A series of lead(II) coordination polymers containing [N(CN)2]? (DCA) or [Au(CN)2]? bridging ligands and substituted terpyridine (terpy) ancillary ligands ([Pb(DCA)2] ( 1 ), [Pb(terpy)(DCA)2] ( 2 ), [Pb(terpy){Au(CN)2}2] ( 3 ), [Pb(4′‐chloro‐terpy){Au(CN)2}2] ( 4 ) and [Pb(4′‐bromo‐terpy)(μ‐OH2)0.5{Au(CN)2}2] ( 5 )) was spectroscopically examined by solid‐state 207Pb MAS NMR spectroscopy in order to characterise the structural and electronic changes associated with lead(II) lone‐pair activity. Two new compounds, 2 and [Pb(4′‐hydroxy‐terpy){Au(CN)2}2] ( 6 ), were prepared and structurally characterised. The series displays contrasting coordination environments, bridging ligands with differing basicities and structural and electronic effects that occur with various substitutions on the terpyridine ligand (for the [Au(CN)2]? polymers). 207Pb NMR spectra show an increase in both isotropic chemical shift and span (Ω) with increasing ligand basicity (from δiso=?3090 ppm and Ω=389 ppm for 1 (the least basic) to δiso=?1553 ppm and Ω=2238 ppm for 3 (the most basic)). The trends observed in 207Pb NMR data correlate with the coordination sphere anisotropy through comparison and quantification of the Pb? N bond lengths about the lead centre. Density functional theory calculations confirm that the more basic ligands result in greater p‐orbital character and show a strong correlation to the 207Pb NMR chemical shift parameters. Preliminary trends suggest that 207Pb NMR chemical shift anisotropy relates to the measured birefringence, given the established correlations with structure and lone‐pair activity. 相似文献
A robust and photoresponsive DNA network has been designed and constructed from branched DNA and molecular glue. The molecular glue is photoswitchable and can specifically bind to G-G mismatched double-stranded DNA. The assembly process can be reversibly controlled by manipulating the wavelength of light. The approach is flexible, allowing tuning of the size, morphology as well as the cavity of the network by variation of the molar ratio and the isotropic/anisotropic character of the branched building blocks. The assembled architectures are versatile and heat tolerant. These properties should allow the use of the network in further applications. 相似文献
We prepared BiOCl(1-x)Br(x) (x=0-1) solid solutions and characterized their structures, morphologies, and photocatalytic properties by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, Raman spectroscopy, photocurrent and photocatalytic activity measurements and also by density functional theory calculations for BiOCl, BiOBr, BiOCl(0.5)Br(0.5). Under visible-light irradiation BiOCl(1-x)Br(x) exhibits a stronger photocatalytic activity than do BiOCl and BiOBr, with the activity reaching the maximum at x=0.5 and decreasing gradually as x is increased toward 1 or decreased toward 0. This trend is closely mimicked by the photogenerated current of BiOCl(1-x)Br(x) , indicating that the enhanced photocatalytic activity of BiOCl(1-x)Br(x) with respect to those of BiOCl and BiOBr originates from the trapping of photogenerated carriers. Our electronic structure calculations for BiOCl(0.5)Br(0.5) with the anion (O(2-), Cl(-), Br(-)) and cation (Bi(3+)) vacancies suggest that the trapping of photogenerated carriers is caused most likely by Bi(3+) cation vacancies, which generate hole states above the conduction band maximum. 相似文献
Quasi‐aligned cylindrical and conical core–shell nanofibers consisting of carbon shells and TiO2 nanowire cores are produced in situ on Ti foils without using a foreign metallic catalyst and template. A cylindrical nanofiber has a TiO2 nanowire core 30–50 nm in diameter and a 5–10 nm‐thick cylindrical carbon shell, while in the conical nanostructure the TiO2 nanowire core has a diameter of 20–40 nm and the thickness of the carbon shell varies from about 200 nm at the bottom to about 5 nm at the tip. Electrochemical analysis reveals well‐defined redox peaks of the [Fe(CN)6]3?/4? redox couple and heterogeneous charge‐transfer rate constants of 0.010 and 0.062 cm s?1 for the cylindrical and conical nanofibers, respectively. The coverage of exposed edge planes on the cylindrical and conical carbon shells is estimated to be 2.5 and 15.5 % respectively. The more abundant exposed edge planes on the conical nanofiber decrease the overpotential and increase the voltammetric resolution during electrochemical detection of uric acid and ascorbic acid. Our results suggest that the density of edge‐plane sites estimated from Raman scattering is not necessarily equal to the density of exposed edge‐plane sites, and only carbon electrodes with a large density of exposed edge planes or free graphene sheet ends exhibit better electrochemical performance. 相似文献
In the last decade, there has been growing interests in studies aimed at delineating the strategies used by various nucleic acid enzymes to facilitate catalysis. Insights gained from such studies would enable the design of better DNA/RNA catalysts for various applications such as biosensing. DNA and RNA catalysts have been shown to be able to catalyze myriads of reactions, including peroxidation reactions, which are catalyzed by G-quadruplexes. In this report, we provide data that clarifies how G-quadruplex peroxidases achieve catalysis. Firstly, we show that by covalently linking a hemin cofactor to DNAzymes, anti-parallel G-quadruplexes, which have been previously shown to be catalytically inefficient, can be "resurrected" to become good peroxidation catalysts. We also reveal that the relative rates of peroxidation by DNAzyme peroxidases depend on the nature of the organic reductant, arguing for a special binding site in the peroxidase-mimicking DNAzymes for catalysis. 相似文献
A HBSP has been designed as a novel bifunctional enzyme model with SOD and GPx activity by host/guest‐directed self‐assembly of MnTPyP‐M‐Ad and 6‐Te‐diCD. The structure of the host/guest complex was elucidated by 1H NMR spectra, and the HBSP was characterized by SEM, DLS and measurement of catalytic properties. In the bifunctional enzyme model, the Mn(III) porphyrins act as efficient SOD active sites and the tellurol moieties endow GPx activity. The SOD‐like activity (IC50) of this new supramolecular catalyst was found to be 1.05 × 10?7 M, which corresponds to 2.82% of the activity of the native SOD enzyme. Besides this, the hyperbranched supramolecular polymer also shows a higher GPx activity (ν0 = 21.7 × 10?6 M · min?1) than other supramolecular enzyme models.
