Hydrophilic oxybathophenanthroline ligands: Synthesis and copper(II) complexation

Article abstract of DOI:10.1039/b805136d

Hydrophilic oxybathophenanthroline dendrons (generation 1-3) have been synthesized by treatment of 4,7-bis(4′-hydroxyphenyl)-1,10-phenanthroline with the corresponding bromo-functionalized etheraryl branching units containing triethylene glycol monomethyl end groups. Radiotracer experiments using ⁶⁴Cu prove the rapid formation of stable copper(ii) complexes in aqueous solution. These ⁶⁴Cu complexes remain unchanged even upon addition of a high excess of glutathione as competing ligand, thus demonstrating the high stability of the formed copper(ii) complexes. Electronic and EPR spectroscopy indicate the formation of [Cu(L)₂(OH₂) ₂]²⁺ (L = ligand) complexes in aqueous solution, confirmed by time-resolved laser fluorescence spectroscopy and supported by molecular mechanics modeling. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008.

Full text of DOI:10.1039/b805136d

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Hydrophilic oxybathophenanthroline ligands: synthesis and copper(II)
complexation
Holger Stephan,*a Stefanie Juran,a Karin Born,b Peter Comba,b Gerhard Geipel,c
d
d
Uwe Hahn,de Nicole Werner and Fritz Vogtle*
¨
Received (in Montpellier, France) 26th March 2008, Accepted 8th May 2008
First published as an Advance Article on the web 16th July 2008
DOI: 10.1039/b805136d
Hydrophilic oxybathophenanthroline dendrons (generation 1–3) have been synthesized by
treatment of 4,7-bis(40-hydroxyphenyl)-1,10-phenanthroline with the corresponding bromo-
functionalized etheraryl branching units containing triethylene glycol monomethyl end groups.
Radiotracer experiments using 64Cu prove the rapid formation of stable copper(II) complexes in
aqueous solution. These 64Cu complexes remain unchanged even upon addition of a high excess
of glutathione as competing ligand, thus demonstrating the high stability of the formed copper(II)
complexes. Electronic and EPR spectroscopy indicate the formation of [Cu(L)2(OH2)2]2+
(L = ligand) complexes in aqueous solution, confirmed by time-resolved laser fluorescence
spectroscopy and supported by molecular mechanics modeling.
methanol.5 Kinetically inert copper(I) complexes with Fre
´
chet-
Introduction
type dendrons, attached adjacent to the metal coordination
center (2,9 positions of 1,10-phenanthroline), have been
observed in dichloromethane.6 Recently, we have described
hydrophobic oxybathophenanthroline derivatives with
Dendrimer chemistry is a rapidly expanding field for both
fundamental studies and applications.1 The typical behavior
of dendritic systems emerges from their compact tree-like
molecular structure, which provides an arrangement of inner
and outer molecular functionalities, making them useful for
applications in medicine, catalytic processes and nano-
technology. The introduction of the structurally reinforced
1,10-phenanthroline unit onto dendritic frameworks leads to
unique material properties. Thus, metallodendrimers based on
ruthenium(II) complexes with bisphenanthroline ligands,
bridged in the 5,6-positions, provide very robust, structurally
rigid and well-defined nanoscopic complexes.2 Dendritic phe-
nanthroline-containing ligands described so far possess hydro-
phobic skeletons, which can be employed in applications that
require an organic environment. Particularly, ruthenium(II)
complexes with branched phenanthroline moieties exhibit inter-
esting absorption, luminescence and redox properties in polar
organic solvents.3 Supramolecular self-assembled structures
with tuneable coordination geometries could be obtained with
amphiphilic dendritic phenanthroline ligands and appropriate
metal ions in acetonitrile.4 Furthermore, a dendrimer with an
arylethynyl scaffold with six peripheral phenanthroline units
showed significant activity in copper-catalyzed reactions in
attached Frechet-type dendrons in the 4,7-positions (Fig. 1),
´
which are able to rapidly form stable copper(II) complexes in
trichloromethane.7
In view of biomedical applications such as the design of
novel diagnostic and therapeutic agents, it was of interest to
develop the corresponding hydrophilic systems.8 In this paper,
we report the synthesis and the copper(II) complexation of
dendritic 4,7-diphenyl-1,10-phenanthroline (dpp) ligands with
attached Frechet-type dendrons, containing triethylene glycol
´
monomethyl ether end groups (Fig. 2).
Results and discussion
Syntheses
The phenanthroline ligand 1 with two peripheral hydroxy
groups was obtained in five steps, according to a previously
reported procedure.7 The dendritic precursors 2–4 with terminal
hydrophilic ethylene glycol chains and a benzylic bromide
functional group (generation 1–3) have also been prepared
a Institut fur Radiopharmazie, Forschungszentrum Dresden-
¨
Rossendorf, Postfach 510119, 01314 Dresden, Germany.
E-mail: h.stephan@fzd.de; Fax: +49 (351) 2603232;
Tel: +49 (351) 2603091
b Universitat Heidelberg, Anorganisch-Chemisches Institut,
¨
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
c Institut fur Radiochemie, Forschungszentrum Dresden-Rossendorf,
Postfach 510119, 01314 Dresden, Germany
¨
d
´
Kekule Institut fur Organische Chemie und Biochemie, Universitat
¨
¨
Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany;
Fax: +49 (228) 735662; Tel: +49 (228) 733495.
