Anthracene-tethered aminomethyl oxadiazole chemosensor: A probe offering selective chromo- and fluorogenic signalings for targeting Cu(II)

Article abstract of DOI:10.1007/s10847-009-9717-4

A new optical chemosensor featuring anthracene as a fluorophore and an aminomethyl oxadiazole moiety as a bidentate chelate has been synthesized. From photophysical studies, we find the probe to offer remarkably selective chromo- and fluorogenic signaling

Full text of DOI:10.1007/s10847-009-9717-4

J Incl Phenom Macrocycl Chem (2010) 67:361–367
DOI 10.1007/s10847-009-9717-4
ORIGINAL ARTICLE
Anthracene-tethered aminomethyl oxadiazole chemosensor:
a probe offering selective chromo- and fluorogenic signalings
for targeting Cu(II)
•
Sabir H. Mashraqui Tabrez Khan
•
•
•
Mukesh Chandiramani Rupesh Betkar
Kiran Poonia
Received: 16 October 2009 / Accepted: 25 November 2009 / Published online: 10 December 2009
Ó Springer Science+Business Media B.V. 2009
Abstract A new optical chemosensor featuring anthra-
cene as a fluorophore and an aminomethyl oxadiazole
moiety as a bidentate chelate has been synthesized. From
photophysical studies, we find the probe to offer remark-
ably selective chromo- and fluorogenic signaling responses
Introduction
The design of artificial sensors capable of selective detection
of biologically and or environmentally significance metal
ions is an area of burgeoning interest in supramolecular
chemistry [1–4]. Copper is an essential mineral in the human
diet with its established role in haemoglobin synthesis,
nerve functions, lipid metabolism, electron transfer pro-
cesses and activation of small molecules [5, 6]. Copper is
also a significant environmental pollutant, and its prolong
exposure beyond the physiological limits is known to cause
gastrointestinal problems and renal dysfunction [7, 8].
Detection of Cu2? has been reported by the classical
atomic absorption spectroscopy as well as by inductively
coupled plasma spectroscopy [9, 10]. In addition, electro-
chemical methods, using ligand modified electrodes have
also been employed [11, 12]. In past decades, optical
spectral techniques, particularly the fluorescence spectros-
copy have gained tremendous popularity owing to its high
sensitivity, inexpensive instrumentations and the possibil-
ity of real time analysis [13–15]. One of the most popular
approaches to construct fluorescence sensors is to connect a
photoemittive unit to a metal ion selective receptor via a
suitable spacer within the fluorophore-spacer-receptor for-
mat [4]. This sensor protocol, initiated by de Silva [16] and
later extensively exploited by others, work on the principle
of photoinduced electron transfer (PET) from the donor
ligand to the excited fluorophore. Binding of the metal ion
could trigger either fluorescence ‘‘on’’ or ‘‘off’’ modula-
tion, depending upon the diamagnetic/paramagnetic char-
acter of the interacting metal ion [1–4, 13–15].
towards biologically and environmentally significant Cu2?
.
In the presence of Cu2?, fluorescence is quenched to the
extent of 95%, while the absorbance due to the anthracene
chromophore is nearly completely bleached out. On the
other hand, Li?, Na?, K?, Ba2?, Ca2?, Zn2?, Mg2?, Cd2?
,
Co2?, Ni2?, Ag?, Pb2? and Hg2? even at 10 times higher
concentration than Cu2? do not cause detectable photo-
physical perturbations. The stability constants, logK for
Cu2? were calculated to be 4.36 and 4.76 on the basis of
spectrophotometric and fluorimetric titrations, respectively.
However, logKs for other metal ions are too low (\0.1) to
pose any interferences in the optical detection of Cu2?
.
Though, not fully defined, the uncommon phenomenon of
the absorbance bleaching by Cu2? is tentatively explained
by invoking the involvement of non-covalent anthracene-
Cu2? complex.
Keywords Chemosensor Á Colorimetry Á Fluorescence Á
Quenching Á Cu2? sensor Á Absorbance bleaching Á
Anthracene-Cu2? interaction
S. H. Mashraqui (&) Á T. Khan Á M. Chandiramani Á
R. Betkar Á K. Poonia
Over past decades, a variety of fluorescence sensors of
Cu2? exhibiting either fluorescence ‘‘on–off’’ or ‘‘off–on’’
signaling has been developed. While the Cu2? sensors
offering fluorescence quenching response generally operate
Department of Chemistry, University of Mumbai, Vidyanagari,
Santacruz (E), Mumbai 400098, India
e-mail: sh_mashraqui@yahoo.com
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J Incl Phenom Macrocycl Chem (2010) 67:361–367
N
N
ClCH COCl
i)
via PET mechanism, on the other hand, the fluorescence
enhancements in a limited number of Cu sensors arise
either via chelation induced blocking of a fluorescence
quenching channel or the change over of the nonemittive n-
p* to the emmitive p–p* state.[17–29] Note withstanding
considerable progress, some of the reported Cu2? sensors
suffer from delayed response and minor, but significant
competitive binding from one or more of the metal ions
such as Zn, Ni, Hg, Cd, Pb and Ag ions [30–36]. In this
paper, we have designed a new chemosensor, designated as
Anthrox to study its potential as an optical sensor for metal
ion(s) of biological/environmental interest.
