Fluorescence signaling of aromatic oxoanion inclusion within metal-ion activated molecular receptor complexes formed from 2-(9-anthracenylmethylamino) ethyl-appended cyclen

Article abstract of DOI:10.1007/s10847-011-9924-7

Our observations that 1-[2-[(9-anthracenylmethylamino)ethyl)-4,7,10- tris[(2S)-2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, L ¹, complexes Cd(II) to form fluorescent [CdL¹] ²⁺ which undergoes a fluorescence change when it acts as an aromatic anion receptor complex has caused us to explore further the potential development of an interesting sequestration/sensor system. Accordingly, three new, octadentate, fluorescent, macrocyclic ligands, 1-[2-[(9-anthracenylmethyl) ((2S)-2-hydroxy-3-phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S) -2-hydroxy-3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L²), 1-[2-[(9-anthracenyl-methyl)((2S)-2-hydroxy-3-(4′-methyl)phenoxypropyl) amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(4′-methyl)phenoxypropyl]-1,4,7, 10-tetraazacyclododecane, (L³), and 1-[2-[(9-anthracenylmethyl)((2S)- 2-hydroxy-3-(4′-t-butyl)phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S) -2-hydroxy-3-(4′-t-butyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L⁴), have been prepared with a view to using their metal complexes to study aromatic anion sequestration. The eight-coordinate Cd(II) complexes of L² and L³, [CdL²](ClO₄) ₂?5H₂O and [CdL³](ClO₄) ₂?2H₂O?2Et₂O are both capable of acting as receptors for a range of aromatic oxoanions. This is demonstrated by perturbation of the anthracene derived fluorescence emission intensity as the guest aromatic oxoanion and the receptor complex combine. In 20% aqueous 1,4-dioxane the receptor complex/aromatic oxoanion association constants are in the range of 10^3.2 M^-1 (guest = p-hydroxybenzoate) to 10^7.3 M^-1 (guest = 3,4,5-trihydroxybenzoate).

Full text of DOI:10.1007/s10847-011-9924-7

J Incl Phenom Macrocycl Chem (2011) 71:567–575
DOI 10.1007/s10847-011-9924-7
ORIGINAL ARTICLE
Fluorescence signaling of aromatic oxoanion inclusion
within metal-ion activated molecular receptor complexes formed
from 2-(9-anthracenylmethylamino)ethyl-appended cyclen
•
Adam J. Bradbury Stephen F. Lincoln
•
Kevin P. Wainwright
Received: 11 November 2010 / Accepted: 9 January 2011 / Published online: 8 February 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Our observations that 1-[2-[(9-anthracenylm-
ethylamino)ethyl)-4,7,10-tris[(2S)-2-hydroxy-3-phenoxypro-
pyl]-1,4,7,10-tetraazacyclododecane, L1, complexes Cd(II)
to form fluorescent [CdL1]2? which undergoes a fluores-
cence change when it acts as an aromatic anion receptor
complex has caused us to explore further the potential
development of an interesting sequestration/sensor system.
Accordingly, three new, octadentate, fluorescent, macro-
cyclic ligands, 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-
3-phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-
3-phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L2), 1-[2-
[(9-anthracenyl-methyl)((2S)-2-hydroxy-3-(40-methyl)phen
oxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-(40-me
thyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane, (L3),
and 1-[2-[(9-anthracenylmethyl)((2S)-2-hydroxy-3-(40-t-butyl)
phenoxypropyl)amino]ethyl]-4,7,10-tris[(2S)-2-hydroxy-3-
(40-t-butyl)phenoxypropyl]-1,4,7,10-tetraazacyclododecane,
(L4), have been prepared with a view to using their metal
complexes to study aromatic anion sequestration. The
eight-coordinate Cd(II) complexes of L2 and L3, [CdL2]
(ClO4)2ꢀ5H2O and [CdL3](ClO4)2ꢀ2H2Oꢀ2Et2O are both
capable of acting as receptors for a range of aromatic
oxoanions. This is demonstrated by perturbation of the
anthracene derived fluorescence emission intensity as the
guest aromatic oxoanion and the receptor complex com-
bine. In 20% aqueous 1,4-dioxane the receptor complex/
aromatic oxoanion association constants are in the range of
103.2 M-1 (guest = p-hydroxybenzoate) to 107.3 M-1 (guest =
3,4,5-trihydroxybenzoate).
Keywords Aromatic oxoanions ꢀ Cyclen derivatives ꢀ
Fluorescence ꢀ Inclusion complex ꢀ Sensors
Introduction
In earlier work we have developed a family of molecular
receptor complexes capable of sequestering aromatic
oxoanions from aqueous and non-aqueous environments
[1–5]. These molecular receptor complexes utilise an eight-
coordinating metal ion, usually Cd(II), to form a metal
complex with a hydrophobic cavity that is defined by the
juxtapositioning of four aromatic moieties that are appen-
ded to the nitrogen atoms of a cyclen (1,4,7,10-tetraaza-
cyclododecane) ligand. This cavity is fringed at its closed
end with three or four hydrogen bond donor moieties that
serve to retain aromatic oxoanions capable of acting as
multiple hydrogen bond acceptors that enter the hydro-
phobic region. If one of the four pendant aromatic moieties
is a fluorophore, such as the 2-(9-anthracenylmethylami-
no)ethyl moiety that forms part of the fluorescent receptor
complex [CdL1]2? shown in Scheme 1, the sequestration
of an aromatic oxoanion triggers a fluorescence perturba-
tion and the receptor complex functions as a sensor [6].
