Lanthanide directed self-assembly of highly luminescent supramolecular "peptide" bundles from α-amino acid functionalized 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligands

Article abstract of DOI:10.1021/ic502384w

Ligands containing the [2,6-bis(1,2,3-triazol-4-yl)pyridine] (btp) motif have recently shown promise in coordination chemistry. The motif is synthesized via the Cu(I)-catalyzed "click" reaction and can be conveniently functionalized when compared to other

Full text of DOI:10.1021/ic502384w

Article
pubs.acs.org/IC
Lanthanide Directed Self-Assembly of Highly Luminescent
Supramolecular “Peptide” Bundles from α‑Amino Acid
Functionalized 2,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) Ligands
Joseph P. Byrne,† Jonathan A. Kitchen,†,‡ John E. O’Brien,† Robert D. Peacock,§
and Thorfinnur Gunnlaugsson*,†
†School of Chemistry and Trinity Biomedical Sciences Institute, Trinity College Dublin, University of Dublin, Pearse Street, Dublin 2,
Ireland
‡Chemistry, Faculty of Natural & Environmental Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, U.K.
§School of Chemistry, University of Glasgow, Glasgow, G12 8QQ, Scotland, U.K.
S
* Supporting Information
ABSTRACT: Ligands containing the [2,6-bis(1,2,3-triazol-4-yl)pyridine] (btp) motif have recently shown promise in
coordination chemistry. The motif is synthesized via the Cu(I)-catalyzed “click” reaction and can be conveniently functionalized
when compared to other terdentate chelating motifs. Ligand 1 was synthesized and shown to sensitize Eu(III) and Tb(III)
excited states effectively. The use of these ions to synthesize self-assembly structures in solution was investigated by carrying out
1
both H NMR and photophysical titrations. The latter were used to determine high binding constants from changes in the
absorption, ligand emission (fluorescence), and lanthanide-centered emission. A small library of amino acid derivatives of 1,
ligands 3, were prepared upon coupling reactions with Gly, Ala, Phe, and Trp methyl esters, with a view to introducing
biologically relevant and chiral moieties into such ligands. All of these derivatives were shown to form stable, emissive Ln(III)
self-assemblies, emitting in the millisecond time range, which were studied by means of probing their photophysical properties in
organic solutions using lanthanide ion titrations. All the Tb(III) complexes, with the exception of Trp based derivatives, gave rise
to highly luminescent and bright complexes, with quantum yields of Tb(III) emission of 46−70% in CH3CN solution. In
contrast, the Eu(III) complexes gave rise to more modest quantum yields of 0.3−3%, reflecting better energy match for the
Tb(III) complexes, and hence, more efficient sensitization, as demonstrated by using low temperature measurements to
determine the triplet state of 1.
synthetically flexible motif has in modern supramolecular
chemistry.17 Herein, we describe our recent efforts into
developing self-assembly structures from amino acid derived
btp ligands, by employing lanthanide directed synthesis. A key
attractive feature of the btp ligands is that they can be prepared
in a facile one-pot synthesis using the Cu(I)-catalyzed alkyne−
azide “click” (CuAAC) reaction from a wide range of azide
substrates, allowing for convenient derivatization and variety in
such ligands.2,10,18,19 The coordination chemistry of ligands
containing this motif has been studied with many metal ions
including Ni(II),20 Cu(I),21 Cu(II),2,22 Zn(II),23 Ag(I),2
INTRODUCTION
■
The 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) motif has attracted
significant attention in recent years1,2 (e.g., from researchers
such as Crowley,2,3 Flood,4−6 Hecht,7−10 and Schubert11−15) as
a class of pyridine-centered terdentate ligands with applications
in supramolecular and coordination chemistry. The btp ligands
possess similar bond lengths and angles to the widely used
2,2′;6′,2″-terpyridine (terpy) binding motif, and as such are
highly desirable alternatives to terpy in coordination chem-
istry;16 however, their exploitation has been somewhat limited
to date. We have recently reviewed the relatively small amount
of literature surrounding the use of the btp motif in
supramolecular and coordination chemistry, and in the process,
have highlighted the potential that such a modular and
Received: October 1, 2014
© XXXX American Chemical Society
A
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a
Scheme 1. Synthesis of Ligands 1−3
a
(i) NaN3, rt, 1 h, DMF/H2O; (ii) CuSO4·5H2O, sodium ascorbate, K2CO3, DMF/H2O, rt, 18 h; (iii) SOCl2, Δ, 18 h; (iv) Et3N, rt, 1 h; (v)
CH2Cl2, rt, 18 h.
Ir(III),20 Pt(II),14,24 Pd(II),25 Pb(II),26 Fe(II),1,10,23 and
Ru(II).1,11−16,18,23,27−29 The most studied of these, by far, is
Ru(II). Hecht and co-workers have prepared a range of mono-
and dileptic Ru(II)−btp complexes and tuned their electro-
chemical properties upon variation of the ligand.23 Schubert
and co-workers compared such systems’ photophysical behavior
with analogous terpy-based systems and also reported mixed
heteroleptic terpy−btp complexes with intermediate proper-
ties.11,12,27 We recently published the synthesis and character-
ization of two btp ligands, 1 and 2, and studied their
coordination chemistry with a number of d-block metals
(namely, Ru(II), Ir(III), Ni(II), and Pt(II)), as well as their
photophysical properties and the electrochemical properties of
the Ru(II) complexes.20 We also demonstrated that these
ligands can give rise to the formation of metallogels with some
of these ions. There is, however, a surprising paucity in the
literature of examples of btp systems coordinating the f-block
lanthanide(III) (Ln(III)) ions. Ln(III) have been exploited for
the formation of elegant self-assembly systems such as
polymetallic helicates.30 They possess unique photophysical
and magnetic properties, which make their study desirable for
optoelectronic and bioimaging applications.31−33 Hence, the
need to explore the btp motif within lanthanide chemistry
prompted us to develop the work presented here, focusing on
the use of Ln(III) ions to direct, through their high
coordination requirements, the formation of novel functional
and luminescent supramolecular self-assembly structures.
In the past, we have shown how Ln(III) is capable of forming
self-assemblies, such as bundles,34 helicates,35 half-helicates,36
and interlocked systems such as a [3]catenane,37 with
dipicolinic acid (dpa) derivatives, as well as luminescent
Langmuir−Blodgett films38,39 and supramolecular gels based on
the terpy motif.40 Indeed, many researchers have shown how
other pyridine-centered terdentate ligands, particularly motifs
which contain heterocyclic rings, have been widely exploited to
form luminescent Ln(III)-directed structures, including the
benzimidazole-based systems studied at length by Piguet,
pyridine-bis(tetrazolate) systems developed by Mazzanti and
co-workers.47,48 We herein present an investigation of the self-
assembly behavior of btp ligands 1, and 3 with Eu(III) and
Tb(III) ions, the outcome of which we describe as lanthanide
directed synthesis of “peptide bundles”. Flood et al. displayed
that btp compounds can form stable coordination compounds
with Eu(III), sensitizing characteristic line-like emission from
the metal center via the “antenna effect”,1 while Hecht and co-
workers also reported Eu(III) complexes.10 “Back-to-back”
ditopic btp ligands have also been used to sensitize Ln(III)
luminescence.49 Brunet and co-workers described covalently
attaching btp-containing organic phosphonates to the surface of
the γ-zirconium phosphate by topotactic exchange to produce a
solid host that could efficiently sensitize the emission of Ln(III)
ions.19,50 O’Reilly and co-workers used Eu(III) coordinated by
btp ligands containing RAFT polymerization agents to
template “star-branched” polymeric structures.18 We herein
present an investigation of the self-assembly behavior of btp
ligand 1 with Eu(III) and Tb(III) ions. More recently, a
number of Ln(III) complexes of bis(benzyl)-btp have been
evaluated as chemically stable bioimaging agents, suggesting the
potential utility of such compounds for biological applica-
tions.51 With the aim of introducing biorelevant moieties into
these compounds, we prepared derivatives of 1 with appended
amino acid methyl ester residues, ligands 3. Amino acids are
small, convenient, and mostly chiral residues, which are
ubiquitous in nature, acting as the building blocks for peptides
and proteins. Their incorporation into btp ligands provides a
facile route toward a range of derivatives 3, which were all
chiral, apart from 3-Gly, which contains the optically inactive
Gly residue. The ligands were prepared through straightforward
amide coupling reactions. The synthesis and characterization of
seven such ligands and their Eu(III) and Tb(III) complexes are
reported as well as their self-assembly behavior in CH3CN
solution, allowing the determination of global stability
constants for various stoichiometric species. Such self-assembly
structures can be considered as ternary structural building units
with the potential to function as a foundation for tertiary
peptide structural mimics; we have recently demonstrated that
peptide conjugates (of up to 20-mers) can form highly ordered
Bunzli, and co-workers,41−43 the pybox ligands (2,6-bis-
̈
(oxazoline)pyridine) employed by the group of de Betten-
court-Dias,44−46 and the highly emissive Ln(III) complexes of
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1
Figure 1. H NMR spectra (600 MHz, DMSO-d6) of ligands (a) 3-Gly, (b) 3-L-Ala, (c) 3-L-Phe and (d) 3-L-Trp (resonance at 10.5 ppm from
indolyl NH not shown). Resonances are labeled as follows: q (amide NH), r (α-protons in amino acid residue), s (−OCH3), t (triazolyl CH), u (3-
○
and 5-pyridyl CH), v (4-pyridyl CH), w and x (phenyl CH), y (CH2), (peaks particular to amino acid side-chain). (Spectra of 3-D-Ala, 3-D-Phe,
and 3-D-Trp were identical to their enantiomers and are shown in Supporting Information.)
