Center Dot OH Research Articles

Molecular Dynamics Simulation of Ozonation of <i>p</i>-Nitrophenol at Room Temperature with ReaxFF Force Field

Understanding the reaction mechanism of phenol ozonation in coking wastewater is very important for industrial applications of the ozonation process. Ozonation of p-nitrophenol in water at 300 K was simulated by ReaxFF force field molecular dynamics (ReaxFF MD) employing the GPU-enabled high-performance code of GMD-Reax and a unique code of VARxMD developed in authors' group. Evolution trends of aromatic ring opening, CO2 generation, dominant radicals (center dot OH, center dot O2, center dot O), and H2O clusters were obtained. The simulated CO2 generation and reduction of aromatic ring could be described with pseudo-first-order kinetics. Moreover, the reaction pathways for the ozonation of p-nitrophenol can be divided into three stages: hydrogen abstraction, opening of the six-membered-ring structure, and the breaking of C-C bonds. The simulations revealed the important role of radicals and water clusters in the ozonation of p-nitrophenol. This work is an attempt to investigate the ozonation mechanism of phenols in aqueous solutions at room temperature using ReaxFF MD, which should be helpful for further experimental or theoretical investigation of the mechanism.

ChemInform Abstract: Syntheses, Structures and Antioxidant Activities of Fullerenols: Knowledge Learned at the Atomistic Level

AbstractReview: 79 refs.

Syntheses, Structures and Antioxidant Activities of Fullerenols: Knowledge Learned at the Atomistic Level

Fullerenol nanoparticles have intriguing potentials in biomedical applications. However, the structures, mechanisms of syntheses and mechanisms of antioxidant activities of fullerenols at the atomistic level, which substantialize their properties and applications, remain opened questions. Here, we review the syntheses, structures and antioxidant activities of fullerenols. Especially, we focus on the knowledge at the atomistic level. Experimentally, fullerenols can be synthesized using oxidation reactions in either acidic conditions or alkaline conditions. The latter reactions yield fullerenols with high hydroxyl numbers and better water solubility. For fullerenol structures, a precision structural model has been recently proposed for C-60 fullerenols, which explain the experimentally-observed radical anion properties and pH-dependent infrared spectroscopic properties. Calculations have suggested that the most thermodynamically stable structures of many fullerenols have hydroxyls located aggregately in islands on the fullerene cages, although the most stable configuration of C-60(OH)(24) has hydroxyls distributed on C-60 equator. Two different center dot OH-scavenging mechanisms are possible for fullerenols. Fullerenols with low degrees of hydroxylation prefer the center dot OH addition mechanism, whereas those with high degrees of hydroxylation prefer the hydrogen abstraction mechanism. The O (2) (a (TM) a') -scavenging mechanism is related to redox potentials, charges and H-bond nets of the fullerenols.

Photo-catalytic properties of doped or substituted polyaniline-coated Fe3O4 nanoparticles

In this work, doped and substituted polyaniline (PANI)-coated Fe3O4 nanoparticles were synthesized. The diameter of Fe3O4 core was similar to 430 nm, and the thickness of PANI shell was similar to 20 nm. Their photo-catalytic properties for methyl orange were investigated under natural light illumination. The photo-catalytic activity sequence of three doped PANI/Fe3O4 nanoparticles is as follows: iodine doping > without doping > graphite powder doping This should be due to the difference of structure, conductivity, and band gap resulting from the dopants. The photo-catalytic activity of five substituted PANI/Fe3O4 nanoparticles followed the order of poly(1,2-diaminobenzene) > poly(o-toluidine) > poly(1,3-diaminobenzene) > PANI > polydiphenylamine. The effects of steric hindrance, activated ability, and conjugation of the substituents on the photo-catalytic properties were discussed. The ESR results suggested that O-2 and H2O2 dissolved in the solutions were important factors on the photo-degradation, and the center dot OH generated via h(+)-mediated pathwaywas the key oxidizing substance.

