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141.
Dr. Werner Fudickar Prof. Dr. Torsten Linker 《Angewandte Chemie (International ed. in English)》2018,57(39):12971-12975
The generation of reactive singlet oxygen under mild conditions is of current interest in chemistry, biology, and medicine. We were able to release oxygen from dipyridylanthracene endoperoxides (EPOs) by using a simple chemical trigger at low temperature. Protonation and methylation of such EPOs strongly accelerated these reactions. Furthermore, the methyl pyridinium derivatives are water soluble and therefore serve as oxygen carriers in aqueous media. Methylation of the EPO of the ortho isomer affords the parent form directly without increasing the temperature under very mild conditions. This exceptional behavior is ascribed to the close contact between the nitrogen atom and the peroxo group. Singlet oxygen is released upon this reaction, and can be used to oxygenate an acceptor such as tetramethylethylene in the dark with no heating. Thus, a new chemical source of singlet oxygen has been found, which is triggered by a simple stimulus. 相似文献
142.
Manganese‐Catalyzed Dehydrogenative Alkylation or α‐Olefination of Alkyl‐Substituted N‐Heteroarenes with Alcohols
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Dr. Guoying Zhang Dr. Torsten Irrgang Thomas Dietel Fabian Kallmeier Prof. Dr. Rhett Kempe 《Angewandte Chemie (International ed. in English)》2018,57(29):9131-9135
Catalysis with earth‐abundant transition metals is an option to help save our rare noble‐metal resources and is especially interesting when novel reactivity or selectivity patterns are observed. We report here on a novel reaction, namely the dehydrogenative alkylation or α‐olefination of alkyl‐substituted N‐heteroarenes with alcohols. Manganese complexes developed in our laboratory catalyze the reaction with high efficiency whereas iron and cobalt complexes stabilized by the same ligands are essentially inactive. Hydrogen is liberated during the reaction, and bromine and iodine functional groups as well as olefins are tolerated. A variety of alkyl‐substituted N‐heteroarenes can be functionalized, and benzylic and aliphatic alcohols undergo the reaction. 相似文献
143.
We present a mild and efficient method for the completely regioselective alcoholysis of styrene oxides utilizing a cooperative Br?nsted acid-type organocatalytic system comprised of mandelic acid (1 mol %) and N,N'-bis-[3,5-bis-(trifluoromethyl)phenyl]-thiourea (1 mol %). Various styrene oxides are readily transformed into their corresponding beta-alkoxy alcohols in good to excellent yields at full conversion. Simple aliphatic and sterically demanding, as well as unsaturated and acid-sensitive alcohols can be employed. 相似文献
144.
Spitzer T 《Analytical and bioanalytical chemistry》2008,391(8):2923-2929
Young lignite from two locations in Sendai City, Japan, were analyzed for polynuclear aromatic compounds (PACs). Lignite samples
were extracted with toluene and PACs were isolated by a compound-class-selective, reactive matrix clean-up. This clean-up
separates all compounds of polynuclear aromatic structure, for example hydrocarbons and ketones and their primary metabolites,
from interfering organic compounds. The result of this isolation procedure is, therefore, a group of a large number of polycyclic
compounds with different functional groups. Further analysis is done by glass capillary gas chromatography. Perylene was identified
as the only compound obtained by the reactive matrix clean-up of lignite samples from both locations. Concentrations were
in the range of 1–10 mg kg−1. Conversely, PACs resulting from particulate emissions from fossil fuel combustion always contain isomeric PAHs (polynuclear
aromatic hydrocarbons) with some polycyclic aromatic ketones and thousands of primary and secondary metabolites at very low
concentrations. This was demonstrated for a sample of urban air particulate matter, which is the source of PAC contamination
of surface soil. The absence of accompanying PAHs and polynuclear aromatic ketones in the lignite samples confirms that perylene
did not originate from a combustion process. It is assumed that the high concentrations of perylene are the result of a reduction
of perylene quinone. Thus, the high perylene content of the lignite samples investigated is of biogenic origin. 相似文献
145.
