The synthesis and dyes complexation properties of novel cyclodextrin derivatives with large conjugate acylhydrazone group

Article abstract of DOI:10.1007/s10847-015-0501-3

By reacting β-cyclodextrin with 4-(prop-2-ynyloxy)benzaldehyde, the cyclodextrins (CDs) aromatic aldehyde derivative 6 was prepared in yield of 80 % via click chemistry of the Huisgen [2 + 3] cycloaddition reaction. Further Schiff-base condensation of com

Full text of DOI:10.1007/s10847-015-0501-3

J Incl Phenom Macrocycl Chem
DOI 10.1007/s10847-015-0501-3
ORIGINAL ARTICLE
The synthesis and dyes complexation properties
of novel cyclodextrin derivatives with large conjugate
acylhydrazone group
Zusheng Wang1 Hongyu Guo1 Fafu Yang1,2 Yingmei Zhang1
•
•
•
Received: 27 January 2015 / Accepted: 18 March 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract By reacting b-cyclodextrin with 4-(prop-2-
ynyloxy)benzaldehyde, the cyclodextrins (CDs) aromatic
aldehyde derivative 6 was prepared in yield of 80 % via
click chemistry of the Huisgen [2 ? 3] cycloaddition re-
action. Further Schiff-base condensation of compound 6
with salicylic hydrazide, nicotinohydrazide, or 2,4-dini-
trophenylhydrazine, novel cyclodextrin derivatives with
large conjugate acylhydrazone group 7a, 7b and 7c were
conveniently obtained in yields of 75–85 %. Their struc-
tures were confirmed by elemental analysis, FT-IR, ESI–
MS and NMR spectra. Their complexation properties for
Orange I and Neutral red were studied by fluorescence
titration spectroscopy and complexation MS spectrum. The
results suggested that these novel CDs derivatives with
large conjugate acylhydrazone group showed excellent
complexation abilities for the tested dyes. The association
constants were higher than 104 and the highest associations
constant was 5.85 9 104 for host 7a with OI. The 1:1
complexes were formed in DMSO solution.
Introduction
In recent years, cyclodextrins (CDs) have been extensively
used in many research fields such as food chemistry, ana-
lytical chemistry, biology, and pharmacy due to their ap-
pealing unique binding properties [1–7]. But the
complexation properties of native CDs are generally lim-
ited and the more elaborated structures are often needed for
binding guests effectively. As a result, various functional
groups and unique structural units were introduced into
CDs to obtain novel CDs derivatives with interesting
binding properties up to now [1–7]. However, due to the
difficulties of selective modifications of the hydroxyl
groups on CDs, the varieties and amounts of CDs deriva-
tives were far fewer than that of other organic supramo-
lecules, such as crown ethers and calixarenes. One pathway
to solve this problem is to synthesize efficiently CDs in-
termediate derivatives containing active-terminal func-
tional groups, which can be used as new synthetic platform
to construct novel CDs derivatives by reacting easily with
other molecules. For example, the CDs derivatives with
terminal amino-group prepared by reacting mono-6-tosyl-
b-CD with corresponding amines, were applied to con-
struct some CDs derivatives by addition reaction or am-
monolysis reaction, etc. [8–10]. It is well known that the
aldehyde group is an important active functional group,
which could be easily transformed to other derivatives by
reducing, oxidizing, addition or condensation reaction.
