Fluorescence-responsive H2PO4- receptor based on macrocyclic boron complex

Article abstract of DOI:10.1246/cl.2006.536

Macrocyclic boron complex showed selective fluorescence response toward H₂PO₄^- via hydrogen-bond network, Lewis acid-base interaction, and inhibition of PET. Copyright

Full text of DOI:10.1246/cl.2006.536

536
Chemistry Letters Vol.35, No.5 (2006)
À
Fluorescence-responsive H2PO4 Receptor Based on Macrocyclic Boron Complex
Naohiro KametaÃ1 and Kazuhisa HirataniÃ2
1Nanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology, AIST
Tsukuba Central 5, 1-1-1 Higashi, Tsukuba 305-8565
2Department of Applied Chemistry, Faculty of Engineering, Utsunomiya University, 7-1-2 Youtou, Utsunomiya 321-8585
(Received February 21, 2006; CL-060213; E-mail: hiratani@cc.utsunomiya-u.ac.jp)
Macrocyclic boron complex showed selective fluorescence
À
zation reaction between dicarboxylic acid dichloride 1 and dia-
mine 2 under high dilution conditions. Then, tandem Claisen re-
arrangement (160 ꢀC, 1 h, in N-methylpyrrolidinone (NMP)) was
carried out to introduce plural hydroxy groups into 3.9 Complex-
ation between 4 and boric acid derivative 5 in the presence of
molecular sieves gave only macrocyclic boron complex 6 in ex-
cellent yield.10
response toward H2PO4 via hydrogen-bond network, Lewis
acid–base interaction, and inhibition of PET.
Various anion sensors having recognition and response sites
have been developed so far.1 Supramolecular metal complexes
are interested in the field of anion binding1,2 and sensing1,3 be-
cause of the unique three-dimensional recognition-site toward
specific anion and the Lewis acidic metal center in the complex
which is possible to interact with anion. Boron compounds such
as boric acid and its ester derivatives have been known to act as
hard acid and strongly interact with anions changing the orbital
from sp2 to sp3.4 Therefore, many boron complexes bearing fluo-
rophore and chromophore as sensing agents for anions and sug-
ars have been synthesized.5–7 Fluorescence response of those
sensing agents utilizes the changing of the photoinduced electron
transfer (PET) between fluorophore and boron moiety, the effi-
ciency of the energy transfer from donor to acceptor. Recently,
we succeeded in the construction of a chromogenic anion recep-
tor based on a noncyclic boron-complex whose central boron
consisted of a four-coordinated structure which was negatively
charged and was not able to interact with anion.8
In this work, we designed and synthesized macrocyclic bor-
on complex having plural hydrogen-bonding sites such as hy-
droxy, amide, oxyethylene, and a fluorophoric anthracene linked
to phenyl borate. We investigated the complexation and the flu-
orescence response abilities of the boron complex toward vari-
ous anions by using fluorescence and 1H NMR spectroscopy.
Scheme 1 shows a synthetic process of novel macrocyclic
boron complex. Macrocyclic compound 3 was obtained by cycli-
Fluorescence response of the boron complex toward various
anions having tetrabutylammonium ion as a counter cation was
investigated. Figure 1a shows fluorescence spectra of the anthra-
cene moiety in Àthe boron complex in the presence and the ab-
sence of H2PO4 in CH3CN/CHCl3 (9/1). The fluorescence iÀn-
tensity increased with increase in the concentration of H2PO4
.
The molar ratio plot in Figure 1b indicated an intersection at the
molar ratio of 1.0, which corresponds to a 1:1 (=Boron com-
plex:H2PO4À) stoichiometry. On the other hand, the variations
of the fluorescÀence intensity of the boron complex in the pres-
ence of HSO4À and CH3COOÀ were remarkably smaller than
that of H2PO4 as shown in Figure 1b. For ClÀ, BrÀ, and IÀ,
the spectral change was not observed at all. The variation of
the fluorescence intensity by the addition of FÀ was strange, al-
though the shape of spectra did not change. The binding constant
(ꢀ1) between the boron complex and anions was determined
by using the general equation10 related to the variation of the
fluorescence intensity in Figure 1b. The ꢀ1 values were in the
À
À
order of H2PO4 (104:89) ꢁ HSO4 (101:90) > CH3COOÀ
(101:75) ꢁ ClÀ, BrÀ, IÀ (no response) which were not corre-
sponding to the order of the basicity of anions. The ꢀ1 value
of FÀ was not able to be calculated because of the strange spec-
tral change.
70
60
50
40
30
20
10
0
80
60
40
20
NH2
-
H
H2PO4
3.0 x 10-7
N
O
M
O
O
O
O
O
O
1
Cl
Cl
O
O
O
O
O
O
O
O
O
O
NEt3
∆
NMP
-
H2PO4
F -
HSO4
+
rt, THF
-
N
H
O
CH3COO-
Cl-, Br-, I-
NH2
0 M
2
3 (36%)
H
H
400 420 440 460 480 500 520
Wavelength/nm
0.0 0.5 1.0 1.5 2.0 2.5 3.0
[Anion]
N
N
HN
O
O
O
O
O
O
O
OH
O
O
HO
B
OH
OH
O
O
total / [Boron complex]total
HN
O
OH
OH
O
HO
5
B
Figure 1. a) Fluorescence spectra of 1:0 Â 10À7 M boron com-
plex in the presence and the absence of 1:0 Â 10À8–3:0 Â
Molecular sieves 4Å
Reflux, CHCl3
O
OH
N
H
N
H
À
10À7 M H2PO4 in CH3CN/CHCl3 (9/1). Excitation at 380
nm. b) Molar ratio plots between boron complex and various
anions. Solid lines except for FÀ were calculated by using the
general equation and the obtained ꢀ1 value.
4 (86%)
6 (95%)
Scheme 1. Synthesis of novel macrocyclic boron complex.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.5 (2006)
537
References and Notes
To clear the above behavior of the boron complex toward
various anions, the interaction and the complexation between
the boron complex and anions were studied by H NMR spec-
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À
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4
5
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À
be inhibited by the complexation with H2PO4 through plural
hydrogen-bond formations and the Lewis acid–base interaction
as illustrated in Figure 2. Although the enhancement of the
fluorescence intensity might occurred commonly in the case of
FÀ which strongly interacts with boron,4,11 the tendency was
remarkably different from that of H2PO4À. This should be
due to the contribution of another PET12 by the hydrogen-bond
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7
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À
H2PO4 which can be detected by the fluorescence response.
8
9
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O
OH
10 Supporting Information available. Synthesis of 5. 1H NMR, IR,
ESI-MS of 3, 4, 5, and 6; General equation for determination
of binding constant; 1H NMR spectra of boron complex in the
N
H
O
P
OH
O
-
O
O
OH
O
O
presence and absence of H2PO4 and FÀ.
À
O
B
H
OH
N
11 Recent issues: S. Arimori, M. G. Davidson, T. M. Fyles, T. G.
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380 nm
¨
O
H
O
N
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PET
414 nm
FigureÀ2. Optical response of the boron complex toward
H2PO4
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.
Published on the web (Advance View) April 22, 2006; DOI: 10.1246/cl.2006.536