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91.
Bencze KZ Yoon T Millán-Pacheco C Bradley PB Pastor N Cowan JA Stemmler TL 《Chemical communications (Cambridge, England)》2007,(18):1798-1800
The coordinated iron structure and ferrochelatase binding surface of human frataxin have been characterized to provide insight into the protein's ability to serve as the iron chaperone during heme biosynthesis. 相似文献
92.
Stoner-Ma D Skinner JM Schneider DK Cowan M Sweet RM Orville AM 《Journal of synchrotron radiation》2011,18(1):37-40
Three-dimensional structures derived from X-ray diffraction of protein crystals provide a wealth of information. Features and interactions important for the function of macromolecules can be deduced and catalytic mechanisms postulated. Still, many questions can remain, for example regarding metal oxidation states and the interpretation of `mystery density', i.e. ambiguous or unknown features within the electron density maps, especially at ~2 ? resolutions typical of most macromolecular structures. Beamline X26-C at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL), provides researchers with the opportunity to not only determine the atomic structure of their samples but also to explore the electronic and vibrational characteristics of the sample before, during and after X-ray diffraction data collection. When samples are maintained under cryo-conditions, an opportunity to promote and follow photochemical reactions in situ as a function of X-ray exposure is also provided. Plans are in place to further expand the capabilities at beamline X26-C and to develop beamlines at NSLS-II, currently under construction at BNL, which will provide users access to a wide array of complementary spectroscopic methods in addition to high-quality X-ray diffraction data. 相似文献
93.
Exchange of [2Fe-2S] centers between Grx2 and the cluster scaffold protein ISU, and characterization of two mutually exclusive Grx2 binding sites on ISU by isothermal titration calorimetry supports a direct link for Grx and glutathione involvement in ISU promoted Fe-S cluster biosynthesis. 相似文献
94.
Pendlebury SR Barroso M Cowan AJ Sivula K Tang J Grätzel M Klug D Durrant JR 《Chemical communications (Cambridge, England)》2011,47(2):716-718
Transient absorption spectroscopy on the μs-s time scale is used to monitor the yield and decay dynamics of photogenerated holes in nanocrystalline hematite photoanodes. In the absence of a positive applied bias, these holes are observed to undergo rapid electron-hole recombination. The application of a positive bias results in the generation of long-lived (3 ± 1 s lifetime) photoholes. 相似文献
95.
The non-symmetric imide ligand Hpypzca (N-(2-pyrazylcarbonyl)-2-pyridinecarboxamide) has been deliberately synthesised and used to produce nine first row transition metal complexes: [M(II)(pypzca)(2)], M = Zn, Cu, Ni, Co, Fe; [M(III)(pypzca)(2)]Y, M = Co and Y = BF(4), M = Fe and Y = ClO(4); [Cu(II)(pypzca)(H(2)O)(2)]BF(4), [Mn(II)(pypzca)(Cl)(2)]HNEt(3). These are the first deliberately prepared complexes of a non-symmetric imide ligand. X-ray crystal structures of [Cu(II)(pypzca)(2)]·H(2)O, [Co(II)(pypzca)(2)], [Co(III)(pypzca)(2)]BF(4), [Cu(II)(pypzca)(H(2)O)(2)]BF(4)·H(2)O and [Mn(II)(pypzca)Cl(2)]HNEt(3) show that each of the (pypzca)(-) ligands binds in a meridional fashion via the N(3) donors. In the first three complexes, two such ligands are bound such that the 'spare' pyrazine nitrogen atoms are positioned approximately orthogonally to one another and also to the imide oxygen atoms. In MeCN the [M(II/III)(pypzca)(2)](0/+) complexes, where M = Ni, Co or Fe, exhibit one reversible metal based M(II/III) process and two distinct, quasi-reversible ligand based reduction processes, the latter also observed for M(II) = Zn. [Mn(II)(pypzca)Cl(2)]HNEt(3) displays a quasi-reversible oxidation process in MeCN, along with several irreversible processes. Both copper(II) complexes show only irreversible processes. Variable temperature magnetic measurements show that [Fe(III)(pypzca)(2)]ClO(4) undergoes a gradual spin crossover from partially high spin at 298 K (3.00 BM) to fully low spin at 2 K (1.96 BM), and that [Co(II)(pypzca)(2)] remains high spin from 298 to 4 K. All of the complexes are weakly coloured, other than [Fe(II)(pypzca)(2)] which is dark purple and absorbs strongly in the visible region. 相似文献
96.
