13 results on '"Wiedmer, Susanne K."'
Search Results
2. Anionic liposomes in capillary electrophoresis: Effect of calcium on 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine / phosphatidylserine-coating in silica capillaries
- Author
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Hautala, Jari T., Wiedmer, Susanne K., and Riekkola, Marja-Liisa
- Published
- 2004
- Full Text
- View/download PDF
3. CE and asymmetrical flow‐field flow fractionation studies of polymer interactions with surfaces and solutes reveal conformation changes of polymers.
- Author
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Witos, Joanna, Karjalainen, Erno, Tenhu, Heikki, and Wiedmer, Susanne K.
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POLYMERIZED ionic liquids ,POLYMER fractionation ,SURFACE interactions ,DIBLOCK copolymers ,POLYMERS ,BLOCK copolymers - Abstract
Amphiphilic diblock copolymers consisting of a hydrophobic core containing a polymerized ionic liquid and an outer shell composed of poly(N‐isoprolylacrylamide) were investigated by capillary electrophoresis and asymmetrical flow‐field flow fractionation. The polymerized ionic liquid comprised poly(2‐(1‐butylimidazolium‐3‐yl)ethyl methacrylate tetrafluoroborate) with a constant block length (n = 24), while the length of the poly(N‐isoprolylacrylamide) block varied (n = 14; 26; 59; 88). Possible adsorption of the block copolymer on the fused silica capillary, due to alterations in the polymeric conformation upon a change in the temperature (25 and 45 °C), was initially studied. For comparison, the effect of temperature on the copolymer conformation/hydrodynamic size was determined with the aid of asymmetrical flow‐field flow fractionation and light scattering. To get more information about the hydrophilic/hydrophobic properties of the synthesized block copolymers, they were used as a pseudostationary phase in electrokinetic chromatography for the separation of some model compounds, that is, benzoates and steroids. Of particular interest was to find out whether a change in the length or concentration of the poly(N‐isoprolylacrylamide) block would affect the separation of the model compounds. Overall, our results show that capillary electrophoresis and asymmetrical flow‐field flow fractionation are suitable methods for characterizing conformational changes of such diblock copolymers. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
4. Novel cationic polyelectrolyte coatings for capillary electrophoresis
- Author
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Dusa, Filip, Witos, Joanna, Karjalainen, Erno, Viitala, Tapani, Tenhu, Heikki, and Wiedmer, Susanne K.
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Capillary electrophoresis ,Polyelectrolytes (cationic ,Coating materials ,Ionic strength ,electrophoresis ,Hydrophobicity ,coating ,cationic ,β-Adrenoceptor antagonists (novel cationic polyelectrolyte coatings for capillary electrophoresis) ,novel cationic polyelectrolyte coatings for capillary electrophoresis) ,Stability ,polyelectrolyte ,capillary - Abstract
The use of bare fused silica capillary in CE can sometimes be inconvenient due to undesirable effects including adsorption of sample or instability of the EOF. This can often be avoided by coating the inner surface of the capillary. In this work, we present and characterize two novel polyelectrolyte coatings (PECs) poly(2-(methacryloyloxy)ethyl trimethylammonium iodide) (PMOTAI) and poly(3-methyl-1-(4-vinylbenzyl)-imidazolium chloride) (PIL-1) for CE. The coated capillaries were studied using a series of aq. buffers of varying pH, ionic strength, and compn. Our results show that the investigated polyelectrolytes are usable as semi-permanent (phys. adsorbed) coatings with at least five runs stability before a short coating regeneration is necessary. Both PECs showed a considerably decreased stability at pH 11.0. The EOF was higher using Good's buffers than with sodium phosphate buffer at the same pH and ionic strength. The thickness of the PEC layers studied by quartz crystal microbalance was 0.83 and 0.52 nm for PMOTAI and PIL-1, resp. The hydrophobicity of the PEC layers was detd. by anal. of a homologous series of alkyl benzoates and expressed as the distribution consts. Our result demonstrates that both PECs had comparable hydrophobicity, which enabled sepn. of compds. with log Po/w > 2. The ability to sep. cationic drugs was shown with β-blockers, compds. often misused in doping. Both coatings were also able to sep. hydrolysis products of the ionic liq. 1,5-diazabicyclo[4.3.0]non-5-ene acetate at highly acidic conditions, where bare fused silica capillaries failed to accomplish the sepn.
- Published
- 2016
5. Potential of liposomes and lipid membranes for the separation of β-blockers by capillary electromigration and liquid chromatographic techniques.
- Author
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Ravald, Henri and Wiedmer, Susanne K.
