad
Published: February 2004

No abstracts.
Separation of capsular polysaccharide K4 and defructosylated K4 by high‐performance capillary electrophoresis
Authors: Volpi Nicola
Published: February 2004

A rapid, highly sensitive and reproducible high‐performance capillary electrophoresis (HPCE) method (electrokinetic chromatography with sodium dodecyl sulfate) is described for the determination of the polysaccharide from the uropathogenic Escherichia coli K4 bacteria (05:K4:H4) and its defructosylated product. The two polyanions, K4 and defructosylated K4, are separated and readily determined within 30 min on an uncoated fused‐silica capillary using normal polarity at 20 kV and detection at 200 nm. A linear relationship was found for the two polysaccharides over a wide range of concentrations, from approximately 30 ng (0.5 μg/μL) to 210 ng (3.5 μg/μL). The described method was used to evaluate the defructosylation process of K4 under drastic acid conditions.
On‐line identification of trans‐resveratrol in red wine using a sweeping technique combined with capillary electrophoresis/77 K fluorescence spectroscopy
Authors: Hsieh Min‐Chi , Lin Cheng‐Huang
Published: February 2004

The feasibility of combining the techniques of on‐line concentration and capillary electrophoresis/low‐temperature fluorescence spectroscopy (CE/LTFS) for the detection and identification of trans‐resveratrol in red wine at 77 K is demonstrated for the first time. This technique, involving sweeping‐micellar electrokinetic chromatography (sweeping‐MEKC), was used for the initial on‐line concentration and separation, after which a cryogenic molecular fluorescence experiment was performed at 77 K. In comparison with normal‐MEKC mode, a ∼1500‐fold improvement in detection sensitivity could be obtained when the sweeping‐MEKC was applied. The proposed method permits not only the separation and detection of trans‐resveratrol from red wine extracts but also ensures that the on‐line spectrum is readily distinguishable and can be unambiguously assigned at 77 K.
Capillary electrophoresis with laser‐induced fluorescence detection as a novel sensitive approach for the analysis of desmosines in real samples
Authors: Annovazzi Laura , Viglio Simona , Perani Eleonora , Luisetti Maurizio , Baraniuk James , Casado Begoña , Cetta Giuseppe , Iadarola Paolo
Published: February 2004

Among various biomarkers believed to behave as descriptors of the disease process in chronic obstructive pulmonary disease (COPD), urinary desmosines are commonly used for monitoring elastin degradation. Given the low concentrations of urinary desmosines, their quantitative determination in this biological matrix often requires preconcentration steps. To minimize both solute losses and effects of sample matrix, and to decrease data variability related to the above‐mentioned manipulation processes, we have developed a capillary electrophoresis approach combined with laser‐induced fluorescence (CE‐LIF) detection system using urine samples not submitted to any pretreatment procedure other than filtering the sample. Urines were hydrolyzed, derivatized with fluoresceine isothiocyanate (FITC) and endogenous desmosines were identified by addition of standard analytes and submitting to mass spectrometry (MS) analysis the material collected from micropreparative runs. The assay showed good linearity, reproducibility and precision, allowing to detect amounts of desmosines as low as 10‐8 M (equivalent to 0.1 fmol on column). We conclude that CE‐LIF technique is a highly sensitive method for detecting urinary desmosines.
Reversed‐phase capillary electrochromatography for the simultaneous determination of acetylsalicylic acid, paracetamol, and caffeine in analgesic tablets
Authors: Pucci Vincenzo , Mandrioli Roberto , Raggi Maria Augusta , Fanali Salvatore
Published: February 2004

