A selective chromogenic reagent for nitrate

Article abstract of DOI:10.1002/1521-3773(20020415)41:8<1416::AID-ANIE1416>3.0.CO;2-2

Nitrate sensing: A selective colorimetric sensing of nitrate by a mercury complex of an oxa-thia-aza macrocycle functionalized with an azo dye is described. The figure shows the color of acetonitrile solutions of the mercury complex in the presence of the

Full text of DOI:10.1002/1521-3773(20020415)41:8<1416::AID-ANIE1416>3.0.CO;2-2

COMMUNICATIONS
[10, 22, 23]
have potential applications as a pigment dispersant,
in the separation and purification of proteins.[
or
A Selective Chromogenic Reagent for
Nitrate**
7, 24]
Received: November 26, 2001 [Z18276]
F e¬ lix Sancen o¬ n, Ram o¬ n MartÌnez-M a¬ nƒ ez,* and
Juan Soto
The selective sensing of anions by natural and synthetic
receptors is an important area of supramolecular chemistry.[
Anions play significant roles in biological and environmental
processes, therefore the development of new chemosensors
for anions is an important topic. Anion-sensing receptors
incorporate into their structures groups that are capable of
interaction with anions, and sensing subunits in which
[
[
[
1] V. B¸t¸n, N. C. Billingham, S. P. Armes, J. Am. Chem. Soc. 1998, 120,
1]
1
1818.
2] V. B¸t¸n, S. P. Armes, N. C. Billingham, Z. Tuzar, A. Rankin, J.
Eastoe, R. K. Heenan, Macromolecules 2001, 34, 1503.
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Angew. Chem. Int. Ed. 2001, 40, 2328.
[
[
4] V. B¸t¸n, S. P. Armes, N. C. Billingham, Polymer 2001, 42, 5993.
5] C. S. Patrickios, W. R. Hertler, N. L. Abbott, T. A. Hatton, Macro-
molecules 1994, 27, 930.
[2]
[3]
spectroscopic or electrochemical features change upon
anion binding. Chemosensors with changes in their spectro-
[
[
[
[
6] W. Chen, P. Alexandridis, C. Su, C. S. Patrickios, W. R. Hertler, T. A.
Hatton, Macromolecules 1995, 28, 8604.
7] C. S. Patrickios, L. R. Sharma, S. P. Armes, N. C. Billingham, Lang-
muir 1999, 15, 1613.
8] S. Creutz, J. van Stam, S. Antoun, F. C. De Schryver, R. Jerome,
Macromolecules 1997, 30, 4078.
9] S. Creutz, J. van Stam, F. C. De Schryver, R. Jerome, Macromolecules
scopic behavior have either fluorogenic[ or chromogenic
4]
[5]
signalling subunits. Chromogenic reagents are especially
attractive because the anion determination can be carried
out by the naked eye, without the use of expensive equipment.
Chromogenic reagents for the selective detection of inorganic
and organic anions have been reported.[ However, it is still a
challenge to find chromogenic receptors for the selective
sensing of poorly coordinating anions such as nitrate. As far as
we know, the only example of nitrate sensing by color change,
by use of receptors coupled to dyes, was reported recently, and
it involved a competitive assay between nitrate and methyl
red or resorufin in binding a polyamide cage, in dichlorome-
thane:methanol 50:50 v/v. The system, however, is not specific
and addition of bromide or perchlorate also produced color
changes, although to a lesser extent.[ We now report a new
and specific chromogenic reagent for nitrate using a p-
nitrophenylazobenzene group as a dye and a mercuric
complex as an anion-binding site. The system shows a
selective change of color in acetonitrile but can also be
applied to the selective determination of nitrate in water.
The aza-oxa-thia macrocycle (see Scheme 1) was obtained
by the cyclization of 3,6-dioxa-1,8-octanedithiol and dimesi-
1
998, 31, 681.
6]
[
[
10] S. Creutz, R. Jerome, Langmuir 1999, 15, 7145.
11] J. F. Gohy, S, Creutz, M. Garcia, B. Mahltig, M. Stamm, R. Jerome,
Macromolecules 2000, 33, 6378.
[
[
[
[
[
12] A. B. Lowe, N. C. Billingham, S. P. Armes, Chem. Commun. 1997,
1
035.
13] A. B. Lowe, N. C. Billingham, S. P. Armes, Macromolecules 1998, 31,
991.
