Publications

*Naohito Urakami, Takehiro Jimbo, Yuka Sakuma and Masayuki Imai,
Molecular mechanism of vesicle division induced by coupling between lipid geometry and membrane curvatures,
Soft Matter 14, 3018-3027 (2018).

[Summary] We investigated effects of lipid geometry on the vesicle division using coarse-grained molecular dynamics simulations.When the vesicle is composed of zero and negative spontaneous curvature lipids (ZSLs and NSLs), the difference in their molecular spontaneous curvatures destabilizes the neck of the limiting shape vesicle. In the vesicle division pathway, the neck developed to the stalk intermediates. The stalk was broken when the NSLs were expelled from the stalk. The free energy analysis shows that the coupling between the lipid geometry and the Gaussian rigidity is responsible for the observed vesicle division.

*Kentaro Suzuki, Koichiro Machida, Kazuo Yamaguchi, and Tadashi Sugawara,
Photo-triggered Recognition between Host and Guest Compounds in a Giant Vesicle Encapsulating Photo-Pierceable Vesicles,
Chemistry and Physics of Lipids 210, 70-75 (2017).

[Summary] Here, we used centrifugal precipitation to construct a giant vesicle (GV) encapsulating smaller giant vesicles (GV-in-GV) which comprises a photo-resistant outer GV and a photo-pierceable inner GV; the outer GV contained a fluorescent probe (SYBR Green I) in its inner water pool, and the inner GV contained double-stranded DNA (dsDNA) in its inner water pool. The phospholipid membrane of the inner GV was made photo-pierceable by inclusion of ca. 15 mol% of a caged phospholipid in its membrane. Immediately after exposure of the GV-in-GVs to UV irradiation, strong fluorescence was detected in the inner water pool of the outer GV, indicating that dsDNA had been released from the inner GV and had complexed with the fluorescent probe. These dynamics can be recognized as a macroscopic representation of the molecular level function of a caged compound.

Shoko Uemoto, Taro Toyota, Luca Chiari, Tomonori Nomoto, *Masanori Fujinami,,
Assemblies of molecular aggregates in the blebbing motion of an oil droplet on an aqueous solution containing surfactant,
Colloids and Surfaces A: Physicochemical and Engineering Aspects 529, 373-379 (2017).

[Summary] The characteristic amoeboid behavior of an oil droplet (decane with dissolved palmitic acid) on an aqueous phase containing a surfactant (stearyltrimethylammonium chloride) has been investigated and discussed. The formation and motion of assemblies of molecular aggregates were observed with the aid of a range of particle tracers. The quasi-elastic laser scattering method was employed to measure the surface tension of the aqueous phase as a function of time. From those measurements we found that the amoeboid behavior occurs in three stages. First, molecular aggregates formed at the oil-water interface and subsequently spread and absorbed at the aqueous surface thanks to a convective flow due to the Marangoni effect. In the second stage, the whole aqueous surface was saturated with those molecular aggregates and a phase transition to a liquid condensed monolayer membrane occurred. Finally, domains formed at the bottom of the oil droplet with permeable boundaries composed of branch-shaped assemblies of molecular aggregates. Blebs grew in those parts of the oil droplet rim with high accumulation of molecular aggregates.

Atsuji Kodama, Yuka Sakuma, *Masayuki Imai, Toshihiro Kawakatsu, Nicolas Puff, and Miglena I. Angelova,
Migration of Phospholipid Vesicles Can Be Selectively Driven by Concentration Gradients of Metal Chloride Solutions,
Langmuir 33, 10698-10706 (2017).

[Summary] We have investigated the migrations of phospholipid vesicles under the concentration gradients of metal ions. We micro-injected metal chloride solutions, monovalent (NaCl and KCl), divalent (CaCl2 and MgCl2), and trivalent (LaCl3) salts, toward phospholipid giant vesicles (GVs) composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). For NaCl, CaCl2, and MgCl2 solutions, the GVs migrated straight toward the tip of the micro-pipette in response to the concentration gradients, whereas for KCl and LaCl3, GVs moved to the opposite direction. Our motion tracking of lipid domains in a vesicle membrane showed no unidirectional flow in the membrane during the vesicle migration, indicating that the Marangoni mechanism is not responsible for the observed vesicle migration. We calculated the diffusiophoretic velocities for symmetric and asymmetrical electrolytes by solving the Stokes’ equation numerically. The theoretical diffusiophoretic velocities well described the observed migration velocities. Thus we can control the migration of vesicle in response to the concentration gradient by adapting the electrolytes and the lipids.