ChemInform Abstract: From Molecular to Supramolecular: An Exploration into the Modes of Self‐Assembly in Conformationally Locked Polycyclitols

AbstractReview: 102 refs.

Degradation of organic pollutants by a Co3O4-graphite composite electrode in an electro-Fenton-like system

A novel composite electrode was constructed by pressing together Co3O4 and graphite and it was used as the cathode in an electro-Fenton-like (EFL) system. The poor electron transport characteristic of Co3O4 was overcome by incorporating graphite. In situ electro-catalytic generation of hydroxyl radicals (center dot OH) occurred at high current efficiencies from pH 2-10, extending the traditional Fenton reaction pH range. Cyclic voltammetry and AC impedance spectrometry were used to characterize the composite electrode. The ability of the EFL system to degrade organic compounds was investigated using sulforhodamine B (SRB) and 2,4-dichlorophenol (2,4-DCP) as probes. Decoloration of SRB (1.0x10(-5) mol/L) was complete (100%) in 150 min and SRB was effectively degraded from pH 2-10. The decomposition of SRB was studied using Fourier transform infrared spectroscopy (FT-IR) and total organic carbon (TOC) analysis and results indicated that the final degradation products were carbon dioxide, carboxylic acids and amines. The EFL system also decomposed 2,4-DCP and the degradation was 98.6% in 240 min. Electro-catalytic degradation of SRB occurs by a center dot OH mechanism. After 5 times reused, the degradation rate of SRB did not significantly slow down. The electrode shows excellent potential for use in advanced oxidation processes (AOPs) used to treat persistent organic pollutants (POPs) in wastewater.

Antioxidant peptides isolated from sea cucumber Stichopus Japonicus

The sea cucumber Stichopus japonicus protein was hydrolyzed by pepsin, trypsin, papain, acid protease and neutral protease, respectively, to get five kinds of peptide fractions: pepsin peptides (PP), trypsin peptides (TP), acid protease peptides (AP), neutral protease peptides (NP) and papain peptide (PAP). Antioxidative activities of all peptide fractions were evaluated by hydroxyl radical( (center dot OH) and Superoxide anion (O-2 (-))-scavenging activity. Trypsin peptide (TP) exhibited the highest antioxidative activity compared to other peptide fractions. In considering scavenging effects on hydroxyl radicals (center dot OH) and Superoxide anions (O-2(-)), TP was employed for isolation, purification and identification of antioxidant peptide. To purify and characterize antioxidative peptide, two steps gel filtration, one-step ion-exchange column chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC) were used. The purified antioxidative peptide TP2b-1 was a novel peptide and was sequenced as GPEPTGPTGAPQWLR, in which the low molecular weight and some amino acid constituents played important role in the radical-scavenging effects according reports. The IC50 values of TP2b-1 were 138.9 mu M on center dot OH and 353.9 mu M on O-2(-).

A unique tetranuclear cubane-like [Ni4O4] complex supported by hydroxyl-rich ligands: Synthesis, crystal structure and magnetic property

The tetranuclear cubane-like complex of the formula [Ni-4(HL1)(3)(HL2)(H2O)(CH3OH)] [CH3COO]center dot 2CH(3)OH center dot CH3CN (1) (H(3)L1=3-(2-hydroxybenzylideneamino)propane-1,2-diol; H(2)L2=3-aminoprppane-1,2-diol) has been prepared by a one-pot reaction of nickel(II) acetate, salicylaldehyde and 3-aminopropane-1,2-diol, where the H(3)L1 ligand was generated in situ via the condensation reaction between salicylaldehyde and 3-aminopropane-1,2-diol. The X-ray diffraction analysis of the complex showed a Ni4O4 cubane arrangement and the coordination environments of four Ni(II) ions are different from each other. Magnetic studies indicated ferromagnetic behavior for the complex. The magnetic data were fitted and the parameters were given as g=2.43, J(1)=15.96, and J(2)=4.116. (C) 2011 Elsevier B.V. All rights reserved.

