Synthesis of β-cyclodextrin-2,4-dihydroxyacetophenone-phenylhydrazine and its application

Article abstract of DOI:10.1002/jccs.200500167

A novel host reagent of β-cyclodextrin-2,4-dihydroxyacetophenone- phenylhydrazine(β-CDP-DHPH) was synthesized and characterized by IR and ¹H NMR spectra. A highly selective and sensitive spectrofluorimetric determination of trace amounts of cad

Full text of DOI:10.1002/jccs.200500167

Journal of the Chinese Chemical Society, 2005, 52, 1165-1170
1165
Synthesis of b-Cyclodextrin-2,4-dihydroxyacetophenone-phenylhydrazine
and Its Application
Jianning Liu* (
Department of Chemistry, Longdong University, Qingyang, Gansu 745000, P. R. China
), Bowan Wu (
) and Bing Zhang (
)
A novel host reagent of b-cyclodextrin-2,4-dihydroxyacetophenone-phenylhydrazine(b-CDP-DHPH)
1
was synthesized and characterized by IR and H NMR spectra. A highly selective and sensitive spectro-
fluorimetric determination of trace amounts of cadmium was proposed based on the reaction between Cd2+
and b-CDP-DHPH at pH 10.0. The molar ratio of b-CDP-DHPH to Cd2+ was 1:1. The linear range of this
method was 0.56-120 mg·L-1 with a detection limit of 0.20 mg·L-1. The interferences of 39 common ions in the
determination of cadmium were investigated, and the results showed that the host reagent had a quite high se-
lectivity. This method was rapid and simple in determination of trace amounts of cadmium in mineral, tap and
river water.
Keywords: Synthesis; Host reagent; Guest; b-Cyclodextrin-2,4-dihydroxyacetophenone-phenyl-
hydrazine; Spectrofluorimetric determination of cadmium.
INTRODUCTION
There has been an increased interest in the development
minium ion recognition by using b-cyclodextrin cross-linked
polymer-Schiff base.8
Cadmium is a widely known chemical pollutant and
even in low concentration levels, its toxicity can be danger-
ous. Therefore, highly sensitive detection of trace cadmium
content in the environment is of great importance. Spectro-
fluorimetry has many advantages. One of them is high sensi-
tivity. Cadmium has been determined spectrofluorimetri-
cally.9-16 Based on the use of the special properties of the b-
cyclodextrin-2,4-dihydroxyacetophenone-phenylhydrazine,
the aim of the present work is to establish an improved sensi-
tised fluorometric method permitting a simple, fast and inex-
pensive measurement of cadmium with high sensitivity and
good accuracy.
of functional molecules that could sensitively and selectively
respond to specific species. The enormous potential of fluo-
rometric methods for the assay of heavy metal cationic ions
requires the development of highly selective and sensitive
fluorescence probes.1 In recent years, the application of
supramolecular complexes has proved to be one of the ap-
proaches to generate new materials with specificity of chemi-
cal sensing or recognition. These supramolecular structures
are expected to produce novel functions which are different
from those found in simple molecules.2-3
Cyclodextrins (CDs) are cyclic oligomers of a-linked
D-glucopyranose. The prime feature of CDs is that the mole-
cule has a hydrophobic cavity and thus possesses the ability
to form inclusion complexes with a variety of guests, which
exerts remarkable effects on important properties of the com-
plexed substances without formation of chemical bonds and
thus without structural changes.4 The inclusion behavior of
CDs has been studied extensively and applied in analytical
chemistry.5-7 It should be pointed out, however, that even
though the number of reports is large, in contrast, there was
little attempt to seek the application of the supramolecular
function of b-cyclodextrin cross-linked polymer-Schiff base
to metal ions detection. One paper has been reported for alu-
EXPERIMENTAL
Apparatus and Reagents
Melting point was obtained using a Beijing X4 micro-
scopic melting point apparatus. C, H and N analyses were ob-
tained using a Perkin-Elmer 240B elemental analysis instru-
ment. Infra-red spectra were measured in KBr pellets on a
Perkin-Elmer 983 spectrophotometer in the range 200-4000
cm-1. Fluorescence measurements were made on a Shimadzu
RF-5000 Spectrofluorimeter equipped with a xenon light
* Corresponding author. E-mail: ljnly@ldxy.com.cn

