A reversible Em-FRET rhodamine-based chemosensor for carboxylate anions using a ditopic receptor strategy

Article abstract of DOI:10.1039/b9nj00594c

A reversible rhodamine-based sensor (L1) capable of undergoing excimer-fluorescent resonance energy transfer (E_m-FRET) was designed and synthesized using a ditopic receptor strategy. Addition of Cu²⁺ ions to a solution of L1 induced a ring-open conformation of spirolactam (E _m-FRET ON), whilst ring closure was induced upon addition of CH ₃COO^- (E_m-FRET OFF).

Full text of DOI:10.1039/b9nj00594c

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PAPER
www.rsc.org/njc | New Journal of Chemistry
A reversible Em-FRET rhodamine-based chemosensor for carboxylate
anions using a ditopic receptor strategyw
Chatthai Kaewtong,*a Jakkapong Noiseephum,a Yuwapon Uppa,b
Nongnit Morakot,a Neramit Morakot,a Banchob Wanno,a Thawatchai Tuntulanic
and Buncha Pulpokac
Received (in Victoria, Australia) 25th October 2009, Accepted 15th January 2010
First published as an Advance Article on the web 29th April 2010
DOI: 10.1039/b9nj00594c
A reversible rhodamine-based sensor (L1) capable of undergoing excimer-fluorescent resonance
energy transfer (Em-FRET) was designed and synthesized using a ditopic receptor strategy.
Addition of Cu2+ ions to a solution of L1 induced a ring-open conformation of spirolactam
(Em-FRET ON), whilst ring closure was induced upon addition of CH3COOꢀ (Em-FRET OFF).
value of them in many biochemical processes.7 Because of the
Introduction
irreversible
Hg2+-promoted
desulfurization
reaction,
Cu2+and Zn2+ were chosen in this work. Herein, we report
rhodamine derivatives (RhBs) based on excimer-fluorescent
resonance energy transfer (Em-FRET), combined with energy
donor from excimer emission (naphthalene excimer)8 and
energy acceptor from dye absorption (rhodamine dye) (L1).
Using L1 as a sensitive and selective chemosensor for anions in
the absence of cation binding, the L1 solution is colorless and
nonfluorescent, yet in the presence of the cation, a visual color
change was observed as well as a fluorescent OFF-ON
observation, which constitutes a ditopic selective fluorescent
chemosensor. Chemosensor L1 was synthesized with two steps
from the reaction of rhodamine B with ethylenediamine, and
the coupling reaction with 1-naphthaleneisothiocyanate and
refluxing in CHCl3 for 72 h to afford L1 at an 84% yield.
As a control experiment, compound 2 was synthesized by
reacting butylamine with 1-naphthaleneisothiocyanate. The
control compound was used in comparative investigation to
explore which structure is preferable to form excimer emission
(B500 nm)8 and can overlap with ring-opened rhodamine
B to undergo the Em-FRET phenomenon (Fig. 1). L1
and 2 were well characterized by 1H NMR, FT-IR and
MALDI-TOF MS.
