Dissociation Of Phenols Research Articles

Metal-free multifunctional nanozymes mimicking endogenous antioxidant system for acute kidney injury alleviation

Cellular redox homeostasis is highly dependent on endogenous antioxidant systems, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). The nanozymes mimicking the catalytic activities of natural antioxidant systems serve as potential candidates for the therapy of reactive oxygen species (ROS)-related diseases. However, previously reported metal-containing nanozymes possessed unsatisfactory catalytic activity and inevitable peroxidase activity, limiting their translational applications. Therefore, inspired by the superior ROS scavenging activities of natural polyphenols and metal-free carbon dots (CDs) with ultra-small size, phenol-functionalized CDs that mimic endogenous antioxidant system have been fabricated. The SOD activity was determined at an extremely high level (18187 U/mg), which was substantially comparable to natural SOD. Notably, this study reveals for the first time that CDs, as selenium-free nanomaterials, show robust GPx activity in vitro. The theory calculation suggests that the bond dissociation of phenols on CDs is considerably lower than selenocysteine of natural GPx, which facilitates the formation of peroxide intermediate to initiate GPx-like reactions. Furthermore, the kidney-targeting and intracellular antioxidant mimicking properties contribute to the effective alleviating cisplatin-induced acute kidney injury via suppressing oxidative stress-mediated ferroptosis in vivo. These results provide an effective polyphenol-functionalized strategy for synthesizing metal-free multifunctional antioxidant nanozyme to treat ROS-related diseases.

The Study on the Generation of Persistent Free Radicals in the Explosive Industry Area

Phenolic compounds and transition metals exist in wastewater having a large number of emissions due to the discharge of polluted wastewater from the explosive industry. And these two substances are important factors that affect the generation of persistent free radicals (PFR). However, the generation of more toxic and harmful PFR is unclear in wastewater from the explosive industry. In this study, the dissociation reaction of phenol on transition metal oxides ZnO to form PFR has been explored by the density functional theory (DFT) calculation. The dissociation of phenol on the ZnO surface is an exothermic and barrierless reaction process, which indicates that PFR can be formed in the wastewater of the explosive industry. Thus, more attention should be paid to the toxicity of PFR in the wastewater produced by the explosive industry.

PHOTODEGRADATION OF PHENOL USING N/TiO2 SYSTEM

In the article the photochemical dissociation of phenol in the participation of TiO2 nano-particles and methyl-3-aminocrotonate was done for the first time, the period was taken as 60 minutes, the processing of photochemical dissociation was verified by the curves drawn for reaction solution in the UV radiation device and the 60% decomposition of phenol was defined. Light absorption of a system with TiO2 is observed only in the UV area, whereas absorption of a system with N/TiO2 falls on the visible area of the spectrum .

Study on hydrodeoxygenation mechanism of anisole over Ni (111) by first-principles calculation

Anisole, as an aromatic oxygenate lignin model compound, which can be selectively cleaved into benzene over Ni/C at high temperature. On the basic of experimental results, the hydrodeoxygenation (HDO) mechanism of anisole was investigated on clean Ni (111) surface by using computational techniques. Based on static energies, the microkinetic modeling on clean Ni (111) and H-covered Ni (111) were built in which the modeling of H-covered Ni (111) approximately simulated the real catalytic system under lower temperature and higher H2 pressure. As a result, the microkinetic analysis proved the phenol was the major product in the anisole decomposition on clean Ni (111) surface. However, the phenol was preferred to decompose rather than desorb from Ni surface because of the high desorption energy, suggesting that the benzene mainly originated from the secondary dissociation of phenol. Differently, the decreasing of energy barrier for anisole hydrogenation led to the formation of methylcyclohexane as main product on H-covered Ni (111) surface by microkinetic analysis. The differences in products distribution between Ni (111) and H-covered Ni (111) provided a mechanistic understanding for anisole conversion under different experimental conditions.

