Protein template effect on hydrotalcite morphology

Layered double hydroxides (LDHs), hydrotalcite‐like compounds, or hydrotalcites are porous materials, which may be used in catalysis, biomedicine, or adsorption as they may work as anion exchangers or drug deliverers. The morphology of hydrotalcites determines their use: in catalysis or in adsorption, reagents and gases have to reach as much surface as possible; in biomedicine, drugs have to be encapsulated and delivered later on. In this work, we synthesize hydrotalcites in presence of protein templates (egg white and yolk) and under two crystallization conditions (conventional and microwave). The obtained materials are hydrotalcites whose morphologies correspond to platelets organized as sand roses. Depending on the template and the preparation procedure, the amount of platelets can be increased. This feature is explained through the template effect of egg components. The resulting materials are promising adsorbers. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactivity of 2‐aryl‐1,3‐dithiane anions towards neopentyl,neophyl and phenyl iodides. New evidence for an SRN1 mechanism

The reactions of 2‐(4‐Z‐phenyl)‐1,3‐dithiane anions (Z = H, OMe, Cl, CN) with neopentyl, neophyl and phenyl iodides were studied in DMSO, taking into consideration the effect of the Z substituent on the dithiane anions reactivity as well as on the product distribution. These substitution reactions proceed by an S_RN1 mechanism with radicals and radical anions as intermediates. Two competitive pathways are possible for the radical anion of the substitution product, namely electron transfer (ET) to the substrate giving the substitution product and C–S bond fragmentation to yield a distonic radical anion. ET is the main pathway for the reactions between dithiane anions bearing electron‐donor substituents and neopentyl or its analogue iodides affording the substitution products in moderate yields (41–53%). Copyright © 2011 John Wiley & Sons, Ltd.     

Nanopowders of ferroic oxides for magnetoelectric composites

Piezoelectric oxides are currently being considered in combination with magnetic materials for the development of magnetoelectric composites, in which stress transfer across the interface is a key issue. In this context, we report here a detailed study of the mechanochemical activation processes of the ferroelectric perovskite BiScO₃–PbTiO₃ and of the ferrimagnetic spinel NiFe₂O₄. Highly sinterable, single-phase nanopowders of both ferroic oxides are synthesised, and used for the preparation of high-density materials and two-phase composites by hot pressing. Emphasis is put on studying chemical reactions at and interdiffusion across the interface between the two phases using high spatial resolution techniques such as micro X-ray diffraction and piezoresponse force microscopy. The feasibility of preparing magnetoelectric composites by this approach is demonstrated, for which the necessity of controlling physicochemical processes at the interface is key to obtain functionality.     

Thickening mechanism of associative polymers

Steady state viscosity and viscoelasticity of HMHEC solutions were studied. Viscosity increases with concentration due to a reinforcement of the micellar network. High shear rate viscosities are independent of temperature. Two relaxation processes were observed, the long one related to the lifetime of the hydrophobic junction and the short related to rapid Rouse-like relaxations of the free chains. When SDS is added, mixed micelles form that reinforce the network up to an optimum [SDS]/[HMHEC] ratio. Above this ratio, the micelles in excess isolate the polymer chains, the long relaxation process disappears and Rouse-like relaxations occur, corresponding to rapid movements of free chains.     

High-Porosity Metal-Organic Framework Glasses

We report a synthetic strategy to link titanium-oxo (Ti-oxo) clusters into metal-organic framework (MOF) glasses with high porosity though the carboxylate linkage. A new series of MOF glasses was synthesized by evaporation of solution containing Ti-oxo clusters Ti₁₆O₁₆(OEt)₃₂, linkers, and m-cresol. The formation of carboxylate linkages between the Ti-oxo clusters and the carboxylate linkers was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The structural integrity of the Ti-oxo clusters within the glasses was evidenced by both X-ray absorption near edge structure (XANES) and ¹⁷O magic-angle spinning (MAS) NMR. After ligand exchange and activation, the fumarate-linked MOF glass, termed Ti-Fum, showed a N₂ Brunauer–Emmett–Teller (BET) surface areas of 923 m² g⁻¹, nearly three times as high as the phenolate-linked MOF glass with the highest BET surface area prior to this report.     

Side-Chain Chemistry Governs Hierarchical Order of Charge-Complementary β-sheet Peptide Coassemblies

Self-assembly of proteinaceous biomolecules into functional materials with ordered structures that span length scales is common in nature yet remains a challenge with designer peptides under ambient conditions. This report demonstrates how charged side-chain chemistry affects the hierarchical co-assembly of a family of charge-complementary β-sheet-forming peptide pairs known as CATCH(X+/Y−) at physiologic pH and ionic strength in water. In a concentration-dependent manner, the CATCH(6K+) (Ac-KQKFKFKFKQK-Am) and CATCH(6D−) (Ac-DQDFDFDFDQD-Am) pair formed either β-sheet-rich microspheres or β-sheet-rich gels with a micron-scale plate-like morphology, which were not observed with other CATCH(X+/Y−) pairs. This hierarchical order was disrupted by replacing D with E, which increased fibril twisting. Replacing K with R, or mutating the N- and C-terminal amino acids in CATCH(6K+) and CATCH(6D−) to Qs, increased observed co-assembly kinetics, which also disrupted hierarchical order. Due to the ambient assembly conditions, active CATCH(6K+)-green fluorescent protein fusions could be incorporated into the β-sheet plates and microspheres formed by the CATCH(6K+/6D−) pair, demonstrating the potential to endow functionality.     

Application of ftir spectroscopy to the study of curing of glass reinforced polyester composites

The effect of glass fiber reinforcements on the curing behavior of unsaturated polyester commercial resins was investigated by Fourier transform infrared spectroscopy. Two different E-glass fibers and two commercial resins were employed. The results indicate that both the glass fiber content and the fiber size have a pronounced effect on the ultimate values of the styrene conversion. Some complications found in the infrared analysis of commercial resins are also presented.