The demand for chemosensors that are selective for specific
target anions or cations is continuously increasing. Especially
important in this regard is a sensor whose receptor can bind
either cations, anions or both.1 A great effort has been
concentrated on the development of selective fluorescent
chemosensors due to their high sensitivity.2,3a Most fluoro-
metric sensors, have been developed to adopt photo-physical
changes produced upon guest complexation, including photo-
induced electron/energy transfer (PET), charge-transfer (CT)
excited state, excimer/exciplex and fluorescence resonance
energy transfer (FRET).3 More recently, FRET has become
an active field in supramolecular chemistry research due to its
potential practical benefits in cell physiology and optical
therapy, as well as the selective and sensitive sensing of specific
targeted molecular or ionic species.4 A variety of chemo-
sensors have been reported based on a FRET signal mechanism.4
For example, a calix[4]arene containing rhodamine dye and
pyrenyl moieties was described as a Hg2+-selective FRET
sensor.5 Recent developments have shown that rhodamine
spirolactam is a promising structural scaffold for the design
of selective chemosensors. Upon metal binding, its structure
can undergo a change from the spirolactam to an open ring
amide, resulting in a magenta-colored, highly fluorescent
compound.4b,6 To date, several rhodamine-modified chemo-
sensors for Hg2+, Cu2+, Pb2+ and Fe3+ ions have been
developed.6 Surprisingly, the potential for a rhodamine-based
ditopic receptor remains unexplored despite the indispensable
The UV-vis spectra and fluorescence intensity changes of L1
were investigated to determine the anion binding abilities, as
a Supramolecular Chemistry Research Unit, Department of Chemistry
and Center of Excellence for Innovation in Chemistry, Faculty of
Science, Mahasarakham University, Mahasarakham, 44150,
Thailand. E-mail: kchatthai@gmail.com; Fax: +66 0437 54246;
Tel: +66 0437 54246
b Department of Chemistry, Faculty of Engineering, Rajamangala
University of Technology Isan Khon Kaen Campus, Khonkaen 40000,
Thailand. Fax: +66 0437 54246; Tel: +66 0433 36371
c Supramolecular Chemistry Research Unit, Department of Chemistry,
Faculty of Science, Chulalongkorn University, Bangkok 10330,
Thailand. Fax: +66 0221 87598; Tel: +66 0221 87643
w Electronic supplementary information (ESI) available: Spectro-
scopic data and compound characterization data including proposed
binding modes. See DOI: 10.1039/b9nj00594c
Fig. 1 Spectral overlap between naphthyl emission (black) and ring-
opened rhodamine B absorption (red).
ꢁc
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demonstrated in Fig. S1 and S2, respectively.w Upon addition
of 30 equiv. of anions to the solution of L1, hypochromic
shifts oꢀf all anions were observed. Moreover, in the case of Fꢀ,
H2PO4 and CH3COOꢀ, the new absorption bands appeared
at 410 nm, red-shifted by a Dlmax of 95 nm. These shifts are
ascribed to the occurrence of the H-bond interaction involving
the two N–H fragments of the thiourea subunit and anions.9
Fluorescent spectra showed a small enhancement in the
monomer and excimer emission at 370 and 490 nm, respec-
tively. UV-vis spectroscopy was employed to determine the
stoichiometry and stability constant for the complexes using
the SIRKO program.1b,8c,10
Fig.
2
Spectral change in the UV-vis absorption of L1
(CL = 10 mM) upon addition of PhCOOꢀ (CA = 0.4 mM) in MeCN
(0 r CA/CL r 30).
According to the extent of the observed absorption spectra
changes, the association constants of L1 were obtained, and
are summarized in Table 1. L1 prefers to bind with PhCOOꢀ
selectively (log b = 4.44, Fig. 2) over all the other anions
which form structurally similar 1 : 1 complexes, suitably
described as 2 : 2 complexes owing to the evident dimeric
fluorescent nature of naphthalene (Fig. 1 and S2w). The
selectivity can be explained by the geometry of PhCOOꢀ and
the p–p stacking interaction as demonstrated in proposed
binding modes in Fig. 3 and S3.w To further elucidate
the binding mode, 1H NMR-titration experiments were
conducted. As shown in Fig. 4, the downfield shift of the
NH thiourea proton and upfield shift of the naphthyl proton
were observed, which may be due to anion complexation and
conformational organization.11 Upon addition of 2 and
5 equiv. of Zn2+ and Cu2+, respectively, to the solution of
L1, the solution turned from colorless to pink (Fig. 4A), and
the absorbance was significantly enhanced with a new peak
appearing at around 558 nm. (Fig. 5), clearly suggesting the
formation of the ring-open amide form of L1 as a result of
cations binding.12
Fig. 3 Proposed binding modes of L1+PhCOOꢀ (2 : 2).
The addition of 5 equiv. of Cu2+ induced a relatively larger
change in both the spectrometric and colorimetric results
than that of 2, 5 equiv. of Zn2+ and 2 equiv. of Cu2+, as
demonstrated in Fig. 5a. The SIRKO program of the UV-vis
titration curve assumed a 1 : 1 stoichiometry for the L1-Cu2+
complex with log b = 5.78. This binding mode was also
supported by the data of Job’s plots and mole ratio plots
evaluated from the absorption and emission spectra of L1 and
Cu2+ (Fig. S4 and S5w).
