Inhibition of trypanothione reductase by substrate analogues

Trypanothione reductase (TR) catalyzes the NAPDH-dependent reduction of the spermidine-glutathione conjugate trypanothione, an antioxidant found in Trypanosomatid parasites. TR plays an essential role in the parasite's defense against oxidative stress and has emerged as a prime target for drug development. Here we report the synthesis of several trypanothione analogues and their inhibitory effects on T. cruzi TR. All are competitive inhibitors with K(i) values ranging from 30 to 91 microM.     

Taking a strategic view of BPR to develop a multidisciplinary framework

Despite undoubtedly being one of the latest fads, Business Process Reengineering (BPR) has provoked much debate about how organisations should be managed if dramatic improvements in performance are to be achieved. This paper takes a multidisciplinary view of BPR and focuses upon a number of the emergent issues. These include the role of strategy making, the promotion of communication and creativity, the role of statistics, and the effective use of performance measurement systems within a learning environment. The paper develops a framework that capitalises on the role of modelling in MS/OR as well as the various disciplines of the authors. As such, the framework draws on recent advances, as well as established thinking, in the areas of strategy development, information systems, quality management and statistical science. More importantly, the framework also provides an iterative approach to BPR enabling organisations to design, implement and monitor progress on an ongoing basis. Emphasis is placed on building effective communications, developing an organisational memory and supporting organisational learning.     

Ordering in an ensemble of nanometer-size Au clusters on a NaCl(100) surface at high deposition rates

The results of experimental studies on pulsed laser deposition of the Au atoms on the NaCl(100) surface are reported. Under the conditions far from thermodynamic equilibrium, the spatial ordering was observed in an ensemble of gold clusters at the initial deposition stage. A mechanism based on the idea of fractal structure decomposition caused by the development of unstable concentration modes in the condensed substance is proposed.     

The percolation transition in filling a nanoporous body by a nonwetting liquid

The paper presents the results of an experimental study of the percolation transition in filling by nonwetting liquids of nanoporous bodies of various natures with different specific surface areas and mean pore and granule sizes. The liquid that we used was an aqueous solution of ethylene glycol. The hysteresis and non-outflow phenomena observed in this transition at various (known) surface energies of liquids were studied by varying the concentration of ethylene glycol. This helped us explain the mechanism of the percolation transition in filling nanoporous bodies with nonwetting liquids. It was shown that, to quantitatively describe the observed dependences in terms of percolation theory taking into account energy barriers to filling, we must use a non-scaling distribution function of clusters of accessible and filled pores that admits the formation of pore clusters of arbitrary dimensions.     

Correlation effects in Auger spectra of Ni and Cu nanoclusters

Results of experimental research of exciton-like two-hole states in nanoclusters of narrow-band metals (Ni, Cu) on surface of high-oriented pyrolitic graphite by X-ray photoelectron and Auger electron spectroscopy are presented. It was found that the evolution of the electronic structure in Ni nanoclusters with the decreasing of their sizes can lead to appearance of long-living two-hole states in the valence band. One-particle and two-particle density of states are analyzed, and the Auger-electron spectra confirming the presence of the bound and localized states are obtained.     

A study of many-body phenomena in metal nanoclusters (Au, Cu) close to their transition to the nonmetallic state

The results of a study of many-body phenomena in gold and copper nanoclusters are presented. The measured conductivity as a function of nanocluster height h was found to have a minimum at h ≈ 0.6 nm. Conductivity was local in character at nanocluster sizes l ≤ l _c ≈ 2.5 nm. Changes in core hole screening and an anomalous increase in the Anderson singularity index α in gold and copper nanoclusters could be caused by changes in permittivity from metallic (? → ∞) to nonmetallic (? ∝ l ²). The many-body phenomenon characteristics observed in the X-ray photoelectron and tunnel spectra of gold and copper nanoclusters as the size of the nanoclusters changed led us to suggest changes in the band structure of the nanoclusters and, therefore, their possible transition from the metallic to nonmetallic state.     

Formation of an ensemble of nanoclusters under rapid deposition of atoms on a surface

The results of an experimental study of the formation of nanometer-size Au clusters on NaCl(100) and HOPG(0001) surfaces under pulsed laser deposition are presented. No clusters of small sizes (d ≤ 1 nm) have been found in the cluster size distribution. The distribution itself at d < 5 nm has the form of a percolation distribution. It has been established that the perimeter of clusters with sizes d < 5 nm has a fractal structure. The fractal dimension of clusters is different for NaCl(100) and HOPG(0001) surfaces with different symmetries; it decreases with increasing cluster size from D _f ≈ 1.2–1.4 at d ≈ 1.5 nm to D _f ≈ 1 at d ≈ 5 nm. A physical mechanism of nanocluster formation is suggested. Under pulsed laser deposition, the attainable densities of adatoms are close to the percolation threshold in the region of thermodynamically unstable states and many-particle correlation regions are formed in a spatially inhomogeneous adsorbate. Clusters are formed on the surface from many-particle correlation regions in several diffusion jumps. The suggested mechanism allows the fractal dimension of the clusters forming on surfaces with different symmetries, its dependence on cluster size, and the cluster size distribution functions to be calculated.     

Thermomagnetic effect in a Knudsen gas at low temperatures

The thermomagnetic effect (TME) in nitrogen interacting with a gold surface is investigated. It has been found that at temperatures T<100K the sign of the effect and the dependence of the heat flux on the magnitude and direction of the field do change.     

On the melting of gold nanoclusters formed by pulsed laser deposition on different substrates

The experimental results are presented for the backscattering of 500-eV electrons on Au nanoclusters formed on the surface of highly oriented pyrolytic graphite HOPG(0001) and amorphous SiO₂. It has been found that the measured intensity of the elastically backscattered electrons nonmonotonically depends on the size of nanoclusters. It has been shown that the observed features can be explained by an increase in the rms deviation of the atoms of the Au nanocluster with a decrease in its size. The difference in the dependence of the rms deviation of atoms on the size of the nanoclusters formed on the surfaces of HOPG(0001) and amorphous SiO₂ is qualitatively explained by an increase in the roughness of the nanocluster surface accompanying their formation under the strongly nonequilibrium conditions of pulsed laser deposition.     

Investigation into the factors affecting accuracy of mass measurements on a time-of-flight mass spectrometer using Design of Experiment

The results of an investigation of the parameters which have the most significant effect on the accuracy of mass measurements on a quadrupole orthogonal acceleration time-of-flight mass spectrometer (q-oaToF) are reported. The influence of eight factors is investigated: ion abundances of reference and analyte compounds, mass difference between analyte and reference compounds, quality of calibration, number of reference acquisitions averaged and TDC (time-to-digital converter) settings (resolution, Np multiplier (number of pushes correction factor), minimum number of points, i.e. minimum acquisition width which defines a peak). To extract the maximum information from as few experiments as possible, a Design of Experiment approach was used. The data will be used as a basis for developing guidance on accurate mass measurement on q-oaToF instruments.