1166 J. Chin. Chem. Soc., Vol. 52, No. 6, 2005
Liu et al.
source and the excitation and emission slits are both 5 nm.
The pH of the solutions used was measured with a pHS-3C
digital pH meter (Shanghai Leici Device Works, Shanghai,
The melting point of DHPH is 160-161 °C. Element
analysis gave a composition of C 69.31, H 5.77, N 11.58%,
which is in good agreement with the theoretical composition
of DHPH, C 69.40, H 5.75, N 11.57%.
1
China) with a combined glass-calomel electrode. H NMR
spectra of 2,4-dihydroxyacetophenone-phenylhydrazine and
b-cyclodextrin-2,4-dihydroxyacetophenone-phenylhydrazin
e were recorded in deuterated dimethyl sulfoxide using a
Varian XL-200 NMR spectrometer with TMS as internal
standard.
The infrared spectrum of DHPH (KBr discs) was ob-
tained and the bands were assigned as follows: OH (3423.46
cm-1), N-H (3280.00 cm-1), C=N (1599.08 cm-1), C-O (1245.70
cm-1) and C-H of the aromatic ring (3180.00 cm-1).
All chemicals used were of analytical or higher grades.
b-CDP (Fig. 1) was prepared and purified as reported previ-
ously.17 Doubly distilled water was used throughout. Stock
cadmium solution (1 mg/mL) was prepared from Cd(NO3)2·
4H2O(Merk) in acidified water (in HNO3 1 mol·L-1). Working
standard solutions were freshly prepared by appropriate dilu-
tion with water. An ammonia-ammonium acetate buffer solu-
tions (pH = 10.0) was used. The 1.0 ´ 10-4 mol·L-1 of b-CDP-
DHPH stock solutions were prepared by dissolving appropri-
ate amount of materials in anhydrous dimethylformamide
(DMF).
Synthesis of host reagent (b-CDP-DHPH)
A 0.50 g amount of 2,4-dihydroxyacetophenone was
dissolved in 20.0 mL methanol. A solution of 15 mL b-CDP
was added dropwise, with stirring. The mixture was heated to
at 40 °C for 30 min, then cooled down to room temperature,
filtered and bathed with doubly distilled water. After being
dried under vacuum, 0.45 g of the b-CDP-DHPH was ob-
tained with a yield of 10%. The melting point is 179-181 °C.
The infrared spectrum of b-CDP-DHPH (KBr discs) was ob-
tained and the bands were assigned as follows: OH (3455.00
cm-1), N-H (3296.00 cm-1), C=N (1590.50 cm-1), C-O (1275.00
cm-1) and C-H of the aromatic ring (3200.00 cm-1).
Synthesis and characterization of 2,4-dihydroxyaceto-
phenone-phenylhydrazine (DHPH)
Characterization of host reagent (b-CDP-DHPH)
Notice from Table 1 that a new host reagent (b-CDP-
DHPH) has been synthesized according to melting point,
crystal and color of (b-CDP-DHPH) as distinguished from
DHPH and b-CDP.
A 1.8 mL amount (about 0.015 mol) of phenylhydra-
zine was dissolved in 20 mL of 50% ethanol. Into this, a
mixed solution of 2.24 g (about 0.015 mol) 2,4-dihydro-
xyacetophenone, 20 mL of 50% ethanol and 2 mL of 36%
acetic acid was added slowly. The mixture was refluxed at 85
°C for 1.5 h. The synthesis reaction is shown in Scheme I. The
mixture was then cooled to room temperature, filtered and
re-crystallized from 50% ethanol. A pale yellow needle
crystalloid was obtained (yield 75%).
1
The H NMR data and assignments of DHPH and b-
CDP-DHPH are presented in Table 2. The 1H NMR spectra of
the DHPH showed the multiplets for the aromatic proton at d
6.86-8.00 ppm. The multiplets of the aromatic proton of the
b-CDP-DHPH is shifted to d 6.75-7.98 ppm, which proved
the suggestion that a new host reagent (b-CDP-DHPH) has
been synthesized. The chemical shift for OH, NH and CH3
protons are almost unchanged in DHPH and b-CDP-DHPH.
The structure of b-CDP-DHPH is shown in Fig. 2.
Analytical procedure of cadmium
A standard solution of cadmium or the sample solution
was placed into a calibrated tube containing 0.6 mL b-CDP-
Fig. 1. Structure of the b-CDP.
Scheme I Synthesis of the DHPH
CH
C
3
CH
C
3
NH
N
OH
HAc
NH
NH
O
OH
2
+
OH
OH

