Metal-organic cyclohelicates as optical receptors for glutathione: Syntheses, structures, and host-guest behaviors

Article abstract of DOI:10.1002/asia.201000733

Two trinuclear zinc-based cyclohelicates, Zn-PDB (PDB=[5-(dibenzylamino)- N1′,N3′-bis(pyridin-2-ylmethylene)isophthalohydrazide]) and Zn-PMB (PMB=[5-(bodipy-oxy)-N1′,N3′-bis(pyridin-2-ylmethylene) isophthalohydrazide]) containing dibenzylamino and BODIPY

Full text of DOI:10.1002/asia.201000733

DOI: 10.1002/asia.201000733
Metal–Organic Cyclohelicates as Optical Receptors for Glutathione:
Syntheses, Structures, and Host–Guest Behaviors
Jian Wang, Hongmei Wu, Cheng He,* Liang Zhao, and Chunying Duan[a]
Abstract: Two trinuclear zinc-based cy-
clohelicates, Zn–PDB (PDB=[5-(di-
benzylamino)-N1’,N3’-bis(pyridin-2-yl-
methylene)isophthalohydrazide]) and
towards
g-glutamyl-cysteinyl-glycine
acted with the amide groups sited in
host molecules through hydrogen-
bonding interactions to produce meas-
urable spectral changes. Fluorescent ti-
trations of Zn–PMB upon the addition
of GSH and ESI-MS investigations of
the titration solutions confirmed the
host–guest interaction modes and re-
vealed the possible 1:1 complexation
stoichiometry. These results showed
(GSH) and its component amino acids
was investigated by spectroscopic titra-
tions. UV/Vis absorption titration and
NMR titrations of Zn–PDB and Zn–
PMB upon addition of the above-men-
tioned guests suggested that the Glu
residue of GSH was positioned within
the cavity. The COOÀ groups interact-
ed with metal ions through static inter-
actions. The Cys moiety of GSH inter-
Zn–PMB
(PMB=[5-(bodipy-oxy)-
N1’,N3’-bis(pyridin-2-ylmethylene)i-
sophthalohydrazide]) containing diben-
zylamino and BODIPY groups, respec-
tively, were generated by incorporating
two amide-containing tridentate chela-
tors into meta-positions of a substituted
phenyl ring. Single-crystal structure
analysis and related spectroscopic char-
acterizations demonstrated the forma-
tion of macrocyclic helicals both in the
solid state and in solution. The host–
guest behavior of the cyclohelical hosts
that the recognition of
within the cavity of functionalized
metal–organic cage-like receptors
a substrate
Keywords: glutathione · host–guest
systems
works · sensors · supramolecular
chemistry
could be a useful method to produce
supramolecular sensors for biomole-
cules.
·
metal–organic frame-
Introduction
sponses and metal-triggered functions is relevantly
small.[26,27] There are still big challenges at stake here related
to our understanding in functionalizing optically active
groups as well as special trigger sites for the efficient guest
interactions with biological small molecules and proper
communication that transduces the recognition informa-
tion.[28–30]
On the other hand, synthetic hosts that recognize peptides
in solution with high affinity would be useful in basic bio-
chemical research, such as the separation of protein mix-
tures and possibly in the diagnosis and treatment of human
diseases.[31–33] Especially, the analysis of GSH (g-glutamyl-
cysteinyl-glycine) is of continuous interest, because GSH is
the most abundant cellular thiol compound and is involved
in many important functions in the body, including the con-
trol of the redox environment in cells.[34–37] Various molecu-
lar probes that use organic small molecules,[38–44] metal com-
plexes,[45,46] gold nanorods,[47–49] and quantum dots[50] have
been developed for GSH and thiol-containing amino acids.
Although these approaches have led to significant contri-
butions to the GSH assay, it is noted that the molecular rec-
ognition step of these approaches is always based on interac-
Supramolecular assembly of predesigned organic and inor-
ganic building blocks is an excellent tool for constructing
well-defined nanosized molecular cavities[1–10] that can en-
capsulate special guest substrates for applications in chemi-
cal sensing,[11,12] molecular separations,[13–15] reactive inter-
mediate isolation,[16–18] and encapsulated reaction chemis-
try.[19,20] Recently, the synthetic strategies for constructing
functional coordination cages with various structures and
novel inclusion properties have been well established, and
substantial developments have been made in the creation of
Werner-type capsules showing interesting molecular recogni-
tion properties;[21–25] however, the number examined as size-
or shape-selective molecular chemosensors with various re-
[a] J. Wang, Dr. H. Wu, C. He, L. Zhao, Prof. C. Duan
State Key Laboratory of Fine Chemicals
Dalian Technology of University
Dalian, 116012 (P. R. China)
Fax : (+86)411-83702355
E-mail: hecheng@dlut.edu.cn
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FULL PAPERS
tions of the thiol of the analyte and the probe molecules
through covalent chemical reactions or metal coordinations.
Such reactions are irreversible and are not fast enough to
allow real-time detection.[51–53] Furthermore, discrimination
of GSH from sulfhydryl-containing amino acids and pep-
tides is hampered because of interference from these struc-
turally related molecules, and the development of biomimet-
ic systems for studying protein–protein interactions is also
very important in academic arenas.[54–56] Therefore, it is de-
sirable to develop a new approach to alleviate these prob-
lems and, more importantly, to allow the direct analysis of
the possible hydrogen-bonding patterns, as the fold struc-
tures of GSH in an enzyme-like assembly cavity have a spe-
cial size, shape, and chemical environment.[57–58]
Tridentate coordinated units are efficient building blocks
for creating metal-variable nanostructures with considerable
stabilities and tunable optical properties.[59,60] By using func-
tionalized amide groups as the trigger sites for efficient
host–guest interaction sites within the modulation tridentate
N2O chelators, we have developed a new strategy for the
preparation of Werner-type capsules for the selective and
sensitive molecular recognition and optical sensing of sever-
al important biological molecules including glucosamine,
natural saccharides, and others.[61–63] As a continuance of our
research work on the construction of metal–organic heli-
cates,[64,65] molecular polygons,[66,67] and molecular poly-
hedrons,[68,69] herein we reported the systematic investiga-
tions of host–guest chemistry corresponding to GSH and
functionalized cyclohelicates (Scheme 1). We reasoned that
these amide groups in the positively charged cages have the
potential to provide a special environment that matched the
static, geometric, coordinative, and functional requirements
for the recognition of special biochemical molecules. In ad-
dition, the formation of hydrogen bonds of the amide
groups is likely to perturb the electronic distribution of the
conjugated backbone of the ligand, leading to significant
changes in optical properties.
