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排序方式: 共有987条查询结果,搜索用时 15 毫秒
1.
Prof. Dr. Jevgenij A. Raskatov Dr. Scott Virgil Dr. Hsiau-Wei Lee Dr. Lawrence M. Henling Ka Chan Ariel J. Kuhn Alejandro R. Foley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4467-4470
Methionine (Met) oxidation is an important biological redox node, with hundreds if not thousands of protein targets. The process yields methionine oxide (MetO). It renders the sulfur chiral, producing two distinct, diastereomerically related products. Despite the biological significance of Met oxidation, a reliable protocol to separate the resultant MetO diastereomers is currently lacking. This hampers our ability to make peptides and proteins that contain stereochemically defined MetO to then study their structural and functional properties. We have developed a facile method that uses supercritical CO2 chromatography and allows obtaining both diastereomers in purities exceeding 99 %. 1H NMR spectra were correlated with X-ray structural information. The stereochemical interconversion barrier at sulfur was calculated as 45.2 kcal mol−1, highlighting the remarkable stereochemical stability of MetO sulfur chirality. Our protocol should open the road to synthesis and study of a wide variety of stereochemically defined MetO-containing proteins and peptides. 相似文献
2.
NMR is a fast method for obtaining a holistic snapshot of the metabolome and also offers quantitative information without separating the compounds present in a complex mixture. Identification of the metabolites present in a plant extract sample is a crucial step for all plant metabolomics studies. In the present work, we used various two dimensional (2D) NMR methods such as J-resolved NMR, total correlation spectroscopy (TOCSY), and heteronuclear single quantum coherence sensitivity enhanced NMR spectroscopy for the identification of 36 common metabolites present in Coriandrum sativum L. seed extract. The identified metabolites belong to the following classes: organic acids, amino acids, and carbohydrates. 1H NMR spectra of such complex mixtures in general display tremendous signal overlap due to the presence of a large number of metabolites with closely resonating multiplet signals. This signal overlapping leads to ambiguity in an assignment, and hence, identification of metabolites becomes tedious or impossible in many cases. Therefore, the utility of pure-shift proton spectrum along the indirect (F1) dimension of the F1-PSYCHE-TOCSY spectrum is demonstrated for overcoming ambiguity in assignment of metabolites in crowded spectral regions from Coriandrum sativum L. seed extract sample. Because pure-shift NMR methods yield ultrahigh resolution spectrum (i.e., a singlet peak per chemical site) along one or more dimensions, such spectra provide better identification of metabolites compared with regular 2D TOCSY where signal overlap and peak distortions lead to ambiguity in the assignment. Nine metabolites were unambiguously assigned by pure-shift F1-PSYCHE-TOCSY spectrum, which was unresolved in regular TOCSY spectrum. 相似文献
3.
4.
G. Yu S. H. Jacobson N. Kiyavash 《Stochastics An International Journal of Probability and Stochastic Processes》2020,92(2):223-264
ABSTRACTWe provide an asymptotic analysis of multi-objective sequential stochastic assignment problems (MOSSAP). In MOSSAP, a fixed number of tasks arrive sequentially, with an n-dimensional value vector revealed upon arrival. Each task is assigned to one of a group of known workers immediately upon arrival, with the reward given by an n-dimensional product-form vector. The objective is to maximize each component of the expected reward vector. We provide expressions for the asymptotic expected reward per task for each component of the reward vector and compare the convergence rates for three classes of Pareto optimal policies. 相似文献
5.
Total Synthesis,Stereochemical Assignment,and Field‐Testing of the Sex Pheromone of the Strepsipteran Xenos peckii 下载免费PDF全文
Dr. Huimin Zhai Michael Hrabar Regine Gries Prof. Gerhard Gries Prof. Robert Britton 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(18):6190-6193
The sex pheromone of the endoparasitoid insect Xenos peckii (Strepsiptera: Xenidae) was recently identified as (7E,11E)‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal. Herein we report the asymmetric synthesis of three candidate stereostructures for this pheromone using a synthetic strategy that relies on an sp3–sp2 Suzuki–Miyaura coupling to construct the correctly configured C7‐alkene function. Comparison of 1H NMR spectra derived from the candidate stereostructures to that of the natural sex pheromone indicated a relative configuration of (3R*,5S*,9R*). Chiral gas chromatographic (GC) analyses of these compounds supported an assignment of (3R,5S,9R) for the natural product. Furthermore, in a 16‐replicate field experiment, traps baited with the synthetic (3R,5S,9R)‐enantiomer alone or in combination with the (3S,5R,9S)‐enantiomer captured 23 and 18 X. peckii males, respectively (mean±SE: 1.4±0.33 and 1.1±0.39), whereas traps baited with the synthetic (3S,5R,9S)‐enantiomer or a solvent control yielded no captures of males. These strong field trapping data, in combination with spectroscopic and chiral GC data, unambiguously demonstrate that (3R,5S,9R,7E,11E)‐3,5,9,11‐tetramethyl‐7,11‐tridecadienal is the X. peckii sex pheromone. 相似文献
6.
