A new Cu2+-induced color reaction of a rhodamine derivative N-(3-carboxy)acryloyl rhodamine B hydrazide

Article abstract of DOI:10.1007/s11426-011-4275-1

A new rhodamine derivative, N-(3-carboxy)acryloyl rhodamine B hydrazide (CARB), has been synthesized, and its unusual spectroscopic reaction with Cu²⁺ has been investigated. The derivative exhibits a rapid and reversible non-fluorescent absorption upon coordination to Cu²⁺, which is a rather unusual phenomenon for rhodamine B derivatives. Stoichiometric measurements using the Job's method and the molar ratio method reveal that one CARB molecule combines two Cu²⁺ ions, and the two Cu²⁺ ions play different roles: one opens the spirocyclic structure and the other quenches the fluorescence of the xanthene moiety. This reaction mechanism is supported by a comparative study on the model compound N-acryloyl rhodamine B hydrazide as well as by the density functional theory calculations. Furthermore, the absorption response of CARB is highly selective for Cu²⁺ over other common ions, which implies that CARB may be used as a colorimetric probe for the rapid visual detection of Cu²⁺.

Full text of DOI:10.1007/s11426-011-4275-1

SCIENCE CHINA
Chemistry
•
ARTICLES •
July 2011 Vol.54 No.7: 1101–1108
doi: 10.1007/s11426-011-4275-1
2
+
A new Cu -induced color reaction of a rhodamine derivative
N-(3-carboxy)acryloyl rhodamine B hydrazide
1
1
1*
2
SUN ChengDong , CHEN JianMing , MA HuiMin , LIU Yang ,
2
2
ZHANG JingHua & LIU QingJun
1
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Analytical Chemistry for Living Biosystems,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
2
Beijing Center for Physical and Chemical Analysis, Beijing 100089, China
Received December 8, 2010; accepted January 24, 2011
A new rhodamine derivative, N-(3-carboxy)acryloyl rhodamine B hydrazide (CARB), has been synthesized, and its unusual
2
+
spectroscopic reaction with Cu has been investigated. The derivative exhibits a rapid and reversible non-fluorescent absorp-
2
+
tion upon coordination to Cu , which is a rather unusual phenomenon for rhodamine B derivatives. Stoichiometric measure-
2
+
ments using the Job’s method and the molar ratio method reveal that one CARB molecule combines two Cu ions, and the
2
+
two Cu ions play different roles: one opens the spirocyclic structure and the other quenches the fluorescence of the xanthene
moiety. This reaction mechanism is supported by a comparative study on the model compound N-acryloyl rhodamine B hy-
drazide as well as by the density functional theory calculations. Furthermore, the absorption response of CARB is highly selec-
2
+
tive for Cu o+ver other common ions, which implies that CARB may be used as a colorimetric probe for the rapid visual de-
2
tection of Cu .
N-(3-carboxy)acryloyl rhodamine B hydrazide, reaction mechanism, colorimetric probe, visual detection, copper,
N-acryloyl rhodamine B hydrazide
1
Introduction
forms, considerable efforts have been directed toward the
development of novel spectroscopic off-on-type probes by
introducing a suitable recognition unit for various analytes,
Rhodamine dyes, like fluorescein dyes, are fluorochromes
that belong to the family of xanthenes. Because rhodamine
dyes have many advantages such as low cost, long-wave-
length absorption/emission, high molar absorption coeffi-
cient, high quantum yield, and photostability [1–10], they
have been widely used as a molecular platform for the de-
sign of new spectroscopic probes. Moreover, rhodamine
derivatives are nonfluorescent and colorless when existing
in spirocylic forms, whereas their ring-opening structures
would give rise to strong fluorescence emission and pink
color [1–8]. Based on the transformation between these two
2+
3+
2+

such as Hg [3, 4], Fe [9], Cu [10–12], ClO [5, 13],
3+
2+
Cr [14], and Pb [15]. On the other hand, some of the
rhodamine derivatives are dependent on the reaction condi-
tions. For example, a simple change in the medium or sol-
vent system may result in switching the selective response
from one analyte to another, thereby enabling the same
rhodamine probe to be used for different detections [1, 16,
1
7]. The above measures have updated a number of tradi-
tional colorimetric methods in terms of selectivity and sim-
2+
plicity. Among the rhodamine probes reported for Cu ,
however, the prolonged reaction time and cross-sensitivities
toward other metal ions remain to be problematic.
*
Corresponding author (email: mahm@iccas.ac.cn)
Copper(II) is known to be an essential trace element in
©
Science China Press and Springer-Verlag Berlin Heidelberg 2011
chem.scichina.com
www.springerlink.com