folded structures through the use of lanthanide directed
synthesis, where the changes in the lanthanide centered
emission were monitored upon folding.52
symmetry, only differing significantly from the previously
reported spectra of 1 and 220 in the presence of resonances
arising from the amino acid moieties, with the spectra of
enantiomeric pairs being identical (cf. Supporting Informa-
tion); hence only the ligands containing two L-amino acid
residues as “arms” will be discussed here. The 1H NMR
spectrum (600 MHz, DMSO-d6) of 3-Gly, shown in Figure 1a,
displayed a resonance relating to the methyl ester protecting
group at 3.65 ppm (labeled s), a doublet arising from the Gly
CH2 at 4.02 ppm (r) and a signal at 5.79 ppm from the
methylene linker between the triazole and phenyl rings (y). The
aromatic region consisted of a pair of phenyl doublets at 7.46
and 7.89 ppm, two pyridyl resonances, overlapping as a
multiplet from 7.93−8.05 ppm (u and v), a triazolyl resonance
at 8.72 ppm (t), and a triplet resonating at 8.97 ppm assigned
to the amide NH protons (q). All NH proton resonances were
assigned by NH COSY, see Supporting Information. ESI MS
analysis confirmed the identity of the desired product. As
expected, the 1H NMR spectrum (600 MHz, DMSO-d6) of 3-L-
Ala was very similar to that of the Gly derivative above,
differing only in the presence of the chiral side-chain,
resonating at 1.40 ppm as a doublet (marked in Figure 1b
with a ○) and a resonance centered at 4.48 ppm arising from
the adjacent chiral CH (r) of the Ala residue. The NH
resonance was also shifted to lower frequency, appearing as a
doublet at 8.81 ppm. Similarly, the 3-L-Phe 1H NMR spectrum
(600 MHz, DMSO-d6, Figure 1c) closely resembled the Ala
derivative described above, the benzyl CH2 protons appearing
as multiplets between 3.05−3.19 ppm and the α-protons at 4.66
RESULTS AND DISCUSSION
■
Ligand Synthesis, Characterization, and Photophys-
ical Properties. Ligands 1 and 2 were prepared using a one-
pot deprotection/“click” CuAAC reaction in high purity and
moderate yields of 53% and 63%, respectively, as previously
reported.20 The carboxylic acid ligand 2 proved to have poor
solubility in many organic solvents. Ligand 1, however, was
readily soluble in a range of solvents. Methyl ester-protected
amino acids were coupled with both carboxylic acid groups of
ligand 2 in order to produce a small library of bis-substituted
btp ligands, 3 (see table in Scheme 1). This was achieved as
shown in Scheme 1 by first converting 2 into its acid chloride
derivative with thionyl chloride. The methyl ester-protected
amino acids (as HCl salts), Gly, Ala, Phe, and Trp (the latter of
which has been employed in the literature as a naturally
occurring antenna for Tb(III) emission53,54) were first stirred
with Et3N in CH2Cl2 for an hour, before being added to the
acid chloride and stirred at room temperature. Both the L- and
the D-enantiomers of the chiral amino acids Ala, Phe, and Trp
were used. Solvent was removed and the product was triturated
with cold CH3OH, furnishing the amide products in moderate
yields (47−61%) and high purity upon filtration (as confirmed
by elemental analysis).
1
The simplicity of the H NMR spectra (600 MHz, DMSO-
d6) of 3 confirmed the formation of ligands possessing C2
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ppm with further resonances occurring at 7.15−7.20 and 7.25−
7.30 ppm, for the aryl protons. Again, the amide NH resonance
(q) appeared at a different chemical shift of 8.86 ppm.
absorption profile with a maximum centered at 223 nm, a
shoulder around 235 nm, and a sharp peak at λmax = 290 nm
overlapping with a broader band resembling the 300 nm-band
in all of the other ligands. This is consistent with the absorption
profile of Trp-containing ligands reported by us previously.55
Upon excitation into either band, 1 displayed a broad
fluorescence band centered at 335 nm. Ligands 3 all showed
a similar emission band. Excitation spectra of this emission
across the range of ligands were practically identical and
matched the general structure of the absorption profiles, the
exception being 3-Trp, where the excitation spectrum
resembled just those bands associated with the btp “core”
and not those assigned to the Trp moieties (viz. the bands at
223 and 290 nm). This suggested that fluorescence arises
largely from the btp moiety of these ligands. CD spectra of
ligands 3 were weak and poorly resolved, but did show subtle
differences between the enantiomers.
Preparation and Photophysical Studies of Ln(III)
Complexes. Having synthesized the above ligands 1 and 3,
both Eu(III) and Tb(III) complexes were prepared from these
ligands. This was achieved using microwave irradiation of 1 or 3
in the presence of 0.35 equiv of Eu(III) or Tb(III) triflate salt in
CH3OH solution at 70 °C for 20 min. The complexes were
recovered as solids upon diffusion of Et2O into the CH3OH
solution, with successful complexation being confirmed by
MALDI+ mass spectrometry, Table 1, where the characteristic
isotopic distribution patterns of the measured peaks matched
the calculated spectra (see Supporting Information). Evidence
was also seen in the MALDI+ spectra of fragmentation into the
1:2 and, in some cases, 1:1 stoichiometries. These peaks are
listed with the experimental details. Unfortunately, we were
unable to obtain crystals of these systems of sufficient quality
for crystal structural analysis, and hence, their structural nature
was probed by using solution state analysis only, such as UV−
vis absorption, emission and NMR analysis.
1
The H NMR spectrum (600 MHz, DMSO-d6) of 3-L-Trp
was the most complicated of the ligands described herein, as is
evident from Figure 1d, with aliphatic resonances similar to
those seen for 3-L-Phe; the indole peaks appeared as a pair of
triplets at 6.98 and 7.06 ppm and three doublets at 7.19, 7.32,
and 7.55 ppm. These resonances were well resolved from the
two phenyl CH doublets at 7.43 and 7.84 ppm (labeled x and
w, respectively), the pyridyl multiplet at 7.96−8.03 ppm and the
triazolyl resonance at 8.70 ppm (t). 3-L-Trp showed two NH
resonances. The amide signal appeared as a doublet at 8.81
ppm, while the indole NH resonated at a higher frequency of
10.80 ppm (see Supporting Information). ESI MS analysis
confirmed the identity of all the aforementioned ligands.
General Photophysical Properties of 3. Ligands 1, 3-
Gly, 3-Ala, and 3-Phe showed broadly similar UV−vis
absorption profiles when recorded in CH3CN solution, Figure
2, with distinct bands centered at 300 nm, tentatively assigned
to n → π* transitions from the btp core, and 235 nm, assigned
to π → π* transitions from the various aromatic rings in the
structures. For 3-Phe, the lower wavelength band was broader
and only slightly shifted by a few nanometres relative to the
parent ligand 1 (λmax = 237 nm). 3-Trp shows a broader
Compared to the UV−vis absorption spectra of the relevant
ligands, upon complexation with either Eu(III) or Tb(III), the
ligand band centered at 300 nm (assigned to the btp center)
was red-shifted to ∼313 nm, indicating the successful formation
of the complexes. IR spectra were also altered upon formation
of the complexes.
All the complexes showed characteristic Ln(III)-centered
emission spectra upon excitation of the pyridine moiety,
confirming the ability of the btp ligands to sensitize the Ln(III)
excited states in these complexes successfully (see Supporting
Information), while, in contrast, ligand fluorescence was
quenched. For Eu(III) complexes, characteristic line-like
emission bands were observed at λ = 579, 593, 617, 650, and
5
7
694 nm, assigned to the D0 → FJ transitions (J = 0−4), as
demonstrated in Figure 3a, for [Eu·(3-L-Phe)3](CF3SO3)3. In
the case of the Tb(III) complexes, Tb(III)-centered emission
bands were observed at 490, 545, 585, and 621 nm, assigned to
5
7
the D4 → FJ transitions (J = 6−3) of Tb(III), as well as
weaker bands arising from the transitions to the J = 2−0 states,
Figure 3b. The sensitization process was further confirmed by
recording the excitation spectra of the various Ln(III)
complexes, which were seen to structurally match the
absorption spectra. Moreover, the complexes were clearly
luminescent to the naked eye, even at low concentrations, upon
irradiation with a hand-held UV lamp, as is demonstrated by
the photographs of CH3CN solutions of Ln(III) complexes
shown as insets in Figure 3.
Figure 2. UV−vis absorption, excitation and fluorescence spectra of
ligands 1, 3-Gly, 3-L-Ala, 3-L-Phe, and 3-L-Trp in CH3CN solution at
23 °C (the spectra of 3-D-Ala, 3-D-Phe, and 3-D-Trp are shown in
Supporting Information).
D
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Table 1. Calculated and Experimental HRMS (MALDI+) Signals for the Various Ln(III) Complexes of Ligands 1 and 3
complex
calculated m/z
experimental m/z, MALDI+
+
[Eu·(1)3](CF3SO3)2
1978.369
2320.498
2404.591
2404.591
2860.779
2860.779
3094.845
3094.845
1978.378
2320.489
2404.599
2404.571
2860.783
2860.787
3094.852
3094.860
+
[Eu·(3-Gly)3](CF3SO3)2
[Eu·(3-L-Ala)3](CF3SO3)2
[Eu·(3-D-Ala)3](CF3SO3)2
[Eu·(3-L-Phe)3](CF3SO3)2
[Eu·(3-D-Phe)3](CF3SO3)2
[Eu·(3-L-Trp)3](CF3SO3)2
[Eu·(3-D-Phe)3](CF3SO3)2
+
+
+
+
+
+
+
[Tb·(1)3](CF3SO3)2
1984.373
2326.502
2410.596
2410.596
2866.783
2866.783
3100.849
3100.849
1984.370
2326.509
2410.602
2410.602
2866.784
2866.773
3100.842
3100.862
+
[Tb·(3-Gly)3](CF3SO3)2
[Tb·(3-L-Ala)3](CF3SO3)2
[Tb·(3-D-Ala)3](CF3SO3)2
[Tb·(3-L-Phe)3](CF3SO3)2
[Tb·(3-DPhe)3](CF3SO3)2
[Tb·(3-L-Trp)3](CF3SO3)2
[Tb·(3-D-Trp)3](CF3SO3)2
+
+
+
+
+
+
Figure 3. (a) UV−vis absorption (red), sensitized Eu(III) luminescence (magenta), and excitation spectra (dashed magenta) of [Eu·(3-L-
Phe)3](CF3SO3)3 in CH3CN; (b) UV−vis absorption (red), sensitized Tb(III) luminescence (magenta), and excitation spectrum (dashed blue) of
[Tb·(1)3](CF3SO3)3 in CH3CN; insets: photographs of the complex solutions under UV irradiation, showing characteristic visible emission.
In our previous work,34−36,39,56−58 we have shown that
acyclic ligands based on the dpa motif, which have been
derivatized with chiral chromophores as antennae, can give rise
to sensitized Ln(III) polarized emission, upon complexation
with visibly emitting Ln(III) ions and subsequent excitation of
the antennae. This we have demonstrated by using circularly
polarized luminescence (CPL) spectroscopy, by observing the
chiroptical emission of Sm(III), Tb(III), and Eu(III), where
such enantiomerically pure complexes give rise to spectra that
are mirror images with opposite signs for the various
transitions. Similarly, other researchers have demonstrated the
same for either cyclic or acyclic ligands.59−66 As all of the
ligands presented here (except 3-Gly) possess chiral amino
acids adjacent to phenyl antennae, we attempted to record the
CPL spectra of these complexes. However, they only gave low
intensity CPL spectra for the Ln(III)-centered emission, the
best results being observed for [Tb·(3-L-Trp)3](CF3SO3)3 and
[Tb·(3-D-Trp)3](CF3SO3)3, showing only very weak signals
(see Supporting Information), sufficient only to confirm these
complexes were formed as a pair of enantiomers. Unlike the
aforementioned complexes, where the chiral antennae were
close to the Ln(III) ion, giving rise to strong CPL emission, in
the case of the complexes reported here, the chirality of the
amino acid side chain seems to be too remote from the binding
site to have any significant impact on the nature of the complex
and hence the CPL signal observed.
