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Edge termination is the key building block in power devices to enable near-ideal, avalanche breakdown voltage (BV). This work presents the design, fabrication, and physics of a GaN guard ring (GR) edge termination formed by selective-area nitrogen implantation through an epitaxial p-GaN layer. The fabrication of this termination only includes a single implantation step that does not require precise control of implant depth, rendering a large process latitude. The selective-area implantation produces p-GaN rings that are separated by the implanted, semi-insulating regions. The number and spacing of the p-type rings are found to determine the BV of the vertical GaN p-n diode. The 16-ring structure enables a BV of 1800 V, being 88% of the theoretical 1-D parallel-plane limit. Avalanche characteristics are observed in devices with a large variety of GR designs. Finally, we present a comprehensive survey on the efficiency, fabrication complexity, real estate, and avalanche capability of various edge termination techniques that have been reported in vertical GaN devices. The high efficiency (among the highest reported in avalanche-capable GaN terminations), simple and robust fabrication process, and uniform avalanche capability make this implanted GR a promising edge termination for high-voltage GaN devices.

The Reaction Mechanism Generator (RMG) database for chemical property prediction is presented. The RMG database consists of curated datasets and estimators for accurately predicting the parameters necessary for constructing a wide variety of chemical kinetic mechanisms. These datasets and estimators are mostly published and enable prediction of thermodynamics, kinetics, solvation effects, and transport properties. For thermochemistry prediction, the RMG database contains 45 libraries of thermochemical parameters with a combination of 4564 entries and a group additivity scheme with 9 types of corrections including radical, polycyclic, and surface absorption corrections with 1580 total curated groups and parameters for a graph convolutional neural network trained using transfer learning from a set of >130 000 DFT calculations to 10 000 high-quality values. Correction schemes for solvent–solute effects, important for thermochemistry in the liquid phase, are available. They include tabulated values for 195 pure solvents and 152 common solutes and a group additivity scheme for predicting the properties of arbitrary solutes. For kinetics estimation, the database contains 92 libraries of kinetic parameters containing a combined 21 000 reactions and contains rate rule schemes for 87 reaction classes trained on 8655 curated training reactions. Additional libraries and estimators are available for transport properties. All of this information is easily accessible through the graphical user interface at https://rmg.mit.edu. Bulk or on-the-fly use can be facilitated by interfacing directly with the RMG Python package which can be installed from Anaconda. The RMG database provides kineticists with easy access to estimates of the many parameters they need to model and analyze kinetic systems. This helps to speed up and facilitate kinetic analysis by enabling easy hypothesis testing on pathways, by providing parameters for model construction, and by providing checks on kinetic parameters from other sources.

Small airways are known to be affected early in the course of COPD; however, traditional spirometric indices may not accurately identify small airways disease.

An efficient general methodology for the synthesis of 4-quinolinyl ethers is demonstrated via a highly reactive SNAr reaction of 4-quinolinyl sulfones with a range of structurally diversified 1°, 2°, and 3° alcohols with a wide substrate scope and high yields. By adapting this methodology, a convergent synthesis of a complex target of HCV NS3/4a protease inhibitor BI 201420was accomplished.

5-Cyanoimidazole was identified as an inexpensive ligand for nickel-catalyzed cross-electrophile couplings by screening a diverse set of pharmaceutical compound library. A strategic screening approach led to the discovery of this novel ligand, which was successfully applied in the preparation of various alkylated arene products with good to high yields. Furthermore, the properties of this ligand allowed expanding the scope of reductive couplings to challenging substrates, such as sterically hindered neopentyl halides, which are known to generate motifs that are prevalent in biologically active molecules.

We report the serendipitous discovery and synthesis of an indigoid “semi-Nindigo” (2) via oxidation of a diindolopyrrole (1). The reaction of 2with BF3Et2O affords the borylated derivative (3). The electronic spectra of 2and 3possess intense long wave absorptions near 600 and 650 nm. Compound 3is weakly emissive in the near-infrared. Thin-film OFETs fabricated with 1and 2both exhibited hole mobility of 10–5and 10–3cm2/(V s), respectively.

A practical and efficient synthesis of the FLAP inhibitor 1was developed addressing multiple scale-up and safety concerns posed by the established synthesis and utilized a resolution strategy (replacing supercritical fluid chromatography (SFC) separation) for expedient access to the key structural component of 1: the challenging chiral quaternary center. Also highlighted are in situ IR monitoring, condensation to form the 1,2,4-oxadiazole ring, and an efficient Suzuki-Miyaura coupling.

