Molecular dynamics in polyester- or polyether-urethane networks based on different diisocyanates

Different non-conventional polyurethane networks crosslinked with a hyperbranched polyester (Boltorn^®H40) were synthesised with an aim to determine the influence of the polyurethane chemical structure as well as of the length of the linear chains between crosslinking centres on molecular relaxations in such systems. For that purpose, both polyether- and polyester-type macrodiols as well as two different diisocyanates were used to synthesise the connecting polyurethane chains between crosslinks. Molecular dynamics were investigated by dielectric spectroscopy and by dynamic mechanical analysis. It was found that the changes of the repeating macrodiol-diisocyanate unit number (i.e. length of the polyurethane linear chains) practically did not affect the molecular relaxations. This effect was explained by the formation by hydrogen bonds between urethane groups of similar, independent of the polyurethane linear chain length, physical networks, which control the molecular mobility. By contrast, the chemical nature of the precursors strongly influences the molecular relaxation associated with glass transition, and to some extent also the sub-glass secondary relaxation processes occurring in the investigated networks.     

A Short Note on Point Singularities for Robot Manipulators

We consider a specific type of singularities for kinematic chains, so-called point singularities. These were characterized in 2005 by Borcea and Streinu. We give a new proof for this result in the framework of the Exterior Algebra. As an illustration we give an exhaustive list of the point singularities of a specific robot manipulator.     

Baceridin,a Cyclic Hexapeptide from an Epiphytic Bacillus Strain,Inhibits the Proteasome

A new cyclic hexapeptide, baceridin ( 1 ), was isolated from the culture medium of a plant‐associated Bacillus strain. The structure of 1 was elucidated by HR‐HPLC‐MS and 1D and 2D NMR experiments and confirmed by ESI MS/MS sequence analysis of the corresponding linear hexapeptide 2 . The absolute configurations of the amino acid residues were determined after derivatization by GC‐MS and Marfey's method. The cyclopeptide 1 consists partially of nonribosomal‐derived D ‐ and allo‐D ‐configured amino acids. The order of the D ‐ and L ‐leucine residues within the sequence cyclo(‐L ‐Trp‐D ‐Ala‐D ‐allo‐Ile‐L ‐Val‐D ‐Leu‐L ‐Leu‐) was assigned by total synthesis of the two possible stereoisomers. Baceridin ( 1 ) was tested for antimicrobial and cytotoxic activity and displayed moderate cytotoxicity (1–2 μg mL^?1) as well as weak activity against Staphylococcus aureus. However, it was identified to be a proteasome inhibitor that inhibits cell cycle progression and induces apoptosis in tumor cells by a p53‐independent pathway.     

Synthesis and Characterization of Block-Graft Copolymers [poly(epichlorohydrin-<Emphasis Type="Italic">b</Emphasis>-styrene)-<Emphasis Type="Italic">g</Emphasis>-poly(methyl methacrylate)] by Combination of Activated Monomer Polymerization,NMP and ATRP

Summary Synthesis of block-graft copolymers, namely poly(epichlorohydrin-b-styrene)-g-poly(methyl methacrylate) (PECH-b-St)-g-PMMA) by combination of Activated Monomer (AM), Nitroxide Mediated Polymerization (NMP) and Atom Transfer Radical Polymerization (ATRP) methods was described. For this purpose, first epichlorohydrin (ECH) was polymerized by using BF₃THF complex in the presence of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyl-1-oxy (HTEMPO) via AM mechanism. The resulting stable radical terminated polymer was subsequently used as a counter radical in the NMP of styrene (St) initiated by benzoyl peroxide to yield block copolymers of ECH and St. Finally, the ATRP of methyl methacrylate (MMA) by using chloromethyl groups of the PECH segment as initiating sites resulted in the formation of (PECH-b-St)-g-PMMA). The structures of the intermediate polymers at various stages were characterized by ¹H-NMR spectral investigations. The thermal behavior and surface morphology of the copolymers were also investigated by DSC and AFM measurements.     