Results and Discussion
Syntheses and Host–Guest Chemistry of Dibenzylamino
Cyclohelicates
Ligands PDB and QDB (QDB=[(N1’E,N3’E)-5-(dibenzyla-
mino)-N1’,N3’-bis(quinolin-2-ylmethylene)isophthalohydra-
zide]) were prepared from the reaction of 1,3-dicarbohydra-
zidobenzene derivatives with 2-pyridinecarboxaldehyde or
2-quinolinecarboxaldehyde in methanol (Scheme 2), respec-
tively. Adding a solution of zinc(II) nitrate in methanol to a
dichloromethane/methanol solution of the ligands PDB or
QDB in the presence of NH4PF6 led to high-yield formation
of the zinc(II) compounds Zn–PDB and Zn–QDB, respec-
tively, similar to that of the cobalt(II) analogies reported in
the literature,[61] whereas the zinc(II) ion with d10 electronic
configuration would benefit the NMR spectroscopic charac-
terization.
Compound Zn–PDB exhibited intense peaks at m/z:
1018.94 and 1091.80 with the isotopic distribution patterns
being separated by 0.50Æ0.01 Dalton in HR-ESI-MS. These
peaks were assigned to the positively charged species [Zn3
(PF6)-3H]2+ and [Zn (PF6)2-2H]2+, respec-
AHCTUNGETRG(NNUN PDB)3ACHUTNGTRENNUG 3ACHTUNGETRNN(GUN PDB)3ACTHNUGTRENNGUN
tively, through the exact comparison of these experimental
peaks with the simulation results obtained on the basis of
natural isotopic abundances (Figure 1top). Similarly, com-
pound Zn–QDB exhibits intense peaks at m/z: 732.19,
Scheme 1. Structures and the constitutive/constructional fragments of the
cyclohelicates showing the potential functional groups and the postulated
recognition of the receptors for GSH, in which R=dibenzylamino (PDB)
and BODIPY groups (PMB), respectively.
Abstract in Chinese:
Figure 1. ESI-MS spectra of Zn–PBD in a DMF solution in the absence (
top) and presence (bottom) of an equivalent molar ratio of GSH.
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Chem. Asian J. 2011, 6, 1225 – 1233

Metal–Organic Cyclohelicates as Optical Receptors
Scheme 2. Synthetic procedure for the synthesis of ligands PDB and QDB.
753.19, and 780.85, with the isotopic distribution patterns
being separated by 0.33Æ0.01 Dalton. These signals were as-
signable to the positive species [Zn CHUTNGTRENNUNG
(QDB)3-3H]3+, [Zn3
3A
(QDB)3AHCNUTGTRENNUNG
(PF6)-2H]3+, respec-
(QDB)
E
N
tively. The coordination of the ligand to the metal ions
could also be characterized by the relatively broadened and
shifted resonance signals in the 1H NMR spectra. At the
same time, only one set of signals was observed in the
1H NMR spectra, which indicated that the ligands in each
complex were in identical environments, equivalently relat-
ed by possible C3 symmetry.
Single-crystal X-ray structural analysis of Zn–QDB con-
firmed the formation of the Zn3ACHTGNUTREN(NUNG QDB)3 helical structure in
the solid state. The macrocycle triple helicate was crystal-
¯
lized in a P1 space group. A positively charged triple heli-
À
À
cate, three PF6 , and one NO3 anion and several solvent
molecules were found in an asymmetric unit. As shown in
Figure 2, the triangle was present in a pseudo-C3-symmetry.
Each zinc centre was octahedrally coordinated by two tri-
dentate groups from two ligands in the mer configuration
(with pairs of amide oxygen atoms and pyridyl nitrogen
atoms each bearing a cis relationship, whereas the imine ni-
trogen atoms are trans to each other) as found in related oc-
tahedral coordinated metal complexes with tridentate chela-
tors.[61,62] The coordination geometry of these zinc centers all
exhibited the same configurations, and the trinuclear metal–
organic macrocycle was thus described as a helicate, as
found in the cobalt(II) analogy MC1 (MC1=Co-[5-(1-(di-
methylamino)naphthalene-5-sulfonamido)-N1’,N3’-bis(pyri-
din-2-ylmethylene)isophthalohydrazide]).[61] The three meta-
substituted benzene rings within the main bone of the heli-
Figure 2. Molecular structure of Zn–QDB with the atomic numbering
scheme; the anions, solvent molecules, and hydrogen atoms were omitted
À
À
for clarity. Selected bond lengths (ꢁ): Zn(1) N(6): 2.048(4), Zn(1)
À
À
À
N(26): 2.061(4), Zn(1) N(27): 2.146(4), Zn(1) O(2): 2.153(3), Zn(1)
À
À
À
N(7): 2.164(4), Zn(1) O(22): 2.286(3), Zn(2) N(13): 2.057(4), Zn(2)
À
À
À
N(3): 2.073(4), Zn(2) N(14): 2.151(3), Zn(2) O(11): 2.166(3), Zn(2)
À
À
À
N(4): 2.178(4), Zn(2) O(1): 2.253(3), Zn(3) N(23): 2.040(4), Zn(3)
À
À
À
N(16): 2.061(4), Zn(3) N(24): 2.142(4), Zn(3) O(21): 2.149(3), Zn(3)
À
À
À
N(17): 2.156(4), Zn(3) O(12): 2.267(3), C(18) O(1): 1.242(6), C(18)
À
À
À
N(2): 1.346(6), C(7) O(2): 1.273(5), C(7) N(5): 1.351(6), CACHTUNGTRENNUNG
À
À
À
1.261(6), C
1.342(6), C
1.226(5), C
G
E
(107) N(15):
À
À
À
(218) O(21): 1.253(5), C
E
(207) O(22):
À
(207) N(25): 1.361(6).
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C. He et al.
FULL PAPERS
cate lay on the same side of the trimetal ions plane, thereby
showing a calix[3]arene feature, whereas the six benzene
rings extended outside of the triangle. Each ligand bridged
two metal ions with the Zn···Zn separation of about 9.65 ꢁ
on average. The upper rim had the diameter of about
11.42 ꢁ (estimated from the separation between the tertiary
amines on the central benzene rings). The depth of the heli-
cate was approximately 4.5 ꢁ from the tertiary amines to
sorbency A300 demonstrated a 1:1 stoichiometric complexa-
tion behavior and the association constant (log Ka) was cal-
culated as 5.20Æ0.18. In the presence of one molar equiva-
lent of glutathione, ESI-MS spectra (Figure 1bottom) of
Zn–PDB in a N,N-dimethylformamide solution exhibited a
new peak at 1262.25 relative to its original one, assignable
to the host–guest complexation species [(Zn–PDB)ꢀGSH]2+
. These results supported the 1:1 stoichiometry of the host–
guest behavior.
