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31.
Frey PA 《Chemical record (New York, N.Y.)》2001,1(4):277-289
Research on the mechanism of action of coenzyme B12, adenosylcobalamin, as a graduate student introduced the author to the field of organic free radicals in enzymology. Twenty years later, related work on S-adenosylmethionine (SAM) as a "poor man's coenzyme B12" was initiated in a detailed analysis of the mechanism of action of lysine 2,3-aminomutase (LAM). The interconversion of L-lysine and L-beta-lysine is catalyzed by LAM, which requires SAM, pyridoxal-5'-phosphate (PLP), and a [4Fe-4S] cluster as coenzymes. The mechanism of this reaction has been delineated as a radical isomerization, in which radical formation is initiated by the [4Fe-4S]-dependent cleavage of the SAM into methionine and the 5'-deoxyadenosyl radical. The mechanism of this process is discussed, together with the role of this radical in hydrogen abstraction from lysine to initiate the substrate radical isomerization. The chemistry underlying the functions of SAM, PLP, and [4Fe-4S] in the action of LAM is novel in all respects, except for the formation of a lysine-PLP aldimine at the active site. Of the four free radicals in the mechanism, three have been characterized by EPR spectroscopy. In the suicide inactivation of adenosylcobalamin-dependent dioldehydrase (DDH) by glycolaldehyde, the formation of cob(II)alamin and 5'-deoxyadenosine is accompanied by the conversion of glycolaldehyde to cis-ethanesemidione radical at the active site. The cis-ethanesemidione radical has been characterized by EPR spectroscopy. Its exceptional stability at the active site is the basis for the inactivation of DDH by glycolaldehyde. 相似文献
32.
Jing XU Lan Hua ZHAO Xin Guo WU Hong Mei WANG Ru Xiu CAI College of Chemistry Molecular Science Wuhan University Wuhan Stuff of Chemistry Yunyang Medical College Shiyan College of Resources Environmental Science Wuhan University Wuhan 《中国化学快报》2006,17(7):949-952
Quantification of free radical formation is critical for evaluation and interpretation of many radical-mediated biological processes1-4. Numerous studies have been devoted to the determination of free radicals, but the most of the reports have been focuse… 相似文献
33.
Heinz Günter Viehe Robert Mernyi Lucien Stella Zdenek Janousek 《Angewandte Chemie (International ed. in English)》1979,18(12):917-932
The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals. 相似文献
34.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(1):81-93
Efficient electrochemical syntheses of “homocoenzyme B12” ( 2 , Coβ‐(5′‐deoxy‐5′‐adenosyl‐methyl)‐cob(III )alamin) and “bishomocoenzyme B12” ( 3 , Coβ‐[2‐(5′‐deoxy‐5′‐adenosyl)‐ethyl]‐cob(III )alamin) are reported here. These syntheses have provided crystalline samples of 2 and 3 in 94 and 77 % yield, respectively. In addition, in‐depth investigations of the structures of 2 and 3 in solution were carried out and a high‐resolution crystal structure of 2 was obtained. The two homologues of coenzyme B12 ( 2 and 3 ) are suggested to function as covalent structural mimics of the hypothetical enzyme‐bound “activated” (that is, “stretched” or even homolytically cleaved) states of the B12 cofactor. From crude molecular models, the crucial distances from the corrin‐bound cobalt center to the C5′ atom of the (homo)adenosine moieties in 2 and 3 were estimated to be about 3.0 and 4.4 Å, respectively. These values are roughly the same as those found in the two “activated” forms of coenzyme B12 in the crystal structure of glutamate mutase. Indeed, in the crystal structure of 2 , the cobalt center was observed to be at a distance of 2.99 Å from the C5′ atom of the homoadenosine moiety and the latter was found to be present in the unusual syn conformation. In solution, the organometallic moieties of 2 and 3 were shown to be rather flexible and to be considerably more dynamic than the equivalent group in coenzyme B12. The homoadenosine moiety of 2 was indicated to occur in both the syn and the anti conformations. 相似文献
35.
D. V. Kazakov D. R. Khusnullina N. N. Kabal'nova S. L. Khursan V. V. Shereshovets 《Russian Chemical Bulletin》1997,46(10):1690-1693
The kinetics of the reaction between dimethyldioxirane and 2-methylbutane in acetone solutions were studied spectrophotometrically
at 25 °C. The radical-chain induced decomposition of dioxirane proceeding with the participation of the carbon-centered radicals
follows the first-order kinetic law. The reaction is inhibited by dioxygen. In the presence of O2, the dimethyldioxirane consumption is due to the homolysis of the O−O bond (at a rate constant of 6.3·10−4 s−1) followed by attack of the C−H bond of 2-methylbutane by the biradical formed. The rate constant of the reaction between
the alkyl radical and dimethyldioxirane was estimated.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1785–1788, October, 1997. 相似文献
36.
