Colorimetric detection of in situ metal acetates and fluorides by a bipyridyl-linked Schiff base

Article abstract of DOI:10.1002/jmr.2393

A new bipyridyl moiety linked Schiff base (bipy-1) was developed and showed selective recognition of dimethyl sulphoxide solution of tetrabutyl ammonium salt of F^- ion with absorbance at 529 nm and interesting binding of aqueous Co, Ni, and Cu acetates/fluorides, as confirmed by distinct color changes from fluorescent green to pink or orange with absorbance at 480-510 nm. However, in situ formation of Co, Ni, and Cu acetates/fluorides also was found to be able to respond to similar color and absorption changes.

Full text of DOI:10.1002/jmr.2393

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
Research Article
Received: 11 February 2014,
Revised: 12 May 2014,
Accepted: 14 May 2014,
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jmr.2393
Colorimetric detection of in situ metal acetates
and fluorides by a bipyridyl-linked Schiff base
Sivalingam Suganyaa, Hye Jin Zob, Jong S. Parkb and Sivan Velmathia*
Here, we present a new bipyridyl moiety linked Schiff base (bipy-1) that is well characterized using spectroscopic
techniques. Colorimetric and UV-vis titrations were used to study the photophysical properties of bipy-1 in the presence
of various tetrabutyl ammonium salt of anions and metal salts containing different counter cations. bipy-1 showed
selective recognition of dimethyl sulphoxide solution of tetrabutyl ammonium salt of FÀ ion accompanied with a UV-
vis band at 529 nm and interesting binding of aqueous Co, Ni, and Cu acetates/fluorides, as confirmed by distinct color
changes from fluorescent green to pink or orange and a strong band around 480–510 nm in the UV-vis spectrum.
However, in the presence of Co, Ni, and Cu countercations, any form of metal acetate/fluorides was found to be able
to respond to similar color changes from fluorescent green to pink or orange, showing a band around 480–510nm. This
type of output clearly indicates that the in situ formation of Co, Ni, and Cu acetates/fluorides also coordinates with
bipyridyl nitrogen atoms. Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: bipyridyl Schiff base; colorimetric analysis; metal acetate/fluoride; in situ analyte detection
2008), imidazole (Zapata et al., 2009), quinoline (Basa & Sykes,
2012), triazole (Maity & Govindaraju, 2012), and naphthalimide
INTRODUCTION
(Satriano et al., 2013)), coumarin (Jung et al., 2009), and rhodamines
(Zhou et al., 2009). In this article, we demonstrate for the first time
the synthesis of bipy-1 and its binding property with Co(OAc/F)2,
Ni(OAc/F)2, and Cu(OAc/F)2 manifested by colorimetric analysis
and UV-vis titration. The surprising concept is that the in situ formed
metal acetates/fluorides can also bind effectively with bipy-1,
showing results similar to those of the original metal acetates/
fluorides. To the best of our knowledge, this is the first report of in
situ formed metal acetate/fluoride binding with organic receptors.
The dual-responsive nature of bipy-1 also makes the system interest-
ing with regard to the selective detection of tetrabutyl ammonium
(TBA) salt of FÀ ion in dimethyl sulphoxide (DMSO) medium.
Molecular recognition is a fascinating and growing research field
for the identification of charged (Ghosh et al., 2006; Mahapatra
et al., 2012; Tang & Cai, 2012; Guo et al., 2013) and neutral
analytes (Buryak & Severin, 2005; Zhou & Yoon, 2012) because
they are cost effective, easy to create, selective for particular
analytes, and show high sensitivity even at trace levels. Design-
ing a single molecule for multiple analytes in the direct as well
as in the in situ form is a highly interesting and new concept in
the molecular recognition field. Among all metal ions, “d” block
metal ions are capable of effective interaction with organic
receptors. In particular, Co2+ (Maity & Govindaraju, 2011; Zhen
et al., 2011), Ni2+ (Aksuner et al., 2012; Wang et al., 2012), and
Cu2+ (Hua et al., 2013; Lin et al., 2013) ions are biologically
important species because of their extraordinary roles in living
organisms. Similarly, fluorides and acetate ions (Zhang et al.,
2009; Hu et al., 2011; Mahapatra et al., 2011) are also biologically
important anions with a wide range of application in medicine,
food preservation, and in enzyme-catalyzed reactions. Deficiency
of such charged analytes leads to severe health risks such as
Alzheimer’s disease, anemia, and heart and nerve problems.
