bluuebunny/crossref_metadata_2025 huggingface dataset:
IR Study of the Interaction of Dioxygen with [meso‐Triphenyl(4‐pyridyl)porphyrinato]cobalt(II)
Authors: Kurtikyan Tigran S. , Ogden J. Steven , Kazaryan Robert K. , Madakyan Valery N.
Published: May 2003

The interaction of O2 (18O2) with [meso‐triphenyl(4‐pyridyl)porphyrinato]cobalt(II) [Co(MPyTPP)] has been investigated by means of IR spectroscopy under matrix‐isolation conditions and by the action of dioxygen on thin sublimed layers. These studies have led to the characterisation of two dioxygen adducts: (1) a very unstable dioxygen adduct similar to that observed earlier for the closely related [meso‐tetraphenylporphyrinato]cobalt(II) Co(TPP), and (2) a new type of coordinated O2 (18O2) complex which is formed after warming Co(MPyTPP) either in pure oxygen matrices, or as sublimed layers in the presence of oxygen. The ν(O2) vibration in this second species is more than 100 cm−1 lower than in the first, and the dioxygen adduct thus formed is thermally stable at 200 K. This adduct is identified as a six‐coordinate dioxygen complex, with one coordination site occupied by the pyridyl group of an adjacent Co(MPyTPP) molecule. In the sublimed layers, the capacity for self‐assembly of Co(MPyTPP) oligomers leads to the formation of microporous solids containing coordinatively unsaturated metal ions which have the ability to bind oxygen reversibly upon storage at ambient conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, Characterisation and Antiamoebic Studies of Dioxovanadium(V) Complexes Containing ONS Donor Ligands Derived from S‐Benzyldithiocarbazate
Authors: Maurya Mannar R. , Khurana Shilpa , Shailendra  , Azam Amir , Zhang Wenjian , Rehder Dieter
Published: May 2003

Three new dioxovanadium(V) compounds, [K(H2O)][VO2(sal‐sbdt)] (1), [K(H2O)2][VO2(Clsal‐sbdt)] (2), and [K(H2O)2][VO2(Brsal‐sbdt)] (3) (where H2sal‐sbdt are the Schiff bases formed between salicylaldehyde and dithiocarbazates) have been synthesised, and the structures of 1 and 2 revealed by X‐ray diffraction analyses. The ligands coordinate in the tridentate ONS fashion out of the enethiolate tautomeric form. The potassium counterions, coordinated to water molecules, the phenolate‐O, the oxo groups on vanadium and, in the case of 1, to the thiolate, provide interlinkages between the anions and thus a complex supramolecular network, further reinforced by intermolecular hydrogen bonds between oxo groups and water molecules. In vitro tests of the antiamoebic activity against the protozoan parasite Entamoeba histolytica showed comparable (1 and 2) or substantially better (3) amoebocidal action than metronidazole, a commonly used drug against amoebobiasis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
ZnII Complex with a Phenanthroline‐Containing Macrocycle as Receptor for Amino Acids and Dipeptides − Hydrolysis of an Activated Peptide Bond
Authors: Bazzicalupi Carla , Bencini Andrea , Berni Emanuela , Bianchi Antonio , Fornasari Patrizia , Giorgi Claudia , Valtancoli Barbara
Published: May 2003

The interaction between several L‐amino acids and dipeptides and the ZnII complex with ligand L, a macrocycle containing a triamine chain linking the 2,9 positions of a phenanthroline moiety, has been studied by means of potentiometric and 1H NMR spectroscopic measurements in aqueous solutions. In the [ZnL]2+ complex, the metal ion displays an unsaturated coordination environment and the metal can act as a binding site for these substrates. Amino acids and dipeptides in their neutral (zwitterionic) form bind to ZnII through the carboxylate function and, when in their anionic form, through the amine group. In this case the carbonyl of the amide function is probably also involved in metal coordination. Amino acids containing aromatic pendants form the most stable complexes, due to hydrophobic and/or π‐stacking interactions between the aromatic subunits of the substrates and the phenanthroline moiety of the metal receptor. The hydrolytic properties of the ZnII complex with L, involving the cleavage of the peptide bond, have been tested by using L‐leucine‐p‐nitroanilide (LNA), which contains an activated peptide bond. This substrate forms stable [ZnL(LNA)]2+ and [ZnL(OH)(LNA)]+ complexes. The formation of the [ZnL(OH)(LNA)]+ complex is followed by LNA hydrolysis, through a nucleophilic attack of the Zn−OH function on the peptide bond. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Quest for Isophosphaalkynes (Isophosphocyanides) C≡P−R — Still an Elusive Class of Compounds
Authors: Weber Lothar
Published: May 2003

This review gives an account on the quest for isophosphaalkynes, a class of compounds that still resists isolation and/or spectroscopic detection. Synthetic attempts toward this target are reported. On the other hand, a number of coordination compounds featuring isophosphaalkyne ligands have been prepared, the syntheses, structures, and chemistry of which are discussed.
Thermodynamics of Complex Formation of Silver(I), Cadmium(II) and Cobalt(II) with Open‐Chain Polyamines in Dimethyl Sulfoxide and Molecular Dioxygen Binding to Cobalt(II) Complexes
Authors: Comuzzi Clara , Melchior Andrea , Polese Pierluigi , Portanova Roberto , Tolazzi Marilena
Published: May 2003

