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301.
Leimkuhler C Fridman M Lupoli T Walker S Walsh CT Kahne D 《Journal of the American Chemical Society》2007,129(34):10546-10550
The tetracyclic core of anthracycline natural products with antitumor activity such as aclacinomycin A are tailored during biosynthesis by regioselective glycosylation. We report the first synthesis of TDP-L-rhodosamine and demonstrate that the glycosyltransferase AknS transfers L-rhodosamine to the aglycone to initiate construction of the side-chain trisaccharide. The partner protein AknT accelerates AknS turnover rate for L-rhodosamine transfer by 200-fold. AknT does not affect the Km but rather affects the kcat. Using these data, we propose that AknT causes a conformational change in AknS that stabilizes the transition state and ultimately enhances transfer. When the subsequent glycosyltransferase AknK and its substrate TDP-L-fucose are also added to the aglycone, the disaccharide and low levels of a fully reconstituted trisaccharide form of aclacinomycin are observed. 相似文献
302.
We report cryogenic scanning tunneling spectroscopy measurements on single crystals of superconducting FeSe1−xTex, at doping levels of x=0.5 and 0.7, with critical temperatures . Atomically resolved topographic images were obtained, showing large-scale density-of-state clustering which appears to have no periodicity and to vary with the doping. Conductance spectra taken at 300 mK showed a generally asymmetric V-shaped background, along with a sharp dip structure within . These spectra appeared to vary over ∼nm length scale, and not correlated with the topography. The overall spectral evolution versus temperature is consistent with the dip structure arising from a superconducting energy gap which closes above Tc, and with the spectral background having a non-superconducting origin. The persistence of finite zero-bias conductance down to 300 mK, well below Tc, indicates the presence of low-energy quasiparticles on parts of the Fermi surface. We discuss our data in light of some other recent spectroscopic measurements of FeSe1−xTex, and in terms of its characteristic band structure. 相似文献
303.
Yang Y Cho YI Friedman G Fridman A Fridman G 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2011,39(11):2060-2061
Observations of atmospheric-pressure dielectric barrier discharge are conducted through a water-filled electrode in atmospheric-pressure argon gas flow. Quasi-symmetric self-organized discharge filaments were observed. The streamers moved with the gas flow, and the migration velocity increased with increasing gas velocity. 相似文献
304.
V. F. Krivorotov G. S. Nuzhdov A. A. Fridman E. V. Charnaya 《Russian Journal of Electrochemistry》2013,49(12):1154-1159
The results of quantum chemical calculations of the potential profile in the LaF3 crystal lattice in the range of superionic phase transition are presented for clusters containing 24 to 1200 ions. It is found that the values of formation energy E a of vacancy-interstitial fluoride ion defects and potential barriers E d hindering the movement of fluoride ions and determining the efficiency of charge transport in the lattice grow monotonously from the minimum values E a = 0.12 eV and E d = 0.22 eV for a 24-ion cluster to the maximum E a = 0.16 eV and E d = 0.26 eV for clusters of 576 and 1200 ions. It is shown that the values of E a and E d obtained for the dielectric phase (T < T c) are several times the values of E a and E d for the superionic state (T ≥ T c) of LaF3. The values of E a and E d obtained by quantum chemical calculations from clusters of 576 and 1200 ions agree well with energies E a and E d obtained from the analysis of the data of the Raman and quasielastic light scattering. 相似文献
305.
Yong Yang Hyoungsup Kim Andrey Starikovskiy Young Cho Alexander Fridman 《Plasma Chemistry and Plasma Processing》2011,31(1):51-66
Direct pulsed spark discharge treatment was found to be able to induce the precipitation of calcium ions in supersaturated
hard water (Yang et al. in Water Res 44:3659, 2010). The present study investigated possible pathways for the plasma-induced
precipitation. Both UV and reactive species were found not the major factors that stimulate the precipitation in present setup.
A transient hot-wire method was used to investigate the effect of plasma-induced local micro-heating. Approximately 15% drop
in the calcium-ion concentration was observed, indicating that the local micro-heating effect could be the major contributing
factor. Additionally, a nanosecond pulsed corona discharge was used to investigate the non-thermal effect of plasma, and a
maximum 7% drop in the calcium hardness was observed. Calcite with rhombohedron morphology was observed in both cases, similar
to the structure observed in the spark discharge treatment case, indicating that calcium-ion precipitation process could be
attributed to both the thermal and non-thermal effects produced by the plasma. 相似文献
306.
Yu. A. Fridman F. N. Klevets A. P. Voitenko 《Journal of Experimental and Theoretical Physics》2011,112(2):261-273
Concentration-induced reorientation phase transitions in thin magnetic films of FeCo alloys have been investigated taking
into account “planar” or “bulk” magnetoelastic interaction. The critical concentrations of Co corresponding to the phase transition
points, as well as the types of the phase transitions, have been determined. The phase diagrams have been plotted. 相似文献
307.
Phase locking, which is achieved by transferring some energy from one oscillator to the others, strongly depends on the coupling strength between the oscillators. Typically, the coupling strength must be above a certain threshold in order to achieve phase locking. Here we show how this threshold can be significantly reduced when phase-dependent losses are introduced into the oscillators. Specifically, the coupling strength can be reduced by at least an order of magnitude, thereby substantially decreasing the needed transfer of energy between oscillators. The resulting enhancement of phase locking does not only influence the laser research area, but also affects many other areas that involve coupled ensembles. 相似文献
308.
309.
Prof. Micha Fridman Prof. Kaori Sakurai 《Angewandte Chemie (International ed. in English)》2023,62(12):e202211927
The growing number of fungal infections caused by pathogens resistant to one or more classes of antifungal drugs emphasizes the threat that these microorganisms pose to animal and human health and global food security. Open questions remain regarding the mechanisms of action of the limited repertoire of antifungal agents, making it challenging to rationally develop more efficacious therapeutics. In recent years, the use of chemical biology approaches has resolved some of these questions and has provided new promising concepts to guide the design of antifungal agents. By focusing on examples from studies carried out in recent years, this minireview describes the key roles that probes based on antifungal agents and their derivatives have played in uncovering details about their activities, in detecting resistance, and in characterizing the interactions between these agents and their targets. 相似文献
310.