Fig. 4 1H NMR spectra (400 MHz, DMSO-d6) of (a) L1, (b) L1 *
PhCOOꢀ 1.5 equiv., (c) L1ꢂZn2+ * CH3COOꢀ 5 equiv., (d) L1ꢂZn2+
after treatment with dilute NaOH and eluted through a silica column.
Inset: Visible color changes of (A) L1 (10 mM) after the addition of
5 equiv. of Cu2+ and L1ꢂCu2+ after the addition of (B) CH3COOꢀ,
Table 1 Stability constants (log b)a of 1 : 1 complexes of L1 and L1ꢂ
Cu2+ with anions in MeCN by UV-visible titration method (T = 25 1C)
Anions
L1
L1ꢂCu2+
ꢀ
PhCOOꢀ, Fꢀ, H2PO4 and (C) other anions.
Fꢀ
Clꢀ
Brꢀ
Iꢀ
2.56 (0.08)
2.59 (0.03)
2.74 (0.09)
2.61 (0.02)
2.76 (0.09)
2.74 (0.01)
2.12 (0.04)
3.12 (0.09)
4.44 (0.09)
4.09 (0.08)
ncb
ncb
Upon irradiation at 300 nm, the fluorescent spectrum of L1
shifted to 584 nm, the region of the energy acceptor
(Em-FRET ON). A statistically significant increase (almost
300-fold enhancement of IF/I0) of fluorescence at 584 nm
was observed, that is, Cu2+ ion induced the formation of
ring-opened RhBs11 with a strong fluorescence Em-FRET
process (Scheme 1, Fig. 5). To confirm that FRET was
originated from excimer formation, Cu2+ was added to 1
at the same condition and the spectrum was recorded.
The spectrum showed no evident emission at 548 nm as
ncb
ncb
ꢀ
NO3 ꢀ
ClO4
H2PO4
ncb
ꢀ
4.05 (0.05)
5.15 (0.07)
3.92 (0.03)
CH3COOꢀ
PhCOOꢀ
a
Mean values derived from at least three independent determinations
b
with the standard deviation sn–1 in parentheses. nc = no observable
change in the UV-vis and fluorescent spectrum upon addition of the
indicated anions.
ꢁc
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Fig. 6 Fluorescence spectra of 1 (10 mM) in MeCN upon addition of
5 equiv. of Cu2+; lex = 300 nm.
Fig. 5 (a) Absorption and fluorescence spectra of L1 (10 mM) in
MeCN upon addition of 2 and 5 equiv. of Cu2+ and Zn2+ ions, and
(b) upon addition of different amounts of Cu2+ ions (lex = 300 nm,
lem = 584 nm).
demonstrated in Fig. 6. In addition, we further investigated the
time evolution of the responses of L1 (10 mM) in the presence
of 5.0 equiv. of Cu2+ in MeCN. As shown in Fig. S6,w the
recognition interaction was completed after addition of the
Cu2+ for 3 h.
In order to verify that L1 can accommodate substrates as a
ditopic receptor, the selectivity of L1 for anions in the present
of Cu2+ was studied. Upon addition of 2.5 equiv. of
CH3COOꢀ to the solution of L1ꢂCu2+, the color changed
from pink to colorless, and the fluorescence and UV-vis
spectra were immediately turned off (Em-FRET OFF), which
Fig. 7 (a) Mole ratio plot of L1ꢂCu2+ with anions at 558 nm,
(b) spectral change in the UV-vis absorption of L1ꢂCu2+ (CL
=
10 mM) upon addition of CH3COOꢀ (CA = 0.4 mM) in MeCN
(0 r CA/CL r 30).
indicates a closed-ring form of RhB (Fig. 4B, 7, 8 and S7w).
