Discovery of a sensitive Cu(ii)-cyanide "off-on" sensor based on new C-glycosyl triazolyl bis-amino acid scaffold

Article abstract of DOI:10.1039/c1ob06242e

A new functional glycosyl peptidomimetic, featuring a C-glucosyl 1,4-dimethoxynaphthalene backbone in conjugation with two triazolyl phenylalanine moieties on its adjacent C3,4-positions, was readily synthesized via click chemistry. Primary optical measur

Full text of DOI:10.1039/c1ob06242e

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Discovery of a sensitive Cu(II)-cyanide “off–on” sensor based on new
C-glycosyl triazolyl bis-amino acid scaffold†
Yan-Hui Tang,a Yi Qu,a Zhuo Song,a Xiao-Peng He,*a,b Juan Xie,b Jianli Hua*a and Guo-Rong Chen*a
Received 24th July 2011, Accepted 19th October 2011
DOI: 10.1039/c1ob06242e
A new functional glycosyl peptidomimetic, featuring a C-glucosyl 1,4-dimethoxynaphthalene
backbone in conjugation with two triazolyl phenylalanine moieties on its adjacent C3,4-positions, was
readily synthesized via click chemistry. Primary optical measurements indicated that the fluorescence of
the ester form of this probe (4) could be selectively quenched by Pb2+. In contrast, the fluorescence
intensity of its analog 5 with released carboxylic groups was uniquely diminished by Cu2+ with
remarkably enhanced sensitivity and selectivity. Moreover, subsequent addition of cyanide to the
methanol solution of the resulting Cu2+-5 complex induced its fluorescence recovery with a nanomolar
detection limit, which was two orders of magnitude smaller than the regulated concentration limit of
CN- in drinking water. This suggests the promising applicability of C-glycosyl bis-triazolyl amino acid
scaffold in the future design and exploration of sensitive “off–on” Cu(II)-cyanide chemosensors.
Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC)14 which is
Introduction
the best paradigm of click chemistry,15,16 we have recently synthe-
Cyanide is acutely toxic toward both environmental and biological
sized a series of bidentate glycomimetics that have bis-triazolyl
systems,1–3 therefore considerable efforts have been devoted to
the development of effective chemosensors.4–9 Among the various
intelligent strategies in designing cyanide sensors, the use of Cu(II)-
compound complexes for sensing CN-, which takes advantage
of the high affinity between copper and cyanide,10 has emerged
as a novel effective approach.11,12 The general rationale behind
this strategy relies on cyanide induced fluorescence recovery of
a chemosensor that has previously been fluorescently deactivated
through complexation with Cu(II). However, since the regulated
concentration of cyanide in drinking water is extraordinarily low
due to its extreme toxicity,3 the majority of currently developed
probes encounter the main drawback of unsatisfactory detection
limits. As a consequence, further exploration of new chemical
entities that are highly sensitive to both copper(II) and cyanide is
fairly desirable.
functional groups on two different sites of a monosaccharide.17
Some of these compounds bearing fluorophores were identified as
new selective metal chelators.
With continued interest in developing sugar-based fluorescent
probes, we report herein our new discovery of a bis-triazolyl C-
glycosyl amino acid derivative that may potentially serve as an
“off–on” Cu(II)–cyanide sensor with desirable sensitivity, however
with moderate selectivity over phosphates. Enlightened by the
structural feature of our previously synthesized C-glycosyl 1,4-
dimethoxynaphthalene that embodies a free sugar moiety and a
naphthalene group (1, Fig. 1), two phenylalaninyl fragments were
further introduced onto the adjacent C3,4-position of the glycosyl
scaffold via CuAAC for embracing ions. The fluorescence of the
ester form of this probe was identified to be selectively quenched
by Pb2+, whereas that of its carboxylic acid-exposed analog was
uniquely diminished by Cu2+ with more enhanced sensitivity.
Subsequent addition of CN- to this Cu2+-probe complex induced
its fluorescence recovery with a nanomolar detection limit.
