Mesomorphic properties, microwave-assisted synthesis, and antimicrobial evaluation of novel Schiff base functionalized resorcin[4]arene derivatives

Article abstract of DOI:10.1080/15421406.2020.1856615

Schiff bases of Resorcin[4]arenes were synthesized under microwave irradiation in high yield and characterized through various spectroscopic techniques. Mesomorphic behavior of synthesized materials (8a-f) were studied by polarizing optical microscope, di

Full text of DOI:10.1080/15421406.2020.1856615

Molecular Crystals and Liquid Crystals
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Mesomorphic properties, microwave-assisted
synthesis, and antimicrobial evaluation of novel
Schiff base functionalized resorcin[4]arene
derivatives
Jinal A. Gajjar, Rajesh H. Vekariya, Vinay S. Sharma, Seema N. Kher, Dhanji P.
Rajani & Hitesh M. Parekh
To cite this article: Jinal A. Gajjar, Rajesh H. Vekariya, Vinay S. Sharma, Seema N. Kher, Dhanji
P. Rajani & Hitesh M. Parekh (2021) Mesomorphic properties, microwave-assisted synthesis, and
antimicrobial evaluation of novel Schiff base functionalized resorcin[4]arene derivatives, Molecular
Crystals and Liquid Crystals, 715:1, 37-55, DOI: 10.1080/15421406.2020.1856615
To link to this article: https://doi.org/10.1080/15421406.2020.1856615
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
2021, VOL. 715, NO. 1, 37–55
https://doi.org/10.1080/15421406.2020.1856615
Mesomorphic properties, microwave-assisted synthesis, and
antimicrobial evaluation of novel Schiff base functionalized
resorcin[4]arene derivatives
Jinal A. Gajjara, Rajesh H. Vekariyaa , Vinay S. Sharmab , Seema N. Khera,
Dhanji P. Rajanic, and Hitesh M. Parekha
b
aSchool of Science, Department of Chemistry, Gujarat University, Ahmedabad, Gujarat, India; Faculty of
Basic and Applied Science, Department of Chemistry, Madhav University, Sirohi, Rajasthan, India;
cMicrocare Laboratory and TRC, Surat, Gujarat, India
KEYWORDS
ABSTRACT
Resorcin[4]arene; microwave
irradiation; resorcin[4]arene;
Schiff bases; antimicrobial;
liquid crystals
Schiff bases of Resorcin[4]arenes were synthesized under microwave
irradiation in high yield and characterized through various spectro-
scopic techniques. Mesomorphic behavior of synthesized materials
(8a-f) were studied by polarizing optical microscope, differential
scanning calorimetry (DSC), and thermal gravimetric analysis. Most of
compounds displayed isotropic phase and nematic mesophase in
enantiotropically manner. Electronic properties of the highest occu-
pied molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) of compound (8a) was simulated for the first time.
Among them, most of derivatives exhibited outstanding antibacterial
activity. Some molecules also displayed excellent antifungal potency.
Introduction
In supramolecular chemistry, studies of macrocycles like calix[4]arenes [1–3] is much
encouraging and growing branch. Resorcin[4]arene is one type of calix[4]arene and its
made from resorcinol units. Resorcin[4]arene is a flexible subclass, having eight
hydroxyl groups at their upper rim, which is the best active site for substitution to
CONTACT Hitesh M. Parekh
keya714@gmail.com
Department of Chemistry, School of Science, Gujarat University,
Ahmedabad, Gujarat, India.
ß 2020 Taylor & Francis Group, LLC

38
J. A. GAJJAR ET AL.
increasing their applications. They are broadly described as a form of their oxygen
bridged derivatives, the cavitands (it is a container shaped molecule), and the different
type of supramolecular assemblies are widely found in literature [4–9].
Resorcin[4]arene and their derivatives were synthesized by different synthetic proto-
cols utilizing different Lewis acid catalysts like concentrated HCl [10], trifluoroacetic
acid [11], TSA (Tungsten sulfuric acid) [12], MSA(molybdate sulfuric acid) [13], iodine
[14], and so on. The resorcinol react with various aldehyde gives all cis cone stereoiso-
mer [15,16], that reported by Niedel and Vogel and their boat, saddle, and chair stereo-
isomer was discovered by Hogberg [17]. In resorcin[4]arene structure, different
aldehyde groups attached in feet to give the ordering of stereoisomers of resorcin[4]ar-
ene [18].
Resorcin[4]arene are popular cyclic tetrameric host compounds for ions, sugars, and
organic molecules thus their applicability is very wide [19]. They are also used as a
starting material for different cavitands [20–24]. Resorcin[4]arenes have a broad range
of applications such as a macrocyclic receptor [25], dendrimers in biological systems
[26], nanoparticles and nano-capsules [27], supramolecular tectonics [28], optical che-
mosensors [29], host-guest complexes [30], components in liquid crystals [31], photore-
sists [32], selective membranes [33], HPLC stationary phases [34], surface reforming
agents [25], ion channel mimics [35], and metal ion extraction agents [36] and also in
host-guest chemistry with Nonlinear optical (NLO) property of material chemistry also
taken consideration [37–42].
Nowadays, liquid crystalline (LC) a state investigation has become a multidisciplinary
research area, due to its exceptional property to flow like a liquid and optical properties
as crystals are beneficial to various industrial applications [43–48]. Study on LC state is
measured with a view to understanding the effect of molecular structure on LC proper-
ties [49–51] as a significance of molecular stiffness and flexibility [52–55]. Liquid crys-
tals can be classified into lyotropic, thermotropic, and metallotropic phases. Lyotropic
and thermotropic liquid crystal state mostly seen in organic compounds, however, few
minerals are also known [56]. Liquid crystals in the nematic group are most extensively
used in the manufacture of liquid crystal displays (LCD) primarily due to their excep-
tional physical properties as well as a wide temperature range.
Calix[4]arene rigid core as liquid crystalline materials was reported and utilized first
time in 1990 [57]. Such type of materials, which are an important part of macrocycles
based liquid crystal materials were examined by some scientist [58–62]. Furthermore,
the calix[4]arene with substitution of long aliphatic side chains showed excellent liquid
crystalline behavior [63,64]. Yonetake and coworkers have prepared two liquid crystal
based on tert-butyl calix[8]arene to show smectic and nematic mesophases [65]. Yang
and associates displayed mesomorphic property with the presence of columnar type
molecular arrangement of calixarene with cholesterol derivatives [30]. Furthermore,
Yang et al. have investigated the liquid crystalline behavior of calix[4]arene-linked tri-
phenylene derivatives [66–69]. In addition, his group has reported the mesomorphic
properties of gallic-calix[4]arene derivatives with stable cone conformation [70]. Menon
and coworkers have disclosed a review on lower rim substituted calixarenes and their
various applications [71]. In addition, her group has synthesized Schiff base and
azoester derivatives of calix[4]arene and studied their liquid crystalline and dielectric

