Preparation and photoactivity of a novel water-soluble, polymerizable zinc phthalocyanine

Article abstract of DOI:10.1016/j.molcata.2008.09.023

A novel water-soluble and polymerizable photosensitizer, zinc tetra(N-carbonylacrylic)aminophthalocyanine (Zn-MPc), was synthesized by the ornament of zinc tetraaminophthalocyanine (Zn-APc) with maleic anhydride and characterized by ¹H NMR, FT-

Full text of DOI:10.1016/j.molcata.2008.09.023

Journal of Molecular Catalysis A: Chemical 298 (2009) 17–22
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Preparation and photoactivity of a novel water-soluble, polymerizable zinc
phthalocyanine
∗
Xiaoyuan Shen, Wangyang Lu, Guihua Feng, Yuyuan Yao, Wenxing Chen
Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education of China, Zhejiang Sci-Tech University, Hangzhou 310018, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 January 2008
Received in revised form
A novel water-soluble and polymerizable photosensitizer, zinc tetra(N-carbonylacrylic)aminophtha-
locyanine (Zn-MPc), was synthesized by the ornament of zinc tetraaminophthalocyanine (Zn-APc) with
1
maleic anhydride and characterized by H NMR, FT-IR, and MALDI-TOF mass spectra. The photoactiv-
18 September 2008
ity of Zn-MPc was determined by tracking the degradation of 1,3-diphenylisobenzofuran (DPBF). The
results indicated that Zn-MPc is an efficient photosensitizer and has a high photostability. The apparent
rate constant, ka, of DPBF photodegradation increased with the increase of the Zn-MPc concentration
or light intensity, but declined with the increase of the initial concentration of DPBF. Furthermore, the
Accepted 23 September 2008
Available online 2 October 2008
Keywords:
Zinc tetra(N-
carbonylacrylic)aminophthalocyanine
Photoactivity
−
5
0.51
0.54 1.35
kinetics equation was deduced as Rd = 1.12 × 10 [DPBF] [Zn-MPc]
E
. The results in this work pro-
vide a basis for the further development of more desirable phtotosensitizers and their applications in
photodynamic therapy (PDT) of cancer.
Water-soluble
Polymerizable
© 2008 Elsevier B.V. All rights reserved.
Singlet oxygen
1. Introduction
ity [15–17]. The effective strategies to prevent such aggregation
involve the introduction of polymeric substituents to the peripheral
Zinc phthalocyanines (Zn-Pcs) as one class of efficient pho-
tosensitizers have attracted considerable interest, which can be
used in the photodynamic therapy of cancer (PDT) [1,2], water
treatment [3–5], and fine chemical synthesis [6–8], etc. Among
these applications, PDT is currently the object of intense inves-
tigation due to their high efficiency to generate singlet oxygen,
intense absorption in the optimally tissue-penetrating spectral
region (630–800 nm) and lack of dark toxicity [9,2]. However,
this application is greatly limited by their insolubility in water,
which strongly influences the bioavailability and in vivo distribu-
tion [10]. Therefore, the enhancement of their water solubility is
the important aim of studies on the chemistry of Zn-Pcs. Several
aqueous soluble Zn-Pcs, such as tetrasulfonated Zn-Pc [11], tetra-
and octa-triethyleneoxysulfonyl substituted Zn-Pc [12], [1,2,3,4-
tetrakis(␣/␤-d-galactopyranos-6-yl)-phthalocyaninato] zinc [13],
Zn-Pc containing four carboxyphenyloxy substituents (p-HPcZn)
benzene rings [18] and conjugation with polymers [19–21]. Fur-
thermore, via adjusting the size of the polymeric substituents and
polymers or incorporating site-selective moieties, the biodistribu-
tion of the photosensitizers can be improved, and these systems
may be used for targeted delivery and release of photosensitiz-
ers [18,22]. Whereas, most of the water-soluble Zn-Pcs reported,
including those mentioned above, are lack of founctional groups
for further design of photosensitizers to satisfy various require-
ments, thus the exploration of Zn-Pcs which have high aqueous
solubility and are facile to chemical modification is particularly
attractive.
