Spectroscopic, structural, electronic and bioactive characteristics of 3,5-bis(2,5-dimethylphenyl)pyridine (1): An experimental and theoretical investigations

Journal Pre-proof Spectroscopic, structural, electronic and bioactive characteristics of 3,5-bis(2,5dimethylphenyl)pyridine (1): An experimental and theoretical investigations Muhammad Akram, Shanawer Niaz, Muhammad Adeel, Muhammad Nawaz Tahir, Irfan Ullah, Malik Aman Ullah, S. Subashchandrabose, Ghias Uddin PII:

S0022-2860(19)31557-1

DOI:

https://doi.org/10.1016/j.molstruc.2019.127448

Reference:

MOLSTR 127448

To appear in:

Journal of Molecular Structure

Received Date: 22 April 2019 Revised Date:

17 November 2019

Accepted Date: 18 November 2019

Please cite this article as: M. Akram, S. Niaz, M. Adeel, M.N. Tahir, I. Ullah, M.A. Ullah, S. Subashchandrabose, G. Uddin, Spectroscopic, structural, electronic and bioactive characteristics of 3,5bis(2,5-dimethylphenyl)pyridine (1): An experimental and theoretical investigations, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.127448. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

Muhammad Akram: Experimentation, Data curation, characterization. Shanawer Niaz: Conceptualization, Methodology, Software, Writing-Original draft preparation. Muhammad Adeel: Visualization, Investigation, Writing-Original draft preparation. Muhammad Nawaz Tahir: Supervision, Data curation. Irfan Ullah: Validation. Malik Aman Ullah: Writing-Reviewing and Editing. S. Subashchandrabose: Methodology, Editing, Validation. Ghias Uddin: Experimentation.

Spectroscopic, Structural, Electronic and Bioactive Characteristics of 3,5-bis(2,5-dimethylphenyl)pyridine (1): An Experimental and Theoretical Investigations Muhammad Akrama,g, Shanawer Niazb,*, Muhammad Adeelc, Muhammad Nawaz Tahird Irfan Ullahe, Malik Aman Ullaha, S. Subashchandrabosef, Ghias Uddina

a

Institute of Chemical Sciences, University of Peshawar, Peshawar, KPK, Pakistan. Department of Physics, University of Sargodha, Sub-campus Bhakkar 30000, Pakistan. c Instittue of Chemical Sciences, Gomal University, Dera Ismail Khan, Khyber Pakhtun Khwa, Pakistan. d Department of Physics, University of Sargodha, Sargodha 40100, Pakistan. e Department of Chemistry, University of Sargodha, Sub-campus Bhakkar 30000, Pakistan. f Department of Physics, Centre for Research and Development, PRIST Deemed University, Thanjavur 613403, Tamilnadu, India. g Medicinal Botanic Centre, PCSIR Laboratories Complex Peshawar, KPK, Pakistan b

* Corresponding author. Tel.: +92 (321) 6020309. E-mail address: [email protected] (S. Niaz). Present address: Department of Physics, University of Sargodha, Sub-campus Bhakkar 30000, Pakistan.

Abstract 3,5-bis(2,5-dimethylphenyl)pyridine (1); a novel derivative of 3,5-dibromopyridine was synthesized via Pd(0) catalyzed cross coupling reaction. The compound under investigation was characterized by XRD and different spectroscopic techniques. Density functional theory (DFT) was applied to compound 1 and experimental XRD data and DFT data are found in good agreement with each other. Calculated FT-IR results are found to be in excellent agreement with experimental FT-IR findings. Chemical shift values for NMR were calculated for compound (1) in the gas phase which show deviation to experimental values might be because of medium affects. Natural bond orbital (NBO) study was also performed which indicates that the methyl groups influence van der Waals interactions among the adjacent bonds, especially, delocalization of energy during the interaction. Energy gap values of HOMO-LUMO calculated through frontier molecular orbital (FMO) analysis provided enough evidence that molecule is biologically active. Molecular electrostatic potential (MEP) mapping indicated that electron density is located on nitrogen whereas carbon and hydrogen atom are favorable sites for nucleophilic attack. Moreover, the bioactivities of compound (1) have been confirmed by the experimental activity in terms of zones of inhibition against bacteria and fungus.

Keywords:

Pyridine derivatives; Synthesis; Natural bond orbitals; Density functional theory; Molecular electrostatic potential; Antimicrobial activities

1. Introduction Present work is the extension of our previous study on the synthesis of a series of arylated pyridines [1]. C-C coupling reactions are of great importance for the synthesis of new compounds. Among these Sonogoshira [2], Heck [3], Stille [4] and Suzuki [5] reactions are the famous ones which result in the formation of Palladium (Pd) catalyzed Carbon-Carbon and Carbon-Heteroatom coupling products. These transition metal catalyzed reaction has found numerous uses in organic synthesis and material synthesis, these reactions also have an important role in pharmaceutical, agrochemical and fine chemical industries [6-10]. Pd catalysis has found its applications in numerous methodologies during the last thirty years like regioselective [11], chemoselective [12] and enantioselective [13]. State of the art transition metal catalysts, novel ligand designs and easily accessible reaction conditions have been developed. Pyridine is nitrogen containing six membered aromatic heterocycle. It is present in many compounds of natural and synthetic origin and voluminous searches have been carried out on the isolation and synthesis of pyridine and its derivatives [14-17]. Pyridine in addition to be an important member of heterocyclic chemistry has found use as strong base as well as catalyst in many synthetic reactions of medicinal values. The literature about pyridine and its derivatives reveal that a large number of these compounds have been evaluated to have therapeutic prospective against countless diseases [18-21]. Plants are the rich source of pyridine containing compounds. Some of the natural products containing pyridine have been explored exhibiting cancer curative activities [22-23]. Number of pyridine derivatives exhibit antifungal activity i.e. 2-Aryl-1,2,4-triazolo[1,5-a]pyridine derivatives have shown excellent antifungal activity. N1-[1-

Aryl-2-(1H-imidazol-1-yl and 1H-1,2,4-triazol-1-yl)-ethylidene]-pyridine-2-carboxamidrazone derivatives have shown good antifungal and antimycobacterial activity [24-26]. Herein, by this research study, we report the synthesis of 3,5-bis(2,5-dimethylphenyl)pyridine (1) by employing Pd (0) catalysed Suzuki-Miyaura cross-coupling reaction (Scheme 1). Synthesized compound (1) characterized by using FT-IR, 1H-NMR, mass spectrometric analysis and single crystal X-ray studies. The synthesized compound was subjected to density functional theory (DFT) studies to explore more about molecular geometry, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), and natural bond orbital (NBO) properties of the synthesized organic structure. This study for the synthesis of this compound has therefore led us not only to synthesize pyridine derivatives, but also to investigate the structural dynamic of geometries of this molecule. Keeping in view of biological activities of arylated pyridines the titled compound 3,5-bis(2,5-dimethylphenyl) pyridine (1) was subjected to antimicrobial activities that has shown promising results.