14] V. B¸t¸n, A. B. Lowe, N. C. Billingham, S. P. Armes, J. Am. Chem.
Soc. 1999, 121, 4288.
5
15] T. Goloub, A, de Keizer, M. A. C. Stuart, Macromolecules 1999, 32,
8
441.
7]
16] At intermediate pH values either side of the IEP, the electrostatic
interaction of the oppositely charged blocks can lead to the formation
of aggregates (soluble polyelectrolyte complexes), which are stabi-
lized by uncompensated cationic charge on the DEA block (below the
IEP) or anionic charge on the VBA block (above the IEP). In
contrast, at pH 2 (or pH 10) the VBA block (or DEA block) is
uncharged; thus hydrophobic interactions of this neutral block should
produce compact, well-defined micelles.
[
[
17] A. V. Kabanov, T. K. Bronich, V. A. Kabanov, K. Yu, A. Eisenberg,
Macromolecules 1996, 29, 6797.
18] M. A. C. Stuart, N. A. M. Besseling, R. G. Fokkink, Langmuir 1998,
lated N,N-diethanolphenylamine in acetonitrile/K CO at
2
3
reflux,[ under high dilution conditions. The macrocycle was
8]
1
4, 6846.
[
[
19] A. Harada, K. Kataoka, Science 1999, 283, 65.
20] J. F. Gohy, S. K. Varshney, S. Antoun, R. Jerome, Macromolecules
obtained in a 40% yield. The macrocycle was coupled with the
1
azonium salt of p-nitroaniline in HCl to obtain L as a red-
2
000, 33, 9298.
1
13
orange powder (80% yield). H NMR and C NMR spectro-
scopy, mass spectrometry, and elemental analysis are consis-
tent with the proposed formulation.
[
[
[
[
21] G. B. Webber, E. J. Wanless, S. P. Armes, F. L. Baines, S. Biggs,
Langmuir 2001, 17, 5551.
22] N. G. Hoogeveen, M. A. C. Stuart, G. J. Fleer, Colloids Surf. A 1996,
1
17, 7 7 .
1
The visible spectrum of the ligand L in acetonitrile is
23] S. Creutz, R. Jerome, G. M. P. Kaptijn, A. W. van der Werf, J. M.
Akkerman, J. Coat. Technol. 1998, 70, 41.
24] C. S. Patrickios, C. J. Jang, W. R. Hertler, T. A. Hatton, ACS. Symp.
Ser. 1994, 548, 257.
characterized by an intense band centered at 490 nm (e ˆ
À1
À1
2
6000m cm ), which is responsible for the orange color of
the solutions and is caused by a charge transfer from the
[
*] Dr. R. MartÌnez-M a¬ nƒ ez, F. Sancen o¬ n, Dr. J. Soto
Departamento de QuÌmica
Universidad Polit e¬ cnica de Valencia
Camino de Vera s/n, 46071 Valencia (Spain)
Fax : (‡34)96-387-9349
E-mail: rmaez@qim.upv.es
[
**] This research was supported by the Ministerio de Ciencia y TecnologÌa
proyecto PB98-1430-C02-02, 1FD97-0508-C03-01, and AMB99-0504-
(
C02-01). F.S. also thanks the Ministerio de Ciencia y TecnologÌa for a
Doctoral Fellowship.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
1416
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4108-1416 $ 20.00+.50/0
Angew. Chem. Int. Ed. 2002, 41, No. 8

COMMUNICATIONS
5
40 nm band to 490 nm with a concomitant change in color
1
2‡
from red to yellow, whereas the [Hg(L ) ] complex gave a
specific response to NO3 ions, as this was the only anion
2
À
which produced a color change of the receptor solution
(
Figure 1). Competitive experiments have been carried out
1
2‡
using the [Hg(L ) ] complex. The same spectral variation
2
was found upon nitrate addition in solutions containing a five-
fold excess of chloride, bromide, iodide, or sulfate. In contrast,
some interference was detected in the presence of an excess of
fluoride or phosphate.
