The function of the Saccharomyces Cerevisiae ribonucleotide reductase second [beta] subunit in DNA repair

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The function of the Saccharomyces Cerevisiae ribonucleotide reductase second [beta] subunit in DNA repair

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

1:1 complex of 4-nitrobenzoic acid and 4-nitropyridine N-oxide

In the title co-crystal, C7H5NO4. C5H4N2O3, the two components are linked by an intermolecular hydrogen band between the O-H and N-O groups [O ... O 2.577(3) Angstrom]. The interplanar angle between the planes of the rings of the molecules is 5.3 (2)degrees. The rings are stacked in the crystal with a mean interplanar distance of 3.279 (3) Angstrom.

Role of neuronal nitric oxide in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic pathway damage similar to that observed in Parkinson disease (PD). To study the role of NO radical in MPTP-induced neurotoxicity, we injected MPTP into mice in which nitric oxide synthase (NOS) was inhibited by 7-nitroindazole (7-NI) in a time- and dose-dependent fashion. 7-NI dramatically protected MPTP-injected mice against indices of severe injury to the nigrostriatal dopaminergic pathway, including reduction in striatal dopamine contents, decreases in numbers of nigral tyrosine hydroxylase-positive neurons, and numerous silver-stained degenerating nigral neurons. The resistance of 7-NI-injected mice to MPTP is not due to alterations in striatal pharmacokinetics or content of 1-methyl-4-phenylpyridinium ion (MPP+), the active metabolite of MPTP. To study specifically the role of neuronal NOS (nNOS), MPTP was administered to mutant mice lacking the nNOS gene. Mutant mice are significantly more resistant to MPTP-induced neurotoxicity compared with wild-type littermates. These results indicate that neuronally derived NO mediates, in part, MPTP-induced neurotoxicity. The similarity between the MPTP model and PD raises the possibility that NO may play a significant role in the etiology of PD.

High performance cobalt-free Cu1.4Mn1.6O4 spinel oxide as an intermediate temperature solid oxide fuel cell cathode

In this work Cu_1.4Mn_1.6O₄ (CMO) spinel oxide is prepared and evaluated as a novel cobalt-free cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). Single phase CMO powder with cubic structure is identified using XRD. XPS results confirm that mixed Cu⁺/Cu²⁺ and Mn³⁺/Mn⁴⁺ couples exist in the CMO sample, and a maximum conductivity of 78 S cm⁻¹ is achieved at 800 °C. Meanwhile, CMO oxide shows good thermal and chemical compatibility with a 10 mol% Sc₂O₃ stabilized ZrO₂ (ScSZ) electrolyte material. Impedance spectroscopy measurements reveals that CMO exhibits a low polarization resistance of 0.143 Ω cm² at 800 °C. Furthermore, a Ni-ScSZ/ScSZ/CMO single cell demonstrates a maximum power density of 1076 mW cm⁻² at 800 °C under H₂ (3% H₂O) as the fuel and ambient air as the oxidant. These results indicate that Cu_1.4Mn_1.6O₄ is a superior and promising cathode material for IT-SOFCs.

Preparation, IR and nuclear magnetic resonance studies on the rare-earth perchlorate complexes of 3-methylpyridine-1-oxide

THE COMPLEXES of pyridine-l-oxide and 2- and 4-substituted pyridine-l-oxides have been investigated previously[l]. The complexes of 3-substituted pyfidine-l-oxides, however, have received little attention. The rare-earth complexes of pyridine-Ioxide[l, 2], 4-methylpyridine- l-oxide [1] and 2,6- dimethylpyfidine-l-oxide[3,4] have been reported earlier. The present paper deals with the isolation and characterisation of 3-methylpyridine-l-oxide (3-Picoline-N-oxide, 3-PicNO) complexes with rare-earth perchlorates.

4-Picoline-N-oxide complexes of rare-earth bromides

In continuation of our work on the effect of the anion on the coordination chemistry of the rare-earth metal ions, we have now extended our studies to 4-picoline-N-oxide (4-Pie NO) complexes of rare-earth bromides. By ohangi~ the method of preparation Harrison and Watsom (1) have prepared two types of Sm(IIl) complexes and three types of Eu(III) complexes of 4-pioollne-N-Oxide in the presence of perchlorate ions. We have isolated two types of pyridine-N-Oxide complexes of rare-earth bromides, also by changing the method of preparation (2). The effect of the change of the preparative method on the composition of the lanthanide complexes is exhibited in the case of other complexes also (3-6). But our attempts to prepare 4-picoline-N-Oxide of rare-earth bromides having different stoichiometries were unsucessful . The composition of the complexes is the same for all the complexes prepared. The results of the physico-chemical studies on these 4-Pic NO complexes of rare-earth bromides are discussed in the present paper.

Nuclear-quadrupole resonance in coordination chemistry- identification of bridiging and therminal chlorines in the mercuric chloride-4-picoline n-oxide complex

The temperature dependence of the chlorine-35 n.q.r. in the mercuric chloride-4-picoline N-oxide complex has been studied from 77 K to room temperature, and the results are used to assign the observed frequencies to terminal and bridging chlorines.

