Benzoate liquid crystals with direct isotropic-smectic transition and antipathogenic activity

C. R. Chimie xxx (2016) 1e10

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ꢀ

Full paper/Memoire

Benzoate liquid crystals with direct isotropicesmectic

transition and antipathogenic activity

,

Daniela Ailincai ^a, Luminita Marin ^{a *}, Sergiu Shova ^a, Cristina Tuchilus ^b

^a“Petru Poni” Institute of Macromolecular Chemistry of Romanian Academy, Grigore Ghica Voda Alley, No. 41A, 700487, Iasi, Romania

^b“Grigore T. Popa” University of Medicine & Pharmacy, Pharmacy Faculty, Universitatii Street, No. 16, 700115, Iasi, Romania

a r t i c l e i n f o

a b s t r a c t

Article history:

A smectogen liquid crystal based on benzoate units has been synthesized and structurally

characterized by FTIR and ¹H NMR spectroscopy. Besides, its structure and supramolecular

arrangement in the crystalline state was demonstrated by single crystal X-ray diffraction

measurements. The thermotropic behaviour, monitored by differential scanning calorim-

etry and polarized light microscopy, consists in the formation of an enantiotropic smectic

mesophase with a direct ﬁrst order transition from the isotropic to smectic mesophase,

and with its thermal stability range superposed on human body temperature. The smec-

togen liquid crystal has moderate wettability e suitable for biocompatible materials and

presents good antipathogenic activity against gram positive and gram negative bacteria

and fungus.

Received 30 October 2015

Accepted 21 January 2016

Available online xxxx

Keywords:

Ester

Smectic liquid crystal

Wettability

Antipathogen

All these properties recommend the understudied liquid crystal to be used in biochemical

and biological applications.

ꢀ

1. Introduction

obtained [13]. The PDLC systems combine valuable proper-

ties of the two components and are designed for a wide

Liquid crystals (LC) based on ester units are an interesting

class of compounds which combine the anisotropic prop-

erties of the liquid crystals with the biological characteristics

of the esters, promising to be a new class of biological

relevant materials for surface functionalization [1], drug

delivery systems [2], protein sorption/desorption [3], bio-

logical sensors [4], wound healing [5] membranes [6], gene

therapy [7] and so on. A signiﬁcant number of ester based

liquid crystals have been mainly synthesized with the aim of

being applied in optoelectronics and photonics as LC dis-

plays [8], ﬁeld effect transistors [9], organic light emitting

diodes [10], optical data storage devices [11], or photovoltaic

cells [12]. Their application ﬁeld is further enlarged by

incorporating them into a polymeric matrix when systems

known as polymer dispersed liquid crystals (PDLCs) are

range of applications, those in high performance biomedical

ﬁeld being especially envisaged in the last years, as artiﬁcial

iris [14], blood sensors or sperm testers [15], smart pack-

aging, and so on [16]. To be applied in such biological ap-

plications, liquid crystals must have the mesophase stability

range at low temperature, eventually superposed on human

body temperature. Moreover, speaking about the particular

case of smectic liquid crystals, a direct isotropicesmectic

transition is required, in order to reach a monomorphic

stable mesophase capable of bistability [17].

Having all these in mind, we designed an ester based

liquid crystal with a benzoate core and two aliphatic end

groups which bring the beneﬁts of the low temperature

mesophase stability and of the direct isotropicesmectic

transition. Besides, the ester groups provide the advantage

of a potential biologically friendly compound, with real

possibilities to be used in biochemistry and biological

applications.

* Corresponding author.

