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吉川研究室主催

Time 2/8(Fri.) 15:00-16:30
Place 理学部5号館413号室 (Kyoto Univ. Science Bldg. V, Rm. 413)
Speaker Dr. Zoher Gueroui
Affiliation Ecole Normale Superieure, Department of Chemistry
Title Spatiotemporal control of microtubule nucleation and assembly using magnetic nanoparticles
Abstract Cell fate decisions and cellular functions are dictated by the spatiotemporal dynamics of molecular signaling networks. However, the techniques available to examine the spatiotemporal properties of these intracellular processes remain limited. Here we report a method to artificially control in space and time such signaling pathways using magnetic nanoparticles conjugated to key regulatory proteins. Using a magnetic field, we modulate the collective behavior of GTPase signaling proteins involved in specifying the morphogenetic properties of the cell’s cytoskeleton. This allows us to design a bio-inspired switch that triggers microtubule nucleation and stabilization. This method demonstrates how bioactive nanoparticles can be used to engineer both signaling networks and spatial self-organization.
Time 12/14(Fri.) 10:30-12:00
Place 理学部5号館401号室 (Kyoto Univ. Science Bldg. V, Rm. 401)
Speaker Ass.Prof. Jens Paasche
Affiliation The University of Potsdam
Title Aggregation behavior of cationic Surfactant and Interaction with DNA
Abstract First part deals with analysis of azobenzene-containing trimethylammonium bromide cationic surfactants C4-Azo-OCnTMAB (for different spacer length n) by UV/vis absorption spectra. Additionally NaCl concentrations were varied and it is interesting how the onset of aggregation will change. Goal here is to show that the surfactants stack in a certain arrangement and build higher structures. These aggregates are to be further investigated through light scattering. Through Dynamic light scattering (DLS) there has been made investigations of the size distribution for C4-Azo-OC6TMAB surfactant above aggregation concentration. Aggregation sizes from 100-200nm could be found. The consecutive part introduces the behavior of surfactant and DNA: A process of initially compacted DNA to an light-induced decompaction will be presented by analysis of absorption measurements for this DNA-surfactant complex.
Time 11/21(Wed.) 10:30-12:00
Place 理学部5号館北棟第二講義室 (Kyoto Univ. Science Bldg V, North Bldg, #2 Lecture Room)
Speaker Prof. Valentina Vasilevskaya
Affiliation Nesmeyanov Institue of organolelement compounds Russian Academy of Sciences
Title Unusual structures of amphiphilic macromolecules: computer modelling.
Abstract Many macromolecules are amphiphilic on a level of individual monomer unit in the meaning that each monomer unit contains both hydrophobic and hydrophilic groups. The duality of the monomer units results in their simultaneous affinity and incompatibility with both polar and organic solvents. Computer simulations of the macromolecules, containing amphiphilic monomer units were carried out by us. It was shown, that amphiphilicity on a scale of individual monomer unit leads to dramatic complication and enrichment of the set of possible conformational transitions, compared to this of ordinary homopolymer macromolecules. In case of amphiphilic macromolecules the coil-to-globule transition normally goes through a stage of necklace conformations. The globules of such macromolecules have the complex core-shell structure: the interiors consist of hydrophobic units, while the outer shell is composed by hydrophilic units. The details of the structure depend considerably on the rigidity of the polymer chain. The flexible chains form cylindrical globules with blob ordering. The rigid chains are compacted into toroidal or collagen-like structures, in which macromolecule folds several times, and different chain branches intertwine around each other. In concentrated solutions upon worsening the solvent quality, the flexible macromolecules condense into individual globules, while the rigid macromolecules tend to aggregate with formation of braid fibrillar-like complexes. The number of chains in the braid cross-section varies along the braid, the total length of braid is much higher than the contour length of chain and as a result all macromolecules in the simulation cell could be assembled into the only fibrillar-like complex. A way was proposed to employ such macromolecules in simple surface recognition systems.
