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111.
Erstmals wurden, in einen intermetallischen Vorläuferansatz, durch In‐situ‐Elektrokonversion von Mangangallid (MnGa4) hochleistungsfähige und langzeitstabile MnOx‐basierte Elektrokatalysatoren für die Wasseroxidation in alkalischem Medium hergestellt. Überraschend führt seine Elektrokorrosion, unter gleichzeitigem Verlust von Ga, gleichzeitig zu drei kristallinen Typen von MnOx‐Mineralien mit verschiedenen Strukturen und induzierten Defekten: Birnessit δ‐MnO2, Feitknechtit β‐MnOOH und Hausmannit α‐Mn3O4. Das Vorkommen und die intrinsische Stabilität von aktiven MnIII/MnIV‐Zentren in den drei gebildeten MnOx‐Phasen erklärt die hervorragende Effizienz und Stabilität des Systems für die elektrokatalytische Wasseroxidation. Nach der elektrophoretischen Abscheidung des MnGa4‐Vorläufers auf elektrisch leitfähigem Nickelschaum wurde ein niedriges Überpotential von 291 mV bei der Stromdichte von 10 mA cm?2 erreicht, das praktisch den Überpotentialen von edelmetallbasierten Katalysatoren entspricht und für mehr als fünf Tage beständig ist.  相似文献   
112.
The synthesis and applications of carboxy‐MIDA‐boronate, a novel C1 building block, are described. This molecule is accessible via a ruthenium tetraoxide‐mediated cleavage of commercially available ethynyl‐MIDA‐boronate. In the course of this study, carboxy‐MIDA‐boronate was found to possess ambident reactivity towards nucleophiles. Carboxylic acid derivatization produces a broad range of previously unknown carbamoyl‐, oxycarbo‐ and thiocarboboronates. Carboxy‐MIDA‐boronate and its derivatives undergo condensations to access borylated heterocycles with boron at positions that are difficult to access using alternate methods. The resulting heterocycles participate in the Suzuki–Miyaura cross‐coupling reaction, enabling entry into diverse bis(heteroaryl) motifs. The carbon monoxide‐releasing capacity of carboxy‐MIDA‐boronate was also examined and applied in palladium‐catalyzed carbonylation.  相似文献   
113.
Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution & Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis “like” macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers.  相似文献   
114.
5-Pyrimidylboronic acid and 2-methoxy-5-pyrimidylboronic acid 4 have been synthesised by lithium-halogen exchange reactions on 5-bromopyrimidine and 2-methoxy-5-bromopyrimidine, respectively, followed by reaction with triisopropylborate. Suzuki cross-coupling reactions of 2 and 4 with heteroaryl halides [Na(2)CO(3), Pd(PPh(3))(2)Cl(2), 1,4-dioxane, 95 degrees C] yield heteroarylpyrimidines (heteroaryl = thienyl, quinolyl and pyrimidyl). Two-fold reaction of 2 with 4,6-dichloropyrimidine 12 gave 4,6-bis(5-pyrimidyl)pyrimidine 8(56% yield). Reaction of 4,6-dichloropyrimidine with 2-methoxy-5-pyridylboronic acid gave 4,6-bis(2-methoxy-5-pyridyl)pyrimidine 14 (84% yield). Conversion of into 4,6-bis(2-chloro-5-pyridyl)pyrimidine 15 (63% yield) followed by two-fold Suzuki reaction with 4-tert-butylbenzeneboronic acid gave the penta-arylene derivative 4,6-bis[2-(4-tert-butyl)phenyl-5-pyridyl]pyrimidine 16 (16% yield). Analogous reaction of 12 with 2-methoxy-3-pyridylboronic acid 17 gave 4,6-bis(2-methoxy-3-pyridyl)pyrimidine 18 (64% yield). The X-ray crystal structures of compound 2.0.5H(2)O and compound 18 are reported. The two hydroxyl H atoms in 2 have the usual exo-endo orientation. However, unlike most arylboronic acids, molecule 2 does not form a centrosymmetric hydrogen-bonded dimer. In molecule 18, the pyridine rings form dihedral angles of 39.9 degrees and 22.8 degrees with the central pyrimidine ring.  相似文献   
115.
