Use of a porphyrin platform and 3,4-HPO chelating units to synthesize ligands with N4 and O4 coordination sites

Article abstract of DOI:10.1016/j.tet.2011.07.063

Piperazine and 1,2-diaminobenzene have been previously used as anchoring molecules to synthesize 3-hydroxy-4-pyridinone (3,4-HPO) tetradentate ligands affording ligands with different flexibility and coordination properties. In order to have a relatively

Full text of DOI:10.1016/j.tet.2011.07.063

Tetrahedron 67 (2011) 7821e7828
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Use of a porphyrin platform and 3,4-HPO chelating units to synthesize ligands
with N4 and O4 coordination sites
,
a
b
c
a
Ana M.G. Silva a , Andreia Leite , Pablo Gonzalez , M. Rosario M. Domingues , Paula Gameiro ,
*
ꢀ
Baltazar de Castro a, Maria Rangel d
,
*
ˇ
a REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciencias, Universidade do Porto, 4169-007 Porto, Portugal
ˇ
b REQUIMTE, Departamento de Química, Faculdade de Ciencias e Tecnologia, UNL, 2829-516 Caparica, Portugal
c Centro de Espectrometria, Departamento de Química, Universidade de Aveiro, 3810-193 Aveiro, Portugal
ˇ
d
ꢀ
REQUIMTE, Instituto de Ciencias Biomedicas de Abel Salazar, Universidade do Porto, 4099-003 Porto, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2011
Received in revised form 16 July 2011
Accepted 21 July 2011
Available online 26 July 2011
Piperazine and 1,2-diaminobenzene have been previously used as anchoring molecules to synthesize 3-
hydroxy-4-pyridinone (3,4-HPO) tetradentate ligands affording ligands with different flexibility and
coordination properties. In order to have a relatively rigid and hindered structure, a porphyrin platform
was selected to anchor one or two 3,4-HPO chelating units. This platform provides an additional N4
coordination sphere and also very interesting optical properties to the synthesized conjugates. De-
pending on the metal ion present in the porphyrin core, conjugates with different spectroscopic prop-
erties are obtained. EPR spectroscopy has been used to characterize the copper(II) metalloporphyrins and
to monitor and identify the species formed upon addition of copper(II) to solutions of two porphyrin
conjugates with one and two 3,4-HPO arms. The porphyrin conjugates having two 3,4-HPO units are
ligands that provide two separate binding sites with N4 and O4 coordination spheres, which allow ac-
commodation of two metal ion centers that may be distinguished by spectroscopic methods.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Porphyrins
3-Hydroxy-4-pyridinones
Fluorescence
EPR Spectroscopy
1. Introduction
Besides the coordination properties, the porphyrin framework
presents very interesting and useful photophysical properties, in-
Porphyrin-type macrocycles keep on catching the attention of
researchers in coordination chemistry.1 Indeed, these compounds
have assumed an important role in numerous areas of chemistry,
biology, medicine, catalysis, and material science.2
cluding high absorption coefficients in the visible region, tunable
fluorescence emission, and high stability against light and chemical
reactions.6 Because of this set of peculiar binding/optical proper-
ties, porphyrins have been utilized in the construction of highly
sensitive and selective fluorescent chemosensors for copper(II) and
zinc(II), through a metal ion bound mechanism to the porphyrin
central core.7 In order to improve the response of the sensor to the
presence of these and others metal ions, the porphyrin chemo-
sensor can be covalently immobilized to the surface of Au at SiO2
core/shell nanoparticles8 or to other matrices.9 Porphyrins and
metalloporphyrins bearing additional chelating units, such as
2-(oxymethyl)pyridine,10 2,20-dipyridylamine,11 and bipyridine
units12 have been also employed as efficient chemosensors for the
detection of copper(II) and zinc(II). In these cases, the porphyrin or
metalloporphyrin acts as a fluorophore due to their excellent
photophysical properties and the peripheral group acts as a recog-
nition and binding site for the metal ions.
Typically, porphyrin macrocycles, which are characterized by
the presence of a central N4 core, are excellent metal-complexing
ligands. However their coordination chemistry is not restricted to
the metal ion bound to the porphyrin central core and may be
extended to the porphyrin periphery through the attachment of
additional metal chelating units. For instance pyridylporphyrins, in
which the pyridine ring is directly attached to the porphyrin
forming a relatively rigid system, have been used in the construc-
tion of supramolecular coordination complexes.3 The pyridyl group
can be also introduced through sulfonamide linkage in order to
achieve less rigid systems.4 In the similar way, porphyrins bearing
pyrazolyl, imidazolyl, and hydroxyl substituents have been applied
as scaffolds for the building of multiporphyrin arrays and other
supramolecular structures.5
An additional important feature of the porphyrin macrocycle is
the fact that it provides a planar or quasi-planar platform to bind
other chelating molecules thus allowing the synthesis of poly-
dentate ligands based on bidentate units. Our group has reported,
very recently, the preparation of three tetradentate 3,4-HPO
* Corresponding authors. E-mail address: ana.silva@fc.up.pt (A.M.G. Silva).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.07.063

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A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
chelators, which exhibit different flexibility due to the use of two
anchor molecules, piperazine, and 1,2-diaminobenzene, and di-
verse length of the 3,4-HPO.13 These ligands revealed to have a very
rich coordination chemistry involving the formation of binuclear
metal ion species, which we are presently exploring in more detail.
In this context we used a porphyrin core as a platform to anchor
3,4-HPO bidentate units thus obtaining bidentate and tetradentate
ligands based on a planar platform, which may include an addi-
tional coordination site. Moreover, the combination of the elec-
tronic and spectroscopic features of porphyrins with the chelating
properties of 3,4-HPO expands the functionality of the system and
provides the synthesis of novel conjugates with enhanced or
complementary electronic, photophysical, and/or coordination
properties.
Previously, 3,4-HPOs and other related families, have been used
in the synthesis of diverse macrocyclic chelators to obtain mono-
and bimetallic complexes in order to mimic the active site of
multinuclear metalloenzymes.14e17 Now, in this work a series of
novel porphyrin and metalloporphyrin conjugates containing one
and two 3,4-HPO chelating units in the periphery of the macrocycle
(Fig. 1), were synthesized using an efficient and selective metal
coordination strategy. This approach relies on the synthesis of
mono- and di-substituted porphyrins with 3,4-HPO protected li-
gands, followed by metalation of the porphyrin core and selective
removal of benzyl protecting groups via hydrogenolysis, leading to
the desired peripherally containing 3,4-HPO metalloporphyrins P2,
P3, P5, and P6. Metal-free porphyrin conjugates P1 and P4 were
prepared using the same strategy but without metalation.
Scheme 1. Synthesis of porphyrin conjugates (P1eP6).
complexes 9a and 10a in good yields (80e90%). The deprotection
final sequence required the use of a selective methodology for re-
moval of benzyl protecting group of the pyridinone skeleton
without exclusion of the metal ion from the core of the macrocycle.
