Synthesis, characterization, antioxidant evaluation, molecular docking and density functional theory studies of phenyl and naphthyl based esters

Journal of Molecular Structure 1207 (2020) 127812

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Synthesis, characterization, antioxidant evaluation, molecular docking and density functional theory studies of phenyl and naphthyl based esters Zaib-un-Nisa a, Muhammad Shabbir a, Zareen Akhter a, *, Muhammad Adeel Asghar a, Vickie Mckee b, Asma Sani a, Faroha Liaqat a, Saima Kalsoom c, Shaista Sabir a, Hammad Ismail d a

Department of Chemistry, Quaid-i-Azam University, Islamabad, 45320, Pakistan School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland c Center for Interdisciplinary Research in Basic Sciences (CIRBS), International Islamic University, Islamabad, Pakistan d Department of Biochemistry & Biotechnology, University of Gujrat, 50700, Gujrat, Pakistan b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 22 September 2019 Received in revised form 26 January 2020 Accepted 28 January 2020 Available online 4 February 2020

Two phenol based esters phenyl benzoate (OE1) and 1-naphthyl benzoate (OE2) were synthesized from phenol/1-naphthol and benzoyl chloride respectively. The structural elucidation of the synthesized compounds was accomplished by spectroscopic studies (FTIR, 1H NMR & GC-MS) and single crystal X-ray diffraction analysis. DPPH (2, 2-diphenyl-1-picryl-hydrazyl-hydrate) free radical and hydrogen peroxide activities were performed to evaluate the antioxidant capabilities of the synthesized esters. The compounds (OE1 & OE2) showed DPPH scavenging activity in concentration dependent manner with IC50 values 605.6 mM and 1138.7 mM correspondingly. Similarly, in hydrogen peroxide assay, OE1 and OE2 exhibited moderate activity with IC50 values 1510.2 mM and 1069.4 mM respectively. Molecular docking of the compounds was carried out to predict their antioxidant binding mechanism against target protein using the MOE suite. The structure
activity relationship analysis showed that replacing the phenyl ring by naphthyl significantly influences their activity. Geometrical studies of the compounds have been performed by both semi-empirical and DFT methods; results reveal an excellent convergence of experimental and theoretical structural parameters. A detailed bonding investigation of each compound has been performed by NBO and Bader’s AIM analysis to obtain inter and intramolecular interactions. © 2020 Published by Elsevier B.V.

Keywords: Esters DPPH free radical activity Hydrogen peroxide activity Molecular docking Density functional theory AIM analysis

1. Introduction Esters, an important class of organic compounds, possess numerous biological and industrial applications. Natural esters form backbone of DNA molecules and are found in pheromones, fats and oils [1]. Synthetic esters have several therapeutic applications like methyl phenidate as nervous system stimulant whereas salicylic acid acetate and phenyl salicylate as analgesics [2e4]. Moreover, they are applied for the preparation of cosmetics, perfumes, surfactants, plastics and as solvents for oils, fats, gums, resins, cellulose, paints and varnishes [5]. In addition, esters have shown significant antioxidant and free radical scavenging activities

* Corresponding author. E-mail addresses: [email protected], [email protected] (Z. Akhter). https://doi.org/10.1016/j.molstruc.2020.127812 0022-2860/© 2020 Published by Elsevier B.V.

[6,7].Due to efficacious biological worth of aromatic esters, phenyl benzoate (OE1) and 1-naphthyl benzoate (OE2) were synthesized from phenol, 1-naphthol and benzoyl chloride. The bioactive nature of these organic esters was evaluated by performing DPPH and hydrogen peroxide activities. Antioxidant behavior of these compounds was investigated computationally through molecular docking to predict the binding orientation of small drug candidates to a target complex, thereby playing an important role in understanding the binding pattern of docked compounds in the active site of target protein [8]. Since the NO free radicals have an important role to play in the immune and nervous systems, their production needs to be regulated [9]. Nitric oxide synthases (NOS) produces nitric oxide (NO) from L-arginine. Various isoforms of NOS have recently been selected as a target for anti-cancer inhibitors [10]. Density Functional studies have been carried out to understand

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Scheme 1. Synthesis of phenolic esters OE1 and OE2.