In order to further understand the energy transfer process of
the Ln(III) complexes, the energy levels of the relevant excited
states of ligand 1 (singlet and triplet states) were determined.
The energy of S1 (singlet state) was estimated by considering
the ligand fluorescence emission with an emission band ranging
from 300−420 nm with a maximum at 335 nm (vide supra),
indicating an energy of ∼32 800 cm−1. Since the energy level of
T1 (triplet state) is insensitive to the identity of Ln(III), a
complex with Gd(III) was prepared, as described above for the
other complexes. The lowest lying excited level of Gd(III) is
located at much higher energy than Eu(III) or Tb(III) and
hence organic ligands like 1 tend not to sensitize Gd(III)-
centered emission, allowing evaluation of T1. The phosphor-
escence spectrum of [Gd·(1)3](CF3SO3)3 in CH3CN, meas-
ured at 77 K, displayed a broad structured emission with
maxima at 408, 434, 454, and 464 nm (shown in Supporting
Information). The energy of T1 was determined as ∼24 500
cm−1. These results are shown schematically in the energy level
diagram in Figure 4, which also shows the simplified energy
transfer process leading to sensitization of Ln(III) emission,
E
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measurements were carried out at low concentration (10−5 M)
due to solubility problems at higher concentrations in aqueous
media. For both ranges of complexes, the 3-Ala complexes
possessed the longest lifetimes in aqueous environment, with τ
= 2.71
0.01 ms and 2.83
0.02 ms in H2O and D2O,
respectively, for [Eu·(3-L-Ala)3](CF3SO3)3, while the Eu(III)
complex of 1 gave τ = 1.06 0.05 ms and 1.98 0.01 ms in
the same solvents. For the Tb(III) complexes, the lifetimes
were generally shorter, with [Tb·(3-D-Ala)3](CF3SO3)3 dis-
playing lifetimes of 1.68 0.08 ms and 1.65 0.03 ms in H2O
and D2O, respectively, and the complex with 1 giving lifetimes
of τ = 0.81 0.14 ms and 0.85 0.28 ms in the same solvents.
These values are similar to those commonly seen for dpa based
ligands. These data were next used to determine hydration
states of these complexes, q, by utilizing the Parker-modified
Horrocks equation.69,70 As can be seen from Table 2, all the
complexes seem to be coordinatively saturated; indicating the
successful formation of 1:3 (metal:ligand) complexes as the
dominant (or the only) stoichiometry, where the hydration
state is ∼0. Here, each of the ligands can act as terdentate
ligands, giving a total coordination of nine around the Ln(III)
ions with no metal bound water molecules.
Figure 4. Schematic energy level diagram of the simplified energy
transfer processes involved in ligand 1 sensitizing Eu(III)- and Tb(III)-
centered luminescence.
occurring via the initial excitation of the S1 followed by
intersystem crossing to T1. The energy of T1 closely matches
5
5
that of the Eu(III) D0 and Tb(III) D4 states, allowing for
energy transfer and population of the Ln(III) excited states.
Analysis of these values show that the energy differences
between the triplet energy level of 1, and the relevant emitting
Ln(III)-centered levels were approximately 7000 and 4000
cm−1 for Eu(III) and Tb(III) respectively; such a difference is
too high to allow effective back energy transfer to either of
these systems.67 This was further demonstrated by recording
the Tb(III) emission in aerated and degassed solution, both of
which gave rise to identical spectra, indicating that no
quenching by O2 was observed.68 However, the T1 level is
also well positioned to sensitize higher energy states of the
Eu(III) 5DJ manifold, which may allow for various nonradiative
The luminescence quantum yields, Φ, were also measured for
the Eu(III)- and Tb(III)-centered emission by a relative
method, by comparison to secondary standards Cs3[Ln·
(dpa)3] in CH3CN, Table 2.71,72 The quantum yields of the
Eu(III) complexes with 1 and 3 were very modest, ranging
from 2.1−3.0% for the Gly, Ala, and Phe derivatives. Ligands 3-
Trp were significantly lower (<0.5%), most likely because the
Trp antenna is a poor sensitizer for Eu(III). These results
demonstrate that these 1:3 complexes possess comparable
photophysical properties to those seen for 1:3 complexes
formed from the dpa systems.56,59,74 To our surprise, however,
the quantum yields of the Tb(III) complexes were much
higher, Table 2, ranging between 6.3−70% in CH3CN (with
the Trp derivatives, once again, being much less bright than the
rest of the systems). These quantum yields are comparable to
those seen for bis(tetrazolate)pyridyl systems reported by
Mazzanti and co-workers.47,48 The formation of such highly
luminescent complexes can possibly be accounted for by the
processes before the 5D0
→
7FJ transitions occur with
associated luminescence, hence the sensitization of the emissive
Ln(III) excited state may prove less efficient for Eu(III) than
Tb(III) complexes.
Luminescence lifetimes (τ) of these complexes were
determined in H2O and D2O by fitting the Ln(III) excited
state decay profiles of the most intense Ln(III) transitions (the
5D0 → 7F2 band centered at 616 nm for Eu(III), and the 5D4 →
7F6 band centered at 490 nm for Tb(III), respectively). These
were best fitted to monoexponential decay, Table 2, but the
5
well matched energy levels for sensitization of the Tb(III) D4
excited state by the btp ligands, as discussed above and
demonstrated in Figure 4. This marked differential between
Tb(III) and Eu(III) complex quantum yields is in contrast to
dpa systems. To further investigate the structure of these
Table 2. Photophysical Properties of Ln(III) Complexes of Ligands 1 and 3: Luminescence Lifetimes, Hydration States, and
Total Quantum Yields in CH3CN
[Eu·(L)3](CF3SO3)3
[Tb·(L)3](CF3SO3)3
a
b
a
b
ligand
τH O (ms)
τD O (ms)
q
( 0.5)
Φ
(%)
τH O (ms)
τD O (ms)
q
( 0.5)
Φ
(%)
70 12
53
2
2
2
2
1
1.06 0.05
1.17 0.39
2.71 0.01
2.80 0.05
2.31 0.04
2.65 0.05
1.07 0.04
0.68 0.03
1.98 0.01
1.81 0.04
2.83 0.02
2.78 0.10
2.28 0.01
2.72 0.01
1.38 0.05
1.25 0.10
0.2
0.1
2.4 0.4
3.0 0.5
2.2 0.4
2.1 0.4
2.2 0.4
2.5 0.4
0.3 0.1
0.4 0.1
0.81 0.14
1.26 0.27
1.66 0.04
1.68 0.08
1.23 0.01
1.24 0.03
0.76 0.02
0.83 0.01
0.85 0.28
1.48 0.12
1.64 0.01
1.65 0.03
1.25 0.01
1.23 0.03
0.85 0.01
0.84 0.01
−0.5
0.3
3-Gly
9
3-L-Ala
3-D-Ala
3-L-Phe
3-D-Phe
3-L-Trp
3-D-Trp
−0.3
−0.3
−0.3
−0.3
−0.1
0.5
−0.3
−0.4
−0.2
−0.3
0.4
54 10
57 10
61 11
46
11
8
2
−0.3
6.3 1.1
a
Hydration states were calculated using the equation q = A((1/τH O − 1/τD O) − B), where for Eu(III), A = 1.2, B = 0.25 and for Tb(III), A = 5.0, B
2
2
= 0.06.31,70 Quantum yields in CH3CN were estimated by a relative method,71,72 compared with Cs3[Ln·(dpa)3]73 according to the equations
b
shown in Supporting Information.
F
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1
Figure 5. H NMR spectrum (400 MHz, CD3OD) of [Eu·(3-Gly)3](CF3SO3)3, showing paramagnetically shifted resonances, compared to the
ligand spectrum.
1
Figure 6. (a) H NMR (400 MHz, CD3CN) titration of ligand 1 upon addition of Eu(CF3SO3) solution; (b) a graph showing ratios of the
integrations of the methylene resonances (labeled y) of each species as a function of equivalents of Eu(III) added; (c) schematic representation of
the interconversion between anti-anti and syn-syn conformation of 1 upon complexation.
1
complexes, we carried out H NMR analysis of 1 with Eu(III)
in CD3CN.
Figure 5 as an example, with the various peaks labeled. Most
notable shifts to lower frequency were seen for pyridyl (labeled
u′ and v′) and triazolyl (labeled t′) proton resonances, with the
3- and 5-pyridyl signal appearing at a chemical shift where
aliphatic protons are usually observed. The fact that the dipolar
shift in proton resonances is minor compared to other Eu(III)
complexes corresponds with the very small splitting observed in
1H NMR Studies of Ligand 1 upon Titration with
Eu(III). The H NMR spectra of Ln(III) complexes are often
1
very difficult to interpret as a result of the paramagnetic nature
of many of the Ln(III) ions, including Eu(III) and Tb(III),
which can broaden and shift proton resonances, sometimes
beyond recognition. In the case of some of the Eu(III)
complexes with ligands 1 and 3, the spectra were relatively well
resolved, albeit paramagnetically shifted, particularly those
resonances close to the btp binding motif. The spectrum
(400 MHz, CD3OD) of [Eu·(3-Gly)3](CF3SO3)3 is shown in
the 5D0
→
7F1 transitions; correlation between these
parameters was described in recent work by Parker and co-
workers.75,76
1
In light of the fact that the complex H NMR spectra differ
significantly from the ligand spectra, titrations were undertaken
G
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Figure 7. Titration plots of 1 v. Eu(III) in CH3CN. (a) UV−vis spectral changes; inset: experimental binding isotherms (×) and calculated isotherms
(solid lines) at various wavelengths; (b) changes in Eu(III) luminescence; inset: experimental binding isotherms (×) and calculated isotherms (solid
lines) at various wavelengths. Fluorescence spectral changes are shown in Supporting Information.
to observe the changes in the spectrum of ligand 1, and the
different self-assembly species formed in a solution of CD3CN
as a function of [Eu(III)] with a view to understanding the
geometry of the free ligand, as compared with the coordinating
ligand.
conformation of the free ligand and the ligand as part of the
complex was obtained. Consistent with the anti-anti structure
seen in the crystal structure of 1, which we have previously
published,20 the triazolyl proton did not show any through-
space interactions with the 3-pyridyl protons. This “horseshoe”
conformation was similar to that seen by other similar
compounds in the literature.2,9,22,23,78 Upon addition of 0.5
equiv of Eu(III), however, the new species showed weak
interactions between the 3-pyridyl protons and the triazolyl
resonance, consistent with the inversion of triazolyl con-
formation in the btp motif to syn-syn geometry (as schemati-
cally represented in Figure 6c), as has been previously reported
for similar systems, resulting from the nitrogen lone-pairs
binding the metal ion.10
As shown in Figure 6a, the changes in the NMR spectra were
in slow exchange on the NMR time scale, the most significant
changes occurring within the addition of 0.0 → 0.5 equiv of
Eu(III), followed thereafter by increased broadening and
complexity of signals. The resonance arising from the methyl
ester resonance in 1 (3.86 ppm, labeled z) underwent a slight
shift to higher frequency upon self-assembly, with the free
ligand signal disappearing completely by the addition of 0.5
equiv and being replaced by a signal at 3.89 ppm (labeled z′).