Geochemical Alteration and Mineralogy of Coals under the Influence of Fault Motion: A Case Study of Qi’nan Colliery, China

Geochemical characteristics of rocks in fault zones have been extensively studied, while there are limited studies on coal occurring in fault zones of underground coal mine. In this study, five coal samples were carefully collected from a reverse fault zone in Qi’nan colliery. Systematical detection methods were employed to analyze the different chemical and physical characteristics of fault-related coal samples. Through comparative analysis, the following insights are obtained. Three subdivided fault zones were classified according to the deformation characteristics of coal samples. Frictional heat and strong ductile deformation generated by fault motion led to the dissociation of phenol and carboxyl groups in coal molecules, which sharply decreased the concentrations of elements Co and Mo bound to these functional groups in zone I. The modified pore-cleat system in zone I with higher pore volume and lower permeability allowed solutions containing enriched trace elements to migrate through zone I locally. Concentrations of HREE, MREE and related elements associated with the invasive solutions showed significant positive anomalies in zone I. Precipitation and smearing of clay minerals in zone I led to poorer connectivity. Disruption and delamination of laminar clay minerals by strong compression-shear stress significantly increased the adsorption sites for related elements, especially the HREE and MREE. Nano-scale clay minerals resulting from stress-induced scaly exfoliation also enhanced the retention capability of REE in zone I.

Photodissociation of phenol in the adiabatic representation: Tunneling, motions of phenyl ring, and kinetic isotope effects

AbstractThe photodissociation of phenol is a prototype of the photoinduced hydrogen detachment reaction. The dissociation rates of phenol through the excited S1 state are calculated with the quantum instanton method in full dimensionality. The Arrhenius plot of the rates shows that the quantum tunneling dominates the OH bond dissociation at low temperatures. The degrees of freedom of phenyl ring (C6H5) play extremely important roles in the dissociation of phenol. Fixing the phenyl ring at the equilibrium geometry can only provide reliable rates between 400 K and 800 K. The motions of phenyl ring have an impact on enhancing the dissociation by lowering the free energy barrier. The larger the amplitudes of the phenyl ring motions are, the more the free energy barrier will be reduced. The dissociation rates of C6H5OH are much larger than those of C6H5OD, which is due to the zero‐point energy and entropy effects.

Selective hydrogenation of phenol to cyclohexanone by SiO2-supported rhodium nanoparticles under mild conditions

A silica-supported rhodium catalyst for the selective hydrogenation of phenol to cyclohexanone under mild conditions has been developed. As the Rh concentration on the catalyst increased from 0.5 to 15 wt%, the conversion (at phenol/Rh mole ratio 100/1) dropped whereas the initial selectivity to cyclohexanone increased. The direct hydrogenation to cyclohexanol occurred in parallel with partial hydrogenation to cyclohexanone. The negative correlation between selectivity and Rh dispersion suggests that direct hydrogenation occurs at low coordination sites whereas dissociation of phenol to phenoxy followed by hydrogenation to cyclohexanone takes place at higher coordinated terrace sites. DFT calculations revealed that the activation barrier for O–H bond cleavage is lower for phenol adsorbed on a Rh(1 1 1) flat surface than on small particles. By blocking the low coordination edge and step sites through grafting with (3-mercaptopropyl)trimethoxysilane, the cyclohexanone selectivity was improved from 82 to 93% at 100% conversion. The catalyst is active at room temperature and 1 atm H2 pressure and can be easily activated by in-situ reduction.

Phenol dissociation on pristine and defective graphene

Phenol (C6H5O‒H) dissociation on both pristine and defective graphene sheets in terms of associated enthalpic requirements of the reaction channels was investigated. Here, we considered three common types of defective graphene, namely, Stone-Wales, monovacancy and divacancy configurations. Theoretical results demonstrate that, graphene with monovacancy creates C atoms with dangling bond (unpaired valence electron), which remains particularly useful for spontaneous dissociation of phenol into phenoxy (C6H5O) and hydrogen (H) atom. The reactions studied herein appear barrierless with reaction exothermicity as high as 2.2eV. Our study offers fundamental insights into another potential application of defective graphene sheets.