2. Experimental

of significant antioxidant target protein. Ten conformations were generated for each docked compound. The software package of Gaussian 03 and Turbomole (2018) has been used to optimize the ground state geometry and evaluation of structural parameters of the compounds OE1 and OE2. The basis sets used for the quantum mechanical calculations are B3LYP-321 G and MO6/def2-TZVPP in Gaussian and Turbomole, respectively. DFT studies act as a supportive tool to experimentally observed values of bond lengths and bond angles. The energies of the frontier orbitals, HOMO and LUMO, have also been computed. Bader’s AIM analysis and NBO analysis have been carried out to obtain bond topological parameters and gauge the strength of inter and intra molecular interactions.

2.1. Materials and methods

2.2. Synthesis of organic esters

Sodium hydroxide, phenol, 1-Napthol were purchased from Fluka, Switzerland, Benzoyl chloride from Panreac, Spain and were used without further purification. Melting points were determined using Gallen Kamp apparatus. Infrared measurements (4000e400 cm
1) were performed on thermoscientific NICOLET 6700 FTIR spectrophotometer. 1H NMR spectra were recorded on Bruker ARX 300 MHz in solution using tetramethylsilane (TMS) as internal reference at room temperature. MS spectra were recorded on Agilent-6210-LC/TOF. The single crystal X-ray analysis data for the compounds was collected at 150(2)K on a Bruker Apex II CCD diffractometer using MoK radiation (l ¼ 0.71073 Å). The structures were solved by direct methods and refined on F2 using all the reflections [15]. DPPH free radical and hydrogen peroxide scavenging activities were performed to evaluate the scavenging ability of the synthesized esters, according to the methods reported in the literature with slight modifications [16,17]. Data was analyzed by two-way ANOVA followed by Tukey’s multiple comparison tests using GraphPad Prism 7.0 software. Results are represented as mean ± SD and p < 0.05 is considered to be significant. The crystal structures of the target protein nitric oxide synthase NOS, PDB id: 5FVP [8] was fetched from Protein Data Bank (www. rcsb.org/pdb). The protein was prepared, protonated and minimized via the MOE 2016 suite. The chemical structures of synthesized compounds were built and saved in their 3D conformations by the Builder tool incorporated in MOE 2016. Further protonation, minimization, charge application and atom-type corrections were also carried out. Before docking, the efficiency of the procedure was validated by redocking the crystallized ligand back into the pocket

2.35g phenol (0.025 mol) for OE1 and 3.61 g of 1-naphthol (0.025 mol) for OE2 was added to 20 ml of 5% NaOH solution in separate flasks. 0.75 g decolorizing carbon was added in each flask and was filtered off. Solutions were separately poured into 100 ml two necked flasks and 7.0 g of benzoyl chloride (2.9 ml, 0.025 mol))

the physical properties of the compounds and more importantly, their quantitative structure-activity relationship [11,12]. The reactivity of each compound is dependent on its electron density (r) and the density distribution, Laplacian of the electron density and electrostatic potential [13].By using Natural Bond Order (NBO) analysis and Quantum Theory of Atoms in Molecules (QTAIM), we have attempted to understand the nature of the chemical bonds in our systems and correlate it to their activity [14]. Bader’s AIM theory has been utilized to find topological parameters at bond critical points (BCP) to predict the strength of various interactions in the organic esters under investigation.

Table 1 Crystal data and structure refinements for compounds OE1 and OE2.

Empirical formula Formula weight Crystal system Space group Unit cell a (Å) b (Å) c (Å) b ( ) Volume (Å3) Z D (calc) (Mg/m3) Abs. coeff. (mm
1) F(000) Crystal size (mm3) Crystal description Reflections collected Independent refl. (Rint) Goodness on F2 R1, wR2 [I > 2s (I)] R1, wR2 (all data)

OE1

OE2

C13 H10 O2 198.21 Monoclinic P21/c

C17 H12 O2 248.27 Monoclinic P21/c

5.6354(5) 14.5076(12) 12.2589(10) 100.8530(10) 984.31(14) 4 1.338 0.090 416 0.33  0.26  0.21 colorless block 9998 2466 (0.0300) 1.065 0.0396, 0.0872 0.0504, 0.0930

8.6286(7) 15.0538(12) 10.3888(8) 108.1510(10) 1282.29(18) 4 1.286 0.084 520 0.29  0.21  0.14 colorless block 11303 2636 (0.0310) 1.039 0.0357, 0.0767 0.0536, 0.0846