The separation and simultaneous determination of caffeine, paracetamol, and acetylsalicylic acid in two analgesic tablet formulations was investigated by capillary electrochromatography (CEC). The effect of mobile phase composition on the separation and peak efficiency of the three analytes was studied and evaluated; in particular, the influence of buffer type, buffer pH, and acetonitrile content of the mobile phase was investigated. The analyses were carried out under optimized separation conditions, using a full‐packed silica capillary (75 μm ID; 30.0 cm and 21.5 cm total and effective lengths, respectively) with a 5 μm C8 stationary phase. A mixture of 25 mM ammonium formate at pH 3.0 and acetonitrile (30:70 v/v) was used as the mobile phase. UV detection was at 210 nm. Good linearity was found in the range of 50–200, 20–160, and 4–20 μg/mL for acetylsalicylic acid (r2 = 0.9988), paracetamol (r2 = 0.9990) and caffeine (r2 = 0.9990), respectively. Intermediate precision (RSD interday) as low as 0.1–0.8% was found for retention times, while the RSD values for the peak area ratios (Aanalyte/AIS) were in the range of 1.9–2.9%. The optimized CEC method was applied to the analysis of the studied compounds present in commercial tablets.
Chiral recognition of binaphthyl derivatives using electrokinetic chromatography and steady‐state fluorescence anisotropy: Effect of temperature
Authors: Billiot Fereshteh Haddadian , McCarroll Matthew C. , Billiot Eugene J. , Warner Isiah M.
Published: February 2004

The effect of temperature on the chiral recognition of binaphthyl derivatives in the presence of poly sodium N‐undecanoyl‐LL‐leucyl‐leucinate (poly LL‐SULL) is examined using electrokinetic chromatography (EKC) and steady‐state fluorescence anisotropy. An examination of the effect of temperature suggests that the chiral recognition of 1,1'‐binaphthyl‐2,2'‐diol enantiomers improves with increasing temperature, whereas lower temperatures resulted in better enantiosolectivity in the case of 1,1'‐binaphthyl‐2,2'‐diyl hydrogen phosphate enantiomers. In addition, steady‐state fluorescence anisotropy results show that the anisotropy of the two enantiomers are different when complexed to poly‐(LL) SULL. As would be expected, the enantiomer that binds stronger to the chiral pseudostationary phase, as evidenced by EKC experiments, had higher anisotropy values. The results of this study suggest that steady‐state fluorescence anisotropy can be used to gain further insight into chiral recognition.
Capillary electrochromatography of Triton X‐100
Authors: Norton Dean , Shamsi Shahab A.
Published: February 2004

Nonionic surfactants such as Triton X‐100 (TX‐100) are comprised of a mixture of oligomers with a varying degree of length in the ethoxylate chain. The development of chromatographic methods for resolution of the various oligomers of TX‐100 is of environmental importance, and can be useful for quality control and characterization in industrial manufacture. Capillary electrochromatography (CEC) is fast becoming a capable separation technique that combines the benefits of both high‐performance liquid chromatography (HPLC) and capillary electrophoresis (CE). This report presents a novel CEC method for separation of the various TX‐100 oligomers. A comparison of monomeric vs. polymeric stationary phases for separation of TX‐100 was conducted. Since the oligomers of TX‐100 were better resolved on a monomeric phase as compared to polymeric phase, a systematic mobile phase tuning was performed utilizing a monomeric CEC‐C18‐3 μm‐100 Å stationary phase. Various mobile phase parameters such as acetonitrile (ACN) content, Tris concentration, pH, voltage, and temperature were manipulated in order to achieve the optimum separation of oligomers in less than 30 min.
Indirect resolution of ß‐blocker agents by reversed‐phase capillary electrochromatography
Authors: Aturki Zeineb , Vichi Francesca , Messina Antonella , Sinibaldi Massimo
Published: February 2004

