Copper(ii) complexes of macrocyclic and open-chain pseudopeptidic ligands: synthesis, characterization and interaction with dicarboxylates

Article abstract of DOI:10.1039/c5dt01496d

Mono- and dinuclear Cu(ii) complexes were prepared with pseudopeptidic open chain and macrocyclic ligands, respectively. They were characterized by UV-vis spectroscopy, EPR, HRMS and X-ray diffraction. The Cu(ii) cation is coordinated by two amines and tw

Full text of DOI:10.1039/c5dt01496d

Dalton
Transactions
View Article Online
View Journal | View Issue
PAPER
Copper(II) complexes of macrocyclic and
open-chain pseudopeptidic ligands: synthesis,
characterization and interaction with
dicarboxylates†
Cite this: Dalton Trans., 2015, 44,
12700
Enrico Faggi,*a Raquel Gavara,b Michael Bolte,c Lluís Fajarí,a Luís Juliá,a
Laura Rodríguezb and Ignacio Alfonso*a
Mono- and dinuclear Cu(II) complexes were prepared with pseudopeptidic open chain and macrocyclic
ligands, respectively. They were characterized by UV-vis spectroscopy, EPR, HRMS and X-ray diffraction.
The Cu(II) cation is coordinated by two amines and two deprotonated amides, in a slightly distorted
square planar coordination geometry. The complexes interact with several substituted dicarboxylates, as
shown by UV-vis titrations and EPR experiments. The interaction of both mono- and dinuclear complexes
with very similar dicarboxylates of biological interest (malate and aspartate) resulted in strikingly different
outcomes: in the first case a ternary complex [ligand⋯metal⋯dicarboxylate] was obtained almost quanti-
tatively, while in the latter, the Cu(II) displacement to form Cu(Asp)2 was predominant.
Received 20th April 2015,
Accepted 29th May 2015
DOI: 10.1039/c5dt01496d
www.rsc.org/dalton
ligands functionalized to achieve metal complexation through
a biomimetic approach is a challenge of current interest. The
Introduction
The Cu(II) cation plays a key role in bioinorganic chemistry as use of oligopeptides7 and simple ligands that contain amino
it is present in many enzymes with a variety of essential func- acid residues8 is a successful strategy to provide the Cu(II) ions
tions.1,2 Copper enzymes usually contain metal ions bound to with a coordination environment similar to that found in
a specific amino acid residue or directly to the amide group – metalloproteins.
carbonyl or nitrogen – in the peptide backbone, offering
In this context, (amino amide) compounds9 are promising
different coordination environments.3 For example, naturally- ligands for several reasons: (i) they contain two kinds of nitro-
occurring cyclic peptides form mono- and dinuclear Cu(II) gen atoms, with different coordination capabilities, connected
complexes, with different coordination geometries.4 The Cu(II) through a chiral backbone; (ii) their properties can be tuned
ion also interacts with αsynuclein (αSyn), and fragments of by the variation of the substituents and the spacers and (iii)
Park9 encoded protein from the Parkinson’s disease gene.5 they can form stable metal complexes with transition metals.10
Additionally, Cu(II) ionophores have been studied recently as On the other hand, different bis(amino amides) have been
potential therapeutic agents.6 Thus, an appropriate design of used as building blocks for the construction of macrocyclic or
small molecules with suitable structural and functional macrobicyclic structures. Some of these systems display inter-
characteristics could be important for biomimetic and reco- esting features, acting as in vivo fluorescent pH probes,11 or as
gnition studies. In this regard, the design and synthesis of selective receptors for substrates of biological relevance.12
Recently, the coordination ability of some C2 symmetrical
bis(amino amides) derived from valine towards Cu(II) and
Zn(II) ions has been reported13 and, for the same family of
ligands, the effect of changes in the amino acidic residue
towards the coordination of Cu(II) was evaluated.14 Here, we
present a study of the Cu(II) binding ability of two open-chain
and two macrocyclic (amino amide) ligands derived from
phenylalanine. This particular amino acid was selected
because some phenylalanine-derived receptors have been
shown to be better hosts for cations than those obtained from
valine.15 In view of the multiple and important roles played by
dicarboxylate anions in living systems,16 we also studied the
aDepartamento de Química Biológica y Modelización Molecular, IQAC–CSIC, Jordi
Girona, 16-26, E-08034 Barcelona, Spain. E-mail: enrico.faggi@iqac.csic.es,
ignacio.alfonso@iqac.csic.es
bDepartament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès
1-11, 08028 Barcelona, Spain
cInstitut für Anorganische Chemie, J.-W.-Goethe-Universität, Max-von-Laue-Str.7,
D-60438 Frankfurt/Main, Germany
†Electronic supplementary information (ESI) available: 1H-NMR, 13C-NMR
spectra of the new ligands, HRMS spectra of the ligands and the complexes, UV-
vis and EPR spectra of the complexes and their adducts with dicarboxylates.
CCDC 1059975 and 1059976. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c5dt01496d
12700 | Dalton Trans., 2015, 44, 12700–12710
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
interaction of the obtained Cu(II) complexes with a series of
dicarboxylates with similar structures and of high biological
interest, such as malate and aspartate.
Results and discussion
Synthesis and characterization of the ligands
For this study we selected four ligands (L1–L4) with closely
related structures. Thus, L1 and L2 are open-chain bis(amino
amide) receptors that differ slightly in the length of the ali-
phatic spacer connecting the amide nitrogens. In principle,
they are designed to coordinate Cu(II) forming mononuclear
complexes. On the other hand, L3 and L4 are tetra(amino
amide) macrocyclic ligands with different geometries of the
aromatic spacer that connect the amine nitrogens. They are
designed to coordinate Cu(II) forming dinuclear complexes.
Overall, the complexes derived from these ligands allowed: (i)
comparison of mononuclear and dinuclear Cu(II) complexes,
determining which molecular architecture was more efficient
in the further coordination of dicarboxylates and (ii) an evalu-
ation of the possible effect of the length of the spacer.
The general structure and synthetic pathways of the con-
sidered ligands are displayed in Scheme 1. Primary diamines 1
and 2, derived from phenylalanine, are easily prepared starting
from the corresponding N-Cbz protected phenylalanine
N-hydroxysuccinimidyl ester, coupled with either 1,2-diamino-
ethane or 1,3-diaminopropane and final N-deprotection fol-
lowing previously reported procedures.17 Diamines 1 and 2
were subjected to a reductive amination process with benz-
aldehyde in methanol, affording the new ligands L1 and L2 in
good yields. On the other hand, macrocyclic ligands L3 and L4
were obtained by reaction of diamine 1 with either terephth-
Fig. 1 X-ray crystal structure of ligand L1. Hydrogens are omitted for
clarity (top). Asymmetric unit of ligand L1 (bottom). Carbon (grey),
oxygen (red), nitrogen (blue), hydrogen bond (pale blue).
aldehyde or isophthaldehyde in the presence of a suitable
template agent (tetrabutylammonium terephthalate or iso-
phthalate, respectively), in a macrocyclization reaction that has
already been described.18
The new ligands L1 and L2 were characterised using stan-
dard techniques (1H-NMR, 13C-NMR, HRMS) and in the
case of L1, crystals suitable for single-crystal X-ray diffraction
analysis were obtained. A rather concentrated solution of L1 in
methanol was left evaporating slowly at room temperature.
After four days, colourless elongated crystals of good quality
were obtained.
