Ionic liquid crystals derived from DL-Phenylalanine: Mesomorphism, optical behavior and evaluation of toxicological profile

Article abstract of DOI:10.1016/j.molliq.2019.111061

Methane sulfonate and p-toluene sulfonate (4-methyl benzene sulfonate) salts of esters of racemic 2-Amino-3-phenylpropanoic acid (DL-Phenylalanine) and fatty alcohols were synthesized in good yields and investigated for their liquid crystalline properties

Full text of DOI:10.1016/j.molliq.2019.111061

Accepted Manuscript
Ionic liquid crystals derived from dl-phenylalanine:
Mesomorphism, optical behavior and evaluation of toxicological
profile
Sheetal Venkatesh, Pushpa Kumari Yadav, Minal Govind
Kolambe, M.M.V. Ramana
PII:
DOI:
Article Number:
Reference:
S0167-7322(19)31479-5
https://doi.org/10.1016/j.molliq.2019.111061
111061
MOLLIQ 111061
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
13 March 2019
22 May 2019
26 May 2019
Please cite this article as: S. Venkatesh, P.K. Yadav, M.G. Kolambe, et al., Ionic liquid
crystals derived from dl-phenylalanine: Mesomorphism, optical behavior and evaluation
of toxicological profile, Journal of Molecular Liquids, https://doi.org/10.1016/
j.molliq.2019.111061
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
Ionic liquid crystals derived from DL-Phenylalanine: mesomorphism, optical
behavior and evaluation of toxicological profile
Sheetal Venkatesh,a Pushpa Kumari Yadav,a Minal Govind Kolambe,a
M. M. V. Ramanaa,*
a,*Department of Chemistry, University of Mumbai, Santacruz (East), Mumbai-400098,
India.
Corresponding author E-mail: mmvramana@yahoo.co.in
Abstract
Methane sulfonate and p-toluene sulfonate (4-methyl benzene sulfonate) salts of esters of
racemic 2-Amino-3-phenylpropanoic acid (DL-Phenylalanine) and fatty alcohols were
synthesized in good yields and investigated for their liquid crystalline properties using Polarizing
Optical Microscopy (POM) and Differential Scanning Calorimetry (DSC). Six out of seven
derivatives were found to be liquid crystalline in the first series while four out of thirteen
derivatives were found to be ionic liquid crystals in the second series. The refractive indices of
one of the ionic liquid crystals were measured at variable wavelengths and temperatures and
found to exhibit a high Abbe number and low dispersive power. For evaluation of the
toxicological profile, binding interactions of hsDNA with one of the derivatives from each series
were recorded under physiological conditions. The experimental studies by UV-Visible and
Fluorescence spectroscopy suggested a weak interaction between the ionic liquid crystal and
hsDNA and, that too, mainly through minor grooves. As the strength of binding seems to be
weak, a safe nature of the reported ionic liquid crystals could be expected.
Keywords
Ionic liquid crystals; Smectic; monotropic; refractive index; enantiotropic; DNA Binding
1. Introduction
Liquid crystals (LCs), being the fourth state of matter [1], have a unique set of properties like
anisotropy [2], optical birefringence [3] and self-organization [4]. Along with ordering, they also
1

ACCEPTED MANUSCRIPT
possess certain degree of fluidity [5]. Thus, they are a special class of self-condensed matter [6]
possessing properties of both solids and liquids [7]. They have long-range positional order in
atleast one dimension [8] along with long-range orientational order [9], without any fixed
positions for the individual molecules [8]. Liquid crystals exhibit a wide variety of phases and
they differ from one another by their physical properties and structures [5]. In recent times, this
new state of matter has become increasingly recognized, thus opening up numerous new and
exciting areas of research.
Ionic liquids (ILs) are another important class of compounds with properties of low or negligible
vapour pressure [10], hydrophobicity, wide electrochemical window [11], high ionic
conductivity, high thermal stabilities, making them good candidates as eco-friendly and green
“designer” solvents [12] for various kinds of reactions and manufacture of chemicals [10]. ILs
can be used to dissolve a wide variety of polymers, inorganic compounds as well as organic
compounds [12]. Due to their high tunabilty and exceptional properties, ionic liquids have
become important players in the fields of chemical transformations [13,14], electrochemistry,
extraction, chemical analysis, sample preparation, separation [15], purification and recovery
[16,17].
Merging of ionic liquids and liquid crystals produces a third and unique class of compounds
exhibiting properties of both called ‘Ionic liquid crystals’ (ILCs). They are formed by the
incorporation of ionic groups into moieties capable of exhibiting liquid crystalline properties or
by inclusion of mesogenic molecules into ionic compounds [18,19]. Thus, ionic liquid crystals
are composed of cationic and anionic groups, just like ionic liquids [20]. The nature of
mesogenic phases is governed by the dimensions of the molecules, molecular interactions,
molecular shape, location of the ionic parts in the molecules and microphase segregation [21].
Important applications of ionic liquid crystals include ion self-assembly [22,23], molecular
electronics [19], directed synthesis [24], anisotropic tribology [25] and sensors [26].
Literature studies revealed that as compared to the vast library of liquid crystals, there are lesser
number of ionic liquid crystals reported. Most of these are based on heterocyclic cores like
imidazolium, pyridinium, pyrrolidinium, morpholinium, amidinium and pyrimidinium [20,21].
However, their synthetic procedures involve multiple steps, use of expensive reactants, tedious
2

ACCEPTED MANUSCRIPT
purification steps and low yields. These compounds mostly being non-biodegradable undergo
bioaccumulation and therefore, are not eco-friendly.
In the present work, we report the preparation of two series of ionic liquid crystals in good yields
with the cationic part based on an α-amino acid, that is racemic 2-Amino-3-phenylpropanoic acid
(DL-Phenylalanine) esterified with fatty alcohols and the anionic part derived from methane
sulfonic acid and p-toluene sulfonic acid (4-methyl benzene sulfonic acid). Amino acids and
their derivatives are bountiful sources of nitrogens and there are only a few reports of them being
used to make up the cationic part in ionic liquid crystals, for e.g. Neidhardt, et al. have reported
some L-Tyrosine based ionic liquid crystals with structural variations on the carboxylic acid,
phenolic –OH and amino functional groups. Similarly, Echue, et. al have prepared building
blocks for ion self-assembly from phenylalanine containing chiral perylene diimides [27-30].
Also, quaternary ammonium salts are more resistant to reduction and oxidation due to which
their ILs & ILCs have much wider electrochemical windows than the corresponding imidazolium
salts [31]. Thus, amino acids have been chosen as the cations in this work. The aliphatic chain
length plays an important role in inducing mesomorphism; this is because, the amphiphilicity of
the ionic compounds needs to be high enough to achieve a proper balance between the strong
electrostatic forces of attraction and Vander Waals interactions [20]. Methane sulfonic acid and
p-toluene sulfonic acid have been chosen as the anions because research has shown that anions
with strong organic character have shown remarkable properties for thermal stabilities and
reduction of phase transition temperatures. Moreover, the reactants involved: amino acid, fatty
alcohols, methane sulfonic acid and p-toluene sulfonic acid easily available, biodegradable [32-
35] and inexpensive. The method adopted for the synthesis enjoys the advantages of one-step,
solvent-free protocol with high atom-economy, easy work-up, simple purification, high yields of
the desired products and is in conjunction with the principles of green chemistry.
2. Experimental Section
2.1 Materials and Methods
Materials obtained from commercial suppliers were used without further purification, unless
otherwise noted. All reactions were carried out in oven-dried glassware. Elemental Analysis was
3

