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761.
Taw FL Mellows H White PS Hollander FJ Bergman RG Brookhart M Heinekey DM 《Journal of the American Chemical Society》2002,124(18):5100-5108
Hydrogenolysis of [Cp(PMe(3))Rh(Me)(CH(2)Cl(2))](+)BAr'(4)(-) (4, Ar' = 3,5-C(6)H(3)(CF(3))(2)) in dichloromethane afforded the nonclassical polyhydride complex [Cp*PMe(3))Rh(H)(H(2))](+)BAr'(4)(-) (1), which exhibits a single hydride resonance at all accessible temperatures in the (1)H NMR spectrum. Exposure of solutions of 1 to D(2) or T(2) gas resulted in partial isotopic substitution in the hydride sites. Formulation of 1 as a hydride/dihydrogen complex was based upon T(1) (T(1)(min) = 23 ms at 150 K, 500 MHz), J(H-D) (ca. 10 Hz), and J(H-T) (ca. 70 Hz) measurements. The barrier (Delta G(++)) to exchange of hydride with dihydrogen sites was determined to be less than ca. 5 kcal/mol. Protonation of Cp(PMe(3))Rh(H)(2) (2) using H(OEt(2))(2)BAr'(4) resulted in binuclear species [(Cp(PMe(3))Rh(H))(2)(mu-H)](+)BAr'(4)(-) (3), which is formed in a reaction involving 1 as an intermediate. Complex 3 contains two terminal hydrides and one bridging hydride ligand which exchange with a barrier of 9.1 kcal/mol as observed by (1)H NMR spectroscopy. Additionally, the structures of 3 and 4, determined by X-ray diffraction, are reported. 相似文献
762.
Chang L Miyata Y Ung PM Bertelsen EB McQuade TJ Carlson HA Zuiderweg ER Gestwicki JE 《Chemistry & biology》2011,18(2):210-221
DnaK is a molecular chaperone responsible for multiple aspects of bacterial proteostasis. The intrinsically slow ATPase activity of DnaK is stimulated by its co-chaperone, DnaJ, and these proteins often work in concert. To identify inhibitors we screened plant-derived extracts against a reconstituted mixture of DnaK and DnaJ. This approach resulted in the identification of flavonoids, including myricetin, which inhibited activity by up to 75%. Interestingly, myricetin prevented DnaJ-mediated stimulation of ATPase activity, with minimal impact on either DnaK's intrinsic turnover rate or its stimulation by another co-chaperone, GrpE. Using NMR, we found that myricetin binds DnaK at an unanticipated site between the IB and IIB subdomains and that it allosterically blocked binding of DnaK to DnaJ. Together, these results highlight a "gray box" screening approach, which might facilitate the identification of inhibitors of other protein-protein interactions. 相似文献
763.
Charles S. Owen Miriam L. Wahl Dennis B. Leeper Heather D. Perry Suzanne B. Bobyock Matthew Russell Wendy Woodward 《Journal of fluorescence》1995,5(4):329-335
Fluorescent measurements of intracellular H+ and Na+ are improved by using whole spectra of the fluorescent indicators BCECF and SBFI, respectively. The extra data in whole spectra enable both an accurate calibration and a ready detection of artifacts which are not possible to identify using a more conventional data analysis that relies upon only two wavelength windows in the fluorescence spectra. The whole-spectrum technique is applicable to cell suspensions in a conventional fluorimeter (as is reported here with SBFI), as well as to attached cells using a fluorimeter combined with an inverted epifluorescence microscope. The spectral method was highly reproducible in that pairs of successive pH measurements differed, on average, by only 0.01±0.02 U. Random uncertainty from sample to sample was estimated numerically from the standard deviation of measurements on ionophore-treated cells. When full-spectrum analysis was employed, this scatter showed a two-fold improvement over results obtained using the two-wavelength ratio method. Because SBFI has a relatively narrow dynamic range, whole-spectrum analysis has been applied to improve the accuracy of sodium determinations. The calibrated system measured [Na+]i with excellent linearity over the range 2–150 mM and with an accuracy of approximately 5 mM. 相似文献
764.
Heather E. Byrne 《Journal of Non》2009,355(9):525-530
SiO2/TiO2 composites were synthesized by adding Degussa P25 TiO2 to a liquid sol that was catalyzed by HNO3 and HF acids. Various composites were synthesized by altering the mass loading of TiO2 and concentration of HF added to the liquid sol before gelation. The resulting materials were characterized by SEM, nitrogen adsorption-desorption, streaming potential, XRD, diffuse reflectance and TiO2 surface area analyses. Approximate characteristics include an isoelectric point of 3, TiO2 particle size of 30 nm, and a band gap energy of 3.2 eV. Small variations in these properties were noted for the different composites. Physical characteristics were largely affected by HF concentration and TiO2 loading. Nitrogen adsorption-desorption isotherms were type IV for all materials and exhibited trends of decreased pore volume with an increase in TiO2 loading and an increase in pore diameter with increased HF concentration. Surface areas of the composites ranged from 167 to 630 m2/g. Available TiO2 surface area of the composite was also dependent upon TiO2 loading and increased as the mass composition of TiO2 increased but was not largely affected by HF concentration. 相似文献
765.
Evans HM Ahmad A Ewert K Pfohl T Martin-Herranz A Bruinsma RF Safinya CR 《Physical review letters》2003,91(7):075501
DNA condensation in vivo relies on electrostatic complexation with small cations or large histones. We report a synchrotron x-ray study of the phase behavior of DNA complexed with synthetic cationic dendrimers of intermediate size and charge. We encounter unexpected structural transitions between columnar mesophases with in-plane square and hexagonal symmetries, as well as liquidlike disorder. The isoelectric point is a locus of structural instability. A simple model is proposed based on competing long-range electrostatic interactions and short-range entropic adhesion by counterion release. 相似文献
766.
767.
768.
Corrigendum: Electronic Transitions in Conformationally Controlled Tetrasilanes with a Wide Range of SiSiSiSi Dihedral Angles 下载免费PDF全文
769.
Liyun Guan Rong Cao Junfei Tian Heather McLiesh Gil Garnier Wei Shen 《Cellulose (London, England)》2014,21(1):717-727
This study investigated the stability of the primary blood typing antibodies (Anti-A, Anti-B and Anti-D IgM) on paper. This knowledge is critical to manufacture a new type of paper-based blood typing device where blood group antibodies must be kept active on paper for extended periods. Two strategies were explored. The first involved mixing additives such as polyvinylpyrrolidone (PVP), dextran and glycerol, with antibodies before sorption onto paper. While all the additives tested improved the antibody stability on paper, their protection for storage at room temperature was limited; dextran provided the longest protection, followed by PVP and then glycerol. The second strategy relied on freeze-drying to stabilize the antibodies in paper. Freeze dried antibodies sorbed into paper could be stored for long periods at ambient conditions without significantly loss of their activity. The thermal stability of antibodies in paper was also improved by freeze-drying. Our work shows that the use of additives and freeze-drying are effective approaches to retain the activities of IgM blood group antibodies on paper. These approaches will be further explored for the large scale development of a new generation of clinical and home-care blood testing devices. 相似文献
770.