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was added in each flask while stirring vigorously for 10e15 min until odor of benzoyl chloride disappeared. Solid products obtained were filtered off using Buckner funnel followed by washing with cold water. The products were then recrystallized from 30 ml rectified spirit. White crystals appeared which were removed from mother liquor by filtration and dried in the air (Scheme 1) [18]. 2.2.1. Phenyl benzoate (OE1) Yield 89%; m.p. 67e71  C; FTIR: (y/cm
1): 3057 (CeH), 1724 (C] O), 1590 (C]C), 1257 (CeOeC); 1H NMR (300 MHz, CDCl3, d ppm): aromatic protons 7.5e8.3 (m, 5H), aromatic protons (-OCO) 6.7e8.2 (m, 5H); MS (m/z): 198(M þ). 2.2.2. 1-Napthyl benzoate (OE2) Yield 86%; m.p. 55e57  C; FTIR: (y/cm
1): 3064 (CeH), 1727 (C] O), 1597 (C]C), 1253 (CeOeC); 1H NMR (300 MHz, CDCl3, d ppm): aromatic protons 7.5e8.3 (m, 5H), aromatic protons(-OCO) 6.7e8.2 (m, 7H); MS (m/z): 248(M þ). 3. Results and discussion The condensation of phenols with benzoyl chloride yielded aromatic esters (OE1 & OE2) (Scheme 1). Both the compounds were isolated as crystalline and characterized by spectroscopic (FTIR, 1H

3

NMR & GC-MS) as well as by single crystal structure analyses. 3.1. Spectral characterization The FTIR spectra of the synthesized esters provided evidence for the presence of all the expected functional groups. The formation of products was confirmed by the appearance of an intense band of carbonyl group (C]O) at 1724-1727 cm
1. The aromatic moieties in the compounds were identified by their characteristic bands. The band at 3057-3064 cm
1 was due to the aromatic CeH stretch. The aromatic C]C stretch in each spectrum was confirmed by bands in a region of 1590e1597 cm
1. The presence of an ester (COeO) linkage was indicated by its absorption band at 1553-1257 cm
1 [19] (Fig. S1). The 1H NMR spectra of organic esters were also consistent with the proposed structures. The aromatic ring attached directly to the carbonyl group of ester linkage depicted multiplets in the range of 7.5e8.3 ppm (m, 5H) for both the compounds. Attachment of aromatic rings (phenyl/naphthyl) directly linked to the oxygen atom of the ester moiety was confirmed by their characteristic signals in the range of 6.7e8.2 ppm (m, 5H for OE1 and m, 7H for OE2) as displayed in Fig. S2. The mass spectral data of the organic esters confirmed their formation with molecular ion peaks at (m/z) 198 for OE1 and 248 for

Fig. 1. Perspective views OE1 (a) and OE2 (b) showing 50% probability ellipsoids. Hydrogen atoms are shown as sticks.

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OE2 respectively which is consistent to their molecular formula masses (Fig. S3).

3.2. Single crystal X-Ray analysis Single crystal X-ray analyses reveal their monoclinic crystal systems with space groups P21/c. All the non-hydrogen atoms were refined using anisotropic atomic displacement parameters and hydrogen atoms were inserted at calculated positions using a riding model. Parameters for data collection and refinement are summarized in Table 1. The perspective views of the molecules are shown in Fig. 1. In compound OE1, the two ring systems are inclined at an angle of 54.89(4) to each other. Surprisingly, there are no p-p interactions in the structure and the most important intermolecular interactions appear to be CH …. O hydrogen bonds. In OE2 the two ring systems are inclined at an angle of 72.59(4) to each other. The main intermolecular interaction is p-p stacking of pairs of anthracene groups (under symmetry operation 2-x, -y, 1-z). There is also an edge-to-edge interaction between phenyl rings (under -x, -y, -z) again linking them in pairs (Fig. 2).

Fig. 3. DPPH free radical scavenging activity of OE1 and OE2 at 50, 100 and 200 ppm. Statistically significant values expressed as ***p < 0.001, and Mean ± SD in comparison with ascorbic acid.

3.3. Biological studies 3.3.1. DPPH free radical scavenging activity The antioxidant potential of synthesized compounds was evaluated by DPPH free radical scavenging assay and the results are presented in Fig. 3 in the form of percentage scavenging. The experiment was performed on three different concentrations (50, 100, 200 ppm) in triplicate and ascorbic acid was used as positive control with IC50 value 75 mM. The compound OE1 showed significant activity with IC50 value 605.6 mM while weak activity was shown by OE2 with IC50 value 1138.7 mM.