*Satoshi Honda and *Taro Toyota,
Photo-triggered solvent-free metamorphosis of polymeric materials.,
Nature Communications 8, 502 (2017).

Naoko Ueno, Taisuke Banno, Arisa Asami, Yuki Kazayama, Yuya Morimoto, Toshihisa Osaki, Shoji Takeuchi, Hiroyuki Kitahata, *Taro Toyota,
Self-propelled motion of monodisperse underwater oil droplets formed by a microfluidic device,
Langmuir 33, 5393-5397 (2017).

[Summary] We evaluated the speed profile of self-propelled underwater oil droplets comprising a hydrophobic aldehyde derivative in terms of their diameter and the surrounding surfactant concentration using a microfluidic device. We found that the speed of the oil droplets is dependent on not only the surfactant concentration but also the droplet size in a certain range of the surfactant concentration. This tendency is interpreted in terms of combination of the oil and surfactant affording spontaneous emulsification in addition to the Marangoni effect.

Takuro Itoh, *Taro Toyota, Hiroyuki Higuchi, Michio M. Matsushita, Kentaro Suzuki, and *Tadashi Sugawara,
Cycle of charge carrier states with formation and extinction of a floating gate in an ambipolar tetracyanoquaterthienoquinoid-based field-effect transistor,
Chemical Physics Letters 671, 71-77 (2017).

[Summary] A tetracyanoquaterthienoquinoid (TCT4Q)-based field effect transistor is characterized by the ambipolar transfer characteristics and the facile shift of the threshold voltage induced by the bias stress. The trapping and detrapping kinetics of charge carriers was investigated in detail by the temperature dependence of the decay of source-drain current (ISD). We found a repeatable formation of a molecular floating gate is derived from a ‘charge carrier-and-gate’ cycle comprising four stages, trapping of mobile carriers, formation of a floating gate, induction of oppositely charged mobile carriers, and recombination between mobile and trapped carriers to restore the initial state.

Taisuke Banno, Arisa Asami, Naoko Ueno, Hiroyuki Kitahata, Yuki Koyano, Kouichi Asakura, *Taro Toyota,
Deformable self-propelled micro-object comprising underwater oil droplets,
Scientific Reports 6, 31292 (2016).

[Summary] The self-propelled motion with deformation of micrometer-sized soft matter in water has potential application not only for underwater carriers or probes in very narrow spaces but also for understanding cell locomotion in terms of non-equilibrium physics. As far as we know, there have been no reports about micrometer-sized self-propelled soft matter mimicking amoeboid motion underwater. Here, we report an artificial molecular system of underwater oil droplets exhibiting self-propelled motion with deformation as an initial experimental model. We describe the heterogeneity in a deformable self-propelled oil droplet system in aqueous and oil phases and at their interface based on the behavior and interaction of surfactant and oil molecules. The current results have great importance for scientific frontiers such as developing deformable micro-swimmers and exploring the emergence of self-locomotion of oil droplet-type protocells.

*Kentaro Suzuki, and Tadashi Sugawara,
Phototaxis of oil droplets comprising a caged fatty acid tightly linked to internal convection,
ChemPhysChem 17, 2300-2303 (2016).

[Summary] We found that novel sub-millimeter-sized photoactive oil droplets of oleic acid bearing a photolabile protecting group, 2-nitrobenzyl oleate (NBO), in basic water exhibited unidirectional motion toward a UV light source. This unidirectional motion can be explained by anisotropic photolysis on a surface of the NBO droplet with low permeability for UV light. Time-dependent changes of the movement under UV irradiation occurred in a cascade manner (still-standing, induction, and active stages). The velocity of the UV-irradiated droplet in the induction stage was small, but it was accelerated sixteen times by the presence of an inner convection structure, which was created by continued photolysis. This characteristic dynamics, which is derived from a supramolecular machinery system towards the external stimulus, may be similar to the phototaxis of a living cell.

