Preferential Formation of Three-layered Host-Guest Complexes of a Planar Dinuclear Metallohost with Alkali Metal Ions.

We synthesized a planar macrocyclic dinuclear nickel(II) metallohost from the corresponding macrocyclic imine ligand containing two NO chelate coordination sites and an O cation binding site like 18-crown-6 as well as peripheral hexyl groups. Due to the lipophilic nature of the hexyl groups, the metallohost was soluble in less polar media where its interaction with alkali metal ions was enhanced. The binding studies by NMR spectroscopy clearly showed its strong tendency to form multi-layered structures.

Non-threaded and rotaxane-type threaded wheel-axle assemblies consisting of dinickel(II) metallomacrocycle and dibenzylammonium axle.

Rotaxanes are typically prepared using covalent bonds to trap a wheel component onto an axle molecule, and rotaxane-type wheel-axle assembly using only noncovalent interactions has been far less explored. Here we show that a dinickel(II) metallomacrocycle forms two different types of wheel-axle assemblies with a dibenzylammonium axle molecule based only on noncovalent interactions. The non-threaded assembly was obtained by introduction of Ni into the macrocycle before the complexation with the axle molecule (metal-first method).

Redox-Triggered Reversible Switching between Dynamic and Quasi-static α-Helical Peptides.

We report the reversible transformation between a singly stapled dynamic α-helical peptide and a doubly stapled quasi-static one through redox-triggered dithiol/disulfide conversions of a stapling moiety. This process allows the rate of interconversion between the right-handed (P) and left-handed (M) α-helices to be altered by a factor of approximately 10 before and after the transformation. An as-obtained doubly stapled α-helical peptide, which is composed of an achiral peptide having an l-valine carboxylic acid residue at the C-terminus, a disulfide-based reversible staple, and a biphenyl-based fixed staple, adopts an (M)-rich form as a kinetically trapped state.

Self-Inclusion Complexation of Electron-Accepting Guest into Electron-Donating Cyclic Host by Photoexcitation.

Self-inclusion complexes consisting of host-guest conjugates are one of the unique supramolecular structures because they form in-state and out-state depending on the external stimuli. Despite many reports of the stimuli-responsive self-inclusion complex formation, study of the structural relaxation from out-state to in-state by photoexcitation has been unexplored. Herein, we report that an electron-donating host and an electron-accepting guest conjugate exhibits the structural relaxation from out-state to in-state by photoexcitation.

Induced chirality at the surface: fixation of a dynamic / invertible helical Co complex on SiO.

Dynamic / invertible helicity was successfully induced at a SiO surface immobilized with a dynamic helical trinuclear cobalt complex, [LCo(NHMe)](OTf), using chiral (() or ())-1-phenylethylamine. Solid-state CD spectra and theoretical calculations suggested that the fixation of the / helical complex on the surface coordination interactions was the key factor of the induced chirality at the surface.

Acceleration and deceleration of chirality inversion speeds in a dynamic helical metallocryptand by alkali metal ion binding.

We report that the chirality inversion kinetics of a trinickel(II) cryptand can be controlled by guest recognition in the cryptand cavity. When the guest was absent, the nickel(II) cryptand underwent a dynamic interconversion between the and forms in solution, preferring the form, with a half-life of = 4.99 min.

Stapling strategy for slowing helicity interconversion of α-helical peptides and isolating chiral auxiliary-free one-handed forms.

In nature, α-helical peptides adopt right-handed conformations that are dictated by L-amino acids. Isolating one-handed α-helical peptides composed of only achiral components remains a significant challenge. Here, this goal is achieved by optical resolution of the corresponding racemic (quasi-)static α-helical peptide with double stapling, which effectively freezes the interconversion between the right-handed (P)- and left-handed (M)-α-helices.

Dynamic-to-Static Planar Chirality Conversion in Pillar[5]arenes Regulated by Guest Solvents or Amplified by Crystallization.

Controlling dynamic chirality and memorizing the controlled chirality are important. Chirality memory has mainly been achieved using noncovalent interactions. However, in many cases, the memorized chirality arising from noncovalent interactions is erased by changing the conditions such as the solvent and temperature.

Speed Tuning of the Formation/Dissociation of a Metallorotaxane.

Switching between the formation/dissociation of rotaxanes is important to control the function of various types of rotaxane-based materials. We have developed a convenient and simple strategy, the so-called "accelerator addition", to make a static rotaxane dynamic without apparently affecting the chemical structure. As an interlocked molecule that enables tuning of the formation/dissociation speed, a metallorotaxane was quantitatively generated by the complexation of a triptycene-based dumbbell-shaped mononuclear complex, [PdL ] (L=2,3-diaminotriptycene), with 27C9.

Synthesis of Isomeric Tb -Phthalocyanine Double-Decker Complexes Depending on the Difference in the Direction of Coordination Plane and Their Magnetic Properties.

Invited for the cover of this issue are Kentaro Tanaka at Nagoya University and co-workers. The image depicts three isomers of a terbium(III) phthalocyanine double-decker complex made from C symmetrically substituted phthalocyanines and their magnetic properties. Read the full text of the article at 10.

A Twisted Chiral Cavitand with 5-Fold Symmetry and Its Length-Selective Binding Properties.

Controlling bottom-up syntheses from chiral seeds to construct architectures with specific chiralities is currently challenging. Herein, a twisted chiral cavitand with 5-fold symmetry was constructed by bottom-up synthesis using corannulene as the chiral seed and pillar[5]arene as the chiral wall. After docking between the seed and the wall, their dynamic chiralities ( and ) are fixed.

