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plexes and phospholipids. The vesicles prepared from proxi-
mal-2 and DOPC (abbreviated as proximal-2/DOPC; DOPC=
1,2-dioleoyl-sn-glycero-3-phosphocholine) are shown in Fig-
ure 2A,B and the Supporting Information, Figure S2. The aver-
age size of the vesicles was 15 mm and giant multilamellar vesi-
cles larger than 50 mm were observed. The dark color of the
vesicle in Figure 2B arises from the concentric lipid layers (see
below). On the other hand, vesicles prepared from DOPC alone
gave multilamellar structures with an average size of 24 mm
(Figure 2C; Supporting Information, Figure S3). Vesicles proxi-
mal-1/DOPC and 3/DOPC are shown in the Supporting Infor-
mation, Figures S4 and S5, and their average sizes were 20 and
9 mm, respectively.
The absorption spectra for the vesicle dispersions of proxi-
mal-2/DOPC showed an absorption band at 537 nm, which is
assigned as metal-to-ligand charge transfer (MLCT) transitions
(Supporting Information, Figure S6). The absorption spectra
changed slightly under the light irradiation of a 100 W halogen
lamp (l>380 nm), with isosbestic points at 276, 303, 435, and
582 nm. The absorbance change at 537 nm was fitted with
a single exponential curve. After light irradiation, the vesicle
dispersions were evaporated at 458C within 5 min, and the
Scheme 2. Ruthenium complexes used in this work, and the photoisomeriza-
tion equilibrium between proximal-2 and distal-2.
observed that the morphological changes in vesicles were
driven by red light (635 nm), which can permeate mammalian
tissues. For comparison, we prepared two kinds of ruthenium
complex with
a single alkyl chain: proximal-1; [Ru(tpy)-
(C10pyqu)OH2]2+ (tpy=2,2’;6’,2”-terpyridine), and 3; [Ru(tpy)-
(C10tpy)]2+. Control experiments suggested that photodissocia-
tion of the aqua ligand in proximal-2, followed by geometrical
change of the two alkyl chains, was an important factor in driv-
ing the morphological changes.
product of the photoreaction was checked by H NMR spec-
1
troscopy (Supporting Information, Figure S7).[40] The formation
of the distal isomer was confirmed in the spectrum of the vesi-
cle dispersions, similar to the case with photoisomerization in
the solution. Thus, photoisomerization of proximal-2 occurred
in the vesicles despite the fact that the photoisomerization re-
action requires photodissociation of an aqua ligand and re-co-
ordination by a solvent water molecule.[36]
In mixed aqueous solutions, both proximal-1 and proximal-2
showed photoisomerization equilibria with the corresponding
1
distal isomers, according to H NMR measurements (Figure 1;
Supporting Information, Figure S1). The ratio of the proximal
and distal isomers in the photostationary state was 54:46 and
40:60 for complexes 1 and 2, respectively. The quantum yields
for forward and back photoisomerizations for proximal- and
distal-2 were determined to be 3.710À3 and 2.510À3, re-
spectively, using monochromic light at 508 nm.
The real-time morphological changes of the giant vesicles
were monitored using a digital microscope. For vesicles proxi-
mal-2/DOPC, various morphological changes were observed
under visible light irradiation, as depicted in Figure 2. The vesi-
cle in Figure 2A showed increases and decreases in size to
give an obscure lamellar structure (see the time courses of size
changes in Supporting Information, Figure S9). On the other
hand, distortion and budding were observed for the vesicle in
Figure 2B. The shape of the vesicle in Figure 2B at 112 min
was traced by small granule vesicles (Supporting Information,
Figure S10). Vesicles prepared from 10 mol% proximal-2 on
DOPC also exhibited various morphological changes, including
budding and division into two vesicles (Supporting Informa-
tion, Figure S11).
Giant vesicles containing ruthenium complexes were pre-
pared by hydration of films containing the ruthenium com-
We then tested morphological changes of the giant vesicles
under red-light irradiation (635 nm). We prepared vesicles con-
taining DOPC, proximal-2, and rhodamine-DOPC as a fluores-
cent dye (rhodamine-DOPC:1,2-dioleoyl-sn-glycero-3-phos-
phoethanolamine-N-(lissamine rhodamine B sulfonyl). The vesi-
cles in Figure 3A,C displayed fluorescence from their edges,
and multilamellar structures were clearly observed from digital
microscopy. On the other hand, a dark colored vesicle in Fig-
ure 3F displayed fluorescence from interior (Figure 3E), indicat-
ing the presence of concentric layers (onion-like structures; see
the sliced fluorescence images of vesicles in the Supporting In-
formation, Figures S12 and S13). For vesicles depicted in
Figure 3, we observed morphological changes of vesicles
1
Figure 1. Left: H NMR spectra of proximal-2 (1.1 mm) in a mixed aqueous
solution (D2O/CD3OD/d-acetone=4:2:1) under light irradiation with a 100 W
halogen lamp (l>380 nm, 70 mWcmÀ2). Right: kinetic profiles of proximal-2
( ) and distal-2 ( ) under light irradiation, where the ratio of proximal and
distal isomers was estimated from peak areas at 6.59 ppm and 6.87 ppm.
The sample solution was prepared by dissolving proximal-
&
*
[Ru(C10tpy)(C10pyqu)Cl]Cl in the mixed solution prior to the measurements.
Chem. Eur. J. 2016, 22, 2590 – 2594
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