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Decarboxylation

About: Decarboxylation is a(n) research topic. Over the lifetime, 9914 publication(s) have been published within this topic receiving 193955 citation(s). The topic is also known as: decarboxylation reaction.
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Journal ArticleDOI
TL;DR: The results suggest that the role of the Cys --> Gln beta-ketoacyl synthases found in the loading domains of some modular polyketide synthases likely is to act as malonyl, or methylmalonyL, decarboxylases that provide a source of primer for the chain extension reactions catalyzed by associated modules containing fully competent beta- ketoacyL synthases.
Abstract: beta-Ketoacyl synthases involved in the biosynthesis of fatty acids and polyketides exhibit extensive sequence similarity and share a common reaction mechanism, in which the carbanion participating in the condensation reaction is generated by decarboxylation of a malonyl or methylmalonyl moiety; normally, the decarboxylation step does not take place readily unless an acyl moiety is positioned on the active-site cysteine residue in readiness for the ensuing condensation reaction. Replacement of the cysteine nucleophile (Cys-161) with glutamine, in the beta-ketoacyl synthase domain of the multifunctional animal fatty acid synthase, completely inhibits the condensation reaction but increases the uncoupled rate of malonyl decarboxylation by more than 2 orders of magnitude. On the other hand, replacement with Ser, Ala, Asn, Gly, and Thr compromises the condensation reaction without having any marked effect on the decarboxylation reaction. The affinity of the beta-ketoacyl synthase for malonyl moieties, in the absence of acetyl moieties, is significantly increased in the Cys161Gln mutant compared to that in the wild type and is similar to that exhibited by the wild-type beta-ketoacyl synthase in the presence of an acetyl primer. These results, together with modeling studies of the Cys --> Gln mutant from the crystal structure of the Escherichia coli beta-ketoacyl synthase II enzyme, suggest that the side chain carbonyl group of the Gln-161 can mimic the carbonyl of the acyl moiety in the acyl-enzyme intermediate so that the mutant adopts a conformation analogous to that of the acyl-enzyme intermediate. Catalysis of the decarboxylation of malonyl-CoA requires the dimeric form of the Cys161Gln fatty acid synthase and involves prior transfer of the malonyl moiety from the CoA ester to the acyl carrier protein domain and subsequent release of the acetyl product by transfer back to a CoA acceptor. These results suggest that the role of the Cys --> Gln beta-ketoacyl synthases found in the loading domains of some modular polyketide synthases likely is to act as malonyl, or methylmalonyl, decarboxylases that provide a source of primer for the chain extension reactions catalyzed by associated modules containing fully competent beta-ketoacyl synthases.

1,009 citations


Journal ArticleDOI
Xingfa Gao1, Joonkyung Jang1, Shigeru Nagase1Institutions (1)
Abstract: The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...

922 citations


Journal ArticleDOI
Abstract: In the liquefaction process, the micellar-like broken down fragments produced by hydrolysis are degraded to smaller compounds by dehydration, dehydrogenation, deoxygenation and decarboxylation. These compounds once produced, rearrange through condensation, cyclization and polymerization, leading to new compounds. Thermal depolymerization and decomposition of biomass, cellulose, hemicelluloses and products were formed as well as a solid residue of charcoal. The mechanism of pyrolytic degradation of structural components of the biomass samples was separately studied. Cleavage of the aromatic C–O bond in lignin led to the formation of one oxygen atom products, and the cleavage of the methyl C–O bond to form two oxygen atom products is the first reaction to occur in the thermolysis of 4-alkylguaiiacol at 600–650 K. Cleavage of the side chain C–C bond occurs between the aromatic ring and the α-carbon atom.

843 citations


Journal ArticleDOI
04 Aug 2006-Science
TL;DR: A safe and convenient cross-coupling strategy for the large-scale synthesis of biaryls, commercially important structures often found in biologically active molecules, using a copper catalyst to generate the carbon nucleophiles in situ via decarboxylation of easily accessible arylcarboxylic acid salts.
Abstract: We present a safe and convenient cross-coupling strategy for the large-scale synthesis of biaryls, commercially important structures often found in biologically active molecules. In contrast to traditional cross-couplings, which require the prior preparation of organometallic reagents, we use a copper catalyst to generate the carbon nucleophiles in situ, via decarboxylation of easily accessible arylcarboxylic acid salts. The scope and potential economic impact of the reaction are demonstrated by the synthesis of 26 biaryls, one of which is an intermediate in the large-scale production of the agricultural fungicide Boscalid.

747 citations


Journal ArticleDOI
J. Hoigné1, Hans-Peter Bader1Institutions (1)
Abstract: Hydroxyl radicals are formed upon the hydroxide-ion catalyzed decomposition of ozone in water as is shown by the relative rates with which organic substrates compete with each other for consuming the oxidative intermediates. The yield of the decarboxylation of 14 C-labelled benzoic acid indicates that up to 0.55 ± 0.08 mol of hydroxyl radicals may be produced from 1 mol ozone at pH 10.5. Published data on hydroxyl radical-reactions can now be applied to describe oxidations initiated by ozonation. Parameters influencing the prior ozone decomposition and protective effects of radical scavengers, such as carbonates, have to be accounted for when optimizing the processes. The solutes present in water influence appreciably the rate of the chain reaction leading to the decomposition of ozone.

740 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20223
2021237
2020244
2019285
2018255
2017289