Thus, the first CD aliphatic aldehyde derivative was re-
ported by oxidation of hydroxyl group as early as in 1994
[11]. Subsequently, several different oxidizing methods for
hydroxyl groups of CDs were reported to prepare the CDs
aliphatic aldehyde derivatives [12–14]. Also, by the further
addition and oxidizing reaction of these aldehyde deriva-
tives, some interesting CDs derivatives with unique
Keywords Cyclodextrin ꢀ Acylhydrazone ꢀ Synthesis ꢀ
Complexation ꢀ Dye
& Fafu Yang
yangfafu@fjnu.edu.cn
1
College of Chemistry and Chemical Engineering, Fujian
Normal University, Fuzhou 350007,
People’s Republic of China
2
Fujian Key Laboratory of Polymer Materials,
Fuzhou 350007, People’s Republic of China
123

J Incl Phenom Macrocycl Chem
functional groups were obtained [15–18]. But no conden-
sation reaction, such as Schiff-base condensation, was re-
ported due to the unstably reversible condensation process
of aliphatic aldehyde. If the aromatic aldehyde group is
introduced into CDs, obviously, the obtained CDs aromatic
aldehyde derivative would possess better reaction activities
and could be transformed effectively to all kinds of CDs
derivatives based on the stable aromatic conjugate structure
comparing with the aliphatic aldehyde. Moreover, it is
expected that this kind of CDs derivatives with aromatic
conjugate group would exhibit better complexation prop-
erties for some guests, such as organic dyes, due to the
effective p–p stacking action between the aromatic con-
jugate structure on CDs and the aromatic conjugate struc-
ture of organic dyes [19–21]. However, no such CDs
derivative was described up to now. On the other hand, it
was well-known that the CuI-catalyzed click chemistry,
which react easily azide group with alkynyl group, had
been used to prepare CDs derivatives effectively [22–27].
Considering the significance of CDs aromatic aldehyde
derivative as the synthetic platform to construct other CDs
derivatives, in this paper, we described the first synthesis of
CDs aromatic aldehyde derivative via a facile click reac-
tion. Moreover, we prepared novel cyclodextrin derivatives
with large conjugate acylhydrazone group for the first time,
and their preliminary complexation properties for organic
dyes were also investigated.
water bath, with excitation and emission slits 10 nm wide.
The excitation wavelengths were 290 nm. In the fluores-
cence titration experiments, the concentrations of hosts
7a,7b and 7c were 1 9 10-4 M and the concentrations of
dyes were 0, 0.2, 0.4, 0.6, 0.8, 1.0, 2.0 9 10-6 M, re-
spectively, in the phosphate buffer (pH = 7.20). The stoi-
chiometry of the complexes was determined by the Job
method of continuous variations. The association constant
was calculated by Benesi–Hilderbrand formula with non-
linear curve fitting procedure [29].
Synthesis of CDs aromatic aldehyde derivative 6
Compound 5 (0.18 g, 1.1 mmol) with compound 3 (1.16 g,
1 mmol) was carried out in DMF (35 mL) in the presence
of CuI generated by the reduction of copper sulfate
(0.28 g,1.1 mmol) with sodium ascorbate (0.48 g, 2.4 mmol).
The mixture was stirred at room temperature for 15 h. TLC
detection indicated the disappearance of materials of
compound 3. After reaction, most of the solvent was
evaporated under reduced pressure and 20 mL of distilled
water was added with vigorous stirring at room tem-
perature. The mixture was stored in the refrigerator over-
night and then the precipitate was collected by filtration.
The precipitate was further purified by recrystallization in
DMF/acetone for three times. Compound 6 was obtained as
grey white solid in yield of 80 %. Compound 6: IR/cm-1
:
1
3387, 2927, 1679, 1599, 1509, 1157, 1031, 756; H NMR
(400 MHz, DMSO-d6) d ppm: 2.78–4.10 (m, 40H, CH and
CH2), 4.25–4.68 (8H, OH and NCH2), 4.69–5.10 (m, 7H,
CH), 5.23 (s, 2H, CH2O), 5.53–5.99 (m, 14H, OH), 7.24 (d,
J = 8.0 Hz, 2H, ArH), 7.88 (d, J = 8.0 Hz, 2H, ArH),
8.22 (s, 3H, NCH); 9.87 (s, 1H, CHO). 13C NMR
(100 MHz, DMSO-d6) d ppm: 191.9, 163.5, 142.4, 132.3,
130.3, 126.2, 115.6, 102.6, 101.7, 83.9, 82.5, 82.1, 81.4,
73.7, 73.6, 73.4, 73.1, 72.9, 72.6, 72.2, 70.5, 61.8, 60.4,
60.0, 59.5, 50.5. MS m/z (%): 1342.3(MNa?, 100). Anal.