To develop sensors such as [CdL1]2? into practical
devices, in which the sensor is immobilised on the surface
of a solid, we plan eventually to use the secondary amine in
the 2-(9-anthracenylmethylamino)ethyl fluorophore (the
anthracenylamine) as an alkylation point for covalently
attaching the sensor to a 3-(glycidoxy)propyl-functional-
ised silica surface [7]. This converts the secondary anth-
racenylamine to a tertiary amine and reduces by one the
A. J. Bradbury ꢀ K. P. Wainwright (&)
School of Chemical and Physical Sciences, Flinders University,
GPO Box 2100, Adelaide, SA 5001, Australia
e-mail: Kevin.Wainwright@flinders.edu.au
S. F. Lincoln
School of Chemistry and Physics, University of Adelaide,
Adelaide, SA 5005, Australia
123

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J Incl Phenom Macrocycl Chem (2011) 71:567–575
Alkylation point to be used for surface immobilisation
CH2OR CH2OR
H
OH
H
OH
O
O
O
O
O
O
H
O
H
H
O
N
N
N
H
N
O
O
O
N
H
O
H
O
O
H
O
H
O
Cd(ClO4)2
H
NH
HO
N
Cd
Cd
N
N
pH 7, 20% aqueous dioxane
N
N
N
N
N
N
(ClO )
ClO4
4 2
CH2OR
Weakly fluorescent
Fluorescent
Fluorescence emission intensity doubles
[CdL1]2+
L1, R = phenyl
Scheme 1
maximum number of hydrogen bonds, albeit the one that is
most likely to be the weakest [8], available for the retention
of the aromatic oxoanion guest. It is, therefore, of impor-
tance to test the effect of alkylation at the anthracenyl-
amine on the ability of this class of receptor complex to
sequester aromatic oxoanions. This is the subject of this
study. Previous study has shown that alkylation of the
anthracenylamine in a similar ligand increases the strength
of complexation of Cd(II) consistent with coordination of
the anthracenylamine still occurring following alkylation
[9].
2-(9-anthracenylmethylamino)ethyl fluorophore as one
pendant arm and have corresponding alkylations at the
macrocyclic secondary amines. L2–L4 were derived from
the known compound 1-(2-(9-anthracenylmethylami-
no)ethyl)-1,4,7,10-tetraazacyclododecane, 1 [9, 10], using
the procedure shown in Scheme 2. The epoxides chosen
generate the required pendant arms on the receptor ligands
that ultimately form the binding cavity necessary for aro-
matic oxoanion retention once the receptor complexes are
formed through coordination to Cd(II). Use of enantiome-
rically pure epoxides is necessary to ensure that the reac-
tion products are formed only as their homochiral
diastereomer. Good yields of L2–L4 were obtained.
Results and discussion
Cd(II) complexes of L2–L4 were readily formed as their
diperchlorate salts by the addition of Cd(ClO4)2 to a
solution of the respective ligand in hot ethanol and were
characterised by NMR spectroscopy, microanalysis and
their fluorescence behaviour. The structures of these
complexes are expected to be broadly as shown in
Synthesis of the receptor ligands and complexes
A series of receptor complexes were prepared from ligands
L2–L4, which are based on cyclen and bear an N-alkylated
Scheme 2
CH2OR CH2OR
H
H
OH
OH
O
R
H
H
H
O
N
N
N
N
N
N
N
H
N
NH
HO
N
H
CH2OR
CH2OR
HO
1
receptor ligand
R
R
Cd(ClO4)2
L2, R = phenyl
R
L3, R = p-tolyl
R
L4, R = p-t-butylphenyl
O
OH
O
O
H
O
O
N
H
H
O
O
N
Cd
N
(ClO4)2
[CdL2]2+, R = H
N
N
[CdL3]2+, R = Me
[CdL4]2+, R = t-butyl
receptor complex
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J Incl Phenom Macrocycl Chem (2011) 71:567–575
569
Schemes 1, 2 and similar to many other eight-coordinate
Cd(II) complexes which have been formed from cyclen
derived ligands that have four appended 2-hydroxyethyl,
carboxymethyl, or carbomoylmethyl moieties where the
structures have been determined by X-ray diffraction [2].
orders of magnitude; from ca 8.4 in L1 and a close deriv-
ative [6], to 4.2 0.4 for L2–L4. This pKa almost certainly
corresponds to the deprotonation of the anthracenylamine,
since the consequent availability of a lone pair of electrons
on this nitrogen atom is known to quench the fluorescence
of anthracene via the photoinduced electron transfer (PET)
effect [11]. The change from a secondary amine to a ter-
tiary amine is expected to lower the basicity, due to weaker
solvation of the protonated form [12], and so the lowering
of the pKa is not unexpected and is consistent with obser-
vations in related work [9]. The decrease in fluorescence at
very low pH seen in Fig. 1 has been noted previously with
anthracene derived fluorophores and is believed to be
associated with protonation of the aromatic ring [13].