E-mail: voegtle@uni-bonn.de
e
Fig.
1 Hydrophobic dendritic oxybathophenanthroline ligand
´
Universidad Autonoma de Madrid, Departamento de Quımica
Organica, Campus de Cantoblanco, 28049 Madrid, Spain
´
´
(generation 1).
ꢀc
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Fig. 3 HPLC trace of 64Cu-LG1 at 12 h in the presence of glutathione:
cligand = 1 mM, cglutathione = 5 mM, pH = 5.4 (MES/NaOH buffer).
Fig.
2 Constitutions of the investigated hydrophilic dendritic
oxybathophenanthroline ligands LG1–LG3
.
copper(II) is completely bound with very low ligand concentra-
tion (1 mM) in aqueous buffer solution (pH range from 5.4 to
7.4) within 1 min at room temperature. The qualitative stability
of the radioactive copper(II)–dpp complexes was deduced from
challenge experiments using glutathione as competing ligand.12
To get reliable results, TLC measurements are unsuitable. It was
not possible to clearly distinguish radiocopper complexes of
glutathione and dpp-ligands LG1–LG2 (64Cu-glutathione, Rf =
0–0.15). Therefore, Radio-HPLC experiments were used to
obtain well-separated Rt-values (64CuCl2, Rt = 2.8 min; 64Cu-
following synthetic routes described in literature.9 The dendritic
diphenylphenanthroline ligands LG1–LG3 were synthesized as
shown in Scheme 1. One equivalent of 4,7-bis(40-hydroxy-
phenyl)-1,10-phenanthroline 1 was dissolved in DMF and
deprotonated by treatment with sodium hydride. Addition of
two equiv. of the corresponding dendritic benzyl bromides 2–4,
followed by purification on silica gel, gave the products in
medium yields as colorless viscous oils in all cases. LG1–LG3
are well soluble in polar solvents such as water and methanol
and can also easily be dissolved in more apolar solvents such as
CH2Cl2, CHCl3, or THF. The structures of all dendritic ligands
could be readily deduced from 1H and 13C NMR spectra as well
as from mass spectrometric analysis (see Experimental section).
glutathione, Rt = 7.6 min; 64Cu-LG1 = 19.7 min; 64Cu-LG2
=
21.1 min; 64Cu-LG3 = 23.8 min). After full complexation, the
64Cu-dpp complexes were reacted with glutathione for 12 h at
room temperature. The radiochromatogram shown in Fig. 3
illustrates the elution profile of 64Cu-LG1. In the presence of even
a large excess of the competing ligand glutathione (5 mM vs.
1 mM), there was no evidence of transchelation (64Cu-gluta-
Radiotracer experiments with 64Cu
thione, Rt = 7.6 min) and demetalation (64CuCl2, Rt
=
Phenanthroline derivatives are able to form strong complexes
with copper(II). In particular, water-soluble phenanthroline
ligands are attractive candidates for the development of copper
radiopharmaceuticals.10 With the increasing dissemination of
copper radionuclides, the use of radiocopper complexes for
imaging and therapy is an emerging field.11 In this perspective,
highly thermodynamically and kinetically stable copper(II) com-
plexes are required. Based on these requirements preliminary
radiolabeling experiments of the dendritic diphenylphenan-
throline ligands LG1–LG3 with 64Cu have been performed.
Initially, the complex formation was studied by thin-layer
chromatography using C18 TLC plates. The Rf-values of free
copper (64CuCl2, Rf = 0) and the dendritic 64Cu-dpp complexes
(Rf = 0.17–0.20) are well-separated. The copper complexation
by the ligands LG1–LG3 is very efficient and rapid. Radio
2.8 min), indicative for a high stability of the 64Cu-dpp
complexes formed.
Information about the lipophilicity was obtained from the
measurement of the distribution of the dendritic copper(II)-
dpp complexes in the water/1-otanol system. Fig. 4 shows the
distribution ratio log DCu as a function of pH.13 As expected,
the 64Cu complexes of LG1–LG3 are rather hydrophilic. With
increasing generation of the covalently linked dendritic
Frechet-type branches the higher number of ethylene glycol
´
groups causes a decreasing lipophilicity in the order 64Cu-LG1
(log P = ꢁ0.02) 4 64Cu-LG2 (log P = ꢁ1.09) 4 64Cu-LG3
(log P = ꢁ1.67). Therefore, the observed lipophilicity data
with the 64Cu complexes of the corresponding dendritic
diphenylphenanthroline ligands are in the typical range of
approved radiopharmaceuticals.10b,14
Geometry of dendritic copper(II) complexes
The complexation behavior and coordination geometry of the
dendritic ligands LG1–LG3 have been examined by UV/Vis
titration and EPR experiments as well as by molecular
mechanics modeling. The UV/Vis titration of the ligands
with Cu(NO3)2 shows the establishment of a 1 : 1 and a 1 : 2
(Cu2+ : ligand) species. Addition of more ligand did not affect
the absorption, thus there is no indication for 1 : 3 complexes.
