Lamellar-lamellar phase separation in phospholipid/salt/water system(Poster session 1, New Frontiers in Colloidal Physics : A Bridge between Micro- and Macroscopic Concepts in Soft Matter)

この論文は国立情報学研究所の電子図書館事業により電子化されました。リン脂質と一価塩を一定の割合で混合して形成したマルチラメラベシクルにおいて観測されるラメラーラメラ相分離(別の面間隔を持つ2種類のラメラ構造が共存する)の要因を明らかにするため、DPPCとNaClの混合系でのそれぞれのラメラ相の面間隔の温度変化に対する応答を、X線小角散乱をもちいて観測した。その結果、この相分離は一価塩濃度の濃いラメラ相と薄いラメラ相に相分離することにより引き起こされることが示唆された

擬似非平衡場としての生体膜：膜上での分子拡散と選択的分子集積

科学研究費助成事業 研究成果報告書：挑戦的萌芽研究2015-2017課題番号 : 15K1354

Phase separation of a ternary lipid vesicle including n-alkane: Rugged vesicle and bilayer flakes formed by separation between highly rigid and flexible domains

We investigate the phase separation of a ternary lipid bilayer including n-alkane and construct the ternary phase diagram. When a certain proportion of a long n-alkane is mixed with a binary mixture of lipids, which exhibit the disordered liquid-crystalline phase and the ordered gel phase at room temperature, we observed the characteristic morphology of bilayers with phase separation. The ordered bilayer forms flat and rigid domains, which is connected or rimmed with flexible domains in the disordered phase. The asymmetric emergence of the phase separation region close to the ordered phase side is interpreted based on the almost equal distribution of the n-alkane to the ordered and disordered phase domains

Electrostatic double-layer interaction between stacked charged bilayers

The inapplicability of the DLVO theory to multilayered anionic bilayers is found in terms of the co-ion-valence dependence of the lamellar repeat distance. Most of the added salt is expelled from the interlamellar space to the bulk due to the Gibbs-Donnan effect on multiple bilayers with the bulk. The electrostatic double-layer interaction is well expressed by the formula recently proposed by Trefalt. The osmotic pressure due to the expelled ions, rather than the van der Waals interaction, is the main origin of the attractive force between the bilayers

Orders Exhibited by Ensemble of Headless Spins Preferring Twisted Alignment: Phase Diagram of Extended Maier–Saupe Model on Simple Cubic Lattice

The effect of the preference for nonparallel alignment without a preferred twist sense of neighboring headless spins is examined through computer simulations on extended Maier–Saupe models on the simple cubic lattice with/without next-nearest-neighbor interactions. Phase diagrams containing four phases are constructed for a varying degree of the preference for the local twist and for a strength of the next-nearest-neighbor interaction. It is shown that the preference for the local twist brings about not only the instability for the nematic (uniaxial) order but also that for a spatial order to reduce the frustration arising from the local twist. The next-nearest-neighbor interaction can produce even a weak spatial order of local chirality. The results are discussed in relation to the formation of a liquid crystalline gyroid phase and chiral phases in ensembles consisting of antispindle molecules that are axially symmetric and achiral

Reassessment of structure of smectic phases: Nano-segregation in smectic E phase in 4-n-alkyl-4′-isothiocyanato-1,1′-biphenyls

Based on new diffraction data from aligned samples of smectic E (SmE) phase of 4-n-alkyl-4′-isothiocyanato-1,1′-biphenyls, systematics against the alkyl chain length n is analyzed. In order to perform the analysis, the molecular form factor approximated by a box-shaped distribution is calculated while taking the rounding of the distribution at corners into account. The analysis clearly shows the nano-segregated layered structure, which does not fit to the traditional structural view of SmE phase but does fit to the model the present authors proposed recently. Some implications of this conclusion are discussed in relation to the importance of the molten state of alkyl chains in most of real mesogens revealed previously through thermodynamic analyses

Cell-quintupling: Structural phase transition in a molecular crystal, bis(trans-4–butylcyclohexyl)methanol

A structural phase transition at 151.6 K of the title compound [bis(trans-4–butylcyclohexyl)methanol] is examined by X-ray diffraction crystallography, Fourier-transform infrared spectroscopy, and adiabatic calorimetry. A general consideration on possible superstructures indicates that a single modulation wave is sufficient to drive this cell-quintupling transition. The entropy of transition determined calorimetrically indicates that two conformations are dominant in the room-temperature phase in contrast to the fivefold disorder expected from the structure of the low-temperature phase

リン シシツ ノ カイソウテキ コウゾウ ケイセイ : シシツマク ノ ネツリキガク オヨビ マク ショウホウ ケイセイ カテイ ノ ソクドロン

京都大学0048新制・課程博士博士(理学)甲第14374号理博第3371号新制||理||1494(附属図書館)UT51-2009-D86京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 吉川 研一, 教授 山本 潤, 教授 太田 隆夫学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

The bending rigidity of lipid bilayers in the anomalous swelling regime determined by neutron spin echo(Poster session 2, New Frontiers in Colloidal Physics : A Bridge between Micro- and Macroscopic Concepts in Soft Matter)

この論文は国立情報学研究所の電子図書館事業により電子化されました。人工リン脂質が水中で形成するラメラ構造は、リン脂質分子の膜内でのpackingの違いにより、温度上昇に応じてゲル相から液晶相に転移する。そしてDMPCやDPPCなどのリン脂質においては、ゲル相/液晶相の転移点直上において膜間距離が増大する「異常膨潤」の現象が見られることが知られていた。今回はその異常膨潤の要因を調べるため、中性子スピンエコー法を用いて二重膜の曲げ弾性係数の変化を調べた。その結果、膜間距離が広がるに従って膜が堅くなる事が分かった。これは、膜が柔らかくなることにより立体斥力が増大して膜間距離が広がる、と言うこれまで考えられていた描像に反する結果となっている。The origin of anomalous swelling in multilamellar vesicles of phospholipids upon approaching the main transition is still a matter of dispute. From the recent small-angle X-ray scattering experiment on DMPC, the decrease of the bending modulus of the lipid bilayers is confirmed to be the origin of the anomalous swelling ; this would increase undulations of lipid bilayers and would increase the steric repulsion between bilayers. However, nobody has any ideas to explain the microscopic origin of the decrease of bending modulus near the main transition so far

13. Spontaneous formation of phospholipid giant vesicles(poster presentation,Soft Matter as Structured Materials)

この論文は国立情報学研究所の電子図書館事業により電子化されました。生体膜を主に形づくるリン脂質は、水中でベシクル構造をとる。特に大きさが1μmを超えるものをgiant vesicle(GV)といい、細胞膜モデルなどとして盛んに応用されている。GVを効率的に生成する方法の一つとして静置水和法がよく知られているが、この方法でなぜ自発的にGVが形成されるのか、そのメカニズムは明らかではなかった。本研究では、静置水和法で用いられるリン脂質Dry Filmの構造に着目し、相の違いによる形態の違いとGV形成に与える影響を調べた。これにより、GVの形成メカニズムに関して重要な知見を得た