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41.
Combining the selectivity of G-quadruplex (G4) ligands with the spatial and temporal control of photochemistry is an emerging strategy to elucidate the biological relevance of these structures. In this work, we developed six novel V-shaped G4 ligands that can, upon irradiation, form stable covalent adducts with G4 structures via the reactive intermediate, quinone methide (QM). We thoroughly investigated the photochemical properties of the ligands and their ability to generate QMs. Subsequently, we analyzed their specificity for various topologies of G4 and discovered a preferential binding towards the human telomeric sequence. Finally, we tested the ligand ability to act as photochemical alkylating agents, identifying the covalent adducts with G4 structures. This work introduces a novel molecular tool in the chemical biology toolkit for G4s.  相似文献   
42.
Due to their remarkable electronic features, recent years have witnessed the emergence of carbones L2C, which consist in two donating L ligands coordinating a central carbon atom bearing two lone pairs. In this context, the phosphine/sulfoxide-supported carbone 4 exhibits a strong nucleophilic character, and here, we describe its ability to coordinate dichlorogermylene. Two original stable coordination complexes were obtained and fully characterized in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis, respectively. At 60 °C, in the presence of 4, the Ge(II)-complex 5 undergoes a slow isomerization that transforms the bis-ylide ligand into an yldiide.  相似文献   
43.
The fractionation of an ethanol extract of the bark of Trichilia adolfi yielded four novel limonoids (trichilinones A-D, 1–4), with five fused rings and related to the hortiolide-type limonoids. Starting with an ε-lactone, which is α,β-unsaturated in trichilinones A and D (1 and 4), attached to a tetrahydrofuran ring that is connected to an unusual bicyclo [5.1.0] hexane system, joined with a cyclopentanone with a 3-furanyl substituent [(2-oxo)-furan-(5H)-3-yl in trichilinone D (4)], the four compounds isolated display a new 7/5/3/5/5 limonoid ring system. Their structures were established based on extensive analysis of NMR spectroscopic data. As the crude extract possessed anti-leishmanial properties, the compounds were assayed for cytotoxic and anti-parasitic activities in vitro in murine macrophages cells (Raw 264.7) and leishmania promastigotes (L. amazoniensis and L. braziliensis), respectively. The compounds showed moderate cytotoxicity (approximately 70 μg/mL), but are not responsible for the leishmanicidal effect of the extract.  相似文献   
44.
Six new lipodepsipeptides and an additional linear derivative named taxlllaids A–G ( 1 – 7 ) have been identified in the entomopathogenic bacterium Xenorhabdus indica. The structures of the main compounds have been solved by detailed NMR spectroscopic analysis and the structures of minor derivatives were elucidated by a combination of labelling experiments and detailed MS experiments. The absolute configuration of the taxlllaids was deduced by using the advanced Marfey method and analysis of the biosynthesis gene cluster showing the presence of epimerisation domains, which was subsequently proved to be correct by solid‐phase peptide synthesis of all taxlllaids. The exchange of a single amino acid in the adenylation domain was shown to be responsible for substrate promiscuity of the third A domain, resulting in the incorporation of leucine, phenylalanine or tyrosine. Bioactivity testing revealed the taxlllaids to be weakly active against Plasmodium falciparum and against a number of eukaryotic cell lines.  相似文献   
45.
In this study, we investigated the inclusion complexation of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and eight monoterpenes (eucalyptol, geraniol, limonene, linalool, α-pinene, β-pinene, pulegone, and thymol) in aqueous solution and solid state. The formation constants (K f) of inclusion complexes were determined using fluorescence spectroscopy and static headspace gas chromatography. The results indicated the formation of 1:1 inclusion complexes between HP-β-CD and all studied guests. A linear relationship was found between K f values and the hydrophobic character of the monoterpenes expressed as logP. Solid complexes were prepared by the freeze-drying method in a 1:1 (HP-β-CD:monoterpene) molar ratio. Physicochemical characterization of solid inclusion complexes was carried out using Fourier transform infrared spectroscopy and differential scanning calorimetry. Finally, the encapsulation efficiency (EE%) of HP-β-CD was determined using HPLC analysis. Noticeable difference in the EE% was observed between monoterpene hydrocarbons and oxygenated monoterpenes. These results suggested that complexation with HP-β-CD could be a promising strategy to enlarge the application of monoterpenes in cosmetic, pharmaceutical and food industries.  相似文献   
46.
Ruthenium nanocatalysis can provide effective deuteration and tritiation of oxazole, imidazole, triazole and carbazole substructures in complex molecules using D2 or T2 gas as isotopic sources. Depending on the substructure considered, this approach does not only represent a significant step forward in practice, with notably higher isotope uptakes, a broader substrate scope and a higher solvent applicability compared to existing procedures, but also the unique way to label important heterocycles using hydrogen isotope exchange. In terms of applications, the high incorporation of deuterium atoms, allows the synthesis of internal standards for LC-MS quantification. Moreover, the efficacy of the catalyst permits, even under subatmospheric pressure of T2 gas, the preparation of complex radiolabeled drugs owning high molar activities. From a fundamental point of view, a detailed DFT-based mechanistic study identifying undisclosed key intermediates, allowed a deeper understanding of C−H (and N−H) activation processes occurring at the surface of metallic nanoclusters.  相似文献   
47.