Time 10/26(Fri.) 10:30-12:00
Place 理学部5号館401号室 (Kyoto Univ. Science Bldg. V, Rm. 401)
Speaker Prof. Marie Pierre Krafft
Affiliation SOFFT Team, Institut Charles Sadron (ICS, UPR CNRS 22) Universite de Strasbourg, 23 rue du Loess, Strasbourg (France)
Title Large organized surface domains self-assembled from non-polar amphiphiles
Abstract The discovery that Langmuir-Blodgett (LB) monolayers of small CnF2n+1CmH2m+1 (FnHm) diblock molecules (e.g. F8H16) consist of ordered arrays of unusually large (~30-60 nm), discrete self-assembled surface domains (or hemimicelles, Figure), and not the presumed continuous, featureless film, had not been anticipated. These surface micelles differ in several essential ways from all previously reported or predicted molecular surface aggregates: they self-assemble spontaneously, even at zero surface pressure, depending solely on a critical surface concentration; are very large (~100 times the length of the diblock); involve thousands of molecules (orders of magnitude more than classical micelles); yet are highly monodisperse; self-organize in close-packed hexagonal patterns (2-dimensional crystals); their size is essentially independent from pressure; they do not coalesce, and are unexpectedly sturdy for soft matter (persisting even beyond surface film collapse). Large surface micelles were observed by us and others for numerous diblocks, using LB transfer, spin-coating, dip-coating techniques, or expulsion from mixed monolayers, and on diverse supports, establishing that hemimicelle formation and ordering are intrinsic properties of (perfluoroalkyl)alkanes. Notably also, they involve “incomplete” surfactants with limited amphiphilic character, further illustrating the outstanding capacity for perfluoroalkyl chains to promote self-assembly and interfacial film structuring. X ray reflectivity determined a perfluoroalkyl-chain-up orientation. Theoretical investigations assigned self-assembly and hemimicelle stability to electrostatic dipole-dipole interactions at the interface between Fn- and Hm-sub-layers. Grazing-incidence small-angle X-ray scattering (GISAXS) data collected directly on the surface of water demonstrated unambiguously the presence of surface micelles in monolayers of diblocks, prior to LB transfer for AFM imaging. An almost perfect 2-dimensional crystal (12 assignable diffraction peaks; Figure), was characterized, definitely establishing that self-assembly, and regular nanopatterning, were not caused by transfer or induced by the solid support, also providing the first direct identification of surface micelles on water, and also of such large-size domains using GISAXS. Revisiting Langmuir film compression behavior after we realized that it actually was a compression of nanometric objects, led to further unanticipated observations: compression could be pursued far beyond the documented film “collapse”, resulting, (e.g. for F8H20) in the building-up of one, and eventually two, superimposed less-organized bilayers of diblocks on top of the initially formed monolayer of hemimicelles. Remarkably, the latter withstood the final irreversible collapse of the composite films. “Gemini” tetrablocks, di(FnHm), with two Fn-chains and two Hm-chains, provided two superposed layers of discrete micelles (Figure, right), apparently the first example of thin films made of stacked discrete self-assembled nanoobjects. Decoration of solid surfaces with domains of predetermined size of these small “non-polar” molecules is straightforward. Initial examples of applications include deposition of metal dots and catalytic oxidation of CO, and use for nanopatterning of SiO2 films.
Time 10/10(Wed.) 10:30-12:00
Place 理学部5号館北棟第二講義室 (Kyoto Univ. Science Bldg V, North Bldg, #2 Lecture Room)
Speaker Mr. Paul Brown
Affiliation School of Chemistry, University of Bristol Cantock’s Close, Bristol BS8 1TS (UK)
Title Magnetic Surfactants
Abstract Recently, a new class of surfactants have been discovered that respond to a magnetic field. These magneto-responsive surfactants are based on common cationic surfactants with metal complex anions, which, because they contain high effective concentrations of metal centres, allows their physico-chemical properties (hydrophbicity, electrical conductivity, etc) to be controlled non-invasively and reversibly by external magnetic fields. It has been shown that the controlled conjugation of these surfactants to DNA (and other biomolecules) is possible, allowing for manipulation in solution simply by switching "on" and "off" a magnetic field. Further to this it has been demonstrated that magnetic emulsions and microemulsions can be readily generated with suggested applications from environmental cleanup to targeted drug delivery. Finally, a combination of small-angle neutron scattering and SQUID magnetometry has shown that magnetic microemulsions (nanoparticle-free ferrofluids) can act as tunable nanomagnets, providing a new method to bridge the gap in our understanding of magnetic behaviour on an intermediate scale between molecular and solid-state bulk objects."
