In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat-soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization-MS (DESI-MS) and desorption atmospheric pressure photoionization-MS (DAPPI-MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M-H](+) ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods.

No abstract

Paracoccus denitrificans is a soil bacterium which can respire aerobically and also denitrify if oxygen is absent. Both processes are highly dependent on copper enzymes and copper is therefore likely to be an essential trace element for the bacterium. If copper is not easily available, a copper-acquisition mechanism would be highly beneficial. In this paper, we have addressed the question of whether Paracoccus secretes a copper-acquisition compound functionally analogous to that found in some methanotrophs. Bacteria were grown both in copper-containing and copper-deficient denitrification media, cells were removed by centrifugation and the supernatant was analysed using chromatography and spectroscopy. Bacterial growth yield in the absence of copper was 70-80% of that in the copper-containing medium. A notable difference between the two culture conditions was that spent copper-deficient medium was pigmented, whereas the copper-containing medium was not. Spectrophotometry indicated that a red compound with an absorption maximum at 405 nm was produced under copper-limited conditions. In addition to the strong 405 nm maximum, the visible spectrum of the purified red molecule had weaker maxima at 535 nm and 570 nm, features typical of metallated tetrapyrroles. Mass spectrometry showed that the purified pigment had a molecular mass of 716.18. Moreover, the fine structure of the mass spectrum suggested the presence of zinc and was consistent with the chemical formula of C(36)H(36)N(4)O(8)Zn. The presence of zinc was also demonstrated using inductively coupled plasma atomic emission spectroscopy. Fragmentation analysis with mass spectrometry showed the release of consecutive 59 Da fragments, assignable to four -CH(2)-COOH moieties. Thin layer chromatography as well as NMR analysis of the C-13/N-15 labelled red pigment suggested that it is predominantly zinc coproporphyrin III with a minor fraction of metal-free coproporphyrin III. We propose that in a copper-poor environment P. denitrificans secretes coproporphyrin III for copper chelation and subsequent uptake of the bound copper into the cell. Consistent with this idea, cell yields of copper-deficient cultures grown in the presence of 1 microM copper-coproporphyrin III were 90-95% of the yields of cultures grown in the normal copper-containing media. Coproporphyrin III may work as a copper-acquisition compound in P. denitrificans.

Patterned chips: Organic self‐assembled monolayers on Si–SiO2 surfaces are patterned with an electric discharge between a patterning tip and the silicon substrate (see picture). The method allows rapid patterning with simple equipment on planar, curved, and textured surfaces. It is used in the fabrication of microfluidic structures for microchip‐based mass spectrometric drug analysis.

Gemusterte Chips: Organische selbstorganisierte Monoschichten auf Si/SiO2‐Oberflächen werden mithilfe einer elektrischen Entladung zwischen einer Spitze und dem Siliciumsubstrat erzeugt (siehe Bild). Die apparativ einfache Methode ermöglicht die schnelle Musterbildung auf ebenen, gebogenen und texturierten Oberflächen und wird zur Herstellung von Mikrofluidikstrukturen für die mikrochipbasierte massenspektrometrische Wirkstoffanalyse genutzt.