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
39
Figure 1. Some bio-active resorcin[4] arene derivatives.
properties at various temperatures [72–74]. Fang et al. have prepared calix[4]arene
hybrid dimeric cholesteryl derivative with the presence of naphthalene linker [75].
Recently, Sharma et al. developed various supramolecular liquid crystals based on cal-
ix[4]arene core and studied their optical and luminescence properties [76].
Due to their simply modifiable framework, resorcin[4]arene is a major class of supra-
molecular host that can be used in the structure to add particular functionality [77,78].
To change the property of resorcin[4]arene system, various functional groups are intro-
duced and used to replace the hydroxyl groups. Resorcin[4]arene has a capability for
molecular identification, interacted maximum guest molecules, modification, and further
manufactured in high amounts [24].
Resorcin[4]arene were used to design and synthesized biological active compounds
[79,80] and also rare host molecules for chemical and biological study [81].
Resorcin[4]arene derivatives (Figure 1) exhibited some bio-active molecules in which
Compound (a) [82] gives moderate antibacterial activity, good antiviral activity, and
antiHSV-1 (Herpes simplex virus) activity, whereas Compound (b) [83] gives good
antibacterial activity. Here, Compound (c) [84] gives excellent antioxidant activity with
low cytotoxicity and Compound (d) [85] gives moderate antimicrobial activity against
Gram-positive bacteria.

40
J. A. GAJJAR ET AL.
Scheme 1. Synthesis of Schiff bases of resorcin[4] arene derivatives (8a–f).
The green preparation of organic compounds in the field of medicinal chemistry can
be recognized as an attractive research prospect, because of energy savings, waste reduc-
tion, atom economy, avoiding the use of hazardous chemicals, and easy work-up proc-
esses are progressive benefits related with these syntheses [86,87].The expansion of
effective anti-microbial derivatives becomes one of the most important areas of antibac-
terial research today, because of their resistance to the existing antibacterial and antifun-
gal drugs [88–90]. Thus, new antimicrobial agents are urgently essential to survive
this situation.
Inspired from the above facts, we have synthesized novel Schiff bases of resorcin[4]ar-
ene derivatives and evaluate their antimicrobial activity. Here, resorcin[4]arene
(3a–f)derivatives were synthesized from the reaction of resorcinol(1) with different alde-
hydes (2a–f) in presence of acatalytic amount of conc. HCl in refluxing ethanol. After
that, we have synthesized Resorcin[4]arene methyl ester (5a–f) and their corresponding
hydrazine derivatives (6a–f) in excellent yield. These hydrazide derivatives finally
reacted with benzaldehyde to form different Schiff bases of resorcin[4]arene derivatives
(8a–f) (Scheme 1).
Result and discussion
Initially, we have synthesized resorcin[4]arene derivatives (3a–f)from the reaction of
resorcinol with a various aldehyde in presence of a catalytic amount of conc. HCl
under-refluxing ethanol for 72 h or under microwave irradiation (MWI) at 300 W for
3 h. Here, we have used only aliphatic aldehydes, which are attached at feet of resorci-
n[4]arene. Further, we have carried out the synthesis of resorcin[4]arene methyl ester
(5a–f) through the reaction of derivatives (3a–f) with methyl 2-bromoacetate in the
presence of K2CO3 in acetonitrile at 70 ꢀC for 36 h or under MWI at 300 W for 2 h. To
optimize the reaction conditions, the same reaction was carried out in the presence
of solvents like DMF and THF. However, in both cases comparatively lower yield of

