共查询到20条相似文献,搜索用时 15 毫秒
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Type III dicopper centres are the heart of the reactive sites of enzymes that catalyze the oxidation of catechols. Numerous synthetic model complexes have been prepared to uncover the fundamental chemistry involved in these processes, but progress is still lagging much behind that for heme enzymes. One reason is that the latter gain very much from the informative spectroscopic features of their porphyrin-based metal-chelating ligand. We now introduce sapphyrin-chelated dicopper complexes and show that they may be isolated in different oxidation states and coordination geometries, with distinctive colors and electronic spectra due to the heme-like ligands. The dicopper(i) complex 1-Cu2 was characterized by 1H and 19F NMR spectroscopy of the metal-chelating sapphyrin, the oxygenated dicopper(ii) complex 1-Cu2O2 by EPR, and crystallographic data was obtained for the tetracopper(ii)-bis-sapphyrin complex [1-Cu2O2]2. This uncovered a non-heme [Cu4(OH)4]4− cluster, held together with the aid of two sapphyrin ligands, with structural features reminiscent of those of catechol oxidase. Biomimetic activity was demonstrated by the 1-Cu2O2 catalyzed aerobic oxidation of catechol to quinone; the sapphyrin ligand aided very much in gaining information about reactive intermediates and the rate-limiting step of the reaction.Di-copper chelation by sapphyrin facilitates reaction mechanism investigations and characterization of reactive intermediates regarding biomimetic catechol oxidation. 相似文献
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Hui Wu Huiling Guo Jiaheng Lei Rongguo Zhang Yong Liu 《Frontiers of Chemistry in China》2007,2(3):322-325
The relationship between the structure and performance of polycarboxylate superplasticizer was analyzed. The respective functions
of the structure units of the main and branched chains were discussed. The progress of synthesis and molecular structure design
and synthesis of polycarboxylate superplasticizer were reviewed according to the difference in the structure unit of the main
chain. Results indicated that their performance is related to the structure unit of the main and branched chains, as well
as the position and species of functional groups. The polycarboxylate superplasticizer, which had suitable graft and block
polymers of polyethylene glycol or polyoxyethylene, and a suitable sulfonic group, had small slump loss besides high water-reducing
performance. On the other hand, the hydroxyl group at the end of the chain causes gelation easily. On the basis of the items
mentioned above, as well as the source and cost of raw materials, esterification of polyethylene glycol and acrylic acid were
first adopted using para-toluene sulfonic acid as catalyst, then polymerized with sodium sulfonate methacrylate. A certain
amount of acrylic was added in order to regulate both the polymerization degree of the main chain and the ratio of carboxyl
and sulfonic groups in the branched chain. As a result, the high performance superplasticizer has been synthesized (was obtained).
The divergence of the cement plasma is about 200 mm when the addition amount of superplasticizer is 0.16%–0.20% of cement
weight, and the ratio of the water and cement is 0.29.
Translated from Journal of Wuhan Uniwersity of Technology, 2006, 28(9): 18–20 [译自: 武汉理工大学学报] 相似文献
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Naismith JH 《Chemical Society reviews》2006,35(9):763-770
Chemistry has once again embraced the study of enzyme mechanism as a core discipline. Chemists are uniquely able to contribute to the analysis of enzymes through their understanding of the reactivity of atoms. In this tutorial review for the Corday-Morgan medal, I will concentrate on the work from my lab over the past six years. I discuss enzymes which transform carbohydrates and incorporate halogens. The tutorial review will emphasise the strengths and limitations of structural biology as a means to deducing the chemical mechanism. 相似文献
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Micklefield J 《Chemistry & biology》2004,11(7):887-888
Daptomycin kills otherwise antibiotic-resistant gram-positive pathogens and is the first lipopeptide antibiotic to reach the clinic. Elucidation of its 3D structure and mechanism of action, reported in this issue of Chemistry & Biology, will facilitate the design and engineering of new, potentially life-saving antibiotics. 相似文献
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In this paper we apply Optimal Control techniques, based on the solution of Hamilton–Jacobi–Bellman equations, to simulate
the action of a drug on some sub-networks of an intracellular signal transduction network. The cost functional to be minimized
is chosen in order to take into account, in the models, different factors, like the toxicity of some reactants, the drug action
and the costs of the drug itself. Numerical results are also shown, to test the model. 相似文献
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E. I. Kulish V. P. Volodina R. R. Fatkullina S. V. Kolesov G. E. Zaikov 《Polymer Science Series B》2008,50(7-8):175-176
The features of the enzymatic degradation process mediated by the nonspecific enzymes collagenase and Lyrase are discussed for chitosan films prepared from acetic acid solutions. It was shown that variations in the acid concentration in the initial solution have a substantial effect on both the structure of chitosan in the film formed and the degree of degradation of film samples. 相似文献
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He Z Stigers Lavoie KD Bartlett PA Toney MD 《Journal of the American Chemical Society》2004,126(8):2378-2385