The indirect resolution of five β‐adrenoreceptor blocking agents (propranolol, oxprenolol, pindolol, metoprolol, and atenolol) using precolumn derivatization with (+)‐1‐(9‐fluorenyl)ethyl chloroformate (FLEC), and capillary electrochromatography (CEC) is reported. Three octadecylsilanized (ODS) silica gel‐based stationary phases, differing in particle diameter and carbon surface density for suitability of determination of the enantiomeric composition of these substances in drugs and biological fluids, were studied. Under optimum separation conditions, all the investigated compounds were baseline‐resolved within acceptable analysis times (i.e., between 10–16 min). The resolution values ranged between 1.80 and 1.14, and the separation factors were in no case less than 1.07. The possible use of the developed CEC method for the determination of enantiomeric composition of β‐adrenoreceptor blocking agents in drug substances was investigated. A study, in which the enantiomers of metoprolol were examined regarding specificity, reproducibility, limit of detection, and ruggedness, was developed in accordance with some analytical procedures for method validation.
Dynamics of interconversion of enantiomers in chiral separation systems: A novel approach for determination of all rate constants involved in the interconversion
Authors: Dubský Pavel , Tesařová Eva , Gaš Bohuslav
Published: February 2004

When enantiomers separated by chromatography or capillary electrophoresis undergo interconversion reaction (enantiomerization) during the separation, it leads to a typical detection pattern: two individual peaks of the separated enantiomers are connected with a plateau consisting of a mixture of both separated enantiomers. We propose a separation method for determination of all individual rate constants (or inversion barriers) of the interconversion. The method enables to distinguish which part of interconversion takes place in the free (unbound) form of the analyte and which part in the complexed (bound) form. Further, we propose a complete dynamic model of capillary electrophoresis of interconverting enantiomers based on solving a complete set of continuity equations for all constituents of the separation system together with complexation and acid‐base equilibria. This allows a simulation of both linear and nonlinear mode of separation and understanding all processes taking place in such enantioseparation systems. We demonstrate the applicability of the method on determination of the rate constants of interconversion of oxazepam enantiomers separated in systems with charged cyclodextrin chiral selectors.
Capillary electrochromatographic analysis of barbiturates in serum
Authors: Ohyama Kaname , Wada Mitsuhiro , Lord Gwyn A. , Ohba Yoshihito , Fujishita Osamu , Nakashima Kenichiro , Lim Chang Kee , Kuroda Naotaka
Published: February 2004

A capillary electrochromatographic method was developed for the separation of barbiturates. The separation was optimized in a 75 μm ID capillary, packed with 3‐(1,8‐naphthalimido)propyl‐modified silyl silica gel (NAIP), studying the effect of buffer pH, buffer concentration, and mobile phase composition. Using an applied voltage of 20 kV and the short‐end injection method (9 cm capillary effective length), the mobile phase of 1.0 mM citrate buffer (pH 5.0) containing 40% methanol provided the baseline separation of barbital, phenobarbital, secobarbital, and thiopental (internal standard) in less than 4.5 min. The method was successfully applied to the analysis of barbiturates in human serum. Under the optimal conditions, good repeatability and linearity were obtained in the range of 2.90–43.29 μg/mL for barbital, phenobarbital, and secobarbital.
Separation of phenylthiohydantoin amino acids by capillary electrochromatography
Authors: Mueller Thomas , Posch Ulrike C. , Lindner Herbert H.
Published: February 2004

Capillary electrochromatography (CEC) was employed as a rapid and high‐efficiency method for the isocratic separation of all 20 important phenylthiohydantoin (PTH) amino acids, the end products of Edman degradation during N‐terminal protein sequencing. For this purpose, 75 μm ID fused‐silica capillaries were packed with standard 3 μm Hypersil octadecyl silica (ODS) particles using a two‐step column fabrication process, which represents a fast, reliable and efficient means of producing long‐term stable columns. The influence of solvent composition, pH, type of buffer cation, buffer concentration, and temperature on retention behavior of PTH amino acids was investigated. Same‐day and day‐to‐day reproducibility of the retention times (over a period of two months) were found to be better than 3%. When comparing this new technique with traditional reversed phase‐high performance liquid chromatography (RP‐HPLC) methods applied in automated protein sequenators, CEC shows essentially shorter separation times and superior resolution.
Novel anionic copolymerized surfactants of mixed achiral and chiral surfactants as pseudostationary phases for micellar electrokinetic chromatography
Authors: Akbay Cevdet , Tarus Jepkoech , Gill Nicole L. , Agbaria Rezik A. , Warner Isiah M.
Published: February 2004