AgI, CdII and CoII complex formation with the primary and tertiary tetraamines 1,4,7,10‐tetraazadecane (trien) and 1,1,4,7,10,10‐hexamethyltriethylenetetraamine (hmtrien) has been studied at 298 K in the aprotic solvent dimethyl sulfoxide (DMSO) and in an ionic medium set to 0.1 mol·dm−3 with Et4NClO4 under anaerobic conditions. UV/Vis spectrophotometric and calorimetric measurements have been carried out to obtain the thermodynamic parameters for the systems investigated. Mononuclear 1:1 complexes are formed for all systems. In addition, trien also forms the ML2 mononuclear complex and a polynuclear M2L3 species with M = Cd2+ and Co2+. All the complexes are enthalpy stabilized, whereas the entropy changes counteract the complex formation. The results are discussed in terms of the different basicities, steric requirements and solvation both of the ligands and of the complexes formed. The influence of N‐alkylation on the selectivity of the ligands towards metal ions is analysed. In the case of the CoII complexes, their ability to take up dioxygen has also been studied by voltammetric and UV/Vis measurements and gasometric absorption. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Formation of Ruthenium−Aminocarbene Complexes from Aldimines and Aminals
Authors: Standfest‐Hauser Christina M. , Mereiter Kurt , Schmid Roland , Kirchner Karl
Published: May 2003

Specific pyridine‐based aldimines and aminals act as chelating ligands towards the RuCpL and RuTpL (Tp = hydrido trispyrazolylborate) fragments giving κ2N,N′‐coordinated cyclic imine complexes. Under particular conditions, as elucidated in this paper, these complexes rearrange into cyclic aminocarbene complexes. Thus, the reaction of [RuCp(L)(CH3CN)2]PF6 (L = CH3CN, PMe3, SbPh3) with 1 equiv. of py−N=CHR [R = Ph (phenyl), Fc (ferrocenyl), Np (naphthyl)] affords the cyclic aminocarbene complexes [RuCp(L)(=C(R)NH−py)]PF6, whereas when L = PPh3, PiPr3, and CO the reaction stops at the stage of the imine complex [RuCp(L)(κ2N,N′‐py−N=CHR)]PF6. Analogously, [RuTp(COD)Cl] (COD = 1,5‐cyclooctadiene) also reacts readily with the imines py−N=CHR (R = Ph, pMeOC6H4, Np) at elevated temperatures to yield the aminocarbene complexes [RuTp{=C(R)NH−py}Cl]. This process may open a new synthetic route for obtaining carbene complexes. The mechanism of the imine−aminocarbene conversion was analyzed by DFT/B3LYP calculations. Accordingly, the operation of a direct 1,2 hydrogen shift can be ruled out; the reaction seems to involve hydrido iminoacyl intermediates resulting from C−H bond activation and deprotonation/protonation steps. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Structures and Thermodynamics of the Sulfuranes SF3CN and SF2(CN)2 as well as of the Persulfurane SF4(CN)2 − An ab initio MO Study by the G3(MP2) Method
Authors: Steudel Yana , Steudel Ralf
Published: May 2003

At the G3(MP2) level of theory the trans isomer 1a of the hypothetical molecule SF4(CN)2 is more stable than the cis isomer 1b by 8 kJ·mol−1. The isomerization of 1a to 1b requires an activation enthalpy of 319 kJ·mol−1 at 298 K. The decomposition of trans‐SF4(CN)2 to SF2(CN)2 and F2 is endothermic (ΔHo298 = 395 kJ·mol−1) but the elimination of FCN from trans‐SF4(CN)2 is exothermic by −7 kJ·mol−1. The elimination of (CN)2 from cis‐SF4(CN)2 is exothermic by −137 kJ·mol−1. The activation enthalpies for the latter two reactions were calculated as 251 and 311 kJ·mol−1, respectively. Thus, SF4(CN)2 should be a thermally stable compound. In the sulfuranes SF3CN and SF2(CN)2 the CN ligands prefer the equatorial positions; mutual exchange of an axial F atom by an equatorial CN group requires a reaction enthalpy of 51 kJ·mol−1 [SF3CN] or 58 kJ·mol−1 [SF2(CN)2]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cubane Complexes with Two (or More) Group 14−Group 16 Double Bonds: Synthesis and X‐ray Structures of Sn4Se2(NtBu)4 and Ge4Se3(NtBu)4
Authors: Chivers Tristram , Clark Timothy J. , Krahn Mark , Parvez Masood , Schatte Gabriele
Published: May 2003

Monomeric complexes with two or three terminal M=Se bonds, Sn4Se2(NtBu)4 or Ge4Se3(NtBu)4, respectively, are produced by oxidation of (MNtBu)4 (M = Sn, Ge) with selenium in hot toluene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: IR Study of the Interaction of Dioxygen with [meso‐Triphenyl(4‐pyridyl)porphyrinato]cobalt(II) (Eur. J. Inorg. Chem. 10/2003)
Authors: Kurtikyan Tigran S. , Ogden J. Steven , Kazaryan Robert K. , Madakyan Valery N.
Published: May 2003

The cover picture shows a schematic view of part of a novel complex that undergoes reversible dioxygen binding. The complex is a zig‐zag oligomer formed in sublimed layers of [meso‐triphenyl(4‐pyridyl)porphyrinato]cobalt(II) and is depicted here with molecular dioxygen coordinated at each cobalt centre. The relatively open, microporous structure of the oligomer arises as a result of pyridine coordination, which inhibits closer‐packed structures (e.g. with parallel contiguous porphyrin rings), and ensures facile transport of molecular oxygen to the coordination site. The zig‐zag chain also inhibits the formation of dioxygen‐bridged centres, with the result that this basic structure is relatively stable. On warming, the Co−dioxygen link may be broken, with the evolution of dioxygen, which can readily diffuse through the microporous structure, leaving the zig‐zag oligomer chain effectively intact. Details are discussed in the article by T. S. Kurtikyan et al. on p. 1861 ff.
Amalgam Electrodes for Electroanalysis
Authors: Mikkelsen Øyvind , Schrøder Knut H.
Published: May 2003