1102
Sun CD, et al. Sci China Chem July (2011) Vol.54 No.7
biosystems and is an important environmental pollutant at
at 400 MHz in CD
.2 Reagents
3
OD.
2+
high concentrations [18]. Therefore, determination of Cu
has attracted wide-spread interests. In particular, colorimet-
2
2
+
ric measurements of Cu have received extensive attention,
because such detections have the advantage of simplicity
Rhodamine B, hydrazine hydrate (85%), maleic anhydride,
and acryloyl chloride were purchased from Beijing Chemi-
[
19], reliability, and visualization. So far, many probes have
2
+
3+
been proposed for the colorimetric sensing of Cu [20–23].
In connection with a program of investigating new spec-
troscopic probes, a series of rhodamine probes have been
developed in our laboratory [3, 5, 24–27]. In the present
study, we report the synthesis of a new rhodamine deriva-
tive, N-(3-carboxy)acryloyl rhodamine B hydrazide (CARB;
cal Reagent Co and used as received. The solutions of Al ,
2+
2+
3+
2+
2+
2+
2+
Ca , Cu , Fe , Hg , Mg , Ni , and Sn were prepared
+
2+
2+
from their chloride salts; the solutions of Ag , Ba , Cd ,
2+
+
3+
2+
2+
Co , K , La , Pb , and Zn were prepared from their ni-
2
+
2+
trate salts; the solutions of Fe and Mn were prepared
2
3


2
4
from their sulphate salts; the solutions of CO , ClO , HPO ,
2+
2
Scheme 1), and its unusual spectroscopic reaction with Cu .
The derivative displays a rapid and reversible non-fluores-
and SiO3 were prepared from their sodium salts. The
Palitzsch’s buffer solution (0.2 mol/L) was prepared with
2
+
cent absorption upon coordination to Cu , which is rather
rare for rhodamine B derivatives. This unusual reaction
mechanism has been investigated by a comparative study on
the model compound N-acryloyl rhodamine B hydrazide
3 3 2 4 7
H BO , NaCl, and Na B O [28]. The stock solutions (1.0
mmol/L) of CARB and ARB were prepared with tetrahy-
drofuran (THF) as solvent. Distilled-deionized water was
used unless otherwise noted. All other reagents were of
analytical grade and used without further purification.
(
ARB, Scheme 1) as well as by the density functional the-
ory calculations. Moreover, compared with many of the
2
+
reported rhodamine probes for Cu , CARB exhibits an im-
proved overall performance in terms of fast reaction time
and good selectivity, which makes it to be of great potential
2
.3 Synthesis of CARB and ARB
CARB was synthesized from rhodamine B via a two-step
reaction (Scheme 1). First, rhodamine B hydrazide was
prepared in 75% yield employing the previously reported
procedure [5]. Then, rhodamine B hydrazide (456 mg, 1.0
mmol) was dissolved in dichloromethane (30 mL), to which
a solution of maleic anhydride (490 mg, 5.0 mmol) in di-
chloromethane (10 mL) was added dropwise. The resulting
solution was stirred at 35 °C for 2 h, and then the solvent
was removed under reduced pressure to get a violet-red
residue, which was purified by silica-gel column chroma-
tography with ethyl acetate-petroleum ether (bp 60–90 °C)
(1:9, v/v) as eluent, affording 194 mg of CARB (yield 35%).
2
+
use in the rapid visual detection of Cu .
2
Experimental
2
.1 Apparatus
The absorption spectra were recorded in 1 × 1 cm quartz
cells on a TU-1900 spectrophotometer (Beijing Purkinje
General Instrument Co., Ltd.). pH Values were measured on
a model HI-98128 pH-meter (Hanna Instruments Inc., USA).
MALDI-TOF mass spectra were measured on a BIFLEX III
mass spectrometer (Bruker, Inc.). Electrospray ionization
mass spectra (ESI-MS) were measured on an LC-MS
1
H NMR (400 MHz, CD OD, 298 K)  7.94 (d, J = 7.2 Hz,
3
1H), 7.61 (m, 2H), 7.12 (d, J = 7.4 Hz, 1H), 6.60 (d, J=8.8
Hz, 2H), 6.42 (s, 2H), 6.38 (d, J = 9.0 Hz, 2H), 6.27 (d, J=
13.2 Hz, 1H), 6.02 (d, J = 13.0 Hz, 1H), 3.40 (q, J=6.8 Hz,
8H), 1.33 (s, 2H), 1.18 (t, J=6.8 Hz, 12H). MALDI-TOF, m/z:
2
010A (Shimadzu, Japan) instrument. Elemental analyses
1
were carried out on a Flash EA 1112 instrument. H NMR
spectra were measured on a Bruker DMX-400 spectrometer
Scheme 1 Synthesis of CARB and ARB.