One disadvantage of amino acid‐based chiral selectors for micellar electrokinetic chromatography (MEKC) is that either they have very low solubility or are insoluble at acidic pHs. In order to increase solubilities at lower pHs, we have synthesized a highly water‐soluble achiral surfactant and copolymerized it with an amino acid‐based chiral surfactant. These two surfactants were polymerized either separately or at various molar rations of binary solutions, yielding pure molecular or copolymerized surfactant (CoPS), respectively. All surfactants were characterized by use of several analytical techniques prior to using them as novel pseudostationary phases in MEKC. The chromatographic performance of the CoPS in MEKC was tested with chiral and achiral analytes. The highly soluble sulfate head group significantly increased the solubility of amino acid‐based CoPS over a wide range of pH. Three chiral binaphthyl derivatives were tested and each surfactant system was found to have different selectivity.
Open‐tubular capillary electrochromatography/electrospray ionization‐mass spectrometry using polymeric surfactant as a stationary phase coating
Authors: Zhu Xiaofeng , Kamande Mary W. , Thiam Serigne , Kapnissi Constantina P. , Mwongela Simon M. , Warner Isiah M.
Published: February 2004

We describe the use of the polymeric surfactant poly(sodium undecylenic sulfate) (poly‐SUS) as a stationary phase coating in open‐tubular capillary electrochromatog raphy (OT‐CEC) coupled with electrospray ionization‐mass spectrometry (ESI‐MS) for the analysis of β‐blocker and benzodiazepine analytes. The production of a polymeric surfactant coating on the capillary inner wall involves (i) adsorption of the cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) to the inner surface of capillary, and (ii) adsorption of the negatively charged poly‐SUS onto the cationic polymer layer via strong physical interaction of the two polymer layers. As compared with micellar electrokinetic chromatography (MEKC) coupled with ESI‐MS, the main advantage of this proposed method is minimization of introduction of the monomeric or polymeric surfactant into the mass spectrometer, thus avoiding the interference of the nonvolatile micelle in ESI‐MS. The effects of buffer pH and applied voltage on the separation of the analytes are also discussed. Under optimum conditions, four of the five β‐blockers and four benzodiazepines are separated.
Combination of cyclodextrins and polymeric surfactants for chiral separations
Authors: Valle Bertha C. , Billiot Fereshteh H. , Shamsi Shahab A. , Zhu Xiaofeng , Powe Aleeta M. , Warner Isiah M.
Published: February 2004

A cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) method was applied to the enantioseparation of three binaphthyl derivatives using neutral CDs (i.e., β‐ and γ‐CD) in combination with various chiral amino acid‐based polymeric surfactants (PSs). Both the D‐ and L‐configurations of poly(sodium N‐undecanoyl alaninate), poly(sodium N‐undecanoyl leucinate), and poly(sodium N‐undecanoyl valinate) (poly(L‐SUV)) were synthesized. The retention behavior of the three binaphthyl derivatives under optimum electrophoretic conditions using a single chiral additive (PS or CD) is discussed. In addition, the effect of CD cavity size and stereochemical configuration of polymeric surfactants on selectivity (α) and resolution (Rs) was investigated. The enantioseparation of (±)1,1'‐binaphthyl‐2,2'‐diamine gave a reversal of enantiomeric order when using β‐CD in combination with any of the three D‐configuration PS. However, better enantioseparation is obtained when using the corresponding L‐configuration PS with β‐CD. A reversal of migration order (RMO) for the enantiomers of (±)1,1'‐bi‐2‐naphthol was observed upon the addition of 10 mM γ‐CD to poly(L‐SUV). However, no RMO of (±)1,1'‐bi‐2‐naphthol was seen when either β‐CD or γ‐CD was combined with D‐PS. The enantiomers of (±)1,1'‐binaphthyl‐2,2'‐diyl hydrogen phosphate showed little enantioselective behavior toward the PS alone. However, combined D‐ or L‐PS and β‐CD or γ‐CD systems gave increased Rs and α values. The chiral recognition of binaphthyl derivatives observed resulting from the various combinations of two chiral selectors is discussed.
Recent advances in the study of biomolecular interactions by capillary electrophoresis
Authors: He Xinya , Ding Yongsheng , Li Dazhi , Lin Bingcheng
Published: February 2004