Herein, we reported a novel water-soluble Zn-Pc with unsat-
urated double bonds, zinc tetra(N-carbonylacrylic)aminophtha-
locyanine (Zn-MPc). Moreover, the special molecular structure of
Zn-MPc supplies extensive space for the further design of flex-
ible molecular, effectively preventing the aggregation of Zn-Pcs
and exhibiting desirable photoactivity. Since PDT activity is mainly
based on singlet oxygen [23], 1,3-dphenyl isobenzofuran (DPBF) as a
specific scavenger of this toxic species [24–26] is chosen to evaluate
the photoactivity of Zn-MPc, and the kinetics of DPBF degradation
is investigated. A thermosensitive macromolecular photosensitizer
with desirable photoactivity and PDT selectivity based on Zn-
MPc is currently being explored in our labs and will be reported
soon.
[
14], have been successfully prepared. However, they tend to aggre-
gate at relatively low concentrations in aqueous media. These
aggregates provide a facile nonradiative energy relaxation pathway
and negatively result in the significant reduce of the photoactiv-
∗ Corresponding author. Tel.: +86 571 8684 3251 fax: +86 571 8684 3251.
E-mail address: chenwxg@yahoo.com.cn (W. Chen).
1381-1169/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2008.09.023

18
X. Shen et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 17–22
Scheme 1. Synthesis of Zn-MPc.
2. Experimental
2.4. Photoactivity studies
2.1. Preparation of Zn-MPc
All experiments were carried out in oxygen-saturated DMF at
5 C, using 1,3-diphenylisobenzofuran (DPBF, Acros Organics) as
◦
2
The synthetic methodology was shown in Scheme 1. Finely
ground zinc tetraaminophthalocyanine (Zn-APc, prepared accord-
ing to the literature method [27]) (3.0 g) was dissolved in 150 ml
chemical quencher. Electronic energy-saving lamps (15, 11, 8, and
5 W, Philips, Shanghai) were used as the irradiation source. A
550 nm glass cut off filter (CB550, Shanghai Seagull Coloured Opti-
cal Glass Co., Ltd., China) was used to filter off ultraviolet light, so
that only the phthalocyanine Q band was irradiated, avoiding direct
photodegradation of DPBF under UV light irradiation. The light
intensity was measured by a luminometer (TES-1339, TES Electrical
Electronic Corp., Taibei). After irradiation for certain interval, the
sample was monitored by a Hitachi UV-3010 spectrophotometer.
For the study on photodegradation kinetics of DPBF, experiments
were performed where one of the initial concentration of DPBF, Zn-
MPc concentration and light intensity changed while the other two
factors were restrained.
DMF, and then maleic anhydride (1.32 g) was added. After stirring
◦
at 60 C for 3 h, the solution was poured into 1000 ml H O and a
2
dark cyan floccule was obtained. The mixture was centrifugated
and the precipitate was collected. The rude product was then dis-
solved in sodium hydroxide solution (0.1 M) and filtrated through
a glass funnel. The filtrate pH was adjusted to 2. When much dark
cyan floccule appeared, centrifugated it again. This procedure was
repeated three times. After washing with water, ethanol and ether,
the final product (Zn-MPc) was dried in vacuo for 24 h.
2.2. Characterization
3. Results and discussion
FT-IR spectra was determined on a Brucker vector 22 spec-
trophotometer using KBr pellets. H NMR spectra was recorded on a
Bruker-400 spectrophotometer (400 MHz) in deuterated dimethyl-
1
3.1. Characterization of Zn-MPc
In the FT-IR spectra (Fig. S1, see supporting information),
for Zn-MPc, the absorption peaks at 1167, 1085, 1045, 840 and
sulfoxide (DMSO-d ), using TMS as internal reference. MALDI-TOF
6
mass spectra was taken on a MALDI-TOF 4700 proteomics Analyzer,
−
1
745 cm
were assigned to phthalocyanine skeleton [28]. Peak
and the sample was dissolved in a 10:90 mixture of DMF:H O.