Concomitantly, shifts were observed in the aromatic region.
Most significant among these was the disappearance of the
triazolyl resonance at 8.40 ppm (t) upon addition of 0.5 equiv
of Eu(III); this resonance was determined by 2D NMR
spectroscopy (see Supporting Information) to overlap with one
of the phenyl CH signals at 7.23 ppm in the complex (t′). The
triplet pertaining the 4-pyridyl proton showed a significant
paramagnetic shift from 7.91 ppm (v) to 6.27 ppm (v′), an
exchange which was also complete by 0.5 equiv; the 3- and 5-
pyridyl proton signal (u) shifted dramatically to lower
frequency as well, but this is less clearly monitored as a result
of the ligand peak overlapping with one of the phenyl proton
signals, only becoming clearly resolved as a doublet (labeled u′)
at 4.54 ppm upon complexation (confirmed by selective
ROESY and HSQC, see Supporting Information). The phenyl
protons (w and x) also became more shielded, but less notably
so. These kinds of pyridyl shifts to lower frequency are similar
to those reported for dpa based ligands previously.77
Interestingly, the CH2 signal at 5.7 ppm (y) split into two
doublets upon complexation; this would suggest a locking of
the ligand “arms” into a conformation where free rotation of
this bond is no longer possible. Figure 6b shows the
interconversion of these two signals by representing the
relative integrations of the resonances marked y and y′ as a
function of equivalents of Eu(III) added.
Having shown the competency of btp ligands for binding
Ln(III) ions through formation of emissive thermal complexes
and monitoring the self-assembly of 1 with Eu(III) in CD3CN
1
by H NMR spectroscopy, more detailed investigations of this
self-assembly were carried out in CH3CN by monitoring the
changes in the UV−vis absorption, fluorescence, and Ln(III)
luminescence spectra upon addition of Eu(III) or Tb(III)
triflate salt solution to ligand solutions at concentrations of ca.
10−5 M (accurate concentrations were determined using the
Beer−Lambert Law).
Observing Ln(III)-Directed Self-Assembly Formation
through Photophysical Studies. The ligands developed
herein were titrated with both Eu(III) and Tb(III) triflate. The
overall changes in the absorption spectrum of a CH3CN
solution of 1 were monitored as a function of [Eu(III)], Figure
7. A slight blue shift and concomitant decrease in absorbance
was observed for the peak at 235 nm, stabilizing at 232 nm,
while the other peak, centered at 300 nm, and assigned to btp n
→ π* transitions, underwent a more significant red shift of 15
nm with an increase in absorbance. Coordination of the metal
ion by the btp motif accounts for this notable change. The
spectra after these changes match the recorded spectra of the
thermally prepared metal complex. Experimental binding
isotherms at various wavelengths are shown as an inset in
Figure 7a, demonstrating that changes to the absorption spectra
were largely finished upon addition of approximately 0.33 equiv
of Eu(CF3SO3)3, signifying the formation of the desired 1:3
Through the use of selective ROESY experiments (shown in
Supporting Information), information about the spatial
H
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a
Table 3. Binding Constants Determined from Titrations of btp Ligands with Ln(III) in CH3CN
Eu(III)
Tb(III)
ligand
logβ1:1
logβ1:2
logβ1:3
logβ1:1
logβ1:2
logβ1:3
b
b
b
b
1
UV
6.0 0.1
13.0
19.8
UV
6.5
13.0
18.9 0.1
b
Fluor.
Lum.
UV
6.9
22.2 0.1
Fluor.
Lum.
UV
b
b
b
b
7.2 0.1
14.8
20.7
6.9
6.9
14.2 0.1
20.2 0.1
22.7 0.7
20.5 0.1
21.6 0.1
22.1 0.1
22.0 0.1
20.0 0.1
20.7 0.1
20.9 0.1
21.6 0.1
20.4 0.1
21.4 0.2
21.4 0.1
b
b
3-Gly
6.5
14.3 0.1
21.2
b
Lum.
UV
7.3 0.1
8.0 0.1
15.2
21.4 0.1
21.8 0.2
21.4 0.1
21.5 0.1
20.1 0.1
21.7 0.1
21.2 0.1
Lum.
UV
6.9 0.14
7.2 0.14
b
3-L-Ala
14.8 0.1
14.4
b
b
b
Fluor.
Lum.
UV
7.4
14.3
Fluor.
Lum.
UV
7.2
b
b
7.3 0.1
7.7 0.1
8.5 0.1
7.1 0.1
7.9 0.1
15.2
6.9 0.1
b
14.6
b
3-D-Ala
3-L-Phe
3-D-Phe
3-L-Trp
14.7
6.9
14.4 0.1
14.6 0.1
b
b
Lum.
UV
15.6
Lum.
UV
7.2
b
b
b
14.9
7.28
b
14.6
b
b
b
Lum.
UV
16.3
21.0
Lum.
UV
7.3
15.2
b
b
b
7.1
14.6
21.5 0.1
23.0 0.4
20.2 0.1
7.6 0.1
6.8 0.1
14.9
Lum.
UV
8.5 0.2
17.3 0.3
Lum.
UV
15.1 0.1
b
b
b
b
6.6
14.2
6.8
14.7
b
b
Fluor.
Lum.
UV
Fluor.
Lum.
UV
6.8
14.9 0.1
20.4
b
b
b
b
7.7
14.9 0.1
14.2 0.2
16.8 0.1
14.6 0.1
19.7
6.8
15.0
21.7 0.1
21.3 0.4
3-D-Trp
6.6 0.1
20.7 0.3
6.8 0.2
14.9 0.3
b
b
Fluor.
7.7
23.7
Fluor.
Phos.
b
b
Lum.
7.7 0.1
19.8 0.1
6.8
16.2 0.2
21.3
a
b
[L] ≈ 10−5 M. Value fixed.
complex. The changes in fluorescence emission spectra were
also recorded, with the ligand fluorescence centered at 335 nm
being quenched upon addition of 0.33 equiv also. The
concomitant emergence of Eu(III) luminescence emission
was monitored by recording the delayed Ln(III) emission
(phosphorescence) upon excitation of the ligand. The overall
changes in the Eu(III) emission profile are shown in Figure 7b,
demonstrating gradual enhancement of the characteristic
Eu(III) luminescence spectrum within the addition of 0−0.33
equiv of metal ion, signifying both the successful sensitization
of the lanthanide excited state and the successful formation of
the Eu(III)-directed self-assembly in solution. The inset in
Figure 7b shows the changes observed over the course of the
titration for various 5D0 → 7FJ transitions; it is clear from these
changes that after the addition of 0.33 equiv of Eu(III), a sharp
decrease in the Eu(III)-centered emission was observed, an
indication of the formation of other self-assemblies in solution,
and that this shift in equilibrium causes the formation of less
emissive species to become the most dominant species in
solution. This is similar to behavior often observed for dpa
based ligands, and has been, in those cases, assigned to the
formation of 1:2 and 1:1 stoichiometries.
Analogous spectroscopic changes for ligands 3 are discussed
in detail in Supporting Information. The changes observed for
ligands 3-Trp are, however, worth commenting on here, as
these possessed more complicated absorption spectra to those
seen above, as the Trp residues give rise to some distinctive
absorption bands not seen in the aforementioned ligands (see
Supporting Information). The Trp-based band centered at 290
nm decreased in intensity upon addition of metal ion until 0.5
equiv, while the shoulder centered at 236 nm disappeared
altogether. Simultaneously, the band centered at 232 nm
decreased in intensity as a function of added Eu(III), whereas a
band centered at 315 nm grew in absorbance. The fluorescence
emission was also quenched upon binding to Eu(III), these
changes being most pronounced up to the addition of 0.5
equiv. As seen above, the Eu(III)-centered luminescence
peaked at 0.33 equiv and was subsequently quenched after
the addition of 1.0 equiv of Eu(III), indicating that the 1:3
stoichiometry was the most emissive species, as was the case for
all ligands discussed thus far. These ligands were not very
efficient, however, at sensitizing Eu(III) luminescence, as can be
seen from the poor resolution of the phosphorescence spectra
and from the quantum yield measurements detailed above. The
results observed for the other ligands developed herein upon
titration with Eu(III) are shown in Supporting Information.
Similarly, we evaluated the changes in the various
spectroscopic properties of these ligands upon titrating with
Tb(III). The results yielded very similar trends to those seen
from the above titrations and are discussed in Supporting
Information.
Quantifying the Binding Affinity and Speciation
Distribution through Photophysical Studies. In order to
gain a better understanding of this solution self-assembly
behavior and obtain a more detailed view on the formation of
different stoichiometric species in solution, the various
spectroscopic changes determined in the above measurements
were analyzed by fitting the global changes using nonlinear
regression analysis (using the ReactLab Equilibria software79)
to various btp:Ln(III) stoichiometries and stability constants
(logβ) for each equilibrium were determined. Global stability
constants were estimated for all ligands, 1 and 3, with Eu(III)
and Tb(III) from the UV−vis absorbance and Ln(III)
luminescence studies, while for some ligands, it was possible
to estimate values from ligand fluorescence titration data as
well, using the following equilibrium processes:
Ln(III) + (btp) ⇌ [Ln(btp)]3+ log β1:1
(1)
Ln(III) + 2(btp) ⇌ [Ln(btp)2]3+ log β1:2
(2)
Ln(III) + 3(btp) ⇌ [Ln(btp)3]3+ log β1:3
(3)
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Across the series of ligands, the estimated values of
equilibrium constants were of similar magnitude (as shown in
Table 3) with logβ1:1 ranging from 6.0−8.5, logβ1:2 of 14.2−
17.3 and logβ1:3 of 19.8−23.7, although in some cases values of
logβ1:2 could not be determined. In all but one case, the
constants estimated from Ln(III)-centered measurements were
higher than those determined from the absorption data.
The binding constants with Ln(III) were in good agreement
with the range of values reported for similar compounds in the
literature and at the upper end of the reported range,56,59,74,80,48
suggesting that these ligands are capable of forming very stable
coordination compounds with Ln(III) in CH3CN solution.