À
À
the plane of the zinc atoms. The C N and N N bond
lengths in the QDB ligand were intermediate between
formal single and double bonds, thus pointing to the exten-
sive electron delocalization over the entire molecular skele-
To make clear the possible interaction patterns between
the Zn–PDB host and the GSH molecule, the UV/Vis titra-
tions of the Zn–PDB solution toward the three-component
amino acids of the GSH were investigated, respectively. The
addition of Cys exhibited almost the same spectral variation
with the absorbance at 300 nm enhanced by approximately
45% when 10 equivalents of Cys were added. The Hill-plot
profile[70] of absorbency (A300) at 300 nm demonstrated a 1:2
stoichiometric complexation with a association constant (log
Ka) of 9.61Æ0.52. However, the addition of Gly or Glu did
not cause any obvious absorption spectral responses. These
results suggested that the interactions corresponding to the
Cys group were the major contributors for the Zn–PDB
host to recognize GSH. The different stoichiometry between
the receptor and the guests should be attributed to the
space effect of the cavity, thereby implying the possibility
that the recognition process occurred inside the cavity. It
seems that the formation of hydrogen bonds between the
amide groups of the receptor and thiol groups of GSH or
Cys itself could favor electronic delocalization, thus leading
to the variation of the electron distribution and the obvious
spectral variation of the cyclohelicate in solution.[29]
À
ton. The six C O bond lengths were divided into two sets,
four of them were close to 1.24 ꢁ, which is within the
normal range of a C=O double bond, and the other two
were about 1.27 ꢁ, which indicates the possible loss of two
of the six amide protons. The presence of four counter-
anions for each cationic helicate supported the fact that only
two amide groups in the three ligands lost their protons
during metal coordination. These amide groups—located
within the positively charged cages—provide static, geomet-
ric, coordinative, and functional properties to the cage-like
capsules, which are important for the recognition of small
molecules, such as GSH.
Ligand PDB exhibited an absorption band at 300 nm (log
e=4.76) in a N,N-dimethylformamide (DMF)/water (9:1)
solution, the coordination with zinc led to the appearance of
a new peak centered at about 380 nm (log e=4.86), and the
maintenance of the ligand-based charge transition band led
to a peak at about 300 nm (log e=5.17). The addition of
GSH to the solution of Zn–PDB (6.5 mm in a DMF/water
9:1 solution) caused a significant absorbance increase at
300 nm and an obvious absorbance decrease at 380 nm. The
absorbance at 300 nm enhanced approximately by 50%
when 10 equivalents of GSH were added. The presence of a
sharp isobestic point at 330 nm indicated that only two spe-
cies coexisted in the equilibrium and the sensing for GSH
was reversible (Figure 3). The individual profile of the ab-
1H NMR spectroscopy of Zn–PDB (10 mm) in
a
[D6]DMSO (dimethyl sulfoxide) solution (Figure 4), upon
addition of GSH (10 mm), exhibited significant downfield
shifts of protons of the Glu residue with the Dd sequence
as: Dd(Ha)=0.60>Dd(Hb)=0.15>Dd(Hg)=0.04 ppm. No
obvious downfield shifts were found corresponding to the
Cys and Gly residues. These results demonstrated that the
Figure 3. Absorption spectra of Zn–PDB (6.5 mm) in a solution of DMF/
H2O (9:1) upon the addition of GSH. The inset shows the absorption re-
sponse of Zn–PDB (6.5 mm) in DMF/H2O (9:1 in volume) toward GSH
and its subcomponents recorded at 300 nm in the presence of 10 equiva-
lents of guest molecules.
Figure 4. Partial 1H NMR spectra of a) Zn–PDB (10 mm) in [D6]DMSO,
b) free Zn–PDB upon the addition of GSH (10 mm), and c) GSH itself.
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Metal–Organic Cyclohelicates as Optical Receptors
terminal Glu residue of the GSH molecule was encapsulated
within the positively charged cage and closed to the metal
centers.[71,72] The two amide-NH signals (H7 and H8) of the
GSH moiety were also upshifted by Dd=À0.18 and
À0.32 ppm. These results precluded the formation of donor-
type hydrogen bonds of these amide groups and, alternative-
ly, demonstrated the interactions corresponding to the
closed aromatic rings or the shield-effect caused by the
closed anionic species.[73,74] By combining the optical titra-
tions and the NMR spectroscopic investigations, it seems
that the configuration of the GSH molecule within the
cavity of the Zn–PDB receptor might be: the residue of the
Glu moiety positioned near to the metal centers with the
COOÀ moiety closed to the metal centers, the thiol group
interacted to the amide groups of the receptor through hy-
drogen bonding, and the two amide groups of GSH possibly
interacted with the aromatic rings of the cyclohelicate back-
bone and/or the dibenzylamino moieties, respectively.
Host–Guest Chemistry of a BODIPY-Functionalized
Triangle
To further investigate the host–guest interaction pattern be-
tween GSH and the tricycle host, new metal–organic analo-
gy Zn–PMB was designed and synthesized by incorporating
a luminescence-active BODIPY group within the meta-site
of the benzene ring to substitute the tertiary amine moiety.
As BODIPY groups were expected to exhibit luminescence
responses towards GSH, we reasoned that the host–guest
chemistry between Zn–PMB and GSH would provide a new
stereochemical performance about the interactions and the
configurations of GSH within the amide-containing recep-
tor.
Ligand PMB was synthesized from the multistep reactions
as listed in Scheme 3. The compound Zn–PMB was synthe-
sized from the same procedure as that for Zn–PDB. ESI-MS
exhibited two intense peaks at m/z: 812.63 and 1218.64, as-
signable to the species of [Zn3ACTHNUTRGNEUNG
(PMB)3-3H]3+ and [Zn3
Scheme 3. Synthetic procedure for the synthesis of ligand PMB.
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C. He et al.
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ACHTUNGTRENNUNG
(PMB)3-4H]2+, respectively, thereby revealing the successful
assembly of a zinc-based trinuclear molecular macrocycle in
the solution. The presence of only one set of signals in its
1H NMR spectrum indicated that the ligands in compound
Zn–PMB were in identical environments. In the case of a
solution of Zn–PMB in the presence of an equimolar
amount of GSH, an exact comparison of the most interest-
ing experimental peak at m/z: 1372.50 revealed that this di-
valently charged species was assignable to [(Zn–
PMB)ꢀGSH]2+ (Figure 5). This result provided solid evi-
dence for a 1:1 stoichiometry of the host–guest interactions.
