Researcher Database

Tetsuya Yamamoto
Creative Research Institution Institute for Chemical Reaction Design and Discovery
Specially Appointed Associate Professor

Researcher Profile and Settings

Affiliation

  • Creative Research Institution Institute for Chemical Reaction Design and Discovery

Job Title

  • Specially Appointed Associate Professor

Research funding number

  • 40610027

J-Global ID

Research Areas

  • Life sciences / Genomics
  • Natural sciences / Bio-, chemical, and soft-matter physics

Academic & Professional Experience

  • 2017/04 - Today Nagoya University Graduate School of Engineering Materials Physics 2 Assistant Professor
  • 2015/04 - 2017/03 Nagoya University NCC Division Assistant Professor

Research Activities

Published Papers

  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi
    Journal of Rheology 64 (4) 933 - 939 0148-6055 2020/07 [Refereed][Not invited]
  • Tetsuya Yamamoto, Tomohiro Yamazaki, Tetsuro Hirose
    Soft Matter 16 (19) 4692 - 4698 1744-683X 2020 [Refereed][Not invited]
     

    We use an extension of the Flory–Huggins theory to predict the phase separation driven by the production dynamics of architectural RNA.

  • Tetsuya Yamamoto, Takahiro Sakaue, Helmut Schiessel
    Europhysics Letters 127 (3) 38002  2019/09/05 [Refereed][Not invited]
     
    The loop extrusion theory predicts that the loops of chromosomes are produced by cohesin molecules that uni-directionally extrude a chromatin fiber. We here use an extension of the Rouse model to predict the chain conformational dynamics driven by the loop extrusion process. Our theory predicts that in a bulk solution, the mean square distance between the starting and ending sites of the loop extrusion process decreases with a constant rate. This is because the tension generated by the loop extrusion process drives the displacement of the starting site towards the ending site. In contrast, when the cohesin is entrapped at an interface, the mean square distance does not decrease until the tension generated by the loop extrusion process arrives at the ending site. This theory highlights the fact that the chain dynamics strongly depends on the mobility of the chain segments bound by cohesin.
  • Tetsuya Yamamoto, Helmut Schiessel
    Soft Matter 15 7635-7643  2019/08/28 [Refereed][Not invited]
     
    The loop extrusion theory predicts that cohesin acts as a molecular motor that extrudes chromatin fibers to produce loops. Hi-C experiments have detected relatively high contact frequencies between superenhancers. These probably result from the fact that superenhancers are localized at condensates of transcriptional activators and coactivators. The contact frequency between superenhancers is enhanced by auxin treatment that removes cohesin from chromatin. Motivated by these experimental results, we here treat chromatin at the surface of a condensate as a loop extruding polymer brush. Our theory predicts that the lateral pressure generated by the brush decreases with decreasing the loading rate of cohesin. This is because loop extrusion actively transfers chain segments at the vicinity of the interface. Our theory thus predicts that the increase of contact frequency by auxin treatment results from the fact that suppressing the loop extrusion process induces the dissolution of molecular components to the nucleoplasm, decreasing the average distance between superenhancers.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi
    Nature Communications 9 (1) 2062  2041-1723 2018/12/01 [Refereed][Not invited]
     
    The equilibrium volume of a thermoresponsive polymer gel changes dramatically across a temperature due to the coil-globule transitions of the polymers. When cofacially oriented nanosheets are embedded in such a gel, the composite gel deforms at the temperature, without changing the volume, and the response time is considerably shorter. We here theoretically predict that the deformation of the composite gel results from the fact that the nanosheets restrain the deformation of some polymers, while other polymers deform relatively freely. The unrestrained polymers collapse due to the coil-globule transitions and this generates the solvent flows to the restrained regions. The response time of this process is rather fast because solvent molecules travel only by the distance of the size of a nanosheet, instead of permeating out to the external solution. This concept may provide insight in the physics of composite gels and the design of thermoresponsive gels of fast response.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi
    SOFT MATTER 13 (37) 6515 - 6520 1744-683X 2017/10 [Refereed][Not invited]
     
    Many biopolymer gels generate negative normal stress, with which the polymer networks shrink in the normal of applied shear. Here we theoretically predict the sliding velocity of such a gel on a solid surface when a constant shear stress is applied to the gel. Our theory predicts that the negative normal stress drives the flow of the solvent in the gel and this produces a solvent layer between the gel and the surface. The sliding velocity of the gel is proportional to the thickness of the solvent layer and is a cubic function of the applied shear stress. With constant applied normal and shear stresses, the thickness of the solvent layer is a non-monotonic function of time with a maximum because the solvent flow from the gel to the solvent layer is dominant in the short time scale and the solvent flow from the solvent layer to the outside is dominant in a longer time scale. The maximum layer thickness depends on the ratio of the time scales of the solvent flow in the gel and in the solvent layer.
  • Tetsuya Yamamoto, Helmut Schiessel
    PHYSICAL REVIEW E 96 (3) 030402(R)  2470-0045 2017/09 [Refereed][Not invited]
     
    The loop extrusion theory assumes that protein factors, such as cohesin rings, act as molecular motors that extrude chromatin loops. However, recent single molecule experiments have shown that cohesin does not show motor activity. To predict the physical mechanism involved in loop extrusion, we here theoretically analyze the dynamics of cohesin rings on a loop, where a cohesin loader is in the middle and unloaders at the ends. Cohesin monomers bind to the loader rather frequently and cohesin dimers bind to this site only occasionally. Our theory predicts that a cohesin dimer extrudes loops by the osmotic pressure of cohesin monomers on the chromatin fiber between the two connected rings. With this mechanism, the frequency of the interactions between chromatin segments depends on the loading and unloading rates of dimers at the corresponding sites.
  • Tetsuya Yamamoto, Helmut Schiessel
    SOFT MATTER 13 (31) 5307 - 5316 1744-683X 2017/08 [Refereed][Not invited]
     
    We use a brush of DNA in a solution of transcriptional machinery and histone proteins to theoretically predict that this brush shows phase separation due to the instability arising from the disassembly of nucleosomes during transcription. In the two-phase coexistent state, collapsed chains (with relatively large nucleosome occupancy) lie at the grafting surface and swollen chains (with relatively small nucleosome occupancy) are distributed at the space above the collapsed chains, analogous to the structure of chromatin in differentiated cells. This layer structure is stabilized by the lateral osmotic pressure of swollen chains. For a relatively small grafting density, DNA brushes show tricritical points because the entropic elasticity with respect to the lateral excursion of swollen chains balances with the lateral osmotic pressure of these chains. At the tricritical points, DNA brushes show large fluctuations of local nucleosome concentration, which may be reminiscent of the fluctuations observed in embryonic stem cells.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi
    MACROMOLECULES 50 (13) 5208 - 5213 0024-9297 2017/07 [Refereed][Not invited]
     
    We use the two-fluid model to theoretically predict the relaxation dynamics of the normal stress of a gel, which is twisted by a rotational rheometer in the parallel plate geometry. We derive the equations of motion of solvent and polymer network by using an expansion of the free energy of the statistical thermodynamic model of polymer gels by the leading order nonlinear terms and solve these equations in the spirit of the lubrication approximation. Our theory predicts that the normal stress of the gel decreases exponentially with time due to the redistribution of solvent. The time scale of the normal stress relaxation scales with the square of the distance between the plates parabolic distribution of network displacements between the plates.
  • Tetsuya Yamamoto, Helmut Schiessel
    Europhysics Letters 118 28003  2017/06/23 [Refereed][Not invited]
     
    We study chromatin gels, model systems for chromatin, to theoretically predict the conditions, under which such gels show negative Poisson's ratios. A chromatin gel shows phase separation due to an instability arising from the disassembly of nucleosomes by RNA polymerases during transcription. We predict a negative Poisson's ratio near a miscibility threshold due to the cooperative assembly and disassembly of nucleosomes. The Poisson's ratio becomes more negative with an increasing number of RNAP because the disassembly rate of nucleosomes increases. In contrast, the chromatin gel shows a positive Poisson's ratio far from the miscibility threshold because the assembly of nucleosomes is arrested by the expiration of freely diffusing histone proteins.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi
    ACS MACRO LETTERS 6 (5) 512 - 514 2161-1653 2017/05 [Refereed][Not invited]
     
