References of "Crommen, Jacques"
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See detailUnusual Amino Acids and Monofluoroacetate from Dichapetalum michelsonii (Umutambasha), a Toxic Plant from Rwanda
Esters, Virginie ULg; Karangwa, Charles; Tits, Monique ULg et al

in Planta Medica (2013), 79

In the course of our investigations on Umutambasha in order to identify its convulsant principles, small quantities of monofluoroacetate were observed in stem bark, leaves, and fruits of this plant newly ... [more ▼]

In the course of our investigations on Umutambasha in order to identify its convulsant principles, small quantities of monofluoroacetate were observed in stem bark, leaves, and fruits of this plant newly identified as Dichapetalum michelsonii Hauman. Conclusive evidence for a monofluoroacetate presence came from its isolation from the freeze-dried extract of stem bark. Three free unusual amino acids, named N-methyl-α-alanine, N-methyl-β-alanine, and 2,7-diaminooctan-1,8-dioic acid, described for the first time in a plant, and known trigonelline were also isolated from the stem bark of D. michelsonii. Structure elucidations were mainly achieved by spectroscopic methods (1H-NMR, 2D-NMR, MS) and by comparison with authentic references. These unusual amino acids were detected by a fast, reliable TLC analysis in all our batches of Umutambasha, suggesting that they could be used for identification purposes in case of human or livestock intoxications. Finally, EEG recordings and behavioural observations performed in mice suggested that the convulsive patterns produced by Umutambasha are the consequence of monofluoroacetate presence in D. michelsonii. [less ▲]

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See detailA facile and efficient strategy to enhance hydrophilicity of zwitterionic sulfoalkylbetaine type monoliths.
Yuan, Guangxin; Peng, Yongbo; Liu, Zhenghua et al

in Journal of chromatography. A (2013), 1301

In order to prepare zwitterionic HILIC monolithic columns with high polarity, the highly hydrophilic monomer N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPDA) and crosslinker N,N ... [more ▼]

In order to prepare zwitterionic HILIC monolithic columns with high polarity, the highly hydrophilic monomer N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPDA) and crosslinker N,N'-methylenebisacrylamide (MBA) were employed for developing a novel sulfoalkylbetaine type stationary phase. The polymerization parameters were systematically optimized in order to obtain a satisfactory performance for column permeability, mechanical stability, hydrophilicity, efficiency and selectivity. Compared to the previously reported poly(N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine-co-ethylene dimethacrylate) (poly(SPE-co-EDMA)) monolith and the poly(SPDA-co-EDMA) monolith that we developed, a significantly enhanced hydrophilicity was obtained on the poly(SPDA-co-MBA) monolithic column, illustrated by the lowered critical composition of the mobile phase corresponding to the transition from the HILIC to the RP mode. Excellent permeability, reproducibility and stability were achieved on this optimized poly(SPDA-co-MBA) monolith. A column efficiency of 70,000plates/m was obtained for the analysis of bases at a linear velocity of 1.95mm/s. As expected, by studying the influence of mobile phase pH and salt concentration on their retention, a weak electrostatic repulsion interaction for negatively charged analytes was also observed at low organic solvent content on the poly(SPDA-co-MBA) monolithic column. The final optimized poly(SPDA-co-MBA) monolith exhibited good selectivity for a series of polar compounds, such as phenols, bases, benzoic acid derivatives, small peptides, urea and allantoin. [less ▲]

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See detailUse of neutral capillaries for the enantioseparation of N-benzoylated amino acids by capillary electrophoresis with bromobalhimycin as chiral selector.
Peng, Yongbo; Zhang, Tingting; Wang, Tingting et al

in Journal of separation science (2013), 36(9-10), 1568-74

In this study, the partial filling technique on both polycationic polymer hexadimethrine bromide (HDB) modified capillary and eCAP neutral capillary were systematically compared in order to enhance the ... [more ▼]

In this study, the partial filling technique on both polycationic polymer hexadimethrine bromide (HDB) modified capillary and eCAP neutral capillary were systematically compared in order to enhance the enantioseparation ability of bromobalhimycin as CE additive. The separation conditions, such as pH, the plug length, and the concentration of bromobalhimycin, etc., were optimized in order to obtain satisfactory separations. As expected, for all tested 28 N-benzoylated amino acids, up to five times higher enantioresolutions were obtained on the eCAP neutral capillary compared to that on the polycationic polymer hexadimethrine bromide modified capillary. Moreover, 26 of 28 tested racemic compounds were almost baseline- resolved without observing any interference from the front of the plug of bromobalhimycin. Although the limitation of longer running time on the neutral capillary, it allows the use of higher content of bromobalhimycin in the running buffer without any interference on the detection of analytes when enantioseparations are more difficult to obtain. [less ▲]

