Evaluation of the Radical-Scavenging Properties of Various Flavonols in Ethanol Environment: an ab initio Study

Raluca Pop

doi:10.5562/cca3449

Abstract

The antioxidant properties of six flavonols -fisetin, galangin, gossipetin, kaempferol, morin and myricetin- have been investigated at HF/6-311G+(d,p) level of theory, using ethanol as solvent. Three known antioxidant mechanisms, namely HAT (hydrogen atom transfer), SET-PT (single electron transfer followed by proton transfer) and SPLET (sequential proton loss electron transfer) have been employed in order to evaluate the radical scavenging abilities of the investigated compounds. Thermodynamic parameters like bond dissociation energy (BDE), proton affinity (PA), electron transfer enthalpy (ETE), ionization potential (IP) and proton dissociation enthalpy (PDE) were calculated and the results were associated with the number and the positions of the hydroxyl groups, the geometry of the parent molecule and of the corresponding radicals, as well as with the electron spin distribution. Also, computations of global reactivity descriptors like HOMO-LUMO gap showed that an increased reactivity is related to the presence of the catechol moiety (gossipetin, myricetin, fisetin). The influence of the catecholic OH groups is also outlined by the HOMO energies, highest electron-donor ability being obtained for gossipetin, the flavonol with two catecholic moieties on rings A and B. According to the HAT mechanism, it has been outlined an enhanced antioxidant character of the 3-OH groups, followed by the hydroxyl groups attached to the phenyl ring B. The calculated values of the condensed Fukui functions, computed for a radical attack, are in good agreement with the above-mentioned results.

Highlights

W ITHIN the last years, there have been performed various studies that have outlined the role of the oxidative stress in neurodegenerative and cardiovascular diseases, metabolic disorders or cancer.[1,2] Defined as the imbalance between prooxidant and antioxidant species,[3] the importance of the oxidative stress in the etiology of the above-mentioned diseases had a significant effect on other research field of great interest, the one of the antioxidants
A brief summarization regarding the number and the position of the hydroxyl groups of the investigated flavonols outlines that one of the investigated structures is characterized by the presence of three OH groups exclusively attached to the rings A and C; two compounds have four OH groups
The second stage of the SET-PT mechanism involves the donation of the proton from the cation radical structure, so the proton dissociation enthalpy (PDE) parameter has been computed for each hydroxyl group; the results presented in Table 8 are in good agreement with the bond dissociation energy (BDE) trend

Summary

Introduction

W ITHIN the last years, there have been performed various studies that have outlined the role of the oxidative stress in neurodegenerative and cardiovascular diseases, metabolic disorders or cancer.[1,2] Defined as the imbalance between prooxidant and antioxidant species,[3] the importance of the oxidative stress in the etiology of the above-mentioned diseases had a significant effect on other research field of great interest, the one of the antioxidants. Due to the fact that the antioxidant activity is based on the capacity of donating one electron or proton, there are various classes of compounds that are successfully used within this field. The polyphenols, the carotenoids, the vitamins A and C are the most frequently encountered

Methods

Results

Conclusion