    We use a statistical thermodynamic model to theoretically predict the normal stress of a polymer gel, which is twisted by a rotational rheometer in the parallel plate geometry. This theory predicts that the normal stress of the gel is positive at a short time scale. At longer time, the normal stress decreases significantly due to the redistribution of solvent, but is still positive when the polymer network is in the neo-Hookean regime. The normal stress becomes negative when the polymer network is greatly prestretched in the swelling process because large tension is generated by shearing already prestretched polymers. Our theory predicts the phase diagram with respect to the direction of normal stress as functions of the aspect ratio and swelling ratio of gels. Experimental tests on this prediction may advance our understanding of the physical mechanisms involved in the negative normal stress generated by polymer gels.
  • Tetsuya Yamamoto, Qingan Meng, Huan Liu, Lei Jiang, Masao Doi
    LANGMUIR 32 (13) 3262 - 3268 0743-7463 2016/04 [Refereed][Not invited]
     
    We theoretically predict the stability of liquid in a model brush made of flexible fibers for cases in which liquid is supplied from an ink reservoir. The volume of the liquid in the brush increases with increasing applied pressure by the reservoir, and the liquid shows instability at a critical pressure. When the fibers are shorter than a critical length, the end of the brush opens continuously with increasing applied pressure. The volume of the liquid that hangs from the open end of the brush increases with increasing applied pressure, and the liquid drops from the brush at the critical pressure, where the weight of the liquid becomes larger than the surface tension. In contrast, when the fibers are longer than the critical length, the end of the brush opens discontinuously to the maximal extent at the critical pressure. The discontinuous unbuckling is driven by the instability arising from the fact that the bending stiffness of the water surface, which bends together with the flexible fibers, decreases as the end of the brush opens, and it is thus a unique feature of brushes of flexible fibers.
  • Tetsuya Yamamoto, Helmut Schiessel
    LANGMUIR 32 (12) 3036 - 3044 0743-7463 2016/03 [Refereed][Not invited]
     
    We. theoretically predict the local density of nucleosomes on DNA brushes in a solution of molecules, which are necessary for transcription and the assembly of nucleosomes. Our theory predicts that in a confined space, DNA brushes show phase separation, where a region of relatively large nucleosomal occupancy coexists with a region of smaller nucleosomal occupancy. This phase separation is driven by an instability arising from the fact that the rate of transcription increases as the nucleosomal occupancy decreases due to the excluded volume interactions between nucleosomes and RNA polymerase during thermal diffusion and, in turn, nucleosomes are (in some cases) desorbed from DNA when RNA polymerase collides with nucleosomes during transcription. The miscibility phase diagram shows critical points, which are sensitive to the rate constants involved in transcription, the changes of interactions of DNA chain segments by assembling nucleosomes, and pressures that are applied to the brushes.
  • Tetsuya Yamamoto, Qing'an Meng, Qianbin Wang, Huan Liu, Lei Jiang, Masao Doi
    NPG ASIA MATERIALS 8 e241  1884-4049 2016/02 [Refereed][Not invited]
     
    When brushes of flexible fibers are removed from liquid baths, these brushes sometimes show unwanted droplets at their ends, depending on the length, rigidity and shape of their fibers. Capillary forces arising from the varying cross-sections of conical fiber tips have been thought to eliminate the droplets. However, these forces may not operate with water, which fills the entire space between the fibers of a brush. Here, we theoretically show that brushes eliminate unwanted droplets with a physical mechanism that is significantly different from a single conical fiber by 'closing' their ends. We analyze the hydrostatics of water in a brush when it is removed from a bath, and we identify the condition under which the end of the brush is closed, emphasizing the roles played by the elastic deformation of the flexible fibers owing to interfacial forces. Moreover, this theory predicts that the volume of water that is captured by brushes is a non-monotonic function of the length of their fibers because the fibers show excluded volume interactions when their ends are 'closed'. This theory may guide the design of liquid-transfer devices that can retain liquids in a controlled manner.
  • Tetsuya Yamamoto, Masao Doi, David Andelman
    EPL 112 (5) 56001  0295-5075 2015/12 [Refereed][Not invited]
     
    We use the Poisson-Boltzmann theory to predict contact angle saturation of aqueous droplets in electrowetting. Our theory predicts that injection of ions from the droplet into its surrounding medium is responsible for the deviation of the apparent contact angle from the Young-Lippmann equation for large applied voltages. The ion injection substantially decreases the Maxwell stress and increases the osmotic pressure at the interface between the two media, leading to saturation of the apparent contact angle. Moreover, we find that the contact angle does not saturate, but only has a broad minimum that increases again upon further increase of the applied voltage, in agreement with experiments. Copyright (C) EPLA, 2015
  • Tetsuya Yamamoto, S. A. Safran
    SOFT MATTER 11 (15) 3017 - 3021 1744-683X 2015 [Refereed][Not invited]
     
    We theoretically predict the rate of transcription (TX) in DNA brushes by introducing the concept of TX dipoles that takes into account the unidirectional motion of enzymes (RNAP) along DNA during transcription as correlated pairs of sources and sinks in the relevant diffusion equation. Our theory predicts that the TX rates dramatically change upon the inversion of the orientation of the TX dipoles relative to the substrate because TX dipoles modulate the concentrations of RNAP in the solution. Comparing our theory with experiments suggests that, in some cases, DNA chain segments are relatively uniformly distributed in the brush, in contrast to the parabolic profile expected for flexible polymer brushes.
  • Tetsuya Yamamoto, Masao Doi
    NATURE COMMUNICATIONS 5 4162  2041-1723 2014/06 [Refereed][Not invited]
     
    Polyelectrolyte gel diodes that are double layers of two oppositely charged polyelectrolyte gels, sandwiched by two symmetric electrodes, are emergent ionic devices. These diodes are designed to rectify ion currents with a physical mechanism that is analogous to conventional semiconductor diodes-the asymmetry in the permeability of ions across the interfaces between the two oppositely charged gels. Here we show that polyelectrolyte gel diodes indeed rectify steady currents with a physical mechanism that is very different from conventional diodes by using a simple electrochemical model; electric currents are limited by electrochemical reactions that are driven by potential drops at electrodes and these potential drops markedly change with changing the direction of applied voltages due to the redistribution of non-reactive counterions, leading to rectified ion currents. This concept is relatively generic and thus may provide insight in the physics of analogous ionic and biomimetic systems that show electrochemical reactions.
  • Dawid Szewczyk, Tetsuya Yamamoto, Daniel Riveline
    New Journal of Physics 15 035031:1-22  2013/03/27 [Refereed][Not invited]
  • Atsuo Sadakata, Tetsuya Yamamoto, Dai Taguchi, Takaaki Manaka, Masahiro Fukuzawa, Mitsumasa Iwamoto
    Molecular Crystals and Liquid Crystals 567 (1) 187 - 192 1542-1406 2012/11/15 [Refereed][Not invited]
     
    We measured the electroluminescence (EL) generated from double-layer ITO/-NPD/Alq 3/Al diodes by applying large A.C. square voltages for understanding carrier behaviors. Two EL modes were identified in high and low frequency regions, relying on the D.C. component of the applied A.C. square voltages. This indicates that two different carrier behaviors are responsible for the EL emission from the double-layer EL diodes. Modeling the two EL modes, we showed the contribution of the D.C. component of applied A.C. square voltages to the two EL modes in terms of the interfacial Maxwell-Wagner charging. © 2012 Taylor & Francis Group, LLC.
  • Atsuo Sadakata, Kenshiro Osada, Dai Taguchi, Tetsuya Yamamoto, Masahiro Fukuzawa, Takaaki Manaka, Mitsumasa Iwamoto
    Journal of Applied Physics 112 (8) 0021-8979 2012/10/15 [Refereed][Not invited]
     
    By using electric field induced optical second harmonic generation measurement, charge accumulation at the double-layer interface of ITO/α-NPD/Alq 3/Al diodes was verified under two electroluminescence (EL) operational modes, which were activated in the low and high frequency regions, respectively, with application of large ac square voltage. Results supported our proposed idea [A. Sadakata, J. Appl. Phys. 110, 103707 (2011)] that accumulated holes suppress hole injection in the low frequency region and lead to the decrease of the EL intensity activated by the recombination of holes and electrons injected from opposite electrodes. On the one hand, the accumulated holes assist electron injection in the high frequency region and result in the increase of EL intensity activated by the recombination of the interfacial accumulated holes and injected electrons from Al electrode. © 2012 American Institute of Physics.
  • Tetsuya Yamamoto, Samuel A. Safran
    SOFT MATTER 8 (20) 5439 - 5442 1744-683X 2012 [Refereed][Not invited]
     
