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991.
Novel, porous NiCo2O4 nanotubes (NCO‐NTs) are prepared by a single‐spinneret electrospinning technique followed by calcination in air. The obtained NCO‐NTs display a one‐dimensional architecture with a porous structure and hollow interiors. The effect of precursor concentration on the morphologies of the products is investigated. Due to their unique structure, the prepared NCO‐NT electrode exhibits a high specific capacitance (1647 F g?1 at 1 A g?1), excellent rate capability (77.3 % capacity retention at 25 A g?1), and outstanding cycling stability (6.4 % loss after 3000 cycles), which indicates it has great potential for high‐performance electrochemical capacitors. The desirable enhanced capacitive performance of NCO‐NTs can be attributed to the relatively large specific surface area of these porous and hollow one‐dimensional nanostructures.  相似文献   
992.
The rare‐earth‐metal? hydride complexes [{(1,7‐Me2TACD)LnH}4] (Ln=La 1 a , Y 1 b ; (1,7‐Me2TACD)H2=1,7‐dimethyl‐1,4,7,10‐tetraazacyclododecane, 1,7‐Me2[12]aneN4) were synthesized by hydrogenolysis of [{(1,7‐Me2TACD)Ln(η3‐C3H5)}2] with 1 bar H2. The tetrameric structures were confirmed by 1H NMR spectroscopy and single‐crystal X‐ray diffraction of compound 1 a . Both complexes catalyze the dehydrogenation of secondary amine? borane Me2NH ? BH3 to afford the cyclic dimer (Me2NBH2)2 and (Me2N)2BH under mild conditions. Whilst the complete conversion of Me2NH ? BH3 was observed within 2 h with lanthanum? hydride 1 a , the yttrium homologue 1 b required 48 h to reach 95 % conversion. Further reactions of compound 1 a with Me2NH ? BH3 in various stoichiometric ratios gave a series of intermediate products, [{(1,7‐Me2TACD)LaH}4](Me2NBH2)2 ( 2 a ), [(1,7‐Me2TACDH)La(Me2NBH3)2] ( 3 a ), [(1,7‐Me2TACD)(Me2NBH2)La(Me2NBH3)] ( 4 a ), and [(1,7‐Me2TACD)(Me2NBH2)2La(Me2NBH3)] ( 5 a ). Complexes 2 a , 3 a , and 5 a were isolated and characterized by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction studies. These intermediates revealed the activation and coordination modes of “Me2NH ? BH3” fragments that were trapped within the coordination sphere of a rare‐earth‐metal center.  相似文献   
993.
Proteins typically have nanoscale dimensions and multiple binding sites with inorganic ions, which facilitates the templated synthesis of nanoparticles to yield nanoparticle–protein hybrids with tailored functionality, water solubility, and tunable frameworks with well‐defined structure. In this work, we report a protein‐templated synthesis of Mn‐doped ZnS quantum dots (QDs) by exploring bovine serum albumin (BSA) as the template. The obtained Mn‐doped ZnS QDs give phosphorescence emission centered at 590 nm, with a decay time of about 1.9 ms. A dual‐channel sensing system for two different proteins was developed through integration of the optical responses (phosphorescence emission and resonant light scattering (RLS)) of Mn‐doped ZnS QDs and recognition of them by surface BSA phosphorescent sensing of trypsin and RLS sensing of lysozyme. Trypsin can digest BSA and remove BSA from the surface of Mn‐doped ZnS QDs, thus quenching the phosphorescence of QDs, whereas lysozyme can assemble with BSA to lead to aggregation of QDs and enhanced RLS intensity. The detection limits for trypsin and lysozyme were 40 and 3 nM , respectively. The selectivity of the respective channel for trypsin and lysozyme was evaluated with a series of other proteins. Unlike other protein sensors based on nanobioconjugates, the proposed dual‐channel sensor employs only one type of QDs but can detect two different proteins. Further, we found the RLS of QDs can also be useful for studying the BSA–lysozyme binding stoichiometry, which has not been reported in the literature. These successful biosensor applications clearly demonstrate that BSA not only serves as a template for growth of Mn‐doped ZnS QDs, but also impacts the QDs for selective recognition of analyte proteins.  相似文献   
994.
