Hydrogen Abstraction Reactions from Phenolic Compounds by Peroxyl Radicals: Multireference Character and Density Functional Theory Rate Constants

Abstract

An assessment of multireference character in transition states is considered to be an important component in establishing the expected reliability of various electronic structure methods. In the present work, the multireference characters of the transition states and the forming and breaking of bonds for a large set of hydrogen abstraction reactions from phenolic compounds by peroxyl radicals have been analyzed using the T1, M, B1, and GB1 diagnostics. The extent of multireference character depends on the system and on the conditions under which the reaction takes place, and some systematic trends are observed. In particular, the multireference character is found to be reduced by solvation, the size of the phenolic compound, and deprotonation in aqueous solution. However, the deviations of calculated rate constants from experimental ones are not correlated with the extent of multireference character. The performance of single-determinant density functional theory was investigated for the kinetics of these reactions by comparing calculated rate constants to experimental data; the results from these analyses showed that the M05 functional performs well for the task at hand.

Probing the Time Scale of FPOP (Fast Photochemical Oxidation of Proteins): Radical Reactions Extend Over Tens of Milliseconds

“…The wider literature suggests that FPOP conditions will favor the formation of various secondary radicals, and that these species can cause oxidation long after ⋅OH has disappeared [25,46,47,49]. The reactivity of secondary radicals is lower than that of ⋅OH, but due to their extended lifetimes they can nonetheless cause significant analyte oxidation [47,51]. The key question is to what extent the measured Cy5 bleaching profiles reflect the protein oxidation kinetics in FPOP.…”

“…Nonetheless, the cumulative oxidation caused by these secondary radicals in biological samples can be significant because of their long lifetimes [47,51].…”

Computational strategies for predicting free radical scavengers' protection against oxidative stress: Where are we and what might follow?

“…In general, considering formal f ‐HAT, RAF, SET, and SPLET is enough for most free radical scavengers. ‐ Using the transition state theory (TST) for calculating the rate constants and using the Marcus theory to estimate the reaction barriers of SET pathways. Conventional TST is frequently accurate enough in this context . It has been shown to produce rate constants of radical‐molecule reactions with uncertainties similar to those arising from experiments …”

The Role of Solvation in the Kinetics and the Mechanism of Hydroperoxide Radicals Addition to π‐Bonds of 1,2‐Diphenylethylene and 1,4‐Diphenylbutadiene‐1,3

“…Hydroperoxide radicals () are carriers of liquid‐phase chain oxidation of organic molecules of different classes . During the oxidation of unsaturated compounds, depending on the substrate structure, the chain propagation takes place either via the addition reaction: + >CC< (M)→ HOOM • (≡M • ) or via the hydrogen atom abstraction from the αCHbond: + RH → HOOH + R • , or these routes are parallel . Along with liquid‐phase reactions, the possibility of formation is also considered in micro‐heterogeneous systems, particularly, the oxidation of methyl linoleate in micelles .…”