ACCEPTED MANUSCRIPT
recorded on EuroVector EUROEA3000 Elemental Analyser. 1H-NMR (300 MHz) and 13C-NMR
(75 MHz) spectra were recorded on Bruker AVANCE spectrometer (Bruker BioSpin AG,
Fallanden, Switzerland; 300 MHz) using CDCl3 or MeOD as solvent and TMS as an internal
standard. Infrared spectra were recorded on a Perkin Elmer (Model – Frontier) spectrometer
(Waltham, MA, USA). Transition temperatures were investigated by POM using Mettler Toledo
FP90 heating stage containing temperature control unit in conjunction with a Carl Zeiss
polarising optical microscope (Carl Zeiss MicroImaging GmbH, Koenigsallee, Goettingen,
Germany). The mesophase type was assigned by visual comparison (under the microscope) with
known phase standards.The samples were prepared in thin films sandwiched between the glass
slide and cover. The phase transition temperatures and enthalpy values were measured by Mettler
Toledo Differential Scanning Calorimeter at heating and cooling rates of 1°C min-1, respectively.
The refractive indices were measured at various temperatures in the visible spectral region using
a multiple wavelength Abbe Refractometer (DSR-λ Schmidt + Haensch). UV absorption spectra
were measured on SHIMADZU UV-2450 PC spectrophotometer. Quartz cuvette with 1 cm path
length was used. The blank corresponding to the buffer was subtracted to correct the absorbance
at room temperature. The fluorescence spectra were recorded using SHIMADZU RF5301 PC
spectrofluorophotometer.
2.2 Synthetic Procedure
2.2.1 Scheme 1: Synthesis of 3a-3g
Racemic 2-Amino-3-phenylpropanoic acid [DL-Phenylalanine] (1) (1 mmol) and fatty alcohol
(2) [n = 18, 16, 14, 12, 10, 9, 8] (1.1 mmol) were taken in a round bottom flask and heated to
120°C. The reaction mixture was stirred at this temperature for about 5 min. To this reaction
mixture, methane sulphonic acid (1.2 mmol) was added dropwise over a period of 5 min. The
reaction mixture was stirred at 130-135°C till the solution became golden brown. After
completion of the reaction (as monitored by TLC), the hot golden brown solution was poured
cautiously into 50 mL of chilled diethyl ether (dry ice-acetone bath). The resultant suspension
was stirred for 2 h at room temperature and filtered to get an insoluble solid. Purification was
carried out by recrystallization from diethyl ether followed by drying in air to afford pure
4

ACCEPTED MANUSCRIPT
product (3a-3g) in good yields. The general scheme is outlined in Scheme. 1. The spectral data
for Compound 3g and the spectral images are given in Electronic Supplementary Information.
[PLEASE INSERT SCHEME 1 HERE]
Scheme 1. Reaction Scheme for synthesis of compounds 3a-3g
Racemic 1-(octadecyloxy)-1-oxo-3-phenylpropan-2-aminium methane sulfonate (3a): as a
white solid in 82% (0.421g) yield. Found: C, 65.59; H, 9.93; N, 2.62; S, 6.28. Calcd. for
C28H51NO5S (513.77): C, 65.46; H, 10.01; N, 2.73; S, 6.24. UV (MeOH, λmax): 215 nm. IR (neat)
νmax/cm-1: 3408.22 (Quat. N-H stretching), 2915.30, 2847.77, 1743.28 (unconj. ester C=O str.),
1601.55 (N-H bending), 1511.07, 1461.76 (-CH2 bending), 1335.87 (Asymm. S=O str.),
1
1211.17, 1146.36 (Symm. S=O str.), 1035.93, 778.24 (S-O str.). H (300MHz, CDCl3): δH =
8.103 (s, 3H, -CH-NH3+), 7.263-7.234 (m, 5H, Ar-H), 4.350 (t, 1H, -CH2-CH-NH3+), 4.034 (t, J
= 6.6 Hz, 2H, -CO-OCH2-), 3.230 (d, 2H, -CH2-CH-NH3+), 2.670 (s, 3H, CH3-SO-), 1.519-
1.456 (m, 2H, -OCH2-CH2-(CH2)15-CH3), 1.258 (m, 30H, -OCH2-CH2-(CH2)15-CH3), 0.879 (t, J
= 6.9 Hz, 3H, -OCH2-CH2-(CH2)15-CH3). 13C (75MHz, CDCl3): δC = 169.224 (ester –C=O),
134.308, 129.567, 128.823, 127.512, 66.466 (-CO-OCH2-), 54.179 (-CH-NH3+), 39.197 (CH3-
SO-), 36.490, 31.941, 29.729, 29.678, 29.642, 29.514, 29.375, 29.240, 28.260, 25.711, 22.701,
+
-
14.119 (-OCH2-CH2-(CH2)15-CH3); m/z calc. for C27H48NO2 [M-(CH3SO3 )]+ = 418.470, obs.
- +
mass [(M+H)-CH3SO3 ] = 419.200.
Racemic 1-(hexadecyloxy)-1-oxo-3-phenylpropan-2-aminium methane sulfonate (3b): as a
white solid in 80% (0.389g) yield. Found: C, 64.14; H, 9.83; N, 2.91; S, 6.56. Calcd. for
C26H47NO5S (485.72): C, 64.29; H, 9.75; N, 2.88; S, 6.60. UV (MeOH, λmax): 215 nm. IR (neat)
νmax/cm-1: 3403.66 (Quat. N-H stretching), 2915.58, 2848.31, 1744.71 (unconj. ester C=O str.),
1623.02 (N-H bending), 1469.69 (-CH2 bending), 1374.44 (-CH3 bending), 1334.40 (Asymm.
1
S=O str.), 1148.97 (Symm. S=O str.), 1038.11, 776.20 (S-O str.). H (300MHz, MeOD): δH=
7.404-7.275 (m, 5H, Ar-H), 4.323 (t, 7.2 Hz, 1H, -CH2-CH-NH3+), 4.175 (t, J = 6.3 Hz, 2H,
-CO-OCH2-), 3.238 (d, 6.9 Hz, 2H, -CH2-CH-NH3+), 2.726 (s, 3H, CH3-SO-), 1.629-1.543 (m,
2H,-OCH2-CH2-(CH2)13-CH3), 1.301 (m, 26H, -OCH2-CH2-(CH2)13-CH3), 0.912 (t, J = 6.9 Hz,
3H, -OCH2-CH2-(CH2)13-CH3). 13C (75MHz, MeOD): δC = 170.346 (ester –C=O), 135.504,
5

