Colorimetric anion sensing by porphyrin-based anion receptors

Article abstract of DOI:10.1016/S0040-4039(01)01876-7

Porphyrin derivatives 1-4 with H-bond donors and/or color-reporting chromophoric unit were synthesized and studied as anion-binding receptors. 1 and 2 exhibited binding selectivity in the order of AcO^->H₂PO₄^-?Cl^-, Br^-, I^- in DMSO-d₆. Color change tests with several different anions for colorimetric anion sensors (3 and 4) resulted in selectivities for F^-, AcO^- and H₂PO₄^- in organic solution. While 1 and 2 exhibited good selectivities for AcO^- and H₂PO₄^-, 3 and 4 showed a dramatic color change for F^- due to increased interaction with a nitrophenylazo phenolic OH group.

Full text of DOI:10.1016/S0040-4039(01)01876-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 8665–8668
Colorimetric anion sensing by porphyrin-based anion receptors
Chanhyo Lee, Dong Hoon Lee and Jong-In Hong*
School of Chemistry and Molecular Engineering, College of Natural Sciences, Seoul National University,
Seoul 151-742, South Korea
Received 5 September 2001; revised 4 October 2001; accepted 9 October 2001
Abstract—Porphyrin derivatives 1–4 with H-bond donors and/or color-reporting chromophoric unit were synthesized and studied
as anion-binding receptors. 1 and 2 exhibited binding selectivity in the order of AcO−>H2PO4−ꢀCl−, Br−, I− in DMSO-d6. Color
change tests with several different anions for colorimetric anion sensors (3 and 4) resulted in selectivities for F−, AcO− and H2PO4
−
in organic solution. While 1 and 2 exhibited good selectivities for AcO− and H2PO4−, 3 and 4 showed a dramatic color change
for F− due to increased interaction with a nitrophenylazo phenolic OH group. © 2001 Elsevier Science Ltd. All rights reserved.
The development of synthetic receptors for anion
recognition has attracted considerable attention in
recent decades within the field of supramolecular chem-
istry due to the fact that a large number of biological
processes involve molecular recognition of anionic spe-
cies.1 Selective colorimetric anion sensing is particularly
challenging since visual detection can give immediate
qualitative information, while absorption spectroscopy
gives quantitative information.2 Most of these sensors
have the chromophore covalently attached to the anion
recognition unit.3 However, there are only a few
reported colorimetric sensors available for anionic sub-
strates.2,3 In this paper we present colorimetric anion
sensing by porphyrin-based receptors. In addition to
the biologically important functions of the porphyrin as
the prosthetic group of heme proteins, porphyrins con-
stitute a suitable framework for artificial receptors due
to their several unique characteristics.4 We used a por-
phyrin scaffold as a rigid spacer for the multiple hydro-
gen bond donors to be predisposed on favorable
positions for anion binding above a porphyrin plane.5
It turns out that the receptors 3 and 4 act as colorimet-
ric sensors for selected anions by means of hydrogen
bonding interactions.
NO2
O2N
NO2
N
N
O2N
N
N
N
N
N
N
HO
HO
HN
OH
H2N
HN HO
OH
OH
O
HO
NH
HN
HN
NH2
OH
NH
O
O
O
a
NH
H2N
NH
NH
HN
HN
O
HN
N
HN
NH
N
O
N
N
O
M
NH
NH2
N
N
NH
O
HN
NH
N
N
N
M
N
H2TamPP
1 M = 2H
2 M = Zn
3 M = 2H
4 M = Zn
b
b
Scheme 1. (a) Triphosgene, TEA, CH2Cl2, rt, 6 (or 7), 76% (79%); (b) Zn(OAc)2, CH2Cl2, MeOH, rt, 95%.