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LIPOSOMES , *ELECTRODIFFUSION , *MEMBRANE separation , *INTRAVENOUS fat emulsions , *LIQUID chromatography , *CAPILLARIES - Abstract
• Capillary electromigration techniques relevant for lipid membrane/β-blocker studies. • Unilamellar vesicles are preferred in liposome electrokinetic chromatography. • New stationary phases for immobilized artificial chromatography are needed. • PC is the most common phospholipid in lipid membrane/β-blocker interaction studies. • Propranolol has been the most studied β-blockers in lipid membrane studies. β-Blockers belong to a frequently used class of drugs primarily used to treat heart and circulatory conditions. Here we describe the use of lipid vesicles and liposomes as cell membrane biomimicking models in capillary electromigration (CE) and liquid chromatography (LC) techniques for the investigation of interactions between lipid membranes and β-blockers. In addition to liposomes, the use of commercial intravenous lipid emulsions, and their interactions with β-blockers are also discussed. Different CE and LC instrumental techniques designed for these purposes are introduced. Other methodologies for studying interactions between β-blockers and lipid membranes are also briefly discussed, and the different methodologies are compared. The aim is to give the reader a good overview on the status of the use of liposomes and lipids in CE and LC for studying β-blocker interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
6. Stabilization of phosphatidylcholine coatings in capillary electrophoresis by increase in membrane rigidity
- Author
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Lindén, Maria V., Wiedmer, Susanne K., Hakala, R.M. Susanna, and Riekkola, Marja-Liisa
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LECITHIN , *PHOSPHOLIPIDS , *ELECTROPHORESIS , *ELECTROCHEMISTRY - Abstract
Divalent cations affect the stability and structure of phospholipid vesicles and also the binding and immobilization of proteins into phospholipid membranes. The effect of calcium, magnesium, and zinc on zwitterionic phosphatidylcholine (PC) coatings in fused silica capillaries for electrophoresis was the primary interest in this work. In addition, the effect of temperature on the coating stability was investigated by coating 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes at temperatures above and below the gel- to fluid-state transition. All coatings were performed with PC large unilamellar vesicles (LUV) in 40mM N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid) (HEPES) at pH 7.4 as basic solution. HEPES (40mM) at pH 7.4 was used as background electrolyte (BGE) throughout the study. The stability of the coating was studied by measuring the electroosmotic flow. A molar ratio of 1:3PC/Ca2+ or PC/Mg2+ gave the best coating stability owing to the increased rigidity of the phospholipid membrane furnished by the divalent metal ions. Better results were obtained with DPPC in the more rigid gel state than in the fluid state: the electroosmotic flow was much suppressed and the PC coating was stabilized. Coating the fused silica capillary with PC liposome–metal ion buffer solutions resulted in good electrophoretic separation of basic model proteins (pI-values 7.8–11.0). The electrophoretic results demonstrate the importance of stabilizing the phospholipid coating on fused silica capillaries, either by the addition of divalent metal ions (Ca2+, Mg2+, or Zn2+) or by working in the gel-state region of the phospholipid. [Copyright &y& Elsevier]
- Published
- 2004
- Full Text
- View/download PDF
7. Potential of capillary electrophoresis with micelles or chiral additives as a purity control method in pharamaceutical industry.
- Author
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Riekkola, Marja-Liisa and Wiedmer, Susanne K.
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CAPILLARY electrophoresis ,CHIRAL drugs ,MICELLES ,PHARMACEUTICAL industry ,HIGH performance liquid chromatography ,QUALITY control - Abstract
Offers a look at the potential of capillary electrophoresis (CE) with micelles or chiral selectors for the determination of drug related impurities. Advantages of CE over high performance liquid chromatography; Determination of chiral reagent purity; Application of CE in the purity quality control of pharmaceuticals.
- Published
- 1997
8. Anionic phospholipid coatings in capillary electrochromatography: Binding of Ca2+ to phospholipid phosphate group
- Author
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Hautala, Jari T., Riekkola, Marja-Liisa, and Wiedmer, Susanne K.