The results of the X-ray diffraction of the crystal structure
are shown in Fig. 1 (top) together with the corresponding
asymmetric unit (Fig. 1, bottom). The asymmetric unit con-
tains two independent molecules that are linked by two hydro-
gen bonds. These H-bonds induce a global parallel disposition
of the molecules (Fig. S23†). Selected bond distances and
angles are summarized in Table S2.† Carbonyl groups from
amides are located in the syn position, pointing to the same
direction, due to the establishment of hydrogen bonds with
neighbouring molecules (Fig. 1 bottom).
Synthesis and characterization of the copper(II) complexes
Scheme 1 Synthetic route and structure of L1–L4 ligands. (a) Tetra-
hydrofuran, 20 h, r.t., 70–90% (b) HBr/AcOH, 1 h, r.t., 70–80%; (c) (i)
benzaldehyde, methanol, 20 h, r.t. (ii) sodium borohydride, 20 h, r.t.,
44–81%; (d) (i) terephthaldehyde, (TBA)2-terephthalate, methanol, 24 h,
r.t. (ii) sodium borohydride, 24 h, r.t., 65%; (e) isophthaldehyde, (TBA)2-
isophthalate, methanol, 24 h, r.t. (ii) sodium borohydride, 24 h, r.t., 30%.
The copper(II) complexes of both open-chain and macrocyclic
ligands were prepared by applying slight modifications to a
previously reported procedure.14 Bis(amino amide) ligands L1
and L2 were reacted with one equivalent of CuSO4 in metha-
nol, in the presence of two equivalents of NaOH, to ensure the
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 12700–12710 | 12701

View Article Online
Paper
Dalton Transactions
Scheme 2 Structures of the four Cu(II) complexes.
Table 1 Absorption maxima (λmax) and molar absorptivity (ε) of the
corresponding Cu(II) complexes of L1–L4 in methanol
ε (M−1 cm−1
)
Fig. 2 X-band EPR spectra of a frozen methanol solution (103 K) of
Complex
λmax (nm)
Cu(II) complexes (black: experimental; red: simulated).
CuL1
CuL2
Cu2L3
Cu2L4
510
498
526
519
226
150a
365
319
a Value obtained at the lowest studied concentration (1 × 10−4 M) since
hyperchromicity was observed upon dilution.
The ε value of CuL2 is concentration-dependent, as further
confirmed by a dilution study (Fig. S70†), indicating that this
complex undergoes self-aggregation in methanol. This unique
feature of CuL2 complicated the study of its binding properties
by UV-vis spectroscopy.
Besides, upon the Cu(II) complex formation, the IR band
corresponding to the stretching of the carbonyl amide of the
ligands suffers a shift (54–63 cm−1) to lower wavenumbers
(Fig. S18–S21†). This indicates the participation of the deproto-
nated amide groups in the coordination to Cu(II), in agreement
with the data obtained by EPR and the X-ray diffraction of the
crystal structure of CuL2 (see below).
The X-band EPR spectrum of a frozen methanol solution at
103 K of Cu(II) complexes is shown in Fig. 2. The Hamiltonian
parameters obtained from the simulated spectra of these com-
pounds are summarized in Table 2 (entries 1–4).
The simulated parameters show excellent agreement with
the experimental spectra. All the spectra show a characteristic
axial symmetry (g∥ > g⊥ > ge = 2.0023), and indicate that the
copper ions have a square planar coordination. In all cases g∥
and A∥ parameters are typical of neutral CuN4 units according
to the Peisach and Blumberg plot19 (Fig. S32†), pointing out
that the metal centres are equatorially coordinated by four
nitrogen atoms (two amines and two deprotonated amides).
The values of the g∥/A∥ ratio can be used as a convenient
empirical index of tetrahedral distortion in Cu(II) complexes;20
complete deprotonation of the ligand amide groups. Bright
purple solutions were obtained, while a white solid was dis-
carded. Solutions were concentrated to afford the mono-
nuclear complexes CuL1 and CuL2 as purple solids. Similarly,
tetra(amino amide) ligands L3 and L4 were reacted with two
equivalents of CuSO4 and four equivalents of NaOH, affording
dinuclear complexes Cu2L3 and Cu2L4. The structures of the
four complexes are displayed in Scheme 2.
All complexes were characterized by means of high resolu-
tion mass spectrometry, affording in all cases the expected
molecular peaks with the correct isotopic patterns (Fig. S9–
S12†).
In the UV-vis spectra, all complexes exhibit intense ligand
to metal charge transfer transitions (LMCT) in the range of
200–315 nm (Fig. S13†). A less intense absorption band,
responsible for the purple-violet colour and due to d–d tran-
sitions, is present in the range 498–526 nm, suggesting Cu(II)
coordination geometries ranging from square-planar to
square-pyramidal.13 Table
1 collects the wavelength of
maximum absorbance for the d–d transitions (λmax) of all com-
plexes together with the corresponding molar absorptivity (ε).
12702 | Dalton Trans., 2015, 44, 12700–12710
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
Table 2 Best fit EPR spectroscopic parameters of Cu complexes in solid solution (MeOH, 103 K)
a
a
a
b
Entry
Complex
A∥
A⊥
AN
g∥
g⊥
g∥/A∥
Type
1
2
3
4
5
6
7
8
9
CuL1
CuL2
Cu2L3
Cu2L4
Cu2L3 + Suc
Cu2L3 + Mal
Cu2L3 + Asp
CuL1 + Asp
CuL1 + Malc
Cu(Asp)2
199.5
200.8
190.4
197.5
191.4
162.8
168.2
167.6
168.6
167.5
23.6
21.0
23.2
24.8
23.2
25.6
17.6
18.9
24.8
17.6
14.7
15.7
14.8
14.7
14.8
12.8
12.3
12.4
12.8
11.3
2.1822
2.1852
2.1884
2.1846
2.1862
2.2422
2.2609
2.2626
2.2377
2.2611
2.0413
2.0414
2.0436
2.0405
2.0486
2.0487
2.0492
2.0475
2.0477
2.0463
107.4
108.8
112.5
108.5
111.9
131.6
127.4
127.8
127.0
127.9
CuN4
CuN4
CuN4
CuN4
CuN4
CuN2O2
CuN2O2
CuN2O2
CuN2O2
CuN2O2
10
a Values of coupling constants in gauss. b Value of A∥ in cm−1. A [cm−1] = 0.46686 × 10−4 g A[G]. c A minor component is also detected (see
Table S3).
in the studied cases, values of g∥/A∥ fall within the 105–135 cm
X-ray diffraction data confirm the formation of the copper
range, typical of Cu(II) complexes possessing a non-distorted complex with a 1 : 1 stoichiometry. The complex crystallizes
square-planar structure with a dx2−y2 ground state. Finally, the with one molecule of methanol that establishes hydrogen
large similarity between EPR spectra of mononuclear and bonds with one amine group of the same molecule and with
dinuclear complexes, and the absence of a half-field signal at the amide carbonyl group of another molecule (Fig. S24†). The
around 1600 G due to the Δms
= 2 transition in both frozen copper(II) cation is coordinated by two amine groups and two
methanol (107 K) and DMF (103 K) solutions (Fig. S27 and deprotonated amide groups, in a slightly distorted square
S28†) rule out any Cu–Cu dipolar interaction; i.e., dinuclear planar geometry, and displays a torsion angle of 11.84°
Cu(II) complexes Cu2L3 and Cu2L4 behave as mononuclear (between the plane containing N4–Cu–N3 and that containing
complexes. This is also confirmed by the absence of the N3–Cu–N2, see Fig. S25†).
specific bands of the triplet state in the spectrum of the Cu2L3
complex in the solid state (103 K, field scan range: 0 to 7000 G, corresponding Cu–Namine being 1.919 and 2.043 Å on average,
Fig. S29†). respectively. This fact was previously observed for analogous
The Cu–Namide distances are slightly shorter than the
Crystals suitable for single-crystal X-ray diffraction analysis Cu–pseudopeptidic complexes and was attributed to the
were obtained in the case of CuL2. A solution of CuL2 in anionic coordination from the deprotonated Namide donors
methanol was left evaporating slowly at room temperature; instead of the neutral donation from the Namine groups.14 The
after two days, square purple crystals of good quality were N–Cu–N angles contained in the five membered rings (N1–Cu–
obtained.