Takehiro Jimbo, Yuka Sakuma, Naohito Urakami, Primož Ziherl, and *Masayuki Imai,
Role of inverse-Cone-Shape Lipids in Temperature-Controlled Self-Reproduction of Binary Vesicles,
Biophysical Journal 110, 1551-1562 (2016).

[Summary] We investigate a temperature-driven recursive division of binary giant unilamellar vesicles (GUVs). During the heating step of the heating-cooling cycle, the spherical mother vesicle deforms to a budded limiting shape using up the excess area produced by the chain melting of the lipids and then splits off into two daughter vesicles. Upon cooling, the daughter vesicle opens a pore and recovers the spherical shape of the mother vesicle. Our GUVs are composed of DLPE (1,2-dilauroyl-sn-glycero-3-phosphoethanolamine) and DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine). During each cycle, vesicle deformation is monitored by a fast confocal microscope and the images are analyzed to obtain the time evolution of reduced volume and reduced monolayer area difference as the key geometric parameters that quantify vesicle shape. By interpreting the deformationpathway using the area-difference elasticity theory, we conclude that vesicle division relies on (1) a tiny asymmetric distribution of DLPE within the bilayer, which controls the observed deformation from the sphere to the budded shape; and (2) redistribution of DLPE during the deformation-division stage, which ensures that the process is recursive. The spontaneous coupling between membrane curvature and PE lipid distribution is responsible for the observed recursive division of GUVs. These results shed light on the mechanisms of vesicle self-reproduction.

Atsuji Kodama, Yuka Sakuma, *Masayuki Imai, Yutaka Oya, Toshihiro Kawakatsu, Nicolas Puff, and Miglena I. Angelova,
Migration of phospholipid vesicles in response to OH- stimuli,
Soft Matter 12, 2877-2886 (2016).

[Summary] We demonstrate migration of phospholipid vesicles in response to a pH gradient. Upon simple microinjectionof a NaOH solution, the vesicles linearly moved to the tip of the micro-pipette and the migration velocity was proportional to the gradient of OH concentration. Vesicle migration was characteristic of OH ions and no migration was observed for monovalent salts or nonionic sucrosesolutions. The migration of vesicles is quantitatively described by the surface tension gradient modelwhere the hydrolysis of the phospholipids by NaOH solution decreases the surface tension of the vesicle. The vesicles move toward a direction where the surface energy decreases. Thus the chemical modification of lipids produces a mechanical force to drive vesicles.

Kensuke Kurihara, Yusaku Okura, Muneyuki Matsuo, Taro Toyota, Kentaro Suzuki, and *Tadashi Sugawara,
A recursive vesicle-based model protocell with a primitive model cell cycle,
Nature Communications 6, 8352 (2015).

[Summary] Self-organized lipid structures (protocells) have been proposed as an intermediate between nonliving material and cellular life. Synthetic production of model protocells can demonstrate the potential processes by which living cells first arose. While we have previously described a giant vesicle (GV)-based model protocell in which amplification of DNA was linked to self-reproduction, the ability of a protocell to recursively self-proliferate for multiple generations has not been demonstrated. Here we show that newborn daughter GVs can be restored to the status of their parental GVs by pH-induced vesicular fusion of daughter GVs with conveyer GVs filled with depleted substrates. We describe a primitive model cell cycle comprising four discrete phases (ingestion, replication, maturity and division), each of which is selectively activated by a specific external stimulus. The production of recursive self-proliferating model protocells represents a step towards eventual production of model protocells that are able to mimic evolution.

Naohito Urakami, Akio Takai, Masayuki Imai and Takashi Yamamoto,
Molecular dynamics simulation for shape change of water-in-oil droplets,
Molecular Simulation 41, 986-992 (2015).

