Synthesis of amphiphilic graft copolymer brush and its use as template film for the preparation of silver nanoparticles

A microphase‐separated, amphiphilic graft copolymer consisting of a poly (vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains, (PVC‐g‐POEM at 62:38 wt %) was synthesized via atom transfer radical polymerization (ATRP). Nuclear magnetic resonance (¹H NMR), FTIR spectroscopy, and transmission electron microscopy (TEM) clearly revealed that the “grafting from” method using ATRP was successful and that the graft copolymer molecularly self‐assembled into discrete nanophase domains of continuous PVC and isolated POEM regions. The self‐assembled graft copolymer film was used to template the growth of silver nanoparticles in solid state by introducing a AgCF₃SO₃ precursor and a UV irradiation process. The in situ formation of silver nanoparticles in the graft copolymer template film was confirmed by TEM, UV–visible spectroscopy, and wide angle X‐ray scattering. FTIR spectroscopy and X‐ray photoelectron spectroscopy also demonstrated the selective incorporation and in situ formation of silver nanoparticles within the hydrophilic POEM domains, presumably due to strong interactions between the silver and the ether oxygen in POEM. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3911–3918, 2008     

Single-Molecule Force Spectroscopy of DNA-Based Reversible Polymer Bridges: Surface Robustness and Homogeneity

Single-molecule force spectroscopy, as implemented in an atomic force microscope, provides a rarely used method by which to monitor dynamic processes that occur near surfaces. Here, a methodology is presented and characterized that facilitates the study of polymer bridging across nanometer-sized gaps. The model system employed is that of DNA-based reversible polymers, and an automated procedure is introduced that allows the AFM tip–surface contact point to be automatically determined, and the distance d between opposing surfaces to be actively controlled. Using this methodology, the importance of several experimental parameters was systematically studied, e.g. the frequency of repeated tip/surface contacts, the area of the substrate surface sampled by the AFM, and the use of multiple AFM tips and substrates. Experiments revealed the surfaces to be robust throughout pulling experiments, so that multiple touches and pulls could be carried out on a single spot with no measurable affect on the results. Differences in observed bridging probabilities were observed, both on different spots on the same surface and, more dramatically, from one day to another. Data normalization via a reference measurement allows data from multiple days to be directly compared.     

Mixed-ligand complexes with trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene terminal and different aromatic polycarboxyl linkers: Synergistic modulation of metallosupramolecular architectures via coordinative and secondary interactions

A series of Co^II, Ni^II, and Cu^II complexes with trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene (bpe) and various polycarboxyl co-ligands have been prepared under general condition and characterized by IR, elemental analysis, and TG-DTA techniques. Single-crystal X-ray diffraction indicates that these complexes display multifarious binuclear, 1-D, and 2-D coordination motifs in virtue of the bridging polycarboxyl building blocks, in which the bpe ligand uniformly adopts the unidentate coordination by using its 4-pyridyl group. Remarkably, higher-dimensional extended networks are further formed with the aid of additional secondary interactions based on bpe (such as H-bonding and π–π stacking). These results demonstrate that bpe is a reliable bifunctional tecton to construct diverse supramolecular architectures via synergistic effect of multiple intermolecular interactions.     

A New Supramolecular Assembly Formed by Melamine and Sulfuric Acid

Polymeric melaminium sulfate [(LH₂)₂(SO₄)₂]_n has been synthesized by reaction of melamine L with sulfuric acid in aqueous solution. The compound was characterized by elemental analysis, ¹H NMR, ESI MS and a single crystal X‐ray diffraction analysis. The architecture of the assembly formed is based on hydrogen bonded dimers of diprotonated melaminium cations (LH₂)²⁺ which are linked by a hydrogen bonded network with sulfate ions forming 2D sheets. A 3D polymeric structure results from the presence of mutual hydrogen bonds between sulfate ions and melaminium cations in different sheets. Significant π‐π stacking is also present between the aromatic cations in this supramolecular arrangement.     

Noncovalent associations in fluorous fluids

Perfluorocarbons (PFCs) are emerging as a new type of liquid phase in which molecular recognition processes can effectively take place. The combination of perfluorocarbons (PFCs) and noncovalent associations, mostly hydrogen bonds, ion pairing, halogen bonds or coordination bonds, has already been successfully exploited for applications in organic synthesis (catalyst recycling, by-product removal), electrochemical sensing, selective extraction/titration processes or to prepare gels. Due to the extreme solvophobic effect in PFCs, the least polar existing fluids, noncovalent associations tend to be enhanced. For instance, quantitative data on the increase in association strength occurring in PFCs have recently been reported for ion-pairing interactions or encapsulation processes. Moreover, several examples show that confining a receptor in a fluorous phase leads to recognition processes with improved selectivity.     