The calculated speciation distribution diagrams for these
titrations are shown in Supporting Information. These
demonstrated that for all the titrations, the 1:3 stoichiometry
was initially formed in high yield, (for instance, in the case of 1
with Eu(III), in ca. 85% yield) after which the formation of the
1:2 species became apparent (in all but a few cases), eventually
followed by the formation of the 1:1 complex at higher Ln(III)
concentrations. This kind of behavior is similar to that seen in
our work using dpa derivatives, demonstrating the similar
coordination properties of the two systems. Hence, the results
demonstrate that amino acid conjugated btp ligands can be
used to form novel self-assembly structures where the final
assembly contains 6, 4, or 2 such monopeptide conjugates.
Since all of these are based on methyl esters, they can be further
modified, with a view to achieving better solubility in aqueous
solution, or with the objective of forming higher order self-
assemblies and novel materials (such as gels) for instance by
simple hydrolysis and interactions with metal ions; an endeavor
that is currently being pursued in our laboratory with a view to
forming novel functional MOFs and soft materials.
assembled species were high, and comparable to dpa based
derivatives previously developed in our laboratory, as well as
other terdentate systems in the literature; these varied very little
throughout the series of compounds. The study herein
demonstrates that the btp ligands are a useful addition to the
chemistry of the lanthanides, possessing three coordination
sites that can be used in the formation of highly ordered self-
assemblies, which can exist in 1:3, 1:2, or 1:1 stoichiometries.
We have further shown that these can be simply functionalized
by using classical organic chemistry and, as such, the btp ligands
are excellent candidates for developing novel structures and
functional Ln(III)-based materials. We are currently working
toward exploring the use of btp derivatives in greater detail for
such applications.
EXPERIMENTAL SECTION
■
Methods and Materials. All chemicals were purchased from
commercial sources and, unless specified, used without further
purification. Melting points were determined using an Electrothermal
IA9000 digital melting point apparatus Elemental analysis was carried
out at the Microanalytical Laboratory, School of Chemistry and
Chemical Biology, University College Dublin using an Exeter
Analytical CE 440 elemental analyzer. Infrared spectra were recorded
on a PerkinElmer Spectrum One FT-IR Spectrometer fitted with a
universal ATR sampling accessory. NMR spectra were recorded using
a Bruker DPX-400 Avance spectrometer or Agilent DD2/LH
1
spectrometer, operating at 400.13 MHz for H NMR, 100.6 MHz
for 13C NMR, or a Bruker AV-600 spectrometer, operating at 600.1
1
MHz for H NMR and 150.2 MHz for 13C NMR. All spectra were
recorded using commercially available deuterated solvents, and were
referenced to solvent residual proton signals. All 1H−1H coupling
constants, J, are quoted with an accuracy of 0.3 Hz. Electrospray
mass spectra were measured on a Micromass LCT spectrometer
calibrated using a leucine enkephaline standard. MALDI Q-Tof mass
spectra were carried out on a MALDI Q-Tof Premier (Waters
Corporation, Micromass MS technologies, Manchester, UK) and high-
resolution mass spectrometry was performed using Glu-Fib as an
internal reference (peak at m/z = 1570.677). All microwave reactions
were carried out in 2−5 mL or 10−20 mL Biotage Microwave Vials in
a Biotage Initiator Eight EXP microwave reactor. Ligands 1 and 2 were
prepared as previously reported.20
Photophysical Measurements. Unless otherwise stated, all
photophysical measurements were carried out at 23 °C in HPLC
CH3CN solution at a concentration of ca. 10−5 M. UV−visible
absorption spectra were measured in 1 cm quartz cuvettes on a Varian
Cary 50 spectrophotometer. Baseline correction was applied for all
spectra. Emission spectra and luminescence lifetimes were measured
on a Varian Cary Eclipse luminescence spectrometer. All the stock
solutions were prepared in CH3CN. Low temperature emission spectra
were recorded on a Fluorolog FL-3-22 spectrometer from Horiba-
Jobin-Yvon Ltd. This instrument was equipped with a dewer of liquid
nitrogen, allowing for measurements at 77 K.
CONCLUSIONS
■
In the work presented in this article, we have developed seven
new btp ligands, 3 (derived from previously reported ligand 1),
their synthesis and characterization being discussed in detail for
a select number of them. All the ligands contained amino acid
residues, which were incorporated at the aryl terminal of these
ligands, enabling further functionalization of these moieties in
the future. Ligands 1 and 3 all formed stable, luminescent
complexes with Ln(III) salts, displaying characteristic Eu(III)
or Tb(III) line-like emission profiles upon sensitization via the
“antenna effect”. A hydration state of q ≈ 0 was determined for
each complex, indicating the absence of water molecules bound
in the first coordination sphere of the metal ion and the ability
of these ligands to satisfy the high coordination requirements of
Ln(III). Of these the Tb(III) complexes were shown to be
highly luminescent with quantum yield for the metal centered
emission being determined to be within the range of 46−70%,
with the exception of Trp derivatives which were significantly
less luminescent. The Eu(III) complexes were much less
luminescent, with a quantum yield of 0.3−3%, reflecting less
efficient sensitization process; this we analzed by measuring the
triplet state of the ligand 1. As in the case of Tb(III) the Trp
derivatives of Eu(III) were the least emissive. The interactions
of ligand 1 with Eu(III) ions in CD3CN were studied through
NMR studies, showing that the btp motif can bind this metal
ion, forming a stable 1:3 self-assembly, which was also
confirmed by HRMS analysis. Spectroscopic titrations of 1
and 3 with Eu(III) and Tb(III) were carried out in CH3CN
solution in order to monitor the self-assembly behavior of these
ligands in solution. The stability constants of the various self-
Sample Procedure for Synthesis of Amino-Acid Derivative,
3-Gly. Ligand 2 (0.20 g, 0.42 mmol) was suspended in 4 mL of SOCl2
and heated to 80 °C for 18 h under a CaCl2 guard tube. SOCl2 was
removed by vacuum distillation, and the acid chloride was suspended
in distilled CH2Cl2 and used without further purification. In a separate
reaction vessel, the relevant amino acid methyl ester HCl salt (3.3
equiv) was suspended in distilled CH2Cl2 and stirred for 1 h with an
excess of triethylamine (0.2 mL) at room temperature. The two
suspensions were added together and stirred at room temperature for
18 h under a CaCl2 guard tube. The reaction mixture was concentrated
under reduced pressure. The product was isolated upon trituration
with CH3OH and collected by filtration, washing with CH3OH and
diethyl ether, yielding the amide as a white or off-white solid.
Yield: 51%. Mp: 136−141 °C. HRMS (m/z) (ESI+): Calculated for
+
C31H30N9O6 m/z = 624.2319 [M + H]+. Found m/z = 624.2308;
calculated for C31H29N9O6·0.75NaCl·0.75H2O, C = 54.68, H = 4.51, N
J
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= 18.51. Found C = 55.02, H = 4.11, N = 18.45; 1H NMR (600 MHz,
DMSO-d6): δ (ppm) = 3.65 (s, 6H, COOCH3), 4.02 (d, 4H, CH2, J =
5.8 Hz), 5.79 (s, 4H, CH2), 7.46 (d, 4H, Ph CH, J = 8.0 Hz), 7.89 (d,
4H, Ph CH, J = 8.0 Hz), 7.93−8.05 (m, 3H, pyr CH), 8.72 (s, 2H,
triazolyl CH), 8.97 (t, 2H, NH, J = 5.8 Hz); 13C NMR (150 MHz,
DMSO-d6): δ (ppm) = 41.5 (Gly CH), 52.1 (CH3), 53.0 (CH2), 118.9
(pyr CH), 124.1 (triazolyl CH), 128.1 (Ph CH), 128.2 (Ph CH),
133.8 (Ph qt), 138.6 (pyr CH), 139.6 (Ph qt), 147.7 (triazolyl qt),
150.1 (pyr qt), 166.5 (amide CO), 170.6 (ester CO); FT-IR
(ATR, cm−1): 3339, 3079, 2956, 2285, 2167, 2080, 1981, 1740, 1645,
1615, 1575, 1544, 1505, 1436, 1402, 1371, 1321, 1303, 1263, 1212,
1160, 1115, 1095, 1052, 1020, 993, 979, 803, 765, 732, 694, 663.
3-L-Ala. Yield: 57%. Mp: 253−254 °C. HRMS (m/z) (ESI+):
Calculated for C33H34N9O6+ m/z = 652.2632 [M + H]+. Found m/z =
652.2653; calculated for C33H33N9O6·H2O, C = 59.19, H = 5.27 N =
(d, 4H, Ph CH adjacent amide bond), 7.96−8.01 (m, 3H, pyr CH),
8.70 (s, 2H, triazolyl CH), 8.86 (d, 2H, NH, J = 7.9 Hz). 13C NMR
(150 MHz, DMSO-d6): δ (ppm) = 36.2 (Phe CH2), 52.0 (COOCH3),
52.7 (CH2), 54.3 (Phe CH), 118.6 (pyr CH), 123.8 (triazolyl CH),
126.5 (Phe o-Ph CH), 127.8 (Ph CH), 127.9 (Ph CH), 128.2 (Phe Ph
CH), 129.0 (Phe Ph CH), 133.5, 137.6, 138.3 (pyr CH) 139.2, 147.4,
149.8, 166.0, 172.1; FT-IR (ATR, cm−1): 3320, 3132, 3055, 3031,
2949, 1736, 1643, 1611, 1575, 1530, 1497, 1456, 1433, 1352, 1279,
1215 (s), 1198, 1175, 1152, 1083, 1043, 1019, 992, 977, 914, 864, 806,
741.