3.3.2. Hydrogen peroxide scavenging activity Hydrogen peroxide assay was performed to determine the scavenging activity of newly synthesized compounds and the results are shown in Fig. 4. The assay was performed in triplicate with the same three different concentrations. Both the compounds (OE1 & OE2) showed weak activity in concentration dependent way with IC50 values 1510.2 mM and 1069.4 mM respectively. Ascorbic acid served as positive control which showed significant activity with IC50 value 55 mM.

Fig. 4. Hydrogen peroxide scavenging activity of OE1 and OE2 at 50, 100 and 200 ppm. Statistically significant values expressed as ***p < 0.001, and Mean ± SD in comparison with ascorbic acid.

Fig. 5. 3D structure of target complex nitric oxide synthase NOS, PDB id: 5FVP. Fig. 2. Edge-edge p interactions in OE2, distances in Å.

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interaction. The binding energy values for OE1 and OE2 are
6.67 and
3.46 kcal/mol, respectively. The carbonyl oxygen of OE1 shows strong hydrogen bonding with the hydroxyl of Ser457 at a distance of 3.02 Å (energy value of 1.9 kcal/mol) in addition to a strong p-p interaction with Trp409. Similarly, the OE2 docked complex has both hydrogen bonding and p-p interactions with Ser457 and Trp409 respectively, as shown in Fig. 9. Comparatively lower antioxidant behavior of OE2 may be due to the presence of steric clashes of naphthalene rings in the proximity contour of target protein. Both organic esters bind in the same vicinity of target complex when compared to ascorbic acid (Fig. 7). The high antioxidant activity of ascorbic acid is due to the major number of strong hydrogen bonds with the key contributing amino acids, Asp597 and Glu592.

3.5. Quantum mechanical studies

Fig. 6. Superimposition of the docked pose of compound OE1 & OE2 (yellow color) and standard ascorbic acid (blue color).

3.4. Molecular docking The most suitable targets and inhibition mechanisms for the antioxidant activity of the newly synthesized ester can be predicted in MOE 2016 software package. The organic esters and the reference compound (ascorbic acid) were docked in the active site of antioxidant target complex, (PDB ID: 5FVP), as shown in Figs. 5 and 6. Ten conformations were generated for each compound and the lowest energy conformation was selected to determine the binding mode of each complex. Root Mean Square Deviation (RMSD) values of these compounds range from 0.12 to 1.60 Å. The ligand interactions of the reference compound (ascorbic acid) can be seen in Fig. 7, while Figs. 8 and 9 show the 2D and 3D docked maps of the organic esters OE1 and OE2 respectively. It is found that the key contributing amino acids in the vicinity of target complexes are Ser457, Gly586, Trp587, Gly417, Trp409, Ser585, Leu424, Phe584, Phe704 and Val567. The antioxidant behavior of organic ester OE1 and OE2 can be attributed to a strong binding

Density functional studies were carried out on the compounds OE1 and OE2 using Gaussian 03 [20] and Turbomole software package [21]. The hybrid exchange density functional with Becke’s three parameter (B3LYP) and 3e21 G basis set has been used to obtain the optimized ground state geometry of each compound (Fig. S4). The AIM analysis and NBO population analysis have been performed with a basis set of MO6/def2-TZVPP in the Turbomole package. The compounds were also studied by the AM1 semiempirical methods in Gaussian 03 and the results were compared to those obtained from DFT studies. A comparison of the theoretically computed and experimental bond lengths is presented in Tables S1 and S3, while the correlation for bond angles can be found in Tables S2 and S4 for OE1 and OE2 respectively. It can be observed that an excellent convergence of structural parameters is observed for both compounds using experimental and theoretical means. The energy of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) has been computed using the DZ basis set of the density functional model (presented in Table 2). The HOMO-LUMO energy gap signifies the chemical reactivity of the studied compounds, as HOMO indicates an electron donation capacity and the LUMO level is associated with the electron affinity of molecules [22]. A schematic of the frontier energy orbitals is depicted for compounds OE1 and OE2 in Figs. S5 and S6 respectively.

Fig. 7. Binding analysis (a) and ligand interactions (b) of reference ascorbic acid.

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Fig. 8. 2D (a) and (b) 3D docking map of organic ester OE1 in active site of target protein 5FVP.

Fig. 9. 2D (a) and 3D (b) docking map of organic ester OE2 in active site of target protein 5FVP.

