Publications

Isala Dueramae, Shingo Fukuzawa, Naoki Shinyashiki, Shin Yagihara, *Rio Kita,
Dynamics of amyloid-like aggregation and gel formation of hen egg-white lysozyme in highly concentrated ethanol solution,
Journal of Biorheology 31, 21-28 (2017).

[Summary] We investigated the mechanisms of amyloidlike aggregation and gel formation in hen egg-white lysozyme (HEWL) in a mixed solvent comprising 90% v/v ethanol in water using dynamic light scattering (DLS) and circular dichroism CD. The mechanism of HEWL in ethanol aqueous solution is interpreted into three stages as: (I) denaturation of HEWL; (II) elongation of amyloid fibrils composed of β-sheet-rich HEWL by lateral aggregation; and (III) gel formation due to the creation of junctions in amyloid fibrils. The transformation of sol to gel can be confirmed by: (1) the oscillation behavior and the rapid increase in the intensity of scattered light; (2) the power-law behavior of the correlation function of scattered light g(2)(t); (3) the appearance of a long-time tail in the distribution function of the decay time G(τ); and (4) the beginning of the reduction in initial amplitude in g(2)(t). The gelation rate was strongly dependent on the protein concentration. The estimated rod length of the amyloid fibrils increased significantly over time. Scanning electron microscopy (SEM) performed on the formation of fibrils in the HEWL gels revealed that the structure was highly heterogeneous, with areas characterized by dense fiber networks interspersed with loose network areas.

Doreen Niether, Tsubasa Kawaguchi, Jana Hovancova, Kazuya Eguchi, Jan K. G. Dhont, *Rio Kita, and *Simone Wiegand,
Role of hydrogen bonding of cyclodextrin-drug complexes probed by thermodiffusion,
Langmuir 33, 8483-8492 (2017).

[Summary] Temperature gradient-induced migration of biomolecules, known as thermophoresis or thermodiffusion, changes upon ligand binding. In recent years, this effect has been used to determine protein−ligand binding constants. The mechanism through which thermodiffusive properties change when complexes are formed, however, is not understood. An important contribution to thermodiffusive properties originates from the thermal response of hydrogen bonds. Because there is a considerable difference between the degree of solvation of the protein−ligand complex and its isolated components, ligand-binding is accompanied by a significant change in hydration. The aim of the present work is therefore to investigate the role played by hydrogen bonding on the change in thermodiffusive behavior upon ligand-binding. As a model system, we use cyclodextrins (CDs) and acetylsalicylic acid (ASA), where quite a significant change in hydration is expected and where no conformational changes occur when a CD/ASA complex is formed in aqueous solution. Thermophoresis was investigated in the temperature range of 10−50 °C by infrared thermal diffusion forced Rayleigh scattering. Nuclear magnetic resonance measurements were performed at 25 °C to obtain information about the structure of the complexes. All CD/ASA complexes show a stronger affinity toward regions of lower temperature compared to the free CDs. We found that the temperature sensitivity of thermophoresis correlates with the 1-octanol/water partition coefficient. This observation not only establishes the relation between thermodiffusion and degree of hydrogen bonding but also opens the possibility to relate thermodiffusive properties of complexes to their partition coefficient, which cannot be determined otherwise. This concept is especially interesting for protein−ligand complexes where the protein undergoes a conformational change, different from the CD/ASA complexes, giving rise to additional changes in their hydrophilicity.

Isala Dueramae, Masaru Yoneyama, Naoki Shinyashiki, Shin Yagihara, and *Rio Kita,
Self-assembly of acetylated dextran with various acetylation degrees in aqueous solutions: Studied by light scattering,
Carbohydrate Polymers 159, 171-177 (2017).