    We present a theory that predicts that cholesterol molecules phase separate from multicomponent lipid bilayer membranes, but not from monolayers of the same composition. In our model, the tilting of cholesterol molecules in monolayers is not energetically favorable because their exocyclic chains are very short. However, in bilayers, two correlated cholesterol molecules in the opposing leaflets of bilayers can form "dimers'', whose chains are effectively twice as long and can tilt cooperatively. Our theory predicts that the cooperative tilting of these dimers drives the phase separations of cholesterol in bilayers.
  • Atsuo Sadakata, Dai Taguchi, Tetsuya Yamamoto, Kenshiro Osada, Masahiro Fukuzawa, Takaaki Manaka, Mitsumasa Iwamoto
    IEEJ Transactions on Electronics, Information and Systems 132 (9) 4 - 1412 1348-8155 2012 [Refereed][Not invited]
     
    By applying large A.C. square voltages to double-layer ITO/á-NPD/ Alq3/Al devices, we studied the generation of electroluminescence (EL) in terms of the carrier injection and transport. The EL intensity gradually decayed with the increase of the frequency of the applied A.C. square voltage, and reached a minimum at the frequency corresponding to the carrier transit time. Interestingly, the EL intensity was again increased by the application of further higher frequency A.C. square voltages, relying on the D.C. component of the A.C. square voltages. The results suggested the presence of two EL modes. Using the Maxwell-Wagner effect model analysis, we proposed a model that accounts for the presence of two EL modes. © 2012 The Institute of Electrical Engineers of Japan.
  • Atsuo Sadakata, Dai Taguchi, Tetsuya Yamamoto, Masahiro Fukuzawa, Takaaki Manaka, Mitsumasa Iwamoto
    Journal of Applied Physics 110 (10) 0021-8979 2011/11/15 [Refereed][Not invited]
     
    By applying large A.C. square voltages to double-layer ITO/ -NPD/ Alq 3 /Al diodes, we studied the generation of electroluminescence (EL) in terms of the carrier injection and transport. The EL intensity gradually decayed with the increase of the frequency of the applied A.C. square voltage, and reached a minimum at the frequency corresponding to the carrier transit time. Interestingly, the EL intensity was again increased by the application of further higher frequency A.C. square voltages, relying on the D.C. component of the A.C. square voltages. The results suggest the presence of two EL modes. Using the Maxwell-Wagner effect model analysis, we have proposed a model that accounts for the two EL modes. © 2011 American Institute of Physics.
  • T. Yamamoto, P. A. Pincus
    EPL 95 (4) 48003: 1-6  0295-5075 2011/08 [Refereed][Not invited]
     
    We predict the collapse of a polyelectrolyte brush grafted on an electrode that is induced by applied electric fields for the limiting cases of low and high salt concentrations. The polyelectrolyte brush collapses locally to screen the charges induced on the electrodes. For low salt concentrations, the height of the polyelectrolyte brush decreases steeply with increasing the voltage between the electrodes because the number of counterions expelled from the brush increases exponentially. However, when the system is in equilibrium with monovalent salts at high concentrations, the brush height decreases almost linearly with increasing the voltage instead of the steep collapse. This is because the voltage drop mainly occurs over the diffuse double layer associated with the distant electrode. Copyright (C) EPLA, 2011
  • Tetsuya Yamamoto, Samuel A. Safran
    SOFT MATTER 7 (15) 7021 - 7033 1744-683X 2011 [Refereed][Not invited]
     
    Hybrid lipids (with one saturated tail and one unsaturated tail) have been proposed as agents that can reduce the line tension between domains. We use a liquid crystal model to predict the effect of the degree of unsaturation in the unsaturated tails of hybrid lipids on the miscibility phase diagram and line tension between domains in membranes comprising saturated lipids (with two saturated tails), hybrid lipids, and cholesterol (SHC membranes). In contrast to SHC membranes containing hybrid lipids with a single (or small) degree of unsaturation, for which the phase diagram shows two distinct two-phase regions, SHC membranes containing hybrid lipids with degrees of unsaturation larger than a threshold value exhibit a single two-phase region. This enables hybrid lipids with larger degrees of unsaturation to steadily increase their chain order with decreasing temperature and enhances the reduction of the line tension. This theory predicts that the line tension between domains in SHC membranes is sensitive to the degrees of unsaturation of hybrid lipids.
  • Tetsuya Yamamoto, Dai Taguchi, Takaaki Manaka, Mitsumasa Iwamoto
    Molecular Crystals and Liquid Crystals 479 (1) 13-31  2010/09/22 [Refereed][Not invited]
     
    Monolayers comprised of banana-shaped achiral molecules are modeled taking into account the hard-core repulsive force and electrostatic interaction between constituent molecules and the water surface. The model predicts the achiral-chiral transition of orientational structure along with in-plane nematic ordering during a monolayer compression due to the 2D geometry of monolayers. This model further reveals that in-plane nematic order is established beforehand of the chiral transition since banana-shaped molecules behave as rod-shaped molecules with variable aspect ratio in 2D geometry. It indicates the importance of in-plane nematic order in the achiral-chiral phase transition of monolayers comprised of banana-shaped achiral molecules.
  • Tetsuya Yamamoto, Said Aranda-Espinoza, Rumiana Dimova, Reinhard Lipowsky
    LANGMUIR 26 (14) 12390 - 12407 0743-7463 2010/07 [Refereed][Not invited]
     
    The stability of spherical vesicles in alternating (ac) electric fields is studied theoretically for asymmetric conductivity conditions across their membranes. The vesicle deformation is obtained from a balance between the curvature elastic energies and the work clone by the Maxwell stresses. The present theory describes and clarifies the mechanisms for the four types of morphological transitions observed experimentally on vesicles exposed to ac fields in the frequency range from 500 to 2 x 10(7) Hz. The displacement currents across the membranes redirect the electric fields toward the membrane normal to accumulate electric charges by the Maxwell-Wagner mechanism. These accumulated electric charges provide the underlying molecular mechanism for the morphological transitions of vesicles as observed on the micrometer scale.
  • T. Yamamoto, R. Brewster, S. A. Safran
    EPL 91 (2) 28002-1-6  0295-5075 2010/07 [Refereed][Not invited]
     
    We use a liquid-crystal model to predict that hybrid lipids (lipids that have one saturated and one unsaturated tail) can stabilize line interfaces between domains in mixed membranes of saturated lipids, hybrid lipids, and cholesterol (SHC membranes). The model predicts the phase separation of SHC membranes with both parabolic and loop binodals depending on the cholesterol concentration, modeled via an effective pressure. In some cases, the hybrid lipids can reduce the line tension to zero in SHC membranes at temperatures that approach the critical temperature as the pressure is increased. The differences in the hybrid saturated tail conformational order in bulk and at the interface are responsible for the reduction of the line tension. Copyright (C) EPLA, 2010
  • T. Yamamoto, T. Manaka, M. Iwamoto
    EUROPEAN PHYSICAL JOURNAL E 29 (1) 1 - 8 1292-8941 2009/05 [Refereed][Not invited]
     
    The free energy of condensed phase domains in monolayers at the air-water interface has been analyzed by taking into account the surface pressure, line tension, and electrostatic energy due to the normal and in-plane spontaneous polarization. We found that this free energy was reduced to the sum of the Frank elastic energy and anisotropic line tension, which were used to reproduce the shapes of domains in fatty acid monolayers, in the limit of small orientational deformation. Domains in monolayers are interesting systems as a meeting point between the physics of liquid crystals and electrostatics.
  • Rumiana Dimova, Natalya Bezlyepkina, Marie Domange Jordo, Roland L. Knorr, Karin A. Riske, Margarita Staykova, Petia M. Vlahovska, Tetsuya Yamamoto, Peng Yang, Reinhard Lipowsky
    SOFT MATTER 5 (17) 3201 - 3212 1744-683X 2009 [Refereed][Not invited]
     
    This review focuses on the effects of electric fields on giant unilamellar vesicles, a cell-size membrane system. We describe various types of behavior of vesicles subjected to either alternating fields or strong direct current pulses, such as electrodeformation, -poration and -fusion. The vesicle response to alternating fields in various medium conditions is introduced and the underlying physical mechanisms are highlighted, supported by theoretical modeling. New aspects of the response of vesicles with charged or neutral membranes, in fluid or gel-phase, and embedded in different solutions, to strong direct current pulses are described including novel applications of vesicle electrofusion for nanoparticle synthesis.
  • Wei Ou-Yang, Martin Weis, Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto
    Journal of Chemical Physics 130 (10) 0021-9606 2009 [Refereed][Not invited]
     