pH Dependence of the fluorescence emission of L2–L4
A preliminary inspection of the UV spectra of protonated
L2–L4 in 20% aqueous 1,4-dioxane (I = 0.1 mol dm-3
,
Et4NClO4) and their variation with pH during titration with
Et4NOH revealed almost identical spectra and the same
minimal variation with pH as was seen previously with L1
under the same conditions [6]. Accordingly, the same
excitation frequency of 350 nm was used for the fluores-
cence studies described here. The variation of the fluores-
cence emission spectra for L2–L4 with pH differed from
that seen with L1, however. In particular, the pKa value
associated with the change from the more highly fluores-
cent, protonated form of the ligand, Fig. 1, to the less
fluorescent form seen at high pH is lowered by about four
The effect of metal ion complexation
on the fluorescence of L2–L4
Since the Cd(II) complexes of L2–L4 are to be used for
aromatic oxoanion sequestration, it is their fluorescence
emission intensities that constitute the baseline data against
which any perturbations associated with aromatic oxoanion
inclusion will be compared. These data were acquired
under the same conditions that were used in the preceding
section for L2–L4 by titrating 10-4 mol dm-3 solutions of
each ligand with a 10-3 mol dm-3 solution of Cd(ClO4)2.
To ensure that fluorescence changes due to metal binding
were not confused with fluorescence changes due to pH
change, arising from aquated Cd(II) hydrolysis, the ligand
solutions were buffered at pH 7.0 using 0.01 mol dm-3
HEPES. It was found that for each ligand the fluorescence
emission intensity increased up to the point where one
equivalent of Cd(II) had been added and then plateaued,
indicating, as was expected from the previous study of
[CdL1]2? [6], strong eight-coordinate binding of Cd(II) by
each ligand. Coordination of the anthracenylamine is
indicated because it is the donation of its lone pair electron
density towards Cd(II) that causes the fluorescence emis-
sion increase by blocking the PET quenching of the fluo-
rophore that otherwise occurs at pH 7.0 [14]. With L2 the
change in quantum yield upon complexation was from
0.061 to 0.251 (311%), for L3 from 0.039 to 0.244 (526%)
and for L4 from 0.055 to 0.241 (338%). These are larger
quantum yield changes than the 45% (from 0.471 to 0.684)
increase seen during the formation of [CdL1]2? and occur
because L1 is more strongly fluorescent at pH 7.0 due to its
protonated anthracenylamine having a pKa of ca. 8.4 rather
than ca. 4.2. However, the relative fluorescence emission
intensities at the wavelength of maximum emission
(416 nm) of the Cd(II) complexes of L2–L4 compared with
[CdL1]2?, are only 28, 27, and 26%, respectively, as may
be seen for L2 in Fig. 2, where the intensities are shown
relative to that of [CdL1]2? under the same conditions. This
Fig. 1 Top fluorescence emission spectra (kex = 350 nm) of proton-
ated L2 (protonated L3 and L4 behaved similarly), 10-6 mol dm-3 in
20% aqueous 1,4-dioxane (I = 0.1 mol dm-3, Et4NClO4) during
titration with Et4NOH at 298 K. Emission maxima are at 403.2,
422.5, and 444.7 nm at pH 2 and at 394.5, 414.5, and 438.2 nm at
pH 10. Bottom fluorescence emission intensity and quantum yields
(U) of L2 at kmax plotted against pH. Intensities in both diagrams are
relative to that of [CdL1]2? at pH 7.0 under the same conditions
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When solutions of receptor complexes [CdL2]2? and
[CdL3]2? at 10-4 or 10-6 mol dm-3 in 20% aqueous 1,4-
dioxane, buffered at pH 7.0 (0.02 mol dm-3 lutidine,
I = 0.1 mol dm-3 (Et4NClO4)) were titrated with the
sodium salts of the aromatic oxoanions indicated in
Table 1 perturbations of the fluorescence emission inten-
sity (DI) were seen in most cases. These ranged from
-66% with p-dimethylaminobenzoate to 250% with
m-hydroxybenzoate. A typical titration curve, that for
[CdL3]2? and monosodium gallate is shown in Fig. 3.
Since no perturbations of fluorescence intensity were seen
in blank titrations where the uncomplexed receptor ligands
L2 and L3 were used, the perturbations in the fluorescence
of the receptor complexes were taken as being indicative of
inclusion of the aromatic oxoanion within the binding
cavity of the receptor complex in the manner shown in
Scheme 1, but without the hydrogen bonding contribution
from the anthracenylamine that is now alkylated. Non-
linear least squares regression analysis of each titration
curve gave the aromatic oxoanion association constants
also shown in Table 1. Since the fluorescence perturbations
span both negative and positive values it should be
appreciated that no fluorescence emission perturbation
does not necessarily imply that there is no aromatic oxo-
anion inclusion, although obviously log Kassoc cannot be
determined in such instances.
Fig. 2 Fluorescence emission spectra (kex = 350 nm) and
quantum yields (U) of L2 alone, lower trace, 10-4 mol dm-3 in
20% aqueous 1,4-dioxane, I = 0.1 mol dm-3 (Et4NClO4) at pH 7.0
(0.01 mol dm-3 HEPES), and with 10-4 mol dm-3 Cd(II), upper
trace. Intensities are relative to that of [CdL1]2? under the same
conditions
may be attributable to weaker binding of the alkylated
anthracenylamine to the Cd(II), consistent with its lower
basicity, which results in less effective suppression of the
PET quenching. The fact that the Cd(II) complexes of L2–
L4 have lower quantum yields than [CdL1]2? renders them
potentially more useful in terms of sensor behaviour since
more scope remains for fluorescence enhancement upon
aromatic oxoanion inclusion. Ligands L2 and L3 were also
investigated with Pb(II), Zn(II), and Hg(II), in the same
way, and found to show similar behaviour producing
complexes with emission intensities at kmax, compared
with [CdL1]2? of 27, 31 and 19%, and 27, 18 and 7%,
respectively.
