Photo-controlled growth of polymeric submicron-sized particles

Article abstract of DOI:10.1039/c9pp00086k

A tripodal coumarin derivative shows complex photoreactivity, changing from intra- to intermolecular photodimerization with increasing concentration. At high concentration, the compound undergoes efficient photopolymerization, resulting in the formation of polymeric submicron-sized particles. The size of these particles can be precisely increased through photoirradiation, without affecting their polydispersity.

Full text of DOI:10.1039/c9pp00086k

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DOI: 10.1039/C9PP00086K
Photochemical & Photobiological Sciences
COMMUNICATION
Photo-controlled growth of polymeric submicron-sized particles
a,b
b
b
João Avó* , João C. Lima , A. Jorge Parola*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A tripodal coumarin derivative shows complex photoreactivity, exempt of elaborate purification steps and without additional
changing from intra- to intermolecular photodimerization with reagents. Using a tripodal motif bearing photodimerizable
increasing concentration. At high concentration, the compound moieties (Scheme 1), the preparation of polymeric particles of
undergoes efficient photopolymerization, resulting in the precise dimensions and narrow size distribution can be
formation of polymeric submicron-sized particles. The size of these achieved. Coumarins, which are naturally occurring
particles can be precisely increased through photoirradiation, chromophores with tunable photophysical and photochemical
without affecting their polydispersity.
properties, are known to undergo photodimerization and make
for ideal candidates for the functionalization of the tripodal
molecules.
Polymeric particles (PPs) have gathered much attention from
the scientific community due to their important role in a wide
spectrum of areas, including electronics and photonics, sensors,
12-14
The synthesis of tripodal precursors bearing a coumarin
chromophore (3) is readily achieved from the derivatization of
coumarin-3-carboxylic acid (1) with thionyl chloride, followed
by condensation with tris(2-aminoethyl)amine, tren, in the
presence of potassium carbonate (Scheme 2). Compound 3 was
obtained in good overall yield (85%) and at high purity after a
simple purification process that does not require column
chromatography (see Supplementary material). Compound 3 is
moderately soluble in acetonitrile and dimethylsulfoxide, and
highly soluble in chloroform. The absorption spectrum of a
freshly prepared solution of 3 exhibits two bands without
vibrational structure in the UV region at approximately 300 and
1
-6
or medicine and biotechnology. A recurring topic in PP
research is the optimization of preparation methods that
greatly influence their final properties. In particular, size and
morphology of PPs are crucial factors that affect their
applicability, since they determine key properties such as
7
-8
viscosity, surface area and packing density. When PPs are
used as drug delivery carriers, size defines their biological effect,
cellular internalization mechanism and the in vivo fate of the
drug.9 Thus, methods that allow the preparation of particles
with specific sizes and structures with high reproducibility and
in relatively high volumes are a major objective of material
science research. Most PP preparation methods involve the
precipitation of preexisting polymers or the polymerization of
monomers in nanosized droplets, which require the addition of
stabilizers and/or additional reagents.
-11
3
50 nm, corresponding to the typical π-π* transitions
associated to the charge transfer from the benzenic cycle to the
15
pyranone moiety of coumarins (Figure 1). Due to the presence
of an electron-withdrawing amide moiety group at position 3,
the absorption maxima of compound
3 are shifted
While this does not pose significant purification problems at
laboratory scale, considerable challenges emerge when large
production volumes are needed. From this perspective, we
envision that in situ photopolymerization can lead to the
formation of polymeric particles from homogenous solutions,
bathochromically (ca. 30–40 nm) in comparison with
16
unsubstituted coumarin. In addition, the calculated molar
-1
-1
absorptivity value ε of ca. 38900 M cm is approximately three
-1
times higher than that of native coumarin (ca. 9000-12500 M
-1
cm , depending on solvent polarity), due to the presence of
1
5,16
three independent chromophores in the tripodal molecule.
a. CQFM-IN and IBB-Institute for Bioengineering and Biosciences, Instituto Superior
Técnico, Universidade de Lisboa, Portugal
b.
LAQV-REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia,
Universidade NOVA de Lisboa, 2829-516, Caparica, Portugal
*
corresponding address: joao.avo@tecnico.ulisboa.pt; ajp@fct.unl.pt
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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DOI: 10.1039/C9PP00086K
Scheme 1 - Representation for light-controlled dendrimeric growth of nanoparticles
from photopolymerizable tripodal molecules
O
O
HN
O
O
O
tren
K2CO3
SOCl2
CHCl3
O
O
O
O
O
O
N
OH
Cl
O
HN
O
CH2Cl2
HN
O
1
2
3
9
0%
Figure 1 - Spectral modifications of 2.6 x 10-5 M 3 in chloroform upon irradiation at 330
nm. Under the experimental setup, the photostationary state was reached after 60 min.