* Corresponding author. Tel.: +82-2-889-1568; fax: +82-2-880-6682; e-mail: jihong@plaza.snu.ac.kr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01876-7

8666
C. Lee et al. / Tetrahedron Letters 42 (2001) 8665–8668
The syntheses of receptors 1–4 are outlined in Scheme
1. Compounds 5 and 6 were prepared by the standard
methods in Scheme 2. Attachment of a p-nitropheny-
lazo group on the para position of the phenolic OH of
5 was accomplished by a general azo-coupling method6
and then removal of a Boc protecting group gave 7
(Scheme 2). The synthesis of 5,10,15,20-meso-tetra-
kis(o-aminophenyl)porphyrin (H2T-amPP) was accom-
plished using the Collman’s method,7 from which the
a,a,a,a-isomer of H2TamPP was obtained using Lind-
sey’s atropisomerization method.8 To a stirred solution
of H2TamPP and TEA in CH2Cl2 was added 1.33 equiv.
triphosgene under N2 with subsequent stirring for 1 h.
The resulting mixture was treated with 6 and stirred for
1 h to give free-base porphyrin receptor 1.9 Receptor
310 was prepared following the above methodology11 in
which 7 was used instead of 6. Zn insertion was accom-
plished by stirring the CH2Cl2 solution of 1 or 3 with
methanol saturated with zinc acetate for 2 h to give rise
to receptors 212 and 4.13 Compounds 1 and 2 have urea
groups and additional phenol groups as H-bond donors
for anionic guest molecules. The association of 1 and 2
with various anion guests in DMSO-d6 was studied by
1H NMR spectroscopy. Downfield shifts of urea NH
resonances (0.3–0.5 ppm) were detected upon complex-
−
Figure 1. UV–vis titration of 2 with H2PO4 in DMSO ([2]=
2×10−6 M, [H2PO4−]=0–520 equiv.).
that urea and phenol groups play an essential role in
the anion recognition process via hydrogen bonding.
Anion binding to 1 and 2 was also investigated with
UV–vis spectroscopy. UV–vis spectral changes for the
receptors were induced by the addition of anion guests
in DMSO. UV–visible titration spectra revealed anion
binding through perturbation of the Soret and visible
Q-bands. The original Soret band at 433 nm shifted to
−
438 nm when H2PO4 was added to 2 and isosbestic
points were observed in the spectra (Fig. 1), indicating
1:1 complexation between host and guest molecules.
The formation constants of complexes between 2 and
various anions were calculated by fitting the binding
curve of absorbance at umax as a function of change in
anion concentration (Table 1).
ation with AcO− and H2PO4 . When 0.2 equiv. of AcO−
−
−
and H2PO4 was added, the phenol OH peak became
broad and almost disappeared. These shifts indicated
a
The selectivity trends in binding affinities of anions for
b
1 and 2 were determined to be AcO−>H2PO4 ꢀCl−,
−
NOH
H
Br−, I−. The selectivity for AcO− and H2PO4 can be
−
OH
O
OH
NHBoc
OH
rationalized based on the guest basicity and structure of
the complex. This result contrasts with those for Burn’s
urea-appended porphyrin which complexes more
strongly with spherical chloride.4c This finding shows
that the phenol unit as an additional H-bond site is
important in anion recognition. As expected from the
5
d
NO2
c
basicity of anions,14 AcO− and H2PO4 form stronger
−
N
N
complexes than other anions. These results lead to the
idea that by introducing another chromophore azophe-
nol, 3 and 4 might cause color changes suitable for the
visual detection of selected anions.3d–f UV–vis spectra
of 3 and 4 with anions show different patterns from
.
NH2 HCl
OH
.
OH NH2 HCl
6
7
−
those of 1 and 2. Upon addition of H2PO4 to 3 in
Scheme 2. (a) NH2OH·HCl, TEA, MeOH, 1 h, 98%; (b) (i)
LAH, THF, 2 h, (ii) di-tert-butyl dicarbonate, H2O, THF, 2
h, 44%; (c) HCl bubbling, 99%; (d) (i) aq. NaOH, MeOH,
RT, (ii) p-nitroaniline, NaNO2, aq. HCl, MeOH, 0°C, (iii)
HCl bubbling, 60%.
