Insights into a novel class of azobenzenes incorporating 4,6- O -protected sugars as photo-responsive organogelators

Article abstract of DOI:10.1039/c9ra08033c

A novel class of 4,6-O-butylidene/ethylidene/benzylidene β-d-glucopyranose gelator functionalized with photo-responsive azobenzene moieties were designed and synthesized and also characterized using different spectral techniques. These azobenzene-based or

Full text of DOI:10.1039/c9ra08033c

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Insights into a novel class of azobenzenes
incorporating 4,6-O-protected sugars as photo-
responsive organogelators†
Cite this: RSC Adv., 2019, 9, 42219
P. V. Bhavya, V. Rabecca Jenifer, Panneerselvam Muthuvel and T. Mohan Das *ab
a
a
b
A novel class of 4,6-O-butylidene/ethylidene/benzylidene b-D-glucopyranose gelator functionalized with
photo-responsive azobenzene moieties were designed and synthesized and also characterized using
different spectral techniques. These azobenzene-based organogelators can gel even at lower
concentrations (critical gelation concentration – 0.5% and 1%). A morphological study of the gels shows
one-dimensional aggregated bundles and helical fibres. The main driving force for the self-assembly is
through cooperative interactions exhibited by the different groups viz., sugar hydroxyl (hydrogen
bonding interaction), azobenzene (aromatic p–p interaction) and alkyl chain of the protecting group
(van der Waals interaction).
Received 3rd October 2019
Accepted 10th December 2019
DOI: 10.1039/c9ra08033c
rsc.li/rsc-advances
as cyclic ketal derivatives are not only transports amphiphilicity
but also supports in the preorganization by constraining the
1
. Introduction
Gels are viscoelastic materials consisting of low molecular conformational freedom for self-assembly. Some of the ketal
1
weight gelator molecules and solvents. Most of the gel forma- derivatives of carbohydrates have been reported as organo-
14
tion takes place by multiple interactions, such as hydrogen gelators. Carbohydrates are hydrophilic building blocks that
2
bonding, p–p stacking, and hydrophobic interactions. Several are able to form multiple H-bonds due to the presence of
class of organogelators have wide-range of applications as hydroxyl groups, which also favour solubilisation in water.
3
4
17
scaffolds for energy transfer, as drug delivery agents, self- Cyclic forms of carbohydrates provide more stable gels due to
5
6
healing
materials,
cosmetic
additives,
enzyme- their directional hydroxyl groups which supports cooperative
7
8
9
immobilization matrices, oil recovery, tissue engineering
networks to have a self-assembled brous structure. Stability
etc. Sugar-based gelators also have a signicant role in many of and gel properties are strongly dependent on the molecular
10
these applications. One of the most interesting and also structure of the gelator. The structural modication of carbo-
inspiring category of low molecular weight gelators (LMWGs), hydrate molecules to obtain LMWGs has been an interesting
18
are multi-stimuli responsive supramolecular gelators (MRSGs). eld of research in recent years. Carbohydrate molecules are
The self-assembly process of these smart materials are affected biocompatible; the gels derived from these molecules have wide
1
9
by some external stimuli such as heat, light, ultrasound, redox, application in biology and also as functional materials.
11
and pH changes. LMWGs are an important class of so Moreover, the abundant availability of saccharides enhances
matters and have received increasing attention in recent years research into the design of novel sugar based gelator molecules
12
due to their easy fabrication into so materials, and also wide I and II (Fig. 1). The incorporation of appropriate external photo
13
applications in the eld of chemosensors drug delivery responsive chromophores into gelator molecules leads to novel
4
14
systems, optical devices, display devices, oil recovery, phase stimuli-responsive gels. For example, the introduction of
1
2
15
selective gelator removal of toxic dye and other applica-
tions.
16
Carbohydrates and other polyhydroxy class of
compounds are partly decorated with hydrophobic and hydro-
philic moieties and were found to be one of the cheap and easy-
to-synthesize LMWGs. The partial protection of carbohydrates
a
Department of Chemistry, School of Basic and Applied Sciences, Central University of
Tamil Nadu (CUTN), Thiruvarur 610005, India. E-mail: tmohandas@cutn.ac.in
b
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai –
6
†
1
00025, India
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra08033c
Fig. 1 Representative examples of sugar-based low molecular weight
organogelators reported in the literature.
1,13
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2
0
21
22
23
azobenzene, stilbene, butadiene, dithienylethene, spi- hydrogen bonding also seems to play a role in the orientation of
24
25
ropyran, and anthracene groups are extensively incorporated molecules within the aggregates. Azobenzene-based choles-
29
30
to from photo-responsive materials. Similarly, the introduction terol and aryl ethers were reported to possess gelating ability
of the p-methoxy group to the benzylidene acetal affects the in organic solvents. In order to obtain a right balance between
gelation property. In the presence of acids, p-methox- hydrophilic and hydrophobic nature of the gelator molecule,
31
32
ybenzylidene acetal readily cleaves which is the resultant effect some of the hydrophilic groups like saccharide, peptide and
26
33
of pH and it triggered to release drug molecules. In general, PEG has been introduced to achieve the desire a hydrogelator
the interactions of LMWGs are dynamic and reversible in property. In continuation to our on-going project in the area of
nature. External stimuli on these gelators can affect the self- the design and synthesis of sugar based gelators here we have
assembly of building blocks which is aggregated through reported the synthesis of sugar-azo derivatives and its organo-
multiple non-covalent interactions (such as hydrogen bonds, p– gelation properties. In order to obtain further insight into the
p stacking, electrostatic interactions, van der Waals forces). structure–function relationships of sugar-based organogelators,
Depends on the functionalities of the gelator molecules, the we have constructed a small library of sugar derivatives that
gel–sol phase transitions have been triggered by pH value, contain aromatic moieties (i.e., azobenzene) linked to the
temperature, mechanical stress, light, ionic species, host–guest saccharide moiety through N-glycosyl bridges.