95%
O
Scheme 2 - Synthetic Pathway for the Preparation of Coumarin Derivative 3
This phenomenon can be rationalized if a simplified model for the
photodimerization reaction, where no photodegradation occurs, is
considered, as depicted in Scheme 3. In this model, M and M*
represent compound 3 in the ground and excited states,
respectively, (MM*) the excimer formed by an excited and a
ground state molecule of 3, D the (ground state) dimer of two
molecules of 3 and d represents compound 3 with two
intramolecularly dimerized coumarin moieties. The quantum
yields for the intramolecular and intermolecular dimerization
processes, Φ퐷 and Φ푑, respectively, are given by equations (1)
Upon irradiation at the absorption maxima, there is a clear decrease
of the absorption of both bands (Figure 1), compatible with a loss of
conjugation length of the coumarin chromophores. In this
wavelength range, only a very small increase below 250 nm is
noticed. The spectral transformations observed are consistent with
1
7
the photodimerization reaction of the coumarin moiety . This
1
hypothesis is further corroborated by H NMR spectroscopy, since
the spectra obtained after irradiation show the characteristic peaks
of the cyclobutane moieties formed upon dimerization of coumarins
(ESI, Figure S1 and S3).
and (2):
Since the photodimerization can occur from both intramolecular and
intermolecular processes, and only intermolecular dimerization can
give rise to the desired photopolymerization, elucidation of the
photochemical mechanism was required. Because photochemical
푘
퐷
푘
퐴
[푀]
Φ =
(1)
(2)
퐷
푘
푑
+ 푘푁푅 + 푘
퐷
푘퐴[푀] + 푘 푘 [푀]
푞 퐴
푘
푑
Φ = 푘푑 + 푘푁푅 + 푘퐴[푀]
푑
bimolecular processes are concentration sensitive,18 irradiation where k and k are the rate constants for unimolecular and
d
D
experiments over a broad concentration range were conducted and bimolecular dimerizations, respectively, k the (MM*) excimer
A
q
the respective photochemical quantum yields calculated (Table 1). formation constant, k the excimer self-quenching rate constant
The results show a clear correlation between the concentration of 3 and kNR is the rate constant for the non-reactive decay of
and the photochemical quantum yield for its disappearance (Φ
R
), compound 3.
The quantum yield for the observed reaction, i.e.,
indicating that there is a significant contribution of intermolecular
photodimerization to the observed photoreactivity.
disappearance of 3, Φ
Φ = Φ + Φ
R
, is given by the sum of both processes:
(3)
푅
퐷
푑
Table 1 -Determined photochemical quantum yield values, Φ
of 3 upon irradiation and calculated values for unimolecular, Φ
reactions at different concentration of 3 in chloroform.
R
, for the disappearance
D
, and bimolecular, Φ ,
Thus, for dilute solutions, the observed photochemical reaction
should arise only from an intramolecular process,
d
푘
푑
0
0
0
Φ = Φ + Φ =
푅
([푀]→0)
(4)
퐷
푑
푘 + 푘푁푅
푑
concentration
(
and for concentrated solutions, the opposite is verified.
Φ푅a
Φ푑b
Φ퐷 c
(
%)
(%)
(%)
10-5 M)
푘
퐷
∞
∞
∞
Φ = Φ + Φ =
([푀]→∞)
(5)
푅
퐷
푑
퐷 푞
푘 + 푘
0
1
3
1
5
.56
.15
.67
1.2
0.2
1.02
1.09
1.21
1.52
1.85
1.99
0.97
0.05
0.95
0.85
0.71
0.34
0.05
0.14
0.36
0.81
1.51
1.94
kD
D
kA
(MM*)
d+M
kNR
4
73.2
*
M+M
M +M
kq
M+M
a) determined by UV-Vis and NMR spectroscopy at conversion rates <5%
b) calculated from equation (2)
c) calculated from equation (3)
kd
푘푑
푘퐷
푘푑
fitting parameters: 푘푁푅=0.01, 푘 =0.02, 푘 =0.37 and = 4630 M-1
푘퐴
푞
퐷
Scheme 3 - Kinetic model for photodimerization reaction occurring in tripod 3
2
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DOI: 10.1039/C9PP00086K
Using equations 1-3, it is possible to fit the experimental values
of Φ
with great accuracy and calculate the contribution of
푅
intra- and intermolecular dimerization at each concentration
value (Figure 2, Table 1). The fitting was achieved using the
푘
푑
푘
퐷
푘
푑
= 4630 M-
kinetic relationships 푘푁푅=0.01, 푘푞=0.02, 푘퐷=0.37 and 푘
퐴
1.
