Xu-Jie Qin

Steroidal saponins with antimicrobial activity from stems and leaves of Paris polyphylla var. yunnanensis

Rhizoma Paridis, the root of Paris polyphylla var. yunnanensis (Trilliaceae), is a Chinese traditional medicine, which resources become less and less. However, the aerial parts of this herb, which can regenerate every year, were discarded. In order to expand the resources, detailed chemical investigation on the stems and leaves of Paris polyphylla var. yunnanensis led to isolation of one sapogenin and 24 steroidal saponins (1-25), including 6 new glycosides, named chonglouosides SL-1-SL-6 (1-6). Their structures were elucidated on the basis of detailed analyses of their 1D and 2D NMR spectra and acid hydrolysis. Among them, compounds 3 and 4 are the first 23,27-dihydroxydiosgenin saponin having a sugar chain attached to C-23 or C-27, while compound 6 is the first 27-hydroxyruscogenin glycoside bearing 1, 27-di-O-sugar chains. The known compounds 10, 12, 14, 19, 20, 22, and 25 were isolated from the genus Paris for the first time. Antimicrobial testing activities of the selected compounds showed that compound 2, 3, 6, 8, 9, 11, 13, 17, 18, 21, and 24 were active against Propionibacterium acnes with MIC values of 62.5, 62.5, 3.9, 16.5, 17.2, 7.8, 39.0, 17.2, 31.3, 62.5, and 31.3 μg/ml, respectively.

Effects of Nb doping on thermoelectric properties of Zn 4 Sb 3 at high temperatures

The thermoelectric properties of Nb-doped Zn 4 Sb 3 compounds, (Zn 1– x Nb x ) 4 Sb 3 ( x = 0, 0.005, and 0.01), were investigated at temperatures ranging from 300 to 685 K. The results showed that by substituting Zn with Nb, the thermal conductivities of all the Nb-doped compounds were lower than that of the pristine β-Zn 4 Sb 3 . Among the compounds studied, the lightly substituted (Zn 0.995 Nb 0.005 ) 4 Sb 3 compound exhibited the best thermoelectric performance due to the improvement in both its electrical resistivity and thermal conductivity. Its figure of merit, ZT, was greater than the undoped Zn 4 Sb 3 compound for the temperature range investigated. In particular, the ZT of (Zn 0.995 Nb 0.005 ) 4 Sb 3 reached a value of 1.1 at 680 K, which was 69% greater than that of the undoped Zn 4 Sb 3 obtained in this study.

Indole alkaloids with new skeleton activating neural stem cells.

Alstoscholarisines A-E (1-5), five unprecedented monoterpenoid indole alkaloids with 6/5/6/6/6 fused-bridge rings, were isolated from Alstonia scholaris. They promoted adult neuronal stem cells (NSCs) proliferation significantly, in which the most active one (1) functioned from a concentration of 0.1 μg/mL in a dosage-dependent manner. Furthermore, 1 enhanced NSC sphere formation and neurogenic fate commitment through activation of a Wnt signaling pathway and promoted NSC differentiation but did not affect proliferation of neuroblastoma cells.

Steroidal saponins from stems and leaves of Paris polyphylla var. yunnanensis.

Phytochemical investigation of the stems and leaves of Paris polyphylla var. yunnanensis led to isolation of 12 steroidal saponins, chonglouosides SL-9-SL-20, which had not been described previously, along with 13 known compounds. Their structures were established on the basis of extensive spectroscopic analysis and chemical methods. Four of the twelve steroidal saponins possessed three steroidal aglycones which have not been reported in nature. Steroidal saponins were also evaluated for their cytotoxicities against two human cancer cell lines (HepG2 and HEK293) and anti-HCV effects. One known steroidal saponin was the most cytotoxic compound overall with IC50 values of 2.9 ± 0.5 μM and 5.0 ± 0.6 μM against HepG2 and HEK293 cell lines, respectively, while none showed anti-HCV activity at a concentration of 20 μM.

Enhanced thermoelectric performance of Cu2Se/Bi0.4Sb1.6Te3 nanocomposites at elevated temperatures

Bi2Te3-based thermoelectric materials with large thermoelectric figure of merit, ZT, at elevated temperatures are advantageous in power generation by using the low-grade waste heat. Here, we show that incorporation of small proportion (0.3 vol. %) of nanophase Cu2Se into BiSbTe matrix causes an enhanced high-temperature thermopower due to elevated energy filtering of carriers and inhibition of minority transport besides enhanced phonon blocking from scattering at interfaces, which concurrently result in an ∼20% increase in the power factor and an ∼60% reduction in the lattice thermal conductivity at 488 K. As a result, ZT = 1.6 is achieved at 488 K in the composite system with 0.3 vol. % of Cu2Se. Significantly, its ZT is larger than unit in broad high-temperature range (e.g., ZT = 1.3 at 400 K and ZT = 1.6 at 488 K), which makes this material to be attractive for applications in energy harvesting from the low-grade waste heat.

