Geobacter species enhances pit depth on 304L stainless steel in a medium lacking with electron donor

Geobacter sulfurreducens bacteria increased the open circuit potential of 304L stainless steel by around 320 mV in only a few hours after inoculation. This represents a significant increase in the corrosion risk. In contrast, the oxidation of acetate, which is catalysed by well-established biofilms, shifted the pitting potential towards positive values. In acetate-lacking media, pitting occurred with and without bacteria in the same range of potential values, but the presence of bacteria drastically increased the size of pits. AFM showed pits more than 10 times broader and deeper due to the presence of bacteria.In the absence of acetate, the masking effect due to acetate oxidation disappeared and the full corrosive effect of the biofilm was revealed.This also fully explains why pitting was predominantly observed close to surface areas where bacterial settlement was the densest.     

Activation of Elemental Sulfur at a Two‐Coordinate Platinum(0) Center

Platinum dichalcogenides have been known to exhibit two‐dimensional layered structures. Herein, we describe the syntheses, isolation, and characterization of air‐stable crystalline cyclic alkyl(amino) carbene (cAAC)‐supported monomeric platinum disulfide three‐membered ring complex [(cAAC)₂Pt(S₂)] ( 2 ). The highly reactive platinum(0) [(cAAC)₂Pt] complex ( 1 ) with two‐coordinate platinum activates elemental sulfur to give 2 . The brown crystals of bis‐carbene platinum(II)monosulfate [(cAAC)₂Pt(SO₄)_x(S₂)_1?x] ( 4 ) have been isolated when the reaction was performed in air. The dioxygen analogue of 2 was formed upon exposing the THF solution of 1 to aerial oxygen (O₂). The binding of oxygen at the Pt⁰ center was found to be reversible. Additionally, DFT study has been performed to elucidate the electronic structure and bonding scenario of 2 , 3 , and 4 . Quantum chemical calculations showed donor–acceptor‐type interaction for the Pt?S bonds in 2 and Pt?O bonds in 3 and 4 .     

Effect of cross-linker density of P(NIPAM-co-AAc) microgels at solid surfaces on the swelling/shrinking behaviour and the Young��s modulus

The effect of the amount of cross-linker in poly(N-isopropylacrylamide-co-acrylic acid) microgel particles on the swelling behaviour and their elasticity is studied. The distribution of the stiffness through the particle is also investigated. Therefore, the swelling ratio obtained from dynamic light scattering measurements in aqueous solutions is compared with the one after adsorption at polycation-coated silicon wafers. The studies of the swelling behaviour at the surface are carried out with scanning force microscopy (SFM) against liquid. The Young??s modulus is determined by indentation experiments with an SFM. With increasing amount of cross-linker, the ability to shrink as well as the shift in the lower critical solution temperature and in particle size (hysteresis) during the heating and cooling processes decreases. In addition, the particles at the surface preserve their height/width ratio at high amount of cross-linker, while at low amounts the shrinking and swelling mainly takes place with respect to changes in height. The particles show their highest Young??s modulus in the centre of the particles and become stiffer with increasing the amount of cross-linker and the temperature.     

