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551.
The synthesis and isolation are reported of a range of terminal aryl- and heteroaryl-butadiynes (ArCC-CCH) 4a-h from 2-methyl-6-(aryl/heteroaryl)hexa-3,5-diyn-2-ol precursors. The stability of 4a-h in solution is concentration dependent: many of the derivatives can be stored as dilute solutions for several days or even weeks. The X-ray crystal structures have been obtained for five ArCC-CCH derivatives [Ar = 2-(9-fluorenonyl), 4-biphenyl, 2-pyridyl, 4-pyridyl, and 2-pyrazyl]. 相似文献
552.
myo-Inositol 1,2,3-trisphosphate [Ins(1,2,3)P3], a component in mammalian cells, possesses the correct chemical properties of an intracellular iron transit ligand. Here we have examined the conformation of the Ins(1,2,3)P3-Fe3+ complex. The synthesis and antioxidant properties of 4,6-carbonate-myo-inositol 1,2,3,5-tetrakisphosphate [4,6-carbonate Ins(1,2,3,5)P4], which is locked in the unstable penta-axial chair conformation and 1,2,3-trisphosphoglycerol, a flexible acyclic analogue of Ins(1,2,3)P3, are reported. 4,6-Carbonate Ins(1,2,3,5)P4 caused complete inhibition of iron-catalysed hydroxyl radical (HO) formation at 100 μM, thereby resembling Ins(1,2,3)P3 and supporting a penta-axial chair binding conformation. In contrast, 1,2,3-trisphosphoglycerol was shown to have incomplete antioxidant properties. In support of experimental observations, we have applied high-level density functional calculations to the binding of Ins(1,2,3)P3 to iron. This study provides evidence that Fe3+ binds tightly to the less stable penta-axial conformation of Ins(1,2,3)P3 using terminal and bridging phosphate oxygens, thought to also contain a tightly bound water molecule or hydroxyl ligand in the complex. 相似文献
553.
Pobelov IV Mészáros G Yoshida K Mishchenko A Gulcur M Bryce MR Wandlowski T 《J Phys Condens Matter》2012,24(16):164210
We describe a new setup for simultaneous measurements of force and current in conductive nanocontacts in a liquid environment with a high sampling rate and resolution. A lab-built current-to-voltage converter allows measurements of the current over seven orders of magnitude. As examples, we studied conductances and mechanical forces upon formation and breaking of gold atomic contacts and of two molecular junctions containing 1,2-di(4-pyridyl)ethyne (M1) and 1,4-di(4-pyridyl)buta-1,3-diyne (M2). We found that the forces required to deform or break gold atomic contacts depend critically on the surrounding medium. Further, they show non-linear behaviour in dependence of the number N of gold atoms detached. The electromechanical properties of the two types of molecular junctions upon stretching were analysed by correlating breaking forces with simultaneously measured junction conductances. A rather complex behaviour in a wide range of forces was discovered. Comparison of the current-probe atomic force microscopy experiments on the rupture of molecular junctions with STM-based break junction experiments enables the assignment of breaking forces of molecular junctions to the corresponding junction conductances. 相似文献
554.
Low-noise, tunable wavelength-conversion through nondegenerate four-wave mixing Bragg scattering in SiN(x) waveguides is experimentally demonstrated. Finite element method simulations of waveguide dispersion are used with the split-step Fourier method to predict device performance. Two 1550 nm wavelength band pulsed pumps are used to achieve tunable conversion of a 980 nm signal over a range of 5 nm with a peak conversion efficiency of ≈5%. The demonstrated Bragg scattering process is suitable for frequency conversion of quantum states of light. 相似文献
555.
L Nugent-Glandorf T Neely F Adler AJ Fleisher KC Cossel B Bjork T Dinneen J Ye SA Diddams 《Optics letters》2012,37(15):3285-3287
We present and characterize a two-dimensional (2D) imaging spectrometer based on a virtually imaged phased array (VIPA) disperser for rapid, high-resolution molecular detection using mid-infrared (MIR) frequency combs at 3.1 and 3.8?μm. We demonstrate detection of CH4 at 3.1?μm with >3750 resolution elements spanning >80 nm with ~600 MHz resolution in a <10 μs acquisition time. In addition to broadband detection, we also demonstrate rapid, time-resolved single-image detection by capturing dynamic concentration changes of CH4 at a rate of ~375 frames per second. Changes in absorption above the noise floor of 5×10-4 are readily detected on the millisecond time scale, leading to important future applications such as real-time monitoring of trace gas concentrations and detection of reactive intermediates. 相似文献
556.
Rebecca J. Holmberg Thomas Burns Samuel M. Greer Dr. Libor Kobera Dr. Sebastian A. Stoian Dr. Ilia Korobkov Prof. Stephen Hill Prof. David L. Bryce Prof. Tom K. Woo Prof. Muralee Murugesu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7711-7715
Coordinatively unsaturated FeIII metal sites were successfully incorporated into the iconic MOF‐5 framework. This new structure, FeIII‐iMOF‐5, is the first example of an interpenetrated MOF linked through intercalated metal ions. Structural characterization was performed with single‐crystal and powder XRD, followed by extensive analysis by spectroscopic methods and solid‐state NMR, which reveals the paramagnetic ion through its interaction with the framework. EPR and Mössbauer spectroscopy confirmed that the intercalated ions were indeed FeIII, whereas DFT calculations were employed to ascertain the unique pentacoordinate architecture around the FeIII ion. Interestingly, this is also the first crystallographic evidence of pentacoordinate ZnII within the MOF‐5 SBU. This new MOF structure displays the potential for metal‐site addition as a framework connector, thus creating further opportunity for the innovative development of new MOF materials. 相似文献
557.
Dr. Luke J. O'Driscoll Dr. Daniel J. Welsh Dr. Steven W. D. Bailey Dr. David Visontai Dr. Harry Frampton Prof. Martin R. Bryce Prof. Colin J. Lambert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):3891-3894
Easily reversible aqueous dispersion/precipitation of multiwalled carbon nanotubes (MWNTs) has been demonstrated using small‐molecule non‐ionic pyrene‐based surfactants, which exhibit lower critical solution temperature (LCST) phase behaviour. The MWNTs are dispersed by means of non‐covalent interactions. The dispersibility can be switched “off” (i.e., MWNTs precipitated) upon heating and switched “on” (i.e., MWNTs re‐dispersed) upon cooling and merely swirling the sample at room temperature, that is, under very mild conditions. This effect is also observed under high ionic strength conditions with NaCl in the aqueous phase. 相似文献