2
CONHNH2
CHCl3 ,
reflux
O
Cl
ii) POCl3
, reflux
1
2
N
N
+
O
Cl
N
H
2
3
Dry Acetone,
KI, reflux 48h
Since, metal binding selectivity depends mainly upon the
nature of the ligand system, it is tempting to manipulate the
structures of the chelates in order improve binding charac-
teristics and selectivity towards a target metal ion. We have
been interested in the photoemittive diaryloxadiazole as an
intrinsic fluorescent ligand and have successfully used this
system to designed sensors for targeting biologically sig-
nificant Zn, Mg, Ca, and Ba ions [37–40]. Besides, a Cd2?
selective fluorescence chemosensor has recently reported by
Lie et al. by incorporating oxadiazole ring as a part of the
chelating ligand [41]. Copper (II) exists as a d9 metal center
of borderline softness, exhibiting binding interactions with
nitrogen-based ligands such as amines, imines, and biden-
tate ligands like aminomethyl pyridine, bipyridine etc [42–
45]. Though, oxadiazole ring is known to coordinate with
Cu2?, however to our knowledge this ring has not been used
to design Cu2? selective fluorescence sensor [46]. We now
extend the application of oxadiazole core as one of the
binding ligands to develop a new fluorescence sensor,
Anthrox. The design of Anthrox is based on the fluorophore-
spacer-receptor format, and carries anthracene core as a
fluorophore, whereas the aminomethyl oxadiazole moiety
constitutes a bidentate metal binding domain. Our photo-
physical results show the probe to be an effective optical
sensor, offering highly selective color bleaching and turn-
N
O
N
N
Anthrox
Scheme 1 Synthesis of the chemosensor, Anthrox
Absorption studies and titrations
Photophysical sensitivity of Anthrox towards selected
metal ions of biological and or environmental relevance viz
Li?, Na?, K?, Ba2?, Ca2?, Zn2?, Mg2?, Cd2?, Cu2?
,
Co2?, Ni2?, Ag?, Pb2? and Hg2? were investigated in
CH3CN (ACN) solvent both spectrophotometrically and
fluorimetrically. All the metal ion titration experiments
were uniformly carried out by adding ACN solution of the
known concentration of metal ions perchlorates into the
ACN solution of Anthrox. The UV–vis spectrum of
Anthrox displayed absorption maxima, characteristic of
anthracene chromophore at 348, 366 and 386 nm, with the
molar extinction coefficient, em of ca. 0.921 9 104 M-1
cm-1. As depicted in Fig. 1, the absorbance of the probe
decrease marginally by 5–15% upon adding Li?, Na?, K?,
Ba2?, Ca2?, Zn2?, Mg2?, Cd2?, Co2?, Ni2?, Ag?, Pb2?
and Hg2? up to 1000 equiv with respect to a fix concen-
tration of Anthrox (2.83 9 10-5 M). However, the ener-
gies of the absorption maxima remained essentially
invariant to the added perchlorates of the above metal ions.
Since, the probe is not a typical donor–acceptor chromo-
phore, the lack of significant changes in the absorbance
profile of the probe does not imply the absence of signifi-
cant metal ion binding interaction.
off signaling response towards Cu2?
.
Result and discussion
Synthesis of Anthrox was readily achieved in two easy
steps as outlined in Scheme 1. Condensation of chloro-
acetyl chloride with the known 4-t-butylphenyl hydrazide
in the presence of phosphorus oxychloride afforded chlo-
romethyl oxadiazole 2. N-alkylation of 2 with the known
N-benzyl aminomethyl anthracene under acetone/K2CO3
condition, followed by SiO2 column chromatographic
purification afforded the target molecule, Anthrox as a
yellow, crystalline solid in about 30% overall yield. The
structure of the probe is fully characterized on the basis of
spectral data and elemental analysis.
By contrast, addition of Cu2? caused progressive decline
in the molar absorbance with increasing concentration of
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J Incl Phenom Macrocycl Chem (2010) 67:361–367
363
0.5
enhancement by ca. 3–12%. These emission enhancements,
probably caused by blocking of the PET process are too
weak to have any sensing implications. For the case of
Hg2?, the quenching effect though by a small margin of ca.
5% is observed at a 1000 equiv with respect to that of the
probe. The insignificant fluorescence perturbations clearly
imply negligible binding affinity of the above studied metal
ions towards the probe.