Scheme 1 Preparation of the hydrophilic dpp-ligands LG1–LG3
Reagents and conditions: (i) NaH (60% in paraffin), rt, 1 d, DMF
(white spheres represent the ether aryl branching units, grey spheres
represent triethylene glycol monoethyl ether end groups).
.
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Fig. 6 Strain energy minimized structure of [Cu(LG1)2(OH2)2], using
the MOMEC97 program and force field.18,19
In agreement with the electronic spectra, the EPR spectra do not
change after addition of more than two equivalents of ligand to
the copper(II) salts (see Fig. 5).
Fig. 4 Distribution of 64Cu complexes of dpp ligands in the system
buffer/1-octanol: cligand =1 mM, pH = 5.4–7.4 (MES/NaOH buffer).
The conclusion, that the assembled Cu(II) complexes have
the composition [Cu(LGn)2(OH2)2]2+ is further supported by
strain energy minimized structures, using the MOMEC
program18 and force field.19 An optimized structure is shown
in Fig. 6 (for clarity, only the Cu(II) complex with LG1 is
shown; the coordination geometry does not change with the
higher generations, and is also largely unchanged for various
possible conformational minima). The Cu–N distances
(ca. 1.97 A) and a tetrahedral twist of the CuN4 chromophores
(ca. 401) are, as expected, very similar to those reported for
other [Cu(phen)2(OH2)2]2+-type structures.20
This is expected since phenanthroline (phen) is known to
preferably form 1 : 2 complexes with Cu(II).15 The electronic
spectra show a broad transition at 711 nm for LG1, 721 nm for
LG2 and 724 nm for LG3, due to transitions from dxy, dxz
and dyz-type orbitals of the copper(II) center. [Cu(dpp)2-
(OH2)2](X)2 (X = Clꢁ, Brꢁ, ClO4ꢁ) has transitions at
714–740 nm in nitromethane, depending on the counter
anion.16 Therefore, it was concluded that [Cu(LGn)2(OH2)2]2+
complexes are formed upon addition of Cu2+ in aqueous
solution.
The assignment of these transitions to CuN4On (n = 0, 1, 2)
chromophores is supported by the EPR spectra of the same
solutions at 120 K. Fig. 5 shows the spectra of the complexes
with LG2 at different Cu : L ratios (1 : 1, 1 : 2, 1 : 3). The
analysis of the spin Hamiltonian (for the 1 : 2 complexes; gx =
gy = 2.065, gz = 2.370, Ax = Ay = 11 ꢂ 10ꢁ4 cmꢁ1, Az =
Luminescence properties
The fluorescence properties of the ligands LG1–LG3 were
characterized by time-resolved fluorescence spectroscopy.
The fluorescence spectra 50 ps after excitation (lexc
266 nm) are given in Fig. 7.
=
135 ꢂ 10ꢁ4 cmꢁ1) are similar to those of [Cu(phen)2(OH2)2]2+ 17
.
Compared to 1,10-phenanthroline, the three dendritic
ligands LG1–LG3 show a shift to higher wavelengths, and with
higher ligand generations a slight hypsochromic shift is
observed. The emission maxima and the decay time of the
ligands investigated are summarized in Table 1. The spectra
cannot be fitted by a single gaussian waveform. With respect
to the fluorescence lifetime, more complex features have been
noticed for the dpp-ligands than for 1,10-phenanthroline. This
may be due to the appended phenyl rings adjacent to the
fluorescence center. Energy transfer between the fluorescence
center and the phenyl rings may lead to multiple fluorescence
lifetimes. In all cases, the fluorescence around 400 nm has the
highest intensity.
Addition of copper(II) to an aqueous solution of the appro-
priate ligands leads to a decrease of fluorescence intensity.
Thus, the complex stability of the copper(II) complexes with
the dpp-ligands can be determined with time-resolved laser-
induced fluorescence.
The determination of the stability constants exploits the
luminescence properties of the non-complexed ligand, and free
metal ion and the complex do not emit. This is well known as a
static quench effect.21 With this assumption, the species
concentration can be calculated from the fluorescence
intensities of the metal-free ligand as a function of metal
Fig. 5 Experimental (spectra 2, 4, 6 from top) and computed (spectra
1, 3, 5 from top) EPR spectra of Cu(II) complexes with LG2 at different
Cu : ligand ratios (from top to bottom: 1 : 1, 1 : 2, 1 : 3); g>, gJ, A>, AJ
values: 2.080, 2.400, 6 ꢂ 10ꢁ4 cmꢁ1, 130 ꢂ 10ꢁ4 cmꢁ1 (1 : 1); 2.065,
2.370, 11 ꢂ 10ꢁ4 cmꢁ1, 135 ꢂ 10ꢁ4 cmꢁ1 (1 : 2) and 2.065, 2.380,
11 ꢂ 10ꢁ4 cmꢁ1, 138 ꢂ 10ꢁ4 cmꢁ1 (1 : 3).
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Fig. 8 Fluorescence intensity of LG3 as function of Cu(II) concentra-
tion, cligand = 30 mM in 0.1 M NaClO4.
Fig. 7 Time-resolved fluorescence spectra of the dpp-ligands and
1,10-phenanthroline, cligand = 10 mM in water.