Sun CD, et al. Sci China Chem July (2011) Vol.54 No.7
1103
+
5
55.2 [M+H] . Elemental analysis, calcd. for C32
H
34
N
4
O
5
:
buffer (pH 7.0) containing 10% (v/v) THF or acetonitrile,
and THF was used as a co-solvent for Cu -CARB com-
plexes.
2+
C 69.30, H 6.18, N 10.10%; found, C 69.46, H 6.37, N
9
.82%.
The model compound ARB was synthesized by treating
Figure 1 shows absorption spectra of CARB and its reac-
2+
rhodamine B hydrazide with acryloyl chloride (Scheme 1).
Acryloyl chloride (450 mg, 5.0 mmol) was added dropwise
to a solution of rhodamine B hydrazide (456 mg, 1.0 mmol)
in dichloromethane (30 mL). The resulting solution was
stirred at 0 °C for 2 h, and then treated with water (50 mL).
The organic layer was separated, and the solvent was re-
moved under reduced pressure to yield a violet-red residue,
which was then purified by silica-gel column chromatogra-
tion solutions with Cu at various concentrations. As can
be seen, CARB itself has nearly no absorption in the visible
region (curve 1), which may be attributed to its closed spi-
2+
rolactam form [1, 2, 25]. Upon gradual addition of Cu
(curves 2–18), however, a pink color appears, with a maxi-
mum absorption at 567 nm and a molar absorptivity of 2 ×
4
1
1
10 (mol/L) cm . This may be ascribed to the opening of
2+
the closed spirolactam structure promoted by Cu com-
plexation. Surprisingly, the reaction system of CARB with
phy with methanol as eluent, affording 153 mg ARB (yield
1
2+
3
7
0%). H NMR (400 MHz, CD
3
OD, 298 K)  7.94 (d, J =
Cu barely produces fluorescence (data not shown), which
2+
.3 Hz, 1H), 7.63 (m, 2H), 7.14 (d, J = 7.4 Hz, 1H), 6.58 (d,
might result from the quenching effect of Cu through a
special binding mode (vide infra, Scheme 2, Section 3.6).
Most notably, the color-on reaction of CARB exhibits a
high selectivity for Cu over other common ions (Figure 2).
This property enables Cu to be distinguished easily from
J = 8.8 Hz, 2H), 6.42 (s, 2H), 6.38 (d, J = 8.9 Hz, 2H), 6.20
m, 2H), 5.64 (dd, J =8.8 Hz, J =2.7 Hz, 1H), 3.39 (q, J=6.8
Hz, 8H), 1.33(s, 1H), 1.18 (t, J=6.9 Hz, 12H). ESI-MS, m/z:
(
1
2
2+
+
2+
5
11.4 [M+H] . Elemental analysis, calcd. for C31
H
34
N
4
O
3
:
C 79.92, H 6.71, N 10.97%; found, C 79.69, H 6.93, N
1
0.80%.
2
.4 General procedure for Cu(II) detection
Unless otherwise noted, all the measurements were per-
formed according to the following procedure. In a 10 mL
tube, 5 mL of 0.2 mol/L Palitzsch’s buffer solution (pH 7.0),
1
.0 mL of THF, and 0.2 mL of CARB stock solution were
mixed, followed by addition of an appropriate volume of
2
+
Cu sample solution. The final volume was adjusted to 10
mL with water, and the reaction solution was thoroughly
mixed. After 5 min at room temperature, a suitable volume
of the reaction solution was transferred into a quartz cell
with 1 cm optical length to measure absorbance at 567 nm.
In the meantime, a blank solution containing no Cu was
prepared and measured under the same conditions for com-
parison.
2+
Figure 1 Absorption spectra of CARB (20 mol/L, curve 1) and its reac-
2
+
tion solutions with Cu at various concentrations (2–50 mol/L, curves
–18) in 0.1 mol/L Palitzsch’s buffer media (pH 7.0) containing 10% (v/v)
THF. The inset depicts the absorbance at 567 nm in curves 2–18 as a func-
2
2
+
tion of Cu concentration.
3
Results and discussion
3
.1 Absorption properties
2
+
The color reaction of CARB with Cu was initially exam-
ined in some pure aqueous buffer solutions such as phos-
phate, Tris-HCl, and Palitzsch’s buffer. No or only weak
color reaction was observed in the two former media, but in
the latter (Palitzsch’s buffer) a much stronger color reaction
occurred immediately. However, the reaction in the Palitzsch’s
buffer was unstable and the absorption spectrum of CARB
2
+
in the presence of Cu was gradually red-shifted with the
increase of time. This may result from the lower water solu-
2+
bility of the Cu -CARB complexes. Then, we examined the
effect of organic solvents (e.g., methanol, acetonitrile, and
THF) on the color reaction. The results show that a stable
pink color-on reaction could be produced in the Palitzsch’s
Figure 2 Absorption spectra of CARB (10 mol/L) reacting with various
ions (20 mol/L). Reactions were conducted at room temperature for 30
min in 0.1 mol/L Palitzsch’s buffer media (pH 7.0) containing 10% (v/v)
THF.