The magnitude of the fluorescence perturbation that
occurs on aromatic oxoanion inclusion within [CdL2]2? is
in some cases larger, both in the positive and negative
sense, than that seen for the receptor complex [CdL1]2?
,
which lacks alkylation at the anthracenylamine. This
indicates that the potential that the [CdL2]2?–[CdL4]2?
receptor complexes have as sensors is not diminished by
anthracenylamine alkylation. Neither do the association
constant values for aromatic oxoanions with [CdL2]2?
and [CdL3]2? show a general pattern of diminution that
might be anticipated due to the loss of the contribution
from the secondary anthracenylamine to the group of
hydrogen bond donors at the base of the binding cavity.
In some cases the association constants are higher for
aromatic oxoanions with [CdL2]2?, most noticeably with
benzoate and benzenesulfonate, which have no para-
substituent to project from the binding cavity, and which
perhaps benefit more fully than some of the other aro-
matic oxoanions studied from the deepening and fuller
enclosure of the cavity by the fifth pendant arm, attached
to the anthracenylamine.
Fluorescence emission perturbation in [CdL2]2?
and [CdL3]2? due to aromatic oxoanion sequestration
Studies of [CdL1]2? in 20% aqueous 1,4-dioxane have
shown that entry of an aromatic oxoanion into its binding
cavity generally leads to a perturbation in its fluorescence
emission intensity [6]. Overall, this may be positive or
negative due to the interplay of several different quenching
and enhancement effects. The principal effects of relevance
to [CdL2]2? and [CdL3]2?, when studied in a solvent that is
partially aqueous, are likely to be, (1) displacement of
hydrogen bonded water molecules from the binding cavity,
which will enhance fluorescence [15, 16], (2) through space
PET quenching, which can occur if the aromatic oxoanion
has significant electron donor (e.g. p-dimethyaminobenzo-
ate) or electron acceptor (e.g. p-nitrobenzoate) properties
with respect to the anthracene moiety [17], and (3) hydro-
gen bonding to the fluorophore, (e.g. O–Hꢀꢀꢀp hydrogen
bonding to the anthracene moiety) which leads to quench-
ing [18].
Conclusion
Alkylation of the anthracenylamine in receptor complexes
formed from 2-(9-anthracenylmethylamino)ethyl-appended
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571
Table 1 Association constants determined from fluorescence intensity monitored titrationsa, expressed as log (Kassoc/M-1), and fluorescence
intensity perturbations at 416 nm (DI)b for the inclusion of guest aromatic oxoanions within the receptor complexes [CdL1]2?, [CdL2]2?, and
[CdL3]2?
Guest
Receptor complex
[CdL1]2?c
[CdL2]2?
[CdL3]2?
log Kassoc
DI (%)
log Kassoc
DI (%)
log Kassoc
DI
Benzoate
2.3
4.5
5.3
7.1
4.9
6.5
4.1
4.6
3.4
117
27
5.2 0.1d
3.2 0.2
5.2 0.1d
7.3 0.5d
3.4 0.1
6.4 0.1d
3.2 0.1
3.3 0.2
5.6 0.2
192
75
e
e
p-Hydroxybenzoate
m-Hydroxybenzoate
Gallate (3,4,5-trihydroxybenzoate)
p-Nitrobenzoate
3.3 0.3
35%
e
21
250
8
e
10
6.9 0.3d
4.7 0.3
e
37%
-9%
5%
-13
59
-48
174
-66
91
p-Aminobenzoate
p-Dimethylaminobenzoate
p-Toluenesulfonate
Benzene sulfonate
-30
8
–
0%
4.2 0.2
3.2 0.3
13%
25%
39
17
a
[Receptor complex] = 10-4 mol dm-3
,
measured at pH 7.0 (0.02 mol dm-3 lutidine) in 20% aqueous 1,4-dioxane, at 298 K,
I = 0.1 mol dm-3 (Et4NClO4). Uncertainties are taken as one SD
b
Values calculated as (IHost–Guest-IHost)/IHost) 9 100 where IHost–Guest is calculated together with K from non-linear least squares regression
analysis of the titration curve
c
Data taken from [6]
[Receptor complex] = 10-6 mol dm-3
d
e
Not measured
Experimental
General information
All syntheses were performed under dry nitrogen. Solvents
were purified using literature methods [19]. Microanalyses
were conducted at the University of Otago, New Zealand.