In fact, when the removal of the benzyl group was tried with the
very labile Zn(II) complex 9a using a solution of BCl3 in dichloro-
methane, the reaction lead to the corresponding metal-free
debenzylated conjugate P1. In order to use a non-acidic method-
ology, the catalytic hydrogenolysis was carried out with H2(g) in the
presence of 10% Pd/C catalyst. Using these conditions the reaction
afforded the desired Zn(II) conjugate P2, in a very good yield.
Similarly, when the same catalytic hydrogenolysis was applied to
Cu(II) complex 10a, conjugate P3 was also obtained in a very good
yield. Even knowing that certain porphyrins can be reduced to
porphyrinogens using H2 and Pd/C catalyst,18 in the present case no
porphyrinogen was obtained. These results show that hydro-
genolysis can be used as a selective and efficient methodology to
remove the benzyl protecting groups from this set of porphyrin and
metalloporphyrin conjugates. The metal-free conjugate P1 was
prepared using a similar strategy but without metalation. Fur-
thermore, such synthetic strategy was successfully extended to di-
substituted porphyrins allowing the synthesis of conjugates
P4eP6.
Fig. 1. Porphyrin conjugates containing one and two peripheral 3,4-HPO units
(P1eP6).
2. Results and discussion
2.1. Synthesis
Bidentate 3,4-HPO ligands show a high affinity toward M(III)
and M(II) metal ions forming complexes of general formula ML3
and ML2. The aim of the present work is to synthesize porphyrin
conjugates with one and two 3,4-HPO arms in order to produce
macrocyclic ligands with additional chelating functions. To achieve
this goal 3,4-HPO units with a flexible spacer were attached to the
porphyrin phenyl rings through amide bonds as its shown in
Scheme 1.
Firstly, the amide coupling reaction of 5-(4-aminophenyl)-
10,15,20-triphenylporphyrin 7a with 3-benzyloxy-1-(30-carbox-
ypropyl)-2-methyl-4-pyridinone was performed in dry DMF at
room temperature, during 24 h, through in situ generation of the
corresponding activated ester using N,N0-dicyclohexylcarbodiimide
(DCC) and 1-hydroxybenzotriazole (HOBt) as coupling reagents.
After purification by flash chromatography and crystallization,
porphyrin 8a was obtained in 68% yield. This porphyrin was then
metalated with Zn(OAc)2 and Cu(OAc)2, in a mixture of dichloro-
methane and methanol to give the desired Zn(II) and Cu(II)
The new compounds were characterized by mass spectrometry,
NMR, absorption, and fluorescence spectroscopy and EPR in the
case of copper(II) containing porphyrins.
2.2. Mass spectrometry
Mass spectrometry, particularly the electrospray ionization
tandem mass spectrometry (ESI-MS/MS) is an important tool in the

A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
7823
structural characterization of porphyrins and metalloporphyrins.19
In the present work, the ESI-MS spectra of porphyrin conjugates
having one or two 3,5-HPO units were obtained in positive ion
mode showed the corresponding protonated molecules [MþH]þ.
For porphyrin conjugates P1eP3 having one 3,4-HPO unit, the MS/
MS spectra revealed several product ions that can be formed by
cleavage in three possible points of fragmentation (a1ea3). The
most intense peak observed corresponds to the fragmentation a1
formed by heterolytic cleavage of the CH2eN bond with the lost of
the pyridinone ring with migration of one proton. The homolytic
cleavage of the COeCH2 bond corresponds to a2 fragmentation.
Fragmentation a3 corresponds to the cleavage of the amide bond
between the C]O and the NHR group, is a common fragmentation
of amides and its present in all MS/MS spectra. Similarly, the cor-
responding porphyrin conjugates having two 3,4-HPO units show
the same fragmentation patterns.
bands occurs and only one component of the Q bands is observed.
However, the delocalized bands of the Zn(II) porphyrins in-
p
creased the average electron density of the porphyrin, which low-
ered the energy for electron transition, leading to a bathochromic
shift in the Soret band and two components of the Q band are
observed.20 In Fig. 2 is depicted absorption spectra of porphyrins
with one 3,4-HPO unit (P1eP3) measured in DMSO at room
temperature.
0,8
P1
P2
P3
0,6
0,4
0,2
0,0
2.3. NMR spectroscopy
The NMR spectra of porphyrin conjugates having one 3,4-HPO
unit are relatively identical, showing the presence of one porphy-
rin macrocycle per pyridinone unit. For Zn(II) conjugate P2 the
most characteristic signals observed in the aromatic region of the
1H NMR spectrum in DMSO are: (i) a broad singlet at 10.47 ppm due
to the resonance of NH proton of the amide bond; (ii) a multiplet
400
500
600
700
λ
(nm)
around 8.80 ppm due to the resonance of the b-pyrrolic protons of
Fig. 2. Electronic absorption spectra of porphyrins P1eP3 obtained in
a DMSO
the porphyrin and (iii) two doublets at 6.22 and 7.71 ppm corre-
sponding to the resonance of H-50 and H-60 protons of the pyr-
idinone. While H-50 shows HMBC correlation with a signal at
145.4 ppm assigned as C-30 (CeOH), H-60 shows HMBC correlation
with a signal at 168.7 ppm assigned to C-40 (C]O). In the aliphatic
region of the spectrum is clear the presence of one singlet at
2.45 ppm corresponding to the methyl group of the pyridinone and
two triplets at 2.97 and 4.40 ppm for the C2H5 spacer. As expected,
the 1H NMR spectra of the corresponding metal-free conjugate P1
is very similar with the characteristic signal of the pyrrole NH
solution.
Fluorescence spectra: The fluorescence spectra of porphyrins
P1eP3 are depicted in Fig. 3 and spectra of porphyrins P4eP6 in
Fig. 4.
400
protons at
d
¼ꢀ2.92 ppm, which is absent in zinc(II) conjugate P2.
300
The NMR spectra of porphyrin conjugates having two 3,4-HPO units
show a similar profile to those of mono-substituted porphyrins,
revealing the presence of one porphyrin macrocycle per two pyr-
idinone units, which are equivalent.
P1
P2
P3
200
2.4. Electronic spectroscopy
100
Absorption spectra: The absorption spectra of all synthesized
porphyrin conjugates are quite similar under the same experi-
mental conditions thus indicating that the number of substituents
does not significantly influence the absorption properties, which
are also similar in the two solvents used (DMSO and acetonitrile,
see Supplementary data). The spectra of the metal-free porphyrins
(P1 and P4) in DMSO show the typical Soret band and four Q bands
with absorption maxima very similar for the two porphyrins. The
band ca. 420 nm was assigned to the Soret band arising from the
0
500
550
600
650
700
750
800
λ
(nm)
Fig. 3. Fluorescence spectra of porphyrins P1eP3 obtained in a 2.5ꢁ10ꢀ7 M DMSO
solution.
