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71.
Lenka Soukupová Alena Komersová Karel Komers árka tpánková Alexander egan 《Reaction Kinetics and Catalysis Letters》2008,95(2):205-211
Mechanism and kinetics of in vitro hydrolysis of acetyl-β-methylcholine by acetylcholinesterase from electric eel in a mixed batch reactor at 25 and 37°C, pH
8, ionic strength 0.11 M and catalytic activity of the enzyme preparat of 3.5 U mL−1 were studied. The optimal kinetic parameters were determined. 相似文献
72.
Trouillas P Marsal P Svobodová A Vostálová J Gazák R Hrbác J Sedmera P Kren V Lazzaroni R Duroux JL Walterová D 《The journal of physical chemistry. A》2008,112(5):1054-1063
Flavonolignans from silymarin, the standardized plant extract obtained from thistle, exhibit various antioxidant activities, which correlate with the other biological and therapeutic properties of that extract. To highlight the mode of action of flavonolignans as free radical scavengers and antioxidants, 10 flavonolignans, selectively methylated at different positions, were tested in vitro for their capacity to scavenge radicals (DPPH and superoxide) and to inhibit the lipid peroxidation induced on microsome membranes. The results are rationalized on the basis of (i) the oxidation potentials experimentally obtained by cyclic voltammetry and (ii) the theoretical redox properties obtained by quantum-chemical calculations (using a polarizable continuum model (PCM)-density functional theory (DFT) approach) of the ionization potentials and the O-H bond dissociation enthalpies (BDEs) of each OH group of the 10 compounds. We clearly establish the importance of the 3-OH and 20-OH groups as H donors, in the presence of the 2,3 double bond and the catechol moiety in the E-ring, respectively. For silybin derivatives (i.e., in the absence of the 2,3 double bond), secondary mechanisms (i.e., electron transfer (ET) mechanism and adduct formation with radicals) could become more important (or predominant) as the active sites for H atom transfer (HAT) mechanism are much less effective (high BDEs). 相似文献
73.
Alena A. Volgusheva Daria A. Todorenko Ivan V. Konyukhov Elena N. Voronova Sergey I. Pogosyan Tatyana Yu Plyusnina Sergey S. Khruschev Taras K. Antal 《Photochemistry and photobiology》2023,99(4):1106-1114
The effect of the toxicant 2,3′,4,4′,6-pentachlorobiphenyl (PCB-119) on the growth, chlorophyll content, and PSII activity of C. sorokiniana cells was investigated. A strong negative effect of the toxicant was observed at PCB concentration of 0.05 μg mL−1, when culture growth ceased, chlorophyll strongly bleached, and cell death occurred. The use of original highly sensitive fluorimeter to measure three types of high-resolution chlorophyll fluorescence kinetics allowed us to detect an initial dramatic decrease in the activity of primary photosynthetic reactions, followed by their almost complete recovery at the end of the incubation period when most cells were dead. The study of the distribution of individual cells in culture in terms of Fv/Fm parameter, which reflects the quantum yield of PSII photochemistry, revealed the existence of 2–3% of cells retaining high Fv/Fm (>0.7) in the presence of the toxicant. The treated cultures were able to resume growth after prolonged incubation in fresh medium. The high sensitivity fluorescence methods used made it possible to identify stress-resistant cells which maintain high photosynthetic activity in the presence of lethal doses of toxic substances; these cells provide recovery of the population after stress. 相似文献
74.
Biospecimens with nearly flat surfaces on a flat stage are typically required for laser-based mass spectrometry imaging (MSI) techniques. However, sampling stages are rarely perfectly level, and accounting for this and the need to accommodate non-flat samples requires a deeper understanding of the laser beam depth of focus. In ablation-based MSI methods, a laser is focused on top of the sample surface, ensuring that the sample is at the focal point or remains within depth of focus. In general, the depth of focus of a given laser is related to the beam quality (M2) and the wavelength (λ). However, because laser is applied on a biological sample, other variables can also impact the depth of focus, which could affect the robustness of the MSI techniques for diverse sample types. When the height of a sample ranges outside of the depth of focus, ablated area and the corresponding ion abundances may vary as well, increasing the variability of results. In this tutorial, we examine the parameters and equations that describe the depth of focus of a Gaussian laser beam. Additionally, we describe several approaches that account for surface roughness exceeding the depth of focus of the laser. 相似文献
75.
