Abstract
In the search for new antioxidants, flavan structures called our attention, as substructures of many important natural compounds, including catechins (flavan-3-ols), simple and dimeric proanthocyanidins, and condensed tannins. In this work the conformational space of the Z-isomers of (4α→6´´, 2α→O→1´´)-phenylflavans substituted with R = H, OH and OCH(3) was scanned in aqueous solution, simulating the solvent by the polarizable continuum model (PCM). Geometry optimizations were performed at B3LYP/6-31 G level. Electronic distributions were analyzed at a better calculation level, thus improving the basis set (6-311++G). A topological study based on Bader´s theory (atoms in molecules) and natural bond orbital (NBO) framework was performed. Furthermore, molecular electrostatic potential maps (MEPs) were obtained and thoroughly analyzed. The stereochemistry was discussed, and the effect of the solvent was addressed. Moreover, intrinsic properties were identified, focusing on factors that may be related to their antioxidant properties. Hyperconjugative and inductive effects were described. The coordinated NBO/AIM analysis allowed us to rationalize the changes of MEPs in a polar solvent. To investigate the molecular and structural properties of these compounds in biological media, the polarizabilities and dipolar moments were predicted which were further used to enlighten stability and reactivity properties. All conformers were taken into account. Relevant stereoelectronic aspects were described for understanding the stabilization and antioxidant function of these structures.
Highlights
The role of flavonoids as antioxidants is the subject of intense theoretical and experimental research
The main substructure of the non-substituted (4α→6 ́ ́, 2α→O→1 ́ ́)-phenylflavan was a [3.1.3]bicycle (Fig. 1), which consisted of two 6-membered rings, C and E, each involved in a benzo-γ-pyran, fused by a CH2-3-containing bridge with bridgehead C-2 and C-4
The stereochemistry of (4α→6 ́ ́,2α→O→1 ́ ́)-phenylflavan was studied in aqueous solution, emphasizing the description of the factors that determine it, and the changes that occur with R=OCH3, R=H, and R=OH, R'=H as substituents
Summary
The role of flavonoids as antioxidants is the subject of intense theoretical and experimental research. The biological and pharmaceutical activities of these compounds have been related to their antioxidant activity as free radical scavengers. Free radicals can damage biomolecules such as lipids, amino acids, proteins, carbohydrates and nucleic acids by the process of oxidative damage resulting in several diseases and aging [1]. They were associated with deterioration of plant tissues, such as fruits and vegetables. The biological activity of flavonoids is governed by electronic interactions of the biomolecules within the cell [2].
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