Off-center rattling and thermoelectric properties of type-II clathrate (K, Ba)(24)(Ga, Sn, square)(136) single crystals

We report the synthesis and temperature-dependent structural, transport, and thermal properties of type-II clathrate K8+xBa16-xGa40-ySn96-z square(y+z) (1.2 <= x <= 2.8, 2.0 <= y <= 3.3, 0.8 <= z <= 6.6, square = framework vacancy). Single-crystal x-ray diffraction analysis reveals that the guest K+ and Ba2+ ions are preferentially incorporated into the hexakaidecahedral cages and dodecahedral cages, respectively. The guest site in the former splits into four sites 0.67 angstrom away from the center to the 32e site of the cage. The splitting is consistent with the presence of four minima in the electrostatic potential in the hexakaidecahedron. The thermopower is negative and relatively large, -50 similar to -120 mu V/K at 300 K, indicating that the dominant charge carriers are electrons. The thermal conductivity displays a glasslike behavior with a plateau at around 20 K. The analysis of the specific heat indicates that the motion of the K+ ion in the hexakaidecahedron can be described by the soft-potential model, including the tunneling term. The characteristic energy of 21 K for the soft mode is as low as that of the off-center rattling of the Ba2+ ion in type-I clathrate Ba8Ga16Sn30. The present result on the type-II clathrate verifies the idea that the low-energy off-center rattling in oversized cages of intermetallic clathrates couples to the acoustic phonons to lead to the glasslike thermal conductivity

Interplay between thermoelectric and structural properties of type-I clathrate K8Ga8Sn38 single crystals

We report structural, transport, and thermal properties of type-I clathrate K8Ga8Sn38 single crystals grown by the self-flux method. Single-crystal x-ray diffraction analysis confirmed that the guest K+ ion locates on the center in the tetrakaidecahedron composed of Ga and Sn atoms. The thermopower is largely negative,-200μ V/K at room temperature, irrespective of the flux used during growth Ga or Sn . The thermal conductivity κ(T) exhibits a large peak at 14 K. These observations in K8Ga8Sn38 are ontrasting with the splitting of the guest site and the glasslike behavior in κ(T) reported for type-I Ba8Ga16Sn30 although the free space for the guest is almost the same in both compounds. The electrostatic potential for the tetrakaidecahedron was calculated using the occupation probabilities of Ga ions in the three sites on the cage. It is found that the off-centered state is stabilized for the Ba2+ ions in Ba8Ga16Sn30 by the partial occupation of Ga anion in the 16i site while the on-center state for K8Ga8Sn38 is stabilized by the strongly preferred occupation of Ga anions in the 6c site. We conclude that the charge distribution on the cage is crucial for the splitting of the guest site into off-center positions in the tetrakaidecahedron of the type-I clathrate

Time-resolved serial femtosecond crystallography reveals early structural changes in channelrhodopsin

X線自由電子レーザーを用いて、光照射によるチャネルロドプシンの構造変化の過程を捉えることに成功. 京都大学プレスリリース. 2021-03-26.Channelrhodopsins (ChRs) are microbial light-gated ion channels utilized in optogenetics to control neural activity with light . Light absorption causes retinal chromophore isomerization and subsequent protein conformational changes visualized as optically distinguished intermediates, coupled with channel opening and closing. However, the detailed molecular events underlying channel gating remain unknown. We performed time-resolved serial femtosecond crystallographic analyses of ChR by using an X-ray free electron laser, which revealed conformational changes following photoactivation. The isomerized retinal adopts a twisted conformation and shifts toward the putative internal proton donor residues, consequently inducing an outward shift of TM3, as well as a local deformation in TM7. These early conformational changes in the pore-forming helices should be the triggers that lead to opening of the ion conducting pore

FISH DIVERSITY DETECTION AT THE INNER PART OF OSAKA BAY USING ENVIRONMENTAL DNA ANALYSIS

大阪湾奥に位置する尼崎運河において，環境DNA調査と捕獲調査を比較して運河内スケールにおける環境DNAの有効性と問題点を検討し，各調査地点の魚類相の比較および環境条件との関連を明らかにした．東堀では1月の表層のORPやDOが回復し，同時期の環境DNAにより検出された種数が最も多かった．このことから，この場所が水質の回復によって魚類の利用場所となるポテンシャルを持っている可能性が示唆された．環境DNA調査はより環境の異なる港湾との比較や季節変化については差の検出が可能であった．環境DNA調査は検出は不安定で，検出できない種もあるが，採捕調査よりも多くの魚種を検出する傾向にあり，直接採捕の調査と合わせると互いの調査方法の結果を補い，魚類相全体の把握に有効な手法であると考えられる．Fish diversity at at Amagasaki canal in the Inner Part of Osaka Bay were investigated by environmental DNA analysis (eDNA) to clarify whether this method is valuable in eutrophic conditions. A ORP and DO was restored in January in Higashi-bori sampling point and the detected fish species was larger number than the other time. The result suggests that Higashi-bori has a potential for fish habitat with a water quality recovery. The number of detected species and fish fauna suggests that eDNA is efficient in comparison among sampling points which has sharp contrast of environmental factors and monitoring seasonal difference. The eDNA is unable to detected a certain species, but allow to detect larger number of species than the conventional sampling methods. eDNA is most effective when used in conjunction with conventional sampling method for investigation of fish diversity

SMAD2/3 signaling regulates initiation of mouse Wolffian ducts and proximal differentiation in Müllerian ducts

Male and female reproductive tracts develop from anterior intermediate mesoderm with similar differentiation processes. The anterior intermediate mesoderm develops into the mesonephros, and the Wolffian duct initiates by epithelialization in the mesonephros. The Müllerian duct invaginates from the coelomic epithelium of the cranial mesonephros for ductal formation and is then regionalized into proximal to caudal female reproductive tracts. In this study, we focused on the epithelialization of the Wolffian duct, initiation of the Müllerian duct, and the regionalization step of the Müllerian ducts as a continuous process. By using intermediate mesodermal cells from mouse pluripotent stem cells, we identified that inhibition of SMAD2/3 signaling might be involved in the differentiation into mesenchymal cells, after which mesonephric cells might be then epithelialized during differentiation of the Wolffian duct. Aggregation of coelomic epithelial cells might be related to initiation of the Müllerian duct. Transcriptomic analysis predicted that consensus sequences of SMAD3/4 were enriched among highly expressed genes in the proximal Müllerian duct. SMAD2/3 signaling to regulate differentiation of the Wolffian duct was continuously activated in the proximal Müllerian duct and was involved in proximal and oviductal regionalization. Therefore, SMAD2/3 signaling may be finely tuned to regulate differentiation from initiation to regionalization steps