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
41
Table 1. Preparation of Schiff base of hydrazine carbonyl methyl Resorcin[4] arene and their
derivatives.
Thermal heating (80 ꢀC)
Microwave irradiation (300 W)
Comp. code
R
Time (h)
Yielda(%)
Time (min)
Yielda(%)
Mp (ꢀC)
8a
8b
8c
8d
8e
8f
C2H5
C3H7
C4H9
C5H11
C6H13
C7H15
72
72
72
72
72
72
64.71
89.36
64.76
54.34
90.00
57.43
3
3
3
3
3
3
82.34
92.60
85.82
76.22
93.56
79.00
121–123
139–140
143–144
134–135
128–130
145–146
aIsolated yields.
product was obtained. After that, hydrazide derivatized resorcin[4]arenes (6a-f) were
prepared by the reaction of derivatives (5a–f) and hydrazine hydride under refluxing
ethanol for 24 h or under MWI at 300 W for 1 h. Finally, the benzaldehyde was treated
with derivatives (6a–f) in ethanol: DMF as a dual solvent media in the presence of a
catalytic amount of acetic acid at 80 ꢀC for 3 days or under MWI at 300 W for 2 h to
obtain the different Schiff base derivatives (8a–f). All the newly synthesized Schiff bases
(8a–f) were purified either by column chromatography or by recrystallization with etha-
nol. Compared to conventional heating, reaction under MWI showed higher proficiency
in terms of product yields and reaction times (Table 1).
The reaction proceeded smoothly and provided excellent yields in all cases (Table 1).
Various long carbon chain aldehydes reacted smoothly with this protocol to afford the
excellent yields of the products. The purity of the synthesized compounds was con-
firmed by TLC and elemental analysis. The structure of the final products was well
1
characterized by using spectral analysis techniques (IR, Mass, H-NMR, and 13C-NMR).
IR spectra displayed characteristic -NH stretching bands between 3200 and
3400 cmꢁ1 is corresponding to -CONH group as well as the peak between 1680 and
1
1700 cmꢁ1 also confirms the presence of amide in the structure. The H-NMR spectrum
showed a singlet nearer 4.4 to 4.7 ppm, which indicated a proton of the –O-CH2-CO-
linkage, while singlet nearer 7.6–8.2 ppm, which indicated a proton of the -CONH
group. In addition, peaks between 6.6 and 8.8 ppm were observed for respective aro-
matic protons. The 13C-NMR spectrum displayed peak nearer 170–176 ppm, which indi-
cated C ¼ O group of amide. The ESI-MS spectra of compounds (8a–f), showed
corresponding (M þ 1)þ peak.
Electronic properties
Electronic properties such as ionization potential (IP), electron affinities (EA), and coef-
ficients of HOMO and LUMO of compound (8a) are simulated at the R83LYP/3-21G
(d,p) level (Figure 2).
The negatives of HOMO and LUMO are estimated as IP and EA, respectively. The
IP and EA of compound (8a) are ꢁ0.20 and ꢁ0.08 eV. The electron transitions occur
from the ground state to the excited state due to their p ! p transition. Here, the nega-
tive value of HOMO–LUMO gap indicates that the molecule is stable. Also, the reason
for the decreasing energy of the HOMO–LUMO energy gap is the eventual charge

42
J. A. GAJJAR ET AL.
Figure 2. The HOMO–LUMO isodensity surface plots for the (8a).
transfer interaction taking place within the molecules because of the strong electron-
accepting ability of the electron acceptor group [91].
POM investigation
The liquid crystalline phase of present synthesized Schiff base based resorcin[4]arene
derivatives (8a–f) were primarily investigated by polarizing optical microscope (POM)
(Figure 3). It can be observed that the texture pattern of nematic phase in compounds
(8a–8b) on heating as well as cooling condition respectively. Compounds (8a) showed
droplets of nematic phase at 112 ꢀC which is further isotropic at 128 ꢀC. Further, a simi-
lar texture pattern is observed in the cooling phase. Compound (8 b) displayed a nem-
atic phase at 126 ꢀC on heating and 121 ꢀC on cooling condition. In addition,
compound (8c–8d) showed a similar texture pattern of the nematic phase. Compound

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
43
Figure 3. (a) Nematic phase at 50 ꢀC for compound 8e; (b) Nematic phase at 80 ꢀC for compound 8c.
Figure 4. Bargraph showing the thermal stability of compounds (8a-f) by POM.
(8e) showed nematic phase at 105 ꢀC on heating and 109 ꢀC on cooling temperature.
Similarly, Compound (8f) shows threaded type texture image of a nematic phase at
98 ꢀC on heating condition. The mesophase temperature range and phase transition
curve is given in below (Figures 4 and 5).
DSC investigation
The mesomorphic behavior of present synthesized Schiff base functionalized resorci-
n[4]arene core based derivatives 8a–8f were preliminarily studied by using differential
scanning calorimetry (DSC) (Figure 6). The transition temperatures along with enthalpy
changes obtained from the DSC scans of second heating and cooling cycles are mention
in Table 2. In DSC scans, compound 8a–8f exhibited two endothermic peaks corre-
sponding to crystal to nematic mesophase and nematic mesophase to isotropic liquid
phase on heating as well as cooling condition. From these results, it can be noted that
all the synthesized derivatives showed enantiotropical nematic mesophase. Compound
8a with ethylchain exhibited two endothermic peaks at 119.2 ꢀC and 131.6 ꢀC on heating

44
J. A. GAJJAR ET AL.
Figure 5. Phase diagram of compound (8a–f) by POM.
Figure 6. The DSC traces of compounds (a) 8a, (b) 8b, (c) 8c, and (d) 8d on first heating and cooling
(scan rate 10 ꢀC/min).

