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•liposome electrokinetic capillary chromatography (LEKC) is reviewed over the last 15 years.•liposomes, lipid aggregates, lipid emulsions, and disks are used as pseudostationary phases.•LEKC is employed for the separation of a variety of different compounds.•LEKC is used for determining lipid membrane-water distribution constants.•LEKC is particularly applied to biomedical applications.

Ionic liquids have the potential to be used for extracting valuable chemicals from raw materials. These processes often involve water, and after extraction, the water or other chemicals must be removed from the ionic liquid, so it can be reused. To help in designing such processes, we present data on the vapor–liquid equilibrium of the system containing protic ionic liquid 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate, water, acetic acid, and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene. Earlier studies have only focused on mixtures of water and an ionic liquid with a stoichiometric ratio of the ions. Here, we also investigated mixtures containing an excess of the acid or base component because in real systems with protic ionic liquids, the amount of acid and base in the mixture can vary. We modeled the data using both the ePC-SAFT and NRTL models, and we compared the performance of different modeling strategies. We also experimentally determined the vapor composition for a few of the samples, but none of the modeling strategies tested could accurately predict the concentration of the acid and base components in the vapor phase.

The aim of this study was to assess what properties of the pseudostationary phases in electrokinetic capillary chromatography affect the interactions between monomethyl auristatin E (MMAE) and hydrophilically modified structural analogues thereof with various lipophilic phases. MMAE is a widely used cytotoxic agent in antibody–drug conjugates (ADC), which are used as selective biopharmaceutical drugs in the treatment of cancers. MMAE and its derivatives are highly lipophilic, yet they fail to interact with biomimicking phosphatidylcholine–phosphatidylserine liposomes. To reveal what properties affect the interaction of the auristatin derivatives with cell plasma membrane-mimicking vesicles, capillary electrokinetic chromatography was used with four different types of micellar and vesicular pseudostationary phases: pure vesicles, mixed vesicles, mixed micelles, and pure micelles. Vesicular phases were composed of pure phospholipids [dimyristoylphosphatidylcholine (DMPC) and dilauroylphosphatidylcholine (DLPC)] and phospholipid–surfactant mixtures [sodium dodecyl sulfate, (SDS) with DMPC and DLPC] while the micellar phases comprised pure surfactant (SDS) and surfactant–phospholipid mixtures (SDS–DMPC and SDS–DLPC). In addition, differential scanning calorimetry and dynamic light scattering were used to monitor the aggregate composition. Our data shows that the interaction between hydrophobic auristatin derivatives and hydrophobic pseudostationary phases critically depends on the type, size, and hydrogen bonding capability of the pseudostationary phases.

Lipidomics is an emerging field of science not only due to its integral part of cell biology and biophysics but also due to the key role of lipids in the modulation of membrane physical properties, signaling, and cell death regulation. The aim of this study was to characterize changes in N‐palmitoyl ceramide concentration and in the global lipid profile in macrophages challenged by oxidized low‐density lipoprotein and nutrient deprived hepatocytes. For this purpose, a quantitative targeted method based on gas chromatography‐mass spectrometry for the determination of total N‐palmitoyl ceramide concentrations in the cellular membranes of cells under stress was used. Ultrahigh‐performance liquid chromatography‐quadrupole‐time of flight mass spectrometry was applied for the comprehensive profiling of lipids. In essence, we found that both models of cellular stress caused an increase in N‐palmitoyl ceramide levels. In addition, increased levels of other ceramides were observed as well as up‐ and down‐regulation of several other lipid species.

