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871.
Tropp J Lupo JM Chen A Calderon P McCune D Grafendorfer T Ozturk-Isik E Larson PE Hu S Yen YF Robb F Bok R Schulte R Xu D Hurd R Vigneron D Nelson S 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,208(1):171-177
We report metabolic images of (13)C, following injection of a bolus of hyperpolarized [1-(13)C] pyruvate in a live rat. The data were acquired on a clinical scanner, using custom coils for volume transmission and array reception. Proton blocking of all carbon resonators enabled proton anatomic imaging with the system body coil, to allow for registration of anatomic and metabolic images, for which good correlation was achieved, with some anatomic features (kidney and heart) clearly visible in a carbon image, without reference to the corresponding proton image. Parallel imaging with sensitivity encoding was used to increase the spatial resolution in the SI direction of the rat. The signal to noise ratio in was in some instances unexpectedly high in the parallel images; variability of the polarization among different trials, plus partial volume effects, are noted as a possible cause of this. 相似文献
872.
V.B. Podobedov D.F. Plusquellic G.T. Fraser R.H. Tipping 《Journal of Quantitative Spectroscopy & Radiative Transfer》2008,109(3):458-467
We present a spectroscopic study of the water vapor continuum absorption in the far-IR region from 10 to 90 cm−1 (0.3-2.7 THz). The experimental technique combines a temperature-stabilized multipass absorption cell, a polarizing (Martin-Puplett) interferometric spectrometer, and a liquid-He-cooled bolometer detector. The contributions to the absorbance resulting from the structureless H2O-H2O and H2O-N2 continua have been measured in the temperature range from 293 to 333 K with spectral resolution of 0.04-0.12 cm−1. The resonant water vapor spectrum was modeled using the HITRAN04 database and a Van Vleck-Weisskopf lineshape function with a 100 cm−1 far-wing cut-off. Within experimental uncertainty, both the H2O-H2O and H2O-N2 continua demonstrate nearly quadratic dependencies of absorbance on frequency with, however, some deviation near the 2.5 THz window. The absorption coefficients of 3.83 and 0.185 (dB/km)/(kPa THz)2 were measured for self- and foreign-gas continuum, respectively. The corresponding temperature exponents were found to be 8.8 and 5.7. The theoretically predicted foreign continuum is presented and a reasonable agreement with experiment is obtained. 相似文献
873.
Fraser MacMillan Christian Lange Matt Bawn Carola Hunte 《Applied magnetic resonance》2010,37(1-4):305-316
Quinone molecules are ubiquitous in living organisms. They are found either within the lipid phase of the biological membrane (quinone pool) or are bound in specific binding sites within membrane-bound protein complexes. The biological function of such bound quinones is determined by their ability to be reduced and/or oxidized in two successive one-electron steps. As a result, quinones are involved as one- or two-electron donors or acceptors in a large number of biological electron-transfer steps occurring during respiratory or photosynthetic processes. The intermediate formed by a one-electron reduction step is a semiquinone, which is paramagnetic and can be studied by electron paramagnetic resonance (EPR) spectroscopy. Detailed studies of such states can provide important structural information on these intermediates in such electron-transfer processes. In this study, we focus on the redox-active ubiquinone-6 of the yeast cytochrome bc 1 complex (QCR, ubiquinol: cytochrome c oxidoreductase) from Saccharomyces cerevisiae at the so-called Qi site. Although the location of the Qi binding pocket is quite well known, details about its exact binding are less clear. Currently, three different X-ray crystallographic studies suggest three different binding geometries for Qi. Recent studies in the bacterial system (Rhodobacter sphaeroides) have suggested a direct coordination to histidine as proposed in the chicken heart crystal structure model. Using the yeast system we apply EPR and especially relaxation filtered hyperfine (REFINE) spectroscopy to study the Qi binding site. 14N-electron spin-echo envelope modulation spectroscopy together with an inversion-recovery filter (REFINE) is applied to resolve the question of whether 14N modulations arise from interactions to Q i ·? or to the Rieske iron–sulphur center. These results are discussed with regard to the location and potential function of Qi in the enzyme. 相似文献
874.
H. J. Fraser 《Analytical and bioanalytical chemistry》1943,125(11-12):444-453
875.
Dr. Bethany R. Hood Dr. Yovan de Coene Afonso V. Torre Do Vale Froes Dr. Claire F. Jones Dr. Pierre Beaujean Dr. Vincent Liégeois Dr. Fraser MacMillan Prof. Benoît Champagne Prof. Koen Clays Dr. John Fielden 《Angewandte Chemie (International ed. in English)》2023,62(5):e202215537
Electrochemically switched 2nd order non-linear optical responses have been demonstrated for the first time in polyoxometalates (POMs), with an arylimido-derivative showing a leading combination of high on/off contrast (94 %), high visible transparency, and cyclability. Spectro-electrochemical and TD-DFT studies indicate that the switch-off results from weakened charge transfer (CT) character of the electronic transitions in the reduced state. This represents the first study of an imido-POM reduced state, and demonstrates the potential of POM hybrids as electrochemically activated molecular switches. 相似文献
876.
877.
The natural phenomenon of self-assembly has been used to make complex unnatural products. These new compounds have taken the form of catenanes and rotaxanes. We have identified several polymeric architectures containing the catenane and rotaxane motifs, and then described how the model structures, which we have identified and actually realized as chemical compounds, can be employed to assess the feasibility of introducing mechanical linkages into novel polymers by means of self-assembly processes. 相似文献
878.
879.
Jessica L. Bender Robert M. Johnson Adam P. Smith Cassandra L. Fraser 《Macromolecular Symposia》2002,186(1):161-164
Polymeric metal complexes exhibiting useful properties were prepared by chelating macroligands to labile and inert metal ions. The specific structures elucidated through this method, as well as potential applications for these complexes are described. By carefully selecting the appropriate metal ion and polymer, these materials can be tuned for a host of applications in fields ranging from biomedicine to nanotechnology. 相似文献
880.