Calcd. For C52H77N3O36: C47.31, H5.88, N3.18; found
C47.38, H5.82, N3.22 %. Mp 288–291 °C (dec).
Experimental
Materials and instruments
All chemicals were purchased from commercial suppliers
and used without further purification. The other organic
solvents and inorganic reagents were purified according to
standard anhydrous methods before use. TLC analysis was
performed using pre-coated silica gel glass plates. IR
spectra were recorded on a Perkin-Elmer PE-983 infrared
spectrometer as KBr pellets with absorption in cm-1.1H
NMR spectra was recorded in DMSO-d6 on a Bruker-ARX
600 instrument at 30 °C. Chemical shifts are reported in
ppm, using tetramethylsilane (TMS) as internal standard.
ESI–MS spectra were obtained from DECAX-30000 LCQ
Deca XP mass spectrometer. Elemental analyses were
performed at Vario EL III Elemental Analyzer. 4-(Prop-2-
ynyloxy)benzaldehyde 5 were conveniently prepared by
reacting 4-hydroxybenzaldehyde, with 3-bromoprop-1-yne
under K2CO3/MeCN system in yields of 87 % [28].
Synthesis of CDs derivatives 7a, 7b and 7c
Under N2 atmosphere, a mixture of compound 6 (0.265 g,
0.2 mmol) and corresponding amino-compound (salicy-
loylhydrazine, nicotinichydrazide or 2,4-dinitrophenylhy-
drazine) (0.4 mmol) was stirred in 15 mL of DMF solution.
The reaction system was heated at 55 °C for 8–18 h. TLC
detection indicated the disappearance of compound 6. Then
the solvent was evaporated by reduced pressure. Fifteen
milliliter of MeOH was added and the precipitation was
formed. The precipitation was recrystallized in MeOH/
Fluorescence spectra were measured in a conventional
quartz cell (10 9 10 9 45 nm) at 25 °C on a Hitachi
F-4500 spectrometer equipped with a constant-temperature
123

J Incl Phenom Macrocycl Chem
CHCl3 and washed by 10 mL of MeOH and 10 mL of
acetone subsequently.
Results and discussion
Compound 7a was obtained by refluxing 8 h as brown
powder in yield of 84 %. Compound 7a: IR/cm-1: 3415,
2927, 1605, 1508, 1306, 1079, 1031, 756; 1H NMR
(400 MHz, DMSO-d6) d ppm: 2.82–4.11 (m, 40H, CH and
CH2), 4.22–4.70 (8H, OH and NCH2), 4.71–5.11 (m, 7H,
CH), 5.18 (s, 2H, CH2O), 5.61–5.97 (m, 15H, OH), 6.92 (s,
2H, ArH), 7.18 (s, 2H, ArH), 7.42 (s, 1H, ArH), 7.71 (s,
2H, ArH), 7.92 (s, 1H, ArH), 8.21 (s, 1H, NCH), 8.41 (s, 1,
CH), 11.86 (s, 1H, NH). 13C NMR (100 MHz, DMSO-d6) d
ppm: 166.1.9, 162.8, 157.1, 142.8, 141.6, 132.8, 131.6,
129.6, 126.7, 122.4, 115.6 110.6, 101.9, 101.8, 101.7,
101.6, 101.1,83.2, 82.1, 81.8, 81.0, 73.3, 73.1, 72.9, 72.7,
72.5, 72.1, 71.7, 70.1, 61.7, 60.1, 59.8, 59.6, 58.7, 50.2. MS
m/z (%): 1452.8(M?, 100). Anal. Calcd. For C59H83N5O37:
C48.73, H5.75, N4.82; found C48.69, H5.71, N4.86 %. Mp
276–279 °C (dec).
Synthesis and characterization
Initially, we tried to prepare the CDs aromatic aldehyde
derivative by the nucleophilic substitution reaction of CD
derivative 2 with 4-hydroxybenzaldehyde as shown in
Scheme 1. However, this reaction failed to afford any
product under all kinds of reaction systems, such as
K2CO3/H2O, K2CO3/DMF, K2CO3/MeCN, NaOH/DMF,
NaOH/THF, NaOH/H2O, etc. The reason might be at-
tributed to the unfavorable influences of the strong hy-
drogen bonding between the phenolate and the multiple
hydroxyl groups of CD.