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
45
Table 2. Phase transition temperatures (ꢀC) and corresponding enthalpies (kJ/mol) of
synthesized compounds.
Phase sequence
Compound
Heating
Cooling
8a
8b
8c
8d
8e
8f
Cr 119.2 (2.3) N 131.6 (9.4) I
Cr 123.5 (1.4) N 147.3 (11.5) I
Cr120.1 (1.9) N 151.8 (8.6) I
Cr108.5 (2.1) N 143.8 (9.6) I
Cr107.3 (3.1) N 131.5 (11.6) I
Cr98.7 (4.2) N 142.6 (12.7) I
I 128.4 (11.3) N 116.3 (2.3) Cr
I 144.6 (9.4) N 124.8 (3.6) Cr
I 149.4 (6.1) N 118.8 (4.2) Cr
I 139.7 (8.4) N 105.7 (3.2) Cr
I 129.4 (6.2) N 104.6 (2.4) Cr
I 139.6 (7.3) N 96.1 (3.1) Cr
aPeak temperatures in the DSC thermograms obtained during the second heating cooling cycles at 10 ꢀC/min;
N ¼ nematic phase; I ¼ isotropic phase.
Figure 7. TGA curves of the compounds 8a–8c carried out at a rate of 10 ꢀC/min.
condition while on cooling condition, two endothermic peaks again traced at 128.4 ꢀC
and 116.3 ꢀC. Compound 8b with propylchain showed two endothermic peaks at 123.5 ꢀC
and 147.3 ꢀC on heating and at 144.6 ꢀC and 124.8 ꢀC on cooling condition respectively.
One can see that the higher value of enthalpy change in N-I phase transition is occurred
as compare to Cr-N phase transition due to disordered molecular arrangement of 3D-
shaped functionalized resorcin[4]arene central core. Compound 8cand compound 8d
showed first endothermic peaks at 120.1 ꢀC and 118.8 ꢀC on heating condition and second
endothermic peaks at 151.8 ꢀC and 149.4 ꢀC with a lower enthalpy change value to form
N-I phase transition peak noticed in DSC scans. It can be noted thatthe compounds
(8d–8f) with higher periphery alkyl chain showed higher mesophase range as compared
to compounds (8a–8c), which contain lower mesophase transition temperature. The result
obtained from DSC study is further confirmed by using POM analysis.
Thermogravimetric analysis
Thermal stability of compounds 8a–8c were studied by thermogravimetric analysis
(TGA) under nitrogen atmosphere mention in Figure 7. All the synthesized Schiff base
functionalized calix[4]resorcinarene based supramolecular derivatives were stable at least
up to ꢂ 230ꢀC and complete degradation occurs at around 320 ꢀC which showed the
good stability of these synthesized compounds, respectively. As there is no loss seen up
to temperature at around 130 ꢀC that means no water or any other solvent entrapped in
mesophase formation. All the synthesized supramolecular compounds show good

46
J. A. GAJJAR ET AL.
Table 3. In vitro antibacterial activity of compounds (8a–f).
MIC (lg/mL)
Comp. Code
E. Coli MTCC 443
P. Aeruginosa MTCC 1688
S. Aureus MTCC 96
S. Pyogenus MTCC 442
8a
8b
8c
8d
8e
8f
100
62.5
100
50
100
25
0.05
100
50
125
200
62.5
100
200
100
1
100
50
25
200
62.5
200
100
125
125
0.25
250
50
250
100
250
125
100
250
0.5
100
50
50
Gentamycine
Ampicillin
Chloramphncol
Ciprofloxacin
Norfloxacin
25
10
50
10
10
10
Figure 8. Graphical representation of antibacterial activity of compound (8a–f).
thermal stability as also confirmed by the POM temperature range as well. From the
POM study, compounds 8a–c showed mesophase temperature range for nematic to iso-
tropic phase is 16ꢀ, 17ꢀ, and 28ꢀ, respectively. Further increasing alkyl chain in func-
tionalized resorcinarene resulted in an increment of the mesophase temperature range.
Pharmacology
In vitro antibacterial activity
The newly synthesized Schiff base of resorcin[4]arene derivatives were screened for their
in vitro antibacterial activity (Table 3). The bioassay results demonstrated that Schiff
bases (8a–f) succeeded to indicate remarkably activity against the mentioned microor-
ganisms as compared to standard drugs (Figure 8). In general, most of the tested deriva-
tives showed better activity against the Gram-positive strain S. aureus as well as the
Gram-negative bacteria E. coli.
Among the Gram-positive bacterial strain, S. aureus exhibited comparatively higher
sensitivity toward the screened derivatives. In this view, the derivative (8b) was found
to be the most active and that inhibits the S. aureus bacterial growth at the lowest min-
imum inhibitory concentration (MIC) value of 62.5 mg/mL than standard drug
Ampicillin (MIC 250 mg/mL). Furthermore, compounds (8e) and (8f) showed excellent

