Rhodium-Catalyzed Synthesis of Silicon-Bridged 1,2-Dialkenylbenzenes via 1,4-Rhodium Migration.

An efficient synthesis of 1,3-dialkylidene-2,3-dihydro-1 H-benzo[ c]siloles, a new type of silicon-bridged π-conjugated compounds, was developed from a simple substrate combination of dialkynylsilanes and arylboronic acids under rhodium catalysis through the use of 1,4-rhodium migration. The reaction pathway was probed by deuterium-labeling experiments, and the use of o-tolylboronic acids led to the formation of 6-membered silacycles via 1,5-rhodium migration.

Blue organic light-emitting diodes realizing external quantum efficiency over 25% using thermally activated delayed fluorescence emitters.

Improving the performance of blue organic light-emitting diodes (OLEDs) is needed for full-colour flat-panel displays and solid-state lighting sources. The use of thermally activated delayed fluorescence (TADF) is a promising approach to efficient blue electroluminescence. However, the difficulty of developing efficient blue TADF emitters lies in finding a molecular structure that simultaneously incorporates (i) a small energy difference between the lowest excited singlet state (S1) and the lowest triplet state (T1), ΔE ST, (ii) a large oscillator strength, f, between S1 and the ground state (S0), and (iii) S1 energy sufficiently high for blue emission. In this study, we develop TADF emitters named CCX-I and CCX-II satisfying the above requirements. They show blue photoluminescence and high triplet-to-singlet up-conversion yield. In addition, their transition dipole moments are horizontally oriented, resulting in further increase of their electroluminescence efficiency. Using CCX-II as an emitting dopant, we achieve a blue OLED showing a high external quantum efficiency of 25.9%, which is one of the highest EQEs in blue OLEDs reported previously.

Nonhost resistance of Arabidopsis thaliana against Alternaria alternata involves both pre- and postinvasive defenses but is collapsed by AAL-toxin in the absence of LOH2.

The tomato pathotype of Alternaria alternata causes Alternaria stem canker on tomato depending upon the production of the host-specific AAL-toxin. Host defense mechanisms to A. alternata, however, are largely unknown. Here, we elucidate some of the mechanisms of nonhost resistance to A. alternata using Arabidopsis mutants. Wild-type Arabidopsis showed either no symptoms or a hypersensitive reaction (HR) when inoculated with both strains of AAL-toxin-producing and non-producing A. alternata. Yet, when these Arabidopsis penetration (pen) mutants, pen2 and pen3, were challenged with both strains of A. alternata, fungal penetration was possible. However, further fungal development and conidiation were limited on these pen mutants by postinvasion defense with HR-like cell death. Meanwhile, only AAL-toxin-producing A. alternata could invade lag one homologue (loh)2 mutants, which have a defect in the AAL-toxin resistance gene, subsequently allowing the fungus to complete its life cycle. Thus, the nonhost resistance of Arabidopsis thaliana to A. alternata consists of multilayered defense systems that include pre-invasion resistance via PEN2 and PEN3 and postinvasion resistance. However, our study also indicates that the pathogen is able to completely overcome the multilayered nonhost resistance if the plant is sensitive to the AAL-toxin, which is an effector of the toxin-dependent necrotrophic pathogen A. alternata.

Gpr1, a putative G-protein-coupled receptor, regulates morphogenesis and hypha formation in the pathogenic fungus Candida albicans.

In response to various extracellular signals, the morphology of the human fungal pathogen Candida albicans switches from yeast to hypha form. Here, we report that GPR1 encoding a putative G-protein-coupled receptor and GPA2 encoding a Galpha subunit are required for hypha formation and morphogenesis in C. albicans. Mutants lacking Gpr1 (gpr1/gpr1) or Gpa2 (gpa2/gpa2) are defective in hypha formation and morphogenesis on solid hypha-inducing media. These phenotypic defects in solid cultures are suppressed by exogenously added dibutyryl-cyclic AMP (dibutyryl-cAMP). Biochemical studies also reveal that GPR1 and GPA2 are required for a glucose-dependent increase in cellular cAMP. An epistasis analysis indicates that Gpr1 functions upstream of Gpa2 in the same signaling pathway, and a two-hybrid assay reveals that the carboxyl-terminal tail of Gpr1 interacts with Gpa2. Moreover, expression levels of HWP1 and ECE1, which are cAMP-dependent hypha-specific genes, are reduced in both mutant strains. These findings support a model that Gpr1, as well as Gpa2, regulates hypha formation and morphogenesis in a cAMP-dependent manner. In contrast, GPR1 and GPA2 are not required for hypha formation in liquid fetal bovine serum (FBS) medium. Furthermore, the gpr1 and the gpa2 mutant strains are fully virulent in a mouse infection. These findings suggest that Gpr1 and Gpa2 are involved in the glucose-sensing machinery that regulates morphogenesis and hypha formation in solid media via a cAMP-dependent mechanism, but they are not required for hypha formation in liquid medium or during invasive candidiasis.