Comparative study of 13,15-[N-(2-hydroxyethyl)]cycloimide chlorin p6 (2), 13,15-(N-acetoxy)cycloimide chlorin p6 (3), 13,15-(N-hydroxy)cycloimide chlorin p6 methyl ester (4) and 13,15-(N-methoxy)cycloimide chlorin p6 methyl ester (5) together with the previously investigated 13,15-[N-(3-hydroxypropyl)]cycloimide chlorin p6 (1) was performed. The dependence of the key photodynamic properties of 1-5 on the introduced substituents was analyzed. The photoinduced cell-killing activity of 4 is 100- and 280-fold higher than that of chlorin p6 and Photogem, respectively, as estimated on A549 human lung adenocarcinoma cells. The activity is reduced eight times in the order 4 > 5 > 1 > 2 > 3. The intracellular accumulation of 1-5 occurs in cytoplasm in a monomeric form bound to the lipids of cellular membranes. This form of 1, 2, 3, 4 and 5 is characterized by the high quantum yield of singlet oxygen generation, which depends on the introduced substituents, 0.66, 0.59, 0.35, 0.51 and 0.73, respectively. The photostability is two-fold less for 1 and four-fold less for 2, 3 and 5 than for 4. The rates of cellular uptake and efflux of 1-5 vary widely, thus providing the way to optimize the pharmacological properties of the photosensitizer (PS) using the respective substituents. Modifying the substituents, 1-5 were targeted to different cellular organelles. The enhanced accumulation in the Golgi apparatus and mitochondria complemented with diffuse staining of intracellular membranous structures is a property of 1-4. Compound 5 accumulates selectively in the lipid droplets and stains weakly perinuclear structures. Temperature-sensitive mechanisms of transport are responsible for the 1-4 uptake. Diffusion can play a role in the internalization of 5 but not of 1-4. Endocytosis via caveolae, clathrin-dependent and adenosine triphosphate-dependent pathways are not noticeably involved in the 1-5 internalization. Independently from their intracellular localization 1, 4 and 5 are highly efficient near-IR PS, which induce predominantly an apoptotic type of cell death under conditions providing ca 50% level of phototoxicity and necrosis at the 100% level of phototoxicity.  相似文献   
116.
Alkoxysilyl derivatives of dibenzoylmethanatoboron difluoride (DBMBF2) are synthesized by the hydrosilylation reaction of the corresponding O‐allyl derivatives of DBMBF2 with triethoxysilane. The photophysical properties of the synthesized O‐allyl and alkoxysilyl derivatives are investigated. It is found that the absorption and fluorescence spectra of the DBMBF2 derivatives essentially depend on the position of the O‐allyl or O‐propyl alkoxysilyl substituent. The highest fluorescence quantum yield is obtained for the para‐position, whereas the substitution at the meta‐position gives the largest bathochromic shift in the fluorescence spectrum. Density functional theory calculations of the structures and time‐dependent density functional theory calculations of the gas‐phase excitation and emission energies of alkoxysilyl derivatives are performed at the PBE0/SVP level of theory. Some spectral features of para‐, ortho‐, and meta‐substituted derivatives can be adequately explained by the overlapping of two absorption bands.  相似文献   
117.
Unprotected aziridine aldehydes belong to the amphoteric class of molecules by virtue of their dual nucleophilicity/electrophilicity. The dimeric nature of these molecules, brought together by a weak and reversible aminal "connection", was found to be an important element of reactivity control. We present evidence that reversible dimer dissociation is instrumental in aziridine aldehyde transformations. We anticipate further developments that will unveil other synthetic consequences of remote control of selectivity through forging reversible covalent interactions.  相似文献   
118.
