Computational Antioxidant Capacity Simulation (CAOCS): A Novel Framework of Antioxidant Capacity Profiling

2014 ◽  
Vol 9 (1) ◽  
pp. 25-43 ◽  
Author(s):  
Sunday O. Idowu
Keyword(s):  
Proton Transfer ◽  
Antioxidant Capacity ◽  
Exponential Decay ◽  
Information Criterion ◽  
Hydrogen Atom Transfer ◽  
Phenol Red ◽  
Linear Free Energy ◽  
Analytical System ◽  
Decay Threshold ◽  
Exponential Decay Equation

Abstract Inconsistent ranking is a well-known drawback of antioxidant capacity (AOC) profiling methodologies that use free-radical species as oxidant. This problem leads to assay results that are not biorelevant. Linear free energy relationships (LFER) theory predicts proton transfer (PT) kinetics as a surrogate for biorelevant hydrogen atom transfer (HAT) kinetics. Computational antioxidant capacity simulation (CAOCS), based on real-time proton transfer kinetics modeling (PTKM) of polyphenols and phenol-like small molecules, inspired a novel AOC profiling methodology. Kinetic data acquired by incremental addition of resorcinol to an oxidized probe (phenol red), was fitted to mono-exponential decay equation (MED). Absorbance decay data from strongly antioxidant phenol-like molecules (e.g. ascorbic acid) and a new chromogenic probe (phenolphthalein) was fitted to MED and bi-exponential decay equation. The preferred model and corresponding best-fit rate constant (Kptt) was identified by comparison of fits, using Akaike’s Information Criterion (AICc). Photometric phenolphthalein assay (PPA)-derived metric was normalized with photometric phenol red assay (PPRA) results by using a function developed from proton concentration differential between phenolphthalein and phenol red, with respect to decay threshold to plateau (assay endpoint) interval. pKa dependence of the CAOCS’ metric is a signature of structure–function relationships, and hence, biorelevance. It is shown, unambiguously, that a combination of two phenolic probe molecules, an analytical system devoid of free radicals, and statistical identification of preferred exponential decay fit to PT kinetics data, constitutes a novel algorithm for AOC profiling of polyphenols and phenol-like molecules. This methodology holds a promise of utility in quality assurance of dietary supplements.

Computational Models for the Determination of Antioxidant Capacity and Phenolics in Dietary Supplements Using Real-Time Proton Transfer Kinetics Data

2009 ◽  
Vol 4 (1) ◽  
Author(s):  
Sunday O Idowu ◽  
Morenikeji A Adeyemo ◽  
Ademola J Itiola
Keyword(s):  
Free Radical ◽  
Proton Transfer ◽  
Antioxidant Capacity ◽  
Dietary Supplement ◽  
Exponential Decay ◽  
Linear Free Energy Relationship ◽  
Phenol Red ◽  
Kinetic Assay ◽  
Hydroxyl Ion ◽  
Chain Breaking

Hydrogen atom transfer (HAT) underlies free-radical chain-breaking by phenolic compounds. Using linear free energy relationship (LFER) analysis, proton transfer kinetics was hypothesized as a surrogate rate process for HAT. Phenol red is a probe that is easily oxidized to highly absorbing specie by hydroxyl ion. Absorbance decay of oxidized phenol red was induced by incremental proton transfer from a model phenolic (resorcinol). Global best-fit kinetics profile of resorcinol approximates a mono-exponential decay model (R2 = 0.991) as a limiting law. Proton transfer rate constant (Kptt) versus concentration reveal the utility of the slope (?aoc) of the linear plot (r2= 0.990) as a sensitive predictor of phenolic antioxidant capacity. Superior antioxidant capacity profile of a polyphenol-rich dietary supplement: Garcinia kola seed extract, optimally obeyed a mixed linear/mono-exponential decay equation. Model robustness and selectivity for phenolics was achieved by specifying mathematical constraints as acceptance criteria. The method is more biologically relevant for chain-breaking antioxidants than free-radical-based assays because it captures antioxidant structure-function relationships. Further validation studies, using structurally diverse polyphenols, are warranted to ascertain general utility of the kinetic assay for achieving quality by design (QbD) in phenolic dietary supplement products.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis

2019 ◽  
Author(s):  
Dominic Di Toro ◽  
Kevin P. Hickey ◽  
Herbert E. Allen ◽  
Richard F. Carbonaro ◽  
Pei C. Chiu
Keyword(s):  
Free Energy ◽  
Hydrogen Atom ◽  
Hydrogen Atom Transfer ◽  
Energy Model ◽  
Second Order ◽  
Transfer Model ◽  
Atom Transfer ◽  
Order Rate ◽  
Linear Free Energy ◽  
Free Energy Model

<div>A linear free energy model is presented that predicts the second order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). For this situation previously presented models use the one electron reduction potential of the NAC reaction. If such value is not available, it has been has been proposed that it could be computed directly or estimated from the electron affinity (EA). The model proposed herein uses the Gibbs free energy of the hydrogen atom transfer (HAT) as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic parameters. The available and proposed models are compared using second order rate constants obtained from five investigations reported in the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the computed hydrogen atom transfer model and the experimental one electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed electron affinity has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed hydrogen transfer reaction free energy produces a more reliable prediction of the NAC abiotic reduction second order rate constant than previously available methods. The advantages of the proposed hydrogen atom transfer model and its mechanistic implications are discussed as well.</div>

Ion-molecule reactions in acetone-water mixtures

1966 ◽  
Vol 19 (1) ◽  
pp. 59 ◽  
Author(s):  
Souza BC de ◽  
JH Green
Keyword(s):  
Hydrogen Atom ◽  
Proton Transfer ◽  
Transfer Process ◽  
Hydrogen Atom Transfer ◽  
Mass Spectrometric ◽  
Transfer Mechanism ◽  
Atom Transfer ◽  
Ion Molecule Reactions ◽  
Acetone Water

Mass-spectrometric studies of ion-molecule reactions in acetone-water mixtures at 70 eV and 20 eV electron energies are described. The results provide evidence in favour of the proton transfer mechanism rather than for a hydrogen atom transfer process for the production of M + 1 ions.

scholarly journals Artificial Intelligence (AI) to the Rescue: Deploying Machine Learning to Bridge the Biorelevance Gap in Antioxidant Assays

2020 ◽  
pp. 247263032096271
Author(s):  
Sunday Olakunle Idowu ◽  
Amos Akintayo Fatokun
Keyword(s):  
Oxidative Stress ◽  
Artificial Intelligence ◽  
Machine Learning ◽  
Antioxidant Capacity ◽  
Unmet Need ◽  
Hydrogen Atom Transfer ◽  
Support Vector ◽  
Antioxidant Action ◽  
Predictive Tool

Oxidative stress induced by excessive levels of reactive oxygen species (ROS) underlies several diseases. Therapeutic strategies to combat oxidative damage are, therefore, a subject of intense scientific investigation to prevent and treat such diseases, with the use of phytochemical antioxidants, especially polyphenols, being a major part. Polyphenols, however, exhibit structural diversity that determines different mechanisms of antioxidant action, such as hydrogen atom transfer (HAT) and single-electron transfer (SET). They also suffer from inadequate in vivo bioavailability, with their antioxidant bioactivity governed by permeability, gut-wall and first-pass metabolism, and HAT-based ROS trapping. Unfortunately, no current antioxidant assay captures these multiple dimensions to be sufficiently “biorelevant,” because the assays tend to be unidimensional, whereas biorelevance requires integration of several inputs. Finding a method to reliably evaluate the antioxidant capacity of these phytochemicals, therefore, remains an unmet need. To address this deficiency, we propose using artificial intelligence (AI)-based machine learning (ML) to relate a polyphenol’s antioxidant action as the output variable to molecular descriptors (factors governing in vivo antioxidant activity) as input variables, in the context of a biomarker selectively produced by lipid peroxidation (a consequence of oxidative stress), for example F2-isoprostanes. Support vector machines, artificial neural networks, and Bayesian probabilistic learning are some key algorithms that could be deployed. Such a model will represent a robust predictive tool in assessing biorelevant antioxidant capacity of polyphenols, and thus facilitate the identification or design of antioxidant molecules. The approach will also help to fulfill the principles of the 3Rs (replacement, reduction, and refinement) in using animals in biomedical research.

