Electroformed giant vesicles from thiophene-containing rod-coil diblock copolymers

Article abstract of DOI:10.1021/ma035789n

Electroformation of giant vesicles from thiophene-containing rod-coil diblock copolymers was analyzed. The giant aggregates were found to have a fluidic membrane and are capable of encapsulating solutes, similar to vesicles prepared by the injection method despite their rigid-rod block copolymer nature. The thiophene group inside the vesicles were found polymerizable. It was found that polymerizable vesicles opens the possibility to regulate the rigidity of the vesicle membrane, freezing them in a desired morphology.

Full text of DOI:10.1021/ma035789n

4736
Macromolecules 2004, 37, 4736-4739
capable of encapsulating solutes, in a manner similar
Electr ofor m ed Gia n t Vesicles fr om
Th iop h en e-Con ta in in g Rod -Coil Diblock
Cop olym er s
to vesicles prepared by the injection method.8
Exp er im en ta l Section
Den n is M. Vr iezem a ,† Alexa n d er Kr os,‡
Ren e´ d e Geld er ,§ J er oen J . L. M. Cor n elissen ,†
Ala n E. Row a n ,*,† a n d Roela n d J . M. Nolte†
Ma ter ia ls. Tetrahydrofuran (THF) was distilled over so-
dium, CH2Cl2 over CaCl2, and methanol over CaH2. â-3-
Thienylethylamine,9 N-formyl-L-alanine,10 tetrakis(tert-butyl
isocyanide)nickel(II) perchlorate ((t-BuNC)4Ni(ClO4)2),11 and
amine-functionalized polystyrene40 (PS40-NH2)12 were synthe-
sized using procedures reported in the literature. All other
chemicals were commercial products and used as obtained.
Department of Organic Chemistry,
NSRIM Institute, University of Nijmegen,
Toernooiveld 1, 6525ED Nijmegen, The Netherlands;
Leiden Institute of Chemistry, Department of Soft
Condensed Matter, Leiden University, P.O. Box 9502,
2300RA Leiden, The Netherlands; and
Department of Inorganic Chemistry,
NSRIM Institute, University of Nijmegen,
Toernooiveld 1, 6525ED Nijmegen, The Netherlands
Syn t h esis of In it ia t or Com p lex (1). PS40-NH2 (1.03 g,
0.242 mmol, Mn ) 4250, Mw/Mn ) 1.04) dissolved in CH2Cl2
(10 mL) was added to a stirred solution of (t-BuNC)4Ni(ClO4)2
(0.143 g, 0.242 mmol) in CH2Cl2 (25 mL) under a nitrogen
atmosphere. After an additional hour of stirring the solvent
was evaporated, yielding a yellow solid (1.17 g, 0.242 mmol,
100%).7 1H NMR (CDCl3): δ ) 7.82 (s, CH2NH), 7.3-6.3 (br,
CHPh), 3.7 (br, OCH2CH2CH2NH), 3.3-2.9 (br, CH2OCH2 and
CH2OCH2), 2.3-1.7 (br, CHPh), 1.54 (s, C(CH3)3), 1.7-1.2 (br,
CH2CHPh), 1.26-0.58 ppm (Bu(CH2CHPh)40). 13C NMR
(CDCl3): δ ) 178 (NCN), 146.5-145 (br, CHPhipso), 130-127
(br, (CHPhortho+meta), 127-124 (br, CHPhpara), 123 (br, Ni-CdN),
75 (br, CH2OCH2CH2CH2NH), 68 (br, CH2OCH2CH2CH2NH),
54.9 (CH2OCH2CH2CH2NH), 41 (CHPh), 46-40 (br, CH2CHPh),
31.7 (CH2CH(CH3)(CH2CHPh)40), 30.3 ((CH3)3CN), 29.5 ((CH3)3-
CNH), 28.2 (br, CH2CH(CH3)(CH2CHPh)40), 26.9 (OCH2CH2-
CH2NH), 22.3 (CH2CH(CH3)(CH2CHPh)40), 13.9 ppm (CH3-
CH2CH(CH3)(CH2CHPh)40). FT-IR (cm-1, KBr): 3282 (NH),
3061, 3026, 2923, 2850 (CH), 2253, 2226 (CdN), 1602 (C-C
aryl), 1575 (NCN), 1493, 1453 (C-C aryl), 1097 (ClO4).