J. P. Stokes T. J. Emge W. A. Bryden J. S. Chappell D. O. Cowan T. O. Poehler 《Molecular Crystals and Liquid Crystals》2013,570(1):683-692
The 2:1 charge-transfer salt (TMTSF)2(2,5-TCNQBr2) has been prepared and its physical properties investigated. Its crystal structure consists of segregated stacks of TMTSF donors (ring-over-bond overlap pattern; mean interplanar spacing of 3.6A) and chains of edge-on and disordered 2,5-TCNQBr2 acceptors. Infrared data are suggestive of unit charge on the 2,5-TCNQBr2 molecule and, therefore, half charge on the TMTSF donor. Resistivity data are successfully interpreted on the basis of a percolation construction. Magnetic data are also presented. 相似文献
97.
D. Broggio J. Bento M. Caldeira E. Cardenas-Mendez J. Farah T. Fonseca C. Konvalinka L. Liu B. Perez K. Capello P. Cowan J.-A. Cruzate L. Freire J.-M. Gómez-Ros S. Gossio B. Heide J. Huikari J. Hunt S. Kinase G.H. Kramer M.-A. Lopez 《Radiation measurements》2012,47(7):492-500
In order to assess the reliability of Monte Carlo (MC)-based numerical calibration of in vivo counting systems the EURADOS network supported a comparison of MC simulation of well-defined experiments. This action also provided training for the use of voxel phantoms. In vivo measurements of enriched uranium in a thoracic phantom have been carried out and the needed information to simulate these measurements was distributed to 17 participants. About half of the participants managed to simulate the measured counting efficiency without support from the organisers. Following additional support all participants managed to simulate the counting efficiencies within a typical agreement of ±5% with experiment. 相似文献
98.
A previous paper [Nave & Hill (2005). J. Synchrotron Rad. 12 , 299–303] examined the possibility of reduced radiation damage for small crystals (10 µm and below in size) under conditions where the photoelectrons could escape from the sample. The conclusion of this paper was that higher‐energy radiation (e.g. 40 keV) could offer an advantage as the photoelectron path length was greater and less energy would be deposited in the crystal. This paper refines these calculations further by including the effects of energy deposited owing to Compton scattering and the energy difference between the incident photon and the emitted photoelectron. An estimate is given for the optimum wavelength for collecting data from a protein crystal of a given size and composition. Another way of reducing radiation damage from a protein crystal is to collect data with a very short pulsed X‐ray source where a single image can be obtained before subsequent radiation damage occurs. A comparison of this approach compared with the use of shorter wavelengths is made. 相似文献
99.
W. R. Miller R. A. Awl E. H. Pryde J. C. Cowan 《Journal of polymer science. Part A, Polymer chemistry》1970,8(2):415-427
Poly(ester-acetals) have been prepared from isopropylideneglyceryl azelaaldehydate dimethyl acetal and from methyl azelaaldehydate glycerol acetal. Acid hydrolysis of isopropylideneglyceryl azelaaldehydate led to oligomeric poly(ester-acetals) with six to seven repeating units and carboxylic acid endgroups from which the sodium salt and the methyl ester could be prepared. The polymer sodium salt showed some surfactant properties. Methyl azelaaldehydate glycerol acetal, a mixture of geometric and structural isomers, was polymerized under typical polyesterification conditions. Lime was the best catalyst found. Molecular weights of 5000 to 12000 were obtained. Some of these polymers contained significant quantities of calcium as the carboxylate salt. A tough elastomer was prepared by heating a poly(ester-acetal) with p-toluenesulfonic acid and zine oxide. 相似文献
100.