Search

Nω‐hydroxy‐l‐arginine amidinohydrolase (EC:3.5.3.25), an enzyme in the d‐cycloserine (d‐CS) biosynthetic pathway of Streptomyces lavendulae, catalyzes the hydrolysis of an arginase inhibitor, Nω‐hydroxy‐l‐arginine, to produce l‐ornithine and hydroxyurea, despite being homologous to arginase. Like arginase, the enzyme (DcsB) possesses two manganese ions (MnA and MnB) essential for the enzymatic reaction at the bottom of the cavity formed within the molecule. However, one of the MnA ligands in DcsB is Cys86, whereas the corresponding residues in arginase are histidine. In this study, we determined the crystal structure of Mn‐free DcsB to elucidate the installation mechanism of the manganese ions. The flipping of the His111 residue after the formation of the coordination bond to the second manganese ion may facilitate the installation of MnB and the closing of the cavity entrance to retain MnA and MnB at the active site. Copper ions, which are known to be a positive regulator of many secondary metabolites in Streptomyces species, were found to irreversibly inactivate the catalytic activity of DcsB. Mass spectrometric and crystallographic analyses of the Cu(II)‐treated DcsB indicated that Cys86 is oxidized to sulfinic acid. The d‐CS biosynthesis in the producing microorganism may be negatively regulated by the concentration of intracellular copper ions, which mediates the oxidative stress. [ABSTRACT FROM AUTHOR]

It is known that X‐ray CT of organic polymer materials usually provides low‐contrast images because of the low X‐ray absorption of these materials. In this paper, we describe a new method to enhance the contrast of X‐ray CT images of organic polymer materials. We demonstrate that gamma‐ray irradiation of poly (ethylene terephthalate) (PET) fibers in dichloromethane containing 2‐bromoethyl methacrylate, 2‐chloroethyl methacrylate, or 4‐bromostyrene results in the grafting of halogen‐containing oligomeric chains onto the PET fibers. Focused ion beam scanning electron microscopy (FIB‐SEM) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) analyses revealed a homogeneous distribution of bromine atoms within the 2‐bromoethyl methacrylate‐modified PET fibers, not only on the surface. This uniform incorporation translated to a significant improvement in X‐ray CT image contrast compared with pristine fibers. Similar treatment of polypropylene pellets also enhanced the contrast of their X‐ray CT images. This is a new simple and effective method to enhance the X‐ray CT image contrast and potentially applicable to various polymer materials including polymer composites and porous polymer materials, readily allowing the observation of their 3D microstructures finely. [ABSTRACT FROM AUTHOR]

Synthetic strategies to access high‐valent iridium complexes usually require use of π donating ligands bearing electronegative atoms (e. g. amide or oxide) or σ donating electropositive atoms (e. g. boryl or hydride). Besides the η5‐(methyl)cyclopentadienyl derivatives, high‐valent η1 carbon‐ligated iridium complexes are challenging to synthesize. To meet this challenge, this work reports the oxidation behavior of an all‐carbon‐ligated anionic bis(CCC‐pincer) IrIII complex. Being both σ and π donating, the diaryl dipyrido‐annulated N‐heterocyclic carbene (dpa‐NHC) IrIII complex allowed a stepwise 4e− oxidation sequence. The first 2e− oxidation led to an oxidative coupling of two adjacent aryl groups, resulting in formation of a cationic chiral IrIII complex bearing a CCCC‐tetradentate ligand. A further 2e− oxidation allowed isolation of a high‐valent tricationic complex with a triplet ground state. These results close a synthetic gap for carbon‐ligated iridium complexes and demonstrate the electronic tuning potential of organic π ligands for unusual electronic properties. [ABSTRACT FROM AUTHOR]

Two new strontium polysulfides, SrS3 and Sr(sub 2)(OH)(sub 2)S(sub 4).10H2O, are obtained by the high-pressure and high-temperature treatment of Sr and sulfur mixtures. The MO calculation of the S(sub 4)(super 2-) anion described the longer central S-S bond distance rather than the terminal bond distance in Sr(sub 2)(OH)(sub 2)S(sub 4).10H2O and this is the first compound that contains the S(sub 4)(super 2-) anion with coplanar and anitgeometry.

High-resolution electron paramagnetic resonance (EPR) spectra of CH3, CH3 and CH2D radicals with their natural abundances were investigated in Ar matrix in the temperature range 4.2-40 K. The high-resolution EPR spectra of CD3 and CHD2 radicals were also obtained under similar conditions using CD4 and CH2D2 instead of CH4, respectively. At the lower temperatures, the EPR lines shapes of these radicals were dominated by hyperfine patterns with anomalous intensity due to quantum effects. The application of the Pauli principle in combination with the D3 point-group symmetry resulted in the exclusion of EPR transitions for both the alpha-proton- and the alpha-deuteron-rotor spectra.

An experimental study was conducted to theoretically calculate the rate constants of the abstraction reactions T + HD(DH) - HT(DT) + D(H) and T + H2(D2) - HT(DT) + H(D) in superfluid and normal fluid 3He-4He mixtures at 1.3 K using the gas-phase reaction model. The tunneling abstraction reaction through van der Waals complex was proposed based on the experimental isotope effects and theoretical rate constants. Other results of the study are discussed.