Here we describe the story behind the link between molecular chirality and macroscopic phenomena, the latter being a probe for the direct assignment of absolute configuration of chiral molecules. First, a brief tour of the history of molecular stereochemistry, starting with the classic experiment reported by Pasteur in 1848 on the separation of enantiomorphous crystals of a salt of tartaric acid, and his conclusion that the molecules of life are chiral of single-handedness. With time, this study raised, inter alia, two fundamental questions: the absolute configuration of chiral molecules and how a molecule of given configuration shapes the enantiomorphous morphology of its crystal. As for the first question, following the beginning of crystal structure determination by X-ray diffraction in 1912, it took almost 40 years before Bijvoet assigned molecular chirality through the esoteric method involving anomalous X-ray scattering. We have been able to address and link both questions through ‘everyday concepts of left and right’ (in the words of Jack Dunitz) by the use of ‘tailor-made’ auxiliaries. By such means, it proved possible to reveal, through morphology, etch patterns, epitaxy and symmetry reduction of both chiral and, paradoxically, centrosymmetric crystals, the basic chiral symmetry of the molecules of life, the α-amino acids and sugars. 相似文献
7.
8.
An automated NMR chemical shift assignment algorithm was developed using multi-objective optimization techniques. The problem is modeled as a combinatorial optimization problem and its objective parameters are defined separately in different score functions. Some of the heuristic approaches of evolutionary optimization are employed in this problem model. Both, a conventional genetic algorithm and multi-objective methods, i.e., the non-dominated sorting genetic algorithms II and III (NSGA2 and NSGA3), are applied to the problem. The multi-objective approaches consider each objective parameter separately, whereas the genetic algorithm followed a conventional way, where all objectives are combined in one score function. Several improvement steps and repetitions on these algorithms are performed and their combinations are also created as a hyper-heuristic approach to the problem. Additionally, a hill-climbing algorithm is also applied after the evolutionary algorithm steps. The algorithms are tested on several different datasets with a set of 11 commonly used spectra. The test results showed that our algorithm could assign both sidechain and backbone atoms fully automatically without any manual interactions. Our approaches could provide around a 65% success rate and could assign some of the atoms that could not be assigned by other methods. 相似文献
9.
Single nucleotide polymorphisms of mitochondrial DNA HVS‐I and HVS‐II in Chinese Bai ethnic group 下载免费PDF全文
Feng Chen Cai‐Yong Yin Xiao‐Qin Qian Han‐Ting Fan Ya‐Jun Deng Yu‐Dang Zhang Hao‐Tian Meng Chun‐Mei Shen Chun‐Hua Yang Rui Jin Bo‐Feng Zhu Peng Xu 《Electrophoresis》2015,36(6):930-936
For forensic and population genetic purposes, a total of 125 unrelated volunteers’ blood samples were collected from Chinese Bai ethnic minority group to analyze sequence variation of two hypervariable segments (HVS‐I and HVS‐II) in the mitochondrial DNA control region. Comparing the HVS‐I and HVS‐II sequences of the 125 Chinese Bais to the Anderson reference sequence, we found 86 polymorphic loci in HVS‐I and 40 in HVS‐II in mitochondrial DNA sequences of the Chinese Bai ethnic minority group, which defined 93 and 53 different haplotypes, respectively. Haplotype diversity and the mean pairwise differences were 0.992 ± 0.003 and 6.553 in HVS‐I, and 0.877 ± 0.027 and 2.407 in HVS‐II, respectively. We defined four macrohaplogroups R, M, N and D with the proportions ranging from 9.6% to 40.0%. With the analysis of the hypervariable domain from nucleotide 16 180–16 193 in HVS‐I, our study revealed new haplotypes of sequence variations. In addition, the Fst metric, phylogenetic tree, and principal component analysis demonstrated a close genetic relationship between the Bai group and Chinese Han populations from South China, Changsha, and Guangdong. The results support that the Bai group is a multiorigin ethnic minority that has merged with the Chinese Han population. 相似文献
10.
Teng‐Shuo Zhang Rui Du Yan‐Yin Zhao Jia‐Dan Xue Hui‐Gang Wang Xuming Zheng 《Journal of Raman spectroscopy : JRS》2016,47(3):299-309
The B‐band resonance Raman spectra of 2(1H)‐pyridinone (NHP) in water and acetonitrile were obtained, and their intensity patterns were found to be significantly different. To explore the underlying excited state tautomeric reaction mechanisms of NHP in water and acetonitrile, the vibrational analysis was carried out for NHP, 2(1D)‐pyridinone (NDP), NHP–(H2O)n (n = 1, 2) clusters, and NDP–(D2O)n (n = 1, 2) clusters on the basis of the FT‐Raman experiments, the B3LYP/6‐311++G(d,p) computations using PCM solvent model, and the normal mode analysis. Good agreements between experimental and theoretically predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands in both the FT‐Raman and the resonance Raman spectra. The results indicated that most of the B‐band resonance Raman spectra in H2O was assignable to the fundamental, overtones, and combination bands of about ten vibration modes of ring‐type NHP–(H2O)2 cluster, while most of the B‐band resonance Raman spectra in CH3CN was assigned to the fundamental, overtones, and combination bands of about eight vibration modes of linear‐type NHP–CH3CN. The solvent effect of the excited state enol‐keto tautomeric reaction mechanisms was explored on the basis of the significant difference in the short‐time structural dynamics of NHP in H2O and CH3CN. The inter‐molecular and intra‐molecular ESPT reaction mechanisms were proposed respectively to explain the Franck–Condon region structural dynamics of NHP in H2O and CH3CN.Copyright © 2015 John Wiley & Sons, Ltd. 相似文献