Glycosidases in carbohydrate synthesis: when organic chemistry falls short

Thanks to the stability, good availability, stereoselectivity and broad substrate specificity, oligosaccharide synthesis catalyzed by glycosidases represents an elegant way to complex carbohydrate structures. Two approaches to glycosidase catalysis are presented: (i) the use of structurally modified substrates that carry various functional moieties in the molecule, and (ii) the design of mutant glycosidases void of hydrolytic activity. Products of glycosidase-catalyzed synthesis are applicable in a range of areas such as immunology, therapy of Alzheimer's or Parkinson's diseases and the synthesis of neoglycoproteins.     

Human NKCC2 cation–Cl– co‐transporter complements lack of Vhc1 transporter in yeast vacuolar membranes

Cation–chloride co‐transporters serve to transport Cl^– and alkali metal cations. Whereas a large family of these exists in higher eukaryotes, yeasts only possess one cation–chloride co‐transporter, Vhc1, localized to the vacuolar membrane. In this study, the human cation–chloride co‐transporter NKCC2 complemented the phenotype of VHC1 deletion in Saccharomyces cerevisiae and its activity controlled the growth of salt‐sensitive yeast cells in the presence of high KCl, NaCl and LiCl. A S. cerevisiae mutant lacking plasma‐membrane alkali–metal cation exporters Nha1 and Ena1‐5 and the vacuolar cation–chloride co‐transporter Vhc1 is highly sensitive to increased concentrations of alkali–metal cations, and it proved to be a suitable model for characterizing the substrate specificity and transport activity of human wild‐type and mutated cation–chloride co‐transporters. Copyright © 2013 John Wiley & Sons, Ltd.     

Fluorescence and structure of methyl red-clay nanocomposites

Two types of clay minerals-montmorillonite and vermiculite have been chosen as a host matrix for the intercalation of methyl red (MR) in order to investigate a possible fluorescence tuning via dye-clay interactions. The effect of silicate layer charge on the structure and fluorescence of dye-clay intercalated hybrid nanostructures was investigated using combination of molecular modeling with experiment. Structure of both intercalates MR-vermiculite (MR-VER) and MR-montmorillonite (MR-MMT) exhibits high degree of structural disorder resulting in broaden emission band. The fluorescence wavelength range of MR intercalated in clays is shifted to lower wavelengths compared with the pristine MR polycrystalline sample (800 nm). Results showed the strong dependence of fluorescence band maximum on the silicate layer charge, lambda(max) = 565 nm for MR-MMT, 645 nm for MR-VER and 800 nm for the methyl red fine crystalline powder, whereas the structural disorder in the arrangement of dye molecules affects the emission band broadening.     

Retrieval of suspended particulate matter concentrations in the Danube River from Landsat ETM data

Alternations in river channel morphology result in a disturbed natural transport of suspended particulate matter (SPM). Suspended particulate matter serves as a transport medium for various pollutants, e.g. heavy metals. It is therefore important to understand how artificial obstructions alter the natural transport of suspended matter. Measurements of SPM in rivers are traditionally carried out during in situ sampling campaigns, which can provide only a limited view of the actual spatial distribution of suspended matter over large distances. Several authors have studied how space-borne remote sensing could be used for mapping of water quality in standing waters, but with only little attention paid to rivers. This paper describes the methodology how a Landsat ETM image was used to map the spatial patterns of SPM in the Slovak portion of the Danube River. Results of our investigation reveal that the Danube River in Slovakia exhibits gradual longitudinal decrease in concentrations of SPM. Based on a strong relationship between the Landsat near-infrared band (TM4) and field measurements, we developed a map of suspended particulate matter in the Danube River with a standard error (SE) of 2.92 mg/L. This study aims to show how archived satellite data and historical water quality data can be used for monitoring of SPM in large rivers. A methodology describing the minimum samples required for sufficiently accurate results is discussed in this paper also.     