1104
Sun CD, et al. Sci China Chem July (2011) Vol.54 No.7
the other ions directly by the naked eye, and such a test is
3.2 Optimization of experimental conditions
2
+
shown in Figure 3. As can be seen, Cu , whether present
alone (b) or in mixed ions (u), displays the expected pink
color, but the other ions do not show any color.
Different experimental conditions, such as THF concentra-
tion, pH, reaction temperature, and time, were examined for
optimization. To stabilize absorption spectra, at least 6%
The reversibility of the reaction was also investigated. As
shown in Figure 4, addition of 1 equiv of EDTA to the reac-
(
v/v) of THF is required, and 10% (v/v) of THF may be used
2
+
in this work. The effect of pH, reaction temperature, and
time on the absorbance is shown in Figure 5. As can be seen
tion solution containing 1 equiv of Cu causes the disap-
pearance of the absorption band at 567 nm (curve c) due to
the stronger binding ability of EDTA. Further introduction
2+
from Figure 5(a), CARB does not react with Cu in the
alkaline media with pH > 7.8, consistent with the behavior
of N-benzoyl rhodamine B hydrazide [5] that possesses the
same reaction group. Because CARB shows the best per-
formance at about pH 7, the combination of pH 7.0 Palitzsch’s
buffer and 10% (v/v) THF is selected for the present reac-
tion system. Change in temperature from 15 to 45 C hardly
affects the absorbance (Figure 5(b)), and thus room tem-
perature may be employed in this experiment. Time course
studies reveal that the color reaction is fast, and is almost
completed in 1 min (Figure 5(c)). Moreover, the formed
pink color is stable and could remain constant for at least 2
days. Based on the above observations, the optimized reac-
2+
of 1 equiv. of Cu into the reaction system re-produces the
pink color (curve d; the incomplete recovery is due to the
presence of EDTA). These results indicate that the com-
2+
plexation of CARB with Cu is reversible, which is impor-
2
+
tant for monitoring dynamic changes of Cu concentration.
2+
tion conditions for Cu analysis include a reaction time of
min at room temperature in 0.1 mol/L Palitzsch’s buffer
5
Figure 3 A photograph of color reactions of CARB (10 mol/L) with
various ions. Reactions were performed at room temperature for 30 min in
0
.1 mol/L Palitzsch’s buffer solution (pH 7.0) containing 10% (v/v) THF.
2
+
(a) CARB only (reagent blank); (b) CARB + 10 mol/L Cu ; (ct) CARB
Figure 4 Effect of EDTA on absorption spectra of CARB reacting with
3
+
+
2+
2+
2+
2+
3+
3+
2+
2+
+
2+
+
20 mol/L of Al , Ag , Ba , Ca , Cd , Co , La , Fe , Fe , Hg , K ,
Cu in 0.1 mol/L Palitzsch’s buffer solution (pH 7.0) containing 10% (v/v)
2
+
2+
2+
2+
2+
2+