2
−
1
around 1706 cm indicated the presence of C O group, and the
band at 3000–3500 cm corresponded to OH of the COOH group;
and for Zn-APc, the absorption peaks at 1136, 1095, 1059, 822
−
1
2
.3. Solubility test
−
1
and 751 cm were also assigned to phthalocyanine skeleton. The
0
.01 g Zn-Pcs were placed into 50 ml of solvent (THF, acetone,
−1
strong absorption bands around 3300 cm were due to the NH2
◦
ethanol, toluene, DMF, H O and CHCl ) and vibrated at 25 C for 24 h
2
3
group on the ring of phthalocyanine, which was diminished in
the spectra of Zn-MPc. It can be concluded that the nucleophilic
reaction had taken place between Zn-APc and maleic anhydride.
in a thermostatic vibrator. The solution was filtered and the insol-
uble substrate was collected, dried and weighed (m). The formula
of dissolution rate (ꢀ) can be expressed as follows:
1
The H NMR spectra of Zn-APc and Zn-MPc (Fig. S2) are consis-
1
tent with the results from FT-IR analysis. In the H NMR spectra
.01 − m
ꢀ
ꢀ
= 0
× 100%
of Zn-APc, the 3-H (Scheme 1) of phthalocyanine ring had the
maximum chemical shift because of the effect of Zn(II) through
the phthalocyanine ring and the easiest solvation, appearing as a
0
.01
< 0.1%, insoluble; 0.1% ≤ ꢀ < 1%, slightly soluble; ꢀ ≥ 1%, soluble.

X. Shen et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 17–22
19
−
6
−1
,
Fig.
5
8
3. Control
experiments:
dark; (b) DPBF: 5.0 × 10 mol l
(a)
Zn-MPc:
5.0 × 10 mol l
DPBF:
Fig. 1. MALDI-TOF mass spectra of Zn-MPc. The inset shows the isotopic distribution
patterns of this molecule.
.0 × 10− mol l
5
−1
,
−5
−1
,
irradiation resource:
−6
−1
−5
−1
W, no Zn-MPc; (c) Zn-MPc: 5.0 × 10 mol l , DPBF: 5.0 × 10 mol l , irradiation
resource: 8 W.
quartet at 8.90–8.96 ppm, the 4-H (Scheme 1) had a smaller chemi-
cal shift at 8.41–8.45 ppm because of the relatively disadvantageous
position, the 1-H (Scheme 1) had the smallest chemical shift at
proof for the proposed structure of Zn-MPc (calculated for
[
C48H28N12O12Zn]: 1030.19). As expected, complex isotopic distri-
7
.38–7.42 ppm for the most difficult solvation and the –NH2 pro-
butions were observed around 1030.20. In addition, a specie with
a MW of 1066.15 was observed, which seemed to be Zn-MPc conju-
1
tons appeared as a typical broad singlet at 6.23 ppm. While in the H
NMR spectra of Zn-MPc, the broad singlet at 6.23 ppm for –NH pro-
2
gated with two H O (+36) in the Zn(II) coordination center. Another
2
tons disappeared and a new singlet at 11.30 ppm for –COOH proton
emerged, indicating the successful preparation of Zn-MPc. Mean-
while, the introduction of functional group (–COCH CHCOOH)
influences the electron cloud of the protons of phthalocyanine ring
and makes the space conformation complicated, hence causing the
spectral broadening.
For the further certification of the structure of Zn-MPc, the
MALDI-TOF mass spectra of the compound were tested. In Fig. 1,
the intense molecular ion peak at m/z 1030.20 provided a definitive
molecular ion peak at m/z 1005.24 may correspond to Zn-MPc (+2
H O-CO -OH: +36-44-17), created by the excess laser power.
2
2
3.2. Solubility test
As shown in Table 1, compared with Zn-APc, which was only
soluble in aprotic polar solvents like DMF, Zn-MPc can also be dis-
solved in basic solution since the dissociated carboxyl groups on
the phthalocyanine rings increase the electrostatic repulsion and
reduce the aggregation of phthalocyanine molecules, improving its
solubility. Moreover, Zn-MPc was partially soluble in THF due to
the enhancement of the solubility by substituting of the functional
groups on the phthalocyanine ring.
Table 1
a
Solubility test of Zn-APc and Zn-MPc .
