共查询到20条相似文献,搜索用时 15 毫秒
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Conformational features of α,β‐disubstituted β2,3‐dipeptide models have been studied with quantum mechanics method. Geometries were optimized with the HF/6‐31G** method, and energies were evaluated with the B3LYP/6‐31G** method. Solvent effect was evaluated with the SCIPCM method. For (2S,3S)‐β2,3‐dipeptide model 1 , a six‐membered‐ring hydrogen bonded structure is most stable. However, the conformation corresponding to the formation of the 14‐helix is only about 1.7 kcal/mol less stable in methanol solution, indicating that the 14‐helix is favored if a (2S,3S)‐β2,3‐polypeptide contains more than 5 residues. On the other hand, the conformation corresponding to the formation of β‐sheet is most stable for (2R,3S)‐β2,3‐dipeptide model 2 , suggesting that this type of β‐peptides is intrinsically favored for the formation of β‐sheet secondary structure. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(8):2119-2123
Peptide foldamers containing both cis ‐β‐aminocyclopentanecarboxylic acid and α‐amino acid residues combined in various sequence patterns (ααβ, αααβ, αβααβ, and ααβαααβ) were screened using CD and NMR spectroscopy for the tendency to form helices. ααβ‐Peptides were found to fold into an unprecedented and well‐defined 16/17/15/18/14/17‐helix. By extending the length of the sequence or shifting a fragment of the sequence from one terminus to another in ααβ‐peptides, the balance between left‐handed and right‐handed helix populations present in the solution can be controlled. Engineering of the peptide sequence could lead to compounds with either a strong propensity for the selected helix sense or a mixture of helical conformations of opposite senses. 相似文献
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Dr. Christofer Lendel Dr. Morten Bjerring Dr. Anatoly Dubnovitsky Robert T. Kelly Dr. Andrei Filippov Prof. Dr. Oleg N. Antzutkin Prof. Dr. Niels Chr. Nielsen Prof. Dr. Torleif Härd 《Angewandte Chemie (International ed. in English)》2014,53(47):12756-12760
Oligomeric and protofibrillar aggregates formed by the amyloid‐β peptide (Aβ) are believed to be involved in the pathology of Alzheimer’s disease. Central to Alzheimer pathology is also the fact that the longer Aβ42 peptide is more prone to aggregation than the more prevalent Aβ40. Detailed structural studies of Aβ oligomers and protofibrils have been impeded by aggregate heterogeneity and instability. We previously engineered a variant of Aβ that forms stable protofibrils and here we use solid‐state NMR spectroscopy and molecular modeling to derive a structural model of these. NMR data are consistent with packing of residues 16 to 42 of Aβ protomers into hexameric barrel‐like oligomers within the protofibril. The core of the oligomers consists of all residues of the central and C‐terminal hydrophobic regions of Aβ, and hairpin loops extend from the core. The model accounts for why Aβ42 forms oligomers and protofibrils more easily than Aβ40. 相似文献
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Atsushi Suenaga Dr. Tetsu Narumi Dr. Noriyuki Futatsugi Dr. Ryoko Yanai Yousuke Ohno Dr. Noriaki Okimoto Dr. Makoto Taiji Dr. 《化学:亚洲杂志》2007,2(5):591-598
Short peptides that fold into β‐hairpins are ideal model systems for investigating the mechanism of protein folding because their folding process shows dynamics typical of proteins. We performed folding, unfolding, and refolding molecular dynamics simulations (total of 2.7 μs) of the 10‐residue β‐hairpin peptide chignolin, which is the smallest β‐hairpin structure known to be stable in solution. Our results revealed the folding mechanism of chignolin, which comprises three steps. First, the folding begins with hydrophobic assembly. It brings the main chain together; subsequently, a nascent turn structure is formed. The second step is the conversion of the nascent turn into a tight turn structure along with interconversion of the hydrophobic packing and interstrand hydrogen bonds. Finally, the formation of the hydrogen‐bond network and the complete hydrophobic core as well as the arrangement of side‐chain–side‐chain interactions occur at approximately the same time. This three‐step mechanism appropriately interprets the folding process as involving a combination of previous inconsistent explanations of the folding mechanism of the β‐hairpin, that the first event of the folding is formation of hydrogen bonds and the second is that of the hydrophobic core, or vice versa. 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(16):4518-4522
Detailed herein is the photochemical organocatalytic enantioselective α‐alkylation of aldehydes with (phenylsulfonyl)alkyl iodides. The chemistry relies on the direct photoexcitation of enamines to trigger the formation of reactive carbon‐centered radicals from iodosulfones, while the ground‐state chiral enamines provide effective stereochemical control over the radical trapping process. The phenylsulfonyl moiety, acting as a redox auxiliary group, facilitates the generation of radicals. In addition, it can eventually be removed under mild reducing conditions to reveal methyl and benzyl groups. 相似文献
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Hongyan Cao Yunyun Wang Yuan Gao Xinli Deng Yulong Cong Ye Liu Xingyu Jiang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(6):1640-1645
Intermolecular forces constrain peptide conformation. However, the role of each intermolecular force in constraining peptide conformation remains poorly understood. In this work, we show that aromatic–aromatic interactions drive peptides into β‐sheets, and the hydrophobic effect determines the assembly speed of peptides. By using intermolecular forces to artificially control the assembly of β‐sheets, a multi‐modal analytical system was developed that allows five readouts and dual qualitative–quantitative analysis, and satisfies both point‐of‐care testing (POCT) and laboratory‐based testing. For Mycoplasma Pneumoniae diagnosis, this system eradicates misdiagnosis (from 30 % to 0 %) and broadens the linear range by three‐fold, both of which are critical for guiding therapy. This work not only illustrates exact roles of intermolecular forces in driving the formation of β‐sheets, but also provides a guideline for the construction of a multi‐modal analytical system for disease diagnosis. 相似文献
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Zhen Lei Arghya Banerjee Elena Kusevska Eric Rizzo Peng Liu Ming‐Yu Ngai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(22):7396-7401
Late‐stage synthesis of α,β‐unsaturated aryl ketones remains an unmet challenge in organic synthesis. Reported herein is a photocatalytic non‐chain‐radical aroyl chlorination of alkenes by a 1,3‐chlorine atom shift to form β‐chloroketones as masked enones that liberate the desired enones upon workup. This strategy suppresses side reactions of the enone products. The reaction tolerates a wide array of functional groups and complex molecules including derivatives of peptides, sugars, natural products, nucleosides, and marketed drugs. Notably, addition of 2,6‐di‐tert‐butyl‐4‐methyl‐pyridine enhances the quantum yield and efficiency of the cross‐coupling reaction. Experimental and computational studies suggest a mechanism involving PCET, formation and reaction of an α‐chloro‐α‐hydroxy benzyl radical, and 1,3‐chlorine atom shift. 相似文献