    The effect of external electrostatic charge on the shapes of liquid condensed (LC) phase domains in monolayer at the air/water interface was investigated. For this reason the thermodynamic properties, domain size, and spontaneous polarization were analyzed by surface pressure-area isotherms, Brewster angle microscopy (BAM), and Maxwell displacement current technique. The analysis indicated magnesium ions preferred to bond with dipalmitoyl phosphatidylcholine negative head group in liquid expanded phase and/or at domain boundary at low ion concentration and got an access to binding with molecules inside of the LC domains for higher ion concentration. Domain size increase characterized by BAM was discussed in respect to the shape equation on the basis of electrostatic energy contribution. Although molecular repulsive force increased by adding of ions into subphase, the growth of domain size exceeded this tendency. Following shape equation analysis it was suggested that this effect corresponded to change in dipole moment orientation represented by increase in spontaneous polarization in normal projection. This demonstrated impact of local electrostatic field on molecular dipoles and free energy of LC domains. © 2009 American Institute of Physics.
  • Mitsumasa Iwamoto, Takaaki Manaka, Tetsuya Yamamoto, Eunju Lim
    Thin Solid Films 517 (4) 1312 - 1316 0040-6090 2008/12/31 [Refereed][Not invited]
     
    Probing and modeling of surface polarization phenomena originating from dipoles and electrons in organic materials are studied. We use an electrical measurement that can directly probe orientational dipolar motion in monolayers by Maxwell Displacement Current, and show that a two-dimensional domain shape is dependent on electrostatic energy stored in the domain owing to the polar orientational alignment of permanent dipoles. Also, we demonstrate a novel optical second harmonic generation technique that allows carrier motion in active layers of organic field-effect transistors to be directly probed as the migration of electric field. We conclude that probing of electric field generated from moving charged particles, e.g., dipoles and electrons, at the interface is a common concept for studying dielectric polarization and its related two-dimensional interfacial phenomena in organic materials. © 2008 Elsevier B.V. All rights reserved.
  • Martin Weis, Wei Ou-Yang, Takahiro Aida, Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto
    Thin Solid Films 517 (4) 1317 - 1320 0040-6090 2008/12/31 [Refereed][Not invited]
     
    Phospholipid organic monolayer at the air-water interface was studied in the presence of magnesium ions. For this reason the domain size by Brewster angle microscopy (BAM) as well as the Gibbs energy by thermodynamic analysis is evaluated. Domain size increase is discussed with respect to the shape equation on the basis of the electrostatic energy contribution. By coupling these techniques it was found that for ion adsorption at first it is preferred domain boundary and liquid expanded (LE) phase. Only after reaching of specific concentration (30 mM) ions are adsorbed also inside of the liquid condensed (LC) domain. Evaluation of BAM images and thermodynamic analysis reveals existence of pure repulsive forces it is illustrated by gradual increase of average domain area. Additionally, in low magnesium ion concentration region it was successful to use Langmuir adsorption isotherm for fitting the observed domain area. © 2008 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Takahiro Aida, Takaaki Manaka, Mitsumasa Iwamoto
    COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 321 (1-3) 151 - 157 0927-7757 2008/05 [Refereed][Not invited]
     
    Domain shape transition of racemic dipalmitoylphosphatidylcholine (DPPC) monolayers indicates the possibility of chiral phase separation in a racemic domain. We have analyzed the chiral phase separation in a racemic domain taking into account the surface pressure, line tension, electrostatic energy due to the spontaneous polarization and electric quadrupole density, and mixing entropy to clarify the mechanism of shape transition of racemic monolayer domains. We derive the condition of the chiral phase separation in an analogous form to the Bragg-Williams theory, and predict that chiral phase separation occurs as the spontaneous polarization in monolayer normal increases in agreement with our experimental results. The electric quadrupole density plays an important role in the chiral phase separation of a racemic monolayer domain. (c) 2008 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Dai Taguchi, Martin Weis, Takaaki Manaka, Mitsumasa Iwamoto
    JOURNAL OF CHEMICAL PHYSICS 128 (20) 204706  0021-9606 2008/05 [Refereed][Not invited]
     
    The formation mechanism of the shapes of condensed phase domains in monolayers at the air-water interface was investigated taking into account the surface pressure, line tension, and electrostatic energy due to the spontaneous polarization generated in normal and in-plane direction. By deriving the shape equation of monolayer domains as the mechanical balance at the domain boundary, we found that the electrostatic energy contributes to the shape equation as electrostatic Maxwell stress. Development of a cusp from condensed phase domains of fatty acid monolayers, which has been experimentally observed, was analyzed by the shape equation. It was found that the development of a cusp originated from the strong Maxwell stress, which was induced by the non-uniform orientational distribution in the fatty acid domain, and that cusped shapes gave a minimum of the free energy of the domain. It demonstrates that the shape equation with Maxwell stress, which is derived in the present study, is useful to study the formation mechanism of the shapes of condensed phase domains in monolayers. (C) 2008 American Institute of Physics.
  • Wei Ou-yang, Tetsuya Yamamoto, Takahiro Aida, Takaaki Manaka, Mitsumasa Iwamoto
    Thin Solid Films 516 (9) 2649 - 2651 0040-6090 2008/03/03 [Refereed][Not invited]
     
    To understand the relationship between molecular chirality and electrical properties of monolayers, Maxwell displacement current (MDC) behaviors and domain shapes of chiral DPPC monolayers composed of dextro- (d-) and levo- (l-) rotatory molecules at the air-water interface are investigated during monolayer compression using MDC measurement and the Brewster angle microscopy (BAM) system. The experimental results show that for DPPC monolayers of the two pure enantiomers, the π-A isotherms and the MDC behaviors are similar to each other, while the domain patterns of them are mirror shapes of different sizes. This reveals that MDC behaviors due to molecular spontaneous polarization have no relation to chirality but domain shapes closely depend on the molecular chirality. Moreover, the observed domain shapes verify the domain shape theory which was recently developed by Iwamoto et al. [M. Iwamoto, Z.C. Ou-Yang, Phy. Rev. Letts, 93 (2004) 206101]. © 2007 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto
    THIN SOLID FILMS 516 (9) 2660 - 2665 0040-6090 2008/03 [Refereed][Not invited]
     
    The electrostatic energy in a dipolar monolayer domain with orientational deformation has been analyzed for the study of monolayer shapes. It is demonstrated that a monolayer domain is viewed as a system of interacting induced electric charges distributed at the inside and boundary of a domain. Since induced charge distribution is determined by orientational deformation and domain shape, the electrostatic energy is represented in the form of Frank splay elastic energy with spontaneous splay and curvature elastic energy with spontaneous curvature. (c) 2007 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto
    JOURNAL OF CHEMICAL PHYSICS 126 (12) 125106  0021-9606 2007/03 [Refereed][Not invited]
     
    Shapes and orientational deformation of a lipid monolayer domain have been analyzed taking into account the surface pressure, line tension, and electrostatic energy due to the spontaneous polarization and electric quadrupole density generated from the domain. The electrostatic energy due to the generation of spontaneous polarization and electric quadrupole density contributes to the formation of orientational deformation as the Frank elastic energy and spontaneous splay, respectively. Since the orientational configuration of the electric quadrupole density and in-plane spontaneous polarization is dependent on the molecular chirality, and the positive splay deformation of electric quadrupole density is induced by the spontaneous splay, the bending direction of in-plane spontaneous polarization depends on the chirality of constituent lipids. The electrostatic energy due to the in-plane spontaneous polarization is dependent on the orientational deformation of in-plane spontaneous polarization, and bends the domain shape towards the bending direction of the in-plane spontaneous polarization. It has been demonstrated that the chiral dependence of the domain shapes of lipid monolayers originated from the chiral dependence of orientational structure due to the electric quadrupole density.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 479 1071 - 1085 1542-1406 2007 [Refereed][Not invited]
     
    The domain shape formation of monolayers comprised of polar molecules with the orientational deformation of spontaneous polarization is investigated by viewing this problem as electrostatic charge effect. The orientational deformation contributes to the domain free energy as the spontaneous curvature, Frank elastic energy, and spontaneous splay, which originate from the effect of diagonal and off-diagonal components of capacitance matrix. Shape equation is extended by introducing the concept of "curvature of polarization" to take into account the spontaneous curvature. It is exemplified that the spontaneous curvature is reasonably understood as the shape formation to optimize the off-diagonal component of electrostatic energy.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto
    COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS 284 154 - 160 0927-7757 2006/08 [Refereed][Not invited]
     