Figure 6. Family of absorption spectra of Zn–PMB (6.5 mm) in an aqueous
solution of DMF/H2O (9:1) upon the addition of GSH. The inset shows
the absorption response of Zn–PMB (6.5 mm) in DMF/H2O (9:1) toward
GSH and its subcomponents recorded at 300 nm in the presence of
10 equivalents of guest molecules.
Accordingly, the spectral responses upon addition of GSH
could also be assigned to the formation of hydrogen bonds
between the amide groups of the Zn–PMB receptor and the
thiol moiety. This kind of host–guest complexation did not
change the ground-state electronic distribution of the
BODIPY moiety.
The presence of BODIPY groups on the ligand allowed
the host–guest interaction between Zn–PMB and GSH to
be evaluated by luminescence titrations. Zn–PMB exhibited
a typical emission of the BODIPY group at about 513 nm in
the N,N-dimethylformamide/water (9:1 v/v) aqueous solu-
tion (20 mm, excitation at 467 nm) with the quantum yield
(FF) at approximately 0.23 under the experimental condi-
tions (by using rhodamine B as the standard).[75] The lower
of the quantum yields corresponding to the free BODIPY
moiety (FF =0.92) under the same experimental conditions
might be an indicator that the luminescence of the
BODIPY moiety was quenched by the amide groups or
imine moieties within the ligand backbones of the triangle.
Upon the addition of GSH to the solution of Zn–PMB, the
luminescence intensity gradually increased and finally
Figure 5. ESI-MS spectra of Zn–PMB in a solution of DMF (top) and
upon the addition of one equivalent of GSH (bottom). The insets exhibit
the measured and simulated isotopic patterns at m/z: 1218.64 and
1372.51 in parts top and bottom, respectively.
Besides the absorption band at 300 nm (log e=4.80),
ligand PMB exhibited a characteristic absorption band of
the BODIPY moiety at 500 nm (log e=5.07) in a N,N-dime-
thylformamide/water (9:1 v/v) solution. The coordination of
zinc caused a new peak at about 380 nm (log e=4.89), but
the absorption band at 300 nm disappeared, with the main-
tenance of the characteristic BODIPY absorption band (log
e=5.39) in the solution of Zn–PMB. The addition of GSH
to the solution of Zn–PMB caused an absorbance increase
at 300 nm and an absorbance decrease at 380 nm, and also
exhibited a sharp isosbestic point at 330 nm (Figure 6). No
significant spectral changes were found corresponding to the
characteristic BODIPY absorption band, therefore this band
could act as an internal standard to determine the concen-
tration fraction of the host–guest species. The Hill-plot pro-
file of the absorbencies A300/A500 demonstrated a 1:1 stoi-
chiometric complexation, with the association constant (log
Ka) being calculated as 4.74Æ0.16 for Zn–PMB. Most im-
portantly, only the addition of Cys to the solution of Zn–
PMB caused the spectral changes, the addition of the other
two component amino acids Glu and Gly did not cause any
spectral variations under the same experimental conditions.
reached
a platform when 0.065 mm GSH was added
(Figure 7). Fitting of the individual profile of the lumines-
cence at 513 nm also demonstrated a 1:1 stoichiometric
host–guest complexation with an association constant (log
Ka) of 4.93Æ0.17. As the addition of GSH did not cause any
change in the absorption spectra corresponding to the
BODIPY moiety, the luminescence enhancement upon addi-
tion of GSH was assigned to the blockage of the PET path
from the amide groups within the ligand backbone to the
BODIPY moiety.[76,77]
As expected, the addition of Cys to the solution of Zn–
PMB also caused a significant luminescence increase with
the emission wavelength fixed. Fitting of the individual pro-
file of the luminescence at 513 nm gave a 1:2 host–guest sto-
ichiometry with an association constant (log Ka) calculated
as 9.2Æ0.6. Clearly, the luminescence response of the Zn–
PMB towards GSH mainly contributed to the interactions
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Metal–Organic Cyclohelicates as Optical Receptors
metal–organic cages could be a useful method to produce
supramolecular sensors for biomolecules.
Experimental Section
Materials and Methods
All chemicals were of reagent grade quality, obtained from commercial
sources, and used without further purification. The elemental analyses of
C, H, and N were performed on a Vario EL III elemental analyzer.
1H NMR spectra were measured on a Varian INOVA 400m spectrometer.
ESI mass spectra were carried out on a HPLC-Q-Tof MS spectrometer
by using methanol as the mobile phase. UV/Vis spectra were measured
on a HP 8453 spectrometer. The fluorescent spectra were measured on a
Edinburgh FS-920 fluorescent spectrometer. Both excitation and emis-
sion slit widths were 2 nm. Solutions of Zn–PDB and Zn–PMB were pre-
pared in DMF/H2O (9:1 v/v), respectively. The high concentration of the
stock solutions of GSH, Cys, Gly, and Glu (1.0ꢂ10À2 m) were prepared di-
rectly in DMF/H2O (1:1 v/v) and added by using a syringe.
Figure 7. The family of fluorescent spectra of Zn–PMB (20 mm) in an
aqueous solution of DMF/H2O (9:1) upon the addition of GSH. The
insert shows the fluorescent response of Zn–PMB (20 mm) in DMF/H2O
(9:1) toward GSH and its subcomponents recorded at 513 nm in the pres-
ence of three equivalents of guest molecules. Excited at 467 nm.
Preparation of dimethyl 5-(dibenzylamino)isophthalate (1)
Benzyl bromide (0.85 g, 5 mmol) in acetonitrile (30 mL) was added to
the acetonitrile solution (50 mL) of dimethyl 5-aminoisophthalate (0.42 g,
2 mmol) in the presence of K2CO3 (0.55 g, 4 mmol). The mixture was re-
fluxed for 24 h. After removing the solvent, the white product was ob-
tained and further used in the next step.
corresponding to the Cys component. Only the species able
to form hydrogen bonds with the amide groups in the ligand
backbones could lead to the absorption spectral variation.
The interactions changed the electron distribution of the
ligand backbone to block the PET efficiency between the
amide group and the BODIPY moiety. As a consequence,
this led to variation in the luminescence.
Preparation of 5-(dibenzylamino)isophthalohydrazide (2)
Compound 1 was mixed with 80% hydrazine hydrate in a solution of
methanol and stirred for 12 h. White precipitates formed were isolated
and further used in the next step.
