Aqueous sol–gel synthesis and thermoanalytical study of the alkaline earth molybdate precursors

The preparation and characterization of the M′–Mo–O nitrate–tartrate (M′ = Mg, Ca, Sr, and Ba) gels, which were produced by the simple aqueous sol–gel method and calcined at 500, 600, 700, 800, 900, and 1,000 °C temperatures are reported. The crystalline alkaline earth metal molybdates (MgMoO₄, CaMoO₄, SrMoO₄, and BaMoO₄) and as-prepared M′–Mo–O nitrate–tartrate gels investigated by thermal analysis (TG/DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). TG/DSC analysis showed the possible decomposition mechanism of synthesized gels. XRD studies allowed the identification of main types of crystalline structures in the MgMoO₄, CaMoO₄, SrMoO₄, and BaMoO₄ systems. Moreover, SEM analysis revealed the changes of surface morphology of the final compounds depending on annealing temperatures.     

N-Aryl-N-Hydroxy Urethanes as Peroxidase Substrates

 N-Aryl-N-hydroxy urethanes (AHUs), which are promising N*OH mediators for oxidoreductase catalysis, are electrochemically active redox compounds with a redox potential of 0.35–0.40 V vs. SCE (0.59–0.64 V vs. NHE). Alkyl substituents in the carbamic acid residue have, as expected, only little influence on the redox potential. The highest potential was noticed for N-hydroxy-N-(4-cyanophenyl)-carbamic acid methyl ester. Recombinant Coprinus cinereus peroxidase (rCiP) catalyzes oxidation of the AHUs with apparent bimolecular constants k _ox of 2.5ċ10⁴–7.5ċ10⁴ M ⁻¹s⁻¹ at pH = 8.5 and 25°C. Structure-function connectivities of the substrates were analysed within the framework of the Marcus cross relationship and by using ab initio quantum chemical calculations. An excellent correlation of the redox potentials and the HOMO energies could be found. However, no correlation of log(k _ox) with redox potential and HOMO energy was indicated as predicted by theory. This was explained by specific docking of the substrates in the active center of rCiP.     

Arithmetical Properties of Powers of Algebraic Numbers

We consider the sequences of fractional parts {ⁿ}, n = 1, 2,3,..., and of integer parts [ⁿ], n = 1, 2, 3,..., where isan arbitrary positive number and > 1 is an algebraic number.We obtain an inequality for the difference between the largestand the smallest limit points of the first sequence. Such aninequality was earlier known for rational only. It is alsoshown that for roots of some irreducible trinomials the sequenceof integer parts contains infinitely many numbers divisibleby either 2 or 3. This is proved, for instance, for , n = 1, 2, 3,.... The fact that thereare infinitely many composite numbers in the sequence of integerparts of powers was proved earlier for Pisot numbers, Salemnumbers and the three rational numbers 3/2, 4/3, 5/4, but nosuch algebraic number having several conjugates outside theunit circle was known. 2000 Mathematics Subject Classification11J71, 11R04, 11R06, 11A41.     

Elastic properties of chemically modified baker's yeast cells studied by AFM

Chemical pretreatment is widely used to facilitate transformation of living cells when foreign components are introduced into a cell through the cell wall. The influence of appropriate chemicals on the wall properties and mechanism of transformation is still a matter of intensive studies. Saccharomyces cerevisiae cells (also known as baker's yeast) were investigated by atomic force microscopy (AFM). The cell walls were modified by lithium acetate and dithiothreitol. The AFM imaging was performed in liquid water‐based environment. The living cells were fixed by trapping into the holes of a polycarbonate membrane. Mechanical and morphological properties of initial intact cells and treated cells were investigated. The increased stiffness of the chemically treated cells was observed. As deduced from the applied theoretical Hertz‐Sneddon model, the treated cells show completely different response mechanism to applied mechanical pressure in comparison with the intact cells. Also, the increased roughness of the cell wall of the treated yeasts was observed. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectroscopic and X-ray diffraction study of high Tc epitaxial YBCO thin films obtained by pulsed laser deposition

We report spectroscopic characterization of epitaxial YBCO thin films grown on LaAlO₃ by pulsed laser deposition. Raman spectroscopy and spectroscopic ellipsometry were used for film characterization and the results were correlated with X-ray diffraction measurements. The mentioned techniques allowed us to analyze crystallographic, micro-structural, and morphological properties of YBCO thin films. We also demonstrated that relatively low resolution Raman spectroscopy and spectroscopic ellipsometry are reliable techniques for a rapid and non-destructive characterization of epitaxial YBCO thin films.     

On the fractional parts of the natural powers of a fixed number

Let ξ ≠ = 0 and α > 1 be reals. We prove that the fractional parts {ξ αⁿ}, n = 1, 2, 3, ..., take every value only finitely many times except for the case when α is the root of an integer: α = q ^1/d, where q ≥ 2 and d ≥ 1 are integers and ξ is a rational factor of a nonnegative integer power of α.     

Warm dense matter at the bench-top: Fs-laser-induced confined micro-explosion

We report the experimental evidence for creation of Warm Dense Matter (WDM) in ultrafast laser-induced micro-explosion inside a sapphire (Al₂O₃) crystal. We show that the WDM can be formed by a 100 nJ fs-pulse if the following conditions are satisfied: (1) the laser pulse is tightly focused to inside of the bulk of transparent material so the intensity at focus is two orders of magnitude higher than the optical breakdown threshold; (2) the pulse duration is shorter than the electron-ion energy exchange time; and, (3) the absorbed energy density is above the Young’s modulus for the material studied. The empty void created inside a sapphire crystal surrounded by a shell of compressed material provides the direct evidence of the maximum pressure above the Young’s modulus of sapphire (∼400 GPa). Synchrotron X-ray diffraction (XRD) analysis of the shell revealed the presence of novel super-dense bcc-Al crystalline phase predicted at pressures above ∼380 GPa theoretically, which has never been observed experimentally before neither in nature in laboratory experiments. These results show that confined micro-explosion induced by tightly focussed fs-laser inside a transparent solid opens new routes for synthesis of new materials and study of WDM at a laboratory bench-top.