Two different reaction pathways in the photooxygenation of 9,10-diarylanthracenes are identified, with strong evidence for polar (forward, singlet oxygen addition) and radical (backward, thermolysis) intermediates. 相似文献
146.
147.
Widely used regression approaches in modeling quantitative structure-property relationships, such as PLS regression, are highly susceptible to outlying observations that will impair the prognostic value of a model. Our aim is to compile homogeneous datasets as the basis for regression modeling by removing outlying compounds and applying variable selection. We investigate different approaches to create robust, outlier-resistant regression models in the field of prediction of drug molecules' permeability. The objective is to join the strength of outlier detection and variable elimination increasing the predictive power of prognostic regression models. In conclusion, outlier detection is employed to identify multiple, homogeneous data subsets for regression modeling. 相似文献
148.
Koch R Finnerty JJ Bruhn T Borget F Wentrup C 《The journal of physical chemistry. A》2008,112(38):8999-9004
The complex reaction of thermally generated iminopropadienones with amines in the gas phase and upon matrix deposition and its varying product composition is investigated using density functional theory. In the high energy gas phase addition a single amine molecule reacts readily with iminopropadienone with the decisive step being a 1,3-hydrogen shift and activation barriers of at least 100 kJ/mol. In accordance with the experiment, the formation of ketenes is favored. In the condensed phase of an amine matrix, the utilization of amine dimers both as reagents and as explicit solvents lowers the activation energy required to a feasible 20-30 kJ/mol and predicts ketenimines as the main products, as observed experimentally. 相似文献
149.
Kinran Lau Felix Niemann Dr. Kaltum Abdiaziz Dr. Markus Heidelmann Yuke Yang Dr. Yujin Tong Dr. Michael Fechtelkord Prof. Torsten C. Schmidt Dr. Alexander Schnegg Prof. R. Kramer Campen Dr. Baoxiang Peng Prof. Martin Muhler Dr. Sven Reichenberger Prof. Stephan Barcikowski 《Angewandte Chemie (International ed. in English)》2023,62(12):e202213968
Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO2 (rutile and P25) with increasing oxygen deficiency and Ti3+ concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution. As indicated by EPR spectroscopy, the laser-generated Ti3+ exist near the surface of rutile, but appear to be deeper in the bulk for P25. Fluoride substitution shows that extra acidic bridging OH are selectively created on rutile, while the surface OH density remains constant for P25. These observations suggest near-surface Ti3+ are highly related to surface bridging OH, presumably the former increasing the electron density of the bridging oxygen to form more of the latter. We anticipate that fluoride substitution will enable better characterization of surface OH and its correlation with defects in metal oxides. 相似文献
150.
We examine how postsynthesis nanoparticle ligand shell modifications as a general approach can help in the understanding of currently proposed mechanisms for gold nanoparticle chirality. We compare the CD response of chirally decorated mixed-monolayer-protected gold nanoparticles synthesized in situ with quasi-identical gold nanoparticles either prepared by place exchange reactions or subjected to an aqueous base, resulting in partial hydrolysis and simultaneous partial racemization. We find that the CD response at wavelengths where the free chiral ligand does not absorb strongly depends on the preparation conditions, i.e., in situ synthesis vs place exchange, and that postsynthesis racemization of the chiral ligand produces racemic nanoparticles with no CD response, i.e., no induction of a chiral bias during reductive nanoparticle formation. Considering all experimental results for the described gold nanoparticle system with a C12H24 spacer between the nanoparticle surface and chiral center, the so-called "vicinal effect" with the formation of a supramolecular assembly of the chiral moieties seems to be active. Finally, we argue that postsynthesis nanoparticle ligand shell modifications such as racemization and/or place exchange reactions are very powerful tools to unravel contributions of the different gold nanoparticle chirality mechanisms. 相似文献