Impact of Anionic Substitution in Yb14MgSb11-x As x Compounds on the Electronic and Thermoelectric Properties.

The effects of anionic site substitution on the electronic transport properties of Yb14MgSb11-x As x compounds were investigated using density functional theory (DFT) with on-site Coulomb interaction correction (PBE+U). By replacing the Sb atoms at the four symmetry sites in Yb14MgSb11 with As, we found that the electronic and thermoelectric properties of the compound can be altered substantially. For most of the cases, the thermoelectric properties improve compared to the base compound Yb14MgSb11. Substitution at the tetrahedral site (Sb2) in particular yields the highest improvement in the thermoelectric properties. Detailed insight into the electronic and structural changes caused by the selective site substitutions is also discussed.

Enhanced Immunogenicity of Adjuvanted Microparticulate HPV16 Vaccines Administered via the Transdermal Route.

Human papillomavirus (HPV) causes cervical cancer among women and is associated with other anogenital cancers in men and women. Prophylactic particulate vaccines that are affordable, self-administered and efficacious could improve uptake of HPV vaccines world-wide. The goal of this research is to develop a microparticulate HPV16 vaccine for transdermal administration using AdminPatch® and assess its immunogenicity in a pre-clinical mouse model. HPV16 microparticles were prepared using a biocompatible polymer and characterized in terms of size, zeta potential, encapsulation efficiency and microparticle yield. Scanning and transmission electron microscopy were conducted to confirm particle image and to visualize the conformation of HPV16 vaccine particles released from microparticle formulation. In vivo studies performed to evaluate the potential of the microparticulate vaccine initiated a robust and sustained immune response. HPV16 IgG antibodies were significantly elevated in the microparticle group compared to antigen solutions administered by the transdermal route. Results show significant expansion of CD4+, CD45R, CD27 and CD62L cell populations in the vaccinated mice group, indicating the high efficacy of the microparticulate vaccine when administered via transdermal route. The findings of this study call attention to the use of minimally invasive, pain-free routes to deliver vaccine.

The small molecule Zaractin activates ZAR1-mediated immunity in Arabidopsis.

Pathogenic effector proteins use a variety of enzymatic activities to manipulate host cellular proteins and favor the infection process. However, these perturbations can be sensed by nucleotide-binding leucine-rich-repeat (NLR) proteins to activate effector-triggered immunity (ETI). Here we have identified a small molecule (Zaractin) that mimics the immune eliciting activity of the Pseudomonas syringae type III secreted effector (T3SE) HopF1r and show that both HopF1r and Zaractin activate the same NLR-mediated immune pathway in Arabidopsis Our results demonstrate that the ETI-inducing action of pathogenic effectors can be harnessed to identify synthetic activators of the eukaryotic immune system.

Discovery of multivalley Fermi surface responsible for the high thermoelectric performance in Yb14MnSb11 and Yb14MgSb11.

The Zintl phases, Yb14 MSb11 (M = Mn, Mg, Al, Zn), are now some of the highest thermoelectric efficiency p-type materials with stability above 873 K. Yb14MnSb11 gained prominence as the first p-type thermoelectric material to double the efficiency of SiGe alloy, the heritage material in radioisotope thermoelectric generators used to power NASA's deep space exploration. This study investigates the solid solution of Yb14Mg1-x Al x Sb11 (0 ≤ x ≤ 1), which enables a full mapping of the metal-to-semiconductor transition. Using a combined theoretical and experimental approach, we show that a second, high valley degeneracy (N v = 8) band is responsible for the groundbreaking performance of Yb14 MSb11 This multiband understanding of the properties provides insight into other thermoelectric systems (La3-x Te4, SnTe, Ag9AlSe6, and Eu9CdSb9), and the model predicts that an increase in carrier concentration can lead to zT > 1.5 in Yb14 MSb11 systems.

Halide-free neodymium phosphate based catalyst for highly cis-1,4 selective polymerization of dienes.