Although many reports are available regarding the individual
detection of different types of metal ions or anions, the specific
binding of metal acetates and fluorides is rarely reported. Recently,
H. J. Zo et al. (Song et al., 2013) reported the selective sensing of Zn
(OAc)2 using a bipyridyl-modified acetylene dye.
EXPERIMENTAL SECTION
Materials and instruments used
Reagents such as o-amino phenol, 5,5′-dimethyl-2,2′-bipyridine,
Bredereck’s reagent, sodium periodate, TBA salt of anions,
and metal salts were received commercially and were used
as such without any further purification. The solvents DMSO,
ethanol (EtOH), and dimethyl formamide, used for the
spectroscopic experiments and synthesis process, were also
* Correspondence to: S. Velmathi, Organic and Polymer Synthesis Laboratory,
Department of Chemistry, National Institute of Technology, Tiruchirappalli-620
015, India. E-mail: velmathis@nitt.edu
Many receptors for charged analytes have recently been
designed using a binding site-signaling unit approach. When a
particular analyte binds with the receptor unit, the electronic
properties of the entire system are distorted upon a conversion
into an optical signal. Common building blocks for charged
analytes are nitrogen-containing compounds (Schiff base
(Udhayakumari et al., 2013), pyridine (Xue et al., 2005), bipyridine
(Beer et al., 2004), and phenanthroline (Wang et al., 2010)), NH
group (pyrrole and indole (Suganya et al., 2013; Martínez et al.,
a S. Suganya, S. Velmathi
Organic and Polymer Synthesis Laboratory, Department of Chemistry,
National Institute of Technology, Tiruchirappalli 620 015, India
b H. J. Zo, J. S. Park
Department of Organic Material and Polymer Engineering, Dong-A University,
Busan 604-714, Korea
J. Mol. Recognit. 2014; 27: 689–695
Copyright © 2014 John Wiley & Sons, Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
S. SUGANYA ET AL.
Scheme 1. Synthesis of bipy-1.
a
b
Figure 1. Color changes observed upon the addition of 2 eq of various metal (a) acetates and (b) fluorides (1.5 × 10À3 M in H2O) to bipy-1 (5 × 10À5 M in DMSO).
purchased and used as such. An Orbitrap Q Exactive mass
spectrometer was used for the molecular weight analysis. The
a
1H and 13C NMR spectra were obtained on a Bruker AV-III 300-
MHz spectrometer using DMSO-d6 as a solvent. The infrared (IR)
spectra were recorded on a Nicolet IS5 instrument using KBr plates.
The UV-vis spectra were recorded on a Shimadzu UV-2600 spectro-
photometer with a quartz cuvette (path length = 1 cm) at room
temperature (r.t.). For all the spectroscopic titrations, a 5 × 10À5 M
solution of bipy-1 in DMSO and 1.5× 10À3 M of all TBA salt of
anions in DMSO and metal salt of acetate, fluoride, chloride, and
nitrate in H2O were prepared and used.
b
c
Experimental procedure
2, 2′-Bipyridine-5,5′-dicarbaldehyde (bipy-CHO) was synthesized
using reported procedure (Hodacova & Budesınsky, 2007). Then,
bipy-1 was prepared by reacting 1 mmol of o-amino phenol with
2 mmol of 2,2′-bipyridine-5,5′-dicarbaldehyde in EtOH medium.
