Metallo-supramolecular Complex Research Articles

Diazananographene with Quadruple [5]Helicene Units: Synthesis, Optical Properties, and Supramolecular Assembly

A helical diazananographene (1) was successfully synthesized by employing sterically hindered t-butyl groups to inhibit further dehydrocyclization of [5]helicene units. These t-butyl groups stabilized the conformation of [5]helicene units, thus resulting in three stable conformers of 1, comprising a pair of enantiomers (1-(P, P, P, P) and 1-(M, M, M, M)) and a mesomer (1-(P, P, M, M)). In comparison to its planar analogs, helical 1 exhibited broadened peaks in both its absorption and emission spectra, leading to an increase in the emission quantum yield from 0.3 to 0.6. The significantly enhanced radiative decay rate (k r) accounted for the increase in the quantum yield of 1. Additionally, it was observed that the compound could be fully protonated upon the addition of an equivalent acid. Furthermore, 1 assembled into a chiral trimeric metallosupramolecular complex upon coordination with the PdII units. Both protonated 1 and the metallosupramolecular complex exhibited an enhanced circular dichroic response. These findings revealed that the incorporation of a helical structure and pyridinic nitrogen-doping into the nanographene can allow the synthesis of responsive chiroptical graphenic materials, which could serve as fundamental components for constructing chiral hierarchical metallosupramolecular structures.

Synthesis, aggregation, and photophysical properties of amphiphilic BODIPY-Pt(II) metallacycles

The construction of metallo-organic macrocycles using transition metals and optoelectronically active donor ligands is a very active area of research due to the potential applicability of these structures as sensors or as drugs for combined photodynamic/chemotherapy treatments. Herein, we report on the synthesis, photophysical properties, and aggregation behavior of a triangular Pt(II)-assembled metallo-supramolecular complex built by the coordination-driven assembly of a BODIPY functionalized with two pyridines at the 2,6 positions and an (R, R)-phenylalanine dipeptide moiety in the meso position. This hydrophilic group provides the metallacycle with water-solubility and self-assembly capabilities, which result in the formation of robust nanoparticles in aqueous solutions with a 50 nm average size.

Hexagonal Microparticles from Hierarchical Self-Organization of Chiral Trigonal Pd3L6 Macrotetracycles

Construction of structurally complex architectures using inherently chiral, asymmetric, or multi-heterotopic ligands is a major challenge in metallosupramolecular chemistry. Moreover, the hierarchical self-organization of such complexes is unique. Here, we introduce a water-soluble, facially amphiphilic, amphoteric, chiral, asymmetric, and hetero-tritopic ligand derived from natural bile acid, ursodeoxycholic acid. We show that via the supramolecular transmetalation reaction, using nitrates of Cu(II) or Fe(III), and subsequently Pd(II), a superchiral Pd 3 L 6 complex can be obtained. Even though several possible constitutional isomers of Pd 3 L 6 could be formed, because of the ligand asymmetry and relative flexibility of carbamate-pyridyl moieties attached to the steroid scaffold, only a single product with C 3 rotational symmetry was obtained. Finally, we demonstrate that these amphiphilic complexes can self-organize into hexagonal microparticles in aqueous media. This finding may lead to the development of novel self-assembled metal-organic functional materials made of natural, abundant, and relatively inexpensive steroidal compounds. Asymmetric, amphiphilic, chiral, and hetero-tritopic ligand from bile acid Supramolecular transmetalation self-assembly leads to symmetric superchiral complex Complexes self-organize in aqueous environment into hexagonal microparticles Materials with high density of chiral centers and optical activity are prepared Jurček et al. report an amphiphilic bile-acid-based ligand (L) used for the preparation of large hollow metallosupramolecular complex Pd 3 L 6 , accomplished via a supramolecular transmetalation process. The complexes prepared can self-organize into hexagonal microparticles upon contact with water.