3.6. Atoms in Molecules (AIM) analysis Bader’s theory of Atoms in Molecules (AIM) enables one to take advantage of the notion of an atom as the volume around the nucleus with zero-flux in the electron density gradient and to predict quantum mechanically, the nature of interactions in crystals, molecules, clusters, etc [14]. It makes use of the charge density in a molecule, which is in turn reliant on the chemical bonding between atoms [23]. A population analysis should therefore reflect the qualitative results of electronegativity, where more electronegative atoms ‘‘draw’’ more electrons to themselves than less electronegative ones. The electronic information in the bonding region is determined from the electron density r, Laplacian of electron density V, and bond critical points [24]. The ellipticity (e) at the Bond Critical Points (BCP) is a sensitivity index to monitor the p-

  character of bond. It is related to l1 and l2 , which correspond to the eigen values of Hessian, by the relationship: ε ¼ l1=l
1. 2 In this study, the optimized geometries of the compounds OE1 and OE2 are analyzed with Bader’s “Atoms in Molecules” (AIM) analysis using a DFT approach with the M-O6/def2-TZVPP basis set in TURBOMOLE software [25]. The topological properties of the electron density distribution, Bond Critical Points (BCPs) and Ring Critical Points (RCP) are determined for both the compounds;

Table 2 Energy values of the frontier orbitals and band gap for compounds OE1 and OE2. Compounds

HOMO (eV)

LUMO (eV)

Energy Gap (eV)

OE1 OE2


2.990
3.911


0.031
0.255


2.959
3.656

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Fig. 10. AIM analysis of OE1 (a) and OE2 (b). The Ring Critical Points (RCP) are shown in red, while the Bond Critical Points (BCP) are depicted green in color. The circles around each atom represent charge density

Fig. 11. NBO analysis of OE1(a) and OE2(b).

Fig. 10 indicates BCPs and RCPs for the compound OE1 and OE2, respectively. The optimized structures of the compounds were used to obtain parameters at the BCPs such as the electron density(rBCP ), Laplacian of electron density (VBCP ), electron kinetic energy density (GBCP), total electron energy density (KBCP), estimated interaction energy (Eint) at bond critical point (BCP). All the calculated

topological parameters are listed in Table S5 (OE1) and S6 (OE2). 3.7. Natural population analysis (NP) In the current study, the NP analysis has been performed to obtain atomic charges and orbital populations using the basis set,

Table 3 Second Order Perturbation Theory Analysis of Fock Matrix in NBO Basis for OE2. Stabilization energy of charge delocalization interactions (E2), Energy difference between donor i and acceptor j NBO orbitals (E(j) e E(i), Fock matrix element between i and j NBO orbitals (Fi, j). Donor NBO (i)

Occupancy (i)

Acceptor NBO (j)

Occupancy (j)

E2 (kcal/mol)

E(j)-E(i) (a.u.)

F (i, j) (a.u.)

O 18 - C 30 C 13 - H 16 C1 O 18 O 18 C3-C4 O 18 e C 30 C 23 - C 30 C 30 - O 31 O 31 C1-C2 C3-C4 O 18 C 30 - O 31 C 22 - C 23 O 18 e C 30

1.99270 1.98408 1.99852 1.94579 1.94579 1.96346 1.99270 1.97795 1.99665 0.00093 1.97998 1.96346 0.00137 1.98064 1.63664 1.99270

C C C C C C C C C C C C C C C C

1.99803 1.74020 1.99127 1.99860 1.98064 1.97999 1.99665 1.99127 0.00038 0.00038 1.98099 1.74020 1.97998 1.63664 1.99848 1.99665

1.80 2.61 0.61 0.58 48.27 264.04 1.32 2.60 2.22 18.64 187.39 264.04 27.08 54.57 0.83 1.32

2.01 1.13 10.22 11.24 0.29 0.01 0.24 0.97 2.00 1.60 0.01 0.01 0.34 0.04 0.84 0.24

0.054 0.049 0.071 0.072 0.107 0.077 0.058 0.045 0.060 0.155 0.078 0.077 0.087 0.072 0.054 0.058

