Visual detection and removal of mercury ions by a ferrocene derivative

Article abstract of DOI:10.1016/j.tetlet.2014.04.093

New ferrocene naphthyridine derivatives were successfully synthesized. The di-substituted ferrocene derivative FecDN behaves as a selective visual chemosensor for mercury ions, exhibiting a rapid and clearly visible precipitation with good selectivity (precipitation) and sensitivity (0.01 μM). The interaction of the ferrocene derivatives and metal ions was investigated by ultraviolet-visible spectroscopy (UV-vis), electrochemical methods, ¹H NMR, as well as infrared (IR), and energy dispersive X-ray spectroscopy (EDX). The application of FecDN in the detection and removal of mercury ions is very simple, rapid, and intuitive.

Full text of DOI:10.1016/j.tetlet.2014.04.093

Accepted Manuscript
Visual detection and removal of mercury ions by a ferrocene derivative
Xiaoqian Peng, Hanping He, Jingping Xia, Zhaowen Lou, Gang Chang, Xiuhua
Zhang, Shengfu Wang
PII:
S0040-4039(14)00730-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.04.093
TETL 44555
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
11 December 2013
8 April 2014
28 April 2014
Please cite this article as: Peng, X., He, H., Xia, J., Lou, Z., Chang, G., Zhang, X., Wang, S., Visual detection and
removal of mercury ions by a ferrocene derivative, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/
j.tetlet.2014.04.093
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Visual detection and removal of mercury
ions by a ferrocene derivative
Xiaoqian Peng, Hanping He, Jingping Xia, Zhaowen Lou, Gang Chang, Xiuhua Zhang, and Shengfu Wang

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Visual detection and removal of mercury ions by a ferrocene derivative
Xiaoqian Penga, Hanping Hea,  Jingping Xiaa, Zhaowen Loua, Gang Changb, , Xiuhua Zhanga, and
Shengfu Wanga
aHubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Ministry of Education Key Laboratory for the
Synthesis and Application of Organic Functional Molecules, College of Chemistry and Chemical Engineering, Hubei University, Youyi
Road 368, Wuchang, Wuhan, Hubei 430062, (PR China)
bMinistry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, College of Materials
Science and Engineering, Hubei University, Youyi Road 368, Wuchang, Wuhan, Hubei 430062, (PR China)
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
New ferrocene naphthyridine derivatives were successfully synthesized. The di-
substituted ferrocene derivative FecDN behaves as a selective visual chemosensor for
mercury ions, exhibiting a rapid and clearly visible precipitation with good selectivity
(precipitation) and sensitivity (0.01 µM). The interaction of the ferrocene derivatives
Available online
and metal ions was investigated by ultraviolet-visible spectroscopy (UV-vis),
electrochemical methods, H NMR, as well as infrared (IR) and energy dispersive X-
ray spectroscopy (EDX). The application of FecDN in the detection and removal of
mercury ions is very simple, rapid and intuitive.
1
Keywords:
Mercury ions
Di-substituted ferrocene derivative
Precipitation
2009 Elsevier Ltd. All rights reserved.
Visual
Removal
An increasing current interest has arisen in the design and
development of selective and sensitive methods for the detection
of heavy-metal ions because of the extensive use of these metal
ions and their detrimental impact on the environment and human
health. Among these heavy-metal ions, mercury ion (Hg2+) poses
severe hazards such as immuno/geno/neurotoxic defects1. It is not
biodegradable and is converted to the organomercury species,
which can be accumulated in the body. Mercury pollution is
widespread, occurring through many pathways from the chemical
industry or natural processes such as burning toxic chemicals,
coal-burning, solid incineration, and oceanic and volcanic
emission2. Even low levels of mercury pollution can be
concentrated through the food chain and the water contamination,
which poses a substantial threat to humans and animals, may be
lead to fatal mercury poisoning 3-5. Much attention has been
focused on developing cost-effective, rapid, and facile detection
Furthermore, numerous ferrocene derivatives have been applied
as chemsensors for the detection of heavy metal ions14. Among
them, some ferrocene-based chemosensors for Hg2+ have already
been reported, in which significant electrochemical changes
occurred at the redox active ferrocenyl moiety upon the addition
of the target ion15. Ferrocenylamide-containing molecules have
played an important role in the development of molecular
sensors16 because of the hydrongen-bonding interaction of the
amide N-H hydrogens with guest species. The 1, 8-naphthyridine
units has been of interest to many research groups because of its
ability to serve as a hydrogen-bonding unit in molecular
recognition and large self-assemblies17.
We have investigated some naphthyridine derivatives as
recognition elements for nucleotides18. As a continuation of our
work with ferrocene derivatives19, we have combined a
ferrocenyl group to 1, 8-naphthyridine by an amide linkage.
Here, the mono- and di-substituted ferrocenylamide-
naphthyridine conjugates, FecMN and FecDN (as shown in
Scheme 1) were synthesized and applied towards the detection
and removal of the heavy metal ion Hg2+. The di-substituted
conjugate FecDN revealed the presence of Hg2+ by forming an
orange precipitate, which is clearly visible to the naked eye,
making it applicable towards the removal of Hg2+.
and removal methods for mercury ions.
A number of
sophisticated signaling systems have been developed to detect
Hg2+ 6, such as atomic absorption spectrometry7, inductively
coupled plasma atomic emission spectrometry8, electrochemical
sensing9,10, and optical detection (emission or color change)11,12
.
Ferrocene derivatives have earned considerable attention from
many researchers due to their outstanding stability, redox
activity, and potential use in catalysis, pharmaceuticals etc.13.
———
Scheme 1 illustrates the synthesis of the mono- and di-
 Corresponding author. Tel.: +86-27-50865319; fax: +86-27-88663043;
 e-mail: hehanping@hubu.edu.cn (H. He) changgang@hubu.edu.cn (G.Chang).

