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A02 SAITO, Kazuya |Proposed Research Projects (2016-2017)

Paper | Original Paper

2017

*Kazuya Saito, Takaaki Ikeda, Yasuhisa Yamamura, Hideki Saitoh, Mafumi Hishida, Yutaro Kobayashi, Takeshi Fujita, and Junji Ichikawa,
Cell-quintupling: Structural phase transition in a molecular crystal, bis(trans-4-butylcyclohexyl)methanol,
The Journal of Chemical Physics 146, 074503 (2017).

[Summary] Astructural phase transition at 151.6Kof 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.

*Kazuya Saito, Mafumi Hishida, Kent Koike, Shigenori Nagatomo, and Yasuhisa Yamamura,
X-ray study of molecular association in alcohols having bulkysubstituents,
Chemical Physics Letters 673, 74-77 (2017).

[Summary] The formation of globular associate on cooling, which was previously claimed on the basis of small dielectric constant, is supported through measuring X-ray scattering from dicyclohexylmethanol (DCHM). Radial distribution function of the DCHM molecules exhibits strong temperature dependence between 65 ℃ and 130 ℃ in contrast to a little change in that of tricyclohexylmethanol (TCHM), which is similar to DCHM but essentially non-associating in experimental conditions (95–160℃).

2016

*Kazuya Saito, Yasuhisa Yamamura, Yohei Miwa, and Shoichi Kutsumizu,
A structural model of the chiral Im3m cubic phase,
Physical Chemistry Chemical Physics 18, 3280-3284 (2016).

[Summary] Assuming the twisted arrangement of rodlike molecules as the origin of the chirality as in the existing model, a new model of the molecular arrangement in the cubic "Im3m" phase is proposed. The adoption of a basic structure different from that assumed in the existing model resolves most difficulties of the model including the random placement of defects concerning the sense of twist.

Mafumi Hishida, Ryuta Yanagisawa, Hatsuho Usuda, Yasuhisa Yamamura, and *Kazuya Saito,
Communication: Rigidification of a lipid bilayer by an incorporated n-alkane,
Journal of Chemical Physics 144, 041103 (2016).

[Summary] Towards a greater understanding of the effects of organic molecules in biomembranes, the effects of a flexible alkyl chain on the morphologies of phospholipid vesicles are investigated. Vesicles composed of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and tetradecane (TD) rupture during cooling from the liquid–crystalline phase to the gel phase. A model calculation based on the size-dependent rupture probability indicates the bending rigidity of the bilayer in the gel phase is more than 10 times higher than that without TD, resulting in the rupture arising from elastic stress. The rigidification is caused by the denser molecular packing in the hydrophobic region by TD. There is little change of the rigidity in the liquid–crystalline phase. Additionally, the rigidification produces a characteristic morphology of the ternary giant vesicles including TD. Reported thermal behaviors imply that molecules with a linear and long alkyl chain, such as trans fatty acids, universally exhibit a similar effect, in contrast to rigid and bulky molecules, such as cholesterol.