Development of fluorescent compounds using small-molecule
sugar units as the core scaffold is a rarely explored but promising
alternative for the discovery of potent chemosensors as naturally
occurring sugars possess substantial merits such as well-defined
stereo-structures, low toxicity and high bioavailability.13 In using
aKey Laboratory for Advanced Materials and Institute of Fine Chemicals,
East China University of Science and Technology, 130 Meilong Road,
Shanghai, 200237, PR China. E-mail: frogmaster_eminem@yahoo.com.cn,
jlhua@ecust.edu.cn, mrs_guorongchen@ecust.edu.cn; Fax: +86-21-
64252758; Tel: +86-21-64253016
bPPSM, Institut d’Alembert, ENS de Cachan, CNRS UMR 8531, 61 Avenue
du Pt Wilson, F-94235, Cachan, France
† Electronic supplementary information (ESI) available: Fig. S1–S3, 1H
Fig. 1 Construction of bis-triazolyl C-glycosyl amino acid derivatives as
new ion chemosensors.
and 13C NMR copies of compounds 3–5. See DOI: 10.1039/c1ob06242e
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Results and discussion
Synthesis
Using our previously prepared aryl C-glucoside 118 as the start-
ing material, 3,4-di-O-propynyl-2,6-O-TBDMS-C-glucosyl 1,4-
dimethoxynaphthalene 2 was readily synthesized via selective 2,6-
silylation by TBDMSCl, and then O-alkylation in the presence of
propargyl bromide and NaH.17c A dual click reaction between this
di-alkynyl C-glycoside and an azido phenylalanine (a)19 promoted
by excessive Na ascorbate and CuSO4·5H2O17c sequentially led to
the bis-triazolyl amino acid-C-glucoside conjugate 3 in a moderate
yield of 65%. Desilylation of compound 3 by AcCl gave the
desired compound in its ester form (4). Subsequent removal of
the methyl esters in the presence of LiOH eventually resulted in
the formation of carboxylic acid-exposed glycosyl bis-amino acid
5 in quantitative yield (Scheme 1).
Fig. 2 (a) Fluorescence quenching rate in the presence of 100 mM of
various metal cations; (b) Fluorescence spectrum in the presence of various
concentrations (10 to 400 mM) of Pb2+; (c) Stern–Volmer plot in the
presence of various concentrations (0 to 400 mM) of Pb2+ of compound 4
(10 mM) in methanol (lex = 242 nm).
ascribable to the broad-range binding ability of the N-rich triazole
moiety with various metal cations.20
A fluorescence titration experiment of 4 in the presence of Pb2+
with varied concentrations was then performed, shown in Fig. 2b
and Fig. 2c. By excitation at 242 nm, a narrow emission band
of probe 4 (10 mM in methanol) ranging from 300 to 500 nm
was observed (Fig. 2b, top curve). Clearly, the gradual increase
of Pb2+ from 10 mM to 400 mM induced the gradual decrease of
fluorescence intensity of 4, while the quenching plateau could be
reached in the presence of 40 equiv. Pb2+. The detection limit of
this probe for Pb2+ in methanol was calculated to be 0.29 mM (Fig.
S1a, ESI†).12d
Having preliminarily determined the metal ion sensitivity of
the ester-form of the designed probe, we sequentially attempted
to study the fluorescence change of its analog 5 with exposed
carboxylic acid groups in the presence of the same selection of
cations as described above (excitation at 242 nm). To our surprise,
by simply releasing the carboxylic acid groups, the resulting
sensitivity as well as specificity of probe 5 was significantly varied.
Fig. 3a depicts the specificity of 5 (10 mM in methanol) toward
various metal cations, which reveals that this probe is sensitive to
binding with Cu2+ as the presence of only 1 equiv. of Cu2+ may
afford a fluorescence quenching rate of approximately 75%. In the
meanwhile, whereas 5 gave almost no response to the addition
of Ba2+, Mg2+ and Cd2+, the presence of other competing cations
such as Co2+, Ni2+, Fe2+ and Pb2+ resulted in its slight fluorescence
decrease by a rate of less than 20%.
Scheme 1 Reagents and conditions: (i) TBDMSCl, DMAP, pyridine;
then propargyl bromide, NaH, DMF; (ii) Na ascorbate, CuSO4·5H2O,
CH2Cl2/H2O; (iii) AcCl, MeOH, then LiOH, MeOH.