Time 7/5(Thu.) 15:00-16:30
Place 理学部5号館413号室 (Kyoto Univ. Science Bldg. V, Rm. 413)
Speaker Dr. Ken-ichiro Kamei
Affiliation Assistant Professor, Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University
Title Artificial regulatory microenvironments (niche) for controlling cell function
Abstract Microenvironmental cues (i.e., soluble factors, extracellular matrices (ECMs) and cell-cell interactions) have critical roles for determining stem cell fates, such as self-renewal, differentiation, survival and apoptosis. Conventional macro-scale techniques can only provide limited controls of microenvironments over cells, therefore, there is a current lack of tools to perform accurate and effective procedures for regulating stem cells. To meet this urgent need, we propose to develop micro- and nanofabrication technologies in combination with material sciences to create artificial microenvironments for a better control of cell function, including human pluripotent stem cells (hPSCs). In my presentation, I will present our researches on i) nanofibrous substrates as cellular scaffolds for hPSC defined culture system for long-term periods, and ii) microfluidic platforms for creating microenvironments to control hPSC functions.
Time 6/29(Fri.) 10:30-12:00
Place 理学部5号館401号室 (Kyoto Univ. Science Bldg. V, Rm. 401)
Speaker 船山 典子 准教授 (Assoc. Prof. Noriko Funayama)
Affiliation 京都大学大学院 理学研究科 生物科学専攻 生物物理教室 分子発生学講座
Title 基本単位を組み上げて自発的に複雑な秩序構造を形成する全く新しいモデル:カイメン骨片骨格形成
Abstract  カイロウドウケツの骨片骨格標本や、ヘッケルのカイメン骨片骨格の美しいスケッ チを見たことがあるだろうか?多様な形の「骨片」というパーツを配置し組み上げら れるこの秩序立った骨片骨格構造は100年以上も私たちを魅了して来た。しかし、 「体を支える建築物」とも言える骨片骨格が、カイメンの体の中でどのように構築さ れるかは全く謎のままである。
 私たちは淡水性のカワカイメンの無性生殖である、「数千個の幹細胞のみの集団 からの個体形成過程」を用い、また骨片の生体内での可視化を工夫し、成熟した骨片 がダイナミックに運ばれて1段目においてはほぼ等間隔な位置に立てられること、こ の骨片を運ぶ大工さんとも言うべき特殊な細胞の存在を見いだした。細胞が骨片とい う単位をどこに配置するべきかを決め、1つ1つ骨片を組みあげ、立体的な秩序構造 を構築するこの機構には、単純な反応拡散だけでは説明出来ない、おそらくは体内空 間の感知、刻々と拡張する体を支える為の機械的な力の感知などを含む仕組みが働い ているのではないかと考えるに至っている。この様に骨片骨格形成解析の手がかりを つかみ、始めの一歩を踏み出した取り組みについて紹介する。物理学的な視点から活 発な助言や議論をいただければ幸いです。
Time 6/1(Fri.) 10:30-12:00
Place 理学部5号館401号室 (Kyoto Univ. Science Bldg. V, Rm. 401)
Speaker Prof. Chwen-Yang Shew
Affiliation Department of Chemistry, College of Staten Island, City University of New York, Staten Island, NY 10314, USA
Title Elucidation of the role counterions on the interaction between macroions: Electrostatic interaction and beyond
Abstract Like-charge attraction remains one of the most intriguing mysteries in science, and revealing its origin is expected to generate a great impact on numerous communities including biophysics, nanomaterials and polymer sciences, etc. This phenomenon is referred to the condition when like-charge macroions induce attraction in solution.