- Subjects
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PHOSPHOLIPIDS , *SURFACE coatings , *CAPILLARY electrophoresis , *LIPOSOMES - Abstract
Abstract: Anionic phospholipids phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidylinositol (PI), and phosphatidylserine (PS) were examined for their effect on 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine (POPC)-containing liposomes used as coating material in capillary electrochromatography. Liposome solvent was N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid) (HEPES) buffer at pH 7.4 with and without 3mM of CaCl2. The background electrolyte solution was HEPES buffer at pH 7.4. The net charge, size, and short-term stability of the liposomes were measured with a Zetasizer. Results showed that calcium interacts with all liposomes but most strongly with POPC/PA. The relative migration times, retention factors, and resolution of the model analytes (one cationic, three uncharged ions, and one anionic) were studied. All liposomes successfully coated the silica capillary. Without calcium the strongest interaction and best separation of the analytes were with the POPC/PI and POPC/PS coatings, while interactions with the POPC/PA coating were weak. Calcium enhanced the interactions of the model analytes with all coatings, and the interactions were then strongest with the POPC/PA coating. In the presence of calcium there appears to be a slight reorganization of the coating with increasing number of runs. Our results indicate strong interactions between calcium and the phosphate groups in phospholipids and demonstrate the significant role of the phospholipid polar head group in phospholipid coatings on silica surfaces. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
9. Small diamines as modifiers for phosphatidylcholine/phosphatidylserine coatings in capillary electrochromatography
- Author
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Varjo, Sami J.O., Hautala, Jari T., Wiedmer, Susanne K., and Riekkola, Marja-Liisa
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LECITHIN , *SILICON compounds , *BUFFER solutions , *PHOSPHOLIPIDS - Abstract
Abstract: Greater stability of liposome coatings and improved resolution of model steroids in capillary electrochromatography (CEC) were sought by adding small diamines (ethylenediamine, diaminopropane, bis-tris-propane, or N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid, HEPES)) to the liposome solution before coating of fused silica capillaries. The phospholipid coatings consisted of 1mM of 8:2mol% phosphatidylcholine (PC)/phosphatidylserine (PS) and 5mM of modifier in buffer solutions (acetate, phosphate, or Tris) at pH 4.0–7.4. The coating was based on a published procedure, and five steroids were used as neutral model analytes in evaluation of the coating. The results showed that under optimal conditions, the small linear diamines increased the packing density of anionic phospholipids, leading to improved separations. In addition, the choice of buffer for the liposome coating and separation appeared to influence the performance of the coatings. While buffers with amino groups take part in the phospholipid bilayer formation, buffers like phosphate may even have negative effect on coating formation. The factors affecting phospholipid coatings with diamines as modifiers are clarified. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
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10. Effect of ionic liquids on the interaction between liposomes and common wastewater pollutants investigated by capillary electrophoresis.
- Author
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Ruokonen, Suvi-Katriina, Duša, Filip, Lokajová, Jana, Kilpeläinen, Ilkka, King, Alistair W.T., and Wiedmer, Susanne K.
- Subjects
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IONIC liquids , *LIPOSOMES , *SEWAGE , *WATER pollution , *CAPILLARY electrophoresis , *PHOSPHONIUM compounds , *IMIDAZOLES - Abstract
The effect of three phosphonium and imidazolium ionic liquids (ILs) on the interaction between liposomes and common pharmaceuticals found in wastewaters was studied. The liposomes comprised zwitterionic phosphatidyl choline and negatively charged phosphatidyl glycerol. A set of common cationic, anionic, and neutral compounds with varying chemical composition and unique structures were included in the study. The electrophoretic mobilities of the analytes were determined using conventional capillary electrophoresis (CE), using CE under reversed electroosmotic flow mobility conditions, and in the presence of ILs in the background electrolyte (BGE) solution by electrokinetic chromatography (EKC). In order to evaluate the impact of ILs on the interaction between the compounds and the liposomes, EKC was performed with liposome dispersions, with and without ILs. The retention factors of the compounds were calculated using BGEs including liposome dispersions with and without ILs. Two phosphonium based ILs, namely tributyl(tetradecyl)phosphonium chloride ([P 14444 ]Cl) and octyltributylphosphonium chloride ([P 8444 ]Cl), were chosen due to their long alkyl chains and their low aggregation concentrations. Another IL, i.e. 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), was chosen based on our previous study, which suggests that it has a minimal or even nonexistent effect on liposomes at the used concentrations. The results indicate that the studied ILs have an effect on the interactions between wastewater compounds and liposomes, but the effect is highly dependent on the concentration of the IL and on the IL alkyl chain lengths. Most of the ILs hindered the interactions between the liposomes and the compounds, indicating strong interaction between ILs and liposomes. In addition, the nature of the studied compounds themselves affected the interactions. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
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11. Antibiotic fusidic acid has strong interactions with negatively charged lipid membranes: An electrokinetic capillary chromatographic study
- Author
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Helle, Anne, Mäkitalo, Johanna, Huhtanen, Jarkko, Holopainen, Juha M., and Wiedmer, Susanne K.