Received November 28, 2003
Revised Manuscript Received April 16, 2004
In tr od u ction
Giant vesicles are very interesting self-assembled
structures since their size and membrane curvature
make them simple model systems for living cells. Over
the past few years several methods have been developed
for the construction of large vesicles with diameters in
the range of 10-200 µm.1,2 Electroformation has proven
to be one of the most useful in this respect, since it
allows the preparation of such vesicles from a large
variety of neutral, charged, and zwitterionic lipids.3
Using this technique, the vesicle size can be readily
controlled by varying the voltage and frequency of the
electric field.2 A more recent approach to construct large,
micrometer-sized vesicles is to use large amphiphiles,
i.e., amphiphiles derived from block copolymers. These
macromolecules have been shown to self-assemble into
vesicles, referred to as polymersomes, which have a
much higher toughness and stability than classical
phospholipid-based vesicles, i.e., liposomes.4 In a fashion
similar to liposomes, polymersomes can be loaded with
synthetic or biological compounds, like dyes and en-
zymes.5,6 The combination of electroformation and block
copolymers may offer an ideal route to prepare stable
giant polymersomes with potentially unique properties.
Discher et al. were the first to demonstrate the feasibil-
ity of such an approach and constructed giant polymer-
somes from poly(ethylene oxide)-b-poly(ethylethylene)
with diameters between 20 and 50 µm.5
Recently, we developed a novel type of amphiphilic
diblock copolymer derived from isocyanopeptides and
styrene.7 Charged diblock copolymers of styrene and
L-isocyanoalanyl-L-alanine and of styrene and L-iso-
cyanoalanyl-L-histidine were found to self-assemble in
water, yielding vesicles, multilayers, and helical ag-
gregates. In this paper we report that this type of
diblock copolymer can generate gigantic vesicles up to
100 µm in diameter by the electroformation method.
Despite their rigid-rod block copolymer nature, these
giant aggregates have a fluidic membrane and are
Syn th esis of N-For m yl-L-alan in e(2-th ioph en -3-yleth yl)-
a m id e (F AT). â-3-Thienylethylamine (0.61 g, 4.8 mmol),
N-formyl-L-alanine (0.56 g, 4.8 mmol), (dimethylamino)pyri-
dine (catalytic amount), and dicyclohexylcarbodiimide (1.19 g,
5.8 mmol) were dissolved in 20 mL of CH2Cl2/EtOAc (3/1 v/v).
The solution was stirred overnight, followed by removal of the
formed dicyclohexylurea by filtration and evaporation of the
solvent. After purification by flash column chromatography on
silica gel (CH2Cl2/MeOH, 95/5 v/v), the product was dissolved
in a minimal amount of CH2Cl2 and precipitated in petroleum
ether (40-65 °C), yielding a white solid (0.65 g, 2.9 mmol,
60%). [R]D (CH2Cl2 c 0.10) ) -40°. 1H NMR (CDCl3): δ )
20
8.13 (s, 1H, C(O)H), 7.29 (m, 1H, thiophene H-5), 7.01 (d, 1H,
thiophene H-2, 3J ) 2.3 Hz), 6.95 (m, 1H, thiophene H-4), 6.29
(br, 1H, NHCO), 6.08 (br, 1H, NHCO), 4.48 (m, 1H, C(O)-
NHCH(CH3)), 3.52 (m, 2H, CH2NH), 2.86 (t, 2H, CH2-
3
3
thiophene, J ) 6.9 Hz), 1.37 ppm (d, 3H, CHCH3, J ) 3.4).
13C NMR (CDCl3): δ ) 171.7 (COH), 160.9 (CdO), 138.9
(thiophene C-3), 128.1 (thiophene C-4), 126.3 (thiophene C-5),
121.8 (thiophene C-2), 47.8 (C(O)NHCH(CH3)), 40.2 (CH2NH),
30.2 (CH2-thiophene), 18.7 ppm (CH3). FT-IR (cm-1, KBr):
3342 (NH), 3092, 2979, 2936, 2864 (CH), 1685, 1655 (amide I)
1547, 1522 (amide II). EI-MS: m/z ) 226 [M]+ (calcd: 226.30).
El anal. calcd for C10H14N2O2S (%): C, 53.08; H, 6.24; N, 12.38;
S, 14.17. Found: C, 53.06; H, 6.23; N, 12.01; S, 14.37.