2
Tetrahedron
substituted ferrocene derivatives. The conjugates FecMD and
Titration experiments were performed using UV-vis
spectroscopy. Free FecDN in ethanol/H2O showed absorption
maxima signal at 220nm and 340nm. As shown in Figure 2(a),
the addition of Hg2+ to the FecDN solution caused a decrease in
both bands, which eventually disappeared due to the formation of
precipitation (Hg-FecDN complex). In the presence of 1-2.6
equiv of Cu2+ (Figure 2(b)), the peak about 210 nm was seen to
increase. The peak about 340 nm showed a noticeable
hypsochromic effect and a red shift (Δλ, 30 nm). This change
may be attributed to the formation of a Cu-FecDN complex,
which affects the conjugation of FecDN itself. In the presence of
other metal ions, the absorption pattern of FecDN has no obvious
changes (Figure S1). For metal ions mixed with FecMN, no
obvious changes in the absorption spectra were found (Figure S2),
which was consistent with the lack of visual change.
FecDN were synthesized by the general reaction of 2-methyl-7-
amine-1, 8-naphthyridine, and either ferrocenecarboxylic acid or
1, 1'-ferrocenedicarboxylic acid under the mild reaction
conditions in the presence of HBTU and DIPEA. The FecMN
and FecDN were characterized by IR, H NMR, 13C{H} NMR
1
and ESI-MS (the details and copies of H NMR, 13C NMR and
1
ESI-MS can be seen in the supporting information).
The job plot analysis was carried out by UV-vis spectra (the
detail experiment was shown in supporting information). The job
plot showed 1:1 complexation stoichiometry (Figure S3).
1
Additionally, a H NMR titration was performed in the absence
and presence of different concentration of Hg2+ in the
CD3OD/D2O, and the spectra were present in the supporting
information (Figure S4). It was found that the all the proton
peaks disappeared after 0.8~1 equiv Hg2+ because of generation
of precipitation.
few seconds
Figure 1. Visual features observed in an ethanol /H2O
solution of FecDN (0.5 mM) after the addition of 10 equiv of
different metal cations in water.
Scheme 1. Synthesis of the ferrocene derivatives, FecMN and FecDN.
The chemosensing behavior of FecMN and FecDN towards
a variety of cations (Hg2+, Cr3+, Mn2+, Co2+, Zn2+, Cu2+, Mg2+,
Ba2+, Pb2+, K+, Ca2+, Na+) was investigated by naked eye
visualization and UV-vis spectroscopy. The different metal
chloride aqueous solutions were added dropwise into 0.5 mM
FecDN and FecMN ethanol/H2O solutions respectively. As
shown in Figure 1, the FecDN solution became noticeably cloudy
when Hg2+ was added. The orange precipitate settled after few
seconds. The yellow FecDN solution became a slightly darker
when Cu2+ added. For the other cations, no obvious changes were
observed in the FecDN solution. Similarly, there were no
changes when these cations were added into the FecMN solution.
The unique and striking orange precipitation indicated the
selective recognition of FecDN for Hg2+.
Ferrocene derivatives exhibited good redox-active
properties, so the interaction between FecDN and metal ions was
studied by SWV in a 1mM FecDN ethanol/H2O solution
containing [(n-Bu)4N]ClO4 as a supporting electrolyte. In the
potential window from 0.4 V to 1.0V, FecDN shows an oxidation
peak potential at 0.752 V with a peak current 2.5 µA (Fig.3(a)).
With the gradual addition of Hg2+, it was found that the peak
current was weakened and disappeared when the molar ratio of
FecDN and Hg2+ was approximately 1:1. These results may
demonstrate that the formation of the Hg-FecDN complex causes
a decrease of the free FecDN in the solution. In the presence of
excess Cu2+, the peak at 0.752V disappeared, and a new peak
about 0.4V appeared with the concomitant reduction of Cu2+ to
Cu+ (Fig.3(b)). After adding excess amounts of other metal ions,