Table 1 Fluorescence properties of phen and dendritic dpp-ligands
Ligand
Emission maxima (lmax)/nm
Decay time/ps
phen
LG1
359, 375, 395, 411, 430
396, 422, 465
1170 ꢃ 23
150 ꢃ 5
670 ꢃ 13
2450 ꢃ 41
403 ꢃ 20
1710 ꢃ 100
554 ꢃ 10
2100 ꢃ 30
LG2
LG3
392, 415, 447
398, 428
concentration. The fluorescence lifetime was also determined
in all solutions to establish dynamic quench effects.
The stability of the copper(II) complex with 1,10-phenan-
throline in 0.1 M NaClO4 and water–MeOH (1 : 1) was
determined for comparison. The formation of a Cu(L)2 com-
plex was established by slope analysis (slope = 1.94 ꢃ 0.23),
Fig. 9 Fluorescence intensity of LG3 as function of Cu(II) : LG3 ratio,
cligand = 30 mM in 0.1 M NaClO4.
and the formation constant was determined to be log b12
=
13.86 ꢃ 0.12, compared to log b12 = 13.7 in 0.1 M NaNO3
and log b12 = 16.14 in 0.1 M KNO3, both in dioxane–water
(1 : 1).22 Therefore, time-resolved fluorescence spectroscopy is
well-suited to determine reliable formation constants for
Cu(II)-phenanthroline complexes.
From the fluorescence intensities the concentration of the
non-complexed ligand LG3 was calculated and the stability data
were determined, assuming a 1 : 2 (metal : ligand) complex
stoichiometry. Slope analysis confirms the formation of
The fluorescence intensity for LG1 and LG2 decreases with
increasing copper concentration. The fluorescence disappears
at metal : ligand ratios of about 1 : 4 and 1 : 3. However, for
LG1 and LG2 it was not possible to determine the complex
stoichiometry and the stability constants. This may be due to
dynamic hydration/dehydration effects of the triethylene
glycol monomethyl ether end groups adjacent to the fluores-
cence center. Increasing the distance of these arms from the
chromophore results in a decrease of the influence on
the fluorescence by energy transfer from the excited state of
the chromophore to the increasing number of phenyl rings.
Hence, the estimation of the stability was possible for the
copper(II) complex formed with LG3. The fluorescence spectra
of LG3 as a function of the total copper concentration are
shown in Fig. 8.
Cu(LG3
) (slope = 1.96). The resulting stability constant is
2
log b2 = 12.27 ꢃ 0.13. It follows that the stability of copper(II)-
phenanthroline complexes is only slightly influenced by the
dendritic modification. On the other hand, with higher genera-
tion the fluorescence lifetime of the ligands is less affected by
copper(II) addition pointing to an increased shielding effect on
the metal center.
Conclusions
A new series of fractal ligands, derived from 4,7-diphenyl-1,
10-phenanthroline with first to third generation poly(aryl
ether) branching units and triethylene glycol monomethyl
ether end groups have been prepared. These water-soluble
oxybathophenanthroline-derived dendritic ligands were
explored by radiotracer experiments using 64Cu, and have
shown spontaneous formation of stable copper(II) complexes
in aqueous solution. Electronic and EPR spectroscopy suggest
There was found a small residual fluorescence intensity at
higher metal concentration, which did not change with
ongoing increase of the metal concentration (cf. Fig. 9).
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the formation of [Cu(LG1–G3)2(OH2)2]2+ species. This is
underscored by molecular modeling and time-resolved laser
fluorescence experiments. The latter revealed that the stability
of the copper(II) complexes is nearly independent of the
dendritic modification of the ligands. However, with higher
generation of the fractal structure the metal center is better
shielded from the environment. The synthetic approach allows
the fine-tuning of the solubility by introduction of appropriate
methoxypolyethoxy groups. Moreover, the mild conditions of
synthesis offers the possibility to introduce and covalently link
biomolecules such as sugars and peptides as surface groups,
hence paving the way to produce new ligands with a potential
in pharmaceutical targeting. That makes this type of phenan-
throline ligands attractive for the development of new (radio)-
diagnostically and (radio)therapeutically relevant metal
complexes as well as hydrophilic DNA intercalating agents.
(400 MHz, CDCl3, 25 1C): d 3.30 (s, 12 H; CH3), 3.46 (m, 8 H;
CH2), 3.60 (m, 16 H; CH2), 3.66 (m, 8 H; CH2), 3.78 (t, J = 5
Hz, 8 H; CH2), 4.07 (t, J = 5 Hz, 8 H; CH2), 5.01 (s, 4 H;
CH2), 6.40 (t, J = 2 Hz, 2 H; Har), 6.47 (d, J = 2 Hz, 2 H;
Har), 6.58 (d, J = 2 Hz, 4 H; Har), 7.04 (AA0 part of the
AA0BB0 system, 4 H; Har), 7.39 (BB0 part of the AA0BB0
system, 4 H; Har), 7.48 (d, J = 4 Hz, 2 H; Har), 7.82 (s, 2 H;
Har), 9.12 (d, J = 5 Hz, 2 H; Har) ppm; 13C NMR (100 MHz,
CDCl3, 25 1C): d 59.0 (CH3), 67.6, 69.7, 70.0, 70.5, 70.6, 70.8,
71.9 (OCH2), 101.1, 106.1, 115.1, 123.5, 124.0, 126.5, 130.5,
131.1, 139.1, 146.9, 148.1, 149.7, 159.0, 160.2 (Car) ppm; MS
(FAB, NBA): m/z (%): 1193.5 ([M + H]+, 62), 663.4 (100),
648.4 (85).