The reaction mixture was allowed to reflux for 3 h at 70°C. After
cooling to r.t., the precipitate formed was filtered, washed with
EtOH, and dried in a vacuum oven (Scheme 1). Yield: 70%; melt-
ing point: 265–270°C. IR (cmÀ1, KBr): 3357.65, 1624.37, 1590.26,
1488.80, 1369.67, 1241.85, and 1150.69. 1H NMR (300 MHz,
DMSO-d6, δ ppm): 9.26 (2H, OH, s), 9.13 (2H, CH=N, imine, s),
8.90 (2H, CH=N, pyridine ring, s), 8.59–8.62 (4H, aro, q), 7.29–
7.33 (2H, aro, dd), 7.11–7.16 (2H, aro, t), 6.91–694 (2H, aro, dd),
and 6.84–6.89 (4H, aro, t). 13C NMR (75 MHz, DMSO-d6, δ ppm):
153.93, 149.38, 148.35, 134.98, 134.15, 130.17, 125.93, 118.71,
117.26, 116.80, and 113.98. HRMS (M + 1): 395.1502 (calculated)
and 395.1502 (observed).
Figure 2. Color changes observed upon the addition of 2 eq of (a) NiCl2,
CoCl2, and CuCl2 to bipy-1 (5 × 10À5 M in DMSO) and the addition of (b)
Ni(OAc)2, Co(OAc)2, and Cu(OAc)2 and (c) NiF2, CoF2, and CuF2
(1.5 × 10À3 M in H2O) to the solution of panel (a).
wileyonlinelibrary.com/journal/jmr
Copyright © 2014 John Wiley & Sons, Ltd.
J. Mol. Recognit. 2014; 27: 689–695

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
MOLECULAR RECOGNITION
a
b
Figure 3. Color changes of bipy-1 (5 × 10À5 M in DMSO) in the presence of Ni2+ (NiCl2) counterion upon the addition of 2 eq of other metal (a) acetates
and (b) fluorides (1.5 × 10À3 M in H2O).
To evaluate the counteranion, UV-vis titration was carried
out with chloride and nitrate salts of Co, Ni, and Cu. No obvi-
RESULTS AND DISCUSSIONS
Bipy-1 consists of an extended conjugation by means of a Schiff
base at two ends of bipyridine ring, which can act as an excellent
chromophore for specific metal acetate, fluoride, and anions inter-
action, showing output in the visible region. The metal acetate
and fluoride binding of bipy-1 was investigated through exposure
to different aqueous metal acetates, fluorides, nitrates, and chlo-
rides. Among the different metal salts, aqueous solution of Co
(OAc/F)2, Ni(OAc/F)2, and Cu(OAc/F)2 showed distinct color changes
from fluorescent green to orange or pink (Figures 1(a)–1(b)).
Whereas aqueous solution of other metal acetates/fluorides, other
metal chloride and nitrate salt including Co, Ni, and Cu did not show
any significant effect, even in the presence of excess quantities un-
der aqueous and organic medium. However, in the presence of Co,
Ni, and Cu chloride/nitrate, the addition of Co(OAc/F)2, Ni(OAc/F)2,
and Cu(OAc/F)2 produced a color change, fluorescent green to
orange or pink. This finding implies that the formed in situ metal
acetate/fluoride binding was successfully achieved by bipy-1 with-
out chloride and nitrate counteranion interference (Figures 2(a)–2
(c)). In order to confirm the in situ metal acetate binding, a colori-
metric titration was carried out with the addition of different metal
acetate salts such as Mn(OAc)2, Co(OAc)2, Cu(OAc)2, Zn(OAc)2, Cd
(OAc)2, Pb(OAc)2, Na(OAc), and TBAAc to the solution of bipy-1:
Ni2+ complex. Similarly, CoF2, CuF2, NaF, and TBAF also used for
the confirmation of in situ metal fluoride binding with bipy-1. In
both cases, yellow color of the bipy-1:Ni2+ complex turned into
pink or orange suggesting the peculiar binding of in situ metal
acetate and fluoride (Figures 3(a)–3(b)). The colorimetric findings
were further confirmed by spectroscopic methods.