Figure 2 evidences that for concentrations of 3 below 10 M,
-4
the efficiency of intramolecular dimerization is higher than that
of intermolecular process, and photopolymerization cannot
occur below this concentration. In addition, to achieve a
D d
significant polymerization degree, Φ must be higher than Φ
at a high conversion range, otherwise, an inversion in the
process relative efficiency can occur during irradiation. Thus,
solutions of 3 with concentrations above 1 mM were irradiated,
D d
as this concentration ensures that Φ >Φ up to 90% conversion
of 3. It was observed that the irradiated solutions turned turbid
due to the formation of an insoluble precipitate. Analysis of the
suspensions by atomic force microscopy (AFM) revealed the
presence of spherical nanoparticles with narrow size
distributions (Figure 3a). These results were corroborated by
Dynamic Light Scattering (DLS), with the particles exhibiting a
mean particle diameter of 100 nm and polydispersity index
(PDI) of 0.2. It is proposed that these results arise from the
photopolymerization of 3 upon irradiation, which leads to the
precipitation of insoluble oligomers. Further irradiation of the
obtained suspensions resulted in a significant increase in
particle size. For instance, after 400 minutes of continuous
irradiation, particles with a mean diameter size of ca. 400 nm
were observed (Figure 3b). It is worth noting that upon this 4-
Figure 3 - Atomic force microscopy images obtained from the irradiation of a 10 mM
solution of 3 in chloroform after 10 (a) and 400 (b) minutes. Scale bar is 1 μm. Insets
show size distribution determined by DLS.
fold increase in particle diameter, the PDI value of the The irradiation-induced growth rate was investigated with DLS
suspension did not vary significantly (ca. 0.23), which suggests spectroscopy and it was evidenced that it was virtually linearly
dependent with the irradiation time (Figure 4). The same
measurements were conducted for solutions of 3 at different
concentrations and it is evidenced that the growth rate of the
polymeric particles is significantly affected by the concentration
of 3.
that the increase in size results from the growth of the initial
particles, rather than their aggregation.19 Therefore, it is
proposed
that
the
growth
mechanism
involves
photodimerization reactions occurring at the surface of the
polymeric particles between their coumarin moieties and free
molecules or small oligomers of 3.
0
0
0
,025
R
0
,02
D
,015

0
,01
,005
d
0
-5
-4
-3
10
-2
10
10
10
concentration of 3 (M)
Φ푅
Figure 2 - Observed photodimerization quantum yield ( , square dots) dependency
with concentration of 3 and theoretical fitting (eqns. 1-3) of overall (solid black line),
intermolecular (dotted red line) and intramolecular (dashed blue line) quantum yields.
Figure 4 - Nanoparticle size dependence with irradiation time and concentration of 3 in
chloroform.
푘푑
푘퐷
푘푑
Fitting parameters: 푘푁푅=0.01, 푘 =0.02, 푘 =0.37 and = 4630 M-1
푘퐴
푞
퐷
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Journal Name
8
9
1
1
C.I.C. Crucho, M.T. Barros, Polymeric nanopartVicielwesA:rtiAclesOtunldinye
on the preparation variables and characterization methods,
DOI: 10.1039/C9PP00086K
In conclusion, the results obtained for tripodal coumarin 3
derivative show that it is possible to obtain particles with the
desired size in the submicron regime by adjusting the duration
of exposure of photopolymerizable compounds to UV light,
under determined irradiated conditions. By tuning the
photoreaction mechanism through concentration adjustment,
efficient photopolymerization was achieved and resulted in the
formation of polymeric nanoparticles. The size of these particles
could be accurately controlled by adjusting irradiation time and
monomer concentration, without affecting the polydispersivity.
The present work evidences the potential of photoresponsive
systems for the preparation of polymeric nano- and
micromaterials with controlled size and morphology using a
simple methodology exempt from additional organic reactants
and purification steps.
Mater. Sci. Eng. C, 2017, 80, 771-784.
M. Kalomiraki, K. Thermos, N.A. Chaniotakis, Dendrimers as
tunable vectors of drug delivery systems and biomedical and
ocular applications, Int. J. Nanomedicine, 2016, 11, 1-12.
0 A.B. Jindal, The effect of particle shape on cellular interaction
and drug delivery applications of micro- and nanoparticles,Int.
J. Pharm., 2017, 532, 450-465.
1 A.S. Gupta, Role of particle size, shape, and stiffness in design
of intravascular drug delivery systems: insights from
computations, experiments, and nature, WIREs Nanomed.
Nanobiotechnol., 2016, 8, 255-270.
1
1
2 K. Tanaka, Supramolecular Photodimerization of Coumarins,
Molecules, 2012, 17, 1408-1418.
