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KM Davis BA Mattern JI Pacold T Zakharova D Brewe I Kosheleva RW Henning TJ Graber SM Heald GT Seidler Y Pushkar 《The journal of physical chemistry letters》2012,3(14):1858-1864
The paradigm of "detection-before-destruction" was tested for a metalloprotein complex exposed at room temperature to the high x-ray flux typical of third generation synchrotron sources. Following the progression of the x-ray induced damage by Mn Kβ x-ray emission spectroscopy, we demonstrated the feasibility of collecting room temperature data on the electronic structure of native Photosystem II, a trans-membrane metalloprotein complex containing a Mn(4)Ca cluster. The determined non-damaging observation timeframe (about 100 milliseconds using continuous monochromatic beam, deposited dose 1*10(7) photons/μm(2) or 1.3*10(4) Gy, and 66 microseconds in pulsed mode using pink beam, deposited dose 4*10(7) photons/μm(2) or 4.2*10(4) Gy) is sufficient for the analysis of this protein's electron dynamics and catalytic mechanism at room temperature. Reported time frames are expected to be representative for other metalloproteins. The described instrumentation, based on the short working distance dispersive spectrometer, and experimental methodology is broadly applicable to time-resolved x-ray emission analysis at synchrotron and x-ray free-electron laser light sources. 相似文献
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Rabindra N. Roy Julie A. Carlsten Jodi Niederschmidt William S. Good J. Michelle Rook Christina Brewe Amanda J. Kilker Lakshmi N. Roy Kathleen M. Kuhler 《Journal of solution chemistry》1997,26(3):309-317
ThepK
2
values for 3-[(l,l-Dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO), and 3-[N,N-Bis(-hydroxyethyl)amino]-2-hydroxypropanesulfonic
acid (DIPSO) have been determined at 12 temperatures over the range 5 to 55‡C by measurements of the emf of cells without
liquid junction containing hydrogen and silver-silver chloride electrodes. The values of pK
2 for AMPSO and DIPSO were found to be 9.138 and 7.576, respectively, at 25‡C. The thermodynamic quantities, δG‡, δH‡, δS‡,
and δC
p
‡
were calculated from the change of the equilibrium constants with temperature. These buffer substances are useful as secondary
pH standards in the physiological region of pH 7 to 9.
Camille and Henry Dreyfus Fellow, 1994–1996. 相似文献
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Andrew M. Crawford Patrick Kurecka Tsz Kwan Yim Claire Kozemchak Aniruddha Deb Lubomír Dostál Cheng-Jun Sun Dale L. Brewe Raul Barrea James E. Penner-Hahn 《Journal of synchrotron radiation》2016,23(4):901-908
An X‐ray fluorescence flow cytometer that can determine the total metal content of single cells has been developed. Capillary action or pressure was used to load cells into hydrophilic or hydrophobic capillaries, respectively. Once loaded, the cells were transported at a fixed vertical velocity past a focused X‐ray beam. X‐ray fluorescence was then used to determine the mass of metal in each cell. By making single‐cell measurements, the population heterogeneity for metals in the µM to mM concentration range on fL sample volumes can be directly measured, a measurement that is difficult using most analytical methods. This approach has been used to determine the metal composition of 936 individual bovine red blood cells (bRBC), 31 individual 3T3 mouse fibroblasts (NIH3T3) and 18 Saccharomyces cerevisiae (yeast) cells with an average measurement frequency of ~4 cells min?1. These data show evidence for surprisingly broad metal distributions. Details of the device design, data analysis and opportunities for further sensitivity improvement are described. 相似文献
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