Syn th esis of L-Isocya n oa la n in e(2-th iop h en -3-yleth yl)-
a m id e (IAT). To a solution of FAT (99.0 mg, 0.438 mmol) in
1.0 mL of CH2Cl2, N-methylmorpholine (0.97 mL, 0.88 mmol)
was added under a nitrogen atmosphere, and the reaction
mixture was cooled to -30 °C. Over a period of 10 min diphos-
gene (43 mg, 0.22 mmol) in 1.0 mL of CH2Cl2 was added. After
keeping the temperature at -30 °C for an additional 30 min,
the temperature was gradually brought to room temperature.
A saturated NaHCO3 solution (5 mL) was added, and the
reaction mixture was stirred vigorously for 5 min. The organic
layer was separated, extracted twice with 10 mL of water, and
dried using Na2SO4. The solvent was evaporated, and the crude
solid was purified by flash column chromatography on silica
gel (CH2Cl2/MeOH, 99.5/0.5 v/v), resulting in a white solid (79
† Department of Organic Chemistry, University of Nijmegen.
‡ Department of Soft Condensed Matter, Leiden University.
§ Department of Inorganic Chemistry, University of Nijmegen.
* Corresponding author: Tel +31 24 3652323; Fax +31 24
3652929; e-mail rowan@sci.kun.nl.
10.1021/ma035789n CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/21/2004

Macromolecules, Vol. 37, No. 12, 2004
Notes 4737
mg, 0.38 mmol, 87%). Single crystals were obtained by slow
evaporation of a diethyl ether solution of the compound. [R]D
X-r a y An a lysis of IAT. Crystals of IAT suitable for X-ray
diffraction studies were obtained from diethyl ether by slow
evaporation of the solvent. A single crystal was mounted in
air on a glass fiber. Intensity data were collected at room
temperature and corrected for Lorentz and polarization effects.
An Enraf-Nonius CAD4 single-crystal diffractometer was used,
Mo KR radiation, omega scan mode. Unit cell dimensions were
determined from the angular setting of 25 reflections. Semi-
empirical absorption correction (ψ-scans) was applied.13 The
structure was solved by the program CRUNCH14 and was
refined with standard methods (refinement against F2 of all
reflections with SHELXL9715) with anisotropic parameters for
the non-hydrogen atoms. The hydrogens of the methyl group
were refined as a rigid rotor with idealized sp3 hybridization
and a C-H bond length of 0.97 Å to match maximum electron
density in a difference Fourier map. All other hydrogens were
placed at calculated positions and were refined riding on the
parent atoms. The thiophene ring is disordered over two
positions. This disorder can be interpreted as a swap of the
ring and can be described by a suitable disorder model.
Crystallographic data for IAT has been deposited with the
Cambridge Crystallographic Data Centre and can be retrieved
under number CCDC 225216.
20
(CH2Cl2 c 0.5) ) +11°. 1H NMR (CDCl3): δ ) 7.31 (m, 1H,
thiophene H-5), 7.04 (d, 1H, thiophene H-2, 3J ) 2.0 Hz), 6.97
(m, 1H, thiophene H-4), 6.43 (br, 1H, NHCO), 4.19 (q, 1H,
C(O)NHCH(CH3), 3J ) 7.1 Hz), 3.58 (m, 2H, CH2NH), 2.91 (t,
2H, CH2-thiophene, 3J ) 6.9 Hz), 1.61 ppm (d, 3H, CHCH3,
3J ) 7.1). 13C NMR (CDCl3): δ ) 166.1 (CdO), 161.5 (NC),
138.5 (thiophene C-3), 128.1 (thiophene C-5), 126.7 (thiophene
C-2), 122.0 (thiophene C-4), 53.7 (C(O)NHCH(CH3)), 40.5 (CH2-
NH), 30.1 (CH2-thiophene), 20.0 ppm (CH3). FT-IR (cm-1
,
KBr): 3282 (NH), 3093 (thiophene), 2145 (CN), 1661 (amide
I), 1567 (amide II). EI-MS: m/z ) 208 [M]+ (calcd: 208.28).
El anal. calcd for C10H12N2OS (%): C, 57.67; H, 5.81; N, 13.45;
S, 15.40. Found: C, 57.91; H, 5.89; N, 13.11; S, 15.58.