    The orientational structure of monolayers comprised of 1-butyl-2,6-bis-[2-(4-dibutylaminophenyl)-vinyl]-pyridiniumiodide (M53) banana-shaped achiral molecules was studied by Maxwell displacement current (MDC) and optical second harmonic generation (SHG) measurements. In the MDC-SHG measurement, gradual increase of the orientational order parameters C-01 equivalent to < cos theta > and C-03 equivalent to (5 cos(3)theta - 3cos theta)/2 (theta : tilt angle, <> : thermodynamic average) was detected as the molecular area was decreased. In order to clarify this result, a model of monolayers comprised of banana-shaped achiral molecules was constructed taking into account the electrostatic Coulomb interaction between constituent molecules and induced image dipole at an air-water interface, and the entropy with respect to positional and orienational distribution of constituent molecules. A good agreement between the model calculation and the experimental result demonstrated that the geometrical constraint imposed on the orientation of constituent molecules at an air-water interface (interfacial binding effect) plays an important role in the determination of orientational structure of monolayers comprised of banana-shaped achiral molecules. (c) 2005 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Takaaki Manaka, Dai Taguchi, Mitsumasa Iwamoto
    JOURNAL OF CHEMICAL PHYSICS 125 (3) 034704  0021-9606 2006/07 [Refereed][Not invited]
     
    Chirality of monolayers comprised of banana-shaped achiral molecules at an air-water interface was investigated theoretically, and a forming mechanism of chiral structure as an assembly of achiral molecules was argued. A model of such monolayers was constructed taking into account the short-range repulsive interaction between constituent banana-shaped achiral molecules, and the free energy density functional of the model was derived as a generalization of Williams-Bragg approach. It was predicted that chiral symmetry breaking occurs by monolayer compression, where two-dimensional characteristics of monolayers at an interface plays an important role in the formation of chiral structure by banana-shaped achiral molecules.
  • R Wagner, T Yamamoto, T Manaka, M Iwamoto
    REVIEW OF SCIENTIFIC INSTRUMENTS 76 (8) 083902  0034-6748 2005/08 [Refereed][Not invited]
     
    An experimental instrument has been developed utilizing Brewster angle reflectometry and Maxwell displacement current (MDC) measurement techniques, which are ascribed to the linear and spontaneous polarization, respectively, to investigate orientational order of Langmuir monolayers at an air-water interface. This system has been demonstrated to be sensitive in detecting the orientational order parameters S-1 and S-2 simultaneously [S-n is defined as the thermodynamic average of Legendre polynomials of nth rank, S-n = < P-n(cos theta)>]. Using this system in conjunction with a previously established system utilizing second harmonic generation and MDC, which is capable of detecting the orientational order parameters S-1 and S-3 simultaneously, all three orientational order parameters S-1, S-2, and S-3 can be obtained for Langmuir monolayers. An experiment using the newly developed instrument was conducted on a monolayer comprised of 4-octyl-4'-n-cyanobiphenyl (8CB) molecules to demonstrate the capability of detecting the orientational order parameters S-1 and S-2 during monolayer compression. (c) 2005 American Institute of Physics.
  • Mitsumasa Iwamoto, Takaaki Manaka, Tetsuya Yamamoto, Zhong-Can Ou-Yang
    Colloids and Surfaces A: Physicochemical and Engineering Aspects 257-258 51 - 56 0927-7757 2005/05/05 [Refereed][Not invited]
     
    With the Maxwell displacement current (MDC) measurement coupled with optical second harmonic generation (SHG) measurement, the dielectric polarization phenomena of monolayers can be investigated. We have been studying the flow behavior of Langmuir-film by the MDC-SHG experimental system. Shear induced phase transition accompanying the monolayer structural change from C∞-symmetry to Cs-symmetry was detected by MDC and SHG measurement under lateral constant monolayer compression. This dynamical behavior of organic monolayer was well explained, taking into account the tilt of directors in monolayers coupled with the lattice structure of organic monolayers. © 2004 Elsevier B.V. All rights reserved.
  • T Yamamoto, D Taguchi, T Manaka, M Iwamoto
    JOURNAL OF CHEMICAL PHYSICS 122 (16) 164703  0021-9606 2005/04 [Refereed][Not invited]
     
    The flexoelectric effect of 4-heptyloxy-4'-cyanobiphenyl (70CB) monolayers at the air-water interface is studied by Maxwell displacement current (MDC) and optical second harmonic generation measurements. Though MDC was expected to increase during the compression of 70CB monolayers in L-2/L-2(') phase from the MDC theory developed previously, decrease of MDC was detected in these phases. This abnormalous phenomenon is found to be due to the quench of flexoelectric effect by the flow orientation of monolayers. (c) 2005 American Institute of Physics.
  • T Yamamoto, A Tojima, T Manaka, M Iwamoto
    CHEMICAL PHYSICS LETTERS 378 (3-4) 428 - 433 0009-2614 2003/09 [Refereed][Not invited]
     
    The flow behavior of 4-heptyloxy-4'-cyanobiphenyl (7OCB) monolayer is studied during compression and expansion by Maxwell displacement current (MDC) and second harmonic generation (SHG) measurement. It is found that in-plane molecular flow induced reorientation of 7OCB monolayer in L-2 and L-2' phases of the monolayer is reversible. It is concluded that the MDC-SHG method is available for exploring the flow behavior of monolayers. (C) 2003 Elsevier B.V. All rights reserved.
  • T Yamamoto, T Manaka, M Iwamoto
    CHEMICAL PHYSICS LETTERS 368 (3-4) 370 - 376 0009-2614 2003/01 [Refereed][Not invited]
     
    The electrostatic charge effect on the orientational distribution of rod-like polar molecules at the air-water interface is analyzed taking into account the induced charge on electrode suspended in the air. The first order orientational order parameter S, is found to change as the electrode approaches monolayers, and approximately expressed as S-1 = S-1(0) + A(*)(2S(2)(0) - 3S(1)(02) + 1)/3, where A(*) characterizes the effect of electrode and S-i(0) (i = 1,2) represents orientational order parameters in the absence of suspended electrode. The molecular area giving the maximum deviation of S-1 from S-1(0) decreases as the interaction between molecules and water surface increases, but it is independent of the position of electrode. (C) 2002 Elsevier Science B.V. All rights reserved.

MISC

  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi  Nature Communications  9-  (1)  2062  2018/12/01  [Refereed][Not invited]
     
    The equilibrium volume of a thermoresponsive polymer gel changes dramatically across a temperature due to the coil-globule transitions of the polymers. When cofacially oriented nanosheets are embedded in such a gel, the composite gel deforms at the temperature, without changing the volume, and the response time is considerably shorter. We here theoretically predict that the deformation of the composite gel results from the fact that the nanosheets restrain the deformation of some polymers, while other polymers deform relatively freely. The unrestrained polymers collapse due to the coil-globule transitions and this generates the solvent flows to the restrained regions. The response time of this process is rather fast because solvent molecules travel only by the distance of the size of a nanosheet, instead of permeating out to the external solution. This concept may provide insight in the physics of composite gels and the design of thermoresponsive gels of fast response.
  • Tetsuya Yamamoto, Helmut Schiessel  PHYSICAL REVIEW E  96-  (3)  030402(R)  2017/09  [Refereed][Not invited]
     
    The loop extrusion theory assumes that protein factors, such as cohesin rings, act as molecular motors that extrude chromatin loops. However, recent single molecule experiments have shown that cohesin does not show motor activity. To predict the physical mechanism involved in loop extrusion, we here theoretically analyze the dynamics of cohesin rings on a loop, where a cohesin loader is in the middle and unloaders at the ends. Cohesin monomers bind to the loader rather frequently and cohesin dimers bind to this site only occasionally. Our theory predicts that a cohesin dimer extrudes loops by the osmotic pressure of cohesin monomers on the chromatin fiber between the two connected rings. With this mechanism, the frequency of the interactions between chromatin segments depends on the loading and unloading rates of dimers at the corresponding sites.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi  Soft Matter  13-  6515-6520  2017/08/18  [Refereed][Not invited]
     