No significant changes were, however, promoted by any
of the other tested anions (Clꢀ, Brꢀ, Iꢀ, NO3ꢀ, ClO4
)
ꢀ
(Fig. 4C and S7w). The order of effect of anions on the
>
Em-FRꢀET OFF process was CH3COOꢀ > Fꢀ E PhCOOꢀ
H2PO4 (Fig. 8). This order is the result of two phenomena,
the strength of hydrogen bonding and the inductive effect. The
stronger the hydrogen bond is, the easier the closure of the ring
is. This also results in the stronger interaction of S of thiourea
with Cu2+
.
The calculated association constants are summarized in
Table 1. In certain cases, the presence of a metal cation
increased the anion affinity of the thiourea subunit by more
than 20 times, except for the PhCOOꢀ. It is possible that the
Scheme 1 Proposed Cu2+-promoted ring opening and CH3COOꢀ-
promoted ring closing of spirolactam on RhBs.
ꢁc
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Fig. 9 Proposed binding modes of L1ꢂCu2+ + CH3COOꢀ (2 : 2).
Experimental
General methods
NMR spectra were recorded on a Varian 400 MHz spectro-
meter in deuterated chloroform and DMSO-d6. MALDI-TOF
mass spectra were recorded on a Biflex Bruker Mass spectro-
meter using 2-cyano-4-hydroxycinnamic acid (CCA) or
2,5-dihydroxy-benzoic acid (DHB) as the matrix. ESI mass
spectra were recorded on a Bruker Daltonics microTOF.
UV-vis absorption measurements were performed on a Perkin
Elmer Lambda 25 UV/VIS spectrometer. Fluorescent spectra
were recorded using a Perkin Elmer luminescence spectro-
meter LS50B. Infrared spectra were obtained on a Nicolet
Impact 410 using KBr pellet. Column chromatography was
carried out using silica gel (Kieselgel 60, 0.063–0.200 mm,
Merck). All reagents were standard analytical grade and used
without further purification.
Fig. 8 Fluorescent spectral change of L1ꢂCu2+ (CL = 10 mM) (a)
upon addition 0.2 equiv. of various anions, (b) upon addition
of different amounts of CH3COOꢀ (CA 0.4 mM) in MeCN
(0 r CA/CL r 30) (lex = 300 nm, lem = 584 nm).
Commercial grade solvents, such as acetone, hexane,
dichloromethane, methanol and ethyl acetate, were distilled
before use. MeCN was dried over CaH2 and freshly distilled
under a nitrogen atmosphere prior to use.
steric hindrance, L1 preorganized to bind with Cu2+, blocks
the PhCOOꢀ anion. However, from the absolute values of
association constants, the following cooperative factors13 can
be calculated: Fꢀ, 1.68; H2PO4ꢀ, 1.91; CH3COOꢀ, 1.65;
PhCOOꢀ, 0.88. A value o1 indicates that host/anion binding
is inhibited by the steric hindrance, whereas a cooperativity
factor >1 reflects host/anion binding enhancement due to the
ion-pair recognition,12 allosteric effects (induced fit)14 and/or
through-bond electrostatic effects.8,15
The 1H-NMR spectrum (Fig. 1c) of L1ꢂZn2+ instantly after
addition of CH3COOꢀ gave rise to two sets of distinguishable
broad signals for the NH thiourea proton at d = 9.65 and
6.84 ppm and at d = 11.98 and 7.67 ppm, respectively. These
peaks were ascribed to the anion-free and acetate-bound
forms L1ꢂZn2+ and were consistent with the anion-binding/
decomplexation equilibrium shown on the 1H-NMR time
scale. Furthermore, after treated with dilute NaOH and eluted
through a silica column, 1H-NMR gave solid evidence for the
reversible process (Fig. 4d).
Syntheses
Synthesis of N-(rhodamine B)lactam-ethylenediamine (1).