Sample
DMF
CHCl3
Toluene
Ethanol
THF
H2O (pH > 7)
Acetone
Zn-APc
Zn-MPc
+
+
−
−
−
−
−
−
−
±
−
−
−
3.3. Photoactivity studies
+
a
(
+) soluble; (± ) partially soluble; (−) insoluble.
As a specific singlet oxygen quencher, DPBF is known to form an
endoperoxide upon cycloaddition with singlet oxygen, resulting in
−4
−1
Fig. 2. Time evolution of the UV–vis spectrum of a DPBF (1.0 × 10 mol l ) and
Zn-MPc (5.0 × 10− mol l ) in DMF solution.
6
−1
Scheme 2. The proposed mechanism of DPBF decomposition.

2
0
X. Shen et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 17–22
Fig. 5. Effect of Zn-MPc concentration on the photodegradation rate of DPBF. All the
Fig. 4. Effect of the initial concentration of DPBF on the photodegradation rate of
−5
−1
reactions were performed in DMF; DPBF: 5.0 × 10 mol l ; irradiation resource:
−6
−1
DPBF. All the reactions were performed in DMF; Zn-MPc: 5.0 × 10 mol l ; irradi-
8
W.
ation resource: 8 W.
of 1O2 generation was almost changeless when the light inten-
sity and the Zn-MPc concentration were fixed. Although the suttle
amount of DPBF degradation increased with the increase of initial
the complete disappearance of its characteristic absorption band
at 415 nm [24]. Fig. 2 shows a family of spectra obtained for the
photodegradation of DPBF in DMF. It can be seen that the absorp-
tion of DPBF (415 nm) decreased significantly and disappeared after
concentration, contrarily, ka, depending on C /C decreased.
0
The effect of the amount of catalyst added on the photodegra-
dation rate of DPBF was shown in Fig. 5. As the concentration of
2
0 min, while the Zn-MPc absorption (698 nm) seldom changed
during the whole process, indicating that Zn-MPc is an efficient
photosensitizer with high photoactivity and photostability.
The concentration change of DPBF under various conditions
−6
−5
−1
−1
Zn-MPc increased from 3 × 10 to 2 × 10 mol l , the relevant
value of ka increased from 0.2267 to 0.8297 min (Table 2). This
could be explained by the fact that increasing amount of catalyst
led to the increasing rate of singlet oxygen generation.
(
Fig. 3) was investigated. The result indicated that light and Zn-MPc
were essential for the efficient degradation of DPBF (Fig. 3c), while
DPBF was hardly degraded in dark (Fig. 3a) or decomposed very
slowly under irradiation without Zn-MPc (Fig. 3b). According to the
well known Type II mechanism [7,29], the excited triplet state sen-
The light intensity is another factor which influences the rate
of photodegradation (Fig. 6). As the illumination increased from
2
100 to 9850 lux, the relevant value of ka increased from 0.05418
−1
to 0.6841 min (Table 2), which was consistent with the Type II
3
*
sitizer MPc was obtained by irradiation and intersysterm crossing
mechanism. Because higher light intensity brings more incident
photons, which will excitated more Zn-MPc.
In order to determine the influences of the initial concentration
of DPBF, Zn-MPc concentration and light intensity on the initial
photodegradation rate of DPBF (Rd) in detail, a dynamics equation
was assumed as follows:
(
(
ISC), which then interacted with the ground state triplet oxygen
3
1
O ) to generate the highly active singlet oxygen ( O ), inducing
2
2
the immediate decomposition of DPBF (Scheme 2). Without irradi-
1
ation, no O2 was formed, thus there was no degradation in dark
(
Fig. 3a). However, trace singlet oxygen may be spontaneously pro-
duced in solvent under the illuminance of visible light even without
Zn-MPc, resulting in the slight decomposition of DPBF.
a
b
c
Rd = k[DPBF] [Zn − MPc] E
Based on the reaction kinetics shown in Fig. 4, which was fitted
well into the first-order kinetic equation ln(C /C) = kat, the apparent
0
rate constant, ka, of DPBF photodegradation decreased from 0.4205
−1
to 0.2173 min as the initial concentration of DPBF increased from
× 10 to 1.05 × 10−4 mol l (Table 2). The reason is that the rate
−
5
−1
3
Table 2
Initial rate (Rd) and the apparent rate constant (ka) of DPBF photodegradation.