Enantioselective synthesis of α-aryl and α-heteroaryl piperidines is reported. The key step is an iridium-catalyzed asymmetric hydrogenation of substituted N-benzylpyridinium salts. High levels of enantioselectivity up to 99.3:0.7 er were obtained for a range of α-heteroaryl piperidines. DFT calculations support an outersphere dissociative mechanism for the pyridinium reduction. Notably, initial protonation of the final enamine intermediate determines the stereochemical outcome of the transformation rather than hydride reduction of the resultant iminium intermediate.

The anaerobic bacterium Geobacter bemidijensisBem has the unique ability to both produce and degrade methylmercury (MeHg). While the adsorption of MeHg onto bacterial surfaces can affect the release of MeHg into aquatic environments as well as the uptake of MeHg for demethylation, the binding of MeHg to the bacterial envelope remains poorly understood. In this study, we quantified the adsorption of MeHg onto G. bemidijensisand applied X-ray absorption spectroscopy (XAS) to elucidate the mechanism of MeHg binding. The results showed MeHg adsorption onto G. bemidijensiscell surfaces was rapid and occurred via complexation to sulfhydryl functional groups. Titration experiments yielded cell surface sulfhydryl concentrations of 3.8 ± 0.2 μmol/g (wet cells). A one-site adsorption model with MeHg binding onto sulfhydryl sites provided excellent fits to adsorption isotherms conducted at different cell densities. The log K binding constant of MeHg onto the sulfhydryl sites was determined to be 10.5 ± 0.4. These findings provide a quantitative framework to describe MeHg binding onto bacterial cell surfaces and elucidate the importance of bacterial cells as possible carriers of adsorbed MeHg in natural aquatic systems.

The Joint Workshop on Induced Special Regions convened scientists and planetary protection experts to assess the potential of inducing special regions through lander or rover activity. An Induced Special Region is defined as a place where the presence of the spacecraft could induce water activity and temperature to be sufficiently high and persist for long enough to plausibly harbor life.

The application of a Buchwald’s third generation palladacycle containing a dihydrobenzooxaphosphole-based ligand (e.g., BIDIME) was reported in the Suzuki cross-coupling reaction. Using flow technology, high yield and reproducible Suzuki cross-coupling reaction for one of our key intermediates was achieved with Pd loadings as low as 0.5 mol %. This continuous flow approach overcomes catalyst deactivation and scale dependence issues that can be a problem in some traditional batch-mode operations and responds to the challenge of improving process greenness.

Systemic administration of antibiotics can cause severe side-effects such as liver and kidney toxicity, destruction of healthy gut bacteria, as well as multidrug resistance. Here, we present a bio-orthogonal chemistry-based strategy toward local prodrug concentration and activation. The strategy is based on the inverse electron-demand Diels–Alder chemistry between trans-cyclooctene and tetrazine and involves a biomaterial that can concentrate and activate multiple doses of systemic antibiotic therapy prodrugs at a local site. We demonstrate that a biomaterial, consisting of alginate hydrogel modified with tetrazine, is efficient at activating multiple doses of prodrugs of vancomycin and daptomycin in vitroas well as in vivo. These results support a drug delivery process that is independent of endogenous environmental markers. This approach is expected to improve therapeutic efficacy with decreased side-effects of antibiotics against bacterial infections. The platform has a wide scope of possible applications such as wound healing, and cancer and immunotherapy.

An efficient, sustainable, and broadly applicable procedure has been developed for Suzuki–Miyaura cross‐coupling reactions in environmentally benign solvent (water) by employing as little as 500 ppm Pd(OAc)2with a monophosphorus BI‐DIME ligand in the presence of inexpensive and commercially available nonionic surfactant Triton X‐100. This method was applied to a broad range of functionalized reaction partners, thereby affording excellent yields of the coupling products, including active pharmaceutical ingredients (APIs). An interesting kinetic study by using reaction calorimetry is also presented, which describes the effect of reaction parameters that enabled the low catalyst loading. Turning on a DIME: A p‐donating BI‐DIME ligand in the presence of Triton X‐100 surfactant in water showed excellent activity for Suzuki–Miyaura cross‐coupling reactions at low Pd(OAc)2loading (500 ppm) to afford various biaryl and heterobiaryl products in high yields. A kinetic study enabled a further decrease in the catalyst loading and this method was successfully applied to the synthesis of active pharmaceutical ingredients (APIs).