On the other hand, addition of Cu2? at 100 equiv caused
remarkably high emission quenching of ca, 95%. Fluori-
metric titration of an ACN solution of Anthrox with
Cu(ClO4)2 is shown in Figs. 2, 3. A steady decline in
emission intensities at 396, 416 and 439 nm maxima is
observed on incremental (0 to 100 equiv) addition of Cu2?
ions. A plateau is reached at a limiting concentration of ca.
100 equiv of Cu2? and under this condition with the
0.4
Anthrox
Li+,Na+,K+,Ca2+,Ba2+,Ni2+,
Ag+,Hg2+,Zn2+,Co2+,Mg2+,
Pb2+.
0.3
}
0.2
0.1
0.0
Cu2+
300
350
400
450
500
Wavelength(nm)
Fig. 1 Absorption spectra of Anthrox (2.83 9 10-5 M) in absence
and presence of each of Li?, Na?, K?, Ba2?, Ca2?, Zn2?, Mg2?
,
Cd2?, Co2?, Ni2?, Ag?, Pb2? and Hg2? (2.83 9 10-2 M) and Cu2?
(2.83 9 10-3 M) in CH3CN
0.30
0.25
Cu2?. The spectrophotometric titration revealed linear
decrease in the absorption maxima due to the anthracene
chromophore, with virtually complete bleaching being
observed after the addition of ca. 100 equiv of Cu2?. The
loss of anthracene absorption occurred immediately upon
mixing the ACN solution of Anthrox and Cu2?, turning the
deep yellow solution into colorless, an event that allows
naked eye sensing of this ion. None of the other metal ions
examined gives rise to detectable color sensitivity even at 10
0
0.20
0.15
0.10
100 equiv
0.05
0.00
times higher concentration than Cu2?
.
300
325
350
375
400
425
450
Wavelength(nm)
Fluorescence spectral studies in the presence of metal
ions
Fig. 2 Spectrophotometric titration of Anthrox (2.83 9 10-5 M) on
incremental addition of Cu(ClO4)2 (0–2.83 9 10-3 M) in CH3CN
Excitation of Anthrox at 330 nm produced a structured
fluorescence spectrum showing emission maxima at 396,
416 and 439 nm, which could be ascribed to the anthracene
fluorophore. The quantum yield, Uf of the probe was
determined to be 0.054 with reference to coumarin 151 in
cyclohexane (Uf = 0.28) [47]. The weakly emissive nature
of Anthrox is presumably due to the PET quenching
operating via electron transfer from the saturated nitrogen
to the excited state of the anthracene fluorophore. On this
ground, we expected that strong binding interaction with
the diamagnetic metal ions should induce chelation
enhanced fluorescence (CHEF), while the paramagnetic
metal ions might lead to fluorescence quenching effects.
Accordingly, we also investigated the fluorescence
modulation of the probe in the presence of different metal
ions. Addition of Li?, Na?, K?, Ca2?, Ba2?, Cd2?, Pb2?
and up to 1000 equiv did not noticeably perturb the excited
350
0
300
250
200
150
100 equivalents
100
50
0
350 375 400 425 450 475 500 525 550 575 600
Wavelength (nm)
Fig. 3 Fluorimetric titration of Anthrox (2.83 9 10-5 M) on incre-
mental addition of Cu(ClO4)2 (0–2.83 9 10-3 M) in CH3CN
(kex = 330 nm)
state behavior of the probe, whereas Mg2?, Co2?, Ni2?
Ag? and Zn2? induced insignificant emission intensity
,
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J Incl Phenom Macrocycl Chem (2010) 67:361–367
quantum yield dropping down to 0.0061 from a value of
0.054 for the unbound probe. This is one of the highest
emission quenching observed among the known fluores-
cence chemosensors for Cu2?. Moreover, the quenching,
like the absorbance bleaching also occurs instantaneously
upon mixing the ACN solution of Anthrox with Cu2?. The
interaction between Cu2? and Anthrox is also found to be
reversible, since the addition 1,4,7,10-tetraazatetradecane,
a strong complexing ligand for Cu2? caused the decom-
plexation of Anthrox-Cu2? system and revived the fluo-
rescence to the original level of the unbound probe. Apart
from Cu2?, Hg2? is the only other metal ion for which
quenching is detected at 1000 equiv, though by a small
margin of ca. 5%.
To check the interferences from other metal ions on the
fluorescence signaling of Cu2?, a competitive fluorescence
experiment was performed by adding 100 equivalent of
Cu2? to the ACN solutions carrying 1000 equivalent of
individual metal ions. As shown in Figs. 4, 5 prior to the
addition of Cu2?, the fluorescence intensity of the probe is
only marginally affected. However, addition of Cu2? cau-
ses a uniformly high fluorescence quenching in the range of
85–95%. This experiment clearly demonstrates that even in
higher concentrations, the presently studied metal ions do
not pose significant interferences in the fluorescent detec-
tion of Cu2?. Inspite the high selectivity of Anthrox
towards Cu2?, a limitation of the probe is its inherent low
sensitivity on account of the its very low quantum yield.