Role of Dissociation of Phenol in Its Selective Hydrogenation on Pt(111) and Pd(111)

The adsorption, dissociation, and hydrogenation of phenol on the Pt(111) and Pd(111) surfaces have been studied using density functional theory slab calculations. The results show that phenol favors adsorption through a mixed σ–π interaction on both surfaces through its phenyl ring, with the hydrogen atoms and hydroxyl tilted away from the surface. The dissociation of phenol to phenoxy is both thermodynamically and kinetically favored on Pd but not on Pt. The phenoxy adsorbs on Pd through both the phenyl ring and the oxygen atom, whereas the O atom points away from the surface on Pt. On Pt, the barrier for adding one hydrogen atom to the adsorbed phenol is 0.49 eV lower than the overall barrier for phenol dissociation to phenoxy followed by adding the hydrogen atom to its phenyl ring, resulting in direct hydrogenation of the adsorbed phenol to cyclohexanol as the dominant reaction pathway. In contrast, on Pd, the barrier for direct hydrogenation (1.22 eV) is higher than the overall barrier of dissociation...

Hydrodynamics, mass transfer, and photocatalytic phenol selective oxidation reaction kinetics in a fixed TiO2 microreactor

Photocatalytic phenol dissociation was studied in a microreactor, with a TiO2 layer immobilized on the reactor inner walls. Experiments were conducted for various residence times, initial concentrations, pH values, and UV light irradiation intensities. The intermediates and products (catechol, hydroquinone, and resorcinol) were quantitatively investigated to determine the predominant reaction pathways for the investigated anatase catalyst. A three‐dimensional mathematical model was used to simulate the heterogeneous photocatalysis reaction conditions with Langmuir–Hinshelwood mechanism, considering the adsorption/desorption thermodynamic equilibria, and for kinetic parameter estimation via regression analysis. The effectiveness factor, Thiele modulus, and the correction function were calculated to determine the pore diffusion effects. The value of pH had the dramatic effect of lowering the reaction rate due to the competitive adsorption of hydroxide ions and protons on the catalyst surface. A phenol conversion of 79.5% was achieved at the residence time of 7.22 min, but without total mineralization. © 2014 American Institute of Chemical Engineers AIChE J, 61: 572–581, 2015

Near-Edge X-ray Absorption Fine Structure Spectra and Site-Selective Dissociation of Phenol

A time-of-flight mass spectrometer with orthogonal acceleration and soft X-rays from synchrotron radiation were utilized to measure near-edge X-ray absorption fine structure (NEXAFS) spectra of carbon and oxygen in phenol and the corresponding ionic fragments following core excitation. The photon energies were in the range of 284-298 eV for the carbon K-edge and 529.5-554.5 eV for the oxygen K-edge. The total ion yield, ion intensity for each ionic fragment, and ion intensity ratio, defined as ion intensity divided by total ion yield, were measured as a function of photon energy. Possible mechanisms of dissociation are proposed and enhancements of specific products of dissociation are reported. In general, the enhancement of these specific products is small in the carbon K-edge region but is clear for some products at the oxygen K-edge. In particular, elimination of the H atom from the hydroxyl group was observed only at the oxygen K-edge. One remarkable result is that an excitation of a core-level electron of oxygen greatly enhanced the cleavage of specific C-C bonds.

Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces

The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).

Influence of organic fouling and operating conditions on nanofiltration membranes to reduce phenol concentration in natural waters

Phenol is a product widely used in manufacturing and as a disinfectant for industrial and medical applications. The treatment of aqueous effluents polluted with phenol and phenolic species has deserved much attention in the last years due to the toxicity and low biodegradability of those organic compounds. Nanofiltration (NF) has a great potential to remove these contaminants. The main objective of this work is to study the influence on the rejection of phenol by a NF90 2540 NF membrane of various operating conditions: pressure (0.3, 0.4 and 0.5 × 106 N/m2); phenol feed concentration (from 0.025 kg/m3 up to 0.150 kg/m3) and pH (from 5.9 to 11.5). The influence of organic fouling is also investigated. Results showed that when different phenol concentrations were compared at the same pressure, permeate fluxes decreased as phenol concentrations increased (from 20% for the highest phenol feed concentration tested to 10% for the lowest); when phenol concentration increased, phenol was probably adsorbed onto the membrane, which led to lower rejection values (from 78 to 59% rejection). Changes in the pH of the solution altered the phenol dissociation equilibrium and membrane rejection characteristics. The reduction in phenol rejection by organic fouling (maximum of 35%) was a consequence of the materials deposited onto the membrane, which led to the formation of a cake layer.