Optical study
The metal cation sensitivity of the ester-form of probe 4 in
methanol was first studied via fluorescence spectroscopy by
excitation at 242 nm, shown in Fig. 2. Upon addition of 10
equiv. of various selected metal cations (100 mM) including Ba2+,
Mn2+, Co2+, Zn2+, Al3+, Ni2+, Cd2+, Ag+, Hg2+, Fe2+, Cu2+ and
Pb2+ to the methanol solution of 4 (10 mM), its fluorescence
intensity altered accordingly (Fig. 2a). We observed that Pb2+
could more compellingly quench the fluorescence of compound
4 by a quenching rate ([F0 - F]/F0, where F0 is the original
fluorescence intensity and F is the varied fluorescence intensity
in the presence of the metal) of about 50% compared with other
competing cations. However, we also noticed that the presence of
Cu2+ and Ag+ may lead to the fluorescence quenching of 4 by a
relatively smaller rate of 20% and 15%, respectively. This should be
It is interesting that the removal of the methyl ester group
of compound 4 has caused its remarkable change in binding
preference from Pb2+ to Cu2+, which is most likely ascribable
to the specific coordination of Cu2+ with the released car-
boxylic acid groups.11d Furthermore, by comparing with several
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The quantum yields (UF) of 4 and 5 in methanol were assigned
to 0.278 and 0.279, respectively, using L-tryptophan (UF = 0.13 in
water) as the reference.
The strategy for the sensing of cyanides using fluorescently
deactivated Cu2+-sensor complexes has been well established in the
literature.11,12 Hence, we further examined whether the successive
addition of CN- to the methanol solution of 5-Cu2+ (10 mM)
complex would result in any variations.
As shown in Fig. 4a, the fluorescence of 5-Cu2+ complex could
be renewed with different fluorescence recovery ratios ([FRR] =
[F - Fmin]/[Fmax - Fmin], where Fmax is the fluorescent intensity of
5 without Cu2+, Fmin is the fluorescent intensity of 5-Cu2+, F is
the fluorescent intensity of 5-Cu2+ with different concentrations
of CN-) in terms of the nature of the anion added (30 mM).
The presence of F-, Br-, Cl-, ClO4 and NO3 induced almost
-
-
no fluorescence change, while the presence of I-, AcO- and HSO4
-
weakly enhanced its fluorescence intensity. In contrast, whereas
-
H2PO4 induced a half fluorescence recovery rate of the complex,
the presence of CN- increased its fluorescence intensity with a
recovery rate of 65%. A detailed fluorescence titration test shown
in Fig. 4b and 4c further implies that with increased concentration
of CN-, the fluorescence intensity of 5 can regress gradually. The
presence of 10 equiv. CN- nearly rendered its full fluorescence
recovery.
Fig. 3 (a) Fluorescence quenching rate in the presence of various metal
cations (10 mM); (b) Fluorescence spectrum in the presence of various
concentrations (0 to 14 mM) of Cu2+; (c) Stern–Volmer plot in the presence
of various concentrations (0 to 14 mM) of Cu2+ of compound 5 (10 mM) in
methanol (lex = 242 nm).
former reports in which the developed fluorescent probes were
generally equally sensitive to Cu2+ and another competing
cation,21 compound 5 takes advantage of its more distinct
selectivity. Meanwhile, the sensitivity of probe 5 is significantly
enhanced (vs. 4) with a low detection limit of 14 nM (Fig.
S1b, ESI†). This value is comparable to recent work wherein
heterocyclic mono-amino acid frameworks were developed as
Cu2+ chelators.21a However, those chelators showed unsatisfactory
selectivity for Cu2+ over Co2+, Ni2+ and especially Zn2+, which
means that the bis-triazolyl amino acid system constructed
herein on a sugar scaffold is advantageous for achieving im-
proved metal-sensing selectivity with simultaneously comparable
sensitivity.