3
the carbonyl stretching frequencies shift from 1682 cm-1 to
the peak at 0.752 V always decreases to some extent (Figure S5).
This observed phenomenon may be attributed to the electrostatic
repulsion between the metal ions and the electro generated
positive charge on the ferrocene unit.
1695 cm-1. No obvious changes were observed in the other peaks.
The results indicate that the amide N in FecDN is involved in the
coordination of the mercury ion. The N in the naphthyridine has
also possible tendency to conjugate to mercury ion.
Figure 3. SWV of spectra of 1mM FecDN (v/v, 1:2 ethanol
/H2O) interaction with (a) Hg2+ and (b) Cu2+, the concentrations
of (a) Hg2+ and (b) Cu2+ increased with the arrow direction: (a)
0(blue), 0.4, 0.5, 0.7, 0.9, 1.2 mM (red) of Hg2+, (b) 0 (blue), 1,
2, 3, 5, 6, 7, 8, 9, 10mM(red) of Cu2+.
Figure 2. UV/Vis spectra of FecDN (50 uM) in ethanol/H2O
after addition of: (a) Hg2+ (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11
equiv concentration with arrow direction) and (b) Cu2+ (0, 0.2,
0.4, 0.6, 0.8, 1.0, 1.4, 1.8, 2.2, 2.6 equiv concentration with
arrow direction).
EDX was used to determine the elemental N, Fe, and Hg
content (Figure S6). Firstly, the EDX analysis shows that the
elemental composition of N, Fe, and Hg in the free FecDN
molecule was 7.02%, 1.02%, and 0 (molar ratio, 6.9:1:0). The
results agreed well with the theoretical molar ratio (N:Fe:Hg,
6:1:0, C30H24FeN6O2). In the precipitate, the elemental
composition of N, Fe, and Hg was N 9.15%, Fe 1.43%, Hg
1.97% respectively, which means the molar ratio close to 6:1:1.
This value indicated that Hg2+ formed a 1:1 complex with FecDN,
The above studies indicate that FecDN possesses significant
potential for the recognition and removal of mercury ions due to
the rapid and clearly visible formation of a precipitation. Here,
the precipitated FecDN-Hg complex was characterized by IR and
EDX to analyze the probable structure. Strong amide protons N-
H and carbonyl stretching frequencies were found at 3406 and
1682 respectively for free FecDN (Figure 4, FecDN, IR (KBr,
cm-1): 3406, 1682, 1612, 1508, 1438, 1390, 1322, 1274, 1133).
The IR bands of the precipitate FecDN-Hg were 3329, 1695,
1611, 1507, 1439, 1387, 1332, 1269, 1129, 851, 790 (KBr, cm-
1). Here, there are very obvious changes in the amide protons N-
H and carbonyl stretching frequencies. The amide protons N-H
frequency was found to shift from 3406 cm-1 to 3329 cm-1, and
1
which is consistent with the job plot measurement, H NMR, and
electrochemical experiment. Considering that the formed Hg-
FecDN complex is insoluble, so we inferred that FecDN and
Hg2+ may form a type of insoluble metal complexes of
macromolecules.