Real-time chirality transfer monitoring from statistically random to discrete homochiral nanotubes.

Real time monitoring of chirality transfer processes is necessary to better understand their kinetic properties. Herein, we monitor an ideal chirality transfer process from a statistically random distribution to a diastereomerically pure assembly in real time. The chirality transfer is based on discrete trimeric tubular assemblies of planar chiral pillar[5]arenes, achieving the construction of diastereomerically pure trimers of pillar[5]arenes through synergistic effect of ion pairing between a racemic rim-differentiated pillar[5]arene pentaacid bearing five benzoic acids on one rim and five alkyl chains on the other, and an optically resolved pillar[5]arene decaamine bearing ten amines.

Synthesis of Isomeric Tb -Phthalocyanine Double-Decker Complexes Depending on the Difference in the Direction of Coordination Plane and Their Magnetic Properties.

A C symmetrically substituted phthalocyanine, 1,8,15,22-tertrakis(2,4-dimethylpent-3-oxy)phthalocyanine (H TdMPPc), was used to synthesize Tb -phthalocyanine double-decker complexes ([Tb(TdMPPc) ]s). Because H TdMPPc has C symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc) ] were obtained depending on the difference in the direction of the coordination plane of two C -type phthalocyanines with respect to a central Tb ion. We investigated the physical properties of these [Tb(TdMPPc) ] isomers, including their single-ion magnetic properties, and found that the spin-reversal energy barrier (U ) of the meso isomer was apparently higher than that of the enantiomers.

Synthesis of amphiphilic chiral salen complexes and their conformational manipulation at the air-water interface.

A series of amphiphilic salen complexes, [L1a,bM] and [L2a,bM], were designed and synthesized. These complexes consist of two or four hydrophilic triethylene glycol (TEG) chains and a hydrophobic π-extended metallosalen core based on naphthalene or phenanthrene. The obtained amphiphilic complexes, [L1bM] (M = Ni, Cu, Zn), formed a monolayer at the air-water interface, while the monocationic [L1bCo(MeNH)](OTf) did not form a well-defined monolayer.

Rotaxane formation by an allosteric pseudomacrocyclic anion receptor utilising kinetically labile copper(I) coordination properties.

Rotaxanes, which are composed of ring and axle components, are important interlocked molecules with wide applications such as molecular machines and switchable catalysts. The construction of interlocked structures targeting anions is an important issue, as evidenced by the fact that anionic groups are usually abundant in many biomacromolecules. We now report an allosteric pseudomacrocyclic anion receptor as a ring that spontaneously generates a rotaxane in an auto-clipping way, which does not require the successive ring forming reaction like usual clipping, in the presence of an axle with an anionic station.

Noncooperative guest binding by metal-free [2 + 2] Schiff-base macrocycles.

Salphen-based [ + ] macrocycles have been widely explored for their unique chemical and topological properties following metal ion coordination. Despite having vastly different reactivity than their coordinated counterparts, fewer studies have focused on metal-free salphen macrocycles. We investigated the binding of [2 + 2] Schiff-base macrocycle host 3, which contains a central 18-crown-6-like cavity and two NO moieties.

State- and water repellency-controllable molecular glass of pillar[5]arenes with fluoroalkyl groups by guest vapors.

Molecular glasses are low-molecular-weight organic compounds that are stable in the amorphous state at room temperature. Herein, we report a state- and water repellency-controllable molecular glass by -alkane guest vapors. We observed that a macrocyclic host compound pillar[5]arene with the CF fluoroalkyl groups changes from the crystalline to the amorphous state (molecular glass) by heating above its melting point and then cooling to room temperature.

Transient chirality inversion during racemization of a helical cobalt(III) complex.

SignificanceWe first observed a transient chirality inversion on a simple unimolecular platform during the racemization of a chiral helical complex [LCo], i.e., the helicity changed from -rich (right-handed) to -rich (left-handed), which then racemized to a / equimolar mixture in spite of the absence of a reagent that could induce the helix.

Metal-dependent selective formation of calix[4]arene assemblies based on dynamic covalent chemistry.

The reaction of calix[4]arene derivatives 1a and 1b bearing four salicylaldehyde moieties with 1,3-propanediamine gave macrocyclic trimers 5a and 5b, respectively, which have intramolecular bridges formed the conformation. In contrast, a capsular-shaped dimeric cage [7a·2Na] was selectively formed when the conformation of the calix[4]arene moiety of 1a was fixed in the conformation by complexation with Na at the lower-rim amide groups.

Synthesis of a monocationic μ-nitrido-bridged iron porphycene dimer and its methane oxidation activity.

Herein, we report the synthesis of a monocationic μ-nitrido-bridged iron porphycene dimer, a structural analogue of a monocationic μ-nitrido-bridged iron phthalocyanine dimer, which is known to be one of the most potent molecule-based catalysts for methane oxidation. H-NMR and single-crystal X-ray structural analyses showed that the porphycene complex includes two Fe(IV) ions, and the structure around the Fe-NFe core is quite similar to that of the monocationic μ-nitrido-bridged iron phthalocyanine dimer. Although methane was oxidized into MeOH, HCHO, and HCOOH in the presence of a silica-supported catalyst of this monocationic μ-nitrido-bridged iron porphycene dimer in an acidic aqueous solution containing excess HO, its reactive intermediate was not a high-valence iron-oxo species, as in the case of a monocationic μ-nitrido-bridged iron phthalocyanine dimer, but ˙OH.