2 9 - C 14 2 - O 18 20 30 - O 31 9 - C 14 30 - O 31 2 - O 18 30 30 5-C6 9 - C 14 1-C2 22 - C 23 23 30 - O 31

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MO6/def2-TZVPP in the TURBOMOLE software. The natural analysis, as an alternative to the conventional Mulliken population analysis, describes accurately the electron distribution in compounds of high ionic character, such as those containing metal atoms. The NP analysis for the compounds OE1 and OE2 are provided in Tables S7 and S8.In the natural bond orbital (NBO) method developed by Weinhold, atomic population is calculated from localized natural atomic orbitals (NAO), therefore the name, natural population (NP) [26]. The occupied (or bond) and unoccupied (or antibond/Rydberg) NBO’s provide an idea of the delocalization of charge densities and charge transfer between donors and acceptors [27,28]. The NBO analysis translates computational solutions of €dinger’s wave equation into familiar chemical bonding conSchro cepts. Using version 3.1 of the NBO program by F. Weinhold and coworkers [29] in Gaussian 03, the NBO analysis the wave function into localized form, corresponding to the one-center (“lone pairs”) and two-center (“bonds”) elements of the Lewis structure [30]. The NBO analysis for the compounds OE1and OE2 (Fig. 11) are given in Tables S9 and S10 respectively. Additionally, the stabilization energy of charge delocalization interactions (E2), Energy difference between donor i and acceptor j NBO orbitals (E(j) e E(i), and the Fock matrix element between i and j NBO orbitals (Fi, j) for OE2 are shown in Table 3. A larger value of stabilization energy indicates an extensive interaction between electron donors and acceptors; a greater E2 value would therefore indicate increased conjugation in the system [28]. For OE2, it can be seen from Table 3, that the largest E2 values of 264 kcal/mol are obtained for C3eC4 donor NBO and C9eC14 acceptor NBO numbering as shown in Fig. 11(b). This supplements the edge p-p interactions observed for OE2 (Fig. 2) in the single crystal XRD analysis. 4. Conclusions Two phenol-based organic esters have been synthesized and characterized successfully. Both the compounds are crystalline in nature possessing monoclinic crystal system. DPPH free radical and hydrogen peroxide activities showed the biological worth of the synthesized compounds that was supported theoretically by molecular docking studies of synthetic esters with target antioxidant protein. Optimized geometry and structural parameters of the two organic esters have been investigated using semi-empirical methods and confirmed with density functional theory. The experimental and theoretical values complement each other well. The HOMO-LUMO band gap is greater for naphthyl benzoate ester suggesting greater stability compared to more reactive phenyl benzoate. The bond topological and the electrostatic properties of OE1 and OE2 have been investigated by Bader’s AIM analysis using the basis set MO6/def2-TZVPP in the Turbomole package. The studies obtained from analyzing the BCP and RCP values of both compounds indicate that OE1 exhibits significantly low Laplacian and electron density values, conforming that bonds are depleted and sensitive to external shocks. Their NBO analysis has also been carried out indicating the population distribution and atomic charges. The experimental findings are fully supported by the quantum mechanical calculations. Author’s contribution Zaib-un-Nisa: They accomplished the synthetic part. Muhammad Shabbir: They accomplished the synthetic part. Zareen Akhter: They accomplished the synthetic part. Muhammad Adeel Asghar: They accomplished the synthetic part. Vickie Mckee: analyzed the single crystals of compounds. Asma Sani: carried out molecular docking and DFT studies. Faroha Liaqat: carried out molecular