Metallo-supramolecular complex of 1,3-di{bis(2-hydroxynaphthyl)}-2-aminothiophenylcalix[4]arene for the detection of L-histidine using secondary interactions

The 1,3-di{bis(2-hydroxynaphthyl)}-2-aminothiophenylcalix [4]arene (L1) has been synthesized and characterized by nmr, mass, uv- vis, fluorescence spectroscopy. The in-situ mixing of receptor L1 and copper ions in 1:1 pattern forms metallo supramolecular complex [L1‐Cu2+] which recognizes l-histidine from among other essential amino acids in the emission spectrum. It seems that receptor L1 act as a primary sensor for cation recognition and as a secondary sensor for l-histidine.

Inert Layered Silicate Improves the Electrochemical Responses of a Metal Complex Polymer

A chemically inert, insulating layered silicate (saponite; SP) and an iron(II)-based metallo-supramolecular complex polymer (polyFe) were combined via electrostatic attraction to improve the electrochromic properties of polyFe. Structural characterization indicated that polyFe was intercalated into the SP nanosheets. Interestingly, the redox potential of polyFe was lowered by combining it with SP, and the current was measurable despite the insulating nature of SP. X-ray photoelectron spectroscopy showed that the decrease in the redox potential observed in the SP-polyFe hybrid was caused by the electrostatic neutralization of the Fe cation in polyFe by the negative charge on SP. Electrochemical analyses indicated that electron transfer occurred through electron hopping across the SP-polyFe hybrid. Control experiments using a metal complex composed of Fe and two 2,2':6',2''-terpyridine ligands (terpyFe) showed that SP contributes to the effective electron hopping. This modulation of the electrochemical properties by the layered silicates could be applied to other electrochemical systems, including hybrids of the redox-active ionic species and ion-exchangeable adsorbents.

Novel calix[4]arene based metallo-supramolecular complex for recognition of cyanide ions in aqueous medium

A novel bis-naphthalimidocalix[4]arene-Cu(II) supramolecular complex has been observed to provide an efficient recognition system for CN− ions in aqueous medium. The binding stoichiometry of bis-naphthalimidocalix[4]arene and copper ion has been found to be 1:1 while that for bis-naphthalimidocalix[4]arene-Cu(II) and cyanide ion it has been determined to be 1:2.

Chiral Metallo-Supramolecular Complex Directed Enantioselective Self-Assembly of β-Sheet Breaker Peptide for Amyloid Inhibition.

Chiral recognition plays an important role for biomacromolecules involved self-assembly and further affects their biological functions. Herein, it is demonstrated that two chiral metal complexes can enantioselectively bind with Aβ15-20, leading to the formation of different self-assembled nanostructures. With the ability of both metal complexes and Aβ15-20 to inhibit Aβ1-40 aggregation, the NiM@P hybrid particles can act as bifunctional Aβ inhibitors.

A new metallo-supramolecular sensor for recognition of sulfide ions

A hydroxynaphthyl hydrazine linked calix[4]arene derivative (4) has been designed, synthesized and evaluated for multi ion recognition. 4 not only recognizes copper ions selectively through a change in color, UV–Vis and fluorescence spectrum but the resultant metallo-supramolecular complex (4·Cu2+) emulates specific recognition of S2− ions as well.

Metallo-supramolecular complexes mediated thermoplastic elastomeric block copolymer

Orthogonal multi-phase strategy has been applied to generate a novel type of thermoplastic elastomeric block copolymer which was obtained via anionic polymerization. Functional terpyridine groups which can potentially form metallo-supramolecular complexes with a variety of metal ions has been introduced to the polystyrene-b-polyisoprene (PS-PI) living chain ends through the termination reaction in an optimized condition. Iron(II), cobalt(II) and zinc(II) metal ions have been used to form metal-ligand complexes with the terpyridine end groups, which can phase separate from the polymer matrix to form hybrid clusters. The formation of metallo-supramolecular hybrid clusters have dramatic effects on the micro-phase separated structures of the PS-PI diblock copolymer, which have been characterized by transmission electron microscopy, small-angle X-ray scattering and atomic force microscopy. This type of hybrid material containing hard PS nanophase and metal-ligand clusters exhibit distinct mechanic properties such as increased modulus, higher yield strength and improved toughness, which is further discussed in light of nature of the metal-ligand bonds and the liability of the clusters. The utilization of metallo-supramolecular complex and its high tunability is potential to fabricate new types of supramolecular nanocomposite materials.

