Metallosupramolecular Complexes Research Articles

Label-free electrochemiluminescent enantioselective sensor for distinguishing between chiral metallosupramolecular complexes.

Chiral molecular recognition of DNA is important for rational drug design and for developing structural probes of DNA conformation. Developing a convenient and inexpensive assay for sensitive and selective identification of DNA-specific binding compounds with rapid, easy manipulation is in ever-increasing demand. Here, we present a "turn-on" and label-free electrochemiluminescent (ECL) biosensor for distinguishing chiral metallosupramolecular complexes based on DNA three-way junction formation selectively induced by the analyte. The fabricated ECL sensor shows excellent performance in the chiral discrimination of two enantiomers with an enantioselective recognition ratio of up to 4.4. More importantly, as a "turn-on" detection system, the ECL chiral sensor does not suffer from false positives and limited signal range of "signal-off" systems. Therefore, this concept may provide a new insight into the design of efficient sensors for distinguishing chiral molecules and for investigating the interactions between DNA and small molecules.

Meso-Helicates with Rigid Angular Tetradentate Ligand: Design, Molecular Structures, and Progress Towards Self-Assembly of Metal–Organic Nanotubes

The self-assembly of two novel metallosupramolecular complexes of the general formulas [L2M2(CH3CN)4][BF4]4 (M = Co, 1a; M = Ni, 1b), where L stands for the tetradentate ligand 3,5-bis[4-(2,2'-dipyridylamino)phenylacetylenyl]toluene, is reported together with their molecular structures ascertained by single-crystal X-ray diffraction studies. Complexes 1a and 1b are isostructural and show the formation of dinuclear meso-helicates with the two octahedral metal centers displaying respectively Δ and Λ configurations. These meso-helicates display large nanocavities with metal---metal separation distance of >2 nm; furthermore, π-π-stacking occurs among individual units to form one-dimensional (1D) polymers which further autoassemble in another direction through π-π contacts among neighboring chains to generate a two-dimensional (2D) network with regular nanocavities. Our approach might be of interest to prepare metal-organic nanotubes via a bottom-up strategy depending on the assembling functional ligand and the geometry of molecular building block.

Metallosupramolecular complex targeting an α/β discordant stretch of amyloid β peptide

The accumulation of amyloid β-peptide (Aβ) is one of the pathological hallmarks of Alzheimer's disease (AD). Developing Aβ amyloid inhibitors has received much attention. Most reported Aβ inhibitors are small organic molecules or peptides. Here we use a cell-based novel Aβ–enhanced cyan fluorescent protein (ECFP) fluorescent fusion inhibitor screen system, biochemical and biophysical approaches and in vivo studies to identify two zinc-finger-like triple-helical metallo-supramolecular cylinders, [Ni2L3]4+ and [Fe2L3]4+, that can strongly inhibit Alzheimer's disease β-amyloid aggregation. Further studies indicate that the two metallo-supramolecular cylinders are specifically targeting the α/β-discordant stretch and reducing Aβ cytotoxicity. In vivo studies demonstrate that these complexes can ameliorate spatial memory deficits in a transgenic mouse model and decrease the insoluble Aβ level. This is the first demonstration that zinc-finger-like metallo-supramolecular cylinders can be Aβ aggregation inhibitors that specifically target an α/β-discordant stretch. Our work will prompt design and screening of metallo-supramolecular complexes as potential therapeutic agents for AD.

Electrochemical DNA three-way junction based sensor for distinguishing chiral metallo-supramolecular complexes

Here we report a signal-on three-way junction based-electrochemical DNA sensor for distinguishing chiral metallo-supramolecular complexes with an enantioselective recognition ratio of about 3.5. This platform is easy to fabricate, simple to operate and readily regenerated.

Metallosupramolecular Architectures of Pseudoterpyridine-Type Ligands and ZnII Metal Ions

This paper reports the solid state structures of two new metallosupramolecular complexes resulting from pseudoterpyridine bis-hydrazone-type 3 and bis-acylhydrazone-type 4 ligands and ZnII metal ions. The complex 32ZnII are quantitatively trapped by crystallization via constitutionally driven selection from binary solutions of 1:1 and 2:1 3:ZnII (mol:mol). The constitutional internal overlap between the phenyl moieties and the central pyridine moiety clearly plays an important role for internal holding and stabilizing the duplex formation by π−π stacking. The crystal 4ZnII*4 heterostructure and its packing reported in this paper present uncommon features with many other similar architectures reported by now. This structure shows a relatively new structural concept: the 4ZnII complex in which the ZnII ions are coordinated by one ligand rolling the axial position of the metal ion, further interacting by H-bonding with the free ligand 4 in the crystal, allowing one to obtain 2D-layered architectures.

