Investigation on spectra (UV–Vis, vibrational, NMR, HRMS), electronic structure (DFT calculations), molecular docking and antidiabetic activity of N-((benzo[d]thiazol-2-ylthio)methyl)-N-cyclohexylcyclohexanamine – A Mannich base

Article abstract of DOI:10.1016/j.molstruc.2020.128604

A new Mannich base molecule of N-((benzo[d]thiazol-2-ylthio)methyl)-N-cyclohexylcyclohexanamine (ICF) has been synthesized and spectroscopic characterization such as FT-IR, FT-Raman, UV–Vis, NMR, mass and TG/DSC were investigated. The spectroscopic quantum chemical calculations namely simulation of vibrational spectrum, UV–Vis, NMR have been carried out and compared with the experimental observations. Other theoretical predictions such as Equilibrium Geometry, chemical reactivity, molecular electrostatic potential, frontier molecular orbital analysis and natural bond orbital analysis (NBO) have been computed and investigated using the density functional theoretical (DFT) methods. The computed entities and experimental results the consistently have good agreement with each other. The excited properties of ICF have been calculated using the TDDFT calculations. The molecular docking studies used to simulate the protein-ligand interactions have been analyzed with Schr?dinger software.

Full text of DOI:10.1016/j.molstruc.2020.128604

Journal Pre-proof
Investigation on spectra (UV–Vis, vibrational, NMR, HRMS), electronic structure (DFT
calculations), molecular docking and antidiabetic activity of N-((benzo[d]thiazol-2-
ylthio)methyl)-N-cyclohexylcyclohexanamine – A Mannich base
Krishnan Sarojini Devi, Palaniappan Subramani, Namadevan Sundaraganesan, Maria
Susai Boobalan, Dhanapal Tamilvendan
PII:
S0022-2860(20)30929-7
DOI:
https://doi.org/10.1016/j.molstruc.2020.128604
MOLSTR 128604
Reference:
To appear in: Journal of Molecular Structure
Received Date: 5 January 2020
Revised Date: 2 June 2020
Accepted Date: 2 June 2020
Please cite this article as: K.S. Devi, P. Subramani, N. Sundaraganesan, M.S. Boobalan, D.
Tamilvendan, Investigation on spectra (UV–Vis, vibrational, NMR, HRMS), electronic structure (DFT
calculations), molecular docking and antidiabetic activity of N-((benzo[d]thiazol-2-ylthio)methyl)-N-
cyclohexylcyclohexanamine – A Mannich base, Journal of Molecular Structure (2020), doi: https://
doi.org/10.1016/j.molstruc.2020.128604.
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2020 Published by Elsevier B.V.

Krishnan Sarojini Devi: Conceptualization, Data curation Methodology, writing- Original
draft preparation, Investigation
Palaniappan Subramani : Supervision
Namadevan Sundaraganesan : Software
Maria Susai Boobalan
Dhanapal Tamilvendan
: writing- Reviewing and Editing
: Visualization

Graphical Abstract

Investigation on spectra (UV-Vis, vibrational, NMR, HRMS), electronic
structure (DFT calculations), molecular docking and antidiabetic activity of N-
(
(benzo[d]thiazol-2-ylthio)methyl)-N-cyclohexylcyclohexanamine – A
Mannich base
a
b,
c
Krishnan Sarojini Devi , Palaniappan Subramani *, Namadevan Sundaraganesan ,
d
e
Maria Susai Boobalan , Dhanapal Tamilvendan
a
Department of Chemistry, Sri-La-Sri Kasivasi Sawaminatha Swamigal Arts College, Thiruppanathal,
Kumbakonam 612504, Tamil Nadu, India
b
Chemistry Section, Faculty of Engineering and Technology, Annamalai University,
Annamalainagar 608 002, Tamil Nadu, India
c
Physics Section, Faculty of Engineering and Technology, Annamalai University, Annamalainagar
608 002, Tamil Nadu, India
d
Department of Chemistry, College of Natural and Computational Sciences (CNCS), Haramaya
University, Dire Dawa, Ethiopia
e
Department of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, Tamil Nadu,
India
*Corresponding author
Dr. P. Subramani
Professor
Chemistry Section
Faculty of Engineering and Technology
Annamalai University
Annamalainagar 608 002.
Tel.: +91 8973522231
E-mail: saro87che@gmail.com

2
ABSTRACT
A
new Mannich base molecule of N-((benzo[d]thiazol-2-ylthio)methyl)-N-
cyclohexylcyclohexanamine (ICF) has been synthesized and spectroscopic characterization such as
FT-IR, FT-Raman, UV-Vis, NMR, mass and TG/DSC were investigated. The spectroscopic
quantum chemical calculations namely simulation of vibrational spectrum, UV-Vis, NMR have been
carried out and compared with the experimental observations. Other theoretical predictions such as
Equilibrium Geometry, chemical reactivity, molecular electrostatic potential, frontier molecular
orbital analysis and natural bond orbital analysis (NBO) have been computed and investigated using
the density functional theoretical (DFT) methods. The computed entities and experimental results the
consistently have good agreement with each other. The excited properties of ICF have been
calculated using the TDDFT calculations. The molecular docking studies used to simulate the
protein-ligand interactions have been analyzed with Schrödinger software.
Keywords: Mannich base, Density functional theory, Basis set, Mass, Natural bond orbital, Molecular
docking

3
1
. Introduction
A novel and a newly synthesized Mannich base molecule of N-((benzo[d]thiazol-2-
ylthio)methyl)-N-cyclohexylcyclohexanamine (ICF), C H N S has been synthesized by
2
0
28
2 2
employing condensation of three reactants secondary amine, formaldehyde and active hydrogen
compound. Generally, Mannich base compounds acting as a potential biological agents have been
reported earlier. They play very significant applications such as analgesic drugs [1],
vasorelaxing [2], anti-malarial [3], anti-tubercular [4] and anticancer [5]. The cyclohexylamine
(CHA) can be used in the synthesis of artificial sweeteners (sodium or calcium cyclamate), metal
corrosion inhibitors, rubber vulcanizing additives, dyestuff, plasticizers and in extracting agents for
natural products [6]. The dicyclohexylamine is used industrially in chemical formulations as anti-
corrosion agents (metal tools and spare parts). Dicyclohexylamine (DCH) is an excipient in
commercial fumagillin formulations used in veterinary medicine. Nowadays, benzothiazoles have
bicycles ring system of scientific interest for their various pharmaceutical applications which play vital
role for the preparation of fused heterocyclic systems [7]. The heterocyclic thialato ligand of 2-
mercaptobenzothiazole has potential N- and S-donors and synthesizes the complex prosperous in
biological activities [8]. Benzothiazole and its derivatives widely display remarkably different
bioactivities in the field of bioorganic and medicinal chemistry in drug discovery and in the
agrochemicals field [9–12]. They are widely used in manufacture of rubber shoes, tyres, other related
rubber articles and rubber vulcanization accelerator [13]. They are used as stabilizer and biocide
commonly act as an inhibitor of copper corrosion within re-circulating of water systems [14].
Furthermore, the benzothiazole has significant interest as a collector of floating and is used for
oxidizing the lead and copper minerals [15]. In the recent years, Lee et al. [16] analyzed the
adsorption orientation of 2-mercaptobenzoxazole (MBO) and 2-mercaptobenzothiazole (MBT) with
surface improved Raman scattering (SERS).
Author report, probably for the first time, the results based on quantum chemical calculations,
FT-IR and FT-Raman spectral studies, HOMO-LUMO and NBO analysis on ICF molecule and also,
for the first time it is reported that the synthesis procedure of ICF molecule using imide, aldehyde
and secondary amine in acetonitrile medium. The ICF molecule is a yellow powder sample which
has a melting point of 166 °C. The molecule ICF based on coarse aqueous suspension shows 7.98 pH
having very less basicity level. Therefore the present work is mainly focused to investigate the
complete vibrational spectra of the ICF molecule and to identify the different vibrational modes with
better accuracy as well as the spectral characterization of the ICF molecule by quantum chemical
method. Density functional theory (DFT) computations have been predicted to support the

