30 research outputs found
Thermal transport properties of IrSbSe
We report a thermal transport study of IrSbSe, which crystallizes in a
noncentrosymmetric cubic structure with the space group and shows a
narrow-gap semiconducting behavior. The large discrepancy between the
activation energy for conductivity [ = 128(2) meV] and for thermopower
[ = 17.7(9) meV] from 200 to 300 K indicates the polaronic transport
mechanism. Electrical resistivity varies as and thermopower
varies as at low temperatures, indicating that it evolves into the
Mott's variable-range hopping dominant conduction with decreasing temperature.
IrSbSe shows relatively low value of thermal conductivity ( 1.65
W/Km) and thermopower of about 0.24 mV/K around 100 K, yet poor
electrical conductivity. On the other hand, high vacancy defect concentration
on both Ir and Sb atomic sites of up to 15\%, suggests high defect tolerance
and points to possibility of future improvement of carrier density by chemical
substitution or defect optimization
Colossal Nernst power factor in topological semimetal NbSb
Today solid-state cooling technologies below liquid nitrogen boiling
temperature (77 K), crucial to quantum information technology and probing
quantum state of matter, are greatly limited due to the lack of good
thermoelectric and/or thermomagnetic materials. Here, we report the discovery
of colossal Nernst power factor of 380010 W m K
under 5 T at 25 K and high Nernst figure-of-merit of 7110
K under 5 T at 20 K in topological semimetal NbSb single crystals.
The observed high thermomagnetic performance is attributed to large Nernst
thermopower and longitudinal electrical conductivity, and relatively low
transverse thermal conductivity. The large and unsaturated Nernst thermopower
is the result of the combination of highly desirable electronic structures of
NbSb having compensated high mobility electrons and holes near Fermi level
and strong phonon-drag effect. This discovery opens an avenue for exploring
material option for the solid-state heat pumping below liquid nitrogen
temperature
Maculosin, a non-toxic antioxidant compound isolated from Streptomyces sp. KTM18
Context Streptomyces species are prolific sources of bioactive secondary metabolites known especially for their antimicrobial and anticancer activities. Objective This study sought to isolate and characterize antioxidant molecules biosynthesized by Streptomyces sp. KTM18. The antioxidant potential of an isolated compound and its toxicity were accessed. Materials and methods The compound was purified using bioassay-guided chromatography techniques. Nuclear magnetic resonance (NMR) experiments were carried out for structure elucidation. The antioxidant potential of the isolated compound was determined using DPPH free radical scavenging assay. The toxicity of the isolated compound was measured using a brine shrimp lethality (BSL) assay. Results Ethyl acetate extract of Streptomyces sp. KTM18 showed more than 90% inhibition of DPPH free radical at 50 mu g/mL of the test concentration. These data were the strongest among 13 Streptomyces isolates (KTM12-KTM24). The active molecule was isolated and characterized as maculosin (molecular formula, C14H16N2O3 as determined by the [M + H](+) peak at 261.1259). The DPPH free radical scavenging activity of pure maculosin was higher (IC50, 2.16 +/- 0.05 mu g/mL) than that of commercial butylated hydroxyanisole (BHA) (IC50, 4.8 +/- 0.05 mu g/mL). No toxicity was observed for maculosin (LD50, <128 mu g/mL) in brine shrimp lethality assay (BSLA) up to the compound's antioxidant activity (IC50) concentration range. The commercial standard, berberine chloride, showed toxicity in BSLA with an LD50 value of 8.63 +/- 0.15 mu g/mL. Conclusions Maculosin may be a leading drug candidate in various cosmetic and therapeutic applications owing to its strong antioxidant and non-toxic properties