Neodymium-based Ziegler-Natta type catalytic systems are known to produce polydienes with high cis-1,4 content. It is generally believed that in Ziegler-Natta catalytic systems, a halide or pseudohalide, whether in the catalyst itself or a separate source, is required for the success of the polymerization. In this work, we have synthesized an unusual halide-free neodymium diethyl phosphate catalyst for diene polymerization. This neodymium complex combined with triisobutylaluminum (TIBA), formed a binary catalytic system and was used to polymerize ß-myrcene. The catalytic system displays high stereospecificity and produces poly(ß-myrcene) with 96% cis-1,4 content and a relatively narrow molecular weight distribution (M w/M n = 1.80). Also, kinetic studies indicated the catalytic system gives a pseudo-living polymerization. The block copolymer poly(ß-myrcene)-b-poly(isoprene) was successfully synthesized by sequential monomer addition, further demonstrating the pseudo-living nature of polymerization with the neodymium diethyl phosphate catalyst.

Synthesis and characterization of vacancy-doped neodymium telluride for thermoelectric applications.

Thermoelectric materials exhibit a voltage under an applied thermal gradient and are the heart of radioisotope thermoelectric generators (RTGs), which are the main power system for space missions such as Voyager I, Voyager II, and the Mars Curiosity rover. However, materials currently in use enable only modest thermal-to-electrical conversion efficiencies near 6.5% at the system level, warranting the development of material systems with improved thermoelectric performance. Previous work has demonstrated large thermoelectric figures of merit for lanthanum telluride (La3-x Te4), a high-temperature n-type material, achieving a peak zT value of 1.1 at 1275 K at an optimum cation vacancy concentration. Here we present an investigation of the thermoelectric properties of neodymium telluride (Nd3-x Te4), another rare-earth telluride with a similar structure to La3-x Te4. Density functional theory (DFT) calculations predicted a significant increase in the Seebeck coefficient over La3-x Te4 at equivalent vacancy concentrations due to an increased density of states (DOS) near the Fermi level from the 4f electrons of Nd. The high temperature electrical resistivity, Seebeck coefficient, and thermal conductivity were measured for Nd3-x Te4 at various carrier concentrations. These measurements were compared to La3-x Te4 in order to elucidate the impact of the four 4f electrons of Nd on the transport properties of Nd3-x Te4. A zT of 1.2 was achieved at 1273 K for Nd2.78Te4, which is a 10% improvement over that of La2.74Te4.

Tolerogenic Nanoparticles Induce Antigen-Specific Regulatory T Cells and Provide Therapeutic Efficacy and Transferrable Tolerance against Experimental Autoimmune Encephalomyelitis.

T cells reacting to self-components can promote tissue damage when escaping tolerogenic control mechanisms which may result in autoimmune disease. The current treatments for these disorders are not antigen (Ag) specific and can compromise host immunity through chronic suppression. We have previously demonstrated that co-administration of encapsulated or free Ag with tolerogenic nanoparticles (tNPs) comprised of biodegradable polymers that encapsulate rapamycin are capable of inhibiting Ag-specific transgenic T cell proliferation and inducing Ag-specific regulatory T cells (Tregs). Here, we further show that tNPs can trigger the expansion of endogenous Tregs specific to a target Ag. The proportion of Ag-specific Treg to total Ag-specific T cells remains constant even after subsequent Ag challenge in combination with a potent TLR7/8 agonist or complete Freund's adjuvant. tNP-treated mice do not develop experimental autoimmune encephalomyelitis (EAE) after adoptive transfer of encephalitogenic T cells; furthermore, tNP treatment provided therapeutic protection in relapsing EAE that was transferred to naïve animals. These findings describe a potent therapy to expand Ag-specific Tregs in vivo and suppress T cell-mediated autoimmunity.

Mechanochemical Synthesis and High Temperature Thermoelectric Properties of Calcium-Doped Lanthanum Telluride La3-xCaxTe4.

The thermoelectric properties from 300 - 1275 K of calcium-doped La3-xTe4 are reported. La3-xTe4 is a high temperature n-type thermoelectric material with a previously reported zTmax ~ 1.1 at 1273 K and x = 0.23. Computational modeling suggests the La atoms define the density of states of the conduction band for La3-xTe4. Doping with Ca2+ on the La3+ site is explored as a means of modifying the density of states to improve the power factor and to achieve a finer control over the carrier concentration. High purity, oxide-free samples are produced by ball milling of the elements and consolidation by spark plasma sintering. Calcium substitution upon the lanthanum site was confirmed by a combination of Rietveld refinements of powder X-ray diffraction data and wave dispersive spectroscopy. A zTmax ~ 1.2 is reached at 1273 K for the composition La2.2Ca0.78Te4 and the relative increase compared to La3-xTe4 is attributed to the finer carrier concentration.

