The Mechanism of Formation of Active Fe-TAMLs Using HClO Enlightens Design for Maximizing Catalytic Activity at Environmentally Optimal, Circumneutral pH.

Fe-TAML/peroxide catalysis provides simple, powerful, ultradilute approaches for removing micropollutants from water. The typically rate-determining interactions of H2O2 with Fe-TAMLs (rate constant kI) are sharply pH-sensitive with rate maxima in the pH 9-10 window. Fe-TAML design or process design that shifts the maximum rates to the pH 6-8 window of most wastewaters would make micropollutant eliminations even more powerful. Here, we show how the different pH dependencies of the interactions of Fe-TAMLs with peroxide or hypochlorite to form active Fe-TAMLs (kI step) illuminate why moving from H2O2 (pKa, ca. 11.6) to hypochlorite (pKa, 7.5) shifts the pH of the fastest catalysis to as low as 8.2. At pH 7, hypochlorite catalysis is 100-1000 times faster than H2O2 catalysis. The pH of maximum catalytic activity is also moderated by the pKa's of the Fe-TAML axial water ligands, 8.8, 9.3, and 10.3, respectively, for [Fe{4-NO2C6H3-1,2-(NCOCMe2NSO2)2CHMe}(H2O)n]- (2) [n = 1-2], [Fe{4-NO2C6H3-1,2-(NCOCMe2NCO)2CF2}(H2O)n]- (1b), and [Fe{C6H4-1,2-(NCOCMe2NCO)2CMe2}(H2O)n]- (1a). The new bis(sulfonamido)-bis(carbonamido)-ligated 2 exhibits the lowest pKa and delivers the largest hypochlorite over peroxide catalytic rate advantage. The fast Fe-TAML/hypochlorite catalysis is accompanied by slow noncatalytic oxidations of Orange II.

PETER-assay: Combined Impedimetric Detection of Permeability (PE) and Resistance (TER) of Barrier-Forming Cell Layers.

Epithelial and endothelial barrier function is typically studied in vitro by growing the cells of interest on permeable supports that are sandwiched between two fluid compartments. This setup mimics the physiological situation with the cell layer as the diffusion barrier at the interface between two chemically distinct fluids. Routinely, the barrier function is quantitatively described by two key parameters: (i) the transepithelial or transendothelial electrical resistance (TER) as a measure of the permeability for small inorganic ions and (ii) the permeability coefficient (PE) as a descriptor of the permeability for molecular tracers. So far the two parameters have been determined in separate experiments. This study introduces a device that allows for simultaneous detection of PE and TER of the very same cell monolayer in one single experiment (PETER-assay). The novel approach is entirely based on AC impedance measurements in two different modes, so that TER and PE become available in real time. The new approach is demonstrated for three epithelial cell lines derived from the kidney (MDCK-I, MDCK-II, NRK) with very different barrier properties under stationary conditions and when challenged by barrier-breaking fungal toxin cytochalasin D. PETER provides an excellent time-resolution and completely automated data collection.

Rhombic organization of microvilli domains found in a cell model of the human intestine.

Symmetry is rarely found on cellular surfaces. An exception is the brush border of microvilli, which are essential for the proper function of transport epithelia. In a healthy intestine, they appear densely packed as a 2D-hexagonal lattice. For in vitro testing of intestinal transport the cell line Caco-2 has been established. As reported by electron microscopy, their microvilli arrange primarily in clusters developing secondly into a 2D-hexagonal lattice. Here, atomic force microscopy (AFM) was employed under aqueous buffer conditions on Caco-2 cells, which were cultivated on permeable filter membranes for optimum differentiation. For analysis, the exact position of each microvillus was detected by computer vision; subsequent Fourier transformation yielded the type of 2D-lattice. It was confirmed, that Caco-2 cells can build a hexagonal lattice of microvilli and form clusters. Moreover, a second type of arrangement was discovered, namely a rhombic lattice, which appeared at sub-maximal densities of microvilli with (29 ± 4) microvilli / µm2. Altogether, the findings indicate the existence of a yet undescribed pattern in cellular organization.

Reaction of human macrophages on protein corona covered TiO2 nanoparticles.

The cytokine secretion of primary cells of human macrophages during the interaction of TiO2 nanoparticles (with an average primary size of 100-120 nm) is investigated down to concentration levels suggested to be relevant for in vivo conditions. We find that high TiO2 concentrations induce the cytokines Interleukin IL-1ß, IL-6, and IL-10 secretion, while at low concentrations only IL-6 secretion is observed. To obtain further evidence on in vivo conditions we investigated the development and structure of the protein corona of the nanoparticles. We demonstrated that the surface of TiO2 particles attract preferably secondary modified proteins which then induce cytokine secretion of macrophages. Our results indicate that concentration of corona covered TiO2 particles below 1 µg/ml induce IL-6 secretion which is reported to be responsible for the development of autoimmune diseases as well as for the secretion of acute phase proteins. FROM THE CLINICAL EDITOR: This study investigates the effects of protein corona covered titanium dioxide nanoparticles on human macrophages, concluding that concentration of such particles below 1 µg/ml induces IL-6 secretion, which may be responsible for the development of autoimmune diseases as well as for the secretion of acute phase proteins. This finding has important implications on future applications of such nanoparticles.

Single beam optical tweezers setup with backscattered light detection for three-dimensional measurements on DNA and nanopores.

We introduce a versatile and high precision three-dimensional optical tweezers setup with minimal optical interference to measure small forces and manipulate single molecules in the vicinity of a weak reflective surface. Our tweezers system integrates an inverted optical microscope with a single IR-laser beam that is spatially filtered in an appropriate way to allow force measurements in three dimensions with remarkably high precision when operated in backscattered light detection mode. The setup was tested by overstretching a lambda-DNA in x and z directions (perpendicular and along the optical axis), and by manipulating individual lambda-DNA molecules in the vicinity of a nanopore that allowed quantitative single molecule threading experiments with minimal optical interference.

Colloid probes with increased tip height for higher sensitivity in friction force microscopy and less cantilever damping in dynamic force microscopy.

We present a method how to glue small spheres to atomic force microscope cantilevers. In difference to an often used approach where the sphere is glued to a tipless cantilever, we suggest to mount small spheres to a conventional cantilever with integrated tips modified by a focused ion beam. In this way it is possible to manufacture a spherical probe with increased tip height which enhances the sensitivity in friction force microscopy and reduces the cantilever damping in dynamic force microscopy. By milling cavities for the spheres at the tip apex the colloid particles can be attached at defined positions and contamination with glue can be prevented.

Investigation of living pancreas tumor cells by digital holographic microscopy.

Digital holographic microscopy provides new facilities for contactless and marker-free quantitative phase contrast imaging. In this work, a digital holographic microscopy method for the integral refractive index determination of living single cells in cell culture medium is presented. Further, the obtained refractive index information is applied to full field thickness and shape determination of adherent pancreas tumor cells, as well as for analysis of drug-induced dynamic changes of a single cell's cytoskeleton. The results demonstrate that digital holographic microscopy is a quantitative phase contrast technique for living cells under conventional laboratory conditions.