Atomic force microscopy study of the interaction of Fusarium solani pisi cutinase with lipid surfaces

We present an atomic force microscopy (AFM) study of a supported triacylglyceride multilayer phase and its interaction with lipolytic enzyme cutinase from Fusarium solani pisi. The multilayer triacylglyceride phase of coconut oil showed a rippled surface structure in the AFM images. Upon enzymatic degradation of the triacylglyceride phase, the ripple structure vanished rapidly. The apparent catalytic rate constants could be estimated based on the AFM image information. Interestingly, in one sample we observed what we interpret as a recurrent structural collapse of the cavity dug out by the protein. We interpret the cavities seen in the AFM images as molten surfaces or surface holes filled with liquidified phase containing product molecules, which appear transparent during the image recording.     

Ion channel mimetic micropore and nanotube membrane sensors

This paper describes synthetic micropore and nanotube membranes that mimic the function of a ligand-gated ion channel; that is, these membranes can be switched from an "off" state (no or low ion current through the membrane) to an "on" state (higher ion current) in response to the presence of a chemical stimulus. Ion channel mimics based on both microporous alumina and Au nanotube membranes were investigated. The off state was obtained by making the membranes hydrophobic by chemisorbing either a C18 silane (alumina membrane) or a C18 thiol (Au nanotube membrane). Water and electrolyte are forbidden from entering these very hydrophobic pores/nanotubes. The transition to the on state was induced by the partitioning of a hydrophobic ionic species (e.g., a drug or a surfactant) into the membrane. The membrane switches to the on state because at a sufficiently high concentration of this ionic analyte species, the pores/nanotubes flood with water and electrolyte. A pH-responsive membrane was also prepared by attaching a hydrophobic alkyl carboxylic acid silane to the alumina membrane.     

Carbon dioxide effects on luminol and 1,10-phenanthroline chemiluminescence

Luminol and 1,10-phenanthroline are widely used chemiluminescent (CL) reagents for the analysis of a wide range of metals and inorganic and organic complexes. While the fundamental mechanism for luminol and 1,10-phenantholine chemiluminescence is understood, the analytical application of these reagents is largely empirical and often poorly described mechanistically. For example, CL signals observed from metal-luminol systems are strongly dependent on the pH of the sample, even though the final pH of the reaction mixture is controlled to a narrow range by a buffer. Other investigators report significant changes in CL signal due to freshness and the acidity of reagents. Our work shows that many of these effects are due to dissolved CO2 present or formed in the analytical system. The hypothesis that carbon dioxide plays a pivotal role in enhancing luminol CL is supported by direct manipulation of CO2(aq) concentrations by the addition of CO2(g) or carbonic anhydrase. In contrast, Cu(II) analysis using the CL reagent 1,10-phenanthroline is completely quenched in the presence of CO2(aq). A plausible mechanism for these observations involves the reaction between superoxide, produced in these analytical systems, and CO2(aq) to form the peroxycarbonate radical, *C04-. The formation of *CO4- has very important analytical implications since this species appears to enhance or quench the CL signal from luminol and 1,10-phenanthroline, respectively.     

A simplified broadband coupling approach applied to chemically robust sol-gel, planar integrated optical waveguides

A new generation waveguide spectrometer with broadband coupling capabilities has been developed. As opposed to previous devices, this attenuated total reflection (ATR) spectrometer is much simpler in design, is more chemically robust, and transmits light down to at least 400 nm. The attenuated total reflection element consists of a single-mode, planar integrated optical waveguide fabricated by dip-coating a approximately 300 nm thick, sol-gel composite layer on a glass substrate. A commercially available prism is used as the incoupler with an integral holographic diffraction grating acting as the dispersive outcoupling element. The transmission of narrow band-pass filters was used to compare the response of the waveguide spectrometer to that of a conventional transmission instrument. Spectral resolution was assessed by measuring the fwhm of various laser lines, which were found to range from 0.5 to 1.3 nm. The measured limits of detection for the waveguide spectrometer from 400 to 600 nm are 8.0 and 10.1 milliabsorbance units for TE and TM polarizations, respectively. Finally, to demonstrate the application of this technology to a molecular film confined to a solid-liquid interface, visible ATR spectra of an adsorbed submonolayer of horse heart cytochrome c were acquired. A procedure to correct the waveguide spectra for the wavelength dependence in ATR path length is described.     