1H NMR spectroscopy of Zn–PMB (10 mm) in the pres-
ence of GSH (10 mm) exhibited a similar downfield shift of
protons within the Glu residues Dd(Ha)=0.61, Dd(Hb)=
0.07, and Dd(Hg)=0.02 ppm, respectively, which suggests
possible static interactions between the Glu residue and
metal centers. No obvious downfield shifts were found cor-
responding to the Cys and Gly residues. The similar upfield
shifts of the two GSH amide-NH signals (H7 and H8) by
Dd=À0.14 and À0.28 ppm, respectively, to those of the
PDB receptor were also attributed to the shield effect. By
Preparation of PDB
Acetic acid (5 drops) was added to the mixture of 2 (0.5 g, 1.3 mm) and 2-
pyridinecarboxaldehyde (0.33 g, 3.12 mm) in a solution of methanol. The
mixture was refluxed for 4 h, after which a yellow precipitate was formed
and isolated by filtration. Total yield (from dimethyl 5-aminoisophtha-
late): 45.2%; 1H NMR (400 MHz, [D6]DMSO): d=12.04 (s, 2H;
À
À
À
À
CONH ), 8.62 (s, 2H; N=CH ), 8.48 (s, 2H; ArH), 7.96 (d, 2H, J=
7.6 Hz; ArH), 7.88 (t, 2H, J=7.6 Hz; ArH), 7.69 (s, 1H; ArH), 7.44–7.26
À
À
(m, 14H; ArH), 4.85 ppm (s, 4H; CH2 ); elemental analysis calcd (%)
for C34H29N7O2: C 71.94, N 17.27, H 5.15; found: C 71.55, N 16.98, H
5.25.
1
combining the optical titration and H NMR spectroscopic
investigations, it seems that the configuration of the GSH
molecule within the cavity of Zn–PMB was as follows: the
residue of the Glu moiety is positioned near to one of the
metal centers with the COOÀ moiety interacted with the
metal center.
Preparation of QDB
Acetic acid (5 drops) was added to the mixture of 2 (0.5 g, 1.3 mm) and 2-
quiolinecarboxaldehyde (0.48 g, 3.12 mm) in a solution of methanol. The
mixture was refluxed for 4 h. The yellow precipitate formed was isolated
by filtration. Total yield (from dimethyl 5-aminoisophthalate): 40.6%;
1
À
À
H NMR (400 MHz, [D6]DMSO): d=12.22 (s, 2H; CONH ), 8.63 (s,
À
À
2H; N=CH ), 8.44 (d, 2H, J=8.4 Hz; ArH), 8.12 (d, 2H, J=8.8 Hz;
ArH), 8.04 (t, 4H, J=8.4 Hz; ArH), 7.80 (t, 2H, J=7.4 Hz; ArH), 7.74
(s, 1H; ArH), 7.65 (t, 2H, J=7.4 Hz; ArH), 7.45 (s, 2H; ArH), 7.39–7.27
Conclusions
À
À
(m, 10H; ArH), 4.87 ppm (s, 4H; CH2 ); elemental analysis calcd (%)
for C42H33N7O2: C 75.54, N 14.68, H 4.98; found: C 75.84, N 14.21, H
5.11.
Two Zinc(II) cycohelicates were synthesized and character-
ized. Host–guest chemistry between these receptors and
GSH molecules was investigated systematically. Electronic
absorption spectra, luminescence spectra, and NMR titra-
tions suggested that the Glu residue was folded within the
Preparation of 4-iodobenzoyl chloride 3
4-iodobenzoic acid (10.0 g, 0.04 mol) was added to thionyl chloride
(25 mL). The mixture was refluxed for 3 h. A white solid was obtained
after removing excess thionyl chloride.
positively charged cavity into
a special configuration
through encapsulation, whereas the thiol group of GSH in-
teracted with the amide groups sited in host molecules
through hydrogen-bonding interactions, thus producing
measurable spectral variations. This result showed that the
recognition of substrate within the cavity of functionalized
Preparation of 4
Compound 3 (5 g, 0.019 mol) and 2,4-dimethylpyrrole (3.6 g, 0.038 mol)
were dissolved in absolute CH2Cl2 (150 mL). The mixture was then
stirred for 5 h at room temperature under an atmosphere of N2. The
Chem. Asian J. 2011, 6, 1225 – 1233
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1231

C. He et al.
FULL PAPERS
black solution was reduced to 50 mL and triethylamine (10 mL) was
added, followed by BF3·OEt2 (15 mL). After the mixture had been stirred
for an additional 4 h at room temperature, the reaction mixture was
washed with water and dried over K2CO3. The crude compound was ob-
tained by removing the solvent and purified by flash column chromatog-
raphy on silica gel (hexanes/CH2Cl2 1:1) to afford a red solid.
Preparation of Zn–PMB
Zn(NO3)2·6H2O (30 mg, 0.10 mmol) and PMB (75 mg, 0.10 mmol) were
dissolved in CH3OH/CH3CN (10:2 in volume) to give a light-red solution.
After addition of NH4PF6, red precipitates formed were isolated and
dried under vacuum. Yield: 45%; 1H NMR (400 MHz, [D6]DMSO): d=
AHCTUNGTRENNUNG
À
À
À
À
12.25 (s, 2H; CONH ), 8.64 (s, 2H; N=CH ), 8.53 (s, 2H; ArH), 8.16
(s, 1H; ArH), 8.00–7.86 (m, 6H; ArH), 7.64 (m, 2H; ArH), 7.44 (m, 4H;
Preparation of 5
À
À
À
À
ArH), 6.18 (s, 2H; =CH ), 5.30 (s, 2H; CH2 ), 2.44 (s, 6H; CH3),
Dimethyl 5-hydroxyisophthalate (0.5 g, 2.4 mmol), K2CO3 (0.66 g,
4.8 mmol), and propargyl bromide (0.75 mL, 9.6 mmol) were mixed in
acetonitrile (30 mL). The mixture was refluxed for 24 h. After removing
the solvent, a white solid was obtained and purified by column chroma-
tography (hexanes/CH2Cl2 1:50).
À
1.35 ppm (s, 6H; CH3); elemental analysis calcd (%) for Zn3(C126H102B3
F6N24O9)
(PF6)3: H 3.58, C 52.66, N 11.70; found: H 3.57, C 52.84, N
11.53; ESI-MS: m/z: 812.63 [Zn
(PMB)3-3H]3+, 1218.64 [Zn
3ACHTUGTNRENNUG 3ACHTUNGTRENNUNG(PMB)3-
4H]2+
.