ACCEPTED MANUSCRIPT
130.500, 130.136, 128.918, 67.641 (-CO-OCH2-), 55.346 (-CH-NH3+), 39.595 (CH3-SO-),
37.677, 37.368, 33.083, 30.782, 30.692, 30.591, 30.478, 30.313, 29.446, 26.850, 23.758, 14.536
(-OCH2-CH2-(CH2)13-CH3).
Racemic 1-(tetradecyloxy)-1-oxo-3-phenylpropan-2-aminium methane sulfonate (3c): as a
white solid in 81% (0.371g) yield. Found: C, 62.82; H, 9.57; N, 3.13; S, 6.96. Calcd. for
C24H43NO5S (457.67): C, 62.98; H, 9.47; N, 3.06; S, 7.01. UV (MeOH, λmax): 215 nm. IR (neat)
νmax/cm-1: 3483.37 (Quat. N-H stretching), 2953.06, 2848.16, 2915.16, 1744.99 (unconj. ester
C=O str.), 1599.24, 1468.22 (-CH2 bending), 1373.59 (-CH3 bending), 1335.30 (Asymm. S=O
str.), 1211.85, 1148.70 (Symm. S=O str.), 1038.08, 776.16 (S-O str.). 1H (300MHz, MeOD): δH
= 7.407-7.274 (m, 5H, Ar-H), 4.324 (t, J = 6.6 Hz, 1H, -CH2-CH-NH3+), 4.180 (t, J = 6.9 Hz,
2H, -CO-OCH2-), 3.234 (d, J = 6.9 Hz, 2H, -CH2-CH-NH3+), 2.715 (s, 3H, CH3-SO-), 1.639-
1.551 (m, 2H, -OCH2-CH2-(CH2)11-CH3), 1.304 (m, 22H, -OCH2-CH2-(CH2)11-CH3), 0.914 (t, J
= 6.9 Hz, 3H, -OCH2-CH2-(CH2)11-CH3).13C (75MHz, MeOD): δC = 170.242 (ester –C=O),
135.458, 130.458, 130.143, 128.935, 67.624 (-CO-OCH2-), 55.210 (-CH-NH3+), 39.521 (CH3-
SO-), 37.616, 37.352, 33.086, 30.772, 30.696, 30.597, 30.483, 30.314, 29.464, 26.850, 23.748,
14.469 (-OCH2-CH2-(CH2)11-CH3).
Racemic 1-(dodecyloxy)-1-oxo-3-phenylpropan-2-aminium methane sulfonate (3d): as a
white solid in 82% (0.352g) yield. Found: C, 61.40; H, 9.23; N, 3.37; S, 7.42. Calcd. for
C22H39NO5S (429.25): C, 61.51; H, 9.15; N, 3.26; S, 7.46. UV (MeOH, λmax): 215 nm. IR (neat)
νmax/cm-1: 3480.59 (Quat. N-H stretching), 2953.65, 2915.45, 2848.66, 1745.35 (unconj. ester
C=O str.), 1599.39 (N-H bending), 1374.09 (-CH3 bending), 1334.48 (Asymm. S=O str.),
1
1212.13, 1149.24 (Symm. S=O str.), 1038.55, 776.96 (S-O str.). H (300MHz, MeOD): δH =
7.414-7.275 (m, 5H, Ar-H), 4.325 (t, J = 7.2 Hz, 1H, -CH2-CH-NH3+), 4.190 (t, J = 6.6 Hz, 2H,
-CO-OCH2-), 3.235 (d, J = 6.9 Hz, 2H, -CH2-CH-NH3+), 2.717 (s, 3H, CH3-SO-), 1.646-1.555
(m, 2H, -OCH2-CH2-(CH2)9-CH3), 1.309 (m, 18H, -OCH2-CH2-(CH2)9-CH3), 0.918 (t, J = 6.9
13
Hz, 3H, -OCH2-CH2-(CH2)9-CH3). C (75MHz, MeOD): δC = 170.242 (ester –C=O), 135.473,
130.467, 130.135, 128.923, 67.615 (-CO-OCH2-), 55.217 (-CH-NH3+), 39.558 (CH3-SO-),
37.615 37.373, 33.085, 30.779, 30.759, 30.698, 30.547, 30.481, 30.315, 25.464, 26.849, 23.746,
-
14.472 (-OCH2-CH2-(CH2)9-CH3). m/z calc. for C21H36NO2 [M-(CH3SO3 )]+ = 334.520, obs.
- +
mass [(M+H)-CH3SO3 ] = 335.300.
6

ACCEPTED MANUSCRIPT
Racemic 1-(decyloxy)-1-oxo-3-phenylpropan-2-aminium methane sulfonate (3e): as a white
solid in 83% (0.332g) yield. Found: C, 59.67; H, 8.89; N, 3.56; S, 7.93. Calcd. for C20H35NO5S
(401.56): C, 59.82; H, 8.79; N, 3.49; S, 7.99. UV (MeOH, λmax): 215 nm. IR (neat) νmax/cm-1:
3433.25 (Quat. N-H stretching), 2953.22, 2915.36, 1745.31 (unconj. ester C=O str.), 1599.64,
1515.58, 1211.81, 1148.59 (Symm. S=O str.), 1037.96, 776.26 (S-O str.). 1H (300MHz, MeOD):
δH = δ 7.414-7.277 (m, 5H, Ar-H), 4.327 (t, J = 6.9 Hz, 1H, -CH2-CH-NH3+), 4.188 (t, J = 6.6
Hz, 2H, -CO-OCH2-), 3.237 (d, J = 7.2 Hz, 2H, -CH2-CH-NH3+), 2.721 (s, 3H, CH3-SO-),
1.647-1.557 (m, 2H, -OCH2-CH2-(CH2)7-CH3), 1.312 (m, 14H, -OCH2-CH2-(CH2)7-CH3), 0.920
(t, J = 6.9 Hz, 3H, -OCH2-CH2-(CH2)7-CH3). 13C (75MHz, MeOD): δC = 170.253 (ester –C=O),
135.540, 130.506, 130.106, 128.876, 67.567 (-CO-OCH2-), 55.233 (-CH-NH3+), 39.658 (CH3-
SO-), 37.604, 37.313, 33.071 30.675, 30.613, 30.461, 30.326, 29.462, 26.851, 23.754, 14.509
(-OCH2-CH2-(CH2)7-CH3).
Racemic 1-(nonyloxy)-1-oxo-3-phenylpropan-2-aminium methane sulfonate (3f): as a white
solid in 82% (0.318g) yield. Found: C, 58.71; H, 8.73; N, 3.69; S, 8.21. Calcd. for C19H33NO5S
(387.53): C, 58.89; H, 8.58; N, 3.61; S, 8.27. UV (MeOH, λmax): 215 nm. IR (neat) νmax/cm-1:
3439.41 (Quat. N-H stretching), 2916.54, 2850.62, 1745.76 (unconj. ester C=O str.), 1375.11
(-CH3 bending), 1334.41 (Asymm. S=O str.), 1213.80, 1148.62 (Symm. S=O str.), 1038.85,
775.91 (S-O str.). 1H (300MHz, MeOD): δH = 7.404-7.275 (m, 5H, Ar-H), 4.325 (t, J = 6.9 Hz,
1H, -CH2-CH-NH3+), 4.173 (t, J = 6.6 Hz, 2H, -CO-OCH2-), 3.237 (d, J = 6.9 Hz, 2H, -CH2-
CH-NH3+), 2.716 (s, 3H, CH3-SO-), 1.630-1.536 (m, 2H, -OCH2-CH2-(CH2)6-CH3), 1.301 (m,
12H, -OCH2-CH2-(CH2)6-CH3), 0.917 (t, J = 6.9 Hz, 3H, -OCH2-CH2-(CH2)6-CH3).
2.2.1 Scheme 2: Synthesis of 4a-4l
Racemic 2-Amino-3-phenylpropanoic acid [DL-Phenylalanine] (1) (1 mmol) and fatty alcohol
(2) [n = 18, 16, 14, 12, 10, 9, 8, 7, 6, 5, 4, 2] (1.1 mmol) were taken in a round bottom flask and
heated to 120°C. The reaction mixture was stirred at this temperature for about 5 min. To this
reaction mixture, p-toluene sulfonic acid (4-methyl benzene sulfonic acid) (1.2 mmol) was added
in portions over a period of 5 min. The reaction mixture was stirred at 130-135°C till the solution
became golden brown. After completion of the reaction (as monitored by TLC), the hot golden
7