Capillary electrophoresis (CE) has been abundantly used in the study of molecular interactions owing to such advantages as short analysis time, low sample size requirement, high separation efficiency, and flexible applications. The focus of this paper is to review recent studies and advances (mainly from 1998 to now) in biomolecular interactions using CE. Five CE modes: zone migration CE, affinity CE, frontal analysis (FA), Hummel‐Dreyer (HD) and vacancy peak (VP) are cited and compared. Quantitative aspects of the thermodynamics and kinetics of biomolecular interaction are reviewed. Several biomolecular binding systems, including protein‐protein (polypeptide), protein‐DNA (RNA), protein(polypeptide)‐carbohydrate, protein‐small molecule, DNA‐small molecule, small molecule‐small molecule, have been well characterized by CE. CE is shown to be a powerful tool for the determination of the binding parameters of various bioaffinity interactions.
Analysis of ephedra‐alkaloids using sweeping and cation‐selective exhaustive injection and sweeping micellar electrokinetic chromatography methods
Authors: Chiang Hui‐Yu , Sheu Shuenn‐Jyi
Published: February 2004

Two stacking methods of capillary electrophoresis (CE) were developed for the separation of very dilute solutions of ephedra‐alkaloids, namely ephedrine, pseudoephedrine, methylephedrine, methylpseudoephedrine, norephedrine, and norpseudoephedrine. A sweeping method which uses a carrier comprised of phosphoric acid, sodium dodecyl sulfate (SDS), diethylamine and acetonitrile permits the detection of the alkaloids down to the 10−1 μg/mL level, and the cation‐selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI‐Sweep‐MEKC) method using phosphoric acid, SDS, and acetronitrile as electrolytes can detect down to the 10−3 μg/mL level. The former requires the conductance of the sample solution to be adjusted beforehand, and only five peaks were observed, two of which were overlapped. The latter is capable of separating the six alkaloids but has a somewhat poorer reproducibility. Using an optimized injection time, it was found that the more diluted a solution is, the greater the sweeping effect will be. The CSEI‐Sweep‐MEKC method with a 600 s injection time and a 10−1 μg/mL solution concentration provides an amplification effect of ∼ 104. The method is suitable for analyses of dilute herb drug extracts and mouse sera. The effect of buffers on the separation and validation of the methods in this study are also discussed.
Development and validation of a robust capillary electrophoresis method for impurity profiling of calcium levofolinate including the (6R,2'S)‐diastereomer using statistical experimental design
Authors: Süß Falko , Harang Valérie , Sänger‐van de Griend Cari E. , Scriba Gerhard K. E.
Published: February 2004

A chiral capillary electrophoresis assay for the simultaneous determination of the optical purity and of related substances of calcium levofolinate has been developed and validated. Using 2,6‐dimethyl‐β‐cyclodextrin as chiral selector at a concentration of 20 mg/mL, the method was optimized using a full factorial design with four factors including pH and concentration of the background electrolyte, column temperature and separation voltage. Optimized conditions were a 40 mM sodium tetraborate buffer, pH 9.9, a capillary temperature of 16°C, and an applied voltage of 21 kV. Methotrexate was used as internal standard to compensate for injection errors and fluctuations of the migration times. A multiple linear regression model was also used to test the robustness of the method. Validation was performed with respect to specificity, linearity, range, limit of quantification and detection, precision, and accuracy. The assay allowed the detection and determination of related substances including the diastereomeric (6R,2'S)‐impurity of levofolinic acid at the 0.1% level, the identification threshold of impurities for orally administered drugs for human use defined by the International Conference on Harmonization guidelines as well as the European Pharmacopoeia.
Preparation and evaluation of molecularly imprinted polymers based on 9‐ethyladenine for the recognition of nucleotide bases in capillary electrochromatography
Authors: Huang Yi‐Chen , Lin Chun‐Chi , Liu Chuen‐Ying
Published: February 2004