3-L-Trp. Yield: 47%. Mp: 170−173 °C. HRMS (m/z) (ESI+):
Calculated for C49H43N11O6Na+ m/z = 904.3295 [M + Na]+. Found
m/z = 904.3250; calculated for C49H43N11O6·1.25H2O, C = 65.07, H =
1
5.07, N = 17.03. Found C = 64.86, H = 4.57, N = 17.09; H NMR
(600 MHz, DMSO-d6): δ (ppm) = 3.22 (dd, 2H, Trp CH2, J = 9.0 Hz,
14.5 Hz), 3.24 (dd, 2H, Trp CH2, J = 5.2 Hz, 14.5 Hz) 3.62 (s, 6H,
COOCH3), 4.69 (ddd, 2H, Trp CH, J = 7.4 Hz, 9.0 Hz, 5.2 Hz), 5.77
(s, 4H, CH2), 6.98 (t, 2H, Trp CH, J = 7.4 Hz), 7.06 (t, 2H, Trp CH, J
= 7.4 Hz), 7.19 (d, 2H, Trp CH, J = 2.2 Hz), 7.32 (d, 2H, Trp CH, J =
8.0 Hz), 7.43 (d, 4H, Ph CH, J = 8.3 Hz), 7.55 (d, 2H, Trp CH, J = 7.9
Hz), 7.84 (d, 4H, Ph CH, J = 8.3 Hz), 7.96−8.03 (m, 3H, pyr CH),
8.70 (s, 2H, triazolyl CH), 8.81 (d, 2H, amide NH, J = 7.6 Hz), 10.80
(s, 2H, Trp NH); 13C NMR (150 MHz, DMSO-d6): δ (ppm) = 26.6
(Trp CH2), 51.9 (CH3), 52.6 (CH2), 53.8 (chiral CH), 109.9 (Trp
qt), 111.4 (Trp CH), 118.0 (Trp CH), 118.4 (Trp CH), 118.6 (pyr
CH), 121.0 (Trp CH), 123.6 (Trp CH), 123.7 (triazolyl CH), 127.0
(Trp qt), 127.7 (Ph CH), 127.9 (Ph CH), 133.5 (Ph qt), 136.1 (Trp
qt), 139.2 (Ph qt), 147.4 (triazolyl qt), 149.8 (pyr qt), 166.0 (amide
CO), 172.4 (ester CO); FT-IR(ATR, cm−1): 3441, 3387, 3155,
3055, 2953, 1737, 1640, 1611, 1575, 1525, 1497, 1458, 1437, 1346,
1279, 1217, 1196, 1176, 1153, 1089, 1045, 1021, 1012, 992, 977, 930,
865, 803, 766, 735, 673.
1
18.82. Found C = 58.86, H = 4.86 N = 18.88; H NMR (600 MHz,
DMSO-d6): δ (ppm) = 1.40 (d, 6H, Ala CH3, J = 7.2 Hz), 3.64 (s, 6H,
COOCH3), 4.48 (quin, 2H, Ala CH, J = 7.2 Hz), 5.79 (s, 4H, CH2),
7.46 (d, 4H, phenyl CH, J = 8.1 Hz), 7.91 (d, 4H, phenyl CH, J = 8.1
Hz), 7.99 (app s, 3H, pyridyl CH), 8.71 (s, 2H, triazolyl CH), 8.81 (d,
2H, NH, J = 7.0 Hz); 13C NMR (150 MHz, DMSO-d6): δ (ppm) =
17.0, 48.6 (Ala CH), 52.2 (COOCH3), 53.0 (CH2), 118.9 (pyr CH),
124.0 (triazolyl CH), 128.1 (Ph CH), 128.3 (Ph CH), 133.9 (qt),
138.6 (pyr CH), 139.5 (qt), 147.7 (qt), 150.1 (qt), 166.1 (qt), 173.4
(qt); FT-IR (ATR, cm−1): 3353, 3169, 2957, 2162, 2050, 1741, 1642,
1609, 1577, 1532, 1505, 1459, 1438, 1426, 1380, 1359, 1320, 1271,
1238, 1212, 1198, 1167, 1096, 1080, 1045, 1021, 993, 980, 939, 876,
849, 801, 790, 776, 759, 742, 660.
3-D-Ala. Yield: 48%. Mp: 254−255 °C. HRMS (m/z) (ESI+):
Calculated for C33H34N9O6+ m/z = 652.2632 [M + H]+. Found m/z =
652.2635; calculated for C33H33N9O6·NaCl·0.5H2O, C = 55.63, H=
1
4.38, N = 17.64. Found C = 55.46, H = 4.73, N = 17.64; H NMR
(600 MHz, DMSO-d6): δ (ppm) = 1.40 (d, 6H, Ala CH3, J = 7.3 Hz),
3.64 (s, 6H, COOCH3), 4.48 (quin, 2H, Ala CH, J = 7.2 Hz), 5.79 (s,
4H, CH2), 7.46 (d, 4H, phenyl CH, J = 8.2 Hz), 7.91 (d, 4H, phenyl
CH, J = 8.3 Hz), 7.94−8.06 (m, 3H, pyridyl CH), 8.71 (s, 2H, triazolyl
CH), 8.81 (d, 2H, NH, J = 7.0 Hz); 13C NMR (150 MHz, DMSO-d6):
δ (ppm) = 16.8, 48.2 (Ala CH), 51.8 (COOCH3), 52.6 (CH2), 118.5
(pyr CH), 123.7 (triazolyl CH), 127.7 (phenyl CH), 127.9 (phenyl
CH), 133.5 (qt), 138.3 (pyr CH), 139.1 (qt), 147.4 (qt), 149.7 (qt),
165.7 (qt), 173.0 (qt); FT-IR (ATR, cm−1): 3351, 3168, 2957, 2162,
2046, 1741, 1642, 1609, 1577, 1532, 1505, 1460, 1438, 1426, 1380,
1359, 1346, 1315, 1271, 1238, 1212, 1198, 1167, 1135, 1096, 1080,
1045, 1021, 993, 980, 938, 876, 849, 801, 790, 759, 742, 660.
3-L-Phe. Yield: 61%. Mp: 139−148 °C. HRMS (m/z) (ESI+):
Calculated for C45H41N9O6Na+ m/z = 826.3078 [M + Na]+. Found
m/z = 826.3071; calculated for C45H41N9O6·0.5NaCl·H2O, C = 63.50,
H = 5.09, N = 14.81. Found C = 64.04, H = 4.84, N = 14.74; 1H NMR
(600 MHz, DMSO-d6): δ (ppm) = 3.05−3.19 (m, 4H, Phe CH2), 3.63
(s, 6H, COOCH3), 4.66 (octet, 2H, Phe CH, J = 3.3 Hz), 5.77 (s, 4H,
CH2), 7.15−7.20 (m, 2H, Phe p-Ph CH), 7.25−7.30 (m, 8H, Phe m-
and o-Ph CH), 7.43 (d, 4H, Ph CH adjacent to CH2, J = 8.3 Hz), 7.82
(d, 4H, phenyl CH adjacent amide bond), 7.96−8.01 (m, 3H, pyr
CH), 8.70 (s, 2H, triazolyl CH), 8.86 (d, 2H, NH, J = 7.9 Hz). 13C
NMR (150 MHz, DMSO-d6): δ (ppm) = 36.5 (Phe CH2), 52.3
(COOCH3), 53.0 (CH2), 54.6 (Phe CH), 118.9 (pyr CH), 124.1
(triazolyl CH), 126.8 (Phe o-Ph CH), 128.1 (Ph CH), 128.2 (Ph CH),
128.5 (Phe Ph CH), 129.4 (Phe Ph CH), 133.8, 137.9, 138.7 (pyr
CH) 139.6, 147.7, 150.1, 166.3, 172.4. FT-IR (ATR, cm−1): 3442,
3375, 3156, 3055, 3031, 2949, 1736, 1639, 1604, 1574, 1524, 1495,
1458, 1436, 1352, 1279, 1217 (s), 1198, 1175, 1152, 1088, 1045, 1021,
992, 977, 921, 864, 803, 736.
3-D-Trp. Yield: 60%. Mp: 168−171 °C. HRMS (m/z) (ESI+):
+
Calculated for C49H44N11O6 m/z = 882.3476 [M + H]+. Found m/z
= 882.3440; calculated for C49H43N11O6·0.5NaCl·2H2O, C = 62.13, H
1
= 5.00, N = 16.27. Found C = 62.40, H = 4.58, N = 16.73; H NMR
(600 MHz, DMSO-d6): δ (ppm) = 3.22 (dd, 2H, Trp CH2, J = 9.0 Hz,
14.5 Hz), 3.24 (dd, 2H, Trp CH2, J = 5.2 Hz, 14.5 Hz), 3.62 (s, 6H,
COOCH3), 4.69 (ddd, 2H, Trp CH, J = 7.4 Hz, 9.0 Hz, 5.2 Hz), 5.77
(s, 4H, CH2), 6.98 (t, 2H, Trp CH, J = 7.4 Hz), 7.06 (t, 2H, Trp CH, J
= 7.4 Hz), 7.19 (d, 2H, Trp CH, J = 2.2 Hz), 7.32 (d, 2H, Trp CH, J =
8.0 Hz), 7.43 (d, 4H, Ph CH, J = 8.3 Hz), 7.55 (d, 2H, Trp CH, J = 7.9
Hz), 7.84 (d, 4H, phenyl CH, J = 8.3 Hz), 7.96−8.03 (m, 3H, pyr
CH), 8.70 (s, 2H, triazolyl CH), 8.81 (d, 2H, amide NH, J = 7.6 Hz),
10.81 (s, 2H, Trp NH); 13C NMR (150 MHz, DMSO): δ (ppm) =
26.9 (Trp CH2), 52.2 (CH3), 53.0 (CH2), 54.1 (chiral CH), 110.2
(Trp qt), 111.8 (Trp CH), 118.3 (Trp CH), 118.7 (Trp CH), 118.9
(pyr CH), 121.3 (Trp CH), 124.0 (Trp CH), 124.1 (triazolyl CH),
127.3 (Trp qt), 128.1 (Ph CH), 128.3 (Ph CH), 133.8 (Ph qt), 136.4
(Trp qt), 139.5 (Ph qt), 147.7 (triazolyl qt), 150.1 (pyr qt), 166.3
(amide CO), 172.8 (ester CO); FT-IR (ATR, cm−1): 3441, 3388,
3158, 3057, 2954, 1738, 1639, 1611, 1576, 1525, 1496, 1459, 1437,
1347, 1280, 1217, 1197, 1176, 1152, 1089, 1046, 1021, 1012, 993, 977,
927, 864, 804, 766, 735, 674.
General Procedure for Synthesis of Ln(III) Complexes of btp
Ligands. Ligand (1 or 3) (1 equiv) and Ln(CF3SO3)3·6(H2O) (0.35
equiv) were suspended in CH3OH (6 mL) and heated to 70 °C under
microwave irradiation for 20 min. The complexes were isolated as
beige solids upon diffusion of diethyl ether into a CH3OH solution.