NMR data were collected using a Varian Gemini 300
spectrometer operating at 300.075 MHz for protons and
1
75.462 MHz for 13C. H NMR chemical shifts were refer-
enced to the residual protonated solvent peak taken as
7.26 ppm for CDCl3, 2.60 ppm for DMSO-d6, and 1.96 ppm
for CD3CN. For 13C NMR spectra, chemical shifts were
referenced to the central resonance of the solvent multiplet
peak taken as 77.00 ppm for CDCl3, 39.52 ppm for DMSO-
d6, and 118.10 ppm for CD3CN (CN resonance). UV–visi-
ble absorbance spectra were measured on a Varian Cary 50
SCAN UV–Visible spectrophotometer. Flash chromatog-
raphy was carried out using Brockman II basic alumina pH
10 0.5 (particle size 100–290 mesh) as the stationary
phase. Thin layer chromatography employed Merck no.
5551 aluminium-backed neutral (type T) alumina 150 F254
plates. (2S)-(?)-3-phenoxy-1,2-epoxypropane [1], (2S)-(?)
-3-[40-(methyl)phenoxy]-1,2-epoxypropane [5], and 1-(2-
(9-anthracenylmethylamino)ethyl)-1,4,7,10-tetraazacyclodo-
decane, 1, [9], were prepared by literature methods. (2S)-(?)
-3-[40-(t-butyl)phenoxy]-1,2-epoxypropane was prepared by
Fig. 3 Molar fluorescence changes (e0) at 416 nm for 10-6 mol
dm-3 [CdL3](ClO4)2 in 20% aqueous 1,4-dioxane at pH 7.0 (0.02 mol
dm-3 lutidine, I = 0.1 mol dm-3 (Et4NClO4)) as it is titrated with
monosodium gallate. Squares indicate the experimental points and the
curve indicates the theoretical e0 values for the calculated values of
K and e0Host–Guest. Error bars are 2%
cyclen derived ligands, as may be used in future work for
the purpose of attaching these sensors to a solid supporting
material such as silica, has insignificant deleterious effects
on the ability of the receptor complex to sequester aromatic
oxoanions. The signalling ability of the sensor is slightly
improved in some cases through the lower basicity of the
alkylated anthracenylamine giving rise to a more weakly
fluorescent receptor complex.
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J Incl Phenom Macrocycl Chem (2011) 71:567–575
a method analogous to that used for (2S)-(?)-3-[40-(methyl)
phenoxy]-1,2-epoxypropane and was a gift from Prof. Xing-
You Xu of the Huaihai Institute of Technology, China.
(866 mg, 55%), m.p. 121–123°. (Found: C, 61.6; H, 7.1; N,
5.6. C61H80Cl5N5O8 requires C, 61.6; H, 6.8; N, 5.9%).
[a]2D98 = -40.9° (c 0.005, EtOH).
Syntheses
1-((N-(2-(9-Anthracenylmethyl)(N-(2S)-2-hydroxy-3-
[(40-methyl)phenoxy]propyl)aminoethyl))-4,7,10-tris((2S)-
2-hydroxy-3-[(40-methyl)phenoxy]propyl)-1,4,7,10-
tetraazacyclododecane, L3
1-((N-(2-(9-Anthracenylmethyl)(N-(2S)-2-hydroxy-3-
phenoxypropyl)aminoethyl))-4,7,10-tris((2S)-2-hydroxy-3-
phenoxypropyl)-1,4,7,10-tetraazacyclododecane, L2
1-(2-(9-anthracenylmethylamino)ethyl)-1,4,7,10-tetraaza-
cyclododecane, 1, (320 mg, 0.789 mmol) was dissolved in
dry EtOH (16 cm3) and the solution stirred whilst heating it
to boiling point. A solution of (2S)-(?)-3-[40-methylphen-
oxy]-1,2-epoxypropane (532 mg, 3.24 mmol) in dry EtOH
(16 cm3) was added dropwise. The reaction was then stir-
red whilst refluxing for 10 days and monitored by TLC
(alumina, 4% MeOH/CH2Cl2). Upon disappearance of the
starting epoxide, the reaction was cooled to room temper-
ature, and the solvent removed to leave an orange oil
(0.91 g). This was purified on a basic alumina column
(10% hexane/CH2Cl2) giving the product as a reddish-
brown oil, (684 mg, 82%). UV–vis (20% aqueous 1,4-
dioxane): kmax/nm 388.7 (e/dm3 mol-1 cm-1 9522), 368.7
(9941), 350.3 (6532), 334.0 (3607), 320.2 (2054). 1H NMR
(CDCl3): d 8.49 (2H, d, J = 8.6 Hz, AnthH); 8.38 (1H, s,
AnthH); 7.97 (2H, distorted d, J = 7.6 Hz, AnthH); 7.46
(4H, m, AnthH); 7.03 (8H, br s, PhH); 6.78 (8H, m, PhH);
4.8–1.2 (46H, br m, –OH, –CH– and –CH2–); 2.26 (12H, s,
–CH3). 13C NMR (CDCl3): d 156.4 (4C, Ph, ipso); 131.8
(2C, Anth, ipso); 131.6 (1C, Anth, ipso); 130.0 (8C, Ph);
129.9 (4C, Ph); 129.0 (2C, Anth, ipso); 128.0 (2C, Anth);
127.9 (2C, Anth); 127.0 (2C, Anth); 126.0 (1C, Anth);
124.8 (2C, Anth); 114.4 (8C, Ph); 70.3 (4C, OCH2); 67.9
(1C, methine); 66.9 (1C, methine); 65.5 (1C, methine);
65.3 (1C, methine); 60.4 (1C, exo-CH2N); 58.3 (1C, exo-
CH2N); 58.0 (1C, exo-CH2N); 57.8 (1C, exo-CH2N); 56.3
(1C, exo-CH2N); 53.8 (1C, exo-CH2N); 53.2 (1C, cyclen
CH2); 53.0 (1C, cyclen CH2); 52.3 (1C, cyclen CH2); 52.1
(1C, cyclen CH2); 51.8 (1C, cyclen CH2); 50.3 (1C, cyclen
CH2); 50.0 (1C, cyclen CH2); 49.8 (1C, cyclen CH2); 47.8
(1C, Anth-CH2N-); 20.1 (4C, CH3). To obtain a sample for
microanalysis L3 was converted to its pentahydrochloride
trihydrate by taking a solution of it (910 mg, 0.86 mmol) in
EtOH (11 cm3) cooled in ice. The stirred solution was
treated dropwise with 36% aqueous HCl (0.6 cm3,
7.6 mmol) and allowed to continue stirring overnight. The
solvent was then evaporated and the residue triturated with
ether. The brown solid was collected by filtration and dried
under vacuum (800 mg, 94%). (Found: C, 60.06; H, 7.13;
N, 5.60. C65H94Cl5N5O11 requires C, 60.11; H, 7.29; N,
5.39%). [a]2D98 = -42.2° (c 0.007, EtOH).