2. Experimental 2.1 General Experimental All of the chemicals were from Acros Organics and were used without purification. The melting points were recorded on digital melting point apparatus (Stuart, UK) and are uncorrected. IR spectra of the compounds were procured on FTIR (Shimadzu Prestige, Japan) with FT-IR (νmax Cm-1): 2916.37, 1500.62, 1415.75, 1394.53, 1161.15, 1026.13, 885.33, 771.53, 717.52. NMR spectra were recorded on 400 MHz NMR (Bruker, Switzerland). EIMS (electron ionization mass spectroscopy) and ESI-MS (electrospray ionization mass spectroscopy) measurements were done on GC-MS (Varian, Japan) and LC-MS (Thermo, USA), respectively.

2.2 Synthesis 2.2.1 Synthesis of 3,5-bis(2,5-dimethylphenyl)pyridine (1) To a pressure tube (25 mL) were added 3,5-dibromopyridne (100 mg, 0.422 mmol), 2,5dimethylphenylboronic acid (0.928 mmol), K3PO4 (0.633 mmol), Pd(PPh3)4 (1.5mol%) and dioxane:water (3:1 v/v ratio) (see Scheme 1). After flushing with dry nitrogen, pressure tube was sealed with screw-cap, placed in the aluminum container and heated at 90-100 °C for a period of 8 hours. After ascertaining the completing of the reaction by TLC the contents of the pressure tube were extracted thrice with ethyl acetate (3×20 mL), the solvent was evaporated on reduced pressure of rota-vapor and the solid material thus obtained was re-dissolved in CH2Cl2 (2-3 mL) and contents taken in small dry and clean glass vial. The crude from reaction mixture was loaded on 50 Cm long Silica-Gel column and eluted with n-hexane: ethyl acetate (98: 2 → 97: 3 → 95: 5). The fractions containing the major compound were combined together and evaporated on Rotavap to get major compound. The major compound was recrystallized to get colorless crystalline solid. Major compound was characterized through NMR, Mass and IR. These studies revealed the structure of titled compound (1); mp 186-188 °C; Yield 73%; 1H-NMR (400 MHz, CDCl3) δ: 8.62 (s, H-2,6), 7.68-7.67 (d, J = 1Hz, H-4), 7.26-7.24 (d, J = 2Hz, H-2', 2''), 7.207.15 (m, H-5',5'',6',6''), 2.42 (Me), 2.33 (Me);

13

C-NMR (150 MHz, CDCl3) δ: 148.1(2CH),

137.8(2C), 137.05(2C), 136.8(2C), 135.6(2C), 132.48 (CH), 130.65 (2CH), 130.58 (2CH), 128.8(2CH), 20.92 (CH3), 19.98 (CH3) FT-IR (νmaxCm-1): 2916, 1500, 1415, 1394, 1161, 1026, 885, 771, 717.

Scheme 1. Synthesis of title compound 3,5-bis(2,5-dimethylphenyl)pyridine (1)

The complete structure of the synthesized compound was determined by X-rays crystallographic data as well as spectroscopic data, which were compatible with the given structure.

2.3 X-ray structure measurements Single crystal X-rays analysis was performed on Bruker Smart APEX-II CCD diffractometer. A colorless prism crystal with approximate dimensions of 0.40 mm × 0.32 mm × 0.30 mm was analyzed by Bruker Apex Kappa-II-CCD- Diffractometer with a MoKa (0.71073 Å) radiation by using an ω scan mode in the range of 3.6<θ<30° at 296 K. Molecular graphics were produced by using Mercury. A total of 10519 reflections were measured, of which 1878 unique reflections [R (int) = 0.0280] were used in the calculation. The maximum and minimum peaks and holes are 0.27 and -0.17 e/Å3 respectively. Table 1 shows further crystallographic information for 3,5-bis(2,5-dimethylphenyl)pyridine (1).

3. Computational Details

The geometry optimization was performed using density functional theory (DFT) by employing hybrid Becke’s 3-parameter functional combined with Lee, Yang, and Parr’s correlation functional (B3LYP) [27] along with 6-311+G(2d,p) basis set [28]. Tight convergence criteria for the Self Consistent Field (SCF) energies and for the electron density (rms of the density matrix) were considered during all calculations. For DFT calculations, the initial geometry of 3,5-bis(2,5-dimethylphenyl)pyridine (1) was obtained from the crystal structure. The geometry optimizations of 3,5-bis(2,5dimethylphenyl)pyridine (1) were carried out in gas phase without any symmetry constraints using B3LYP/6-311+G(2d,p) level of theory. The ground state structure was confirmed by frequency analysis, which yielded only positive frequencies. The stability of the structure was confirmed after analyzing the calculated vibrational frequencies. The FT-IR, NBO, FMOs, NMR and MEP analyses of the 3,5-bis(2,5-dimethylphenyl)pyridine (1) were calculated at B3LYP/6311+G(2d,p) level of theory. The Turbomole 7.0.1 program package and GAMESS software [29-30] were used for all the theoretical calculations. The Avogadro [31] molecular visualization program was used to edit/interpret the input/output files and results. The 1H and 13C NMR chemical shifts values for 3,5-bis(2,5-dimethylphenyl)pyridine (1) has been determined experimentally in CDCl3 whereas both 1H and

13

C NMR chemical shift

values were calculated with B3LYP/6-311+G(2d,p) level of theory using polarizable continuum model (PCM) solvent method in chloroform.

4. Results and Discussion

4.1. Molecular geometry 4.1.1 Crystallography Figure 1 represents (a) ORTEP diagram with thermal ellipsoids drawn at 50% probability level. The Hydrogen atoms are represented as small circles of arbitrary radii. Symmetry code i = x, -y+1/2, z (b) The packing diagram showing the arrangement of molecules in the unit cell and (c) Optimized molecular structure of 3,5-bis(2,5-dimethylphenyl)pyridine (1) respectively. The asymmetric unit consists of half of the molecule which is shown in ORTEP diagram without symmetry codes. The mirror plane passes through C11 and N1 atoms. In this structure, the 2,5dimethylphenyl A (C1-C8) is planar with r. m. s. deviation of 0.0090 Å. The half of the central pyridine ring B (C9/C10/C11/N1) is also planar with r.m.s. deviation of 0.0001 Å. The dihedral angle between A/B is 56.27 (6)°. The molecules are mainly stabilized due to van der Waals forces.

Fig. 1. (a) ORTEP diagram with thermal ellipsoids drawn at 50% probability level. The Hydrogen atoms are represented as small circles of arbitrary radii. Symmetry code i = x, -y+1/2, z (b) The packing diagram showing the arrangement of molecules in the unit cell and (c) Optimized molecular structure of 3,5-bis(2,5-dimethylphenyl)pyridine (1) respectively.