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
47
Table 4. In vitro antifungal activity of compounds (8a–f).
MIC (lg/mL)
Compound code
C. albicans MTCC 227
A. niger MTCC 282
A. clavatus MTCC 1323
8a
8b
8c
8d
8e
8f
250
50
500
>1000
500
>1000
500
1000
100
100
500
>1000
1000
>1000
500
1000
100
100
250
100
500
250
100
500
Nystatin
Greseofulvin
activity with MIC value 125 mg/mL against S. aureus as compared to standard drug
Ampicillin. Furthermore, molecules (8d) showed excellent potency (MIC 100 mg/mL) against
S. aureus as compared to standard reference Ampicillin (MIC 250 mg/mL), but 50% less
active than Chloramphenicol (MIC 50 mg/mL), and Ciprofloxacin (MIC 50 mg/mL). With
regard to the activity against S. pyogenes, derivatives(8b) and (8e) showed good activity
(MIC 100 mg/mL), which is equally potent to the Ampicillin (MIC 100 mg/mL) but 50% less
active than Chloramphenicol (MIC 50 mg/mL) and Ciprofloxacin (MIC 50 mg/mL). Rest of
the compounds displayed moderate activity against S. pyogenus bacterial strain.
On the other hand, activity against the two tested Gram-negative strains revealed that
derivative(8f) (MIC 25 mg/mL) displayed outstanding activity against E. coli as compared
to standard drug Ampicillin (MIC 100 mg/mL). Furthermore, derivative(8d) (MIC 50 mg/
mL) and derivative(8b) (MIC 62.5 mg/mL) exhibited excellent potency against E. coli as
compared to standard drug Ampicillin. Furthermore, compounds (8a), (8c), and (8e)
were showed equipotent activity to Ampicillin (MIC 100 mg/mL) against E. coli, but 50%
less active than Chloramphenicol (MIC 50 mg/mL). Moreover, compound (8c) was
inhibits the Gram-negative P. Aeruginosa bacterial growth at the lowest minimum
inhibitory concentration (MIC) value of 62.5 mg/mL as compared to standard reference
ampicillin (MIC 100 mg/mL). Furthermore, compound (8f) was showed equipotent
activity to Ampicillin (MIC 100 mg/mL) against P. aeruginosa bacterial strain.
In vitro antifungal activity
Antifungal activity data (Table 4) displayed that among the derivatives (8a–f), com-
pound (8b) displayed excellent activity with MIC 50 lg/mL against C. albicans as com-
pared to Nystatin (MIC 100 mg/mL) and Greseofulvin (MIC 500 mg/mL). Furthermore,
compound (8d) showed excellent activity with MIC 100 lg/mL against C. albicans
equipotent to Nystatin (MIC 100 mg/mL). Moreover, compounds (8a), (8c), and (8f)
exerted good inhibitory efficiency (MIC 200 mg/mL) against the C. albicans as compared
to standard drug Greseofulvin (MIC 500 mg/mL). Moreover, compounds (8a–f), exhib-
ited moderate inhibitory activity against the A. niger and A. clavatus (Figure 9).
Experimental
Materials and methods
All chemicals of the highest purity available were purchased from commercial sources
and used as received. The progress of the reaction was monitored by thin layer

48
J. A. GAJJAR ET AL.
Figure 9. Graphical representation of antifungal activity of compound (8a–f).
chromatography (TLC) on Merck precoated silicagel 60 F254 aluminum sheets, visual-
ized by UV light.
The reactions were performed under Samsung modified microwave oven. Melting
points were measured on an Optimelt MPA 100 melting point apparatus and are uncor-
rected. FTIR spectra were taken on a Perkin-Elmer FT-IR 377 spectrometer using KBr
pellets in cmꢁ1. Microanalysis was performed on Perkin-Elmer PE 2400 CHN analyzer.
The texture images were studied on a trinocular optical polarizing microscope (POM)
equipped with a heating stage. The phase transition temperatures were measured using
Shimadzu DSC-50 at heating and cooling rates of 10 ꢀC min–1. The samples were heated
1
from room temperature to 550 ꢀC at 10 ꢀC/min. H NMR spectra were recorded on a
Bruker AV 400 MHz spectrometer using CDCl3 as a solvent, TMS as an internal refer-
ence. Mass spectra were recorded on Advion appearance CMS, USA. Ethyl acetate was
utilized as mobile phase and electron spray ionization (ESI) is used as the ion source.
Elemental analysis was performed on a CHNS elemental analyzer. Resorcin[4]arene
derivatives (3a–f) were prepared according to previously reported methodology [92].
The resorcin[4]arene methyl esters (5a–f) were prepared according to procedure
reported by Pansuriya and coworker [23].
General process for preparation of Resorcin[4]arene derivatives (3a–f)
Take ethanolic solution of resorcinol (1 mol) in RBF and add con. HCl (1.81 mol) drop-
wise with constant stirring during 15 min at 0 ꢀC. Now, add aldehyde (1 mol) (Propanal,
Butanal, Pentanal, Hexanal, Heptanal, Octanal) into the reaction mixture at same tem-
perature. After that, reaction mixture was stirred for 3 days at reflux temperature or irri-
tated under microwave oven at 300 W for 3 h. After completion of reaction, indicated
by TLC, the reaction mixture was cooled to room temperature and poured into crushed
ice-water mixture. Obtained precipitates were filtered and washed with ethanol/water
(1:1) and dried in oven at 45 ꢀC for 24 h.
General process for preparation of Resorcin[4]arene methyl ester (5a–f)
In three neck RBF take resorcin[4]arenes (1 mol) in dry acetonitrile. Anhydrous potassium
carbonate (20 mol) was added into the reaction mixture and stirred for 10 min at 70 ꢀC.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
49
After that, methyl acetyl bromide (16 mol) was added drop-wise into the reaction mixture
and heated 70 ꢀC for 2 days or irritated under microwave oven at 300 W for 2 h. After com-
pletion of reaction, indicated by TLC, solvent was removed under vacuum. The residue
extracted with MDC and water. The organic layer was separated and dried over anhydrous
magnesium sulfate (MgSO4) to remove the water molecules. Remove the solvent under vac-
uum and obtained solid was enough pure and no further purification was needed.
General process for preparation of hydrazide derivative of carbonyl methyl resor-
cin[4] arene (6a-f)
Take ethanolic solution of resorcin[4]arene methyl ester (1 mol) in RBF. Then add hydra-
zine hydrate (25mol) with constant stirring. The reaction mixture was refluxed for 24h
or irritated under microwave oven at 300 W for 1 h. After completion of reaction, indi-
cated by TLC, cool the reaction mixture at room temperature. The obtained precipitates
were filtered out and washed with Ethanol/water (1:1) and dried the product in oven.
General process for preparation of Schiff base of resorcin[4] arene (8a-f)
Take hydrazide derivative of carbonyl methyl resorcin[4]arene (1 mmol) into EtOH:
DMF (4:1) as dual solvent media in RBF, add benzaldehyde (16 mol) into the reaction
mixture followed by few drops (3–4 drops) of acetic acid. The reaction mixture was
then heated 80 ꢀC for 3 days or irritated under microwave 2 h with a fixed power of
300 W. The reaction progress was monitored by TLC. After completion of the reaction,
the mixture was added into cold water. Obtained precipitates were filtered and washed
with Ethanol/water (1:1) and dried in oven. All compounds were purified by either col-
umn chromatography or by crystallization with ethanol.
Antibacterial and antifungal activity
Mueller-Hinton broth and Sabouraud’s broth were used as nutrient medium to grow bac-
teria and fungus, respectively. Inoculum size for the test strain was adjusted to 106 col-
ony-forming unit (CFU) per milliliter by comparing the turbidity. Serial dilutions were
prepared in primary and secondary screening. The control tube containing no antibiotic
was immediately subcultured (before inoculation) by spreading a loopful evenly over a
quarter of plate of medium suitable for the growth of test organism and incubated at
37ꢀC for bacteria and 22ꢀC for fungi overnight. The MIC of the control organism was
read to check the accuracy of the drug concentrations. The lowest concentration inhibit-
ing growth of the organism was recorded as the MIC. Each test compound was diluted,
obtaining 2,000 mg/mL concentration, as a stock solution. In primary screening 1000, 500,
250, and 125 mg/mL concentrations of the test compounds were taken. The active synthe-
sized compounds found in this primary screening were further tested in a second set of
dilution against all organisms. The drugs found active in primary screening were similarly
diluted to obtain 100, 50, 62.5, 25, 12.5, and 6.25mg/mL concentrations. The highest dilu-
tion showing at least 99% inhibition is taken as MIC.
All newly synthesized Schiff base of resorcin[4]arene derivatives(8a-f)were examined
for antimicrobial activity against two gram-positive bacterial strains (Staphylococcus aureus
MTCC 96 and Streptococcus pyogenes MTCC 442), two gram-negative bacterial strains

