In Situ Strain Tuning of the Dirac Surface States in Bi2Se3 Films.

Elastic strain has the potential for a controlled manipulation of the band gap and spin-polarized Dirac states of topological materials, which can lead to pseudomagnetic field effects, helical flat bands, and topological phase transitions. However, practical realization of these exotic phenomena is challenging and yet to be achieved. Here we show that the Dirac surface states of the topological insulator Bi2Se3 can be reversibly tuned by an externally applied elastic strain. Performing in situ X-ray diffraction and in situ angle-resolved photoemission spectroscopy measurements during tensile testing of epitaxial Bi2Se3 films bonded onto a flexible substrate, we demonstrate elastic strains of up to 2.1% and quantify the resulting changes in the topological surface state. Our study establishes the functional relationship between the lattice and electronic structures of Bi2Se3 and, more generally, demonstrates a new route toward momentum-resolved mapping of strain-induced band structure changes.

Composition, irregular terpenoids, chemical variability and antibacterial activity of the essential oil from Santolina corsica Jordan et Fourr.

A detailed analysis of Santolina corsica essential oil was carried out by combination of GC (RI), GC-MS and 13C NMR spectroscopy. After fractionation by column chromatography, 50 components were identified, accounting for 88.2% of the total amount of the oil. The chemical composition was dominated by monoterpene hydrocarbons, myrcene (34.6%), santolina triene (13.5%) and beta-phellandrene (11.7%). Beside the main compounds, we noted the occurrence of irregular mono and sesquiterpenes belonging to five families: santolinane, artemisane, chrysanthemane, lavandulane and sesquilavandulane. Three compounds, lyratyl butyrate, isolyratone and epi-isolyratol were isolated and their structure elucidated by 2D NMR. Antibacterial activity was tested against six bacteria strains. The essential oil was effective against Staphylococcus aureus and C. jejuni. Lyratol was identified as main responsive of the antibacterial activity. The content of lyratol was measured in 33 oil samples isolated from individual plants.

(E)-Methylisoeugenol and elemicin: antibacterial components of Daucus carota L. essential oil against Campylobacter jejuni.

The essential oil of wild Daucus carota L. obtained from aerial parts at the end of the flowering stage (DCEO) was reported as antimicrobial against the human enteropathogen Campylobacter jejuni. The aim of the present study was to extend this analysis to other Campylobacter species and to identify the active compounds of the essential oil, subjected to GC, GC-MS, and (13)C NMR analysis. A minimum inhibitory concentration assay was used to quantify the antimicrobial activity of DCEO and the major components, isolated on column chromatography. Growth of all the C. jejuni, Campylobacter coli, and Campylobacter lari strains tested, including one multidrug resistant C. jejuni, was inhibited to the same extent by DCEO. Molecules that were responsible for the antibacterial activity were identified as (E)-methylisoeugenol and elemicin. Moreover, the use of structural analogues of these compounds allowed us to identify important features that may account for the activity.