Polymer-assisted formation of giant polyoxomolybdate structures

A functional mesoporous ionic crystal based on polyoxometalate

A mesoporous ionic crystal is synthesized with a polyoxometalate and a macrocation with polar cyano groups. The compound possesses one-dimensional mesopores and shows high proton conductivity and catalytic activity, which are due to the water molecules in the mesopores.

Biomimetic design and performance of polymerizable lipids

Bilayer lipid membranes (BLMs) have received significant attention over the past several decades because of their applications in biological and material sciences. BLMs consist of two amphiphilic lipid layers arranged with their hydrophilic head region exposed to the surrounding aqueous environment and hydrophobic domains in the core. In biology, lipid membranes confine and support the cell structure while selectively controlling the diffusion of ions and proteins between the intra- and extracellular matrix (ECM). Naturally derived lipid monomers spontaneously self-assemble to develop smart gateways that recognize and incorporate desired protein transporters or ion channels. BLMs are useful research models of lamellar lipid assemblies and associated protein receptors in cell membranes. The transport properties of lipid membranes can be tuned through careful consideration of the solution medium, transporter functionality, and pH, as well as other environmental conditions. BLMs are of particular interest in the design of biofunctional coatings, controlled release technologies, and biosensors; however, high-performance applications require lipid membranes to remain stable under harsh denaturing conditions. Accordingly, synthetic strategies are often proposed to increase the chemical and mechanical stability of lipid assemblies. The polymerization of self-assembled lipid structures is a strategy that results in robust biocompatible architectures, and diverse reactive functional groups are available for the synthesis of monomeric lipids. The selection of the polymerizable functionality and its precise location within the lipid assembly influences the ultimate supramolecular microstructure and polymerization efficiency. The biomimetic potential of polymerized lipids depends on the stability and robustness of the self-assembled membranes, and it is essential that the polymerizable functionality not disturb the amphiphilic nature of the lipid to maintain biocompatibility. Innovative applications are the motivational force for the development of durable polylipid compositions. Surface modification with biocompatible polylipids provides the opportunity for specific binding of biological molecules for applications as sensors or controlled release delivery vehicles. The ability to create stable lipid assemblies requires a comprehensive understanding of the mechanism of lipid polymerization in confined supramolecular geometries. The future is exciting as researchers begin to fully understand the morphology of polylipids in an effort to successfully produce naturally derived sustainable materials. In this Account, we highlight recent efforts to covalently stabilize lipid membranes and discuss emerging applications of mechanically robust self-assembled lipid architectures.

Polymer-assisted growth of molybdenum oxide whiskers via a sonochemical process

Whiskers of molybdenum oxides with high aspect ratios were synthesized from peroxomolybdate precursor solutions in the presence of small amounts of poly(ethylene glycol) (PEG) via a sonochemical process at temperatures of 25-70 degrees C. Irradiation with ultrasound reduces the time needed for the growth of micrometer-sized whiskers from weeks to a few hours. The simplicity of the sonochemical approach also compares favorably to a hydrothermal/solvothermal process. The morphology, crystal structure, and other characteristics of the whiskers were characterized by scanning electron microscopy, transmission electron microscopy, selective area electron diffraction, energy-dispersive X-ray spectroscopy, wide-angle X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and the Brunauer-Emmett-Teller method. The surface area of the calcified molybdenum oxide whiskers (55.4 m2/g) was found to be much higher than those of molybdenum oxide nanofibers (35 m2/g) or nanorods (13.4 m2/g) The growth rate of various crystal faces could be postulated to be controlled by the binding of peroxomolybdate ions to pseudo-crown ether cavities formed by PEG. The reduction of molybdenum oxide to produce mixed-valent oxides and their growth could also be controlled by the reducing ability of PEG. The aspect ratio of the molybdenum oxide whiskers increased with decreasing concentration in the initial peroxomolybdate precursor solution. Whether the precursor solution species was H2Mo2O3(O2)4(H2O)2, H2MoO2(O2)2, or MoO2(OH)(OOH), the peroxide group in all the species disproportionates to give the final product MoO3 by a catalytic process. On the basis of experimental evidence of the dual role of glycols, a mechanism for the growth of the molybdenum oxide whiskers is proposed.

Solution-phase synthesis of spherical zinc sulfide nanostructures

A facile solution-phase method has been developed to synthesize specially hollow and solid ZnS nanospheres. High-resolution TEM images on the nanospheres suggest their formation via the oriented aggregation of the primary ZnS nanocrystals. The morphology and size of the ZnS nanospheres can also be tuned easily by controlling the experimental conditions. These special spherical structures are very easily encapsulated within a uniform silica layer without any surface modification, suggesting potential applications in biochemistry and biodiagnostics.

Morphogenesis of Highly Ordered Mixed-Valent Mesoporous Molybdenum Oxides

Control of the size, shape, and structure of mesoporous transition metal oxide materials is important in their correlations with corresponding optoelectronic and photocatalytic properties. Highly ordered cubic phases of mixed-valent mesoporous molybdenum oxides have been prepared by the reduction and decomposition of aqueous molybdenum precursor solution in the presence of poly(ethylene oxide) under ultrasonic irradiation. Large-scale uniform molybdenum oxide particles with well-defined crystal-like morphologies (ball-like, rhombic dodecahedral, and cubic shapes) were synthesized and found to be controllable by modifying the molecular chain length of the polymeric additive. Molybdenum oxides with an average oxidation state of 4.8 form a cubic lattice of open mesoporous structures.

Molybdenum blue: Binding to collagen fibres and microcrystal formation

Collagen fibres have been shown by transmission electron microscopy to progressively bind the polyoxomolybdate ring-complex, termed molybdenum blue. Nucleation of cuboidal molybdenum blue microcrystals occurs on the surface of the collagen fibres, leading eventually to extensive coating of the fibres with microcrystals.

Self-assembly of microporous manganese oxide octahedral molecular sieve hexagonal flakes into mesoporous hollow nanospheres

Manganese oxide hollow nanospheres were prepared using a straightforward, template-free synthesis. The resulting material was mesoporous, crystalline, and of uniform diameter. The nanospheres were characterized by XRD, HR-SEM, and HR-TEM, and pore size distributions were calculated from nitrogen desorption. Unlike previous synthesis methods that use an inorganic template, this procedure requires no separation after synthesis to remove the template. The nanospheres are composed of hexagonal gamma-manganese oxide flakes and are approximately 400 nm in diameter. gamma-MnO2 is composed of a ramsdellite matrix (1 x 2 tunnels) with randomly distributed microdomains of pyrolusite (1 x 1 tunnels). These materials could have applications as cathodic battery materials, oxidation catalysts, catalyst supports, and adsorbents for pollutants.

Supramolecular structures of polyoxomolybdate-based giant molecules in aqueous solution

A combination of static and dynamic laser light-scattering techniques was employed to study the supramolecular structures of polyoxomolybdate-based giant molecules in aqueous solution. Convincing evidences indicate that the spherical aggregates have unique vesicle-like structures. A model is built up based on solid experimental results. It is the first time that a clear explanation is presented for the long-time enigma in inorganic chemistry: the nature of the polyoxomolybdate aggregates in "molybdenum blue solution".