Artificial Evolution of Graphene Oxide Chemzyme with Enantioselectivity and Near‐Infrared Photothermal Effect for Cascade Biocatalysis Reactions

It is highly desirable and challenging when the chemzyme can be not only simply duplicating and imitating the properties of natural enzymes, but also introducing additional new features for practical applications. Herein, we report a zinc-finger-protein like α-helical chiral metallo-supramolecular complex ([Fe2L3](4+)) functionalized graphene oxide (GO-COOH) as a peroxidase mimic. This artificial enzyme integrates the characteristics of both chiral metallo-supramolecular complex and GO-COOH, and shows excellent catalytic activity. More intriguingly, the novel chemzyme turn out to have enantioselectivity and near-infrared photothermal effect. To the best of our knowledge, this is the first example that the chemzyme has such new features. Based on these properties, we have demonstrated three examples for the applications of our designed enzyme: 1) Intracellular H2O2 detection in PC12 cells against Alzheimer's disease; 2) Discrimination between the chiral drug, Levodopa (L-dopa), the gold standard for treating Parkinson's disease and its enantiomer, D-dopa. This is important because L-dopa is the most effective drug at present used to combat Parkinson's disease while D-dopa is inactive and can even cause side effects, thus for drug efficacy it must be free of D-dopa in the formulation; 3) Remote control of enzyme cascade biocatalysis reactions using high transparent, bio-friendly near-infrared (NIR) light. NIR allows remote activation with relatively high spatial and temporal precision. Our work will provide new insights into design and construction of novel chemzyme with more advanced features beyond intrinsic enzyme property.

G-Quadruplex binding enantiomers show chiral selective interactions with human telomere

Chiral recognition of DNA molecules is important because DNA chiral transition and its different conformations are involved in a series of important life events. Among them, polymorphic human telomere DNA has attracted great interests in recent years because of its important roles in chromosome structural integrity. In this report, we examine the short-term effect of chiral metallo-supramolecular complex enantiomers treatment on tumor cells, and find that a zinc-finger-like alpha helical chiral metallo-supramolecular complex, [Ni2L3]4+-P enantiomer (NiP), can selectively provoke the rapid telomere uncapping, trigger DNA damage responses at telomere and degradation of G-overhang and the delocalization of telomeric protein from telomeres. Further studies indicate that NiP can induce an acute cellular apoptosis and senescence in cancer cells rather than normal cells. These results are further evidenced by the upregulation of p21 and p16 proteins. Moreover, NiP can cause translocation of hTERT from nuclear to cytoplasm through Tyr 707 phosphorylation. While its enantiomer, [Ni2L3]4+-M (NiM), has no such mentioned effects, these results clearly demonstrate the compound’s chiral selectivity in cancer cells. Our work will shed light on design of chiral anticancer drugs targeting G-quadruplex DNA, and developing telomere and telomerase modulation agents.

Electron capture dissociation of a self-assembled tetranuclear metallosupramolecular complex in the gas phase

A self-assembled tetranuclear metallosupramolecular complex was brought into the gas phase by electrospray ionization (ESI), mass-selected, and fragmented via infrared multi-photon dissociation (IRMPD) and electron capture dissociation (ECD) in a Fourier-transform ion-cyclotron resonance mass spectrometer (FT-ICR). The resulting spectra were compared. The ECD spectra show some identical fragments to IRMPD which suggest similar fragmentation pathways, but also different fragments which can be assigned to radical cations. Further experiments were performed to investigate the location of the captured electron and results hint at the formation of complexes containing a bipyridyl anion.

ChemInform Abstract: Five Thermodynamic Describers for Addressing Serendipity in the Self‐Assembly of Polynuclear Complexes in Solution

AbstractReview: 57 refs.