4
vibrational frequencies in the FT-Raman and FT-IR spectra of the ICF molecule. Due to the diverse
potential biological activity of the ICF molecule, the molecular docking of the ICF molecule has also
been reported.
2. Experimental details
2.1. Synthesis of N-((benzo[d]thiazol-2-ylthio)methyl)-N-cyclohexylcyclohexanamine (ICF)
About 0.01 M of 2-mercaptobenzothiazole was dissolved in minimum quantity of ethanol and
added steadily to saturated aqua solution of 0.01 M dicyclohexylamine with constant stirring. In
addition to this mixture, about 0.01 M of formaldehyde was added gradually with continuous
stirring. The mixture was stirred at room temperature for 2h and the progress of the reaction has been
monitored by TLC. After 6 h, the greenish yellow colour solid product was obtained and washed
several times with ethanol and water. It was then recrystallized with acetone. About 84% of the yield
has been obtained. The melting point of the ICF molecule is 166 °C (Fig. 1).
2.2. Spectroscopy measurements
The FT-IR spectrum was carried out using the Perkin Elmer spectrophotometer with a resolution
–
1
–1
of 2 cm and the scanning region from 4000–450 cm besides having 100 numbers of scans by
analyte the KBr pellet. The FT-Raman spectrum was obtained using the Bruker RFS 27: Stand-alone
–
1
FT-Raman spectrometer by Nd:YAG laser source of wavelength 1064 nm with 1.0 cm resolution in
–
1
the span of 4000–50 cm and 100 number of scans. The NMR spectra were conducted on a Bruker
1
13
Avance spectrometer at 500 MHz for H and C NMR. The chemical shift values (δ) in the NMR
spectrum were measured in parts per million (ppm) with comparative analysis to the reference
sample as the TMS molecule. The mass spectrum was recorded using the Agilent 7890A GC system.
Vario EL III Elementar was used to carry out the CHNS analysis. The UV-Vis spectrum was given
by using Perkin Elmer Lambda 35 spectrometer between 250 to 700 nm. The TGA/DSC was
recorded in TGA-50 Shimadzu-00652 instrument at a heating rate of 10 °C/min under atmospheric
nitrogen.
2.3. Theoretical calculations
Theoretical calculations, evaluated with the Khon-Sham’s DFT method, were subjected to the
gradient-corrected hybrid density functional B3LYP method [17–19]. For the structure, the 6-
1G(d, p) basis set was used for a full geometry optimization using the published function which was
3
implemented by the Gaussian 09 package [20]. All the produced geometries were done by
GaussView 5.0.9 [21] and/or Chemcraft 1.6 software packages [22]. The vibrational modes were
assigned on the basis of PED analysis using VEDA4 program [23]. It should be noted that the
Gaussian 09W package was able to calculate the Raman activity. The Raman activities were

5
1
13
transformed into Raman intensities using Raint program [24]. The H and C NMR chemical shifts
of the ICF molecule have been obtained from the gauge-independent atomic orbital (GIAO) [25,26]
approach by subtracting the shielding constants of TMS. The UV spectra were calculated using the
TD-B3LYP-FC functional with 6-31G(d, p) basis set in methanol using TD-DFT model [27,28]. The
DOS were computed by GaussSum 3.0 software [29]. The RDG calculation were made by Multiwfn
[
30] and VMD program [31]. The NBO calculation has been performed with NBO 3.1 program [32].
.4. Raman intensities
The predicted Raman intensities (I ) were determined by Raman activities (S ) which were
2
R
i
i
calculated using the Gaussian 09 package. Raman intensities can be described by the mathematical
formula [33,34].
R
4
–1
–1
(
I ) = C(ν –ν ) ν B S
i
(1)
i
0
i
i
i
where the B is the temperature factor which interprets the intensity contribution of excited
i
vibrational states, denoted by the Boltzmann appropriation.
B = 1–(exp–hν c/KT)
(2)
i
i
2.5. Docking studies
The molecular docking study was investigated by using the diabetic proteins to find the active
binding sites and interaction properties of the amino acids with synthesized molecules. The 3D
crystal structure of protein complex (PDB format) was downloaded from Protein Data Bank
(www.rcsb.com). The protein complex and ligand were organized after pre-processing by protein
preparation wizard and ligand preparation wizard [35] in Maestro 9.3.5 version of Schrödinger
software.
2
2
.6. In vivo antidiabetic assay
.6.1. Animals and maintenance
Adult male albino Wistar rats (6 weeks), weighing 150 to 200 g were used for the present
antidiabetic study. The animals were housed in clean polypropylene cages and maintained in a well-
ventilated temperature controlled animal house with a constant 12 h light/dark schedule. The animals
were fed with standard rat pelleted diet and clean drinking water was made available ad libitum. All
the animal procedures were performed after approval from the ethical committee and in accordance
with the recommendations for the proper care and use of laboratory animals.
2.6.2. Ethical statement
Antidiabetic procedures were carried out at Department of Pharmacology, KMCH College of
Pharmacy, Coimbatore, with no anti-ethical statements.
.6.3. Induction of diabetes
2

6
The animals were divided into five groups of six animals each. The animals were kept over night
fasting and the initial fasting blood glucose was checked from the tip of rat-tail vein. Sterptozotocin
(STZ) was dissolved in citrate buffer (pH 4.5) and nicotinamide (NA) was dissolved in normal
saline. Non-insulin dependent diabetes mellitus was induced in overnight fasted rats by a single
intraperitoneal (i.p) injection of 60 mg/kg STZ and 15 min after the i.p administration 120 mg/kg of
NA was induced. After 72 h, the hyperglycemia was confirmed by the elevated levels of blood
glucose. The animals with blood glucose concentration more than 250 mg/dL were used for the study
[
36].
2.6.3.1. Study design
After the acclimation for a period of one week, they were divided randomly among five groups
consisting of six rats each. The following groups were maintained for a total period of 28 days.
Group 1 : Animals received normal pellet feed (Control)
Group 2 : Streptozotocin (STZ) (60 mg/kg bw) + nicotinamide (NA) (120 mg/kg bw)
Group 3 : STZ (60 mg/kg bw) + NA (120 mg/kg bw) rats treated with Metformin (MF)
(
10 mg/kg bw)
Group 4 : STZ (60 mg/kg bw) + NA (120 mg/kg bw) rats treated with ICF and TBF
10 mg/kg bw – low dose (L.D))
Group 5 : STZ (60 mg/kg bw) + NA (120 mg/kg bw) rats treated with ICF and TBF
20 mg/kg bw – high dose (H.D))
(
(
The vehicle (saline), standard Metformin (MF) and the test compounds were administered on the
respective group animals for 28 days. Throughout the study period, the MF and test compounds were
freshly dispersed in normal saline and distilled water before the administration. The fasting animal
st th
th
st
th
body, blood glucose level was estimated from tip of rat tail vein on 1 , 7 , 14 , 21 and 28 day.
2.6.3.2. Estimation of blood glucose
Blood samples were collected from the tip of rat-tail vein and the glucose levels were
estimated using a glucose oxidase-peroxidase reactive strips and a glucometer (Accu-Chek,
Roche Diagnostics, USA).
2.6.3.3. Determination of body weight
The body weight of each animal in every group was additionally noted during the investigation
duration.
2.7. Statistical analysis
All the tests of fasting blood glucose and body weight estimations were carried out in
triplicates. The values expressed as the Mean±SD (n=3) were analyzed with one-way analysis of