DMSO, the absorbance of the original Soret band
decreased with little shift of umax, and increased in a
new peak at about 600 nm (Fig. 2). This results from
the stronger basicity of the p-nitrophenyl-azophenolic
OH of 3. As can be expected from UV–vis data, a color
Table 1. Association constants (M−1) for complexes of 1–3 with anionic guestsa
−
−
F−
H2PO4
AcO−
HSO4
Cl−
1
2
3
NDT
4.5×104 b
NDT
1.6×105 b
ND
NDT
2.0×104 b (1.6×104)c
1.4×104 b (2.5×105)d
4.4×104 b (6.4×104)c
3.5×104 b (3.3×105)d
9.5×104 b (9.7×104)c
(4.1×104)d
2400c
ND
(3.6×104)d
a Anions were added as their tetrabutylammonium salts except for Cl−, which was used as tetraethylammonium salt. Association constants were
determined by UV–vis titration in b DMSO, c DMSO:H2O=93:7, d CHCl3 at rt. NDT=not determined (binding constants are too large to
determine), ND=not detected. In case of 4, UV-titration curves for all anions were not well fitted to 1:1 binding isotherm.

C. Lee et al. / Tetrahedron Letters 42 (2001) 8665–8668
8667
In summary, we have developed new colorimetric
azophenolurea-introduced porphyrin sensors for
anions, which show a selective coloration for F−,
H2PO4 and AcO−. Color responses for selected anions
−
(F−, H2PO4 , AcO−) arise from basicity of the anions
−
and effective binding between the azophenolic OH
function of 3 (or 4) and the anion.
Acknowledgements
−
Figure 2. UV–vis titration of 3 with H2PO4 in DMSO ([3]=
2×10−6 M, [H2PO4−]=0–520 equiv.).
Financial support from CMDS (KOSEF) is gratefully
acknowledged. C.L. and D.H.L. thank the Ministry of
Education for award of the BK 21 fellowship.
change occurs by addition of anions to the solution of
3 and 4. More pronounced spectral changes for 3 and 4
were induced by addition of F−, H2PO4 and AcO− in
−
References
CH3CN (Fig. 4). Similarly, F−, H2PO4 and AcO−
−
induced the most distinguishable color changes upon
complexation in CH3CN. However, no detectable color
1. (a) Brzo´zka, Z. In Comprehensive Supramolecular Chem-
istry; Atwood, J. L.; Davies, J. E. D.; MacNicol, D. D.;
Vo¨gtle, F.; Suslick, K. S., Eds.; Pergamon: Oxford, 1996;
pp. 187–212; (b) Chemosensors of Ion and Molecular
Recognition; Desvergne, J.-P.; Czarnik, A. W., Eds.;
Kluwer: Dordrecht, 1997; Vol. 492; (c) Niikura, K.;
Metzger, A.; Anslyn, E. V. J. Am. Chem. Soc. 1998, 120,
8533–8534; (d) Metzger, A.; Anslyn, E. V. Angew. Chem.,
Int. Ed. Engl. 1998, 37, 649–652; (e) Kubo, Y.; Maeda, S.;
Tokita, S.; Kubo, M. Nature 1996, 382, 522–523.
2. (a) Lavigene, J. J.; Anslyn, E. V. Angew. Chem., Int. Ed.
1999, 38, 3666–3669; (b) Gale, P. A.; Twyman, L. J.;
Handlin, C. I.; Sessler, J. L. Chem. Commun. 1999,
1851–1852; (c) Black, C. B.; Andrioletti, B.; Try, A. C.;
Ruiperez, C.; Sessler, J. L. J. Am. Chem. Soc. 1999, 121,
10438–10439; (d) Miyaji, H.; Sato, W.; Sessler, J. L.
Angew. Chem., Int. Ed. 2000, 39, 1777–1780; (e) Anzen-
bacher, Jr., P.; Jurs´ıkova´, K.; Sessler, J. L. J. Am. Chem.
Soc. 2000, 122, 9350–9351; (f) Anzenbacher, Jr., P.; Try,
A. C.; Miyaji, H.; Jurs´ıkova´, K.; Lynch, V. M.; Marquez,
M.; Sessler, J. L. J. Am. Chem. Soc. 2000, 122, 10268–
10272.
