Preparation and characterization of SDS-stabilized hydrophobic porphyrinic nanoaggregates in water

Article abstract of DOI:10.1142/S1088424612500320

Porphyrin nanoaggregates formed in the interior of colloidal suspensions can be considered as examples of supramolecular systems with self-organized architecture. Due to their peculiar optical and electrochemical properties such as decrease of fluorescenc

Full text of DOI:10.1142/S1088424612500320

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 267–272
DOI: 10.1142/S1088424612500320
Published at http://www.worldscinet.com/jpp/
Preparation and characterization of SDS-stabilized
hydrophobic porphyrinic nanoaggregates in water
L. Maqueiraa,b,*,†, A. Iribarrenb, A. C. Valdésb, Celso P. de Meloc and
Clécio G. dos Santosd
a Departamento de Química Analítica, Facultad de Química, Universidad de La Habana, Zapata y G, Vedado, C.P.
10400, La Habana, Cuba
b Instituto de Ciencia y Tecnología de Materiales, Universidad de La Habana, Zapata y G, Vedado, C.P. 10400, La
Habana, Cuba
c Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, PE Brazil
d Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, 50670-901 Recife, PE Brazil
Received 8 August 2011
Accepted 23 December 2011
ABSTRACT: Porphyrin nanoaggregates formed in the interior of colloidal suspensions can be considered
as examples of supramolecular systems with self-organized architecture. Due to their peculiar optical
and electrochemical properties such as decrease of fluorescence, increase of conductivity and possible
electron transfer, these aggregates can be used in the design and fabrication of optoelectronic devices,
such as organic solar cells and optical and electrochemical sensors. In this paper, we first describe the
synthesis of a series of hydrophobic tetraphenylporphyrins by a change in the order of reagents addition
that results in high yields of the desired products. These products were then employed to obtain stable
suspensions of porphyrinic nanoaggregates in aqueous solutions of sodium dodecyl sulfate (SDS). The
aggregates resulting of the encapsulation of the tetraphenylporphyrins into the micelles of the surfactant
were studied by dynamic light scattering (DLS), atomic force microscopy (AFM) and UV-vis and
fluorescence spectroscopies. The results indicate that the nanoggregates have a spherical morphology
with particles whose average size ranges between 46–78 nm and z-potential values (higher than 55 mV),
indicative of excellent stability. Optical characterization was used to determine the classification of
nanoaggregates, according to the observed shifts on the absorption spectra.
KEYWORDS: porphyrin, SDS, porphyrinic nanoaggregates.
their metallo derivatives are well-described in the
INTRODUCTION
literature [6–9], and have been extensively exploited in
Porphyrins are excellent examples of the versatility of
the fabrication of a variety of devices such as solar cells
the supramolecular organic chemistry [1–4] because, as
[10–12] and optical and electrochemical sensors [13–15].
macrocycles of tetrapyrroles with a chemical structure
In fact, porphyrins present structural and chemical
of high conjugation and rigidity that can be obtained
characteristics that favor self-assembly in different ways,
by well-established synthetic methods, they enable the
creation of a large number of derivatives with diverse
by use of intermolecular H-bonding, p–p or electrostatic
interactions and direct coordination to the central
functionalities [5]. The remarkable photo-, catalytic-,
metal ion, and these particular properties have been
electro-, and biochemical properties of porphyrins and
extensively used to prepare self-assembled monolayers
(SAM) and thin films and porphyrin nanoparticles (i.e.
nanoscale aggregates) [5, 16, 17]. Those nanoaggregates
can be prepared through the use of several methods,
such as (1) the rapid exchange of solvent, (2) host/
*Correspondence to: Luis Maqueira, email: maqueira@fq.uh.