Five thermodynamic describers for addressing serendipity in the self-assembly of polynuclear complexes in solution

The thermodynamic self-assembly of any metallo-supramolecular complex [M(pm)L(pn)] in solution can be dissected into five additive free energy contributions. According to a hierarchical energetic order, the two microscopic describers f(inter) and f(intra), which refer to the hetero-component metal-ligand connections, bring the main driving forces to the complexation process. Combined with the statistical factor omega of the self-assembly, which measures the changes in intrinsic rotational entropies accompanying the complexation process, these three parameters provide a satisfying description of the statistical binding leading to [M(pm)L(pn)] in solution. Deviations from statistics, i.e. cooperativity, has then two different origins. Firstly, the preorganization controlling the intramolecular connection events may vary along the assembly process, thus affecting f(intra). Secondly, the homo-component interactions brought by the specific location of the different components in the final assembly (M...M interactions: DeltaE(M,M), and L...L interactions: DeltaE(L,L)), may additionally contribute to the total free energy change and affect f(inter). Beyond the determination of quantitative experimental values for these five parameters operating in various metal-containing assemblies, considerable efforts have been focused on their physico-chemical origins, with the ultimate goal of unravelling their chemical design. In this Feature Article, the bases are first considered leading to the emergence of the free additive thermodynamic model in metallo-supramolecular chemistry. A tutorial discussion of the current level of understanding of each microscopic thermodynamic describer follows, together with some selected practical applications in the field of polynuclear d-block and f-block complexes.

Dimerization Boosts One-Dimensional Mobility of Conformationally Adapted Porphyrins on a Hexagonal Surface Atomic Lattice

We employed temperature-controlled fast-scanning tunneling microscopy to monitor the diffusion of tetrapyridylporphyrin molecules on the Cu(111) surface. The data reveal unidirectional thermal migration of conformationally adapted monomers in the 300-360 K temperature range. Surprisingly equally oriented molecules spontaneously form dimers that feature a drastically increased one-dimensional diffusivity. The analysis of the bonding and mobility characteristics indicates that this boost is driven by a collective transport mechanism of a metallosupramolecular complex.

Predicting speciation in the multi-component equilibrium self-assembly of a metallosupramolecular complex

A practical method to predict the speciation in a multi-component equilibrium self-assembly process has been developed and applied to the formation of the square macrocyclic complex formed from (ethylenediamine)Pd(II) and 4,4′-bipyridyl. The method is based on an additive free energy approach that derives the cumulative formation constants of all 56 species at equilibrium from a set of five pair-wise interactions. Estimates for the required values of the pair-wise interactions were derived from potentiometric titration of (ethylenediamine)Pd(II) and 3-phenylpyridine, and from (diethylenetriamine)Pd(II) and 4,4′-bipyridyl systems. The method calculates the equilibrium speciation as a function of reactant concentrations and pH and produces a map of the range of compositions in which the square complex and competing species are dominant. The predictions of the method closely correlate with available experimental data.

Stimuli-Responsive Aqueous Micelles from an ABC Metallo-Supramolecular Triblock Copolymer

A metallo-supramolecular ABC triblock copolymer containing a bis(2,2′:6′,2″-terpyridine)-ruthenium(II) complex as a supramolecular connection between the constituting poly(styrene)-block-poly-(2-vinylpyridine) diblock and poly(ethylene oxide) block (PS 32-b-P2VP 13-[Ru]-PEO 70) has been prepared. This copolymer was further utilized in order to prepare aqueous micelles consisting of a PS core, a pH-sensitive P2VP shell, and a PEO corona. The accordingly formed micelles have been characterized by a combination of dynamic light scattering, transmission electron microscopy, and atomic force microscopy. Spherical micelles and a minor fraction of bigger aggregates were observed by these three independent techniques. The pH sensitivity of the P2VP shell could be demonstrated and the reversibility of the metallo-supramolecular complex investigated utilizing a strong competitive ligand.