[Summary] Self-assembly of acetylated dextran (Ac-DEXs) was investigated with a modified dextran with acetic anhydride in the presence of pyridine. The effect of acetylation degree on solution properties has been investigated by static and dynamic light scattering (DLS). Molecular weight (Mw) and the radius of gyration (Rg) of dextran significantly increased with acetylation degree due to the aggregates formation. However, those aggregates noticeably reduced with further increase of acetylation degree. It suggested that the aggregates have shrinkage. The aggregate formation is clearly confirmed by DLS analysis in the presence of the bimodal relaxation distribution for Ac-DEXs. The hydrodynamic radius (Rh) of fast and slow mode is distinctly corresponded with single dextran macromolecules and aggregates, respectively. The Rh of aggregates varied slightly with increasing acetylation degree. The aggregates of Ac-DEXs represent hard spherical nanoparticles whereas the random coil structure is found in dextran. Formation of gel nanoparticles was monitored at the highest acetylated substitution.

Kazuya Eguchi, Doreen Niether, Simone Wiegand, and *Rio Kita,
Thermophoresis of cyclic oligosaccharides in polar solvents,
European Physical Journal E 39, 86/1-8 (2016).

[Summary] Cyclodextrins are cyclic oligosaccharides which are interesting as drug delivery systems, because they can be used as containers for pharmaceutical substances. We studied the Ludwig-Soret effect of α-, β-, γ- and methyl-β-cyclodextrin in water and formamide by infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS). In water the Soret coefficient, ST, of α-, β- and γ-cyclodextrin increases with increasing temperature and shows a sign change from negative to positive around T = 35 ◦C, while ST of methyl-β-cyclodextrin is positive in the entire investigated temperature. In formamide ST-values of all cyclodextrins coincide and show a slight decrease with temperature. We discuss the obtained results and relate the ST-values to the different hydrogen bonding capabilities of the cyclodextrins and the used solvents. It turns out that the change of ST with temperature correlates with the partition coefficient, log P, which indicates that more hydrophilic substances show a more pronounced temperature sensitivity of ST. Additionally we obtained a surprising result measuring the refractive index contrast factor with temperature, (∂n/∂T)c,p of cyclodextrins in formamide, which might be explained by a complex formation between cyclodextrins and formamide.

Kaito Sasaki, Yurika Matsui, Masahiko Miyara, Rio Kita, Naoki Shinyashiki, and Shin Yagihara,
Glass transition and dynamics of the polymer and water in the poly(vinylpyrrolidone)−ｗater ｍixtures studied by dielectricrelaxation spectroscopy,
Journal of Physical Chemistry B 120, 6882-6889 (2016).

[Summary] In this study, broadband dielectric spectroscopy and differential scanning calorimetry (DSC) measurements are performed to study the dynamics of water and polymers in an aqueous solution of poly(vinylpyrrolidone) (PVP) with concentrations of 60, 65, and 70 wt % PVP in a temperature range of 123-298 K. Two distinct relaxation processes, l- and h-processes, which originate from the segmental chain motion of PVP and the primary relaxation process of water, respectively, are observed simultaneously. The relationship between l- and h-processes and their temperature dependences mimic those of the α-process and Johari-Goldstein β-process, which are observed in ordinal glass formers. The relaxation time of the l-process, τl, obeys the Vogel-Fulcher (VF)-type temperature dependence, and the glass-transition temperature of the l-process, Tg,l, which is defined by the temperature that is reached in a τl of 100-1000 s, shows good agreement with the calorimetric Tg obtained by DSC. The temperature dependence of the relaxation time of the h-process, τh, exhibits a crossover from VF to Arrhenius behavior at the so-called fragile-to-strong transition (FST) of water at Tg,l. The temperature dependence of the relaxation strength of the h-process, Δϵh, increases with a decrease in temperature from 298 K to Tg,l. Below Tg,l, Δϵh is nearly constant or slightly decreases with decreasing temperature. According to previous studies on aqueous solutions of sugars and alcohols, the Δϵ of the ν-process, which originates from local motion of water, decreases with decreasing temperature above the Tg of the α-process, which originates from the cooperative motion of the solute and water. Therefore, the l-process in the PVP-water mixture is not a result of the cooperative motion of PVP and water but rather a result of the polymer-polymer cooperative motion of PVP. In addition, agreement among Tg,l, the temperature of the FST of water, and calorimetric Tg suggests that the FST of water occurs at Tg.