Metallo-Supramolecular Self-Assembly: the Case of Triangle-Square Equilibria

For the efficient self-assembly of metallo-supramolecular complexes, not only reversibility is required but also two other properties have to be controlled as well: (i) The right binding sites need to be programmed into the building blocks at the appropriate positions. (ii) The building blocks must be rigid enough to support the geometrical arrangement and to avoid the unfavorable entropy effects connected with the conformational fixation of flexible molecules. A series of different bis-pyridyl ligands is reported which self-assemble with (dppp)M(OTf) 2 complexes (dppp = 1,3-bis-(diphenylphosphino)propane; M = Pd (II), Pt (II)) to yield squares and/or triangles as the products. Enthalpic contributions (higher strain in the triangle) and entropic contributions (higher number of triangles from the same building blocks) determine the equilibrium. The effects of concentration, temperature, and solvent properties on the equilibrium have been studied. To characterize the complexes under study, a combination of (1)H, (31)P, and diffusion-ordered NMR spectroscopy, electrospray-ionization Fourier-transform ion-cyclotron-resonance mass spectrometry, and X-ray crystallography is needed. Variable-temperature NMR spectroscopy provides evidence for fast ligand-exchange processes occurring for the Pd complexes, while the Pt complexes exchange ligands much more slowly.

様々な分野で応用可能な広範囲波長領域の光を吸収するスクアリリウム系機能性色素

Novel bis-squaraine dyes have been synthesized in which two squaraine moieties are conjuga-tively linked by a methine group, thiophene, oligothiophene or arene spacer. New unsymmetrical squarylium dyes have been also prepared by condensation of mono-substituted squaric acid (semi-squaraine acid) with heterocyclic compounds with active methyl group or arylamines. These dyes exhibit large and intense absorption in the near-infrared region, and the X-ray structural analyses of these dyes show a planar structure. Semi-squaraine acids are key precursors for the synthesis of unsymmetrical squarylium dyes, and exhibited their absorption maxima at the shorter wavelength. Applications of squarylium dyes to photoconductive materials, photovoltatic devices, biological and environmental analysis are described. A Ca2+ ion-induced allostreic assem-bling of the squarylium dimmer was confirming by ESI-MS measurement showing the formation of metallo supramolecular complexes, that is the H-aggregate composed of at least three units.

Self-Optimizing Charge-Transfer Energy Phenomena in Metallosupramolecular Complexes by Dynamic Constitutional Self-Sorting

In this paper we report an extended series of 2,6-(iminoarene)pyridine-type ZnII complexes [(Lii)2Zn]II, which were surveyed for their ability to self-exchange both their ligands and their aromatic arms and to form different homoduplex and heteroduplex complexes in solution. The self-sorting of heteroduplex complexes is likely to be the result of geometric constraints. Whereas the imine-exchange process occurs quantitatively in 1:1 mixtures of [(Lii)2Zn]II complexes, the octahedral coordination process around the metal ion defines spatial-frustrated exchanges that involve the selective formation of heterocomplexes of two, by two different substituents; the bulkiest ones (pyrene in principle) specifically interact with the pseudoterpyridine core, sterically hindering the least bulky ones, which are intermolecularly stacked with similar ligands of neighboring molecules. Such a self-sorting process defined by the specific self-constitution of the ligands exchanging their aromatic substituents is self-optimized by a specific control over their spatial orientation around a metal center within the complex. They ultimately show an improved charge-transfer energy function by virtue of the dynamic amplification of self-optimized heteroduplex architectures. These systems therefore illustrate the convergence of the combinatorial self-sorting of the dynamic combinatorial libraries (DCLs) strategy and the constitutional self-optimized function.

