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Fine-tuning of the ratio of two different states is important in controlling the structures and functions of crystalline materials. Here we report that clathrated guest molecules inside a tubular host crystal formed via halogen and hydrogen bonding exhibit reversible temperature-dependent orientational isomerisation in equilibrium. [ABSTRACT FROM AUTHOR]

The synthesis of branched gold nanoparticles (AuNPs) with shape- and size-specific optical properties requires effective control of the particle formation mechanism using appropriate reducing agents and protective agents that prevent particle aggregation in solution. In this context, the heterogeneous synthesis of AuNPs using solid surfaces of graphene oxides and metal–organic frameworks has attracted much attention. These materials are characterized by their ability to immobilize and stabilize the particles grown on the surface without the need for additional protective agents. However, the shape- and size-selective synthesis of AuNPs using solid surfaces remains challenging. Herein, we report the shape-selective one-step synthesis of monodisperse branched AuNPs using a metal–macrocycle framework (MMF), a porous molecular crystal of Pd II3 -tris(phenylenediamine) macrocycle. Konpeito-Shaped branched AuNPs with uniform size were obtained on the surface of MMF by mixing HAuCl4·4H2O, L -ascorbic acid and MMF microcrystals. Spectroscopic and microscopic observations confirmed that MMF promoted the reduction of gold by its reductive activity as well as acted as a solid support to electrostatically immobilize the pseudo-seed particles for further growth on the crystal surface. In addition, the MMF also served as a substrate for in situ high-speed AFM imaging due to the effective immobilization of AuNPs on the surface, allowing direct visualization of the particle growth. Since the chemical structural features of MMF allow the growth of branched AuNPs via pseudo-seeding, this approach would provide new synthetic methods for obtaining a variety of gold nanostructures. [ABSTRACT FROM AUTHOR]

Porous crystals with well‐defined active metal centers on the pore surface have high potential as heterogeneous metal catalysts. We have recently demonstrated that a porous molecular crystal, metal‐macrocycle framework (MMF), catalyzes olefin migration reactions by photoactivation of its PdIICl2 moieties exposed on the crystalline channel surface. Herein we report a mechanistic study of the photoinduced olefin migration reactions at the PdII active centers of MMF. Several experiments, including a deuterium scrambling study, revealed that olefin migration is catalyzed via an alkyl mechanism by in situ generated Pd−H species on the channel surface during photoirradiation. This proposed mechanism was further supported by DFT and ONIOM calculations. [ABSTRACT FROM AUTHOR]

Molecular adsorption on a surface is a unique way to break the mirror-symmetry of prochiral molecules, and therefore the use of chiral surfaces is an effective strategy for achieving highly selective chiral separation and asymmetric catalytic reactions based on molecular adsorption with high diastereoselectivity. We have previously reported a porous metal–macrocycle framework (MMF) with an enantiomeric pair of chiral pore-surfaces derived from Pd II3 -helical macrocycles as the ingredients of the framework. Aiming at applying the chiral pore-surface of the MMF to asymmetric reactions and chiral separation, herein we propose a strategy to utilize one of the enantiomerically paired pore-surfaces as a homochiral pore-surface with the aid of chiral auxiliaries that can block only one side of the enantiomeric pore-surfaces in a site-selective manner. Single-crystal X-ray diffraction analysis revealed that a chiral auxiliary, (1R)- or (1S)-1-(3-chlorophenyl)ethanol, and a prochiral guest molecule, 2′-hydroxyacetophenone, were cooperatively arranged in each pore unit so that the prochiral guest molecule can face-selectively bind to the homochiral pore-surface. [ABSTRACT FROM AUTHOR]

One-dimensional self-assembly of macrocycles is one of the important strategies for constructing fibrous nanomaterials with anisotropic functions such as one-dimensional transport and accumulation of molecules and ions. Herein we report on the synthesis and properties of self-assembled nanofibers using macrocycles to develop a multipurpose template for one-dimensional array of noble metal ions. The nanofibers were prepared by protonation-induced self-assembly of bis-phenanthroline macrocycles, which have enabled the accumulation of some metal-containing anions, such as tetrachloroaurate, hexachloroplatinate and phosphomolybdate. Microscopic observations have demonstrated that the supramolecular nanofibers were reproducibly formed in a similar way, regardless of the structures and charge numbers of the anions. Moreover, the resulting nanofibers, arrayed with several metal ions, were chemically reduced, producing dispersible gold nanoparticles and mixed-valence nanofibers. [ABSTRACT FROM AUTHOR]

Designing unique core–shell porous crystals is key to the development of anisotropically functionalised materials. Herein we report the facile preparation of a core–shell metal–macrocycle framework (MMF) containing continuous 1D-channels via an epitaxial growth procedure. Methyl orange loaded in the core was found to be anisotropically transported to the shell along the heterogeneously hybridised 1D-channels. [ABSTRACT FROM AUTHOR]

Highly soluble, PEGylated cage derivative is used for showing the full reversibility of the light-driven encapsulation/release process. X-ray structure analysis has confirmed the guest molecules having left the cavity of the host and on the contrary joining the cages into a polymeric material by binding to their Pd(II) centers from outside.