7
variance (ANOVA) and the post hoc Dunnett’s test. The difference between the groups were
considered to be significant at P<0.05.
3. Result and discussion
3.1. Molecular geometry
The computed optimized parameters like bond lengths, bond angles, and dihedral angles given
in Table 1 and compared with their related molecule data as given in literature [37,38]. The ICF
molecule contains the electronegatively sulfur groups bonded with the carbon C11 atom of
dicyclohexylamine amine moiety. The sulfur group (C–S) along with the benzothiazole moiety with
termination is considered as an electron acceptor group. The ICF molecule consisting of one C=N
bond, four C–S bonds, four C–N bonds, eighteen C–C bonds and twenty six C–H bonds is shown in
Fig. 2. The bond distance of N =C (1.297/1.285 Å) in the ICF molecule shows equivalent value for
7
8
the normal value of double C=N (1.22 Å) and lower than the single bond value C–N (1.47 Å) as
given in the literature [39]. The bond length of C –N (1.389/1.340 Å) is greater than normal value
4
7
of double C=N (1.22 Å) and lower than the single bond value C–N (1.47 Å) as given in the relevant
literature [39]. Similarly, the bond length of N –C (1.485/1.506 Å) and N –C (1.477/1.506 Å)
1
2
13
12
14
for dicyclohexylamine moiety are greater than normal value of double C=N (1.22 Å) and equivalent
value for single bond C–N (1.47 Å) as given in the relevant literature [39]. Those values have
resemblance with the 2-mercaptobenzothiazole due to the presence of resonance between –NH–C=S
and –N=C–SH (thione-thiol tautomerism) reported earlier [40,41]. The bond lengths of C –S for
5
9
benzothiazole moiety 1.758/1.718 Å, C –S (1.792/1.743 Å) and C –S (1.754/1.743 Å) are found
8
9
8
10
intermediate compared to the single bond and double bond character, due to the attachment of
neighbouring C=S group. In cyclohexyl ring, the C–C–C bond angle varies from 110.7–111.5°, so
the cyclohexyl ring act as a chair configuration. The benzothiazole ring being essentially planar
makes a bond angle around 120° with the dicyclohexylamine ring. The C–C bond length of
2
benzothiazole ring with sp character intermediate values are found between single and double bonds
due to the presence of delocalization of electron within the ring C –C , C –C , C –C , C –C , C –C ,
1
2
1
6
2
3
3
4
4
5
C –C such as 1.404, 1.394, 1.391, 1.401, 1.416 and 1.395 Å while those values are found
5
6
concurrence with theoretical data 1.347, 1.366, 1.380, 1.415, 1.410 and 1.367 Å, respectively. In
dicyclohexylamine ring, the bond length of C –C (1.544/1.519 Å), C –C (1.539/1.518 Å),
1
3
20
13
24
C –C (1.540/1.519 Å), C –C (1.546/1.518 Å), C –C (1.537/1.525 Å), C –C (1.536/1.515 Å),
14
15
14
19
15
16
16
17
C –C (1.535/1.512 Å), C –C (1.537/1.526 Å) are slightly deviated from the single bond properties
17
18
18
19
due to the attachment of electronegative group nitrogen and oxygen atom. The C–H bond length of
benzothiazole ring varies from 1.085–1.086 Å which is compared to the observed values (0.93

8
Å). In benzothiazole ring, the C–H bond distances are C –H (1.086/0.930 Å), C –H (1.086/0.930
1
25
2
26
Å), C –H (1.085/0.930 Å), C –H (1.085/0.930 Å). In dicyclohexylamine ring, the C–H bond
3
27
6
28
length varies from 1.094–1.107 Å which is compared with the observed values 0.970–0.980 Å. In
dicyclohexylamine ring, the C–H bond values are C –H (1.107/0.980 Å), C –H (1.097/0.970 Å),
13
31
15
33
C –H (1.095/0.970 Å), C –H (1.099/0.970 Å), C –H (1.099/0.970 Å), C –H (1.099/0.970 Å),
15
34
16
35
16
36
17
37
C –H (1.096/0.970 Å), C –H (1.098/0.970 Å), C –H (1.098/0.970 Å) and C –H
42
17
38
18
40
19
41
19
(1.097/0.970 Å).
3
.2. Potential energy surface (PES) scan
Due to the flexibility of N-((benzo[d]thiazol-2-ylthio)methyl)-N-cyclohexylcyclohexanamine and
possible rotational isomerism, the potential energy surface (PES) scans about C –S –C –H
8
10
11
29
(
scan coordinate–1 (SC–1)) and H –C –N –C (scan coordinate–2 (SC–2)) were performed to
30 11 12 13
confirm the theoretical approximation for the molecule. The torsion angle of C –S –C –H
29
8
10
11
and H –C –N –C are found as the relevant coordinate for the conformation flexibility within the
3
0
11
12
13
molecule. The PES calculation has been performed using PM3 semi-empirical method since the
ab-initio and the DFT methods are costly for 10° interval scan with each step optimization. During
the calculation all the geometrical parameters were simultaneously relaxed while the C –S –C –H
8
10
11
29
and H –C –N –C torsion angles were found varying in steps of 0°, 10°, 20°, 30°, … 360°.
3
0
11
12
13
For the SC–1 and SC–2 rotations, the maximum energy conformer has been appeared at 118.42 and
04.31 with 0.06964 Hartree energy on PES (Table 2). It’s clearly mentioned in Fig. 3 with steep
1
down apex red region. Around four different minimal energy conformers has been generated, namely C1,
C , C and C with 0.00007 Hartree energy difference. The conformers C , C and C , C have the
2
3
4
1
3
2
4
same energy having different stereo chemical orientations. Although, the SC–1 and SC–2 of C , C and
1
3
C , C are different, the energy is same. Interestingly, the ground state structure of ICF by DFT
2
4
method simply reproduces the structure of C conformer rather than the C conformer with different
1
3
dihedral value.
.3. Vibrational analysis
There are 52 atoms present in the ICF molecule which exhibit 150 normal modes of vibrations
3
with 52 stretching and 98 bending vibrations. The fundamental vibrational modes were calculated by
using B3LYP/6-31G(d, p) basis set and compared with the experimental vibrational spectra. The
entire spectral assignments with total energy distribution (TED) contributions are collected in Table
3. The experimental and theoretical FT-IR and FT-Raman spectra of the ICF molecule are shown in
Figs. S1 and S2 for visual comparison. The vibrational modes of the functional groups in ICF
molecule are described below:
3.3.1. C–S vibrations

