Analysis of selected withanolides in plant extract by capillary electrochromatography and microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) coupled with a diode-array detector was developed for the simultaneous analysis of natural steroidal compounds, withanolides including withaferin A, withacnistin and iochromolide. Optimal resolution was obtained with a microemulsion consisting of 70 mM octane, 800 mM 1-butanol, 100 mM sodium dodecyl sulfate (SDS), and 10 mM phosphate-borate buffer (pH 7) using a fused-silica capillary at 25 kV and 40 degrees C. Since this technique is not compatible with mass spectrometry detection, a capillary electrochromatographic method was developed to separate the investigated withanolides. The effects of mobile phase composition and pH were systematically investigated. Complete separation was obtained with a capillary electrochromatography (CEC) Hypersil C18 bonded silica column (packed length, 25 cmx100 microm ID and 375 microm OD), packed with 3 microm particles. The mobile phase consisted of formic acid-ammonia, pH 8 / acetonitrile (40/60 v/v); the voltage was set at 25 kV and the temperature at 20 degrees C. Under these conditions, resolution of these closely related compounds, including the critical pair withacnistin and iochromolide, was achieved in less than 5 min. The separations by MEEKC and CEC were compared with that obtained by reversed-phase liquid chromatography and showed similar retention order, indicating the analogy of the retention mechanism of these techniques. To further improve specificity and sensitivity, the developed CEC method was interfaced with electrospray ionization mass spectrometry using a Teflon connection between the CEC column and a void fused-silica capillary. Finally, the described methods were applied to the qualitative analysis of withanolides in Iochroma gesnerioides plant extract.     

Use of the Gaussian Distribution Function as a Tool to Estimate Continuous Heterogeneity in Adsorbing Systems

In environmental engineering, adsorption and desorption are phenomena commonly referred to as responsible for pollution dispersion, retention, or retardation in soils, aquifers, and hydrologic systems. They are also used to remove organic pollutants from water or odorous compounds in gas deodorization. Most often, the characterization of the aqueous adsorption systems that are of engineering interest involves a narrow adsorbate concentration range and low values of the adsorbate concentration. The practice is to use the Freundlich equation that best fits most data and is considered sufficient to design adsorption contactors. However, no physical or chemical meaning can be associated with the values taken by the parameters. The present paper gives a new way of analyzing adsorption data, using an extension of the Freundlich equation and the Gaussian distribution function that makes it possible to associate parameter values of this extension with the adsorbate–adsorbent normal interaction energy, its heterogeneity, and to some extent the adsorbate–adsorbate lateral interaction energy.     

Immobilization as a tool for the stabilization of lignin peroxidase produced byPhanerochaete chrysosporium INA-12

Lignin peroxidase immobilization was achieved by covalent coupling on CNBr-Sepharose 4B. Protein immobilization yield was around 80%. For veratryl alcohol oxidation, in the presence of hydrogen peroxide, both soluble and bound enzymes exhibited the same pH profile with an optimum near 2.5. Catalytic parameters (kc andK _m ) were seriously affected by immobilization. On the other hand, immobilization provided a noticeable stabilization of the enzyme against acidic pH and high temperatures. A 15–20 increase in the half-inactivation times at pH 2.2 and 2.7, respectively, could be observed. Bound enzyme was also much more thermostable than soluble.     

Copper(II)—dialkyldithiocarbamate—silica precolumn for the enrichment of complexing analytes in natural media coupled on-line with liquid chromatography

A chemically modified silica (dialkyldithiocarbamate, DDTC) has been developed which strongly binds copper(II) ion. This metallic surface has been shown to be an effective means for the preconcentration of complexing analytes in natural media (e.g., amino acids chosen as model compounds). The Si-DDTC is more stable than other dithiocarbamate functions previously tested, and no copper or silane leaching occurred with this surface. The possibility of on-line coupling of the enrichment precolumn packed with the copper-loaded silica with an RP-18 analytical column allowed the direct liquid chromatographic analysis of some aqueous media containing amino acids at the 10^?7?10^?9M level and of some complex matrices as urine or blood serum. The total analysis procedure takes not more than 40 min. The method minimizes manipulation errors, contamination, losses and the total analysis time, and enhances the selectivity.     

Solvent extraction of organic molecules of exobiological interest for in situ analysis of the Martian soil

A solid-liquid extraction method able to perform in situ extraction of organic compounds on Mars is proposed. The extraction efficiency of various organic solvents was tested and compared to that of water. The selected key compounds are molecules of exobiological interest: glycine, alanine, serine, glutamic acid, oxalic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid and 1,3,5-benzenetricarboxylic acid. Among the organic solvents, propanol gives the highest yield of extraction for all the targeted compounds except for benzoic acid. A mixture of propanol and ethyl acetate increases significantly the extraction yield of benzoic acid. The extraction time was considerably reduced (140 h to 15 min) by using sonication. The method is discussed for an easy automation with coupling to an in situ GC-MS space instrument.     

Synthesis and Biological Activity of Four Adrenocorticotropin-(1-24)-tetracosapeptide Analogues with N-Terminal Deletions of Four to Seven Amino-Acid Residues

The syntheses of adrenocorticotropin-(5–24)-eicosapeptide, -(6–24)-nonadecapeptide, -(7–24)-octadecapeptide, and -(8–24)-heptadecapeptide are described. Their biological activities on isolated adrenal cortex cells and adipocytes, on superfused adrenal tissue, as well as on the adenylate cyclase system of isolated cell membranes are summarized.