A simple and rapid chemical method for the determination of cephalosporins

A simple and rapid chemical assay for cephalosporins is described. It is a simple modification of the colorimetric determination of penicillins in which the narrow spectrum beta-lactamase (penicillinase) is replaced by a broad spectrum beta-lactamase (cephalosporinase) produced by Enterobacter cloacae. The method can be used for assay of fermentation broths as well as for pure cephalosporins.     

Sodium‐Naphthalenide‐Driven Synthesis of Base‐Metal Nanoparticles and Follow‐up Reactions

Mo⁰, W⁰, Fe⁰, Ru⁰, Re⁰, and Zn⁰ nanoparticles—essentially base metals—are prepared as a general strategy by a sodium naphthalenide ([NaNaph])‐driven reduction of simple metal chlorides in ethers (1,2‐dimethoxyethane (DME), tetrahydrofuran (THF)). All the nanoparticles have diameters ≤10 nm, and they can be obtained either as powder samples or long‐term stable suspensions. Direct follow‐up reactions (e.g., Mo⁰+S₈, FeCl₃+AsCl₃, ReCl₅+MoCl₅), moreover, allow the preparation of MoS₂, FeAs₂, or Re₄Mo nanoparticles of similar size as the pristine metals (≤10 nm).     

Influence of long-chain branches in polyethylenes on linear viscoelastic flow properties in shear

 This contribution presents a survey on the influence of long-chain branching on the linear viscoelastic properties zero shear-rate viscosity and steady-state recoverable compliance of polyethylene melts. The materials chosen are linear and slightly long-chain branched metallocene-catalyzed polyethylenes of narrow molecular mass distribution as well as linear and highly long-chain branched polyethylenes of broad molecular mass distribution. The linear viscoelastic flow properties are determined in shear creep and recovery experiments by means of a magnetic bearing torsional creep apparatus. The analysis of the molecular structure of the polyethylenes is performed by a coupled size exclusion chromatography and multi-angle laser light scattering device. Polyethylenes with a slight degree of long-chain branching exhibit a surprisingly high zero shear-rate viscosity in comparison to linear polyethylenes whereas the highly branched polyethylenes have a much lower viscosity compared to linear samples. Slightly branched polyethylenes have got a higher steady-state compliance in comparison to linear products of similar polydispersity, whereas the highly branched polyethylenes of broad molecular mass distribution exhibit a surprisingly low elasticity in comparison to linear polyethylenes of broad molecular mass distribution. In addition sparse levels of long-chain branching cause a different time dependence in comparison to linear polyethylenes. The experimental findings are interpreted by comparison with rheological results from literature on model branched polymers of different molecular topography and chemical composition. Received: 12 July 2001 Accepted: 30 October 2001     

Free-standing biomimetic polymer membrane imaged with atomic force microscopy

Fluid polymeric biomimetic membranes are probed with atomic force microscopy (AFM) using probes with both normal tetrahedrally shaped tips and nanoneedle-shaped Ag(2)Ga rods. When using nanoneedle probes, the collected force volume data show three distinct membrane regions which match the expected membrane structure when spanning an aperture in a hydrophobic scaffold. The method used provides a general method for mapping attractive fluid surfaces. In particular, the nanoneedle probing allows for characterization of free-standing biomimetic membranes with thickness on the nanometer scale suspended over 300-μm-wide apertures, where the membranes are stable toward hundreds of nanoindentations without breakage.     

Reduced protein adsorption by osmolytes

Osmolytes are substances that affect osmosis and are used by cells to adapt to environmental stress. Here, we report a neutron reflectivity study on the influence of some osmolytes on protein adsorption at solid-liquid interfaces. Bovine ribonuclease A (RNase) and bovine insulin were used as model proteins adsorbing at a hydrophilic silica and at a hydrophobic polystyrene surface. From the neutron reflectivity data, the adsorbed protein layers were characterized in terms of layer thickness, protein packing density, and adsorbed protein mass in the absence and presence of urea, trehalose, sucrose, and glycerol. All data point to the clear effect of these nonionic cosolvents on the degree of protein adsorption. For example, 1 M sucrose leads to a reduction of the adsorbed amount of RNase by 39% on a silica surface and by 71% on a polystyrene surface. Trehalose was found to exhibit activity similar to that of sucrose. The changes in adsorbed protein mass can be attributed to a decreased packing density of the proteins in the adsorbed layers. Moreover, we investigated insulin adsorption at a hydrophobic surface in the absence and presence of glycerol. The degree of insulin adsorption is decreased by even 80% in the presence of 4 M of glycerol. The results of this study demonstrate that nonionic cosolvents can be used to tune and control nonspecific protein adsorption at aqueous-solid interfaces, which might be relevant for biomedical applications.     

Biomimetic membrane arrays on cast hydrogel supports

Lipid bilayers are intrinsically fragile and require mechanical support in technical applications based on biomimetic membranes. Tethering the lipid bilayer membranes to solid substrates, either directly through covalent or ionic substrate-lipid links or indirectly on substrate-supported cushions, provides mechanical support but at the cost of small molecule transport through the membrane-support sandwich. To stabilize biomimetic membranes while allowing transport through a membrane-support sandwich, we have investigated the feasibility of using an ethylene tetrafluoroethylene (ETFE)/hydrogel sandwich as the support. The sandwich is realized as a perforated surface-treated ETFE film onto which a hydrogel composite support structure is cast. We report a simple method to prepare arrays of lipid bilayer membranes with low intrinsic electrical conductance on the highly permeable, self-supporting ETFE/hydrogel sandwiches. We demonstrate how the ETFE/hydrogel sandwich support promotes rapid self-thinning of lipid bilayers suitable for hosting membrane-spanning proteins.