A molecularly imprinted polymer (MIP) comprising 9‐ethyladenine was polymerized in situ inside the capillary for the electrochromatographic separation of nucleotide bases. The capillary wall was first functionalized with 3‐trimethoxysilylpropyl methacrylate (10% v/v) and 1,1‐diphenyl‐2‐picrylhydrazyl (0.01% w/v) in toluene. Following this treatment, the capillary was filled with acetonitrile containing 9‐ethyladenine, methacrylic acid, ethylene glycol dimethacrylate, and initiator. After polymerization, the MIP was shrunk into a film against the inner wall of the capillary with the syringe pump. The template was then removed with methanol under nitrogen flow. For evaluation the feasibility of the MIP column for the separation of nucleotide bases, some parameters including the pH, concentration of the background electrolyte, the applied voltage as well as the effect of organic modifier were studied. The migration behavior of nucleotide bases on the MIP column was also compared with that on the bare fused‐silica column. The results indicated that the MIP columns demonstrated better recognition properties at a pH range of 6–8. The efficiency (plates/m) at pH 8 for the nonimprinted analyte was 75 300 for cytosine, 50 200 for thymine, and 14 800 for guanine. However, the efficiency for the imprinted analyte, adenine, was quite low. This was evidenced by the broad peak, yielding only 2600 plates/m.
Effect of oil substitution in chiral microemulsion electrokinetic chromatography
Authors: Mertzman Melissa D. , Foley Joe P.
Published: February 2004

In a previous publication (Pascoe, R., Foley, J. P., Analyst 2002, 127, 710–714 [1]), a novel chiral microemulsion based on 1.0% w/v dodecoxycarbonylvaline (DDCV), 0.50% v/v ethyl acetate and 1.2% v/v 1‐butanol, was shown to provide rapid enantiomeric separations of various pharmaceutical compounds. The two deficiencies noted with this method were that the peak shapes obtained were asymmetric and the efficiencies were lower than those previously obtained using DDCV micelles (Peterson, A. G., Ahuja, E. S., Foley, J. P., J. Chromatogr. B 1996, 683, 15–28 [2]). This study examines the use of three alternative low‐interfacial‐tension oils (methyl acetate, methyl propionate, and methyl formate), in combination with DDCV, to characterize their effect on the elution range, efficiency, resolution, and enantioselectivity of various pharmaceutical enantiomers. The oils were evaluated in both the same volume percentage and the same molar concentration as ethyl acetate in the original DDCV microemulsion system. Including ethyl acetate, a total of seven microemulsion systems were examined. For the compounds that were separated, average enantioselectivities ranged from 1.09 to 1.28, with corresponding efficiencies of 14 000–20 000. While some interesting differences were observed, ethyl acetate still proved to be the most advantageous in terms of enantioselectivity, resolution, and elution range.
Dual opposite injection electrokinetic chromatography: Nonionic microemulsion pseudostationary phase and novel approach to electrokinetic sampling bias
Authors: Zhou Marilyn X. , Foley Joe P.
Published: February 2004

