Molecular Spectroscopy and Molecular Docking Studies on ( E )-1-( 4-Bromobenzylidene ) Thiourea

The organic molecule (E)-1-(4-bromobenzylidene)thiourea (BBTU) have been synthesized and characterized using FT-IR and FT-Raman spectral studies. The quantum chemical calculations of BBTU have been studied using DFT/B3LYP/6-31G(d,p) level of theory. The stable conformer is identified by the potential energy surface scan. The complete vibrational assignments were performed on the basis of PED analysis with the help of SQM method. NBO analysis was carried out to explore the various conjucative/hyperconjucative interactions within the molecule and their second order stabilization energy. The NLO activity of BBTU is calculated and compared with the standard Urea molecule. The energies of the FMOs are used for the determination of global reactivity descriptors. The electrophilic and nucleophilic charge sites were identified by the molecular electrostatic potential mapped surface. The molecular docking of BBTU is carried out with the receptors of 3U2D and 1JIJ to screen the bacterial activity. DOI : 10.14302/issn.2377-2549.jndc-18-1933 Corresponding Author: S. Bharanidharan, Department of Physics, Bharath Institute of Higher Education and Research, Bharath University, Chennai-600 073, India. Tel: +91 9843225234, E-mail: bharani.dharan0@gmail.com


Introduction
The consideration products of carbonyl compounds and primary amines are often named as Schiff bases. They are also known as azomethines or anils or imines. The >C=N-group is present in organic molecules of fundamental importance. They have got extensive application in biological and industrial fields.
Schiff bases with potential pharmaceutical use were synthesized [1,2]. Schiff bases have been reported for their biological properties, such as anti-bacterial, anti-fungal, anti-inflammatory, analgesic, anti-convulsant, anti-tubercular, anti-cancer, anti-oxidant and anti-helmintic activities [3][4][5][6][7][8][9][10][11]. Schiff base metal complexes have applications in the areas from material science to biological sciences. They have been widely studied because they have anti-cancer and herbicidal applications [12,13]. Schiff base complexes show greater biological activity than free ligands. The DNA binding, cytotoxicity and apoptosis induction activity were studied for Schiff base copper(II) complexes [14]. phenyl]ethanone with trans-1,2-diaminocyclohexane by C. Balakrishnan et al (2015) [22]. The single crystal analysis shows that the compound exists in enolimine form with monoclinic crystal lattice system and space group C2/c. Density functional calculation on L reveals that the enolimine form is more stable than the ketoamine form in gas phase.
The mixture was shaken to make homogenous solution.
Few drops of catalyst acetic acid was added to increase the rate of reaction. The content was refluxed at 90°C for 3 hours. The completion of the reaction was monitored by thin layer chromatography. After the reaction was completed, the content was cooled the mixture was poured into water. The solid product obtained was filtered and purified using absolute ethanol.

FT-IR and FT-Raman Spectra
The FT-IR spectrum of the synthesized BBTU was measured in the 4000-400 cm −1 region at the spectral resolution of 4 cm −1 using on SHIMADZU FT-IR Where I i is the Raman intensity, RA i is the Raman scattering activities, ν i is the wavenumber of the normal modes and ν 0 denotes the wavenumber of the excitation laser [27].

Identification of Stable Conformer
After

Vibrational Assignments
The observed FT-IR, FT-Raman, computed harmonic wavenumber along with intensities and their assignments for the present compound are illustrated in

C-Br Vibrations
Bromine compounds absorb strongly in the region 650-485 cm -1 due to the C-Br stretching vibrations [29]. The theoretical wavenumbers of C-Br stretching vibration coupled with other group vibrations.
According to PED, there is no pure C-Br band vibration.
In our present study, the C-Br vibration was calculated at 659 cm -1 along with CCC and CNC bending vibrations.
The 90% of PED contribution confirms the corresponding wavenumber. The C-Br out-of-plane bending and in-plane bending vibrations are assigned to the Raman bands at 298 and 218 cm −1 , respectively.

C=S Vibrations
The C=S is less polar than the C=O group and encountered great difficulty due to vibrational mixings between C=S stretching the other vibrational modes.
The C=S group is found over the wide range of 1035-245 cm -1 whereas, C-S stretching vibration results strong bands in Raman spectra which are normally easy to identify and is difficult in Infrared region [29]. In consequence, the band is not intense, and it falls at lower frequencies, where it is much more susceptible to coupling effects and identification is therefore difficult and uncertain [30]. In our present study the C=S band is observed in FT-IR at 740 cm -1 and in FT-Raman spectrum at 733 cm -1 as strong bands. Its theoretical wavenumber calculated at 750 cm -1 with 67% of PED contribution.

C-N Vibrations
The C=N stretching skeletal bands are observed in the range 1650-1550 cm -1 [31]. For BBTU, the C=N Where, qi is the donor orbital occupancy, εi and εj are diagonal elements (orbital energies) and F(i, j) is off diagonal NBO Fock matrix elements.  Table 3 reveals

Non-Linear Optics
The first order hyperpolarizabilities (β 0 , α 0 and Δ α ) of BBTU is calculated using DFT/B3LYP/6-31G(d,p) basis set, based on the finite-field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. First hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to Kleinman symmetry [41]. It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3x3x3 matrix is a tetrahedral. The components of β are defined as the coefficients in the Taylor series expansion of the energy in the external electric field.
When the external electric field is weak and homogeneous, this expansion becomes: Where E 0 is the energy of the unperturbed molecules, F α is the field at the origin, and µ α , α αβ and β αβγ are the components of the dipole moment, polarizability and the first hyperpolarizabilities, respectively. The total static dipole moment μ, the mean polarizability α0, the anisotropy of polarizability Δ α and the mean first hyperpolarizability β 0 , using the x, y, z components [42] are defined as Raman activity strong at the same time [47].
Theoretical investigation plays an important role in understanding the structure -property relationship, which is able to assist in designing novel NLO materials.
It is well known that the higher values of dipole moment, molecular polarizability and hyperpolarizability are important for more active NLO properties. It is evident from Table 4 As seen from Fig. 5, the HOMO is localized over

Molecular Docking Studies
Protein-ligand interactions play a critical role in the distribution, metabolism and transport of small molecules in biological systems and processes [52].
AutoDock is a suite of automated docking tools designed to predict how small molecules, such as substrates or drug candidates, bind to a receptor of known threedimensional structure. With the aim to investigate the binding mode, molecular modeling study was performed using AutoDock Tools for docking [53]. 5NI was chosen to be docked into the active site of different receptors     algorithm [54] was applied to search for protein-ligand interaction with and for visualization performed using PyMOL [55].
The objective of present study was to evaluate the drug activity and binding affinity of BBTU with a target protein using the program of AutoDock. The resulting free energy of binding and inhibition constant of BBTU with protein 3U2D and IJIJ observed at the end of docking simulation is shown in Table 6