Synthetic β‑Barrel by Metal-Induced Folding and Assembly

The de novo construction of repeat proteins has received much attention from biologists and chemists, yet that of a β-barrel structure, one of the most well-known classes, has not been accomplished to date. Here, we report the first chemical construction of a β-barrel tertiary structure with a pore through a combination of peptide folding and metal-directed self-assembly. Coordination of zinc salts to an eight-residue peptide fragment bearing β-strand- and loop-forming sequences resulted in a β-barrel in which six-stranded cylindrical antiparallel β-sheets formed a hydrophobic pore with a specific shape

Metal–Organic Proximity in a Synthetic Pocket

Proximity between a noninteractive organic substrate and a transition metal (<i>trans</i>-MCl₂(PEt₃)₂; M = Pd or Pt) is achieved by their co-encapsulation within a synthetic cage, as revealed by X-ray crystallographic analysis and NOESY experiments. Through co-encapsulation with a Pd­(II) complex, a terminal alkyne was activated within the cage to give a σ-alkynylpalladium complex

Size‑, Mass‑, and Density-Controlled Preparation of TiO₂ Nanoparticles in a Spherical Coordination Template

TiO₂ nanoparticles were prepared with strict control of the size, molecular mass (PDI = 1.02), and mass density by hydrolyzing a precursor, Ti­(acac)₂(biphen), in the presence of a well-defined hollow Pd₁₂L₂₄ spherical endotemplate. The formation of highly monodisperse TiO₂ nanoparticles was confirmed by ¹H NMR spectroscopy, MALDI–TOF mass spectrometry, transmission electron microscopy, and atomic force microscopy. The template was easily removed by treating the sphere with a metal scavenger followed by calcination to give crystalline TiO₂ nanoparticles (2.0 ± 0.2 nm in diameter), which showed photocatalytic activity

Cage-Catalyzed Knoevenagel Condensation under Neutral Conditions in Water

A cationic coordination cage dramatically accelerates the Knoevenagel condensation of aromatic aldehydes in water under neutral conditions. The addition of a nucleophile to the aldehyde to generate anionic intermediates seems to be facilitated by the cationic environment of the cavity. The products are ejected from the cage as a result of the host–guest size discrepancy. As a result, the condensation is promoted by a catalytic amount of the cage

Temporary and Permanent Trapping of the Metastable Twisted Conformer of an Overcrowded Chromic Alkene via Encapsulation

An overcrowded alkene with an anti-folded conformation was converted to its twisted conformer, accompanied by a dramatic color change from yellow to deep purple, by inclusion in a self-assembled <i>T</i>_<i>d</i>-symmetric coordination cage. The shape of the caged cavity was suitable and desirable for trapping of the twisted conformer. The twisted conformation was temporarily memorized in the alkene even after guest ejection. Permanent trapping of the twisted conformation was achieved by bromination of the twisted conformer formed in situ in the cage

Temporary and Permanent Trapping of the Metastable Twisted Conformer of an Overcrowded Chromic Alkene via Encapsulation

An overcrowded alkene with an anti-folded conformation was converted to its twisted conformer, accompanied by a dramatic color change from yellow to deep purple, by inclusion in a self-assembled <i>T</i>_<i>d</i>-symmetric coordination cage. The shape of the caged cavity was suitable and desirable for trapping of the twisted conformer. The twisted conformation was temporarily memorized in the alkene even after guest ejection. Permanent trapping of the twisted conformation was achieved by bromination of the twisted conformer formed in situ in the cage

Diels–Alder via Molecular Recognition in a Crystalline Molecular Flask

In the pore of a porous coordination network, Diels–Alder reactants, a diene and a dienophile, are recognized by donor–acceptor and multiple H-bond interactions, respectively, and fixed at ideal positions for the reaction. Heating the crystals promoted the Diels–Alder reactions with enhanced reactivity and controlled regioselectivity as clearly monitored by in situ X-ray crystallography

Synthetic β‑Barrel by Metal-Induced Folding and Assembly

The de novo construction of repeat proteins has received much attention from biologists and chemists, yet that of a β-barrel structure, one of the most well-known classes, has not been accomplished to date. Here, we report the first chemical construction of a β-barrel tertiary structure with a pore through a combination of peptide folding and metal-directed self-assembly. Coordination of zinc salts to an eight-residue peptide fragment bearing β-strand- and loop-forming sequences resulted in a β-barrel in which six-stranded cylindrical antiparallel β-sheets formed a hydrophobic pore with a specific shape

Synthetic β‑Barrel by Metal-Induced Folding and Assembly

The de novo construction of repeat proteins has received much attention from biologists and chemists, yet that of a β-barrel structure, one of the most well-known classes, has not been accomplished to date. Here, we report the first chemical construction of a β-barrel tertiary structure with a pore through a combination of peptide folding and metal-directed self-assembly. Coordination of zinc salts to an eight-residue peptide fragment bearing β-strand- and loop-forming sequences resulted in a β-barrel in which six-stranded cylindrical antiparallel β-sheets formed a hydrophobic pore with a specific shape

Mutual Induced Fit in a Synthetic Host–Guest System

Mutual induced fit is an important phenomenon in biological molecular recognition, but it is still rare in artificial systems. Here we report an artificial host–guest system in which a flexible calix[4]­arene is enclathrated in a dynamic self-assembled host and both molecules mutually adopt specific three-dimensional structures. NMR data revealed the conformational changes, and crystallographic studies clearly established the precise structures at each stage