Dual opposite injection capillary electrophoresis (DOI‐CE) is a family of CE techniques in which the sample is introduced into both ends of the capillary. For the analysis of compounds with widely varying pKa values using a voltage‐driven separation scheme, DOI‐CE is superior to conventional CE with sample introduction at only one end of the capillary due to DOI‐CE's broader elution window. To enhance the DOI‐CE separation, a running buffer with a microemulsion system was developed. Since DOI‐CE works best under conditions of low electroosmotic flow (EOF), the suppression of EOF via the addition of a multiply charged cation (e.g., Zn2+) to the buffer was investigated, and was found to suppress the EOF effectively at moderate concentrations (2.5–10 mM). Three different dual opposite injection modes were studied: simultaneous electrokinetic injection, sequential electrokinetic injection, and sequential hydrodynamic injection. The injection bias in the first two electrokinetic injection modes was compared with the sequential hydrodynamic injection. Corrections in the bias of the electrokinetic injections were discussed, and an improved approach was suggested. Finally, the effect of the relative concentration of the multiply charged cation in the sample plug and running buffer on the peak shape of co‐electroosmotic and counter‐electroosmotic ions was examined, and found to be much more influential on the latter.
Determination of basic pharmaceuticals in human serum by hydrophilic interaction capillary electrochromatography
Authors: Fu Hongjing , Jin Wenhai , Xiao Hua , Xie Chuanhui , Guo Baochuan , Zou Hanfa
Published: February 2004

Hydrophilic interaction capillary electrochromatography (HI‐CEC) for the determination of basic pharmaceuticals spiked in human serum is described. The organic modifier content, ionic strength, and pH value of the mobile phase as well as the applied voltage are optimized for separation and elution of these drug analytes. Excellent separation was achieved for drugs using a mobile phase composition of 80% v/v acetonitrile in 100 mM triethylamine phosphate (TEAP) buffer at pH 2.8 with column efficiencies for analytes more than 200 000 plates/m. The samples of human serum spiked with basic drugs were directly injected after a simple acetonitrile treatment. The linear range and reproducibility of these basic drugs using an external and internal standard method were compared. As a result, the reproducibility could be greatly improved by using the internal standard method. Good calibration curves with regression coefficients more than 0.998 in the range of 5–160 μg/mL were observed with the internal standard method. The limits of quantitation, based on standards with acceptable relative standard deviations (RSDs), were below 5 μg/mL. The intra‐ and inter‐day precisions, determined as RSDs, were less than 4.57%.
Stir bar sorptive extraction‐liquid desorption applied to the analysis of hop‐derived bitter acids in beer by micellar electrokinetic chromatography
Authors: De Villiers André , Vanhoenacker Gerd , Lynen Fréderic , Sandra Pat
Published: February 2004

Stir bar sorptive extraction‐liquid desorption (SBSE‐LD) has been applied as an efficient sample preparation method for the analysis of beer bitter acids. Extracts free of almost all interfering compounds were obtained, allowing simultaneous analysis of iso‐α‐acids and reduced iso‐α‐acids. A robust micellar electrokinetic chromatography (MEKC) method was developed that enables fast separation of iso‐α‐acids and reduced iso‐α‐acids. Quantitative data are in good agreement with results obtained by high‐performance liquid chromatography (HPLC) using direct beer injection.
Polymeric sulfated surfactants with varied hydrocarbon tail: I. Synthesis, characterization, and application in micellar electrokinetic chromatography
Authors: Akbay Cevdet , Shamsi Shahab A.
Published: February 2004

