Search

We synthesized a planar macrocyclic dinuclear nickel(II) metallohost from the corresponding macrocyclic imine ligand containing two N2O2 chelate coordination sites and an O6 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. The metallohost formed 2 : 1 and 1 : 1 (host/guest) complexes with Na+ with the two‐step binding constants of logK1=6.6 and logK2=3.0. In contrast, its complexation with larger alkali metal ions (K+, Rb+, Cs+) preferentially gave 3 : 2 (host/guest) complexes when 2/3 equiv. of the guest was present. The three‐layered structures of these 3 : 2 complexes were well characterized by mass spectrometry and 2D COSY/ROESY experiments as well as DFT calculations, elucidating their unique structural feature with three chemically different environments due to the oppositely curved two [Ni(saloph)] moieties of the metallohost. Therefore, the three‐layered structures were preferentially formed when larger alkali metal ions (K+, Rb+, Cs+) were complexed with the metallohost. [ABSTRACT FROM AUTHOR]

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 103 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. The (M)‐rich helix was subsequently transformed into the thermodynamically stable (P)‐rich form in 1,1,2,2‐tetrachloroethane with the half‐life time (t1/2) of approximately 44 days at 25 °C. Reduction of the doubly stapled peptide with tri‐n‐butylphosphine in tetrahydrofuran/water (10/1, v/v) produced the corresponding singly stapled dynamic α‐helical peptide bearing two thiol groups at the side chains, which underwent solvent‐induced reversible helicity inversion. The resulting dithiol of the singly stapled peptide could be reoxidized to form the original doubly stapled form using 4,4'‐dithiodipyridine. Furthermore, the P/M interconversion of a doubly stapled peptide with two flexible hydrocarbon‐based staples is considerably more rapid than that with more rigid staples. [ABSTRACT FROM AUTHOR]

The article in Chemistry - A European Journal discusses the preferential formation of three-layered host-guest complexes by complexing a macrocyclic dinickel metallohost with larger alkali metal ions (K+, Rb+, Cs+). Spectroscopic and theoretical investigations confirm the unique structure of these complexes, where three metallohost molecules are stacked in a parallel manner with oppositely curved nickel complex moieties. The research was conducted by S. Akine and co-workers, providing further details in the Research Article (DOI: 10.1002/chem.202403071). [Extracted from the article]

A C4h symmetrically substituted phthalocyanine, 1,8,15,22‐tertrakis(2,4‐dimethylpent‐3‐oxy)phthalocyanine (H2TdMPPc), was used to synthesize Tb3+‐phthalocyanine double‐decker complexes ([Tb(TdMPPc)2]s). Because H2TdMPPc has C4h symmetry, S,S, R,R, and meso isomers of [Tb(TdMPPc)2] were obtained depending on the difference in the direction of the coordination plane of two C4h‐type phthalocyanines with respect to a central Tb3+ ion. We investigated the physical properties of these [Tb(TdMPPc)2] isomers, including their single‐ion magnetic properties, and found that the spin‐reversal energy barrier (Ueff) of the meso isomer was apparently higher than that of the enantiomers. Detailed crystal structural analyses indicated that the meso isomer has a more symmetrical structure than do the enantiomers, thereby suggesting that the higher Ueff of the meso isomer originated from the more highly symmetrical structure. [ABSTRACT FROM AUTHOR]

Host–guest binding behavior of macrocyclic hosts is significantly influenced by the shapes and sizes of the hosts. In particular, closing/opening the apertures of the hosts controls the guest uptake/release. A post‐metalation modification method was used to achieve the open/close conversions. The starting open complex, [LCo2(pip)4](OTf)2, was efficiently converted to the closed complex, [LCo2(hda)2](OTf)2, which has a doubly bridged structure. The conversion of this closed complex to the open complex [LCo2(hda)2(OAc)]+ was too slow to be completed, but this gate‐opening was dramatically accelerated by the addition of Na+. The Na+ binding was also significantly enhanced by the gate‐opening, that is, conversion of [LCo2(hda)2]2+ to [LCo2(hda)2(OAc)]+. [ABSTRACT FROM AUTHOR]

Interactions between designed charged species are important for the ordered arrangements of π-electron systems in assembled structures. As precursors of π-electron anion units, new arylethynyl-substituted dipyrrolyldiketone boron complexes, which showed anion-responsive behavior, were synthesized. They formed a variety of receptor-anion complexes ([1+1] and [2+1] types) in solution, and the stabilities of these complexes were discussed in terms of their thermodynamic parameters. Solid-state ion-pairing assemblies of [1+1]- and [2+1]-type complexes with countercations were also revealed by single-crystal X-ray analysis. In particular, a totally charge-segregated assembly was constructed based on negatively and positively charged layers fabricated from [2+1]-type receptor-anion complexes and tetrabutylammonium cations, respectively. Furthermore, the [1+1]-type anion complex of the receptor possessing long alkyl chains exhibited mesophases based on columnar assembled structures with contributions from charge-by-charge and charge-segregated arrangements, which exhibited charge-carrier transporting properties. [ABSTRACT FROM AUTHOR]

Keywords: cobalt; host-guest systems; ion recognition; macrocyclic ligands; metallohost EN cobalt host-guest systems ion recognition macrocyclic ligands metallohost 2220 2220 1 02/03/21 20210201 NES 210201 B The recognition of a guest Na SP + sp ion b significantly accelerated the AcO SP - sp -mediated gate-opening of a closed dicobalt(III) macrocyclic metallohost [LCo SB 2 sb (hda) SB 2 sb ] SP 2+ sp , which has two bridging 1,6-hexanediamine (hda) ligands, yielding an open host - guest complex [LCo SB 2 sb (hda) SB 2 sb (OAc) B - b Na] SP 2+ sp . Cobalt, host-guest systems, ion recognition, macrocyclic ligands, metallohost. [Extracted from the article]

A ligand exchange strategy was successfully utilized for tuning the response speeds of helicity induction and inversion of a metal‐containing helical structure. The helicity changes were driven by the exchange of six axial amine ligands that are introduced into the three Co3+ centers in the metallocryptands, and the response speeds were efficiently controlled by using different combinations of the starting and entering amine ligands. More information can be found in the Communication by Shigehisa Akine et al. on page 2962. [ABSTRACT FROM AUTHOR]

A reversible open/close function based on disulfide exchange was successfully incorporated in a metallomolecular cage that has a tris(saloph) organic framework and three cobalt(III) ions. To close the cage structure, bridging diamine ligands having a disulfide bond were introduced. These bridging ligands efficiently blocked the uptake of a guest, Cs+, but the presence of a thiolate anion significantly accelerated the guest uptake. Thus, the cage complex became open by the thiolate anion, because the cage closure becomes more dynamic due to the disulfide exchange. More information can be found in the Communication by S. Akine, T. Nabeshima, and M. Miyashita on page 1432. [ABSTRACT FROM AUTHOR]