Structural-Electronic Properties and Antioxidant Relations—A Case of DFT Study
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Hindawi Journal of Chemistry Volume 2019, Article ID 4360175, 12 pages https://doi.org/10.1155/2019/4360175 Research Article Isoflavones and Isoflavone Glycosides: Structural-Electronic Properties and Antioxidant Relations—A Case of DFT Study Son Ninh The ,1 Thanh Do Minh,2 and Trang Nguyen Van 2 1Institute of Natural Products Chemistry, Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Caugiay, Hanoi, Vietnam 2Institute for Tropical Technology, Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet, Caugiay, Hanoi, Vietnam Correspondence should be addressed to Son Ninh e; [email protected] and Trang Nguyen Van; [email protected] Received 8 January 2019; Revised 13 February 2019; Accepted 24 February 2019; Published 24 June 2019 Academic Editor: Artur M. S. Silva Copyright © 2019 Son Ninh e et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Isoflavonoids and isoflavonoid glycosides have drawn much attention because of their antioxidant radical-scavenging capacity. Based on computational methods, we now present the antioxidant potential results of genistein (1), biochanin A (2), ambocin (3), and tectorigenin 7-O-[β-D-apiofuranosyl-(1-6)-β-D-glucopyranoside] (4). e optimized structures of the neutral and radical forms have been determined by the DFT-B3LYP method with the 6-311G(d) basis set. From the findings and thermodynamic point of view, the ring B system of isoflavones is considered as an active center in facilitating antioxidant reactions. Antioxidant activities are mostly driven by O-H bond dissociation enthalpy (BDE) following hydrogen atom transfer (HAT) mechanism. Antioxidant ability can be arranged in the following order: compounds (4) > (3) > (2) > (1). Of comprehensive structural analysis, flavonoids with 4′-meth- ylation and 6-methoxylation, especially 7-glycosylation would claim responsibility for antioxidant enhancement. 1. Introduction apiofuranosyl-(1-6)-β-D-glucopyranoside] (4) (Figure 1) [4, 5]. A vast data showed that the substitutions at C-5, C-7, and C-4′ Naturally occurring isoflavone compounds fall into the class of in isoflavonoid rings have been playing a key role in structural flavonoid phenolic compounds, which consists of a molecular features of bioactive isoflavones, especially in terms of anti- structure of 3-phenylchromen-4-one backbone, and are widely oxidants [4]. For instance, genistein (1) revealed much more distributed in the plant kingdom, particularly in Fabaceae significance in the powerful antioxidant when compared to family [1]. Isoflavone derivatives were found to involve in other isoflavones like daidzein and glycitein due to the de- various biological experiments and have been employed in pendence on its functional hydroxyl groups [5]. Likewise, a pharmacological drugs to treat cancer, Alzheimer’s disease, survey conducted by Dowling et al. proposed that with regards atherosclerosis, and so on [2]. Basically, the reactive oxygen to DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, both genstein radicals such as hydroxyls (·OH) presenting in living organ- (1) and its 4′-methoxylation biochanin A (2) successfully isms can be seen as the reason for the changes in the body and chelated to Cu (II) and Fe (III) with a 1 : 2 M/L stoichiometry in one of the main causes of various diseases [3]. Numerous methanol phase, whereas daidzein fails to do so [6]. evidence suggests that either flavonoids or typical isoflavones Using B3LYP functional with 6-311G(d) basis set for have been shown to be associated with good antioxidant studied mediums gas and methanol, the current DFT capacities due to their radical-scavenging activities. (density functional theory) study will provide an insight into Of computational compounds 1–4, we herein select the best structural features, conformational analyses, and electronic isoflavones and their 7-glycosylation principally based on the properties of the selective isoflavones 1-2, in which the result good results in their biological experiments, including genistein intensively related to explaining their reactivity with free (1), biochanin A (2), ambocin (3), and tectorigenin 7-O-[β-D- radicals. Ambocin (3) was isolated from the root of Pueraria 2 Journal of Chemistry HO 8a O θ HO 5′′′ 2 2 7 ′′′ O AC3 ′ 4 ′′′ 1′ 2 1 4a 2′′′ O 5 4 B ″ ′ OHOH 6 OH O 4 ″O OR HO 5″ 2 ″ 2 HO 1 O 8a O θ OH 2 1 R = H 7 2 ′ 2 R = Me 3 2 1′ 4a 4 R 5 ′ OH O 4 OH 3 R = H 4 R = OMe (a) (b) Figure 1: General structures of studied compounds 1–4 with atom numbering. mirica, while its 6-methoxylation compound (4) had re- (2) SET-PT pathway was recognized by two steps cently been identied as a new compound existing in (Equation (3)). In details, the rst step accounted Dalbergia sissoo stem bark [4, 7]. To the best of our for the process of losing an electron to form