This was synthesized in a manner similar to literature procedure.16
Rhodamine B (0.20 g, 0.42 mmol) was dissolved in 30 mL of
ethanol and ethylenediamine (0.22 mL, excess) was added
dropwise to the solution and refluxed overnight (24 h) until
the solution lost its red color. The solvent was removed by
evaporation. Water (20 mL) was added to the resultant residue
and the solution extracted with CH2Cl2 (20 mL ꢃ 2). The
combined organic phase was washed twice with water and
dried over Na2SO4. The solvent was removed by evaporation
and dried in vacuo, affording a pale-yellow solid of 1
(0.17 g, yield 84%). 1H NMR (400 MHz, CDCl3) d
7.86–7.81 (m, 1H, ArH), 7.45–7.32 (m, 2H, ArH), 7.08–7.03
(m, 1H, ArH), 6.42 (s, 1H, ArH), 6.39 (s, 1H, ArH) 6.37
(s, 2H, ArH), 6.38–6.21 (m, 2H, ArH), 3.32 (q, J = 6.8 Hz,
8H, NCH2CH3), 3.12 (t, J = 6.8 Hz, 2H, NCH2CH2), 2.23
In conclusion, a reversible-ditopic fluorescent and colori-
metric chemosensor based on RhBs has been discovered and
used as an Em-FRET probe. Complexation studies showed
that L1 was a selective chemosensor for PhCOOꢀ due to the
geometry of PhCOOꢀ and p–p stacking interaction and turned
out to bind CH3COOꢀ in the presence of Cu2+ due to the
allosteric effect, ion-pair recognition and/or through-bond
electrostatic effects (Table 1, Fig. 9). The results provided a
useful design strategy for the future synthesis and application
of new fluorescent sensors as ditopic receptors.
(t,
J = 6.8 Hz, 2H, NCH2CH2NH2), 2.05 (s, 2H,
CH2CH2NH2) and 1.16 (t, J = 7.2 Hz, 12H, NCH2CH3).
MS (MALDI-TOF); Calcd for [C30H36N4O2]+: m/z 484.63.
Found: m/z 485.91 [M+H]+.
Synthesis of N-(Rhodamine B)lactam-N0-naphthylthiourea-
ethylenediamine (L1). A portion of 1 (0.17 g, 0.35 mmol) and
1-naphthyl isothiocyanate (0.08 g, 0.46 mmol) were combined
in fresh distilled acetonitrile (30 mL). The reaction solution
was refluxed for 24 h under a N2 atmosphere and stirred for
ꢁc
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another 2 h at room temperature to form a white precipitate.
The solid was filtrated, washed with acetonitrile three times.
Crude product was purified by recrystallization from aceto-
nitrile to give 0.15 g of L1 (white crystal) in 65% yield. 1H
NMR (400 MHz, DMSO-d6) d 9.74 (s, 1H, NHCS), 7.92 (d, J =
7.2 Hz, 1H, ArH), 7.83 (d, J = 7.2 Hz, 1H, ArH), 7.79–7.73
(m, 2H, ArH), 7.50–7.21 (m, 6H, ArH), 7.00 (s, 1H, CSNH),
6.30 (s, 2H, ArH), 6.09 (d, J = 7.2 Hz, 4H, ArH) 3.23 (t, J =
9.6 Hz, 8H, NCH2CH3), 3.17–3.08 (m, 4H, NCH2CH2NH)
and 1.03 (t, J = 6.8 Hz, 12H, NCH2CH3). 13C NMR
(100 MHZ, DMSO-d6) d 182.0, 168.0, 154.0, 152.9, 148.8,
134.5, 133.3, 130.3,128.7, 128.6, 128.3, 127.5, 126.9, 126.7,
126.2, 125.9, 123.9, 123.2, 122.9, 108.5, 105.1, 97.8, 64.4, 44.1,
42.9, 38.8 and 12.8. IR (KBr) n 3367, 3249, 2972, 1683, 1616,
Notes and references
1 (a) J. L. Sessler, P. A. Gale and W.-S. Cho, Anion Receptor Chemistry,
Royal Society of Chemistry, Cambridge, UK, 2006, pp. 259–293;