Biaryl‐Monophosphorligandenmit einem 2,3‐Dihydrobenzo[d][1,3]oxaphosphol‐Gerüst ergeben hoch effiziente palladiumkatalysierte Suzuki‐Miyaura‐Kreuzkupplungen mit verschiedenartigen Substraten. Der Ligand 1eignet sich außerordentlich gut für Kupplungen von sterisch stark gehinderten Arylboronsäuren.

An unexpected highly exothermic decomposition was observed during routine safety analysis of the magnesium-iodine exchange reaction of 2-iodo-4-fluorotoluene (3) with commercially available i-PrMgCl (2.0 M solution in THF). When the reaction mixture was scanned in an adiabatic calorimeter with the use of a 2 °C/min temperature ramp, a rapid exothermic decomposition with an onset temperature of approximately 80 °C was observed. The system temperature rapidly rose to 210 °C at a peak rate of 200 °C/min. Subsequent testing of three simplified substrates showed the same type of exothermic decomposition for all cases. Control experiments indicated that the decomposition requires both aryl iodide and i-PrMgCl (or arylMgCl and i-PrI). While the onset temperatures for all cases studied were generally well above the typical operating temperature for these reactions (0-10 °C), it is nonetheless important to cautiously evaluate these types of processes and install proper engineering controls for analogous decomposition events.

Supercritical CO2was used to remove ruthenium catalyst and its derived by-products from a crude ring-closing metathesis reaction. The method was implemented in a semi-continuous fashion and allowed for efficient removal of the toxic metal impurities to meet the specifications for the final drug substance.

In this study, we quantified the rate of ferrihydrite conversion to goethite via the Fe(II) pathway using synchrotron radiation-based energy dispersive X-ray diffraction (ED-XRD). Ferrihydrite transformation experiments were conducted in oxygen-free solutions at neutral pH with synthetic 2-line ferrihydrite reacting with 100 mM Fe(II). The kinetics of goethite crystallization was measured in situ at temperatures ranging from 21 to 90 °C. The results showed that in the presence of ferrous iron, the transformation of poorly ordered ferrihydrite into crystalline goethite is rapid and highly dependent on temperature. The time-resolved peak area data fitted using a Johnson-Mehl-Avrami-Kolmogorov (JMAK) kinetic model yielded rate constants of 4.0 x 10-5, 1.3 x 10-4, 3.3 x 10-4, 2.27 x 10-3, and 3.14 x 10-31/s at reaction temperatures of 21, 45, 60, 85, and 90 °C respectively. The activation energy for the transformation was determined to be 56 ± 4 kJ/mol. Comparison with the activation energy predicted for the phase conversion in the absence of ferrous iron indicates that Fe(II) acts as a catalyst that decreases the activation energy barrier by approximately 38 kJ/mol. The kinetic parameters derived from the experimental data suggest that goethite crystallization is controlled by a 1-D phase boundary growth mechanism with a constant nucleation rate occurring during the reaction

1-Aryl-1H-indazoles were synthesized by the palladium-catalyzed intramolecular amination [Pd(OAc)2/dppf/tBuONa (150 mol%)/toluene/90°C] of the corresponding N-aryl-N′-(o-bromobenzyl)hydrazines. It was further demonstrated that cyclization of [N-aryl-N′-(o-bromobenzyl)-hydrazinato-N′]-triphenylphosphonium bromides under the conditions of [Pd(OAc)2/dppf/tBuONa (250 mol%)/dioxane/90°C] also led to the formation of the corresponding 1-aryl-1H-indazoles. These methods were applied to a group of representative substrates to give indazole products in moderate to very good yields.

A practical and general method for the stereoselective synthesis of trans-4,5-disubstituted 2-pyrrolidinones was developed. Hydride reduction of these pyrrolidinones gave the corresponding pyrrolidines.