The fluorescence spectrum excited at 242 nm of compound 5
shown in Fig. 3b similarly interprets a narrow emission band from
300 to 500 nm (top curve). Upon addition of Cu2+ with gradually
increased concentration (0–14 mM) to the methanol solution of
5 (10 mM), the corresponding fluorescence intensity gradually
decreased till quenching plateau at the highest concentration,
shown in Fig. 3b and 3c. To test the potential practicality of
5, a fluorescence titration experiment in the presence of various
concentrations of Cu2+ was further performed in pure water. As
shown in Fig. S2a (ESI†), the emission band ranging from 300
to 500 nm of 5 was equally observed by excitation at 242 nm in
water, while the gradual addition of Cu2+ to this aqueous solution
led to the gradual decrease in fluorescence intensity. Eventually,
the presence of 50 equiv. of Cu2+ caused a quenching rate of
about 50%. The corresponding detection limit calculated through
Fig. S2b (ESI†) was assigned to 44 mM. Despite the diminished
sensitivity, probe 5 has proven useful in the direct sensing of Cu2+
in pure water, unravelling the applicability of glycosyl bis-triazolyl
amino acid framework for the development of water soluble
chemosensors.
Fig. 4 (a) Fluorescence recovery rate in the presence of TBA (tetrabuty-
lammonium) salts of various anions (30 mM); (b) Fluorescence spectrum
in the presence of various concentrations (0 to 100 mM) of CN-; (c)
Fluorescence recovery plot in the presence of various concentrations (0
to 20 mM) of CN- of compound 5 (10 mM) in methanol (lex = 242 nm).
Such a phenomenon is most likely caused by the association
of CN- with Cu2+ which then positively sets free the original
fluorescence of probe 5 (Fig. 4, top curve).11d However, 5 may
-
similarly be isolated by H2PO4 that is also known to have high
binding affinity with Cu2+. We subsequently examined the impact
2-
of several other anions including CO3 and the phosphates such
-
2-
3-
as H2PO4 , HPO4 and PO4 toward the fluorescence change of
5-Cu2+ (10 mM) in aqueous media (MeOH/water = 9 : 1, v/v),
shown in Fig. S3 (ESI†).
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The fluorescence of 5 could similarly be recovered by CN-
(30 mM) in this new aqueous ambiance by 65%, while the presence
solvent mixture of CH2Cl2 (5 mL) and H2O (5 mL), were added
sodium ascorbate (1073 mg, 5.4 mmol) and CuSO4·5H2O (867 mg,
3.5 mmol). This mixture was stirred at rt for 12 h, and was then
diluted directly with CH2Cl2 and washed with brine and deionized
water. The combined organic layer was dried over MgSO4, filtered
and then concentrated under vacuum. The resulting residue was
purified by column chromatography (petroleum ether/EtOAc =
3 : 1) to afford compound 3 as a white solid (189 mg, 65.2%). 1H
NMR (400 MHz, CDCl3): d = 8.21 (dd, J = 1.6, 6.8 Hz, 1H),
8.01 (dd, J = 1.6, 7.2 Hz, 1H), 7.56 (s, 1H), 7.52–7.44 (m, 2H),
7.27–7.21 (m, 3H), 7.20–7.18 (m, 3H), 7.04 (dd, J = 2.4, 7.6 Hz,
1H), 6.94 (dd, J = 2.0, 7.2 Hz, 1H), 6.86 (s, 1H), 6.80 (s, 1H), 5.56
(dd, J = 6.8, 8.4 Hz, 1H), 5.13 (dd, J = 7.2, 8.0 Hz, 1H), 4.94 (d,
J = 11.2 Hz, 1H), 4.88 (d, J = 11.6 Hz, 1H), 4.58 (d, J = 11.6 Hz,
1H), 3.97 (s, 3H), 3.94 (dd, J = 3.6, 12.4 Hz, 1H), 3.88 (d, J = 8.4
Hz, 1H), 3.86–3.82 (m, 2H), 3.82 (s, 3H), 3.74 (s, 3H), 3.71–3.63
(m, 2H), 3.58 (s, 3H), 3.52 (dd, J = 6.8, 14.4 Hz, 2H), 3.47–3.39
(m, 2H), 3.31 (dd, J = 6.8, 14.0 Hz, 1H), 3.31 (dd, J = 8.4, 14.0 Hz,
1H), 0.92 (s, 9H), 0.88 (s, 9H), 0.06 (s, 3H), 0.05 (s, 3H), 0.04 (s,
3H), 0.02 (s, 3H). 13C NMR (100 MHz, CDCl3): d = 168.8, 168.4,
152.1, 147.8, 145.7, 145.2, 134.9, 134.8, 129.0, 128.9, 128.7, 128.3,
127.6, 127.4, 127.2, 126.7, 126.5, 125.8, 122.6, 122.3, 122.2, 122.1,
104.1, 83.9, 80.4, 79.0, 78.7, 75.1, 66.5, 66.4, 64.0, 63.7, 63.3, 62.5,
55.7, 53.1, 52.9, 39.0, 38.5, 26.2, 26.1, 18.4, 18.1, -3.8, -3.9, -4.7,
-5.0.
