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排序方式: 共有309条查询结果,搜索用时 31 毫秒
91.
Miloš Buděšínský Václav Vaněk Martin Dračínský Radek Pohl Lenka Poštová-Slavětínská Vladimír Sychrovský Jan Pícha Ivana Císařová 《Tetrahedron》2014
The six-membered saturated heterocycles—4-tert-butyl-1-methylpiperidine, 4-tert-butyl-1-methylphosphine, 4-tert-butyl-tetrahydro-2H-thiopyran, and 4-tert-butyl-tetrahydro-2H-selenopyran—were prepared as suitable model compounds with well-defined geometry for an NMR study of their oxidation products. The corresponding epimeric N-oxides, phosphinoxides, sulfoxides, and selenoxides were obtained by standard chemical preparation and also by in situ oxidation with meta-chloroperbenzoic acid directly in the NMR tube. The experimental 1H and 13C chemical shifts were compared with corresponding calculated data obtained by GIAO approach with DFT, MP2, and HF methods and various basis sets. The correlation of experimental versus calculated data showed the possibility to determine the stereochemistry of the epimeric oxidation products using fast DFT B3LYP/6-31G* method for both geometry optimization and NMR chemical shifts calculation. 相似文献
92.
Radek Žlebčík Karel Černý Alice Valkárová 《The European Physical Journal C - Particles and Fields》2011,71(9):1741
Recent experimental data on dijet cross sections in diffractive photoproduction at HERA collider are analysed with an emphasis
on QCD factorisation breaking effects. The possible sources of the different conclusions of H1 and ZEUS collaborations are
studied. 相似文献
93.
Utilization of metallic nanoparticles in various biotechnological and medical applications represents one of the most extensively investigated areas of the current materials science. These advanced applications require the appropriate chemical functionalization of the nanoparticles with organic molecules or their incorporation in suitable polymer matrices. The intensified interest in polymer nanocomposites with silver nanoparticles is due to the high antimicrobial effect of nanosilver as well as the unique characteristics of polymers which include their excellent structural uniformity, multivalency, high degree of branching, miscellaneous morphologies and architectures, and highly variable chemical composition. In this review, we explore several aspects of antimicrobial polymer silver nanocomposites, giving special focus to the critical analysis of the reported synthetic routes including their advantages, drawbacks, possible improvements, and real applicability in antibacterial and antifungal therapy. A special attention is given to "green" synthetic routes exploiting the biopolymeric matrix and to the methods allowing preparing magnetically controllable antimicrobial polymers for targeting to an active place. The controversial mechanism of the action of silver against bacteria, fungi and yeasts as well as perspectives and new applications of silver polymeric nanocomposites is also briefly discussed. 相似文献
94.
Michal imek Kateina Brtov Radek Pohl Ivana Císaov Ullrich Jahn 《Angewandte Chemie (International ed. in English)》2020,59(15):6160-6165
Tandem anionic oxy‐Cope rearrangement/radical oxygenation reactions provide δ,?‐unsaturated α‐(aminoxy) carbonyl compounds, which serve as convenient precursors to diverse compound classes. Functionalized carbocycles are accessible by very rare all‐carbon 5‐endo‐trig cyclizations, but also common 5‐exo‐trig radical cyclizations, based on the persistent radical effect. The tandem reactions can be further extended by highly diastereoselective allylation or reduction steps to give complex scaffolds. 相似文献
95.