9
Generally, it is difficult to identify the C–S stretching vibrational modes for various compounds
in FT-IR spectrum. The absorption of C–S vibration has variable intensity which depends on the
–
1
nature of the molecules which might be found with wide range 1035–245 cm for aliphatic as well
as aromatic [42]. The C–S group is less polar than the carbonyl group, so the peak appears in the
weaker band in FT-IR. Since, the peak shows in lower frequencies, the less intense, coupling with
other vibrational modes are not easily identified with this vibration. Xiao-Hong et al. [43] have
–
1
reported, the C–S stretching vibrational mode was observed at 716–609 cm . Similarly, the C–S
–1
stretching vibrational mode is observed at 690 cm in the FT-IR spectrum and 691, 678, 495, 384
–
1
cm in FT-Raman spectrum. The corresponding simulated values for C–S stretching vibrational
–
1
mode were observed at 692, 679, 495 and 389 cm .
3.3.2. C=N vibrations
–
1
Benzon et al. [44] have previously reported at 1463 cm for simulated and observed value at
–
1
1
463 cm in FT-IR spectrum. In ICF molecule, the C=N stretching vibrational mode was observed
–
1
–1
at 1470 cm in FT-IR and at 1469 cm in FT-Raman spectrum. The simulated value was
–
1
observed at 1470 cm with corresponding TED contribution 72%. The in-plane vibration of –C=N,
–1
–1
displayed at 630 cm in FT-IR and at 629 cm in FT-Raman was compared with the theoretical
–1
wavenumber at 631 cm with a TED of 31%. The normal vibrational modes of a title molecule were
overlapping with some bending vibration and C–C, C–S, C–H vibrations.
3.3.3. C–N vibrations
It is difficult to identify the C–N vibration due to mixing of several modes possible in this
–1
region. The C−N stretching vibrational mode was in the range from 1362–1266 cm [45]. The
–1
assignment of C–N stretching vibrations of ICF molecule were observed at 1261, 1131 cm in FT-IR and
–
1
at 1263 cm in FT-Raman spectrum. The correlated simulated spectrum was observed at 1263, 1132
–
1
cm with corresponding TED contribution of 17, 24% respectively. The in-plane vibration of –C–
–
1
–1
N, displayed at 456 cm in FT-IR and at 235 cm in FT-Raman was compared with the
–
1
theoretical wavenumber at 466, 240 cm with a TED of ~15%. The vibration is exposed towards
overlapping with some bending vibration and C–C, C–S, C–H vibrations.
3.3.4. C–C vibrations
In aromatic ring, the C=C, C–C stretching vibration modes are usually in the region 1650–1400
–
1
cm [46,47]. In the present study, the C–C stretching vibration mode of benzothiazole ring fall in the
–
1
–1
frequency region of 1588 cm in FT-IR spectrum and at 1560 cm in FT-Raman spectrum. The
–1
corresponding C–C stretching vibration mode of theoretical counterpart appeared at 1593, 1561 cm
with TED contribution 60, 67%. Similarly, the C–C stretching vibration modes of dicyclohexylamine
–
1
–1
appeared at 1311, 1123, 1060, 1034, 756 cm in FT-IR and at 1064, 1028, 986 cm in FT-Raman

1
0
spectrum. The related theoretical counterpart of C–C stretching vibration modes of dicyclohexylamine
–1
were observed at 1315, 1128, 1065, 1061, 1035, 1028, 994, 756 cm . The in-plane vibrations of C–C
–1
–1
vibration were assigned at 1048, 443 cm in FT-IR and 1042, 407 cm in FT-Raman which were
–
1
correlated value at 1050, 444, 408 cm theoretically with contribution of ~35%. The out-plane
–
1
–1
vibration of C–C vibration was observed at 874 cm in FT-Raman which are correlated at 877 cm
theoretically with contribution of 45%. The torsion vibration modes of C–C vibration appeared at
–
1
–1
9
98, 834, 582, 567 cm in FT-IR and 1000, 817, 506 cm in FT-Raman which were concurrent with
–
1
the theoretical counterparts at 1007, 840, 817, 582, 578, 514 cm with the contribution of ~60%.
3.3.5. C–H vibrations
The C–H stretching vibration of aromatic ring exhibited the multiplicity of weak to moderate
bands, when compared with the aliphatic C–H stretching vibration [48]. Klots and Collier [49]
–1
have previously reported about the vibrational modes at 3085, 3074, 3065 and 3045 cm for
–1
benzoxazole. The C–H stretching vibrations of phenyl ring are observed in the 3120–3000 cm
Roeges [50]. In current study, the C–H stretching vibrations of benzothiazole ring are observed at
–
1
–1
3
055, 2999 cm in FT-IR and at 3074, 2998 cm in FT-Raman spectrum. The corresponding C–H
stretching vibrations of benzothiazole ring for simulated spectrum appear at 3081, 3055 and 2999
–
1
cm with TED contributions of above 75%. Commonly, the coordinate investigation exhibits that
the aromatic C–H bending vibrational modes as overlapped with some stretching, in-plane and out-
of-plane vibration mode (Table 3).
3
.3.6. CH vibrations
2
–1
Generally, the C–H stretching vibrations appear in the region 2980–2900 cm in FT-IR for
–
1
aliphatic amine molecule [51]. In present study, the vibrational band appears at 2970, 2818 cm in
–
1
FT-Raman and in FT-IR at 2959, 2924, 2817 cm is due to assignment of C–H stretching vibration
for dicyclohexylamine. The related simulated wavenumber is coherent to the experimental and the
–1
reported data at 2971, 2965, 2927, 2819 cm (with greater than 75% TED) by employing the B3LYP/6-
3
1G(d, p) method. The fundamental vibrations of CH owing to twisting, rocking, wagging, and
2
–1
scissoring are observed in the range from 1500–800 cm and the bands show deviation in these
wavenumbers owing to the presence of atom in nature and substituent of molecule linked to
CH group [52]. For dicyclohexylamine, the in-plane bending vibrations are assigned at 1450, 1311,
2
–1
–1
1
241 cm in FT-IR while the related simulating frequencies are found at 1456, 1315, 1244 cm with
pure vibration mode of TED greater than 70% [53]. The most vital point is that certain CH modes
2
are generally coupled with some stretching and bending vibrations (Table 3).
3.4. NMR spectral analysis

1
1
The molecular geometry of ICF molecule is optimized by DFT method with B3LYP/6-31G(d, p)
1
13
basis level. The chemical shifts of H and C NMR have been carried out with the help of gauge
invariant atomic orbital (GIAO) calculations. The experimental and simulated chemical shifts of ICF
1
13
molecule in H and C chemical shifts values are noted in Table 4 and NMR spectra are exhibited in
1
13
Fig. 4. The values show good agreement with the computed and experimented H and C chemical
shifts.
1
3
.4.1. H NMR
1
The H NMR chemical shift value of N–CH –S appears at 3.36 ppm deshielded region (high
2
chemical shift value) indicating the presence of electronegative atom like Sulfur and Nitrogen atom.
A multiplet peak was displayed in the deshielded region of 3.11–3.10 ppm with two protons (H and
31
H ), which were assigned to the cyclohexane ring protons due to the attachment of electron withdrawing
32
group nitrogen atom. Another multiplet peak is assigned to eight equivalent aliphatic protons at 1.80–
.78 ppm (H , H , H , H , H , H , H , H ) with eight protons of cyclohexane ring. Similarly,
1
3
3
34
41
42
43
44
51
52
yet another multiplet peak was displayed at 1.90–1.88 ppm, which assigned to eight equivalent
aliphatic hydrogens (H , H , H , H , H , H , H , H ) of cyclohexane ring. The next multiplet
3
5
36
39
40
45
46
49
50
peak was assigned as four equivalent aliphatic protons of cyclohexane ring at 1.77–1.66 ppm (H ,
3
7
H , H , H ). The two set triplet peaks were presented at 7.16 (H ) and 7.27 (H ) ppm with
3
8
47
48
25
26
integral value corresponding to the two aromatic protons having the coupling constant 6.4 and 6.6
Hz. A two set of doublet peaks were shown at 7.57 (H , J = 7.1 Hz) and 7.46 (H , J = 7.2 Hz) for
2
7
28
aromatic protons in benzothiazole ring. The calculated values of proton chemical shifts were
summarized in Table 4.
1
3
3
.4.2. C NMR
Generally, the C NMR spectrum of aromatic compounds appear in the typical the region
1
3
1
3
>
100 ppm [54,55]. In the C NMR spectrum of ICF molecule, the peak at 188.3 ppm (high chemical
shift value) was assigned to the C linked with electronegative sulfur atom and nitrogen atoms.
8
Similarly, the signal at 148.3 ppm was assigned to be C connected with electron withdrawing
4
nitrogen atom. The chemical shift value of C has a higher value, which happens due to bonding with
5
the electronegative nitrogen atom, appeared deshielded region at 136.9 ppm. The three aromatic
carbons were displayed at 121.0–126.4 ppm in carbon NMR spectrum. The signal at 121.0 ppm is
assigned as C position in benzothiazole ring. Another aromatic carbon C of benzothiazole ring is
3
2
exhibited at 126.4 ppm. The signal at 123.6 ppm was assigned as C position in benzothiazole ring.
1
The C and C were displayed at 64.8 ppm in the deshielded region due to the attachment of
1
3
14
electronegative group nitrogen atom. The carbon C appears at 54.4 ppm, which had high chemical
1
1
shift value (deshielded region) due to the attachment neighbouring electron withdrawing of sulfur and

