Microbial metabolomics with gas chromatography/mass spectrometry

An analytical method was set up suitable for the analysis of microbial metabolomes, consisting of an oximation and silylation derivatization reaction and subsequent analysis by gas chromatography coupled to mass spectrometry. Microbial matrixes contain many compounds that potentially interfere with either the derivatization procedure or analysis, such as high concentrations of salts, complex media or buffer components, or extremely high substrate and product concentrations. The developed method was extensively validated using different microorganisms, i.e., Bacillus subtilis, Propionibacterium freudenreichii, and Escherichia coli. Many metabolite classes could be analyzed with the method: alcohols, aldehydes, amino acids, amines, fatty acids, (phospho-) organic acids, sugars, sugar acids, (acyl-) sugar amines, sugar phosphate, purines, pyrimidines, and aromatic compounds. The derivatization reaction proved to be efficient (>50% transferred to derivatized form) and repeatable (relative standard deviations <10%). Linearity for most metabolites was satisfactory with regression coefficients better than 0.996. Quantification limits were 40-500 pg on-column or 0.1-0.7 mmol/g of microbial cells (dry weight). Generally, intrabatch precision (repeatability) and interbatch precision (reproducibility) for the analysis of metabolites in cell extracts was better than 10 and 15%, respectively. Notwithstanding the nontargeted character of the method and complex microbial matrix, analytical performance for most metabolites fit the requirements for target analysis in bioanalysis. The suitability of the method was demonstrated by analysis of E. coli samples harvested at different growth phases.     

Stereochemische Gesichtspunkte zu der Reaktion zwischen Cyclohexylidenacetaldehyden und Mercaptanen

Some Stereochemical Aspects of the Reaction between Cyclohexylidene Acetaldehydes and Thiols The reaction between cyclohexylidene acetaldehyde, 4-methyl-cyclohexylidene acetaldehyde resp. 4-tert.-butylcyclohexylidene acetaldehyde and thioglycolic acid thioglycolic acid methylester, benzylthiol resp. isopropylthiol and catalytical amounts of conc. HCl gave 60% cyclohexylidene acetaldehyde dimercaptales 1 – 3 . In addition to these compounds i t was also obtained in 40% a mixture of 46% cis and 54% trans forms of the cyclohexane derivatives 4–9. Double magnetic non equivalent methylenic protons were found in the compounds 2a – 2c and 3a – 3c and double magnetic non equivalent geminal methyl groups in the compounds 2d and 3d . ⁴J_H,H couplings were observed in 1–3. The reaction mechanisms of the formation of the compounds 4–9 as well as the ¹H-n.m.r. spectra of the compounds 1–9 were discussed.     

Comparison of Rheological Methods to Obtain a Sufficient Sensitivity with Shear Interfacial Rheology in the Presence of Nanoparticles at Liquid/Liquid Interfaces

Silicon - Interfacial shear rheology can give a lot of information on the organization of the nanoparticles at the liquid/liquid and at the liquid/air interfaces. The measurements are challenging...