Kaito Sasaki, Rio Kita, *Naoki Shinyashiki, and Shin Yagihara,
Dielectric relaxation time of ice-Ih with different preparation,
Journal of Physical Chemistry B 120, 3950-3953 (2016).

[Summary] Dielectric relaxation process of ice-Ih has been investigated by many researchers. Pioneering studies focused on the temperature dependence of the dielectric relaxation time, τice, were reported by Auty in 1952 [Auty, R. P.; Cole, R. H. J. Chem. Phys. 1952, 120, 1309] and Johari in 1981 [Johari, G. P.; Whalley, E. J. Chem. Phys. 1981, 75, 1333]. However, the temperature dependences of τice found in these studies are not in agreement. While Auty et al. reported a single Arrhenius temperature dependence of τice for the entire 207−273 K temperature range, Johari et al. reported changes in the temperature dependence of ice at 230 and 140 K. In this study, the temperature dependence of τice is investigated by broadband dielectric spectroscopy for ice prepared by three different procedures. For all investigated ices, a dielectric relaxation process is observed, and τice decreases with increasing temperature. Temperature dependence of τice with rapid crystallization shows the same properties at temperatures down to 140 K as that reported by Johari et al. On the other hand, ice obtained by slow crystallization exhibits the same temperature dependence of τice as those reported by Auty et al. We suggest that the difference between the temperature dependences of τice found by Auty et al. and Johari et al. can be controlled by preparation conditions. That is, the growth rate of the ice crystal can affect τice because a slow growth speed of the ice crystal induces a smaller impurity content of ice, giving rise to an Arrhenius temperature dependence of τice.

Yasutaka Ohnishi, Rio Kita, Kazuyoshi Tsuchiya and *Satoru Iwamori,
Optical characteristics of poly(tetrafluoroethylene) thin film prepared by a vacuum evaporation,
Japanese Journal of Applied Physics 55, 02BB04/1-5 (2016).

[Summary] Poly(tetrafluoroethylene) (PTFE) thin films were deposited onto a glass slide substrate by a heat-resistance type vacuum evaporation apparatus due to changing the evaporation conditions. Transparency of the PTFE thin films prepared by the vacuum evaporation depended on the deposition conditions, i.e., temperatures of the basket, and distance between the evaporation source and substrate. To elucidate relationship between the molecular structure and transparency of the PTFE thin film prepared by the vacuum evaporation, chemical structures, crystallinity and thermophysical property were investigated. The chemical bonding state of the PTFE thin film prepared by the vacuum evaporation was almost the same as that of the pristine PTFE, however, the crystalinity was different. Although the pristine PTFE was crystal structure, the transparent evaporated thin film was estimated to be microcrystal structure. In addition, endothermic peaks in a differential scanning calorimeter (DSC) spectrum of the PTFE thin film were different from that of the pristine PTFE. These endothermic peaks of the PTFE thin film prepared by the vacuum evaporation shifted lower temperature compared to the pristine PTFE, which suggests that molecular weight of the PTFE thin film prepared by the vacuum evaporation decreased compared with that of the pristine PTFE.

Kousaku Maeda, Naoki Shinyashiki, Shin Yagihara, Simone Wiegand, and *Rio Kita,
Ludwig-Soret effect of aqueous solutions of ethylene glycol oligomers, crown ethers, and glycerol: Temperature, molecular weight, and hydrogen bond effect,
Journal of Chemical Physics 143, 124504/1-7 (2015).