[Eu·(1)3](CF3SO3)3. HRMS (m/z) (MALDI+): Calculated for
C83H69N21O18S2F6Eu+ m/z = 1978.369 [EuL3(CF3SO3)2]+. Found
m/z = 1978.378; calculated for C56H46EuF6N14O14S2+ m/z = 1469.187
[EuL2(CF3SO3)2]+. Found m/z = 1469.175; calculated for
3-D-Phe. Yield: 47%. Mp: 141−149 °C. HRMS (m/z) (ESI−):
−
Calculated for C45H40N9O6 m/z = 802.3107 [M − H]−. Found m/z
+
C29H23EuF6N7O10S2 m/z = 960.006 [EuL(CF3SO3)2]+. Found m/z
= 802.3115; calculated for C45H41N9O6·1.5H2O, C = 65.05, H = 5.34,
1
= 960.003; calculated for C84H69N21O21S3F9Eu·6CH2Cl2·1.5-
N = 15.17. Found C = 64.88, H = 5.08, N = 14.69; H NMR (600
(CH3)2NCOH, C = 50.57, H = 4.10, N = 14.04. Found C = 50.89,
H = 3.60, N = 14.49. H NMR (400 MHz, CD3CN): δ = 3.91 (s,
−OCH3), 4.57 (d, 3- and 5-pyr CH), 5.52 (d, CH2), 6.00 (d, CH2),
6.28 (m, 4-pyr CH), 7.24 (m, Ph CH and triazolyl CH), 7.89 (d, Ph
MHz, DMSO-d6): δ (ppm) = 3.05−3.19 (m, 4H, Phe CH2), 3.63 (s,
6H, COOCH3), 4.66 (octet, 2H, Phe CH, J = 3.3 Hz), 5.77 (s, 4H,
CH2), 7.15−7.20 (m, 2H, Phe p-Ph CH), 7.25−7.30 (m, 8H, Phe m-
and o-Ph CH), 7.43 (d, 4H, Ph CH adjacent to CH2, J = 8.3 Hz), 7.81
1
K
DOI: 10.1021/ic502384w
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
CH); FT-IR (ATR, cm−1): 3112, 2955, 1719, 1615, 1589, 1468, 1435,
1275, 1254, 1223, 1156, 1109, 1067, 1029, 963, 875, 808, 727.
[Eu·(3-Gly)3](CF3SO3)3. HRMS (m/z) (MALDI+): Calculated for
C95H87N27O24S2F6Eu+ m/z = 2320.498 [EuL3(CF3SO3)2]+. Found m/
z = 2320.489; calculated for C64H58N18O18S2F6Eu+ m/z = 1697.273
[EuL2(CF3SO3)2]+. Found m/z = 1697.282; calculated for
C96H87N27O27S3F9Eu·1.25NaCl, C = 45.32, H = 3.45, N = 14.87.
Found C = 45.67, H = 2.92, N = 14.74; 1H NMR (400 MHz,
CD3OD): δ = 3.72 (s, 6H, OCH3), 4.15 (m, 4H, Gly CH2), 4.50 (d,
2H, 3- and 5-pyr CH, J = 7.9 Hz), 5.63 (d, 2H, CH2, J = 14.3 Hz), 6.19
(d, 2H, CH2, J = 14.3 Hz), 6.28 (t, 1H, 4-pyr CH, J = 7.8 Hz), 7.30 (d,
4H, Ph CH, J = 8.0 Hz), 7.47 (br s, 2H, triazolyl CH), 7.79 (d, 4H, Ph
CH, J = 8.0 Hz); FTIR (ATR, cm−1): 3345, 3101, 2956, 1737, 1643,
1617, 1572, 1541, 1504, 1467, 1454, 1438, 1248, 1222, 1160, 1122,
1067, 1029, 1011, 993, 951, 867, 847, 806, 773, 728, 659.
[Eu·(3-D-Trp)3](CF3SO3)3. Mp: 168−173 °C. HRMS (m/z) (MALDI
+): Calculated for C149H129N33O24F6S2Eu+ m/z = 3094.845
[EuL3(CF3SO3)2]+. Found m/z = 3094.860; Calculated for
C100H86N22O18F6S2Eu+ m/z = 2212.497 [EuL2(CF3SO3)2]+. Found
1
m/z = 2212.502; H NMR (400 MHz, CD3OD): δ = 0.90 (m), 1.16
(t), 1.27 (m), 2.13 (s), 2.78 (br s), 3.11 (s), 3.29 (m), 3.46 (s), 3.67
(m), 4.31 (d), 4.55 (s), 4.83 (br s), 5.47 (d), 5.71 (s), 5.94 (d), 6.37
(s), 6.95 (t), 7.03 (m), 7.12 (m), 7.20 (m), 7.27 (d), 7.40 (d), 7.52
(d), 7.61 (m), 7.72 (d), 7.94 (br s), 8.55 (br s); FTIR (ATR, cm−1):
3312, 3110, 2953, 1735, 1642, 1618, 1573, 1534, 1500, 1458, 1437,
1341, 1249, 1222, 1156, 1123, 1097, 1066, 1029, 1010, 993, 806, 741,
660.
[Tb·(1)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C83H69N21O18S2F6Tb+ m/z = 1984.373 [TbL3(CF3SO3)2]+. Found
m/z = 1984.370; Calculated for C56H46N14O14S2F6Tb+ m/z =
1475.192 [TbL2(CF3SO3)2]+. Found m/z = 1475.191; calculated for
C84H69N21O21S3F9Tb·2.5NaCl·4CH3OH, C = 43.88, H = 3.56, N =
[Eu·(3-L-Ala)3](CF3SO3)3. Mp: 154−160 °C. HRMS (m/z) (MALDI
+): Calculated for C101H99N27O24S2F6Eu+ m/z = 2404.591 [Eu-
1
L3(CF3SO3)2]+. Found m/z
= 2404.599; Calculated for
12.21. Found C = 44.10, H = 3.26, N = 11.67; H NMR (400 MHz,
C68H66N18O18S2F6Eu+ m/z = 1753.336 [EuL2(CF3SO3)2]+. Found
m/z = 1753.330; 1H NMR (400 MHz, CD3OD): δ = 1.45−1.58 (m),
3.71 (d), 3.72 (s), 4.54 (d), 4.58−4.68 (m), 5.58−5.67 (m), 6.15 (d),
6.30 (q), 7.26−7.35 (m), 7.47 (s), 7.80 (t), 8.05 (d); FTIR (ATR,
cm−1): 3340, 3107, 1737, 1645, 1617, 1574, 1538, 1504, 1454, 1250,
1223, 1160, 1122, 1067, 1029, 994, 807, 774, 728, 661.
CD3CN): δ = −0.41 (br s), 1.77 (s), 2.68 (br s), 2.78 (s), 2.90 (s),
3.25 (br s), 3.89 (s), 5.02 (br s), 5.71 (s), 6.16 (br s), 6.63 (br s), 7.28
(s), 7.43 (d), 7.59 (s), 8.01 (d), 8.37 (s), 9.61 (br s); FTIR (ATR,
cm−1): 3119, 2956, 1716, 1616, 1589, 1435, 1253, 1223, 1154, 1108,
1068, 1028, 807, 727, 661.
[Tb·(3-Gly)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C95H87N27O24S2F6Tb+ m/z = 2326.502 [TbL3(CF3SO3)2]+. Found m/
z = 2326.509; calculated for C64H58N18O18S2F6Tb+ m/z = 1703.278
[TbL2(CF3SO3)2]+. Found m/z = 1703.273; calculated for
C96H87N27O27S3F9Tb·NaCl, C = 45.48, H = 3.46, N = 14.92. Found
[Eu·(3-D-Ala)3](CF3SO3)3. Mp: 151−157 °C. HRMS (m/z) (MALDI
+): Calculated for C101H99N27O24F6S2Eu+ m/z = 2404.591 [Eu-
L3(CF3SO3)2]+. Found m/z
= 2404.571; Calculated for
C68H66N18O18F6S2Eu+ m/z = 1753.336 [EuL2(CF3SO3)2]+. Found
1
C = 45.67, H = 2.92, N = 14.74; H NMR (400 MHz, CD3CN): δ =
1
m/z = 1753.337; H NMR(400 MHz, CD3OD): δ = 1.45−1.58 (m),
1.39 (br s), 1.77 (m), 2.57 (br s), 3.70 (br s), 3.88 (br s), 4.22 (br m),
4.90 (br s), 5.45 (s), 5.69 (s), 6.49 (br s), 7.12 (br s), 7.91 (br m),
10.77 (br s); FTIR (ATR, cm−1): 3345, 3106, 2953, 1741, 1649, 1618,
1589, 1574, 1541, 1505, 1469, 1455, 1438, 1408, 1370, 1247, 1213,
1183, 1158, 1123, 1068, 1060, 1029, 1011, 995, 976, 867, 849, 807,
773, 757, 729, 709, 691, 660.
3.71 (d), 3.72 (s), 4.54 (d), 4.58−4.68 (m), 5.58−5.67 (m), 6.15 (d),
6.30 (q), 7.26−7.35 (m), 7.47 (s), 7.80 (t), 8.05 (m); FTIR (ATR,
cm−1): 3340, 3107, 1737, 1644, 1617, 1574, 1538, 1505, 1456, 1250,
1223, 1161, 1124, 1067, 1029, 994, 951, 807, 773, 728, 659.
[Eu·(3-L-Phe)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C137H123N27O24S2F6Eu+ m/z = 2860.7792 [EuL3(CF3SO3)2]+. Found
m/z = 2860.7832; calculated for C92H82N18O18S2F6Eu+ m/z =
2057.461 [EuL2(CF3SO3)2]+. Found m/z = 2057.453; calculated for
C138H123N27O27F9S3Eu·NaCl·3H2O, C = 53.05, H = 4.16, N = 12.10.
Found C = 52.62, H = 3.63, N = 11.91; 1H NMR (400 MHz,
CD3OD): δ = 1.99 (m), 2.76 (br s), 3.06−3.19 (m), 3.45−3.47 (m),
3.69 (d), 3.73 (s), 4.45 (d), 4.86−4.97 (m), 5.51−5.60 (m), 5.96−6.13
(m), 7.01 (t), 7.10−7.18 (m), 7.19−7.31 (m), 7.42 (d), 7.63−7.72
(m), 7.77 (br s), 7.93 (d); FTIR (ATR, cm−1): 3330, 3107, 1737,
1649, 1617, 1575, 1536, 1498, 1468, 1455, 1437, 1250, 1223, 1153,
1120, 1067, 1029, 994, 857, 806, 726, 700, 661.
[Tb·(3-L-Ala)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C101H99N27O24S2F6Tb+ m/z = 2410.596 [TbL3(CF3SO3)2]+. Found
m/z = 2410.602; calculated for C102H99N27O27S3F9Tb·3.1-
(CH3)2NCOH, C = 47.95, H = 4.36, N = 15.12. Found C = 48.50,
H = 3.83, N = 14.90; 1H NMR (400 MHz, CD3OD): δ = −2.48, 1.77,
2.65 (br s), 3.70 (s), 3.79 (s), 4.32−4.52 (m), 5.45 (s), 5.69 (s), 6.65−
6.75 (br m), 7.18 (br s), 7.29 (br s), 7.42 (d), 7.59 (s), 7.83 (d), 8.02
(d), 8.36 (s), 10.30 (br s); FTIR (ATR, cm−1): 3348, 3170, 2957,
1741, 1642, 1617, 1577, 1531, 1504, 1458, 1438, 1425, 1379, 1358,
1346, 1271, 1238, 1213, 1163, 1095, 1080, 1068, 1045, 1029, 1021,
993, 980, 938, 876, 849, 841, 801, 790, 775, 759, 742, 730, 660.