27
interactions, redox processes, enzymes, etc.
The so materials fabricated from the azobenzene groups
2
. Result and discussion
containing molecules can potentially be applied in message
28
2.1. Synthesis and characterization of sugar-azo derivatives
storage and increased charge transport process, etc. In several
organogels, hydrophobic interactions such as aromatic p–p Azobenzene based N-glycosylamine derivatives (5–7, 9–11 & 13–
stacking and van-der Waals interactions are indispensable for 15) were synthesized from amino azobenzene derivatives (4, 8,
34
35,36
the formation of oriented aggregates and are most probably the 12) and 4,6-O-protected-D-glucose (1a–c) (Scheme 1).
The
initial driving force for the self-assembly process. Furthermore, reactants were chosen preferentially to have
a desired
ꢀ
Scheme 1 Synthesis of sugar-azo derivatives 5–7, 9–11 & 13–15. Reagents and reaction conditions: (i) toluene, AcOH, 60 C, 21 h, 70% (ii) 4,6-
ꢀ
O-protected D-glucose, 81–88% 1(a–c), ethanol, rt, (iii) KOH, 90 C, 1 h, 94% (iv) 4,6-O-protected D-glucose 1(a–c), ethanol, rt, 71–83% (v)
ꢀ
compound 3, toluene, AcOH, 60 C, 16% (vi) 4,6-O-protected D-glucose 1(a–c), ethanol, rt, 66–85%.
42220 | RSC Adv., 2019, 9, 42219–42227
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functional groups, such as the primary amine in the aromatic compounds (5–7, 9–11 & 13–15). The identities of all the
1
moiety and active hydroxyl group in the 4,6-O-protected-D- synthesized N-glycosylamines were conrmed using NMR ( H
1
3
glucose. All the new resulting azobenzene N-glycosylamine and C) and elemental analysis. All the synthesized compounds
compounds (5–7, 9–11 & 13–15) were identied through spectral were subjected to gelation studies with a wide range of solvents
techniques. During the synthesis of different N-glycosylamines and the gels thus obtained were characterized using micro-
37
using partially protected saccharide, gel formation were scopic techniques, viz., SEM and HR-TEM analysis.
1
observed and this observation prompted us to go for the study
Using H NMR the presence of acetyl methyl proton was
of the gelation property of azobenzene containing saccharide conrmed as sharp singlet in the region of 1.88–2.90 ppm. The
protons of the glucose moiety resonate at around 3.00–
5.60 ppm, the b-anomeric form of the glycosidic unit was
conrmed by the triplet in the range of 4.41–4.90 ppm with
a coupling constant between 4.8–6.6 Hz (ref. 38) (Table 1). The
NH proton appears as a doublet in the region of 4.03–4.54 ppm
with a coupling constant between 4.8–6.9 Hz (see ESI for further
details†).
Table 1 Synthesis of azobenzene based N-glycosylamines, (5–7, 9–11
13–15)
&
1
3
From C NMR analysis of compounds (5–7, 9–11 & 13–15)
the methyl carbon atoms of the acetyl group appear in the range
of 22.1–29.6 ppm. 107.0 ppm corresponds to acetal carbon of
ethylidene, benzylidene and butylidene derivatives, respec-
tively. The presence of azobenzene moiety can be conrmed
from the appearance of the peaks in the range of 107.0–
Structure
of the
compound
Compd
no.
d (ano-H),
d (gly-NH),
J ,H2/Hz
H1
Yield
(%)
150.0 ppm. In addition, the presence of the carbonyl carbons
3
3
J
H1
,
H2/Hz
was identied from the appearance of the peak at 168.0–
174.0 ppm.
1
5
6
7
R ]C
3
H
7
4.90, 5.1
4.43, 5.1
4.64, 6.6
4.51, 5.4
4.24, 7.8
4.03, 4.8
82
81
88
R]NHAc
1
R ]CH
R]NHAc
3
2.2. Organogel formation
1
R ]C
6
H
5
The gelation ability of these compounds in different solvents
was determined by “stable to inversion of the container”
R]NHAc
39
method. A weighed amount of the corresponding azo-benzene
based N-glycosylamines (5 mg) in 1 mL of an organic solvent
was heated in a septum-capped test tube until the solid dis-
solved; the resultant mixture was then cooled to room temper-
ature, and when the tube could be inverted without any ow, it
was determined to be a “gel” (Fig. 2). Furthermore, critical
gelation concentration (CGC) refers to the concentration at
which a minimum amount of compound forms a gel (Table 2).
The more gelating ability of butylidene protected N-glycosyl-
amines (5, 9 & 13), seems to be due to the presence of the long
9
4.82, 4.8
4.72, 4.8
4.97, (—)
4.18, 6.9
4.54, 5.7
4.38, (—)
71
78
83
1
1
0
1
alkyl chain in these compounds (in ethylidene only one –CH
a
a
3
40
group is present), as a result of higher van der Waals force and
such interactions are expected to be less in ethylidene protected
N-glycosylamines (6, 10 & 14) and the corresponding gelation
would be low.
1
3
4.54, 5.1
4.10, 4.8
66
2.3. Sol–gel transition
The benzylidene protected N-glycosylamines (7, 11 & 15) and the
corresponding gelation would be moderate. However, in methyl
substituted N-glycosylamines (7, 11 & 15) the steric interactions
seem to be largely responsible for hampering the gelation
properties. These results support that alkyl group present at
ortho position inuences the formation of intermolecular H-
bonding which is responsible for gelation process in partially
protected N-glycosylamines. The presence of signicant
involvement of van der Waals forces and the structural
arrangement that enhances the p–p interactions are some of
the factors responsible for good gelation abilities. Among the
a
a
1
4
5
4.73, 4.8
4.41, (—)
4.15, (—)
76
85
a
1
4.59, (—)
a
Peaks overlapped with saccharide protons.