[Summary] The thermal diffusion, also called the Ludwig-Soret effect, of aqueous solutions of ethylene glycol oligomers, crown ethers, and glycerol is investigated as a function of temperature by thermal diffusion forced Rayleigh scattering. The Soret coefficient, S_T, and the thermal diffusion coefficient, D_T, show a linear temperature dependence for all studied compounds in the investigated temperature range. The magnitudes and the slopes of S_T and D_T vary with the chemical structure of the solute molecules. All studied molecules contain ether and/or hydroxyl groups, which can act as acceptor or donor to form hydrogen bonds, respectively. By introducing the number of donor and acceptor sites of each solute molecule, we can express their hydrogen bond capability. S_T and D_T can be described by an empirical equation depending on the difference of donor minus acceptor sites and the molecular weight of the solute molecule.

S. K. Kundu, S. Choe, K. Sasaki, Rio Kita, N. Shinyashiki, and *S. Yagihara,
Relaxation dynamics of liposomes in an aqueous solution,
Physical Chemistry Chemical Physics 17, 18449-18455 (2015).

[Summary] The gel–liquid crystal phase transition has been studied by the temperature and frequency dependent dielectric relaxation behavior of liposomes in an aqueous solution (40 g L^{-1} DPPC–water mixture). Four relaxation processes were observed in the frequency range from 40 Hz to 30 GHz which were ascribed to different molecular mechanisms, related to the structural units of the system. The gel–liquid crystal phase transition was also described very accurately from the temperature-dependent dielectric relaxation strength, relaxation time and symmetric shape parameter of the relaxation functions obtained from the fitting procedure. Relaxation process 3, obtained from the dielectric fitting procedure, was confirmed by dielectric modulus analysis. A comparison of the lipid membrane with non-biological systems like liquid crystals was performed. It was determined that the lipid membrane has a ferroelectric liquid crystal like behavior. Process 3 is comparable to the soft mode relaxation process observed in ferroelectric liquid crystals which was detected close to the smectic-C*–smectic-A phase transition. Differential scanning calorimetry was also used to confirm the gel–liquid crystal phase transition of this mixture.

Wataru Yamamoto, Kaito Sasaki, Rio Kita, Shin Yagihara, and *Naoki Shinyashiki,
Dielectric study on temperature-concentration superposition of liquid to glass in fructose-water mixtures,
Journal of Molecular Liquids 206, 39–46 (2015).

[Summary] Broadband dielectric measurements of fructose-water mixtures with various fructose concentrations, Cf (wt%), in the range of 5 - 94.6 wt% were carried out in the frequency range of 2 mHz - 50 GHz at 25 and 0 degreeC, to clarify the dynamics of water and fructose molecules in the mixtures from the liquid to glass states as a function of Cf. For the mixtures with Cf below 45 wt%, a single relaxation process originating from the reorientational motion of water, i.e., "mu"-relaxation, was observed. In contrast, in the mixtures with Cf above 45 wt%, in addition to the "mu"-relaxation, "alpha"-relaxation resulting from the cooperative motion of two components appears at a lower frequency than that of the "mu"-relaxation. Due to the facts of the precise analyses, the temperature-concentration superposition appears to be valid for the "mu"- and "alpha"- relaxations.

Kousaku Maeda, Naoki Shinyashiki, Shin Yagihara, Simone Wiegand, *Rio Kita,
How does thermodiffusion of aqueous solutions depend on concentration and hydrophobicity?,
European Physical Journal E 37, 94（6pages） (2014).

[Summary] The thermal diffusion of aqueous solutions of mono-, di-ethylene glycols, poly(ethylene glycol), methanol, and glycerol is investigated systematically as a function of concentration using the Thermal Diffusion Forced Rayleigh Scattering (TDFRS). For all investigated binary mixtures, the Soret coefficient, ST , decays with increasing concentration of the non-aqueous component showing two regions. For aqueous solution of ethylene glycol, at a very low solute content the decay is steep, while it becomes less steep for higher solute concentration. All mixtures show a sign change of ST with concentration. The sign change concentration is discussed with respect to chemical structures of solute molecules and the partition coefficient, log p . It turns out that the number of hydroxyl groups plays an important role. For the investigated aqueous mixtures, we find empirical linear relations between the sign change concentration and the ratio of the number of hydroxyl groups to the number of carbon atoms as well as the partition coefficient, log p.