3 J. He, L. Tremblay, S. Lacelle, Y. Zhao, Preparation of polymer
single
chain
nanoparticles
using
intramolecular
photodimerization of coumarin, Soft Matter, 2011, 7, 2380-
386.
2
1
1
4 J. Ling, M.Z. Rong, M.Q. Zhang, Photo-stimulated self-healing
polyurethane containing dihydroxyl coumarin derivatives,
Polymer, 2012, 53, 2691-2698.
Conflicts of interest
There are no conflicts to declare.
5 J.S. Seixas de Melo, R.S. Becker, A.L. Maçanita, Photophysical
Behavior of Coumarins as a Function of Substitution and
Solvent: Experimental Evidence for the Existence of a Lowest
Lying (n,pi*) State, J. Phys. Chem., 1994, 98, 6054-6058.
6 M. Taniguchi, J.S. Lindsey, Database of Absorption and
Fluorescence Spectra of >300 Common Compounds for use in
PhotochemCAD, Photochem. Photobiol., 2018, 94, 290-327.
7 R. Hoffman, P. Wells, H. Morrison, Organic photochemistry.
XII. Further studies on the mechanism of coumarin
photodimerization, observation of an unusual "heavy atom"
effect, J. Org. Chem., 1971, 36, 102-108.
1
1
Acknowledgements
This work was supported by the Associate Laboratory for Green
Chemistry - LAQV which is financed by national funds from
FCT/MCTES (UID/QUI/50006/2013) and co-financed by the
ERDF under the PT2020 Partnership Agreement (POCI-01-0145-
FEDER - 007265). FCT/MCTES is acknowledged for Projects
PTDC/QUI-QFI/30951/2017 and PTDC/QUI-QFI/32007/2017,
grants SFRH/BD/65127/2009 (JA) and SFRH/BPD/120599/2016
1
8 H. Bouas-Laurent, A. Castellan, J.P. Desvergne, R. Lapouyade,
Photodimerization of anthracenes in fluid solutions: (part 2)
mechanistic aspects of the photocycloaddition and of the
photochemical and thermal cleavage, Chem. Soc. Rev., 2001,
(JA). Jorge Caldeira (LAQV-REQUIMTE and ISSEM) is
3
0, 248-263.
acknowledged for the help with AFM measurements.
19 M.J. Masarudin, S.M. Cutts, B.J. Evison, D.R. Phillips, P.J.
Pigram, Factors determining the stability, size distribution,
and cellular accumulation of small, monodisperse chitosan
nanoparticles as candidate vectors for anticancer drug
Notes and references
1
4
delivery: application to the passive encapsulation of [ C]-
1
T. Patel, J.B. Zhou, J.M. Peipmeier, W.M. Saltzman, Polymeric
nanoparticles for drug delivery to the central nervous system,
Adv. Drug Deliv. Rev., 2012, 64, 701-705
doxorubicin, Nanotech. Sci. Appl., 2015, 8, 67-80.
2
N. Kamaly, B. Yameen, J. Wu, O.C. Farokhzad, Degradable
Controlled-Release Polymers and Polymeric Nanoparticles:
Mechanisms of Controlling Drug Release, Chem. Rev., 2016,
1
16, 2602-2663.
3
4
X. Xing, Q. Zeng, M. Vagin, M. Fahlman, F.L. Zhang, Fast
switching polymeric electrochromics with facile processed
water dispersed nanoparticles, Nano Energy, 2018, 47, 123-
1
29.
C.K. Lim, J. Shin, Y.D. Lee, J. Kim, K.S. Oh, S.H. Yuk, S.Y. Jeong,
I.C. Kwon, S. Kim, Phthalocyanine-aggregated polymeric
nanoparticles as tumor-homing near-infrared absorbers for
photothermal therapy of cancer, Theranostics, 2012, 2, 871-
8
79.
5
6
7
M.A.J. Gillissen, I.K. Voets, E.W. Meijer, A.R.A. Palmans, Single
chain polymeric nanoparticles as compartmentalised sensors
for metal ions, Polymer Chem., 2012, 3, 3166-3174.
V. Jain, P.V. Bharatam, Pharmacoinformatic approaches to
understand complexation of dendrimeric nanoparticles with
drugs, Nanoscale, 2014, 6, 2476-2501.
C.I.C. Crucho, Stimuli-Responsive Polymeric Nanoparticles for
Nanomedicine, ChemMedChem, 2015, 10, 24-38.
4
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Photochemical & Photobiological Sciences
A tripodal coumarin derivative is photopolymerized into polymeric nanoparticles with 100 nm. The size
of the polymeric particles can be accurately tuned within the submicron range with irradiation time.