1,10-Phenanthroline(4,7)-phenyl(40):{1-oxa-3-(phenyl-300,500-
diylpropyl(300,500)}G1,G2/2x,4x:(1-oxa-4-oxa-7-oxa-10-oxaun-
decane)8-cascadane (LG2). Prepared from 1 (35.0 mg, 96 mmol),
and dendritic bromide 3 (208.2 mg, 0.20 mmol). Gradient
column chromatography (SiO2, CH2Cl2/MeOH, 70 : 1 to
10 : 1) yielded LG2 (146.0 mg, 67%) as a colourless oil. 1H
NMR (400 MHz, CDCl3, 25 1C): d 3.30 (s, 24 H; CH3), 3.48
(m, 16 H; CH2), 3.58 (m, 32 H; CH2), 3.66 (m, 16 H; CH2),
3.79 (t, J = 5 Hz, 16 H; CH2), 4.05 (t, J = 5 Hz, 16 H; CH2),
4.92 (s, 8 H; CH2), 5.04 (s, 4 H; CH2), 6.40 (t, J = 2 Hz, 6 H;
Har), 6.47 (d, J = 2 Hz, 4 H; Har), 6.58 (d, J = 2 Hz, 8 H; Har),
7.09 (AA0 part of the AA0BB0 system, 4 H; Har), 7.32 (BB0 part
of the AA0BB0 system, 4 H; Har), 7.51 (d, J = 5 Hz, 2 H; Har),
7.88 (s, 2 H; Har), 9.14 (d, J = 5 Hz, 2 H; Har) ppm; 13C NMR
(100 MHz, CDCl3, 25 1C): d 59.0 (CH3), 67.5, 69.7, 70.0, 70.1,
70.5, 70.6, 70.8, 71.9 (OCH2), 101.2, 101.6, 106.1, 106.4, 115.1,
123.5, 124.0, 126.5, 130.6, 131.0, 139.0, 139.2, 147.0, 148.1,
149.7, 159.1, 160.1, 160.2 (Car) ppm; MS (FAB, NBA): m/z
(%): 2267.1 ([M + H]+, 64), 1010.5 (58), 307.1 (100).
Experimental
Materials and methods
All starting materials were purchased from commercial
sources and used without further purification. The dpp-ligand7
1 and the dendritic bromides9 2–4 have been prepared
according to literature procedures. The solvents were dried
using standard techniques. Reactions were monitored by thin-
layer chromatography using TLC plates pre-coated with silica
gel 60F254 (Merck) and compounds detected by UV-light
(254 nm). Column chromatography was carried out using
silica gel (Merck 15101). 1H and 13C NMR spectra were
recorded using a AM 400 MHz Bruker instrument; the solvent
signal was used for internal calibration. FAB mass spectra
were recorded using a Concept 1H from Kratos Analytical
Ltd., Manchester, GB. 64Cu was produced on the PET
cyclotron ‘‘Cyclone 18/9’’ of the FZ Dresden-Rossendorf by
the 64Ni(p,n) - 64Cu nuclear reaction. The specific activity
was 4370 MBq mgꢁ1
.
1,10-Phenanthroline(4,7)-phenyl(40):{1-oxa-3-(phenyl-300,500-
diyl)propyl(300,500)}G1,G2,G3/2x,4x,8x:(1-oxa-4-oxa-7-oxa-10-
oxa-undecane)16cascadane (LG3). Prepared from 1 (41.2 mg,
0.11 mmol), and dendritic bromide 4 (500.0 mg, 0.24 mmol).
Gradient column chromatography (SiO2, CH2Cl2/MeOH,
70 : 1 to 10 : 1) yielded LG3 (209.8 mg, 42%) as a colourless
oil. 1H NMR (400 MHz, CDCl3, 25 1C): d 3.28 (s, 48 H; CH3),
3.42 (t, J = 5 Hz, 32 H; CH2), 3.53–3.66 (m, 96 H; CH2), 3.74
(t, J = 5 Hz, 32 H; CH2), 4.03 (t, J = 5 Hz, 32 H; CH2), 4.86
(s, 16 H; CH2), 4.92 (s, 8 H; CH2), 5.04 (s, 4 H; CH2), 6.36
(t, J = 2 Hz, 8 H; Har), 6.47 (t, J = 2 Hz, 4 H; Har), 6.50 (d, J =
2 Hz, 16 H; Har), 6.53 (t, J = 2 Hz, 2 H; Har), 6.60 (d, J =
2 Hz, 8 H; Har), 6.66 (d, J = 2 Hz, 4 H; Har), 7.06 (AA0 part of
the AA0BB0 system, 4 H; Har), 7.39 (BB0 part of the AA0BB0
system, 4 H; Har), 7.48 (d, J = 5 Hz, 2 H; Har), 7.85 (s, 2 H;
Har), 9.14 (d, J = 5 Hz, 2 H; Har) ppm; 13C NMR (100 MHz,
CDCl3, 25 1C): d 59.0 (CH3), 67.5, 69.7, 70.0, 70.1, 70.6, 70.71,
70.75, 70.8, 71.9 (OCH2), 101.2, 101.5, 101.6, 106.2, 106.46,
106.53, 115.1, 123.6, 124.0, 126.5, 130.6, 131.0, 139.1, 139.17,
139.21, 147.0, 148.1, 149.7, 159.1, 160.10, 160.13, 160.2 (Car)
ppm; MS (FAB, NBA): m/z (%): 4413.2 ([M + H]+, 64),
1010.5 (58), 307.1 (100).