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See detailA facile and efficient one-step strategy for the preparation of beta-cyclodextrin monoliths.
Guo, Jialiang; Zhang, Qiaoxuan; Peng, Yongbo et al

in Journal of separation science (2013), 36(15), 2441-9

A novel, facile, and efficient one-step copolymerization strategy was developed for the preparation of beta-cyclodextrin (beta-CD) methacrylate monolithic columns using click chemistry. The novel mono-(1H ... [more ▼]

A novel, facile, and efficient one-step copolymerization strategy was developed for the preparation of beta-cyclodextrin (beta-CD) methacrylate monolithic columns using click chemistry. The novel mono-(1H-1,2,3-triazol-4-ylmethyl)-2-methylacryl-beta-CD monomer was synthesized by a click reaction between propargyl methacrylate and mono-6-azido-beta-CD, and then monolithic columns were prepared through a one-step in situ copolymerization of the mono-(1H-1,2,3-triazol-4-ylmethyl)-2-methylacryl-beta-CD monomer and ethylene dimethacrylate. The physicochemical properties and column performance of the fabricated monolithic columns were characterized by elemental analysis, SEM, and micro-HPLC. Satisfactory column permeability, efficiency, and separation performance were obtained for the optimized poly(mono-(1H-1,2,3-triazol-4-ylmethyl)-2-methylacryl-beta-CD-co-ethylene dimethacrylate) monolithic columns. Additionally, typical hydrophilic interaction chromatography retention behavior was observed on the monoliths at high acetonitrile content in the mobile phase. Although the enantioselectivity of our monolithic columns did not meet the level of other reported beta-CD monolithic columns, this one-step strategy based on click chemistry still provides an interesting and effective model as it offers the possibility to easily prepare related novel CD methacrylate monoliths through a one-step copolymerization strategy. [less ▲]

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See detailSimultaneous determination of insulin and its analogues in pharmaceutical formulations by micellar electrokinetic chromatography (MEKC)
Lamalle, Caroline ULg; Servais, Anne-Catherine ULg; Crommen, Jacques ULg et al

Poster (2013)

Insulin plays an important role in the homeostasis of blood glucose concentration. A deficiency of this hormone causes diabetes, which can be treated by subcutaneous injection of synthetic insulin ... [more ▼]

Insulin plays an important role in the homeostasis of blood glucose concentration. A deficiency of this hormone causes diabetes, which can be treated by subcutaneous injection of synthetic insulin. Besides human regular insulin, several modified analogues have been developed to accelerate (Lispro, Aspart, Glulisin) or delay (Glargin, Detemir) its absorption. Moreover, protamine is sometimes associated with human, Lispro or Aspart insulin to give a crystalline form, which delays the action of insulin, providing it with a prolonged absorption profile after injection. Diabetes is one of the most common metabolic diseases in the world; its prevalence increases continuously. A lot of patients are therefore concerned with the treatment, which is relatively expensive and requires a prescription. Some pharmaceutical formulations can sometimes be found without prescription on the parallel market but the risk of drug counterfeiting is then considerably increased. The poor quality of these drugs can lead to harmful consequences for the public health. It is therefore essential to develop a suitable method for the identification and quantification of human insulin and its analogues. Ortner et al. have already proposed micellar electrokinetic chromatography (MEKC) methods to analyse simultaneously human insulin and its five analogues but formulations containing protamine were not tested. Since the number of these formulations is significant, we included them in our study. The first optimisation step involved the sample preparation procedure. An acidic sample solution (0.01 M HCl) was finally selected to solubilise protamine and Glargin. Then the background electrolyte composition was investigated to separate the components present in the formulations. A basic buffer (50 mM ammonium acetate pH 9) was selected, providing an important and stable electroosmotic flow, a negative charge to insulin and related compounds and avoiding any adsorption to the capillary wall. The addition of sodium dodecyl sulfate and acetonitrile were also found crucial for selectivity. The six insulins and the two major excipients (phenol and m-cresol) were fully separated within 15 minutes The aforementioned method was then adapted to permit the separation of each insulin from its degradation products. [less ▲]

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See detailHigh inorganic triphosphatase activities in bacteria and mammalian cells: Identification of the enzymes involved.
Kohn, Grégory ULg; Delvaux, David ULg; Lakaye, Bernard ULg et al

in PLoS ONE (2012), 7(9), 43879

Background: We recently characterized a specific inorganic triphosphatase (PPPase) from Nitrosomonas europaea. This enzyme belongs to the CYTH superfamily of proteins. Many bacterial members of this ... [more ▼]