cu, tel: +537 873-8222 and Augusto Iribarren, email: augusto@
imre.oc.uh.cu, tel: +537 8781004/06 ext. 221
†Bolsista da CAPES
Copyright © 2012 World Scientific Publishing Company

268
L. MAQUEIRA ET AL.
guest solvents whereby aggregation occurs by mixing of
solutions containing porphyrins with miscible solvents
in which they are not soluble (e.g. CHCl3/H2O) and
stabilized by surfactants or amphipathic molecules, (3)
interfacial precipitation, and (4) the rapid expansion of
supercritical solvents [1]. Besides, porphyrin nanorods
have been obtained by employing sonication [18].
slits at 1 mm and lamp current at 15 A. Particles size and
z-potential were measured by dynamic light scattering
using a Zetasizer NanoSeries, Model Nano-ZS290
(Malvern Instruments). AFM images were recorded with
a PicoScan 2500 (Molecular Imaging). Nuclear magnetic
resonance (NMR) spectra were recorded on a Bruker
100-MHz (AMX 100) FT-NMR instrument and were
carried out using CDCl3.
In general terms, porphyrin aggregates could be of two
types, depending on the order of the adopted molecular
arrangement, i.e. H-aggregates, when the arrangement is
face-to-face and J-aggregates if side-by-side (or edge-to-
edge) [1]. The occurrence of these two types of aggregates
could be in principle identified by optical spectroscopy,
since the H-aggregates produce a blue shift in the Soret
band whereas a red shift is observed if J-aggregates are
present, both in comparison to the spectra of monomeric
porphyrin [1, 19, 20]. Once formed, the aggregates
can favor electron transfer in these supramolecular
systems, leading to noticeable changes in the optical
and electrochemical properties that contribute to extend
the range of possible applications of these materials.
For example, porphyrin-doped polymer films can be
prospectively used in optoelectronics and sensor [21].
On the other hand, to obtain stable nanoaggregate
suspensions of porphyrins in water is also relevant
because of its possible use in biological applications
photosensitizer in polymer/porphyrins complex with
antibacterial activity [22]. However, the preparation of
hydrophobic porphyrin suspensions could be difficult.
Due to this it is necessary the search for new methods to
obtain stable dispersions of hydrophobic porphyrins and
metalloporpyrins in water [23].
Materials
Propionic acid (Sigma-Aldrich, 99%), aldehydes
(o-methoxybenzaldehyde, o,p-dimethoxybenzaldehyde
and benzaldehyde (Sigma-Aldrich, 99%)) of analytical
grade were used. Pyrrole (Sigma-Aldrich, 99%) was
distilled prior to synthesis.
Synthesis of porphyrins and its metallic derivatives
Porphyins were synthesized according to the procedure
reported by Adler et al. [24], but with the modification
in the order of reagents addition suggested by Ortega
et al. [25] to increase the reaction yield (see Supporting
information section).
Metallic derivatives were obtained by refluxing the
corresponding metal acetate together with porphyrin
in DMF for 20 min, with subsequent precipitation on
cold water and vacuum filtering. All products were
characterized by UV-vis, and the nonmetallic derivatives
by NMR-1H and NMR 13C. The corresponding structures
of the synthesized porphyrins are presented in Table 1.
NMR -1H and 13C of nonmetallic porphyrins were
carried out, and the corresponding results were:
In this work, a series of hydrophobic porphyrins and
metalloporphyrins substituted by different functional
groups was synthesized and used to obtain porphyrin
nanoaggregatesinwater,throughanovelmethodthatallows
the formation of highly stable hydrophobic porphyrinic
nanoaggregates dispersed in an aqueous medium. The
optical, morphological properties and the stability of these
nanoaggregates suspensions were studied by dynamic light
scattering (DLS), UV-vis and fluorescence spectroscopies
and by atomic force microscopy (AFM).
