排序方式: 共有52条查询结果,搜索用时 13 毫秒
41.
Karma Yeshi Darren Crayn Edita Ritmejeryt Phurpa Wangchuk 《Molecules (Basel, Switzerland)》2022,27(1)
Plant secondary metabolites (PSMs) are vital for human health and constitute the skeletal framework of many pharmaceutical drugs. Indeed, more than 25% of the existing drugs belong to PSMs. One of the continuing challenges for drug discovery and pharmaceutical industries is gaining access to natural products, including medicinal plants. This bottleneck is heightened for endangered species prohibited for large sample collection, even if they show biological hits. While cultivating the pharmaceutically interesting plant species may be a solution, it is not always possible to grow the organism outside its natural habitat. Plants affected by abiotic stress present a potential alternative source for drug discovery. In order to overcome abiotic environmental stressors, plants may mount a defense response by producing a diversity of PSMs to avoid cells and tissue damage. Plants either synthesize new chemicals or increase the concentration (in most instances) of existing chemicals, including the prominent bioactive lead compounds morphine, camptothecin, catharanthine, epicatechin-3-gallate (EGCG), quercetin, resveratrol, and kaempferol. Most PSMs produced under various abiotic stress conditions are plant defense chemicals and are functionally anti-inflammatory and antioxidative. The major PSM groups are terpenoids, followed by alkaloids and phenolic compounds. We have searched the literature on plants affected by abiotic stress (primarily studied in the simulated growth conditions) and their PSMs (including pharmacological activities) from PubMed, Scopus, MEDLINE Ovid, Google Scholar, Databases, and journal websites. We used search keywords: “stress-affected plants,” “plant secondary metabolites, “abiotic stress,” “climatic influence,” “pharmacological activities,” “bioactive compounds,” “drug discovery,” and “medicinal plants” and retrieved published literature between 1973 to 2021. This review provides an overview of variation in bioactive phytochemical production in plants under various abiotic stress and their potential in the biodiscovery of therapeutic drugs. We excluded studies on the effects of biotic stress on PSMs. 相似文献
42.
A shortest cycle cover of a graph G is a family of cycles which together cover all the edges of G and the sum of their lengths is minimum. In this article we present upper bounds to the length of shortest cycle covers, associated with the existence of two types of nowhere‐zero flows—circular flows and Fano flows. Fano flows, or Fano colorings, are nowhere‐zero ?‐flows on cubic graphs, with certain restrictions on the flow values meeting at a vertex. Such flows are conjectured to exist on every bridgless cubic graph. Copyright © 2011 Wiley Periodicals, Inc. J Graph Theory 68:340‐348, 2011 相似文献
43.
Edita Sakyte Rita Palivonaite Algiment Aleksa Minvydas Ragulskis 《Optics Communications》2011,284(16-17):3954-3964
Image hiding based on time-averaged fringes produced by non-harmonic oscillations and near-optimal moiré gratings is presented in this paper. The secret image is embedded into the background moiré grating. Phase matching and initial stochastic phase scrambling algorithms are used to encrypt the image. The decoding of the image is completely visual. The embedded secret image appears when the encrypted image is oscillated in a predefined direction, according to a predefined law of motion. No secret is leaked when the encrypted image is oscillated harmonically at any amplitude of oscillation. The criterion of the optimality of a moiré grating serves as a fitness function for evolutionary algorithms which are used to identify a near-optimal moiré grating for image hiding applications. Numerical experiments are used to illustrate the functionality of the method. 相似文献
44.
The circumference of a graph G is the length of a longest cycle. By exploiting our recent results on resistance of snarks, we construct infinite classes of cyclically 4‐, 5‐, and 6‐edge‐connected cubic graphs with circumference ratio bounded from above by 0.876, 0.960, and 0.990, respectively. In contrast, the dominating cycle conjecture implies that the circumference ratio of a cyclically 4‐edge‐connected cubic graph is at least 0.75. Up to our knowledge, no upper bounds on this ratio have been known before for cubic graphs with cyclic edge‐connectivity above 3. In addition, we construct snarks with large girth and large circumference deficit, solving Problem 1 proposed in [J. Hägglund and K. Markström, On stable cycles and cycle double covers of graphs with large circumference, Disc Math 312 (2012), 2540–2544]. 相似文献
45.
An acyclic edge‐coloring of a graph is a proper edge‐coloring such that the subgraph induced by the edges of any two colors is acyclic. The acyclic chromatic index of a graph G is the smallest number of colors in an acyclic edge‐coloring of G. We prove that the acyclic chromatic index of a connected cubic graph G is 4, unless G is K4 or K3,3; the acyclic chromatic index of K4 and K3,3 is 5. This result has previously been published by Fiam?ík, but his published proof was erroneous. 相似文献
46.
