Separation of chitosan oligomers by immobilized metal affinity chromatography

A novel approach for chitosan oligosaccharide (COS) separation by immobilized metal affinity chromatography (IMAC) based on the differences in the interactions of chelated copper (II) ions with various COS (dimers, trimers, tetramers) is described. Polyhydroxylic chromatographic supports (agarose CL-6B and silica) were functionalized with various chelating functions such as iminodiacetate (IDA), carboxymethyl-aspartate (CM-Asp) and tris(carboxymethyl)ethylenediamine (TED). The COS retention capacities of the columns were between 2 and 6 mg/cm(3), depending on the chelating group. The COS were separated and/or enriched up to 95% for dimer and trimer and 90% for the tetramer, with yields of 60-95%.     

Oxidative coupling of acridinones: Synthesis of new C2‐symmetry atropisomers

The preparation of symmetric 2,2′‐dimethoxy‐10,10′‐biacridinyl‐9,9′‐dione atropisomers were obtained by the oxidative coupling of 9(10H)‐acridinone with 1,3‐dibromo‐5,5‐dimethyl‐imidazolidine‐2,4‐dione     

NIR‐to‐NIR Two‐Photon Scanning Laser Microscopy Imaging of Single Nanoparticles Doped by YbIII Complexes

The photophysical and nonlinear optical properties of water‐soluble chromophore‐functionalised tris‐dipicolinate complexes [LnL₃]^3? (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb^III luminescence can be sensitized by a two‐photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu₄]₃[YbL₃] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two‐photon microscopy setup in a NIR‐to‐NIR configuration.     

Suitability of different containers for the sampling and storage of biogas and biomethane for the determination of the trace-level impurities – A review

The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement.     

Standard thermodynamic properties of H3PO4(aq) over a wide range of temperatures and pressures

The densities and heat capacities of solutions of phosphoric acid, 0.05 to 1 mol kg-1, were measured using flow vibrating tube densitometry and differential Picker-type calorimetry at temperatures up to 623 K and at pressures up to 28 MPa. The standard molar volumes and heat capacities of molecular H3PO4(aq) were obtained, via the apparent molar properties corrected for partial dissociation, by extrapolation to infinite dilution. The data on standard derivative properties were correlated simultaneously with the dissociation constants of phosphoric acid from the literature using the theoretically founded SOCW model. This made it possible to describe the standard thermodynamic properties, particularly the standard chemical potential, of both molecular and ionized phosphoric acid at temperatures up to at least 623 K and at pressures up to 200 MPa. This representation allows one to easily calculate the first-degree dissociation constant of H3PO4(aq). The performance of the SOCW model was compared with the other approaches for calculating the high-temperature dissociation constant of the phosphoric acid. Using the standard derivative properties, sensitively reflecting the interactions between the solute and the solvent, the high-temperature behavior of H3PO4(aq) is compared with that of other weak acids.     

AFM imaging of immobilized fibronectin: does the surface conjugation scheme affect the protein orientation/conformation?

Covalent grafting of biomolecules could potentially improve the biocompatibility of materials. However, these molecules have to be grafted in an active conformation to play their biological roles. The present work aims at verifying if the surface conjugation scheme of fibronectin (FN) affects the protein orientation/conformation and activity. FN was grafted onto plasma-treated fused silica using two different crosslinkers, glutaric anhydride (GA) or sulfosuccinimidyl 4-(p-maleimidophenyl)butyrate (SMPB). Fused silica was chosen as a model surface material because it presents a roughness well below the dimensions of FN, therefore allowing AFM analyses with appropriate depth resolution. Cell adhesion assays were performed to evaluate the bioactivity of grafted FN. Cell adhesion was found to be higher on GA-FN than on SMPB-FN. Since FN-radiolabeling assays allowed us to rule out a surface concentration effect (approximately 80 ng/cm2 of FN on both crosslinkers), it was hypothesized that FN adopted a more active conformation when grafted via GA. In this context, the FN conformation on both crosslinkers was investigated through AFM and contact angle analyses. Before FN grafting, GA- and SMPB-modified surfaces had a similar water contact angle, topography, and roughness. However, water contact angles of GA-FN and SMPB-FN surfaces clearly show differences in surface hydrophilicity, therefore indicating a dependence of protein organization toward the conjugation strategy. Furthermore, AFM results demonstrated that surface topography and roughness of both FN-conjugated surfaces were significantly different. Distribution analysis of FN height and diameter confirmed this observation as the protein dimensions were significantly larger on GA than SMPB. This study confirmed that the covalent immobilization scheme of biomolecules influences their conformation and, hence, their activity. Consequently, selecting the appropriate conjugation strategy is of paramount importance in retaining molecule bioactivity.     

Methods to Analyse the Texture of Alginate Aerogel Microspheres

Nitrogen adsorption at 77 K has been applied to the study of the texture of alginate aerogel microspheres obtained by CO₂ supercritical drying of alcogels. The limited volume shrinkage suggests that the aerogels preserve the texture of the hydrogels. Alginate aerogels presents a N₂ adsorption at small pressure higher than reference non-porous silica, to be attributed to the polarity of the surface or to a small microporous volume. The aggregated nanobead strings of the guluronic-rich gels accounts for a significant mesoporosity. The N₂ adsorption results correspond to electron microscopy observations for features smaller than 50 nm.     

Synthesis of Polystyrene‐block‐poly(butyl acrylate) Copolymers Using Nitroxide‐Mediated Living Radical Polymerization in Miniemulsion

Living free‐radical butyl acrylate polymerization in miniemulsion was initiated by polystyrene bearing a nitroxyl end group to yield polystyrene‐block‐poly(butyl acrylate) block copolymers. Polystyrene macroinitiator was obtained using different initiating systems (potassium persulfate or benzoyl peroxide) in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) or the more water‐soluble 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐N‐oxyl (OH‐TEMPO). The nitroxide water‐solubility has an important influence in determining molecular weight distribution and controlling the growth of the second block.     

DNS and LES of spark ignition with an automotive coil

The cycle to cycle combustion variability which is observed in spark-ignition engines is often caused by fluctuations of the early flame development. LES can be exploited for a better understanding and mastering of their origins. For that purpose appropriate models taking into account energy deposition, mixture ignition and transition to propagation are necessary requirements. This paper presents first DNS and LES of spark ignition with a real automotive coil and simplified pin-pin electrodes. The electrical circuit characteristics are provided by ISSIM while the energy deposition is modelled by Lagrangian particles. The ignition model is first evaluated in terms of initial spark radius on a pin-pin ignition experiment in pure air performed at CORIA and EM2C laboratories, showing that it pilots the radius of the torus formed by the initial shock wave. DNS of a quiescent lean propane/air mixture are then performed with this ignition system and a two-step mechanism. The impact of the modelled transferred energy during glow phase as well as the initial arc radius on the minimum ignition energy (MIE) are examined and compared to experimental values. Replacing the two-step chemistry by an analytically reduced mechanism leads to similar MIE but shows a different ignition kernel shape. Finally, LES of turbulent ignition using a Lagrangian arc model show a realistic prediction of the arc shape and its important role on the energy transfer location and thus on the flame kernel shape.