N2 and N3–Cu–N4) are ca. 10° smaller than the others (N2–
The X-ray crystal structure is presented in Fig. 3 and Cu–N3 and N1–Cu–N4), as expected for a smaller ring size
selected bond distances and angles are presented in Table S2.† with a tighter environment. These values are slightly shorter
than those obtained for an analogous copper complex with a
three methylene chain spacer between the amide groups. The
corresponding N1–Cu–N3 and N2–Cu–N4 distances are shorter
than linear symmetry and also slightly shorter than in a pre-
vious analogous copper complex.14
Unfortunately, we were not able to obtain suitable crystals
for X-ray diffraction with the Cu(II) complexes of the other
ligands. However, the very similar UV-vis and EPR spectro-
scopic data support that the coordination environment of the
copper ion is virtually identical for all the complexes.
Interaction of the copper complexes with dicarboxylates
Many short-chain dicarboxylates play a role in biotransform-
ations. For example, succinate (Suc) acts as an electron donor
in the citric acid cycle and plays a crucial role in adenosine tri-
phosphate (ATP) generation in mitochondria.21 Malate (Mal)
also takes part in the citric acid cycle and is a source of CO2 in
the Calvin cycle.22 Aspartate (Asp) is the precursor to several
Fig. 3 X-ray crystal structure of CuL2. Carbon (grey), oxygen (red),
nitrogen (blue) and copper (orange).
amino acids, including four that are essential for humans:
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 12700–12710 | 12703

View Article Online
Paper
Dalton Transactions
methionine, threonine, isoleucine, and lysine;23 it is also an
important neurotransmitter.24
Among others,25 a variety of receptors and sensors for dicarb-
oxylates containing two Cu(II) centres have been reported due
to the bidentate nature of these anions and the good affinity of
the carboxylate group for the Cu(II) ion.26 Most of the reported
systems are dicopper complexes of polyamine macrocycles27
and cryptands.28 In this study we investigate the coordination
properties of Cu(II) complexes coordinated by both amine and
amide nitrogens present in pseudopeptidic ligands, in an
environment that resembles more closely a metalloprotein.
We started our study with Cu2L3, as we reasoned that the
presence of two Cu(II) ions at a close distance in its structure
would make this complex a good receptor for short-chain
dicarboxylate anions. We carried out an initial screening of
various dicarboxylates (aliphatic dicarboxylic acids, amino
acids and hydroxy acids) as potential guests for the complex by
comparing the absorbance of the CuL3 complex alone and in
the presence of 2 equivalents of dicarboxylate. Interestingly, in
most cases the absorption spectrum was not affected by the
addition of the dicarboxylate, while in a few cases the initial
purple solution turned light blue or light green. We then
focused on some particular cases and studied them in depth,
by accurate UV-vis titration experiments in methanol. Unfortu-
nately, solubility issues of the metal complexes prevented us
Fig. 4 UV-vis absorption spectra of Cu2L3 (1 × 10−3 M, methanol) in
the absence and in the presence of increasing amounts of bis(TBA) salts
of Asp, (top, left) and Mal, (top, right); changes in the normalized absor-
bance at 525 nm of Cu2L3 upon addition of dicarboxylates (bottom;
blue: Suc; pink: N-Ac-Asp; black: Glu; green: Asp; red: Mal).
from performing this study in water. Also, all the dicarboxylate the deprotonated L3 ligand rendered two significantly
substrates were used as the corresponding bis(tetrabutyl- different spectra. The first has a λmax = 691 nm (ε = 43 M−1
ammonium) (TBA) salts for a better solubility in methanol.
cm−1) while the second has a λmax = 649 nm (ε = 41 M−1 cm−1
)
The most striking cases were those of Mal, Asp and Glu (Fig. S39†). These combined data are consistent with the for-
(throughout the study, the naturally occurring L isomers were mation of a ternary complex with the formula Cu2L3Mal2.
always used). Titration of Cu2L3 with Mal showed a bathochro-
The case of aspartate is different: the Job plot shows a
mic shift in λmax from 526 to 575 nm (Fig. 4, top right) result- maximum for χanion = 0.56 (Fig. S44†). This value is intermedi-
ing in a change in colour from intense purple to light green. A ate between 0.5 and 0.66, suggesting the simultaneous pres-
similar trend from purple to pale blue was observed in the ence of different species, with Cu : Asp ratios of 1 : 1 and 1 : 2.‡
case of the of the corresponding TBA salts of Asp and Glu: the The comparison of the absorption spectrum of CuAsp2
λmax shifted to 628 nm (Fig. 4, top left) and 604 nm, respecti- (obtained by addition of 2.0 equivalents of Asp to a solution of
vely. In contrast, addition of succinate had no effect on the CuSO4), with that obtained after the addition of the deproto-
absorption spectrum of the system (Fig. S34†). The case of nated L3 ligand returned two almost identical spectra: the first
N-acetyl-L-aspartate (N-Ac-Asp) was intermediate: the intensity has λmax = 634 nm (ε = 47 M−1 cm−1) while the second has λmax
of the absorption band at 526 nm decreased, but only to a low = 635 nm (ε = 49 M−1 cm−1) (Fig. S45†). These combined data
extent (≈20% of the initial value). A general trend clearly suggest the presence of both Cu2L3Asp2 and CuAsp2 species,
emerged from these titrations: complex Cu2L3 was able to the latter being predominant. In other words, aspartate is able
coordinate dicarboxylates with a heteroatom in the α position to displace a high fraction of the Cu(II) ion from the macro-
to one COO− group. However, the dicarboxylates having the cyclic ligand L3.
protected heteroatom were weakly coordinated and those
lacking the heteroatom were not coordinated at all.
These conclusions are supported by the EPR studies.
Addition of Suc did not affect the EPR spectrum of the Cu2L3
Following this, the titration curves of malate and aspartate complex, while addition of a small excess (ca. 3 eq.) of Mal and
were analysed more in-depth. Job plots were built by reporting Asp altered it (Table 2, entries 3, 5–7 and Fig. 5). The value of
ΔAbs/χanion as a function of χanion (calculated with respect to A∥ decreased from 190.4 G to 162.8 G (Mal) and 168.2 G (Asp)
Cu). In the case of malate, the plot shows a maximum for while that of g∥ increased from 2.1884 to 2.2422 (Mal) and
χanion = 0.50 (Fig. S38†) thus indicating that the Cu : Mal ratio 2.2609 (Asp). These changes of the EPR parameters imply a
in the formed species is 1 : 1. Accordingly, this result implies modification of the coordination environment of the metal
the binding of two equivalents of Mal per Cu2L3 complex
molecule. Moreover, comparison of the absorption spectrum
of Cu(Mal)2 (obtained by addition of 2.0 equivalents of Mal to
‡Analysis of the titration data with Glu rendered the same result (Job plot
a solution of CuSO4), with that obtained after the addition of maximum for χanion = 0.60).