Tetraphenylporphyrin (TPP). In 20 mL of propionic
acid 0.32 mL of pyrrole (5 mmol) and benzaldehyde
(5 mmol) were added and refluxed by 1 hour. The obtained
dark solid was vacuum filtered and dried to give 79% yield
of TPP. 1H NMR (CDCl3): d, ppm 8.89 (s, 8H, Hb), 8.27–
7.79 (m, 20H, H aromatics), -2.73 (s, 2H, NH). 13C NMR
(CDCl3): d, ppm 142.23 (C1), 134.63 (C2,6), ≈131.3 (Cb),
127.78 (C4), 126.76 (C3,5), 120.22 (C meso).
o-methoxy-tetraphenylporphyrin (OMTPP). In 20
mL of propionic acid 0.32 mL of pyrrole (5 mmol) and
o-methoxy-benzaldehyde (530 mg, 5 mmol) dissolved in
1 mL of propionic acid were added and refluxed by 1 h.
The obtained dark solid was vacuum filtered and dried
to give 56% yield of OMTPP. 1H NMR (CDCl3): d, ppm
8.74 (s, 8H, Hb), 8.01–7.25 (m, 20H, H aromatics), 3.56
(s, 3H, OCH3), -2.60 (s, 2H, NH).
EXPERIMENTAL
Equipments
o,p-dimethoxy-tetraphenylphyrin (OPMTPP). In
20 mL of propionic acid 0.32 mL of pyrrole (5 mmol)
and o,p-methoxy-benzaldehyde (681 mg, 5 mmol)
dissolved in 1 mL of propionic acid were added and
refluxed by 1 h. The obtained dark solid was vacuum
The porphyrin aqueous microemulsions solutions
were prepared by use of an ultrasonic probe (Ultrasonic
Processor Sonics, Vibra.cell), with a regime of 130 watts
power and 20 KHz frequency. Samples were treated with
an Ultracentrifuge Hermle Z300.
UV-vis spectra were recorded by using a Varian
Cary5E UV/vis/NIR spectrophotometer. Fluorescence
measurement were carried out on an ISS Vinci Model
PC1 spectrofluorimeter with excitation and emission
1
filtered and dried to give 62% yield of OMTPP. H
NMR (CDCl3): d, ppm 8.74 (s, 8H, Hb), 7.94–6.87 (m,
20H, H aromatics), 3.55 (s, 3H, OCH3), 3.52 (s, 3H,
OCH3), -2.66 (s, 2H, NH).
Copyright © 2012 World Scientific Publishing Company
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PREPARATION AND CHARACTERIZATION OF SDS-STABILIZED HYDROPHOBIC PORPHYRINIC
269
Table 1. Structures and abbreviation of the porphyrins synthetized
Abbreviation
TPP
R1
H
R2
H
R3
H
M
—
Zn
Cu
—
R3
R2
R2
R1
ZnTPP
H
H
H
R3
CuTPP
H
H
H
N
OMTPP
-OCH3
H
H
R1
M
N
N
R1
N
R3
OPMTPP
-OCH3 -OCH3
H
—
R1
R2
R2
R3
Preparation of hydrophobic porphyrin water
dispersions stabilized with SDS
into the surfactant (SDS) dispersed in water, whereas
the greyish layer is the mixing between water, SDS
and porphyrin dissolved in chloroform. Later, this
pre-emulsion is sonicated (Fig. 1(b)) to obtain a stable
suspension of porphyrin nanoaggregates in water, which
is the dark layer in Fig. 1(c), where the greyish layer is
the unstable layer produced. Afterwards, this unstable
layer fully disappears after a rotoevaporing step for
eliminating chloroform from the suspension.
Although a similar method has been reported to
produce nanoparticles of water-soluble polymers [26],
to our knowledge, this procedure had not been used
before for the preparation of porphyrin nanoaggregates.
In fact, the method here adopted can be considered as
a combination of two other procedures independently
used for the preparation of porphyrinic nanoaggregates:
while one of them, employs surfactants, the other one
uses sonication with ultrasonic bath [1, 18]. In our
case, the use of ultrasonic probe guarantees the full
introduction of the dissolved porphyrin in the interior
of the SDS micelles, a factor that leads to highly stable
suspensions.
