Phenolate Anion (phenolate + anion)

Distribution by Scientific Domains


Selected Abstracts


Computational studies of electron-transfer processes in old yellow enzyme

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2001
Ginger M. Chateauneuf
Abstract Old Yellow Enzyme (OYE) is a flavoenzyme that was first isolated from brewer's bottom yeast. Homologues have been identified in other strains of yeast, bacteria, and plants. In plants, the OYE homologue functions enzymatically in the synthesis of plant hormones, but the biological function of OYE in yeast is still unknown. Flavin mononucleotide (FMN) is the cofactor that is noncovalently bound in the enzyme. OYE binds several phenolic ligands that serve as models for reactive biological substrates. These complexes have broad long-wavelength absorption bands, which have been ascribed to charge-transfer interactions, with the phenolate anion acting as the electron donor and the FMN as the acceptor [Abramovitz, A. S.; Massey, V. J Bio Chem 1976, 251, 5327,5336]. The computational characterization of these electronic transitions in the active site will help in understanding the biological processes in the enzyme. It was found that at several levels of computational methods, and through computationally mutating relevant amino acids, a charge-transfer process is occurring. This result agrees with previous experimental work and is consistent with all ultraviolet,visible spectrophotometric data. The preliminary results for the computational studies of these electron-transfer processes will be presented. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source]


Primary kinetic hydrogen isotope effects in deprotonations of a nitroalkane by intramolecular phenolate groups

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2010
Nicholas Backstrom
Abstract Rate constants and kinetic isotope effects have been determined for the formation of nitronate anions from the ethers 1-(2-methoxyphenyl)-2-nitropropane, 7(X,=,H, L,=,H and D) and 1-(2-methoxy-5-nitrophenyl)-2-nitropropane, 7(X,=,NO2, L,=,H and D), and from the corresponding phenols, 1-(2-hydroxyphenyl)-2-nitropropane, 3(X,=,H, L,=,H and D), and 1-(2-hydroxy-5-nitrophenyl)-2-nitropropane, 3(X,=,NO2, L,=,H and D), in aqueous basic medium. For the ethers 7, rates of deprotonation by hydroxide are comparable with those found for deprotonations of 2-nitropropane, with kH/kD (25,°C),=,7.7 and 7.8, respectively. In both the cases, the isotope effects are conventionally temperature dependent. For the corresponding phenols 3, conditions have been established under which the deprotonations of the nitroalkane are dominated by intramolecular deprotonation by the kinetically first-formed phenolate anion, with an estimated effective molarity EM,,,250. For 3 (X,=,H, L,=,H or D), kH/kD (25,°C),=,7.8, with E,,,E,=,6.9,kJ,mol,1 and AH/AD,=,0.5. For 3(X,=,NO2, L,=,H or D), rates of intramolecular deprotonation are reduced 30-fold, and an elevated kinetic isotope effect is found (kH/kD (25,°C),=,10.7). Activation parameters (E,,,E,=,17.8,kJ,mol,1 and AH/AD,=,0.008) are compatible with an enhanced tunnelling contribution to reactivity in the H-isotopomer. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Hydroxycinnamic Acids as DNA-Cleaving Agents in the Presence of CuII Ions: Mechanism, Structure,Activity Relationship, and Biological Implications

CHEMISTRY - A EUROPEAN JOURNAL, Issue 46 2009
Gui-Juan Fan
Abstract The effectiveness of hydroxycinnamic acids (HCAs), that is, caffeic acid (CaA), chlorogenic acid (ChA), sinapic acid (SA), ferulic acid (FA), 3-hydroxycinnamic acid (3-HCA), and 4-hydroxycinnamic acid (4-HCA), as pBR322 plasmid DNA-cleaving agents in the presence of CuII ions was investigated. Compounds bearing o -hydroxy or 3,5-dimethoxy groups on phenolic rings (CaA, SA, and ChA) were remarkably more effective at causing DNA damage than the compounds bearing no such groups; furthermore, CaA was the most active among the HCAs examined. The involvement of reactive oxygen species (ROS) and CuI ions in the DNA damage was affirmed by the inhibition of the DNA breakage by using specific scavengers of ROS and a CuI chelator. The interaction between CaA and CuII ions and the influence of ethylenediaminetetraacetic acid (EDTA), the solvent, and pH value on the interaction were also studied to help elucidate the detailed prooxidant mechanism by using UV/Vis spectroscopic analysis. On the basis of these observations, it is proposed that it is the CaA phenolate anion, instead of the parent molecule, that chelates with the CuII ion as a bidentate ligand, hence facilitating the intramolecular electron transfer to form the corresponding CaA semiquinone radical intermediate. The latter undergoes a second electron transfer with oxygen to form the corresponding o -quinone and a superoxide, which play a pivotal role in the DNA damage. The intermediacy of the semiquinone radical was supported by isolation of its dimer from the CuII -mediated oxidation products. Intriguingly, CaA was also the most cytotoxic compound among the HCAs toward human promyelocytic leukemia (HL-60) cell proliferation. Addition of exogenous CuII ions resulted in an effect dichotomy on cell viability depending on the concentration of CaA; that is, low concentrations of CaA enhanced the cell viability and, conversely, high concentrations of CaA almost completely inhibited the cell proliferation. On the other hand, when superoxide dismutase was added before, the two stimulation effects of exogenous CuII ions were significantly ameliorated, thus clearly indicating that the oxidative-stress level regulates cell proliferation and death. These findings provide direct evidence for the antioxidant/prooxidant mechanism of cancer chemoprevention. [source]


Synthesis and Crystal Structure of the Copper Complex of 7,16-Bis(2-hydroxy-5-methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane

CHINESE JOURNAL OF CHEMISTRY, Issue 1 2004
Shu-Lan Ma
Abstract A lariat crown ether ligand 7.16-bis (2-hydroxy-5-methylbenzyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (Ll) has been prepared via one-pot Mannich reaction. Its copper(II) complex Cu-Ll was synthesized and characterized by elemental analysis, IR and UV-visible spectroscopy. The crystal structure of the complex has been determined by X-ray diffraction analysis. The result shows that the copper(II) ion is six-coordinated by two nitrogen and four oxygen atoms, two from the crown ether and the other two from the deprotonated phenolate anions, forming an elongated octahedral complex. Electrochemical study indicates that the complex undergoes reversible reduction in DMF solution. [source]