scholarly journals Proton-Coupled Electron Transfer in the Reaction of 3,4-Dihydroxyphenylpyruvic Acid with Reactive Species in Various Media

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
J. J. Fifen ◽  
Z. Dhaouadi ◽  
M. Nsangou ◽  
O. Holtomo ◽  
N. Jaidane
Keyword(s):  
Electron Transfer ◽  
Proton Transfer ◽  
Activation Barrier ◽  
Bond Cleavage ◽  
Hydrogen Atom Transfer ◽  
Free Energies ◽  
Solvent Interactions ◽  
Proton Coupled Electron Transfer ◽  
Nonpolar Solvents ◽  
One Step

The distinction of concerted proton-coupled electron transfer (CPCET) from sequential one as well as proton transfer-electron transfer (PT-ET) from electron transfer-proton transfer (ET-PT) in the O–H bond cleavage reactions in various media has always been a difficult task. In this work, the activation barrier of the CPCET mechanism, its rate constants, and reaction free energies related to ET-PT and PT-ET involving coreactive species were presented as good parameters to attempt the problem. DFT calculations were carried out studying the described pathways subsequent to the scavenging of OH• and OBr- by the 3,4-DHPPA in various media. The solvation was described in a hybrid manner using IEF-PCM model conjointly with a model that takes into account some solute-solvent interactions. As a result, we found that the scavenging of hydroxyl radical by 3,4-DHPPA is thermodynamically governed by a one-step hydrogen atom transfer (CPCET) from the acid to the radical in all media. In kinetic viewpoint, CPCET still dominates in the vacuum and in nonpolar solvents, but in polar solvents it could compete strongly with the ET-PT mechanism so that the latter could slightly dominate.

Selected-ion flow tube studies of reactions of the radical cation (HC3N)+• in the interstellar chemical synthesis of cyanoacetylene

1986 ◽  
Vol 64 (2) ◽  
pp. 399-403 ◽  
Author(s):  
A. Fox ◽  
A. B. Raksit ◽  
S. Dheandhanoo ◽  
D. K. Bohme
Keyword(s):  
Hydrogen Atom ◽  
Proton Transfer ◽  
Radical Cation ◽  
Covalent Bond ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Flow Tube ◽  
Ion Flow ◽  
Wide Range ◽  
Selected Ion Flow Tube

The radical cation (HC3N)+• was produced in a Selected-Ion Flow Tube (SIFT) apparatus from cyanoacetylene by electron impact and reacted at room temperature in helium buffer gas with a selection of molecules including H2, CO, HCN, CH4, H2O, O2, HC3N, C2H2, OCS, C2H4, and C4H2. The observed reactions exhibited a wide range of reactivity and a variety of pathways including charge transfer, hydrogen atom transfer, proton transfer, and association. Association reactions were observed with CO, O2, HCN, and HC3N. With the latter two molecules association was observed to proceed close to the collision limit, which is suggestive of covalent bond formation perhaps involving azine-like N—N bonds. For HC3N an equally rapid association has been observed by Buckley etal. with ICR (Ion Cyclotron Resonance) measurements at low pressures and this is suggestive of radiative association. The hydrogen atom transfer reaction of ionized cyanoacetylene with H2 is slow while similar reactions with CH4 and H2O are fast. The reaction with CO fails to transfer a proton. These results have implications for synthetic schemes for cyanoacetylene as proposed in recent models of the chemistry of interstellar gas clouds. Proton transfer was also observed to be curiously unfavourable with all other molecules having a proton affinity higher than (C3N)•. Also, hydrogen-atom transfer was inefficient with the polar molecules HCN and HC3N. These results suggest that interactions at close separations may lead to preferential alignment of the reacting ion and molecule which is not suited for proton transfer or hydrogen atom transfer.