mo- knowledge, there have been no specic theoretically useful lecular radical cation Flav-OH•+. After that, Flav- account reports on their glycosides 3-4. erefore, we also OH•+ was deprotonated. e rst action was set out a computational work on 7-glycosylated compound evaluated by the sum of the ionization potential (3) and 6-methoxylated-7-glycosylated compound (4), (IP), whereas deprotonation was characterized by within the aim of nding the eects of chemical structure on heterolytic bond dissociation enthalpy (PDE) the antioxidant capacity. Hopefully, the ndings will lay the (Equations (4) and (5)). ground for future research. • • Flav-OH R Flav-OH + R + + Flav-O• ROH− ( ) 1.1. eoretical Parameters and Computational Procedure. ⟶ + DFT calculation is carried out with Gaussian 09 software • 3 IP ⟶H Flav-OH + He package [8]. In order to optimize the structure, the B3LYP + () H Flav-OH − ( ) exchange correlation functional level without constraints ( ) has been utilized and has been linked to 6-311G(d) basis set • 4 in the gas phase (dielectric constant, ε 1) and in methanol PDE −H Flav-O HH+ + solvent (ε 32.613) [9, 10]. Vibrational frequencies are • H Flav-OH + ( ) calculated at the same level to correct zero-point energy (ZPE). e result conrms the presence of ground states •+ 5 H(Flav-OH ) presents− the enthalpies of avonoid without imaginary frequency. e self-consistent reaction radical cation Flav-OH•+ after electron abstraction of eld polarizable continuum model (SCRF-PCM) has been original avonoid. e calculated gaseous phase employed for estimating solvent eects [9]. enthalpy values, which are 0.75 kcal/mol and From literature, there have been three known mecha- 1.48 kcal/mol, are normally used for H(e–) and nisms HAT (H-atom Transfer), SET-PT (Single electron H(H+), respectively [11, 12]. transfer-proton transfer), and SPLET (Sequential proton loss electron transfer), which concern radical-scavenging (3) e third mechanical SPLET is briey described properties of the parent molecular (Flav-OH) [11–17]: when avonoid is deprotonated to aord a typical anion Flav-O– and the sequential electron transfer (1) HAT mechanical route (Equation (1)) involves in from this anion happens (Equation (6)). Proton O-H bond breaking of Flav-OH, then transfers to a¤nity (PA) and the electron transfer enthalpy radicals, and is often controlled by homolytic bond (ETE) are two conceptual parameters which corre- dissociation enthalpy (BDE) (Equation (2)). spond to deprotonation and electron transfer, re- spectively (Equations (7) and (8)). Flav-OH RO• Flav-O• ROH + + ( ) • Flav-OH Flav-O H+; Flav-O R • • + + BDE ⟶H Flav-O HH 1 • + Flav-O− R ;R H−+ RH H Flav-OH ( ) ⟶ + + ( ) − − ( ) • • 2 ⟶ ⟶ H(Flav-O ), H(H ),− and H(Flav-OH) are the en- • PA H Flav-O HH+ thalpies of Flav-O , hydrogen radical atom, and the ()+ 6 H Flav-OH− ( ) parent avonoid molecule, respectively. ( ) 7 − Journal of Chemistry 3 + · − − associate with nucleophilic (fk ), electrophilic (fk ), and/or ETE � H Flav-O � + H() e 0 − (8) radical attacks (fk) and were possibly described by the − H() Flav-O following equilibriums [20]: f+ � q (N + ) q (N); H(Flav-O−) is the enthalpy of flavonoid anion after k k 1 − k proton abstraction of original molecule. f− � q (N) − q (N − 1); k k k (11) Antioxidant activities have been explained by DFT-based reactivity descriptors [11], including energies of highest oc- �q (N + 1) − q (N − 1)� f0 � k k ; cupied molecular orbital (HOMO) and lowest unoccupied k 2 molecular orbital (LUMO), dipole moments, atomic charges, where qk(N): electronic population of atom k in a neutral electron affinity A, the ionization potential Io, the global hardness η, the electronegativity χ, the chemical potential µ, molecule, qk(N + 1): electronic population of atom k in an global electrophilicity index ω, and Fukui chemical parameters. anionic molecule, and qk(N − 1): electronic population of Based on the theoretical approach of DFT, Janak’s atom k in a cationic molecule. theorem, and the finite difference approximation, these descriptors can be proposed by the related equations given as 2. Results and Discussion follows [18]: 2.1. Geometrical Analysis. e comprehension of isoflavone conformational analysis is an important method to prove the Io ≈ −EH; relationship between the antioxidant activities and structural A ≈ −EL; aspects since the HAT, SET-PT, and SPLETpathways closely depend on the behaviors of differential hydroxyl groups and Io − A � EL − EH � the geometric features. From Figures 2 and S1 and Table 1, η ≈ ≈ ; we reported the optimized structures with patterns of 2 2 (9) intramolecular hydrogen bonds (IHBs) between 5-OH and I + A � E + E � 4-CO, along with selective characters of bonds, bond angles, χ ≈ o ≈ L H ; 2 2 and dihedral angles. As of local minimum energies, there is no distinction in each compound between gaseous state and I + A � −E + E � methanol (Table 2).