scholarly journals Theoretical Calculation on the Reaction Mechanisms, Kinetics and Toxicity of Acetaminophen Degradation Initiated by Hydroxyl and Sulfate Radicals in the Aqueous Phase

Toxics ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 234
Author(s):  
Mengmeng Xu ◽  
Junfang Yao ◽  
Simei Sun ◽  
Suding Yan ◽  
Jingyu Sun
Keyword(s):  
Rate Constants ◽  
Reaction Mechanisms ◽  
Theoretical Calculations ◽  
Aquatic Organism ◽  
Vital Role ◽  
Hydrogen Atom Transfer ◽  
Point Of View ◽  
Diffusion Limited ◽  
Radical Adduct ◽  
Degradation Intermediates

The •OH and SO4•− play a vital role on degrading pharmaceutical contaminants in water. In this paper, theoretical calculations have been used to discuss the degradation mechanisms, kinetics and ecotoxicity of acetaminophen (AAP) initiated by •OH and SO4•−. Two significant reaction mechanisms of radical adduct formation (RAF) and formal hydrogen atom transfer (FHAT) were investigated deeply. The results showed that the RAF takes precedence over FHAT in both •OH and SO4•− with AAP reactions. The whole and branched rate constants were calculated in a suitable temperature range of 198–338 K and 1 atm by using the KiSThelP program. At 298 K and 1 atm, the total rate constants of •OH and SO4•− with AAP were 3.23 × 109 M−1 s−1 and 4.60 × 1010 M−1 s−1, respectively, considering the diffusion-limited effect. The chronic toxicity showed that the main degradation intermediates were harmless to three aquatic organism, namely, fish, daphnia, and green algae. From point of view of the acute toxicity, some degradation intermediates were still at harmful or toxic level. These results provide theoretical guidance on the practical degradation of AAP in the water.

Reactivity and photophysical behavior of chromone triplet. A laser flash photolysis study

1987 ◽  
Vol 65 (9) ◽  
pp. 2277-2285 ◽  
Author(s):  
S. Rajadurai ◽  
P. K. Das
Keyword(s):  
Rate Constants ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Hydrogen Atom Transfer ◽  
Oxidation Potential ◽  
Pulse Excitation ◽  
Quenching Rate ◽  
Diffusion Limited ◽  
Photophysical Behavior

The chromone triplet ([Formula: see text] in acetonitrile) is produced in quantitative yields upon 308- or 337.1-nm laser pulse excitation and is characterized by submicrosecond lifetimes in solutions at room temperature. The short-lived nature of the triplet is attributable to intrinsically fast T1 [Formula: see text] S0 intersystem crossing, nearly diffusion-limited self-quenching, and facile interactions with solvents in the form of charge and hydrogen-atom transfer. The unusually high self-quenching rate constants, (0.9–4.0) × 109 M−1 s−1, are related in a major part to the presence of the ene double bond at which the photocycloaddition of the triplet may occur; this is supported by large bimolecular rate constants [Formula: see text] observed for chromone triplet quenching by various alkene derivatives. Although, based on low-temperature photophysical behaviors, the lowest triplet state of chromone in polar solvents is expected to be of reduced n,π* character, the reactivity of the triplet toward hydrogen donors is very pronounced in acetonitrile (for example, [Formula: see text] for tri-n-butylstannane and 2-propanol, respectively). Carbon tetrachloride and benzene prove to be facile quenchers of chromone triplet; the quenching interactions probably involve charge transfer, the carbonyl triplet acting as a donor and an acceptor, respectively. The electrophilic role of chromone triplet in the quenching by benzene derivatives is supported by a good correlation between [Formula: see text] and quencher oxidation potential.

scholarly journals Reaction Mechanisms and Rate Constants of Auto‐Catalytic Urethane Formation and Cleavage Reactions

