Cation control of dimensionality in isothiocyanate coordination polymers constructed from conformationally flexible 3,3′-bipyridine tethers

Two isothiocyanate coordination polymers constructed from the conformationally flexible tethering ligand 3,3′-bipyridine (3,3′-bpy) and divalent metal cations have been prepared and characterized via single crystal X-ray diffraction, infrared spectroscopy and elemental analysis. [Co(NCS)₂(3,3′-bpy)₂] (1), wherein the isothiocyanate ligands are coordinated in a trans fashion, manifests stacked two-dimensional (2-D) rhomboid grid layered motifs. In contrast, [Ni(NCS)₂(3,3′-bpy)₂] (2) possesses a doubly interpenetrated adamantoid three-dimensional (3-D) network despite the presence of trans isothiocyanate ligands. Thus, a metal cation-based control of coordination polymer dimensionality has been revealed in this system, reflective of different donor dispositions allowed by the conformational flexibility of the exobidentate 3,3′-bpy ligand. The 3-D framework of 2 decomposes at a temperature ∼40 °C higher than the 2-D network of 1.     

Syntheses, crystal structures and photoluminescences of two (4,4) topological coordination networks derived from the flexible bipyridyl ligands

Two new 2D coordination polymers, [Ag₄(μ-4,4′-bpp)₃(1,3-bdc)₂]_n · 2nH₂O (1) and [Ag(μ-4,4′-bpp)₂ClO₄]_n(2) (4,4′-bpp = 2,2′-bis(4-pyridylmethyleneoxy)-1,1′-biphenylene; 1,3-bdc = 1,3-benzenedicarboxylate) have been synthesized using three-layer diffusion methods. Single-crystal X-ray analyses reveal that they are both extended grid networks of the (4,4) topology. In complex 1, a chain built by Ag(I) centers with T-shaped and linear geometries is further connected by the interesting ligand-unsupported Ag?Ag interactions as well as the conjugated π systems to form an interdigitated 2-D coordination network. The corrugated (4,4) sheets of 2 are packed in the ab planes and stacked along the c direction with the anions occupying the gaps in the squares.     

Hydrothermal synthesis and characterization of a new 1-D polymeric lanthanum ethylenediaminetetraacetate with less metal-aqua coordination: {[La(EDTA)(H2O)]2}n

A new lanthanum ethylenediaminetetraacetate (EDTA) coordination polymer, {[La(EDTA)(H₂O)]₂}_n (EDTA³⁻ = [(CH₂N)₂(CH₂COOH)(CH₂COO⁻)₃]), was hydrothermally prepared from LaCl₃ solution and ethylenediaminetetracetic acid at 448 K. The compound was characterized by elemental analysis, FTIR, TG-DTA, and X-ray crystallography. The structure consists of ladder-like chains of [La(EDTA)(H₂O)]₂ dimers bridged by O-C-O groups. Hydrothermal method successfully reduced the high number of La-aqua coordinations in known lanthanum EDTA to one giving rise to relatively compact structure. It has high thermal stability up to 550 K. Every EDTA ligand with COOH group is involved in eight La-O(N) bonds to three nine-coordinated La centers.     

One-dimensional coordination polymer and its hydrogen bonded 2D network generated from dimeric Ag(I) building units

A new dimeric silver(I) complex [Ag(PhPPy₂)(CH₃CN)]₂(ClO₄)₂ (1) (PhPPy₂ = bis(2-pyridyl)phenylphosphine) was synthesized by a direct reaction of [Ag(CH₃CN)₄]ClO₄ with ligand PhPPy₂. X-ray crystallographical studies revealed that in 1, two silver atoms are bridged by two PhPPy₂ ligands and bonded to each other. Each Ag(I) adopts a distorted trigonally bi-pyramidal geometry, and axially coordinated acetonitrile molecules are collinear with two silver atoms. By using 1 as a building block precursor, a 1D coordination polymer, [Ag₂(PhPPy₂)₂(1,3,5-C₆H₃(CO₂)₂(CO₂H))]_∞ (2) was prepared by replacing axially coordinated acetonitrile molecules in 1 with two carboxylate groups of a bridging ligand, 1,3,5-benzenetricarboxylate. In solid state, linear polymeric chains are oriented parallel to each other and interestingly interact by hydrogen bonding through their carboxylic/carboxylate groups to construct a novel wave-shaped 2D network. Both 1 and 2 exhibit similar photoluminescent properties in solid state at room temperature.     