Chorismate is the end-product of the shikimate pathway for biosynthesis of carbocyclic aromatic compounds in plants, bacteria, fungi, and some parasites. Anthranilate synthase (AS), 4-amino-4-deoxychorismate synthase (ADCS), and isochorismate synthase (IS) are homologous enzymes that carry out the initial transformations on chorismate in the biosynthesis of tryptophan, p-aminobenzoate, and enterobactin, respectively, and are expected to share a common mechanism. Poor binding to ADCS of two potential transition state analogues for addition of a nucleophile to C6 of chorismate implies that it, like AS and IS, initiates reaction by addition of a nucleophile to C2. Molecular modeling based on the X-ray structures of AS and ADCS suggests that the active site residue K274 is the nucleophile employed by ADCS to initiate the reaction, forming a covalent intermediate. The K274A and K274R mutants were shown to have 265- and 640-fold reduced k(cat) values when PabA (the cognate amidotransferase) + glutamine are used as the nitrogen source. Under conditions of saturating chorismate and NH(4)(+), ADCS and the K274A mutant have identical k(cat) values, suggesting the participation of NH(4)(+) as a rescue agent. Such participation was confirmed by the buildup of 2-amino-2-deoxyisochorismate in the reactions of the K274A mutant but not ADCS, when either NH(4)(+) or PabA + glutamine is used as the nitrogen source. Additionally, the inclusion of ethylamine in the reactions of K274A yields the N-ethyl derivative of 2-amino-2-deoxyisochorismate. A unifying mechanism for AS, ADCS, and IS entailing nucleophile addition to C2 of chorismate in an S(N)2' ' process is proposed. 相似文献
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S Nochi N Shimomura T Hattori T Sato Y Miyake K Tanizawa 《Chemical & pharmaceutical bulletin》1989,37(10):2855-2857
It was found that [4-(2-succinimidoethylthio)phenyl 4-guanidinobenzoate]methanesulfonate (E-3123) inhibits trypsin, thrombin and kallikrein, and its inhibitory activity is most potent toward trypsin. The interactions of these enzymes with E-3123 were studied mainly by using stopped-flow spectrophotometry. E-3123 behaved as a quasi-substrate of the enzymes and the inhibitory property was due to the efficient production of the stable acyl-enzyme. The acylation process with trypsin was exceedingly effective, and the resulting acyl-enzyme was the most stable among the three enzymes tested. This observation affords a rational basis for explaining the action of E-3123, which is a transient inhibitor most active toward trypsin. 相似文献
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含有官能机制特殊树枝状聚合物可作为生物有机分子, 如蛋白质及酵素的模型。本文将介绍这类型官能性树枝聚合物的制备方法。 相似文献
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Cysteine dioxygenase (CDO) is a vital enzyme for human health involved in the biodegradation of toxic cysteine and thereby regulation of the cysteine concentration in the body. The enzyme belongs to the group of nonheme iron dioxygenases and utilizes molecular oxygen to transfer two oxygen atoms to cysteinate to form cysteine sulfinic acid products. The mechanism for this reaction is currently disputed, with crystallographic studies implicating a persulfenate intermediate in the catalytic cycle. To resolve the dispute we have performed quantum mechanics/molecular mechanics (QM/MM) calculations on substrate activation by CDO enzymes using an enzyme monomer and a large QM active region. We find a stepwise mechanism, whereby the distal oxygen atom of the iron(II)-superoxo complex attacks the sulfur atom of cysteinate to form a ring structure, followed by dioxygen bond breaking and the formation of a sulfoxide bound to an iron(IV)-oxo complex. A sulfoxide rotation precedes the second oxygen atom transfer to the substrate to give cysteine sulfinic acid products. The reaction takes place on several low-lying spin-state surfaces via multistate reactivity patterns. It starts in the singlet ground state of the iron(II)-superoxo reactant and then proceeds mainly on the quintet and triplet surfaces. The initial and rate-determining attack of the superoxo group on the cysteinate sulfur atom involves a spin-state crossing from singlet to quintet. We have also investigated an alternative mechanism via a persulfenate intermediate, with a realignment of hydrogen bonding interactions in the substrate binding pocket. However, this alternative mechanism of proximal oxygen atom attack on the sulfur atom of cysteinate is computed to be a high-energy pathway, and therefore, the persulfenate intermediate is unlikely to participate in the catalytic cycle of CDO enzymes. 相似文献
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A. G. Taranto J. W. de M. Carneiro F. G. de Oliveira M. T. de Araujo C. R. Correa 《Journal of Molecular Structure》2002,580(1-3):207-215
Artemisinin is a sesquiterpene lactone with an endoperoxide function that is essential for its antimalarial activity. Endoperoxides are supposed to act on heme leading to the reduction of the peroxide bond and production of radicals, which can be responsible for killing the parasite. The geometries of artemisinin, radical anions and neutral species generated by rearrangement after reduction of the peroxide bond were fully optimized with the AM1 and PM3 semi-empirical methods, in order to characterize the intermediates formed during the process. Among the radicals calculated along the pathway for reductive decomposition of artemisinin, the secondary radical centered on carbon C4 has the highest stability when compared to other radicals that can be achieved either by hydrogen migration to the original O-centered radical or by homolytic break of C–C bond. This suggests that the C4-centered radical may be the species responsible for killing the parasite, as has been indicated previously in experimental studies. 相似文献