ChemistryOpen ◽  
2021 ◽  
Author(s):  
Christoph Gertig ◽  
Eric Erdkamp ◽  
Andreas Ernst ◽  
Carl Hemprich ◽  
Leif C. Kröger ◽  
...  
Keyword(s):  
Rate Constants ◽  
Reaction Mechanisms ◽  
Urethane Formation ◽  
Cleavage Reactions

scholarly journals The Diffusion Mechanism of Megaproject Citizenship Behavior: The Role of Institutional Isomorphism

2021 ◽  
Vol 13 (15) ◽  
pp. 8123
Author(s):  
Delei Yang ◽  
Jun Zhu ◽  
Qingbin Cui ◽  
Qinghua He ◽  
Xian Zheng
Keyword(s):  
Structural Equation ◽  
Diffusion Mechanism ◽  
Vital Role ◽  
Citizenship Behavior ◽  
Equation Modeling ◽  
Positive Effects ◽  
Diffusion Limited ◽  
The Relationship ◽  
Mimetic Isomorphism

Megaproject citizenship behavior (MCB) has been confirmed to a play vital role on megaproject performance. Although current research has argued that institution elements have had an impact on MCB diffusion, limited studies have empirically investigated the distinct effectiveness of various institution elements on driving MCB’s widespread diffusion in construction megaprojects. Based on institution theory, this study proposes a theoretical model comprising institutional elements (i.e., normative and mimetic isomorphism), owner’s support, relationship-based trust, and their effect or impact on MCB’s diffusion. Based on 171 industrial questionnaires collected from managers of contractors and designers in megaprojects. Partial least squares structural equation modeling (PLS-SEM) was used to validate the established model. The results indicated that both normative and mimetic isomorphism have positive effects on facilitating MCB diffusion, and owner’s support has shown partial mediation in promoting MCB diffusion through normative isomorphism, as well as full mediation in the promoting of MCB diffusion through mimetic isomorphism. Meanwhile, relationship-based trust exerts a positive moderating effect on the relationship between mimetic isomorphism and MCB. This study extends current literature on driving MCB diffusion from the perspective of institutional theory, contributing by providing four implications for megaprojects managers to “buy in” more extensive MCB.

scholarly journals Sustaining Rice Production through Biofertilization with N2-Fixing Cyanobacteria

2021 ◽  
Vol 11 (10) ◽  
pp. 4628
Author(s):  
Macarena Iniesta-Pallarés ◽  
Consolación Álvarez ◽  
Francisco M. Gordillo-Cantón ◽  
Carmen Ramírez-Moncayo ◽  
Pilar Alves-Martínez ◽  
...  
Keyword(s):  
Agricultural Practices ◽  
Vital Role ◽  
Rice Production ◽  
Point Of View ◽  
Paddy Fields ◽  
Nitrogen Fertilizers ◽  
Trophic Chain ◽  
Agricultural Practice ◽  
Biotechnological Potential

Current agricultural productivity depends on an exogenous nutrient supply to crops. This is of special relevance in cereal production, a fundamental part of the trophic chain that plays a vital role in the human diet. However, our agricultural practices entail highly detrimental side-effects from an environmental point of view. Long-term nitrogen fertilization in croplands results in degradation of soil, water, and air quality, producing eutrophication and subsequently contributing to global warming. In accordance with this, there is a biotechnological interest in using nitrogen-fixing microorganisms to enhance crop growth without adding chemically synthesized nitrogen fertilizers. This is particularly beneficial in paddy fields, where about 60% of the synthetic fertilizer that has been applied is dissolved in the water and washed away. In these agricultural systems, N2-fixing cyanobacteria show a promising biotechnological potential as biofertilizers, improving soil fertility while reducing the environmental impact of the agricultural practice. In the current study, Andalusian paddy fields have been explored to isolate N2-fixing cyanobacteria. These endogenous microorganisms have been subsequently re-introduced in a field trial in order to enhance rice production. Our results provide valuable insights regarding the use of an alternative natural source of nitrogen for rice production.

scholarly journals Influence of TEM-1 β-Lactamase on the Pharmacodynamic Activity of Simulated Total versus Free-Drug Serum Concentrations of Cefditoren (400 Milligrams) versus Amoxicillin-Clavulanic Acid (2,000/125 Milligrams) against Haemophilus influenzae Strains Exhibiting an N526K Mutation in the ftsI Gene