Synthesis of b-CDP-DHPH and Its Application
J. Chin. Chem. Soc., Vol. 52, No. 6, 2005 1167
Table 1. Physical properties of DHPH, b-CDP and b-CDP-DHPH
Compound
Melting point (°C)
Crystal
Color
DHPH
b-CDP
b-CDP-DHPH
160-161
240 Decomposition
179-181
Needle crystal
Powdery
Rod crystal
Pale yellow
White
Shade yellow
Table 2. 1H NMR spectra of DHPH and b-CDP-DHPH (d, ppm)
environment; the freedom of movement of the formed fluo-
rescent complex molecule and the relaxation effect of the wa-
ter molecule were both greatly depressed, which reduced the
mutual collision of molecules and the non-radiative transi-
tion. The complexometric effect of Cd2+ with DHPH made
the rigidity and plane of b-CDP-DHPH improve. Further-
more, the b-CD cavity could also protect the fluorescent sin-
gle state molecule of b-CDP-DHPH-Cd2+ from the quenching
of water and soluble oxygen.
Compound
OH
N-H
Aromatic
CH3
DHPH
b-CDP-DHPH
12.05
12.03
11.03
11.02
6.86-8.00
6.75-7.98
2.36
2.35
DHPH (1 ´ 10-4 mol/L), 2.0 mL ammonia-ammonium acetate
buffer solution (pH = 10.0) and 3.0 mL of dimethylform-
amide. The final volume was made up to 10.0 mL with sec-
ondary distilled water. The solution was mixed and equili-
brated at room temperature for 20 min. The relative fluores-
cence intensity of the b-CDP-DHPH-Cd2+ complex was mea-
sured within 0.33-4 h at an emission wavelength of 442.0 nm
in a 1 cm quartz cell, keeping the excitation wavelength max-
imum at 368.0 nm.
If we simply added the same dosage of b-CDP and
DHPH into the reaction system rather than b-CDP-DHPH,
b-CDP could still offer a feasible microenvironment of weaker
polarity and stronger rigidity, so the quenching effect of wa-
ter and soluble oxygen on the fluorescent single state mole-
cule of DHPH-Cd2+ was reduced and the fluorescence inten-
sity was improved, compared to the system without b-CDP.
However, the steric effect of b-CDP restrained DHPH-Cd2+
RESULTS AND DISCUSSION
Excitation and emission spectra
Under the selected conditions, the maximum excitation
and emission wavelengths were 368.0 and 442.0 nm, respec-
tively (Fig. 3). We found that the complex of the b-CDP-
DHPH-Cd2+ had very strong fluorescence intensity while the
reagent blank had a low signal, which indicated that b-CDP-
DHPH had a higher signal-to-noise than DHPH in the deter-
mination of cadmium. With the driving force of hydrophobic
interaction, van der Waals force and hydrogen bond, the
DHPH molecule entered into the b-CDP cavities and formed
a supermolecule host reagent b-CDP-DHPH. Two b-CD
units of the b-CDP cooperated to include two phenyl rings of
DHPH, which improved the rigidity of the host reagent. The
b-CD cavities in b-CDP-DHPH offered a non-polar micro-
Fig. 3. (a) Excitation and (b) emission spectra. 1 and 1’
are the fluorescence spectra of b-CDP-DHPH-
Cd2+ complex and its blank; 2 and 2’ are the flu-
orescence spectra of DHPH-Cd2+ complex and
its blank; 3 and 3’ are the fluorescence spectra
of b-CDP + DHPH + Cd2+ and its blank; Buffer
medium of pH 10.0; DMF as organic solvent;
6.0 ´ 10-5 mol·l-1 of b-CDP-DHPH; 5.0 ´ 10-4
mol·l-1 of DHPH; 1.0 ´ 10-4 mol·l-1 of b-CDP;
40 mg·l-1 of Cd2+.
Fig. 2. Structure of the b-CDP-DHPH.

