Synthesis of blood group Forssman pentasaccharide GalNAcα1-3GalNAcβ1-3Galα1-4Galβ1-4Glcβ–R

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Do complex matrices modify the sorptive properties of polydimethylsiloxane (PDMS) for non-polar organic chemicals?

The partitioning of non-polar analytes into the silicone polydimethylsiloxane (PDMS) is the basis for many analytical approaches such as solid phase microextraction (SPME), stir bar sorptive extraction (SBSE) and environmental passive sampling. Recently, the methods have been applied to increasingly complex sample matrices. The present work investigated the possible effect of complex matrices on the sorptive properties of PDMS. First, SPME fibers with a 30 μm PDMS coating were immersed in 15 different matrices, including sediment, suspensions of soil and humic substances, mayonnaise, meat, fish, olive oil and fish oil. Second, the surface of the fibers was wiped clean, and together with matrix-free control fibers, they were exposed via headspace to 7 non-polar halogenated organic chemicals in spiked olive oil. The fibers were then solvent-extracted, analyzed, and the ratios of the mean concentrations in the matrix-immersed fibers to the control fibers were determined for all matrices. These ratios ranged from 92% to 112% for the four analytes with the highest analytical precision (i.e. polychlorinated biphenyls (PCBs) 3, 28, 52 and brominated diphenyl ether (BDE) 3), and they ranged from 74% to 133% for the other three compounds (i.e. PCBs 101, 105 and γ-hexachlorocyclohexane (HCH)). We conclude that, for non-polar, hydrophobic chemicals, the sorptive properties of the PDMS were not modified by the diverse investigated media and consequently that PDMS is suited for sampling of these analytes even in highly complex matrices.     

Thin films of cross-linked metallo-supramolecular coordination polyelectrolytes

We report on the synthesis of a new tristerpyridine ligand, tris(2,2':6',2' '-terpyridinyl-4'-oxymethyl)ethane (tritpy), as well as its introduction into metal ion induced self-assembly of cross-linked metallo-supramolecular coordination polyelectrolytes (MEPE). For cross-linking degrees of 9.5% and below, soluble homogeneous networks are obtained. The molar mass of the networks is large and depends on the cross-linking degree. Due to the charges in the MEPE, the soluble networks are suitable for film formation on the basis of layer-by-layer self-assembly and to study the details of film growth. UV-vis spectroscopy, X-ray reflectivity, AFM, and ellipsometry show that the film growth is linear and continuous. The multilayers exhibit no inner structure and have a very low surface roughness. The thickness of the adsorbed layer of MEPE networks is in the range of 3 nm. The important point is that an influence of cross-linking is not seen in multilayers, which is the opposite of what is observed for the MEPE in solution. Our experiments did not reveal an influence of the preparation procedure on the adsorption process, e.g., increasing the layer thickness.     

Quantification of Polymer Fouling on Heat Transfer Surfaces During Synthesis

During the synthesis and processing of polymers, a significant amount of polymer may be deposited on the heat transfer surfaces. This deposit is unwanted and is usually named fouling. This study deals with the fouling behavior of a vinyl acetate/vinyl ester copolymer during emulsion polymerization and compares this to fouling of an already reacted vinyl acetate/ethylene copolymer dispersion. Besides the state of polymerization, also the influence of the wall temperature is investigated. The experiments are performed on cooled and heated surfaces. The deposition process is quantified by the mass‐based fouling resistance, the height of the fouling layer, and the surface coverage using a digital microscope. It is found that the state of polymerization and the temperature gradient between wall and bulk exert a strong influence on the fouling behavior, especially on the structure of the fouling layer.     

Upconverting nanophosphors as reporters in a highly sensitive heterogeneous immunoassay for cardiac troponin I

Photon upconverting nanophosphors (UCNPs) have a unique capability to produce anti-Stokes emission at visible wavelengths via sequential multiphoton absorption upon infrared excitation. Since the anti-Stokes emission can be easily spectrally resolved from the Stokes' shifted autofluorescence, the upconversion luminescence (UCL) is a highly attractive reporter technology for optical biosensors and biomolecular binding assays – potentially enabling unprecedented sensitivity in separation-based solid-phase immunoassays.     