E-mail address: lmarin@icmpp.ro (L. Marin).

http://dx.doi.org/10.1016/j.crci.2016.01.008

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Please cite this article in press as: D. Ailincai, et al., Benzoate liquid crystals with direct isotropicesmectic transition and anti-

pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

2

D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

2. Experimental

¹H NMR (400.13 MHz, DMSO-d₆, ppm)

d

¼ 8.12, 8.10 (d,

2H, H3,H5); 8.09, 8.07 (d, 2H, H20,H22); 7.47, 7.45 (d, 2H,

H19,H23); 7.16, 7.14 (d, 2H, H2,H6); 4.34, 4.32, 4.30 (t, 2H,

H27); 4.13, 4.11, 4.10 (t, 2H, H8); 1.79, 1.77, 1.75, 1.74, 1.71 (m,

4H, H9,H28); 1.49, 1.47, 1.45, 1.44, 1.42 (m, 4H, H10,H29);

1.40e1.24 (overlapped peaks, 8H, H11,H12,H13,H14); 0.99,

0.97, 0.95 (t, 3H, H30); 0.91, 0.89, 0.87 (t, 3H, H15)

2.1. Reagents

4-Hydroxybenzoic acid ꢀ99%, butyl 4-hydroxybenzoate

ꢀ99%, 1-bromooctane 99%, thionyl chloride 99%, anhydrous

pyridine 99.8%, potassium hydroxide >85% were purchased

from Aldrich and used as received. All the solvents of high

purity were purchased from Carl Roth and used without

any other puriﬁcation.

FTIR (KBr, cm^ꢁ1): 2954, 2921, 2855 (n_CH3

_C]_O), 1602 n_C¼Caromatic), 1252 n_CeOeC), 845, 760

d_CHaromatic).

, n_CH2), 1720

(

n

(

Crystal data C₅₂H₆₈O₁₀(M_r¼ 853.06 g mol^ꢁ1), triclinic,

a ¼ 5.7447(6) Å, b ¼ 14.5648(14) Å, c ¼ 28.725(2) Å,

a

¼ 98.673(7)^ꢂ,

b

¼

94.343(7)^ꢂ,

g

¼

91.478(8)^ꢂ;

2.2. Synthesis

V ¼ 2367.4(4) Å³, T ¼ 160 K, space group Pꢁ1, Z ¼ 2, 1652

coll. reﬂ., 8053 indep. (R_int

R₁¼ 0.0935, wR(F²) ¼ 0.2132.

¼

0.0779), G_of

¼

1.000,

The smectic liquid crystal has been synthesized using an

input from published procedures [18] and optimized to the

best yield, as can be seen in Scheme 1.

2.3. Equipment

2.2.1. p-Octyloxy-benzoic acid (2)

In a round bottom ﬂask, solutions of 4-hydroxybenzoic

acid (1.1 g, 8 mmol) in 15 mL dry ethanol, and KOH

(0.89 g, 16 mmol) in 5 mL dry ethanol were introduced, and

over the resulted mixture n-bromooctyl (1 mL, 8 mmol)

reagent was added drop wise, under vigorous stirring. The

reaction mixture was reﬂuxed for 14 h under nitrogen at-

mosphere, and then allowed to reach room temperature.

The solid inorganic salts were removed by ﬁltration and the

pH of the resulted solution was adjusted to 2 by adding

diluted HCl (0.1M). The crude product was ﬁltered off,

washed with water and recrystallized from acetic acid and

then toluene, to give a white powder with a yield of 67%.

Infrared (IR) spectrum of the solid BBO was recorded on

a FTIR Bruker Vertex 70 Spectrophotometer in the trans-

mission mode, by using KBr pellets.

¹H-NMR spectrum was recorded on a BRUKER Avance

DRX 400 MHz spectrometer, equipped with a 5 mm direct

detection QNP probe with z-gradients. The chemical shifts

are reported as

DMSO solvent.

d (ppm) relative to the residual peak of the

Crystallographic measurements on the BBO single

crystal were carried out with an Oxford-Diffraction XCA-

LIBUR E CCD diffractometer using graphite-monochromatic

MoKa radiation, under the conditions described in the

literature [19]. Crystallographic data for BBO have been

deposited at the Cambridge Crystallographic Data Centre as

Supplementary Publications No. CCDC-1416309. Copies of

the data can be obtained free of charge from CCDC (12

Union Road, Cambridge CB2 1EZ, UK; Tel.: þ44 1223 336

408; fax: þ44 1223 336 033; e-mail: deposit@ccdc.cam.ac.

uk; www:http://ccdc.cam.ac.uk).