Background: We recently characterized a specific inorganic triphosphatase (PPPase) from Nitrosomonas europaea. This enzyme belongs to the CYTH superfamily of proteins. Many bacterial members of this family are annotated as predicted adenylate cyclases, because one of the founding members is CyaB adenylate cyclase from A. hydrophila. The aim of the present study is to determine whether other members of the CYTH protein family also have a PPPase activity, if there are PPPase activities in animal tissues and what enzymes are responsible for these activities. Methodology/Principal Findings: Recombinant enzymes were expressed and purified as GST- or His-tagged fusion proteins and the enzyme activities were determined by measuring the release of inorganic phosphate. We show that the hitherto uncharacterized E. coli CYTH protein ygiF is a specific PPPase, but it contributes only marginally to the total PPPase activity in this organism, where the main enzyme responsible for hydrolysis of inorganic triphosphate (PPPi) is inorganic pyrophosphatase. We further show that CyaB hydrolyzes PPPi but this activity is low compared to its adenylate cyclase activity. Finally we demonstrate a high PPPase activity in mammalian and quail tissue, particularly in the brain. We show that this activity is mainly due to Prune, an exopolyphosphatase overexpressed in metastatic tumors where it promotes cell motility. Conclusions and General Significance: We show for the first time that PPPase activities are widespread in bacteria and animals. We identified the enzymes responsible for these activities but we were unable to detect significant amounts of PPPi in E. coli or brain extracts using ion chromatography and capillary electrophoresis. The role of these enzymes may be to hydrolyze PPPi, which could be cytotoxic because of its high affinity for Ca2+, thereby interfering with Ca2+ signaling. [less ▲]

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See detailDevelopment of a generic micellar electrokinetic chromatography method for the separation of 15 antimalarial drugs as a tool to detect medicine counterfeiting
Lamalle, Caroline ULg; Marini Djang'Eing'A, Roland ULg; Debrus, Benjamin ULg et al

in Electrophoresis (2012), 33

Since antimalarial drugs counterfeiting is dramatically present on the African market, the development of simple analytical methods for their quality control is of great importance. This work consists in ... [more ▼]

Since antimalarial drugs counterfeiting is dramatically present on the African market, the development of simple analytical methods for their quality control is of great importance. This work consists in the CE analysis of 15 antimalarials (artesunate, artemether, amodiaquine, chloroquine, piperaquine, primaquine, quinine, cinchonine, mefloquine, halofantrine, sulfadoxine, sulfalen, atovaquone, proguanil, and pyrimethamine). Since all these molecules cannot be ionized at the same pH, MEKC was preferred because it also allows separation of neutral compounds. Preliminary experiments were first carried out to select the most crucial factors affecting the antimalarials separation. Several conditions were tested and four parameters as well as their investigation domain were chosen: pH (5–10), SDS concentration (20–90 mM), ACN proportion (10–40%), and temperature (20–35°C). Then, the experimental design methodology was used and a central composite design was selected. Mathematical modeling of the migration times allowed the prediction of optimal conditions (29°C, pH 6.6, 29 mM SDS, 36% ACN) regarding analyte separation. The prediction at this optimum was verified experimentally and led to the separation of 13 compounds within 8 min. Finally, the method was successfully applied to the quality control of African antimalarial medicines for their qualitative and quantitative content. [less ▲]

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See detailMigration behaviour study of charged and uncharged compounds in micellar electrokinetic chromatography systems containing various proportions of SDS micelles and acetonitrile as organic modifier
Lamalle, Caroline ULg; Servais, Anne-Catherine ULg; Crommen, Jacques ULg et al

Poster (2012)

In 1984, Terabe and co-workers introduced a modified version of CZE, called micellar electrokinetic chromatography (MEKC), in which surfactant-formed micelles are included in the running buffer providing ... [more ▼]