Figure 4 shows the graphical representation of the
steady changes in the emission profile of Anthrox giving an
indication of stoichiometric complex formation between
Anthrox and Cu2?. The Job plot analysis performed on the
basis of fluorimetric titration confirmed 1:1 binding stoi-
chiometry. The stability constant, logK, determined using
the nonlinear square curve fitting using data both spectro-
photometric and fluorimetric titrations gave the values of
4.36 and 4.76, respectively. This observation suggests that
the binding interactions in both the ground and excited
states are of similar magnitude. However, owing to insig-
nificant absorbance and fluorescence perturbations, the
Comments on Cu2? binding interaction
The probe, Anthrox has been found to serve as a highly
selective chemosensor, offering naked eye detection by
color bleaching as well as fluorescence ‘turn-off’ signaling
in the presence of Cu2?. Noteworthily, trace biological
metal ions Zn2?, Mg2? and Co2?, abundantly existing
cellular ions, Na?, K? and Ca2?, as well as toxic, Cd2?
,
Pb2? and Hg2? displayed none or negligible binding
interactions. As far as fluorescence quenching alone is
concerned, one can rationalize it by taking into account the
paramagnetic nature of Cu2?. However, in the present
circumstance the fluorescence quenching cannot be con-
sidered in isolation, since it is also accompanied by the
absorbance bleaching, a feature which is essentially rooted
in the ground state interaction. Consequently, the observed
quenching in the presence of Cu2? may not be simply the
result of either electron or energy transfer mechanism,
operating only in the excited states [48]. Based on this
stability constants for Li?, Na?, K?, Ba2?, Ca2?, Zn2?
,
Mg2?, Cd2?, Co2?, Ni2?, Ag?, Pb2? and Hg2? are too
small (\0.1) to be reliably determined. The significant
perturbation in optical spectral properties of Anthrox with
Cu2? signifies its superior binding interaction and selec-
tivity compared to several metal ions examined. Conse-
quently, the probe allows for the selective detection of
Cu2? both by means of absorption bleaching and drastic
fluorescence ‘on–off’ response.
B
C
1.2
350
300
250
200
150
100
50
1.0
0.8
0.6
0.4
0.2
0.0
0
Li Na
K
Ba Ca Hg Ag Mg Co Ni Cd Zn Pb
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Metal ions
Conc of Cu2+ [mM]
Fig. 5 Fluorescence response of Anthrox (2.83 9 10-5 M) in the
Fig. 4 Variation in fluorescence intensity of a solution of Anthrox
(2.83 9 10-5 M) in CH3CN at 416 nm as a function of change in
Cu2? ion concentration
presence of Li?, Na?, K?, Ba2?, Ca2?, Zn2?, Mg2?, Cd2?, Co2?
,
Ni2?, Ag?, Pb2? and Hg2? (2.83 9 10-2 M) alone and after adding
of Cu(ClO4)2 (2.83 9 10-3 M) in CH3CN
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J Incl Phenom Macrocycl Chem (2010) 67:361–367
365
reasoning, we propose that the fluorescence quenching may
be a direct consequence of the absorbance bleaching.
Though, precedence for the absorbance bleaching has
been earlier encountered by Kumar et al. in their study of
certain anthracene based Cu2? chemosensor [49], however
no explanation was offered regarding the mechanism of the
absorption bleaching. The cation-p interaction, a nonco-
valent electrostatic interaction between a cation and p-
electron-rich systems is increasingly recognized as an
important force influencing the structures and functions of
molecules including proteins. Unlike other metal cations,
up until recently Cu2? was believed not to participate in a
cation-p interaction because of its tendency to oxidize the
p-electron rich systems. However, a recent report provides
the first direct spectral evidence for the reversible cation-p
interaction between Cu2? and the electron rich indole ring
of tryptophane [50]. In the present case, the interaction of
Cu2? with the probe is reversible, meaning the interaction
does not lead to any chemical reaction. Thus, on grounds of
the absorbance bleaching and the reversible nature of the
Cu2? binding interaction, the possibility of the involve-
ment of noncovalent anthracene-Cu2? interaction in this
intriguing phenomenon can not be ruled out. Such an
interaction might disrupt the electronic transition and cause
the absorption due to the anthracene chromophore to
vanish.
and spectral grade solvents were purchased from S.D. fine
Chemicals (India) and used as received. IR spectra were
1
recorded on Shimadzu FTIR-420 spectrophotometer. H-
NMR spectra were recorded in CDCl3 solution on a Bruker
300 MHz spectrometer with TMS as an internal standard.
Elemental analyses were performed on Carlo Erba instru-
ment EA-1108 Elemental analyzer. UV–vis spectra were
recorded on Jasco V-530 UV–vis spectrophotometer and
fluorescence spectra were recorded on Hitachi F-4500
Fluorescence spectrophotometer. The slit width was set at
3 nm for both excitation and emission and the PMT
detector voltage was 700 V.