docking and DFT studies. Saima Kalsoom: carried out molecular docking and DFT studies. Shaista Sabir: carried out molecular docking and DFT studies. Hammad Ismail: Performed the biological activities of the compounds. Declaration of competing interest The authors have declared no conflict of interest. Acknowledgements The authors are highly grateful to Chemistry department Quaidi-Azam University Islamabad, Pakistan and School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland for providing technical support and laboratory facilities. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.molstruc.2020.127812. References [1] Y. Han, D. Diao, Z. Lu, X. Li, Q. Guo, Y. Huo, Q. Xu, Y. Li, S. Cao, J. Wang, Y. Wang, Selection of group-specific phthalic acid esters binding DNA aptamers via rationally designed target immobilization and applications for ultrasensitive and highly selective detection of phthalic acid esters, Anal. Chem. 89 (10) (2017) 5270e5277, https://doi.org/10.1021/acs.analchem.6b04808. [2] U.K. Maji, P. Jana, M. Chatterjee, S. Karmakar, A. Saha, T.K. Ghosh, Role of acetyl salicylic acid in controlling the DOCA-salt induced hypertension in rats by stimulating the synthesis of r-cortexin in the kidney, High Blood Press. Cardiovasc. Prev. 25 (1) (2018) 79e88, https://doi.org/10.1007/s40292-0170241-0. [3] G. Kuriakose, N. Nagaraju, Selective synthesis of phenyl salicylate (salol) by esterification reaction over solid acid catalysts, J. Mol. Catal. Chem. 223 (1e2) (2004) 155e159, https://doi.org/10.1016/j.molcata.2004.03.057. [4] W.O. Cooper, Shedding light on the risks of methylphenidate and amphetamine in pregnancy, JAMA psychiatry 75 (2) (2018) 127e128, https://doi.org/ 10.1001/jamapsychiatry.2017.3882. [5] H. Watanabe, A. Morigaki, M. Yuba, K. Yamada, M. Miyake, N. Tobori, K. Aramaki, Structural analyses of hydrated crystals in mixed green surfactant systems: a-sulfonated fatty acid methyl ester salt and fatty acid soap mixtures, J. Surfactants Deterg. 21 (2) (2018) 221e229, https://doi.org/10.1002/ jsde.12010. [6] B. Hasdemir, H. Yas¸a, Y. Akkamıs¸, Synthesis and antioxidant activities of novel N-aryl (and N-alkyl) g- and d-imino esters and ketimines, J. Chin. Chem. Soc. 66 (2019) 197e204, https://doi.org/10.1002/jccs.201800126. [7] J. Qian, L. Gou, Y. Chen, J. Ding, J. Xu, H. Guo, Enzymatic acylation of flavone isolated from extractive of bamboo leaves with oleic acid and antioxidant activity of acylated product, Eng. Life Sci. 19 (2019) 66e72. https://doi:10. 1002/elsc.201800096. [8] R. Sudha, G. Nithya, D. Brindha, P. Charles, C. Kanakam, Docking antioxidant activity on hydroxy (diphenyl) aceticacid and its derivatives, Asian J. Pharmceut. Clin. Res. 10 (7) (2017) 263e265, https://doi.org/10.22159/ ajpcr.2017.v10i7.18299. [9] M.A. Marletta, A.R. Hurshman, K.M. Rusche, Catalysis by nitric oxide synthase, Curr. Opin. Chem. Biol. 2 (5) (1998) 656e663, https://doi.org/10.1016/s13675931(98)80098-7. [10] M. Kojima, T. Morisaki, Y. Tsukahara, A. Uchiyama, Y. Matsunari, R. Mibu, M. Tanaka, Nitric oxide synthase expression and nitric oxide production in human colon carcinoma tissue, J. Surg. Oncol. 70 (4) (1999) 222e229, https:// doi.org/10.1002/(SICI)1096-9098, 199904)70:4<222::AID-JSO5>3.0.CO;2-G. [11] Y. Minenkov, D.I. Sharapa, L. Cavallo, Application of semiempirical methods to transition metal complexes: fast results but hard-to-predict accuracy, J. Chem. Theor. Comput. 14 (2018), https://doi.org/10.1021/acs.jctc.8b00018, 3428
343. [12] O. Tamer, M.H. Bhatti, U. Yunus, M. Nadeem, D. Avci, Y. Atalay, A. Yaqub, R. Quershi, Structure-property relationship of 3-(N-phthalimidomethyl)-4amino-1, 2, 4-triazole-5-thione: a structural, spectroscopic and DFT study, J. Mol. Struct. 1133 (2017) 329e337, https://doi.org/10.1016/ j.molstruc.2016.12.017. [13] V. Anbu, K.E. Vijayalakshmi, R. Karunathan, A.D. Stephen, P.V. Nidhin, Explosives properties of high energetic trinitrophenyl nitramide molecules: a DFT and AIM analysis, Arab. J. Chem. 12 (2019) 621e632, https://doi.org/10.1016/ j.arabjc.2016.09.023. [14] R.F. Bader, Atoms in molecules, Acc. Chem. Res. 18 (1) (1985) 9e15, https:// doi.org/10.1021/ar00109a003. [15] G.M. Sheldrick, Crystal structure refinement with SHELXL, Acta Crystallogr.