Scheme 1. Synthesis of L1.
donor nitrogen atom of the macrocycle to the acceptor nitro
moiety.[ No changes were observed in the UV/Vis spectrum
9]
‡
‡
in acetonitrile, upon addition of one equivalent of Li , Na ,
‡
2‡
2‡
2‡
K , Ca , Ba , and Mg (perchlorate salts) or upon addition
À
À
À
À
À
of up to 100 equivalents of the anions F , Cl , Br , I , H PO ,
2
4
À
À
HSO , and NO (tetra-N-butylammonium salts). Whereas
4
3
1
2‡
À5
À3
2‡
2‡
2‡
2‡
2‡
Figure 1. Color changes induced in [Hg(L ) ] (9.6 Â 10 moldm ) in
the addition of the metal ions Ni , Zn , Cd , Pb , Fe , and
2
À
À
À
À
À
À
4
‡
2‡
acetonitrile. From left to right: no anion, F , Cl , Br , I , H
2
PO
4
, HSO
,
Ag did not have any significant effect, the presence of Cu ,
À
and NO
3
.
2
‡
3‡
1
Hg , and Fe cations induced a red shift of the L visible
band to 520 ± 540 nm, which resulted in a color change of the
solution from orange to red. The 520 nm band intensity
Titration of acetonitrile solutions of the complexes
1
2‡
1
2‡
[Cu(L )] , [Hg(L ) ] , and [Fe(L ) ] by addition of aliquots
2
1
3‡
1
À4
2
(
concentration of L 1.0 Â 10 m in acetonitrile) was moni-
2 2‡ 3‡
‡
of the corresponding anion solution gave isosbestic points in
all cases, which indicate the formation of 1:1 anion:receptor
complexes. From the titration data, stability constants for the
formation of anion ± receptor complexes were determined
tored upon addition of the metal ions Cu , Hg , and Fe ,
which allowed us to determine complex stability constants.
1
2‡
Titration of L with Cu indicated the formation of 1:1 ligand-
to-metal complexes. The log K value for the complex-
formation equilibrium, calculated through nonlinear least-
(
Table 1).[ . The receptor [Cu(L )] forms strong complexes
10]
1
2‡
[10]
with all the anions studied. Stability constants are in the
squares treatment of the titration profiles, was 5.9 Æ 0.2. For
À
À
À
À
À
À
À
Hg2 and Fe ions, the titration data suggested the formation
‡
3‡
order F > H
[
2
PO
4
> NO
3
> Cl ˆI > HSO
3‡
2
4
ˆBr . The
1
2‡
1
Hg(L ) ] and [Fe(L ) ] receptors, though they show a
2
of sandwichlike complexes with 2:1 ligand:metal stoichiome-
more selective response, also form strong complexes with
values of the stability constants of the same order of those of
the copper receptor.
tries. Calculated log K values were 11.2 Æ 0.3 and 10.9 Æ 0.2
1
2‡
1
3‡
2
for the formation of the [Hg(L ) ] and [Fe(L ) ] com-
2
plexes, respectively. Additional 1H and C NMR spectro-
scopic studies were carried out on the Hg ± L system. NMR
13
2‡
1
Table 1. Stability constants from titration experiments in acetonitrile for
the formation of 1:1 anion:receptor complexes.[
spectroscopy confirmed the formation of the 1:2 metal:ligand
a]
1
2‡
complex [Hg(L ) ] with significant shifts of the signals
2
1
À
À
À
À
À
À
À
4
NO
3
F
Cl
Br
I
HSO
4
H
2
PO
arising from the protons and carbons of the L aza-oxa-thia
ring, in the presence of the mercuric cation.
[Cu(L
1
)]2‡
3‡
6.2(2) 7.5(5) 4.7(1) 3.4(1) 4.6(2) 3.7(1)
7.1(2)
±
±
1
2‡
1
2‡
1
3‡
2
1
These [Cu(L )] , [Hg(L ) ] , and [Fe(L ) ] complexes
[Fe(L )
2
]
5.7(1)
6.2(2)
±
±
±
±
±
±
4.8(1)
±
±
±
2
1
2‡
[
Hg(L )
2
]
have proved to be suitable chromogenic receptors for anion
sensing. Thus, changes in the visible spectrum were recorded
in acetonitrile solutions of these receptors upon addition of
[a] Values in parentheses are the standard deviations in the last significant
digit.
