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951.
Felipe Wodtke Fernando R. Xavier Samuel R. Mendes Alfredo R.M. de Oliveira Rogério A. Gariani 《Tetrahedron letters》2017,58(3):231-234
A novel application of the highly stable niobium oxide phosphate (NbOPO4) as an efficient catalyst for the synthesis of β-enamino ketones under solvent-free conditions is described. This protocol, exhibits attractive yields, short reaction periods, lower loading of catalyst and high chemoselectivity. 相似文献
952.
Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions in soils results in the formation of both N2O and N2, whereby highly nitrogen-fertilized agricultural soils contribute to a considerable extent of the N2O emission. Latest results in the literature indicate that nitrous oxide can also be formed as a byproduct of the microbial nitrification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semiaride climate. This study was conducted to measure the path of N2O formation in Haplic Phaeozen: using [15N] ammonium and [15N] nitrat and a GC-MS aided incubation system. The kinetic isotope method was used to evaluate the experimental data. The results are: - Under anaerobic conditions (~ 90% of the water holding capacity = WHC) N2O originates mainly from the nitrate pool by denitrification. - As expected, the N2O formation is low under aerobic conditions (~ 80% WHC) but the gas originates directly from the ammonium and not from the nitrate pool, probably as a byproduct of the nitrification process. 相似文献
953.
Dr. Nadja A. Simeth Thomas Kinateder Dr. Chitra Rajendran Julian Nazet Prof. Dr. Rainer Merkl Prof. Dr. Reinhard Sterner Prof. Dr. Burkhard König Dr. Andrea C. Kneuttinger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(7):2439-2451
Light regulation of drug molecules has gained growing interest in biochemical and pharmacological research in recent years. In addition, a serious need for novel molecular targets of antibiotics has emerged presently. Herein, the development of a photocontrollable, azobenzene-based antibiotic precursor towards tryptophan synthase (TS), an essential metabolic multienzyme complex in bacteria, is presented. The compound exhibited moderately strong inhibition of TS in its E configuration and five times lower inhibition strength in its Z configuration. A combination of biochemical, crystallographic, and computational analyses was used to characterize the inhibition mode of this compound. Remarkably, binding of the inhibitor to a hitherto-unconsidered cavity results in an unproductive conformation of TS leading to noncompetitive inhibition of tryptophan production. In conclusion, we created a promising lead compound for combatting bacterial diseases, which targets an essential metabolic enzyme, and whose inhibition strength can be controlled with light. 相似文献
954.
Differences and Commonalities in the Gas‐Phase Reactions of Closed‐Shell Metal Dioxide Clusters [MO2]+ (M=V,Nb, and Ta) with Methane 下载免费PDF全文
Dr. Shaodong Zhou Dr. Jilai Li Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(21):7225-7228
High‐level electronic structure calculations, in combination with Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometric studies, permit the mechanism by which closed‐shell, “naked” [TaO2]+ brings about C?H bond activation of methane to be revealed. These studies also help to understand why the lighter congeners of [MO2]+ (M=V, Nb) are unreactive under ambient conditions. 相似文献
955.
B. Johannsen 《Isotopes in environmental and health studies》2013,49(9):293-300
1. Einleitung 2. Tracerdarstellung 3. Geuinnung von Antiseren 4. Methoden zur Trennung von freier und antikörpergebundener Radioaktivität 5. Analysengang 6. Spezifität 7. Empfindlichkeit 8. Anwendungsbeispiele 9. Literatur 相似文献
956.
957.
The study toward the total synthesis of (R)‐(+)‐harmicine is reported in this paper. The enantioselective synthesis of pyrrolidinone, the main backbone of of (R)‐(+)‐harmicine, has been completed by the methodology based on photo‐induced Wolff rearrangement of α‐diazo‐β‐carbonyl compounds. 相似文献
958.
Data describing the insertion of sulphur dioxide into the carbon―tin bond of a range of substituted phenyltrimethyltin compounds in methanol and benzene solvents have been reconsidered. The reaction in methanol is cleanly second order, but the reaction in benzene has both a second‐order and third‐order component, the latter ascribable to an initial equilibrium formation of a SO2 complex with the phenyl ring followed by the insertion of a second SO2 molecule into the carbon–tin bond. Molecular orbital calculations have identified the transition states (TS) and the favoured reaction pathways for the second‐order and third‐order reaction pathways in benzene. The effects of solvents on TS and enthalpies of reaction have also been examined. New insights into the types of TS involved in electrophilic substitution reactions are revealed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
959.
Back Cover: Aqueous Sulfate Separation by Sequestration of [(SO4)2(H2O)4]4− Clusters within Highly Insoluble Imine‐Linked Bis‐Guanidinium Crystals (Chem. Eur. J. 6/2016) 下载免费PDF全文
960.
Generation of an N→B Ladder‐type Structure by Regioselective Hydroboration of an Alkenyl‐Functionalized Quaterpyridine 下载免费PDF全文
Markus Grandl Dr. Yu Sun Dr. Frank Pammer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):3976-3980
An unusual reactivity of 2‐(1‐alkenyl)‐pyridines towards hydroboration with 9H‐borabicyclo[3.3.1]nonane (9H‐BBN) has been employed to selectively introduce two borane groups into a conjugated quaterpyridine. Quantitative conversion of the substrate was observed with exclusive regioselectivity. A molecular structure that allows intramolecular N→B coordination was generated. The effect of the ladder formation on the molecular structure and the electronic properties of the conjugated system have been investigated. The synthetic strategy demonstrated herein offers a facile access to N→B ladder‐type structures from readily available substrates, and allows to simultaneously introduce several boron centers under mild conditions. 相似文献