Characterization and Purification of Kinase Activities against Arabidopsis COP9 Signalosome Subunit 7

The COP9 signalosome (CSN) is a multisubunit protein complex that intersects the ubiquitin (Ub)–proteasome pathway at several junctions. The CSN associates with several protein kinases that target key regulatory proteins that themselves are targets for Ub-dependent degradation, and several subunits themselves are phosphoproteins. We previously reported that Arabidopsis CSN7 is a phosphoprotein. To identify the kinases responsible for CSN7 phosphorylation, we biochemically purified CSN7-kinsae activities from cauliflower through a four-step purification procedure that resulted in a ca. 300-fold enrichment. One of these activities is Ca²⁺ dependent, while the second is not. Peptide fingerprint analysis of the purified proteins identified three putative CSN7 kinases.     

Investigation of the polyurethane chain length influence on the molecular dynamics in networks crosslinked by hyperbranched polyester

Several non-conventional polyurethane (PU) networks crosslinked with hyperbranched polyester (Boltorn^®H40) were synthesised with an aim to determine an influence of the PU chain length on molecular relaxations in such systems. The PU chain length was regulated by changing the macrodiol length or by changing the number of the repeating macrodiol/diisocyanate units n. Molecular dynamics were investigated by broadband dielectric spectroscopy and by dynamic mechanical analysis. It was found that the macrodiol length has a strong influence on the glass transition and the α-relaxation, and also on the crystallization. By contrast, the changes of n practically do not affect the molecular relaxations. This effect was explained by the formation of a physical network by hydrogen bonds between urethane groups, controlling the molecular mobility. The rheological measurements have shown, that at temperatures above 150 °C, when hydrogen bonds were thermally destroyed, not only macrodiol length but also n had strong influence on the flowing point.     

Dynamic Programming Problem for Fractional Discrete-Time Dynamic Systems. Quadratic Index of Performance Case

Dynamic programming problem for discrete-time fractional order systems with quadratic performance index has been formulated and solved. A new method for numerical computation of optimal dynamic programming problem has been presented. The efficiency of the method has been demonstrated on numerical example and illustrated by graphs. Graphs also show the differences between the fractional and classical (standard) systems theory. Results for other cases of the coefficient \(\alpha \) , and not illustrated with numerical examples, have been obtained through a computer algorithm written for this purpose.     

Structural Determinants of Substrate Specificity of SplF Protease from Staphylococcus aureus

Accumulating evidence suggests that six proteases encoded in the spl operon of a dangerous human pathogen, Staphylococcus aureus, may play a role in virulence. Interestingly, SplA, B, D, and E have complementary substrate specificities while SplF remains to be characterized in this regard. Here, we describe the prerequisites of a heterologous expression system for active SplF protease and characterize the enzyme in terms of substrate specificity and its structural determinants. Substrate specificity of SplF is comprehensively profiled using combinatorial libraries of peptide substrates demonstrating strict preference for long aliphatic sidechains at the P1 subsite and significant selectivity for aromatic residues at P3. The crystal structure of SplF was provided at 1.7 Å resolution to define the structural basis of substrate specificity of SplF. The obtained results were compared and contrasted with the characteristics of other Spl proteases determined to date to conclude that the spl operon encodes a unique extracellular proteolytic system.     

Genome Study of a Novel Virulent Phage vB_SspS_KASIA and Mu-like Prophages of Shewanella sp. M16 Provides Insights into the Genetic Diversity of the Shewanella Virome

Shewanella is a ubiquitous bacterial genus of aquatic ecosystems, and its bacteriophages are also isolated from aquatic environments (oceans, lakes, ice, and wastewater). In this study, the isolation and characterization of a novel virulent Shewanella phage vB_SspS_KASIA and the identification of three prophages of its host, Shewanella sp. M16, including a mitomycin-inducible Mu-like siphovirus, vB_SspS_MuM16-1, became the starting point for comparative analyses of phages infecting Shewanella spp. and the determination of their position among the known bacterial viruses. A similarity networking analysis revealed the high diversity of Shewanella phages in general, with vB_SspS_KASIA clustering exclusively with Colwellia phage 9A, with which it forms a single viral cluster composed of two separate viral subclusters. Furthermore, vB_SspS_MuM16-1 presented itself as being significantly different from the phages deposited in public databases, expanding the diversity of the known Mu-like phages and giving potential molecular markers for the identification of Mu-like prophages in bacterial genomes. Moreover, the functional analysis performed for vB_SspS_KASIA suggested that, despite the KASIA host, the M16 strain grows better in a rich medium and at 30 °C the phage replication cycle seems to be optimal in restrictive culture conditions mimicking their natural environment, the Zloty Stok gold and arsenic mine.