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2.5. Thermal analysis
To understand the thermal properties of compound 13, the
comparative study of the gelator in the solid and xerogel states
were studied using differential scanning calorimetric (DSC)
technique. DSC graphs of azobenzene based N-glycosylamine
1
3 and its xerogel are shown in Fig. 4 p-xylene gel (0.5%) was
utilized for DSC studies, upon heating the gel at the rate of
ꢁ
1
1
0 min the evaporation of solvent will take place and result
in formation of the xerogel. The solid and the xerogel of N-
ꢀ
Fig. 2 Picture of sol–gel transition of compound 13 in p-xylene glycosylamine 13 show the phase transition at 152.10 C (74.2 J
ꢁ
1
(
0.5 mg mL ).
ꢁ1
ꢀ
ꢁ1
g
) and 46.10 C (116.9 J g ) respectively. From the DSC
graph it was evidenced that N-glycosylamine 13 is thermally
more stable in the xerogel state than in the solid state. This is
due to the ordered arrangement of gelator in the self-
assembled state and which is not available in the solid
various polar and nonpolar solvents used for gelation of N-gly-
cosylamines (5–7, 9–11 & 13–15) benzene, p-xylene, m-xylene, o-
xylene and nitrobenzene were found to be best solvents for the
gelation process which may be attributed to a strong solute–
solvent interaction.
42
state. The phase transition temperature of compound 13 and
ꢀ
ꢁ1
its corresponding gel are T s ( C) 147 and DH (J g ) 116. The
g
melting temperature of the gelator and gel are obtained from
DSC experiments.
2
.4. Morphological studies
The morphology of azo-benzene based N-glycosylamines in the
solution and gel states were studied with SEM and HR-TEM Generally, the self-assembly of the molecules in the gel state
analysis (Fig. 3). was studied using powder X-ray diffraction studies of the
2
.6. Powder XRD analysis
4
3
SEM image (Fig. 3a) of N-glycosylamine 13, recorded imme- xerogel. The gel of azobenzene N-glycosylamine, 13 was
diately aer heating the compound 13 (0.5% w/v) in p-xylene, prepared at the concentration of 0.5% in p-xylene and
shows a bundles-like structure which is due to the identical allowed to stand at ambient temperature to obtain the xero-
state of the N-glycosylamine molecules in solution state. gel. From the XRD (Fig. 5) pattern, it was conrmed that the
However, cooling the solution to room temperature and led to self-assembly of gelator 13 was due to van der Waals force
the formation of a gel, which shows a nano-brous network between the alkyl chain and p–p interaction between the
(Fig. 3b). Therefore the SEM analysis revealed the conversion of azobenzene core. The strong diffraction at a low q angle of
bundle-like structure into nano-brous upon self-assembly in 6.969 corresponds to van der Waals force and a broad peak at
41
the gel state and HR-TEM image of compound 13 also showed 25.761 arises from p–p interaction of the azobenzene unit.
bers network (Fig. 3c and d). The SEM and HR-TEM analysis Peaks at q ¼ 6.002, 9.351, 12.811, 13.551, 14.384, 16.901,
clearly indicates the formation of gels due to self-assembly of 17.633 and 23.398 show the crystalline nature of the gel
the molecules. bers.

Table 2 Gelation studies of azo-benzene based N-glycosylamines (5–7, 9–11 & 13–15)
a
Status of compound (CGC%)
Solvent
5
6
7
9
10
11
13
14
15
CHCl
DCM
3
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
Hexane
EtOH
I
P
I
P
I
P
I
P
I
P
I
P
I
P
I
P
I
P
MeOH
DMF
P
S
P
S
P
S
P
S
P
S
P
S
P
S
P
S
P
S
THF
P
P
P
P
P
P
P
P
P
EtOAc
S
S
S
S
S
S
S
S
S
Toluene
p-Xylene
m-Xylene
o-Xylene
Benzene
PG
PG
PG
G (1)
G (1)
G (0.5)
G (1)
PG
PG
PG
PG
G (1)
PG
G (1)
PG
G (0.5)
PG
PG
PG
G (1)
G (1)
PG
G (1)
PG
G (0.5)
G (1)
PG
G (0.5)
G (0.5)
G (1.5)
G (1.5)
PG
G (2)
PG
G (0.5)
G (0.5)
G (1)
G (0.5)
G (0.5)
G (1.5)
G (2)
G (1)
G (2)
G (1)
G (0.5)
G (0.5)
G (1)
PG
G (1.5)
G (1.5)
G (2)
G (2)
G (2)
NO
2
-benzene
G (0.5)
a
G – gelation, PG – partial gelation, S – soluble, I – insoluble, P – precipitation, CGC – Critical Gelation Concentration.
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Fig. 6 Absorption spectra of compounds 12 (a), 13 (b) and 15 (c) in
ꢁ5
acetonitrile (1 ꢂ 10 M).
Fig. 3 SEM and HR-TEM images of compound, 13 from p-xylene: (a)
(
0.5% w/v p-xylene) solution; (b–d) gel.