[Tb·(3-D-Ala)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C101H99N27O24S2F6Tb+ m/z = 2410.596 [TbL3(CF3SO3)2]+. Found
m/z = 2410.602; 1H NMR (400 MHz, CD3OD): δ = −2.48 1.77, 2.65
(br s), 3.67 (m), 3.77 (s), 4.10−4.50 (m), 5.45 (s), 5.69 (s), 6.06 (br
s), 6.58 (br s), 7.05 (br s), 7.18 (br s), 7.29 (br s), 7.42 (d), 7.59 (s),
7.83 (d), 8.02 (d), 8.36 (s), 10.15 (br s); FTIR (ATR, cm−1): 3350,
3167, 2957, 1741, 1642, 1617, 1577, 1534, 1504, 1457, 1438, 1426,
1379, 1358, 1346, 1271, 1239, 1214, 1163, 1095, 1080, 1068, 1045,
1029, 1021, 993, 980, 938, 876, 849, 841, 802, 790, 775, 759, 742, 730,
660.
[Eu·(3-D-Phe)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C137H123N27O24S2F6Eu+ m/z = 2860.779 [EuL3(CF3SO3)2]+. Found
m/z = 2860.787; calculated for C92H82N18O18S2F6Eu+ m/z = 2057.461
[EuL2(CF3SO3)2]+. Found m/z = 2057.458; calculated for
C138H123N27O27F9S3Eu·1.25NaCl·3H2O, C = 52.81, H = 4.14, N =
1
12.05. Found C = 53.22, H = 3.65, N = 11.92; H NMR (400 MHz,
CD3OD): δ = 1.99 (m), 2.76 (br s), 3.06−3.19 (m), 3.45−3.47 (m),
3.69 (d), 3.73 (s), 4.45 (d), 4.86−4.97 (m), 5.51−5.60 (m), 5.96−6.13
(m), 7.01 (m), 7.10−7.18 (m), 7.19−7.31 (m), 7.42 (d), 7.63−7.72
(m), 7.77 (br s), 7.93 (d); FTIR (ATR, cm−1): 3330, 3107, 1735,
1648, 1617, 1575, 1536, 1498, 1468, 1455, 1437, 1251, 1223, 1153,
1120, 1067, 1029, 993, 857, 806, 726, 701, 661.
[Tb·(3-L-Phe)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C137H123N27O24S2F6Tb+ m/z = 2866.783 [TbL3(CF3SO3)2]+. Found
m/z = 2866.784; calculated for C138H123N27O27F9S3Tb·1.25NaCl·
0.5H2O, C = 53.47, H = 4.03, N = 12.20. Found C = 53.25, H = 3.50,
[Eu·(3-L-Trp)3](CF3SO3)3. Mp: 164−171 °C. HRMS (m/z) (MALDI
+): Calculated for C149H129N33O24F6S2Eu+ m/z = 3094.845
[EuL3(CF3SO3)2]+. Found m/z = 3094.852; Calculated for
C100H86N22O18F6S2Eu+ m/z = 2212.497 [EuL2(CF3SO3)2]+. Found
1
N = 12.01; H NMR (400 MHz, CD3CN): δ = 1.00 (s), 1.25 (m),
1.77 (s), 2.58 (br m), 2.82 (m), 3.00−3.22 (m), 3.52 (s), 3.68 (s), 3.72
(s), 4.59 (br s), 4.71 (br s), 5.68 (s), 6.11 (br s), 6.57 (br s), 6.75 (br
s), 7.08−7.25 (m), 7.73 (m), 8.35 (s), 9.60 (br s); FTIR (ATR, cm−1):
3312, 2955, 1737, 1645, 1617, 1573, 1536, 1498, 1469, 1455, 1436,
1250, 1222, 1154, 1121, 1097, 1067, 1029, 994, 875, 806, 727, 700,
660.
[Tb·(3-D-Phe)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C137H123N27O24S2F6Tb+ m/z = 2866.783 [TbL3(CF3SO3)2]+. Found
m/z = 2866.773; calculated for C92H82N18O18F6S2Tb+ m/z = 2063.465
1
m/z = 2212.507; H NMR (400 MHz, CD3OD): δ = 0.88 (m), 1.15
(t), 1.27 (m), 2.13 (s), 2.76 (br s), 3.11 (s), 3.28 (m), 3.46 (s), 3.66
(m), 4.31 (d), 4.55 (s), 4.82 (br s), 5.47 (d), 5.70 (s), 5.94 (d), 6.37
(s), 6.93 (t), 7.03 (m), 7.11 (m), 7.18 (m), 7.26 (d), 7.38 (d), 7.50
(d), 7.59 (m), 7.71 (d), 7.93 (br s), 8.54 (br s); FTIR (ATR, cm−1):
3313, 3101, 2953, 1736, 1648, 1618, 1573, 1535, 1500, 1458, 1435,
1341, 1249, 1223, 1156, 1121, 1097, 1067, 1029, 1010, 994, 806, 742,
660.
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Article
[EuL2(CF3SO3)2]+. Found m/z = 2063.465; calculated for
C138H123N27O27F9S3Tb·NaCl·2.5H2O, C = 53.01, H = 4.13, N =
(3) Crowley, J. D.; Bandeen, P. H. Dalton Trans. 2010, 39, 612−623.
(4) Li, Y.; Flood, A. H. Angew. Chem., Int. Ed. 2008, 47, 2649−2652.
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Chem. 2011, 83, 3455−3461.
1
12.12. Found C = 52.62, H = 3.63, N = 11.91; H NMR (400 MHz,
CD3CN): δ = 1.00 (s), 1.25 (m), 1.77 (quin), 2.25 (br m), 2.70 (br
m), 2.85 (m), 3.00−3.28 (m), 3.51 (s), 3.68 (s), 3.73 (s), 4.58 (br s),
4.71 (br s), 5.68 (s), 6.10 (br s), 6.59 (br s), 6.72 (br s), 7.08−7.25
(m), 7.72 (m), 8.35 (s), 9.70 (s); FTIR (ATR, cm−1): 3313, 2981,
1736, 1643, 1617, 1573, 1535, 1498, 1469, 1456, 1437, 1249, 1222,
1153, 1121, 1096, 1067, 1029, 994, 859, 806, 727, 700, 660.
[Tb·(3-L-Trp)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C149H129N33O24F6S2Tb+ m/z = 3100.849 [TbL3(CF3SO3)2]+. Found
m/z = 3100.842; calculated for C150H129N33O27F9S3Tb·NaCl·6H2O, C
= 52.70, H = 4.16, N = 13.52. Found C = 52.91, H = 3.61, N = 13.44;
1H NMR (400 MHz, CD3CN): δ = 9.48 (br d), 8.33 (br s), 8.01 (m),
7.73 (d), 7.57 (m), 7.47 (m), 7.37 (d), 7.21 (m), 7.14 (m), 7.02 (m),
6.80 (s), 6.48 (br s), 5.67 (br s), 5.45 (s), 4.89 (m), 4.07 (q), 3.76 (br
s), 3.66 (br s), 3.61 (br s), 3.28 (m), 1.77 (q), 1.19 (t), 1.00 (s), −2.48
(s); FTIR (ATR, cm−1): 3311, 2981, 1736, 1648, 1618, 1573, 1534,
1500, 1458, 1437, 1342, 1250, 1223, 1157, 1124, 1097, 1067, 1029,
994, 807, 743, 659.
[Tb·(3-D-Trp)3](CF3SO3)3. HRMS (m/z) MALDI+: Calculated for
C149H129N33O24F6S2Tb+ m/z = 3100.849 [TbL3(CF3SO3)2]+. Found
m/z = 3100.862; calculated for C150H129N33O27S3F9Tb·0.75H2O, C =
55.17, H = 4.03, N = 14.15. Found C = 54.68, H = 3.83, N = 13.98; 1H
NMR (400 MHz, CD3CN): δ = 9.66 (br s), 9.19 (s), 8.33 (br s), 8.01
(m), 7.73 (d) 7.56 (m), 7.37 (d), 7.26 (m), 7.19 (m), 7.12 (m), 7.02
(m), 6.79 (s), 6.66 (br s), 5.67 (br s), 5.45 (s), 4.90 (m), 4.07 (q), 3.82
(br s), 3.67 (d), 3.56 (m), 3.28 (d), 1.77 (q), 1.21 (t), 1.00 (s), −2.48
(s); FTIR (ATR, cm−1): 3327, 2981, 1734, 1645, 1618, 1574, 1532,
1501, 1458, 1436, 1343, 1250, 1223, 1157, 1124, 1097, 1067, 1029,
994, 806, 742, 660.
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ASSOCIATED CONTENT
* Supporting Information
■
(20) Byrne, J. P.; Kitchen, J. A.; Kotova, O.; Leigh, V.; Bell, A.;
Boland, J. J.; Albrecht, M.; Gunnlaugsson, T. Dalton Trans. 2014, 43,
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S
1H NMR, 13C NMR, and 2D NMR spectra of ligands; 1H NMR
spectra of complexes; selective ROESY and TOCSY spectra of
1 and [Eu(1)3](CF3SO3)3; IR spectra; HRMS isotopic pattern
matching; UV−vis absorption, luminescence and excitation
spectra of ligands and complexes; CPL spectra of [Tb·(3-
Trp)3]CF3SO3); further discussion of spectroscopic titrations;
and full titration data, calculated binding isotherms and
speciation diagrams. This material is available free of charge
via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: gunnlaut@tcd.ie. Fax: +353 1 716 2628. Tel: +353 1
896 3459.
■
(27) Schulze, B.; Escudero, D.; Friebe, C.; Siebert, R.; Gorls, H.;
̈
Notes
Kohn, U.; Altuntas, E.; Baumgaertel, A.; Hager, M. D.; Winter, A.;
̈
The authors declare no competing financial interest.
Dietzek, B.; Popp, J.; Gonzal
2011, 17, 5494−5498.
(28) Schulze, B.; Escudero, D.; Friebe, C.; Siebert, R.; Gorls, H.;
́
ez, L.; Schubert, U. S. Chem.Eur. J.
ACKNOWLEDGMENTS
̈
■
́
Sinn, S.; Thomas, M.; Mai, S.; Popp, J.; Dietzek, B.; Gonzalez, L.;
We thank the Irish Research Council (Embark Initiative) and
TCD School of Chemistry for studentships funding this work
(J.P.B.), IRCSET for postdoctoral fellowship (J.A.K.) and
Science Foundation Ireland (SFI) for SFI PI 2010 (10/IN.1/
B2999) and SFI PI 2013 (13/IA/1865) funding. We thank Dr.
Martin Feeney for HRMS measurements, Dr. Manuel Ruether
for technical assistance, and Dr. Oxana Kotova and Dr. Salvador
Blasco for useful discussions.
Schubert, U. S. Chem.Eur. J. 2012, 18, 4010−4025.
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