Site-dependent Local Spin Susceptibility and Low-energy Excitation in a Weyl Semimetal WTe2_2

Site-dependent local spin susceptibility is investigated with $^{125}$Te nuclear magnetic resonance in a Weyl semimetal WTe$_2$. The nuclear spin-lattice relaxation rate $1/T_1T$ shows a dependence of the square of temperature $T$ at high temperatures, followed by a constant behavior below 50 K. The temperature dependence features Weyl fermions appearing around the linearly crossing bands. The Knight shift $K$ scales to the square root of $1/T_1T$, corroborating a predominant spin contribution in low-lying excitation. The observed dependence of $K$ and $1/T_1T$ on the four Te sites shows the site-dependent electron correlation and density of states. The angular profile of the NMR spectrum gives the anisotropic hyperfine coupling tensor, consistent with $5p$ hole occupations on Te sites.Comment: 6 pages, 5 figure

Substellar Companions to Seven Evolved Intermediate-Mass Stars

We report the detections of substellar companions orbiting around seven evolved intermediate-mass stars from precise Doppler measurements at Okayama Astrophysical Observatory. o UMa (G4 II-III) is a giant with a mass of 3.1 M_sun and hosts a planet with minimum mass of m_2sini=4.1 M_J in an orbit with a period P=1630 d and an eccentricity e=0.13. This is the first planet candidate (< 13 M_J) ever discovered around stars more massive than 3 M_sun. o CrB (K0 III) is a 2.1 M_sun giant and has a planet of m_2sini=1.5 M_J in a 187.8 d orbit with e=0.19. This is one of the least massive planets ever discovered around ~2 M_sun stars. HD 5608 (K0 IV) is an 1.6 M_sun subgiant hosting a planet of m_2sini=1.4 M_J in a 793 d orbit with e=0.19. The star also exhibits a linear velocity trend suggesting the existence of an outer, more massive companion. 75 Cet (G3 III:) is a 2.5 M_sun giant hosting a planet of m_2sini=3.0 M_J in a 692 d orbit with e=0.12. The star also shows possible additional periodicity of about 200 d and 1880 d with velocity amplitude of ~7--10 m/s, although these are not significant at this stage. nu Oph (K0 III) is a 3.0 M_sun giant and has two brown-dwarf companions of m_2sini= 24 M_J and 27 M_J, in orbits with P=530.3 d and 3190 d, and e=0.126 and 0.17, respectively, which were independently announced by Quirrenbach et al. (2011). The ratio of the periods is close to 1:6, suggesting that the companions are in mean motion resonance. We also independently confirmed planets around k CrB (K0 III-IV) and HD 210702 (K1 IV), which had been announced by Johnson et al. (2008) and Johnson et al. (2007a), respectively. All of the orbital parameters we obtained are consistent with the previous results.Comment: 21 pages, 14 figures, accepted for publication in PAS

Regioselective biooxidation of (+)-valencene by recombinant E. coli expressing CYP109B1 from Bacillus subtilis in a two-liquid-phase system

<p>Abstract</p> <p>Background</p> <p>(+)-Nootkatone (<b>4</b>) is a high added-value compound found in grapefruit juice. Allylic oxidation of the sesquiterpene (+)-valencene (<b>1</b>) provides an attractive route to this sought-after flavoring. So far, chemical methods to produce (+)-nootkatone (<b>4</b>) from (+)-valencene (<b>1</b>) involve unsafe toxic compounds, whereas several biotechnological approaches applied yield large amounts of undesirable byproducts. In the present work 125 cytochrome P450 enzymes from bacteria were tested for regioselective oxidation of (+)-valencene (<b>1</b>) at allylic C2-position to produce (+)-nootkatone (<b>4</b>) via <it>cis</it>- (<b>2</b>) or <it>trans</it>-nootkatol (<b>3</b>). The P450 activity was supported by the co-expression of putidaredoxin reductase (PdR) and putidaredoxin (Pdx) from <it>Pseudomonas putida </it>in <it>Escherichia coli</it>.</p> <p>Results</p> <p>Addressing the whole-cell system, the cytochrome CYP109B1 from <it>Bacillus subtilis </it>was found to catalyze the oxidation of (+)-valencene (<b>1</b>) yielding nootkatol (<b>2 </b>and <b>3</b>) and (+)-nootkatone (<b>4</b>). However, when the <it>in vivo </it>biooxidation of (+)-valencene (<b>1</b>) with CYP109B1 was carried out in an aqueous milieu, a number of undesired multi-oxygenated products has also been observed accounting for approximately 35% of the total product. The formation of these byproducts was significantly reduced when aqueous-organic two-liquid-phase systems with four water immiscible organic solvents – isooctane, <it>n</it>-octane, dodecane or hexadecane – were set up, resulting in accumulation of nootkatol (<b>2 </b>and <b>3</b>) and (+)-nootkatone (<b>4</b>) of up to 97% of the total product. The best productivity of 120 mg l^-1of desired products was achieved within 8 h in the system comprising 10% dodecane.</p> <p>Conclusion</p> <p>This study demonstrates that the identification of new P450s capable of producing valuable compounds can basically be achieved by screening of recombinant P450 libraries. The biphasic reaction system described in this work presents an attractive way for the production of (+)-nootkatone (<b>4</b>), as it is safe and can easily be controlled and scaled up.</p