Synthesis and characterization of metal ion imprinted nano-porous polymer for the selective recognition of copper

Selective recognition of metal ions utilizing metal ion-imprinted polymers (MIIPs) received much importance in diverse fields owing to their high selectivity for the target metal ions. In the present study, a copper ion imprinted polymer was synthesized without an additional complexing ligand or complex with a broad aim to avoid the conventional extra metal ion complexing ligand during the synthesis of MIIP. The complete removal of the copper metal ion from the MIIP was confirmed by AAS and SEM–EDX. SEM image of the MIIP exhibited nano-patterns and it was also found to be entirely different from that of non-imprinted polymer and polymer with copper metal ions. BET surface area analysis revealed more surface area (47.96 m²/g) for the Cu(II)-MIIP than non-imprinted control polymer (41.43 m²/g). TGA result of polymer with copper metal ion indicated more char yield (18.41%) when compared to non-imprinted control polymer (8.3%) and Cu(II)-MIIP (less than 1%). FTIR study confirmed the complexation between Cu(II)-MIIP and Cu(II) metal ion through carbonyl oxygen of acryl amide. The Cu(II)-MIIP exhibited an imprinting efficiency of 2.0 and it was showing 8% interference from a mixture of Zn, Ni and Co ions. A potentiometric ion selective electrode devised with Cu(II)-MIIP showed more potential response for Cu(II) ion than that was fabricated from non-imprinted polymer.     

Molecularly imprinted polymer films for reflectometric interference spectroscopic sensors

Reflectometric interference spectroscopic measurements were performed on molecularly imprinted polymer (MIP) films with the herbicide atrazine as the template molecule. A conventional imprinting protocol was used relying on non-covalent interactions between the functional monomers and the template. The MIPs were deposited on glass transducers by two different methods: spin-coating followed by in situ polymerization of thin films of monomers containing a sacrificial polymeric porogen, and autoassembly of MIP nanoparticles with the aid of an associative linear polymer. Reproducible results were obtained upon measurements of atrazine solutions in toluene with both films. Atrazine concentrations as low as 1.7 ppm could be detected with the autoassembled particle film. No or very little analyte adsorption was observed onto non-imprinted control films made by spin-coating and by particle assembly, respectively. We believe that these MIP layers in combination with the general reflectrometric transduction scheme could be a versatile sensing tool for the detection of environmentally important and other analytes.     

Heparin/polypyrrole (PPy) composite on gold-coated matrix for the neurite outgrowth of PC12 cells by electrical stimulation

A heparin/polypyrrole (PPy) composite, an electrical conducting polymer, was designed to enhance the interactions between a gold-coated matrix and nerve cells, with the cell (PC12 cells) interactions investigated under different conditions, both with and without electrical stimulation. The heparin concentration in the composites increased with increasing current density under the preparation condition, indicating that the heparin concentration in the composite could be controlled by managing the current density. Optical imaging showed that PC12 cells well attached to the PPy surfaces covered with heparin, but were poorly interacted to PPy surfaces without the heparin and gold coated matrix. The neurite length of the PC12 cells on the surfaces with an electrical stimulation (100 mV for 1h) significantly increased, with a median length of 77.5 μm; whereas, that without electrical stimulation was 10∼20 μm. Therefore, the heparin/polypyrrole (PPy) composite may provide insight for the development of an ideal nerve guidance channel.     

Conformation of ring single-stranded DNA measured by DNA origami structures

Measuring the mechanical properties of single-stranded DNA (ssDNA) is a complex challenge that has been addressed lately by different methods. We measured the persistence length of ring ssDNA using a combination of a special DNA origami structure, a self-avoiding ring polymer simulation model, and nonparametric estimation statistics. The method overcomes the complexities set forth by previously used methods. We designed the DNA origami nano structures and measured the ring ssDNA polymer conformations using atomic force microscopy. We then calculated their radius of gyration, which was used as a fitting parameter for finding the persistence length. As there is no simple formulation for the radius of gyration distribution, we developed a simulation program consisting of a self-avoiding ring polymer to fit the persistence length to the experimental data. ssDNA naturally forms stem-loops, which should be taken into account in fitting a model to the experimental measurement. To overcome that hurdle, we found the possible loops using minimal energy considerations and used them in our fitting procedure of the persistence length. Due to the statistical nature of the loops formation, we calculated the persistence length for different percentages of loops that are formed. In the range of 25–75% loop formation, we found the persistence length to be 1.9–4.4 nm, and for 50% loop formation we get a persistence length of 2.83 ± 0.63 nm. This estimation narrows the previously known persistence length and provides tools for finding the conformations of ssDNA.     

Inducing enantioselective crystallization with and self-assembly of star-shaped hybrid polymers prepared via “grafting to” strategy

Helical polymers present some interesting and distinctive properties, and one of the most distinguished applications of them is the chiral recognition and resolution of enantiomers. In this work, star-shaped hybrid helical poly (phenyl isocyanide) (PPI) with polyhedral oligomeric silsesquioxanes (POSS) as the core was designed and synthesized by “grafting to” strategy. The homoarm star-shaped hybrid POSS-(PPI)₈ was first obtained by the click reaction between azide-modified POSS (POSS-(N₃)₈) and alkynyl-modified PPI (PPI-Alkynyl). The hybrid POSS-(PPI)₈ was with predominated left-handed helical conformation and exhibited excellent ability in the enantioselective crystallization of racemic compounds. In the meantime, heteroarm star-shaped hybrid (PEG)₄-POSS-(PPI)₄ was prepared by the click reaction of POSS-(N₃)₈ with PPI-Alkynyl and alkynyl-modified poly (ethylene glycol) (PEG-Alkynyl). The hybrid (PEG)₄-POSS-(PPI)₄ was amphiphilic, and it could self-assemble to form spherical micelles in aqueous solutions.