Intrinsic Defects and Electronic Conductivity of TaON: First-Principles Insights

As a compound in between the tantalum oxide and nitride, the tantalum oxynitride TaON is expected to combine their advantages and act as an efficient visible-light-driven photocatalyst. In this letter, using hybrid functional calculations we show that TaON has different defect properties from the binary tantalum oxide and nitride: (i) instead of O or N vacancies or Ta interstitials, the $O_N$ antisite is the dominant defect, which determines its intrinsic n-type conductivity and the p-type doping difficulty; (ii) the $O_N$ antisite has a shallower donor level than O or N vacancies, with a delocalized distribution composed mainly of the Ta $5d$ orbitals, which gives rise to better electronic conductivity in the oxynitride than in the oxide and nitride. The phase stability analysis reveals that the easy oxidation of TaON is inevitable under O rich conditions, and a relatively O poor condition is required to synthesize stoichiometric TaON samples

Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution

We introduce an approach to calculate the thermodynamic oxidation and reduction potentials of semiconductors in aqueous solution. By combining a newly-developed ab initio calculation for compound formation energy and band alignment with electrochemistry experimental data, this approach can be used to predict the stability of almost any compound semiconductor in aqueous solution. 30 photocatalytic semiconductors have been studied, and a graph (a simplified Pourbaix diagram) showing their valence/conduction band levels and oxidation/reduction potentials is produced. Based on this graph, we have studied the stabilities and trends against the oxidative and reductive photocorrosion for compound semiconductors. We found that, only metal oxides can be thermodynamically stable when used as the n-type photoanodes. All the non-oxides are unstable due to easy oxidation by the photogenerated holes, but they can be resistant to the reduction by electrons, thus stable as the p-type photocathodes

Phytochemistry of Camptotheca Decaisne

To date, chemical investigations of the genus Camptotheca have been primarily focused on C. acuminata. Total 78 compounds have been isolated from the species, including alkaloids (1-28), ellagic acids (29-40), flavonoids (41-46), sterols (47-48), terpenes (49-55), tannins (56-71), polyphenols and fatty acids (65-72), iridoid (73), lignan (74), polyols (75 and 76), amide (77), and sacchardide (78). The contents of camptothecin (CPT, 1), the major active alkaloid varies significantly with Camptotheca species and varieties, tissue and tree age and seasonal changes. Among all taxa of Camptotheca, C. acuminata var. acuminata has the lowest CPT contents (0.2249-0.3162% in young leaves, and 0.0392- 0.0572% in older leaves). C. lowreyana “Hicksii” has the highest CPT contents in both young and old leaves, approximately 1.5-2 folds higher than those in C. acuminata var. acuminata. Young leaves and mature fruits have high CPT contents than other tissues in Camptotheca. In young tissues of C. acuminata var. acuminata, the lowest CPT levels were found in March and April (0.074% and 0.081%, respectively) and highest in June (0.265%)

Endocidal Regulation of Secondary Metabolites in the Producing Organisms

Secondary metabolites are defined as organic compounds that are not directly involved in the normal growth, development, and reproduction of an organism. They are widely believed to be responsible for interactions between the producing organism and its environment, with the producer avoiding their toxicities. In our experiments, however, none of the randomly selected 44 species representing different groups of plants and insects can avoid autotoxicity by its endogenous metabolites once made available. We coined the term endocides (endogenous biocides) to describe such metabolites that can poison or inhibit the parent via induced biosynthesis or external applications. Dosage-dependent endocides can selectively induce morphological mutations in the parent organism (e.g., shrubbiness/dwarfism, pleiocotyly, abnormal leaf morphogenesis, disturbed phyllotaxis, fasciated stems, and variegation in plants), inhibit its growth, development, and reproduction and cause death than non-closely related species. The propagule, as well as the organism itself contains or produces adequate endocides to kill itself

Genetic Diversity in Camptotheca Decaisne

RAPD markers were used to reveal the genetic diversity of the genus Camptotheca. Three primers (OPA02, OPA03, and OPA04), generating 44 polymorphic bands using randomly amplified polymorphic DNA (RAPD) markers, were able to discriminate among 25 Camptotheca populations. The band size varied from 268-4,411bp, with an average of 15 bands/primer. Of these populations, cultivars ‘Katie’ (KT) and ‘Ang’ (AG) of C. lowreyana and cultivated A1a (HJ) of C. acuminata can be easily distinguished by their unique bands. Population differentiation of Camptotheca was found to be higher than in other species with similar breeding systems. Cluster analysis of the genetic distance values and dendrogram from RAPD markers were consistent with the phenotypic data and both support the current taxonomic treatment of Camptotheca. Camptotheca acuminata var. acuminata appeared as the closest relative of C. yunnanensis, followed at some distance by C. lowreyana and, further away, C. acuminata var. tenuifolia

National Center for Pharmaceutical Crops

The mission of the National Center for Pharmaceutical Crops is to develop crops for the production of pharmaceutical and other bioactive compounds. The NCPC, located in the Arthur Temple College of Forestry and Agriculture, is the only one of its kind in the U.S. and it seeks to improve human health, revitalize rural economies and enhance U.S. security in strategic pharmaceuticals. This poster provides a background to the department, its functions and activities and notable achievements

Trichome Management to Enhance Camptothecins in Camptotheca Decaisne

Inducible chemical defenses of plants have received much attention in the last three decades, and these defenses often involve trichomes. It is known that some plant secondary metabolites may accumulate in trichomes which can protect plants from damage by herbivores. However, studies on plant trichomes are largely limited to some major vegetable or cash crops and model species with large glandular trichomes (e.g., Nictotiana and Arabidopsis). In fact, the existing studies on the effect of damage (pruning or defoliation) on trichome density or chemical production in plants are partial and even contradictory. Management strategies to maximize chemical induction in medicinal plants or pharmaceutical crops have not been developed well. Our experiments showed that camptothecins (CPTs) are primarily accumulated in glandular trichomes in Camptotheca. We found that pruning, particularly decapitation pruning (T-pruning) can effectively induce contents and derivatization of CPTs in Camptotheca, and the leveled CPTs caused induced endogenous autotoxicity (abnormal morphogenesis) in the plants. Auxin reduction is a trigging factor for such induced biosynthesis and endogenous autotoxicity. Because trichomes are visible to the naked eye and can be much more easily targeted and measured than CPTs, the term “Trichome Management” is used for strategy development to induce CPTs in Camptotheca