Syntheses
General procedure for the preparation of the dendritic ligands
LG1–LG3. To a suspension of 4,7-bis(40-hydroxyphenyl)-1,
10-phenanthroline7 1 (0.1 mmol) in dry DMF (10 mL) was
added NaH (0.22 mmol, 60% in paraffin). The reaction
mixture turned to red. After 5 min a solution of the corres-
ponding bromides9 2–4 (0.21 mmol) in dry DMF (5 mL) was
added and the suspension stirred for 1 d at rt. The residual
NaH was deactivated by slow addition of water at 0 1C.
CH2Cl2 (30 mL) was added, the suspension neutralized with
aq. HCl (2 M), and the aqueous phase extracted several times
with CH2Cl2. The collected organic phase was washed with
conc. aq. NaHCO3, water, dried with MgSO4 and the solvent
removed under reduced pressure. The crude product was
purified as outlined in the following text.
1,10-Phenanthroline(4,7)-phenyl(40):{1-oxa-3-(phenyl-300,500-
diylpropyl(300,500}G1/2x:(1-oxa-4-oxa-7-oxa-10-oxaundecane)4-
cascadane (LG1)23. Prepared from 1 (70.0 mg, 0.19 mmol), and
dendritic bromide 2 (199.8 mg, 0.40 mmol). Gradient column
chromatography (SiO2, CH2Cl2–MeOH, 70 : 1 to 10 : 1)
yielded LG1 (158.0 mg, 69%) as a colourless oil. 1H NMR
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Radiotracer experiments
recorded in time domain mode. The gate width of the intensi-
fier was set to be 2 ns and the stepwidth between the single
spectra were 25 ps. For details of the used system see also
ref. 25.
Dpp-ligands were labelled with 64Cu using 64CuCl2. To 200 ml of
the ligand solution (1 mM ligand in 0.05 M 2-[N-morpholino]-
ethanesulfonic acid (MES)–NaOH buffer, pH = 5.4–7.4)
250 kBq of 64CuCl2 dissolved in buffer was added. Formation
kinetics and labelling yields of the copper complexes were
assayed using reverse phase C18 TLC plates developed in
acetonitrile (0.1% TFA)–water (0.1% TFA) = 4 : 1. Radio-
TLC chromatograms were scanned using a Radioisotope Thin
Layer Analyzer (Rita Star, raytest). HPLC runs were performed
on a Knauer WellChrom system consisting of an interface box, a
Acknowledgements
This work is part of D31 COST action ‘‘Organising
Non-Covalent Chemical Systems with Selected Functions’’.
The authors are indebted to Ms K. Landrock for their careful
experimental assistance.
HPLC-pump K-1001,
UV-detector U-2501 and
a
Solvent Organizer K-1500, an
a
home-made g-ray detector
References
(well-type, NaI(Tl) crystal). Eluent A: acetonitrile containing
0.1% trifluoroacetic acid, eluent B: water containing 0.1%
trifluoroacetic acid. Column: Jupiter 4 m C18 90 A (Pheno-
menex), 250 mm ꢂ 4.6 mm; gradient elution: 10 to 70% A in 20
min, 70 to 100% A in 25 min, 1 mL minꢁ1. Information about
the lipophilicity of the 64Cu complexes of the dendritic ligands
has been obtained by distribution measurements in water/
1-octanol systems. The experiments were performed with
1 mM solution of the ligands in buffered solution (0.05 M
MES/NaOH, pH = 5.4–7.4). The aqueous solution was spiked
with 64CuCl2. The distribution experiments were carried out at
25 ꢃ 1 1C in microcentrifuge tubes (2 cm3) by means of
mechanical shaking. The phase ratio V(1-octanol) : V(aq) was
1 : 1 (0.5 cm3 each). The shaking time was chosen as 30 min.
After extraction, all samples were centrifuged and the phases
separated. The copper concentration in both phases was deter-
mined radiometrically using g-radiation [64Cu, NaI(Tl) scintilla-
tion automatic gamma counter 1480, Wizard 300, PerkinElmer].
The results are means of three independent experiments.
1 (a) G. R. Newkome, C. N. Moorefield and F. Vogtle, Dendrimers
¨
and Dendrons, Wiley-VCH, Weinheim, 2001; (b) Dendrimers and
Other Dendritic Polymers, ed. J. M. J. Frechet and D. A. Tomalia,
´
Wiley, Chichester, 2001; (c) Dendrimers V, Top. Curr. Chem., ed.