2007 ◽  
Vol 51 (10) ◽  
pp. 3699-3706 ◽  
Author(s):  
M. Torrico ◽  
L. Aguilar ◽  
N. González ◽  
M. J. Giménez ◽  
O. Echeverría ◽  
...  
Keyword(s):  
Haemophilus Influenzae ◽  
Oral Administration ◽  
Clavulanic Acid ◽  
Bactericidal Activity ◽  
Theoretical Calculations ◽  
Point Of View ◽  
Release Formulation ◽  
Extended Release Formulation ◽  
Amoxicillin Clavulanic Acid ◽  
Free Serum

ABSTRACT The aim of this study was to explore bactericidal activity of total and free serum simulated concentrations after the oral administration of cefditoren (400 mg, twice daily [bid]) versus the oral administration of amoxicillin-clavulanic acid extended release formulation (2,000/125 mg bid) against Haemophilus influenzae. A computerized pharmacodynamic simulation was performed, and colony counts and β-lactamase activity were determined over 48 h. Three strains were used: ampicillin-susceptible, β-lactamase-negative ampicillin-resistant (BLNAR) (also resistant to amoxicillin-clavulanic acid) and β-lactamase-positive amoxicillin-clavulanic acid-resistant (BLPACR) strains, with cefditoren MICs of ≤0.12 μg/ml and amoxicillin-clavulanic acid MICs of 2, 8, and 8 μg/ml, respectively. Against the ampicillin-susceptible and BLNAR strains, bactericidal activity (≥3 log10 reduction) was obtained from 6 h on with either total and free cefditoren or amoxicillin-clavulanic acid. Against the BLPACR strain, free cefditoren showed bactericidal activity from 8 h on. In amoxicillin-clavulanic acid simulations the increase in colony counts from 4 h on occurred in parallel with the increase in β-lactamase activity for the BLPACR strain. Since both BLNAR and BLPACR strains exhibited the same MIC, this was due to the significantly lower (P ≤ 0.012) amoxicillin concentrations from 4 h on in simulations with β-lactamase positive versus negative strains, thus decreasing the time above MIC (T>MIC). From a pharmacodynamic point of view, the theoretical amoxicillin T>MIC against strains with elevated ampicillin/amoxicillin-clavulanic acid MICs should be considered with caution since the presence of β-lactamase inactivates the antibiotic, thus rendering inaccurate theoretical calculations. The experimental bactericidal activity of cefditoren is maintained over the dosing interval regardless of the presence of a mutation in the ftsI gene or β-lactamase production.

Hydrogen exchange and isomerization in ortho substituted benzamides. On the question of free rotation in an N-protonated amide

1979 ◽  
Vol 57 (22) ◽  
pp. 2896-2901 ◽  
Author(s):  
Robert A. McClelland ◽  
William F. Reynolds
Keyword(s):  
Exchange Reaction ◽  
Rate Constants ◽  
Hydrogen Exchange ◽  
Isomerization Reaction ◽  
Free Rotation ◽  
Bond Rotation ◽  
Diffusion Limited ◽  
Deprotonation Reaction ◽  
Substituted Benzamides ◽  
Acid Catalyzed

Rate constants have been obtained for the acid-catalyzed N–H exchange of N-methyl, 2,N-dimethyl, and 2,4,6,N-tetramethylbenzamide and the acid-catalyzed isomerization of the three corresponding N,N-dimethylbenzamides. The ratio [Formula: see text] increases significantly with increased number of ortho methyl substituents. This is explained in terms of a suggestion of Perrin, that C—N bond rotation is not completely free in the N-protonated amide, since it must compete with a diffusion limited deprotonation reaction. The isomerization reaction, which requires such a rotation, is therefore slowed by ortho methyl substituents which hinder rotation, relative to the exchange reaction, which does not require rotation.

