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141.
142.
Aromatic amides bearing 2-azulenyl group on the amide nitrogen were synthesized and their structures were investigated. The π-electron density of the N-aryl group was found to influence the cis-trans conformational preferences of these compounds in solution. X-ray crystallography revealed that the plane of the 2-azulenyl ring has a strong tendency to lie coplanar with the amide plane when the azulene group is located on the same side as the amide oxygen atom.  相似文献   
143.
The effects of multi-step rapid thermal annealing (RTA) for the self-assembled InAs quantum dots (QDs), which were grown by a molecular beam epitaxy (MBE), were investigated through photoluminescence (PL) and transmission electron microscopy (TEM). Postgrowth multi-step RTA was used to modify the structural and optical properties of the self-assembled InAs QDs. Postgrowth multi-step RTAs are as follows: one step (20 s at 750 °C); two step (20 s at 650 °C, 20 s at 750 °C); three step (30 s at 450 °C, 20 s at 650 °C, 20 s at 750 °C). It is found that significant narrowing of the luminescence linewidth (from 132 to 31 meV) from the InAs QDs occurs together with about 150 meV blueshift by two-step annealing, compared to as-grown InAs QDs. Observation of transmission electron microscopy (TEM) shows the existence of the dots under one- and two-step annealing but the disappearance of the dots by three-step annealing. Comparing with the samples under only one-step annealing, we demonstrate a significant enhancement of the interdiffusion in the dot layer under multi-step annealing.  相似文献   
144.
Choi MG  Ryu de H  Jeon HL  Cha S  Cho J  Joo HH  Hong KS  Lee C  Ahn S  Chang SK 《Organic letters》2008,10(17):3717-3720
The chemodosimetric behavior of dichlorofluorescein derivatives toward Hg(2+) ions was investigated. Simple chemodosimetric systems showed selective and efficient signaling behaviors toward micromolar concentrations of Hg(2+) ions over other common interfering metal ions in an aqueous environment. The signaling mechanism is selective mercuration of the 4',5'-position of the xanthene moiety, which results in efficient chromogenic and fluorogenic signaling of Hg(2+) ions in aqueous environment.  相似文献   
145.
New N-aryl-4-(pyridin-3-yl)pyrimidin-2-amine derivatives were synthesized from the corresponding amines, applying optimized Buchwald-Hartwig amination conditions using dichlorobis(triphenylphosphine)Pd(II), xantphos and sodium tertbutoxide in refluxing toluene under a nitrogen atmosphere. The target N-aryl derivatives were obtained in moderate to good yields ranging from 27% to 82%. The procedure described could be widely employed for the preparation of new heterocyclic compounds. The structures of the new compounds were confirmed by FT-NMR, FT-IR and elemental analysis.  相似文献   
146.
Ultra-sharp nano-probes and customized atomic force microscopy (AFM) have previously been developed in our laboratory for in situ sub-cellular probing of electrochemical phenomena in living plant cells during their photosynthesis. However, this AFM-based electrochemical probing still has numerous engineering challenges such as immobilization of the live cells, compatibility of the immobilization procedure with AFM manipulation of the probe, maintenance of biological activity of the cells for an extended time while performing the measurements, and minimization of electrochemical noise. Thus, we have developed an open micro-fluidic channel system (OMFC) in which individual cells can be immobilized in micro-traps by capillary flow. This system affords easy AFM access and allows for maintenance of the cells in a well-defined chemical environment, which sustains their biological activity. The use of micro-channels for making the electrochemical measurements significantly reduces parasitic electrical capacitances and allows for current detection in the sub-pico-ampere range at high signal bandwidths. The OMFC was further studied using simulation packages for optimal design conditions. This system was successfully used to measure light-dependent oxidation currents of a few pico-amperes from the green alga Chlamydomonas reinhardtii.  相似文献   
147.
Novel axially chiral benzopolysulfides were synthesized on biaryls by sulfurization of dithiastannoles. Pentathiepin, trithiole, and trithiole 2-oxide rings were observed as single isomer on 1,1′-biaryls. The rotational energy barrier of chiral axis was increased by incorporation of a methyl group at ortho-position. In that case, both trithiole oxide and pentathiepin rings appeared as diastereomer. ortho-Tolyl functionality was also replaced by naphthyl moiety to create more rotational hindrance. Chiral axis was incorporated at the neighborhood of polysulfide functionality by Suzuki-Miyaura cross-coupling reaction. Calculated rotational energy barriers were very much consistent with experimental observations to show atropisomerism. Energy barrier for the inversion of pentathiepin ring was experimentally determined by variable temperature 1H NMR. The kinetic data suggested that pentathiepin ring inversion was prompt in solution. Insufficient rotational energy barriers of chiral axis and pentathiepin ring inversion make substantially impossible to separate optically pure diastereomer even by chiral chromatography [Preliminary report: Sato, R.; Ohta, H.; Yamamoto T.; Nakajo, S.; Ogawa, S.; Alam, A. Tetrahedron Lett.2007, 48, 4991-4994.].  相似文献   
148.
An enantioselective rhodium(I)-catalyzed Pauson–Khand reaction (PKR) using 1,6-chloroenynes that contain challenging 1,1-disubstituted olefins is described. In contrast to the previous studies with these types of substrates, which are only suitable for a single type of tether and alkyne substituent, the new approach results in a more expansive substrate scope, including carbon and heteroatom tethers with polar and non-polar substituents on the alkene. DFT calculations provide critical insight into the role of the halide, which pre-polarizes the alkyne to lower the barrier for metallacycle formation and provides the proper steric profile to promote a favorable enantiodetermining interaction between substrate and chiral diphosphine ligand. Hence, the chloroalkyne enables the efficient and enantioselective PKR with 1,6-enynes that contain challenging 1,1-disubstituted olefins, thereby representing a new paradigm for enantioselective reactions involving 1,6-enynes.  相似文献   
149.
Inducing strong metal-support interaction (SMSI) has been a useful way to control the structure of surface active sites. The SMSI often causes the encapsulation of metal particles with an oxide layer. Herein, an amorphous ceria shell was formed on Cu nanoparticles under a mild gas condition with high activity and durability for surface reaction. Cu−Ce solid solution promoted the transfer of surface oxygen species, which induced the ceria shell formation on Cu nanoparticles. This catalyst was used for CO2 hydrogenation, selectively producing CO with high low-temperature activity and good durability for operation at high temperature. CO2 activation and H2 spillover could occur at low temperatures, enhancing the activity. The shell prevented the sintering, assuring durability. This catalyst was applied to a bench-scale reactor without loss in performance, resulting in high CO productivity in all temperature ranges.  相似文献   
150.
Phenolic glycolipids (PGLs) are polyketide-derived virulence factors produced by Mycobacterium tuberculosis, M. leprae, and other mycobacterial pathogens. We have combined bioinformatic, genetic, biochemical, and chemical biology approaches to illuminate the mechanism of chain initiation required for assembly of the p-hydroxyphenyl-polyketide moiety of PGLs. Our studies have led to the identification of a stand-alone, didomain initiation module, FadD22, comprised of a p-hydroxybenzoic acid adenylation domain and an aroyl carrier protein domain. FadD22 forms an acyl-S-enzyme covalent intermediate in the p-hydroxyphenyl-polyketide chain assembly line. We also used this information to develop a small-molecule inhibitor of PGL biosynthesis. Overall, these studies provide insights into the biosynthesis of an important group of small-molecule mycobacterial virulence factors and support the feasibility of targeting PGL biosynthesis to develop new drugs to treat mycobacterial infections.  相似文献   
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