Short peptides are induced into [alpha]-helix conformations in water through enclathration to an artificial hydrophobic cavity. Peptides with two aromatic residues have displayed high affinity for the host and these intermolecular aromatic-aromatic interactions have driven the helical folding of short peptides.

The syntheses of novel nucleosides, mercaptopyridone-bearing nucleoside (M) and hydroxypyridinethione-bearing nucleoside (S), possessing O,S-donor atoms as a bidentate ligand, are described. These nucleosides have efficiently formed metal-mediated base pairs with soft transition metal ions such as [Pd.sup.2+] and [Pt.sup.2+].

The synthesis of a macrocyclic tetranuclear Ni(II) complex of artificial [beta]-dipeptides with two sets of tridentate ligands is described. The cyclic twisted-boat structure of the complex provides well-defined isolated spaces for in-line molecular arrangement of water and anion molecules.

Study is conducted to show that even a three-residue peptide fragment, Ac-Ala-Ala-Ala-NH2 can be folded into a beta-[turn.sup.3] through encapsulation by a porphyrin-assembled synthetic host. It is suggested that peptide recognition within the large cavity of self-assembled [cages.sup.11,12] is a powerful method to produce the secondary structures of peptides even if the peptide fragment is considerably short.

Sequence-selective recognition of peptides is expected to be an essential process for the site-specific recognition of protein surfaces, which leads to the control of protein functions and to the understanding of biological events at protein surfaces such as protein-protein or protein-oligopeptide interactions. The study aiming at the pinpoint recognition of protein surfaces by the self-assembled hollow receptors is presented.

The self-assembly of a 3.5-nm coordination nanotube is described. The characterization of nanotubes is studied by NMR spectroscopy.

Aiming at precisely arranging several proteinogenic α-amino acids on a folded scaffold, we have developed a cyclic hexapeptide comprising an alternate sequence of biphenyl-cored ζ-amino acids and proteinogenic α-amino acids such as l-leucine. The amino acids were connected by typical peptide synthesis, and the resultant linear hexapeptide was intramolecularly cyclized to form a target cyclic peptide. Theoretical analyses and NMR spectroscopy suggested that the cyclic peptide was folded into an unsymmetrical conformation, and the structure was likely to be flexible in CHCl3. The optical properties including UV/Vis absorption, fluorescence, and circular dichroism (CD) were also evaluated. Furthermore, the cyclic peptide became soluble in water by introducing three carboxylate groups at the periphery of the cyclic skeleton. This α/ζ-alternating cyclic peptide is therefore expected to serve as a unique scaffold for arranging several functionalities. [ABSTRACT FROM AUTHOR]

Non-covalent immobilisation of catalysts in nanoporous materials is a promising way to apply homogeneous catalysts to heterogeneous catalytic reactions. Herein we report a size-specific catalytic reaction with an acid catalyst, p-toluenesulfonic acid, immobilised in a porous molecular crystal, metal–macrocycle framework (MMF), composed of metallo-macrocycles. A tritylated substrate which is smaller than the pore dimension of MMF was deprotected by the heterogeneous catalyst, whereas the reaction with a larger substrate was completely suppressed due to the steric restriction. [ABSTRACT FROM AUTHOR]

Host-guest complexation driven by metal-to-metal dative bonding was studied using a mono-nuclear AgI complex of 2,9-bis(9-anthracenyl)-1,10-phenanthroline as a simple metallo-host. This host molecule can capture a ruthenocene with a Ru-Ag dative bond in solution as revealed by NMR spectroscopy and ESI-TOF MS spectrometry. Single-crystal XRD analysis of the host-guest complex revealed a Ru-Ag type dative bond with a significant change in the coordination arrangement of the central Ru atom of ruthenocene. The binding constant for the host-guest complexation was estimated to be over 104 M-1 in CD2Cl2 at 300 K. [ABSTRACT FROM AUTHOR]

The cleavage of CC bonds in π-conjugated systems is an important method for controlling their shape and coplanarity. An efficient way for the cleavage of an aromatic CC bond in a typical buckybowl corannulene skeleton is reported. The reaction of 2-pyridylcorannulene with a catalytic amount of IrCl3⋅ n H2O in ethylene glycol at 250 °C resulted in a structural transformation from the curved corannulene skeleton to a strain-free flat benzo[ ghi]fluoranthene skeleton through a site-selective CC cleavage reaction. This cleavage reaction was found to be driven by both the coordination of the 2-pyridyl substituent to iridium and the relief of strain in the curved corannulene skeleton. This finding should facilitate the design of carbon nanomaterials based on CC bond cleavage reactions. [ABSTRACT FROM AUTHOR]

