共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
Tim Görlich Dr. Peter Coburger Eric S. Yang Prof. Dr. Jose M. Goicoechea Prof. Dr. Hansjörg Grützmacher Prof. Dr. Christian Müller 《Angewandte Chemie (International ed. in English)》2023,62(32):e202217749
We review the known chemistry of the cyaphide ion, (C≡P)−. This remarkable diatomic anion has been the subject of study since the late nineteenth century, however its isolation and characterization eluded chemists for almost a hundred years. In this mini-review, we explore the pioneering synthetic experiments that first allowed for its isolation, as well as more recent developments demonstrating that cyaphide transfer is viable in well-established salt-metathesis protocols. The physical properties of the cyaphide ion are also explored in depth, allowing us to compare and contrast the chemistry of this ion with that of its lighter congener cyanide (an archetypal strong field ligand and important organic functional group). Recent studies show that the cyaphide ion has the potential to be used as a versatile chemical regent for the synthesis of novel molecules and materials, hinting at many interesting future avenues of investigation. 相似文献
4.
5.
6.
Kerim Samedov Yannic Heider Yuanjing Cai Philipp Willmes Daniel Mühlhausen Volker Huch Robert West David Scheschkewitz Paul W. Percival 《Angewandte Chemie (International ed. in English)》2020,59(37):16007-16012
Understanding the characteristics of radicals formed from silicon‐containing heavy analogues of alkenes is of great importance for their application in radical polymerization. Steric and electronic substituent effects in compounds such as phosphasilenes not only stabilize the Si=P double bond, but also influence the structure and species of the formed radicals. Herein we report our first investigations of radicals derived from phosphasilenes with Mes, Tip, Dur, and NMe2 substituents on the P atom, using muon spin spectroscopy and DFT calculations. Adding muonium (a light isotope of hydrogen) to phosphasilenes reveals that: a) the electron‐donor NMe2 and the bulkiest Tip‐substituted phosphasilenes form several muoniated radicals with different rotamer conformations; b) bulky Dur‐substituted phosphasilene forms two radicals (Si‐ and P‐centred); and c) Mes‐substituted phosphasilene mainly forms one species of radical, at the P centre. These significant differences result from intramolecular substituent effects. 相似文献
7.
Prof. Armido Studer Prof. Dennis P. Curran 《Angewandte Chemie (International ed. in English)》2016,55(1):58-102
The area of catalysis of radical reactions has recently flourished. Various reaction conditions have been discovered and explained in terms of catalytic cycles. These cycles rarely stand alone as unique paths from substrates to products. Instead, most radical reactions have innate chains which form products without any catalyst. How do we know if a species added in “catalytic amounts” is a catalyst, an initiator, or something else? Herein we critically address both catalyst‐free and catalytic radical reactions through the lens of radical chemistry. Basic principles of kinetics and thermodynamics are used to address problems of initiation, propagation, and inhibition of radical chains. The catalysis of radical reactions differs from other areas of catalysis. Whereas efficient innate chain reactions are difficult to catalyze because individual steps are fast, both inefficient chain processes and non‐chain processes afford diverse opportunities for catalysis, as illustrated with selected examples. 相似文献
8.
GUO Li-li WANG Dong-xia Roger W. Roeske 《高等学校化学研究》2006,22(2):265-266
Introduction PeptidesmadeupofalternatingL andD amino acidscanformβhelicesasingramicidinAorcyclic peptidesthataggregatetoformtubes[1].Inbothcases thestructuresarehollowwithallthesidechainspro jectingoutwards.Kennedyetal.[2]postulatedthat peptideshavingthe… 相似文献
9.