The tear fluid protects the corneal epithelium from drying out as well as from invasion by pathogens. It also provides cell nutrients. Similarly to lung surfactant, it is composed of an aqueous phase covered by a lipid layer. Here we describe the molecular organization of the anterior lipid layer of the tear film. Artificial tear fluid lipid layers (ATFLLs) composed of egg yolk phosphatidylcholine (60 mol %), free fatty acids (20 mol %), cholesteryl oleate (10 mol %), and triglycerides (10 mol %) were deposited on the air-water interface and their physico-chemical behavior was compared to egg-yolk phosphatidylcholine monolayers by using Langmuir-film balance techniques, x-ray diffraction, and imaging techniques as well as in silico molecular level simulations. At low surface pressures, ATFLLs were organized at the air-water interface as heterogeneous monomolecular films. Upon compression the ATFLLs collapsed toward the air phase and formed hemispherelike lipid aggregates. This transition was reversible upon relaxation. These results were confirmed by molecular-level simulations of ATFLL, which further provided molecular-scale insight into the molecular distributions inside and dynamics of the tear film. Similar type of behavior is observed in lung surfactant but the folding takes place toward the aqueous phase. The results provide novel information of the function of lipids in the tear fluid.

The intraocular lens contains high levels of both cholesterol and sphingolipids, which are believed to be functionally important for normal lens physiology. The aim of this study was to explore the spatial distribution of sphingolipids in the ocular lens using mass spectrometry imaging (MSI). Matrix-assisted laser desorption/ionization (MALDI) imaging with ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to visualize the lipid spatial distribution. Equatorially-cryosectioned, 12 μm thick slices of tissue were thaw-mounted to an indium-tin oxide (ITO) glass slide by soft-landing to an ethanol layer. This procedure maintained the tissue integrity. After the automated MALDI matrix deposition, the entire lens section was examined by MALDI MSI in a 150 μm raster. We obtained spatial- and concentration-dependent distributions of seven lens sphingomyelins (SM) and two ceramide-1-phosphates (CerP), which are important lipid second messengers. Glycosylated sphingolipids or sphingolipid breakdown products were not observed. Owing to ultra high resolution MS, all lipids were identified with high confidence, and distinct distribution patterns for each of them are presented. The distribution patterns of SMs provide an understanding of the physiological functioning of these lipids in clear lenses and offer a novel pathophysiological means for understanding diseases of the lens.

The intraocular lens contains high levels of both cholesterol and sphingolipids, which are believed to be functionally important for normal lens physiology. The aim of this study was to explore the spatial distribution of sphingolipids in the ocular lens using mass spectrometry imaging (MSI). Matrix-assisted laser desorption/ionization (MALDI) imaging with ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to visualize the lipid spatial distribution. Equatorially-cryosectioned, 12 µm thick slices of tissue were thaw-mounted to an indium-tin oxide (ITO) glass slide by soft-landing to an ethanol layer. This procedure maintained the tissue integrity. After the automated MALDI matrix deposition, the entire lens section was examined by MALDI MSI in a 150 µm raster. We obtained spatial- and concentration-dependent distributions of seven lens sphingomyelins (SM) and two ceramide-1-phosphates (CerP), which are important lipid second messengers. Glycosylated sphingolipids or sphingolipid breakdown products were not observed. Owing to ultra high resolution MS, all lipids were identified with high confidence, and distinct distribution patterns for each of them are presented. The distribution patterns of SMs provide an understanding of the physiological functioning of these lipids in clear lenses and offer a novel pathophysiological means for understanding diseases of the lens.

EKC and its sub‐techniques, such as MEKC and microemulsion EKC, have attracted wide interest in recent years. Investigations on this topic have covered several analytical applications, but attention has also been paid more and more to basic studies. This review provides an overview of the different approaches to calculating retention factors, which express the ratio of the amount of sample component in the pseudostationary and mobile phases. Special attention is given to the selection of markers for the determination of the electrophoretic mobility or migration time of a marker describing the behavior of the pseudostationary phase in EKC. Introduction of a hydrophobic marker is by far the most common approach, but the use of a homologous series of compounds is also quite popular. In addition, other possible approaches found in the literature will be described.

Nonylphenol ethoxylates (NPEOx) are surfactants which are used worldwide and can be transformed in the environment by microorganisms to form nonylphenol (NP). Analysis of these compounds was carried out with micellar electrokinetic capillary chromatography (MEKC). Different parameters such as background electrolyte (BGE) solution, pH, type of surfactant, and sample stacking were optimized. The use of CHES (20 mM, pH 9.1) in combination with 50 mM sodium cholate as a surfactant as BGE solution, together with sample stacking using 50 mM NaCl in the sample and an injection time of 20 s, provided the best separation of the compounds studied. The method was applied to the determination of target analytes in two types of sludge water coming from two steps of a wastewater treatment plant. Liquid–liquid extraction was carried out using toluene as solvent, resulting in recoveries around 100% for all studied analytes. The presence of NPEOxwas observed in the first step of the sludge water treatment, based on migration time and UV spectra. Identification was confirmed using tandem MS. LOQs of the studied compounds were in the range of 12.7 to 30.8 ng/mL, which is satisfactory for the analysis of real wastewater samples.