Crystallography
Preparation of 6
A crystal of Zn–QDB (suitable for X-ray single-crystal analysis) was ob-
tained by slow evaporation of Zn—QDB in a DMF solution over several
days. Intensities of Zn–QDB were collected on a Bruker SMART APEX
CCD diffractometer, with graphite- monochromated MoKa radiation (l=
0.71073 ꢁ), by using the SMART and SAINT programs. The structures
were solved by direct methods and refined on F2 by full-matrix least-
squares methods with SHELXTL version 5.1.
Compounds
iodide (0.57 mg), and bis(triphenyl phosphine)dichloropalladium(II)
[PdCl2A(PPh3)2] (7.0 mg) were added to a solution of THF (8 mL) in the
presence of triethylamine (2 mL). The reaction mixture was stirred for
2 h at 408C under an atmosphere of N2. After removing the solvent, the
orange solid obtained was purified by column chromatography (hexanes/
CH2Cl2 1:1).
4 (50 mg, 0.01 mmol), 5 (5.0 mg, 0.02 mmol), copper(I)
CHTUNGTRENNUNG
Crystal
(NO3)·11CH3OH·3H2O; M=3100.79; triclinic; space group PÀ1; red
block; a=18.266(1), b=18.313(1), c=27.911(2) ꢁ; a=94.8(1), b=
data
for
Zn–QDB:
Zn3(C126H97N21O6)ACHTUNGTRENNUNG(PF6)3
Preparation of 7
ACHTUNGTRENNUNG
Compound 6 was mixed with 80% hydrazine hydrate in a methanol solu-
tion and stirred for 24 h. The orange precipitates obtained were isolated
and used further in the next step.
92.2(1), g=119.3(1)8; V=8078.5(7) ꢁ3; Z=2; 1calcd =1.277 gcmÀ3
;
m-
A
;
T=180(2) K; 28285 unique reflections [Rint
=
0.0728]; final R1 [with I>2s(I)]=0.0865; wR2 (all data)=0.2841;
GOOF=0.915. CCDC-795194 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Non-hydrogen atoms were refined anisotropically,
except for the solvent molecules. Hydrogen atoms were fixed geometri-
cally at calculated distances and allowed to ride on the parent non-hydro-
gen atoms with the isotropic displacement being fixed at 1.2 and
1.5 times of the aromatic and methyl carbon atoms attached, respectively.
One of the pyridine rings was disordered into two parts with the site oc-
cupancy factor (s.o.f.) being refined as free variables. A phosphorus atom
in a hexafluorophosphate anion was disordered into two parts with the
s.o.f. of each part being fixed at 0.5. The fluoride atoms on another group
of hexafluorophosphate anions were disordered into two parts with the
s.o.f. being refined by free values.
Preparation of PMB
Acetic acid (5 drops) was added to the mixture of 7 (0.5 g, 0.88 mm) and
2-pyridinecarboxaldehyde (0.23 g, 2.11 mm) in a solution of methanol.
The mixture was refluxed over 24 h and an orange precipitate was isolat-
ed by filtration. Total yield (from dimethyl 5-hydroxyisophthalate):
20.6%; 1H NMR (400 MHz, [D6]DMSO): d=12.22 (s, 2H; CONH ),
À
À
À
À
8.64 (s, 2H; N=CH ), 8.53 (s, 2H; ArH), 8.16 (s, 1H; ArH), 8.01 (d,
2H, J=8.0 Hz; ArH), 7.93–7.86 (m, 4H; ArH), 7.65 (d, 2H, J=7.6 Hz;
À
À
ArH), 7.44 (t, 4H, J=8.4 Hz; ArH), 6.18 (s, 2H; =CH ), 5.30 (s, 2H;
À
À
À
CH2 ), 2.44 (s, 6H; CH3), 1.35 ppm (s, 6H; CH3); elemental analysis
calcd (%) for C42H35BF2N8O3: C 67.39, N 14.97, H 4.71; found: C 67.32,
N 15.01, H 4.94.
Preparation of Zn–PDB
ZnACHTUNGTRENNUNG(NO3)2·6H2O (30 mg, 0.10 mmol) and PDB (60 mg, 0. 10 mmol) were
dissolved in CH3OH/CH2Cl2 (2:10 in volume) to give a light-yellow solu-
tion. After addition of NH4PF6, yellow precipitates formed were isolated
and dried under vacuum. Yield: 60%; 1H NMR (400 MHz, [D6]DMSO):
Acknowledgements
À
À
À
À
d=12.17 (s, 2H; CONH ), 8.61 (s, 2H; N=CH ), 8.49 (s, 2H; ArH),
7.96–7.93 (m, 4H; ArH), 7.71 (s, 1H; ArH), 7.45–7.24 (m, 14H; ArH),
This work is supported by the National Natural Science Foundation of
China (20923006 and 20801008).
À
À
4.85 ppm (s, 4H;
Zn3(C102H87N21O6)(PF6)6: H 3.17, C 44.25, N 10.62; found: H 3.32, C
44.14, N 10.75; ESI-MS: m/z: 1018.94 [Zn3A(PDB)3A
(PF6)-3H]2+, 1091.80
[Zn3A(PDB)3A
(PF6)2-2H]2+
CH2 ); elemental analysis calcd (%) for
ACHTUNGTRENNUNG
E
CHTUNGTRENNUNG
[1] M. Schmittel, V. Kalsani, Top. Curr. Chem. 2005, 245, 1–53.
[2] M. Fujita, M. Tominaga, A. Hori, B. Therrien, Acc. Chem. Res.
2005, 38, 371–380.
C
E
.
Preparation of Zn–QDB
[3] B. H. Northrop, Y. R. Zheng, K. W. Chi, P. J. Stang, Acc. Chem. Res.
2009, 42, 1554–1563.
[4] M. D. Ward, Chem. Commun. 2009, 4487–4499.
[5] D. Fiedler, D. H. Leung, R. G. Bergman, K. N. Raymond, Acc.
Chem. Res. 2005, 38, 349–360.
[6] D. M. Vriezema, M. C. Aragones, J. A. A. W. Elemans, J. J. L. M.
Cornelissen, A. E. Rowan, R. J. M. Nolte, Chem. Rev. 2005, 105,
1445–1489.
[7] I. M. Mꢃller, D. Moller, Angew. Chem. 2005, 117, 3029–3033;
Angew. Chem. Int. Ed. 2005, 44, 2969–2973.