Syn th esis of P olystyr en e40-b-p oly(L-isocya n oa la n in e-
(2-th iop h en -3-yleth yl)a m id e) (P S-P IAT). To a stirred
solution of IAT (50.0 mg, 0.240 mmol) in CH2Cl2 (25 mL) a
solution of initiator complex 1 (22.9 mg, 4.79 µmol) in CH2Cl2
(5 mL) was added. Complete consumption of IAT, as observed
by IR spectroscopy, was achieved after 2 days stirring. The
reaction mixture was evaporated to dryness, and the resulting
polymer was dissolved in a minimal amount of CH2Cl2. The
polymer was then precipitated by dropping this solution into
a well-stirred mixture of methanol/water (1/1 v/v, 10 mL). The
product was filtered off and washed with methanol/water (1/1
v/v, 20 mL). After drying in vacuo the polymer was obtained
as an orange/brown solid (40 mg, 60%). 1H NMR (300 MHz,
CDCl3): δ ) 7.3-6.3 (br, CHPh), 6.94 (br, thiophene H-5), 6.83
(br, thiophene H-2), 6.79 (br, thiophene H-4), 4.3-4.1 (br, Cd
NCH(CH3)), 3.9-3.3 (br, CH2CH2-thiophene), 3.7 (br, OCH2-
CH2CH2NH), 3.3-2.9 (br, CH2OCH2 and CH2OCH2), 3.1-2.6
(br, CH2-thiophene), 2.1-1.7 (br, CH2CHPh), 1.7 (br, C(CH3)3),
1.7-1.2 (br, CH2CHPh), 1.62 (br, NHCH(CH3)CO), 1.0-0.6
ppm (Bu(CH2CHPh)40). 13C NMR (75 MHz, CDCl3): δ ) 155.2
(CdN), 147-143 (br, CHPhipso), 140 (thiophene C-3), 130-127
(br, (CHPhortho+meta), 127-124 (br, thiophene C-4, C-5 and
CHPhpara), 113 (br, thiophene C-2), 72 (br, CH2OCH2CH2CH2-
NH), 68 (br, CH2OCH2CH2CH2NH), 63 (br, CdNCH(CH3)),
42-38 (br, CHPh and CH2CHPh), 39.8 (br, CH2CH2NHCO),
37.5-34 (br, CH2OCH2CH2CH2NH), 32-30 (CdNC(CH3)3) and
CH2CH(CH3)(CH2CHPh)40), 28.7 (CH2CH2NHCO), 25.9 (br,
CH2CH(CH3)(CH2CHPh)40), 22.6 (CH2CH(CH3)(CH2CHPh)40),
21.4 (CH(CH3)), 13.4 ppm (CH3CH2CH(CH3)(CH2CHPh)40). FT-
IR (cm-1, KBr): 3288 (NH), 3060, 3027, 2950, 2924, 2850 (CH),
1660 (amide I), 1604 (C-C aryl), 1532 (amide II).
P r ep a r a tion of Aggr ega tes. In a typical aggregation
experiment 1.0 mL of a 1.0 mg/mL PS-PIAT solution in THF
was injected into 5 mL of ultrapure water at room tempera-
ture, and the dispersion was left to equilibrate. No additional
energy was applied to induce aggregate formation. SEM
samples were prepared by drying a drop of the dispersion on
a microscopy glass, which was cleaned by sonication for 15
min in CH2Cl2. The samples were left to dry for a day in a
desiccator before studying them.
Electr ofor m a tion . The used electroformation setup con-
sisted of a bath with two platinum electrode wires (5 × 1 mm),
which were separated 5 mm from each other and were
connected to an external alternating or direct current supply.
A thin film of PS-PIAT in CHCl3 was dried on the electrodes,
the bath was filled with a 0.1 M sucrose solution, and an
alternating current potential of 10 V with a frequency of 10
Hz was applied for 6 h. Thereafter, the frequency was lowered
to 2 Hz for 12 h to release the vesicles from the electrodes,
followed by dilution into an isoosmotic sucrose solution. The
setup was mounted on the stage of a light microscope for
optical observation.
Resu lts a n d Discu ssion
In recent studies it has been found that peptide-based
polyisocyanides have an enhanced stability and rigidity
of the helical polymer backbone, when compared to
other polyisocyanides. This rigidity is the result of a
hydrogen-bonding network between the stacking amide
groups of the peptide side chains. This additional
stabilization increases the persistence length of these
types of macromolecules, which were found to be even
more rigid than DNA.16,17 In this study we used the
rod-coil diblock copolymer polystyrene40-b-poly(L-iso-
cyanoalanine(2-thiophen-3-ylethyl)amide) (PS-PIAT).
Its synthesis was carried out in four steps as outlined
in Scheme 1.
Isocyanides are polymerized using Ni(II)-based cata-
lysts, in which nucleophiles, i.e., alcohols or amines, act
as initiators.18,19 These nucleophiles are also incorpo-
rated as the first unit in the resulting polyisocyanide.