4
Tetrahedron
nm became weak and finally disappeared after 90 µM (the values
of absorbance peak: 0.165, 0.084, 0.049, 0.021, 0.006, 0.006,
respectively). The results indicated that the Hg2+ in water was
removed by treatment of FecDN.
In conclusion, we have successfully synthesized new mono-
and di-substituted ferrocene derivatives, FecMN and FecDN. It
was found that di-substituted ferrocene derivatives (FecDN) may
be used as visual chemosensors for Hg2+ based on precipitation.
In the presence of FecDN, an Hg2+ aqueous solution rapidly
forms a precipitate with the molar ration of 1:1. FecDN was also
successfully used to remove mercury ions from water. The
application of FecDN in the detection with very good selectivity
and sensitivity and removal of mercury ions is very simple, fast
and intuitive.
Figure 4. IR spectra of FecDN (a) before and (b) after
interaction with Hg2+.
Owing to the selective recognition of FecDN to mercury ions
with fast precipitate, we were able to detect and removal Hg2+ in
aqueous solution using FecDN compound. When a FecDN
ethanol stock solution is added into a test aqueous solution, if the
test solution becomes turbid, it means that the solution is polluted
by Hg2+. We tested Hg2+ polluted water containing different
concentrations of mercury. As shown in Figure S7, 10 µM Hg2+
water immediately became cloudy after adding FecDN. After a
few seconds, an orange precipitate was observed at the bottom of
the testing solution (Figure S7b). When the Hg2+ concentration
was decreased to 5 µM, the water also became cloudy. If the
Figure 5. UV-vis spectra of the filtrate. The concentration of
FecDN increased in the direction of the arrow: 0, 15 uM, 30
uM, 60 uM, 90 uM, 120 uM.
0
solution was left at 3-5 C for 10min, we could observe a thin
layer of orange precipitate. When the concentration of Hg2+ was
further reduced to 1 µM, 0.1 µM and 0.01 µM, the turbidity
could no longer be seen by the naked eye, which may be
attributed to too little precipitate. However we see the orange-
yellow precipitate after the solution was rotated centrifugal with
high speed, or 80%~90% of water was evaporated. To eliminate
the possibility of interference, FecDN and Hg2+ aqueous
solutions were tested separately in the same manner. No turbidity
or precipitation was observed, which indicated that the formed
precipitate may be observed by concentrating or rotating the
aqueous solution. For other metal ions, we did not observe any
turbidity. So the chemical sensor FecDN can be used detect
Hg2+with low concentration 0.01µM. In addition, the detection of
Hg2+ water containing mixed metal ions was performed (Figure
S7c). When the mixed metal ions (Cr3+, Mn2+, Co2+, Zn2+, Mg2+,
Ba2+, Pb2+, K+, Na+) didn’t contain Hg2+, we did not observe any
precipitation or turbidity after addition of FecDN. Importantly
when the mixed metal ions contain Hg2+, the orange precipitation
was clearly found. These phenomenons show that FecDN can be
used as a chemical probe to selectively detect Hg2+ even in the
presence of the competitive mixed-ions.
Acknowledgments
Authors gratefully acknowledge support from Educational
Commission of Hubei Province of China (D20131007), the
national Science of Foundation of China (Grant 21002024), and
the National Science Fund for Creative Research Groups of
Hubei Province of China (2011CDA111).
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