3
. Experimental section
3
.1. Materials and methods
D-Glucose and O-phenylene diamine were purchased from Sd-
ne, India. Benzaldehyde, dimethyl acetal was purchased

from Sigma Aldrich chemicals Pvt. Ltd, USA. Paraldehyde,
potassium hydroxide, acetic anhydride, acetic acid and butyr-
aldehyde were purchased from SRL, India. Toluene and ethanol
were used aer distillation. Column chromatography was per-
formed on silica gel (100–200 mesh). NMR spectra were recor-
ded on a Bruker DRX 300 MHz, spectrometer. Elemental
analysis was performed by using PerkinElmer 2400 series
CHNS/O analyser. The gels were imaged with a HITACHI-S-
3400W Scanning Electron. Thermal transitions for gelators
and gels were determined on a NETZSCH DSC 204 instrument.
Diffractograms of the dried lms were recorded on XRD RINT
Fig. 4 DSC spectra of compound 13 and its gel in p-xylene.
2
500 diffractometer using Ni ltered Cu Ka radiation X-ray
2.7. Absorption studies
diffractograms of the dried lms were recorded on XRD RINT
2
500 diffractometer using Ni ltered Cu Ka radiation.
The chromophoric nature of the azobenzene based N-glycosyl-
amines 12, 13 & 15 was investigated using absorption spectros-
copy. The absorption spectra of N-glycosylamines have been
recorded at the concentration of 1 ꢂ 10 M in acetonitrile. The
compounds 12, 13 & 15 show characteristic absorption bands at
around 279 nm and 440 nm (Fig. 6). The change in the number of
methylene units in the alkyl chain and the 4, 6-O-protecting group
in the D-glucose unit does not inuence the absorption maxima.
0
3
.2. Synthesis of 2-acetamido-2 -amino-ortho-azobenzene (4)
ꢁ
5
33
Compound, 4 was prepared according to literature procedures
from o-phenylenediamine 2 (0.821 g, 7.58 mmol) and 2-nitro-
soacetanilide 3 (1.25 g, 7.71 mmol). The residue was puried
by ash column chromatography (SiO , hexane/EtOAc, 1 : 1),
43
2
and it was obtained as red solid in 70% yield (1.35 g): mp 148–
ꢀ
ꢀ
1
1
8
50 C (lit. 143 C); H NMR (300 MHz, CDCl
.63 (d, J ¼ 8.3 Hz, 1H), 7.70 (dd, J ¼ 8.1, 1.6 Hz, 1H), 7.62 (dd, J
8.1, 1.3 Hz, 1H), 7.45–7.37 (m, 1H), 7.29–7.22 (m, 1H), 7.18–
3
) d 9.95 (s, 1H),
¼
1
3
7
.10 (m, 1H), 6.87–6.71 (m, 2H), 5.40 (s, 2H), 2.27 (s, 3H);
C
3
NMR (75 MHz, CDCl ) d 168.6, 145.0, 137.5, 135.5, 133.2, 131.8,
1
24.4, 123.5, 122.2, 120.5, 120.2, 118.0, 117.4, 25.5. HRMS (ESI)
+
m/z calcd [M + Na] : 277.10517 found 277.10598.
0
3
.3. Synthesis of 2,2 -diamino-ortho-azobenzene (8)
Compound, 8 was prepared according to the literature proce-
33
0
dures. A solution of 2-acetamido-2 -amino-ortho-azobenzene 4
740 mg, 2.91 mmol) in 138 mL of ethanol was treated with
(
a solution of KOH (12.1 g, 215 mmol) in 80 mL of ethanol and
ꢀ
Fig. 5 Powder XRD diffraction of xerogel, 13 (p-xylene 0.5%).
32 mL of water. The mixture was heated to 90 C. Aer 1 h, the
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mixture was poured into 500 g of ice and extracted with CH
2
Cl
2
.
and 4,6-O-ethylidene-b-D-glucopyranose 1b (1.0 mmol, 0.5 g) as
ꢀ
1
It was dried over Na SO and concentrated to yield 0.583 g a red solid. Yield: 0.50 g (81%); mp 142–144 C; H NMR (CDCl
3
2
4
ꢀ
1
(
8
4
94%): mp 136–138 C; H NMR (300 MHz, CDCl ) d 7.68 (dd, J ¼ + DMSO-d , 300 MHz), d 8.89 (d, J ¼ 8.1 Hz, 1H, Ar-H), 8.09 (d, J
3
6
.0, 1.4 Hz, 2H), 7.21–7.14 (m, 2H), 6.83–6.74 (m, 4H), 5.49 (s, ¼ 7.8 Hz, 1H, Ar-H), 8.03 (d, J ¼ 8.4 Hz, 1H, Ar-H), 7.84 (s, 1H, Ar-
37
H). The analytical data corresponds to the literature. HRMS H), 7.76 (t, J ¼ 7.8 Hz, 1H, Ar-H), 7.50–7.63 (m, 2H, Ar-H), 7.23
+
(
ESI) m/z calcd [M + H] : 213.11275 found 213.11347.
(d, J ¼ 8.1 Hz, 1H, –NH), 7.13 (t, J ¼ 7.5 Hz, 1H, Ace-H), 5.54 (s,
1
H, Sac-H), 4.40–4.51 (m, 2H, Sac-H), 4.43 (t, J ¼ 5.1 Hz, 1H,
00
.4. Synthesis of 2-acetamido-2 -amino-ortho-
Ano-H), 4.24 (t, J ¼ 7.8 Hz, 1H, –NH), 3.87 (d, J ¼ 12 Hz, 2H, Sac-
3
H), 3.85–3.94 (m, 2H, Sac-H), 3.62–3.70 (m, 2H, Sac-OH), 2.63 (s,
bisazobenzene (12)
1
3
3
H, –NHCOCH ), 1.72 (d, J ¼ 6 Hz, 3H, Sac-CH ). C NMR
3
3
Compound, 12 was prepared according to the literature proce-
(CDCl + DMSO-d , 75 MHz) d 177.07, 148.98, 146.66, 142.52,
33
0
3 6
dures from a solution of 2,2 -diaminodiazobenzene 8 (300 mg,
.41 mmol) and 2-nitrosoacetanilide 3 (230 mg, 1.41 mmol).