Novel Aspergillus hemicellulases enhance performance of commercial cellulases in lignocellulose hydrolysis.

A novel hemicellulase-producing fungal strain was isolated from a local soil sample. The organism is identified as Aspergillus fumigatus based on ribosomal RNA analyses. The Aspergillus strain, designated as 2NB, produces both enzymes acting on xylan backbone (xylanase and ß-xylosidase), and those acting on side chains (or accessory enzymes) notably α-arabinofuranosidase and acetyl-xylan esterase. The Asperigillus hemicellulases are characterized as having relatively low xylanase and ß-xylosidase activities but high side chain removal activities. The activity ratio of side-chain acting enzymes to xylanase is higher than that of the Multifect enzyme, a commercial hemicellulase product. The potential of the novel hemicellulases in lignocelluloses bioprocessing was demonstrated with alkaline-pretreated switchgrass as lignocellulose substrate with hemicellulase supplemented with a ratio of xylanase activity to filter paper unit of 2:1. Supplement of Aspergillus hemicellulases to commercial cellulases significantly enhanced the hydrolysis of lignocellulose, achieving a 94% hydrolysis yield based on reducing sugar measurement, compared to 60% when no hemicellulase or 75% when Multifect enzyme was used under otherwise identical conditions. The significant improvement resulting from supplementing a hemicellulase mix with high side-chain removal activities suggests the importance of accessory hemicellulases in lignocellulose processing.

Escherichia coli binary culture engineered for direct fermentation of hemicellulose to a biofuel.

Metabolic engineering has created several Escherichia coli biocatalysts for production of biofuels and other useful molecules. However, the inability of these biocatalysts to directly use polymeric substrates necessitates costly pretreatment and enzymatic hydrolysis prior to fermentation. Consolidated bioprocessing has the potential to simplify the process by combining enzyme production, hydrolysis, and fermentation into a single step but requires a fermenting organism to multitask by producing both necessary enzymes and target molecules. We demonstrate here a binary strategy for consolidated bioprocessing of xylan, a complex substrate requiring six hemicellulases for complete hydrolysis. An integrated modular approach was used to design the two strains to function cooperatively in the process of transforming xylan into ethanol. The first strain was engineered to coexpress two hemicellulases. Recombinant enzymes were secreted to the growth medium by a method of lpp deletion with over 90% efficiency. Secreted enzymes hydrolyzed xylan into xylooligosaccharides, which were taken in by the second strain, designed to use the xylooligosaccharides for ethanol production. Cocultivation of the two strains converted xylan hemicellulose to ethanol with a yield about 55% of the theoretical value. Inclusion of other three hemicellulases improved the ethanol yield to 70%. Analysis of the culture broth showed that xylooligosaccharides with four or more xylose units were not utilized, suggesting that improving the use of higher xyloogligomers should be the focus in future efforts. This is the first demonstration of an engineered binary culture for consolidated bioprocessing of xylan. The modular design should allow the strategy to be adopted for a broad range of biofuel and biorefinery products.

Atomistic design of thermoelectric properties of silicon nanowires.

We present predictions of the thermoelectric figure of merit ( ZT) of Si nanowires with diameter up to 3 nm, based upon the Boltzman transport equation and ab initio electronic structure calculations. We find that ZT depends significantly on the wire growth direction and surface reconstruction, and we discuss how these properties can be tuned to select silicon based nanostructures with combined n-type and p-type optimal ZT. Our calculations show that only by reducing the ionic thermal conductivity by about 2 or 3 orders of magnitudes with respect to bulk values, one may attain ZT larger than 1, for 1 or 3 nm wires, respectively. We also find that ZT of p-doped wires is considerably smaller than that of their n-doped counterparts with the same size and geometry.