12704 | Dalton Trans., 2015, 44, 12700–12710
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
the aromatic spacer. In principle, L4 would set the Cu(II) ions
at a closer distance. To find out if this small variation had an
effect on the interaction with dicarboxylates, we investigated
the coordination properties of the Cu2L4 complex. However,
both EPR and UV-vis spectra showed no substantial
differences.
Although less studied, mononuclear Cu(II) complexes have
also been employed in dicarboxylate binding.30 For this
reason, and to gain further insight into the binding character-
istics of the complexes, the coordination abilities of the open-
chain mononuclear analogue of Cu2L3, CuL1, were studied.
According to UV-vis titrations, the coordination properties
of CuL1 towards Suc, Mal and Asp are very similar to those of
Cu2L3, apart from the differences in the stoichiometry of the
binding.
Titration of CuL1 with Mal showed a bathochromic shift in
λmax from 508 to 646 nm, resulting in a change in color from
intense purple to light green (Fig. S56†). In the case of Asp, it
changed to light blue and the λmax shifted to 631 nm
(Fig. S61†). In contrast, addition of succinate had no effect on
the absorption spectrum of the system (Fig. S54†). However,
the titration curves for Mal and Asp (Fig. 6) are different; the
first one is much steeper and reaches a plateau for 1.25 equi-
valents of Mal, while the latter one shows that saturation, if
reached, requires a larger number of equivalents. The differ-
ence between Mal and Asp titration curves is clearer from the
respective Job plots (inset in Fig. 6). Job plots were built by
reporting ΔAbs/χanion as a function of χanion. In the case of Mal,
the plot shows a maximum for χanion = 0.50 thus indicating
that the Cu : Mal ratio in the formed species is 1 : 1 (Fig. S58†).
We also compared the absorption spectrum of CuMal2
obtained by addition of 2.0 equivalents of Mal to a solution of
CuSO4 in methanol, with that obtained after the addition of
one equivalent of the deprotonated L1 ligand. The two spectra
are different: the first has λmax = 697 nm while the second has
Fig. 5 X-band EPR spectra of a frozen methanol solution (103 K) of
Cu2L3 alone and in the presence of different dicarboxylate anions
(black: experimental; red: simulated).
centre from CuN4 to CuN2O2, maintaining the overall neutral
charge (Fig. S33†). Since Mal has no nitrogen atoms in its
structure, this result suggests that Mal coordinates to Cu(II)
through its alcohol and carboxylate groups, displacing one
(amino amide) moiety of L3. On the other hand, the amino
acids, Asp and Glu, can coordinate the Cu(II) ion via the
carboxylate and the amine groups, thus displacing L3 almost
completely.
Due to the paramagnetic nature of the Cu(II) ion, its
complexes are usually difficult to study by means of NMR
spectroscopy, as their spectra show severe broadening of the
signals.29 However, we undertook a 1H-NMR study of Cu2L3
and its Asp and Mal adducts. All the signals in the 1H-NMR
spectrum of Cu2L3 (Fig. S71,† bottom) were broad and poorly
resolved, suggesting a close connection of the organic ligand
with the Cu(II) ion. Upon the addition of 2.0 equivalents of
Asp, some very broad signals of L3 sharpened (doublets at 3.60
and 3.30 ppm, doublets of doublets at 2.75 and 2.95 ppm
Fig. S71,† top). Addition of 2.0 equivalents of Mal (Fig. S71,†
middle) provoked a similar transformation on the signals of
L3, but to a lesser extent. This different behaviour supports
the observation that Mal has a minor tendency to displace
Cu(II) ions from L3, as it mainly forms the ternary species
Cu2L3Mal2.
Fig. 6 Changes in the normalized absorbance at 508 nm of CuL1 upon
addition of dicarboxylates (black: Suc; blue: Asp; red: Mal). Inset: Job
plots for CuL1 + Asp (blue) and CuL1 + Mal (red).
Ligand L4 is a macrocyclic structure that slightly differs
from L3, due to the meta instead of the para substitution of
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 12700–12710 | 12705

View Article Online
Paper
Dalton Transactions
λmax = 666 nm (Fig. S59†). These combined data suggest the
formation of a ternary complex with the formula CuL1Mal as
the predominant species.
Table 3 Stepwise and cumulative formation constants determined by
UV-vis titrations in methanol at 298 K. The standard deviations are
reported in parentheses as uncertainties on the last significant figure
The case of Asp is quite different: the Job plot shows a
maximum for χanion = 0.60 and the comparison of the absorp-
tion spectrum of CuAsp2 with that obtained after the addition
of one equivalent of the deprotonated L1 ligand rendered two
almost identical spectra (Fig. S63–S64†). Similarly to its macro-
cyclic analogue, the combined UV-vis data suggest the co-exist-
ence of a ternary complex (CuL1Asp) together with the CuAsp2
complex. However, the percentage of CuAsp2 in this case
should be higher (the Job plot maximum now is 0.60; for
Cu2L3 it was 0.56). Not surprisingly, it would be easier for Asp
to displace the Cu(II) ion from the open-chain ligand L1 than
from the macrocyclic ligand L3.
Entry
Reactiona
Log β
Log K
1
2
3
4
5
6
7
8
Cu + Asp → CuAsp
6.08 (3)
10.75 (3)
Cu + 2Asp → CuAsp2
CuAsp + Asp → CuAsp2
Cu + Mal → CuMal
Cu + 2Mal → CuMal2
CuMal + Mal → CuMal2
Cu + L1 → CuL1
4.67
4.31
5.77 (4)
10.08 (4)
5.40 (4)
9.25 (4)
2Cu + L1 → Cu2L1
9
Cu + CuL1 → Cu2L1
Cu + L1 + Asp → CuL1Asp
CuL1 + Asp → CuL1Asp
Cu + L1 + Mal → CuL1Mal
CuL1 + Mal → CuL1Mal
3.85
4.50
5.61
10
11
12
13
9.90 (1)
11.01 (3)
The 1H-NMR study of CuL1 and its aspartate and malate
adducts rendered similar results to those found for its macro-
cyclic counterpart Cu2L3 (Fig. S72†). The different aspect of
the spectra supports the hypothesis that Mal forms mainly the
ternary species CuL1Mal, while Asp has a higher tendency to
displace Cu(II) ions from the pseudopeptidic ligand, leading
mainly to the formation of the CuAsp2 complex, together with
a small amount of CuL1Asp ternary species.
a Charges have been omitted for simplicity.
vs. Mal and Asp were carried out, allowing the determination
of the stability constants for the corresponding ternary com-
plexes (entries 10 and 12 in Table 3). Interestingly, the ternary
complex with Mal is one order of magnitude more stable than
the one with Asp, which is evident when comparing the corres-
ponding stepwise equilibrium constants (entries 11 and 13 in
Table 3). Thus, the analysis of the data reported in Table 3
underscores the different behaviour of CuL1 in the presence of
Mal and Asp anions. This difference is clearer by plotting the
species distribution during the titration of the CuL1 complex
with either Mal or Asp dicarboxylates (Fig. 7). In the case of
Mal, the addition of one equivalent of dicarboxylate mainly led
to the formation of the ternary species (CuL1Mal) while for
Asp, a complex mixture was obtained, due to the efficient dis-
placement of the Cu ion from CuL1, produced by the Asp
ligand.
