Synthesis of functional polyolefins using cationic bisphosphine monoxide-palladium complexes

The copolymerization of ethylene with polar vinyl monomers, such as vinyl acetate, acrylonitrile, vinyl ethers, and allyl monomers, was accomplished using cationic palladium complexes ligated by a bisphosphine monoxide (BPMO). The copolymers formed by these catalysts have highly linear microstructures and a random distribution of polar functional groups throughout the polymer chain. Our data demonstrate that cationic palladium complexes can exhibit good activity for polymerizations of polar monomers, in contrast to cationic α-diimine palladium complexes (Brookhart-type) that are not applicable to industrially relevant polar monomers beyond acrylates. Additionally, the studies reported here point out that phosphine-sulfonate ligated palladium complexes are no longer the singular family of catalysts that can promote the reaction of ethylene with many polar vinyl monomers to form linear functional polyolefins.     

Intercalation of n-Alkylamines and n-Alkyldiamines into γ-Zirconium Phenylphosphonate Phosphate

Crystalline -zirconium phenylphosphonate phosphate was prepared according to Yamanaka's method and the intercalation behavior of n-alkylamines and n-alkyldiamines were investigated. In the case of n-alkylamines, a linear increase in interlayer distance was observed up to a carbon atom number of 12, whereas in n-alkyldiamines, only two di-amines, ethylenediamine and propylenediamine, were intercalated with respective increases in the interlayer distance. The increment of interlayer distance in both monoamines and diamines indicates the formation of a monomolecular layer in the interlayer region of the host, in contrast to the case in -zirconium phosphate as a host.     

A novel total synthesis of isocryptolepine based on a microwave-assisted tandem Curtius rearrangement and aza-electrocyclic reaction

A new entry to the total synthesis of isocryptolepine (cryptosanguinolentine), isolated from Cryptolepis sanguinolenta, was achieved by constructing a tetracyclic ring system through a microwave-assisted tandem Curtius rearrangement and electrocyclic reaction of an aza 6π-electron system. The tetracyclic lactam was converted to isocryptolepine in a four-step sequence.     

Novel antiviral fucoidan from sporophyll of Undaria pinnatifida (Mekabu)

Structural characterization and antiviral activities of fucoidan from sporophyll of Undaria pinnatifida (Mekabu) was examined. The fucoidan was composed of fucose and galactose with an approximately ratio of 1.0:1.1. Degree of substitution of sulfate was 0.72 and its apparent molecular weight was 9,000. Methylation analyses showed that fucoidan had various sugar linkages, and revealed that the fucoidan might have complicated structure. This fucoidan showed potent antiviral activities against herpes simplex virus type 1 (HSV-1), HSV-2, and human cytomegalovirus.     

Bundling mRNA Strands to Prepare Nano‐Assemblies with Enhanced Stability Towards RNase for In Vivo Delivery

Ribonuclease (RNase)‐mediated degradation of messenger RNA (mRNA) poses a huge obstruction to in vivo mRNA delivery. Herein, we propose a novel strategy to protect mRNA by structuring mRNA to prevent RNase attack through steric hinderance. Bundling of mRNA strands through hybridization of RNA oligonucleotide linkers allowed the preparation of mRNA nano‐assemblies (R‐NAs) comprised of 7.7 mRNA strands on average, mostly below 100 nm in diameter. R‐NA formation boosted RNase stability by around 100‐fold compared to naïve mRNA and preserved translational activity, allowing protein production. A mechanistic analysis suggests that an endogenous mRNA unwinding mechanism triggered by 5′‐cap‐dependent translation may induce selective R‐NA dissociation intracellularly, leading to smooth translation. R‐NAs showed efficient mRNA transfection in mouse brain, demonstrating the feasibility for in vivo administration.     

Molecular dynamics simulations of nucleation from vapor to solid composed of Lennard-Jones molecules

We performed molecular dynamics (MD) simulations of nucleation from vapor at temperatures below the triple point for systems consisting of 10(4)-10(5) Lennard-Jones (L-J) type molecules in order to test nucleation theories at relatively low temperatures. Simulations are performed for a wide range of initial supersaturation ratio (S(0) ? 10-10(8)) and temperature (kT = 0.2-0.6ε), where ε and k are the depth of the L-J potential and the Boltzmann constant, respectively. Clusters are nucleated as supercooled liquid droplets because of their small size. Crystallization of the supercooled liquid nuclei is observed after their growth slows. The classical nucleation theory (CNT) significantly underestimates the nucleation rates (or the number density of critical clusters) in the low-T region. The semi-phenomenological (SP) model, which corrects the CNT prediction of the formation energy of clusters using the second virial coefficient of a vapor, reproduces the nucleation rate and the cluster size distributions with good accuracy in the low-T region, as well as in the higher-T cases considered in our previous study. The sticking probability of vapor molecules onto the clusters is also obtained in the present MD simulations. Using the obtained values of sticking probability in the SP model, we can further refine the accuracy of the SP model.     

Solvent-free asymmetric olefin hydroformylation catalyzed by highly cross-linked polystyrene-supported (R,S)-BINAPHOS-Rh(I) complex

Using an (R,S)-BINAPHOS-Rh(I) catalyst that is covalently anchored to a highly cross-linked polystyrene support, asymmetric hydroformylation of olefins was performed in the absence of organic solvents. The reaction of cis-2-butene, a gaseous substrate, provided (S)-2-methylbutanal with 100% regioselectivity and 82% ee upon treatment with H(2) (12 atm) and CO (12 atm) in a batchwise reactor equipped with a fixed bed. The polymer-supported catalyst was applicable to a continuous vapor-flow column reactor, and thus, 3,3,3-trifluoropropene was converted into (S)-2-trifluoromethylpropanal with an iso/normal ratio of 95/5 and 90% ee. Less volatile olefins, such as styrene, vinyl acetate, 1-alkenes, and fluorinated alkenes, were successfully converted into the corresponding isoaldehydes with high ee values, when they were injected through a supercritical CO(2)-flow column reactor. Successive injection of a series of olefins realized the conversion of an olefin library into an optically active aldehyde library.