Zaib-un-Nisa et al. / Journal of Molecular Structure 1207 (2020) 127812 C71 (1) (2015) 3e8, https://doi.org/10.1107/S2053229614026540. [16] E. Pick, Y. Keisari, A simple colorimetric method for the measurement of hydrogen peroxide produced by cells in culture, J. Immunol. Methods (1e2) (1980) 161e170, https://doi.org/10.1016/0022-1759(80)90340-3. [17] M. Shabbir, Z. Akhter, I. Ahmad, S. Ahmed, M. Shafiq, B. Mirza, V. McKee, K.S. Munawar, A.R. Ashraf, Schiff base triphenylphosphine palladium (II) complexes: synthesis, structural elucidation, electrochemical and biological evaluation, J. Mol. Struct. 1118 (2016) 250e258, https://doi.org/10.1016/ j.molstruc.2016.04.003. [18] F. Zhu, X.F. Wu, Selectivity controlled palladium-catalyzed carbonylative synthesis of propiolates and chromenones from phenols and alkynes, Org. let. 20 (11) (2018) 3422e3425, https://doi.org/10.1021/acs.orglett.8b01368. [19] B.F. Tjeerdsma, H. Militz, Chemical changes in hydrothermal treated wood: FTIR analysis of combined hydrothermal and dry heat-treated wood, Holz als roh-und Werkstoff 63 (2) (2005) 102e111, https://doi.org/10.1007/s00107004-0532-8. [20] S. Chandrasekar, V. Balachandran, H. Evans, A. Latha, Synthesis, crystal structures HOMOeLUMO analysis and DFT calculation of new complexes of psubstituted dibenzyltin chlorides and 1,10-phenanthroline, Spectrochim. Acta A Mol. Biomol. Spectrosc. 143 (2015) 136e146, https://doi.org/10.1016/ j.saa.2015.01.112. €ttig, W. Klopper, M. Sierka, F. Weigend, Turbomole. [21] F. Furche, R. Ahlrichs, C. Ha Wiley Interdiscip. Rev. Comput. Mol. Sci. 4 (2) (2014) 91e100, https://doi.org/ 10.1002/wcms.1162. [22] D. Avci, Y. Ataly, H. Comert, D. Muharrem, DFT Calculations on the Molecular Structure, Vibrational and Chemical Shift Assignments of 4-Allyl-2-(morpholin-4-ylmethyl)-5-(pyridin-4-yl)-2,4-Dihydro-3H-1,2,4-Triazole-3-Thione, Arabian J. Sci. Eng. 36 (2011) 607e620, https://doi.org/10.1007/s13369-0110059-3.

9

[23] P.S.V. Kumar, V. Raghavendra, V. Subramanian, Bader’s theory of atoms in molecules (AIM) and its applications to chemical bonding, J. Chem. Sci. 128 (10) (2016) 1527e1536, https://doi.org/10.1007/s12039-016-1172-3. [24] B.G. Oliveira, F.S. Pereira, R.C.M.U. de Araújo, M.N. Ramos, The hydrogen bond strength: new proposals to evaluate the intermolecular interaction using DFT calculations and the AIM theory, Chem. Phys. Lett. 427 (1e3) (2006) 181e184, https://doi.org/10.1016/j.cplett.2006.06.019. €ttig, W. Klopper, M. Sierka, F. Weigend, Turbomole. [25] F. Furche, R. Ahlrichs, C. Ha Wiley Interdiscip. Rev. Comput. Mol. Sci. 4 (2) (2014) 91e100, https://doi.org/ 10.1002/wcms.1162. [26] A.E. Reed, R.B. Weinstock, F. Weinhold, Natural population analysis, J. Chem. Phys. 83 (2) (1985) 735e746, https://doi.org/10.1063/1.449486. [27] R.V. Singh, A. Kumar, R.K. Tiwari, P. Rawat, A combined experimental andtheoretical (DFT and AIM) studies on synthesis, molecular structure, spectroscopic properties and multiple interactions analysis in a novel Ethyl-4-[2(thiocarbamoyl)hydrazinylidene]-3,5 dimethyl-1H-pyrrole-2-carboxylate and its dimer, Spectrochim. Acta A Mol. Biomol. Spectrosc. 112 (2013) 182e190, https://doi.org/10.1016/j.saa.2013.04.002. [28] M. Snehalatha, C. Ravikumar, H. Joe, N. Sekar, V.S. Jayakumar, Spectroscopic analysis and DFT calculations of a food additive carmoisine, Spectrochim. Acta A Mol. Biomol. Spectrosc. 72 (3) (2009) 654e662, https://doi.org/10.1016/ j.saa.2008.11.017. [29] R. Ghiasi, E.E. Mokaram, Natural bond orbital (NBO) population analysis of iridabenzene (C5H5Ir)(PH3)3, J. Appl.Chem. Res. 6 (1) (2012) 7e13. [30] A.E. Reed, F. Weinhold, L.A. Curtiss, D.J. Pochatko, Natural bond orbital analysis of molecular interactions: theoretical studies of binary complexes of HF, H2O, NH3, N2, O2, F2, CO, and CO2 with HF, H2O, and NH3, J. Chem. Phys. 84 (10) (1986) 5687e5705. https://doi:10.1063/1.449928.