2.2.2. p-n-Octyloxy benzoyl chloride (3)

Thionyl chloride (1.5 g, 25 mmol) was added dropwise,

at room temperature, to a solution of p-octyloxybenzoic

acid (2.2 g, 13 mmol) in dimethylchloride (25 mL) with few

drops of dimethylformamide, and the resulted mixture was

stirred for 2 h. After that, the solvent was removed by

distillation to give an ochre powder which was further used

without any puriﬁcation.

The textures of the BBO liquid crystal were investigated

by polarized light microscopy, with an Olympus BH-2 mi-

croscope equipped with a Linkam THMS 600/HSF9I heating

stage and a TMS91 control unit. The samples were observed

during a heating/cooling/heating scan, at a heating/cooling

2.2.3. Butyl-p-[p⁰-n-octyloxy benzoyloxy]benzoate (BBO)

The ﬁnal product butyl-p-[p⁰-n-octyloxy benzoyloxy]

benzoate (BBO) was obtained by reaction of the p-n-octy-

loxy benzoyl chloride (3) with the commercial p-hydroxy

butyl benzoate (4). The crude product has been recrystal-

lized from ethyl acetate when ﬁne white single crystals

suitable for crystallographic measurements were obtained.

ꢁ1

ꢂ

rate of 5 C min

.

Differential scanning calorimetric (DSC) measurements

were performed on a DSC 200 F3 Maia device (Netzsch,

Germany), under nitrogen purge (nitrogen ﬂow 50 mL/

min). The device temperature and sensitivity was

O

31

20

23

25

27

29

19

18

21

22

28

O

CH₃

30

24

26

5

16

6

4

3

O

17

14

12

10

8

1

13

11

9

2

H₃C

O

15

7

Please cite this article in press as: D. Ailincai, et al., Benzoate liquid crystals with direct isotropicesmectic transition and anti-

pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

3

O

C₈H₁₇-Br

EtOH, reflux

HO

O

2

OH

1

SOCl₂

CH₂Cl₂

O

Cl

3

O

HO

C₄H₉

4

pyridine

O

BBO

Scheme 1. Synthesis of BBO butyl-p-[p⁰-n-octyloxy benzoyloxy]benzoate.

calibrated with indium, according to the standard pro-

cedures. Around 5 mg of BBO sample was loaded in a

punched and sealed aluminium crucible and DSC curves

have been registered on a heatingecoolingeheating scan,

at a 5^ꢂC min^ꢁ1rate. The transition temperatures were read

at the top of the endothermic and exothermic peaks.

The static contact angle for the BBO deposition was

obtained using a CAM-200 instrument from KSV Finland,

by the sessile drop method, at room temperature and

2950 and Candida parapsilosis ATCC 22019 fungus. Stainless

steel cylinders, with an inner diameter of 6 mm, were

placed in Petri dishes containing Mueller-Hinton agar

medium for bacteria, and Sabourand medium for fungus.

The medium (Oxoid, UK) was inoculated with the micro-

organism suspension. Afterwards, the cylinders were ﬁlled

with 100 ml solution of BBO in DMSO (10 mg/mL). After

incubation at 37 ^ꢂC for 24 h, the diameter of the inhibition

zone was measured. The results are expressed as the mean

value of three different measurements. Two disks, one of

controlled humidity. A drop of 1 mL was placed on the BBO

ﬁlm surface and the measurement was performed within

10 s. The contact angle was measured 5 times on random

locations of the surface, the average value being consid-

ered. To calculate the components of the free surface en-

ergy and the total free surface energy, the contact angle at

equilibrium between the studied surface and three pure

liquids e twice distilled water, formamide and diiodo-

methane e was measured [16c,20].

25

used as etalons for the antimicrobial activity, while a disk of

myconazol of 50 g, and one of nystatin of 100 g were

mg ampicillin and one of 30 mg chloramphenicol were

m

used as etalons for the antifungal activity.

3. Results and discussions

3.1. Synthesis and structure

The UVevis absorption and photoluminescence spectra

were recorded on a Carl Zeiss Jena SPECORD M42 spec-

trophotometer and Perkin Elmer LS 55 spectrophotometer

respectively. The UVevis spectrum of the BBO was regis-

tered in diluted chloroform solution (y10^ꢁ5%) using

10 mm quartz cells ﬁtted with poly(tetraﬂuoroethylene)

stoppers. The photoluminescence spectrum of the BBO was

obtained by exciting the ﬁlm with a light wavelength cor-

responding to the absorption maximum.

The antimicrobial activity of the BBO compound was

evaluated against both gram positive and gram negative

bacteria and also against fungus, using the agar diffusion

method [21]. The used microorganisms were: Staphylo-

coccus aureus ATCC 2592 and Sarcina lutea ATCC 9341 gram

positive bacteria; Escherichia coli ATCC 25922 and Pseudo-

monas aeruginosa ATCC 27853 gram negative bacteria; and

Candida albicans ATCC 10231, Candida glabrata ATCC MYA

A thermotropic smectic liquid crystal containing ester

linkages named butyl-p-[p⁰-n-octyloxy benzoyloxy]benzo-

ate] (BBO) has been synthesized by an esteriﬁcation reac-

tion starting from p-hydroxy benzoic acid (Scheme 1). The

right structure of the liquid crystal has been proved by ¹H

NMR and FTIR spectroscopy and further by single crystal X-

ray diffraction measurements.

The FTIR spectrum of the BBO revealed all the charac-

teristic absorption bands of the new formed compound,

conﬁrming the reaction pathway. Thus, in the ﬁnger print

region, signiﬁcant bands are seen at 1720 cm^ꢁ1assigned to

the stretching vibration of COO groups and at 1602 cm^ꢁ1

attributed to the stretching vibration of the double bond in

the aromatic ring. Symmetric and anti-symmetric stretch-

ing vibrations of the CeH bond of CH₂and CH₃units are

also present at 2954, 2921 and 2855 cm^ꢁ1(Fig. 1).

Please cite this article in press as: D. Ailincai, et al., Benzoate liquid crystals with direct isotropicesmectic transition and anti-

pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

4

D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

chemically identical molecules as the asymmetric part of

the unit cell. Both molecules (A and B) exhibit very close

geometric parameters listed in Table 1S.

The crystal structure essentially results from the pack-

ing of two-dimensional layers parallel to the (110) plane. A

fragment of the crystal structure viewed along the a axis is

shown in Fig. 4. Each layer has a thickness of approximately

27 Å, being constructed due to the antiparallel arrangement

of the asymmetric molecules A and B along the c crystal-

lographic axis. There are two types of inter-molecular in-

teractions, which caused the formation of supramolecular

layers: molecules A and B in an antiparallel orientation are

linked through short contacts, evidenced for numerous (i)

pep, and (ii) CeH/p interactions (Fig. 5) [22]. In addition,

along the perpendicular direction the supramolecular

layers are additionally sustained via a system of similar

CeH/O inter-molecular hydrogen bonding comprising

separately A and B molecules. As an example, the H-

bondings which occur between molecules A are shown in

Fig. 6.

Fig. 1. FTIR spectrum of the BBO liquid crystal.

This bonding network facilitates a rigid-ﬂexible self-

assembly which further plays an important role in the

thermotropic behaviour.

Further, the NMR spectrum of the BBO exhibits all the

chemical shifts characteristic of the aromatic and aliphatic

protons, in the right integral ratio, conﬁrming the right

structure and the high degree of purity (Fig. 2).

3.2. Liquid crystalline behaviour

Single crystal X-ray diffraction of the BBO, clearly indi-

cated the targeted structure and moreover, gave a view on

the driving forces to the supramolecular arrangement of

the molecules in the crystal structure. Fig. 3 presents a

perspective view of two crystallographic independent but

The thermotropic behaviour of the BBO has been ﬁrstly

monitored by differential scanning calorimetry. As can be

seen in Fig. 7, during the heating scans, two endothermic

peaks e a more intense one at 54 ^ꢂC (~ 80 J/g) and a less

intense one at 70 ^ꢂC (15.38 J/g) e indicate the presence of a

Fig. 2. NMR spectrum of the BBO liquid crystal.

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pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

5

Fig. 3. Two crystallographic independent molecules (A and B) in the asymmetric part of the unit cell. Thermal ellipsoids are drawn at 50% probability level.

Fig. 4. The crystal structure of the BBO viewed along the a axis.

Please cite this article in press as: D. Ailincai, et al., Benzoate liquid crystals with direct isotropicesmectic transition and anti-

pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

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D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

Fig. 7. DSC curves of the butyl-p-[p⁰-n-octyloxy benzoyloxy]benzoate.

Fig. 5. View of the crystal structure showing (i)

pep, and (ii) CeH/p in-

teractions in the crystal structure of the BBO. The centroid-to-centroid and

CeH/ distances are in the range of 3.885÷3.892 Å and 2.759÷2.993 Å,

p

respectively.

from the viscous smectic ﬂuid into the complex crystalline

structure, most probably due to the weaker H-bond in-

teractions among the supramolecular layers, related to

their low dipole moment [24].

mesophase. In the cooling scans, in a reverse manner, two

exothermic peaks occur too, at 69 ^ꢂC (ꢁ15,51 J/g) and 29 ^ꢂC

(ꢁ68.08 J/g), respectively. The enthalpy change of the

exothermic processes has similar value with that of the

corresponding endothermic processes. Taking into consid-

eration the high values of enthalpy changes, it can be

assumed that BBO forms an enantiotropic smectic meso-

phase, being known that smecticeisotropic transition in-

volves more energy compared to the nematic-isotropic one

[23]. The high hysteresis of the lower temperature transi-

tion is characteristic of a difﬁcult crystallization process

To gain deeper insight into the mesophase type, polar-

ized light microscopy (POM) was performed under similar

conditions with DSC measurements. Under polarized light,

at room temperature, the BBO shows strong birefringent

needle crystals (Fig. 8a). During the ﬁrst heating cycle, the

needle-like crystals suffered a transition to a ﬂuid, striated

marble texture difﬁcult to be ascribed (Fig. 8b), which

further became isotropic. The two transitions occurred at

temperatures corresponding to the DSC endotherms. In the

cooling scan, from the isotropic ﬂuid, a clear fan shape

texture, characteristic of the smectic

A mesophase

appeared (Fig. 8c), and crystallized at further cooling

(Fig. 8d). Both transitions occurred at temperatures corre-

sponding to the DSC exotherms. No other transition could

be observed before crystallization, even after decreasing

the cooling speed to 3, 1, or 0.1 ^ꢂC min^ꢁ1. It can be remarked

that the smectic mesophase formed during the cooling is

stable on a larger temperature range (40 ^ꢂC) compared to

that occurred during the heating (16 ^ꢂC).

Taking into consideration the crystalline structure as

demonstrated by single crystal X-ray diffraction, the for-

mation of the smectic mesophase was explained by the

tendency of the BBO molecules to form layered structures

by rigid-ﬂexible segregation, which appeared to be the

principal driving force in keeping crystal integrity. As the

temperature increased the weaker H-bonds interactions

were destroyed and the

gained enough energy to rotate competing with the

and CeH/ cohesion forces between the rigid parts, and

s bonds of the ﬂexible spacer

pep

p

thus a smectic mesophase was formed. As the temperature

increased more, the molecules gained enough energy for

translational moving, and thus the layered ordering of the

smectic mesophase was lost. The direct smecticeisotropic

transition without a transition via a nematic mesophase,

appeared to be the result of the short inter-molecular

distances and consequently strong inter-molecular forces

Fig. 6. CeH/O hydrogen bonding within the two-dimensional layer. H-

bond parameters: C17AeH/O2A [C17AeH 0.93 Å, H/O2A 2.42 Å,

C17A/O2A(ꢁ1 þ x, y, z) 3.333(6) Å, C17AeH/O2A 166.1^ꢂ]; : C24AeH/O4A

[C24AeH 0.97 Å, H/O4A 2.65 Å, C24A/O2A(1 þ x, y, z) 3.568(67) Å,

C24AeH/O2A 157.2^ꢂ]; C21BeH/O2B [C21BeH 0.93 Å, H/O2B 2.41 Å,

C21B/O2B(1 þ x, y, z) 3.303(6) Å, C21BeH/O2B 162.0^ꢂ]; C24BeH/O4B

[C24BeH 0.97 Å, H/O4B 2.54 Å, C24B/O4B(-1

C24BeH/O4B 160.7^ꢂ].

þ

x, y, z) 3.472(6) Å,

Please cite this article in press as: D. Ailincai, et al., Benzoate liquid crystals with direct isotropicesmectic transition and anti-

pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

7

Fig. 8. POM images revealing thermotropic behaviour of the BBO smectic liquid crystal.

between the rigid cores. This kind of interaction was

completely vanished by increasing the temperature at a

value at which the molecules gained enough energy for

translational moving. In the cooling scan, the smectic

mesophase appeared directly from the isotopic state, due

maximum around 266 nm in the UVevis spectrum, char-

acteristic of the benzenoid transition. By exciting with

pep

light of wavelength corresponding to the absorption

maximum, the BBO ﬁlm exhibits a large emission band

expanding from the UV to green light domain (Fig. 9b), with

emission maxima lying in principal in the blue light

domain. The emission proﬁle has a structured shape indi-

cating the crystallization in crystals of different size and in

different amounts. It is important to underline that no su-

perposing of the absorption and emission bands was

registered, pointing to no reabsorption phenomena and

consequently potential use in biochemical and biological

applications [25].

to the strong

pep and CeH/p cohesion forces between

the rigid cores which favoured the layer formation.

Comparing the data from the three methods (single

crystal X-ray diffraction, POM and DSC), it can be concluded

that the BBO ester based compound is a smectic liquid

crystal with a direct isotropicesmectic transition and large

mesophase stability range superposing with human body

temperature. The smectic mesophase appears due to the

tendency of BBO to aggregate in layered structures because

of rigid-ﬂexible self-assembling. The short inter-molecular

distances indicate strong inter-molecular forces which

disfavour the BBO molecule arrangement in a nematic

mesophase and, on the other hand, favour the molecule

arrangement in a layered structure and the direct iso-

tropicesmectic transition. Besides, considering the bio-

logically friendly building blocks [18a,b] used for obtaining

BBO , the new liquid crystal appears to have potential use in

biomedical applications.

3.4. Surface characteristics

As the surface of a material is the ﬁrst coming into

contact with biological ﬂuids, its characteristics in terms of

wettability and surface energy are very important param-

eters when the level of biocompatibility of a material is

investigated. The water contact angle of the BBO liquid

crystal has the medium value of 68.4 degree which is

comprised in the moderate wettability range of 60e90

degree e characteristic of the biocompatible materials

[16,19,26]. Moreover, this contact angle value is close to the

value of 60 degree of the corneal surface [27] indicating the

BBO as potential candidate for ocular biomedical

applications.

3.3. Photophysical properties

The absorption behaviour of the BBO liquid crystal was

studied in diluted solution of chloroform (10^ꢁ5M), when

no interactions between molecules are possible and so they

can be considered isolated. As can be seen in Fig. 9a, the

BBO liquid crystal shows an absorption band with a

The BBO liquid crystal based on benzoate units has high

surface energy value of 42.8 mN/m, given by higher

dispersive Lisfshitz

e

van der Waals contribution

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D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

Fig. 9. a) UVevis and b) photoluminescence spectra of the BBO.

(

g^L_S^W¼ 40.32) and less important polar forces (g^a¼ 2.48) as

react with the ester groups of the BBO via a trans-

esteriﬁcation reaction. This should disrupt the membrane

function and thus inhibit the culture growth.

result of almost missing electron accepting (g^þ_S¼ 0.08)

contributions despite important electron donating

(

g^ꢁ_S¼ 18.22) contribution. This is in agreement with the

Related to the gram negative bacteria, stagnation of the

bacterial growth was observed only in the case of E. coli,

while no activity could be seen against P. aeruginosa. This

observation comes in line with other reported data which

evidenced the catabolic activity of P. aeruginosa against a

large variety of organic molecules including benzoates [30].

The good activity of the BBO against E. coli is remarkable,

taking into consideration the high resistance of this bac-

terium to antibiotics [31].

Considerable activity of the BBO liquid crystal was also

observed against fungus. Inhibition zone diameter between

14 and 19 mm for the three tested Candida fungus com-

petes with the one obtained for the used Nystatin etalon e

a well-known antifungal agent.

structure of the BBO consisting of electron rich ester groups

and nonpolar aliphatic units. The surface energy value of

the BBO liquid crystal is higher than 22 mN/m e value over

which the cellular adhesion and the maintainance of the

tissue multicellular structure was demonstrated to be fav-

oured [28].

3.5. Antipathogenic tests

As the BBO compound was designed for being used in

biomedical applications, a preliminary screening of its

antimicrobial activity was performed against common and

virulent pathogen agents related to human healthcare,

such as S. aureus ATCC 25923 and S. lutea ATCC 9341 gram

positive bacteria, E. coli ATCC 25922 and P. aeruginosa ATCC

27853 gram negative bacteria and C. albicans ATCC 10231, C.

glabrata ATCC MYA 2950 and C. parapsilosis ATCC 22019

fungus.

4. Conclusions

A smectogen liquid crystal based on benzoate units has

been designed and successfully synthesised. The liquid

The antimicrobial activity was measured by the agar

diffusion method in Petri dishes containing Mueller-Hinton

agar medium for bacteria, and Sabourand medium for

fungus. Except P. aeruginosa, the BBO liquid crystal

exhibited strong antimicrobial activity against all the tested

microorganisms, as can be observed in Fig. 10. Represen-

tative images of the inhibition area could be observed in

Fig. 11.

Firstly, it can be observed that BBO reduces the culture

of viable gram positive S. aureus and S. lutea bacteria on a

large area around, with an inhibition zone about 15 mm,

activity comparable with that of sugar fatty acid esters used

as multifunctional food additives in food industries [29]. A

plausible explanation of this good activity could be given

taking into consideration the chemical structure of both

interacting components. Thus, the cell surface of the gram

positive bacteria contains lipoteichoic acid which could

Fig. 10. The inhibition area (mm) of the BBO liquid crystal.

Please cite this article in press as: D. Ailincai, et al., Benzoate liquid crystals with direct isotropicesmectic transition and anti-

pathogenic activity, Comptes Rendus Chimie (2016), http://dx.doi.org/10.1016/j.crci.2016.01.008

D. Ailincai et al. / C. R. Chimie xxx (2016) 1e10

9

Fig. 11. The antimicrobial activity of the BBO liquid crystal against a) Candida albicans, b) Candida glabrata, c) Candida parapsilosis, d) Staphilococus aureus.

[5] (a) C.F. Soon, M. Yousef ﬁ , R.F. Berends, N. Blagden, M.C.T. Denye,

Biosens. Bioelectron. 39 (2013) 14e20;

crystal has a direct isotropicesmectic transition and its

thermal stability mesophase range superposes on human

body temperature. The liquid crystal has excellent anti-

pathogenic activity and its surface properties in terms of

wettability and surface energy indicate it as a potential

biocompatible material.

(b) Y. Bouligand, C. R. Chimie 11 (2008) 281e296;

(c) M.-M. Giraud-Guille, E. Belamie, G. Mosser, C. Helary,

F. Gobeaux, S. Vigier, C. R. Chimie 11 (2008) 245e252.

[6] W. Han, M. Tu, R. Zeng, J. Zhao, C. Zhou, Carbohydr. Polym. 90 (2012)