2+
Mg , Mn , Ni , Pb , Sn , Zn and ClO , respectively; (u) the sample b
+
Fe , Fe , Hg , K , Mg , Mn , Ni , Pb , Sn , Zn and ClO ).
THF. (a) CARB (20 mol/L) alone; (b) CARB (20 mol/L) + Cu (40
3
+
+
2+
2+
2+
2+
3+
2+
other mixed ions (20 mol/L of Al , Ag , Ba , Ca , Cd , Co , La ,
mol/L); (c) the sample b + EDTA (40 mol/L); (d) the sample c + Cu
3
+
2+
2+
+
2+
2+
2+
2+
2+
2+

(40 mol/L).
2
+
Figure 5 Effect of pH (a), reaction temperature (b) and time (c) on the absorbance at 567 nm of CARB (10 mol/L) reacting with Cu (20 mol/L). Con-
ditions: (a) the reaction was carried out at room temperature for 5 min in 0.1 mol/L Palitzsch’s buffer solution containing 10% (v/v) THF with different pH
values; (b) the reaction was performed in 0.1 mol/L Palitzsch’s buffer solution (pH 7.0) containing 10% (v/v) THF at different temperatures for 5 min; (c) the
reaction was conducted at room temperature for different time in 0.1 mol/L Palitzsch’s buffer solution (pH 7.0) containing 10% (v/v) THF.

Sun CD, et al. Sci China Chem July (2011) Vol.54 No.7
1105
solution (pH 7.0) containing 10% (v/v) THF.
.3 Linearity
3
Under the optimized condition, a linear relationship was
determined by plotting the absorbance of CARB against
2
+
Cu concentration. A linear equation of A
= 0.0675 +
567nm
2+
2
0
.0248 × [Cu ] (n = 16, R = 0.990) was obtained in the
concentration range of 4–40 mol/L Cu (see also the inset
of Figure 1). The detection limit for Cu was 4.5 × 10
2
+
2
+
7
mol/L based on 11 blank determinations (S/N = 3).
3
.4 Binding stoichiometry of CARB with Cu(II)
To determine the binding stoichiometry, the continuous
variation method (Job’s plot) [29] was used by measuring
the absorbance of the reaction system at 567 nm. As shown
in Figure 6(a), a maximum absorbance is produced when
2
+
the molecular fraction of Cu is close to 67%, indicating
2
+
that the binding ratio of CARB to Cu is 1:2. This result is
also supported by the molar ratio method (Figure 6(b))
[
30–32]. On the basis of 1:2 stoichiometery, the stability
2
+
constant of the CARB-Cu complex is estimated to be 4.9 ×
1
1
5
2
0 (mol/L) .
2
+
Figure 6 Binding stoichiometry of CARB and Cu . (a) Job’s plot for the
2
+
2+
system of CARB with Cu (the total concentration of Cu and CARB was
kept constant at 30 mol/L); (b) molar ratio method (the concentration of
CARB was constant at 20 mol/L). The absorbance was measured at 567 nm.
3
.5 Interference studies
The effects of various ions on the absorbance were investi-
gated by analyzing the CARB solutions containing 20

the criterion at which a species gave a relative error of no
more than 10% in recovery for 20 mol/L Cu . As shown
in Table 1, high-valent cations such as Al and Fe seem
to have lower tolerable concentrations. However, higher
levels of these ions in the media of pH 7.0 would lead to
precipitation of metal hydroxides, which can be removed
through filtration. In addition, all the other common ions
2+
mol/L Cu . The tolerable concentration was estimated by
2
+
Table 1 Recovery of 20 mol/L Cu in the presence of various coexist-
ing ions
2
+
3
+
3+
Concentration
mmol/L)
Molar ratio of the
added ion to Cu
Ions
2+
Recovery (%)
(
+
K
4
12
20
0.4
0.2
2
200
600
1000
20
108
106
101
93
2
+
Ca
Mg
2
+
3
+
Al
2+
+
produce little influence on the determination of Cu , indi-
cating a highly selective feature of the present system.
Ag
10
99
2
+
Ba
Cd
Co
100
100
100
5
98
2
2
+
2
101
102
94
+
2
3
.6 Reaction mechanism
3+
Fe
Fe
0.1
0.4
1
2
+
2+
20
97
As described above, the color reaction of CARB with Cu
is attributed to the ring-opening of the spirolactam structure
promoted by Cu complexation. However, the reaction
system hardly shows fluorescence, which is rather different
from that of the common rhodamine spirolactam derivatives
2
+
Hg
50
98
3
+
La
1
50
102
102
95
2
+
2+
Mn
2+
4
200
200
150
15
Ni
Pb
Sn
Zn
4
2+
2+
3
104
95
[
1, 2, 33]. To explore the reaction mechanism of CARB
0.3
2
2+
2
+
with Cu , the model compound ARB, which only lacks the
extra carboxyl group (Scheme 1), was synthesized for com-
parison. Interestingly, ARB does not show any color re-
sponse to Cu under the same conditions. This strongly
indicates that the extra carboxyl group in CARB plays a
crucial role in the color-on reaction, and without it the reac-
tion can not occur. Considering the above result of 1:2
100
20
103
108
103
95