Sphingolipids are key lipid regulators of cell viability: ceramide is one of the key molecules in inducing programmed cell death (apoptosis), whereas other sphingolipids, such as ceramide 1-phosphate, are mitogenic. The thermotropic and structural behavior of binary systems of N-hexadecanoyl-D-erythro-ceramide (C16-ceramide) or N-hexadecanoyl-D-erythro-ceramide-1-phosphate (C16-ceramide-1-phosphate; C16-C1P) with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was studied with DSC and deuterium nuclear magnetic resonance (2H-NMR). Partial-phase diagrams (up to a mole fraction of sphingolipids X= 0.40) for both mixtures were constructed based on DSC and 2H-NMR observations. For C16-ceramide-containing bilayers DSC heating scans showed already at Xcer= 0.025 a complex structure of the main-phase transition peak suggestive of lateral-phase separation. The transition width increased significantly upon increasing Xcer, and the upper-phase boundary temperature of the mixture shifted to ∼65°C at Xcer= 0.40. The temperature range over which 2H-NMR spectra of C16-ceramide/DPPC-d62mixtures displayed coexistence of gel and liquid crystalline domains increased from ∼10° for Xcer= 0.1 to ∼21° for Xcer= 0.4. For C16-C1P/DPPC mixtures, DSC and 2H-NMR observations indicated that two-phase coexistence was limited to significantly narrower temperature ranges for corresponding C1P concentrations. To complement these findings, C16-ceramide/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and C16-C1P/POPC mixtures were also studied by 2H-NMR and fluorescence techniques. These observations indicate that DPPC and POPC bilayers are significantly less perturbed by C16-C1P than by C16-ceramide and that C16-C1P is miscible within DPPC bilayers at least up to XC1P= 0.30.

•Potential of capillary electromigration techniques for biointeraction studies are introduced•Basic principles of relevant CE techniques for interaction studies are described•Experimental bimolecular interaction approaches are enlighted•Affinity constants for some selective important interactions are given

Interactions between low‐molar mass analytes and phospholipid membranes were studied by liposome electrokinetic capillary chromatography (LEKC). The analytes were pesticides, some degradation products, and compounds associated with the manufacture of pesticides. Negatively charged liposome dispersions with different zwitterionic lipids (PC) were applied to the determination of retention factors (k) of 15 charged and uncharged compounds. The liposome dispersions consisted of 80:20 mol% of 1,2‐dilauroyl‐sn‐glycero‐3‐phosphocholine (DLPC)/1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phospho‐L‐serine (POPS), 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine (DMPC)/POPS, and 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC)/POPS. Retention factors were calculated from the effective electrophoretic mobilities of the analytes under LEKC and CZE conditions and from the effective electrophoretic mobilities of the liposomes, determined by CZE with a polyacrylamide‐coated capillary. Determining the liposome mobilities in this way proved to be a good alternative to the conventional method employing a liposome marker compound. The log k values of the analytes for the different liposome dispersed phases were correlated with one another. In addition, correlation curves were determined between log kand calculated octanol–water partition coefficients. The results showed that the zwitterionic phospholipid in the liposome has a major impact on the interactions between the tested compounds and the lipid membranes.