The fluorescence spectra of the free porphyrins (P1 and P4)
show Q(0,0) and Q(0,1) bands (Figs. 3 and 4). The asymmetric
porphyrin P1 shows a third component of the Q band and that can
be assigned to a Q(1,0) transition, which is observed as a conse-
quence of a decrease in molecular symmetry. The fluorescence
spectra observed for the metalloporphyrins (P2, P3, P5, P6) illus-
trate the usual variation upon metal ion chelation. For the para-
magnetic Cu(II) metalloporphyrins (P3, P6) fluorescence is
quenched, a result, that is, in agreement with Gouterman’s theory
confirming the purity of the copper complexes synthesized in this
work.6 The fluorescence spectra of the diamagnetic Zn(II) metal-
loporphyrins (P2, P5) display fluorescence originated from the first
excited singlet state, S1 or Q state. This Q band has two peaks at
about 605.0 (Q(0,0)) and 655.0 nm (Q(0,1)) for porphyrins P2 and
transition a1u
(516, 553, 594, and 648 nm) were attributed to the Q bands
(Qy(1,0), Qy(0,0), Qx(1,0), Qx(0,0)) that correspond to the a2u )e
eg*(
) transition.20 The substituents do not change the transition
(p)eeg*(p), and the other four absorption maxima
(p
p
mode of the porphyrin molecules. For the metalloporphyrins (P2,
P3, P5, and P6) the spectra are also typical of porphyrin complexes
of the two metal ions used. For metalloporphyrins, due to the easy
flow of electrons within the delocalized
p system and to the in-
crease of the molecular symmetry, the UVevis spectra exhibit one
Soret band and either one or two Q bands. For Cu(II) porphyrins,
their delocalized
p bonds decreased the average electron density
on the metalloporphyrins thus increasing the energy available for
electron transition. As a result, a hypsochromic shift of the Soret

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A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
800
700
600
500
400
300
200
100
0
exp
P4
P5
P6
500
550
600
650
700
750
800
λ
(nm)
sim
Fig. 4. Fluorescence spectra of porphyrins P4eP6 obtained in a 2.5ꢁ10ꢀ7 M DMSO
solution.
P5, respectively. The fluorescence maxima of these porphyrins
show the usual hypsochromic shift relative to the free porphyrin.21
For the asymmetric zinc(II) porphyrin P2 the fluorescence intensity
lies within the same order of magnitude of the free porphyrin while
for the symmetric porphyrin P5 a slight decrease is observed.
2.5. EPR spectroscopy
The EPR spectroscopy has been utilized to characterize the
copper(II) metalloporphyrins (P3, P6 and 7c, see Fig. 1 and Scheme
1) and also to get information about the species formed upon ad-
dition of copper(II) to solutions of the porphyrinepyridinone con-
jugates. The spectra of compounds P3, P6, and 7c, which are,
respectively, the copper complexes of the mono- and di-
functionalized porphyrins and the non-derivatized starting por-
phyrin, are very similar and the X-band EPR spectrum of porphyrin
P6 obtained in a toluene frozen matrix is depicted in Fig. 5. The
spectrum is typical of an one electron (S¼1/2) system and clearly
exhibits lines due to the hyperfine interaction of the unpaired
electron with the copper nucleus (I¼3/2) and with the four nitrogen
(I¼1) nuclei. The computer simulation of the spectrum was
obtained considering the interaction of the unpaired electron with
one copper nucleus and two sets of equivalent nitrogen atoms in
the porphyrin ring. The values of the Spin-Hamiltonian parameters
obtained upon simulation are registered in Table 1 and are con-
sistent with a dx2ey2 ground state. These parameters are identical to
those obtained for porphyrin P3 and virtually identical those of
porphyrin 7c thus indicating that the functionalization of the por-
phyrin core with the pyridinone arms does not significantly change
the electronic density on the copper ion. Porphyrin 7c has a higher
2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700
Magnetic Field (G)
Fig. 5. Frozen solution EPR spectrum of porphyrin P6 obtained in toluene at 77 K and
computer simulation.
Table 1
Spin-Hamiltonian parameters for copper(II) porphyrins. The components of the
hyperfine tensor are expressed in Gauss
Porphyrin
gxx
2.045
Axx
50
19
15
gyy
2.045
Ayy
50
15
19
gzz
2.190
Azz
210
15
15
7c
63Cu
14
N
1,3
14
N
2,4
P6
11
gxx
2.069
Axx
35
19
15
gyy
2.065
Ayy
35
15
19
gzz
2.188
Azz
210
15
15
63Cu
14
N
1,3
14
N
2,4
gxx
2.055
Axx
10
gyy
2.06
Ayy
10
gzz
2.264
Azz
211
182
symmetry, which is reflected in the coincident values of gxx and gyy
.
In order to characterize the EPR signal characteristic of a copper
(II) complex formed by chelation with the 3,4-HPO arms of the
porphyrins we prepared the copper complex of P5, which bears
two 3,4-HPO arms and in which the porphyrinic center is occupied
by zinc(II), designated as porphyrin 11. The spectrum obtained in
a DMSO matrix is depicted in Fig. 6. The signal is clearly different
from that shown in Fig. 5 and very similar to the EPR spectra
obtained for copper(II) complexes of N-alkyl-3-hydroxy-4-
pyridinone bidentate ligands.22 The spectrum is typical of a (S¼1/
2) system and only exhibits lines due to the interaction of the un-
paired electron with the copper nucleus (I¼3/2) as expected for the
O4 coordination sphere provided by the two 3,4-HPO bidentate li-
gands. The values of the Spin-Hamiltonian parameters obtained
upon simulation are registered in Table 1 and are consistent with
a dx2-y2 ground state.
65Cu
63Cu
10
10
Chelation properties of porphyrin conjugates toward copper(II): In
order to understand the chelation properties of the new ligands
toward copper(II), we registered EPR spectra of solutions of some of
the porphyrin conjugates upon addition of copper(II) in 1:1, 1:2,
and 1:4 molar ratios. We started with the metal free porphyrin P4
that possesses two different coordination sites provided by the
porphyrin ring (N4 coordination sphere) and by the 3,4-HPO
bidentate ligands (O4 coordination sphere). The spectra obtained
upon addition of copper(II) to a porphyrin P4 DMSO solution are
depicted in Fig. 7. In this figure the black line is the spectrum
obtained upon addition of copper(II) in a 1:1 molar ratio, which

A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
7825
exp
sim
2400 2600 2800 3000 3200 3400 3600 3800 4000 4200
Magnetic Field (G)
Fig. 6. Frozen solution EPR spectrum of the copper complex of porphyrin 11 obtained
in DMSO at 77 K and computer simulation.
Fig. 8. Possible structures of the binuclear species formed by the di-substituted
porphyrins.
1:1
1:0
1:1
1:2
1:4
1:2
1:4
2600
2800
3000
3200
3400
3600
3800
Magnetic Field (Gauss)
2600
2800
3000
3200
3400
3600
3800
Fig. 7. Frozen solution EPR spectra of porphyrin P4 upon addition of copper(II) in 1:1
(black line), 1:2 (red line), and 1:4 (green line) obtained in DMSO at 20K.