−
changes were observed upon addition of excess HSO4 ,
Cl−, Br− or I− to the CH3CN solution of 3 (Fig. 3).
The absorption intensities of F−-3, AcO−-3 and
−
H2PO4 -3 are well correlated with the intensity of the
color change in the order of F−>AcO−>H2PO4 (Figs. 3
−
and 4). While 1 and 2 have the greatest binding affinity
for AcO−, 3 and 4 have a detectable selectivity for F−
because F− interacts more effectively with azophenol
groups. The selectivity trends of anion-induced color
changes for 3 and 4 were determined to be F−>AcO−>
H2PO4 ꢀHSO4 , Cl−, Br−, I−. As a result of the basic-
−
−
ity order of anions, F−, H2PO4 and AcO− form
−
stronger complexes than other anions and show notice-
able color changes compared to other anions.
3. (a) Black, C. B.; Andrioletti, B.; Try, A. C.; Ruiperez, C.;
Sessler, J. L. J. Am. Chem. Soc. 1999, 121, 10438–10439;
(b) Miyaji, H.; Sato, W.; Sessler, J. L. Angew. Chem., Int.
Ed. 2000, 39, 1777–1780; (c) Anzenbacher, Jr., P.; Jur-
s´ıkova´, K.; Sessler, J. L. J. Am. Chem. Soc. 2000, 122,
9350–9351; (d) Lee, D. H.; Lee, K. H.; Hong, J.-I. Org.
Lett. 2001, 3, 5–8; (e) Lee, D. H.; Lee, K. H.; Lee, H. Y.;
Hong, J.-I. Chem. Commun. 2001, 1188–1189; (f) Lee, K.
H.; Lee, H.-Y.; Lee, D. H.; Hong, J.-I. Tetrahedron Lett.
2001, 42, 5447–5449.
Figure 3. Color changes of 3 in CH3CN. [3]=2.0×10−5 M,
[anion]=5 equiv.; (a) 3 only; (b) F−; (c) H2PO4−; (d) AcO−; (e)
HSO4−; (f) Cl−; (g) Br−; (h) I−.
4. (a) The Porphyrins; Dolphin, D., Ed.; Academic Press:
New York, 1978; (b) Kuroda, Y.; Kado, Y.; Higashioji,
T.; Hasegawa, J.; Kawannami, S.; Takahshi, M.; Shi-
raishi, N.; Tanabe, K.; Ogoshi, H. J. Am. Chem. Soc.
1995, 117, 10950–10958; (c) Jagessar, R. C.; Shang, M.;
Scheidt, W. R.; Burns, D. H. J. Am. Chem. Soc. 1998,
120, 11684–11692; (d) Ogoshi, H.; Mizutani, T. Acc.
Chem. Res. 1998, 31, 81–89.
5. Kim, Y.-H.; Hong, J.-I. Tetrahedron Lett. 2000, 41, 4419–
4424.
6. Tsuge, A.; Moriguchi, T.; Mataka, S.; Tachiro, M. J.
Chem. Soc., Perkin Trans. 1993, 2211.
Figure 4. UV–vis changes of 3 operated in CH3CN (5.0×10−6
M) after the addition of 20 equiv. of anions.

8668
C. Lee et al. / Tetrahedron Letters 42 (2001) 8665–8668
11. Collman, J. P.; Wang, Z.; Straumanis, A. J. Org. Chem.
7. Collman, J. P.; Gagne, R. R.; Reed, C. A.; Halbert, T.
1998, 63, 2424–2425.
R.; Long, G.; Robinson, W. T. J. Am. Chem. Soc. 1975,
97, 1424–1439.