(b) C. Kaewtong, S. Fuangswasdi, N. Muangsin, N. Chaichit,
J. Vicens and B. Pulpoka, Org. Lett., 2006, 8, 1561; (c) W. W. H.
Wong, D. Curiel, S.-W. Lai, M. G. B. Drew and P. D. Beer, Dalton
Trans., 2005, 774; (d) M. D. Lankshear, I. M. Dudley, K.-M. Chan,
A. R. Cowley, S. M. Santos, V. Felix and P. D. Beer, Chem.–Eur. J.,
2008, 14, 2248; (e) T. Gunnlaugsson, M. Glynn, G. M. Tocci,
P. E. Kruger and F. M. Pfeffer, Coord. Chem. Rev., 2006, 250, 3094;
(f) L. Fabbrizzi and A. Poggi, Chem. Soc. Rev., 1995, 24, 197;
(g) M. H. Filby, S. J. Dickson, N. Zaccheroni, L. Prodi,
S. Bonacchi, M. Montalti, M. J. Paterson, T. D. Humphries,
C. Chiorboli and J. W. Steed, J. Am. Chem. Soc., 2008, 130, 4105.
2 (a) B. Valeur, Molecular Fluorescence: Principles and Applications,
Wiley-VCH, Weinheim, Germany, 2002; (b) E. M. Nolan and
S. J. Lippard, Chem. Rev., 2008, 108, 3443; (c) L. Fabbrizzi and
A. Poggi, Chem. Soc. Rev., 1995, 24, 197.
1559, 1519, 1386, 1333, 1267, 1222, 1119, 786 and 701 cmꢀ1
.
MS (MALDI-TOF) Calcd for [C41H43N5O2S]+: m/z 669.3137.
Found: m/z 670.94 [M+H]+. EI-MS m/z 670.3301 (M+H)+,
m/z 692.3131 (M + Na)+.
3 (a) A. P. de Silva, H. Q. Gunaratne, T. Gunnlaugsson, A. J. M.
Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice, Chem.
Rev., 1997, 97, 1515; (b) Z. Zhou, M. Yu, H. Yang, K. Huang,
F. Li, T. Yi and C. Huang, Chem. Commun., 2008, 3387;
(c) J. S. Kim and D. T. Quang, Chem. Rev., 2007, 107, 3780.
4 (a) R. P. Haugland, M. T. Z. Spence, I. D. Johnson and A. Basey,
The Handbook: A Guide to Fluorescent Probes and Labeling
Technologies, Molecular Probes, Eugene, OR, 10th edn, 2005;
(b) M. Beija, C. A. M. Afonso and J. M. G. Martinho, Chem.
Soc. Rev., 2009, 38(8), 2410; (c) M. J. Ruedas-Rama, X. J. Wang
and E. A. H. Hall, Chem. Commun., 2007, 1544; (d) S. W. Thomas,
G. D. Joly and T. M. Swager, Chem. Rev., 2007, 107, 1339.
5 A. B. Othman, J. W. Lee, J.-S. Wu, J. S. Kim, R. Rym Abidi,
´
P. Thuery, J. M. Strub, A. V. Dorsselaer and J. Vicens, J. Org.
Chem., 2007, 72, 7634.
6 H. N. Kim, M. H. Lee, H. J. Kim, J. S. Kim and J. Yoon, Chem.
Soc. Rev., 2008, 37, 1465 and reference their in.
7 B. D. Smith, in Macrocyclic Chemistry: Current Trends and Future
Perspectives, ed. K. Gloe, Springer, Dordrecht, The Netherlands,
2005, pp. 137–152.
8 (a) F. Galindo, J. Becerril, M. I. Burguete, S. V. Luis and
L. Vigara, Tetrahedron Lett., 2004, 45, 1659; (b) M. B. Roy,
S. Samanta, G. Chattopadhyay and S. Ghosh, J. Lumin., 2004,
106, 141; (c) C. Kaewtong, N. Muangsin, N. Chaichit and
B. Pulpoka, J. Org. Chem., 2008, 73, 5574.
Synthesis of 1-butyl-3-(naphthalen-1-yl)thiourea (2). This was
synthesized by a modified literature method.17 To a solution of
butylamine (0.50 g, 0.68 mL, 6.76 mmol) in dried CHCl3ꢂ(20 mL)
was added 1-naphthyl isothiocyanate (1.0 g, 5.41 mmol). The
reaction mixture was stirred at room temperature for 15 h and
then water (40 mL) was added. The organic layer was
separated, washed with brine (40 mL), dried with anhydrous
MgSO4 and the product purified by recrystallization from
acetonitrile to give 0.15 g of 2 (white crystal) in 87% yield.
