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991.
Ana Diniz Dr. Helena Coelho Dr. Jorge S. Dias Dr. Sandra J. van Vliet Prof. Dr. Jesús Jiménez-Barbero Prof. Dr. Francisco Corzana Prof. Dr. Eurico J. Cabrita Dr. Filipa Marcelo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(61):13945-13955
The human macrophage galactose-type lectin (MGL), expressed on macrophages and dendritic cells (DCs), modulates distinct immune cell responses by recognizing N-acetylgalactosamine (GalNAc) containing structures present on pathogens, self-glycoproteins, and tumor cells. Herein, NMR spectroscopy and molecular dynamics (MD) simulations were used to investigate the structural preferences of MGL against different GalNAc-containing structures derived from the blood group A antigen, the Forssman antigen, and the GM2 glycolipid. NMR spectroscopic analysis of the MGL carbohydrate recognition domain (MGL-CRD, C181-H316) in the absence and presence of methyl α-GalNAc (α-MeGalNAc), a simple monosaccharide, shows that the MGL-CRD is highly dynamic and its structure is strongly altered upon ligand binding. This plasticity of the MGL-CRD structure explains the ability of MGL to accommodate different GalNAc-containing molecules. However, key differences are observed in the recognition process depending on whether the GalNAc is part of the blood group A antigen, the Forssman antigen, or GM2-derived structures. These results are in accordance with molecular dynamics simulations that suggest the existence of a distinct MGL binding mechanism depending on the context of GalNAc moiety presentation. These results afford new perspectives for the rational design of GalNAc modifications that fine tune MGL immune responses in distinct biological contexts, especially in malignancy. 相似文献
992.
Prof. Piotr Bałczewski Dr. Emilia Kowalska Dr. Ewa Różycka-Sokołowska Dr. Joanna Skalik Dr. Krzysztof Owsianik Dr. Marek Koprowski Dr. Bernard Marciniak Dr. Dariusz Guziejewski Prof. Witold Ciesielski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14148-14161
The highly substituted mono-aryl/alkylthio-(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di-aryl/alkylthio-substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio-anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG-substituted anthracenes (EDG=electron-donating group, EWG=electron-withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio-Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o-(1,3-dithian-2-yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono-aryl/alkylthio-substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD-DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono-aryl/alkylthio-substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen. 相似文献
993.
Nadine Wellington Sabrina Macklai Prof. Philip Britz-McKibbin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(67):15277-15280
A zwitterionic heterocyclic boronic acid based on 4-isoquinolineboronic acid (IQBA) exhibits the highest reported binding affinity for sialic acid or N-acetylneuraminic acid (Neu5Ac, K=5390±190 m −1) through the formation of a cyclic boronate ester complex under acidic conditions (pH 3). This anomalous pH-dependent binding enhancement does not occur with common neutral saccharides (e.g., glucose, fructose, sorbitiol), because it is mediated via selective complexation to a α-hydroxycarboxylate moiety forming a stable ion pair and ternary complex with Neu5Ac in phosphate buffer. IQBA expands biorecognition beyond classical vicinal diols under neutral or alkaline buffer conditions, which enables the direct analysis of Neu5Ac by native fluorescence with sub-micromolar detection limits. 相似文献
994.
ABSTRACTThe Coupled-Cluster (CC) theory is one of the most successful high precision methods used to solve the stationary Schrödinger equation. In this article, we address the mathematical foundation of this theory with focus on the advances made in the past decade. Rather than solely relying on spectral gap assumptions (non-degeneracy of the ground state), we highlight the importance of coercivity assumptions – Gårding type inequalities – for the local uniqueness of the CC solution. Based on local strong monotonicity, different sufficient conditions for a local unique solution are suggested. One of the criteria assumes the relative smallness of the total cluster amplitudes (after possibly removing the single amplitudes) compared to the Gårding constants. In the extended CC theory the Lagrange multipliers are wave function parameters and, by means of the bivariational principle, we here derive a connection between the exact cluster amplitudes and the Lagrange multipliers. This relation might prove useful when determining the quality of a CC solution. Furthermore, the use of an Aubin–Nitsche duality type method in different CC approaches is discussed and contrasted with the bivariational principle. 相似文献
995.