An increasing number of proteins are found to contain a knot in their polypeptide chain. Although some studies have looked into the folding mechanism of knotted proteins, why and how these complex topologies form are still far from being fully answered. Moreover, no experimental information about how the knot moves during the protein‐folding process is available. Herein, by combining single‐molecule fluorescence resonance energy transfer (smFRET) experiments with molecular dynamics (MD) simulations, we performed a detailed study to characterize the knot in the denatured state of TrmD, a knotted tRNA (guanosine‐1) methyltransferase from Escherichia coli, as a model system. We found that the knot still existed in the unfolded state of TrmD, consistent with the results for two other knotted proteins, YibK and YbeA. More interestingly, both smFRET experiments and MD simulations revealed that the knot slid towards the C‐terminal during the unfolding process, which could be explained by the relatively strong interactions between the β‐sheet core at the N terminal of the native knot region. The size of the knot in the unfolded state is not larger than that in the native state. In addition, the knot slid in a “downhill” mode with simultaneous chain collapse in the denatured state.  相似文献   
995.
A series of arylboronic esters containing different aromatic substituents and various benzylic leaving groups (Br or N+Me3Br?) have been synthesized. The substituent effects on their reactivity with H2O2 and formation of quinone methide (QM) have been investigated. NMR spectroscopy and ethyl vinyl ether (EVE) trapping experiments were used to determine the reaction mechanism and QM formation, respectively. QMs were not generated during oxidative cleavage of the boronic esters but by subsequent transformation of the phenol products under physiological conditions. The oxidative deboronation is facilitated by electron‐withdrawing substituents, such as aromatic F, NO2, or benzylic N+Me3Br?, whereas electron‐donating substituents or a better leaving group favor QM generation. Compounds containing an aromatic CH3 or OMe group, or a good leaving group (Br), efficiently generate QMs under physiological conditions. Finally, a quantitative relationship between the structure and activity has been established for the arylboronic esters by using a Hammett plot. The reactivity of the arylboronic acids/esters and the inhibition or facilitation of QM formation can now be predictably adjusted. This adjustment is important as some applications may benefit and others may be limited by QM generation.  相似文献   
996.
Herein, we report a “threading followed by shrinking” approach for the synthesis of rotaxanes by using an “oxygen‐deficient” macrocycle that contained two arylmethyl sulfone units and the dumbbell‐shaped salt bis(3,5‐dimethylbenzyl)ammonium tetrakis(3,5‐trifluoromethylphenyl)borate as the host and guest components, respectively. The extrusion of SO2 from both of the arylmethyl sulfone units of the macrocyclic component in the corresponding [2]pseudorotaxane resulted in a [2]rotaxane that was sufficiently stable to maintain its molecular integrity in CD3SOCD3 at 393 K for at least 5 h.  相似文献   
997.
This paper reports the facile design and synthesis of a series of lipidic organoalkoxysilanes with different numbers of triethoxysilane headgroups and hydrophobic alkyl chains linked by glycerol and pentaerythritol for the construction of cerasomes with regulated surface siloxane density and controlled release behavior. It was found that the number of triethoxysilane headgroups affected the properties of the cerasomes for encapsulation efficiency, drug loading capacity, and release behavior. For both water‐soluble doxorubicin (DOX) and water‐insoluble paclitaxel (PTX), the release rate from the cerasomes decreased as the number of triethoxysilane headgroups increased. The slower release rate from the cerasomes was attributed to the higher density of the siloxane network on the surface of the cerasomes, which blocks the drug release channels. In contrast to the release results with DOX, the introduction of one more hydrophobic alkyl chain into the cerasome‐forming lipid resulted in a slower release rate of PTX from the cerasomes due to the formation of a more compact cerasome bilayer. An MTT viability assay showed that all of these drug‐loaded cerasomes inhibited proliferation of the HepG2 cancer cell line. The fine tuning of the chemical structure of the cerasome‐forming lipids would foster a new strategy to precisely regulate the release rate of drugs from cerasomes.  相似文献   
998.
999.
以取代苯酚、多聚甲醛和取代苯胺为原料,在无催化剂的条件下,通过Mannich缩合反应合成了一系列新型3,6(8)-二取代-2,4-二氢-1,3-苯并(口恶)嗪类化合物.结果表明,取代苯酚和取代苯胺的取代基为供电子基时,合成产物的产率高于吸电子取代基的.产物的结构用1H NMR、13C NMR、IR和MS等进行了表征.初步测试了目标化合物的杀菌活性,部分化合物具有较好的杀菌活性.当浓度为25 mg/L时,化合物4j和4d对菌核病菌的抑制率分别为86.1%和81.5%,化合物4i对灰霉病菌的抑制率为81.6%.  相似文献   
1000.
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