[Summary] We performed molecular dynamics (MD) simulations of water-in-oil droplet shape transformations induced by the addition of polymer chains. In a prior experiment, transformations of spherical droplets to rod-like, worm-like and network-like droplets were observed. In our previous study, we reproduced rod-like droplets via coarse-grained MD simulations, and the mechanism for the droplet shape change was elucidated by considering the contact area between the chains and the surfactant head groups. However, in that simulation model, we could not reproduce the worm-like and network-like droplets. In this study, we improved the simulation model. For a small number of chains, several spherical droplets were obtained. As the number of chains increased, the spherical droplets were transformed to rod-like, worm-like and networklikeshapes by coalescence of the droplets. The calculated and experimental results agreed well, and we verified that themechanism for the droplet shape transformations observed in the present simulations could be explained by the mechanism suggested in the previous study.

Keita Ikari, Yuka Sakuma, Takehiro Jimbo, Atsuji Kodama, *Masayuki Imai, Pierre-Alain Monnard, and Steen Rasmussen,
Dynamics of fatty acid vesicles in response to pH stimuli,
Soft Matter 11, 6327-6334 (2015).

[Summary] We investigate the dynamics of decanoic acid/decanoate (DA) vesicles in response to pH stimuli. Twotypes of dynamic processes induced by the micro-injection of NaOH solutions are sequentiallyobserved: deformations and topological transitions. In the deformation stage, DA vesicles show a seriesof shape deformations, i.e., prolate–oblate–stomatocyte-sphere. In the topological transition stage,spherical DA vesicles follow either of the two pathways, pore formation and vesicle fusion. The pHstimuli modify a critical aggregation concentration of DA molecules, which causes the solubilization ofDA molecules in the outer leaflet of the vesicle bilayers. This solubilization decreases the outer surfacearea of the vesicle, thereby increasing surface tension. A kinetic model based on area differenceelasticity theory can accurately describe the dynamics of DA vesicles triggered by pH stimuli.

*Yoshiyuki Kageyama, Tomonori Ikegami, Natsuko Hiramatsu, *Sadamu Takeda, and Tadashi Sugawara,
Structure and growth behavior of centimeter-sized helical oleate assemblies formed with assistance of medium-length carboxylic acids,
Soft Matter 11, 3550-3558 (2015).

[Summary] The nonequilibrium organization of self-assemblies from small building-block molecules offers an attractive and essential means to develop advanced functional materials and to understand the intrinsic nature of life systems. Fatty acids are well-known amphiphiles that form self-assemblies of several shapes. Here, we found that the lengths of helical structures of oleic acid formed in a buffered aqueous solution are dramatically different by the presence or absence of certain amphiphilic carboxylic acids. For example, under the coexistence of a small amount of N-decanoyl-L-alanine, we observed the formation of over 1 centimeter-long helical assemblies of oleate with a regular pitch and radius, whereas mainly less than 100 μm-long helices formed without this additive. Such long helical assemblies are unique in terms of their highly dimensional helical structure and growth dynamics. Results from the real-time observation of self-assembly formation, site-selective small-angle X-ray scattering, high-performance liquid chromatography analysis, and pH titration experiments suggested that the coexisting carboxylates assist in elongation by supplying oleate molecules to a scaffold for oleate helical assembly.

Masahiro Mizuno, Taro Toyota, Miki Konishi, Yoshiyuki Kageyama, *Masumi Yamada, and Minoru Seki,
Formation of monodisperse hierarchical lipid particles utilizing microfluidic droplets in a non-equilibrium state,
Langmuir 31, 2334-2341 (2015).

*Hiroshi Noguchi, Ai Sakashita and Masayuki Imai,
Shape transformations of toroidal vesicles,
Soft Matter 11, 193-201 (2015).

[Summary] Morphologies of genus-1 and 2 toroidal vesicles are studied numerically by dynamically triangulatedmembrane models and experimentally by confocal laser microscopy. Our simulation results reproduceshape transformations observed in our experiments well. At large reduced volumes of the genus-1vesicles, obtained vesicle shapes agree with the previous theoretical prediction, in which axisymmetricshapes are assumed: double-necked stomatocyte, discoidal toroid, and circular toroid. However, forsmall reduced volumes, it is revealed that a non-axisymmetric discoidal toroid and handled discocyteexist in thermal equilibrium in the parameter range, in which the previous theory predicts axisymmetricdiscoidal shapes. Polygonal toroidal vesicles and subsequent budding transitions are also found. Theentropy caused by shape fluctuations slightly modifies the stability of the vesicle shapes.