A. Bande 《Molecular physics》2019,117(15-16):2014-2028
ABSTRACTRecently, highly accurate multi-configuration time-dependent Hartree electron dynamics calculations demonstrated the efficient long-range energy transfer inter-Coulombic decay (ICD) process to happen in charged semiconductor quantum dot (QD) pairs. ICD is initiated by intraband photoexcitation of one of the QDs and leads to electron emission from the other within a duration of about 150 ps. On the same time scale electronically excited states are reported to relax due to the coupling of electrons to acoustic phonons. Likewise, phonons promote ionisation. Here, the QDs' acoustic breathing mode is implemented in a frozen-phonon approach. A detailed comparison of the phonon effects on electron relaxation and emission as well as on the full ICD process is presented, which supports the previous empirical finding of ICD being the dominant decay channel in paired QDs. In addition the relative importance of phonon–phonon, phonon–electron and electron–electron interaction is analysed. 相似文献
996.
997.
998.
999.
Iain J. W. McKean Joanna C. Sadler Anibal Cuetos Amina Frese Luke D. Humphreys Gideon Grogan Paul A. Hoskisson Glenn A. Burley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):17747-17752
A tandem enzymatic strategy to enhance the scope of C‐alkylation of small molecules via the in situ formation of S‐adenosyl methionine (SAM) cofactor analogues is described. A solvent‐exposed channel present in the SAM‐forming enzyme SalL tolerates 5′‐chloro‐5′‐deoxyadenosine (ClDA) analogues modified at the 2‐position of the adenine nucleobase. Coupling SalL‐catalyzed cofactor production with C‐(m)ethyl transfer to coumarin substrates catalyzed by the methyltransferase (MTase) NovO forms C‐(m)ethylated coumarins in superior yield and greater substrate scope relative to that obtained using cofactors lacking nucleobase modifications. Establishing the molecular determinants that influence C‐alkylation provides the basis to develop a late‐stage enzymatic platform for the preparation of high value small molecules. 相似文献
1000.
New carbohydrazone ligand derived from the condensation of carbohydrazide and ethyl acetoacetate, diethyl 3,3′‐(carbonylbis (hydrazin‐2‐yl‐1‐ylidene))(3E,3′E)‐dibutyrate (H4EBC), and its divalent Co, Ni and Cu chelates have been isolated and characterized utilizing convenient methods. 1H‐NMR spectrum of H4EBC revealed the abundance of the enol isomer in solution, which was the opposite to what was shown by the solid IR. This was supported by comparing the theoretical IR of both keto and enol forms. In [Ni(H4EBC)Cl2(H2O)]·2H2O, H4EBC acts as a neutral NON tridentate ligand via the (C=O)carbonyl oxygen atom besides the two (C=N)azomethine nitrogen atoms, while in [Co(H4EBC)Cl2(2H2O)]·2H2O, H4EBC behaves as a neutral NN bidentate ligand through the two azomethine groups. Magnetic measurements inherent to their electronic spectra show that both Ni (II) and Co (II) chelates have octahedron coordination frameworks. On the other hand, the ligand behaves as a binegative tetradentate in [Cu2(H4EBC)Cl2]·H2O via the deprotonated (C=O)carbonyl groups of the ethyl acetoacetate framework and the two (C=N)azomethine groups. In the latter complex, the carbonyl group of the carbohydrazide moiety is converted to hydroxyl group. Cu (II) complex has a tetrahedral geometry according to ESR and electronic spectral data. The reaction of H4EBC with SmCl3·6H2O or LnCl3·7H2O gave single crystals of abnormal product (C16H16N4O4). The packing diagram of this crystal has a chain structure. The photoluminescence spectra of [Cu 2 (H 4 EBC)Cl 2 ]·H 2 O , [Co(H 4 EBC)Cl 2 (H 2 O) 2 ]·2H 2 O and [Ni(H 4 EBC)Cl 2 (H 2 O)]·2H 2 O display emission broad‐bands at 342, 321 and 337 nm, respectively. The microbial behavior of the synthesized moieties was investigated against various bacterial and fungal strains. [Cu2(H4EBC)Cl2]·H2O complex shows the same activity as ampicillin towards Escherichia coli and Staphylococcus aureus with inhibition zones of 26 and 22 mm, respectively. Antioxidant activity is determined using bleomycin‐dependent DNA damage assay besides erythrocyte hemolysis. Finally, in vitro cytotoxic activities against two different cell lines have been examined. 相似文献