1
1
2
42.18, 136.44, 136.32, 129.86, 127.48, 123.06 (2C), 121.86,
18.30, 107.07, 90.36, 85.19, 79.26, 79.01, 73.14, 72.26, 41.01,
2.19. Anal. calcd for C22H N O : C, 59.72; H, 5.92; N, 12.66.
26 4 6
1
Aer 2.5 days, the solvent was removed under reduced pressure,
and the residue was puried by ash column chromatography
Found: C, 59.54; H, 5.90; N, 12.55. HRMS (ESI) m/z calcd [M +
(
SiO , hexane/EtOAc, 2 : 1). The product was obtained as a red
2
+
Na] : 465.17401 found 465.17446.
ꢀ
1
solid (80.3 mg, 16%): mp 158–162 C; H NMR (300 MHz,
3
.5.3. Physicochemical and spectral data for 4,6-O-benzy-
CDCl ) d 10.12 (s, 1H), 8.69 (d, J ¼ 8.3 Hz, 1H), 7.88 (dd, J ¼ 8.1,
3
0
lidene-N-(2-acetamido-2 -amino-ortho-azobenzyl)-b-D-glucopyr-
1
1
.5 Hz, 1H), 7.85 (dd, J ¼ 8.1, 1.5 Hz, 1H), 7.81 (dd, J ¼ 7.9,
.5 Hz, 1H), 7.72 (dd, J ¼ 7.7, 1.6 Hz, 1H), 7.62–7.44 (m, 3H), 7.20
anosyl amine, 7. Compound, 7 was obtained by the reaction of
0
2
-acetamido-2 -amino-ortho-azobenzene 4 (1.2 mmol, 0.56 g)
(
8
dd, J ¼ 15.3, 8.4, 1.4 Hz, 2H), 6.87–6.81 (m, 1H), 6.74 (dd, J ¼
and 4,6-O-benzylidene-b-D-glucopyranose 1c (1.0 mmol, 0.5 g) as
.2, 1.0 Hz, 1H), 6.31 (s, 2H), 2.00 (s, 3H). The analytical data
ꢀ
1
a red solid. Yield: 0.40 g (88%); mp 140–143 C; H NMR (CDCl
3
37
+
correspond to the literature. HRMS (ESI) m/z calcd [M + Na] :
+
8
2
6
DMSO-d
6
, 300 MHz), d 8.69 (d, J ¼ 8.4 Hz, 1H Ar-H), 7.91 (d, J ¼
381.14265 found 381.14343.
.1 Hz, 1H, Ar-H), 7.64–7.73 (m, 2H, Ar-H), 7.48 (d, J ¼ 5.4 Hz,
H, Ar-H), 7.15–7.21 (m, 2H, Ar-H), 6.85 (d, J ¼ 8.4 Hz, 3H, Ar-H),
.74 (t, J ¼ 8.1 Hz, 2H, Ar-H), 5.52 (s, 2H, Ace-H), 5.1 (s, 1H, Sac-
3.5. General procedure for the synthesis of N-glycosylamines
(
5–7, 9–11 & 13–15)
H), 4.64 (t, J ¼ 6.6 Hz, 1H, Ano-H), 4.20–4.30 (m, 2H, Sac-H),
To a solution of 1.0 mmol of the 4,6-O-protected-b-D-glucopyr- 3.91–4.02 (d, J ¼ 4.8 Hz, 1H, –NH), 3.70–3.75 (m, 2H, Sac-OH),
1
3
anose 1a–c in 10 mL of ethanol, was added 1.2 mmol of the azo- 3.44–3.51 (m, 3H, Sac-H), 2.50 (s, 3H, –NHCOCH
3
). C NMR
benzene based amine 4, 8, 12. The reaction was then stirred at (CDCl + DMSO-d , 75 MHz) d 173.6, 150.0, 141.6, 140.0 (2C),
3
6
room temperature, the reactants dissolved within 5–10 minutes. 137.6, 135.5, 133.7, 132.8 (2C), 131.3 (2C), 127.8, 126.4, 123.5,
Progress of the reaction was monitored by TLC, which was then 122.1, 121.5, 120.6 (2C), 106.4, 98.6, 86.6, 80.8, 73.9, 71.1, 66.9,

ltered and dried.
29.6. Anal. calcd for C27
H
28
N
4
O
6
: C, 64.27; H, 5.59; N, 11.10.
3
.5.1. Physicochemical and spectral data for 4,6-O-butyli- Found: C, 64.10; H, 5.20; N, 11.05.