Yuka Takeuchi, Yoko Sugawara, Tadashi Sugawara, and *Masakazu Iwasaka,
Magnetic rotation of monosodium urate and urinary tract stones for clinical treatment applications,
Magnetics, IEEE Transactions on 50, 6101204 (2014).

[Summary] In recent years, diseases such as gout and urinary tract calculi, caused by crystals in vivo, are rapidly increasing due to excess intake of alcohol, salt, and so forth. Crystals causing gout are compounds of uric acid with sodium in the blood, which are called monosodium urate (MSU) crystals. On the other hand, urinary tract calculus is caused by calcium oxalate crystal. In this paper, we focused on the behaviors of MSU crystals and oxalic acid crystals under magnetic fields of several hundreds of mT (Tesla), and developed a method for new medical treatments by using a magnetic field. MSU crystals and oxalic acid crystals were prepared by a recrystallization from the aqueous solution. We observed these crystals using a charge-coupled device microscope under horizontal magnetic fields (maximum of 500 mT). While the magnetic fields were applied, the MSU crystals were oriented by the magnetic fields. In addition, oxalic acid crystals were oriented perpendicularly to the magnetic field. The dynamic rotation of MSU crystal was observed quantitatively by measuring the time course of the lightscattering intensities of the MSU suspension. The results show that the diamagnetic anisotropy in the MSU crystals controlled the rotational responses. As a possible medical application, a remote control of the MSU crystals and oxalic acid crystals in living body by the magnetic fields is proposed.

Yuri Mizukawa, Kentaro Suzuki, Shigefumi Yamamura, Yoko Sugawara, Tadashi Sugawara, and *Masakazu Iwasaka,
Magnetic manipulation of nucleic acid base microcrystals for DNA sensing,
Magnetics, IEEE Transactions on 50, 5001904 (2014).

[Summary] This paper develops a magneto-DNA sensing device composed of a crystalline nucleic acid base, which is a component of DNA on the basis of the dynamic rotation due to its diamagnetic anisotropy under a magnetic field of the mT order. As a basic study, recrystallized nucleic acid bases, such as cytosine, adenine, and guanine, were used for the measurement. We focused on the induced dynamic orientation effect on the nucleic acid base crystals by exposure of the magnetic field at 0.5 T. The morphologically long axis of a cytosine crystal oriented parallel to the applied magnetic fields, while those of adenine and guanine oriented perpendicular to the magnetic field. As a next stage, we traced the angular difference of the magnetic rotation of DNA adhered to guanine crystals comparing the rotation angles of the pre-exposure sample and the during exposure sample with and without DNA. It was revealed that the degree of the magnetic rotation of guanine crystals with DNA was seemingly less than that of guanine crystals without DNA. The difference in angle of the magnetic rotation of the guanine crystal may allow to detect the adhesion of DNA. The method obtained by detecting precise magnetic rotation of nucleic acid base crystals can be applied to the manipulation and sensing of macromolecules in dispersion containing nucleic acid bases, such as DNA and RNA.

Ai Sakashita, Masayuki Imai, and *Hiroshi Noguchi,
Morphological variation of a lipid vesicle confined in a spherical vesicle,
Physical Review E 89, 040701/1-4 (2014).

[Summary] Morphologies of a double-bilayer vesicle were explored experimentally by fast confocal laser microscopy andnumerically by a dynamically triangulated membrane model with area-difference elasticity. The confinement wasfound to induce several shapes of the inner vesicles that had not been observed in unilamellar vesicles: doubleand quadruple stomatocytes, slit vesicle, and vesicles of two or three compartments with various shapes. Thesimulations reproduced the experimental results very well and some of the shape transitions can be understoodby a simple theoretical model for axisymmetric shapes.