Stability and reactivity of active sites for direct benzene oxidation to phenol in Fe/ZSM-5: A comprehensive periodic DFT study

The stability of isolated extraframework Fe 2+ ions in ZSM-5 zeolite and their reactivity in the benzene to phenol oxidation were studied by periodic DFT calculations. Mononuclear iron(II) cations can only be stabilized at very specific exchange sites of ZSM-5 zeolite. Accordingly, iron will be predominantly present as oxygenated/hydroxylated mono- and binuclear iron complexes in Fe/ZSM-5. The reactivity of isolated Fe 2+ does not depend on the local coordination environment around iron, whereas the steric constraints imposed by the zeolite lattice are important for the overall catalytic reactivity. [FeO] +, [HOFe(μ-O)FeOH] 2+, [Fe(μ-O) 2Fe] 2+, [Fe(μ-O)Fe] 2+ extraframework complexes are also potential sites for benzene activation. The reaction is however not catalytic in these cases because the vacant active site cannot be regenerated. The presence of basic extraframework O ligands in these complexes favors phenol dissociation resulting in the formation of stable grafted phenolate species, and ultimately, to the deactivation of the oxygenated iron complexes.

Influence of humic acids of different origins on oxidation of phenol and chlorophenols by permanganate

The influences of humic acids (HAs) of different origins, including two commercial HAs, three soil HAs and one aquatic HA, on phenols oxidation by permanganate were studied. The apparent second-order rate constants of 2-chlorophenol (2-CP)/phenol oxidation by permanganate in the presence of HAs at pH 7 followed the order of commercial HA (Shanghai) > soil HAs > commercial HA (Fluka) > aquatic HA. Moreover, the commercial HA (Shanghai) could accelerate the oxidation of different chlorophenols (CP) significantly under neutral condition. The FTIR analysis demonstrated greater content of C C moieties and less amount of carboxylate, aliphatic groups and polysaccharide-like substances in soil HAs than in aqueous HA, suggesting that the increase of aromaticity in HA was beneficial to the oxidation of phenols by permanganate. The apparent second-order rate constants of 2-CP/phenol oxidation by permanganate in the presence of HAs correlated well with specific visible absorption (SVA) at 665 nm of HAs. High positive correlation coefficients ( R 2 > 0.75) implied that π-electrons of HA strongly influenced the reactivity of 2-CP/phenol towards permanganate oxidation, which agreed well with positive correlation between Fluorescence Regional Integration (FRI) and the apparent second-order rate constants. The π–π interaction between HAs and phenols, the steric hindrance effect and the dissociation of phenols may affect the oxidation of phenols by permanganate in the presence of HA at pH = 7.0.

Ligand Escape Pathways and (Un)Binding Free Energy Calculations for the Hexameric Insulin-Phenol Complex

Cooperative binding of phenolic species to insulin hexamers is known to stabilize pharmaceutical preparations of the hormone. Phenol dissociation is rapid on hexamer dissolution timescales, and phenol unbinding upon dilution is likely the first step in the conversion of (pharmaceutical) hexameric insulin to the active monomeric form upon injection. However, a clear understanding of the determinants of the rates of phenol unbinding remains obscure, chiefly because residues implicated in phenol exchange as determined by NMR are not all associated with likely unbinding routes suggested by the best-resolved hexamer structures. We apply random acceleration molecular dynamics simulation to identify potential escape routes of phenol from hydrophobic cavities in the hexameric insulin-phenol complex. We find three major pathways, which provide new insights into (un)binding mechanisms for phenol. We identify several residues directly participating in escape events that serve to resolve ambiguities from recent NMR experiments. Reaction coordinates for dissociation of phenol are developed based on these exit pathways. Potentials of mean force along the reaction coordinate for each pathway are resolved using multiple independent steered molecular dynamics simulations with second-order cumulant expansion of Jarzynski's equality. Our results for Δ F agree reasonably well within the range of known experimental and previous simulation magnitudes of this quantity. Based on structural analysis and energetic barriers for each pathway, we suggest a plausible preferred mechanism of phenolic exchange that differs from previous mechanisms. Several weakly-bound metastable states are also observed for the first time in the phenol dissociation reaction.

