Rapid analysis of long‐chain glycolipids in heterocystous cyanobacteria using high‐performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry

Under nitrogen‐depleted conditions, N₂‐fixing cyanobacteria of the order Nostocales and Stigonematales differentiate vegetative cells into heterocysts. The cell envelope of these specialized cells contains unique glycolipids, consisting of a sugar moiety glycosidically bound to long‐chain diols, triols and hydroxyketones. Only few reports have been published on these glycolipids in cultured cyanobacteria and none has reported them in natural environments. Here we show that heterocyst glycolipids can be rapidly and sensitively analyzed using high‐performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC/ESI‐MS²). Positive ion mass spectra of the glycolipids consisted of protonated molecules and diagnostic product ions, indicating losses of sugar groups as well as hydroxyl and carbonyl functionalities from an alkyl chain. Using this method, heterocyst glycolipids were for the first time identified in a natural ecosystem, i.e., a microbial mat from the North Sea barrier island Schiermonnikoog, The Netherlands. This technique will facilitate the quick screening of cyanobacterial cultures and natural environments for the presence of heterocyst glycolipids, which may aid in assessing the role of heterocystous cyanobacteria in the global nitrogen cycle. Copyright © 2009 John Wiley & Sons, Ltd.     

Regional and modular expression of morphogenetic factors in the demosponge Lubomirskia baicalensis

Some sponges [phylum Porifera], e.g. the demosponges Lubomirskia baicalensis or Axinella polypoides, show an arborescent growth form. In the freshwater sponge L. baicalensis this morphotype is seen mostly in depths below 4m while in more shallow regions it grows as a crust. The different growth forms are determined in nature very likely by water current and/or light. The branches of this species are composed of modules, arranged along the apical-basal axis. The modules are delimited by a precise architecture of the spicule bundles; longitudinal bundles originate from the apex of the earlier module, while at the basis of each module these bundles are cross-linked by traverse bundles under formation of annuli. Genes encoding putative morphogenetic factors, myotrophin and epidermal growth factor (EGF)-like molecules, and one gene of an antagonist for the Wnt signaling pathway, the soluble frizzled molecule, have been identified and characterized. Their expression levels as well as those of silicatein, one major spicule-forming molecule, have been studied in the crusts and the modules. The data revealed that at the apices of each module higher level of expression of myotrophin and EGF can be detected, while the base of each module is characterized by a high steady-state expression level of soluble frizzled molecule. These results suggest that module formation in L. baicalensis is controlled by a tuned interaction of agonistic (e.g., myotrophin and EGF) as well as antagonistic morphogenetic factors (e.g., soluble frizzled molecule).     

Phosphanyl Cyanophosphide Salts: Versatile PCN Building Blocks

The facile preparation of alkali salts of phosphanyl cyanophosphides [NHP‐PCN]^? (NHP=N‐heterocyclic phosphenium) is reported. Their formation is achieved by isoelectronic replacement of O for [N]^? in the phosphaketenes NHP‐PCO using alkaline hexamethyldisilazide M[N(SiMe₃)₂] (M=Na, K) as reagent. The new anionic entities are versatile PCN building blocks which allow the formation of a diversity of new cyanophosphine derivates including the first example of a PCNB hetero‐cumulene and a PCN‐ligated transition metal complex.     

UV-Vis microspectroscopy: probing the initial stages of supported metal oxide catalyst preparation

A UV-vis microspectroscopy methodology for monitoring the speciation and macrodistribution of catalyst-precursor species inside catalyst-support bodies at the initial stages of catalyst preparation has been developed. The setup is based upon optical-fiber technology and allows spatially resolved analysis of bisected catalyst bodies. The potential of this tool is demonstrated by two pore-volume impregnation studies involving Ni2+ d-d transition bands and Cr6+ charge-transfer bands.     

Identification of non-cross-linked compounds in methanolic extracts of cured and aged linseed oil-based paint films using gas chromatography-mass spectrometry

Methanolic extracts of paint samples of different composition and age were qualitatively investigated by GC–MS using an on-column injector after off-line methylation or trimethylsilyl derivatisation, and on-line thermally assisted (trans)methylation with tetramethylammonium hydroxide using Curie-point pyrolysis–GC–MS. The combination of these three analytical strategies led to the identification of typical oxidation products of unsaturated fatty acids by interpretation of their mass spectrum. Some of the identified compounds have not been reported before. Both the off-line and on-line GC–MS strategy show series of short-chain fatty (di)acids and C₁₆ and (oxidised) C₁₈ fatty acids. The major advantage of the on-line pyrolysis–GC–MS approach is that chemical work-up is minimal and very quick. With this technique both the carboxylic acid functionalities, and hydroxyl groups are methylated. Young paint films are shown to contain relatively more oxidised C₁₈ fatty acids and less diacids compared to older paints, which is indicative for the on-going oxidation processes within the paint. After trimethylsilylation, monoacylglycerols are detected indicative for hydrolytic processes, which reflect the relative distribution of the most prominent silylated fatty acids present. Relatively more C₁₆ and C₁₈ monoacylglycerols are found in young paints, whereas older paints contain higher amounts of monoacylglycerols of diacids.     

Ultrafast vibrational dynamics and stability of deuterated amorphous silicon

Infrared four-wave mixing experiments performed upon deuterated amorphous silicon layers (a-Si:D) reveal profound differences in the dynamics of Si-D stretch vibrations compared to those of analogous Si-H vibrational modes in hydrogenated amorphous silicon (a-Si:H). Remarkably, transient-grating measurements of the population decay rate of the Si-D vibrations show single-exponential decay directly into collective modes of the a-Si host, bypassing the local bending modes of the defect into which the Si-H vibrations decay. Photon-echo measurements of the vibrational dephasing suggest at low temperature contributions from TO nonequilibrium phonons and at elevated temperatures elastic phonon scattering of TA phonons.     

Spontaneous disproportionation of rhodium(I) bisoxazolinates to rhodium(II)

[RhI(t-Bu2-boxate)(C2H4)2] spontaneously disproportionates to the mononuclear [RhII(t-Bu2-boxate)2], whereas [RhI(Ph2-boxate)(C2H4)2] is stable against disproportionation.     

Determination of maduramicin in feedingstuffs and premixtures by liquid chromatography: development, validation, and interlaboratory study

A reversed-phase liquid chromatography method for determination of maduramicin in feedingstuffs and premixtures was developed, validated, and interlaboratory studied. The extraction solvent was methanol. Maduramicin was detected at 520 nm after postcolumn derivatization with vanillin. Recovery was >90%. The repeatability relative standard deviation (RSDr) in feeds (1-5 mg/kg) and premixtures (500 mg/kg) ranged between 2.7 and 7.7%; the within-laboratory reproducibility was between 3.7 and 8.5%. The limit of quantitation was 2 mg/kg. Other feed additives did not interfere in the assay. The method showed ruggedness against small changes in the extraction conditions, eluant composition, and conditions for postcolumn derivatization. The presence of water in the extraction solvent negatively affected the recovery. In the collaborative study, 5 feeds (4 positive at 2.5-9 mg/kg, 1 blank) and 1 premixture (450 mg/kg) were analyzed by 10 laboratories. The RSDr of the feedingstuffs varied between 3.29 and 8.53%. The HORRAT ranged between 1.10 and 1.98. Recoveries were >90%, except for one participant (80%). One laboratory detected small signals in the blank sample, corresponding to 0.7 and 0.8 mg/kg. For the premixture, the RSDr was 3.15% and the HORRAT was 1.80.