A New Multiresponsive Drug Delivery System using Smart Nanogels

This paper addresses the synthesis and characterization of a novel temperature‐ and pH‐responsive nanogel system based on poly(vinylcaprolactam‐co‐2‐dimethylaminoethyl methacrylate) [P(VCL‐co‐DMAEMA)] by using a surfactant‐free emulsion polymerization procedure for the multiresponsive drug delivery of hydrophobic drugs. The effects of solvent, monomer, pH, and temperature were studied to tailor the average particle hydrodynamic diameters and the polydispersity index of the final particles. According to dynamic light‐scattering measurements, the obtained nanogels show a narrow particle‐size distribution and their hydrodynamic diameters can be varied from 81 to 368 nm. The nanogels display a re‐entrant phase‐transition state, and the equilibrium volume swelling ratio of the nanogels decreases drastically down to 47 °C and then increases up to 65 °C. In addition, the nanogels show pH‐dependent behavior. They exhibit a maximum size at pH 5.0. Rhodamine B (RhB) was chosen as a model compound for drug loading and release studies from P(VCL‐co‐DMAEMA) on the basis of particles in different phosphate buffer solutions at different temperatures. The temperature/pH‐dependent cumulative release and ultrasound‐enhanced pulsatile release properties were investigated for RhB‐loaded nanogels for long‐term and one‐shot delivery. The nanogels display efficient delivery for both long‐term and one‐shot delivery systems. We provide here a proof of concept for the novel use of multiresponsive nanogels having an overall size below 200 nm as a cargo system for hydrophobic drugs and for controlled release mediated by temperature/pH and ultrasound.     

Development of an optical biosensor assay for detection of β-lactam antibiotics in milk using the penicillin-binding protein 2x*

An assay was developed for the detection of residues of penicillins and cephalosporins in milk using a surface plasmon resonance (SPR) biosensor. The assay was based on the inhibition of the binding of digoxigenin-labelled ampicillin (DIG-AMPI) to a soluble penicillin-binding protein 2x derivative (PBP 2x*) of Streptococcus pneumoniae. Samples were incubated with PBP 2x* in a first step, whereby β-lactams in positive samples would bind to the PBP 2x*. Non-complexed PBP 2x* was then allowed to form a complex with DIG-AMPI in a second incubation step. The formed DIG-AMPI/PBP 2x*-complexes were detected in a SPR-based biospecific interaction assay (BIA) for digoxigenin with an antibody against digoxigenin immobilised on the sensor chip. Although binding of matrix components to the sensor chip (non-specific binding) occurred, benzylpenicillin, ampicillin, amoxicillin, cloxacillin, cephalexin and cefoperazone could be detected in defatted bulk raw milk samples at concentrations corresponding to the maximum residue limits (MRL) set by the European Union. The influence of matrix components on the performance of the assay was examined in more detail by analysing individual raw milk samples from 19 cows. Compared to bulk raw milk samples, individual samples showed a higher level and variation of matrix interferences. Non-specific binding could be reduced to a lower and more constant level by a heat-treatment step, a centrifugation step and the addition of carboxymethylated dextran to the samples. With this sample preparation, benzylpenicillin could be detected at MRL (4 μg kg⁻¹) in individual raw milk samples. Thus, the assay could be the basis for a screening test for routine use.     

Nitridation of niobium films by rapid thermal processing: different behaviour of films on oxydized silicon and monocrystalline sapphire substrates

By electron beam evaporation and RF magnetron sputtering 500 nm thick niobium films were deposited on thermally oxidized Si-(100)-wafers and by RF magnetron sputtering on monocrystalline sapphire-(1-102)-wafers. Investigations by scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed differences of the film morphology depending on the substrate used: films deposited on SiO₂ exhibited an even surface with small crystallites, films on sapphire showed parallel surface structures with relatively large and well-shaped crystallites pointing at regular crystal growth influenced by the substrate. These differences in film morphology were also reflected in different reflection intensities of the films in XRD patterns, indicating that the films deposited on sapphire were strongly textured. In a first set of experiments nitridation in molecular nitrogen and ammonia was investigated. In a second set of experiments, it was tried to form oxynitrides of niobium by annealing the nitrided films in molecular oxygen. Particularly by X-ray-diffraction the formation of different nitride and oxide phases in dependence of the reaction temperature was examined. Further, elemental depth profiles were recorded by secondary ion mass spectrometry (SIMS) to track the position of the phases formed in the film. The different substrates led to disparate film reactivities, resulting in different nitridation grades of the films at similar reaction temperatures. In general, larger crystallite sizes resulted in less chemical reactivity of the films: even after nitridation at 1000 °C metallic niobium was still present in films deposited on sapphire. However, no evidence was obtained for the formation of oxynitrides by the process sequence observed.