Liquid mercury is a unique material for the indicator electrode in voltammetry. One reason for this is the high overvoltage for hydrogen formation, thus extending the actual potential window. Diluted amalgams are important reaction products in voltammetric (polarographic) processes, however liquid amalgams are rarely used directly as electrode material for analytical purposes. Because of the fact that voltammetry is very suitable for field and remote monitoring, issues concerning the use of mercury electrodes in environmental analyses have led to considerable research effort aimed at finding alternative tools with acceptable performance. Solid electrodes are such alternatives. Different types of electrodes are reviewed. In particular, solid amalgam electrodes are very promising, with acceptable low toxicity to be used for field measurements. Solid amalgam electrodes are easy and cheap to construct and are stable over a reasonable time up to several weeks. Assessment of the toxicity risk and the long time stability for remote and unattended monitoring is discussed. The differences between solid dental amalgam electrodes, made by using techniques known from dental clinical practice, and mercury film or mercury layer electrodes on solid substrates are reviewed. In particular the dental technique for constructing solid amalgam electrodes gives advantage because it's fast and inexpensive. Also the technique for making dental amalgam has been explored and optimized over years by dentists, giving advantage when the same technique is used for constructing electrodes. Dental amalgam electrodes has been found to act similar to a silver electrodes, but with high overvoltage towards hydrogen. This make it possible to use the dental amalgam electrode for detection of zinc, cobalt and nickel in additions to other metals like lead, copper, thallium, cadmium, bismuth, iron etc. Also the use for reducible organic compounds is expected to be promising.
Reaction with N,N‐Diethyl‐p‐phenylenediamine: A Procedure for the Sensitive Square‐Wave Voltammetric Detection of Chlorine
Authors: Seymour E. Hugo , Lawrence Nathan S. , Compton Richard G.
Published: May 2003

The reaction of chlorine and N,N‐diethyl‐p‐phenylenediamine has been studied as a means of generating an analytical voltammetric signal of much improved sensitivity and selectivity for the detection of the former than is possible via direct electrolysis. A reaction mechanism is suggested whereby the chlorine attacks the primary amine of DEPD to form the N‐chlorinated product that shows a much enhanced signal under conditions of square‐wave voltammetry than does chlorine itself. The analytical parameters were found to vary with concentration of DEPD and a linear range from 17 to 495 μM was achievable with a corresponding limit of detection of 6.8 μM
Differential Pulse Techniques on Modified Conventional‐Size and Microelectrodes. Electroactivity of Poly[4,4′‐bis(butylsulfanyl)‐2,2′‐bithiophene] Coating Towards Dopamine and Ascorbic Acid Oxidation
Authors: Lupu S. , Parenti F. , Pigani L. , Seeber R. , Zanardi C.
Published: May 2003

Poly[4,4′‐bis(butylsulfanyl)‐2,2′‐bithiophene] modified conventional‐size and (ultra)microelectrodes are first investigated in acetonitrile and quasi‐neutral aqueous solution with respect to the repeatability of the responses obtained both in cyclic voltammetry and in differential pulse voltammetry. The reactivity towards ferrocene and hydroquinone, chosen as benchmark oxidizable substances in the two media, respectively, is considered. Comparison is made with the behavior of poly(3‐methylthiophene) as electrode coating, which is one of the most commonly used redox mediators in amperometric sensors based on coatings consisting of conducting polymers. The results confirm the appealing properties of poly[4,4′‐bis(butylsulfanyl)‐2,2′‐bithiophene], previously evidenced by us in different electrochemical studies: it exhibits particularly high stability and the characteristics of the current/potential curves obtained make it particularly suitable for analytical purposes. After performing these tests, the quantitative determination of dopamine by modified microelectrode is examined and the simultaneous voltammetric determination of ascorbic acid and dopamine is considered. The possibility of working profitably with a microelectrode at very low buffer‐supporting electrolyte concentration is ascertained.
Capillary zone electrophoresis in methanol: Migration behavior and background electrolytes
Authors: Beckers Jozef L. , Ackermans Mariëtte T. , Boček Petr
Published: May 2003

Nonaqueous (NA) solutions are often used as background electrolytes (BGEs) and NA solvents are added to aqueous BGEs as organic modifiers in capillary zone electrophoresis (CZE), in order to optimize the separations. This can be tricky, however, because the pH* and pK* concepts may be totally different in NA solvents, whereas often less knowledge is available concerning phenomena, such as system zones, applying NA solvents. In this paper, the concepts of pH* and pK* are considered for methanol as a solvent and pK* values are determined for several components in mixtures of water and methanol. With a mathematical model, adapted for calculations in methanol, parameters are calculated describing the fronting or tailing character of peaks and the question of peaks or dips, and the existence of system zones is discussed for pure methanol as a solvent. These aspects are experimentally verified, applying BGEs useful for the separation of cationic species in the indirect UV mode. It can be concluded that the mathematical model developed for aqueous BGEs is applicable to BGEs in methanol, too, and that the behavior of BGEs in methanol is comparable with that in water concerning the fronting or tailing character of peaks and the question of peaks and dips, although the mobilities and pK values can change significantly.
Modeling the zeta potential of silica capillaries in relation to the background electrolyte composition
Authors: Berli Claudio L. A. , Piaggio María V. , Deiber Julio A.
Published: May 2003