Multielement analysis in cereals and pulses by k0 instrumental neutron activation analysis

The concentrations of some elements in a few varieties of cereals and pulses are determined by Instrumental Neutron Activation Analysis using a single comparator method (k0-standardised NAA method). A total of 15 elements are measured. The method was validated by analysing the Standard Reference Material (SRM-1571) of NIST; the results are within +/-10% of the reported values for the majority of the elements. The measured concentrations of major and minor elements are analysed in terms of the average intake of mineral content and the role of these elements in terms of the nutritional value.     

Coherent and incoherent components of a synchrotron radiation spot produced by separate capillaries

We discuss soft-x-ray focusing properties of separate capillaries. It is shown that a nonnegligible fraction of the synchrotron radiation beam transmitted by the capillary is modal. Experimental and theoretical data are discussed to explain the superposition pattern of x rays in the focal plane due to the interference phenomena of electromagnetic radiation propagating through separate capillaries.     

Evidence for roles of the activating function in electric stimulation

The hypothesis that the activating function drives transmembrane voltage changes (delta Vm) has been tested in hearts. Optical delta Vm were measured during activating functions produced with nonuniform and uniform transparent electrodes. When a nonuniform electrode was used to produce [equation: see text], the signs of delta Vm and [equation: see text] matched. The extracellular voltage gradients, often assumed important, did not predict delta Vm. When a uniform electrode was used to eliminate [equation: see text], the signs of delta Vm matched the signs of [equation: see text] estimated from variations in heart width. Demonstration of the activating function as a determinant of stimulation may improve research and therapy that use electric stimulation.     

Single-reflection regime of X rays that travel into a monocapillary

We present an analysis of the transmission of x rays through a single monocapillary under the single-reflection regime. Because ray tracing does not provide an explanation for experimental data, we give a qualitative interpretation of the observed behavior within the framework of wave theory.     

Gradient surface porosity in titanium dental implants: relation between processing parameters and microstructure

To be successful, an implant should be biocompatible, strong and contain surface pores to promote osseointegration. A one-step microwave sintering procedure of titanium powders was attempted in this work. The idea was to take advantage of the peculiar way microwave couple with metallic powders, i.e. generating heat in the interior of the sample and dissipating it away through the surface. This non-conventional heating of titanium powder produced a dense core with surface porosity. The dense core provides the strength while the surface pores promote bone growth. The experiments were carried out in a semi-industrial grade microwave cavity using a alpha-SiC susceptor. Power levels of 1-1.5 kW, and soaking periods of approximately 30 min were used. Microstructural characterization was carried out by a scanning electron microscope. The sintered titanium had gradient porosity on the surface with a thickness of about 100-200 microm depending on the microwave power. The pores were interconnected with size ranging from 30 to 100 microm. This kind of microstructure is favorable for cell growth. Tensile strength values as high as 400 MPa were obtained for these samples.     

Error analysis of pure rotation-based self-calibration

Self-calibration using pure rotation is a well-known technique and has been shown to be a reliable means for recovering intrinsic camera parameters. However, in practice, it is virtually impossible to ensure that the camera motion for this type of self-calibration is a pure rotation. In this paper, we present an error analysis of recovered intrinsic camera parameters due to the presence of translation. We derived closed-form error expressions for a single pair of images with nondegenerate motion; for multiple rotations for which there are no closed-form solutions, analysis was done through repeated experiments. Among others, we show that translation-independent solutions do exist under certain practical conditions. Our analysis can be used to help choose the least error-prone approach (if multiple approaches exist) for a given set of conditions.