2-(2-Bromophenyl)ethyl groups have been used as building blocks in radical cyclisation reactions onto azoles to synthesise tri- and tetra-cyclic heterocycles. 2-(2-Bromophenyl)ethyl methanesulfonate was used to alkylate azoles (imidazoles, pyrroles, indoles and pyrazoles) for the synthesis of the radical precursors. Cyclisations of the intermediate aryl radicals yield new 6-membered rings attached to the azoles. The aryl radicals undergo intramolecular homolytic aromatic substitution onto the azole rings. Tributylgermanium hydride has been used with success to replace the toxic and troublesome tributyltin hydride. Initial studies show that the protocol can be used on solid phase resins. The molecular and crystal structures of methyl 5,6-dihydroimidazo[5,1-a]iso-quinoline-1-carboxylate and methyl 5,6-dihydroimidazo[2,1-a]isoquinoline-3-carboxylate were determined by X-ray crystallography. 相似文献
37.
Antonio Alberola 《Journal of organometallic chemistry》2007,692(13):2750-2760
Dithiazolyl radicals with π-stacking motifs have attracted particular interest because of their ability to exhibit spin-switching between diamagnetic distorted π-stacks and paramagnetic regular π-stacked structures through a solid state phase transition. Previous studies indicate that inclusion of electronegative heteroatoms into the backbone favours lamellar structures. This methodology has been extended to the synthesis and characterisation of the title compound, 4′-cyanobenzo-1,3,2-dithiazolyl (4-NCBDTA). Its electronic structure is probed through DFT calculations, cyclic voltammetry and EPR spectroscopy and its crystal structure determined by X-ray powder diffraction at room temperature. Variable temperature SQUID magnetometry reveals that 4-NCBDTA undergoes two phase transitions, each exhibiting bistability; a high temperature phase transition occurs at room temperature (TC↓ = 291 K, TC↑ = 304 K, ΔT = 13 K); whilst the low temperature phase transition occurs below liquid nitrogen temperatures (TC↓ = 37 K, TC↑ = 28 K;ΔT = 9 K). 相似文献
38.
Masanori Sakamoto Takashi Tachikawa Sung Sik Kim Mamoru Fujitsuka Tetsuro Majima 《Chemphyschem》2007,8(11):1701-1706
The association behavior of the dyes 5(6)-carboxyfluorescein and nitrilotriacetic acid (NTA)-modified 5(6)-carboxyfluorescein (F-NTA) in a poly(vinyl alcohol) (PVA) film and in a PVA film containing metal nanoparticles is investigated. Well-dispersed gold nanoparticles (AuNps) and Ni(II)-adsorbed AuNps are formed in the PVA film using in situ photochemical fabrication method. 5(6)-carboxyfluorescein and F-NTA are doped into the films. The F-NTA forms an H-aggregate in the PVA film containing Ni(II)-adsorbed AuNps. It is suggested that the interaction between NTA and Ni(II) adsorbed on the AuNps promotes the formation of the H-aggregate. 相似文献
39.
Bo Jiang Lixing Yang Yong Zhou Guanglin Huang Libin Lin 《Radiation Physics and Chemistry》2002,63(3-6):469-473
The radiation-induced hybrid polymerization in the presence of the N-alkoxypyridinium salt having relatively stable nonnucleophilic anion (PF6−) has been investigated in the paper. Based on the analysis of experimental data and the GPC spectrum, the onium salts not only oxidize -alkoxyalkyl radicals, produced from IBVE in dichloromethane by irradiation, to the corresponding cations, but also give nonnucleophilic anions PF6− for the polymerization system. The experimental results clearly demonstrate that free radical and cationic polymerization mechanisms occurred simultaneously in IBVE/EMP+PF6−/CH2Cl2 systems on irradiation with γ-ray. 相似文献
40.
Yoshitaka Uenoyama Takahide Fukuyama Keisuke Morimoto Osamu Nobuta Hidefumi Nagai Ilhyong Ryu 《Helvetica chimica acta》2006,89(10):2483-2494
The carbonylation of alkanes 1 under radical‐reaction conditions was examined by using ethynyl triflone A as the unimolecular chain‐transfer (UMCT) reagent. Good to moderate yields of ethynyl ketones 2 were prepared by means of this three‐component coupling reaction. Higher CO pressures as well as lower concentrations of triflone A improved the efficiency of the reaction over the direct addition, the latter leading to alkylated ethynes 3 . In contrast to the reaction with A , the reaction of cyclohexane ( 1a ) with allyl triflone B (= ethyl 2‐methylene‐3‐[(trifluoromethyl)sulfonyl]propanoate) in the presence of CO gave a mixture of carbonylation products, including 8a formed from two molecules each of cyclohexane, CO, and allyl triflone B . 相似文献