ACCEPTED MANUSCRIPT
brown solution was poured cautiously into 50 mL of chilled diethyl ether (dry ice-acetone bath).
The resultant suspension was stirred for 2 h at room temperature and filtered to get an insoluble
solid. Purification was carried out by recrystallization from diethyl ether followed by drying in
air to afford pure product (4a-4l) in good yields. The general scheme is outlined in Scheme 2.
The spectral data for Compounds 4e-4l and the spectral images are given in Electronic
Supplementary Information.
[PLEASE INSERT SCHEME 2 HERE]
Scheme 2. Reaction Scheme for synthesis of compounds 4a-4l
Racemic 1-(octadecyloxy)-1-oxo-3-phenylpropan-2-aminium 4-methyl benzene sulfonate
(4a): as a white solid in 83% (0.489g) yield. Found: C, 69.11; H, 9.53; N, 2.48; S, 5.39. Calcd.
for C34H55NO5S (589.87): C, 69.23; H, 9.40; N, 2.37; S, 5.44. UV (MeOH, λmax): 220 nm. IR
(neat) νmax/cm-1: 3240.30 (Quat. N-H stretching), 3065.88, 2915.57, 2848.98, 1737.10 (unconj.
ester C=O str.), 1596.77, 1508.83, 1469.71 (-CH2 bending), 1378.90, 1124.42 (Symm. S=O
str.), 1035.73, 813.17 (S-O str.). 1H (300MHz, MeOD): δH = δ 7.748 (d, J = 8.1 Hz, 2H, Ar-H),
7.393-7.231 (m, 5H, Ar-H), 7.257 (d, J = 7.8, 2H, Ar-H), 4.310 (t, J = 6.9 Hz, 1H, -CH2-CH-
NH3+), 4.153 (t, J = 6.6 Hz, 2H, -CO-OCH2-), 3.223 (d, J = 6.9 Hz, 2H, -CH2-CH-NH3+), 2.382
(s, 3H, CH3-Ar-SO-), 1.611-1.443 (m, 2H, -OCH2-CH2-(CH2)15-CH3), 1.309 (m, 30H, -OCH2-
13
CH2-(CH2)15-CH3), 0.918 (t, J = 6.6 Hz, 3H, -OCH2-CH2-(CH2)15-CH3). C (75MHz, MeOD):
δC = 170.195 (ester –C=O), 143.556, 141.705, 135.475, 130.478, 130.110, 129.861, 128.890,
127.015, 67.599 (-CO-OCH2-), 55.239 (-CH-NH3+), 37.617, 33.111, 30.823, 30.630, 30.347,
30.512, 29.472, 26.867, 23.773, 21.400 (CH3-Ar-SO-), 14.519 (-OCH2-CH2-(CH2)15-CH3). m/z
+
-
- +
calc. for C27H48NO2 [M-(CH3-Ar-SO3 )]+ = 418.470, obs. mass [(M+H)-CH3-Ar-SO3 ] =
419.300.
Racemic 1-(hexadecyloxy)-1-oxo-3-phenylpropan-2-aminium 4-methyl benzene sulfonate
(4b): as a white solid in 81% (0.455g) yield. Found: C, 68.24; H, 9.27; N, 2.55; S, 5.67. UV
(MeOH, λmax): 220 nm. Calcd. for C32H51NO5S (561.82): C, 68.41; H, 9.15; N, 2.49; S, 5.71. IR
(neat) νmax/cm-1: 3243.90 (Quat. N-H stretching), 3064.85, 2916.74, 2850.43, 1737.86 (unconj.
ester C=O str.), 1596.88, 1471.00 (-CH2 bending), 1381.48, 1218.98, 1123.96 (Symm. S=O
8

ACCEPTED MANUSCRIPT
1
str.), 1035.33, 811.82 (S-O str.). H (300MHz, MeOD): δH = 7.737 (d, J = 8.1 Hz, 2H, Ar-H),
7.383- 7.281 (m, 5H, Ar-H), 7.261 (d, J = 7.8 Hz, 2H, Ar-H), 4.314 (t, J = 7.2 Hz, 1H, -CH2-
CH-NH3+), 4.181 (t, J = 6.9 Hz, 2H, -CO-OCH2-), 3.226 (d, J = 7.2 Hz, 2H, -CH2-CH-NH3+),
2.385 (s, 3H, CH3-Ar-SO-), 1.639-1.548 (m, 2H, -OCH2-CH2-(CH2)13-CH3), 1.304 (m, 26H,
-OCH2-CH2-(CH2)13-CH3), 0.915 (t, J = 7.2 Hz, 3H, -OCH2-CH2-(CH2)13-CH3). 13C (75MHz,
MeOD): δC = 170.221 (ester –C=O), 143.534, 141.669, 135.432, 130.440, 130.137, 129.834,
128.931, 126.983, 67.618 (-CO-OCH2-), 55.201 (-CH-NH3+), 37.622, 33.092, 30.800, 30.703,
30.605, 30.493, 30.321, 29.462, 26.850, 23.756, 21.341 (CH3-Ar-SO-), 14.469 (-OCH2-CH2-
+
-
(CH2)13-CH3). m/z calc. for C25H44NO2 [M-(CH3-Ar-SO3 )]+ = 390.620, obs. mass = [(M+H)-
- +
CH3-Ar-SO3 ] = 391.200.
Racemic 1-(tetradecyloxy)-1-oxo-3-phenylpropan-2-aminium 4-methyl benzene sulfonate
(4c): as a buff-colored solid in 81% (0.432g) yield. Found: C, 67.39; H, 8.98; N, 2.69; S, 5.92.
Calcd. for C30H47NO5S (533.76): C, 67.51; H, 8.88; N, 2.62; S, 6.01. UV (MeOH, λmax): 220 nm.
IR (neat) νmax/cm-1: 3468.94 (Quat. N-H stretching), 3063.62, 2916.81, 2851.33, 1737.61
(unconj. ester C=O str.), 1597.99, 1470.95 (-CH2 bending), 1381.58, 1217.42, 1123.82 (Symm.
S=O str.), 1034.88, 812.03 (S-O str.). 1H (300MHz, MeOD): δH = 7.739 (d, J = 8.1 Hz, 2H, Ar-
H), 7.389-7.287 (m, 5H, Ar-H), 7.264 (d, J = 7.8, 2H, Ar-H), 4.317 (t, J = 6.9 Hz, 1H, -CH2-
CH-NH3+), 4.188 (t, J = 6.6 Hz, 2H, -CO-OCH2-), 3.229 (d, J = 6.3 Hz, 2H, -CH2-CH-NH3+),
2.388 (s, 3H, CH3-Ar-SO-), 1.627-1.561 (m, 2H, -OCH2-CH2-(CH2)11-CH3), 1.309 (m, 22H,
-OCH2-CH2-(CH2)11-CH3), 0.918 (t, J = 6.3 Hz, 3H, -OCH2-CH2-(CH2)11-CH3). 13C (75MHz,
MeOD): δC = 170.209 (ester –C=O), 143.516, 141.744, 135.467, 130.473, 130.116, 129.868,
128.897, 127.003, 67.598 (-CO-OCH2), 55.227 (-CH-NH3+), 37.607, 37.350, 33.101, 30.791,
30.718, 30.614, 30.501, 30.331, 29.457, 26.853, 23.766, 21.381 (CH3-Ar-SO-), 14.502 (-OCH2-
+
-
CH2-(CH2)11-CH3). m/z calc. for C23H40NO2 [M-(CH3-Ar-SO3 )]+ = 362.570, obs. mass [M-
-
- +
(CH3-Ar-SO3 )]+ = 362.200. [(M+H)-CH3-Ar-SO3 ] = 363.200.
Racemic 1-(dodecyloxy)-1-oxo-3-phenylpropan-2-aminium 4-methyl benzene sulfonate
(4d): as a white solid in 82% (0.414g) yield. Found: C, 66.38; H, 8.67; N, 2.84; S, 6.29. Calcd.
for C28H43NO5S (505.71): C, 66.50; H, 8.57; N, 2.77; S, 6.34. UV (MeOH, λmax): 220 nm. IR
(neat) νmax/cm-1: 3244.12 (Quat. N-H stretching), 2916.71, 2850.16, 1738.80 (unconj. ester C=O
9