Alternately, because the click reaction had been con-
firmed as a useful reaction mode in introducing other
functional groups on CDs [22–27], it was chosen as the
linking reaction for aromatic aldehyde with CDs. Scheme 2
showed the synthetic route of cyclodextrin aromatic alde-
hyde derivative 6 via click chemistry and its acylhydrazone
derivatives 7a, 7b and 7c. The mono-6-azido-b-CD 3 was
obtained from the readily available mono-6-tosyl-b-CDs
according to references [28, 30]. Also, 4-(prop-2-yny-
loxy)benzaldehyde 5 was prepared in yield of 87 % by
reacting 4-hydroxybenzaldehyde with 3-bromoprop-1-yne
under K2CO3/MeCN system according to literatures [28,
31]. After the reactants 3 and 5 had been prepared, the
coupling reaction of b-CDs azido derivative 3 and com-
pound 5 was carried out by click chemistry of the Huisgen
[2 ? 3] cycloaddition reaction. The mol ratio of com-
pounds 3 and 5 was 1:1.1, using 1.1 equiv. CuSO4ꢀ5H2O
and 2.4 equiv. sodium ascorbate (with respect to the CD) as
catalyst. This procedure was accomplished at room tem-
perature in DMF solution in 15 h. The first example of CD
aromatic aldehyde derivative 6 was obtained conveniently
after simple purifying procedure of recrystallization in
DMF/acetone and the yield was as high as 80 %.
Compound 7b was obtained by refluxing 12 h as of-
fwhite powder in yield of 85 %. Compound 7b: IR/cm-1
:
1
3408, 2923, 1668, 1599, 1508, 1156, 1030, 579; H NMR
(400 MHz, DMSO-d6) d ppm: 2.81–4.07 (m, 40H, CH and
CH2), 4.21–4.69 (8H, OH and NCH2), 4.70–5.13 (m, 7H,
CH), 5.21 (s, 2H, CH2O), 5.60–5.94 (m, 14H, OH), 7.22 (s,
2H, ArH), 7.49 (s, 1H, ArH), 7.88 (s, 2H, ArH), 8.21(s, 1H,
NCH), 8.32 (s, 1H, ArH), 8.42 (s, 1H, CH), 8.89 (s, 1H,
ArH), 9.17 (s, 1H, ArH), 9.89 (s, 1H, NH). 13C NMR
(100 MHz, DMSO-d6) d ppm: 167.4, 162.9, 151.1, 146.5,
141.7, 138.1, 131.7, 129.7, 128.2, 125.5, 123.4, 115.1,
102.1, 101.9, 101.8, 101.7, 83.3, 81.9, 81.5, 81.4, 81.3,
73.1, 73.0, 72.9, 72.8, 72.7, 72.5, 72.3, 72.0, 71.9, 71.8,
71.6, 61.2, 60.0, 59.9, 59.8, 58.7, 59.6, 58.8, 50.3. MS m/z (%):
1438.2(M?, 100). Anal. Calcd. For C58H82N6O36: C48.40,
H5.74, N5.84; found C48.47, H5.69, N5.90 %. Mp
278–281 °C (dec).