1
2
nitrogen. The chemical shifts of cyclohexane ring are observed in the range from 25.7–31.2 ppm.
The simulated and observed NMR results showed some deviations, because the computed
calculation was done in gas phase and experimental work takes place in solid.
3.5. Mass spectrum
The mass spectrum of ICF molecule was obtained on HRMS. The mass spectrum of the ICF
molecule is shown in Fig. 5a. The Fig. 4a illustrates the molecular ion peak at m/z = 399.1304
which confirms the molecular mass of the ICF molecule with K ion (C H N S ), when compared
20
28
2 2
with the calculated mass m/z = 399.1331.The peak appearing at m/z = 400.1304 corresponds to the
1
3
15
33
protonated peak (M+1), C H N S . The C, N, and S mainly contribute to the M+1 peak, of
20
29
2 2
1
3
which the C is found the most significant. If the M has the range up to 100%, the M+1
intensity/1.1% will give an approximation for the quantity of carbon atom present in the molecule.
3.6. TG/DSC analysis
The thermal characters of the solid ICF molecule were carried out by recording TG-DSC
curve in the temperature which varied from 0 to 550 °C using the NETZSCH STA 449 F3 thermal
analyzer under the nitrogen atmosphere and the heating was carried out at a rate of 20 °C/min.
Fig. 5b indicates that the thermal decomposition of ICF molecule occuring in three consecutive steps.
The initial step in TG curve illustrated the weight loss of 50.73% in the temperature range of 171.4–
2
84.0 °C due to the exclusion of the methanethiol and hydrogen molecule groups from the title
molecule, the second step showed the weight loss of 45.51% in the temperature range of 284.0–360.0
C due to the decomposition of the ethanamine molecule from the former ICF molecule, the third
°
step showed the mass loss of 99.13% in the temperature range of 360.0–516.5 °C due to the
liberation of C H N (cyclohexanamine) group and the complete decomposition of the molecule
6
13
was finished. The nature of mass loss shows that there was neither volatilization nor fragmentation. A
result of TG plot shows that the ICF molecule was stable up to 171.4 °C, when the fusion process
beginning, followed by evaporation and no phase transition occurs till the melting point of the
sample. The sample was defined as the unreality of crystallization from solvent or impurity and the
most specific thermal steadiness of ICF up to beginning of melting point. The smooth response of the
TGA curve behind its melting point represented the thermal liberation of ICF with the creation of
reaction products [56]. The last residual carbon mass at 516.5 °C indicated the last part of the
decomposition reaction is 0.87%. The second broad exothermic curve was shown at 273.1 °C and
after this step the weight loss in TGA plot occured progressively. The progress weight loss illustrated
the elimination of stable cyclohexanamine fragments [57].

1
3
The thermal decomposition temperature established as 284.0 °C in TGA graph, behind its
melting point, indicates the thermal stability of the ICF molecule. There was no mass loss around
284.0 °C which represents the state at which no crystallization of phase transmission was possible.
The DSC peak illustrates how the sample undergoes an irreversible exothermic transition where
onsets of melting point and the peaks appeared at 168.2 and 273.1 °C. The initial exothermic weak
peak appeared at 168.2 °C might be the melting point of the ICF molecule. The next exothermic peak
appeared at 273.1 °C happens due to the decomposition of ethanamine. The definition of purity was
based on the postulation that the contamination samples lower the melting point of a pure material.
The melting point of a pure, high degree (100%) crystalline material have sharpness, but the impure
sample or defects in the crystal structure will widen the melting point range and lower the melting
point [58]. The material seemed to be appropriate for transparency determination by the DSC
analysis; the material was established to be very pure (99.13%). The purity of the sample was
confirmed by the obtained DSC result, less impurity content and also showed the acceptable results
for the melting transition of the used material under various methods.
3.7. UV-Visible spectral analysis
The UV-Vis spectral analysis was carried out to explain the electronic transition within the
molecule. In this study, to find out the maximum wavelengths, energy gap, oscillator strength and
excitation energies of the ICF molecule which were obtained from B3LYP/6-31G(d, p) method. The
observed UV-Vis spectra of the ICF molecule were carried out in chloroform as a solvent and
computational calculations were used in gas and solvent phase as shown in Figs. S3 and S4. The
broad peak and the maximum intensity of the title molecule clearly show that the charge transfer of
interaction involved in the molecule. The molecular geometry calculation shows the maximum
absorption wavelength of the ICF molecule which resembles the electron excitation from the top
level of the occupied molecular orbital (HOMO) to lowest level of unoccupied orbital (LUMO).
The experimental value and computed value of UV-Visible spectral results were compared in
Table 5. The predicted maximum excitation wavelength at 282 nm (f = 0.0069) in gas phase and 292 nm
(f = 0.0047) were compared with the measured value at 326 nm (blue shift), it is represented as H-
1
→L (98%) electronic transition. The calculated and observed values show deviation and expected
tolerance limit 34 nm. The experimental values mostly depend on the solvent effect. Therefore, the
ICF molecule indicates the influence of solvent in optical activity as present in the molecule. The
HOMO-LUMO electronic transformation occurs from the highest level of occupied molecular orbital
at 97 level of molecular orbital number to lowest level of unoccupied orbital at 98 level, this occurs
due to possible electronic transition in ICF molecule. In ICF molecule under chloroform condition, it