Table 1 Single crystal XRD data of 3,5-bis(2,5-dimethylphenyl)pyridine (1). Crystal data CCDC Chemical formula Mr Crystal system, space group Temperature (K) a, b, c (Å) Angle (°) V (Å3) Z Radiation type µ (mm−1) Crystal size (mm) Data Collection Diffractometer Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 2σ(I)] reflections Rint (sin θ/λ)max (Å−1) Refinement R[F2 > 2σ(F2)], wR(F2), S No. of reflections No. of parameters H-atom treatment ∆ρmax, ∆ρmin (e Å−3)

Compound 1914740 C21H21N 287.39 Orthorhombic, Pnma 296 8.5123 (6), 27.4008 (19), 7.1987 (5) α = β = γ = 90 1679.1 (2) 4 Mo Kα 0.07 0.40 × 0.32 × 0.30 Bruker Kappa APEXII CCD Multi-scan (SADABS; Bruker, 2005) 0.974, 0.981 10519, 1878, 1427 0.028 0.639 0.044, 0.137, 1.06 1878 105 H-atom parameters constrained 0.27, −0.17

The two phenyl rings attached to central pyridine ring are out of plane due to steric repulsion. Therefore, the experimental bond lengths between N(41)-C(39), C(39)-C(38), C(38)C(28) and C(29)-C(28) are found to be 1.33 Å, 1.39 Å, 1.49 Å and 1.41 Å. The bond angles between C(39)-N(41)-C(19), C(28)-C(38)-C(42), C(28)-C(38)-C(39), C(38)-C(28)-C(29) and C(38)-C(28)-C(26) are 116.77°, 122.91°, 120.08°, 121.99° and 118.51° respectively. The experimental and theoretical crystal parameters, bond lengths and bond angles values are summarized in Table 2.

Table 2 Summary of the experimental and theoretical crystal parameters i.e. bond lengths, bond angles of 3,5-bis(2,5-dimethylphenyl)pyridine (1)

Parameters Bond lengths (Å) H(43)-C(42) C(42)-C(38) N(41)-C(39) C(39)-C(38) C(38)-C(28) H(37)-C(34) H(36)-C(34) H(35)-C(34) C(34)-C(29) H(33)-C(32) C(32)-C(30) C(32)-C(25) H(31)-C(30) C(30)-C(29) C(29)-C(28) C(28)-C(26) H(27)-C(26)

Experimental

Theory B3LYP/6-311+G(2d,p)

0.9298 1.3912 1.3340 1.3934 1.4915 0.9600 0.9606 0.9604 1.5060 0.9307 1.3809 1.3843 0.9300 1.3987 1.4046 1.3969 0.9301

1.0833 1.3947 1.3322 1.3993 1.4888 1.0939 1.0911 1.0912 1.5101 1.0849 1.3938 1.3884 1.0848 1.3957 1.4071 1.3994 1.0850

C(26)-C(25) C(25)-C(21) H(24)-C(21) H(23)-C(21) H(22)-C(21) Bond angles (°) H(43)-C(42)-C(38) C(38)-C(42)-C(18) C(39)-N(41)-C(19) H(40)-C(39)-N(41) H(40)-C(39)-C(38) N(41)-C(39)-C(38) C(28)-C(38)-C(42) C(28)-C(38)-C(39) C(42)-C(38)-C(39) C(29)-C(34)-H(35) C(29)-C(34)-H(36) C(29)-C(34)-H(37) H(35)-C(34)-H(36) H(35)-C(34)-H(37) H(36)-C(34)-H(37) H(33)-C(32)-C(30) H(33)-C(32)-C(25) C(30)-C(32)-C(25) H(31)-C(30)-C(32) H(31)-C(30)-C(29) C(32)-C(30)-C(29) C(34)-C(29)-C(30) C(34)-C(29)-C(28) C(30)-C(29)-C(28) C(38)-C(28)-C(29) C(38)-C(28)-C(26) C(29)-C(28)-C(26) H(27)-C(26)-C(28) H(27)-C(26)-C(25) C(28)-C(26)-C(25) C(21)-C(25)-C(32) C(21)-C(25)-C(26) C(32)-C(25)-C(26) H(22)-C(21)-H(23) H(22)-C(21)-H(24) H(22)-C(21)-C(25) H(23)-C(21)-H(24)

1.3924 1.5087 0.9599 0.9598 0.9596

1.3929 1.5080 1.0946 1.0914 1.0918

119.8887 120.2225 116.7731 117.7845 117.7172 124.4983 122.9057 120.0799 116.9977 109.5129 109.4521 109.5063 109.4581 109.4532 109.4446 119.4225 119.4954 121.0821 118.9786 118.9783 122.0431 119.8568 122.6489 117.4754 121.9894 118.5132 119.4934 118.6612 118.8072 122.5315 121.7325 120.9019 117.3651 109.5008 109.4180 109.4727 109.4539

119.7621 120.4279 117.7942 116.3185 119.7188 123.9616 122.6420 120.3836 116.9263 111.8646 110.4071 111.9536 108.1134 107.1035 107.1826 119.8213 119.5371 120.6386 119.1630 118.8250 122.0059 119.3899 122.6928 117.8973 122.4982 118.1200 119.3732 118.4280 119.0664 122.5014 121.3179 121.0938 117.5792 108.0617 107.3222 111.3360 107.4005

H(23)-C(21)-C(25) H(24)-C(21)-C(25) H(20)-C(19)-N(41) H(20)-C(19)-C(18)

109.4875 109.4944 117.7845 117.7172

111.4276 111.0977 116.3185 119.7188

As is shown in Table 2 that the theoretical bond lengths with B3LYP/6-311+G(2d,p) method between N(41)-C(39), C(39)-C(38), C(38)-C(28) and C(29)-C(28) are found to be 1.33 Å, 1.40 Å, 1.49 Å and 1.41 Å. The bond angles between C(39)-N(41)-C(19), C(28)-C(38)-C(42), C(28)-C(38)-C(39), C(38)-C(28)-C(29) and C(38)-C(28)-C(26) are 117.79°, 122.64°, 120.38°, 122.50° and 118.12° respectively. In general, the comparative study clearly shows that all the theoretical bond lengths and bond angles agree with the experimentally determined values apart from some little deviations.

4.2. FT-IR analysis The FT-IR spectrum also supported the structure of the synthesized compound. The compound showed peaks in its FT-IR spectrum at 2916 Cm-1 and indicated the presence of aromatic C-H and methyl C-H stretching. Aromatic C=C and C=N were identified by stretching vibrations in the double bond region of the spectrum at 1500, 1415, 1394 and 1161 Cm-1. Moreover, the presence of methyl group was established by C-H bending vibrations appearing at 771 Cm-1 and 717 Cm-1. In methyl group, the C-H stretching vibrations appears at lower wavenumber than those of aromatic C-H stretching vibrations. Moreover, the asymmetric stretching vibrations are usually found higher wavenumber than the symmetric stretching vibrations. Band predicted at

2916 Cm−1 by FT-IR (ATR (Attenuated Total Reflectance), Cm-1) is assigned to symmetric CH3 stretching vibrations of the methyl group attached with the Phenyl ring. On the other hand, the computed wavenumber by B3LYP/6-311+G(2d,p) level of calculation is about 2908 Cm-1, on comparing the both results it shows excellent agreement each other also agrees well with literature [32]. The rocking mode of τCH3 has obtained at 1026 Cm-1 in FT-IR spectrum, whereas the calculated wavenumber is about 1022 Cm-1.