    Many biopolymer gels generate negative normal stress, with which the polymer networks shrink in the normal of applied shear. Here we theoretically predict the sliding velocity of such a gel on a solid surface when a constant shear stress is applied to the gel. Our theory predicts that the negative normal stress drives the flow of the solvent in the gel and this produces a solvent layer between the gel and the surface. The sliding velocity of the gel is proportional to the thickness of the solvent layer and is a cubic function of the applied shear stress. With constant applied normal and shear stresses, the thickness of the solvent layer is a non-monotonic function of time with a maximum because the solvent flow from the gel to the solvent layer is dominant in the short time scale and the solvent flow from the solvent layer to the outside is dominant in a longer time scale. The maximum layer thickness depends on the ratio of the time scales of the solvent flow in the gel and in the solvent layer.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi  Macromolecules  50-  (13)  5208  -5213  2017/07/11  [Refereed][Not invited]
     
    We use the two-fluid model to theoretically predict the relaxation dynamics of the normal stress of a gel, which is twisted by a rotational rheometer in the parallel plate geometry. We derive the equations of motion of solvent and polymer network by using an expansion of the free energy of the statistical thermodynamic model of polymer gels by the leading order nonlinear terms and solve these equations in the spirit of the lubrication approximation. Our theory predicts that the normal stress of the gel decreases exponentially with time due to the redistribution of solvent. The time scale of the normal stress relaxation scales with the square of the distance between the plates because the solvent redistribution results in the parabolic distribution of network displacements between the plates.
  • Tetsuya Yamamoto, Helmut Schiessel  Soft Matter  13-  5307 - 5316  2017/06/29  [Refereed][Not invited]
     
    We use a brush of DNA in a solution of transcriptional machinery and histone proteins to theoretically predict that this brush shows phase separation due to the instability arising from the disassembly of nucleosomes during transcription. In the two-phase coexistent state, collapsed chains (with relatively large nucleosome occupancy) lie at the grafting surface and swollen chains (with relatively small nucleosome occupancy) are distributed at the space above the collapsed chains, analogous to the structure of chromatin in differentiated cells. This layer structure is stabilized by the lateral osmotic pressure of swollen chains. For a relatively small grafting density, DNA brushes show tricritical points because the entropic elasticity with respect to the lateral excursion of swollen chains balances with the lateral osmotic pressure of these chains. At the tricritical points, DNA brushes show large fluctuations of local nucleosome concentration, which may be reminiscent of the fluctuations observed in embryonic stem cells.
  • Tetsuya Yamamoto, Helmut Schiessel  Europhysics Letters  118-  28003  2017/06/23  [Refereed][Not invited]
     
    We study chromatin gels, model systems for chromatin, to theoretically predict the conditions, under which such gels show negative Poisson's ratios. A chromatin gel shows phase separation due to an instability arising from the disassembly of nucleosomes by RNA polymerases during transcription. We predict a negative Poisson's ratio near a miscibility threshold due to the cooperative assembly and disassembly of nucleosomes. The Poisson's ratio becomes more negative with an increasing number of RNAP because the disassembly rate of nucleosomes increases. In contrast, the chromatin gel shows a positive Poisson's ratio far from the miscibility threshold because the assembly of nucleosomes is arrested by the expiration of freely diffusing histone proteins.
  • Tetsuya Yamamoto, Yuichi Masubuchi, Masao Doi  ACS Macro Letters  6-  512-514  2017/04/21  [Refereed][Not invited]
     
    We use a statistical thermodynamic model to theoretically predict the normal stress of a polymer gel, which is twisted by a rotational rheometer in the parallel plate geometry. This theory predicts that the normal stress of the gel is positive at a short time scale. At longer time, the normal stress decreases significantly due to the redistribution of solvent, but is still positive when the polymer network is in the neo-Hookean regime. The normal stress becomes negative when the polymer network is greatly prestretched in the swelling process because large tension is generated by shearing already prestretched polymers. Our theory predicts the phase diagram with respect to the direction of normal stress as functions of the aspect ratio and swelling ratio of gels. Experimental tests on this prediction may advance our understanding of the physical mechanisms involved in the negative normal stress generated by polymer gels.
  • Tetsuya Yamamoto, Qingan Meng, Huan Liu, Lei Jiang, Masao Doi  LANGMUIR  32-  (13)  3262  -3268  2016/04  [Refereed][Not invited]
     
    We theoretically predict the stability of liquid in a model brush made of flexible fibers for cases in which liquid is supplied from an ink reservoir. The volume of the liquid in the brush increases with increasing applied pressure by the reservoir, and the liquid shows instability at a critical pressure. When the fibers are shorter than a critical length, the end of the brush opens continuously with increasing applied pressure. The volume of the liquid that hangs from the open end of the brush increases with increasing applied pressure, and the liquid drops from the brush at the critical pressure, where the weight of the liquid becomes larger than the surface tension. In contrast, when the fibers are longer than the critical length, the end of the brush opens discontinuously to the maximal extent at the critical pressure. The discontinuous unbuckling is driven by the instability arising from the fact that the bending stiffness of the water surface, which bends together with the flexible fibers, decreases as the end of the brush opens, and it is thus a unique feature of brushes of flexible fibers.
  • Tetsuya Yamamoto, Helmut Schiessel  LANGMUIR  32-  (12)  3036  -3044  2016/03  [Refereed][Not invited]
     
    We. theoretically predict the local density of nucleosomes on DNA brushes in a solution of molecules, which are necessary for transcription and the assembly of nucleosomes. Our theory predicts that in a confined space, DNA brushes show phase separation, where a region of relatively large nucleosomal occupancy coexists with a region of smaller nucleosomal occupancy. This phase separation is driven by an instability arising from the fact that the rate of transcription increases as the nucleosomal occupancy decreases due to the excluded volume interactions between nucleosomes and RNA polymerase during thermal diffusion and, in turn, nucleosomes are (in some cases) desorbed from DNA when RNA polymerase collides with nucleosomes during transcription. The miscibility phase diagram shows critical points, which are sensitive to the rate constants involved in transcription, the changes of interactions of DNA chain segments by assembling nucleosomes, and pressures that are applied to the brushes.
  • Tetsuya Yamamoto, Qing'an Meng, Qianbin Wang, Huan Liu, Lei Jiang, Masao Doi  NPG ASIA MATERIALS  8-  e241  2016/02  [Refereed][Not invited]
     
    When brushes of flexible fibers are removed from liquid baths, these brushes sometimes show unwanted droplets at their ends, depending on the length, rigidity and shape of their fibers. Capillary forces arising from the varying cross-sections of conical fiber tips have been thought to eliminate the droplets. However, these forces may not operate with water, which fills the entire space between the fibers of a brush. Here, we theoretically show that brushes eliminate unwanted droplets with a physical mechanism that is significantly different from a single conical fiber by 'closing' their ends. We analyze the hydrostatics of water in a brush when it is removed from a bath, and we identify the condition under which the end of the brush is closed, emphasizing the roles played by the elastic deformation of the flexible fibers owing to interfacial forces. Moreover, this theory predicts that the volume of water that is captured by brushes is a non-monotonic function of the length of their fibers because the fibers show excluded volume interactions when their ends are 'closed'. This theory may guide the design of liquid-transfer devices that can retain liquids in a controlled manner.
  • Tetsuya Yamamoto, Masao Doi, David Andelman  EPL  112-  (5)  56001  2015/12  [Refereed][Not invited]
     
    We use the Poisson-Boltzmann theory to predict contact angle saturation of aqueous droplets in electrowetting. Our theory predicts that injection of ions from the droplet into its surrounding medium is responsible for the deviation of the apparent contact angle from the Young-Lippmann equation for large applied voltages. The ion injection substantially decreases the Maxwell stress and increases the osmotic pressure at the interface between the two media, leading to saturation of the apparent contact angle. Moreover, we find that the contact angle does not saturate, but only has a broad minimum that increases again upon further increase of the applied voltage, in agreement with experiments. Copyright (C) EPLA, 2015
  • Tetsuya Yamamoto, S. A. Safran  SOFT MATTER  11-  (15)  3017  -3021  2015  [Refereed][Not invited]
     
    We theoretically predict the rate of transcription (TX) in DNA brushes by introducing the concept of TX dipoles that takes into account the unidirectional motion of enzymes (RNAP) along DNA during transcription as correlated pairs of sources and sinks in the relevant diffusion equation. Our theory predicts that the TX rates dramatically change upon the inversion of the orientation of the TX dipoles relative to the substrate because TX dipoles modulate the concentrations of RNAP in the solution. Comparing our theory with experiments suggests that, in some cases, DNA chain segments are relatively uniformly distributed in the brush, in contrast to the parabolic profile expected for flexible polymer brushes.
  • Tetsuya Yamamoto, Masao Doi  NATURE COMMUNICATIONS  5-  4162  2014/06  [Refereed][Not invited]
     
