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91.
Flavin-zinc(II)-cyclen 10 contains a covalently linked substrate binding site (zinc(II)-cyclen) and a chromophore unit (flavin). Upon irradiation, compound 10 effectively oxidizes 4-methoxybenzyl alcohol (11-OCH3) to the corresponding benzaldehyde both in water and in acetonitrile. In the presence of air, the reduced flavin 10-H2 is reoxidized, and so catalytic amounts of 10 are sufficient for alcohol conversion. The mechanism of oxidation is based on photoinduced electron transfer from the coordinated benzyl alcohol to the flavin chromophore. This intramolecular process provides a much higher photooxidation efficiency, with quantum yields 30 times those of the comparable intermolecular process with a flavin chromophore without a binding site. For the reaction in buffered aqueous solution a quantum yield of Phi = 0.4 is observed. The turnover number in acetonitrile is increased (up to 20) by high benzyl alcohol concentrations. The results show that the covalent combination of a chromophore and a suitable binding site may lead to photomediators more efficient than classical sensitizer molecules. 相似文献
92.
Dr. Mariana Amaro Dr. Radek Šachl Gokcan Aydogan Dr. Ilya I. Mikhalyov Dr. Robert Vácha Prof. Martin Hof 《Angewandte Chemie (International ed. in English)》2016,55(32):9411-9415
β‐Amyloid (Aβ) oligomers are neurotoxic and implicated in Alzheimer's disease. Neuronal plasma membranes may mediate formation of Aβ oligomers in vivo. Membrane components sphingomyelin and GM1 have been shown to promote aggregation of Aβ; however, these studies were performed under extreme, non‐physiological conditions. We demonstrate that physiological levels of GM1, organized in nanodomains do not seed oligomerization of Aβ40 monomers. We show that sphingomyelin triggers oligomerization of Aβ40 and that GM1 is counteractive thus preventing oligomerization. We propose a molecular explanation that is supported by all‐atom molecular dynamics simulations. The preventive role of GM1 in the oligomerization of Aβ40 suggests that decreasing levels of GM1 in the brain, for example, due to aging, could reduce protection against Aβ oligomerization and contribute to the onset of Alzheimer's disease. 相似文献
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Petr Řepa Ladislav Peksa Tomáš Gronych Radek Ulman Jan Wild Oldřich Schneeweiss 《Czechoslovak Journal of Physics》2006,56(12):1389-1399
This article describes a measuring system that was proposed so as to enable measurement of the content of dissolved gas in
samples, whose shape is determined by the specific requirements of the simultaneous measurements and cannot be modified to
satisfy the requirements on solubility measurements. The apparatus — a dynamic UHV vacuum system — consists of a measuring
chamber fitted with a heater based on electron bombardment, which permits a change in the sample temperature according to
the selected schedule. The design of the heater permits reduction of additional heating in the actual measuring chamber, so
that the increase in pressure caused by the action of the heater can be neglected. The measuring part of the system permits
recording of changes in the overall pressure and partial pressures of selected gases in the measuring chamber. The lowest
detectable amount of dissolved gas is less than 10−5 Pa m3.
The results of measurement of the solubility of hydrogen in Ti and Fe aluminides in samples that are simultaneously used to
measure the electrical conductivity are given as an example of the suitability of the apparatus for such measurements.
This work is a part of research plan MSM 0021620834 financed by the Ministry of Education, Youth and Sports of the Czech Republic. 相似文献
96.
Resolving Electronic Transitions in Synthetic Fluorescent Protein Chromophores by Magnetic Circular Dichroism 下载免费PDF全文
Petr Štěpánek Thomas Y. Cowie Dr. Martin Šafařík Dr. Jaroslav Šebestík Dr. Radek Pohl Prof. Petr Bouř 《Chemphyschem》2016,17(15):2348-2354
The detailed electronic structures of fluorescent chromophores are important for their use in imaging of living cells. A series of green fluorescent protein chromophore derivatives is examined by magnetic circular dichroism (MCD) spectroscopy, which allows the resolution of more bands than plain absorption and fluorescence. Observed spectral patterns are rationalized with the aid of time‐dependent density functional theory (TDDFT) computations and the sum‐over‐state (SOS) formalism, which also reveals a significant dependence of MCD intensities on chromophore conformation. The combination of organic and theoretical chemistry with spectroscopic techniques also appears useful in the rational design of fluorescence labels and understanding of the chromophore's properties. For example, the absorption threshold can be heavily affected by substitution on the phenyl ring but not much on the five‐member ring, and methoxy groups can be used to further tune the electronic levels. 相似文献
97.
Martin Robinson Chong Luo Patrick E. Farrell Radek Erban Apala Majumdar 《Liquid crystals》2017,44(14-15):2267-2284
We study nematic equilibria on a square with tangent Dirichlet conditions on the edges, in three different modelling frameworks: (i) the off-lattice Hard Gaussian Overlap and Gay–Berne models; (ii) the lattice-based Lebwohl–Lasher model; and the (iii) two-dimensional Landau-de Gennes model. We compare the modelling predictions, identify regimes of agreement and in the Landau-de Gennes case, find up to 21 different equilibria. Of these, two are physically stable. 相似文献
98.
Supramolecular shuttle based on inclusion complex between cucurbit[6]uril and bispyridinium ethylene
Cucurbit[6]uril (CB6) and bispyridinium ethylene form a stable inclusion complex. A rotaxane derived from this complex was prepared in which a CB6 wheel shuttles along an axle in an NMR time-resolved regime. 相似文献
99.
Syntax of natural language has been the focus of linguistics for decades. The complex network theory, being one of new research tools, opens new perspectives on syntax properties of the language. Despite numerous partial achievements, some fundamental problems remain unsolved. Specifically, although statistical properties typical for complex networks can be observed in all syntactic networks, the impact of syntax itself on these properties is still unclear. The aim of the present study is to shed more light on the role of syntax in the syntactic network structure. In particular, we concentrate on the impact of the syntactic function of a verb in the sentence on the complex network structure. Verbs play the decisive role in the sentence structure (“local” importance). From this fact we hypothesize the importance of verbs in the complex network (“global” importance). The importance of verb in the complex network is assessed by the number of links which are directed from the node representing verb to other nodes in the network. Six languages (Catalan, Czech, Dutch, Hungarian, Italian, Portuguese) were used for testing the hypothesis. 相似文献
100.
We studied the effects of the number of crystal water molecules on the magnetic behavior of {[Ni(en)(2)](3)[Fe(CN)(6)](2)·xH(2)O}(n) (1-3) (where en = ethylenediamine and x = 3, 2, or 0) coordination polymers by (57)Fe M?ssbauer spectroscopy, single-crystal X-ray diffraction, and magnetization measurements. Magnetic phase diagrams constructed for all three compounds indicate that they behave as metamagnets exhibiting very rare field-induced antiferro-ferro-paramagnetic transitions. The number of crystal water molecules has a major effect on the Néel temperature, critical field, and magnetic hardness of the compounds in the ferromagnetic state. Moreover, the systems behave as molecular magnetic sponges, changing their magnetic properties due to the controllable and reversible dehydration/hydration process. 相似文献