To construct PS-PIAT, an amine-functionalized poly-
styrene40 (PS40-NH2) was used to prepare the macromo-
lecular initiator complex 1 (see Experimental Section),
which was subsequently treated with 50 equiv of IAT
to give PS-PIAT in a yield of 60%. Attempts to deter-
mine the molecular weight by GPC and MALDI-TOF
spectrometry were unsuccessful because these types of
polyisocyanides do not run on a GPC column and they
do not fly in a MALDI spectrometer. However, using
1H NMR, an estimation of the molecular weight could
be made by comparing integrals of the polystyrene block,
of which the molecular weight and polydispersity were
known, with integrals of the polyisocyanide block. In
this way the PIAT block was estimated to consist of 62
( 15 repeating units, corresponding to a total molecular
weight for PS-PIAT of 18 ( 4 kg/mol. The crystal
structure of IAT already revealed the preference of this
molecule to form hydrogen-bonding networks between
the amide groups of stacked molecules (Figure 1).
The existence of a hydrogen-bonding network in PS-
PIAT was confirmed by IR studies in an analogous way
as described previously.16 The thiophene groups were
included in the block copolymer so that once a 3D
architecture had been self-assembled, it could be cross-
linked by polymerization of the fore-mentioned groups,
resulting in stable and potentially conductive nanom-
eter-sized vesicles and fibers.8
Mea su r em en ts. 1H NMR and 13C NMR spectra were
recorded on a Bruker AC-300 instrument (1H/300 MHz, 13C/
75 MHz) at room temperature. Infrared spectra were measured
on a BioRad FTS 25 spectrometer. For SEM studies a J EOL
J SM-6330F was used. A 1.5 nm layer of Pd/Au was sputtered
on the SEM samples before studying by using a Cressington
208 HR sputter coater. Light and fluorescence micrographs
were made with a Zeiss Axiovert 100.

4738 Notes
Macromolecules, Vol. 37, No. 12, 2004
Sch em e 1. Syn th etic Rou te to P S-P IAT; th e Im a ge on th e Righ t Bottom Is a Sch em a tic Illu str a tion of P S-P IAT
Assemblies of this amphiphilic diblock copolymer were
initially prepared via the injection method.20 PS-PIAT
was dissolved in a good solvent (THF) and then injected
into a poor solvent (water). Immediately after addition
of the PS-PIAT solution very small vesicles (<100 nm)
were observed by electron microscopy. Upon standing,
these vesicles fused over a period of 50 h to give vesicles
with a final average diameter of 1.5 µm (Figure 2a).8
Removing the THF immediately after injection into
water resulted in vesicles with a small average diameter
of 80 nm, which was retained over a period of weeks.8
Giant vesicles of PS-PIAT were prepared by electro-
formation as described in the Experimental Section.
Using this approach, large quantities of well-defined
aggregates were obtained. Their diameters ranged from
1 to 100 µm (Figure 2b,c), which is significantly larger
than the vesicles prepared via the injection method and
about 2 times larger than the polymersomes reported
by Discher and Dimova.5,21 The electroformation pro-
cedure used to form the giant vesicles is that commonly
used in the electroformation of phospholipid vesicles.
In contrast to the approach of Dimova et al., who
prepared vesicles in water while applying an increasing
potential, the giant vesicles described here were as-
sembled in a 0.1 M sucrose solution while applying a
constant potential. This latter approach is similar to
that developed by Discher et al. and only differs in the
method of dissociation of the vesicles from the electrode.2
A standard method for the preparation of vesicles from
low molecular weight amphiphiles, e.g., dioleoylphos-
phatidylcholine (DOPC), is the hydration method,22
which was used to check whether vesicles of PS-PIAT
could be formed under the same conditions. A drop of a
PS-PIAT solution in CHCl3 was dried on a roughened
Teflon surface and subsequently immersed into a 0.1
M sucrose solution of 40 °C. This experiment can be
considered as a blank experiment since the electro-
formed vesicles were also prepared in a sucrose solution.
This approach did not result in the formation of vesicles.
The lack of vesicle formation by the hydration method
is likely the result of the low mobility of the polysty-
rene40 chains below their glass transition temperature
(Tg ∼ 70 °C). The mechanism of the electroformation of
giant vesicles is not yet fully understood; however, it is
believed that the electroosmotic motion of water induces
bilayer separation and vesicle growth.3 Since the elec-
troformation experiments were done at a temperature
below the Tg of polystyrene40, it is assumed that the
applied alternating current supplies the energy that is
needed to plasticize the polystyrene chains, resulting
in the growth of the vesicles.
