Morphological Changes of Kinetically Trapped Tubular Vesicles Driven by the
Production of Synthetic Phospholipids in a Vesicular Membrane
Ibuki Ishii,
1
Yuka Ominato,
1
Akane Karasawa,
1
Tatsuya Takahashi,
1
Muneyuki Matsuo,
2,3
Kentaro Suzuki,*
1
and Tadashi Sugawara*
1
1
Department of Chemistry, Faculty of Science, Kanagawa University,
Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan
2
Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo,
Komaba, Meguro, Tokyo 153-8902, Japan
3
Department of Life and Coordination-Complex Molecular Science, Biomolecular Functions, Institute for Molecular Science,
Myodaiji, Okazaki,Aichi 444-8585, Japan
E-mail: suzuken@kanagawa-u.ac.jp (K. Suzuki), sugawara-t@kanagawa-u.ac.jp (T. Sugawara)
A tubulation of giant vesicles (GVs) composed of
zwitterionic phospholipids was induced by the addition of the
precursor of the phospholipid. The generated tubular GVs can be
regarded as a kinetically-trapped structure because it was
converted to more stable spherical GVs by heating through the
one-way deformation. Such a morphologicalinterconversion
is the first example to be rationalized by the concept of the
thermodynamically and kinetically controlled formation of
molecular self-assemblies.
Keywords: Giant vesicle | Morphological change |
Kinetically trapped structure
It isoften observed that a crystal structure of ablock shape
is generated inaslow cooling process as a thermally stable
crystalline form if an equilibrium between a crystallization of
constituent molecules onto the surface of a growing crystal and
adissolution from the surface is achieved. On the other hand,
a thin needle crystalis formed as a kinetically trapped product
in a rapid crystallization with no equilibrium between these
two processes. Control of these processes is indispensable for
crystal engineering
1
or for regulating polymorphism to express
physical properties or specific functions.
2
Asimilar phenomenon
is observed in the case of giant molecules e.g., fullerenes and
carbon nanotubes derived from a covalent bond formation
between carbon atoms.
3
Recently, vesicles, which are self-assembled closed struc-
tures of amphiphiles in water, have drawn considerable attention
as molecular capsules for enzymatic reactions,
4,5
drug delivery
systems (DDS),
6
and compartments for model protocells.
7,8
Control of morphologies e.g., tubulation and budding deforma-
tions of giant vesicles (GVs), which is defined as a vesiclewith
adiameter larger than 1 ¯m, is important not only from the
standpoint of membrane dynamics but also from expressing
their functions as above mentioned.
911
These deformations are
mainly caused by external physical stimuli,
10,12
such as changes
in the osmotic pressure,
13
temperature,
14
electric field,
15
mag-
netic field
16
and mechanicalforce from biochemical material,
17
and the morphological changes have been successfully ration-
alized in terms of the area-difference elasticity (ADE) model
theory.
18
However, these morphological changes are not accom-
panied by the growth of GVs because even if membrane lipids
are supplied to an exterior water phase containing pre-existing
GVs, added lipids predominantly form new GVs, not dissolving
into the pre-existing GVs. Recently, we have proposed a
different way to induce morphological changes of the pre-
existing GVs as a resultof the increase in the number of
membrane lipids within a GV by adding a precursor of the
membrane lipid (Figure 1a).
1922
Thistime we focused on phospholipids with a head group
of a phosphocholine-type because the hydrophilic head
groups of major phospholipids of living cells are zwitterionic
e.g., 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC).
Those phospholipids are characterized by an extremely low
critical aggregate concentration (cac).
23
To examine the mor-
phological changes in GVs constituted by synthesized phos-
pholipids, we prepared artificial zwitterionic phospholipids
(Figure 1b, a detailed description of the synthesis is provided
in the Supporting Information):
24,25
V
PC
(D), 1,2-di(10-(4-for-
mylphenoxy)decanoyl)-sn-glycero-3-phosphocholine, that bears
a phosphocholine group as a hydrophilic head, while the termini
of the dual hydrophobic tails bear a benzaldehyde group, and
C@GV
V
PC
(D): R =
V
PC
(S): R =
V
PC
(D)*: R =
V
PC
(S)*: R =
C@GV
+ nE
C E
V
PC
-GV
C C
C C
Precursor (V
PC
*)
V
PC
* V
PC
(a)
(b)
Morphological
Change
n = 2
n = 1
Figure 1. (a) Schematic illustration of morphological changes
of GV, induced by internal chemical stimuli. (b) Scheme of
hydrolysis precursor V
PC
* to yield membrane lipidV
PC
in the
vesicular membrane containing the lipophilic acid catalyst C.
CL-190260 Received: March 29, 2019 | Accepted: May 16, 2019 | Web Released: June 4, 2019
932 | Chem. Lett. 2019, 48, 932–935 | doi:10.1246/cl.190260 © 2019 The Chemical Society of Japan