2-
of excessive CO3 only resulted in a recovery rate of 30%.
Since phosphates exist extensively in biological systems, an excess
-
2-
3-
of, respectively, H2PO4 , HPO4 and PO4 were added to the
solution, which led to maximal renewed fluorescence of 5 by a
rate of approximately 60%. Although the selectivity of 5-Cu2+
between phosphates and cyanide is not adequate, there is a clear
tendency that this complex has a recognition preference to the
latter. Future efforts could be made to achieve better specificity
for CN- over other anions by appropriate structural modifications.
Additionally, this probe is remarkably more selective to cyanide
over F- compared with previously developed amide-type cyanide
sensors, probably due to the lack of NH protons sensitive to
halogens.12d
Notably, the detection limit of complex 5-Cu2+ is assigned to a
favorable value of 37.5 nM (Fig. S1c, ESI†), which is two orders
of magnitude lower than the regulated concentration of cyanide
in drinking water (around 200 nM).3 This could be a substantial
merit for the further exploration of sensitive cyanide sensors.
Conclusions
To summarize, a unique C-glycosyl bis-triazolyl amino acid
derivative was readily synthesized by taking advantage of the
modular and selective CuAAC as the key step. This fluorescent
molecule with exposed di-carboxylic acid functional groups was
subsequently identified as a new “off–on” Cu(II)-cyanide sensor
with a satisfactorily nanomolar detection limit, albeit with moder-
ate selectivity over phosphates. Our study would therefore set out
a unique basis for the future design and development of sensitive
and potentially biocompatible cyanide sensors based on the double
“clicked” C-glycosyl bis-amino acids. Programs related to this
subject are currently underway.
Synthesis of 3,4-di-O-{1-[1(S)-methoxycarbonyl-2-phenylethyl]-
4-methyl-1H-1,2,3-triazol-4-yl}-b-D-glucopyranosyl 1,4-dimeth-
oxynaphthalene (4). To a soln. of 3 (189 mg, 0.2 mmol) in
MeOH (5 mL) was added AcCl (30 mL, 0.3 mmol), stirring at
rt for 12 h. The solvent was removed under vacuum and the
residue was then diluted with EtOAc and washed successively
with sat. NaHCO3 and brine. The combined organic layer was
dried over MgSO4, filtered and then concentrated under vacuum.
The resulting residue was purified by column chromatography
(petroleum ether/EtOAc = 1 : 1) to afford compound 4 as a white
solid (136 mg, 91.5%). [a]2D5 = +14 (c = 0.02, MeOH); UV-vis
Experimental section
1
(MeOH) lmax: 211, 242, 301, 313, 327 nm; H NMR (400 MHz,
General techniques and materials
CDCl3): d = 8.23 (dd, J = 0.8, 7.6 Hz, 1H), 8.01 (dd, J = 1.2,
7.6 Hz, 1H), 7.63 (s, 1H), 7.56–7.47 (m, 2H), 7.28–7.25 (m, 1H),
7.24–7.17 (m, 5H), 7.06 (s, 1H), 7.05 (dd, J = 1.6, 7.6 Hz, 2H), 6.94
(dd, J = 1.6, 7.6 Hz, 2H), 6.75 (s, 1H), 5.56 (dd, J = 6.8, 8.8 Hz,
1H), 5.34 (dd, J = 6.4, 8.8 Hz, 1H), 5.03 (d, J = 13.2 Hz, 1H), 4.99
(d, J = 12.8 Hz, 1H), 4.88 (d, J = 9.6 Hz, 1H), 4.27 (d, J = 13.2
Hz, 1H), 4.21 (d, J = 13.6 Hz, 1H), 4.02 (d, J = 8.8 Hz, 1H), 3.97
(s, 3H), 3.89 (s, 3H), 3.80 (dd, J = 2.8, 12.4 Hz, 1H), 3.77–3.72 (m,
2H), 3.74 (s, 3H), 3.70–3.65 (m, 1H), 3.66 (s, 3H), 3.55–3.51 (m,
1H), 3.50 (d, J = 6.4 Hz, 1H), 3.45 (dd, J = 8.4, 14.0 Hz, 1H), 3.45
(dd, J = 6.4, 14.4 Hz, 1H), 3.24 (dd, J = 8.8, 14.4 Hz, 1H). 13C
NMR (100 MHz, CDCl3): d = 168.7, 168.4, 152.4, 148.2, 145.6,
145.3, 134.8, 134.7, 129.0, 128.9, 128.8, 128.4, 127.7, 127.6, 126.9,
126.8, 126.4, 126.1, 122.6, 122.4, 122.0, 101.8, 83.7, 79.4, 79.1,
78.7, 74.9, 65.4, 65.2, 64.2, 64.0, 63.4, 62.4, 55.9, 53.2, 53.1, 38.9,
38.7. HRESIMS m/z: [M + H]+ calcd. for C42H45N6O11: 837.3459;
found: 837.3458.