ACCEPTED MANUSCRIPT
str.), 1509.03, 1469.73 (-CH2 bending), 1381.27 (-CH3 bending), 1218.12, 1124.53 Symm. S=O
str.), 1035.79, 1011.86, 812.67 (S-O str.). 1H (300MHz, MeOD): δH = 7.741 (d, J = 8.1 Hz, 2H,
Ar-H), 7.388-7.285 (m, 5H, Ar-H), 7.264 (d, J = 8.1 Hz, 2H, Ar-H), 4.306 (t, J = 7.5 Hz, 1H,
-CH2-CH-NH3+), 4.187 (t, J = 6.6 Hz, 2H, -CO-OCH2-), 3.225 (d, J = 6.3 Hz, 2H, -CH2-CH-
NH3+), 2.388 (s, 3H, CH3-Ar-SO-), 1.651-1.554 (m, 2H, -OCH2-CH2-(CH2)9-CH3), 1.310 (m,
18H, -OCH2-CH2-(CH2)9-CH3), 0.918 (t, J = 6.9 Hz, 3H, -OCH2-CH2-(CH2)9-CH3). 13C
(75MHz, MeOD): δC = 170.234 (ester –C=O), 143.556, 141.686, 135.431, 130.431, 130.141,
129.824, 128.936, 126.984, 126.984, 67.624 (-CO-OCH2-), 55.207 (-CH-NH3+), 37.636 (CH3-
Ar-SO-), 33.084, 30.778, 30.758, 30.696, 30.596, 30.480, 30.310, 29.459, 26.843, 23.742,
21.327 (CH3-Ar-SO-), 14.449 (-OCH2-CH2-(CH2)9-CH3).
3. Results & Discussion
3.1 Chemistry
Two series of compounds were synthesized: 3a-3g with the methane sulfonate anion and 4a-4l
with the p-toluene sulfonate anion and different alkyl chain lengths were synthesized by a neat,
one-step process by esterification of DL-Phenylalanine with fatty alcohols and their
simultaneous salt formation using methane sulfonic acid and p-toluene sulfonic acid respectively
resulted in good yields. The acids enabled the esterification of the amino acid with the fatty
alcohols and also salt formation, by quaternization of the amino group of the amino acid.
Evaluation of liquid crystalline properties was carried out by a combination of Differential
Scanning Calorimetry (DSC) and hot-stage thermo-optical polarized microscopy (POM)
analysis.
3.2 Physical characterization
1
In order to substantiate the formation of the final compounds 3a-3g & 4a-4l, FT-IR, H-NMR
and 13C-NMR were recorded for all the compounds while DEPT-135, 2D-COSY and 2D-HMQC
(Heteronuclear Multiple-Quantum Correlation) were recorded for the compound 3d from the
10

ACCEPTED MANUSCRIPT
first series and 4b from the second series. The related figures, tables and relevant explanation for
the same are given in the Electronic Supplementary Information document.
3.3 Thermal & Mesophase behaviour
The thermal and phase behaviour of the derivatives was studied by POM, DSC and TG.
According to information from DSC and POM compounds 3a-3f from the first series and 4a-4d
from the second series were able to form mesophases and are therefore, thermotropic ionic liquid
crystals, while compound 3g from the first series and compounds 4e-4l from the second series
did not exhibit liquid crystalline properties.
3.3.1 Thermal properties
The liquid crystalline property was confirmed using Differential Scanning Calorimetry (DSC)
analysis. DSC thermograms were recorded at a scan rate of 1°C/min for the compounds.
Compound 3a from the first series with an octadecyl side chain, obtained as a white solid at
room temperature, changed from a crystalline solid state to a mesophase finally passing to a
molten liquid state without further thermal transitions during the heating cycle, while during the
cooling cycle, transitions were observed from an isotropic liquid to a mesophase and finally to a
crystalline solid. Compound 3b with the hexadecyl chain, showed two endothermic peaks during
heating, representing transitions from a crystalline solid to mesophase at 77.28 °C and
mesophase to an isotropic liquid at 92.63°C. Similarly, two exothermic peaks were observed for
compound 3b indicating transitions from isotropic liquid to a mesophase at 73.11°C and finally
to a crystalline solid at 66.83°C.
For compound 4a from the second series with the octadecyl chain showed two endothermic
peaks representing solid-mesophase at 68.34°C with an enthalpy of 15.02 kJ/mol and mesophase
to isotropic liquid transition at 76.82°C with an enthalpy of 7.56 kJ/mol. The reason behind high
enthalpy values could be that strongly polar liquid crystals tend to exhibit larger enthalpy values
[36] broadening of peaks. A very broad exothermic peak was observed during the cooling cycle,
at 53.47°C, starting from 56.46°C and complete crystallization occurring at 49.66°C. Compound
4b displayed two endothermic peaks at 60.87°C and 81.43°C and a broad exothermic peak at
64.90°C. Compound 4c showed only two endothermic peaks at 55.49°Cand 84.98°C and no
11

ACCEPTED MANUSCRIPT
peaks during cooling. Compound 4d showed two endothermic peaks at 79.53°C and 89.67°C
with enthalpies of 8.20 kJ/mol and 17.82 kJ/mol respectively during the heating cycle and three
exothermic peaks at 73.59°C, 71.17°C and 62.15°C with enthalpies of 2.56 kJ/mol, 1.11 kJ/mol
and 3.33 kJ/mol during the cooling cycle. Compound 4e showed single and comparatively
narrow peaks during heating and cooling, indicating no tendency to form liquid crystalline states.
It is clearly indicative that in comparison with the strong electrostatic interactions between the
ionic head groups, the Vander Waals forces between the non-polar decyl chains could not
satisfactorily create a balance necessary to induce formation of a liquid crystalline phase.
The DSC thermograms of selected compounds are shown in Fig. 1 & Fig. 2.
[PLEASE INSERT FIG. 1 HERE]
Fig. 1. (a)-(b) DSC thermograms of compounds 3a & 3b recorded at a scan rate of 1°C/min
during heating and cooling
[PLEASE INSERT FIG. 2 HERE]
Fig. 2. (a)-(c) DSC thermograms of compounds 4a, 4d & 4e recorded at a scan rate of 1°C/min
during heating and cooling
3.3.2 Mesophase investigation with POM
The temperature ranges and existence / absence of the aforementioned liquid crystalline phases
for compounds 3a-3f and 4a-4l were evaluated using Polarizing Optical Microscopy (POM).
POM images were recorded at a scan rate of 1°C/min. Identification of mesophases have been
carried out by the comparison of the POM textures exhibited by the compounds (during heating
and cooling cycles) with the reported [37,38] textures. All the compounds 3a-3e and 4a-4d
displayed Smectic A phases during cooling. Selected POM images for compounds 3a-3f during
heating and cooling are as shown in Fig. 3 (a)-(c) and Fig. 4 (a)-(f) while Fig. 5 (a)-(c) and Fig.
6(a)-(d) display some selected POM images for compounds 4a-4d. Compounds 3g and 4e-4l
exhibited no phase transitions during the heating as well as cooling cycles confirming them to be
non-liquid crystalline.
12

ACCEPTED MANUSCRIPT
[PLEASE INSERT FIG. 3 HERE]
Fig. 3. (a) Thermal optical micrograph of the SmA texture displayed by compound 3b at
75.90°C during heating (b) Thermal optical micrograph of the SmA texture displayed by
compound 3f at 84.50°C during heating
[PLEASE INSERT FIG. 4 HERE]
Fig. 4. (a) Thermal optical micrograph of the SmA fan shaped texture displayed by compound
3a at 95.30°C during cooling (b) Thermal optical micrograph of the SmA batonnets displayed
bycompound 3b at 73.10°C during cooling (c) Thermal optical micrograph of the SmA fan
shaped texture displayed by compound 3c at 83.5°C during cooling (d) Thermal optical
micrograph of the SmA texture displayed by compound 3d at 75.70°C during cooling (e)
Thermal optical micrograph of the SmA batonnets displayed by compound 3e at 50.40°C during
cooling (f) Thermal optical micrograph of the SmA texture displayed by compound 3f at
74.40°C during cooling
From the results of both POM and DSC analysis, compounds 3a, 3b & 3f can be concluded to be
enantiotropic ionic liquid crystals while compounds 3c, 3d & 3e are monotropic ionic liquid
crystals. Compound 3g was found to be non-mesomorphic.
[PLEASE INSERT FIG. 5 HERE]
Fig. 5. (a) Thermal optical micrograph of the SmA texture displayed by compound 4b at
62.10°C during heating (b) Thermal optical micrograph of the SmA texture displayed by
compound 4c-4d at 81.2°C during heating
[PLEASE INSERT FIG. 6 HERE]
Fig. 6. (a) Thermal optical micrograph of the SmA fan shaped texture displayed by compound
4a at 51.60°C during cooling (b) Thermal optical micrograph of the SmA fan shaped texture
displayed by compound 4b at 45.70°C during cooling (c) Thermal optical micrograph of the
13