Magnetic Field (Gauss)
Fig. 9. Frozen solution EPR spectra of porphyrin P3 (black line), and upon addition of
copper(II) in 1:1 (red line), 1:2 (green line), and 1:4 (blue line) obtained in DMSO at
20 K.
clearly indicates the coordination of the metal ion to the porphyrin
nitrogen atoms as can be seen by comparison with Fig. 5 and
demonstrates the preference of the metal ion for the N4 co-
ordination sphere. The signal obtained upon addition of copper(II)
in a 1:2 molar ratio (red line) shows the presence of a new signal
superimposed with the previous one and, which exhibits features
recognizable in Fig. 6. This observation provides evidence for che-
lation of copper(II) by the two 3,4-HPO arms. The EPR spectrum
obtained after addition of the metal ion in a 1:4 molar ratio (green
line) is identical to the one previously observed (red line) thus
signifying that the fulfillment of both coordination sites is achieved
upon addition of copper(II) in a 1:2 molar ratio.
In this case the signal of the copper on the porphyrin site is
predominant at 1:1 and 1:2 molar ratios and at 1:4 the signal
characteristic of copper in the 3,4-HPO coordination environment,
although clearly visible seems to reflect a smaller number of
paramagnetic centers. The results illustrate the fact that porphyrin
P3 is a bidentate ligand while porphyrin P6 is a tetradentate one. A
tentative structure of the trinuclear species formed is presented in
Fig. 10.
Taking into account the structure of porphyrin P4 we believe
that both structures presented in Fig. 8 are possible for the com-
plexes formed although at present we cannot rule out one of them.
EPR signals characteristic of the existence of a magnetic interaction
between two paramagnetic centers were not observed, in any of the
spectra, thus indicating that the two copper centers they must be
far apart. These results confirm those we have previously found for
other tetradentate 3,4-HPO ligands in which a relatively rigid and
planar platform does not provide sufficient proximity between the
copper centers to allow magnetic interaction while for a more
flexible platform such interaction is observed.13
Fig. 10. Possible structure of the trinuclear species formed by the mono-substituted
porphyrins.
3. Conclusions
Considering the previously observed preference of copper for
the porphyrin ring we monitored by EPR the species formed by
porphyrin P3 upon addition of copper(II) in 1:1, 1:2, and 1:4 molar
ratios and the spectra obtained are shown in Fig. 9.
Metal free, zinc(II) and copper(II) porphyrins were successfully
functionalized with one and two 3,4-HPO bidentate ligands. In the
latter case a ligand with separate binding sites that provides two
types of coordination spheres (N4 and O4) was produced. EPR

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A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
spectra obtained upon addition of copper(II) to the di-substituted
porphyrin allowed us to monitor the coordination of copper to
the available binding sites and demonstrated that the porphyrin
core is preferred by the copper ion. The set of porphyrins synthe-
sized permit the formation of both homo- and hetero- binuclear
complexes in which the metal centers do not interact magnetically
has shown by the absence of EPR features at g¼4. These results also
confirm that the flexibility of the anchor platform is crucial to de-
sign polidentate ligands that allow the formation of binuclear metal
complexes as has been observed for other tetradentate 3,4-HPO
ligands. It is important to mention that, once again, EPR spectros-
copy proved to be of value to monitor and characterize the para-
magnetic species formed by the new ligands.
The new set of bifunctional porphyrin ligands also has charac-
teristics that allow the use of the pyridinone arms as anchoring
tools that permit the immobilization of the metal free porphyrin
core in surfaces of several types of materials. Such a possibility is
important as the porphyrin ligand may be used to trap metal ions
that can be further removed in acid conditions9c thus allowing its
recycle. Moreover, the detection of metal ion binding to the por-
phyrin core may be easily monitored by absorption or fluorescence
electronic spectroscopy. More detailed information can be gathered
by EPR.
dichloromethane as eluent in order to remove reaction side-
products and then a mixture of dichloromethane/methanol (95:5)
to give the porphyrin 8a (145 mg, 68%) as purple solid. 1H NMR
(DMSO-d6, 400 MHz, ppm):
d
ꢀ2.92 (s, 2H, NH), 2.36 (s, 3H, CH3),
2.94 (t, J¼6.8 Hz, 2H, 300-H), 4.34 (t, J¼6.8 Hz, 2H, 200-H), 5.07 (s, 2H,
CH2C6H5), 6.24 (d, J¼7.6 Hz, 1H, H-50), 7.34e7.41 and 7.45e7.48
(2 m, 5H, CH2C6H5), 7.74 (d, J¼7.6 Hz, 1H, 60-H), 7.81e7.88 (m, 9H,
10,15,20-PheHmþp), 8.02 (d, J¼8.6 Hz, 2H, 5-AreHm), 8.16 (d,
J¼8.6 Hz, 2H, 5-AreHo), 8.21e8.24 (m, 6H, 10,15,20-PheHo),
8.81e8.88 (m, 8H, H-
100 MHz, ppm)
b
), 10.49 (s, 1H, NH). 13C NMR (DMSO-d6,
d
: 13.4 (CH3), 38.6 (300-C), 50.4 (200-C), 73.3
(CH2C6H5), 117.5 (50-C), 118.9, 121.4, 128.4, 129.2, 129.5, 129.6, 129.7,
135.6, 136.1, 137.5, 139.2, 140.2 (60-C), 141.0 (20-C), 142.0, 142.6, 143.þ1,
146.8 (30-C), 169.9 (100-C),173.3 (40-C). ESI-MS/MS m/z: 899 [MþH] .