À
À
À
À
À
À
À
F , Cl , Br , I , H PO , HSO , and NO ions. Each
2
4
4
3
complex showed quite different behavior in the presence of
the anions studied, the most remarkable effect being observed
These results show that dye-containing metal complexes
can act as efficient and selective chromogenic reagents for
anion sensing. Additionally, there is a remarkable control of
1
2‡
[11]
with the [Hg(L ) ] complex. Hence, while addition of every
2
1
2‡
anion to the [Cu(L )] complex solution resulted in a shift of
the selectivity by simple selection of the metal cation. Thus,
3
‡
2‡
2‡
the visible band of the complex and color change (the color
metal ions such as Fe , Cu , and Hg are able to change the
À
À
À
À
1
variation is more remarkable for F , Cl , I , H PO , and
color of the dye L probably by a suitable coordination with
2
4
À
À
À
3‡
2‡
2‡
NO3 ions than Br and HSO
ions, see Supporting
the aza-oxa-thia ring. In fact, Fe , Cu , and Hg ions, among
the metals studied, give the strongest complexes with amines
and therefore an effective coordination between the metals
and the nitrogen atom of the aza-oxa-thia ring of the dye
4
1
3‡
1
2‡
Information), the [Fe(L ) ]
and [Hg(L ) ]
complexes
2
2
1
3‡
showed a more selective response. For [Fe(L ) ] , only
addition of I and NO3 ions resulted in a shift of the
2
À
À
Angew. Chem. Int. Ed. 2002, 41, No. 8
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4108-1417 $ 20.00+.50/0
1417

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would be expected.[ This interaction causes the disappear-
12]
sulfate, chloride, calcium, magnesium, and sodium in typical
1
À3
À4
ance of the L charge-transfer band and the appearance of a
concentration ranges 1 Â 10 ±5 Â 10 ). Table 2 shows the
nitrate concentration in water determined by addition of
50 mL of the aqueous sample to 10 mL of acetonitrile solutions
new red-shifted band that probably arises from a new charge-
transfer transition, in which orbitals of the metal centers are
involved. This metal ± dye interaction is very sensitive to local
electronic disturbances produced by the presence of the
anions and hence, coordination or formation of ion-pairs
between certain anions and [Cu(L )] , [Hg(L ) ] , and
Fe(L ) ] receptors could induce the observed color changes.
NMR spectroscopic studies of the [Hg(L ) ] -nitrate system
1
2‡
of [Hg(L ) ] and further measurement of the absorption
2
band. The method is easy to carry out and allows colorimetric
determination of nitrate in the presence of the other anions
and cations typically present in water. We also found that
lower concentrations of nitrate can also be determined by the
simple preconcentration of diluted aqueous samples.
1
2‡
1
2‡
2
1
3‡
[
2
1
2‡
2
showed a slight shift of the signals assigned to the protons
ortho to the azo group, in the presence of nitrate ions. This
shift could be related to the presence of p-stacking inter-
actions between the nitrate ion and the p-nitrophenylazoben-
À
Table 2. Concentration of nitrate (Àlog [NO
3
]) in different samples of
Determined [
water.
a]
Real
concentration
1
zene group. Therefore, as both the nitrate anion and the L
1
2‡
with [Hg(L )
2
]
molecule are planar, and nitrate forms equally strong com-
2
.36
2.40
2.70
3.10
3.50
1
2‡
1
2‡
plexes with all three receptors [Cu(L )] , [Hg(L ) ] , and
2
2.66
3.02
3.43
1
3‡
À
[
Fe(L ) ] , we suggest that the interaction between the NO
2
3
1
ions and the receptors must proceed through the L molecule
and not through the cationic metal center. Hence, though the
interaction between nitrate and the receptors must be favored
by electrostatic forces, p-stacking interactions between the
planar nitrate and the also planar p-nitrophenylazobenzene
could be responsible for the color changes observed in the
presence of nitrate.
[
a] Concentration of nitrate was determined using the calibration curve
(Figure 2).
2‡
3‡
2‡
In conclusion, Cu , Fe , and Hg complexes with the
1
receptor L are very sensitive to the electronic perturbations
produced by anions and have proved to be suitable chromo-
genic reagents for anion sensing. The selective detection of
the poorly coordinating anion nitrate, and the possibility of its
direct quantification in water using a simple color change are
especially significant. These findings might open up new
opportunities in the chromogenic sensing of traditionally
poorly coordinating anions by synthetic receptors.
1
2‡
The selective nitrate sensing using the [Hg(L ) ] complex
2
is a remarkable effect, thus some preliminary studies were
carried out to use this color change as a method for direct
nitrate determination in water. We realized that the addition
of small quantities of water (up to 0.5%) to acetonitrile
1
2‡
solutions of [Hg(L ) ] did not have any effect in the selective
2
color change from red to yellow observed in the presence of
nitrate. Therefore, using a calibration curve for nitrate in an
acetonitrile:water solution (Figure 2), nitrate concentration in
aqueous solutions can be approximately determined by the
addition of small aliquots of aqueous nitrate ions (few mL) to
Received: December 7, 2001 [Z18347]
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2‡
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1
2‡
acetonitrile:water 99.5:0.5 v/v. Concentration of [Hg(L )
2
]
:
9.6 Â
À5
À3
1
0
moldm .