A theoretical relation between the zeta potential of silica capillaries and the composition of the background electrolyte (BGE) is presented in order to be used in capillary zone electrophoresis (CZE). This relation is derived on the basis of the Poisson‐Boltzmann equation and considering the equilibrium dissociation of silanol groups at the capillary wall as the mechanism of charge generation. The resulting model involves the relevant physicochemical parameters of the BGE‐capillary interface. Special attention is paid to the characterization of the BGE, which can be either salt or/and buffer solutions. The model is successfully applied to electroosmotic flow (EOF) experimental data of different aqueous solutions, covering a wide range of pH and ionic strength. Numerical predictions are also presented showing the capability of the model to quantify the EOF, the control of which is relevant to improve analyte separation performance in CZE.
Influence of electrolyte nature on the separation selectivity of amphetamines in nonaqueous capillary electrophoresis: Protonation degree versus ion pairing effects
Authors: Descroix Stéphanie , Varenne Anne , Geiser Laurent , Cherkaoui Samir , Veuthey Jean‐Luc , Gareil Pierre
Published: May 2003

The simultaneous analysis of Ecstasy and its derivatives in an acetonitrile‐methanol (80:20 v/v) mixture was previously shown to be strongly dependent on the nature of the electrolyte (acetate versus formate). To elucidate the phenomena involved, systematic experiments were conducted in this solvent medium. Conductivity measurements allowed to evaluate the ion‐pairing rate in the background electrolyte (BGE) and thereby distinguish between electrolyte concentration and ionic strength. The influence of electrolyte concentration on analyte effective mobilities (μeff) was studied by capillary electrophoresis (CE). As μeff extrapolated to infinite dilution proved to be independent of the nature of the electrolyte, selectivity changes could not be attributed to a modification in the protonation degree of amphetamines. Experimental mobility data were then confronted to existing theoretical mobility models to discriminate between ion pairing or simple ionic strength effect. Ion‐pair formation in a BGE containing acetate was highlighted with an ion‐pairing model and ion‐pair formation constants between each amphetamine and acetate ion were calculated.
The principles of migration and dispersion in capillary zone electrophoresis in nonaqueous solvents
Authors: Porras Simo P. , Riekkola Marja‐Liisa , Kenndler Ernst
Published: May 2003

Nonaqueous solvents are interesting media for capillary zone electrophoresis as they can affect all relevant parameters governing the separation of sample zones. However, for a rational planning of the working conditions and an appropriate interpretation of the results obtained, the basic principles of ion migration and zone dispersion must be understood. Many solvent induced effects need to be carefully considered and recognized before full exploitation of nonaqueous solvents can take place. It is the goal of this overview to present the fundamental physicochemical aspects of capillary zone electrophoresis in nonaqueous solvent systems. Therefore, the detailed discussion is related to the effect of organic solvents on electrophoretic mobilities (based on the theory of conductance), acid‐base dissociation behavior (based on the transfer activity coefficient and medium effect), pH, separation efficiency (with regard to mobility and diffusion coefficient in dilute solutions), resolution, and electroosmotic flow.
Enantioselective strong cation‐exchange molecular recognition materials: Design of novel chiral stationary phases and their application for enantioseparation of chiral bases by nonaqueous capillary electrochromatography
Authors: Constantin Stéphane , Bicker Wolfgang , Zarbl Elfriede , Lämmerhofer Michael , Lindner Wolfgang
Published: May 2003

New chiral stationary phases derived from enantiomerically pure derivatives of cysteine carrying sulfonic acid groups are synthesized and evaluated for enantiomer separation of chiral bases by non aqueous capillary electrochromatography after bonding to a linker and grafting upon thiol‐modified silica particles. Structural modifications of these low molecular weight chiral selectors are investigated and discussed in terms of apparent enantioselectivities and resolution factors based on the enantiomeric separations of a set of chiral bases including β‐blockers, β‐sympathomimetics and other basic drugs. The influence of the mobile phase constitution and its flow velocity on the enantioseparation by nonaqueous capillary electrochromatography is also briefly evaluated and discussed for the chiral substances investigated.
Heteroconjugation‐based capillary electrophoretic separation of phenolic compounds in acetonitrile and propylene carbonate
Authors: Kuldvee Ruth , Vaher Merike , Koel Mihkel , Kaljurand Mihkel
Published: May 2003

A mixture of methyl‐ and hydroxy‐substituted phenols was separated by capillary electrophoresis in pure acetonitrile and propylene carbonate. Interactions between undissociated phenolic compounds and the background electrolytes were investigated. In the present work, benzyltriethylammonium chloride, tetrabutylammonium acetate, and two room temperature‐molten salts, 1‐butyl‐3‐methyl imidazolium trifluoroacetate and 1‐butyl‐3‐methyl imidazolium heptafluorobutanoate, were used as background electrolytes. The formation of a negative complex between background electrolyte anion and neutral phenolic compound was observed and the formation constant calculated. The formation constants for anion‐analyte complexes were approximately the same in propylene carbonate and in acetonitrile. In both solvents the formation constants were the highest for acetate and the lowest for trifluoroacetate. The separation of analytes was slightly influenced by the nature of the solvent: in acetonitrile the resolution between peaks was higher for 1,3‐dihydroxyphenol and 1,3,5‐trihydroxyphenol, in propylene carbonate 3‐methylphenol and phenol were better separated. It was demonstrated that traces of water influence the mobilities of anion‐phenol complexes in propylene carbonate.
Solvent effects in microemulsion electrokinetic chromatography
Authors: Klampfl Christian W.
Published: May 2003

