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The present work addresses the quantitative structure–antioxidant activity relationship in a series of 148 sulfur-containing alkylphenols, natural phenols, chromane, betulonic and betulinic acids, and 20-hydroxyecdysone using GUSAR2019 software. Statistically significant valid models were constructed to predict the parameter logk7, where k7 is the rate constant for the oxidation chain termination by the antioxidant molecule. These results can be used to search for new potentially effective antioxidants in virtual libraries and databases and adequately predict logk7 for test samples. A combination of MNA- and QNA-descriptors with three whole molecule descriptors (topological length, topological volume, and lipophilicity) was used to develop six statistically significant valid consensus QSPR models, which have a satisfactory accuracy in predicting logk7 for training and test set structures: R2TR > 0.6; Q2TR > 0.5; R2TS > 0.5. Our theoretical prediction of logk7 for antioxidants AO1 and AO2, based on consensus models agrees well with the experimental value of the measure in this paper. Thus, the descriptor calculation algorithms implemented in the GUSAR2019 software allowed us to model the kinetic parameters of the reactions underlying the liquid-phase oxidation of organic hydrocarbons. [ABSTRACT FROM AUTHOR]

The antioxidant properties of a series of biologically active polysubstituted tetrahydroquinolines containing chromanyl fragments have been experimentally studied in the liquid phase. Probed was the ability of the substrates to kinetically retard the initiator‐induced radical chain oxidation by O2 of the model compounds 1,4‐dioxane or isopropyl alcohol. The oxidation reactions were monitored at 348 K using a manometric technique, measuring under various initial conditions the time‐dependent concentration of oxygen in the gas phase above a reaction mixture containing the radical‐chain initiator azobisisobutylnitrile and the substrates under study. When tetrahydroquinolines were present, the kinetic curves of oxygen absorption exhibited characteristic induction periods (τ) wherein the reaction rate is immeasurably small. The dependence of τ on the initial concentration of the introduced antioxidants has been determined and the results interpreted within the framework of a classical scheme describing the radical‐chain oxidation of organic compounds in the presence of an inhibitor. Values of the stoichiometric coefficient of inhibition, f, which is related to the number of chain propagating radicals destroyed by each antioxidant molecule, is >>2 for all the studied antioxidants. Consistent with the existing literature, it is inferred that the original antioxidant molecule is regenerated from its radical inhibition product during reaction. Previous studies suggest that oxyperoxy radicals play an important role in the inhibitor regeneration process due to their ability to act either as an oxidizer (in chain propagation) or as a reducing agent (in regeneration of the inhibitor from its corresponding radical). In the presently studied systems containing 1,4‐dioxane, it is argued that the source of oxyperoxy radicals is 2‐hydroxy‐1,4‐dioxane. A reaction mechanism that includes the stages of inhibitor regeneration and that is quantitatively consistent with the present results has been developed. It is suggested that the high antioxidant capacity of the tetrahydroquinoline derivatives is due to their large chain breaking rate constants in conjunction with regeneration of the inhibitor during chain termination processes. The relationship of the studied chemical structures and their antioxidant capacity is discussed. [ABSTRACT FROM AUTHOR]

A quantitative analysis of the structure-antioxidant activity relationship was performed for 128 derivatives of phenols, amines, uracil, benzopyrane, and benzofuran using the GUSAR 2013 program. Nine statistically significant QSAR consensus models characterized by a high accuracy of prediction of the chain termination rate constant of oxidation on the antioxidant molecules were constructed. The results of the structural analysis performed in the GUSAR 2013 program are in good agreement with the literature data. [ABSTRACT FROM AUTHOR]

The free-radical chain oxidation of 1,4-dioxane in the presence of an inhibitor has been investigated by mathematical modeling. The forward kinetic problem has been solved, and complete kinetic information about the reaction has been gained, including the variation of the concentrations of all reaction participants. The inverse kinetic problem has also been solved to determine the rate constants of all elementary steps. [ABSTRACT FROM AUTHOR]

ABSTRACT This article addresses mathematical modeling of the reaction of inhibited organic compounds oxidation. It was proposed to solve the inverse problems of chemical kinetics by using the index method of constrained global minimization of the deviation between the calculated and experimental data. This approach allows us to use more complete information about the chemical process which, in its turn, reduces the range of possible solutions, narrows down the domain of uncertainty, and improves the quality of mathematical model of chemical reactions. The index method was applied to solving inverse kinetic problem for the reaction of n-decane oxidation in the presence of a p-oxydiphenylamine/n-decyl alcohol inhibitory composition. [ABSTRACT FROM AUTHOR]

We designed an algorithm and software for inverse kinetic problem solving by conditional global minimization of the deviation of calculated data from experimental data. This approach allows use of more complete information on the process, which narrows the region of feasibility and increases the quality of mathematical simulation of chemical reactions. The algorithms designed were tested in the kinetic description of a complex liquid-phase chain reaction, specifically, the oxidation of n-decane in the presence of an inhibiting composition, viz., para-oxydiphenylamine + n-decanol. [ABSTRACT FROM AUTHOR]

A new software package is suggested for solving the inverse kinetic problem for inhibited oxidation reactions of organic compounds. The software has been developed using inhibited n-decane oxidation as the model reaction. [ABSTRACT FROM AUTHOR]