We have studied the effects of cholesterol and steroid-based antibiotic fusidic acid (FA) on the behavior of lipid bilayers using a variety of experimental techniques together with atomic-scale molecular dynamics simulations. Capillary electrophoretic measurements showed that FA was incorporated into fluid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes. Differential scanning calorimetry in turn showed that FA only slightly altered the thermodynamic properties of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers, whereas cholesterol abolished all endotherms when the mole fraction of cholesterol (Xchol) was 0.20. Fluorescence spectroscopy was then used to further characterize the influence of these two steroids on DPPC large unilamellar vesicles. In the case of FA, our result strongly suggested that FA was organized into lateral microdomains with increased water penetration into the membrane. For cholesterol/DPPC mixtures, fluorescence spectroscopy results were compatible with the formation of the liquid-ordered phase. A comparison of FA and cholesterol-induced effects on DPPC bilayers through atomistic molecular dynamics simulations showed that both FA and cholesterol tend to order neighboring lipid chains. However, the ordering effect of FA was slightly weaker than that of cholesterol, and especially for deprotonated FA the difference was significant. Summarizing, our results show that FA is readily incorporated into the lipid bilayer where it is likely to be enriched into lateral microdomains. These domains could facilitate the association of elongation factor-G into lipid rafts in living bacteria, enhancing markedly the antibiotic efficacy of FA.

Unilamellar liposomes were investigated by capillary electrophoresis, light scattering, and monolayer penetration techniques. Zwitterionic liposomes with and without cholesterol were compared and the effects of pH (7.40 and 8.25) and buffer (various sulfonic acid buffers, Tricine, and phosphate) on the electrophoretic mobilities and sizes of the liposomes were studied. Anionic liposomes containing phosphatidylserine with and without various amounts of cholesterol were used as dispersed phase in electrokinetic capillary chromatography in the separation of six steroidal hormones, with a focus on selectivity differences with increasing amounts of cholesterol in the liposomes. The results were confirmed by monolayer penetration measurements.

An efficient and fast method was developed for the determination of phenols in pyrolysis oils. Microporous membrane liquid‐liquid extraction (MMLLE) was applied in sample pretreatment and samples were analyzed by multidimensional liquid chromatography. The pyrolysis oil was dissolved in a suitable organic solvent and then continuously pumped through the donor side of the MMLLE system. The acceptor solution was a highly basic aqueous solution, which was kept stagnant during the extraction. The extract was transferred via a loop to the multidimensional LC system. Capillary electrophoresis was investigated for qualitative analysis of the extract. After separation, the phenols were identified by diode array detection and mass spectrometry. The method was quantitative, repeatable and linear, and limits of detection were in the range of 0.01–0.12%w/w.

The preparation and catalytic potential of a camphor derivative, 1,7,7-trimethyl-3-(pyrid-2-ylmethyl)bicyclo- [2.2.1]heptan-2-ol, were investigated. The potential of this novel camphor-based 4-amino alcohol to control the addition of organozincs to aldehydes was of particular interest. Several spectroscopic and analytical methods were applied, and major focus was placed on the data obtained by capillary electrophoresis and capillary electrophoresis-electrospray ionization-mass spectrometry; the latter proved to be a fast, reliable and applicable tool in the study of these novel organic synthesis products. The new 4-amino alcohol, 1,7,7-trimethyl-3-(pyrid-2-ylmethyl)bicyclo[2.2.1]heptan-2-ol, was shown to work well as a catalyst in the enantioselective addition of diethylzinc to benzaldehyde.

The applicability of a polyelectrolyte, Elvacite 2669, as a pseudostationary phase in capillary electrokinetic chromatography for the separation of some neutral hydrophobic compounds was investigated. In addition, its behavior in buffer solutions for capillary electrophoretic separations was studied by dynamic light scattering. With the polymer concentration held constant and the methanol–water ratio varied, study was made of the viscosity, the migration times of some neutral hydrophobic compounds, and the light scattering properties of the buffers. The effect of varying the polymer concentration on the separation of the compounds was also investigated. All studies were made under basic conditions. Data on the aggregation behavior, including the size and aggregation number of the polyelectrolyte under different conditions, are given and the capillary electrophoretic results are interpreted in terms of the dynamic light scattering data. In addition, the interaction of Elvacite 2669 with the fused silica wall was investigated, and the results showed that polymer adsorption onto the capillary wall occurred at polymer concentrations at and above 0.5 wt%. Both the capillary electrophoretic and dynamic light scattering results showed the behavior of Elvacite 2669 to be highly dependent on the methanol–water ratio in the buffer. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 557–565, 1998