Antibacterial monoterpenoid indole alkaloids from Alstonia scholaris cultivated in temperate zone

Three new monoterpenoid indole alkaloids, named normavacurine-21-one (1), 5-hydroxy-19, 20-E-alschomine (2), and 5-hydroxy-19, 20-Z-alschomine (3), together with thirteen known indole alkaloids (4-16) were isolated from the leaves of Alstonia scholaris cultivated in Kunming. Their structures were elucidated on the basis of extensive spectroscopic analysis, as well as by comparison with the reported spectroscopic data. The leaves of A. scholaris cultivated in Kunming, contained picrinine-type alkaloids, scholaricin-type alkaloids and nareline as major alkaloids. New compounds 1-3 might be derived from a common biogenetic precursor (5). Compounds 1, 5 and 10 exhibited significant antibacterial activity against Enterococcus faecalis, and 3, 9 and 14 against Pseudomonas aeruginosa with an MIC value of 0.781 μg/mL, while 14 showed moderate activity against Klepsiella pneumonia with an MIC value of 1.56 μg/mL.

Effects of Bi doping on the thermoelectric properties of β-Zn4Sb3

The thermoelectric properties of Bi-doped compounds (Zn1−xBix)4Sb3 (x=0,0.0025,0.005,0.01) were studied experimentally as well as theoretically. The results indicate that low-temperature (T<300 K) thermal conductivity of moderately doped (Zn0.9975Bi0.0025)4Sb3 reduces remarkably as compared with that of Zn4Sb3 due to enhanced phonon scattering of impurity (dopant). Electrical resistivity and Seebeck coefficient increase monotonically with increase in the Bi content resulting mainly from decrease in carrier concentration. Moreover, first-principle calculations were performed on the occupation options of Bi atoms in β-Zn4Sb3, which show that Bi will preferentially occupy the Zn sites and not Sb sites and act as donors, being consistent with the experimental observations. In addition, the lightly doped compound (Zn0.9975Bi0.0025)4Sb3 exhibits the best thermoelectric performance due to the improvement in both its thermal conductivity and Seebeck coefficient, whose figure of merit, ZT, is about 1.5 times large...

Electrical transport and thermoelectric properties of double filled compounds Ca0.1CexCo4Sb12 at low temperatures

The electrical transport and thermoelectric properties of CoSb3 and double filled compounds Ca0.1CexCo4Sb12 (x=0.05, 0.1, and 0.15) were investigated in the temperature range from 5 to 300 K. The results indicated that double filling of Ca and Ce has a strong influence on the temperature dependence of the electrical resistivity. For samples CoSb3 and Ca0.1Ce0.05Co4Sb12, the relationship of ln ρ∝1/T existed only in the temperature regimes of 100–200 and 160–300 K, respectively, while Mott’s law ln ρ∝T−1/4 was obeyed at lower temperatures below 100 and 160 K for CoSb3 and Ca0.1Ce0.05Co4Sb12, respectively. The results suggested a localization of charge carriers. Moreover, a transition from the semiconducting state (i.e., dρ/dT 0) (0.05 0.5) was observed to be smaller than that of CoSb3. However, the increase in carrier concen...

Enhanced thermoelectric performance of BiSbTe-based composites incorporated with amorphous Si3N4 nanoparticles

Thermoelectric properties of BiSbTe-based composites dispersed with a small amount (<1 vol%) of amorphous Si3N4 (a-Si3N4) nanoparticles (∼25 nm) were investigated in the temperature range from 303 K to 483 K. The results indicate that with a-Si3N4 content increasing, the thermopower (S) of the a-Si3N4/BiSbTe composites increases substantially at T < ∼370 K, due to the decreased carrier concentrations and the enhanced energy-dependent scattering of the carrier at the heterojunction potential. Simultaneously, a-Si3N4 nanodispersion causes ∼20–30% reduction in thermal conductivity (κ) owing to phonon scattering of nanoparticles as well as phase boundaries. As a result, high dimensionless figure of merit (ZT) values of up to 1.20 (∼303 K) and 1.38 (∼383 K) are obtained in Bi0.4Sb1.6Te3 incorporated with only 0.44 vol% a-Si3N4 nanoparticles, demonstrating that the thermoelectric performance of the BiSbTe alloy can be improved effectively through incorporation of a-Si3N4 nanoparticles.

Enhancement of thermopower and thermoelectric performance through resonant distortion of electronic density of states of b-Zn4Sb3 doped with Sm

Thermoelectric properties of Sm-doped compounds β-(Zn1−xSmx)4Sb3 (x = 0, 0.001, 0.002, and 0.003) (at 300-615 K) were investigated. The results indicate that Sm doping causes the resonant distortion of density of states of β-Zn4Sb3, as manifested by almost 2-fold increase in effective mass md* of β-Zn4Sb3, which results in ∼40 μV/K increase of the thermopower for all the doped samples. Besides, thermal conductivity decreases substantially by Sm doping. As a result, figure of merit ZT of β-(Zn0.008Sm0.002)4Sb3 is ∼53% larger than that of the un-doped one and reaches 1.1 at 615 K, suggesting that Sm doping is an effective approach to improve ZT of β-Zn4Sb3.