Preparation of 2-(chloromethyl)-5-(4-t-butylphenyl)-
1,3,4-oxadiazole (2)
To
a solution of chloroacetyl chloride (0.626 mL,
7.8 mmol) in dry CHCl3 (20 mL) was added 4-t-butyl
benzoic acid hydrazide (1.5 g, 7.8 mmol) and the reaction
was heated on water-bath for about 2 h till evolution of
HCl gas ceased. At this time, freshly distilled POCl3
(1 mL, 9.5 mmol) was added all at once and the reaction
continued to be refluxed for further 3 h to effect the
cyclization of the intermediate dihydrazide. After cooling
to room-temperature, the reaction mixture was poured
carefully over crushed ice and the mixture was treated with
gradual addition of solid Na2CO3 till basic. The basified
reaction mixture was refrigerated to deposit a brown solid,
which was collected by filtration. The filtered solid was
thoroughly washed with water and air dried. Crystallization
from CHCl3- petroleum ether (1:3) afforded chloromethyl
oxadiazole (2) as a colorless solid in 62% yield (1.08 g) mp
152–155 °C; IR (KBr)/cm-1 : 3033, 2966, 1616, 1586,
1569, 1495, 1416, 1362, 1251, 1112, 1083, 1011, 841, 758,
708, 647 and 554; 1H-NMR (CDCl3) d : 7.92 (d, 2H,
J = 7.2 Hz Ar–H), 7.49 (d, 2H, J = 7.2 Hz Ar–H), 4.67
(s, 2H, Ar–CH2–Cl), 1.38 (s, 9H, Ar–C(CH3)3). Anal.
Calcd for C13H15ClN2O: C, 62.27; H, 5.98; N, 11.17; Cl,
14.17. Found: C, 62.35; H, 6.05; N, 11.23; Cl, 14.24%.
Conclusion
In conclusion, we have synthesized a new optical probe,
Anthrox which offers highly selective and fast chromo- and
fluorogenic ‘turn-off’ signaling responses in the presence
of Cu2?. Our work demonstrates that oxadiazole motif can
be exploited as a binding motif to design Cu selective
chemosensors. By contrast, the probe exhibits none or
negligible optical sensitivity towards various metal ions of
biological and or environmental significant such as Li?,
Na?, K?, Ba2?, Ca2?, Zn2?, Mg2?, Cd2?, Co2?, Ni2?
,
Ag?, Pb2? and Hg2?. Consequently, these metal ions pose
no detectable interference in targeting Cu2?. In spite the
excellent selectivity, its organic working medium forms a
limitation for biological studies, though potential is avail-
able for environmental sensing applications. Work is in
progress to modify the present design by replacing the
anthracene with other suitable fluorophores to render the
probe compatible for aqueous measurements.
Preparation of N-benzyl aminomethyl anthracene (3)
9-anthraldehyde (515 mg, 2.5 mmol) was condensed with
benzyl amine (0. 28 mL, 2.5 mmol) in absolute ethanol
(10 mL) by heating the mixture on water-bath for 1 h. On
cooling the reaction mixture, the crude Schiff base precip-
itated out as a light yellow solid. Without further purifica-
tion, the crude Schiff base was reduced in dry THF by
portion-wise addition of NaBH4 (114 mg, 3 mmol) during
30 min at room temperature. The reaction, after stirring for
5 h was poured in water and the precipitated solid filtered,
washed with water and air dried. Crystallization from
alcohol gave the product 3 in 81% yield (480 mg) mp 262–
Experimental
Metal perchlorates were prepared as described in the lit-
erature and dried under vacuum prior to use. The chemicals
123

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J Incl Phenom Macrocycl Chem (2010) 67:361–367
265 °C; IR (KBr)/cm-1: 3057, 2905, 2779, 1583, 1438,
1412, 1262, 1210, 1006, 968, 952, 890, 785 and 732; H-
8. Sarkar, B.: Transport of copper. Met. Ions Biol. Syst. 12, 233–281
(1981)
1
9. Fuller, C.W.: Electrochemical Atomization for Atomic Absorp-
tion Spectroscopy. Royal Society of Chemistry, London (1977)
10. Fassel, V.A., Kniseley, R.N.: Inductively coupled plasma-optical
emission analytical spectrometry. Anal. Chem. 46, 75–80 (1974)
11. Herzog, G.D.W.M.: Application of disorganized monolayer films
on gold electrodes to the prevention of surfactant inhibition of the
voltammetric detection of trace metals via anodic stripping of
under potential deposits: detection of copper Arrigan. Anal.