50
J. A. GAJJAR ET AL.
(Escherichia Coli MTCC 443, Pseudomonas aeruginosa MTCC 1688) as well as three fun-
gal strains (Aspergillus clavatus MTCC 1323, Candida albicans MTCC 227 and Aspergillus
niger MTCC 282) using the agar dilution method [93]. Ampicillin, Ciprofloxacin, and
Chloramphenicol were used as standard control drugs for antibacterial activity, whereas
Nystatin and Greseofulvin were used as standard control drugs for antifungal activity.
Physical and spectral data of compounds
N0-(phenylmethylidene)-2-f[2, 8, 14, 20 – tetraethyl – 6, 10, 12, 16, 18, 22, 24 –
heptakis (f[N0-phenylmethylidene) hydrazinecarbonyl] methoxyg] pentacyclo
[19.3.1.13,7.19,13.115,19] octacosa – 1 (24), 3 (28), 4, 6, 9 (27), 10, 12, 15 (26), 16,
18, 21 (25) dodecaen-4-yl] oxyg acetohydrazide (8a)
White solid. IR (KBr) (kmax) cmꢁ1: 3443.63 (-N-H), 1696.20 (>C ¼ O), 3028.16 (Ar-
CH), 1443.27 (-CH2), 1365.95 (-CH3), 1696.90 (-C ¼ O-NH-), 3028.16 (¼C-H), 1224.19
(-C-O-C-), 1498.17 (-C ¼ C-Ar).1H NMR(400 MHz, CDCl3, d ppm): 8.25 (s, 8H, -N-H-
), 7.64-7.52(s, 8H, -N ¼ CH-), 7.35–7.19 (m, 40H, Ar-H),7.10 (s, 4H, Ar-H), 6.32–6.08
(s, 4H, Ar-H), 4.54–4.12 (s, 16H, -OCH2CO-), 3.60–3.50 (t, 4H, -Ar-CH-Ar-), 1.95–1.86
(q, 8H, -CH2), 0.78–0.76 (s, 12H, -CH3). 13C-NMR (100 MHz, DMSO, d ppm): 12.7,
26.9, 37.3, 69.3, 95.5, 125.7, 126.0, 156.3, 128.8, 129.2, 131.0, 133.71, 144.1, 156.3, 171.0.
Mass (m/z): 1883.20 [M þ 1]þ. Elemental Analysis: Calculated for C108H104N16O16
(1882.08): C 68.92%, H 5.57%, N 11.91%; Found: C 68.90%, H 5.55%, N 11.90%.
2-f[6,10, 12, 16, 18, 22, 24 – Heptakis (f[N0- (phenylmethylidene) hydrazinecarbonyl]
methoxyg) -2, 8, 14, 20 tetrapropyl-pentacyclo[19.3.1.13,7.19,13.115,19] octacosa-1
(24), 3 (28), 4, 6, 9 (27), 10, 12, 15 (26), 16, 18, 21 (25), 22 – dodecaen– 4 - ylg -
N0- phenylmethylidene acetohydrazide (8b)
White solid. IR (KBr) (kmax) cmꢁ1: 3417.27 (-N-H), 1686.18 (>C ¼ O), 2955.18 (Ar-
CH), 1499.21 (-CH2), 1383.11 (-CH3), 1596.02 (-C ¼ O-NH), 759.42 (¼C-H), 1090.92
1
(-C-O-C-), 1596.02 (-C ¼ C-Ar). H NMR (400 MHz, CDCl3, d ppm): 8.22 (s, 8H, -N-
H-), 7.69–7.63 (s, 8H, -N ¼ CH-), 7.32-7.16 (m, 40H, Ar-H),7.14 (s, 4H, Ar-H),
6.34–6.11 (s, 4H, Ar-H), 4.59–4.14 (s, 16H, -OCH2CO-), 3.65–4.49 (t, 4H, -Ar-CH-Ar-),
1.93–1.84 (q, 8H, -CH2), 1.38–1.13 (m, 8H, -CH2), 0.80–0.78 (s, 12H, -CH3).13C-NMR
(100 MHz, DMSO, d ppm): 14.4, 19.7, 34.8, 41.4, 69.3, 96.5, 125.7, 126.0, 128.8, 129.2,
131.0, 133.7, 144.1, 156.3, 171.0. Mass (m/z): 1938.7 [M]þ, 1939.77 [M þ 1]þ, 1940.7
[M þ 2]þ. Elemental Analysis: Calculated for C112H112N16O16 (1938.19): C 69.41%, H
5.82%, N 11.56%; Found: C 69.40%, H 5.80%, N 11.55%.
N0-(phenylmethylidene)-2-f[2, 8, 14, 20 – tetrabutyl – 6, 10, 12, 16, 18, 22, 24 –
heptakis (f[N0-(phenylmethylidene) hydrazinecarbonyl] methoxyg) pentacyclo
[19.3.1.13,7.19,13.115,19] octacosa – 1 (24), 3 (28), 4, 6, 9 (27), 10, 12, 15 (26), 16,
18, 21 (25), 22 – dodecaen – 4 - yl] oxyg acetohydrazide (8c)
White solid. IR (KBr) (kmax) cmꢁ1: 3060.37 (-N-H), 1697.22 (>C ¼ O), 1441.59 (-CH2-
), 1352.27(-CH3), 1628.23 (-C ¼ O-NH), 3060.37 (¼C-H), 1071.80 (-C-O-C-), 1498.40
(-C ¼ C-).1H NMR (400 MHz, CDCl3, d ppm): 8.26 (s, 8H, -N-H-), 7.70-7.62 (s, 8H,