C. A. Schalley and F. Vogtle, 2003, vol. 228, and previous volumes
¨
I–IV; (d) C. R. Chim., ed. D. Astruc, 2003, vol. 6, pp. 709–1212; (e)
Tetrahedron, ed. D. K. Smith, 2003, vol. 59, pp. 3787–4024; (f) P. J.
Gittings and L. J. Twyman, Supramol. Chem., 2003, 15, 15–23; (g)
F. Vogtle, G. Richardt and N. Werner, Dendritische Molekule,
¨
Teubner, Wiesbaden, 2007.
¨
2 (a) F. M. MacDonnel and S. Bodige, Inorg. Chem., 1996, 35,
5758–5759; (b) S. Bodige, A. S. Torres, D. J. Maloney, D. Tate, G.
R. Kinsel, A. K. Walker and F. M. MacDonnel, J. Am. Chem.
Soc., 1997, 119, 10364–10369; (c) F. M. MacDonnel, M.-J. Kim
and S. Bodige, Coord. Chem. Rev., 1999, 185/186, 535–549; (d)
M.-J. Kim, F. M. MacDonnel, M. E. Gimon-Kinsel, T. Du Bois,
N. Asgharian and J. C. Griener, Angew. Chem., Int. Ed., 2000, 39,
615–619; (e) F. M. MacDonnel, M. D. Meser Ali and M.-J. Kim,
Comments Inorg. Chem., 2000, 22, 203–225; (f) F. M. MacDonnell,
M. J. Kim, K. K. Wouters and R. Konduri, Coord. Chem. Rev.,
2003, 242, 47–58.
3 (a) S. Serroni, S. Campagna, A. Juris, M. Venturi, V. Balzani and
D. Denti, Gazz. Chim. Ital., 1994, 124, 423–427; (b) M. Kimura, T.
Shiba, T. Muto, K. Hanabusa and H. Shirai, Tetrahedron Lett.,
2000, 41, 6809–6813; (c) N. D. McClenaghan, R. Passalacqua, F.
Loiseau, S. Campagna, B. Verheyde, A. Hameurlaine and W.
Dehaen, J. Am. Chem. Soc., 2003, 125, 5356–5365; (d) H. Chao,
Z.-R. Qiu, L.-R. Cai, H. Zhang, X.-Y. Li, K.-S. Wong and L.-N.
Ji, Inorg. Chem., 2003, 42, 8823–8830.
4 (a) D. Tzalis and Y. Tor, Tetrahedron Lett., 1996, 46, 8293–8296;
(b) Y. Tor, C. R. Chim., 2003, 6, 755–766.
5 U. Luning, J. P. W. Eggert and K. Hagemann, Eur. J. Org. Chem.,
¨
2006, 2747–2752.
6 (a) J.-F. Nierengarten, D. Felder and J.-F. Nicoud, Tetrahedron
Lett., 1999, 40, 273–276; (b) N. Armaroli, C. Boudon, D. Felder,
J.-P. Gisselbrecht, M. Gross, G. Marconi, J.-F. Nicoud, J.-F.
Nierengarten and V. Vicinelli, Angew. Chem., Int. Ed., 1999, 38,
3730–3733; (c) J.-F. Nierengarten, C. R. Chim., 2003, 6, 725–733;
(d) E. Gumienna-Kontecka, Y. Rio, C. Bourgogne, M. Elhabiri, R.
Louis, A.-M. Albrecht-Gary and J.-F. Nierengarten, Inorg. Chem.,
2004, 43, 3200–3209.
UV/Vis and EPR spectroscopy
UV/Vis spectra were measured on a double beam Jasco Cary
instrument in a thermostated sample holder. Titration experi-
ments were done in aqueous solution at 20 1C in a standard
quartz cell. To 2 ml of a 0.1 mM Cu(NO3)2 solution were
added 1–5 equivalents of ligand in 0.02 ml portions of a 1 mM
ligand solution. After each step 0.2 ml of the sample were
diluted in 1 : 1 ratio with DMF and frozen in liquid nitrogen
for the EPR measurement. EPR spectra were recorded on a
Bruker Elexsys E500 spectrometer at 120 K. Spectral
parameters were determined by simulation using the program
XSophe.24
7 H. Stephan, G. Geipel, G. Bernhard, P. Comba, G. Rajaraman, U.
Hahn and F. Vogtle, Eur. J. Inorg. Chem., 2005, 4501–4508.
Time-resolved laser-induced fluorescence spectroscopy (TRLFS)
¨
8 For hydrophilic bipyridine based dendrons see: J. Issberner, F.
For time resolved fluorescence measurements the samples were
excited with laser pulses of 130 femtoseonds pulse duration
and 1 kHz repetition rate. For generation of the laserpulses an
oscillator (Millenia pumped Tsunami, Spectra Physics) –
amplifire (Merlin pumped Spitfire, Spectra Physics) system
was used. The excitation wavelength was set to be 266 nm (3rd
harmonic of the 800 nm Spitfire output). The energy of the
laser pulses was B150 mJ. The emitted fluorescence was
measured in a right angle setup using a combination of a
spectrograph (2300i, Acton Research) and an intensified CCD
camera system (PicoStar HR, LaVision). The spectra were
¨
Vogtle, L. De Cola and V. Balzani, Chem.–Eur. J., 1997, 3,
706–712.