The influence of surfactant hydrocarbon tail on the solute/pseudostationary phase interactions was examined. Four anionic sulfated surfactants with 8‐, 9‐, 10‐, and 11‐carbon chains having a polymerizable double bond at the end of the hydrocarbon chain were synthesized and characterized before and after polymerization. The critical micelle concentration (CMC), polarity, and aggregation number of the four sodium alkenyl sulfate (SAlS) surfactants were determined using fluorescence spectroscopy. The partial specific volume of the polymeric SAlS (poly‐SAlS) surfactants was estimated by density measurements and capillary electrophoresis (CE) was employed for determination of methylene selectivity as well as for elution window. The CMC of the monomers of SAlS surfactants decrease with increase in chain length and correlated well when fluorescence method was compared to CE. The physicochemical properties (partial specific volume, methylene selectivity, electrophoretic mobility, and elution window) increased with an increase in chain length. However, no direct relationship was found between the aggregation number and the length of hydrophobic tail of poly‐SAlS surfactants. These polymeric surfactants were then used as pseudostationary phases in micellar electrokinetic chromatography (MEKC) to study the retention behavior and selectivity factor of 36 benzene derivatives with different chemical characteristics. Although variation in chain length of the polymeric surfactants significantly affects the retention of nonhydrogen bonding (NHB) benzene derivatives, these effects were less pronounced for hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) benzene derivatives. Therefore, hydrophobicity of poly‐SAlS surfactants was found to be a major driving force for retention of NHB derivatives. However, for several benzene derivatives (NHB, HBA, and HBD) significantly higher selectivity factor was observed with longest chain polymeric surfactant (e.g., poly(sodium 10‐undecenyl sulfate), poly‐SUS) compared to shorter chain polymeric surfactant (e.g., poly(sodium 7‐octenyl sulfate), poly‐SOcS). In addition, the effect of the surfactant hydrophobic chain was also found to have some impact on migration order of NHB, HBA, and HBD benzene derivatives.
Polymeric sulfated surfactants with varied hydrocarbon tail: II. Chemical selectivity in micellar electrokinetic chromatography using linear solvation energy relationships study
Authors: Akbay Cevdet , Shamsi Shahab A.
Published: February 2004

The effect of hydrocarbon chain length on chemical selectivity in micellar electrokinetic chromatography (MEKC) was investigated using polymeric sulfated surfactants: poly‐(sodium 7‐octenyl sulfate), poly(sodium 8‐nonenyl sulfate), poly(sodium 9‐decenyl sulfate), and poly(sodium 10‐undecenyl sulfate). Linear solvation energy relationships (LSERs) and free energy of transfer studies were conducted to predict the selectivity differences between the four polymeric surfactants. The overall nature of the solute/ polymeric micelle interactions was found to be different despite the fact that all polymeric surfactants have the same head group. The polar character and acidic strength of the polymeric surfactant are found to decrease as the hydrocarbon chain length of the surfactant is increased. On the other hand, the polarizability of the polymeric sulfated surfactants increases (upon interacting with solute lone‐pair electrons) with increasing hydrocarbon chain length. The LSER results show that the solute size and hydrogen bond accepting ability play the key roles in MEKC retention.
Capillary electrochromatography of peptides on a neutral porous monolith with annular electroosmotic flow generation
Authors: Li Yan , Xiang Rong , Horváth Csaba , Wilkins James A.
Published: February 2004

A new kind of monolithic capillary column was prepared for capillary electrochromatography (CEC) with a positively charged polymer layer on the inner wall of a fused‐silica capillary and a neutral monolithic packing as the bulk stationary phase. The fused‐silica capillary was first silanized with 3‐glycidoxypropyltrimethoxysilane (GPTMS). Polyethyleneimine (PEI) was then covalently bonded to the GPTMS coating to form an annular positively charged polymer layer for the generation of electroosmotic flow (EOF). A neutral bulk monolithic stationary phase was then prepared by in situ copolymerization of vinylbenzyl chloride (VBC) and ethylene glycol dimethacrylate in the presence of 1‐propanol and formamide as porogens. Benzyl chloride functionalities on the monolith were subsequently hydrolyzed to benzyl alcohol groups. Effects of pH on the EOF mobility of the column were measured to monitor the completion of reactions. Using a column with this design, we expected general problems in CEC such as irreversible adsorption and electrostatic interaction between stationary phase and analytes to be reduced. A peptide mixture was successfully separated in counter‐directional mode CEC. Comparison of peptide separations in isocratic monolithic CEC, gradient HPLC and capillary zone electrophoresis (CZE) indicated that the separation in CEC is governed by a dual mechanism that involves a complex interplay between selective chromatographic retention and differential electrophoretic migration.