Analysis of Metallo‐Supramolecular Systems Using Single‐Molecule Force Spectroscopy

AbstractSingle‐molecule force spectroscopy has been used for the investigation of the rupture behavior of individual metallo‐supramolecular systems. For this purpose, a specifically designed unsymmetrical α,ω‐functionalized poly(ethylene oxide) has been employed for mono‐termination with a terpyridine ligand and subsequently for the attachment onto atomic force microscopy (AFM) tips and microscope slide substrates. Metallo‐supramolecular complexes were formed by the use of ruthenium(III)–ruthenium(II) chemistry. Vertical stretching with the AFM cantilever ruptured the coordinative bonds. The rupture force of individual bisterpyridine ruthenium(II) complexes was determined to be 95 pN at a force loading rate of 1 nN s–1. Simultaneous rupturing of multiple parallel metallo‐supramolecular bonds was also observed. Monte Carlo simulations corroborated the experimental observations. The presented results lay the basis for the application of such metallo‐supramolecular systems in advanced functional nanomaterials.

Silver(I) complexes with quinoline based linear multidentate ligands: self-assembly of sulfur-bridged tetrametallotricyclic boxes †

The flexible linear multidentate ligands 1,5-bis(8-quinolylsulfanyl)-3-oxapentane (OESQ) and 1,8-bis(8-quinolylsulfanyl)-3,6-dioxaoctane (ODSQ) reacted with silver(I) perchlorate affording the simple mononuclear complexes [Ag(OESQ)]ClO41 and [Ag(ODSQ)]ClO42, respectively. However, with silver(I) nitrate, novel metallosupramolecular complexes [Ag4(ODSQ)2(η1-NO3)2(η2-NO3)2] 3 and [Ag4(OESQ)(ODSQ)(η1-NO3)2(η2-NO3)2]·H2O 4 were obtained, in which the co-ordination motifs [Ag(OESQ)]+ and [Ag(ODSQ)]+ are spontaneously self-assembled by sulfur-bridged silver(I) ions into tetrametallotricyclic molecules containing the same or mixed building blocks. All four complexes have been characterized by elemental analyses, IR and 1H NMR spectroscopy, and single crystal X-ray diffraction methods. The possible self-assembly process has been discussed with the aid of electrospray mass spectrometry.

Supramolecular and metallosupramolecular coordination compounds of nickel(II) with the half units of vicinal oxime–imine ligands; mixed ligand complexes of the metal ion

The [1+1] condensation of isonitrosoacetylacetone (Hisoacac) with o-phenylenediamine produces the diazepine (HLBD) (1), which reacts with Ni(OAc)2· 4H2O (1:1 molar ratio) to produce the mixed ligand complex (LBDN)Ni(OAc) (2); where LBDN is the anion of the half unit obtained by hydrolysis of one HLBD imine linkage. The reaction of (2) (1 mol) with mono-, bi- and trichloroethanoic acid (1mol) or picric acid (1mol) led to the exchange of the acetate in (2) with the anion of the added acid [(3)–(6), respectively]. The supramolecular structure of (2)–(6) is achieved through the dimerization of these complexes via intermolecular hydrogen bonding of the LBDN –NH2 group of one molecule and the monodentate acetate group of another molecule. The template reaction of o-phen with Hisoacac in the presence of Ni(OAc)2·4H2O (1:2:2 and 1:2:1 molar ratios, respectively) led to the formation of (LBDN)Ni(OAc)2Ni(isoacac) (7) and (isophen)Ni (8), respectively; H2isophen is a symmetrical Schiff base ligand formed by the (2:1) in situ condensation of Hisoacac with o-phen. The (1:1) condensation of Hisoacac with p-phen produced the half unit Hisopphen (9), whose 1:1 molar ratio reaction with Ni(OAc)2·4H2O led to the formation of (isopphen)Ni(OAc)·2H2O (10). The amino group of the isopphen ligand is available for further coordination with the nickel(II) ion to produce the metallosupramolecular complexes {[two molecules of complex (10)] [Ni(OAc)2]} and {[complex (10)] [Ni(OAc)2·H2O]} from the 2:1 and 1:1 molar ratio reactions, respectively, of (10) with Ni(OAc)2·4H2O. The 1:1 molar ratio reaction of (10) with Hisoacac led to replacement of OAc by isoacac. The suggested structures of the ligands and their coordination compounds are based on analytical, chemical, spectral data and magnetic moments.

Monolayer of metallo-supramolecular complexes

Self-assembled thin films of metallo-supramolecular complexes were prepared and characterized by synchrotron based X-ray reflectivity and fluorescence techniques.