0
dene-N-(2-acetamido-2 -amino-ortho-azobenzyl)-b-D-glucopyr-
3.5.4. Physicochemical and spectral data for 4,6-O-butyli-
anosyl amine, 5. Compound, 5 was obtained by the reaction of dene-N-(2,2 -diamino-ortho-azobenzyl)-b-D-glucopyranosyl
0
0
0
2
-acetamido-2 -amino-ortho-azobenzene 4 (1.2 mmol, 0.65 g) amine, 9. Compound, 9 was obtained by the reaction of 2,2 -
and 4,6-O-butylidene-b-D-glucopyranose 1a (1.0 mmol, 0.5 g) as diamino-ortho-azobenzene 8 (0.50 mmol, 0.3 g) and 4,6-O-
ꢀ
1
a red solid. Yield: 0.82 g (82%); mp 140–143 C; H NMR (CDCl
butylidene-b-D-glucopyranose 1a (1.0 mmol, 0.54 g) as a red
3
ꢀ
1
+
DMSO-d
m, 2H, Ar-H), 7.58 (t, 1H, Ar-H), 7.47 (m, 1H, Ar-H), 7.27–7.30 DMSO-d
d, J ¼ 9 Hz, 1H, Ar-H), 7.12–7.18 (m, 1H, Ar-H), 6.09 (s, 2H, Ar- 7.5 Hz, 2H, Ar-H), 6.80 (d, J ¼ 7.8 Hz, 3H, Ar-H), 6.70 (t, J ¼
6
, 300 MHz), d 8.61 (d, J ¼ 6 Hz, 1H, Ar-H), 7.96–8.03 solid. Yield: 0.50 g (71%); mp 140–142 C; H NMR (CDCl
3
+
(
(
6
, 300 MHz), d 7.62 (d, J ¼ 9.0 Hz, 2H Ar-H), 7.12 (t, J ¼
H), 5.67 (s, 1H, Ace-H), 5.19 (d, J ¼ 3 Hz, 1H, Sac-H), 5.09 (t, J ¼ 7.5 Hz, 1H, –NH), 6.29 (s, 1H, Ar-H), 5.99 (s, 2H, Ace-H), 4.82 (d, J
3
1
2
Hz, 1H, Sac-H), 4.90 (t, J ¼ 6 Hz, 1H, Ano-H), 4.51 (d, J ¼ 6 Hz, ¼ 4.8, 2H, Ano-H), 4.74–5.12 (m, 3H, Sac-H), 4.55 (d, J ¼ 11.4 Hz,
H, –NH), 3.81–3.84 (m, 2H, Sac-H), 3.66 (s, 2H, Sac-OH), 2.90 (s, 4H, Sac-H), 4.00–4.19 (m, 3H, Sac-H), 4.18 (d, J ¼ 6.9 Hz, 1H,
H, Sac-H), 2.63 (s, 3H, –NHCOCH ), 1.97 (t, J ¼ 4.5 Hz, 2H, Sac- –NH), 3.59 (d, J ¼ 9.3 Hz, 2H, Sac-H), 3.41–3.56 (m, 4H, Sac-OH),
3
1
3
CH ), 1.77 (m, 2H, Sac-CH ), 0.45 (s, 3H, Sac-CH ). C NMR 1.58 (d, J ¼ 4.8 Hz, 4H, Sac-CH
2
), 1.37–1.44 (m, 4H, Sac-CH
2
),
2
2
3
1
3
(CDCl
3
+ DMSO-d
6
, 75 MHz) d 173.6, 149.8, 141.8, 139.9, 138.0, 0.92 (t, J ¼ 7.5 Hz, 6H, Sac-CH
3 3 6
). C NMR (CDCl + DMSO-d
, 75
1
7
37.7, 135.8, 128.3, 127.7, 125.6, 124.3, 122.1, 121.9, 107.1, 85.0, MHz) d 142.7, 130.2, 123.1, 116.1, 115.85 101.2, 96.6, 92.1, 80.1,
9.2, 78.1, 73.4, 73.1, 67.0, 35.7, 29.8, 22.1, 18.7. Anal. calcd for 77.1, 75.0, 72.4, 69.6, 35.3, 16.4, 13.0. Anal. calcd for
C
6
4
24
H
30
N
4
O
6
: C, 61.26; H, 6.43; N, 11.91. Found: C, 60.54; H,
C H N O10: C, 59.61; H, 6.88; N, 8.69. Found: C, 58.60; H,
32 44 4
+
+
.33; N, 11.85. HRMS (ESI) m/z calcd [M + Na] : 493.20544 found 6.60; N, 8.50. HRMS (ESI) m/z calcd [M + Na] : 667.29244 found
93.20516.
667.29496.
.5.2. Physicochemical and spectral data for 4,6-O-ethyl- 3.5.5. Physicochemical and spectral data for 4,6-O-ethyl-
3
0
0
idene-N-(2-acetamido-2 -amino-ortho-azobenzyl)-b-D-glucopyr-
idene-N-(2,2 -diamino-ortho-azobenzyl)-b-D-glucopyranosyl
anosyl amine, 6. Compound, 6 was obtained by the reaction of amine, 10. Compound, 10 was obtained by the reaction of 2,2 -
0
0
2
-acetamido-2 -amino-ortho-azobenzene 4 (1.2 mmol, 0.73 g) diamino-ortho-azobenzene 8 (0.50 mmol, 0.3 g) and 4,6-O-
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ethylidene-b-D-glucopyranose 1b (1.0 mmol, 0.48 g) as a red (0.5 mmol, 0.5 g) as a red solid. Yield: 1.00 g (76%); mp 152–
ꢀ
1
ꢀ
1
solid. Yield: 0.50 g (78%); mp 141–143 C; H NMR (CDCl + 154 C; H NMR (CDCl + DMSO-d , 300 MHz), d 8.65 (d, J ¼
3
3
6
DMSO-d , 300 MHz), d 8.23 (d, J ¼ 6.0 Hz, 1H Ar-H), 7.61–7.83 8.1 Hz, 2H, Ar-H), 7.76–7.93 (m, 3H, Ar-H), 7.60 (t, J ¼ 7.5 Hz,
6
(
m, 3H, Ar-H), 7.10–7.20 (m, 2H, Ar-H), 6.98 (d, J ¼ 8.4 Hz, 2H, 1H, Ar-H), 7.54 (t, J ¼ 6.3 Hz, 1H, Ar-H), 7.21–7.35 (m, 2H, Ar-H),