1-(2-(9-anthracenylmethylamino)ethyl)-1,4,7,10-tetraaza-
cyclododecane, 1, (366 mg, 0.9 mmol) was dissolved in
dry EtOH (23 cm3) and the solution stirred whilst warming
it to boiling point. A solution of (2S)-(?)-3-phenoxy-1,2-
epoxypropane (550 mg, 3.7 mmol) in dry EtOH (26 cm3)
was added dropwise. The reaction mixture was then stirred
whilst refluxing for 7 d and monitored by TLC (alumina,
MeOH/CH2Cl2 4:96). Upon disappearance of the epoxide,
the reaction was cooled to room temperature and the sol-
vent removed to leave a reddish-brown oil. This was
purified on a basic alumina column (hexane/CH2Cl2 1:9) to
remove three impurity bands, then flushed with MeOH to
recover the product. Removal of solvent from the final
fraction, and drying under vacuum gave the product as a
reddish-brown oil (684 mg, 75%). UV–vis (20% aqueous
1,4-dioxane): kmax/nm 386.4 (e/dm3 mol-1 cm-1 7891),
366.5 (8562), 348.6 (5580), 332.4 (2947), 319.8 (sh)
(1360). 1H NMR (CD3CN): d 8.55 (2H, d, J = 8 Hz,
AnthH); 8.39 (1H, s, AnthH); 8.00 (2H, d, J = 8 Hz,
AnthH); 7.47 (4H, m, AnthH); 7.35 (8H, m, PhH); 7.00
(10H, m, PhH); 6.71 (2H, d, J = 8 Hz, PhH); 4.8–1.8
(46H, br m, –OH, –CH–, and –CH2–). 13C NMR (CDCl3):
d 157.8 (4C, Ph, ipso); 130.9 (2C, Anth, ipso); 130.8 (2C,
Anth, ipso); 129.3 (1C, Anth, ipso); 129.0 (8C, Ph); 128.8
(2C, Anth); 127.4 (1C, Anth); 125.6 (2C, Anth); 124.5 (2C,
Anth); 124.1 (2C, Anth); 120.4 (4C, Ph); 114.2 (8C, Ph);
71.1 (1C, OCH2); 69.8 (1C, OCH2); 69.4 (1C, OCH2); 68.7
(1C, OCH2); 68.4 (1C, methine); 67.2 (1C, methine); 66.6
(1C, methine); 65.8 (1C, methine); 65.2 (1C, exo-CH2N);
60.1 (1C, exo-CH2N); 58.2 (1C, exo-CH2N); 57.5 (1C,
exo-CH2N); 55.0 (1C, exo-CH2N); 54.2 (1C, exo-CH2N);
52.8 (2C, cyclen CH2); 51.8 (2C, cyclen CH2); 51.4 (2C,
cyclen CH2); 50.1 (2C, cyclen CH2); 46.0 (1C, Anth-
CH2N-). To obtain a sample for microanalysis L2 was
converted to its pentahydrochloride by taking a solution of
it (960 mg, 1.12 mmol) in EtOH (14 cm3), cooled in ice
and treating it dropwise with 36% aqueous HCl (0.76 cm3,
9.9 mmol). The mixture was allowed to stir overnight then
the solvent was evaporated. The residue was triturated with
ether. The white solid was collected by filtration, and dried
under vacuum to yield the product as an off-white powder
123

J Incl Phenom Macrocycl Chem (2011) 71:567–575
573
dropwise over 5 min to a refluxing solution of L2 (232 mg,
0.23 mmol) in dry EtOH (5 cm3). A white precipitate
formed instantly. The suspension was left refluxing for 1 h,
then cooled to room temperature. The solvent was con-
centrated by rotary evaporation and then the residue was
triturated with ether to produce a light cream powder. This
was collected by filtration, washed with ice-cold water
(1 cm3) and dried under vacuum to give the product,
(252 mg, 83%). (Found: C, 51.85; H, 5.98; N, 4.97.
C61H85CdCl2N5O21 requires C, 52.05; H, 6.09; N, 4.98%).