Fluorographites (CFx)n Exhibit Improved Heterogeneous Electron‐Transfer Rates with Increasing Level of Fluorination: Towards the Sensing of Biomolecules
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Xinyi Chia Dr. Adriano Ambrosi Prof. Michal Otyepka Prof. Radek Zbořil Prof. Martin Pumera 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6665-6671
Halogenated sp2 materials are of high interest owing to their important electronic and electrochemical properties. Although methods for graphite and graphene fluorination have been extensively researched, the fundamental electrochemical properties of fluorinated graphite are not well established. In this paper, the electrochemistry of three fluorographite materials of different carbon‐to‐fluorine ratio were studied: (CF0.33)n, (CF0.47)n, and (CF0.75)n. Our findings reveal that the carbon‐to‐fluorine ratio of fluorographite will impact the electrochemical performance. Faster heterogeneous electron‐transfer (HET) rates and lowered oxidation potentials for ascorbic acid and uric acid are progressively obtained with increasing fluorine content. The fluorographite (CF0.75)n was in fact found to exhibit the most improved electrochemical performances with the fastest HET rates and significantly lowered overpotentials in the oxidation of ascorbic acid. Analytical parameters such as sensitivity and linearity were subsequently investigated by applying the fluorographite (CF0.75)n in the analysis of ascorbic acid and uric acid, which can be simultaneously detected. We determined good linear responses towards the detection of both ascorbic and uric acid. Fluorographites outperform graphites in sensing applications, which will have a profound impact on applications of fluorographites and fluorographene in sensing and biosensing. 相似文献
96.
Toward a Consistent Interpretation of the QTAIM: Tortuous Link between Chemical Bonds,Interactions, and Bond/Line Paths
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Dr. Cina Foroutan‐Nejad Prof. Dr. Shant Shahbazian Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):10140-10152
Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, “misinterpretations” of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM’s topological analysis of the one‐electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the “interaction” to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed “line paths” in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some “problematic” molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new “interpretation” of data is performed. 相似文献
97.
The Use of Cobalt‐Mediated Cycloisomerisation of Ynedinitriles in the Synthesis of Pyridazinohelicenes
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Dr. Serghei Chercheja Jiří Klívar Andrej Jančařík Dr. Jiří Rybáček Simon Salzl Dr. Ján Tarábek Prof. Dr. Lubomír Pospíšil Dr. Jana Vacek Chocholoušová Dr. Jaroslav Vacek Dr. Radek Pohl Dr. Ivana Císařová Dr. Ivo Starý Dr. Irena G. Stará 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(27):8477-8482
A cobalt‐mediated [2+2+2] cycloisomerisation of ynedinitriles to helical pyridazines in good to high yields was developed. The construction of the pyridazine nucleus from one alkyne and two nitrile units is proposed to follow either a conventional organometallic mechanism or to be triggered by a single‐electron transfer from a CoII species. Various [5]‐, [6]‐ and [7]helicene pyridazines were prepared. 相似文献
98.
Miroslav Janicek Martina Polaskova Radek Holubar Roman Cermak 《Cellulose (London, England)》2014,21(6):4039-4048
Cellulose powders hydrophobized by surface esterification with carboxylic acids with different chain lengths (3, 10 and 18 carbons) were dispersed in a polypropylene matrix. Quality of the dispersion and nucleation activity of the filler were investigated by means of differential scanning calorimetry and optical microscopy. The results showed that the esterification decreases the crystallization rate in case of cellulose esterified with propionic or decanoic acid. On the other hand, the oleic acid ester demonstrated slightly higher crystallization rates than the unmodified cellulose, which was ascribed primarily to the newly arisen non-esterified surface after disintegration of the filler. Optical microscopy with hot stage showed the high nucleation ability of the natural cellulose fiber and its suppression in case of esterified surfaces. A complete inability to nucleate polypropylene crystallization was observed in case of decanoyl ester, while the other two retained some activity, but lower than that of the natural fiber. Finally, analysis of the filler dispersion and distribution revealed that the decanoyl and octadecanoyl esters disintegrate during melt mixing, while both dispersion and distribution of the fibers modified with propionic acid are poor. 相似文献
99.
100.
José M. Hidalgo Michal Zbuzek Radek Černý Petr Jíša 《Central European Journal of Chemistry》2014,12(2):281-281
The original version of the article was published in Cent. Eur. J. Chem. 12(1) (2014) pp. 1–13. Unfortunately, the original version of this article contains some mistakes in the text:
- The caption of Figure 7. A fixed bed unit converted to the UOP Par-Isom Process?
- Par Isom Process should be written as Par-Isom Process?
- everywhere in the text LCC should be written as LLC