4.1.2. Synthesis of porphyrin (8b). A mixture of 3-benzyloxy-1-(30-
carboxypropyl)-2-methyl-4-pyridinone
(87.0 mg,
0.30 mmol,
2.3 equiv), DCC (65.0 mg, 0.32 mmol, 2.4 equiv), HOBt (43.0 mg,
0.32 mmol, 2.4 equiv), and DMF (2 mL) was stirred at room tem-
perature under argon atmosphere during 30 min. After that time,
porphyrin 7b (85 mg, 0.13 mmol) was added. The resulting reaction
mixture was protected from light and it was allowed to stir at room
temperature under argon atmosphere for 2 days. Upon filtration
and removal of the solvent under reduced pressure, the residue was
purified by flash chromatography using firstly dichloromethane as
eluent in order to remove reaction side-products and then a mix-
ture of dichloromethane/methanol (9:1) to give the porphyrin 8b
4. Experimental section
4.1. General information
(109 mg, 70% yield). 1H NMR (DMSO-d6, 400 MHz, ppm)
d
: ꢀ2.92 (s,
Reagents and solvents were purchased as reagent-grade and
used without further purification unless otherwise stated. NMR
spectra were recorded with Bruker Avance III 400 spectrometer
2H, NH), 2.36 (s, 6H, 2ꢁ CH3), 2.94 (t, J¼6.8 Hz, 4H, 2ꢁ300-H), 4.33 (t,
J¼6.8 Hz, 4H, 2ꢁ200-H), 5.06 (s, 4H, 2ꢁ CH2C6H5), 6.24 (d, J¼7.6 Hz,
2H, 2ꢁ H-50), 7.37e7.41 and 7.45e7.48 (2 m, 10H, 2ꢁ CH2C6H5), 7.74
(d, J¼7.6 Hz, 2H, 2ꢁ60-H), 7.81e7.86 (m, 6H, 15,20-PheHmþp), 8.02
(d, J¼8.6 Hz, 4H, 5,10-AreHm), 8.16 (d, J¼8.6 Hz, 4H, 5,10-AreHo),
(400.15 MHz for 1H and 100.63 MHz for 13C). Chemical shifts (
d) are
reported in parts per million and coupling constants (J) in hertz;
internal standard was TMS. Unequivocal 1H assignments were
made with aid of 2D gCOSY (1H/1H), while 13C assignments were
made on the basis of 2D gHSQC (1H/13C) and gHMBC experiments
(delay for long range J C/H couplings were optimized for 7 Hz). The
electrospray mass spectra (ESI-MS and ESI-MS/MS) were acquired
using an electrospray Q-ToF2 (Micromass, Manchester) operating in
the positive ion mode and using a MassLynx software system
(version 4.0). The needle voltage was set at 3000 V, the cone volt-
age at 35 V and the ion source at 80 ꢂC. Tandem mass spectra (MS/
MS) of [MþH]þ ions produced under ESI conditions were obtained
by collision induced decomposition and varying the collision en-
ergy between 40 and 50 eV. Microanalyses were carried out by
8.21e8.23 (m, 4H, 15,20-PheHo), 8.80e8.87 (m, 8H, H-
b), 10.50 (s,
2H, 2ꢁ NH). 13C NMR (DMSO-d6, 100 MHz, ppm)
d: 12.0 (CH3), 37.2
(C-300), 49.0 (C-200), 71.9 (CH2C6H5), 116.2, 117.5, 119.80, 119.85, 127.0,
127.8,128.1,128.2,128.3,134.2,134.7,136.1,137.8,138.8,139.6,140.6,
141.2 (C-20), 145.4 (C-30), 168.5 (C-100), 171.9 (C-40).
4.2. General metalation procedure
Metalation of porphyrins with Zn(II) or Cu(II) was accomplished
by refluxing zinc acetate hydrate or copper acetate hydrate
(2 equiv) in a mixture of chloroform/methanol (5:2). The solutions
were heated under reflux for 2 h (until UVevis indicated comple-
tion of the reactions). After evaporation of the solvent, the resulting
residues were dissolved in chloroform and washed with deionized
water several times to remove excess metal salt. The organic phase
was dried over anhydrous Na2SO4 and reduced to dryness.
ꢀ
Unidad De Analisis Elemental of Santiago de Compostela.
5-(4-Aminophenyl)-10,15,20-triphenylporphyrin 7a and 5,10-
bis(4-aminophenyl)-15,20-diphenylporphyrin 7b were prepared
according to the literature method.23 Porphyrin 7b was further
converted into porphyrin 7c by metalation with copper acetate
hydrate as described in general procedure. The 3-benzyloxy-1-(30-
carboxypropyl)-2-methyl-4-pyridinone was synthesized from the
initial benzylation of OH group of maltol (3-hydroxy-2-methyl-4-
pyrone), followed by reaction with 4-amino-butyric acid, using
a similar procedure to the one described in the literature.24
4.2.1. Synthesis of zinc(II) complex (9a). Metalation of porphyrin 8a
(70.0 mg, 78.0
mmol) with Zn(II) was accomplished by refluxing
zinc acetate hydrate (34.2 mg, 0.16 mmol, 2 equiv) in 40 mL of
a mixture of chloroform/methanol (5:2), using the general protocol.
The zinc(II) complex 9a (66.9 mg, 89%) was crystallized from
4.1.1. Synthesis of porphyrin (8a). A mixture of 3-benzyloxy-1-(30-
chloroform/methanol. 1H NMR (DMSO-d6, 400 MHz, ppm)
d: 2.36
carboxypropyl)-2-methyl-4-pyridinone
(82.0 mg,
0.29 mmol,
(s, 3H, CH3), 2.93 (t, J¼6.8 Hz, 2H, 300-H), 4.34 (t, J¼6.8 Hz, 2H, 200-H),
5.06 (s, 2H, CH2C6H5), 6.23 (d, J¼7.6 Hz, 1H, 50-H), 7.34e7.41 and
7.45e7.47 (2 m, 5H, CH2C6H5), 7.74 (d, J¼7.6 Hz, 1H, 60-H), 7.78e7.81
(m, 9H, 10,15,20-PheHmþp), 7.98 (d, J¼8.8 Hz, 2H, 5-AreHm), 8.11 (d,
J¼8.8 Hz, 2H, 5-AreHo), 8.17e8.19 (m, 6H, 10,15,20-PheHo),
1.2 equiv), DCC (64.0 mg, 0.31 mmol, 1.3 equiv), HOBt (42.0 mg,
0.31 mmol, 1.3 equiv), and DMF (2 mL) was stirred at room tem-
perature under argon atmosphere during 30 min. After that time,
porphyrin 7a (0.15 g, 0.24 mmol) was added. The resulting reaction
mixture was protected from light mixture and it was allowed to stir
at room temperature under argon atmosphere for 24 h. Upon fil-
tration and removal of the solvent under reduced pressure, the
residue was purified by flash chromatography using firstly
8.75e8.81 (m, 8H, H-b
), 10.46 (s, 1H, NH). 13C NMR (DMSO-d6,
100 MHz, ppm)
d:
11.9 (CH3), 37.1 (300-C), 48.9 (200-C), 71.8
(CH2C6H5), 116.1 (50-C), 117.1, 120.0, 120.2, 126.5, 127.4, 127.7, 128.1,
128.3, 131.5, 134.0, 134.5, 139.5 (60-C), 140.6 (20-C), 142.6, 145.3 (30-

A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
7827
C), 149.1, 149.2, 149.3, 168.3 (100-C), 171.8 (40-C). ESI-MS/MS m/z: 961
(DMSO), lmax nm (log
NMR (DMSO-d6, 400 MHz, ppm)
3
): 429 (5.77), 561 (4.29) and 601 (4.05). 1H
: 2.45 (s, 3H, CH3), 2.97 (t,
[MþH]þ.
d
J¼6.8 Hz, 2H, 300-H), 4.40 (t, J¼6.8 Hz, 2H, 300-H), 6.22 (d, J¼7.2 Hz,
1H, 50-H), 7.71 (d, J¼7.2 Hz, 1H, 60-H), 7.79e7.80 (m, 9H, 10,15,20-
PheHmþp), 7.98 (d, J¼8.4 Hz, 2H, 5-AreHm), 8.11 (d, J¼8.4 Hz, 2H,
5-AreHo), 8.17e8.19 (m, 6H, 10,15,20-PheHo), 8.76e8.82 (m, 8H, H-
4.2.2. Synthesis of copper(II) complex (10a). Metalation of porphy-
rin 8a (70.0 mg, 78.0
mmol) with Cu(II) was accomplished by
refluxing copper acetate hydrate (31.2 mg, 0.156 mmol, 2 equiv) in
40 mL of a mixture of chloroform/methanol (5:2), using the general
protocol. Cu(II) complex 10a (64.3 mg) was obtained in 86% yield.