The contribution of organic solvents to the mechanisms responsible for separation in microemulsion electrokinetic chromatography (MEEKC) is reviewed. Organic solvents are needed as constituents of microemulsions for a series of reasons. (i) A water‐immiscible organic substance is used to form the actual oil phase of the microemulsion, (ii) a less hydrophobic solvent is commonly employed as a so‐called cosurfactant, and (iii) in many cases an organic modifier is added to influence the solubility of the analytes in the aqueous phase of the microemulsion. All these organic solvents do not only participate in the separation in their actual function, but also interact with each other and the analytes. Variations in separation selectivities triggered by changes in the nature and/or concentration of these organic solvents present in microemulsions suitable for MEEKC are discussed in this work.
Capillary electrophoretic study of the binding of zinc(II) ion to bacitracin A1 in water‐2,2,2‐trifluoroethanol
Authors: Castagnola Massimo , Rossetti Diana Valeria , Inzitari Rosanna , Vitali Alberto , Lupi Alessandro , Zuppi Cecilia , Cabras Tiziana , Fadda Maria Benedetta , Podda Ilaria , Petruzzelli Raffaele , Giardina Bruno , Messana Irene
Published: May 2003

Binding of Zn2+ to bacitracin A1 was studied by capillary electrophoresis in water/2,2,2‐trifluoroethanol (70/30 v/v) at different apparent pH values in order to estimate the association constant of metal, the acidic dissociation constants and the Stokes radii of both free and bounded peptide in apolar environment. The Stokes radii of the free peptide species were compared with those in aqueous solution, as obtained in a recent study performed by our group, indicating that apolar environment stabilizes bacitracin A1 in a conformational structure with the lateral chain of apolar amino acids exposed on the external surface. This conformation of the macrocyclic dodecapeptide is ready to interact with Zn2+ ion, as pointed out by the strong increase of the association constant measured in water/2,2,2‐trifluoroethanol with respect to the value obtained in aqueous solution. In addition, whereas Zn2+ ion binding in aqueous solution provides a sensible reduction of peptide Stokes radius, no sensible variations following to ion binding were observed in hydro‐organic solution. The present results suggest that the apolar environment, rather than the metal ion binding, could be responsible for the conformational transition that brings bacitracin A1 towards its biologically active structure.*
Peak dispersion and contributions to plate height in nonaqueous capillary electrophoresis at high electric field strengths: Propanol as background electrolyte solvent
Authors: Palonen Sami , Porras Simo P. , Jussila Matti , Riekkola Marja‐Liisa
Published: May 2003

Peak dispersion effects in nonaqueous capillary electrophoretic separations of aromatic anionic analytes were investigated in a propanolic background electrolyte solution. Poly(glycidylmethacrylate‐co‐N‐vinylpyrrolidone) coating was applied to the capillary to suppress the electroosmotic flow and to improve the repeatability of the migration times. Electrical field strengths up to 2000 Vcm−1 were applied in separations and the separation efficiencies were compared with theoretical values calculated on the basis of plate height theory. The contributions to the total plate height were calculated for injection plug length, diffusion, Joule heating, electromigration dispersion, analyte adsorption to the capillary wall, and detector slit aperture length. Analyte diffusion coefficients were measured by Taylor dispersion method, while distribution constants were measured chromatographically. Agreement between the calculated and empirical results was fairly good even though some approximations were required. In most cases the longitudinal diffusion contribution governed the total plate height, while the contribution of Joule heating was insignificant even at exceptionally high field strengths used. The relatively long detection slit aperture was found to influence the separation efficiency strongly, while the other dispersion sources that were investigated were of minor importance, except for adsorption in the case of one analyte. With all analytes, the dispersive effect of longitudinal diffusion was reduced as the field strength was increased, leading to enhanced migration velocities and faster separations.
Microemulsion electrokinetic chromatography for the analysis of green tea catechins: Effect of the cosurfactant on the separation selectivity
Authors: Pomponio Romeo , Gotti Roberto , Luppi Barbara , Cavrini Vanni
Published: May 2003

Microemulsion electrokinetic chromatography (MEEKC) was applied to the separation of six catechins and caffeine, the major constituents of the green tea. The developed methods involved the use of sodium dodecyl sulfate (SDS) as surfactant, n‐heptane as organic solvent and an alcohol as cosurfactant. The separations were performed under acidic conditions (pH 2.5 phosphate buffer, 50 mM) to ensure good stability of the catechins, with reversed polarity (anodic outlet). The effect of the alcohol nature on the MEEKC selectivity was evaluated; nine alcohols were used as cosurfactant: 1‐butanol, tert‐butanol, 1‐pentanol, 2‐pentanol, 3‐pentanol, cyclopentanol, 1‐hexanol, 2‐hexanol, and cyclohexanol. The migration order of (+)‐catechin (C), (−)‐epicatechin (EC), (−)‐epigallocatechin (EGC), (−)‐gallocatechin (GC), (−)‐epigallocatechin gallate (EGCG), (−)‐epicatechin gallate (ECG), caffeine and theophylline was significantly affected by the alcohol used as cosurfactant. Using nine microemulsions, four different selectivities were achieved: A (cyclohexanol); B (2‐pentanol, 3‐pentanol, 1‐hexanol, 2‐hexanol); C (1‐butanol, 1‐pentanol, cyclopentanol); D (tert‐butanol). MEEKC methods, based on 2‐hexanol and cyclohexanol as cosurfactant were validated and successfully applied to the analysis of catechins and caffeine in commercial green tea products.
Effect of diluting agent on sensitivity in capillary electrophoresis with amperometric detection
Authors: Wang Qingjiang , Ding Fei , Li Hui , He Pingang , Fang Yuzhi
Published: May 2003