All chemicals and reagents as well as Ba(OAc)2, Mn(OAc)2,
Co(OAc)2, ZnSO4, Al(NO3)3, Ni(OAc)2, Cd(NO3), AgNO3,
Hg(OAc)2, FeSO4, CuSO4 and Pb(OAc)2, and all K and TBA salts
used for fluorescence studies are of high commercially available
1
grade. H and 13C NMR spectra were recorded on a Jeol-400
MHz spectrometer in CDCl3 or CD3OD solutions. Analytical thin-
layer chromatography was performed on E. Merck aluminium
precoated plates of Silica Gel 60F-254 with detection by UV and
by spraying with 6 N H2SO4 and heating at 300 ◦C. High resolution
mass spectra (HRMS) were recorded on an MA1212 instrument
using standard conditions (ESI, 70 eV). Optical rotations were
measured using a Perkin–Elmer 241 polarimeter at room tem-
perature and 10 cm/1 mL cell. All UV-Vis absorption spectra
were measured on a Varian Cary 500 UV-Vis spectrophotometer
and fluorescence spectra measured on a Varian Cary Eclipse
Fluorescence spectrophotometer.
Synthesis of 2,6-di-O-TBDMS-3,4-di-O-{1-[1(S)-methoxycar-
bonyl-2-phenylethyl]-4-methyl-1H-1,2,3-triazol-4-yl}-b-D-gluco-
pyranosyl 1,4-dimethoxynaphthalene (3). To a soln. of alkyne
2 (257 mg, 0.4 mmol) and azide a (202 mg, 1.0 mmol) in a
Synthesis of 3,4-di-O-{1-[1(S)-carboxy-2-phenylethyl]-4-methyl-
1H-1,2,3-triazol-4-yl}-b-D-glucopyranosyl 1,4-dimethoxynaphtha-
lene (5). To a soln. of 4 (65 mg, 0.08 mmol) in a solvent mixture of
MeOH (3 mL) and H2O (3 mL) was added LiOH (6 mg, 0.2 mmol),
558 | Org. Biomol. Chem., 2012, 10, 555–560
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stirring at rt for 3 h. H+ resin was then added for neutralization
and the mixture was filtered. The filtrate was concentrated under
vacuum to give the pure product 5 as a white solid (62.7 mg,
Acknowledgements
Generous funding was provided by the Natural Science Foun-
dation of China (Grant No. 21176076), Shanghai Science and
Technology Community (No. 10410702700) and the Fundamental
Research Funds for the Central Universities (No. WK1013002).