    Polyelectrolyte gel diodes that are double layers of two oppositely charged polyelectrolyte gels, sandwiched by two symmetric electrodes, are emergent ionic devices. These diodes are designed to rectify ion currents with a physical mechanism that is analogous to conventional semiconductor diodes-the asymmetry in the permeability of ions across the interfaces between the two oppositely charged gels. Here we show that polyelectrolyte gel diodes indeed rectify steady currents with a physical mechanism that is very different from conventional diodes by using a simple electrochemical model; electric currents are limited by electrochemical reactions that are driven by potential drops at electrodes and these potential drops markedly change with changing the direction of applied voltages due to the redistribution of non-reactive counterions, leading to rectified ion currents. This concept is relatively generic and thus may provide insight in the physics of analogous ionic and biomimetic systems that show electrochemical reactions.
  • Dawid Szewczyk, Tetsuya Yamamoto, Daniel Riveline  New Journal of Physics  15-  035031:1-22  2013/03/27  [Refereed][Not invited]
  • Tetsuya Yamamoto, Samuel A. Safran  SOFT MATTER  8-  (20)  5439  -5442  2012  [Refereed][Not invited]
     
    We present a theory that predicts that cholesterol molecules phase separate from multicomponent lipid bilayer membranes, but not from monolayers of the same composition. In our model, the tilting of cholesterol molecules in monolayers is not energetically favorable because their exocyclic chains are very short. However, in bilayers, two correlated cholesterol molecules in the opposing leaflets of bilayers can form "dimers'', whose chains are effectively twice as long and can tilt cooperatively. Our theory predicts that the cooperative tilting of these dimers drives the phase separations of cholesterol in bilayers.
  • T. Yamamoto, P. A. Pincus  EPL  95-  (4)  48003: 1-6  2011/08  [Refereed][Not invited]
     
    We predict the collapse of a polyelectrolyte brush grafted on an electrode that is induced by applied electric fields for the limiting cases of low and high salt concentrations. The polyelectrolyte brush collapses locally to screen the charges induced on the electrodes. For low salt concentrations, the height of the polyelectrolyte brush decreases steeply with increasing the voltage between the electrodes because the number of counterions expelled from the brush increases exponentially. However, when the system is in equilibrium with monovalent salts at high concentrations, the brush height decreases almost linearly with increasing the voltage instead of the steep collapse. This is because the voltage drop mainly occurs over the diffuse double layer associated with the distant electrode. Copyright (C) EPLA, 2011
  • Tetsuya Yamamoto, Samuel A. Safran  SOFT MATTER  7-  (15)  7021  -7033  2011  [Refereed][Not invited]
     
    Hybrid lipids (with one saturated tail and one unsaturated tail) have been proposed as agents that can reduce the line tension between domains. We use a liquid crystal model to predict the effect of the degree of unsaturation in the unsaturated tails of hybrid lipids on the miscibility phase diagram and line tension between domains in membranes comprising saturated lipids (with two saturated tails), hybrid lipids, and cholesterol (SHC membranes). In contrast to SHC membranes containing hybrid lipids with a single (or small) degree of unsaturation, for which the phase diagram shows two distinct two-phase regions, SHC membranes containing hybrid lipids with degrees of unsaturation larger than a threshold value exhibit a single two-phase region. This enables hybrid lipids with larger degrees of unsaturation to steadily increase their chain order with decreasing temperature and enhances the reduction of the line tension. This theory predicts that the line tension between domains in SHC membranes is sensitive to the degrees of unsaturation of hybrid lipids.
  • Tetsuya Yamamoto, Dai Taguchi, Takaaki Manaka, Mitsumasa Iwamoto  Molecular Crystals and Liquid Crystals  479-  (1)  13-31  2010/09/22  [Refereed][Not invited]
     
    Monolayers comprised of banana-shaped achiral molecules are modeled taking into account the hard-core repulsive force and electrostatic interaction between constituent molecules and the water surface. The model predicts the achiral-chiral transition of orientational structure along with in-plane nematic ordering during a monolayer compression due to the 2D geometry of monolayers. This model further reveals that in-plane nematic order is established beforehand of the chiral transition since banana-shaped molecules behave as rod-shaped molecules with variable aspect ratio in 2D geometry. It indicates the importance of in-plane nematic order in the achiral-chiral phase transition of monolayers comprised of banana-shaped achiral molecules.
  • Tetsuya Yamamoto, Said Aranda-Espinoza, Rumiana Dimova, Reinhard Lipowsky  LANGMUIR  26-  (14)  12390  -12407  2010/07  [Refereed][Not invited]
     
    The stability of spherical vesicles in alternating (ac) electric fields is studied theoretically for asymmetric conductivity conditions across their membranes. The vesicle deformation is obtained from a balance between the curvature elastic energies and the work clone by the Maxwell stresses. The present theory describes and clarifies the mechanisms for the four types of morphological transitions observed experimentally on vesicles exposed to ac fields in the frequency range from 500 to 2 x 10(7) Hz. The displacement currents across the membranes redirect the electric fields toward the membrane normal to accumulate electric charges by the Maxwell-Wagner mechanism. These accumulated electric charges provide the underlying molecular mechanism for the morphological transitions of vesicles as observed on the micrometer scale.
  • T. Yamamoto, R. Brewster, S. A. Safran  EPL  91-  (2)  28002-1-6  2010/07  [Refereed][Not invited]
     
    We use a liquid-crystal model to predict that hybrid lipids (lipids that have one saturated and one unsaturated tail) can stabilize line interfaces between domains in mixed membranes of saturated lipids, hybrid lipids, and cholesterol (SHC membranes). The model predicts the phase separation of SHC membranes with both parabolic and loop binodals depending on the cholesterol concentration, modeled via an effective pressure. In some cases, the hybrid lipids can reduce the line tension to zero in SHC membranes at temperatures that approach the critical temperature as the pressure is increased. The differences in the hybrid saturated tail conformational order in bulk and at the interface are responsible for the reduction of the line tension. Copyright (C) EPLA, 2010
  • T. Yamamoto, T. Manaka, M. Iwamoto  The European Physical Journal E  29-  (1)  1-8  2009/04/03  [Refereed][Not invited]
     
    The free energy of condensed phase domains in monolayers at the air-water interface has been analyzed by taking into account the surface pressure, line tension, and electrostatic energy due to the normal and in-plane spontaneous polarization. We found that this free energy was reduced to the sum of the Frank elastic energy and anisotropic line tension, which were used to reproduce the shapes of domains in fatty acid monolayers, in the limit of small orientational deformation. Domains in monolayers are interesting systems as a meeting point between the physics of liquid crystals and electrostatics.
  • Rumiana Dimova, Natalya Bezlyepkina, Marie Domange Jordo, Roland L. Knorr, Karin A. Riske, Margarita Staykova, Petia M. Vlahovska, Tetsuya Yamamoto, Peng Yang, Reinhard Lipowsky  SOFT MATTER  5-  (17)  3201  -3212  2009  [Refereed][Not invited]
     
    This review focuses on the effects of electric fields on giant unilamellar vesicles, a cell-size membrane system. We describe various types of behavior of vesicles subjected to either alternating fields or strong direct current pulses, such as electrodeformation, -poration and -fusion. The vesicle response to alternating fields in various medium conditions is introduced and the underlying physical mechanisms are highlighted, supported by theoretical modeling. New aspects of the response of vesicles with charged or neutral membranes, in fluid or gel-phase, and embedded in different solutions, to strong direct current pulses are described including novel applications of vesicle electrofusion for nanoparticle synthesis.
  • Tetsuya Yamamoto, Takahiro Aida, Takaaki Manaka, Mitsumasa Iwamoto  Colloids and Surfaces A: Physicochemical and Engineering Aspects  321-  (1-3)  151  -157  2008/05/15  [Refereed][Not invited]
     
    Domain shape transition of racemic dipalmitoylphosphatidylcholine (DPPC) monolayers indicates the possibility of chiral phase separation in a racemic domain. We have analyzed the chiral phase separation in a racemic domain taking into account the surface pressure, line tension, electrostatic energy due to the spontaneous polarization and electric quadrupole density, and mixing entropy to clarify the mechanism of shape transition of racemic monolayer domains. We derive the condition of the chiral phase separation in an analogous form to the Bragg-Williams theory, and predict that chiral phase separation occurs as the spontaneous polarization in monolayer normal increases in agreement with our experimental results. The electric quadrupole density plays an important role in the chiral phase separation of a racemic monolayer domain. © 2008 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Dai Taguchi, Martin Weis, Takaaki Manaka, Mitsumasa Iwamoto  JOURNAL OF CHEMICAL PHYSICS  128-  (20)  204706  2008/05  [Refereed][Not invited]
     