9 (a) D. K. Smith, J. Chem. Soc., Perkin Trans. 2, 1999, 1563–1565;
(b) Y. Rio, J.-F. Nicoud, J.-L. Rehspringer and J.-F. Nierengarten,
Tetrahedron Lett., 2000, 41, 10207–10210.
10 (a) P. J. Blower and J. S. Zweit, Nucl. Med. Biol., 1996, 23,
957–980; (b) Handbook of Radiopharmaceuticals: Radiochemistry
and Applications, ed. M. J. Welch and C. S. Redvanly, J. Wiley &
Sons, Chichester, 2003.
11 (a) J. S. Lewis and M. J. Welch, in Technetium, Rhenium and other
Metals in Chemistry and Nuclear Medicine, ed. M. Nicolini and
U. Mazzi, SGE Editoriali, Padova, Italy, 2002, pp. 23–33; (b) I.
Novak-Hofer and P. A. Schubiger, Eur. J. Nucl. Med. Mol.
ꢀc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2008 New J. Chem., 2008, 32, 2016–2022 | 2021

View Article Online
Imaging, 2002, 29, 821–830; (c) S. V. Smith, J. Inorg. Biochem.,
2004, 98, 1874–1901; (d) H. A. Williams, S. Robinson, P. Julyan,
J. Zweit and D. Hastings, Eur. J. Nucl. Med. Mol. Imaging, 2005,
32, 1473–1480; (e) Technetium, Rhenium and other Metals in
Chemistry and Nuclear Medicine, ed. U. Mazzi, SGE Editoriali,
Padova, Italy, 2006.
18 P. Comba, T. W. Hambley and N. Okon, ‘‘MOMEC, a molecular
modeling package for inorganic compounds’’, University of
Heidelberg, www.comba-group.uni-hd.de, 1997.
19 P. V. Bernhardt and P. Comba, Inorg. Chem., 1992, 31, 2638–2644.
20 (a) K. Amournjarusiri and B. J. Hathaway, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1991, 47, 1383–1385; (b) M. T. Miller, P. K.
Gantzel and T. B. Karpishin, Inorg. Chem., 1998, 37, 2285–2290; (c)
K. J. Catalan, S. Jackson, J. D. Zubkowski, D. L. Perry, E. J. Valente,
L. A. Felin and A. Polanco, Polyhedron, 1995, 14, 2165–2171.
21 D. Vulpius, G. Geipel, L. Baraniak and G. Bernhard, Spectrochim.
Acta, Part A, 2006, 63, 603–608.
22 (a) M. S. Reddy, K. Ram and M. G. R. Reddy, Indian J. Chem.,
Sect. A: Inorg., Bio-inorg., Phys., Theor. Anal. Chem., 1989, 28,
437–439; (b) G. Anderegg, Helv. Chim. Acta, 1959, 42, 344–349; (c)
D. Chakraborty and P. Bhattacharya, Indian J. Chem., Sect. A:
Inorg., Bio-inorg., Phys., Theor. Anal. Chem., 1996, 35, 37–40; (d)
S. Abbasi, Pol. J. Chem., 1984, 58, 61–64.
12 A. Gupta, S. Seifert, R. Syhre, M. Scheunemann, P. Brust and B.
Johannsen, Radiochim. Acta, 2001, 89, 43–49.
13 DCu is defined as the ratio of the relative amounts of the CuII
species present in the organic and aqueous phase. Radio-TLC and
Radio-HPLC gave no evidence of free copper(II) in the aqueous
and organic phase. Thus, DCu represents the distribution coefficient
of the 64CuII-dpp complexes.
14 K. Schwochau, Technetium. Chemistry and Radiopharmaceutical
Applications, Wiley-VCH, Weinheim, 2000.
15 (a) B. J. Hathaway, in Comprehensive Coordination Chemistry, ed.
G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon,
Oxford, 1987, vol. 5, pp. 533–594; (b) R. Mukherjee, in
Comprehensive Coordination Chemistry II: From Biology to Nano-
technology, ed. J. A. McCleverty and T. J. Meyer, Elsevier–
Pergamon, New York, 2004, vol. 5, pp. 747–910.
16 H. C. Lip and R. A. Plowman, Aust. J. Chem., 1975, 28, 779–792.
17 G. Murphy, C. Murphy, B. Murphy and B. J. Hathaway, J. Chem.
Soc., Dalton Trans., 1997, 2653–2660.
23 Cascadane-nomenclature according to J. H. Friedhofen and F.
Vogtle, New J. Chem., 2006, 30, 32–43.
¨
24 (a) D. Wang and G. R. Hanson, J. Magn. Reson., Ser. A, 1995,
117, 1–8; (b) D. Wang and G. R. Hanson, Appl. Magn. Reson.,
1996, 11, 401–415.
25 G. Geipel, M. Acker, D. Vulpius, G. Bernhard, H. Nitsche and T.
Fanghanel, Spectrochim. Acta, Part A, 2004, 60, 417–424.
¨
ꢀc
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2022 | New J. Chem., 2008, 32, 2016–2022