[FeFe]‐Hydrogenase with Chalcogenide Substitutions at the H‐Cluster Maintains Full H2 Evolution Activity

The [FeFe]‐hydrogenase HYDA1 from Chlamydomonas reinhardtii is particularly amenable to biochemical and biophysical characterization because the H‐cluster in the active site is the only inorganic cofactor present. Herein, we present the complete chemical incorporation of the H‐cluster into the HYDA1‐apoprotein scaffold and, furthermore, the successful replacement of sulfur in the native [4Fe_H] cluster with selenium. The crystal structure of the reconstituted pre‐mature HYDA1[4Fe4Se]_H protein was determined, and a catalytically intact artificial H‐cluster variant was generated upon in vitro maturation. Full hydrogen evolution activity as well as native‐like composition and behavior of the redesigned enzyme were verified through kinetic assays, FTIR spectroscopy, and X‐ray structure analysis. These findings reveal that even a bioinorganic active site with exceptional complexity can exhibit a surprising level of compositional plasticity.     

Overall approaches and experiences of first-time participants in the Nuclear Forensics International Technical Working Group’s Fourth Collaborative Material Exercise (CMX-4)

Journal of Radioanalytical and Nuclear Chemistry - The Fourth Collaborative Material Exercise (CMX-4) of the Nuclear Forensics International Technical Working Group (ITWG) registered the largest...     

Proteome analysis of conditioned medium from cultured adult hippocampal progenitors

It is known that proliferation and survival of neural stem/progenitor cells in vitro not only depend on exogenous factors, but also on autocrine factors secreted into the conditioned medium. It is also well known that the identification of bioactive proteins secreted into the conditioned medium poses a substantial challenge. Recently, neural stem/progenitor cells were shown to secrete a survival factor, cystatin C, into the conditioned medium. Here, we demonstrate an approach to identify other low molecular weight proteins in conditioned medium from cultured adult rat hippocampal progenitor cells. A combination of preparative two-dimensional gel electrophoresis (2-DE) and mass spectrometry was utilized in the analysis. We were able to identify a number of proteins, which include Rho-guanine nucleotide dissociation inhibitor 1, phosphatidylethanolamine binding protein (PEBP), also termed Raf-1 kinase interacting protein, polyubiquitin, immunophilin FK506 binding protein 12 (FKBP12) and cystatin C. The presence of PEBP and FKBP12 in conditioned medium was confirmed immunologically. All nestin-positive progenitor cells showed immunoreactivity for antibodies against PEBP and FKBP12. To our knowledge we are the first to use this preparative proteomic approach to search for stem cell factors in conditioned medium. The method could be used to identify novel bioactive proteins secreted by stem/progenitor cells in vitro. Identification of bioactive proteins in vitro is of potential importance for the understanding of the regulatory mechanisms of the cells in vivo.     

Synthesis of R-(-)-imperanene from the natural lignan hydroxymatairesinol

A convenient and high yielding method for the synthesis of R-(-)-imperanene, starting from the readily available natural lignan hydroxymatairesinol from Norway spruce, was developed. Hydroxymatairesinol was degraded in strongly basic aqueous conditions to (E)-4-(4-hydroxy-3-methoxyphenyl)-2-(4-hydroxy-3-methoxyphenylmethyl)but-3-enoic acid, which was esterified and then reduced by LiAlH(4) to afford R-(-)-imperanene. The configuration at the crucial stereocenter was preserved in the synthesis, and the obtained product was identified by optical rotation measurements and chiral HPLC analyses as the R-(-)-enantiomer (ee 86-92%).     

Peracid dependent stereoselectivity and functional group contribution to the stereocontrol of epoxidation of (E)-alkene dipeptide isosteres

Twelve Boc-protected phenylalanyl-phenylalanine and phenylalanyl-glycine trans-vinyl isosteres were epoxidised with magnesium monoperoxyphtalate hexahydrate (MMPP) and trifluoroperacetic acid, and the results have been compared with those from earlier studies on epoxidations with m-CPBA. The alkenes were synthesised in high yields with high E/Z-selectivities using either the Julia or Schlosser reactions. The formation of threo isomers was favoured in all epoxidation reactions except with CF₃CO₃H on substrates containing two allylic/homoallylic functional groups directing the peracid to opposite faces of the alkene. The switch to erythro selectivity observed with CF₃CO₃H is suggested to emanate from coordination to the allylic ester functionalities via hydrogen bond donation from the peracid. The other peracid reagents seem to be preferentially coordinated to the allylic carbamate function. The contribution of individual functional groups to the stereopreference was also investigated.