分类: 物理学 >> 核物理学 提交时间: 2023-06-25
摘要: The ion motions in a Penning trap have been studied in detail in the presence of azimuthal dipolar and quadrupolar radio-frequency excitations and buffer gas cooling. The numerical solutions by using the Runge-Kutta method and thus the pictures of the ion trajectories in the trap have been obtained for different cases and summarized in graphical form. For the recentering of the ion of interest and to perform the purification of the ion species, one has to set a reasonable buffer gas pressure in the trap and apply azimuthal quadrupolar excitation at frequency rf = c.
分类: 化学 >> 核化学 提交时间: 2023-06-06
摘要: N,N,N,N-Tetraoctyl diglycolamide (TODGA) is one of the most promising extractants tailored for high-level liquid radioactive waste treatment during nuclear fuel reprocessing. The -radiolysis of TODGA (0.2 mol/L) in n-dodecane (nDD) solution with and without pre-equilibrated 3.0 mol/L HNO3 was investigated using HPLC and UPLC-QTOF-MS and compared with the -radiolysis of neat TODGA in this study. With increased absorbed doses, the concentration of TODGA decreased exponentially for the studied systems. Moreover, pre-equilibration with HNO3 (3.0 mol/L) slightly influenced the -radiolysis of TODGA in nDD. Seven radiolytic products generated from the rupture of the C C, C O, and C N bonds in TODGA were identified in the studied extraction system. The influence of -radiation on TODGA/nDD for the extraction of Eu(III) was evaluated using the first combination of extraction experiments and density functional theory (DFT) calculations, in which the complexations of Eu(III) with TODGA and its radiolytic products were systematically compared. Based on the radiolysis kinetic model of TODGA, the slope curve of the distribution ratio of Eu(III) (DEu ) and the absorbed dose, and fluorescence titration analysis, the empirical equation of the absorbed dose and DEu was obtained successfully. Below 300 kGy, the experimental DEu agreed well with the obtained empirical equation for TODGA/nDD. Conversely, at a high absorbed dose, the experimental DEu was higher than the theoretical DEu based on the empirical equation because the radiolytic products of TODGA with similar coordination structures still possessed partial complexation toward Eu(III), which was confirmed by DFT calculations. This work provides a method to predict the extraction distribution ratio of an irradiated extractant system and to understand the complex extraction process.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-11
摘要: Inflammatory caspases (caspase-1, -4, -5 and -11) are critical for innate defences. Caspase-1 is activated by ligands of various canonical inflammasomes, and caspase-4, -5 and -11 directly recognize bacterial lipopolysaccharide, both of which trigger pyroptosis. Despite the crucial role in immunity and endotoxic shock, the mechanism for pyroptosis induction by inflammatory caspases is unknown. Here we identify gasdermin D (Gsdmd) by genome-wide clustered regularly interspaced palindromic repeat (CRISPR)-Cas9 nuclease screens of caspase-11- and caspase-1-mediated pyroptosis in mouse bone marrow macrophages. GSDMD-deficient cells resisted the induction of pyroptosis by cytosolic lipopolysaccharide and known canonical inflammasome ligands. Interleukin-1 beta release was also diminished in Gsdmd(-/-) cells, despite intact processing by caspase-1. Caspase-1 and caspase-4/5/11 specifically cleaved the linker between the amino-terminal gasdermin-N and carboxy-terminal gasdermin-C domains in GSDMD, which was required and sufficient for pyroptosis. The cleavage released the intramolecular inhibition on the gasdermin-N domain that showed intrinsic pyroptosis-inducing activity. Other gasdermin family members were not cleaved by inflammatory caspases but shared the autoinhibition; gain-of-function mutations in Gsdma3 that cause alopecia and skin defects disrupted the autoinhibition, allowing its gasdermin-N domain to trigger pyroptosis. These findings offer insight into inflammasome-mediated immunity/diseases and also change our understanding of pyroptosis and programmed necrosis.
分类: 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间: 2016-05-11
摘要: Growing evidence suggests a strong association between cardiovascular risk factors and incidence of Alzheimer disease (AD). Asymmetric dimethylarginine (ADMA), the endogenous nitric oxide synthase inhibitor, has been identified as an independent cardiovascular risk factor and is also increased in plasma of patients with AD. However, whether ADMA is involved in the pathogenesis of AD is unknown. In this study, we found that ADMA content was increased in a transgenic Caenorhabditis elegans beta-amyloid (A beta) overexpression model, strain CL2006, and in human SH-SY5Y cells overexpressing the Swedish mutant form of human A beta precursor protein (APPsw). Moreover, ADMA treatment exacerbated A beta-induced paralysis and oxidative stress in CL2006 worms and further elevated oxidative stress and A beta secretion in APPsw cells. Knockdown of type 1 protein arginine N-methyltransferase to reduce ADMA production failed to show a protective effect against A beta toxicity, but resulted in more paralysis in CL2006 worms as well as increased oxidative stress and A beta secretion in APPsw cells. However, overexpression of dimethylarginine dimethylaminohydrolase 1 (DDAH1) to promote ADMA degradation significantly attenuated oxidative stress and A beta secretion in APPsw cells. Collectively, our data support the hypothesis that elevated ADMA contributes to the pathogenesis of AD. Our findings suggest that strategies to increase DDAH1 activity in neuronal cells may be a novel approach to attenuating AD development. (C) 2014 Elsevier Inc. All rights reserved.