Zn(NO3)2·6H2O (30 mg, 0.10 mmol) and QDB (70 mg, 0.10 mmol) were
ACHTUNGTRENNUNG
dissolved in CH3OH/CH2Cl2 (2:10 in volume) to give a light-yellow solu-
tion. After addition of NH4PF6, yellow precipitates formed and were iso-
lated and dried under vacuum. Yield: 55%; 1H NMR (400 MHz,
À
À
À
À
[D6]DMSO): d=12.24 (s, 2H; CONH ), 8.63 (s, 2H; N=CH ), 8.45
(m, 2H; ArH), 8.13 (m, 2H; ArH), 8.04 (m, 4H; ArH), 7.80 (m, 2H;
ArH), 7.75 (s, 1H; ArH), 7.65 (m, 2H; ArH), 7.45 (s, 2H; ArH), 7.39–
À
À
7.27 (m, 10H; ArH), 4.87 ppm (s, 4H; CH2 ); elemental analysis calcd
(%) for Zn3(C126H97N21O6)(PF6)3NO3: H 3.63, C 56.17, N 11.44; found: H
3.52, C 56.14, N 11.23; ESI-MS: m/z: 732.19 [Zn3A
(QDB)3-3H]3+, 753.19
[Zn3A(QDB)3A 3A(QDB)3A
(NO3)-2H]3+, 780.85 [Zn (PF6)-2H]3+
AHCTUNGTRENNUNG
CTHUNGTRENNUNG
[8] H. Yang, N. Das, F. Huang, A. M. Hawkridge, D. C. Muddiman, P. J.
Stang, J. Am. Chem. Soc. 2006, 128, 10014–10015.
G
E
G
C
.
[9] I. S. Tidmarsh, T. B. Faust, H. Adams, L. P. Harding, L. Russo, W.
Clegg, M. D. Ward, J. Am. Chem. Soc. 2008, 130, 15167–15175.
[10] X. J. Liu, R. Warmuth, J. Am. Chem. Soc. 2006, 128, 14120–14127.
1232
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1225 – 1233

Metal–Organic Cyclohelicates as Optical Receptors
[11] B. C. Tzeng, Y. F. Chen, C. C. Wu, C. C. Hu, Y. T. Chang, C. K.
Chen, New J. Chem. 2007, 31, 202–209.
[45] C. F. Chow, B. K. W. Chiu, M. H. W. Lam, W. Y. Wong, J. Am.
Chem. Soc. 2003, 125, 7802–7803.
[12] Y. Q. Chen, X. Z. Wang, X. B. Shao, J. L. Hou, X. Z. Chen, X. K.
Jiang, Z. T. Li, Tetrahedron 2004, 60, 10253–10260.
[13] P. Mal, B. Breiner, K. Rissanen, J. R. Nitschke, Science 2009, 324,
1697–1699.
[46] H. Chen, Q. Zhao, Y. Wu, F. Li, H. Yang, T. Yi, C. Huang, Inorg.
Chem. 2007, 46, 11075–11081.
[47] P. K. Sudeep, S. T. Joseph, K. G. Thomas, J. Am. Chem. Soc. 2005,
127, 6516–6517.
[14] J. Recker, W. M. Muller, U. Muller, T. Kubota, Y. Okamoto, M.
Nieger, F. Vgtle, Chem. Eur. J. 2002, 8, 4434–4442.
[15] D. Dubbeldam, C. J. Galvin, K. S. Walton, D. E. Ellis, R. Q. Snurr, J.
Am. Chem. Soc. 2008, 130, 10884–10885.
[16] M. D. Pluth, R. G. Bergman, K. N. Raymond, J. Am. Chem. Soc.
2008, 130, 6362–6366.
[48] S. J. Chen, H. T. Chang, Anal. Chem. 2004, 76, 3727–3734.
[49] C. C. Huang, W. L. Tseng, Anal. Chem. 2008, 80, 6345–6350.
[50] B. Y. Han, J. P. Yuan, E. K. Wang, Anal. Chem. 2009, 81, 5569–5573.
[51] Y. Fujikawa, Y. Urano, T. Komatsu, K. Hanaoka, H. Kojima, T.
Terai, H. Inoue, T. Nagano, J. Am. Chem. Soc. 2008, 130, 14533–
14543.
[17] S. Tashiro, M. Tominaga, Y. Yamaguchi, K. Kato, M. Fujita, Angew.
Chem. 2006, 118, 247–250; Angew. Chem. Int. Ed. 2006, 45, 241–
244.
[18] K. Nakabayashi, M. Kawano, M. Fujita, Angew. Chem. 2005, 117,
5456–5459; Angew. Chem. Int. Ed. 2005, 44, 5322–5325.
[19] M. D. Pluth, R. G. Bergman, K. N. Raymond, Science 2007, 316, 85–
88.
[20] T. Kawamichi, T. Haneda, M. Kawano, M. Fujita, Nature 2009, 461,
633–635.
[21] L. Cronin, Angew. Chem. 2006, 118, 3656–3658; Angew. Chem. Int.
Ed. 2006, 45, 3576–3578.
[52] X. Chen, Y. Zhou, X. Peng, J. Yoon, Chem. Soc. Rev. 2010, 39,
2120–2135.
[53] Y. H. Ahn, J. S. Lee, Y. T. Chang, J. Am. Chem. Soc. 2007, 129,
4510–4511.
[54] G. L. Hornyak, Otolaryngologic Clinics of North America 2005, 38,
273–293.
[55] P. Wu, D. W. Grainger, Biomaterials 2006, 27, 2450–2467.
[56] A. I. Scott, Bioorg. Med. Chem. 1996, 4, 965–985.
[57] Y. Hatakeyama, T. Sawada, M. Kawano, M. Fujita, Angew. Chem.
2009, 121, 8851–8854; Angew. Chem. Int. Ed. 2009, 48, 8695–8698.
[58] A. C. Laungani, J. M. Slattery, I. Krossing, B. Breit, Chem. Eur. J.
2008, 14, 4488–4502.
[59] M. Ruben, J. Rojo, F. J. Romero-Salguero, L. H. Uppadine, J. M.
Lehn, Angew. Chem. 2004, 116, 3728–3747; Angew. Chem. Int. Ed.
2004, 43, 3644–3662.
[22] C. Schmuck, Angew. Chem. 2007, 119, 5932–5935; Angew. Chem.
Int. Ed. 2007, 46, 5830–5833.
[23] T. Sawada, M. Yoshizawa, S. Sato, M. Fujita, Nat. Chem. 2009, 1,
53–58.