The antioxidant properties of 2,4-diphenyl-7,8-benzo-5,6-dihydro(4H)selenochromene, some of its chlorine-containing derivatives, and selected chromilium salts based on these derivatives have been investigated using the initiated oxidation of 1,4-dioxane as a model reaction. The antioxidant activity of these compounds is quantitatively characterized by the apparent inhibition rate constant fk. [ABSTRACT FROM AUTHOR]

The antioxidant properties of conjugates of betulonic and betulinic acids with amido derivatives of the acid Trolox were studied for initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the compounds was characterized in terms of the apparent inhibition rate constant fk. [ABSTRACT FROM AUTHOR]

The antiradical properties of a number of uracil derivatives are studied in initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the uracil derivatives as inhibitors is estimated. The antiradical activity of the compounds is quantitatively characterized in terms of the effective rate constant of inhibition, fk. [ABSTRACT FROM AUTHOR]

The antioxidant properties of 20-hydroxyecdysone and its conjugates with (6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)acetaldehyde are reported for initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of these compounds is characterized in terms of the effective rate constant of inhibition, fk. [ABSTRACT FROM AUTHOR]

The kinetics of 1,4-dioxane oxidation initiated by azodiisobutyronitrile in the temperature range from 323 to 353 K are studied from the rate of oxygen absorption. The oxidation proceeds in the regime of a nonbranched chain reaction with quadratic-law chain termination. The apparent rate constants ( fk 7) of 1,4-dioxane oxidation inhibition by 2,6-ditert-butyl-4-methylphenol and quercitin are measured. Quercitin is not inferior to ionol in inhibition efficiency. [ABSTRACT FROM AUTHOR]

Antioxidant properties of caffeic, ferulic, vanillic, and 4-hydroxybenzoic acids isolated from Larix sibirica Ledeb. bark were studied using model radical-chain reactions for oxidation of propan-2-ol and 1,4-dioxane under kinetic control. Quantitative characteristics of the antioxidant activities were determined as effective rate constants fkIn for oxidation chain termination of the phenolcarboxylic acids. It was found that caffeic acid had the highest antioxidant activity among the investigated natural compounds. [ABSTRACT FROM AUTHOR]

The antioxidant [AO] properties of the ethylacetate extract of Larix sibirica bark and the flavonoids quercetin and dihydroquercetin found in it were studied using a model radical-chain oxidation of propan-2-ol in the kinetic regime. The quantitative characteristics of their AO activity were determined as effective rate constants fkln. It was found that dihydroquercetin had the highest AO activity among the studied natural compounds. [ABSTRACT FROM AUTHOR]

The kinetics of the reactions of ozone with 12 substituted olefins in aqueous solutions at 293 K are studied by the stopped-flow method. Second-order rate constants are determined for these reactions. The dependence of the reactivity of olefins in H2O on their structure can be described by the Taft equation. [ABSTRACT FROM AUTHOR]

Using the GUSAR 2013 program, the quantitative structure–antioxidant activity relationship has been studied for 74 phenols, aminophenols, aromatic amines and uracils having lgk7 = 0.01–6.65 (where k7 is the rate constant for the reaction of antioxidants with peroxyl radicals generated upon oxidation). Based on the atomic descriptors (Quantitative Neighborhood of Atoms (QNA) and Multilevel Neighborhoods of Atoms (MNA)) and molecular (topological length, topological volume and lipophilicity) descriptors, we have developed 9 statistically significant QSAR consensus models that demonstrate high accuracy in predicting the lgk7 values for the compounds of training sets and appropriately predict lgk7 for the test samples. Moderate predictive power of these models is demonstrated using metrics of two categories: (1) based on the determination coefficients R2 (R2TSi, R20, Q2(F1), Q2(F2), R mTSi 2 ¯ ) and based on the concordance correlation coefficient (CCC)); or (2) based on the prediction lgk7 errors (root mean square error (RMSEP), mean absolute error (MAE) and standard deviation (S.D.)) The RBF-SCR method has been used for selecting the descriptors. Our theoretical prognosis of the lgk7 for 8-PPDA, a known antioxidant, based on the consensus models well agrees with the experimental value measure in the present work. Thus, the algorithms for calculating the descriptors implemented in the GUSAR 2013 program allow simulating kinetic parameters of the reactions underling the liquid-phase oxidation of hydrocarbons. [ABSTRACT FROM AUTHOR]

The antioxidant activity of extracts from a series of plants of Geraniaceae and Rosaceae families was studied as a function of the solution concentration and characterized by their ability to inhibit the model reaction of isopropyl alcohol oxidation. The activity of extracts was evaluated in terms of the inhibition rate constants. The influence of extractant (aqueous ethanol versus water) on the relative activity variation in the series of plant extracts was studied. [ABSTRACT FROM AUTHOR]

Discusses the study which examined the oxidation of 2-propanol in the presence of a mixture of uracils and hydrogen peroxide and found an anomalous influence of hydrogen peroxide on the inhibition of oxidation. Use of uracils as antioxidants; Decrease in the initial rate of oxygen absorption.

The antioxidant properties of humic substances of low-mineralization sulfidic muds (peloids) were investigated using initiated oxidation of 1,4-dioxane as a model reaction. Four groups of substances including humic, himatomelanic, fulvic, and humus acids were studied. Kinetic characteristics of the oxidation of humic substances were determined in terms of effective inhibition rate constants fk. It is established that himatomelanic acids of peloids exhibit the maximum antioxidant activity among the studied substances. [ABSTRACT FROM AUTHOR]