*Tomoyuki Mochida, Yusuke Funasako, Kousuke Takazawa, Masashi Takahashi, Michio M. Matsushita, and Tadashi Sugawara,
Chemical control of the monovalent-divalent electron-transfer phase transition in biferrocenium-TCNQ salts,
Chemical Communications 50, 5473-5475 (2014).

[Summary] An ionic molecular crystal of (1',1'''-dineopentylbiferrocene)(F₁TCNQ)₃ exhibits a first-order phase transition from a monovalent state (D⁺A₃⁻) to a divalent state (D²⁺A₃²⁻) at around 120 K. The transition was successfully controlled by modulation of the redox potentials using F_nTCNQ (n = 0-2) and by chemical-pressure effects.successfully controlled by modulation of the redox potentials using F_{nTCNQ (n = 0–2) and by chemical-pressure effects.}

*Katsuto Takakura, Takahiko Yamamoto, Kensuke Kurihara, Taro Toytota, Kiyoshi Ohnuma, and *Tadashi Sugawara,
Spontaneous Transformation from Micelles to Vesicles Associated with Sequential Conversionsof Comprising Amphiphiles within Assemblies,
Chemical Communications 50, 2190-2192 (2014).

[Summary] A morphological transformation from hybrid micelles to giant vesicles was observed in aqueous dispersion associated with formation of a double-chained amphiphile as a result of themigration of dodecylamine from the amphiphilic imine to the amphiphilic aldehyde within the hydrophobic environment of amphiphilic aggregates.

*Yuka Sakuma, Takashi Taniguchi, Toshihiro Kawakatsu, and Masayuki Imai,
Tubular membrane formation of binary giant unilamellar vesicles composed of cylinder and inverse-cone-shaped lipids,
Biophysical Journal 105, 2074-2081 (2013).

[Summary] We have succeeded in controlling tubular membrane formations in binary giant unilamellar vesicles (GUVs) using a simple temperature changing between the homogeneous one-phase region and the two-phase coexistence region. The binary GUV is composed of inverse-cone (bulky hydrocarbon chains and a small headgroup) and cylinder-shaped lipids. When the temperature was set in the two-phase coexistence region, the binary GUV had a spherical shape with solidlike domains. By increasing the temperature to the homogeneous one-phase region, the excess area created by the chain melting of the lipid produced tubes inside the GUV. The tubes had a radius on the micrometer scale and were stable in the one-phase region. When we again decreased the temperature to the two-phase coexisting region, the tubes regressed and the GUVs recovered their phaseseparated spherical shape. We infer that the tubular formation was based on the mechanical balance of the vesicle membrane (spontaneous tension) coupled with the asymmetric distribution of the inverse-cone-shaped lipids between the inner and outer leaflets of the vesicle (lipid sorting).

*Yoshiyuki Kageyama, Naruho Tanigake, Yuta Kurokome, Sachiko Iwaki, *Sadamu Takeda, Kentaro Suzuki, and *Tadashi Sugawara,
Macroscopic motion of supramolecular assemblies actuated by photoisomerization of azobenzene derivatives,
Chemical Communications 49, 9386-9388 (2013).

[Summary] Submillimetre size self-assemblies composed of oleate and azobenzene derivatives show forceful motions such as screw-type coiling–recoiling motion by photoirradiation.

*Masakazu Iwasaka, Yuito Miyashita, Yuri Mizukawa, Kentaro Suzuki, Taro Toyota, and Tadashi Sugawara,
Biaxial Alignment Control of Guanine Crystals by Diamagnetic Orientation,
Applied Physics Express 6, 037002/1-4 (2013).

[Summary] The present study provides evidence that a kind of nucleic acid base crystal, guanine crystal, shows a distinct magnetic orientation. Under thecondition where the guanine crystal boards were lying on the glass surface due to gravity, the boards gradually oriented their length to the appliedhorizontal magnetic fields of 400 mT. On the other hand, the vertical magnetic fields parallel to Earth’s gravity caused their width to be orientedalong the applied magnetic fields. Moreover, combining both vertical and horizontal magnetic fields produced a rapid alignment of the length to thehorizontal magnetic fields.