Compound 7c was obtained by refluxing 18 h as car-
mine powder in yield of 75 %. Compound 7c: IR/cm-1
:
3418, 2921, 1662, 1614, 1502, 1332, 831; 1H NMR
(400 MHz, DMSO-d6) d ppm: 2.84–4.08 (m, 40H, CH and
CH2), 4.23–4.70 (8H, OH and NCH2), 4.72–5.09 (m, 7H,
CH), 5.20 (s, 2H, CH2O), 5.62–5.93 (m, 14H, OH), 7.18 (d,
J = 8.0 Hz, 2H, ArH),7.78 (d, J = 8.0 Hz, 2H, ArH), 8.11
(d, d, J = 8.0 Hz, 1H, ArH), 8.20 (s, 1H, NCH), 8.35 (d,
J = 8.0 Hz, 1H, ArH), 8.66 (s, 1H, ArH), 8.88 (s, 1H,
ArH), 10.05 (s, 1H, NH). 13C NMR (100 MHz, DMSO-d6)
d ppm: 163.0, 158.9, 141.8, 139.8, 134.3, 131.7, 129.7,
125.6, 122.8, 120.7, 118.8, 115.1, 102.1, 102.0, 101.9,
101.8, 101.2, 83.4, 82.0, 81.6, 81.4, 81.3, 80.9, 73.1, 73.0,
72.9, 72.8, 72.5, 72.4, 72.3, 72.1, 72.0, 71.7, 70.0, 61.2,
60.1, 60.0, 59.9, 59.8, 58.9, 50.3. MS m/z (%):
1523.1(MNa?, 100). Anal. Calcd. For C58H81N7O39:
C46.43, H5.44, N6.54; found C46.48, H5.48, N6.50 %. Mp
282–285 °C (dec).
OH
O
HO
OH
TsCl
6
HO
OTs
NaN3
HO
6
N3
6
OH
*
O
OH
*
7
OH
OH
2
14
OH
3
14
14
1
HO
O
CHO
6
HO
2 +
CHO
under various conditions
4
OH
14
Scheme 1 The unsuccessful synthetic route of compound 4
123

J Incl Phenom Macrocycl Chem
Scheme 2 The synthetic route
of compounds 7a, 7b and 7c
Br
OHC
O
OHC
OH
K2CO3 / CH3CN
5
HO
6
O
CHO
N
CuSO4
sodium ascorbate
N
N
3
+
5
6
OH
14
RNH2
HO
N
6
O
CH N R
N
N
7
OH
14
O2N
O
N C
O
N C
N
H
H
7a: R=
7c: R=
N
NO2
7b: R=
H
HO
Aromatic aldehyde group is an effective functional group
to construct the stable large aromatic conjugate structures
by the Schiff-base condensation. By stirring compound 6
with salicylic hydrazide, nicotinohydrazide, or 2,4-dinitro-
phenylhydrazine in DMF at 55 °C, the corresponding con-
densation products were obtained. The mol ratios of
reactants were 1:2 and no catalyst, such as acetic acid, was
needed. The TLC showed that almost all of compound 6
disappeared and only one new dot of product emerged.
After distillation of most DMF under vacuum, the residue
was recrystallized in MeOH/CHCl3 and the residue of hy-
drazides was washed by small amount of MeOH and ace-
tone for several times. Then compounds 7a, 7b and 7c were
prepared in yields of 84, 85 and 75 %, respectively. Both
CDs aromatic aldehyde derivative 6 and its Schiff-base
derivatives 7a, 7b and 7c were obtained conveniently by
recrystallization to remove some excess of materials, which
were seldom applied in the syntheses of CDs derivatives.
The yields were as high as 75–85 % and their purifications
were confirmed by TLC and spectral characterization.
Moreover, it is worthy of noting that compounds 7a, 7b and
7c are novel cyclodextrin derivatives with large conjugate
acylhydrazone group, which were not reported before
among all kinds of cyclodextrin derivatives [1–7].
