Anisotropic Optical Conductivity Accompanied by a Small Energy Gap in One-Dimensional Thermoelectric Telluride Ta4SiTe4

We investigated the optical properties of single crystals of one-dimensional telluride Ta4SiTe4, which shows high thermoelectric performance below room temperature. Optical conductivity estimated from reflectivity spectra indicates the presence of a small energy gap of 0.1-0.15 eV at the Fermi energy. At the lowest energy, optical conductivity along the Ta4SiTe4 chain is an order of magnitude higher than that perpendicular to this direction, reflecting the anisotropic electron conduction in Ta4SiTe4. These results indicate that coexistence of a very small band gap and anisotropic electron conduction is a promising strategy to develop a high-performance thermoelectric material for low temperature applications.Comment: 6 pages, 4 figure

Positron Emission Tomography to Elucidate Pharmacokinetic Differences of Regioisomeric Retinoid X Receptor Agonists

RXR partial agonist NEt-4IB (<b>2a</b>, 6-[ethyl-(4-isobutoxy-3-isopropylphenyl)­amino]­pyridine-3-carboxylic acid: EC₅₀ = 169 nM, <i>E</i>_max = 55%) showed a blood concentration higher than its <i>E</i>_max after single oral administration at 30 mg/kg to mice, and repeated oral administration at 10 mg/kg/day to KK-A^y mice afforded antitype 2 diabetes activity without the side effects caused by RXR full agonists. However, RXR full agonist NEt-3IB (<b>1a</b>), in which the isobutoxy and isopropyl groups of <b>2a</b> are interchanged, gave a much lower blood concentration than <b>2a</b>. Here we used positron emission tomography (PET) with tracers [¹¹C]<b>1a</b>, [¹¹C]<b>2a</b> and fluorinated derivatives [¹⁸F]<b>1b</b>, [¹⁸F]<b>2b</b>, which have longer half-lives, to examine the reason why <b>1a</b> and <b>2a</b> exhibited significantly different blood concentrations. As a result, the reason for the high blood concentration of <b>2a</b> after oral administration was found to be linked to higher intestinal absorbability together with lower biliary excretion, compared with <b>1a</b>