Topology-Dependent Dissociation Mode of the O–H Bond in Monohydroxycoumarins

Abstract

All possible monohydroxycoumarin derivatives are modeled using density functional theory computations in order to investigate the role of the hydroxyl group position for the radical-scavenging and antioxidant activity of these compounds. Geometry optimization is performed using the B3LYP functional with the 6-311++G­(d,p) basis set. The enthalpy changes are assessed in gas phase and in implicit water using the polarized continuum model. Structure–reactivity patterns are delineated. The most reactive isomers as well as the most probable mechanism of interaction between monohydroxycoumarins and free radicals are outlined.

Mechanism of Antioxidant Activity of Betanin, Betanidin and Respective C15-Epimers via Shape Theory, Molecular Dynamics, Density Functional Theory and Infrared Spectroscopy

“…The compounds’ ETE value in kcal/mol increases in the following order: Bn < IsoBn < Bd < IsoBd. The fact that IsoBd loses hydrogen easier than the rest and at the same time corresponds to the highest value of the ETE descriptor could imply that the anion form is long-living, which would allow various transformations, thus being able to lose antioxidant capacity [ 32 ]. However, in general terms, the difference between the ETE values and all the descriptors is not very wide, and as discussed above, the most favorable antioxidant mechanism in water is the SPLET mechanism for all the compounds studied, IsoBd is the first compound to loss of hydrogen.…”

“…The capacity to scavenge free radicals (R ) through a hydrogen atom transfer (H ) from phenolic hydroxyl groups to the free radical, either in one step or in two steps, was mainly approached through three mechanisms (i) HAT, a direct Hydrogen Atom Transfer between the antioxidant and the active radical (Equation ( 1 )), (ii) SPLET (Sequential Proton Loss Electron Transfer): deprotonation of the antioxidant which resulting anion, followed by an electron transfer to the active radical, the final step is protonation of the anion of the active radical (Equation ( 2 )) and (iii) SET-PT (Single Electron Transfer Proton Transfer): an electron is transferred from the antioxidant to the active radical, yielding a cation-radical and an anion, followed by proton transfer from the cation-radical to the anion (Equation ( 3 )). These mechanisms may occur parallel but with different rates [ 11 , 29 , 32 , 33 , 34 , 35 ]. …”

“…In addition, PubChem’s repository facilitates the download files of the structures of Betanin and Betanidin used for the DFT studies, and from them, the stereoisomers were obtained [ 37 ]. The free radical-scavenging activity can be determined via studies with different levels of theory and have reported that the computational level DFT B3LYP/631+G(d,p) has allowed analyzing the system quite well at a low computational cost [ 11 , 16 , 32 , 38 ].…”

“…All enthalpies-calculated at 298 K and 1.0 atm. Previous reports provide the enthalpies in the water of the hydrogen atom, proton, and electron: the enthalpy of the proton H(H+) is −259.00 kcal/mol, the enthalpy of the electron H(e−) is −55.61 kcal/mol, and the enthalpy of the hydrogen atom H(H−) is −314.65 kcal/mol [ 32 , 42 ]. The IR-simulated spectra via the Gaussian 09 package for the parent molecules Bn, Bd, IsoBn, and IsoBd.…”

Topology delimited radical‐scavenging propensity of monohydroxycinnamic acids

“…Yet the calculated BDE values are in good agreement with those obtained by other authors or in our earlier studies for these or analogous compounds. [25][26][27][28][29]…”