of compound 6 exhibited strong absorption peak at
1680 cm-1, indicating the existence of C=O of aromatic
aldehyde group. After Schiff-base condensation, the peak at
1680 cm-1 disappeared utterly and new peaks for C=N
groups were observed in the IR spectra of compounds 7a,
7b and 7c. Their ESI–MS spectra exhibited the corre-
sponding molecular ion peaks at 1342.3 (MNa?), 1452.8
(M?), and 1523.1 (MNa?), respectively (Fig. 1). In their 1H
NMR spectra, the characteristic peaks were assigned well
for triazole proton and phenyl proton. For example, in the
1H NMR spectrum of compound 7a, all the protons of the
functional groups, especially for the aromatic groups, were
well assigned as shown in Fig. 2. On the other hand, as
generally observed for substituted CDs, the proton signals at
sugar units were hardly exploitable due to overlapping and
broadening [28, 31]. This phenomenon suggested a
modification of the conical CD structures leading to non-
equivalent glucopyranose units [28, 31]. As a result, com-
plete signal assignment was therefore difficult for CD units
of compounds 6, 7a, 7b and 7c. By contrast, in their
13C NMR spectra, the characteristic signals were detected
distinctly for carbon atoms of aldehyde group, Schiff-base
groups, triazole cycle and aromatic groups. For instance, the
13C NMR spectrum of mono CD aromatic aldehyde
derivative 6 showed the signals of carbon atoms for alde-
hyde and triazole cycle at 191, 163 and 142 ppm, respec-
tively. The results of elemental analysis were also in
The novel CD aromatic aldehyde derivative 6 and its
derivatives 7a, 7b and 7c were characterized by elemental
analysis, FT-IR, ESI–MS and NMR spectra. The IR spectra
123

J Incl Phenom Macrocycl Chem
Fig. 1 1H NMR spectrum of
compound 7a
Fig. 2 The structures of tested
organic dyes
N
H3C
H2N
CH3
Cl-
N+
CH3
HO
N
N
SO3 Na+
-
N
H
Neutral red (NR)
Orange¢ñ(OI)
2000
accordance with their structures. As to the cis/trans con-
formers of C(O)–N bond and E/Z geometrical isomers re-
spect to the C=N double bonds of compounds 7a–7c, it was
reasonable to deduce the existence of isomers by referring
to the similar structural analysis in literature [32]. However,
it was difficult to determine the percentage of different
isomers for compounds 7a–7c due to the overlapped signal
of NH and OH in IR spectra and the absence of CH2 groups
beside the C(O)–N bond and C=N double bond which were
crucial to study the percentages of different isomers [32].
Based on all these characteristic data of IR, ESI–MS, NMR
and elemental analysis, compounds 6, 7a, 7b and 7c possess
the corresponding structures as shown in Scheme 2.
-8
Y =0.00123+4.63306*10
R=0.995
X
0.0ml
0.02
0.01
0.00
1500
1000
500
0
0
100000 200000 300000 400000 500000
1/[G]
2.0ml
350
400
450
500
Wavelength/nm
Complexation studies for dyes
Fig. 3 Fluorescence titration spectra of host 7a (1 9 10-4 M) with
OI (0, 0.2, 0.6, 0.8, 1.0, 2.0 9 10-6 M) in phosphate buffer
(pH = 7.20)
The formation of inclusion complexes between cyclodex-
trin derivatives and guests, such as dyes, were reported
123

J Incl Phenom Macrocycl Chem
stacking action for dyes. Thus, the preliminary binding
properties of hosts 7a, 7b and 7c for two normal dyes of
Orange I and Neutral red were investigated by fluorescence
titration spectroscopy. The change of fluorescence spectra
of host 7a for OI was shown as representative ones in
Fig. 3. It could be seen that the emission intensity
gradually decreased as the concentration of guest in-
creased, indicating a substantial association of these two
components. These phenomena might be explained that the
fluorescence was quenched directly by the interaction of
host and guest, such as p–p stacking action interaction
between large conjugate acylhydrazone group and planar
aromatic structures of organic dyes. Moreover, based on
the changes of emission intensity at maximal wavelength,
the association constants and correlation coefficients were
calculated by Benesi–Hildebrand equation, which was
Table 1 Association constants (Ks) and compexation ratios of
compounds 7a–7c with two dyes
Dyes
7a
7b
7c
n
Ks
n
Ks
n
Ks
OI
1
1
5.85 9 104
2.65 9 104
1
1
3.98 9 104
4.82 9 104
1
1
5.35 9 104
4.45 9 104
NR
widely for the potential application on sensors and probes
studies [33, 34]. As to novel CDs derivatives 7a, 7b and 7c,
it is expected that they showed good binding abilities for
dyes based on the cooperation complexation of CDs unit
and large conjugate acylhydrazone group with good p–p
Fig. 4 The ESI–MS spectra of compound 7a with NR (1:4)
123

J Incl Phenom Macrocycl Chem
usually used to study the complexation behaviors of host–
guest [29]. The calculated formula was as follows:
the results of complexation fluorescence spectra and com-
plexation ESI–MS spectrum suggested that compounds 7a,
7b and 7c possessed excellent complexation abilities for
dyes and 1:1 complexes were formed in DMSO solution.