Hydrophobic porphyrinic dispersed in aqueous
solutions were obtained using sodium dodecyl sulfate
(SDS) as surfactant and after sonication. Initially a pre-
emulsion of the porphyrin dissolved in chlorophorm
and the SDS aqueous solution (0.1 g in 10 mL) was
prepared and then stirred for about 1 h. Later, a
microemulsion was obtained by ultrasonication of the
pre-dispersion for 3 min at 70% amplitude. Finally,
the material was rotoevaporated to remove the organic
solvent, and centrifuged for 30 min at 10,000 rpm, and
then filtered through a 0.22 mm membrane.
RESULTS AND DISCUSSION
Nanoaggregates suspension: particle size, morphology
and stability
A stable suspension of porphyrins remained dis-
persed in the aqueous medium. Figure 1 shows the
porphyrin dispersions before, during and after soni-
cation. Figure 1(a) shows the pre-emulsion obtained
after magnetic stirring, but before sonication, where the
clear layer corresponds to a few porphyrin encapsuled
To examine the stability of each suspention, we have
measured the average size of the dispersed particles
and their z-potential by DLS, and the corresponding
results are shown in Table 2, where the full width at
half maximum (fwhm) values are also shown. Figure 2
exemplifies the size distribution with that of ZnTPP
Table 2. Particle size and z-potential of water-
dispersed porphyrins
Porphyrins d, nm fwhm, nm z-potential, mV
TPP
64
65
59
78
46
62
41
53
55
54
-55.9
-70.1
-68.9
-70.9
-73.6
ZnTPP
CuTPP
OMTPP
OPMTPP
Fig. 1. Pictures of porphyrinic dispersions (CHCl3/SDS/H2O),
before (a) during (b) and after (c) sonication
Copyright © 2012 World Scientific Publishing Company
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270
L. MAQUEIRA ET AL.
Characterization of porphyrin nanoaggregates in
water by UV-vis and fluorescence
In general, porphyrins have very strong absorption bands
around 400–450 nm (Soret band) with an extinction molar
coefficient (e) of about 105 M-1.cm-1 and four Q-bands
between 500 and 700 nm with values of e 10–20 times
lower. Their metallo-derivatives present only one or two
Q-bands with similar e, depending on the metal [1]. The
UV-visible spectrum of each nanoaggregate suspension
in water were recorded and compared with those obtained
with chloroform-dissolved porphyrins (see supporting
information). In order to establish such comparison, all
samples were adjusted to the same concentration value.
In Table 3, the Soret and Q-bands of porphyrin dispersed
in chloroform and water, respectively, are presented. All
spectra of water-dispersed porphyrins showed that the Soret
band broadens and the absorbance decreases in comparison
tonon-aggregatedporphyrinsinchloroform(seeSupporting
information section). In general, no significant shifts were
observed from the region, and so it was not possible to
assign them as J- or H-aggregates [5, 19].
However, in the case of the metallic derivatives one
could observe the existence of small red shifts, which
were more significant in the Zn substituted porphyrin,
(see Fig. 4); a fact suggestive of the presence of J-type
aggregate [1]. On the other hand, in the case of non-metal
porphyrins, only the methoxyl disubstituted porphyrins
were the ones to present some variation on absorption
spectra, with blue-shifts — characteristic of the existence
of H-type aggregates — on the Soret band.
Fig. 2. DLS characterization of ZnTPP nanoaggregates, mean
diameter = 65 nm
nanoaggregate, where it is noticed the distribution skewed
shape. A similar shape of distribution was obtained
for all porphyrin nanoaggregates. See the supporting
information for results of DLS characterization of the
other studied porphyrins.
In general, average particle sizes for each porphyrin
change between 46 nm and 78 nm. Fwhm values indicate
relatively high dispersion in comparison to other reports
[16], where ZnTPP distribution was the narrowest one.
However, in all cases, the absolute value of the measured
z-potential of the suspended particles was higher than
50 mV, in an indication that the corresponding colloidal
solutions presented a high stability. As it should be
expected, these z-potentials had negative values because
the negatively charged dodecylsulphate ions form the
most external shell of the aggregates.
