One‐Pot Evolution of Ageladine A through a Bio‐Inspired Cascade towards Selective Modulators of Neuronal Differentiation

A bio‐inspired cascade reaction has been developed for the construction of the marine natural product ageladine A and a de novo array of its N1‐substituted derivatives. This cascade features a 2‐aminoimidazole formation that is modeled after an arginine post‐translational modification and an aza‐electrocyclization. It can be effectively carried out in a one‐pot procedure from simple anilines or guanidines, leading to structural analogues of ageladine A that had been otherwise synthetically inaccessible. We found that some compounds out of this structurally novel library show a significant activity in modulating the neural differentiation. Namely, these compounds selectively activate or inhibit the differentiation of neural stem cells to neurons, while being negligible in the differentiation to astrocytes. This study represents a successful case in which the native biofunction of a natural product could be altered by structural modifications.     

Molecular Recognition of Medium-size Lactones by Enclathration of Cholic Acid

Abstract

Molecular recognitions of medium size lactones by enclathration of cholic acid (CA) are described. Size and location of the substituents on the lactone rings play an important role for enclathration. Lactones within the limited steric dimensions are included in CA, and larger or smaller ones are not included to give guest-free crystals of CA. Moreover, CA partially separates one enantiomer from racemic lactones by recystallization. X-ray crystallographic studies reveal that all included lactones form the β-trans type bilayer structure having a pentagonal void channel with a side pocket. The cross-sections illustrate that the lactone rings are incorporated in the center of the channel and that the substituents of the guests are fixed in the side pockets. The asymmetric channel enables CA to discriminate size and chirality of medium size lactones.     

Thermo-responsive mending of polymers crosslinked by thermally reversible covalent bond: Polymers from bisfuranic terminated poly(ethylene adipate) and tris-maleimide

Remending properties of a network polymer with reversible reactivity are described. The network structure is constructed by a Diels-Alder (DA) reaction between furyl-telechelic poly(ethylene adipate) (PEAF₂) and a tris-maleimide, M₃. When a film sample was cut into two pieces and the cut surfaces were kept in contact with each other at 60 °C, rejoining of the cut pieces was observed. This mending was induced by the reversible cross-linking reaction bridging the cut surfaces. At the cut front, the “weak” DA adducts are selectively dissociated sacrificially to release the stress so as to protect the chemical structure of the prepolymer and the linker against the scission or degradation. The dissociated furan and maleimide readily reconnect by forward DA reaction to mend the material. The remending was also observed for the samples kept at room temperature after melting at 60 °C. So, the PEAF₂ network polymer is a thermo-responsive mendable material in which crack healing is induced by a prompt thermal stimulus.     

The structure of an Al–Rh–Cu decagonal quasicrystal studied by spherical aberration (Cs)-corrected scanning transmission electron microscopy

The structure of an Al–Rh–Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al₆₃Rh_18.5Cu_18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76 nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in τ²(τ: golden ratio)-inflated pentagonal tiling with a bond-length of 2 nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2 nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed.     

A Simple Fabrication Method for Three‐Dimensional Gold Nanoparticle Electrodes and Their Application to the Study of the Direct Electrochemistry of Cytochrome c

A simple method for constructing gold nanoparticle‐modified electrodes with three‐dimensional nanostructures is demonstrated. The electrodes were prepared by casting citrate‐reduced AuNPs onto polycrystalline gold electrodes. The resultant electrodes had a large surface area‐to‐volume ratio, adequate for high protein loading and conferring high stability. The gold nanoparticle electrodes were covered with a self‐assembled monolayer of 11‐mercaptoundecanoic acid for electrostatic immobilization of cytochrome c (cyt c). At the electrode, direct, reversible electron transfer from cyt c was observed with remarkable stability. Moreover, an extremely high surface coverage of electrochemically active cyt c, 167 fully packed monolayers, was obtained through use of the electrode.     

Construction of superhydrophobic surfaces by fibrous aggregation of perfluoroalkyl chain-containing organogelators

Superhydrophobic surfaces, characterized by water contact angles greater than 150 degrees, can be produced by means of intermediate organogels, which were formed by perfluoroalkyl chain-containing organogelators with volatile organic solvents.