Detailed analysis of the interaction of CuL1 with Asp and Mal
In view of the intricacy of the different equilibria taking place
between the studied Cu(II) complexes and dicarboxylate
anions, we undertook a detailed and quantitative study of the
interaction between the simple mononuclear CuL1 complex
and the Asp/Mal pair. First of all, we determined the binding
constants and the stoichiometry of binding of Asp and Mal
anions to the Cu(II) cation under our experimental conditions.
In fact, amino acids and hydroxy acids are known to form
stable complexes with Cu(II),31 with a CuL2 general formula. A
solution of CuSO4 in methanol was titrated with Asp or Mal.
The UV-vis spectral variations regarding the titration with Asp
are shown in Fig. S67.† The results are compatible with the for-
mation of two complexes, CuAsp and CuAsp2. The absorption
is blue shifted upon complexation giving a maximum around
700 nm for the 1 : 1 complex and 637 nm for the 1 : 2 complex.
The stability constants obtained by fitting the data to this equi-
librium pattern are reported in Table 3 (entries 1–3).
Thus, as described in Fig. 7, CuL1 can form a ternary
complex with both Mal and Asp, but while in the first case this
complex is relatively stable, in the latter the equilibrium is
shifted towards the formation of CuAsp2 and the free L1
ligand (Scheme 3). EPR spectra of CuL1 in the presence of a
slight excess (ca. 2 equivalents) of Asp and Mal supported this
Similar results were obtained regarding the Cu(II) complexa-
tion with Mal (Fig. S68†). In this case the 1 : 1 complex absorbs
mainly in the 700–800 nm region whereas the 1 : 2 complex
has a maximum around 694 nm (Table 3, entries 4–6). In both
cases, the stability constants are high enough to allow the for-
mation of the 1 : 2 complexes (CuL2) under the conditions
used for the UV-vis study ([Cu2+] ≈ 1 × 10−3 M; [dicarboxylate]
up to 4 × 10−3 M). Besides, the stability of the complexes
formed by Cu(II) with Asp was seen to be slightly higher than
those formed with Mal.
Following this, we determined the equilibrium constant for
the formation of the CuL1 complex (entries 7–9 in Table 3).
The titration revealed the formation of a transient complex
Fig. 7 Species distribution for the titration of the CuL1 complex with
Mal (left) or Asp (right). The plot was generated using the stability con-
with a 2 : 1 stoichiometry, Cu2L1. Finally the titrations of CuL1 stants reported in Table 3 and [Cu] = [L1] = 1 × 10−3 M.
12706 | Dalton Trans., 2015, 44, 12700–12710
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
bath and the reaction mixture was stirred at room temperature
for16 hours. Aqueous 4 M HCl was added, and a white solid
formed. After 1 hour the solvents were evaporated at reduced
pressure, affording a solid that was suspended in aqueous 4 M
NaOH. The product was extracted twice with DCM and once
with AcOEt. Organic layers were combined, dried over MgSO4
and concentrated at reduced pressure. The resulting thick oil
was suspended in diethyl ether, triturated, filtered and washed
with additional diethyl ether, affording L1 as a white solid
(440 mg, 0.82 mmol, 81% yield).
1H-NMR (400 MHz, CDCl3) δ 7.29 (bs, 2H), 7.26–7.15
(m, 12H), 7.12–7.09 (m, 4H), 7.05 (dd, J = 7.5, 1.9 Hz, 4H), 3.66
(d, J = 13.4 Hz, 2H), 3.48 (d, J = 13.4 Hz, 2H), 3.37–3.21 (m,
4H), 3.29 (dd, J = 9.1, 4.8 Hz, 2H), 3.13 (dd, J = 13.8, 4.7 Hz,
2H), 2.71 (dd, J = 13.8, 9.1 Hz, 2H), 1.65 (bs, 2H). 13C-NMR
(101 MHz, CDCl3) δ 174.4, 139.2, 137.5, 129.3, 128.8, 128.6,
128.0, 127.3, 127.0, 63.2, 52.7, 39.5, 39.3. HRMS (ESI-TOF) m/z
[L1 − H]− Calcd for (C34H37N4O2) 535.3073, found 535.3080. IR
(KBr, ν cm−1): 3345, 3282, 1652, 1522, 745, 697.
Scheme 3 Proposed model of interaction of CuL1 with malate (X =
OH) and aspartate (X = NH2).
L2: Obtained following the same procedure described for
L1, using 2 (400 mg, 0.82 mmol) as the starting material. L2
was obtained as a waxy solid (240 mg, 0.82 mmol, 44% yield).
1H-NMR (400 MHz, CDCl3) δ 7.52 (t, J = 6.4 Hz, 2H), 7.35–7.18
(m, 12H), 7.14 (d, J = 6.6 Hz, 4H), 7.07 (d, J = 7.4 Hz, 4H), 3.70
(d, J = 13.4 Hz, 2H), 3.53 (d, J = 13.4 Hz, 2H), 3.36 (dd, J = 9.3,
4.4 Hz, 2H), 3.20–3.09 (m, 6H), 2.73 (dd, J = 13.8, 9.3 Hz, 2H),
1.75 (bs, 2H), 1.54 (p, J = 6.4 Hz, 2H). 13C-NMR (101 MHz,
CDCl3) δ 174.0, 139.2, 137.4, 129.1, 128.7, 128.5, 128.0, 127.1,
126.8, 63.2, 52.6, 39.4, 35.6, 30.0. HRMS (ESI-TOF) m/z
[L2 − H]− Calcd for (C35H39N4O2) 547.3076, found 547.3073. IR
(KBr, ν cm−1): 3415, 3229, 1638, 1617, 1398.
hypothesis, as they showed the formation, in both cases, of
Cu(II) species with CuN2O2 coordination, and overall zero
charge (Table 2, entries 1, 8, 9 and Fig. S26†). In particular, the
EPR spectrum of the CuL1/Asp system is very similar to that of
CuAsp2 (obtained by mixing CuSO4 and Asp in methanol)
(Fig. S30†) with close spectral parameters (entry 10, Table 2).
In the case of Mal, the EPR spectrum (Fig. S31†) shows two
components of different intensities, both assignable to
CuN2O2 coordination. This may be due to two different dis-
positions of the Mal anion in the ternary complex; in fact, the
carboxylate ligand can be in a cis or trans position relative to
the amino ligand in the Cu complex. The structure proposed
for the ternary supramolecular complex CuL1Mal also fits well
the ATR-IR spectrum (Fig. S22†), which shows for the ternary
complex a broad band with two major components: 1650 and
1593 cm−1, relative to free and metal-coordinated amides,
respectively. The complexity of the equilibria prevented us to
undertake the same detailed study for the dinuclear Cu2L3
complex. In particular, the stability constant of the macrocyclic
Cu2L3 complex was too high to be accurately determined by
UV-vis titrations in the required concentration range. However,
the main difference between CuL1 and Cu2L3 seems to be the
lower tendency of the macrocyclic ligand to transfer the metal
to Asp anions, probably due to the higher stability of the
Cu2L3 complex due to the macrocyclic effect.
L3 and L4 were prepared as already described.18 L3: IR
(KBr, ν cm−1): 3415, 1653, 1521, 702. L4: IR (KBr, ν cm−1):
3417, 3232, 1643, 1520, 1397, 699.