Although constructed from rigid diblock copolymers,
fusion of two giant vesicles was possible when they were
brought in close proximity using a micropipet. This
suggests that despite the high Tg value of the polysty-
rene block, the vesicle membranes are still highly fluidic
in nature and behave like the membranes of simple lipid
molecules (Figure 2d). One of the requirements for
fusion is thought to be a good contact between the two
membranes and a pressure above a certain threshold.
The large size of the giant vesicles means that the
curvature of the membranes is small, which is known
to more readily enable the diblock copolymers to easily
insert into the membrane of the adjacent vesicle without
disruptive reorganization. It is most remarkable that
this process so readily occurs, given that the polystyrene
is probably in a glassy state. The precise mechanism of
this fusion is currently being further investigated. This
fusion behavior is in contrast to vesicles prepared via
the injection method, where THF is an essential com-
F igu r e 1. (a) PLUTON representation of the single-crystal
X-ray structure of IAT, showing the most abundant conforma-
tion of the thiophene ring.25 (b) Computer modeled image of
the PIAT block.

Macromolecules, Vol. 37, No. 12, 2004
Notes 4739
F igu r e 2. (a) Scanning electron micrograph of PS-PIAT vesicles, formed by the injection method, after 2 days in dispersion; the
scale bar represents 5 µm. (b, c) Optical micrographs of electroformed giant vesicles of PS-PIAT; the image width corresponds
to 60 µm. (d) Two giant vesicles fuse into one vesicle with the help of a micropipet. The width of the optical micrographs amounts
to 80 µm.
with the injection method are polymerizable as we
showed previously, opening the possibility to regulate
the rigidity of the vesicle membrane, in that way
freezing them in a desired morphology.8
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic files for IAT in CIF format. This information is
available free of charge via the Internet at http://pubs.acs.org.
Refer en ces a n d Notes
F igu r e 3. Fluorescence micrographs of fluorescein-labeled
(1) Bangham, A. D., Ed. Liposome Letters; Academic Press:
dextran inside electroformed giant vesicles of PS-PIAT. (a)
London, 1983.
Multicompartmental giant vesicle; the width of the image
(2) Luisi, P. L., Walde, P., Eds. Giant Vesicles; J ohn Wiley &
corresponds to 80 µm. (b) Multilamellar giant vesicle; the width
Sons: Chichester, 2000.
of the image corresponds to 45 µm.
(3) Menger, F. M.; Angelova, M. I. Acc. Chem. Res. 1998, 31,
789-797.
ponent for fusion by dissolving the polystyrene block,
(4) Discher, D. E.; Eisenberg, A. Science 2002, 297, 967-973.
allowing it to reorganize.8
(5) Discher, B. M.; Won, Y.-Y.; Ege, D. S.; Lee, J . C.-M.; Bates,
These giant vesicles have the potential to be used
as microcapsules, as was demonstrated in a separate
experiment. Giant vesicles of PS-PIAT were prepared
by electroformation in a 0.1 M sucrose solution contain-
ing fluorescein-labeled dextran (Mw ) 104 g/mol). The
vesicles that grew from the electrode surface were found
to encapsulate the dye, as could be observed by fluo-
rescence microscopy. The encapsulation of the labeled
biopolymer allowed the observation of two distinct types
of giant vesicles, viz. multicompartment ones (Figure
3a) and multilamellar ones (Figure 3b).
These results are in contrast to experiments carried
out with classical phospholipids and with block copoly-
mers studied by Discher et al. In both cases the giant
vesicles were unilamellar in nature.5,23 The mechanism
of formation of the compartmental vesicles shown in
Figure 3 requires further study, but it is likely that the
structure of PS-PIAT plays an important role. Both
blocks of PS-PIAT have a very low solubility in water,
in contrast to the classical phospholipids and the poly-
(ethylene oxide)-b-poly(ethylethylene) block copolymers
studied by Discher and co-workers, which are more
water compatible. The multilamellar vesicles are prob-
ably formed from a multilayer sheet of PS-PIAT, which
shrinks at a rate that is similar for the whole sheet,
yielding the observed “onion type” vesicles.24 Encapsula-
tion of smaller, clustered vesicles on the electrode
surface by a giant vesicle could explain the formation
of the multicompartmental vesicles.
F. S.; Discher, D. E.; Hammer, D. A. Science 1999, 284,
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(6) Graff, A.; Sauer, M.; van Gelder, P.; Meier, W. Proc. Natl.
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