Besides the running buffer, pH of buffer, separation voltage and sampling time, the diluting agent was studied in this paper as one of the important factors influencing the sensitivity in capillary electrophoresis (CE) with amperometric detection (AD) when electrokinectic sampling was used. Clonidine hydrochloride, hydrochlorothiazide and rutin, which are positively charged, neutral and negatively charged, respectively, in aqueous solutions, could be perfectly separated by CE with 25 mmol·L−1 Na2B4O7 ‐ 50 mmol·L−1 NaH2PO4 as running buffer and detected by measuring their current responses with AD. Before CE running, some kinds of diluents including water, methanol, formamide, running buffer, hydrochloric acid and sodium hydroxide were, respectively, applied to dilute the stock solutions of above three analytes and their effects on the sensitivity of CE‐AD were investigated. The results showed that for electrokinetic injection, the current responses of these three analytes were greatly affected in different ways when different diluting agents were used. This method was applied to simultaneously determine the active ingredients in one Chinese compound hypotensor named Zhen Ju Jiang Ya Pian, in which the contents of clonidine hydrochloride, hydrochlorothiazide and rutin is very different as 0.03 mg : 5 mg : 20 mg per tablet, and satisfactory results were obtained by adjusting their sensitivity by selecting the suitable diluting agent.
Method development for the analysis of trans‐fatty acids in hydrogenated oils by capillary electrophoresis
Authors: de Oliveira Marcone A. L. , Solis Victor E. S. , Gioielli Luiz A. , Polakiewicz Bronislaw , Tavares Marina F. M.
Published: May 2003

A novel capillary electrophoresis methodology using UV indirect detection (224 nm) for the analysis of trans‐fatty acids in hydrogenated oils was proposed. The electrolyte consisted of a pH 7 phosphate buffer at 15 mmol·L−1 concentration containing 4 mmol·L−1 sodium dodecylbenzenesulfonate, 10 mmol·L−1 polyoxyethylene 23 lauryl ether (Brij 35), 2% 1‐octanol and 45% acetonitrile. Under the optimized conditions, ten fatty acids, C12:0, C13:0 (internal standard), C14:0, C16:0, C18:0, C18:1c, C18:1t, C18:2cc, C18:2tt and C18:3ccc were baseline‐separated in less than 12 min. The proposed methodology was applied to monitor the formation of trans‐fatty acids during hydrogenation of Brazilnut oil. A crude oil sample (42.1% linoleic acid, 37.3% oleic acid, 13.4% palmitic acid, and 7.0% stearic acid) was mixed with 0.25% of a nickel‐based catalyst and submitted to two independent hydrogenation conditions: 175°C, 3 atm, 545 rpm for 60 min (GH1 sample), and 150°C, 1 atm, 545 rpm for 30 min (GH2 sample). For the most severe hydrogenation condition (higher temperature and pressure, under longer reactional period), a more complete conversion of linoleic and oleic acids into stearic acid occurred with concomitant formation of the trans‐species, elaidic acid (C18:1t). For the milder hydrogenation procedure that generated sample GH2, larger amounts of linoleic and oleic acids remained, in addition to the transformations already observed in the GH1 sample.
Electrophoretic analysis of quinone anion radicals in acetonitrile solutions using an on‐line radical generator
Authors: Esaka Yukihiro , Okumura Noriko , Uno Bunji , Goto Masashi
Published: May 2003

We have investigated analysis of anion radicals of phenanthrenequinone (PhQ) and anthraquinone (AQ) using acetonitrile‐capillary electrophoresis (CE) under anaerobic conditions. PhQ and AQ have relatively high negative reduction potentials meaning that their anion radicals are re‐oxidized quite readily by the surrounding O2 to disappear during analysis and we failed to detect them with our previous system. In this work, we have developed an on‐line system combining a unique electrolysis cell for generation of the radicals and a CE unit to keep the analysis system free from external O2 molecules and to reduce analysis time remarkably. As a result, electrophoretic detection of the anion radicals of PhQ and AQ has been achieved. Furthermore, we have observed hydrogen‐bonding interaction between the anion radicals and dimethylurea (DMU) using the present system and have indicated a characteristic interaction of the anion radical of PhQ as an ortho‐quinone with DMU.
Effects of organic solvents on sample pretreatment and separation performances in capillary electrophoresis
Authors: Huie Carmen W.
Published: May 2003

A review of recent developments in theoretical as well as application studies concerning the use of organic solvents, either as purely nonaqueous solvents, hydro‐organic mixtures, or a combination of an organic solvent with another organic modifier(s), in the sample matrix and/or separation buffer for effecting sample pretreatment and/or improving separation performances in capillary electrophoresis (CE) is presented. In particular, recent advances made in furthering the basic understanding of selectivity changes that occur in capillary zone electrophoresis due the presence of organic solvents in the separation medium, based on in‐depth studies of fundamental processes, such as acid‐base chemistry, ion‐ion and ion‐solvent interactions, were discussed in detail. The utilization of organic solvents for improving the resolution of highly challenging and important separations, i.e., those involving the separation of positional and optical isomers, was also critically reviewed. Furthermore, a comprehensive survey of the use of organic solvents for on‐line sample pretreatment, e.g., minimizing aggregration and maximizing solubilization of hydrophobic analytes, improving concentration detection sensitivity for analytes via the use of sample stacking, was presented and discussed. Moreover, recent applications involving the use of organic solvents for improving the CE separations of a variety of molecular species with significance in various disciplines, including biological, environmental and pharmaceutical areas, were summarized and tabulated.
The role of organic solvents in the separation of nonionic compounds by capillary electrophoresis
Authors: Fritz James S.
Published: May 2003