Fig. 2. The FTIR spectrum of 3,5-bis(2,5-dimethylphenyl)pyridine (1). The stretching wavenumber of νC−N functional group identification is indeed a difficult task due to the problems in identification. Since there are mixing of bands is possible in this

region. Usually C−N lies in the region 1400-1200 Cm−1. Therefore, the identification of C−N wavenumber from other vibrations is problematic one. For the title compound, the C−N stretching vibrations are identified at 1500 Cm-1, stretching modes associated with the bending vibrations of βCNH modes appeared in the range of 772 and 717 Cm−1 in FT-IR and calculated at 1525 and 761 and 717 Cm-1 respectively. The ring CCC vibration found at 885 Cm-1 the counterpart wavenumber calculated at 900 Cm-1. The ring βCCH in-plane bending vibrations observed in the region 1161 Cm-1 and γCCH the out of plane bending vibration appeared at 810, and this vibration coupled with C-N vibrations at the 772 and 717 Cm-1. The corresponding calculated wavenumber for βCCH is 1163 Cm-1, and the γCCH wavenumbers are 794 Cm-1, 761 Cm-1, 717 Cm-1. Vibrational wavenumbers are listed in Table 3 whereas IR spectrum of 3,5bis(2,5-dimethylphenyl)pyridine (1) is shown in Figure 3.

Fig. 3. The calculated IR spectrum of 3,5-bis(2,5-dimethylphenyl)pyridine (1)

Table 3 Experimental and theoretical vibrational analysis along with vibrational assignments of 3,5bis(2,5-dimethylphenyl)pyridine (1). S. No.

1.

Experimental Unhormonic Harmonic Vibrational frequencies frequencies frequencies assignments -1 (Cm ) (Cm-1) (Cm-1) 2916.37 3026 2908 νCH3 sym stre

2. 3. 4. 5. 6. 7. 8. 9.

1500.62 1415.75 1161.15 1026.13 885.33 810.10 771.53 717.52

1587 1469 1210 1064 937 826 791 746

1525 1411 1163 1022 900 794 761 717

βN-CH bending νCC βCCH τCH3 rocking νCCC in ring γCCH bending γCCH obp, NCH γCCH obp, NCH

4.3 NMR analysis The symmetry in the molecule was revealed by fewer NMR signals. In 1HNMR (Figure 4a) five different sets of peaks were observed. A singlet at δ 2.33 was assigned to 6 hydrogen of two methyl groups present at 2′ & 2′′ positions of benzene. Another singlet at δ 2.42 was assigned to 6 hydrogen of remaining two methyl groups present at 5′ & 5′′ positions of benzene. Hence, these two peaks correspond to twelve CH3 protons present in compound. A multiplet arising at δ 7.20 - 7.15 due to four hydrogens was assigned to four hydrogens present at 3' & 3'', 4' & 4'' positions of benzene. A doublet at δ 7.26 - 7.24 (J = 2Hz) was assigned to two hydrogens attached to 6' & 6'' carbons of benzene. A hydrogen attached with carbon-4 of pyridine ring appeared as doubled at δ 7.68 - 7.67 (J = 1Hz). A low field singlet at δ 8.62 was attributed to two hydrogens attached to 2 & 6 carbons of pyridine ring. In comparison, the theoretical 1H-NMR spectrum is shown in Figure 4b of 3,5-bis(2,5-dimethylphenyl)pyridine (1), where five singlet peaks were observed in the range of 2.16 ppm - 2.74 ppm and assigned to twelve CH3 protons. Singlets at 7.32 ppm, 7.40 ppm and 7.49 ppm were assigned to CH aromatic hydrogens present at 6' & 6'', 4' & 4'' and 3' & 3'' positions of benzene respectively. Singlet peak at 7.67 ppm was

due to one CH proton of pyridine ring, while two CH protons of pyridine ring nearing to nitrogen atom appeared downfield at 8.73 ppm as singlet peak.

Fig. 4. (a) Experimental and (b) theoretical 1HNMR spectra of molecule of 3,5-bis(2,5dimethylphenyl)pyridine (1).

Fig. 5.

(a) Experimental and (b) theoretical

dimethylphenyl)pyridine (1).

13

CNMR spectra of molecule of 3,5-bis(2,5-

In

13

CNMR (Figure 5a) two peaks for four CH3 groups at 2nd and 5th position of phenyl

rings are resonating at 19.98 ppm and 20.98 ppm respectively. Signals at 137.8 ppm, 137.05 ppm, 136.8 ppm and 135.6 ppm are corresponding to eight quaternary carbons while signals at 148.1 ppm, 132.48 ppm, 130.65 ppm, 130.58 ppm, 128.8 ppm are resonating for nine CH carbons. In comparison, theoretical 13CNMR spectra (Figure 5b) show that the two peaks for four CH3 groups of phenyl rings are resonating at 21.49 ppm and 21.68 ppm respectively. Signals at 139.25 ppm, 142.70 ppm, 143.29 ppm and 145.15 ppm are corresponding to eight quaternary carbons while signals at 132.66 ppm, 134.27 ppm, 135.21 ppm, 143.95 ppm, 153.84 ppm are resonating for nine CH carbons.

4.4. Natural bond orbital (NBO) analysis The hyperconjugation gives as stabilizing effect that arises from an overlap between an occupied orbital with another neighboring electron deficient orbital, when these orbitals are properly oriented. This non-covalent bonding (antibonding) interaction can be quantitatively described in terms of the NBO analysis, which is expressed by means of the second-order perturbation interaction energy (E(2)) [33-35]. This energy represents the estimate of the offdiagonal NBO Fock matrix elements. It can be deduced from the second-order perturbation approach [36]: ‫( ܧ‬ଶ) = ߂‫ܧ‬௜௝ = ‫ݍ‬௜

ி(௜,௝)మ ఌೕ ିఌ೔

(1)

where ‫ݍ‬௜ is the donor orbital occupancy, ߝ௝ and ߝ௜ are diagonal elements (orbital energies) and ‫݅(ܨ‬, ݆) is the off diagonal NBO Fock matrix elements. The NBO analysis was performed using B3LYP/6-311+G(2d,p) level of theory calculation. The Natural atomic orbital (NAO) and Natural bond orbital (NBO) analysis were performed using Gaussian NBO version 3.1. The obtained results are presented in Table S1. In which, the core level atomic orbital population has calculated about 43.98e, and valence orbital population has calculated about 109.56e, whereas the total minimal basis is about 153.54e and Rydberg basis (Non-Lewis- NL) has calculated about 0.454e. The importance of the NBO method is originated from it gives information about the intra- and inter-molecular bonding and interactions among bonds. Furthermore, it provides a convenient basis for investigating the interactions in both filled and virtual orbital spaces along with charge transfer and conjugative interactions in molecular system [37]. Natural (localized) orbital used in computational chemistry to calculate the distribution of electron density in atoms in a bond. They have the “maximum occupancy character” in localized 1-center and 2-center regions of the molecule. As

is

mentioned

earlier,

NBO

analysis

was

performed

for

3,5-bis(2,5-

dimethylphenyl)pyridine (1) by using B3LYP level with the 6-311+G(2d,p) basis set in order to elucidate the intra-molecular, hybridization and delocalization of electron density within 3,5bis(2,5-dimethylphenyl)pyridine

(1).

It

is

revealed

that

the

strong

intra-molecular

hyperconjugative interaction of the σ and π electrons of C−C to the anti C−C bond of the benzene ring leads to stabilization of some part of the benzene ring [36].