E (lux)
Initial concentration
Initial rate (Rd)
(×10 mol l min
ka (min−1)
−5
−1
−5
−1
−1
)
(×10 mol L
)
DPBF
Zn-MPc
6
6
6
6
6
6
6
6
9
350
350
350
350
350
350
350
350
850
10.5
10.0
5.0
3.0
8.0
8.0
8.0
8.0
5.0
5.0
5.0
0.5
0.5
0.5
0.5
2.0
1.0
0.5
0.3
0.5
0.5
0.5
1.68
1.58
1.28
0.88
3.27
2.11
1.62
1.12
2.07
1.72
0.27
0.2173
0.3277
0.3861
0.4205
0.8297
0.4671
0.3566
0.2267
0.6841
0.4736
0.05418
7
900
100
Fig. 6. Effect of light intensity on the photodegradation rate of DPBF. All the reactions
2
were performed in DMF; DPBF: 5.0 × 10− mol l ; Zn-MPc: 5.0 × 10 mol l
5
−1
−6
−1
.

X. Shen et al. / Journal of Molecular Catalysis A: Chemical 298 (2009) 17–22
21
Table 3
Orders with respect to the reactants and rate constants of DPBF degradation.
−1
−0.05
−1.35
min
−1
Variable
R2
Order
Rate constant (k) (mol l
1.31 × 10−
)
(lux)
5
DPBF
Zn-MPc
E
0.9863
0.9940
0.9983
0.51
0.54
1.35
−5
1.00 × 10
1.05 × 10−
5
where a, b and c were the reaction orders of DPBF concentration,
Zn-MPc concentration and light intensity, respectively, k the rate
constant of the photodegradation of DPBF, E the illuminance of irra-
diation source. The initial degradation rate of DPBF, Rd (Table 2),
was calculated from the decreased concentration at initial 1 min
of irradiation according to the reported method [5,30]. When two
of [DPBF], [Zn-MPc] and E were fixed, using a plot of ln Rd ver-
sus ln[DPBF], ln Rd ∼ ln[Zn-MPc] and ln Rd ∼ ln E, the values of a,
b, c and k could be obtained from the slope and intercept, respec-
tively (Fig. 7). As shown in Table 3, the results of linear fitting were
2
fine (R > 0.98) and the three constants of k varied slightly from
each other, which indicated that the assumed dynamics model was
reasonable. The final equation was obtained as follows:
Rd = 1.12 × 10− [DPBF]0.51[Zn − MPc]0.54E1.35
5
in which the unit of E is lux.
This equation shows that the light intensity is the most impor-
tant influencing factor to the photosensitizing efficiency. The
results also shed some light on the understanding of the action
of light irradiation, and on the design of highly efficient photosen-
sitizers for the potential utility in PDT. Moreover, DPBF is a singlet
oxygen trapper extensively used in research of photoactivity of var-
ious photosensitizers, and to the best of our knowledge, no similar
dynamic equations have been reported.
4. Conclusion
A novel aqueous soluble polymerizable phthalocyanine, Zn-
MPc, with high photoactivity and photostability, was successfully
synthesized and characterized. The increase of the Zn-MPc con-
centration or light intensity resulted in an increased efficiency of
photosensitivity, while the increase of the initial concentration of
substrate decreased it. The kinetics equation of the initial degra-
−
5
0.51
0.54 1.35
dation rate of DPBF is Rd = 1.12 × 10 [DPBF]
[Zn-MPc]
E
,
which can provide a novel thought for the potential application of
photosensitizers in PDT and the further design of highly efficient
photosensitizers.
Acknowledgements
This work was supported by the National natural science
foundation of China (Nos. 20574061 and 50872124), Program for
Changjiang Scholars and Innovative Research Team in University
(
IRT 0654) and Zhejiang Provincial Natural Science Foundation of
China (Y4080341).
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.molcata.2008.09.023.
Fig. 7. Regression lines of ln Rd ∼ ln[DPBF] (A), ln Rd ∼ ln[Zn-MPc] (B) and ln Rd ∼ ln E
C).
(
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