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
51
-N ¼ CH-), 7.35–7.19 (m, 40H, Ar-H),7.12 (s, 4H, Ar-H), 6.28–6.05 (s, 4H, Ar-H),
4.64–4.14 (s, 16H, -OCH2CO-), 3.69–3.49 (t, 4H, -Ar-CH-Ar-), 2.02–1.72 (q, 8H, -CH2),
1.35–1.08 (m, 16H, -CH2), 0.85–0.80 (s, 12H, -CH3).13C-NMR (100 MHz, DMSO, d
ppm): 14.1, 23.0, 34.4, 35.1, 38.9, 69.3, 95.5, 125.7, 128.8, 129.2, 131.0, 133.7, 144.1,
156.3, 171.0. Mass (m/z): 1994.8 [M]þ, 1995.7 [M þ 1]þ. Elemental Analysis: Calculated
for C116H120N16O16 (1994.33): C 69.86%, H 6.07%, N 11.24%; Found: C 69.85%, H
6.05%, N 11.22.
N0- (phenylmethylidene) – 2 - f[2, 8, 14, 20 – tetrapentyl – 6, 10, 12, 16, 18, 22, 24 –
heptakis (f[N0-(phenylmethylidene) hydrazinecarbonyl] methoxyg) pentacyclo
[19.3.1.13,7.19,13.115,19] octacosa – 1 (24), 3 (28), 4, 6, 9 (27), 10, 12, 15 (26), 16,
18, 21 (25), 22 – dodecaen – 4 – yl] oxyg acetohydrazide (8d)
White solid. IR (KBr) (kmax) cmꢁ1: 3213.58 (-N-H), 1694.36 (>C ¼ O), 3061.28 (Ar-
CH), 3213.58 (-C ¼ O-NH-), 3061.28 (¼C-H), 1442.66 (-CH2-), 1070.86 (-C-O-C-),
1498.14 (-C ¼ C-Ar).1H NMR (400 MHz, CDCl3, d ppm): 8.20 (s, 8H, -N-H-), 7.68-7.63
(s, 8H, -N ¼ CH-), 7.51-7.19 (m, 40H, Ar-H), 7.10 (s, 4H, Ar-H), 6.23-6.09 (s, 4H, Ar-
H), 4.63-4.11 (s, 16H, -OCH2CO-), 3.67–3.51 (t, 4H, -Ar-CH-Ar-), 2.00–1.74 (q, 8H,
-CH2), 1.37–1.07 (m, 24H, -CH2), 0.84–0.78 (s, 12H, -CH3).13C-NMR (100 MHz,
DMSO, d ppm): 14.1, 22.7, 26.3, 32.1, 35.1, 39.2, 69.3, 96.5, 125.7, 126.0, 128.8, 129.2,
131.0, 133.7, 144.1, 156.3, 171.0.Mass (m/z): 2050.8 [M]þ, 2051.87 [M þ 1]þ. Elemental
Analysis: Calculated for C120H128N16O16 (2050.44): C 70.29%, H 6.29%, N 10.93%;
Found: C 70.26%, H 6.27%, N 10.92%.
N0 - (phenylmethylidene) – 2 - f[2, 8, 14, 20 – tetrahexyl – 6, 10, 12, 16, 18, 22, 24 –
heptakis (f[N0- (phenylmethylidene) hydrazinecarbonyl] methoxyg) pentacyclo
[19.3.1.13,7.19,13.115,19] octacosa – 1 (24), 3 (28), 4, 6, 9 (27), 10, 12, 15 (26), 16,
18, 21 (25), 22 – dodecaen – 4 - yl] oxyg acetohydrazide (8e)
White solid. IR (KBr) (kmax) cmꢁ1: 3211.78 (-N-H), 1693.81 (>C ¼ O), 3061.73 (Ar-
CH), 3211.78 (-C ¼ O-NH), 693.17 (¼C-H), 1444.96 (-CH2-), 1071.19 (-C-O-C-),
1497.78 (-C ¼ C-Ar).1H NMR (400 MHz, CDCl3, d ppm): 8.24 (s, 8H, -N-H-), 7.71–7.64
(s, 8H, -N ¼ CH-), 7.34–7.15 (m, 40H, Ar-H), 7.15 (s, 4H, Ar-H), 6.25–6.07 (s, 4H, Ar-
H), 4.62–4.09 (s, 16H, -OCH2CO-), 3.67–3.52 (t, 4H, -Ar-CH-Ar-), 2.05–1.77 (q, 8H,
-CH2), 1.37–1.06 (m, 16H, -CH2), 0.89–0.82 (s, 12H, -CH3).13C-NMR (100 MHz,
DMSO, d ppm): 14.1, 22.7, 26.6, 29.6, 31.8, 35.8, 39.2, 69.3, 96.5, 125.7, 126.6, 128.8,
129.2, 131.0, 133.7, 144.1, 156.3, 171.0.Mass (m/z): 2106.06 [M]þ, 2107.8 [M þ 1]þ.
Elemental Analysis: Calculated for C124H136N16O16 (2106.55): C 70.70%, H 6.51%, N
10.64%; Found: C 70.69%, H 6.50%, N 10.62%.
N0-(phenylmethylidene) – 2 - f[2, 8, 14, 20 – tetraheptyl - 6, 10, 12, 16, 18, 22,
2heptakis (f[N0 - (phenylmethylidene) hydrazinecarbonyl] methoxyg) pentacyclo
[19.3.1.13,7.19,13.115,19] octacosa – 1 (24), 3 (28), 4, 6, 9 (27), 10, 12, 15 (26), 16, 18,
21 (25), 22 – dodecaen – 4 - yl] oxyg acetohydrazide (8f)
White solid. IR (KBr) (kmax) cmꢁ1: 3403.20 (-N-H), 1693.77 (>C ¼ O), 1598.91
(-C ¼ O-NH), 758.80 (¼C-H), 1439.48 (-CH2-), 1382.01 (-CH3), 1071.29 (-C-O-C-),