Predictive QSPR modeling of the acidic dissociation constant (pKa) of phenols in different solvents

AbstractGiven the importance of ionization constant (pKa) of phenols in explaining the mechanism of their toxicity, it is of interest to develop theoretical models for the prediction of pKa values of phenols in different solvent systems. In the present communication, we developed predictive QSPR models for pKa values of substituted phenols in seven different solvent systems such as water, dimethyl sulfoxide (DMSO), methanol, dimethylformamide (DMF), acetonitrile (AN), isopropanol, and tert‐butanol using quantum topological molecular similarity (QTMS) descriptors. The data set was divided into training and test sets, and models were developed using partial least squares (PLS) regression from the training set. The predictive potential of the developed models was assessed by the prediction of pKa values of the test set compounds. Root mean square error of prediction (RMSEP) values were used as objective function for selection of the best models in different solvent systems. Good predictive models were developed in all solvent systems except isopropanol. Considering all seven solvent systems, distance descriptors give consistently good results whereas ellipticity descriptors are of less importance. Moreover, plots of ‘variable importance in the projection’ (VIP) for the best models highlight the importance of the bond connecting the phenolic oxygen to the aromatic ring. This suggests the diagnostic nature of QTMS descriptors in identifying the reaction center in acidic dissociation of phenols. Copyright © 2008 John Wiley & Sons, Ltd.

Adsorption Behavior of Chlorophenols on Natural Zeolite

The adsorption of aqueous organic pollutants, i.e., phenol, monochlorophenols (2‐and 4‐), and dichlorophenols (2,4‐and 3,5‐) on natural Jordanian zeolitic tuff was studied. Three simplified kinetic models, viz., pseudo‐first order, pseudo‐second order, and intraparticle diffusion models were used to fit the kinetics data. The results revealed that at earlier stages of adsorption of phenols onto zeolite, the pseudo‐second order and the bulk diffusion rate constants are dependent on the acidity and the hydrophobicity of phenols. Whereas at later stages of adsorption, the adsorption capacity and the intraparticle diffusion rate constants are affected by the molecular size and the extent of dissociation of phenols.

New insights into the interconversion mechanism between phenol and its isomers

We have studied the tautomerization reactions of 2,4-cyclohexadienone and 2,5-cyclohexadienone to phenol and the phenol dissociation to phenoxy radical using ab initio calculations. For the tautomerization mechanisms, the geometries were optimized at the CASSCF(8,8)/6-31G* level and the energetics were recalculated at the CASPT2(8,8)/cc-pVDZ level. For the dissociation reaction, the computational requirements for achieving comparable accuracy were stricter. In this case, the geometry optimizations were carried out at the CASSCF(10,9)/6-31G* level and the energetics were tuned with CASPT2(10,9)/aug-cc-pVTZ calculations. The tautomerization of 2,4-cyclohexadienone to phenol involved a one-step mechanism with a barrier of 53.3 kcal mol −1, while the interconversion from 2,4-cyclohexadienone to 2,5-cyclohexadienone involved a two-step mechanism, which disagreed with previous theoretical results. This interconversion occurs through a diradical intermediate. The highest barrier, between the reactant and the intermediate, was of 42.7 kcal mol −1. The best result for O–H bond dissociation enthalpy (BDE) of phenol to phenoxy was 86.2 kcal mol −1, which is within the interval proposed for this reaction by experimentalist authors. The height barrier corresponding to the rotation through the O–H bond was 3.3 kcal mol −1, which is very close to the experimental value of 3.4 kcal mol −1.

Direct Observation of an Intermediate State for a Surface Photochemical Reaction Initiated by Hot Electron Transfer

The photoinduced charge transfer that had been suggested to result in the dissociation of phenol on Ag(111) was investigated by two-photon photoemission spectroscopy. An unoccupied intermediate state was positively identified, which was found to be located 3.22 eV above the Fermi level. From the photoelectron energy dispersion, the effective mass of the intermediate state was determined to be (15 +/- 10)m(e) for a 1 ML coverage of phenol. This implies that the excited electron is localized mainly on the adsorbed phenol, forming a molecular resonance state. Polarization dependence of the photoelectron intensity suggested that the initial photoexcitation of the substrate produces hot electrons that scatter into the molecular resonance state, leading ultimately to the dissociation of the adsorbate. These results are the first two-photon photoemission study to characterize the transient anionic state involved in photodissociation of a molecule adsorbed on a metal surface.