Some of the most interesting aspects of free radical chemistry that emerged in the last two decades are radical enzyme mechanisms, cell signaling cascades, antioxidant activities, and free radical-induced damage of biomolecules. In addition, identification of modified biomolecules opened the way for the evaluation of in vivo damage through biomarkers. When studying free radical-based chemical mechanisms, it is very important to establish biomimetic models, which allow the experiments to be performed in a simplified environment, but suitably designed to be in strict connection with cellular conditions. The 28 papers (11 reviews and 17 articles) published in the two Special Issues of Molecules on “Biomimetic Radical Chemistry and Applications (2019 and 2021)” show a remarkable range of research in this area. The biomimetic approach is presented with new insights and reviews of the current knowledge in the field of radical-based processes relevant to health, such as biomolecular damages and repair, signaling and biomarkers, biotechnological applications, and novel synthetic approaches. 相似文献
10.
离子交换树脂在分析化学中的应用 总被引:1,自引:0,他引:1
简要评述了离子交换树脂在分析化学中的应用。包括离子交换树脂预富集技术从稀溶液中浓缩痕量离子,离子交换树脂相分光光度法测定微量离子,离子色谱在无机分析中的应用,以及离子交换树脂在有机分析与生化分析中的应用。 相似文献
11.
Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexants and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R•+), carbon-centered radicals (R•), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R•+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with various ligands. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. 相似文献
12.
氨基酸、多肽的环糊精化学 总被引:7,自引:0,他引:7
本文着重介绍了氨基酸、多肽-环糊精连接物的合成,分子识别和自组装,对环糊精及其衍生物与氨基酸、多肽的包合行为,异构体识别和仿酶合成作了简要概述。 相似文献
13.
Daiki Shimizu Dr. Keisuke Fujimoto Prof. Dr. Atsuhiro Osuka 《Angewandte Chemie (International ed. in English)》2018,57(30):9434-9438
Nitrenium ions, isoelectronic nitrogen counterparts of carbenes, are important intermediates in various biological and chemical processes. Herein we describe the first synthesis and characterization of a stable nitrenium ion without resonance stabilization by adjoining amino groups. Namely, a stable salt of a diporphyrinylnitrenium ion was synthesized by stepwise oxidation of the corresponding diporphyrinylamine through a stable aminyl radical. The nitrenium ion exhibits characteristic features such as a singlet ground state, enhanced double‐bond character of the central C?N bonds, no reactivity toward water and methanol, and negative solvatochromic behavior. 相似文献
14.
Michael G. Leeming Jonathan M. White Richard A. J. O’Hair William A. Donald 《Journal of the American Society for Mass Spectrometry》2014,25(3):427-438
Protonated nitroarginine, [RNO2 + H]+, which contains the nitroguanidine ‘explosophore,’ undergoes homolytic N – N nitro-imine bond cleavage to expel NO2 ? and form a radical cation of arginine in high yield (100 % relative abundance) upon low-energy collision-induced dissociation (CID). Other ionization states of nitroarginine, including [RNO2 - H]–, and a fixed-charge derivative of nitroarginine do not expel NO2 ? (<1 %), but instead dissociate via heterolytic bond cleavage with abundant losses of small molecules (N2O and H2N2O2) from the nitroguanidine group. The effects of proton mobility on the CID reactions of nitroarginine containing peptides was investigated for peptide derivatives of leucine enkephalin, including XYGGFLRNO2, X = D, G, K, and R, by examining the different protonation states: [M – H]–; [M + H]+; and [M + 2H]2+. For [M + H]+ containing the less basic N-terminal residues (X = D, G) and all [M + 2H]2+, mobile proton fragmentation reactions that result in peptide sequence ions dominate. In contrast, for peptides containing the basic N-terminal residues (R and K), the CID spectra of both the [M – H]– and [M + H]+ are dominated by the losses of small even-electron neutrals from the nitroarginine side-chain. The fraction of nitroguanidine directed fragmentation of the nitroarginine side chain that results in bond homolysis to form [XYGGFLR]+? by expulsion of NO2 ? increases by more than 10 times as the protonation state changes from [M – H]– (<10 %) to [M + 2H]2+ (ca. 90 %) and by about four times as the acidity of the [M + H]+ N-terminal residue increases from R (19.0 %) to D (76.5 %). These results indicate that protonated peptides containing nitroarginine can undergo non-canonical mobile proton triggered radical fragmentation. Figure
? 相似文献
15.