Dr. Zi Wang Dr. Alena M. Sheveleva Dr. Daniel Lee Yinlin Chen Dr. Dinu Iuga Dr. W. Trent Franks Dr. Yujie Ma Dr. Jiangnan Li Dr. Lei Li Dr. Yongqiang Cheng Dr. Luke L. Daemen Dr. Sarah J. Days Dr. Anibal J. Ramirez-Cuesta Bing Han Dr. Alexander S. Eggeman Prof. Eric J. L. McInnes Dr. Floriana Tuna Prof. Sihai Yang Prof. Martin Schröder 《Angewandte Chemie (International ed. in English)》2023,62(28):e202302602
We report the modulation of reactivity of nitrogen dioxide (NO2) in a charged metal–organic framework (MOF) material, MFM-305-CH3 in which unbound N-centres are methylated and the cationic charge counter-balanced by Cl− ions in the pores. Uptake of NO2 into MFM-305-CH3 leads to reaction between NO2 and Cl− to give nitrosyl chloride (NOCl) and NO3− anions. A high dynamic uptake of 6.58 mmol g−1 at 298 K is observed for MFM-305-CH3 as measured using a flow of 500 ppm NO2 in He. In contrast, the analogous neutral material, MFM-305, shows a much lower uptake of 2.38 mmol g−1. The binding domains and reactivity of adsorbed NO2 molecules within MFM-305-CH3 and MFM-305 have been probed using in situ synchrotron X-ray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, high-field solid-state nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants. 相似文献
76.
A generalisation of the classical Halton sequence \((\phi _{\beta }(n))_{n\in \mathbb {N}}\) has emerged in recent years based on \(\beta \)-adic expansions of elements of [0, 1). In the case where \(\beta \) is a natural number greater than 1, this reduces to the classical Halton sequence. In this paper, we use ergodic and analytic methods to prove the uniform distribution of a sequence \((\phi _{\beta }(k_j))_{j\in \mathbb {N}}\) for the sequence of integers \((k_j)_{j\ge 0}\), which is both Hartman uniformly distributed and good universal. This builds on earlier work of M. Hofer, M. R. Iaco and R. Tichy in the special case \(k_j =j \ (j=0,1, \ldots )\). Variants of this phenomenon are also studied. 相似文献
77.
Karolína Pádrová Irena Kolouchová Tomáš Řezanka Alena Čejková 《Chemical Papers》2016,70(10):1351-1359
Yeast responses to stress conditions include an increase in lipid content and concomitant changes in content of saturated and unsaturated fatty acids. Some fatty acids are among the dietetically important fatty acids and new possibilities are sought for their biotechnological production in addition to those already exploited from marine organisms, nuts and other sources. The possibility of the production of palmitoleic and linoleic acids resulting from new approaches to traditional biotechnologically useful yeast species (Kluyveromyces polysporus, Saccharomyces cerevisiae, Torulospora delbrueckii) and species capable of high accumulation of lipids (Rhodotorula glutinis, Trichosporon cutaneum, Candida sp., Yarrowia lipolytica) was explored. The most promising was the combination of two stress factors: limitation of N-sources (C/N mass ratio of 70: 1) and oxidative stress induced by zero- valent iron nanoparticles. These conditions were conducive to the production of palmitoleic acid commonly used in cosmetics and medicine and ω-6-linoleic acid, a precursor of thromboxanes, prostaglandins and leucotrienes. The yield of these two fatty acids in T. cutaneum was more than 500 mg g?1 (dry mass) and in Candida sp. more than 600 mg g-1 (dry mass). 相似文献
78.
79.
Xiangyu Teng Dr. Alena Sheveleva Dr. Floriana Tuna Prof. Keith R. Willison Dr. Liming Ying 《Chemphyschem》2021,22(23):2413-2419
The interaction between α-synuclein (αSyn) and Cu2+ has been suggested to be closely linked to brain copper homeostasis. Disruption of copper levels could induce misfolding and aggregation of αSyn, and thus contribute to the progression of Parkinson's disease (PD). Understanding the molecular mechanism of αSyn-Cu2+ interaction is important and controversies in Cu2+ coordination geometry with αSyn still exists. Herein, we find that the pathological H50Q mutation has no impact on the kinetics of Cu2+ binding to the high-affinity site of wild type αSyn (WT-αSyn), indicating the non-involvement of His50 in high-affinity Cu2+ binding to WT-αSyn. In contrast, the physiological N-terminally acetylated αSyn (NAc-αSyn) displays several orders of magnitude weaker Cu2+ binding affinity than WT-αSyn. Cu2+ coordination mode to NAc-αSyn has also been proposed based on EPR spectrum. In addition, we find that Cu2+ coordinated WT-αSyn is reduction-active in the presence of GSH, but essentially inactive towards ascorbate. Our work provides new insights into αSyn-Cu2+ interaction, which may help understand the multifaceted normal functions of αSyn as well as pathological consequences of αSyn aggregation. 相似文献
80.
Alena Haddley Poj Lertchoosakul Radhakrishnan Nair 《Periodica Mathematica Hungarica》2017,74(1):128-136
Let \(\kappa \) be an infinite cardinal, and \(2^\kappa <\lambda \le 2^{\kappa ^+}\). We prove that if there is a weak diamond on \(\kappa ^+\) then every \(\{C_\alpha :\alpha <\lambda \}\subseteq \mathcal {D}_{\kappa ^+}\) satisfies Galvin’s property. On the other hand, Galvin’s property is consistent with the failure of the weak diamond (and even with Martin’s axiom in the case of \(\aleph _1\)). We derive some consequences about weakly inaccessible cardinals. We also prove that the negation of a similar property follows from the proper forcing axiom. 相似文献