Chem. 75, 319–323 (2003)
NMR (CDCl3) d: 8.3 (s, 1H, Ar–H), 8.06–7.3 (m, 13H, Ar–
H), 4.88 (s, 2H, Ar–CH2–N–), 4.16 (s, 2H, Ar–CH2–N–).
13C-NMR (DMSO-d6) 40.77, 41.73, 51.13, 123.55, 124.67,
125.88, 127.35, 129.15, 129.47, 129.56, 130.16, 131.06,
131.10, 131.26, 132.37. Anal. Calcd for C22H19N: C, 88.88;
H, 6.39; N, 4.71. Found: C, 89.06; H, 6.42; N, 4.83%.
12. Zen, J.M., Wang, H.F., Kumar, A.S., Yang, H.H., Dharuman, V.:
Preconcentration and electroanalysis of copper(II) in ammoniacal
medium on nontronite/cellulose acetate modified electrodes.
Electroanalysis 14, 99–105 (2002)
13. Valeur, B.: Molecular Fluorescence. Wiley-VCH, Weinheim
(2002)
14. Amendola, V., Fabbrizzi, I., Forti, F., Pallavicini, P., Poggi, A.,
Sacchi, D., Tagleitti, A.: Light-emitting molecular devices based
on transition metals. Coord. Chem. Rev. 250, 273–299 (2006)
15. Wolfbeis, O.S., Bohmer, M., Durkop, A., Enderlein, L., Gruber,
M., Klimant, I., Krause, C., Kurner, J., Liebsch, G., Lin, Z.,
Oswald, B., Kraayenhof, R., Visser, A.J.W.G., Gerritsen, H.C.,
Wu, M.: Fluorescence Spectroscopy, Imaging and Probes: New
Tools in Chemical Physical and Life Sciences. Springer, Berlin
(2002)
16. De Silva, A. P., De Silva, S. A.: Fluorescent signalling crown
ethers; switching on–off fluorescence by alkali metal ion recog-
nition and binding in situ. J. Chem. Soc. Chem. Commun. 1709–
1710 (1986)
17. Kramer, R.: Fluorescent chemosensors for Cu2? ions: fast,
selective, and highly sensitive. Angew. Chem. Int. Ed. 37, 772–
773 (1998)
18. Roy, B.C., Chandra, B., Hromas, D., Mallik, S.: Synthesis of new,
pyrene-containing, metal-chelating lipids and sensing of cupric
ions. Org. Lett. 5, 11–14 (2003)
19. Zheng, Y., Orbulescu, J., Ji, X., Andreopoulos, F.M., Pham, S.M.,
Leblanc, R.M.: Development of fluorescent film sensors for the
detection of divalent copper. J. Am. Chem. Soc. 125, 2680–2686
(2003)
Synthesis of chemosensor, Anthrox
N-benzyl aminomethyl anthracene 3 (445 mg, 1.5 mmol),
chloromethyl oxadiazole derivative 2 (376 mg, 1.5 mmol),
K2CO3 (150 mg) and KI (250 mg) were refluxed in dry
acetone for 48 h. After cooling to room temperature, the
reaction mixture was filtered to remove insoluble inorganic
salts and the filtrate was concentrated. The crude solid
product was subjected to purification by SiO2 column
chromatography using CHCl3: methanol (98:2) as eluant.
The target product, Anthrox was obtained as a yellow solid
in 58% yield (446 g), mp 174–176 °C; IR (KBr)/cm-1
:
3050, 2958, 1615, 1583, 1559, 1496, 1445, 1366, 1252,
1208, 1110, 1011, 957, 889, 857, 730; 1H-NMR (CDCl3) d:
8.45 (m, 3H, Ar–H), 8.0 (d, 2H, 5.7 Hz, Ar–H), 7.92 (d,
2H, 6.3 Hz, Ar–H), 7.54 (d, 2H, J = 6.3 Hz, Ar–H), 7.46
(m, 4H, Ar–H), 7.30 (m, 5H, Ar–H), 4.88 (s, 2H), 3.99 (s,
2H), 3.92 (s, 2H), 1.38 (s, 9H, Ar–C(CH3)3). Anal. Calcd
for C35H33N3O: C, 82.19; H, 6.45; N, 8.21. Found: C,
82.25; H, 6.55; N, 8.24%. 13C-NMR (DMSO-d6) 31.27,
35.27, 46.71, 50.12, 57.01, 121.16, 125.25, 125.50, 126.34,
126.68, 126.74, 127.58, 128.13, 128.60, 129.14, 129.33,
129.67, 131.35, 131.40, 138.81, 155.28, 164.22, 164.52.