ACCEPTED MANUSCRIPT
SmA batonnets displayed by compound 4c at 44.3°C during cooling (d) Thermal optical
micrograph of the SmA batonnets displayed by compound 4d at 71.90°C during cooling
From the results of both POM and DSC analysis, compounds 4a-4d can be concluded to be
enantiotropic ionic liquid crystals. Compounds 4e-4l were found to be non-mesomorphic.
No clear trend is observed on changing the alkyl chain lengths. The melting points and
mesophase ranges vary in no particular order as the R group is changed. The packing of the alkyl
chains could be responsible for this behaviour. In case of the first series with methane sulfonate
as the anion, we observed enantiotropic behaviour for 3a, 3b & 3f and monotropic behaviour for
3c, 3d & 3e, while 3g was found to be non-mesomorphic as we changed the alkyl chain length
from octadecyl to octyl. When the anion was changed from methane sulfonate to p-toluene
sulfonate in the second series, enantiotropic behaviour was observed for 4a-4d, while 4e-4l were
found to be non-mesomorphic for alkyl chains-octadecyl to ethyl.
3.3.3 Thermogravimetric analysis
Compound 3a-3b and 4a-4b were analyzed for their thermal stabilities by subjecting them to TG
/ DTA analysis. The scan rate was 10°C / min. Fig. 7 (a)-(b) shows the TG / DTA spectra of
compounds 3a & 3b while Fig. 7 (c)-(d) represents the TG / DTA spectra of compounds 4a &
4b. From Fig. 7 (a)-(d), it can be seen that the compounds showed almost no loss in weight
between 50°C to 110°C. Since this temperature range corresponds to the melting point range of
the compounds, it can safely be concluded that they are not undergoing decomposition during
heating and thermally stable upto a temperature of 250°C.The compounds exhibited good
stabilities, with their decomposition temperatures ranging from 250°C to 400°C.
[PLEASE INSERT FIG. 7 HERE]
Fig.7. (a) TG / DTA of Compound 3a at a scan rate of 10°C / min (b) TG / DTA of Compound
3b at a scan rate of 10°C / min (c) TG / DTA of Compound 4a at a scan rate of 10°C / min (d)
TG / DTA of Compound 4b at a scan rate of 10°C / min
14

ACCEPTED MANUSCRIPT
3.3.4. Study of Refractive Indices
A liquid crystalline compound is uniaxial and anisotropic [2]; as a result, the polarized light
encounters different refractive indices. This is due to the different polarizations of the incident
light. It is possible to measure the refractive indices of a LC compound at discrete wavelengths,
but difficult to measure them continuously in the entire visible spectrum region. The refractive
indices change as the operating temperature changes [39]. The refractive indices of the liquid
crystalline compounds are mostly measured as a function of the operating temperatures and
wavelength of the incident light and are influenced by the phase transition temperatures of the
LC molecules. They increase or decrease accordingly due to the occurrence of reorientation of
the LC molecules [40,41]. These temperature and wavelength dependent refractive indices are
absolutely essential in photonic applications like high-temperature gradient LCs, high thermal
tunable LC photonic crystal fibres and thermally induced photonic band-gap tuning. Most of the
liquid crystal light modulators utilize the electric-field-induced refractive index change to
modulate light. Hence, the two most important parameters affecting the LC refractive indices are
wavelength and temperature, apart from molecular constituents [39,41].
The refractive indices were measured in the visible region using a multiple wavelength Abbe
Refractometer (DSR-λ Schmidt + Haensch) for the wavelengths: 404.7, 435.8, 486.1, 546.1,
587.6, 589.3, 632.8, 656.3 and 706.5 nm. The refractive indices were recorded by varying the
temperature from 20°C to 80° C at an interval of 5°C.
The plots of Refractive Indices v/s Wavelength and Refractive Index v/s Temperature for
compounds 4a are displayed in Fig. 8 (a)-(b). This refractometer gives the average of both
parallel and perpendicular refractive indices and hence, the refractive indices values are average
of the two (Eq. 1).
(
)
< 푛 >= 풏풆 + ퟐ풏풐 /ퟑ………….(Eq. 1)
[PLEASE INSERT FIG. 8 HERE]
Fig. 8. (a) Plot of Refractive Indices v/s Temperature at different wavelengths for compound 4a
(b) Plot of Refractive Indices v/s Wavelength at 75°C for compound 4a
15

ACCEPTED MANUSCRIPT
From Fig. 8 (a)-(b), it is clear that the refractive indices decrease with an increase in the
temperature and wavelength. For Compound 4a, in the temperature ranges of 45-65°C & 70-
80°C which correspond to the ranges in which the liquid crystalline properties were observed, a
decline in the refractive indices can be observed, which further confirms the existence of these
intermediate liquid crystalline phases. It can be noted that the refractive indices increase towards
the blue region of the visible spectra.
A term called ‘Abbe number’ was calculated for better characterization of this behaviour. The
equation to calculate Abbe number is given below (Eq. 2):
푛
퐷
Abbe number = 푛 −−푛1 ………(Eq. 2)
퐹
퐶
where 푛퐷, 푛퐹 and 푛퐶 are R.I at 587.6 nm, 486.1 nm and 656.3 nm respectively.
Abbe number is a measure of a material’s dispersion, with high values of Abbe number
indicating low dispersion [42]. Abbe number is a measure of the degree to which light is
dispersed or separated when passing through a lens. Abbe numbers are helpful in classifying
glass and other optical materials in terms of chromicity. A material with high Abbe number
produces less chromatic aberration than the one with a lower Abbe number [40]. Higher the
values, better will be the peripheral optics. Abbe numbers are taken into account while designing
achromatic lenses.
The reciprocal of Abbe number corresponds to the Dispersive Power [40]. Dispersion is a
measure of how much, the colors that make up a white light, are spread out.
The Abbe number and Dispersive Power of compound 4a are calculated and tabulated in Table
1.
Table 1
Optical parameters calculated from the refractive indices data
[PLEASE INSERT TABLE 1 HERE]
From Table 1, it can be noted that the Abbe number of compound 4a is quite high and that the
dispersive power is quite low, which could be beneficial when it comes to its applications in
optics and lens design, electrically tunable lenses, tunable lasers, etc. It could also be used in
16

ACCEPTED MANUSCRIPT
preparing extra low dispersion glasses. LC lenses in turn have many applications such as
holographic projection systems, ophthalmic lenses for myopia, pico-projection systems, imaging
systems of portable devices, etc [43].
4. DNA Binding Studies
Most of the carcinogenic agents bind with DNA in an irreversible manner, causing mutation of
the genome. Hence, it is important to evaluate the nature of binding as well as the mode of
binding of new molecules to predict their toxicity [44]. Since the synthesized derivatives 3a-3f
from the first series and 4a-4d from the second series are confirmed to be liquid crystalline and
quite likely to be used on a commercial scale for different applications, it is important to
investigate their safety aspects. For this, we have carried out DNA binding studies. There have
been quite a few reports of toxicity evaluation of ionic liquids [45,46]; however, to the best of
our knowledge, DNA binding studies have hardly been performed and reported for ionic liquid
crystals, which prompted us to carry out the same for our synthesized ILCs. The toxicological
profiles were determined by recording the interactions of compounds 3b from the first series and
compound 4a from the second series with hsDNA, using techniques like UV-Visible and
Fluorescence spectroscopy, under physiological conditions. From literature studies, it is clear
that macromolecules generally bind to the major groove of DNA while smaller molecules bind to
the minor groove of DNA.
The detailed study, preparation of stock solutions, related figures, tables and relevant explanation
for the same are given in the Electronic Supplementary Information document.
5. Conclusion
Two series- methane sulfonate and p-toluene sulfonate salts of esters of DL-Phenylalanine have
been successfully synthesised using readily available, biodegradable and inexpensive raw
materials in good yields. The synthesized derivatives were analyzed for their phase morphology
17