scholarly journals THE PROBLEM OF NARRATION IN NOTES FROM A DEAD HOUSE BY FYODOR DOSTOEVSKY

2021 ◽  
Vol 19 (1) ◽  
pp. 221-238
Author(s):  
Tamara Batalova
Keyword(s):  
Sense Of Self ◽  
Self Esteem ◽  
Vital Role ◽  
Point Of View ◽  
Christian Faith ◽  
Fyodor Dostoevsky ◽  
Theatrical Performance ◽  
Essential Idea ◽  
The Dead

Within the framework of Pavel Medvedev’s sociological poetics, the article identifies and studies the features of the narrative in Fyodor Dostoevsky’s Notes from a Dead House, and examines the role of these features in expressing the key idea of this novel, namely the desire of convicts for freedom, for “resurrection from the dead”. From this point of view, the author examines the significance of the narrator’s duality (Goryanchikov and Goryanchikov-Dostoevsky) and the juxtaposition of the characters in the narrative (positive and negative). He also analyzes the compositional function of the XI chapter of the first part of Notes from a Dead House, “Presentation”, in the plot. The Christian faith plays the vital role in the expression of the essential idea of the work. An open-minded attitude to people, a friendly, Christian approach towards them is a distinctive feature of Goryanchikov-Dostoevsky and all the positive characters in the book. Inspired by the celebration of the Nativity of Christ, the convicts staged a theatrical performance, which alters the moral state of both the actors and the audience, fortifies their sense of self-esteem required to resist the prison orders that “deaden” people, and strengthens the prisoners’ desire for freedom, for “resurrection from the dead”. The article concludes that Notes from a Dead House is the beginning of aesthetic and artistic changes that manifested themselves in Dostoevsky’s post-prison works.

scholarly journals Radical-Scavenging and UV-Radiation Absorption Activities of Aaptamine Derivatives: DFT and TD-DFT Studies

2021 ◽  
Author(s):  
Thi Hoai Nam Doan ◽  
Thi Le Anh Nguyen ◽  
Nguyen Thi Ai Nhung ◽  
Duong Tuan Quang ◽  
Duy Quang Dao
Keyword(s):  
Density Functional ◽  
Antioxidant Activities ◽  
Radical Scavenging Activity ◽  
Radical Scavenging ◽  
Hydrogen Atom Transfer ◽  
Radiation Absorption ◽  
Functional Theory ◽  
Radical Adduct ◽  
Td Dft ◽  
Potential Applications

Antioxidant and UV absorption activities of three aaptamine derivatives including piperidine[3,2-b]demethyl(oxy)aaptamine (C1), 9-amino-2-ethoxy-8-methoxy-3H-benzo[de][1,6]naphthyridine-3-one (C2), and 2-(sec-butyl)-7,8-dimethoxybenzo[de]imidazo[4,5,1-ij][1,6]-naphthyridin-10(9H)-one (C3) were theoretically studied by density functional theory (DFT). Optimized geometries of C1C3 and theirs intrinsic thermochemical properties such as bond dissociation energy, proton affinity, and ionization potential were calculated at DFT/M05-2X/6-311++G(d,p) level of theory in vacuo and in water. The results show that C1C3 exhibited similar potent antioxidant activities, which are comparable to well-known antioxidants such as Trolox or cembrene. The radical scavenging activity of the antioxidants were then investigated by evaluation the Gibbs free energy (ΔrG0) of the reaction between C1C3 and the HOO●/HO● radicals via four mechanisms, including: hydrogen atom transfer (HAT), single electron transfer (SET), proton loss (PL) and radical adduct formation (RAF). Kinetic calculation reveals that HOO● scavenging in water is occurred via HAT mechanism with C1@C19 while RAF is more dominant with C2 and C3. Antioxidant activity of aaptamine derivatives can be classified as C1 > C3 > C2. In addition, all compounds are active in UV-Vis absorption; the excitations of which are determined as π-π* transition. Overall, the results suggest the potential applications of the aaptamines in pharmaceutics and cosmetics, i.e. as sunscreen and antioxidant ingredient<br>

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