Number Of Zinc Atoms Research Articles

Thermal and chemical unfolding pathways of PaSdsA1 sulfatase, a homo-dimer with topologically interlinked chains.

Understanding the mechanisms as to how interlinked proteins entangle and fold is a challenge. PaSdsA1 sulfatase is a homo-dimer containing two zinc atoms per monomer. The monomer chains are interlinked in a dimerization domain. To study the unfolding pathways denaturation experiments were performed. In the native protein three forms coexist in chemical equilibrium, each with a different number of zinc atoms. In the chemical unfolding of the holo-dimers the entanglement of the chains is preserved and acts as a 'folding seed', allowing the unfolding process to be reversible. Thermal irreversible unfolding of the holo-dimers favours dissociation, producing monomers that are SDS-stabilized. The thermal unfolding of these monomers is reversible. However, it is not possible to form dimers from unfolded monomers.

The coordination polyhedra ZnS n in crystal structures

Voronoi-Dirichlet polyhedra (VDP) and the intersecting sphere method were used to analyze the coordination of zinc atoms in the structures of all known compounds containing ZnS n polyhedra. The Zn(II) atoms were found to coordinate 6, 5, 4, 3, or 2 sulfur atoms to form coordination octahedra or trigonal prisms (n = 6), trigonal bipyramids (n = 5), tetrahedra (n = 4), triangles ZnS3, or dumbbells ZnS2. The effect of the coordination number of zinc atoms on the key parameters of zinc VDP is considered. A common linear dependence of the solid angles of the VDP faces corresponding to both valence and non-valence Zn-S contacts on the interatomic distances was established to exist. Although the Zn-S bond lengths vary over a broad range (2.39 to 3.29 A), the Zn VDP volume almost does not depend on its C.N. with respect to sulfur. Some characteristic features of Zn stereochemistry are considered from the 18-electron rule standpoint.

Deconvolution of tip affected atomic force microscope images and comparison to Rutherford backscattering spectrometry

There is distortion in atomic force microscope (AFM) images caused by a nonideal shape and size of the probe tip. This is called tip effect and is due to the convolution of the tip and sample. AFM images of nanometer size islands of zinc deposited on silicon substrates by the ionized cluster beam deposition technique were used to investigate this effect. The number of zinc atoms per unit area determined by each of two methods, the AFM images and Rutherford backscattering spectrometry (RBS) are compared and the AFM reported more zinc than RBS. A partial explanation for this difference is that the convolution of the tip and sample makes the islands appear larger in the AFM data. Previously reported convolution and deconvolution algorithms were implemented to study and simulate the interaction between tip and sample in the AFM. The deconvolution algorithm removes part of the distortion by taking into account the physical volume occupied by the tip which exposes a more accurate image. After deconvolution of the zinc islands images there was better agreement between AFM and RBS results. Deconvolution of other images will also be discussed.

Comparison of atomic force microscope and Rutherford backscattering spectrometry data of nanometre size zinc islands

Atomic force microscopes (AFM) form images by sliding a sharp tip over a surface in a raster pattern and recording the height of the tip at each position. There is distortion in these images caused by a non-ideal shape and the size of the probe tips. Previously reported convolution and deconvolution algorithms have been implemented to study and simulate the interaction between the tip and the sample. The first part of this work is a comparison between AFM and Rutherford backscattering spectrometry (RBS) data taken on nanometre size zinc islands on a flat substrate. Zinc islands were deposited on a silicon substrate using the ionized cluster beam deposition technique. An algorithm was developed to calculate the volume of the islands and the number of zinc atoms present from AFM images. The number of zinc atoms per unit area of the same samples was also measured by RBS. The AFM and RBS results agree qualitatively but there is an offset with AFM reporting more zinc than RBS. A possible explanation for this difference is a convolution of the tip and sample making the islands appear larger. After deconvolution of the AFM images there was better agreement between AFM and RBS on the number of zinc atoms per unit area.

The electrical properties of zinc diffused indium phosphide

The electrical properties of p -type layers of InP, formed by the diffusion of zinc into n -type material, are studied. A wide range of diffusion conditions are used and both homogeneously doped specimens and those containing a zinc atom concentration gradient are produced. The impurity atom distribution of the diffused crystals is characterised by radiotracer analysis. p − n junction measurements on non-homogeneously doped specimens indicate that the number of zinc atoms in a diffused layer is much greater than the number of shallow acceptors. This non-correspondence of atom and carrier concentrations is confirmed by four point resistivity, Hall effect and capacitance-voltage measurements. The first two of these techniques are used to produce carrier concentration profiles which are compared with corresponding radio-tracer profiles. The carrier profiles are achieved by both serial sectioning and multiple specimen techniques. A gold probe point contacting procedure is developed for the Hall Effect measurements from which a plot of carrier mobility versus carrier concentration, in the range 5 × 10 18 – 5 × 10 19 cm −3 , is produced for p -type InP.

Diffusion of zinc in indium phosphide at 700°C

Abstract The diffusion of zinc into n -type InP at 700°C is described for a variety of experimental conditions. Radioactive zinc was used and radio-tracer profiles were plotted. Observations were made of the semiconductor surfaces after each diffusion. The p - n junction depths were also measured and some electrical measurements were taken. For some experimental conditions, very high values of zinc surface concentration were found. The samples showing high surface concentrations also exhibited surface features after diffusion, and these were studied using optical microscopy and an X-ray probe microanalyser. In some cases very small changes in diffusion conditions produced large variations in the measured profile. This is attributed to a boundary being crossed in the In/P/Zn ternary phase diagram. A comparison of the radio-tracer and p - n junction measurements shows that the number of zinc atoms in a sample is much greater than the number of shallow acceptors. For diffusions in which excess phosphorus was used, evidence is presented to suggest that the diffusion coefficient varies with zinc concentrations at low densities of zinc, but saturates to a constant value at zinc concentrations above 10 19 cm −3 .

Estimates of the Zinc Requirements of Marine Organisms

The amount of enzyme-bound zinc is calculated from estimates of total enzyme concentrations and the number of zinc atoms per mole of these enzymes. This estimate is shown to be smaller than measured concentrations in marine organisms, indicating that zinc is accumulated in excess of the organisms' immediate needs. A minimum "potential fertility" for zinc is calculated; the results indicate that zinc is not limiting in the marine environment.