Synthesis of Breathing Metallopolymer Hollow Spheres for Redox-Controlled Release.

A convenient synthetic approach for the preparation of uniform metallopolymer-containing hollow spheres based on 2-(methacryloyloxy)ethyl ferrocenecarboxylate (FcMA) as monomer by sequential starved feed emulsion polymerization is described. Core/shell particles consisting of a noncrosslinked poly(methyl methacrylate) core and a slightly crosslinked ferrocene-containing shell allows for the simple dissolution of core material and, thus, monodisperse metallopolymer hollow spheres are obtained. Since PFcMA is incorporated in the particle shell, herein investigated hollow spheres can be addressed by external triggers, i.e., solvent variation and redox chemistry in order to change the particle swelling capability. PFcMA-containing core/shell particles and hollow spheres are characterized by transmission electron microscope (TEM), scanning electron microscopy, cryogenic TEM, thermogravimetric analysis, and dynamic light scattering in terms of size, size distribution, hollow sphere character, redox-responsiveness, and composition. Moreover, the general suitability of prepared stimulus-responsive nanocapsules for the use in catch-release systems is demonstrated by loading the nanocapsules with malachite green as model payload followed by release studies.

Metallopolymer-Based Shape Anisotropic Nanoparticles.

The formation of nanostructured shape anisotropic nanoparticles from poly(ferrocenylsilane)-b-poly(2-vinylpyridine) (PFS-b-P2VP) block copolymers is presented. Ellipsoidal particles with an axially stacked lamellar structure and nanosheets with a hexagonal structure of PFS cylinders are obtained under neutral wetting conditions through the use of a mixed surfactant system during self-assembly. In contrast to traditional systems, the resulting particle structure is strongly influenced by crystallization of the PFS domains under colloidal confinement with lamella-forming PFS-b-P2VP block copolymers leading to cylindrical morphologies. A blending approach was developed to control this morphological change and by the addition of PFS homopolymers, ellipsoidal particles with a lamellar structure could also be obtained. Ultimately, the spatial control over two orthogonal functionalities was exploited to demonstrate morphology transitions for nanosheets upon the exposure to methanol as solvent for P2VP and FeCl3 as a redox stimulus, opening up a variety of applications in the field of stimuli-responsive materials.

Single-source magnetic nanorattles by using convenient emulsion polymerization protocols.

A novel strategy to achieve easily scalable magneto-responsive nanoceramics with core/shell and nanorattle-type or yolk/shell architectures based on a ferrocene-containing polymer precursor is described. Monodisperse nanorattle-type magnetic particles are obtained by using convenient semicontinuous emulsion polymerization and Stöber process protocols followed by thermal treatment. The particles are characterized by TGA, TEM, WAXS, DLS, XPS, and Raman spectroscopy. Herein, established synthetic protocols widen opportunities for the convenient bottom-up strategies of various ferrocene-precursor-based spherical architectures for advanced ceramics with potential applications within fields of sensing and stimuli-responsive nanophotonics.

Identification of rice root associated nitrate, sulfate and ferric iron reducing bacteria during root decomposition.

Leakage of O(2) from roots of aquatic plants supports the oxidation of ammonia to nitrate and of sulfide to sulfate in the rhizosphere, so that these electron acceptors may become available to the root microbial communities and affect their activity. We studied the composition of the bacterial community active in anoxically incubated rice roots by analysis of terminal restriction fragment length polymorphism (T-RFLP) and by cloning and sequencing targeting bacterial 16S rRNA. The bacterial ribosomal abundance in unamended rice roots, which were naturally encrusted with ferric iron, were initially dominated (about 65% of total 16S rRNA) by Clostridium, Bacillus and Geobacter/Pelobacter, but after 5 d clostridia decreased and members of the Cytophaga-Flavobacterium-Bacteroides (CFB) phylum increased (up to 30% of total 16S rRNA). Addition of nitrate or sulfate to the root incubations resulted in bacterial growth detected by fluorescent in situ hybridization (FISH). It also affected the steady state concentrations of H(2), acetate, propionate and butyrate that were measured in the root incubations. Nitrate reducers were apparently involved in consumption of all of these compounds. Sulfate reducers, on the other hand, showed net production of acetate during utilization of propionate. Nitrate stimulated populations of Bacillus and Dechloromonas to become active, the latter temporarily increasing to 25% of total 16S rRNA, but suppressed the increase of CFB bacteria. Sulfate, on the other hand, stimulated Desulfosporosinus and Geobacter/Pelobacter, increasing to about 15% of total 16S rRNA, and suppressed CFB bacteria to become active. In conclusion, our study showed the potential effect of exogenous electron acceptors on the composition and activity of the bacterial community in rice root incubations, and identified the phylogenetic groups of the root microbial communities that respond to an increased availability of nitrate or sulfate.

Effects of nitrate- and sulfate-amendment on the methanogenic populations in rice root incubations.

Abstract Potential interactions between methanogenic archaea and nitrate- and sulfate-reducing bacteria were studied in anoxic incubations of excised rice roots as a model system, by following changes in the concentrations of electron donors and acceptors and in the methanogenic community structure. The relative abundances of methanogenic groups were determined by analyses of terminal restriction fragment length polymorphism targeting archaeal SSU rRNA. Nitrate and sulfate amendment both resulted in suppression of CH(4) production. Suppression by nitrate was initially due to substrate competition for H(2) but eventually also resulted in the suppression of rRNA synthesis of methanogens, in particular of Methanosarcina spp., which was most probably caused by toxic N-compounds (e.g. nitrite). Sulfate-reducing bacteria also successfully competed with methanogens for H(2) and retarded the growth (and/or rRNA synthesis) of the methanogenic populations belonging to the hydrogenotrophic Rice cluster I/Methanomicrobiaceae-group. Our results thus show the potential effect of competition and substrate toxicity on growth and/or synthesis of ribosomes in the two major functional groups of methanogens in a natural habitat.