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191.
Langer R Iron MA Konstantinovski L Diskin-Posner Y Leitus G Ben-David Y Milstein D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(23):7196-7209
The new, structurally characterized hydrido carbonyl tetrahydridoborate iron pincer complex [(iPr-PNP)Fe(H)(CO)(η(1)-BH(4))] (1) catalyzes the base-free hydrogenation of ketones to their corresponding alcohols employing only 4.1 atm hydrogen pressure. Turnover numbers up to 1980 at complete conversion of ketone were reached with this system. Treatment of 1 with aniline (as a BH(3) scavenger) resulted in a mixture of trans-[(iPr-PNP)Fe(H)(2)(CO)] (4a) and cis-[(iPr-PNP)Fe(H)(2)(CO)] (4b). The dihydrido complexes 4a and 4b do not react with acetophenone or benzaldehyde, indicating that these complexes are not intermediates in the catalytic reduction of ketones. NMR studies indicate that the tetrahydridoborate ligand in 1 dissociates prior to ketone reduction. DFT calculations show that the mechanism of the iron-catalyzed hydrogenation of ketones involves alcohol-assisted aromatization of the dearomatized complex [(iPr-PNP*)Fe(H)(CO)] (7) to initially give the Fe(0) complex [(iPr-PNP)Fe(CO)] (21) and subsequently [(iPr-PNP)Fe(CO)(EtOH)] (38). Concerted coordination of acetophenone and dual hydrogen-atom transfer from the PNP arm and the coordinated ethanol to, respectively, the carbonyl carbon and oxygen atoms, leads to the dearomatized complex [(iPr-PNP*)Fe(CO)(EtO)(MeCH(OH)Ph)] (32). The catalyst is regenerated by release of 1-phenylethanol, followed by dihydrogen coordination and proton transfer to the coordinated ethoxide ligand. 相似文献
192.
193.
We study the asymmetry of the Lipschitz metric d on Outer space. We introduce an (asymmetric) Finsler norm \({\|\cdot\|^L}\) that induces d. There is an Out(F n )-invariant “potential” Ψ defined on Outer space such that when \({\|\cdot\|^L}\) is corrected by dΨ, the resulting norm is quasi-symmetric. As an application, we give new proofs of two theorems of Handel-Mosher, that d is quasi-symmetric when restricted to a thick part of Outer space, and that there is a uniform bound, depending only on the rank, on the ratio of logs of growth rates of any irreducible \({f\in Out(F_n)}\) and its inverse. 相似文献
194.
Kaplan-Neeman R Kishon-Rabin L Henkin Y Muchnik C 《The Journal of the Acoustical Society of America》2006,120(2):926-933
This study was designed to characterize the effect of background noise on the identification of syllables using behavioral and electrophysiological measures. Twenty normal-hearing adults (18-30 years) performed an identification task in a two-alternative forced-choice paradigm. Stimuli consisted of naturally produced syllables [da] and [ga] embedded in white noise. The noise was initiated 1000 ms before the onset of the speech stimuli in order to separate the auditory event related potentials (AERP) response to noise onset from that to the speech. Syllables were presented in quiet and in five SNRs: +15, +3, 0, -3, and -6 dB. Results show that (1) performance accuracy, d', and reaction time were affected by the noise, more so for reaction time; (2) both N1 and P3 latency were prolonged as noise levels increased, more so for P3; (3) [ga] was better identified than [da], in all noise conditions; and (4) P3 latency was longer for [da] than for [ga] for SNR 0 through -6 dB, while N1 latency was longer for [ga] than for [da] in most listening conditions. In conclusion, the unique stimuli structure utilized in this study demonstrated the effects of noise on speech recognition at both the physical and the perceptual processing levels. 相似文献
195.
