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241.
The mechanism of 1,2-aryl shifts in the Wittig rearrangement of α-metallated benzyl aryl ethers has been investigated by a detailed examination of the behavior of the following ethers: benzyl phenyl ether, benzyl para-tert-butyl- and meta-tert-butyl-phenyl ethers, benzyl 2-bromo-4-tert-butylphenyl ether and dibenzo[b,d] pyran. The failure to trap any aldehyde intermediate, the ease of rearrangement for the pyran, the lack of evidence for an aryne intermediate with the benzyl butyl ethers and other circumstantial evidence have led to the proposal of an intramolecular pathway in which radical pairs are generated and then collapse to the isomeric carbinolate. 相似文献
242.
Mihaly Mezei 《International journal of quantum chemistry》1994,52(1):147-152
An iso-energy cutoff scheme is introduced for the calculation of the potential of mean force between two ions in water. The cutoff criterion is based on the optimal interaction of the water dipole with the ion pair, for which analytical expressions are derived. Formulas are also derived to characterize the solvent reorganization contribution to the potential of mean force. Treatment of the contributions from waters outside the cutoff is also discussed. © 1994 John Wiley & Sons, Inc. 相似文献
243.
Dynamic characteristics of protein surfaces are among the factors determining their functional properties, including their potential participation in protein‐protein interactions. The presence of clusters of static residues—“stability patches” (SPs)—is a characteristic of protein surfaces involved in intermolecular recognition. The mechanism, by with SPs facilitate molecular recognition, however, remains unclear. Analyzing the surface dynamic properties of the growth hormone and of its high‐affinity variant we demonstrated that reshaping of the SPs landscape may be among the factors accountable for the improved affinity of this variant to the receptor. We hypothesized that SPs facilitate molecular recognition by moderating the conformational entropy of the unbound state, diminishing enthalpy–entropy compensation upon binding, and by augmenting the favorable entropy of desolvation. SPs mapping emerges as a valuable tool for investigating the structural basis of the stability of protein complexes and for rationalizing experimental approaches, such as affinity maturation, aimed at improving it. © 2015 Wiley Periodicals, Inc. 相似文献
244.
Both the Hall effect and the ab(')-plane conduction anisotropy are directly addressing the unconventional normal phase properties of the Bechgaard salt (TMTSF)2PF6. We found that the dramatic reduction of the carrier density deduced from recent optical data is not reflected in an enhanced Hall resistance. The pressure and temperature dependence of the b(')-direction resistivity reveal isotropic relaxation time and do not require explanations beyond the Fermi liquid theory. Our results allow a coherent-diffusive transition in the interchain carrier propagation, however the possible crossover to Luttinger liquid behavior is placed at an energy scale above room temperature. 相似文献
245.
Moisescu MG Leveque P Bertrand JR Kovacs E Mir LM 《Bioelectrochemistry (Amsterdam, Netherlands)》2008,74(1):9-15
Studying cell behaviour under irradiation with radiofrequency electromagnetic fields (RF-EMF) is often impeded by the difficulty to monitor cell characteristics during irradiation. Here we report the design and the application of a complete device for continuous microscopic observation of cells exposed to modulated EMF similar to mobile phones signals. The system allows the follow up of cell progression into mitosis under controlled temperature and CO(2) environment. Protocols are proposed in which the same cells are the controls before and after the EMF exposure and we demonstrate the interest of the "before exposure" controls. The exposure system was validated by cell endocytosis measurements. While the endocytosis rate was increased, no alteration of mitosis progression and mitosis duration was observed in cells exposed to 900 MHz modulated EMF for 1 h, at 30 degrees C and at a Specific Absorption Rate of 2.2 W/kg. 相似文献
246.
McIntee JW Sundararajan C Donovan AC Kovacs MS Capretta A Valliant JF 《The Journal of organic chemistry》2008,73(21):8236-8243
A convenient method for the preparation of fluorous aryl stannanes was developed as a means of expanding the general utility of the fluorous labeling strategy (FLS). Following the synthesis of a novel fluorous distannane, a palladium-catalyzed cross-coupling reaction was used to prepare the target compounds from aryl halides. The scope of the reaction was investigated by preparing a small library of model compounds where the reaction yields were similar to those reported for the analogous procedures employing hexamethyl- or hexabutyldistannanes. The utility of the reported methodology was demonstrated through the successful synthesis of fluorous precursors to two established molecular imaging and therapy agents (FIAU, IUdR). These were radiolabeled with iodine-125 and the desired products isolated in high yield and effective specific activity. 相似文献
247.
Marin Senila Emilia Neag Oana Cadar Emoke Dalma Kovacs Ioan Aschilean Melinda Haydee Kovacs 《Molecules (Basel, Switzerland)》2022,27(12)
Increased concentrations of heavy metals in the environment are of public health concern, their removal from waters receiving considerable interest. The aim of this paper was to study the simultaneous adsorption of heavy metals (Cu, Cd, Cr, Ni, Zn and Pb) from aqueous solutions using the zeolitic volcanic tuffs as adsorbents. The effect of thermal treatment temperature, particle size and initial metal concentrations on the metal ions sorption was investigated. The selectivity of used zeolite for the adsorption of studied heavy metals followed the order: Pb > Cr > Cu > Zn > Cd > Ni. The removal efficiency of the heavy metals was strongly influenced by the particle sizes, the samples with smaller particle size (0–0.05 mm) being more efficient in heavy metals removal than those with larger particle size (1–3 mm). Generally, no relevant changes were observed in heavy metals removal efficiency for the treatment temperatures of 200 °C and 350 °C. Moreover, at a higher temperature (550 °C), a decrease in the removal efficiencies was observed. The Cd, Zn, Cu, Cr, Zn and Ni sorption was best described by Langmuir model according to the high values of correlation coefficient. The pseudo-first-order kinetic model presented the best correlation of the experimental data. 相似文献
248.
249.
S. Ebraheem W. B. Beshir A. Kovacs L. Wojnarovits W. L. McLaughlin 《Radiation Physics and Chemistry》1999,55(5-6):785-787
The electron spin resonance (ESR) readout of radical concentration in irradiated L-alanine is well known as a transfer dosimetry system, however, the high cost of the ESR equipment is a serious handicap for large-scale routine application. In this study the reaction between irradiated L-alanine powder and aqueous solution of triphenyl tetrazolium chloride (TTC) was studied. The radical produced by irradiation of alanine reacts during the dissolution with TTC forming pink-colored formazans with absorption maxima around 401 and 487 nm. This readout method can be used in the 2–200 kGy dose range. 相似文献
250.
Mihaly Mezei 《Journal of computational chemistry》1997,18(6):812-815
It is shown that, by optimizing the placement of a solute in a solvent droplet or in a periodic simulation cell, the number of solvent molecules can be reduced without affecting the quality of the simulation. © 1997 by John Wiley & Sons, Inc. J Comput Chem 18: 812–815, 1997 相似文献