52
J. A. GAJJAR ET AL.
1
1498.71 (-C ¼ C-). H NMR (400 MHz, CDCl3, d ppm): 8.22 (s, 8H, -N-H-), 7.72-7.64
(s, 8H, -N ¼ CH-), 7.34–7.18 (m, 40H, Ar-H), 7.17 (s, 4H, Ar-H), 6.24–6.03 (s, 4H, Ar-
H), 4.62–4.07 (s, 16H, -OCH2CO-), 3.69–3.51 (t, 4H, -Ar-CH-Ar-), 2.03–1.79 (q, 8H,
-CH2), 1.37–1.04 (m, 16H, -CH2), 0.88–0.80 (s, 12H, -CH3).13C-NMR (100 MHz,
DMSO, d ppm): 14.1, 22.7, 26.6, 29.3, 31.9, 35.1, 39.2, 69.3, 96.5, 125.7, 126.0, 128.8,
129.2, 131.0, 133.7, 144.1, 156.3, 171.0. Mass (m/z): 2162.9 [M]þ, 2163.9 [M þ 1]þ.
Elemental Analysis: Calculated for C128H144N16O16 (2162.61): C 71.09%, H 6.71%, N
10.36%; Found: C 71.08%, H 6.70%, N 10.35%.
Conclusion
The Schiff base of resorcin[4] arene derivatives were synthesized in excellent yield via
microwave assisted methodology. All synthesized compounds displayed nematic meso-
phase due to the presence of short alkyl spacer and flexibility in Schiff base in alkoxy tail
group. Themesogenic behavior of newly synthesized compounds were investigated by
POM and DSC study. The electronic properties of compound (8a) was simulated for the
first time. Compared to conventional heating, reaction under MWI showed higher profi-
ciency in terms of product yields and reaction times. From the bioassays it is clear that
the all Schiff base of resorcin[4]arene derivatives leads to outstanding antimicrobial
potency. In the present study, derivatives (8b), (8d), and (8f) exhibited highly potent
activity against most of the tested bacteria. In addition, derivative (8b) displayed excellent
activity with MIC 50lg/mL against C. albicans as compared to standard drug Nystatin.
Acknowledgments
The authors are thankful to the Department of Chemistry, Gujarat University, Ahmedabad, for
providing the necessary laboratory facilities. UGC-Info net and INFLIBNET Gujarat University
are acknowledged for providing the e-resource facilities, the NFDD, Rajkot for proton NMR and
carbon NMR, and the MNIT, Jaipur for mass spectrometry.
Disclosure statement
The authors declare no conflict of interest.
ORCID
Rajesh H. Vekariya
Vinay S. Sharma
Hitesh M. Parekh
http://orcid.org/0000-0002-7145-3774
http://orcid.org/0000-0002-8834-702X
http://orcid.org/0000-0002-2949-0280
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