Blue light-emitting polymer with polyfluorene as the host and highly fluorescent 4-dimethylamino-1,8-naphthalimide as the dopant in the sidechain

The dopant/host concept, which is an efficient approach to enhance the electroluminescence (EL) efficiency and stability for organic light-emitting diodes (OLEDs) devices, has been applied to design efficient and stable blue light-emitting polymers. By covalently attaching 0.2 mol % highly fluorescent 4-dimethylamino-1,8-naphthalimide (DMAN) unit (photoluminescence quantum efficiency: Phi(PL)=0.84) to the pendant chain of polyfluorene, an efficient and colorfast blue light-emitting polymer with a dopant/host system and a molecular dispersion feature was developed. The single-layer device (indium tin oxide/PEDOT/polymer/Ca/Al) exhibited the maximum luminance efficiency of 6.85 cd/A and maximum power efficiency of 5.38 lm/W with the CIE coordinates of (0.15, 0.19). Moreover, no undesired long-wavelength green emission was observed in the EL spectra when the device was thermal annealed in air at 180 degrees C for 1 h before cathode deposition. These significant improvements in both efficiency and color stability are due to the charge trapping and energy transfer from polyfluorene host to highly fluorescent DMAN dopant in the molecular level.

Connective tissue mast cells are the target of formaldehyde to induce tracheal hyperresponsiveness in rats: Putative role of leukotriene B(4) and nitric oxide

Formaldehyde (FA) exposure induces upper airways irritation and respiratory abnormalities, but its mechanisms are not understood. Since mast cells are widely distributed in the airways, we hypothesized that FA might modify the airways reactivity by mechanism involving their activation. Tracheal rings of rats were incubated with Dulbecco`s modified medium culture containing FA (0.1 ppm) in 96-well plastic microplates in a humid atmosphere. After 30 min, 6 h, and 24-72 h, the rings were suspended in an organ bath and dose-response curve to methacholine (MCh) were determined. incubation with FA caused a transient tracheal hyperresponsiveness to MCh that was independent from tracheal epithelium integrity. Connective tissue mast cell depletion caused by compound 48/80 or mast cell activation by the allergic reaction, before exposure of tracheal rings to FA prevented the increased responsiveness to MCh. LTB(4) concentrations were increased in the culture medium of tracheas incubated with FA for 48 h, whereas the LTB(4)-receptor antagonist MK886 (1 mu M) added before FA exposure rendered the tracheal rings normoreactive to MCh. In addition, FA exposure did not cause hyperresponsiveness in tracheal segments incubated with L-arginine (1 mu M). We suggest that airway connective tissue mast cells constitute the target and may provide the increased LTB(4) generation as well as an elevated consumption of NO leading to tracheal hyperresponsiveness to MCh. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

1,4-Diamino-2-butanone, a wide-spectrum microbicide, yields reactive species by metal-catalyzed oxidation

The alpha-aminoketone 1,4-diamino-2-butanone (DAB), a putrescine analogue, is highly toxic to various microorganisms, including Trypanosoma cruzi. However, little is known about the molecular mechanisms underlying DAB`s cytotoxic properties. We report here that DAB (pK(a) 7.5 and 9.5) undergoes aerobic oxidation in phosphate buffer, pH 7.4, at 37 degrees C, catalyzed by Fe(II) and Cu(II) ions yielding NH(4)(+) ion, H(2)O(2), and 4-amino-2-oxobutanal (oxoDAB). OxoDAB, like methylglyoxal and other alpha-oxoaldehydes, is expected to cause protein aggregation and nucleobase lesions. Propagation of DAB oxidation by superoxide radical was confirmed by the inhibitory effect of added SOD (50 U ml(-1)) and stimulatory effect of xanthine/xanthine oxidase, a source of superoxide radical. EPR spin trapping studies with 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) revealed an adduct attributable to DMPO-HO(center dot), and those with alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 3,5-dibromo-4-nitrosobenzenesulfonic acid, a six-line adduct assignable to a DAB(center dot) resonant enoyl radical adduct. Added horse spleen ferritin (HoSF) and bovine apo-transferrin underwent oxidative changes in tryptophan residues in the presence of 1.0-10 mM DAB. Iron release from HoSF was observed as well. Assays performed with fluorescein-encapsulated liposomes of cardiolipin and phosphatidylcholine (20:80) incubated with DAB resulted in extensive lipid peroxidation and consequent vesicle permeabilization. DAB (0-10 mM) administration to cultured LLC-MK2 epithelial cells caused a decline in cell viability, which was inhibited by preaddition of either catalase (4.5 mu M) or aminoguanidine (25 mM). Our findings support the hypothesis that DAB toxicity to several pathogenic microorganisms previously described may involve not only reported inhibition of polyamine metabolism but also DAB pro-oxidant activity. (C) 2011 Elsevier Inc. All rights reserved.

Tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato]aluminium(III)-tris[4,4,4-trifluoro-1-(2-thienyl)butane-1,3-dionato]iron(III) (3/1)

In the title compound, [Al(C8H4F3O2S)3]3[Fe(C8H4F3O2S)3], the metal centre is statistically occupied by AlIII and FeIII cations in a 3:1 ratio. The metal centre is within an octahedral O6 donor set defined by three chelating substituted acetoacetonate anions. The ligands are arranged around the periphery of the molecule with a mer geometry of the S atoms.