We present a comprehensive theoretical study of the quantum solvation of the HF molecule by small clusters of the H2 isotopomers, p-H2, HD, and o-D2, with up to 13 hydrogen solvent molecules. This complements our earlier work on the HF-doped parahydrogen clusters [H. Jiang and Z. Bacic, J. Chem. Phys. 122, 244306 (2005)]. The ground-state properties of the clusters are calculated exactly using the diffusion Monte Carlo method. Detailed information is obtained regarding the size and isotopomer dependences of the energetics, vibrationally averaged structures, and their rigidity. The rigidity of these clusters is investigated further by analyzing the distributions of their principal moments of inertia from the diffusion Monte Carlo simulations. The clusters are found to be rather rigid, especially when compared with the pure parahydrogen clusters of the same size. Extensive comparison is made with the quantum Monte Carlo results for the CO-doped parahydrogen clusters and significant differences are observed in the size evolution of certain properties, notably the chemical potential. 相似文献
196.
197.
Revital Sasson Dan Vaknin Avihai Bross Efraim Lavie 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):753-756
A practical and reliable HPLC method was used for the determination of 2-[4-N-(2-hydroxyethyl)-1-piperazinyl]-N′-ethanesulfonic acid (HEPES) content in the 68Ga-labeled [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-Nal3-octreotide (DOTANOC). Linearity of this method
was observed in a concentration range of 0.01–10 mg mL−1 and the quantitative limit (signal to noise = 11) was determined as 10 μg mL−1. The HEPES concentration in the final products of 68Ga-DOTANOC was typically lower than the detection limit. Pure water and HEPES buffer as reaction medium were investigated
using various activities of gallium-68. It was demonstrated that the presence of HEPES buffer consistently furnished very
high radiochemical purity of 68Ga-DOTANOC, which remained stable for several hours post-labeling. Evidence is provided that in addition to its role as a
buffer, HEPES also functions as a radioprotectant agent. 相似文献
198.
In this article we establish an exponential lower bound on the Graver complexity of integer programs. This provides new type
of evidence supporting the presumable intractability of integer programming. Specifically, we show that the Graver complexity
of the incidence matrix of the complete bipartite graph K
3,m satisfies g(m) = Ω(2
m
), with g(m) ≥ 17·2
m−3 –7 for every m > 3. 相似文献
199.
Bat-El Oded Yael Diskin-Posner Dr. Vered Marks Prof. Haya Kornweitz Prof. Flavio Grynszpan 《European journal of organic chemistry》2023,26(39):e202300697
Theoretical and experimental mixed approaches are complementary and valuable. Our DFT calculations support the mechanism suggested by Kosower, adding to it a key diaziridine intermediate that determines the relative product distribution of this reaction. Our results are consistent with the formation of the diazoketene intermediate as the rate-limiting step. Based on curve fittings, first or second-order kinetics cannot be ruled out. This may indicate that more than one mechanism is simultaneously at play in this transformation. This unexpected outcome led us to study an alternative cyclopropenone intermediate. Although cyclopropenone is not likely to be formed under thermal conditions, adding it to the reaction mixture results in bimane structures. The most staggering finding from this investigation was the unanticipated generation of the unsymmetrical anti-(Me,Me)(Ph,Ph)bimane. The optimization of this route towards unsymmetrical bimanes will require additional investigation. 相似文献
200.
Noy Cohen Dr. Dror Shamir Prof. Haya Kornweitz Dr. Yael Albo Prof. Ariela Burg 《Chemphyschem》2023,24(18):e202300130
Para chloro aniline (PCA) is a common toxic pollutant found in pharmaceutical wastewater. Our study suggests a novel PCA treatment method based on a heterogeneous advanced oxidation process (AOP) that proceeds in an electron exchange matrix (EEM) prepared by the incorporation of redox-active specie in silica matrices using the sol-gel synthesis route. The results, which are supported by DFT calculations, show that the silicon skeleton of the EEM has two important roles, both as a porous matrix that hosts the redox species and as an oxidant species involved in the AOP. The calculations indicate that the formation of a radical on the nitrogen is favored. The suggested mechanism could shed light on the AOP, which proceeds in a heterogenous system, and on its application inside the understudied EEMs that, until now, have been a virtual black box. A better understanding of the mechanism could lead to improved control over the heterogeneous processes that can play a critical role in industries with the need to treat small amounts of toxic compounds at low concentrations, such as in the pharmaceutical industry. 相似文献