ClO
CO
0.4
2
2
3

100
40
2+
2
4
HPO
0.8
6

NO
300
200
500
104
102
106
3
2

SO4
4
2

SiO3
10

1106
Sun CD, et al. Sci China Chem July (2011) Vol.54 No.7
mized at the B3LYP/6-31G level by the Gaussian 03 pro-
2+
gram [37], shows that one Cu is located in a caged struc-
ture by coordinating with two oxygen atoms and two nitro-
2+
gen atoms. The other Cu is coordinated with the extra
carboxyl group and interacts with the -conjugated benzene
ring of xanthene.
3
.7 Comparison with other rhodamine probes
A summary of the rhodamine-based probes for the detection
2+
of Cu is given in Table 2. As can be seen, each probe has
its own charactersistic. Compared with most of the probes,
2
+
Scheme 2 The possible reaction mechanism of CARB with Cu .
2+
stoichiometery, the color-on reaction of CARB with Cu
may be explained by the route depicted in Scheme 2: the
carboxyl and hydrazide groups in CARB produce a coop-
eration effect, leading to the formation of a 1:2 complex.
2+
The two Cu ions in the complex may play different roles:
one induces the opening of the spirocyclic structure and the
other quenches the fluorescence of the xanthene moiety
[
34–36]. It is noted that the curve in Figure 6(b) appears
2+
somewhat in an S-shape, suggesting that the two Cu ions
might also have a cooperation effect in the reaction. More-
over, density functional theory calculations provide further
structural evidence for the CARB-Cu 1:2 complex. As
depicted in Figure 7, the geometry of the complex, opti-
2+
Figure 7 The calculated structure of the 1:2 CARB-Cu complex. Gray,
2
+
red, blue and green atoms denote C, O, N and Cu atoms, respectively,
where H atoms are omitted for clarity.
2
+
Table 2 Comparison of different rhodamine probes for the determination of Cu
Probes
Reaction medium
Reaction time (min) Interfering ion
Reversibility
Yes
Ref.
[11]
2
+
CH
3
CN
60
Hg
Rhodamine B hydroxylamide
Rhodamine B hydrazide
pH 6.0 Tris-HCl with 60% (v/v)
CH CN
120
2
No
No
No
[25]
[36]
3
a
2+
pH 7.0 HEPES with 80% (v/v)
CH CN
Hg
3
pH 7.0 Tris-HCl with 90% (v/v)
CH CN
2+
4
0
Zn
Not available
[38]
3
(To be continued on the next page)

Sun CD, et al. Sci China Chem July (2011) Vol.54 No.7
1107
(Continued)
Probes
Reaction medium
pH 7.4 HEPES
Reaction time (min) Interfering ion
Reversibility
Yes
Ref.
Rhodamine B boronic acid
30
No
[39]
pH 7.2 HEPES with 30% (v/v)
2+
1
Hg
No
[40]
3
CH CN
Platinum film-immobilized rhodamine
Salicylaldehyde rhodamine B hydrazone
methanol
30
20
No
Yes
Yes
[41]
[42]
2
+
pH 7.0 Tris-HCl with 50% (v/v)
Fe
CH
N-(3-Carboxy)acryloyl rhodamine B hydrazide pH 7.0 Palitzsch’s buffer with 10%
v/v) THF
3
CN
5
No
Yes
This work
(
a) HEPES: 4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid.
J, 2008, 14: 4719–4724
however, CARB exhibits an improved overall performance
in terms of fast reaction time and good selectivity.
6
7
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