ACCEPTED MANUSCRIPT
and optical behaviour. Six derivatives from the first series and four from the second series were
found to be liquid crystalline. The refractive indices of one the derivatives show a decrease with
an increase in wavelength and temperatures. A decline in the R.I. values in temperature ranges of
45-65°C & 70-80°C, further confirms the presence of these intermediate mesophases. A high
Abbe number and low dispersive power were obtained making them promising candidates in
potential applications such as LC lenses, optics, electrically tunable laser sources, extra-low
dispersion glasses, projection systems, etc. Finally, DNA binding studies revealed a weak
interaction between the compounds and hsDNA by formation of an unstable complex occurring
through minor grooves, mainly via electrostatic interactions. From the results, a safe and non-
toxic nature of the compounds can be predicted.
Acknowledgement
The authors thank the Department of Chemistry, University of Mumbai for financial support and
facilities. Sheetal Venkatesh, Pushpa Kumari Yadav and Minal Govind Kolambe also thank
UGC, New Delhi for Ph. D Research Fellowship.
References
[1] F. D. Saeva, Liquid crystals: the fourth state of matter, J. Chem. Educ. 58 (3) (1981)
A118.
[2] S. Soni, D, Dharniya, Liquid Crystals And Applications Of Choletsteric Liquid Crystal
In
Laser,
Int.
J.
Mod.
Phys.
22
(2013)
736–740.
https://doi.org/10.1142/S2010194513010957.
[3] G. Pelzl, A. Hauser, Birefringence and phase transitions in liquid crystals, Phase
Transitions, 37 (1991) 33-62. https://doi.org/10.1080/01411599108203447.
[4] L. Schmidt-Mende, A. Fechtenkotter, K. Mullen, E. Moons, R. H. Friend, J. D.
MacKenzie, Self-organized Discotic Liquid Crystals for High-Efficiency Organic
18

ACCEPTED MANUSCRIPT
Photovoltaics,
Science,
293(5532)
(2001)
1119-1122.
https://doi.org/10.1126/science.293.5532.1119.
[5] J. An, Hina, Y. Yang, M. Xue, Y. Liu, Characterization of Liquid Crystals: A Literature
Review, Rev. Adv. Mater. Sci. 44 (2016) 398-406.
[6] M. M. Prasad, M. L. N. Mohan, P. V. Chalapathi, A. V. N. A. Kumar, D. M. Potukuchi,
Influence of spacer and flexible chain on polymorphism in complementary hydrogen
bonded liquid crystal dimers, SA:nOBAs, J. Mol. Liq., 207 (2015) 294-308.
https://doi.org/10.1016/j.molliq.2015.03.025.
[7] S. Chandrasekhar, Liquid Crystals; Cambridge University Press, Cambridge, 1992.
[8] C. Tschierske, Development of Structural Complexity by Liquid-Crystal Self-assembly,
Angew. Chem., Int. Ed. 52 (2013) 8828−8878. https://doi.org/10.1002/anie.201300872.
[9] G. R. Luckhurst, Oriental Order in Liquid Crystals: Experiment and Theory, Ber.
Bunsenges. Phys. Chem. 97 (1993) 1169- 1187.
[10] N. D. Khupse, A. Kumar, Ionic liquids: New materials with wide applications, Ind. J.
Chem. 49A (2010) 635-648.
[11] V. V. Singh, A. K. Nigam, A. Batra, M. Boopathi, B. Singh, R. Vijayaraghavan,
Applications of Ionic liquids in Electrochemical Sensors and Biosensors, Int. J.
Electrochem.
Article
ID
165683
(2012)
19
pages.
http://dx.doi.org/10.1155/2012/165683.
[12] J. Hulsbosch, E. D. De Vos, L. Binnemans, R. Aameloot, Biobased Ionic liquids:
Solvents for a Green Processing Industry? ACS Sus. Chem. Eng. 4(6) (2016)
2917−2931. https://doi.org/10.1021.acssuschemeng.6b00553.
[13] H. Olivier-Bourbigou, L. Magna, D. Morvan, Ionic Liquids and Catalysis: Recent
Progress from Knowledge to Applications, Appl. Catal. A373 (2010) 1−56.
http://dx.doi.org/10.1016/j.apcata.2009.10.008.
[14] P. Dominguez de María, “Nonsolvent” Applications of Ionic liquids in
Biotransformations and Organocatalysis, Angew. Chem. 47(37) (2008) 6960−6968.
https://doi.org/10.1002anie.200703305.
[15] P. Sun, D. W. Armstrong, Ionic Liquid in Analytical Chemistry, Anal. Chim. Acta, 661
(2010) 1−16. https://doi.org/10.1016/j.aca.2009.12.007.
19

ACCEPTED MANUSCRIPT
[16] O. Kuzmina, J. Hallett, Application, Purification, and Recovery of Ionic Liquids, 1st
Ed., Elsevier, Oxford, 2016.
[17] N. L. Mai, K. Ahn, Y. M. Koo, Methods for recovery of ionic liquids-A review, Process
Biochem. 49 (2014) 872− 881. https://doi.org/10.1016/j.procbio.2014.01.016.
[18] C. M. Paleos, Thermotropic Liquid Crystals Derived from Amphiphilic Mesogens, Mol.
Cryst. Liq. Cryst. 243 (1994) 159-183. https://doi.org/ 10.1080/10587259408037768.
[19] P. J. Kouwer, A. A. Fernandez, Key Developments in Ionic liquid crystals, Int. J. Mol.
Sci.17 (2016) 731. https://doi.org/10.3390/ijms17050731.
[20] K. Binnemans, K. Goossens, K. Lava, C. W. Bielawski, Ionic liquid crystals: Versatile
Materials, Chem. Rev. 116 (2016) 4643−4807. https://doi.org/10.1021/cr400334b.
[21] K. Binnemans, Ionic liquid crystals, Chem. Rev. 105 (2005) 4148−4204.
https://doi.org/10.1021/cr0400919.
[22] C. F. J. Faul, Ionic Self-assembly for Functional Hierarchical Nanostructured Materials,
Acc. Chem. Res. 47(12) (2014) 3428–3438. https://doi.org/10.1021/ar500162a.
[23] M. Santella, F. Amini, K. B. Andreasen, D. S. Aswad, H. Ausar, L. M. Austin, I. Bora,
I. M. I. Boye, N. K. Brinkenfeldt, M. F. Boe, Template-Guided Ionic Self-Assembled
Molecular Materials And Thin Films With Nanoscopic Order, Chem. Nano. Mat.1
(2015) 253–258. https://doi.org/10.1002/cnma.201500064.
[24] T. D. Do, A. R. Schmitzer, Intramolecular Diels Alder reactions in highly organized
imidazolium salt-based ionic liquid crystals, RSC Adv. 5 (2015) 635–639.
https://doi.org.10.1039/C4RA11693C.
[25] T. Amann, C. Dold, A. Kailer, Rheological characterization of ionic liquids and ionic
liquid crystals with promising tribological performance, Soft Matter, 8 (2012) 9840–
9846. https://doi.org/10.1039/C2SM26030A.
[26] S. J. Woltman, G. D. Jay, G. P. Crawford, Liquid-crystal materials find new order in
biomedical applications, Nat. Mater. 6(12) (2007) 929–938. https://doi.org/
10.1038/nmat2010.
[27] K. V. Axenov, S. Laschat, Thermotropic ionic liquid crystals, Materials 4 (2011) 206-
259. https://doi.org/0.3390/ma4010206.
20

ACCEPTED MANUSCRIPT
[28] G. Echue, G. Llyod-Jones, C. F. J. Faul, Chiral Perylene Diimides: Building Blocks for
Ionic
Self-Assembly,
Chem.
Eur.
J.
21
(2015)
5118-5128.
https://doi.org/10.1002/chem.201406094
[29] M. M. Neidhardt, W. Wolfrum, S. Breadsworth, T. Wohrle, W. Frey, A. Baro, C.
Stubenrauch, F. Giesselmann, S. Laschat, Tyrosine-Based Ionic Liquid Crystals:
Switching
from
a
Smectic
A,
Chem.
Eur.
J.
22
(2016)
1-
12.https://doi.org/10.1002/chem.201602937.
[30] M. M. Neidhardt, K. Schmitt, A. Baro, C. Schneider, U. Bilitewski, S. Laschat, Self-
assembly and biological activities of ionic liquid crystals derived from aromatic amino
acids, Phys. Chem. Chem. Phys. 20 (2018) 20371. https://doi.org/10.1039/C8CP03404D.
[31] Z. Wie; X. Wei, X. Wang; Z. Wang, J. Liua, ionic liquid crystals of quaternary
ammonium salts with a 2-hydroxypropoxy insertion group, J. Mater. Chem. 21 (2011)
6875-6882. https://doi.org/10.1039/C1JM10236B.
[32] B. Chen, J. Fang, J. Wu, W. Huang, J. Wang, N. Zhang, The Influence of Amino Acids
on Biodegradability, Oxidation Stability, and Corrosiveness of Lubricating Oil, J. Pet.
Sci. Technol. 31 (2013) 185–191. https://doi.org/10.1080/10916466.2010.525578.
[33] UK/ICCA"SIDS Initial Assessment Profile", OECD Existing Chemicals Database,
2006.
[34] P. Kulkarni, Methane Sulphonic Acid is Green Catalyst in Organic Synthesis, Orient. J.
Chem. 31(1) (2015) 447-451. http://dx.doi.org/10.13005/ojc/310154.
[35] B. Stoffler, G. Luft, Oxidative biodegradation of p-toluenesulfonic acid using hydrogen
peroxide, Chemosphere, 38(5) (1999) 1035-1047. https://doi.org/10.1016/S0045-
6535(98)00357-9.
[36] S. Kumar, Liquid Crystals: Experimental Study of Physical Properties and Phase
Transitions, Cambridge University Press, UK, 2001.
[37] M. Yang, K. Stappert A. Mudring, Bis-cationic ionic liquid crystals, J. Mater. Chem. 2
(2014) 458.
[38] D. Demus, L. Richter, Textures of Liquid Crystals, VEB Deutscher Verlag Chemie,
1978.
[39] J. Li, Refractive Indices of Liquid Crystals And Their Applications In Display And
Photonic Devices, Electronic Theses and Dissertations, (2005) 4460.
21

ACCEPTED MANUSCRIPT
[40] P. J. Jessy, S. Radha, N. Patel, Morphological, optical and dielectric behavior of chiral
nematic liquid crystal mixture: Study on effect of different amount of chirality, J. Mol.
Liq. 255 (2018) 215–223. https://doi.org/10.1016/j.molliq.2018.01.160.
[41] P. J. Jessy, S. Radha, N. Patel, Highly improved dielectric behaviour of ferronematic
nanocomposite for display application, Liq. Cryst. (2018)
https://doi.org/10.1080/02678292.2018.1528642.
[42] Y. Suzuki, T. Higashihara, S. Ando, M. Ueda, Synthesis and Characterization of High
Refractive Index and High Abbe’s Number Poly(thioether sulfone)s based on Tricyclo
[5.2.1.02,6]decane
https://doi.org/10.1021/ma300379w.
[43] Y. Lin, H. Chen, M. Chen, Electrically Tunable Liquid Crystal Lenses and
Applications, Mol. Cryst. Liq. Cryst. 596(1) (2014)12–21.
https://dx.doi.org/10.1080/15421406.2014.918243.
moiety,
Macromol.
45(8)
(2012)
3402−3408.
[44] A. Haque, I. Khan, I. H. Syed, M. S. Khan, Interaction studies of cholinium-based ionic
liquids with calf thymus DNA: Spectrophotometric and computational methods, J. Mol.
Liq. 237 (2017) 201-207. https://doi.org/10.1016/j.molliq.2017.04.068.
[45] A. Pabbathi, A. Samanta, Spectroscopic and Molecular Docking Study of the
Interaction of DNA with a Morpholinium Ionic Liquid, J. Phys. Chem. DOI:
10.1021/acs.jpcb.5b02939.
[46] D. Chandra, Effect of Ionic Liquids on DNA-Ligands Interaction: studied by
Fluorescence, Asian J. Sci. Tech. 6(12) (2015) 2100-2103.
22

ACCEPTED MANUSCRIPT
Figure Captions
Fig. 1. (a)-(b) DSC thermograms of compounds 3a & 3b recorded at a scan rate of 1°C/min
during heating and cooling
Fig. 2. (a)-(c) DSC thermograms of compounds 4a, 4d & 4e recorded at a scan rate of 1°C / min
during heating and cooling
Fig. 3. (a) Thermal optical micrograph of the SmA texture displayed by compound 3b at
75.90°C during heating (b) Thermal optical micrograph of the SmA texture displayed by
compound 3f at 84.50°C during heating
Fig. 4. (a) Thermal optical micrograph of the SmA fan shaped texture displayed by compound
3a at 95.30°C during cooling (b) Thermal optical micrograph of the SmA batonnets displayed by
compound 3b at 73.10°C during cooling (c) Thermal optical micrograph of the SmA fan shaped
texture displayed by compound 3c at 83.5°C during cooling (d) Thermal optical micrograph of
the SmA texture displayed by compound 3d at 75.70°C during cooling (e) Thermal optical
micrograph of the SmA batonnets displayed by compound 3e at 50.40°C during cooling (f)
Thermal optical micrograph of the SmA texture displayed by compound 3f at 74.40°C during
cooling
Fig. 5. (a) Thermal optical micrograph of the SmA texture displayed by compound 4b at
62.10°C during heating (b) Thermal optical micrograph of the SmA texture displayed by
compound 4c at 81.2°C during heating
Fig. 6. (a) Thermal optical micrograph of the SmA fan shaped texture displayed by compound
4a at 51.60°C during cooling (b) Thermal optical micrograph of the SmA fan shaped texture
displayed by compound 4b at 45.70°C during cooling (c) Thermal optical micrograph of the
SmA batonnets displayed by compound 4c at 44.3°C during cooling (d) Thermal optical
micrograph of the SmA batonnets displayed by compound 4d at 71.90°C during cooling
Fig. 7. (a) TG / DTA of Compound 3a at a scan rate of 10°C / min (b) TG / DTA of Compound
3b at a scan rate of 10°C / min (c) TG / DTA of Compound 4a at a scan rate of 10°C / min (d)
TG / DTA of Compound 4b at a scan rate of 10°C / min
23

ACCEPTED MANUSCRIPT
Fig. 8. (a) Plot of Refractive Indices v/s Temperature at different wavelengths for compound 4a
(b) Plot of Refractive Indices v/s Wavelength at 75°C for compound 4a
Scheme Captions
Scheme 1. Reaction Scheme for synthesis of compounds 3a-3g
Scheme 2. Reaction Scheme for synthesis of compounds 4a-4l
Table Captions
Table 1
Optical parameters calculated from the refractive indices data
24

ACCEPTED MANUSCRIPT
Table 1
Optical parameters calculated from the refractive indices data
Compound Abbe Number Dispersive Power
45.25
0.0221
4a
25

ACCEPTED MANUSCRIPT
Highlights
 Methane sulfonate & p-toluene sulfonate salts of esters of DL-Phenylalanine as ILCs
 Refractive indices showed an increase towards the blue region of visible spectrum
 High Abbe number and low Dispersive Power
 Promising candidates for applications in electrically tunable LC lenses and optics
 Non-toxic & safe for large scale applications as proved by DNA binding studies
26

Figure 1

Figure 2

Figure 3