Linking Bridged Tetracopper Complexes with Neutral Dipyridyl Compounds to Coordination Polymers and Discrete Metalacages

The bridged tetracopper(I) complex [{Cu₂(μ‐dppm)₂}₂(μ‐(1,3‐O₂CC₆H₄ (CO₂ )₂)](BF₄ )₂ ( 2 (BF₄ )₂) was prepared. This complex and the neutral dipyridyl compounds (NN ; NN = 4,4′‐bipyridine (bpy), 1,2‐bis(4‐pyridyl)ethane (bpa), 4,4′‐trimethylenedipyridine (tmp)) can form dynamic equilibria in CH₂Cl₂ . From the equilibrium mixtures containing 2 (BF₄ )₂ and NN with 2 (BF₄ )₂/NN = 1:1, different supramolecular compounds were obtained as single crystals, and their structure were determined by X‐ray crystallography. The flexibility of NN is found to be important in determining the outcome of the reactions with a rigid bpy, leading to the formation of the coordination polymer [{Cu₂(μ‐dppm)₂}₂(μ‐1,3‐C₆H₄ (CO₂ )₂)(μ‐bpy)] _n (BF₄ )_2n ( 3 (BF₄ )_2n ), whereas with flexible bpa and tmp direct the formation of the metalacages [{Cu₂(μ‐dppm)₂}₂(μ‐1,3‐C₆H₄ (CO₂ )₂)(μ‐NN )](BF₄ )₂ (NN = bpa, 4 (BF₄ )₂; tmp, 5 (BF₄ )₂), respectively, as supported by density functional theory (DFT ) calculation results.     

A cationic water-soluble pillar[7]arene: Synthesis and its fluorescent host−guest complex in water

The first cationic water-soluble pillar[7]arene CWP7 was prepared. ¹H NMR, ¹³C NMR, and MALDI-TOF-MS were performed to provide converging evidences of the structure of obtained CWP7. Host–guest complexation between this novel pillar[7]arene-based host and sodium pyren-1-olate guest G was fully investigated in aqueous solution. Increased fluorescence intensity was observed during the inclusion complexation. Driven by the cooperativity of electrostatic interactions, π-stacking interactions and hydrophilic/hydrophobic interactions, the guest penetrated into the cavity of CWP7 to form a pseudorotaxane-type inclusion complex with relatively high binding affinity.     

PS-b-PEO block copolymer thin films as structured reservoirs for nanoscale precipitation reactions

Thin films of PS-b-PEO block copolymers were utilized as structured reservoirs for localized nanoscale precipitation reactions. By consecutively immersing the film into solutions of thioacetamide and cadmium chloride, we were able to obtain a monolayer of cadmium sulfide nanostructures on top of the block copolymer film. AFM and grazing incidence small angle X-ray scattering revealed spherical nanostructures (d = 15 nm) corresponding to the dimensions given by the block copolymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1569–1573, 2010     

Preparation and gelling properties of sugar-contained low-molecular-mass gelators: Combination of cholesterol and linear glucose

Four novel amphiphilic cholesterol-based and sugar-contained low-molecular-mass gelators (LMMGs) were designed and prepared. According to the structures of the linkers, which are ethylenediamine, 1,3-propanediamine, 1,4-butanediamine, and 1,6-hexane- diamine, these compounds are denoted as 1, 2, 3 and 4, respectively. Gelation tests revealed that 2, 3 and 4 start to gel xylene at concentrations of 0.090%, 0.022%, and 0.016% (w/v), respectively, which are typical ‘super-gelators’. Moreover, these xylene gel systems also possess film formation property. Scanning electron microscopy (SEM) measurements demonstrated that the aggregation behaviors of the compounds are greatly affected by the structures of the linkers. ¹H NMR spectroscopy studies revealed that intermolecular hydrogen bonding formation plays an important role for the formation of the gels. X-ray diffraction (XRD) studies showed that 1 possesses a layered structure in its 1-pentanol gel, a similar structure to that of it in solid state. Gelator 3 also possesses a similar structure in its THF gel, but different from that of it in solid state. Transmission electron microscopy (TEM) observation revealed the helical nature of the nanobelt assemblies of 1 in its 1-pentanol gel.     

Synthesis and Molecular Structures of Tetrasilyl Ethers of Calix[4]arenes

The tetrasilyl ethers calix[4]areneOSiMe₂R (R = Me, H, vinyl, allyl) were prepared by salt elimination; the calix[4]arene was deprotonated with sodium hydride and subsequently reacted with chlorosilanes ClSiMe₂R. In general, DMF was chosen as solvent in order to steer the reactions in terms of a preference for the cone‐conformation of the products. In the case of calix[4]areneOSiMe₃ both, partial‐cone‐ and cone‐conformers, were synthesised. All products were characterised by NMR (¹H, ¹³C, ²⁹Si) spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction.