Self-assembly of a renewable nano-sized triterpenoid 18β-glycyrrhetinic acid

Article abstract of DOI:10.1039/c2ra21051g

The nano-sized triterpenoid 18β-glycyrrhetinic acid extractable from Glycyrrhiza glabra self assembled in different liquids affording mostly nano to microsized spherical and flower like objects consisting of fibrillar networks yielding thermoreversible gels. The self-assemblies have been utilized for the templated growth of CdS nanoparticles.

Full text of DOI:10.1039/c2ra21051g

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Electronic Supplementary Information
Self-assembly of a renewable nano-sized triterpenoid 18β-
glycyrrhetinic acid
*
Braja Gopal Bag and Rakhi Majumadar
Department of Chemistry and Chemical Technology
Vidyasagar University
Midnapore 721102
West Bengal, India
Fax: 0091 3222275297
Email: braja@mail.vidyasagar.ac.in

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Additional Analytical Data for 18β-glycyrrhetinic acid 1: R
dichloromethane), Mp = 284 °C. FTIR( KBr, cm ): 3483, 3466, 3427, 3300 – 3600 (br.) 2970 (m),
f
= 0.3 (20% ethyl acetae-
-
1
2
98
2
8
4
928 (m), 2868 (w), 1705 (s), 1666 (s), 1620 (w), 1541 (w), 1456 (m), 1386 (m), 1326 (m). [α]
2.7 (methanol, 0.222 g/100 mL) Reversed-phase HPLC analysis (conditions: C -column, 250 mm x
.6 mm, mobile phase: methanol (flow rate 0.4 mL/minute, UV-Vis detection at 206 nm.) tR = 8.83
D
= +
1
8
min.
Fig S1: Energy minized structure of 18β-glycyrrhetinic acid 1 using MMX force field as
®
implemented
in
PCMODEL
version
9.2
(serena
software)

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Figure S2: FESEM Image of the xerogel of 1 from o-dichlorobenzene gel (0.25% w/v).These
images are recorded in Zeiss FESEM.
Figure S3: FESEM of the xerogels of 1 from nitrobenzene gel (0.25% w/v). These images are
recorded in Zeiss FESEM.

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Figure S4: FESEM of the xerogels of 1 from 5:2 DMSO-water gel (0.045% w/v). These
images are recorded in Zeiss FESEM.
Figure S5. Polarizing Optical microscopic images of 18β-glycyrrhetinic acid 1 gel (recorded in
NIKON ECLIPSE LV100POL instrument.): (a) OPM images of ethylene glycol partial gel of 1 (0.91
%
w/v) (b) OPM image of p-methoxy benzaldehyde partial gel of 1 (1.25 % w/v) (c) OPM image of the
o-dichloro benzene partial gel of 1 (3.33% w/v), (d) OPM image of a nitrobenzene partial gel of 1
2.5% w/v). The aliquot of sample taken on a cover slip was covered with another cover slip and placed
under the microscope.
(

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AFM IMAGES
Figure S6: AFM images of 18β-glycyrrhetinic acid in p-methoxybenzaldehyde (1.25% w/v). In image
c) the diameters of the left and right spherical objects are 63.54 and 64.98 nm respectively. Images
(
were captured in atomic force microscopy VEECO, dicp-II, Model no. AP0100. A solution of the
sample (1.25% w/v) was coated on a glass plate and allowed to dry in air for over night and then under
reduced pressure.

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Fig S7: AFM Images of 1in DMSO-water
Images were captured in atomic force microscopy VEECO, dicp-II, Model no. AP0100. A hot solution
of sample in DMSO - water (0.045% w/v, ratio 5:2) was allowed to cool at room temperature and then
coated on a glass plate and allowed to dry in air for over night and then under reduced pressure.
Fig S8: AFM images of 1 in nitrobenzene: Images were captured in atomic force microscopy
VEECO, dicp-II, Model no. AP0100. A solution of the sample in nitrobenzene (0.25 %w/v) was
coated on a glass plate and allowed to dry in air for over night and then under reduced pressure.
Spherical shape objects of nano-meter –micrometer ranges were obtained.

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1
Thermodynamic parameters
Calculation:
The thermoreversible melting of a gel can be expressed as :
Gel
liquid
The equilibrium constant can be expressed as :
K = [Gelator]/ [Gel]
Assuming unit activity of the gel, the equilibrium constant can be expressed as :
K = [Gelator]
The Gibbs free energy change during gel melting can be expressed as:
0
0
0
0
0
∆
G = - RTlnK = ∆H – T∆S , Hence, lnK = -∆H /R. (1/T) + ∆S /R
“
”
The gel melting temperature (Tgel) increases with increasing concentration of the solutes . A plot of
lnK vs 1/T allowed us to calculate the thermodynamic parameters . A representative plot for a gel in
chlorobenzene is given in the figure below:
-
-
-
-
-
-
-
2.2
2.4
2.6
2.8
3.0
3.2
3.4
0.00295 0.00300 0.00305 0.00310 0.00315 0.00320 0.00325 0.00330
1
/T ( K)
o
Figure S9
0
From the slope we obtain -∆H /R = - 3379.00237 and from the intercept we obtain
0
∆
S /R = 7.7784
0
°
0
The thermodynamic parameters are : ∆S = 64.67 J/mol/ K, ∆H = 28.09 kJ/mol
0
and ∆G = 8.82 kJ/mol
1
Rizkov, D.; Gun, J.; Lev, O.; Sicsic, R.; Melman, A. Langmuir 2005, 21, 12130.

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Fig. S 10: X-RAY diffractograms have been recorded in a Bruker X-ray diffractometer at room
°
temperature (25 C) using Cu-Kα filament (λ = 1.54 Å) .

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Table S1: Wide angle X-ray diffraction data of 18β-glycyrrhetinic acid under different
conditions
Sample
d (Å)
Xerogel from PhNO
Xerogel from PhCl
Xerogel from PhBr
2
10.6, 6.5, 5.9, 5.4, 5.3, 4.9, 4.4, 4.3, 3.7, 3.6, 3.4, 3.3, 3.2, 2.7, 2.5
10.7, 6.5, 5.9, 5.4, 5.3, 4.9, 4.5, 4.3, 4.2, 3.7, 3.6, 3.4, 3.3, 2.5
10.7, 6.5, 5.9, 5.4, 5.3, 4.9, 4.5, 4.4, 4.3, 4.2, 3.7, 3.5, 3.4, 3.3, 3.2, 2.5
10.7, 6.6, 5.9, 5.4, 5.3, 4.9, 4.4, 4.3, 4.2, 3.7, 3.6, 3.4, 3.3, 3.2, 2.8, 2.5
15.3, 12.7, 10.8, 9.0, 6.5, 6.4, 6.0, 5.8, 5.6, 4.9, 4.5, 4.4, 4.3, 3.6, 3.2, 2.7, 2.5
15.2, 12.9, 9.1, 8.7, 7.6, 6.3, 5.9, 5.3, 4.9, 4.7, 4.4, 4.2, 4.0, 3.8, 3.7, 3.6, 3.5, 3.2, 3.0, 2.9,
Xerogel from o-PhCl
Xerogel from DMSO
Powder
2
2.8, 2.6
Gel in
10.8, 6.5, 5.5, 5.2, 5.1, 3.8, 3.7
o-dichlorobenzene
Figure S11a: Overlay of FTIR spectra showing the shift of ‘C=O’ stretching frequency of the
carboxyl group of glycyrrhetinic acid from 1705 cm in a powder sample to 1695 cm in a gel
sample in o-dichlorobenzene (4% w/v).
-1
-1

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Figure S 11b: Overlay of FTIR spectra (KBr) of the xerogels obtained from different solvents

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Figure S12. (a-f) Epifluorescent microscopy images of a partial gel of 18β-glycyrrhetinic acid
in ethylene glycol (1% w/v) containing CdS nano particle: (a,d) bright field images, (b,e)
overlay images, (c,f) fluorescent images.
Figure S13: (a) UV-Vis spectrum of templated CdS nanoparticle on self-assembled 18β-
glycyrrhetinic acid (0.1% w/v) in ethylene glycol, (b) fluorescence emission spectrum upon
excitation at 395 nm, (c) UV-Vis spectrum of 18β-glycyrrhetinic acid (0.21 mM) in ethylene
glycol; (d) fluorescence emission spectrum of 18β-glycyrrhetinic acid upon excitation at 252
nm.

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Figure S14: Transmission electron microscopy images of CdS nanoparticles deposited
on the self-assemblies of 18β-glycyrrhetinic acid (1% w/v).
Figure S15: (a) Energy dispersive X-ray spectrum of templated CdS nanoparticles embedded
on the self-assemblies of 18β-glycyrrhetinic acid (1% w/v) in ethylene glycol; (b) X-ray
diffractogram of CdS nanoparticles (ref. JCPDS 030-65-2887 for cubic CdS and JCPDS File
No. 2-549 for hexagonal CdS) embedded on 18β-glycyrrnetinic acid self-assemblies.