In Table 4 one can note the shift of the emission
bands of water-dispersed ZnTPP, which is in agreement
with the result obtained in the absorption spectrum
of this porphyrin. The methoxylated products show
increases in the emission intensity when compared to
non-functionalized porphyrins, because this functional
group produces a positive mesomeric effect on the
porphyrin ring, increasing the average electron density
and the transition p–p* [27].
On the other hand, morphological studies of the TPP
nanoaggregates by AFM, employing the drop dispersed
method to prepared sample. AFM images reveal spherical
particles with size ranging between 50 nm and 90 nm, as
shown in Fig. 3.
Fig. 3. Morphology of porphyrin nanoaggregates as revealed by AFM
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PREPARATION AND CHARACTERIZATION OF SDS-STABILIZED HYDROPHOBIC PORPHYRINIC
271
Table 3. Comparison of the absorption band maxima between water-suspended nanoaggregates
and chloroform-dissolved non-aggregate porphyrins (in nm)
Porphyrins
Porphyrins in CHCl3
Porphyrins in H2O
Soret band
Q-bands
Soret band
Q-bands
TPP
418
419
416
419
422
515 549 588 646
419
427
415
421
417
517 549 590 646
ZnTPP
CuTPP
OMTPP
OPMTPP
547 581
538
—
—
—
—
557 599
540
—
—
—
—
—
—
515 549 590 652
516 550 592 651
515 551 591 652
517 552 590 646
Table 4. Emission wavelength of porphyrin in organic and
aqueous media (in nm)
Porphyrins
Porphyrins in CHCl3
Porphyrins in H2O
lemission(1)
lemission(2)
l
emission(1)
l
emission(2)
TPP
653
597
655
653
715
645
715
715
654
603
655
654
715
654
715
715
ZnTPP
OMTPP
OPMTPP
Fig. 5. Fluorescence spectra of OPMTPP water-suspensions
(A) and OPMTPP in CHCl3-dissolved (B), c = 1.58 × 10-5
and excited at 420 nm in both case
M
CONCLUSIONS AND PERSPECTIVES
We have developed a simple modified procedure for
preparation of porphyrin nanoaggregates that allowed
us to obtain aqueous suspensions of hydrophobic
porphyrins with excellent colloidal stability. DLS and
AFM measurements showed that the aggregates exhibit
spherical morphology and are nanostructured. UV-vis
and fluorescence spectroscopic characterization has
permitted us to discern the dispersed porphyrin particles
in suspension as of J- or H-type nanoaggregates.
Recently, the light harvesting properties of con-
ducting polymers have been exploited in the design of
(conjugated polymers)/porphyrin complexes that could
be used in the detection of heavy metals ions [28] or
as light-activated antibacterial agents [22]. It would be
of special interest to examine the equivalent properties
of complexes formed by water-soluble conjugated
polymers and the porphyrin derivatives described in the
present work.
Fig. 4. Absorption spectra of ZnTPP (solid line) and ZnTPP
nanoaggregate (dashed line)
Fluorescence signals in the 600–800 nm region
were not observed for Cu porphyrin, in agreement
with previous reports [27]. The fluorescence spectra of
the water-dispersed nanoaggregates and chloroform-
dissolved porphyrins are compared in Fig. 5. In order
to attain such comparison, the same concentration
(c = 1.58 × 10-5 M) and similar instrumental conditions
were used in all cases. The fluorescence intensity in
water-suspended porphyrins decreases in comparison
to those of the chloroform-dissolved ones. Porphyrin
nanoaggregates usually present a quenching of the
fluorescence due to several factors, such as non-radiative
pathways and photoscreening of chromophores.
Particles with sizes lower than 150 nm are reported to
present anomalous and depressed fluorescence [5] (see
Supporting information section).
Acknowledgements
This work was partially supported by Project 040/07
CAPES, Brasil – MES, Cuba and it is also under Project
PNCIT-DES 00613457.
Copyright © 2012 World Scientific Publishing Company
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L. MAQUEIRA ET AL.