H þ nG ꢀ H ꢁ nG
1
1
1
¼
n þ
DF KsDf½Hꢂ½Gꢂ
Df½Hꢂ
Conclusions
where H is host; G is guest; n is the ratio of complexation;
[H] and [G] are the concentration of host and guest, re-
spectively; Ks is association constant; Df is the fraction of
accessible fluorophore guest to a host; DF is the change of
emission intensity at maximal wavelength.
In the paper, we described the facile synthesis of CDs
aromatic aldehyde derivative via a facile click reaction.
Moreover, the novel cyclodextrin derivatives with large
conjugate acylhydrazone group were reported for the first
time by Schiff-base condensation of CDs aromatic alde-
hyde derivative with series phenyl hydrazine or acyl hy-
drazide derivatives in yields of 75–85 %. Their structures
were confirmed by elemental analysis, FT-IR, ESI–MS and
NMR spectra. Their complexation properties for two or-
ganic dyes were investigated by fluorescence titration
spectroscopy and complexation MS spectrum. The results
suggested these novel CDs derivatives with large conjugate
acylhydrazone group possess excellent complexation abil-
ities comparing with the raw CDs and other CDs deriva-
tives. The associations constants were higher than 104 and
the highest associations constant was 5.85 9 104 for host
7a with OI. Both fluorescence titration spectroscopy and
complexation MS spectrum indicated that 1:1 complexes
were formed in DMSO solution. These dyes complexation
results indicated that the large acylhydrazone conjugate p-
electronic systems in novel CDs derivatives play important
roles in binding dyes based on the p–p stacking action,
which extend a new strategy to the design and synthesis of
new CDs derivatives with excellent complexation abilities
for dyes.
The calculated results were summarized in Table 1.
These results indicated the formation of 1:1 host–guest
complexes for compounds 7a, 7b and 7c with dyes. The
association constants were higher than 104 and the highest
associations constant was 5.85 9 104 for host 7a with OI.
Comparing with the literature reports, the complexation
constants of compounds 7a, 7b and 7c were outstanding.
For examples, as to the complexation constants of CDs or
its derivatives for NR, the associations constants of native
CDs, organoselenium-bridged Bis-CDs and triazinylanili-
no-bridged Bis-CDs were 480, 5090 and 1546, respectively
[10, 35], which were far lower than the data in this work. It
can be seen that the although the large conjugate acylhy-
drazone group in compounds 7a, 7b and 7c showed some
difference structures, their association constants for dyes
were close in the scope of 2.65–5.85 9 104. These phe-
nomena might indicate that the similar large acylhydrazone
conjugate p-electronic systems, resulting in good p–p
stacking action with planar organic dyes, play more im-
portant roles in binding dyes than the influences of other
functional groups such as hydroxyl and nitro group.
Further, the complexation behavior of compound 7a
with NR was studied by ESI–MS spectrum. The com-
plexation of compound 7a with excess Neutral red (mol
ratio = 1:4) was studied in DMSO solution. The result was
illustrated in Fig. 4. Before complexation, compound 7a
showed clear molecular ion peak at 1458.2. After com-
plexation with NR, the spectrum exhibited three peaks for
host 7a ? H? at 1453.9, host 7a with Na? at 1476.4 and
host 7a with NR at 1705.8. The dye complexation peak
showed the relative abundance of 100 %, indicating the
strong molecular interaction between host and guest.
Moreover, it can be seen that although the excess NR was
added, only the 1:1 complexation peak was observed. This
result was in accordance with the result of 1:1 com-
plexation of fluorescence titration spectra. We also tried to
Acknowledgments Financial support from the National Natural
Science Foundation of China (No: 21406036), Fujian Natural Science
Foundation of China (No. 2014J01034), Fujian province science and
technology key project (2014N0025) and the Program for Innovative
Research Team in Science and Technology in Fujian Province
University were greatly acknowledged.
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