In 1984, Terabe and co-workers introduced a modified version of CZE, called micellar electrokinetic chromatography (MEKC), in which surfactant-formed micelles are included in the running buffer providing a two phases chromatographic system for the separation of neutral compounds. Depending on their hydrophobicity, compounds can interact with the core of the micelles. Many MEKC methods have been described for the separation of neutral and basic compounds and for various applications. However, the migration behaviour of cationic, anionic and neutral analytes mixture is not well established regarding to the surfactant concentration and to the proportion of organic solvent in the background electrolyte (BGE). With such a mixture, it is important to remember that the separation of charged solutes in MEKC involves a combination of chromatographic and electrophoretic separation mechanisms. Moreover, it is worth noting that with charged analytes, two kinds of interactions with the micelles may occur; not only with the hydrophobic core but also with the head groups of the micelles through electrostatic interactions. In systems in which the surfactant has an opposite charge to that of the solute, ion pairing may occur. On the contrary, when a solute and the surfactant have similar charges, coulombic forces may cause the repulsion of these molecules. The goal of this study is to improve our understanding of the migration behaviour of charged and uncharged analytes in MEKC systems. With this aim in view, effective mobility (electrophoretic mobility under the influence of micelles) of neutrals, cations and anions were mesured at neutral, basic and acidic pH with BGE containing different SDS concentrations and ACN proportions. This study is also focused on the changes of migration order between CZE and MEKC systems using different BGE compositions. In the MEKC systems investigated in the study, SDS concentration and ACN proportion show a tremendous effect on the effective mobilities and migration order of the model compounds. While anions interact very weakly with SDS micelles, neutrals and cations interact with SDS through hydrophobic and ionic bonds. These interactions become stronger with the increase of SDS concentration and weaker with high ACN proportion. With 20 mM of SDS in the BGE, CZE behaviour is observed till 40% of ACN. But, when the SDS concentration is high and the ACN proportion is low, the migration order of analytes is reversed compared to CZE: EOF first, then the anions, followed by the neutrals and finally the cations. The migration order inside each group (cations, neutrals and anions) depends on the hydrophobicity of the analytes. Different organic solvents were also investigated to study the ion-pair formation. Those observations confirm the interest of using MEKC not only for the separation of neutral compounds but also variously charged analytes. [less ▲]

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See detailMicellar electrokinetic chromatography (MEKC) systems for the separation of mixtures of charged and uncharged compounds
Lamalle, Caroline ULg; Servais, Anne-Catherine ULg; Fradi, Inès et al

Poster (2012)

The migration behaviour of charged and uncharged analytes in MEKC was investigated under different conditions. Effective mobilities – electrophoretic mobilities under the influence of the negatively ... [more ▼]

The migration behaviour of charged and uncharged analytes in MEKC was investigated under different conditions. Effective mobilities – electrophoretic mobilities under the influence of the negatively charged micelles – of cations, anions and neutrals were measured at neutral, basic and acidic pH values (7.5, 11 and 2.2) using background electrolytes containing different sodium dodecyl sulfate (SDS) concentrations (0-90 mM) and acetonitrile proportions (0-75 %, v/v). The SDS concentration and acetonitrile proportion were found to have a tremendous effect on the effective mobilities and the migration order of the tested compounds. Although the SDS micelles interact more strongly with neutrals and cations, the migration of anionic compounds is also affected by the SDS concentration, indicating that hydrophobic interactions can occur between the micelles and these compounds. Since cationic, anionic and neutral solutes exhibit rather different migration behaviours, it is possible to considerably enhance the separation selectivity by properly adjusting the SDS concentration and the acetonitrile proportion in the background electrolyte. These observations confirm the interest of using MEKC not only for the separation of neutral substances but also for the analysis of mixtures of charged compounds. [less ▲]

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See detailMicellar electrokinetic chromatography systems for the separation of mixtures of charged and uncharged compounds
Lamalle, Caroline ULg; Servais, Anne-Catherine ULg; Fradi, Ines ULg et al

in Journal of Separation Science (2012), 35(15), 1933-1939

In this study, the migration behavior of charged and uncharged analytes was investigated under different conditions. Effective mobilities - electrophoretic mobilities under the influence of micelles - of ... [more ▼]

In this study, the migration behavior of charged and uncharged analytes was investigated under different conditions. Effective mobilities - electrophoretic mobilities under the influence of micelles - of cations, anions, and neutrals were measured at neutral, basic, and acidic pH (7.5, 11, and 2.2) using background electrolytes containing different sodium dodecyl sulfate (SDS) concentrations (0-90 mM) and acetonitrile (ACN) proportions (0-75%). SDS concentration and ACN proportion were found to have a tremendous effect on the effective mobilities and migration order of the model compounds. Although the SDS micelles preferably interact with neutrals and cations, hydrophobic bonds can also occur with anions. Cations, anions, and neutrals having rather different migration behaviors, it is possible to considerably enhance the selectivity of the method by adjusting properly the SDS concentration and the ACN proportion. These observations confirm the interest of using micellar electrokinetic chromatography not only for the separation of neutral substances but also to analyze charged compounds. [less ▲]

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