ESI-MS/MS m/z: 960 [MþH]þ.
b
), 10.47 (s, 1H, NH). 13C NMR (DMSO-d6, 100 MHz, ppm)
d: 11.4
(CH3), 37.2 (300-C), 49.1 (200-C), 110.7 (50-C), 117.2, 120.0, 120.1, 120.2,
126.5, 127.4, 128.8 (20-C), 131.5, 131.6, 134.1, 134.5, 137.6, 137.8 (60-C),
138.1, 142.6, 145.4 (30-C), 149.12, 149.16, 149.4, 168.3 (100C), 168.7 (40-
C). ESI-MS/MS m/z: 871 [MþH]þ.
4.2.3. Synthesis of zinc(II) complex (9b). Metalation of porphyrin 8b
(35.0 mg, 30
mmol) with Zn(II) was accomplished by refluxing zinc
acetate hydrate (13.0 mg, 60
chloroform/methanol (5:2), using the general protocol. The Zn(II)
m
mol, 2 equiv) in 20 mL of a mixture of
4.3.3. Synthesis of copper(II) complex (P3). Pd/C (10%) (catalytic
amount) was added to a solution of porphyrin 10a (63.2 mg,
complex 9b (36.0 mg 98% yield) was crystallized from chloroform/
65.9 mmol) in DMF (20 mL) and the resulting mixture was subjected
methanol. 1H NMR (DMSO-d6, 400 MHz, ppm)
d: 2.43 (s, 6H, 2ꢁ
to hydrogenolysis, following general procedure. The resulting resi-
due was recrystallized from chloroform/methanol to give P3
(40.3 mg, 70%). [Found: C, 71.38; H, 4.07; N, 9.41. C53H38CuN6O3$H2O
CH3), 2.98 (t, J¼6.8 Hz, 4H, 2ꢁ300-H), 4.44 (t, J¼6.8 Hz, 4H, 2ꢁ200-H),
5.08 (s, 4H, 2ꢁ CH2C6H5), 6.48 (d, J¼7.0 Hz, 2H, 2ꢁ H-50), 7.35e7.43
and 7.47e7.49 (2 m, 10H, 2ꢁ CH2C6H5), 7.79e7.81 (m, 6H, 15,20-
PheHmþp), 7.93 (d, J¼7.0 Hz, 2H, 2ꢁ60-H), 7.98 (d, J¼8.4 Hz, 4H,
5,10-AreHm), 8.11 (d, J¼8.4 Hz, 4H, 5,10-AreHo), 8.16e8.19 (m, 4H,
requires C, 71.65; H, 4.54; N, 9.46%]; UVevis (DMSO), lmax nm (log
3 ):
419 (5.59) and 542 (4.28). ESI-MS/MS m/z: 870 [MþH]þ.
15,20-PheHo), 8.74e8.80 (m, 8H, H-
b
), 10.48 (s, 2H, 2ꢁ NH). 13C
4.3.4. Synthesis of porphyrin (P4). Pd/C (10%) (catalytic amount)
was added to a solution of porphyrin 8b (30 mg, 25.4 mol) in DMF
NMR (DMSO-d6, 100 MHz, ppm)
d
: 12.3 (CH3), 36.9 (C-300) 49.7 (C-
m
200), 72.4 (CH2C6H5), 115.4, 117.2, 120.0, 120.2, 126.6, 128.0, 128.3,
128.4, 131.6, 134.1, 134.5, 137.5, 137.7, 138.2, 140.4, 142.7 (C-20), 144.9
(C-30), 149.24, 149.42, 168.3 (C-100), 171.0 (C-40).
(20 mL) and the resulting mixture was subjected to hydrogenolysis,
following general procedure. The resulting residue was recrystal-
lized from chloroform/methanol to give P4 (19 mg, 75%). [Found: C,
56.69; H, 4.60; N, 8.83. C62H50N8O6$4H2O$4HCl CHCl3 requires C,
4.2.4. Synthesis of copper(II) complex (10b). Metalation of porphy-
56.45; H, 4.74; N, 8.36; UVevis (DMSO), lmax nm (log
3
): 422 (5.52),
rin 8b (35.0 mg, 0.30
mmol) with Cu(II) was accomplished by
516 (4.15), 554 (3.95), 592 (3.69) and 648 (3.73). 1H NMR (DMSO-
refluxing copper acetate hydrate (11.8 mg, 0.60
20 mL of a mixture of chloroform/methanol (5:2), using the general
procedure. Cu(II) complex 10b (36.0 mg) was obtained in 98% yield.
m
mol, 2 equiv) in
d6þTFA, 400 MHz, ppm) : 2.71 (s, 6H, 2ꢁ CH3), 3.19e3.22 (m, 4H,
d
2ꢁ300-H), 4.79e4.82 (m, 4H, 2ꢁ300-H), 7.25 (d, J¼7.0 Hz, 2H, 2ꢁ H-
50), 8.03e8.08 (m, 6H, 15,20-PheHmþp), 8.33 (d, J¼8.4 Hz, 4H, 5,10-
AreHm), 8.36 (d, J¼7.0 Hz, 2H, 2ꢁ H-60), 8.62e8.71 (m, 16H, 5,10-
4.3. General hydrogenolysis procedure
AreHo and 15,20-PheHo and H-
b
), 10.85 (s, 2H, 2ꢁ NH). ESI-MS/
MS m/z: 1003 [MþH]þ.
Pd/C (10%) (catalytic amount) was added to a solution of por-
phyrin in DMF (minimal volume) and the resulting mixture was
subjected to hydrogenolysis (H2, 5 bar) until hydrogen uptake
ceased. The resulting solution was filtered to remove the catalyst (in
case of hydrogenolysis with porphyrins 1 and 4, a few drops of HCl
were added in order to solubilize the porphyrins in DMF). The
solvent was removed under reduced pressure and the resulting
residue was crystallized.
4.3.5. Synthesis of zinc(II) complex (P5). Pd/C (10%) (catalytic
amount) was added to a solution of porphyrin 9b (35.0 mg, 28 mol)
in DMF (20 mL) and the resulting mixture was subjected to hydro-
genolysis, following general procedure. The resulting residue was
recrystallized from chloroform/methanol to give P5 (14.6 mg, 49%).