UV–vis (20% aqueous 1,4-dioxane): kmax/nm 388.7 (e/
dm3 mol-1 cm-1 9481), 368.7 (9935), 350.3 (6423), 334.4
(3364), 320.2 (sh) (1763). 1H NMR (DMSO-d6):d 8.61
(3H, br s, AnthH); 8.09 (2H, br s, AnthH); 7.52 (4H, br s,
AnthH); 7.28 (8H, br m, PhH); 7.0–6.4 (12H, br m, PhH);
5.1–1.8 (46H, br m, –OH, –CH– and –CH2–). 13C NMR
(DMSO-d6):d 158.5 (1C, Ph, ipso); 158.2 (3C, Ph, ipso);
131.0 (2C, Anth); 130.9 (1C, Anth); 130.3 (8C, Ph); 129.6
(2C, Anth); 127.6 (2C, Anth); 126.8 (1C, Anth); 126.1 (2C,
Anth); 125.1 (2C, Anth); 124 (2C, Anth); 121.3 (3C, Ph);
121.0 (1C, Ph); 115.6 (8C, Ph); 71.0 (1C, OCH2); 70.6 (1C,
OCH2); 70.3 (2C, OCH2); 67.7 (1C, methine); 67.0 (1C,
methine); 66.2 (1C, methine); 64.4 (1C, methine); 61.5
(1C, exo-CH2N); 60.0 (1C, exo-CH2N); 57.5 (1C, exo-
CH2N); 56.1 (1C, exo-CH2N); 54.2 (1C, exo-CH2N); 52.0
(1C, exo-CH2N); 51.3 (2C, cyclen CH2); 50.2 (2C, cyclen
CH2); 49.0 (2C, cyclen CH2); 48.2 (2C, cyclen CH2); 44.8
(1C, Anth-CH2-N-).
1-((N-(2-(9-Anthracenylmethyl)(N-(2S)-(-)-2-hydroxy-3-
[(40-t-butyl)phenoxy]propyl)aminoethyl))-4,7,10-tris((2S)-
(-)-2-hydroxy-3-[40-(t-butyl)phenoxypropyl)-1,4,7,10-
tetraazacyclododecane, L4
1-(2-(9-anthracenylmethylamino)ethyl)-1,4,7,10-tetraaza-
cyclododecane, 1, (268 mg, 0.66 mmol) was dissolved in
dry EtOH (20 cm3) and stirred. (2S)-(?)-3-[40-(t-butyl)
phenoxy]-1,2-epoxy propane (541 mg, 2.61 mmol) was
added in EtOH (20 cm3). The reaction mixture was heated
under reflux for 10 days, whilst monitoring by TLC
(CH2Cl2/hexane, 9:1). Upon loss of starting material the
reaction was cooled to room temperature, filtered and the
filtrate was evaporated to leave the product as a reddish oil
(700 mg, 86%). UV–vis (20% aqueous 1,4-dioxane): kmax
/
nm 388.6 (e/dm3 mol-1 cm-1 7753), 368.5 (8159), 350.2
(5350), 334.1 (2786), 319.0 (sh) (1444). 1H NMR
(CD3CN): d 8.51 (2H, d, J = 5.8 Hz, AnthH); 8.43 (1H, d,
J = 5.8 Hz, AnthH); 7.99 (2H, d, J = 6.4 Hz, AnthH); 7.45
(4H, br s, AnthH); 7.4–7.1 (8H, m, PhH); 7.0–6.4 (8H, m.
PhH); 4.62 (4H, br s, –OH); 4.50–1.80 (42H, br m, –CH- and –
CH2–); 1.27 (36H, br s, –CH3). 13C NMR (CD3CN): d 157.7
(3C, Ph, ipso); 157.5 (1C, Ph, ipso); 144.3 (4C, Ph, ipso);
135.3 (2C, Anth, ipso); 132.4 (2C, Anth, ipso); 131.4 (1C,
Anth, ipso); 130.0 (2C, Anth); 128.6 (2C, Anth); 127.8 (1C,
Anth); 127.2 (6C, Ph); 127.0 (2C, Ph), 126.1 (2C, Anth); 124.5
(2C, Anth); 118.3 (4C, Ph); 115.0 (4C, Ph); 72.5 (1C, OCH2);
71.3 (1C, OCH2); 70.5 (1C, OCH2); 70.2 (1C, OCH2); 69.8
(1C, methine); 68.6 (1C, methine); 67.3 (1C, methine); 67.2
(1C, methine); 66.6 (1C, exo-NCH2); 64.1 (1C, exo-CH2N);
61.5 (1C, exo-CH2N); 58.8 (1C, exo-CH2N); 57.7 (1C, exo-
CH2N); 54.4 (1C, exo-CH2N); 52.9 (2C, cyclen CH2); 52.6
(2C, cyclen CH2); 52.3 (2C, cyclen CH2); 51.7 (2C, cyclen
CH2); 47.4 (1C, Anth-CH2N-); 34.7 (4C, -C(CH3)3); 31.8
(12C, -CH3). To obtain a sample for microanalysis L4 was
converted to its pentahydrobromide monohydrate by taking a
solution of it (100 mg, 0.08 mmol) in EtOH (5 cm3) and
treating it with 48% HBr (100 lL) and allowing it to stir for
1 h. The solvent was evaporated and the residue was triturated
with ether. The light brown solid was collected by filtration
and dried under vacuum. Yield:(94 mg, 71%). (Found C, 55.8;
H, 7.2; N, 4.15. C77H114Br5N5O9 requires C, 55.94; H, 6.95;
N, 4.24%). [a]2D98 = -29.3° (c 0.008, EtOH).
