Mineralized collagen fibrils constitute a basic structural unit of collagenous mineralized tissues such as dentin and bone. Understanding of the mechanisms of collagen mineralization is vital for development of new materials for the hard tissue repair. We carried out bio-inspired mineralization of reconstituted collagen fibrils using poly-l-aspartic acid, as an analog of non-collagenous acidic proteins. Transmission electron microscopy and electron diffraction studies of the reaction products revealed stacks of ribbon-shaped apatitic crystals, deposited within the fibrils with their c-axes coaligned with the fibril axes. Such structural organization closely resembles mineralized collagen of bone and dentin. Initial mineral deposits formed in the fibrils lacked a long range crystallographic order and transformed into crystals with time. Interestingly, the shape and organization of these amorphous deposits was similar to the crystals found in the mature mineralized fibrils. We demonstrate that the interactions between collagen and poly-l-aspartic acid are essential for the mineralized collagen fibrils formation, while collagen alone does not affect mineral formation and poly-l-aspartic acid inhibits mineralization in a concentration dependant manner. These results provide new insights into basic mechanisms of collagen mineralization and can lead to the development of novel bio-inspired nanostructured materials.

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Abstract:Ce 1-x Zr x O 2 nanoparticle sols (x = 0-1) are synthesized by hydroxide coprecipitation of a mixed precursor solution of cerium ammonium nitrate and zirconyl chloride followed by redispersion in an aqueous medium by sonication using nitric acid as the peptizing agent. The obtained sols are highly concentrated and stable for weeks. Analytical ultracentrifugation measurements show a particularly narrow particle distribution with an average particle size of about 3.5 nm for pure CeO 2 and 2.5 nm for pure ZrO 2 nanoparticles. Wide-angle X-ray scattering (XRD) as well as high-resolution transmission electron microscopy give evidence that all of the as-synthesized nanoparticle sols with a ceria content larger than 20 mol % are well crystalline. The formation of a solid solution with an increasing amount of Zr was monitored by XRD and Raman spectroscopy.

SIBLING (Small Integrin-Binding Ligand N-linked Glycoproteins) family is the major group of noncollagenous proteins in bone and dentin. These extremely acidic and highly phosphorylated extracellular proteins play critical roles in the formation of collagenous mineralized tissues. While the lack of individual SIBLINGs causes significant mineralization defects in vivo, none of them led to a complete cessation of mineralization suggesting that these proteins have overlapping functions. To assess whether different SIBLINGs regulate biomineralization in a similar manner, and how phosphorylation impacts their activity, we studied the effects of two SIBLINGs, dentin matrix protein 1 (DMP1) and dentin phosphophoryn (DPP), on mineral morphology and organization in vitro. Our results demonstrate distinct differences in the effects of these proteins on mineralization. We show that phosphorylation has a profound effect on the regulation of mineralization by both proteins. Specifically, both phosphorylated proteins facilitated organized mineralization of collagen fibrils and phosphorylated DMP1 induced formation of organized mineral bundles in the absence of collagen. In summary, these results indicate that the primary structure and phosphorylation uniquely determine functions of individual SIBLINGs in regulation of mineral morphology and organization.

Steam reforming of methanol (SRM) was investigated over Cu/ZrO 2 /CeO 2 (CZC) catalysts prepared via a novel synthetic method based on coprecipitation and polymer templating. Structural characterization of the samples was performed by N 2 adsorption-desorption, N 2 O decomposition, and X-ray diffraction. The variation of the Cu loading resulted in an increased Cu crystallite size and a decreased specific surface area of the active particles. Catalytic investigations were carried out in a fixed bed reactor at 10 5 Pa, by applying a CH 3 OH:H 2 O = 1:1 ratio. The samples with Cu contents higher than 5 % exhibited good long-term stabilities and low CO levels during continuous operation. The kinetic model suggested for the transformation involved the reverse water-gas shift (RWGS) and methanol decomposition (MD), in addition to the SRM reaction. Kinetic measurements were accomplished in the temperature range 503-573 K and the experimental results could be well simulated. The highest methanol conversions and the lowest CO levels were observed in the temperature range 523-543 K. The apparent activation energies for the individual reactions were found to depend on the Cu content of the catalyst. Since the influence of mass transport limitations on the kinetic data could be excluded, it was established that the variation of the Cu concentration in the precursor material altered the microstructure of the Cu particles and, accordingly, the active Cu surface, which resulted in the formation of significantly different catalysts.Keywords: steam reforming of methanol, copper, zirconia, ceria, N 2 O chemisorption, long term stability, CO formation, kinetic model, reverse water-gas shift reaction, methanol decomposition, activation energy 1.IntroductionIn the past decade, considerable attention has been focused on the reduction of the significant emissions originating from mobile sources, such as internal combustion engines [1][2][3][4]. For environmental reasons, the development of proton-exchange membrane fuel cells (PEMFCs) has gained in increasing importance [5,6]. As compared with conventional heat engines, several advantages of fuel cell application have been established, including a higher efficiency and a more convenient operation, the absence of moving parts and the low emission of hazardous compounds [1,5]. The combustion of hydrogen in a fuel cell is regarded as a clean process, releasing energy and providing only water as an exhaust material [4,7,8]. However, hydrogen is not a natural energy source and must be generated by consuming a large amount of energy, either from natural gas or via the electrolysis of water [4]. Furthermore, for a fuel cell vehicle, the storage and the supply of hydrogen, a volatile and explosive gas, imposes mechanical problems and safety hazards on a commercial level [1,4,8].Several liquid fuel candidates have been discussed for on-board reforming, including methanol, ethanol, gasoline and diesel [1], of which methanol is considered the most favourable alternative [1,9]. Although mo...