For bipy-1, strong bands at 375 and 325 nm were observed,
corresponding to the n–π* and π–π* transitions occurring within
the molecule. No significant band was observed in the visible
region for bipy-1. An addition of different metal acetate and
fluoride solutions to bipy-1, Co(OAc/F)2, Ni(OAc/F)2, and Cu
(OAc/F)2 individually showed a readily apparent, characteristic
band around 485–510 nm detailing the interaction with bipy-1
through a charge or electron transfer process (Figures 4(a)–4
(b)). For a complete understanding of the metal acetate
binding of bipy-1, UV-vis titrations were carried out as incre-
mental additions. Upon the addition of 0–2 eq of Co(OAc)2,
Ni(OAc)2, and Cu(OAc)2, a uniform formation of a new band
at 487, 516 and 487 nm, respectively, was observed with a
concomitant decrease in the bands at 375 and 325 nm (Figures
5(a)–5(c)).
ous changes in the absorption band of bipy-1 were observed
in the presence of Ni/CoCl2 and Ni/Co(NO3)2; however, CuCl2
and Cu(NO3)2 showed a reduction in the band at 375 nm
(Figure 6). Similarly, the influence of the countercation was
also evaluated in the presence of NiCl2 with other metal
bipy-1
TBAAc
Na(OAc)
Mn(OAc)2
1.5
1.0
0.5
0.0
a
Co(OAc)2
Ni(OAc)2
Cu(OAc)2
Zn(OAc)2
Cd(OAc)2
Pb(OAc)2
300
400
500
600
700
Wavelength(nm)
1.5
1.0
0.5
0.0
b
bi py-1
CoF2
NiF2
CuF2
TBAF
NaF
300
350
400
450
500
550
600
650
Wavelength(nm)
Figure 4. UV-vis changes observed upon the addition of 2 eq of various
metal (a) acetates and (b) fluorides (1.5 × 10À3 M in H2O) to bipy-1
(5 × 10À5 M in DMSO).
J. Mol. Recognit. 2014; 27: 689–695
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/jmr

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
S. SUGANYA ET AL.
1.5
1.5
1.0
0.5
0.0
a
b
1.0
2 eq. Co(OAc)2
2 eq. Ni(OAc)2
0 eq. Ni(OAc)2
0 eq. Co(OAc)2
0.5
0.0
300
400
500
600
300
400
500
600
Wavelength(nm)
Wavelength(nm)
1.5
1.0
0.5
0.0
c
2 eq. Cu(OAc)2
0 eq. Cu(OAc)2
300
400
500
600
Wavelength(nm)
Figure 5. UV-vis changes observed upon the addition of 2 eq of (a) Co(OAc)2, (b) Ni(OAc)2, and (c) Cu(OAc)2 (1.5 × 10À3 M in H2O) to bipy-1 (5 × 10À5 M
in DMSO).
1.5
bipy-1
CoCl2
Co(NO3)2
1.0
0.5
0.0
CuCl2
Cu(NO3)2
NiCl2
Ni(NO3)2
300
400
500
600
Wavelength(nm)
Figure 6. UV-vis changes observed upon the addition of 2 eq of various
metal salts (1.5 × 10À3 M in H2O) to bipy-1 (5 × 10À5 M in DMSO).
acetates and fluorides; bipy-1 responds with a band in the
visible region, precisely matching the Ni(OAc/F)2 complex of
bipy-1 without any countercation or anion interference
(Figures 7(a)–7(b)). The same effect was reflected in the case
of Co/CuCl2 and Ni/Co/Cu(NO3)2. This type of metal acetate/
fluoride binding even in the in situ form over other metal salts
indicates that the structure of metal acetates/fluorides prefers
to bind with the electron-rich bipy-1. In addition to the metal
acetate/fluoride binding, bipy-1 can selectively bind TBAF in DMSO
Figure 7. UV-vis changes of bipy-1 (5 × 10À5 M in DMSO) in the
presence of Ni2+ (NiCl2) counterion upon the addition of 2 eq of different
metal (a) acetates and (b) fluorides (1.5 × 10À3 M in H2O).
wileyonlinelibrary.com/journal/jmr
Copyright © 2014 John Wiley & Sons, Ltd.
J. Mol. Recognit. 2014; 27: 689–695