Observation of photoinduced polarons in semimetal 1T-TiSe2.

In this work, ultrafast carrier dynamics of mechanically exfoliated 1T-TiSe2flakes from the high-quality single crystals with self-intercalated Ti atoms are investigated by femtosecond transient absorption spectroscopy. The observed coherent acoustic and optical phonon oscillations after ultrafast photoexcitation reveal the strong electron-phonon coupling in 1T-TiSe2. The ultrafast carrier dynamics probed in both visible and mid-infrared regions indicate that some photogenerated carriers localize near the intercalated Ti atoms and form small polarons rapidly within several picoseconds after photoexcitation due to the strong and short-range electron-phonon coupling. The formation of polarons leads to a reduction of carrier mobility and a long-time relaxation process of photoexcited carriers for several nanoseconds. The formation and dissociation rates of the photoinduced polarons are dependent on both the pump fluence and the thickness of TiSe2sample. This work offers new insights into the photogenerated carrier dynamics of 1T-TiSe2, and emphasizes the effects of intercalated atoms on the electron and lattice dynamics after photoexcitation.

Factors affecting the occurrence and accumulation of perfluoroalkyl acids in indoor dust in Tainan, Taiwan.

Perfluoroalkyl acids (PFAAs) are environmentally and biologically persistent chemicals. In this study, we investigated the concentrations of six PFAAs in dust samples collected from different indoor environments in a college campus in Tainan, Taiwan, and assessed the health risk of PFAAs exposure to college students. We also analyzed the effects of dust characteristics (total organic carbon, moisture content, and dust content) on PFAAs levels. With regard to the space type, the median of total PFAAs concentrations were in the order of laboratories (528.9 µg kg-1) > offices (304.2 µg kg-1) > dormitories (180.1 µg kg-1) > classrooms (105.1 µg kg-1). With regard to the height from the ground, the median total PFAAs concentrations were in the order of dust near the floors (>2 m; 383.6 µg kg-1) > near the ceiling (0-2 m; 202.5 µg kg-1) > on the ground (0 m; 145.6 µg kg-1). The main species of PFAAs, perfluorooctane sulfonate and short-chain perfluoroalkyl carboxylates, accounted for respectively 30%-60% and ∼20%-37% of total PFAAs pollution in the indoor space types and sampling heights under consideration. The average daily intake (ADI) values of six PFAAs for college students were found to be 0.059-0.126 ng kg-1 BW day-1 (BW: body weight), with dormitories and workplaces (i.e., laboratories and offices) accounting for over 40% and ∼50% of the ADI, respectively. The estimated hazard quotient ranged from 0.0029 to 0.0063, three orders of magnitude lower than 1, suggesting relatively low risks for college students exposed to the six PFAAs monitored in indoor dust. The analysis of dust characteristics revealed that total organic carbon did not have a significant effect on PFAAs levels as we expected. In contrast, dust moisture and cation content dominated PFAAs accumulation.

Investigation of antimicrobial model of Hemsleya pengxianensis W.J. Chang and its main active component by metabolomics technique.

AIM OF THE STUDY: H.pengxianensi is a native plant in China. Dihydrocucurbitacin F-25-O-acetate is one of the major chemical components in H.pengxianensis. In this investigation, we attempted to quantify the content of dihydrocucurbitacin F-25-O-acetate in H.pengxianensis and find the possible antibacterial mode of dihydrocucurbitacin F-25-O-acetate and H.pengxianensis. MATERIAL AND METHODS: First, the content of dihydrocucurbitacin F-25-O-acetate was quantified by HPLC. Then, metabolic profiles of Staphylococcus aureus treated by dihydrocucurbitacin F-25-O-acetate, extract of H.pengxianensis and nine antibacterial substances with the known modes of action were acquired by HPLC/DAD/ESI-MS. Principal component analysis was carried out upon all metabolic profiles to classify those drugs according to their mechanisms. RESULTS AND CONCLUSION: The HPLC result show the content of dihydrocucurbitacin F-25-O-acetate in H.pengxianensis (5.3+/-0.4 mg/g). From the result obtained by principal component analysis, dihydrocucurbitacin F-25-O-acetate was found to be the component playing the main antimicrobial roles on Staphylococcus aureus in H.pengxianensis and the possible antibacterial mode of dihydrocucurbitacin F-25-O-acetate and H.pengxianensis may be to inhibit cell wall synthesis.