- Subjects
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CAPILLARY electrophoresis , *ATYPICAL mycobacteria , *BILAYER lipid membranes , *PHASE partition - Abstract
Abstract: Fusidic acid (FA), a narrow spectrum steroidal antibiotic, is useful for treatment of most skin, conjunctival, and corneal infections and also in infections caused by atypical microbes in the surface of the eye. Liposome electrokinetic capillary chromatography (LEKC) was used to study the interactions between FA and lipid membranes. Liposomes prepared by extrusion were composed of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleyl-sn-glysero-3-phosphor-l-serine (POPS), cholesterol, FA, and sphingomyelin (SM) in various molar ratios. 26 different liposome dispersions were studied as dispersed (pseudostationary) phase in LEKC. The hydrophobicities of the liposomes were evaluated by calculating the retention factors of model neutral steroids. The retention factors were calculated using the EOF and the effective electrophoretic mobilities of the analytes and the liposomes. The latter were separately determined by capillary electrophoresis with a polyacrylamide (PAA)-coated capillary. FA–lipid membrane interactions were studied by determining the retention factor of FA. In addition, liposomes prepared from lipids extracted from Escherichia coli bacterium were studied and used as dispersed phase in LEKC for interaction studies between FA and lipid membranes. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
12. Quantitative determination of drug encapsulation in poly(lactic acid) nanoparticles by capillary electrophoresis
- Author
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Helle, Anne, Hirsjärvi, Samuli, Peltonen, Leena, Hirvonen, Jouni, and Wiedmer, Susanne K.
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BECLOMETHASONE dipropionate , *BRONCHODILATOR agents , *SYNTHETIC drugs , *SPECTRUM analysis - Abstract
Abstract: Capillary electrophoretic (CE) methods were used for the quantitative determination of model drugs [salbutamol sulphate (SS), sodium cromoglycate (SCG) and beclomethasone dipropionate (BDP)] in poly(d,l-lactic acid) (PLA) nanoparticles, which were prepared by the nanoprecipitation method. Zeta potential and size distribution of the nanoparticles were determined by electrophoretic mobility determinations and photon correlation spectroscopy, respectively. Interactions between the drugs, the PLA nanoparticles and the fused-silica capillary were investigated by electrokinetic capillary chromatography (EKC). A quantitative CE method was developed for salbutamol sulphate and sodium cromoglycate, and the linearity and repeatability of migration times, peak areas and peak heights were determined. Microemulsion electrokinetic chromatography was used for the quantitative determination of beclomethasone dipropionate. According to this study, the applied electromigration techniques were suitable for the interaction, drug entrapment and dissolution studies of pharmaceutical nanoparticles. The results suggest that even quantitation of the drug located inside the nanoparticles was possible. Encapsulation of the more hydrophilic model drugs (SS, SCG) in the PLA nanoparticles was less efficient than in the case of BDP. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
- View/download PDF
13. Stability of phospholipid vesicles studied by asymmetrical flow field-flow fractionation and capillary electrophoresis
- Author
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Yohannes, Gebrenegus, Pystynen, Kati-Henna, Riekkola, Marja-Liisa, and Wiedmer, Susanne K.
- Subjects
- *
PHOSPHOLIPIDS , *GEL electrophoresis , *ISOPENTENOIDS , *LOW-cholesterol diet - Abstract
Abstract: The stability of zwitterionic phosphatidylcholine vesicles in the presence of 20mol% phosphatidyl serine (PS), phosphatidic acid (PA), phosphatidyl inositol (PI), and diacylphosphatidyl glycerol (PG) phospholipid vesicles, and cholesterol or calcium chloride was investigated by asymmetrical flow field-flow fractionation (AsFlFFF). Large unilamellar vesicles (LUV, diameter 100nm) prepared by extrusion at 25°C were used. Phospholipid vesicles (liposomes) were stored at +4 and −18°C over an extended period of time. Extruded egg yolk phosphatidylcholine (EPC) particle diameters at peak maximum and mean measured by AsFlFFF were 101±3nm and 122±5nm, respectively. No significant change in diameter was observed after storage at +4°C for about 5 months. When the storage period was extended to about 8 months (250 days) larger destabilized aggregates were formed (172 and 215nm at peak maximum and mean diameters, respectively). When EPC was stored at −18°C, large particles with diameters of 700–800nm were formed as a result of dehydration, aggregation, and fusion processes. In the presence of calcium chloride, EPC alone did not form large aggregates. Addition of 20mol% of negatively charged phospholipids (PS, PA, PI, or PG) to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) vesicles increased the electrostatic interactions between calcium ion and the vesicles and large aggregates were formed. In the presence of cholesterol, large aggregates of about 250–350nm appeared during storage at +4 and −18°C for more than 1 day. The effect of liposome storage temperature on phospholipid coatings applied in capillary electrophoresis (CE) was studied by measuring the electroosmotic flow (EOF). EPC coatings with and without cholesterol, PS, or calcium chloride, prepared from liposomes stored at +25, +4, and −18°C, were studied at 25°C. The performances of the coatings were further evaluated with three uncharged compounds. Only minor differences were observed between the same phospholipid coatings, showing that phospholipid coatings in CE are relatively insensitive to storage at +25, +4°C or −18°C. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
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