Molecular adsorption is a fundamental phenomenon in porous materials and is usually characterized by the efficiency and selectivity of molecular separations and reactions. However, for functional porous materials, analysis of the dynamic behaviour of molecular adsorbents is a major challenge. Here, we use in situ single-crystal X-ray diffraction to analyse multi-step molecular adsorption in a crystalline nanochannel of a metal-macrocycle framework. The pore surface of the metal-macrocycle framework crystal contains five different enantiomerically paired binding pockets, to which the adsorption of a (1R)-1-(3-chlorophenyl)ethanol solution was monitored with time. The resulting X-ray snapshot analyses suggest that the guest adsorption process takes a two-step pathway before equilibrium, in which the guest molecule is temporarily trapped by a neighbouring binding site. This demonstrates the potential for using X-ray analyses to visualize a transient state during a non-covalent self-assembly process. [ABSTRACT FROM AUTHOR]

Porous crystals are excellent materials with potential spatial functions through molecular encapsulation within the pores. Co-encapsulation of multiple different molecules further expands their usability and designability. Herein we report the simultaneous arrangement of up to three different guest molecules, TTF (tetrathiafulvalene), ferrocene, and fluorene, on the pore surfaces of a porous crystalline metal-macrocycle framework (MMF). The position and orientation of adsorbed molecules arranged in the pore were determined by single-crystal X-ray diffraction analysis. The anchoring effect of hydrogen bonds between the hydroxy groups of the guest molecules and inter-guest cooperation and competition are significant factors in the adsorption behaviors of the guest molecules. This finding would serve as a design basis of multicomponent functionalized nanospaces for elaborate reactions that are realized in enzymes. [ABSTRACT FROM AUTHOR]

Synthetic amphiphiles have been found to self-assemble into a variety of structures such as micelles, vesicles, cylinders and lamellae in aqueous media over many length scales. We report herein cation-induced aggregation of hexaaza-cyclophanes in water. Pd2+- or proton-induced formation of submicro spherical aggregates was observed by several spectroscopic and microscopic methods. [ABSTRACT FROM AUTHOR]

Stacked rings: A diamond ‐ shaped macrocycle with two inward phenanthroline ligands and outward long alkyl chains, and its PdII complex form organic and organometallic fibrous aggregates, respectively, as revealed by NMR, UV/Vis, AFM, and TEM measurements. The most likely structures are face ‐ to ‐ face stacked macrocycles, generating nanotubes. [ABSTRACT FROM AUTHOR]

Recently, we have reported a metal-macrocycle framework (MMF) with five enantiomerically paired molecular binding pockets that exhibit site-selective guest arrangement on the nano-channel surface in soaking experiments using a variety of guest molecules. The guest inclusion is based largely on molecular exchange between solvent molecules such as CH3CN and guest molecules on the surface. Herein, we report that the molecular arrangement on the nano-channel surface varies with size, shape and/or chemical properties of functional groups of guests, mono-substituted benzene derivatives, such as benzonitrile, acetophenone and nitrobenzene. In their inclusion complexes, polar nitrile, acetyl and nitro groups serve as molecular anchors to a macrocyclic cavity through hydrogen bonding. Notably, benzonitrile and benzenesulphonic acid bind only to one pair of enantiomeric binding pockets. Such a highly site-selective binding would enable further multi-component surface modifications in the MMF. [ABSTRACT FROM AUTHOR]

Hollow nanostructures for the functional assembly of chemical groups with inner surface geometry and regulable stoichiometry enable steric design of interior reaction centers. Herein we report a metal-macrocycle framework (MMF) that forms single-crystalline nanochannels with five distinct enantiomeric pairs of guest binding pockets. During crystal-soaking experiments, the MMF crystals can encapsulate aromatic molecules with high site selectivity. First, constitutional isomers of dibromobenzene are captured and sorted into different binding pockets. Second, each of the optical isomers of (1R/1S)-1-(3-chlorophenyl)ethanol is included diastereoselectively into one of an enantiomeric pair of binding pockets. An advantage of this strategy is that the interior walls can be "repainted" via replacement of the trapped molecules with alternatives. Such guest uptake behaviors would allow highly regioselective or stereoselective reactions within the nanochannel. [ABSTRACT FROM AUTHOR]

