Thermal Conductivity of poly-p-phenylene-2,6-benzobisoxazole Film along the In-Plane Axis in the 10–300 K Temperature Range

The thermal conductivities of compression molded thin films of poly-p-phenylene-2,6-benzobisoxazole (PBO) were measured in directions along an in-plane axis in the 10–300?K temperature range by a steady-state heat flow method, with interest in the use of the material for superconductivity applications. The thermal conductivities of the PBO films increased from 0.3?W/mK to 9.0?W/mK with increasing temperature from 10?K to 300?K and these were much higher than those of polyimide films, epoxy resin and glass fiber reinforced plastics at all temperatures. The 9.0?W/mK at 300?K was 60% of that of stainless steel (SUS304). It was 6?W/mK at 150?K, which was half that of SUS304 and was 3.3?W/mK at 77?K, which was 33% of that of SUS304. The thermal conductivities of the PBO films were lower than those of a cloth of high strength ultrahigh molecular weight polyethylene fiber reinforced plastics in the 30?K–180?K temperature range and were almost equivalent to its values in the 180?K–300?K temperature range. The main contribution to the thermal conduction in the PBO films was from thermal phonon conduction along the molecular chains. Although many kinds of high thermal conductivity polymeric materials have been prepared by a uni-directional drawing process or by adding high thermal conductive additives, the PBO film showed high thermal conductivity without a uni-directional drawing process or high thermal conductive additive.     

Disulfide‐Unit Conjugation Enables Ultrafast Cytosolic Internalization of Antisense DNA and siRNA

Development of intracellular delivery methods for antisense DNA and siRNA is important. Previously reported methods using liposomes or receptor‐ligands take several hours or more to deliver oligonucleotides to the cytoplasm due to their retention in endosomes. Oligonucleotides modified with low molecular weight disulfide units at a terminus reach the cytoplasm 10 minutes after administration to cultured cells. This rapid cytoplasmic internalization of disulfide‐modified oligonucleotides suggests the existence of an uptake pathway other than endocytosis. Mechanistic analysis revealed that the modified oligonucleotides are efficiently internalized into the cytoplasm through disulfide exchange reactions with the thiol groups on the cellular surface. This approach solves several critical problems with the currently available methods for enhancing cellular uptake of oligonucleotides and may be an effective approach in the medicinal application of antisense DNA and siRNA.     

Hydrogen bond donors and acceptors are generally depolarized in α-helices as revealed by a molecular tailoring approach

Hydrogen-bond (H-bond) interaction energies in α-helices of short alanine peptides were systematically examined by precise density functional theory calculations, followed by a molecular tailoring approach. The contribution of each H-bond interaction in α-helices was estimated in detail from the entire conformation energies, and the results were compared with those in the minimal H-bond models, in which only H-bond donors and acceptors exist with the capping methyl groups. The former interaction energies were always significantly weaker than the latter energies, when the same geometries of the H-bond donors and acceptors were applied. The chemical origin of this phenomenon was investigated by analyzing the differences among the electronic structures of the local peptide backbones of the α-helices and those of the minimal H-bond models. Consequently, we found that the reduced H-bond energy originated from the depolarizations of both the H-bond donor and acceptor groups, due to the repulsive interactions with the neighboring polar peptide groups in the α-helix backbone. The classical force fields provide similar H-bond energies to those in the minimal H-bond models, which ignore the current depolarization effect, and thus they overestimate the actual H-bond energies in α-helices. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.     

Search for lepton-flavor-violating decays of the neutral kaon

The Fermilab KTeV experiment has searched for lepton-flavor-violating decays of the K(L) meson in three decay modes. We observe no events in the signal region for any of the modes studied, and we set the following upper limits for their branching ratios at the 90% C.L.: BR(K(L) --> pi(0) micro(+/-) e(-/+)) <7.6 x 10(-11); BR(K(L) --> pi(0)pi(0) micro(+/-) e(-/+)) <1.7 x 10(-10); BR(pi(0) --> micro(+/-) e(-/+)) <3.6 x 10(-10). This result represents a factor of 82 improvement in the branching ratio limit for K(L) --> pi(0) micro(+/-) e(-/+) and is the first reported limit for K(L) --> pi(0)pi(0) micro(+/-) e(-/+).     

Redox‐Driven Symmetry Change for Terbium(III) Bis(porphyrinato) Double‐Decker Complexes by the Azimuthal Rotation of the Porphyrin Macrocycles

Molecular structures for three oxidation forms (anion, radical, and cation) of terbium(III) bis(porphyrinato) double‐decker complexes have been systematically studied. We found that the redox state controls the azimuthal rotation angle (φ) between the two porphyrin macrocycles. For [Tb^III(tpp)₂]ⁿ (tpp: tetraphenylporphyrinato, n=?1, 0, and +1), φ decreases at each stage of the oxidation process. The decrease in φ is due to the higher steric repulsion between the phenyl rings on the porphyrin macrocycle and the β hydrogen atoms on the other porphyrin macrocycle, which results from the shorter interfacial distance between the two porphyrin macrocycles. Conversely, φ=45° for both [Tb^III(oep)₂]^?1 and [Tb^III(oep)₂]⁰ (oep: octaethylporphyrinato), but φ=36° for [Tb^III(oep)₂]⁺¹. Theoretical calculations suggest that the smaller azimuthal rotation angle of the cation form is due to the electronic interaction in the doubly oxidized ligand system.     

Chiral Carboxylic Acid Enabled Achiral Rhodium(III)‐Catalyzed Enantioselective C−H Functionalization

Reported is an achiral Cp^xRh^III/chiral carboxylic acid catalyzed asymmetric C?H alkylation of diarylmethanamines with a diazomalonate, followed by cyclization and decarboxylation to afford 1,4‐dihydroisoquinolin‐3(2H)‐one. Secondary alkylamines as well as nonprotected primary alkylamines underwent the transformation with high enantioselectivities (up to 98.5:1.5 e.r.) by using a newly developed chiral carboxylic acid as the sole source of chirality to achieve enantioselective C?H cleavage by a concerted metalation‐deprotonation mechanism.     

An Efficient Method for the Conjugation of Hydrophilic and Hydrophobic Components by Solid‐Phase‐Assisted Disulfide Ligation

Chemical conjugation between hydrophilic and hydrophobic components is difficult because of their extremely different solubility. Herein, we report a new versatile method with a solid‐phase‐assisted disulfide ligation to overcome the difficulty of conjugation attributed to solubility. The method involves two steps in a one‐pot process: 1) loading of a hydrophobic molecule onto a resin in an organic solvent, and 2) release of the solid‐supported hydrophobic molecule as a conjugate with a hydrophilic molecule into an aqueous solvent. This strategy allows the use of a suitable solvent system for the substrates in each step. Conjugates of a water‐insoluble drug, plinabulin, with hydrophilic carriers that could not be prepared by solution‐phase reactions were obtained in moderate yields (29–45 %). This strategy is widely applicable to the conjugation of compounds with solubility problems.