In Table S1 donor and acceptor bonds, electron densities and hyperconjugative (E2) interaction energies are given. In NBO investigation, we mainly concentrate on σ-σ* and π- π*

interactions, where σ and π are donor (i) and σ* and π* is acceptor (j). This investigation indicates that the methyl groups influence van der Waals interactions among the adjacent bonds, especially; delocalization of energy during the interaction of methyl group attached bonds such as CH3-C5, C9-CH3, C29-CH3 and C25-CH3 are playing major role in the electron delocalization to the neighboring bonds and non-bonded groups. For example, the C42-H43 in pyridine ring and C34-H37 in Phenyl ring reveals more E2 energy (671.79 kcal/mol). Whereas, the lone pair nitrogen (41) show maximum energy (878.63 kcal/mol) with C38-H42 bond. Moreover, the Carbon-Carbon bond interactions also obtained considerable E2 energy, during the π-π* interactions. Finally, it can be concluded, for this section, based on outcomes that extended conjugation exists in the title compound i.e. 3,5-bis(2,5-dimethylphenyl)pyridine (1) which is responsible for the intra-molecular charge transfer. Therefore, clearly, the reason of ambient stability in the system is due to the strong intra-molecular hyper-conjugative interactions.

4.5. Frontier molecular orbital (FMOs) analysis The FMO theory is typically practiced describing various properties such as electronic and optical characteristics of a molecule. For example, the HOMO energy, LUMO energy and energy difference between them can predict the nature of reactivity of the structure in question and this information can be used to explain the intramolecular-charge-transfer effect [38]. In general, the value of HOMO energy effectively explain ability of a molecule to donate electron which further explains the oxidation procedures (i.e. higher the HOMO-energy, the easier the oxidation process). Furthermore, a system having large electronic gap energies are considered as less reactive i.e. more stable compared with the system containing smaller electronic energy gap

that is assumed to be less stable and more reactive [39]. Frontier molecular orbital energies and gap energies are represented in Table 4. Table 4 Frontier molecular orbital energies and gap energies (∆E) of 3,5-bis(2,5-dimethylphenyl)pyridine (1) in Hartree (Eh) units. FMOs HOMO LUMO HOMO-1 LUMO+1 HOMO-2 LUMO+2 HOMO-3 LUMO+3

Fig.

6.

Graphical

representation

Energy -0.23617 -0.04427 -0.24114 -0.03899 -0.24968 -0.01737 -0.25209 -0.01604

of

Frontier

∆E 0.19190 0.20215 0.23231 0.23605

Molecular

Orbitals

of

3,5-bis(2,5-

dimethylphenyl)pyridine (1).

With B3LYP/6-311+G(2d,p) level of theory we computed the energies of HOMOs, LUMOs and other frontier molecular orbitals of 3,5-bis(2,5-dimethylphenyl)pyridine (1). We

have represented (graphically) several frontier molecular orbitals in Figure 6, for example, HOMO-3, HOMO-2, HOMO-1, HOMO, LUMO, LUMO+1, LUMO+2, and LUMO+3 respectively. The gap energy values from various FMOs can be very useful information in order to extract numerous vital properties regarding energetics, dynamic stability and chemical reactivity of molecule. As is mentioned earlier, all eight FMO’s energies and gap energies (i.e. ∆E = ELUMO - EHOMO ) are represented in Table 4. Clearly, in Figure 6, the HOMO is localized on both left and right phenyl rings and a portion of connecting central pyridine ring except its nitrogen whereas LUMO on the other hand is localized everywhere except methyl group which may indicate a significant charge transfer. Which is enough evidence along with HOMO-LUMO energy gap values that the molecule is biological active which has been further confirmed after the molecular electrostatic potential analysis and then antimicrobial activity tests (see section 4.6 and 4.7 below).

Table 5 Electron affinity (EA), Ionization potential (IP), global hardness (η), global softness (S), electro negativity (χ), global electrophilicity (ω) and chemical potential (µ) of title compound i.e. 3,5bis(2,5-dimethylphenyl)pyridine (1) in electron volts (eV) units. Property Ionization potential (IP) Electron affinity (EA) Electro negativity (χ) Chemical potential (µ) Global hardness (η) Global softness (S) Global electrophilicity (ω)

Calculated results 6.43 1.20 3.82 -3.82 2.61 0.19 2.79

We have also calculated the global reactivity descriptors such as global softness (S), hardness (η), electrophilicity index (ω) electron affinity (EA), the chemical potential (µ), ionization potential (IP) and electro negativity (χ) [40-44]. These global parameters are defined as: ‫ = ܲܫ‬−‫ܧ‬ுைெை

(2)

‫ = ܣܧ‬−‫ܧ‬௅௎ெை

(3)

ଵ

−ߤ = (‫ ܲܫ‬+ ‫߯ = )ܣܧ‬ ଶ

ଵ

ߟ = (‫ ܲܫ‬− ‫)ܣܧ‬ ଶ

ଵ

ܵ = ଶఎ

߱=

ఓమ ଶఎ

(4)

(5)

(6)

(7)

Calculated values of all above-mentioned descriptors of the title compound can be seen in Table 5. These descriptors are very much appreciable considering biological-activities. It is well established that the compounds having the +ve electron affinity (or electron acceptors) can be an example of charge-transfer reactions. Therefore, electron affinity value for 3,5-bis(2,5dimethylphenyl)pyridine (1) is found to be positive. By knowing ionization potential energy, which is the amount energy required to remove an electron from the HOMO level, one can calculate electron donation strength for a compound whereas electro negativity is the quality of specie to attract electrons towards it. Chemical potential (µ) summaries the escaping tendency of electrons from an equilibrium system. We have calculated the value of (µ) using equation (4). Usually, if the electronic chemical potential is greater then compound is less stable or more

reactive, which is, in fact true for our case. Chemical hardness describes the resistance to change in the electron distribution in a collection of nuclei and electrons, which is calculated by using of equation (5). Moreover, electrophilicity index (ω) measures the ability of the species to accept electrons hence a good (more reactive) nucleophile has a lower value of (ω). The electrophilicity index values are calculated by equation (7). Clearly, the values of global chemical descriptors shown in Figure 5 predict that the title compound possess reactive behavior (i.e. biological active) that we have also studied in next sections.

4.6. Molecular electrostatic potential (MEP) Theoretical 3-D visualized mapping with molecular electrostatic potential analysis not only propose reactivity of the molecule but also help representing charge distribution and related properties. The MEP can also be a very important parameter to predict bioactivities in the compounds. Moreover, MEP is an important tool, which help figuring out electrophilic and nucleophilic attack sites, biological gratitude and H-bonding interactions depending upon the size/shape of the molecule and magnitude of the electrostatic potential (colour code). At the surface of molecules, the magnitude (value) of electrostatic potential can be represented by the colour scheme. For example, green colour shows the value of electrostatic potential equal to zero (or close to zero), blue colour represents the area of most +ve potential (i.e. nucleophilic region) and finally red colour shows the area of most -ve potential (i.e. electrophilic region). The intensities of MEP surfaces (i.e. negative to all the way positive potentials) can be judged with the color codes and increases in the order: red < orange < yellow < green < blue [45].

Fig. 7. (A) front (B) side view of molecular electrostatic potential map for 3,5-bis(2,5dimethylphenyl)pyridine (1) at isoval=0.004, whereas (C) represents contour map of the same.