    The formation mechanism of the shapes of condensed phase domains in monolayers at the air-water interface was investigated taking into account the surface pressure, line tension, and electrostatic energy due to the spontaneous polarization generated in normal and in-plane direction. By deriving the shape equation of monolayer domains as the mechanical balance at the domain boundary, we found that the electrostatic energy contributes to the shape equation as electrostatic Maxwell stress. Development of a cusp from condensed phase domains of fatty acid monolayers, which has been experimentally observed, was analyzed by the shape equation. It was found that the development of a cusp originated from the strong Maxwell stress, which was induced by the non-uniform orientational distribution in the fatty acid domain, and that cusped shapes gave a minimum of the free energy of the domain. It demonstrates that the shape equation with Maxwell stress, which is derived in the present study, is useful to study the formation mechanism of the shapes of condensed phase domains in monolayers. (C) 2008 American Institute of Physics.
  • T. Yamamoto, T. Manaka, M. Iwamoto  Thin Solid Films  516-  (9)  2660-2665  2008/03/03  [Refereed][Not invited]
     
    The electrostatic energy in a dipolar monolayer domain with orientational deformation has been analyzed for the study of monolayer shapes. It is demonstrated that a monolayer domain is viewed as a system of interacting induced electric charges distributed at the inside and boundary of a domain. Since induced charge distribution is determined by orientational deformation and domain shape, the electrostatic energy is represented in the form of Frank splay elastic energy with spontaneous splay and curvature elastic energy with spontaneous curvature.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto  JOURNAL OF CHEMICAL PHYSICS  126-  (12)  125106  2007/03  [Refereed][Not invited]
     
    Shapes and orientational deformation of a lipid monolayer domain have been analyzed taking into account the surface pressure, line tension, and electrostatic energy due to the spontaneous polarization and electric quadrupole density generated from the domain. The electrostatic energy due to the generation of spontaneous polarization and electric quadrupole density contributes to the formation of orientational deformation as the Frank elastic energy and spontaneous splay, respectively. Since the orientational configuration of the electric quadrupole density and in-plane spontaneous polarization is dependent on the molecular chirality, and the positive splay deformation of electric quadrupole density is induced by the spontaneous splay, the bending direction of in-plane spontaneous polarization depends on the chirality of constituent lipids. The electrostatic energy due to the in-plane spontaneous polarization is dependent on the orientational deformation of in-plane spontaneous polarization, and bends the domain shape towards the bending direction of the in-plane spontaneous polarization. It has been demonstrated that the chiral dependence of the domain shapes of lipid monolayers originated from the chiral dependence of orientational structure due to the electric quadrupole density.
  • Robert Wagner, Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto  Colloids and Surfaces A: Physicochemical and Engineering Aspects  284-285-  147  -153  2006/08/15  [Not refereed][Not invited]
     
    The dielectric polarizations, i.e. spontaneous, linear, and second order non-linear polarizations, generated from Langmuir monolayers comprised of rod-shaped molecules were analyzed, and represented as functions of the orientational order parameters S1, S2, and S3 (Sn = 〈 Pn (cos θ) 〉, θ: molecular tilt angle, 〈 〉: thermodynamic average, Pn (cos θ): Legendre polynomial of n th order). It has been shown that the Maxwell displacement current (MDC), Brewster angle reflectometry (BAR), and optical second harmonic generation (SHG), which are attributed to the spontaneous, linear, and non-linear polarization, respectively, are capable of detecting the orientational order parameter S1, S2, and S3 of Langmuir monolayers. An experiment using the MDC-BAR-SHG was conducted on Langmuir monolayers comprised of 4-octyl-4′-cyanobiphenyl rod-shaped molecules. It is shown that the MDC-BAR-SHG measurements are useful to investigate the orientational structure of Langmuir monolayers. © 2005 Elsevier B.V. All rights reserved.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto  Colloids and Surfaces A: Physicochemical and Engineering Aspects  284-285-  154-160  2006/08/15  [Refereed][Not invited]
  • Tetsuya Yamamoto, Takaaki Manaka, Dai Taguchi, Mitsumasa Iwamoto  JOURNAL OF CHEMICAL PHYSICS  125-  (3)  034704  2006/07  [Refereed][Not invited]
     
    Chirality of monolayers comprised of banana-shaped achiral molecules at an air-water interface was investigated theoretically, and a forming mechanism of chiral structure as an assembly of achiral molecules was argued. A model of such monolayers was constructed taking into account the short-range repulsive interaction between constituent banana-shaped achiral molecules, and the free energy density functional of the model was derived as a generalization of Williams-Bragg approach. It was predicted that chiral symmetry breaking occurs by monolayer compression, where two-dimensional characteristics of monolayers at an interface plays an important role in the formation of chiral structure by banana-shaped achiral molecules.
  • R Wagner, T Yamamoto, T Manaka, M Iwamoto  REVIEW OF SCIENTIFIC INSTRUMENTS  76-  (8)  083902  2005/08  [Refereed][Not invited]
     
    An experimental instrument has been developed utilizing Brewster angle reflectometry and Maxwell displacement current (MDC) measurement techniques, which are ascribed to the linear and spontaneous polarization, respectively, to investigate orientational order of Langmuir monolayers at an air-water interface. This system has been demonstrated to be sensitive in detecting the orientational order parameters S-1 and S-2 simultaneously [S-n is defined as the thermodynamic average of Legendre polynomials of nth rank, S-n = < P-n(cos theta)>]. Using this system in conjunction with a previously established system utilizing second harmonic generation and MDC, which is capable of detecting the orientational order parameters S-1 and S-3 simultaneously, all three orientational order parameters S-1, S-2, and S-3 can be obtained for Langmuir monolayers. An experiment using the newly developed instrument was conducted on a monolayer comprised of 4-octyl-4'-n-cyanobiphenyl (8CB) molecules to demonstrate the capability of detecting the orientational order parameters S-1 and S-2 during monolayer compression. (c) 2005 American Institute of Physics.
  • T Yamamoto, D Taguchi, T Manaka, M Iwamoto  JOURNAL OF CHEMICAL PHYSICS  122-  (16)  164703  2005/04  [Refereed][Not invited]
     
    The flexoelectric effect of 4-heptyloxy-4'-cyanobiphenyl (70CB) monolayers at the air-water interface is studied by Maxwell displacement current (MDC) and optical second harmonic generation measurements. Though MDC was expected to increase during the compression of 70CB monolayers in L-2/L-2(') phase from the MDC theory developed previously, decrease of MDC was detected in these phases. This abnormalous phenomenon is found to be due to the quench of flexoelectric effect by the flow orientation of monolayers. (c) 2005 American Institute of Physics.
  • Tetsuya Yamamoto, Atsushi Tojima, Takaaki Manaka, Mitsumasa Iwamoto  Chemical Physics Letters  378-  (3-4)  428-433  2003/09/05  [Refereed][Not invited]
     
    The flow behavior of 4-heptyloxy-4'-cyanobiphenyl (7OCB) monolayer is studied during compression and expansion by Maxwell displacement current (MDC) and second harmonic generation (SHG) measurement. It is found that in-plane molecular flow induced reorientation of 7OCB monolayer in L<sub>2</sub> and L<sub>2</sub>' phases of the monolayer is reversible. It is concluded that the MDC-SHG method is available for exploring the flow behavior of monolayers.
  • Tetsuya Yamamoto, Takaaki Manaka, Mitsumasa Iwamoto  Chemical Physics Letters  368-  (3-4)  370  -376  2003/01/17  [Refereed][Not invited]
     
    The electrostatic charge effect on the orientational distribution of rod-like polar molecules at the air-water interface is analyzed taking into account the induced charge on electrode suspended in the air. The first order orientational order parameter S1 is found to change as the electrode approaches monolayers, and approximately expressed as S1 = S1 0 + A*(2S1 02 - 3S1 02 + 1)/3, where A* characterizes the effect of electrode and Si 0 (i = 1,2) represents orientational order parameters in the absence of suspended electrode. The molecular area giving the maximum deviation of S1 from S1 0 decreases as the interaction between molecules and water surface increases, but it is independent of the position of electrode. © 2002 Elsevier Science B.V. All rights reserved.


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