Supporting information
13. D’Souza F, Hsieh Y-Y, Wickman H and Kutner W.
Chem. Commun. 1997: 1191–1192.
The results of UV-visible absorption spectra, fluo-
rescent spectra and DLS characterization of porphyrins
nanoaggregates are given in the supplementary material.
This material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
14. Deviprasad GR, Keshavan B and D’Souza F. J.
Chem. Soc., Perkin Trans. 1 1998: 3133–3135.
15. Rakow NA, Sen A, Janzen MC, Ponder JB and
Suslick KS. Angew. Chem., Int. Ed. 2005; 44:
4528–4532.
16. Gong X, Milic T, Xu C, Batteas JD and Drain CM.
J. Am. Chem. Soc. 2002; 124: 14290–14291.
17. Bazzan G, Smith W, Francesconi LC and Drain
CM. Langmuir 2008; 24: 3244–3249.
18. Hasobe T, Oki H, Sandanayaka ASD and Murata H.
Chem. Commun. 2008: 724–726.
19. Maiti NC, Mazumdar S and Periasamy N. J. Phys.
Chem. B 1998; 102: 1528–1538.
20. Barber DC, Freitagbeeston RA and Whitten DG.
J J. Phys. Chem. B 1991; 95: 4074–4086.
21. Egawa Y, Hayashida R and Anzai JI. Langmuir
2007; 23: 13146–13150.
22. Xing CF, Xu QL, Tang HW, Liu LB and Wang S. J.
Am. Chem. Soc. 2009; 131: 13117–13124.
23. Chen C-Y, Tian Y, Cheng Y-J, Young AC, Ka
J-W and Jen AKY. J. Am. Chem. Soc. 2007; 129:
7220–7221.
24. Adler AD, Longo FR, Finarell. Jd, Goldmach J,
Assour J and Korsakof L. J. Org. Chem. 1967; 32:
476-&.
REFERENCES
1. Drain CM, Varotto A and Radivojevic I. Chem. Rev.
2009; 109: 1630–1658.
2. Mohnani S and Bonifazi D. Coord. Chem. Rev.
2010; 254: 2342–2362.
3. Schmittel M, He B and Mal P. Org. Lett. 2008; 10:
2513–2516.
4. Jurow M, Schuckman AE, Batteas JD and Drain
CM. Coord. Chem. Rev. 2010; 254: 2297–2310.
5. Drain CM, Smeureanu G, Patel S, Gong XC,
Garno J and Arijeloye J. New J. Chem. 2006; 30:
1834–1843.
6. Chen W, Wang Y, Bruckner C, Li CM and Lei Y.
Sens. Actuators, B 2010; 147: 191–197.
7. Mazzotta E and Malitesta C. Sens. Actuators, B
2010; 148: 186–194.
8. Bai D, Wang Q, Song Y, Li B and Jing H. Catal.
Commun. 2011; 12: 684–688.
25. León-Cedeño F, Menes-Arzate M and García-
Ortega H. Rev. Cubana Quí. 2006; XVIII.
26. Kietzke T, Neher D, Landfester K, Montenegro
R, Guntner R and Scherf U. Nat. Mater. 2003; 2:
408–U407.
27. Zheng WQ, Shan N, Yu LX and Wang XQ. Dyes
Pigm. 2008; 77: 153–157.
28. Fang Z, Pu KY and Liu B. Macromolecules 2008;
41: 8380–8387.
9. Rezaeifard A, Jafarpour M, Raissi H, Ghiamati E
and Tootoonchi A. Polyhedron 2011; 30: 592–598.
10. Kim H-S, Kim C-H, Ha C-S and Lee J-K. Synth.
Met. 2001; 117: 289–291.
11. Watson DF, Hasselmann GM and Meyer GJ.
“NCPV and Solar Program Review Meeting” 2003.
12. Maree CHM, Roosendaal SJ, Savenije TJ, Schropp
REI, Schaafsma TJ and Habraken F. J. Appl. Phys.
1996; 80: 3381–3389.
Copyright © 2012 World Scientific Publishing Company
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