20. Wu, Q., Anslyn, E.V.: Catalytic signal amplification using a heck
reaction. An example in the fluorescence sensing of Cu(II).
J. Am. Chem. Soc. 126, 14682–14683 (2004)
Acknowledgments Thanks are due to the B.R.N.S., Government of
India for generous financial support and the UGC for providing
research fellowship to R. B. and M. C.
21. Kaur, S., Kumar, S.: Photoactive chemosensors 4: a Cu2? protein
cavity mimicking fluorescent chemosensor for selective Cu2?
recognition. Tetrahedron Lett. 45, 5081–5085 (2004)
22. Bag, B., Bharadwaj, P.K.: Attachment of electron-withdrawing 2,
4-dinitrobenzene groups to a cryptand-based receptor for Cu(II)/
H ? -specific exciplex and monomer emissions. Org. Lett. 7,
1573–1576 (2005)
References
1. Schraderr, T., Hamilton, A.D. (eds.): Functional Synthetic
Receptors. Wiley-VCH, Weinheim (2005)
23. Royzen, M., Dai, Z., Canary, J.W.: Ratiometric displacement
approach to Cu(II) sensing by fluorescence. J. Am. Chem. Soc.
127, 1612–1613 (2005)
24. Xu, Z., Xiao, Y., Qian, X., Cui, J.N., Cui, D.: Ratiometric and
selective fluorescent sensor for CuII based on internal charge
transfer (ICT). Org. Lett. 7, 889–892 (2005)
25. Zeng, L., Miller, E.W., Pralle, A., Isacoff, E.Y., Chang, C.-J.:
A selective turn-on fluorescent sensor for imaging copper in
living cells. J. Am. Chem. Soc. 128, 10–11 (2006)
26. Jun, E.J., Won, H.N., Kim, J.S., Lee, K.-H., Yoon, J.: Unique
blue shift due to the formation of static pyrene excimer: highly
selective fluorescent chemosensor for Cu2?. Tetrahedron Lett. 47,
4577–4580 (2006)
2. Desvergne, J.P., Czarnik, A.W.: Chemosensors of Ion and Mol-
ecule Recognition. Kluwer, Dordrecht (1997)
3. Beer, P.D., Gale, P.A.: Anion recognition and sensing: the state
of the art and future perspectives. Angew. Chem. Int. Ed. 40,
486–516 (2001)
4. De Silva, A.P., Gunaratne, H.Q.N., Gunnlaugsson, T., Huxley,
A.J.M., McCoy, C.P., Rademacher, J.T., Rice, T.E.: Signaling
recognition events with fluorescent sensors and switches. Chem.
Rev. 97, 1515–1566 (1997)
5. Harris, E.D.: Copper and iron: a landmark connection of two
essential metals. J. Trace Elem. Exp. Med. 14, 207–210 (2001)
6. Saltman, P.D., Strause, L.G.: The role of trace minerals in oste-
oporosis. J. Am. Coll. Nutr. 12, 384–390 (1993)
27. Wen, Z.-C., Yang, R., He, H., Jiang, Y.-B.: A highly selective
charge transfer fluoroionophore for Cu2?. Chem. Commun. 106–
107 (2006)
7. Frieden, E., Osaki, S., Kobayashi, H.: Copper proteins and oxy-
gen; correlations between structure and function of the copper
oxidases. J. Gen. Physiol. 49, 213–252 (1965)
123

J Incl Phenom Macrocycl Chem (2010) 67:361–367
367
28. Weng, Y.-Q., Yue, F., Zhong, Y.-R., Ye, B.-H.: A new selective
fluorescent chemosensor for Cu(II) ion based on zinc porphyrin-
dipyridylamino. Inorg. Chem. Commun. 10, 443–446 (2007)
29. Que, E.L., Chang, C.J.: A smart magnetic resonance contrast
agent for selective copper sensing. J. Am. Chem. Soc. 128,
15942–15943 (2006)
30. Kovbasyuk, L., Kramer, R.: A selective fluorescent sensor for
Cu2? and its immobilization on CPG beads. Inorg. Chem.
Commun. 9, 586–590 (2006)
40. Mashraqui, S.H., Sundaram, S., Khan, T., Ghadigaonkar, S.,
Poonia, K.: New PCT probes featuring N-phenylmonoaza-18-
crown-6 and aryl/pyridyl oxadiazoles: optical spectral studies of
solvent effects and selected metal ions. J. Incl. Phenom. Macro-
cycl. Chem. 62, 81–90 (2008)
41. Tang, X.-L., Peng, X.-H., Dou, W., Mao, J., Zheng, J.-R., Qin,
W.-W., Liu, W.-S., Chang, J., Yao, X.-J.: Design of a Semirigid
Molecule as a Selective fluorescent Chemosensor for Recognition
of Cd(II). Org. lett. 10, 3653–3656 (2008)
31. He, X., Liu, H., Li, Y., Wang, S., Wang, N., Xiao, J., Xu, X., Zhu,
D.: Gold nanoparticle-based fluorometric and colorimetric sens-
ing of copper (II) ions. Adv. Mater. 17, 2811–2815 (2005)
42. He, Z., Craig, D. C., Colbran, S. B.: Structures and properties of
6-aryl substituted tris(2-pyridylmethyl)amine transition metal
complexes. J. Chem. Soc. Dalton Trans. 4224–4235 (2002)
43. Collman, J.P., Zhong, M., Zhang, C., Costazo, S.: Catalytic
activities of Cu(II) complexes with nitrogen-chelating bidentate
ligands in the coupling of imidazoles with arylboronic acids.