Synthesis of the Cu(II) complexes
CuL1: To a solution of L1 (105 mg, 0.197 mmol) in MeOH
(20 mL) were added CuSO4·5H2O (50 mg, 0.200 mmol) and
NaOH (16 mg, 0.40 mmol). A colour change from blue to
purple was observed. The reaction mixture was stirred for
30 minutes at room temperature and then centrifuged for
10 minutes. The white solid was discarded while the purple
solution was concentrated at reduced pressure. CuL1 was
obtained as a purple solid (94 mg, 0.157 mmol, 80%
yield). UV-vis (1 × 10−3 M, MeOH) λmax = 510 nm; ε = 226 M−1
cm−1
. HRMS (ESI-TOF) m/z [CuL1 +
Cl]− Calcd for
(C34H3635Cl63CuN4O2) 630.1823, found 630.1899; [CuL1
+
HCOO]− Calcd for (C35H3763CuN4O4) 640.2111, found
640.2189. IR (KBr, ν cm−1): 3406, 1598, 1454, 751, 700. Elemen-
tal analysis: found: C: 64.75%, H: 5.93%; N: 8.75%; calculated
Experimental
Synthesis of the ligands
Primary diamines
described.17
1
and
2
were prepared as already for CuL1 + 2H2O; C: 64.59%, H: 6.38%, N: 8.86%.
CuL2: Prepared following the same procedure described for
L1: To a solution of 1 (360 mg, 1.01 mmol) in methanol CuL1. CuL2 was obtained as a pink solid. 76% yield. UV-vis
(15 ml) was added benzaldehyde (454 µl, 4.46 mmol) and the (2.4 × 10−3 M, MeOH) λmax = 498 nm; ε = 94 M−1 cm−1. HRMS
resulting solution was stirred at room temperature for 6 hours. (ESI-TOF) m/z [CuL2 + Cl]− Calcd for (C35H3835Cl63CuN4O2)
Sodium borohydride (470 mg, 12.2 mmol) was added in an ice 644.1979, found 644.2072; [CuL2
+
HCOO]− Calcd for
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 12700–12710 | 12707

View Article Online
Paper
Dalton Transactions
(C36H3963CuN4O4) 654.2267, found 654.2340. IR (KBr, ν cm−1): several samples containing 1 mL of the Cu(II) solution and
3405, 3229, 1576, 1398. Elemental analysis: found: C: 63.66%, increasing amounts of the L1 solution (from 0 to 3.0 equi-
H: 6.35%; N: 8.43%; calculated for CuL2 + 3H2O; C: 63.28%, valents) were prepared and left to equilibrate for 24 hours
H: 6.68%, N: 8.43%.
prior to the measurement in the spectrophotometer.
Cu2L3: To a solution of L3 (215 mg, 0.228 mmol) in MeOH
CuL1 vs. dicarboxylates: a solution of 1 × 10−3 M CuL1 was
(25 mL) were added CuSO4·5H2O (115 mg, 0.46 mmol) and titrated with 2.0 × 10−2 M (TBA)2-dicarboxylate (from 0 to 3.0
NaOH (37 mg, 0.92 mmol). A colour change from blue to equivalents). In the case of malate and aspartate, the associ-
purple was observed. The reaction mixture was stirred for ation constants were calculated fitting the absorption vari-
30 minutes at room temperature and then centrifuged for ations from 450 to 750 nm. For these fittings, the
10 minutes. The white solid was discarded while the purple corresponding stability constants for CuL1 and the Cu-dicarb-
solution was concentrated at reduced pressure. Cu2L3 was oxylate complexes were introduced as constant fixed values.
obtained as a purple solid (175 mg, 0.164 mmol, 72% yield).
UV-vis (7 × 10−4 M, MeOH) λmax = 526 nm; ε = 365 M−1 cm−1
HRMS (ESI-TOF) m/z [Cu2L3
Cu2L3 and Cu2L4 vs. dicarboxylates: a solution of 7 × 10−4
M Cu2L3 (or Cu2L4) was titrated with 1.4 × 10−3 M (TBA)2-
.
+
HCOO]− Calcd for dicarboxylate (from 0 to 4.0 equivalents).
(C57H6163Cu2N8O6) 1081.3304, found 1081.3602. IR (KBr, ν
cm−1): 3404, 1599, 702. Elemental analysis: found: C: 64.15%,
H: 6.21%; N: 10.43%; calculated for: Cu2L3 + 1H2O; C: 63.80%,
H: 5.93%, N: 10.63%.
Crystal structure determination
Cu2L4: Prepared following the same procedure described
for Cu2L3. Cu2L4 was obtained as a pink solid. 81% yield. UV-
Data for all structures were collected on a STOE IPDS II two-
circle diffractometer with a Genix Microfocus tube with mirror
optics using MoKα radiation (λ = 0.71073 Å) and were scaled
using the frame scaling procedure in the X-AREA program
system.33
The structures were solved by direct methods using the
program SHELXS and refined against F2 with full-matrix least-
squares techniques using the program SHELXL-97.34
All H atoms in L1 were refined using a riding model. Due to
the absence of anomalous scatterers, the absolute configur-
ation could not be determined.
The H atoms bonded to N and O in CuL2 were freely
refined. The absolute configuration was determined by refin-
ing the Flack-x-parameter, x = −0.025(13) (Table 4).
CCDC 1059976 (L1) and CCDC 1059975 (CuL2) contain the
supplementary crystallographic data for this paper.
vis (5 × 10−4 M, MeOH) λmax = 519 nm; ε = 319 M−1 cm−1
.
HRMS (ESI-TOF) m/z [Cu2L4
+
HCOO]− Calcd for
(C57H6163Cu2N8O6) 1081.3304, found 1081.3629. IR (KBr, ν
cm−1): 3414, 3229, 1614, 1397. Elemental analysis: found: C:
63.75%, H: 5.95%; N: 10.38%; calculated for Cu2L4 + 1H2O; C:
63.80%, H: 5.93%, N: 10.63%.
EPR experiments
EPR spectra of Cu(II) complexes in methanol at 103 K were
recorded on a Bruker EMX-Plus 10/12 Bruker BioSpin spectro-
meter with an X-band microwave bridge EMX Premium X, a
10″ERO73 magnet and a power supply of 12 kW (ERO83). The
temperature was controlled by a Bruker ER 4111 VT tempera-
ture control system. Spectrometer parameters for acquiring
spectra were: magnetic field, 3300 G with a sweep width of
2000 G. A 15.170 mW microwave power at a frequency of 9.442
GHz was used with a modulation amplitude of 1.60 G and a
frequency of 100 kHz. The EPR spectra were simulated with
software from Bruker WIN-EPR system (v 2.22 Rev. 12) and
WIN-EPR SimFonia (v 1.26 beta).
Table 4 Crystal data and structure refinement for L1 and CuL2
Compounds
L1
CuL2
Empirical formula
Form. weight [g cm−3
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C34H38N4O2
534.68
C36H42CuN4O3
642.27
]
UV-vis titrations
Triclinic
P1 (no. 1)
9.631(3)
10.027(3)
15.551(4)
86.83(2)
87.67(2)
78.27(2)
1467.5(7)
0.076
11 889
8265
0.1832
8265/3/721
0.148
Orthorhombic
P212121 (no. 19)
10.0943(8)
15.9068(10)
19.5472(13)
90
90
90
3138.7(4)
0.739
13 262
5861
0.0591
5861/0/410
0.0365
0.0821
1.002
0.315
−0.451
All the titrations were carried out in methanol. UV-vis spectra
were recorded on a SpectraMax M5 spectrophotometer. The
association constants were calculated using the HypSpec
1.1.33 software for Windows.32 Species distributions of Fig. 7
were made with the HySS software (http://www.hyperquad.co.
uk/hyss.htm).