[CdL3](ClO4)2ꢀ2Et2Oꢀ2H2O
A solution of cadmium(II) perchlorate hexahydrate(1.152 g,
3.0 mmol) in EtOH (20 cm3) was added dropwise over
5 min to a refluxing solution of L3 (1.911 g, 2.5 mmol) in
EtOH (63 cm3). A white precipitate formed instantly. The
suspension was left refluxing for 1 h, then cooled to RT. The
solvent was evaporated and trituration of the residue with
ether produced a light cream powder. This was collected by
filtration, washed with water (1 cm3) and dried under vac-
uum to give the pure product (1.831 g, 74%). (Found: C,
56.09; H, 7.09; N, 4.20. C73H107CdCl2N5O20 requires C,
56.28; H, 6.92; N, 4.50%). UV/vis (20% aqueous 1,4-diox-
ane): kmax/nm 388.7 (e/dm3 mol-1 cm-1 9596), 368.7
(10120), 350.3 (6678), 334.1 (3644), 320.4 (sh) (2038). 1H
NMR (DMSO-d6): d 8.90 (3H, br s, AnthH); 8.39 (2H, br s,
AnthH); 7.81 (4H, br s, AnthH); 7.35 (8H, br m, PhH);
7.4–6.6 (8H, br m, PhH); 5.6–2.0 (58H, br m, –OH, –CH–,
–CH2– and CH2 of ether); 2.30 (12H, br s, –CH3); 1.10 (6H,
m, CH3 of ether). 13C NMR (DMSO-d6): d 156.5 (2C, Ph,
ipso); 156.2 (2C, Ph, ipso); 131.1 (2C, Anth, ipso); 131.0
(2C, Anth, ipso); 130.0 (8C, Ph); 129.1 (4C, Ph); 128.6 (2C,
Anth, ipso); 127.6 (2C, Anth); 127.1 (2C, Anth); 126.2 (2C,
Anth); 125.2 (2C, Anth); 114.5 (8C, Ph); 72.0 (2C, OCH2);
Safety note: perchlorate salts are potentially explo-
sive. Although no problems were encountered in the
synthesis or use of the following compounds extreme
care should be taken when handling them.
[CdL2](ClO4)2ꢀ5H2O
A
solution of cadmium(II) perchlorate hexahydrate
(106 mg, 0.26 mmol) in dry EtOH (5 cm3) was added
123

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J Incl Phenom Macrocycl Chem (2011) 71:567–575
70.0 (1C, OCH2); 69.1 (1C, OCH2); 67.9 (2C, methine); 66.0
(2C, methine); 65.0 (1C, exo-CH2N); 64.8 (1C, exo-CH2N);
64.2 (1C, exo-CH2N); 62.5 (1C, exo-CH2N); 57.5 (4C, CH2
of ether); 57.0 (1C, exo-CH2N); 53.0 (1C, exo-CH2N); 51.4
(2C, cyclen CH2), 50.5 (2C, cyclen CH2); 49.4 (2C, cyclen
CH2); 48.0 (2C, cyclen CH2); 45.1 (1C, Anth-CH2N-); 20.2
(4C, -CH3); 15.3 (4C, CH3 of ether).
at pH 7.0 (0.02 M lutidine). The fluorescence emission
spectra at 298 0.1 K were recorded on a Varian Cary
Eclipse fluorescence spectrophotometer, using stoppered
10 mm quartz cells, over a wavelength range of 370–550 nm
at 0.15 nm intervals, with a scan rate of 40 nm min-1. Both
the excitation and emission monochromator slit widths were
set at 5 nm, and due to the highly fluorescent nature of the
compounds, a 1.5 absorbance attenuator was used for
10-4 mol dm-3 solutions, while 10-6 mol dm-3 solutions
required no attenuation. All samples were purged with N2
prior to use. Quantum yields were calculated with respect to
quinine in 0.5 mol dm-3 H2SO4 according to the method of
Demas [20], and are corrected for solvent refractive indices.
[CdL4](ClO4)2ꢀCH3CN
A
solution of cadmium(II) perchlorate hexahydrate
(0.183 g, 0.43 mmol) in dry EtOH (3.5 cm3) was added
dropwise over 5 min to a refluxing solution of L4 (0.35 g,
0.39 mmol) in dry EtOH (11 cm3). A white precipitate
formed instantly. The suspension was left refluxing for 1 h,
then cooled to room temperature. The solvent was evapo-
rated and then trituration of the residue with ether produced
a light cream powder. This was collected by filtration,
washed with ice-cold MeCN, followed by drying under
vacuum, to give the pure product (0.272 g, 45%). (Found
C, 60.06; H, 7.13; N, 5.60. C79H110CdCl2N6O16 requires:
C, 59.94; H, 7.00; N, 5.31%.). UV–vis (20% aqueous 1,4-
dioxane): kmax/nm 388.2 (e/dm3 mol-1 cm-1 4865), 367.8
Acknowledgment Funding of this study by the Australian Research
Council is gratefully acknowledged.
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