Although nonionic compounds can be separated by micellar electrokinetic chromatography (MEKC), application of this technique is restricted by a somewhat limited elution range. Incorporation of organic solvents in the background electrolyte (BGE) greatly extends the scope of MEKC and provides a major variable in optimizing the separation of neutral analytes. This paper provides a systematic review of the principles and scope of the separation of neutral analytes by capillary electrophoresis (CE) in organic‐aqueous solution. The methods surveyed include those that use tetraalkylammonium salts, dioctyl sulfosuccinate, lauryl poly(oxyethylene) sulfate. Polyaromatic hydrocarbon (PAH) compounds can be separated using sodium hexadecyl sulfate in 70% methanol (30% aqueous) to 100% methanol.
Dual stacking of unbuffered saline samples, transient isotachophoresis plus induced pH junction focusing
Authors: Shim Sang‐Hee , Riaz Asif , Choi Kihwan , Chung Doo Soo
Published: May 2003

A dual stacking mechanism based on transient isotachophoresis (TITP) and induced pH junction focusing is demonstrated as a means to increase the concentration sensitivity in capillary electrophoresis of highly saline samples. When stacking was carried out with an unbuffered saline sample of fluorescein between two zones of low mobility background electrolyte at high pH under an electric field of reverse polarity, two transient peaks at both boundaries of the sample zone were observed. One peak at the rear boundary could be inferred as a transient isotachophoretic stacked zone. Through computer simulations of an unbuffered sample with a high concentration of sodium chloride, we showed that the fast moving zones of sodium and chloride ions induced pH changes at both boundaries to satisfy the electroneutrality condition and that the peak at the front boundary was due to the induced pH junction. To verify the pH changes, an indicator, thymol blue, was added to an NaCl solution and the color changes under an electric field were observed. The proposed mechanism was supported by observing the dual stacking procedure for an unbuffered sample of 4‐nitrophenol and measuring additional sensitivity enhancements by dual stacking for ten weakly acidic compounds. For the ten analytes including nucleoside phosphates, every dual stacking of an unbuffered sample exhibited an additional enhancement up to 86% larger than that of usual transient isotachophoresis of the corresponding buffered sample without loss of separation efficiency and reproducibility. Therefore, it would be useful to skip over buffering in sample preparation for TITP, contrary to the general recommendation.
Effects of background electrolyte composition and addition of selectors on separation selectivity in nonaqueous capillary electrophoresis
Authors: Fillet Marianne , Servais Anne‐Catherine , Crommen Jacques
Published: May 2003

This review gives a survey of the approaches employed to obtain, enhance and tune selectivity in nonaqueous capillary electrophoresis (NACE). Recent developments in NACE are described and the effects of background electrolyte composition and addition of selectors on separation selectivity are discussed. The use of one organic solvent, a mixture of several organic solvents or the use of additives to tune separation selectivity in NACE is presented and a list of relevant applications is included.
Comparison of different algorithms to calculate electrophoretic mobility of analytes as a function of binary solvent composition
Authors: Jouyban Abolghasem , Chan Hak‐Kim , Clark Brian John , Kenndler Ernst
Published: May 2003

Ten different mathematical models representing the electrophoretic mobility of analytes in capillary electrophoresis in mixed solvents of different composition have been compared using 32 experimental data sets. The solvents are binary mixtures of water‐methanol, water‐ethanol and methanol‐ethanol, respectively. Mean percentage deviation (MPD), overall MPD (OMPD) and individual percentage deviation (IPD) have been considered as comparison criteria. The results showed that a reorganized solution model, namely the combined nearly ideal binary solvent/Redlich‐Kister equation, is the most accurate model among other similar models concerning both correlation ability and prediction capability.
Salt dependence on vancomycin‐herbicide enantiomer binding: Capillary electrophoresis study and theoretical approach
Authors: André Claire , Guillaume Yves‐Claude
Published: May 2003

In a previous paper, a mathematical model was developed for the estimation of binding constants by capillary electrophoresis (Guillaume and Peyrin, Anal. Chem. 1999, 71, 2046–2052). This model was applied to determinate the binding constant of the guest‐vancomycin complex as well as the degree of complexation nc (percent of complexed guest). In this work, the guest molecule were a series of acid herbicide enantiomers (aryloxypropionic, aryloxyphenoxypropionic, and aminopropionic acid). The effects of the run buffer salt concentration on the herbicide‐vancomycin binding was clearly described by the determination of specific physicochemical parameters as well as thermodynamic data. These results demonstrate that a better understanding of the interactions involved in the guest molecule‐vancomycin binding allows to optimize the enantiomeric separation of this chiral guest molecule.
Influence of solvent on temperature and thermal peak broadening in capillary zone electrophoresis
Authors: Porras Simo P. , Marziali Ettore , Gaš Bohuslav , Kenndler Ernst
Published: May 2003