[Found: C, 62.59; H, 3.81; N, 9.19. C62H48N8O6Zn$CHCl3$H2O re-
m
quires C, 62.85; H, 4.27; N, 9.31%]; UVevis (DMSO), lmax nm (log ):
3
430 (5.72), 562 (4.25) and 602 (4.04). 1H NMR (DMSO-d6, 400 MHz,
4.3.1. Synthesis of porphyrin (P1). Pd/C (10%) (catalytic amount)
ppm)
d
: 2.45 (s, 6H, 2ꢁ CH3), 2.94e3.01 (m, 4H, 2ꢁ300-H), 4.36e4.43
was added to a solution of porphyrin 8a (8.5 mg, 9.46
mmol) in DMF
(m, 4H, 2ꢁ300-H), 6.21 (d, J¼7.2 Hz, 2H, 2ꢁ H-50), 7.69 (d, J¼7.2 Hz,
2H, 2ꢁ H-60), 7.77e7.84 (m, 6H, 15,20-PheHmþp), 7.98 (d, J¼8.0 Hz,
4H, 5,10-AreHm), 8.11 (d, J¼8.0 Hz, 4H, 5,10-AreHo), 8.17e8.18 (m,
(3 mL) and the resulting mixture was subjected to hydrogenolysis,
following general procedure. The resulting residue was crystallized
from chloroform/methanol to give P1 (6.3 mg, 83%). [Found: C
71.55; H, 5.62; N, 9.56. C53H40N6O3$9/2H2O requires: C, 71.53; H,
4H, 15,20-PheHo), 8.75e8.82 (m, 8H, H-
b
), 10.47 (s, 2H, 2ꢁ NH). 13
C
NMR (DMSO-d6, 100 MHz, ppm) d
: 11.4 (CH3), 37.3 (C-300), 49.2
5.55; N, 9.44%]; UVevis (DMSO), lmax nm (log
(4.01), 554 (3.88) 596 (3.62) and 648 (3.51). 1H NMR (DMSO-d6,
400 MHz, ppm)
3
) 421 (5.42), 516
(C-200),110.5 (C-50),117.2,120.0,120.1,120.6,126.5,127.4,128.6 (C-20),
131.4,131.6,134.1,134.5,137.6 (C-60),138.1,142.6,145.4 (C-30),149.10,
149.14, 149.29, 149.33, 168.3 (C-100), 169.0 (C-40). ESI-MS/MS m/z:
1065 [MþH]þ.
d
: ꢀ2.92 (s, 2H, NH), 2.53 (s, 3H, CH3), 3.00 (t,
J¼6.8 Hz, 2H, 300-H), 4.47 (t, J¼6.8 Hz, 2H, 300-H), 6.34 (d, J¼6.4 Hz,
1H, 50-H), 7.54 (d, J¼6.4 Hz, 1H, 60-H), 7.79e7.85 (m, 9H, 10,15,20-
PheHmþp), 8.03 (d, J¼8.4 Hz, 2H, 5-AreHm), 8.17 (d, J¼8.4 Hz, 2H,
5-AreHo), 8.20e8.23 (m, 6H,10,15,20-PheHo), 8.76e8.82 (m, 8H, H-
4.3.6. Synthesis of copper(II) complex (P6). Pd/C (10%) (catalytic
amount) was added to a solution of porphyrin 10b (34.7 mg,
0.28 mmol) in DMF (20 mL) and the resulting mixture was subjected
to hydrogenolysis, following general procedure. P6 (18.8 mg) was
obtained in 63% of yield. [Found: C, 64.07; H, 4.25; N, 9.58.
C62H48CuN8O6. CHCl3 requires C, 63.91; H, 4.17; N, 9.46%]; UVevis
b
), 10.50 (s, 1H, NH). ESI-MS/MS m/z: 809 [MþH]þ.
4.3.2. Synthesis of zinc(II) complex (P2). Pd/C (10%) (catalytic
amount) was added to a solution of porphyrin 9a (63.6 mg,
66.3
m
mol) in DMF (20 mL) and the resulting mixture was subjected
(DMSO), lmax nm (log
3
): 421 (5.53), 543 (4.23). ESI-MS/MS m/z:
to hydrogenolysis, following general procedure. The resulting
obtained residue was recrystallized from chloroform/methanol to
give P2 (40.3 mg, 70%). [Found: C, 68.01; H, 4.57; N, 8.65.
C53H38N6O3Zn. CH2Cl2 requires: C, 67.75; H, 4.21; N, 8.78%]; UVevis
1064 [MþH]þ.
4.3.7. Synthesis of copper(II) complex (11). Complexation of met-
alloporphyrin P5 was accomplished by refluxing a mixture of P5:

7828
A.M.G. Silva et al. / Tetrahedron 67 (2011) 7821e7828
copper acetate hydrate (1:1) in chloroform/methanol (5:2), fol-
lowing the general procedure. The resulting complex 11 was fil-
tered, dried and characterized by EPR spectroscopy.
Supplementary data
The supplementary data contains selected NMR spectra (1H, 13C,
COSY, HMBC, and HSQC) and mass spectra of compounds. Fluo-
rescence spectra in acetonitrile are also available. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.tet.2011.07.063.
4.4. Spectroscopic studies
UVevis measurements: Electronic absorption spectra were
recorded with a Varian Cary bio50 spectrophotometer, equipped
with a Varian Cary single cell Peltier accessory. Spectra were
recorded at 25 ꢂC in 1 cm path length quartz cells with a slit width
of 1 nm, in the range 350e750 nm. Spectra were record in dried
DMSO and acetonitrile. Stock solutions of the compounds were
obtained by dissolution in DMSO. Samples were prepared by dis-
solving of a known volume of the DMSO stock solution (the per-
centage of the DMSO in the final volume in case of the acetonitrile
solutions was always less than 1% in the final volume). Typical
solution concentrations for the determination of the molar ex-
tinction coefficient were 8ꢁ10ꢀ5e2ꢁ10ꢀ6 M.
References and notes
1. (a) Cuesta, L.; Sessler, J. L. Chem. Soc. Rev. 2009, 38, 2716; (b) Matano, Y.;
Imahori, H. Acc. Chem. Res. 2009, 42, 1193.
2. The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic:
New York, NY, 2000; Vol. 6.
3. (a) Scandola, F.; Chiorboli, C.; Prodi, A.; Iengo, E.; Alessio, E. Coord. Chem. Rev.
2006, 250, 1471; (b) Iengo, E.; Marzilli, L. G. Supramol. Chem. 2002, 14, 103; (c)
Alessio, E.; Macchi, M.; Heath, S. L.; Marzilli, L. G. Inorg. Chem. 1997, 36, 5614.
4. Manono, J.; Marzilli, P. A.; Fronczek, F. R.; Marzilli, L. G. Inorg. Chem. 2009, 48,
5626.
ꢀ
_ ꢀ
5. (a) Wojaczynski, J.; Latos-Grazynski, L. Coord. Chem. Rev. 2000, 204, 113; (b)
Beletskaya, I.; Tyurin, V. S.; Tsivadze, A. Y.; Guilard, R.; Stern, C. Chem. Rev. 2009,
109, 1659.
Fluorescence measurements: Fluorescence measurements were
carried out in a Varian spectrofluorometer, model Cary Eclipse,
equipped with a constant-temperature cell holder (Peltier single
cell holder). Stock solutions of the compounds were obtained by
dissolution in DMSO. All solutions were prepared by dilution of the
right amount of the stock solution in the solvent (% DMSO less than
1% when the solvent was acetonitrile). The spectra in DMSO and
acetonitrile were obtained using lexc in the range 421 nme430 nm
and emission between 550 and 800 nm. The slit width values used
for excitation end emission processes were 5 for porphyrins P1, P2,
P3, P4, and P5 and 10 for porphyrin P3 and P6 in DMSO and
acetonitrile.
6. Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic: New York, 1978;
Vol. 3.
ꢁ
7. (a) Bellacchio, E.; Lauceri, R.; Magrõ, A.; Purrello, R.; Bellacchio, E.; Gurrieri, S.;
Scolaro, L. M.; Romeo, A. Chem. Commun. 1998, 1333; (b) Purrello, R.; Gurrieri,
S.; Lauceri, R. Coord. Chem. Rev. 1999, 190e192, 683; (c) Natale, C. D.; Monti, D.;
Paolesse, R. Mater. Today 2010, 13, 46.
8. Cho, Y.; Lee, S. S.; Jung, J. H. Analyst 2010, 135, 1551.
9. (a) Balaji, T.; Sasidharan, M.; Matsunaga, H. Analyst 2005, 130, 1162; (b) Del-
ꢀ
marre, D.; Meallet, R.; Bied-Charreton, C.; Pansu, R. B. J. Photochem. Photobiol., A
1999, 124, 23; (c) Buntem, R.; Intasiri, A.; Lueangchaichaweng, W. J. Colloid
Interface Sci. 2010, 347, 8.
10. Li, C.-Y.; Zhang, X.-B.; Dong, Y.-Y.; Ma, Q.-J.; Han, Z.-X.; Zhao, Y.; Shen, G.-L.; Yu,
R.-Q. Anal. Chim. Acta 2008, 616, 214.
11. (a) Weng, Y.-Q.; Yue, F.; Zhong, Y.-R.; Ye, B.-H. Inorg. Chem. 2007, 46, 7749; (b)
Weng, Y.-Q.; Teng, Y.-L.; Yue, F.; Zhong, Y.-R.; Ye, B.-H. Inorg. Chem. Commun
2007, 10, 443.
Electron paramagnetic resonance: EPR spectra were recorded in
frozen solution in the temperature range 20e77 K using an X-band
(9 GHz) Bruker EMX spectrometer equipped with a variable tem-
perature unit (Oxford ESR900) and a frequency meter. The samples
were prepared by dissolution of compound in dried toluene or
DMSO, placed in quartz tubes and frozen. Regarding the samples for
the titration of porphyrin P4 with copper (II), different solutions
were prepared by mixing the right amounts of porphyrin and
copper (II) solution in the ratios 1:0.5, 1:1, 1:2, and 1:4. The copper
(II) solution was prepared by dissolution of its acetate salt in
methanol, while the porphyrin was dissolved in DMSO. A concen-
tration range of 1e5ꢁ10ꢀ3 M was used. The Spin-Hamiltonian pa-
rameters were determined by simulation of the experimental
spectra using the computer suite Bruker WinEPR/SimFonia.
12. Luo, H.-Y.; Zhang, X.-B.; Jiang, J.-H.; Li, C.-Y.; Peng, J.; Shen, G.-L.; Yu, R.-Q. Anal.
Sci. 2007, 23, 551.
13. Leite, A.; Silva, AM. G.; Nunes, A.; Andrade, M.; Sousa, C.; Cunha-Silva, L.;
Gameiro, P.; de Castro, B.; Rangel, M. Tetrahedron 2011, 4009.
14. Gavrilova, A. L.; Bosnich, B. Chem. Rev. 2004, 104, 349.
15. Yang, C.-T.; Sreerama, S. G.; Hsieh, W.-Y.; Liu, S. Inorg. Chem. 2008, 47, 2719.
16. Ambrosi, G.; Formica, M.; Fusi, V.; Giorgi, L.; Guerri, A.; Lucarini, S.; Micheloni,
M.; Paoli, P.; Rossi, P.; Zappia, G. Inorg. Chem. 2005, 44, 3249.
17. Guerra, K. P.; Delgado, R. Dalton Trans. 2008, 539.
18. Bergonia, H. A.; Phillips, J. D.; Kushner, J. P. Anal. Biochem. 2009, 384, 74.
19. (a) Domingues, M. R. M.; Marques, M. G. O. S.; Alonso, C.; Neves, M. G. P. M. S.;
Cavaleiro, J. A. S.; Ferrer-Correia, A. J.; Nemirovskiy, O. V.; Gross, M. L. J. Am. Soc.
Mass Spectrom. 2002, 13, 1427; (b) Silva, E. M. P.; Domingues, M. R. M.; Barros,
ꢀ
ꢀ
C.; Faustino, M. A. F.; Tome, J. P. C.; Neves, M. G. P. M. S.; Tome, A. C.; Santana-
Marques, M. G.; Cavaleiro, J. A. S.; Ferrer-Correia, A. J. J. Mass Spectrom. 2005, 40,
ꢀ
117; (c) Silva, E. M. P.; Domingues, P.; Tome, J. P. C.; Faustino, M. A. F.; Neves, M.
ꢀ
G. P. M. S.; Tome, A. C.; Dauzonne, D.; Silva, A. M. S.; Cavaleiro, J. A. S.; Ferrer-
Correia, A. J.; Domingues, M. R. M. Eur. J. Mass Spectrom. 2008, 14, 49; (d)
ꢀ
Domingues, M. R. M.; Domingues, P.; Neves, M. G. P. M. S.; Tome, A. C.;
Cavaleiro, J. A. S. J. Porphyrins Phthalocyanines 2009, 13, 524; (e) Lourenc¸ o, L. M.
Acknowledgements
ꢀ
ꢀ
O.; Tome, J. P. C.; Domingues, M. R. M.; Domingues, P.; Costa, P. J.; Felix, V.;
Neves, M. G. P. M. S.; Cavaleiro, J. A. S. Rapid Commun. Mass Spectrom. 2009, 23,
3478.
Financial support from FCT through project PTDC/QUI/67915/
2006 is gratefully acknowledged. A.L. thanks FCT for a Ph.D. grant
(SFRH/BD/30083/2006). The Bruker Avance II 400 spectrometer is
part of the National NMR network and was purchased under the
framework of the National Programme for Scientific Re-equipment,
contracREDE/1517/RMN/2005, with funds from POCI 2010 (FEDER)
and (FCT).
20. Zheng, W.; Shan, N.; Yu, L.; Wang, X. Dyes Pigm. 2008, 77, 153.
21. Uttamlal, M.; Holmes-Smith, A. S. Chem. Phys. Lett. 2008, 454, 223.
22. Leite, A.; Silva, A.; Amorim, M. J.; Silva, A. M. G.; Nunes, A.; Cunha-Silva, L.;
Gameiro, P.; de Castro, B.; Burgess, J.; Rangel, M.; submitted for publication.
23. Luguya, R.; Jaquinod, L.; Fronczek, F. R.; Vicente, M. G. H.; Smith, K. M. Tetra-
hedron 2004, 60, 2757.
24. Santos, M. A.; Gil, M.; Marques, S.; Gano, L.; Cantinho, G.; Chaves, S. J. Inorg.
Biochem. 2002, 92, 43.