In order to investigate the electrostatic physiochemical properties and potential regions of the 3,5-bis(2,5-dimethylphenyl)pyridine (1) molecule, DFT calculations were carried out on the optimized geometry using B3LYP/6-311+G(2d,p) method and the graphical representation is shown in Fig. 7. This is clearly shown in Fig. 7 that most of the –ve electrostatic potential is distributed over the nitrogen atom which is attached with in the pyridine ring is actually favorable region in 3,5-bis(2,5-dimethylphenyl)pyridine (1) molecule for electrophilic attack. On the other hand, most of the +ve electrostatic potential (explains the donor nature) is distributed over the carbon and hydrogen atoms present in the same ring is favorable region in 3,5-bis(2,5dimethylphenyl)pyridine (1) molecule for nucleophile attack.

4.7. Antimicrobial activity 4.7.1. Antimicrobial activities measured in terms of mm zone of inhibition 3,5-bis(2,5-dimethylphenyl)pyridine (1) sample was tested against various Gram negative (E.coli, P. aeroginosa, Citrobacter spp. and K. pneumoniae) and Gram positive bacteria (S. aureus and B. atrophoeus). Moreover, the sample was also tested for its anticandidal activity. Two concentrations of the sample was applied (0.1mg, 0.2mg) against each microorganism. The results were calculated in terms of millimeter (mm) of zones of inhibition formed against each microorganism. While using lower concentration (0.1mg) of 3,5-bis(2,5-dimethylphenyl)pyridine (1), it has exhibited maximum antimicrobial activity against S. aureus (16mm) followed by P. aeruginosa (12mm) and C. albicans (11mm). Similar activities (10mm) were shown against Gram negative Citrobacter and Gram positive B. atrophoeus. Similarly, alike activities (9mm)

were also exhibited against E. coli and K. pneumonia. However, by increasing the concentration of the sample the activities were equally increased, at 0.2mg maximum activity was also recorded against S. aureus (19mm) followed by P. aeruginosa (14mm). However, this time B. atrophoeus and C. albicans have shown same results (13mm), followed by Citrobacter (12mm). Similarly, at higher concentrations as well, E. coli and K. pneumonia were the less effected bacterial cultures showing 11mm zone of inhibition against each of them. The current results were at par with the findings of Fazal et al. [46]. They reported that crude extract of Parthenium hysterophorus scored (13, 14, 16, 17mm) against E. coli, P. aeroginosa, B. subtilus respectively. Stevia rebaudiana showed inhibition of E. coli, K. pneumoniae, and S. aureus as 26, 16, and 12mm respectively. Moreover, Ginkgo biloba extracts was found inactive against E. coli, B. subtilus and S. aureus [46]. Similarly, Shad et al. reported that hexane fraction of Ajuga bracteosa was best active against C. albicans (25.86) followed by S. typhi (25mm) [47]. Similarly, it is also reported [48] that Artemisia scoparia and Echinacea purpurea illustrated marked antimicrobial activity. Iqbal et al., [49] found that Methoxysubsitutedbenzyl 4ketohexanoates (1-8) as well as halogen substitutedbenzyl 4-ketohexanoates (9-17) exhibited good activities against B. cereus, M. luteus, A. niger and C. albicans.

Fig.

8.

Antimicrobial

activities

of

3,5-bis(2,5-dimethylphenyl)pyridine

(1)

against

Staphylococcus aureus, Pseudomonas aeruginosa, scherichia coli, Klebsiella pneumoniae, Citrobacter spp., Bacillus atrophoeus and Candida albicans.

4.7.2. Antimicrobial Activities of Standard Antibiotics

The standard antibiotics (30µg) were tested against microorganism to check their susceptibility and resistance. Azithromycin and Ciprofloxacin were used against Gram positive and Gram-negative bacteria respectively. Clotrimazole was used against the fungus C. albicans. These antibiotics were applied as positive control for the said organisms. Azithromycin showed (23mm, 25mm) zones against S. aureus and B. atrophoeus respectively. Moreover, Ciprofloxacin showed (43mm, 34mm, 29mm, 29mm) zones against E.coli, P. aeroginosa, Citrobacter spp. and K. pneumoniae respectively, while Clotrimazole showed (32mm) inhibitory zone against C. albicans (Figure 8) similar to the results of Ahmad et al. [50]. Previously, tetracycline was found active against E. coli (15.5mm) and P. aeroginosa (11 mm). However, K. pneumoniae was found resistant to tetracycline and showed 29 mm zones against ciprofloxacin. Similarly erythromycin was equally effective against S. aureus and B. atrophaeus [50]. Furthermore, it is reported [49] that standard drugs including imipenem and ketoconazole exhibit promising zones of inhibition against B. cereus, M. luteus, A. niger and C. albicans (36.3 , 38.6, 30.4 and 31.5mm) respectively.

5. Conclusions A novel compound 3,5-bis(2,5-dimethylphenyl)pyridine (1) was synthesized via Pd (0) catalyzed Suzuki-Miyaura cross coupling reaction in excellent yield. Compound (1) was characterized by XRD, NMR, FT-IR and mass spectrometric analysis. Experimental spectroscopic findings were compared with DFT studies. The XRD studies suggest that the crystal structure of compound (1) is orthorhombic shape with space group Pnma respectively. XRD studies were compared with density functional theory calculations, which are in close

agreement with each other. Calculated FT-IR results are found to be in excellent agreement with experimental FT-IR findings. Natural bond orbital (NBO) study was performed using B3LYP/6311+G(2d,p) method which indicates that the methyl groups influence van der Waals interactions among the adjacent bonds, especially, delocalization of energy during the interaction. Energy gap values of HOMO-LUMO calculated through frontier molecular orbital (FMO) analysis provided enough evidence that molecule is biologically active. Molecular electrostatic potential (MEP) mapping indicated that electron density is located on nitrogen whereas carbon and hydrogen atom are favorable sites for nucleophilic attack. Moreover, the bioactivities of compound (1) have been confirmed by the experimental activity in terms of zones of inhibition against bacteria and fungus.

Acknowledgments Computational resources from the Department of Physics, University of Sargodha (HEC Project No. 172) Pakistan are gratefully acknowledged.

