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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(33):9974-9978
From DNA base pairs to drug–receptor binding, hydrogen (H‐)bonding and aromaticity are common features of heterocycles. Herein, the interplay of these bonding aspects is explored. H‐bond strength modulation due to enhancement or disruption of aromaticity of heterocycles is experimentally revealed by comparing homodimer H‐bond energies of aromatic heterocycles with analogs that have the same H‐bonding moieties but lack cyclic π‐conjugation. NMR studies of dimerization in C6D6 find aromaticity‐modulated H‐bonding (AMHB) energy effects of approximately ±30 %, depending on whether they enhance or weaken aromatic delocalization. The attendant ring current perturbations expected from such modulation are confirmed by chemical shift changes in both observed ring C−H and calculated nucleus‐independent sites. In silico modeling confirms that AMHB effects outweigh those of hybridization or dipole–dipole interaction. 相似文献
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Emmanuel O. Awosanya Joel Lapin Prof. Alexander A. Nevzorov 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3582-3585
In oriented-sample (OS) solid-state NMR of membrane proteins, the angular-dependent dipolar couplings and chemical shifts provide a direct input for structure calculations. However, so far only 1H–15N dipolar couplings and 15N chemical shifts have been routinely assessed in oriented 15N-labeled samples. The main obstacle for extending this technique to membrane proteins of arbitrary topology has remained in the lack of additional experimental restraints. We have developed a new experimental triple-resonance NMR technique, which was applied to uniformly doubly (15N, 13C)-labeled Pf1 coat protein in magnetically aligned DMPC/DHPC bicelles. The previously inaccessible 1Hα–13Cα dipolar couplings have been measured, which make it possible to determine the torsion angles between the peptide planes without assuming α-helical structure a priori. The fitting of three angular restraints per peptide plane and filtering by Rosetta scoring functions has yielded a consensus α-helical transmembrane structure for Pf1 protein. 相似文献
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Thi Hong Anh Truong Fernaldo Richtia Winnerdy Anh Tun Phan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(39):13972-13977
A knot‐like G‐quadruplex peripheral structure is formed by a 7‐nt DNA sequence DL7 (TGTTGGT), in which six out of its seven nucleobases participate in compact base‐pairing interactions. Here, the solution NMR structure of a 24‐nt DNA oligonucleotide containing the DL7 sequence shows the interaction between a two‐layer anti‐parallel G‐quadruplex core and the peripheral knot‐like structure, including the construction of two sharp turns in the DNA backbone. The formation of this novel structural element highlights the intricate properties of single‐stranded DNA folding in presence of G‐quadruplex‐forming motifs. We demonstrated the compatibility of the DL7 knot‐like structure with various G‐quadruplexes, which could have implications in drug design and DNA engineering. 相似文献
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Tomas Orlando Rza Derviolu Marcel Levien Igor Tkach Thomas F. Prisner Loren B. Andreas Vasyl P. Denysenkov Marina Bennati 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1416-1420
Nuclear magnetic resonance (NMR) techniques play an essential role in natural science and medicine. In spite of the tremendous utility associated with the small energies detected, the most severe limitation is the low signal‐to‐noise ratio. Dynamic nuclear polarization (DNP), a technique based on transfer of polarization from electron to nuclear spins, has emerged as a tool to enhance sensitivity of NMR. However, the approach in liquids still faces several challenges. Herein we report the observation of room‐temperature, liquid DNP 13C signal enhancements in organic small molecules as high as 600 at 9.4 Tesla and 800 at 1.2 Tesla. A mechanistic investigation of the 13C‐DNP field dependence shows that DNP efficiency is raised by proper choice of the polarizing agent (paramagnetic center) and by halogen atoms as mediators of scalar hyperfine interaction. Observation of sizable DNP of 13CH2 and 13CH3 groups in organic molecules at 9.4 T opens perspective for a broader application of this method. 相似文献
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Jasmine Viger‐Gravel Claudia E. Avalos Dominik J. Kubicki David Gajan Moreno Lelli Olivier Ouari Anne Lesage Lyndon Emsley 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7327-7331
The introduction of high‐frequency, high‐power microwave sources, tailored biradicals, and low‐temperature magic angle spinning (MAS) probes has led to a rapid development of hyperpolarization strategies for solids and frozen solutions, leading to large gains in NMR sensitivity. Here, we introduce a protocol for efficient hyperpolarization of 19F nuclei in MAS DNP enhanced NMR spectroscopy. We identified trifluoroethanol‐d3 as a versatile glassy matrix and show that 12 mm AMUPol (with microcrystalline KBr) provides direct 19F DNP enhancements of over 100 at 9.4 T. We applied this protocol to obtain DNP‐enhanced 19F and 19F–13C cross‐polarization (CP) spectra for an active pharmaceutical ingredient and a fluorinated mesostructured hybrid material, using incipient wetness impregnation, with enhancements of approximately 25 and 10 in the bulk solid, respectively. This strategy is a general and straightforward method for obtaining enhanced 19F MAS spectra from fluorinated materials. 相似文献
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Hidde Elferink Rens A. Mensink Wilke W. A. Castelijns Oscar Jansen Jeroen P. J. Bruekers Jonathan Martens Jos Oomens Anouk M. Rijs Thomas J. Boltje 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(26):8838-8843
Uronic acids are important constituents of polysaccharides found on the cell membranes of different organisms. To prepare uronic‐acid‐containing oligosaccharides, uronic acid 6,3‐lactones can be employed as they display a fixed conformation and a unique reactivity and stereoselectivity. Herein, we report a highly β‐selective and efficient mannosyl donor based on C‐4 acetyl mannuronic acid 6,3‐lactone donors. The mechanism of glycosylation is established using a combination of techniques, including infrared ion spectroscopy combined with quantum‐chemical calculations and variable‐temperature nuclear magnetic resonance (VT NMR) spectroscopy. The role of these intermediates in glycosylation is assayed by varying the activation protocol and acceptor nucleophilicity. The observed trends are analogous to the well‐studied 4,6‐benzylidene glycosides and may be used to guide the development of next‐generation stereoselective glycosyl donors. 相似文献
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Terra Sztain Ashay Patel D. John Lee Tony D. Davis J. Andrew McCammon Michael D. Burkart 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(32):11004-11008
At the center of many complex biosynthetic pathways, the acyl carrier protein (ACP) shuttles substrates to appropriate enzymatic partners to produce fatty acids and polyketides. Carrier proteins covalently tether their cargo via a thioester linkage to a phosphopantetheine cofactor. Due to the labile nature of this linkage, chemoenzymatic methods have been developed that involve replacement of the thioester with a more stable amide or ester bond. We explored the importance of the thioester bond to the structure of the carrier protein by using solution NMR spectroscopy and molecular dynamics simulations. Remarkably, the replacement of sulfur with other heteroatoms results in significant structural changes, thus suggesting more rigorous selections of isosteric substitutes is needed. 相似文献
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