The present paper deals with the role of the solvent on thermal peak broadening. One main solvent property that determines the magnitude of the temperature gradient due to the generation of Joule heat in capillary zone electrophoresis is the thermal conductivity. As organic solvents have lower thermal conductivity than water (methanol and acetonitrile, e.g., nearly by a factor of 3) it can be hypothesized that the temperature gradient inside the capillary is more pronounced in organic solvents compared to an aqueous solution. On the other hand, the temperature dependence of the ion mobility (which is responsible for the velocity profile and thus for thermal peak broadening) is smaller in organic solvents. To get insight into the thermal effect of the solvent, first the temperature of a solution in a cylindrical tube was calculated utilizing the heat balance equation. It was shown that the two theoretical models most common in the literature (based on the analytical solution or on an assumption of the parabolic temperature profile in the tube, respectively) give the same results. The latter model was chosen for the further calculations, adding a quadratic term to express the electric conductivity as a function of the temperature. The temperature at the inner capillary wall and center as function of the capillary dimensions and the electric power was computed for electrolytes with a given conductivity at 25.0°C with water, methanol, and acetonitrile as solvents. Capillary cooling systems used were circulating liquid cooling, enforced air‐cooling, and natural convection in still air. The mean temperature (averaged over the cross section) resulting from Joule heating was compared with experimentally determined temperatures established upon application of an electric field; the latter temperature was derived from the measurement of the electric conductance of the background electrolyte solution and its (measured) temperature dependence. All investigations were carried out with solutions of the same initial electric conductivity (about 0.5 S·m−1 at 25.0°C). Agreement is found for natural convection conditions, and the deviation between theoretical and experimental results for the forced air and circulated liquid cooling systems can be related to the poorly defined thermal conditions of the capillaries in commercial instrumentation (with a part in a thermostated cassette and a part outside). For given conditions the temperature gradients in the organic solvents exceed largely those in water, independent of the type of cooling. As a consequence, the thermal plate height is significantly larger in organic solvents, at least under conditions where the deviation from the Nernst‐Einstein limiting case is not too high. However, even for the maximum applicable field strengths the thermal plate height contributions are negligible compared to longitudinal diffusion in all solvents.
Separation of (Z)‐ and (E)‐isomers of thioxanthene and dibenz[b,e]oxepin derivatives with calixarenes and resorcinarenes as additives in nonaqueous capillary electrophoresis
Authors: Sokoließ Torsten , Gronau Michael , Menyes Ulf , Roth Ullrich , Jira Thomas
Published: May 2003

Five acidic calix[4]arenes with carboxylic or sulfonic groups at either the upper or lower rim of the cavity and one resorc[4]arene were investigated to separate three thioxanthenes (flupentixol, clopenthixol, chlorprothixene) and a dibenz[b,e]oxepin derivative (doxepin) with cis‐/trans‐isomerism by nonaqueous capillary electrophoresis (NACE). Partial filling of the capillary with the UV‐absorbing selectors led to a low detection limit and an advantageous signal‐to‐noise ratio (S/N). A sufficient electrophoretic mobility of the calixarenes towards the anode was necessary to outweigh the oppositely directed electroosmotic flow (EOF). This depended from the functional groups, the dissociation and the hydrodynamic radius of the cyclophanes. In contrast, the resorcinarene was useable only by addition of sodium dodecyl sulfate (SDS) because only the complex of the two selectors had an anodic apparent electrophoretic mobility. p‐Sulfonyl‐calix[4]arene (ss‐a1) was the most capable selector for all E/Z‐isomers with maximal α‐values ranging from 1.056 for doxepin to 1.224 for chlorprothixene. This was due to the sufficient migration in reversed direction to the EOF even at low pH* values of 3.0. Otherwise, electrostatic as well as hydrophobic interactions with the positively charged isomers seem to contribute to a superior recognition. Increasing the concentration up to 15 mM ss‐a1 and using acidic media (pH* 5.0) led to high separation efficiency. Changing the organic solvent provides a powerful tool to improve selectivity with N,N‐dimethylformamide‐methanol (DMF‐MeOH)‐mixtures for thioxanthenes. Further electrophoretic parameters were optimized, such as the concentration of the electrolytes, the addition of SDS, the kind of electrolytes and the voltage. Distinct differences in selectivities were found between the derivatives with thioxanthene and dibenzo[b,e]oxepin ring system, respectively. Further, the different basic side chain was responsible for the different selectivity at higher pH* values. In contrast, the substitution at position 2 of the thioxanthenes played a secondary role. Based on the studies of single parameters a method for a simultaneous separation of the four pairs of isomers within 13 min was developed.
Capillary electrophoresis of cardiolipin with on‐line dye interaction and spectrophotometric detection
Authors: Qi Lining , Danielson Neil D. , Dai Qiang , Lee Ray M.
Published: May 2003

Cardiolipin is an important phospholipid present in the mitochondrial inner membrane. It plays a key function in mitochondrial respiration by interacting with many enzymes or cofactors related to oxidative phosphorylation complexes. We have determined the concentration of cardiolipin using on‐line 10‐N‐nonyl acridine orange (NAO) dye interaction capillary electrophoresis (CE) and spectrophotometric detection with a sample throughput of 3 min. In addition to the presence of 0.1 mM NAO, the background electrolyte (BGE) composition has been set at 80% methanol‐10% acetonitrile‐10% H2O (all v/v) to provide both good solubility and the maximum absorbance enhancement at 497 nm for the NAO‐cardiolipin complex as compared to NAO alone. Sample consumption for each injection is about 57 nL. A calibration curve is established from 0.5 μM to 0.1 mM with R 2 = 0.9912 with a detection limit of 0.05 μM for cardiolipin. In a blind study, actual mitochondrial cell membrane samples in the μL range before or after UV light exposure were analyzed using the CE method. Cardiolipin concentration decreased in the different parts of the membrane sample upon UV photolysis of the cells. Support for the theory that UV light can induce cardiolipin translocation from the inner membrane (IM) to the outer membrane (OM) was indicated by a significant percentage increase of cardiolipin (as measured by the cardiolipin in the OM as compared to the sum total in the OM and IM) from 30.7 ± 2.4% before UV light photolysis to 38.3 ± 2.2% after UV irradiation.