α [°]
β [°]
γ [°]
Volume [Å3]
Absorption coeff.
Reflections collected
Unique reflections
R(int)
Formation of CuAsp2 and CuMal2: a solution of 1.4 × 10−3
M CuSO4·5H2O was titrated respectively with 1.4 × 10−2
M
(TBA)2-L-aspartate and 1.4 × 10−2 M (TBA)2-L-malate (from 0 to
3.0 equivalents). The absorption variations from 500 to
800 nm were fitted to 1 : 1 and 1 : 2 models.
Data/restraints/parm.
R1 [I > 2σ(I)]
wR2 [all data]
GooF
0.418
1.064
0.544
−0.661
Formation of CuL1: a solution of CuSO4 7 × 10−4 M was
titrated in batch with a solution of L1 7.0 × 10−3 M containing
2.2 equivalents of TBAOH. The next procedure was followed:
Diff. peak [e Å−1
]
Diff. hole [e Å−1
]
12708 | Dalton Trans., 2015, 44, 12700–12710
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
M. Metz, S.-K. Lee and A. E. Palmer, Angew. Chem., Int. Ed.,
2001, 40, 4570; (c) G. Henkel and B. Krebs, Chem. Rev.,
2004, 104, 801; (d) E. I. Solomon, R. K. Szilagyi, S. DeBeer
George and L. Basumallick, Chem. Rev., 2004, 104, 419;
(e) P. C. Ford, B. O. Fernandez and M. D. Lim, Chem. Rev.,
2005, 105, 2439; (f) M. L. Zastrow and V. L. Pecoraro, Coord.
Chem. Rev., 2013, 257, 2565.
Conclusions
The present study reports the synthesis and the characteriz-
ation of mononuclear Cu(II) complexes with bis(amino amide)
ligands (L1 and L2) and dinuclear Cu(II) complexes with tetra-
(amino amide) ligands (L3 and L4). The metal ion always dis-
plays the square planar coordination geometry, being
connected to four nitrogen atoms (two amines and two
deprotonated amides).
The complexes interact with hydroxy- and amino-dicarboxy-
late substrates, and this event provokes a strong change in the
visible absorption spectra. In particular, the interaction with
two biologically important dicarboxylates possessing very
similar structures (malate and aspartate) has a completely
different outcome. In the case of malate, a ternary complex
[ligand⋯metal⋯dicarboxylate] is formed almost quantitat-
ively; while in the case of aspartate, the anion is able to dis-
place Cu(II) from the ligand to form, mainly, the Cu(Asp)2
complex. These complexes are model compounds that mimic
the ligand exchange observed in natural systems and especially
the function of metal ionophores. In fact, ionophores are
specific ligands that bind a metal cation, transport it across a
cellular membrane, and then release it in response to different
stimuli (for example lower pH or presence of competitive
ligands).
3 (a) R. H. Holm, P. Kennepohl and E. I. Solomon, Chem.
Rev., 1996, 96, 2239; (b) J. T. Rubino and K. J. Franz,
J. Inorg. Biochem., 2012, 107, 129; (c) E. I. Solomon,
D. E. Heppner, E. M. Johnston, J. W. Ginsbach, J. Cirera,
M. Qayyum, M. T. Kieber-Emmons, C. H. Kjaergaard,
R. G. Hadt and L. Tian, Chem. Rev., 2014, 114, 3659.
4 (a) A. L. van den Brenk, D. P. Fairlie, G. R. Hanson,
L. R. Gahan, C. J. Hawkins and A. Jones, Inorg. Chem.,
1994, 33, 2280; (b) P. V. Bernhardt, P. Comba, D. P. Fairlie,
L. R. Gahan, G. R. Hanson and L. Lötzbeyer, Chem. – Eur.
J., 2002, 8, 1527; (c) P. Comba, L. R. Gahan, G. Haberhauer,
G. R. Hanson, C. J. Noble, B. Seibold and A. L. van den
Brenk, Chem. – Eur. J., 2008, 14, 4393; (d) P. Comba,
N. Dovalil, L. R. Gahan, G. Haberhauer, G. R. Hanson,
C. J. Noble, B. Seibold and P. Vadivelu, Chem. – Eur. J.,
2012, 18, 2578; (e) P. Comba, N. Dovalil, L. R. Gahan,
G. R. Hanson and M. Westphal, Dalton Trans., 2014, 43,
1935.
We are currently exploiting the modularity of the structure
of the pseudopeptidic ligands, that allow changes in the
spacer, the amino acid residue and the amine substituent, in
order to improve the solubility of the Cu(II) complexes in water
and tune their stability.
5 (a) M. Remelli, M. Peana, S. Medici, L. G. Delogu and
M. A. Zoroddu, Dalton Trans., 2013, 42, 5964; (b) S. C. Drew,
Chem. – Eur. J., 2015, 21, 7111.
6 (a) J. L. Hickey, P. J. Crouch, S. Mey, A. Caragounis,
J. M. White, A. R. White and P. S. Donnelly, Dalton Trans.,
2011, 40, 1338; (b) S. Tardito, I. Bassanetti, C. Bignardi,
L. Elviri, M. Tegoni, C. Mucchino, O. Bussolati, R. Franchi-
Gazzola and L. Marchiò, J. Am. Chem. Soc., 2011, 133, 6235;
(c) V. Oliveri, M. Viale, G. Caron, C. Aiello, R. Gangemi and
G. Vecchio, Dalton Trans., 2013, 42, 2023.
Acknowledgements
This work was supported by the Spanish Ministry of Economy
and Competitiveness (MINECO, CTQ2012-38543-C03-03 and
CTQ2012-36074) and Generalitat de Catalunya (2014 SGR 231).
This research was also supported by a Marie Curie Intra Euro-
pean Fellowship within the 7th European Community Frame-
work Programme (R. G.). E. F. thanks CSIC for the concession
of a JAE-Doc grant, a program co-funded by the European
Social Fund. We thank Daniel Heras, Mari Carmen Alcalá,
Miquel Sintes and Sandra Bassas for performing some
experiments.
7 (a) R. Österberg, Coord. Chem. Rev., 1974, 12, 309;
(b) V. Lillo and J. R. Galán-Mascarós, Dalton Trans., 2014,
43, 9821.
8 (a) B. Gyurcsik, T. Gajda, L. Nagy and K. Burger, J. Chem.
Soc., Dalton Trans., 1992, 2787; (b) T. Gajda, B. Henry,
A. Aubry and J.-J. Delpuech, Inorg. Chem., 1996, 35, 586;
(c) H. Kurosaki, R. K. Sharma, S. Aoki, T. Inoue,
Y. Okamoto, Y. Sugiura, M. Doi, T. Ishida, M. Otsuka and
M. Goto, J. Chem. Soc., Dalton Trans., 2001, 441;
(d) H. B. Albada, F. Soulimani, B. M. Weckhuysen and
R. M. J. Liskamp, Chem. Commun., 2007, 4895;
(e) S. Bhattacharyya, A. Sarkar, S. K. Dey, G. P. Jose,
A. Mukherjee and T. K. Sengupta, Dalton Trans., 2013, 42,
11709; (f) A.-S. Felten, N. Pellegrini-Moïse, K. Selmeczi,
B. Henry and Y. Chapleur, Eur. J. Org. Chem., 2013, 5645;
(g) S. Zhu, Z. Qiu, T. Ni, X. Zhao, S. Yan, F. Xing, Y. Zhao,
Y. Bai and M. Li, Dalton Trans., 2013, 42, 10898.
Notes and references
1 (a) M. C. Linder, Biochemistry of Copper, Springer, US, 1991;
(b) E. D. Harris, Annu. Rev. Nutr., 2000, 20, 291;
(c) H.-B. Kraatz and N. Metzler-Nolte, Concepts and models
in bioinorganic chemistry, Wiley-VCH Weinheim, Germany,
2006; (d) I. Bertini, Biological inorganic chemistry: structure
and reactivity, University Science Books, 2007.