1168 J. Chin. Chem. Soc., Vol. 52, No. 6, 2005
Liu et al.
from entering into the cavities of b-CDP, so the rigidity and
plane of DHPH-Cd2+ could not be improved further. In b-
CDP-DHPH, the steric effect made it easy to include with an
appropriate guest (for example Cd2+),18 so the selectivity was
improved greatly.
above. The fluorescent intensity increased with an increasing
amount of b-CDP-DHPH up to 0.4 mL (1 ´ 10-4 mol·l-1), re-
mained constant between 0.4 and 0.8 mL, and decreased
slowly thereafter. Thus 0.6 mL was selected to ensure a suffi-
cient excess of the reagent through the experimental work.
The results are shown in Fig. 5.
Effect of temperature and time
The results show that temperature has little effect on the
fluorescence intensity of the b-CDP-DHPH-Cd2+ complex.
The experiment can be carried out at room temperature. The
fluorescence intensity of the complex reached a maximum af-
ter 20 min and remained constant for at least 4 h.
Influence of amount of dimethylformamide
As b-CDP-DHPH is insoluble in water but soluble in
dimethylformamide, the effect of this solvent on the fluores-
cent intensity of the Cd2+-b-CDP-DHPH system was studied.
The experimental results show that the fluorescent intensity
of the complex increased when the dimethylformamide con-
tent in the medium increased from 0.5-2.0 mL and remained
constant between 2.0 and 4.0 mL. Therefore, a medium con-
taining 3.0 mL of dimethylformamide in a total volume of 10
mL was selected.
Effect of pH
The pH of the medium had a great effect on the form of
the reagent and also affected the fluorescence intensity of the
b-CDP-DHPH-Cd2+ complex. The experimental results show
that the optimum pH range for complex formation is between
9.0 and 11.0. Therefore, a pH of 10.0 was fixed with the use of
ammonia-ammonium acetate buffer solution. The volume of
the buffer solution added (from 1.0 to 3.0 mL) had little effect
on the fluorescence intensity, so 2.0 mL was used in the fol-
lowing experiments. The results are shown in Fig. 4.
Effect of foreign ions
A systematic study of the interferences of foreign ions
in the determination of cadmium (0.03 mg·mL-1) was carried
out. For this study, various amounts of different ions were
added by firstly testing a 1000-fold interference with cad-
mium (m/m). If interference occurred, the ratio was reduced
gradually until the interference ceased. The criterion for in-
terference was fixed at a ±5% variation of the average fluo-
rescent intensity calculated for the established level of cad-
mium. The results are shown in Table 3.
Effect of amount of the host reagent b-CDP-DHPH
The influence of the amount of b-CDP-DHPH on the
fluorescent intensities of the solutions containing 40 mg·L-1
of cadmium was studied under the conditions established
Fig. 5. Effect of amount of the host reagent b-CDP-
Fig. 4. Effect of pH on the difference of the fluores-
cence intensities (DF) of the b-CDP-DHPH-
Cd2+ complex and the b-CDP-DHPH. Solution
DHPH on the difference of the fluorescence in-
tensities (DF) of the b-CDP-DHPH-Cd2+ com-
2+
(CCd = 40 mg·l-1, Cb-CDP-DHPH = 6.0 ´ 10-5
plex and the b-CDP-DHPH. Solution (CCd
40 mg·l-1, pH = 10.0).
=
2+
mol·l-1).