Ar-H), 6.69 (t, J ¼ 7.8 Hz, 1H, Aro-H), 6.42 (s, 2H, Ace-H), 5.03 (d, 6.97 (d, J ¼ 8.7 Hz, 1H, Ar-H), 6.71–6.91 (m, 2H, Ar-H), 6.16 (s,
J ¼ 6.8 Hz, 3H, Sac-H), 4.90 (s, 2H, Sac-H), 4.72 (t, J ¼ 4.8 Hz, 1H, 1H, –NH), 5.16 (s, 1H, Ace-H), 4.71–4.76 (q, J ¼ 4.8 Hz, 1H, Ano-
Ano-H), 4.54 (t, J ¼ 5.7 Hz, 1H, –NH), 3.98–4.09 (m, 2H, Sac-H), H), 4.41 (s, 1H, –NH), 4.61 (s, 3H, Sac-H), 4.02–4.12 (m, 1H, Sac-
3
¼
.77–3.82 (m, 4H, Sac-OH), 3.19–3.3.26 (m, 4H, Sac-H), 1.33 (t, J H), 3.83–3.89 (q, J ¼ 4.2 Hz, 2H, Sac-OH), 3.46–3.54 (m, 1H, Sac-
1
3
3 3 6 3
4.8 Hz, 6H, Sac-CH ). C NMR (CDCl + DMSO-d , 75 MHz) H), 3.21–3.32 (m, 1H, Sac-H), 1.88 (s, 3H, –NHCOCH ), 1.37 (t, J
1
3
d 139.9, 137.7, 135.8, 128.3, 124.2 (2C), 104.1, 97.8, 85.6, 80.7, ¼ 4.8 Hz, 3H, Sac-CH ). C NMR (CDCl + DMSO-d , 75 MHz)
3
3
6
7
8.1, 75.4, 66.8, 29.8. Anal. calcd for C H N O : C, 57.13; H, d 174.2, 152.3, 147.7, 142.6, 140.3, 138.4, 136.3 (2C), 134.8, 132.4
28 36 4 10
6
.16; N, 9.52. Found: C, 56.80; H, 5.90; N, 8.90. HRMS (ESI) m/z (2C), 128.0 (2C), 125.5, 124.0, 123.2, 118.5 (2C), 104.1, 102.2,
+
calcd [M ꢁ H] : 588.24314 found 587.23621.
97.8, 85.6, 80.8, 78.2, 73.3, 66.8, 29.5, 25.1. Anal. calcd for
28 30 6 6
C H N O : C, 61.53; H, 5.53; N, 15.38. Found: C, 61.20; H,
5.40; N, 15.20.
3
.5.6. Physicochemical and spectral data for 4,6-O-benzy-
0
lidene-N-(2,2 -diamino-ortho-azobenzyl)-b-D-glucopyranosyl
amine, 11. Compound, 11 was obtained by the reaction of 2,2 -
diamino-ortho-azobenzene 8 (0.50 mmol, 0.3 g) and 4,6-O-ben- lidene-N-(2-acetamido-2 -amino-ortho-bisazobenzyl)-b-D-gluco-
zylidene-b-D-glucopyranose 1c (1.0 mmol, 0.63 g) as a red solid. pyranosyl amine, 15. Compound, 15 was obtained by the
Yield: 0.65 g (83%); mp 142–144 C; H NMR (CDCl + DMSO-d , reaction of 2-acetamido-2 -amino-ortho-bisazobenzene, 12
0
3.5.9. Physicochemical and spectral data for 4,6-O-benzy-
0
0
ꢀ
1
00
3
6
3
00 MHz), d 7.60 (d, J ¼ 8.1 Hz, 2H, Ar-H), 7.50 (d, 2H, Ar-H), (0.52 mmol, 0.54 g) and 4,6-O-ethylidene-b-D-glucopyranose 1c
7
.47 (d, J ¼ 3.9 Hz, 4H, Ar-H), 7.32 (t, J ¼ 6 Hz, 4H, Ar-H), 7.11 (0.5 mmol, 0.5 g) as a red solid. Yield: 0.85 g (85%); mp 153–
ꢀ
1
(
1
t, J ¼ 6.9 Hz, 1H, Ar-H), 6.93 (s, 2H, Ar-H), 6.80 (d, J ¼ 8.1 Hz, 155 C; H NMR (CDCl
3
+ DMSO-d
6
, 300 MHz), d 8.52 (d, J ¼
H, Ar-H), 6.68 (t, J ¼ 7.2 Hz, 1H, Ar-H), 6.45 (s, 1H, Ar-H), 6.05 8.1 Hz, 1H, Ar-H), 8.10 (t, 3H, Ar-H), 7.73 (d, J ¼ 5.4 Hz, 1H, Ar-
(
4
5
s, 1H, Ace-H), 5.10 (d, J ¼ 7.8 Hz, 2H, –NH), 4.97 (s, 2H, Ano-H), H), 7.65 (d, J ¼ 7.5 Hz, 2H, Ar-H), 7.40–7.51 (m, 3H, Ar-H), 7.25
.59 (d, J ¼ 3.3 Hz, 1H, Sac-H), 4.38 (s, 1H, –NH), 4.15–4.27 (m, (d, J ¼ 3.3 Hz, 3H, Ar-H), 7.10 (t, J ¼ 7.5 Hz, 2H, Ar-H), 6.69–6.76
H, Sac-H), 3.86 (t, J ¼ 8.4 Hz, 2H, Sac-H), 3.63–3.94 (m, 6H, Sac- (m, 4H, Ar-H, –NH), 6.10 (s, 1H, Ar-H), 5.43 (s, 1H, Ace-H), 5.12
1
3
H, Sac-OH), 3.48 (s, 2H, Sac-H). C NMR (CDCl + DMSO-d , 75 (s, 1H, –NH), 4.59 (s, 1H, Ano-H), 4.41 (d, 1H, Sac-H), 4.11–4.20
3
6
MHz) d 136.8, 136.7, 128.0 (2C), 127.1 (2C), 125.6 (2C), 125.6, (m, 1H, –NH), 3.77–3.97 (m, 1H, Sac-H), 3.66 (d, J ¼ 6.6 Hz, 2H,
1
3
1
23.0, 100.7, 100.6, 92.3, 80.8, 80.1, 75.0, 72.3, 69.5, 68.2. Anal. Sac-H), 3.37–3.67 (m, 2H, Sac-OH), 1.95 (s, 3H, –NHCOCH
calcd for C38 10: C, 64.04; H, 5.66; N, 7.86. Found: C, NMR (CDCl + DMSO-d , 75 MHz) d 168.9, 147.5 (2C), 142.5,
3.80; H, 5.60; N, 7.50. 139.6, 137.3, 136.0 (2C), 132.7, 132.5 (2C), 131.4, 130.7, 129.9,
.5.7. Physicochemical and spectral data for 4,6-O-butyli- 128.8, 127.9, 126.3, 123.3 (2C), 120.5, 118.1, 117.1, 116.9 (2C),
3
).
