Helical chirality of poly(quinoxaline-2,3-diyl)s bearing a boronyl pendant at the 5-position of the quinoxaline ring was induced by condensation with chiral guests such as a diol, diamine, and ...amino alcohol. Reversible induction of a single-handed helical structure was achieved by using less than an equimolar amount of chiral amino alcohols to the boronyl pendants. Majority-rule-effect-based chiral amplification on the polyquinoxaline main chain was demonstrated with chiral amino alcohols with low enantiomeric excess (ee). The helical macromolecular scaffold whose helicity was thus induced was utilized in palladium-catalyzed asymmetric silaboration of meso-methylenecyclopropane (up to 92% ee) by introducing (diarylphosphino)phenyl pendants at their side chains.
Argonaute proteins are key players in the gene silencing mechanisms mediated by small nucleic acids in all domains of life from bacteria to eukaryotes. However, little is known about the Argonaute ...protein that recognizes guide RNA/target DNA. Here, we determine the 2 Å crystal structure of Rhodobacter sphaeroides Argonaute (RsAgo) in a complex with 18-nucleotide guide RNA and its complementary target DNA. The heteroduplex maintains Watson-Crick base-pairing even in the 3'-region of the guide RNA between the N-terminal and PIWI domains, suggesting a recognition mode by RsAgo for stable interaction with the target strand. In addition, the MID/PIWI interface of RsAgo has a system that specifically recognizes the 5' base-U of the guide RNA, and the duplex-recognition loop of the PAZ domain is important for the DNA silencing activity. Furthermore, we show that Argonaute discriminates the nucleic acid type (RNA/DNA) by recognition of the duplex structure of the seed region.
Display omitted
•Syntheses of Au complexes featuring L2/Z-type ligands.•Analysis of interaction between Au and Z-type ligand.•Activation of catalytic reactions using L2/Z-Au complexes.
In the long ...history regarding the development of the transition metal-catalyzed reactions, almost all ligands in metals are classified as the covalent X-type and/or dative L-type ligands. Therefore, exploring the reactivity of the metal complexes bearing the σ-acceptor, i.e., the Z-ligand, is required. This digest briefly describes our recent results regarding 1) the syntheses of gold complexes featuring the Z-type ligand, and 2) their catalytic reactions, which would be speculated that the electron-withdrawing effect of the Z-ligand on the neighboring gold activated the catalytic reactivity due to the increase in the Lewis acidity.
Small particles attached to liquid surfaces arise in many products and processes, including crude-oil emulsions and food foams and in flotation, and there is a revival of interest in studying their ...behaviour. Colloidal particles of suitable wettability adsorb strongly to liquid-liquid and liquid-vapour interfaces, and can be sole stabilizers of emulsions and foams, respectively. New materials, including colloidosomes, anisotropic particles and porous solids, have been prepared by assembling particles at such interfaces. Phase inversion of particle-stabilized emulsions from oil in water to water in oil can be achieved either by variation of the particle hydrophobicity (transitional) or by variation of the oil/water ratio (catastrophic). Here we describe the phase inversion of particle-stabilized air-water systems, from air-in-water foams to water-in-air powders and vice versa. This inversion can be driven either by a progressive change in silica-particle hydrophobicity at constant air/water ratio or by changing the air/water ratio at fixed particle wettability, and has not been observed in the corresponding systems stabilized by surfactants. The simplicity of the work is that this novel inversion is achieved in a single system. The resultant materials in which either air or water become encapsulated have potential applications in the food, pharmaceutical and cosmetics industries.