Synthesis of b-CDP-DHPH and Its Application
J. Chin. Chem. Soc., Vol. 52, No. 6, 2005 1169
Table 3. Effect of foreign ions on the spectrofluorimetric determination of cadmium (0.03
mg·mL-1); tolerance error ±5%
Tolerance ratio (m/m)
Foreign ions
-
-
-
-
-
³ 1000
K+, Na+, Cl-, Br-, I-, NO3 , NO2 , CO32-, HCO3 , ClO4 , H2PO4 ,
HPO42-, PO43-, B4O72-, SO42-, SO32-, CH3COO-
Ca2+, Mg2+, F-, SiO32-, Ba2+
500
250
200
100
20
EDTA
Be2+, Fe2+, Fe3+
Co2+, Mn2+, Ni2+, Zn2+, Cr3+, CrO4
2-
Ag+, Sr2+, Pb2+, Ga2+
MoO42-, Cu2+
Al3+
10
5
Stoichiometry of the complex
From Table 4, it can be seen that the sensitivity and se-
lectivity of the new method are better than the other methods
and the method can be easily carried out.
The stoichiometry of the complex was studied under
the established experimental conditions by the molar ratio
and continuous variation method.19 The result is shown in
Fig. 6. The two methods showed that the composition ratio of
Cd2+ and b-CDP-DHPH is 1:1 in the complex.
Calibration curve
Under the experimental conditions, there is a linear re-
lationship between fluorescence intensity and Cd2+ concen-
tration in the range 0.56-120 mg·L-1 with a correlation coeffi-
cient(r) of 0.9976. The regression equation is DF = 1.78 C
(mg·L-1) + 1.43. The detection limit, as defined by IUPAC,
was determined to be 0.20 mg·L-1, when the K value was taken
as 3 and the standard deviation was 0.119 obtained from a se-
ries of 11 reagent blanks. The relative standard deviation was
1.08% obtained from a series of 11 standards each containing
50 mg·L-1 cadmium. In Table 4, the method characteristics are
compared with those of similar fluorescence-based methods
for cadmium determination reported previously.
Fig. 6. Composition determination of the complex.
[b-CDP-DHPH] = 1 ´ 10-6 mol·L-1, pH = 10.0,
lex = 368.0 nm, lem = 442.0 nm.
Table 4. Characteristics of fluorimetric method for cadminm
Linear range Detection limit
Reagent
lex/em (nm)
Major interferences
Ref.
(mg·l-1)
(ppb)
2-(o-hydroxyphenyl)-benzoxazole
8-hydroxyquinoline-5-sulphonic acid
3,5¢-bis(dicarboxymethyllamino-
methyl)-4,4¢-dihydroxytrans-stilbene
fluorexon
Benzyl-2-pyridylketone 2-guinolyl-
hydrazone
Calcein
100-200
1-250
20-1000
100
1.0
20
Cu2+, Co2+, Ni2+
[9]
[10]
[11]
360/520
3600/4400
Zn2+, Mg2+, Al3+, Ca2+, La3+, Sn2+
Al3+, Be2+, Cd2+, Zn2+
490/520
465/545
2.24
0.8
Cu2+, Zn2+, Fe2+, Pb2+, Hg2+
Al3+, Zn3+, Zn2+
[12]
[13]
6-40
519/535
536/555
365/592
368/442
7-80
0.5-15
4-200
7
Pb2+, Zn2+, Fe2+, Co2+
Cd2+, Hg2+
Pb2+, Hg2+
[14]
[15]
[16]
Cryptand 2.2.1
Rhodamine B
b-CDP-DHPH
0.5
4.0
0.20
0.56-120
Al3+
This work

1170 J. Chin. Chem. Soc., Vol. 52, No. 6, 2005
Liu et al.
Table 5. Analytical results of cadmium determination in natural waters by the proposed
method (mg·L-1)
Sample
Known value
Found
R.S.D (%)
Recovery (%)
Mineral water
0.50
1.00
0.50
1.00
0.50
1.00
0.49 ± 0.01
0.99 ± 0.02
0.51 ± 0.01
1.01 ± 0.01
0.53 ± 0.03
1.04 ± 0.02
1.85
2.16
3.11
1.58
2.63
1.75
098
099
102
101
106
104
Tap water
River water
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Determination of cadmium in mineral, tap and river
water
The proposed method was applied to the analysis of
mineral water, tap water and river water samples. Natural wa-
ter samples were filtered through 0.45 mm membrane filters.
1 mL sample solution was placed into a calibrated tube con-
taining 0.6 mL b-CDP-DHPH (1 ´ 10-4 mol/L), 2.0 mL am-
monia-ammonium acetate buffer solution (pH = 10.0) and 3.0
mL of dimethylformamide. The final volume was made up to
10.0 mL with secondary distilled water. The solution was
mixed and equilibrated at room temperature for 20 min. The
relative fluorescence intensity of the b-CDP-DHPH-Cd2+
complex was measured within 0.33-4 h at an emission wave-
length of 442.0 nm in a 1 cm quartz cell, keeping the excita-
tion wavelength maximum at 368.0 nm. The results are pre-
sented in Table 5. The obtained recovery varied from 98 to
106% showing that the method was very good in determina-
tion of cadmium in mineral water, tap water and river water.
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