A reaction exemplifying migration of boron-substituted carbon is described. We show that α-boroalkyl groups of transient boroalkyl acyl azide intermediates readily migrate from carbon to nitrogen. This process allows access to a new class of stable molecules, α-boryl isocyanates, from α-borylcarboxylic acid precursors. The methodology facilitates synthesis of a wide range of α-aminoboronic acid derivatives, including α,α-disubstituted analogues.  相似文献   
119.
An efficient synthetic route to 2- and 2,7-substituted pyrenes is described. The regiospecific direct C-H borylation of pyrene with an iridium-based catalyst, prepared in situ by the reaction of [{Ir(μ-OMe)cod}(2)] (cod = 1,5-cyclooctadiene) with 4,4'-di-tert-butyl-2,2'-bipyridine, gives 2,7-bis(Bpin)pyrene (1) and 2-(Bpin)pyrene (2, pin = OCMe(2)CMe(2)O). From 1, by simple derivatization strategies, we synthesized 2,7-bis(R)-pyrenes with R = BF(3)K (3), Br (4), OH (5), B(OH)(2) (6), and OTf (7). Using these nominally nucleophilic and electrophilic derivatives as coupling partners in Suzuki-Miyaura, Sonogashira, and Buchwald-Hartwig cross-coupling reactions, we obtained 2,7-bis(R)-pyrenes with R = (4-CO(2)C(8)H(17))C(6)H(4) (8), Ph (9), C≡CPh (10), C≡C[{4-B(Mes)(2)}C(6)H(4)] (11), C≡CTMS (12), C≡C[(4-NMe(2))C(6)H(4)] (14), C≡CH (15), N(Ph)[(4-OMe)C(6)H(4)] (16), and R = OTf, R' = C≡CTMS (13). Lithiation of 4, followed by reaction with CO(2), yielded pyrene-2,7-dicarboxylic acid (17), whilst borylation of 2-tBu-pyrene gave 2-tBu-7-Bpin-pyrene (18) selectively. By similar routes (including Negishi cross-coupling reactions), monosubstituted 2-R-pyrenes with R = BF(3)K (19), Br (20), OH (21), B(OH)(2) (22), [4-B(Mes)(2)]C(6)H(4) (23), B(Mes)(2) (24), OTf (25), C≡CPh (26), C≡CTMS (27), (4-CO(2)Me)C(6)H(4) (28), C≡CH (29), C(3)H(6)CO(2)Me (30), OC(3)H(6)CO(2)Me (31), C(3)H(6)CO(2)H (32), OC(3)H(6)CO(2)H (33), and O(CH(2))(12)Br (34) were obtained from 2. These derivatives are of synthetic and photophysical interest because they contain donor, acceptor, and conjugated substituents. The crystal structures of compounds 4, 5, 7, 12, 18, 19, 21, 23, 26, and 28-31 have also been obtained from single-crystal X-ray diffraction data, revealing a diversity of packing modes, which are described in the Supporting Information. A detailed discussion of the structures of 1 and 2, their polymorphs, solvates, and co-crystals is reported separately.  相似文献   
120.
Detailed kinetic and computational investigation of the enantio‐ and diastereoselective allylation of aldehydes 1 with allyltrichlorosilanes 5 , employing the pyridine N‐oxides METHOX ( 9 ) and QUINOX ( 10 ) as chiral organocatalysts, indicate that the reaction can proceed through a dissociative (cationic) or associative (neutral) mechanism: METHOX apparently favors a pentacoordinate cationic transition state, while the less sterically demanding QUINOX is likely to operate via a hexacoordinate neutral complex. In both pathways, only one molecule of the catalyst is involved in the rate‐ and selectivity‐determining step, which is supported by both experimental and computational data.  相似文献   
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