Abstract
Insect-induced galls are microhabitats distinct from the outer environment that support inhabitants by providing improved nutrients, defence against enemies, and other unique features. It is ...intriguing as to how insects reprogram and modify plant morphogenesis. Because most of the gall systems are formed on trees, it is difficult to maintain them in laboratories and to comprehend the mechanisms operative in them through experimental manipulations. Herein, we propose a new model insect,
Smicronyx madaranus
, for studying the mechanisms of gall formation. This weevil forms spherical galls on the shoots of
Cuscuta campestris
, an obligate parasitic plant. We established a stable system for breeding and maintaining this ecologically intriguing insect in the laboratory, and succeeded in detailed analyses of the gall-forming behaviour, gall formation process, and histochemical and physiological features. Parasitic
C. campestris
depends on host plants for its nutrients, and usually shows low chlorophyll content and photosynthetic activity. We demonstrate that
S. madaranus-
induced galls have significantly increased CO
2
absorbance. Moreover, chloroplasts and starch accumulated in gall tissues at locations inhabited by the weevil larvae. These results suggest that the gall-inducing weevils enhance the photosynthetic activity in
C. campestris
, and modify the plant tissue to a nutrient-rich shelter for them.
Display omitted
The (P+B-P+)CuCl3-2 complex (P+B-P+ = phosphonium-borate-phosphonium) featuring the dication-monoanion-type counterion was synthesized. The resulting cationic copper catalyst enhanced ...the Mukaiyama-Aldol reaction of ketene silyl acetals and ketones for the formation of protected tertiary alcohols.
Oil (liquids with low surface tension and practically immiscible with water) drops can be dispersed in air if relatively oleophobic particles are available. However, such particles with oil‐repellent ...surfaces cannot simply be prepared by controlling the particle surface chemistry alone. Herein the preparation of oil‐in‐air materials (oil marbles, dry oils) by changing the wetting behavior of particles by tuning the oil properties, which allows the formation of the metastable Cassie–Baxter wetting state of particle assemblies on oil drop surfaces, is presented. The oil‐in‐air materials can be converted to air‐in‐oil materials (non‐aqueous foams) by tailoring the oil properties, as the robustness of the metastable Cassie–Baxter state of the particle assemblies critically depends on the particle wettability. This conversion implies the phase inversion of dispersed systems consisting of air and oils. It is also shown that particle‐stabilized non‐aqueous foams can be utilized as template to produce macroporous polymers.
Fluid‐dispersed systems consisting of air and oils are stabilized by adsorption of colloidal particles at air–oil surfaces. Particle assemblies with oil‐repellent surfaces produced by utilizing metastable Cassie–Baxter state stabilize oil drops dispersed in air, such as dry oils. Air bubbles dispersed in oil (non‐aqueous foams) are formed by controlling the particle wetting behavior.
The palladium‐catalyzed asymmetric side‐chain C(α)‐allylation of 2‐alkylpyridines, without using an external base, was developed. The high linear selectivities and enantioselectivities were achieved ...using new chiral diamidophosphite monodentate ligands. Given that the reaction conditions do not require an external base, this catalyst system enabled chemoselective C(α)‐allylation of 2‐alkylpyridines containing α‐carbonyl C−H bonds, which are more acidic than α‐pyridyl C−H bonds.
No branching out: The palladium‐catalyzed asymmetric side‐chain C(α)‐allylation of 2‐alkylpyridines was developed. The high linear selectivities and enantioselectivities were achieved using a new chiral ligand. This catalyst system enabled chemoselective C(α)‐allylation of 2‐alkylpyridines containing α‐carbonyl C−H bonds, which are more acidic than α‐pyridyl C−H bonds.
The synthesis of 2,2-dimethyloxepane frameworks based on the 7-endo-trig cyclization of ene-diol using a catalytic amount of metal catalysts (Au, Ag) or Brønsted acid (TfOH) has been developed. Also, ...the spiro-type dioxabicyclic products were also derived from the diene-diols. For the condition using metal catalysts, the cyclization selectively reacted between the 1,1,3-trisubstituted alkenes and alcohols to form the 2,2-dimethyloxepane frameworks. On the other hand, the TfOH reacted with not only the 1,1,2-trisubstituted alkene, but also the 1-substituted and 1,2-disubstituted alkenes providing the corresponding cyclic ethers, which is quite different from the conditions of the metal catalysts.
PDF