The biosynthesis of diterpene hydrocarbons with enzyme extracts from rice cell suspension cultures was investigated to verify proposed pathways and intermediates in the production of the momilactone and oryzalexin phytoalexins. Diterpene synthase activity in cells treated with chitin to elicit the phytoalexin response was compared with the activity in untreated cells using the acyclic substrates [1-3H](E,E,E)- and [1-3H](E,Z,E)-geranylgeranyl diphosphates (GGPPs 4-OPP and 11-OPP) as well as the bicyclic substrates [15-3H]ent-copalyl and [15-3H]syn-copalyl diphosphates (CPPs, 5-OPP, and 6-OPP).ent-kaurene (7),ent-sandaracopimaradiene (8), 9βH-pimara-7,15-diene (9), and stemar-13-ene (10) were identified as major products by comparisons with authentic standards. Marked increases in diterpene synthase activities were observed with enzyme from chitin-treated cells: (E,E,E)-GGPP (∼100 fold),ent-CPP (∼3 fold), andsyn-CPP (∼60 fold). The very low conversions of (E,Z,E)-GGPP to hydrocarbon products excludes its role in the biosynthesis of 9,10-syn-diterpenes in rice cells.ent-Kaurene was the major diterpene formed froment-CPP with enzyme from unelicited cells. In contrast the enzyme from chitin-treated cells convertedent-CPP to a mixture ofent-kaurene,ent-sandaracopimaradiene, and a third unidentified diterpene. Withsyn-CPP as substrate the induced synthases afforded a mixture of 9β-pimaradiene, stemarene, and a third, unidentifiedsyn-diterpene. Overall the results are consistent with the hypothesis that rice cells respond to treatment with chitin fragments by producing new diterpene synthases not present in the untreated cells. These induced cyclases initiate phytoalexin biosynthesis by diverting (E,E,E)-GGPP into new cyclization modes that produceent-sandaracopimaradiene, stemarene, and 9β-pimaradiene, the presumed precursors to oryzalexins A–F, oryzalexin S, and momilactones A–C, respectively. The intermediate role of 9,10-syn-CPP in syn diterpene biosynthesis is verified.

Tellurium (Te) is an emerging contaminant and its chemical transformation in the environment is strongly influenced by microbial processes. In this study, we investigated the adsorption of tellurite [Te(IV), TeO32–] onto the common soil bacterium Bacillus subtilis. Thiol-blocking experiments were carried out to investigate the role of cell surface sulfhydryl sites in tellurite binding, and extended X-ray absorption fine structure (EXAFS) spectroscopy was performed to determine the chemical speciation of the adsorbed tellurite. The results indicate that tellurite reacts with sulfhydryl functional groups in the extracellular polymeric substances (EPS) produced by B. subtilis. Upon binding to sulfhydryl sites in the EPS, the Te changes from Te–O bonds to Te–S coordination. Further analysis of the surface-associated molecules shows that the EPS of B. subtiliscontain proteins. Removal of the proteinaceous EPS dramatically decreases tellurite adsorption and the sulfhydryl surface site concentration. These findings indicate that sulfhydryl binding in EPS plays a key role in tellurite adsorption on bacterial surfaces.

We report a comparative study of two structurally similar donor–acceptor complexes with (1a) and without (2a) H-bonding using X-ray crystallography, spectroscopic analysis, and density functional theory calculations. H-Bonding enhances the donor–acceptor interactions, as manifested in a narrower band gap and shorter π-stacking distance in 1aversus 2a, despite 2being a stronger donor than 1. Thin-film transistors of 1ashowed ambipolar charge transport with “double dip” characteristics, whereas no transistor behavior was observed for 2a.

In chemical kinetics research, kinetic models containing hundreds of species and tens of thousands of elementary reactions are commonly used to understand and predict the behavior of reactive chemical systems. Reaction Mechanism Generator (RMG) is a software suite developed to automatically generate such models by incorporating and extrapolating from a database of known thermochemical and kinetic parameters. Here, we present the recent version 3 release of RMG and highlight improvements since the previously published description of RMG v1.0. Most notably, RMG can now generate heterogeneous catalysis models in addition to the previously available gas- and liquid-phase capabilities. For model analysis, new methods for local and global uncertainty analysis have been implemented to supplement first-order sensitivity analysis. The RMG database of thermochemical and kinetic parameters has been significantly expanded to cover more types of chemistry. The present release includes parallelization for faster model generation and a new molecule isomorphism approach to improve computational performance. RMG has also been updated to use Python 3, ensuring compatibility with the latest cheminformatics and machine learning packages. Overall, RMG v3.0 includes many changes which improve the accuracy of the generated chemical mechanisms and allow for exploration of a wider range of chemical systems.

Sterically hindered aryl bromides and chlorides are converted with very low catalyst loadings using the new monophosphorus ligand (Ia) and Bedford′s Pd precursor (II).

Compared to the most common cross‐coupling electrophiles, triflate as counterion has the highest reactivity.

The method utilizes low catalyst loadings with very short reaction times.

Based on the regioselective Suzuki‐type N‐arylation of the imidazole (I), an alternative route to the p38 MAP kinase inhibitor BIRB796 (IIIa) and different analogues is developed.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.