[24] H. Clever, S. Tashiro, M. Shionoya, Angew. Chem. 2009, 121, 7144–
7146; Angew. Chem. Int. Ed. 2009, 48, 7010–7012.
[25] M. D. Pluth, D. Fiedler, J. S. Mugridge, R. G. Bergman, K. N. Ray-
mond, Proc. Natl. Acad. Sci. USA 2009, 106, 10438–10443.
[26] K. Harano, S. Hiraoka, M. Shionoya, J. Am. Chem. Soc. 2007, 129,
5300–5301.
[27] K. Ono, J. K. Klosterman, M. Yoshizawa, K. Sekiguchi, T. Tahara,
M. Fujita, J. Am. Chem. Soc. 2009, 131, 12526–12527.
[28] Y. Ferrand, M. P. Crump, A. P. Davis, Science 2007, 318, 619–622.
[29] T. Gunnlaugsson, M. Glynn, G. M. Tocci (nꢄe Hussey), P. E. F.
Kruger, M. Pfeffer, Coord. Chem. Rev. 2006, 250, 3094–3117.
[30] S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki, Y.
Kinoshita, S. Kitagawa, J. Am. Chem. Soc. 2007, 129, 2607–2614.
[31] E. J. Cohn, L. E. Strong, W. L. Hughes, Jr. D. J. Mulford, J. N. Ash-
worth, M. Melin, H. I. Taylor, J. Am. Chem. Soc. 1946, 68, 459–475.
[32] H. C. Kang, B. M. Chung, J. H. Chae, S. I. Yang, C. G. Kim, C. G.
Kim, FEBS J. 2005, 272, 1265–1277.
[60] M. S. Alam, S. Stromsdorfer, V. Dremov, P. Muller, J. Kortus, M.
Ruben, J. M. Lehn, Angew. Chem. 2005, 117, 8109–8113; Angew.
Chem. Int. Ed. 2005, 44, 7896–7899.
[61] H. Wu, C. He, Z. Lin, Y. Liu, C. Duan, Inorg. Chem. 2009, 48, 408–
410.
[62] C. He, Z. Lin, Z. He, C. Duan, C. Xu, Z. Wang, C. Yan, Angew.
Chem. 2008, 120, 891–895; Angew. Chem. Int. Ed. 2008, 47, 877–
881.
[63] Y. Liu, X. Wu, C. He, Y. Jiao, C. Duan, Chem. Commun. 2009,
7554–7556.
[64] D. Guo, K. Pang, C. Duan, C. He, Q. Meng, Inorg. Chem. 2002, 41,
5978–5985.
[65] Y. Bai, C. Duan, P. Cai, D. Dang, Q. Meng, Dalton Trans. 2005,
2678–2680.
[66] Y. Zhao, D. Guo, Y. Liu, C. He, C. Duan, Chem. Commun. 2008,
5725–5727.
[67] D. Guo, C. Qian, C. Duan, K. Pang, Q. Meng, Inorg. Chem. 2003,
42, 2024–2030.
[33] R. Bischoff, T. M. Luider, J. Chromatogr. B 2004, 803, 27–40.
[34] A. Meister, M. E. Anderson, Annu. Rev. Biochem. 1983, 52, 711–
760.
[68] B. Zhang, P. Cai, C. Duan, R. Miao, L. Zhu, T. Niitsu, H. Inoue,
Chem. Commun. 2004, 2206–2207.
[35] M. E. Anderson, Chem.-Biol. Interact. 1998, 112, 1–14.
[36] H. Wakabayashi, M. Miyagawa, Y. Koshi, Y. Takaoka, S. Tsukiji, I.
Hamachi, Chem. Asian J. 2008, 3, 1134–1139.
[37] F. Q. Schafer, G. R. Buettner, Free Radical Biol. Med. 2001, 30,
1191–1212.
[38] X. Chen, S. Ko, M. Kim, I. Shin, J. Yoon, Chem. Commun. 2010, 46,
2751–2753.
[39] J. H. Lee, C. S. Lim, Y. S. Tian, J. H. Han, B. R. Cho, J. Am. Chem.
Soc. 2010, 132, 1216–1217.
[69] Y. Bai, D. Guo, C. Duan, D. Dang, K. Pang, Q. Meng, Chem.
Commun. 2004, 186–187.
[70] K. A. Connors, Binding Contants, Wiley, New York, 1987.
[71] A. B. Descalzo, K. Rurack, H. Weisshoff, R. Martunez, M. D.
Marcos, P. Amorrs, K. Hoffmann, J. Soto, J. Am. Chem. Soc. 2005,
127, 184–200.
[72] F. Hibbert, J. Emsley, Adv. Phys. Org. Chem. 1991, 26, 255–379.
[73] S. Tashiro, M. Tominaga, Y. Yamaguchi, K. Kato, M. Fujita, Angew.
Chem. 2006, 118, 247–250; Angew. Chem. Int. Ed. 2006, 45, 241–
244.
[74] S. Tashiro, M. Tominaga, Y. Yamaguchi, K. Kato, M. Fujita, Chem.
Eur. J. 2006, 12, 3211–3217.
[75] S. Diring, F. Puntoriero, F. Nastasi, S. Campagna, R. Ziessel, J. Am.
Chem. Soc. 2009, 131, 6108–6110.
[76] P. Jiang, Z. Guo, Coord. Chem. Rev. 2004, 248, 205–229.
[77] H. Sunahara, Y. Urano, H. Kojima, T. Nagano, J. Am. Chem. Soc.
2007, 129, 5597–5604.
[40] H. S. Hewage, E. V. Anslyn, J. Am. Chem. Soc. 2009, 131, 13099–
13106.
[41] L. Yi, H. Y. Li, L. L. Liu, C. H. Zhang, Z. Xi, Angew. Chem. 2009,
121, 4094–4097; Angew. Chem. Int. Ed. 2009, 48, 4034–4037.
[42] H. Maeda, H. Matsuno, M. Ushida, K. Katayama, K. Saeki, N. Itoh,
Angew. Chem. 2005, 117, 2982–2985; Angew. Chem. Int. Ed. 2005,
44, 2922–2925.
[43] T. Matsumoto, Y. Urano, T. Shoda, H. Kojima, T. Nagano, Org. Lett.
2007, 9, 3375–3377.
[44] N. Shao, J. Jin, H. Wang, J. Zheng, R. Yang, W. Chan, Z. Abliz, J.
Am. Chem. Soc. 2010, 132, 725–736.
Received: October 8, 2010
Published online: March 1, 2011
Chem. Asian J. 2011, 6, 1225 – 1233
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1233