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91.
Kyounghoon Lee Anastasia V. Blake Courtney M. Donahue Kyle D. Spielvogel Brian J. Bellott Scott R. Daly 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(36):12581-12585
Bond distance is a common structural metric used to assess changes in metal–ligand bonds, but it is not clear how sensitive changes in bond distances are with respect to changes in metal–ligand covalency. Here we report ligand K‐edge XAS studies on Ni and Pd complexes containing different phosphorus(III) ligands. Despite the large number of electronic and structural permutations, P K‐edge pre‐edge peak intensities reveal a remarkable correlation that spectroscopically quantifies the linear interdependence of covalent M?P σ bonding and bond distance. Cl K‐edge studies conducted on many of the same Ni and Pd compounds revealed a poor correlation between M?Cl bond distance and covalency, but a strong correlation was established by analyzing Cl K‐edge data for Ti complexes with a wider range of Ti?Cl bond distances. Together these results establish a quantitative framework to begin making more accurate assessments of metal–ligand covalency using bond distances from readily‐available crystallographic data. 相似文献
92.
Munce NR Mariampillai A Standish BA Pop M Anderson KJ Liu GY Luk T Courtney BK Wright GA Vitkin IA Yang VX 《Optics letters》2008,33(7):657-659
A novel flexible scanning optical probe is constructed with a finely etched optical fiber strung through a platinum coil in the lumen of a dissipative polymer. The packaged probe is 2.2 mm in diameter with a rigid length of 6mm when using a ball lens or 12 mm when scanning the fiber proximal to a gradient-index (GRIN) lens. Driven by constant high voltage (1-3 kV) at low current (< 5 microA), the probe oscillates to provide wide forward-viewing angle (13 degrees and 33 degrees with ball and GRIN lens designs, respectively) and high-frame-rate (10-140 fps) operation. Motion of the probe tip is observed with a high-speed camera and compared with theory. Optical coherence tomography (OCT) imaging with the probe is demonstrated with a wavelength-swept source laser. Images of an IR card as well as in vivo Doppler OCT images of a tadpole heart are presented. This optomechanical design offers a simple, inexpensive method to obtain a high-frame-rate forward-viewing scanning probe. 相似文献
93.
94.
95.
F. F. Hopkins W. J. Courtney W. R. Coker C. F. Moore P. Richard 《Zeitschrift für Physik A Hadrons and Nuclei》1971,243(5):446-451
The (p, α) reaction was studied on a208Pb target at 16.475 MeV. Nineteen states were observed in205Tl, up to 3.6 MeV in excitation. Angular distributions were obtained for five strong proton-hole transitions, and DWBA fits made to determinelj values. Results are compared with previous206Pb(t, α)205Tl,206Pb(d,3He)205Tl,205Tl(p, p′), and205Tl(n, n′) work. 相似文献
96.
97.
Lee Courtney Paul A. Sermon Jenny Towers Dost Halepoto Angela F. Danil de Namor Ian R. Collins 《Journal of Sol-Gel Science and Technology》2004,32(1-3):229-236
Work on the development of a Ba2 +-sensitive sol–gel based optical fiber (OF) for use in oil wells is described. The optical fiber (OF) has on its surface a Ba2 + chelating ligand (L) immobilized at a 2–16 wt% loading immobilized in a porous SiO2 sol–gel host. The authors report sol–gel routes to these SiO2 and L/SiO2 nanocomposites and describe their characterization by XPS, fluorescence, NMR, UV-vis and BET methods. They also report on the sol–gel coating and its selectivity to Ba2 +(aq). 相似文献
98.
Beck BJ Aldrich CC Fecik RA Reynolds KA Sherman DH 《Journal of the American Chemical Society》2003,125(16):4682-4683
The unique ability of the pikromycin polyketide synthase (Pik PKS) to generate 12- and 14-membered ring macrolactones presents an opportunity to explore the fundamental processes of polyketide synthesis, specifically, the mechanistic details of the chain extension process. We have overexpressed and purified PikAIII and PikAIV and demonstrated the ability of these proteins to generate triketide lactone products using (14)C-methylmalonyl-CoA as the sole substrate. Monomodular PikAIII generates TKL (1) when reacted alone, and synthesizes TKL (2) upon reaction in combination with PikAIV. Product formation remains dependent on the enzymatic decarboxylation of methylmalonyl-CoA and transfer of the acyl chain within the enzyme rather than acylation by propionyl-CoA from spontaneous decarboxylation. We propose that synthesis of TKL (1) by PikAIII involves iterative assembly of the triketide chain within a PikAIII homodimer analogous to the nonmodular type I PKS systems. 相似文献
99.
Prof. Bhajan Lal Karam B. Idrees Dr. Haomiao Xie Courtney S. Smoljan Saman Shafaie Prof. Timur Islamoglu Prof. Omar K. Farha 《Angewandte Chemie (International ed. in English)》2023,62(16):e202219053
Metal–organic frameworks (MOFs) have been proposed as a promising material for non-thermal chemical separations owing to their high structural diversity and tunability. Here, we report the synthesis of a zinc-based MOF containing a three-dimensional (3D) linker, bicyclo[2.2.2]octane-1,4-dicarboxylic acid, with high thermal stability towards the separation of hexane isomers. The incorporation of the 3D linker enhances the structural stability and provides well-defined pore apertures/channels with sub-Ångstrom precision. This precision allowed for the separation of similarly sized hexane isomers based on subtle differences in their kinetic diameters. Multi-component liquid phase batch experiments confirmed the separation of hexanes mixture into linear, monobranched, and dibranched isomers. This work represents a significant milestone in the construction of stable Zn-based MOFs and the incorporation of 3D linkers as a potential solution to challenging separations. 相似文献
100.
Younker JM Krest CM Jiang W Krebs C Bollinger JM Green MT 《Journal of the American Chemical Society》2008,130(45):15022-15027
The class Ic ribonucleotide reductase from Chlamydia trachomatis ( Ct) uses a stable Mn(IV)/Fe(III) cofactor to initiate nucleotide reduction by a free-radical mechanism. Extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculations are used to postulate a structure for this cofactor. Fe and Mn K-edge EXAFS data yield an intermetallic distance of approximately 2.92 A. The Mn data also suggest the presence of a short 1.74 A Mn-O bond. These metrics are compared to the results of DFT calculations on 12 cofactor models derived from the crystal structure of the inactive Fe 2(III/III) form of the protein. Models are differentiated by the protonation states of their bridging and terminal OH X ligands as well as the location of the Mn(IV) ion (site 1 or 2). The models that agree best with experimental observation feature a mu-1,3-carboxylate bridge (E120), terminal solvent (H 2O/OH) to site 1, one mu-O bridge, and one mu-OH bridge. The site-placement of the metal ions cannot be discerned from the available data. 相似文献