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Raju S.,University Utrecht | Jastrzebski J.T.B.H.,University Utrecht | Lutz M.,Bijvoet Center for Biomolecular Research | Klein Gebbink R.J.M.,University Utrecht
ChemSusChem | Year: 2013

A bulky cyclopentadienyl (Cp)-based trioxorhenium compound was developed for the catalytic deoxydehydration of vicinal diols to olefins. The 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium (2) catalyst was synthesised in a two-step synthesis procedure. Dirhenium decacarbonyl was converted into 1,2,4-tri(tert-butyl)cyclopentadienyl tricarbonyl rhenium, followed by a biphasic oxidation with H2O2. These two new three-legged compounds with a 'piano-stool' configuration were fully characterised, including their single crystal X-ray structures. Deoxydehydration reaction conditions were optimised by using 2 mol % loading of 2 for the conversion of 1,2-octanediol into 1-octene. Different phosphine-based and other, more conventional, reductants were tested in combination with 2. Under optimised conditions, a variety of vicinal diols (aromatic and aliphatic, internal and terminal) were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. A high turnover number of 1400 per Re was achieved for the deoxydehydration of 1,2-octanediol. Furthermore, the biomass-derived polyols (glycerol and erythritol) were converted into their corresponding olefinic products by 2 as the catalyst. In the bulk of it: Bulky 1,2,4-tri(tert-butyl)cyclopentadienyl trioxorhenium was studied as a catalyst for the deoxydehydration of different vicinal diols. Under optimised conditions, a variety of vicinal diols were converted into olefins in good to excellent yields, and with minimal olefin isomerisation. Biomass-derived polyols were also converted into their corresponding olefinic products. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dzik W.I.,University of Amsterdam | Calvo S.E.,University of Amsterdam | Reek J.N.H.,University of Amsterdam | Lutz M.,Bijvoet Center for Biomolecular Research | And 4 more authors.
Organometallics | Year: 2011

The binuclear iridium complex [(cod)(Cl)Ir(bpi)Ir(cod)]PF 6 (bpi = (pyridin-2-ylmethyl)(pyridin-2-ylmethylene)amine; cod = 1,5-cyclooctadiene) reveals a noteworthy asymmetric binuclear coordination geometry, wherein the bpi ligand acts as a heteroditopic ligand and has an unusual π-coordinated imine moiety. This species is an effective precatalyst for water oxidation. After a short incubation time the catalyst reveals a turnover frequency of 3400 mol mol -1 s -1 with an overall turnover number >1000. © 2011 American Chemical Society.

Munoz J.,Bijvoet Center for Biomolecular Research | Munoz J.,University Utrecht | Heck A.J.R.,Bijvoet Center for Biomolecular Research
Methods in Molecular Biology | Year: 2011

Understanding the signaling pathways governing pluripotency and self-renewal is a prerequisite for better controlling stem cell differentiation to specific fates. Reversible protein phosphorylation is one of the most important posttranslational modifications regulating signaling pathways in biological processes. Global analysis of dynamic changes in protein phosphorylation is, therefore, key to understanding signaling at the system level. Here, we describe a generic mass spectrometry (MS)-based phosphoproteomics strategy applied to monitor phosphorylation dynamics after bone morphogenetic protein 4 (BMP4)-induced differentiation of human embryonic stem cells (hESCs). Our method combines the use of strong cation exchange (SCX) and titanium dioxide (TiO 2) for phosphopeptide enrichment, high-resolution MS for peptide and protein identification, and stable isotope labeling by amino acids in cell culture (SILAC) for quantification. This approach allows us to identify thousands of phosphorylation sites and profile their relative abundance during differentiation. This systems-biology-based approach provides new insights into how human pluripotent stem cells exit the pluripotent state. © 2011 Springer Science+Business Media, LLC.

Scheidelaar S.,Bijvoet Center for Biomolecular Research | Koorengevel M.C.,Bijvoet Center for Biomolecular Research | Pardo J.D.,Bijvoet Center for Biomolecular Research | Meeldijk J.D.,University Utrecht | And 2 more authors.
Biophysical Journal | Year: 2015

A recent discovery in membrane research is the ability of styrene-maleic acid (SMA) copolymers to solubilize membranes in the form of nanodisks allowing extraction and purification of membrane proteins from their native environment in a single detergent-free step. This has important implications for membrane research because it allows isolation as well as characterization of proteins and lipids in a near-native environment. Here, we aimed to unravel the molecular mode of action of SMA copolymers by performing systematic studies using model membranes of varying compositions and employing complementary biophysical approaches. We found that the SMA copolymer is a highly efficient membrane-solubilizing agent and that lipid bilayer properties such as fluidity, thickness, lateral pressure profile, and charge density all play distinct roles in the kinetics of solubilization. More specifically, relatively thin membranes, decreased lateral chain pressure, low charge density at the membrane surface, and increased salt concentration promote the speed and yield of vesicle solubilization. Experiments using a native membrane lipid extract showed that the SMA copolymer does not discriminate between different lipids and thus retains the native lipid composition in the solubilized particles. A model is proposed for the mode of action of SMA copolymers in which membrane solubilization is mainly driven by the hydrophobic effect and is further favored by physical properties of the polymer such as its relatively small cross-sectional area and rigid pendant groups. These results may be helpful for development of novel applications for this new type of solubilizing agent, and for optimization of the SMA technology for solubilization of the wide variety of cell membranes found in nature. © 2015 Biophysical Society.

Intemann J.,Stratingh Institute for Chemistry | Intemann J.,Friedrich - Alexander - University, Erlangen - Nuremberg | Lutz M.,Bijvoet Center for Biomolecular Research | Harder S.,Friedrich - Alexander - University, Erlangen - Nuremberg
Organometallics | Year: 2014

Multinuclear magnesium hydride complexes react with pyridine, forming 1,2- and 1,4-dihydropyridide (DHP) complexes. Reaction of PARA3Mg8H10 with pyridine initially formed 1,2-DHP and 1,4-DHP product mixtures which converted at 60 °C into PARA-[Mg(1,4-DHP)]2·(pyridine)2 (PARA = [(2,6-iPr2C6H3)NC(Me)C(H)C(Me)N]2-(p-C6H4)). Reaction of [NN-(MgH)2]2 with pyridine gave exclusive formation of the 1,2-DHP product NN-[Mg(1,2-DHP)]2·(pyridine)2 (NN = [(2,6-iPr2C6H3)NC(Me)CHC(Me)N-]2). Both products were characterized by crystal structure determinations. The unusual preference for 1,2-addition is likely caused by secondary intramolecular interactions based on mutual communication between the metal coordination geometries: an extended network of C-H···C π-interactions and π-stacking interactions is found. Whereas PARA3Mg8H10 is hardly active in magnesium-catalyzed hydroboration of pyridines with pinacolborane, [NN-(MgH)2]2 shows efficient coupling. However, the regioselectivity of the stoichiometric reaction is not translated to the catalytic regime. This result is taken as an indication for a potential alternative mechanism in which magnesium hydride intermediates do not play a role but the hydride is transferred from an intermediate borate complex. © 2014 American Chemical Society.

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