Appendix A. Supplementary data

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Table 1 Single crystal XRD data of 3,5-bis(2,5-dimethylphenyl)pyridine (1). Crystal data CCDC Chemical formula Mr Crystal system, space group Temperature (K) a, b, c (Å) Angle (°) V (Å3) Z Radiation type µ (mm−1) Crystal size (mm) Data Collection Diffractometer Absorption correction Tmin, Tmax No. of measured, independent and observed [I > 2σ(I)] reflections Rint (sin θ/λ)max (Å−1) Refinement R[F2 > 2σ(F2)], wR(F2), S No. of reflections No. of parameters H-atom treatment ∆ρmax, ∆ρmin (e Å−3)

Compound 1914740 C21H21N 287.39 Orthorhombic, Pnma 296 8.5123 (6), 27.4008 (19), 7.1987 (5) α = β = γ = 90 1679.1 (2) 4 Mo Kα 0.07 0.40 × 0.32 × 0.30 Bruker Kappa APEXII CCD Multi-scan (SADABS; Bruker, 2005) 0.974, 0.981 10519, 1878, 1427 0.028 0.639 0.044, 0.137, 1.06 1878 105 H-atom parameters constrained 0.27, −0.17

Table 2 Summary of experimental and theoretical crystal parameters i.e. bond lengths, bond angles of 3,5-bis(2,5-dimethylphenyl)pyridine (1)

Parameters Bond lengths (Å) H(43)-C(42) C(42)-C(38) N(41)-C(39) C(39)-C(38) C(38)-C(28) H(37)-C(34) H(36)-C(34) H(35)-C(34) C(34)-C(29) H(33)-C(32) C(32)-C(30) C(32)-C(25) H(31)-C(30) C(30)-C(29) C(29)-C(28) C(28)-C(26) H(27)-C(26) C(26)-C(25) C(25)-C(21) H(24)-C(21) H(23)-C(21) H(22)-C(21) Bond angles (°) H(43)-C(42)-C(38) C(38)-C(42)-C(18) C(39)-N(41)-C(19) H(40)-C(39)-N(41) H(40)-C(39)-C(38) N(41)-C(39)-C(38) C(28)-C(38)-C(42) C(28)-C(38)-C(39) C(42)-C(38)-C(39) C(29)-C(34)-H(35)

Experimental

Theory B3LYP/6-311+G(2d,p)

0.9298 1.3912 1.3340 1.3934 1.4915 0.9600 0.9606 0.9604 1.5060 0.9307 1.3809 1.3843 0.9300 1.3987 1.4046 1.3969 0.9301 1.3924 1.5087 0.9599 0.9598 0.9596

1.0833 1.3947 1.3322 1.3993 1.4888 1.0939 1.0911 1.0912 1.5101 1.0849 1.3938 1.3884 1.0848 1.3957 1.4071 1.3994 1.0850 1.3929 1.5080 1.0946 1.0914 1.0918

119.8887 120.2225 116.7731 117.7845 117.7172 124.4983 122.9057 120.0799 116.9977 109.5129

119.7621 120.4279 117.7942 116.3185 119.7188 123.9616 122.6420 120.3836 116.9263 111.8646

C(29)-C(34)-H(36) C(29)-C(34)-H(37) H(35)-C(34)-H(36) H(35)-C(34)-H(37) H(36)-C(34)-H(37) H(33)-C(32)-C(30) H(33)-C(32)-C(25) C(30)-C(32)-C(25) H(31)-C(30)-C(32) H(31)-C(30)-C(29) C(32)-C(30)-C(29) C(34)-C(29)-C(30) C(34)-C(29)-C(28) C(30)-C(29)-C(28) C(38)-C(28)-C(29) C(38)-C(28)-C(26) C(29)-C(28)-C(26) H(27)-C(26)-C(28) H(27)-C(26)-C(25) C(28)-C(26)-C(25) C(21)-C(25)-C(32) C(21)-C(25)-C(26) C(32)-C(25)-C(26) H(22)-C(21)-H(23) H(22)-C(21)-H(24) H(22)-C(21)-C(25) H(23)-C(21)-H(24) H(23)-C(21)-C(25) H(24)-C(21)-C(25) H(20)-C(19)-N(41) H(20)-C(19)-C(18)

109.4521 109.5063 109.4581 109.4532 109.4446 119.4225 119.4954 121.0821 118.9786 118.9783 122.0431 119.8568 122.6489 117.4754 121.9894 118.5132 119.4934 118.6612 118.8072 122.5315 121.7325 120.9019 117.3651 109.5008 109.4180 109.4727 109.4539 109.4875 109.4944 117.7845 117.7172

110.4071 111.9536 108.1134 107.1035 107.1826 119.8213 119.5371 120.6386 119.1630 118.8250 122.0059 119.3899 122.6928 117.8973 122.4982 118.1200 119.3732 118.4280 119.0664 122.5014 121.3179 121.0938 117.5792 108.0617 107.3222 111.3360 107.4005 111.4276 111.0977 116.3185 119.7188

Table 3

Experimental and theoretical vibrational analysis along with vibrational assignments

of 3,5-bis(2,5-dimethylphenyl)pyridine (1). S. No.

1. 2. 3. 4. 5. 6. 7. 8. 9.

Experimental Unhormonic Harmonic Vibrational frequencies frequencies frequencies assignments -1 (cm ) (cm-1) (cm-1) 2916.37 3026 2908 νCH3 sym stre 1500.62 1587 1525 βN-CH bending 1415.75 1469 1411 ν CC 1161.15 1210 1163 βCCH 1026.13 1064 1022 τCH3 rocking 885.33 937 900 νCCC in ring 810.10 826 794 γCCH bending 771.53 791 761 γCCH obp, NCH 717.52 746 717 γCCH obp, NCH

Table 4 Frontier molecular orbital energies and gap energies (∆E) of 3,5-bis(2,5-dimethylphenyl)pyridine (1) in Hartree (Eh) units. FMOs HOMO LUMO HOMO-1 LUMO+1 HOMO-2 LUMO+2 HOMO-3 LUMO+3

Energy -0.23617 -0.04427 -0.24114 -0.03899 -0.24968 -0.01737 -0.25209 -0.01604

∆E 0.19190 0.20215 0.23231 0.23605

Table 5 Electron affinity (EA), Ionization potential (IP), global hardness (η), global softness (S), electro negativity (χ), global electrophilicity (ω) and chemical potential (µ) of title compound i.e. 3,5bis(2,5-dimethylphenyl)pyridine (1) in electron volts (eV) units. Property Ionization potential (IP) Electron affinity (EA) Electro negativity (χ) Chemical potential (µ) Global hardness (η) Global softness (S) Global electrophilicity (ω)

Calculated result 6.43 1.20 3.82 -3.82 2.61 0.19 2.79

Table S1 The Second order perturbation analysis of Fock Matrix in NBO basis for 3,5-bis(2,5dimethylphenyl)pyridine (1). a

Type

Donor (i)

ED/e

π*

Acceptor (j)

π* π* σ σ* σ* σ* σ* σ* σ* σ* π* π* σ* σ* σ* σ* σ* σ* σ* σ* σ* π* σ* σ* π* π* σ* π* π* σ* σ* σ* σ* σ* π*

C5 - C6 C18 - C19 C18 - C42 C26 - H27 C29 - C30 C34 - H35 C34 - H37 C38 - C39 C38 - C42 C42 - H43 C5 - C6 C18 - C19 C18 - C42 C26 - H27 C29 - C30 C34 - H35 C34 - H37 C38 - C39 C38 - C42 C39 - H40 C42 - H43 C5 - C6 C29 - C30 C38 - C42 C8 - C9 C10 - C12 C38 - C42 C10 - C12 C5 - C6 C21 - C25 C38 - C42 C29 - C30 C34 - H37 C38 - C42 C5 - C6