1
4
is observed that the initial peak from the n–π* electronic excitation due to electron transfer from
dicyclohexylamine ring to benzothiazole ring. This is evidence for the n–π* electronic transition
involved in the dicyclohexylamine ring where n determines the highest filled orbital while π*
demonstrates the lowest unfilled level. The other two calculated values are 271, 261 with oscillator
strength of 0.3548, 0.0722 in gas phase and 274, 261 nm with oscillator strength 0.5154, 0.0972 in
solution phase respectively. These assignments correspond to the H-1→L (86%), H-2→L (6%), H-2→L
(2%), H→L+2 (2%) and H-2→L (53%), H-1→L+1 (36%), H-1→L (7%) electronic transition. There
is no peak of absorption in the entire visible region which evidently tells about its applicability
towards frequency doubling process. The absorption of maximum of λmax is the utility of
substitution; the more electrons pushed into the ring, shows the higher value of λmax
.8. Frontier molecular orbital analysis
The most important part of FMO was helpful in defining the chemical hardness-softness, optical
.
3
polarizability and the chemical reactivity of the particular molecule. To define the various reaction
types, the calculating reaction position in π-conjugated systems, MO and related their properties like
energy are commonly used. The molecule having low energy gap has more polarizable property,
which was associated with high chemical reactivity and low kinetic stability. These properties
facilitate the chemists and physicists to know about the main role taking place in the chemical
reaction. The energy of the HOMO is related to ionization potential and the LUMO is related to
electron affinity of the molecule. Nowadays, the energy of HOMO, LUMO and their energy gap resolve
the biological activity of the molecule from ICT [59,60].
In presence of conjugated molecules, the highest filled and lowest unfilled molecular orbital are
characterized by charge separation of HOMO-LUMO as a result of the important role of
intermolecular charge transfer (ICT) from end-capping electron of donor groups via π-conjugated
way. The strong ICT that originates on the π-conjugated bridge results as a substantial ground state
mixing of electron donor-acceptor groups, the charge transfer band appear in the absorption
spectrum. As a result of FMO, the ED transfer from aromatic part of the π-conjugated system
that act as an electron donor side to electron accepting part of MO. As a result of DFT calculations, the
total number of molecular orbital consists of 410 FMOs and 98 occupied MOs and 312 unoccupied
orbitals. The HOMO is mainly located on benzothiazole ring, dicyclohexylamine ring and the LUMO
is mainly located on the same ring except sulfur (S ), N and dicyclohexylamine ring. In experimental
10
12
work, the common formula; E = hc/λ is used to calculate the energy gap value. Here h and c are constant,
2
λ is the cut-off wavelength. By ploting the hν against (αhν) to obtain an observed energy gap at
3
.14 eV and compared with 4.41 eV (gas phase) and 4.24 eV (solvent phase) which are shown in

1
5
Table 6 and Fig. 6. The energy values of HOMO and LUMO in DOS spectrum are used to predict
the global chemical reactivity description of the ICF molecule as shown in Table 7 and Fig. 7a. The
energy values of HOMO, LUMO and the energy gap are –5.69, –0.68 and 5.01 eV in gas phase and
5.72, 0.85 and 4.87 eV in solvent phase, respectively. The higher ionization potential implies the
high reactivity of a molecule. The hardness and softness are used to explain the stability and
reactivity of a molecule. A large energy gap defined as hard molecule and low value indicates soft
molecule [61]. In ICF molecule, the value of chemical hardness is higher than the softness, so the
title molecule becomes more kinetically stable and less reactive as shown in Table 7. The
electronegativity of a molecule is used to define the electrons attraction of an atom in a covalent
bond. When two dissimilar atoms are covalently bonded, the sharing of electron will be more
strongly attracted with each other, so the electronegativity becomes greater. The electrophilicity
index was helpful to explain the lowering of energy based on the maximum number of electron
transfer from HOMO to LUMO. As shown in Table 7, the ICF molecule had higher value which
implied the strong electron excitation between HOMO and LUMO [62]. The electronic absorption
mainly was explained by the electron excitation from the HOMO to LUMO which increased the
stability of a molecule and decrease the ICT that makes the molecule as NLO active.
3.9. Total, partial and overlap population density of states
The vital role of DOS spectrum is used to describe the molecular orbital compositions and their
percentage of contribution to chemical bonding via OPDOS peaks based on the COOP diagram in
the literature. The PDOS spectrum explains the fragment orbital composition of atoms or groups
which involve in the molecular orbital. The total, partial and overlapped populations in the density of
states, defined as TDOS, PDOS and OPDOS spectrum can be got from GaussSum software by
convoluting the molecular orbital information with Gaussian curves of unit height and full width at
half maximum (FWHM) of 0.3 eV. The DOS, OPDOS and PDOS spectra are shown in Fig. 7. The
OPDOS or COOP spectrum results, by multiplying of the DOS by overlapping population, are
similar of DOS spectrum. The OPDOS spectrum displays the bonding, antibonding, non-bonding
interaction between two atoms groups, orbitals. The positive value of COOP represented as the
interaction of atoms or groups involves in bonding orbital and the negative value described as
interaction of atoms or groups involves in antibonding orbital, zero value defined as interaction of atoms
or groups involves in non-bonding orbital [63]. Both HOMO and LUMO are in FMO; they play vital role
in chemical reaction of a molecule. The HOMO-LUMO energy gap is used to determine the electron
transfer properties, so it is useful to calculate the electrical conductivity property of a title molecule
[
64]. The OPDOS is based on the Mulliken population with the help of GaussSum software. As a
result of PDOS spectrum, the ICF molecule can be fragmented into four groups which are assigned

1
6
as nitrogen, sulfur, carbon and hydrogen as shown in Fig. 6c. The highest contribution comes from
the nitrogen and sulfur and the least contributions come from carbon and hydrogen. Thus, the
HOMO orbitals (H, C, S and N) are represented as (15% + 83% + 0% + 1% = 100%) whereas
LUMO (H, C, O and N) are represented as (1% + 75% + 15% + 9% = 100%). However, the
percentage contribution of atomic or molecular orbitals in the molecule is very hard to establish the
bonding and antibonding character. So, the OPDOS diagram can be used as some of its orbitals of
energy data results of interaction among the selected groups which are obtained from figure easily to
identify the particular group of interactions as shown in Fig. 7b. In OPDOS spectrum, six groups
were selected such as H overlap with C, H overlap with S, H overlap with N, C overlap with S, C
overlap with N and S overlap with N.
3.10. Reduced density gradient (RDG) analysis
The weak interaction in real space of a molecule based on the electron density and their
derivatives is described by Johnson et al. [65]. The RDG is a dimensionless quantity coming from
the electron density with its first derivative. The weak interaction is defined as a position having
electron density with low RDG value. The density value appears on the low-gradient spikes (the plot
of RDG against ρ) which is explained as the strength of interaction of a molecule. The value of sign
λ is used to fully distinguish between bonding (λ <0) and non-bonding interaction (λ >0). The plot
2
2
2
of RDG against electron density of ρ value multiplied by the sign of λ can allow displaying the
2
several interaction types present in the molecule. The RDG results are predicted by using Multiwfn
and graphed by VMD program. The large positive value shows strong electron repulsion like steric
effect and large negative value explains the strong non-covalent interaction for hydrogen bonding.
Even either small positive or negative value describes the van der Waals interactions within a
molecule. As a result of RDG, one or more spikes are present in low-density, low-gradient place as
shown in Fig. 8a. The presence of weak interaction that implies to generated RDG isosurfaces which
cover the related position in the real molecular space are shown in Fig. 8b.
3.11. NBO analysis
The results of the NBO analysis based on the second order perturbation are summarized in
Tables S1 and S2. In the present study, the NBO analysis of ICF molecule shows six types of
transitions such as strong σ–σ*, n–σ*, n–π*, π–π*, π–σ*, π*–π*, the hyperconjugative intra-
molecular interactions produced by orbital interaction between bonding C–C, C–N, C=N, C=C, C–S
and antibondings C–S, C–C, C–N, C=N, C=C and the bonding of lone pair atoms like N, S, with C–
N, N=C, C–S and C=C antibonding orbitals contact with antibonding orbitals C=N, C=C which
provide an intra-molecular electron density delocalization and creates the stability of a system.

1
7
As seen from Table S1, the highest stabilization energy value of ICF molecule for antibonding
orbital shows antibonding (π orbital) C –C to antibonding (π orbital) C –C predicted at 180.61
4
5
2
3
kcal/mol (ED = 0.47592e) which implies the strong delocalized designate with the donor and
i
acceptor groups. The other similar transitions are antibonding (π orbital) C –C to antibonding (π
4
5
orbital) C –C and antibonding (π orbital) N –C to antibonding (π orbital) C –C and the related ED
i
2
3
7
8
4
5
values are found as 0.47592, 0.38722e and stabilization energies are 153.99, 85.23 kcal/mol,
respectively.
In lone pair, the highest stabilization energy value of ICF molecule shows LP(2)S →π*(N –
1
0
7
C ), LP(2)S →π*(N –C ), LP(2)S →π*(C –C ), LP(1)N →σ*(C –S ), LP(1)N →σ*(S –C ) and
8
9
7
8
9
4
5
7
8
9
12
10
11
the related ED values are 1.80826, 1.70798 (2 and 3 are equal value), 1.87934 1.83606e and
i
stabilization energy at 29.00, 24.67, 17.35, 17.25, 13.26 kcal/mol. In bonding (π) orbital, the highest
stabilization energy value of ICF molecule shows π(C –C )→π*(C –C ), π(C –C )→π*(C –C ),
2
3
4
5
4
5
1
6
π(C –C )→π*(C –C ) and the related ED values are 1.69909, 1.63254, 1.69909e and stabilization
2
3
1
6
i
energy at 21.03, 19.67, 19.58 kcal/mol. In bonding (σ) orbital, the highest stabilization energy value
of ICF molecule shows σ(C –N )→σ*(S –C ), and the related ED value is 1.97376e with the
4
7
8
10
i
stabilization energy at 6.24 kcal/mol. The NBO analysis is used to define the hybridization of a title
molecule as shown in Table S2. Table S2 shows the orbital type i.e., bond like (single or double) and
the occupancy number of electrons range from 0.00 to 2.000. The types of orbital get bonded with
lone pair of electron and antibonding orbital. The antibonding orbital is termed as non-Lewis
structure. The ICF molecule shows some deviation due to the presence of electronegative atom like
sulfur and nitrogen. The results of Table S2 show the bond of C –N has electron density 1.97376
4
7
2
.45
2.05
2.45
with 28.99% C character in sp
and 70.95% N character in sp hybrid. The sp hybrid on
7
4
2
.05
carbon (C ) has 28.99% of p-character and sp hybrid has 70.95% on nitrogen (N) p-character. It is
4
3
efficient to identify sp has 70% p-character as referred from given literature [66].
ICF molecule consisting of electronegative atoms sulfur and nitrogen get the higher value of
polarization coefficients and also the atom connected with electronegative atom (sulfur and
nitrogen) give low value of polarization coefficients. The percentage compositions of a title
molecule are obtained from square of the polarization coefficient value involving in the natural
bonding. From the NBO results, I have predicted the subsequent bonds such as C –N , C –S , N –C ,
4
7
5
9
7
8
N –S , C –N , C –S , S –C , C –N , N –C and N –C . The σ bond character of C –N is
7
9
7
37
8
10
10
11
11
12
12
13
12
14
4
7
2.45
2.05
composed of 0.6417C(sp ) + 0.7669N(sp ). The numbers 0.6417C + 0.7669N describe the
polarization coefficient. The higher value of polarization coefficient indicates the higher electron
density (%) of the NBO and also the increasing the electronegativity character of the atom [67]. The

1
8
2
weights are given from the squares of the polarization coefficient as (0.6417) = 0.2899,
corresponding to 28.99% localization on carbon atom. In an analogous method, the 70.95% on
nitrogen atom is obtained. The NBO method was more polarized towards nitrogen atom, indicating
the electronegative properties of nitrogen as noted in atomic charge analysis. The other bonds are
explained in Table S2 along with polarization coefficient and their hybridization. The theoretical
calculations were prepared by the available literature [68,69].
The natural hybrid orbitals with lower energies and high occupation numbers are: n (S ), n (S ),
1
10
1
9
σ(N –C ), σ(C –C ), σ(C –C ) and σ(C –C ). The corresponding energy values such as –0.24566, –
7
8
2
3
1
2
4
5
0
6
1
.65418, –0.88404, –0.68687, –0.68038, –0.69310 a.u, the considerable p-characters 31.38, 33.45,
1.99, 64.21, 64.71, 66.38%, the lower occupation numbers 1.98230, 1.98424, 1.98949, 1.97873,
.98090, 1.97422 and the higher energy values with lower occupation number are π(C –C ), π(C –C ),
4
5
2
3
π(C –C ), n (S ) and π(N –C ). The corresponding energies are –0.69310, –0.68687, –0.24434, –
1
6
1
10
7
8
0.62975, –0.32600 and considerable p-character 99.97, 99.96, 99.94, 99.92% and occupation
numbers are 1.63254, 1.69909, 1.69582, 1.80826, 1.90265. Thus, a very near to pure p-type lone pair
orbital participates in the electron donation to the n (S )→π*(C –C ), n (S )→π*(N –C ),
2
9
4
5
2
9
7
8
n (S )→π*(N –C ), π(C –C )→π*(C –C ), π(C –C )→π*(C –C ), π(C –C )→π*(C –C ), π(C –
2
10
7
8
1
6
2
3
1
6
4
5
2
3
1
6
2
C )→π*(C –C ), π(C –C )→π*(C –C ), π(C –C )→π*(C –C ), π(C –C )→π*(N –C ), π(N7–
3
4
5
4
5
1
6
4
5
2
3
4
5
7
8
C )→π*(C –C ) interactions in the molecule.
8
4
5
3.12. Mulliken population analysis
The Mulliken population atomic charges have an enormous role in the field of DFT studies
based on quantum chemical calculation through the entire molecular structure. The simulated
Mulliken charge for the ICF molecule by B3LYP compared with the compositional groups such as
N-methylbenzothiazole and N-methyldicyclohexylamine summarized in Table S3. The horizontal
bar diagram of comparative Mulliken atomic charges are shown in Fig. S5. The comparison of the
Mulliken atomic charge distribution in the ICF molecule and its individual N-methylbenzothiazole
moiety represent the Mulliken atomic charge distribution as nearly equal in the aromatic ring and the
carbon C , C , C having greater negative charge value; but the C undergoes more opposite charge for
5
8
11
5
ICF molecule than the separated N-methylbenzothiazole molecule. The Mulliken charge analysis of
S and S in ICF molecule has greater positive value than N-methylbenzothiazole molecule. This
9
10
concludes the attachment of the N-methylbenzothiazole ring in the ICF molecule. Similarly, the N-
methyldicyclohexylamine ring in the ICF molecule shows deviation of Mulliken atomic charges from
that of the individual N-methyldicyclohexylamine in the carbon atoms like C13 and C14 i.e., +I
indicative effect. This is due to attachment of N-methylbenzothiazole moiety in the ICF molecule.