Porous polymer beads have been used as templates in which sol–gel chemistry was conducted for the formation of porous titanium dioxide and titania/aluminum, gallium, or indium oxide spheres. The addition of 5, 10, and 15 wt.‐% of the second metal oxide to titania was studied, resulting in little variation in the final porous‐sphere diameter, but in a decreased titania nanocrystal size and an increased specific surface area of the material. The crystallinity of the samples was observed after heating at 550, 750, and 950 °C as anatase to rutile phase transitions became apparent and peaks from the added metal oxide were observed with the increase in temperature. Photocatalytic decomposition of 2‐chlorophenol was monitored in the presence of the titania and titania/metal‐oxide spheres showing that a 5 wt.‐% addition of the second metal oxide gave best photocatalytic results for all the metal oxides studied. At a pH of 6 the pure titania spheres were less photocatalytically active than the Degussa P25 titania, however the mixed titania/5 wt.‐% metal‐oxide samples were more active than the standard in the order In (least active), Ga, then Al (most active). Variation of the solution pH (between pH 2 and 10) had little influence on the photocatalytic activity of the titania/5 wt.‐% aluminum oxide material, more effect on the titanium/5 wt. % gallium oxide, and the most pronounced effect on the titanium/5 wt.‐% indium oxide, with increased activity at higher pH values. The adsorption of pyridine to the titania samples containing the second metal oxide indicated the presence of Lewis‐acid sites.

High‐precision nanocasting using crystalline ceria/zirconia nanoparticle sols is employed for successful replication of hierarchical wood tissue. Full retention of the spiraling cellulose microfibril orientation after template removal is unambiguously proved for the first time using small angle X‐ray scattering (see figure). Electron microscopy reveals that the morphological details of the wood template are well preserved over four levels of hierarchy.

Collagen and amelogenin are two major extracellular organic matrix proteins of dentin and enamel, the mineralized tissues comprising a tooth crown. They both are present at the dentinenamel boundary (DEB), a remarkably robust interface holding dentin and enamel together. It is believed that interactions of dentin and enamel protein assemblies regulate growth and structural organization of mineral crystals at the DEB, leading to a continuum at the molecular level between dentin and enamel organic and mineral phases. To gain insight into the mechanisms of the DEB formation and structural basis of its mechanical resiliency we have studied the interactions between collagen fibrils, amelogenin assemblies, and forming mineral in vitro, using electron microscopy. Our data indicate that collagen fibrils guide assembly of amelogenin into elongated chain or filament-like structures oriented along the long axes of the fibrils. We also show that the interactions between collagen fibrils and amelogenin-calcium phosphate mineral complexes lead to oriented deposition of elongated amorphous mineral particles along the fibril axes, triggering mineralization of the bulk of collagen fibril. The resulting structure was similar to the mineralized collagen fibrils found at the DEB, with arrays of smaller well organized crystals inside the collagen fibrils and bundles of larger crystals on the outside of the fibrils. These data suggest that interactions between collagen and amelogenin might play an important role in the formation of the DEB providing structural continuity between dentin and enamel.Dentin and enamel, the two mineralized tissues that comprise a tooth crown, are strikingly different in terms of their compositional, structural, and mechanical properties (1). Despite these differences, dentin and enamel work together for decades under severe mechanical stress, without delamination or catastrophic failure.Dentin is a mineralized tissue similar to bone, comprised primarily of fibrillar collagen type I, carbonated apatite and water (2). There are other so-called noncollagenous macromolecules present that, in total, represent less then 10% by mass of organic material, although they play important roles in the formation and function of these tissues. All bone materials share the same basic building block, a collagen fibril, in which plateshaped apatitic crystals are organized in parallel arrays with their c-axes co-aligned with the long axis of the fibril (2-4). Collagen type I triple helical molecules, are super-coiled assemblies of two identical ␣1-chains and one ␣2-chain with a different sequence (5, 6). Each chain contains more than 1000 amino acids and is primarily composed of Gly-X-Y repeats, where amino acids proline (Pro) and hydroxyproline (Hyp) predominantly occupy X and Y positions. All three chains in the molecule adopt a polyproline II (PPII)-like structure, which is stabilized by direct and water mediated inter-and intra-chain hydrogen bonds (5, 6). Collagen fibrils form via a self-assembly process in which collag...