9 S. V. Luis and I. Alfonso, Acc. Chem. Res., 2014, 47, 112.
10 (a) R. Marchelli, A. Dossena, G. Casnati, G. G. Fava and
M. F. Belicchi, J. Chem. Soc., Chem. Commun., 1985, 1672;
(b) T. R. Wagler, Y. Fang and C. J. Burrows, J. Org. Chem.,
2 (a) A. C. Rosenzweig and T. V. O’Halloran, Curr. Opin.
Chem. Biol., 2000, 4, 140; (b) E. I. Solomon, P. Chen,
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 12700–12710 | 12709

View Article Online
Paper
Dalton Transactions
1989, 54, 1584; (c) B. Dangel, M. Clarke, J. Haley, D. Sames 25 D. Curiel, M. Más-Montoya and G. Sánchez, Coord. Chem.
and R. Polt, J. Am. Chem. Soc., 1997, 119, 10865; Rev., 2015, 284, 19.
(d) C. L. Weeks, P. Turner, R. R. Fenton and P. A. Lay, 26 L. Fabbrizzi and A. Poggi, Chem. Soc. Rev., 2013, 42, 1681.
J. Chem. Soc., Dalton Trans., 2002, 931; (e) M. I. Burguete, 27 (a) Q. Lu, J. J. Reibenspies, A. E. Martell and
F. Galindo, S. V. Luis and L. Vigara, Dalton Trans., 2007,
4027.
11 F. Galindo, M. I. Burguete, L. Vigara, S. V. Luis, N. Kabir,
J. Gavrilovic and D. A. Russell, Angew. Chem., Int. Ed., 2005,
44, 6504.
12 (a) I. Alfonso, M. Bolte, M. Bru, M. I. Burguete, S. V. Luis
and C. Vicent, Org. Biomol. Chem., 2010, 8, 1329;
(b) E. Faggi, A. Moure, M. Bolte, C. Vicent, S. V. Luis and
I. Alfonso, J. Org. Chem., 2014, 79, 4590.
13 S. Blasco, M. I. Burguete, M. P. Clares, E. García-España,
J. Escorihuela and S. V. Luis, Inorg. Chem., 2010, 49, 7841.
14 I. Marti, A. Ferrer, J. Escorihuela, M. I. Burguete and
S. V. Luis, Dalton Trans., 2012, 41, 6764.
R. J. Motekaitis, Inorg. Chem., 1996, 35, 2630;
(b) C. Bazzicalupi, A. Bencini, A. Bianchi, V. Fusi, E. Garcia-
España, C. Giorgi, J. M. Llinares, J. A. Ramirez and
B. Valtancoli, Inorg. Chem., 1999, 38, 620; (c) S. Carvalho,
C. Cruz, R. Delgado, M. G. B. Drew and V. Felix, Dalton
Trans., 2003, 4261; (d) F. Li, R. Delgado and V. Félix,
Eur. J. Inorg. Chem., 2005, 4550; (e) M. Boiocchi,
M. Bonizzoni, A. Moletti, D. Pasini and A. Taglietti, New
J. Chem., 2007, 31, 352; (f) S. l. Carvalho, R. Delgado,
M. G. B. Drew and V. Félix, Dalton Trans., 2007, 2431;
(g) L. Tang, J. Park, H.-J. Kim, Y. Kim, S. J. Kim, J. Chin and
K. M. Kim, J. Am. Chem. Soc., 2008, 130, 12606; (h) F. Li,
S. Carvalho, R. Delgado, M. G. Drew and V. Félix, Dalton
Trans., 2010, 39, 9579; (i) M. Hu and G. Feng, Chem.
Commun., 2012, 48, 6951.
15 I. Alfonso, I. Burguete, S. V. Luis, J. F. Miravet, P. Seliger
and E. Tomal, Org. Biomol. Chem., 2006, 4, 853.
16 (a) J. Berg, J. Tymoczko and L. Stryer, Biochemistry, 28 (a) M. Boiocchi, M. Bonizzoni, L. Fabbrizzi, G. Piovani and
Freeman, 5th edn, 2002; (b) D. L. Nelson, A. L. Lehninger
and M. M. Cox, Lehninger principles of biochemistry,
Macmillan, 2008.
A. Taglietti, Angew. Chem., Int. Ed., 2004, 43, 3847;
(b) G. Y. Xie, L. Jiang and T. B. Lu, Dalton Trans., 2013, 42,
14092; (c) P. Mateus, R. Delgado, V. Andre and
M. T. Duarte, Inorg. Chem., 2015, 54, 229.
17 J. Becerril, M. Bolte, M. I. Burguete, F. Galindo, E. García-
España, S. V. Luis and J. F. Miravet, J. Am. Chem. Soc., 2003, 29 T. Gärtner and R. M. Gschwind, in PATAI’S Chemistry of
125, 6677. Functional Groups, John Wiley & Sons, Ltd, 2009.
18 I. Alfonso, M. Bolte, M. Bru, M. I. Burguete, S. V. Luis and 30 (a) L.-J. Tang and M.-H. Liu, Bull. Korean Chem. Soc., 2010,
J. Rubio, J. Am. Chem. Soc., 2008, 130, 6137.
19 J. Peisach and W. E. Blumberg, Arch. Biochem. Biophys.,
1974, 165, 691.
20 U. Sakaguchi and A. W. Addison, J. Chem. Soc., Dalton
Trans., 1979, 600.
21 E. Mills and L. A. O’Neill, Trends Cell Biol., 2014, 24, 313.
22 M. J. West-Eberhard, J. A. C. Smith and K. Winter, Science,
2011, 332, 311.
31, 3159; (b) P. Mateus, R. Delgado, P. Brandao and
V. Felix, Chem. – Eur. J., 2011, 17, 702.
31 (a) K. S. Rajan and A. E. Martell, J. Inorg. Nucl. Chem., 1967,
29, 463; (b) H. Sigel, Metal Ions in Biological Systems: Amino
Acids and Derivatives as Ambivalent Ligands, Marcel Dekker,
1979; (c) A. Manceau and A. Matynia, Geochim. Cosmochim.
Acta, 2010, 74, 2556.
32 P. Gans, A. Sabatini and A. Vacca, Talanta, 1996, 1739.
23 B. J. Miflin and P. J. Lea, Annu. Rev. Plant Physiol., 1977, 28, 33 S. Cie, X-AREA., Diffractometer control program system, Stoe &
299. Cie, Darmstadt, Germany, 2002.
24 A. Cavallero, A. Marte and E. Fedele, J. Neurochem., 2009, 34 G. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr.,
110, 924.
2008, 64, 112.
12710 | Dalton Trans., 2015, 44, 12700–12710
This journal is © The Royal Society of Chemistry 2015