A Novel Mechanism for Metal-independent Hydroxyl Radical Production by Hydrogen Peroxide and Halogenated Quinones

The hydroxyl radical ((center dot)OH) has been considered to be one of the most reactive oxygen species that are produced in biological systems. Frequently, (center dot)OH formation is ascribed to the transition metal-catalyzed Fenton reaction. During the study of the molecular mechanism for the genotoxicity of the wood preservative pentachlorophenol (PCP), we found that (center dot)OH could be produced by H(2)O(2) and PCP metabolite tetrachloro-1,4-benzoquinone (TCBQ) independent of transition metal ions. Further studies showed that TCBQ, but not its corresponding semiquinone radical, is essential for (center dot)OH production. Metal-independent production of (center dot)OH could also be observed with other halogenated quinones and H(2)O(2). Based on these data, we propose that (center dot)OH production by TCBQ and H(2)O(2) is not through a semiquinone-dependent organic Fenton reaction, but rather through a novel nucleophilic substitution and homolytical decomposition mechanism. This represents a novel mechanism for (center dot)OH production not requiring the catalysis of redox-active transition metal ions, and may partly explain the potential carcinogenicity of the widely used biocides such as PCP and other polyhalogenated aromatic compounds.

The influence of the cation of quaternized chitosans on antioxidant activity

Various quaternized chitosans (QCSs) were synthesized according to previous method. Their reducing power and antioxidant potency against hydroxyl radicals ((center dot)OH) and hydrogen peroxide (H(2)O(2)) were explored by the established systems in vitro. The QCSs exhibited markedly antioxidant activity, especially TCEDMCS, whose IC(50) on hydroxyl radicals was 0.235 mg/mL. They showed 65-80% scavenging effect on hydrogen peroxide at a dose of 0.5 mg/mL. Generally, the antioxidant activity decreased in the order TCEDMCS > TBEDMCS > EDMCS > PDMCS > IBDMCS > Chitosan. Furthermore, the order of their (center dot)OH and H(2)O(2) scavenging activity was consistent with the electronegativity of different substituted groups in the QCSs. The QCSs showed much stronger antioxidant activity than that of chitosan may be due to the positive charge density of the nitrogen atoms in QCSs strengthened by the substituted groups. (C) 2009 Elsevier Ltd. All rights reserved.

The preparation and antioxidant activity of glucosamine sulfate

Glucosamine sulfate was prepared from glucosamine hydrochloride that was produced by acidic hydrolysis of chitin by ion-exchange method. Optical rotation and elemental analysis characterized the degree of its purity. In addition, the antioxidant potency of chitosan derivative-glucosamine sulfate was investigated in various established in vitro systems, such as superoxide (O (2) (-) )/hydroxyl (center dot OH) radicals scavenging, reducing power, iron ion chelating. The following results are obtained: first, glucosamine sulfate had pronounced scavenging effect on superoxide radical. For example the O (2) (-) scavenging activity of glucosamine sulfate was 92.11% at 0.8 mg/mL. Second, the center dot OH scavenging activity of glucosamine sulfate was also strong, and was about 50% at 3.2 mg/mL. Third, the reducing power of glucosamine sulfate was more pronounced. The reducing power of glucosamine sulfate was 0.643 at 0.75 mg/mL. However, its potency for ferrous ion chelating was weak. Furthermore, except for ferrous ion chelating potency, the scavenging rate of radical and reducing power of glucosamine sulfate were concentration-dependent and increased with their increasing concentrations, but its ferrous ion chelating potency decreased with the increasing concentration. The multiple antioxidant activities of glucosamine sulfate were evidents of reducing power and superoxide/hydroxyl radicals scavenging ability. These in vitro results suggest the possibility that glucosamine sulfate could be used effectively as an ingredient in health or functional food, to alleviate oxidative stress.