Search results for "carboxylation"
showing 10 items of 81 documents
Ribulose-1,5-bisphosphate Carboxylase-Oxygenase: New Aspects Respective the pH-Dependance of the Carboxylation Reaction
1983
The investigation was directed towards the effects of reaction conditions, substrates and pH on the carboxylation reaction of ribulose-1 ,5-bisphosphate carboxylase-oxygenase in the crude enzyme extracts from several plants. Optimal substrate concentrations (HCO3 - and RubP) were determined. The highest carboxylase activity was attained with Tris/HCl buffer. The pH activity profile was quite sharp with an optimum at pH 7.8. Purified and crystallized carboxylase yielded a broad optimum curve under the same reaction conditions
Electrocatalytic carboxylation of chloroacetonitrile at a silver cathode for the synthesis of cyanoacetic acid
2008
Abstract The electrocatalytic carboxylation of chloroacetonitrile to cyanoacetic acid performed at silver cathodes was investigated both theoretically and experimentally. Silver exhibits powerful electrocatalytic activities towards the reduction of chloroacetonitrile. In CO 2 -saturated CH 3 CN, reduction of NCCH 2 Cl occurs at potentials that are about 0.7 V more positive than those observed at glassy carbon and gives cyanoacetic acid in good yields. Theoretical considerations on the effect of operative parameters on the performances of the process were confirmed by electrocarboxylation experiments performed in undivided cells equipped with sacrificial anodes both in a bench-scale electroc…
Nickel-catalyzed carboxylation of aryl zinc reagent with CO2: A theoretical and experimental study
2019
Abstract Two Ni-complexes with 1,1′-bis(diphenylphosphino)ferrocene (dppf) and tricyclohexylphosphine (PCy3) ligands were tested for the Ni-catalyzed cross-coupling of aryl zinc reagent with CO2 to form aryl carboxylic acid. Theoretical study with the aid of density functional theory (DFT) was carried out to understand the detailed reaction mechanism. The reasonable reaction pathway was deduced. The simulation results suggested that the free energy barrier of the rate-limiting step with (dppf)Ni is only 1.64 kcal mol−1 higher than the barrier with (PCy3)2Ni. However, our experiment provided an unexpectedly low yield by using (dppf)Ni complex as the catalyst. Further theoretical study ascrib…
Analysis of the Decarboxylation Step in Mammalian Histidine Decarboxylase
2008
We report a hybrid quantum mechanics/molecular mechanics theoretical study on the reaction mechanism of mammalian histidine decarboxylase that allows us to obtain valuable insights on the structure of the cofactor-substrate adduct (external aldimine) in the active site of rat histidine decarboxylase. By means of molecular dynamics simulations, we traced the potential of mean force corresponding to the decarboxylation reaction of the adduct both in the active site of the enzyme and in aqueous solution. By comparing this process in both media, we have identified the key electrostatic interactions that explain the lowering of the free energy barrier in the enzyme. Our analysis also offers a va…
The influence of aluminium cations on electrocarboxylation processes in undivided cells with Al sacrificial anodes
2005
Abstract The influence of Al cations on the electrochemical carboxylation of acenaphthylene ( 1 ), benzophenone ( 2 ), 6-methoxy-2-acetonaphthone ( 3 ), and benzyl chloride ( 4 ) has been investigated in dimethylformamide at a glassy carbon cathode. The Al 3+ ions were either added at the beginning of the experiment or were released from the anode during electrocarboxylation. It has been found that when Al cations are added to the reaction medium, they strongly influence the reduction process, in most cases leading to a complete change of the mechanism. For example, in the case of 1 , the radical anion ( 1 − ) formed upon 1e − reduction rapidly reacts with Al 3+ to give an Al(III) adduct, w…
Activity and activation state of ribulose-1,5-bisphosphate carboxylase of spruce trees with varying degrees of damage relative to the occurrence of n…
1989
The aim was to determine whether a reduced carboxylation efficiency in needles of damaged spruce trees (Picea abies), is derived from a direct impairment of the ribulose-1,5-bisphosphate carboxylase (RuBP carboxylase) or there is an indirect inhibition of the RuBP carboxylase. In 1985, 1986 and 1987 measurements of RuBP carboxylase activity were carried out at three locations. Trees of different ages and degrees of damage were examined. RuBP carboxylase was assayed using both a rapid extraction method to determine the initial activity and an in vitro test after total activation to determine the total activity. The activation state was calculated as the ratio of initial activity to total act…
DFT studies of COOH tip-functionalized zigzag and armchair single wall carbon nanotubes
2011
Structure and energy calculations of pristine and COOH-modified model single wall carbon nanotubes (SWCNTs) of different length were performed at B3LYP/6-31G* level of theory. From 1 to 9 COOH groups were added at the end of the nanotube. The differences in structure and energetics of partially and fully functionalized SWCNTs at one end of the nanotube are observed. Up to nine COOH groups could be added at one end of (9,0) zigzag SWCNT in case of full functionalization. However, for (5,5) armchair SWCNT, the full functionalization was impossible due to steric crowding and rim deformation. The dependence of substituent attachment energy on the number of substituents at the carbon nanotube ri…
Durch sterische effekte stabilisierte ß-ketocarbonsäuren
1989
Abstract Increasing steric hindrance in β-keto carboxylic acids leads to an increasing kinetic stability towards decarboxylation, till systems are reached which are completely stable at room temperature. Simultaneously the tautomeric equilibrium is changed in favour of the (Z)-enol, and finally in favour of the (E)-configurated enol.
ChemInform Abstract: Photoinduced Functionalization of the C-20 Methyl Group of the Nor-diterpene Atractyligenin.
2010
Abstract Irradiation of the nor-diterpene atractyligenin at λ =254 nm in methanol gave, on one hand, the decarboxylation product, and provided, on the other hand, the transformation of the C-20 angular methyl into a methylene-carbomethoxy group. A photochemical pathway involving formation of C-19/C-20 bond is suggested.
Catalytic aerobic oxidative decarboxylation of α-trifluoromethyl-α-hydroxy acids to trifluoromethyl ketones
2003
Abstract The oxidative decarboxylation of α-trifluoromethyl-α-hydroxy acids to trifluoromethyl ketones is carried out under mild catalytic aerobic conditions using a cobalt(III) complex in the presence of pivalaldehyde.