σ

C1 - H4

1.97612

σ

C1 - C5

1.98245

σ

C5 - C6

1.97216

π

C5 - C6

1.65046

σ π

C6 - H7 C8 - C9

1.97826 1.96472

σ

C10 - H11

1.97871

σ

C10 - C12

1.97595

ED/e 0.34382 0.32753 0.02579 0.01470 0.02204 0.00761 0.01161 0.03542 0.02582 0.01564 0.34382 0.32753 0.02579 0.01470 0.02204 0.00761 0.01161 0.03542 0.02582 0.02524 0.01564 0.34382 0.32753 0.02579 0.37397 0.33479 0.02582 0.33479 0.34382 0.01628 0.02582 0.02204 0.01161 0.02582 0.34382

E(2) kcal/mol 659.06 11.54 26.22 26.1 135.39 41.33 127.57 21.38 435.11 31.73 378.86 11.64 24.39 25.42 119.62 38.94 106.12 23 344.37 13.05 34.7 37.3 11.01 29.88 20.77 19.93 29.24 20.44 17.14 11.39 22.33 12.13 11.33 36.8 92.18

b

ε(j)-ε(i) 0.07 0.58 1.05 1.05 1.44 0.78 0.72 1.05 0.32 3.44 0.23 0.74 1.21 1.21 1.6 0.93 0.88 1.2 0.48 3.39 3.59 0.16 1.53 0.41 0.29 0.28 0.23 0.29 0.09 1.25 0.34 1.35 0.63 0.23 0.18

c

f(i,j)

0.208 0.08 0.148 0.148 0.394 0.161 0.272 0.134 0.334 0.295 0.286 0.09 0.153 0.157 0.391 0.171 0.273 0.149 0.363 0.188 0.315 0.075 0.116 0.099 0.07 0.067 0.072 0.069 0.037 0.107 0.078 0.114 0.075 0.082 0.126

π σ σ

C10 - C12 C14 - H17 C18 - C19

1.67501 1.97652 1.97292

σ

C18 - C42

1.96742

σ π σ

C19 - N41 C28 - C29 C28 - C38

1.98346 1.63677 1.96813

σ σ

C34 - H37 C38 - C42

1.97663 1.96763

π

C38 - C42

1.63417

σ* σ* σ* π* σ* π* σ* σ* σ* σ* σ* σ* π* σ* π* σ* σ* σ* σ* σ* σ* σ* σ* σ* σ* σ* π* π* σ* σ* σ* π* σ* σ* σ* σ* σ* σ* σ* σ* σ* σ* σ*

C29 - C30 C34 - H37 C38 - C42 C8 - C9 C38 - C42 C5 - C6 C21 - C25 C29 - C30 C29 - C34 C34 - H37 C1 - H2 C1 - H4 C5 - C6 C5 - C12 C18 - C19 C18 - C42 C21 - C25 C26 - H27 C29 - C30 C34 - H35 C34 - H37 C38 - C39 C38 - C42 C39 - H40 C42 - H43 C29 - C30 C30 - C32 C5 - C6 C21 - C25 C38 - C42 C38 - C42 C18 - C19 C18 - C42 C26 - H27 C29 - C30 C29 - C34 C34 - H35 C34 - H37 C38 - C39 C38 - C42 C42 - H43 C29 - C30 C34 - H35

0.02204 0.01161 0.02582 0.37397 0.02582 0.34382 0.01628 0.02204 0.01647 0.01161 0.00589 0.01074 0.34382 0.02440 0.32753 0.02579 0.01628 0.01470 0.02204 0.00761 0.01161 0.03542 0.02582 0.02524 0.01564 0.02204 0.33481 0.34382 0.01628 0.02582 0.02582 0.32753 0.02579 0.01628 0.01470 0.02204 0.00761 0.01161 0.03542 0.02582 0.02204 0.33481 0.00761

38.46 30.29 72.24 19.76 32.33 43.05 12.98 68.26 19.7 36.51 14.41 14.92 761.39 10.3 15.32 47.93 14.52 39.8 114.76 43.93 95.25 30 309.56 34.89 81.17 12 20.26 179.09 10.55 74.35 19.11 25.84 92.76 51.66 494.34 17.71 118.68 460.77 24.97 1359.34 107.02 21.25 13.1

1.55 0.83 0.43 0.29 0.22 0.16 1.33 1.54 2.31 0.82 1.15 1.16 0.25 1.36 0.77 1.23 1.42 1.24 1.62 0.96 0.9 1.23 0.5 3.41 3.62 1.66 0.28 0.1 1.27 0.35 0.21 0.47 0.94 0.94 1.33 2.1 0.67 0.61 0.93 0.21 3.32 1.12 0.46

0.218 0.142 0.158 0.069 0.075 0.082 0.118 0.289 0.191 0.155 0.115 0.118 0.426 0.106 0.105 0.217 0.129 0.199 0.386 0.184 0.263 0.171 0.353 0.309 0.486 0.126 0.068 0.132 0.104 0.145 0.057 0.107 0.264 0.198 0.726 0.173 0.253 0.476 0.136 0.477 0.535 0.152 0.077

0.01161 σ* C34 - H37 31.87 0.02582 σ C39 - H40 1.98043 σ* C38 - C42 24.22 0.02204 σ C39 - N41 1.98350 σ* C29 - C30 16.61 0.32753 σ C42 - H43 1.97922 π* C18 - C19 139.68 0.02579 σ* C18 - C42 35.52 0.01470 σ* C26 - H27 26.77 0.02204 σ* C29 - C30 246.78 0.00761 σ* C34 - H35 175.9 0.01161 σ* C34 - H37 671.79 0.03542 σ* C38 - C39 53.7 0.02524 σ* C39 - H40 20.37 0.01564 σ* C42 - H43 25.45 0.03536 σ N41 1.91629 σ* C18 - C19 12.94 0.32753 π* C18 - C19 17.42 0.02579 σ* C18 - C42 27.86 0.01470 σ* C26 - H27 28.48 0.02204 σ* C29 - C30 123.66 0.00761 σ* C34 - H35 50.16 0.01161 σ* C34 - H37 144.75 0.03542 σ* C38 - C39 61.32 0.02582 σ* C38 - C42 878.63 0.02524 σ* C39 - H 40 14.15 0.01564 σ* C42 - H43 38.26 a (2) E means energy of hyper conjugative interaction (stabilization energy). b Energy difference between donor(i) and acceptor(j) NBO orbitals. c F(i,j) is the fork matrix element between i and j NBO orbitals.

0.41 0.23 1.65 0.06 0.52 0.53 0.91 0.25 0.19 0.52 2.7 2.91 0.99 0.43 0.89 0.9 1.28 0.62 0.56 0.89 0.16 3.07 3.28

0.112 0.066 0.148 0.086 0.121 0.106 0.424 0.188 0.323 0.149 0.21 0.243 0.102 0.082 0.143 0.145 0.361 0.16 0.26 0.211 0.343 0.189 0.322

Highlights

➢ 3,5-bis(2,5-dimethylphenyl)pyridine (1); a novel derivative of 3,5-dibrommopyridine was synthesized via Pd(0) catalyzed cross coupling reaction. ➢ The compound was characterized by XRD and NMR, FT-IR spectroscopic techniques. ➢ DFT calculations were performed for various molecular properties like NBO, FMO analysis and MEP mapping etc. ➢ Calculated FT-IR results are found to be in excellent agreement with experimental FT-IR findings. ➢ Bioactivities of the compound are confirmed experimentally (and theoretically) in terms of zones of inhibition against bacteria and fungus.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: