Nonlinear Response of a Continuous Wave NMR Spectrometer for Samples with a Large Magnetization

We present a new insight in the response of a CW NMR spectrometer for highly magnetized samples above 100 MHz. The spectrometer is a bridge made of a magic T. The output of the bridge is proportional to the reflection coefficient, , of a resonant circuit, which is built with a coil containing the sample. The sensitivity of the reflection coefficient to the complex susceptibility of the sample, () = () – j(), depends on the quality factor, Q, of the circuit and filling factor, . When the condition Q 1 is not fulfilled, we show indeed that the use of a simple crystal detector, which is only sensitive to || gives rise to a strong nonlinear response of the spectrometer. Measurements of the complex value of by means of phase sensitive detection allow to recover a linear behavior. We discuss and illustrate those issues with a few circuits we designed for our measurements on liquid ³ He with spin polarizations up to 15 %. A method is described to build in a reproducible and predictable way resonant circuits matched to 50 in the frequency range 100 – 400 MHz with a quality factor as high as 1000 at 4 K.     

The role of complement and gp120-specific antibodies in virus lysis and CD4+ T cell depletion in HIV-1-infected patients

The substantial virus lysis was induced by HIV-1-infected patient serum and normal human complement serum in the presence of purified patient IgG. Non-infected CD4+ T cells coated with the whole virus or with a recombinant HIV-1 envelope gp120 and sensitised with patient IgG were also shown to be susceptible to complement-dependent lysis. The serum level of complement regulatory protein in a fluid phase, the C1-esterase inhibitor, was significantly correlated with serum concentration of C1q-circulating immune complexes (P=0.0062), but inversely with CD4+ T cell count (P < 0.0001). Accordingly, the disease progression in HIV-1-infected patients was significantly correlated with the level of complement activation as determined by serum level of C1-esterase inhibitor (P=0.0001), and inversely correlated with CD4+ cell count (P < 0. 0001) and gp120-specific antibody titre (P=0.0086). These results strongly suggest that the complement activation by gp120-specific antibodies play a very important role in virus clearance, but also in depletion of infected as well as gp120-coated non-infected CD4+ bystander T cells during the course of HIV-1 infection.     

A Flexible and Energy-Efficient Coarse-Grained Reconfigurable Architecture for Mobile Systems

Two of the most important design issues for next generation handheld devices are wireless networking and the processing of multimedia content. Both applications rely heavily on computationally intensive digital signal processing algorithms. Programmable architectures that keep pace with the increasing performance requirements become more and more power hungry. This is problematic for a battery powered mobile device, since it has only a limited amount of energy available. Conversely, dedicated architectures are too inflexible to keep pace with changing standards and feature sets. A mobile device requires high-performance, flexibility and (energy-)efficiency. These contradicting requirements need to be balanced in the system architecture of a mobile device. In this paper a heterogeneous architecture of domain specific processing tiles is proposed. The focal point is the coarse-grained reconfigurable architecture of the Montium processing tile, which is designed to execute digital signal processing algorithms energy-efficiently.     

Liquid-phase methanol synthesis in apolar (squalane) and polar (tetraethylene glycol dimethylether) solvents

The kinetics of the three-phase methanol synthesis over a commercial Cu–Zn–Al₂O₃ catalyst were studied in an apolar solvent, squalane and a polar solvent, tetraethylene glycol dimethylether (TEGDME). Experimental conditions were varied as follows: P=3.0–5.3 MPa, T=488–533 K and Φ_vG/w=7.5×10⁻³–8×10⁻³ Nm³ s⁻¹kg⁻¹_cat. The nature of the slurry–liquid influences the activation energy and the kinetic rate constant by interaction between adsorbed species and solvent and by competitive adsorption of the solvent on the catalyst surface. The rate of reaction to methanol observed in TEGDME appeared to be about 10 times lower than in squalane. TEGDME reduces the reaction rate, which is a disadvantage for its use as a solvent.     

Synthesis and isolation of added‐value milk fat derivatives using lipase‐catalyzed reactions and supercritical carbon dioxide

Lipase‐catalyzed reactions and supercritical technology are powerful tools that can be effectively combined for the modification and processing of fats. In addition, both are “green” technologies, which can produce high‐quality, food‐grade products without the need of additional solvents. We show two examples in which milk fat was used as raw material for the production of added‐value derivatives: short‐chain fatty acid ethyl esters, which are natural flavor agents; and a diacylglycerol‐based, potentially superior dietary fat. In both cases we applied a combination of lipases and supercritical carbon dioxide extraction for the synthesis and separation of products.     

Rheological and crystallization behaviors of low processing temperature poly(aryl ether ketone)

A new low melting temperature poly(aryl ether ketone) (PAEK) thermoplastic polymer (Victrex AE 250) was investigated through thermal and rheological analysis of films and flakes. DSC was assigned to evaluate the influence of cooling rate on crystallinity and thermal transitions. Rheometry was used to assess its flowing behavior through the evaluation of dynamic moduli and complex viscosity in the melted state. The relaxation times were found from the rheological curves: they are between a few ms to 200 ms for AE 250, lower than those found for PEEK 450, meaning a faster mobility of macromolecules. The thermal activation energy, E_a obtained from Time Temperature Superposition is the same for films and flakes in spite of a lower viscosity for flakes. The molecular weight between entanglements is evaluated at 8000 g.mol⁻¹ for FMc and 13,000 for FLc, it is compared to the value of about 2000 g.mol⁻¹ found for PEEK 450 with the same procedure. Also, the viscosity was compared to other commercial PAEK such as PEEK and PEKK based on data from the literature. This polymer appears very efficient to compete with high performance thermoplastics to be processed by compression molding, out of autoclave consolidation, additive manufacturing, and welding.     

Activity-Based Protein Profiling of Chitin Catabolism

The microbial catabolism of chitin, an abundant and ubiquitous environmental organic polymer, is a fundamental cog in terrestrial and aquatic carbon and nitrogen cycles. Despite the importance of this critical bio-geochemical function, there is a limited understanding of the synergy between the various hydrolytic and accessory enzymes involved in chitin catabolism. To address this deficit, we synthesized activity-based probes (ABPs) designed to target active chitinolytic enzymes by modifying the chitin subunits N-acetyl glucosamine and chitotriose. The ABPs were used to determine the active complement of chitinolytic enzymes produced over time by the soil bacterium Cellvibrio japonicus treated with various C substrates. We demonstrate the utility of these ABPs in determining the synergy between various enzymes involved in chitin catabolism. The strategy can be used to gain molecular-level insights that can be used to better understand microbial roles in soil bio-geochemical cycling in the face of a changing climate.     

Binding Specificity of Recombinant Odorant-Binding Protein Isoforms is Driven by Phosphorylation

Native porcine odorant-binding protein (OBP) bears eleven sites of phosphorylation, which are not always occupied in the molecular population, suggesting that different isoforms could co-exist in animal tissues. As phosphorylation is a dynamic process resulting in temporary conformational changes that regulate the function of target proteins, we investigated the possibility that OBP isoforms could display different binding affinities to biologically relevant ligands. The availability of recombinant proteins is of particular interest for the study of protein/ligand structure-function relationships, but prokaryotic expression systems do not perform eukaryotic post-translational modifications. To investigate the role of phosphorylation in the binding capacities of OBP isoforms, we produced recombinant porcine OBP in two eukaryotic systems, the yeast, Pichia pastoris, and the mammalian CHO cell line. Isoforms were separated by anion exchange HPLC, and their phosphorylation sites were mapped by MALDI-TOF mass spectrometry and compared to those of the native protein. Binding experiments with ligands of biological relevance in the pig, Sus scrofa, were performed by fluorescence spectroscopy on two isoforms of recombinant OBP expressed in the yeast. The two isoforms, differing only by their phosphorylation pattern, displayed different binding properties, suggesting that binding specificity is driven by phosphorylation.     

Ruthenacycles and Iridacycles as Catalysts for Asymmetric Transfer Hydrogenation and Racemisation

Ruthenacycles, which are easily prepared in a single step by reaction between enantiopure aromatic amines and [Ru(arene)Cl₂]₂ in the presence of NaOH and KPF₆, are very good asymmetric transfer hydrogenation catalysts. A range of aromatic ketones were reduced using isopropanol in good yields with ee’s up to 98%. Iridacycles, which are prepared in similar fashion from [IrCp*Cl₂]₂ are excellent catalysts for the racemisation of secondary alcohols and chlorohydrins at room temperature. This allowed the development of a new dynamic kinetic resolution of chlorohydrins to the enantiopure epoxides in up to 90% yield and 98% enantiomeric excess (ee) using a mutant of the enzyme Haloalcohol dehalogenase C and an iridacycle as racemisation catalyst.