1418
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4108-1418 $ 20.00+.50/0
Angew. Chem. Int. Ed. 2002, 41, No. 8

COMMUNICATIONS
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inside a three-dimensional host compound. The accessibility
of the Li center is controlled by the steric requirements of
‡
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whereas larger anions are efficiently blocked. Since the radius
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1
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À
‡
the hard base F appears to be very attractive, but so far Li -
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there is not even structural data available on complexes
containing molecular LiF,[ although numerous examples of
other alkali metal halide complexes are known. The difficulty
of stabilizing molecular LiF arises from its very high lattice
energy which makes crystalline LiF a thermodynamic trap.[
Recently, we have described the synthesis of trimeric
organometallic complexes of the general formula
1
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[
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[
12] M. J. Choi, M. Y. Kim, S. K. Chang, Chem. Commun. 2001, 1664 ±
1
665; M. Inouye, Color. Non-Text. Appl. 2000, 238 ± 274; Q. Ma, H.
[
L M(C H NO )] (L M ˆ arene-Ru or Cp*Rh; Cp* ˆ
n
5
[5]
3
2
3
n
Ma, Z. Wang, M. Su, H. Xiao, S. Liang, Chem. Lett. 2001, 100 ± 101; T.
Gunnlaugsson, M. Nieuwenhuyzen, L. Richard, V. Thoss, Tetrahedron
Lett. 2001, 42, 4725 ± 4728.
[6]
C Me ). These analogues of [12]crown-3 were shown to
5
5
bind alkali metal halides with remarkable affinity and
selectivity. In an extension of this work we have investigated
the reaction of [{Cp*IrCl } ] with 3-hydroxy-2-pyridone in the
2
2
presence of base. As in the cases with the analogous
ruthenium and rhodium complexes, a trimeric complex
[
Cp*Ir(C H NO )] (1) was obtained. The metallamacrocycle
5 3 2 3
1
13
Selective Recognition of Fluoride Anion Using
was characterized by NMR spectroscopy ( H, C), elemental
analysis, and single-crystal X-ray analysis (Figure 2).
‡
[7]
a Li ± Metallacrown Complex
A
pseudo-C -symmetric geometry is observed in the solid state,
with dianionic pyridonate ligands bridging the Cp*Ir frag-
3
Marie-Line Lehaire, Rosario Scopelliti,
Holger Piotrowski, and Kay Severin*
III
With the final goal of constructing specific chemosensors
for fluoride anions, considerable efforts have been put into the
synthesis of compounds that are able to bind fluoride ions
with high affinity and selectivity. The receptors described
include organic macrocycles with convergent H-bond donor
groups and compounds containing Lewis acidic boron, silicon,
or tin atoms.[ Here we report a conceptually new fluoride
receptor, the basic principle of which is shown in Figure 1. A
lithium ion, which serves as a binding site, is coordinated
1, 2]
*] Prof. K. Severin, M.-L. Lehaire, Dr. R. Scopelliti[
‡]
[
Institut de Chimie Mol e¬ culaire et Biologique
¬
Ecole Polytechnique F e¬ d e¬ rale de Lausanne, BCH
015 Lausanne (Switzerland)
1
Fax : (‡41)21-693-9305
E-mail: kay.severin@epfl.ch
Dr. H. Piotrowski[
‡]
Department Chemie
Ludwig-Maximilians Universit‰t M¸nchen
Butenandtstrasse 5 ± 13, 81377 M¸nchen (Germany)
Figure 2. a) The molecular structure of 1 in the crystal; b) view along the
pseudo-C
filling representation); c) the molecular structure of 1 ¥ LiF in the crystal;
d) view along the pseudo-C axis of 1 ¥ LiF. Four very short CH ¥¥¥ F contacts
3
axis of 1 highlighting the sterically shielded binding site (space
‡
[
] X-ray structural analyses.
3
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
are observed (the water molecule is omitted in the space filling
representation).
Angew. Chem. Int. Ed. 2002, 41, No. 8
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
1433-7851/02/4108-1419 $ 20.00+.50/0
1419