16.
Radical anions are reactive intermediates in a variety of organic reactions. They make possible several unique synthetic conversions and provide an opportunity for investigating structural relationships. Examples of such reactions are given and current mechanistic views are discussed. 相似文献
17.
Victor Adebomi Ryan D. Cohen Rachel Wills Holland Andrew Hays Chavers Gary E. Martin Monika Raj 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):19249-19256
Here, we report a novel “CyClick” strategy for the macrocyclization of peptides that works in an exclusively intramolecular fashion thereby precluding the formation of dimers and oligomers via intermolecular reactions. The CyClick chemistry is highly chemoselective for the N‐terminus of the peptide with a C‐terminal aldehyde. In this protocol, the peptide conformation internally directs activation of the backbone amide bond and thereby facilitates formation of a stable 4‐imidazolidinone‐fused cyclic peptide with high diastereoselectivity (>99 %). This method is tolerant to a variety of peptide aldehydes and has been applied for the synthesis of 12‐ to 23‐membered rings with varying amino acid compositions in one pot under mild reaction conditions. The reaction generated peptide macrocycles featuring a 4‐imidazolidinone in their scaffolds, which acts as an endocyclic control element that promotes intramolecular hydrogen bonding and leads to macrocycles with conformationally rigid turn structures. 相似文献
18.
Akihiko Ueno Tomoko Shimizu Hisakazu Mihara Keita Hamasaki K. Pitchumani 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):49-52
AC17, which is composed of 17 amino acids and has an azobenzene moiety but has no cyclodextrin (CD) unit in the side chain, exhibits 54% helix content. However, AC17, which has both trans-azobenzene and -CD, shows 82% helix content. This result suggests that the helix structure is stabilized by host (CD)-guest (azobenzene) bridge in the side chain of the peptide. The helix content changed by trans-cis photoisomerization as shown by 64% helix content for AC17 in its cis form. This result suggests that cis-azobenzene unit is excluded from the -CD cavity, thus resulting in the smaller helix content. The helix contents for AC17, which has both azobenzene and -CD, are 94% in the cis form and 87% in the trans form, suggesting that the cis form is included in the -CD cavity. Azobenzene-tagged CD-peptide hybrids with histidine unit were also prepared and photoregulation of catalytic activity in ester hydrolysis was examined. 相似文献
19.
20.
Moore B Sun Q Hsu JC Lee AH Yoo GC Ly T Julian RR 《Journal of the American Society for Mass Spectrometry》2012,23(3):460-468
The fragmentation chemistry of anionic deprotonated hydrogen-deficient radical peptides is investigated. Homolytic photodissociation
of carbon–iodine bonds with 266 nm light is used to generate the radical species, which are subsequently subjected to collisional
activation to induce further dissociation. The charges do not play a central role in the fragmentation chemistry; hence deprotonated
peptides that fragment via radical directed dissociation do so via mechanisms which have been reported previously for protonated
peptides. However, charge polarity does influence the overall fragmentation of the peptide. For example, the absence of mobile
protons favors radical directed dissociation for singly deprotonated peptides. Similarly, a favorable dissociation mechanism
initiated at the N-terminus is more notable for anionic peptides where the N-terminus is not protonated (which inhibits the
mechanism). In addition, collisional activation of the anionic peptides containing carbon–iodine bonds leads to homolytic
cleavage and generation of the radical species, which is not observed for protonated peptides presumably due to competition
from lower energy dissociation channels. Finally, for multiply deprotonated radical peptides, electron detachment becomes
a competitive channel both during the initial photoactivation and following subsequent collisional activation of the radical.
Possible mechanisms that might account for this novel collision-induced electron detachment are discussed. 相似文献