C
H
40
N
4
O
3
6
6
3
0
0
dene-N-(2-acetamido-2 -amino-ortho-bisazobenzyl)-b-D-gluco-
116.5, 101.6, 97.4, 93.0, 81.4, 73.2, 68.6, 62.0, 24.8. Anal. calcd
pyranosyl amine, 13. Compound, 13 was obtained by the for C H N O : C, 65.12; H, 5.30; N, 13.81. Found: C, 64.90; H,
3
3
32
6
6
0
0
reaction of 2-acetamido-2 -amino-ortho-bisazobenzene 12 5.20; N, 13.60.
(1.2 mmol, 0.91 g) and 4,6-O-butylidene-b-D-glucopyranose 1a
(
1
8
1.0 mmol, 0.5 g) as a red solid. Yield: 0.80 g (66%); mp 156–
ꢀ
1
4. Conclusion
, 300 MHz), d 8.63 (d, J ¼
58 C; H NMR (CDCl
.4 Hz, 1H, Ar-H), 7.79–7.85 (m, 2H, Ar-H), 7.72 (t, J ¼ 5.7 Hz, 1H,
3
+ DMSO-d
6
By introducing 4,6-O-protected glucose core into azobenzene
moiety, we obtained a versatile gelator which can widely gel
varieties of organic solvents. The electron microscopy and
spectral studies showed that the gel formation is due to aggre-
gation of molecules into aggregated bundles or helical bres
through cooperative interactions of hydrogen bonding of sugar
moiety, p–p interactions of azobenzene groups, and hydro-
phobicity of alkyl chains. From this we have obtained new
insight toward the molecular design in more effective organo-
gelator for organic solvents. Despite from the wide study of
azobenzenes this class of molecules shows exciting activities.
The biological evaluation of the compounds are under progress
and we are planing to reveal those informations in our
upcoming research paper.
Ar-H), 7.53–7.59 (m, 2H, Ar-H), 7.40–7.47 (m, 2H, Ar-H), 7.19 (d, J
5.1 Hz, 3H, Ar-H), 6.80 (t, J ¼ 6.0 Hz, 2H, Ar-H), 5.87 (s, 1H,
¼
Ace-H), 4.54 (t, J ¼ 5.1 Hz, 1H, Ano-H), 4.05–4.10 (q, J ¼ 4.8 Hz,
1
3
–
H, –NH), 3.84–3.90 (m, 3H, Sac-H), 3.47–3.51 (m, 2H, Sac-OH),
.20–3.33 (m, 2H, Sac-H), 2.70 (s, 1H, Sac-H), 2.02 (s, 3H,
NHCOCH
3
), 1.62 (t, J ¼ 4.5 Hz, 2H, Sac-H), 1.39–1.46 (q, J ¼
.2 Hz, J ¼ 7.5 Hz, 2H, Sac-H), 0.91 (t, J ¼ 7.5 Hz, 3H, Sac-CH ).
, 75 MHz) d 168.6, 147.2, 147.1,
7
3
1
3
3 6
C NMR (CDCl + DMSO-d
1
1
7
42.1, 139.3, 137.1, 135.7, 132.5 (2C), 132.3, 131.1, 130.3, 129.6,
23.0, 120.1, 118.0, 116.8, 116.7, 116.4, 101.9, 97.0, 80.4, 73.0,
0.6, 68.3, 61.9, 35.9, 24.6, 17.0, 13.5. Anal. calcd for
C H N O : C, 62.71; H, 5.96; N, 14.63. Found: C, 61.90; H,
5
3
0
34 6 6
.80; N, 14.50.
3
.5.8. Physicochemical and spectral data for 4,6-O-ethyl-
0
0
idene-N-(2-acetamido-2 -amino-ortho-bisazobenzyl)-b-D-gluco-
pyranosyl amine, 14. Compound, 14 was obtained by the
reaction of 2-acetamido-2 -amino-ortho-bisazobenzene, 12
Conflicts of interest
0
0
(0.52 mmol, 1.04 g) and 4,6-O-ethylidene-b-D-glucopyranose 1b There are no conicts to declare.
This journal is © The Royal Society of Chemistry 2019
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G. V. Bochicchio and S. R. Raghavan, Biomaterials, 2011,
Acknowledgements
32, 3351.
T. M. thank Central University of Tamil Nadu (CUTN), Thir- 20 N. Koumura, M. Kudo and N. Tamaoki, Langmuir, 2004, 20,
uvarur, Tamil Nadu for the infrastructure facility. P. V. B. & V. R.
J. acknowledges CUTN for research fellowship.
9895.
21 J. Seo, J. W. Chung, J. E. Kwon and S. Y. Park, Chem. Sci.,
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2 (a) N. S. S. Kumar, S. Varghese, G. Narayan and S. Das,
Angew. Chem., Int. Ed., 2006, 45, 6317; (b) S. Abraham,
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