Hideyuki Tatsuno  Kasper S. Kjr  Kristjan Kunnus  Tobias C. B. Harlang  Cornelia Timm  Meiyuan Guo  Pavel Chbera  Lisa A. Fredin  Robert W. Hartsock  Marco E. Reinhard  Sergey Koroidov  Lin Li  Amy A. Cordones  Olga Gordivska  Om Prakash  Yizhu Liu  Mads G. Laursen  Elisa Biasin  Frederik B. Hansen  Peter Vester  Morten Christensen  Kristoffer Haldrup  Zoltn Nmeth  Dorottya Srosin Szemes   va Bajnczi  Gyrgy Vank  Tim B. Van Driel  Roberto Alonso‐Mori  James M. Glownia  Silke Nelson  Marcin Sikorski  Henrik T. Lemke  Dimosthenis Sokaras  Sophie E. Canton  Asmus O. Dohn  Klaus B. Mller  Martin M. Nielsen  Kelly J. Gaffney  Kenneth Wrnmark  Villy Sundstrm  Petter Persson  Jens Uhlig 《Angewandte Chemie (International ed. in English)》2020,59(1):364-372
Iron N‐heterocyclic carbene (NHC) complexes have received a great deal of attention recently because of their growing potential as light sensitizers or photocatalysts. We present a sub‐ps X‐ray spectroscopy study of an FeIINHC complex that identifies and quantifies the states involved in the deactivation cascade after light absorption. Excited molecules relax back to the ground state along two pathways: After population of a hot 3MLCT state, from the initially excited 1MLCT state, 30 % of the molecules undergo ultrafast (150 fs) relaxation to the 3MC state, in competition with vibrational relaxation and cooling to the relaxed 3MLCT state. The relaxed 3MLCT state then decays much more slowly (7.6 ps) to the 3MC state. The 3MC state is rapidly (2.2 ps) deactivated to the ground state. The 5MC state is not involved in the deactivation pathway. The ultrafast partial deactivation of the 3MLCT state constitutes a loss channel from the point of view of photochemical efficiency and highlights the necessity to screen transition‐metal complexes for similar ultrafast decays to optimize photochemical performance.  相似文献   
48.
The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices.  相似文献   
49.
Hot carrier (HC) cooling accounts for the significant energy loss in lead halide perovskite (LHP) solar cells. Here, we study HC relaxation dynamics in Mn-doped LHP CsPbI3 nanocrystals (NCs), combining transient absorption spectroscopy and density functional theory (DFT) calculations. We demonstrate that Mn2+ doping (1) enlarges the longitudinal optical (LO)–acoustic phonon bandgap, (2) enhances the electron–LO phonon coupling strength, and (3) adds HC relaxation pathways via Mn orbitals within the bands. The spectroscopic study shows that the HC cooling process is decelerated after doping under band-edge excitation due to the dominant phonon bandgap enlargement. When the excitation photon energy is larger than the optical bandgap and the Mn2+ transition gap, the doping accelerates the cooling rate owing to the dominant effect of enhanced carrier–phonon coupling and relaxation pathways. We demonstrate that such a phenomenon is optimal for the application of hot carrier solar cells. The enhanced electron–LO phonon coupling and accelerated cooling of high-temperature hot carriers efficiently establish a high-temperature thermal quasi-equilibrium where the excessive energy of the hot carriers is transferred to heat the cold carriers. On the other hand, the enlarged phononic band-gap prevents further cooling of such a quasi-equilibrium, which facilitates the energy conversion process. Our results manifest a straightforward methodology to optimize the HC dynamics for hot carrier solar cells by element doping.

Mn doping modulates the hot carrier dynamics in all-inorganic lead halide perovskite nanocrystals according to the excitation energy.  相似文献   
50.
The electrophilic ipso-reactions of a tBu-calix[6]arene that presents alternate O-methyl and O-2-methylen-N-methyl-imidazolyl groups (1) at the small rim have been studied. Whereas 1 underwent per-sulfonation in sulfuric acid, it selectively reacted with nitric acid to yield a tris-nitro derivative. The ipso-nitration occurred regioselectively on the calixarene anisol units. The reaction has been studied with various tBu-calixarenes (2-11) presenting alternate anisol and phenol ether units. The regioselectivity of the process appeared to be correlated to the presence of a protonable site on the O-substituent. It is proposed that the corresponding protonated heteroatom (N for the amines, O for the amides and the carboxylic acid), situated in the gamma or epsilon position of the phenoxy moieties, deactivates the corresponding aromatic ring by removing electron density through intramolecular hydrogen bonding. The high control operated by the O-substituents at the small rim even allowed the selective ipso-nitration of partially detertiobutylated calixarene 1(H3). Hence, these findings open new routes to a wide range of nonsymmetrically substituted calixarenes at the large rim.  相似文献   
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