X.-P. H. also gratefully acknowledges the French Embassy in
Beijing, PR China for a co-tutored doctoral fellowship.
quantitative). [a]D25 = +5 (c = 0.02, MeOH); UV-vis (MeOH) lmax
:
211, 242, 301, 313, 327 nm; 1H NMR (400 MHz, CD3OD): d = 8.20
(d, J = 8.4 Hz, 1H), 8.04–8.00 (m, 2H), 7.55–7.45 (m, 2H), 7.21–
7.05 (m, 8H), 6.98 (brs, 1H), 6.93 (dd, J = 2.0, 6.0 Hz, 2H), 6.80
(dd, J = 2.0, 5.6 Hz, 1H), 5.55 (dd, J = 3.6, 10.4 Hz, 1H), 5.24–5.17
(m, 1H), 5.00 (d, J = 12.0 Hz, 1H), 4.87–4.81 (m, 2H), 4.61–4.46
(m, 1H), 4.18 (dd, J = 3.2, 12.4 Hz, 1H), 4.01–3.94 (m, 3H), 3.86 (t,
J = 8.4 Hz, 1H), 3.79 (s, 3H), 3.72 (dd, J = 7.2, 13.6 Hz, 1H), 3.69–
3.59 (m, 3H), 3.55 (dd, J = 2.4, 9.2 Hz, 1H), 3.49 (dd, J = 3.2, 14.4
Hz, 1H), 3.45–3.43 (m, 1H), 3.41 (dd, J = 4.8, 14.0 Hz, 1H), 3.32
(brs, 2H). 13C NMR (100 MHz, CD3OD): d = 170.9, 170.4, 152.1,
148.0, 144.4, 143.3, 136.4, 136.1, 128.6, 128.5, 128.2, 128.1, 127.1,
127.0, 125.6, 124.1, 124.0, 123.1, 123.0, 122.2, 122.1, 102.3, 83.1,
82.5, 80.1, 78.9, 78.2, 77.9, 74.8, 65.6, 65.1, 62.6, 61.8, 55.0, 38.0,
37.7. HRESIMS m/z: [M + H]+ calcd. for C42H49N6O11: 809.3146;
found: 809.3146.
Notes and references
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The fluorescence measurements were carried out on a Varian Cary
Eclipse Fluorescence spectrophotometer by using a path length of
10 mm and excitation at 242 nm by scanning the emission spectra
between 250 and 650 nm. The bandwidth for both excitation and
emission spectra was 5 nm.
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Preparation of sample solutions for the evaluation of ion
specificity. Stock solutions of 0.01 M of Hg(OAc)2, Ba(OAc)2,
Mn(OAc)2, Co(OAc)2, Ni(OAc)2, Cu(OAc)2, Zn(SO4)2, Cd(NO3)2,
Pb(OAc)2, FeSO4 and AgNO3 were prepared in de-ionized water.
Stock solutions of 0.01 M of F-, Br-, Cl-, I-, ClO4 , NO3 , AcO-,
-
-
HSO4 , H2PO4 , CN- were prepared in acetonitrile and stock
solutions of sensors (2 ¥ 10-4 M) 4 and 5 prepared in methanol or
in water or methanol/water (90 : 1, v/v). Stock solutions of 0.01 M
-
-
2-
-
2-
3-
of CO3 and excessive H2PO4 , HPO4 and PO4 were prepared
in water. For the selectivity experiment of sensor 4, test solutions
were prepared by adding 30 mL of each metal stock to 3 mL test
solution of sensor 4 ([4] = 10 mM). For the selectivity experiment
of sensor 5, test solutions were prepared by adding 3 mL of each
of metal stock to 3 mL test solution of sensor 5 ([5] = 10 mM).
For the selectivity experiment of sensor Cu2+-5, test solutions were
prepared by adding 3 mL of Cu2+ stock to 3 mL test solution of
sensor 5 ([5] = 10 mM). Then, 9 mL of different anion stock were
added in the test solutions.
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Preparation of stock solutions and samples for the titration
experiments. Stock solutions of 0.01 M of Pb(OAc)2, CuSO4 and
TBACN in de-ionized water or acetonitrile were prepared. For the
titration experiment of sensor 4 with Pb2+, to 3 mL test solution of
sensor 4 ([4] = 10 mM) was added 0–120 mL of Pb(OAc)2 solution.
For the titration experiment of sensor 5 with Cu2+, to 3 mL test
solution of sensor 5 ([5] = 10 mM) was added 0–4.2 mL of CuSO4
solution. For the titration experiment of sensor Cu2+-5 with CN-,
to 3 mL of test solution of sensor Cu2+-5 ([Cu2+-5] = 10 mM) was
added 0–30 mL of TBACN solution.
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The Royal Society of Chemistry 2012
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