1
9
The highest negative value is observed at carbon (C ) atom and this occurs due to the dislocation of
1
electron, sulfur atom. The highest positive value is observed at C carbon atom. This is influence the
4
attachment of neighbouring nitrogen atom. Almost the entire hydrogen atoms exhibit positive charge
and the maximum of carbon, sulfur, nitrogen atoms possess the negative charge. As a result of the
electronegative character atoms, I have recognized the atoms which can take place electrophilic
substitution at these centers.
3.13. Fukui function
The concept of generalized philicity [70] contains almost all the information about the known
different global and local reactivity and selectivity descriptor, in addition to the information
regarding electrophilic/nucleophilic power of a given atomic site in a molecule. Under this situation,
the reactivity descriptor ∆f(r) provides useful information on both stabilizing and destabilizing
interactions between a nucleophile and an electrophile, which helps in identifying the
electrophilic/nucleophilic behaviour of a specific site within a molecule. It provides positive value
(positive value i.e., ∆f(r)>0) for site prone for nucleophilic attack and a negative value (negative
value i.e., ∆f(r)<0) prone for electrophilic attack and these values are summarized in Table S4.
From the Fig. 9, the purple or bluish colour indicates the positive colour, i.e., the areas represent
as a function positive, while red colour indicates the negative colour, i.e., the areas represents as a
+
function negative. It can be seen from Fig. 9 that positive values of Fukui f function of the title
k
molecule are located at sulfur atom, which indicates the increase of electron density in this region, so
–
the molecule acts as a nucleophilic attack. On the other side, the negative values of Fukui fk
functions are situated at the N–CH –N, which implies that the electron density losses, so the
2
molecule acts as an electrophilic attack.
3.14. Local reactivity descriptors analysis
The local reactivity descriptors of a molecule based on the electron density are helpful to predict
the probable reactive sites of the molecule, which are a significant for designing a medicinal
+
k
–
k
0
k
+
k
–
k
0
k
compound. The softness (sf , sf , sf ) and electrophilicity indices (ωf , ωf , ωf ) were computed
for the ICF molecule using Mulliken charge analysis to determine the possible electrophilic and
nucleophilic reactive sites of atoms with in a molecule [71].
The values of local reactivity descriptors of a molecule for selected atomic reactive sites of using
Mulliken charge distribution analyses are listed in Table S5. In ICF molecule, the highest values of
+
+
the electrophilic reactivity descriptors (s , ω ) at C of benzothiazole ring moiety confirm that this
k
k
3
is the most electrophilic site. Therefore, the C is the most active site for nucleophilic attack and
3
favour the formation of new heterocyclic compounds by an attack of nucleophilic part of the dipolar
–
reagent. In the same way, the maximum values of the local nucleophilic reactivity descriptors (s ,
k

2
0
–
k
ω ) at N of cyclohexane ring moiety indicate that this is the most nucleophilic site. Therefore, this
12
site is more prone to electrophilic attack and favours the formation of Schiff base. The C position of
4
benzothiazole ring is proved to be free radical attack.
3.15. Molecular electrostatic potential
The molecular electrostatic potential (MEP) is found very useful tool to reactive sites of a
molecule related with electron density [72]. The MEP surface of the ICF molecule is mapped with
colour code range from 0.3199 to –0.3199 a.u as shown in Fig. S6. The MEP image of ICF
molecule displays two major negative potential regions around sulfur of benzothiazole (represented
by red colour) and around the sulfur atom of methylene group (yellow colour) and the most positive
potential located on nitrogen atom, cyclohexylamine ring and all hydrogen atom (blue colour). With
the result of MEP diagram, they can infer that the H atom implying presence of strong attraction and
sulfur implies the strong repulsion. The MEP mapped (vdW) surface is shown in Fig. S6b. It is used
to describe the global maxima and minima of MEP on vdW surface. The contour plot of molecular
electrostatic potential of ICF molecule has been made by the DFT method as shown in Fig. S6c. This
conforms the positive and negative potential sites of a molecule according to the electron density
surface.
3.16. Molecular docking studies
The molecular docking studies were used to resolve the binding reactive sites and the
interactions among the synthesized molecule (ligand) and the protein. The target proteins are
downloaded from the protein data bank. The ligand is prepared from the optimized molecular
structure of the ICF molecule. The strength of the drug-receptor complex was successfully made by
several features like hydrogen bond interactions, van der Waals forces, π–π stacking,
hydrophilic and hydrophobic interactions. These interactions among the ligand and protein depend
upon the nature of functional groups present in the ligand. The docking score of the ICF molecule
with diabetic proteins 1Z32 and 3G7V are –5.56 and –5.53 as presented in Table S6. In 3D and 2D
structure of docking results were clearly explained in the tested compound display of π–π stacking
interactions of benzothiazole ring in ICF molecule with TRP 59 amino acids present in the active site
of 1Z32 and 3G7V as shown in Fig. 10. The result of docking of ICF molecule shows the activity
against the diabetic as compared to the experimental results.
3.17. In vivo antidiabetic activity
Organization of Streptozotocin (STZ) + Nicotinamide (NA) in animals speedily destroy the
pancreatic β-cells, therefore, it provides approximately a decrease of discharge of insulin indicating

2
1
the type 2 diabetics [73] for insulin resistance. In our current study, it is found an increase in blood
glucose level along with diabetic animals confirmed the installation of diabetic mellitus.
3.17.1. Analysis of blood glucose level
The effect of ICF on plasma glucose was exhibited in Table S7 and Fig. 11. The STZ (60 mg/kg
bw) + NA (120 mg/kg bw) fed rats showed significant increase in the level of plasma glucose.
Treatment with ICF decreased the levels of plasma glucose. With the two tested doses of ICF at a
dose of 20 mg/kg show more significant decrease with plasma glucose level than the low dose.
3.17.2. Analysis of body weight
Table S8 and Fig. 12 show the changes in the levels of body weight in the control and
experimental groups. At the end of the experimental period, the body weight was found significantly
decreased in diabetic rats when compared to the normal rats (control), due to excessive catabolism of
protein which provides amino acids for gluconeogenesis. Insulin deficiency resulted in muscle wasting
decreases the body weight. The treatment with different doses of ICF (10 and 20 mg/kg bw)
significantly increased the body weight among treated the diabetic rats.
4. Conclusion
DFT tools may useful to calculate the feasible activity spectrum of a reasonable drug
molecule. The novel Mannich base ICF molecule was synthesized by using thiazole, aldehyde, amine
and ethanol as a solvent. The synthesized molecule was characterized using various spectral
techniques. The optimized molecular structure of the ICF molecule showed some deviation for
bond lengths (C–S, C–N) and bond angles (C–C–C, C–C–N, H–C–C) due to the presence of
benzothiazole and dicyclohexylamine moiety linked by methylene derivative (–N–CH –N–). Mulliken
2
charge in the sulfur and carbon atom might contribute positively to show the biological activity of
the ICF molecule. In UV-Vis spectrum, the λmax corresponds to electron excitation from HOMO-
LUMO with 98% contribution. The DOS spectrum and RDG diagram are also support for
intramolecular interactions with in the molecule. The gradients of H, S and C increase with the
v
increase of temperature owing to the enhancement of vibration of molecule. Almost all proposed and
the synthesized ICF molecule has good docking score as diabetic proteins 1Z32 and 3G7V. These
diabetic proteins can be confirmed as the most appropriate target protein through which the
anticipated molecules, as well as planned prepared novel molecule show their diabetic activity.
Virtual screening modelling best pharmacokinetics and ADME properties have positive potential
bioactivity score against human receptors. The metabolic site likely to undergo metabolism were also
performed. Docking results clearly shows ICF molecule (Hydrogen bonding, and Van der Waals
interaction with ligand and target protein) to be an encouraging anti-diabetic agent and it might be
referred as potential “lead molecule” for the synthesized of the novel anti-diabetic drug candidate.

2
2
Additionally, these data range predicted that title molecule has best oral bioavailability. The results
obtained from this study may be valuable, which may be helpful to strategize out the further
synthesis, in vivo testings which could lead to the appearance of novel inhibitors against diabetic
activity. This study is helpful to report antidiabetic activity of novel ICF molecule. This synthesized
ICF molecule showed better hypoglycemic activity. These results indicate that benzothiazole could
be served as potential antidiabetic agents in the similar manner as thiazole derivatives. In diabetic
activity, I have concluded that the administration of ICF dose dependently to STZ + NA induced
type 2 diabetic rats ameliorated blood glucose and improved body weight. The overall quantum
chemical spectral studies, electronic structure, various interactions and thermochemical property on
antidiabetic active of ICF molecule were to extend the application in the field of medicinal and
molecular modeling.

2
3
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