Application of burnt clay shale as pozzolan addition to lime mortar

Burnt Czech clay shale of different grain fineness is applied as a new pozzolan addition to lime mortar. Experimental results show that the new lime-pozzolan mortars have significantly better mechanical properties and frost resistance than the reference lime mortar. The fineness of burnt Czech clay shale is a very important parameter affecting the properties of lime-pozzolan mortars; the best results are achieved with an average particle size of 4 μm. In a comparison with a lime-metakaolin mortar of the same composition, the frost resistance of the new lime-pozzolan mortars is significantly better, the mechanical, fracture-mechanical, hygric and thermal properties are either comparable or slightly better. Therefore, it can be concluded that the burnt Czech clay shale has a good potential to be used in lime-pozzolan mortars for renovation of historical buildings.     

Chelating polymeric particles intended for the therapy of Wilson’s disease

Wilson’s disease is a genetic disorder that leads to a high accumulation of copper in multiple organs with subsequent toxic effects. In this paper, a gentle therapy to eliminate harmful copper concentrations in patients with Wilson’s disease is proposed using an oral administration of insoluble polymeric sorbents containing selective chelating groups for copper(II). The sorbents contained triethylenetetramine, N,N-di(2-pyridylmethyl)amine, 8-hydroxyquinoline or 8-hydroxyquinoline-5-sulfonic acid chelating groups bound to a methacrylate-based macroporous support. Nearly quantitative copper(II) uptake within minutes was achieved in buffers modeling the pH range present in the gastric environment (pH 2.0 and 4.0). The sorbents demonstrated chelating selectivity for copper(II) against zinc(II) with ratios of up to 1321. The sorbents demonstrated sufficient stability of the copper complexes against rechelation using studies in a model environment for the small intestine (the presence of chelating amino acids, pH 6.8).     

CycloSal‐phosphate Pronucleotides of Cytostatic 6‐(Het)aryl‐7‐deazapurine Ribonucleosides: Synthesis,Cytostatic Activity,and Inhibition of Adenosine Kinases

A series of cycloSal‐phosphate prodrugs of a recently described new class of nucleoside cytostatics (6‐hetaryl‐7‐deazapurine ribonucleosides) was prepared. The corresponding 2′,3′‐isopropylidene 6‐chloro‐7‐deazapurine nucleosides were converted into 5‐O′‐cycloSal‐phosphates. These underwent a series of Stille or Suzuki cross‐couplings with diverse (het)arylstannanes or ‐boronic acids to yield the protected 6‐(het)aryl‐7‐deazapurine pronucleotides that were subsequently deprotected to give 12 derivatives of free pronucleotides. The in vitro cytostatic effect of the pronucleotides was compared with parent nucleoside analogues. In most cases, the activity of the pronucleotide was similar to or somewhat lower than that of the corresponding parent nucleosides, with the exception of 7‐fluoro pronucleotides 13 a , 13 b , and 13 d , which had exhibited GIC₅₀ values that were improved by one order of magnitude (to the low nanomolar range). The presence of a cycloSal‐phosphate group also influenced selectivity toward various cell lines. Several pronucleotides were found which strongly inhibit human adenosine kinase but only weakly inhibit the MTB adenosine kinase.     

Classification of spectra of emission line stars using machine learning techniques

Advances in the technology of astronomical spectra acquisition have resulted in an enormous amount of data available in world-wide telescope archives. It is no longer feasible to analyze them using classical approaches, so a new astronomical discipline,astroinformatics, has emerged. We describe the initial experiments in the investigation of spectral line profiles of emission line stars using machine learning with attempt to automatically identify Be and B[e] stars spectra in large archives and classify their types in an automatic manner. Due to the size of spectra collections, the dimension reduction techniques based on wavelet transformation are studied as well. The result clearly justifies that machine learning is able to distinguish different shapes of line profiles even after drastic dimension reduction.     

Different approaches to superhard coatings and nanocomposites

Different approaches to the preparation of superhard coatings such as intrinsically superhard materials, coatings whose hardness is enhanced by energetic ion bombardment during deposition, and nanostructured superhard materials are discussed with the emphasis on the question of how to distinguish between the different mechanisms of hardness enhancement in thin coatings. We compare the thermal and long-term stability in air and some further properties of such coatings. The lack of success of some workers to reproduce the high value of hardness reported by Veprek et al. is explained in terms of inappropriate choice of the deposition conditions and/or impurities.