A phenanthroline-based macrocycle 1 has been newly developed which has two chemically equivalent metal chelating sites within the spatially restricted cavity for dinuclear metal arrangement. The macrocycle 1 reacts with Zn(CF3CO2)2 or ZnCl2 to form homodinuclear Zn(II)-complexes. A single-crystal X-ray structural analysis of the resulting Zn21(CF3CO2)4 determined the complex structure in which two Zn(II) ions are bound by two phenanthroline sites and two CF3CO2- ions bind to each Zn(II) ion in a tetrahedral geometry. Similarly, a homodinuclear Cu(I)-macrocycle was formed from 1 and Cu(CH3CN)4BF4. Notably, from 1 and an equimolar mixture of Cu(CH3CN)4BF4 and Zn(CF3CO2)2, a heterodinuclear Cu(I)-Zn(II)-macrocycle was exclusively formed in high yield (>90%) because of the relatively low stability of the dinuclear Cu(I)-macrocycle. A heterodinuclear Ag(I)-Zn(II)-macrocycle was similarly formed with fairly high selectivity from a mixture of Ag(I) and Zn(II) ions. Such selective heterodinuclear metal arrangement was not observed with other combinations of M-Zn(II) (M = Li(I), Mg(II), Pd(II), Hg(II), La(III), and Tb(III)). [ABSTRACT FROM AUTHOR]

Keywords: mechanism; metallacycles; olefin migration; palladium; photoactivation EN mechanism metallacycles olefin migration palladium photoactivation 174 174 1 02/03/21 20210201 NES 210201 B One-dimensional crystalline channels b with well-defined active metal centers hold great potential as heterogeneous catalysts. Experimental and theoretical studies revealed that the olefin migration was catalyzed via an alkyl mechanism by in situ generated Pd-H species on the channel ceiling through photoirradiation. Mechanism, metallacycles, olefin migration, palladium, photoactivation. [Extracted from the article]

The optically active cobalt(III) complex with chiral cyclen, (2S,5S,8S,11S)-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane, preferentially binds to d-phenylglycine (D-Phg) or D-t-leucine (D-t-Leu) rather than L-Phg or L-t-Leu, respectively, with 20% de in dimethyl sulfoxide at 293 K. Comparative studies on the crystal structures of cobalt(III) complexes with D-Phg and L-Phg revealed that the diastereoselectivity is due to the difference in the steric hindrance that should occur between the amino group of Phg and the ethyl group of cyclen. [ABSTRACT FROM AUTHOR]

A water ‐ soluble cyclic hexapeptide comprising an alternate sequence of biphenyl ‐ cored ζ ‐ amino acids and proteinogenic α ‐ amino acids such as l ‐ leucine has been developed. The amino acids were connected by typical peptide synthesis, and the resultant linear hexapeptide was intramolecularly cyclized to form the target cyclic peptide. Theoretical and NMR spectroscopic analyses suggested that the cyclic peptide was folded into an unsymmetrical conformation, and the structure was likely to be flexible. Furthermore, the cyclic peptide became soluble in water by introducing three carboxylate groups. More information can be found in the Full Paper by Mitsuhiko Shionoya et al. on page   1087 in Issue 10, 2017 (DOI: 10.1002/asia.201700203). [ABSTRACT FROM AUTHOR]

Stackable metallomacrocycles can form supramolecular micrometer ‐ long metallo ‐ fibers or ‐ tubes, thus providing novel structural motifs for supramolecular architectures. In their Communication on page 1368   ff., Mitsuhiko Shionoya et   al. report the formation of organic and organometallic fibrous aggregates by the assembly of diamond ‐ shaped macrocyclic ligands and their palladium complexes, respectively, as revealed by AFM, TEM, NMR, and UV/Vis measurements. In the Cover picture, the stacked structure of bis(cyclopalladated) macrocycles is expressed as a “supramolecular dragon” taking a moonlight swim. [ABSTRACT FROM AUTHOR]

The article synthesizes a macrocyclic tetranuclear Ni(II) complex of an artificial β-dipeptide 1 which possesses two sets of tridendate ligands for in-line molecular arrangement. Researchers focused on biorelated molecular building blocks such as amino acids and nucleosides in constructing a more sophisticated molecular functions. They discovered that β-dipeptide 1 forms a cyclic trinuclear ZN(II) complex.

The article presents information on the β-turn structures of peptides. The turn structure can be constituted by four amino acid residues via hydrogen bonding between CO(i) and NH(i+3). A three-residue peptide fragment, Ac-Ala-Ala-Ala-NH2, can be folded into a turn3 through encapsulation by a porphyrin-assembled synthetic host. Despite the presence of only one intramolecular hydrogen bond, the turn conformation is very stable because of efficient host-guest interaction.

Review: [76 refs. [ABSTRACT FROM AUTHOR]