1H NMR (400 MHz, CDCl3) d 9.94 (s, 1H, ArNHCS),
7.87–7.78 (m, 3H, ArH), 7.54–7.36 (m, 4H, ArH), 5.60
(s, 1H, CSNHCH2), 3.51 (t, J = 7.2 Hz, 2H, NCH2CH3),
1.39–1.32 (m, 4H, NCH2CH2CH2), 1.18 (m, 2H, CH2CH2CH3)
and 0.76 (t, J = 7.2 Hz, 3H, CH2CH2CH3). IR (KBr) n 3391,
3155, 2934, 1676, 1559, 1536, 1509, 1277, 1203, 788 and
640 cmꢀ1
.
´
9 V. Amendola, D. Esteban-Gomez, L. Fabbrizzi, M. Licchelli,
E. Monzani and F. Sancenon, Inorg. Chem., 2005, 44, 8690.
´
10 V. I. Vetrogon, N. G. Lukyanenko, M. J. Schwing-well and
F. Arnaud-Neu, Talanta, 1994, 41, 2105.
Complexation studies of ligands by using UV-vis titrations
11 (a) H. Maeda, Y. Haketa and T. Nakanishi, J. Am. Chem. Soc.,
2007, 129, 13661; (b) L. Kovbasyuk and R. Krmer, Chem. Rev.,
2004, 104, 3161.
12 (a) W. Shi and H. Ma, Chem. Commun., 2008, 1856;
(b) X.-Q. Zhan, Z.-H. Qian, H. Zheng, B.-Y. Su, Z. Lan and
J.-G. Xu, Chem. Commun., 2008, 1859; (c) X. Zhang, Y. Shiraishi
and T. Hirai, Org. Lett., 2007, 9, 5039; (d) M. H. Lee, H. J. Kim,
S. Yoon, N. Park and J. S. Kim, Org. Lett., 2008, 10, 213.
13 R. Shukla, T. Toshiyuki Kida and B. D. Smith, Org. Lett., 2000, 2,
3099.
14 (a) S. Kubik and R. Goddard, J. Org. Chem., 1999, 64, 9475;
(b) P. D. Beer, P. K. Hopkins and J. D. McKinney, Chem.
Commun., 1999, 1253.
15 (a) N. Pelizzi, A. Casnati, A. Friggeri and R. Ungaro, J. Chem.
Soc., Perkin Trans. 2, 1998, 1307; (b) P. D. Beer and J. B. Cooper,
Chem. Commun., 1998, 129; (c) T. Tozawa, Y. Misawa, S. Tokita
and Y. Kubo, Tetrahedron Lett., 2000, 41, 5219.
The complexation abilities of ligand L1 with anions in the
presence and absence of bound cations were investigated by
spectrophotometric titration in MeCN at 25 1C. 2 mL of the
10 mMꢂL1 solution were placed in a spectrophotometric cell
(1 cm path length) and the spectrum was recorded from
250–650 nm. The solutions of a cation or an anion were added
successively into the cell from a microburette. The mixture was
stirred for 40 s after each addition and its spectral variation
was recorded. The stability constants were calculated from
spectrometric data using program SIRKO.10
Acknowledgements
16 (a) X. Zhang, Y. Shiraishi and T. Hirai, Org. Lett., 2007, 9, 5039;
(b) Y. Shiraishi, R. Miyamoto, X. Zhang and T. Hirai, Org. Lett.,
2007, 9, 3921; (c) J. H. Soh, K. M. K. Swamy, S. K. Kim, S. Kim,
S.-H. Lee and J. Yoon, Tetrahedron Lett., 2007, 48, 5966.
17 C. M. Suter and Eugene W. Moffett, J. Am. Chem. Soc., 1933, 55, 2497.
The authors gratefully acknowledge financial support from
Faculty of Science, Mahasarakham University and the center
of excellence for innovation in chemistry (PERCH-CIC).
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1108 | New J. Chem., 2010, 34, 1104–1108