Agáta Smieková Edita Rojasová Pavol Hudec Lubo abo 《Reaction Kinetics and Catalysis Letters》2004,82(2):227-234
The role of Zn2+ in ZnZSM-5 catalyst in the process of aromatization of alkanes has been studied with the probe molecules - n-hexane, cyclohexane and 1-hexene. IR measurements showed that the parent HZSM-5 zeolite contains predominantly Br?nsted acid
sites, while Zn cations in ZnZSM-5 catalyst represent Lewis sites. From the results it follows, that Zn cations in ZnZSM-5
catalyst as Lewis acid sites have strong hydro-dehydrogenation activity and they catalyze the dehydrogenation of n-hexane as well as of cyclic intermediates into the corresponding aromatics. From the results of catalytic tests we conclude
that the hydro-dehydrogenation activity of the catalyst plays an essential role in aromatization of light alkanes. The results
indicate that for improving the yields of aromatics in aromatization of light alkanes on bifunctional catalysts it is inevitable
to increase the participation of the dehydrogenation reactions in the activation of alkane as well as in the formation of
the corresponding aromatics from cyclic intermediates.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
47.
Edita Voitechovi
Aura Vektarien Gytis Vektaris Regina Jan
ien Julija Razumien Vidut Gurevi
ien 《Electroanalysis》2020,32(5):1005-1016
D‐fructose amount in food and beverages should be carefully controlled in order to avoid its overconsumption by human, which can lead to various metabolic diseases. Thus, the development of a low‐cost and portable (bio)sensors, which realize the on‐site monitoring of D‐fructose, is still highly required. In this work, we proposed several reagentless bioelectrochemical systems (BioESs) based on fructose dehydrogenase EC1.1.99.11 from Gluconobacter japonicus (FDH) and on 2‐arylamine‐1,4‐benzoquinone (ABQ) derivatives as a platform for the development of D‐fructose electrochemical biosensor. To design a reliable and easily reproducible BioES, we used the simple physical sorption as the electrode modification strategy for ABQs and FDH immobilization that is suitable for low‐cost mass production of the biosensors by standard microfabrication techniques. To choose the most suitable ABQ compounds for BioESs design, we proposed a novel theoretical approach of potential ET mediator evaluation through its electrochemical properties. A set of newly synthesized and of previously applied ABQs was characterized both electrochemically and using the density functional theory (DFT). It was shown that results obtained by quantum chemical analysis were in a good agreement with the ABQ characteristics obtained in electrochemical measurements. We suggest that the calculated local ionization energy values and theoretical redox potential obtained by DFT are a powerful tool for prediction of ABQs electrochemical properties. The performance of the BioESs with FDH under study was determined by electrochemical and electronic properties of ABQ derivatives and FDH orientation and stabilization on the electrode surface. The most promising BioES was based on carbon paste electrodes and 2‐(3‐nitro(phenyl)amino)‐ cyclohexa‐2,5‐dien‐1,4‐dione as ET mediator, which accelerated FDH catalysis and improved its stability better, then other studied ABQs. The bioelectrocatalytic process was characterized by initial apparent maximum current density of 7.1 μA cm?2 at the optimal conditions (+400 mV vs. Ag/AgCl, McIlvaine's buffer, pH 5.0 and 20 °C). The findings of this research open new possibilities for development of cost‐effective biosensors with FDH and, potentially, with other redox enzymes. 相似文献
48.
For arbitrary polynomial loading and a sufficient finite number of nodal points N, the solution for the 3D Timoshenko beam differential equations is polynomial and given as \({{\varvec \theta} = \sum_{i=1}^N I_i {\varvec \theta}_i}\) for the rotation field and \({{\bf u} = \sum_{i=1}^{N+1} J_i {\bf u}_i}\) for the displacement field, where I i and J i are the Lagrangian polynomials of order N?1 and N, respectively. It has been demonstrated in this work that the exact solution for the displacement field may be also written in a number of alternative ways involving contributions of the nodal rotations including \({{\bf u} = \sum_{i=1}^N I_i \left[ {\bf u}_i + \frac 1 N ( {\varvec \theta} - {\varvec \theta}_i ) \times {\bf R}_i \right]}\), where R i are the beam nodal positions. 相似文献
49.
Mike J. Grannell Terry S. Griggs Edita Máčajová Martin Škoviera 《Journal of Graph Theory》2013,74(2):163-181
An ‐coloring of a cubic graph G is an edge coloring of G by points of a Steiner triple system such that the colors of any three edges meeting at a vertex form a block of . A Steiner triple system that colors every simple cubic graph is said to be universal. It is known that every nontrivial point‐transitive Steiner triple system that is neither projective nor affine is universal. In this article, we present the following results.
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50.