scholarly journals Defining a standardized methodology for the determination of the antioxidant capacity: case study of Pistacia atlantica leaves

The Analyst ◽  
2020 ◽  
Vol 145 (2) ◽  
pp. 557-571 ◽  
Author(s):  
Ziyad Ben Ahmed ◽  
Yousfi Mohamed ◽  
Viaene Johan ◽  
Bieke Dejaegher ◽  
Kristiaan Demeyer ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Electron Transfer ◽  
Hydrogen Atom ◽  
Antioxidant Capacity ◽  
Hydrogen Atom Transfer ◽  
Single Electron ◽  
Single Electron Transfer ◽  
Pistacia Atlantica

Antioxidant activity can be measured by a variety of methods, that include hydrogen atom transfer (HAT) and single electron transfer (ET) methods.

scholarly journals Antioxidant Capacity and Phenolic Content of four Myrtaceae Plants of the South of Brazil

2011 ◽  
Vol 6 (7) ◽  
pp. 1934578X1100600 ◽  
Author(s):  
Marcos José Salvador ◽  
Caroline C. de Lourenço ◽  
Nathalia Luiza Andreazza ◽  
Aislan C.R.F. Pascoal ◽  
Maria Élida Alves Stefanello
Keyword(s):  
Antioxidant Activity ◽  
Antioxidant Capacity ◽  
Transfer Reaction ◽  
Phenolic Content ◽  
Hydrogen Atom Transfer ◽  
Preliminary Evaluation ◽  
Dpph Assay ◽  
The South ◽  
Ethanolic Extracts ◽  
South Of Brazil

Antioxidant compounds can be useful to prevent several degenerative diseases or as preservative in food and toiletries. Species of the Myrtaceae family are able to accumulate phenolic substances and those are closely related to the antioxidant activity due to their capacity to scavenge free radicals, protect against lipid peroxidation and quench reactive oxygen species. These facts prompted us to investigate the antioxidant capacity of the ethanolic extracts of the leaves of four Myrtaceae plants collected of the south of Brazil: Eugenia chlorophylla O. Berg., Eugenia pyriformis Cambess, Myrcia laruotteana Cambess and Myrcia obtecta (Berg) Kiacrsk. The antioxidant potential was performed using the DPPH (a single electron transfer reaction based assay) and ORAC (Oxygen Radical Absorbance Capacity, a hydrogen atom transfer reaction based assay) assays. Moreover, the total soluble phenolic content was also measured using the Folin-Ciocalteu reagent. A preliminary evaluation of the ethanolic extracts of these Myrtaceae plants revealed high levels of phenolic compounds (343.7-429.3 mg GAE) as well as high antioxidant activity according to both methods (1338 a 3785 μmol of TE/g of extract in ORAC and SC50 in the range of 1.70 and 33.7 μg/mL in the DPPH). The highest antioxidant activity obtained by DPPH assay was exhibited by ethanol extract of the leaves of E. pyriformis (1.70 μg/mL), followed by extracts of M. laruotteana (3.38 μg/mL) and M. obtecta (6.66 μg/mL). In comparison with controls, in the DPPH assay, the extract of E. pyriformis was more active than trolox (SC50 = 2.55 μg/mL), while the extracts of M. laruotteana and M. obtecta were more actives than quercetin (SC50 = 7.80 μg/mL). In the ORAC assay, all species also show good antioxidant capacity (>1000 μmol of TE/g). Initial HPLC-UV/DAD and ESIMS confirmed the presence of phenolic acids constituents in the ethanol extracts. The results indicate the presence of compounds possessing promising antioxidant/free-radical scavenging activity in the analyzed extracts of Myrcia and Eugenia plants of the south of Brazil.

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