Such a concept is somewhat counterintuitive because like-charge objects are supposed to repel each other. The unique role of like-charge attraction lies in the fact that it yields a driving force to induce self-assembly processes. In biological systems, like-charge attraction is ubiquitous partly because the majority of biomolecules are macroions, for instance aggregation of actin filaments, in the form of bundles. Besides, nano-scaled polyoxometalates (polyanions) self-assemble into a much larger hollow sphere with a near uniform size while the solvent dielectric constant is decreased.
Unlike other aggregation processes with infinity aggregate size, like-charge aggregates share a common feature, that is, their aggregate size becomes leveled-off at a finite size. One scenario for finite aggregate size is attributed to the survival charge of aggregates that prevents charged aggregates from growing. Through our studies by using integral equation theories and simulations, we suggest that the specific binding between counterion and macroion may play an important for like-charge attraction. Incorporating specific binding into models allows us to better understand the solution structure of short DNA segments and polyoxometalates. Furthermore, changing the specific binding affinity from macroions to their aggregates manifests a possible mechanism to account for the finite aggregate growth.
Time 5/23(Wed.) 13:30-14:30
Place 理学部5号館525号室 (Kyoto Univ. Science Bldg. V, Rm. 525)
Speaker Mr. Michael Benzaquen
Affiliation PCT Laboratory UMR Gulliver 1083 CNRS/ESPCI, Paris, France
Title On Capillary Gravity Waves
Abstract Water waves are both fascinating and of great practical importance. For these reasons, they have attracted the attention of scientists and engineers for many decades. Water waves can for instance be generated by the wind blowing over the ocean, by a moving ship on a calm lake, or simply by throwing a pebble into a pond. Their propagation at the surface of water is driven by a balance between the liquid inertia and its tendency, under the action of gravity or of surface tension (or a combination of both in the case of capillary gravity waves), to return to a state of stable equilibrium. We here look into the theoretical features of the capillary gravity waves created at the waterair interface by a small external perturbation (pressure distribution) moving at constant velocity along a linear trajectory. This theoretical study was justified by a substantial experimental work on the same topic. Such experiments are notably led by Christophe Clanet at Ecole Polytechnique (France) and Victor Steinberg at Weizmann Institute (Israel). Firstly, we consider the case of a two-dimensional perturbation and assume that a depthdependent current is initially present in the fluid. Within the framework of linear wave theory, we derive a general expression of the wave resistance experienced by the perturbation as a function of the current profile in the case of an inviscid fluid. We then analyze and discuss in details the behavior of the wave resistance in the particular case of a linear current, a valid approximation for some wind generated currents.
Secondly, we focus on the three-dimensional case in which the pressure distribution is symmetrical about a point. We calculate the wave resistance experienced by the perturbation as a function of its size (compared to the capillary length). In particular, we analyze how the amplitude of the jump occurring at the minimum phase speed c depends on the size of the perturbation, including liquid density, the water-air surface tension, acceleration due to gravity). We also show how for pressure distributions broader than a few capillary lengths, thewave resistance in the particular case of pure gravity waves is progressively recovered.
Time 4/9(Mon.) 16:00-17:30
Place 理学部5号館401号室 (Kyoto Univ. Science Bldg. V, Rm. 401)
Speaker Prof. Arun Yethiraj
Affiliation Department of University of Wisconsin - Madison
Title Self-assembly in complex fluids
Abstract The self-assembly of molecules into nano-structured materials is a fascinating process because small changes in intermolecular interactions can have a large impact on the final mesoscopic structures. An interesting goal is the directed self-assembly of molecules where the chemical nature of the molecules is altered to drive the assembly into specific nanostructures. In this talk I will discuss two classes of molecules: -peptides and Gemini surfactants. In the former, some sequences assemble into long hollow cylinders, but other similar sequences do not. The latter form lyotropic liquid crystalline phases. Using computer simulation I will show that interactions between three molecules play an important role in the assembly of -peptides and electrostatic interactions play an important role in the self-assembly of Gemini surfactants. Both systems show promise for chemistry directed self-assembly.

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セミナー主催研究室について

京都大学大学院 理学研究科  物理学第一教室 
吉川研究室



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