8. Lindsey, J. S. J. Org. Chem. 1980, 45, 5215.
12. Selected spectral data for 2: 1H NMR (300 MHz,
DMSO-d6, ppm): l 3.75 (s, 8H), 6.26 (br, 4H), 6.39–6.44
(t, 4H), 6.53–6.56 (d, 4H), 6.61–6.63 (d, 4H), 6.81–6.86 (t,
4H), 7.07 (s, 4H), 7.30–7.35 (t, 4H), 7.69–7.74 (m, 8H),
8.40–8.43 (d, 4H), 8.68 (s, 8H), 9.27 (s, 4H); 13C NMR
(75 MHz, DMSO-d6, ppm): l 37.84, 114.80, 115.60,
118.50, 120.62, 120.78, 125.32, 127.72, 128.32, 128.56,
131.62, 131.84, 135.31, 139.42, 149.63, 154.52, 155.46; LR
FAB-MS (m-NBA) m/z=1334 (found), 1332.39 (calcu-
lated for major isotope peak for [C76H60N12O8Zn]+); UV–
vis umax (DMSO, nm): 433 (Soret), 563.
9. Selected spectral data for 1: 1H NMR (300 MHz,
DMSO-d6, ppm): l −2.69 (s, 2H), 3.85–3.87 (d, 8H), 6.38
(br, 4H), 6.48–6.51 (t, 4H), 6.57–6.59 (d, 4H), 6.74–6.77
(d, 4H), 6.86–6.88 (t, 4H), 7.29–7.31 (t, 4H), 7.51–7.56
(m, 8H), 7.73–7.76 (t, 4H), 8.44–8.47 (d, 4H), 8.71 (s,
8H), 9.32 (s, 4H); 13C NMR (75 MHz, DMSO-d6, ppm):
l 38.96, 115.76, 116.70, 119.48, 121.81, 122.00, 126.07,
128.83, 129.65, 129.96, 131.50, 132.40, 136.46, 140.38,
155.59, 156.46; LR FAB-MS (m-NBA) m/z=1271
(found), 1270.48 (calculated for [C76H62N12O8]+); UV–vis
umax (DMSO, nm): 433 (Soret), 519, 563.
13. Selected spectral data for 4: 1H NMR (300 MHz,
DMSO-d6, ppm): l 3.68 (s, 8H), 6.28 (br, 4H), 6.66–6.69
(d, 4H), 6.95 (s, 4H), 7.27–7.49 (m, 12H), 7.62–7.75 (m,
16H), 8.18–8.21 (d, 8H), 8.31–8.34 (d, 4H), 8.71 (s, 8H),
10.47 (s, 4H); 13C NMR (75 MHz, DMSO-d6, ppm): l
37.74, 115.40, 115.54, 120.82, 122.71, 123.40, 124.71,
126.82, 128.53, 131.71, 131.98, 135.15, 139.29, 144.85,
147.44, 149.63, 155.24, 155.31, 159.55; LR FAB-MS (m-
NBA) m/z=1931 (found), 1928.48 (calculated for major
isotope peak for [C100H72N24O16Zn]+); UV–vis umax
(DMSO, nm): 433 (Soret), 518.
10. Selected spectral data for 3: 1H NMR (300 MHz,
DMSO-d6, ppm): l −2.67 (s, 2H), 3.81 (s, 8H), 6.43 (br,
4H), 6.68–6.71 (d, 4H), 6.71–7.52 (m, 36H), 8.19–8.22 (d,
8H), 8.36–8.39 (d, 4H), 8.75 (s, 8H), 10.58 (br, 4H); 13C
NMR (75 MHz, DMSO-d6, ppm): l 38.76, 116.38,
116.60, 122.12, 123.56, 124.22, 124.46, 125.61, 125.86,
127.62, 130.02, 131.83, 136.33, 140.21, 145.66, 148.31,
156.09, 156.38, 160.59; MALDI-TOF-MS m/z=1866.27
(found), 1866.57 (calculated for [C100H74N24O16]); UV–vis
umax (CHCl3, nm): 424 (Soret), 518, 591.
14. (a) Nishizawa, S.; Bu¨hlmann, P.; Iwao, M.; Umezawa, Y.
Tetrahedron Lett. 1995, 36, 6483; (b) Kelly, T. R.; Kim,
M. H. J. Am. Chem. Soc. 1994, 116, 7072–7080.