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991.
Amy Lea Schumacher Jonathan P. Hill Katsuhiko Ariga Francis DSouza 《Electrochemistry communications》2007,9(12):2751-2754
The effect of anion binding on the oxidation potential of an anion receptor, N21,N23-dibenzyl-5,10,15,20-(3,5-di-t-butyl-4-oxo-cyclohexa-2,5-dienylidene)porphyrinogen, 1 in o-dichlorobenzene is reported. The anion binding site of 1, at its inner pyrrolic amine hydrogens, is an integral part of the highly conjugated macrocycle, thus predicting larger potential shifts upon anion binding. Accordingly, cathodic shifts up to 600 mV are observed upon anion binding and such potential shifts correlate well with the anion binding constants. 相似文献
992.
Heterologous expression of a myxobacterial natural products assembly line in pseudomonads via red/ET recombineering 总被引:10,自引:0,他引:10
Natural products of microbial origin are widely used as pharmaceuticals and in agrochemistry. These compounds are often biosynthesized by multifunctional megasynthetases whose genetic engineering and heterologous expression offer considerable promise, especially if the natural hosts are genetically difficult to handle, slow growing, unculturable, or even unknown. We describe a straightforward strategy that combines the power of advanced DNA engineering (recombiogenic cloning) in Escherichia coli with the utility of pseudomonads as the heterologous host for the analysis and mutagenesis of known and unknown secondary metabolite pathways. The myxochromide S biosynthetic gene cluster from Stigmatella aurantiaca was rebuilt and engineered in E. coli to contain the elements required for expression in pseudomonads. The successful production in Pseudomonas putida, at unprecedented levels, demonstrates the feasibility of the new approach to the analysis and mutagenesis of these important pathways. 相似文献
993.
The internal model principle for linear multivariable regulators 总被引:20,自引:0,他引:20
Necessary structural criteria are obtained for linear multivariable regulators which retain loop stability and output regulation in the presence of small perturbations, of specified types, in system parameters. It is shown that structural stability thus defined requires feedback of the regulated variable, together with a suitably reduplicated model, internal to the feedback loop, of the dynamic structure of the exogenous reference and disturbance signals which the regulator is required to process. Necessity of these structural features constitutes the internal model principle.This research was partially supported by the National Research Council of Canada, Grant No. A-7399. 相似文献
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996.
Baafour Nyantekyi-Kwakye Mark Francis Tachie Shawn Paul Clark 《Journal of Turbulence》2016,17(8):727-757
A three-dimensional offset jet flow over a surface mounted square rib was investigated using particle image velocimetry at Reynolds number of 7600. The square rib was mounted at three different locations downstream of the nozzle exit. Contour and profile plots in the symmetry plane were used to investigate the effect of the rib on the mean flow distribution and turbulence statistics. Changing the rib location enhanced the mixing and entrainment characteristics of the jet thereby leading to larger wall-normal spread rates. The quadrant analysis revealed a significant contribution of all events towards the Reynolds shear stress. The joint probability density function analysis showed that the structures within the outer shear layer of the jet differed from those of boundary layers. Results from the two-point correlation analysis indicated that the introduction of a surface mounted rib modified the flow structures within the developing region. However, there was no significant structural difference between the flow with mounted rib and the no rib case within the self-similar region. The proper orthogonal decomposition was used to examine how changes in rib location modified the dynamics of the energetic modes towards the turbulent kinetic energy and Reynolds shear stress within the developing and self-similar regions. 相似文献
997.
William E. Evenson M. Adams Austin Bunker Jeffery A. Hodges P. L. Matheson Tyler Park Michael Stufflebeam Francis P. Sullivan M. O. Zacate 《Hyperfine Interactions》2016,237(1):119
Inhomogeneous broadening (IHB) of hyperfine interactions in materials arises from a distribution of electric field gradients (EFGs) due to randomly distributed defects contributing non-uniformly to the EFG at probe sites. Hyperfine experiments reflect the inhomogeneous distribution of defects through the joint probability distribution function (PDF) of Vzz and η determined by the defect concentration, crystal structure, and defect sites in the crystal. Czjzek showed how to choose coordinates in the (Vzz, η) plane that are consistent with the physical constraints and ordering convention for these EFG parameters. Here we show how to transform to a new set of coordinates that decreases the distortion inherent in Czjzek’s representation. These new coordinates allow one to express the joint PDF for random distributions of defects in a form reasonably approximated by the product of two independent marginal distributions. This paper focuses on these topologically appropriate coordinates, with simple examples drawn from Czjzek’s work and from our simulations of point defects in cubic lattices as well as random amorphous distributions of defects. Detailed simulations have been carried out for IHB in cubic structures and point charge models relevant to perturbed angular correlation (PAC) experiments. 相似文献
998.
Panchromatic Light Capture and Efficient Excitation Transfer Leading to Near‐IR Emission of BODIPY Oligomers 下载免费PDF全文
Ritambhara Sharma Habtom B. Gobeze Prof. Dr. Francis D'Souza Prof. Dr. Mangalampalli Ravikanth 《Chemphyschem》2016,17(16):2516-2524
All‐BODIPY‐based (BODIPY=boron‐dipyrromethene) donor–acceptor systems capable of wide‐band absorbance leading to efficient energy transfer in the near‐IR region are reported. A covalently linked 3‐pyrrolyl BODIPY–BODIPY dimer building block bearing an ethynyl group at the meso‐aryl position is synthesized and coupled with three different monomeric BODIPY/pyrrolyl BODIPY building blocks with a bromo/iodo group under Pd0 coupling conditions to obtain three covalently linked 3‐pyrrolyl‐BODIPY‐based donor–acceptor oligomers in 19–29 % yield. The oligomers are characterized in detail by 1D and 2D NMR spectroscopy, high‐resolution mass spectrometry, and optical spectroscopy. Due to the presence of different functionalized BODIPY derivatives in the oligomers, panchromatic light capture (300–725 nm) is witnessed. Fluorescence studies reveal singlet–singlet energy transfer from BODIPY monomer to BODIPY dimer leading to emission in the 700–800 nm range. Theoretical modeling according to the Förster mechanism predicts ultrafast energy transfer due to good spectral overlap of the donor and acceptor entities. Femtosecond transient absorption studies confirm this to be the case and thus show the relevance of the currently developed all‐BODIPY‐based energy‐funneling supramolecular sytems with near‐IR emission to solar‐energy harvesting applications. 相似文献
999.
Armstrong AF Oakley N Parker S Causey PW Lemon J Capretta A Zimmerman C Joyal J Appoh F Zubieta J Babich JW Singh G Valliant JF 《Chemical communications (Cambridge, England)》2008,(43):5532-5534
A robust method for synthesizing structurally diverse metallopeptide libraries using a Re(i) complex of a non-natural amino acid was developed as a way to accelerate the discovery of novel molecular imaging probes. 相似文献
1000.
Carrico ZM Romanini DW Mehl RA Francis MB 《Chemical communications (Cambridge, England)》2008,(10):1205-1207
This Communication describes the chemo- and site-selective coupling of cell type-specific targeting peptides to a virus capsid containing aminophenylalanine residues. 相似文献