J. Org. Chem. 66, 7892–7897 (2001)
44. Creaven, B.S., Mahon, M.F., McGinley, J., Moore, A.-M.: Cop-
per(II) complex of a tridentate N-donor ligand with unexpected
Cu–H interaction. Inorg. Chem. Commun. 9, 231–234 (2006)
45. Taki, M., Teramae, S., Nagatomo, S., Tachi, Y., Kitagawa, T.,
Itoh, S., Fukuzumi, S.: Fine-tuning of copper(I)-dioxygen reac-
tivity by 2-(2-Pyridyl)ethylamine bidentate ligands unusual.
J. Am. Chem. Soc. 124, 6367–6377 (2002)
32. Kubo, K.: Mori A.: PET fluoroionophores for Zn2? and Cu2?
:
complexation and fluorescence behavior of anthracene deriva-
tives having diethylamine, N-methylpiperazine and N, N-bis(2-
picolyl)amine units. J. Mater. Chem. 15, 2902–2907 (2005)
33. Wu, J.-S., Wang, P.-F., Zhang, X.-H., Wu, S.-K.: Novel fluo-
rescent sensor for detection of Cu(II) in aqueous solution.
Spectrochim. Acta Part A 65, 749–752 (2006)
34. Bolletta, F., Garelli, A., Montalti, M., Prodi, L., Romano, S.:
Synthesis, photophysical characterization and metal ion binding
properties of new ligands containing anthracene chromophores.
Inorg. Chim. Acta 357, 4078–4084 (2004)
35. De Santis, G., Fabbrizzi, L., Licchelli, M., Mangano, C., Sacchi,
D., Sardone, N.: A fluorescent chemosensor for the copper(II)
ion. Inorg. Chim. Acta 257, 69–76 (1997)
36. Zeng, Q., Cai, P., Li, Z., Qina, J., Tang, B. Z.: An imidazole-
functionalized polyacetylene: convenient synthesis and selective
chemosensor for metal ions and cyanide. Chem. Commun. 1094–
1096 (2008)
37. Mashraqui, S.H., Kumar, S., Vashi, D.: Synthesis, cation-binding
and optical spectral studies of photoemissive benzothiazole
crown ethers. J. Incl. Phenom. Macrocycl. Chem. 48, 125 (2004)
38. Mashraqui, S.H., Sundaram, S., Bhasikuttan, A.C.: New ICT
probes: synthesis and photophysical studies of N-phenylaza-15-
crown-5 aryl/heteroaryl oxadiazoles under acidic condition and in
the presence of selected metal ions. Tetrahedron 63, 1680–1688
(2007)
39. Mashraqui, S.H., Khan, T., Sundaram, S., Betkar, R., Chandira-
mani, M.: A new intramolecular charge transfer receptor as a
selective ratiometric ‘off-on’ sensor for Zn2?. Tetrahedron Lett.
48, 8487–8490 (2007)
46. Incarvito, C., Rheingold, A.L., Qin, C.J., Gavrilova, A.L., Bos-
nich, B.: Bimetallic reactivity. On the use of oxadiazoles as
binucleating ligands. Inorg. Chem. 40, 1386–1390 (2001)
47. Nad, S., Pal, H.: Unusual photophysical properties of coumarin-
151. J. Phys. Chem. 105, 1097–1106 (2001)
48. Klein, G., Kaufmann, D., Schurch, S., Reymond, J.-L.: A fluo-
rescent metal sensor based on macrocyclic chelation. Chem.
Commun. 6, 561–562 (2001)
49. Kumar, S., Singh, P., Kaur, S.: A Cu2? protein cavity mimicking
fluorescent chemosensor for selective Cu2? recognition: tuning of
fluorescence quenching to enhancement through spatial place-
ment of anthracene unit. Tetrahedron 63, 11724–11732 (2007)
50. Yorita, H., Otomo, K., Hiramatsu, H., Toyama, A., Miura, T.,
Takeuchi, H.: Evidence for the cation–p Interaction between
Cu2? and tryptophan. J. Am. Chem. Soc. 130, 15266–15277
(2008)
123